GB2568151A

GB2568151A - Actuator system

Info

Publication number: GB2568151A
Application number: GB1815131.6A
Authority: GB
Inventors: Neilson Robert; Robertson James; Slater Barry
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2017-09-19
Filing date: 2018-09-17
Publication date: 2019-05-08
Anticipated expiration: 2038-09-17
Also published as: GB201815131D0; DE102018215589A1; GB2568151B; GB201715063D0

Abstract

An active suspension system 14A for a vehicle (10, Figure 1) is provided. The active suspension system 14A comprises a plurality of actuator systems 17 each of which couples a body of the vehicle 10 to a wheel 12. Each actuator system 17 comprises an actuator 18 having a piston 24 and first fluid chamber C1 separated from a second chamber C2 by the piston 24. The actuator 18 further comprises: a pump P having an inlet port P2 and an outlet port P1, the outlet port P1 of the pump P being selectively connectable to the first and second fluid chambers C1, C2; and a first variable pressure relief valve V1 having a first port V1A connected or connectable to the outlet port P1 of the pump P and a second port V1B connected or connectable to the inlet port P2 of the pump P. The variable relief valve V1 being arranged to selectively vary a pressure in one of the first and second fluid chambers C1, C2. A vehicle comprising such an active suspension system, and a method of controlling an active suspension system are also disclosed.

Description

TECHNICAL FIELD

The present disclosure relates to an actuator system. Particularly, but not exclusively, the disclosure relates to an actuator system for a vehicle suspension system. Aspects of the invention relate to an active suspension system, a vehicle comprising the active suspension system and a method of controlling an active suspension system.

BACKGROUND

Suspension systems on vehicles are known to improve the ride quality of the vehicle compared to a vehicle without any suspension. As such, suspension systems are provided to filter or isolate the vehicle body from vertical road surface irregularities as well as to control body and wheel motion. They are also used to maintain stability during manoeuvring of a vehicle.

Passive suspension vehicles are known, wherein the system reacts to driver induced inputs and/or road induced inputs. This classic system includes a spring and a damping device, which are arranged in parallel and located between the vehicle body and the drive axis/wheels. The damping devices typically shock absorbers, which are used in conjunction with conventional springs to absorb unwanted vibration during driving. To absorb vibration, the shock absorber includes a piston located within a pressure cylinder, which is connected to the body of the automobile via a piston rod. The piston divides the pressure cylinder into two separate chambers and is able to restrict the flow of damping fluid between these two chambers when the piston/piston rod is displaced. By means of restricting the flow of damping fluid between the chambers, the shock absorber/damper produces a damping force which counteracts the aforementioned, unwanted vibrations.

A known disadvantage of conventional passive suspension systems is that the damping force created by the damping device are dependent on the impact force and thereby the flow of damping fluid within the working chambers of the cylinder, making it difficult to achieve an acceptable compromise between all modes of operation.

In view of the above, more recent vehicle suspension systems include intelligent active suspensions systems, capable of electronically controlling the suspension forces generated by hydraulic actuators. In said active suspension systems, hydraulic actuators are arranged in parallel with the aforementioned classic spring and damping device of passive suspension 1 systems. Active suspension systems need to deal with various types of demands, such as dynamic or fast acting forces and static or slowly changing forces. Driver induced inputs, for example, tend to be relatively low frequency that is, they will change slowly. By contrast, road induced inputs tend to be of a relatively high frequency, requiring the actuator to act against the movement of the piston more rapidly. It is a known problem that common active suspension systems have difficulties in dealing with the high frequency, dynamic forces created by road induced inputs, such as road surface irregularities.

It is an aim of the present invention to address the disadvantages associated with the prior art. In particular, it is an object of the present invention to provide an actuator system for a vehicle suspension, which enables faster reaction times and, at the same time, exhibits low power consumption.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide an actuator system, an active suspension system, a vehicle and a method of controlling an active suspension system as claimed in the independent claims.

According to an aspect of the present invention, there is provided an actuator system for a vehicle suspension system comprising an actuator having a piston and a first fluid chamber separated from a second fluid chamber by the piston. The actuator system comprises a pump having an inlet port and outlet port, the outlet port of the pump being selectively connectable to the first and second fluid chambers, wherein the actuator system further comprises a first variable pressure relief valve having a first port connected or connectable to the outlet port of the pump and a second port connected to or connectable to the inlet port of the pump, the variable relief valve being arranged to selectively vary a pressure in one of the first and second fluid chambers.

According to an aspect of the present invention, there is provided an active suspension system for a vehicle, the active suspension system comprising a plurality of actuator systems for each coupling a body of the vehicle to a wheel, wherein each actuator system comprises an actuator having a piston and a first fluid chamber separated from a second fluid chamber by the piston, a pump having an inlet port and an outlet port, the outlet port of the pump being selectively connectable to the first and second fluid chambers, a first variable pressure relief valve having a first port connected or connectable to the outlet port of the pump and a second port connected or connectable to the inlet port of the pump, the first variable pressure relief valve being arranged to selectively vary a pressure in one of the first and second fluid chambers.

In contrast to the prior art, the pressure in the first and second fluid chambers is not varied directly by means of the pump, e.g. by increasing and decreasing flow provided by a variable displacement pump; rather, the variable pressure relief valve of the present invention enables the actuator system to utilise any pump type. The pump of the actuator system may be arranged to permanently create a fluid flow, which is provided to the first variable pressure relief valve. Depending on the flow resistance of the first variable pressure relief valve, different pressures may be provided in the first and/or second fluid chamber. It is thus not necessary to vary the output flow provided by the pump in order to vary the suspension force provided by the actuator. Since the flow resistance of the first variable pressure relief valve can be adjusted significantly quicker than the flow rate of conventional pumps, the actuator system of the present invention is able to react faster than prior art solutions.

According to another embodiment of the present invention, the or each actuator system comprises a first accumulator adapted to maintain a system pre-charge. The first accumulator will act to maintain a base pressure within the first and/or fluid chambers, such that reaction times are further improved. The first accumulator also acts to accommodate changes in volume due to rod displacement and/or temperature.

The first accumulator of the or each actuator system may have an inlet port connected to the second port of the pressure relief valve. The inlet port of the first accumulator may also be connected to the inlet port of the pump. This will dictate the working pressure on the low pressure side of the system, that is, at the inlet port of the pump.

