Vehicle steering control system and method

Abstract

A control system for a vehicle is described. The control system includes one or more controllers and is configured to receive a speed-dependent signal from a wheel speed sensor, the speed-dependent signal being dependent on a speed at which a gear tooth passes in front of the wheel speed sensor, and depending on the speed-dependent signal, enabling rear wheel steering of the vehicle. In this manner, rear wheel steering can be enabled from low speeds where a vehicle or wheel speed signal is not typically available. By utilizing the number of teeth, such low speeds, or at least an indication that the vehicle is moving, can be estimated.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to a control system, a control method for vehicle steering, a computer program, and a vehicle. [Background technology]

[0002] It is known to provide vehicles with rear wheel steering in addition to the usual front wheel steering, which may improve agility. When the vehicle is stationary, it is undesirable to rotate (steer) the rear wheels, as the rear wheel steering system may not be designed to withstand continuous use in this condition.

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

[0004] Aspects and embodiments of the present invention provide a control system, a method for controlling steering of a vehicle, a computer program product, and a vehicle, as set out in the accompanying claims.

[0005] In one aspect, a control system for a vehicle is provided, the control system including one or more controllers, the control system configured to receive a speed-dependent signal from a wheel speed sensor, where the speed-dependent signal is dependent on a speed at which a gear tooth passes in front of the wheel speed sensor, and to enable rear wheel steering of the vehicle in dependence on the speed-dependent signal.

[0006] In this way, rear wheel steering can be permitted from very low speeds where vehicle or wheel speed signals are not typically available, and by using the number of teeth, such low speeds, or at least an indication that the vehicle is moving, can be extrapolated.

[0007] One or more controllers can at least one electronic processor having an electrical input for receiving a speed dependent signal; at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein; At least one electronic processor may be configured to access and execute instructions in the at least one memory device to enable rear wheel steering of the vehicle in dependence on the speed dependent signal.

[0008] The speed dependent signal may be a time dependent waveform that has a respective characteristic generated each time a tooth of the toothed wheel passes the wheel speed sensor. The time dependent waveform may be, for example, a sine wave, a sawtooth wave, or a square wave.

[0009] The controller may be configured to permit rear wheel steering in dependence on a plurality of consecutive features in the speed-dependent signal occurring within a predetermined time interval. Viewed alternatively, the controller may be configured to permit rear wheel steering in dependence 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.

[0010] Each feature may be a peak or a valley in a repeating waveform.

[0011] The control system may be configured to estimate the speed of the road wheels or vehicle based on the speed-dependent signal and allow rear wheel steering if the estimated speed is greater than a threshold. The estimate calculated in this manner may differ from speed calculations used for different purposes (e.g., by the vehicle's antilock braking system (ABS)).

[0012] The speed estimation may be performed using less than 10 features of the speed dependent signal, preferably less than 5 features of the speed dependent signal, and more preferably only 2 features of the speed dependent signal. In this way, the speed estimate (and therefore the decision whether to allow rear wheel steering) may be obtained very early and at very slow speeds.

[0013] The controller may be configured to generate a vehicle speed signal or a wheel speed signal from the speed-dependent signal, and at least below a predetermined speed, a decision to allow rear wheel steering of the vehicle is made in dependence on the speed-dependent signal rather than the speed signal.

[0014] The controller may be configured to receive speed-dependent signals from a plurality of sensors associated with different road wheels of the vehicle, the controller enabling rear wheel steering in dependence on the speed-dependent signals generated by each of the plurality of sensors. Preferably, the controller enables rear wheel steering only if the speed-dependent signals for all of the plurality of sensors indicate that the respective road wheel is in motion.

[0015] The controller may be configured to permit rear wheel steering in dependence on the speed dependent signal only in a subset of the vehicle's driving modes, in particular some vehicle modes may permit rear wheel steering from very low speeds, some modes may permit low speed rear wheel steering from somewhat higher speeds, and some modes may not permit low speed rear wheel steering at all.

[0016] 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.

[0017] The vehicle includes a front wheel steering system, and the control system is configured to allow steering via the front wheel steering system mode while not allowing steering via the rear wheel steering system based on the speed-dependent signal.

[0018] According to another aspect, there is provided a control method for steering a vehicle, the control method comprising: receiving a speed dependent signal from a wheel speed sensor, where the speed dependent signal is dependent on a speed at which a gear tooth passes in front of the wheel speed sensor; and enabling rear wheel steering of the vehicle in dependence on the speed dependent signal.

