Patent Description:
In known vehicle speed control systems, typically referred to as cruise control systems, the vehicle speed is maintained on-road once set by the user without further intervention by the user so as to improve the driving experience for the user by reducing workload.

With typical cruise control systems, the user selects a speed at which the vehicle is to be maintained, referred to as a set-speed, and the vehicle is maintained at a target speed that is set equal to the set-speed for as long as the user does not apply a brake or, in the case of a vehicle having a manual transmission, depress a clutch pedal. The cruise control system takes its speed signal from a driveshaft speed sensor or wheel speed sensors. When the brake or the clutch is depressed, the cruise control system is disabled so that the user can override the cruise control system to change the vehicle speed without resistance from the system. If the user depresses the accelerator pedal by a sufficient amount the vehicle speed will increase, but once the user removes his foot from the accelerator pedal the vehicle reverts to the preset cruise speed (set-speed) by coasting.

Such systems are usually operable only above a certain speed, typically around <NUM>-20kph, and are ideal in circumstances in which the vehicle is travelling in steady traffic conditions, and particularly on highways or motorways. In congested traffic conditions, however, where vehicle speed tends to vary widely, cruise control systems are ineffective, and especially where the systems are inoperable because of a minimum speed requirement. A minimum speed requirement is often imposed on cruise control systems so as to reduce the likelihood of low speed collision, for example when parking. Such systems are therefore ineffective in certain driving conditions (e.g. low speed) and are set to be automatically disabled in circumstances in which a user may not consider it to be desirable to do so.

<CIT>) discloses a cruise control for an off-highway condition that sets a maximum cruise control speed appropriate to the off-highway condition, which may reflect the terrain across which the vehicle is travelling. The condition may be selected manually by a driver of automatically by an electronic control unit associated with a terrain sensor. The maximum speed may be varied for different terrain types.

More sophisticated cruise control systems are integrated into the engine management system and may include an adaptive functionality which takes into account the distance to the vehicle in front using a radar-based system. For example, the vehicle may be provided with a forward-looking radar detection system so that the speed and distance of the vehicle in front is detected and a safe following speed and distance is maintained automatically without the need for user input. If the lead vehicle slows down, or another object is detected by the radar detection system, the system sends a signal to the engine or the braking system to slow the vehicle down accordingly, to maintain a safe following distance.

Known cruise control systems also cancel in the event that a wheel slip event is detected requiring intervention by a traction control system (TC system or TCS) or stability control system (SCS). Accordingly, they are not well suited to maintaining vehicle progress when driving in off road conditions where such events may be relatively common.

<CIT> primarily discloses a transmission control system that sets a transmission shift pattern for driving on a curve. It also discloses a different shift pattern for when it is detected that the vehicle is operating in a cold environment and when it is in a "snow" mode.

<CIT> discloses a traction control system that changes to using a different transmission shift map when traction is being controlled.

It is an aim of embodiments of the present invention to address disadvantages associated with the prior art.

In one aspect of the invention for which protection is sought there is provided a system comprising:.

Optionally, suspending a gear downshift comprises reducing the engine speed at which a transmission controller is permitted to cause a gear downshift to zero whilst the vehicle is in motion.

This feature has the advantage that a problem that locking of one or more wheels driven by a powertrain due to a downshift when operating on surfaces offering relatively low traction may be reduced.

Optionally, the gear shift limit signal is configured to reduce the engine speed at which a transmission controller causes a downshift.

Optionally, the gear shift limit signal is configured to substantially prevent a transmission controller from causing a downshift by reducing the engine speed at which a transmission controller causes a downshift.

Optionally, the at least one traction indicator signal is a signal indicative of an amount of torque that may be applied to a wheel before slip of the wheel occurs.

Optionally, at least one said at least one traction indicator signal is indicative of a normal force between a wheel and a driving surface.

It is to be understood that, the lower the normal force on a wheel, the lower the tractive force that may be developed between a wheel and a driving surface. Similarly, the lower the surface coefficient of friction between a wheel and a driving surface, the lower the tractive force that may be developed.

Optionally, at least one said at least one traction indicator signal is indicative of a surface coefficient of friction between a wheel and a driving surface.

Optionally, the first controller is configured to perform a mu-check operation when in one of the plurality of states, the system being configured to perform a mu-check operation by causing a transmission controller to cause a downshift and monitoring a speed of one or more wheels in response to the downshift.

This feature has the advantage that the first controller may obtain an indication of the value of surface coefficient between a wheel and a driving surface.

Optionally, when performing a mu-check operation the first controller is configured to calculate an estimated value of surface coefficient of friction between a wheel and a driving surface in dependence on a change in a speed of one or more wheels in response to the downshift.

The system may take into account a change in speed of one or more wheels due to a reduction in speed of the ground when estimating a value of surface coefficient of friction. For example, in some embodiments if a change in wheel speed corresponds substantially to a change in vehicle speed over ground when a mu-check is performed the first controller may determine that the surface coefficient of friction corresponds substantially to unity. In contrast, if wheel speed reduces more rapidly than vehicle speed over ground, for example if wheel speed falls substantially to zero whilst the vehicle is still moving over ground, the system may determine that the surface coefficient of friction is less than unity.

Optionally, the system may be configured to perform a mu-check operation when one or more predetermined conditions are met during operation in one of said plurality of states.

Optionally, the system may be configured to perform a mu-check at predetermined intervals of time.

Optionally, the system may be configured to perform a mu-check following a torque control intervention event in which a torque intervention system intervenes to cause change in an amount of torque applied to one or more wheels.

It is to be understood that the torque invention system may be a system that is configured to intervene and cause a change in an amount of torque applied to one or more wheels under certain predetermined conditions, not being configured to cause a vehicle to operate in accordance with a target speed value. For the present purposes a torque intervention system performs functionality that is in addition to that of the first controller. Examples of torque intervention systems include traction control systems (TCS), stability control systems (SCS) and anti-lock braking systems (ABS).

Optionally, the system may be configured wherein the at least one traction indicator signal is indicative of an amount of torque that may be applied to a wheel before slip of the wheel slip exceeding a predetermined amount occurs.

Optionally, the system may be further configured, when causing a vehicle to operate in accordance with the target speed value, to generate a brake request signal to command a brake system to deliver an amount of brake torque.

Optionally, the system may be configured wherein said plurality of states includes a first one or more first states in which the system is configured to generate a powertrain request signal in order to cause a powertrain to deliver drive torque and cause a vehicle to operate in accordance with a target speed value, and a second state wherein the system is configured to cause a vehicle to operate in accordance with a target speed value by generating the brake request signal and not to generate a powertrain request signal in order to cause a powertrain to deliver drive torque.

It is to be understood that the system may generate a nominal powertrain request signal even when in the second state, for example a request for an amount of torque corresponding to a released position of an accelerator pedal. However the first controller does not actively cause a powertrain to develop positive drive torque, that is the first controller does not cause an increase in the amount of any positive drive torque developed by a powertrain, or a reduction in an amount of negative torque developed by a powertrain. Other arrangements are also useful.

In a further aspect of the invention for which protection is sought there is provided a motor vehicle comprising a system according to said one aspect. The vehicle may comprise a chassis, a body attached to said chassis, a plurality of wheels, a powertrain to drive said wheels, and a braking system to brake said wheels.

In another aspect of the invention for which protection is sought there is provided a method of operating a vehicle implemented by means of a control system comprising:
causing a powertrain to deliver drive torque and cause a vehicle to operate in accordance with a target speed value;.

In one aspect of the invention for which protection is sought there is provided a processor arranged to implement the method of said another aspect.

It is to be understood that the controller or controllers described herein may comprise a control unit or computational device having one or more electronic processors. The system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term "control unit" will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide the stated control functionality. A set of instructions could be provided which, when executed, cause said computational device to implement the control techniques described herein. The set of instructions could be embedded in said one or more electronic processors. Alternatively, the set of instructions could be provided as software to be executed on said computational device. The controller may be implemented in software run on one or more processors. One or more other controllers may be implemented in software run on one or more processors, optionally the same one or more processors as the controller. Other arrangements are also useful.

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying figures in which:.

References herein to a block such as a function block are to be understood to include reference to software code for performing the function or action specified which may be an output that is provided responsive to one or more inputs. The code may be in the form of a software routine or function called by a main computer program, or may be code forming part of a flow of code not being a separate routine or function. Reference to function block is made for ease of explanation of the manner of operation of embodiments of the present invention.

<FIG> shows a vehicle <NUM> according to an embodiment of the present invention. The vehicle <NUM> has a powertrain <NUM> that includes an engine <NUM> that is connected to a driveline <NUM> having an automatic transmission <NUM>. It is to be understood that embodiments of the present invention are also suitable for use in vehicles with manual transmissions, continuously variable transmissions or any other suitable transmission.

In the embodiment of <FIG> the transmission <NUM> may be set to one of a plurality of transmission operating modes, being a park mode P, a reverse mode R, a neutral mode N, a drive mode D or a sport mode S, by means of a transmission mode selector dial <NUM>. The selector dial <NUM> provides an output signal to a powertrain controller <NUM> in response to which the powertrain controller <NUM> causes the transmission <NUM> to operate in accordance with the selected transmission mode.

