DUAL PISTON STRUT

Abstract: A vehicular suspension system incorporates, at each wheel (14), a liquid spring (12) which internally utilizes a compressible liquid to generate spring and damping forces that yieldingly resist vertical wheel deflection relative to the vehicle frame. The liquid spring includes a dual piston assembly (36) which divides a main cylinder into bounce (38) and rebound (40) chambers. A rotary metering valve (80) is interposed between the bounce (38) and rebound (40) chambers for controlling the flow of compressible liquid from one chamber to the other during bounce and rebound. The dual piston assembly includes a tubular piston (48) having a modulation chamber (52) coupled in flow communication with the bounce chamber (38). The spring and damping characteristics of each liquid spring are computer adjusted during vehicle operation by modulating the bounce chamber pressure in response to sensed variations in various liquid spring and vehicle operating parameters.

Description: SPECIFICATION accompanying TITLE: "DUAL PISTON STRUT" Field of the Invention This invention relates generally to suspension systems for land vehicles and, in a preferred embodiment thereof, to a liquid . spring suspension system in which the spring and damping ι: characteristics of each liquid spring are computer adjusted, during vehicle operation, in response to sensed variations in ϊ liquid spring and vehicle operating parameters. j; Background of the Invention Various proposals have been made for replacing the conventional hydraulic shock abβorber and exterior coil spring assemblies in vehicular suspension systems with more compact devices known as liquid springs. A conventional liquid spring includes a cylindrical housing having an internal chamber with a compressible liquid therein, a piston reciprocally disposed in the chamber, a rod structure secured to the piston and axially movable into and out of the chamber, and having an external strut projecting outwardly of one of the housing ends. With the liquid spring operatively interconnected between the vehicle frame and an associated wheel support structure, the compresβible working liquid generates both spring and damping forces in the suspension system in response to relative axial translation between the rod structure and housing of the liquid Bpring cauβed by relative 1 vertical displacement between the wheel and the f ame. 2 The compressible working liquid permits the system to j exhibit a non-linear force/deflection curve. This non-linear 4 behavior is important because it o fers lower spring rates during 5 normal operation and higher spring rates when the vehicle strikes β a bump. Non-linearity in the system is provided by the 7 compressibility of the silicone-based working liquid, which iε 8 approximately 1.5 to 2 times more compressible than conventional 9 , hydraulic fluid. In operation, the non-linear system provides a 0 : spring rate which increases exponentially when the strut moves '.: from its normal static position to full compression. This j: increase permits the suspension unit to absorb sharp bumps without :| bottoming out. In contrast, if the spring rate were linear, a " substantially greater piston stroke would be required to enable the suspension unit to absorb comparable bounce forces. Conventional liquid spring suspensions can be tuned and _ i: readily adjusted for differing vehicle weights (springing force) i; and different ride characteristics (dampening) . It will be r* \l appreciated that non-linear struts that utilize a compressible [j working liquid for both springing and dampening have a potential for superior performance. Description of the Prior Art Various arrangements have been proposed for selectively .. adjusting the spring force and/or damping force characteristics of : liquid springs to settings which remain essentially constant V during vehicle operation until readjusted when the vehicle is at ■■ rest. These essentially fixed spring force and damping force characteristics represent at best compromise settings adapted to i handle an often wide range of road conditions and vehicle operational inputs (such as steering input, braking forces, . vehicle speed and the like) encountered during operation of the • vehicle. I Conventional non-linear suspension systems, for example gas-over-oil systems, are too bulky and heavy for certain commercial and military vehicles . There is a continuing interest ; in reducing the size and weight of such non-linear suspension systems, as well as improving the operational performance. Examples of the general structure and operation of a liquid spring incorporated in a vehicular suspension system are disclosed in the following patents: • 4,741,516 4,877,222 4,735,402 4,652,008 I ' ,_ Object of the Invention ' The principal object of the present invention is to provide . an improved liquid spring vehicular suspension system in which the i spring force and damping force characteristics of the liquid > springs are automatically adjusted, during vehicle operation, to compensate for variations in both road conditions, vehicle load changes and vehicle operational inputs, or any combination ,i thereof. !' |i Summary of the Invention Practicing the present invention, and in accordance with a preferred embodiment thereof, an improved liquid spring vehicular ', suspension system is provided in which the spring and damping ;, force characteristics of each liquid spring are continuously computer adjusted, during vehicle operation, in response to sensed variations in either or both liquid spring and vehicle operating parameters. Each liquid spring comprises a main cylinder housing having a pressure chamber formed therein in which a dual piston assembly is reciprocally disposed and axially divides the main pressure chamber into bounce and rebound chambers. The dual piston assembly includes a support piston secured to the main housing and coaxially disposed within the mam pressure cnamber. A separation piston nead is coaxially secured to the static support piston ana is slidably ana sealingly engaged against the main housing chamber bore fcr axial movement relative thereto into and out of the pressure chamber. The separation piston head is secured to a tubular piston which includes a tubular Btrut portion which projects outwardly of the housing ana which has a longitudinal bore defining a pressure modulation chamber. A compressible working liquid is disposed within the bounce and rebound chambers and within the pressure modulation chamber of the tubular piston. An annular flow passage is defined in the annulus between the static support piston and the tubular piston. Flow transfer