Control system and method for vehicle steering

Abstract

A control system for a vehicle is described. The control system includes one or more controllers, the control system configured to: receive a speed related signal from the wheel speed sensor, the speed related signal depending on a rate at which teeth of the gear move past the wheel speed sensor; and allowing a rear wheel of the vehicle to steer according to the speed-related signal. In this manner, the rear wheels may be allowed to steer from a very low speed at which vehicle or wheel speed signals are typically unavailable. By using tooth counts, such low speed or at least an indication that the vehicle is moving may be estimated.

Description

Technical Field

[0001] The present disclosure relates to a control system and method for vehicle steering.Aspects of the invention relate to a control system, a method of controlling vehicle steering, a computer program and a vehicle. Background Art

[0002] It is known to provide a vehicle with rear wheel steering in addition to the usual front wheel steering. This can provide improved maneuverability. When the vehicle is stationary, it is not desirable to turn (steer) the rear wheels, as rear wheel steering systems may not be rated for continuous use in this state.

[0003] It is an object of the present invention to address one or more of the disadvantages associated with the prior art. Summary of the invention

[0004] Aspects and embodiments of the invention provide a control system, a method of controlling vehicle steering, a computer program and a vehicle as claimed in the appended claims.

[0005] In one aspect, a control system for a vehicle is provided, the control system comprising one or more controllers, the control system being configured to:

[0006] receiving a speed-dependent signal from a wheel speed sensor, the speed-dependent signal being dependent on a rate at which teeth of a gear move past the wheel speed sensor; and

[0007] Based on the speed-related signal, the vehicle's rear wheels are allowed to steer.

[0008] In this way, rear wheel steering can be allowed from very low speeds, where vehicle or wheel speed signals are not normally available. By using tooth counts, such low speeds, or at least an indication that the vehicle is moving, can be estimated.

[0009] The one or more controllers may collectively include:

[0010] at least one electronic processor having an electrical input for receiving the speed-related signal; and

[0011] at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein;

[0012] And wherein the at least one electronic processor is configured to access the at least one memory device and execute instructions on the at least one memory device to allow rear wheel steering of the vehicle based on the speed related signal.

[0013] The speed-dependent signal may be a time-dependent waveform that generates a corresponding characteristic each time a tooth of a gear moves past the wheel speed sensor. The time-dependent waveform may be, for example, a sine wave, a sawtooth wave, or a square wave.

[0014] The controller may be configured to allow rear wheel steering based on a plurality of consecutive features within the speed-related signal occurring within a predetermined time interval. Viewed differently, the controller may be configured to allow rear wheel steering based on a second feature within the speed-related signal occurring within a predetermined time interval relative to a first feature within the speed-related signal.

[0015] The corresponding features may be peaks or valleys of a repeating waveform.

[0016] The control system may be configured to estimate the speed of the wheel or vehicle based on the speed-related signal and allow rear wheel steering if the estimated speed is greater than a threshold value. The estimate calculated in this manner may be different from a speed calculation used for a different purpose (e.g., by an anti-lock braking system (ABS) of the vehicle).

[0017] The estimation of speed may be performed using features of less than ten speed-dependent signals, preferably features of less than five speed-dependent signals, and even more preferably features of only two speed-dependent signals. In this way, a speed estimate (and therefore a determination whether to allow rear-wheel steering) may be obtained very early and at very low speeds.

[0018] The controller may be configured to generate a vehicle or wheel speed signal based on the speed related signal, and wherein, at least below a predetermined speed, the decision to allow rear wheel steering of the vehicle is made based on the speed related signal rather than the speed signal.

[0019] The controller may be configured to receive speed-related signals from a plurality of sensors, each sensor being associated with a different wheel of the vehicle, and wherein the controller enables rear wheel steering in dependence on the speed-related signals generated by each of the plurality of sensors. Preferably, the controller enables rear wheel steering only if the speed-related signals for all of the plurality of sensors indicate that the corresponding wheel is in motion.

