Tax system for a motor vehicle and procedures

Abstract

Motor vehicle control system (210C, 220) for controlling an electric drive motor (230) for driving a wheel (290, 290F) of the vehicle (200), wherein the motor vehicle control system (210C, 220) is configured to be operated in a first and a second mode at least partially depending on a slip quantity perceived by at least one driven wheel, wherein the motor vehicle control system (210C, 220) is configured in the first mode to cause the at least one electric drive motor (230) to generate a predetermined amount of drive torque, wherein the motor vehicle control system (210C, 220) is configured in the second mode motor vehicle control system to cause the at least one electric drive motor (230) to rotate at a predetermined speed by controlling the conversion of the drive motor (230) in order to exert a desired speed on the rotation of the magnetic field of the drive motor (230), wherein the motor vehicle control system (210C, 220) is configured to operate in the first mode when the amount of slip detected by at least one driven wheel is below a predetermined amount of slip and to operate in the second mode when the amount of slip detected by at least one driven wheel exceeds the predetermined amount of slip.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a vehicle control system and a method for controlling an electric drive motor. Aspects of the invention relate to a vehicle, a method, and a non-transitory computer-readable storage medium. STATE OF THE ART

[0002] It is known to provide a control device for controlling a drive motor of a motor vehicle. Modern (converter) motors, and in particular synchronous motors, such as switched reluctance motors and permanent magnet DC motors, are controlled by power electronics with conversion, controlled in response to an estimate of the motor's angular position. Local speed control algorithms can be implemented within the control device to estimate motor speed using the motor position information. Essentially, the conversion control device aligns the stator magnetic field (or rotor magnetic field—some machines are constructed with a fixed field in the stator, others have the constant field (or permanent magnet) in the rotor) with respect to the magnetic field on the rotor (stator). The magnitude and offset of the fields generates torque in the motor.In a standard conversion approach, the offset is maintained at a fixed angle as the motor rotates. Two other approaches can be used: . 1) a local speed controller can be implemented that uses a closed-loop speed control algorithm, such as a proportional-integral-derivative (PID) algorithm to control the motor torque; or 2) a position request can be used to fix the absolute position of the stator (rotor) magnetic field, with position deviations towards and away from it generating a torque, for example a position-controlled stepper motor.

[0003] Electric motors can be used to provide both torque and braking torque, thereby implementing regenerative braking functionality. Known control systems for electric motors for motor vehicles employ a control structure similar to conventional anti-lock brake (ABS) control systems. In these, the braking torque is modulated (cancelled and reapplied) in response to sudden drops in wheel speed, indicating wheel slip on the road.

[0004] Fig. 1 illustrates a known arrangement for controlling a wheel 190 of a vehicle. A control device 110C receives a signal 155 indicative of the travel of an accelerator pedal of the vehicle and a signal 156 indicative of the speed of the wheel 190. The control device 110C calculates an amount of torque to be developed by an electric machine 130 to drive the wheel, in the illustrated example via a transmission 140. The control device 110C transmits a signal 151 to an inverter 120, which supplies power to the electric machine 130 to develop the required torque. The inverter 120 includes a control device for controlling the power supplied to the electric machine 130.

[0005] The controller 110C monitors the wheel speed signal 156 and compares the signal 156 to a vehicle reference speed value calculated by the controller 110C. The reference speed value is an estimate of the vehicle speed. Methods for calculating a vehicle speed value are known and include calculating an average of the vehicle's wheel speeds, taking the speed of the fastest-rotating wheel or the speed of the second-fastest-rotating wheel. A change in the wheel torque value is then calculated taking into account the amount of slip of the wheel 190 to control the amount of slip and prevent excess slip, and a wheel torque signal 151 generated to enable the inverter to cause the motor 130 to develop the required amount of slip.The actual torque required to control wheel 190 to avoid excess slip is not immediately known, as it depends on the variable nature of the surface, and accordingly, a feedback loop attempts to control wheel speed by varying the torque until the desired speed / slip is achieved. Thus, by attempting to prevent excess wheel slip, controller 110C implements torque control functionality.

[0006] Fig. Figure 2 is an example of a graphical representation of wheel speed versus time (upper trace) and corresponding braking torque versus time (lower trace) during braking in a vehicle with the wheel control arrangement of Fig. 1. The electric machine 130 is operated as a generator to effect regenerative braking to develop negative (braking) torque. At a time t1, the wheel speed is depicted as falling dramatically, and a reduction in braking torque occurs due to the wheel traveling over a surface with a relatively low surface friction coefficient. The controller 110C responds to this change in wheel speed by decreasing the amount of negative torque commanded by the torque signal 151, which causes the wheel speed to slowly increase again to a speed closer to the base speed of the vehicle 1 due to the (limited) road grip.Once the wheel speed has been reset to a speed similar to the vehicle speed—that is, when the wheel stops slipping—the regenerative braking torque can be reapplied. It is clear that wheel speed oscillations occur when the controller 110C continually attempts to maintain control over the wheel speed during braking. This can lead to increased noise, vibration, and harshness (NVH), which are associated with a user's driving experience as well as poor vehicle deceleration. Prior art documents include US Pat. No. 5,511,866 A and WO 2015 / 151193 A1.

