Vehicle control device and control method

Abstract

Controller and Control Method for Vehicles. One aspect of the invention relates to a control system for controlling an actuator of a rear wheel steering system of a vehicle. The control system is configured to receive first and second input signals indicative of a vehicle speed and a power mode of a power plant of the vehicle. The control system determines the vehicle speed and determines whether the power mode has changed. If the vehicle speed is greater than zero and the power mode changes from on to off, the control system outputs an actuator control signal with an actuator displacement position request equal to zero. Aspects of the invention also relate to methods, systems, vehicles, and computer software and hardware for controlling a rear wheel steering system.

Description

[Technical field]

[0001] The present disclosure relates to vehicle control devices and methods, and in particular, but not exclusively, to a control device and method for controlling a rear wheel steering system of a vehicle. Aspects of the invention relate to a control system, a system constituting the control system, a method, a vehicle constituting the control system and / or a system, computer software arranged for performing the method, and a non-transitory computer readable storage medium storing instructions for performing the method. [Background technology]

[0002] Road vehicles are known to be equipped with front wheel steering systems, which typically involve a driver-operated steering wheel connected through a pinion gear to a steering rack that controls the angular position of the vehicle's front wheels, sometimes referred to as the "front wheel steering angle," which is the angle between each front wheel and a straight ahead position in which the vehicle is aligned.

[0003] Recently, rear-wheel steering (used in conjunction with front-wheel steering) has become popular to improve low-speed maneuverability and vehicle stability at high speeds. Rear-wheel steering systems typically use a drive-by-wire system, where steering inputs by the driver through the steering wheel are converted into electronic signals and transmitted through a control system to motorized actuators that control the angular position of the vehicle's rear wheels, thus providing the rear-wheel steering function. The angular position of the rear wheels is sometimes referred to as the "rear-wheel steering angle", which is the angle between the straight-ahead position in which each rear wheel is aligned with the vehicle.

[0004] The steering angle of the rear wheels is typically less than the steering angle of the front wheels, and the steering direction of the vehicle is determined by the combination of the steering angles of the front and rear wheels. The front and rear wheel steering systems are typically configured so that the wheel steering angles on each side of the vehicle are not identical to avoid scrubbing at the faster or slower turning wheels.

[0005] It may become necessary to restart the vehicle's powerplant while the vehicle is in motion. For vehicles equipped with rear wheel steering, it is important that the rear wheel steering system remains under proper control during the powerplant restart cycle. This avoids unexpected steering sensations and ensures that the rear wheel steering function is fully available after powerplant operation is resumed. Summary of the Invention

[0006] SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to address one or more of the shortcomings associated with the prior art.

[0007] Aspects and embodiments of the present invention provide a control system, a system, a method, a vehicle, computer software, and a non-transitory, computer readable storage medium as set forth in the accompanying claims.

[0008] According to one aspect of the invention, there is provided a control system for controlling an actuator of a rear wheel steering system of a vehicle, the control system including one or more controllers and configured to receive a first input signal indicative of a vehicle speed and determine the vehicle speed in dependence on the first input signal. The control system also receives a second input signal indicative of a power mode of a power plant of the vehicle. The second input signal has a first state corresponding to a power mode ON and a second state corresponding to a power mode OFF, and determines whether the power mode changes from ON to OFF in dependence on the second input signal and outputs an actuator control signal for controlling the actuator of the rear wheel steering system. The actuator control signal includes an actuator displacement position request equal to zero when the vehicle speed is greater than zero and the power mode changes from ON to OFF.

[0009] The present invention has the advantage that control of the rear wheel steering system is maintained even when the vehicle's power plant is turned off and / or restarted while the vehicle is moving. By controlling the rear wheel steering system to move to a zero or home displacement position when the vehicle ignition is turned off while the vehicle is moving, proper steering feel is maintained.

[0010] In an embodiment, the one or more controllers include at least one electronic processor having an electrical input for receiving the first and / or second input signals; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored thereon. The at least one electronic processor is configured to access the at least one memory device and execute the instructions stored in the memory device to determine a vehicle speed, determine a power mode, and output actuator control signals in response to the determined vehicle speed and power mode.

