Vehicle controller and control method

Abstract

Aspects of the present invention relate 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 unit of the vehicle. The control system determines whether a speed of the vehicle and a power mode change. Where the vehicle speed is greater than zero and the power mode changes from on to off, the control system outputs an actuator control signal including 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 the rear wheel steering system.

Description

Technical Field

[0001] The present disclosure relates to vehicle controllers and control methods, and in particular, but not exclusively, to controllers and methods for controlling a rear wheel steering system of a vehicle. Aspects of the invention relate to control systems, systems including control systems, methods, vehicles including the systems and / or control systems, computer software arranged to execute the methods, and non-transitory computer readable storage media storing instructions for executing the methods. Background Art

[0002] It is known to provide road-going vehicles with front wheel steering systems which typically include a driver-operated steering wheel connected by a pinion to a steering rack which controls the angular position of the front running wheels of the vehicle, thereby controlling the direction in which the vehicle is turned. The angular position of the front running wheels may be referred to as the 'front running wheel steering angle', which is the angle between each front running wheel and a straight ahead position in which the running wheels are aligned with the vehicle.

[0003] Recently, rear wheel steering (rear wheel steering used in combination with front wheel steering) has become popular because it can be used to provide improved low speed maneuverability and high speed vehicle stability. Rear wheel steering systems typically use a drive-by-wire system in which the steering input made by the driver via the steering wheel is converted into an electronic signal that is relayed via a control system to a motor driven actuator that controls the angular position of the rear wheels of the vehicle, thereby providing the rear wheel steering function. The angular position of the rear wheels may be referred to as the 'rear wheel steering angle', which is the angle between each rear wheel and the straight ahead position, where the wheels are aligned with the vehicle.

[0004] The rear wheel steering angle is usually less than the front wheel steering angle, and it is the combination of the front and rear wheel steering angles that determines the direction the vehicle turns. Front and rear wheel steering systems are usually configured so that the wheel steering angles are different on each side of the vehicle to avoid rubbing against faster or slower rotating wheels.

[0005] When the vehicle is moving, it is sometimes necessary to restart the vehicle's power unit. For vehicles equipped with rear-wheel steering, it is important that the rear-wheel steering system remains under proper control during the power unit restart period to avoid an undesirable steering feel and to ensure that the rear-wheel steering function is fully available once the power unit resumes operation. Summary of the invention

[0006] It is an object of the present invention to address one or more of the disadvantages 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 claimed in the appended claims.

[0008] According to one aspect of the present invention, a control system for controlling an actuator of a rear-wheel steering system of a vehicle is provided, the control system comprising one or more controllers, the control system being configured to: receive a first input signal indicating a vehicle speed, and determine the vehicle speed based on the first input signal; receive a second input signal indicating a power mode of a power unit of the vehicle, wherein the second input signal has a first state corresponding to the power mode being on and a second state corresponding to the power mode being off; determine whether the power mode has changed from on to off based on the second input signal; and output an actuator control signal to control the actuator of the rear-wheel steering system, wherein when the vehicle speed is greater than zero and the power mode is changed from on to off, the actuator control signal comprises an actuator displacement position request equal to zero.

[0009] The present invention is advantageous because control of the rear wheel steering system can be maintained even when the vehicle's power unit is powered off and / or restarted while the vehicle is moving. Proper steering feel is maintained by controlling the rear wheel steering system to move to a zero displacement position or an original displacement position when the ignition of the moving vehicle is turned off.

[0010] In an embodiment, one or more controllers collectively include: at least one electronic processor, the at least one electronic processor having an electrical input for receiving a first input signal and / or a second input signal; and at least one storage device, the at least one storage device being 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 storage device and execute the instructions on the at least one storage device in order to: determine a vehicle speed; determine a power mode; and output an actuator control signal based on the determined vehicle speed and power mode.

