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

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

Background Art

[0002] It is well known to provide rear-wheel steering in addition to normal front-wheel steering in a vehicle. This may improve agility. When the vehicle is stationary, it may not be desirable to rotate (steer) the rear wheels because the rear-wheel steering system may not be designed to withstand continuous use in this state.

[0003] The object of the present invention is to address one or more of the drawbacks 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 the steering of a vehicle, a computer program, and a vehicle as described in the appended 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 depends on the speed at which the teeth of a gear pass in front of the wheel speed sensor), and to permit rear-wheel steering of the vehicle depending on the speed-dependent signal. ​​​​​​​ At least one electronic processor having an electrical input for receiving a speed-dependent signal, It includes at least one memory device electrically coupled to at least one electronic processor, in which instructions are stored, At least one electronic processor may be configured to access and execute instructions for at least one memory device to enable rear-wheel steering of the vehicle in a manner dependent on a speed-dependent signal.

[0008] The speed-dependent signal may be a time-dependent waveform in which a characteristic is generated each time a tooth of a toothed wheel passes a 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 allow rear-wheel steering depending on a series of consecutive features in a speed-dependent signal occurring within a predetermined time interval. Alternatively, the controller may be configured to allow rear-wheel steering depending 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 trough in a repeating waveform.

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

[0012] Speed ​​estimation may be performed using fewer than 10 features of the speed-dependent signal, preferably fewer than 5 features of the speed-dependent signal, and even more preferably only 2 features of the speed-dependent signal. In this way, the speed estimate (and thus the determination of whether to allow rear-wheel steering) may be obtained at a very early stage and at a very low speed.

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

[0014] The controller may be configured to receive speed-dependent signals from multiple sensors associated with different load wheels of the vehicle, and the controller may enable rear-wheel steering depending on the speed-dependent signal generated by each of the multiple sensors. Preferably, the controller enables rear-wheel steering only if the speed-dependent signals for all of the multiple sensors indicate that each load wheel is in motion.

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

[0016] From another perspective, a vehicle is provided 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 described in any of the prior claims.

[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 a speed-dependent signal.

[0018] In another embodiment, a control method for the steering of a vehicle is provided, the method being: Receiving a speed-dependent signal from the wheel speed sensor (where the speed-dependent signal depends on the speed at which the gear teeth pass in front of the wheel speed sensor), This includes allowing rear-wheel steering of the vehicle based on a speed-dependent signal.

[0019] In another embodiment, computer software is provided that, when executed, is configured to perform the method described 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 adopted independently or in any combination. That is, any embodiments and / or features may be combined in any way and / or combination, provided that such features are not incompatible. The applicant reserves the right to modify the claims originally filed, or to file new claims accordingly. This includes the right to modify the claims originally filed to rely on and / or incorporate any features of other claims, even if they were not originally claimed as such. [Brief explanation of the drawing]

[0021] Hereinafter, with reference to the attached drawings, one or more embodiments of the present invention will be described as an example.

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

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

[0024] [Figure 3] FIG. 3 schematically shows a steering control system and method for rear wheels.

[0025] [Figure 4] FIG. 4 shows a schematic flow chart of the control method.