[0020] The controller may be configured to allow rear wheel steering based on the speed-related signal only in a subset of the vehicle's driving modes. In particular, in some vehicle modes, rear wheel steering may be allowed from very low speeds, in some modes, low speed rear steering is allowed from slightly higher speeds, and in some modes, low speed rear steering is not allowed at all.

[0021] According to another aspect, there is provided a vehicle comprising a rear wheel steering system, one or more wheel speed sensors associated with at least the rear wheels of the vehicle and a control system according to any preceding claim.

[0022] The vehicle may include a front wheel steering system, wherein the control system is configured to enable steering via the front wheel steering system mode while disabling steering via the rear wheel steering system based on the speed related signal.

[0023] According to another aspect, there is provided a control method for steering a vehicle, the method comprising:

[0024] receiving a speed-dependent signal from a wheel speed sensor, the speed-dependent signal being dependent on a rate at which teeth of a gear move past the wheel speed sensor; and

[0025] Based on the speed-related signal, the vehicle's rear wheels are allowed to steer.

[0026] In another aspect, there is provided computer software which, when executed, is arranged to perform a method according to above.

[0027] 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 their individual features 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

[0028] 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:

[0029] Figure 1 A schematic representation of a vehicle having an anti-lock braking system (ABS), front and rear steering systems, and a controller is shown;

[0030] Figure 2 A wheel speed sensor for use with the present technology is shown;

[0031] Figure 3 A rear wheel steering control system and method are schematically shown; and

[0032] Figure 4 A schematic flow chart of the control method is shown. DETAILED DESCRIPTION

[0033] This article refers to the attached Figure 1A vehicle 1 according to an embodiment of the invention is described. The vehicle 1 comprises respective wheel speed sensors 14a to 14d, each associated with one of the wheels (not shown) of the vehicle 1. The wheel speed sensors 14a to 14d each output a speed-related signal to a control system 10, and in particular to an electronic stability program (ESP) 12 of the control system 10, which includes an anti-lock braking system (ABS) function and other functions related to stability control of the vehicle. The control system 10 further comprises a rear-wheel steering controller 13. In the present case, there are respective wheel speed sensors associated with all four wheels of the vehicle. The wheel speed sensors 14a to 14d may be mounted at or near the wheels (e.g., in a bearing unit of the wheels), or on an axle or drive shaft that provides torque to the wheels. The vehicle 1 further comprises a front wheel steering actuator 16 and a rear wheel steering actuator 18, which actuate the steering mechanism to affect the steering of the front and rear wheels, respectively. The rear wheel steering actuator 18 is driven to actuate, dependent upon the rear wheels of the vehicle 1 being in motion (not stationary) as determined using sensor data from wheel speed sensors 14b, 14d associated with the rear wheels of the vehicle 1. The front wheel steering actuator 16 is driven to move independently of the wheel speed, and in particular even when the vehicle is stationary and the wheels are not rotating.

[0034] Several different forms of wheel speed sensors are available and can be used in the present method. These wheel speed sensors typically have two main parts: a wheel or ring that rotates with the wheel (or with the axle or drive shaft that drives the wheel); and a fixed sensor mounted near the wheel or ring that generates a signal when the wheel or ring moves past the sensor. The wheel or ring can be a ferromagnetic gear or an alternating magnetic pole ring. For illustration purposes, Figure 2 An example wheel speed sensor 14 using a fixed sensor 142 and a gear 144 is shown. It can be seen that the periphery of the gear 144 includes teeth 144a and gaps 144b, which are alternating around the periphery of the gear 144. The fixed sensor 142 is arranged relative to the gear 144 so that the alternating teeth 144a and gaps 144b pass through the magnetic field generated by the fixed sensor 142 when the gear 144 rotates. The fixed sensor 142 may include a coil wound around a magnetic core and a permanent magnet. When the gear 144 rotates and the teeth and gaps alternately pass through the magnetic field, this causes an AC voltage to be induced in the coil, and the frequency and amplitude of the AC voltage are related to the wheel speed. Therefore, the output of the sensor is an AC sinusoidal signal that changes frequency when the wheel speed changes.