The driveline <NUM> is arranged to drive a pair of front vehicle wheels <NUM>,<NUM> by means of a front differential <NUM> and a pair of front drive shafts <NUM>. The driveline <NUM> also comprises an auxiliary driveline portion <NUM> arranged to drive a pair of rear wheels <NUM>, <NUM> by means of an auxiliary driveshaft or prop-shaft <NUM>, a rear differential <NUM> and a pair of rear driveshafts <NUM>. The front wheels <NUM>, <NUM> in combination with the front drive shafts <NUM> and front differential <NUM> may be referred to as a front axle 136F. The rear wheels <NUM>, <NUM> in combination with rear drive shafts <NUM> and rear differential <NUM> may be referred to as a rear axle 136R.

The wheels <NUM>, <NUM>, <NUM>, <NUM> each have a respective brake 111B, 112B, 114B, 115B. Respective speed sensors <NUM>, <NUM>, <NUM>, <NUM> are associated with each wheel <NUM>, <NUM>, <NUM>, <NUM> of the vehicle <NUM>. The sensors <NUM>, <NUM>, <NUM>, <NUM> are mounted to a chassis 100C of the vehicle <NUM> and arranged to measure a speed of the corresponding wheel.

Embodiments of the invention are suitable for use with vehicles in which the transmission is arranged to drive only a pair of front wheels or only a pair of rear wheels (i.e. front wheel drive vehicles or rear wheel drive vehicles) or selectable two wheel drive/four wheel drive vehicles. In the embodiment of <FIG> the transmission <NUM> is releasably connectable to the auxiliary driveline portion <NUM> by means of a power transfer unit (PTU) 131P, allowing operation in a two wheel drive mode or a four wheel drive mode. It is to be understood that embodiments of the invention may be suitable for vehicles having more than four wheels or where only two wheels are driven, for example two wheels of a three wheeled vehicle or four wheeled vehicle or a vehicle with more than four wheels.

A control system for the vehicle engine <NUM> includes a central controller <NUM>, referred to as a vehicle control unit (VCU) <NUM>, the powertrain controller <NUM>, a brake controller <NUM> and a steering controller 170C. The brake controller <NUM> is an anti-lock braking system (ABS) controller <NUM> and forms part of a braking system <NUM> (<FIG>). The VCU <NUM> receives and outputs a plurality of signals to and from various sensors and subsystems (not shown) provided on the vehicle. The VCU <NUM> includes a low-speed progress (LSP) control system <NUM> shown in <FIG>, a stability control system (SCS) <NUM>, a traction control system (TCS) 14T, a cruise control system <NUM> and a Hill Descent Control (HDC) system 12HD. The SCS <NUM> improves stability of the vehicle <NUM> by detecting and managing loss of traction when cornering. When a reduction in steering control is detected, the SCS <NUM> is configured automatically to command a brake controller <NUM> to apply one or more brakes 111B, 112B, 114B, 115B of the vehicle <NUM> to help to steer the vehicle <NUM> in the direction the user wishes to travel. If excessive wheel spin is detected, the TCS <NUM> is configured to reduce wheel spin by application of brake force in combination with a reduction in powertrain drive torque. In the embodiment shown the SCS <NUM> and TCS 14T are implemented by the VCU <NUM>. In some alternative embodiments the SCS <NUM> and/or TCS 14T may be implemented by the brake controller <NUM>. Further alternatively, the SCS <NUM> and/or TCS 14T may be implemented by separate controllers.

Similarly, one or more of the controllers <NUM>, <NUM>, <NUM>, 170C may be implemented in software run on a respective one or more computing devices such as one or more electronic control units (ECUs). In some embodiments two or more controllers may be implemented in software run on one or more common computing devices. Two or more controllers may be implemented in software in the form of a combined software module, or a plurality of respective modules each implementing only one controller.

One or more computing devices may be configured to permit a plurality of software modules to be run on the same computing device without interference between the modules. For example the computing devices may be configured to allow the modules to run such that if execution of software code embodying one module terminates erroneously, or the computing device enters an unintended endless loop in respect of one of the modules, it does not affect execution by one or more computing devices of software code comprised by a software module embodying the second controller.

It is to be understood that one or more of the controllers <NUM>, <NUM>, <NUM>, 170C may be configured to have substantially no single point failure modes, i.e. one or more of the controllers may have dual or multiple redundancy. It is to be understood that robust partitioning technologies are known for enabling redundancy to be introduced, such as technologies enabling isolation of software modules being executed on a common computing device. It is to be understood that the common computing device will typically comprise at least one microprocessor, optionally a plurality of processors, which may operate in parallel with one another. In some embodiments a monitor may be provided, the monitor being optionally implemented in software code and configured to raise an alert in the event a software module is determined to have malfunctioned.

The SCS <NUM>, TCS 14T, ABS controller 22C and HDC system 12HD provide outputs indicative of, for example, SCS activity, TCS activity and ABS activity including brake interventions on individual wheels and engine torque requests from the VCU <NUM> to the engine <NUM>, for example in the event a wheel slip event occurs. Each of the aforementioned events indicate that a wheel slip event has occurred. Other vehicle sub-systems such as a roll stability control system or the like may also be present.

As noted above the vehicle <NUM> includes a cruise control system <NUM> which is operable to automatically maintain vehicle speed at a selected speed when the vehicle is travelling at speeds in excess of <NUM> kph. The cruise control system <NUM> is provided with a cruise control HMI (human machine interface) <NUM> by which means the user can input a target vehicle speed to the cruise control system <NUM> in a known manner. In one embodiment of the invention, cruise control system input controls are mounted to a steering wheel <NUM> (<FIG>). The cruise control system <NUM> may be switched on by pressing a cruise control system selector button <NUM>. When the cruise control system <NUM> is switched on, depression of a 'set-speed' control <NUM> sets the current value of a cruise control set-speed parameter, cruise_set-speed to the current vehicle speed. Depression of a `+' button <NUM> allows the value of cruise_set-speed to be increased whilst depression of a '-' button <NUM> allows the value of cruise_set-speed to be decreased. A resume button 173R is provided that is operable to control the cruise control system <NUM> to resume speed control at the instant value of cruise_set-speed following driver over-ride. It is to be understood that known on-highway cruise control systems including the present system <NUM> are configured so that, in the event that the user depresses the brake or, in the case of vehicles with a manual transmission, a clutch pedal, the cruise control function is cancelled and the vehicle <NUM> reverts to a manual mode of operation which requires accelerator pedal input by a user in order to maintain vehicle speed. In addition, detection of a wheel slip event, as may be initiated by a loss of traction, also has the effect of cancelling the cruise control function. Speed control by the system <NUM> is resumed if the driver subsequently depresses the resume button 173R.

The cruise control system <NUM> monitors vehicle speed and any deviation from the target vehicle speed is adjusted automatically so that the vehicle speed is maintained at a substantially constant value, typically in excess of <NUM> kph. In other words, the cruise control system is ineffective at speeds lower than <NUM> kph. The cruise control HMI <NUM> may also be configured to provide an alert to the user about the status of the cruise control system <NUM> via a visual display of the HMI <NUM>. In the present embodiment the cruise control system <NUM> is configured to allow the value of cruise_set-speed to be set to any value in the range <NUM>-150kph.

The LSP control system <NUM> also provides a speed-based control system for the user which enables the user to select a very low target speed at which the vehicle can progress without any pedal inputs being required by the user. Low-speed speed control (or progress control) functionality is not provided by the on-highway cruise control system <NUM> which operates only at speeds above <NUM> kph.

The LSP control system <NUM> is activated by means of a LSP control system selector button <NUM> mounted on the steering wheel <NUM>. The system <NUM> is operable to apply selective powertrain, traction control and braking actions to one or more wheels of the vehicle <NUM>, collectively or individually, to maintain the vehicle <NUM> at the desired speed.

The LSP control system <NUM> is configured to allow a user to input a desired value of set-speed parameter, LSP_set-speed to the LSP control system <NUM> via a low-speed progress control HMI (LSP HMI) <NUM> (<FIG>, <FIG>) which shares certain input buttons <NUM>-<NUM> with the cruise control system <NUM> and HDC control system 12HD. Provided the vehicle speed is within the allowable range of operation of the LSP control system (which is the range from <NUM> to 30kph in the present embodiment although other ranges are also useful) the LSP control system <NUM> controls vehicle speed in accordance with the value of LSP_set-speed. Unlike the cruise control system <NUM>, the LSP control system <NUM> is configured to operate independently of the occurrence of a traction event. That is, the LSP control system <NUM> does not cancel speed control upon detection of wheel slip. Rather, the LSP control system <NUM> actively manages vehicle behaviour when slip is detected.

The LSP control HMI <NUM> is provided in the vehicle cabin so as to be readily accessible to the user. The user of the vehicle <NUM> is able to input to the LSP control system <NUM>, via the LSP HMI <NUM>, an indication of the speed at which the user desires the vehicle to travel (referred to as "the target speed") by means of the 'set-speed' button <NUM> and the `+'/ `-` buttons <NUM>, <NUM> in a similar manner to the cruise control system <NUM>. The LSP HMI <NUM> also includes a visual display upon which information and guidance can be provided to the user about the status of the LSP control system <NUM>.

