CA1143579A - Gas turbine engine fuel governor - Google Patents

Abstract

ABSTRACT

a recuperated gas turbine engine fuel governor which controls fuel flow in response to both mechanical and elec-tronic input signals.

Description

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BACXGROU'`~D OF TIIE INVE~rrIO~
This invention relates to gas turbine engines, and xelates more particularly to an improved gas turbine engine and method and control thexefor particularly useful as the power plant for S a ground vehicle.
Recent advances in gas turbine engine technology have improved their overall efficiency and economy to such an extent that this type of power plant has become competitive in many instances with more conventional internal com~ustion type power plants such as Otto or Diesel cycle engines. For instance, gas turbine technology has made significant inroads as the power plant:
for aircraft engines. Similarly, attempts have been made to develop a gas turbine engine which would be competitive with the more conventional internal combustion engines in high-production ground vehicles such as on-the-road automobiles and heavy trucks.
The gas turbine offers signiicant advantayes of equivalent or better operational e~ficiency, fuel savings, and less emissions as well as being able to utiliz.e a variety of diferent fuels on an economic basis. Further, the gas turbine engine in many instances offers greater overall economy over the entire operational lie of a vehicle.
The inherent operational characteristics of a gas turbine~
engine present, however, certain problcmx w~len utiliæed in a ground vehicle. More specifically, A gas turbine encJinc gcnercllly includes a gas genexator section which prov;ides a large presc;uriGed air flow to a combustor wherein the air flow is mixed and ignited with fuel to greatly increase the temperature oE th~ resulting gas flow. Hot pres~urized cJas flow then drives one or more turbines to produce useful rotary mechanical output power. Normally one o these turbines is a portion cf the gas generator section for driving

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the fan which provides the high volume pressurized air inlet flow. Downstream power output turbines then generate -the useful mechanical power output. Conventionally, the high speed, high vol~Ime gas flow from the gas genera~or drives the ~urbines at relatively high speeds. Other inherent characteristics of such gas turbine engines relates to the thermodynamic and aerodynamic processes carried out therewithin which dictate that operational efficiency of -the engine increases substantially with increasing maximum temperatur~ of the gas flow.
These operating characteristics of a gas turbine engine present certain disadvantages in comparison to the normal operation of reciprocatiny or rotary pist.on type internal combustion engines for ground vehicles. More particularly, the internal combustion engine inherently provides a substantial amount of deceleration horsepower for the vehicle upon reduc.inc~' fuel flow thereto through the drag imposed by the reciprocating portio~ of the engine. In contrast, the high rotational inertia`
of the turbines of the gas turbine engine normally do not permit such immediate, relatively high horsepower braking for a ground vehicle simply upon reducing fuel flow to the combustor of the gas turbine enyine. To overcome this disadvantacJe, a variety of proposals have been offered in the past to increase the~ bra~inc3 characteristics of a gas turb:ine eng.ine when u~ilized Eor drivincr a ground vehicle. Primarily, these concc~t~ relake to completely extinguishincJ the combusti.on process within the combust.or to produce ma~imum dynamic braki.ny. Ilowever, operational l..ife oE
gas turbine engine is su~stantially reduced by continllal thermal cycling of the entire eny.ine as created upon extinyuishing the combustion process. Furthe.r, such approaches adversely affect emissions. Other concepts re].ating to improvinc3 the dynamic hrakinc3 characteristics of a gas turbine engine revolve around the utilization of a "fixed shaft" type of gas turbine engine ~3~79 wherein the gas generator section and the po~er drive section are mechanically interconnected to drive the vehicle. While such an arrangement improves the dynamic bra~ing, it greatly - reduces the adaptability of t~e engine to perform various other processes for driving a ground vehicle, and due to this limited adaptability has met with limited success in use as the power source for a high-production type of ground vehicle. An example of such prior art structure is found in U. S. Patent No. 3,237,40~. The no~nal method for dyn~nic braking in gas turbine powered aircraft, thrust reversal, is of course not readily applicable to ground vehicles.
Prior arrangements for gas turbine engines for ground vehicles also have suEfered from the disadvantage of not providing efficient, yet highly responsive acceleration in lS comparison to internal combustion engines. Inherently, a free tuxbine engine nonnally requires a substantially longer time in developing the maximum torque required during acceleration of the ground vehicle. Prior attemp-ts to solve this prohlem have centered about methods such as operating the gas generator at a constant, maximum speed, or other techniques which are equally inefficient in utilization of fuel. Overall, prior ga~ turbine engines for ground vehicles normally have suf~ered from a reduced operational efficiency .in attemptlng to improve the accel~ration or deceleration characterist.ics of the engine, and or resulted in reduced efficiency by substantially varyincJ the turbine inlet temperature of the gas turbine engine which i5 a primary fclctor in the fuel conswnption of the engine. Further, prior art attempts have generally been deficient in providing a relia~le type of control system which is effective throughout all 57~
operational modes of a gas turbine engine when operating a ground vehicle to produce safe, reliable, operatiny charac-teristics. ~urther, such prior art gas turbine engines have resulted in control arrangements which present a sl~stantial change in required operator actions in comparison to dri~ing an internal combustion powered vehicle.
Other problems related to prior art atternpts to produce a gas turbine engine fox ground vehicle relate to the safety and reliability of the control system in various failure modes, safe and reliable types of controls, and in the overall operational efficiency of the engine. A majority of these problems may be considered as an outgrowth of attempts t~ provide a gas turbin~ engine presenting operational char-acteristics duplicative of the desirable, inherent actions of an internal combustion engine.
Accordingly, it will be seen that it would be highly desirable to provide a gas turbine engine and associated con-trols which incorporate the desirable operational features of both a gas turbine and internal cornbustion engine, but while providing an economical end product of sufficiently rcliable and sae design for hic~h volume production basis for grourld vehicles.
Discussiolls of exemplary prior art structure relating to the engine of the pre~ent invcntion may be found in U. S.
Patents No. 3,237,404 discusscd above; 3,660,976i 3,899,~77;

3,941,015 all of whioh appear to relate to ;chelne~s for trans-mitting motive power from the gas generator to tlle er,c3ine out-put shaft, and 3,688,605; 3,771,916 and 3,938,321 that relate to other concepts for vehicular gas turbine engines. Examples of concepts for variable nozzle engines may also be found in U. S. Patents 3,686,860; 3,780,527 and 3,777,479. Prior art fuel governor controls in the general class of that contcm-plated by the present invention may be found in U.S. Patents 3,400,535; 3,50~,395; 3,568,439; 3,712,055; .~ ..........

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3,777,480 and 3,913,316, none of which incorporate reset ~nd override features as conternplated by the present invention;
and 3,521,446 which discloses a substanti~lly more complcx fuel reset feature than that of the present invention. Exa~ples of other fuel controls less pertinent to the present invention may be found in Patents 3,851,464 and 3,888,078. Patent 3,733,815 relates to the automatic idle reset feature of the present inven-tion while patents ~,976,683; 3,183,667 and 31820b323 relate to the scheduling valve controls.
SUMM~Y OF TE~E INVENTION
An important object of the present invention is to provide an improved gas turbine engine and method and more particularly arrangements exhibiting desirable operakional features normall~
inherent to piston encJines.
Another important object is to provide provisions producing improved fuel performance .in a variety of operations of a ground vehicle driven by a gas turbine engine.
Another important object of the present invention is -to provide improved acceleration, deceleration characteristics for a gas turbine driven ground vehicle, and to provicle a more reliable, longer life y~s ~urbi.ne engine for propuls.ion or power generating purpose~.
In summary, the invention contemplatcc: a recuperated, ~ree tuxbine typ~ engine w:i.t:h separatc ga~, generator and power turbine sections. A ~uel gove.rnor cont.rol~ uel flow to the combustor to se~ gas generator speecl in relation to thu throttle lever. Rc~t soleno:ids can overr.ide and adju~t fuel flow in response to certain opexat.ing parameters or conditions oE cnyine operation. For instance, in response to low speecl on the output shaft of the drive train clutch which is indicat;.ve of an impending desireA
encJine accelera-tion for increased torque output, a rese-t solenoid 357~
increases fuel flow ana the ga~ generator idle speed to sub-stantially reduce time required in increasing engine tor~3ue output. A scheduling valve is effective to control fuel flow during engine acceleration to prevent excessive recuperator inlet temperature and maintain turbine inlet temperature at a substantially constant, high level for maximum engine per-formance. The scheduling valve is responsive to combustor inlet gauge pressure an~ temperature, and also c~ntrols fuel flow during deceleration in a manner maintaining combustion.
Variable turbine guide vanes are shifted first to maximize power delivered to the gas generator during its acceleration, and subsequently are shifted toward a position delivering maximum power to the power turbine section. The variable guide vane control includes a hydromechanical portion capable of controlling power turbine section speed in relation to throttle position, and has an electromechanical portion co-operable therewith to place the guide vanes in a braking mode for deceleration. Power feedback is incorporated to provide yet greater brakiny characteristics. When such is selected, .0 the gas generator speed is automatically adjusted to approach power turbine speed, then through a relatively low power rated clutch the gas generator and power turbine sections are mechanically interconnected such that the rotational inertia of the gas generator sectiorl a~sist~ in retardirlg the ~ngin~
output shaft.
More specifically the present invention contemplates a gas turbine engine fuel control system comprising a housing ~aving an inlet ~:o~ receiving pressurized fuel flow and an outlet for delivering Euel flow to the enyine; a fuel lever pivotally mounted to said housing with first and second arms extending oppositely Erom the pivo-t point, said first arm movable toward and away from an opening carrying said fuel flow to define a variable orifice for variably me-tering fuel ~ 7 -~143S~9 flow to said outlet; means for continuously sensing a preselec~ed parameter of engine operation and exerting a firs-t force on said lever in relation to the value of said sensed parameter; throttle means for continuously exerting a variable second force on said lever opposing said first force, and second force being indicative of a desired value for said preselected parameter; means for selectively exerting a third force on said lever opposing said second force upon occurrence of one preselected condition of engine operation;
and means for selectively exerting a fourth force on said lever upon occurrence of another preselected condition of engine operation, said lever operable to mechanically sum said first through fourth forces.
These and other objects and advantages of the present invention are set forth in or will become apparent from the following detailed description oE a preferred embodi-ment when read in conjunction with the accompanying drawings.

- 7a -~3~7'3 BRIEF DESCRIPTION OF T~IE DRA~INGS
In the drawin~s:
Fig. 1 is a left front perspective illustration of a gas turbine engine and associated drive train embodying the principles of the present invention;
Fig. 2 is a perspective illustration of the power feedback drive train as incorporated in the engine with po~tions of the engine shown in outline form;
Fig. 3 is a fragmentary, partially schematic, elevational cross-section of the power feedback clutch and associated hydraulic system, taken generally along lines 3-3 of Fig. 2;
Fig. ~ is a partiall~ schematic cross-sectional representa-tion o the rotating yroup oE the engine with controls associated the~ewith shown in schematic, block diayram form;
Fiy. 5 is a right front perspective view of a portion of the housing, ducting passages and combustor of the engine with portions broken away to reveal in~ernal details of construction;
Fiy. 6 is a partially schematic, plan cross-sectional view o the fuel governor 60 with portions shown perspectively for 20 better clarity of operational interrelationships;
Fig. 6a is an enlarged partial elevational cross-sectiollal view of the fuel pump taken yenerally along lines 6a-6a of FicJ. 6;
Figs. 6b, 6c, 6d are enlarged cross-section.ll views of a portion of the ~uel yc)ve~nor control show:ing different operational positions of solenoid 257;
Fig~ 7 is a ~chemat:ic, cross-sect:ional and parspective functional representat~on of sched~ll:incJ valve 62;
Fiy. 8 is a plan cross-6ectional view through one port.ion of the scheduliny valve~;
Fiy. 9 is a plan cross-sectional view of the scheduling valve taken generally along lines 9-9 of Fig. 8;
Figs. 10 and 11 are enlarged views of portions of valve 282 showing the interrelationship of fuel metering passages as would be viewed respectively along lines 10-10 and 11-11 of Fig. 7;

~ _ ~3~'3 Fi~. 12 is a schematic cross-sectional representation of guide vane control 66;
Fig. 13 is an exploded perspective illustration of the guide vanes and actuator linkage;
Figs. 14, 15 and 16 are circumferential views showing various operational relationships between the variable yuide vanes and the power turbine blades;
Fig. 17 is a schematic logic representation of a portion of the electronic control module 68;
Fig. 18 is a graphical representation oE the area ratio across the power turbines as a function of guide vane angle;
Fig. 19 is a graphical representation of the desired gas generator section and power turbine section speeds selected in relation to throttle position; and 1.5 F.ig. 20 is a graphical representation of the relationship of fuel flow pennitted by the scheduling valve as a function of combustor pressure along lines of constant com~ustor inlet temperature.
DETAILED nESCRIPTION OF THL: PREFER~cED EMBODIMENT
With reference to the fiyures, listed below are the abbreviations uti:Lizecl in the following detailecl descript.ion to denote var:ious parameters:
Np~ - Power Turbine 54 Speecl Ngg o Ga~ Genercltc)r 52 Speecl NgcJ* ~ Preselectecl G~s Gener~tor 52 Speecl Nti = Tr~nsmissioll Input Sha:Et 36 Speecl e - Predetermined Minirnum Speecl of Transmission Input ShaEt 36 Wf = Fuel flow B = Stator Vane 120, 122 Angle B* = Predetermined S-tator Vane Angle a = Throttle 184 Position `'. 11~57g a* = Preaetexmined Throttle Position T2 - = Compressor Inlet Temperature P2 - ~mbient Pressure T3.5 Combustor Inlet Temperature p3 5 = Combustor Pressure p3 5* = Preselected Intermediate Value of Combustor Pressure T4 = Turbine Inlet Temperature T6 = Turbine Exhaust Temperature Engine 30 Referring now more parti.cularly to the drawings, an improved gas turbine engine as contemplated by the present invention is generally denoted by the numeral 30. As depicted in F.ig. 1 the enyine is coupled to a subskantially standard drive train for a vehicle, particularly a truck in the 450 to 600 horsepower class, with a power output shaft 32 as the input to a drive train clutch 34- A transmission input shaft 36 extends between the clutch 34 and a "change speed" type of tran.smission 38. Transmission 38 is of the manually shiftable gear type; however, it is to be under-stood that various improvements of the present invention are equally usable with other types of speed varying transmissions.
As is conventional the tran~miss:ion 3~ has A var.iety of differen~
positions including severll forward gears, reverse gec-ring, and a neukral positioll. Xn the neut:ral po~.ition no power is transmitted between the transm.~ssion .input s}la~t 36 arld the tr~rlsml~ision ou~put shaf~ 40 which conventionally extends ko the final clrive ~2 and drive wheels 44 of the vehicle. A manual shifting lever 46 provides selection of the desired gear ratio, and a speed sensor 48 generates a signal indicative of the speed oE transmission input shaft 36. As schematically depicted in Fig. 1 and described in greater detail hereinbelow, the speed sensor 4~ may be of any type compa-tible with the control medium of the engine 30. Preferably, speed sensor 48 ,,, ,, , . . . . . , .. ,,, ~, ,, , . .. ,, . , . ", .. .. ... . .

