TRACTION CONTROL CONSIDERING WHEEL SLIP, PITCH AND HEAVE

Abstract

A traction control system for a motor vehicle includes a controller configured to initiate a traction control intervention at one or more vehicle wheels. The controller is configured to inhibit the traction control intervention in dependence on a reduced wheel load condition in said one or more wheels. The reduced wheel load condition is identified based on at least one of a signal indicative of vehicle pitch and a signal indicative of vehicle heave.

Claims

1. A traction control system for a motor vehicle, the traction control system comprising an electronic controller configured to identify a wheelslip condition and initiate a traction control intervention at one or more vehicle wheels in dependence on the wheelslip condition, wherein the electronic controller is configured to modify the traction control intervention in dependence on a reduced wheel load condition in said one or more wheels, the reduced wheel load condition being identified based on at least one of: a signal indicative of vehicle pitch; and a signal indicative of vehicle heave, wherein the controller is configured to modify the traction control intervention by inhibiting the traction control intervention.

2. (canceled)

3. The traction control system of claim 1, wherein the controller is configured to inhibit the traction control intervention such that the severity of the traction control intervention is reduced based on the reduced wheel load condition.

4. The traction control system of claim 1, wherein the controller is configured to inhibit the traction control intervention such that the traction control intervention is eliminated based on the reduced wheel load condition.

5. The traction control system of claim claim 1, wherein the controller is configured to scale or customize inhibition of the traction control intervention in dependence on the identified reduced wheel load condition.

6. The traction control system of claim 1, wherein the controller is configured to carry out at least one of: omit inhibition of the traction control intervention in an off-road mode of the vehicle; and modify the traction control intervention by enhancing the traction control intervention in an off-road mode of the vehicle.

7-8. (canceled)

9. The traction control system of claim 1, wherein the reduced wheel load condition is an airborne wheel condition.

10. The traction control system of claim 1, wherein the traction control intervention comprises one or more of: braking said one or more wheels; and a reduction in an engine torque driving said one or more wheels.

11-12. (canceled)

13. The traction control system of claim 1, wherein the signal indicative of vehicle pitch comprises vehicle pitch data and/or the signal indicative of vehicle heave comprises vehicle heave data.

14. The traction control system of claim 13 wherein the vehicle pitch data comprise a pitch profile over time associated with the reduced wheel load condition, wherein the pitch data comprise an inertial pitch sensor signal, wherein the heave data comprise a heave profile over time associated with the reduced wheel load condition, and/or wherein the heave data comprise an inertial heave sensor signal.

15-17. (canceled)

18. The traction control system of claim 13, wherein the reduced wheel load condition is also identified based on additional data selected from one or more of yaw data, roll data, longitudinal acceleration, lateral acceleration, and speed data of the vehicle.

19. The traction control system of claim 13, wherein the controller is configured to receive at least one of the pitch data and the heave data, and optionally additional data, and to identify the reduced wheel load condition based on the received data, wherein the controller is configured to identify the reduced wheel load condition by comparing the received data with reference data, and/or wherein the controller is configured to compare a profile over time associated with the received data with a reference profile to identify the reduced wheel load condition.

20-21. (canceled)

22. The traction control system of claim 1, wherein the controller is configured to initiate a plurality of distinct traction control interventions in a plurality of wheels and to modify each intervention in dependence on an identified wheel load condition in the associated wheel or wheels.

23. A vehicle comprising a plurality of wheels, a powertrain, a brake system, sensing means for sensing at least one of vehicle pitch data and vehicle heave data, and a traction control system according to claim 1, the traction control system being configured to initiate traction control intervention in at least one of the plurality of wheels.

24. A method of controlling traction at one or more wheels of a motor vehicle, the method comprising: identifying a wheelslip condition in said one or more wheels, identifying a reduced wheel load condition in said one or more wheels based on at least one of vehicle pitch data and vehicle heave data; and determining a modified traction control intervention in dependence on the wheelslip condition and the reduced wheel load condition, wherein determining a modified traction control intervention comprises inhibiting the traction control intervention.

