CA2074514A1 - Digital suspension system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A digital suspension system for a wheeled vehicle incorporates digital hydraulic actuators at each wheel and includes a system for sensing lateral and longitudinal accelerations of a body portion of the vehicle and the positionof each wheel relative to the body and provides this information to a computer.
The computer computes the forces required at each wheel and controls the digitalhydraulic actuator at each wheel by adjusting in increments the force applied ateach actuator between the wheel and the body to maintain the body portion of the vehicle in a substantially stable position. Preferably the hydraulic actuator used in the suspension system will be, formed by an assembly including a first element, a cylinder, a body section and a chamber. The first element is providedwith a first set of a plurality of different sized piston cavities and piston elements which cooperate with a second set of piston elements and piston cavities respectively formed on a second element. The second element forms a piston in cylinder. The body sides incorporates preferably in symmetrical relationship around the axis, of the assembly a plurality of valves, one valve for each of the pairs of cooperating pistons and cavities. A piston divides the chamber into a high pressure reservoir and a low pressure reservoir with the piston being urgedtoward the high pressure reservoir to maintain a difference in pressure between the high and low pressure reservoirs. Passages connect each of the valves to thehigh and low pressure reservoir and each valve with respective of the cavity adapted to selectively connect its respective cavity to either the high pressurereservoir or the low pressure reservoir.

Description

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nlGlTAI, S~JSI~l~NSION SY$TEM
Fielcl Or ihc Invention The present invention relates to a hydraulic suspension system and to digital actuators suitable for use therein. More particularly the present S invention relates to a digital force adjustillg computer controlled hydraulic sllspension system and an actuator ther~,for.

Backgrollnd of the Present Inv~ntlon The use of computers tn control hydraulie systems in the suspension 10 of motor vehicles has been discussed an~ various arrangements ~or controlling the suspension and for constructibn o~ ihe hydraulic actuator have been described and patente~l.
U.S Patent 4,333,668 issued June 8, 1982 to Hendrickson et al discloses a shock absorber with damping orifices that are contro]led by sole7l0ids lS which in turn are activated by a compllter control in response to ~he rate ofcbange of the extension of the absorber. Pitch and roll of the vehicle are also imposed on the control which en~rgizes th~ solenoid to vary the opening and closing of the Yalves and maintain the Yehicle substantially stable.
IJ.S~ Patent 4,639,Q13 issued January 27, 1987 to Williams et al 20 describes an active vehicle suspension incorpor~ting a double acting hydraulic actuatar in parallel with a gas spring. An actllal change in load is sensed and an appropriate adjustment of th~ actuator is made to compensate for the sensed loadchange.
Canadian patent 1,230,657 issued I)ecember 22, 1987 to Williams 25 et al describes an active vehicle suspension system using hydraulic actuators for each wheel to generate signals in accordance with their displacements and forcesapplied thereto and controls the displacemeni OI the hydraulic actuator in accordance with the il3terpretation of these signals to maintain vehicle stability.
U.S. Patent 4,753,328-is.sued June 28, 1988 to Wil}iams is a further 33 modificatinn of the systems dsscribed in the preceding YJilliam's IJ.S. and .
Canad;an patents ancl furtller discloses a damping ~ystem to selectively apply positive or negative dampin~ to ~ile movel1lent nf ~he pistnns of the actuators.
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Dig;tal hydraulic actuatnrs are also kno~n. IJ.S. Paient 4,6Q2,481 -~

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issued Jl~ly 29, 1986 to Robinson describes a particular form of digital actuator utilizing piston areas of ciifferent sizçs to selectively apply forces of a preselected magnitude. The force applied is controlled by adjus~ing the ratio of piston areasubjected to the source pressure $o that subjected to return pressure. The S pressllres may selectively be ~pplied to force the a~uator in opposite directions.
By changing the piston area subjected to source (higher) presslare dri~ ing the actuator in one direction relative to the area under similar pressure driving the actuator in the opposit~ direction one can adjwst the force to be posltive in either direction and to have a selected value dependin~ on th~ combination of areas 10 subjected to source pressure or return pr ~sure.
Generally linear digital hy~raulic actuators are limi~ed in those cases where a double aetion arrangernent is required as the total area or range of pressures that may be applie~ are limit~d since the forces mlsst be applied to move in both directions. This limits the variation in pressure that may be applie~
15 in any one direction or increases signiîicantly the size of the actuator, see IJ.~.
Patent 4,602,481 issuel3 July 29, 1986 to Robinson which discloses a linear double acting digital system of the kind described.
U.S~ patent 3,068,841 issued December 18, 1962 to Robbins et al discloses a system to permit rapid advance of a ram toward a workpiece urlder 20 low power and low pumping volume requirements arld for ef~ecting full force against the work piece after the ram is positioned by utilizing di~ferent piston and cylinder sizes to obtain the desired rç~ults.
Generally digital actbators are separate elements and are connected .
to discrete valves and separate res~rvoir systems all arranged in positions remote 2S from the actuator itself.

BrJe~ l~escription o~ the Present InYention It is an object of the present invention to provide a suspension system for wheeled vehicles wherein the forco be~ween the body oE the vehicle 30 and each wheel is adjusted independent of displacement of the ac~uator to maintain the stability of the vehicle.
Broadly the present in~ention relates to a suspension system for a wheeled ~ehicle ha~in~ a body portion comprising means for sensing lateral and ' .

~ ~ 7 !~ ri longituàinal ~cceleration of saill bo~ly portion, a cligital llydraulic actuatorsupporting said body portion from each of said wheels, each said actuator includillg a plurality of dif~erent ef~ective area actlla~or sect;ons, a first source of hydraulic fl-lid at a first pressure, a second source of hydraulic fluid at a second 5 pressure, sa;~3 second pressure bein~ differetlt from said first pressure, valve means for selectively connecting said first and said second sources to selected of said actuator sections thereby to va~y the amount of said effective area of saidactuator subjected to said first and said second pressures to vary the force applie ;l by each said actuator indepçndent of the extension of said actllator, computer 10 means for controlling said valves to adjust ~he number of said actuator sections nf each said digital hydraulic ac~uator subjected to saicl first and said secon~pressures based on anticipated forces at each sa;d actuator as determined by said computer means based on conditions sensed by said means for sensing lateral and longitudinal acceleration thereby to maintain said body portion substantially 1S stable.
Pre~erably means to measure the displacement of each said actuator w;ll provide a signal representing the displacement of each said actuator to said compllter means and said campu~er means will ~ontrol said valvcs to tend ~o maintain said actuator means in a position wherein said ~aS~h said actuator has 2Q a preselected de~ree of extension.
Preferable the hydraulic actua~or comprises a housing, a rotor ex$ending through said h~using, a plurality of a~cially extendlllg radially projecting circumferentially spaced lugs oll said housing and defining a plurali~ of circumferentially extending spaces therebetween, a pair of circurnferentially 2S apposed surfaces nn an a~Ua~ent pair of said lugs defining opposite circumferentially spaced ends of each of said spaces, each of surfaces of said pairs of opposed surfaces o:E an adjacen~ pair lugs having different area~, axially extending radially projecting space~l bosses on said rotor, each said boss beingreceived within a different one of sai(l ~spaces ancl dividing its respec~ive said 30 space into a pair OI actuator sections one on ~ach side of said bnss, each said boss ~ having each of its radial circm~erentially spaced sides substantially the same area ~: as its adjacent opposed surface of said Jug forming the adjacent circumferential end of said space in which it is receivecl, said lugs havin~ end faces conperating , ~ ~ 7 1~ V.~

