Vehicle speed control system

Abstract

A control system (50) for controlling a powertrain (22) of a vehicle is configured to receive a desired occupant comfort level (62) and to receive occupant excitation information (63) indicative of movement of the vehicle and / or movement of an occupant of the vehicle. The control system is configured to determine an occupant comfort level (53) based on a time-average of the occupant excitation information (63) and to determine a target vehicle speed in dependence on the occupant comfort level and the desired occupant comfort level. The control system is configured to output a vehicle speed control signal (71) based on the target vehicle speed. The control system is configured to output the vehicle speed control signal (71) independent of the target vehicle speed during an override period when an accelerator of the vehicle is actuated (67), and wherein, following the override period, the control system is configured to determine an updated value of the occupant comfort level by ignoring occupant excitation information (63) for at least part of the override period.

Description

[0001] VEHICLE SPEED CONTROL SYSTEM

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a control system for a vehicle. Aspects of the invention relate to a control system for a vehicle, a vehicle comprising the control system, a method for controlling a vehicle and a non- transitory computer readable medium.

[0004] BACKGROUND

[0005] It is known to provide a low speed cruise control system for automatically controlling vehicle speed when a vehicle is driving over off-road terrain. This allows the user to concentrate on the terrain. There are some situations when it is desirable to manually override a speed which the control system has selected.

[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 system for a vehicle, a vehicle comprising the control system, a method for controlling a vehicle and a non-transitory computer readable medium as claimed in the appended claims.

[0009] According to an aspect of the present invention there is provided a control system for controlling a powertrain of a vehicle, the control system comprising one or more processors collectively configured to: receive occupant excitation information indicative of movement of the vehicle and / or movement of an occupant of the vehicle; receive a desired occupant comfort level; determine an occupant comfort level based on a time-average of the occupant excitation information; determine a target vehicle speed in dependence on the occupant comfort level and the desired occupant comfort level, and output a vehicle speed control signal based on the target vehicle speed, wherein the control system is configured to output the vehicle speed control signal independent of the target vehicle speed during an override period when an accelerator of the vehicle is actuated, and wherein, following the override period, the control system is configured to determine an updated value of the occupant comfort level by ignoring occupant excitation information for at least part of the override period.

[0010] An advantage of the control system is avoiding an undesirable reduction in vehicle speed after the override period. During the override period, the driver of the vehicle purposely accelerates the vehicle. For example, the driver may wish to power through a region of sandy terrain at a speed greater than a speed which has been automatically set by the control system. During the override period, the vehicle may experience significant movement if the terrain is uneven. This could significantly reduce the comfort level, and therefore the target vehicle speed automatically set by the control system, immediately following the override period. The reduction in target vehicle speed may be undesirable, particularly on high-drag surfaces such as sand, since the vehicle may lose momentum and may be placed in a condition in which it is unable to progress over terrain. Embodiments of the invention have the advantage that this undesirable decrease in target vehicle speed may be prevented or reduced. The vehicle can maintain momentum following the end of the override period and thereby safely progress over terrain. By determining the occupant comfort level without using occupant excitation level information for at least part of the override period, the determination of target speed is not unduly affected by high levels of occupant excitation level information during the override period.

[0011] The “desired occupant comfort level” may also be considered as a “desired occupant excitation level”, where “comfort level” and “excitation level” are inversely related.

[0012] Optionally, the control system is configured to determine the occupant comfort level independent of the occupant excitation information for all of the override period.

[0013] Optionally, the control system is configured to: during the override period, store the occupant excitation information for a window period preceding the override period; and following the override period, determine the occupant comfort level using the stored occupant excitation information.

[0014] Optionally, the occupant comfort level is a moving average value of the received occupant excitation information. The occupant comfort level may be calculated as a root mean square (RMS) moving average value of the received occupant excitation level information. The RMS may be calculated over a period of around 4 seconds (e.g. 3.8 seconds) or any other suitable period such as 1 second, 2 seconds, 3 seconds, 5 seconds, 10 seconds.

[0015] Optionally, the control system is configured to: receive vehicle set speed information indicative of a desired vehicle speed; and determine the target vehicle speed in dependence on the vehicle set speed information, the occupant comfort level and the desired occupant comfort level information.

[0016] Optionally, the control system is configured to determine the target vehicle speed based on a lower of: the vehicle set speed information; and a vehicle speed at which the occupant comfort level is above the desired occupant comfort level.