The LSP control system <NUM> receives an input from the braking system <NUM> of the vehicle indicative of the extent to which the user has applied braking by means of the brake pedal <NUM>. The LSP control system <NUM> also receives an input from an accelerator pedal <NUM> indicative of the extent to which the user has depressed the accelerator pedal <NUM>. An input is also provided to the LSP control system <NUM> from the transmission or gearbox <NUM>. This input may include signals representative of, for example, the speed of an output shaft of the gearbox <NUM>, torque converter slip and a gear ratio request. Other inputs to the LSP control system <NUM> include an input from the cruise control HMI <NUM> which is representative of the status (ON/OFF) of the cruise control system <NUM>, and an input from the LSP control HMI <NUM>.

The HDC system 12HD is configured to limit vehicle speed when descending a gradient. When the HDC system 12HD is active, the system 12HD controls the braking system <NUM> (via brake controller <NUM>) in order to limit vehicle speed to a value corresponding to that of a HDC set-speed parameter HDC_set-speed which may be set by a user. The HDC set-speed may also be referred to as an HDC target speed. Provided the user does not override the HDC system by depressing the accelerator pedal when the HDC system 12HD is active, the HDC system 12HD controls the braking system <NUM> to prevent vehicle speed from exceeding the value of HDC_set-speed. In the present embodiment the HDC system 12HD is not operable to apply positive drive torque. Rather, the HDC system 12HD is only operable to apply negative brake torque by means of the braking system <NUM>.

A HDC system HMI 20HD is provided by means of which a user may control the HDC system 12HD, including setting the value of HDC_set-speed. An HDC system selector button <NUM> is provided on the steering wheel <NUM> by means of which a user may activate the HDC system 12HD to control vehicle speed.

As noted above, the HDC system 12HD is operable to allow a user to set a value of HDC set-speed parameter HDC_set-speed and to adjust the value of HDC_set-speed using the same controls as the cruise control system <NUM> and LSP control system <NUM>. Thus, in the present embodiment, when the HDC system 12HD is controlling vehicle speed, the HDC system set-speed may be increased, decreased or set to an instant speed of the vehicle in a similar manner to the set-speed of the cruise control system <NUM> and LSP control system <NUM>, using the same control buttons <NUM>, 173R, <NUM>, <NUM>. The HDC system 12HD is operable to allow the value of HDC_set-speed to be set to any value in the range from <NUM>-30kph.

If the HDC system 12HD is selected when the vehicle <NUM> is travelling at a speed of 50kph or less and no other speed control system is in operation, the HDC system 12HD sets the value of HDC_set-speed to a value selected from a look-up table. The value output by the look-up table is determined in dependence on the identity of the currently selected transmission gear, the currently selected PTU gear ratio (Hi/LO) and the currently selected driving mode. The HDC system 12HD then applies the powertrain <NUM> and/or braking system <NUM> to slow the vehicle <NUM> to the HDC system set-speed provided the driver does not override the HDC system 12HD by depressing the accelerator pedal <NUM>. The HDC system 12HD is configured to slow the vehicle <NUM> to the set-speed value at a deceleration rate not exceeding a maximum allowable rate although as noted elsewhere the HDC system 12HD is not able to cause positive drive torque to be applied by the powertrain <NUM> in order to reduce a rate of deceleration of the vehicle <NUM>. The rate is set at <NUM>-<NUM> in the present embodiment, however other values are also useful. If the user subsequently presses the 'set-speed' button <NUM> the HDC system 12HD sets the value of HDC_set-speed to the instant vehicle speed provided the instant speed is 30kph or less. If the HDC system 12HD is selected when the vehicle <NUM> is travelling at a speed exceeding 50kph, the HDC system 12HD ignores the request and provides an indication to the user that the request has been ignored.

In the present embodiment the vehicle <NUM> is configured to assume one of a plurality of power modes PM at a given moment in time. In each power mode the vehicle <NUM> may be operable to allow a predetermined set of one or more operations to be performed. For example, the vehicle <NUM> may allow a predetermined one or more vehicle subsystems such as an infotainment system, a windscreen demist subsystem and a windscreen wiper control system to be activated only in a respective one or more predetermined power modes. In one or more of the power modes the vehicle <NUM> may be configured to inhibit one or more operations, such as turning on of the infotainment system.

The identity of the power mode in which the vehicle <NUM> is to operate at a given moment in time is transmitted to each controller <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, 12HD, of the vehicle <NUM> by the central controller <NUM>. The controllers respond by assuming a predetermined state associated with that power mode and that controller. In the present embodiment each controller may assume an ON state in which the controller is configured to execute computer program code associated with that controller, and an OFF state in which supply of power to the controller is terminated. In the present embodiment, the central controller <NUM> is also operable to assume a quiescent state. The quiescent state is assumed by the central controller <NUM> when the vehicle is in power mode PM0 and the controller <NUM> has confirmed that the other controllers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, 12HD have successfully assumed the OFF state following receipt of the command to assume power mode PM0.

In the present embodiment the vehicle <NUM> is provided with a known key fob <NUM> (<FIG>) that has a radio frequency identification device (RFID) 190R embedded therein. The key fob <NUM> has first and second control buttons <NUM>, <NUM>. The key fob <NUM> is configured to generate a respective electromagnetic signal in response to depression of the first or second control buttons <NUM>, <NUM>. The central controller <NUM> detects the electromagnetic signal by means of a receiver module forming part of the controller <NUM> and triggers locking or unlocking of door locks <NUM> of the vehicle <NUM>. Each door 100D of the vehicle <NUM> is provided with a respective door lock <NUM> as shown in <FIG>.

Pressing of the first control button <NUM> generates a door unlock signal, which triggers unlocking of the door locks <NUM>, whilst pressing of the second control button <NUM> triggers a door lock signal, which triggers locking of the door locks <NUM>.

When the controller <NUM> is in the quiescent state, consumption of power by the central controller <NUM> is reduced and the controller <NUM> monitors receipt of a door unlock signal from the key fob <NUM>. It is to be understood that in some embodiments one or more vehicle controllers may be configured to remain in the ON or quiescent state, to allow one or more essential functions to be performed, when the vehicle is in power mode PM0. For example in vehicles fitted with an intruder alarm system an intruder alarm controller may be permitted to remain in the ON or a quiescent state pending detection of an intrusion. Upon detection of an intrusion the intruder alarm controller may cause the central controller <NUM> to assume the ON state if it is not already in that state.

The central controller <NUM> is also configured to transmit a radio frequency (RF) 'interrogation' signal that causes the RFID device 190R of the key fob <NUM> to generate an RF 'acknowledgement' signal in response to receipt of the interrogation signal. In the present embodiment the RFID device 190R is a passive device, not requiring battery power in order to generate the acknowledgement signal. The controller <NUM> is configured to detect the acknowledgment signal transmitted by the RFID device 190R provided the RFID device 190R is within range. By the term 'within range' is meant that the RFID device 190R or fob <NUM> is sufficiently close to the controller <NUM> to receive the interrogation signal and generate an acknowledgement signal that is detectable by the controller <NUM>.

The vehicle <NUM> is also provided with a start/stop button <NUM>. The start/stop button <NUM> is configured to transmit a signal to the central controller <NUM> when pressed in order to trigger an engine start operation, provided certain predetermined conditions are met. In response to pressing of the start/stop button <NUM> the central controller <NUM> causes the vehicle <NUM> to be placed in a condition in which if the transmission <NUM> is subsequently placed in the forward driving mode D or reverse driving mode R, the vehicle <NUM> may be driven by depressing accelerator pedal <NUM>. In the present embodiment, the central controller <NUM> is configured to perform a pre-start verification operation before commanding the powertrain controller <NUM> to trigger an engine start operation. In performing the pre-start verification operation the controller <NUM> verifies (a) that the vehicle <NUM> is in a predetermined power mode as described in more detail below, (b) that the controller <NUM> is receiving an acknowledgement signal from the key fob <NUM> in response to transmission of the interrogation signal by the controller <NUM>, and (c) that the transmission <NUM> is in either the park P or neutral N modes. Thus, the controller <NUM> requires that the RFID device 190R is within range of the controller <NUM> before permitting an engine start. If any of conditions (a) to (c) are not met the controller causes the vehicle <NUM> to remain in its current power mode.

It is to be understood that the central controller <NUM> is configured to cause the vehicle <NUM> to assume a predetermined one of a plurality of power modes in dependence at least in part on actuation of a control button <NUM>, <NUM> of the key fob <NUM> and actuation of the start/stop button <NUM>. In some embodiments the vehicle <NUM> may be configured such that the central controller <NUM> responds to voice commands from a user in addition to or instead of signals received from the key fob <NUM>.

The various power modes in which the vehicle <NUM> of the embodiment of <FIG> may be operated will now be described. As noted above, the key fob <NUM> is operable to cause the door locks <NUM> of the vehicle <NUM> to be locked and unlocked. When the doors 100D of the vehicle <NUM> (<FIG>) are closed and the locks <NUM> are in the locked condition, the vehicle <NUM> assumes power mode PM0.

