A control system for controlling a foundation brake and a powertrain of a vehicle

Abstract

Aspects of the present invention relate to the control of a vehicle when descending and ascending a slope, in particular when the vehicle is beginning to ascend or descent starting from rest. The present invention relates to improved control of a vehicle to allow a better controlled ascent or descent.

Description

[0001] A CONTROL SYSTEM FOR CONTROLLING A FOUNDATION BRAKE AND A POWERTRAIN OF A VEHICLE

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a control system for controlling a foundation brake and a powertrain of a vehicle. Aspects of the invention relate to a vehicle, to a method of for controlling the foundation brake and the powertrain of the vehicle, and to computer readable instructions which, when executed by a computer, are arranged to perform the method.

[0004] BACKGROUND

[0005] If a vehicle is at rest on a slope and held at rest by foundation brakes, it may begin moving due to the brakes being disengaged. However, where a vehicle is to travel downhill, it may be difficult to control the acceleration of the vehicle down the slope by selectively applying braking force via the foundation brakes.

[0006] Further, when a vehicle is to travel uphill, it is a known problem to avoid “roll-back” or “roll-against-gear”. To this end, some vehicles include hill-start assist functionality, which may release brakes automatically upon detecting an input to an accelerator pedal. However, in cases where there is a small, positive pressure applied to the accelerator pedal, this may result in the brakes being released without a sufficient propulsive force being provided to prevent roll-back.

[0007] It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

[0008] SUMMARY OF THE INVENTION

[0009] Aspects of the invention relate to a control system for controlling a foundation brake and a powertrain of a vehicle, a vehicle, to a method of for controlling the foundation brake and the powertrain of the vehicle, and to computer readable instructions which, when executed by a computer, are arranged to perform the method as claimed in the appended claims. Friction brakes including disc and drum brakes are examples of foundation brakes.

[0010] According to an aspect of the present invention there is provided a control system for controlling a foundation brake and a powertrain of a vehicle, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, the control system comprising one or more processors collectively configured to: receive a signal comprising information indicating that the vehicle is to transition from the stationary state to a moving state; determine a first torque, the first torque being in a direction to resist movement of the vehicle; output a first torque signal to request the power source to generate a torque equal to the first torque; and subsequent to outputting the first torque signal, output a brake release signal to cause the vehicle foundation brake to be released.

[0011] The processors may be collectively configured to receive the signal comprising information indicating that the vehicle is to transition from the stationary state to a moving state when the vehicle is in a stationary state with a vehicle foundation brake applied; determine if the vehicle is to descend in the moving state; and, in response to determining that the vehicle is to descend in the moving state, determine the first torque.

[0012] The control system comprises one or more controllers collectively comprising at least one electronic processor having an electrical input for receiving an input signal; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to:

[0013] The vehicle may apply a braking torque via the power source before disengaging the foundation brakes. In this way, the vehicle may be controlled better as it transitions from a stationary state to a moving state when descending.

[0014] The foundation brakes may also comprise eddy current brakes. The foundation brakes may also be referred to as friction brakes. Friction brakes include disk brakes and drum brakes. The signal comprising information indicating that the vehicle is to transition from the stationary state to a moving state may come from a range of sources. For instance, the signal may be a signal from an accelerator pedal being depressed, from a gear stick being moved into a driving gear, or the release of a brake pedal.

[0015] The one or more processors may be collectively configured to: receive a first torque output signal, the first torque output signal comprising information indicative of a torque applied by the power source; determine whether the torque applied by the power source is greater in magnitude than a control torque threshold; and output the brake release signal based on a determination that the torque output by the power source is greater in magnitude than the control torque threshold.

[0016] By ensuring that a sufficient torque is applied to the wheels by the electric machine before the foundation brakes are released, undesired acceleration of the vehicle in a downhill direction may be avoided. This may allow improved control of the vehicle.

[0017] The one or more processors may be collectively configured to: receive a gradient signal comprising information indicative of a gradient of a surface the vehicle is on; and determine the control torque threshold at least partially on the gradient of the surface the vehicle is on.

[0018] It will be understood that the downhill component of the weight force will increase with surface gradient and therefore, by receiving a gradient signal such as from an inertial measurement unit (IMU), the vehicle may be better controlled as it descends.

[0019] The one or more processors may be collectively configured to: receive a vehicle mass signal comprising information indicative of the mass of the vehicle; and determine the control torque threshold such that the control torque threshold equals the torque on the wheels due to the weight of the vehicle and the gradient of the surface the vehicle is on, based on the gradient of the surface and the mass of the vehicle. In this way, there may be reduced movement of the vehicle due to release of the brakes, and the brakes may have zero torque load when released. This may reduce noise, vibration and harshness of the vehicle, improving passenger comfort.