[0007] It is an object of the present invention to address disadvantages associated with the prior art. SUMMARY OF THE INVENTION

[0008] Aspects and embodiments of the present invention provide a motor vehicle control system, a vehicle, a method, and a carrier medium. Embodiments of the invention may be understood with reference to the appended claims.

[0009] The above object is at least partly achieved by the subject matter of the independent claims.

[0010] In one aspect of the invention for which protection is claimed, there is provided a motor vehicle control system for controlling an electric drive motor for driving a wheel of the vehicle, the motor vehicle control system being configured to operate in first and second modes depending at least in part on an amount of slip experienced by at least one driven wheel, wherein the motor vehicle control system is configured in the first mode to cause the at least one electric drive motor to generate a predetermined amount of drive torque, wherein the motor vehicle control system is configured in the second mode to cause the at least one electric drive motor to rotate at a predetermined speed by controlling the conversion of the drive motor to exert a desired speed on the rotation of the magnetic field of the drive motor, wherein the motor vehicle control system is configured to operate in the first mode when the amount of slip experienced by the at least one driven wheel is less than a predetermined amount of slip and to operate in the second mode when the amount of slip experienced by the at least one driven wheel exceeds the predetermined amount of slip.

[0011] Optionally, in the second mode, the motor vehicle control system may be configured to cause the at least one electric drive motor to rotate at a predetermined speed by controlling the conversion of the motor to impart a desired speed to the rotation of the magnetic field of the motor. For example, the conversion speed may be set to be equal to a speed corresponding to a rotational speed of the magnetic field equal to the predetermined speed, thereby causing the rotor of the electric drive motor to rotate at a predetermined speed.

[0012] Optionally, the electric drive motor is a synchronous motor, for example, a switched reluctance motor or an electric DC motor with a permanent magnet. Advantageously, the rotational speed of such motors is typically equal to the rotational speed of the magnetic field.

[0013] In one embodiment, control of the motor in the first mode is performed depending on an estimate of an angular position of a rotor of the electric drive motor. In contrast, the conversion is preferably independent of the rotor position when the motor vehicle control system is operated in the second mode.

[0014] Embodiments of the present invention have the advantage that unwanted oscillations in wheel speed, which can occur when a motor vehicle control system is operated only in the first mode, which may be referred to as a torque control mode, can be prevented or substantially reduced. It should be noted that switching between the first mode, which may be referred to as a torque control mode, and the second mode, which may be referred to as a speed control mode, can be accomplished quickly, thereby enabling highly effective traction control to be implemented. The motor vehicle control system, in some embodiments, may include a powertrain control device. In some embodiments, the motor vehicle control system may include a traction control system control device.

[0015] The motor vehicle control system may be configured to calculate the amount of slip of the at least one driven wheel in dependence on a reference speed signal indicative of a traveling speed of the vehicle over ground / ground and on at least one wheel speed signal, wherein the system is configured to operate in the first or second mode in dependence on an amount of slip.

[0016] The motor vehicle control system may be configured to receive information indicative of a surface friction coefficient between the wheel and a driving surface, wherein the motor vehicle control system is configured to adjust the predetermined amount of slip in dependence on the information indicative of a surface friction coefficient.

[0017] The vehicle control system may be configured wherein the predetermined amount of slip is calculated depending on whether the vehicle control system causes a positive torque to be applied to the wheel or a negative torque to be applied to the wheel.

[0018] Optionally, the predetermined amount of slip is set to a first value when the vehicle control system causes a positive torque to be applied to the wheel and to a second value when the vehicle control system causes a negative torque to be applied to the wheel.

[0019] Accordingly, in some embodiments, the predetermined slip amount is set to the first value when the vehicle control system causes the vehicle to accelerate. Conversely, the predetermined slip amount is set to the second value when the vehicle control system causes the vehicle to decelerate.

[0020] The motor vehicle control system may be configured to receive the information indicative of a surface friction coefficient between the wheel and a driving surface, comprising the motor vehicle control system being configured to receive information indicative of a driving mode in which the vehicle is operated.

[0021] Optionally, the motor vehicle control system being configured to receive information indicative of a drive mode comprises the motor vehicle control system being configured to receive information indicative of a state of a user-operable drive mode control input for selecting a drive mode of the vehicle.