If the first button <NUM> of the key fob <NUM> is subsequently actuated, the controller <NUM> causes the door locks <NUM> to assume the unlocked condition. Once the door locks <NUM> are in the unlocked condition and the controller <NUM> detects the acknowledgement signal from the key fob <NUM>, the controller <NUM> causes the vehicle <NUM> to assume power mode PM4. In power mode PM4 the controller <NUM> permits a predetermined number of electrical systems to become active, including an infotainment system. Power mode PM4 may also be referred to as a convenience mode or accessory mode. If a user subsequently presses the second button <NUM> of the key fob <NUM>, the controller <NUM> causes the vehicle <NUM> to revert to power mode PM0.

If, whilst the vehicle is in power mode PM4 a user presses the starter button <NUM> and maintains the button <NUM> in a depressed condition, the controller <NUM> performs the pre-start verification operation described above. Provided conditions (a) to (c) of the pre-start verification operation are met, the controller <NUM> places the vehicle <NUM> in power mode PM6. When the vehicle <NUM> is in power mode PM6 the powertrain controller <NUM> is permitted to activate a starter device. In the present embodiment the starter device is a starter motor <NUM>. The powertrain controller <NUM> is then commanded to perform an engine start operation in which the engine <NUM> is cranked by means of the starter motor <NUM> to cause the engine <NUM> to start. Once the controller <NUM> determines that the engine <NUM> is running, the controller <NUM> places the vehicle <NUM> in power mode PM7.

In power mode PM6 the controller <NUM> disables certain non-critical electrical systems including the infotainment system. This is at least in part so as to reduce the magnitude of the electrical load on a battery 100B of the vehicle during cranking in order to permit an increase in the amount of electrical current available for engine starting. Isolation of non-critical electrical systems also reduces a risk of damage to the systems when a relatively large current drain is placed on the battery 100B by the starter motor <NUM>.

If whilst the vehicle is in power mode PM7, with the engine <NUM> running, a user again actuates the start/stop button <NUM>, the controller <NUM> causes the powertrain controller <NUM> to switch off the engine <NUM> and the controller <NUM> causes the vehicle <NUM> to transition to power mode PM4. A user may then cause the vehicle to assume power mode PM0 by pressing the first button <NUM> of the key fob <NUM> provided each of the doors 100D is closed. It is to be understood that in some embodiments the user may trigger assumption of power mode PM0 whilst remaining in the vehicle <NUM> and locking the doors <NUM> by means of the key fob <NUM>. In some embodiments the vehicle <NUM> may be configured to assume power mode PM0 regardless of whether the controller is receiving the acknowledgement signal from the key fob <NUM>. Other arrangements are also useful.

It is to be understood that assumption of power mode PM0 by the vehicle <NUM> may be referred to as 'key off', whilst assumption of power mode PM4 from power mode PM0 may be referred to as 'key on'. A sequence of transitions of the vehicle from power mode PM0 to PM4, and back to power mode PM0, optionally including one or more transitions to power mode PM6 and power mode PM7 prior to assumption of power mode PM0, may be referred to as a 'key cycle'. Thus a key cycle begins and ends with the vehicle <NUM> in power mode PM0. In some embodiments, assumption of power mode PM6 or PM7 from power mode PM0 may be required in order to complete a key cycle, starting with power mode PM0.

It is to be understood that the VCU <NUM> is configured to implement a known Terrain Response (TR) (RTM) System of the kind described above in which the VCU <NUM> controls settings of one or more vehicle systems or sub-systems such as the powertrain controller <NUM> in dependence on a selected driving mode. The driving mode may be selected by a user by means of a driving mode selector <NUM> (<FIG>). The driving modes may also be referred to as terrain modes, terrain response modes, or control modes. In the embodiment of <FIG> four driving modes are provided: an 'on-highway' driving mode suitable for driving 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; a 'grass, gravel or snow' driving mode suitable for driving over grass, gravel or snow, a 'rock crawl' driving mode suitable for driving slowly over a rocky surface; and a 'mud and ruts' driving mode suitable for driving in muddy, rutted terrain. Other driving modes may be provided in addition or instead.

In the present embodiment, at any given moment in time the LSP control system <NUM> is in one of a plurality of allowable 'on' modes (also referred to as conditions or states) selected from amongst an active or full function (FF) mode, a descent control (DC) mode, also referred to as an intermediate mode and a standby mode. The LSP control system may also assume an `off' mode or condition. The active mode, DC mode and standby mode may be considered to be different 'on' modes or conditions of the vehicle, i.e. different modes in which the LSP control system is in an 'on' mode or condition as opposed to an 'off' mode or condition. In the off condition the LSP control system <NUM> only responds to pressing of the LSP selector button <NUM>, which causes the LSP control system <NUM> to assume the on condition and the DC mode. When the LSP control system <NUM> assumes the on mode from the off mode in response to pressing of the LSP selector button, the value of LSP_set-speed is set to the instant speed of the vehicle <NUM> provided it is in the allowable range of speeds for operation of the LSP control system <NUM>. If the vehicle speed <NUM> is above this range the value of LSP_set-speed is set to the highest allowable speed for operation of the LSP control system <NUM>, i.e. 30kph.

In the active or full function mode, the LSP control system <NUM> actively manages vehicle speed in accordance with the value of LSP set-speed, LSP_set-speed, by causing the application of positive powertrain drive torque to one or more driving wheels or negative braking system torque to one or more braked wheels.

In the DC mode the LSP control system <NUM> operates in a similar manner to that in which it operates when in the active mode except that the LSP control system <NUM> is prevented from commanding the application of positive drive torque by means of the powertrain <NUM>. Rather, only braking torque may be applied, by means of the braking system <NUM> and/or powertrain <NUM>. The LSP control system <NUM> is configured to increase or decrease the amount of brake torque applied to one or more wheels in order to cause the vehicle to maintain the LSP set-speed to the extent possible without application of positive drive torque. It is to be understood that, in the present embodiment, operation of the LSP control system <NUM> in the DC mode is very similar to operation of the HDC system 12HD, except that the LSP control system <NUM> continues to employ the LSP control system <NUM> set-speed value LSP_set-speed rather than the HDC control system set-speed value HDC_set-speed.

In the standby mode, the LSP control system <NUM> is unable to cause application of positive drive torque or negative brake torque to a wheel.

As noted above, in the 'off' mode the LSP control system <NUM> is not responsive to any LSP input controls except the LSP control system selector button <NUM>. Pressing of the LSP control system selector button <NUM> when the system <NUM> is in the off mode causes the system <NUM> to assume the 'on' condition and the DC mode.

When the LSP control system <NUM> is initially switched on by means of the LSP selector button <NUM>, the LSP control system <NUM> assumes the DC mode.

If whilst in DC mode the 'set +' button <NUM> is pressed, the LSP control system <NUM> sets the value of LSP_set-speed to the instant value of vehicle speed according to vehicle speed signal <NUM> (<FIG>, discussed in more detail below) and assumes the active mode. If the vehicle speed is above 30kph, being the maximum allowable value of LSP_set-speed, the LSP control system <NUM> remains in the DC mode and ignores the request to assume the active mode. A signal may be provided to the driver indicating that the LSP control system <NUM> cannot be activated due to the vehicle speed exceeding the maximum allowable value of LSP_set-speed. The signal may be provided by means of a text message provided on the LSP control HMI <NUM>, by means of an indicator lamp, an audible alert or any other suitable means.

If the resume button 173R is depressed whilst in the DC mode, the LSP control system assumes the active mode and causes the vehicle to operate in accordance with the stored value of LSP_set-speed provided the vehicle speed does not exceed 30kph.

If vehicle speed is above 30kph but less than or substantially equal to 50kph when the resume button 173R is pressed the LSP control system <NUM> remains in the DC mode until vehicle speed falls below 30kph. In the DC mode, provided the driver does not depress the accelerator pedal <NUM> the LSP control system <NUM> deploys the braking system <NUM> to slow the vehicle <NUM> to a value of set-speed corresponding to the value of parameter LSP_set-speed. Once the vehicle speed falls to 30kph or below, the LSP control system <NUM> assumes the active mode in which it is operable to cause a required amount of positive powertrain drive torque to be applied to one or more wheels via the powertrain <NUM>, as well as negative torque via the powertrain <NUM> (via engine braking) and brake torque via the braking system <NUM> in order to control the vehicle in accordance with the LSP_set-speed value. The LSP control system <NUM> may generate a virtual accelerator pedal signal in order to cause the powertrain129 to develop a required amount of powertrain torque in some embodiments. The virtual accelerator pedal signal may correspond to that which would be generated by an accelerator pedal controller in response to depression of the accelerator pedal <NUM> by an amount corresponding to the amount of powertrain torque required at a given moment in time. The accelerator pedal controller may form part of a powertrain controller <NUM> although other arrangements are also useful.

With the LSP control system <NUM> in the active mode, the user may increase or decrease the value of LSP_set-speed by means of the `+' and `-` buttons <NUM>, <NUM>. In addition, the user may optionally also increase or decrease the value of LSP_ set-speed by lightly pressing the accelerator or brake pedals <NUM>, <NUM> respectively. In some embodiments, with the LSP control system <NUM> in the active mode the `+' and '-' buttons <NUM>, <NUM> may be disabled such that adjustment of the value of LSP_set-speed can only be made by means of the accelerator and brake pedals <NUM>, <NUM>. This latter feature may prevent unintentional changes in set-speed from occurring, for example due to accidental pressing of one of the '+' or `-` buttons <NUM>, <NUM>. Accidental pressing may occur for example when negotiating difficult terrain where relatively large and frequent changes in steering angle may be required. Other arrangements are also useful.

