GB2577090A

GB2577090A - Powertrain control method and apparatus

Info

Publication number: GB2577090A
Application number: GB1814898.1A
Authority: GB
Inventors: Richards Karl; Owen Simon
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2018-09-13
Filing date: 2018-09-13
Publication date: 2020-03-18
Anticipated expiration: 2038-09-13
Also published as: GB2577090B; GB201814898D0

Abstract

A powertrain controller to implement a hill start control strategy. The strategy including reducing a braking torque 115 applied to a vehicle’s wheels, identifying which wheels are in a slip condition and a non-slip condition 155 as a driving torque transmitted to the wheels is increased 130, and controlling the braking torque applied to the wheels identified as being in a non-slip condition 160 in dependence on identification of the wheels in the slip condition. The brake torque control may include increasing or maintain the torque, or implementing a braking profile. The brake torque may be proportional to the detected wheel slip. When the detected wheel slip decreases, the controller may be configured to reduce the braking torque. The braking torque could be applied to a wheel disposed on a side of the vehicle opposite to the side with the wheel in a slip condition. A method for carrying out the strategy is included, and is stored on a non-transitory computer-readable medium.

Description

(71) Applicant(s):

Jaguar Land Rover Limited

Abbey Road, Whitley, Coventry, Warwickshire, CV3 4LF, United Kingdom (72) Inventor(s):

Karl Richards

Simon Owen (56) Documents Cited:

WO 2005/009814 A1

US 20070050120 A1 (58) Field of Search:

INT CL B60L, B60T, B60W Other: EPODOC, WPI

CN 108162800 A US 20020099489 A1 (74) Agent and/or Address for Service:

JAGUAR LAND ROVER

Patents Department W/1/073, Abbey Road, Whitley, Coventry, Warwickshire, CV3 4LF, United Kingdom (54) Title of the Invention: Powertrain control method and apparatus

Abstract Title: A vehicle hill start controller configured to adjust a braking torque based on a wheel being in a non-slip condition (57) A powertrain controller to implement a hill start control strategy. The strategy including reducing a braking torque 115 applied to a vehicle’s wheels, identifying which wheels are in a slip condition and a non-slip condition 155 as a driving torque transmitted to the wheels is increased 130, and controlling the braking torque applied to the wheels identified as being in a non-slip condition 160 in dependence on identification of the wheels in the slip condition. The brake torque control may include increasing or maintain the torque, or implementing a braking profile. The brake torque may be proportional to the detected wheel slip. When the detected wheel slip decreases, the controller may be configured to reduce the braking torque. The braking torque could be applied to a wheel disposed on a side of the vehicle opposite to the side with the wheel in a slip condition. A method for carrying out the strategy is included, and is stored on a non-transitory computer-readable medium.

1/7

W3

W4

2/7

IG. 2

3/7

4/7

TIME (Dia) anOaoi DNixvaa

FIG. 4B (Dia) anOaoi DNixvaa

FIG. 4C (019) anOaoi DNixvaa

7/7

100

VEHICLE >l STATIONARY

ON SLOPE

IDENTIFY SLIPPING/ NON-SLIPPING WHEEL(S)

155

HOLD/'INC REASE

BRAKING TORQUE ON

NON-SLIPPING WHEEL(S) i

INCREASE DRIVETRAIN TORQUE

160

165

HG. 5

POWERTRAIN CONTROL METHOD AND APPARATUS

TECHNICAL FIELD

The present disclosure relates to a powertrain control method and apparatus. More particularly, but not exclusively, the present disclosure relates to a powertrain control method and apparatus for implementing a hill start assist control strategy.

BACKGROUND

It is known to provide a powertrain controller to provide a hill start assist function for a wheeled vehicle. The hill start assist function facilitates starting the vehicle from a stationary position on a slope, such as a hill, a ramp or other inclined surface, to continue progress up the slope. The powertrain controller is configured to control a braking torque and a driving torque applied to the wheels of the vehicle during the hill start. Known hill start assist functions use a torque look up table to balance the amount of driving torque required to accelerate the mass of the vehicle up the slope. The hill start assist function assumes a homogenous, high-grip surface for all wheels of the vehicle. When the vehicle is on a slope, the powertrain controller calculates a braking torque and a release point for a given gradient in dependence on the driving torque. The driving torque is controlled in dependence on a driver-generated torque request, for example as a throttle is applied. When the braking torque and the driving torque balance, the braking torque is released at a pre-defined ramp rate and the driving torque increased.

