ACTIVE SUSPENSION SYSTEMS

Abstract

An active suspension system 1 for a vehicle. The suspension system 1 comprises a hydraulic actuator 4 for connection to the vehicle, an accumulator 30 arranged to provide fluid to the actuator 4 and a spool valve 16. The spool valve 16 comprises a spool 18 mounted for movement between a first position in which the flow of fluid from the accumulator 30 to the actuator 4 is prevented and a second position in which fluid can flow from the accumulator 30 to the actuator 4 via the spool 18 thereby causing movement of the actuator 4.

Claims

1. An active suspension system for a vehicle, the suspension system comprising a hydraulic actuator for connection to the vehicle, an accumulator arranged to provide fluid to the actuator and a spool valve comprising a spool mounted for movement between a first position in which the flow of fluid from the accumulator to the actuator is prevented and a second position in which fluid can flow from the accumulator to the actuator via the spool thereby causing movement of the actuator.

2. An active suspension system according to claim 1, wherein the accumulator forms part of a high-pressure sub-system and the suspension system further comprises a low-pressure sub-system, and wherein fluid can flow from the hydraulic actuator to the low-pressure sub-system via the spool when the spool is in the second position.

3. An active suspension system according to claim 2, wherein the spool is mounted for movement between the first position and a third position in which fluid can flow from the hydraulic actuator to the low-pressure sub-system via the spool and wherein the flow of fluid from the high-pressure sub-system to the hydraulic actuator is prevented by the spool when the spool is in the third position.

4. An active suspension system according to claim 3, wherein the spool passes through the third position when the spool moves from the first position to the second position.

5. An active suspension system according to claim 1, wherein the suspension system comprises a pump arranged to provide fluid to the accumulator.

6. An active suspension system according to claim 5, wherein the accumulator is located on a flow path between the pump and the spool valve.

7. An active suspension system according to claim 1, wherein the spool valve is a direct drive spool valve.

8. An active suspension system according to claim 1, wherein the spool valve is an Electro-Hydraulic Servo Valve.

9. An active suspension system according to claim 1, wherein the spool valve includes a plurality of internal ports spaced apart along the longitudinal axis of the spool, and the ports and spool are arranged such that the distance that the spool must move in a given direction to create a flow path between a service port and the corresponding return port is less than the distance the spool must move in the same direction to create a flow path between another service port and its corresponding high-pressure port.

10. An active suspension system according to claim 1, wherein the control system is arranged to alter the target position of the actuator arm from a first target position to a second target position thereby changing the ride height of the vehicle.

11. A method of actively controlling the suspension of a vehicle using an active suspension system, the suspension system comprising a spool valve including a spool, an accumulator and a hydraulic actuator, the method comprising the step of moving the spool from a first position to a second position to alter the flow of fluid to the actuator from the accumulator in response to a road event.

12. A method of actively controlling the suspension of a vehicle according to claim 11, wherein the suspension system further comprises a pump and the method includes operating the pump to provide pressurised fluid to the accumulator while the spool is in the first position.

13. A method of actively controlling the suspension of a vehicle according to claim 11, wherein the method includes the step of using an additive manufacturing process to make at least part of the active suspension system.

14. A method of controlling the movement of a wheel of a vehicle using an active suspension system comprising a hydraulic actuator suitable for connection between the wheel and the chassis of the vehicle, a control valve arranged to control the flow of fluid to the actuator, an accumulator in fluid communication with the control valve and a pump arranged to provide fluid to the accumulator, the method comprising moving the control valve from a closed position in which fluid cannot flow from the accumulator to the actuator to an open position in which fluid can flow from the accumulator to the actuator via the valve in response to a road event, and wherein the method further includes operating the pump to provide high pressure fluid to the accumulator when the control valve is in the closed position.

15. A method of controlling the movement of a wheel in accordance with claim 14, wherein the accumulator forms part of a high-pressure sub-system and the method comprises the step of periodically operating the pump to provide fluid to the accumulator when the control valve is in the closed position in order to maintain pressure in the high-pressure sub-system.

