A control system for controlling a powertrain of a vehicle

Abstract

Aspects of the present invention relate to a control system for controlling a powertrain of a vehicle to bring the vehicle to rest using an open loop deceleration control scheme based on an estimate of the vehicle speed and a measured road gradient.

Description

[0001] A CONTROL SYSTEM FOR CONTROLLING A POWERTRAIN OF A VEHICLE

[0002] TECHNICAL FIELD

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

[0004] BACKGROUND

[0005] For bringing vehicles to rest, a driver must usually reduce the pressure on an accelerator pedal and apply pressure to a brake pedal, adjusting their inputs so as to bring the vehicle to rest comfortably. ADAS systems may bring a vehicle to rest based on external factors such as a distance measurement to an adjacent object. However, such systems require either significant driver input or may be uncomfortable for passengers due to high or inconsistent rates of acceleration.

[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] According to an aspect of the present invention, there is provided a control system for controlling a powertrain of a vehicle, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, the control system comprising one or more processors collectively configured to: receive an acceleration signal comprising information indicative of a proper acceleration of the vehicle; determine a road gradient based at least partially on the proper acceleration of the vehicle; determine a torque demand based on the road gradient; and output a torque demand signal in order to cause the power source to generate a torque equal to the torque demand.

[0009] The processors may be collectively configured to: receive a first vehicle speed signal comprising information indicative of a first vehicle speed at a first time; receive a second vehicle speed signal comprising information indicative of a second vehicle speed at a second time; determine a vehicle acceleration based on the first vehicle speed and the second vehicle speed; and determine the road gradient based at least partially on the proper acceleration of the vehicle and the vehicle acceleration.

[0010] The control system may comprise 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 the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to carry out the disclosed function of the control system.

[0011] By determining the road gradient, a more accurate determination of the torque required for providing a desired acceleration or deceleration of the vehicle may be made. This may in some cases allow the vehicle to be brought to rest with less driver input and improved comfort. By using a proper acceleration value which accounts for acceleration due to gravity, the gradient and the mass of the vehicle may be determined more precisely, improving the accuracy of the determination of the torque demand.

[0012] The one or more processors may be collectively configured to: receive a vehicle mass signal, the vehicle mass signal comprising information indicative of an estimated mass of the vehicle; and determine the torque demand based on the vehicle mass and the road gradient.

[0013] By determining a torque requirement based on an estimated vehicle mass and the road gradient, the torque demand may be determined more precisely. In particular, this may allow the control system to control a range of different vehicles accurately.

[0014] The one or more processors may be collectively configured to: receive a torque signal comprising information indicative of a torque generated by the power source; and determine, when the vehicle has been brought to rest by a torque generated by the power source, a corrected estimated vehicle mass based on the torque generated by the power source.

[0015] By determining a corrected estimated mass based on the torque generated by the power source, the estimated vehicle mass may be corrected, allowing improved determination of the required torque subsequently. This may improve control of the vehicle for example when the vehicle is transporting a greater load than expected during normal use.

[0016] The one or more processors may be collectively configured to: receive a further first vehicle speed signal comprising information indicative of a further first vehicle speed at a further first time; receive a further second vehicle speed signal comprising information indicative of a further second vehicle speed at a further second time; determine a further vehicle acceleration based on the further first vehicle speed and the further second vehicle speed; receive a further acceleration signal comprising information indicative of a further proper acceleration of the vehicle; determine a further road gradient based at least partially on the further vehicle acceleration and the further proper acceleration of the vehicle; determine a further torque demand based on the further road gradient and the corrected estimated vehicle mass; and output a further torque demand signal in order to cause the power source to generate a torque equal to the further torque demand.

[0017] Using the corrected estimated vehicle mass to determine torque requirements for further acceleration and / or deceleration requests may provide more accurate determined torque requirements.

[0018] Determining the torque demand may comprise determining a torque required to bring the vehicle to rest.

[0019] The estimation of vehicle mass and road gradient may be particularly useful where the vehicle is brought to rest as a more accurate determination of the torque demand may allow the vehicle to stop in the desired location more precisely. Determining the torque demand may comprise determining the torque required to decelerate the vehicle at a rate of between 1 ms-2and 8 ms-2, preferably between 2ms-2and 7ms-2, further preferably between 3 ms-2and 6 ms-2.

