TECHNICAL FIELD

The present disclosure relates to steering control method and apparatus. In particular, but not exclusively, the present disclosure relates to a method of controlling a power assisted steering (PAS) system; and a system for controlling a PAS system.

BACKGROUND OF THE INVENTION

It is known to provide a vehicle with an adjustable suspension, for example an adjustable air suspension. For the purpose of improvements in fuel economy and C0 ₂ reduction, it is known to alter the vehicle ride height or suspension characteristics during driving, for example to reduce vehicle ride height at highway speeds. It may also be possible to alter the vehicle ride height or suspension characteristics to assist with off-road driving. This reconfiguration may be done manually (in response to a driver selection) or automatically (selected by an electronic control unit in the vehicle). The reconfiguration of the vehicle suspension typically changes suspension kinematics. There is a consequential change in vehicle dynamics/response and this may result in a change in the feel and/or responses via the vehicle steering system. In certain cases, these changes may be perceptible to the driver. In particular, the driver may detect changes in the steering feel as a result in changes in the configuration of the vehicle suspension.

At least in certain embodiments the present invention relates to a method and apparatus for improving consistency of a power assisted steering system. SUMMARY OF THE INVENTION

Aspects of the present invention relate to a method of controlling a vehicle power assisted steering (PAS) system; a system for controlling a vehicle power assisted steering (PAS) system; a carrier medium carrying computer readable code; a computer program product; a computer readable medium; a non-transitory, computer-readable storage medium; a processor; and a vehicle as claimed in the appended claims.

According to a further aspect of the present invention there is provided a method of controlling a vehicle power assisted steering (PAS) system, the vehicle PAS system being configured to access at least one PAS variable, wherein the method comprises:

modifying one or more of said at least one PAS variable in dependence on a change in a configuration of a vehicle suspension. The steering power assistance behaviour may be modified in line with a changes in a ride height of the suspension, for example as the vehicle's speed changes. At least in certain embodiments, the steering feel and/or efforts remain consistent, independently of the selected suspension configuration. By modifying the PAS variable(s) in dependence on the configuration of the vehicle suspension, the behaviour of the steering power assistance may be adapted dynamically to match the current configuration of the vehicle suspension.

The method may be implemented in a PAS system having electronic control. The PAS system may be an electromechanical (EPAS) system, an electrohydraulic system (where the hydraulic pump is powered by an electric motor), or a conventional hydraulic PAS system that uses either an engine driven pump with electronically regulated flow control or electronic control of the steering gear valve. The method may, for example, be implemented by electronically switching between two steering parameter sets (tunes). The steering parameter sets may be stored in a memory device connected to an electronic control unit (ECU) associated with the PAS system. A first steering parameter set may relate to a first tune for a first suspension configuration which defines a ("normal") default first ride height; and a second steering parameter set may relate to a second suspension configuration which defines a second ride height. Alternatively, or in addition, the method may apply a blending algorithm between the first and second steering parameter sets, such that the changeover is more progressive in nature.

The modification of one or more of said at least one PAS variable may comprise selecting one or more PAS variable from a first PAS profile and changing the selected one or more PAS variable. The first PAS profile may be predefined. The selected one or more PAS variable may be changed by applying a modifier to the one or more PAS variable. Alternatively, the selected one or more PAS variable may be substituted with one or more predefined alternatives.

Alternatively, a first steering parameter set may be stored in a first PAS profile; and a second steering parameter set may be stored in a second PAS profile. The first steering parameter set may comprise or consist of said at least one PAS variable. The second steering parameter set may comprise or consist of said at least one PAS variable. The modification of one or more of said at least one PAS variable may comprise configuring the PAS system to access said first PAS profile rather than said second PAS profile; or to access said second PAS profile rather than said first PAS profile. The method may comprise configuring the PAS system to access the first PAS profile or the second PAS profile in dependence on the configuration of the vehicle suspension. In other words, the first and second PAS profiles may be interchangeable to implement the required change. In this arrangement the first and second PAS profiles are different from each other. The first PAS profile may be predefined; and/or the second PAS profile may be predefined.