with said rotor and said bosses having sllrfaces cooperating with circumferentially extendin~s surfaces of said spaces to seal one said actuator section of said pair of sections in said space in which said boss is receivesl from the other of said pair of actua~or sections, said rotor being rotatably mounted within said housing so S that eacll boss may rotate ~Yithin its respective space throu~h a preselected angle of rotation and means for directing ~luicl under preselected pressures into each of said actuator sections.
It is a further object of the present invention to provide a compact, easily in~talled, cligital hy~lraulic actuator a~sembly wherein the various components are provided in a single assembly having a hy~lraulic ou~put that maybe coupled to a suitable hydraulic actuator.
Broadly the present invention alsn relates to a digital hydraulic actuator assembly comprising a cylinder, a body portion including a firs~ element and a chamber integrally interconnected, a second element ~orming a piston in said cylinder, said first and secolld elements haYing sets of cooperating pairs of pistons and cavities, a p;stnn div;d;n~ said chamber into a high pressure reservoir and a low pressure reselvoir, means larging sairl piston toward said high pressure reservoir thereby to tend to increase the size o~ the low pressur~ reservoir an~~: reduce the size of the high pressllr~ reser~oir and thereby genera~e a pressure :~ 20 differential between hydraulic fluid in sakl high and saici low pressure reselvoirs, set of valves in said body portion, said set of valves inclNding one valve ~r each of said cooperating pairs of piston and cavities, first passage means ~hrough sai~
- body portion connecting each of said valv~s to said l~igh pressure reservoir, second passage means eonnecting said low prcssure resesvoir to each of said va]ves, individual passages connecting ead~ o~ said cavities of said cooperating pairs of pistons and caYities with its respective sai~3 valve of said set of valves.
Preferably said cylinder will he hydraulically connected to one side o~ a hyclraulic actuator to drive said actuator in accordance with the pressure in said cylinder.
Pre~erably said chamber and said cylinder will be positioned at opposite axial ends nf said assembly.
Preferably further valYe means will be provided in said body portion~ ~urther first passage means will cl~nnçct said further valve means w~th ~ .

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said high pressure reservoir, a futther second passage means will connect said further valve means with said low pressure reservoir and wherein a hydraulic connector will connect to said hydraulic actuator to said further valve means whereby said further valve means may selectively connect said hydraulic actuatorS to saitl higll or said low pressure reservoir to drive said ac~uator in the opposite direction to the pressure applied from said cylinder.
Broadly the present invention also relates eo a digital hydrauli~
actuator comprising a fixed elçment, a driven ,~iston cooperating with a first cy]inder formed by said fixe(l element, means to digitally vary the pressure acting 10 between said fixed element and said ~riven pis~on tending to displace said driven piston in said first cylinder, a second cylinder, a hydraulic coupling hydraulically ~onnecting said first cylinder to said secon~ cylin~er, sai~ second cylinder ha~ing a cross sectional area different from said first cylinder, a wQrking piston in said second cylinder adapted to apply a ~orGe det¢rmined by the ratio of the cross 15 sectional areas of said first and second cylinders.
Preferably said means to digitally ~ary the pressure acting between said f~xed element and said driven pi~ton includes a first set of differsnt cross sectional area piston cavities and a first set of differ~nt cross section area pistons on said` fixed element, a s~cond set of different cross sectional area pistons and 20 a second set of different cross sec~i~nal ~rea piston cavities orl said d~en piston, each piston OI said second set of pistons being received vvithin said one of said ca~ities of said first set of piston cavities and each cavity of said second set ~f piston cavities receiving a piston of said first set of pis~ons, and means to : . selectively apply fluid under selected pr~ssures to each cavi~ of said first arld said 25 seco~id sets of cavities.
Preferably saicl means to sele~tively appiy fluid pressure will apply : fluid under a ~irst pressure or a sec(~nd pressur¢ differgnt ~om said first p~essure to each `caYi~ in said f~'rst and said second sets of c~Yities.
Preferably said operatin~ pist~n will be a double acting piston and 30 - m~ans wIll be provided to apply fluid un~er pressure under ~he side of said piston ;: ~ remote from said fluid coupling Preferal~ly said hydralllic collplin~ will comprise a straight tubular passage section interconnecting ~aid first and second ~ylinders and hav~ng a ; ~ .
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portion changing the cross sectional size of said passage from a cross sec~ionalarea equal to that of saicl first cylinder to a cross sectional area equal to that of said secon(l cylinder.
Pre~rably said first set of cylinders and said first set of pistons will S be concentric and pistons of sailJ first set will separate aald form the walls of cavities of said first set.
PreEerably saicl second set of cylinders and said second set o~pistons w~ll be concentric and pistons of sa;d second set will separate and form the walls of cavities of said secon~l set.
Preferably means will be provided to adjust the amount of fluid in said fluid coupling to maintain the spacing between said dri~en and said workingpistons within a preselected range.

Brlef I~escription of the Drnwlngs Further features, objects an~ advantage will be evident from the following detailed descript;on of the pre~rred embodiments of the present ~; invention taken in conjullction with the accompanying drawings in which ~: Figure 1 is a schemati$ illustration of a wheeled vehicle illustrating a suspension system constructed in accordan~e with the present inYention.
Fi~lre 2 is a scbematic illus~ration of a dig~tal hydraulic actuator in - ~ ~ position sllpporting one of the wheeJs ~f the vehicle relative to the chassis.
Figure 3 is a view ~imilar to Figure 2 but illustrating a pre~erred ;~ fnrm of hydralllic actuator.
Fig~lre 4 is a schematic illustration of one form of hydraulic actuator that may be used with the present inyentiDn~
Figure S is a schematic illustration o~ a control valve ~hat may bg : , .
used to control the pressure applied to secti~ns of the actuator~
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Figure 6 is a schematic radi~l cross sectional illustration of preferred hydraulic actuator~
Figure 7 is a ~oss-section through a preferred form of digi~l actuator constructed in accordanc~ with the present invontion~
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~: Figure 8 is a cross s~ction ~hrough a preferred form of actuator constructed in accord~nce with tlle present inv~ntioll~
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I;igure 9 is a section along the lines 9~9 of Fi~ure 8.
Figure 10 is a section along the lint~ 10-10 of Figllre 8.
Figurt-~ 11 is a seetion along the linç 11-11 of Pigure 8.
Figure 12 is a schemaffs illustration of a system constNcted in S accorclan~e with tbe present invention and filrther including an actuator throttle.