25. (canceled)

26. The method of claim 24 wherein the intervention is entirely inhibited.

27. The method of claim 24, wherein the inhibited traction control intervention comprises at least one of braking said one or more wheels and a reduction in an engine torque driving said one or more wheels.

28-31. (canceled)

32. The method of claim 24, comprising identifying the reduced wheel load condition based on additional data selected from one or more of yaw data, roll data, longitudinal acceleration, lateral acceleration, and speed data of the vehicle.

33-34. (canceled)

35. The method of claim 24, wherein the reduced wheel load condition is an airborne wheel condition.

36. A non-transitory carrier medium carrying computer readable code for controlling a vehicle to carry out a method according to claim 24.

37-38. (canceled)

39. An electronic controller for a vehicle having a storage medium associated therewith storing instructions that when executed by the controller cause the determination of a modified traction control intervention in accordance with a method comprising: identifying a wheelslip condition in said one or more wheels, identifying a reduced wheel load condition in said one or more wheels based on at least one of vehicle pitch data and vehicle heave data; and determining a modified traction control intervention in dependence on the wheelslip condition and the reduced wheel load condition, wherein the controller is configured to modify the traction control intervention by inhibiting the traction control intervention.

40-41. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0070] FIG. 1 is a schematic view of a vehicle comprising a traction control system in accordance with an embodiment of the invention;

[0071] FIG. 2 is a flow diagram illustrating traction control functions carried out in an electronic control unit of the vehicle of FIG. 1; and

[0072] FIG. 3 is an illustration of pitch data obtained while the vehicle of FIG. 1 travelled over a speed bump.

DETAILED DESCRIPTION

[0073] With reference to FIG. 1, a motor vehicle 2 according to an embodiment of the invention comprises a pair of front wheels 4, a pair of rear wheels 6, a powertrain 8, a brake system 10, vehicle sensors 12, and a traction control system 14.

[0074] The powertrain 8 comprises an engine 16 for generating torque and a driveline 18 having a transmission 20 for transmitting the torque to the wheels 4, 6. The driveline 18 is arranged to drive the front wheels 4 by means of a front differential 22 and a pair of front drive shafts 24. The driveline 18 also comprises an auxiliary driveline portion 26 arranged to drive the rear wheels 6 by means of an auxiliary driveshaft or prop-shaft 28, a rear differential 30 and a pair of rear driveshafts 32. Embodiments of the invention are suitable for use with vehicles in which the engine is arranged to drive only a pair of front wheels or only a pair of rear wheels (i.e. front wheel drive vehicles or rear wheel drive vehicles) or selectable two wheel drive/four wheel drive vehicles. In the embodiment of FIG. 1 the engine 16 is releasably connectable to the auxiliary driveline portion 26 by means of a power transfer unit (PTU) 34, allowing selectable two wheel drive or four wheel drive operation. It is to be understood that embodiments of the invention may be suitable for vehicles having more than four wheels or where only two wheels are driven, for example two wheels of a three wheeled vehicle or four wheeled vehicle or a vehicle with more than four wheels.

[0075] The PTU 34 is operable in a ‘high ratio’ or a ‘low ratio’ configuration, in which a gear ratio between an input shaft and an output shaft thereof is selected to be a high or low ratio. The high ratio configuration is suitable for general on-road or ‘on-highway’ operations in an on-road mode of the vehicle, while the low ratio configuration is more suitable for negotiating certain off-road terrain conditions, e.g. in an off-road mode of the vehicle.

[0076] The brake system 10 of the vehicle 2 comprises four hydraulic disc brakes 36, one for each wheel 4, 6 of the vehicle. The disc brakes 36 are individually operable by imparting hydraulic pressure via hydraulic lines 38 connecting each brake to a master cylinder 40. Each hydraulic line 38 is in communication with hydraulic pressure control means 42 for increasing or decreasing hydraulic pressure in the line 38 based on electronic commands. Such hydraulic pressure control means 42 are well known in the art and may, for example comprise pumps and valves.

[0077] The vehicle 2 has an accelerator pedal 44 for indicating a demanded torque output of the powertrain 8, a brake pedal 46 for indicating a desired braking effort to be supplied by the brake system 10, and a steering wheel 48 for steering the front wheels 4.