~ 3~79 generates an electrical signal transmltted by conductor 50 to the electronic control module of the engine.
Referring to Figs~ 1-4, engine 30 is of the free turbine, recuperated type incorporating a gas generalor sec-tion:52, a power turbirle 54 mounted on a shaft separate rom that of the gas generator 52, and a recupera~or 56 that sca-vanges waste heat from the exhaust flow from the engi~e fox preheating the compressed fluid prior to the combustion process.
The engine further generally includes a source 58 of combus-tible fuel, a fuel governor generally denoted by n-~eral 60 wh~ch also includes the fuel pump therein, a scheduliny valve 62 for controlling fuel flow normally during accelerat.ion or deceleration of the engine through a fuel line 64 extending to the gas generator section 52, and a control 66 for variably positioning variable stator vanes included in the power tur-bine section 54. An electronic control module 68 receives and processes various input pararneter signals and produces output control signals to the governor 60 and vane actuator control 66.
Conventi.onally, there is inc:luded an electrical 6to-rage batt~ry 70 and associat~d starter motor 72 which .i.~ prc-ferably s~l.ectively coupled to both the gas generator S2 and a starter air pump 74. During ~;tartiny ~peration, ~.he motor 72 is energized to drive both an air starter purrlp 74 as well as the main gas generator shaEt 76. As clearly illustrated i.n Fig. 2, the preferred forrn of the invention also includes a drive train 78 associated with gas generator shaft 76, and another drive train 80.associated with and driven by a main shaft 82 of the power turbine 54. The two drive trains 78 and 80 are selectively interengageable through a relatively low power, wet clutch generally denoted by the numeral 84. This clutch is generally referred to as the power feedback clutch and the structure thereof is described in detail below with respect to Fig. 3, ........... ............................ ~

~1~35~9 while its ~unctional operation is described further below with regard to the power feedback operation of the present invention.
Gas generator 52 generally includes an appropriately fi~tered air inlet 86 through which ambient air is supplied to a pair of series arranged centrifugal compressors 88 and 9o. Cross-over ducting 92 carries the compressed air flow from the first compressor 88 to the second compressor 90. The gas yenerator 52 further includes ducting 94 as depicted in Fig. 5 which surrounds and collects the compressed air flow exhaust from the circular periphery o the second stage compressor 90, and carries this compressed air flow in a pair of feeder ducts 95 to recuperator 56 in non-mixing, heat exchange relationship with the recuperator.
While various ~orms o~ recuperator structure may be utilized in conjunction with the present invention, an exemplary form is as described in U. S. Patent No. 3,894,581 entitled "Metllod of Manifold Construction for Formed Tube-Sheet Heat Exchanger", dated July 15, 1975, issued to Fred W. Jacobsen et al. Though not necessa:ry to the understanding of the present invention, re~erence may be made to the above referenced pa-tent ~or a detailed descri.ption of a recuperator and it~ operation. For purposes o~
the present inventi.on, it is su~ficienk to state that thc compressed air flow from ducts 95 :is prellellt-ed in the recuperator by the waste heat from khe exhaust 10w ~xom khe cny.in~. The prehc~ated, compressed air 10w is then clucted thrc,ugh du~t 96 to a can-type ~S combustor 98. ~3 be,st scen in Fig. 5, he~clted flow Erorn khe recuperator passes throuyh a pluralit~ o~ openincJs 97 into a plenum portion o duct 96, then through openings 97-a in a portion of the housing structure supporting combustor 98. Combustor 98 has a perforated inner liner 99, and airflow ~rom openings 97-a passes into the zone between the i,nner and outer liner to then pass through the perforated inner liner 99 into the combustor zone.
One or more electrical ignition pluys 100 are suitably connected to a source o~ high vol-tage electrical energy in a conventional manner. The igni-ter plug i5 operable to ~aintain a continuous - 12 ~

~3~79 combustion process within the interior of the combustor wherein the fuel delivered from line 64 is mixed and burned with the compressed air flow from duct 96.
The gas generator 52 further incluaes a gas genera-tor turbine 102 of the radial inflow type. The compressed, heated gas flow from combustor 98 is delivered across turbine inlet choke nozæles 104 disposed in a circular array about the annularly shaped inlet 106 to the gas generator turbine section. During engine operation, nozzles 104 maintain pressure in combustor 98 at a level higher than ambient. Flow of this heated, compressed gas across turbine 102 causes high speed rotation of the turbine and the gas generator main shaft 76. This rotation of course drives the two centrifugal compressors 88 and 90. Shaft 76 is appropriately mounted by bearings 108 to the stationary housing 15 . 110 of the engine.
Power turbine section 54 generally includes a duct section 112 and appropriate vanes 114 therein for directing the flow o gases from the gas generator power -turbine 102 -toward a pair o~
axial power turbines 116 and 1].8 mounted to the power turbine main sha.ft 82. The power turbine section further includes sets 120 and 122 of variably pos.itionable guid~ v~lnes rcspectively disposed ups~ream of a~soci.ated axial turbines 116, 1:l.8 and th~ir associ.ated blaclec; ].17, 119. As d~picted irl Fi~J. 13, each of the set~ o~ var:iable gulde vanes 120 and 122 are disposed .in an annular array within the gas flow path and are both mounted to a comrnon actuati.n~ mecharl.isr.l generally r~ferrcd to by the numeral 124. The actuatincJ mechanism 124 comprises a pair of ring years 126 and 128, one for each set of variable vanes, a link 129 affixed to ring gear 126 and secured to rincJ gcar 128 via plate 129-a. Pivotally mourlted to the housing is a bell crank 130, and a t~isted link ].31 has opposite ends pivotally attached to ~1~357~
link 129 and one arm o~ ~ell cran~ 130. A linearl~ shiftable input shaft 368 acts through a pivot link 132 and another arm of the bell crank to cause rotation of cran}; 130 a~out its axis 133 and consequent simultaneous rotation of both ring years 126, 128. Rotation of input shaft 368 rotates each of the ring gears 126, 128 about an axis coincident with the rotational axis of power driven shaft 82 to cause rotation of the two sets of guide vanes in unison to various positions relative to the direction of gas flow passing thereby. As shown in Figs. 14-16, guide vanes 120 are positioned in a central or "neutral" position of Fig. 14 causing substantially max.unum area ratio and minimum pressure ratio across the downstream power turbine wheel blades 117 of wheel 116 in order to minimize the amount of power transferred by the gas flow into rotation of the turbine 116. The Fig. 14 position is graphically illustrated by the position arbitrarily denoted O in Fig. 18. The guide vanes 120 are variably positioned toward the Fic3. 15 position, noted as the +20 position in Fig. 18, wherein high pressure ratio exists across blades 117 and maximum power is transmitted frorn the gas flow to turbine 116 to rotate the latter and transmit maximum power to shaft 82. Also, the vanes are oppositely rotatable to the Fig. 16 position, noted as the -95 position of Fiy. 18, wherein the gas flow is directed by the variable vanes 120 to oppose and tcnd to retard the rotation of wheel 116. While only vanes 120 and blades 117 are illustrated in Figs. 14-16, it will be understood by those skilled in the art that substantially identical operati.onal relation3hips e~ist between vanes 122 and turbine blades 119 of -turbinc 118.
The gas ~l~w uporl ex.iting the last axial turbine 118 i5 collected in an exhaust duct 13~ wh:ich leads to the recuperator 56. The power turbine output shaft 82 is a part of or operably connected with the power output shaft 32 of the engine through appropriate speed reduction gearinCJ. An air or water cooler 87 is also included to cool the lubricating fluid in engine 30 and co~unicates with fluid reservoir 89 through hose 9~.

Fuel Governor 60 Referring now more particularly to Figs. 4, 6, 6A-6D, the fuel governor 60 receives fuel from source 58 through an appropriate filter 136 into an inlet port 138 of a fuel pump housing 140. It will be apparent to those skilled in the art that the housing 140 is attached to and may be integrally formed with another portion .
of the main engine housing 110. The governor is operable to schedule fuel flow output through either or both of the output ducts 142, 144 for delivery to the scheduling valve 62. The governor 60 is hydromechanical in nature but capable of being ; responsive to externally applied mecharical and electrical siynals, and includes an appropriate drive connection schematically illustrated by line 1~6, and associated speed reducing gearing 1~8 , as necessary to drive a gear 150 and drive shaft 152. Shaft 152 drives a fuel pumy in the form of a positive displac~ment rotary gear pump 154 which receives fuel from inlet port 138 and displaces it at a substantially higher pressure through an output conduit 156.
As clearly illustrated in Fig. 6A, the gear pump cornprises a pair of intermeshing yeats 158 and 160, one of which is driven by drive shaft 152 and the other of which is mounted to an idler shaft 162 journaled within housing 140. Supplied in parallel flow arrange-ment from output conduit 156 are three passages, i.e. output duct 142, bypass bore 16~, and main flow metering passay~ 166. Contained in bypass bore 164 is a bypass regulating valve poppet 168 slidable within bore 16~ to variably meter excess flow frorn output condui~
156 to a return passage 170 connectcd back to the fuel inlet port 138. Pressure of fuel in bore 16~ urges poppet 168 downwardly to increase bypass flow thrcugh passage 170, while a helical coil compression spring means 172 acts against the pressure of fuel to urge poppet 168 upwardly to reduce volume of flow from bore 164 to passage 170. Through a pressure passage 182 the lower end of bypass bore 16~ communicates with fuel supply conduit 64. Thus, pressure of fluid in conduit 6~ is exerted upon the lower side of bypass valve poppet 168 to assist spring 172 in opposing the force created by the high pressure fluid in output conduit 156.

-- 15 -- .

