GB2560590A

GB2560590A - Improvements in traction control to aid launch in friction-limited terrains

Info

Publication number: GB2560590A
Application number: GB1707073.1A
Authority: GB
Inventors: Raveendran Arun
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2017-03-17
Filing date: 2017-05-04
Publication date: 2018-09-19
Anticipated expiration: 2037-05-04
Also published as: WO2018166862A1; GB201707073D0; GB2560590B

Abstract

A method and controller for launching a wheeled vehicle (100 fig. 3) from a standstill, comprising receiving input indicative of an anticipated wheel slip event at a drive wheel (318 fig. 4) of the vehicle, applying a preload braking force to at least one drive wheel in dependence on the input; and applying drive torque to at least one of the drive wheels in dependence on the input and on the preload braking force so as to launch the vehicle from a standstill. The input indicative of an anticipated wheel slip event may be a user input device where a user selects the wheel(s) with the least amount of traction or it may comprise data relating to one or more vehicle sensors. The input indicative of an anticipated wheel slip event may also be saved data from a failed launch attempt or may be saved data from an ABS event as the vehicle came to rest prior to launching.

Description

(54) Title of the Invention: Improvements in traction control to aid launch in friction-limited terrains Abstract Title: Vehicle launch control for friction-limited terrains (57) A method and controller for launching a wheeled vehicle (100 fig. 3) from a standstill, comprising receiving input indicative of an anticipated wheel slip event at a drive wheel (318 fig. 4) of the vehicle, applying a preload braking force to at least one drive wheel in dependence on the input; and applying drive torque to at least one of the drive wheels in dependence on the input and on the preload braking force so as to launch the vehicle from a standstill. The input indicative of an anticipated wheel slip event may be a user input device where a user selects the wheel(s) with the least amount of traction or it may comprise data relating to one or more vehicle sensors. The input indicative of an anticipated wheel slip event may also be saved data from a failed launch attempt or may be saved data from an ABS event as the vehicle came to rest prior to launching.

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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IMPROVEMENTS IN TRACTION CONTROL TO AID LAUNCH IN FRICTION-LIMITED TERRAINS

TECHNICAL FIELD

The present disclosure relates to improvements in traction control to aid launch in frictionlimited terrains and particularly, but not exclusively, to a controller and a method of launching a vehicle from a standstill. Aspects of the invention relate to a method, a computer program and a controller to launch a vehicle from a standstill.

BACKGROUND

Currently, vehicles use traction control systems to improve traction when travelling over slippery ground, and if a vehicle has become stuck and needs to move off from a standstill on a split-friction surface. Traction control systems generally operate by detecting one or more driven wheels spinning faster than the others and artificially retarding said wheels. As traction control is a purely reactive system, attempts to move the vehicle involve providing drive to all drive wheels until a wheel slip is detected. Detecting wheel slip is even more difficult when all drive wheels are rotating at different speeds, as it becomes difficult to calculate a reference speed for the vehicle, especially when the vehicle is at a standstill, because there will be no reference ground speed. When a vehicle is on a low friction surface, it may be relatively easy to cause excessive wheel spin and lose traction, particularly if the surface friction changes as the vehicle progresses.

In low friction launch events it can be difficult to determine the correct vehicle reference speed, resulting in a delay in traction control taking retarding action on the wheels which are slipping. This is illustrated by the shaded region R in Figure 1. This delay reduces the chances of recovery as a bigger hole may be dug around the driven wheels. The situation is exacerbated if there is no locking differential, the car is on a gradient or side-slope and the vehicle slips backwards before traction control kicks in, or if some steering lock is needed to move the car in the right direction. The problem to be solved by the present invention is increasing the chance of recovery when a vehicle is stuck with wheels over low friction surfaces.

It is an object of embodiments of the invention to at least mitigate one or more of the problems of the prior art. Embodiments of the invention provide a method of launching a wheeled vehicle from a standstill. Other embodiments of the invention provide a controller for controlling a launch of a wheeled vehicle from a standstill. Other aims and advantages of the invention will become apparent from the following description, claims and drawings.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a method of launching a vehicle from a standstill, a controller for controlling a launch of a vehicle from a standstill and a vehicle as claimed in the appended claims.

According to an aspect of the invention, there is provided a method of launching a wheeled vehicle from a standstill, comprising receiving input indicative of an anticipated wheel slip event at a drive wheel of the vehicle, applying a preload braking force to at least one drive wheel in dependence on the input; and applying drive torque to at least one of the drive wheels in dependence on the input and on the preload braking force so as to launch the vehicle from a standstill.

This is advantageous over the prior art because the wheel or wheels most likely to slip can be identified in advance, and by suitable application of preload braking force that slippage can be prevented or at least reduced. Advantageously, the preload braking force is applied before the drive torque is applied, thus mitigating against the drive wheel or wheels digging into soft terrain.

In an embodiment of the present invention, receiving input indicative of an anticipated wheel slip event at a drive wheel of the vehicle may comprise determining which of multiple drive wheels has the least traction and applying a greatest preload braking force to that drive wheel with the least traction.

Embodiments of the present invention may also comprise determining an order of the drive wheels according to their traction, and applying preload braking forces to each respective drive wheel in dependence on the ranking of that drive wheel in the order of traction. This is advantageous in that all drive wheels can be treated independently, with suitable preload braking forces applied dependent on the traction of each wheel.

Embodiments of the present invention may comprise receiving input indicative of an anticipated wheel slip event at a drive wheel of the vehicle comprising a manual input via a user interface. Advantageously, this allows a driver to inspect the terrain and identify which of the drive wheels is most likely to slip, and input that information for use by the method in determining the appropriate preload braking force(s) to be applied.

Embodiments of the present invention may comprise receiving input indicative of an anticipated wheel slip event at a drive wheel of the vehicle comprising receiving input automatically in dependence on data signals output by at least one vehicle sensor. Advantageously, this facilitates an automated process, by which the method can take input from vehicle sensors.