[0020] The one or more processors may be collectively configured to receive a gradient signal comprising information indicative of a gradient of a surface the vehicle is on; and determining if the vehicle is to descend in the moving state may comprise comparing the gradient of the surface the vehicle is on to a descent control threshold. The control system may therefore determine whether a vehicle is facing downhill in a drive mode or uphill in a reversing mode, and may apply the control method when it is determined that the vehicle is to descend. In some cases, the descent control threshold may be non-zero as a shallow gradient may not require descent control using the power source.

[0021] The one or more processors may be collectively configured to determine the first torque based at least partially on the or a gradient of the or a surface the vehicle is on. In this way, the torque applied to the wheels may resist rolling of the vehicle and allow more controlled descent.

[0022] The one or more processors may be collectively configured to: receive a vehicle mass signal comprising information indicative of the mass of the vehicle, and determine the first torque based at least partially on the vehicle mass signal. In this way, the torque applied to the wheels may resist rolling of the vehicle and allow more controlled descent. In particular, the first torque may be determined based on the mass of the vehicle and the gradient of the surface such that the first torque approximately resists downhill acceleration of the vehicle, to cause a descent at a constant speed.

[0023] In the moving state, the one or more processors may be collectively configured to: receive a torque demand signal, the torque demand signal comprising information indicative of a torque demand, determine a further torque based on the torque demand, the further torque having a magnitude different from the magnitude of the first torque; and output a further torque signal to request the power source to generate a torque equal to the furthertorque. The torque demand may be from a driver input device such as an accelerator pedal. By varying the torque demand, the descent may be controlled and variable in speed, by adjusting the braking torque provided by the power source.

[0024] The one or more processors may be collectively configured to determine the first torque such that the magnitude of the first torque changes at or below a predetermined rate of change of torque. By limiting the rate of change of power source torque, vehicle graunching may be reduced. This may improve passenger comfort.

[0025] The one or more processors may be collectively configured to output the brake release signal to cause the vehicle foundation brake to be released such that the braking torque imparted by the vehicle foundation brake decreases at or below a predetermined rate of change of brake torque. By limiting the rate of change of brake torque, vehicle graunching may be reduced. This may improve passenger comfort. The vehicle may have a front axle and a rear axle, and the one or more processors may be collectively configured to: determine which of the front and rear axles are a tractive axle and which is a non-tractive axle based on the or a gradient of the or a surface the vehicle is on; and output the first torque signal to cause the power source to apply a torque to the tractive axle.

[0026] The tractive axle may be an axle with a greater normal reaction force with the surface on which the vehicle is located. The determination of the tractive axle may be based on load data from the vehicle suspension, or by a value of the gradient of the surface and a knowledge of the longitudinal position of the centre of gravity of the vehicle. By applying a torque to the tractive axle, which may be a downhill axle, the chance of the wheel slipping may be reduced, as the downhill axle may have greater normal reaction force with the ground, increasing the traction of that axle.

[0027] The one or more processors may be collectively configured to output the first torque signal to cause the power source to apply a tractive axle torque to the tractive axle and a non-tractive axle torque to the non-tractive axle, the tractive axle torque having a magnitude greater than the magnitude of the non-tractive axle torque. In this way, where both axles are driven, the tractive axle may be driven with a greater torque in order to improve traction. The risk of wheel slip is therefore reduced.

[0028] According to a further aspect of the invention, there is provided a vehicle comprising a powertrain, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, and the control system of the first-mentioned aspect.

[0029] The power source may be an electric machine.

[0030] According to a still further aspect of the invention, there is provided a method for controlling a foundation brake and a powertrain of a vehicle, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, the method comprising: when the vehicle is in a stationary state with a vehicle foundation brake applied, receiving a signal comprising information indicating that the vehicle is to transition from the stationary state to a moving state; determining if the vehicle is to descend in the moving state; in response to determining that the vehicle is to descend in the moving state: determining a first torque, the first torque being in a direction to resist downhill movement of the vehicle; outputting a first torque signal to request the power source to generate a torque equal to the first torque; subsequent to outputting the first torque signal, outputting a brake release signal to cause the vehicle foundation brake to be released.

[0031] According to a yet still further aspect of the invention, there is provided computer readable instructions which, when executed by a computer, are arranged to perform a method according to the still further aspect of the invention.

[0032] According to another aspect of the invention, there is provided a control system for controlling a powertrain of a vehicle and a foundation brake of the vehicle, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, the control system comprising one or more processors collectively configured to: receive a torque demand signal comprising information indicative of a torque demand; select a required torque for the power source, wherein the required torque is selected to be the greater of an anti-roll torque value and the torque demand; and output a required torque signal to cause the power source to generate a torque equal to the required torque.

[0033] The control system may be arranged to receive a foundation brake release signal and to select the required torque in response to the foundation brake release signal.

[0034] A torque demand signal may be received from a driver input device such as an accelerator pedal or from ADAS. In situations where a vehicle encounters significant forces in an opposite direction to the direction of travel, such as on a steep upward slope, a torque demand intended to move the vehicle forwards slowly may in fact result in the vehicle moving backwards. This can be damaging for the vehicle and may be unsettling for a driver. By comparing the torque demand to a threshold, and setting the torque demand to a minimum amount, this undesired phenomenon may be reduced or avoided.