The control of a vehicle powertrain to implement a hill start assist control strategy is illustrated by a first chart 50 shown in Figure 4A. A braking torque is represented by a first braking torque plot BTQ1; and a driving torque is represented by a first driving torque plot DTQ1. This example assumes that the vehicle is on a homogenous surface and no wheel slip occurs during the hill start. The vehicle is initially located on the slope and is held stationary by a braking torque applied in response to a driver applied brake pressure (PERIOD P1). The driver then releases the brake pressure (PERIOD P2). The hill start assist function calculates a holding torque TQHOLD required to hold the vehicle in station on the slope (PERIOD P3). The holding torque TQHOLD is calculated based on a gradient of the slope, vehicle mass and driver input. The holding torque TQHOLD is generated by application of the braking torque. As represented by the first driving torque plot DTQ1, a driving torque is generated in dependence on a driver request, for example by depressing the throttle pedal. The driving torque increases and the powertrain controller implements a corresponding reduction in the generated braking torque (PERIOD P4). As the driving torque is increased, the powertrain controller reduces the braking torque and balances the braking torque and the driving torque to hold the vehicle in a ‘neutral’ torque state (thereby avoiding sticking brakes). The reduction in the braking torque is controlled to ensure that the combined driving torque and braking torque is sufficient to hold the vehicle stationary on the slope. The driving torque increases until there is sufficient driving torque to propel the vehicle up the slope. The point at which there is sufficient propulsion torque from the power train to ascend the slope is represented as a first transition point TP1 in Figure 4A. The powertrain controller thereafter reduces the braking torque until the braking torque is completely removed (PERIOD P5). In this exemplary scenario, there is no wheel slip and all wheels follow the reference speed (PERIOD P4 and P5). The driving torque increases after the first transition point TP1 and the resulting traction torque transmitted by the wheels propels the vehicle up the slope. The powertrain controller thereafter reduces the braking torque until the braking torque is completely removed (PERIOD P5). In this exemplary scenario, there is no wheel slip and all wheels follow the reference speed (PERIOD P4 and P5).

A potential limitation of known hill start control strategies may occur when one of more wheel spin during the transition from braking torque to driving torque. This may, for example, occur if the vehicle is on a mixed surface having varying surface level grips. On a mixed surface, the wheels may have different grip levels which may result on one or more wheel experiencing a slip condition. Driving torque may be lost on a spinning wheel and the vehicle may roll backwards. In a scenario where the grip levels are split, for example dry tarmac on one side of the vehicle and ice on the other, this affect may be very pronounced.

At least in certain embodiments, the present invention seeks to overcome or ameliorate some of the limitations associated with the prior art.

SUMMARY OF THE INVENTION

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

According to a further aspect of the present invention there is provided a powertrain controller for controlling a vehicle to perform a hill start, the vehicle having a plurality of wheels and at least one of said wheels being a driven wheel for transmitting a driving torque to propel the vehicle; the powertrain controller comprising a processor coupled to a memory device, the processor being configured to implement a hill start control strategy comprising:

reducing a braking torque applied to one or more of said wheels;

identifying one or more wheel in a slip condition and one or more wheel in a non-slip condition as the driving torque transmitted to the at least one driven wheel is increased; and controlling the braking torque applied to the one or more wheel identified as being in a non-slip condition in dependence on identification of the one or more wheel in the slip condition.

The slip condition indicates that the one or more wheel is experiencing wheel slip. The no slip condition indicates that the one or more wheel is not experiencing wheel slip. The driving torque may be controlled in dependence on a user input, for example actuation of a throttle pedal. As the driving torque increases, one or more wheel may undergo slip which reduces the driving torque available to accelerate the vehicle. In use, the braking torque applied to one or more of the wheels identified as having a non-slip condition may be controlled at least partially compensate for a decrease in the torque transmitted by the one or more wheel in a slip condition. At least in certain embodiments, the powertrain controller may implement a hill start assist control strategy to facilitate vehicle pull away with wheel slip while reducing vehicle rollback.

The processor may be configured to receive a wheel speed signal from each wheel of the vehicle. The wheel speed signal may indicate a wheel speed of each wheel. By comparing the wheel speed to a reference speed of the vehicle, the processor may identify whether each wheel is in a slip condition or a non-slip condition. The processor may control the braking torque by outputting a brake pressure control signal to control the braking torque generated by a brake system associated with each wheel.

