System, vehicle and method

Abstract

A system for generating a terrain parameter indicative of a surface topography of a driving surface comprises one or more processors configured to receive information relating to the pitch angle and r

Description

TECHNICAL FIELD The present disclosure relates to a system, vehicle and method. Aspects of the invention relate to a system for generating a terrain parameter indicative of a surface topography of a driving surface, to a vehicle comprising the system and to a method of generating a terrain parameter indicative of a surface topography of a driving surface. BACKGROUND It is known to provide a control system for a motor vehicle for controlling one or more vehicle subsystems in accordance with one or more characteristics of the terrain or ground surface type over which the vehicle is travelling. US7349776 discloses a vehicle control system comprising a plurality of subsystem controllers including an engine management system, a transmission controller, a steering controller, a brakes controller and a suspension controller. The subsystem controllers are each operable in a plurality of subsystem function or configuration modes. The subsystem controllers are connected to a vehicle mode controller which controls the subsystem controllers to assume a required function mode so as to provide a number of driving modes for the vehicle. Each of the driving modes corresponds to a particular driving condition or set of driving conditions, and in each mode each of the subsystems is set to the function mode most appropriate to those conditions. Such conditions are linked to types of terrain over which the vehicle may be driven such as grass / gravel / snow, mud ruts, rock crawl, sand and a highway mode known as 'special programs off (SPO). The vehicle mode controller may be referred to as a Terrain Response (TR) (RTM) System or controller. The driving modes may also be referred to as terrain modes, terrain response modes, or control modes. GB2492655B discloses a control system for a motor vehicle in which the most appropriate terrain mode for the prevailing terrain over which the vehicle is driving is determined automatically by the control system. The control system then causes the vehicle to operate in the terrain mode determined to be the most appropriate. In these examples, an estimate of the surface roughness may be used to determine a driving condition or driving mode of the vehicle. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. STATEMENTS OF THE INVENTION In an aspect of the invention there is provided a system for generating a terrain parameter indicative of a surface topography of a driving surface, the system configured to generated the terrain parameter in dependence at least in part on received pitch information and roll information. The system calculates and store successive values of change of pitch angle and change of roll angle as the vehicle progresses over terrain and determines the terrain parameter in dependence on the stored values of change of pitch angle and stored values of change of roll angle. Optionally, the system is configured to determine a driving mode selection in dependence at least in part on the determined terrain parameter. The system may output a signal indicative of the driving mode selection. In an aspect of the invention there is provided a system for generating a terrain parameter indicative of a surface topography of a driving surface, the system comprising one or more processors collectively configured to: receive pitch information indicative of a pitch angle of a motor vehicle; receive roll information indicative of a roll angle of the motor vehicle; in dependence on the received pitch information and roll information, calculate and store successive values of change of pitch angle and change of roll angle as the vehicle progresses over terrain; determine the terrain parameter in dependence on the stored values of change of pitch angle and stored values of change of roll angle; determine a driving mode selection in dependence at least in part on the determined terrain parameter; and output a signal indicative of the driving mode selection. Embodiments of the present invention have the advantage that a parameter indicative of a surface topography of a driving surface may be generated based on measurements of changes in vehicle pitch angle and changes in vehicle roll angle as the vehicle progresses overterrain. Such measurements have been found to provide a reliable means for characterizing surface topography that may be used, in turn, to identify a type of terrain over which the vehicle is driving and select an appropriate configuration of one or more vehicle subsystems for that terrain. Respective different configurations of the one or more vehicle subsystems may in some embodiments be referred to as respective different driving modes. A problem associated with the use of vehicle pitch information and vehicle roll information to characterise a driving surface is that instantaneous values of vehicle pitch angle and vehicle roll angle may vary considerably as a vehicle progresses over terrain. The present applicant has determined, however, that accumulated values of changes in pitch angle and accumulated values of changes in roll angle as the vehicle progresses over terrain may be used to generate a terrain parameter that provides a reliable indication of a surface topography of a driving surface such that a suitable driving mode may be selected in a reliable manner based on the terrain parameter. The system may be configured to calculate and store successive values of maximum change of pitch angle and successive values of maximum change of roll angle over successive first distance intervals as the vehicle progresses over terrain. This feature has the advantage that a surprisingly accurate measure of surface topography of a driving surface may be obtained comparable to that obtainable from suspension articulation information without the requirement for suspension articulation information to be provided. The distance intervals may correspond to a prescribed portion of a wheelbase, such as a prescribed percentage, such as 5%, 10%, 20% or any other suitable percentage. This feature has the advantage that surface topography information to be obtained on a scale enabling the system to respond relatively quickly to changes in surface topography. It is to be understood that the maximum change of pitch (or roll) angle corresponds to the angle between extremes of vehicle pitch (or roll) angle experienced by the vehicle over a given first distance interval. The system may be configured to determine the terrain parameter at least in part in dependence on the stored values of maximum change of pitch angle and stored values of maximum change of roll angle over a second prescribed distance which is equal to a prescribed number of the first distance intervals. Optionally, the second prescribed distance corresponds to a vehicle wheelbase. This feature has the advantage that the system may respond to changes in surface topography in a timely and reliable manner. The vehicle wheelbase may be a centre-to-centre longitudinal distance between front and rear wheels of the vehicle. The system may be further configured to determine the terrain parameter at least in