In a further embodiment, the signals may comprise data relating to one or more of: wheel load; wheel rotational speed; locking torque applied on a differential; suspension height; vehicle orientation; steering angle; vehicle speed; driving mode; and vehicle acceleration and deceleration.

In a yet further embodiment, the signals are input to an algorithm which determines the preload braking force to be applied to the at least one drive wheel. Advantageously, the algorithm can determine the appropriate braking forces to be applied to the respective drive wheels dependent on the vehicle data, including historical data, such as that taken in a leadup to the vehicle coming to a standstill.

Embodiments of the method may comprise the algorithm further determining the drive torque to be applied to the at least one drive wheel. Advantageously, the algorithm may determine not only the appropriate preload braking forces, but also associated drive torques for each drive wheel.

In embodiments of the present invention, the algorithm determines the preload braking force to be applied to each drive wheel in dependence on vehicle data obtained during an Antilock Braking System (ABS) event at the terrain where the vehicle has come to a standstill. In such embodiments, the method comprises: determining if the terrain is friction-limited in dependence on the vehicle velocity, brake interventions and deceleration rate during the ABS event; and, if the terrain is determined to be friction-limited: capturing the brake torques and brake pressures for each drive wheel as the vehicle is stopping during the ABS event; and determining the order of traction of the drive wheels in dependence on which of the drive wheels has the highest ABS intervention and/or the lowest brake torque during the ABS event. This is advantageous over prior art which does not take into account vehicle data during an ABS event, as the vehicle data obtained during an ABS event provides a more accurate estimate of each wheel’s traction which will more effectively aid a launch event from standstill.

In embodiments of the present invention, the method may also comprise saving the determined preload braking forces to be applied, and vehicle data obtained during the ABS event to a processor memory.

In embodiments of the present invention, the algorithm may determine the preload braking force to be applied to each drive wheel in dependence on vehicle data obtained during a preceding failed launch event at the terrain where the vehicle has come to a standstill.

Embodiments of the present invention may further comprise, where there has been a traction control intervention during the preceding failed launch event, filtering the brake torques of each wheel during the traction control intervention and compensating for losses and inertia associated with the failed launch event; determining the powertrain torque at which each drive wheel began to slip during the failed launch event; and determining the preload braking forces for each drive wheel in dependence on the filtered preload brake torques and the determined powertrain torques. By filtering the preload brake torques and compensating for losses and inertia, a more accurate determination of the preload braking forces can be made.

Embodiments of the present invention may further comprise determining the order of traction of the drive wheels by determining, from the vehicle sensor signals, which of the drive wheels began to slip first as the engine torque rose during the preceding failed launch event.

Embodiments of the present invention may comprise applying an increasing drive torque to all the drive wheels with all differentials open; detecting a first drive wheel to slip; applying a braking torque to that first slipping wheel to maintain rotation of the wheel at a set speed; detecting a second drive wheel to slip and applying a braking torque to that second slipping wheel to maintain rotation of the wheel at a set speed; and repeating until the drive wheel with the most traction is determined.

Embodiments of the present invention may further comprise estimating the drive torque applied to each wheel during the preceding failed launch event and determining the preload braking forces for each drive wheel in dependence on the engine torque, the wheel speeds and the estimated drive torques.

Embodiments of the present invention may further comprise determining the preload braking forces for each wheel in dependence both on the filtered preload brake torques and the determined powertrain torques, as well as on the engine torque, the wheel speeds and the calculated drive torques, based on a level of confidence in each determination.

Embodiments of the present invention may comprise saving the determined preload braking forces to be applied to a processor memory.

In embodiments of the present invention, the algorithm may comprise determining the preload braking force to be applied by: retrieving saved values of preload braking force along with supporting data for each drive wheel, wherein the supporting data includes data pertaining to at least: driving mode, vehicle orientation, weight distribution, wheel articulation, or steering angle; modifying the preload brake forces based on the supporting data; scaling the preload brake force values based on the current driving mode; and assessing the preload brake forces and supporting data to determine whether the vehicle is ready to attempt a launch from standstill. In such embodiments, the method comprises: applying the scaled preload brake forces to each drive wheel in synchronisation with the application of rising drive torque; when the wheels move above a predetermined amount, introducing normal traction control and/or cross-axle slip control with the applied preload as the starting point; and if the current launch event fails, saving the vehicle data for use in a subsequent launch event. The wheels moving more than a predetermined amount ensures that the vehicle has actually begun to move, rather than, for example, rocking on the spot with otherwise insubstantial wheel movements.

Embodiments of the present invention may further comprise limiting the drive torque rise when the drive torque is near a torque value at which a wheel slip event was previously detected.

In embodiments of the present invention, wherein the at least one drive wheel comprises one of a pair of drive wheels on opposite ends of a common axle, the method may comprise: applying the preload braking force to the drive wheel having the least traction; applying a drive torque to the pair of drive wheels until the other of the pair, which is not subject to a braking force, begins to rotate; and modulating the preload braking force on the low traction wheel such that its rotational speed is matched to that of the non-braked wheel.

Embodiments of the present invention may comprise determining the maximum tractive force of at least one drive wheel of a vehicle comprising: generating a slip curve for at least one drive wheel when a traction-limited wheel slips following increasing drive torque; using said slip curve to determine the optimum speed for the traction-limited wheel; setting the traction-limited wheel speed to said optimum speed; and increasing drive torque further, resulting in either a successful pull-away attempt or a subsequent wheel slipping; and, if a subsequent wheel slip is detected, generating a new slip curve for the subsequently tractionlimited wheel, wherein the method can be repeated to determine slip curves and optimum speeds for each drive wheel to generate maximum tractive force for the vehicle in subsequent launch attempts.

In embodiments of the present invention, the method may be terminated by one or more of: the vehicle having moved a given distance in the intended direction; the vehicle having sufficient longitudinal acceleration, indicating the vehicle may have been recovered; a sudden change in vehicle weight distribution, orientation or composure; and the safety limits of brake pressure modulation being reached.