[0035] The foundation brake release signal may be output by the control system to a brake actuator and also received by a further part of the control system, so that the foundation brake release signal is a command to disengage foundation brakes or may be a signal output by a brake actuator indicating that the foundation brakes have been released, in response to a received command.

[0036] The one or more processors may be collectively configured to: receive a torque generation signal comprising information indicative of a torque output by the power source; compare, in response to the foundation brake release signal, the information indicative of the torque output by the power source to a brake release torque threshold; based on a determination that the torque output by the power source is greater than the brake release torque threshold, output a foundation brake release signal to cause the foundation brake to be released.

[0037] Where a vehicle may be stopped on a hill and held at rest by the foundation brakes, there is the possibility that the vehicle may roll down the hill undesirably when the brakes are released. This is particularly common where there may be a low torque demand or where the torque generated by the power source might not match the torque demand, such as due to a lag in the torque generated by the power source relative to the demanded torque. By considering the torque generated by the power source and releasing the brakes dependent on the torque generated by the power source exceeding a threshold, this issue may be reduced.

[0038] Overall, the processors may be collectively configured to: receive a torque demand signal comprising information indicative of a torque demand; based on the torque demand signal, output a required torque signal to cause the power source to generate a torque equal to the demanded torque; receive a torque generation signal comprising information indicative of a torque output by the power source; compare, the information indicative of the torque output by the power source to a brake release torque threshold, and based on a determination that the torque output by the power source is greater than the brake release torque threshold, output a foundation brake release signal to cause the foundation brake to be released.

[0039] The processors may be collectively configured to: after outputting the foundation brake release signal determine a required torque. Determining the required torque may comprise, in response to the foundation brake release signal, selecting a required torque for the power source, wherein the required torque is selected to be the greater of an anti-roll torque value and the torque demand; and outputting a required torque signal to cause the power source to generate a torque equal to the required torque.

[0040] The one or more processors may be collectively configured to: receive a gradient signal comprising information indicative of the gradient of a surface the vehicle is on, and determine the brake release torque threshold based on the information indicative of the gradient of the surface. As the vehicle may be more likely to roll back on a steeper road, or lurch forward on brake release on a less steep road, by considering the gradient when determining the brake release torque threshold, the vehicle may move as desired in a wider range of situations.

[0041] The one or more processors may be collectively configured to: receive a vehicle mass signal comprising information indicative of the mass of the vehicle, and determine the brake release torque threshold based at least partially on the information indicative of the mass of the vehicle. A heavier vehicle may be more likely to roll back on a steep road, and a light vehicle may accelerate more quickly. By considering the vehicle mass, and in turn the weight, when determining the brake release torque threshold, the vehicle may move as desired in a wider range of situations.

[0042] The brake release torque threshold may be equal to or less than the anti-roll torque threshold. This may allow the vehicle to remain stationary or creep forward slowly upon brake release. In particular, it may allow vehicles to mimic the creep that is a known feature of vehicles having torque converters where no torque converter is present.

[0043] The foundation brake release signal may be arranged to cause the foundation brake to be released such that a braking torque imparted by the foundation brake decreases at or below a predetermined rate of change of brake torque. By limiting the rate of change of brake torque, i.e. limiting how quickly the brakes may be released, the transition from being stationary and held by the foundation brakes to being propelled forward by the power source may be made smoother, improving driver comfort.

[0044] The one or more processors are collectively configured to: receive the or a gradient signal comprising information indicative of the gradient of the or a surface the vehicle is on; and determine the anti-roll torque threshold based on the information indicative of the gradient of the surface. As the vehicle may require more torque to creep forward on a steeper road, by considering the gradient when determining the anti-roll torque, the vehicle may move with a similar speed or acceleration profile in a wider range of situations.

[0045] The one or more processors may be collectively configured to: receive the or a vehicle mass signal comprising information indicative of the mass of the vehicle, and determine the anti-roll torque threshold based at least partially on the information indicative of the mass of the vehicle. A heavier vehicle may require more torque to creep forward on a steep road, by considering the mass and weight of the vehicle when determining the antiroll torque, the vehicle may move with a similar speed or acceleration profile in a wider range of situations.

[0046] The required torque signal may be arranged to cause the torque generated by the power source to increase at or above a predetermined rate of change of torque. By increasing the torque generated by the power source at a rate above a threshold, the vehicle may respond more quickly to a driver demand, meaning that the delay between a driver requesting an acceleration and the acceleration occurring may be reduced.

[0047] According to an additional aspect of the invention, there is provided a vehicle comprising: a powertrain, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, a foundation brake, and the control system of the another aspect.

[0048] The power source may be an electric machine.