Passage 166 terminates in a metering no~,zle 174 secured by plate 176 to the housing, and having a reducecl diamete~ opening 17 communicating with a central cavity 180.
The fuel governor 60 further includes a manual throttle input in the foxm of a throttle lever 184 shiftable between opposed adjustable stops 186, 188 adjustably secured to housing 140. Through an appropriate bearing 190 a shaft 192 extending within internal cavity 180 is rotatable relative to housiny 140.
Integrally carried by shaft 192 in an open-sided camming section 194 into which are pressed fit a pair of stub shafts 196 that respectively carry rollers 198. Rollers 198 are engacJeable with the lower shoulder of a spring stop 200 such that rotation of the throttle lever 184 and shaft 192 causes consequent rotation of stub shafts 196 which are non-aligned with the main rotational axis of shaft 192, and thus vertical shifting of spring stop 200 through rollers 198. During its vertical or longitudinal shiftincJ, spring s~op 200 is guided by a yuide shaft 202 which has an upper guide roll pin 204 slidably extending through a central bore oE
spring stop 200. Guide rod 202 is threadably received and secured such as by lock nut 206 to housiny 1~0.
The governor 60 fu.rther includes a mechanical speed ~ensor which includes a flyweic~ht carr:icr 208 rigidly secur~d to rotate with shaft 152. RotatincJ w.;.th carrier 208 are a plurality of regularly sp~c~d flyweicJIIts 210 mountcd for pivotal movemen~ upon pins 212 securin~ the wel.ghts 210 to carr:ier 208. Dependent upon the speed of shcl~t :l52, the centri~ugcll f.orce cau.C,;es rotation o~
weiyhts 210 about pins 212 to cause the i.nner ends thcreof to shiEt downwardly as viewed in E`ig. 6 and drive the inner rotating race 214 oE a roller bearing assembly also downwardly. Through ball bearings 216 this downward force is transmitted to the non-rotating outer race 218 of the bearing assembly to cause downward shifting of non-rotating se~ment 220. At its lower end segment 220 carries a spriny stop shoulder 222, and a speeder spriny 224 operably extends between the s-top 222 of segmerlt 220 and the spring 35~9 stop 200 associated with the throttle input mechanism. Through a prelo~d of ~pring 224 acting on segment 220 the flyweights are normally urged upward to the zero or low speed position illustrated in Fig. 6. Increasing speed of shaft 152 causes downward shifting of segment 220. Thus it will be apparent that throttle lever 184 ac-ts essentially to select gas generator speed - as reflected by the speed of shaft 152, since the compression of spring 224 is set by rotation of throttle lever 184 and then opposed by the centrifugal force created by the rotation of shaft 152. The vertical position of segment 220 therefore becomes indicative of the difference between selected speed (position of input throttle 184) and actual gas generator speed as sensed through flyweights 210. Fig. 19 illustrates the action of spring 22~ in requesting different levels of yas generator speed Ngg, as lS the throttle is moved through different positions, a.
Governor 60 further includes a main fuel throttle lever 226 pivotally mounted by pin 228 to housing 140. One arm 230 of lever 226 terminates in a spherically shaped end 230 within a receiving groove 232 on segment 220 of the speed error signal mechanism.
An opposite arm 234 of lever 226 i~ movable toward and away from meteriny orifice 178 in response to shifting of segrnent 220 to thereby variably meter fue.l flow from passagc 166 into internal cavity 180. It will be apparent that the rec3ulatinc3 valve poppet 168 is variably positioned .in response to the precisuxe differ~ntial between passage 168 and conduit 64 downstrcam of the meter.in~
orifice 178 to variably meter b~pass fluld flow throuc3h passage 170 in order to maintain a substantially const~nt pressure differential across the fluid metering oriEice cre~ted between metering opening 178 and the arm 23~ of fuel lever 226. Thus the xate of fuel flow delivered from passage 166 to cavity 180 and output duct 144 is a function only substantially of the position of arm 234 relative to meterincJ opening 178 whenever the latter is 57~
the fuel flow controlling parameter. As appropriate, ~ dam2ing orifice 236 may be incorporated in pressure sensing line 1~2 to stabilize the movement of bypass valve poppet 168.
A uni-directional proportional solenoid 239 has an outer housing 238 inte~ral with plate 176 or other~lise affix~d in stationary xelationship to housing 140. Disposed within the housing 238 is a coi- 240, and a centrally arranged armature 2~2.
Rigidly secured to form a portion of armature 2A2 is a central plunger shaft 244 which has an upper end engageable with lever arm 234. Linear gradient springs 246, 248 operably extend between stops on housing 238 to engage associated shoulders on the plunger shaft 244 to normally urge the latter to its de-energized position illustrated. Energization of the solenoid through appropriate electrical lead lines 250 causes upward shifting of the armature 242 and plunger shaft 244 so that the latter engages and exerts an upward force on lever arm 234 opposinq and subtracting from the fo.rce exerted by speeder spring 224 upon lever 226.
While the plunger shaft 244 could, if desired directly engacJe the lever arm 234; in the preferred form a "flo.dting face"
arrangement for arm 234 is utilixed. In this arrangement a floating flat poppet-type face 252 is carriccl within arm 234 in alignment with metering opening 178. Thi~ float.ing face is normal.ly spxing loaded toward the metering orifice, and the upper ~ncl of plunger shaft 2~4 .is eng~geable thexewith. The purposc o floati.ncJ
face 252 is to compensate for manuEacturing tolerallces and to assure that a relatively flat surface .i5 directly aligned with metering opening 178 and l~ing perpendicular to the Eluid fl.ow therefrom to assure proper metering of fuel thercacross. The spring 25~ loads floating face 252 toward opening 178. Pivoting of arm 234 against spring 254 to increase fuel flow is permitted until face 252 contacts the upper end of 245 of plunger 244. This stroking of arm 234 is quite limited bu-t sufficient to create flow ~1~357~
saturation of the annular orifice defined between opening 178 and face 252.
Disposed on the opposite side of lever arm 234 from solenoid 239 is a housing 256 of another directional, one-~ay solenoid 257 shown in ~igs. 6B-6D. Solénoid 257 includes a coil 258, armature 260, and plunger shaft 262 secured for movement therewith. Through appropriate stops, centering springs 264, 266 normally urge the plungex shaft 262 to the de-ènergized position illustrated. Upon energization of thè coil 258 through appropriate leader lines 268, the armature 260 and plunger shaft 262 are shifted downwardly such th~t the plunger shaft: engages the lever arm 234 in a manner exerting a force thereon tending to add to the force created b~
speeder spring 224 and rotating lever 226 to shift arrn 234 away from opening 178. Housing 256 of solenoid 257 is rigidly secured such as by bolts 272 to securement plate 176. Similar to floatincJ
face 252, in the preferred form the plunger 262 does not directly engage the lever arm 234, but rather acts through a floatlng-type pin 272 to e.xert a force on arm 234. The pin 272 is pre-loaded by a spring 274 to give a floating action thereto in order to assure that plunger 262 can properly engage and exert. a force on lever arm 234 regardlesc. of var.iation6 in manufacturin~ tolerances, and/or the position of lever 226 relative to its pivotal shaft 228.
Both solenoi.ds are urged to their de-energ.ized pc~ition by linear gradi.ent sprinc3s, and unlike on-o~f, d:igital-type solenoids, vaxiatiorl in current and/or voltage input to their coils will cause an analog increment:al pOsition.i.nCJ o:E the plunger 2~4 of ~olenoid 239, and will move plunger 262 to either its Fig. 6-~ or 6-D position.
The plunger 262 of solenoid 257 can be shiftecl away from its de-energi~ed Fig. 6-B state, to two different enercJized states shown in Figs. 6-C and 6-D. One electrical input signal of preselected,intermediate power causes the armature 262 to shift to ~143~79 the Fig. 6-C position moving plunger 262 until the face of i-ts -adjustable stop nut 263 contacts the spring stop 267. This travel of plunger piston 262 depresses plunger 272 ancl compresses spring 274 to shift arm 234 ~way from opening 178 and increase fuel flow s until gas generator speed incre~.ses to a level corresponding to the signal force generated by solenoid 257. Thus the plunger 272 spring 274 configuration assists in pe~nitting a less-than-maximum power signal to produce a force of preselected magnitude on arm 234.
Another electrical input signal of greater power causes the armature to shift to the end of its stroke with face 261 thereof contact the adjacent stop face 259 of the housing 256 as shown in Fig. 6-D. This travel causes piston plunger 262 to compress centering spring 266 and cause its lower encl to come into direct contact with arm 234 and urge the latter to permit maximum flow through the orifice presented between opening 178 and piston 252. As described in greater detail below energization of solenoid 257 to its Fig. 6 D position is essentially a false throttle signal duplicating the speed desired from the gas generator when the throttle is depressed to its maximum fuel flow maximum power position.
Schedulinc~ Valve 62 R~ferring now more particulclrly to Figs. 7~ cheduling valve 62 generally includec; a housincJ 276 which m~y be intec3ral wi.kh both housinys 1~0 and thc ~tationary engirle housing 110.
Preferabl~ housinc~ 276 ix disposed in close proximity to both the fuel governor 60 and the combustor 98. ~lousing 276 includes an internal bore 278 into which open the two fuel ducts 142 144 as well as the fuel line 6~ and a low pressure return conduit 280 which returns fuel back to the source. Mounted for longitudinal sliding and rotation within bore 278 is a metering valve 282 having liL 1 ~3579 "windowed" irregularly shaped openings 284, 286 that open into the hollowed interior cavity 288 of valve 282. Fuel line 144 continuously communicates with interior cavity 288. Valve 282 further includes an opening 290 in continuous cornmunication with fuel line 64. Deceleration window 286 is in general - alignment with fuel duct 142, and acceleration window gener~lly aligns with opening 290. The particular configuration of each of the windows 284, 286 is clearly illustrated in Figs. 10 and 11.
Metering valve 282 is urged in one longitudinal direction by a biasing spring 292 which reacts against the housing 276 through a spring stop 294 acting on an alignment point 296 of a sealed block 298 mounted to housing 276 such as by snap ring 300.
The preferred construction as illustrated in Fig. 9; however, the alignment point arrangement permitting rotation of valve 282 relative to housing 276 at the end o~ spxing 292 may alternately be accomplished via a ball 302 configuration as shown schematically in Fi.g. 7. At the opposite end of valve 282 is a spherical ball 304 permitting rotation of valve 282 relative to a piston ~06 carried in bore 278. Attached to housing 276 is a temperature sensitive element 312, 308, for example a thermally responsive cylinder, whose longitudinal length varies with respect to the temperature imposed thereon by the cJa~ or other fluid in the temperature sensincJ chamher 310 within cylinder 312. Thc housinc3 276 is mounted relative to the cn~3ine 6uch that a portion thcrcof, particularly cyl.inder 312 and Lhe a~90ciated chamber 310 ar~ in communication w.ith and rnaintained at the same temperature, T3.5, as the compre~sed air Elow b~incJ delivered into the combustor.
Thermally insulative material 311 is incorporated as necessary to avoid overheating of valve 62. For example the rightward end of Fig. 9 and the perforated cylindrical wall 312 may be disposed at the air inlet to the combustor and/or at the duct 96 carrying air from the recuperator 56 to cornbustor 98. In any case the scheduling 3~7~
valve is so arranged that cylinder 312 expands and contracts longitudinall~ with respect to increase and decrease of combustor inlet temperature. Valve 288 is operably engaged by the thermally responsive element 312 through a relatively non-thermally respon-sive ceramic rod 308. Accordingly, valve 288 is shifted loncJitudi-' nally relative to input port 142 and opening 290 in relation to the sensed combustor inlet temperature. Thus the metering fuel flow accomplised by window 284 is varied in relation to the sensed combustor inlet temperature as this window moves longitudi-nally re].ative to opening 290.
I ~Iousing 276 further includes another transverse bore 314 j which crosses and intersects generally with the longitudinal bore ~ 276. Mounted for lonyitudinal reciprocation within this transverse ! bore 314 is a rod and piston configuration 316 which includes a ¦15 pair of diaphrac3m-type seals 318, 320 having outer ends rigidly secured to houxing 276 by being compressed between the housing, an intermediate sect.ion 322 and a closing plug 32~ -threadably or otherwise secured to housinc~ 276. The inner ends of the sec~ls 1 320 are secured on the movable piston, rod conficJur~tion 316. The seal 320 in conjunction with the cnd closing plug 32~ define an interior pressur~ sensin~ charnber 326 to wh:ich one end oE the piston 316 is expo.cd. Throuqh a sensinc3 ]..i.ne 328 tho cornbu.c;tor pressuxe P3 5 such a5 COnlbU5tO.r i.nlet pre~i5ur~ iS trarlsmitted into chamber 326 to act upon one encl of p:i.storl 316. At the opposite end of bore 31~, a helical coil b:iLIs:;ncJ sprin~ meanF; 330, ~roundcd to housing 276 throuyh a stationary stop 332, acts to urye the piston, rod conficJuration 316 in opposition to the pressure in char~ex 326. The opposite end 334 of the piston configurcltion 316 is vented to atmospheric pressure through an appropriate port 336.
A seal schematically showIl at 335, which may be of a structure like seals 318, 320 and section 348, is also included at this opposite end 334. Thus ~auge pressure in the combustor, i.e. the difference S'~9 bett~een ambient pressure and the absolute pressure maintained in combustor 98, acts upon piston 316 to shift the latter within bore 314.
~n arm 338 is threadably secured wi-thin a transverse bore in metering valve 282 at one end, and at its other end the rod 338 has a spherical ball 340 mounted thereon which is received in a groove 342 in rod, piston 316. It will therefore be apparent that shifting of piston, rod 316 within bore 314 is translated into rotat.ion of metering valve 282 about its major longitudinal axis. Accordingly, the respecti.ve openings between windows 284, 286 and the input ports 142 and opening 290 are also varied in relation to the magnitude of gauge pressure in compressor 98 by virtue of this rotational translation of meteriny valve 282.
Groove 3~2 permits axial translation of arm 338 along with valve 282. While the rod, piston configuration 316 ma~ be of varied arrangements, the preferred form as illustrated in Fiy. 8 incorporates a threaded end section 3~ which acts through appropriate spaces 346 to compress and secure the inner ends of seals 318, 320 to rod 316 throuyh an intermed:iate section 343.
Thus, the schedulincJ valve acts as a mechanical analog computer in multiplyiny the parametcrs of combustor pre.ssure, P3 5 and combustor inlet temperature, T3 5, ~uch tha-t the positioning of valve 232 and the windowc; 2~, 2~6 is a Eunction oE the product quantity of combusto:r pressure multi.plied by combuskor inlet 2~ temperature.
Conventionally, as shown in Fiy. q the controls for enyine 30 further includes a normally open, solenoid operated fuel sequenciny solenoid valve 350 as well as a manually or electrical solenoid operated shut-off valve 352. These valves are disposed downstream of schecluling va].ve 62 and in the preEerred form may be included within and/or adjacent to the housing 276 ~of scheduling valve 62.

~3~79 The configuration of each of the windows 284, 286 as illustratea in Figs ~ and 9 are determined to ~olve a qualitative empirical formula of the following fo~n:
Wf (Kl 2 3.5) 3.5 3 3 5 where: Kl, K2 and K3 are constants determined by the operational characteristics of a particular gas turbine engine and are reflected by the configuration of wind~w 284 and associated opening 290.
By proper formulation of the window 2a4 and opening 290, the solution to this equation as accomplished by schedu-ling valve 62 holds a constant ma~imum turbine inlet tempera-ture T4 during all or at least a portion of gas generator acceleration. Accordingly, when window Z84 is the controlling parameter for fuel flow, scheduling valve 62 empirically by mechanical analogr controls fuel flow to maintain a substanti-ally constant turbine inlet temperature, T4. Window 284 i5 the primary operating parameter during acceleration of the enyine as described in greater detail below. In contrast, window 286 is the controlling parameter during enyine decelera-tion. While acceleration window 284 is contourcd to Jnaintain a substantially constant maximwn yas generator turbine inlet temperature to provide maximwn acceleration pcr~ormance within tlle tem~erature limitations of the enyine, the deceleration window 286 is contollred to limit and control fuel fluw to pre-vent loss o~ combustion while af~ordin~3 suhstantial decc-lera-tion of the engine. ~n extensive di~cussion of operation of a similar type of tur~ine inlet temperature computing valve, but which utilizes absolute rather than gauge col~ustor pres-sure, may be found in United States Patent Application No.
30 689,339 of Rheinhold Werner, filed May 24, 1976, now V. S.
Patent No. 4,057,960.