[0035] In the alternative case of a magnetic pole ring (not shown), the fixed sensor does not include a magnet, but rather the wheel itself includes a series of magnets arranged with alternating magnetic poles at the periphery of the ring. The alternating magnetic poles around the circumference of the ring are similar to the alternating teeth and gaps of a gear. As the magnet ring rotates, the magnetic field generated by the magnetic poles interacts with the fixed sensor and induces a current in the coil of the fixed sensor, the frequency and amplitude of which are related to the wheel speed. The output of the sensor is an AC square wave (approximately) signal that changes frequency as the wheel speed changes.

[0036] In some cases, the output of the sensor may also indicate the direction of rotation - for example because the shape of the waveform feature is asymmetric. This can be achieved, for example, by positioning the fixed sensor at an angle relative to the radius of the wheel, such as Figure 2 shown.

[0037] In the following description, the term "gear" will be used for the sake of brevity and clarity. However, it should be understood that the present technology is equally applicable to alternating magnetic pole rings as discussed above, or to any wheel speed sensor that outputs a speed-related signal.

[0038] ESP 12 uses these time-varying (e.g., AC) signals to calculate various parameters including wheel speed, tooth count (or pole count in the case of magnetic rings), and (optional) wheel rotation direction. These parameters are generated (individually) for each wheel of the vehicle. At very low speeds (wheels rotate slowly), the calculation of wheel speed is inaccurate. At least in some cases, EPS functions such as ABS do not calculate and / or output wheel speed at all at very low speeds. Usually this is not a problem, because the main purpose of wheel speed is for ABS braking, which is only relevant at relatively high speeds.

[0039] The present technology is concerned with allowing rear wheel steering only when the (rear) wheels of the vehicle are in motion (turning / rotating). This is because the rear wheel steering system (actuator) may not be optimized to allow steering when the rear wheels are completely stationary, contrary to the front wheel steering system, which requires steering to be allowed even when the vehicle (and in particular its front wheels) is stationary. Implementing rear wheel steering on a stationary vehicle may result in rear tire scraping and excessive load on the rear wheel steering actuator. It also avoids unnecessary battery load when rear wheel steering is not needed.

[0040] Due to the fact that wheel speed is calculated and / or output by ESP 12 only at (usual) 0.7kph or higher speed, it is not possible to easily allow or reject rear wheel steering based on wheel speed values ​​calculated by ESP 12 at very low speeds. However, these low speeds are suitable for or at least may be suitable for allowing rear wheel steering. In some implementations, the present technology does not require accurate wheel speeds, but only requires a relatively rough indication that the wheel is moving (rotating). In such cases, it has been recognized that other wheel motion related signals can be used to infer wheel motion, and thus form the basis for the decision to allow or reject rear wheel steering. In this case, roughly means that the actual wheel speed does not need to be accurately known, but the indication should be reliable, that is to say it accurately indicates whether the wheel is moving or not. In other examples, the actual speed may be more important, particularly in the implementation where the steering rate depends on the vehicle or wheel speed. In these implementations, a relatively low steering rate can be allowed at a relatively low speed, and a relatively high steering rate can be allowed at a relatively high speed. Typically, the wheel speed calculated by the ESP 12 (at least when below a certain speed threshold, such as 0.7kph, and possibly always) is not used explicitly to determine whether to perform rear-wheel steering, but rather an alternative measurement indicative of wheel movement but still obtained (directly or indirectly) from a wheel speed sensor is used to determine whether to perform rear-wheel steering.