[0049] According to a further additional aspect of the invention, there is provided a method for controlling a foundation brake and a powertrain of a vehicle, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, the method comprising: receiving a foundation brake release signal; receiving a torque demand signal comprising information indicative of a torque demand; selecting, in response to the foundation brake release signal, a required torque for the power source, wherein the required torque is selected to be the greater of an anti-roll torque value and the torque demand; and outputting a required torque signal to cause the power source to generate a torque equal to the required torque.

[0050] The method may further comprise: receiving a torque generation signal comprising information indicative of a torque output by the power source; comparing, in response to the foundation brake release signal, the information indicative of the torque output by the power source to a brake release torque threshold; based on a determination that the torque output by the power source is greater than the brake release torque threshold, outputting a foundation brake release signal to cause the foundation brake to be released.

[0051] According to a still further additional aspect of the invention, there is provided computer readable instructions which, when executed by a computer, are arranged to perform a method according to the further additional aspect of the invention.

[0052] 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

[0053] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0054] Figure 1 shows a vehicle in accordance with an embodiment of the invention;

[0055] Figure 2 shows a block diagram illustrating components of a vehicle in accordance with an embodiment of the invention;

[0056] Figure 3 shows a block diagram illustrating components of a vehicle in accordance with a further embodiment of the invention; and

[0057] Figures 4 to 8 show flow charts illustrating methods of controlling the powertrain and the foundation brakes of the vehicle in accordance with embodiments of the invention.

[0058] DETAILED DESCRIPTION

[0059] Figure 1 illustrates a vehicle according to an embodiment of the present invention to provide context for the invention.

[0060] The vehicle 10 includes a control system 110, a powertrain 120 and a foundation braking system 130. The control system 110 is arranged to control the powertrain 120 and the foundation braking system 130. The vehicle 10 may be a hybrid electric vehicle having an electric machine and an internal combustion engine both arranged to drive the wheels of the vehicle or may be a battery electric vehicle powered by an electric machine only. In some cases, the vehicle 10 may have multiple electric machines arranged to drive the wheels. The vehicle 10 may be a mild hybrid electric vehicle (MHEV) or a plug-in hybrid electric vehicle (PHEV). The foundation braking system 130 may comprise disc brakes or drum brakes.

[0061] Figure 2 shows a schematic diagram of components of the vehicle 10. The vehicle 10 has the control system 110, the control system 110 comprising a plurality of controllers. The controllers are collectively configured to receive data from different sensors, systems, and input devices of the vehicle, to process the data and to output commands for controlling the vehicle. The controllers may each or may communally comprise processing means and memory means. The processing means may be one or more electronic processing devices which operably execute computer readable instructions. The memory means may be one or more memory devices. The memory means is electrically coupled to the processing means. The memory means is configured to store instructions, and the processing means may be configured to access memory means and to execute the instructions stored thereon.

[0062] The control system 110 is arranged to control a powertrain 120. The powertrain comprises a power source 122. The power source 122 may be an electric machine and in some cases the powertrain 120 may have two power sources 122 which are an electric machine and an internal combustion engine. The powertrain 120 also comprises a drivetrain 124 that is arranged to receive torque 125 from the power source 122, to convert the torque and to provide a converted torque 127 to the wheels 140. The drivetrain 124 may be a direct-drive drivetrain or may have a gearbox and a differential for increasing the torque 125 delivered from the power source 122 so that a higher torque 127 may be delivered to the wheels 140 of the vehicle.

[0063] The powertrain 120 is controlled by and monitored by the control system 110. The control system 110 is arranged to output an electric machine torque requirement signal 121 , which may also be referred to as a required torque signal 121 , to the powertrain 120 to cause the power source 122 to generate a required amount of torque 125. The control system 110 is also arranged to receive data 123, such as a torque generation signal 123, from the powertrain 120. The received data 123 may include a rotational speed of the power source 122 and may include a torque generated by the power source 122. The control system 110 may also receive data 123 and transmit commands 121 related to the drivetrain 124. The control system 110 may transmit commands 123 to the powertrain 120, such as a gear change command to change a torque ratio of the drivetrain 124. The control system 1 10 may also receive data 123 that may include a rotational speed of one or more components of the drivetrain 124, or an amount of torque received by the drivetrain 124 or output by the drivetrain 124. The torque ratio of the drivetrain may be transmitted from the drivetrain 124 to the control system 110 as part of data 123 or may be stored as a value in the control system 110, as the control system 110 may command the drivetrain 124 in order to control the torque ratio of the drivetrain 124.

[0064] The vehicle 10 also has a foundation braking system 130. The term “foundation brake” is generally used herein to mean any braking system that may decelerate the vehicle by converting kinetic energy into heat, as opposedo a regenerative brake, such as may be provided by an electric machine. In this specific example the foundation braking system 130 comprises a brake actuator 132 and a foundation brake 134. The brake actuator 132 may be a hydraulic pump or an electromechanical actuator for moving components of the foundation brake 134 that are arranged to engage frictionally in order to provide a braking torque. The brake actuator 132 may therefore apply a force 135 to the foundation brake 134. The foundation brakes 134 may be any friction brake, such as brake discs with moveable brake callipers or drum brakes with moveable brake shoes. By moving components of the foundation brakes 134 into engagement, the foundation braking system 130 may provide a braking torque 137 to the wheels 140 to decelerate the vehicle.