16. An active suspension system for a vehicle, the active suspension system comprising a hydraulic actuator for connection between a wheel and the chassis of the vehicle, a control valve arranged to control the flow of fluid to the actuator, a high pressure sub-system including an accumulator in fluid communication with the control valve and a pump arranged to provide high pressure fluid to the high pressure sub-system.

17. An active suspension system according to claim 16, wherein the control valve is a spool valve.

18. A strut for connection between a chassis and a wheel of a vehicle wherein the strut comprises a main housing, the main housing forming at least part of one of the components of the active suspension system according to claim 1.

19. A vehicle including an active suspension system in accordance with claim 1.

Description

DESCRIPTION OF THE DRAWINGS

[0103] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0104] FIGS. 1(a) and (b) show schematic plots of the force-velocity performance envelope for (a) an active damping system and (b) an active suspension system;

[0105] FIG. 2 shows a schematic view of an active suspension system according to a first embodiment of the invention;

[0106] FIGS. 3 (a), (b) and (c) show a close up of part of the servo valve of the active suspension system according of the first embodiment when the spool is in (a) a null position, (b) a intermediate position and (c) an extended position;

[0107] FIG. 4 shows a flow chart of a method of controlling the movement of the wheel of a vehicle using the active suspension of the first embodiment;

[0108] FIG. 5 shows a strut for use in an active suspension system according to a second embodiment of the invention; and

[0109] FIGS. 6 (a) and (b) show schematic plan views of a car including an active suspension system according to a further embodiment of the invention.

DETAILED DESCRIPTION

[0110] FIG. 2 shows a cross-sectional schematic view of an active suspension system 1 according to a first example embodiment of the invention. The active suspension system 1 includes a hydraulic actuator 4 concentrically located with a coil spring 6. The actuator 4 is connected to the chassis 3 of a car at one end and to a wheel 5 of the car at the other end.

[0111] The main body of the actuator 4 includes a cavity 10. The actuator 4 also comprises an actuator arm 8. The lower end 8a of the actuator arm 8 (i.e. the end of the actuator arm 8 furthest from the chassis 3) is in the form of a piston head which divides the cavity 10 into two chambers; lower chamber 10a (the chamber furthest from the chassis) and upper chamber 10b (the chamber closest to the chassis). A service flow passage 12.sub.a, 12.sub.b extends between each chamber 10a, 10b and a corresponding service port S.sub.a, S.sub.b which forms part of a direct drive servo valve 16. The servo valve 16 is denoted by a dashed line in FIG. 2 and its internal structure is shown in more detail in FIG. 3. The servo valve 16 also comprises a moveable spool 18. On the opposite side of the spool 18 to the service ports S.sub.a, S.sub.b are two return ports R.sub.a, R.sub.b and a high-pressure port P. Both return ports R.sub.a, R.sub.b are connected via a low-pressure sub-system 20 with the input of a pump 22. A check valve 26.sub.a, 26.sub.b connects the low-pressure sub-system 20 with each service flow passage 12.sub.a, 12.sub.b. The high-pressure port P is connected via a high-pressure sub-system 28 with an accumulator 30 and the output of the pump 22. The system also comprises a bootstrap reservoir 32 comprising a bootstrap piston 34 extending between the high and low-pressure sub-systems 28, 20. The system further includes a control unit, a sensor, a spool motor and a pump motor which along with other elements of the system not mentioned here have been omitted from FIG. 2 for the sake of clarity.