[0041] In one example, a tooth count is used. The tooth count as an integer is generated (by the ESP) by detecting individual waveform peaks (and / or valleys, or other repeating features, such as rising or falling edges) in the signal generated by the wheel speed sensor and incrementing a counter each time such a peak and / or valley occurs. In other words, the tooth count is incremented each time a tooth and / or gap of a gear passes a fixed sensor. The number may be reset (or wrapped around to zero) periodically. The ESP uses the tooth count as part of the wheel speed calculation, for example, by measuring the increase in the tooth count relative to time. The wheel speed (expressed in terms of the linear ground speed of the wheel) can be easily calculated based on the total number of teeth on the gear, the number of teeth counted in a predetermined interval, the length of the predetermined interval, and the diameter of the wheel. For wheel speed with respect to angular velocity (radians per second), the diameter of the wheel is not required. In order to ensure accurate measurement of wheel speed, a relatively large number of tooth counts per unit time is required. As indicated above, this means that speed values ​​calculated at very low wheel speeds are considered unreliable - because there are very few increments of tooth counts within a given time frame, and therefore the speed value is not generated and / or output. However, the ESP not only uses the tooth count itself to generate a speed value, but is also able to output the tooth count directly (in this case to the controller 13). The present technique exploits this to infer wheel motion based on the incrementing tooth count and / or based on a rough speed estimate generated outside (and downstream) of the ESP using a small number (and preferably only two) of tooth count increments.

[0042] The present technology can use this tooth count signal directly (independent of its use to calculate wheel speed) to allow or deny rear wheel steering.

[0043] In its simplest case, rear wheel steering can be permitted based on detection of any increase in the tooth count signal. For example, the controller may permit rear wheel steering if the tooth count increases at least once in a predetermined time interval (e.g., in the first half second).

[0044] Alternatively, the controller may be configured to allow rear wheel steering based on the tooth count incrementing a predetermined number of times (e.g., two or three times) within a predetermined time interval (e.g., within the first half second). Equivalently, in this case, rear wheel steering is allowed based on a predetermined number of consecutive features appearing in the speed-related signal within a predetermined time interval. This can be determined by determining that the tooth count increments (increases) by at least a certain (predetermined) amount within a predetermined time period. Using only two consecutive features is preferred because it allows determinations to be made at lower speeds and the actual speed is relatively unimportant for this purpose. In one implementation, the tooth count signal is generated by the ABS and output from the ABS. However, in an alternative implementation, the controller may operate directly on the speed-related signal by detecting peaks or other features, rather than using the tooth count as an intermediary.

[0045] Where only two features are used, it will be appreciated that the controller may be configured to allow rear wheel steering based on the tooth count being incremented a second time within a predetermined time interval relative to the first increment of the tooth count. Equivalently, in this case, rear wheel steering is allowed based on the second feature in the speed-related signal occurring within a predetermined time interval relative to the first feature in the speed-related signal. This may be determined by starting a timer when the tooth count is incremented once, and allowing rear wheel steering if the tooth count is incremented again within a predetermined time interval.

[0046] Although absolute wheel speed is not required to determine whether to allow rear wheel steering, preferably, the control system can be configured to estimate the speed of the wheel or vehicle based on the speed-related signal (using tooth counts) and allow rear wheel steering if the estimated speed is greater than a threshold value, which can be set to be very low (e.g., 0.1 km / h). However, unlike the complete calculation conventionally performed by the ESP system 12 (for example), the wheel speed estimation is performed using a relatively small number of features of the speed-related signal (i.e., a small number of increments of tooth counts), such as less than ten features, preferably less than five features of the speed-related signal, and more preferably only two features of the speed-related signal. This results in a relatively inaccurate speed estimate, but it is generated very early from standstill (only two teeth need to pass the fixed sensor, corresponding to a very low proportion of a complete rotation of the vehicle wheel), and can be generated for very low speeds.

[0047] Meanwhile, as mentioned above, for conventional purposes, the ESP 12 is configured to generate a vehicle or wheel speed signal based on the speed-related signals of the wheel speed sensors 14a to 14d. However, at least below a predetermined speed (the predetermined speed may be the speed at which the ESP 12 begins to generate and / or output speed values), a decision to allow the rear wheels of the vehicle 1 to be steered is made based on the count signal (or an equivalent raw signal indicating wheel movement) without using the calculated speed of the vehicle or wheel output by the ESP.