[0020] By decelerating the vehicle at this rate, the passenger may experience a more comfortable ride and the vehicle may be brought to rest at an acceptable rate.

[0021] The one or more processors may be collectively configured to: determine or receive an expected vehicle speed signal comprising information indicative of an expected vehicle speed at a third time; receive a third vehicle speed signal comprising information indicative of a third vehicle speed at the third time; compare the expected vehicle speed at the third time to the third vehicle speed at the third time; determine a corrective torque demand based on the comparison of the expected vehicle speed at the third time and the third vehicle speed at the third time; and output a corrective torque demand signal in order to cause the power source to generate a torque equal to the corrective torque demand.

[0022] By comparing vehicle speed to an expected vehicle speed, progress of the vehicle may be compared to that expected. This may be used to bring the vehicle to rest precisely and with a varying acceleration that may improve passenger comfort.

[0023] The one or more processors may be collectively configured to: determine a vehicle mass error based on the comparison of the expected vehicle speed at the third time and the third vehicle speed at the third time.

[0024] By determining a vehicle mass error, the system may be able to adjust the torque demand or apply brakes as necessary to accelerate or decelerate the vehicle as desired.

[0025] The one or more processors may be collectively configured to determine a corrected vehicle mass based on the vehicle mass and the vehicle mass error.

[0026] By determining a corrected vehicle mass, the system may adjust the expected speed or the torque demand to provide desired vehicle motion and improve passenger comfort.

[0027] The one or more processors may be collectively configured to: determine a road gradient error based on the comparison of the expected vehicle speed at the third time and the third vehicle speed at the third time; and determine a corrected road gradient based on the road gradient and the road gradient error.

[0028] By determining a corrected road gradient, the system may adjust the expected speed or the torque demand to provide desired vehicle motion and improve passenger comfort.

[0029] The one or more processors may be collectively configured to: determine a corrected torque demand based on the corrected vehicle mass and / or the corrected road gradient; and output a corrected torque demand signal in order to cause the power source to generate a torque equal to the corrected torque demand. By determining a corrected torque demand, the vehicle may move more closely in line with the expected vehicle speed.

[0030] The vehicle speed signals may each comprise a power source speed signal indicative of a rotational speed of the power source and a torque ratio signal indicative of a torque ratio of the drivetrain. The one or more processors may be collectively configured to determine the vehicle speed based on the rotational speed of the power source and the torque ratio of the drivetrain.

[0031] Speed sensors based on road wheel speed may become inaccurate at low speed. Therefore, by using a speed sensor linked to the power source, the vehicle speed may be determined more accurately at low speed.

[0032] Another aspect of the invention provides a vehicle comprising a powertrain, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, and the control system of the aspect of the present invention.

[0033] The power source may be an electric machine.

[0034] A further aspect of the invention provides a method for controlling a powertrain of a vehicle, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, the method comprising: receiving a first vehicle speed signal comprising information indicative of a first vehicle speed at a first time; receiving a second vehicle speed signal comprising information indicative of a second vehicle speed at a second time; determining a vehicle acceleration based on the first vehicle speed and the second vehicle speed; receiving an acceleration signal comprising information indicative of a proper acceleration of the vehicle; determining a road gradient based at least partially on the vehicle acceleration and the proper acceleration of the vehicle; determining a torque demand based on the road gradient; and outputting a torque demand signal in order to cause the power source to generate a torque equal to the torque demand.

[0035] A still further aspect of the invention provides computer readable instructions which, when executed by a computer, are arranged to perform a method according to the further aspect of the present invention.

[0036] 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.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0038] Figure 1 shows a vehicle in accordance with an embodiment of the invention;

[0039] Figure 2 shows a block diagram illustrating a control system in accordance with an embodiment of the invention;

[0040] Figure 3 shows a block diagram illustrating a control system in accordance with a further embodiment of the invention;

[0041] Figure 4 shows a flowchart illustrating a method in accordance with an embodiment of the invention;

[0042] Figure 5 is a graph illustrating an expected speed profile for use in a control system according to the invention;

[0043] Figure 6 shows a flowchart illustrating a method in accordance with a further embodiment of the invention; and

[0044] Figure 7 shows a flowchart illustrating a method in accordance with a still further embodiment of the invention.