[0011] Optionally, the control system may be configured to determine whether vehicle speed remains greater than zero after the powered mode is changed from ON to OFF; determine whether the powered mode remains OFF; and if vehicle speed remains greater than zero and the powered mode remains OFF, output an actuator control signal with an actuator displacement position request equal to zero. Thus, the control system can continue to control the displacement of the rear wheel steering system even if the powered unit remains OFF for an extended period of time during which other vehicle control systems may shut down.

[0012] The control system may optionally be configured to: determine if vehicle speed is zero after the power mode is changed from on to off; determine if the power mode is off; and stop outputting the actuator control signals when the vehicle speed is zero and the power mode is off, thereby conserving power when the power unit is off and the vehicle speed is zero.

[0013] The control system may be configured to receive a third input signal indicative of the steering system input, determine the actuator displacement position setpoint in dependence on the third input signal, determine whether the vehicle speed is greater than zero, determine whether the power mode has changed from OFF to ON, and output an actuator control signal equal to the actuator displacement position setpoint as an actuator displacement position request if the vehicle speed is greater than zero and the power mode has changed from OFF to ON. This is advantageous because the displacement position of the rear wheel steering system can be moved to the driver requested displacement position as soon as the power unit is turned on again.

[0014] In an embodiment, the control system may be configured to: receive a fourth input signal indicative of an actual actuator displacement; determine a magnitude of a difference between an actuator displacement position setpoint and the actual actuator displacement; use the determined magnitude of the difference between the actuator displacement position setpoint and the actual actuator displacement to determine a rate of change of the actuator displacement; and output an actuator control signal including a request to operate the actuator at the determined rate of change. This has the advantage that the displacement position of the rear wheel steering system is blended at a rate appropriate to the driver requested displacement position so that the driver does not notice the change and does not experience an unexpected steering feel.

[0015] Optionally, the control system may be configured to use the determined vehicle speed to determine a rate of change of the actuator displacement; and output an actuator control signal including a request to operate the actuator at the determined rate of change. As above, this has the advantage that the displacement position of the rear wheel steering system can be blended at an appropriate rate to the driver requested displacement position, so that the driver does not notice the change and experience an unexpected steering feel. Optionally, both the difference between the actuator displacement position setpoint and the actual actuator displacement, and the vehicle speed may be used to determine the rate of change of the actuator displacement.

[0016] According to another aspect of the invention, there is provided a system including an actuator having a movable actuator element, where a displacement of the actuator element from a zero position determines a steering position of the rear wheel steering system. A control system according to any preceding claim includes at least a first controller, where the at least first controller is arranged to output an actuator control signal for causing movement of the actuator element. The actuator receives the actuator control signal and moves the actuator element in dependence on the actuator control signal.

[0017] Further, according to one aspect of the present invention, there is provided a method for controlling an actuator of a rear wheel steering system of a vehicle, the method comprising the steps of: receiving a signal indicative of a vehicle speed and determining the vehicle speed in dependence on the signal indicative of the vehicle speed; receiving a second input signal indicative of a power mode of a power unit of the vehicle, the second input signal having a first state corresponding to a power mode ON and a second state corresponding to a power mode OFF; determining whether the power mode changes from ON to OFF in dependence on the second input signal; and outputting an actuator control signal for controlling an actuator of the rear wheel steering system, When the vehicle speed is greater than zero and the power mode changes from ON to OFF, the actuator control signal includes an actuator displacement position request equal to zero.

[0018] Optionally, the method includes determining whether the vehicle speed remains greater than zero after the power mode changes from ON to OFF; determining whether the power mode remains OFF; and if the vehicle speed remains greater than zero and the power mode remains OFF, outputting an actuator control signal with an actuator displacement position request equal to zero.

[0019] The method may optionally include determining whether the vehicle speed is zero after the power mode is changed from on to off; determining whether the power mode is off; and stopping output of the actuator control signals when the vehicle speed is zero and the power mode is off.

[0020] The method includes receiving a third input signal indicative of a steering system input, determining an actuator displacement position set point value depending on the third input signal; determining whether the vehicle speed is greater than zero; determining whether the power mode has changed from off to on; and outputting an actuator control signal equal to the actuator displacement position set point value as an actuator displacement position request if the vehicle speed is greater than zero and the power mode has changed from off to on.

