TECHNICAL FIELD

The present invention relates to an apparatus and method for use in vehicle control to improve vehicle traction. Aspects of the invention relate to an apparatus, to a vehicle, to a method, to a computer program product, to a computer readable medium, and to a processor.

BACKGROUND

It can be difficult for vehicle tyres to achieve traction on a low friction surface such as wet grass or ice. This can lead to wheel spin when attempting to accelerate, or skidding of the vehicle as wheels lock under braking when attempting to decelerate.

These are particular issues for vehicles driving off-road, which are more likely to encounter such surfaces, although all vehicles are vulnerable to these problems.

Spinning and/or skidding of the vehicle wheels causes excessive wear of the tyres, and can also damage the surface on which the wheel spins/skids. Furthermore, each of these problems represents a reduction in control of the vehicle. It is therefore desirable to implement measures to prevent loss of traction.

Examples of conventional measures for preventing loss of traction include traction control systems and anti-lock braking systems (ABS). Operating on the principle that un- driven wheels do not spin, and un-braked wheels do not skid, wheels to which neither drive force nor braking force is applied therefore rotate at a speed that is directly proportional to the vehicle speed, and so can be used as a reference in order to determine when other wheels have lost traction.

Accordingly, traction control and anti-lock braking systems compare wheel speed data derived from wheel speed sensors attached to different wheels to determine when a wheel is locked or spinning. For example, if the system detects that the un-driven wheels are stationary while the driven wheels are moving, this indicates that the driven wheels are spinning. In this event, the traction control system typically mitigates this by applying braking to the spinning wheels. Alternatively, in other systems the power sent to spinning wheels is reduced. This approach is effective for vehicles in which not all wheels are powered and/or braked, for example front-wheel drive or rear-wheel drive vehicles. However, for vehicles in which all wheels are driven and/or braked, or in which wheel speed data is unavailable for un-driven wheels, this approach is less effective, as all of the wheels may spin or lock simultaneously. Known systems for such vehicles depend on identifying subtle differences in wheel speed between different wheels of the vehicle. However, if all of the vehicle's wheels are rotating at the same speed, the traction control system has no means for determining whether the vehicle is moving or if all of the wheels are spinning (or both). Correspondingly, if all of the vehicle wheels are stationary, the traction control system cannot determine whether the vehicle is stationary or if the wheels are locked and the vehicle is skidding.

A further consideration for conventional traction control systems or ABS is that the wheel speed sensors are typically electromagnetic sensors which have significantly reduced sensitivity at low speeds, and often cannot detect speeds below 3km/h. Therefore, if the vehicle moves below this speed, the traction control system/ABS may be disabled or may operate with reduced functionality or reliability.

It is against this background that the invention has been devised.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided apparatus for use in a vehicle, comprising a wheel speed sensing system comprising a wheel speed sensor, the wheel speed sensing system being arranged to provide a first metric indicative of a rotational speed of a respective wheel. The apparatus further comprises a ground speed sensing system configured to determine, independently of the wheel speed sensor, a second metric indicative of a ground speed of the vehicle. The apparatus also comprises processing means configured to compare the first metric to the second metric to determine if the wheel is in a loss of traction condition.

The term 'metric' is used to denote a measurement unit that is common to both the wheel speed measurement and the vehicle ground speed measurement. This is indicative of the fact that while a rotational wheel speed is directly related to a linear vehicle speed, the two cannot be compared directly: at least one of these measurements must be converted into a format that allows for comparison with the other. Such a conversion would be apparent to the persons skilled in the art. Accordingly, the terms 'first metric' and 'second metric' are intended to cover both rotational speed and linear speed, with the implication that both the first and second metrics are in the same format, thereby enabling direct comparison. For example, both the first and second metrics could be linear speeds, or both could be rotational speeds.

By determining the first metric indicative of the ground speed of the vehicle without reference to a wheel speed measurement, the first metric provides a reliable indication of the vehicle ground speed which can be used as a reference. Therefore, the second metric can be compared with the first metric in order to determine a loss of traction condition for the respective wheel. The second metric relates to an individual wheel of the vehicle, and therefore the apparatus enables identification of instances of the monitored wheel falling into a loss of traction condition. Since the wheel is monitored independently of other wheels of the vehicle, the severity of traction loss in the wheel can also be determined, through analysing the difference between the first metric and the respective second metric.

Accordingly, the first metric may be an indicated vehicle ground speed, associated with a particular wheel, derived from a respective measured wheel speed, in which case the second metric is a measured vehicle ground speed. Alternatively, the first metric may be a measured wheel speed, in which case the second metric is an indicated wheel speed that is derived from a measurement of a ground speed of the vehicle. By enabling the apparatus to work in two alternative modes, the first and second metrics provide flexibility to the system. The ground speed sensing system may comprise at least one vehicle-mounted sensor associated with a respective vehicle subsystem. In this embodiment, the at least one vehicle mounted sensor may be at least one of: a radar sensor associated with an active cruise control subsystem; an acoustic sensor associated with a parking assist subsystem of the vehicle; and a GNSS sensor associated with a navigation subsystem of the vehicle. The apparatus may comprise a controller for calculating the ground speed of the vehicle, the controller being configured to receive a data input from the or each vehicle- mounted sensor, and to calculate a ground speed parameter based on the received data input. The processing means may be configured to output a signal if a wheel of the vehicle is in a loss of traction condition. This beneficially enables other systems of the vehicle to take corrective action. According to another aspect of the invention there is provided a traction control system for a vehicle, the traction control system comprising an apparatus according to the above aspect of the invention, and further comprising a control means configured to, in response to a detected discrepancy between said first metric and said second metric, output at least one of: a signal to a powertrain controller to reduce positive drive torque at said at least one wheel; a signal to a brakes controller to reduce a braking effort to said at least one wheel; or a signal to a brakes controller to increase a braking effort to said at least one wheel.