l)escription of the Prererred Embodiments In the illustration of rigure 1 the systern of the present invention 10 is applied to a four wheeled vehi~le having wheels 10, 12, 14 and 16 each of which is supported ~rom ch~ssis (not sl:aown in Figllre l.) The system includes a plurality of accelerometers measuring thç verticle, lateral and fore and aft acceleration of the vehicle as well as the pitt,h and roll. In the illustrated system five accelerometers indicated at 18, 20, 22, ~ and 26 have been provided. The lS accelerometer 18 measllres fore and aft acceleration, tbe accelerometer 20 measures vertical accelerat;on at t~ne end of t~e vehicle, acceleromcters ~2 and26 measure vertical acceleration at opposite sides of ~he vehicle and the accelerometer 24 measures hor}z~ntal lateral acceleration. ~ach of ths accelerometers 18 to 26 inclusive as above described ~ransmit signals representing 20 measured accelerations to the colltrol ct)mputer or colltroller 28. 1l~e corltroller ` ~ 28 iD~ turn sends signals to eash of the control Yalves systems 30, 32 and 34 a~d 3~ (each of wh;eh is composed of a plurality of valves as will be described belgYY) used to control the hydraulic actuator 42 (57 and 200) at each of the wheels 10,I2,~14 and lfi respectively. Th~ hydraulic Gircuits for each of the 2S actuators 42 in the ;llustrated arrangement inclllde a high pre~sure tank 38 and a iow pres~llre :tank 40 which are connected to the valve fiystems 30, 32, 34~ 36 which ~ontrol tbe forces generated by the digital hydraulic actuator 42 at each of th~ wheels 1Q, 12, 14 and 16 respectJYely~ The actuators 42 will be described inmore~:detail hereinbelow with respect t~ ac~uat~r~ S7 and 20û shown in Figures -30~ 4 and 6 respectively.
In the illustrated arrangement the hydraulic pump 44 supplies high pressure Pl., flui.d to tlle iligh pressur¢ cylinders 38 and maintains the low pressure cylinders 40 ~It ~ significnntly lower pressure, P,.

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Any suital)le type of hydraulic actuator provided it is digital hydraulic actllator permitting adJustment of applied force independently of extension may he used. Obvinusly the computer control 28 will operate the valvesfor actllators 42 in accor(lance with the type of digital hyclraulic astllator S employe(l, in particlllar, the contrf)3 wili be different if a single acting actuator (force ~pplied in a single direction only) is ~sed than when a double acting actuator (force applied in two opposite directions) is used. ~xamples of the twodifferent types are shown in figures 4 and 6.
An example of the mounting of an axially acting hydraulic actuator 10 is shown in Fi~l~res 2. In Figure 2 a piston and cylinder type actuator 42 (Figure 4) which changes i~s axial or longitudinal extension between the body 46 and thesuspension 48 to which the wheel ~10, 12, 14 or 16) is mounted has been sho~, In Figure 3 a torsl.ue type digital actllator 42A ~eg. the double acting torque ~e actuator 200 in Figure 6) has been shown interposed between the body 46 and the I5 suspension system 48 ~r e,ach wheel (1(), 12, 14 and 16.) The actuator 42 (or42A) may be a single or a double acting actuator, a single acting axial extens;on - actuator ;s shown in ~igure 4 (actuator 57) and a double acti~g axial extension actuator is shnwn in said IJ.$. patene 4,602,481.
Generally when a double acting actuator is used as is pre~rred a 20 suitable suspension spring such as that illustrated at 43 will bc used in parallel with the digital hydraulic actua~or to support the body 46 at each of the wheels(10,12,14 and 16.) A single acting piston and cylinder type actuator 57 has been illustrated in Figure 4. In this system two high pressure sources 38 h~ve b en 25 shown; one for the actuator sections of the upper portion 59 of the actuator 57 and one fnr the actuator sections jn the lower por~ion 76 of the actuator. The deseription below will only refer to a bigh pres~sure source 38 and a low pressure source 40 as separate sollrces need not be provided for each section. The source38 is at a pressure p" whereas the low pressure reservoir or source 40 is at a n lower press.lre pl.
The high pressure sour~ 38 is connected via a manifol~ 50 with valves S2, 54 and 56 which will form part OI each the v~lve system 30, 3~, ~4 or36. These vah~es are also ~onneeted via a low pressurç m~nifold 58 with the low , .

pressure reservoir 40. E~ach of valve 52, 54 and ~6 is connected respectively toactuator sections in this case formçd by annular, concentric cham~ers 60, 62 and64 respeçtively in the upper pnrtion 59 of ~he actuator 57. The chambers or sections 60, 62 and ~4 have different ef~ective cross sectional areas measured in S a plane radial to the axis 6fi around which the chamhers, 60, 62 and 64 are . concentric.
Sim;larly the anmll~r rin~ dividers separating the chambers or sections 60, 62 and 64 are receiveci within a second set of aImul~r chambers 68,71 72 and 74 concentric witb the axis 6~ formed in second or bottom section 76 10 of the actuator 57. The ef~ective cross sectional areas of the sections 60, 62, 64, fi8, 70, 72 and 74 are related su~h that for example th¢
effective are~ of chamber 60 is preferably twice that of chamber 62 and chamber 62 is twice that of chamber 64 etc., howevgr i~ ;s not essential tbat the effec~ive areas of tbese chambers be steppçd in this manner but i~ is important that the 15 areas be d;f~erent.
~: Each of these chamhers 60, 62 and 64 formed tn ~he upper portion 59 of the actuator 57 is connected re~ectively to the valve 50, 52 and 56 while the ehaml)er 68, 70, 72 and 74 in the lo~er section 76 are connectcd to valves, 78, 80, and 82 respective]y (there are valves 78, 8û1 82 in each of the Yalve syste~ns - 20 30~ 32, 34 ~r ~6) which valves are c~nnected via a high pres~ure manifold 86 to the high pressure reservoir 38 and ~ria manifold 88 and the low pressure source or reservoir 40.
The controller 28 actuates each of the valves 52, 54, 56, 78, B0, 82 and 84 to connect the various scctions 60, 62, 64, 68, 7û, 72 and 74 either to the 25 high pressure source 38 or the low pressllre source 40 so that the total force tending to separate the two units 59 and 76 is goYerned by the sum ~f t~e forcesin the cylinders 60, 62~ ~4, 68, 70, 72 and 74. The sum of these forces is dependent :directly on the area of each chamber multiplied by the pressure in each chamber which pressures are s~lected as P~, or PL depending on which 3n ~ source of fluid i~s connected thereto.
he Va1VeS 52, 54, 56, 78, 80, 82 and 84 may be any suitable valve connecting the actuator section to one pressllre source or the other, however the operation of the system will be described with respeçt to the valYe shown in ' ~

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Fig~lre 5. In this system the valve has a control solenoid indicated a~ 90 whichmay be any suitable solenoid or the like ~o xnove the body of the valve, formed by two interc~ nected cylin~lers 92 and 94, back and forth to open and close thetwo inlet ports 96 and 983 one f~r high pressure (96) and one for low pressure S (9~). Intermediatç port 1()0 connects the, valve to its respectiYe section or chamber 60, 62, 64, 68, 7n, 72 nr 74. It will be apparent that as the valve moves to close off say port 96 and open port ~8 it opens port 98 before it totally c!oses off port 96 as indicated by the dimension x. Obviously a similar phenomena - occurs when the v~lve is moved in th~ opposite direction to close off port 98 and 1~ open port 96. The rate of movement of the cylinders 92 and 94 to open and close the ports 96 and ~8 is relatively rapid, thus the time period in which both ports are simultaneol]sly cracked open is small and is provides to ensure that there is no significant build up o~ pressure dl!ring the transition between the high and low pressure sources.
15It will be apparent that any of the c~linders 60, ~, 64, 68, 70, 72, and 74 may be cs~nnected ei~her ~o the IQW pressure source 40 or tbe high pressure source 38. If the ratio of effective areas in the various sections or :: ~ chambers, i.e. tlle ef~ectiv~ cross sectional ar~as oî the chambers are in multiples of two a convenient stepping of the pres~sures applied tendlng to force the tu~o20 sections 59 and 76 apart can bç established by appropriately connecting the various chambers to the high pressure source PH or the low pressure source p,.