[0011] Optionally, the control system may be configured to: determine if the vehicle speed remains greater than zero after the power mode is changed from on to off; determine if the power mode remains off; and if the vehicle speed remains greater than zero and the power mode remains off, output an actuator control signal including an actuator displacement position request equal to zero. Thus, the control system can advantageously continue to control the displacement of the rear wheel steering system even if the power unit remains off for an extended period of time when other vehicle control systems may be off.

[0012] The control system may optionally be configured to: determine whether the vehicle speed is zero after the power mode is changed from on to off; determine whether the power mode is off; and stop outputting the actuator control signal when the vehicle speed is zero and the power mode is off. Thus, when the power unit is turned off and the speed is zero, power is saved.

[0013] The control system may be configured to: receive a third input signal indicative of a steering system input, and determine an actuator displacement position set point based 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 if the vehicle speed is greater than zero and the power mode has changed from off to on, output an actuator control signal including an actuator displacement position request equal to the actuator displacement position set point. This is advantageous because the displacement position of the rear wheel steering system can be moved to the displacement position requested by the driver as soon as the power unit is restored.

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

[0015] Alternatively, the control system may be configured to: determine the rate of change of the actuator displacement using the determined vehicle speed; and output an actuator control signal including a request to operate the actuator at the determined rate of change. As above, this is advantageous because the displacement position of the rear wheel steering system may be blended to the driver requested displacement position at an appropriate rate so that the driver does not notice the change and does not experience an undesirable steering feel. Alternatively, the rate of change of the actuator displacement may be determined using both the difference between the actuator displacement position set point and the actual actuator displacement and the vehicle speed.

[0016] According to another aspect of the invention, a system is provided, the system comprising: an actuator having a movable actuator element, wherein a displacement of the actuator element relative to a zero position determines a steering position of a rear-wheel steering system; and a control system according to any preceding claim, the control system comprising at least a first controller, wherein at least the first controller is arranged to output an actuator control signal for causing movement of the actuator element, wherein the actuator is configured to receive the actuator control signal and to move the actuator element in accordance with the actuator control signal.

[0017] According to another aspect of the present invention, a method for controlling an actuator of a rear-wheel steering system of a vehicle is provided, the method comprising: receiving a signal indicating a vehicle speed, and determining the vehicle speed based on the signal indicating the vehicle speed; receiving a second input signal indicating a power mode of a power unit of the vehicle, wherein the second input signal has a first state corresponding to the power mode being on and a second state corresponding to the power mode being off; determining whether the power mode has changed from on to off based on the second input signal; and outputting an actuator control signal to control the actuator of the rear-wheel steering system, wherein 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 is changed from on to off; determining whether the power mode remains off; and outputting an actuator control signal including an actuator displacement position request equal to zero when the vehicle speed remains greater than zero and the power mode remains off.

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

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

[0021] In an embodiment, a method may include: 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 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 including a request to operate the actuator at the determined rate of change.

[0022] Optionally, the method comprises: determining a rate of change of actuator displacement using the determined vehicle speed; and outputting an actuator control signal comprising a request to operate the actuator at the determined rate of change.

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

[0024] According to yet another further aspect of the present invention, there is provided computer software which, when executed, is arranged to perform the method described above.

[0025] According to yet another aspect of the present invention, a non-transitory computer-readable storage medium is provided, on which instructions are stored. When the instructions are executed by one or more electronic processors, the one or more electronic processors are caused to perform the method described above.

[0026] It is expressly intended that the various aspects, embodiments, examples and alternatives set forth in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular individual features thereof, may be employed independently or in any combination within the scope of the present application. That is, all embodiments and / or features of any embodiment may be combined in any manner and / or combination, unless such features are incompatible. Applicants reserve the right to change any originally filed claim or to file any new claim accordingly, including the right to amend any originally filed claim to be subordinate to any other claim and / or to incorporate any features of any other claim, even though protection was not originally claimed in this manner. 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, in which:

[0028] Figure 1 shows a schematic diagram of a vehicle according to an embodiment of the present invention;

[0029] Figure 2 A block diagram of a control system that may be adapted, for example, according to an embodiment of the present invention is shown;

[0030] Figure 3 A flowchart illustrating an example logic flow according to an embodiment of the present invention is shown;

[0031] Figure 4 shows a flowchart illustrating another example logic flow according to an embodiment of the present invention; and

[0032] Figure 5 A simplified example of a control system that may be adapted, for example, according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0033] In this article, refer to Figure 1 A vehicle 1 according to an embodiment of the present invention is described.