In another embodiment, the first variable pressure relief valve is an electronically adjustable relief valve. Of course, the variable pressure relief valve may alternatively be constructed as a mechanically adjusted relief valve, however electronically adjustable relief valves have the advantage that an electronic control unit of the actuator system may act directly, and therefore more quickly, on the first variable relief valve.

The or each actuator system may comprise a first directional control valve arranged to connect the outlet port of the pump with a first fluid chamber of the actuator, in a first state, and arranged to connect the outlet port of the pump with a second fluid chamber, in a second state. In other words, the first directional control valve may be used to connect the high pressure side of the actuator system selectively with the first or second chamber.

In another embodiment, the first directional control valve is arranged to connect the second fluid chamber with the inlet port of the pump, in its first state, and arranged to connect the fluid chamber with the inlet port of the pump, in its second state. In this embodiment, the remaining fluid chamber, which is connected to the high pressure side of the system, is then connected to the low pressure side. To this end, the first directional control valve may be constructed as a 4/2-way valve or a 4/3-way valve.

The first directional control valve may comprise a third state, in which the first and second fluid chambers are disconnected from the outlet port of the pump. According to this embodiment, the first directional control valve may be constructed as a 4/3-way valve. In said third state, the first and second fluid chambers may be directly connected to the inlet port of the pump, for example via the first accumulator. This third state of the first directional control valve may be arranged as a failsafe state, which is set if the actuator system experiences a power cut. In other words, the first directional control valve may be in its third state in a zero position.

According to an alternative embodiment, the or each actuator system may comprise a second directional control valve arranged to connect the outlet port of the pump with the inlet port in the event of an electrical power failure. In this variant, the first directional control valve is not provided with a third, failsafe state. Rather, an independent, second directional control valve is provided to fulfil the failsafe requirements. For as long as the actuator system is supplied with power, the second directional control valve remains in a blocking position, that is, it does not alter the fluid flow through the system in any way. However, if the actuator system experiences a power cut, the second directional control valve switches into its zero position, which connects the chambers directly with the low pressure side of the system, such that the actuator system is transparent to the vehicle suspension.

According to another embodiment, the or each actuator system comprises a first anticavitation accumulator mounted on a housing of the actuator and fluidly connected to the fluid chamber and/or wherein the actuator system comprises a second anti-cavitation accumulator mounted on a housing of the actuator and fluidly connected to the second fluid chamber. The first and/or second anti-cavitation accumulators of this embodiment are arranged in close proximity to the actuator housing. Therefore, the first and/or second anti-cavitation accumulators are part of the sprung mass of the actuator system, as will be described in more detail below.

The first and/or second anti-cavitation accumulator is any of a diaphragm type accumulator, an enclosed bladder type accumulator, a floating piston type accumulator, and a spring type accumulator. The first and/or second anti-cavitation accumulator may be sized to be saturated at a pre-determined system pressure of the actuator system. The term saturated in this context refers to the fact that the first and/or second anti-cavitation accumulator, at a predetermined system pressure, is filled to a point that no significant amounts of fluid can enter the anti-cavitation accumulators, when the system is at or above the predetermined system pressure. As such, the anti-cavitation accumulators are not arranged to receive more working fluid during use of the actuator system but only to provide pressurised fluid if necessary. As will be described in more detail below, fluid from the anti-cavitation accumulators will be provided to the first and/or second fluid chambers if air holes are created therein due to cavitation.

According to another embodiment, the or each actuator system comprises a high pressure recovery accumulator, said recovery accumulator being connectable to the inlet port of the pump and selectively connectable to the first and second fluid chambers. As such, the high pressure recovery accumulator may be used to recover some of the pressurised fluid within the chambers when no active suspension is required. The high pressure recovery accumulator, therefore, will further reduce the power consumption and increase reaction times of the present actuator system.

In another embodiment, the or each actuator system comprises a head-pressure accumulator, said head-pressure accumulator being connected to the outlet port of the pump and to a first port of a head-pressure relief valve. The head-pressure relief valve may have a second port connected to the first port of the first variable pressure relief valve. The head-pressure relief valve may act as a charging valve, which controls the fluid pressure stored in the headpressure accumulator. This set up will further increase the reaction speed of the present actuator system.

The or each actuator system may comprise a second variable pressure relief valve having a first port connectable to the outlet port of the pump and a second port connectable to the inlet port of the pump, wherein the first variable relief valve is arranged to selectively vary the pressure in the first fluid chamber, and the first port of the first variable pressure relief valve is 5 connected to the first fluid chamber, wherein the second variable relief valve is arranged to selectively vary the pressure in the second fluid chamber, and the first port of the second variable pressure relief valve is connected to the second fluid chamber. According to this embodiment, the pressure in the first and second fluid chambers may be varied individually with separate variable relief valves. As such, this embodiment offers a different packaging possibility and reduces fluid inertia between the piston and the variable relief valves.

The active suspension system may comprise each actuator system arranged in parallel with a spring and a damper.

The active suspension system optionally comprises a control unit for, in use, controlling each of the plurality of actuator systems to stabilise the body of the vehicle. Advantageously the plurality of actuator systems may be controlled in a synchronised manner to stabilise the body of the vehicle.

The control unit may be arranged to control the first variable pressure relief valve of each actuator system to vary the pressure in one of the first and second fluid chambers of the actuator system. Advantageously the flow resistance of the first variable pressure relief valve can be rapidly adjusted by the control unit.

Each of the plurality of actuator systems may be independently controlled to stabilise the body of the vehicle. Advantageously each actuator system may be controlled to stabilise a respective portion of the vehicle. Advantageously some of the plurality of actuator systems may be controlled in concert to stabilise the body of the vehicle.

In another aspect of the present invention there is provided a vehicle comprising the active suspension system arranged between a vehicle wheel and a vehicle chassis.

