CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 of International Application No. PCT/EP2019/054517, filed Feb. 25, 2019, which claims priority to GB Patent Application 1803043.7, filed Feb. 26, 2018, the contents of both of which are incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present disclosure relates to a vehicle control method and apparatus. More particularly, but not exclusively, the present disclosure relates to a powertrain controller for controlling a torque distribution between a front axle and a rear axle of a vehicle. The present disclosure also relates to a method of controlling a torque distribution between a front axle and a rear axle of a vehicle.

Aspects of the invention relate to a powertrain controller, a vehicle, a method, and a non-transitory computer-readable medium.

BACKGROUND

It has been recognised that the appropriate powertrain-torque distribution between the front and rear axles is dependent, at least partially, on a surface grip level (represented as a coefficient of friction p (mu)). The vehicle may deviate from an intended course during a turning manoeuvre as a result of a change from a positive torque request to a negative torque request, for example as a result of a lift-off event when the driver lifts off the throttle pedal. This change in the torque request may result in the vehicle oversteering or understeering depending on the powertrain-torque distribution between the front and rear axle; and/or the surface grip level (mu). In order to provide a consistent vehicle response, a stability margin (or stability margins) used to control the torque distribution between the front and rear axles may be defined below a tyre adhesion point. The stability margins may be triggered early to improve vehicle response on high and low surface grip level (mu), thereby reducing the occurrences of torque transfer between the front and rear axles. However, this may reduce the opportunities for energy recuperation and potentially provides a non-optimal torque distribution between the front and rear axles.

The present invention, at least in certain embodiments, seeks to overcome at least some of the problems associated with the prior art systems.

SUMMARY OF THE INVENTION

Aspects and embodiments of the present invention relate to a powertrain controller, a vehicle, a method and a non-transitory computer-readable medium as claimed in the appended claims.

According to an aspect of the present invention there is provided a powertrain controller for controlling a torque distribution between a front axle and a rear axle of a vehicle; the powertrain controller comprising a processor and a memory device, the processor being configured selectively to implement first and second torque distribution profiles defining the torque distribution between the front axle and the rear axle; wherein the processor is configured to:determine when one or more vehicle dynamics parameter is within one or more predefined stability margin and when the one or more vehicle dynamics parameter is outside the one or more predefined stability margin;monitor a torque request signal to identify a change in a torque request;implement the first torque distribution profile when the one or more vehicle dynamics parameter is within the one or more predefined stability margin; andimplement the second torque distribution profile when the one or more vehicle dynamics parameter is outside the one or more predefined stability margin and the identified change in the torque request comprises a decrease in the torque request. The decrease in the torque request may, for example, indicate an overrun torque which is generated when a driver of the vehicle lifts off a throttle pedal (also known as an accelerator pedal). The first and second torque distribution profiles control the distribution of a powertrain torque between the front and rear axles (i.e. the torque split between the front and rear axles).

The processor may be configured to implement the second torque distribution profile when the magnitude of the decrease in the torque request is greater than a predefined torque change threshold. The predefined torque change threshold may correspond to a change in the torque request which may affect vehicle stability when the one or more vehicle dynamics parameter is outside the one or more predefined stability margin. The predefined torque change threshold may be calibrated for a vehicle.

Alternatively, or in addition, the processor may be configured to implement the second torque distribution profile when a rate of change of the torque request during the identified change is greater than a predefined rate of change threshold. The predefined rate of change threshold may correspond to a rate of change in the torque request which may affect vehicle stability when the one or more vehicle dynamics parameter is outside the one or more predefined stability margin. The predefined rate of change threshold may be calibrated for a vehicle.

The decrease in the torque request may result in the torque request changing to a negative torque request; or an increase in a magnitude of a negative torque request. The second torque distribution profile may be implemented when the identified change in the torque request results in a negative torque request or an increase in a magnitude of a negative torque request. The processor may be configured to implement the second torque distribution profile when the decrease in the torque request comprises a change from a positive torque request to a negative torque request. Alternatively, or in addition, the processor may be configured to implement the second torque distribution profile when the decrease in the torque request comprises a change from a substantially neutral torque request to a negative torque request. Alternatively, or in addition, the processor may be configured to implement the second torque distribution profile when the decrease in the torque request comprises an increase in a magnitude of a negative torque request.

The first and second torque distribution profiles may be implemented in dependence on a surface grip level. To reduce a tendency for the vehicle to oversteer, the distribution of a negative torque towards the front axle may be prioritised when the vehicle is travelling over a surface providing a high surface grip level. To reduce a tendency for the vehicle to understeer or oversteer, the distribution of a negative torque may be distributed more evenly between the front and rear axles when the vehicle is travelling on a surface providing a low surface grip level. The surface grip level may be assessed in dependence on a lateral acceleration of the vehicle.

The first torque distribution profile may comprise a first fixed torque distribution between the front axle and the rear axle of the vehicle.

The controller may be configured to determine a lateral acceleration of the vehicle. The second torque distribution profile may control the torque distribution between the front axle and the rear axle in dependence on the determined lateral acceleration of the vehicle.

The second torque distribution profile may increase the torque distributed to the front axle in dependence on the determined lateral acceleration of the vehicle. The second torque distribution profile may control the torque distributed to the front axle in direct proportion to the determined lateral acceleration. The second torque distribution profile may control the torque distributed to the rear axle in dependence on the determined lateral acceleration of the vehicle. The second torque distribution profile may decrease the torque distributed to the rear axle in direct proportion to the determined lateral acceleration.

The second torque distribution profile may comprise a lateral acceleration threshold. The control of the torque distribution between the front axle and the rear axle in dependence on the determined lateral acceleration of the vehicle may optionally be implemented when the lateral acceleration of the vehicle is greater than the lateral acceleration threshold.