[0021] In an embodiment, the method includes receiving a fourth input signal indicative of an actual actuator displacement; determining a magnitude of a difference between an actuator displacement position setpoint and the actual actuator displacement; determining a magnitude of the difference between the actuator displacement position setpoint and the actual actuator displacement; determining a rate of change of the actuator displacement using the determined magnitude of the difference between the actuator displacement position setpoint and the actual actuator displacement; and outputting an actuator control signal requesting actuation of the actuator at the determined rate of change.

[0022] Optionally, the method includes determining a rate of change of actuator displacement using the determined vehicle speed, and outputting an actuator control signal requesting actuation of the actuator at the determined rate of change.

[0023] According to yet another aspect, there is provided a vehicle comprising a control system according to the invention or a system as described above.

[0024] According to yet another aspect, there is provided computer software configured, when executed, to perform the above-described method.

[0025] According to yet another aspect, a non-transitory computer-readable storage medium is provided having stored thereon instructions that, when executed by one or more electronic processors, cause the one or more electronic processors to perform the above-described method.

[0026] Within the scope of this application, the various aspects, embodiments, examples, and alternatives described in the preceding paragraphs, claims, and / or the following description and drawings, in particular their individual features, are expressly intended to be taken independently or in any combination. That is, any embodiment and / or feature may be combined in any manner and / or combination, unless such features are incompatible. The applicant reserves the right to modify the claims originally filed or to submit new claims accordingly, including the right to amend the claims originally filed to rely on and / or incorporate features of other claims, even if they were not originally so claimed. [Brief description of the drawings]

[0027] One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings.

[0028] [Figure 1] FIG. 1 shows a schematic diagram of a vehicle according to one embodiment of the present invention.

[0029] [Diagram 2] FIG. 2 shows a block diagram of a control system that may be adapted in accordance with one embodiment of the present invention.

[0030] [Diagram 3] FIG. 3 shows a flow diagram illustrating an example of a logic flow according to one embodiment of the present invention.

[0031] [Figure 4] FIG. 4 depicts a flow diagram illustrating another example logic flow according to an embodiment of the present invention.

[0032] [Diagram 5] FIG. 5 shows a simplified example of a control system that may be adapted in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] A vehicle 1 according to an embodiment of the present invention is herein described with reference to accompanying FIG.

[0034] The vehicle 1 includes a pair of front road wheels 3 and a pair of rear road wheels 5, each of which is rotatably supported by a sub-structure (not shown) of the vehicle 1.

[0035] The steering direction of the front road wheels 3 is controlled by movement of the driver-operated steering wheel 7, which is connected to a steering rack 9 via a steering column 8. The steering rack 9 is connected to each front steering knuckle (not shown) by tie rods 10. Rotation of the steering wheel 7 by the driver causes linear movement of the steering rack 9, which is transmitted to the front steering knuckles by the tie rods 10, changing the steering angle of the front road wheels in response to the rotation of the steering wheel 7.

[0036] The steering direction of the rear road wheels 5 is adjusted by an actuator 15 (see FIG. 2). The actuator 15 is controlled by a rear wheel steering control system 20, which will be described in detail below with reference to FIGS. 2 to 5. The actuator 15 has a movable actuator element (not shown) driven by an electric motor (not shown). The actuator element is connected to a rear steering knuckle (not shown) via a mechanical linkage 13. When the actuator element is displaced from a home or zero position, the displacement is transmitted to the rear steering knuckle via the mechanical linkage 13, and the steering angle of the rear road wheels changes according to the movement of the actuator element. In an alternative embodiment (not shown), the steering angle of the rear road wheels is controlled by a separate actuator, or the actuator 15 may include multiple actuator elements corresponding to each rear road wheel 5.

[0037] With reference to Fig. 2, the rear wheel steering control system 20 comprises a first controller 22 and a second controller 32. The first controller 22 is configured to receive a speed input signal 23 indicative of the vehicle speed. The speed input signal 23 may consist of a measurement signal obtained by the wheel rotation speed sensor 11, in which case the controller 22 is configured to determine the vehicle speed from the measurement signal received from the wheel rotation speed sensor 11. In an alternative embodiment, the measurement signal from the wheel rotation speed sensor 11 may be pre-processed such that the speed input signal 23 consists of the vehicle speed determined by a pre-processing device. In either case, the first controller 22 determines the vehicle speed depending on the speed input signal 23.

