VEHICLE SUSPENSION SYSTEMS

Abstract: A vehicle suspension system comprises a springing means, e.g. an anti-roll torsion bar (15) common to at least two vehicle wheels, means (20) for adjusting the springing means to change its loading, means for sensing vehicle acceleration, means for measuring the adjusted position of the springing means, and control means (26, 27) which respond to the vehicle acceleration to determine the required adjustment of the springing means and to cause it to be adjusted until the required setting of the springing means is reached.

Description: VEHICLE SUSPENSION SYSTEMS This invention relates to vehicle suspension systems, and more particularly to the active control of vehicle suspension systems, that is to say the automatic adjustment of a system part or parts in response to vehicle operating parameters in order to provide an improved suspension performance. One aspect of the design of vehicle suspension systems to which considerable ef ort has been devoted is that of attempting to minimise changes in vehicle attitude as a result of acceleration of the vehicle. Acceleration or deceleration of the vehicle while travelling in a straight line cause changes in the attitude of the vehicle in pitch, while lateral acceleration of the vehicle during cornering causes the vehicle to roll. One well known way in which vehicle roll can be controlled is by the use of a so-called torsional stabiliser bar or anti-roll bar, comprising a torsionally resilient member extending transversely of the vehicle, the opposite ends of which member are connected to appropriate suspension parts for the wheels of the vehicle at its opposite sides so that when the wheels are displaced vertically relative to the vehicle structure by different amounts the transverse resilient member is torsionally loaded. Thus such wheel displacement, and hence vehicle roll, is resisted. However, the design of such an anti-roll bar is a compromise because if it is too stiff the vehicle ride quality on uneven surfaces will deteriorate. Therefore, proposals have been made that the simple anti-roll bar as above described should be controlled so that its behaviour is modified under certain conditions. For example, EP-A-0152914 discloses a stabiliser bar attached to a vehicle body by extensible hydraulic cylinders, to change the effectiveness of the stabiliser bar in accordance with variations in the running conditions of the vehicle. In accordance with sensed inputs such as vehicle steering angle or acceleration, a control system causes the hydraulic cylinders to extend or contract to vary the attitude of the stabiliser bar where it is attached to the vehicle body. However, such attitude of the stabiliser bar is not detected by the system, and therefore the degree by which the effectiveness of the stabiliser bar is varied cannot be precisely controlled to achieve a fully effective stabilisation of the vehicle. Further examples of systems which provide a degree of control over roll of a vehicle are disclosed in GB-1075481 and GB-1037312. However, there is a need for improvements in these previous systems, and the object of the present invention is to provide such improvements. According to the invention we provide a vehicle suspension system comprising springing means which is common to at least two vehicle wheels; adjustment means operable on said springing means to effect a positional adjustment thereof, thereby to change the loading of the spring means; acceleration sensing means for sensing vehicle acceleration and providing a signal representative of said acceleration; means for measuring the position of said springing means as determined by said adjustment means and providing a signal representative of said position; and control means for controlling the operation of said adjustment means, said control means being responsive to said acceleration signal to determine a required position of said springing means, and operable to cause said adjustment means to adjust the position of the springing means until the required position thereof is reached. In the embodiments of the invention first described hereafter, the system is intended to control roll of a vehicle when the vehicle is cornering, and the springing means comprises an anti-roll torsion bar, having opposite ends connected to the wheels at opposite sides of the vehicle. The acceleration sensing means is responsive to vehicle lateral acceleration which occurs when the vehicle is cornering. The positional adjustment which is effected in the springing means is then a torsional adjustment between the opposite ends of the torsion bar. The torsional adjustment between the opposite ends of the torsion bar may be effected directly by a suitable actuator, e.g. a fluid pressure actuator, having a torsional output operative between respective parts of the torsion bar. Alternatively an actuator may adjust the position relative to the structure of the vehicle of a portion of the torsion bar, between said opposite ends thereof, which is mounted to the structure of the vehicle. Whether the torsional adjustment in the torsion bar is effected directly by an actuator which has a torsional output, or by an actuator which adjusts the position of a portion of the torsion bar relative to the vehicle structure, the adjusted position of the torsion bar is measured (e.g. by measuring the position set by the actuator which causes such adjustment) and a signal representative of such measured position is fed back to the control means of the system. The control means stores a range of required values of the position corresponding to the magnitude of sensed vehicle acceleration, and operates so that the adjusted position corresponds to the acceleration. The relationship between acceleration and adjusted position may be a linear