[0048] The ESP 12 outputs wheel speed, tooth count and wheel rotation direction for each of the wheels of the vehicle 1. Typically, the present technology uses only these values ​​for each of the rear wheels of the vehicle. In order to allow rear wheel steering, it should be determined that all wheels of the vehicle are in motion. Therefore, if any of the rear wheels is stationary, rear wheel steering is not allowed, which will cause excessive tire wear due to scratching and excessive peak loads on the actuators that perform the steering.

[0049] It is also possible to infer that a wheel is in motion based on a wheel direction signal indicating forward or reverse rotation rather than indicating a stationary state. Thus, wheel direction as an output from ESPABS can be used instead of tooth count. However, the wheel direction signal does not provide any indication of actual rotational speed, and therefore in some cases it is possible that a determination based on wheel direction alone may not be appropriate.

[0050] Preferably, the tooth count and wheel direction are used together, wherein the wheel direction is used to confirm the determination based on the tooth count. In other words, the controller can be configured to allow rear wheel steering only if the tooth count (or the derived speed estimate) satisfies the condition for each of the rear wheels and only if the wheel direction indicated for each of the rear wheels indicates wheel motion.

[0051] In some implementations, the controller is configured to allow rear wheel steering based on speed related signals only in a subset of the vehicle's driving modes. For example, rear wheel steering may not be allowed at all in a "comfort" mode on the road, while it may be allowed in an off-road mode, such as when driving on mud or sand or in a rock crawling mode. In these modes, rear wheel steering is allowed under the conditions of the wheel movement requirements of the application of the present technology. In principle, other implementations can provide driving modes in which rear wheel steering is provided and the wheel movement requirements are not enforced.

[0052] It will be appreciated that the vehicle also includes a front wheel steering system. The front wheel steering system does not have the same limitations as the rear wheel steering system and is specifically rated to operate when the front wheels are stationary. Therefore, the control system is configured to allow steering via the front wheel steering system mode based on the speed related signal while not allowing steering via the rear wheel steering system. It will be appreciated that separate controllers may be provided for the front wheel steering and rear wheel steering.

[0053] Reference Figure 3 , provides a schematic block diagram illustrating vehicle components and signal flows involved in the present technology.

[0054] Wheel speed sensors 14b, 14d are shown and output corresponding AC signals to ESP 12 for each of the left and right rear wheels. ESP 12 processes the received AC signals and generates tooth count TCL, wheel speed WSL and wheel direction WDL for the left rear wheel, and generates tooth count TCR, wheel speed WSR and wheel direction WDR for the right rear wheel. These are provided to the rear-wheel steering controller 13. A driving mode selector 19 configured to select a driving mode for the vehicle 1 is provided. Different driving modes of the vehicle can have different characteristics, such as suspension stiffness, ABS use, acceleration or braking curves, etc. The selection of the driving mode can be made manually by the driver, or automatically based on vehicle sensor data. The selected driving mode is provided to the rear-wheel steering controller 13. A steering module 20 is also provided, which generates a steering request based on a manual driving input (via a steering wheel) or an automatic driving input. The steering request is provided to the rear-wheel steering controller 13. The rear-wheel steering controller 13 is configured to determine whether the rear-wheel steering is available according to the selected driving mode, determine whether the rear-wheel steering is available according to the tooth count signal TCL regarding the left rear wheel and the tooth count signal TCR regarding the right rear wheel and the wheel direction signal WDL regarding the left rear wheel and the wheel direction signal WDR regarding the right rear wheel, and if it is determined that the rear-wheel steering is available, the rear-wheel steering controller issues a steering request to the steering actuator 18 to adjust the orientation of the rear wheels based on the steering request from the steering module 20.