part by calculating a surface articulation, SA, value by summing the stored values of maximum change of pitch angle and stored values of maximum change of roll angle over the first prescribed distance. The system may be configured to calculate the surface articulation, SA, value by summing the stored values of maximum change of pitch angle and stored values of maximum change of roll angle over the first prescribed distance and scaling the sum to a value in the range from 0 to 100. Optionally, the step of determining the terrain parameter in dependence on the stored values of maximum change of pitch angle and stored values of maximum change of roll angle comprises multiplying the surface articulation, SA, value by a gain factor, the gain factor being selected in dependence at least in part on at least one previously calculated value of surface articulation value, wherein the selected gain factor is lower for lower values of surface articulation value. This feature has the advantage that the system may be made resilient to isolated peaks in the value of terrain parameter that are not indicative of travel over rough terrain. For example, in the case of a vehicle driving in an urban environment over smooth asphalt, the system would typically select a relatively low value of gain, thus reducing the value of terrain parameter. In the event that the vehicle mounts a kerb whilst parking, transient peaks in roll angle and pitch angle would be attenuated when the stored values of maximum change of pitch angle and stored values of maximum change of roll angle are multiplied by the gain factor. The value of terrain parameter generated by the system, based on accumulated values of maximum change of pitch angle and values of maximum change of roll angle, would therefore be more likely to remain at a relatively low value. The system will thereby continue to indicate, correctly, that the vehicle is travelling over a relatively smooth surface. However, in the event that the vehicle begins to travel over a relatively rough surface, the prevailing value of terrain parameter will increase, and a higher gain factor may be selected if the value increases sufficiently. Optionally, the gain factor is selected in dependence on previously calculated values of surface articulation over a prescribed distance travelled, wherein the prescribed distance is selected in dependence on one or more calculated values of surface articulation, the prescribed distance being lower for higher values of surface articulation. This feature has the advantage that the system may respond relatively quickly and change the value of surface articulation generated when the surface of the terrain becomes less smooth, but responds less quickly to reduce the generated surface articulation value when the surface of the terrain becomes smoother, as a precaution. The prescribed distance may be referred to as a transition distance. Optionally, a higher gain factor is selected in further dependence on calculated values of maximum change in pitch angle and / or roll angle as the vehicle progresses over terrain, the system being configured to select a higher gain value when calculated values of maximum change in pitch angle and / or roll angle exceed a threshold value. This feature has the advantage that the system may be made more highly responsive to changes in pitch angle and / or roll angle that are determined not to be isolated changes on an otherwise relatively smooth surface. The system may be further configured to control the configuration of at least one vehicle system in dependence on the terrain parameter. In an aspect of the invention there is provided a vehicle comprising a system according a preceding aspect. In a further aspect of the invention there is provided a vehicle according to a preceding aspect, wherein the vehicle control system is configured to control the configuration of at least one vehicle system selected from amongst: (i) a suspension system; (ii) a steering system; (iii) a powertrain of the vehicle; (iv) a braking system; and (v) a stability control system (SCS). In a further aspect of the invention there is provided a method for generating a terrain parameter indicative of a surface topography of a driving surface by means of a system comprising one or more processors, the method comprising: receiving pitch information indicative of a pitch angle of a motor vehicle; receiving roll information indicative of a roll angle of the motor vehicle; in dependence on the received pitch information and roll information, calculating and storing successive values of change of pitch angle and change of roll angle as the vehicle progresses over terrain; determining the terrain parameter in dependence on the stored values of change of pitch angle and stored values of change of roll angle; determining a driving mode selection in dependence at least in part on the determined terrain parameter; and outputting a signal indicative of the driving mode selection. The comprising calculating and storing successive values of maximum change of pitch angle and successive values of maximum change of roll angle over predetermined distance intervals as the vehicle progresses over terrain, the method comprising determining the terrain parameter at least in part in dependence on the stored values of maximum change of pitch angle and stored values of maximum change of roll angle over a first prescribed distance which is equal to a prescribed number of the predetermined distance intervals, the method further comprising determining the terrain parameter at least in part by calculating a surface articulation, SA, value by summing the stored values of maximum change of pitch angle and stored values of maximum change of roll angle over the first prescribed distance. In an aspect of the invention there is provided computer readable instructions which, when executed by a computer, are arranged to perform a method according to a preceding aspect. In an aspect of the invention there is provided a system for generating a terrain parameter indicative of a surface topography of a driving surface, the system comprising one or more processors collectively configured to: receive pitch information indicative of a pitch angle of a motor vehicle; receive roll information indicative of a roll angle of the motor vehicle; in dependence on the received pitch information and roll information, calculate and store successive values of change of pitch angle and change of roll angle as the vehicle progresses over terrain; and determine the terrain parameter in dependence on the stored values of change of pitch angle and stored values of change of roll angle; determine a driving mode selection in dependence on the determined terrain parameter; output a signal indicative of the driving mode selection, wherein the step of determining the terrain parameter in dependence on the stored values of change of pitch angle and stored values of change of roll angle comprises multiplying the stored values of change of pitch angle and stored values of change of roll angle by a gain factor, the gain factor being selected in dependence on at least one previously calculated value of terrain parameter, wherein the selected gain factor is lower for lower values of terrain parameter. A system for generating a surface articulation parameter indicative of a surface topography of a driving surface, the system comprising one or more processors collectively configured to: receive pitch information indicative of a pitch angle of a motor vehicle; receive roll information indicative of a roll angle of the motor vehicle; in dependence on the received pitch information and roll information, calculate and store successive values of change of pitch angle and change of roll angle as the vehicle progresses over terrain; and determine the surface articulation parameter in dependence on the stored values of change of pitch angle and stored values of change of roll angle; determine a driving mode selection in dependence at least in part on the surface articulation parameter; output a signal indicative of the driving mode selection. 