[0034] The vehicle 1 includes a pair of front running wheels 3 and a pair of rear running wheels 5 , each of which is supported for rotation by a substructure (not shown) of the vehicle 1 .

[0035] The direction in which the front running wheels 3 are steered is controlled by the movement of a steering wheel 7 operated by the driver, and the steering wheel 7 is connected to a steering rack 9 via a steering column 8. The steering rack 9 is connected to each of the front steering knuckles (not shown) through a tie rod 10. The rotation of the steering wheel 7 by the driver causes the linear movement of the steering rack 9, which is transmitted to the front steering knuckles through the tie rod 10, so that the front running wheel steering angle changes in response to the movement of the steering wheel 7.

[0036] The direction of the rear running wheel 5 is adjusted by the actuator 15 (see Figure 2 ). The actuator 15 is referred to below Figures 2 to 5 The rear wheel steering control system 20 described in detail is controlled. The actuator 15 includes a movable actuator element (not shown) driven by an electric motor (not shown). The actuator element is connected to the rear steering knuckle (not shown) via a mechanical linkage 13. The displacement of the actuator element relative to the original position or zero position is transmitted to the rear steering knuckle through the mechanical linkage 13 so that the rear running wheel steering angle changes in response to the movement of the actuator element. In an alternative embodiment (not shown), the rear running wheel steering angle can be controlled by a separate actuator, or the actuator 15 can include more than one actuator element, with one actuator element for each rear running wheel 5.

[0037] Reference Figure 2 , the rear-wheel steering control system 20 includes a first controller 22 and a second controller 32. The first controller 22 is configured to receive a speed input signal 23 indicating a vehicle speed. The speed input signal 23 may include a measurement signal obtained by the wheel rotation speed sensor 11, in which case the controller 22 is configured to determine the vehicle speed based on 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 preprocessed so that the speed input signal 23 includes the vehicle speed as determined by the preprocessor. In each case, the first controller 22 determines the vehicle speed based on the speed input signal 23.

[0038] The first controller 22 is also configured to receive a steering input signal 24 indicative of an angular position of the steering wheel 7. The first controller 22 is configured to determine an actuator displacement position set point based 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 set point, 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 set point.

[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 a power unit 16 of the vehicle 1. The power mode input signal 17 has a first state corresponding to the power mode of the power unit being on and a second state corresponding to the power mode of the power unit being off. The power mode input signal 17 is directly associated with the operating state of the power unit of the vehicle, so that a power mode input signal 17 equivalent to on corresponds to the power unit being on and being operated to provide power for driving the vehicle; and a power mode input signal 17 equivalent to off corresponds to the power unit being off. The first controller 22 and the second controller 32 are configured to determine whether the power mode of the power unit is on or off, or whether the power mode of the power unit is changed from on to off or from off to on, based on the power mode input signal 17.

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

[0041] The second controller 32 is also configured to receive a speed input signal 23 indicative of a vehicle speed. As described above with respect to the first controller 22, the speed input signal 23 may include a measurement signal obtained by the wheel rotation speed sensor 11, or the measurement signal obtained by the wheel rotation speed sensor 11 may be preprocessed so that the speed input signal 23 includes the vehicle speed as determined by the preprocessor. In each case, the second controller 32 determines the vehicle speed based on the speed input signal 23.

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

[0043] The actuator 15 includes a displacement sensor (not shown) configured to measure the actual displacement of the actuator element relative to an original or zero position. The displacement sensor is configured to output a signal 34 indicative of the actual actuator displacement. 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 actuator displacement.