[0045] DETAILED DESCRIPTION

[0046] With reference to Figure 1 , there is illustrated a control system 100 for controlling a powertrain 120 of a vehicle 10. As shown in Figure 2, the control system 100 comprises one or more controllers 160, and the powertrain 120 at least comprises a power source 130 and a drivetrain 140. The drivetrain 140 is arranged to receive torque 133 generated by the power source 130. The power source 130 and drivetrain 140 together form a powertrain 120 of the vehicle 10.

[0047] The control system 100 is configured to receive an acceleration signal 151 from an inertial measurement unit (IMU) 150 and speed data 1 11 from a speed sensor 100, and to determine an acceleration of the vehicle 10, a road gradient and a torque demand. The control system 100 may then output a torque demand signal 101 to cause the power source 130 to generate a torque equal to the torque demand.

[0048] The control system 100 as Illustrated in Figure 2 comprises one controller 160, although it will be appreciated that this is merely illustrative. The controller 160 comprises processing means 162 and memory means 164. The processing means may be one or more electronic processing device 162 which operably executes computer-readable instructions. The memory means 164 may be one or more memory device 164. The memory means 164 is electrically coupled to the processing means 162. The memory means 164 is configured to store instructions, and the processing means 162 is configured to access the memory means 164 and execute the instructions stored thereon.

[0049] The controller 160 comprises an input means 166 and an output means 168. The input means 166 may comprise an electrical input of the controller 160 arranged to receive data such as a vehicle speed 111 from a vehicle speed sensor 110. The output means 168 may comprise an electrical output of the controller 160 arranged to output commands, such as a required torque signal 101 to cause the power source 130 to generate a required torque. As illustrated in Figure 2, the control system 100 is configured to receive vehicle speed signals 1 11 from a vehicle speed sensor 100. The control system 100 is arranged to receive a plurality of vehicle speed signals 11 1 over time, the vehicle speed signals comprising data indicative of a speed of the vehicle. In particular, the control system 100 is arranged to receive a first vehicle speed signal and a second vehicle speed signal. The first vehicle speed signal may contain information indicative of a first vehicle speed at a first time. The second vehicle speed signal may contain information indicative of a second vehicle speed at a second time. A speed sensor 1 10 may be used to measure the first and second vehicle speeds. The speed sensor 110 may form part of the control system 100 or may be part of a separate system within the vehicle 10. The speed sensor 110 may detect a rotational speed of a wheel of the vehicle or may detect a rotational speed of the power source 130 and determine a vehicle speed based on the rotational speed of the power source 130 and a known torque ratio of the drivetrain.

[0050] The control system 100 is further configured to receive an acceleration signal 151 from an inertial measurement unit 150. The acceleration signal 151 may be referred to as a gradient signal containing information indicative of the gradient of the road which the vehicle is on. While the road gradient may be determined based on data received from an inertial measurement unit (IMU) 150 as illustrated in Figure 2, it will be understood that the road gradient may alternatively be determined based on data from different sensors, such as suspension loading data 171 from suspension sensors 170 or GPS data (see also Figure 3). The road gradient is used to determine the torque demand. Using the road gradient may improve the accuracy of the determined torque demand as changes in road gradient may be accounted for in determining the torque required to achieve a specified acceleration and / or deceleration. (As used herein, acceleration is the general term for change in velocity, both increase and decrease, whereas deceleration is restricted to reducing velocity. Where the context requires, however, acceleration may be interpreted as increasing velocity.)

[0051] The road gradient may be determined using a proper acceleration of the vehicle output by the IMU 150. Proper acceleration here is defined as acceleration relative to free-fall, i.e. acceleration measured relative to acceleration due to gravity. The proper acceleration of the vehicle 10 may be communicated to the control system as an acceleration signal containing information indicative of a proper acceleration of the vehicle 10.