[0038] The first controller 22 is configured to receive a steering input signal 24 indicative of the angular position of the steering wheel 7. The first controller 22 is configured to determine an actuator displacement position setpoint in dependence on the steering input signal 24 and the speed input signal 23. The first controller 22 is configured to output a signal 25 indicative of the actuator displacement position setpoint, and the second controller 32 is configured to receive the output signal 25 from the first controller 22 as an input signal 27 indicative of the actuator displacement position setpoint.

[0039] The first controller 22 and the second controller 32 are configured to receive a power mode input signal 17 indicating a power mode of the power unit 16 of the vehicle 1. The power mode input signal 17 has a first state corresponding to a power unit power mode ON and a second state corresponding to a power unit power mode OFF. The power mode input signal 17 is directly linked to the operating state of the power unit of the vehicle, such that when the power mode input signal 17 is equal to ON, it corresponds to an operating state in which the power unit is ON and supplies power to drive the vehicle, and when the power mode input signal 17 is equal to OFF, it corresponds to a state in which the power unit is OFF. The 122nd and 232nd controllers are configured to determine, depending on the power mode input signal 17, whether the power mode of the power unit is ON or OFF, or has changed from ON to OFF or from OFF to ON.

[0040] It will be appreciated that the power mode input signal 17 may be provided to the steering control system 20 from the power unit itself, a cockpit mounted driver controlled switch, a vehicle control unit (not shown), or any other suitable vehicle system. Similarly, the speed input signal 23 and the steering input signal 24 may be provided to the steering control system 20 from a vehicle control unit (not shown) or other suitable vehicle system.

[0041] The second controller 32 is configured to receive a speed input signal 23 indicative of the vehicle speed. As described above with respect to the first controller 22, the speed input signal 23 may consist of a measurement signal obtained by the wheel rotation speed sensor 11, or the measurement signal obtained by the wheel rotation speed sensor 11 may have been pre-processed such that the speed input signal 23 constitutes the vehicle speed determined by a pre-processing device. In either case, the second controller 32 depends on the speed input signal 23 to determine the vehicle speed.

[0042] In an alternative embodiment (not shown), the first controller 22 may be configured to output vehicle speed as an output signal indicative of vehicle speed, and the control system 20 may be configured such that the output signal indicative of vehicle speed from the first controller 22 is received by the second controller 32 as an input indicative of vehicle speed.

[0043] The actuator 15 includes a displacement sensor (not shown) configured to measure the actual displacement of the actuator element from a home or zero position. The displacement sensor is configured to output a signal 34 indicative of the actual displacement of the actuator. The second controller 32 is configured to receive the output signal 34 from the displacement sensor as an input signal 37 indicative of the actual displacement of the actuator.

[0044] The second controller 32 is configured to determine the magnitude of the difference between the actuator displacement position setpoint and the actual actuator displacement in response to an input signal 27 indicative of the actuator displacement position setpoint and an input signal 37 indicative of the actual actuator displacement.

[0045] The second controller 32 is configured to output an actuator control signal 35 for controlling the displacement of the actuator element from a home or zero position. The actuator control signal 35 includes an actuator displacement position demand determined by the control system 20 depending on the control system inputs described above. Figure 3 is a flow diagram illustrating an example of a logic flow executed by the control system 20.

[0046] 3, in a first step 40, the first controller 22 determines whether the vehicle speed is greater than zero. If the vehicle speed is not greater than zero, the control system 20 performs control of the actuator 15 according to a control method that is not the subject of this application.

[0047] If the vehicle speed is greater than zero, the logic flow proceeds to step 41 where the first controller 22 determines whether and in what sense the power unit power mode has changed to a different state. If the power unit power mode has not changed, the control system 20 implements control of the actuator 15 via a control methodology that is not the subject of this application.

[0048] If the power mode of the power plant is changed from on to off, the logic flow moves to step 42 where the second controller 32 outputs an actuator control signal 35 consisting of an actuator displacement position request equal to zero, which instructs the actuator 15 to return the actuator element to the home or zero position, or to maintain the actuator element in the home or zero position if the actuator element is already in that position.

[0049] The logic flow then proceeds to step 43 where it is determined by the first controller 22 and / or the second controller 32 whether the vehicle speed is above zero. If the vehicle speed is above zero, the logic flow proceeds to step 44 where it is determined by the first controller 22 and / or the second controller 32 whether the power unit's power mode remains OFF. If the power mode remains OFF, the logic flow moves to step 45 where the second controller 32 outputs an actuator control signal 35 consisting of an actuator displacement position request equal to zero such that the actuator element is maintained in a home or zero position.