ports are formed radially through the tubular piston closely adjacent the reDound chamber side of the separator piston head, and radially extending flow transfer ports are formed '' through the static support piston in communication with the bounce and rebound chambers, respectively. The static support piston is intersected by a longitudinal flow passage which is coupled in flow communication with the bounce and rebound cnambers by the j- flow transfer ports. A rotary metering valve is interposed f between the bounce and rebound chambers and is independently : operable to respectively meter compressible liquid flow . therebetween. The piston modulation chamber is coupled in flow communication with the bounce chamber through a check valve. Each of the liquid springs has its cylinder housing piston ■ secured to an associated wheel structure, and haβ its strut secured to the vehicle frame in a manner βuch that vertical ι[ deflection of the wheel structure relative to the frame causes relative axial displacement between the rod structure and the housing and causes the compressible working liquid to exert spring and damping forces that yieldingly and reactively resist vertical wheel displacement. Control means are provided and are respectively operable to selectively and independently operate the rotary metering valve to meter compressible liquid flow through tne piston roα ports, to selectively varv tne effective volume of the compressible liquid and to selectively vary the pressure of the compressible liquid in the pounce and rebound chambers by modulating tne pressure of the compressible liquid in the modulation chamber. Means are provided for generating liquid spring operating parameter signals including a first signal indicative of the relative axial position of the piston within the housing chamber, and a second signal indicative of the compressible liquid pressure in the bounce chamber. Additionally, means are provided for generating vehicle operating parameter signals which represent- atively include signals indicative of the sense and magnitude of steering input to the vehicle, the speed of the vehicle, and the braking force being exerted on the vehicle. Computer means receive the liquid spring operating parameter signals, and the vehicle operating parameter signals, and responsively generate output signals that are used to operate the metering valve and a proportional flow control valve in a manner automatically adjusting the spring and damping characteristics of each liquid spring to maintain a desired ride height deflection and optimum damping force to maximize ride performance characteristics. Brief Description of the Drawings The features of the invention which are believed to be novel are particularly pointed out and distinctly claimed in the concluding portion of this specification. The invention, however, both as to its operation and organization, together with objects and advantages thereof, may best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings, wherein: Figure 1 is a longitudinal view, and full section, of a αuai piston strut ' constructed according to the teachings of the present invention; Figure 2 is an enlarged view, partially broken away, ___, showing the relative Dosition of the dual piston components in the 2 maximum ride height αeflecrion position: 2 Figure 3 is similar to Figure 2 showing the relative 4 positions of the dual piston components illustrating the relative 5 positions of the dual piston components in response to bounce 5 extension of the mam tubular piston relative to the static support piston; B Figure 4 is a simplified electrical, nydraulic and 9 mechanical scnematic diagram which illustrates interconnection of 0 the various components of a liquid spring suspension system 1 constructed according to a preferred embodiment of the present 2 invention; 3 Figure 5 is a simplified sectional view of a metering valve ■ taken through the line 5-5 of Figure 3; Figure 6 is a performance curve which illustrates strut deflection as a function of dynamic loading; Figure 7 is a simplified schematic diagram showing the liquid spring of Figure 1 in a double wishbone (A-frame) assembly; Figure 8 is a sectional view of the double wishbone (A- ■ frame) assembly of Figure 7 taken along the line 8-8. ' Detailed Description of the Preferred Embodiment : In the description which follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily drawn to scale and the proportions of certain parts have been exaggerated for purposes of clarity. Referring now to Figure 1 and Figure 4, an improved liquid spring vehicular suspension system 10 incorporates a generally vertically oriented dual piston liquid spring 12 at each wheel 14 of the vehicle. The liquid spring 12 is adapted for attachment at its upper end to a vehicle frame F. and at its lower end to the axle spindle 16 of its associated wheel 14. The liquid spring 12 is operable to provide the requisite suspension spring and damping forces at each wheel location. As αescribed below, the liquid spring 12 is controlled by a co Duter IB wnicn continuously ana automatically adjusts key operational aspects of the liquid spring 12 in response to sensed variations in selected vehicle and liquid spring operating parameters. The liquid spring 12 includes an elongated main cylinder housing 20 having an upper housing end 20A and a lower housing end 20B. A spherical bearing 22 is secured to the lower housing end 20B and is connected to the wheel support structure 16 as shown in Figure 4. A spherical bearing 24 is secured to a cylindrical housing boot 26 n which the main housing 20 is telescopically received. The spherical bearing assembly 24 is adapted for attachment to a vehicle frame (not shown) . An annular gland ■' member 28 is connected into the upper housing end 20A of the main cylinder housing 20 by a threaded union T. Interposed between the gland 28 and the upper housing sidewall 20A is an annular, • elastomer seal 30. The main cylinder housing 20 has a cylindrical ■' bore 32 which defines a pressure chamber 34 for receiving compressible silicone-based working liquid. A dual piston assembly 36 is reciprocally disposed in and axially divides the main pressure chamber 34 into a bounce chamber 38 and a rebound chamber 40. The dual piston assembly 36 includes a static support piston 42 which is secured to the lower end 20B of the main housing 20 and is coaxially disposed within the main pressure chamber 3 . A separation piston head 44 is coaxially secured to the static support piston 42 and is slidingly and seaiingly engaged against the main housing chamber bore 32 for axial extension and retraction movement relative thereto into and out of the pressure chamber 3 . The separation piston head 44 is sealed against the main housing chamoer bore 32 by an annular seal 46. The separation piston head 44 is attached to a tubular piston 48 navinσ a longitudinal Pore 50 defining a pressure modulation chamoer 52. The tubular piston 48 has a tubular strut portion 48S projecting outwardly of the main cylinder housing 20 and is mechanically connected to tne housing boot 26 and the spherical 1 . bearing 2 . 