~1~3S79 Vane Ac-tuator 66 Details of the vane actuator control 66 are illustrated in Figs. 12 and 13. The vane control is hydromechanical in nature and generally includes a housing 354 having a pair of hydraulic pressure fluid supply ports 356, 358 respectively receiving pressuri~ed fluid from a high pressure pump source 360 and lower pressure pump source 362 each of which are driven through the auxiliary power system of the engine. It is understood that the pumps 360, 362 may provide various other functions within -the engines also such as lubrication.
Housing 354 has an internal, fluid receiving cylinder 364 in which is reciprocally mounted a piston 366 dividing the cylinder into opposed fluid pressure chambers. Rod or shaft 368 carried with piston 366 extends exteriorly of housing 354 and is operably connected with the bell crank 130 of Fig. 13 so that, as described previously, linear reciprocation of rod 368 causes rotation of bell crank 130, ring gears 126, 128 and the sets of variable guide vanes 120, 122.
High pressure hydraulic fluid from inlet port 356 is delivered into a bore 370 within housing 354 located adjacent cylinder 364. Also intersecting at sp~ced location~ along bore 370 are a high pressure fluid exhaust duct 372, and a pair of fluid work conduits 37~, 376 re~pectively communicatiny with the cylindex 364 on opposed sides of pi~ton 366. Mounted for reciprocation within bore 370 i5 ~ dir~ctional fluid control valve element 380 which is nominally yositionable in the open center po ition illustrated wherein high pressure hydraulic fluid from duct 356 communicates only with the eYhaust port 372. A series of centering springs 382, 383, 384, 385 normally urge valve 380 to the position shown. Valve 380 i5 of the-four-way type and is shiftable one direc-tion to direct high pressure fluid from ~3~i79 port 356 to conduit 374 and the uppe~ side of piston 366, while through conduit 376 the lower side of the cylinder carryin~ piston 366 is vented to a low pr~ssure return 386 via bore 370, and communicating conduit 388. Valve 380 is shiftable in an opposite direction to direct pressure fluid from inlet 356 to conduit 376 and the lower side of piston 366, while conduit 374 communicates with return 386 throuyh a chamber 378 and return line 379. It will be noted that piston 366 cooperates with housing 354, such as with a circular wall protrusion 390 thereof to prevent fluid communication between chamber 378 and c~linder 364.
Spring 382 acts to sense the position of piston 366 and the guide vane angle, and as a feedback device in acting upon valve 380. The relative compression rates of spring 382 in comparison to the springs 383-38S provides a high gain response requiring large movement of piston 366 (e.g. 14 times) to counteract as initial movement of valve 380 and return the valve to its center position. Thus it will be apparent that piston 366 acts in servo-type following movément to the movement of an "input piston" in the form of valve 380.
In bore 370 is a stepped d.iameter piston mech~nisln 392 shiftable in response to the rnagnitud~ of fluid pressure from a conduit 39~ acting upon a shoul,der 393 of p:iston 392. ~iston 392 presents an adju.stable stop Eo.r vary:inc3 the compressive forcc of spr.iny 383. Pressure ac-t:iny on shouldor 393 is opposed by a spriny 385. Slidably extending through the cerltc:r o~ element 392 is a rod 395 which acts as a vari~bly positionabl~ ~:top upon the spring 384 extending between the upper end of rod 395 ar-d valve 380. Rod 395 is longituclin~lly shiftable in response to rotation of a fulcrum type lever 396 pivotally mounted to housiny 354 at pivot 398.

~3~7~3 Vane actuator control 66 further includes another bore 400 in which is mounted a control pressure throttling valve 402.
An input from the throttle lever 18~ of the engine ~cts to depress a variably positionable spring stop 404 to increase the force exerted by compression spring 406 in urging valve 402 downwarclly. Opposing spring 406 is a gradient compression, helical coil spring 408 Valve 402 is variably positionable to me~er hydraulic flow from port 358 to conduit 410. It wil:L be noted that conduit 410 also communicates with the lower end of throttling valve 402 via a conduit 412 having a damping orifice 414 therein. Conduit 410 leads to the larger face o~ a stepped piston 416 reciproc~lly mount-ed within another bore 418 in housing 354. One end on bore 418 is in restricted fluid co~nunication with return 387 through an orifice 419. 'rhe smaller diarneter section of stepped piston 416 receives pressuri~ed 1uid from conduit 420. Through an appropriate exhaust conduik 424 the intermediate section of the stepped piston, as well as the upper end of valve 402 are exhausted to low pressure return 3~6 through the conduit 388.
Conduit ~20 provides a hydraulic sicJnal indicative. of the speed of the power tu~hine shaft 82. In this collnect:ion, the vane actuator inc:ludes a non-posi.tive clisp~ cernent type hydrLIul.ic purnp, such as a ccnt.r:ifuc3cll purnp ~2? moullted to and rotated by power turbine shaEt 82. Being a non~posit.ive d:ic;pLcrcernent type pulnp, the pump 422 de:L:ivers pres~;ur:ized hydrclul.ic ~I.ow thrc~ugh concluit 420 such that the pressure mainta:irled on the smaLler diarneter oE st~pped piston 416 is a square funct.ion of the sp~ed of power turbine shaft 82. Sirni:Larly, -the act.ion of throttling valve 402 dev~lops a pressure on the large diameter of piston 416 in relation to ~ desired or selected speed reflected by the position of the thxottle 184.

5~9 The valve 402 and piston ~]6 act as input signal means and as a comparator to vary the compressive force of spring 384 as a function of the difference or error bet~een actual power turbine speed and the power turbine speed requested by throttle position. The requested ~pt is graphicall~ illustrated in Fig. 19.
The vane actuator control 65 further includes a linear, proportional solenoid ac-tuator 426 operably connected by electrical connector lines 427 to electronic control module 68.

Actuator 426 includes a housing 428 enclosing a coil 430, and a centrally arranged armature which carries therewlth a hydraul:ic directional control valve 432. Valve 432 is normally urged upwardly by spring 434 to the position communicating conduit 394 with return 386. Valve 432 is proportionàlly shiftable do~nwardl~

in response to the magnitude of the energization signal to proportionally increase communication between conduits 372 and 394 while decreasing communication between conduit 394 and drain.
As a result, pressure in conduit 39~ increases proportionately to the magnitude of the electronic signal, such pressure heing essentially zero .in the absence of an energizati.on signal to solenoid 426. It wi].l be noted that minimum pressure in conduit 39~ allows spr.ing.s 383 and 385 to exert maxirnum upward force on valve 380, and that increasillg pressure in conduit 39~ 6hifts piston 392 downwardly to reduce the forcc exerted hy sprincJs 333 r 385 upon valve 380, thus c1evelopilly arl over.ride force in the form of reduced force from spring 383.
In the absence of an elec-tri.cal signal to solenold ~26 minimum pressure ifi exerted on shoulder 393 causing the guide ~anes to be controlled by power turbine speed. Thus, the guide vane~ during start-up are at their Fig. 14 position and at other conditions of engine operation are normally urged to maximum power, Fig. 15 position.

As shown in Pig. 18, vane actuator 66 is operable to vary guide vane angle, B, from O to +20 to alter t~e positive incidence of gas flow upon the pOwer turbine blades and thus alter power transmitted fro~,l the gas ~low to xotate the power turbine wheels in a direction transmitting motive power to the vehicle. The vane actuator 66 is also operable to shift the guide vanes to a negative incidence position and modulate the guide vane position within zone "d" of Fig. 18. In these negative incidence positions, gas flow is directed to oppose and thus tend to decelerate the rotation of the power turbine wheels.
Electronic Control 68 A portion of the control logic of the electronic control module 68 is illustrated in Fig. 17. The electronic control module receives input electrical signals indicative of power turbine speed (Npt) through a chopper 436 secured to power turbine shaft 82 and an appropriate magnetic monopole 438 which transmitsan electronic signal indicative of power turbine speed through lead line 440. Similarly, gas generator speed, Nggl is sensed through a chopper 44Z, monopole 444 and lead lines 446. Trans-ducers 448, 450, and 452 respectively generatc electrical input signals indicative of the respective temperature sensed thereby, i.e. compressor inlct temperature T2, turbine inlet temperature T4, and turbine exhaust temperatuxe T6. As illustrated these temperature signals are transmitted through l.inecs 454, ~56 and 458. The electronic control module also receivec; from an ambient pressure sensor ~60 and assoc;.ated llne ~62 an electrical .
signal indicativc- o~ ambient pressure P2. The electronic control module further receivcs from an appropria-te sens.incJ device an electrical signal through lines 464 indicative of throttle 184 pcsition, "a." ~lso, a switch 466 is manually settable by the vehicle operator when power feedback braking (described more in greater detail below) is desired. A transducer 544 generates a signal to an inverter 546 whenever the variable guide vanes are ~3~79 moved past a predetermined positîon B*.
¦ The electronic control module includes several output signals ! to energize and/or de-energize the various logic solenoids and ' relays including solenoid 518 through line 519, solenoid 257 .5 through line 268, fuel sequencing solenoid 350 through associatedline 351, fuel trim solenoid 239 through line 250, and the vane ~ solenoid 426 through line 427. The electronic control module ¦ includes function generators 514, 550 and 552. Box $14 is denotedas a "flat rating and torque limiting" func-tion and generates a signal indicative of maximum allowable gas generator speed as a function of ambient conditions T2 and P2 and power turbine speed Npt. Element 550 transforms the throttle position signal "a" into an electronic gas generator speed request signal, and function ~ generator 552 produces a signal as a function of gas generator ¦ 15 speed Ngg from line 446. The module further includes comparators 497, 534, 540, 554, 556 as well as the logical elements 498, 500 and 538. The logical elements are of the "lowest wins" type, i.e.
' they pass the algebraically lowest input signal.
The logic element 498 selects rom the signals 536 and 542 which have been generated in comparators 534 and 540 inclicating the amount of over or undertemperature for T~ and 'r6. An additional input Erom 456 is provided to lo~ic elernent 498 so as to provide an indic~ltion of excessive T~ figures in the case o a failed T4 sensor signal. The loqic element 500 receives inputs from 497 and 498. Comparatox 497 compares the electronic ~peed re~quest with the actual yas generator speed ~46 to detcrmine if the engine has been requested to accelerate or is in steady stcl~e. The output of loyic element 500 is fed to inverter 546, generating an appropriate signal in solenoid driver 558 which then moves trim solenoid 426 a distance proportional to the magnitude of signal 427.

~_ 30 -~ ~35~3 The logic element 538 receives its inputs from comparators 554 and 556, logic element 49~ and a differentiator 548. As noted, logical element 498 indica~es the lower of the two temperature errors T~ and T6. The output of comparator 556 is the error between the operator requested power turbine sp~ed Npt and the actual power turbine speed Npt. The output of comparator 554 is indicative o~ the difference between the maxim~n allowable gas generator speed determined by function generator 514 and the actual gas generator speed 446. The logic element 538 selects the algebraically lowest signal and outputs it to solenoid driver 560 with an output on line 250 which is passed on to the governor reset decrease solenoid 239 in the fuel control 60.
As depicted in Fig. 17, the electronic control module includes a comparator 468 and s~nthesizers or function generators

4~0, 472 and 474. Function generator 470 produces an output signal in line 478 indicative of whether the difference between power turbine speed and gas generator speed is less than a preselected maximum such as five percent. Function generator 472 produces a siynal in line ~80 showing whether or not power turb.ine speed i5 greater than gas generator speed, while function generator 47~ gerlerates a signal in lines ~2 showing whether or not gas generator speed is c3reclter tharl ~5 percent of its ma~.irnum speed. The control log:;c further inc:Ludes functiorl yenerator ~6 and 488 which respectively gen~rate siynals in associated l:ine 490 and 492 showing whether or not translnissiorl :input speed i.s above a preselected m.in.imum "e" and whether thxottle position is below a preselected throttle posit.ion a*. Throttle position "a"
is obtained from a suitable pos;.tion sensor such as a variable resistance potentiometer. Thus, output signal 464 is indi.cative of throttle position "a."

- 30~ -~1~35~

The electronic control module further includes the logical gates 502, 504, 506, 508 and 562. Logical AND gate 502 receives inputs from line 478 and ~ND gate 50O to produce an output signal to solenoid driver 516 to activate power feedback clutch 84.
Logical AND gate 506 receive~ its inputs from line 482~ switch 466 and line 492 and produces an input signal to AND gates 502 and 504. Logical AND gate 504 receives an input from line 480 and the inverted input from line 478. Its output generates a 50~O gas generator speed signal and also enables solenoid driver 56~ through OR gate 562 to produce the "a" signal in line 268 which is the result of a constant 50% si.gnal plus the output of element 566.
Signal 26B then activates the governor reset increase solenoid 257 in the fuel control 60. Logical AND gate 508 receives its inputs from lines 490 and 492. Its output signal generates a :15 20% gas generator signal through function generator 568 which, added to the constant 50% signal by su~ner 570 results in a fast idle signal (7.0% gas genercltor speed) to the governor reset increase solenoid 257. The output of AND gate 508 also generates the enable signal to solenoid driver 564.