According to another aspect of the invention, there is provided a computer program that, when run on a processor, performs a method as described above.

According to another aspect of the invention, there is provided a controller for controlling a launch of a wheeled vehicle from a standstill, comprising: means for receiving an input indicative of an anticipated wheel slip event at a drive wheel of the vehicle, means for applying a preload braking force to at least one drive wheel in dependence on the input; and means for applying drive torque to at least one of the drive wheels in dependence on the input and on the preload braking force so as to launch the vehicle from a standstill.

According to an aspect of the invention, there is provided a controller for controlling a launch of a wheeled vehicle from a standstill, as described above, wherein the means for receiving an input indicative of an anticipated wheel slip event at a drive wheel of the vehicle comprises an electronic processor having an electrical input for receiving one or more signals indicative of said anticipated wheel slip event; and an electronic memory device electrically coupled to the electronic processor and having instructions stored therein; wherein the means for applying a preload braking force to at least one drive wheel in dependence on the input and the means for applying drive torque to at least one of the drive wheels in dependence on the input and on the preload braking force so as to launch the vehicle from a standstill comprises the processor being configured to access the memory device and execute the instructions stored therein such that it is operable to cause the application of said braking force and said drive torque.

In embodiments of the present invention, the controller may comprise input means comprising a user interface, wherein the user interface comprises one or more of: a visual display or touch screen, a button, a keypad or D-pad, and a voice-activated console.

In embodiments of the present invention, the controller may also comprise input means comprising at least one vehicle sensor configured to detect one or more of: wheel load, wheel rotational speed; suspension height, vehicle orientation; steering angle; vehicle speed; driving mode; and vehicle acceleration and deceleration.

In a further embodiment, the controller may be configured to carry out the method of the present invention described above.

According to yet another aspect of the present invention, there is provided a vehicle comprising a controller as described above.

Within the scope of the 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 files 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 invention will now be described, by way of example only, with reference to the accompanying drawing, in which:

Figure 1 shows a graph illustrating brake pressure and wheel speeds during split friction acceleration both with and without traction control in operation;

Figure 2 shows a slip curve with an ABS slip target range;

Figure 3 shows an example of a user interface according to an embodiment of the invention where the user manually selects which wheel is anticipated to undergo a wheel slip event;

Figure 4 shows a wheeled vehicle according to an embodiment of the invention;

Figure 5 shows a flowchart of the data captured for calculating brake preloads on ABS braking according to an embodiment of the invention;

Figure 6 shows a flowchart of the data captured for calculating brake preloads on failed pullaway according to an embodiment of the invention;

Figure 7 shows a flowchart of applying pre-emptive brake torque on pull-away according to an embodiment of the invention;

Figure 8 shows a schematic view of a vehicle suitable for launching from a standstill using a method according to the invention; and

Figure 9 shows a block diagram of control systems of a vehicle.

DETAILED DESCRIPTION

Vehicles use traction control systems to improve traction in slippery, low or varying friction conditions. Such traction control systems generally operate by detecting one or more driven wheels spinning faster than the others and artificially retarding said wheels. Such a scenario is illustrated in Figure 1. In order for such systems to operate reliably and to determine which of the driven wheels is in fact slipping the most (i.e. has the least traction), it can be necessary to determine a reference ground speed of the vehicle. In low friction launch events it can be difficult to determine the correct reference speed because the vehicle is, at least initially, at a standstill, so there is accordingly no such ground speed to reference. Embodiments of the present invention provide a method of launching a wheeled vehicle from a standstill by determining which wheel or wheels have the least traction and diverting powertrain torque to the wheels with more traction.

Recognising which wheels have the least traction may be performed manually by the driver of the vehicle by visual inspection of the terrain. Once the driver has assessed the situation of the vehicle and selected which wheels are likely to be traction-limited and slip in an attempted pull-away, a user may manually select which wheels should not spin or which wheels appear to have the least traction from a user interface. As explained below, in dependence on the user input, the wheel or wheels identified as being most likely to slip can have appropriately calculated braking forces applied to them and/or the drive torques applied to the respective wheels can be adjusted and balanced so as to divert powertrain drive torque to the wheel or wheels having the most grip, thereby minimising the likelihood of wheel slip occurring in a launch (or pull-away) event. This is advantageous over the prior art because the wheel or wheels most likely to slip can be identified in advance, and by suitable application of preload braking force that slippage can be prevented or at least reduced. Advantageously, the preload braking force is applied before the drive torque is applied, thus mitigating against the drive wheel or wheels digging into soft terrain.

FIG. 8 shows a vehicle 100 according to an embodiment of the present invention. The vehicle 100 has a powertrain 129 that includes an engine 121 that is connected to a driveline 130 having an automatic transmission 124, and an accelerator pedal 161. A control system for the vehicle 100 includes a central controller 10, referred to as a vehicle control unit (VCU) 10, a powertrain controller 11, a brake controller 13 and a steering controller 170C in communication with a steering wheel 171. It is to be understood that embodiments of the present invention are also suitable for use in vehicles with manual transmissions, continuously variable transmissions or any other suitable transmission. Moreover, embodiments of the invention are suitable for use in vehicles having other types of powertrain, such as battery electric vehicles, fuel cell powered vehicles, and hybrids.

In the embodiment of FIG. 8 the transmission 124 may be set to one of a plurality of transmission operating modes, being a park mode P, a reverse mode R, a neutral mode N, a drive mode D or a sport mode S, by means of a transmission mode selector dial 124S. The selector dial 124S provides an output signal to the powertrain controller 11 in response to which the powertrain controller 11 causes the transmission 124 to operate in accordance with the selected transmission mode. Accordingly, in this embodiment a transmission controller (not shown) is incorporated into the powertrain controller 11. However, in other embodiments the transmission controller may be a separate element in operable communication with the central controller 10.