The method may comprise transitioning between said first and second PAS profiles in one or more intermediate steps. The method may comprise progressively transitioning between said first and second PAS profiles. The method may, for example, comprise applying a blending algorithm to transition between said first and second PAS profiles.

The method may comprise detecting a change in the configuration of the vehicle suspension; and modifying one or more of said least one PAS variable in dependence on detection of said change. Detecting the change in the configuration of the vehicle suspension may, for example, comprise monitoring a pneumatic pressure in an air suspension system. The vehicle suspension may change from a first suspension configuration to a second suspension configuration. The method may comprise modifying one or more of said least one PAS variable when the vehicle suspension changes from the first suspension configuration to the second suspension configuration. The first and second suspension configurations are different from each other.

The changes in the configuration of the vehicle suspension could be implemented in response to a user input, for example in response to operation of a human machine interface (HMI). Alternatively, the changes in the configuration of the vehicle suspension may be implemented automatically or semi-automatically. For example, the first and second suspension configurations may be implemented in dependence on a vehicle speed. The first suspension configuration being implemented when the vehicle speed is less than a first speed threshold and the second suspension configuration being implemented when the vehicle speed is greater than the first speed threshold. The first speed threshold may, for example, be defined as 50kph, 60kph, 70kph or 80kph.

The first suspension configuration may correspond to a first ride height; and the second configuration may correspond to a second ride height. The first ride height may be less than or greater than the second ride height. Alternatively, or in addition, the first and second suspension configurations may correspond to other aspects of the vehicle suspension. For example, the first and second suspension configurations may correspond to stiffness and/or response settings of the vehicle suspension.

According to a further aspect of the present invention there is provided a method of controlling a vehicle power assisted steering (PAS) system, the vehicle PAS system being configured to access at least one PAS variable; wherein, in dependence on a vehicle speed, the method comprises:

modifying one or more of said at least one PAS variable; and

changing a configuration of a vehicle suspension.

The modification of the PAS variable(s) and the changes in the vehicle suspension configuration may be implemented automatically in dependence on the vehicle speed, for example based on a predefined first speed threshold. The method may comprise modifying the PAS variable(s) and changing the vehicle suspension configuration when the vehicle speed is less than or greater than the first speed threshold. The first speed threshold may, for example, be defined as 50kph, 60kph, 70kph or 80kph. The modification of the PAS variable(s) and the changes in the vehicle suspension configuration may be implemented concurrently. Alternatively, the modification of the PAS variable(s) may be implemented after the changes in the vehicle suspension configuration. The at least one PAS variable may include one or more of the following: a level of PAS assist; a level of PAS damping; and a level of steering wheel return. Other PAS variables may be useful.

The vehicle PAS system may be an electrical PAS system.

The vehicle PAS system may be a hydraulic PAS system. The vehicle PAS system may include an electric motor to power a rotary pump.

According to a further aspect of the present invention there is provided a system for controlling a power assisted steering (PAS) system, the system comprising:

an electronic control unit (ECU) that includes a processor, a non-transient computer-readable medium for storing data, and a communication input for receiving an indicator that alerts the ECU of a change in a configuration of a vehicle suspension, wherein the ECU is configured to:

access a PAS profile stored in the non-transient computer-readable medium; and modify one or more PAS variable in the PAS profile in dependence on a change in the suspension configuration. The ECU may be configured to modify said one or more PAS variable by selecting one or more PAS variable from the PAS profile and changing the selected one or more PAS variable. Changing the selected one or more PAS variable may comprise applying a modifier to the one or more PAS variable. Alternatively, the selected one or more PAS variable may be substituted with one or more predefined alternatives.

A first PAS profile and a second PAS profile may be stored in the non-transient computer- readable medium. The modification of said one or more PAS variable may comprise accessing the second PAS profile rather than the first PAS profile; or accessing the first PAS profile rather than the second PAS profile.

