GB2500932A

GB2500932A - A method of producing a control output from a clutch position sensing system

Info

Publication number: GB2500932A
Application number: GB1206179.2A
Authority: GB
Inventors: Chris Edward Pedlar; Ian Halleron; David Hesketh; Themi Philemon Petridis
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2012-04-05
Filing date: 2012-04-05
Publication date: 2013-10-09
Anticipated expiration: 2032-04-05
Also published as: RU2013115132A; CN103362664B; GB201206179D0; GB2500932B; RU2627952C2; CN103362664A; DE102013205315A1

Abstract

A method and system of producing a control output from a clutch position sensing system comprises monitoring, via signals from a sensor 26, a position of a clutch pedal 25. An electronic clutch pedal position processor 16C processes the signal from the senor 26 and defines several operating zones including a transition zone between a clutch pedal 25 release state and a clutch pedal 25 pressed state. The clutch pedal position processor 16C is operable to set a moveable or tracking or trailing offset (Th1, fig 6) from a clutch pedal starting position that if crossed when the clutch pedal 25 is within the transition zone will result in clutch pedal 25 state changing from one to the other state, e.g. from released to pressed or vice versa. An engine (10, fig 1) is controlled by an electronic control unit 16 which receives signals from, for example, a gear selector sensor (12) and the clutch pedal position processor 16C and controls the engine (10) in stop-start running mode.

Description

A Method for Producing a Control Output from a Clutch Position Sensing System of a Motor Vehicle.

This invention relates to a motor vehicle having an internal combustion engine and in particular to a motor vehicle having a system to automatically stop and start the internal combustion engine based at least partially on clutch engagement state.

It is known to provide a motor vehicle having a manual transmission with a stop-start system for automatically stopping and starting an internal combustion engine used to provide motive power for the motor vehiole.

A stop-start system automatically stops the engine whenever it is determined that there is an opportunity to do so in order to improve fuel consumption and reduce emissions from the engine.

For manual transmission start-stop applications, a clutch pedal pressed/clutch pedal released' threshold is normally used to indicate the driver's intention to drive away when the clutch is pressed, so that the start-stop system can trigger an engine start. The same threshold can also be used to indicate when the driver has released the clutch pedal and is intending to remain stationary long enough that the start-stop system can switch the engine off to conserve fuel.

The clutch pedal released state is often used as a condition for the start-stop system to run plausibility checks relating to the stop-start system. Such plausibility tests are set which must be passed once in every key-cycle prior to start-stop being enabled. One example of such a plausibility test is to oheck whether a gear sensor signal agrees with an estimation of the current driven gear based on the ratio of engine speed to vehicle speed for a known drive ratio. This test, if passed, will indicate that the gear sensor is funotioning correctly.

In order to sucoessfully perform such a comparison test, at the time the test is run, there must be no slipping between the clutch plates that is to say the clutch must be engaged. A condition to indicate that the driveline is fully engaged is to check whether the clutch pedal is released past the bite-point. Therefore, as long as the olutoh pedal pressed/clutch pedal released' threshold is set to occur at a more-released pedal position than the bite point, the clutch pedal released state can be used as a condition to run the test.

The issue with using such a fixed clutch pedal pressed/clutch pedal released threshold is that there exists a start/stop availability versus drivability attribute trade-off based on the calibrated threshold value. In order to provide as much time as possible to start the engine when the driver presses the clutch pedal, it is desirable to set the threshold as high up the pedal travel as possible such as 10% pressed. That is a position where the driver does not have to press the clutch pedal very far from a fully released position in order to trigger an engine start. This arrangement improves the perceived engine start performance, or eagerness of start. One problem with setting the threshold near to the top of pedal travel is that many drivers (real life testing indicates somewhere in the order of 35 to 40%) rest their foot on the clutch pedal sometimes referred to as riding the clutch, either whilst driving in gear with the clutch fully engaged and/ or when the vehicle is stationary with the transmission in neutral with the clutch engaged and so the threshold would always be exceeded.

Figure 2 depicts three clutch states, Released, Pressed and Depressed, and the transition thresholds between the states. These three states are typicaiiy used in Stop-in-Neutral start-stop applications today.

In the zone "R" a clutch pedal is oonsidered to be released that is to say the olutch will definitely be engaged, in the zone "D" the clutch pedal is considered to be depressed and the clutch will definitely be disengaged and in the zone "P" the olutch pedal is considered to be pressed and the clutch could be disengaged or engaged depending upon the location of the clutch pedal in the zone

P

The most significant threshold is that between the pressed and the released state indicted by ThRP on Fig.2.

Consider now four possible scenarios, in the first scenario Thu is set to 10% of clutch pedal travel and the driver fully removes their foot from the clutch pedal, in the second scenario ThRP is set to 30% of clutch pedal travel and the driver fully removes their foot from the clutch pedal, in the third scenario ThRP is set to 10% of clutch pedal travel and the driver rides the clutch pedal so that it remains pressed by 25% of clutch pedal travel, in the fourth scenario Thkp is set to 30% of clutch pedal travel and the driver rides the clutch pedal so that it remains pressed by 25% of clutch pedal travel.

With the first scenario start-up will be prompt and time is available for plausibility testing; With the second scenario start-up will be non-responsive because the clutch pedal has to be depressed 30% to achieve this. However there is plenty of time for plausibility testing; With the third scenario the engine will not stop because the threshold Th1 will normally not be crossed and plausibility checking can therefore not occur; and With the fourth scenario start-up will be prompt and there is time for plausibility testing.

Problems therefore exist with scenarios two and three in that they can result in one or more of poor perceived stop-start performance, reduced availability of start-stop operation and can lead to driver confusion if plausibility testing is not possible resulting in deactivation of the stop-start system.

It is an object of this invention to provide an improved method and apparatus for controlling the stop-start operation of an engine fitted to a motor vehicle having a manual transmission that minimises or eliminates the above referred to problems.

According to a first aspect of the invention there is provided a method of producing a control output from a clutch position sensing system wherein the method comprises monitoring the position of a clutch pedal of the motor vehicle, defining a transition zone defined by a range of clutch pedal positions in which the control output is one of two alternative clutch pedal position states comprised of a clutch pedal released state and a clutch pedal pressed state, setting a moveable threshold offset from a clutch pedal starting position that if crossed when the clutch pedal position is within the transition zone will result in a change in clutch pedal position state and changing the control output from the current state to the alternative state if the moveable threshold is crossed.

The method may further oomprise setting a maximum offset of the moveable threshold from the clutch pedal position.

If the state of clutch pedal is the released state at the clutch pedal starting position, then the magnitude of the moveable threshold may have a magnitude greater than the magnitude of the clutch pedal starting position.

If the state of clutch pedal is the pressed state at the clutch pedal starting position, then the magnitude of the mcveable threshold may have a magnitude less than the magnitude of the clutch pedal starting position.

If the clutch pedal position is within the transition zone, the method may further comprise defining the clutch pedal position state as released if the final clutch pedal position is less than the moveable threshold.

If the clutch pedal position is within the transition zone, the method may further comprise defining the clutch pedal position state as pressed if the final clutch pedal position is greater than or equal to the moveable threshold.

When the clutch pedal position and the moveable threshold are both within the transition zone, the method may further comprise moving the moveable threshold so as to maintain a predefined offset from the clutch pedal position if the clutch pedal position moves from the clutch pedal starting position away from the moveable threshold.

If the clutch pedal position moves from the clutch pedal starting position towards the moveable threshold, the magnitude of the moveable threshold may remain the same until the clutch pedal position has moved a predefined distance past the moveable threshold.