[0065] The control system 110 is arranged to output brake command signals 131 to the foundation braking system 130. The brake command signals 131 include a foundation brake release signal that is arranged to cause the foundation brake actuator 132 to disengage the foundation brake 134, such that a braking torque is reduced. The brake command signals 131 also include a brake engagement signal that is arranged to cause the brake actuator 132 to engage the foundation brake 134 to cause an increase in braking torque 137 applied to the wheels.

[0066] The control system 1 10 may receive brake data 133 from the foundation brake system 130. The foundation brake data 133 may include information of a generated brake torque, which may differ from the commanded brake torque due to a lag in the activation of the brake actuator 132. The data 133 may include data that a brake release has been effected, such that a negligible brake torque is being provided by the foundation brake 134. This signal may also be referred to as a brake release signal. The control system 110 is also arranged to receive further input signals. The control system 110 is arranged to receive an acceleration or deceleration request 103 from a speed control device 102. The speed control device 102 may be a driver's accelerator pedal or may be an autonomous driving system. The control system 110 is also arranged to receive a proper acceleration signal 105 from an inertial measurement unit 104. The proper acceleration may be used to determine a gradient of a road the vehicle is on and may be used in determination of a mass of the vehicle, in conjunction with a torque value received from the powertrain 120. Proper acceleration is acceleration relative to freefall and is the acceleration provided by an accelerometer, or a plurality of accelerometers, such as the inertial measurement unit 104. The control system 110 may also receive a driving mode input value 107 from a driving mode selection switch 106. The driving mode may include information such as a desired driving style, or a terrain over which the vehicle is travelling. The driving mode selection switch 106 may indicate that a single pedal driving mode is to be effected. In a single pedal driving mode, the control system 110 may instruct the power source 122 to exert a braking torque to decelerate the vehicle based on an input from an accelerator pedal, without any input from a brake pedal.

[0067] It will be understood that the inertial measurement unit 104 and / or the driving mode selection switch 106 may be omitted in some cases.

[0068] The control system 110 may also receive further inputs from further input devices that are not shown. For example, a gear stick may provide an input signal to select a driving mode, a reversing mode or a parking mode. The control system 110 may also receive suspension loading data from suspension sensors, which may be strain sensors. The loading sensors may provide information about the pitch of the vehicle and / or the mass and mass distribution of the vehicle. This may be used in a determination of the mass of the vehicle and / or in the determination of the gradient of a surface the vehicle is located on.

[0069] It will be understood that the control system 1 10 may be formed of a plurality of separate controllers or processors, and that signals which are described as being received by the control system or output by the control system may be published on a central CAN bus or output by one portion of a computer program and received by a further portion of the computer program. Signals described as being received may also be retrieved from an internal memory or determined by a program within the control system 110.

[0070] Figure 3 shows a further possible architecture of a vehicle 10.

[0071] The control system 110, input devices 102, 104, 106, and signals 103, 105, 107 may be substantially similar to those described above with reference to figure 2 and so their descriptions are not repeated here for brevity.

[0072] As can be seen in Figure 3, the vehicle 10 may have multiple powertrains 120a, 120b and multiple foundation braking systems 130a, 130b. The separate powertrains 120a, 120b and foundation braking systems 130a, 130b may control separate wheels or separate axles 140a, 140b. For example, a first powertrain 120a and a first braking system 130a may control a first pair of wheels 140a and a second powertrain 120b and a second braking system 130b may control a second set of wheels 140b. The first set of wheels 140a may be front wheels of a vehicle, and the second set of wheels 140b may be a rear set of wheels. The first powertrain 120a has a first power source 122a arranged to transfer a first torque 125a to a first drivetrain 124a. The first drivetrain 124a is arranged to receive the first torque 125a, to convert the first torque 125a such as via a gearbox, and to transmit a first wheel torque 127a to the first wheels 140a. The vehicle 10 also has a first foundation braking system 130a comprising a first brake actuator 132a arranged to transfer a braking force 135a to first foundation brake 134a, such that a first braking torque 137a is transmitted to the first wheels 140a.

[0073] The vehicle 10 has a second powertrain 120b and a second foundation braking system 130b arranged to transmit second wheel torque 127b and second braking torque 137b to the second wheels 140b respectively. The second powertrain 120b has a second power source 122b, arranged to transfer a second torque 125b to a second drivetrain 124b, and the second foundation braking system 130b has a second brake actuator 132b arranged to transfer a second braking force 135b to a second foundation brake 134b.

[0074] It will be understood that the power trains 120a, 120b described with reference to Figure 3 may be substantially similar to the powertrain 120 described with reference to Figure 2 and that the braking systems 130a, 130b may be substantially similar to the braking system 130 of Figure 2.