It is to be understood that in the present embodiment the LSP control system <NUM> is operable to cause the vehicle to travel in accordance with a value of set-speed in the range from <NUM>-30kph whilst the cruise control system is operable to cause the vehicle to travel in accordance with a value of set-speed in the range from <NUM>-150kph although other values are also useful, such as <NUM>-120kph or any other suitable range of values.

It is to be understood that if the LSP control system <NUM> is in the active mode, operation of the cruise control system <NUM> is inhibited. The two speed control systems <NUM>, <NUM> therefore operate independently of one another, so that only one can be operable at any one time.

In some embodiments, the cruise control HMI <NUM> and the LSP control HMI <NUM> may be configured within the same hardware so that, for example, the speed selection is input via the same hardware, with one or more separate switches being provided to switch between the LSP control HMI <NUM> and the cruise control HMI <NUM>.

When in the active mode, the LSP control system <NUM> is configured to command application of positive powertrain torque and negative brake torque, as required, by transmitting a request for (positive) drive torque in the form of a powertrain torque signal and/or a request for (negative) brake torque in the form of a brake torque signal to the brake controller <NUM>. The brake controller <NUM> arbitrates any demand for positive powertrain torque, determining whether the request for positive powertrain torque is allowable. If a request for positive powertrain torque is allowable the brake controller <NUM> issues the request to the powertrain controller <NUM>. In some embodiments, the request for brake torque may correspond to an amount of brake torque (or brake fluid pressure) to be developed by the braking system <NUM>. In some alternative embodiments the request for brake torque may be for an amount of negative torque to be applied to one or more wheels. The brake controller <NUM> may in some embodiments determined whether the requested negative torque is to be supplied by means of powertrain braking alone, for example engine overrun braking, by means of powertrain braking and brake torque developed by the braking system <NUM>, or by means of the braking system <NUM> alone. In some embodiments the brake controller <NUM> or LSP control system <NUM> may be configured to cause a required amount of net negative torque to be applied to one or more wheels by applying negative torque by means of the braking system <NUM> against positive drive torque generated by the powertrain <NUM>. Application of positive drive torque generated by means of the powertrain <NUM> against negative brake torque generated by means of the braking system <NUM> may be made in order to reduce wheel flare when driving on surfaces of relatively low surface coefficient of friction such as during off-road driving. By wheel flare is meant excessive wheel slip as a result of the application of excess positive net torque to a wheel.

In the present embodiment the brake controller <NUM> also receives from the LSP control system <NUM> a signal S_mode indicative of the mode in which the LSP control system <NUM> is operating, i.e. whether the LSP control system <NUM> is operating in the active mode, DC mode, standby mode or off mode.

If the brake controller <NUM> receives a signal S_mode indicating that the LSP control system <NUM> is operating in the DC mode, standby mode or off mode, the brake controller <NUM> sets a powertrain torque request inhibit flag in a memory thereof. The powertrain torque request inhibit flag indicates that positive torque requests to the powertrain controller <NUM> from the brake controller <NUM> in response to positive torque requests from the LSP control system <NUM> are forbidden. Accordingly, if a request for positive powertrain torque is received by the brake controller <NUM> from the LSP control system <NUM> whilst the LSP control system <NUM> is operating in the DC mode, standby mode or off mode, the positive torque request is ignored by the brake controller <NUM>.

In some embodiments, the powertrain controller <NUM> is also provided with signal S_mode indicating the mode in which the LSP control system <NUM> is operating. If the LSP control system <NUM> is operating in a mode other than the active mode, such as the DC mode, standby mode or off mode, positive powertrain torque requests received as a consequence of a command from the LSP control system <NUM> are ignored by the powertrain controller <NUM>.

In some embodiments, if the powertrain controller <NUM> receives a request for positive powertrain torque from the brake controller <NUM> as a consequence of a command from the LSP control system <NUM> and the request is received more than a predetermined period after the LSP control system <NUM> has transitioned to a mode other than the active mode, the powertrain controller <NUM> causes the LSP control system <NUM> to assume a disabled off mode. In the disabled off mode the LSP control system <NUM> is effectively locked into the off condition or mode for the remainder of the current key cycle and the LSP control system <NUM> does not assume the DC mode in response to pressing of the LSP selector button <NUM>. The predetermined period may be any suitable period such as <NUM>, <NUM>, <NUM>, <NUM> or any other suitable period. The period may be set to a value such that any delay in receipt of a positive torque request issued by the LSP control system <NUM> immediately prior to a transition from the active mode to a mode other than the active mode (and in which positive torque requests are not permitted) that is consistent with normal system operation will not trigger a transition to the disabled off mode. However, the powertrain controller <NUM> is configured such that any request for positive powertrain torque received by the powertrain controller <NUM> as a consequence of a request issued by the LSP control system <NUM> after assuming a mode other than the active mode (and in which positive torque requests are not permitted) will trigger a transition to the disabled off mode.

It is to be understood that other arrangements may also be useful. For example, in some embodiments, in the disabled off mode the LSP control system <NUM> may be configured not to respond to the LSP selector button <NUM> by assuming the DC mode until after the vehicle has transitioned from power mode PM7 to power mode PM4. As described above, a transition from power mode PM7 to power mode PM4 may be accomplished by depressing the start/stop button <NUM>. When the vehicle <NUM> is subsequently restarted and assumes power mode PM7, the LSP control system <NUM> may be permitted to assume operation in the active mode as required.

It is to be understood that some vehicles may be provided with known automatic engine stop/start functionality. In vehicles with this functionality, the powertrain controller <NUM> is configured to command stopping and starting of the engine <NUM> according to a stop/start control methodology when the vehicle <NUM> is being held stationary by means of brake pedal <NUM> with the transmission in the drive mode D. The process of automatically commanding stopping and restarting of the engine <NUM> may be referred to as an automatic stop/start cycle. In vehicles having automatic engine stop/start functionality, the controller <NUM> may be configured to cause the vehicle <NUM> to assume a power mode PM6A when the engine <NUM> is stopped during a stop/start cycle. Power mode PM6A is similar to power mode <NUM>, except that disabling of certain vehicle systems such as the infotainment system is not performed when in power mode PM6A. In power mode PM6A, the powertrain controller <NUM> is configured to restart the engine <NUM> upon receipt of a signal indicating a user has released the brake pedal <NUM>. It is to be understood that in some embodiments, a vehicle <NUM> may be configured to require an engine restart before the LSP control system <NUM> may exit the DC fault mode but an engine restart as part of an automatic stop/start cycle may be configured not to qualify as an engine restart permitting the system <NUM> to exit the DC fault mode. In some embodiments therefore, a transition from power mode PM7 to power mode PM6A and back to power mode PM7 does not permit the LSP control system <NUM> to exit the disabled off mode.

In some embodiments the LSP control system <NUM> may be configured such that it can assume one of a number of different further modes such as:.

The DC fault mode corresponds to the DC mode except that if the DC fault mode is assumed by the LSP control system <NUM>, the LSP control system <NUM> is unable subsequently to assume the active mode for the remainder of the current key cycle. Thus, when the next key-on procedure is performed, following the next key-off procedure, the LSP control system <NUM> is permitted to assume the active mode when required. The vehicle <NUM> may be configured wherein the LSP control system <NUM> may assume the DC fault mode if a fault is detected indicating that the LSP control system <NUM> should not be permitted to request positive powertrain drive torque but where it is determined that it may be desirable for the benefits of DC mode to be enjoyed. Thus a transition from active mode to DC fault mode may be preferable to a transition to the off mode, particularly when negotiating off road conditions, in the event of a relatively minor fault in respect of the LSP control system <NUM>.

In some embodiments, if a transition to DC fault mode occurs with more than a predetermined frequency, the LSP control system <NUM> may become latched in the DC fault mode until a reset procedure is performed requiring action other than a key-off and subsequent key-on procedure in order to permit the active mode to be assumed again. In some embodiments, the LSP control system <NUM> may require a predetermined code to be provided to it. In some embodiments, the LSP control system <NUM> may be configured to receive the code via a computing device external to the vehicle <NUM> that temporarily communicates with the LSP control system <NUM> in order to provide the code. The computing device may be a device maintained by a vehicle servicing organisation such as a dealer certified by a manufacturer of the vehicle <NUM>. The computing device may be in the form of a laptop or other computing device, and be configured to communicate wirelessly with the LSP control system <NUM> or via a wired connection.

The predetermined frequency may be defined in terms of a predetermined number of occurrences in a predetermined number of key cycles, or a predetermined distance driven, or be time based such as a predetermined number of occurrences in a predetermined period in which the vehicle is in power mode <NUM> (or power mode 6A in addition to power mode <NUM>, in the case of a vehicle with stop/start functionality) over one or more key cycles, or a predetermined number of occurrences in a given calendar period, such as a day, a week, a month or any other suitable frequency.