In a further aspect of the invention there is provided a vehicle comprising the apparatus or the system of the above aspects.

The wheel speed sensing system may comprise a respective wheel speed sensor for each wheel of the vehicle. This beneficially allows for monitoring of all of the wheels of the vehicle. In this embodiment the vehicle may be arranged to determine that the vehicle is in a loss of traction condition in the event that the measured speed of none of said vehicle wheels corresponds to the measured ground speed of the vehicle. This advantageously enables corrective action to be taken automatically in a total loss of traction event, for example if all wheels are slipping, or all wheels are locked and skidding.

In another aspect of the invention there is provided a method for controlling a vehicle, comprising: (i) determining a first metric indicative of a rotational speed of a respective wheel of the vehicle; (ii) determining a second metric indicative of a ground speed of the vehicle independent of the rotational wheel speed; (iv) comparing the first metric to the second metric to determine if the respective wheel is in a loss of traction condition; and (v) controlling the vehicle so as to regain traction of the wheel.

The measured vehicle ground speed may be determined using a vehicle-mounted sensor including at least one of: a radar sensor, and acoustic sensor, or a GNSS sensor.

The method may include outputting an alert if a wheel is in a loss of traction condition. The invention also embraces a computer program product executable on a processor so as to implement the method of the above aspect, to a computer readable medium loaded with the computer program product, to a processor arranged to implement the method or the computer program product of the above aspects, and also to a vehicle arranged to implement the method, or comprising the processor of the above aspects.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a vehicle apparatus;

Figure 2 is a schematic block diagram of a processing module of the vehicle apparatus;

Figure 3 is a flow chart of a method that may be implemented by the processing module of Figure 2;

Figure 4 is a schematic block diagram of a further processing module of the vehicle apparatus; and Figure 5 is a flow chart of a method that may be implemented by the processing module of Figure 2.

Detailed description Figure 1 shows in schematic form a vehicle 2 having a plurality of vehicle systems. It will be appreciated that Figure 1 is simplified for the purposes of this description and so is not meant to represent a complete electrical system of a vehicle. However, suitable components and functional modules are shown in order to provide an understanding of the inventive concept. In the following description it should be noted that where a controller or processor is described as being configured to perform a described function, this should be considered to mean that the processor includes a means for performing that function, for example that the processor may be programmed with a program, or may execute a program stored in an associated memory unit that causes the processor to perform that function.

In overview, the vehicle 2 comprises a plurality of acoustic sensors 6, a forward-looking radar sensor 8, and a GNSS sensor/receiver 10 that are interfaced with a vehicle local area network (LAN) 12. The system 4 also includes a navigation control module 14, an adaptive cruise control module 16, a park assist module 18, a ground speed determination module 20, a HMI module (human-machine interface) 22 and a vehicle control module 24, all of the aforesaid modules being interfaced to the LAN 12 so as to be able to communicate bi- directionally with various other vehicle sub-systems in accordance with a suitable communications protocol such as the CAN (controller area network) protocol which is well known in the art.

Typically, the HMI module 22 incorporates a display screen and an interface device such as a rotary selection dial, four-way directional selection buttons or a touchscreen interface, although other input means may also be used, for example voice activation. The HMI 22 is used to display alerts to the vehicle user regarding the appropriate vehicle set-up, and in response to which the user can adjust various vehicle settings, as appropriate. For example, the HMI module 22 may be used by the park assist module 18 to display information on the rear-facing view from the vehicle, or the navigation module 14 may display map and route information via the HMI module 22.

By way of further example, a vehicle user may use the HMI module 22 to access in-car entertainment systems or to access functionality provided by the vehicle control module 24. In some vehicles the vehicle control module 24 is configured to allow adjustments to be made to the ride characteristics of the vehicle. For example, in the context of a vehicle terrain response function 26 associated with the vehicle control module 24, data from vehicle-mounted sensors 28 (wheel speed sensors, tyre pressure sensors, brake force sensors, suspension articulation sensors, pitch sensors, yaw sensors and the like) relating to the terrain over which the vehicle is travelling are received by the vehicle control module 24 which is operable to process the data and transmit control commands to one or more further subsystems 30 of the vehicle (such as a suspension system, anti- lock braking system, engine torque vectoring system, stability control system or ride height adjustment system) and a conventional traction control system 32, so as to allow adjustment of the vehicle setup accordingly. The vehicle setup may be initiated by the user via the HMI module 22 or it may be controlled automatically by the vehicle control module 24. A traction detection module 34 is also provided within the system 4, the traction detection module 34 being used to detect a loss of traction of any of the wheels of the vehicle, as will be described later.

Although shown as a single control module for simplicity, it will be appreciated that the functions of the vehicle control module 24 may be performed by a plurality of electronic control units/modules (ECUs) each performing a specific function (e.g. Terrain Response function) and communicating with one another via the CAN protocol.

The above discussion provides a broad overview of the configuration of the electrical systems in the vehicle and, as has been mentioned, the vehicle 2 includes cruise control functionality provided by the adaptive cruise control module 16 and parking assistance functionality provided by the park assist module 18. Details of both of these functions will now be described in more detail. Adaptive cruise control function

Adaptive cruise control (ACC) functions for vehicles are known, and are operable to adjust the vehicle speed to maintain a defined distance from vehicle in the road ahead. Commonly, radar sensors are used to generate data about the traffic ahead of the vehicle for processing by a suitable processing system, although it should be noted that non-radar based systems are also in use, for example using video camera technology, lasers or acoustic-based sensing systems. Since adaptive cruise control functionality is generally known in the art, only a brief explanation will be described here. In the vehicle 2 described with reference to Figure 1 , the vehicle-mounted radar sensor 8 associated with the adaptive cruise control (ACC) module 16 is mounted in the centre of the front of the vehicle so that it has an unobstructed view of the road ahead. The radar sensor 8 has a radar transmitter 8a and a radar receiver 8b. Such radar sensors are known in the art, for example as part of the 'ACC Stop & Go' system provided by Bosch, and the multimode electronically scanning radar provided by Delphi Corporation.

