GB2282784A

GB2282784A - Vehicle suspension system

Info

Publication number: GB2282784A
Application number: GB9417494A
Authority: GB
Inventors: Scott Wilson Badenoch; Geoffrey William Burgess; Gary Chris Fulks
Original assignee: ACG France SAS
Current assignee: ACG France SAS
Priority date: 1993-10-08
Filing date: 1994-08-31
Publication date: 1995-04-19
Also published as: GB9321056D0; GB9417494D0; DE4433142A1

Description

VEHICLE SUSPENSION SYSTEM 2282784 The present invention relates to a

vehicle suspension system.

A number of "advanced" suspension components and techniques have recently been developed for improving vehicle ride quality. These have allowed a variety of controlled suspension systems to be developed. However, these systems have generally been complex and costly and therefore limited to the luxury segment of the market.

The present invention seeks to provide an improved vehicle suspension system.

According to an aspect of the present invention, there is provided a vehicle suspension system including a controllable shock absorber coupled proximate each corner of the vehicle body and to a respective wheel, a plurality of sensors including at least two sensors coupled so as to detect movement of the vehicle body relative to two or more of the wheels, the sensors being operative to measure activity on the vehicle suspension or body of the type which causes resonance of the vehicle body, and control means for controlling the degree of damping provided by the shock absorbers; the control means including analysing means operable to analyse the sensor outputs to derive therefrom one or more signals representative of activity on the vehicle suspension or body of the type which causes resonance of the vehicle body, and processing means operable to generate a shock absorber control signal having a magnitude related to the particular type or types of activity analysed.

The sensors may be arranged to sense wheel resonance which may cause body resonance, such as heave, roll and pitch resonance.

2 It has been discovered that use can be made of activity on the vehicle suspension or vehicle body which typically leads to resonance of the vehicle body, including activity which is not directly related to vehicle body movement, such as wheel movement and movement of the steering actuator. For example, when the wheels are jolted as a result of a bump or other protrusion on the road surface, the effect of the wheel jolt on the suspension can lead to subsequent body resonance. More specifically, wheel travel as a result of a bump or other road protrusion can lead to body resonance and can be detected by analysing the suspension travel. Thus, by analysing and detecting wheel jolt, the shock absorbers can be adjusted is immediately so as to reduce vehicle body movement.

Moreover, in preferred embodiments, it is possible to separate types of movement of the vehicle body relative to the wheels, which can simplify considerably the amount of control required for the shock absorbers to provide optimised handling and comfort. The use of only two sensors, in the preferred embodiment, can reduce the complexity of the system.

It is possible with the present invention to provide normal damper work at body spring resonance and increased isolation, that is reduced damping forces, when damping is not necessary. The degree of damping is preferably tuneable and not limited to the requirements for primary damping. 30 In effect the system looks at the potential for the shock absorbers to do work in response to activity on the vehicle suspension. Advantageously, the analysing means includes vehicle body resonance detecting means comprising a 335 bandpass filter adapted to detect resonance of the 3 vehicle body, the processing means being operative to generate a shock absorber control signal having a magnitude related to the detected vehicle body resonance. Preferably, the shock absorber control signal has a magnitude related to the magnitude of the detected vehicle body resonance. Vehicle body resonance is one of the vehicle motions which reduces ride quality and vehicle handling.

Preferably, the analysing means comprises jolt detecting means adapted to generate a jolt signal on detection of a jolt at one or more wheels of the vehicle, the processing means being operative to generate a shock absorber control signal having a magnitude related to the jolt signal. The jolt detecting means may be operative to maintain the jolt signal at a high level for a predetermined period after detection of a jolt at the wheel or wheels.

Advantageously, the analysing means comprises wheel resonance detecting means including a bandpass filter adapted to provide a wheel resonance signal representative of resonance of one or more of the vehicle wheels, the processing means being operative to generate a shock absorber control signal having a magnitude related to the wheel resonance signal. The wheel resonance signal may have a magnitude related to the magnitude of the detected wheel resonance.

Preferably, the wheel resonance detecting means is operative to maintain the wheel resonance signal at a high level for a predetermined time after detection of a resonance of the wheel or wheels.