The first PAS profile may be predefined; and/or the second PAS profile may be predefined. The ECU may be configured to transition between said first and second PAS profiles in one or more intermediate steps. The ECU may be configured to implement a progressive transition between said first and second PAS profiles. The ECU may be configured to apply a blending algorithm to transition between said first and second PAS profiles. The ECU may be configured to detect a change in the suspension configuration of the vehicle suspension using the communication input; and to modify said one or more PAS variable in dependence on detection of said change.

The ECU may be configured to modify one or more of said at least one PAS variable when the vehicle suspension changes from a first suspension configuration to a second suspension configuration. The first and second suspension configurations are different from each other.

The changes in the configuration of the vehicle suspension could be implemented in response to a user input, for example in response to operation of a human machine interface (HMI). Alternatively, the changes in the configuration of the vehicle suspension may be implemented automatically or semi-automatically. The first and second suspension configurations may be implemented in dependence on a vehicle speed; the first suspension configuration being implemented when the vehicle speed is less than a first speed threshold and the second suspension configuration being implemented when the vehicle speed is greater than the first speed threshold. The first suspension configuration may correspond to a first ride height; and the second configuration may correspond to a second ride height.

Alternatively, or in addition, the first and second suspension configurations may correspond to other aspects of the vehicle suspension. For example, the first and second suspension configurations may correspond to stiffness and/or response settings of the vehicle suspension.

According to a further aspect of the present invention there is provided a system for controlling a power assisted steering (PAS) system, the system comprising:

an electronic control unit (ECU) that includes a processor, a non-transient computer-readable medium for storing data; wherein, in dependence on a vehicle speed, the ECU is configured to:

access a PAS profile stored in the non-transient computer-readable medium and modify one or more PAS variable in the PAS profile; and

output a suspension control signal to change a configuration of a vehicle suspension. The modification of the PAS variable(s) and the suspension control signal may be implemented automatically in dependence on the vehicle speed, for example based on a predefined first speed threshold. The ECU may be configured to modify the PAS variable(s) and to output the suspension control signal when the vehicle speed is less than or greater than the first speed threshold. The first speed threshold may, for example, be defined as 50kph, 60kph, 70kph or 80kph. The ECU may be configured to modify the PAS variable(s) and to change the vehicle suspension configuration concurrently. Alternatively, the ECU may be configured to modify of the PAS variable(s) after changing the vehicle suspension configuration.

The at least one PAS variable may include one or more of the following: a level of PAS assist; a level of PAS damping; and a level of steering wheel return. The vehicle PAS system may be an electrical PAS system.

The vehicle PAS system may be a hydraulic PAS system. The vehicle PAS system may include an electric motor to power a rotary pump. According to a further aspect of the present invention there is provided a carrier medium carrying computer readable code for controlling a vehicle to carry out the method described herein. According to a still further aspect of the present invention there is provided a computer program product executable on a processor so as to implement the method described herein.

According to a yet further aspect of the present invention there is provided a computer readable medium loaded with the computer program product described herein.

According to a further aspect of the present invention there is provided a non-transitory, computer-readable storage medium storing instructions thereon that when executed by one or more electronic processors causes the one or more electronic processors to carry out the method described herein.

According to a still further aspect of the present invention there is provided a processor arranged to implement the method described herein, or the computer program product described herein.

According to a further aspect of the present invention there is provided a vehicle comprising a system as described herein.

Any control unit or controller described herein may suitably comprise a computational device having one or more electronic processors. The system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term "controller" or "control unit" will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide any stated control functionality. To configure a controller or control unit, a suitable set of instructions may be provided which, when executed, cause said control unit or computational device to implement the control techniques specified herein. The set of instructions may suitably be embedded in said one or more electronic processors. Alternatively, the set of instructions may be provided as software saved on one or more memory associated with said controller to be executed on said computational device. The control unit or controller may be implemented in software run on one or more processors. One or more other control unit or controller may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller. Other suitable arrangements may also be used. BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 shows a schematic representation of a vehicle incorporating a electronic control unit in accordance with an embodiment of the present invention;

Figure 2 shows a schematic representation of a power assisted steering (PAS) system for use in the vehicle shown in Figure 1 ;

Figure 3 is a first graph illustrating the relationship between steering weight and steering angle at first and second ride heights; and

Figure 4 is a second graph illustrating the relationship between lateral acceleration and steering angle at first and second ride heights.