By identifying a slip condition, the processor may identify one or more wheel which is spinning. The controller may be configured to control said braking torque to inhibit or reduce rollback of the vehicle during the hill start. At least in certain embodiments, the controller may be configured to control said braking torque to hold the vehicle at least substantially stationary during the hill start. The braking torque may be controlled by a brake pressure, for example using an anti-lock brake system (ABS) pump. The driver may thereafter request additional driving torque to ascend the slope. In this situation once the wheel spin has been detected there needs to be a handover between the hill start assist brake pressure to a traction control system (TCS) brake pressure as the driver requests an increase in the driving torque.

The control of the braking torque may comprise increasing or maintaining the braking torque applied to one or more wheel identified as having a non-slip condition.

The control of the braking torque may comprise implementing a predetermined braking profile. The braking profile may be maintained while other vehicle systems are activated to control wheel spin. The vehicle systems may, for example, comprise a traction control unit and/or a differential. The predetermined braking profile may comprise increasing the braking torque for a predetermined period of time; and/or maintaining the braking torque substantially constant for a predetermined period of time.

The controller may be configured to control the braking torque in dependence on a detected wheel slip. The controller may be configured to control the braking torque in proportion to the detected wheel slip. The braking torque may be directly proportional to the detected wheel slip. The braking torque may be increased in direct proportion to increase in wheel slip.

The control of the braking torque may comprise increasing the braking torque at each wheel where no slip is detected.

The controller may be configured to reduce the braking torque when the detected wheel slip at one or more of said at least one driven wheel decreases.

The controller may be configured to control the braking torque applied to one of the wheels disposed on a side of the vehicle which is opposite to a side of the vehicle on which the one or more wheel identified as having a slip condition is located. The braking torque may be controlled on a wheel on the same axle and/or a different axle.

A user may configure the powertrain controller to implement the hill start control strategy. Alternatively, or in addition, the powertrain controller may automatically or semi-automatically implement the hill start control strategy.

According to a further aspect of the present invention there is provided a vehicle comprising a powertrain controller as described herein.

According to a further aspect of the present invention there is provided a method of controlling a vehicle to perform a hill start, the vehicle having a plurality of wheels and at least one of said wheels being a driven wheel for transmitting a driving torque to propel the vehicle, wherein the method comprises:

reducing a braking torque applied to one or more of said wheels;

increasing the driving torque transmitted to the at least one driven wheel;

identifying one or more wheel in a slip condition and one or more wheel in a non-slip condition; and controlling a braking torque applied to the one or more wheel identified as being in a non-slip condition in dependence on identification of the one or more wheel in the slip condition.

The method may comprise controlling said braking torque to inhibit or reduce rollback of the vehicle during the hill start.

The method may comprise controlling said braking torque to hold the vehicle at least substantially stationary during the hill start.

The method may comprise controlling the braking torque comprises increasing or maintaining the braking torque applied to the one or more wheel identified as having a non-slip condition.

The method may comprise controlling the braking torque comprises implementing a predetermined braking profile. The predetermined braking profile may comprise increasing the braking torque for a predetermined period of time; and/or maintaining the braking torque substantially constant for a predetermined period of time.

The method may comprise controlling the braking torque in dependence on the detected wheel slip. The method may comprise controlling the braking torque in proportion to the detected wheel slip. The braking torque may be directly proportional to the detected wheel slip.

The method may comprise controlling the braking torque comprises increasing the braking torque at each wheel where no slip is detected.

The method may comprise reducing the braking torque when the detected wheel slip at one or more of said at least one driven wheel decreases.

The method may comprise controlling the braking torque applied to one of the wheels disposed on a side of the vehicle which is opposite to a side of the vehicle on which the one or more wheel having a slip condition located.

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.

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 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.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

Figure 1 shows a schematic representation of a vehicle comprising a powertrain controller in accordance with an embodiment of the present invention;

Figure 2 shows a schematic representation of the powertrain controller shown in Figure 1;

Figure 3 shows a schematic representation of the vehicle shown in Figure 1 performing a hill start on a slope having a mixed surface;

Figure 4A shows a first chart representing a hill start performed on a homogenous surface without wheel slip;

Figure 4B shows a second chart representing a hill start performed on a mixed surface with wheel slip resulting in vehicle rollback;

Figure 4C shows a second chart representing a hill start performed on a mixed surface with wheel slip with application of a compensating braking torque to suppress vehicle rollback; and

Figure 5 shows a block diagram representing operation of the powertrain controller in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

A vehicle 1 comprising a powertrain (denoted generally by the reference numeral 2) and a powertrain controller 3 in accordance with an embodiment of the present invention will now be described with reference to the accompanying figures. As described herein, the powertrain controller 3 is configured to implement a hill start assist (HSA) control strategy for the vehicle 1 to facilitate ascent of a slope SL. As described herein, the HSA control strategy in the present embodiment is implemented when the vehicle 1 is starting from a stationary position on the slope (commonly referred to as a hill start). The HSA control strategy has particular application in a scenario where the vehicle 1 is on a slope having a mixed surface with different grip levels.