2 The upper enα of the support piston 42 is received in 3 telescoping engagement within the bore 50 of the tubular piston 4 48. As can best be seen in Figure 3, a damping flow annulus 54 is 5 formed between the overlapping end portions of the static support 6 piston 42 and the tubular piston 48. The annulus 54 between the 7 static support piston and the tubular piston is sealed by an 8 annular gland seal 56. The tubular piston 48 is sealed against 9 ! the bore of the annular housing gland 28 by an annular gland seal 0 i 58. A flow port 60 is formed through the head of the tubular 1 piston 48 and is engaged by a hydraulic fitting 62 for permitting 2 i the flow of compressible working liquid into and out of the 3 .j pressure modulation chamber as indicated by the double arrow 64. 4 The tubular piston 8 and separator pieton head 44 are thus 5 extendable into and retractable out of the main cylinder chamber 6 34 in response to differential pressure conditions which are 7 imposed within the bounce chamber 38 relative to the rebound , ' 8 chamber 40, and relative to the pressure modulation chamber 52. 9 The deflection position of the separation piston head 44 is 0 detected by a position sensor 66 which is mounted onto the housing 1 boot 26. The position sensor 66 carries a conductor which forms ϊ 2 j one plate of a capacitor, while the second plate of the capacitor 3 ' is formed by a tapered conductive strip 68 attached to the . 4 external side surface of the main cylinder housing 20. The . 5 capacitance produced by the sensor plate and the tapered conductor 6 strip 68 varies substantially linearly as the sensor head is moved 7 :. along the tapered strip. The effective capacitor value produced B li by this arrangement forms a portion of an electronic bridge • 9 - " . circuit which generates an electrical analog output signal 70 0 , which is directly proportional to the radial displacement of the 1 sensor head 66 from the tapered strip 68. Since the strip 58 has a linear taper, the radial displacement of the sensor plate is • : directly proportional to axial displacement of the sensor head from a reference position D 0 (Figure 2). The analog electrical - output signal 70 forms one of the vehicle operating parameter signals which is input to the computer 18. Interchamber flow communication between the Pounce chamber 38 and the rebound chamber 40 is provided by flow transfer ports 72 which are formed radially through the static support piston ■ closely adjacent the lower housing end portion 2OB on the bounce chamber side of the piston, and by flow transfer ports 74 which are formed radially through the static support piston closely adjacent the upper housing end portion 20A on the rebound chamber side of the separator piston head 44. The upper flow transfer ports 74 are in flow communication with the damping flow annulus 54. The flow transfer ports 76 are formed radially through the • tubular piston 48 closely adjacent to the rebound chamber side of ' the separator piston head, in flow communication with the rebound chamber 40 and with the damping flow annulus 54. The static . support piston 42 is intersected by a longitudinal flow passage 78 ii which is in flow communication with the radial flow ports 72 and ■ the bounce chamber 38, and also in flow communication with the upper flow transfer ports 74 and damping flow annulus 54. According to one aspect of the invention, a variable flow ' restrictor 80 is interposed between the bounce chamber 38 and the j rebound chamber 40. Preferably, the variable flow restrictor 80 ' is a rotary metering valve which is independently operable to meter compressible liquid flow from the bounce chamber 38 to the rebound chamber 40, and from the rebound chamber 40 to the bounce chamber 38, respectively. The metering valve 80 includes a D.C. electrical stepping motor 82 having a rotor 82R mounted for rotation about a tubular mandrel 84. Connected to the rotor 82R for rotation on the tubular ; • mandrel 84 is a metering valve body 86 having axially extending . peripheral passages 86A, 86B which, upon appropriate rotation of the rotor 82R, may be moved into and out of metering registration with the flow transfer ports 74 to thereby selectively meter ■ compressible liquid flow between the bounce chamber 38 and the rebound chamber 40. The rotor 02R of the stepping motor 82 is rotatable through nine step increments of ten degrees each so that 1 the valve body metering passages are selectively poεitionable from 2 partially open (maximum αampmg), as snown in Figure 5, to fully 3 open (minimum damping1. 4 The tubular mandrel 84 has a central bore 88 disposed in • 5 flow communication with the flow passage 78 and extends C longitudinally through the support piston 42. The metering valve 7 80 is mounted within a counteroore 90 which is formed in the upper 8 end of the static support piston 42. The metering valve assembly 9 ■ 80 is confined within the counter bore 90 by a threaded retainer 0 cap 92. D.C. electrical power for operating the stepping motor 82 is provided by a conductor 94 which is routed through a . longitudinal bore 96 formed through the sidewall of the support • piston 42. The piston rod 42 and the main housing cylinder 20 . form the D.C. return conductor. A check valve 98 is mounted within a pocket in the retainer cap and is spring loaded to close a discharge flow passage 100 and ■ is yieldable to connect the pressure modulation chamber 52 in fluid communication with the central bore 88 of the tubular , !