The transition zone may be bounded at a lower end by a lower clutch pedal position limit and at an upper end by an upper clutch pedal position limit.

A released zone may be defined by a range of clutch pedal positions bounded at one end by a clutch pedal fully released position and at an upper end by the lower clutch pedal position limit and the control output may always be indicative of a released clutch pedal position state whenever the clutch pedal position is within the released zone and a pressed zone may be defined by a range of clutch pedal positions bounded at one end by the upper clutch pedal position limit and bounded at an opposite end by a fixed upper threshold and the control output may always be indicative of a pressed clutch pedal position state whenever the clutch pedal position is within the pressed zone.

A depressed zone may be defined by a range of clutch pedal positions bounded at one end by the fixed upper threshold and at an opposite end by a clutch pedal fully depressed position and the control output may always be indicative of a depressed clutch pedal position state whenever the clutch pedal position is within the depressed zone.

The offset of the moveable threshold from the clutch pedal starting position may define a transition window bounded at one end by the position of the moveable threshold and at an opposite end by the starting clutch position and the transition window may always be positioned to the side of the starting clutch position towards the clutch position zone of the alternative clutch position state.

The method may further comprise adjusting the moveable threshold by a very small amount each time the moveable threshold is calculated to allow for unintentional clutch pedal position changes.

Adjusting the moveable threshold may comprise increasing the offset from the starting clutch pedal position to the moveable threshold by the very small amount each time the moveable threshold is calculated.

If the magnitude of the moveable threshold is greater than the starting clutch position, the offset may be increased by adding the very small amount to the current value of the moveable threshold.

Alternatively, if the magnitude of the moveable threshold is less than the starting clutch position, the offset may be increased by subtracting the very small amount from the current value of the moveable threshold.

The very small amount may be less than 1% of the value of the offset.

The method may further comprise supplying the control output from the clutch position sensing system to a stop-start system of a motor vehicle for use in controlling the stopping and starting of an engine of the motor vehicle.

According to a second aspect of the invention there is provided a clutch position sensing system for sensing the position of a clutch pedal of a motor vehicle and providing a control output indicative of the positional state of the clutch pedal, the system comprising a position sensing means to provide a signal indicative of a current clutch pedal position and an electronic clutch pedal position processor to process the signal from the position sensing means wherein if the clutch pedal position is within a transition zone bounded by a fixed lower limit of clutch pedal position and an upper fixed limit of clutch pedal position in which the state of the clutch pedal position is one of released and pressed, the electronic clutch pedal position processor is operable to set a moveable threshold offset from a clutoh pedal starting position that if crossed when the clutch pedal position is within the transition zone will result in a change in clutch pedal position state and change the control output from indicative of the current clutch pedal position state to indicative of the alternative clutch pedal position state if the moveable threshold is crossed.

If the clutch pedal is in the released state at the clutch pedal starting position, the electronic clutch pedal position processor may be operable to set the moveable threshold value so as to have a magnitude greater than the magnitude of the clutch pedal starting position and if the clutch pedal is in the pressed state at the clutch pedal starting position, the electronic clutch pedal position processor may be operable to set the moveable threshold value so as to have a magnitude less than the magnitude of the clutch pedal starting position.

The electronic clutch pedal position processor may be operable to set a maximum offset of the moveable threshold from the clutch pedal position.

The electronic clutch pedal position processor may be further operable to adjust the moveable threshold by a very small amount each time the moveable threshold is calculated to allow for unintentional clutch pedal position changes.

If the magnitude of the moveable threshold is less than the starting olutch position, the offset may be inoreased by subtraoting the very small amount from the ourrent value of the moveable threshold.

The very small amount may be less than 1% of the value of the offset.

The electronio clutch pedal position prooessor may be operable to supply the control output from the clutch position sensing system to a stop-start system of a motor vehicle for use in controlling the stopping and starting of an engine of the motor vehicle.

According to a third aspect of the invention there is provided a motor vehicle having an engine, a clutch the engagement state of which is controlled by a clutch pedal, a system to automatically stop and start the engine based upon at least changes in the position of the clutch pedal and a clutch position sensing system for sensing the position of the clutch pedal constructed in accordance with said second aspect of the invention.

The invention will now be described by way of example with reference to the accompanying drawing of which:-Fig.1A is a schematic representation of a motor vehicle having a stop-start system according to the invention; Fig.1B is a schematic representation of a clutch actuation system forming part of the stop-start system of Fig.1; -10 -Fig.2 is a schematic representation of the operational range of movement of a clutch pedal showing three predefined zones In accordance with the prior art; Fig.3 is a schematic chart showing the operating range of movement of a clutch pedal showing four predefined zones in accordance with the invention; Fig.4 is a flow chart showing a first embodiment of a method of producing a control output from a clutch position sensing system according to the invention; Fig.5 is a flow chart showing a second embodiment of a method of producing a control output from a clutch position sensing system according to the invention; Fig.6 is a schematic chart showing six clutch position changes and the resulting state transitions.

With reference to Figs.1A and lB there is shown & motor vehicle 5 having an engine 10 driving a multi-speed transmission 11. The transmission 11 is driveably connected to the engine 10 by a clutch 8 (not shown on Fig.1A) which is manually engaged or released by a driver of the motor vehicle 5 and has a gear selector (not shown) . The gear selector is mcveable between several positions including at least one position where a gear forming part of the multi-speed transmission is selected and a neutral position in which no gears of the multi-speed transmission are selected.

When the gear selector is moved to the neutral position the multi-speed transmission 11 is said to be in a neutral state in which drive cannot be transmitted by the multi-speed transmission and when the gear selector is moved to an in gear position the multi-speed transmission 11 is said to be in an in gear state in which drive can be transmitted by the multi-speed transmission.

-11 - An engine starter in the form of an integrated starter-generator 13 is driveably connected to the engine 10 and in this case is connected by a flexible drive in the form of a drive belt or chain drive 14 to a crankshaft of the engine 10. The starter-generator 13 is connected to a source of electrical energy in the form of a battery 15 and is used to start the engine 10 and which is recharged by the starter-generator when it is operating as an electrical generator.

The invention is not limited to the use of a starter-generator 13 and the starter-generator 13 could be replaced by a starter motor for starting the engine 10.

It will be appreciated that during starting of the engine 10 the starter-generator 13 drives the crankshaft of the engine 10 and that at other times the starter-generator is driven by the engine 10 to generate electrical power.

A driver operable on/ off device in the form of a key operable ignition switch 17 is used to control the overall operation of the engine 10. That is to say, when the engine is running the ignition switch 17 is in a key-on' position and when the ignition switch 17 is in a key-off' position the engine 10 is not able to run. The ignition switch 17 also includes a third momentary position used to manually start the engine 10. It will be appreciated that other devices may be used to provide this functionality and that the invention is not limited to the use of an ignition switch.

An electronic control unit 16 is connected to the starter-generator 13, to the engine 10, to a gear selector sensor 12 used to monitor whether the transmission 11 is in neutral or in gear, to a road speed sensor 21 used to measure the rotational speed of a road wheel 20, to a brake pedal position sensor 24 used to monitor the position of a brake pedal 23, to a clutch pedal position sensing system used to monitor the position of a clutch pedal 25 and to a -12 -throttle position sensor 19 used to monitor the position of an accelerator pedal 18. The accelerator pedal 18 provides a driver input of required power output from the engine 10.