The powertrain controller 3 comprises but is not limited to a processor 4 connected to a memory device 5. In use, the processor 4 executes a set of computational instructions stored on the memory device 5. The powertrain controller 3 in the present embodiment is coupled to an engine control unit (ECU) 6 and a brake control unit 7. As described herein, the ECU 6 is configured to control the generation of a driving torque DTQ; and the brake control unit 7 is configured to control the generation of a braking torque BTQ. In a variant, the engine control unit (ECU) 6 and/or the brake control unit 7 may be separate control units which are coupled to the powertrain controller 3. A schematic representation of the powertrain controller 3 is shown in Figure 1.

The vehicle 1 is described herein with reference to a frame comprising a longitudinal axis X, a transverse axis Y and a vertical axis Z. The vehicle 1 in the present embodiment is a road vehicle, such as an automobile, a sports utility vehicle (SUV) or a utility vehicle. As shown in Figure 2, the vehicle 1 comprises but is not limited to first and second wheels W1, W2 mounted on a front axle 8; and third and fourth wheels W3, W4 mounted on a rear axle 9. The vehicle 1 in the present embodiment is a four-wheel drive vehicle, but aspects of the present invention may be applied to a two-wheel drive vehicle. The vehicle 1 may have permanent four-wheel drive, or the four-wheel drive may be selectively engaged. The powertrain 2 comprises but is not limited to an internal combustion engine 10 operable to generate a driving torque DTQ which is transmitted to the front and rear axles 8, 9. In use, the driving torque DTQ is output to the wheels W1-4 to propel the vehicle 1. The powertrain controller 3 is operative to control a powertrain-torque distribution to the front and rear axles 8, 9 of the vehicle 1. In particular, the powertrain controller 3 is configured to determine a torque split ratio (Front/Rear) to control the powertrain-torque distribution between the front axle 8 and the rear axle 9. A requested driving torque DTQR is determined in dependence on driver actuation of a throttle pedal 11 (also known as an accelerator pedal). A throttle pedal position sensor 12 determines the position of the throttle pedal 11 and outputs a driving torque request signal DTQRS to the powertrain controller 3. The ECU 6 is configured to control operation of the internal combustion engine 10 in dependence on the driving torque request signal DTQRS. Other configurations of the powertrain 2 are also useful. For example, the powertrain 2 may comprise of but is not limited to one or more electric motor and/or an internal combustion engine.

The first, second, third and fourth wheels W1-4 have first, second, third and fourth brake systems B1-4 respectively. The brake systems B1-4 are operable to generate the braking torque BTQ for retarding rotation of the wheels W1-4. In the present embodiment, the brake systems B1 -4 each comprise a friction brake, for example comprising a disc brake and an associated brake calliper (not shown). A hydraulic cylinder (not shown) is provided to generate a hydraulic brake pressure to actuate the brake callipers. Other brake systems may usefully be employed. For example, one or more electric motor provided on the vehicle 1 may generate a braking torque at each wheel W1-4. The brake systems B1-4 are operable independently of each other to provide selective control of the braking torque BTQ applied to each wheel W14. The brake control unit 7 is configured to control the braking torque BTQ generated by each brake system B1-4, thereby controlling the braking torque BTQ applied at each wheel W1-4 of the vehicle 1. A requested braking torque BTQR is generated in dependence on actuation of a brake pedal 14. A brake pedal position sensor 15 determines the position of the brake pedal 14 and outputs a braking torque request signal BTQRS to the brake control unit 7. In use, the brake control unit 7 controls a brake pressure applied to each brake system B1 -4 to control the braking torque BTQ applied at each wheel W1-4. In use, the brake control unit 7 is configured to output separate brake pressure signals BTQS1 -4 to provide independent control of the braking torque BTQ generated by each brake system B1-4. The brake control unit 7 is configured to control actuation of each of the brake systems B1-4 in dependence on the braking torque request signal BTQRS. As described herein, the brake control unit 7 is configured also to control the braking torque BTQ generated by each brake system B1-4 as part of the HSA control strategy.

