US3389640A - Hydraulic control mechanism having viscosity independent restoring mechanism - Google Patents

Description

June 25, 1968 s. G. BEST ETAL HYDRAULIC CONTROL MECHANISM HAVING VISCOSIT INDEPENDENT RESTORING MECHANISM Filed Aug. 3l, 1966 United States Patent O "ice 3,389,640 HYDRAULIC CONTROL MECHANISM HAV- ING VISCOSITY INDEPENDENT RESTOR- ING MECHANISM Stanley G. Best, Manchester, Kermit I. Hamer, Windsor, and Donald P. Ramaker, Glastonbury, Conn., assignors to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Aug. 31, 1966, Ser. No. 576,299 7 Claims. (Cl. 91-366) ABSTRACT OF THE DISCLQSURE A hydraulic ilyball governor for propeller pitch changing mechanism having a hydraulic feed back from the pitch changing mechanism which changes the pressure on one side of the governor pilot valve to restore the valve to a null position by opposing the governor action. A by-pass passage across the pilot valve gradually restores the equal pressure on opposite Sides of the pilot valve. A chopper valve in the by-pass passage is opened periodically for a time less than that required for the fluid to attain terminal 'velocity in the passage so that the restoring rate is independent of viscosity variation of the hydraulic fluid.

This invention relates to hydraulic control mechanism having viscosity independent restoring mechanism and particularly to control mechanism incorporating a stabilizing system.

An object of this invention is a governing System with improved compensation.

A further object iS a speed governing system utilizing the effect of fluid inertia to provide stability over a Wide range of fluid viscosities.

Other and additional objects will be apparent from the following Specification and claims and from the accompanying drawing in which the single figure is a schematic representation of a turbine driven propeller system incorporating various controls including a centrifugal governor and the associated stabilizing System of the invention.

This invention is described in connection with an aeronautical propeller and a pitch changing speed control mechanism associated therewith. It will be appreciated however that the invention is not limited to Such specio mechanism.

A propeller shown generally at 16 is driven through a gear box shown generally at 12 by an engine 14 which may be a well-known single spool compressor-turbine engine well known in the art. The propeller, which may be of a well-known type, iS Shown as a hydraulically actuated propeller having a hydraulically actuated piston 16 movable to the left as shown in the drawing by hydrauiic fluid admitted to the chamber 18 to reduce the pitch of the propeller. Piston 16 is urged to the right as shown in the drawing by the spring 20 and the counterweights 22 to increase the pitch of the propeller when pressure uid is drained from the chamber 18. A yoke 24 is connected with the shaft 26 forming a part of the piston 16 and coacts with a roller 28 connected eccentric of the propeller blade 30- to turn the propeller on its longitudinal axis and change its pitch upon reciprocating movement of the piston 16. The piston 16 reciprocates in a cylinder 32 secured to the forward end of the hub 34 in which the propeller blade 30 is mounted. The yoke 24 reciprocates on a rod 36 secured in the hub 34 and is held against rotation relative to the hub by the rod 36.

A gear 38 is drivingly connected with the hub 34 and is driven by a gear 40 which in turn is driven by the turbine 14. Suitable packing, not shown, is provided between the hub 34 and the gear box 12 to prevent the 3,389,648 Patented .lune 25, 1968 escape of hydraulic uid discharged from time to time into the gear box.

The rear end of the gear box 12 contains a beta valve shown generally at 42. The beta valve comprises a sleeve 44 closed at the right hand end, concentric with the shaft 26, and reciprocable longitudinally of the center line of Shaft 26 which iS also the center line about which the propeller rotates. The closed end 46 of the beta valve sleeve 44 forms a chamber 48 into which the Shaft 26 projects. A land Sil extending inward from the sleeve 44 serves as a guide between the sleeve and the shaft 26 and closes the left hand end of chamber 48 so that reciprocation of the Shaft 26 will change the free volume of the chamber 48, i.e. displacement of the shaft 26 to the right as seen in the figure while the sleeve 44 is held stationary will displace fluid from the chamber 48.

The propeller Speed governor shown generally at 52 serves to connect line 54 and through port 56 and 58 the chamber 18 with either pressure fluid or a drain to control the propeller pitch. The chamber at the left of piston 16 and the interior of the hub are connected by means of a line 60' to the interior of the gear housing 12 which may be either connected with or act as an atmospheric sump for collecting drained fluid.