Mode for Carrying Out the Invention

[0026] A vehicle 1 according to one embodiment of the present invention is described herein with reference to attached Figure 1. Vehicle 1 comprises a wheel speed sensor 14a-14d, each associated with one of the vehicle's driving wheels (not shown). Each wheel speed sensor 14a-14d outputs a speed-dependent signal to a control system 10, specifically an electronic stabilization program (ESP) 12 of the control system 10, which includes anti-lock braking system (ABS) functions and other functions related to vehicle stability control. The control system 10 also includes a rear wheel steering controller 13. In this embodiment, there is a wheel speed sensor associated with all four wheels of the vehicle. The wheel speed sensors 14a-14d may be mounted on the road wheels or on the axle or drive shaft that torques the road wheels (for example, they may be located within the wheel bearing unit). Vehicle 1 also includes 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 and operates depending on whether the rear wheels of vehicle 1 are moving (not stationary), as determined using sensor data from wheel speed sensors 14b and 14d associated with the rear wheels of vehicle 1. The front wheel steering actuator 16 is driven independently of wheel speed and 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 this method. These generally comprise two main parts: a wheel or ring that rotates with the drive wheel (or axle or drive shaft driving the drive wheel), and a stationary sensor mounted near the wheel or ring that generates a signal as the wheel or ring passes the sensor. This wheel or ring may be a ferromagnetic toothed wheel or a ring with alternating magnetic poles. For illustrative purposes, Figure 2 shows an example of a wheel speed sensor 14 using a stationary sensor 142 and a toothed wheel 144. The outer circumference of the gear 144 is shown to have alternating teeth 144a and gaps 144b. The stationary 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 stationary sensor 142. The stationary sensor 142 may consist of a magnetic core and a wire coil wound around a permanent magnet. As gear 144 rotates, the teeth and gaps alternately pass through the magnetic field, generating an alternating current voltage induced in the wire coil, the frequency and amplitude of which are related to the gear speed. Therefore, the sensor output is an alternating current sinusoidal signal whose frequency changes as the gear speed changes.

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

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

[0030] In the following explanation, for the sake of brevity and clarity, the term "toothed wheel" will be used. However, it should be understood that this technology can be applied equally to the alternating pole rings described above, as well as to any wheel speed sensor that outputs a speed-dependent signal.

[0031] The ESP12 uses these time-varying (e.g., AC) signals to calculate various parameters, including wheel speed, number of teeth (or poles in the case of magnetic rings), and (optionally) direction of rotation of the wheel. These are generated individually for each load wheel of the vehicle. At very low speeds (when the load wheels are rotating slowly), the calculation of wheel speed is inaccurate. In at least some cases, EPS functions such as ABS do not calculate and / or output wheel speed at all at extremely low speeds. This is usually not a problem because the primary use of wheel speed is for ABS braking, which is only relevant at relatively high speeds.

[0032] This technology relates to allowing rear-wheel steering only when the vehicle's (rear) wheels are moving (rotating / turning). This is because the rear-wheel steering system (actuator) may not be optimized to enable steering when the rear wheels are completely stationary. This is in contrast to the front-wheel steering system, which is required to enable steering even when the vehicle (especially its front wheels) is stationary. Forcing rear-wheel steering on a stationary vehicle can cause scrubbing on the rear tires or place excessive load on the rear-wheel steering actuator. Additionally, if rear-wheel steering is not required, it can avoid unnecessary battery load.

[0033] The fact that wheel speed is calculated and / or output by ESP12 only at speeds of (typically) 0.7 km / h or higher means that rear-wheel steering cannot be easily permitted or denied based on wheel speed values ​​calculated by ESP12 at very low speeds. However, these low speeds may be suitable for permitting rear-wheel steering. In some implementations, the technology does not require precise wheel speed, but instead only a relatively coarse indication that the wheels are moving (rotating). In such cases, it is recognized that signals dependent on the movement of other wheels are used to infer the movement of the wheels and form the basis for the decision to permit or deny rear-wheel steering. Coarseness in this case means that the indication must be reliable in the sense that it is not necessary to know the actual wheel speed precisely, but that it accurately indicates whether the wheels are moving or stationary. In other examples, actual speed may be more important, especially in implementations where the steering rate depends on 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. Generally, the wheel speed calculated by ESP12 is not explicitly used to determine whether rear-wheel steering is performed (at least below a certain speed threshold, e.g., 0.7 km / h, and potentially always). Instead, alternative measurements indicating wheel movement are used, which are still obtained (directly or indirectly) from the wheel speed sensor.