In yet another aspect, a method of controlling an active suspension system is provided. The active suspension system comprises at least one actuator, the actuator having a piston and first fluid chamber separated from a second fluid chamber by the piston and a first variable pressure relief valve. The method comprises:

providing an active suspension system with at least one actuator, the actuator having a piston and first fluid chamber separated from a second fluid chamber by the piston;

providing the first fluid chamber with working fluid at a predetermined first pressure; determining or predicting a load acting to compress the actuator;

providing the first fluid chamber with working fluid at a second pressure if said load exceeds a predetermined threshold, wherein the first and second pressure in the first chamber is determined by a variable relief valve.

In still further aspect, there is provided a method of controlling an active suspension system, the active suspension system comprising a plurality of actuator systems coupling a body of a vehicle to a wheel, wherein each actuator system comprises an actuator having a piston and first fluid chamber separated from a second fluid chamber by the piston and a first variable pressure relief valve, the method comprising for each actuator system:

providing the first fluid chamber with working fluid at a second pressure if said load exceeds a predetermined threshold, wherein the first and second pressure in the first chamber is determined by adjusting the first variable pressure relief valve.

In the aforementioned method, determining a load acting to compress the actuator of course requires one or more sensors, which are arranged to measure the force acting on the vehicle suspension. The sensor data may be fed back to the aforementioned control unit which, in turn, regulates the first variable pressure relief valve to control the pressure in the first chamber. Predicting a load acting to compress the actuator may be facilitated by sensors measuring driver induced inputs, such as steering, braking or acceleration. Alternatively, predicting a load acting to compress the actuator may utilise the information of a satellite navigation system, which will be able to predict steering events before they occur. For example, the degree of an upcoming bend and the vehicle speed may be used to calculate or look up a predicted load acting to compress the actuator as soon as the vehicle enters the upcoming turn.

In another embodiment, the second pressure is determined on basis of the determined or predicted load acting to compress the actuator. As such, it will be appreciated that the second pressure is not a fixed pre-determined value but should be understood as a dynamic value, which is dependent on a plurality of factors such as the vehicle speed, vehicle weight, inclination of the road surface, etc.

The method may comprise independently controlling the first variable pressure relief valve of each actuator system.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows an embodiment of a vehicle according to the present invention;

Figure 2 shows a schematic circuit diagram of an embodiment of the active suspension system according to the present invention;

Figure 3 shows a schematic circuit diagram of another embodiment of the active suspension system according to the present invention;

Figure 4 shows a schematic circuit diagram of another embodiment of the active suspension system according to the present invention;

Figure 5 shows a schematic circuit diagram of another embodiment of the active suspension system according to the present invention;

Figure 6 shows a schematic circuit diagram of another embodiment of the active suspension system according to the present invention;

Figure 7 shows a schematic circuit diagram of another embodiment of the active suspension system according to the present invention; and

Figure 8 shows a schematic circuit diagram of yet another embodiment of the active suspension system according to the present invention.

DETAILED DESCRIPTION

Turning to Figure 1, there is shown a vehicle 10 having ground engaging structure, in this case in the form of four wheels 12. An active suspension system 14 is arranged between each wheel 12 and a body 16 of the vehicle 10. The vehicle 10, therefore, defines a sprung mass which includes body 16 and further components which will be described below and an unsprung mass which includes wheels 12 and further components which will be described below. Each of the four wheels 12 is connected to the body 16 by an individual active suspension system 14. However, each active suspension system 14 is connected to a control unit 15 as indicated in Figure 1. The control unit 15 centrally controls each of the active suspension systems 14 so as to stabilise the vehicle body 16 during the entire journey. For example, if the vehicle 10 turns into a sharp left turn, the active suspension systems 14 on the right of the vehicle 10 may both be used to simultaneously produce an extension force via a control signal from a control unit 15. At the same time, the active suspension systems on the left of the vehicle (not shown in Figure 1) may be used to simultaneously produce a compression force to help the vehicle body 16 lean towards the bend.

Each active suspension system 14 includes an actuator system 17 shown in Figure 2, for example. Thus, the vehicle 10 comprises a plurality of actuator systems 17. In some embodiments each actuator system 17 is associated with a respective wheel 12 of the vehicle

10. Each of the plurality of actuator systems 17 may be independently controlled by the control unit 15 to stabilise the body of the vehicle 10. Reference will now be made to one of the plurality of actuator systems 17 with it being appreciated that each of the plurality of actuator systems 17 of the vehicle may be identical.

The actuator system 17 has an actuator 18, specifically a hydraulic actuator, which couples the body 16 to the associated wheel 12 or other components of the vehicle. The suspension system also includes a spring 20, which couples the body 16 to the associated wheel 12. The spring 20 can be any type of spring, for example a helical spring or an Air-spring.

As will be appreciated from Figure 2, the actuator 18 and spring 20 act in parallel. Each active suspension system 14 also includes a damper/shock absorber 21, which couples the body to the associated wheel 12. The damper/shock absorber 21 may be of any type, such as twintube or mono-tube types and upright/inverted shock absorbers. It will also be appreciated from the embodiment in Figure 2 that the actuator 18, the spring 20 and the damper 21 act in parallel.

The actuator 18 includes a cylinder 22, containing a piston 24. The cylinder 22 is connected to the wheel 12 and the piston 24 is connected to the body 16 via a piston rod 26. The piston 24 separates the cylinder 22 into a first fluid chamber C1 and a second fluid chamber C2. The piston fluidly isolates the first fluid chamber C1 from the second fluid chamber C2. To this end, the piston 24 may comprise any kind of annular seal between its outer parameter and the inner surface of the hydraulic cylinder 22.

The actuator system 17 further includes a pump P having an outlet port P1 and an inlet port P2. In this embodiment, the pump P is a mono-directional, fixed displacement pump, driven by a prime mover, which is not shown in Figure 2. It will be understood that in the embodiment of Figure 2, each of the four individual active suspension systems 14a comprises a separate pump P. The pump P in the embodiment of Figure 2 is a mono-directional, fixed displacement pump. However, it is also feasible to implement bi-directional and/or variable displacement pumps should this be required. The advantage of using mono-directional, fixed displacement pumps is a significant cost reduction and longer wear life.

