Suspension system for an automotive vehicle

1 . A suspension system for an automotive vehicle, the suspension system comprising:

a hydraulic actuator for mounting between a wheel assembly and a body of the automotive vehicle, and

a hydraulic system configured to provide a supply of fluid to the hydraulic actuator, wherein the hydraulic system is configured during normal operation to provide fluid at a total pressure greater than 7 MPa (70 Bar) to the hydraulic actuator;

wherein the hydraulic system comprises:

a plurality of gas accumulators,

a common flow path connecting the hydraulic system to the hydraulic actuator,

and one or more valves;

wherein each gas accumulator of said plurality of gas accumulators is connected to the common flow path via an associated valve, each associated valve being associated with one or more gas accumulators and independently actuatable to place one or more of said associated gas accumulators in fluid communication with said common flow path, such that, when said associated valve is in an open position corresponding to a selected gas accumulator, pressure changes in said common flow path are transmitted to gas in said selected gas accumulator,

wherein the hydraulic system is arranged to be switched between a first configuration in which an associated valve of a first gas accumulator of said plurality of gas accumulators is in an open position and an associated valve of a second gas accumulator of said plurality of gas accumulators is in a closed position, and a second configuration in which the associated valve of the first gas accumulator is in a closed position and/or the associated valve of the second gas accumulator is in an open position; and

wherein the hydraulic actuator comprises:

a piston comprising a rod and a piston head mounted on the rod, and

a piston housing,

wherein:

the piston is mounted for movement within a cavity formed within the piston housing, and

a first side and a second side of the piston head divides the cavity into a first chamber and a second chamber, wherein an effective surface area of the first side of the piston head is larger than an effective surface area of the second side of the piston head; and

wherein the first chamber is connected to the common flow path via at least one first piston flow path, and the second chamber is connected to the common flow path via at least one second piston flow path, such that a change in pressure in the common flow path is transmitted to both the first chamber and the second chamber.

2 . The suspension system according to claim 1 , wherein the suspension system is an active suspension system.

3 . The suspension system according to claim 1 , wherein the suspension system is configured to transmit changes in fluid pressure between the hydraulic actuator, the common flow path, the first gas accumulator and the second gas accumulator such that the hydraulic actuator has a first stiffness when the hydraulic system is in the first configuration and a second, different, stiffness when the hydraulic system in the second configuration.

4 . The suspension system according to claim 1 , wherein the plurality of gas accumulators comprises a third gas accumulator, and the hydraulic system is arranged to be switched between further configurations by opening or closing the associated valve of the third gas accumulator, and wherein the third gas accumulator is a variable accumulator, and the variable accumulator is connected to a pump of the hydraulic system, and the hydraulic system is configured such that fluid can flow between the pump and the variable accumulator in a first direction, and in a second direction, opposite to the first direction.

5 . The suspension system according to claim 1 , wherein each of said one or more valves comprises a spool configured to move with respect to a sleeve, wherein a position of the spool relative to the sleeve determines for each of the first gas accumulator and the second gas accumulator whether said first gas accumulator and said second gas accumulator are in fluid communication with the common flow path.

6 . The suspension system according to claim 1 , wherein a proportional valve is located on a flow path between at least one of the first gas accumulator and the second gas accumulator and the common flow path, and the suspension system is configured such that varying a position of said proportional valve from a first, non-zero, position to a second, non-zero, position varies a damping ratio of the hydraulic actuator.

7 . The suspension system as claimed in claim 1 , wherein the suspension system comprises at least one variable resistance valve located on either (i) the at least one first piston flow path or (ii) the at least one second piston flow path, wherein, when more than one first piston flow path is present, each first piston flow path comprises a variable resistance valve, and when more than one second piston flow path is present, each second piston flow path comprises a variable resistance valve, such that varying a resistance of a variable resistance value varies a damping rate of the hydraulic actuator.

8 . The suspension system according to claim 1 , wherein a first portion of the rod is located within the first or second chamber and a second portion of the rod is located outside of the piston housing and the piston housing comprises a sealing region, the sealing region being the region of the housing between said first or second chamber and the exterior of the housing through which the rod extends; at least one seal located in the sealing region and arranged to form a seal between the piston housing and the rod; and at least one scavenge port, said at least one scavenge port being located in the sealing region and between the at least one seal and the first or second piston chamber such that, in use, fluid that enters the sealing region from a piston chamber can exit the sealing region via the at least one scavenge port, the suspension system optionally further comprising a scavenge accumulator connected to the at least one scavenge port and to the common flow path such that fluid can flow from the scavenge port(s) to the common flow path via the scavenge accumulator.