[0034] In one example, a tooth count is used. The tooth count is an integer generated (by the ESP) by detecting individual waveform peaks (and / or troughs, 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 trough occurs. In other words, the tooth count is incremented each time a gear or gear gap passes a fixed sensor. This number is periodically reset (or returned to zero). The ESP uses the tooth count as part of the wheel speed calculation, for example, measuring the increase in the number of teeth over time. Wheel speed (expressed as the linear velocity of the wheel) can be easily calculated based on the total number of teeth on the gear, the number of teeth counted at a given interval, the length of a given interval, and the diameter of the road wheel. The road wheel diameter is not needed when expressing wheel speed in angular velocity (radians per second). A relatively large tooth count per unit time is required to ensure accurate measurement of wheel speed. As mentioned above, this means that speed values ​​calculated at very low wheel speeds are considered unreliable because the increment in tooth counts occurring within a given time frame is very small, and therefore are not generated and / or output. However, the ESP can not only generate speed values ​​using the tooth count itself, but can also output the tooth count directly (to the controller 13 in this case). This technique takes advantage of this to estimate wheel movement based on the increase in tooth count and / or the approximate speed generated outside (and downstream) of the ESP. The increase in tooth count is small (preferably only two).

[0035] This technology allows the number of teeth signal to be used directly (independent of its use in calculating wheel speed) to enable or deny rear-wheel steering.

[0036] In its simplest form, rear-wheel steering can be enabled by relying on detecting an increase in the tooth count signal. For example, the controller may enable rear-wheel steering on the condition that the tooth count has been incremented at least once within a given time interval (e.g., the preceding 0.5 seconds).

[0037] Alternatively, the controller may be configured to allow rear-wheel steering depending on whether the tooth count has been incremented by a predetermined number of times (e.g., two or three times) within a predetermined time interval (e.g., the preceding half-second). Similarly, in this case, rear-wheel steering is allowed depending on a predetermined sequence of features occurring within the speed-dependent signal within a predetermined time interval. This can be determined by determining that the tooth count has increased by at least a certain number of times within a predetermined time period. It is preferable to use only two sequence of features, as this allows the determination to be made at lower speeds, and the actual speed is relatively unimportant for this purpose. In one embodiment, the tooth count signal is generated and output from the ABS. However, in an alternative embodiment, the controller may process the speed-dependent signal directly by detecting peaks or other features, rather than using the tooth count as an intermediate value.

[0038] If only two features are used, it is understood that the controller may be configured to allow rear-wheel steering depending on whether the tooth count is incremented a second time within a predetermined time interval after the first increment. Similarly, in this case, rear-wheel steering is permitted depending on the second feature in the speed-dependent signal occurring within a predetermined time interval with respect to the first feature in the speed-dependent signal. This can be determined by starting a timer when the tooth count has increased once, and if the tooth count increases again within the predetermined time interval, rear-wheel steering is permitted.

[0039] While absolute wheel speed is not required to determine whether to allow rear-wheel steering, preferably the control system is configured to estimate the speed of the road wheels or vehicle based on a speed-dependent signal (using a 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 calculations conventionally performed by, for example, ESP systems 12, the wheel speed estimation is performed using a relatively small number of features of the speed-dependent signal (i.e., a small increment of the tooth count). For example, the number of features of the speed-dependent signal is less than 10, preferably less than 5, and even more preferably only 2. This results in a relatively inaccurate speed estimate, but it can be generated very early from a stationary state (corresponding to a very small percentage of the full rotation of the vehicle wheel, with only 2 teeth passing the fixed sensor) and can be generated even at very low speeds.

[0040] On the other hand, as described above, ESP12 is configured to generate a wheel speed signal from the speed-dependent signals of the wheel speed sensors 14a-14d for conventional purposes. However, below a certain speed (which may be the speed at which ESP12 begins to generate and / or output speed values), the decision to allow rear-wheel steering of vehicle 1 is made based on the count signal (or an equivalent raw signal indicating the movement of the wheels), and does not use the calculated speed of the vehicle or wheels output by the ESP.