The actuator system 17 also includes a first variable pressure relief valve V1 having a first port V1A connected to the outlet port P1 of the pump P via first gallery G1 and fluid line 31. The first variable pressure relief valve V1 also comprises a second port V1B connected to the inlet port P2 of the pump P via fluid return line 33. As will be described in more detail below, the first variable pressure relief valve V1 is arranged to selectively vary a pressure in one of the first and second fluid chambers C1, C2. To this end, the pressure relief valve sets the pressure in gallery G1, depending on a predetermined set pressure. When the set pressure in gallery G1 is exceeded, the first variable pressure relief valve V1 becomes the path of least resistance as the variable pressure relief valve V1 is forced open and a portion of the fluid is diverted back to the inlet port P2 via fluid line 33.

The set relief pressure of the first variable pressure relief valve V1 is electronically adjustable so as to regulate the pressure within gallery G1. As such, the first variable pressure relief valve V1 is electrically connected to the control unit 15 described with reference to Figure 1.

A first directional control valve V2 is arranged to select which of the fluid chambers C1 or C2 shall be pressurised. The first directional control valve V2 of the embodiment shown in Figure 2 is constructed as a 4/3-way valve. As such, the first directional control valve V2 comprises four ports V2A, V2B, V2C and V2D. A first port V2A is connected to the outlet port P1 of the pump P via fluid gallery G1. The second fluid port V2B is connected to the inlet port P2 of the pump P via fluid return line 33. The third port V2C of the first directional control valve V2 is connected to the first fluid chamber C2 of the hydraulic actuator 18 via fluid line 35. The fourth fluid port V2D is connected to the second fluid chamber C2 of the hydraulic actuator 18 via fluid line 37.

In a first state shown in Figure 2, the first and third ports V2A and V2C are connected and the second and fourth ports V2B and V2D are connected too. As such, in the first state, the first directional control valve V2 connects the gallery G1 with the first fluid chamber C1 via fluid line 35. The second fluid chamber C2, on the other hand, is connected to the fluid return line 33 via fluid line 37. In this configuration, the pressure in gallery G1 is supplied to the first fluid chamber C1 in order to create a compression force on the hydraulic actuator 18. Due to the increase in pressure in fluid chamber C1, the piston 24 moves towards the second fluid chamber C2 and thereby pushes some of the fluid within chamber C2 out of the cylinder 22 towards fluid return line 33.

In a second state of the first directional control valve V2, the first fluid port V2A is connected to the fourth fluid port V2D and the second fluid port V2b is connected to the third fluid port V2C. In this condition, the pressure in gallery G1 is applied to chamber C2 and chamber C1 is connected to the fluid return line 33. As such, an extension force is generated by the actuator 18, trying to push the piston 24 towards chamber C1.

The first directional control valve V2 of the actuator system 17 shown in Figure 2 has a third state, in which both fluid chambers C1 and C2 are connected to the fluid return line 33. Accordingly, none of the fluid chambers C1 and C2 are supplied with the pressured fluid in gallery G1. Rather, both chambers C1 and C2 are connected to fluid return line 33 and therefore exhibit the system pressure determined by the first accumulator A1, which will be described in more detail below. The third state is a so-called the failsafe state. In other words, if the actuator system 17 is subject to a power cut, the directional control valve V2 will move into the third, failsafe state, such that the actuator 18 is a transparent part of the vehicle suspension 14. It should be understood that even in the third state of the directional control valve V2, the actuator 17 will cause a small amount of parasitic damping losses due to the working fluid being forced through the fluid lines and orifices.

The third state is the resting position of the first directional control valve V2, in which the pressure in chambers C1 and C2 is equalised and therefore, the hydraulic actuator 18 will not significantly contribute to the suspension effect of system 14, as there are only small net forces acting on the piston 24, due to a difference in surface area between a rod side and a rod-free side of the piston. Alternatively, the valves of the hydraulic actuator 18 could be set up to act as a deliberate flow restriction, such that the hydraulic actuator is not transparent in its third state but rather acts as a further shock absorber.

As mentioned hereinbefore, the actuator system also includes a first accumulator A1 adapted to maintain resistant pre-charge. The first accumulator A1 is connected to the fluid return line 33. The first accumulator A1 shown in Figure 2 is of diaphragm type but may also be constructed as an enclosed bladder type, a floating piston type or a spring type connector. The skilled person will understand that the fluid volume within the cylinder 22 of actuator 18 varies slightly depending on the position of the piston 24, due to the variable rod volume of piston rod 26 within the cylinder 22. For example, if piston 24 moves towards chamber C2, a larger part of piston rod 26 will be received in chamber C1, thereby reducing the fluid volume within cylinder 22 and pushing the difference in fluid into the closed circuit. The first accumulator A1 is adapted to account for such volume differences within the closed loop of the circuit shown in Figure 2. As such, the volume of the fluid as well as the pressure within the first accumulator A1 will vary depending on the temperature of the fluid and the position of the piston 24 within the cylinder 22 of the hydraulic actuator 18.

The actuator system 17 also comprises pressure sensors 40 and 42. The first pressure sensor 40 is arranged within fluid line 35 and, therefore connected to the first fluid chamber C1 of the hydraulic cylinder 22. The second pressure sensor 42 is arranged within fluid line 37 and thus connected to the fluid chamber C2. Both pressure sensors 40 and 42 are connected to the control unit 15 to allow the system to continuously monitor the pressure within chambers C1 and C2. Depending on the pressure measurements of the pressure sensors 40 or 42, the control unit 15 may vary the pressure setting of the first variable pressure relief valve V1, to regulate the compression/extension forces created by the hydraulic actuator.

Figure 2 also shows that anti-cavitation accumulators A2 and A3 are arranged in close proximity to the first and second fluid chambers C1 and C2. A first anti-cavitation accumulator A2 is located in the fluid line 35 and configured to prevent cavitation within chamber C1. A second anti-cavitation accumulator A3 is located in fluid line 37 and adapted to prevent cavitation within chamber C2. Both anti-cavitation accumulators A2 and A3 are preferably mounted directly onto the cylinder housing of the actuator 18 and are therefore part of the unsprung mass of the active suspension system 14.

