A control scheme for controlling acceleration of a vehicle

Abstract

Aspects of the present invention relate to a control system (100) for controlling a torque output of a torque system (240) of a vehicle (900) to control vehicle acceleration on a gradient, the control system (100) comprising one or more processors (120) collectively configured to: receive a torque demand signal (160) indicative of a requested torque; receive a vehicle speed signal (162) indicative of a speed of the vehicle (900); determine, in dependence on the torque demand signal (160) and the vehicle speed signal (162), an expected acceleration of the vehicle (900), wherein the expected acceleration is indicative of an expected acceleration of the vehicle (900) in response to the requested torque being provided to the vehicle (900) while the vehicle (900) is on a flat surface; determine, in dependence on the vehicle speed, an actual acceleration of the vehicle (900); compare the expected acceleration and the actual acceleration of the vehicle (900); and output, in dependence on the comparison, a torque control signal (170) to control the torque output (231) of the torque system (240). Aspects of the invention are also related to a torque system (240) incorporating a control system (100) and a powertrain (210), a vehicle (900) incorporating a control system (100), and a method (300) of controlling a torque system (240) a vehicle (900).

Description

[0001] A CONTROL SCHEME FOR CONTROLLING ACCELERATION OF A VEHICLE

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a control scheme for controlling acceleration of a vehicle. Aspects of the invention relate to a control system for controlling a torque output of a torque system of a vehicle to control vehicle acceleration on a gradient, to a torque system of a vehicle, to a vehicle, and to a method for controlling a control system for controlling a torque output of a torque system of a vehicle.

[0004] BACKGROUND

[0005] It is known to provide vehicles including systems for providing torque to drive the vehicle. Torque demand is conventionally based on a demand from a driver of the vehicle, such as by measuring the position of accelerator and brake pedals to determine whether the driver wishes to change an acceleration of the vehicle. It is also known to provide systems for vehicles which introduce additional positive torque to accelerate the vehicle beyond any acceleration requested by the driver using the accelerator pedal. Such systems can include creep functions which maintain a low vehicle speed without any pedal input from the driver, or systems for one-pedal driving which introduce positive or negative torque to control a speed of the vehicle to enable a driver to operate the vehicle using only the accelerator pedal. For example, a one-pedal driving mode may introduce torque to the system when the vehicle is traveling on an uphill gradient so as to control a slow-down of the vehicle when the driver removes pressure from an accelerator pedal, and may remove torque from the system when the vehicle is traveling on a downhill gradient so as to bring the vehicle to rest when the driver removes pressure from the accelerator pedal. It is important to manage addition of positive torque to the vehicle, and traditional systems are therefore constrained to add a limited amount of positive torque or to only operate at low vehicle speed.

[0006] It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

[0007] SUMMARY OF THE INVENTION

[0008] Aspects and embodiments of the invention provide a control scheme for controlling acceleration of a vehicle. Aspects of the invention relate to a control system for controlling a torque output of a torque system of a vehicle to control vehicle acceleration on a gradient, a torque system of a vehicle, a vehicle, and a method for controlling a control system for controlling a torque output of a torque system of a vehicle as claimed in the appended claims.

[0009] According to an aspect of the present invention, there is provided a control system for controlling a torque output of a torque system of a vehicle to adjust the torque output to compensate for a difference between an actual acceleration of a vehicle and an expected acceleration of the vehicle if the vehicle was driving on a flat surface, based on a speed of the vehicle and a demand for torque.

[0010] According to an aspect of the present invention there is provided a control system for controlling a torque output of a torque system of a vehicle to control vehicle acceleration on a gradient, the control system comprising one or more processors collectively configured to: receive a torque demand signal indicative of a requested torque; receive a vehicle speed signal indicative of a speed of the vehicle; determine, in dependence on the torque demand signal and the vehicle speed signal, an expected acceleration of the vehicle, wherein the expected acceleration is indicative of an expected acceleration of the vehicle in response to the requested torque being provided to the vehicle while the vehicle is on a flat surface; determine, in dependence on the vehicle speed, an actual acceleration of the vehicle; compare the expected acceleration and the actual acceleration of the vehicle; and output, in dependence on the comparison, a torque control signal to control the torque output of the torque system.

[0011] The control system controls to adjust a torque output by the torque system when the expected acceleration of the vehicle in response to the requested torque being applied on a flat surface does not match the actual acceleration of the vehicle. This may be the case for several example situations, such as due to a gradient, an overrun to rest feature, or adaptive pedal progression feature on a gradient. For example, an overrun to rest feature may request torque which causes the vehicle to accelerate more than would be expected based on the accelerator pedal position. The overrun to rest feature may be a feature of the vehicle which controls the vehicle to exhibit particular behaviours which require the addition or removal of torque from the torque output of the torque system. For example, the overrun to rest feature may introduce positive torque to increase the torque output to prevent the vehicle from rolling backwards downhill when a single pedal driving mode is engaged and when the driver does not use a brake to slow the vehicle when driving on an uphill gradient. If too much positive torque is added by the overrun to rest feature, the vehicle may accelerate unpredictably. The control system thus prevents unintended acceleration by removing positive torque. Consequently, the driver is not subjected to undesired acceleration. Further, limitations on the amount of positive torque which can be introduced to the torque system by features such as overrun to rest, creep, and adaptive pedal progression features can be increased or removed, as the control system acts to prevent undesired excessive acceleration.

[0012] The torque output of the system may be a sum of positive torque output by a torque generator (such as an engine or a motor) and a negative torque output by a braking system. The torque output may therefore represent a net torque which applies to the vehicle and causes the vehicle to speed up or slow down.

[0013] Optionally, the expected acceleration of the vehicle on a flat surface is indicative of a calculated acceleration of the vehicle when torque corresponding to the torque demand signal is applied to the vehicle traveling at the vehicle speed on a flat surface. The control scheme therefore determines an expected acceleration of the vehicle absent any influence from a surface gradient or systems that introduce a positive torque. This expected acceleration can then be compared to the actual acceleration of the vehicle to determine if the torque output of the torque system requires adjustment.

[0014] 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: receive a torque demand signal indicative of a requested torque; receive a vehicle speed signal indicative of a speed of the vehicle; determine, in dependence on the torque demand signal and the vehicle speed signal, an expected acceleration of the vehicle, wherein the expected acceleration is indicative of an expected acceleration of the vehicle in response to the requested torque being provided to the vehicle while the vehicle is on a flat surface; determine, in dependence on the vehicle speed, an actual acceleration of the vehicle; compare the expected acceleration and the actual acceleration of the vehicle; and output, in dependence on the comparison, a torque control signal to control the torque output of the torque system.

[0015] Optionally, the flat surface comprises a surface having a zero percent gradient.

[0016] Optionally, the actual acceleration exceeding the expected acceleration is indicative of the vehicle being on a gradient.

[0017] Optionally, the torque demand signal is indicative of a pedal position of one or more pedals of the vehicle.

[0018] Optionally, the pedal position is indicative of a driver request for torque.

[0019] Optionally, an association between pedal position and requested torque is determined in dependence on a gradient of the vehicle. That is, a pedal position may correspond to a particular amount of torque requested by the driver, and the amount of torque for different pedal positions may vary according to a gradient of a surface where the vehicle is located. For example, the vehicle may comprise features such as an adaptive pedal progression mode where, when the vehicle is on an uphill gradient, the requested torque increases more rapidly with depression of the pedal than when the vehicle is on a flat surface, to thereby reduce the requirement of the driver to depress the pedal further than they would need to on a flat surface to accelerate the vehicle up a hill.

[0020] Optionally, the requested torque may include a torque component which is requested by a vehicle system in addition to torque identified as requested torque based on the accelerator pedal position. For example, the requested torque may include a torque component requested by an overrun to rest feature.

[0021] Optionally, the one or more processors are collectively configured to output the control signal to control the torque output of the torque system such that the actual acceleration of the vehicle is controlled to reduce a difference between the expected acceleration of the vehicle. Advantageously, the torque output is controlled to prevent unintended acceleration of the vehicle due to features which introduce positive torque. Optionally, the one or more processors are collectively configured to output the control signal to control the torque output of the torque system such that the actual acceleration of the vehicle is controlled to equal the expected acceleration of the vehicle. Advantageously, acceleration of the vehicle more closely corresponds to the intention of the driver.