- mandrel 84 in response to a predetermined pressure differential. " According to this arrangement, a positive pressure differential in ■ ' - the pressure modulation chamber 52 relative to the bounce chamber 38 causes the check valve 98 to open and thereby permit the bounce i chamber 38 to be pressurized to the pressure level of the pressure , modulation chamber 52. The check valve 98 is thus operable to : permit one way interchamber flow from the modulation chamber to the bounce chamber 38, but blocks reverse flow. The tubular piston 48 is slidably and sealingly engaged against the annular housing gland 28, and the sl dable union is further sealed by an annular wiper seal 102. The rebound chamber is further sealed by an 0-riπg seal 104 which is mounted in an annular slot 106 formed in the housing gland 28. Impact forces applied by the separator piston 44 against the annular housing gland 28 are reacted by a resilient bounce pad 108. When the vehicle is at rest, the portion of its weight , supported by the wheel structure and the liquid spring 12 exerts a αownwarά axiai force on tne tubular piston 48 whicn tends to force the separator head 44 further into the main pressure chamber 34, thereby reducing the volume o£ the Pounce chamber 38. Downward movement of the separator piston also reαuces the volume of the pressure modulation chamber, tnereby compressing and pressurizing the working liquid within the pressure modulation chamber 52. As the separator piston 44 strokes downwardly, the compressible working liquid is forced through the flow ports 72 upwardly through the flow passage 78 where it is discharged through the rotary metering valve 80 into the flow transfer ports 74, 76. When the net upwardly directed fluid pressure on the face of the static support piston 42 and on the face of the separator piston 44 equals the load of the vehicle weight Porn by its wheel structure, the tubular piston 48 is at a vertical equilibrium deflection point D l within the main pressure chamber 34 (Figure 3). This equilibrium point established the ride height of the vehicle when it is at rest or travelling along essentially level terrain. hen an additional, upwardly directed bounce force is imposed on the wheel structure, the main cylinder housing 20 is ■■ moved further upwardly along the tubular piston 48 and the flow of compressible working liquid is metered through the metering valve 80 to equalize the pressures in the bounce and rebound chambers. According to an important feature of the invention, the pressure of the bounce chamber 38 is modulated by flow from the pressure modulation chamber 52 to restore the deflection of the separator piston 44 to a desired ride height D- . This is accomplished by the computer 18 which receives the analog signal 70 which is representative of the instantaneous ride height deflection. In response to the ride height deflection signal 70, as well as other vehicle operation parameters, the computer 18 directs an increase or αecrease in the pressure of the pressure modulation chamber 52 by directing the flow cf compressible working liquid from a accumulator through a proportional flow control valve 112 and a directional flow control valve 11 . The accumulator 110 is cnarged from a compressible liquid reservoir 115 by a hydraulic intens ier 117- Referring now to Figure 6, the load deflection response of the liquid spring 12 is illustrated. In this example, the piston ' of the liquid spring 12 is at a vertical equilibrium deflection point A, which corresponds with a stroke deflection D t of three inches, and a precharged pressure level P of about 1800 psi in the bounce and rebound chambers. In response to a bounce impact, and in the absence of a modulating pressure, the tubular piston 48 will stroke through the main pressure chamber 34, with the < • operating point following along the non-linear load deflection it curve X. ithout pressure modulating compensation, the piston {, will continue its stroke until bottoming occurs. However, upon : the application of a high presβure boost of compressible liquid si from the pressure modulation chamber 52 through the check valve 98 ι π into the bounce chamber 38, the piston stroke is reversed at point I: B, with the tubular piston 48 being retracted until equilibrium is _ι reached at the desired ride height deflection Dj at point C on the I !; load deflection curve Y. As the bounce forces are reacted, the i, ( [ pressure within the bounce chamber equalizes with the pressure in t: the rebound chamber, thereby causing the operating point to return ύ to point A on the load deflection curve X. The load deflection ■ . curves X, Y generally define the limits cf an operational load deflection envelope. The operating point A can be established and i, maintained at any point within the operational envelope by .. appropriate modulation of the pressure level within the modulation ,; pressure chamber 52. The proportioning flow control valve 112 is controlled by . a flow rate control signal 116 generated by the computer 18. The proportioning control valve is driven by a pilot actuator 118. The pilot actuator 118 moves a shuttle within the valve "to provide . flow rate proportioning control cf compressible liquid from tne : reservoir 110 to the directional control valve 114 from a- first : i position m which its inputs are fully blocked, to a second position in which both input ports are fully open to receive pressurized working liquid from the reservoir 110, to a third • position which one output port is vented and one output port is blocked. The three position, four way proportioning control valve 112 is also operable to provide continuously variable flow rate control from fully closed (blocked) to fully open (vented) . The directional flow control valve 114 is responsive to computer control signals 120, 122 for selectively charging the - bottom port 124 which is in flow communication with the bounce ' chamber 38, while venting the top port 60 which is in flow i communication with the modulation chamber 52 in a first position, and is movable to a second position in which the bounce chamber 38 is blocked and the modulation chamber 52 is open to receive ; ■ pressurized working liquid from the accumulator 110, and movable to a third position in which the pressure modulation chamber 52 is ' charged and the bounce chamber 38 is vented to permit pressurized working fluid to be returned to the hydraulic supply reservoir 110. ' According to this arrangement, the directional control ! valve 114 is operable to switch the flow through the hydraulic conduits 62, 126 so that the pressure modulation chamber 52 can be switched from charge to discharge, and the bounce chamber 38 can i be switched from charge to discharge according to computer ■ control. Moreover, both the pressure modulation chamber 52 and the bounce chamber 38 may be charged at the same time and both can be blocked at the same time. The pressure modulation chamber 52 and the bounce chamber 38 can be selectively blocked or opened for ; charging and venting, as determined by the vehicle operating parameters. The vehicle operating parameters include input signals developed by a manually/automatic settable ride height controller 128, a vehicle speed transducer 132, a steering transducer 134, a braking force transducer 136 and a manually settable damping .