GB2491697A

GB2491697A - A method and apparatus of controlling a clutch during a free rolling start

Info

Publication number: GB2491697A
Application number: GB1208981.9A
Authority: GB
Inventors: Ian Halleron; Themi Philemon Petridis; Peter George Brittle; Martin Robekowski
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2011-06-09
Filing date: 2012-05-22
Publication date: 2012-12-12
Anticipated expiration: 2032-05-22
Also published as: RU2012123984A; CN102818012B; GB2491697B; DE102012208996A1; GB201109670D0; CN102818012A; RU2599860C2; GB2491628A; GB201208981D0

Abstract

A method and apparatus of controlling an engagement of a clutch 53 of a motor vehicle 51 in which during a free rolling start, if a transmission ratio of a manual transmission 55 selected for the engagement is currently unsuitable, the engagement of the clutch 53 is inhibited. The engagement of the clutch 53 may be inhibited by preventing engagement of the clutch 53 until a speed of an engine 52 connected to the manual transmission 55 is predicted to fall within a predefined speed range. A human machine interface 66 is connected to an electronic control unit 60 which controls the clutch, e.g. an e-clutch 53, and provides to a driver an indication that the selected gear is unsuitable. The clutch 52 is engaged/disengaged by a hydraulically operated slave cylinder 59 and inhibiting engagement of the clutch 53 comprises preventing release of hydraulic pressure from the cylinder 59.

Description

A METHOD AND APPARATUS FOR CONTROLLING

THE ENGAGEMENT OF A CLUTCH

This invention relates to a motor vehicle having stop-start control and in particular to the control of a clutch of such a motor vehicle during a free rolling start.

For a manual transmission motor vehicle that uses Rolling Stop-Start (RSS) technology, in which the engine is shut off whilst the vehicle is moving so as to effect free rolling', there is a risk that the driver may selects an unsuitable gear and engage the clutch when effecting a free rolling start (FR) A free rolling start as meant herein is a restarting of the engine while the motor vehicle is moving and the engagement of the clutch so as to provide a drive path from the engine to the road. As discussed below, the transmission may either remain in gear while the vehicle is free rolling or may be placed in neutral while the vehicle is free rolling.

There are two main types of manual transmission RSS system which are referred to as Stop-in-Neutral RSS (SIN) and Stop-in-Gear RSS (SIG) For one type of RSS (SIN) system, the stop conditions are that the driver must select neutral and release the clutch pedal for the engine to shut down whilst the vehicle is moving. The start conditions reguired in order to effect an engine restart are that the driver must depress the clutch pedal to trigger the restart.

For one type of RSS (SIG) system the conditions for engine shut-down are that the clutch pedal is depressed, a gear remains selected and the accelerator pedal is not being pressed. In this case the conditicn for an engine restart is typically the driver pressing the accelerator pedal.

If an e-clutch is used for a RSS (SIG) system to disconnect the driveline whilst the transmission remains in gear, the engine shut-down conditions are that the accelerator pedal is not being pressed (the e-clutch being automatically dis-engaged) and the start conditions are the driver requesting torque by pressing the accelerator pedal or the driver pressing the clutch pedal.

An e-clutch is an electronically controlled clutch in which the clutch pedal position is monitored using a sensor and the actual clutch engagement/disengagement is performed via an electronically controlled actuator.

For a RSS (SIN) system without an e-clutch, the engine will always be restarted when the clutch pedal is pressed, however if a higher gear than is suitable is selected, for example fifth gear is selected when the vehicle speed is say only 2Okph, when the clutch pedal is released by the driver and the clutch is engaged the vehicle will judder and struggle to transmit requested torque.

Conversely, if a lower gear than is suitable is selected, for example if second gear is selected when the vehicle speed is say 6Okph, when the clutch is engaged by the driver there is a risk of engine and or transmission damage and potential drivability issues (e.g. skidding or loss of control) may occur.