[0022] Optionally, the one or more processors are collectively configured to: determine that the actual acceleration of the vehicle exceeds the expected acceleration of the vehicle, and in dependence on the determination, output the torque control signal to reduce torque from the torque output of the torque system.

[0023] Optionally, the one or more processors are collectively configured to: determine a difference between the actual acceleration of the vehicle and the expected acceleration of the vehicle; and in dependence on the actual acceleration of the vehicle exceeding the expected acceleration of the vehicle, output the torque control signal to reduce torque from the torque output of the torque system, wherein an amount of torque to be removed is determined in dependence on the determined difference.

[0024] Optionally, the one or more processors are collectively configured to determine the expected acceleration of the vehicle in dependence on an accelerative torque component, wherein the one or more processors are collectively configured to: subtract one or more of a road load torque or a brake torque from the requested torque of the torque demand signal to thereby determine the accelerative torque component; the road load torque comprises an amount of torque corresponding to a resistance to a movement of the vehicle; and the road load torque is determined in dependence on the vehicle speed. Advantageously, the current state of the vehicle is considered when determining the expected acceleration of the vehicle, and opposing forces to the movement of the vehicle are taken into account when determining the expected acceleration.

[0025] Optionally, the road load torque comprises an amount of torque required to maintain a velocity of the vehicle. In an embodiment, the resistance to the movement of the vehicle is based on one or more of a rolling resistance, air resistance, and gravitation.

[0026] Advantageously, by considering purely accelerative torque, the control system does not erroneously detect a difference between the actual and expected accelerations being resolved due to driver braking. That is, when the driver brakes, the actual acceleration may decrease to less than the expected acceleration, and a system could incorrectly determine that over-torque has been resolved if not accounting for the brake torque.

[0027] Optionally, the one or more processors are collectively configured to convert the accelerative torque into the expected acceleration of the vehicle in dependence on a predetermined tyre rolling radius and a predetermined vehicle mass.

[0028] Optionally, the one or more processors are collectively configured to determine the expected acceleration of the vehicle in dependence on an expected acceleration maximum.

[0029] Optionally the one or more processors are collectively configured to determine the expected acceleration of the vehicle in dependence an expected acceleration minimum.

[0030] Optionally the one or more processors are collectively configured to determine the expected acceleration of the vehicle in dependence on one or more of an expected acceleration maximum and an expected acceleration minimum.

[0031] Optionally, the expected acceleration maximum is determined based on the vehicle speed. Advantageously, at low speed the control system can allow positive torque to bring acceleration up to 0 (or slightly above) to prevent roll-back of the vehicle. At higher speeds, deviation from decelerative request is detected as a trigger for controlling the torque output. Optionally, the one or more processors are collectively configured to output the torque control signal in dependence on a minimum torque output of the torque system; and the minimum torque output of the torque system is based on one or more of: a creep torque associated with a creep function of the vehicle; the requested torque; and zero torque.

[0032] Optionally, the creep torque comprises an amount of torque requested by the creep function of the vehicle; wherein the creep function of the vehicle requests the creep torque to maintain a vehicle creep velocity while the requested torque is zero.

[0033] Optionally, the creep velocity is between Opkh and 6kph. Advantageously, embodiments of the present invention are complementary with other vehicle functions, by providing an adaptive target for torque and / or vehicle acceleration in dependence on the function of other vehicle features.

[0034] Optionally, the one or more processors are collectively configured to: generate the torque control signal in dependence on one or more of: a proportional term determined in dependence on the comparison of the actual acceleration of the vehicle and the expected acceleration of the vehicle, and a first gain factor; and an integrator term determined in dependence on the comparison of the actual acceleration of the vehicle and the expected acceleration of the vehicle, a second gain factor, and an integrator execution rate.

[0035] Optionally, the first gain factor is implemented as a curve with a dependence on the current difference between the expected acceleration and the actual acceleration of the vehicle. This allows the first gain factor to increase if there is a large difference so that the control system response is more severe.

[0036] Optionally, the second gain factor is a different curve to the first gain factor. However, it should be understood that the first and second gain factors share the same input of the current difference between the expected acceleration and the actual acceleration of the vehicle. This allows the integrator term to behave differently for different amounts of the difference.

[0037] Optionally, the proportional term is determined by multiplying a difference between the actual acceleration of the vehicle and the expected acceleration of the vehicle by the first gain factor.

[0038] Optionally, the proportional term is saturated to be between 0 and a negative controller allowance. This is so that the control system cannot add positive torque back in to the system, which may be undesirable for a driver of the vehicle.

[0039] Advantageously, according to these embodiments, the integrator has memory of previous differences between the actual acceleration of the vehicle and the expected acceleration of the vehicle. The control system can therefore correct for steady state controller error based on the difference between the actual and expected acceleration of the vehicle over time.

[0040] Optionally, the integrator term is determined further in dependence on a maximum integrator term and a previous integrator term, the previous integrator term comprising an integrator term for a preceding execution of the integrator term determination; and the maximum integrator term is determined in dependence on the previous integrator term and the integrator execution rate.

[0041] Optionally, the integrator term is determined by multiplying a difference between the actual acceleration of the vehicle and the expected acceleration of the vehicle by the second gain factor and the execution rate, adding a result of the multiplication to the previous integrator term, and capping a result of the addition based on the maximum integrator term.

[0042] Optionally, the integrator term is saturated to be between 0 and a negative controller allowance. This is so that the control system cannot add positive torque back in to the system, which may be undesirable for a driver of the vehicle.

[0043] Optionally, the one or more processors are collectively configured to output the torque control signal to re-allocate at least a portion of the requested torque to a brake of the vehicle in dependence on the comparison. Advantageously, when the driver is not depressing the accelerator, rollback of the vehicle (i.e. , the vehicle unintentionally rolling backwards on a gradient) is prevented even when positive torque is reduced in the torque output of the torque system.

[0044] Optionally, the one or more processors are collectively configured to: generate an overrun to rest control signal in dependence on the torque control signal; and output the overrun to rest control signal to an overrun to rest controller to control a torque demand of the overrun to rest controller.

[0045] Optionally, the overrun to rest controller is configured to operate an overrun to rest function of the vehicle; wherein the overrun to rest function of the vehicle comprises requesting positive torque to enable a single-pedal driving mode of the vehicle.

[0046] Advantageously, positive torque which is removed from the torque output of the torque system is not reintroduced by downstream controllers or functions such as the overrun to rest controller.

[0047] According to another aspect of the present invention, there is provided a torque system of a vehicle, the torque system comprising the control system according to any preceding statement and a powertrain configured to generate and output the torque output in dependence on the torque control signal.

[0048] According to another aspect of the present invention, there is provided a vehicle comprising the control system of any preceding statement or the torque system.

[0049] According to another aspect of the present invention, there is provided a method for controlling a torque output of a torque system of a vehicle to control vehicle acceleration on a gradient, the method comprising: receiving a torque demand signal indicative of a requested torque; receiving a vehicle speed signal indicative of a speed of the vehicle; determining, in dependence on the torque demand signal and the vehicle speed signal, an expected acceleration of the vehicle, wherein the expected acceleration is indicative of an expected acceleration of the vehicle in response to the requested torque being provided to the vehicle while the vehicle is on a flat surface; determining, in dependence on the vehicle speed, an actual acceleration of the vehicle; comparing the expected acceleration and the actual acceleration of the vehicle; and outputting, in dependence on the comparison, a torque control signal to control the torque output of the torque system.

[0050] According to another aspect of the present invention, there is provided computer readable instructions which, when executed by a computer, are arranged to perform the method.

[0051] 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.

[0052] 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 block diagram illustrating a control system;

[0055] Figure 2 shows a block diagram illustrating a torque system;

[0056] Figures 3 to 7 show flowcharts illustrating methods of operating a control system;

[0057] Figure 8 shows a graph illustrating a simulation of a method of operating a control system; and

[0058] Figure 9 shows a vehicle in accordance with an embodiment of the invention. DETAILED DESCRIPTION

[0059] The present disclosure relates to a control system for a torque system and to a method of controlling the control system. The control system is provided to control a torque output of the torque system, and particularly to determine whether to remove torque from the torque output of the torque system. It is known to provide features to vehicles which introduce positive torque beyond an amount of torque explicitly requested by the driver (typically through driver control of an accelerator pedal). These systems aim to support the driver and improve the driving experience by modifying the control of the vehicle based on various conditions, such as a road surface gradient or a single pedal driving mode. However, it is important that these systems do not introduce excessive positive torque which may be undesirable for the driver. Therefore, these systems are typically constrained with respect to additions of positive torque to prevent unexpected vehicle acceleration. The present invention relates to methods and means for monitoring the vehicle speed and torque requested by the driver of a vehicle, and controlling a torque output of a torque system of the vehicle based on a comparison of the actual acceleration of the vehicle with an expected acceleration of the vehicle as if the vehicle was on a flat surface. By determining the expected acceleration of the vehicle and comparing it to the actual acceleration of the vehicle, the control system can control the torque system to reduce positive torque from the torque output to prevent unintended acceleration of the vehicle beyond what would reasonably be expected by the driver. Various examples of the present invention are described below and include methods and means for determining the expected acceleration of the vehicle, comparing the expected acceleration of the vehicle to the actual acceleration of the vehicle and generating and transmitting one or more torque control signals to control a torque output of the torque system of the vehicle.