[0112] In use, prior to the detection of any road event by the control system and sensors (not shown) the pump 22 is operated to move fluid from the low-pressure sub-system 20 to the accumulator 30 via the high-pressure sub-system 28. Once a target pressure of 20 MPa is reached in the high-pressure sub-system 28 the pump 22 is switched off. While waiting for a road event to occur the pump 22 is periodically reactivated to compensate for any quiescent leakage from the high-pressure sub-system 28 and maintain the high-pressure sub-system 28 at or near the target pressure. When a road event is detected the spool 18 is moved to provide active or semi-active suspension by allowing fluid to move between the actuator chambers 10a, 10b and the high-pressure 28 and/or low-pressure 20 sub-systems. During and after a road event the pump 22 is operated to supply high-pressure fluid to the high-pressure sub-system 28 in order to replenish that sub-system.

[0113] FIG. 3 shows a close up view of part of the spool valve 16 in accordance with the first embodiment. The spool valve comprises a spool 18 concentrically located within a cavity 14 formed in a manifold 15. The inner surface of the manifold 15 that defines the cavity 14 includes a plurality of internal ports of which only five are shown here for clarity. The inner surface of the manifold includes a pressure port P, two return ports R.sub.a and R.sub.b, and two service ports S.sub.a and S.sub.b. The ports are spaced apart along the length of the cylindrical spool 18. The mid-point of the spool 18 is denoted by a dashed line labelled A in FIG. 3. The pressure port P is shown located on the lower side of the spool 18 on the midline A in FIG. 3 Return ports R.sub.a and R.sub.b are located either side of the pressure port P on the left- and right-hand side of port P respectively. On the upper side of the spool 18, a service port S.sub.a, S.sub.b is located between each return port R.sub.a, R.sub.b and the central pressure port P. Each service port S is located closer (in terms of distance along the longitudinal axis of the spool) to a return port R than a high-pressure port P. The outer surface of the spool 18 includes three grooves 19 spaced between four lands 21 which are in contact with the inner surface of the manifold 15 which defines the cavity 14.

[0114] In use, when the spool is in the null position (as shown in FIG. 3(a)) a land 21 of the spool 18 closes off each service port S while each of the return and pressure ports R, P are aligned with a different one of the three grooves 19. With the spool in this position the only fluid that flows via the spool valve is the small amount that leaks around the side of the spool. Thus, active suspension systems in accordance with the present embodiment may have a lower rate of quiescent leakage from the high-pressure sub-system compared to active suspension systems incorporating other types of control valves.

[0115] Moving the spool to the left of the position shown in FIG. 3(b) uncovers a portion of the right-hand side service port S.sub.b such that fluid may flow from the right hand service port S.sub.b to the return port R.sub.b. This allows fluid to flow from the upper actuator chamber 10.sub.a to the low-pressure sub-system 20. The left hand service port S.sub.a remains closed off by the land 21 in this intermediate position. The precise flow rate through the spool valve may be varied by controlling the extent to which the service port S.sub.b is uncovered when the spool is in the intermediate position. In use this intermediate position may be used to slow the rate at which the wheel 3 moves towards the chassis 5 when the wheel is subject to an external force or to allow the wheel 3 to return downwards towards its normal position following a severe road event.

[0116] Continuing the movement of the spool 18 to the left to the position shown in FIG. 3(c) then uncovers the left-hand service port S.sub.a such that fluid may flow from the high-pressure port P to the service port S.sub.a via the central groove on the spool 18. Thus, fluid may flow from the high-pressure sub-system 28 to the lower chamber 10a of the actuator as well as from the higher chamber 10b of the actuator to the low-pressure sub-system 20 when the spool 18 is in this fully extended position. The resulting pressure imbalance in the actuator chambers 10 causes the wheel to be pulled upwards.

[0117] Similarly when moving the spool to the right, the spool first passes through an intermediate position in which a flow path exits between the left-hand side service port S.sub.a and the left-hand return port Ra, while continued movement in that direction subsequently creates a flow path between the right-hand side return port S.sub.b and the high-pressure port S.sub.b (while maintaining the flow path between S.sub.a and R.sub.a). The fluid flow in the intermediate positions when the spool has been moved to the right results in a pressure imbalance in the actuator that acts to slow a movement of the wheel 5 away from the chassis 3 in response to an external force or allow the wheel 5 to return upwards towards its normal position following a severe road event. The fluid flow in the fully extended position when the spool has been moved to the right results in a pressure imbalance in the actuator that acts to move the wheel 5 away from the chassis 3 (i.e. pushes the wheel down).