The radar sensor 8 may be mounted in any suitable position, such as in the grille of the vehicle or, alternatively, mounted behind or integrated into a suitable trim-piece such as a bumper (fender), or fog lamp unit. Although the radar sensor 8 is described as being centrally mounted it is also acceptable for it to be mounted in an off-centre position.

At this point it should be appreciated that in principle any frequency of radar signal is applicable, although in the automotive industries the use of radar is currently licensed to the spectrum extending between 21 .65 to 26.65 GHz and 76 to 81 GHz. A particularly suitable type of radar sensor may be a frequency-modulated continuous-wave (FMCW) radar sensor.

In the embodiment of Figure 1 , the radar transmitter 8a and radar receiver 8b are oriented in alignment with a longitudinal axis L of the vehicle 2 such that a field of view of the radar receiver 8b is substantially symmetrical about the axis L and that the emission beam of the radar transmitter 8a irradiates a region ahead of the vehicle 2 that is also substantially symmetrical about the axis L. The irradiated region and the field of view are both shown here by a substantially conical region identified as reference '42'.

In order to detect vehicles in the road ahead accurately and at suitable distances in excess of 100 metres away it is preferred that the radar sensor has a relatively narrow beamwidth in the region of 10 degrees cone angle, by way of example. One example of a suitable system is the multimode electronically scanning radar as provided by Delphi Corporation which implements a narrow-beam long-range (approx. 174m) radar coverage in conjunction with a wide-beam mid-range radar coverage.

The ACC module 16 is configured to determine the range of objects (i.e. vehicles) ahead of the vehicle 2 by measuring a frequency difference between the signal transmitted by the radar transmitter 8a and the signal received by the radar receiver 8b. It is to be noted that alternative embodiments may be based on a time-of-flight analysis of the reflected radar signal to determine the range of objects. The ACC module 16 is further configured to determine the velocity of the objects in the road ahead relative to the velocity of the vehicle 2 based on the difference between the frequency of the radar return signal and the frequency of the transmitted radar signal. Due to the Doppler effect, the frequency of the radar signal return will be different to the emitted signal and so the ACC module 16 is able to calculate the speed of the object ahead relative to the speed of the vehicle in dependence on the frequency shift between the emitted and returned signals.

When the ACC module 16 is activated, which is usually on the demand of the user, it is operable to maintain the speed of the vehicle 2 whilst also maintaining a desired distance from another vehicle in the road ahead. The 'desired distance' is a predetermined distance between vehicles and may be a pre-programmed parameter within a suitable memory unit of the ACC module 16. The desired distance parameter may be adjustable by the user of the vehicle or, alternatively, manual adjustment may be limited (e.g. by a minimum separation distance) or prohibited in order to prevent possible abuse of the system.

In order to maintain the desired distance from the vehicle in front, the ACC module 16 communicates with other systems of the vehicle (throttle control, brake control etc. via the vehicle control module 24) and the necessary action is taken by those systems to maintain a constant distance to the vehicle in front.

Radar sensors may be positioned at other locations on the vehicle to collect data to be input to other systems, for example blind spot detection (BSD) systems, lane departure warning systems, or detection systems for detecting external static or portable speed measurement systems, such as those used for detecting vehicles exceeding speed limits.

As a known example of a lane change warning system, sometimes referred to as 'lane change merge aid', two 24 GHz radar sensors are mounted in the rear bumper of the vehicle (one on each side) that look in a 90 degree arc covering the side and the rear of the vehicle. These radar sensors look for targets at ranges of up to 80 m behind the vehicle to enable a warning to be given if a vehicle is approaching from behind when the driver chooses to change lanes. They are also able to offer the shorter range blind spot function. In the embodiment in Figure 1 a single radar sensor is provided, although it should be noted that more than one radar sensor is possible. For example, a combination of long range radar sensors and short range radar sensors could be employed, the short range radar sensors being particularly adept at providing information in the flank regions of the vehicle, for use in blind spot protection systems, lane change warning systems and the like.

Park assist function It is known to provide vehicles with systems that aid the driver of the vehicle to park in tight spaces, particularly during parallel parking manoeuvres. Relatively simple systems are based around providing an array of parking distance control (PDC) sensors on the rear edge of a vehicle, typically integrated within the bumper/fender. More recently, however, more sophisticated systems have been developed which provide the vehicle with an all-round sensing capability and which are operable to identify a suitable space in which a vehicle should be able to park and to control the vehicle automatically to park within the identified space. In the art, such systems may be referred to by a variety of terms such as 'parking assist systems', 'intelligent parking systems', and 'smart parking systems'.

With reference to Figure 1 , the vehicle is provided with a parking assist function by the park assist module 18 that is provided with data regarding the vicinity of the vehicle by the acoustic sensors 6. The acoustic sensors 6 are ultrasonic transceivers that are positioned at respective locations around the periphery of the vehicle 2. In the embodiment shown, four ultrasonic sensors 6a are installed in the front edge of the vehicle (for example integrated in the bumper), one either side of the radar sensor 8. Four ultrasonic sensors 6b are positioned on the rear edge of the vehicle 2 (e.g. integrated into the rear bumper), two ultrasonic sensors 6c are mounted at spaced apart locations on the right hand side of the vehicle and two ultrasonic sensors 6d are mounted at spaced apart locations on the left hand side of the vehicle. All of the ultrasonic sensors 6 are linked to the LAN 12 and so are able to communicate with the park assist module 18. The ultrasonic sensors 6a installed at the front of the vehicle 2 are oriented to direct an ultrasonic signal in a forwards direction. Likewise, the ultrasonic sensors 6a are arranged to direct respective signals rearwards of the vehicle and the ultrasonic sensors installed 6c, 6d in the sides of the vehicle are arranged to emit respective signals perpendicularly away from the longitudinal axis L of the vehicle 2. Also, it should be noted that the ultrasonic sensors 6c, 6d are inclined towards the road surface so as to be able to pick up low-lying obstacles in the road such as kerbs. The sensors 6c, 6d may be inclined at a range of angles, but it is currently envisaged that the sensors are angled 45 degrees to the horizontal.