[0019] In another aspect, there is provided computer software configured, when executed, to perform the method according to the above.

[0020] 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 any feature of another claim, even if not originally so claimed. [Brief description of the drawings]

[0021] One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings.

[0022] [Figure 1]FIG. 1 shows a schematic diagram of a vehicle having an anti-lock braking system (ABS), front and rear steering systems, and a controller.

[0023] [Diagram 2] FIG. 2 shows a wheel speed sensor for use in the present technology.

[0024] [Diagram 3] FIG. 3 illustrates a schematic of a rear wheel steering control system and method.

[0025] [Figure 4] FIG. 4 shows a schematic flow diagram of the control method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] A vehicle 1 according to an embodiment of the present invention is described herein with reference to accompanying FIG. 1. The vehicle 1 includes respective wheel speed sensors 14a-14d of the vehicle 1, each associated with one of the running wheels (not shown) of the vehicle 1. Each of the wheel speed sensors 14a-14d outputs a speed-dependent signal to a control system 10, 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 also includes a rear wheel steering controller 13. In this embodiment, there are respective wheel speed sensors associated with all four wheels of the vehicle. The wheel speed sensors 14a-14d may be mounted on the road wheels or on axles or drive shafts that provide torque to the road wheels (e.g., may be provided within the bearing units of the wheels). The vehicle 1 also includes a front wheel steering actuator 16 and a rear wheel steering actuator 18, which actuate steering mechanisms to affect the steering of the front and rear wheels, respectively. The rear wheel steering actuator 18 is driven to operate dependently on 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 independent of wheel speed, and in particular is driven even when the vehicle is stationary and the wheels are not rotating.

[0027] Wheel speed sensors come in several different forms and can be used in the present method. They generally have two main parts: a wheel or ring that rotates with the drive wheel (or the axle or drive shaft that drives the drive wheel), and a fixed sensor that is mounted near the wheel or ring and generates a signal as the wheel or ring passes the sensor. The wheel or ring may be a ferromagnetic toothed wheel, or a ring with alternating magnetic poles. For illustrative purposes, FIG. 2 shows an example of a wheel speed sensor 14 using a fixed sensor 142 and a toothed wheel 144. It can be seen that the outer circumference of the gear 144 has alternating teeth 144a and gaps 144b. The fixed sensor 142 is positioned relative to the gear 144 such that as the gear 144 rotates, the alternating teeth 144a and gaps 144b pass through the magnetic field generated by the fixed sensor 142. The fixed sensor 142 may consist of a wire coil wound around a magnetic core and a permanent magnet. As the gear 144 rotates, alternating teeth and gaps pass through a magnetic field, which induces an AC voltage in the wire coil whose frequency and amplitude are related to the gear's speed. The output of the sensor is therefore an AC sinusoidal signal whose frequency changes as the gear's speed changes.

[0028] In the alternative case of a ring of magnetic poles (not shown), the fixed sensor does not include a magnet; instead the wheel itself has a series of magnets arranged with alternating poles around the periphery of the ring. The alternating magnetic poles around the periphery of the ring are similar to the alternating teeth and gaps on a gear. As the ring of magnets rotates, the magnetic field generated by the magnetic poles interacts with the fixed sensor, inducing a current in the fixed sensor's wire coil, the frequency and amplitude of which are related to the wheel speed. The output of the sensor is an AC square wave (approximately) signal whose frequency changes as the wheel speed changes.

[0029] In some cases, the sensor output may also indicate the direction of rotation, for example due to asymmetric waveform characteristics. This can be achieved, for example, by placing a fixed sensor at an angle to the wheel radius, as shown in Figure 2.

[0030] In the following description, the term "toothed wheel" will be used for simplicity and clarity, however, it will be understood that the present technique is equally applicable to the alternating pole ring described above, as well as any wheel speed sensor that outputs a speed dependent signal.

[0031] ESP 12 uses these time-varying (e.g. AC) signals to calculate various parameters including wheel speed, number of teeth (or number of poles in the case of magnetic rings), and (optionally) direction of wheel rotation. These are generated separately for each road wheel on the vehicle. At very low speeds (road wheels rotating slowly), the wheel speed calculation is inaccurate. In at least some cases, EPS features such as ABS do not calculate and / or output wheel speed at all at very low speeds. Normally, this is not a problem, since the primary use of wheel speed is ABS braking, which is only relevant at relatively high speeds.

