GB2623970A

GB2623970A - Control system and method for an active suspension system

Info

Publication number: GB2623970A
Application number: GB2216205.1A
Authority: GB
Inventors: Lauwerys Christophe
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2022-11-01
Filing date: 2022-11-01
Publication date: 2024-05-08
Also published as: GB202216205D0

Abstract

A control system (200, Fig. 2) and a method 600 for controlling an active suspension system (104, Fig. 2) of a vehicle (1, Fig.1 ) are provided. The active suspension system comprises a hydraulic circuit (17, Fig. 5). The hydraulic circuit comprises a hydraulic pump (P) and an accumulator (A1, A3). The control system comprises one or more controllers (201, Fig. 2). The control system is configured to obtain 602 a variable setpoint (p_ref) indicative of required hydraulic pressure in the hydraulic circuit of the active suspension system. The control system is configured to determine 604 a flow control parameter (Q_pump_dyn) for controlling hydraulic pressure to track the variable setpoint. The control system is configured to output 606 the flow control parameter to control the hydraulic pump of the active suspension system. The flow control parameter is proportional to a rate of change of the variable setpoint and inversely proportional to an instant value of the variable setpoint. An active suspension system (104, Fig. 4) including such a control system, a vehicle and computer software (208, Fig. 2) are also disclosed.

Description

CONTROL SYSTEM AND METHOD FOR AN ACTIVE SUSPENSION SYSTEM

TECHNICAL FIELD

The present disclosure relates to a control system and method for an active suspension system. In particular, but not exclusively it relates to a control system for an active suspension system of a vehicle, and relates to an active suspension system, a vehicle, a method, and computer software.

BACKGROUND

An active suspension system can comprise a hydraulic circuit arrangement comprising a hydraulic actuator, a hydraulic pump, a variable valve, and an accumulator. Choosing the correct operating points for the hydraulic pump and the variable valve is an optimisation challenge, with regard to responsiveness and control stability.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a control system, an active suspension system, a vehicle, a method, and computer software as claimed in the appended claims.

According to an aspect of the invention there is provided a control system for controlling an active suspension system of a vehicle, the active suspension system comprising a hydraulic circuit, the hydraulic circuit comprising a hydraulic pump and an accumulator, the control system comprising one or more controllers, the control system configured to: obtain a variable setpoint indicative of required hydraulic pressure in the hydraulic circuit of the active suspension system; determine a flow control parameter for controlling hydraulic pressure to track the variable setpoint; and output the flow control parameter to control the hydraulic pump of the active suspension system, wherein the flow control parameter is proportional to a rate of change of the variable setpoint and inversely proportional to an instant value of the variable setpoint.

An advantage of this proportionality is an improved control scheme for an active suspension system. Control speed and accuracy are improved because the control scheme is simple enough to be implemented on a real-time system, yet accurate enough to result in accurate tracking of dynamic pressure setpoint variations, without needing excessive experimental calibration data.

The one or more controllers may collectively comprise: at least one electronic processor having an electrical input for receiving one or more input signals; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to cause, at least in part, execution of any one or more of the methods described herein.

In some examples, the flow control parameter is configured to control how much additional pumping by the hydraulic pump is required to keep the accumulator charged during a change of the variable setpoint.

In some examples, the flow control parameter comprises a feedforward component to control the additional pumping by of the hydraulic pump to keep the accumulator charged during the change of the variable setpoint, wherein the feedforward component is proportional to a rate of change of the variable setpoint and inversely proportional to the instant value of the variable setpoint.

In some examples, the feedforward component is a calibration value, and wherein the calibration value corresponds to the rate of change of the variable setpoint divided by the instant value of the variable setpoint.

In some examples, determining the feedforward component comprises determining the calibration value in dependence on a plurality of predetermined calibration values, based on the rate of change of the variable setpoint divided by the instant value of the variable setpoint.

In some examples, determining the feedforward component comprises determining an interpolated value of the rate of change of the variable setpoint divided by the instant value of the variable setpoint, in dependence on the plurality of predetermined calibration values.

In some examples, determining the flow control parameter comprises looking up the calibration value from a lookup table, the lookup table comprising the plurality of predetermined calibration values, each corresponding to a different range of values of the rate of change of the variable setpoint divided by the instant value of the variable setpoint.

In some examples, the control system is configured to determine a valve control parameter for controlling flow through a pressure control valve, in dependence on the variable setpoint and on a selected operating point of the hydraulic pump.

In some examples, the hydraulic pump is a bidirectional pump, and wherein the control signal is configured to control the hydraulic pump in either direction of the hydraulic pump.

According to a further aspect of the invention there is provided a method of controlling an active suspension system of a vehicle, the active suspension system comprising a hydraulic circuit, the hydraulic circuit comprising a hydraulic pump and an accumulator, the method comprising: obtaining a variable setpoint indicative of required hydraulic pressure in the hydraulic circuit of the active suspension system; determining a flow control parameter for controlling hydraulic pressure to track the variable setpoint; and outputting the flow control parameter to control the hydraulic pump of the active suspension system, wherein the flow control parameter is proportional to a rate of change of the variable setpoint and inversely proportional to an instant value of the variable setpoint.

According to another aspect of the invention there is provided a second control system for controlling an active suspension system of a vehicle, the active suspension system comprising a hydraulic circuit connected to an actuator, the hydraulic circuit comprising a hydraulic pump operable to control flow rate in the hydraulic circuit, wherein the flow rate is related to hydraulic pressure in the hydraulic circuit, wherein displacement of the actuator affects hydraulic pressure in the hydraulic circuit, wherein hydraulic pressure within a first range has a first relationship with flow rate, wherein hydraulic pressure greater than the first range has a second relationship with flow rate, and wherein the control system comprises one or more controllers, the control system configured to: receive information indicative of displacement of the actuator by external forces originating from outside the active suspension system; determine a metric dependent on the information indicative of displacement of the actuator over a time period, the metric indicating potential future actuator displacement; modify a flow control parameter for the hydraulic pump, in dependence on the metric, to control the amount by which the hydraulic pressure is greater than the first range; and output the modified flow control parameter to control the hydraulic pump of the active suspension system.

An advantage of the above adaptive predictive control scheme is that it enables an improved trade-off between control stability and power consumption. This balances the objective to avoid unexpected pressure dips against the competing objective of running the hydraulic pump at a low flow rate (i.e., close to the minimum at which pressure dips can occur).

In some examples of the second control system, the flow control parameter is calculated by an energy optimiser configured to minimise an energy consumption of the hydraulic pump while keeping steady state hydraulic pressure above the first range, and wherein modifying the flow control parameter comprises increasing the flow control parameter to increase the steady state hydraulic pressure, in dependence on the metric, to reduce a likelihood of the hydraulic pressure falling into the first range.