[0060] A vehicle typically has a plurality of wheels, for example four wheels. In some examples the vehicle is provided with a traction control system which manages wheel rotation rate of individual wheels in order to optimise the driving experience for the driver. A vehicle speed signal may be derived from an average of the rate of rotation of the wheels or by other means such as GPS, visual or other sensors.

[0061] A control system 100 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figure 1 and a torque system 240 of a vehicle 900 in accordance with an embodiment of the present invention is described herein with reference to accompanying Figure 2. As shown in Figure 9, the control system 100 and / or the torque system 240 (having components 210, 220 described further below) can be installed in a vehicle 900.

[0062] With reference to Figure 1 , there is illustrated a control system 100 for controlling a torque system 240, such as the torque system 240 shown in Figure 2, which is described in detail below.

[0063] The control system 100 as illustrated in Figure 1 comprises one controller 110, although it will be appreciated that this is merely illustrative. The controller 110 comprises processing means 120 and memory means 130. The processing means 120 may be one or more electronic processing device 120 which operably executes computer-readable instructions. The memory means 130 may be one or more memory devices 130. The memory means 130 is electrically coupled to the processing means 120. The memory means 130 is configured to store instructions, and the processing means 120 is configured to access the memory means 130 and execute the instructions stored thereon.

[0064] The controller 110 comprises an input means 140 and an output means 150. The input means 140 may comprise an electrical input of the controller 110. The output means 150 may comprise an electrical output of the controller 110. The input means 140 is arranged to receive one or more input signals. The input means 140 is arranged to receive at least a torque demand signal 160 indicative of a requested torque and a vehicle speed signal 162 indicative of a speed of the vehicle 900. The torque demand signal 160 may be indicative of a requested torque. The requested torque comprises an amount of torque, and may correspond to a pedal position of an accelerator pedal and / or a brake pedal. The requested torque may be provided absent any influence of a gradient, a single pedal driving model, an adaptive pedal progression mode, or the like, (i.e. , may represent only the driver’s input on a pedal or the like), or may be provided including one or more torque components corresponding to one or more of these influences. The requested torque may comprise a positive torque when the request corresponds to a pedal position of the accelerator pedal, and may comprise a negative torque when the request corresponds to a pedal position of the brake pedal. It should be understood that the requested torque may be a net torque being the sum of positive and negative torque requested by the driver, although the driver may be unlikely to request positive and negative torque at the same time. The processing means 120 is configured to determine, in dependence on the torque demand signal 160 and the vehicle speed signal 162, an expected acceleration of the vehicle 900. The expected acceleration is indicative of an expected acceleration of the vehicle 900 in response to the requested torque being provided to the vehicle 900 while the vehicle 900 is on a flat surface. It should be understood that the flat surface comprises a surface having a zero or near zero percent gradient. In some examples, the expected acceleration is determined using one or more assumptions to reflect a situation where the vehicle 900 is on a flat surface, but it should be understood that in this example the control system 100 does not actually determine whether the vehicle 900 is on a flat surface. That is, the processing means 120 may determine the expected acceleration as if the vehicle 900 is on a flat surface without determining or measuring a surface gradient. In another example, the control system 100 may determine or receive information indicative of a gradient of a road surface in the vehicle’s location.

[0065] The expected acceleration in some examples may be determined by determining an accelerative torque based on a driver demand for torque (i.e. , the requested torque of the torque demand signal 160). The driver demand for torque may correspond to a pedal position of an accelerator pedal. It should be understood that in some examples, a greater depression of the accelerator pedal by the driver corresponds to a request for greater torque. In some examples, the driver demand for torque may be based on the position of the accelerator pedal and a scaling factor. For example, a progressive pedal mode (or an adaptive pedal progression mode) may be provided in which driver request for torque is scaled more rapidly with pedal position. In this example, the vehicle 900 may be configured such that when the accelerator pedal is depressed by the driver, a request for torque is increased compared to a request for torque at the same accelerator pedal position when the progressive pedal mode is turned off. The progressive pedal mode may be activated in several ways, as would be understood. For example, the progressive pedal mode may be activated or deactivated based on a user setting, a road surface gradient, a vehicle speed, or any other suitable means. In some examples, the driver demand on the flat (excluding any influence of anti-rollback features or progressive pedal mode) may be filtered for decreasing demands. In this example, the processing means 120 ensures that unintended accelerations during normal operation are not mis-detected, as there is an expected level of delay to the torque request decreasing, to the actual vehicle acceleration decreasing.

[0066] The processing means 120 may also be configured to determine a road load torque based on the vehicle speed indicated by the vehicle speed signal 162. The road load torque may be indicative of a torque requirement to overcome opposing forces to the movement of the vehicle 900 at the vehicle speed. It should be understood that opposing forces to the movement of the vehicle 900 may be different at different vehicle speeds, for example due to varying surface friction, air resistance, or gravitational components (e.g. , on a gradient). The processing means 120 may determine the accelerative torque by subtracting the road load torque from the requested torque. In some examples, the processing means 120 may further subtract a brake torque corresponding to a pedal position of a brake pedal to determine the accelerative torque.

[0067] The processing means 120 in some examples is configured to determine the expected acceleration of the vehicle 900 by converting the accelerative torque to an acceleration. It should be understood how this conversion is performed. In an example, the accelerative torque is converted to the expected acceleration based on the formula F=ma, where F is a force corresponding to the accelerative torque, m is the mass of the vehicle 900, and a is the expected acceleration. The accelerative torque is converted to the force based on a tyre rolling radius. The tyre rolling radius and the vehicle mass may be preconfigured for the vehicle 900, or may be assumed by the control system 110.

[0068] In some examples, the processing means 120 is configured to apply one or more caps to the expected acceleration. It should be understood that a “cap” may be a maximum or a minimum value, to which the expected acceleration is controlled not be greater than or less than. For example, the processing means 120 may determine, receive or be pre-configured with a minimum and / or a maximum value for the expected acceleration. The processing means 120 may determine the expected acceleration such that the expected acceleration is not greater than or less than the maximum and / or minimum values respectively. In some examples, the one or more caps to the expected acceleration ensure that at a low speed (for example, less than 15 kph) where an anti-rollback feature may be active to prevent the vehicle 900 from rolling backwards on a gradient, the control system 110 may allow the expected acceleration to increase to zero ms2(or above) without then determining to control the torque output due to a difference between the expected acceleration and the actual acceleration, as this corresponds to the expected vehicle behaviour. That is, when the driver does not depress an accelerator pedal, an expected acceleration of the vehicle may be zero in some situations. However, when a function such as the creep function is active, the creep function may introduce positive torque to the torque output to prevent the vehicle from rolling backwards on an uphill gradient. In this example, the expected acceleration may be determined to account for the creep function so as to prevent the torque output being reduced due to a difference between the expected acceleration and the actual acceleration due to the creep function, to thereby prevent the vehicle from rolling backwards downhill absent driver input on the pedals. The inverse situation may apply for a maximum value, to prevent the vehicle from accelerating when coming to rest on a downhill gradient. At the same time, at higher vehicle speeds where the anti-rollback feature is not expected to be active, the one or more caps may have a lesser influence so deviation from the driver’s decelerative request results in the control system 100 controlling the torque output of the torque system 240 to reduce. The one or more caps to the expected acceleration therefore prevent interference by the control system 100 with the normal operation of other vehicle systems.