The powertrain controller 3 is configured to determine awheel slip WS1-4 of each wheel W14 as the driving torque DTQ transmitted to the wheels W1-4 is increased. In particular, the powertrain controller 3 is configured to identify one or more wheel W1-4 in a slip condition; and one or more wheel W1 -4 in a non-slip condition. The wheel slip WS1 -4 may, for example, occur where the available surface grip level (defined as the coefficient of friction “μ” or Mu) is different for different wheels W1-4 of the vehicle 1. A surface having different grip levels may be referred to as a mixed surface or a split Mu surface. A wheel speed sensor 16-n (shown schematically in Figure 2) is associated with each wheel W1-4. Each wheel speed sensor measures the rotational speed of the associated wheel W1-4 which is used to determine the wheel slip WSS(n) to the powertrain controller 3. The powertrain controller 3 compares the measured rotational speed of each wheel W1 -4 to an expected rotational speed of that wheel W1-4 to detect wheel slip. The powertrain controller 3 determines and monitors a wheel slip of each wheel W1-4. The expected rotational speed may, for example, be determined by comparing the rotational speed of the wheels W1-4 on the same axle 8, 9 or the rotational speed of the wheels W1-4 on different axles 8, 9. Other techniques are known for detecting wheel slip. A consequence of wheel slip is a reduction in the ability of that wheel W1-4 to generate a tractive force for propelling the vehicle 1. Unless a limited-slip differential is fitted, the wheel W1-4 which is experiencing slip will receive the majority of the power transmitted to that axle 8, 9. Rather than transmit the driving torque DTQ, the wheel W1-4 may break traction and spin. When performing a hill start, the reduction in the transmittal of the driving torque DTQ may cause an initial rollback of the vehicle 1. The powertrain controller 3 is configured to generate a compensating braking torque BTQCOMP at least partially to compensate for the reduction in the traction torque delivered by the wheels W1-4 when one or more wheel W1-4 spin during a hill start. The operation of the powertrain controller 3 will now be described in more detail.

In the scenario illustrated in Figure 4A, the vehicle 1 is on a homogenous surface and no wheel slip occurs during the hill start. If, however, the vehicle 1 is on a slope having a mixed surface (i.e. a surface having non-uniform grip levels), one or more wheel W1-4 of the vehicle may experience wheel slip as the driving torque DTQ is increased in response to an increase in the driver torque request. For example, one or more wheel W1-4 on the left or right side of the vehicle 1 may be in contact with a low grip surface and one or more wheel W1-4 on the other side of the vehicle 1 may be in contact with a high grip surface. The operation of the powertrain controller 3 to implement the HSA control strategy on a mixed surface will now be described with reference to a second chart 60 shown in Figure 4B.

The braking torque is represented by a second braking torque plot BTQ2; and the driving torque is represented by a second driving torque plot DTQ2. The vehicle 1 is initially located on the slope and is held stationary by a braking torque applied in response to a driver applied brake pressure (PERIOD PT). The driver then releases the brake pressure (PERIOD P2’). The HSA control strategy calculates a holding torque TQHOLD required to hold the vehicle in station on the slope (PERIOD P3’). The holding torque TQHOLD is calculated based on a gradient of the slope, vehicle mass and driver input. The holding torque TQHOLD is generated by application of the braking torque. As represented by the second driving torque plot DTQ1, a driving torque is generated in dependence on a driver request, for example by depressing the throttle pedal. The driving torque DTQ increases and the powertrain controller 3 implements a corresponding reduction in the generated braking torque BTQ (PERIOD P4j. As the driving torque DTQ is increased, the powertrain controller 2 reduces the braking torque BTQ and balances the braking torque BTQ and the driving torque DTQ to hold the vehicle 1 in a ‘neutral’ torque state (thereby avoiding sticking brakes). The driving torque DTQ increases until there is sufficient traction torque to propel the vehicle up the slope. The point at which there is sufficient driving torque DTQ to ascend the slope is represented as a second transition point TP2 in Figure 4B. The braking torque BTQ at each wheel W1-4 is reduced after the second transition point TP2-1 in anticipation of the continued increase in the driving torque DTQ transmitted by the wheels W1-4. In the illustrated scenario, one or more of the wheels W1-4 of the vehicle 1 experiences wheel slip after the second transition point TP2-1. Although sufficient driving torque DTQ is generated by the powertrain 2 to ascend the slope, the driving torque DTQ is sufficient to break traction on the low grip surface and to spin one or more wheel W1-4. At least some of the driving torque DTQ is effectively lost due to the spinning wheel(s), and there is no longer enough traction torque for the vehicle 1 to ascend the slope. The traction torque transmitted by the wheels decreases below the holding torque TQHOLD and the vehicle may roll backwards (PERIOD P5’). The traction control and/or differentials (if present) are effective in directing driving torque DTQ from the spinning wheel(s) to those wheels that have grip resulting in an increase in the driving torque (PERIOD P6’). As illustrated by the second driving torque plot DTQ2, the driving torque DTQ transmitted by the wheels increases above the holding torque TQHOLD, as represented by a second transition point TP2-2. When the driving torque is greater than the holding torque TQHOLD, the vehicle will begin to ascend the slope (PERIOD P7’). However, it will be understood that for the time period between the second transition points TP2-1, TP2-2, the traction torque is less than the balance torque TQBAL and the vehicle 1 may roll backwards on the slope. This delay is at least partially caused by the relatively slow response of the internal combustion engine 10 to the request for an increase in the driving torque DTQ.