[0050] If the vehicle speed in step 43 is not greater than zero, the logic flow moves to step 47 where it is determined whether the power unit power mode remains OFF. If the power mode remains OFF in step 47, the logic flow moves to step 48 where the control system 20 stops outputting control signals to the actuator 15 and the actuator 15 shuts down. If the power mode is not OFF in step 47, the control system 20 performs control of the actuator 15 according to a control method that is not the subject of this application.

[0051] Returning to step 41 of the logic flow, if the power mode of the power unit is changed from OFF to ON (after the vehicle speed is determined to be greater than zero in step 40), the logic flow proceeds to step 46 where the second controller 32 outputs an actuator control signal 35 comprising an actuator displacement position demand equal to the actuator displacement position setpoint. This situation occurs if, in step 44, it is determined that the power unit is no longer OFF. This is illustrated in the logic flow of FIG. 3 by the connector arrow connecting step 44 to step 41 when, in step 44, the power unit is no longer OFF.

[0052] Figure 4 illustrates another example logic flow that may be executed by control system 20. The logic flow of Figure 4 is in all respects the same as the logic flow of Figure 3, except that step 46 of Figure 3 has been replaced by steps 54 through 56.

[0053] Beginning at step 41 in Figure 4, when the power mode of the power unit is changed from off to on (after vehicle speed is determined to be greater than zero in step 40), the logic flow moves to step 54 where the second controller 32 determines the difference in magnitude between the actuator displacement position setpoint and the actual actuator displacement. The logic flow then moves to step 55 where the second controller 32 determines an appropriate rate of change of the actuator element depending on the magnitude of the difference between the actuator displacement position setpoint and the actual actuator displacement and / or the vehicle speed. A calibration table stored in memory 130 (see Figure 5) of the control system 20 may be used to determine the rate of change of the actuator element.

[0054] Once the rate of change of the actuator element has been determined in step 55, the logic flow proceeds to step 56 where the second controller 32 outputs an actuator control signal 35 consisting of an actuator displacement position demand equal to the actuator displacement position setpoint and a demand to operate the actuator at the determined rate of change.

[0055] If only vehicle speed is used to determine the rate of change of the actuator element in step 55, then step 54 may be omitted.

[0056] Referring to Fig. 5, a simplified example of a control system 100 that may be adapted to implement the method of Fig. 3 or Fig. 4 described above is shown. The control system 100 has one or more controllers 110, receives a first input signal 123 indicative of a vehicle speed, determines the vehicle speed in dependence on the first input signal 123, and receives a second input signal 117 indicative of a power mode of the power plant of the vehicle. The second input signal 117 has a first state corresponding to a power mode ON and a second state corresponding to a power mode OFF. Then, in dependence on the second input signal 117, determines whether the power mode changes from ON to OFF and outputs an actuator control signal 135 for controlling the actuator 15 of the rear wheel steering system. The actuator control signal 135 includes an actuator displacement position request equal to zero when the vehicle speed is greater than zero and the power mode changes from ON to OFF.

[0057] The control system 100 receives a third input signal 124 indicative of a steering system input, determines an actuator displacement position setpoint in dependence on the third input signal 124, determines whether the power mode is to change from OFF to ON, and outputs an actuator control signal 135 including an actuator displacement position request equal to the actuator displacement position setpoint if the vehicle speed is greater than zero and the power mode is to change from OFF to ON.

[0058] The control system 100 receives a fourth input signal 137 indicative of the actual displacement of the actuator, determines a magnitude of a difference between the actuator displacement position setpoint and the actual displacement of the actuator, uses the determined magnitude of the difference between the actuator displacement position setpoint and the actual actuator displacement to determine a rate of change of the actuator displacement, and outputs an actuator control signal including a request to operate the actuator at the determined rate of change.