[0017] Optionally, the control system is configured to determine the occupant comfort level based on occupant excitation information from at least two orthogonal axes. For example, the occupant excitation information may comprise: vehicle body pitch angular acceleration about a y-axis (transverse axis) through a centre of the vehicle; vehicle body roll angular acceleration about an x-axis (longitudinal axis) through a centre of the vehicle; vehicle body heave acceleration along a z-axis (vertical axis). The control system may be configured to individually determine a time-averaged value of each type of the occupant excitation information, and then to determine the occupant comfort level based on a combination of the time-averaged values. Optionally, the control system is configured to selectively operate in: a first mode in which, following the override period, the control system is configured to determine the occupant comfort level by ignoring occupant excitation information for all of the override period; and a second mode in which, following the override period, the control system is configured to determine the occupant comfort level by using at least some of the occupant excitation information for at least part of the override period.

[0018] The first mode may be advantageous when the vehicle crosses terrain which has limited traction, such as sand. This is because, at the end of the override period, it is undesirable for the control system to decrease the target vehicle speed and lose momentum. The second mode may be advantageous when the vehicle crosses terrain with greater traction. The second mode may be advantageous when the occupant favours ride comfort.

[0019] Optionally, the control system is configured to receive at least one of: an occupant selection of a drive mode; an automated determination of terrain type, and the control system, is configured to select between the first mode and the second mode based on the terrain drive mode or the terrain type.

[0020] The drive mode may indicate a type of terrain, such as: sand; grass, gravel or snow; mud and ruts driving mode; rock crawl. The drive mode may indicate a type of driving, such as sport mode.

[0021] Optionally, the control system comprises a store configured to store the occupant excitation information.

[0022] According to another aspect of the invention, there is provided a system comprising control system of the previous aspect and at least one sensor configured to detect movement of the vehicle and / or movement of an occupant of the vehicle.

[0023] According to another aspect of the invention, there is provided a vehicle comprising the control system, or the system, of any of the previous aspects.

[0024] According to another aspect of the invention, there is provided a method for controlling a powertrain of a vehicle, the method comprising: receiving occupant excitation information indicative of movement of the vehicle and / or movement of an occupant of the vehicle; receiving a desired occupant comfort level indicative of a desired occupant comfort level; determining an occupant comfort level based on a time-average of the occupant excitation information; determining a target vehicle speed in dependence on the occupant comfort level and the desired occupant comfort level information, and outputting a vehicle speed control signal based on the target speed, wherein the method comprises overriding the target vehicle speed during an override period when an accelerator of the vehicle is actuated, and following the override period, determining an updated value of the occupant comfort level by ignoring occupant excitation information for at least part of the override period.

[0025] An advantage of the control system is avoiding an undesirable reduction in vehicle speed after the override period. During the override period, the driver of the vehicle purposely accelerates the vehicle.

[0026] Optionally, the method comprises determining the occupant comfort level independent of the occupant excitation information for all of the override period.

[0027] Optionally, the method comprises: during the override period, storing the occupant excitation information for a window period preceding the override period; and following the override period, determining the occupant comfort level using the stored occupant excitation information.

[0028] According to another aspect of the invention, there is provided computer readable instructions which, when executed by a computer, are arranged to perform the method.

[0029] According to an aspect of the present invention there is provided a control system for controlling a powertrain of a vehicle, the control system comprising one or more processors collectively configured to: receive occupant excitation information indicative of movement of the vehicle and / or movement of an occupant of the vehicle; receive a desired occupant comfort level; determine an occupant comfort level based on a time-average of the occupant excitation information; determine a target vehicle speed in dependence on the occupant comfort level and the desired occupant comfort level, and output a vehicle speed control signal based on the target vehicle speed, wherein the control system is configured to output the vehicle speed control signal independent of the target vehicle speed during an override period when an accelerator of the vehicle is actuated, and wherein, following the override period, the control system is configured to determine an updated value of the occupant comfort level.

[0030] Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0032] Figure 1 shows an example of a vehicle in which speed control may be implemented;

[0033] Figure 2 schematically shows functional units and a control system of the vehicle;

[0034] Figure 3 shows the control system in more detail;

[0035] Figure 4 shows an example of determining a comfort level;

[0036] Figure 5 shows some example of control strategies for speed control;

[0037] Figure 6 shows another example of a control strategy for speed control;

[0038] Figure 7 shows a method of speed control;

[0039] Figure 8 schematically shows an example of a controller for use in the control system.

[0040] DETAILED DESCRIPTION

[0041] Figures 1 and 2 show an example of a vehicle 10 on which a control system according to embodiments of the invention may be implemented. The vehicle 10 may be a passenger vehicle or an automobile. The vehicle 10 may be intended for on-road use, such as a saloon vehicle, or may be intended for at least some off-road use, such as a sports utility vehicle (SUV) or a four-wheel drive (4x4) vehicle. The vehicle 10 may be a commercial vehicle.