ι controller 138. The ride height controller 128, the vehicle speed • . transducer, steering transduc r, brake transducer, ride height 1 sensor and manual damping controller each produce analog signals 2 which are subsequently digitized by an analog-to-digital converter 3 (ADC) for input to the computer 18. The computer 18 receives 4 these analog and digital vehicle operating parameter signals and 5 generates control signals to the proportioning flow controller 112 ό and the directional flow controller 114, as well as a D.C. 7 . metering control signal 140 which is electrically connected to the 8 power conductor 94 by a connector 142 (Figure 1) and applied to the electrical stepping motor of the metering valve 80 for ■ automatically adjusting the spring and damping characteristics of I- the liquid spring 12 to maintain a desired ride height deflection. !; The use of the proportioning flow control valve 112 and v directional flow control valve 120 in conjunction with the . pressure modulation chamber 52 and the bounce chamber 38 permits •"- the bounce and rebound damping characteristics of the liquid ' spring 12 to be selectively, independently and quickly varied over ,. a wide adjustment range. For example, with the metering valve 80 ; ■ rotated to its maximum position relative to the flow control ports " 74, 76 the damping forces on the static support piston 42 and the , tubular piston 48 are at their minimum magnitudes, with the valve :-■ body 86 being positioned at its least restrictive setting. At the other extreme of the damping range, when the metering valve body . 86 is in its fully closed position as shown in Figure 5, the available bounce and rebound damping forces are maximized. Between those two extremes are an infinite number of relative . valve positions and correspondingly available bounce and rebound damping force settings. . Not only may the metering flow be variably restricted by the metering valve 80, but the pressure modulation chamber 52 and • the bounce chamber 38 may be selectively charged or vented and opened or closed with respect to the output of the proportioning flow controller valve 112, whereby the bounce chamber 38 can be modulated instantaneously by pressure changes in the pressure modulation chamber 52 to further modify the damping 1 characteristics or tne liquid soring 12. This permits the Z pressure modulation cnamoer Ξ2 to oe usec, ror example, to store 3 compression energy as tne housing 20 is deflecteα in one vertical 4 direction, and to release the storeα compression energy as the 5 housing deflects in the opposite vertical direction. 6 Operation of the liquid spring 12 is uniquely controlled 7 during vehicle operation by the control input signals 128 (ride 8 height setting), 132Λ (vehicle speed), 134A . steering), 136A 9 (braking rate), 138A (manual damping) and 70 (deflection height). 0 The deflection signal 70 which is transmitted from the position 1 sensor 66 has a magnitude which is proportional to the deflection 2 distance D : (Figure 3) as measured from the fully extended 3 position D 0 , and is therefore indicative of the axial position of the piston nead 44 relative to the opposite ends of the main cylinder pressure chamber 34. 6 According to this embodiment, both the spring force characteristics and the bounce and rebound damping characteristics • of the liquid spring 12 are continuously monitored and .. automatically varied in response to variations in the vehicle ■■ operating parameters and the deflection operating parameter of the 1 liquid spring itself. For example, the previously described continuous sensing of the deflection position of the piston head 44 enables the computer 18 to compute, at any given instant, the direction of relative travel of the piston 48, its velocity, and its acceleration relative to the main cylinder housing 20, and responsively vary the controller signals 116, 120 to the proportioning flow control valve 112 and the flow direction control valve 114 to substantially instantaneously adjust the . effective piston velocity and/or acceleration during either a bounce or rebound stroke of the wneel 14. It will be appreciated that the suspension system 10 may be conveniently utilized to continuously and automatically adiust the sprmc and damping characteristics of the liquid spring 12 to generally optimize the suspension performance over a wide range of road conditions the vehicle may encounter at any αiven instant. The suspension system 10 takes full advantage of tne instantaneous compliance and compressibility of the εilicone compressible working liquid. Because of the compressible nature of the εilicone working liquid, the suspension system 10 can respond faster to bounce impulses than gas/oil systems because the silicone working liquid does not require hydraulic flow before compliance can occur. The instantaneous reaction and greater damping power reduces not only the magnitude of impact but also • significantly reduces the number of sequential impact cycles i transmitted to the frame, which improves all aspects of handling and ride comfort. Moreover, the improved suspension system 10 is ;' characterized by lighter mass weight and package βize, thereby | i providing lighter unsprung weight which further enhances ride handling characteristics. The improved suspension system 10 is thus capable of f . carrying a wide range of loads and of varying the load force ιi relationship of the liquid spring slowly and instantaneously to ;ι permit a vehicle to travel over rough courses with the suspended t. chassis remaining stable and comfortable. The system thuβ ι! accommodates large variations of static and dynamic loading with •• reduced dynamic affect on the suspended chassis. The suspension t| system has the ability to sense the movement of the piston strut ! 48 including its direction, its instantaneous position and acceleration, and modifies the damping function and bounce or rebound to maximize its reduction of transmitted force to the chassis and thereby improve ride comfort. The ride height sensor signals are read by the computer which generates appropriate output signals the proportional flow controller and the directional flow controller valves to produce the desired pressure force and the required damping level to optimize the chassis ride. For a four wheeled vehicle, the outputs of the four load ride height deflection sensors represent the chassis dynamic motions and describe the heave, pitch, roll ana warp modes cf the chassis relative to the road. The suspension βystem 10 uses the damping force to counteract the _. acceleration forces ana proauces an increase or αecrease in the 2 modulation of the spring lorces to reαuce or increase the 3 displacement at the appropriate strut to affect a more stable ride 4 over an uneven course. 