[0069] The processing means 120 is further configured to determine, in dependence on the vehicle speed, an actual acceleration of the vehicle 900. The actual acceleration of the vehicle 900 is determined based on the vehicle speed signal 162. It should be understood that acceleration is a derivative of velocity. In some examples, the actual acceleration of the vehicle 900 is determined as the derivative of the vehicle speed. That is, the actual acceleration of the vehicle may be determined based on changes in the vehicle speed over time. In some examples, the processing means 120 are configured to filter this derivative, where an amount of filtering may be based on a difference between the unfiltered acceleration and the filtered acceleration. For example, this allows the filtering to be reduced when there is a large difference, and the amount of filtering to be different for an increasing acceleration versus a decreasing deceleration. In an example, the unfiltered acceleration is a derivative of the vehicle velocity, and the filtered acceleration is the unfiltered acceleration passed through a filter which may be a low pass filter in some examples. The time constant of the low pass filter may be based on the unfiltered acceleration subtracted from the filtered acceleration at a previous time step.

[0070] The processing means 120 is further configured to compare the expected acceleration and the actual acceleration of the vehicle 900. In some examples, the processing means 120 is configured to determine a difference between the expected acceleration of the vehicle 900 and the actual acceleration of the vehicle 900.

[0071] The processing means 120 is further configured to generate, in dependence on the comparison, a torque control signal 170 to control the torque output of the torque system 240. In an example, the processing means 120 is configured to generate the torque control signal 170 to control the torque output of the torque system 240 such that the actual acceleration of the vehicle 900 is controlled to reduce a difference between the expected acceleration of the vehicle 900 and the actual acceleration of the vehicle 900. In an example, the processing means 120 is configured to generate the torque control signal 170 to control the torque output of the torque system 240 such that the actual acceleration of the vehicle 900 is controlled to equal the expected acceleration of the vehicle 900. In an example, the torque control signal 170 is configured so as to control the torque system 240 to reduce a positive torque in the torque output of the torque system 240.

[0072] In some examples the processing means is configured to not generate the torque control signal 170 if the rate of rotation of the plurality of wheels of the vehicle varies significantly. Alternatively the processing means may set the torque control signal 170 to zero if the rate of rotation of different wheels varies significantly. Thus the torque output of the torque system is not controlled to reduce a difference between the expected acceleration of the vehicle 900 and the actual acceleration of the vehicle 900. For example, the rate of rotation of different wheels may differ due to differential surface conditions at different wheels (e.g. one or two wheels on a patch of ice on an otherwise dry tarmac road). In some situations a fraction control system of the vehicle may cause one or more wheels to be stationary or to rotate in the opposite direction to other wheels of the vehicle. In any of these conditions the actual acceleration of the vehicle calculated by means of the vehicle speed signal may be deemed to be unmeasurable or of insufficient accuracy or quality. The processing means may prevent generation of the torque control signal 170 and / or may set the torque control signal 170 to zero. Such steps may only be taken providing the estimated acceleration is within predetermined limits, and / or providing the estimated speed of the vehicle is not exceeding a threshold value. For example, providing the estimated speed of the vehicle is less than 5 kph (which may occur on some difficult terrains), or less than 10kph or less than 15kph (which may accommodate some generally good quality terrains).

[0073] In some examples, the processing means 120 is configured to apply one or more caps to a torque output of the torque system 240 and to generate the torque control signal 170 in dependence on the one or more caps. For example, the processing means 120 may determine, receive or be preconfigured with a minimum and / or a maximum value for the torque output of the torque system 240. The processing means 120 may generate the torque control signal 170 such that the torque output is not greater than or less than the maximum and / or minimum torque values respectively. In an example, the minimum torque output of the torque system may be based on one or more of a creep torque associated with a creep function of the vehicle 900, the requested torque indicated in the torque demand signal 160, and / or zero torque. It should be understood that the requested torque indicated in the torque demand signal 160 may correspond to a driver demand for acceleration on a flat surface, and may be absent any influence of other vehicle features which may subsequently add in or remove torque from the driver demand. In an example, the creep torque comprises an amount of torque requested by the creep function of the vehicle 900, where the creep function of the vehicle requests the creep torque to maintain a vehicle creep velocity while the requested torque (being the torque requested by a driver using the accelerator and / or brake pedals) is zero. In one example, the creep velocity is between Okph and 6kph, but it should be understood that the invention is not limited thereto. Advantageously, the maximum and / or minimum torque outputs applied when determining the torque control signal 170 ensure compatibility of the present invention with other vehicle systems by providing an adaptive target for the torque (or acceleration) based on other vehicle system settings. In other words, the torque control signal 170 of the present invention may be determined using the one or more torque output caps so as to account for target torque and / or acceleration associated with other vehicle functions. For example, the maximum and / or minimum torque outputs may be determined at least in part based on other functions of the vehicle 900. For example, the control system 100 may determine a minimum torque output to correspond to a creep function of the vehicle 900, where the creep function maintains a low vehicle speed absent any driver requested torque. In this case, the torque control signal of the present invention is prevented from controlling the vehicle acceleration such that the speed of the vehicle decreases below the creep velocity. It should be understood that the maximum and / or minimum torque outputs may be determined based on other functions, or may be determined based on a combination of functions.

[0074] In some examples, the processing means 120 is configured to generate the torque control signal 170 in dependence on one or more of a proportional term and an integrator term. The processing means 120 may be configured to add the proportional term to the integrator term. The proportional term may be indicative of a real-time difference between the expected acceleration and the actual acceleration of the vehicle 900. The integrator term may be indicative of a difference between the expected acceleration and the actual acceleration of the vehicle 900 over time. By considering both the proportional term and the integrator term, the control system 100 advantageously may correct for a steady state error of the control system 100.

[0075] To determine the proportional term, the processing means 120 may be configured to multiple the difference between the actual acceleration of the vehicle 900 and the expected acceleration of the vehicle 900 by a first gain factor. In some examples, the first gain factor is implemented as a curve with a dependence on the current difference between the expected acceleration and the actual acceleration of the vehicle 900. This allows the first gain factor to increase if there is a large difference so that the control system 100 response is more severe. In some examples, the proportional term is limited to be between 0 and a negative controller allowance. This is so that the control system 100 cannot add positive torque back into the system, which may be undesirable for a driver of the vehicle 900.

[0076] To determine the integrator term, the processing means 120 may be configured to, for a first time window, multiple the difference between the actual acceleration of the vehicle 900 and the expected acceleration of the vehicle 900 by a second gain factor and by an execution rate. The second gain factor may be different to the first gain factor or may be equivalent to the first gain factor. In an example, the second gain factor is a different curve to the first gain factor. However, it should be understood that the first and second gain factors share the same input of the current difference between the expected acceleration and the actual acceleration of the vehicle 900. This allows the integrator term to behave differently for different amounts of the difference.

[0077] The processing means 120 may be further configured to determine the integrator term based on the integrator term for the first time window and an integrator term for a second time window preceding the first time window. For example, the processing means 120 may add the integrator term for the first time window to the integrator term for the second time window. The processing means 120 may further be configured to determine the integrator term in dependence on a maximum integrator term. The maximum integrator term may be determined in dependence on the previous integrator term and the integrator execution rate. In some examples, the processing means 120 may further limit the integrator term by zero and / or a minimum limit.

[0078] The output means 150 is arranged to output the torque control signal 170 to the torque system 240. The torque control signal 170 is configured to control a torque output of the torque system 240 as described above. In some examples, the torque control signal 170 may be output to the torque system 240 to reduce a torque output of the torque system 240. In another example, the torque control signal 170 may also control the torque system 240 to allocate at least a portion of the requested torque to a brake of the vehicle 900 in dependence on the comparison of the expected acceleration and the actual acceleration of the vehicle 900. Advantageously, this may prevent the vehicle 900 from rolling back when on a gradient and when torque is removed from the torque output of the torque system 240.

[0079] The output means 150 and the processing means 120 in some examples may further be configured to generate an overrun to rest control signal in dependence on the torque control signal 170. The overrun to rest signal is output to an overrun to rest controller to control a torque demand of the overrun to rest controller. The overrun to rest controller is configured to operate an overrun to rest function of the vehicle 900. The overrun to rest function of the vehicle 900 may comprise a function which requests positive torque to enable a single-pedal driving mode of the vehicle 900. In an example, the overrun to rest function may comprise at least the two following functions: anti-rollback to prevent the vehicle 900 rolling backwards when the vehicle 900 is on an uphill gradient; and bringing the vehicle 900 to rest when the driver releases the accelerator pedal while going downhill. In some examples, the overrun to rest controller is logically upstream of the control system 100 of Figure 1 . The control system 100 may therefore be configured to output the overrun to rest signal to correct the outputs of the overrun to rest controller if it is requesting too much positive torque.