In some examples of the second control system, if the metric increases, the modified flow control parameter increases, and wherein if the metric decreases, the modified flow control parameter decreases.

In some examples of the second control system, the time period is a value selected from the range greater than or equal to one second and less than or equal to 20 seconds.

In some examples of the second control system, the control system is configured to modify the flow control parameter in realtime, wherein the information is realtime information, and wherein the time period is a realtime moving time period.

In some examples of the second control system, the metric indicates a measure of central tendency of a statistical distribution of actuator displacement over the time period, and/or wherein the metric indicates a statistical dispersion of actuator position over the time period.

In some examples of the second control system, the control system is further configured to determine a valve control parameter for controlling flow through a pressure control valve, in dependence on a hydraulic pressure setpoint and a selected operating point of the hydraulic pump.

In some examples of the second control system, the hydraulic pump is a bidirectional pump, and wherein the flow control parameter is configured to control the hydraulic pump in either direction of the hydraulic pump.

According to a further aspect of the invention there is provided an active suspension system comprising the control system and/or the second control system.

The active suspension system may comprise an independent hydraulic circuit for each one of corners of the vehicle, wherein the control system or second control system is configured to determine independent control signals for each of the independent hydraulic circuits to provide a Fully Active Suspension (FAS) function, or wherein the hydraulic circuit is shared between a pair of laterally separated wheels of the vehicle, such that the active suspension system is configured to provide an Active Roll Control (ARC) function.

According to a further aspect of the invention there is provided a vehicle comprising the control system and/or the second control system or the active suspension system comprising the control system and/or the second control system.

According to a further aspect of the invention there is provided a method of controlling an active suspension system of a vehicle, the active suspension system comprising a hydraulic circuit connected to an actuator, the hydraulic circuit comprising a hydraulic pump operable to control flow rate in the hydraulic circuit, wherein the flow rate is related to hydraulic pressure in the hydraulic circuit, wherein displacement of the actuator affects hydraulic pressure in the hydraulic circuit, wherein hydraulic pressure within a first range has a first relationship with flow rate, wherein hydraulic pressure greater than the first range has a second relationship with flow rate, the method comprising: receiving information indicative of displacement of the actuator by external forces originating from outside the active suspension system; determining a metric dependent on the information indicative of displacement of the actuator over a time period, the metric indicating potential future actuator displacement; modifying a flow control parameter for the hydraulic pump, in dependence on the metric, to control the amount by which the hydraulic pressure is greater than the first range; and outputting the modified flow control parameter to control the hydraulic pump of the active suspension system.

The control system, first described above, and the second control system may be integrated in a single combined control system displaying the features of both control systems.

According to a further aspect of the invention there is provided computer software that, when executed, is arranged to perform any one or more of the methods described herein. According to a further aspect of the invention there is provided a non-transitory computer readable medium comprising computer readable instructions that, when executed by one or more electronic processors, causes the one or more electronic processors to carry out any one or more of the methods described herein.

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 falls within the scope of the appended claims. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination that falls within the scope of the appended claims, 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: FIG. 1 illustrates an example of a vehicle FIG. 2 illustrates an example of a control system; FIG. 3 illustrates an example of a non-transitory computer-readable storage medium; FIG. 4 illustrates an example of an active suspension system; FIG. 5 illustrates an example of a hydraulic circuit arrangement; FIG. 6 illustrates an example of a method; FIG. 7 illustrates an example of a method; and FIG. 8 illustrates an example graph of hydraulic pressure and flow rate in a suspension hydraulic circuit arrangement.

DETAILED DESCRIPTION

FIG. 1 illustrates an example of a vehicle 1 in which embodiments of the invention can be implemented. In some, but not necessarily all examples, the vehicle 1 is a passenger vehicle, also referred to as a passenger car or as an automobile. In other examples, embodiments of the invention can be implemented for other applications, such as commercial vehicles.

FIG. 1 is a front perspective view and illustrates a longitudinal x-axis between the front and rear of the vehicle 1 representing a centreline, an orthogonal lateral y-axis between left and right lateral sides of the vehicle 1, and a vertical z-axis. A forward/fore direction typically faced by a driver's seat is in the negative x-direction; rearward/aft is -frx. A rightward direction as seen from the driver's seat is in the positive y-direction; leftward is -y. These are a first lateral direction and a second lateral direction.

FIG. 2 illustrates an example control system 200 for controlling an active suspension system 104 of the vehicle 1. The control system 200 is configured to implement one or more aspects of the invention. The control system 200 of FIG. 2 comprises a controller 201. In other examples, the control system 200 may comprise a plurality of controllers on-board and/or off-board the vehicle 1.

The controller 201 of FIG. 2 includes at least one processor 204; and at least one memory device 206 electrically coupled to the electronic processor 204 and having instructions (e.g. a computer program 208) stored therein, the at least one memory device 206 and the instructions configured to, with the at least one processor 204, cause any one or more of the methods described herein to be performed. The controller 201 may have an interface 202 comprising an electrical input/output I/O 210, 212, or an electrical input 210, or an electrical output 212, for receiving information and interacting with external components.

FIG. 3 illustrates a non-transitory computer-readable storage medium 300 comprising the instructions (computer software).

FIG. 4 illustrates an example implementation of the active suspension system 104, connecting a vehicle body 102 to vehicle wheels 12.

The active suspension system 104 comprises front left active suspension 106 for a front left wheel FL, front right active suspension 116 for a front right wheel FR, rear left active suspension 108 for a rear left wheel RL, and rear right active suspension 118 for a rear right wheel RR. The active suspension for each wheel (e.g. quarter/corner) of the vehicle 1 may be individually controllable.

FIG. 4 also shows a torque source 103 such as an internal combustion engine or electric machine, for driving at least some of the vehicle wheels 12.

The active suspension 106, 116, 108, 118 for each corner of the vehicle 1 comprises an actuator 502.

The actuator 502 may be a hydraulic actuator such as a hydraulic fluid-filled chamber containing a piston. The fluid may comprise hydraulic oil. One end of the actuator 502 is coupled to a vehicle wheel 12 and the other end is coupled to the vehicle body 102. A spring 504 (e.g. coil or pneumatic) may be in equilibrium and acting in parallel with the actuator 502.

When the vehicle suspension is undisturbed, the piston of the hydraulic actuator 502 sits at a particular neutral position in the chamber.

The piston can move in either direction inside the chamber, e.g. due to a road disturbance compressing the actuator 502. The piston can displace fluid out of the chamber into a hydraulic circuit (not shown). The fluid imparts a restoring force against movement of the piston. Energy can be added to and/or extracted from the actuator 502 by pumping fluid and/or controlling valves to regulate fluid pressure to either side of the piston.

The damping of the actuator 502 can be modified by controlling a damper valve at a constriction, which regulates the force realized by the fluid transferred in and out of the actuator 502 by movement of the piston. Bump and rebound damping rates could be controlled independently in some examples.