[0042] In this example, the vehicle 10 comprises a pair of front wheels 12 and a pair of rear wheels 14. A powertrain 20 is provided to drive the wheels of the vehicle. The powertrain 20 comprises a drive unit 22, a transmission 24 and drive shafts 25. The drive unit 22 may comprise an internal combustion engine, an electric motor / generator with battery energy storage, a hybrid arrangement of an ICE and an electric motor / generator with battery energy storage, or some other unit for providing propulsion.

[0043] For clarity, Figure 2 only shows the powertrain 20 driving the front wheels 12. This represents a vehicle with front wheel drive (FWD). The powertrain 20 may drive the rear wheels 14 in a rear wheel drive (RWD) vehicle. The powertrain may be capable of driving all of the wheels 12, 14 in a four-wheel drive (4WD) or an all-wheel drive (AWD) vehicle. In the case of 4WD / AWD, a single engine or electric motor / generator 22 may be connected to the front wheels 12 and the rear wheels 14 via a drivetrain. Alternatively, the front wheels 12 may be driven by a dedicated front electric motor / generator 22 and the rear wheels 14 may be driven via a dedicated rear electric motor / generator. A braking system 30 is provided for applying a braking force to each of the wheels 12, 14. The braking system 30 is capable of applying a different amount of braking force to each of the wheels 12, 14.

[0044] A control system is provided for controlling operation of the vehicle. The control system comprises one or more controller 50. The one or more controller 50 receives input signals 60. The one or more controller 50 outputs a vehicle speed control signal 71 . The one or more controller 50 may be located in a plurality of vehicle locations, or within one physical controller.

[0045] The vehicle speed control signal 71 may be output directly to the powertrain 20 and the braking system 30 of the vehicle. Alternatively, one or more additional control modules may receive the vehicle speed control signal 71 and interpret how to meet the increase or decrease in vehicle speed. The overall control system of the vehicle may comprise a Powertrain Controller (PTC) and a Braking Controller (BC) (not shown) which receive the vehicle speed control signal 71 .

[0046] The control system is configured to implement a cruise control for use at low speeds on a variety of terrains. This will be called Adaptive Off-road Cruise Control (AOCC). AOCC acts as a low speed cruise control for offroad driving. AOCC is configured to automatically maintain a speed set by a user (called a ’’set speed”) without any pedal inputs being required by the user. It allows the user to concentrate on steering the vehicle and assessing the terrain ahead. The control system is configured to apply selective powertrain, traction control and braking actions to one or more wheels of the vehicle 10, collectively or individually, to maintain the vehicle 10 at the desired speed.

[0047] Figure 3 shows the controller 50 in more detail. While the control system shown in Figure 3 comprises one controller 50, it will be appreciated that this is merely illustrative. The control system may comprise a plurality of controllers which are electrically connected together, and collectively perform the described functionality. The input signals 60 provide various information to the controller 50. One input signal 61 provides an indication that the user wishes to activate the AOCC mode or that the user wishes to de-activate the AOCC mode. AOCC mode may be activated by a button, a virtual button or other form of input device on a human machine interface of the vehicle.

[0048] Another input signal 62 provides information about a desired occupant comfort level. This is an indication of an amount of physical disturbance which is acceptable to the user. Desired comfort level can range from low to high. For example, desired comfort level may be defined by a numerical range from 1 (low comfort) to 4 (high comfort). Another way of considering comfort level is as “excitation level”, where excitation level is the inverse of comfort level. For example, excitation level may be defined by a numerical range from 1 (low excitation) to 5 (high excitation). “Comfort level” and “excitation level” are both ways of indicating an acceptable level of disturbance to the user. “Comfort level” and “excitation level” are inversely related: a high comfort level maps to a low excitation level; a low comfort level maps to a high excitation level. To avoid confusion, the term “comfort level” will be used in the remainder of the description. However, it will be understood that any reference to “comfort level” could be implemented as “excitation level”.

[0049] “Comfort level” may be set by a user of the vehicle, by use of a user interface. For example, controls may be provided on the steering wheel to allow the user to increment and decrement the “Comfort level”. Controls may be provided to the user on another part of the vehicle, such as the dashboard or control panel, or in any other suitable way. The user interface may include a visual display which indicates the selected level of “Comfort level”.