As described hereinbefore, both anti-cavitation accumulators A2 and A3 are sized to be saturated at a pre-determined system pressure of the actuator system 17. In other words, the system pre-charge provided by the first accumulator A1 will be sufficient to maintain both anticavitation accumulator A2 and A3 in a nearly full state, that is, neither of the two anti-cavitation accumulators A2 or A3 is able to receive any more volume of working fluid. Accordingly, if the pressure in fluid line 351 chamber C1 or in fluid line 371 chamber C2 increases, no more fluid will be pumped into the anti-cavitation accumulators. Rather, the pressure in the anti-cavitation cylinders A2 and A3 will increase together with the pressure within the respective chambers C1 or C2 and so will provide a back-up reservoir for sudden pressure losses due to cavitation within one of the two chambers C2 or C2.

The anti-cavitation accumulators A2 and A3 shown in Figure 2 are of a diaphragm type. However, it is also feasible to use any other type of accumulator, such as a spring-type accumulator (Figure 3), floating-piston-type accumulators (Figure 4) or bladder-type accumulators (not shown).

Another embodiment of the active suspension system 14B according to the present invention is shown in Figure 3. Parts of the embodiment in Figure three with identical function as described hereinbefore are labelled with the same reference numbers as the corresponding parts parts of the embodiment in Figure 2. The embodiment of Figure 3 is substantially identical to the embodiment of Figure 2, however, the anti-cavitation accumulators A2A and A3A are constructed as spring-type accumulators, instead of diaphragm type accumulators shown in Figure 2.

Figure 4 shows another embodiment of an actuator system according to the present invention. Parts of the active suspension system 14C in Figure 4, which are identical to parts of the active suspension system 14A in Figure 2 are labelled with corresponding reference signs. In 13 contrast to the embodiment shown in Figure 2, the active suspension system 14C of Figure 4 shows two anti-cavitation accumulators A2B and A3B constructed as floating-piston-type accumulators, instead of the diaphragm type accumulators shown in Figure 2. The remaining parts of the embodiment shown in Figure 4 are identical to the embodiment of Figure 2.

Operation of the active suspensions systems 14A to 14C shown in Figures 2 to 4 is as follows:

Example 1

In this example, the wheel 12 shown in Figure 2 is a front left wheel. The vehicle is being driven along a straight road. The front left of the vehicle is being supported entirely by spring 20 and damper/shock absorber 21, and as such actuator 18 is not creating any force, i.e. it does not create an extension force and nor does it create a contraction force.

The driver then creates a driver induced input by turning the steering wheel of the vehicle clockwise, which causes the vehicle to turn to the right, which, in turn, will tend to cause the vehicle to roll to the left. In order to prevent, minimise or control roll to the left, the suspension system causes the second fluid chamber C2 to be pressurised to a target pressure, which causes an extension force to be generated by the actuator 18, thereby reducing the leftward roll.

In more detail, sensors (not shown) in association with an algorithm and the control unit 15 determine an appropriate target pressure in the second fluid chamber C2. The target pressure may be based on multiple variables, by way of example forward vehicle speed, vehicle weight, load within the vehicle, comfort mode settings of the suspension, radius of the turn, etc. When it is determined by the second pressure sensor 42 that the actual pressure in the second fluid chamber C2 is below the target pressure, then the first variable pressure relief valve V1 is adjusted by the control unit 15 so as to increase the pressure within gallery G1. At the same time, the control unit 15 will move the first directional control valve V2 into its second state, in which gallery G1 is connected to the second fluid chamber C2 via fluid line 37. As the pressure in gallery G1 rises, hydraulic fluid will flow past the first directional control valve V2 causing the hydraulic pressure in fluid line 37 and hence in the second fluid chamber C2 to rise. The hydraulic pressure in anti-cavitation accumulator A3 will similarly rise.

As the pressure in the second fluid chamber C2 increases, the piston 24 may rise (when viewing Figure 2) causing hydraulic fluid to be expelled from the first fluid chamber C1. The 14 expelled fluid will flow from fluid line 35 towards return fluid line 33 via the first directional control valve V2. The actuator system 17 will uphold the target pressure within chamber C2 until the control unit 15 determines that an extension force is no longer required to avoid/minimize the leftward roll. At this point, the target pressure in chamber C2 can either be slowly reduced by adjusting the pressure in gallery G1 via the first pressure relief valve V1. Alternatively, the fluid in both chambers C1 and C2 can be vented towards the fluid return line 33 by transferring the first directional control valve V2 into its third state, such that the hydraulic actuator 18 instantly becomes a transparent part of the active suspension system.

Now imagine that the vehicle continues to negotiate the right-hand bend, and the wheel 12 hits a bump. As described hereinbefore, the active suspension system 17 causes the second fluid chamber C2 to be pressurised to a target pressure during cornering, by means of adjusting the first pressure relief valve V1. While the target pressure in the second fluid chamber C2 is retained by relief valve V1 to extend the actuator, the bump in the road will cause the actuator to contract thereby causing a transient hydraulic fluid flow at a pressure higher than the target pressure set by relief valve V1. The first variable pressure relieve valve V1 permits said transient flow between the second fluid chamber C2 and the first fluid chamber C1. Fluid flowing to the first fluid chamber C1 is provided primarily by hydraulic fluid from pump P or accumulator A1. If the transient response of the pump P or first accumulator A1 is not adequate, cavitation will be prevented to occur within fluid chamber C1 by means of anticavitation accumulator A2. The bump will create a high frequency road induced input.

Example 2

In this example, the wheel 12 shown in Figure 2 is again a front left wheel, similar to Example

1. In contrast to the first example, however, the driver creates a driver induced input by turning the steering wheel in an opposite direction (in an anti-clockwise direction) which causes the vehicle to turn to the left which, in turn, causes the vehicle to roll in the opposite direction, in this case to the right. The wheel 12 shown in Figure 2 therefore becomes an inside wheel of the turn and under these circumstances, instead of creating a target pressure for the second fluid chamber C2, a target pressure is created for the first fluid chamber C1. Where it is determined by the first pressure sensor 40 that the actual pressure in the first fluid chamber C1 is below the target pressure, the gallery pressure G1 is increased to the target pressure by varying the flow resistance of the first directional control valve V1 and transferring the first directional control valve V2 into its first state. As the pressure in gallery G1 rises, hydraulic fluid will flow past the first directional control valve V2, causing the hydraulic pressure in fluid 15 line 35 and hence in the first fluid chamber C1 to also rise. Hydraulic pressure in the anticavitation accumulator A2 will similarly rise.