Further, energy can be added to or removed from the actuator 502 in order to control various suspension characteristics including, but not limited to the damping curve (force-velocity relationship) of the actuator 502.

In FIG. 4 but not necessarily all examples, the spring 504 comprises an active spring such as a pneumatic spring, enabling control of ride height. The control system 200 may be configured to pump gas (e.g. air) in or out of the pneumatic spring 504 to control ride height.

Energy can be added to or removed from the pneumatic spring 504 in order to increase or decrease the volume of the pneumatic spring 504. Increasing the volume can lift the vehicle body 102 in the z-axis. In FIG. 4 this enables the wheel-to-body distance to be changed independently at different ends and/or at different corners of the vehicle 1.

Additionally or alternatively, the spring 504 comprises a passive spring (e.g. coil) or is omitted entirely.

Control of the active suspension system 104 relies on one or more sensors. Wheel travel may be sensed by a wheel-to-body displacement sensor 514 (suspension displacement-based sensor), for example. The wheel-to-body displacement sensor 514 is placed somewhere on the active suspension 106, 116, 108, 118 and can sense the position of the wheel 12 along an arc defined by suspension geometry. An example of a wheel-to-body displacement sensor 514 is a rotary potentiometer attached to a lever, wherein one end of the lever is coupled to the vehicle body 102, and the other end is coupled to a suspension link.

In some examples, the control system 200 more accurately determines the wheel travel and/or its associated derivatives by fusing information from the wheel-to-body displacement sensor 514 with information from hub accelerometers.

In at least some examples the control system 200 is configured to control the active suspension system 104 by transmitting a force request to the active suspension 106, 116, 108, 118 or to a low-level controller thereof. The force request may be an arbitrated force request based on requests from various requestors and information from various sensors.

FIG. 4 illustrates additional features that may interact with the control system 200 to influence force request calculation. These include any one or more of: - A hub-mounted accelerometer 516 for each wheel 12, coupled to the unsprung mass of the vehicle 1.

- At least one vehicle body accelerometer 522 coupled to the vehicle body 102 (sprung mass). A particular example includes a 3DOF or 6DOF inertial measurement unit (IMU). A unit may comprise an accelerometer or a multi-axis set of accelerometers.

FIG. 5 illustrates an example topology of a hydraulic circuit arrangement 17 for each active suspension 106, 108, 116, 118. The active suspension system 104 comprises an independent hydraulic circuit arrangement 17 for each corner of the vehicle 1, wherein the control system 200 is configured to determine independent control signals for each of the independent hydraulic circuits to provide a Fully Active Suspension (FAS) function.

However, the hydraulic circuit arrangement 17 is not limited to that shown in FIG. 5, which is for illustrative purposes only. Aspects of the invention are applicable to a wide range of suspension circuits having a variable hydraulic pump P, a variable valve V2, an accumulator Al, and a substantially incompressible fluid. For example, aspects of the invention may be applicable to a semi-active system such as a system in which a hydraulic circuit is shared between a pair of laterally separated wheels 12 of the vehicle 1, such that the active suspension system 104 is configured to provide an Active Roll Control (ARC) function.

In FIG. 5, the actuator 502 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 vehicle body 102 via a rod 26. The piston 24 defines a first fluid chamber Cl and a second fluid chamber C2. The piston 24 fluidly isolates the first fluid chamber Cl from the second fluid chamber C2. In the illustrated example, the first fluid chamber Cl is an annulus chamber and the second fluid chamber C2 is a piston chamber.

The hydraulic circuit arrangement 17 also includes a hydraulic pump P having a first port P1 and a second port P2. In the illustrated example, the pump P is bidirectional so as to selectively generate flow out of the first port P1 or second port P2. In other examples, separate single-direction pumps are provided, or a single-direction pump is connected to a direction-controlling valve.

The hydraulic circuit arrangement 17 includes valves V1, V2, V3 and V4. The valves may be electromagnetically controlled.

Valve V1 includes a damper valve V1A and a check valve Vi B. Similarly valve V3 includes a damper valve V3A and a check valve V3B.

Valves V2 and V4 are both variable pressure control valves (PCVs). Alternatively, they may comprise a different type of hydraulic valve.

The hydraulic circuit arrangement 17 also includes hydraulic accumulators Al, A2, A3 and hydraulic galleries G1, G2 and G3.

The hydraulic circuit arrangement 17 also includes check valves X1 and X2.

Gallery G1 fluidly connects port P1 of pump P, outlet X10 of check valve X1, inlet V2I of valve V2, hydraulic accumulator Al, and port V1C of valve V1.

Similarly, gallery G3 connects port P2 of pump P with outlet X20 of check valve X2, inlet V4I of valve V4, hydraulic accumulator A3, and port V3C of valve V3.

Gallery 30 connects the first fluid chamber Cl with port VlD of valve Vi. Similarly gallery 32 connects the second fluid chamber C2 with port V3D of valve V3.

Gallery G2 connects hydraulic accumulator A2 with outlet V20 of valve V2, outlet V40 of valve V4, inlet Xll of check valve Xl, and inlet X2I of check valve X2.

As can be seen from FIG. 5, a first hydraulic circuit 28 defined at least by gallery G1 and gallery 30 connect the first port P1 of the hydraulic pump P to the first chamber Cl. Where the first chamber 01 is an annulus chamber, the first hydraulic circuit 28 can be described as an annulus circuit.

Similarly, a second hydraulic circuit 29 defined at least by gallery G3 and gallery 32 connect the second port P2 of the hydraulic pump Al with the second chamber C2. Where the second chamber C2 is a piston chamber, the second hydraulic circuit 29 can be described as a piston circuit.

In operation, the control system 200 is configured to determine an appropriate setpoint indicative of required hydraulic pressure in one or both of chambers Cl, C2. The setpoint obtained (received or calculated) by the control system 200 may be a pressure setpoint or an actuator force setpoint, for example.

In an example, the control system 200 may increase the setpoint for the second fluid chamber 02 when it is desired to cause an extension force to be generated by the actuator 502, for example to counter vehicle body roll in a particular direction. When it is determined that the actual pressure in second fluid chamber 02 is below the setpoint, then the pump P is operated so as to pump fluid from first gallery G1 into the third gallery G3. As the pressure in gallery G3 rises, hydraulic fluid may flow past check valve V3B causing the hydraulic pressure in gallery 32 and hence in the second fluid chamber 02 to also rise. Hydraulic pressure in hydraulic accumulator A3 will similarly rise. As the pressure in gallery G3 increases, so the pressure in gallery Cl may fall. Check valve X2 will prevent fluid flow through the valve from gallery G3 to gallery G2 when the pressure in gallery G3 is greater than the pressure in gallery G2. As the pressure in gallery G1 drops, in particular to a pressure below the pressure in gallery G2 then check valve X1 will open, thereby equalising the pressure in galleries G1 and G2.