[0050] Another input signal 63, or plurality of input signals, provide occupant excitation information. The occupant excitation information is indicative of movement of the vehicle and / or movement of an occupant of the vehicle. Figure 1 shows some examples of quantities which can be measured. Input signals 63 may be indicative of one or more of: vehicle body pitch angular acceleration 15 about a y-axis (transverse axis) through a centre of the vehicle 10; vehicle body roll angular acceleration 16 about an x-axis (longitudinal axis) through a centre of the vehicle 10; vehicle body heave acceleration 17 along a z-axis (vertical axis) through a centre of the vehicle 10.

[0051] Each of these quantities may be measured by an accelerometer or any other suitable sensing device 40. It is possible to measure one or more different quantities in addition to, or instead of, the ones listed here. An alternative to measuring movement of the vehicle itself is to measure movement (of an occupant) within the cabin of the vehicle. For example, a camera within the vehicle may be provided to monitor movement of an occupant.

[0052] Another input signal 64 provides a set speed. The set speed is selected by the user. It represents the speed at which the user wishes the vehicle to operate. The set speed may be input by the user via a user interface, such as “Speed Up” and “Speed Down” inputs on the steering wheel.

[0053] Another input signal 65 provides an indication of the current vehicle speed. This is the actual speed of the vehicle. Vehicle speed may be obtained from wheel rotation sensors.

[0054] Another input signal 66 provides an indication that a user has depressed the accelerator pedal of the vehicle, or some other user control which the user can operate to accelerate the vehicle. Optionally, this input signal may also indicate a magnitude of the acceleration required (e.g. gentle / hard acceleration). This indicates the degree to which the user is overriding the automated speed control.

[0055] Another input signal 67 provides an indication that a user has depressed the brake pedal of the vehicle, or some other user control which the user can operate to brake or decelerate the vehicle. Optionally, this input signal may also indicate a magnitude of the braking / deceleration required. This indicates the degree to which the user is overriding the automated speed control. Another input signal 68 provides an indication of a selection of a driver mode for terrain type. For example, driving modes may include one or more of: on-highway driving mode; sand driving mode; grass, gravel or snow driving mode; mud and ruts driving mode; rock crawl driving mode. The controller 50 may use the input signal 67 to vary acceleration rates. For example, acceleration rate in the on-highway driving mode may be higher than the acceleration rate in the grass, gravel or snow driving mode.

[0056] Another input signal 69 provides an indication of terrain. For example, information from one or more sensors and / or from a camera may indicate a type of terrain. Alternatively, the controller 50 may determine terrain type from other received information, such as one or more of: the occupant excitation information 63; wheel slip; gradient.

[0057] Controller 50 has a module 52 which is configured to determine a comfort level 53 based on the signal(s) 63 indicative of movement of the vehicle. Module 52 is configured to determine the comfort level 53 based on a time-average of the vehicle movement information 63.

[0058] Controller 50 has a module 54 which is configured to determine a target vehicle speed. Module 54 is configured to determine a target vehicle speed in dependence on the occupant comfort level (determined by module 52) and the desired occupant comfort level 62. Module 54 is also configured to determine the target vehicle speed in dependence on the set speed 64. For example, if the user has requested a set speed of 15 kph, the controller 50 will attempt to reach a target speed of 15 kph, if travelling at that speed also meets other limitations, such as the desired comfort level 62.

[0059] Module 54 of the controller 50 outputs a vehicle speed control signal 71 . The vehicle speed control signal 71 may indicate the required vehicle speed, e.g. 15 kph. Alternatively, the vehicle speed control signal 71 may indicate whether an increase in speed or a decrease in speed is required. If the module 54 determines a target speed which is higherthan the current vehicle speed, the vehicle speed control signal 71 indicates an increase in speed. If the module 54 of the controller 50 determines a target speed which is lower than the current vehicle speed, the vehicle speed control signal 71 indicates a decrease in speed.

[0060] As noted above, the vehicle speed control signal 71 may be output directly to the powertrain 20 and the braking system 30 of the vehicle. Alternatively, one or more additional control modules may receive the vehicle speed control signal 71 and interpret how to meet the increase or decrease in vehicle speed. The overall control system of the vehicle may comprise a Powertrain Controller (PTC) and a Braking Controller (BC) (not shown) which receive the vehicle speed control signal 71 .