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 anyway 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 One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a battery electric vehicle (BEV) according to an embodiment of the present invention; Figure 2 is a schematic illustration of the BEV of Fig. 1 in plan view; Figure 3 shows (a) a schematic illustration of a vehicle control unit (VCU) according to an embodiment of the present invention and (b) a schematic illustration of the VCU in component form showing two processors comprised by the VCU; Figure 4 is a flow diagram illustrating operation of a topography estimator according to an embodiment of the present invention; Figure 5 is a plot of distance required for transition to a rough road driving mode as a function of surface roughness (%); and Figure 6 is a flow diagram of a method according to an embodiment of the present invention. DETAILED DESCRIPTION Two Terrain Response (TR) modes are arranged to configure vehicle subsystems for particularly rough terrain, being the ‘rock crawl mode’ and ‘mud ruts mode’. These modes are adapted for surfaces that require significant suspension travel to maintain ground contact at the tyres; the surfaces may involve severe articulations of the suspension where a wheel lifts off the ground, being at ‘full droop’, i.e., the lowest position of suspension travel. Travel over such surfaces typically occurs at extremely low speeds (<2m / s). Two known methods for estimating the articulation of the surface are outlined herein. The first involves the measurement of vehicle suspension ‘cross articulation’ and requires the vehicle to be equipped with suspension position or ‘ride height’ sensors (see below). Such sensors are typically fitted to vehicles with air suspension and to some vehicles with actively damped suspension. Suspension position sensors are arranged to provide a signal indicative of the position of each wheel of a vehicle with respect to a range of vertical movement of the wheel provided by a suspension system of the vehicle. The suspension position sensors may also be referred to as ride height sensors. When the wheel is at a position corresponding to an upper limit of travel the wheel suspension is said to be at the position of ‘lowest ride height’. When the wheel is at a position corresponding to a lower limit of travel the wheel suspension is said to be at the position of ‘highest ride height’ and the wheel said to be at ‘full droop’. By cross-articulation is meant a measure of the displacement, with respect to one another, of diagonally opposite wheels at a given moment in time. If diagonally opposite wheels are at the same level of displacement with respect to the range of travel of a portion of the suspension element 111a, 112a, 114a, 115a associated with a given wheel 111, 112, 114, 115, then the vehicle 100 may be said to be in a state of zero crossarticulation with respect to that diagonal pair. Such a state is typical of driving on a relatively smooth road such as a motorway or highway. In contrast, if one wheel is at full droop and a diagonally opposite wheel is at full travel in an upward direction, the vehicle 100 may be said to be in a state of highest cross-articulation with respect to that diagonal pair. A state of high cross articulation can occur for example in the case that one wheel is not in contact with ground (and therefore at full droop) whilst the diagonally opposite wheel is in full contact with ground. Vehicle cross-articulation may be defined as follows: Cross-articulation = h(FL) - h(FR) - h(RL) + h(RR) where h(FL) is the height of the front left wheel, h(FR) is the height of the front right wheel, h(RL) is the height of the rear left wheel and h(RR) is the height of the rear right wheel. In some vehicles, the value of cross-articulated surface topography is used to determine an appropriate driving mode for the vehicle. For vehicles not having ride height sensors, then a second method of estimating the articulation of the surface involves measuring vehicle ‘cross acceleration’. Cross acceleration logic is arranged to multiply vehicle vertical and lateral acceleration together in order to characterise the driving surface. The inventors have recognised that there disadvantages associated with this method. FIG.1 shows a motor vehicle 100 according to an embodiment of the present invention. The vehicle 100 has an associated vertical axis z, a longitudinal axis x generally parallel or co-axial with the length of the vehicle and the direction of travel of the vehicle, and a lateral axis y. Conventionally the axes x, y, z are mutually perpendicular. References to vertical, longitudinal and lateral acceleration refer to acceleration of the vehicle in a direction along or parallel to the respective axis. Also illustrated in FIG. 1 by means of arrows are the directions of positive roll, pitch and yaw about the x, y and z axes respectively. Yaw rate, wz, is defined as the rotational speed around the z-axis. A positive yaw rate value exists when the vehicle is rotated counter-clockwise around the z-axis as seen from above the vehicle, i.e. positive when vehicle is in a left hand turn. Roll rate, wx is defined as the rotational speed around the x-axis. A positive roll rate value is given when the vehicle is rotated counter-clockwise around the x-axis as seen from in front of the vehicle i.e. positive when the vehicle is in a left hand turn. Pitch rate, coy is defined as the rotational speed around the y-axis. A positive pitch rate value is given when the vehicle is rotated counter-clockwise around the y-axis as seen from the left side of the vehicle i.e. positive when the vehicle is slowing down. FIG. 2 is a schematic illustration of the vehicle 100 of FIG. 1. In the embodiment shown the vehicle is a battery electric vehicle (BEV) in which a vehicle battery 130 is configured to supply power to each of four hub electric machines 117, each hub electric machine 117 being associated with a respective one of four wheels 111,112, 114, 115 of the vehicle 100. A vehicle control unit (VCU) 110 provides control signals to control an amount of positive (drive) torque or negative (brake) torque generated by each electric machine 117. Embodiments of the present invention are not limited to BEVs but are also suitable for use in hybrid electric vehicles (HEVs) having an internal combustion engine and vehicles having only an internal combustion engine to provide motive power. Embodiments of the invention are also suitable for