The brake controller 13 is an anti-lock braking system (ABS) controller 13 and forms part of a braking system 22 (FIG. 9), together with a brake pedal 163. The VCU 10 receives and outputs a plurality of signals to and from various sensors and subsystems (not shown) provided on the vehicle. The VCU 10 includes a low-speed progress (LSP) control system 12 shown in FIG. 9, a stability control system (SCS) 14S, a traction control system (TCS) 14T, a cruise control system 16 and a Hill Descent Control (HDC) system 12HD. The SCS 14S improves stability of the vehicle 100 by detecting and managing loss of traction when cornering. When a reduction in steering control is detected, the SCS 14S is configured automatically to command the brake controller 13 to apply one or more brakes 111 Β, 112B,

114B, 115B of the vehicle 100 to help to steer the vehicle 100 in the direction the user wishes to travel. If excessive wheel spin is detected, the TCS 14S is configured to reduce wheel spin by application of brake force in combination with a reduction in powertrain drive torque. In the embodiment shown the SCS 14S and TCS 14T are implemented by the VCU 10. In some alternative embodiments the SCS 14S and/or TCS 14T may be implemented by the brake controller 13. Further alternatively, the SCS 14S and/or TCS 14T may be implemented by one or more further controllers.

The driveline 130 is arranged to drive a pair of front vehicle wheels 111,112 by means of a front differential 137 and a pair of front drive shafts 118. The driveline 130 also comprises an auxiliary driveline portion 131 arranged to drive a pair of rear wheels 114, 115 by means of an auxiliary driveshaft or prop-shaft 132, a rear differential 135 and a pair of rear driveshafts 139. The front wheels 111, 112 in combination with the front drive shafts 118 and front differential 137 may be referred to as a front axle 136F. The rear wheels 114, 115 in combination with rear drive shafts 139 and rear differential 135 may be referred to as a rear axle 136R.

The wheels 111, 112, 114, 115 each have a respective brake 111 Β, 112B, 114B, 115B. Respective speed sensors 111S, 112S, 114S, 115S are associated with each wheel 111, 112, 114, 115 of the vehicle 100. The sensors 111S, 112S, 114S, 115S are mounted to the vehicle 100 and arranged to measure a speed of the corresponding wheel.

Embodiments of the invention are suitable for use with vehicles in which the transmission 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. 8, the transmission 124 is releasably connectable to the auxiliary driveline portion 131 by means of a power transfer unit (PTU) 131P, allowing operation in a two-wheel drive mode or a four-wheel drive mode. 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.

One or more of the controllers 10, 11, 13, 170C may be implemented in software run on a respective one or more computing devices such as one or more electronic control units (ECUs). In some embodiments two or more of the controllers 10, 11, 13, 170C may be implemented in software run on one or more common computing devices. Two or more controllers 10, 11, 13, 170C may be implemented in software in the form of a combined software module.

It is to be understood that one or more computing devices may be configured to permit a plurality of software modules to be run on the same computing device without interference between the modules. For example the computing devices may be configured to allow the modules to run such that if execution of software code embodying a first controller terminates erroneously, or the computing device enters an unintended endless loop in respect of one of the modules, it does not affect execution of software code comprised by a software module embodying a second controller.

It is to be understood that one or more of the controllers 10, 11, 13, 170C may be configured to have substantially no single point failure modes, i.e. one or more of the controllers may have dual or multiple redundancy. It is to be understood that robust partitioning technologies are known for enabling redundancy to be introduced, such as technologies enabling isolation of software modules being executed on a common computing device. It is to be understood that the common computing device will typically comprise at least one microprocessor, optionally a plurality of processors, which may operate in parallel with one another. In some embodiments a monitor may be provided, the monitor being optionally implemented in software code and configured to raise an alert in the event a software module is determined to have malfunctioned.

The SCS 14S, TCS 14T, ABS controller 22C and HDC system 12HD provide outputs indicative of, for example, SCS activity, TCS activity and ABS activity including brake interventions on individual wheels and engine torque requests from the VCU 10 to the engine 121, for example in the event a wheel slip event occurs. Each of the aforementioned events indicate that a wheel slip event has occurred. Other vehicle sub-systems such as a roll stability control system or the like may also be present.

It is to be understood that the VCU 10 is configured to implement a Terrain Response (TR) (RTM) System of the kind described above in which the VCU 10 controls settings of one or more vehicle systems or sub-systems such as the powertrain controller 11 in dependence on a selected driving mode. The driving mode may be selected by a user by means of a driving mode selector 141S (FIG. 8). The driving modes may also be referred to as terrain modes, terrain response modes, or control modes. In the embodiment of FIG. 8, four driving modes are provided: an ‘on-highway’ driving mode or ‘special programs off’ (SPO) mode suitable for driving on a relatively hard, smooth driving surface where a relatively high surface coefficient of friction exists between the driving surface and wheels of the vehicle; a ‘sand’ driving mode (SAND) suitable for driving over sandy terrain; a ‘grass, gravel or snow’ (GGS) driving mode suitable for driving over grass, gravel or snow, a ‘rock crawl’ (RC) driving mode suitable for driving slowly over a rocky surface; and a ‘mud and ruts’ (MR) driving mode suitable for driving in muddy, rutted terrain. Other driving modes may be provided in addition or instead.

The sensors on the vehicle 100 include sensors which provide continuous sensor outputs to the VCU 10, including wheel speed sensors 111S, 112S, 114S, 115S, as mentioned previously and as shown in FIG. 8, and other sensors (not shown) such as an ambient temperature sensor, an atmospheric pressure sensor, tyre pressure sensors, wheel articulation sensors, gyroscopic sensors to detect vehicular yaw, roll and pitch angle and rate, a vehicle speed sensor, a longitudinal acceleration sensor, an engine torque sensor (or engine torque estimator), a steering angle sensor, a steering wheel speed sensor, a gradient sensor (or gradient estimator), a lateral acceleration sensor which may be part of the SCS 14S, a brake pedal position sensor, a brake pressure sensor, an accelerator pedal position sensor, longitudinal, lateral and vertical motion sensors, an inertial measurement unit (IMU), and water detection sensors forming part of a vehicle wading assistance system (not shown). In other embodiments, only a selection of the aforementioned sensors may be used. Other sensors may be useful in addition or instead in some embodiments.