The DC fault mode fade-out mode is a mode assumed by the LSP control system <NUM> when transitioning from the DC fault mode to an off mode such as disabled off, unless an immediate ('binary') transition to an off mode is required in which case the DC fault mode fade-out mode is not assumed. Thus, under certain conditions, rather than abruptly terminate commanding application of brake torque by means of the braking system <NUM> when ceasing operation in the DC fault mode and transitioning to an off mode such as 'off' or 'disabled off', the LSP control system <NUM> gradually fades out the application of any brake torque applied by the braking system <NUM> as a consequence of being in the DC fault mode, before assuming the off or disabled off mode. This is at least in part so as to allow a driver time to adapt to driving without the system <NUM> applying brake torque automatically.

Similarly, if the LSP control system <NUM> transitions from the DC mode to a mode in which the LSP control system <NUM> is unable to command application of brake torque such as the standby mode, off mode or disabled off mode, the LSP control system <NUM> may assume the DC fade-out mode as an intermediate mode. In the DC fade-out mode, like the DC fault mode fade-out mode, the LSP control system <NUM> gradually reduces the amount of any brake torque commanded by the LSP control system <NUM>, before assuming the target mode such as standby mode, off mode or disabled off mode.

The active standby mode is a mode assumed by the LSP control system <NUM> from the active mode if the driver over-rides the LSP control system <NUM> by depressing the accelerator pedal <NUM> to increase vehicle speed. If the driver subsequently releases the accelerator pedal with vehicle speed within the allowable range for the LSP control system <NUM> to operate in the active mode (i.e. a speed in the range <NUM>-30kph), the LSP control system <NUM> resumes operation in the active mode.

The DC standby mode is a mode assumed by the LSP control system <NUM> if whilst operating in the DC mode the driver over-rides the LSP control system <NUM> by depressing the accelerator pedal <NUM>. If the driver subsequently releases the accelerator pedal, then when vehicle speed is within the allowable range for the LSP control system <NUM> to operate in the DC mode (i.e. a speed in the range <NUM>-30kph), the LSP control system <NUM> resumes operation in the DC mode. Other arrangements are also useful. In some embodiments the LSP control system <NUM> may be configured to assume DC mode from the DC standby mode and cause application of brake torque to slow the vehicle <NUM> when a driver releases the accelerator pedal <NUM> even at speeds above 30kph. In some embodiments the LSP control system <NUM> may be configured to cause application of brake torque at speeds of up to 50kph, 80kph or any other suitable speed in order to cause vehicle speed to reduce to the LSP target speed LSP_set-speed. The LSP control system <NUM> may be configured to take into account negative torque applied by a powertrain due for example to engine over-run braking in determining an amount of brake torque required in order to cause a vehicle to slow at a desired rate. The LSP control system <NUM> may be configured to cause a vehicle to slow at a desired rate according to a predetermined deceleration profile.

In some embodiments, if the powertrain controller <NUM> receives a request for positive powertrain torque from the brake controller <NUM> as a consequence of a command from the LSP control system <NUM> and the LSP control system <NUM> is in the DC mode, the powertrain controller <NUM> causes the LSP control system <NUM> to assume the DC fault mode if the positive torque request is received more than a predetermined period after the LSP control system <NUM> has transitioned to the DC mode. As noted above, in the DC fault mode the LSP control system <NUM> is permitted to cause application of brake torque by the braking system <NUM> to control vehicle speed but is prevented from assuming the active or FF mode for the remainder of the current key cycle. In these circumstances, the LSP control system <NUM> assumes the DC fault mode substantially immediately with no requirement to blend the transition between the DC mode and DC fault mode.

As noted above, the predetermined period may be any suitable period such as <NUM>, <NUM>, <NUM>, <NUM> or any other suitable period. The period may be set to a value such that any inherent system delay in receipt by the powertrain controller <NUM> of a torque request from the brake controller <NUM> as a consequence of a request issued by the LSP control system <NUM> prior to a transition from the active mode to the DC mode will not trigger a transition to the DC fault mode. It is to be understood that by inherent system delay is meant a delay in signal receipt that occurs during normal operation, for example due to a requirement to synchronise timing signals, or to transmit commands from the LSP control system <NUM> to the powertrain controller <NUM> at predetermined intervals as part of an inter-controller communications protocol.

In some embodiments, if the powertrain controller <NUM> receives a request for positive powertrain torque from the brake controller <NUM> as a consequence of a command from the LSP control system <NUM> and the LSP control system <NUM> is in the DC fault mode or DC fault mode fade out mode only, the powertrain controller <NUM> causes the LSP control system <NUM> to assume the disabled off mode if the positive torque request is received more than a predetermined period after the LSP control system <NUM> has transitioned to the DC fault mode or DC fault mode fade out mode. In the present embodiment the predetermined period is a period of <NUM>. However the predetermined period may be any suitable period such as <NUM>, <NUM>, <NUM> or any other suitable period. The LSP control system <NUM> may be configured substantially abruptly to terminate application of any negative (brake) torque requested by the LSP control system <NUM> when the transition to the disabled off mode is commanded even if the system <NUM> is in the processes of fading out any negative brake torque that is being applied as a result of a request issued by the LSP control system <NUM>.

In some embodiments, in addition or instead, if the powertrain controller <NUM> receives a request for positive powertrain torque from the brake controller <NUM> as a consequence of a command from the LSP control system <NUM> and the signal S_mode indicates that the LSP control system <NUM> is in the DC mode, DC standby mode, DC mode fade-out mode or active standby mode, the powertrain controller <NUM> causes the LSP control system <NUM> to assume the disabled off mode if the positive torque request is received over a sustained period of more than a predetermined period. In the present embodiment the predetermined period is substantially <NUM>. However the predetermined period may be any suitable period such as <NUM>, <NUM> or any other suitable period. The LSP control system <NUM> is configured gradually to cause fade-out of any negative (brake) torque being applied as a consequence of a command from the LSP control system <NUM> when the transition to the disabled off mode is commanded. The fade-out of brake torque may be accomplished by assuming the DC mode fade-out mode or DC fault mode fade-out mode if they have not already been assumed.

In some embodiments, the LSP control system <NUM> is caused to assume the disabled off mode if the powertrain controller <NUM> receives a request for positive powertrain torque from the brake controller <NUM> as a consequence of a command from the LSP control system <NUM> and signal S_mode indicates that the LSP control system <NUM> is in the DC fault mode or DC fault mode fade-out mode, as well as when the signal indicates the LSP control system <NUM> is in the DC mode, DC standby mode, DC mode fade-out mode or active standby mode.

It is to be understood that in some embodiments, instead of gradually fading out negative brake torque, the LSP control system <NUM> may be configured to abruptly terminate application of any negative brake torque as a consequence of a command by the LSP control system <NUM>. Thus, if a request for positive powertrain torque is received over a sustained period of more than the predetermined period when the LSP control system <NUM> is in the DC mode, DC standby mode, DC fault mode, DC mode fade-out mode, DC fault mode fade-out mode or active standby mode the system may abruptly terminate application of brake torque caused by the LSP control system <NUM>. It is to be understood that the braking system <NUM> continues to respond to driver brake commands via the brake pedal <NUM>.

It is to be understood that in the present embodiment if a driver switches off the LSP control system <NUM> manually, the LSP control system <NUM> is configured gradually to cause fade-out of any negative (brake) torque being applied as a consequence of a command from the LSP control system <NUM>. This feature has the advantage that vehicle composure may be enhanced.

<FIG> illustrates the means by which vehicle speed is controlled in the LSP control system <NUM>. As described above, a speed selected by a user (set-speed) is input to the LSP control system <NUM> via the LSP control HMI <NUM>. A vehicle speed calculator <NUM> provides a vehicle speed signal <NUM> indicative of vehicle speed to the LSP control system <NUM>. The speed calculator <NUM> determines vehicle speed based on wheel speed signals provided by wheel speed sensors <NUM>, <NUM>, <NUM>, <NUM>. The LSP control system <NUM> includes a comparator <NUM> which compares the LSP control system set-speed LSP_set-speed <NUM> (also referred to as a 'target speed' <NUM>) selected by the user with the measured speed <NUM> and provides an output signal <NUM> indicative of the comparison. The output signal <NUM> is provided to an evaluator unit <NUM> of the VCU <NUM> which interprets the output signal <NUM> as either a demand for additional torque to be applied to the vehicle wheels <NUM>-<NUM>, or for a reduction in torque applied to the vehicle wheels <NUM>-<NUM>, depending on whether the vehicle speed needs to be increased or decreased to maintain the speed LSP_set-speed. An increase in torque is generally accomplished by increasing the amount of powertrain torque delivered to a given position of the powertrain, for example an engine output shaft, a wheel or any other suitable location. A decrease in torque at a given wheel to a value that is less positive or more negative may be accomplished by decreasing the amount of any positive powertrain torque delivered to a wheel, by increasing the amount of any negative powertrain torque delivered to a wheel, for example by reducing an amount of air and/or fuel supplied to an engine <NUM>, and/or by increasing a braking force on a wheel. It is to be understood that in some embodiments in which a powertrain <NUM> has one or more electric machines operable as a generator, negative torque may be applied by the powertrain <NUM> to one or more wheels by means of the electric machine. As noted above negative torque may also be applied by means of engine braking in some circumstances, depending at least in part on the speed at which the vehicle <NUM> is moving. If one or more electric machines are provided that are operable as propulsion motors, positive drive torque may be applied by means of the one or more electric machines.