[0061] For example, if the vehicle speed control signal 71 indicates an increase in speed, the powertrain 20 or the PTC interpret this as requiring an increase in positive torque from the powertrain 20. If the vehicle speed control signal 71 indicates a decrease in speed, the braking system 30 or the BC interpret this as requiring the braking system 30 to apply a braking force (i.e. negative torque) to one or more of the wheels 12, 14. If the vehicle speed control signal 71 indicates a decrease in speed, the powertrain 20 or the PTC may interpret this as requiring a negative torque at the powertrain 20, such as regenerative braking. In a vehicle with Four- Wheel Drive (4WD) or All-Wheel Drive (AWD) the control system of the vehicle may determine how to meet the target vehicle speed, or the increase or decrease in vehicle speed, by driving the front wheels 12 and / or the rear wheels 14 of the vehicle.

[0062] Controller 50 is configured to allow a user to (temporarily) override the target vehicle speed by accelerating the vehicle. A period during which the accelerator is actuated will be called an override period. Automatic control of the vehicle speed is suspended during the override period. There are various reasons why the user may wish to override the speed. For example, the user may consider that a higher speed is required to ride through a patch of sandy terrain. The AOCC would restrict speed to a lower level to meet an acceptable level of excitation / comfort to the user. However, the user may be willing to tolerate a higher level of disturbance to negotiate the terrain. Another example is traversing very muddy terrain or other surfaces where greater momentum is required in order to maintain progress and the customer is actively deciding to temporarily accept more discomfort to maintain progress.

[0063] During the override period, module 54 is configured to output the powertrain control signal 71 in response to the accelerator input signal 66. This controls the vehicle speed independently of the normal determination of the target vehicle speed. Following the override period, the module 54 is configured to determine an updated value of the occupant comfort level. Module 54 is configured to determine an updated value of the occupant comfort level by ignoring occupant comfort level information for at least part of the override period.

[0064] Figure 4 shows an example of operation of module 52 of the controller. In figure 4, (A) shows occupant excitation information 63(x) over a period of time. Signal 63(x) indicates movement of the vehicle. Signal 63(x) represents one of the plurality of measured quantities (e.g. vehicle body roll angular acceleration 16 about the x-axis). In a vehicle which measures quantities about the x, y and z axes, there will be similar timevarying measurements 63(y) and 63(z) for the other measured quantities. A time-averaging function is performed on the occupant excitation information 63(x) over a time window. The value 81 T(x) represents a time-averaged value of the measured quantity 63(x) over the window 81 . The time-averaging is performed repeatedly, at small shifts of the time window. This technique can be described as calculating a moving average value. One example way of calculating the time-average is by calculating a Root Mean Square (RMS) of the occupant excitation information 63 during the window period.

[0065] In one example, each of the individual measured quantities is separately time-averaged in this way. Therefore, there is also a value 81T(y) which represents a time-averaged value of the measured quantity 63(y) over the same time window 81 and a value 81T(z) which represents a time-averaged value of the measured quantity 63(z) over the window 81 .

[0066] Then, the time-averaged values 81T(x), 81T(y) and 81 T(z) are combined. The combined output is a value of comfort level 53 over the period of the time window. One example way of combining measurements in orthogonal directions is described in International Standard ISO 2631-1 1997 “Mechanical Vibration and shock - Evaluation of human exposure to whole-body vibration”. Section 6.5 of this document describes a way of combining vibration measurements in different orthogonal directions. It uses a root sum of squares calculation, with linear gains applied to each direction. Other types of combining operation are possible.

[0067] In Figure 4, (B) shows some discrete values of the comfort level 53. Each of the values is the result of the time-averaging function and combining performed over respective time windows. For example: 81 C is the value of the comfort level for window period 81 . The comfort level varies with the amount of measured excitation. The comfort level is repeatedly calculated at spaced apart times. For example, the comfort level 53 may be calculated at a rate of 100 Hz, i.e. one hundred times every second. An example length of the window period is around 4 seconds, such as 3.8 seconds. Other values for the window period may be used.

[0068] Figure 5 shows an example of operation of the control system. Figure 5(A) schematically shows a surface profile over which the vehicle is driven.

[0069] Figure 5(B) shows speed of the vehicle and Figure 5(C) shows a comfort level when the control system uses a first control strategy. Figure 5(D) shows speed of the vehicle and Figure 5(E) shows a comfort level when the control system uses a second control strategy.

