Patent ID: 12233838

DETAILED DESCRIPTION

A road vehicle100embodying the present invention is shown inFIG.1. In the present embodiment the vehicle100is a car having an electric motor102arranged to provide torque to front wheels101via a transmission system104under the control of a powertrain control module103. The vehicle100also has a second electric motor105arranged to provide torque to rear wheels107via a second transmission system106, but it will be appreciated that in other embodiments, the vehicle100may just have a single electric motor that drives either the front wheels101or the rear wheels107.

The vehicle100is shown inFIG.1after having been stopped on a road with a slight uphill gradient of 1 or 2 degrees to the horizontal. The vehicle100was brought to rest by the driver (not shown) releasing the accelerator pedal108and without depressing the brake pedal109. The vehicle100may be momentarily kept in its present position by frictional resistance to rolling, but the vehicle100may start to roll unexpectedly, for example, triggered by movement of people in the vehicle100or a gust of wind. If the driver is not paying attention, the movement of the vehicle100may go unnoticed. However, the vehicle100is provided with a system (200shown inFIG.2) which automatically causes the brakes (209inFIG.2) of the vehicle100to be applied to hold the vehicle100stationary and prevent undesirable movement of the vehicle100.

A schematic diagram of a system200for automatically causing brakes209of the vehicle100to be applied to hold the vehicle100stationary is shown inFIG.2. The system200comprises a controller201. The controller201comprises an electronic processor202and an electronic memory device203having instructions204stored therein. The electronic processor202is electrically coupled to the electronic memory device203and it is configured to access the electronic memory device203and execute the instructions204, to cause the controller201to perform the processes that will be described below.

The controller201comprises input/output means211to enable signals to be received by the controller201from other components of the vehicle100and to enable the controller201to transmit signals to other components of the vehicle100. In an embodiment, the input/output means211may be provided by a transceiver configured to enable communication over a data bus.

The controller201is configured to receive signals from a brake pedal sensor206configured to detect pressure being applied to the brake pedal109and provide a signal to the controller201indicative of whether or not the brake pedal109has been pressed.

The controller201is also configured to receive signals indicative of whether or not the driver of the vehicle100is requesting torque by depression of the accelerator pedal108. In the present embodiment, these signals are received from an accelerator pedal sensor207configured to detect the position of the accelerator pedal108and provide signals indicative of depression or release of the accelerator pedal108to the controller201.

The controller201is also configured to receive signals from a motor speed sensor208indicative of the rotational velocity of the electric motor102, which is also indicative of the speed of the vehicle100. Due to the gear ratio of the transmission system104, the electric motor102turns many times for each revolution of the driven wheels101. Consequently, measurement of the rotational velocity of the electric motor102provides a very accurate indication of speed of the vehicle100, even at very low speeds of the vehicle100. This enables the controller201to determine from the received signals when the vehicle100is stationary with a relatively small measurement error.

It is noted that the word “speed” generally refers to a scalar quantity equal to the magnitude of a velocity, and therefore it is always positive. However, “speed of the vehicle”, “measured speed” or “vehicle speed” as used herein refers to a scalar quantity with a positive sign for forward motion of the vehicle100and a negative sign for backward motion of the vehicle.

The vehicle100comprises a user input device210configured to enable a user to select a direction of travel, i.e. drive or reverse (D or R), or alternatively neutral or park (N or P). The controller201is configured to receive signals indicative of whether a direction of travel is currently selected. In the present embodiment the indication of the selected direction of travel is received from the user input device210but in alternative embodiments it may be received from the powertrain control module103.

The controller201is configured to provide output signals to a brake system205to cause the brakes209of the vehicle100to be applied to hold the vehicle100stationary. The brake system205may be an antilock braking system. The output signals are provided by the controller201in dependence on the indications of speed received from the motor speed sensor208and a determination that the gradient on which the vehicle100is positioned is less than a threshold gradient. In the present embodiment, the controller201determines that the gradient is less than a threshold gradient when the magnitude of the speed of the vehicle100is less than a threshold speed throughout a predefined period of time. For example, the threshold speed may be set at 1 kilometre per hour. In some embodiments, the threshold speed is dependent on the direction of movement of the vehicle100, but in either case the controller201determines that the gradient is less than a threshold gradient when the speed of the vehicle100remains within a first range of speeds that includes zero during the predefined period. For example, in an embodiment the first range is from −1 kilometer per hour to +1 kilometer per hour.