An output <NUM> from the evaluator unit <NUM> is provided to the brake controller <NUM>. The brake controller <NUM> in turn controls a net torque applied to the vehicle wheels <NUM>-<NUM> by commanding application of brake torque via the brakes 111B, 112B, 114B, 115B and/or positive drive torque by commanding powertrain controller <NUM> to deliver a required amount of powertrain torque. The net torque may be increased or decreased depending on whether the evaluator unit <NUM> demands positive or negative torque. In order to cause application of the necessary positive or negative torque to the wheels, the brake controller <NUM> may command that positive or negative torque is applied to the vehicle wheels by the powertrain <NUM> and/or that a braking force is applied to the vehicle wheels by the braking system <NUM>, either or both of which may be used to implement the change in torque that is necessary to attain and maintain a required vehicle speed. In the illustrated embodiment the torque is applied to the vehicle wheels individually so as to maintain the vehicle <NUM> at the required speed, but in another embodiment torque may be applied to the wheels collectively to maintain the required speed. In some embodiments, the powertrain controller <NUM> may be operable to control an amount of torque applied to one or more wheels at least in part by controlling a driveline component such as a rear drive unit, front drive unit, differential or any other suitable component. For example, one or more components of the driveline <NUM> may include one or more clutches operable to allow an amount of torque applied to wheels of a given axle to be controlled independently of the torque applied to wheels of another axle, and/or the amount of torque applied to one or more individual wheels to be controlled independently of other wheels. Other arrangements are also useful.

Where a powertrain <NUM> includes one or more electric machines, for example one or more propulsion motors and/or generators, the powertrain controller <NUM> may be operable to modulate or control the amount of torque applied to one or more wheels at least in part by means of the one or more electric machines.

The LSP control system <NUM> also receives a signal <NUM> indicative of a wheel slip event having occurred. This may be the same signal <NUM> that is supplied to the on-highway cruise control system <NUM> of the vehicle, and which in the case of the latter triggers an override or inhibit mode of operation of the on-highway cruise control system <NUM> so that automatic control of vehicle speed by the on-highway cruise control system <NUM> is suspended or cancelled. However, the LSP control system <NUM> is not arranged to cancel or suspend operation in dependence on receipt of a wheel slip signal <NUM> indicative of wheel slip. Rather, the system <NUM> is arranged to monitor and subsequently manage wheel slip so as to reduce driver workload. During a slip event, the LSP control system <NUM> continues to compare the measured vehicle speed with the value of LSP_set-speed, and continues to control automatically the torque applied to the vehicle wheels so as to maintain vehicle speed at the selected value. It is to be understood therefore that the LSP control system <NUM> is configured differently to the cruise control system <NUM>, for which a wheel slip event has the effect of overriding the cruise control function so that manual operation of the vehicle <NUM> must be resumed, or speed control by the cruise control system <NUM> resumed by pressing the resume button 173R or set-speed button <NUM>.

In a further embodiment of the present invention (not shown) a wheel slip signal <NUM> is derived not just from a comparison of wheel speeds, but further refined using sensor data indicative of the vehicle's speed over ground. Such a speed over ground determination may be made via global positioning (GPS) data, or via a vehicle mounted radar or laser based system arranged to determine the relative movement of the vehicle <NUM> and the ground over which it is travelling. A camera system may be employed for determining speed over ground in some embodiments.

At any stage of the LSP control process the user can override the LSP function by depressing the accelerator pedal <NUM> and/or brake pedal <NUM> to adjust the vehicle speed in a positive or negative sense. However, absent any override by a user, in the event that a wheel slip event is detected via signal <NUM>, the LSP control system <NUM> remains active and control of vehicle speed by the LSP control system <NUM> is not terminated. As shown in <FIG>, this may be implemented by providing a wheel slip event signal <NUM> to the LSP control system <NUM> which is then managed by the LSP control system <NUM> and/or brake controller <NUM>. In the embodiment shown in <FIG> the SCS <NUM> generates the wheel slip event signal <NUM> and supplies it to the LSP control system <NUM> and cruise control system <NUM>.

A wheel slip event is triggered when a loss of traction occurs at any one of the vehicle wheels. Wheels and tyres may be more prone to losing traction when travelling for example on snow, ice, mud or sand and/or on steep gradients or cross-slopes. A vehicle <NUM> may also be more prone to losing traction in environments where the terrain is more uneven or slippery compared with driving on a highway in normal on-road conditions. Embodiments of the present invention therefore find particular benefit when the vehicle <NUM> is being driven in an off-road environment, or in conditions in which wheel slip may commonly occur. Manual operation in such conditions can be a difficult and often stressful experience for the driver and may result in an uncomfortable ride.

The vehicle <NUM> is also provided with additional sensors (not shown) which are representative of a variety of different parameters associated with vehicle motion and status. 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 is travelling. Suitable sensor data may be provided by inertial systems unique to the LSP or HDC control system <NUM>, 12HD or systems that form part of another vehicle sub-system such as an occupant restraint system or any other sub-system 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 <NUM>, 12HD.

The sensors on the vehicle <NUM> include sensors which provide continuous sensor outputs to the VCU <NUM>, including wheel speed sensors, as mentioned previously and as shown in <FIG>, and other sensors (not shown) such as an ambient temperature sensor, an atmospheric pressure sensor, tyre pressure sensors, wheel articulation sensors, gyroscopic sensors to detect vehicular yaw, roll and pitch angle and rate, a vehicle speed sensor, a longitudinal acceleration sensor, an engine torque sensor (or engine torque estimator), a steering angle sensor, a steering wheel speed sensor, a gradient sensor (or gradient estimator), a lateral acceleration sensor which may be part of the SCS <NUM>, a brake pedal position sensor, a brake pressure sensor, an accelerator pedal position sensor, longitudinal, lateral and vertical motion sensors, 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. Other sensors may be useful in addition or instead in some embodiments.

The VCU <NUM> also receives a signal from the steering controller 170C. The steering controller 170C is in the form of an electronic power assisted steering unit (ePAS unit). The steering controller 170C provides a signal to the VCU <NUM> indicative of the steering force being applied to steerable road wheels <NUM>, <NUM> of the vehicle <NUM>. This force corresponds to that applied by a user to the steering wheel <NUM> in combination with steering force generated by the ePAS unit 170C.

The VCU <NUM> evaluates the various sensor inputs to determine the probability that each of a plurality of different control modes (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 and ruts, sand, grass/gravel/snow).

If the user has selected operation of the vehicle in an automatic driving mode selection condition, the VCU <NUM> then selects the most appropriate one of the control modes and is configured automatically to control the subsystems according to the selected mode.

The nature of the terrain over which the vehicle is travelling (as determined by reference to the selected control mode) may also be utilised in the LSP control system <NUM> to determine an appropriate increase or decrease in vehicle speed. For example, if the user selects a value of LSP_set-speed that is not suitable for the nature of the terrain over which the vehicle is travelling, the system <NUM> is operable to automatically adjust the vehicle speed downwards by reducing the speed of the vehicle wheels. In some cases, for example, the user selected speed may not be achievable or appropriate over certain terrain types, particularly in the case of uneven or rough surfaces. If the system <NUM> selects a set-speed that differs from the user-selected set-speed, a visual indication of the speed constraint is provided to the user via the LSP HMI <NUM> to indicate that an alternative speed has been adopted.

In the present embodiment, the LSP control system <NUM> is configured to monitor signals indicative of an amount of tractive force available between each wheel <NUM>, <NUM>, <NUM>, <NUM> and a driving surface. The LSP control system <NUM> accomplishes this by receiving the following signals as shown in <FIG>:.

The LSP control system <NUM> also receives a signal hi_lo indicative whether the PTU 131P is in a HI or LO ratio and a signal tq_interv indicative that a torque intervention event is in progress in which the ABS function, TCS 14T or SCS <NUM> intervenes to change an amount of torque applied to one or more wheels.

The LSP control system <NUM> is configured to estimate an amount of tractive force that may be developed between each road wheel <NUM>, <NUM>, <NUM>, <NUM> and the driving surface and generate a transmission control signal LSP_trans in dependence on the estimate.

The signal LSP_trans is output to a transmission controller 124C as also shown in <FIG>. The transmission controller 124C is configured to receive the signal LSP_trans. In addition the transmission controller 124C receives a signal acc_pos indicative of an accelerator pedal position and a signal eng_spd indicative of an instant speed of rotation of the output shaft of the engine <NUM>.

It is to be understood that, when the LSP control system <NUM> is in the active mode the LSP control system <NUM> generates a virtual accelerator pedal position signal acc_pos_virt which is fed to the transmission controller 124C and powertrain controller <NUM> in addition to the signal acc_pos. The powertrain controller <NUM> develops an amount of powertrain torque in dependence on the accelerator pedal position signal acc_pos or virtual accelerator pedal position signal acc_pos_virt, whichever is the greatest, when the LSP control system <NUM> is in the active mode.