[0041] The ESP12 outputs the wheel speed, number of teeth, and rotation direction for each wheel of vehicle 1. Generally, this technology uses only these values ​​for each of the vehicle's rear wheels. In order to allow rear-wheel steering, it is necessary to determine that all of the vehicle's wheels are moving. As a result, if any of the rear wheels are stationary, rear-wheel steering is not permitted, leading to excessive tire wear due to scrubbing and excessive peak load on the steering actuator.

[0042] If the wheel direction signal indicates forward or reverse rotation rather than a stationary state, it is possible to infer that the wheel is moving. Therefore, the wheel direction output from ESPABS can be used instead of the tooth count. However, since the wheel direction signal is not an indicator of actual rotational speed, wheel direction-based determination may not be appropriate in some cases.

[0043] Preferably, the tooth count and wheel direction are used in combination, with the wheel direction used to verify the determination based on the tooth count. That is, the controller may be configured to allow rear-wheel steering only if the tooth count (or derived speed estimate) satisfies the conditions for each rear wheel, and the indicated wheel direction for each rear wheel indicates the movement of the wheel.

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

[0045] It is understood that the vehicle also has a front-wheel steering system. The front-wheel steering system does not have the same limitations as the rear-wheel steering system and is evaluated to be operated in particular when the front wheels are stationary. Therefore, 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 a speed-dependent signal. It is understood that separate controllers may be provided for the steering of the front and rear wheels.

[0046] Referring to Figure 3, a schematic block diagram is shown illustrating the vehicle components and signal flow related to this technology.

[0047] Wheel speed sensors 14b and 14d are shown, outputting AC signals to the ESP 12 for each of the left and right rear wheels. The ESP 12 processes the received AC signals and generates the number of teeth TCL, wheel speed WSL, and wheel direction WDL for the left rear wheel, and the number of teeth 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 is provided, configured to select a driving mode for vehicle 1. Different driving modes of the vehicle may have different characteristics, such as suspension stiffness, ABS use, and acceleration or braking profile. 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. A steering module 20 is also provided, which generates steering requests based on either manual driving input (via the steering wheel) or automatic driving input. The steering requests are 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 count 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. 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 direction 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 should be understood that a controller or each controller in the control system of this application may consist of a control unit or arithmetic processing unit having one or more electronic processors (e.g., a microprocessor, microcontroller, application-specific integrated circuit (ASIC), etc.), or may consist of a single control unit or arithmetic processing unit, or different functions of a controller or each controller in the control system may be embodied in different control units or arithmetic processing units, or hosted in different control units or arithmetic processing units. As used herein, the terms “controller,” “control unit,” or “arithmetic processing unit” are understood to encompass a single controller, control unit, or arithmetic processing unit, and a plurality of controllers, control units, or arithmetic processing units operating 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 instruction set may be incorporated into the one or more electronic processors of the controller, or it may be provided as software that runs on the controller. A first controller or control unit may be implemented as software that runs on one or more processors. One or more other controllers or control units can be implemented as software running on one or more processors, and optionally, as software running on the same one or more 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 other controllers) and one or more electrical outputs for outputting one or more output signals (to one or more other controllers). The electronic processor may consist of any suitable electronic processor (e.g., a microprocessor, microcontroller, ASIC, etc.) configured to execute electronic instructions. The electronic memory device may consist of any suitable memory device and may store various data, information, thresholds, lookup 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., which may govern all or part of the methodologies described herein. The processor, or each electronic processor, may access the memory device and execute and / or use its instructions and information to perform or implement some or all of the functions and methodologies described herein.