The ultrasonic transceivers 6 preferably operate at a frequency between 40 and 55 kHz, more specifically about 51 kHz. One such sensor that may be used in such a system is available from Knowles Acoustics Ltd, model number SPM0204UD5.

The park assist module 18 is operable to receive data from all of the ultrasonic sensors 6 over the LAN 12 and process the received data to build up an image of the obstacles surrounding the vehicle. In particular the side-mounted sensors 6c, 6d are operable to determine the location of gaps in rows of parked cars, but also to determine the location of other obstructions such as kerbs which the park assist module 18 can use in order to position the vehicle correctly in a parking space. The parking assist module 18 is operable to warn a vehicle user, either by visual or audible means, of the vehicle's proximity to an obstacle. In the case of an audible warning, a warning tone may sound at an increasing rate or volume as an obstacle becomes closer to the vehicle. The acoustic sensors used for parking assistance systems are typically able to detect obstacles at short-range (0.25-2.5 metres) but at a wide angle from the direction in which the sensor is pointed.

It is to be noted that in general parking assist system are known in the art so a detailed explanation of such a system will not be provided here.

The data generated by the ultrasonic sensors 6a-d may also be used to provide information relating to the ground speed of the vehicle since, due to the Doppler effect, the signal return to the sensors will have a frequency shift compared to the signal emitted by the sensors 6a-d. This data may therefore be used by the ground speed determination module to calculate the ground speed of the vehicle in a manner that will now be described.

Determination of vehicle ground speed The above described systems are regularly included in vehicles as standard options. Each system is generally only used for short periods during driving, for example during a parking manoeuvre. Therefore, the sensors and processors associated with each system are idle for long periods. Accordingly, there is an opportunity to use these sensors for other purposes during these periods. One such use will now be described.

Indicated vehicle speed is usually presented to the vehicle user by a speedometer which is often mounted in an instrument cluster located in front of the driver and behind the steering wheel in a visible position. Typically the speedometer will base the presented vehicle speed on data that is gathered from rotation sensors integrated into the wheels of the vehicle or, alternatively, on the vehicle drive shaft downstream of the gearbox.

However, this vehicle speed data may not be a reliable indication of the true ground speed of the vehicle in all circumstances because it is based in the assumption that wheel rotation will always be translated directly into vehicle movement. As noted previously, in many circumstances, particularly during slippery conditions or during off- road driving, this is not the case and reliance on the speed of rotation of the wheels to provide true ground speed data provides a misleading indication of vehicle speed. Furthermore, speed sensing systems that are based on wheel speed rotation generally are not able to detect speeds lower than about 3kph, which limits how that data can be used by other systems of the vehicle.

Accurate knowledge of the ground speed of the vehicle is desirable to enhance the controllability of the vehicle during low traction conditions, for example when the vehicle is travelling on icy or wet/muddy ground, and/ or when the vehicle is in a skid situation. To this end, the ground speed determination module 20 is operable to receive data from a plurality of sensing systems of the vehicle and provide as an output a value of vehicle ground speed to a plurality of client systems of the vehicle.

The ground speed determination module 20 (hereinafter 'GSD module') is shown in Figure 1 in the context of the vehicle, and is illustrated schematically in more detail in Figure 2 as incorporating a hardware configuration including at least a processing means or 'controller' 50 that is operable to perform control processing, a ROM (read only memory) 52 in which control programs for implementation by the controller 50 are stored, and a RAM (random access memory) 54 for the purposes of the temporary storage of data during the operation of the GSD module 20. The GSD module 20 also includes an I/O unit (input/output) 56 which acts as an interface between the LAN 12 and the controller. The ROM 52, RAM 54, controller 50 and I/O unit 56 are linked by suitable data buses 58 or, alternatively, they may be incorporated into a single solid-state device.

The GSD module 20 is operable to calculate the absolute ground speed of the vehicle independent of the rotational speed of the wheels and, to this end, the GSD module 20 receives data from a plurality of vehicle sensor systems into the I/O unit 56. As illustrated, the GSD module 20 receives a first data input 60 from the GNSS receiver 10 (GNSS data input), a second data input 62 from the radar sensor 8 (radar data input) and a third data input 64 from one or more ultrasonic sensors 6 (ultrasonic data input).

Although the GSD module 20 is shown here as accepting three data inputs, it should be appreciated that the GSD module 20 may be configured to receive further input data from systems that are capable of providing measurements of the ground speed of the vehicle. For example, the vehicle may incorporate an inertial measurement unit (IMU) that uses accelerometers and gyroscopes to calculate by way of dead reckoning the position, orientation and velocity of the vehicle, or may use optical tracking methods, for example using data streams from pre-existing cameras already placed on the vehicle. Alternatively a radio location system could be used to obtain location information and therefore derive a ground speed from, for example by triangulation from WiFi, DAB radio signals, DTV transmissions etc.

It should be noted that none of the vehicle sensor systems that provide data to the GSD module 20 are intended primarily for that purpose. For example, the radar sensor 8 forms part of the adaptive cruise control function and the ultrasonic sensors 6 form part of the park assist function. The functionality of the GSD module 20 in this embodiment is therefore provided for the vehicle with minimal further hardware costs since dedicated sensor suites are not required.

In overview, the GSD module 20 receivers several sources of ground speed data through the plurality of data inputs 60,62,64 and arbitrates between the different data inputs to provide a ground speed data output 66 to various client systems of the vehicles. In this embodiment the process of arbitrating between the data inputs 60-64 is based partly upon the suitability of the prevailing vehicle operating condition and partly on the determined reliability of the data inputs. Note that the prevailing vehicle operating condition is determined from a plurality of vehicle operating parameters, identified here by the general reference 68.