[0022] Alternatively, the vehicle control system may be configured to receive information indicative of a driving mode automatically selected by an automatic driving mode selection means, optionally the vehicle control system or one or more other vehicle control devices or vehicle control systems.

[0023] Optionally, the driving modes are control modes of at least one subsystem of the vehicle.

[0024] Optionally, the driving modes are control modes of at least one subsystem selected from an engine management system, a transmission system, a steering system, a braking system and a suspension system.

[0025] Optionally, the motor vehicle control system may be further configured to initiate controlling the or each vehicle subsystem in the selected one of the plurality of subsystem control modes, wherein each of the subsystem control modes corresponds to one or more different driving surfaces.

[0026] The motor vehicle control system may be configured to control a plurality of electric drive motors, each configured to drive a respective wheel of the vehicle.

[0027] The vehicle control system may be configured to receive a conversion feedback signal from the electric drive motor, wherein the vehicle control system, when operating in the second mode, is configured to control the motor to rotate at a predetermined speed depending at least in part on the conversion feedback signal.

[0028] In a further aspect of the invention for which protection is claimed, there is provided a vehicle comprising a body, a plurality of wheels, a drive train for driving the wheels, a braking system for braking the wheels, and a motor vehicle control system according to any preceding aspect.

[0029] In one aspect of the invention for which protection is claimed, there is provided a method of controlling an electric drive motor by a motor vehicle control system to drive at least one wheel of a vehicle, the method comprising causing the motor vehicle control system to operate in one of a first and a second mode depending at least in part on an amount of slip experienced by the at least one wheel, wherein the method in the first mode comprises causing the at least one electric drive motor to produce a predetermined amount of torque, and the method in the second mode comprises causing the at least one electric drive motor to rotate at a predetermined speed, wherein the motor vehicle control system is configured to operate in the first mode when a wheel slip amount is less than a predetermined slip amount and to operate in the second mode when a wheel slip amount exceeds the predetermined slip amount.

[0030] In a further aspect of the invention for which protection is claimed, a non-transitory computer-readable carrier medium is provided carrying computer-readable code for controlling a vehicle to carry out the method of a preceding aspect.

[0031] It should be noted that the control device or devices described herein may comprise a control unit or a computing device having one or more electronic processors. The system may comprise a single control unit or electronic control device, or alternatively, different functions of the control device may be performed or incorporated in different control units or devices. It should be noted that the term "control unit" as used herein includes both a single control unit or device and multiple control units or devices operated collectively to provide the implemented control functionality. A set of instructions may be provided which, when executed, causes the computing device to implement the control techniques described herein.The set of instructions may be embedded in the one or more electronic processors. Alternatively, the set of instructions may be provided as software to be executed on the computing device. The controller may be implemented in software running on one or more processors. One or more controllers may be implemented in software running on one or more processors, optionally on the same processor(s) as the controller. Other arrangements are also useful.

[0032] In one aspect of the invention for which protection is claimed, there is provided a motor vehicle control system for controlling an electric drive motor for driving a wheel of the vehicle, the motor vehicle control system being configured to operate in first and second modes depending at least in part on an amount of slip experienced by at least one driven wheel, wherein the motor vehicle control system is configured in the first mode to cause the at least one electric drive motor to generate a predetermined amount of drive torque, wherein the motor vehicle control system is configured in the second mode to cause the at least one electric drive motor to rotate at a predetermined speed, wherein the motor vehicle control system is configured to operate in the first mode when the amount of slip experienced by the at least one driven wheel is less than a predetermined amount of slip and to operate in the second mode when the amount of slip experienced by the at least one driven wheel exceeds the predetermined amount of slip, and wherein the motor vehicle control system is configured to determine that the amount of slip experienced by the wheel exceeds the predetermined amount if a speed of the wheel exceeds a speed indicated by a speed control signal.

[0033] Advantageously, such a system can provide traction control capable of correcting a loss of traction during acceleration more quickly than prior art traction control systems.

[0034] Some embodiments of the present invention provide a motor vehicle control system for controlling an electric drive motor to drive a wheel of the vehicle, the motor vehicle control system being configured to operate in either a first (torque control) mode or a second (speed control) mode depending at least in part on an amount of slip experienced by at least one driven wheel. If the amount of slip experienced by the at least one driven wheel is less than a predetermined amount of slip, the system causes the at least one electric drive motor to produce a predetermined amount of torque. This means that the motor vehicle control system is operating in the torque control mode (the first mode).Conversely, the vehicle control system is configured to operate in the second mode if the amount of slip experienced by the at least one driven wheel exceeds the predetermined amount of slip. In the second mode, the vehicle control system causes the at least one electric drive motor to rotate at a predetermined speed. That is, the vehicle control system operates in a 'speed control mode'. Some embodiments of the present invention have the advantage that the amount of slip experienced by a wheel can be limited and cannot become excessive because the vehicle control system switches to the speed control mode when the amount of slip exceeds the predetermined amount of slip.In some embodiments, the amount of slip experienced by a wheel may be limited to a predetermined upper limit by setting the rotational speed of the wheel in the speed control mode of operation to a value determined as a function at least in part of the speed of the vehicle over the ground.