The time at which the output signal is provided by the controller201depends on whether the brake pedal sensor206indicates that the brake pedal109is depressed and/or the accelerator pedal sensor208indicating that the accelerator pedal108is depressed.

In some embodiments, the powertrain control module103has a creep function that causes the motor102to provide a small amount of torque when drive is selected and the accelerator pedal is not depressed. In such an embodiment, the creep function may be switched on or off by a user input device, and the controller is only configured to automatically cause the brakes to be applied, when the creep function is switched off. Similarly, in some embodiments, the vehicle100has a driver assist function, such as an autonomous cruise control system, and a user input device to enable a user to switch on or off the driver assist function. In such an embodiment the controller201is only configured to automatically cause the brakes to be applied, when the driver assist function is switched off.

A functional flow block diagram illustrating operations performed by the controller201is shown inFIG.3. The controller201is configured to receive the measured speed of the vehicle100and perform a low speed detection function301to detect when the speed of the vehicle100is within a first range of speeds that includes zero. When the measured speed is within the first range of speeds, an indication of this is provided to a first timer302and also to a second timer303.

The first timer302and the second timer303are arranged to start only when they receive an indication that the measured speed is within the first range of speeds and that the drive or reverse directions of travel have been selected by the driver. If the measured speed goes outside of the first range of speeds and/or the drive or reverse are deselected, the timers302and303are stopped and reset.

The first timer302times a first period that has a predefined first duration and the second timer times a second period having a predefined second duration that is longer than the predefined first duration. Typically the predefined first duration is about 2 seconds.

The first timer302is arranged to provide an output to indicate when the first period has expired and the output is maintained by the first timer302while ever the measured speed remains within the first range of speeds and the drive/reverse selection is maintained. Similarly, the second timer303provides an output to indicate when the second period has expired and the output is maintained by the second timer while ever the measured speed remains within the first range of speeds and the drive/reverse selection is maintained.

The controller201is also configured to perform a zero speed detection function304in which the measured speeds received by the controller201are compared to a second range of speeds that includes zero. The second range of speeds is substantially smaller than the first range of speeds and is typically arranged to be approximately equal to zero plus or minus the measurement accuracy of the motor speed sensor208. For example, the second range of speeds may be from −0.1 to +0.1 kilometres per hour, or even smaller. The zero speed detection function304is configured to provide an output indicating that the vehicle100is stationary when a measured speed is within the second range of speeds.

In instances when the vehicle100is driven forwards and stopped, and then it rolls backwards, the measured speed changes from a positive value to a negative value indicating that the speed of the vehicle100has crossed zero. Similarly when the vehicle100is driven in reverse and stopped, and then it rolls forwards, the measured speed changes from a negative value to a positive value indicating that the speed of the vehicle100has crossed zero. The zero speed detection function304is also configured to detect when the speed of the vehicle100has crossed zero and provide an indication that the vehicle100is stationary when this is detected.

When the second timer303provides an output indicating that the second period of second duration has been exceeded and the zero speed detection function304indicates that the vehicle100is stationary, the controller201is configured to provide an output signal305to the brake system205to request that the brake system205to apply the brakes209to hold the vehicle100stationary.

The request for brakes to be applied is latched until any one of a second set of requirements is met. The second set of requirements may comprise: the brake system205confirming that the brakes209have been applied; selection of neutral (rather than drive or reverse); confirmation that the park pawl is engaged when park is selected (rather than drive or reverse); a driver pressing the accelerator pedal to cause the vehicle to be moved in the selected direction of travel; a driver pressing the brake pedal, which indicates that the driver is taking control of the vehicle; creep function or a driver assist function being switched on.

The controller201is also configured to receive a signal from the accelerator pedal sensor208indicative of when the accelerator pedal108is being depressed, and, in the present embodiment, receive a signal from the brake pedal sensor206indicative of when the brake pedal109is being depressed. The controller201comprises a pedal release timer306arranged to: start when these signals both indicate that the pedals108and109have gone from a pressed state to a released state; and stop and reset when the signals indicate that either of the pedals108and109has gone from a released state to a pressed state.

The pedal release timer306is configure to provide an output when the period from it being started exceeds a predefined pedal release duration, and to maintain the output while ever both the accelerator pedal108and the brake pedal109continue to be released. In the present embodiment, the predefined pedal release duration is about 0.5 seconds.