vehicles with automatic transmissions, manual transmissions, continuously variable transmissions or any other suitable transmission. In the embodiment illustrated in Fig. 2 the driver may select one of a plurality of powertrain operating modes (or “driving modes”), being a park mode, a reverse mode, a neutral mode, a drive mode or a sport mode, by means of a mode selector dial 104S. The selector dial 104S provides an output signal to the VCU 110 in response to which the VCU 110 causes the powertrain 117 to operate in accordance with the selected powertrain operating mode. In the present embodiment the powertrain 117 comprises the hub electric machines 117, which drive the respective wheel 111,112,114,115 directly. It is to be understood that in some embodiments the powertrain 117 may comprise one or more driveline components that transfer power from the hub electric machines 117 to the wheels 111, 112, 114, 115. Embodiments of the invention are suitable for use in vehicles in which not all wheels of the vehicle are driven, for example four wheels of a four wheel vehicle, or in which less than four wheels are driven, such as four or three wheel vehicles having only two-wheel-drive. In addition to the VCU 110, the vehicle 100 has a brake controller 106 (an anti-lock braking system (ABS) controller) and a steering controller 107. The VCU 110 receives and outputs a plurality of signals to and from various sensors and subsystems (not shown) provided on the vehicle. The VCU 110 includes a low-speed progress (LSP) control system 120, a stability control system (SCS) 121, a cruise control system 122 and a hill descent control (HDC) system 123. The SCS 121 improves the safety of the vehicle 100 by detecting and managing loss of traction or steering control. When a reduction in traction or steering control is detected, the SCS 121 is operable automatically to command the ABS controller 106 to apply one or more brakes of the vehicle 100 or cause one or more hub electric machines to apply negative torque or reduced positive torque, in order to help to steer the vehicle 100 in the direction the user wishes to travel. In the embodiment shown the SCS 121 is implemented by the VCU 110. In some alternative embodiments the SCS 121 may be implemented by the ABS controller 106. As noted above the vehicle 100 also includes a cruise control system 122 which is operable to automatically maintain vehicle speed at a selected speed when the vehicle is travelling at speeds in excess of a predetermined minimum speed of operation of the system 122, in the present embodiment a speed of 25 kph. The cruise control system 122 is provided with a cruise control HMI (human machine interface) 128 by which means the user can input a target vehicle speed to the cruise control system 122 in a known manner. In one embodiment of the invention, cruise control system input controls are mounted to a steering wheel 171. It is to be understood that the VCU 110 is configured to implement a known Terrain Response (TR) (RTM) system of the kind described above in which the VCU 110 controls settings of one or more vehicle systems or sub-systems in dependence on a selected driving mode. The driving mode may be selected by a user by means of a driving mode selector 141S (Fig. 2); the user may also select an ‘automatic driving mode selection mode’ or ‘condition’ of the VCU 110. The driving modes may also be referred to as terrain modes, terrain response (TR) modes, or control modes. Vehicle systems underthe control of the TR system include the SCS system 121, steering controller 107 and powertrain 117. It is to be understood that the vehicle of the embodiment of FIG. 2 is fitted with a coil spring suspension system as opposed to an air suspension system. Air suspension systems generally have an associated suspension system controller configured to control the air suspension system to allow vehicle ride height to be set to one of four settings corresponding to different heights of the vehicle 100 above level ground. In such vehicles, in each driving mode, the VCU 110 may set the value of ride height of the vehicle to a predetermined value associated with the selected driving mode. In the embodiment of Fig. 2 five driving modes are provided: an 'on-highway’ driving mode suitable fordriving on a relatively hard, smooth driving surface where a relatively high surface coefficient of friction exists between the driving surface and wheels of the vehicle; a 'sand' driving mode suitable for driving over sandy terrain, being terrain characterised at least in part by relatively high drag, relatively high deformability or compliance and relatively low surface coefficient of friction; a 'grass, gravel or snow' (GGS) driving mode suitable fordriving over grass, gravel or snow, being relatively slippery surfaces (i.e. having a relatively low coefficient of friction between surface and wheel and, typically, lower drag than sand); a 'rock crawl' (RC) driving mode suitable for driving slowly over a rocky surface; and a 'mud ruts' (MR) driving mode suitable for driving in muddy, rutted terrain. Other driving modes may be provided in addition or instead. As noted above, in the present embodiment the selector 141S also allows a user to select an 'automatic driving mode selection mode’ or ‘condition' of operation in which the VCU 10 selects automatically the most appropriate driving mode as described in more detail below. The on-highway driving mode may be referred to as a 'special programs off (SPO) mode in some embodiments since it corresponds to a standard or default driving mode, and is not required to take account of special factors such as relatively low surface coefficient of friction, or surfaces of high roughness. The vehicle 100 is also provided with additional sensors (not shown) which are representative of a variety of different parameters associated with vehicle motion and status. These may be inertial systems unique to the LSP or HDC control systems 120, 123 or part of an occupant restraint system or any other system or subsystem which may provide data from sensors such as gyros and / or accelerometers that may be indicative of vehicle body movement and may provide a useful input to the LSP and / or HDC control systems 120,123. The signals from the sensors provide, or are used to calculate, a plurality of driving condition indicators (also referred to as terrain indicators) which are indicative of the nature of the terrain conditions over which the vehicle 100 is travelling. The sensors (not shown) on the vehicle 100 include, but are not limited to, sensors which provide continuous sensor outputs to the VCU 10, including wheel speed sensors, an ambient temperature sensor, an atmospheric pressure sensor, tyre pressure sensors, a steering angle sensor, a steering wheel speed sensor, a brake pedal position sensor, a brake pressure sensor, an accelerator pedal position sensor, and water detection sensors forming part of a vehicle wading assistance system (not shown). In other embodiments, only a selection of the aforementioned sensors may be used. As shown in Fig. 2 and Fig. 3(a), the vehicle 100 has an inertial measurement unit (IMU) 200 configured to output to the VCU 110 signals indicative of longitudinal, lateral and vertical acceleration of the vehicle, and of yaw rate, pitch rate