For a RSS (SIG) system without an e-clutch, from the stop in gear restart conditions when the vehicle is moving, the clutch pedal is already pressed and a gear is already selected, if the clutch pedal is released before the accelerator pedal is pressed, then the driveline will be engaged directly without the engine being started via the starter motor.

If IRSS (SIG) is employed with an e-clutch, from the engine-off condition a driver could select an unsuitable gear either with or without pressing the clutch pedal.

Therefore with all types of RSS system there is the risk of the clutch being frequently engaged with a large speed differential across it which will cause excessive wear of the clutch.

It is an object of the invention to provide a method and apparatus for overcoming the above referred to problems associated with a free rolling start.

According to a first aspect of the invention there is provided a method of controlling the engagement of a clutch of a motor vehicle during a free rolling start, the motor vehicle having an engine driving a manual transmission via the clutch wherein the method comprises determining whether a transmission ratio selected for the free rolling start is suitable and, if the selected transmission ratio is unsuitable, inhibiting engagement of the clutch.

A transmission ratio may be unsuitable if the engine speed following the engagement of the clutch is predicted to be outside a predefined engine speed range.

If the selected transmission ratio is not suitable, the method may further comprise providing an indication to a driver of the motor vehicle that the selected gear is

unsuitable.

The method may further comprise inhibiting engagement of the clutch if a speed differential across the clutch is above a predefined differential speed limit.

The clutch may be engaged and disengaged by a hydraulically operated slave cylinder and inhibiting engagement of the clutch may comprise preventing the release of hydraulic pressure from the hydraulic slave cylinder so as to maintain the clutch in a disengaged state.

Inhibiting engagement of the clutch by the actuator may alternatively comprise one of delaying and slowing down engagement of the clutch.

Alternatively, the clutch may be an e-clutch and inhibiting engagement of the clutch may comprise maintaining the e-clutch in a disengaged state.

According to a second aspect of the invention there is provided an apparatus for controlling during a free rolling start the engagement of a clutch of a motor vehicle having an engine driving a manual transmission via the clutch, wherein the apparatus comprises an actuator to engage and disengage the clutch and an electronic control unit, wherein the electronic control unit is operable to determine whether a selected transmission ratio is suitable for clutch engagement and, if the selected transmission ratio is unsuitable, is further operable to inhibit engagement of the clutch by the actuator.

A transmission ratio may be unsuitable if the engine speed following engagement of the clutch is predicted to be outside a predefined engine speed range.

The apparatus may further comprise a Human Machine Interface operably connected to the electronic control unit and, if the selected transmission ratio is unsuitable, the electronic control unit may be operable to provide an indication to a driver of the motor vehicle via the Human Machine Interface that the selected gear is unsuitable.

The apparatus may further comprise an engine speed sensor and a means for determining the input speed of the manual transmission and the electronic control unit may be further operable to inhibit clutch engagement if the differential speed across the clutch is unacceptably high.

The actuator may be a hydraulically operated slave cylinder, the apparatus further comprises an electronically controlled valve operable by the electronic control unit to selectively control the flow of hydraulic fluid into and out of the slave cylinder and the electronic control unit may be operable to inhibit engagement of the clutch by the actuator by closing the electronically controlled valve when the clutch is in an engaged state to prevent the release of hydraulic pressure from the hydraulic slave cylinder thereby maintaining the clutch in the disengaged state.

Inhibiting engagement of the clutch by the actuator may comprise one of delaying and slowing down engagement of the clutch.

Alternatively, the clutch may be an e-clutch, the actuator may be an electronically controlled actuator controlled by the electronic control unit and the electronic control unit may be operable to inhibit engagement of the clutch by using the electronically controlled actuator to maintain the clutch in a disengaged state.