relationship, or otherwise to suit the vehicle. By virtue of such controlled relationship between vehicle acceleration and adjusted position of the torsion bar, a much improved suspension performance is obtained. Althgugh it is possible to rely on the torsional resilience of the torsion bar to return the adjustment means therefor to its previous state upon cessation of vehicle acceleration, it is preferred that the control means is operable positively to cause such return. A quicker response is thereby obtained. When applied to a vehicle having first and second pairs of wheels, a suspension system according to the invention may be provided for one only of such pairs, or both such pairs, in which case a common acceleration sensing means and control means may be provided. It is also possible to provide a suspension system for one pair of wheels of the vehicle, and connect the wheels of the other pair thereto so that the springing means also acts on the other pair of wheels. There is also described hereafter a suspension system in which fluid pressure is used as the suspension medium instead of mechanical springs, and in which the system is effective to control movement of the vehicle in pitch as well as roll thereof. The invention further provides a vehicle suspension system comprising any novel feature or combination of features herein disclosed. The invention will now be described by way of example with reference to the accompanying drawings, in which:- Figure 1 is a diagrammatic front elevation of a suspension for a pair of wheels of a vehicle, incorporating an adjustable anti-roll torsion bar in accordance with the invention. Figure 2 is a plan view of the suspension of Figure 1. Figure 3 is a schematic diagram of a suspension according to the invention. Figure 4 is a diagrammatic front elevation of a further embodiment of suspension according to the invention. Figure 5 is a diagrammatic plan view of the suspension of Figure 4. Figures 6 & 7 are enlarged diagrammatic side and front elevations of the torsion bar assembly of the suspension of Figure 4. Figure 8 is a schematic diagram of a further suspension according to the invention. Referring firstly to Figures 1, 2 and 3 of the drawings, there is shown a vehicle chassis 10 to which a pair of wheels, front or rear, rota able on axles 11, are connected by upper and lower wishbones 12, 13. The wishbones 12, 13 are pivotally connected to the chassis 10 and to wheel carrier members in known manner. A respective spring 14 acts between each of the wishbones 12 and the chassis 10. An anti-roll bar in the form of a torsion bar spring 15 extends transversely of the vehicle, the spring 15 having each end portion cranked to form levers pivotally connected through rigid links 16 to the upper wishbones 12. Between its cranked end portions, the central portion of the torsion bar spring 15 is pivotally supported in bearings 17.for angular movement about its axis. Bearings 17 are attached to an adjustable mounting plate 18 extending transversely of the vehicle, one end of the mounting plate being pivotally connected by a pivot 19 to the vehicle chassis. The other end of the mounting plate 18 is connected to the output element of a double acting hydraulic actuating ram 20, the ram 20 being connected at 30 to the vehicle chassis. The ram 20 also incorporates a position transducer, not shown, which gives an electrical output signal representative of the position of the output element of the ram. When the mounting plate 18 is in a horizontal position relative to the chassis 10, as illustrated, no torsional load exists in the torsion bar spring 15 assuming that no such load is imposed due to different relative vertical movements of the wheels relative to the vehicle chassis. Referring now to Figure 3 of the drawings, there is shown diagrammatically a suspension system wherein a first anti-roll torsion bar spring 15 is provided at one end, front or rear, of the vehicle to interconnect the wheels at that end, and a further anti-roll torsion bar spring 15' is provided at the other end of the vehicle to interconnect the other pair of wheels of the vehicle. Respective hydraulic actuating rams 20, 20' are associated with the springs 15, 15'. The suspension includes an hydraulic circuit comprising a reservoir 24 for hydraulic fluid, and a pump 23 delivering the fluid at high pressure to an accumulator 25. The pump 23 may be driven from the vehicle's engine, with a re-circulating valve operable to prevent further delivery of fluid to the accumulator 25 when the accumulator has been charged to its operative pressure. From the accumulator, a pipe leads to a valve unit 26 from which output pipes 28, 29 lead to the rams 20, 20'. The pipe 28 connects to the. upper operating chambers of the rams 20, 20' and the pipe 29 to the lower operating chambers of the ' rams, so that the fluid may be transferred to and from the rams together to control the position thereof, the pressures in the rams being balanced by their hydraulic connection through pipes 28, 29. Also from the valve unit a pipe leads to the fluid reservoir 24, for the return of fluid released from the rams. Electrical connections 31, 32 lead from the position transducers provided in the rams 20, 20', to a control unit 27. The control unit also receives a signal from an accelerometer A, which is arranged to detect lateral acceleration of the vehicle. The mode of operation of the control unit 27 is that it stores a table of values of lateral acceleration and, associated therewith, required positions of the actuating rams 20, 20' . When a lateral acceleration is detected by the accelerometer A and the corresponding output signal applied to the control unit 27, the control unit compares the average position of the rams 20, 20' with the required position thereof