[0050] At least one memory device may include any mechanism for storing information in a format readable by a mechanical or electronic processor / arithmetic unit, comprising a computer-readable storage medium (e.g., non-temporary or non-temporary storage medium). This includes, but is 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 and programmable memory (e.g., EPROMs, e.g., floppy disks); optical storage media (e.g., CD-ROMs), magneto-optical storage media; read-only memory (ROMs), random access memory (RAM); erasable and programmable memory (e.g., EPROMs and EEPROMs); flash memory; or any other type of electrical or other medium 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, such that the execution of the electronic processor(s) carries out the method described above. A similar configuration may be provided in each controller. However, it will be understood that embodiments of the present invention can be implemented in any suitable form of hardware, software, or a combination of hardware and software. For example, the present invention is not limited to being implemented by a programmable processing unit, and in at least some, and in all of some embodiments, the functions and / or method steps of the present invention can also be implemented by non-programmable hardware, such as non-programmable ASICs, Boolean logic circuits, etc.

[0052] Referring to Figure 4, a schematic flowchart illustrating one embodiment of the method is provided. In step S1, speed-dependent signals are generated at each of the wheel speed sensors 14a-14d and provided to the ESP 12. In step S2, the ESP 12 generates the number of teeth, wheel direction, and wheel speed for each (rear) wheel and provides these to the rear wheel steering controller 13. In step S3, the driving mode selector provides the rear wheel steering controller with an indication of the vehicle's current driving mode. 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, depending on the current driving mode, whether rear wheel steering is permitted from very low speeds or from standard minimum speeds. If it is determined that the current driving mode is one in which rear wheel steering is not permitted, in step S5, rear wheel steering is not permitted (denied), and the process returns to step S1. If it is determined that the current driving mode is one in which rear wheel steering is permitted, in step S6, an estimated wheel speed for each wheel is obtained based on the number of teeth. The estimated wheel speed of each wheel is compared to a speed threshold in step S7. Optionally, the speed threshold may depend on the driving mode (see step S4 above). If the estimated wheel speed of either or both wheels does not exceed the speed threshold, rear-wheel steering is denied in step S5. If the estimated wheel speeds of both rear wheels exceed the speed threshold, in step S8, it is determined whether the wheel direction parameter of each rear wheel indicates movement (i.e., forward or reverse rotation). If it does not, rear-wheel steering is denied in step S5. If the wheel direction parameter of both rear wheels indicates movement, the process proceeds to step S9, and rear-wheel steering of the vehicle is permitted. The process then returns to step S1. Thus, rear-wheel steering is permitted when the actuator operation is unlikely to cause problems with scrubbing or actuator load (because the wheels are moving), and denied when it is likely to cause problems with actuator operation (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 this application. For example, all features disclosed herein (including the appended claims, abstract and drawings) and / or all steps of any method or process so herein can be combined in any combination, except for any combination in which at least some of such features and / or steps are mutually exclusive.

[0054] Each feature disclosed herein (including the attached claims, abstract, and drawings) may be replaced by an alternative feature serving the same, equivalent, or similar purpose unless otherwise expressly stated. Accordingly, unless otherwise expressly stated, each disclosed feature is merely an example of a general set of equivalent or similar features.

[0055] The present invention is not limited to any of the embodiments described above. It extends to novel features or combinations of features disclosed herein (including the appended claims, abstract and drawings), or novel methods or steps of processes disclosed herein. The claims should not be construed as merely covering the embodiments described above, but as covering all embodiments that fall within the scope of the claims.

Claims

1. A vehicle control system comprising one or more controllers, The process involves receiving a speed-dependent signal from a wheel speed sensor, wherein the speed-dependent signal depends on the speed at which the teeth of the toothed wheel pass in front of the wheel speed sensor. In a vehicle control system configured to enable rear-wheel steering of the vehicle depending on the speed-dependent signal, The wheel speed sensor includes a left rear wheel speed sensor and a right rear wheel speed sensor, respectively, associated with the left rear wheel and the right rear wheel. A vehicle control system wherein, when speed-dependent signals from the left rear wheel speed sensor and the right rear wheel speed sensor indicate that the left rear wheel and the right rear wheel are moving, the controller allows the rear wheel steering.