and roll rate. In the present embodiment, the VCU 110 evaluates the various sensor inputs to determine the probability that each of the plurality of different TR modes (control modes or driving modes) for the vehicle subsystems is appropriate, with each control mode corresponding to a particular terrain type over which the vehicle is travelling (for example, mud ruts, sand, grass / gravel / snow) as described above. If the user has selected operation of the vehicle in the automatic driving mode selection condition, the VCU 110 then selects the most appropriate one of the control modes and is configured automatically to control the vehicle systems or subsystems according to the selected mode. This aspect of the invention is described in further detail in patent applications GB2492748, GB2492655 and GB2499279, the contents of each of which is incorporated herein by reference. Surface topography estimator In the embodiment of Fig’s. 1-3, the VCU 110 includes a surface topography estimator 190 (Fig. 3(a)) that is configured to employ vehicle pitch information and roll information in the form of pitch angle PA and roll angle RA signals output by the IMU 200 to generate a value of ‘cross articulation’ (also referred to as ‘surface articulation’) indicative of a surface topography of the driving surface. The topography estimator 190 also generates an off-road gain signal indicative of whether the vehicle is travelling on an on-road surface or an off road surface and a vehicle speed adjustment gam signal that is lower at higher vehicle speeds than at lower vehicle speeds as will described in further detail below. It is to be understood that by on-road surface is meant a relative smooth surface having a relatively high coefficient of friction with respect to wheels (111,112, 114, 115) of the vehicle 100. As will also described in further detail below, the VCU 110 is configured to generate a value of a terrain parameter TP in dependence on the value of cross articulation, the gain signal indicating whether the vehicle 100 is travelling on-road or off-road, and the vehicle speed adjustment gain signal. In the embodiment of Fig.’s 1-3 the surface topography estimator 190 is provided as a software module 190 executed by the VCU 110 (Fig. 3(a)). Alternatively, or in addition, the software module may be executed by one or more other computing devices. In some embodiments the surface topography estimator 190 may be provided by means of a dedicated computing module forming part of the VCU 110 or located in any other suitable part of the vehicle or its control system. The VCU 110 comprises processing means 112 and memory means 114 as illustrated in Fig. 3(b) and discussed in further detail below. Fig. 4 illustrates the operation of the topography estimator 190. As noted above, the topography estimator 190 is configured to receive vehicle pitch angle PA and roll angle RA signals output by the IMU 200 (Fig. 3(a)), together with a vehicle speed signal V, indicative of vehicle speed over terrain. At block 191 the topography estimator 190 receives pitch angle and roll angle information from IMU 200 and information in respect of vehicle speed over ground. From vehicle speed over ground information the block 191 is able to determine distance travelled by the vehicle 100 since a given moment in time. Block 191 outputs pitch angle, roll angle and distance travelled information to block 193. At block 192, based on the received vehicle pitch angle and roll angle signals PA, RA, the topography estimator 190 calculates the maximum change in pitch angle and roll angle, respectively, over a series of successive predetermined distance intervals (or “successive distances”) as the vehicle progresses over terrain. In the present embodiment each successive distance is equal to a first distance equal to one tenth of a second distance that is equal to the vehicle wheelbase or‘wheelbase distance’ WB. That is, the first distance is 0.1 WB or ten percent of the second distance. The first distance may therefore be referred to as a ‘sub-distance’ of the second distance. By wheelbase WB is meant a centre-to-centre distance between front and rear wheels of the vehicle 100 with the steerable wheels in a ‘straight ahead’ position. It is to be understood that block 192 determines distance travelled by the vehicle 100 based on the speed signal V. The maximum change in pitch angle and the maximum change in roll angle over each successive first distance are stored by the topography estimator 190 in a memory thereof. Once ten values of maximum change in pitch angle and ten values of maximum change in roll angle have been accumulated, over ten successive subdistances (which correspond to a distance of travel of one wheelbase WB as noted above), the ten values of maximum change in roll angle over each of the 10 sub-distances are summed togetherto form an accumulated change in roll angle value over the ten successive sub-distances. Similarly, the ten values of maximum change in pitch angle over each of the 10 sub-distances are summed togetherto form an accumulated change in pitch angle value over the ten successive sub-distances. The accumulated change in roll angle value and accumulated change in pitch angle value are then summed togetherto form a combined accumulated change in pitch and roll angle value. Other ways of combining the values may be useful in some embodiments. Thus, it is to be understood that the topography estimator 190 measures changes in pitch and roll angle over the last wheelbase distance WB that the vehicle 100 travelled using 10 points along the wheelbase distance WB (although other numbers may be useful in other embodiments). The vehicle wheelbase WB may thus be considered to be sliced into 10 sections. In order to accomplish this, in the present embodiment a trigger pulse is generated by block 192 every 1 / 1 Oth of the vehicle wheelbase WB as the vehicle 100 progresses over terrain (although other fractions of the wheelbase WB may be useful in some embodiments). When each trigger pulse occurs, the topography estimator 190 calculates the greatest difference in pitch angle and greatest difference in roll angle that the vehicle 100 experienced since the previous trigger pulse. That is, the topography estimator 190 calculates the difference between the most “pitch up” (or “pitch down”) attitude and the least “pitch up” (or “pitch down”) attitude of the vehicle 100 since the last trigger pulse was generated, and stores this value in memory. The topography estimator 190 then sums the stored values for the previous 10 sub-distances (equal to one vehicle wheelbase) to generate an accumulated change in pitch angle value and an accumulated change in roll angle value. The accumulated change in pitch angle value and accumulated change in roll angle value are then combined (by calculating the sum of the values) to form a combined accumulated change in pitch and roll angle value. The present applicant has found that this value provides a remarkably accurate measure of surface articulation SA. The combined accumulated change in pitch and roll angle value will hereinafter be referred to as a surface articulation value SA. In the present embodiment, the surface articulation value SA is scaled to a value from 0 to 100, and may therefore be expressed as a percentage. This