[0032] The technology concerns allowing rear wheel steering only when the (rear) wheels of the vehicle are moving (turning / spinning). This is because rear wheel steering systems (actuators) may not be optimized to allow steering with the rear wheels completely stationary. This is in contrast to front wheel steering systems, which are required to allow steering even when the vehicle (especially its front wheels) is stationary. Forcing rear wheel steering on a stationary vehicle may cause scrubbing of the rear tires and / or excessive load on the rear wheel steering actuators. It also avoids unnecessary battery load when rear wheel steering is not required.

[0033] Due to the fact that wheel speeds are (typically) only calculated and / or output by ESP 12 at speeds above 0.7 km / h, rear wheel steering cannot be easily permitted or denied based on wheel speed values ​​calculated by ESP 12 at very low speeds. However, these low speeds may at least be suitable for permitting rear wheel steering. In some implementations, the technique does not require precise wheel speeds, but instead only a relatively coarse indication that the wheels are moving (turning). In such cases, it is recognized that signals that depend on the movement of other wheels are used to infer the movement of the wheels and form the basis of the decision to permit or deny rear wheel steering. Coarse in this case means that the actual wheel speeds do not need to be known precisely, but the indication must be reliable in the sense of accurately indicating whether the wheels are moving or stationary. In other instances, the actual speed may be more important, particularly in implementations where the steering rate depends on the vehicle speed or wheel speed. In such implementations, a relatively low steering rate may be permitted at relatively low speeds, and a relatively high steering rate may be permitted at relatively high speeds. Typically, the wheel speeds calculated by ESP 12 are not explicitly used to determine whether to implement rear wheel steering (at least below a certain speed threshold, e.g., 0.7 kilometers per hour, and potentially always). Instead, a proxy measurement indicative of wheel movement is used, which is still obtained (directly or indirectly) from wheel speed sensors.

[0034] In one example, tooth counting is used. The tooth count is an integer number and is generated (by the ESP) by detecting individual waveform peaks (and / or valleys, or other repeating features such as rising and falling edges) in the signal generated by the wheel speed sensor and incrementing a counter each time such a peak and / or valley occurs. That is, each time a gear or gear gap passes the fixed sensor, a tooth count is incremented. This number is periodically reset (or reset back to zero). The ESP uses the tooth count as part of its calculation of wheel speed, for example, measuring the increase in tooth count over time. The wheel speed (expressed as the linear speed of the wheel) can be easily calculated based on the total number of gear teeth, the number of teeth counted in a given interval, the length of the given interval, and the diameter of the road wheel. If the wheel speed is expressed as angular velocity (radians per second), the diameter of the road wheel is not necessary. A relatively large number of tooth counts per unit time is required to ensure an accurate measurement of the wheel speed. As mentioned above, this means that speed values ​​calculated at very low wheel speeds are deemed unreliable as very few tooth count increments occur within a given time frame, and therefore are not generated and / or output. However, the ESP can use the tooth count itself to generate speed values, as well as output the tooth count directly (in this case to controller 13). The present technique takes advantage of this to infer wheel movement based on tooth count increments and / or speed estimates generated outside (and downstream) of the ESP, with only a small number of tooth count increments (preferably only two).

[0035] In the present technology, this tooth number signal can be used directly (independent of its use in calculating wheel speed) to allow or deny rear wheel steering.

[0036] In the simplest case, rear wheel steering can be permitted depending on detecting an increase in the tooth number signal. For example, the controller can permit rear wheel steering conditional on the tooth number being incremented at least once within a predefined time interval (e.g., the last 0.5 seconds).

[0037] Alternatively, the controller may be configured to permit rear wheel steering dependent on the tooth count being incremented a predetermined number of times (e.g., two or three times) within a predetermined time interval (e.g., the last half second). Similarly, in this case, rear wheel steering is permitted dependent on a predetermined consecutive feature occurring in the speed-dependent signal within a predetermined time interval. This may be determined by determining that the tooth count has increased (increased) by at least a certain (predetermined) number within a predetermined time period. Using only two consecutive features is desirable, as this allows the determination to be made at slower speeds, the actual speed being relatively unimportant for the present purposes. In one embodiment, the tooth number signal is generated by and output from the ABS. However, in an alternative implementation, the controller may directly process the speed-dependent signal by detecting peaks or other features, rather than utilizing the tooth count as an intermediate value.