According to a third aspect of the invention there is provided a motor vehicle having a clutch control apparatus 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.1 is a schematic block diagram of a motor vehicle having a clutch control apparatus according to a first embodiment of a second aspect of the invention; Fig.2 is a schematic block diagram of a motor vehicle having a clutch control apparatus according to a second embodiment of the second aspect of the invention; Fig.3 is a flow chart of a first embodiment of a method for controlling the engagement of a clutch according to a first aspect of the invention; and Fig.4 is a flow chart of a second embodiment of a method for controlling the engagement of a clutch according to a first aspect of the invention.

Referring firstly to Fig.1 there is shown a motor vehicle 1 having a rolling stop-start system (RSS) . The motor vehicle 1 comprises an engine 2 driving a clutch 3, a multi-speed manual transmission 5 having an input shaft (not shown) driven by the clutch and a clutch control apparatus.

The term manual transmission' as meant herein is a transmission in which the various gear ratios are manually selected by a driver of the motor vehicle.

The clutch control apparatus comprises a hydraulic actuation system having a master cylinder 8 operable by a clutch pedal 7, a slave cylinder 9, an electronically controlled valve 12 and a actuation mechanism 4 in the form of a release lever and release bearing and an electronic control unit 10. The electronic control unit 10 has a number of inputs which include an engine speed input from an engine speed sensor 11, a selected gear sensor 6, a vehicle speed input from a wheel sensor 13 and various other inputs such as, for example, accelerator pedal position and brake pedal position as indicated generally on Fig.1 by the reference number 15.

The electronic control unit 10 is also connected to a Human Machine Interface 16 that can be used to provide information to a driver of the motor vehicle 1.

As is well known in the art, when a driver depresses the clutch pedal 7, the clutch master cylinder 8 is operated SO as to generate hydraulic pressure in a hydraulic path linking the master cylinder 8 to the slave cylinder 9 and the slave cylinder 9 in response to this increased hydraulic pressure moves the release lever of the release mechanism 4 thereby causing the release bearing to act against the clutch 3 thereby disengaging it. When the driver releases the clutch pedal 7 the hydraulic pressure in the system falls and the clutch 3 is engaged thereby facilitating drive from the engine 2 to the input shaft of the transmission 5.

In a first means for determining the input speed of the manual transmission 5 the selected gear sensor 6 provides a signal indicative of the currently selected gear to the electronic control unit 10 and the vehicle speed sensor 13 provides a signal indicative of the current vehicle speed and from these two signals, along with information regarding the final drive ratio of the motor vehicle 1 and the rolling radius of the tyres, the electronic control unit 10 determines the rotational speed of the input shaft of the transmission 5. As an alternative means for determining the input speed of the manual transmission 5, the motor vehicle 1 can be provided with a direct measurement of input shaft speed from a rotational speed sensor associated with the input shaft of the transmission 5.

In either case, the electronic control unit 10 determines whether the speed of the input shaft falls within a predefined rotational speed range bounded by an upper speed limit and a lower speed limit.

The upper speed limit is a speed that if the clutch 3 were engaged would result in the engine 2 rotating at an unacceptably high speed.

As an addition to the upper speed limit there could also be a speed differential limit to prevent engagement of the clutch 3 when the differential speed across the clutch 3 is unacceptably high. This requires knowledge of the current engine speed which can be obtained from the engine speed sensor 11.

The lower speed limit is a speed that if the clutch 3 were engaged would result in the engine 2 rotating at an unacceptably low speed, that is to say, an engine speed where insufficient torque would be produced by the engine 2 to enable a smooth pull away to occur.

The electronic control unit 10 is operable when a free rolling start is occurring to check whether the input shaft speed is within the predetermined speed range, if it is, no further action is taken but, if it is not, the electronic control unit 10 inhibits clutch engagement by closing the electronically operated valve 12 while the clutch 3 is disengaged and maintaining it closed until the input shaft speed falls within the predetermined speed range. This prevents the clutch 3 from being engaged while the unfavourable input speed conditions exist because the high hydraulic pressure is trapped in the slave cylinder 9 by the closed electronically controlled valve 12.