Tf the accelerator pedal 18 has been moved from a rest position it is said to be in a pressed position or in a pressed state.

Although the measurement of motor vehicle speed is described above with reference to the use of a road wheel sensor 21 because such sensors are often already present on a motor vehicle as part of a brake anti-lock system it will be appreciated that other suitable means can be used to determine the speed of the motor vehicle 5 such as, for example, a sensor measuring the rotational speed of an output shaft from the transmission 11.

It will be appreciated that the term gear selector sensor is not limited to a sensor that monitors the position of the gear seleotor but rather is any device which oan provide & feedback of whether the transmission 11 is in gear or in neutral.

Similarly, the term brake pedal sensor is not limited to a sensor that monitors the position of the brake pedal but rather is any device that provides feedback of whether an operator of the motor vehicle 5 has applied pressure to the brake pedal 23 to apply the brakes of the motor vehicle 5. For example the brake pedal sensor could monitor the pressure of the fluid in one or more brake lines. When the brake pedal 23 has been pressed sufficiently to apply the brakes it is said to be in a pressed state or in a pressed position.

In this case the clutch pedal position sensing system comprises a linear position sensor 26 used to monitor the actual position of the clutch pedal 25 and an electronic clutch pedal position processor (EC3P) 160 used to process -13 -the position signal from the olutoh position sensor 26 into a control output for use by the electronic control unit 16 using logic stored in the EO3P 160.

The clutch position sensor 26 may comprise one or more position sensors such as rotary potentiometers.

The determination of the state of the clutch pedal 25 as pressed or released is performed by the EO3P 160 forming part of the electronic control unit 16 using the clutch position signal received from the position sensor 26. The clutch position signal represents the current position (CP) of the clutch pedal 25.

As shown in Fig.lB a clutch actuation system is formed in this case by the clutch pedal 25, a hydraulic master cylinder 27, a hydraulic slave cylinder 28 and a clutch release lever 29 which engages and releases the clutch 8 via a release bearing 9. It will however be appreoiated that other means could be used for converting movement of the clutch pedal 25 into engagement or disengagement of the clutch 8 and that the invention is not limited to the use of a hydraulic clutch actuation system.

It will also be appreciated that the electronic clutch pedal position processor (FC3P) 160 could be a separate unit and may not be formed as part of the main stop-start electronio control unit 16.

The electronic control unit 16 receives several signals from the engine 10 including a signal indicative of the rotational speed of the engine 10 from a speed sensor (not shown) and sends signals to the engine used to control shutdown and start-up of the engine 10. In this case the engine 10 is a spark ignited engine 10 and the signals sent from the electronic control unit 16 are used to control a fuel supply system (not shown) for the engine 10 and an -14 -ignition system (not shown) for the engine 10. If the engine 10 were to be a diesel engine then only the fuel supply to the engine would be controlled. The electronic control unit 16 comprises of various components including a central processing unit, memory devices, timers and signal processing devices to oonvert the signals from the sensors connected to the electronic control unit 16 into data which is used by the electronic control unit 16 to control the operation and, in particular, the automatic stopping and starting of the engine 10.

During normal engine running the electronic control unit 16 is operable to control the fuel supplied to the engine 10 and to adjust the ignition system so that sparks are supplied to the engine 10 from spark plugs at the correct timing to produce the desired engine torque.

The electronic control unit 16 controls the operation of the engine 10 whioh is operable in two modes, a first or automatic stop-start running mode and a second or continuous running mode. However, it will be appreciated that one or more separate electronic controllers could be used to control the normal running of the engine 10 and the electronic controller 16 may only control the switching of the engine 10 between the two modes of operation and the automatic stopping and starting of the engine 10.

The electronio oontrol unit 16 is further operable to determine whether it is appropriate to run the engine 10 in the first mode by checking one or more engine operating parameters before permitting operation in the first mode.

These engine operating parameters include the engine coolant temperature, whether any catalytic converters associated with the engine are lit-off and whether the engine is rotating within a predetermined speed range. For example, if the coolant temperature is less than say 65°C or -15 -the catalytic converter is nct lit-cff or the engine speed is greater than say 1100 revolutions per minute (RPM) then entry to the first mode is barred and the electronic control unit 16 is operable to operate the engine 10 in a warm up mode in which the engine 10 is run continuously irrespective of whether the motor vehicle 5 is moving or is stationary.

As soon as it is determined that the engine operating conditions have been met then the stop-start system is placed in the first mode of operation when one or more predetermined engine stop and start conditions exist.

These engine stop and start oonditions are for a stop in neutral system based upon the signals received by the electronic control unit 16 from the gear selector sensor 12 and the EC3P 160. If the control output from the EC3P 160 indicates that the clutch pedal 25 is not being pressed and the signal from the gear selector sensor 12 indicates that neutral has been selected then the engine 10 is stopped and when the control output from the EC3P 160 indicates that the clutch pedal 25 is being pressed then the engine 10 is re-started either immediately or when the gear selector sensor indicates that neutral is no longer selected.

It will be appreciated that a further operating condition that is used by many systems is whether the motor vehicle 5 is moving. In such a case, operation in the first mode is inhibited if the speed of the motor vehicle 5 is above a predefined low speed.

Referring now to Fig.3 there is shown in a diagrammatic manner how the FC3P 160 processes the output signal from the clutch pedal position sensor 26 into zones of operation based upon a percentage of the fully depressed position.

-16 -In a zone "11" the control output from the EC3P 16C will indicate that the clutch pedal 25 is released that is to say the clutch 8 is engaged.

In a zone "D" the control output from the EC3P 160 will indicate that the clutch pedal 25 is being depressed and the clutch 8 is disengaged.

In a zone "F" in which the bite point of the clutch 8 is located, the control output from the EC3P 160 will indicate that the clutch pedal 25 is being pressed.

In a transition zcne "P cr R" the contrcl output from the EC3P 160 will be dependent upon the location and motion of the clutch pedal 25.

The released zone "R" is defined by a lower limit of 0% and an upper predefined fixed limit of Li which in this case is 10%.

The depressed zone "D" is defined by an upper limit of 100% and a predefined fixed threshold of 1h2 which in this case is 70%.

The transition zone "P or R" is defined by the lower predefined fixed limit Ll and by an upper predefined fixed limit Lu which in this case is 30%. The upper predefined fixed limit Lu is chosen such that it has a positional value less than an expected bite point of the clutch 8 but greater than the positional value due to displacement of the clutch pedal 25 due to a driver riding the clutch pedal 25.

The pressed zone "P" is defined by the lower predefined fixed limit Lu and by the predefined fixed threshold Th2.

A further moveable tracking threshold Thi operates within the transition zone P or R' and is constrained by -17 -the lower limit Ll and by the upper limit Lu. That is to say, Lu »= Thl »= Ll.

Overall operation of the FC3P 160 will now be explained with reference to six example state transitions numbered "A" to "F" on Fig.3.

State transition "A" shows a transition in clutch pedal position (CP) out of Pressed, in the direction of Released.

The crossing the upper limit Lu of the transition zone in this direction will result in a change in state of the control output from the EC3P 16C from pressed to released.

The state transition "C" in which the clutch pedal position moves from the transition zone into the pressed zone will always result in a pressed output. Whether a change in state occurs when the upper fixed limit LU is crossed will depend upon whether the original state is released or pressed.

The state transition "E" in which the clutch pedal position OP crosses the lower limit Ll from the released zone into the transition zone results in a transition in the control output from the EC3P 160 from released to pressed.