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

[0045] The second controller 32 is configured to output an actuator control signal 35 to control the displacement of the actuator element relative to its home or zero position. The actuator control signal 35 comprises an actuator displacement position request determined by the control system 20 based on the control system inputs described above. Figure 3 A flow chart illustrating an example logic flow implemented by the control system 20 is shown.

[0046] Reference Figure 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 implements control of the actuator 15 via a control method that is not the subject of the present application.

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

[0048] If the power unit power mode is changed from on to off, the logic flow moves to step 42 where the second controller 32 outputs the actuator control signal 35 including an actuator displacement position request equal to zero. The actuator 15 is thereby instructed to return the actuator element to its original or zero position, or to maintain the actuator element at its original or zero position if the actuator element is already in the original or zero position.

[0049] The logic flow then moves to step 43 where it is determined by the first controller 22 and / or the second controller 32 whether the vehicle speed remains above zero. If the speed remains 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 power mode remains off. If the power mode remains off, the logic flow moves to step 45 where the second controller 32 outputs the actuator control signal 35 including an actuator displacement position request equal to zero so that the actuator element is maintained at its original 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 is turned off. If the power mode is not off in step 47, the control system 20 implements control of the actuator 15 via a control method that is not the subject of the present application.

[0051] Returning now to step 41 of the logic flow, if (after having determined in step 40 that the vehicle speed is greater than zero) the power unit power mode has changed from off to on, the logic flow moves to step 46 where the second controller 32 outputs the actuator control signal 35 including an actuator displacement position request equal to the actuator displacement position set point. This occurs after step 44 if it is determined in step 44 that the power unit is no longer off. This occurs after step 44. Figure 3 This is illustrated in the logic flow by the connector arrow connecting step 44 to step 41 in the event that the power unit is no longer off in step 44 .

[0052] Figure 4 Another example logic flow that may be implemented by the control system 20 is illustrated. Figure 3 Step 46 is replaced by steps 54 to 56, Figure 4 The logical flow is consistent in all respects with Figure 3 The logical flow is the same.

[0053] exist Figure 4 Starting at step 41, if (after it has been determined in step 40 that the vehicle speed is greater than zero) the power unit power mode is changed from off to on, the logic flow moves to step 54, in which the second controller 32 determines the magnitude of the difference between the actuator displacement position set point and the actual actuator displacement. The logic flow then moves to step 55, in which the second controller 32 determines the appropriate rate of change of the actuator element based on the magnitude of the difference between the actuator displacement position set point and the actual actuator displacement and / or vehicle speed. The memory 130 of the control system 20 (see Figure 5 ) can 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 including an actuator displacement position request equal to the actuator displacement position set point and a request 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 , step 54 may be omitted.

[0056] Reference Figure 5 , which illustrates an example that can be suitable for implementing the above-described Figure 3 or Figure 4 The control system 100 includes one or more controllers 110 and is configured to: receive a first input signal 123 indicating a vehicle speed and determine the vehicle speed based on the first input signal 123; receive a second input signal 117 indicating a power mode of a power unit of the vehicle, wherein the second input signal 117 has a first state corresponding to the power mode on and a second state corresponding to the power mode off; determine whether the power mode is changed from on to off based on the second input signal 117; and output an actuator control signal 135 to control an actuator 15 of a rear-wheel steering system, wherein 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 is changed from on to off.

[0057] The control system 100 is further configured to: receive a third input signal 124 indicative of a steering system input, and determine an actuator displacement position set point based on the third input signal 124; determine whether the power mode has changed from off to on; and output an actuator control signal 135 including an actuator displacement position request equal to the actuator displacement position set point if the vehicle speed is greater than zero and the power mode has changed from off to on.

[0058] The control system 100 is also configured to receive a fourth input signal 137 indicative of actual actuator displacement; determine a magnitude of a difference between an actuator displacement position set point and the actual actuator displacement; determine a rate of change of the actuator displacement using the determined magnitude of the difference between the actuator displacement position set point and the actual actuator displacement; and output an actuator control signal including a request to operate the actuator at the determined rate of change.