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 Cl. The expelled fluid will flow into gallery G1 dependent upon the flow characteristics of valve VIA, thus replacing some of the fluid lost from gallery G1 to gallery G3 via pump P. Fluid from hydraulic accumulator Al may pass into gallery Gl.

After a period of time a steady equilibrium will be reached wherein the pressure in gallery G3, accumulator A3, gallery 322nd in the second fluid chamber 02 are all equal. The magnitude of this steady state pressure, equal to the setpoint, will determine the appropriate pump speed bearing in mind the leakage characteristics of the pump P. In the interest of system performance, it is desirable to minimise the time taken to reach the setpoint, and to minimise the energy used to charge accumulator A3. To this end, accumulator A3 is a relatively small capacity accumulator.

Consider the scenario where there is a disturbance input in the form of the wheel 12 hitting a bump. Whilst the target pressure in the second fluid chamber C2 is tending to extend the actuator 502, the bump in the road will cause the actuator 502 to contract thereby causing hydraulic fluid to flow out of the second fluid chamber C2 and consequently into the first fluid chamber Cl. Fluid flow into the first fluid chamber Cl is provided primarily by hydraulic fluid from accumulator Al flowing through valve V1 B. However, hydraulic fluid flowing out of the second fluid chamber C2 is damped by valve V3A. Thus valve V3A acts as a damper valve under these circumstances.

Hydraulic fluid passing through valve V3A will primarily cause fluid to flow into accumulator A3. Once the bump has been negotiated the piston 24 will return to its steady state position. The bump will create a high frequency road induced input which is accommodated primarily by accumulator A3 which is close to second fluid chamber C2 when compared with accumulator A2 (as will be discussed further below).

However, if the bump is sufficiently big, movement of the piston 24 within the cylinder 22 may cause the pressure in chamber C2 and gallery G3 to increase above the relief valve pressure setting of valve V4 in which case valve V4 will momentarily open so as to limit the pressure in gallery G3. Simultaneously the large bump will cause the volume of chamber Cl to increase in size and hydraulic fluid may, in addition to flowing out of accumulator Al into gallery G1 and on to gallery 30 via valve VI B, also flow out of accumulator A2 into gallery G1 via check valve X1 and on to gallery 30 via valve V1 B. The volume of the second accumulator A2 may be greater than the full stroke differential volume of the actuator 502 As will be appreciated, the first fluid chamber Cl can vent fluid to hydraulic accumulators Al and/or A2. As will be appreciated, the second fluid chamber C2 can vent fluid to hydraulic accumulators A3 and/or A2. The hydraulic accumulators Al and A3 are relatively close both physically and hydraulically to the fluid chambers Cl and C2, so these accumulators Al, A3 can accommodate high frequency road induced inputs which tend to require relatively low amounts of hydraulic fluid to accommodate. If the setpoint is moving, the accumulators Al and A3 may need to be filled more. Conversely the hydraulic accumulator A2, being larger, is better able to accommodate larger volumes of hydraulic fluid associated with larger relative movements of the piston 24 within the cylinder 22 often associated with low frequency driver induced inputs.

As mentioned above, valve V2 is a variable pressure control valve and the valve pressure setting of valve V2 can be electronically varied to suit the particular circumstances. The valve V2 may comprise a variable restriction (variable orifice). In particular, the valve pressure setting of valve V2 may be dependent upon the setpoint for the first chamber Cl. The valve pressure setting of valve V2 may further be dependent upon the operating point of the pump P. The more electrical current is applied to the pressure control valve V2, the more counteracting force restricts the flow. The pressure control valve V2 needs constant electrical current to counteract that pressure.

As mentioned above, valve V4 is a variable pressure control valve and the valve pressure setting of valve V4 can be electronically varied to suit the particular circumstances. The valve V4 may comprise a variable restriction (variable orifice). In particular, the valve pressure setting of valve V4 may be dependent upon the setpoint in the second chamber C2. The valve pressure setting of valve V4 may further be dependent upon the operating point of the pump P. The more electrical current is applied to the pressure control valve V4, the more counteracting force restricts the flow. The pressure control valve V4 needs constant electrical current to counteract that pressure.

In steady state conditions, hydraulic fluid pumped in a first direction flows through the pressure control valve V2, past the check valve X2, and back to the pump P. Hydraulic fluid pumped in the opposite direction flows through the pressure control valve V4, past the check valve Xl, and back to the pump P. The hydraulic pressure in each circuit is determined predominantly or entirely by the pressure through the pressure control valves V2, V4.

The control problem for a given hydraulic circuit 28 or 29 is to track the setpoint to control the force in the actuator 502. This comprises controlling the pressures in the annulus and piston side accumulators Al and A3. The means by which pressure can be controlled comprise the pump P and the pressure control valves V2 and V4. The control problem is challenging because this is a highly nonlinear, dynamically coupled system. As will be explained later, a fast feedback controller would introduce undesired dynamics, whereas a non-adaptive feedforward controller requires the calculation of the inverse dynamics of the system which is practically difficult for realtime deployment.

The below description makes an abstraction of the hydraulic circuit arrangement 17 as only one branch (e.g., circuit 28, pressure control valve V2) and reduces the control problem to tracking a desired accumulator pressure in the accumulator (Al) of that branch 28. The approach for branch 29 would be similar. High level aspects such as the translation of an actuator force target into a pressure target (setpoint) is outside the scope of this disclosure.

In a steady state scenario, the relationship between the pressure (p) on the one hand, and the pump flow and state of the pressure control valve V2 on the other hand, is less challenging. The forward relationship is uniquely defined by the pressure-flow characteristics of the pressure control valve V2 (f control valve) for different electric currents (i) applied to the pressure control valve V2 to control its restrictiveness.

p = f_control_valve(Q_valve, i) Eq. 1 In steady-state, the accumulator pressures and volumes are constant, hence the flow (Q valve) through the pressure control valve V2 is equal to the flow through the pump P (Q pump). Q pump is a flow control parameter configured to control the operating point of the pump P. Therefore, the steady-state generated pressure (p) is directly related to the pump flow (Q_pump) and the control current (i).

p = f control valve(Q pump, i) Eq. 2 This equation uniquely defines the relationship between the pump flow (Q_pump), the control current (i), and the accumulator pressure (p).

In real-life dynamic conditions, the relationship is complicated because the accumulator pressure is a function of the volume of hydraulic fluid present which may be time-varying.

The accumulator pressure (p) is still related to the flow through the pressure control valve V2 (Q_valve) and the control current (i).

p = f control valve(Q valve, i) Eq. 3 However, this flow (Q_valve) is no longer equal to the pump flow (Q_pump) since hydraulic fluid can also flow in or out of the accumulator Al (Q acc).