DETAILED DESCRIPTION OF AN EMBODIMENT

A vehicle 1 comprising a power assisted steering (PAS) system 2 having an electronic control unit (ECU) 3 in accordance with an embodiment of the present invention will now be described with reference to the accompanying figures.

The vehicle 1 in the present embodiment is a motor vehicle, such as a sports utility vehicle (SUV). Although the following description is provided in the context of the vehicle 1 illustrated in Figure 1 , it will be appreciated that this vehicle is merely an example and that other vehicles may certainly be used instead. For instance, in various embodiments, the method and system described herein may be used with any type of vehicle having an automatic, manual, or continuously variable transmission, including traditional vehicles, hybrid electric vehicles (HEVs), extended-range electric vehicles (EREVs), battery electrical vehicles (BEVs), passenger cars, utility vehicles, cross-over vehicles, and trucks, to cite a few possibilities.

As shown in Figure 1 , the vehicle 1 comprises a vehicle body 4, including an occupant compartment. The vehicle 1 has four (4) wheels 5-n which are mounted to the vehicle body 4 by a vehicle suspension (denoted generally by the reference numeral 6). A steering angle of the front wheels 5-1 , 5-2 is controlled via a steering wheel 7. The vehicle suspension 6 comprises four (4) suspension units 8-n each associated with a respective one of the wheels 5-n. The vehicle suspension 6 is adjustable to change the ride height H of the vehicle body 4. In the present embodiment the vehicle suspension 6 is an air suspension. The suspension units 8-n each comprise a pneumatic bag (not shown) selectively connected to a pneumatic compressor and/or reservoir via a valve block. The air pressure in the pneumatic bags is controlled to adjust the geometry of the respective suspension units 8-n. The vehicle 1 comprises a suspension control unit 9 for controlling operation of the vehicle suspension 6. In use, the suspension control unit 9 controls the valve block to control the supply/release of compressed air to/from each of the suspension units 8-n to adjust the ride height H. The vehicle suspension 6 is described herein as an air suspension, but this is not limiting on the scope of the present invention. Other adjustable suspension systems may be used, for example an electromechanical actuator may be provided to adjust the geometry of the vehicle suspension 6.