The analysing means may comprise float detecting means operative to provide a float signal on detection of floating of the vehicle body, the processing means being operative to generate a shock 4 absorber control signal having a magnitude related to the float signal. The float detecting means is preferably operative to generate a float signal only when the speed of the vehicle relative to the wheels is less than a predetermined amount, in other words when the rate of damper movement is above a predetermined threshold. In practice, a float signal is generated when the rate of damper movement is above a float control threshold and less than a body control threshold.

In a preferred embodiment, there is provided a steering actuator sensor, the analysing means being operative to analyse the steering actuator sensor output to derive a signal representative of movement of the steering actuator, the processing means being operative to generate a shock absorber control signal having a magnitude related to the steering actuator movement signal. The analysing means may be operative to derive a steering actuator movement signal only when the steering actuator sensor output exceeds a predetermined threshold level, which may be representative of a threshold steering velocity. Any significant movement of the steering actuator, which may be a steering wheel, will affect the vehicle body.

Thus, by controlling the suspension upon a change in the position of the steering actuator, it is possible to prevent or significantly reduce any effect on the vehicle body.

It has been found that the above five types of vehicle body and wheel movement represent the most important types of disturbances on a vehicle.

In a preferred embodiment, the analysing means is operable to derive from the sensor outputs a plurality of signals representative of a plurality of particular types of activity on the vehicle suspension or body, the processing means including summing means for summing together the signals related to each detected type of activity, the sum forming the shock absorber control signal.

Advantageously, the processing means comprises gain means effective on the derived signals to determine the contribution of each derived signal on the shock absorber control signal.

The degree of damping provided by the shock absorbers may be set at or within maximum and minimum damping levels. The maximum damping level is preferably chosen for optimisation of vehicle handling, while the minimum damping level is preferably chosen for optimisation of comfort.

In the preferred embodiment, the sensors include displacement sensors disposed to measure the relative displacement of the shock absorbers. Advantageously, only two sensors are provided, disposed on shock absorbers at the front of the vehicle.

According to another aspect of the present invention, there is provided a vehicle suspension system comprising a controllable shock absorber coupled proximate each corner of the vehicle body and to a respective wheel, first and second sensors operative to sense operation of the shock absorbers coupled to the two front wheels of the vehicle, and control means for controlling the degree of damping provided by the shock absorbers; the control means including analysing means operative to analyse the sensor outputs to derive first and second signals representative of the operation of said front shock absorbers, and processing means operative to generate a shock absorber control signal having a magnitude related to the detected operation of said two front 6 shock absorbers. In alternative aspects of the present invention, the first and second sensors may be operative to sense operation of two shock absorbers coupled respectively to front and rear wheels of the vehicle, said two shock absorbers being either on the same side or on opposing sides of the vehicle.

Preferably, the first and second sensors are displacement sensors operative to sense the movement of the vehicle body relative to the two front wheels.

Alternatively, the first and second sensors may be pressure sensors operative to sense pressure inside said two front shock absorbers. It has been found that the use of only two such sensors can provide sufficient data to enable effective and relatively cheap suspension control. It has also been found that the system could also work satisfactorily with a single sensor.

According to another aspect of the present invention, there is provided a vehicle suspension system comprising a controllable shock absorber coupled proximate each corner of the vehicle body and to a respective wheel, a steering actuator sensor, and control means for controlling the degree of damping provided by the shock absorbers; the control means including analysing means operative to analyse the steering actuator sensor output to derive a signal representative of movement of the steering actuator, and processing means operative to generate a shock absorber control signal having a magnitude related to the analysed movement of the steering actuator. Significant steering changes effect the vehicle body. Thus, suspension control which is commenced as soon as a steering change is detected can significantly reduce body movement caused by the steering change.

7 The system may include bi-state shock absorbers or continuously variable shock absorbers. In either case, the maximum and minimum damping level provided by the shock absorbers is preferably determined by experiment. Advantageously, the maximum damping level is substantially at or slightly higher than the acceptable level for the particular vehicle (for example between 0.3 and 0.5 of critical damping). The minimum damping level may be substantially between 0.05 and 0.1 of critical damping, the system attempting to keep this level of damping whenever vehicle body control is not required.

Experimental tests have shown that it is possible, both with bi-state and continuously variable shock absorbers, to reduce the average damping level to around 0.15 of critical damping without significant loss of vehicle body control. Moreover, it has been found that continuously variable shock absorbers can exhibit good performance in both the time and frequency domains, and that it is possible to provide satisfactory damping even when the control signal is limited to 10 Hz and a shock absorber of similar bandwidth is used.