[0052] The control system 100 may be further configured to receive a vehicle mass signal from the memory 164. The vehicle mass signal may alternatively be generated by the processor 162 based on a load condition of the vehicle 10, optionally wherein the load condition of the vehicle is provided by a user input or is based on a resistance of the vehicle to acceleration based on a known torque. The torque demand may therefore be determined based on the estimated mass of the vehicle 10 and the road gradient.

[0053] The control system 100 may be still further configured to receive a torque signal 131 containing information indicative of a torque generated by the power source 130 as shown in Figure 3. The torque signal 131 is shown in Figure 3 as being output by the power source 130, however it will be appreciated that a further controller (not shown) may be used to communicate this information. Alternatively, the torque signal 131 may be published on a CAN bus, and a torque command from the control system 100 may be used, as the torque command will be indicative of the torque 133 generated by the power source 130. Once the vehicle 10 has been brought to rest by a torque generated by the power source 130, a corrected estimated vehicle mass may be determined by the control system 100 based on the torque generated by the power source 130. To further improve accuracy of the corrected estimated vehicle mass, the road gradient may also be used to determine the corrected vehicle mass. The corrected estimated vehicle mass may be determined based on any combination of the vehicle acceleration, the proper acceleration and the torque 133 generated by the power source 130.

[0054] The control system 100 may alternatively determine a vehicle load, based on the vehicle acceleration and the power source torque 133. The vehicle load may be based on a resistance to acceleration of the vehicle and so may account for mass, road gradient and air resistance. Determining an estimation of the vehicle mass or load for determining a torque demand may allow desired accelerations and / or decelerations to be more accurately achieved. As a result, this may require less input from a driver of the vehicle 10 since there may be less need for them to adjust their input to account for the mass and inertia of the vehicle 10.

[0055] Having determined a corrected vehicle mass, the corrected vehicle mass may then be used during future acceleration and / or deceleration requests in place of the initial estimated vehicle mass. It will be appreciated that the corrected estimated vehicle mass may be determined each time the vehicle 10 is brought to rest by a torque 133 generated by the power source 130. In this way any changes in the vehicle mass and / or vehicle load may be accounted for in determining the torque required to achieve a requested acceleration and / or deceleration.

[0056] Figure 4 is a flowchart illustrating a method 200 for determining a torque demand according to an embodiment of the invention. The method 200 is a method of controlling a powertrain 120 of a vehicle 10, such as the vehicle 10 illustrated in Figure 1 . The method 200 may be performed by the control system 100 illustrated in Figures 1 and 2. In particular, the memory 164 may comprise computer-readable instructions which, when executed by the processor 162, perform the method 200 according to an embodiment of the invention.

[0057] At step 210, the control system receives a vehicle speed signal 111 . The vehicle speed signal 11 1 may be received from a sensor arranged to sense a rotation speed of a wheel of the vehicle or may be determined based on a signal received from a sensor arranged to sense a rotational speed of an electric machine and a torque ratio of the drivetrain. In particular, the control system receives a first vehicle speed signal comprising information indicative of a first vehicle speed at a first time and a second vehicle speed signal comprising information indicative of a second vehicle speed at a second time.

[0058] At step 220, the control system is arranged to receive an acceleration signal 151 . The acceleration signal 151 may be received from an IMU 150. The vehicle acceleration signal 151 contains information indicative of a proper acceleration of the vehicle 10.

[0059] At step 230, the control system 100 is configured to determine a vehicle acceleration based on the first vehicle speed and the second vehicle speed. As discussed above, the vehicle speed signal 1 11 may further contain information indicative of the time between the first vehicle speed and the second vehicle speed being recorded. Acceleration of the vehicle 10 may therefore be determined as the difference between the first vehicle speed and the second vehicle speed divided by the time between the first and second vehicle speed recording.

[0060] At step 240, the control system 100 determines a road gradient based at least partially on the proper acceleration of the vehicle 10 and the vehicle acceleration determined at step 230.