The governor includes flyweights 62 driven in timed relation with the propeller 10 and mounted to reciprocate a pilot valve 64 and balance the action of Speeder spring 66 by the effect of centrifugal force upon the flyweights 62. The force of the Speeder spring may be varied by a lever 68 controlled by a cam actuated arm 7i). The pilot valve 64 is mounted for reciprocation in a housing 72 having a port 74 therein through which pressure fluid may be admitted and a port 76 connected with a drain. A port 78 in the housing 72 coacts with a land on the pilot valve 64 so that reciprocation of the pilot valve will selectively connect the port 78 and the line 54 leading to the propeller with either the drain port 76 or the pressure port 74 to thereby control pitch changing movements of the propeller. Oil is supplied to the governor through a line 80 from a suitable supply source such as the lubricating oil supply of the engine which may be at say 1GO pounds per square inch, This pressure iS boosted by the governor pump 82 to a pressure Such as 600 pounds per square inch and supplied to the pressure port 74. A line 84 is provided to which an auxiliary pump may be connected for supplying oil under special circumstances. The pump pressure is regulated by a pressure regulating valve 86. lf desired, a feathering valve shown generally at 88 may be installed between the line 54 and the line 99 connected with the governor valve to disconnect the governor from the propeller, connect chamber 18- with drain and feather the propeller if desired.

The yweights 62 are enclosed in a chamber 92 which is filled with the lubricating oil from the line 8tl at about pounds per square inch. The Speeder spring 66 is enclosed in a chamber 94 which is connected by means of line 96 and a port 98 in the bcta valve sleeve 44 with the chamber 48 in the beta valve sleeve. A line 108 and a line 102 in beta sleeve 44 leads lubricating oil from the chamber 92 to the joint between the Shaft 26 and the land 50 of the beta valve sleeve. A buffer piston 184 is mounted for reciprocation in a housing 186 and is normally centered between chambers 108 and 11)` by springs acting on opposite sides of the piston. Chamber 11i) iS connected with the supply line 80 through the chamber 92 and is thus maintained at substantially constant pressure. The chamber 168 is connected through the Speeder Spring housing chamber 94 with the chamber 48 in the beta valve sleeve and is thus subjected to a pressure which will vary with the reciprocation of the Shaft 26 and the displacement of oil thereby in the chamber 48. Buffer piston 104 acts as a relief valve to limit the pressure in chambers 108, 94 and 48 by opening port 112 and connecting those chambers with the supply oilv line when the pressure in those chambers exceeds a predetermined amount.

Pilot valve 64 separates chambers 92 and 94 and acts as a piston whose opposite sides are subject to the pressures in those chambers. The pilot valve 64 is provided adjacent one end with a slot or groove 114 which is connected with one end of a passage 116 extending longitudinally through the pilot valve 64. Adjacent the other end of the pilot valve the passageway 116 is connected with the chamber 92 by a port 118 extending through the side of the pilot valve. A port 120 in the pilot valve housing 72 and longitudinally aligned with the slot 114 is connected with the chamber 94. As the pilot valve rotates and the slot 114 registers with the port 126, chamber 92 will be connected with the chamber 94 through the passageway 116 so that any pressure difference between the two charnbers will tend to be equalized.

The propeller, governor and engine are controlled by two sets of levers identified as a power lever and a condition lever. The condition lever is connected to operate cams 122, 124 and 126. The power lever is connected to operate the fuel control valve 12S and cams 130, 132, and 134. The condition lever will generally control the propeller condition for feathering, taxiing and take-off and landing. The ypower lever in addition to controlling the fuel control will coordinate the fuel control and the propeller blade pitch in the beta range of manual pitch control between the forward governing range and the reverse position of the propeller. When the propeller is in the beta range, the beta valve is actuated by the power lever and the governor speeder spring is set by the power lever in a high speed position by compressing the spring 66, forcing the pilot valve 64 to the left to connect the line 54 with pressure and force the piston 16 to the left to decrease the propeller pitch. Movement of shaft 26 to the left will bring port 137 into alignment with land 138 on beta sleeve 44 and cut off the flow of pressure and if the shaft 26 moves far enough to the left will connect port 137 with the sump or drain pressure existing in the gear housing 22 and thus tend to move the propeller back towards high pitch. The position of the beta valve sleeve 44 will thus determine the position of shaft 26 and the pitch of the propeller blades. As the pilot valve 64 has already been forced to the left by the action of spring 66 under the high speed setting imposed by the power lever the change in volume in the chamber 48 will have no material effect on the position of the pilot valve while the propeller is under beta control.