It will be appreciated that the input shaft speed could be brought into the predefined speed range by the driver changing gear to one that brings the input shaft speed within the predefined speed range or, if the transmission gear selected was unacceptably low so that the input shaft speed was too high, then the natural slowing of the motor vehicle 1 due to the lack of drive will eventually bring the input shaft speed within the predefined range.

If the speed differential across the clutch is also used to test the suitability for engagement of the clutch 3, then the act of the driver applying pressure to the accelerator pedal thereby increasing the engine speed may bring the speed differential below a maximum acceptable predefined differential speed limit.

To assist the driver of the motor vehicle 1, when the input shaft speed falls outside the predefined range, the electronic control unit 10 provides an indication to the driver that a gear change is required in order to perform the free rolling start.

In one embodiment, the electronic control unit provides via the Human Machine Interface 16 a graphical representation in the form of an illuminated up arrow or down arrow to show the driver the corrective action required.

In another embodiment, an alphanumeric message is displayed via the Human Machine Interface (HMI) such as, for example, "Select second gear" or "Select a lower gear". It wiil be appreciated that the HMI could take many different forms and that the invention is not limited to the driver alerts described above.

Although in the embodiment described above the term inhibit engagement of the clutch by the actuator is fulfilled by the electronic control unit 10 via the use of the electronically controlled valve 12 it will be appreciated that other means could be used.

-10 -For example and without limitation, an electronically controlled lock could be associated with the clutch pedal 7 to lock it in a clutch disengaged position in response to a control signal from the electronic control unit 10.

With reference to Fig.3 there is shown a method for controlling the clutch as embodied in the electronic control unit 10.

Steps 90 to 95 are the steps reguired to reach the point where a free rolling start may occur and comprise of at step 90 the engine running, at step 92 whether a reguest for a free rolling stop has been issued and at step 95 the engine stopped. If a free rolling stop has not been reguested then the method loops back from step 92 to step 90.

Then at step 100 the method proper commences with a check of whether a request for a free rolling start has been issued. Any known combination of driver inputs can be used for this test and the invention is not limited to any particular driver action. If this test is passed the method advances to step 110 and if it is failed the method loops back to step 95.

If the method has advanced to step 110 it is determined whether the currently selected transmission ratio is suitable for the free rolling start or more precisely whether the input speed of the transmission 6 will produce an acceptable engine speed if the clutch 3 were currently fully engaged.

The test at step 110 could therefore take the form:-Is < IS < ISrnx (Test 1) Or -11 -Is 5rnji < s < 5m&x and Njff < Ndjffrnax (Test2) Where: -IS = Transmission input shaft speed; = Minimum permissible speed limit; ISmax = Maximum permissible speed limit; = Potential Speed differential across the clutch; and = Maximum permissible difference in speed between the transmission input shaft and the engine.

If the test at step 110 is passed, no additional action is taken, as indicated by step 120, the clutch 3 is engaged normally at step 130 and the method ends at step 200.

If the test at step 110 is failed, then the method advancos to step 140 whoro engagement of tho clutch 3 is blocked by in this case, the closing of the electronically controlled valve 12.

The method then advances to step 150 where the driver is alerted to the fact that the currently selected gear is not suitable for a free rolling start. The method then loops back to step 110 and will continue to loop through steps 110, 140 and 150 until eventually the test at step 110 is passed and then steps 120, 130 and 200 are performed.

Table 1 below shows the speed per 1000RPM for a typical motor vehicle, Table 2 shows the results for the motor vehicle using (Test 1) if 15mm is set at 1200RPM and ISmax is set at 2800RPM with a Y' indicating a suitable transmission ratio for the rolling start and N' indicating

an unsuitable ratio.