The user interface may include at least one of: a visual display or touch screen, a button, a keypad or D-pad, and a voice-activated console. Figure 3 is an exemplary user interface for selecting a traction-limited wheel in embodiments of the present invention. A user-interface 310 comprising a touch screen 312 showing a schematic layout of the vehicle drivetrain 314 allows the user to select the traction-limited wheel 318 by pressing the touch screen 312. A cursor 316 may be displayed on the touch screen 312 to indicate to the user which wheel was selected as the traction-limited wheel 318. After selecting the wheel most likely to spin i.e. that considered to have the least traction, the user may select others of the wheels, in turn, to determine an order of traction of the wheels. This is advantageous in that all drive wheels can be treated independently, with suitable preload braking forces applied dependent on the traction of each wheel.

Alternatively or additionally, the method may receive input data automatically from one or more vehicle sensors and feed this data into an algorithm to anticipate a wheel-slip event. The vehicle sensors may provide data including: wheel load; wheel rotational speed; locking torque applied on a differential; suspension height; vehicle orientation; steering angle; vehicle speed; driving mode; and vehicle acceleration and deceleration. The data may be indicative of the instantaneous situation during a launch attempt or may be indicative of a situation preceding a launch event, such as data captured whilst the vehicle was coming to a standstill on that particular terrain. Advantageously, the algorithm can determine the appropriate braking forces to be applied to the respective drive wheels dependent on the vehicle data, including historical data, such as that taken in a lead-up to the vehicle coming to a standstill. As such, where data from a preceding event is taken into account, the algorithm can be considered as a ‘learning algorithm’, which is able to make improved determinations by learning from the historical data. Advantageously, the algorithm may determine not only the appropriate preload braking forces, but also associated drive torques for each drive wheel.

In one example, and with reference to the flowchart of Figure 5, where the vehicle has come to a stop using ABS braking, the algorithm compares, at block 502, data including vehicle velocity, braking interventions, and vehicle deceleration as occurred during the ABS braking event to determine, at block 504, whether or not the terrain is friction-limited. If the terrain is determined to be friction-limited, data including brake torques and pressures for each wheel are captured, at block 506, while the vehicle is stopping during ABS the braking event, for input to the algorithm.

Once the vehicle has fully stopped, at block 508, the wheel having the least traction is determined by detecting which of the drive wheels had the highest ABS intervention and/or the lowest braking torque during the ABS event. This can be repeated to find the wheel having the next-lowest traction and so on, until a complete order of traction of the drive wheels has been determined. Based on this data, the algorithm can calculate and assign appropriate preload braking forces to be applied to the respective wheels, with a highest preload braking force being assigned to the wheel determined to have the least traction, and with the wheel determined to have the most traction having no preload braking force applied to it. This is advantageous over prior art which does not take into account vehicle data during an ABS event, as the vehicle data obtained during an ABS event provides a more accurate estimate of each wheel’s traction which will more effectively aid a launch event from standstill.

The preload braking forces for all the drive wheels and the vehicle data captured during the ABS event and used by the algorithm to determine the preload braking forces are saved, at block 510, to a processor memory. Supporting information including driving mode and detection confidence may also be saved to a processor memory. That data can be retrieved and used as input for subsequent launch events, either at the same patch of terrain or elsewhere. According to certain embodiments, there may therefore be a learning aspect to the algorithm, in that it can improve upon initial estimations of wheel-slip events and associated determination of preload braking forces and drive torques for subsequent launch attempts.

A launch event may be initiated in response to a user request, which request may be input through one or more of: an input to the user interface 310, for example by selecting a launch control mode; actuation of a button; and actuation of a pedal, such as the accelerator pedal 161. A current launch event may be defined as actions taken in response to an initial launch attempt request until a successful pull away has been achieved. This may include one or more launch attempts that are initiated automatically after an initial launch attempt if the vehicle has not yet made a successful pull away, which may be considered as continuation attempts of the initial launch attempt or as separate subsequent launch events. A subsequent launch event may be defined as any attempt made after an initial launch event responsive to the user request. This may include such automatic attempts. Alternatively, only launch events made in response to a further user launch attempt request are considered as subsequent launch events. Further alternatively, only launch attempts made after an ignition cycle (and a further user launch attempt request) are considered as subsequent launch events.

Where a vehicle has come to a standstill without any ABS intervention, an alternative routine may be employed. This is illustrated in the flowchart of Figure 6.

When attempting to pull away normally (block 602), vehicle sensor data is monitored, at block 604, as powertrain torque is initially applied to the drive wheels in gently increasing amounts. The actual torque rate changes applied may be based on the conditions, such as: track inclination, rolling resistances, net available traction, TR mode, etc., and may be based on a target acceleration rate of, for example, 0.02 m/s² to 2 m/s².

One embodiment is set out on the left-hand branch of the flowchart. Based on that vehicle data, a determination is made by the algorithm, at block 606, as to whether conventional traction control intervention is necessary. Sensor data may include wheel speeds, engine torque, inertial measurement unit (IMU) acceleration signals, and locking torques in the differentials. If traction control intervention is required, then the algorithm may filter, at block 608, the brake torques of each wheel during the traction control intervention and may compensate for losses and inertia.

When in challenging off-road pull away situations, the wheel speed and intervention torques may vary rapidly and considerably, for example due to the type of terrain - e.g. if a wheel is digging in to muddy ground and reaches a stone it will gain some traction, but when the stone dislodges, that traction may be lost instantly. In such a terrain, the brake torque over a brief period of, for example, a few seconds may be averaged to provide a more consistent and confident braking pre-preload torque to be applied to the wheel by the brake controller. The filtering corresponds to this averaging over time.