corresponding to such acceleration. Any error between the actual positions of the rams and the pre-determined required position thereof will cause the valve unit 26 to operate, to deliver and allow release of the fluid appropriately to the rams until the rams assume the required positions and the error is eliminated. Thus the anti-roll torsion bars are loaded to counteract the effect on the vehicle of the lateral acceleration. By way of example, if Figure 1 is considered to be a rear elevation of the vehicle which is cornering to the right, the vehicle will tend to roll to the left due to centrifugal force acting through its centre of gravity, which normally will be above the roll a_?is of the vehicle. To counteract this requires an extension of the ram 20 (and the ' ram 20' at the other end of the vehicle), and hydraulic fluid is applied to the rams to cause them to extend until they reach a position corresponding to the particular lateral acceleration experienced by the vehicle- The extension of the ram 20 alters the angle of the mounting plate 18 relative to the vehicle chassis, and establishes a torsional loading in the bar 15 which counteracts the attempted roll of the vehicle. Similarly should the vehicle corner in the opposite direction, the rams are caused to retract and load the torsion bars in the opposite sense. When cornering has ceased, and the lateral acceleration of the vehicle, as detected by the accelerometer, reduces to zero, the control unit determines that the rams 20, 20' are required to return to their positions they had before the cornering maneouvre began. The control unit causes the valve unit to operate so that the rams return to such positions. This may be by allowing fluid to flow to and from the appropriate operating chambers of the rams, so that they return to their previous positions by virtue of the relaxation of the torsional loading applied to the torsion bars 15, 15' during cornering. Preferably, however, the valve unit is caused to deliver fluid under pressure to the rams, positively to return them to their previous positions, thereby achieving a faster response to the end of the cornering maneouvre. Although the suspension system shown in Figure 3 has respective anti-roll torsion bars provided for the wheels at both front and rear of the vehicle, the same mode of operation would apply if only one anti-roll torsion bar were provided. A further possibility, if an anti-roll torsion bar can only be accommodated in a vehicle at a position adjacent one of the pairs of wheels thereof, either front or rear, would be to provide respective hydraulic actuators at the other transverse pair of wheels of the vehicle, operative between the chassis of the vehicle and the wheels or suspension parts which move with the wheels. Such actuators would be hydraulically connected together so as to present no resistance to simultaneous bump or rebound movement of the wheels of the pair, but would be hydraulically connected to the actuator associated with the anti-roll torsion bar so that the torsion bar is effective to resist roll at such other pair of wheels as well as at the pair of wheels where it is provided. For example, if the wheels of the other pair are connected to respective piston-cylinder actuators the above-piston space of one such actuator would be connected to the below-piston space of the other actuator, and vice-versa, while one such connection would itself be connected to the lower operating chamber of the ram for loading the torsion bar and the other such connection to the upper operating chamber of the ram. Compensation for lateral acceleration would be applied in the above described manner to the ram operable on the torsion bar, which by virtue of the above described connection would also operate on the other pair of wheels. Referring now to Figures 4 - 7 of the drawings, these show details of a suspension system which differs from that above described in respect of the mounting of the or each anti-roll torsion bar, and the manner in which torsional loads are established therein to resist vehicle roll. A control arrangement as described in relation to Figure 3 would be utilized. In Figures 4 - 7, an anti-roll torsion bar 33 is enclosed and supported with rotational freedom at each end in a tubular housing 34 connected to the vehicle chassis. One end of the torsion bar 33 is rigidly connected to a lever arm 35, thus to be connected by a link 16 to the upper wishbone at one side of the vehicle. The other end of the torsion bar is rigidly connected to a sector pinion 36. The housing 34 for the torsion bar 33 is rotationally mounted in bearing blocks 37 to the vehicle chassis. To one end of the housing 34 is fixed an hydraulic cylinder 38 containing a double ended piston 39, having a central portion gear cut to form a rack engaged with the sector pinion 36. Ports 40, 41 provide for hydraulic connection to chambers 42, 43 respectively defined between the two ends of the piston 39 and the cylinder 38. In the hydraulic circuit shown in Figure 3, port 40 would be connected to the pipe 28, and port 41 to the pipe 29. Rigidly connected to the cylinder 38 is a lever arm 44 which is connected, by a rigid link 16, to the upper wishbone at the side of the vehicle opposite the wishbone connected to the lever arm 35. A position-detecting transducer 45 is secured to the cylinder 38, to detect the position of the piston 39 within the cylinder and provide an output signal representative of such position. In use, the way in which the suspension shown in Figures 4 - 7 operates is substantially the same as that above described in relation to Figure 1 - 3, differing only in respect of the way in which the anti-roll torsion bar spring 33 is adjusted in response to vehicle lateral acceleration during cornering. Instead of