5 The liquid spring suspension units function both as a 6 spring and as a shock absorber in which both functions are capable of modulation within desired ranges to increase or decrease G damping to provide harder or softer performance and increase or 9 decrease the spring force to respond to dynamic road conditions, 0 unsprung mass and chassis motions to effectively reduce the 1 chassis dynamic motions and to produce a smoother, more 2 comfortable ride. The signal from the ride height sensors at each 3 strut are sensed by direction and position in relation to a 4 • desired ride height, thereby providing real time adjustment by the 5 computer. The ride height position signals are continuously 6 : monitored and are used in the control system to compare to other struts indicating chassis, heave, roll and warp modes of operation • and corrective damping and spring forces are instantaneously i' modified within the struts to obtain the desired ride and vehicle I' control. It will be appreciated that the suspension system 10 , provides greater damping force capability and the ability to ' change spring force rapidly. This provides improved performance capability over prior art suspension systems. Moreover, the suspension system of the present invention simplifies assembly by reducing both the numbers and complexity of the liquid spring ■ components. The overall system cost and weight are reduced • correspondingly. Moreover, improved ride quality i's provided over a greater load variation, therepy reducing friction-and improving reliability. Consequently, many of the factors which have impeded tne αeveiopment of practical αynam c ride control suspension system? nave oeen overcome. The suspension system of the present invention is aαaptable to a wiαe variety of applications, in whicn tne following capaoi-ities are provided: a provide fast compliance tor levelling system able to bank into corners level ride on a curve reduce nose dive when braking reduce nose rise when accelerating decrease chassis pitch g decrease chassis roll h reduce chassis bounce cycles reduce peak bounce forces transmitted to the chasβis j. since.,,,the spring force is riding on compressible liquid, J the steering • bearing reaction ±aBaββøaπEZf ' thereby eliminating a separate bearing which would otherwise be required for conventional steel spring reaction and rotation. k. riding on compressible fluidreduces noise and high frequency vibration to_the chassis by better isolation - _ t . r r. ^ ____'"' .. _- _. rr -'r. I. J- ■: 1. electronic damping control can tune the , ' damping forces to provide optimum system requirement for a smooth • ride with damping differential in bounce and rebound m. electronic hydraulic pressure in flow control provides spring force changes in real time so that forces can be modulated for chassis pitch, roll, and vertical (heave) motion cancellation n. reduced stroke length provides a better ride than conventional suspension Bince there is no required stroke to accommodate changes in load capacity of the vehicle t should be noted that the suspension system 10 shown in Figure ■_ is representative for a single wheel assembly in a McPnerson configuration, and that except for common components sucr. as tne computer and nyαraulic reservoir, accumulator and intensifier, corresponding components including the liquid spring are reαuireα rcr eacn wneel. The liαuid spring of the present __. invention may Pe installed in otner suspension configuration, sucn 2 as the double wishbone (A-frame) configuration of Figure 7. The 3 sensing of the piston deflection position may De achieved by otner 4 means, for example by a photoelectric position sensor, a agnetoresistive sensor, or an inductive sensor. It is therefore 6 contemplated that the appended claims are intended to cover ail embodiments of inventions and modifications thereof which do not depart from the sphere and scope of the invention.

Claims: What is claimed is: I. A strut for suspending a wheel assembly from a vehicle frame comprising, in combination: a main cylinder houβing adapted for attachment to a wheel assembly, said main cylinder housing having a bore defining a pressure chamber and having an inlet port for admitting a compressible liquid into said housing pressure chamber; a tubular piston adapted for attachment to a vehicle frame, said tubular piston having a bore defining a pressure modulation chamber and having an inlet port for admitting compressible liquid into the pressure modulation chamber, said tubular piston having an annular head disposed in slidable, sealing engagement against the main cylinder housing bore thereby dividing the main cylinder housing chamber into a bounce chamber ■ and a rebound chamber; a piston rod mounted on the main cylinder housing and projecting through the main cylinder housing chamber into slidable, sealing engagement against the bore of the tubular piston; said piston rod and tubular piston being intersected by flow passages for connecting the 'bounce chamber into flow communication with the rebound chamber; and. valve apparatus coupled in fluid communication with the bounce chamber, rebound chamber and modulation chamber for controlling the flow cf compressible liquid from one chamber to another. . A strut as defined in Claim 1, saiα vaive apparatus comprising: a variable flow restrictor interposed between the bounce chamber and the repound chamber for adjusting the rate of flow of compressible liquid from the bounce chamoer to the rebound chamber and from tne reoound chamoer to the Pounce chamber, respectively; ana, a check valve interposed etween the pressure modulation chamber and the pounce chamber for permitting one way flow of compressible liquid from the pressure modulation chamber into the bounce chamber, and for blocking reverse flow thereof. 3. A strut as defined in Claim 2, said variable flow • restrictor comprising a rotary metering valve having flow passages which are rotatable into and out of flow communication with the bounce chamber and the rebound chamber. 4. A strut as defined in Claim 1, said piston rod being intersected by a longitudinal bore and radial flow transfer ports providing flow communication between the bounce chamber and the rebound chamber, said valve apparatus including a variable flow restrictor interposed between the longitudinal flow passage and the radial flow ports. 