As the pressure in the first fluid chamber C1 increases, the piston 24 may move towards the second chamber C2 (down, when viewing Figure 2), causing hydraulic fluid to be expelled from the second fluid chamber C2. The expelled fluid will flow into fluid line 37 and towards the fluid return line 33 via the first directional control valve V2.

Similar to Example 1, if, during negotiating the left-hand bend, the inside wheel hits a bump, hydraulic fluid flowing out of the second fluid chamber will be transferred into the first accumulator A1, while a transient lack of fluid in chamber C1, due to inertia/flow restrictions will be replaced by the first anti-cavitation accumulator A2 to prevent noise and cavitation damages in the hydraulic actuator 18.

Example 3

In this case, the vehicle is being driven in a straight line and the weight of the vehicle associated with wheel 12 is entirely carried by spring 20 and damper/shock absorber 21, and hence the actuator 18 is not generating any force along its longitudinal axis, i.e. the actuator is not generating an extension force in a vertical direction of the vehicle, nor is it generating a contraction force. In this case, the first directional control valve V2 is in its third state and so the actuator 18 is transparent. In the event that wheel 12 hits a bump, the wheel moves up relative to the body 16 causing contraction of the actuator 18, thus resulting in hydraulic fluid being expelled from chamber C2 and passing through the directional control valve V2 into the first accumulator A1. Simultaneously, hydraulic fluid will flow into fluid chamber C1, via first accumulator A1 and anti-cavitation accumulator A2.

As will be appreciated, when the vehicle travels in a straight line and the wheel hits a pot-hole then the actuator will tend to extend resulting in fluid being expelled from chamber C1 and passing through the first directional control valve V2 into the first accumulator A1. Simultaneously, hydraulic fluid will flow into fluid chamber C2 via first accumulator A1 and the second anti-cavitation accumulator A3.

As can be seen from Figure 2, parts of the actuator system 17 (those parts to the right of line D-D in Figure 2) define sprung mass of the vehicle, and another parts of the actuator system 17 (those parts to the left of D-D when viewing Figure 2) define unsprung mass of the vehicle.

As such, parts of fluid lines 35 and 37 are at least partly constructed as flexible hydraulic lines having a first end defined in a sprung mass and a second end defined in an unsprung mass.

As mentioned above, the first variable pressure relief valve V1 can be varied to suit particular circumstances. In particular, the relief valve pressure setting of valve V1 may be dependent upon a target pressure determined by the control unit 15, the pressure setting of the variable pressure relief valve V1 will therefore define the pressure in gallery G1, which can be applied to either of the chambers C1 or C2 via the first directional control valve V2.

Another embodiment of the active suspension system according to the present invention is shown in Figure 5. Parts of the embodiment shown in Figure 5, which are identical to parts of the embodiment shown in Figure 2 are labelled with corresponding reference signs. In contrast to the embodiment shown in Figure 2, the first directional control valve V21 of the embodiment shown in Figure 5 is a 4/2-way valve. As such, the first directional control valve V21 in Figure 5 only comprises a first and second state. In the first state, the first directional control valve V21 connects the gallery G1 with the first fluid chamber C1 and the second chamber C2 with the fluid return line 33. In its second state, the first directional control valve V21 connects the gallery G1 with the second fluid chamber C2 and the first fluid chamber C1 with the fluid return line 33.

The failsafe function of the embodiment shown in Figure 5 is obtained by a second directional control valve V3. The second directional control valve V3 is constructed as a 3/2-way valve. The second directional control valve V3 comprises a first port V3A, a second port V3B and a third port V3C. In its zero position, the second directional control valve connects the second and third ports V3B and V3C with the first port V3A, as shown in Figure 5. In this position, the gallery pressure G1 is vented towards the fluid return line 33 and so are the fluid chambers C1 and C2 of the hydraulic actuator 18. This guarantees that during a power cut, the hydraulic actuator 18 is a transparent part of the active suspension system 14D (expect for parasitic losses within the fluid lines and orifices). Alternatively, the valves of the hydraulic actuator 18 could be set up to act as a deliberate flow restriction, such that the hydraulic actuator is not transparent in its third state but rather acts as a further shock absorber. In order to compensate for driver induced forces, such as driving around bends, the second directional control valve V3 of the actuator system 17 shown in Figure 5 is powered and so remains in its second state, in which the first, second and third ports V3A, V3B and V3C are disconnected. The first variable pressure relief valve V1 can then be used to set the target pressure in chamber C1 or C2 respectively. When the vehicle is driven in a straight line only road induced 17 forces will need to be compensated by the active suspension system 14. In this case, the second direction control valve V3 may be switched to its first, unpowered state, in which the hydraulic actuator is transparent and the active suspension system 14 substantially acts as a passive suspension 14.

Turning to Figure 6, there is provided another embodiment of an active suspension system 14E. Parts of the system in Figure 6, which are identical to parts of the active suspension system 14A of Figure 2 are labelled with corresponding reference signs. The general function of the actuator system 17 of Figure 6 is substantially identical to the actuator system of Figure

2. However, in addition, the actuator system 17 of the active suspension system 14E is provided with a high pressure recovery accumulator A4. The high pressure recovery accumulator A4 is arranged to recover pressurised fluid from the fluid chambers C1 and C2, after use of the hydraulic actuator 18. To this end, the actuator system 17 comprises a second directional valve V4, which acts as a shut-off valve for the inlet of the high pressure recovery accumulator A4.

The second directional control valve V4 of Figure 6 is located within the fluid recovery line 33 and is constructed as a 3/2-way valve. The second directional control valve V4 comprises a first port V4A, a second port V4b and a third port V4C. In a first state, the first port V4A is connected to the second port V4B, such that the fluid return line 33 is uninterrupted. At the same time, the third port V4C is blocked. In a second state, the first port V4A is connected to the third port V4C and the second port V4B is blocked, so that fluid returning from either chamber C1 or C2 may be returned into the high pressure recovery accumulator A4. A check valve V6 stops fluid from exiting the high pressure recovery accumulator A4 in the direction of the third port V4C. In an alternative embodiment, the second direction control valve V4 of Figure 6 may be omitted, leaving only check valve V6 between the fluid return line 33 and the high pressure recovery accumulator A4. In this embodiment, whenever a fluid pressure in the fluid return line 33 exceeds the fluid pressure in pressure recovery accumulator A4, fluid will automatically flow into the pressure accumulator. The skilled person will understand that the construction of the second directional control valve V4 is not limited to the illustrated 2/3 valve structure but may be implemented in other suitable ways, such as an arrangement of check valves.