-12 -Transmission FIRST SECOND THIRD FOURTH FIFTH SIXTH Ratio _________ _________ _________ _________ _________ _________ Vehicle speed kph 7.5 10.0 15.0 20.0 25.0 40.0 per 1000 RPM ________ ________ ________ ________ ________ ________

Table 1

________________ ________________ ________________ ________________

Vehicle Speed FIRST SECOND THIRD FOURTH FIFTH SIXTH kph _________ _________ _________ _________ _________ _________

Y Y N N N N

Y Y Y N N N

N N Y Y Y N

N N N N Y Y

Table 2

Table 3 below shows how the test result at step 110 is modified for an input shaft speed of 2750RPM if (Test 2) is used instead of test (1) and Ndjffmax is set to 1300RPM with y' indicating no change, that is to say, a pass and N' indicating a fail.

Engine Speed Input Shaft Speed _________________________ 275 0RPM 1200 N 1400 N 1600 Y 1800 Y 2000 Y

Table 3

Therefore by using (Test 2) the test at 110 will be failed if the engine speed is below 1500 Rpm because in -13 -those oases the speed differential is too high but in the oase of (Test 1) the test would be passed beoause the input shaft speed is below the maximum permissible speed limit of 2800RPM.

Referring now to Fig.2 there is shown a seoond embodiment of a motor vehiole 51 having a rolling stop-start system. The motor vehiole 51 oomprises an engine 52 driving a olutoh 53, a multi-speed manual transmission 55 having an input shaft (not shown) driven by the olutoh 53 and a olutoh oontrol apparatus.

The olutoh oontrol apparatus oomprises of a driver input devioe in the form of a olutoh pedal 57, a olutoh pedal sensor 58 to sense the position of the olutoh pedal 57, an eleotronioally oontrolled aotuator 59, an aotuation meohanism 54 in the form of a release lever and release bearing and an eleotronio oontrol unit 60. As before the eleotronio oontrol unit 60 has a number of inputs whioh may inolude an engine speed input from an engine speed sensor 61, a seleoted gear sensor 56, a vehiole speed input from a wheel sensor 63 and various other inputs suoh as, for example, aooelerator position and brake pedal position as indioated generally on F'ig.2 by the referenoe number 65.

The olutoh 53 is in this oase therefore of the type often referred to as an e-olutoh in whioh engagement and disengagement is performed by the eleotronio oontrol unit 60 using the aotuator 59 in response to the signal reoeived from the olutoh position sensor 58.

The eleotronio oontrol unit 60 is also oonneoted to a Human Maohine Interfaoe 66 that oan be used to provide information to a driver of the motor vehiole 51.

As before, a first means for determining the input speed of the manual transmission is formed by the seleoted -14 -gear sensor 56 which provides a signal indicative of the currently selected gear to the electronic control unit 60 and the vehicle speed sensor 63 which provides a signal indicative of the current vehicle speed and from these two signals, along with information regarding the final drive ratio of the motor vehicle 51 and the rolling radius of the tyres, the electronic control unit 60 determines the rotational speed of the input shaft of the transmission 55.

As before, the motor vehicle 51 could alternatively be provided with a means for determining the input speed of the manual transmission 5 by direct measurement of input shaft speed from a rotational speed sensor associated with the input shaft to the transmission 55.

In either case, the electronic control unit 60 determines whether the speed of the input shaft falls within a predefined rotational speed range bounded by an upper speod limit and a lowor spoed limit.

The upper speed limit is a speed that, if the clutch were engaged, would result in the engine 52 rotating at an unacceptably high speed. This upper limit is not necessarily the maximum safe operating speed of the engine 52 or a speed that would produce unacceptable clutch wear but could be an engine speed above which the noise generated by such a sudden increase in engine speed would be unacceptable to a driver of the motor vehicle 51, that is to say, the upper speed limit could be a driveability limit and not a mechanical limit.

In addition to the upper speed limit there could also be a check of the expected differential speed across the clutch 53 to determine whether it would be unacceptably high (Test 2) . This reguires knowledge of the current engine speed which can be obtained from the engine speed sensor 61.