[0080] In one example, the proportional term and / or the integrator term may be determined be one or more of a proportional integrator (PI) controller or a proportional-integral-derivative (PID) controller, but it should be understood that the present invention is not limited thereto, and that the control system 100 may comprise any number and type of suitable controllers. In one example, the processing means 120 comprises a PI controller configured to minimise the difference between the actual acceleration of the vehicle 900 and the expected acceleration of the vehicle 900.

[0081] Figure 2 shows a schematic diagram of components of a vehicle 900 including a torque system 240. The vehicle 900 includes a control system 100, a powertrain 210 and a foundation braking system 220. The control system 100 is arranged to control the powertrain 210 and the foundation braking system 220. The vehicle 900 may be a hybrid electric vehicle having an electric machine and an internal combustion engine both arranged to drive the wheels of the vehicle 900, or may be a battery electric vehicle powered by an electric machine only, or may be a vehicle powered by an internal combustion engine only. In some cases, the vehicle 900 may have multiple electric machines arranged to drive the wheels. The vehicle 900 may also be a mild hybrid electric vehicle (MHEV) or a plug-in hybrid electric vehicle (PHEV).

[0082] The vehicle 900 has a control system 100, the control system 100 comprising a plurality of controllers. The controllers are collectively configured to receive data from different sensors, systems, and input devices of the vehicle 900, to process the data and to output commands for controlling the vehicle 900. 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. The control system 100 may be the control system 100 of Figure 1 .

[0083] The control system 100 is arranged to control a powertrain 210. The powertrain comprises a power source 212. The power source 212 may be an electric machine and in some cases the powertrain 210 may have two power sources 212 which are an electric machine and an internal combustion engine. In another example the powertrain 210 may comprise a single power source 212 being an internal combustion engine. The powertrain 210 also comprises a drivetrain 214 that is arranged to receive torque 215 from the power source 212, to convert the torque and to provide a converted torque to the wheels. The drivetrain 214 may be a direct-drive drivetrain or may have a gearbox and a differential for increasing the torque 215 delivered from the power source 212 so that a higher torque may be delivered to the wheels of the vehicle 900. The power train 210 may thereby output a positive torque.

[0084] The powertrain 210 is controlled by and monitored by the control system 100. The control system 100 is arranged to output an electric machine torque requirement signal 211 , which may also be referred to as a required torque signal 211 , to the powertrain 210 to cause the power source 212 to generate a required amount of torque 215. The control system 100 is also arranged to receive data 213, such as a torque generation signal 213, from the powertrain 210. The received data 213 may include a rotational speed of the power source 212 and may include a torque generated by the power source 212. The control system 100 may also receive data 213 and transmit commands 211 related to the drivetrain 214. The control system 100 may transmit commands 213 to the powertrain 210, such as a gear change command to change a torque ratio of the drivetrain 214. The control system 100 may also receive data 213 that may include a rotational speed of one or more components of the drivetrain 214, or an amount of torque received by the drivetrain 214 or output by the drivetrain 214. The torque ratio of the drivetrain may be transmitted from the drivetrain 214 to the control system 100 as part of data 213 or may be stored as a value in the control system 100, as the control system 100 may command the drivetrain 214 in order to control the torque ratio of the drivetrain 214.

[0085] The vehicle 900 also has a foundation braking system 220. The foundation braking system 220 comprises a brake actuator 222 and a foundation brake 224. The brake actuator 222 may be a hydraulic pump or an electromechanical actuator for moving components of the foundation brake 224 that are arranged to engage frictionally in order to provide a braking torque (or a negative torque). The brake actuator 222 may therefore apply a force 225 to the foundation brake 224. The foundation brakes 224 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 224 into engagement, the foundation braking system 220 may provide a braking torque to the wheels to decelerate the vehicle.

[0086] The term “foundation brake” is generally used herein to mean any frictional brake that may decelerate the vehicle by converting mechanical energy into heat by friction, as opposed to a regenerative brake, such as may be provided by an electric machine. It should be understood that in another example, the foundation braking system 220 may further comprise one or more regenerative braking systems.

[0087] The control system 100 is arranged to output brake command signals 221 to the foundation braking system 220. The brake command signals 221 include a foundation brake release signal that is arranged to cause the foundation brake actuator 222 to disengage the foundation brake 224, such that a braking torque is reduced. The brake command signals 221 also include a brake engagement signal that is arranged to cause the brake actuator 222 to engage the foundation brake 224 to cause an increase in braking torque applied to the wheels.

[0088] The control system 100 may receive brake data 223 from the foundation brake system 220. The foundation brake data 223 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 222. The data 223 may include data that a brake release has been effected, such that a negligible brake torque is being provided by the friction brake 224. This signal may also be referred to as a brake release signal.

[0089] The powertrain 210 and the foundation brake system 220 may together be considered a torque system 240, as indicated by the dashed line in Figure 2. The torque system 240 may be configured to output an output torque 231 to one or more wheels 230 of the vehicle. The output torque 231 may be based on positive torque associated with the powertrain 210 and negative torque associated with the foundation brake system 220. The output torque 231 is determined by the control system 100 as explained above in respect of Figure 1 . The commands 211 , 221 output by the control system 100 to the powertrain 210 and the foundation brake system 220 may be considered as part of the torque control signals 170 output by the control system 100 of Figure 1.

[0090] The control system 100 of Figure 1 may be configured to output torque control signals 170 to control one or both of the powertrain 210 and the foundation braking system 220. For example, the torque control signal 170 may be configured to remove positive torque from torque output of the powertrain 210, and / or to allocate torque from the powertrain 210 to the foundation braking system 220.

[0091] The control system 100 is also arranged to receive further input signals. The control system 100 is arranged to receive the vehicle speed signal 162 and the torque demand signal 160 as explained above in respect of Figure 1 . The control system 100 in some examples may be configured to receive one or more signals indicative of an activation or deactivation of one or more of a creep function, an adaptive pedal progression function, an off-road function, a single-pedal driving mode, or an overrun to rest feature.

[0092] The control system 100 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 100 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.

[0093] It will be understood that the control system 100 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 100.

[0094] Figure 3 is a flowchart illustrating a method 300 according to an embodiment of the present invention. The method 300 of Figure 3 may be performed by the control system 100 of Figure 1 and / or the torque system 240 of Figure 2. The method 300 of Figure 3 may be a method for generating one or more torque control signals for controlling a torque output of a torque system 240 such as the torque system 240 of Figure 2.

[0095] The method 300 comprises receiving 310 a torque demand signal 160 indicative of a requested torque. The torque demand signal 160 may also be indicative of a pedal position of one or more of an accelerator pedal and / or a brake pedal. In some examples, the requested torque corresponds to a position of the accelerator pedal and may be further dependent on whether vehicle features such as an adaptive pedal progression mode is activated. As explained above, the adaptive pedal progression mode may be a vehicle function in which the torque request associated with accelerator pedal position is scaled differently depending on one or more factors such as a surface gradient.

[0096] The method 300 comprises receiving 320 a vehicle speed signal 162 indicative of a speed of the vehicle. The speed of the vehicle may be monitored by one or more sensors, which as would be understood may comprise one or more sensors configured to monitor a position of the vehicle (such as a GPS sensor), a rate of rotation of the wheels of the vehicle, an accelerometer, or any other suitable sensor.

[0097] Optionally the method 300 includes a step to ensure the quality of the vehicle speed signal 325 is sufficient for it to be used. If the rate of rotation of different wheels varies significantly then the calculation of the actual acceleration of the vehicle may be deemed to be of insufficient quality or unmeasurable. For example, wheel rotation rate from a first wheel may indicate wheel rotation in a first direction whilst wheel rotation rate from a second wheel indicates wheel rotation in a second direction, the first direction being opposite to the second direction. In this case, the method 300 prevents the generation of the torque control signal and there are no further steps in the process 325. Consequently, the torque control signal 170 is not generated or is set to zero such that the torque control signal does not control or change the torque output of the torque system when the first direction is opposite to the second direction.