[0078] The functionality of the traction control system 14 is performed by a brake controller of the vehicle, for example by an electronic Anti-lock Brake System (ABS) controller 50.

[0079] The ABS controller 50 may suitably comprise a control unit or computational device having one or more electronic processors.

[0080] The ABS controller 50 provides advanced braking functionality in the vehicle 2 by controlling the brake system 10 and engine 16, via an electronic brake controller 52 and an electronic engine management controller 54. The ABS controller 50 is in communication with the brake and engine management controllers 52, 54, and other controllers and components of the vehicle 2, using a CAN interface or similar. Such communication may be facilitated via any suitable wired or wireless connection, such as, for example, a controller area network (CAN) bus, FlexRay communication bus, a system management bus (SMBus), a proprietary communication link, or through some other arrangement known in the art.

[0081] For purposes of this disclosure, and notwithstanding the above, it is to be understood that the controller(s) or electronic control units (ECUs) described herein may each comprise a control unit or computational device having one or more electronic processors. Vehicle 2 and/or a subsystem thereof may comprise a single control unit or electronic controller or alternatively different functions of the controller(s) may be embodied in, or hosted in, different control units or controllers. As used herein, the term “control unit” will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide the required control functionality. A set of instructions could be provided which, when executed, cause said controller(s) or control unit(s) to implement the control techniques described herein (including the method(s) described below). The set of instructions may be embedded in one or more electronic processors, or alternatively, may be provided as software to be executed by one or more electronic processor(s). For example, a first controller may be implemented in software run on one or more electronic processors, and one or more other controllers may also be implemented in software run on or more electronic processors, optionally the same one or more processors as the first controller. It will be appreciated, however, that other arrangements are also useful, and therefore, the present invention is not intended to be limited to any particular arrangement. In any event, a set of instructions may be embedded in a computer-readable storage medium (e.g., a non-transitory storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors/computational device, including, without limitation: a magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM ad EEPROM); flash memory; or electrical or other types of medium for storing such information/instructions.

[0082] The ABS controller 50 receives information from the vehicle sensors 12. The information may be received by the ABS controller 50 directly, or indirectly via one or more other subsystem controllers associated with the sensors. For example the subsystem controllers may communicate with the sensors 12 and then publish a signal therefrom to the CAN.

[0083] To allow the ABS controller 50 to provide a traction control function, the vehicle sensors 12 include wheel speed sensors 56, a vehicle reference speed sensor 58, an engine torque sensor 60, and a six degree of freedom inertial measurement unit (IMU) 62. The vehicle may of course comprise other sensors that are not illustrated. The IMU 62 provides the ABS controller 50 with pitch data, yaw data, roll data, longitudinal acceleration, lateral acceleration and heave data for the vehicle 2. Suitable IMUs are known in the art. One non-limiting example of a suitable IMU is the BMI055 available from Bosch Sensortec.

[0084] The ABS controller 50 acts as an electronic controller of the traction control system 14 of the vehicle 2. The ABS controller 50 is able to initiate traction control interventions by virtue of controlling relevant vehicle subsystems, in particular the brake controller 52 and the engine management controller 54. Intervention commands can be sent by the ABS controller 50 to the brake controller 52 and the engine management controller 54 as may be required, which in turn control the powertrain 8 and brake system 10 as commanded.

[0085] Referring now to FIG. 2, in one non-limiting operational mode, the ABS controller 50 is configured to identify a wheelslip condition in at least one wheel based on a signal from the wheel speed sensors 56 and vehicle reference speed sensor 58. In particular, the ABS controller 50 accesses wheel speed data from the wheel speed sensors 56 and vehicle reference speed data from the vehicle reference speed sensor 58. If no wheelslip condition is identified, the identification step is repeated as long as the system 14 remains active.

[0086] If a wheelslip condition is identified, the ABS controller 50 checks whether a reduced vehicle load condition has been identified based on at least one of pitch data and vehicle heave data obtained from the IMU 62.