[0061] Based on the road gradient, a torque demand is determined by the control system 100 at step 250. The torque demand determined by the control system 100 may be equal to a torque required to bring the vehicle to rest. The torque demand may be determined so as to decelerate the vehicle at a required rate, optionally at a constant rate throughout the deceleration. The rate of deceleration of the vehicle may be between 1 ms-2and 8 ms-2, preferably between 2ms-2and 7ms-2, further preferably between 3 ms-2and 6 ms-2. Alternatively, the control system 100 may be configured to determine a varying torque demand to decelerate the vehicle 10 at a varying rate. The rate of deceleration of the vehicle 10 will affect ride comfort for a user of the vehicle 10. As such, the rate of deceleration of the vehicle 10 may be limited to improve perceived ride comfort for a user of the vehicle 10.

[0062] The control system 100 outputs a torque demand signal 101 at step 260 arranged to cause the power source 130 to generate a torque 133 equal to the torque demand.

[0063] Where the torque 133 generated by the power source 130 has brought the vehicle 10 to rest, an additional step 270 may be performed. At step 270, the control system determines a corrected estimated vehicle mass based on the torque generated by the power source 130. To further improve accuracy of the corrected estimated vehicle mass, the road gradient may also be used to determine the corrected vehicle mass. The corrected estimated vehicle mass may be determined based on any combination of the vehicle acceleration, the proper acceleration, and the torque 133 generated by the power source 130.

[0064] Figure 5 illustrates an expected vehicle speed profile and a real vehicle speed s against time t, showing how the vehicle speed may be corrected based on a determined deviation from an expected vehicle speed.

[0065] An expected vehicle speed may be used to control the speed of the vehicle 10. An example of an expected vehicle speed profile 310 is illustrated in Figure 5, the expected vehicle speed profile comprising a plurality of expected vehicle speed values varying over time. The control system 100 may be configured to determine and / or receive an expected vehicle speed profile 310. The torque demand required to change the vehicle speed to match an expected vehicle speed may then be determined.

[0066] The real vehicle speed is shown as line 320. As illustrated, the vehicle speed 320 may deviate from the expected vehicle speed profile 310. This may be determined based on a vehicle speed measurement taken at time A which may be referred to as a third vehicle speed measurement, showing a deviation D, for example due to a determined vehicle load used to determine the torque demand being different from the real vehicle load. The expected vehicle speed profile 310 may be compared to the vehicle speed at time A, and the difference between the two may be used to determine a vehicle mass error ora road gradient error. The vehicle mass, vehicle gradient and / or vehicle load may be corrected based on the deviation D, and the torque demand may also be corrected. This may be achieved by outputting a corrective torque demand signal which forms part of the torque demand signal 101 . The control system 100 may be configured to output the torque demand signal 101 to cause the power source 130 to generate a torque 133 equal to the torque demand required to change the vehicle speed to match the expected vehicle speed. This may result in the deviation D between the expected vehicle speed profile 310 and the realised vehicle speed profile 320 reducing with time as illustrated in Figure 5.

[0067] Figure 6 illustrates a further method 400 according to an embodiment of the invention. The method 400 is a method for controlling powertrain 120 of a vehicle 10, such as the vehicle 10 illustrated in Figure 1 . In particular, the method 400 provides a method for determining a torque demand in response to an expected vehicle speed profile using a corrected vehicle mass and a corrected road gradient. The method 400 may be performed by the control system 100 illustrated in Figures 1 and 2. In particular, the memory 164 may comprise computer- readable instructions which, when executed by the processor 162, perform the method 400 according to an embodiment of the invention.

[0068] Steps 410, 420 and 430 are identical to steps 210, 220 and 230 of Figure 4 and so are not described again here. At step 440, the control system 100 receives a vehicle mass signal which contains information indicative of an estimated mass of the vehicle 10. The estimated mass of the vehicle may be a predetermined value or may be a corrected estimated vehicle mass determined based on a previously determined torque 133 generated by the power source 130 and a rate of acceleration or deceleration of the vehicle 10, for example when bringing the vehicle to rest.

[0069] At step 450 the control system 100 determines or receives an expected vehicle speed or an expected vehicle speed profile such as the example illustrated in Figure 5. The expected vehicle speed or expected vehicle speed profile may be determined based on the estimated mass and the gradient of the surface the vehicle is on. A third vehicle speed, at a third time subsequent to the first and second times is received at step 460 and this is compared to the expected vehicle speed or the expected vehicle speed profile at step 470.