value is output to multiplier block 195. At block 193 the topography estimator 190 is configured to determine whether the vehicle is travelling on a relatively rough surface (i.e. on an off-road surface) or on a relatively smooth surface (i.e. an on-road surface) and to output a gain value in dependence on the determination. The determination is made using two independent methods in parallel. If either method indicates that the vehicle is travelling on an off-road surface, the topography estimator concludes that the vehicle 100 is travelling on an off-road surface. According to the first method, the topography estimator 190 at block 193 determines that the vehicle 100 is travelling off-road if at any time the value of the change of pitch angle or change of roll angle calculated by the topography estimator 190 over each 0.1 WB distance exceeds an extreme threshold value ETV. It is to be understood that the value of ETV used by the topography estimator 190 may be determined empirically. In the present embodiment the pitch ETV is 0.2 radians and the roll threshold is 0.2 radians. Other values of ETV may be useful in some embodiments, such as values in the range from 0.15 radians to 0.25 radians. According to the second method, at block 193 the topography estimator 190 determines that the vehicle is travelling off-road if the surface articulation value SA is sufficiently high over a sufficiently long distance of travel. If the surface articulation value SA exceeds a medium threshold value MTV then at block 193, the topography estimator 190 employs a look-up table (LUT) to determine, for the prevailing value of surface articulation SA, the distance of travel required at that value of surface articulation SA for the topography estimator 190 to decide that the vehicle 100 is travelling off-road. This distance is referred to herein as the ‘transition distance’ TD. Fig. 5 illustrates the relationship between the value of surface articulation SA and transition distance TD. Fig. 5 is a plot of the transition distance TD that the vehicle 100 must travel fora given value of surface articulation SA in order for the topography estimator 190 to determine that the vehicle 100 is travelling on an off-road surface. It can be seen from the graph that, in the present embodiment, the MTV surface articulation SA value is 40%. It can be seen that, if the surface articulation SA value is 60%, the transition distance TD is 8m. Block 193 determines whether the vehicle 100 is travelling on-road or off-road according to the methodology described above and outputs a gain signal indicating whether the vehicle 100 is travelling on-road or off-road to multiplier block 195. In the present embodiment a higher gain signal is output if the block 193 determines that the vehicle is travelling off-road compared to the gain signal output when the block 193 determines that the vehicle is travelling on-road. The gain signal provides a gain factor by which multiplier block 195 is able to adjust the value of surface articulation, SA, output by block 192. Block 194 receives the vehicle speed signal V and generates a gain signal that reduces as a function of increasing vehicle speed. That is, the gain signal output by block 194 is lower for higher vehicle speeds than the signal output for lower vehicle speeds. The gain signal is output to multiplier block 195 and provides a gain factor by which multiplier block 195 is able to adjust the value of surface articulation, SA, output by block 192. This signal assists the topography estimator 190 in reducing the risk that the terrain parameter signal TP output at block 195 is excessively high in the event that the vehicle 100 negotiates an isolated area of relatively rough terrain when travelling at speed on-road, such as a kerb or pot-hole in a highway. By pot-hole is meant a relatively small area of a highway that is of reduced surface height due to removal of a portion of the surface. A pot hole may be considered typically to be less than 1 square meter in area and of a depth of at least 10cm. Block 195 multiplies the signals received from blocks 192, 193 and 194 and outputs a value of terrain parameter TP that is indicative of vehicle terrain roughness and is in the range from 0 to 100. The parameter TP is used by the VCU 110 to determine in which driving mode the vehicle 100 should be driven at a given moment in time. A scenario is now described by way of example to illustrate operation of the topography estimator 190, with reference to the graph of Fig. 5. In a first example, the vehicle 100 proceeds onto a rough track from a relatively smooth highway. The vehicle 100 is operating in the on-road (or “on-highway”) driving mode (special programs off) and notan off-road mode. In the present embodiment the MTV has a value of 40%. Whilst driving along the track, the topography estimator 190 determines that the surface articulation value SA has a value of 41%, thus exceeding the MTV. The topography estimator 190 thus determines, with reference to stored data (represented graphically in Fig. 5), that the vehicle must travel a distance of 20m before a determination will be made that the vehicle 100 is travelling on a rough surface. Provided the surface articulation value SA does not fall below the MTV over this distance, the topography estimator 190 will determine at block 193 that the vehicle 100 is travelling off-road and output a corresponding gain signal to block 195. If, in this scenario, as the vehicle 100 proceeds along the track the surface articulation value SA increases to a value of 60%, block 193 of the topography estimator 190 determines that the distance required before the topography estimator 190 can determine that the vehicle 100 is travelling on a rough surface is 8m. Block 193 of the topography estimator 190 thus determines that the vehicle 100 is travelling off-road if the vehicle 100 travels a distance of 8m from the point at which block 193 determined that the value of surface articulation SA exceeded the MTV. Fig. 5 may be considered to be a graph of ‘gain’ as a function of surface roughness. The value of ‘gain’ (y-value of the graph) is used to determine the distance that the vehicle must travel, fora given surface articulation value SA (corresponding to the x-value on the graph), before a determination is made that the vehicle is travelling on a rough surface. It is to be understood that the requirement for the value of value of surface articulation SA to exceed the MTV fora predetermined transition distance TD assists in suppressing the influence of transient peaks in the value of surface articulation SA when the vehicle is travelling over relatively smooth terrain. This is in order to reduce the likelihood that the value of terrain parameter TP indicative of surface topography that is finally output by the topography estimator 190 triggers a change in vehicle driving mode from an on-highway driving mode that is normally assumed when the vehicle is driving on smooth asphalt, to an off-highway driving mode such as a ‘mud ruts’ or ‘rock crawl’ driving mode, when the vehicle is in fact not driving off-highway. For example, a vehicle travelling on a highway may mount a kerb when manoeuvring into a parking space or negotiate a speed bump. It would typically be inappropriate for the vehicle to switch