actuating ram 20 being adjusted, the position of piston 39 within cylinder 38 is adjusted to a pre-determined required position in accordance with the lateral acceleration of the vehicle as detected by the accelerometer. As for the system of Figures 1 to 3, after cornering has ceased, the piston 39 is preferably positively returned to its previous position within cylinder 38 by supply of fluid under pressure to the appropriate chamber 42 or 43 while fluid is released from the other of the chambers. As an alternative to detecting the position of the piston 39 in the cylinder 38, to provide a signal representing the positional adjustment applied to the torsion bar spring 33, it would be possible to detect and measure a torsional displacement occurring between spaced parts of the torsion bar as a result of movement of the piston 39. For example, a rotary potentiometer could be arranged to be moved directly by such torsional displacement. A further possibility is that a rotary hydraulic actuator could be used instead of the arrangement of cylinder 38, piston 39, and sector pinion 36, to adjust torsionally the torsion bar 33. Referring now to Figure 8 of the drawings, this shows diagrammatically the arrangement of a complete suspension system in a vehicle in which fluid pressure is used as the suspension medium instead of mechanical springs. In the system shown in Figure 8, the four wheels of a vehicle are suspended relative to the chassis of the vehicle by respective hydraulic actuators 100, 101, 102, 103. Such actuators take the place of the mechanical springs in the embodiments above described, and it will be appreciated that the wheels are also connected to the vehicle chassis by suitable linkages, eg upper ' and lower wishbones for each wheel as above described. The actuator 100 comprises a body 104 connected to the vehicle chassis, and an output element in the form of a piston rod 105 connected at its free end 106 to the vehicle wheel carrier, wishbone or other appropriate part of the wheel-supporting linkage. A piston 107 is reciprocable within a cylinder defined in the actuator body 104, to define two variable volume chambers respectively on opposite sides (herein referred to for convenience as above and beneath) of the piston. A position transducer 108 is mounted to the actuator body 104 to detect the position of the piston 107, and provides an output signal representing such position. The actuators 101, 102, 103 are of the same construction as actuator 100, each having a position transducer. Actuators 100, 101 are connected to the front wheels of the vehicle, and actuators 102, 103 to the rear wheels of the vehicle. The cylinder spaces above the pistons of the actuators 100, 101 are connected, by pipes 109, 110, to the space below the piston 111 of a fluid pressure accumulator 112. A spring 113 above the piston 111 presses down on the piston so as to pressurize the fluid contained above the pistons of the actuators 100, 101 and in the pipes 109, 110. A further pipe 114 connects this fluid-filled system to a valve unit 115. . The accumulator 112 has a position transducer 116, responsive to the position of the piston 111 in the accumulator and to provide an output signal representing such position. The actuators 102, 103 connected to the rear wheels of the vehicle have their chambers above their pistons connected to a further accumulator 117 the same as the accumulator 112. A pipe 118 connects the pressurized fluid in accumulator 117 to the valve unit 115, separately from the pipe 114 leading from the actuators and accumulators for the vehicles front wheels. The system further comprises two more fluid pressure accumulators 119, 120. These are of the same construction as the accumulator 112, but have fluid connection with the variable volume chambers beneath the pistons of the actuators 100 - 103. Accumulator 119 is connected to the beneath-piston chambers of the actuators 100, 102 connected to the wheels at the left hand side of the vehicle, whilst accumulator 120 is similarly connected to the actuators 101, 103, at the right hand side of the vehicle. Fluid connections are established, independently of one another, from the accumulators 119, 120 to a further valve unit 121. Accumulators 119, 120 are provided with respective position transducers, and the outputs from these transducers together with those from all the other position transducers within the system are connected to a central control unit 122. The control unit 122 is a computer arranged and programmed to operate in the manner hereafter described. The control unit 122 has a further input from an accelerometer unit 123 which contains two individual accelerometers, one oriented so as to respond to the lateral acceleration of the vehicle and the other oriented so as to respond to longitudinal acceleration of the vehicle, which accelerations would cause, unless compensated for by the suspension system, roll and pitch of the vehicle respectively. The control unit 122 produces output signals which are applied to the valve units 115, 121. The fluid circuit of this suspension system further comprises a reservoir 124 for hydraulic fluid, a pump 125, and a main accumulator 126 from which supply pipes lead to the valve units 115, 121 to deliver fluid under pressure thereto. Return pipes from the valve units lead back to the fluid reservoir 124. The operation of the system is as follows. It will be appreciated that, for each wheel, the springing force resisting displacement of the wheel relative to the chassis is dependant on the difference between the fluid pressures above and beneath the piston of the respective actuator 100 - 103, acting on the different piston areas above and beneath the pistons. For the front wheels of the vehicle, this is related to the difference between the