The state transition "F" shows a transition out of transition zone across the lower fixed limit Ll in the direction of Released. Crossing the lower limit Ll of the transition zone in this direction will always result in a transition in the control output from the EC3P 160 from pressed to released if the original state was pressed or maintain the state as released if the original state was released.

State transition "B" shows a movement of the clutoh pedal position within the transition zone towards the depressed position (depression increasing) following a -18 -reduction in clutch pedal depression such as the clutch transition "A". That is to say the clutch was released to a clutch pedal position XC, where XC represents the most-released clutch pedal position within the bounds of the transition zone and is now being moved in the opposite direction so that olutoh pedal depression inoreasing. Xl is the final resting position of the clutch pedal and x' is the displacement of the clutch pedal.

A transition window (not shown on Fig.3) lies to the pressed side of the clutch pedal position XO the width of the transition window is in this oase a predefined small amount w' whioh is the offset between the original position XC and the tracking threshold Ihi. The location of the transition window to the pressed side of XC is because the tracking threshold Ihl follows or trails the position of the clutch pedal 25 by the offset w' and the motion to arrive at XC was from Pressed towards Released. In the example shown Xl is shown displaced from XC by a distance x' equal to w' so it lies at the threshold TM and the clutch state remains released because the tracking threshold Thl has not been crossed. If the tracking threshold Ihl had been crossed that is to say x' > w' the state would have changed to pressed because the tracking threshold TM has been crossed.

Continued movement of the clutch pedal position in the same direction as that discussed above will not move the tracking threshold Ihi until the clutch pedal position has moved in the clutch depressing direction more than the width w' of the transition window past the current position of the tracking threshold Thl. Note that the transition window will then flip so as to lie to the released side of the clutch pedal position as soon as the trailing Threshold Thi is traversed.

-19 -Because no transition window is present to the released side of the clutch pedal position XC no change in state will occur if the clutch pedal position continues to move from the position XC. The tracking threshold Thl will follow it a distance w' behind so as to maintain a small transition window to the pressed side of the clutch pedal position.

State transition "C" shows a movement of the clutch pedal position within the transition zone towards the released position (depression reducing) that follows a movement towards the depressed state such as "d".

In such a case the transition window will lie to the released side of the clutch pedal position ZO because it has moved from a more released position towards a less released position and in this case a previous tracking threshold has been crossed resulting in the state being pressed. If the clutch pedal is moved from ZO to Z1 in a clutch pedal releasing direction a distance of z' then no change in state will occur because in this case z' = w' where w' is the width of the transition window bounded at the released end by the tracking threshold Ihi. If however z' increases more than w' that is to say the clutch pedal position traverses the tracking threshold Thl then the state will change from pressed to released and the transition window will lie to the pressed side of the clutch pedal position.

Continued movement of the clutch pedal position in the sane direction as that discussed above will not move the tracking threshold Thl until the clutch pedal position has moved in the clutch releasing direction more than the width w' of the transition window past the current position of the tracking threshold Thi.

Because no transition window is present to the pressed side of the clutch pedal position ZC no change in state will occur if the clutch pedal position moves from the position -20 -ZO in the pressed direction. The tracking threshold Thi will follow it a distance w' behind so as to maintain a small transition window to the released side of the clutch pedal position until the value of the tracking threshold is equal to the upper fixed limit Lu. Note that the upper fixed limit Lu will have no effect in this case because the state is already pressed.

Therefore, a moveable tracking threshold Thi is set that follows the actual position of the clutch pedal 25 (OP on Figures 4 and 5) as the driver presses and releases the clutch pedal 25 and this tracking threshold Thi is used while the clutch pedal position remains within the transition zone to effect changes in state when a small clutch pedal position change occurs in an opposite direction to the previous clutch pedal direction.

By setting the offset of the tracking threshold Thi to be a small number such as for example 5% of total clutch pedal position travel relatively small changes in clutch pedal position can be used to effect clutch pedal position state changes.

The tracking threshold Thl follows the clutch pedal position at a fixed distance referred to as a transition offset w' when the clutch pedal position is moving away from the trailing threshold Thl. The trailing threshold Thi will then start to track clutch pedal position when the clutch pedal position has moved more than the offset w' past the previous trailing threshold Thi. The moving threshold Thi is at all times constrained to remain between the lower limit Ll and the upper limit Lu.

To the driver of the motor vehicle 5 who rides the clutch pedal 25, movement of the clutch pedal 25 towards pressed, which is commonly used to trigger an engine start through the stop-start system, is a consistent distance (w%) -21 -of pedal travel away irrespective of the actual magnitude of clutch pedal depression due to the riding of the clutch pedal 25 within normal expected limits such as 15 to 25%.

Therefore improvements in the operation of the stop-start system can be produced by setting a trailing threshold Thl offset by a small value such as wI of clutch pedal position from a controlling value of clutch pedal position which if crossed causes a change in state.

The value of w-could for example be selected as 51-, which is a value large enough to avoid false transitions triggered by signal noise or unintentional driver's foot movements caused by vibration or twitches, but small enough to provide a sensation of eagerness of engine-start to the driver.

Note that to avoid rapid repeated transitions across boundaries hysteresis is provided to prevent rapid flip-flopping between states. That is to say two trailing thresholds are provided not one as discussed above.

A further refinement is to adaptively learn XO and ZO.

This allows for a driver's foot to creep in either direction while trying to hold the pedal still. Unintentional clutch pedal position changes are often referred to as clutch pedal creep. Using a time-based learning element, XO and ZO are allowed to slowly adapt to help avoid unnecessary state transitions. In this way, the start-stop system can differentiate between a tired foot and clear driver intentions. A clear driver's intention to further press or release the pedal indicating desire to pull away, change gear or fully engage the clutch would be defined as when a movement of magnitude greater than w% has been detected within a short pre-defined time period.

-22 -Referring now to Fig.6 there is shown in greater detail six clutch pedal position changes and how the trailing threshold Thi is arranged so as to define one end of a transition window having an opposite end located at the clutch pedal position used to set the trailing threshold ThI. Movement of clutch pedal position within the transition window will not produce a ohange in clutch pedal position state and will not move the position of the moveable trailing threshold Thl.

It will be appreciated that all determined states are supplied as an output from the 3C3P 16C to the electronic control unit 16 for use in controlling the stop-start system of the motor vehicle 5.

Transition Ti starts with OP = 100% and ends with CP=24. When the magnitude of OP falls below 70% corresponding to the fixed threshold Th2 the state changes from depressed to pressed. As the magnitude of the clutch pedal position OP continues to reduce the state remains as pressed until the upped fixed limit Lu is crossed at 30% at which point the state changes to released and will stay in the released state until it reaches the end of its change in position where the clutch pedal position is 24%. Note that in this case the transition window lies to the pressed side of the clutch pedal position Op =24% and that the trailing threshold Thi is offset towards the pressed direction by a distance of 5% so that Thi = 29%.

The transition window always lies to the side of the clutch pedal position that will cause a change in state from released to pressed or pressed to released.

Transition T2 is a clutch pedal position movement from 24% to 0% and follows transition Ti. In this case there will be no change in state because the state is already released and the clutch pedal position is moving towards the -23 -fully released position. The transition window will follow the clutch pedal position towards the released position but because the trailing threshold Thi lies to the pressed side of the clutch pedal position there is no state change threshold to be crossed.

Transition 13 is a clutch pedal position movement from 24% to 100% and follows transition Ti.

As the magnitude of clutch pedal position increases there is no change in state until the clutch pedal position is greater than the position of the trailing threshold TH1.