The client systems may be any vehicle system that is able to make use of an accurate and precise measurement of the absolute ground speed of the vehicle. Although not described specifically here, examples of such client systems may be: a hill descent system in which the vehicle is controlled to descend a hill at a predetermined speed, a controlled stop system in which the vehicle is controlled to come to a halt at a predetermined low rate of deceleration, a launch control system in which the vehicle traction control system is controlled to accelerate the vehicle at an optimal rate according to the surface conditions, a stability control system, a torque vectoring system, and a terrain response system.

In one embodiment, the controller 50 is operable to implement a method by which it arbitrates between the multiple data inputs 60-64 in dependence on one or more of (i) the reliability of the data inputs and (ii) a vehicle operating condition, and then provides priority to one of the data inputs in order to calculate the ground speed of the vehicle. This embodiment will now be described with reference to Figure 3. The process 100 begins at step 102 upon activation of the vehicle ignition. At step 104 the controller 50 begins the process of monitoring the ground speed data inputs 60-64 to identify which data inputs are available to it over the LAN 12. The controller 50 also monitors the vehicle operating condition by analysing the plurality of vehicle operating parameters 68. One such vehicle operating parameter may be vehicle speed as indicated by one or more of the wheel speed sensors 28.

At step 106 the controller 50 selects one of the data inputs 60-64 and allocates this data input priority for use in downstream calculations. Then, at step 108, the prioritised data input is used to calculate a ground speed parameter which is therefore provided to one or more client systems via data output 66. By way of example, if the controller 50 determines that the indicated speed of the vehicle 2 is over a first predetermined threshold, for example 5mph, the controller 50 may be configured to prioritise the GNSS data input 60, calculate a ground speed parameter from the GNSS data input 60 and output the ground speed parameter to the client systems via data output 66. It should be appreciated that at vehicle speeds over 5mph, the ground speed data provided by the GNSS receiver 10 is considered to be accurate to within 5% which is an acceptable precision to the client systems.

Following the determination of which data input 60-64 should be prioritised for use in the calculation of the ground speed data output 66, the controller 50 then checks, at step 1 10, the reliability of the prioritised data input source 60-64, which in this example is GNSS data 60.

In order to provide a metric of the reliability of data, most input data sources are provided with a confidence level indication. For example, in a GPS system (a type of GNSS), a 'dilution of precision' or DOP is provided. Such a metric indicates the confidence in the data source which may be used to rank data sources in terms of their reliability.

The process 100 then enters a decision step 1 12 the output of which depends on the reliability of the prioritised data input 60. If the data input 60 is determined not to be reliable, the process returns to step 108 through step 1 14. At step 1 12 a different data input source 60-64 is prioritised for the purposes of calculating the ground speed data output 66 at step 108. By way of example, the radar data input 62 may be identified as the next data input to be prioritised in preference to the GNSS data input 60 if said GNSS data is determined to be unreliable, for example, if the vehicle has limited satellite coverage as would be the case if the vehicle enters a tunnel or travels under a thick tree canopy. One option is for the multiple data inputs to have a dynamic Order of preference' that depends on the reliability of the data inputs. So, more reliable data inputs will have a higher rank in the order of preference than less reliable data inputs.

If, however, the reliability of the selected data input 60 is determined to be acceptable at step 1 12, then the process continues to step 1 16 at which step the operating condition of the vehicle is checked to confirm that the prioritised data input 60 is suitable for use in calculating the ground speed data output 66. It should be noted that in order to determine the vehicle operating condition, the controller 50 may be provided with a suitable database in ROM 52 that cross-references a plurality of predefined vehicle operating conditions to one or more of the associated vehicle operating parameters 68. For example, a vehicle operating condition 'high speed travel' may be associated with an indicated vehicle speed of greater than 5mph. Some examples of other vehicle operating conditions that may be useful for determining whether the prioritised data input is suitable are high/low range gearing; ambient temperature thresholds; suspension ride height, GPS position and water wading.

The process then enters decision step 1 18 the output of which depends on the suitability of the prioritised data input 60 for the current vehicle operating condition. If the prioritised data input is determined not to be suitable for the current vehicle operating condition, the process moves to step 120 where the controller re-prioritises the data input 60-64 that is used to calculate the ground speed data output 66 subsequently at step 108. As an example of this, consider the case where the currently prioritised data input source is GNSS data 60. If the vehicle is travelling at greater than 5mph, the controller 50 may determine that GNSS data input source 60 is suitable for calculating the ground speed data output 66. However, if the vehicle speed falls below 5mph, the controller 50 may determine that GNSS data is not sufficiently accurate to be suitable for the current vehicle operating condition and may therefore re-prioritise the radar data input source 62 for calculation of the ground speed data output 66.

Returning to the decision step 1 18, if it is determined that the currently prioritised data input 60 is suitable for the current vehicle operating condition, the process moves to step 122 at which the controller 50 maintains the selection of the currently prioritised data input 60. The process then terminates at step 124.

The above embodiment describes the process 100 as it operates once from start to finish and it should be noted that the process may be configured to be run repeatedly at a suitable frequency in order to ensure that the appropriate data source is prioritised for calculation of accurate ground speed data. It is currently envisaged that a repeat frequency of 1 Hz would be acceptable, although a faster or slower rate would also be acceptable. However, the calculation of the ground speed data output 66 at 108 may run as a background task at a higher rate and it is currently envisaged that the controller 50 will output the ground speed data output 66 at a frequency of between 5 and 10 Hz.

Traction control system

The traction control system 32 is a further example of a system that may be included on modern vehicles. In this embodiment, the traction control system 32 has reduced responsibility relative to a conventional vehicle system, in that it receives an input from the traction detection system 34 which indicates when a wheel of the vehicle has lost traction, as will be described below. Therefore, in this embodiment the traction control system 32 is used only for effecting corrective action in the event that traction loss of one or more wheels is detected. To this end, the traction control system 32 outputs control signals to the vehicle control module 24 through the LAN 12.