[0098] The method 300 comprises determining 330 the expected acceleration of the vehicle. The expected acceleration of the vehicle is determined based on an assumption of the vehicle being on a flat surface. That is, the expected acceleration of the vehicle is determined as if the vehicle is being driven on a flat surface (i.e. absent a gradient factor), and is determined based on the vehicle speed and the requested torque. In some examples, the expected acceleration of the vehicle is determined by determining an accelerative torque by subtracting a road load torque and / or a brake torque from the requested torque. The accelerative torque may then be converted to an acceleration based on a vehicle mass and a vehicle tyre rolling radius, as will be explained in more detail in respect of Figure 4.

[0099] The method 300 comprises determining 340 an actual acceleration of the vehicle. The actual acceleration of the vehicle is determined based on the vehicle speed indicated by the vehicle speed signal 162. The actual acceleration of the vehicle is determined based on the derivative of the vehicle speed. It should be understood that various filtering may be applied to the vehicle speed, as has been explained with respect to Figures 1 and 2. For example, the vehicle speed may be filtered so as to detect decreasing vehicle speed corresponding to a driver engaging vehicle brakes.

[0100] The method 300 comprises comparing 350 the determined expected acceleration of the vehicle with the actual acceleration of the vehicle. In some examples, the method 300 comprises determining a difference between the expected acceleration and the actual acceleration of the vehicle. The method 300 comprises generating 360 a torque control signal 170 in dependence on the comparison. For example, the torque control signal 170 may be generated in dependence on a determination that the actual acceleration of the vehicle exceeds the expected acceleration of the vehicle on the flat surface. The torque control signal 170 is a control signal for controlling a torque output of a torque system, as has been explained. In some examples, the torque control signal 170 may be generated to control the torque system 240 to reduce positive torque output by the torque system 240. For example, the torque control signal 170 may be generated to control the torque output of the torque system 240 such that the actual acceleration of the vehicle is reduced to reduce a difference between the actual acceleration of the vehicle and the expected acceleration of the vehicle on the flat surface.

[0101] It should be understood that one or more steps of the method 300 of Figure 3 may be omitted, or that the method 300 may comprise additional steps not illustrated. For example, the method 300 may be implemented such that a difference between the expected acceleration and the actual acceleration of the vehicle is received, while the determination of the difference, the determination of the expected acceleration and the determination of the actual acceleration is performed elsewhere and thus may be omitted. In another example, the actual acceleration of the vehicle may be directly received from an accelerometer, and the step of determining 340 an actual acceleration of the vehicle may be omitted. Further, it should be understood that although Figure 3 illustrates method steps being performed in a particular order, the invention should not be limited thereto. For example, the determination of the expected acceleration of the vehicle and the actual acceleration of the vehicle may be performed in a different order, or may be performed simultaneously.

[0102] Figure 4 is a flow chart illustrating a method 400 of determining the expected acceleration of the vehicle on the flat surface according to an embodiment of the present invention. The method 400 of Figure 4 may be performed by the control system 100 of Figure 1 and / or the torque system 240 of Figure 2. The method 400 of Figure 4 may be a method for performing step 330 of the method 300 of Figure 3 of determining the expected acceleration of the vehicle on the flat surface according to an embodiment of the present invention.

[0103] The method 400 of Figure 4 comprises determining 410 a road load torque in dependence on a vehicle speed, such as the vehicle speed of the vehicle speed signal 162. The road load torque is a torque corresponding to forces opposing a motion of the vehicle at the current vehicle speed. For example, the motion of the vehicle may be opposed by forces including friction, air resistance. The sum of these opposing forces to the motion of the vehicle may correspond to a road load torque which is a torque required to overcome the opposing forces and to maintain the vehicle speed. It should be understood that such opposing forces may vary in dependence on the vehicle speed.

[0104] The method 400 further comprises receiving 420 braking torque information. The braking torque information may be received from the torque system 240, for example from the foundation braking system 220, and may be indicative of a driver request for braking or negative torque. The driver request for braking torque may be associated with a pedal position of a brake pedal.

[0105] The method 400 further comprises determining 430 an accelerative torque. The accelerative torque may be determined by subtracting the road load torque and / or the braking torque from the requested torque of the torque demand signal 160. The accelerative torque should be understood to correspond to a torque which is net of any negative torque in the system, including but not limited to the road load torque and the braking torque. The accelerative torque may also be understood as an amount of torque which when output by the torque system 240 results in an acceleration of the vehicle 900.

[0106] The method 400 further comprises converting 440 the accelerative torque into the expected acceleration of the vehicle on the flat surface. The conversion of the accelerative torque into the expected acceleration is performed based on the equation F=ma as has been explained. It should be understood that the accelerative torque may be converted to the expected acceleration based on the vehicle speed, a vehicle mass and a tyre rolling radius. The vehicle mass and the tyre rolling radius may be predetermined, received from another vehicle system, or may be estimated by the control system 100.

[0107] The method 400 may further comprise applying 450 one or more of a maximum or minimum value to the expected acceleration of the vehicle. The maximum and / or minimum value may otherwise be known as a cap. In some examples, the maximum or minimum value of the expected acceleration of the vehicle may be determined based on the vehicle speed. In an example, at low speeds, method 400 may allow positive torque to bring the vehicle acceleration up to zero or slightly above zero to prevent rollback of the vehicle on a gradient. In this example, at higher speeds the maximum or minimum value of the expected acceleration of the vehicle may be determined to have a reduced influence, such that a deviation from a driver’s decelerative request is detected as a trigger for removing torque from the torque output of the torque system 240.

[0108] It should be understood that one or more steps of the method 400 of Figure 4 may be omitted, or that the method 400 may include further steps beyond those illustrated. Further, that certain steps of the method 400 of Figure 4 may be performed in a different order to that illustrated.

[0109] Figure 5 is a flowchart illustrating a method 500 according to an embodiment of the present invention. The method 500 of Figure 5 may be performed by the control system 100 of Figure 1 and / or the torque system 240 of Figure 2. The method 500 of Figure 5 may be a method for performing step 360 of the method 300 of Figure 3 of generating the torque control signal 170 according to an embodiment of the present invention.

[0110] The method 500 of Figure 5 comprises comparing 510 the actual acceleration of the vehicle and the expected acceleration of the vehicle on the flat surface. The method step 510 may comprise determining a difference between the actual acceleration and the expected acceleration of the vehicle on the flat surface.

[0111] The method 500 of Figure 5 further comprises determining 520 one or more of a proportional term and an integrator term. The determination of the proportional term may be based on the difference between the actual acceleration of the vehicle and the expected acceleration of the vehicle, and a first gain factor. The determination of the proportional term is explained in more detail with respect to Figure 6. The determination of the integrator term may be based on the difference between the actual acceleration of the vehicle and the expected acceleration of the vehicle, a second gain factor, and an execution rate. The integrator term may be indicative of a difference between the actual acceleration of the vehicle and the expected acceleration of the vehicle over time. The determination of the integrator term is explained in more detail with respect to Figure ?.

[0112] The method 500 of Figure 5 further comprises generating 530 the torque control signal 170. The torque control signal 170 may be determined by summing the proportional term and the integrator term. It should be understood that one or more weightings may be applied to either or both of the proportional term and the integrator term before their sum is taken. The torque control signal 170 is indicative of an amount of torque to be removed from the torque output of the torque system 240, in dependence on the difference between the actual acceleration of the vehicle and the expected acceleration of the vehicle on the flat surface, as has been explained above.

[0113] The method 500 of Figure 5 may further comprise outputting 540 the torque control signal to the torque system 240 to control the torque output of the torque system 240. The method 500 may further comprise outputting the torque control signal to one or more downstream torque control systems. The one or more downstream torque control systems may include any system which is configured to add or remove torque from the torque output of the torque system 240. For example, including but not limited to an overrun to rest controller. The overrun to rest controller may be a controller which introduces or removes torque from the torque output of the torque system 240 to support a single pedal driving mode, to thereby bring the vehicle to a stop or a predetermined vehicle speed (e.g., on a downhill gradient) or to prevent a vehicle from rolling backwards (e.g . , on an uphill gradient). The torque control signal 170 may be output to the overrun to rest controller to prevent reinfroduction of torque removed from the torque output of the torque system 240 by downstream control systems.

[0114] In another example, the method 500 may further comprise outputting a torque control signal 170 configured to re-arbitrate torque from a torque output of the torque system 240 to one or more braking systems such as the foundation braking system 220 of Figure 2. In this example, the re-arbitrated torque may be applied to a brake of the vehicle to prevent rollback of the vehicle on a gradient due to the removal of torque from the torque output of the torque system 240.