In the scenario illustrated in Figure 4B, the reduction in the driving torque caused by wheel spin on the mixed surface may result in vehicle rollback until the traction control and/or differentials are effective in directing driving torque DTQ away from the spinning wheel(s). The powertrain controller 3 in accordance with the present embodiment is configured to compensate for the torque lost by the slip condition on one or more wheel W1-4. The powertrain controller 3 is configured to increase the braking torque BTQ generated by the nonspinning wheel(s) at least partially to compensate for the lost torque. The operation of the powertrain controller 3 on a mixed surface will now be described with reference to a third chart 70 shown in Figure 4C. The vehicle 1 is on a slope having a mixed surface which provides a non-uniform grip level. One or more wheels W1-4 of the vehicle 1 experience slip as the driving torque DTQ is increased in response to the driver torque request increase. The braking torque BTQ is represented by a third braking torque plot BTQ3; and the driving torque is represented by a third driving torque plot DTQ3. The vehicle is initially located on the slope and is held stationary by a braking torque applied in response to a driver applied brake pressure (PERIOD P1”). The driver then releases the brake pressure (PERIOD P2”). The HSA control strategy calculates a holding torque TQHOLD required to hold the vehicle in station on the slope (PERIOD P3”). The holding torque TQHOLD is calculated based on a gradient of the slope, vehicle mass and driver input. The holding torque TQHOLD is generated by application of the braking torque. As represented by the first driving torque plot DTQ1, a driving torque DTQ is generated in dependence on a driver request, for example by depressing the throttle pedal

11. The driving torque DTQ increases and the powertrain controller 3 implements a corresponding reduction in the generated braking torque BTQ (PERIOD P4”). As the driving torque DTQ is increased, the powertrain controller 3 reduces the braking torque BTQ and balances the braking torque BTQ and the driving torque DTQ to hold the vehicle 1 in a ‘neutral’ torque state (thereby avoiding sticking brakes). The driving torque DTQ increases until there is sufficient traction torque to accelerate the vehicle 1. The point at which there is sufficient driving torque DTQ from the powertrain 2 to accelerate the vehicle 1 to cause the vehicle 1 to ascend the slope is represented as a third transition point TP3-1 in Figure 4C. In this example, one of the wheels W1-4 of the vehicle 1 experiences wheel slip after the third transition point TP3-1. Although there is sufficient driving torque DTQ from the powertrain 2 to accelerate the vehicle 1, the driving torque DTQ is sufficient to break traction on the low grip surface and to spin one or more wheel W1-4. The powertrain controller 3 identifies wheel slip against a reference speed. The powertrain controller 3 identifies each spinning wheel (i.e. each wheel(s) is/are on a low grip surface); and each non-spinning wheel (i.e. each wheel(s) is/are on a high grip surface). In response to the wheel slip, the powertrain controller 3 modifies the first brake pressure profile BTQ1 by increasing or maintaining a brake holding pressure on the wheel(s) having a high grip level (i.e. a high mu surface), rather than continuing to release the braking torque BTQ. A compensating braking torque BTQCOMP is illustrated in Figure 4C. The compensating braking torque BTQCOMP is profiled to maintain the total powertrain torque (comprising the driving torque DTQ and the braking torque BTQ) at least substantially equal to or greater than the balance torque TQBAL, thereby inhibiting or suppressing rollback of the vehicle 1. The compensating braking torque BTQCOMP increases progressively (PERIOD P5”) corresponding to an initial reduction in the driving torque DTQ transmitted by the wheels due to wheel slip. The compensating braking torque BTQCOMP is then maintained at a substantially constant level (PERIOD P6”) when the driving torque DTQ stabilises. As the driving torque DTQ increases, the compensating braking torque BTQCOMP is reduced (PERIOD P7”). The driving torque DTQ increases until it is substantially equal to the balance torque TQBAL, as represented by the third transition point TP3-2. The compensating braking torque BTQCOMP is thereafter reduced to zero (0) and the driving torque DTQ increases in dependence on the driver torque request (PERIOD P8”). The vehicle 1 accelerates from stationary and ascends the slope. The compensating braking torque BTQCOMP may be predefined or may be calculated dynamically. For example, the compensating braking torque BTQCOMP may be read from a look-up table in dependence on the measured gradient of the slope and/or a determined surface grip level.