Q pump = Q valve + Q acc Eq. 4 As an example, consider the system in equilibrium at a certain pressure (p1), pump flow (Q pump) and control current (i1). Since the system is in equilibrium there is no flow into or out of the accumulator Al (Q_acc=0).

p1 = f_control_valve(Q_pump, il) Eq. 5 Then, the control current is changed from il to i2 corresponding to an increase in hydraulic restriction.

This new setpoint will result in a higher steady state pressure. However, to reach that increased pressure, first the accumulator Al needs to be filled with an additional volume of hydraulic fluid to match that pressure.

Consequently, immediately after the step change in control current, the pump flow will split, partially flowing to the accumulator Al, partially through the pressure control valve V2.

p = f control valve(Q valve, i2) Eq. 6 Q_valve = Q_pump -Q_acc Eq. 7 During this transient phase, the accumulator Al gradually fills with hydraulic fluid until it reaches the volume that corresponds to the same pressure as the pressure generated by the pressure control valve V2. At that time the new steady state is reached wherein all pump flow goes through the pressure control valve V2.

p2 = f control valve(Q pump, i2) Eq. 8 Various control philosophies can be used. The control target is to track a certain setpoint (p ref) by changing the current (i) to the pressure control valve V2 and the flow of the pump P (Q pump). A distinction is made below between the steady state and dynamic behaviour of the system. The control design is focussed on the more challenging dynamic part.

The steady-state control problem is relatively straightforward. The relation between the setpoint (p ref) on one hand, and the pump flow (Q pump) and the control current (i) on the other can be experimentally identified and inverted to achieve the inverse mapping from pressure (p) and the selected pump flow (Q_pump), to the control current (i valve).This inversion involves a choice about which combination of Q pump and i valve to use to achieve a certain pressure.

i valve = f control valve(Q pump, p ref) Eq. 9 This inverse mapping (f_control_valve) can be implemented in several forms such as a lookup table, a multivariate polynomial, a multidimensional piecewise spline, etc. In a dynamic situation, the main challenge is tracking fast-varying setpoints. The reason is that dynamically, an extra volume of hydraulic fluid is required to flow into or out of the accumulator Al to reach the desired setpoint.

The difficulty is in tracking the moving target without any unwanted oscillation (moving target problem). The road disturbances through the wheels 12 introduce a second variable. It is difficult to achieve a certain force in a fast way, because a certain volume in the accumulator Al needs to be filled or emptied in a certain time to achieve the required setpoint. Optimal control of the pump flow and the flow control valve is desirable. It is difficult to calculate how much hydraulic fluid is required and by when, to fill the accumulator Al properly and achieve the setpoint.

This depends on pressure, on the rate of change of the setpoint, and on wheel disturbances.

Feedforward control relies on an approximation of the inverse system dynamics, and uses only the tracking references (setpoint) as an input without using measurements of any system variables. The advantage of feedforward control is that it does not change the system dynamics hence also cannot induce system instabilities.

However, the disadvantages of feedforward control are that: a) It requires an accurate model of the system dynamics; b) inverting system dynamics is complex; and c) inaccuracies in the inverse system dynamics are not compensated, leading to errors. For a practical active suspension system 104, accurate models are too complex to invert and simple invertible models are not sufficiently accurate.

Feedback control consists of a loop from measured system variables back to the controller input. The advantages of feedback control are that: a) No description of the system is required although it can help in the design process; and b) Very simple controllers can improve low-bandwidth system behaviour. The disadvantage of feedback control is that it changes system dynamics, potentially introducing unpredictable and undesired behaviour. In practice, feedback control is suitable for tracking slowly varying setpoints or compensating for slowly varying disturbances.

However, tracking faster varying setpoints requires higher feedback gains that introduce undesired dynamics in the system which are detrimental for passenger comfort.

Instead of trying to invert the system dynamics itself, this disclosure proposes an adaptive feedforward control scheme that adds an adaptive feedforward component (dQ pump) to the base component (Q pump) of the flow control parameter. The control scheme can be experimentally calibrated to match the desired performance. This approach identifies the inverse model of the active suspension system 104 based on predetermined manufacturer experimental measurements, instead of inversion of a computational model. The measurements are of valve currents, the pump flow, and the actuator force.

The required additional pump flow (dQ_pump) to charge the accumulator Al during a ramp pressure setpoint increase, is proportional to the rate of change of the setpoint (p dot) and inversely proportional to the instant value of the setpoint (p ref), that is to say the absolute value of the setpoint itself and not the rate of change thereof.

dQ_pump p_dot / p_ref Eq. 10 By outputting a modified flow control parameter (Q_pump_dyn) comprising a base component (Q_pump) and an additional adaptive feedforward component (do pump), the system is able to control how much additional flow through the hydraulic pump P is required to keep the accumulator Al charged during a change of the variable setpoint. However, when the setpoint is changing slowly or constant, dQ pump tends to zero and the control scheme reverts to steady state behaviour.

What is missing in this feedforward control scheme is the scalar gain (g).

dQ pump = g *p dot / p ref Eq. 11 Because this is just a crude approximation of the real system that does not take into account for instance pump inefficiencies or leakage (which increases with pressure), the feedforward control scheme may be upgraded from a linear gain (g) to a lookup table (tab) or similar data structure. ;dQ pump = lookup table of (p dot / p ref) Eq. 12 At runtime, the control system 200 may calculate a value of p dot divided by p ref, and then use the value to look up dQ pump from the lookup table stored in an electronic memory device 206. The lookup table comprises a plurality of experimentally-derived predetermined calibration values, each calibration value corresponding to a particular value of p dot/p ref. The lookup table in this example is one-dimensional. In other implementations, a multi-dimensional lookup table could potentially be used. ;Each calibration value in the lookup table corresponds to a particular range of values of p doUp ref. dQ pump can be calculated by interpolating the reference p dot/p ref ratio using the identified lookup table. The interpolation scheme may be a nearest interpolation scheme, a binning scheme, and/or a linear interpolation scheme. Linear interpolation may comprise looking up the calibration values below and above the calculated p dot/p ref, and linearly interpolating the corresponding dQ_pump. ;The performance of this control scheme is relatively smooth. ;A numerical example is provided. The control system 200 may require a particular actuator force such as 1kN. This may be converted to a pressure setpoint such as 30bar. A force of 2kN may correspond to a pressure of 40bar. If the actuator force is required to increase from 1kN to 2k N in one second, the pressure must increase from 30bar to 40bar in one second. This results in p dot of 10 bar/second. This results in a decreasing extra pump flow dQ_pump, by looking up dQ_pump in a table with breakpoints from p_dot/p_ref = 10/30 = 0.33 to p_dot/p_ref = 10/40 = 0.25. ;For the steady state base component (Q pump), an inverse lookup table can be relied upon as described earlier. ;For a fast-moving setpoint, the above-described adaptive feedforward control scheme can be used. For a slow-moving setpoint, the above-described control scheme can be used, or a different control scheme such as an integral feedback control scheme based on the setpoint tracking error. ;The unknown shape of the lookup table relating the additional pump flow d() pump to the ratio between the setpoint rate of change and absolute value of the setpoint p_dot/p_ref can be obtained experimentally on a test rig. The test rig can comprise the pump P and valves of FIG. 5, and sensors for measuring pressure and/or force. The experiments can be undertaken as follows: - Reset the test rig to be at its static pressure; -Generate a set of dynamically varying pressure setpoints. The set may be according to the following differential equation: p dot = g * p ref. This generates exponentially increasing pressure setpoints p ref with time constants proportional to g.