[0059] It should be understood that the controller 110 or each controller 110 may include a control unit or computing device having one or more electronic processors (e.g., a microprocessor, a microcontroller, an application specific integrated circuit (ASIC), etc.), and may include a single control unit or computing device, or alternatively, different functions of the controller 110 or each controller 110 may be embodied or hosted in different control units or computing devices. As used herein, the terms "controller", "control unit" or "computing device" will be understood to include a single controller, control unit or computing device, as well as multiple controllers, control units or computing devices that operate together to provide the required control functions. A set of instructions may be provided that, when executed, causes the controller 110 to implement the control techniques described herein (including some or all of the functions required by the methods described herein). The set of instructions may be embedded in the one or more electronic processors of the controller 110; or alternatively, the set of instructions may be provided as software to be executed in the controller 110. The first controller or control unit may be implemented in software, which runs on one or more processors. The one or more further controllers or control units may be implemented in software running on one or more processors, optionally the same one or more processors as the first controller or control unit.Other arrangements are also useful.

[0060] exist Figure 5 In the example illustrated in , the controller 110 or each controller 110 includes at least one electronic processor 120 having: one or more electrical inputs 122 for receiving one or more of the first input signal 123, the second input signal 117, the third input signal 124 and / or the fourth input signal 137, and one or more electrical outputs 124 for outputting one or more output signals 135. The controller or each controller 110 also includes at least one storage device 130 electrically coupled to the at least one electronic processor 120 and having instructions 140 stored therein. The at least one electronic processor 120 is configured to access the at least one storage device 130 and execute the instructions 140 thereon to: determine the vehicle speed; determine the power mode; and output the actuator control signal according to the determined vehicle speed and power mode.

[0061] The electronic processor 120 or each electronic processor 120 may include any suitable electronic processor (e.g., a microprocessor, a microcontroller, an ASIC, etc.) configured to execute electronic instructions. The electronic storage device 130 or each electronic storage device 130 may include any suitable storage device and may store various data, information, thresholds, lookup tables or other data structures and / or instructions therein or thereon. In an embodiment, the storage device 130 has information and instructions for software, firmware, programs, algorithms, scripts, applications, etc. stored therein or thereon, which may govern all or part of the methods described herein. The processor or each electronic processor 120 may access the storage device 130 and execute and / or use the instructions and information or those instructions and information to perform or execute some or all of the functions and methods described herein. At least one storage device 130 may include a computer-readable storage medium (e.g., a non-transitory or non-transitory storage medium), which may include any mechanism for storing information in a form readable by a machine or electronic processor / computing device, including but not limited to: magnetic storage media (e.g., floppy disks); optical storage media (e.g., CD-ROMs); magneto-optical storage media; read-only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or an electronic medium or other type of medium for storing such information / instructions. An example controller 110 has been described that includes at least one electronic processor 120 that is configured to execute electronic instructions stored in at least one storage device 130 that, when executed, cause the electronic processor 120 to perform the methods described above. However, it is contemplated that the present invention is not limited to being implemented by means of a programmable processing device, and at least some of the functions and / or method steps of the present invention, and in some embodiments, all of the functions and / or method steps, may be equivalently implemented by means of non-programmable hardware, such as by means of a non-programmable ASIC, Boolean logic circuits, etc. It should be understood that various changes and modifications may be made to the present invention without departing from the scope of the present application.

Claims

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 being configured to: receiving a first input signal indicative of a vehicle speed, and determining the vehicle speed based on the first input signal; receiving a second input signal indicative of a power mode of a power unit of the vehicle, wherein The second input signal has a first state corresponding to the power mode being on and a second state corresponding to the power mode being off; determining whether the power mode is changed from on to off according to the second input signal; as well as An actuator control signal is output to control the actuator of the rear wheel steering system, the actuator control signal including an actuator displacement position request equal to zero when the vehicle speed is greater than zero and the power mode is changed from on to off.

2. The control system according to claim 1, wherein: The one or more controllers collectively include: at least one electronic processor having an electrical input for receiving the first input signal and / or the second input signal; and at least one storage 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 storage device and execute the instructions on the at least one storage device to: determining a speed of the vehicle; determining the power mode; and The actuator control signal is output based on the determined vehicle speed and power mode.