[0075] The first and second power trains 120a, 120b also arrange to transfer data 123a, 123b to the control system 110 and to receive commands 121 a, 121 b from the control system 110. Similarly, the braking systems 130a, 130b are arranged to receive commands 131 a, 131 b from the control system 110 and to transmit data 133a, 133b to the control system 110.

[0076] By providing two separate powertrains 120a, 120b and two separate braking systems 130a, 130b, the braking torques provided by the powertrains and / or the braking systems may be selected for different wheels deliberately so as to improve traction of the vehicle. Stability of the vehicle may also be improved during a transition from a braking torque provided by the powertrains 120a, 120b to a braking torque provided by the foundation brakes 130a, 130b.

[0077] In cases of travel on an incline, such as the ascents and descents described below, the torques 127a, 127b provided by the powertrains 120a, 120b may be different. In particular, a tractive axle, which is an axle having a greater normal reaction force with the ground, may be selected to have a greater torque applied to it, than the other, non-tractive axle.

[0078] Figures 4 to 8 illustrate methods according to embodiments of the invention. The methods are methods of controlling a powertrain and a foundation brake of a vehicle, such as the vehicle 10 illustrated in Figures 1 , 2 and 3. The methods may be performed by the control system 1 10 illustrated in Figures 1 , 2 and 3. In particular, the control system may comprise a memory, which may comprise computer-readable instructions which, when executed by a processor, perform the methods according to the embodiments of the invention. Figure 4 shows a method 150 of controlling a vehicle. The method 150 is a method of controlling a vehicle when the vehicle transitions from a stationary mode to a driving mode and in particular is a method of controlling a vehicle when the vehicle begins driving on an inclined surface.

[0079] At step 160, the control system is arranged to receive a torque request. The torque request may be a signal from a speed control device such as an accelerator pedal 102 or may be a change in driving mode from a gear stick, such as a change to a driving or a reversing mode from a park or neutral mode.

[0080] At step 170, the control system is configured to determine whether the vehicle is to ascend or descend along a slope. To this end, the control system may receive a gradient signal, which may also be referred to as a surface signal, from an inertial measurement unit 104. The information from the inertial measurement unit may be combined with suspension data indicating the pitch of the vehicle, such that it can be determined whether the vehicle is due to ascend or descend. The gradient signal may alternatively be received from other means, such as from a suspension loading sensor. The determination as to whether the vehicle is to ascend or descend may also be based on a driving direction of the vehicle, i.e. whether the vehicle is to drive forward or reverse. The vehicle may ascend by reversing uphill while facing downhill, or by driving uphill while facing uphill, and may descend when travelling forwards or in reverse also.

[0081] Based on the determination at step 170, the vehicle may enter an ascending mode 180, which is discussed below with reference to Figures 5 and 6, or a descending mode 190, which is discussed below with reference to Figures 7 and 8.

[0082] Figure 5 shows a method 200 of controlling a vehicle. In particular, Figure 5 shows a method of controlling a vehicle where the vehicle is to ascend a slope. The method 200 may be selected at step 180 of method 150. The ascension may be performed by the vehicle driving forward in a drive mode while facing uphill or may be performed by the vehicle reversing, in a reversing mode, when the vehicle is facing downhill.

[0083] At step 210, the control system is arranged to receive a foundation brake release signal. The foundation brake release signal may be output by the control system and published on a CAN bus or may be received from a further control system. Generally, at step 210, it may be determined that the vehicle is to transition from a stationary mode to a moving mode.

[0084] At step 220, a torque demand signal is received by the control system. The torque demand signal may be received from a driver input device such as an accelerator pedal or may be received from an advanced driver assistance system (ADAS) such as adaptive cruise control. Generally, the torque demand signal may indicate that the vehicle should provide a propulsive torque. Step 220 may be interchanged with step 160 of method 150 where the two methods are combined.

[0085] At step 230, the control system is configured to determine a minimum torque value. The minimum torque value may be described as an anti-roll torque and may be a minimum torque that prevents the vehicle from travelling downhill under gravity, which may be undesirable as it may damage internal components of the drivetrain and may be disconcerting for a driver of the vehicle. The anti-roll torque may be determined based on a gradient of the surface on which the vehicle is located and on a known or estimated mass of the vehicle. The gradient may be determined similarly to that discussed above with reference to step 170.

[0086] Determining the anti-roll torque may comprise determining an anti-roll torque that varies over time. The antiroll torque may vary overtime in orderto reduce graunching of the vehicle and to provide a smoother transition to movement for passengers in the vehicle. The anti-roll torque may therefore increase over time at a predetermined rate. The rate may be selected to balance responsiveness of the vehicle and smoothness of the movement.

[0087] At step 240, the control system is configured to select a required torque. The required torque is selected to be the lower of the torque demand and the minimum torque value. This allows the torque to be controlled by the driver when a higher torque is required, and prevents damage to the vehicle or an undesired downhill travel in the alternative.

[0088] Generally, after release of the brakes, the required torque may be maintained at or above the anti-roll torque in order to prevent downhill movement of the vehicle.