[0035] Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples, and alternatives presented in the preceding paragraphs, in the claims, and / or in the following description and drawings, and in particular their individual features, may be considered independently of one another or in any combination. This means that all embodiments and / or features of any embodiment may be combined in any manner and / or combination, provided such features are not incompatible.The applicant reserves the right to amend any originally filed claim or to file any new claim accordingly, including the right to amend any originally filed claim to depend on and / or incorporate any feature of any other claim even though it was not originally so claimed.

[0036] For the avoidance of doubt, it is understood that features described in relation to one aspect of the invention may be included within any other aspect of the invention, alone or in appropriate combination with one or more other features. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] One or more embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a schematic representation of a known vehicle drive motor control arrangement; Fig. 2 a graphical representation of wheel speed as a function of time (upper trace) and of corresponding braking torque as a function of time (lower trace) during regenerative braking in a vehicle with the wheel control arrangement of Fig. 1; Fig. 3 is a schematic representation of (a) a vehicle drive motor control assembly 205 according to an embodiment of the present invention and (b) a vehicle in which the assembly shown in (a) is installed; Fig. 4 is a graphical representation of wheel speed versus time during regenerative braking in a vehicle with the wheel control arrangement of Fig. 3; and Fig. 5 is a graphical representation of wheel speed versus time during acceleration in a vehicle with the wheel control arrangement of Fig. 3. DETAILED DESCRIPTION

[0038] Fig. Figure 3(a) is a schematic representation of a vehicle drive motor control assembly 205 according to an embodiment of the present invention. Features of the embodiment of Fig. 3(a), which is in accordance with Order 190 of Fig. 1 are represented with similar reference symbols, incremented by 100 each. Fig. Figure 3(b) is a schematic representation of a vehicle 200 in which the assembly 205 is installed. It should be noted that the assembly 205 shown in Fig. 3(a), at each front left and front right wheel 290F, 290F' and at each rear left and rear right wheel 290, 290' of the vehicle 200, wherein the respective assemblies 205F, 205F', 205, 205' share a common control device 210C. In the illustrated embodiment, the electric machine 230 is a permanent magnet DC electric machine having stator coils configured to establish a rotating magnetic field, although it should be understood that the present invention may be practiced using other types of electric machines, including, but not limited to, other types of synchronous electric machines.

[0039] The controller 210C may be referred to as a powertrain controller 210C in some embodiments. In some embodiments, the controller 210C may be referred to as an engine controller.

[0040] The controller 210C is configured to receive a signal 255 indicative of the travel length of an accelerator pedal 280 of the vehicle 200, and signals 256, 256', 256F, 256F' indicative of the speed of each wheel 290F, 290F', 290, 290' of the vehicle 200. The controller 210C also receives a signal 257 from a brake control device 212C indicative of the amount of braking torque that must be provided by the motor control assemblies 205, 205', 205F, 205F' to meet a driver's braking force request. The braking force request is determined by the brake controller 212C at least in part according to a signal 258 received by the brake controller 212C indicative of the travel length of an accelerator pedal 282 of the vehicle 200.

[0041] Operation of the controller 210C with respect to the control of a single motor control assembly 205 will now be described. Control of the remaining assemblies 205', 205F, 205F' can be understood by way of addition.

[0042] The motor control assembly 205 includes an inverter 220 to control the individual stator windings of the machine, a permanent magnet DC electric machine 230, and a gearbox 240 arranged to drive the rear left wheel 290. It should be noted that the invention may be operated with other types of electric machines, and that for other types of electric machines, the inverter may instead control the rotor windings and possibly also the field windings (stator or rotor) in the case of a separately excited motor.

[0043] The electric machine 230 is configured to provide a conversion feedback signal 231 to the inverter 220 indicative of the position (and thus also the rotational speed) of the electric machine 230.

[0044] The controller 210C monitors a wheel speed signal 256 and compares the signal 256 to a vehicle reference speed value calculated by the brake controller 212C. The reference speed value is an estimate of the vehicle speed and is set by the brake controller 212C to be, for example, the speed of the fastest-rotating wheel 290F, 290F', 290, 290' of the vehicle 200. It should be noted that when the vehicle is decelerating, the fastest-rotating wheel is typically indicative of the true speed of the vehicle, whereas when the vehicle is accelerating, the slowest wheel is typically indicative of the true speed of the vehicle.Other methods, for example, the use of accelerometers, radar, vision systems, or GPS, may be used to provide estimates of true vehicle speed in some embodiments.