[0070] In the first control strategy, the control system determines a target vehicle speed (solid line) based on comfort level. The comfort level is based on a time-average of occupant excitation information (i.e. a time-average of information which indicates disturbance). Between times TO and T1 the control system sets a target vehicle speed S1. The vehicle is driving over a smooth surface 102 and the target speed, based on the estimated comfort level, has a high value. At T1 the vehicle begins to travel over an uneven surface 104. The uneven surface reduces the target speed, based on the estimated comfort level. As the control system determines the target vehicle speed based on the comfort level, the target vehicle speed reduces 112 due to the decreasing comfort level 122. At T2 the vehicle begins to travel over a smooth surface 106. The comfort level increases 123. The target vehicle speed increases 113 due to the increasing comfort level. At T4 the comfort level reaches a steady value. This is because the window of occupant excitation information used to calculate the comfort level is constant. The target vehicle speed eventually levels off due to the steady comfort level.

[0071] In Figure 5(B), the target vehicle speed is shown by a dashed line and the actual vehicle speed is shown by a solid line. The target vehicle speed determined by the control system is overridden, such as by a user pressing the accelerator pedal. An override period begins at T1 and ends at T3. In this example, the override period begins at the same time as the vehicle begins to travel over the uneven surface 104. During the override period T1-T3, the control system is configured to control the vehicle speed independently of the target vehicle speed. This means the control system does not use the target vehicle speed between T1 and T3. In this example, the actual vehicle speed remains at a constant value 115 during the override period. In other examples, the vehicle speed may vary during the override period. During the override period the vehicle speed 115 is higher than the target vehicle speed 112, 113. At the end of the override period T3, there is a discrepancy between the actual vehicle speed 116 and the target vehicle speed 113 calculated by the control system based on the comfort level. This can cause a change of vehicle speed at T3 when the control system regains control of vehicle speed. In this example, vehicle speed reduces after T3 and converges towards the target vehicle speed.

[0072] In the second control strategy, the control system determines a target vehicle speed based on comfort level. However, there is a difference in how comfort level is calculated during an override period. The comfort level is based on a time-average of occupant excitation information (i.e. an indication of disturbance). The control system is configured to determine an updated value of the comfort level by ignoring occupant excitation information for at least part of the override period.

[0073] The control system begins at a target vehicle speed 131 as the vehicle is driving over a smooth surface 102, and the comfort level 141 has a high value. At T1 the vehicle begins to travel over an uneven surface 104. Also at T1 , the target vehicle speed is overridden, such as by a user pressing the accelerator pedal. The override period begins at T1 and ends at T3. The actual vehicle speed is maintained at a constant value 5.

[0074] At T3, the control system initially uses the comfort level calculated at T1 (i.e. before the start of the override period). The control system calculates a target vehicle speed based on the comfort level. As the surface 102 was smooth prior to T1 , the calculated comfort level is high and the calculated target vehicle speed is also high. Therefore, at T3 the target vehicle speed 133 is a better match to the actual vehicle speed. In this example, the target vehicle speed 133 is equal to the actual vehicle speed, although they can be different. This results in a smoother control of vehicle speed as the control system regains control of the target vehicle speed. After T3, the control system calculates comfort level based on a window of excitation information which excludes the override period. The window of time will initially comprise a combination of (i) some excitation information immediately before T1 , and (ii) some excitation information immediately after T3.

[0075] During the override period, the control system does not calculate the comfort level. Excitation information during the override period is ignored.

[0076] In this example, the comfort level at time T3 is the same as at time T1 . In another example (not shown) the comfort level at time T3 is greater than at time T1 . The control system will increase the vehicle speed after the override period, based on the new comfort level data after the override period. In another example (not shown) the comfort level at time T3 is less than at time T1 . The control system will decrease the vehicle speed after the override period, based on the new comfort level data after the override period.

[0077] Figure 6 shows another example of operation of the control system. Figure 6(A) schematically shows a surface profile over which the vehicle is driven. This is the same as shown in Figure 5(A). Figure 6(B) shows speed of the vehicle and Figure 6(C) shows a comfort level when the control system uses the second control strategy. In Figure 6(B) and 6(C) the user override period begins later than shown in Figure 5(D) and 5(E).

[0078] Initially, the vehicle is driving over a smooth surface 102, and the comfort level has a high value. The control system sets at a target vehicle speed S1 . At T1 the vehicle begins to travel over an uneven surface 104. At T1 the comfort level begins to fall due to the uneven surface. The vehicle speed beings to fall 152. The user presses the accelerator pedal at T2. This overrides the target vehicle speed set by AOCC. The vehicle speed returns to S1 . The override period ends at T4 when the user releases the accelerator pedal.

[0079] At T4, the control system calculates comfort level using a window of occupant excitation information for the period immediately prior to T2 (i.e. before the start of the override period). The control system calculates a target vehicle speed 155 (dashed line) based on the comfort level. The calculated comfort level is initially the value at T2. This may cause a slight reduction in vehicle speed after T4, as the target vehicle speed 155 is lower than the actual vehicle speed 154. However, the target vehicle speed will be a better match to the actual vehicle speed compared to the first control strategy of Figures 5(B) and (C) . This results in a smoother control of vehicle speed as the control system regains control of the target vehicle speed.