It should be understood that control unit 15 is configured to control the second directional control valve V4 such that the second state is only set when the first directional control valve

V2 is in its third, failsafe state. In other words, V4 only allows fluid in return line 33 to be added to the high pressure recovery accumulator A4, when the hydraulic actuator 18 is in its transparent state, i.e. when the pump P is disconnected from the chambers C1, C2.

Pressurised fluid of the high pressure recover accumulator A4 can only leave the accumulator A4 in direction of the inlet port P2 of pump P. To this end, a check valve V7 prevents high pressure fluid flow from the accumulator A4 from flowing towards second port V4B of the second directional control valve V4. Release of the pressurised fluid stored within the high pressure recovery unit A4 can be regulated by shut-off valve V5. Shut-off valve V5 may be constructed as 2/2-way valve, which is controlled by the control unit 15 to regulate release of high pressure fluid from the recovery accumulator A4.

Turning now to Figure 7, there is provided another embodiment of the active suspension system 14F according to the present invention. In the active suspension system 14F of Figure 7, parts which are identical to parts of the active suspension system 14A of Figure 2 are labelled with corresponding reference signs. The active suspension system 14F corresponds mainly to the active suspension system 14A of Figure 2. However, in addition to the parts of the active suspension system 14A, there is provided a head-pressure accumulator A5 and a head-pressure relief valve V8. The head-pressure relief valve V8 is located within gallery G1 and has a first port V8A connected to the outlet port P1 of the pump P and a second port V8B connected to the first port V2A of the first directional control valve V2. The second port V8B is further connected to the first port V1A of the first pressure relief valve V1. The head-pressure accumulator A5 is arranged between the outlet port P1 of the pump P and the first port V8A of the head-pressure relief valve V8.

It will be appreciated that the head-pressure relief valve V8 is variable to determine the amount of pressure stored within the head-pressure accumulator A5. In other words, the higher the pressure to overcome the head-pressure relief valve V8, the more pressure will be stored in head-high pressure accumulator A5. The pressure in the gallery G1 is, however, still set by the first variable pressure relief valve V1, which is arranged downstream of the head-pressure relief valve V8. It should be understood that the control unit 15 is configured to adjust the pressure necessary to open the variable head-pressure relief valve V8 such that said pressure is lower than or equal to a set pressure necessary to open the first variable relief valve V1, when use of the actuator 18 is required. Otherwise, if the actuator 18 is not in use, i.e. while the first directional control valve V1 is in its third state, the control unit 15 may adjust the pressure necessary to open the variable head-pressure relief valve V8 such that said pressure is higher than the set pressure necessary to open the first variable relief valve V1.

When the vehicle is being driven in a straight line, the suspension associated with wheel 12 is entirely carried by the spring end 20 and damper 21, the actuator 18 is not generating any force along its longitudinal axis, i.e. the actuator is not generating an extension force, nor is it generating a contraction force. At this time, the first directional control valve V2 is in its third state and chambers C1 and C2 do not need to be pressurised so that the fluid flow created by pump P is temporarily not required. At this time, the pump P can be used to fill the headpressure accumulator up to a pressure level that is set by the head-pressure relief valve V8 via the control unit 15. Once the pre-set pressure of the head-pressure relief valve V8 has been reached, the head-pressure accumulator A5 is no longer filled with flow from the pump P and so pressurised fluid crossing the head-pressure relief valve V8 will be recirculated via the first variable pressure relief valve V1 into accumulator A1 and back to the inlet port P2 of the pump P.

Once the driver creates a driver induced input by turning the steering wheel, a target pressure will be required in one of the first or second fluid chambers C1, C2. As described hereinbefore, the control unit 15 will then adjust the first directional control valve V2 accordingly and, at the same time, set the relief pressure of the first adjustable pressure relief valve V1 to the required target pressure. While in the embodiment according to Figure 2, the pump P was used to provide fluid flow until the target pressure is reached within the respective fluid chamber C1 or C2, the active suspension system 14F of Figure 7 now utilises the pressurised fluid from head-pressure accumulator A5 to set the target pressure within gallery G1 and, depending on the state of the first directional control valve V2, in the respective one of the first and second chambers C1, C2.

Since pre-charged high-pressure fluid from accumulator A5 can be used to obtain the target pressure within the hydraulic actuator 18, the actuator system 17 of Figure 7 can be adjusted significantly faster than the systems described hereinbefore. The pump P of this embodiment may only be required to re-charge the head-pressure accumulator A5 intermittently and so it is feasible to use one pump P for two, three or all four active suspension systems 14 of the vehicle 10.

The active suspension system 14G of Figure 8 differs from the active suspension system 14a of Figure 2 in that two variable pressure relief valves are provided. Parts of Figure 8, which are identical to parts of Figure 2 are labelled with corresponding reference signs.

In addition to the accumulators A1, A2 and A3, the first directional control valve V2 and pump P, the actuator system 17 of the active suspension system 14G shown in Figure 8 comprises a first and a second variable pressure relief valve V9 and V10. The first variable pressure relief valve V9 has a first port V9A connected to the third port V2C of the first directional control valve V2. A second port V9B of the first pressure relief valve V9 is connected to the fluid return line 33 and the first accumulator A1.

The second variable pressure relief valve V10 has a first port V10A connected to the fourth port V2D of the first directional control valve V2. A second port V2B is, in turn, connected to the fluid return line 33 and the first accumulator A1. The first and second variable pressure relief valves are electronically adjustable via the control unit 15.

The pressure in fluid line 35 is determined by the pressure setting of the first variable pressure relief valve V9. The pressure in fluid line 37 is adjustable by the pressure setting of the second variable pressure relief valve V10. As such, the first variable pressure relief valve V9 may only change the pressure within the first fluid chamber C1, whereas the second variable pressure relief valve V10 may only adjust the pressure within the second fluid chamber C2.