The controller201is also configured to provide a low torque detection function306, in which a received signal indicating the current powertrain torque demand is compared to a small threshold value and to indicate when the powertrain torque demand is low, i.e. less than that threshold value.

The controller201is configured to provide an output signal305to the brake system205to cause the brake system205to apply the brakes209to hold the vehicle100stationary when: the first timer302provides an output indicating that the first period of first duration has been exceeded; the zero speed detection function304indicates that the vehicle100is stationary; the pedal release timer306indicates that the pedals108and109have been released for at least the predefined pedal release duration; and the low torque detection function307indicates that the powertrain torque demand is low.

Thus, the controller201is configured to automatically provide an output signal305to the brake system205to cause the brake system205to apply the brakes209to hold the vehicle100stationary, after a period of time of defined duration has elapsed beginning when the measured speed is within the first range of speeds. If the powertrain torque demand is low, and the accelerator pedal108and the brake pedal109are both released, the output signal305may be provided after a relatively short first period of time measured by the first timer302. Alternatively, if either of the pedals108and109is depressed and/or the torque demand of the powertrain is high, the output signal305may be provided only after a relatively longer second period of time measured by the second timer303.

It may be noted that if the brake pedal109and accelerator pedal108are both released and the speed of the vehicle100remains less than a threshold speed for the duration of the first period, timed by the first timer302, this indicates that the gradient on which the vehicle100is positioned is less than a threshold gradient. i.e. if the vehicle100were on a steeper slope it would accelerate more rapidly and its speed would not remain within the first range of speeds used by the low speed detection function301for the whole period measured by the first timer302.

In an alternative embodiment, the controller201is configured to receive a signal from a gradient sensing means which may comprise an inertial measurement unit. The gradient sensing means or the controller201may be configured to determine when the gradient measured by the gradient sensing means is less than a predefined threshold gradient. The controller201may then be arranged to provide the output signal305to the brake system205when: the sensed gradient is below the threshold gradient; the measured speed is below a threshold speed (or within a first range); and a direction of travel (drive/reverse) is selected. Therefore, in such an embodiment, the first timer302is not necessary. It will be understood that the implementation of the second timer is also optional.

In alternative embodiments, the second timer303is omitted and the controller201only provides an output signal when: the first timer302has exceeded its predefined duration; the measured speed remains within the first range; the measured speed has been zero or crossed zero since the first timer was started; a direction of travel (drive/reverse) is selected; and at least the accelerator pedal is not depressed. In other alternative embodiments, the first timer302is omitted and the controller201only provides an output signal when: the second timer303has exceeded its predefined duration; the measured speed remains within the first range; the measured speed has been zero or crossed zero since the second timer303was started; and a direction of travel (drive/reverse) is selected.

In addition or alternatively, the controller201may not include the zero speed detection function304and it may be configured to provide the output signal305whenever drive or reverse are selected and either the second timer303has timed out or the first timer302and the pedal release timer306have timed out.

In an alternative embodiment, the pedal release timer306is started in dependence on receiving an indication of the accelerator pedal108being released and does not depend on the brake pedal109being released.

Graphs illustrating some examples of the behavior of the controller201are shown inFIGS.4to7. Each one ofFIGS.4to7shows four graphs with time along the horizontal axis. Along the vertical axis the graphs show, from top graph to bottom graph: vehicle speed; accelerator pedal pressure; brake pedal pressure; and the output signal305from the controller201to the brake system205to request application of the brakes209.

InFIG.4, the vehicle100is slowing down from a speed of 5 kilometres per hour. When the speed becomes less than a threshold speed of 1 kilometre per hour at time t1, the first timer302is started and it continues to run as the speed remains below the 1 kilometre per hour threshold speed. At time t2the first timer exceeds its predefined first duration, in this case 2 seconds, and the vehicle100is still not stationary. Consequently, in terms ofFIG.3, the zero speed detection function304has not yet provided a necessary output to enable the controller201to provide its output signal305to the brake system205. Shortly after t2, at time t3the vehicle100becomes stationary as determined by the zero speed detection function304. The brake pedal109and the accelerator pedal108are never depressed during this example, and therefore when the vehicle100becomes stationary at t3, the controller201provides an output signal305to request the brake system205to apply the brakes209.