[0059] Alternatively, each controller 110 may be comprised of a control unit or processing unit having one or more electronic processors (e.g., microprocessors, microcontrollers, application specific integrated circuits (ASICs), etc.), may be comprised of a single control unit or processing unit, or different functions of each controller 110 may be embodied in different control units or processing units, or different functions of each controller 110 may be hosted in different control units or processing units. As used herein, the terms "controller", "control unit", or "processing unit" are understood to be inclusive of a single controller, control unit, or processing unit, as well as multiple controllers, control units, or processing units operating to provide the necessary control functions. A set of instructions may be provided that, when executed, directs the controller 110 to perform the control techniques described herein, including some or all of the functions required for the methods described herein. The set of instructions may be embedded in the one or more electronic processors of the controller 110, or may be provided as software executing on the controller 110. The first controller or control unit may be implemented as software executing on one or more processors. The one or more other controllers or control units may be implemented as software running on one or more processors, optionally the same processor or processors as the first controller or control unit. Other configurations are also useful.

[0060] 5, each controller 110 has one or more electrical inputs 122 for receiving one or more of a first input signal 123, a second input signal 117, a third input signal 124 and / or a fourth input signal 137, and one or more electrical outputs 124 for outputting one or more output signals 135. The or each controller 110 further includes at least one memory device 130 electrically coupled to the at least one electronic processor 120 and having instructions 140 stored thereon. The at least one electronic processor 120 is configured to access the at least one memory device 130 and execute the instructions 140 thereon to determine a vehicle speed, determine a power mode, and output actuator control signals depending on the determined vehicle speed and power mode.

[0061] The electronic processor 120 may be comprised of any suitable electronic processor (e.g., microprocessor, microcontroller, ASIC, etc.) configured to execute electronic instructions. The electronic memory device 130 may be comprised of any suitable memory device and may store therein or thereon various data, information, thresholds, look-up tables or other data structures, and / or instructions. In one embodiment, the memory device 130 stores information and instructions, such as software, firmware, programs, algorithms, scripts, applications, etc., that may govern all or a portion of the methodologies described herein. The processor, or each electronic processor 120, may access the memory device 130 and execute and / or use the instructions and information therein to perform or implement some or all of the functions and methodologies described herein. At least one memory device 130 may include a computer-readable storage medium (e.g., a non-transitory or non-transitory storage medium) and any mechanism for storing information in a form readable by a machine or electronic processor / computing device. This includes, but is not limited to, magnetic storage media (such as floppy disks), optical storage media (such as CD-ROMs), magneto-optical storage media, read-only memory (ROM), random access memory (RAM), erasable programmable memory (such as EPROM or EEPROM), flash memory, or electrical or other types of media for storing such information or instructions. The exemplary controller 110 includes at least one electronic processor 120 configured to execute electronic instructions stored in at least one memory device 130 that, when executed, configures the electronic processor(s) 120 to perform the methods described above. However, the present invention is not limited to being implemented by programmable processing devices, and at least in part, and in some embodiments, all of the functions and / or method steps of the present invention may be implemented by non-programmable hardware, such as non-programmable ASICs, Boolean logic circuits, etc.It will be understood that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

1. 1. A control system for controlling an actuator of a rear wheel steering system of a vehicle, the control system comprising one or more controllers, the control system comprising: receiving a first input signal indicative of a vehicle speed and determining the vehicle speed dependent on the first input signal; receiving a second input signal indicative of a power mode of the vehicle power plant, the second input signal having a first state corresponding to a power mode ON and a second state corresponding to a power mode OFF; determining whether the power mode changes from the power mode ON to the power mode OFF in response to the second input signal; outputting an actuator control signal for controlling an actuator of the rear wheel steering system, the actuator control signal including an actuator displacement position request equal to zero when both vehicle speeds are greater than zero and the power mode changes from the power mode ON to the power mode OFF.

2. the one or more controllers: at least one electronic processor having an electrical input for receiving the first input signal and / or the second input signal; at least one memory device electrically coupled to the at least one electronic processor, the memory device having instructions stored thereon; The at least one electronic processor accesses the at least one memory device and executes the instructions, determining a speed of the vehicle; determining the power mode; The control system of claim 1 configured to output the actuator control signals in response to the determined vehicle speed and power mode.

3. determining whether the vehicle speed remains greater than zero after the power mode is changed from the power mode ON to the power mode OFF; determining whether the power mode remains in the power mode OFF state; 3. The control system of claim 1 or 2, configured to output an actuator control signal where the actuator displacement position request is equal to zero if the vehicle speed remains greater than zero and the power mode remains in the power mode OFF.

4. determining whether the vehicle speed is zero after the power mode is changed from the power mode ON to the power mode OFF; Determining whether the power mode is the power mode OFF; A control system according to any one of claims 1 to 3, configured to stop outputting the actuator control signals when the vehicle speed is zero and the power mode is the power mode OFF.