~r ; Each of the sources PH an~l p~ are substantially constant pressure sources in that they maintain a s~bseantially cons~ant pressure eg. by a pneumatic pressuTe at the top of the fluid so that the amount of flow fluid does no~
2S significantly aff~ct the pressure. The low pressure PL may ~imply be atmospheric pressure.
l~e pressure ~our~e~ 38 and 40 are o~ the type that maintain essentially the same pressure to the valves subs~antially irrespective of ihe flow to or extension of the actllator eg. ~eparation of the portions 59 and 76 of 30 actuator S7 or as w.ill be described below relativ~ rotatic~n of tho rotor and ~ousing of Figure 6, ~or example hy maintaining substantially constant pnellmatic pressures in the reservoirs 38 and 40.
Control nf the valYes S2, 54, 56, 78, 80, 82 or 84 t~ direct the 7 ~

appropriate pressure into the v~rious chambers 60, 62, 64, 68, 70, 72 or 74 is by the computer contrnller 2g and is based on the anticipated movement of the chassis as determined by calclllations based on the signals from the accelerometers l8, 20, 22, 24 alld 2~ to define the expected movement of the chassis relative to the wheels and using the weight and centre of graYity (assumed or determined) calculate the force require(3 to resist movement of the body 46 at each of the wheels.
In order to calculate the forces involved so that the forces can be matche(l in the actuatorl it is necessary not only to know ~he acceleration but also 10 the weight and centre of gravity o~ ~he vehicle rnust be assumed or deterrnined.
l~us appropriate means may be prov;ded in each of the suspension systems to determine the weight of the vehiçle This weight o~ the vehicle may easily be obtained based on the measured clispla~ement of ~he suspsr3sion system eg. the actuators 42 or 42A at each o~ the wheels 10, 1~, 14 and 1~ measured by a 5 suitable measllring device such as that indicated at 104 in Figure 2 or the angular position of the wheel by the measuring deYice as indicated at 106 in Figure 3.
Tlle signals ~rom the aceelerometers 18, 20, 22, 24 and 26, thc sigl1als from the actuatl)r extension measurement devices on each wheel 104 or 106 and s;gnals from such other measuring devices as may be used are presented 20 ~o the controller or control computer 28. The control computer 28 ealculates the fnrce to be applied by each actuator an~ the positions of each of the valves S2,54, 56, 78, 80, 82 ancl 84 of each of the valve blocks 34.
In the preferred embodiment of the present invention, the force to be applied by each actuator is cal~ulated as a weighted sum of the most recent, 25 and preferably some preceding values o ea~h of the accelerome~er and- extension signals. The weight;ng coefficients are determined using known modern linear contro! theory, preferably the Ricatti equation of optimal linear quadrat;c contsol ~; theory, and a knowledge of the vehicle parameters. The parameters describing tbe vehicl¢ inc~ude mass, mass moments of iner~ia and dimensions are 30 prs)grammed into the compllter when the ~system is lnstalled.
In a pre~erred case the vehicle parameters are identified from ~he accelerometer and extension signals and the actuator forces, for example a maximum likelihood method of parameter estimation from statis~ical theory may " 2 l2 be appliecl tn generate appr()pliate calclllation procedures. Tn this case, the control computer would, in addiltion to calculating actuator forees, periodically perform ~he calclllatiolls to idelltify the paramet~rs of the vehicle and perform the calculations to determine the weighting coefficients mentioned previously and inS the manner compensate for dfflerent loadin~ conditions of the vehicle. Normally . ehe calculations of actuator forces will be repeated at least eve~y 0.1 seconds while the calculatiolls to determine weighting coefficients may be done less frequently preferable at least evel~ In seconds.
Calculating the actuator foree at least eue~y 0.1 seconds is lO suef;ciently rapid to respnnd to turning, accel~ration and brakin~ of the vehicle as well as to variatiolls in the road surface over which the vehicle is travelling.
The prime filnction of the suspension system is to respond to variations in road snrface, thereby to substantially isolate ~he body 46 ~om theroad surface. HoweYer if the wheel is displaced too far ~orn its nominal position 15 (generally in about the middl~ of the wheel well) the susp~nsion may reach the lin~it of its travel and a strong shock will be ~ransmitted to the body 46. To avoid this the suspension must move the body 46 sufficiently to maintain sllspension (wheel relative to the bocly) in its nnrmal position. A stiff suspension holA the wheel near the normal position, but at the expense of a lot of road roughness 20 being transmitted to the body 46, a soPt suspension on the otller hand permits freer movement of tl~e whee] relative to the body 46 and better isolates the body from ~he road but at the expense of more likelihood of the suspension reaching the limits of its travel and transmitting shocks to the body. The computer eontrol must control the active suspension sy~stem to provide the kind OI suspension :: 25 system selected and in any evellt mllst rea~t a~ least as well as a conuentional ; ~ ~ suspension system to pre~ent the suspension from reaching its lim~ts and transmitting shocks to the body 46.
In the preferred embodiment ~f the present invention hydraulic ~ ~ actuator wi]l be a torsional actuator ~ indiçat~d at 200 in Figures 3 and 6. The :: ~ 30 torsional actuator has an outer housing 202 anci a rotor 204 contained ther¢in.
Rotor 204 has an axially extending shaft 2Q8 that is clamped to the suspension arm 48 for a wheel so that the anglllar posi~ion of the arm 48 relative to the body 46 is adjusted by ro~ating thC rotor 2()4 relatiu~ to th~ housing 202.