The transmission controller 124C is configured to command the transmission <NUM> to assume a required gear according to shift map data stored in a memory of the transmission controller 124C in dependence on acc_pos or acc_pos_virt. The shift map data is stored in the form of a look-up table LUT that allows the controller 124C to determine the gear that the transmission <NUM> should be operated in at a given moment in time. The data is stored in the form of values of engine output shaft speed and accelerator pedal position (acc_pos or acc_pos_virt) as a proportion of maximum allowable range of travel of the accelerator pedal <NUM>, at which a transmission gear upshift or downshift should take place. The data stored is plotted graphically in <FIG>, where downshift points are shown with dashed lines and upshift points are shown with solid lines.

By way of example of operation of the transmission controller 124C, if the vehicle <NUM> is travelling under steady state conditions with an engine output shaft speed of 3000rpm and a virtual accelerator pedal position of <NUM>% of maximum stroke or range (point P1 of <FIG>), the transmission <NUM> may be in (say) gear number <NUM>, each transmission gear causing a predetermined gear ratio to be established between input and output shafts of the transmission <NUM> in the conventional manner. If the engine output shaft speed falls to around 2200rpm (point S_D), the transmission controller 124C forces a downshift in gear. The transmission <NUM> therefore assumes gear number <NUM>, causing a larger gear ratio to be established between the input and output shafts of the transmission <NUM>.

The transmission controller 124C receives the signal LSP_trans from the LSP control system <NUM>. The signal LSP_trans may be in the form of a downshift_modify signal, downshift_suspend signal or downshift_temp signal.

The downshift_modify signal causes the value of engine output shaft speed at which a given downshift occurs, for a given value of acc_pos_virt and eng_spd, to be reduced by the transmission controller 124C by a predetermined amount that is indicated by the signal downshift_modify.

The downshift_suspend signal causes the transmission controller 124C to suspend all downshifts by the transmission <NUM> until the signal downshift_suspend is terminated. Other arrangements for suspending downshifts to lower output shaft speed values may also be useful. Other arrangements for suspending downshifts altogether may also be useful.

In response to receipt of signal downshift_temp, the transmission controller 124C performs a mu-check operation in which the transmission controller 124C forces the transmission <NUM> to downshift by one gear number from the current operating gear for a predetermined period downshift_temp_period before reverting to the current operating gear. Thus, in response to signal downshift_temp the transmission controller 124C forces the transmission <NUM> to downshift by one gear number for <NUM> before upshifting by one gear number. In the present embodiment the period downshift_temp_period is of length <NUM> although other lengths are also useful such as <NUM>, <NUM> or any other suitable length. In some embodiments the transmission controller 124C may cause a downshift by more than one gear number when s mu-check operation is performed, optionally in dependence on one or more conditions such as the value of a current gear number, the value of sfc mu_LSP described below, or any other suitable condition.

Whilst the transmission <NUM> is in the downshifted state during a mu-check operation, the LSP control system <NUM> monitors a change in speed of any of the vehicle road wheels by reference to the wheel speed signals 36W. If the LSP control system <NUM> determines that a speed of any of the wheels is no longer consistent with vehicle reference speed signal <NUM> due to an excessive reduction in wheel speed, the LSP control system <NUM> updates an estimate of the surface coefficient of friction between each wheel and a driving surface, sfc_mu_LSP. The parameter sfc_mu_LSP is maintained by the LSP control system <NUM> independently of the value of parameter sfc_mu that is received by the LSP control system <NUM> from the VCU <NUM>. The LSP control system <NUM> may employ the value sfc_mu_LSP in preference to the value sfc_mu received by the LSP control system <NUM> from another source such as a brake controller <NUM> or other controller when deciding whether to adjust a speed at which a transmission downshift may take place.

In the present embodiment the LSP control system <NUM> is configured to transmit the signal downshift_temp to the transmission controller 124C at the expiry of a predetermined interval downshift temp_interval since the last issuance of a downshift_temp signal, or after the vehicle covers a predetermined distance of downshift_temp_distance since the last issuance of a downshift_temp signal, whichever event occurs first, and the LSP control system <NUM> is issuing a virtual accelerator pedal position signal acc_pos_virt having a value that corresponds to pedal lift-off, i.e. to a released position of the pedal <NUM>. In the present embodiment downshift_temp_interval is of length <NUM> (<NUM> minutes) and downshift_temp_distance is <NUM>. Other values of downshift temp_interval and downshift_temp_distance may also be useful, such as <NUM> and <NUM> mile (approximately <NUM>). When the LSP control system <NUM> determines that a mu-check operation is due, the system <NUM> causes the mu-check operation to be performed at the earliest opportunity, i.e. when the condition is met that acc_pos_virt corresponds to a released accelerator pedal <NUM>.

It is to be understood that if the signal tq_interv indicates that a torque intervention event is occurring, the LSP control system <NUM> is configured to perform a mu-check operation at the earliest opportunity once the signal tq_interv indicates that a torque intervention event is no longer occurring. Optionally the system <NUM> may perform a mu-check once the signal tq_interv indicates that a torque intervention event is no longer occurring even if the signal acc_pos_virt does not correspond to a released position of the accelerator pedal <NUM>.

When the LSP control system <NUM> transmits the signal downshift_temp to the transmission controller 124C, the system <NUM> monitors the vehicle speed signal <NUM> and wheel speed signals 36W and determines whether any difference between the vehicle speed signal <NUM> and wheel speed signals 36W is indicative of locking of a wheel due to increased rotational resistance of a wheel when the transmission <NUM> is in a lower gear. In some embodiments if when a mu-check operation is in progress a speed of one or more wheels falls to a value that is lower than vehicle reference speed <NUM> by more than a predetermined proportion of the vehicle reference speed <NUM>, for example that is less than <NUM>% of vehicle reference speed, the LSP control system <NUM> reduces the estimate of surface coefficient of friction sfc mu_LSP by a predetermined amount, optionally by an amount corresponding to the proportion of vehicle reference speed <NUM> by which wheel speed has decreased, such as <NUM>% in the case of a <NUM>% reduction in wheels speed. In the case that wheel lock is experienced, i.e. a wheel becomes substantially stationary, the system <NUM> may set the value of sfc_mu_LSP to a minimum allowable baseline value such as <NUM>. Other values are also useful. It is to be understood that reducing the value of sfc mu_LSP has the effect of reducing an estimated value of tractive force between the driving surface and road wheel, tract_force_LSP, since the tractive force available at a given wheel is a function of surface coefficient of friction and normal force acting on the wheel.

The LSP control system <NUM> is configured to further refine the value of sfc mu_LSP by reference to the signal amb_temp. If the value of amb_temp falls below a predetermined value such as 3C, the LSP control system <NUM> may reduce the value of sfc mu_LSP by a predetermined amount, for example by a predetermined value such as <NUM>, <NUM> or any other value, or by a predetermined proportion of the instant value of sfc_mu_LSP. Other arrangements are also useful.

The LSP control system <NUM> is further configured to refine the value of tract_force_LSP in respect of each wheel by reference to the signals susp_art, wade_depth and sfc_grad which are indicative of a normal force acting on each wheel.

In the case of signal susp_art, the LSP control system <NUM> is configured to increase or decrease the estimate of tract_force_LSP in dependence on whether the signal indicates that a suspension arm in respect of a given wheel is deflected in a positive sense (corresponding to greater weight on a given wheel) or negative sense (corresponding to less weight on a given wheel) with respect to a reference position of the suspension. Positive deflections may result in an increase in tract_force_LSP for a given wheel, whilst negative deflections may result in a decrease in tract_force_LSP for a given wheel. This feature may be particularly useful when a vehicle is negotiating very rough terrain, and the suspension becomes highly deflected, or highly 'articulated', increasing a risk that one or more wheels may suffer excessive slip.

The signal wade_depth is employed to determine an apparent weight of the vehicle <NUM> taking into account buoyancy, and thereby reduce the value of tract_force_LSP accordingly.

The signal sfc_grad is employed to determine a change in distribution of weight over wheels of the vehicle <NUM> due to the gradient, since a proportion of a weight of the vehicle borne by downhill wheels typically increases relative to the proportion borne by uphill wheels. An amount of tractive force available at downhill wheels may therefore be increased, and/or that available at uphill wheels reduced.

The signal hi_lo may be employed to determine an overall driveline gear ratio and enable correlation of engine output shaft speed with vehicle speed.

Claim 1:
A system comprising:
a first controller (<NUM>) configured in each of a predetermined plurality of states to generate a torque request signal in order to cause a vehicle (<NUM>) to operate in accordance with a target speed value,
the system being configured, to:
in dependence on a signal (sfc_mu) having a value indicative of a surface coefficient of friction between each wheel and a driving surface, estimate an amount of tractive force that may be developed between each wheel (<NUM>, <NUM>, <NUM>, <NUM>) and a driving surface, and
when the first controller (<NUM>) is one of said plurality of states to generate a gear shift limit signal to cause a change in an engine speed at which a transmission controller (124C) is permitted to cause a gear downshift, the gear shift limit signal being generated in dependence on the estimated amount of tractive force,
wherein the gear shift limit signal is further configured to suspend a gear downshift if the estimated tractive force between the vehicle (<NUM>) and a driving surface is below a first threshold.