An embodiment of the present invention is described below, by way of illustration only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of an embodiment of vehicle damping system; Figure 2 is a block diagram of an embodiment of control system; Figure 3 is a graph illustrating suspension movement and shock absorber control during jolt of the vehicle wheels; and 8 Figure 4 is a graph illustrating suspension movement and shock absorber control during wheel resonance.

Referring to Figure 1, a vehicle 10, shown in schematic form, includes four hydraulic shock absorbers 12-18, each connected at a first end to the vehicle body and at the opposite end to the unsprung mass of the vehicle, adjacent a respective wheel (not shown). Each shock absorber 12-18 includes a control valve 20-26 coupled to an electronic control unit 28 for controlling the magnitude of damping provided by each shock absorber.

In the preferred embodiment, the shock absorbers 12-18 are controllable to provide continuously variable damping. Alternatively, the shock absorbers 12-18 may be of the bi-state type, being controllable either to maximum or minimum damping levels.

The damping system also includes two displacement sensors 30,32 coupled to the two shock absorbers 12,14 at the front of the vehicle. These displacement sensors 30,32 measure the relative displacement of the shock absorbers, thereby obtaining a measure of the displacement of the front wheels of the vehicle relative to the vehicle body. In an alternative, two sensors across the front may allow roll resonance level to be detected; two sensors, one front and one rear, may allow heave and pitch to be detected; while two sensors, one front and one rear on the opposite side of the vehicle may allow some measure of heave, pitch and roll.

In an alternative embodiment, the two displacement sensors may be replaced by two pressure sensors arranged to sense the quasi-static pressure of their respective shock absorber; or any other sensor 1 9 which can measure activity on the vehicle suspension or body of the type which may cause resonance of the vehicle body.

In addition to the two sensors shown, the preferred embodiment includes a steering actuator sensor, in this case a steering wheel sensor, for detecting movement of, and in particular acceleration of, the steering actuator.

The electronic control unit 28, which is of any suitable type, is coupled to receive the signals from the two sensors 30,32 and to transmit control signals to the four control valves 20-26. The general structure of the electronic control unit will be readily apparent to the skilled person, so will not be described in any further detail herein.

The control unit 28 reads the signals received from the two sensors 30,32 in order to determine if there is displacement of the two front shock absorbers 12,14. When such displacement is detected, the control unit 28 analyses the signals to determine the character of the displacement which has occurred, in other words the manner in which the vehicle body or vehicle wheels are or will move.

From the analysis of the character of the displacement, the electronic control unit 28 carries out one or more of a series of control procedures for changing the degree of damping provided by the shock absorbers 12-18. The degree of damping is varied between maximum and minimum values determined by experiment for the specific vehicle. When the shock absorbers 12-18 are of the continuously variable type, the control unit 28 varies their damping level between the predetermined maximum and minimum levels. On the other hand, when bi-state shock absorbers are used, these are chosen to have damping levels equivalent to the predetermined maximum and minimum levels.

The maximum and minimum damping levels are chosen to optimise the damping forces for each of the separate handling and comfort requirements for particular road inputs. In practice, vehicle parameter inputs are used to determine the necessary effective damping coefficients which will result in optimised handling and comfort. A realistic range of frequency and displacement amplitudes, obtained from road tests, is obtained for wheel and vehicle body motions and a matrix of damping force versus shock absorber velocity input is derived. From these calculations, it is then possible to determine the maximum (hard) and minimum (soft) damping calibration levels. In practice, it has been found that the maximum damping level is substantially at or slightly higher than the acceptable level for the particular vehicle (for example between 0.3 and 0.5 of critical damping), while the minimum damping level is substantially between 0.05 and 0.1 of critical damping. The minimum damping level is maintained whenever vehicle body control is not required.

Figure 2 shows in block diagram form a embodiment of control procedures for changing the degree of damping provided by the shock absorbers 12-18, which in this embodiment are of the continuously variable type. The embodiment disclosed below is described in terms of electronic hardware, although it will be apparent to the skilled person that it could equally be implemented in software form. It will be apparent that the signal from one sensor will be processed independently of the other sensor, the result then being combined if appropriate, thereby 11 to produce a control output which is effective on all the shock absorbers.