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The torsional actuator 2no shown in Figur~ 6 also includes the same valve systems as with tl~e a~ial actuator S7 and like parts have been indicated with like numerals in the Fi~ures 4 and 6 embodiments. In th~ torsional actuator 200 a plural;ty of circumfererltially extending spaces 208, 210, 212 and 214 are S provided. The space 208 is formecl bet~1ueen lugs 216 and 218, the space 210 between the lugs 218 and ~20 and space 212 between the lugs 220 and æ2. A
further space 214 is formed be!tween the lug 222 altd ~ fa~e 224 formed on the rotor 204.
The rotor 204 is provided with circum&rentially spaced bosses 242, 244 and 246 which are circumferentially shorter than and are received w~thin thespaces 208, 210 and 212 respectively and divide the spaces into actuator sections or chambers 20RA, 208B; 210A, 2101~; and ~12A, 21233 respectively.
In the illustrated arrangsment the ports 228, 230 are provtded leading to the sections 208A and 208B adjacent the lugs 218 and 216 respectivelylS and are connected to the valves 80 and 56 respectively. Similarly the sections 2,1013 and 210A are connected by ports 232 and 234 positio~ed adjacent the lugs 218 and 220 respectively tls the valves 54 and 82 re~cpeetiYe1y. The sections 21?B
and 212A are connected by ports 236 and 238 posi~ioned adjacent the lugs æo and 222 to the valves 52 and 84 respectively. The space (section) 214 is :: : 20 connected via port 240 with t~e valve 78.
: It will he notecl that th~ face 24~ of the bos~ 242 ~acing the fare 2S0 on the abutment 2lfi have essentially the same effectiYe area measured rad;ally to the axis of rotation of the rotor 204. Similarly the ~aces 252 and 254 on theboss 242 and lug 218 are of the same radial area as are the adjacen~ faces on each of the respective acljacent lugs an(l bosses.
The periphery of the bosses 24~, 244 and ~46 are in wiping relationship with the circllm~ere,nccs t)f ~h~ spaees 208, 210 and 212 re~pectively : ~ ~ and form a seal l~etween the se.ctions 208A and 208~: 210~ and 210B; and 212a and 212B respectively, Similarly ~he lugs 216, 2J8, 22û, ~22 are in sealing relationship with th~ circumference of the ~otor 204 to ~urther seal sides of the vari~us sections 208A and 208B: 210A and 210~; and 21~A and 212B and 214.
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It will be apparent that the area of the face 224 oî the space 214 is ,~
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substantially eqllal to the area of ~he facing sulface of the lug ~22. It can be seen that a plllrality of different ra~lial ef~ctive cross sectional are~ actuator sections are provi~ed circllm~eren~ially spaced around the rotor. Preferably the radial area o~ the corresponcling pairs of adjacent ~aces wîll be in a specific ratio to ~he are~s S of o~her corresponding pairs of radial area6 so that the cross sectional areas subject to different pressures may be combined to produc~ the desired resultant force by selectively connec,ting the sections 208A, 208B, 210A, 2101~, 212A, 212B
and 214 to PH or P, via the valves 80, 56, 82, S4. 84, 52 and 78 respe ~ively.
The torsional actuator 200 is a double acting actl!ator in that as viewed in Figure 4 it may be used to apply pressure to tend to ~otate the suspens;on 48 either in a clockwise or a counterclockwise under control of ~he computer 28 to maintain the suspension in the desired position relatiYe to the body 46. A single acting aetllator can only be manipulated to keep the suspension in its normal position by changing the magnitude hut not the direction of the forces applied hetween each wheel and the body 46.
111B digital hydraulic a¢tuator 310 illustrated ;n Figure 8 includes a first or fixed element 312 haYing a plurality of annular piston cavities 314, 31~, 318 and 320 forming a first set nf piston cavities separated (surrounded) by plurality o~ annular pistons 322, 324, 3~6 and 328 ~rming a first set of pistons.
A driven piston or second elem~nt 330 is formed with a plurali~ of - ~ annular pistons 332, 33~ and 336 forming a secs)nd set oP pistons an~ a second set of discrete annular piston cavities 338, ~4(~, 342 and 344. I'he second set of pistoos 332, 334 and 336 ar~ received wi~hin the first set of piston cavities 314, 316 and 318 while the first set ~f pisto~s 322l 324, 326 and 328 are received within ~he second set nf piston cavitiçs 338, 3~0, 342 and 344 respectively. Eacb OI the cavities 314, 316, 3:18, 334, 340, 342, and 344 are connerted via lines 346, 34~, 35~, 352, 354, 356 and 358 respectfvely to their respBctive valves 360, 366, ~: 368, 370 and 372 respectively. Each of ~hese valves are essentially the same and ~: ~ are essentially the same as the valve described above and illustrated in Figur~ S.
Eacb i5 adapted to be moved from first positio~ connecting its respectiv~ ~linder to the high pressure line 374 (equivalen~ to line 50 or 86 described above) leading .~
from a high pressure tank 376 (tank ~ above) and designated by the symbol PH
or~ to the low pressure iine 378 (line 58 or 88 ahove? connected to the low . ~

..

2 07 '~ ~ ;L ~
pressure ~ollrce of hydraulic fluid 38û (tnak 40 above~ as symbolized by the symbol P,. lllese valves 360, 362, 364, 366, 368, 370 an~ 372 are controlled viaa controller 382 as iodicated by the dot/dash lines 384 to apply either a hi8h pressure or a low pressllre to each of the cavities and thereby vary the total 5 pressure tending to separate the two elements 312 and 330.
It is preferre(l that there by a direct r~latiollship between the cross sectional areas of the various cavities of the first and second sets of cavitiesforming the actuator 310 to obtaill a digital ef~ect by properly connecting the various cavities to either the source of high or low pressure to increase the 10 pressure in selected steps, i.e, each c~vity will have a cross sectional area that is a direct ratio to the cross seetional areas of the other cavities, e.g. multiples of two.
The actuator 310 incorporates an annular exter!sion to the element 312 which forms a first cylinder 38fi in which the driven piston or second element ~S 330 mates to form a hydr7lulic piston 330 and c;ylinder 38~5. The axial length of the cylinder 3B6 ;s sufflcient to accommoda~e movement of ~he piston 330 for t~efull extension of the pistons o~ the first and second sets of pistnns in the second and first sets of piston cavities respectively. The cooperation of the piston 330 in the cylinder 3g~ guides and bettçr ensllres that the small piston elements ie. the 20 pistons of the first and second se~s of pistons extending between the driven piston 330 and the first element 312 are not broken.
The cylinder 3~6 is connected via a hydraulic coupling section 388 to a second cylinder 392 aceommodating a secon~l or working piston 3~0. In the illustrated arrangement this couplin~ is ~ straight tubular passage as is preferred, 25 however i~ could if desired be bent or form¢d by a hydrau]ic hose connection or : the like. The cross sectional area of the pis~on 390 in ~he illustrated arrangement : ~ ~ is significantly less tban the sross se~tional area of the piston 3~0 thus a ~he - ~ ~ pressure applied by the piston 330 through the fluid coupling 388 will result in a corresponûing plessure applied ts) the pisSorl 390 and the piston rod 394 30 colmected thereto. I~ the ratio of th~ areas of the piston 330 and 390 are 10 ~o 1 then the ~orce applied to the piston 39~ will be 1/10 times that of piston 330(the total pressllres will he essentially the same) and the movement, if the pisgon 390 is free to move will be sllch that a 1/10 of an inch movement of the piston ~: ' 2 ~ '7 330 will result in a full inch of travel of the piston 390, Thus a significant increase in the travel of the working piston 390 can be obtained tbrough the useo~ different cross sectional areas of the pistons 330 and 390.
Tn accommodate the differences in cross section~l areas of the first and second cylinder~ 386 and ~92 the hydraulic collpling 388 has a tapered section 387 gradllally chan~ing the cross se~tional area from the larger area of cylinder 386 to the smaller area of cylinder 392 To move the element 330 toward the element 312 the side of ~he piston 390 remote from the coupling 3~8 is connected via line 396 to a further two position valve 398 that may be connected to the high pressure source while a sufficient mlmber of the cavi~ies s)f thç first and second sets n~ cavities between the elemellts 3l2 and 330 are connected to a low pressure source whereby the pressure acting on the piston 3~0 in the directi~n toward the piston 330 is suf~icient to force the piston 390 upward in Figure 7 and force the element or piston 330 to approaeh the element 312.
As above indicated th~ valves 360, 362, 365, 366, 3~8, 370, 372 and 39~ may be any suitable valve to c~nnect ~he actuator to onç pressure sourcc o~
another such as tha~ described hereinabove with respect to Figure S.
The hydraulic conn~ctor 388 may be provided wi~h a system for ~: 20 adding or removing fluid via vent 408 which is controlled ~ia the computer 8~ to add or subtract iluid as indicated by arrows 412 and 414 respectively in accordance with the relative positions of the pistons 330 and 390 as measured bythe sensorw 400 and 40~ respectively.
~: : The descriptism has ~ealt with nnly two hydraulic pressures, it w~ll be apparent that more than twa could b~ llsed with ~ppropriate Yalve changes so :: that any one pressure of a numl)er of dif~erent pressures could be applied selectively tothe cavities.
e~erring now tQ Figure 8 which illu~trates a preferred ~orm of the : ~ : present invention wherein all of ~be Yalves~ high and low pressure reservoirs and i 30 the output cylinder are neatly combined and arranged in an assembly 450.
In Figure g like parts to tbose illus~rated in Figure 7 have been designated by the same referencq nuMerals followed by th~ letter A and thus a detailed description of the digital hydraulic system will not be repeated (however, : : , 17 ~f~
it shollld be noted that there is one less piston ~nd cavity in the two elements312A and 33ûA than with the arrangement shown in Figure 7, i.e. the piston 328 and its corresponding cavity 344 are not providet! in the arrangement shown in Figure 8). Some of the valve,s have been general]y designated with dif~erent numerals than thnse used in Figure 7.
The compact digital actua~or assembly 450 as shown in ~igure 8 is prov~ded at one axial en(l with a cylinder sectioll 452 which defines the pressure cylinder 386A which is substant;ally eq~ al&nt to this cylind~r 386 of the Figure 7 embodiment. At the opposite ~xial end of the unit 450 chamber 454 is provided.
Interposed hetween the cylinder 42 and chamber 454 is a body portion 4SS made up of the first elements 312A ~which cooperates with the moveable elemerlt 330A (second element) or piston) and ~ plurali~ of disc shaped elements 456, 458 and 460 which combine to de~ne the various passagcs and ~o hold or contain the valves as will be described hereinbel~w.
The assembly 450 has a Inn~itudinal axis 462 about which various elements of the assembly are sllbstantially symmetrically positioned.
The chamber 454 is divkied into a high pressure chamber Pl, as : ~ : indicated at 376A and a low pressure chamber P, 380A by a piston 454. A sprin~
~: 20 or other suitable means 466 bias~s the piston 464 toward the high pressure chamber 376A to maintain a pressur~ differen~ial be~ween the high pressure chamber 376A and the low press~lre chamber 3BOA, i.e. the spring 466 biases tb~
piston 464 to or to tend to reduce the size of the high pressure chamber 376 andincrease the size of the low pressure ~hamber 380A and thereby m~intai~l the pressure di~ferential between the high pressure P~l and the low pressure PL
In the illustrated arrangement the disc 456 has an axial extension 4~ ~hrough which a longitudin~l passa~e 470 extends. The piston 464 slides in sealing relationsh;p the axial extension to 368.
The various valves (descr;bed hereinabove as valves 360, 362, 36~, 366, etc. generally indieated by th~ reference numeral 472 (all of the valves are indicated with the same refcrence mlmeral) are moun~ed in the body portions 455 in the elemen~s ~12~ 460) 458 ancl 456 and as well be apparent frc)m Figures 9, ~: 10 and ll are symmetrically positiol1etl ahout ~he axis 462 ;n the cavities 474.