[0070] At step 472, a vehicle mass error may be determined based on the comparison made previously at step 470. The vehicle mass and the vehicle mass error may be used to determine a corrected vehicle mass at step 474. Optionally, the corrected vehicle mass may be the sum of the estimated vehicle mass or the corrected estimated vehicle mass and the vehicle mass error. Providing a corrected vehicle mass may allow the expected vehicle speed profile and / or the torque demand output by the control system to be adjusted to provide the desired acceleration and / or deceleration and improve comfort for the vehicle user.

[0071] At step 476, a road gradient error may be determined based on the comparison made previously at step 470. An error between the expected vehicle speed and realised vehicle speed may result from an error in determining the gradient of the road. From this, a corrected road gradient may be determined at step 478 based on the road gradient and the road gradient error. Optionally, the corrected road gradient may be the sum of the road gradient and the road gradient error.

[0072] The corrected vehicle mass and / or the corrected road gradient may be used to determine a corrected torque demand at step 480, the corrected torque demand being the torque required to change the vehicle speed to match the expected vehicle speed. A corrected torque demand signal is then output by the control system 100 at step 490 to cause the power source 130 to generate a torque 133 equal to the corrected torque demand.

[0073] It will be understood that steps 460 to 490 may be repeated continually. The vehicle mass, road gradient and / or vehicle load may be re-evaluated and corrected based on an error such that the vehicle speed may remain close to the desired vehicle speed profile.

[0074] In some cases, the control system 100 may not be configured to determine a corrected vehicle mass and / or a corrected road gradient as detailed in steps 472 to 478 of Figure 6. The control system 100 instead may operate as a closed loop control system and determine a corrected torque demand at step 490 based on the comparison between the third vehicle speed and the expected vehicle speed profile made at step 480.

[0075] Figure 7 shows a flow chart illustrating a further method 405 of bringing a vehicle to rest.

[0076] Steps 410 to 450 of method 405 are substantially similar to the identically numbered steps of method 400. At step 455, a torque demand signal is output to cause the power source to output the demanded torque, in order to decelerate the vehicle.

[0077] At step 465, a third vehicle speed is received and compared to a predetermined low speed threshold to determine whether the method should enter a closed loop control scheme. If the third vehicle speed is above the low speed threshold, the control system continues to command the power source to output the demanded torque at step 455. However, if the third vehicle speed is less than the predetermined low speed threshold, the method proceeds to step 475..The low speed threshold may be determined based on the road gradient. The low speed threshold may be less than 15 kilometres per hour, optionally less than 3 kilometres per hour, further optionally less than 0.5 kilometres per hour.

[0078] At step 475, a fourth vehicle speed is received, and based on the fourth vehicle speed, a furthertorque demand is determined at step 485. The torque demand is output at step 495.

[0079] At step 505, it is determined whether the vehicle has come to rest. If the vehicle has not come to rest, the torque demand is recalculated and output. Otherwise, the method may move to step 515, where the vehicle may be held stationary and optionally friction brakes may be applied to hold the vehicle.

[0080] Each of the first, second, third and fourth vehicle speed signals comprised within the vehicle speed signal 11 1 may comprise a power source speed signal and a torque ratio signal. The power source speed signal contains information indicative of a rotational speed of the power source 130. The torque ratio signal contains information indicative of a torque ratio of the drivetrain 140. In this case, the control system 100 is configured to determine the vehicle speed based on the rotational speed of the power source 130 and the torque ratio of the drivetrain 140. While the above disclosure relates to bringing a vehicle to rest, the method may be applied to any deceleration of a vehicle to a chosen target speed. For instance, the method may be employed when implementing cruise control or using adaptive cruise control. In such cases, the method may control deceleration and the low speed threshold determined use at step 465 and the threshold speed for ending the deceleration at step 505 may be altered accordingly.