[0055] Typically, vehicle controller systems are modular in both structure and function. It should be understood that the controller or each controller within the control system of the present application may include a control unit or computing device having one or more electronic processors (e.g., microprocessors, microcontrollers, application specific integrated circuits (ASICs), etc.), and may include a single control unit or computing device, or alternatively, the different functions of the controller or each controller in the control system 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; and 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, enables the controller 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; or alternatively, the set of instructions may be provided as software to be executed in the controller. 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.

[0056] Each of the controllers may include at least one electronic processor having one or more electrical inputs for receiving one or more input signals (from one or more of the other controllers), and one or more electrical outputs for outputting one or more output signals (to one or more of the other controllers). The electronic processor or each electronic processor may include any suitable electronic processor (e.g., a microprocessor, a microcontroller, an ASIC, etc.) configured to execute electronic instructions. The electronic memory device or each electronic memory device may include any suitable memory device, and various data, information, thresholds, lookup tables or other data structures and / or instructions may be stored therein or thereon. In an embodiment, the memory device has information and instructions for software, firmware, programs, algorithms, scripts, applications, etc. stored therein or thereon, which may manage all or part of the methods described herein. The processor or each electronic processor may access the memory device 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.

[0057] At least one memory device may include a computer-readable storage medium (e.g., a non-transitory or non-volatile storage medium) that 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 or other type of medium for storing such information / instructions.

[0058] The controller or each controller may include at least one electronic processor, the at least one electronic processor being configured to execute electronic instructions stored in at least one memory device, the electronic instructions causing (one or more) electronic processors to perform the method as described above when executed. A similar structure may be provided for each controller. However, it should be understood that embodiments of the present invention may be implemented in any suitable form of hardware, software, or a combination of hardware and software. For example, it is contemplated that the present invention is not limited to being implemented by means of a programmable processing device, and at least some of the functions and / or method steps of the present invention, and all of the functions and / or method steps in some embodiments may be equivalently implemented by means of non-programmable hardware, such as by means of non-programmable ASICs, Boolean logic circuits, and the like.

[0059] Reference Figure 4, a schematic flow chart illustrating one implementation of the method is provided. At step S1, a speed-related signal is generated at each of the wheel speed sensors 14a to 14d, and the speed-related signal is provided to the ESP 12. At step S2, the ESP 12 generates a tooth count, wheel direction and wheel speed for each (rear wheel), and provides these to the rear-wheel steering controller 13. At step S3, the driving mode selector provides an indication of the current driving mode of the vehicle to the rear-wheel steering controller. At step S4, the rear-wheel steering controller determines whether rear-wheel steering is allowed based on the current driving mode. In some implementations, the rear-wheel steering controller also determines whether rear-wheel steering is allowed from very low speeds or from a standard minimum speed based on the current driving mode. In the case where the current driving mode is determined to be a mode that does not allow rear-wheel steering, then at step S5, rear-wheel steering is not allowed (rejected), and processing returns to step S1. In the case where the current driving mode is determined to be a mode that allows rear-wheel steering, then at step S6, wheel speed estimates for each wheel are obtained based on tooth counts. The wheel speed estimates for each wheel are then compared to a speed threshold at step S7. Optionally, the speed threshold may depend on the driving mode (see step S4 above). If the wheel speed estimates for one or both of the wheels do not exceed the speed threshold, then at step S5, rear wheel steering is rejected. If the wheel speed estimates for both rear wheels exceed the speed threshold, then at step S8, it is determined whether the wheel direction parameters for each rear wheel indicate movement (i.e., indicate forward or reverse rotation). If not, rear wheel steering is rejected at step S5. If the wheel direction parameters for both rear wheels indicate movement, processing proceeds to step S9, in which rear wheel steering of the vehicle is allowed. Processing then returns to step S1. In this way, rear wheel steering is allowed in situations where actuation is unlikely to cause scratching or actuator load problems (because the wheels are in motion), and rear wheel steering is rejected in situations where actuation may be problematic (because the wheels are not in motion).