Brake torques applied to a wheel to slow it down comprise an addition of engine torque to the wheel and inertia torque of the wheel. Also, engine torque needs to be compensated for losses in drivetrain. Depending on drivetrain architecture, losses and inertia on the path to different wheels may be different. Once these factors have been compensated for, a closer estimate of tractive torque of that wheel can be established. The compensations for losses and inertia therefore result in an improved estimate of brake torque to be applied to the wheels to work against the torque from engine and how much torque is acting on the contact patch of the tyre. So a flared up wheel will have higher losses associated with it not affecting wheels on other axles. Similarly, wheels being accelerated will in effect absorb torque in the form of inertia and release it on braking.

The vehicle may make a successful pull-away, in which case no special launch program is required, although the data collected during the pull-away may be saved for subsequent retrieval, as possible input for subsequent launch events.

If, however, the pull-away is unsuccessful, as determined at block 610, then the algorithm will, in dependence on the data collected during the traction control intervention, determine at block 612 an order of traction of the drive wheels, and will assign appropriate preload braking forces to be applied to the respective wheels, with a highest preload braking force being assigned to the wheel determined to have the least traction, and with the wheel determined to have the most traction having no preload braking force applied to it.

The determination of the preload braking forces to be applied to a drive wheel may, in particular, be made on the basis of one or more of: the ranking of the wheel in the order of traction; the engine torque; the wheel speeds; the drive torque being applied to the wheel; the driving mode; and the powertrain torque at which the wheel started slipping during the traction control event.

Another embodiment is set out on the right-hand branch of the flowchart of Figure 6. During the attempted pull-away, as the powertrain torque is initially applied to the drive wheels in gently increasing amounts and based on the vehicle data captured in block 604, a determination is made by the algorithm, at block 607, as to which of the drive wheels has the least traction by virtue of having been the first to encounter a wheel slip event. An increasing drive torque is applied to the drive wheels with all differentials open. When a first drive wheel to slip is detected, a braking torque is applied to that first slipping wheel to maintain rotation of the wheel at a set speed. The process continues to detect a second drive wheel to slip, whereupon a braking torque is applied to the second slipping wheel to maintain rotation of the wheel at a set speed, which may be the same set speed as for the first slipping wheel or may be a different set speed. The process may be repeated, if necessary, until the drive wheel with the most traction is determined. The amount of drive torque going to each wheel is determined, optionally through an estimate or a calculation.

It will be understood that in variant embodiments, locking torques in the or each differential may be controlled in conjunction with control of the braking forces and drive torques applied to the respective drive wheels.

The vehicle may make a successful pull-away, in which case no special launch program is required, although the data collected during the pull-away may be saved for subsequent retrieval, as possible input for subsequent launch events, the algorithm in this case ‘learning’ from the previous data and thus being able to make a more accurate or faster determination of the brake forces and drive torques to be applied.

If, however, the pull-away is unsuccessful, as determined at block 609, then the algorithm will, in dependence on the data collected during the rising power torque phase of block 607, assign at block 611 appropriate preload braking forces to be applied to the respective drive wheels, with a highest preload braking force being assigned to the wheel determined to have the least traction, and with the wheel determined to have the most traction having no preload braking force applied to it. The determination of the preload braking forces to be applied to a drive wheel may, in particular, be made on the basis of one or more of: the ranking of the wheel in the order of traction; the engine torque; the wheel speeds; the driving mode; and the drive torque being applied to the wheel.

The preload braking forces for all the drive wheels and the vehicle data captured during the failed launch event and used by the algorithm to determine the preload braking forces are saved, at block 614, to a processor memory. Supporting information including driving mode and detection confidence may also be saved to a processor memory. That data can be retrieved and used as input for subsequent launch attempts, either at the same patch of terrain or elsewhere.

The algorithm may, at block 614, merge the preload braking torques as determined for each drive wheel at block 612 with the preload braking forces as determined for each drive wheel at block 611 based on a level of confidence in each determination.

A vehicle pull-away or launch attempt can be made using pre-emptive braking applied to the drive wheels. This is particularly advantageous where a failed launch attempt has previously been made, and where vehicle data is available to calculate the pre-emptive braking forces to be applied. Examples of the collection of such vehicle data, and how the preload braking forces are assigned to the drive wheels are set out above in relation to Figures 5 and 6.

A method of launching a vehicle using pre-emptive brake torques is illustrated in the flowchart of Figure 7. The algorithm determines the preload braking forces to be applied by retrieving, at block 702, saved values of preload data for each drive wheel along with supporting data. Supporting data may include at least: driving mode, vehicle orientation, weight distribution, wheel articulation, or steering angle data. The preload brake torques are optionally subsequently modified, by the algorithm, at block 704, based on the supporting data. The preload brake torques are also optionally scaled, by the algorithm, at block 706, based on the current driving mode. An assessment is performed by the algorithm, at block 708, to determine if the vehicle is ready to attempt a pull-away. If the vehicle is ready to attempt a pull-away, the preload braking forces as determined by the algorithm are applied, at block 710, to each drive wheel in synchronisation with increasing drive torque. The preload braking forces would be applied by the braking system 22 under the control of the VCU 10, which in turn will have the determination of the algorithm as an input. When the wheels start moving (more than a predetermined amount), normal traction control and/or cross-axle slip control is introduced, with the applied preload as the starting point, at block 712. If the vehicle successfully pulls-away, as determined at block 714, the vehicle data is saved at block 716 for possible use in a subsequent launch attempt. This new vehicle data may overwrite the existing data or may be added to it. The wheels moving more than a predetermined amount ensures that the vehicle 100 has actually begun to move, rather than, for example, rocking on the spot with otherwise insubstantial wheel movements.