The operation of the powertrain controller 3 to implement the hill start assist function will now be described with reference to a flow chart 100 shown in Figure 5. The hill start assist is initiated (BLOCK 105). The vehicle 1 is on a slope having a mixed surface which provides a non-uniform grip level. The vehicle 1 is held stationary on the slope by application of a braking torque BTQ (BLOCK 110). The braking torque BTQ may, for example, be applied in dependence on a driver request by depressing the brake pedal 14. The driver reduces the braking torque (BLOCK 115). The powertrain controller 3 calculates a holding torque TQHOLD for holding the vehicle 1 stationary on the slope. The holding torque TQHOLD is calculated in dependence on a mass of the vehicle 1 and an incline angle of the slope. The incline angle may be determined in dependence on a measured attitude of the vehicle 1, for example a measured pitch angle and/or roll angle of the vehicle 1. Other parameters may be used to determine the holding torque TQHOLD. The powertrain controller 3 controls the powertrain 2 to generate the holding torque TQHOLD. The holding torque TQHOLD comprises the braking torque BTQ. The powertrain controller 3 calculates a brake pressure hold required to generate the braking torque BTQ (BLOCK 120). The powertrain controller 3 detects a driver torque request when the throttle pedal 11 is depressed (BLOCK 125). The powertrain controller 3 increases the driving torque DTQ in dependence on actuation of the throttle pedal 11 (BLOCK 130). In dependence on the increase in the driving torque DTQ, the powertrain controller 3 reduces the braking torque BTQ (BLOCK 135). The powertrain controller 3 balances the braking torque BTQ and the driving torque DTQ at least substantially to maintain the holding torque TQHOLD, thereby holding the vehicle 1 stationary (BLOCK 140). The driving torque DTQ is increased until there is sufficient driving torque DTQ to ascend the slope. However, on a mixed surface, the driving torque DTQ may be sufficient to break traction on the low grip surface and to spin one or more wheel W1-4. The powertrain controller 3 monitors each wheel W1-4 to detect a slip condition on one or more wheel (BLOCK 145). If a wheel W1-4 experiences slip, the driving torque DTQ may spin that wheel W1-4 and the traction torque transmitted by the wheels W1-4 may be reduced. If wheel spin is not detected on any of the wheels W1-4, the powertrain controller 3 continues to increase the driving torque DTQ and the vehicle 1 ascends the slope (BLOCK 150). If wheel spin is detected on any of the wheels W1 -4, the powertrain controller 3 identifies each wheel W1 -4 experiencing slip and each wheel W1-4 which is not experiencing slip (BLOCK 155). The powertrain controller 3 identifies each wheel W1-4 experiencing slip; and each wheel W1-4 which is not experiencing slip (BLOCK 155). The powertrain controller 3 increases or maintains the braking torque BTQ applied to each wheel W1-4 which is not experiencing slip (BLOCK 160). The increase in the braking torque BTQ may, for example, correspond to the compensating braking torque BTQCOMP described herein with reference to Figure 4C. The increased braking torque BTQ at least partially compensates for the reduction in the traction torque caused by wheel spin. The powertrain controller 3 increases the driving torque DTQ (BLOCK 165). The powertrain controller 3 continues to monitor each wheel W1-4 to identify wheel slip (BLOCK 170). If the powertrain controller 3 detects wheel slip, the braking torque BTQ applied to each wheel W14 which is not experiencing slip is increased or maintained (BLOCK 160). If the powertrain controller 3 does not detect wheel slip, the braking torque BTQ is reduced on each wheel W14 previously identified as being in a non-slip condition (BLOCK 175). The powertrain controller 3 continues to increase the driving torque DTQ and the vehicle 1 ascends the slope (BLOCK 180).

The powertrain controller 3 described herein implements a HAS control strategy comprising generating a compensating braking torque BTQCOMP to inhibit or reduce vehicle rollback. The compensating braking torque BTQCOMP is applied upon identification of wheel slip on one or more wheel W1-4 of the vehicle 1. The compensating braking torque BTQCOMP is applied to each wheel W1-4 identified as being in a non-slip condition. The compensating braking torque BTQCOMP is maintained until the driving torque DTQ increases and the effective traction force is sufficient for the vehicle 1 to ascend the slope.