[0115] It should be understood that one or more steps of the method 500 of Figure 5 may be omitted, or that the method 500 may include further steps beyond those illustrated. For example, the method 500 may further comprise outputting the torque control signal 170 to one or more other systems or controllers other than those mentioned above. The method 500 may further comprise applying one or more minimum or maximum values to the torque control signal 170 corresponding to a minimum or maximum torque output in some examples. In one example, a minimum torque output may be determined based on one or more of a creep torque associated with a creep function, a driver’s requested torque, and zero torque. As explained in respect of Figure 1 , the driver’s requested torque may correspond to a driver demand on a flat surface, absent any influence of other vehicle functions which may add in or removal torque. The creep torque may be a torque associated with a creep function, and the creep function may be a vehicle function which requests torque from the torque system 240 to maintain a vehicle creep velocity. The vehicle creep velocity may be a low velocity such as between 0 and 5 kph which is maintained by the creep function absent driver input on the accelerator pedal. It should be understood that other maximum or minimum values for the torque output of the torque system 240 may be configured. In one example, the minimum torque output described in the example above may be implemented during the determination of one or more of the proportional or integrator terms, as will be explained below.

[0116] Figure 6 is a flowchart illustrating a method 600 according to an embodiment of the present invention. The method 600 of Figure 6 may be performed by the control system 100 of Figure 1 and / or the torque system 240 of Figure 2. The method 600 of Figure 6 is a method for determining the proportional term, and may be considered a method for performing part of step 520 of the method 500 of Figure 5 according to an embodiment of the present invention.

[0117] The method 600 of Figure 6 comprises comparing 610 the expected acceleration of the vehicle and the actual acceleration of the vehicle. Step 610 of Figure 6 may be the same as step 510 of Figure 5. Comparing 610 the expected acceleration of the vehicle and the actual acceleration of the vehicle may comprise determining a difference between the expected acceleration of the vehicle and the actual acceleration of the vehicle.

[0118] The method 600 comprises determining 620 or receiving a minimum torque authority of the control system 100. The minimum torque authority is indicative of a minimum torque output of the torque system 240 according to an embodiment of the present invention. As explained above, in one example the minimum torque authority may correspond to one or more of a creep torque, a driver’s requested torque (in some examples, corresponding to a driver’s demand on a flat surface, absent any input from adaptive features such as the adaptive pedal progression mode or the overrun to rest function, discussed above and in respect of Figure 1), or zero torque. In one example, the minimum torque authority may be the lowest among these exemplified minimum torques. In another example, the minimum torque authority may be the highest among these exemplified minimum torques. It should be understood that other minimum torque values may be included beyond those exemplified above.

[0119] The method 600 further comprises determining 630 the proportional term. The proportional term is determined by multiplying the difference between the expected acceleration of the vehicle and the actual acceleration of the vehicle by a first gain factor. In some examples, the first gain factor is implemented as a curve with a dependence on the current difference between the expected acceleration and the actual acceleration of the vehicle. This allows the first gain factor to increase if there is a large difference so that the control system 100 response is more severe. In some examples, the proportional term is saturated to be between 0 and a negative controller allowance. This is so that the control system 100 cannot add positive torque back in to the system, which may be undesirable for a driver of the vehicle.

[0120] In some examples, the determining 630 of the proportional term comprises applying one or more of a minimum or maximum limit to the proportional term. In one example, the minimum limit is the minimum torque authority described above. In an example, the maximum limit is predetermined. In an example, the maximum limit is 0 Nm so as to not allow the proportional term to add positive torque to the torque output of the torque system 240.

[0121] The method 600 further comprises outputting 640 the proportional term. It should be understood that the proportional term may be “output’ from one part of the control system 100 to another, or may be stored in temporary or permanent memory of the control system 100.

[0122] It should be understood that one or more steps of the method 600 of Figure 6 may be omitted, or that the method 600 may include further steps beyond those illustrated.

[0123] Figure 7 is a flowchart illustrating a method 700 according to an embodiment of the present invention. The method 700 of Figure 7 may be performed by the control system 100 of Figure 1 and / or the torque system 240 of Figure 2. The method 700 of Figure 7 is a method for determining the integrator term, and may be considered a method for performing part of step 520 of the method 500 of Figure 5 according to an embodiment of the present invention. It should be understood that the method 700 of Figure 7 may be performed sequentially or simultaneously with the method 600 of Figure 6. In another example, the torque control signal 170 may be determined based on only one of the proportional term or the integrator term.

[0124] The method 700 of Figure 7 comprises comparing 710 the expected acceleration of the vehicle and the actual acceleration of the vehicle. Step 710 of Figure 7 may be the same as step 510 of Figure 5 and / or step 610 of Figure 6. It should be understood that the comparison may be performed only once rather than as part of each of the methods of Figures 5, 6 and 7, but that the comparison is described as part of each method for completeness. Comparing 710 the expected acceleration of the vehicle and the actual acceleration of the vehicle may comprise determining a difference between the expected acceleration of the vehicle and the actual acceleration of the vehicle.

[0125] The method 700 comprises receiving 720 or determining 720 the minimum torque authority of the control system 100. The minimum torque authority may be received or determined in the same way as described in respect of the method 600 of Figure 6. The minimum torque authority is indicative of a minimum torque output of the torque system 240 according to an embodiment of the present invention. As explained above, in one example the minimum torque authority may correspond to one or more of a creep torque, a driver’s requested torque, or zero torque. In one example, the minimum torque authority may be the lowest among these exemplified minimum torques. In another example, the minimum torque authority may be the highest among these exemplified minimum torques. It should be understood that other minimum torque values may be included beyond those exemplified above.

[0126] In an example, the method 700 may further comprise receiving the proportional term determined according to the method 600 of Figure 6. As will be explained, the integrator term for a particular time period may be determined by multiplying the difference between the expected acceleration of the vehicle and the actual acceleration of the vehicle by a second gain factor and by an execution rate of the integrator. In one example, the second gain factor and the first gain factor are the same, and the integrator term can be determined by multiplying the proportional term by the execution rate of the integrator. In an example, the second gain factor is a different curve to the first gain factor. However, it should be understood that the first and second gain factors share the same input of the current difference between the expected acceleration and the actual acceleration of the vehicle. This allows the integrator term to behave differently for different amounts of the difference.

[0127] The method 700 comprises determining 730 the integrator term for a particular time period. The integrator term may be determined for particular time periods. The time periods may be delimited by multiples of the integrator execution rate. In one example, the integrator execution rate may be 10ms, but it should be understood that the present disclosure is not limited thereto. For a particular time period, the integrator term is determined by multiplying the difference between the expected acceleration of the vehicle and the actual acceleration of the vehicle by the second gain factor and the execution rate of the integrator.

[0128] The integrator term in some examples is then limited by one or more of a minimum value or a maximum value. The minimum value and / or maximum value of the integrator term may be determined similarly to the minimum value and / or maximum value of the proportional term as explained above in respect of Figure 6. For example, the minimum value of the integrator term may be at least partially based on a minimum torque authority of the control system 100.

[0129] In one example, one or more of a minimum value and / or a maximum value of the integrator term may be determined according to one or more other factors. In one example, a maximum value of the integrator term is determined based on one or more control signals indicating particular vehicle conditions. For example, the vehicle conditions may include a driver input on a brake pedal, or the vehicle speed being zero. These vehicle conditions may be considered to prevent the integrator term from increasing in certain situations.

[0130] In another example, a minimum value and / or a maximum value of the integrator term may be determined based on an integrator term for a current time period. For example, the integrator term for a first time period may be limited to prevent the integrator term for the first time period by increasing by more than an integrator term for a second time period preceding the first time period. The method 700 further comprises adding 740 the determined integrator term for the particular time period to an integrator term for a preceding time period. Advantageously, the integrator term may be considered to have memory of the difference between the expected acceleration of the vehicle and the actual acceleration of the vehicle across a period of time. Thus, the integrator term is able to prevent steady state controller error. The summed integrator term may then be limited by one or more further minimum or maximum values in some examples. For example, the summed integrator term may be limited by a controller minimum limit such as the minimum torque authority, or a zero value. It should be understood that the sum of the integrator term for the particular time period and the integrator term for the preceding time period is referred to as the “integrator term” in this description.

[0131] The method 700 may further comprise outputting the integrator term. It should be understood that the integrator term may be “output” from one part of the control system 100 to another, or may be stored in temporary or permanent memory of the control system 100.