As the drive torque is increased during the pull-away attempt, the method may include limiting, at block 711, the drive torque when the current engine torque approaches the drive torque value at which a wheel slip event was previously detected.

Once the level of traction of each wheel has been determined, the method includes distributing drive torque to the driven wheels based on the traction available to each wheel to improve the chances of recovering a vehicle.

Where at least one drive wheel is part of a pair of wheels on opposite ends of a common axle, embodiments of the invention may distribute torque by: applying the preload braking force to the drive wheel having the least traction; applying a drive torque to the pair of drive wheels until the other wheel of the pair, which is not subjected to a braking force, or is subject to a lesser braking force, begins to rotate; and modulating the preload braking force on the low traction wheel such that its rotational speed is matched to that of the non-braked wheel.

In another embodiment, the maximum tractive force of at least one drive wheel of the vehicle is determined by: generating a slip curve for the first wheel to slip in a pull-away attempt, such as shown in Figure 2. The slip curve shows the slip vs. tractive forces of a specific wheel and can be used to determine the optimum speed for that wheel (the ‘AMS slip Target Range’). By controlling the lowest traction wheel to this speed, the engine torque can be increased until the other wheel of the axle begins to rotate and successfully pull the vehicle away. If the vehicle detects a subsequent wheel slip of the other wheel, the same technique of determining the optimum wheel speed through a slip curve may be used to determine the maximum tractive force possible for the subsequently slipping wheel. This approach can be repeated for all driven wheels of a vehicle, with all differentials open, to generate the maximum tractive force for the vehicle in subsequent launch events.

All of the embodiments described herein may be influenced by the terrain response modes and engine torque controls of the vehicle.

The algorithm may terminate the launching of a vehicle from a standstill and hand over control of the vehicle to normal traction control if a combination of conditions are met. The conditions may include the vehicle detecting: movement of a given distance in the intended direction; sufficient longitudinal acceleration, indicating the vehicle may have been recovered; a sudden change in vehicle weight distribution, orientation or composure, indicating the scenario of the vehicle has changed; and safety limits of brake pressure modulation being reached.

The above-described processes for launching a wheeled vehicle are carried out by means of a controller. The controller may form a part of a vehicle control system, for example comprising an ECU thereof. The controller comprises a processor and an associated memory. The controller is in operative communication with an input means for providing the controller with information relating to the expected traction of the drive wheels. The input means may be in the form of a user interface, for manual input, which may for example be in the form of a visual display or touch screen, a button, a keypad or D-pad, and a voiceactivated console. Alternatively, the controller may be provided with means to automatically receive input data from at least one vehicle sensor. The means to receive input data may therefore be in the form of vehicle sensors configured to provide data indicative of one or more of: wheel load; wheel rotational speed; locking torque applied on a differential; suspension height; vehicle orientation; steering angle; vehicle speed; driving mode; and vehicle acceleration and deceleration.

The controller is operative to cause the application of a preload braking force to at least one drive wheel in dependence on the received input. The vehicle may have a braking controller and the controller may therefore be in operative communication with the braking controller to achieve this. The controller is also operative to cause the application of a drive torque to at least one of the drive wheels in dependence on the input and on the preload braking force so as to launch the vehicle from a standstill. The vehicle may have a powertrain controller and the controller may therefore be in operative communication with the powertrain controller to achieve this.

A vehicle 100 comprising the controller is shown in Figures 4 and 8.

Any controller or controllers described herein may suitably comprise a control unit or computational device having one or more electronic processors. Thus 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, 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. A first controller may be implemented in software run on one or more processors. One or more other controllers 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.

It will be appreciated that embodiments of the present invention can be realised in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs that, when executed, implement embodiments of the present invention. Accordingly, embodiments provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine readable storage storing such a program. Still further, embodiments of the present invention may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. The claims should not be construed to cover merely the foregoing embodiments, but also any embodiments which fall within the scope of the claims.

Claims

1.

2.

3.

20

4.

5.

6.

7.

8.

A method of launching a wheeled vehicle from a standstill, comprising:

receiving input indicative of an anticipated wheel slip event at a drive wheel of the vehicle, applying a preload braking force to at least one drive wheel in dependence on the input; and applying drive torque to at least one of the drive wheels in dependence on the input and on the preload braking force so as to launch the vehicle from a standstill.

The method of claim 1, wherein receiving input indicative of an anticipated wheel slip event at a drive wheel of the vehicle comprises determining which of multiple drive wheels has the least traction and applying a greatest preload braking force to that drive wheel with the least traction.

The method of claim 2, comprising determining an order of the drive wheels according to their traction, and applying preload braking forces to each respective drive wheel in dependence on the ranking of that drive wheel in the order of traction.

The method of claim 1, 2 or 3, wherein receiving input indicative of an anticipated wheel slip event at a drive wheel of the vehicle comprises a manual input via a user interface.

The method of claim 1, 2 or 3, wherein receiving input indicative of an anticipated wheel slip event at a drive wheel of the vehicle comprises receiving input automatically in dependence on data signals output by at least one vehicle sensor.

The method of claim 5, wherein the signals comprise data relating to one or more of: wheel load; wheel rotational speed; locking torque applied on a differential; suspension height; vehicle orientation; steering angle; vehicle speed; driving mode; and vehicle acceleration and deceleration.

The method of claim 5 or claim 6, wherein the signals are input to an algorithm which determines the preload braking force to be applied to the at least one drive wheel.

The method of claim 7, wherein the algorithm further determines the drive torque to be applied to the at least one drive wheel.

The method of claim 7 or claim 8, when dependent on claim 3, wherein the algorithm determines the preload braking force to be applied to each drive wheel in dependence on vehicle data obtained during an Anti-lock Braking System braking event at the terrain where the vehicle has come to a standstill, the method comprising:

determining if the terrain is friction-limited in dependence on the vehicle velocity, brake interventions and deceleration rate during the ABS event; and, if the terrain is determined to be friction-limited:

capturing the brake torques and brake pressures for each drive wheel as the vehicle is stopping during the ABS event; and determining the order of traction of the drive wheels in dependence on which of the drive wheels has the highest ABS intervention and/or the lowest brake torque during the ABS event.