2. Includes one or more controllers, The one or more of the aforementioned contrauras At least one electronic processor having an electrical input for receiving the speed-dependent signal; At least one memory device electrically coupled to the at least one electronic processor and storing instructions; 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 in order to enable rear-wheel steering of the vehicle, depending on the speed-dependent signal. A vehicle control system according to claim 1.

3. The vehicle control system according to claim 1, wherein the speed-dependent signal is a time-dependent waveform in which each characteristic is generated each time the teeth of the toothed wheel pass the wheel speed sensor.

4. The control system for a vehicle according to claim 3, wherein the controller is configured to allow rear-wheel steering depending on a plurality of consecutive features occurring within a predetermined time interval in the speed-dependent signal.

5. The vehicle control system according to claim 3, wherein the controller is configured to allow rear-wheel steering depending on a second feature in the speed-dependent signal that occurs within a predetermined time interval with respect to a first feature in the speed-dependent signal.

6. The vehicle control system according to claim 3, wherein the aforementioned feature is a peak or trough of a repeating waveform.

7. The control system is configured to estimate the speed of the road wheels or the vehicle based on the speed-dependent signal, A control system for a vehicle according to claim 1, configured to allow rear-wheel steering if the estimated speed is greater than a threshold.

8. The vehicle control system according to claim 7, wherein the speed is estimated using fewer than 10 features, preferably fewer than 5 features, and more preferably only 2 features of the speed-dependent signal.

9. The controller is configured to generate a vehicle speed signal or a wheel speed signal from the speed-dependent signal. A control system for a vehicle according to claim 1, wherein, at least below a predetermined speed, a decision is made to permit the rear wheel steering of the vehicle, depending on the speed-dependent signal but without depending on the vehicle speed signal or the wheel speed signal.

10. The wheel speed sensor further includes a left front wheel speed sensor and a right front wheel speed sensor associated with the left front wheel and the right front wheel, respectively. The controller is configured to receive the speed-dependent signals from each of the left rear wheel speed sensor, the right rear wheel speed sensor, the left front wheel speed sensor, and the right front wheel speed sensor. The control system according to claim 1, wherein the controller allows rear wheel steering depending on the speed-dependent signals generated by each of the left rear wheel speed sensors, the right rear wheel speed sensor, the left front wheel speed sensor, and the right front wheel speed sensor.

11. A control system for a vehicle according to claim 10, wherein the controller permits rear wheel steering only when the speed-dependent signals for all of the left rear wheel speed sensor, the right rear wheel speed sensor, the left front wheel speed sensor, and the right front wheel speed sensor indicate that each of the left rear wheel, the right rear wheel, the left front wheel, and the right front wheel is moving.

12. The vehicle control system according to claim 1, wherein the controller is configured to allow rear-wheel steering in accordance with the speed-dependent signal only in a subset of the vehicle's driving modes.

13. One or more wheel speed sensors associated with at least the rear wheels of the vehicle, A vehicle comprising the control system described in claim 1.

14. A vehicle according to claim 13, comprising a front wheel steering system, A vehicle in which 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. A step of receiving speed-dependent signals from a left rear wheel speed sensor and a right rear wheel speed sensor, respectively, associated with the left rear wheel and the right rear wheel, wherein the speed-dependent signals depend on the speed at which the teeth of a toothed wheel pass in front of the left rear wheel speed sensor and the right rear wheel speed sensor. A control method for steering a vehicle, comprising the step of allowing rear wheel steering of the vehicle when, depending on the speed-dependent signals, the speed-dependent signals from the left rear wheel speed sensor and the right rear wheel speed sensor indicate that the left rear wheel and the right rear wheel are moving.

16. Computer software configured to perform the method described in claim 15 when executed.

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