The suspension control unit 9 is configured to control the vehicle suspension 6. The vehicle suspension 6 may, for example, be controlled to reduce aerodynamic drag on the vehicle 1 . Alternatively, or in addition, the vehicle suspension 6 may be controlled to enhance vehicle stability, for example during highway driving and/or cornering. The vehicle suspension 6 may be controlled to lower the vehicle body 4 when the vehicle speed VS is greater than a predefined speed threshold S1 , and raised when the vehicle speed VS is less than the predefined speed threshold S1 . The speed threshold S1 may, for example, be defined as 80kph. The suspension control unit 9 according to the present embodiment controls the vehicle suspension 6 to implement: (a) a first suspension configuration SC1 in which the vehicle body 4 is at a first ride height H1 ; and (b) a second suspension configuration SC2 in which the vehicle body 4 is at a second ride height H2. The first ride height H1 is a "normal" or default ride height in the present embodiment. As shown in Figure 2, the first ride height H1 is greater than the second ride height H2. Thus, the vehicle suspension 6 is lowered to change from said first ride height H1 to said second height H2. The suspension control unit 9 is configured to activate the first suspension configuration SC1 when the vehicle speed VS is less than the speed threshold S1 ; and to activate the second suspension configuration SC2 when the vehicle speed VS is greater than the speed threshold S1 . The ride height H of the vehicle body 4 is thereby reduced at higher speeds to reduce aerodynamic drag. The changes between said first and second suspension configurations SC1 , SC2 may be performed automatically without any direct input from the driver of the vehicle 1 . The suspension control unit 9 publishes a suspension status signal SS1 to a communication bus 10 to indicate the current status of the vehicle suspension 6. The communication bus 10 may, for example, comprise a controller area network (CAN) bus, a system management bus (SMBus), a Flexray bus, a proprietary communication link, or through some other arrangement known in the art. The suspension status signal SS1 indicates whether the vehicle suspension 6 is in said first suspension configuration SC1 or said second suspension configuration SC2. As illustrated in Figure 2, the ECU 3 may comprise any suitable dedicated electronic processor 1 1 or microprocessor as well as any variety of other electronic processing devices, memory devices, input/output (I/O) devices, and/or other known components, and perform various control and/or communication related functions. In one embodiment, the ECU 3 includes a non-transient computer-readable medium, such as an electronic memory device 12, that may store various sensor readings (e.g., such as those generated by vehicle sensors), look-up tables or other data structures, algorithms (e.g., the algorithms embodied in the method described below), etc. The memory device 12 may also store pertinent characteristics and background information pertaining to the vehicle 1 and vehicle subsystems. The electronic processor 1 1 can be implemented as an electronic processing device (e.g., a microprocessor, a microcontroller, an application specific integrated circuit (ASIC), etc.) that executes instructions for software, firmware, programs, algorithms, scripts, applications, etc. that are stored in memory device 12 and may govern the methods described herein. As described above, ECU 3 may be electronically connected to other vehicle devices, modules, subsystems, and components (e.g., sensors) via suitable vehicle communications and can interact with them when required. These are, of course, only some of the possible arrangements, functions, and capabilities of ECU 3, as other embodiments could also be used. Depending on the particular embodiment, the ECU 3 may be a standalone vehicle electronic module, may be incorporated or included within another vehicle electronic module, or may be otherwise arranged and configured in a manner known in the art. Accordingly, the ECU 3 is not limited to any one particular embodiment or arrangement. The ECU 3 can be electronically and/or communicatively connected to other vehicle subsystems, such as the suspension control unit 9. The PAS system 2 is operative to reduce the effort to operate the steering wheel 7 of the vehicle 1 relative to operating the steering wheel 7 without assistance. The PAS system 2 of the vehicle 1 can be implemented using a hydraulic system, an electrical system, or some hybrid of hydraulic and electrical systems (sometimes called electro-hydraulic) as is known in the art. An electrical implementation of the PAS system 2 is shown in Figure 2. The electrical implementation includes a rack and pinion gear 13, a steering angle sensor 14, and a torque sensor 15. The steering angle sensor 14 may be mounted to the steering column, for example packaged behind the steering wheel 7. The rack and pinion gear 13 is coupled to an electric motor 16 that provides torque to the rack of the rack and pinion gear 13 at the direction of the ECU 3. A driver can rotate the steering wheel 7 and the steering angle sensor 14 can detect the steering wheel position while the torque sensor 15 can detect the amount of torque the driver applies to the steering wheel 7. The steering angle sensor 14 and the torque sensor 15 can provide data reflecting the motion of the steering wheel 7 to the ECU 3, which then uses that data to determine how much force or assistance the electric motor 16 should provide to the rack and pinion gear 13. The ECU 3 can also be electrically connected to a speed sensor 17 that detects the vehicle speed VS and communicates data reflecting the vehicle speed VS to the ECU 3.