[0081] 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 powertrain of a vehicle, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, the control system comprising one or more processors collectively configured to: receive a first vehicle speed signal comprising information indicative of a first vehicle speed at a first time; receive a second vehicle speed signal comprising information indicative of a second vehicle speed at a second time; determine a vehicle acceleration based on the first vehicle speed and the second vehicle speed; receive an acceleration signal comprising information indicative of a proper acceleration of the vehicle; determine a road gradient based at least partially on the vehicle acceleration and the proper acceleration of the vehicle; determine a torque demand based on the road gradient; and output a torque demand signal in order to cause the power source to generate a torque equal to the torque demand.

2. The control system of claim 1 , wherein the one or more processors are collectively configured to: receive a vehicle mass signal, the vehicle mass signal comprising information indicative of an estimated mass of the vehicle; and determine the torque demand based on the estimated vehicle mass and the road gradient.

3. The control system of claim 2, wherein the one or more processors are collectively configured to: receive a torque signal comprising information indicative of a torque generated by the power source; and determine, when the vehicle has been brought to rest by a torque generated by the power source, a corrected estimated vehicle mass based on the torque generated by the power source.

4. The control system of claim 3, wherein the one or more processors are collectively configured to: receive a further first vehicle speed signal comprising information indicative of a further first vehicle speed at a further first time; receive a further second vehicle speed signal comprising information indicative of a further second vehicle speed at a further second time; determine a further vehicle acceleration based on the further first vehicle speed and the further second vehicle speed; receive a further acceleration signal comprising information indicative of a further proper acceleration of the vehicle; determine a further road gradient based at least partially on the further vehicle acceleration and the further proper acceleration of the vehicle;determine a further torque demand based on the further road gradient and the corrected estimated vehicle mass; and output a further torque demand signal in order to cause the power source to generate a torque equal to the further torque demand.

5. The control system of any preceding claim wherein determining the torque demand comprises determining a torque required to bring the vehicle to rest.

6. The control system of claim 5, wherein determining the torque demand comprises determining the torque required to decelerate the vehicle at a rate of between 1 ms-2and 8 ms-2, preferably between 2ms-2and 7ms-2, further preferably between 3 ms-2and 6 ms-2.

7. The control system of any preceding claim, wherein the one or more processors are collectively configured to: determine or receive an expected vehicle speed signal comprising information indicative of an expected vehicle speed at a third time; receive a third vehicle speed signal comprising information indicative of a third vehicle speed at the third time; compare the expected vehicle speed at the third time to the third vehicle speed at the third time; determine a corrective torque demand based on the comparison of the expected vehicle speed at the third time and the third vehicle speed at the third time; and output a corrective torque demand signal in order to cause the power source to generate a torque equal to the corrective torque demand.

8. The control system of claim 7, wherein the one or more processors are collectively configured to determine a vehicle mass error based on the comparison of the expected vehicle speed at the third time and the third vehicle speed at the third time.

9. The control system of claim 8, wherein the one or more processors are collectively configured to determine a corrected vehicle mass based on the estimated vehicle mass and the vehicle mass error.

10. The control system of claim 7, 8 or 9, wherein the one or more processors are collectively configured to: determine a road gradient error based on the comparison of the expected vehicle speed at the third time and the third vehicle speed at the third time; and determine a corrected road gradient based on the road gradient and the road gradient error.11 . The control system of claim 9 or 10, wherein the one or more processors are collectively configured to: determine a corrected torque demand based on the corrected vehicle mass and / or the corrected road gradient; andoutput a corrected torque demand signal in order to cause the power source to generate a torque equal to the corrected torque demand.

12. A vehicle comprising a powertrain, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, and the control system of any of claims 1 to 11 .

13. The vehicle of claim 12, wherein the power source is an electric machine.

14. A method for controlling a powertrain of a vehicle, the powertrain comprising a power source and a drivetrain arranged to receive torque from the power source, the method comprising: receiving a first vehicle speed signal comprising information indicative of a first vehicle speed at a first time; receiving a second vehicle speed signal comprising information indicative of a second vehicle speed at a second time; determining a vehicle acceleration based on the first vehicle speed and the second vehicle speed; receiving an acceleration signal comprising information indicative of a proper acceleration of the vehicle; determining a road gradient based at least partially on the vehicle acceleration and the proper acceleration of the vehicle; determining a torque demand based on the road gradient; and outputting a torque demand signal in order to cause the power source to generate a torque equal to the torque demand.

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

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