9 . The suspension system according to claim 1 , wherein the hydraulic system further comprises a pump, the pump being a bidirectional pump that can run both forward and backwards, and the suspension system is configured such that fluid can flow from the pump to the common flow path in (i) a first direction and (ii) in a second direction, the second direction being opposite to the first direction, such that the pump can increase and decrease the pressure in the common flow path.

10 . A suspension unit for mounting between a wheel assembly and a body of the automotive vehicle, the suspension unit comprising the suspension system of claim 1 , wherein the hydraulic system is contained within a housing of the suspension unit, and at least part of the hydraulic actuator is located partially within the housing of the suspension unit.

11 . The suspension unit according to claim 10 , wherein a rod is mounted for axial movement within the housing of the suspension unit and extends parallel to a longitudinal axis of the suspension unit, and wherein the hydraulic system comprises the first gas accumulator, the second gas accumulator and a third gas accumulator, wherein the first gas accumulator, the second gas accumulator and the third gas accumulator are arranged in a row along a portion of the length of the suspension unit.

12 . An automotive vehicle comprising the suspension system of claim 1 wherein the automotive vehicle comprises a plurality of wheels connected to a chassis and a plurality of suspension systems, one of said plurality of suspension systems being associated with each wheel.

13 . A method of controlling a relative movement of a wheel assembly and a body of an automotive vehicle using a suspension system comprising:

a hydraulic actuator connecting the wheel assembly and the body; and

a hydraulic system configured to provide a supply of fluid to the hydraulic actuator,

wherein the hydraulic system comprises:

a plurality of gas accumulators,

a common flow path connecting the hydraulic system to the hydraulic actuator,

and one or more valves;

wherein each gas accumulator of said plurality of gas accumulators is connected to the common flow path via an associated valve, each associated valve being associated with one or more gas accumulators and independently actuatable to place one or more of said associated gas accumulators in fluid communication with said common flow path, such that, when said associated valve is in an open position corresponding to a selected gas accumulator, pressure changes in said common flow path are transmitted to gas in the selected gas accumulator, and when said associated valve is in a closed position corresponding to said selected gas accumulator, pressure changes in said common flow path are not transmitted to gas in said selected gas accumulator;

wherein the hydraulic actuator comprises:

a piston comprising a rod and a piston head mounted on the rod, and

a piston housing,

wherein:

the piston is mounted for movement within a cavity formed within the piston housing, and

a first side and a second side of the piston head divides the cavity into a first chamber and a second chamber, wherein an effective surface area of the first side of the piston head is larger than an effective surface area of the second side of the piston head,

the first chamber is connected to the common flow path via at least one first piston flow path, and

the second chamber is connected to the common flow path via at least one second piston flow path;

wherein controlling the relative movement of the wheel assembly and the body is performed by:

providing fluid via the hydraulic system to the hydraulic actuator via the common flow path at a total pressure equal to or greater than 7 MPa (70 Bar) for a first time period, and

during the first time period:

(1) causing one or more changes in the total pressure in the common flow path, and

(2) transmitting each of the one or more changes in the total pressure in the common flow path to (i) the first chamber via the at least one first piston flow path and (ii) the second chamber via the at least one second piston flow path; and

the method further comprising, during the first time period, changing a stiffness of the hydraulic actuator by actuating the associated valve to switch the hydraulic system between a first configuration in which the associated valve of a first gas accumulator of said plurality of gas accumulators is in an open position and the associated valve of a second gas accumulator of said plurality of gas accumulators is in a closed position, and a second configuration in which the associated valve of the first gas accumulator is in a closed position and/or the associated valve of the second gas accumulator is in an open position.

14 . The method according to claim 13 , wherein the method comprises, during the first time period, changing a damping rate of the hydraulic actuator by varying a position of a variable resistance valve located on one of (i) the, or each, at least one first piston flow path and (ii) the, or each, at least one second piston flow path.

15 . The method according to claim 13 , wherein, during the first time period, a pump operates in a first direction to increase a total pressure in the common flow path and the pump operates in a second direction, opposite to the first direction, to decrease the total pressure in the common flow path.

16 . The method according to claim 13 , wherein the hydraulic system further comprises a pump, and the method comprises, during the first time period, operating the pump in a forward direction such that fluid flows from the pump towards the common flow path and thereby increases the pressure in the common flow path, and operating the pump in a backward direction, such that fluid flows away from the common flow path and into the pump and thereby decreases the pressure in the common flow path.