When the determined lateral acceleration is less than the lateral acceleration threshold, the second torque distribution profile may comprise a second fixed torque distribution between the front axle and the rear axle of the vehicle. The second fixed torque distribution of the second torque distribution profile may distribute more torque to the rear axle of the vehicle than the first fixed torque distribution profile of the first torque distribution profile. The first fixed torque distribution may distribute less torque to the rear axle than the second fixed torque distribution.

The identified change in the torque request may correspond to an overrun torque. The overrun torque may, for example, correspond to a throttle pedal lift-off event.

The identified change in the torque request may correspond to a braking event.

The vehicle dynamics parameters may comprise one or more of the following: the longitudinal acceleration, the lateral acceleration, the vertical acceleration, the rotational movement about the longitudinal axis, the rotational movement about the transverse axis, and the rotational movement about the vertical axis. The vehicle dynamics parameters may comprise one or more of the following: a powertrain torque request, a braking torque request, one or more wheel speed signal, and one or more wheel slip signal.

The powertrain controller may be configured to analyse the vehicle dynamics parameters to generate one or more index. For example, the powertrain controller may be configured to generate one or more of the following: an over-braking index; a dynamic traction control stability index; and a yaw stability index. Each index may be generated for an axle of the vehicle. Thus, separate indices may be generated for the front and rear axles of the vehicle. The one or more index may be used to determine if the one or more vehicle dynamics parameter are within the one or more predefined stability margin. Each index may indicate a stable condition or an unstable condition. If one or more index indicate an unstable condition, the powertrain controller may determine that the one or more vehicle dynamics parameter is outside the one or more predefined stability margin. If each index indicates a stable condition, the powertrain controller may determine that the one or more vehicle dynamics parameter is within the one or more predefined stability margin.

According to a further aspect of the present invention there is provided a vehicle comprising a powertrain controller as described herein. The vehicle may comprise one or more electric traction motor.

According to a further aspect of the present invention there is provided a method of controlling a torque distribution between a front axle and a rear axle of a vehicle by selectively implementing at least first and second torque distribution profiles, the first and second torque distribution profiles defining the torque distribution between the front axle and the rear axle; wherein the method comprises:determining when one or more vehicle dynamics parameter is within one or more predefined stability margin and when the one or more vehicle dynamics parameter is outside the one or more predefined stability margin;monitoring a torque request to identify a change in the torque request;implement the first torque distribution profile when the one or more vehicle dynamics parameter is within the one or more predefined stability margin; andimplement the second torque distribution profile when the one or more vehicle dynamics parameter is outside the one or more predefined stability margin and the identified change in the torque request comprises a decrease in the torque request.

The second torque distribution profile may be implemented when the magnitude of the decrease in the torque request is greater than a predefined torque change threshold.

Alternatively, or in addition, the second torque distribution profile may be implemented when a rate of change of the torque request during the identified change is greater than a predefined rate of change threshold.

The method may comprise implementing the second torque distribution profile when the decrease in the torque request comprises a change from a positive torque request to a negative torque request; or when the decrease in the torque request comprises a change from a substantially neutral torque request to the negative torque request; or when the decrease in the torque request comprises an increase in a magnitude of a negative torque request.

The method may comprise determining a lateral acceleration of the vehicle. The second torque distribution profile may control the torque distribution between the front axle and the rear axle in dependence on the determined lateral acceleration of the vehicle. The second torque distribution profile may increase the torque distributed to the front axle in dependence on the determined lateral acceleration of the vehicle. The second torque distribution profile may control the torque distributed to the front axle in direct proportion to the determined lateral acceleration. The second torque distribution profile may control the torque distributed to the rear axle in dependence on the determined lateral acceleration of the vehicle. The second torque distribution profile may decrease the torque distributed to the rear axle in direct proportion to the determined lateral acceleration.

The second torque distribution profile may comprise a lateral acceleration threshold. The control of the torque distribution between the front axle and the rear axle in dependence on the determined lateral acceleration of the vehicle may optionally be implemented when the lateral acceleration of the vehicle is greater than the lateral acceleration threshold.

The first torque distribution profile may comprise a first fixed torque distribution between the front axle and the rear axle of the vehicle.

When the determined lateral acceleration is less than the lateral acceleration threshold, the second torque distribution profile may comprise a second fixed torque distribution between the front axle and the rear axle of the vehicle. The second fixed torque distribution of the second torque distribution profile may distribute more torque to the rear axle of the vehicle than the first torque distribution profile. The first fixed torque distribution may distribute less torque to the rear axle than the second fixed torque distribution.

The decrease in the torque request may correspond to an overrun torque. The overrun torque may correspond to a throttle pedal lift-off event.

The decrease in the torque request identified by the processor may correspond to a braking event.

According to a further aspect of the present invention there is provided a non-transitory computer-readable medium having a set of instructions stored therein which, when executed, cause a processor to perform the method described herein.

The memory device is electrically coupled to the electronic processor and has instructions stored therein. The processor is configured to access the memory device and execute the instructions stored therein.

Any control unit or controller described herein may suitably comprise a computational device having one or more electronic processors. The system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term “controller” or “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 any stated control functionality. To configure a vehicle controller or control unit, a suitable set of instructions may be provided which, when executed, cause said control unit or computational device to implement the control techniques specified herein. The set of instructions may suitably be embedded in said one or more electronic processors. Alternatively, the set of instructions may be provided as software saved on one or more memory associated with said controller to be executed on said computational device. The control unit or controller may be implemented in software run on one or more processors. One or more other control unit or controller may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller. Other suitable arrangements may also be used.

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. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