- 30b --3S7~
Power Feedback Clutch 84 While various forms of clutches could be utilized for power feedback clutch 84, the preferred form shown in Fiq.
3 comprises a "wet" type hydraulically actuated clutch which incluaes a shaft 520 from the gear train ~8 associatea with gas generator shaft 76, and a shaft 522 interconnected with the gear train 80 associated with the power turbine output shaft 82. The clutch operates in a continual bath of lubri-cating cooling fluid. The ges generator shaft 520 drives a plurality of discs 524, which are interposed in discs 526 con-nected to the output shaft 522. The clutch actuator is in a form of a solenoided operated directional hydraulic control valve 518 which, in t:he energized position illustrated, ports pressurized fluid such as from source 362 into a fluid pres-sure chamber 528 to urye piston 530 against the urgings of a xeturn spring 532 to force the plates 524, 526 into inter-engagement such that the power from ~haft 522 may be fed back to s~as generator shaft 520 to assist in braking. When the solenoid actuator 518 is de-energized, the chamber 528 i6 ex-20 hausted to a low pres;ure drain to permit the spring 532 to shift piston 530 away from the position shown and disengaye the plates 524, 526.
OPE ~AT-.tON
Starting -In a conv~antiorlal maTIner start mot:or 72 is electri-cally energized to initiate rotation of ga~; clenerator drive shaft 76 and the input shaft 152 of fuel governor 60~ The control module 68 energizes the normally open fuel sequence solenoid 350, and solenoid 352 is also in an open position to 30 clear fuel line 64 for delivery to the combustor. As neces-sary, an assist pneumatic pump 74 delivers pressurized air into cornbustor 98 along with the action of ignition plugs 100.
Motor 72 is utilized to drive the various components described --~1--~ .t~
until the gas generator ~ection reaches its self-sustaini~g speed, normally in the range of approximately 40% of maximum rated gas generator speed.
During initial rotation and starting of the engine, the low speed of rotation of fuel governor drive shaft 152 cannot overcome the bias of speeder spring 224, and thus fuel lever 226 is disposed away from and clearing orifice 1~8 to permit fuel flow from line 166 to output line 144. Also during this initial starting, the combustor temperature ~T3 5) and combustor pressure (P3 5) are both relatively low such that scheduling valve 62 also permits significant fuel flow through line 64 to the col~ustor.
Low Idle As gas generator shaft 76 speed climbs beyond the self-sustaining speed, start motor 72 is shut off and the combustion process permits self-sustaining operation of the gas generator. Speeder spring 224 is normally set to maintain a low idle value of approximately 50~ of maximum gas generator rated speed. Accordingly, the mechanical flyw~iyht governor operates in opposition to speeder spring 224 to adjust ~uel lever 226 and maintain fue~l flow t:hrough orifice 178 to hold gas genercltor speed at a nomirlal 50% of maximum. This 50% low idl~ speed is eff~ctive whenever ~:>roportional solcnoid 257 i~
in the de-energi.zed state i.llustrated in Fiy. f,.
The electronic control module 68 normally maintai.Jls solenoid 257 in the de-energized state to ~elect the low idle gas generator speed whenever the transmission input shaft speed of shaft 36, as sensed by speed sensor 48, is rotating. Such normally occurs whenever the clutch 34 is engaged with transmis-sion 38~in its neutral position~ or whenever the vehicle ismoving regardless of whether or not the clutch 34 is engaged or disengaged. Accordingly, during idlin~ when not anticipating ac-celeration o~ the engine, the comparator 486 of ~he electronic _3~_ ~ ~3~79 col~trol module 68 not~s that the speed of shaft 36 is ab~ve a pre-determined minimum, "e", such that no signal is trans-m:itied from comparator 486 to AND gate 508. Solenoid 257 remains de-energized, and the gas generator speed is ~ontrol~
led by the governor to approximately 50% its maximum speed, Hi~h Idle Maximum power is normally required to be developed from an en~ine driving a ground vehicle upon initiating acce-leration of the vehicle from a stationary or su~stantially stationary start. As a natural consequence of normal engine operator action upon starting from a stationary start, trans-mission input shaft 36 comes to a zero or very low rotational speed as clutch 34 is disengaged while gear shift lever,46 is articulated to shift the transmission into gear, Once the speed of shaEt 36 drops below a predetermined speed, "e", comparator 486 of the electronic control module generates an output signal to AND gate 508. Since accelerator lever 184 is still at its idle position, the sensor associated with line 464 generates a signal to energize comparator 488 and also send a positive signal to AND gate 508. The output of AND gate 508 energizes function generator 568 to add 20% to the constant idle command of 50%, ~o that ~u~ner 570 provide~ a 70% con~and signal to solenoid driver 564 that has been abled through the output of AND gate 508 and OR yate S6'~. Accordingly, solenoid 257 is energized by an appropriate current signal throu~h line 268 to shift to its Fig. 6C posikion. In this position the solenoid 257 has been sufficiently energizecl to drive shaft 262 and,plunger 272 downwardly as viewed in Fig. 6C and exert a force on fuel lever 226 tending to rotate the latter away froïn and increase the size of orifice 178. The additional force exerted by solenoid 257 is sufficient to incrcase fuel flow through orifice 178 to increase gas generator speed to a pre-determinedhigher level such as 70% of maximum gas generator :~-33-~3~i7~
speed. The flyweight governor operates to hold -the yas gene-rator speed constant at this level.
In this manner, the idle speed of the ~as generator section is reset to a higher value in anticipation of a re-quired accelexation such that more power will be instantly available for accelerating the vehicle. At the same time, when acceleration is not anticipated; ........................

-33a-1~35~3 as determined by whether or not transmissio~ input shaft 36 is rotatinc~ or station~ry, the electronic control module 6~ is operable to de-energize solenoid 257 and reduce gas generator speed to a lower idle value just above that necessary to maintain a self-sustaining operation of the gas generator section. In this manner power necessary for acceleration is available when needed;
however during other idling operations the fuel flow and thus ~uel consumption of the engine is maintained at a substantially lowex value. This is accomplished by producing a signal, minimum speed of shaft 36, which is anticipatory of a later signal (rotation of accelerator lever 184~ requesting significant increase in power transmitted to drive the vehicle.
Acceleration .
Acceleration of the gas turbine engine is manually selected by depressing the accelerator 184. To fuel governor 60 this generates a gas generator section speed error signal in that the depression of lever 184 rotates shaft 192 to increase compression of speeder spring 224 beyond tha-t force being generated by the mechanical flyweight speed sensor. Fuel lever 226 rotates in a 20 direction substantially clearing the openiny 178 to increase fue]
flow to the combustor.
At the same time, depression of throttle lever 184 generates a power turbine section speed error s.ic3nal to vane ackuator control 66. More particularly, depre~s.ion of throttle 18~ compresses sprin~
406 to shi~t valvc ~02 downwardly and .increase the pressurc main-ta.ined in cha~lber 41~ substantially beyond that beincJ g~nerated by the hydraulic speed signal generator of pressure developed by pump 422 and exerted on the other side of the step piston ~16.
Accordingly, lever 396 is rotated generally cloc~wise about its pivot 3~8 in Fiy. 12, allowing downward retraction, if necessary, ; of plunger 395 and reduction of compression on spring 384.

-- 3~ -Summer 497 of the electronic control m~dl~le deter-mines a large disparity between accelerator position and gas generator speed to develop an elec-tronic signal to element 500 overriding other signals thereto and reducing the siynal in line 42~ to zerO to de-erlergize the solenoid 426 of guiae vane control 65. The spring bias urges plunger 430 and valve 432 to the posi~ion shown in Fig. 12 to minimize hydr~ulic pressure developed in conduit 394 and exerted on piston shoul-der 393. As discussecl above in the vane control 66 descrip-10 tion, springs 382-385 position valve 380 to cause following movement of piston 366 to its nominal or "neutral" position.
In this position vane piston 366 and rod 368, the guide vanes 120 are disposed in their Fig. 14 position wherein the gas flow from the combustor is directed onto the power turbine vanes in a manner rninimizing power transfer to the power tur-bine vanes. ~ore particularly, the guide vanes 120 are disposed in their Fig. 14 position to reduce the pressure drop or pres-sure ratio across turbine blade~ ll7 to a minim~n value, this position correspondirlg to the 0 position of Fig. 18.
Since the nozzles 104 maintain the combustor 98 in a choked cond.ition, this reduction in pressure ratio acrc~ss the turbine blades 117 creates a ~;ubstarlti.al increasc i.n pressllre ratio across the radial inflow turbi.ne 102 of the cJas, genera-tor section. Accordin(31y posi.ti.oning of the gui.de vanes in their Fig. 1~ position by allow.iny the springs 382-385 to position valve 3S0 and piston 366 in its "neutral" poSitiQn~
alters the power spli.t between the gas generator turbine 102 and the power turbines 116, 118 such that a preselçcted maxi-mum portion of power from the motive gas flow is transmitted to the gas generator turbine 102. As a result, ~aximum acce-leration of the gas generator section from either its low or high idle setting towarcl-its maximum speed ... .... .......

~35~
is achieved. As noted previously, the requirement fo~ impending acceleration has been sensed, and the engine is normally already at its high idle setting so that gas generator speed promptly nears its maximum value.
As gas generator speed increases, the combustor pressure P3 5 accordingly increases. This causes rotation of the metering valve 282 of the fuel schedule control 62 to increase the amount of overlap between acceleration schedule window 284 and opening 298 in the fuel scheduling valve. Increase in this opening causes a consequent increase in fuel flow to combustor 98 and an ultimate resulting increase in the inlet temperature T3 5 through the actions of recuperator 56.
To the operation of engine 30, increase in T3 5 is in practical effect the same as a further fuel flow increase. Accordingly, in solving the above described equation the windo~ 284 shifts to reduce fuel flow with increasing T3 5 to produce an "effective" fuel flow, i.e. one combining the effects of actual fuel flow and inlet temperature T3.s, at the sensed gauge pressure P3 5 ~o produce a desired combustor exhaust or gas generator turbine inlet temperature T4.
This increase ln fuel 10w created by the rotation of valve 282 and as compensatcd by axial translation of the v~lve provides an "effective" fuel Plow ~hat increases power de~ve10ped and transmitted from the gas 10w to ga5 gerlerat:or turbine 102. ~r)lls then causes another increase in c3as generator speed, and colnbustor pressure P3 S again increases. Scheduling valve thus acts in regenerative fashion to further accelerate the gas generator section.
As noted previously, the scheduling valve is so contoured to satisfy the equation discussed previously and allow continued increase in P3 5 while maintaining combustor outlet temperature T4 at a relatively constant, high value. In this manner the gas generator section is accelerated most rapidly and at maximum efficiency since the turbine inlet temperature T4 is maintained at a high, constant value.

43~
While the accelera-tion window 284 and openi~ 2~0 may be relatively arran~ed and configured to maintain a constant T~
throughout acceleration, a preferred form contemplates maintaining a substantially constant T4 once the power turbine has initia-ted ; rotation, while limiting turbine outlet or recuperat~r inlet temperature during a first part of the acceleration operation. In this manner excessive T6 is avoided when the power turbine section is at or near stall. More specifically, it will be noted that upon starting acceleration of the vehicle, the free power turbine secti.on 54 and its shaft 82 are st.a-tionary or rotating at a very low speed due to the inertia of the vehicle. Thus there is little temperature drop in the gas flow while flowing through the power turbine section, and the recuperator inlet temperature T6 starts approaching the temperature of gas flow exiting the gas generator radial tuxbine 102.

If combustor exhaust or gas generator turbine inlet temperature T4 is maintained at its maximum constant value at this time, it is possible that T6 may become excessively high in instances of high inertial load which lengthens the time of this substantial "stall"
condition on the power turbine sec tion. Of course, as the pow~r turbine sect.ion overcomcs the inertia and reaches higher speeds, temperatu.re drop ac.ross the power turbines increaseC; to ho:Ld down recuperator inlet tempcrature T6.
For such free turbine type ~ngines, rc:lative].y compl.icated : and cxpense controls, electronic and/or mechan:lcal, are normal.:Ly expected in order to avoicl exces~:ive T6 while p.rovid.ing responsive acceleration under the cond:itions in questioIl. ~n i.mportan-t discovery of the present invention, as ~mbodied in schedul.ing valve 62, is in providing an extremely simple, economical, mechanical structure capable of limiting T6 during the critical turbine section stall period but yet still promoting very responsive engine acceleration.

At the same time this improved arrangement has eliminated the need for compensation for substantial variations in ambi.ent pressure and thus the need to compensate for the variations in altitude that would be expected to be enc~untered by a ground vehic1.e.
In this connection it woul.d be expected that absolute combustor pressure P3 5 must be the pararneter in solving the eq~ation described previously such that the scheduling valve could reliably compute the turbine inlet temperature T4 created by a particular combination of combustor pressure, P3 5, and in-let temperature, T3 ~.
However, a discovery of the present invention is 10 that by proper selection of the constants Kl, K2 as embodied in the si.æe and configuration of openinys 284, 290, and by utilization of coJ~bustor gauye pressure rather than combustor absolute pressure~ mechanically simple and economical struc-ture with minimum control complexity can accomplish the desired control of both T6 and T4 durin~ acceleration. Window ~84 and opening 290 are relatively arranyed such that when valve 282 rotates to a minimum P3 5, a slight overlap remains between the window and opening. Thus, a minimum fuel flow, Wf, is maintained at this condition which is a function of T3 5 since 20 valve 282 is still capable of translating axially. This gi~es rise to the thi.rd term, K3T3 5, in the equcltion set forth above and dictates an initial condîtion of fuel flow when window 284 becomes the controlling uel flow parameter upon ~tarting acceleration.
The constants Kl, K2 are chose~n, thei.r ~ct:ual ValllCs beiny determined by the aerodynalnic and thcrmodyn.~nic charac-teristics of the engine, such .that ~t a prese].eeted value, P3 5*, intermediate the maximum and minimum values thereof, the acceleration window controls fuel flow to maintain a con-30 stant T4. At combustor pressures below this preselected value, the acceleration window provides fuel flow allowing T4 to re-duce ~elow the preselected maximum desired level therefor. It has been found that an inherent function of using gauge com-bustor pressure rather than absolute . ~ t 57~
pressure, in combination with these chosen values of ~ K2 and a preselected minimum f~lel flow at minimum P3 5 ~sdetermined by K3 , is that fuel flow is controlled by the acceleration window to prevent recuperator inlet temperature T6 from exceeding a preselec-ted value. This approach still utilizes the simple geometry of window 284 and 290, both rectangles, that mechanically compute the product j of T3 5 multiplied by P3 5. Accordingly, at pressureslower than P3 5*
which are characteristic of the conditions under which the turbine I section "stalling" occurs, the utilization of gauge combustor pressure prevents potentially damaging excessive T6 . The design point for window 284 is, of course, the condition of maximum vehicle inertia experienced on turbine shaft 82, lesser values of such inertia naturally permittincJ more rapid turbine shaft speed increase and less time in the "stalling" condition above described.
~15 From inspec-tion of the equati.on solved by valve 282 it will be ¦ apparent that Euel flow Wf is a linear or straight line function of ¦ P3 5 asshown in Fi.g. 20, with a slope determined by Kl and K2, an t intercept specified by K3, and pasSincJ through the po.int produclng ~ the preselected turbine inlet temperature T4 at the selected 120 intermediate value P3 5*. Of course, a fam.ily o such straight line I curves o~ W~ vs. P3 5 results ~or d:iferent values of T3 5 While, j if desired, curve itting o~ w.indow 2~4 and opening 290 could be utilixed ~o maintain T~ at prec.isely ~he same value at pressures at and above thc preselected interrllecli.ate P3 5*, in the preferred Eorm eompound curva~ure of the window and openi.ncJ is not utilized.
Instead, the winclow and opel-ing are of rectancJular conigurati.on thus permi-tting T~ to increase very slightly at cornbustor pressures above P3 5*. However, it has been found that such arrangement affords an excellent, praetical approximation to the theoretieal.ly desired precisely constant T4 , resulting in practical effect in maintaining a substantially constant T4 at a desired maximum value once combustor gauge pressure exceeds the preselected level P3 5*.