The first control block 100 is designed to deal with resonance of the vehicle body, caused for example by an uneven road surface, by increasing the damping level when vehicle body resonance is detected.

The body resonance control block 100 includes a bandpass filter 102 set to pass those frequencies of the input signal which are around the natural resonance frequency of the specific vehicle. Coupled to the bandpass filter 102 is a rectifying circuit 104 for converting the filtered signal into a voltage level.

A smoothing circuit 106 is connected to the output of the rectifying circuit 104 to smooth the signal output therefrom. In this embodiment, the smoothing circuit 106 is formed of a diode coupled in series between the input and output of the smoothing circuit and a capacitor and resistor coupled in parallel to one another. First terminals of the capacitor and resistor are connected between the diode and output of the smoothing circuit, while their second terminals are connected to ground.

The output from the smoothing circuit 106 is a voltage level proportional to the degree of resonance of the vehicle body. This output is coupled to a multiplier 108 for multiplying the voltage level by a gain factor 110. The adjusted voltage level is then fed through a hysteresis circuit 112.

The output from the hysteresis circuit 116, that is the output from the body resonance control block 100, is a signal proportional to the amount of damping which should be provided by the shock absorbers 12-18. The gain factor 110, which is determined by experiment, adjusts the level of the 12 signal to provide the most appropriate amount of damping for the specific vehicle.

The second control procedure is a wheel jolt control block 120 designed to deal with the effect on the vehicle of a bump in the road surface which causes a jolt in the front wheels.

The jolt control block 120 includes a differentiator 122 coupled to its input for producing a signal related to the velocity of the displacement.

The output of the differentiator is coupled to a rectifier circuit 124 for producing a voltage level, which is fed to a re-triggerable monostable 126. The monostable 126 is triggered to a high state when the input from the rectifier 124 is above a predetermined trigger level, and remains at this high state until the input falls below the predetermined trigger level.

The monostable 126 is set to remain at the high state for a predetermined time period after the input falls below the predetermined trigger level.

The output of the jolt control block 120 is a two-level signal indicative of the maximum or minimum damping level which can be provided by the system. The signal remains high, that is at the maximum damping level, for a predetermined period after detection of a bump in the road surface, to retain vehicle body control.

The third control procedure shown is a wheel resonance control block 130 designed to deal with the effects of resonance of the vehicle wheels. The control block 130 includes a bandpass filter 132 set to pass those components of the sensor signals around the resonance frequency of the vehicle wheels.

Coupled to the bandpass filter 132 is a rectifier 134 for converting the filtered signal into a voltage level. The output of the rectifier 134 is coupled to l 13 a re-triggerable monostable 136. The monostable 136 is triggered to a high state when the input from the rectifier 134 is above a predetermined trigger level and remains at this high state until the input falls below the predetermined trigger level. The monostable 136 is set to remain at the high state for a predetermined time period after the input falls below the predetermined trigger level.

In similar manner to the bump control block 120, the output of the wheel resonance control block 130 is a two-level signal indicative of the maximum or minimum damping level which can be provided by the system. The signal remains high, that is at the maximum damping level, for a predetermined period after detection of wheel resonance, to retain vehicle body control.

The fourth control procedure shown in Figure 2 is a float control block 140 designed to deal with the effects of floating of the vehicle body when the shock absorbers 12-18 are set at low damping levels. The float control block includes a differentiator 142 which obtains a measure of the velocity of the displacement of the front shock absorbers 12,14, in other words the velocity of the displacement of the vehicle body relative to the wheels. The differentiator 142 is coupled to a comparator 144 which is triggered high when the displacement velocity signal is below a predetermined velocity V, in other words when the relative vehicle body velocity is less than a predetermined velocity.

The output of comparator 144 is coupled to a monostable 146 which has a trigger level determined by capacitor 148 and variable resistor 150. The resistor 150 is varied in proportion to the amount of damping 35 to be provided to control floating of the vehicle 14 body. In practice, the resistor 150 is set experimentally for the specific vehicle and then retained at this setting. In an alternative embodiment, the resistor 150 may be adjustable by the driver or electronically in dependence upon chosen control parameters.

The outputs of the four illustrated control blocks 100,120,130,140 are coupled to a summing circuit 160. The signal output from the summing circuit 160 is a voltage level composed of components derived from each of the control blocks 100,120,130,140 and is used to control the control valves 20A26 to set the degree of damping of the shock absorbers.