[0080] Figure 7 shows an example of a method 200 of controlling a powertrain of a vehicle. In block 202, the method is activated by a user. For example, in response to receiving an AOCC on instruction 61 from a user interface of the vehicle. The method receives a desired occupant comfort level, which is an indication of an amount of disturbance acceptable to the user. The method receives a set speed, which is the speed at which the user wishes to travel.

[0081] In block 204, the method determines if the vehicle speed is less than a predetermined threshold speed value. The method may only proceed if the speed is less than the threshold speed value. For example, the threshold may be 30 kph. If the speed is above the threshold speed value then the method exits 205.

[0082] In block 206, the method receives occupant excitation information indicative of movement of the vehicle and / or movement of an occupant of the vehicle. In block 208 the method determines an occupant comfort level based on a time-average of the occupant excitation information.

[0083] In block 210 the method determines a target vehicle speed in dependence on the occupant comfort level and the desired occupant comfort level. Block 210 outputs a vehicle speed control signal based on the target vehicle speed. Block 212 determines the target vehicle speed based on a lower of: (i) the vehicle set speed information; and (ii) a vehicle speed at which the occupant comfort level is below a maximum desired occupant comfort level. For example, if the minimum desired occupant comfort level is 2 (out of 5) and the occupant comfort level is 3, the amount of disturbance is less than the desired maximum and the vehicle may travel at the set speed. However, if the minimum desired occupant comfort level is 4 (out of 5) and the occupant excitation level is less than 4, the amount of disturbance is more than the desired maximum and the vehicle speed is reduced to bring the amount of disturbance to within the desired amount. This may require the vehicle speed to be less than the set speed.

[0084] In block 214, the method determines if a user has actuated the accelerator of the vehicle. If the accelerator has been actuated, speed control is overridden. An override period begins. The method proceeds to block 216. If the accelerator has not been actuated, the method continues to perform control of the target vehicle speed. The method returns to block 206. In block 216, vehicle speed is controlled by the user. The vehicle speed is responsive to the input signal from the accelerator pedal (or other input device).

[0085] In block 218, the method determines if the accelerator is still actuated. If the accelerator is still being actuated, the override period continues. The method returns to block 216. If the accelerator is no longer being actuated, the override period ends. The method returns to block 206. On returning to block 206, the method uses the value of the occupant comfort level from the end of the last period of speed control. The method does not use any occupant comfort information from the override period.

[0086] The method may vary how speed is controlled based on the type of terrain and / or the terrain driving mode selected by the user.

[0087] In a modification to the control system and the method described above, the controller may store at least some of the excitation information during the override period and the comfort level is based on some of the excitation information during the override period. The control system may be configured to operate in a first mode in which, following the override period, the control system is configured to determine the occupant comfort level 53 by ignoring occupant excitation information 63 for all of the override period. The control system may also be configured to operate in a second mode in which, following the override period, the control system is configured to determine the occupant comfort level 53 by using at least some of the occupant excitation information 63 for at least part of the override period. The second mode may be the same, or similar, to the “first control strategy” shown in Figures 5(B) and (C). The control system may be configured to determine the occupant comfort level 53 by using all of the occupant excitation information 63 for all, or at least part of, the duration of the override period. The control system may be configured to determine the occupant comfort level 53 by using some of the occupant excitation information 63 for all, or at least part of, the duration of the override period. For example, the control system may be configured to determine the occupant comfort level 53 by using a sub-set ofthe total set of received occupant excitation information 63 (e.g. information fortwo directions of movement instead of all three directions of movement) for at least part of the override period. Another possibility is to modify the filtering applied to the occupant excitation information 63 and / or the duration of the time window which is used to determine the time-average of the occupant excitation information 63. This can allow some variation in determining the occupant comfort level 53.

[0088] The control system may be configured to select between the first mode and the second mode based on an occupant selection of a drive mode (e.g. a terrain driving mode) or an automated determination of terrain type. For example, the control system may be configured to select the first mode in sandy terrain, where there is a priority of maintaining vehicle momentum.