5. receiving a third input signal indicative of a steering system input and determining an actuator displacement position set point dependent on said third input signal; determining whether the vehicle speed is greater than zero; determining whether the power mode changes from the power mode OFF to the power mode ON; A control system as claimed in any one of claims 1 to 4, wherein when the vehicle speed is greater than zero and the power mode changes from the power mode OFF to the power mode ON, outputting an actuator control signal including an actuator displacement position request equal to the actuator displacement position setpoint.

6. receiving a fourth input signal indicative of an actual actuator displacement; determining a magnitude of a difference between the actuator displacement position setpoint and the actual actuator displacement; determining a rate of change of actuator displacement using a magnitude of the difference between the actuator displacement position setpoint and the actual actuator displacement; The control system of claim 5 , which outputs an actuator control signal comprising a request to operate the actuator at the determined rate of change.

7. determining a rate of change of actuator displacement using the determined vehicle velocity; A control system as claimed in claim 5 or 6, which outputs an actuator control signal comprising a request to operate the actuator at the determined rate of change.

8. an actuator having a moveable actuator element; a displacement of the actuator element from a zero position determines a steering position of the rear wheel steering system; A control system according to any one of claims 1 to 7, comprising at least a first controller, the at least first controller is configured to output an actuator control signal to cause movement of the actuator element; The actuator is configured to receive the actuator control signal and to move the actuator element in dependence on the actuator control signal.

9. 1. A method for controlling an actuator of a rear wheel steering system of a vehicle, comprising: receiving a signal indicative of a vehicle speed and determining the vehicle speed in dependence on the signal indicative of the vehicle speed; receiving a second input signal indicative of a power mode of the vehicle power plant, the second input signal having a first state corresponding to a power mode ON and a second state corresponding to a power mode OFF; determining whether the power mode changes from the power mode ON to the power mode OFF in dependence on the second input signal; 1. A method for controlling a vehicle with a rear wheel steering system, the method comprising: outputting an actuator control signal to control the actuator of a rear wheel steering system, the actuator control signal including an actuator displacement position demand equal to zero when the vehicle speed is greater than zero and the power mode changes from the power mode ON to the power mode OFF.

10. determining whether vehicle speed remains greater than zero after the power mode is changed from the power mode ON to the power mode OFF; Determining whether the power mode remains in the power mode OFF state:

10. The method of claim 9, further comprising outputting an actuator control signal where the actuator displacement position request is equal to zero if the vehicle speed remains greater than zero and the power mode remains in the power mode OFF.

11. determining whether the vehicle speed is zero after the power mode is changed from the power mode ON to the power mode OFF; Determining whether the power mode is the power mode OFF; 11. The method of claim 9 or 10, further comprising ceasing output of the actuator control signals when the vehicle speed is zero and the power mode is the power mode OFF.

12. receiving a third input signal indicative of a steering system input and determining an actuator displacement position set point dependent on said third input signal; determining whether the vehicle speed is greater than zero; determining whether the power mode has changed from the power mode OFF to the power mode ON; 12. The method according to claim 9, further comprising: outputting an actuator control signal equal to the actuator displacement position setpoint as the actuator displacement position request when the vehicle speed is greater than zero and the power mode changes from the power mode OFF to the power mode ON.

13. receiving a fourth input signal indicative of an actual actuator displacement; determining a magnitude of a difference between the actuator displacement position setpoint and the actual actuator displacement; using the determined magnitude of the difference between the actuator displacement position setpoint and the actual actuator displacement to determine a rate of change of actuator displacement; The method of claim 12 , further comprising outputting an actuator control signal comprising a request to operate the actuator at the determined rate of change.

14. determining a rate of change of actuator displacement using the determined vehicle velocity; 14. A method according to claim 12 or 13, comprising outputting an actuator control signal comprising a request to operate the actuator at the determined rate of change.

15. A vehicle including a control system according to any one of claims 1 to 7 or a system according to claim 8.

16. Computer software arranged, when executed, to perform the method according to any of claims 9 to 14.

17. A non-transitory, computer-readable storage medium having stored thereon instructions that, when executed by one or more electronic processors, cause the one or more electronic processors to perform a method according to any of claims 9 to 14.

Images