The relative contribution made by the individual control blocks 100,120,130,140 to the final output signal is dependent upon the gain factor 110 of control block 100 and the trigger levels of the monostables 126,136,146.

In the case of bi-state shock absorbers, the summing circuit 160 will provide a two-state signal, being either high or low in dependence upon the outputs from the control blocks.

Referring to Figure 3, the series of graphs illustrated shows the response of the system to a jolt of the vehicle wheels caused by a bump or other protrusion on the road surface. Reference is made to the scales of the graphs, which change from graph to graph.

Graphs Wpos and RFpos show the position of the left and right front vehicle wheels relative to the vehicle body, while graphs LFvel and RFvel show the corresponding velocities. Around time 2.00 the front wheels are jolted as a result of a road the left and right 3 obstruction. Almost immediately, J is control algorithms ALG - L and ALG-R, that is the respective shock absorber control signals, react by increasing in magnitude, causing the control valve solenoid signals LFsol and RFsol to go high to increase the stiffness of the shock absorbers. A predetermined time after the end of the jolt, at around time 3.00, the right and left control algorithms fall to zero, causing the control solenoids to toggle low, thereby causing the shock absorbers to become softer.

As will be apparent, the system reacted to wheel jolt, measuring suspension displacement and filtering this displacement to detect wheel movement, without waiting for movement in the vehicle body.

Figure 4 shows a similar graph, in which the two front wheels begin to resonate. As a result, the left and right suspension displacement and velocity signals, Wpos, RFpos, LFvel and RFvel show oscillation around the natural resonance frequency of the vehicle wheels, typically in the region of 10 HZ.

Such wheel resonance can lead to resonance of the vehicle body. As a result, the left and right control signals ALG - L and ALG - R go high upon detection of wheel resonance by the wheel resonance control procedure 130 of Figure 2. The state of the control signals causes the solenoids LFsol, RFsol to set the shock absorbers into a stiff state. The left control signal ALG - L goes low during the control period, although this does not affect the left control solenoid which is also controlled, in part, by the right control signal.

As with jolt control, wheel resonance is used to adjust the vehicle suspension characteristics even before vehicle body movement is detected.

16 is Not shown in Figure 2 is a control procedure in respect of the steering actuator sensor. This control procedure is similar to jolt control block 120 in that the output from the steering actuator sensor, in the case where this is a displacement sensor, is differentiated to obtain a velocity signal. A filter allows velocity signals above a predetermined level to pass to a monostable which produces a high level output which is included in the output control signal by summing block 160. The monostable retains a high output for a preset time after its input goes low.

It will be apparent to the skilled person that the degree of damping provided by the shock absorbers may be common to all the shock absorbers, but preferably set individually for each shock absorber.

The electronic control unit 28 may include an accelerometer for isolating other types of vehicl body movements, for example lateral or heave acceleration.

17

Claims

Claims:

1. A vehicle suspension system including a controllable shock absorber coupled proximate each corner of the vehicle body and to a respective wheel, a plurality of sensors including at least two sensors coupled so as to detect movement of the vehicle body relative to two or more of the wheels, the sensors being operative to measure activity on the vehicle suspension or body of the type which causes resonance of the vehicle body, and control means for controlling the degree of damping provided by the shock absorbers; the control means including analysing means operable to analyse the sensor outputs to derive therefrom one or more signals representative of activity on the vehicle suspension or body of the type which causes resonance of the vehicle body, and processing means operable to generate a shock absorber control signal having a magnitude related to the particular type or types of activity analysed.

2. A vehicle suspension system according to claim 1, wherein the analysing means includes vehicle body resonance detecting means comprising a bandpass filter adapted to detect resonance of the vehicle body, the processing means being operative to generate a shock absorber control signal having a magnitude related to the detected vehicle body resonance.

3. A vehicle suspension system according to claim 1 or 2, wherein the analysing means comprises jolt detecting means adapted to generate a jolt signal on detection of a jolt at one or more wheels of the vehicle, the processing means being operative to generate a shock absorber control signal having a magnitude related to the jolt signal.

4. A vehicle suspension system according to claim 3, wherein the jolt detecting means is operative 18 3 0 to maintain the jolt signal at a high level for a predetermined period after detection of a jolt at the wheel or wheels.