-18 ~ ~ 7 ~
A ~irst passage system connecting the valves 472 to the highpressure chamber 376A is provided hy the longitudinal passage 470 which connects to cavi~ies 474 via radial passages 47fi, 478, 480, 482, 484 and 486.
In reviewing Figure 9, ;t will be noted ~hat there is an extra cavity 5 474 whicJl is adapted to contain a ~urther valve. In this case the valve substantially eqllivalent to tbe valve 398 of the previous embodiment, i.e. the f~lrther ~irst passag~ 490 connects the high pressure reservoir or chamber 376A
with the valve 472 substantially equivalent to the valve 396.
Each of the valves 472 is connected via a separate passage namely lO the passages 492, 494, 496, SOO an~l 502 wllich connect with their respective axially extending passages 504, SOfi, 508, 510, 512 and S14 respectively, to their respective cavity of the digital actuator fnrmed by the elements 312A and 330A (see Figure 11).
Referring again to Figllre lQ, the ca~ 474 housing the valve 15 equivalent to the valve 396 is proYided with a radial passage 516 which cormçcts to an axial passage 518 which in turn connects to fitting 520 ~or coupling to a hydraulic hose or the like as ~ill be described helow.
Ls)w pressure chamher 380A is connected via axial passage 322 (see Fi~ures 9 and 10) to a circum~er~.ntially extending c~annel 524 which 20 interconnects the cavities 474 (see Pigure 11).
To ensure proper ~unet;ol1ing, piston 330A has been provided with a .system for limiting free piston travel to ensllre that the pistnn 330A does not ~: bottom out against the elemellt 312A ~r against the cylinder end of the cylinder section 452. This travel limiter is formed by an anmllar groove 526 (see Fig~re 25 8) which connects via axial passage 528, radial extension 530, radial passage 582, passage 470 and thus the high pressure chamber 376A (see Figures 8 and 9).
A second annular grnove 53~ is also prov~ded in the ~linder wall ~:~ 452, spaced axially from the groove 526 and is connected to a axial passage 534 wliich conneces to a radial passage 53~5, the interconnec~ing passage 524, the axial 30 passage sæ and thus to the low pressllre rese~voir 380A (see lFigures 8, 9 and 11).
The pis~on 33~ is provided on its ollter surface, i.e. around its peripheral w;th a circumferential groo~e 538 whic)l is connected v~a an L shapedpassa~e 540 with the inside of ths cylincler 386A.

, :