In the first state of the first directional control valve V2, shown in Figure 8, the outlet P1 of pump P is connected to fluid line 35 and therefore also to the first inlet port V9A of the first variable pressure relief valve V9. Depending on the pressure setting of the first variable pressure relief valve V9, the pressure in chamber C1 can be regulated. In this first state of the first directional control valve V2, the second variable pressure relief valve V10 does not perform any function and will be bypassed by fluid expelled from the second chamber C2 via the first directional control valve V2.

In the second state of the first directional control valve V2, the outlet port P1 of pump P is connected with fluid line 37 and, therefore, with the first port V10A of the second variable pressure relief valve V10. In this state, it is the second variable pressure relief valve V10, which determines the pressure within fluid line 37 and the second fluid chamber C2 of the cylinder 22. In this configuration, the first variable pressure relief valve V9 does not perform a function and is bypassed by fluid being expelled from the first chamber C1 via the first directional control valve V2.

As mentioned hereinbefore, it is intended that all embodiments and/or features of an embodiment can be combined in any way or combination, unless such features are incompatible. In particular, each of the active suspension systems 14D, 14E, 14F and 14G may include anti-cavitation accumulators as shown in Figures 3 and 4. Furthermore, the embodiments of Figure 5, 7 and 8 may all include the pressure recovery accumulator A4 and the corresponding valves described in Figure 6. Finally, each of the embodiments shown in 10 Figures 5, 6 and 8 may also include the head-pressure accumulator A5 and the corresponding head-pressure relief valve V8.

Claims

1. An active suspension system for a vehicle, the active suspension system comprising a plurality of actuator systems for each coupling a body of the vehicle to a wheel, wherein each actuator system comprises:

an actuator having a piston and a first fluid chamber separated from a second fluid chamber by the piston;

a pump having an inlet port and an outlet port, the outlet port of the pump being selectively connectable to the first and second fluid chambers;

a first variable pressure relief valve having a first port connected or connectable to the outlet port of the pump and a second port connected or connectable to the inlet port of the pump, the first variable pressure relief valve being arranged to selectively vary a pressure in one of the first and second fluid chambers.

2. The active suspension system of claim 1, wherein the actuator system comprises a first accumulator adapted to maintain a system pre-charge.

3. The active suspension system of claim 2, wherein the first accumulator has an inlet port connected to the second port of the first variable pressure relief valve.

4. The active suspension system of claim 3, wherein the inlet port of the first accumulator is connected to the inlet port of the pump.

5. The active suspension system of any of claims 1 to 4, wherein the first variable pressure relief valve is an electronically adjustable relief valve.

6. The active suspension system of any of claims 1 to 5, wherein the actuator system comprises a first directional control valve arranged to connect the outlet port of the pump with the first fluid chamber of the actuator, in a first state, and arranged to connect the outlet port of the pump with the second fluid chamber, in a second state.

7. The active suspension system of claim 6, wherein the first directional control valve is arranged to connect the second fluid chamber with the inlet port of the pump, in its first state, and arranged to connect the first fluid chamber with the inlet port of the pump, in its second state.

8. The active suspension system of claim 6 or 7, wherein the first directional control valve comprises a third state, in which the first and second fluid chambers are disconnected from the outlet port of the pump.

9. The active suspension system of claim 6 or 7, wherein the actuator system comprises a second directional control valve arranged to connect the outlet port of the pump with the inlet port in the event of an electrical power failure.

10. The active suspension system of any of claims 1 to 9, wherein the actuator system comprises a first anti-cavitation accumulator mounted on a housing of the actuator and fluidly connected to the first fluid chamber and/or wherein the actuator system comprises a second anti-cavitation accumulator mounted on a housing of the actuator and fluidly connected to the second fluid chamber.

11. The active suspension system of claim 10, wherein the first and/or second anti-cavitation accumulator is any of a diaphragm type accumulator, an enclosed bladder type accumulator, a floating piston type accumulator, and a spring type accumulator.

12. The active suspension system of claim 10 or 11, wherein the first and/or second anticavitation accumulator is sized to be saturated at a predetermined system pressure of the actuator system.

13. The active suspension system of any of claims 1 to 12, wherein the actuator system comprises a high pressure recovery accumulator, said recovery accumulator being connectable to the inlet port of the pump and selectively connectable the first and second fluid chambers.

14. The active suspension system of any of claims 1 to 12, wherein the actuator system comprises a head-pressure accumulator, said head-pressure accumulator being connected to the outlet port of the pump and to a first port of a head-pressure relief valve.

15. The active suspension system of claim 14, wherein the head-pressure relief valve has a second port connected to the first port of the first variable pressure relief valve.

16. The active suspension system of any of claims 1 to 12, wherein the actuator system comprises a second variable pressure relief valve having a first port connectable to the outlet port of the pump and a second port connectable to the inlet port of the pump, and wherein the first variable relief valve is arranged to selectively vary a pressure in the first fluid chamber, and the first port of the first variable pressure relief valve is connected to the first fluid chamber, and wherein the second variable relief valve is arranged to selectively vary a pressure in the second fluid chamber, and the first port of the second variable pressure relief valve is connected to the second fluid chamber.

17. The active suspension system of any preceding claim, wherein the actuator system is arranged in parallel with a spring and a damper.

18. The active suspension system of any preceding claim comprising a control unit for, in use, controlling each of the plurality of actuator systems to stabilise the body of the vehicle.

19. The active suspension system of claim 18, wherein the control unit is arranged to control the first variable pressure relief valve of each actuator system to vary the pressure in one of the first and second fluid chambers of the actuator system.

20. The active suspension system of any preceding claim, wherein each of the plurality of actuator systems is independently controlled to stabilise the body of the vehicle.

21. A vehicle comprising the active suspension system of any preceding claim, arranged between a vehicle wheel and a vehicle body.

22. A method of controlling an active suspension system, the active suspension system comprising a plurality of actuator systems coupling a body of a vehicle to a wheel, wherein each actuator system comprises an actuator having a piston and first fluid chamber separated from a second fluid chamber by the piston and a first variable pressure relief valve, the method comprising for each actuator system:

23. The method of claim 22, wherein the second pressure is determined on basis of the 5 determined or predicted load acting to compress the actuator.

24. The method of claim 22 or 23, wherein the first variable pressure relief valve of each actuator system is independently controlled.