As shown in Figure 1 , the traction control system 32 is connected to the LAN 12, and so receives input from other components belonging to the vehicle system 4.

By way of providing context for the invention, in a conventional vehicle a traction control system receives data input from wheel speed sensors, and analyses the data to detect loss of traction of any of the wheels of the vehicle. This is primarily achieved by comparing the individual wheel speeds to identify differences between them. In contrast however, the present invention detects loss of traction and the extent of loss of traction by comparing a signal indicative of the wheel speed to a signal indicative of a directly measured speed over the ground which is independent of the rotational speed of the wheels.

As noted previously, the known approach is effective for vehicles in which some wheels are not driven and/or braked, as the traction control system can use such wheels as a reference in to determine when the driven/braked wheels are in either: a wheel spin condition, in which the wheel spins relative to the driving surface; or a locked condition, in which the wheel does not rotate and skids on the driving surface. However, in a vehicle in which all wheels are driven and/or braked, this approach cannot be used, since it is possible for all wheels to spin/lock simultaneously. Therefore, such systems may rely on detecting developing trends in wheel speed differences in order to estimate when a wheel has lost traction, which is less effective.

Returning to the Figure 1 embodiment, as noted above the traction control system 32 relies on an input provided by the traction detection system 34 to indicate when a wheel has lost traction. The traction control system 32 also receives wheel speed data input from the wheel speed sensors 28, but in this embodiment this data is used only to aid control during an intervention procedure when the traction control system 32 attempts to regain traction. Once it has been established that a wheel has lost traction, the traction control system 32 implements appropriate measures to regain traction. In this embodiment, the traction control system 32 intervenes in the same manner as in the conventional arrangement in order to maintain traction.

If a wheel is spinning, the traction control system 32 mitigates this by reducing the torque applied to the wheel. This is achieved by applying braking force to the wheel, reducing the power transmitted to the wheel, or a combination of the two. Incoming data from the wheel speed sensors 28 provides feedback enabling the traction control system 32 to control the intervention more effectively. In the reverse scenario where a wheel has locked under braking, the traction control system 32 (or an anti-lock braking system, a variant of conventional traction control systems) intervenes by reducing the brake force applied to the wheel. Typically, the traction control system 32 then pumps the brake in order to slow the vehicle whilst avoiding another occurrence of wheel locking. As above, wheel speed feedback can be used to refine the process.

Traction detection function

The above described system beneficially provides a measurement of the vehicle ground speed independently of data obtained from the wheel speed sensors. In this way, vehicle speed measurement is decoupled from wheel speed measurement.

The vehicle ground speed output from the GSD module 20 can be used in combination with the known diameter of each wheel to calculate respective expected wheel speeds. Typically, each wheel of the vehicle is of substantially the same diameter, and so a common expected wheel speed is calculated. Wheel speed data obtained from each wheel of the vehicle can then be converted into respective parameters or 'metrics' of indicated vehicle ground speeds corresponding to each wheel, which can be compared with the measured vehicle ground speed in order to identify discrepancies, which are indicative of loss of traction of one or more of the wheels. Conveniently, the conversion of wheel speed into an indicated vehicle speed is already handled by a conventional speedometer system, although this is only applicable when the wheel speeds are in agreement. For example, if an indicated vehicle speed is higher than the measured ground speed, assuming there has not been an error, this indicates that the wheel has lost traction and is spinning. This is particularly the case if the GSD module 20 indicates that the vehicle is stationary.

In the reverse situation, if a wheel speed sensor indicates that the respective wheel is not rotating while the GSD module 20 indicates that the vehicle is moving, or the wheel is rotating at a slower rate than expected based on the GSD module 20, this indicates that the wheel has locked and/or the vehicle is skidding.

Advantageously, outputs from each individual wheel speed sensor 28 can be compared with the vehicle ground speed in order to establish which wheels have lost traction at any particular moment. Furthermore, since traction loss is detected by reference to the vehicle ground speed, the system is more responsive than conventional systems for four wheel drive vehicles which rely on identifying developing differences in wheel speeds between individual wheels.

It is an added advantage that if, for example, a vehicle is experiencing side slip, the current system which measures speed over ground will identify this component of vehicle movement. In contrast, in a conventional system side slip would have little impact on wheel speed sensors, and so the implied speed over ground derived from wheel speed sensors will not reflect any element of vehicle motion due to side slip.

Once it has been determined that a wheel has lost traction, this information is passed to the traction control system 32, enabling the vehicle to take corrective action in conventional manner as described above. For example, reduced torque can be applied to a spinning wheel, or a brake can be released and subsequently pumped on a wheel that is locking.

In this embodiment, the determination of loss of traction is performed by the traction detection module 34. However, in other embodiments this function can be performed by an adapted traction control module, or by the vehicle control module 24.

Figure 4 illustrates a traction detection module 34 according to an embodiment of the invention. The traction detection module 34 incorporates a hardware configuration including at least a processing means or 'controller' 130 that is operable to perform control processing, a ROM (read only memory) 132 in which control programs for implementation by the controller 130 are stored, and a RAM (random access memory) 134 for the purposes of the temporary storage of data during the operation of the traction detection module 34. The traction detection module 34 also includes an I/O unit (input/output) 136 which acts as an interface between the LAN 12 and the controller. The ROM 132, RAM 134, controller 130 and I/O unit 136 are linked by suitable data buses 138 or, alternatively, they may be incorporated into a single solid-state device.

The traction detection module 34 is operable to detect a loss of traction of a vehicle wheel through comparing wheel speed data and vehicle ground speed data. To this end, the traction detection module 34 receives data from a plurality of vehicle sensor systems into the I/O unit 136. As illustrated, the traction detection module 34 receives a first data input 140 from the GSD module 20 (ground speed data input), and a second data input 142 from the wheel speed sensors 28 (wheel speed data input).