[0045] The controller 210C calculates two parameters that are transmitted to the inverter 220. The first parameter is a respective torque command in the form of a torque command signal 251, indicating the amount of torque to be developed by the respective electric machine 230. This is determined by the controller 210C individually for each wheel to meet a driver's torque request. The second is a speed command in the form of a speed signal 253, indicating the maximum or minimum allowable respective wheel speed, depending on whether the vehicle 200 is accelerating (in which case, the speed command signal indicates the maximum allowable wheel speed) or decelerating (in which case, the speed command signal indicates the minimum allowable wheel speed).

[0046] When the vehicle accelerates, the speed command signal 253 is calculated to indicate a wheel speed that exceeds the ground speed of the respective wheel (taking cornering into account) by a predetermined acceleration slip value S1. When the vehicle decelerates, the speed command signal 253 is calculated to indicate a wheel speed that is less than the ground speed of the wheel (taking cornering into account) by a predetermined deceleration slip value S2. In the present embodiment, the values ​​S1 and S2 are set to the same value of slip. The ground speed of a particular wheel is calculated by the controller depending on the vehicle reference speed, which is an indication of the vehicle ground speed.

[0047] In the present embodiment, the values ​​of slip S1, S2 are set depending on an estimated value of surface friction coefficient, 'mu', between a particular wheel and the traveling surface at a particular time. Note that the estimated value of mu is maintained by the brake control device 212C and communicated to the control device 210C. Methods for estimating surface mu are well known. In the present embodiment, the brake control device 212C calculates the value of mu depending on the values ​​of the vehicle reference speed, the individual wheel speed, and the amount of torque applied to a wheel at a particular time.

[0048] The inverter 220 is arranged to monitor the speed of the electric machine 230 with reference to the conversion signal 231 and to compare this speed with the speed value indicated by the speed command signal 253. If the inverter 220 determines that the vehicle 200 is accelerating and the conversion signal 231 indicates that the motor speed corresponds to a wheel speed less than or equal to the speed indicated by a speed command signal 253, the inverter 220 controls the electric machine 230 to develop an amount of torque corresponding to that indicated by the torque request signal.However, if the wheel speed at any time exceeds that indicated by the speed command signal 253, the inverter 220 transitions control of the electric machine 230 from a torque control mode to a speed control mode. In the speed control mode, the inverter 220 controls the electric machine 230 to maintain a substantially constant speed substantially equal to that indicated by the speed command signal, unless the amount of torque required to be developed by the electric machine 230 to do so is caused to exceed that indicated by the torque request signal.

[0049] When operating in the speed control mode, the controller 210C controls the inverter 220 to adjust the conversion speed (or conversion frequency) to correspond to a desired speed without considering the current position of the motor. This may be referred to as "staggering" the conversion.It should be noted that in a synchronous electric machine, such as a permanent magnet DC electric machine 230, controlling the conversion speed of the motor to correspond to a desired speed is achieved by applying a desired rotational speed to the magnetic field produced by the motor (in the illustrated embodiment, the rotating magnetic field is produced by supplying current to the windings on the stator, although it should be noted that in other types of electric machine, the rotating magnetic field may be produced by supplying current to the windings on the rotor).

[0050] The rotor of the permanent magnet DC electric machine 230, and thus the wheel, aligns with the rotational speed of the magnetic field because a difference between the rotational speed of the rotor and the magnetic field causes an increasing offset between the rotor and the magnetic field. This offset causes a torque to act on the rotor in a direction that decreases the offset between the rotor and the magnetic field. The torque acting on the rotor increases with increasing offset between the rotating magnetic field and the rotor, so that if the rotor rotates slower than the magnetic field created by the stator, the torque applied to the rotor increases until it is sufficient to cause the rotor to rotate at the same speed as the magnetic field.

[0051] It should be noted that in a conventional control methodology for a drive motor, the conversion is controlled to establish a target torque, as indicated by a torque control signal. This is typically achieved by essentially continuously estimating the rotor position and controlling the conversion to maintain a target offset between the position of the magnetic field and the rotor position. The target offset typically corresponds to the offset required to establish the target torque.Direct control of the converter to impose a desired speed on the rotation of the magnetic field is not used because imposing a speed on the converter could result in excess charge being applied to the rotor if more torque than the motor is designed to produce is required to cause the rotor to rotate at a rotational speed imposed by the converter control. Imposing a speed on the converter can also cause very significant slip to occur if it results in a high torque demand, causing the wheels to lose traction.