-15 -As before, the lower speed limit is a speed below which, if the clutch were engaged, would result in the engine 52 rotating at an unacceptably low speed. That is to say, an engine speed where insufficient torgue could be produced by the engine 52 to enable a smooth pull away to occur. This speed limit will therefore depend upon the specific engine and the relationship between torque and speed for that engine but in general the lower speed limit is likely to be lower for a diesel engine than it is for an equivalent capacity normally aspirated spark ignition engine.

When a free rolling start is occurring, the electronic control unit 60 is operable to check whether the input shaft speed is within the predetermined speed range, if it is, operation of the actuator 59 mimics the motion of the clutch pedal 57 so that the clutch is engaged and disengaged in response to driver inputs but, if it is not, the electronic control unit 60 is operable to maintain the clutch 53 disengaged even if the driver has fully removed their foot from the clutch pedal 57. This prevents the clutch 53 from being engaged while the unfavourable input shaft speed conditions exist. As previously referred to, the input shaft speed can be brought into the predefined speed range by the driver changing gear to one that brings the input shaft speed within the predefined speed range or, if the transmission gear selected was unacceptably low so that the input shaft speed was too high, then the natural slowing of the motor vehicle 51 due to the lack of drive will eventually bring the input shaft speed within the predefined range.

When the input shaft speed is brought within the predefined range then the electronic control unit 60 engages the clutch 53 in controlled manner to provide a smooth engagement of the clutch 53 and then control of the clutch 53 by the driver returns to normal.

-16 -It will be appreciated that, if the differential speed across the clutch 53 is also used, the act of the driver applying pressure to the accelerator pedal thereby increasing the engine speed will potentially bring the input shaft speed into the predefined speed range.

To assist the driver of the motor vehicle 51 the electronic control unit 60 provides via the HIll 66, as discussed above with respect to Fig.1, an indication to the driver that a gear change is required in order to perform the free rolling start.

With reference to Fig.4 there is shown a method for controlling the clutch as embodied in the electronic control unit 60.

Steps 90 to 95 are the same steps as described with reference to Fig.3 and so will not be described again in detail.

The method proper commences at step 300 with a check of whether a request for a free rolling start has been issued.

As before, any known combination of driver inputs can be used for this test and the invention is not limited to any particular driver action. If this test is passed the method advances to step 310 and if it is failed the method loops back to step 95.

If the method has advanced to step 310 it is determined whether the currently selected transmission ratio is suitable for the free rolling start or more precisely whether the input speed of the transmission 55 will produce an acceptable engine speed if the clutch 53 were currently fully engaged.

-17 -The test at step 310 could take the same form as those set out above and referred to as (Test 1) and (Test 2) If the test at step 310 is passed no action is taken, as indicated in step 320, and the clutch 3 is engaged normally at step 330 and the method continues to step 500 where it ends.

If the test at step 310 is failed, then the method advances to step 340 where engagement of the clutch 3 is blocked, by in this case, the electronic control unit 60 failing to operate the actuator 59 to engage the clutch 53.

The method then advances to step 350 where the driver is alerted to the fact that the currently selected gear is not suitable for a free rolling start. The method then loops back to step 310 and will continue to loop through steps 310, 340 and 350 until eventually the test at step 310 is passed and then steps 320, 330 and 500 are performed.

The values and results given in Tables 1, 2 and 3 are egually applicable to the second embodiments shown in Figs, 2 and 4.

It will appreciated that the invention is applicable to any transmission arrangement in which a drive gear is directly selectable by the driver and drive is transmitted to the transmission via a driver operable clutch.

Although the invention has been described above with respect to embodiments in which a single clutch is used to provide a selectable drive between the engine and the transmission it will be appreciated that it is egually applicable to so called twin or dual clutch arrangements in which there are two drive clutches connecting the transmission to the engine. In such an arrangement one of the clutches is normally used to provide drive from the -18 -engine to the odd gears of the transmission and the other to the even gears of the transmission. If such a transmission is used it will be appreciated that the phrase inhibiting engagement of the clutch' means inhibiting engagement of the respective clutch for the engaged gear and the phrase inhibit engagement of the clutch by the actuator' means inhibiting engagement of the respective clutch for the selected gear by the respective actuator.