The data collected from the inputs 140, 142 is analysed by the controller 130 in order to produce an output 144 which indicates which wheels of the vehicle have lost traction. Although not shown here, it is envisaged that the output 144 is transmitted onto the vehicle network for use by the traction control system 32 as described above, which may make use of such information in order to regulate power supplied to the driven wheels of the vehicle to avoid loss of traction under slippery conditions.

With reference now to Figure 5, a process 150 for determining loss of traction of a vehicle wheel is described, the process 150 being implemented by the traction detection module 34. For clarity, the process 150 is described in relation to a single wheel, although it will be appreciated that in reality each wheel of the vehicle is monitored.

The process 150 begins at Step 152 upon activation of the vehicle ignition, with the traction detection module 34 receiving at Step 154 from the GSD module 20 an input indicating the vehicle ground speed. For example, this input may be a result from the process 100 described above with reference to Figure 3.

Returning to Figure 5, during the time in which Step 154 completes, a concurrent process obtains at Step 156 a wheel speed data input to indicate the rotational speed of the wheel. The traction detection module 34 then uses the rotational speed of the wheel to calculate at Step 158 an indicated vehicle speed. Note that the term 'indicated vehicle speed' is used here to mean a predicted value for the vehicle speed based on the measured rotational speed of the wheel. Next, the indicated vehicle speed calculated at Step 158 is compared at Step 160 with the measured vehicle speed obtained at Step 154. The traction detection module 34 then determines at Step 162 whether the difference between the indicated vehicle speed and the measured vehicle speed is within an acceptable deviation range. Due to the tolerances associated with such measurements, the acceptable deviation range is required in order to prevent erroneous triggering of a traction loss alert. The acceptable deviation range is typically relatively small in order to maintain a satisfactory level of control.

If the traction detection module 34 finds at Step 162 that the difference between the measured vehicle speed and the indicated wheel speed is within the deviation range, the process 150 returns to Step 152 and re-commences. If it is found that the measured vehicle speed is outside the deviation range, the traction detection module 34 then determines at Step 164 the category of traction loss, i.e. whether the wheel is spinning or skidding. The traction detection module 34 then outputs at Step 166 a traction loss alert to the traction control module 32, which can then take corrective action in order to regain traction. The process 150 then ends at Step 168. After completion, the process 150 re-iterates continuously in order to monitor for loss of traction of the wheel and thereby provide real-time traction data.

It is noted that although in the above described process 150, Steps 154 and 156 are conducted concurrently. Steps 154 and 156 may have dissimilar refresh rates. For example, the vehicle ground speed may be updated every second, while the wheel speed data refreshes at a rate of 10Hz. In this instance, the process 150 loops at a rate equal to the fastest sub process, in this example 10Hz. The previous result from the slower sub process, in this case the ground speed determination, is used in each iteration of the process 140 until that measurement is next updated. As such, each of Steps 154 and 158 can entail either receiving data from external inputs, or receiving data from the previous iteration of the process 140.

Alternatively, the process 140 may iterate at the rate of the slower sub-process in order to avoid re-using previous data, providing acceptable performance is maintained. The above process provides a particular benefit in identifying when a vehicle is in an 'all wheel lock' or an 'all wheel spin' condition. Since the process compares metrics relating to the indicated vehicle speed, that is to say wheel speed data as received from the wheel speed sensors, with a metric relating to the true ground speed of the vehicle that is independent of the speed of the wheels, the behaviour of the wheels in an 'all wheel lock' or an 'all wheel spin' condition can be determined rapidly and corrective action can be taken. Such capability is particularly helpful when launching the vehicle from a standstill in very slippery condition such as on wet grass, and even more so when the vehicle is towing a trailer for example.

The measured wheel speed may be adjusted to take into account a steering angle of the vehicle. This is due to the fact that, during a turning manoeuvre in which the vehicle follows a curved path, the inside wheels follow a shorter path than the outside wheels. Consequently, the outside wheels rotate faster than the inside wheels. Therefore, for example, an indicated vehicle speed based on an outside wheel during cornering will be too high unless this effect is accounted for.

It will be appreciated that variations to the above embodiments may be made without departing from the scope of invention as defined by the claims.

For example, in the above process 100 the selection that is made between ground speed data input sources is dependent on both of: (i) the prevailing vehicle operating condition; and (ii) the reliability of the data input source. However, it should be appreciated that the process may also be implemented so that the selection that is made between ground speed data input sources is dependent on only one of: (i) the prevailing vehicle operating condition; or (ii) the reliability of the data input source.

The embodiment described above discusses radar and acoustic sensors that are used for other purposes on the vehicle which minimises the manufacturing cost of adding the ground speed calculating function to the vehicle. However, it should be appreciated that dedicated sensing hardware may also be added to the vehicle. Alternatively, existing sensing hardware may be modified to optimise it for dual-use in multiple systems. In one embodiment, for example, a sensor data package combining radar and ultrasonic sensors may be arranged on each of the four corners of the vehicle. This is illustrated in schematic form in Figure 1 by the ghosted components referenced as 70. To optimise the sensor packages 70 for reception of Doppler data, the sensor packages may be angled so that they point towards the ground.

In the description above, the traction detection module 34, the ground speed determination module 20, the park assist module 18, the adaptive cruise control module 16 and the navigation module 14 have been described as distinct functional modules. As such, they should be considered to represent separate processing functions provided by suitable electronic equipment in the vehicle. However, it will be appreciated that the functions may not be provided by physically separate processing entities and may instead be provided by an integrated processing entity such as a vehicle control module as is generally known in the art.

As a further example, in another embodiment of the above process 150 for detection of loss of traction, the traction detection module 34 uses the measured vehicle ground speed to calculate an expected wheel speed, and then compares this with the measured wheel speed to identify instances of loss of traction.