to an off-highway TR mode such as ‘mud ruts’ or ‘rock crawl’ in either circumstance. Accordingly, by requiring the vehicle 100 to travel a certain distance, that is dependent on the value of surface articulation SA, the likelihood that the vehicle 100 transitions to an off-highway mode from an on-highway mode in this situation is reduced. It is to be understood that the speed correction factor output by block 194 (which scales from a value of 1 to a value of 0 as speed increases) reduces the final value of combined accumulated change in pitch and roll angle value by an amount that is greater as the speed of the vehicle 100 increases. The topography estimator 190 thereby assists in the selection of an appropriate driving mode when the vehicle 100 is travelling at the relatively low speeds appropriate to the ‘mud ruts’ and Tock crawl’ driving modes. In the present embodiment, the topography estimator 190 is configured to generate a value of terrain parameter TP that is in the range from Oto 100. Thus, the topography estimator 190 of the present embodiment will not output a value of TP that exceeds 100. The VCU 110 as illustrated in Fig. 3(a) comprises one controller 110, although it will be appreciated that this is merely illustrative. As shown in Fig. 3(b) the controller 110 comprises processing means 112 and memory means 114. The processing means 112 may be one or more electronic processing devices 112 which operably executes computer-readable instructions (two are illustrated in Fig. 3(b)). The memory means 114 may be one or more memory devices 114. The memory means 114 is electrically coupled to the processing means 112. The memory means 114 is configured to store instructions, and the processing means 112 is configured to access the memory means 114 and execute the instructions stored thereon. The controller 110 comprises an input means 115 and an output means 116. In the embodiment of FIG. 3 the input means 115 comprises an electrical input 115 of the controller 110. The output means 116 comprises an electrical output 116 of the controller 110. The input 115 is arranged to receive the signals indicative of longitudinal, lateral and vertical acceleration of the vehicle, and of yaw rate, pitch rate and roll rate from the IMU 200. The input 115 also receives the vehicle speed signal V indicative of vehicle speed overground. The output 116 is arranged to output the terrain parameter TP indicative of surface topography for controlling the driving mode selection. Fig. 6 is a flow diagram illustrating a method according to the present embodiment. At step S101 the topography estimator 190 receives the vehicle speed signal V, vehicle pitch angle signal PA and vehicle roll angle signal VA. It is to be understood that signals PA, VA are received from IMU 200. The raw signals received may be pitch and roll angles of the vehicle 100 relative to datum pitch and roll positions. In some embodiments the raw signals received may be acceleration signals indicative of vehicle pitch and roll acceleration rates, respectively. At step S103 the topography estimator 190 calculates the value of surface articulation SA, also referred to herein as vehicle cross articulation value, based on the signals V, SA and PA. At step S105 the topography estimator 190 determines whether the vehicle 100 is travelling on-road or offroad and outputs an off-road gain value in dependence on the determination, as described above. The offroad gain value has a relatively high value if it is determined that the vehicle is travelling off-road, (in some embodiments a value of ‘1’ although other values may be useful in some embodiments) and a relatively low value if it is determined that the vehicle 100 is travelling on-road (in some embodiments a value of ‘0’ or ‘0.1 ’ although other values may be useful in some embodiments). As described above, the topography estimator 190 uses two methods in parallel to determine whether the vehicle 100 is travelling off-road. According to the first method, the topography estimator 190 at block 193 determines that the vehicle 100 is travelling off-road if at any time the value of the change of pitch angle or change of roll angle calculated by the topography estimator 190 over each 0.1 WB distance exceeds an extreme threshold value ETV. According to the second method, at block 193 the topography estimator 190 determines that the vehicle is travelling off-road if the surface articulation value SA is sufficiently high over a sufficiently long distance of travel. If the surface articulation value SA exceeds a medium threshold value MTV then at block 193, the topography estimator 190 employs a look-up table (LUT) to determine, for the prevailing value of surface articulation SA, the distance of travel required at that value of surface articulation SA for the topography estimator 190 to decide that the vehicle 100 is travelling off-road. This distance is referred to herein as the ‘transition distance’ TD as noted above (Fig. 5). At step S107, multiplier block 195 of the topography estimator 190 multiples the surface articulation value SA (which is in the range from Oto 1), the off-road gain value and the vehicle speed adjustment gain signal together and outputs a terrain parameter value TP that is in the range from 0 to 100, the TP having a value of zero for travel over perfectly flat terrain and a value of 100 for travel over terrain that causes the surface articulation to have its maximum possible value. In the present embodiment the TP value is higher for relatively rough terrain and lower for relatively smooth terrain although other arrangements may be useful in some embodiments. After step S107 the method continues at step S101. It is to be understood that in the embodiment of Fig.’s 1 to 6, the VCU 110 is configured to cause the vehicle 100 to assume an off-road driving mode if the vehicle is not already in an off-road driving mode in dependence on the value of TP generated by the topography estimator 190. The VCU 110 is configured such that, if the terrain is determined by the surface topography estimator 190 to be sufficiently rough, i.e. if the value of TP is sufficiently high, the VCU 110 causes the vehicle to operate in either the ‘mud ruts’ or‘rock crawl’ driving mode provided the conditions fortravel in such a mode are met. In the present embodiment, when the vehicle 100 is parked and shut down, the VCU 110 retains the current values of parameters associated with determining the prevailing values of surface articulation, SA, and terrain parameter, TP, such that the vehicle 100 may resume travel over terrain with those values. In some alternative embodiments, the VCU 110 resets the values of parameters associated with determining the prevailing values of surface articulation, SA, and terrain parameter, TP, to default values, for example a value of surface articulation, SA, and terrain parameter, TP corresponding to a substantially flat driving surface such as a smooth asphalt highway. In some embodiments, the default values may be dependent on the driving mode in which the vehicle 100 resumes operation when restarted. As described herein, in some embodiments the driving mode may be driver selected or selected automatically by a vehicle control system such as the VCU 110. 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