~3~79 ~ccordincJl~, the presen-t invention inherently limits recuperator temperature T6 to solve the probl~n of recuperator overheati.ng when starting to accelerate a high inertial load, yet still maintains a maximum T~ for high engine efficiency throughout the remainder of acceleration oncc the inertia is substantially overcome ancl for the majority of time during acceleration. ~t the same time, and contrary to what might normally be e.xpected, it has been found that the need for altitude compensation is obviated since there exists a minimum fuel flow at minimum co~bustor pressure, which minirnum fuel flow varies linearly with combustor inlet temperature T3 5. Thus the present invention provides a simple mecha~ical solution to the interdependent and complex problems of limitiny two different temperatures T4, T6 for different purposes, i.e. avoidinq recuperakor overheating while affording high engine operating eficiency and thus highly responsive accelerati.on.
: As the yas yenerator cont:inues to accelerate, the fl.yweight governor 208 of the fuel governor 60 begins exerting greater downward force to counte:ract the bias of speeder sprinq 224.
Accordingly, the fuel lever 226 begins rotating in a generally counter~clockwise direction in ~ig. 6 to begin meter:ing fuel flow through opening 178. O11Ce the opening 178 becomes smaller than that afforded by meter:iny window 2~ in schedulding valve 62, the operation of the scheduling valve i~ overr.idden and the fuel governor 60 begins controlliny ~uel flow ko the combustor in a manner ~ri.mmirlcJ gas ~enerator speel to match the speed selected by the .rotatiorl oE th~
sha~t 192 as~oci.at.ecl witl1 thc-~ acce].exation lever 18~ :in the fuel governor 60.
Similarly, this increase in gas generator speed is sensed in the electronic control module 68 by summer 497 such that once :; 30 gas generator speed Ngg approaches that selected by the position of ; the accelerator pedal as sensed electronical.ly through line 46~, the ?. override signal generated by surnmer 497 is cut oEf. In response, ~; elernent 500 is allowed to generate a signal energizing the proportional solenoid 426 of the guide vane control 66. Valve 432 . .

~1~3579 ~sscciated with solenoid 426 is shifted to increase pressure exerted upon piston shoulder 393 to permit the piston 366 and the suide vanes to shift from the Fig. 14 disposition thereof towards the Fig. 15 position. This shifting of the guide vanes from the Fig. 14 to the Fig. 15 position again alters the wor~
split between the gas generator turbine 102 and the power output turbines 116, 118 such that g~eater power is developed across the output turbines and transmitted to output shaft 82 while a lesser portion is transmitted to turbine 102~
Thus it will be apparent that acceleration of the engine and vehicle occurs by first altering the work split so that maximum power is developed acxoss the gas generator turbine 102, then increasing fuel 10w alony a preselected schedule to regenera-tively further increase power developed across the gas generator while main:taining turbine combustor exhaust temperature T4 at a substar;tially constant, preselected maximum. Once substantial acceleration of the gas generator section has been accomplished, the guide vanes are then rotated to alter the power or work split so as to develop a greater pressure ratio across and transmit more power to the power turbines 116, 118 and the power output shaft 82.
Cruise ~ uring normal cruise operation (i.e. traveliny along at a relatively constant speed or power output level) the ~uide vane control 66 acts primarily to al~er the work split bekween the gas generator turbine 102 and the power output turb:ines 11~, 118 so as to maintain a substantially constan~ combustor exhaust temperature T4 . This is accomplished by the electronlc control module which includes a summer 534 developiny an output signal in llne 536 to the logic box 4~8 indicative of the difference between the actual and desired turbine inlet temperature T4. ~lore particularly, solenoid 426, as discussed previously, is maintained normally energized to gene-rate maximum pressure upon the piston shoulder 393 of the guide vaneactuator. For instance, assuming that ~4 is above the preselected .

,357~
desired value thereof, a signal is generated to line 536 and element 498 to reduce the mac~nitude of the electric signal through line 427 to solenoid 426. Accordingly, the spring bias 43-l of the solenoid be~ins urging val~e 432 in a direction reducing fluid communication between conduits 372 and 394 while correspondingly increasing communication between conduit 394 and exhaust conduit 386. The reduction in pressure exerted upon piston 393 accordingly allows spring 385 to increase the spriny bias of spring 383 to cause upward travel of valve 380 and corresponding downward travel of piston 366 to drive the vanes backwards from their Fig. 13 disposi-tion (-~20 position of Fig. 18) toward a wider open position increasing the area ratio and reducing the pressure ratio across the vanes of the turbines 116, 118.
Accordingly, in response to T4 over-temperature, the guide vanes ~5 are slightly opened up to reduce the pressure ratio across the turbines 116, 118. In response the increased pressure ratio across gas generator turbine 102 causes an increase in gas generator speed.
Such increase in gas generator speed is then sensed by the flywe.i~ht governor 208 of the fuel governor 60 to cause counter-clockwise rotation of fuel lever 226 and reduce fuel flow through opening 178.
The reduc-tion in fuel to the combustor 98 accordingl.y reduces the combustor exhaust or turbine inlet tempcrature T4 toward the pre-selected value thereoE. ~hus, ~he guidc vane con~:rol operates to adjust the ~uide vaneC; as necessary and causes a conseq-lent adjust-~5 ment in fuel flow by the fuel governor 60 clue to charlcJc in ya5 generator speed ~gg so as to rnaintain the com~ustor exhauc;t temperature T4 at the precelected, maximurn value. It will be apparent also frorn the forec3Oing that reduction in turbine inlet ~ ternperature T~ below the preselected desired value thereof causes a t'~ o corresponding movement of the guide vanes 120, 122 to increase the pressure ratio across the power turbines 116, 118. Accordingly '~!~, this causes a reduction in pressure ra-tio across gas generator , - ~2 -~ ~35~
turbine 102 to reduce gas generator spee~. In respons~ t:he fue~.
governor shits fuel lever 226 in a clockwise rotation as vie~ed in Fig. 6 to increase fuel flow to the combusto~ and tllus increase turbine inlet temperature T4 back to the desired value. It will be apparent that the change in guide vane position also directly alters the combustor exhaust temperature T4 due to the difference in air flow therefrom; however, the major alteration of combustor exhaust temperature is effected by altering the fuel flow thereto as described above.
0 During the cruise operation therefore, it should now be apparent that fuel governor 60 acts to adjust fuel flow in such a manner as to maintain a gas yenerator speed in relation to the position of the accelerator lever 18~. Clearly, the fuel governor 60 operates i.n conjunction w~th or independently of the vane control 66, dependent only upon the gas generator speed Ngg~
While the electronic control rnodu].e operates the guide vane controJ. solenoid 426 to trim turbine inlet temperature T~ durincJ
cruise, the hydromechanical por-tion of the guicle vane control 66 acts in a more direct feedback loop to trim the speed of power !0 turbine output shaft 82. More particularly, the actual powex turbine speed as sensed by the pressure developed .in line ~20 is continuously compared to the acceleratc)r leve:r position as re1ected by the pressure developed in li.ne ~10. ~ gr,lphical reurc-;en~.at:lon of the action of valve ~02 and piston ~16 in compressincJ qpring 384 and recluestinc3 different desirecl powc~r turbine speeds Npt in relation to the throttle position, a, is shown in Fi~ . Thus, in response to an i.ncrease in speed of power turbi.ne shclft 82 beyond that selected by the rotation of accelerator lever 184, pressure at the lower d.iameter of piston ~16 becomes substantially greater than that on the larger face thereof to rota-te lever 396 so as to increase compression of the biasing spring 384 ac-ting on , .

. - ~3 -

5~7~
valve 380. The resultinc~ up~7ard movement of valve 380 causes a correspondinc~S downt~ard movement of piston 366 and accordingly shifts the guide vanes toward the Fig. 14 position, i.e. opens ~he guide vanes to increase the area ratio and reduce the pressure ratio across the vanes 117, 119 of the two po~er turbine wheels.
This reduces the power transmitted from the gas flow to the power turbine wheel and thus causes a slight decrease in power turbine output shaft speed back to that selected by the accelerator lever 184. It will be apparent that whenever the speed of the power turbine sha~t 82 is belo~i that selected by accelerator lever 184, Z the compression of spring 384 is reduced to tend to increase the pressure ratio across the power turbine vanes 117, 119 to tend to s, increase power turbine speed Npt.
I The portion of vane control 66 for trimming power turbine sl]5 speed in relation to accelerator position is preferably primaril~
digital in action since as shown in Fig. 19, a small change in throttle lever position increases the requested Npt from 25~ to 100%. The actions of valve 402, piston 416 and plunger 395 are I such that when the accelerator is at a position greater than a*, this portion of the control continually requests approximately j 105~ power turbine speed Npt. Through a small amount of rotation of the accelerator below a*, the control provides a request of power turbine speed proportional to the ~ccelerator position.
Positioninc3 of the accelerator to an anglc below this small arc ?5 causes the con~rol to request only approxlmately 25~ of maY.imum P
Thus, in normal cruise thc-~ gui.de vanes control operc-.tes in conjuncticn with the fue]. governor to maintain a substarltially constant turbine exhaust ternperature T4; fuel governor 60 operates to trim gas generator speed N~c~ to a value selected by the accelerator - 4~ -35~
lever 18~; and the hydromechanical portion of guide ~iane 66 operates to trim power turhine outpt speed Npt to a ].evel i.n relation to the position of accelerator pedal 184. It will further be apparent that durin~ the cruise mode of operation, the orifice created at opening 178 of the fuel governor is substantially smaller than the openings to fuel flow provided in the scheduling valve 62 so that the scheduling valve 62 normally does not enter into the control of the engine in this phase.
Safety Override During the cruise or other operating modes of the engine discussed herein, several safety overrides are continually opera~le.
For instance solenoid 239 of the uel governor 60 operates to essentially reduce or counteract the effect of speeder spring 22~
and cause a consequent reduction in fuel flow from orifice 178 by exerting a force on fuel lever 22F, tend.ing to rotate the latter in a counter-clockwise direction in Fig. 6. As illustrated in Fig. 17, the electronic control module includes a logic element 538 which is , responsive to power turbine speed Npt, gas qenerator speed N~g/
turbine inlet temperature T4, and ~urbine exhaust or recuperator inlet temperature T6. Thus if turbine lnle~ tempera-ture T~ exceeds the preselected maxim~n, a proportional electrical .s.ignal is trans-mitted to lines 250 to energize solenold 239 and reduce fuel flow ', to the engine. Similarly, excessive turbine exhaust temperature T6 results in proportionately energizinc3 'the solenoid 239 to reduce fuel flow to the combustor and thus ultimately reduce turbine exhaust temperature T6. Also, logic element ~38 is responsive to '; power turbine speed so as to proportionately energize solenoid 239 whenever power turbine speed exceeds a preselected maximum. Simi-larly, the electronic control module opera-tes to energiæe solenoid 239 whenever gas generator speed exceeds a preselected maximum ; established by function generator 514 as a function of P2, T2 and Npt.
Normally the preselected max,imum parameter values discussed with regard to these safety override operations, are slightly above the - ~5 -normal operating values of the parameters so that the solenoid 239 is normally inoperable except in inst~nces of one of these parameters substantially exceeding the desired value thereof.
Thus, for instance, during a cruise mode of operation or "coasting"
when the vehicle is traveling do~mhill being dei~en to a certain extent by its own inertia, the solenoid 239 is operable in response to increase of power turbine output shaft 82 beyond that desired to cut back on fuel flow to the combustor to tend to control the po~ler turbine-output speed, While as discussed previously with regard to the cruise operation of the vehicle, the guide vane control normally is responsive to combustor exhaust temperature T4 as reflected in the signal generator by element 435, the logic element 498 is also responsive to the turbine exhaust temperature T6 in comparison to a preselected maximum thereof as determined by summer 540 which generates a signal through line 542 to element 498 whenever turbine exhaust temperature T6 exceeds the preselected maximum.
Logic element 498 is responsive to signal from either line 542 or 536 to reduce the magnitude of the electronic signal supplied throuyh line 427 to solenoid 426 and thus reduce the pressure ratio across the turbine wheels 116, 118. ~s discussed previously, this change in pressure ratio tendr; to increase gas genercltor speed and in response the Euel governor 60 redtlces uel flow to the combustor so that turbine exhaust temperature T6 is pxcvented from increasing beyond a preselected maximum limi~.
As desired, the solenoid 23~ may be ener~izcd in response to other override parameters, For instance, to protect the recupexator 56 from excessive thermal stresses, thc logic element 538 may incorporate a differentiator 548 associatcd with thc signal from the turbine exhaust temperature T6 so as to generate a signal indicative of rate of change of turbine e~haust temperature T6.