- Apply the dynamically varying pressure setpoint p ref and track the force and/or pressure.

- For each value of g in a range of feasible time constants, the engineer tunes the corresponding point in the lookup table in such a way that the resulting additional pump flow (dQ pump) results in a system pressure that optimally tracks the pressure setpoint.

To give an example, the test rig may start at a static pressure of 20 bar. Choosing g = 5 generates an exponentially increasing pressure p ref that satisfies the differential equation p dot = 5 " p ref. For this reference pressure setpoint, the ratio p dot/p ref used as an input to the feedforward lookup table is exactly equal to g = 5. The additional pump flow dQ pump corresponding to this table breakpoint g = 5 is now experimentally tuned in order to make the real measured pressure p optimally match the requested reference pressure p ref.

The above described control scheme leads to fast and accurate performance in theory and in practice because: - The feedforward model is simple enough to be implemented on a real-time system - The feedforward model is accurate enough to result in accurate tracking of dynamic pressure setpoint variations; - This high accuracy is obtained by experimental identification; - The unknown element in the model can be reduced to a single one-dimensional lookup table; and -Each element of the lookup table may be identified uniquely by one simple experiment.

FIG. 6 is a flowchart illustrating a computer-implemented method 600 of implementing the above-described adaptive feedforward control scheme. The control system 200 may implement the method 600.

At block 602, the method 600 comprises obtaining a varlable setpoint indicative of required hydraulic pressure in the hydraulic circuit 28 of the active suspension system 104. The variable setpoint may comprise a pressure target (p_ref) as described earlier, or some other unit indicative of a required hydraulic pressure in the hydraulic circuit 28.

Obtaining the variable setpoint can comprise either calculating the setpoint or receiving the setpoint from another controller.

At block 604, the method 600 comprises determining a modified flow control parameter (Q pump dyn) for controlling hydraulic pressure to track the variable setpoint. The flow control parameter may comprise the sum of a base component (Q pump) and an adaptive feedforward component (dQ pump) as described earlier. The base component may be a steady state target. The adaptive feedforward component requests additional flow through the pump P to keep the accumulator Al charged during the dynamic change of the variable setpoint. The adaptive feedforward component may be determined via a lookup table as described above in relation to Equation 12.

Once the modified flow control parameter (Q pump dyn=Q pump+dQ pump) has been determined, the valve control parameter (i valve) for the pressure control valve V2 can be determined based on the modified flow control parameter (Q_pump_dyn) and the instant value of the setpoint (prep, using the earlier described Equation 9 for i valve.

At block 608, the method 600 comprises outputting the modified flow control parameter to control the hydraulic pump P of the active suspension system 104. In an example, this comprises outputting the modified flow control parameter to a pump controller, which converts the modified flow control parameter to a low-level signal to change the operating point of the pump P. The adapted value may correspond to the sum of the base component (Q_pump) and the adaptive feedforward component (dQ pump).

In the following sections of the disclosure relating to FIGS. 7-8, there is also provided an advantageous method of calculating the base component (Q pump) of the flow control parameter. This method is not dependent on the above method of calculating the adaptive feedforward component (dQ pump), or is necessarily employed in conjunction with the above method to further improve performance.

As set out earlier in Equation 3, the accumulator pressure (p) is related to the flow through the pressure control valve V2 (Q valve) and the control current (i).

Earlier Equation 4 omits the actuator-initiated flow caused by movement of the actuator 502. By taking actuator-induced flow into account, the relationship becomes: Q pump = Q valve + Q acc + Q damper Eq. 13 The flow (Q valve) through the pressure control valve V2 is coming from the pump P (Q_pump) minus what is flowing to the accumulator Al (Q_acc) minus what is going to the actuator 502 (Q_damper), The motion of the actuator 502 causes hydraulic fluid to flow in and out of the hydraulic circuit 28, causing variations in flow through the pressure control valve V2 in turn leading to undesired variations in pressure and force.

The variations in pressure, caused by variations in flow through the pressure control valve V2, can be reduced in the following way.

In steady state, the flow from the accumulator Al (Q acc) and from the actuator 502 (Q damper) are both zero, and the flow through the valve (Q valve) is equal to the flow from the pump P (Q pump).

Q valve = Q pump Eq. 14 When the actuator 502 moves, an additional flow (dQ damper) is created, either adding or extracting hydraulic fluid from the hydraulic circuit 28. Assuming a constant pump flow (Q pump), this additional flow (dQ damper) is compensated for by a fraction of the flow originally flowing to the pressure control valve V2 (dQ valve) and a flow to the accumulator Al (dQ acc).

dQ_damper = -dQ_valve -dQ_acc Eq. 15 Short, dynamic actuator flow variations (dQ_damper) are partially compensated for by the accumulator Al (dQ acc). However, longer flow variations (dQ damper) unavoidably influence the differential flow through the valve (dQ valve) as well.

dQ_valve = -dQ_damper ( -dQ_acc) Eq. 16 In at least some examples, the pressure control valve V2 has been designed to have a flow-pressure characteristic in which the pressure is substantially independent of the flow rate. FIG. 8 illustrates pressure on the y-axis and flow on the x-axis. For a flow-pressure setpoint greater than (01, p1), the flow rate may remain approximately constant as the pressure control valve V2 is controlled to vary the pressure. The flow rate may increase slightly with pressure, as illustrated, but the relationship may be near-horizontal.

However, as shown in FIG. 8, the flow rate and pressure must cross the origin of the pressure-flow relation (Q = 0, p = 0). The pressure is less independent of flow rate at a range of low values -between (0, 0) and (01, p1). The point (01, p1) can be regarded as a knee point (breakpoint) at which the relationship changes between a first relationship (low-flow regime) in which pressure is less independent of flow rate, and a second relationship (high-flow regime) in which pressure is more independent of flow rate. The second relationship enables the pressure to be controlled solely by the control valve substantially independently of the total flow through the valve, as long as it remains always above the breakpoint flow Ql.

In FIG. 8, the target flow rate (Q valve) through the pressure control valve V2 (Q valve) is denoted 800. The target flow rate is calculated by an energy optimiser for minimising an energy consumption of the pump P. The energy optimiser may be a function in the control system 200. The energy optimiser may be configured to determine a minimum flow rate that still enables Equation 9 (i valve) to achieve a required pressure.