That is to say when the clutch pedal position CP is greater than 29% the state will change from released to pressed. As the magnitude of clutch pedal position OP continues to increase the state will remain pressed until the fixed threshold Th2 is crossed at 70%. Above 70% the state will change to depressed and remain in that state until the clutch pedal position reaches 100%.

Transition 14 starts with OP = 0% and ends with OP=24%.

As soon as the lower fixed limit Ll is crossed at 10% the state changes from released to pressed and will remain in that state until the clutch pedal position reaches 24%.

Because the clutch pedal position has moved from the released state towards the depressed state the transition window lies to the released side of the clutch pedal position OP and the trailing threshold Thl is offset 5% towards the released state from the clutch pedal position OP. Therefore although the clutch pedal position is the sane as that for transition Ti the location of the transition window is on the opposite side of the clutch pedal position OP.

-24 -Transition TO is from 24% to 0% and follows 14.

The clutch pedal position state after the transition 14 is initially pressed unlike the result from transition Tl to 24% which produced a released state.

As the magnitude of clutch pedal position reduces the state remains the same until the trailing threshold Thl is reached at 19%. As soon as the trailing threshold Thi is crossed the state changes to released and will stay in the sane state until the clutch pedal position reaches 0% the fully released position of the clutch pedal 25.

When the clutch pedal position magnitude falls below the current trailing threshold Thi it will cause the trailing threshold Ihl to flip to the pressed side of the clutch pedal position and the trailing threshold will then track the clutch pedal position CF trailing by 5% after the clutch pedal position has moved more than 5% past the previously set trailing threshold Thi until the trailing threshold Thi reaches the lower limit TA.

Transition 16 follows transition 14.

The initial state is pressed and this state is maintained until the fixed threshold Th2 is crossed at 70% after which it changes to depressed and remains in the depressed state as the clutch pedal is further depressed to the fully depressed position having a magnitude of 100%.

Note that because the trailing threshold Thl lies to the released side of the clutch pedal position it cannot be crossed. However when the magnitude of clutch pedal position increases from 24% the trailing threshold will follow until it reaches a maximum permitted value of 30% when the upper fixed limit Lu is reached.

-25 -The position of the transition window and henoe the trailing threshold Thl is therefore always to the side of the clutch pedal position that if the trailing threshold Thi is crossed while the clutch pedal position is within the transition zone will produce a change in state from pressed to released or vice-versa.

Referring now to Fig.4 there is shown a first embodiment of a method for producing a control output from the FC3P 16C employing a dynamic clutch function according to this invention.

The method in outline comprises initially setting the moving threshold Thl at the upper limit Lu of its permitted range. The function is then repeatedly executed, and at each execution a new location for the moving threshold (Thresh trnp) is calculated to be a fixed offset which in this case is 5% away from the current position of the clutch pedal (CP) . If the new location (Thresh tmp) , calculated, would be closer to the current pedal position (CP) then the new location is accepted as the Released to Pressed threshold position (Thi), otherwise the prior value of the threshold Thi is retained. In either event, the value for the threshold Thi is constrained to the upper and lower limits Lu, Ll which in this case are 30% and 10% respectively.

In detail the method starts at step 100 in which the motor vehicle 5 is not operating, then at step 105 a key-on event occurs switching on the power to the motor vehicle systems and in particular to the electronic control unit 16, the clutch pedal sensor 26 and the EC3P 160.

Then in step 110 the EC3P 160 is initialised by setting ThI equal to the fixed upper limit Lu namely 30% this is normally achieved by ensuring that the clutch pedal 25 has been fully depressed before the method can commence proper.

-26 -That is to say in practice there is a further step 107 (nct shown) in which it is tested whether the clutch pedal 25 has been fully depressed and, if it has not, the method loops back to step 105 and, if it has, the method advances to step 110 with the trailing threshold set to Lu. After step 110 the method advances to decision step 115.

In decision step 115 the current clutch pedal position (OP) is compared to the moving threshold Thl. If the magnitude of CP is the same or greater than Thl, then the result is to advance to step 120, whereas, if the magnitude of CF is less than Thi, the result is to advance to step 130.

Dealing first with a case where OP is greater than or equal to the moving threshold Thl the method continues in step 120 with a comparison of OP with Th2 which is the lower threshold for the depressed zone. If CF is greater or equal to Th2 the state is resolved in step 124 as being Depressed' and a corresponding control output is provided to the electronic control unit 16 and, if OP is less than Th2 the state is resolved in step 122 as being Pressed' and a corresponding control output is provided to the electronic control unit 16. The nature of the control output will depend upon the specific design of the EC3P 160 but could for example be a two bit output having the following designations [00] is indicative of a Released Clutch pedal position State; [01] is indicative of a Pressed Clutch pedal position State and [11] is indicative of a Depressed Clutch pedal position State.

Then from steps 122 and 124 the method advances to step where a temporary threshold Thresh tmp is set equal to OP minus the transition offset (wI) The method then advances to step 126 where the temporary threshold Thresh tmp is compared to the current -27 -value of the tracking threshold Thl and, if the value of Thresh tmp is greater than Thl the method advances to step 128 where Thl is set to Thresh_tmp and if Thresh tmp is not greater than Thl, then in step 127 Thl remains unchanged.

Reverting back to step 130, where the state is resolved as being Released' and a corresponding control output is provided from the EC3P 160 to the electronic control unit 16, the method advances from step 130 to step 132.

In step 132 the temporary threshold Thresh_tmp is set equal to OP plus the transition offset (wI) The method then advances to step 134 where the temporary threshold Thresh tmp is compared to the current value of the tracking threshold Thl and, if the value of Thresh tmp is less than Thl the method advances to step 138 where Thl is set to Thresh tmp and, if Thresh_tmp is not less than Thi, then in step 136 Thi remains unchanged.

Following on from any of the steps 127, 128, 136 and 138 the method advances to step 140 where it is ensured that the value of Thl produced from the preceding step 127 or 128 or 136 or 138 is within the upper and lower limits Lu and Ll respectively. That is to say if Thl greater than Lu its value is reduced to be equal to Lu and similarly if the value of Thi is less than Ll its value is increased to be equal to Ll.

The method then advances from step 140 to step 150 where it is tested whether the key-on state is still present. If the key-on' state is still present indicating that the power remains on then the method returns to step and the steps 115 to 150 are repeated otherwise it ends at step 160. The method steps 115 to 150 are repetitively executed every 20 to SOms so long as the power remains on.

-28 -Numerical examples of the operation of the method shown in Fig.1 are set out below based on the transitions given in Fig. 6 Transition Ti in which CP goes from 100% to 24% Where: -CP = 100% CP* is the olutch pedal position value upon which the calculations are based.

In this case the clutch pedal position value has a magnitude of 100.