[0052] The inventors concerned have recognized that when excess wheel slip is already occurring, the conversion rate can be directly controlled without causing excess load to be applied to the electric machine or causing excess slip, since the first occurrence of excess wheel slip is associated with a loss in the torque applied to the slipping wheel, and the loss in torque is maintained until the excess slip ceases to occur. Accordingly, directly controlling the conversion rate of an electric machine associated with an already slipping wheel to return the wheel to a speed closer to the speed at which the wheel would rotate for the immediate vehicle speed if the wheel were not slipping would not cause excess torque to be demanded from the electric machine.In addition, this approach can quickly reduce wheel slip to an acceptable level, thereby improving vehicle stability.

[0053] It should be noted that during normal driving on a surface where the value of mu is substantially uniform, the speed of each wheel is close to the vehicle reference speed, and the speed of each wheel does not reach the speed indicated by the speed command signal (whether above or below the reference speed).

[0054] In one example of a braking scenario, the electric machine 230 may be controlled by the inverter 220 to operate as a generator to develop the required (negative) braking torque. The inverter 220 attempts to cause the electric machine 230 to develop the required amount of braking torque according to the torque command signal 251. However, if the speed of the wheel 290, as determined by reference to the conversion signal 231, falls below that indicated by the speed command signal 253, the inverter 220 switches to controlling the speed of the electric machine by setting the conversion speed to a value that causes the magnetic field to rotate at a speed substantially equal to that indicated by the speed command signal 253.This initially causes the electric machine to apply positive torque to the slipping wheel to increase its speed back to that indicated by speed command signal 253. At this point, the wheel is able to grip the driving surface and establish braking at the optimal slip value, S2. As the vehicle decelerates, the vehicle reference speed drops, and that indicated by speed command signal 253 also drops.

[0055] It should also be noted that, unlike conventional friction brakes, additional torque can be automatically (inherently) applied by the engine to accelerate the wheel back to the desired slip level without relying on road grip. This can be important, for example, when lateral stability is required and a large deviation in slip levels would be detrimental to vehicle safety.

[0056] When the wheel 290 encounters a surface with a higher surface mu value while the controller 210C is operating in the speed control mode, the braking torque (measured by the inverter 220) naturally increases. When the braking torque reaches a value corresponding to the torque command signal 251, the inverter 220 returns to the torque control mode and controls the electric machine 230 to develop an amount of torque corresponding to the torque command signal 251. Similarly, if a user reduces pressure on the brake pedal when operating in the speed control mode, the torque command signal 251 may be reduced to a value below that provided in the speed control mode (as measured by the inverter 220), after which the inverter returns to the torque control mode.

[0057] Fig. 4 is a graphical representation of wheel speed versus time in a braking scenario similar to that shown in Fig. 2 for the known motor control arrangement. During a braking operation, beginning at time t0, the inverter 220 is initially operated in a torque control mode, causing the electric machine 230 to develop an amount of braking torque corresponding to that indicated by the torque command signal 251. At time t1, after a time period P1 has elapsed, the speed of the wheel 290 falls below that indicated by the speed command signal 253. The inverter detects the loss of wheel speed and enters a speed control mode of operation in which the inverter is controlled to maintain the wheel 290 at a speed corresponding to that indicated by the speed command signal 253 by controlling the conversion such that the magnetic field generated by the stator rotates at a speed indicated by the speed command signal 253.Accordingly, the inverter 220 causes the electric machine 230 to maintain a speed that is below the vehicle reference speed by the predetermined slip value S2, which is the same as the value S1 specified above.

[0058] Notably, the electric machine speed control implemented by controlling inverter 220 in some embodiments allows the conversion speed to be adjusted such that the magnetic field rotates at a desired speed, correcting excess slip much more quickly than in a conventional ABS (torque-based) control setup. Accordingly, the performance of the motor control arrangement 205 demonstrates a significant improvement over known vehicle control systems.

[0059] Fig.5 is an exemplary graphical representation of wheel speed versus time in a scenario where the vehicle 200 is accelerating rather than decelerating. During an acceleration period beginning at time t0, the driver increases the amount of requested torque by pressing the accelerator pedal 280. In response, the inverter 220 initially operates in a torque control mode, which causes the electric machine 230 to develop an amount of torque corresponding to that indicated by the torque command signal 251. At time t1, after a time period P1 has elapsed, the vehicle passes through a zone of relatively low surface mu during time period P2. The speed of the wheel 290 increases above that indicated by the speed command signal 253.The inverter 220 detects the increase in wheel speed and switches to a speed control mode of operation, in which the inverter maintains the wheel 290 at a speed corresponding to the speed indicated by the speed command signal 253 by controlling the conversion so that the magnetic field generated by the stator rotates at a speed indicated by the speed command signal 253. Accordingly, the inverter 220 causes the electric machine 230 to maintain a speed higher than the vehicle reference speed by the predetermined slip value S1, as described above.