A positive flow offset (dQ valve) shifts the operating point towards the bar labelled 804, on the right of the target operating point 800. As shown, this flow offset only marginally increases the pressure. Note that the terms 'positive' and 'negative' are arbitrarily defined in relation to the direction of actuator displacement.

A negative flow offset (dQ valve) of the same magnitude shifts the operating point towards the lower bar labelled 802, on the left of the target operating point 800. As shown, this flow offset only marginally decreases the pressure.

It would be appreciated that a large negative flow offset (c1()_valve) that moves the operating point towards the steep slope part of the curve of FIG. 8, results in a significant drop in pressure. The resulting control instability may result in noise, vibration and harshness.

Therefore, a problem with pump energy optimisation is a lack of robustness to negative flow offsets, due to the proximity of the operating point to the knee point of FIG. 8.

A classic approach to compensate for pressure variations would be to measure the pressure and control the pump flow to keep the pressure at its setpoint. However, very small flow variations cause relatively large pressure variations because of the high flow sensitivity below the knee point. Despite the highly dynamic pump characteristics, a pressure feedback controller will introduce undesired dynamics in the system. Instead, a more adaptive approach is proposed.

The adaptive approach is configured to modify the energy optimised flow rate to control the amount by which the hydraulic pressure is greater than the knee point. The objective is to keep the operating point high enough, away from the knee point, such that negative flow variations induced by actuator motions remain in the quasi-horizontal part, right of the kneepoint, of the curve of FIG. 8, avoiding large pressure variations.

Wheel motions are stochastic events, hence it is difficult to determine a positive flow rate offset that guarantees avoiding all possible pressure dips. Maximising the flow offset at all times would be the most guaranteed to succeed, however, this would result in unacceptably increased power consumption.

The adaptive approach enables a trade-off between comfort and power consumption, balancing the objective to avoid unexpected pressure dips against the competing objective of running the pump P at a low flow rate.

The adaptive approach is predictive, and is configured to predict worst case flow variations based on measured information indicative of displacement of the actuator 502 by external forces originating from outside the active suspension system 104 (e.g., wheel motions due to road disturbances). Such measurements can originate from a wheel-to-body displacement sensor 514, or at least one accelerometer 516, 522, for example.

In order to predict worst case flow variations, the adaptive approach is configured to determine a metric dependent on the measured information over a time period, the metric indicating potential future actuator displacement.

The metric indicates a statistic of measured movement of the suspension. For example, the metric may indicate a velocity, acceleration or jerk of the actuator 502. The metric may be based on a statistical distribution of the measurement over the time period. For example, the statistical distribution could indicate the actuator velocity distribution over the time period. The indicated actuator velocity is closely related to the actuator flow rate (Q_damper = constant x velocity). In an example implementation, the control system 200 is configured to determine the statistical distribution of the measurement by counting the number of occurrences of the measurement within each of a plurality of bins, in the manner of a histogram.

The metric may indicate a measure of central tendency of the statistical distribution, such as average, median or mode. Additionally, or alternatively, the metric may indicate a statistical dispersion of the statistical distribution, such as variance, standard deviation, or interquartile range.

The control system 200 is then configured to modify the pump flow rate in dependence on the metric, to control the amount by which the hydraulic pressure and pump flow rate are greater than the range (0, 0) to (Q1, p1). For example, the control system 200 may be configured to apply a positive offset to the energy-optimised pump flow rate in realtime, to compensate for realtime additional actuator movement, to reduce a likelihood of the hydraulic pressure falling into the range (0-p1) and pump flow rate falling into the range (0-Q1).

In an example implementation, the required pump flow offset can be based on a predetermined percentile of the statistical distribution. The pump flow offset could be based on a 90'in percentile. Alternatively, to further reduce the likelihood of a pressure dip, the pump flow offset could be based on a 99'h percentile.

By selecting a time period (memory) of an appropriate duration for collecting the statistics, the metric will reactively indicate a probability of potential future actuator displacement for a given road that the vehicle 1 is driving on, in realtime. For example, if the vehicle 1 drives on a potholed suburban road for a mile before turning onto a smooth highway, it is desirable for the metric to quickly detect the high average actuator velocity and/or a wide actuator velocity distribution, and then quickly detect the reduction in actuator velocity after the vehicle 1 has entered the smooth road. The time window should not be so short that one-off transient events result in a long-term change of the metric.

The time window may be selected from the range 1 seconds to 20 seconds, or from the sub-range 7 seconds to 15 seconds. In an implementation, the time window is approximately 10 seconds. The time window is responsive enough to react to road type changes. The time window is not too short, to prevent the pump P from spinning up and down too regularly and rapidly, which can be felt as noise, vibration and harshness. The time window may comprise a moving time period such as a moving data collection window defining a horizon from which the statistical distribution and metric are calculated.

FIG. 7 is a flowchart illustrating a computer-implemented method 700 of implementing the above-described control scheme for ensuring that flow is high enough to tolerate dips. The control system 200 may implement the method 700.

At block 702, the method 700 comprises receiving information indicative of displacement of the actuator 502 by external forces originating from outside the active suspension system 104. As described above, the information may indicate wheel motions due to road disturbances. As described above, the information can originate from a wheel-to-body displacement sensor 514, or at least one accelerometer 516, 522, for example. In other examples, direct measurement of actuator position may be possible by a sensor of the actuator 502.

At block 704, the method 700 comprises determining a metric dependent on the information indicative of displacement of the actuator 502 over a time period, the metric indicating potential future actuator displacement.

As described above, determining the metric may comprise first determining a statistical distribution of the information, and then determining the metric as a representative statistic of the statistical distribution.

At data block 706, the method 700 comprises obtaining the flow control parameter, for example the pump flow rate, from an energy optimiser. The energy optimiser may be a function within the control system 200 or another control system. At block 708, the method 700 comprises modifying the flow control parameter from data block 706, in dependence on the metric, to control the amount by which the hydraulic pressure is greater than the range. As described above, this can comprise applying an offset to increase the flow control parameter to increase the steady state hydraulic pressure, in dependence on the metric, to reduce a likelihood of the hydraulic pressure falling into the range (ft 0) to (01, p1). However, if the metric indicates decreasing actuator movement, the offset could be reduced.

At block 710, the method comprises outputting the modified flow control parameter to control the hydraulic pump P of the active suspension system 104. As described above, this can comprise outputting the modified required pump flow rate, with the offset applied, to control the pump flow rate. In an implementation, the modified required pump flow rate (Q pump) may be provided to the control method of FIG. 6, where the adaptive feedforward component (dQ pump) may be added. The final value of Q pump dyn may then be applied to the pump P and the valve operating point may then be determined according to Equation 9.