- ~6 -,3579 Loc3ic element 538 can thus cJenerate a signal energ;~inc~ solenoid 239 whenever the rate of change of turbine exhaust temperature T6 e~cceeds a preselected maximum. In this manner solenoid 239 can control maximum rate of change of temperature in the recuperator ancd thus the thermal stress imposed thereon. Similarly, ti-e logic element 538 may operate to limit maximum horsepower developed across the power turbine and/or gas yenerator shafts.
Gear Shift Because turbine engine 30 is of the free turbine type with a power output shaft 82 not physically connecked to the gas yenerator shaft 76, the power turbine shaft 82 would normally tend to greatly ; overspeed during a gear shifting operation wherein upon disengage-ment of the drive clutch 34 to permit gear shifting in box 38, substantially all i.nertial retard.ing loads are removed from the power turbine drive shaft 82 and associated power shaft 32. of course, during normal rnanual operation upon gear shiftiny, the accelerator levex 184 is released so that the fuel governor 60 ; immed:iately begins substantially reducing fuel flow to combustor 98. Yet becau~e of the hic3h rotati.onal inertia of the power turbine shaft ~2 as wel]. as thc- hi~h volumetric gas flow thereacross from the combustor, the power turbine shclft would stlll terld to over speed.
Accordingly, the control ~y;tem as contelnplclt~d by the present in~en-tion ut.i]..iz.es th~ yu:idc! vane actuator control 66 to shift the gui~ vanes 120, 122 toward their F:icJ. 16 "reveLc:e" position such that the gas 10w from tl~e eng.ine impin~e; oppos.itely on the vanes 117, 119 of the power turbine wheels in a manner opposing rotation of these power turbine wheels. Thus the gas flow from the engine is used to decelerate, rather than power, the tur~ine shaft 82.
As a result, the power turbine shaft tends to reduce in speed -to the point where synchronous shifting of gear box 38 and consequent . - ~7 -~ ~3S~9 re-engagement of drive clutch 36 may be conveniently ~nd speedil~
accomplished without damage to the engine or drive train.
~ore particularly the hydromechanical nortion of guide -~ane control 66 is so arranged that upon release of accelerator lever S 184 such as during gear shifting a very large error signal is created by the high pressure from the po~er turbine speed sensor line 420 to rotate lever 396 counter-clockwise and substantially greatly increase the compression of spring 384. Sufficient compression of spring 384 results to urge valve 380 upwardly and drive piston 366 downwardly to its position illustrated in Fig. 12.
This position of piston 366 corresponds to position.ing the guide vanes 120 122 in their Fig. 16 disposition. The gas flow from the combustor is then directed by the guidc vane across the t~lrbine wheel vanes 117 119 in opposition to the rotation thereof to dec~lerate the power turbine shaft 82. Since the drive clutch 34 is disengaged during this year shifting operation the power turbine shaft 82 rather rapid-ly decelerates by virtue of the opposing gas flow created by the positioning of guide vanes 120 in their Fig. 16 position. Yet more specifically the arrangement of springs 406 ~08 and the relative magnLtude of pressure developed in condui.t ~10 and 420 cau~es the hydromechanical portion of vane actuator control 66 to operate in the manrler ~bove describecl to shift the guide vanes 120 to their nec3ative or rcverse disE)osition ill-lstrated in Fig. 16 and modulatc yuide vane position withirl ~one d o Fig. 18 in relation to the m~(3ni-tude o~ Npt excess whenever the accelerator lever 18~ i~ movcd to less than a preselected accelerator lever position a*. ~s the speed oE power turbine shaft 82 reduces the piston 416 beyins shift.ing in an opposite direction to reduce compression of spriny 38~ once turbine speed reduces to a preselec-ted value. The action of piston 416 is in the preferred form capable of modulating the degree of compression of spring 384 in relation to the magnitude of the Npt error. The greater the speed _ 48 -~357~

error, the more the guide vanes are rotated to a "harcler"
braking position. Thus, the positionof the guide vanes are maintained in a reverse braking mode and are modulated through zone "d" near the maximum braking position -9S of Fig. 1~ in relation to the power turbine speed error. Once gear shifting is completed, of course, the control system operates through the acceleration operation discussed previously to again increase power turbine speed.
Deceleration A first mode of deceleration of the gas turbine engine is aecomplished by reduction in fuel flow along the deeeleration sehedule afEorded by deceleration window 286 of scheduling valve 62. More particularly, the release of accelerator lever 184 causes the fuel governor 60 to severely restrict fuel flow through opening 17~. As a consequence the minimum fuel flow to the gas turbine engine is provided throuc~h deceleration fuel line 142 and the associated deceleration window ~6 of the scheduling valve. As noted previously deceleration window 286 is particularly eonfigured to the gas tuxbine engine so as to continually reduce fuel,flow along a,sche~ule which maintains combustion in the eombustor 98, i.e., substantially alonc~ the oper~ting line of the gas turbin~ encJine to maintain eombustion but below the "re~uired to run line." A., noted previously, even without rotation of accelerator l~v~r 18~, the solcIIoicl 239 ean be enercJized in partieular instanees to cJener~te a false accelerator lever signal to fuel lever 226 to aecomplish deceleration by severely r~strictincJ
fuel flow.
This deceleration by limitincJ fuel flow is accomplished by reducin~ the accelerator lever to a position at or just above a preselec-ted aecelerator position, a*. This accelerator position is normally just slicjhtly above the minimum accelerator p~sition, _ ~9 _ ~3579 a~l g^nerally cc-respor.ds to the position of the accelerator lever during the "coasting" condition wherein the engine i5 somewhat driven by the inertia of the vehicle such as when coasting downhill. Since this deceleration by restricting fuel flow is acting onl~ through governor 60, it will be apparent that the guide vane control is unaffectred thereby and continues operating in the modes and conditions discussed previ~usly. This is particularly true since the accelerator has been brought down to, but not below the preselected acce-lerator position a* to which the hydromechanical portion ofvane actuator 66 is responsive.
~ pon further rotatiny accelerator lever 184 below the position a* and towards it minimum position, a second mode ; of decelerativn or braking of the vehicle occurs. In this mode, the movement of the accelerator lever below the position a* causes the hydromechanical portion of guide vane actuator 66 to generate a suhstantially large error signal with regard to power turbine speed so as to rotate the guide vanes 120 to their Fig. 16 reverse or "brakiny" position. More particular-ly, as discussed above with regard to the gear shift operation of the vehicle, this large error signal of the power turbine speed in compariæon to the accelerator lever position causes significant counter-clockwise rotation of lever 3~6 and conse-quent compression of spring 38~. Thi~ drives the piston 366 and the guide vanes toward the Fig~ 16 position thereof. ~s a result, the cyas flow from the gas turb;ne enyine oppose~
rotation of the turbine wheels 116, 118 and produces substan-tial tendency for deceleration of output shaft 82. It has been found that for a gas turbine engine in the 450 to 600 horsepower class, that this reversiny of the guide vanes in combination with minimum fuel flow to the combustor as permit-ted by deceleration window 286 provides on the order of 200 or more horsepower braking onto the turbine output shaft B2.

It will be noted that during this second mode of deceleration, as well as during the gear shift operation dis-cussed previously that since the guide vanes are now in a reversed disposition; the ]ogic accomplished by the electronic control module 68 in controlling solenoid 426 to prevent over ternperature of T4 or T6 is n~w opposite to that r~quired.
Accordingly, the electronic control logic further includes a transducer 544 which senses whenever the guide vanes pâSS o~ver centre as noted by the predetennined angle B* of Fig. 18, and are in a negative incidence disposition. This signal generlted by transducer 544 energizes a reversing device such as an in-; verter 546 which reverses the signal to the solenoid 426. More pa~ticularly, if ~luriny this deceleration operation with the guide vanes in the negative incidence position of Fig. 16, there occurs an excess combustor exhaust temperature T4 or ex-cess turbine exhaust temperature T6, the signal generated by element 500 to reduce the magnitude of the current ~ignal is reversed by element 546. Accordingly occurrence high T4 or high T6 while element 5~6 is eneryized generates an electrical signal of increasing strength to solenoid 426. Ln response, the solenoid 4~6 drives valve 432 in a direction increasing pressure in conduit 394 and upon shoulder 393; rrhis reduces the magrlitude of the biasinc3 sprirly 383 and causcs valvç 3~0 to move downwarclly. ~n a followin~J movement the pi~ton 366 moves upwardly to reduce the c:ompression of spring 3~2. Thus the yuide vanes 120 are rever;ely t:rilMned away ~rolu the maximum braking position shown in Fig. 16 back towards the neutral position of Fig. 14. This movement of course reduces the ma~-nitude of power transrnitted from the gas flow in opposing rota-tion of the guide vanes 117 to cause a consequent reduction infuel flow as discussed previously. The reduced fuel flow then reduces the magnitude of the over temperature parameter T~ or T6. Such action to control T4 or T6 will ........ ~

35'7~

substantially only occur when ~uel flow being delivered to the combustor is more than permitted by the deceleration schedule ~86.
Thus such action is more likely to occur during the "coasting"
operation than during hard br~king during the second mode o~
deceleration. Such is natural with operation of the engine, ho~.ever, since durlng hard deceleration, fuel flow to the combustor is at a minimum and combustor exhaust temperature is relatively low. However, during unusual conditions, and even with the guide vanes in a negative incidence position, the electronic control module is still operable to return the guide vanes toward their neutral position to tend to reduce any over temperature conditions.
Power Feedback B a ~
A third mode of deceleration of the vehicle can be manually selected by the operator. Such will norrnally occur when, after initiation of the first two modes of decelera-tion described above, the vehicle still is being driven by its own inertia at too high a speed, i~e. power turbine shaft 82 speed Npt is still -too hiyh.
Thus power turbine ~haEt speed Npt may be in a ranye of approxi-mately 90~ of its maximum speed while the gas generator speed N~g has been brought down to at or neclr its low idle speed of approxi-mately S0~ maximum gas generator spced.
This third mode of deceler-ltiorl, ternled ~owe~ feedhack braking, i5 manual.ly selccted by closing power feedback swi.tch ~G6.
In response the electronic control module. 68 gellerates signals whi~h ultimately reslllt in mechanical intercollnection o the c3as generator sh~Et ~ith the power turhine shaft such that the inertia of the gas generator shaft is imposed upon the drive train oE the vehicle to produce additional braking ef~ects thereon. More particularly, upon closing switch 466, AND gate 506 generates a signal to AND gate 504 since the accelerator level is below a ~ ~3 :i7~
~-^se'cc'cd point a* ^ausing ~unc-~ic~n ~c~nerato~ A ~8 to ycnelat2 a signal to ~ND gate 506, and since the gas generator is opera~
ting at a speed above 45~ of its ra-ted value as deterrnined by element 474. Element 472 develops a signal through line 480 to AND gate 504 since power turbine speed is greater than gas gen~rator speed in this operational mode. Eleme~t 470 also notes that the effective relative speeds of the gas generator shaft_and power turbine shaft are outside a preselected limit, such as the plus or minus 5% noted at cornparator ~70. Accor-dingly element 470 does not yenerate a signal to AND gates 502, 504. More specifically the element 470 is not necessarily com-paring the actual relative speeds of the gas yene~ator power turbine shafts. Rather, the element is so arranged that it only yenerates a signal to ~ND gates 502, 504 whenever the relative speeds of the shafts 520, 522 in the power feedback clutch 84 are within the preselected predeterlnined limits of one another. Thus the comparator 468 will compensate, as re-quired, for differences in the actual speeds of the gas c3eIlera-tor and power turbine shaft, as well as the gec-~r ratios of the two respective drive trains 7~ and 80 associated with the two shafts 502~52~ of the feedback clutch 8q~
Beause of the dif~rerlce between Npt ancl N~3cJ~ no sic3nal frorn element 470 is ~raIlcmitted to either ~ND g~te~ 5t)2 or 504~ As noted schematically b.y the circle ac;c;ocic~ted with the input from elcment 470 to ~N~ gat~ 504, that inpllt i5 :in-verted and ~ND gate 50~ is now e~fective to generatc an OlltpUt signal since rlo signal is comlng from el~ment ~70, and since signals are being received from AND gate 506 and element 472.
The output signal from AN~ gate 504 accomplishes two unctions.
First, a signal of 50% Ngg magnitude is generated in function generator 566 and added to the constant 50% bias signal of sum-mer 570. The resulting signal is equivalent to a 100% ~gg speed command. Secondly, the output frclm AND gate 504 passes throucgh OR gate 562 to produce a signal to solenoid 257. This siynal is of sufficient magnitude to shi~t 3~7~
solenoid 257 to its Fig. 6D position cleariny opening 178 for substantial fuel flow to the combustor. It will be apparent that full ener~ization of solenoid 257 to its Fig. 6D position is essentially a false accelerator lever sign~l to the ~uel lever ~2G
causing lever 226 to rotate to a position normally caused by depressing accelerating lever 1~4 to its maximum flow position.
Secondly, the signal from summer 570 is also an input to element 497 such that an artificial full throttle si~nal is generated which overrides the energization signal which is maintaining the guide vanes in their Fig. 16 braking position during the I second mode of deceleration discussed previously. The energiza-, tion o the guide vane solenoid 426 causes increase of pressure j in conduit 394 allowing the springs 382-385 to shift the piston ~ 366 and the associated guide vanes toward their Fig. 14 "neutral"
¦15 position.
Accordingly, it will be seen that the sic~nal from AND gate ~ 504 produces an acceleration signal to the engine, placing the l~ cJuide vanes 120, 122 in their neutral position such that maximum pressure ratio is developed across the cJas yencrator tur~ine 102, ~20 and at the same ti.me ~uel fl.ow to the combustor 98 ha~ heen greatly increased. In responC;e~ the gas ~enerator section bec~ins incr~asing in speed rapidly toward a value such that the speed of shaft 522 of the feedback clutch approaches the~ spced of its other shait 520.
Once the power twrbine and gas ~enerator sha~-t speeds are ~25 ap~ropriately matched such that the two sha~-tc; 520, 522 oE the feedback clutch are within the pre~electcd limits dctermined by element 470 of the electronic control module, electronic control module develops a positive signal to both AND cJates 502, 504.
This positive signal immediately stops the output signal from AND
gate 504 to de-energize the proportional solenoid 257 of the fuel c~overnor and again reduce fuel Elow back toward a minimum value, and at the same time stops the overri.de signal to element 500 .