[0089] Figure 8 schematically shows the controller 50. The control system may comprise one controller 50, or a plurality of controllers which are electrically connected together, and collectively perform the described functionality. The controller 50 comprises at least one processor 302 which may be any type of processor for executing instructions to control the operation of the system. The processor 302 is electrically connected to other components of the controller via one or more buses 301. Processor-executable instructions 304 may be provided using any data storage device or computer-readable media, such as memory 303. The processorexecutable instructions 304 comprise instructions for implementing the functionality of the described methods, such as the method of Figure 7. The storage / memory 303 is of any suitable type such as non-volatile memory, a magnetic or optical storage device. The processor 302 is configured to access the memory 303 and execute the stored instructions 304. Memory 303, or a separate memory / storage stores data 305 used by the processor 302. Data 305 may comprise occupant excitation information 63 received for a period of time.

[0090] The controller 50 comprises an input interface 306. The input interface 56 is configured to receive one or more input signals 60. The controller 50 comprises an output interface 307. The output interface 307 is configured to output the vehicle speed control signal 71 which controls the powertrain of the vehicle.

[0091] 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 (50) for controlling a powertrain of a vehicle, the control system (50) comprising one or more processors collectively configured to: receive occupant excitation information (63) indicative of movement of the vehicle and / or movement of an occupant of the vehicle; receive a desired occupant comfort level (62); determine an occupant comfort level (53) based on a time-average of the occupant excitation information (63); determine a target vehicle speed in dependence on the occupant comfort level and the desired occupant comfort level, and output a vehicle speed control signal (71) based on the target vehicle speed, wherein the control system is configured to output the vehicle speed control signal (71) independent of the target vehicle speed during an override period when an accelerator of the vehicle is actuated (67), and wherein, following the override period, the control system is configured to determine an updated value of the occupant comfort level by ignoring occupant excitation information (63) for at least part of the override period.

2. The control system of claim 1 configured to determine the occupant comfort level (53) independent of the occupant excitation information (63) for all of the override period.

3. The control system of claim 1 or 2 configured to: during the override period, store the occupant excitation information (63) for a window period preceding the override period; and following the override period, determine the occupant comfort level (53) using the stored occupant excitation information (63).

4. The control system of any one of the preceding claims wherein the occupant comfort level (53) is a moving average value of the received occupant excitation information (63).

5. The control system of any one of the preceding claims configured to: receive vehicle set speed information (64) indicative of a desired vehicle speed; and determine the target vehicle speed in dependence on the vehicle set speed information (64), the occupant comfort level (53) and the desired occupant comfort level information (62).

6. The control system of claim 5 configured to determine the target vehicle speed based on a lower of: the vehicle set speed information (64); and a vehicle speed at which the determined occupant comfort level (53) is above the desired occupant comfort level (62).

7. The control system of any one of the preceding claims configured to selectively operate in:a first mode in which, following the override period, the control system is configured to determine the occupant comfort level (53) by ignoring occupant excitation information (63) for all of the override period; and a second mode in which, following the override period, the control system is configured to determine the occupant comfort level (53) by using at least some of the occupant excitation information (63) for at least part of the override period.

8. The control system of claim 7 configured to receive at least one of: an occupant selection of a drive mode (68); an automated determination of terrain type, and the control system, is configured to select between the first mode and the second mode based on the terrain drive mode or the terrain type.

9. The control system of any one of the preceding claims comprising a store (303) configured to store the occupant excitation information (63).

10. A system comprising control system of any one of the preceding claims and at least one sensor (40) configured to detect movement of the vehicle and / or movement of an occupant of the vehicle.11 . A vehicle comprising the control system (50) of any one of the preceding claims or the system of claim 10.

12. A method for controlling a powertrain of a vehicle, the method comprising: receiving occupant excitation information (63) indicative of movement of the vehicle and / or movement of an occupant of the vehicle; receiving a desired occupant comfort level (62) indicative of a desired occupant comfort level; determining an occupant comfort level (53) based on a time-average of the occupant excitation information; determining a target vehicle speed in dependence on the occupant comfort level (53) and the desired occupant comfort level information (62), and outputting a vehicle speed control signal (71) based on the target speed, wherein the method comprises overriding the target vehicle speed during an override period when an accelerator of the vehicle is actuated, and following the override period, determining an updated value of the occupant comfort level (53) by ignoring occupant excitation information (63) for at least part of the override period.

13. The method of claim 12 comprising determining the occupant comfort level (53) independent of the occupant excitation information (63) for all of the override period.

14. The method of claim 12 or 13 comprising: during the override period, storing the occupant excitation information (63) for a window period preceding the override period; andfollowing the override period, determining the occupant comfort level (53) using the stored occupant excitation information (63).

15. Computer readable instructions which, when executed by a computer, are arranged to perform the method according to any one of claims 12 to 14.

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