pressure in the accumulator 112 connected to the above- piston spaces of the actuators 100, 101 and the pressures in the accumulators 119, 120 connected to the below piston spaces of these actuators. For the rear wheels of the vehicle, the relevant difference in pressure is that between that of the accumulator 117 and, again, the accumulators 119, 120. The control unit 122 is programmed so that when it has no input signal from either of the accelerometers in the unit 123, all the valves in the valve units 115, 121 are closed so that the volume of fluid in the respective circuits connected to the accumulators 112, 117, 119, 120 are all constant. If the vehicle is travelling and one of the front wheels thereof encounters a bump, movement of the piston in the appropriate actuator 100, 101 will cause a corresponding movement of the piston in the accumulator 112, and the control unit 122 will receive signals from the transducers associated with the actuator and accumulator.' The control unit will detect that the signals are of equal magnitude, and thus represent a situation which requires no compensatory action in the suspension system. If both front wheels of the vehicle encounter the same bump, generally equal displacements of the pistons of the actuators 100, 101 will result in a displacement of the piston in the accumulator double that produced when only one wheel encounters the bump. Again, the control unit detects that this is a situation requiring no compensatory action in the suspension. Of course, similar displacements occur in the actuator and accumulator at the rear wheels of the vehicle, again producing output signals from their position transducers which require no compensatory action in the suspension. It will be appreciated, of course, that the accumulators 119, 120 connected to the below-piston spaces of the actuators also undergo corresponding displacements which are observed by the control unit. If the vehicle should undergo acceleration or de- acceleration, which could tend to cause pitch movements of the vehicle, this will be detected by the accelerometer in the accelerometer unit 123 responsive to fore and aft acceleration. In response to such a condition the control unit applies a signal to the valve unit 115 to deliver additional fluid to or release fluid from the accumulators 112, 117 so that they are, in effect, adjusted to compensate for such acceleration so that the vehicle maintains a substantially level attitude. Because the volume of fluid in the fluid circuits of the accumulators 112, 117 is being altered, the combined signal from the position transducers of these accumulators and the actuators connected thereto are not substantially equal as in the case of wheel bump above described. The control unit operates so that the valve unit 115 changes the volume of fluid in the accumulators until the combined signal from the position transducers reaches a pre-determined value corresponding to the magnitude of the vehicle's acceleration. When the acceleration ceases, the control unit causes valve unit 115 to supply and release fluid from the systems associated with the accumulators 112, 117 until the required steady-state fluid content for the systems is achieved, whereafter the appropriate valves in the valve unit 115 are closed and remain closed until further vehicle accelerated or de-acceleration occurs to be compensated for in the above manner. At the same time, of course, the control unit will respond to any lateral acceleration as detected by the other accelerometer in the accelerometer unit 123. If there is no lateral acceleration, all valves in the valve unit 121 are closed so that constant volumes of fluid are contained in the hydraulic systems connecting the accumulator 119 and the below-piston spaces of actuators 100, 102; and the accumulator 120 and the below-piston spaces of the actuators 101, 103. If lateral acceleration of the vehicle is detected, the control unit will apply a signal to the valve unit 121 to cause a suitable adjustment in the fluid volumes of the systems at the two sides of the vehicle to compensate for roll of the vehicle which would otherwise occur. For example, if the vehicle were to roll to the left in response to lateral acceleration to the right release of some fluid from the fluid circuit of accumulator 119 and the below-piston spaces of actuators 100, 102 would result in an effective increase in the spring force exerted by these accumulators (because the net force exerted thereby is the result of the difference between their above and below-piston pressures, acting on the different areas presented above and below the pistons). Thus such roll of the vehicle is resisted. After such lateral acceleration has ceased, restoration of the previously existing fluid volumes restores the vehicle suspension to its normal condition. The system can also compensate for changes in the ride height of the vehicle due to changes in the load carried thereby. The control unit can be programmed to detect any change in the mean positions of the pistons in the actuators of the system, but take no account of any transient such change. In the case of any such change existing for more than a pre-determined period of time,' however, the control unit can cause the valve unit 115 to deliver some additional fluid to the circuits of the front and rear accumulators 112, 117, thereby to restore the vehicle to its desired ride height. Although piston-cylinder type of actuators and accumulators have been described above, it will appreciated that these are exemplary only and in practice there are alternative forms of such units which may be utilized. For example, actuator units incorporating diaphragms rather than pistons could be employed, and the accumulators may be gas pressurized rather than spring pressurised.