3. The control system according to claim 1 or 2, wherein the control system is configured to: determining whether the vehicle speed remains greater than zero after the power mode is changed from on to off; determining whether the power mode remains off; and An actuator control signal including an actuator displacement position request equal to zero is outputted while the vehicle speed remains greater than zero and the power mode remains off.

4. A control system according to any preceding claim, configured to: 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 When the vehicle speed is zero and the power mode is off, output of the actuator control signal is stopped.

5. A control system according to any preceding claim, configured to: receiving a third input signal indicative of a steering system input, and determining an actuator displacement position set point based 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; as well as When the vehicle speed is greater than zero and the power mode is changed from off to on, an actuator control signal including an actuator displacement position request equal to the actuator displacement position set point is output.

6. The control system according to claim 5, wherein the control system is configured to: receiving a fourth input signal indicative of actual actuator displacement; determining a magnitude of a difference between the actuator displacement position set point and the actual actuator displacement; determining a rate of change of actuator displacement using a magnitude of a difference between the determined actuator displacement position set point and the actual actuator displacement; as well as The output comprises a requested actuator control signal for operating the actuator at the determined rate of change.

7. The control system according to claim 5 or 6, wherein the control system is configured to: determining a rate of change of actuator displacement using the determined vehicle speed; and The output includes a requested actuator control signal for operating the actuator at the determined rate of change.

8. A system comprising: an actuator having a movable actuator element, wherein a displacement of the actuator element relative to a zero position determines a steering position of a rear wheel steering system; and A control system according to any preceding claim, the control system comprising at least a first controller, wherein the at least first controller is arranged to output an actuator control signal for causing movement of the actuator element, wherein the actuator is configured to receive the actuator control signal and to move the actuator element in accordance with the actuator control signal.

9. A method for controlling an actuator of a rear wheel steering system of a vehicle, the method comprising: receiving a signal indicative of a vehicle speed, and determining a vehicle speed based on said signal indicative of the vehicle speed; receiving a second input signal indicative of a power mode of a power unit of the vehicle, wherein the second input signal has a first state corresponding to a power mode on and a second state corresponding to a power mode off; determining whether the power mode is changed from on to off according to the second input signal; An actuator control signal is output to control the actuator of the rear wheel steering system, the actuator control signal including an actuator displacement position request equal to zero when the vehicle speed is greater than zero and the power mode is changed from on to off.

10. The method according to claim 9, comprising: determining whether the vehicle speed remains greater than zero after the power mode is changed from on to off; determining whether the power mode remains off; as well as An actuator control signal including an actuator displacement position request equal to zero is outputted while the vehicle speed remains greater than zero and the power mode remains off.

11. The method according to claim 9 or 10, comprising: determining whether the vehicle speed is zero after the power mode is changed from on to off; determining whether the power mode is off; as well as When the vehicle speed is zero and the power mode is off, output of the actuator control signal is stopped.

12. The method according to any one of claims 9 to 11, comprising: receiving a third input signal indicative of a steering system input, and determining an actuator displacement position set point based 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; When the vehicle speed is greater than zero and the power mode is changed from off to on, an actuator control signal including an actuator displacement position request equal to the actuator displacement position set point is output.

13. The method according to claim 12, comprising: receiving a fourth input signal indicative of actual actuator displacement; determining a magnitude of a difference between the actuator displacement position set point and the actual actuator displacement; determining a rate of change of actuator displacement using a magnitude of a difference between the determined actuator displacement position set point and the actual actuator displacement; as well as The output comprises a requested actuator control signal for operating the actuator at the determined rate of change.

14. The method according to claim 12 or 13, comprising: determining a rate of change of actuator displacement using the determined vehicle speed; as well as The output comprises a requested actuator control signal for operating the actuator at the determined rate of change.

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

16. Computer software which, when executed, is configured to perform the method according to any one of claims 9 to 14.

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

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