The PAS system 2 is calibrated for the first ride height H1 . Changes in the geometry of the vehicle suspension 6 affect the relationship between the vehicle steering and the dynamic behaviour of the vehicle 1 . The relationship between a steering weight (Nm) at the steering wheel 7 and a steering angle (a) is illustrated in a first graph 100 in Figure 3. A target steering weight when the vehicle 1 is at said default first ride height H1 is shown as a first continuous curve 105 in the first graph 100. Changing the ride height affects the relationship between the steering weight (Nm) and the steering angle (a). When the vehicle suspension 6 changes from said first suspension configuration SC1 to said second suspension configuration SC2 (lowering the vehicle body 4 from said first ride height H1 to said second ride height H2), the steering weight (Nm) may increase more quickly with steering angle (a). A first dashed curve 1 10 in the first graph 100 represents the relationship between the steering weight (Nm) and the steering angle (a) when the vehicle suspension 6 is in said second suspension configuration SC2 and the vehicle body 4 is at said second ride height H2 (which is lower than the first ride height H1 ). The first dashed curve 1 10 is offset to the right of the first continuous curve 105 indicating that the steering weight (Nm) increases more slowly with steering angle (a). This offset is at least partially caused by the lowering of the centre of gravity of the vehicle 1 when the vehicle suspension 6 is in said second suspension configuration SC2, resulting in a quicker dynamic response to steering inputs. It will be understood that in certain suspension configurations the change in ride height may have the opposite outcome on the steering weight (Nm). In particular, when the vehicle suspension 6 changes from said first suspension configuration SC1 to said second suspension configuration SC2 (lowering the vehicle body 4 from said first ride height H1 to said second ride height H2), the steering weight (Nm) may increase more quickly with steering angle (a). In this arrangement, the first dashed curve 1 10 in the first graph 10Owould offset to the left of the first continuous curve 105.

The relationship between the lateral acceleration (degrees/second) of the vehicle 1 and the steering angle (a) is illustrated in a second graph 200 in Figure 4. The lateral acceleration of the vehicle 1 at the default ride height is illustrated by a second continuous curve 205 in the second graph 200. The lateral acceleration (degrees/second) of the vehicle 1 when the vehicle suspension 6 is in said second suspension configuration SC2 (such that the vehicle body 4 is at said second ride height H2) is illustrated by a second dashed curve 210 in the second graph 200. The second dashed curve 210 is steeper than the second continuous curve 205 indicating that the lateral acceleration (degrees/second) responds more quickly to steering inputs. Thus, the relationship between the steering weight (Nm) and the steering angle (a) is affected by the configuration of the vehicle suspension 6. The change in the steering weight and lateral acceleration may be noticed by a driver of the vehicle 1 as a change in the "steering feel". Since the ride height may be changed automatically, for example in relation to the vehicle speed VS, the change in the steering feel may prove disconcerting. The ECU 3 according to the present embodiment is configured to reduce or minimise any change in the steering feel as a result of the change in the configuration of the vehicle suspension 6. The ECU 3 controls operation of the PAS system 2 in conjunction with changes in the configuration of the vehicle suspension 6. The ECU 3 is configured to control the PAS system 2 selectively to access a first PAS profile P1 or a second PAS profile P2. The first and second PAS profiles P1 , P2 each comprise a plurality of pre-defined PAS variables for controlling operation of the PAS system 2. The PAS variables may control one or more of the following: (a) a level or amount of assistance provided by the PAS system 2; (b) a level or amount of damping provided by the PAS system 2; and (c) a level or amount of assistance provided by the PAS system 2 to return the steering wheel 7 to its centre position. The first PAS profile P1 comprises a first steering parameter set S1 of said PAS variables for access when the vehicle suspension 6 is in said first suspension configuration SC1 . The second PAS profile P2 comprises a second steering parameter set S2 of said PAS variables for access when the vehicle suspension 6 is in said second suspension configuration SC2. The first PAS profile P1 may be referred to as a default PAS profile; and the second PAS profile P2 may be referred to as a lowered PAS profile. The PAS variables in the first steering parameter set S1 are different from those in the second steering parameter set S2 such that operation of the PAS system 2 changes depending on which of the first and second PAS profiles P1 , P2 is accessed. In the present embodiment, the PAS variables in the second steering parameter set S2 define a lower level of assistance by the PAS system 2. Thus, when the PAS system 2 accesses the second PAS profile P2, the assistance provided for steering inputs is reduced. As described herein, the ECU 3 controls the PAS system 2 to access either the first PAS profile P1 or the second PAS profiles P2 to control the steering behaviour and/or characteristics. It will be appreciated that the PAS variables associated with damping and/or steering wheel centring may also differ in the first and second PAS profiles P1 , P2. The elements shown in Figure 1 can be electrically and/or communicatively connected to the ECU 3 via the communication bus 10. The ECU 3 includes a communication input for receiving the suspension status signal SS1 that alerts the ECU 3 of a change between the first and second suspension configurations SC1 , SC2. In an alternative embodiment, the ECU 3 may be configured to instruct the suspension control unit 9 to change between said first and second configurations SC1 , SC2. For example, the ECU 3 can receive data from one or more vehicle sensors and based on that data initiate the change in configuration of the vehicle suspension 6. In accordance with an aspect of the present invention, the selection of the first and second PAS profiles P1 , P2 is dependent on the configuration of the vehicle suspension 6. The ECU 3 is in communication with the vehicle bus 10 and reads the suspension status signal SS1 to monitor the status of the vehicle suspension 6. The ECU 3 detects when the configuration of the vehicle suspension 6 changes, either from the first suspension configuration SC1 to the second suspension configuration SC2; or from the second suspension configuration SC2 to the first suspension configuration SC1 . The ECU 3 configures the PAS system 2 in dependence on the suspension status signal SS1 . In particular, The ECU 3 is configured to access the first PAS profile P1 when the vehicle suspension 6 is in said first suspension configuration SC1 ; and to access the second PAS profile P2 when the vehicle suspension 6 is in said second suspension configuration SC2.