[0087] The ABS controller 50 is configured to identify reduced wheel load conditions based on at least one of vehicle pitch data and vehicle heave data, comprised in an output of the IMU 62. In particular the ABS controller 50 is configured to store vehicle pitch data and vehicle heave data in a memory 51 to determine pitch profiles and heave profiles over time. The pitch and heave profiles are compared by the ABS controller 50 with a lookup table including a reference profiles mapped to normal wheel load conditions and reduced wheel load conditions. If a compared profile is found by the ABS controller 50 to match a reference profile associated with a reduced wheel load condition then the ABS controller 50 concludes that a reduced wheel load condition has been identified.

[0088] By way of further illustration, an example of pitch data received from the IMU 62 as a vehicle travels over a speed bump at high speed is shown in FIG. 3. The pitch rate of the vehicle is subject to a clearly identifiable spike S in this scenario, representing a pitch profile associated with a reduced load condition for the wheels of the vehicle.

[0089] The ABS controller 50 consults the lookup table based on the detected pitch profile and finds a matching reference profile mapped to a reduced wheel load (speed bump) condition. Particular characteristics of the reduced wheel load condition, such as its duration and which wheels are affected, are also mapped. Accordingly, the ABS controller 50 is able to conclude that a particular reduced wheel load condition exists, for example for a particular wheel for a particular duration and with a particular severity.

[0090] A similar determination may be made by the ABS controller 50 by using the heave data instead of or in addition to the pitch data. Additional data from the IMU 62 or other sensors may also be used in the determination, to aid accurate identification and differentiation of reduced wheel load conditions.

[0091] As an alternative to a lookup table, an algorithm may be used, for example based on pitch or heave gradients. The lookup table or algorithm will vary from vehicle to vehicle and may be created based on calculations and/or obtained by calibration.

[0092] Referring again to FIG. 2, if no reduced wheel load condition is identified, then the ABS controller 50 initiates a standard traction control intervention. The intervention may comprise braking one or more wheels 4, 6 and/or a reduction in the torque of the engine. The ABS controller 50 can initiate such interventions by sending commands to the engine controller 54 and brake controller 52 respectively, which in turn act to control the engine 16 or brake system 10 as required.

[0093] By virtue of identifying reduced wheel load conditions, the ABS controller 50 is able to avoid unhelpful traction control interventions and/or to enhance the efficiency of interventions.

[0094] If a reduced wheel load condition is identified, the ABS controller 50 modifies the traction control intervention in dependence on the reduced wheel load condition.

[0095] In the on-road mode, the ABS controller is configured to inhibit any traction control intervention in dependence on the reduced wheel load condition, i.e. to trigger inhibition of the traction control intervention when the reduced wheel load condition is identified: [0096] For reduced wheel load conditions of low severity, the ABS controller 50 is configured to inhibit the traction control intervention such that the severity of the traction control intervention is reduced. For example, the braking force applied by the intervention may be reduced and/or the engine torque may be reduced less by the intervention. [0097] For more severe reduced wheel load conditions, for example those where one or more wheels is airborne, the ABS controller 50 is configured to inhibit the traction control intervention such that the traction control intervention is eliminated. For example, no braking force may be applied by the intervention and/or the engine torque may not be reduced by the intervention.

[0098] It will be appreciated that the particular nature or scale of the inhibition(s) may be readily modified as desired.

[0099] Referring still to FIG. 2, in the off-road mode, the ABS controller 50 is configured to enhance a braking traction control intervention in dependence on the reduced wheel load condition, i.e. to trigger enhancement of the traction control intervention when the reduced wheel load condition is identified. In particular, on identification of a reduced wheel load condition, the ABS controller 50 is configured to enhance braking force applied by any traction control intervention.

[0100] It will be appreciated that many modifications can be made to this embodiment without departing from the scope of the invention as defined in the appended claims.

[0101] For example, while the ABS controller 50 has been described as inhibiting traction control intervention in an on-road mode of the vehicle and enhancing traction control intervention in an off-road mode of the vehicle, inhibition or enhancement can also be implemented independently. For example, the ABS controller 50 could be configured to inhibit traction control intervention in an on-road mode and to initiate a standard traction control intervention in an off-road mode.