1~ 2 0 7 ~
'I'lle lravel limiter operates as ~ollo\~s: if tlle pisk~n 330A moves too close to the cylinder end, i.e. extended too far from the fixed e,lement 312A the groove 538 aligns with the groove 526 thereby connecting inside, of the cylinder386A to the high pressllre chamber ~76A via the passage 5'28, etc. thereby forcing S the piston 330A towards the çlemen~ 312A. On the other hand if the piston 330Aapproaches too closely the element 312A, the groove 538 will align with the groove 532 and connect the cylinder 386A via the line 534, 536, and 538, etc. tothe low pressure reservoir 380A ss) that if there is any of the piston and cavities of the digital actuator system at hi~h pressure the pis~on 330,A will be forced into 10 the cy]inder 386A away ~rom the fixed element 312A.
If the present invention were to be incorporated in an a~tive suspension system wherein each wheel of a vehicle would be supporsed by a~
actuator 399 formed by, ~or exampl~, a piston an~ cylinder arrangement such as tbe piStO11 and cylin(!er 390A, 392A with for example, shaft of the piston as 15 indicated at 394A connected tQ the wheel and the body of the cylinder 392A
connected to the body of the vehicle, Regardless of the use to which the ~systemmay be applied, the high pressure fluid from the cylinder 386A may be connected tQ one side Qf a double piston and cylinder 390A, 392A by a line 388A providing a unit pressure to ghe piston 390A essentially equal to the unit pressure wi~hin the 20 cylinder 38~A, ~: On the opposite en~l of the piston and cylinder 3~0A, 392A, i.e. thc chamher 392,A is cnnnected by a sultable coupling such as a hose coupling as indicated at 396A to the connectors 52Q and thus equivalent to valve 396 which will normally be connected to th~ low pressure reservoir 380A~. To drive the 25 :pist~n 390~ in the opposite direction valve, equivalent to the valve 396 will be shifted to direct high pressure fluid in~o the chamber 39~A as above described.
:~ : Figure 1~ pr~vides a schematic illustration somewhat similar to Figure 8 further incorporating a pump 60Q that is connected Yia a valve 602 to the : ~ ~ ; high and low pressure lines 374 (374A~ 378 (378A) respectively which in turn are 30 connected to the high and low pressure reservoir 376 (376A) and 380 (380A) respectively.
The systern illustrated in Figure 12 further includes an actuator : ~ throttle 604 the purpose o~ whiGh is to limit the speed of the ~vnrking piston ~90 2 ~ 7 ~31 2() (390A), 394 (394A) whcl1 tllcre is no load on the working piston.
The actuator throttle fiO4 j~GIUdeS a throttle valve 606 which is adapted to connects the pressure line from the cylinder 38~, 386A through a throttling orifice schen1aticaJly illustrated at 608 or in the position illustrated to S bypass this thrs)ttling oriPice 60~ and be connected direc~ly wi~h the cylinder 386, 386A. Similarly the return line 396, 3~6A may be conne~ted through to the low pressllre reservoir 380, 38nA vla an orifice 610 as illu~trated by shifting the valve 606 directly to the low pressure reservoir 38(), 380A.
Shif~ing of the valve 6D6 is attained by the di~erence in hydraulic 10 pressure applied to opposite ends of the valve 606 ~ia the valve control pressure lines 6l2 and 614 connected to the lines 3~6 (396A) and 3B8 ~388A) respectively.The throttle 604 operate~ as follows. With no load applied to the working piston390 (390A), there is no pressure dfflerential across the working piston an~
therefore the entire pressure dif~erçntial is applied across the throttle. The flow 15 rate through the throttle, hence the speed of the piston is a function of the size of the throttle orifice 608 or 6tO and the pressure differential applied across i~.
In the extreme case, with no motion of the piston there can be no pressure differential across the throttle and the full pressure differential is applied across the work;ng pistnn. Ihe valve 606 insures that the throttle is always applied 20 across the flow line 388 or 396 from the actuator 399 whi~ is at the higher pressure, This throttle also helps to prevent cavitation, -It will be evident ~hat to in~orporate the assembly into a system four ~:connections are required, namely one to cylinder 386A ~i.e. Iine 388A), one tofitting 5~0, a low pressure line to the rçservoir 380A and a high pressure line to 25 reservoir 376A.
' Having described the in~en~ion modiications will be evident to those sk;lled in the art without departing from the sp;rit of the invention as defined in the appended cla;ms.

.~ .

Claims (14)

Claims

1. A suspension system for a wheeled vehicle having a body portion comprising means for sensing lateral and longitudinal acceleration (18, 20, 22, 24, 26) of said body portion characterized in that, a digital hydraulic actuator (42, 42A, 57, 200, 310, 450) supports said body portion from each of said wheels (10, 12, 14, 16), each said actuator (42, 42A, 57, 200, 310, 450) including a plurality of different effective area actuator sections (60, 62, 64, 68, 70, 72, 74, 208, 210, 212, 214, 314, 316, 318, 338, 340, 342, 344, 314A, 316A, 318A, 338A, 340A, 342A), a first source of hydraulic fluid at a first pressure (PH), a second source of hydraulic fluid at a second pressure PL, said second pressure (PL) being significantly different from said first pressure (PH), valve means (30, 32, 34, 36, 52, 54, 56, 78, 80, 82, 84, 360, 362, 364, 366, 368, 370, 372, 472) for selectively connecting either one or the other of said first source (PH) and said second source (PL) to selected of said actuator sections (60, 62, 64, 68, 70, 72, 74, 208, 210, 212, 214, 314, 316, 318, 338, 340, 342, 344, 314A, 316A, 318A, 338A, 340A, 342A) thereby to vary the number of said actuator sections (60, 62, 64, 68, 70, 72, 74, 208, 210, 212, 214, 314, 316, 318, 338, 340, 342, 344, 314A, 316A, 318A, 338A, 340A, 342A) and thereby the amount of said effective area of each said actuator (42, 42A, 57, 200, 310, 450) subjected to said first (PH) and said second (PL) pressure sources to selectively vary the force applied by each said actuator (42, 42A, 57, 200, 310, 450) independent of the extension of said actuator (42, 42A, 57, 200, 310, 450), computer means (28, 382) for controlling said valve means (30, 32, 34, 36, 52, 54, 56, 78, 80, 82, 84, 360, 362, 364, 366, 368, 370, 372, 472) to adjust the number of said actuator sections (60, 62, 64, 64, 70, 72, 74, 208, 210, 212, 214, 314,316, 318, 338, 340, 342, 344, 314A, 316A, 318A, 338A, 340A, 342A) of each said digital hydraulic actuator (42, 42A, 57, 200, 310, 450) subjected to said first and said second pressures based on anticipated forces at each said actuator (42, 42A, 57, 200, 310, 450) as determined by said computer means (28, 382) based on conditions sensed by said means for sensing lateral and longitudinal acceleration thereby to maintain said body portion substantially stable.

2. A suspension system as defined in claim 1 further comprising means to measure (104) the displacement of each said actuator (42, 42A, 57, 200, 310, 450) to provide a signal representing the displacement of each said actuator (42, 42A, 57, 200, 310, 450) to said computer means (28, 382) and said computer means (28, 382) controlling said valve means (30, 32, 34, 36, 52, 54, 56, 78, 80, 82, 84, 360, 362, 364, 366, 368, 370, 372, 472) to tend to maintain said actuator (42, 42A, 57, 200, 310, 450) in a position wherein said each said actuator (42, 42A, 57, 200, 310, 450) has a preselected degree of extension.

3. A suspension system as defined in claim 2 wherein each said actuator (42, 42A, 57, 200, 310, 450) is a double acting actuator.

4. A suspension system as defined m claims 1, 2 or 3 wherein hydraulic actuator (42, 42A, 57, 200 310, 450) comprises a housing (202), a rotor (204) extending through said housing (202), a plurality of axially extending radially projecting circumferentially spaced lugs (216, 218, 200 222) on said housing (202) and defining a plurality of circumferentially extending spaces (208, 210, 212, 214) therebetween, a pair of circumferentially opposed surfaces (250, 254) on an adjacent pair of said lugs (216, 218) defining opposite circumferentially spacedends of each of said spaces (208, 210, 212, 214), each of surfaces (250, 254) ofsaid pairs of opposed surfaces (250, 254) of an adjacent pair lugs (216, 218, 220, 222) having different areas, axially extending radially projecting spaced bosses(242, 244, 246) on said rotor (204), each said boss (242, 244, 246) being received within a different one of said spaces (208, 210, 212, 214) and dividing its respective said space (208, 210, 212, 214) into a pair of said actuator sections(208A, 208B, 210A, 210B, 212A, 212B) one on each side of said boss (242, 244, 246), each said boss (242, 244, 246) having each of its radial circumferentiallyspaced sides substantially the same area as its adjacent opposed surface of saidlug (216, 218, 220, 222) forming the adjacent circumferential end of said space in which it is received, said lugs (216, 218, 220, 222) having end faces cooperating with said rotor (204) and said bosses (242, 244, 246) having surfaces cooperating with circumferentially extending surfaces of said spaces (208, 210, 212,214) to seal one said actuator section (208A, 208B, 210A, 210B, 212A, 212B) of said pair of sections (208A, 208B, 210A, 210B, 212A, 212B) in said space (208, 210, 212, 214)in which said boss (242, 244, 246) is received from the other of said pair of actuator sections (208A, 208B, 210A, 210B, 212A, 212B), said rotor (204) being rotatable mounted within said housing (202) so that each boss (242,244, 246) mayrotate within its respective space (208, 210, 212, 214)through a preselected angle of rotation and said valve means (52, 54, 56, 78, 80, 82, 84) fluid under said first (PH) or said second (PL) pressure into each of said actuator sections (208A, 208B, 210A, 210B, 212A, 212B).