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 alternative embodiments could be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

-19 -Claims 1. A method of controlling the engagement of a clutch of a motor vehicle during a free rolling start, the motor vehicle having an engine driving a manual transmission via the clutch wherein the method comprises determining whether a transmission ratio selected for the free rolling start is suitable and, if the selected transmission ratio is unsuitable, inhibiting engagement of the clutch.
2. A method as claimed in claim 1 wherein a transmission ratio is unsuitable if the engine speed following the engagement of the clutch is predicted to be outside a predefined engine speed range.
3. A method as claimed in claim 2 wherein, if the selected transmission ratio is not suitable, the method further comprises providing an indication to a driver of the motor vehicle that the selected gear is unsuitable.
4. A method as claimed in claim 2 or in claim 3 wherein the method further comprises inhibiting engagement of the clutch if a speed differential across the clutch is above a predefined differential speed limit.
5. A method as claimed in any of claims 2 to 4 wherein the clutch is engaged and disengaged by a hydraulically operated slave cylinder and inhibiting engagement of the clutch comprises preventing the release of hydraulic pressure from the hydraulic slave cylinder so as to maintain the clutch in a disengaged state.
6. A method as claimed in any of claims 2 to 4 wherein the clutch is an e-clutch and inhibiting engagement of the clutch comprises maintaining the e-clutch in a disengaged state.

-20 -
7. An apparatus for controlling during a free rolling start the engagement of a clutch of a motor vehicle having an engine driving a manual transmission via the clutch, wherein the apparatus comprises an actuator to engage and disengage the clutch and an electronic control unit, wherein the electronic control unit is operable to determine whether a selected transmission ratio is suitable for clutch engagement and, if the selected transmission ratio is unsuitable, is further operable to inhibit engagement of the clutch by the actuator.
8. An apparatus as claimed in claim 7 wherein a transmission ratio is unsuitable if the engine speed following engagement of the clutch is predicted to be is outside a predefined engine speed range.
9. An apparatus as claimed in claim 8 in which the apparatus further comprisos a Human Machino Interfaco operably connected to the electronic control unit and, if the selected transmission ratio is unsuitable, the electronic control unit is operable to provide an indication to a driver of the motor vehicle via the Human Machine Interface that the selected gear is unsuitable.
10. An apparatus as claimed in claim 8 or in claim 9 wherein the apparatus further comprises an engine speed sensor and a means for determining the input speed of the manual transmission and the electronic control unit is further operable to inhibit clutch engagement if the differential speed across the clutch is unacceptably high.
11. An apparatus as claimed in any of claims 7 to 10 wherein the actuator is a hydraulically operated slave cylinder, the apparatus further comprises an electronically controlled valve operable by the electronic control unit to selectively control the flow of hydraulic fluid into and out of the slave cylinder and the electronic control unit is -21 -operable to inhibit engagement of the clutch by the actuator by closing the electronically controlled valve when the clutch is in an engaged state to prevent the release of hydraulic pressure from the hydraulic slave cylinder thereby maintaining the clutch in the disengaged state.
12. An apparatus as claimed in any of claims 7 to 10 wherein the clutch is an e-clutch, the actuator is an electronically controlled actuator controlled by the electronic control unit and the electronic control unit is operable to inhibit engagement of the clutch by using the electronically controlled actuator to maintain the clutch in a disengaged state.
13. A motor vehicle having a clutch control apparatus as claimed in any of claims 7 to 12.
14. A method for controlling the engagement of a clutch substantially as described herein with reference to the accompanying drawing.
15. A clutch control apparatus substantially as described herein with reference to the accompanying drawing.
16. A motor vehicle substantially as described herein with reference to the accompanying drawing.