1. A system for generating a terrain parameter indicative of a surface topography of a driving surface, the system comprising one or more processors collectively configured to:receive pitch information indicative of a pitch angle of a motor vehicle;receive roll information indicative of a roll angle of the motor vehicle;in dependence on the received pitch information and roll information, calculate and store successive values of change of pitch angle and change of roll angle as the vehicle progresses over terrain;determine the terrain parameter in dependence on the stored values of change of pitch angle and stored values of change of roll angle;determine a driving mode selection in dependence at least in part on the determined terrain parameter; andoutput a signal indicative of the driving mode selection.

2. A system according to claim 1 configured to calculate and store successive values of maximum change of pitch angle and successive values of maximum change of roll angle over successive first distance intervals as the vehicle progresses over terrain.

3. A system according to claim 2 configured to determine the terrain parameter at least in part in dependence on the stored values of maximum change of pitch angle and stored values of maximum change of roll angle over a second prescribed distance which is equal to a prescribed number of the first distance intervals.

4. A system according to claim 3 wherein the second prescribed distance corresponds to a vehicle wheelbase.

5. A system according to claim 3 or claim 4 further configured to determine the terrain parameter at least in part by calculating a surface articulation, SA, value by summing the stored values of maximum change of pitch angle and stored values of maximum change of roll angle over the first prescribed distance.

6. A system according to claim 5 further configured to calculate the surface articulation, SA, value by summing the stored values of maximum change of pitch angle and stored values of maximum change of roll angle over the first prescribed distance and scaling the sum to a value in the range from 0 to 100.

7. A system according to claim 5 or 6 wherein the step of determining the terrain parameter in dependence on the stored values of maximum change of pitch angle and stored values of maximum change of roll angle comprises multiplying the surface articulation, SA, value by a gain factor, the gain factor being selected in dependence at least in part on at least one previously calculated value of surface articulation value, wherein the selected gain factor is lower for lower values of surface articulation value.

8. A system according to claim 7 wherein the gain factor is selected in dependence on previously calculated values of surface articulation over a prescribed distance travelled, wherein the prescribed distance is selected in dependence on one or more calculated values of surface articulation, the prescribed distance being lower for higher values of surface articulation.

9. A system according to claim 8 wherein a higher gain factor is selected in further dependence on calculated values of maximum change in pitch angle and / or roll angle as the vehicle progresses over terrain, the system being configured to select a higher gain value when calculated values of maximum change in pitch angle and / or roll angle exceed a threshold value.

10. A system according to any preceding claim further configured to control the configuration of at least one vehicle system in dependence on the terrain parameter.

11. A vehicle comprising a system according any one of claims 1 to 10.

12. A vehicle according to claim 11 as dependent on claim 10, wherein the vehicle control system isconfigured to control the configuration of at least one vehicle system selected from amongst:(i) a suspension system;(ii) a steering system;(iii) a powertrain of the vehicle;(iv) a braking system; and(v) a stability control system, SCS,.

13. A method for generating a terrain parameter indicative of a surface topography of a driving surface by means of a system comprising one or more processors, the method comprising:receiving pitch information indicative of a pitch angle of a motor vehicle;receiving roll information indicative of a roll angle of the motor vehicle;in dependence on the received pitch information and roll information, calculating and storing successive values of change of pitch angle and change of roll angle as the vehicle progresses over terrain;determining the terrain parameter in dependence on the stored values of change of pitch angle and stored values of change of roll angle;determining a driving mode selection in dependence at least in part on the determined terrain parameter; andoutputting a signal indicative of the driving mode selection.

14. A method according to claim 13 comprising calculating and storing successive values of maximum change of pitch angle and successive values of maximum change of roll angle over predetermined distance intervals as the vehicle progresses over terrain, the method comprising determining the terrain parameter at least in part in dependence on the stored values of maximum change of pitch angle and stored values of maximum change of roll angle over a first prescribed distance which is equal to a prescribed number of the predetermined distance intervals, the method further comprising determining the terrain parameter at least inpart by calculating a surface articulation, SA, value by summing the stored values of maximum change of pitch angle and stored values of maximum change of roll angle over the first prescribed distance.

15. Computer readable instructions which, when executed by a computer, are arranged to perform a 5 method according to claim 13 or 14.

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