5. A suspension system as defined in claims 1, 2 or 3 wherein said digital hydraulic actuator (310, 450) comprises a fixed element (312, 312A), a driven piston (330, 330A) cooperating with a first cylinder (386, 386A) formed by said fixed element (312, 312A), said digital actuator (310, 319A) digitally adjusting the pressure between said fixed element (312, 312A) and said driven piston (330,330A) tending to displace said driven piston (3307 330A) in said first cylinder (386, 386A), a second cylinder (392, 392A), a hydraulic coupling (388, 388A) hydraulically connecting said first cylinder (386, 386A) to said second cylinder, said second cylinder (392, 392A) having a cross sectional area different from said first cylinder (386, 386A), a working piston (390, 390A) in said second cylinder(392, 392A) adapted to apply a force determined by the ratio of the cross sectional areas of said first (386, 386A) and second (392, 392A) cylinders.

6. A suspension system as defined in claims 1, 2 or 3 wherein said digital hydraulic actuator (45) comprising a cylinder (386A), a body member (312A) having a fixed element (312A) having a chamber (376A, 380A), said fixed element (312A) cooperating with a piston (330A) in said cylinder (386A), said fixed element (312A) said digital hydraulic actuator digitally adjusting the pressure between said fixed element (312A) and said piston (330A), a second piston (364) dividing said chamber (376A, 380A) into a high pressure chamber (376A PH) and a low pressure reservoir (380, PL), means for urging said second piston (364) toward said high pressure reservoir (376A, PH) to generate said differential in pressure in hydraulic fluid filling said high (376A, PH) and said low pressure reservoir (380A, PL), said valve means (472) set of valves (472) in said body member (312A), a first passage means (470) through said body member (312A) connecting each of said valves (472) to said high pressure (376A, PH)a second passage means (522) in said body member connecting said low pressure reservoir (380, PL) to each of said valves (472), individual passages (504, 506, 508, 510, 512, 514) through said body member (312A) connecting each of said actuator sections (314A, 316A, 318A, 338A, 340A, 342A) with its respective valve (472) ofsaid set of valves (472).

7. A digital hydraulic actuator comprising a fixed member (312, 312A), a driven member (330, 330A) cooperating with a first cylinder (386, 386A) formedby said fixed member (312, 312a) means to digitally vary the pressure acting between said fixed member (312, 312A) and said driven member (330, 330A) tending to displace said driven member (330, 330A) in said first cylinder (386, 386A), characterized in that;
a hydraulic coupling (388, 388A) hydraulically connects said first cylinder (386, 386A) to said second cylinder (392, 392A), said second cylinder (392, 392A) having a cross sectional area different from said first cylinder (386, 386A), a working piston (390, 390A) in said second cylinder (392, 392A) adapted to apply a force determined by the ratio of the cross sectional areas of said first (386, 386A) and second (392, 392A) cylinders.

8. A digital hydraulic actuator as defined in claim 7 wherein said means to digitally vary the pressure acting between said fixed member (312, 312A) and said driven piston (330, 330A) includes a first set of different crosssectional area piston cavities (314, 316, 318, 314A, 316A, 318A) and a first set of different cross section area pistons (322, 324, 326, 322A, 324A, 326A) on said fixed member (312, 312A), a second set of different cross sectional area pistons(332, 334, 336, 332A, 334A, 336A) and a second set of different cross sectional area piston cavities (338, 340, 342, 344, 338A, 340A, 342A) on said driven piston (330, 330A), each piston of said second set of pistons (332, 334, 336, 332A, 334A, 336A) being received within said one of said cavities of said first set of piston cavities (314, 316, 318, 314A, 316A, 318A) and each cavity of said second set ofpiston cavities (338, 340, 342, 344, 338A, 340A, 342A) receiving a piston of said first set of pistons (322, 324, 326, 322A, 324A, 326A), and means to selectivelyapply fluid (360, 362, 364, 366, 368, 370, 372, 472) under selected pressures (PH, PL) to each cavity (314, 316, 318, 314A, 316A, 318A, 338, 340, 342, 344, 338A, 340A, 342A) of said first and said second sets of cavities.

9. A digital hydraulic actuator as defined in claim 8 wherein said means to selectively apply fluid (360, 362, 364, 366, 368, 370, 372, 472) under selected pressure applies one of a first (PH) or a second (PL) pressure to each of said cavities (314, 316, 318, 314A, 316A, 318A, 338, 340, 342, 344, 338A, 340A, 342A), said first (PH) and second (PL) pressures being significantly different.

10. A digital hydraulic actuator as defined in claims 7, 8 or 9 said fixedmember has a chamber (376A, 380A, PH, PL), piston element (464) dividing said chamber (376A, 380A, PH, PL) into a high pressure chamber (376A PH) and a low pressure reservoir (380A, PL), means for urging (466) said piston (464) toward said high pressure chamber (374A, PH) to generate a differential in pressure in hydraulic fluid filling said high (374A, PH) and said low pressure (380A, PL) reservoirs, set of valves (472) in said fixed member (312A), said set of valves (472) including one valve (342) for each of said cavities (314A 316A, 318A, 338A, 340A, 342A), a first passage means (370) through said fixed member (312A) connecting each of said valves (472) to said high pressure chamber (374A, PH), a second passage means (522) in said fixed member (312A) connecting said low pressure reservoir (380A, PL) to each of said valves (472), individual passages through said fixed member (312A) correcting each of said cavities (314A, 316A, 318A, 338A, 340A, 342A) with its respective valve (472) of said set of valves (472).

11. An actuator assembly as defined in claim 10 wherein said valves (472) of said set of valves (472) are symmetrically positioned around the longitudinal axis of said fixed member (312A).

12. An actuator assembly as defined in claim 11 further comprising means for coupling (388A) said cylinder (386A) to a hydraulic actuator (392A) to deliver hydraulic fluid under pressure from said cylinder (386A) to one side of said hydraulic actuator (392A).

13. An assembly as defined in claim 12 wherein said chamber (376A, 380A, PH, PL) and said cylinder (386A) are at axial opposite ends of said fixed member (312A).

14. An assembly as defined in claim 11, 12 or 13 wherein said first passage means (370) includes a passage (370) extending substantially along the longitudinal axis of said fixed member (312A) through a shaft (468) projecting into said chamber (376A, 380A, PH, PL) and wherein said piston element (464) surrounds and slides axially along said shaft (468) in sealed relationship thereto.