Thl = 30% -(ti asnnc he!preater Than 3O dine nno the chinn!pina step 14C) Th2 = 70% Li = 10% Lu = 30% Offset w' = 5% Step No. Test or Action Result 100 > 30 Yes Go to 120 100 > 70 Yes go to 124 124 SiaLe = D OuLpul SLaLe Depressed 100 -5 Thresh tmp = 95 126 95 > 30 Yes Go to 128 128 Set Thi = 95 Thi = 95 Clip Thl Thi = 30 Transition Ti in which CD goes from 100% to 50% Where: -CP' = 50% Thl = 30% . (!_!t1 canncu ho grcatcr Than SOb duo on tho o.hiopincr stop 140) Th2 = 70% Ll = 10% Lu = 30% Offset w' = 5% -29 -Step No. Test or Action Result 50 > 30 Yes Go to 120 50 > 70 No go to 122 122 State = P Output State Pressed 50 -5 Thresh tmp = 45 126 45 > 30 Yes Go to 128 128 Set Thi = 45 Thl = 45 Clip Thl Thl = 30 Transition Ti in which the magnitude of OP goes from 50% to 24% Where:-CP* = 24% Thl = 30%. (ti armor he greater hor 3 ()dre go the o lopina step i-i'::) Th2 = 70% Li = 10% Lu = 30% Offset w' = 5% Step No. Test or Action Result 24 > 30 No Go to 130 State = R Output State Released 132 24 -I-5 Thresh tmp = 29 134 29 < 30 Yes Go to 138 138 Set Thi = 29 Thi = 29 Therefore at the end of transition Tl the clutch state is released, the clutch pedal position is 24%, the transition window lies to the pressed side of the clutch pedal position with the trailing threshold Thi positioned a distance 5% from the clutch pedal position.

Transition T2 in which OP goes from 24% to 20% Where: -CP = 20% Thl = 29% Th2 = 70% Ll = 10% Lu = 30% Offset w' = 5% -30 -Step No. Test or Action Result 20 > 29 No Go to 130 State = R Output State Released 132 20 -I-5 Thresh tmp = 25 134 25 C 29 Yes Go to 138 138 Set Thi = 25 Thl = 25 Therefore there has been no change in state but the tracking threshold has followed the clutch pedal position so as to remain 5% offset with the transition window to the pressed side of the clutch pedal position.

Transition 12 in which CP goes from 20% to 0% Where: -CP = 0% Thl = 25% Th2 = 70% Ll = 10% Lu = 30% Offset w' = 5% Step No. Test or Action Result 0 > 25 No Go to 130 State = R Output State Released 132 0 + 5 Thresh tmp = 5 134 5 < 25 Yes Go to 138 138 Set Thi = 5 Thl = 5 Clip Thl Thl = 10 Therefore there has been no change in state and the tracking threshold Thl has been prevented from falling below 10%) the transition window remains on the pressed side of the clutch pedal position but in this case is positioned 10% away due to the olipping effeot of step 140.

Transition 13 in which OP goes from 24% to 28% Where: - CP = 28% Thl = 29%-Th2 = 70%-Ll = 10% Lu = 30% Offset w' = 5% -31 -Step No. Test or Action Result 28 > 29 No Go to 130 State = R Output State Released 132 28 -I-5 Thresh tmp = 33 134 33 C 29 No Go to 136 136 Set Thi = Thi Thl = 29 Therefore there has been no change in state and the tracking threshold Thl has not moved but in this case is positioned 1% away.

Transition 13 in which CP goes from 28% to 29.5% Where: -CP = 29.5% Thi = 29% Th2 = 70% Li = 10% Lu = 30% Offset w' = 5% Step No. Test or Action Result 29.5 > 29 Yes Go to 120 29.5 > 70 No go to 122 122 State = P Output State Pressed 29.5 -5 Thresh tmp = 24.5 126 24.5 > 29 No Go to 127 127 Set Thl = Thl Thl = 29 There has been a change in state and the tracking threshold Thl has remained the same. The transition window has flipped from the pressed side of the clutch pedal position to the released side of the clutch pedal position so that the tracking threshold remains on the side of the clutch pedal position in which a state change will occur if it crossed.

Note that in this case the tracking threshold is positioned 0.5% away. In practice a hysteresis band is used to prevent flip-flopping when the clutch pedal position is located within say 3l of the tracking threshold after the tracking threshold has been crossed.

-32 -Transition T3 in which OP goes from 29.5% to 50 Where: -ON = 50% Thl = 29% Th2 = 70% Li = 10 Lu = 30 Offset w' = 5 Step No. Test or Action Result 50 > 29 Yes Go to 120 50 > 70 No go to 122 122 State = P Output State Pressed 50 -5 Thresh tmp = 45 126 45 > 29 Yes Go to 128 128 Set Thi = 45 Thi = 45 Clip Thl Thi = 30 There has been no change in state and the tracking threshold Thi has been clipped to 30. The transition window 13 has remained on the released side of the clutch pedal position so that the traoking threshold remains on the side of the clutch pedal position in which a state change will occur if it crossed.

Transition T3 in which CP goes from 50% to 100% Where: -CP = 100% Thl = 30% Th2 = 70% Ll = 10% Lu = 30% Offset w' = 5% Step No. Test or Action Result 100 > 30 Yes Go to 120 100 > 70 Yes go to 124 124 State = D Output State Depressed 100 -5 Thresh tmp = 95 126 95 > 30 Yes Go to 128 128 Set Thi = 95 Thl = 95 Clip Thl Thi = 30 -33 -There has been a change in state from pressed tc depressed because the upper fixed threshold Th2 has been crossed and the tracking threshold Thl has been clipped to 30. The transition window remains on the side of the clutch pedal position in which a state change will occur if it crossed.

Transition T4 in which CP goes from 0% to 14% Where: -ON = 14% Thl = 10% (Due to Clipping) Th2 = 70% Ll = 10% Lu = 30% Offset w' = 5% Step No. Test or Action Result 14 > 10 Yes Go to 120 14 > 70 No go to 122 122 State = P Output State Pressed 14 -5 Thresh tmp = 9 126 9 > 10 No Go to 127 127 Set Thl = Thl Thl = 10 There has been a change in state from released to pressed because the lower limit Ll has been crossed and the tracking threshold Thl remains at 10. The transition window remains on the side of the clutch pedal position in which a state change will occur if it crossed but has flipped compared to its original position it now lies to the released side of the clutch pedal position.

Transition T4 in which OP goes from 14% to 18% Where: -ON = 18% Thl = 10% (Due to Clipping) Th2 = 70% Ll = 10% Lu = 30% Offset w' = 5% -34 -Step No. Test or Action Result 18 > 10 Yes Go to 120 18 > 70 No go to 122 122 State = P Output State Pressed 18 -5 Thresh tmp = 13 126 13 > 10 Yes Go to 128 128 Set Thl = 13 Thl = 13 The state of the clutch pedal remains pressed because the trailing threshold has not been crossed because the clutch pedal position is moving away from the trailing threshold Thl. The threshold Thl is now spaced 5% from the clutch pedal position to the side of the clutch pedal position that if crossed would cause a change in state.

Transition T4 in which CP goes from 18% to 24% Where: -CP = 24% Thl = 13% Th2 = 70% Ll = 10% Lu = 30% Offset w' = 5% Step No. Test or Action Result 24 > 13 Yes Go to 120 24 > 70 No go to 122 122 State = P Output State Pressed 24 -5 Thresh tmp = 19 126 19 > 13 Yes Go to 128 128 Set Thl = 19 Thl = 19 The state of the clutch pedal position has remained unchanged and the trailing threshold has tracked the clutch pedal position to remain 5% offset from it. The transition window lies to the released side of the clutch pedal position.

Note that in this case the trailing threshold is positioned to the released side of the clutch pedal position -35 -at a location of 19% whereas in the case of transition 1 for the same clutch pedal position the trailing threshold lies to the pressed side of the clutch pedal position at a location of 29%.