5. A strut as defined in Claim 1, said valve apparatus including a tubular mandrel connecting the pressure modulation chamber in flow communication with the bounce chamber, and including a variable flow restrictor mounted for rotation on said tubular mandrel, said variable flow restrictor oeing operably intemosed between the Dounce chamber and the reoound chamPer. 6- A suspension system for use on a vehicle having a frame, a wheel structure, and means for generating a vehicle operating parameter signal, said suspension system comprising: a liquid spring adapted to be operably interposed between the vehicle frame and wheel structure for utilizing a compressible liquid to exert spring and damping forces to reactively control relative vertical displacement between the vehicle frame and wheel structure, said liquid spring including a main cylinder having a bore defining a main pressure chamber and a dual piston assembly disposed within said main pressure chamber, said dual piston assembly including a piston rod attached to the ; main cylinder and a tubular piston movably mounted on the piston ' rod, said tubular piston having a head portion dividing the main - pressure chamber into a bounce chamber and a rebound chamber, a ' tubular strut portion projecting out of the main pressure chamber, i. and a bore formed in the tubular strut portion defining a i modulation chamber; i valve apparatus coupled in fluid communication with the bounce chamber, rebound chamber and modulation chamber for ■ controlling the interchamber flow of compressible liquid from one chamber to another; and, control apparatus coupled to said liquid spring for ' controlling the bounce chamber pressure, modulation chamber preβsure and interchamber flow rate in response to a sensed . variation in a vehicle operating parameter signal 1 . 7. A suspension system as defined in Claim 6, wherein said control apparatus includes: means for generating a liquid spring operating parameter signal; and, a computer coupled to the liquid spring and vehicle operating parameter signals and to the control apparatus for adjusting the bounce chamber pressure, modulation chamber presβure and interchamber flow rate in response to a sensed variation in the vehicle operating parameter signal and in response to a sensed variation in the liquid spring operating parameter signal. 8. A suspension as defined in Claim 7 wherein: the liquid spring operating parameter generating means being operable to produce a signal indicative of the position of the movable piston head relative to the piston rod .! within Baid housing chamber. ._,.__ .- • ■ 9. A suspension system as defined in Claim 6 wherein: said vehicle operating parameter generating means > includes a manually operable controller being operable to produce " an adjustable output signal indicative of the desired ride height 'i deflection of the vehicle. . ' , 10. A suspension system as defined in Claim 6 wherein: I' said vehicle operating parameter generating means : includes a transducer being operable to produce an output signal , proportional to the Bteering input to tne vehicle. 1 II. A suspension system as defined in Claim 6 wherein: 2 said vehicle operating parameter includes a trans- 3 ducer being operable to produce an output signal proportional to 4 the speed of the vehicle. 1 12. A suspension system as defined in Claim 6 wherein: 2 said vehicle operating parameter generating meanβ 3 includes a transducer being operable to produce an output signal 4 proportional to the braking force exerted on the vehicle. 1 13. A suεpenεion system as defined in claim 5 wherein: 2 said vehicle operating parameter generator means 3 includes a manual controller being operable to produce an 4 .. adjustable output signal indicative of a predetermined damping 5 factor. 1 14. a liquid spring suspension βyBtem for use on a 2 vehicle having a frame and a wheel structure, said suspension j • ; system comprising: _> _. 4 ,: a liquid spring including a tubular housing having a main chamber disposed therein for containing a compressible liquid, a tubular piston reciprocally disposed in said chamber having a head portion dividing the main chamber into bounce and rebound chambers, a piston rod mounted on said housing and slidably and sealingly engaged against the bore of the tubular . piston, said tubular piston having an external end portion disposed outwardly of said housing, and damping flow annulus defined between the bounce and rebound chambers; means for operatively associating said liquid spring with said frame and said wheel structure in a manner such that I k AMENDED CLAIMS [received by the International Bureau on 19 August 1992 (19.08.92); original claims 2,6 and 14 amended; other claims unchanged (5 pages)] 2. A strut for suspending a wheel assembly from a vehicle frame comprising, in combination: a main cylinder housing adapted for attachment to a wheel assembly, said main cylinder housing having a bore defining a pressure chamber and having an inlet port for admitting a compressible liquid into said housing pressure chamber; a tubular piston adapted for attachment to a vehicle frame, said tubular piston having a bore defining a pressure modulation chamber and having an inlet port for admitting compressible liquid into the pressure modulation chamber, said tubular piston having an annular head disposed in slidable, sealing engagement against the main cylinder housing bore thereby dividing the main cylinder housing chamber into a bounce chamber and rebound chamber; a piston rod mounted on the main cylinder housing and projecting through the main cylinder housing chamber into slidable, sealing engagement against the bore of the tubular piston; said piston rod and tubular piston being intersected by flow passages for connecting the bounce chamber into flow communication with the rebound chamber; valve apparatus coupled in fluid communication with the bounce chamber, rebound chamber and modulation chamber for controlling the flow of compressible liquid from one chamber to another, said valve apparatus including a variable flow restrictor interposed between the bounce chamber and the rebound chamber for adjusting the rate of flow of compressible liquid from the bounce chamber to the rebound chamber and from the rebound chamber to the bounce chamber, respectively; and, a check valve interposed between the pressure modulation chamber and the bounce chamber for permitting one way flow of compressible liquid from the pressure modulation chamber into the bounce chamber, and for blocking reverse flow thereof. 3. A strut as defined in Claim 2, said variable flow restrictor comprising a rotary metering valve having flow passages which are rotatable into and out of flow communication with the bounce chamber and the rebound chambe . 