InFIG.5, the vehicle100is slowing down from a speed of 5 kilometres per hour. When the speed becomes less than a threshold speed of 1 kilometre per hour at time t4, the first timer302is started and it continues to run as the speed remains below the 1 kilometre per hour threshold speed. In less than 2 seconds of t4, at time t5, the speed goes through 0 kilometres per hour and becomes negative as the vehicle100rolls backwards in the opposite direction to its initial direction of travel. Therefore, in terms ofFIG.3, the zero speed detection function304detects that the speed has crossed zero at time t5and provides an output signal to indicate this. Then at time t6, the first timer302reaches its predefined duration of 2 seconds, and because the accelerator pedal108and the brake pedal109have not been depressed, and the magnitude of the speed of the vehicle100has been below the threshold speed of 1 kilometre per hour since the first timer started at time t4, the controller201provides an output signal305at time t6. The application of the brakes209at t6, caused by the output signal305, slows the vehicle100back down to zero kilometres per hour at time t7.

InFIG.6, the graphs illustrate the vehicle100slowing down on an uphill gradient while a small input is received at the accelerator pedal108. The speed of the vehicle100goes below a threshold speed of the 1 kilometre per hour at time t8and the first and second timers302and303are started. The speed then becomes at time t9, and remains at 0 kilometres per hour because the torque generated by the electric motor102is just sufficient to hold the vehicle100stationary on the uphill gradient. Following t9, at t10, which is 2 seconds after time t8, the first timer302times out but the controller201is unable to provide an output signal305to the brake system205because the driver is still pressing the accelerator pedal108to keep the vehicle100stationary. Later, at t11the second timer303times out and consequently the controller201provides the output signal305to the brake system.

InFIG.7, the vehicle100is slowing down while a small input is received at the accelerator pedal. The speed of the vehicle100goes below a threshold speed of the 1 kilometre per hour at time t12, but it never becomes stationary. Consequently in terms ofFIG.3, the zero speed detection function304does not provide an output indicating that the vehicle100is stationary and so the controller201is not enabled to provide an output signal305. The driver is therefore able to drive the vehicle100at very low speeds without interference of automatic brake application.

A flowchart illustrating a method800performable by the controller201is shown inFIG.8. At block801of the method800, an indication of measured speed of the vehicle100is received. At block802it is determined whether the measured speed is in a first range of speeds that includes zero. If the measured speed is not in the first range, then the processes at blocks801and802are repeated. If the measured speed is determined to be in the first range at block802, an output signal is provided to a brake system205at block803in dependence on a determination that a gradient on which the vehicle100is positioned is less than a threshold gradient. The method800may then be repeated.

A flowchart illustrating a second method900performable by the controller201is shown inFIG.9, in which the determination that the gradient is less than a threshold gradient is achieved by monitoring speed of the vehicle100. At block901of the method900, an indication of measured speed of the vehicle100is received. At block902it is determined whether the measured speed is in a first range of speeds that includes zero. If the measured speed is not in the first range, then the processes at blocks901and902are repeated.

If the measured speed is determined to be in the first range at block902, a first timer is started at block903and another indication of measured speed is received at block904. At block905it is determined if the measured speed is still in the first range and if it is not the processes at blocks901and902are repeated until the speed is once again in the first range.

If it is determined at block905that the speed is still in the first range, it is determined at block906whether the first timer302has exceeded a first duration. If it has not, then the processes at blocks904,905and906are repeated until it is determined at block906that the first timer has exceeded the first duration. When that happens, at block907an output signal is provided to the brake system205to cause it to apply the brakes209.

A flowchart illustrating a third method1000performable by the controller201is shown inFIGS.10and11. At block1001of the method1000, an indication of measured speed of the vehicle1000is received. At block1002it is determined whether the measured speed is in a first range of speeds that includes zero. If the measured speed is not in the first range, then the processes at blocks1001and1002are repeated.

If the measured speed is determined to be in the first range at block1002, a first timer302and a second timer303are reset and started at block1003and a zero speed flag is reset to zero at block1004. A pedal release timer306is then reset to zero and started at block1005. At block1006it is determined whether a pedal is depressed. As described above with reference toFIG.3, the pedal concerned may be the accelerator pedal but in the present embodiment it is determined at block1006whether either of the accelerator pedal or the brake pedal is depressed. If the pedals concerned are both released, then it is determined at block1007whether or not drive or reverse has been selected by the driver. If the drive or reverse has been deselected, for example if the user has selected neutral or park, the method1000returns to block1001.