When the propeller is under governor control and the pilot valve is balanced between the speeder spring 66 and the effect of centrifugal force on the flyweights 62 any change in the differential pressure between chambers 92 and 94 will tend to assist or substract from the effect of speeder spring 66 and require a change in the propeller speed and the effect of centrifugal force on the flyweights 62 to again bring the pilot valve into a balanced condition. Considered in another way a change in propeller speed and the consequent change in the centrifugal force acting on the flyweights 62 will cause reciprocation of the pilot valve 64 and a change in the propeller pitch and the position of shaft 26 in the chamber 48% and a consequent change in the volume and pressure of the uid in chamber 48. This change in volume and pressure will cause a change in the differential pressures in chambers 92 and 94 in a direction which will restore the pilot valve 64 to its neutral position while the propeller is still at its changed speed. However because the propeller has changed its pitch the load on the System has changed in a direction which will tend to restore the system to the condition in which it was before the speed disturbance occurred.

As long as a pressure differential exists between the chambers 92 and 94, cach revolution of the pilot valve 64, when the slot 114 registers with the port 124i, will permit a slight amount of fluid to flow from the higher pressure chamber to the lower pressure chamber' and thus tend to equalize the pressure in the two chambers and reduce the pressure differential. The passageway 116 is a cornparatively long narrow passageway in which an appreciable amount of time is required to bring the fluid flow through the passageway to its terminal velocity. This time and the terminal velocity will vary materially with the viscosity of the fiuid, or in this case oil, being fed to the passageway. However, starting with the column of oil in the passageway 116 substantially at rest and with the pressure differential suddenly applied it has been found that the ow velocity in the passageway 116 during the first small interval of time is substantially the same over a wide range of uid viscosity. Hence by making the width of the slot 114 and the width of the port 120 small enough so that the time that the pressure differential is applied to the passageway 116 at a selected governor speed is quite small with respect to the time required to attain terminal velocity with a selected pressure differential and the range of viscosities to be encountered it is possible to obtain a flow rate through the passageway 116 which is substantially independent of the viscosity of the fiuid being handled. This becomes of particular importance in a turbine propeller combination in which the temperatures encountered and the resulting temperatures of the oil in the propeller control system varies over an extremely wide range with a resulting wide variation in the viscosity of the oil. This becomes even more important in the turbine propeller application where the controls must be extremely sensitive and rapid and any delay or sluggishness in the response of the controls would seriously impair their efficiency. This becomes particularly important in some installations in which the engine fuel is controlled by mechanism indicative of the temperature of the turbine to maintain that temperature at a selected high limit for any given speed and thus obtain maximum engine eiliciency. Under such conditions with the propeller maintained at a selected fixed pitch an increase in speed of rotation will produce a greater increase in engine power available than is absorbed by the propeller. This will result in an unstable condition in which the engine power will continue to increase at a faster rate than the propeller absorbs and hence will cause a run-away or unstable condition. The reverse condition would exist upon a decrease in speed in which the engine aavilable power would decrease faster than the power absorbed by the propeller and hence would load the engine up and stall it. In order to avoid such a run-away or stall, it is necessary to have a propeller which will change pitch very rapidly and load or unload the turbine faster than it can change power. Such a high gain propeller control system itself tends to be unstable to the extent that it may overshoot and hunt and thus requires a rapidly responding negative feedback system to reset the governor and provide a temporary speed droop with a time delay in eliminating that droop and restoring the original speed setting. If the time delay were subject to variation because of changes in the viscosity in the fluid system the regulation of the governor would be seriously impaired, overshooting and hunting under some conditions and undershooting and hunting in other conditions. Applicants have provided a materially improved control in which the restoring time delay is substantially independent of viscosity and relies substantially entirely upon the inertia of the fluid in the passageway 116, forming what is known as an inertia tube 116, and the time interval it is exposed to the pressure differential in the chambers 92 and 94. For an explanation of the theory of operation of the inertia tube feature of passageway 116 and the chopper 114, 120, reference may be made to application Ser. No. 529,797 for Viscosity Independent Hydraulic Flow Regulator, filed Feb. 24, 1966, by Kermit I. Harrier.

Passageway 162 in the beta -valve sleeve 44 and port 136 in the pilot valve 64 are always subject to supply oil pressure and serve to minimize leakage into chambers 48 and 94 respectively. The outlet of line 1'02 leads to an annulus located between the blade actuator servo preassure land and chamber 48 and port 136 leads to an annulus between a high pressure source and the chamber 94 and hence prevent leakage from the high pressure lands from having any elect on the pressure in the chamber 94.