such that the c~uide vane 120, 122 are again shifted back to their Fi~. 16 bra~in~ disposition in accord with the operation discussed above with respec-t with the second mode of deceleration.
The logic element AND gate 502 now develops a positive output signal to operate to driver 516 and energize clutch actuator solenoid valve 518. In response the clutch 34 beco~es engaged to mechanically interloc~ the shafts 520 and 522 as ~ell as the gas generator and power turbine shafts 76, 82. Incorporation of the logic element 470 in the electronic control module, in addition to the other functions described previously, also assures that since the two shafts 520, 522 are in near synchronous speed, relatively small torque miss-mateh across the plates 524, 526 of I the elutch is experienced. Aecordingly, the size of clutch 8~ can be relatively small. Thus it will ~e seen that the electronic eontrol module 68 operates automatically first to increase gas - generator speed to essentially mateh power turbine speed, and then to automatically return the guide vanes to their Fig. 16 braking disposition at the sc~ne time as cluteh 84 is enyayed.
This interconnection of the CJas turbine enyine drive train .20 with the gas genera-tor ~haft 76 eauses the rotational iner-tia of yas generator 76 to ass.ist i.n dec~leratincJ the vellic].e. It ha~
been found that ~or a 450 to 600 horsepower class cr-cJine described, this power feedback braki.ng mode addc; in th~ nc1.c~llborhood oE 200 to 250 horsepower bxaki.ng .in additiorl to thc 200 hor.c;epower braking effects produeed by the position~ g of gllide vane 120, 122 in their Fi.g~ 16 position. Because thc' fuc'l CJOVerrlOr iS
again severely restrictiJIcJ flow throucJh orifi.ec 178, the fuel flow is eontrolled by deceleration window 286 permittincJ the yas yenerator section to decelerate while maintaining the combustion s~9 process in combustor 98. Thus reduction of fuel flow provides the decelera-tion effect of the rotational inertia of the yas generator upon the drive train of the vehicle.
It will be apparent from the foregoing that the present invention provides substantial braking for deceleration purposes while still utilizing the optimum operating characteristics of a free turbine type of a gas turbine engine with the yas genera-tor section mechanically interconnected with the power turbine section ' only in a specific instance of a manually selected "severe" thi~d mode type oE deceleration operation. Throughout all deceleration modes and engine operation, a continuous combustion process is , maintained in the combustor. Thus substantial deceleration occurs without exti.nyuishing the combustion process therein.
I This power feedback braking operation can be deactivated in several ways: manually by openiny switch 466 to stop the output signal from AND gate 506;providing a NOT siynal to turn o~f driver 516 and solenoid 51~ to disenyage clutch 8~. Furthermore, i the manual switch is not opened and the engine continues -to decelerate, elem~nt 47~ also opera-tes to deactivat~ the power feedback operation whene,ver gas generator speed NCJcJ reduces to a value below 45% o~ its mE~ximum rate o~ speed. Also, deE)resslon o~' the accelerator to a value o~ a}-~ove a* also declctivates the power feedback operation by ~3~0pp:in~J an outE~ut s:ignal frorn AND
gate 506.
From the foregoing it wi;ll now he apparent that the present invention provides an improved cycle of ope~ratiorl for a gas turbine engine peculiarly adapted for operating a ground vehicle in a safe, familiar manner while still retaining the inherent beneEits of a gas turbine engine. More speciCically~ by utilization of a free turbine type engine yreater adaptability and variability o~
engine operation is provided. ~t the same time the engine can operate ~357~
throuc3hoUt its entire operatinCJ cycle while maintainirly a continuous combustion process within the combustor 98. Tllis avoids various problems of operation and service life associated with repeal:ed start and stop o~ the cc,mbustion prGcess. The novel cycle contemplates a utilization of a combustor 98 having choked nozzles 102 to provide a variable pressure within the combustor as the speed of the gas generator section varies. Gas generator section speed is normally trimmed to a preselected value relative to the position of the accelerator lever 184, while the guide vanes 120, 122 operate to trim the turbine inlet temperature T4 to a preselected substantially constant value to maintain hic3h engine operational efficiency. Further, the guide vane control operates indirectly to alter the fuel f]ow through fuel governor 60 by altering the speed of the gas generator section such that L5 the various controls are operable in an integral manner without counteracting one another. ~t the same time a trim of power turbine shaft speed Npt is provided by the guide vane control 66.
Furthermore it will be seen that the present invention provides the gas turbine engine peculiarly adapted for drivinc3 a ~round vehicle in that responsive acceleration similar to that produced by an internal combustion enginc is prov:ided by both the automatic high idle operation as well as by the manner of accelerat:ion of the gas turbine engine. Such is accolllplished by first: alter:in~
the work split to develop maximum power to the CJaS yCnercltOr ~5 section. The scheduling valve con~rol 62 therl acts in rec3enercltive fash:ion to incre~C;e fuel ~low to the combustor in such a manner that gas generator sE)eed is incre~ascd whlle mailltLIin.illcJ a substan-tially congtant maximum turbine :inlet temperature T~ thereby produ~
cing maximum acceleration without overheating the engine. Yet the scheduling valve also limits T~ durinc3 the initial por-tion of acceleration when turbine "stalling" conditions are prevalent.
~ccelera-tion is therl completed once substantial acceleration of s7g t~e gas generator section i5 accomplished, by re-alteriny the power split to d~velop greater power ~cross the po~er turbine wheels 116, 118.
It is further noted that the present invention pro~Jides an improved method and apparatus for decelerating the vehicle in a three stage type of operation by first reducing fuel flow, then by placing the guide vanes in the braking mode, and ~hen by manually selecting the power feedback operation.
The primary operating elements of the fuel governor 60, scheduling valve 62, and guide vane control 66 are hydromechanical in nature. This, in conjunction with the operation of solenoid ~26 of the guide vane control which is normally ~nergized, provides an engine and control system peculiarly adapted to prov.ide safe engine operation in the event of various failure modes. More particularly, in the event of complete loss of electrical power to the electronic control module 68, the mechanical portion of ~uel governor 60 continues to adjust fuel flow in relation to that selected by accelerator lever 184.
Scheduling valve 62 is in no way affected by such electrical failure and is capable of controlling acceleration and/or deceleration to both prevent over heating oE the encJine durlng acceleration as well clS to rna:intain combustion during deceleration.
The hydromechanical port:ion of the vane ~ctuator control will still b~ operable in the evcnt of olectr,ical failure and c~pable of adju~ting the cJuicle vanes c15 appropriate to maintain funct.ional cngine op~r~tlon. Upon electrical failure thc ~olenoid ~26 of the guide vane control becomes dc-energized causinc3 1055 of pressure upon face 393 of the control piston 392. Ilowever, the speed control afforded by lever 396 is still maintained and the quide vanes can be appropriately positioned to maintain functional engine operation during this failure of the electrical system. Thus, while certain desirable features of the engine control will be lost in the event of e].ectrical failure, the engine can still function properly with 3~9 ; ' appropriate acceleration and deceleration so that the vehicle m~y still be operated in a safe manner even though ~t a possible loss of operational efficiency and loss of the ability to provide power feedback braking.
From the foxegoing it will be apparent that the presellt , invention provides an improved method of automatically setting and resetting the idle of the gas generator section so that the ' engine is highly responsive in developing an increase in output power such as when contemplatinc3 acceleration of the vehicle.
Further the present invention pxovides an improved method of controlli.ng fuel flow hydromechanically in relation to gas genera~ox speed, as well as overriding normal speed control operation of the fuel governor to increase or decrease fuel flow in response to occurrence of various conditions which energize either of the solenoids 239, 257. Further the present invent:i,on provi.des an improved method for controlling fuel flow to the combustor durinc3 acceleration such that constant turbine inlet temperature T4 is maintained throughout, while also controllinc3 fuel flow during deceleration to avoid extinguishiny the combust.ion process within a combustor. The invention further contemplates an improved ~nethod of con~rollincJ c3uide vane position in such an engine both by hydxomechani.cal operation to corltrc)l ~peed of a rotor such a5 tu.rbine wheels 11.6, 118, and by electrical. overricie oper~tion depen~ent upon thc~ amount of enerc3ization o~ t:he~
proportional ~olenoi.d ~26.
The fo.recJoiny has clescribed a preferxed cmbod:iment of th~
invent,ion in sufficient detail that those skillecl in -the art may make and use it. However, this detailed description should be considered exemplary in nature and not as limitincJ to the scope and spirit of the present invention as set forth in the appended '~ claims.

" .

3S~3 E~avin~ described the invention with sufficient clarity tha~:
those skilled in the art may make and use it, what is claimed as ne~ and desired to ~e secured by LetteFs Patent is:

- 60 - .

Claims (19)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A gas turbine engine fuel control system comprising:
a housing having an inlet for receiving pressurized fuel flow and an outlet for delivering fuel flow to the engine;
a fuel lever pivotally mounted to said housing with first and second arms extending oppositely from the pivot point, said first arm movable toward and away from an opening carrying said fuel flow to define a variable orifice for variably metering fuel flow to said outlet;
means for continuously sensing a preselected parameter of engine operation and exerting a first force on said lever in relation to the value of said sensed parameter;
throttle means for continuously exerting a variable second force on said lever opposing said first force, said second force being indicative of a desired value for said preselected parameter;
means for selectively exerting a third force on said lever opposing said second force upon occurrence of one preselected condition of engine operation; and means for selectively exerting a fourth force on said lever upon occurrence of another preselected condition of engine operation, said lever operable to mechanically sum said first through fourth forces.

2. A fuel control system as set forth in Claim 1, wherein said first and second forces are exerted in opposing relation on one of said first and second arms, said third and fourth forces being exerted in opposing relation on the other of said first and second arms.

3. A fuel control system as set forth in Claim 2, wherein said first and second forces act upon said second arm, and said third and fourth forces act upon said first arm.

4. A fuel governor for controlling fuel flow to a gas generator section of a free turbine type gas turbine engine having a power output section rotatable independently of a drive shaft of the gas turbine section, said governor comprising:
a housing having an inlet port adapted to be connected to a fuel source, an outlet port for delivering fuel flow to said gas generator section, and an internal passage received pressurized fuel flow from said inlet port and terminating in an opening through which metered fuel flow is delivered to said outlet port;
a governor shaft journalled to said housing and operably connected to be driven by said gas generator section shaft;
a lever pivotally mounted to said housing having first and second arms extending oppositely from the pivot point, said first arm movable toward and away from said opening upon lever pivoting to variably meter fuel flow to said outlet port;
a speed sensor operably associated with said governor shaft and said second arm for exerting a first force on said lever in relation to the speed of said gas generator shaft, said first force acting in a direction tending to reduce fuel flow;
resilient biasing means exerting a second force on said second arm opposing said first force;
an electronic control generating electrical command signals;
a first solenoid mounted to said housing on one side of said first arm and energized in response to a first command signal from said electronic control, said first solenoid having a plunger shiftable into engagement with said one side of the first arm to exert a third force on said lever opposing said second force in response to said first command signal; and a second solenoid mounted to said housing on an opposite side of said first arm and energized in response to a second command signal from said electronic control, said second solenoid having an associated plunger shiftable into engagement with said opposite side of the first arm to exert a fourth force on said lever opposing said first force in response to said second command signal.

5. A fuel governor as set forth in Claim 5, wherein said second solenoid includes a biasing member to engage the associated plunger upon movement thereof in response to said second command signal to resist further movement of the plunger.

6. A fuel governor as set forth in Claim 5, wherein said electronic control is operable to generate a third command signal greater in strength than said second command signal and sufficient to overcome said biasing member and produce further movement of the associated plunger and a greater magnitude fourth force on said lever.

7. A fuel governor as set forth in Claim 3, further including a throttle and cam means extending between said throttle and said resilient biasing means whereby the magnitude of said second force is varied in relation to the position of said throttle.

8. A fuel control system as set forth in Claim 1, further including means responsive to fuel pressure upstream and downstream of said orifice for altering the rate of fuel flow to said orifice to maintain a substantially constant pressure differential thereacross.

9. A fuel control system as set forth in Claim 1, wherein said preselected parameter is engine speed.

10. A fuel control system as set forth in Claim 1, wherein said engine includes independently rotatable gas generator and power turbine sections, said preselected parameter being the speed of said gas generator section.

11. A fuel control system, as set forth in Claim 9, wherein said means for sensing said preselected parameter comprises a mechanical flyweight speed sensor developing said first force with a magnitude proportional to said engine speed.

12. A fuel control system as set forth in Claim 10, wherein said throttle means includes a manually positionable throttle lever, a compression speeder spring operably extending between said throttle lever and said adjustable element to exert said second force, movement of said throttle lever varying compression of said speeder spring to select said desired value of said gas generator speed, whereby said adjust-able element in response to said first and second forces varies said orifice to maintain gas generator section speed at said desired value.

13. A fuel control system as set forth in Claim 12, further including an electronic control developing a first electrical signal upon occurrence of said one condition of engine operation, said means exerting said third force comprising a first electromechanical transducer operable when energized by said first electrical signal to exert said third mechanical force on said adjustable element whereby fuel flow is altered to reset said gas generator section speed to a value lower than said desired value selected by throttle lever position.

14. A fuel control system as set forth in Claim 13, wherein said electronic control develops a second electrical signal upon occurrence of said another condition of engine operation, said means exerting said fourth force comprising a second electromechanical transducer operable when energized by said second electrical signal to exert said fourth mechanical force on said adjustable element whereby fuel flow is altered to change said gas generator speed to a value higher than said desired value selected by throttle lever position.

15. A fuel control system as set forth in Claim 14, wherein said first and second electromechanical transducers are first and second solenoids having associated plungers shift table to engage and exert said third and fourth forces on said adjustable element.

16. A fuel control system as set forth in Claim 15, wherein said first solenoid is a proportional solenoid whereby the magnitude of said third force varies with the strength of said first electrical signal.

17. A fuel control system as set forth in Claim 15, wherein said second solenoid includes a biasing member engaging and opposing movement of the associated plunger when said second solenoid is energized by said second electrical signal.

18. A fuel control system as set forth in claim 17, wherein said electronic control develops a third electrical signal upon occurrence of a third preselected condition of engine operation to increase the magnitude of said fourth force to overcome said biasing member of the second solenoid and further move the associated plunger to change said gas generator speed to a preselected maximum value regardless of throttle lever position.

19. A gas turbine engine fuel control system comprising:
a pivotal fuel lever having first and second arms extending oppositely from the pivot point thereof, said first arm movable toward and away from an opening carrying said fuel flow to define a variable orifice for variably metering fuel flow to said engine;
means for sensing a preselected parameter of engine operation and exerting a first force on said lever in relation to the value of said sensed parameter;
means for exerting a second force on said lever opposing said first force, said second force being indicative of a desired value for said preselected parameter;
means for exerting a third force on said lever opposing said second force upon occurrence of one preselected condition of engine operation; and means for exerting a fourth force on said element upon occurrence of another preselected condition of engine operation, said lever operable to mechanically sum said first through fourth forces.