5. A vehicle suspension system according to any one of claims 1 to 4, wherein the analysing means comprises wheel resonance detecting means including a bandpass filter adapted to provide a wheel resonance signal representative of resonance of one or more of the vehicle wheels, the processing means being operative to generate a shock absorber control signal having a magnitude related to the wheel resonance signal.

6. A vehicle suspension system according to claim 5, wherein the wheel resonance detecting means is operative to maintain the wheel resonance signal at a high level for a predetermined time after detection of a resonance of the wheel or wheels.

7. A vehicle suspension system according to any one of claims 1 to 6, wherein the analysing means comprises float detecting means operative to provide a float signal on detection of floating of the vehicle body, the processing means being operative to generate a shock absorber control signal having a magnitude related to the float signal.

8. A vehicle suspension system according to claim 7, wherein the float detecting means is operative to generate a float signal only when the speed of the vehicle relative to the wheels is less than a predetermined amount.

9. A vehicle suspension system according to any preceding claim, comprising a steering. actuator sensor, the analysing means being operative to analyse the steering actuator sensor output to derive a signal representative of movement of the steering actuator, the processing means being operative to generate a 19 shock absorber control signal having a magnitude related to the steering actuator movement signal.

10. A vehicle suspension system according to claim 9, wherein the analysing means is operative to derive a steering actuator movement signal only when the steering actuator sensor output exceeds a predetermined threshold level.

11. A vehicle suspension system according to any preceding claim, wherein the analysing means is operable to derive from the sensor outputs a plurality of signals representative of a plurality of particular types of activity on the vehicle suspension or body, the processing means including summing means for summing together the signals related to each detected type of activity, the sum forming the shock absorber control signal.

12. A vehicle suspension system according to claim 11, wherein the processing means comprises gain means effective on the derived signals to determine the contribution of each derived signal on the shock absorber control signal.

13. A vehicle suspension system according to any preceding claim, wherein the degree of damping provided by the shock absorbers is set at or within maximum and minimum damping levels.

14. A vehicle suspension system according to claim 13, wherein the maximum damping level is chosen for optimisation of vehicle handling, and the minimum damping level is chosen for optimisation of comfort.

15. A vehicle suspension system according to any preceding claim, wherein the sensors include displacement sensors disposed to measure the relative displacement of the shock absorbers.

16. A vehicle suspension system according to any preceding claim, comprising two sensors disposed on shock absorbers at the front of the vehicle.

17. A vehicle suspension system according to claim 16, wherein the two sensors are disposed on shock absorbers at the front of the vehicle.

18. A vehicle suspension system according to claim 16, wherein one sensor is disposed on a shock absorber at the front of the vehicle and the second sensor is disposed on a shock absorber at the rear of the vehicle.

19. A vehicle suspension system according to claim 18, wherein the two sensors are disposed on the same side of the vehicle.

20. A vehicle suspension system according to claim 18, wherein the two sensors are disposed on opposite sides of the vehicle.

21. A vehicle suspension system comprising a controllable shock absorber coupled proximate each corner of the vehicle body and to a respective wheel, first and second sensors operative to sense operation of the shock absorbers coupled to the two front wheels of the vehicle, and control means for controlling the degree of damping provided by the shock absorbers; the control means including analysing means operative to analyse the sensor outputs to derive first and second signals representative of the operation of said front shock absorbers, and processing means operative to generate a shock absorber control signal having a magnitude related to the detected operation of said two front shock absorbers.

22. A vehicle suspension system according to claim 21, wherein the first and second sensors are 21 displacement sensors operative to sense the movement of the vehicle body relative to the two front wheels.

23. A vehicle suspension system according to claim 21, wherein the first and second sensors are pressure sensors operative to sense pressure inside said two front shock absorbers.

24. A vehicle suspension system comprising a controllable shock absorber coupled proximate each corner of the vehicle body and to a respective wheel, a steering actuator sensor, and control means for controlling the degree of damping provided by the shock absorbers; the control means including analysing means operative to analyse the steering actuator sensor output to derive a signal representative of movement of the steering actuator, and processing means operative to generate a shock absorber control signal having a magnitude related to the analysed movement of the steering actuator.

25. A vehicle suspension system according to claim 24, wherein the analysing means is operative to derive a signal representative of movement of the steering actuator only when the sensor output exceeds a predetermined threshold level.

26. A vehicle suspension system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.