It will be appreciated that various modifications may be made to the embodiment(s) described herein without departing from the scope of the appended claims.

Claims

1. A powertrain controller for controlling a vehicle to perform a hill start, the vehicle having a plurality of wheels and at least one of said wheels being a driven wheel for transmitting a driving torque to propel the vehicle; the powertrain controller comprising a processor coupled to a memory device, the processor being configured to implement a hill start control strategy comprising:

reducing a braking torque applied to one or more of said wheels;

2. A powertrain controller as claimed in claim 1, wherein the controller is configured to control said braking torque to inhibit or reduce rollback of the vehicle during the hill start.

3. A powertrain controller as claimed in claim 1 or claim 2, wherein the controller is configured to control said braking torque to hold the vehicle at least substantially stationary during the hill start.

4. A powertrain controller as claimed in any one of claims 1 to 3, wherein controlling the braking torque comprises increasing or maintaining the braking torque applied to one or more wheel identified as having a non-slip condition.

5. A powertrain controller as claimed in any one of the preceding claims, wherein controlling the braking torque comprises implementing a predetermined braking profile.

6. A powertrain controller as claimed in claim 5, wherein the predetermined braking profile comprises increasing the braking torque for a predetermined period of time; and/or maintaining the braking torque substantially constant for a predetermined period of time.

7. A powertrain controller as claimed in any one of the preceding claims, wherein the controller is configured to control the braking torque in dependence on a detected wheel slip.

8. A powertrain controller as claimed in claim 7, wherein the controller is configured to control the braking torque in proportion to the detected wheel slip.

9. A powertrain controller as claimed in any one of the preceding claims, wherein controlling the braking torque comprises increasing the braking torque at each wheel where no slip is detected.

10. A powertrain controller as claimed in any one of the preceding claims, wherein the controller is configured to reduce the braking torque when the detected wheel slip at one or more of said at least one driven wheel decreases.

11. A powertrain controller as claimed in any one of the preceding claims, wherein the controller is configured to control the braking torque applied to one of the wheels disposed on a side of the vehicle which is opposite to a side of the vehicle on which the one or more wheel identified as having a slip condition is located.

12. A vehicle comprising a powertrain controller as claimed in any one of the preceding claims.

13. A method of controlling a vehicle to perform a hill start, the vehicle having a plurality of wheels and at least one of said wheels being a driven wheel for transmitting a driving torque to propel the vehicle, wherein the method comprises:

reducing a braking torque applied to one or more of said wheels;

identifying one or more wheel in a slip condition and one or more wheel in a non-slip condition as the driving torque transmitted to the at least one driven wheel is increased; and controlling a braking torque applied to the one or more wheel identified as being in a non-slip condition in dependence on identification of the one or more wheel in the slip condition.

14. A method as claimed in claim 13 comprising controlling said braking torque to inhibit or reduce rollback of the vehicle during the hill start.

15. A method as claimed in claim 13 or claim 14 comprising controlling said braking torque to hold the vehicle at least substantially stationary during the hill start.

16. A method as claimed in any one of claims 13 to 15, wherein controlling the braking torque comprises increasing or maintaining the braking torque applied to the one or more wheel identified as having a non-slip condition.

17. A method as claimed in any one of claims 13 to 16, wherein controlling the braking torque comprises implementing a predetermined braking profile.

18. A method as claimed in claim 17, wherein the predetermined braking profile comprises increasing the braking torque for a predetermined period of time; and/or maintaining the braking torque substantially constant for a predetermined period of time.

19. A method as claimed in any one of claims 13 to 18 comprising controlling the braking torque in dependence on the detected wheel slip.

20. A method as claimed in claim 19 comprising controlling the braking torque in proportion to the detected wheel slip.

21. A method as claimed in any one of claims 13 to 20, wherein controlling the braking torque comprises increasing the braking torque at each wheel where no slip is detected.

22. A method as claimed in any one of claims 13 to 21 comprising reducing the braking torque when the detected wheel slip at one or more of said at least one driven wheel decreases.

23. A method as claimed in any one of claims 13 to 22 comprising controlling the braking torque applied to one of the wheels disposed on a side of the vehicle which is opposite to a side of the vehicle on which the one or more wheel having a slip condition is located.

24. A non-transitory computer-readable medium having a set of instructions stored therein which, when executed, cause a processor to perform the method claimed in any one of claims 13 to 23.

Intellectual

Property

Office

Application No: GB1814898.1