[0089] The anti-roll torque may be re-calculated periodically as the control system may receive updated, further gradient information. Steps 230 and 240 may therefore be repeated periodically.

[0090] At step 250, the required torque is output to the one or more power sources in order that the required torque is generated.

[0091] As described above, the torque may be generated by one power source or may be generated by multiple power sources, in particular a tractive axle may be determined by the control system and a greater torque may be applied with the tractive axle.

[0092] Figure 6 shows a further method of ascending a hill with a vehicle. The method 202 begins at step 215, where a torque demand or other instruction to change from a stationary state to a moving state is received by the control system. Step 215 may be interchanged with step 220 of method 200 or step 160 of method 150.

[0093] Subsequently, steps 220, 230, 240 and 250 are substantially similar to those described above with reference to Figure 5.

[0094] At step 260, the control system receives a torque generation signal comprising information indicative of a torque output by the power source. The torque output by the power source may lag relative to the torque required from the power source and so it may be desirable to check the actual torque produced by the power source before releasing the foundation brakes. At step 260, the torque output by the power source is compared to a brake release torque threshold. The brake release torque threshold may be the required power source torque for holding the vehicle stationary on the slope or for slowly accelerating the vehicle uphill. The brake release torque threshold may be determined based on a known or estimated mass of the vehicle, and a gradient of the slope the vehicle is on. The gradient may be determined similarly to that discussed above with reference to step 170.

[0095] Once the torque produced by the power source is greater than the brake release torque threshold, the method moves to step 270.

[0096] At step 270, a foundation brake release signal is output by the control system to cause the foundation brakes to be released.

[0097] Subsequently, at step 280 the requirement that the required torque is the greater of an anti-roll torque and the torque demand may be maintained. This allows the vehicle to creep forward at low speed and prevents the vehicle from rolling downhill. Step 280 is an optional step of the method 250.

[0098] Above a speed threshold, the requirement for the required torque to be the greater of the anti-roll torque and the torque demand may be removed, to allow the vehicle to decelerate.

[0099] Figure 7 shows a flow chart illustrating a method 300 of allowing a vehicle to descend a slope in a controlled manner. The method 300 may be selected at step 190 of method 150.

[0100] At step 310, where the control system determines that the vehicle is in a stationary state with a vehicle foundation brake applied, the control system receives a signal indicating that the vehicle should transition from a stationary state to a moving state. The received signal may be an acceleration signal from an accelerator pedal or may be a signal from a gear stick changing from a park mode to a drive mode. It will be understood that the descent may be made by the vehicle facing forwards down a hill in a forward driving mode or by a vehicle facing uphill that is reversing down the slope. Step 310 may be interchanged with step 160 of method 150.

[0101] At step 320, in response to the determination that the vehicle is to descend, the control system determines a first torque. The first torque is determined in order to resist downhill movement of the vehicle using a power source. The first torque may be determined based on the mass of the vehicle and / or the gradient of the slope. The first torque may be a single torque to be generated by a single power source or may be a plurality of torques to be generated by a plurality of power sources. For example, the first torque may comprise a first front axle torque and a first rear axle torque. The gradient may be determined similarly to that discussed above with reference to step 170.

[0102] At step 330, the control system outputs a first torque signal to request the power source to generate a torque equal to the first torque. The first torque signal may be output to cause one power source to generate a torque, or to cause a plurality of power sources to generate a plurality of torques. At step 340, after the outputting of the first torque signal, the control system outputs a brake release signal to cause the vehicle foundation brake to be released.

[0103] By outputting the torque signal to cause the power source to generate torque before the brake release signal, the prospect of an uncontrolled downhill acceleration of the vehicle after brake release may be reduced.

[0104] Figure 8 illustrates a further method 350 of descending a slope with a vehicle in a controlled manner.

[0105] Steps 310, 320, 330 and 340 may be substantially similar to the identically numbered steps previously described steps.

[0106] At step 360, the control system receives a first torque output signal. The first torque output signal may also be described as a torque generation signal and comprises information indicative of a torque output by the power source. The first torque output signal may be output by an encoder or torque sensor coupled to the power source, and so may represent a real value of torque, which may vary relative to a torque required from the power source, such as due to a lag in response of the power source after a torque is requested.

[0107] At step 370, the torque applied or output by the power source is compared to a control torque threshold. The control torque threshold is a torque value that is required for resisting uncontrolled downhill acceleration of the vehicle. The control torque threshold may be determined based on the mass of the vehicle and / or a gradient of the slope on which the vehicle is located.

[0108] The control system is arranged to hold the vehicle at this state until the torque generated by the power source is sufficient to resist downhill acceleration of the vehicle.

[0109] Once the torque generated by the power source is greaterthan the control torque threshold, the method moves to step 340, where a brake release signal is output, to release the brakes and allow the vehicle to descend under control of the power source.