[0038] It will be appreciated that if only two features are used, the controller may be configured to permit rear wheel steering in dependence on the tooth count being incremented a second time within a predefined time interval after the first increment. Similarly, rear wheel steering in this case is permitted in dependence on a second feature in the speed-dependent signal occurring within a predefined time interval with respect to the first feature in the speed-dependent signal. This may be determined by starting a timer once the tooth count has increased once, and if the tooth count increases again within the predefined time interval, rear wheel steering is permitted.

[0039] Although absolute wheel speed is not required in deciding whether to allow rear wheel steering, preferably the control system may be configured to estimate road wheel or vehicle speed based on the speed dependent signal (using tooth count) and to allow rear wheel steering if the estimated speed is greater than a threshold (e.g. set to a very low value, e.g. 0.1 km / h). However, unlike the full calculation conventionally performed, e.g. by the ESP system 12, the wheel speed estimation is performed using a relatively small number of features of the speed dependent signal (i.e. a small number of increments of tooth count). For example, there are less than 10 features of the speed dependent signal, preferably less than 5 features, and even more preferably there are only 2 features of the speed dependent signal. This allows the speed estimate to be relatively inaccurate, but can be generated very early from standstill (only 2 teeth pass a fixed sensor, corresponding to a very low proportion of a complete rotation of the vehicle wheel) and at very low speeds.

[0040] On the other hand, the ESP 12 is configured to generate wheel speed signals from the speed-dependent signals of the wheel speed sensors 14a-14d for conventional purposes, as described above, but at least below a predetermined speed (which may be a speed at which the ESP 12 starts to generate and / or output speed values), the decision to allow rear wheel steering of the vehicle 1 is made in dependence on the count signals (or equivalent raw signals indicative of wheel movement) and not using the calculated vehicle or wheel speeds output by the ESP.

[0041] The ESP 12 outputs the wheel speed, number of teeth, and direction of rotation for each wheel of the vehicle 1. Typically, the technique uses only these values ​​for each of the rear wheels of the vehicle. In order to allow rear wheel steering, it must be determined that all wheels of the vehicle are moving. As a result, if any of the rear wheels are stationary, rear wheel steering is not allowed, resulting in excessive tire wear from scrubbing and excessive peak loads on the actuators that perform the steering.

[0042] If the wheel direction signal does not indicate stationary but indicates forward or reverse rotation, it can also be inferred that the wheels are moving. Therefore, the wheel direction output from ESPABS can be used in place of tooth counting. However, the wheel direction signal is not an indication of actual rotational speed, so in some cases a decision based on wheel direction alone may not be appropriate.

[0043] Preferably, tooth count and wheel direction are used in combination, with wheel direction being used to confirm the decision based on tooth count, i.e. the controller may be configured to allow rear wheel steering only if the tooth count (or derived speed estimate) meets a condition for each of the rear wheels and the commanded wheel direction for each of the rear wheels indicates wheel movement.

[0044] In some implementations, the controller is configured to allow rear wheel steering depending on the speed-dependent signal, and is allowed only in a subset of the vehicle's driving modes. For example, rear wheel steering may not be allowed at all in an on-road "comfort" mode, but may be allowed in off-road modes, such as when driving on mud or sand, or in a rock driving mode. In these modes, rear wheel steering is allowed subject to wheel motion requirements applied by the present technology. In principle, other implementations may provide driving modes in which rear wheel steering is provided and in which the wheel motion requirements are waived.

[0045] It is understood that the vehicle also includes a front wheel steering system, which does not have the same limitations as the rear wheel steering system and is specifically rated to be operated with the front wheels stationary. Thus, the control system is configured to allow steering via the front wheel steering system mode while not allowing steering via the rear wheel steering system based on the speed dependent signal. It is understood that separate controllers may be provided for front and rear wheel steering.

[0046] Referring to FIG. 3, a schematic block diagram showing the vehicle components and signal flow involved in the present technology is shown.

[0047] Wheel speed sensors 14b, 14d are shown outputting AC signals to the ESP 12 for the left and right rear wheels respectively. The ESP 12 processes the received AC signals and generates a tooth count TCL, a wheel speed WSL, a wheel direction WDL for the left rear wheel and a tooth count TCR, a wheel speed WSR, a wheel direction WDR for the right rear wheel. These are provided to the rear wheel steering controller 13. A driving mode selector 19 is provided configured to select a driving mode of the vehicle 1. Different driving modes of the vehicle may have different characteristics such as suspension stiffness, use of ABS, acceleration or braking profile, etc. The selection of the driving mode may be done manually by the driver or automatically based on vehicle sensor data. The selected driving mode is provided to the rear wheel steering controller 13. Also provided is a steering module 20 which generates a steering request based on either a manual driving input (via the 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 rear wheel steering is possible from the selected driving mode, and to determine whether rear wheel steering is possible from the tooth number signals TCL and TCR for the left and right rear wheels and the wheel direction signals WDL and WDR for the left and right rear wheels. After determining whether rear wheel steering is possible, if it is determined that rear wheel steering is possible, 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.