Transition 15 in which CP goes from 24% to 18% Where: -ON = 18% Thl = 19% Th2 = 70%: Ll = 10% Lu = 30% Offset w' = 5% Step No. Test or Action Result 18 > 19 No Go to 130 State = R Output State Released 132 18 + 5 Thresh tmp = 23 134 23 C 19 No Go to 136 136 Set Thl = Thl Thi = 19 Because the trailing threshold Thl has been crossed the state has changed from pressed to released but the threshold has not been moved because the olutch pedal position is not more than 5% lower than the current trailing threshold position. Note that the transition window now lies to the pressed side of the clutch pedal position having flipped when the trailing threshold Thi was crossed. Note that in practice a hysteresis band would be provided so that small changes back towards the pressed state would not cause flip flopping.

Transition IS in which OP goes from 18% to 12% Where: - CP = 12% Thl = 19% 1h2 = 70%-Li = 10% Lu = 30% Offset w' = 5% -36 -Step No. Test or Action Result 12 > 19 No Go to 130 State = R Output State Released 132 12 + 5 Thresh tmp = 17 134 17 C 19 Yes Go to 138 138 Set Thl = 17 Thl = 17 No change in state has occurred and the transition window remains on the pressed side of the clutch pedal position but the trailing threshold has begun to track the clutch pedal position so as to trail it by 5%.

Transition 15 in which CP goes from 12% to 0% Where: -CP = 0% Thl = 17% Th2 = 70% Ll = 10% Lu = 30% Offset w' = 5% Step No. Test or Action Result 0 > 17 No Go to 130 State = R Output State Released 132 0 + S Thresh tmp = 5 134 5 < 17 Yes Go to 138 138 Set Thl = 5 Thl = 5 Clip Thl Thl = 10 The state of the clutch pedal position has not changed and the transition window remains to the pressed side of clutch pedal position but the trailing threshold is constrained to remain at 10%.

Transition 16 in which CP goes from 24% to 28% Where: -CP = 28% Thl = 19% 1h2 = 70% Ll = 10% Lu = 30% Offset w' = 5% -37 -Step No. Test or Action Result 28 > 19 Yes Go to 120 28 > 70 No go to 122 122 State = P Output State Pressed 28 -5 Thresh tmp = 23 126 23 > 19 Yes Go to 128 128 Set Thi = 23 Thi = 23 There has been no change in state but the trailing threshold has moved so as to track the clutch pedal position.

Transition 16 in which OP goes from 28% to 50% Where: -CP = 50% Thl = 23%-Th2 = 70% Li = 10% Lu = 30% Offset w' = 5% Step No. Test or Action Result 50 > 23 Yes Go to 120 50 > 70 No go to 122 122 State = P Output State Pressed 50 -5 Thresh tmp = 45 126 45 > 23 Yes Go to 128 128 Set Thl = 45 Thl = 45 Clip Thl Thi = 30 There has been no change in state, the transition window still lies to the released side of the clutch pedal position but the trailing threshold is now fixed to the upper limit Lu due to clipping.

Transition T6 in which OP goes from 50% to 100% Where: -CP = 100% Thi = 30% Th2 = 70% Ll = 10% Lu = 30% Offset w' = 5% -38 -Step No. Test or Action Result 100 > 30 Yes Go to 120 100 > 70 Yes go to 124 124 State = D Output State Depressed 100 -5 Thresh tmp = 95 126 95 > 30 Yes Go to 128 128 Set Thi = 95 Thl = 95 Clip Thl Thl = 30 The trailing threshold Thl remains constrained by clipping at the upper limit Lu but there has been a change of state due to the clutch pedal position crossing the fixed upper threshold Th2.

In accordance with a second embodiment of the invention a small adjustment (6), which might typically be 0.01%, is made to the position of the threshold (Thl) at each execution cycle to move the threshold away from the current clutch pedal position (CP) . The intention of this is to increase the separation between the moving threshold Thl and the current clutch pedal position CP up to the offset value if, for example, the driver's foot has moved (crept) slowly towards the moving threshold Thi. Unintentional clutch pedal position changes are often referred to as clutch pedal creep' . The effect of the adjustment is negligible in comparison to changes resulting from normal pedal movements but prevents incorrect changes of state from occurring due to gradual creep rather than positive driver intention.

The flowchart in Figure 5 shows in more detail the second embodiment of the method utilising a dynamic clutch function with the creep' adjustment added.

The method starts at step 200 in which the motor vehicle 5 is not operating, then at step 205 a key-on event occurs switching on the power to the motor vehicle systems -39 -and in particular to the electronic control unit 16, the clutch pedal sensor 26 and the EO3P 160.

Then in step 210 the FO3P 160 is initialised by setting Th equal to the fixed upper limit Lu namely 30% this is normally achieved by ensuring that the clutch pedal 25 has been fully depressed before the method can commence proper.

That is to say in practice there is a further step 207 (not shown) in which it is tested whether the clutch pedal 25 has been fully depressed and, if it has not, the method 1oops back to step 205 and, if it has, the method advances to step 210 with the trailing threshold set to Lu. After step 210 the method advances to decision step 215.

In decision step 215 the current clutch pedal position (OP) is compared to the moving threshold Thl. If OP is the sane or greater than Thl, then the result is to advance to step 220 and, if OP is less than Thl, the method advances to step 230.

Dealing first with a case where OP is greater than or equal to the moving threshold Thl the method continues in step 220 with a comparison of OP with Th2 which is the lower threshold for the depressed zone. If OP is greater or equal to Th2 the state is resolved in step 224 as being Depressed' and a corresponding control output is provided to the electronic control unit 16 and, if OP is less than Th2 the state is resolved in step 222 as being Pressed' and a corresponding control output is provided to the electronic control unit 16.

Then from steps 222 and 224 the method advances to step 225 where a temporary threshold Thresh tmp is set equal to OP minus the transition offset (wI) The method then advances to step 227 where the temporary threshold Thresh tmp is compared to the current -40 -value of the tracking threshold Thi minus the creep adjustment 6 and, if the value of Thresh tmp is greater than ThI minus 6 the method advances to step 229 where TM is set to Thresh_tmp and, if in step 227 Thresh_tmp is not greater than Thi minus 5, then in step 228 TM is set to Thi minus 5.

Reverting back to step 230, where the state is resolved as being Released' and a corresponding control output is provided from the EC3P 160 to the electronic control unit 16, the method then advances from step 230 to step 232.

In step 232 the temporary threshold Thresh tmp is set equal to OP plus the transition offset (wI) The method then advances to step 235 where the temporary threshold Thresh tmp is compared to the current value of the tracking threshold Thl plus the creep adjustment S and, if the value of Thresh tmp is less than ThI plus 6 the method advances to step 239 where Thi is set to Thresh tmp and, if in step 235 the value of Thresh tmp is not less than Thi plus 6, then in step 237 Thi is set to Thi plus 6.

Following on from any of the steps 228, 229, 237 and 239 the method advances to step 240 where it is ensured that the value of Thl produced from the preceding step 228 or 229 or 237 or 239 is within the upper and lower limits Lu and Ll respectively. That is to say if Thi greater than Lu its value is reduced to be equal to Lu and similarly if the value of Thl is less than Ll its value is increased to be equal to Id.

The method then advances from step 240 to step 250 where it is tested whether the key-on state is still present. If the key-on' state is still present indicating that the power remains on then the method returns to step -41 - 215 and the steps 215 to 250 are repeated otherwise it ends at step 260. The method steps 215 to 250 are repetitively executed every 20 to SOms so long as the power remains on.

It will be appreciated by those skilled in the art that, although the invention has been described by way of example with reference to one or more embodiments, it is not limited to the disclosed embodiments and that one or more modifications to the disclosed embodiments or alternative embodiments could be constructed without departing from the scope of the invention.