4. A strut as defined in Claim 1, said piston rod being intersected by a longitudinal bore and radial flow transfer ports providing flow communication between the bounce chamber and the rebound chamber, said valve apparatus including a variable flow restrictor interposed between the longitudinal flow passage and the radial flow ports. 5. A strut as defined in Claim 1, said valve apparatus including a tubular mandrel connecting the pressure modulation chamber in flow communication with the bounce chamber, and including a variable flow restrictor mounted for rotation on said tubular mandrel, said variable flow restrictor being operably interposed between the bounce chamber and the rebound chamber. 6. A suspension system for use on a vehicle having a frame, a wheel structure, and means for generating a vehicle operating parameter signal, said suspension system comprising; a liquid spring adapted to be operably interposed between the vehicle frame and wheel structure for utilizing a compressible liquid to exert spring and damping forces to reactively control relative vertical displacement between the vehicle frame and wheel structure, said liquid spring including a main cylinder having a bore defining a main pressure chamber and a dual piston assembly disposed within said main pressure chamber, said dual piston assembly including a piston rod attached to the main cylinder and a tubular piston movably mounted on the piston rod, said tubular piston having a head portion dividing the main pressure chamber into a bounce chamber and a rebound chamber, a tubular strut portion projecting out of the main pressure chamber, and a bore formed in the tubular strut portion defining a pressure modulation chamber, said pressure modulation chamber having an inlet port for admitting compressible liquid into said pressure modulation chamber; valve apparatus coupled in fluid communication with the bounce chamber, rebound chamber, and pressure modulation chamber for controlling the interchamber flow of compressible liquid from one chamber to another; and, control apparatus coupled to said liquid spring for controlling, the bounce chamber pressure, pressure modulation chamber pressure and interchamber flow rate in response to a sensed variation in a vehicle operating parameter signal. 7. A suspension system as defined in Claim 6, wherein said control apparatus includes: means for generating a liquid spring operating parameter signal; and, a computer coupled to the liquid spring and vehicle operating parameter signals and to the control apparatus for adjusting the bounce chamber pressure, modulation chamber pressure and interchamber flow rate in response to a sensed variation in the vehicle operating parameter signal and in response to a sensed variation in the liquid spring operating parameter signal. 8. A suspension as defined in Claim 7 wherein: the liquid spring operating parameter generating means being operable to produce a signal indicative of the position of the moveable piston head relative to the piston rod within said housing chamber. 9. A suspension system as defined in Claim 6 wherein: said vehicle operating parameter generating means includes a manually operable controller being operable to _ produce an adjustable output signal indicative of the desired ride height deflection of the vehicle. 10. A suspension system as defined in Claim 6 wherein: said vehicle operating parameter generating means includes a transducer being operable to produce an output signal proportional to the steering input to the vehicle. 11. A suspension system as defined in Claim 6 wherein: said vehicle operating parameter includes a transducer being operable to produce an output signal proportional to the speed of the vehicle. 12. A suspension system as defined in Claim 6 wherein: said vehicle operating parameter generating means includes a transducer being operable to produce an output signal proportional to the braking force exerted on the vehicle. 13. A suspension system as defined in Claim 6 wherein: said vehicle operating parameter generator means includes a manual controller being operable to produce an adjustable output signal indicative of a predetermined damping actor. 14. A liquid spring suspension system for use on a vehicle having a frame and a wheel structure, said suspension system comprising: a liquid spring including a tubular housing having a main chamber disposed therein for containing a compressible liquid, a tubular piston reciprocally disposed in said chamber and having a head portion dividing the main chamber into bounce and rebound chambers, and having a bore, a piston rod mounted on said housing and slidably and sealingly engaged against the bore of the tubular piston, said tubular piston having an external end portion disposed outwardly of said housing, and internally defining a pressure modulation chamber having a flow port through which a compressible liquid may be flowed into and out of said pressure modulation chamber, and a damping flow annulus defined between the bounce and rebound chambers; means for operatively associating said liquid spring with said frame and said wheel structure in a manner such that relative vertical movement between said frame and said wheel structure causes relative axial translation between said tubular piston and said housing; and, means for adjustably restricting interchamber flow between the bounce and rebound chambers in response to variation in at least one vehicle operating parameter, to thereby selectively vary the damping force of said liquid spring. STATEMENTUNDERARTICLE19 In order to conform enclosed claim 2, 6 and 14 with the allowed claims of priority application USSN 608,235 filed 2 November 1990, they include the following changes: 1. Original dependent claim 2 has been rendered independent and for which lines 1-27 have been newly added. 2. Original claim 6 has been amended by inserting -- pressure — in lines 19 and 28; and inserting — said pressure modulation chamber having an inlet port for admitting compressible liquid into said pressure modulation chamber -- in lines 19-21 after "chamber". 3. Original claim 14 has been changed at line 1 by changing "a" to — A —; in line 7 -- and — was inserted after "chamber"; in lines 8-S — and having a bore — was inserted aftei "chambers,"; and in lines 12-15 — , and internally defining a pressure modulation chamber having a flow port through whicn E compressible liquid may be flowed into and out of said pressure modulation chamber, -- was inserted after "housing". The remaining claims continue unamended.

Inventors: DAVIS LEO W, DAVIS, LEO, W.
Applicants: DAVIS LEO W, DAVIS, LEO, W.
Application year: 1991
Main classification: F16F5
IPC codes: B60G17, B60G23, F16F5, F16F9