[0048] Generally, vehicle control systems are modular in structure and function. It is to be understood that the or each controller in the control system of the present application may be comprised of a control unit or processing device 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 device, or different functions of the or each controller in the control system may be embodied in or hosted on different control units or processing devices. As used herein, the terms "controller", "control unit", or "processing device" are understood to be inclusive of a single controller, control unit, or processing device, as well as multiple controllers, control units, or processing devices that operate to provide the required control functions. A set of instructions may be provided that, when executed, causes the controller to perform the control techniques described herein, including some or all of the functions required for the methods described herein. This set of instructions may be embedded in the one or more electronic processors of the controller or may be provided as software executed by the controller. The first controller or control unit may be implemented as software executed 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, and optionally may be implemented as software running on the same processor or processors as the first controller or control unit. Other configurations are also useful.

[0049] Each controller 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 may be comprised of any suitable electronic processor (e.g., microprocessor, microcontroller, ASIC, etc.) configured to execute electronic instructions. The electronic memory device may be comprised of any suitable memory device and may store various data, information, thresholds, look-up tables, or other data structures, and / or instructions. In one embodiment, the memory device stores information and instructions, such as software, firmware, programs, algorithms, scripts, applications, etc., that may manage all or a portion of the methodologies described herein. The processor, or each electronic processor, may access the memory device and execute and / or use the instructions and information therein to execute or implement some or all of the functions and methodologies described herein.

[0050] At least one memory device may include a computer readable storage medium (e.g., non-transitory or non-transient storage medium) and 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-ROM); magneto-optical storage media; read-only memory (ROM); random access memory (RAM); erasable and programmable memory (e.g., EPROM). For example, floppy disks, etc.; optical storage media (e.g., CD-ROM), magneto-optical storage media; read-only memory (ROM), random access memory (RAM); erasable and programmable memory (e.g., EPROM and EEPROM); flash memory; or electrical or other type of media for storing such information / instructions.

[0051] Alternatively, each controller may include at least one electronic processor configured to execute electronic instructions stored in at least one memory device, the execution of which causes the electronic processor(s) to perform the methods described above. Similar structures may be provided in each controller. However, it will be appreciated that embodiments of the invention may be implemented in any suitable form of hardware, software, or combinations of hardware and software. For example, the invention is not limited to being implemented by programmable processing devices, and it is contemplated that at least some, and in some embodiments all, functions and / or method steps of the invention may be implemented by non-programmable hardware, such as non-programmable ASICs, Boolean logic circuits, etc., as well.

[0052] Referring to FIG. 4, a schematic flow diagram illustrating an embodiment of the method is provided. In step S1, a speed-dependent signal is generated at each of the wheel speed sensors 14a-14d and provided to the ESP 12. In step S2, the ESP 12 generates a tooth number, a wheel direction, and a wheel speed for each (rear) wheel and provides them to the rear wheel steering controller 13. In step S3, the driving mode selector provides an indication of the current driving mode of the vehicle to the rear wheel steering controller. In step S4, the rear wheel steering controller determines whether rear wheel steering is permitted or not depending on the current driving mode. In some implementations, the rear wheel steering controller further determines whether rear wheel steering is permitted from a very low speed or a standard minimum speed depending on the current driving mode. If it is determined that the current driving mode is a mode in which rear wheel steering is not permitted, then in step S5, rear wheel steering is not permitted (rejected) and the process returns to step S1. If it is determined that the current driving mode is a mode in which rear wheel steering is permitted, then in step S6, a wheel speed estimate is obtained for each wheel based on the tooth number. The estimated wheel speed for each wheel is compared to a speed threshold in step S7. Optionally, the speed threshold may be driving mode dependent (see step S4 above). If the estimated wheel speed for either or both wheels does not exceed the speed threshold, rear wheel steering is rejected in step S5. If the wheel speed estimates for both rear wheels exceed the speed threshold, it is determined in step S8 whether the wheel direction parameters for each rear wheel indicate movement (i.e., forward or reverse rotation). If not, rear wheel steering is rejected in step S5. If the wheel direction parameters for both rear wheels indicate movement, processing proceeds to step S9, where rear wheel steering of the vehicle is permitted. Processing then returns to step S1. In this manner, rear wheel steering is permitted when actuator operation is unlikely to cause problems with scrubbing or actuator loading (because the wheels are moving) and rear wheel steering is rejected when actuator operation is likely to cause problems (because the wheels are not moving).