It is to be understood that the or each controller 201 can comprise a control unit or computational device having one or more electronic processors (e.g., a microprocessor, a microcontroller, an application specific integrated circuit (ASIC), etc.), and may comprise a single control unit or computational device, or alternatively different functions of the or each controller 201 may be embodied in, or hosted in, different control units or computational devices. As used herein, the term "controller," "control unit," or "computational device" will be understood to include a single controller, control unit, or computational device, and a plurality of controllers, control units, or computational devices collectively operating to provide the required control functionality. A set of instructions could be provided which, when executed, cause the controller 201 to implement the control techniques described herein (including some or all of the functionality required for the method described herein). The set of instructions could be embedded in said one or more electronic processors of the controller 201; or alternatively, the set of instructions could be provided as software to be executed in the controller 201. A first controller or control unit may be implemented in software run on one or more processors. One or more other controllers or control units may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller or control unit. Other arrangements are also useful.

In the example illustrated in Figure 2, the or each controller 201 comprises at least one electronic processor 204 having one or more electrical input(s) 210 for receiving one or more input signals indicative of the setpoint (FIG. 6) and/or the measurement (FIG. 7), and one or more electrical output(s) 212 for outputting a flow control parameter as determined in FIG. 6 and/or 7. The or each controller 201 further comprises at least one memory device 206 electrically coupled to the at least one electronic processor 204 and having instructions 208 stored therein. The at least one electronic processor 204 is configured to access the at least one memory device 206 and execute the instructions 208 thereon so as to execute the steps of FIGS. 6 and/or 7.

The, or each, electronic processor 204 may comprise any suitable electronic processor (e.g., a microprocessor, a microcontroller, an ASIC, etc.) that is configured to execute electronic instructions. The, or each, electronic memory device 206 may comprise any suitable memory device and may store a variety of data, information, threshold value(s), lookup tables or other data structures, and/or instructions therein or thereon. In an embodiment, the memory device 206 has information and instructions for software, firmware, programs, algorithms, scripts, applications, etc. stored therein or thereon that may govern all or part of the methodology described herein. The processor, or each, electronic processor 204 may access the memory device 206 and execute and/or use that or those instructions and information to carry out or perform some or all of the functionality and methodology describe herein.

The at least one memory device 206 may comprise a computer-readable storage medium (e.g. a non-transitory or non-transient storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors/computational devices, including, without limitation: a magnetic storage medium (e.g. floppy diskette); optical storage medium (e.g. CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g. EPROM ad EEPROM); flash memory; or electrical or other types of medium for storing such information/instructions.

Example controllers 201 have been described comprising at least one electronic processor 204 configured to execute electronic instructions stored within at least one memory device 206, which when executed causes the electronic processor(s) 204 to carry out the method as hereinbefore described. However, it will be appreciated that embodiments of the present invention can be realised in any suitable form of hardware, software or a combination of hardware and software. For example, it is contemplated that the present invention is not limited to being implemented by way of programmable processing devices, and that at least some of, and in some embodiments all of, the functionality and or method steps of the present invention may equally be implemented by way of non-programmable hardware, such as by way of non-programmable ASIC, Boolean logic circuitry, etc. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

The blocks illustrated in FIGS. 6-7 may represent steps in a method and/or sections of code in the computer program 212 The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some steps to be omitted.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS1. A control system for controlling an active suspension system of a vehicle, the active suspension system comprising a hydraulic circuit, the hydraulic circuit comprising a hydraulic pump and an accumulator, the control system comprising one or more controllers, the control system configured to: obtain a variable setpoint (p ref) indicative of required hydraulic pressure in the hydraulic circuit of the active suspension system; determine a flow control parameter (Q pump dyn) for controlling hydraulic pressure to track the variable setpoint. and output the flow control parameter to control the hydraulic pump of the active suspenslon system, wherein the flow control parameter is proportional to a rate of change of the variable setpoint and inversely proportional to an instant value of the variable setpoint.
2. The control system of claim 1, wherein the flow control parameter is configured to control how much additional pumping by the hydraulic pump is required to keep the accumulator charged during a change of the variable setpoint.
3. The control system of claim 2, wherein the flow control parameter comprises a feedforward component (dC) pump) to control the additional pumping by of the hydraulic pump to keep the accumulator charged during the change of the variable setpoint, wherein the feedforward component is proportional to a rate of change of the variable setpoint and inversely proportional to the instant value of the variable setpoint.
4. The control system of claim 3, wherein the feedforward component is a calibration value, and wherein the calibration value corresponds to the rate of change of the variable setpoint divided by the instant value of the variable setpoint.
5. The control system of claim 4, wherein determining the feedforward component comprises determining the calibration value in dependence on a plurality of predetermined calibration values, based on the rate of change of the variable setpoint divided by the instant value of the variable setpoint.
6. The control system of claim 5, wherein determining the feedforward component comprises determining an interpolated value of the rate of change of the variable setpoint divided by the instant value of the variable setpoint, in dependence on the plurality of predetermined calibration values.
7. The control system of 5 or 6, wherein determining the flow control parameter comprises looking up the calibration value from a lookup table, the lookup table comprising the plurality of predetermined calibration values, each corresponding to a different range of values of the rate of change of the variable setpoint divided by the instant value of the variable setpoint.
8. The control system of any preceding claim, configured to determine a valve control parameter (i valve) for controlling flow through a pressure control valve, in dependence on the variable setpoint and on a selected operating point of the hydraulic pump.
9. The control system of any preceding claim, wherein the hydraulic pump is a bidirectional pump, and wherein the control signal is configured to control the hydraulic pump in either direction of the hydraulic pump.
10. An active suspension system comprising the control system of any preceding claim.
11. The active suspension system of claim 10, comprising an independent hydraulic circuit for each corner of the vehicle, wherein the control system is configured to determine independent control signals for each of the independent hydraulic circuits to provide a Fully Active Suspension (FAS) function, or wherein the hydraulic circuit is shared between a pair of laterally separated wheels of the vehicle, such that the active suspension system is configured to provide an Active Roll Control (ARC) function.
12. A vehicle comprising the control system of any one of claims 1 to 9 or the active suspension system of claim 10 or 11.
13. A method of controlling an active suspension system of a vehicle, the active suspension system comprising a hydraulic circuit, the hydraulic circuit comprising a hydraulic pump and an accumulator, the method comprising: obtaining a variable setpoint indicative of required hydraulic pressure in the hydraulic circuit of the active suspension system; determining a flow control parameter for controlling hydraulic pressure to track the variable setpoint; and outputting the flow control parameter to control the hydraulic pump of the active suspension system, wherein the flow control parameter is proportional to a rate of change of the variable setpoint and inversely proportional to an instant value of the variable setpoint.
14. Computer software that, when executed, is arranged to perform a method according to claim 13. 29