[0060] A particular advantage of this arrangement is that when the speed of wheel 290 is above that indicated by speed control signal 253, controlling electric machine 230 in the speed control mode inevitably causes a negative torque to be applied to wheel 290 by electric machine 230. This causes the speed of the wheel to rapidly reduce to the speed indicated by the speed command signal, thereby reducing the amount of time during which excess slip occurs.

[0061] An alternative approach to implementing speed control mode would be for inverter 220 to execute a local speed control algorithm using the motor position information provided by conversion signal 231 to estimate the speed of electric machine 230. An internal closed-loop control algorithm, such as a proportional-integral-derivative (PID) algorithm, can be used to control motor torque and implement a local speed controller. However, this approach may produce a slower response to the occurrence of wheel slip than directly controlling the conversion speed as described above.

[0062] More sophisticated control methodologies may be employed in some embodiments. For example, in some embodiments, the speed control loop employed by inverter 220 may be further enhanced by controlling or directly influencing the rotor position using the stiffness provided by magnetic alignment.

[0063] In this configuration, preferably employed by a pole-biasing structure, the electrical current in the windings is directly controlled to orient the magnetic flux in a manner that inherently performs the conversion function and controls the overall rotational states of the compliantly coupled drivetrain, wheel, tire, and the nonlinear slip characterizing the road.

[0064] In this form, the following primary information sources are combined to form an overall state estimate of the vehicle's movement over the road surface and of internal states of the winding system of compliant elements (such as engine mounts or suspension movements): • Motor rotor position • Wheel speed or position sensors • Vehicle inertia measurements, possibly self-calibrated by GPS signals • Other vehicle movement detection devices, such as radar, vision and map matching techniques.

[0065] Based on this state estimation, the motor conversion, that is, the current applied by the power electronics to the motor windings, is determined for best control and driver (or autonomous system) control.

[0066] Extensions can be applied to cover uneven (terrain) surfaces, deformable surfaces, and varying surface properties, including predictions (predictive measurements) or anticipation (from a priori knowledge of either on- or off-board maps). TR modes

[0067] In some embodiments, vehicle 200 may include a drive mode controller for implementing a Terrain Response (TR) (RTM) system, in which the drive mode controller controls settings of one or more vehicle systems or subsystems, such as settings associated with a powertrain controller 210C, a transmission system (if present), a steering system such as an electric power assisted steering system (EPAS) (if present), settings of the braking system via a braking controller 212C, and a suspension system (if present), depending on a selected drive mode. The drive mode may be selected by a driver via a drive mode selection dial. Alternatively, the drive mode may be automatically selected by the drive mode controller. The drive modes may also be referred to as terrain modes, terrain response modes, or control modes.

[0068] In one embodiment, four driving modes are provided: a "road" driving mode or a "special programs off" (SPO) mode, suitable for driving on a relatively hard, smooth driving surface where there is a relatively high surface coefficient of friction between the driving surface and the vehicle's wheels; a "sand" (SAND) mode, suitable for driving over sandy terrain; a "grass, gravel, or snow" (GGS) driving mode, suitable for driving over grass, gravel, or snow; a "rock crawl" (RC) driving mode, suitable for driving slowly over rocky terrain; and a "muds and ruts" (MR) driving mode, suitable for driving on muddy, uneven terrain. Other driving modes may be provided in addition to or instead.

[0069] It should be noted that the powertrain controller 210C may be configured to determine the value of surface mu of the driving surface depending at least in part on the selected drive mode in which the vehicle is caused to operate by the drive mode controller. Accordingly, in some embodiments, the predetermined slip value may be determined according to the selected drive mode.

[0070] Throughout the description and claims of this specification, the words "comprise" and "include" and variations of the words, for example, "comprising" and "comprises," mean "including, but not limited to," and are not intended to be (and do not) exclude other components, integers, or steps.

[0071] Throughout the description and claims of this patent specification, the singular includes the plural unless the context otherwise requires. In particular, when the indefinite article is used, the patent specification should be understood to encompass both the plurality and the singular, unless the context otherwise requires.