[0110] It will be understood that the vehicle may have two or more axles and, based on data such as gradient data from an inertial measurement unit, suspension loading data from one or more suspension sensors and known vehicle properties, the control system may determine the vehicle weight on each axle. The weight on each axle may be the normal reaction force with the surface on which the vehicle is located. Based on the force on the axles, an axle with a greater loading may be termed a tractive axle, as it is an axle that can provide a greater traction than the other axle and torque requirements on each axle may be selected based on the loading of the axles. In particular, the control system may be arranged to determine tractive axle torque and non-tractive axle torque, with the tractive axle torque being greater than the non-tractive axle torque, so that the torque can be distributed between the axles unequally to improve stability of the vehicle and reduce the prospect of wheel slippage. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

CLAIMS1. A control system for controlling a foundation brake and a powertrain of a vehicle, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, the control system comprising one or more processors collectively configured to: when the vehicle is in a stationary state with a vehicle foundation brake applied, receive a signal comprising information indicating that the vehicle is to transition from the stationary state to a moving state; determine if the vehicle is to descend in the moving state; in response to determining that the vehicle is to descend in the moving state: determine a first torque, the first torque being in a direction to resist downhill movement of the vehicle; output a first torque signal to request the power source to generate a torque equal to the first torque; and subsequent to outputting the first torque signal, output a brake release signal to cause the vehicle foundation brake to be released.

2. The control system of claim 1 , wherein the one or more processors are collectively configured to: receive a first torque output signal, the first torque output signal comprising information indicative of a torque applied by the power source; determine whether the torque applied by the power source is greater in magnitude than a control torque threshold; and output the brake release signal based on a determination that the torque output by the power source is greater in magnitude than the control torque threshold.

3. The control system of claim 2, wherein the one or more processors are collectively configured to: receive a gradient signal comprising information indicative of a gradient of a surface the vehicle is on; and determine the control torque threshold at least partially on the gradient of the surface the vehicle is on.

4. The control system of claim 3, wherein the one or more processors are collectively configured to: receive a vehicle mass signal comprising information indicative of the mass of the vehicle; and determine the control torque threshold based on the gradient of the surface and the mass of the vehicle such that the control torque threshold equals the torque on the wheels due to the weight of the vehicle and the gradient of the surface the vehicle is on.

5. The control system of any preceding claim, wherein the one or more processors are collectively configured to receive a gradient signal comprising information indicative of a gradient of a surface the vehicle is on; and wherein determining if the vehicle is to descend in the moving state comprises comparing the gradient of the surface the vehicle is on to a descent control threshold.

6. The control system of any preceding claim, wherein the one or more processors are collectively configured to determine the first torque based at least partially on the or a gradient of the or a surface the vehicle is on.

7. The control system of any preceding claim, wherein the one or more processors are collectively configured to: receive a vehicle mass signal comprising information indicative of the mass of the vehicle, and determine the first torque based at least partially on the vehicle mass signal.

8. The control system of any preceding claim, wherein, in the moving state, the one or more processors are collectively configured to: receive a torque demand signal, the torque demand signal comprising information indicative of a torque demand, determine a further torque based on the torque demand, the further torque having a magnitude different from the magnitude of the first torque; and output a further torque signal to request the power source to generate a torque equal to the further torque.

9. The control system of any preceding claim, wherein the one or more processors are collectively configured to determine the first torque such that the magnitude of the first torque changes at or below a predetermined rate of change of torque.

10. The control system of any preceding claim, wherein the one or more processors are collectively configured to output the brake release signal to cause the vehicle foundation brake to be released such that the braking torque imparted by the vehicle foundation brake decreases at or below a predetermined rate of change of brake torque.11 . The control system of any preceding claim, wherein the vehicle has a front axle and a rear axle, and wherein the one or more processors are collectively configured to: determine which of the front and rear axles are a tractive axle and which is a non-tractive axle based on the or a gradient of the or a surface the vehicle is on; and output the first torque signal to cause the power source to apply a torque to the tractive axle.

12. The control system of claim 11 , wherein the one or more processors are collectively configured to output the first torque signal to cause the power source to apply a tractive axle torque to the tractive axle and a non-tractive axle torque to the non-tractive axle, the tractive axle torque having a magnitude greater than the magnitude of the non-tractive axle torque.

13. A vehicle comprising a powertrain, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, and the control system of any preceding claim.

14. A method for controlling a foundation brake and a powertrain of a vehicle, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, the method comprising: when the vehicle is in a stationary state with a vehicle foundation brake applied, receiving a signal comprising information indicating that the vehicle is to transition from the stationary state to a moving state; determining if the vehicle is to descend in the moving state; in response to determining that the vehicle is to descend in the moving state: determining a first torque, the first torque being in a direction to resist downhill movement of the vehicle; outputting a first torque signal to request the power source to generate a torque equal to the first torque; subsequent to outputting the first torque signal, outputting a brake release signal to cause the vehicle foundation brake to be released.

15. Computer readable instructions which, when executed by a computer, are arranged to perform a method according to claim 14.

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