[0053] 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. For example, all of the features disclosed in this specification (including the accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, can be combined in any combination, except where at least some of such features and / or steps are mutually exclusive.

[0054] Each feature disclosed in this specification (including the accompanying claims, abstract and drawings), unless expressly stated otherwise, may be replaced by alternative features serving the same, equivalent or similar purpose, and thus, unless expressly stated otherwise, each feature disclosed is merely an example of a generic series of equivalent or similar features.

[0055] The present invention is not limited to the details of any of the above-described embodiments. It extends to any novel or novel combination of features disclosed in this specification (including the accompanying claims, abstract and drawings), or any novel or novel combination of steps of the method or process so disclosed. The claims should not be construed to cover merely the above-described embodiments, but also any embodiment falling within the scope of the claims.

Claims

1. 1. A control system for a vehicle having one or more controllers, comprising: receiving a speed dependent signal from a wheel speed sensor, said speed dependent signal being dependent on the speed at which a tooth of a toothed wheel passes in front of said wheel speed sensor; A control system for a vehicle configured to enable rear wheel steering of the vehicle in dependence on the speed dependent signal.

2. one or more controllers; The one or more contra-uras are at least one electronic processor having an electrical input for receiving said speed dependent signal; 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 on the at least one memory device to enable rear wheel steering of the vehicle in dependence on the speed dependent signal.

10. The control system for a vehicle according to claim 1.

3. 3. A control system for a vehicle as claimed in claim 1 or claim 2, wherein the speed dependent signal is a time dependent waveform having a respective characteristic produced each time a tooth of the toothed wheel passes the wheel speed sensor.

4. 4. A control system for a vehicle as claimed in claim 3, wherein the controller is configured to permit rear wheel steering in dependence on a number of consecutive said features occurring within a predetermined time interval in the speed dependent signal.

5. 4. The control system for a vehicle of claim 3, wherein the controller is configured to permit rear wheel steering in dependence upon 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. 6. A control system for a vehicle as claimed in any one of claims 3 to 5, wherein the feature is a peak or a valley of a repetitive waveform.

7. the control system is configured to estimate a speed of a road wheel or the vehicle based on the speed-dependent signal; 7. A control system for a vehicle as claimed in any preceding claim, configured to allow rear wheel steering if the estimated speed is greater than a threshold.

8. 8. A control system for a vehicle as claimed in claim 7, wherein the estimation of speed is performed using less than 10 features of the speed dependent signal, preferably less than 5 features, more preferably only 2 features.

9. the controller is configured to generate a vehicle speed signal or a wheel speed signal from the speed-dependent signal; 9. A control system for a vehicle as claimed in claim 1, wherein the decision to allow rear wheel steering of the vehicle is made depending on the speed dependent signal but not depending on the vehicle speed signal or the wheel speed signal, at least below a predetermined speed.

10. the controller is configured to receive the speed-dependent signals from a plurality of sensors; each of the plurality of sensors associated with a different one of the plurality of wheels of the vehicle; 10. A control system as claimed in any preceding claim, wherein the controller enables rear wheel steering in dependence on the speed dependent signal produced by each of the plurality of sensors.

11. 11. The control system for a vehicle of claim 10, wherein the controller enables rear wheel steering only if the speed dependent signals for all of the plurality of sensors indicate that the respective wheel is moving.

12. 12. A control system for a vehicle as claimed in any preceding claim, wherein the controller is configured to enable rear wheel steering in dependence on the speed dependent signal only in a subset of driving modes of the vehicle.

13. one or more wheel speed sensors associated with at least the rear wheels of the vehicle; A vehicle comprising a control system according to any one of claims 1 to 12.

14. 14. A vehicle as claimed in claim 13, comprising a front wheel steering system, The vehicle, wherein the control system is configured to allow steering via the front wheel steering system while not allowing steering via the rear wheel steering system based on the speed-dependent signal.

15. receiving a speed dependent signal from a wheel speed sensor, said speed dependent signal being dependent on the rate at which a tooth of a toothed wheel passes in front of said wheel speed sensor; enabling rear wheel steering of the vehicle in dependence on said speed dependent signal.

16. Computer software configured to, when executed, perform the method of claim 15.

Images