Claims

[1] A motor vehicle control system (210C, 220) for controlling an electric drive motor (230) for driving a wheel (290, 290F) of the vehicle (200), the motor vehicle control system (210C, 220) being configured to operate in first and second modes at least in part depending on an amount of slip experienced by at least one driven wheel, wherein the motor vehicle control system (210C, 220) is configured in the first mode to cause the at least one electric drive motor (230) to generate a predetermined amount of drive torque, wherein the motor vehicle control system (210C, 220) is configured in the second mode of the motor vehicle control system to cause the at least one electric drive motor (230) to rotate at a predetermined speed by controlling the conversion of the drive motor (230) to exert a desired speed on the rotation of the magnetic field of the drive motor (230), wherein the motor vehicle control system (210C, 220) is configured to operate in the first mode when the amount of slip experienced by at least one driven wheel is below a predetermined amount of slip and to operate in the second mode when the amount of slip experienced by at least one driven wheel exceeds the predetermined amount of slip. [2] The motor vehicle control system (210C, 220) of claim 1, wherein the electric drive motor (230) is a synchronous motor. [3] The motor vehicle control system (210C, 220) of claim 2, wherein the electric drive motor (230) is a switched reluctance motor or a permanent magnet DC electric motor. [4] The motor vehicle control system (210C, 220) according to any one of claims 1 to 3, wherein the control of the motor in the first mode is performed in dependence on an estimation of an angular position of a rotor of the electric drive motor. [5] A motor vehicle control system (210C, 220) according to any one of the preceding claims, configured to calculate the amount of slip of the at least one driven wheel in dependence on a reference speed signal indicative of a traveling speed of the vehicle (200) over ground / ground and at least one wheel speed signal (256), the system being configured to operate in the first or second mode in dependence on an amount of slip. [6] The motor vehicle control system (210C, 220) according to any one of the preceding claims, configured to receive information indicative of a surface friction coefficient between the wheel (290, 290F) and a driving surface, wherein the motor vehicle control system (210C, 220) is configured to adjust the predetermined slip amount in dependence on the information indicative of a surface friction coefficient. [7] The motor vehicle control system (210C, 220) of claim 6, wherein the motor vehicle control system (210C, 220) configured to receive the information indicative of a surface friction coefficient between the wheel (290, 290F) and a driving surface comprises the motor vehicle control system (210C, 220) configured to receive information indicative of a driving mode in which the vehicle (200) is operated, and optionally; wherein the motor vehicle control system (210C, 220) configured to receive information indicative of a driving mode comprises the motor vehicle control system (210C, 220) configured to receive information indicative of a state of a user-operable driving mode control input for selecting a driving mode of the vehicle (200). [8] The motor vehicle control system (210C, 220) of claim 7, wherein the driving modes are control modes of at least one subsystem of the vehicle (200), and optionally; wherein the driving modes are control modes of at least one subsystem selected from an engine management system, a transmission system, a steering system, a braking system, and a suspension system. [9] The motor vehicle control system (210C, 220) of claim 8, further configured to initiate controlling the or each vehicle subsystem in the selected one of the plurality of subsystem control modes, each of the subsystem control modes corresponding to one or more different driving surfaces. [10] A motor vehicle control system (210C, 220) configured according to any one of the preceding claims, wherein the predetermined amount of slip is calculated depending on whether the motor vehicle control system (210C, 220) causes a positive torque to be applied to the wheel (290, 290F) or a negative torque to be applied to the wheel (290, 290F). [11] The motor vehicle control system (210C, 220) of any preceding claim, wherein the predetermined amount of slip is set to a first value when the motor vehicle control system (210C, 220) causes a positive torque to be applied to the wheel (290, 290F) and to a second value when the motor vehicle control system (210C, 220) causes a negative torque to be applied to the wheel (290, 290F). [12] The motor vehicle control system (210C, 220) of any preceding claim, configured to control a plurality of electric drive motors, each configured to drive a respective wheel (290, 290F) of the vehicle (200), and optionally wherein the motor vehicle control system (210C, 220) is configured to determine that the amount of slip experienced by the wheel (290, 290F) exceeds the predetermined amount when a speed of the wheel (290, 290F) exceeds a speed indicated by a speed control signal (253). [13] A vehicle (200) comprising a body, a plurality of wheels (290, 290F), a drive train for driving the wheels (290, 290F), a braking system for braking the wheels (290, 290F), and a motor vehicle control system (210C, 220) according to any one of the preceding claims. [14] A method for controlling an electric drive motor (230) by a motor vehicle control system (210C, 220) to drive at least one wheel (290, 290F) of a vehicle (200), the method causing the motor vehicle control system (210C, 220) to operate in one of a first and a second mode depending at least in part on an amount of slip experienced by the at least one wheel (290, 290F), wherein the method in the first mode comprises causing the at least one electric drive motor (230) to generate a predetermined amount of torque, and wherein the method in the second mode comprises causing the at least one electric drive motor (230) to rotate at a predetermined speed by controlling the conversion of the drive motor (230) to exert a desired speed on the rotation of the magnetic field of the drive motor (230), wherein the motor vehicle control system (210C, 220) is configured to operate in the first mode when a wheel slip amount is below a predetermined slip amount and to operate in the second mode when a wheel slip amount exceeds the predetermined slip amount. [15] A non-transitory computer-readable carrier medium containing computer-readable code for controlling a vehicle (200) to perform the method of claim 14.

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