[0132] It should be understood that one or more steps of the method 700 of Figure 7 may be omitted, or that the method 700 may include further steps beyond those illustrated.

[0133] Figure 8 is a line chart illustrating a simulation 800 of a torque system 240 according to an embodiment of the present invention. In Figure 8, there is illustrated a line showing an output torque 810 of a vehicle, a vehicle speed 820, an actual acceleration of a vehicle 830, an expected acceleration of the vehicle 840, a difference 850 between the actual acceleration and the expected acceleration, a proportional term 860 output by a control system such as the control system 100 of Figure 1 , an integrator term 870 output by the control system 100, and a sum 880 of the proportional term 860 and the integrator term 870. In the example of Figure 8, a scenario is illustrated in which positive torque is injected into the torque output 810 beyond what is requested by a driver’s input such as an input by depressing an accelerator pedal. One example of such a scenario is the injection of positive torque by a vehicle function such as an overrun to rest function into the output torque 810. In the example of Figure 8, the requested torque (corresponding to the driver’s input on the pedals) is constant, shown by the flat line in the top section.

[0134] As can be seen in Figure 8, initially a significant positive torque is introduced into the output torque 810, shown by the sharp increase in the output torque 810. Figure 8 shows a simulation where the positive torque is introduced into the output torque 810, but in a real-life situation this may correspond to a vehicle system erroneously introducing excessive torque. In Figure 8, it can be seen that the vehicle speed 820 initially decays until it reaches a value at which point the positive torque is introduced to the output torque 810. As can be seen in Figure 8, the vehicle speed 820 is increased in response to the increase in the output torque 810. This also results in a large increase in the actual acceleration 830 of the vehicle as the vehicle accelerates in response to the introduced torque. The actual acceleration 830 then which exceeds the expected acceleration 840 of the vehicle resulting in a negative difference 850 between the actual acceleration 830 and the expected acceleration 840. It should be understood that there may be a time delay between the introduction of positive torque to the torque output 810 and changes in the vehicle speed 820 and acceleration 830 which may vary between different vehicles and at different speeds. As the torque introduced to the output torque 810 was not requested by the driver, the expected acceleration is unchanged.

[0135] Figure 8 shows that the proportional term 860 rapidly responds to the difference 850 between the actual acceleration 830 and the expected acceleration 840. The actual acceleration 830 of the vehicle begins to reduce and the difference 850 between the actual acceleration 830 and the expected acceleration 840 also reduces. The integrator term 870 takes more time than the proportional term 860 to respond to the difference 850 between the actual acceleration 830 and the expected acceleration 840, but also continues to provide an effect once the difference 850 between the actual acceleration 830 and the expected acceleration 840 has reduced. It should be understood from Figure 8 that the present invention provides a robust and effective method for managing torque output of a torque system 240, particularly in cases where the torque system 240 outputs positive torque in response to control signals from vehicle functions which add positive torque beyond an explicitly requested torque from a driver of the vehicle. In such scenarios, the present invention outputs the torque control signal 170 to reduce a difference 850 between the actual acceleration 830 and the expected acceleration 840.

[0136] Figure 9 illustrates a vehicle 900 according to an embodiment of the present invention. The vehicle 900 may comprise the control system 100 of Figure 1 , and the torque system 240 of Figure 2. The vehicle 900 may also comprise the powertrain 210 and the foundation braking system 220 of Figure 2 as illustrated. As has been explained, the vehicle 900 may be an internal combustion engine vehicle, a mild hybrid electric vehicle, a plug-in hybrid electric vehicle, or a battery electric vehicle.

[0137] 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 torque output of a torque system of a vehicle to control vehicle acceleration on a gradient, the control system comprising one or more processors collectively configured to: receive a torque demand signal indicative of a requested torque; receive a vehicle speed signal indicative of a speed of the vehicle; determine, in dependence on the torque demand signal and the vehicle speed signal, an expected acceleration of the vehicle, wherein the expected acceleration is indicative of an expected acceleration of the vehicle in response to the requested torque being provided to the vehicle while the vehicle is on a flat surface; determine, in dependence on the vehicle speed, an actual acceleration of the vehicle; compare the expected acceleration and the actual acceleration of the vehicle; and output, in dependence on the comparison, a torque control signal to control the torque output of the torque system.

2. The control system according to claim 1 , wherein the one or more processors are collectively configured to output the torque control signal to control the torque output of the torque system such that the actual acceleration of the vehicle is controlled to reduce a difference between the expected acceleration of the vehicle and the actual acceleration of the vehicle.

3. The control system according to any preceding claim, wherein the one or more processors are collectively configured to: determine that the actual acceleration of the vehicle exceeds the expected acceleration of the vehicle; and in dependence on the determination, output the torque control signal to reduce torque from the torque output of the torque system.

4. The control system according to any preceding claim, wherein the one or more processors are collectively configured to: determine a difference between the actual acceleration of the vehicle and the expected acceleration of the vehicle; and in dependence on the actual acceleration of the vehicle exceeding the expected acceleration of the vehicle, output the torque control signal to reduce torque from the torque output of the torque system, wherein an amount of torque to be removed is determined in dependence on the determined difference.

5. The control system according to any preceding claim, wherein the one or more processors are collectively configured to determine the expected acceleration of the vehicle in dependence on an accelerative torque component, wherein the one or more processors are collectively configured to: subtract one or more of a road load torque or a brake torque from the requested torque of the torque demand signal to thereby determine the accelerative torque component; wherein the road load torque comprises an amount of torque corresponding to a resistance to a movement of the vehicle; and wherein the road load torque is determined in dependence on the vehicle speed.

6. The control system according to any preceding claim, wherein the vehicle speed signal comprises a plurality of wheel rotation rates from a respective plurality of vehicle wheels, and the one or more processors are collectively configured to: determine a first vehicle wheel rotation rate in a first direction; determine a second vehicle wheel rotation rate in a second direction; and set the torque control signal to not control the torque output of the torque system when the first direction is opposite to the second direction.

7. The control system according to any preceding claim, wherein the one or more processors are collectively configured to determine the expected acceleration of the vehicle in dependence on one or more of an expected acceleration maximum and an expected acceleration minimum.

8. The control system according to any preceding claim, wherein the one or more processors are collectively configured to output the torque control signal in dependence on a minimum torque output of the torque system; wherein the minimum torque output of the torque system is based on one or more of: a creep torque associated with a creep function of the vehicle; the requested torque; and zero torque.

9. The control system according to any preceding claim, wherein the one or more processors are collectively configured to: generate the torque control signal in dependence on one or more of: a proportional term determined in dependence on the comparison of the actual acceleration of the vehicle and the expected acceleration of the vehicle, and a first gain factor; and an integrator term determined in dependence on the comparison of the actual acceleration of the vehicle and the expected acceleration of the vehicle, a second gain factor, and an integrator execution rate.

10. The control system according to claim 9, wherein the integrator term is determined further in dependence on a maximum integrator term and a previous integrator term, the previous integrator term comprising an integrator term for a preceding execution of the integrator term determination; and wherein the maximum integrator term is determined in dependence on the previous integrator term and the integrator execution rate.11 The control system according to any preceding claim, wherein the one or more processors are collectively configured to output the torque control signal to re-allocate at least a portion of the requested torque to a brake of the vehicle in dependence on the comparison.

12. The control system according to any preceding claim, wherein the one or more processors are collectively configured to: generate an overrun to rest control signal in dependence on the torque control signal; and output the overrun to rest control signal to an overrun to rest controller to control a torque demand of the overrun to rest controller.

13. A torque system of a vehicle, the torque system comprising the control system according to any preceding claim and a powertrain configured to generate and output the torque output of the powertrain in dependence on the torque control signal.

14. A vehicle comprising the control system of any of claims 1 to 12 or the torque system according to claim 13.

15. A method for controlling a torque output of a torque system of a vehicle to control vehicle acceleration on a gradient, the method comprising: receiving a torque demand signal indicative of a requested torque; receiving a vehicle speed signal indicative of a speed of the vehicle; determining, in dependence on the torque demand signal and the vehicle speed signal, an expected acceleration of the vehicle, wherein the expected acceleration is indicative of an expected acceleration of the vehicle in response to the requested torque being provided to the vehicle while the vehicle is on a flat surface; determining, in dependence on the vehicle speed, an actual acceleration of the vehicle; comparing the expected acceleration and the actual acceleration of the vehicle; and outputting, in dependence on the comparison, a torque control signal to control the torque output of the torque system.

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