[0118] In use, the active suspension system is operated in the semi-active mode by moving the spool 18 between the null and intermediate position, and in the active mode when the spool 18 is moved between the null and fully extended positions. Thus, in suspension systems in accordance with the present embodiment there is no need for a control system to actively switch the system between those two modes.

[0119] FIG. 4 shows a flow diagram of the process for controlling the movement of a car wheel using an active suspension. A road event is detected 52. When the road event is moderate the spool 18 is moved to the left intermediate position 56 or moved to the right intermediate position 58 such that fluid may escape from one or other of the actuator chambers. Thus, active suspension systems in accordance with the present embodiment may function in a semi-active mode without using fluid from the high-pressure sub-system, thereby improving the energy efficiency of the system.

[0120] When the road event is categorised as severe the spool 18 is moved to the far left 60 or far right 62 positions such that fluid may move between the actuator and both the high-pressure and low-pressure sub-systems. Thus, active suspension systems in accordance with the present embodiment may switch between active and semi-active modes simply by increasing the distance travelled by the spool.

[0121] Following the road event the spool returns to the null position 64. When the road event was severe, the spool returns to the null position via the appropriate intermediate position in order to allow the wheel to return to its normal position. The pump is then operated to return the pressure in the high-pressure sub-system to its normal value (if necessary). The pump is then operated periodically 66 to maintain the pressure in the high-pressure sub-system at its normal value.

[0122] FIG. 5 shows a cross-sectional view of a strut 191 in accordance with a second example embodiment of the invention. The strut 191 comprises a main housing 192 concentrically located with a coil spring 106 and attached at one end to the chassis 103 of a car and at the other end to the wheel 105 of a car. Within the main housing 192 is an actuator cavity 110 in which one end of an actuator arm 108 is located. Concentrically located around the actuator chamber 110 is a first cavity forming part of a bootstrap reservoir 132 and a second cavity forming part of an accumulator 130. A control valve 116 and pump 120 are also located within, and formed at least in part by, the main housing of the strut 191. Flow galleries (not shown) in the main housing 192 link the components. The main housing 192 of the strut is produced using an additive manufacturing process. Other aspects of the active suspension system are as described above.

[0123] Providing several components of the active suspension system in a strut means active suspension systems in accordance with the present invention may be easier to install and maintain and/or more compact.

[0124] FIG. 6 (a) shows a schematic view of the underside of a car 298 including an active suspension system in accordance with further embodiments of the invention. The car has four wheels 296. A strut 291, substantially as described with reference to FIG. 5, connects each wheel 296 to the chassis (not shown) of the car 298. A first accelerometer 297 is located forward of each wheel 296 and supplies information to the centrally located control system (not shown) of the car 298. A second accelerometer (not shown) is connected to each wheel 296 and also supplies information to the centrally located control system. The control system controls the movement of the spool of each strut 291 in response to the difference in acceleration measured by the two accelerometers 297 associated with each wheel 296.

[0125] FIG. 6 (b) shows a schematic view of the underside of a car 298 including an active suspension system. In contrast to the embodiment of FIG. 6 (a), the system of FIG. 6 (b) has a centrally located pump 222 which supplies fluid to accumulators 230 which are formed in a strut 291, wherein each strut connects a wheel 296 to the chassis (not shown) of the car 298.

[0126] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described. For example, while the above embodiments all comprise a servo valve, other types of control valve may be used. Alternatively, a servo valve (or other control valve) may be used with an active suspension system in which fluid is supplied to the valve by a pump without passing through an accumulator. The pump and control valve may be provided as a single component, produced using an additive manufacturing process and located locally to each strut.

[0127] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.