The configuration of the PAS system 2 is modified to accommodate changes in the dynamic behaviour of the vehicle 1 resulting from changes in the vehicle suspension 6. The PAS variables stored in the first and second PAS profiles P1 , P2 define different assistance levels provided by the PAS system 2. As outlined above, the second PAS profile P2 comprises PAS variables which define a lower level of assistance than the PAS variables in the first PAS profile P1 . When the vehicle suspension 6 is in said second suspension configuration SC2, the ECU2 accesses the second PAS profile P2. The PAS variables in the second PAS profile P2 define a lower level of assistance. Thus, when the vehicle body 4 is at said second ride height H2, the assistance provided by the PAS system 2 is reduced. Due to the changing dynamic parameters of the vehicle 1 when the vehicle suspension 6 is in said second suspension configuration SC2, the total effort needed to change the steering angle remains substantially constant. Thus, the steering feel is at least substantially unchanged. Alternatively, or in addition, the PAS variables associated with the amount of damping, and/ or the amount of assistance for returning the steering wheel to centre may differ in said first and second PAS profiles P1 , P2. For example, the amount of damping and/or assistance for returning the steering wheel to centre may be reduced in said second PAS profile P2. Thus, the first and second PAS profiles P1 , P2 may define different amounts of damping and/or the amount of assistance for returning the steering wheel 7 back to its centre position. The first PAS profile P1 could include not only a greater amount of assistance but it could also specify more damping and/or centring assistance. Other combinations of variables are possible.

At least in certain embodiments, the ECU 3 in accordance with the present embodiment is operative to change the steering characteristics of the vehicle 1 in conjunction with changes in the configuration of the vehicle suspension 6. It will be appreciated that the PAS variables defined in said first and second PAS profiles P1 , P2 may be tuned for a particular vehicle and/or suspension configuration. At least in certain embodiments, the first and second PAS profiles P1 , P2 may be configured to reduce or minimise changes in steering feel as a result of changes in the vehicle suspension 6. The vehicle 1 may require a substantially uniform steering effort irrespective of whether the vehicle suspension 6 is in said first suspension configuration SC1 or said second suspension configuration SC2.