Otherwise, if drive or reverse are found to be selected at block1007, it is determined at block1008whether the current measured speed is zero or if the measured speed has crossed zero, i.e. the measured speed has changed sign indicating a change in direction of the vehicle100. If the current measured speed is zero or if the measured speed has crossed zero, the zero speed flag is set to 1 at block1009.

At block1010it is determined whether the current measured speed is still in the first range, and if it is not then the method returns to block1001. If the current measured speed is still in the range, then at block1011it is determined whether the zero speed flag is set to 1. If it is, then it is determined at block1012whether the pedal release timer306has exceeded a pedal timer duration, i.e. it is determined whether a predefined pedal release period (for example, with a duration of 0.5 seconds) has elapsed since the pedal release timer306was started at block1005. If it has, then it is determined at block1013whether the first timer has exceeded a first duration. If it has, then an output signal is provided at block1014, for example to the brake system206to cause application of brakes209.

If any of the determinations at blocks1011,1012or1013give a negative result, then the processes at blocks1006to1013are repeated as necessary. If during the repeating of the processes at blocks1007and1010it is determined that the drive or reverse are no longer selected, or the speed is no longer within the first range, then the method1000returns to block1001.

In an alternative embodiment, if it is determined at block1006that a pedal is depressed, then the method1000simply returns to block1001. However, in the present embodiment, if it is determined at block1006that a pedal is depressed, then a process at block1015is performed, which is shown onFIG.11. At block1015it is determined whether the current measured speed is still in the first range and, if it is, it is determined at block1016whether drive or reverse are selected. If it is, then the process at block1017is performed. However, if either of the processes at blocks1015and1016provide a negative result, then the method1000returns to block1001(FIG.10).

At block1017it is determined whether a pedal is still being depressed and, if it is, it is determined at block1018whether the current measured speed is zero or if the speed has crossed zero. The process at block1018is therefore like that of block1008. If the current measured speed is zero or if the speed has crossed zero then the zero speed flag is set to 1 at block1019.

At block1020it is determined whether the zero speed flag is set to 1 and, if it is, it is determined at block1021if the second timer303has exceed a second duration. As mentioned above, the second duration is longer than the first duration. If the second timer303has exceeded the second duration, then the output is provided at block1014to cause the brakes209to be applied. If the processes at blocks1020or1021provide a negative result, the method returns to block1015and the processes at blocks1015to1020and1021are repeated.

If it is determined at block1017that no pedal is being depressed then the pedal release timer306is reset and started at block1005(shown inFIG.10) and the method1000may continue with the processes of blocks1006to1014as described above. When returning to block1005from block1017it is possible that the first timer has already timed out and that the vehicle100has been noted as being stationary at blocks1018and1019. In such a case, the expiry of the pedal release timer306may be all that is still required for the output signal to be provided at block1014. Therefore, for example, if the pedal timer duration is 0.5 seconds, then the brakes209may be automatically applied in accordance with block1014, 0.5 seconds after the pedals are released.

For purposes of this disclosure, it is to be understood that the controller(s) described herein can each comprise a control unit or computational device having one or more electronic processors. A vehicle and/or a system thereof may comprise a single control unit or electronic controller or alternatively different functions of the controller(s) may be embodied in, or hosted in, different control units or controllers. A set of instructions could be provided which, when executed, cause said controller(s) or control unit(s) to implement the control techniques described herein (including the described method(s)). The set of instructions may be embedded in one or more electronic processors, or alternatively, the set of instructions could be provided as software to be executed by one or more electronic processor(s). For example, a first controller may be implemented in software run on one or more electronic processors, and one or more other controllers may also be implemented in software run on or more electronic processors, optionally the same one or more processors as the first controller. It will be appreciated, however, that other arrangements are also useful, and therefore, the present disclosure is not intended to be limited to any particular arrangement. In any event, the set of instructions described above may be embedded in a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors/computational device, including, without limitation: a magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM or EEPROM); flash memory; or electrical or other types of medium for storing such information/instructions.

The blocks illustrated in theFIGS.8to11may represent steps in a method and/or sections of code in the computer program204. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some steps to be omitted.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.