For example, the engagement state of the clutch could be inferred not directly from the clutch pedal but from a clutch release lever or another part of the clutch release mechanism.

Although the invention has been described above in reThtion to the use of a simple single value for the threshold between the Pressed and Released regions, it will be appreciated by those skilled in the art that as inferred above a single value for the moveable threshold can beneficially be replaced with two values working as a hysteresis pair. In this way, the Pressed to Released threshold would be slightly different to the Released to Pressed threshold and this would prevent rapid changing of the indicated clutch pedal state between Released and Pressed or vice-versa if the pedal were held close to a moveable threshold.

Furthermore, although the invention has been described with reference to a particularly advantageous use in respect of a stop-start system of a motor vehicle, it will be appreciated that other motor vehicle based systems may require an indication of clutch pedal position and that the invention can be applied to any such motor vehicle uses where clutch pedal position state is required.

Claims

Claims 1. A method of producing a control output from a clutch position sensing system wherein the method comprises monitoring the position of a clutch pedal of the motor vehicle, defining a transition zone defined by a range of clutch pedal positions in which the control output is one of two alternative clutch pedal position states comprised of a clutch pedal released state and a clutch pedal pressed state, setting a moveabie threshold offset from a clutch pedal starting position that if crossed when the clutch pedal position is within the transition zone will result in a change in clutch pedal position state and ohanging the control output from the current state to the alternative state if the moveable threshold is crossed.
2. A method as claimed in claim 1 wherein the method further comprises setting a maximum offset of the moveable threshold from the clutch pedal position.
3. A method as claimed in claim 1 or in claim 2 wherein, if the state of clutch pedal is the released state at the clutch pedal starting position, then the magnitude of the moveable threshold will have a magnitude greater than the magnitude of the clutch pedal starting position.
4. A method as claimed in any of claims 1 to 3 wherein, if the state of clutch pedal is the pressed state at the clutch pedal starting position, then the magnitude of the moveable threshold will have a magnitude less than the magnitude of the clutch pedal starting position.
5. A method as claimed in any of claims 1 to 4 wherein when the clutch pedal position and the moveable threshold are both within the transition zone, the method further comprises moving the moveable threshold so as to maintain a predefined offset from the clutch pedal position if the clutch pedal position moves from the clutch pedal starting position away from the moveable threshold.
6. A method as claimed in any of claims 1 to 5 wherein, if the clutch pedal position moves from the clutch pedal starting position towards the moveable threshold, the magnitude of the moveable threshold remains the same until the clutch pedal position has moved a predefined distance past the moveable threshold.
7. A method as claimed in any of claims 1 to 6 wherein the transition zone is bounded at a lower end by a lower clutch pedal position limit and at an upper end by an upper clutch pedal position limit.
8. A method as claimed in claim 7 wherein a released zone is defined by a range of clutch pedal positions bounded at one end by a clutch pedal fully released position and at an upper end by the lower clutch pedal position limit and the control output is always indicative of a released clutch pedal position state whenever the clutch pedal position is within the released zone and a pressed zone is defined by a range of clutch pedal positions bounded at one end by the upper clutch pedal position limit and bounded at an opposite end by a fixed upper threshold and the control output is always indicative of a pressed clutch pedal position state whenever the clutch pedal position is within the pressed zone.
9. A method as claimed in claim 8 wherein a depressed zone is defined by a range of clutch pedal positions bounded at one end by the fixed upper threshold and at an opposite end by a clutch pedal fully depressed position and the control output is always indicative of a depressed clutch pedal position state whenever the clutch pedal position is within the depressed zone.
10. A method as claimed in claim B or in claim 9 wherein the offset of the moveable threshold from the clutch pedal starting position defines a transition window bounded at one end by the position of the moveable threshold and at an opposite end by the starting clutch position and the transition window is always positioned to the side of the starting clutch position towards the clutch position zone of the alternative clutch position state.
11. A method as claimed in any preceding claim wherein the method further comprises adjusting the moveable threshold by a very small amount each time the moveable threshold is caloulated to allow for unintentional clutch pedal position changes.
12. A method as claimed in claim 11 wherein adjusting the moveable threshold comprises increasing the offset from the starting clutch pedal position to the moveable threshold by the very small amount each time the moveable threshold is calculated.
13. A method as claimed in claim 12 wherein, if the magnitude of the moveable threshold is greater than the starting clutch position, the offset is increased by adding the very small amount to the current value of the moveable threshold.
14. A method as olaimed in olaim 12 wherein, if the magnitude of the moveable threshold is less than the starting clutch position, the offset is increased by subtracting the very small amount from the current value of the moveable threshold.
15. A method as olaimed in any of claims 11 to 14 wherein the very small amount is less than 1% of the value of the offset.
16. A method as olaimed in any of claims 1 to 15 wherein the method further comprises supplying the control output from the clutch position sensing system to a stop-start system of a motor vehicle for use in controlling the stopping and starting of an engine of the motor vehicle.
17. A clutch position sensing system for sensing the position of a clutch pedal of a motor vehicle and providing a control output indicative of the positional state of the clutch pedal, the system comprising a position sensing means to provide a signal indicative of a current clutch pedal position and an electronic clutch pedal position processor to process the signal from the position sensing means wherein if the clutch pedal position is within a transition zone bounded by a fixed lower limit of clutch pedal position and an upper fixed limit of clutch pedal position in which the state of the clutch pedal position is one of released and pressed, the electronic clutch pedal position processor is operable to set a moveable threshold offset from a clutch pedal starting position that if crossed when the clutch pedal position is within the transition zone will result in a change in clutch pedal position state and change the control output from indicative of the current clutch pedal position state to indicative of the alternative clutch pedal position state if the moveable threshold is crossed.
18. A system as claimed in claim 17 wherein, if the clutch pedal is in the released state at the clutch pedal starting position, the electronic clutch pedal position processor is operable to set the moveable threshold value so as to have a magnitude greater than the magnitude of the clutch pedal starting position and if the clutch pedal is in the pressed state at the clutch pedal starting position, the electronic clutch pedal position processor is operable to set the moveable threshold value so as to have a magnitude less than the magnitude of the clutch pedal starting position.
19. 7 system as claimed in claim 17 or in claim 18 wherein the electronic clutch pedal position processor is operable to set a maximum offset of the moveable threshold from the clutch pedal position.
20. A system as claimed in any of claims 17 to 19 wherein the electronic clutch pedal position processor is further operable to adjust the moveable threshold by a very small amount each time the moveable threshold is calculated to allow for unintentional clutch pedal position changes.
21. A system as claimed in any of claims 17 to 20 wherein the electronic clutch pedal position processor is operable to supply the control output from the clutch position sensing system to a stop-start system of a motor vehicle for use in controlling the stopping and starting of an engine of the motor vehicle.
22. A motor vehicle having an engine, a clutch the engagement state of which is controlled by a clutch pedal, a system to automatically stop and start the engine based upon at least changes in the position of the clutch pedal and a clutch position sensing system for sensing the position of the clutch pedal as claimed in any of claims 17 to 21.
23. A method of producing a control output from a clutch position sensing system substantially as described herein with reference to Figs.3 to 6 of the accompanying drawing.
24. r clutch position sensing system for sensing the position of a clutch pedal substantially as described herein with reference to Figs.1A and 13 of the accompanying drawing.
25. A motor vehicle substantially as described herein with reference to Figs.1A and 13 of the accompanying drawing.