In another embodiment, two sensors are arranged on the vehicle at different orientations so as to determine a speed vector, i.e. an indication of both speed and direction. For example, the two sensors could be orthogonally positioned. By pointing out at different angles, the sensors provide vehicle ground speed data in two different directions. These two readings can be resolved to obtain a true speed vector for the vehicle.

Equally, a sensor having a wide field of view and a fine angular orientation can be used to similar effect, in that a beam can be scanned to effectively provide readings in different directions.

The invention will now be expressed in the following numbered clauses: 1 . Apparatus for use in a vehicle, comprising: a wheel speed sensing system comprising a wheel speed sensor, the wheel speed sensing system being arranged to provide a first metric indicative of a rotational speed of a respective wheel; a ground speed sensing system configured to determine a second metric indicative of a ground speed of the vehicle independent of the wheel speed sensor; and a processor configured to compare the first metric to the second metric to determine if the wheel is in a loss of traction condition.

The apparatus of clause 1 , wherein the first metric is an indicated vehicle ground speed derived from a measured wheel speed, and the second metric is a measured vehicle ground speed.

The apparatus of clause 1 , wherein the first metric is a measured wheel speed, and the second metric is an indicated wheel speed that is derived from a measurement of a ground speed of the vehicle.

The apparatus of clause 1 , wherein the ground speed sensing system comprises at least one vehicle-mounted sensor associated with a respective vehicle subsystem.

The apparatus of clause 4, wherein the at least one vehicle mounted sensor is at least one of: a radar sensor associated with an active cruise control subsystem; an acoustic sensor associated with a parking assist subsystem of the vehicle; and a GNSS sensor associated with a navigation subsystem of the vehicle.

The apparatus of clause 4, comprising a controller for calculating the ground speed of the vehicle, wherein the controller is configured to receive a data input from the or each vehicle-mounted sensor, and to calculate a ground speed parameter based on the received data input.

The apparatus of clause 1 , wherein the processor is configured to output a signal if the wheel of the vehicle is in a loss of traction condition.

A vehicle traction control system comprising: a wheel speed sensing system comprising a wheel speed sensor, the wheel speed sensing system being arranged to provide a first metric indicative of a rotational speed of a respective wheel; a ground speed sensing system configured to determine a second metric indicative of a ground speed of the vehicle independent of the wheel speed sensor; and a processor configured to compare the first metric to the second metric to determine if the wheel is in a loss of traction condition; the traction control system further comprising a controller configured to, in response to a detected discrepancy between said first metric and said second metric, output at least one of: a signal to a powertrain controller to reduce positive drive torque at said at least one wheel; a signal to a brakes controller to reduce a braking effort to said wheel; or a signal to a brakes controller to increase a braking effort to said wheel.

A vehicle comprising: a wheel speed sensing system comprising a wheel speed sensor, the wheel speed sensing system being arranged to provide a first metric indicative of a rotational speed of a respective wheel; a ground speed sensing system configured to determine a second metric indicative of a ground speed of the vehicle independent of the wheel speed sensor; and a processor configured to compare the first metric to the second metric to determine if the wheel is in a loss of traction condition.

A vehicle comprising a traction control system, the traction control system comprising: a wheel speed sensing system comprising a wheel speed sensor, the wheel speed sensing system being arranged to provide a first metric indicative of a rotational speed of a respective wheel; a ground speed sensing system configured to determine a second metric indicative of a ground speed of the vehicle independent of the wheel speed sensor; and a processor configured to compare the first metric to the second metric to determine if the wheel is in a loss of traction condition; the traction control system further comprising a controller configured to, in response to a detected discrepancy between said first metric and said second metric, output at least one of: a signal to a powertrain controller to reduce positive drive torque at said at least one wheel; a signal to a brakes controller to reduce a braking effort to said wheel; or a signal to a brakes controller to increase a braking effort to said wheel.

The vehicle of clause 9, wherein the wheel speed sensing system comprises a respective wheel speed sensor for each wheel of the vehicle.

The vehicle of clause 10, wherein the wheel speed sensing system comprises a respective wheel speed sensor for each wheel of the vehicle.

The vehicle of clause 1 1 , arranged to determine that the vehicle is in a loss of traction condition in the event that the measured speed of none of said vehicle wheels corresponds to the measured ground speed of the vehicle.

The vehicle of clause 12, arranged to determine that the vehicle is in a loss of traction condition in the event that the measured speed of none of said vehicle wheels corresponds to the measured ground speed of the vehicle.

A method for controlling a vehicle, comprising: i. determining a first metric indicative of a rotational speed of a wheel of the vehicle; ii. determining a second metric indicative of a ground speed of the vehicle independent of the rotational wheel speed; iii. comparing the first metric to the second metric to determine if the wheel is in a loss of traction condition; and iv. controlling the vehicle so as to regain traction of the wheel.

The method of clause 15, wherein the first metric is an indicated vehicle ground speed based on a measured wheel speed, and the second metric is a measured vehicle ground speed. The method of clause 15, wherein the first metric is a measured wheel speed, and the second metric is an indicated wheel speed that is derived from a measurement of a ground speed of the vehicle.

The method of clause 16 or clause 17, wherein the measured vehicle ground speed is determined using a vehicle-mounted sensor including at least one of: a radar sensor, and acoustic sensor, or a GNSS sensor.

The method of clause 15, including outputting an alert if the wheel is in a loss of traction condition.

A computer program product executable on a processor so as to implement a method for controlling a vehicle, comprising: i. determining a first metric indicative of a rotational speed of a wheel of the vehicle; ii. determining a second metric indicative of a ground speed of the vehicle independent of the rotational wheel speed; iii. comparing the first metric to the second metric to determine if the wheel is in a loss of traction condition; and iv. controlling the vehicle so as to regain traction of the wheel.

A non-transitory computer readable medium loaded with the computer program product of clause 20. A processor arranged to implement the method of clause 15, or the computer program product of clause 20. A vehicle arranged to implement the method of clause 15, or comprising the processor of clause 22.