The method of claim

9, comprising saving the determined preload braking forces to be applied, and vehicle data obtained during the ABS event to a processor memory.

The method of claim 7 or claim 8, when dependent on claim 3, wherein the algorithm determines the preload braking force to be applied to each drive wheel in dependence on vehicle data obtained during a preceding failed launch event at the terrain where the vehicle has come to a standstill.

The method of claim 11, comprising, where there has been a traction control intervention during the preceding failed launch event:

filtering the brake torques of each wheel during the traction control intervention and compensating for losses and inertia associated with the failed launch event;

determining the powertrain torque at which each drive wheel began to slip during the failed launch event; and determining the preload braking forces for each drive wheel in dependence on the filtered preload brake torques and the determined powertrain torques.

13. The method of claim 11, wherein determining the order of traction of the drive wheels comprises determining, from the vehicle sensor signals, which of the drive wheels began to slip first as the engine torque rose during the preceding failed launch event.

5 14. The method of claim 12, comprising:

applying an increasing drive torque to all the drive wheels with all differentials open;

detecting a first drive wheel to slip;

applying a braking torque to that first slipping wheel to maintain rotation of the 10 wheel at a set speed;

detecting a second drive wheel to slip and applying a braking torque to that second slipping wheel to maintain rotation of the wheel at a set speed; and repeating until the drive wheel with the most traction is determined.

15. The method of any of claims 12 to 14, comprising:

15 calculating the drive torque applied to each wheel during the preceding failed launch event; and determining the preload braking forces for each drive wheel in dependence on the engine torque, the wheel speeds and the calculated drive torques.

16. The method of claim 15, when dependent on claim 12, wherein determining the

20 preload braking forces for each drive wheel is in dependence both on the filtered preload brake torques and the determined powertrain torques as per claim 12, as well as on the engine torque, the wheel speeds and the calculated drive torques as per claim 15, based on a level of confidence in each determination.

25 17. The method of any of claims 12 to 16, comprising saving the determined preload braking forces to be applied to a processor memory.

18. The method of any of claims 7 to 17, wherein the algorithm determines the preload braking force to be applied by:

30 retrieving saved values of preload braking force along with supporting data for each drive wheel, wherein the supporting data includes data pertaining to at least: driving mode, vehicle orientation, weight distribution, wheel articulation, or steering angle;

modifying the preload brake forces based on the supporting data;

scaling the preload brake force values based on the current driving mode;

and assessing the preload brake forces and supporting data to determine whether the vehicle is ready to attempt a launch from standstill; and wherein the method comprises:

applying the scaled preload brake forces to each drive wheel in synchronisation with the application of rising drive torque;

when the wheels move above a predetermined amount, introducing normal traction control and/or cross-axle slip control with the applied preload as the starting point; and if the current launch event fails, saving the vehicle data for use in a subsequent launch event.

The method of claim 18, comprising limiting the drive torque rise when the drive torque is near a torque value at which a wheel slip event was previously detected.

The method of any of claims 2 to 19, wherein the at least one drive wheel comprises one of a pair of drive wheels on opposite ends of a common axle, the method comprising:

applying the preload braking force to the drive wheel having the least traction;

applying a drive torque to the pair of drive wheels until the other of the pair, which is not subject to a braking force, begins to rotate; and modulating the preload braking force on the low traction wheel such that its rotational speed is matched to that of the non-braked wheel.

The method of any of claims 7 to 20, wherein determining the maximum tractive force of at least one drive wheel of a vehicle comprises:

generating a slip curve for at least one drive wheel when a traction-limited wheel slips following increasing drive torque;

using said slip curve to determine the optimum speed for the traction-limited wheel;

setting the traction-limited wheel speed to said optimum speed; and increasing drive torque further, resulting in either a successful pull-away attempt or a subsequent wheel slipping; and, if a subsequent wheel slip is detected, generating a new slip curve for the subsequently traction-limited wheel, wherein the method can be repeated to determine slip curves and optimum speeds for each drive wheel to generate maximum tractive force for the vehicle in subsequent launch events.

22. The method according to any preceding claim, wherein the method is terminated by

5 one or more of:

the vehicle having moved a given distance in the intended direction;

the vehicle having sufficient longitudinal acceleration, indicating the vehicle may have been recovered;

a sudden change in vehicle weight distribution, orientation or composure; and

10 the safety limits of brake pressure modulation being reached.

23. A computer program that, when run on a processor, performs a method in accordance with any preceding claim.

24. A controller for controlling a launch of a wheeled vehicle from a standstill, comprising:

15 means for receiving an input indicative of an anticipated wheel slip event at a drive wheel of the vehicle, means for applying a preload braking force to at least one drive wheel in dependence on the input; and means for applying drive torque to at least one of the drive wheels in 20 dependence on the input and on the preload braking force so as to launch the vehicle from a standstill.

25. The controller of claim 24, wherein the input means comprises a user interface, wherein the user interface comprises one or more of: a visual display or touch screen, a button, a keypad or D-pad, and a voice-activated console.

26. The controller of claim 24, wherein the input means comprises at least one vehicle sensor configured to detect one or more of: wheel load; wheel rotational speed; locking torque applied on a differential; suspension height; vehicle orientation; steering angle; vehicle speed; driving mode; and vehicle acceleration and

30 deceleration.

27. The controller of any of claims 24 to 26, configured to carry out the method according to any of claims 1 to 22.

29.

A vehicle comprising the controller of any of claims 24 to 27.

An apparatus, a controller, a system, or a vehicle as described herein with regard to the figures.

Intellectual

Property

Office

Mr Michael Bate

24 October 2017