Assuming that the propeller and the governor are in a steady state condition as shown in the figure and a disturbancecauses an increase in speed which will cause the ylweights 62 to move outward and the pilot valve 64 to move to the right. Oil will then be drained through port 76 from the chamber 18 in the propeller and the piston 16 forced by the spring 20 and counterweight 22 to the right. Shaft 26 will thus be forced into chamber 48 displacing iluid which will llow into chamber 94 increasing the pressure therein and move buler piston 104 to the left to accommodate the displaced fluid. The increased pressure in chamber 94 acting on the end of the pilot valve 64 exposed to that pressure will produce a force on the end of the pilot valve substantially greater than the force produced on the end of the pilot valve in chamber 92 and exposed to the substantially constant pressure in chamber 92. This will result in a movement of the pilot valve 64 to the left restoring the balance between the force on the pilot valve produced by the counterweights, the Speeder spring 66 and the pressures in the chambers 92 and 94. This movement of the pilot valve will return the pilot valve toward a neutral or null position and stop further pitch changing movement and temporarily restore the system to a balanced condition at a new speed. The pilot valve will be forced to the left at a rate proportional to the rate of pitch change until the balanced condition is attained. Fluid will then be bled from the chamber 94 at a substantially constant rate independent of viscosity which rate will very nearly or substantially compensate for the reduction in speed that will gradually occur due to he increased pitch position of the propeller blades so that the speed will return to its normal preselected value, selected by the arm 70y and p the lever 68 with the blades in a new pitch position to neutralize the disturbance which caused the original increase in speed.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described but may be used in other ways without departing from its spirit and various changes can be made which will come within the scope of the invention which is limited only by the appended claims.

We claim:

1. In combination a movable control member having a null position and controlling a servo motor, means applying a control force to said control member, said control member movable from said null position by a variation in said control force to thereby effect movement of said servo motor, said control member including means separating two fluid chambers, means maintaining a selected uid pressure in one chamber, means, actuated by said movement of said servo motor, varying the uid pressure in the other chamber above and below said selected pressure, thereby applying a separate force, opposing said control force, to said control member and urging said control member back toward said null position, a passageway forming an inertia tube having one end exposed to said selected fluid pressure, means connecting the other end of said passageway with the other chamber, valve means in said connecting means, means periodically opening and closing said lvalve each periodic opening being for a time period less than that required for the fluid flow in said passage to reach terminal veloci ity to gradually equalize the pressure in said chambers at a rate substantially independent of the viscosity variation of the iluid in said chambers.

2. A combination as claimed in claim 1 in Iwhich the control member is rotatable in a housing andthe valve means comprises ports in said control member and said housing intermittently brought into registration by rotation of said control member.

3. A combination as claimed in claim 1 in which the control member is an elongated member and said passageway forming the inertia tube is in said member.

4. A combination as claimed in claim 2 in which said control member includes a reciprocable spool valve member and said passageway forming the inertia tube is located in said spool valve member.

5. A combination as claimed in claim 1 in which the control member is rotatable and reciprocable in a housing having a bore receivng said member, and one said chamber is located at one end of said bore and said other chamber is located at the other end of said bore and said member is exposed at opposite ends of a respective chamber, ilyweights in one chamber urging said Imember in one direction under the eect of centrifugal force and a Speeder spring in the other chamber opposing the action of said llyweights and urging said member in the opposite direction.

6. A combination as claimed in claim 1 in which said servo motor is the pitch changing motor of a controllable pitch propeller and the control mechanism for said motor includes a manually actuatable valve sleeve having a valve chamber formed therein connected with said other chamber and said fluid pressure varying means includes a plunger actuatable by said motor reciprocable in said valve chamber.

7. A combination as claimed in claim 6 in which said control mechanism includes means holding said valve sleeve against movement while said servo motor is under control of said control member, a iluid line controlled by said control member connecting said control member with said motor, said valve sleeve cooperating with a port in said plunger to form a valve in said fluid line,\me'ans disabling the control function of said control member and opening said liuid line to a source of fluid pressure and moving said valve sleeve to control said motor.

References Cited UNITED STATES PATENTS 1,669,108 5/1928 Warner 91-366 1,994,121 3/1935 cuningham 91-366 2,261,925 11/1941 salzer 91-388 2,986,126 5/1961 Wens 91-336 FOREIGN PATENTS 233,110 3/1911 Germany. 40,416 12/1964 Norway.

PAUL E. MASLOUSKY, Primary Examiner.

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