Claims: CLAIMS 1. A vehicle suspension system comprising springing means which is common to at least two vehicle wheels; adjustment means operable on said springing means to effect a positional adjustment thereof, thereby to change the loading of the spring means; acceleration sensing means for sensing vehicle acceleration and providing a signal representative of said acceleration; means for measuring the position of said springing means as determined by said adjustment means and providing a signal representative of said position; and control means for controlling the operation of said adjustment means, said control means being responsive to said acceleration signal to determine a required position of said springing means, and operable to cause said adjustment means to adjust the position of the springing means until the required position thereof is reached. 2. A suspension system according to Claim 1 wherein said springing means comprises an anti-roll torsion bar, having opposite ends connected to the wheels at opposite sides of the vehicle. 3. A suspension system according to Claim 2 wherein said adjustment means comprises an actuator having a torsional output operative between respective parts of the torsion bar. 4. A suspension system according to Claim 2 wherein said adjustment means comprises an actuator operable to adjust the position relative to the structure of the vehicle, of a portion of the torsion bar mounted to the structure of the vehicle. 5. A suspension system according to Claim 3 or Claim 4 wherein said adjustment means comprises a fluid pressure actuator. 6. A suspension system according to any one of Claims 2 to 5 wherein said control means is operable to cause the adjustment means positively to return the torsion bar to a previous state of torsional adjustment upon cessation of vehicle acceleration. 7. A vehicle comprising a first pair of wheels on opposite sides of the vehicle, a second pair of wheels on opposite sides of the vehicle, and a suspension system according to any one of Claims 2 to 6 for at least one of said pairs of wheels. 8. A vehicle according to Claim 7 when appendant to Claim 5 wherein the suspension system is provided for one of said pairs of wheels, and the wheels of the other pair are connected to actuators which have fluid connection to the actuator of the suspension system, whereby the springing means also acts on the wheels of the other pair. 9. A vehicle according to Claim 7 wherein a respective suspension system is provided for each of said pairs of wheels with a common acceleration sensing means and control means. 10. A suspension system according to Claim 1 wherein said springing means comprises a fluid pressure spring, and said adjustment means affects a positional adjustment of a fluid interface thereof. 11. A suspension system according to Claim 10 wherein said springing means comprises an hydraulic accumulator having hydraulic connection to actuators associated with and operable on the wheels, and the adjustment means effects an adjustment of the quantity of fluid in the accumulator, actuators, and connection therebetween. 12. A suspension system according to Claim 11 further comprising means for measuring the position of members of the actuators connected to the wheels and for providing signals representative thereof to the control means in addition to the signal from the accumulator. 13. A suspension system for a first pair of vehicle wheels and for a second pair of vehicle wheels spaced from the first pair, comprising a respective system according to Claim 11 or Claim 12 for each pair of wheels and a common control means therefor. 14. A suspension system according to Claim 13 further comprising respective further hydraulic accumulators having hydraulic connections to the actuators associated with corresponding wheels of each pair, pressure exerted by the further hydraulic accumulators opposing the pressure exerted by the first said accumulators. 15. A suspension system according to Claim 14 wherein the acceleration sensing means is responsive firstly to fore-and-aft vehicle acceleration and secondly to lateral vehicle acceleration and the control means effects an adjustment in the first said accumulators in response to one of said accelerations and in the further accumulators in response to the other of said accelerations.

Inventors: MUMFORD MICHAEL ANTHONY, MUMFORD, MICHAEL, ANTHONY
Applicants: GKN TECHNOLOGY LTD, GKN TECHNOLOGY LIMITED
Application year: 1988
Main classification: B60G21
IPC codes: B60G17, B60G21