The PAS system 2 is described herein as implementing the first and second PAS profiles P1 , P2 as discrete profiles. In a variant, the PAS system 2 may be configured to implement a phased or progressive transition between the PAS variables defined in the first and second PAS profiles P1 , P2. By implementing a progressive transition, the changes in the operation of the PAS system 2 may be coordinated with the changes in the ride height H of the vehicle body 4, for example as the vehicle suspension 6 changes from said first suspension configuration to said second suspension configuration. The transition between said first and second PAS profiles P1 , P2 could be predefined or could be controlled by a suitable algorithm. For example, a blending algorithm may progressively change the PAS variables in said first PAS profile P1 to those in the second PAS profile P2 and vice versa. Alternatively, the ECU 3 may be configured to modify the PAS variables in proportion to the ride height H of the vehicle body 4. In a further alternative, rather than implement separate first and second PAS profiles P1 , P2, the ECU 3 may be configured to apply a modifier to one or more of the PAS variables stored in the first steering parameter set S1 to modify the control functions implemented by the PAS system 2. The modifier could, for example, be applied in conjunction with the vehicle suspension 6 changes from said first suspension configuration to said second suspension configuration. It will be appreciated that the systems and methods described herein can be used with other types of power assisted-steering systems and also that other implementations of electrical power assisted-steering systems can be used other than the one shown in FIG. 2. The PAS system 2 can also be implemented as a hydraulic system. Hydraulic PAS systems commonly include a rotary pump that supplies hydraulic fluid under pressure via a valve to a steering rack. These elements can be implemented in various ways. For example, the rotary pump can be powered by a powertrain. But in another implementation the rotary pump can be powered by a separate electric motor. The pressure applied to the steering rack can be regulated in various ways. In one implementation, the ECU 3 can regulate the assistance the hydraulic PAS system 2 provides by controlling the valve supplying hydraulic fluid from the rotary pump to the steering rack. In another implementation, the ECU 3 can regulate the speed of the separate electric motor powering the rotary pump. As one skilled in the art will appreciate, the PAS system 2 can be implemented in a variety of different configurations.

The suspension control unit 9 has been described herein as configuring the vehicle suspension 6 in first and second configurations SC1 , SC2. It will be understood that the suspension control unit 9 may be operable to configure the vehicle suspension 6 in one or more additional configuration, for example to implement a third suspension configuration SC3. The ride height H of the vehicle body 4 may be greater than or less than the first ride height H1 when the vehicle suspension 6 is in said third suspension configuration SC3.

The present invention has been described with particular reference to the scenario in which the suspension control unit 9 controls the vehicle suspension 6 to reduce aerodynamic drag on the vehicle 1 . The system and method described herein are not limited to this mode of operation. The suspension control unit 9 may be operable to control the vehicle suspension 6 to change the ride height H to increase ground clearance, for example when the vehicle 1 is driven off-road and/or through water. Alternatively, or in addition, the vehicle suspension 6 may be controlled to change dynamic behaviour of the vehicle. The ECU 3 may be configured to control the PAS system 2 to access an alternative PAS profile for one or more of these scenarios.

The present invention has been described with reference to the PAS system 2 for providing power-assisted steering for the front wheels 5-1 , 5-2 of the vehicle 1 . It will be appreciated that the rear wheels 5-3, 5-4 may also provide steering inputs, for example in a four-wheel steering arrangement. Aspects of the present invention may also be applied to control a PAS system associated with the rear wheels 5-3, 5-4. The PAS system associated with the rear wheels 5-3, 5-4 may be controlled in dependence on changes in the configuration of the vehicle suspension (6). The PAS system may, for example, modify the control strategy applied to one or more rear-wheel steering actuator in dependence on the vehicle suspension configuration. In a vehicle having four-wheel steering, the changes applied to the PAS system for the rear wheels 5-3, 5-4 may be the same as or different from those applied to the PAS system for the front wheels 5-1 , 5-2.

It will be understood that the embodiment(s) described above are given by way of example only and are not intended to limit the invention, the scope of which is defined in the appended claims. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims. As used in this specification and claims, the terms "for example," "e.g.," "for instance," "such as," and "like," and the verbs "comprising," "having," "including," and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that that the listing is not to be considered as excluding other, additional components or items. Further, the terms "electrically connected" or "electrically coupled" and the variations thereof are intended to encompass both wireless electrical connections and electrical connections made via one or more wires, cables, or conductors (wired connections). Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.