[0060] 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. For example, all of the features disclosed in this specification (including any attached claims, abstracts and drawings) and / or all of the steps in any method or process disclosed in this specification may be combined in any combination, except that at least some of such features and / or steps are mutually exclusive combinations.

[0061] Each feature disclosed in this specification (including any accompanying claims, abstracts and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Therefore, each feature disclosed is only an example of a general series of equivalent or similar features, unless expressly stated otherwise.

[0062] The invention is not limited to the details of any foregoing embodiments. The invention extends to any novel one or any novel combination of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one or any novel combination of the steps of any method or process so disclosed. The claims should not be construed as covering only the foregoing embodiments, but also any embodiments falling within the scope of the claims.

Claims

1. A control system for a vehicle, the control system comprising one or more controllers, the control system being configured to: receiving a speed-dependent signal from a wheel speed sensor, the speed-dependent signal being dependent on a rate at which teeth of a gear move past the wheel speed sensor; and Rear wheel steering of the vehicle is enabled in dependence on the speed related signal.

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 speed-related signal; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein; And wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions on the at least one memory device to allow the rear wheels of the vehicle to steer based on the speed-related signal.

3. A control system according to claim 1 or claim 2, wherein: The speed-dependent signal is a time-dependent waveform that generates a corresponding characteristic each time a tooth of the gear moves past the wheel speed sensor.

4. The control system according to claim 3, wherein: The controller is configured to enable steering of the rear wheels based on a plurality of consecutive features in the speed-related signal occurring within a predetermined time interval.

5. The control system according to claim 3, wherein: The controller is configured to enable steering of the rear wheels based on a second feature in the speed-dependent signal occurring within a predetermined time interval relative to a first feature in the speed-dependent signal.

6. A control system according to any one of claims 3 to 5, wherein: The corresponding features are peaks or valleys of the repeating waveform.

7. A control system according to any preceding claim, wherein: The control system is configured to estimate a speed of a wheel or the vehicle based on the speed-related signal and to allow steering of the rear wheels if the estimated speed is greater than a threshold.

8. The control system according to claim 7, wherein: Said estimation of speed is performed using less than ten features of said speed-dependent signals, preferably less than five features of said speed-dependent signals, and even more preferably only two features of said speed-dependent signals.

9. A control system according to any preceding claim, wherein: The controller is configured to generate a vehicle speed signal or a wheel speed signal based on the speed-related signal, and wherein, at least below a predetermined speed, a decision to allow steering of the rear wheels of the vehicle is made based on the speed-related signal instead of the speed signal.

10. A control system according to any preceding claim, wherein: The controller is configured to receive speed-related signals from a plurality of sensors, each sensor being associated with a different wheel of the vehicle, and wherein the controller permits steering of the rear wheels based on the speed-related signals generated by each of the plurality of sensors.

11. The control system according to claim 10, wherein: The controller allows the rear wheel to be steered only if the speed-related signals for all sensors of the plurality of sensors indicate that the corresponding wheel is in motion.

12. A control system according to any preceding claim, wherein: The controller is configured to enable steering of the rear wheels based on the speed-related signal only in a subset of driving modes of the vehicle.

13. A vehicle comprising a rear wheel steering system, one or more wheel speed sensors associated with at least the rear wheels of the vehicle and a control system according to any preceding claim.

14. The vehicle of claim 13, comprising a front wheel steering system, wherein: The control system is configured to enable steering via the front-wheel steering system mode while disabling steering via the rear-wheel steering system based on the speed-related signal.

15. A control method for steering a vehicle, the method comprising: receiving a speed-related signal from a wheel speed sensor, the speed-related signal being dependent on a rate at which teeth of a gear move past the wheel speed sensor; as well as Rear wheel steering of the vehicle is enabled in dependence on the speed related signal.

16. Computer software which, when executed, is configured to perform the method according to claim 15.

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