The present invention relates to a clutch control system for a motor vehicle.

The applicant has developed a power hydraulic circuit for use in a clutch control system, and which comprises a reservoir of hydraulic fluid, an accumulator, a pump, and a control valve. Such a system is disclosed in WO 89/08786.

The power hydraulic circuit is controlled by a control unit which is responsive to predetermined vehicle parameters to operate the friction clutch.

A problem with such systems is that if the vehicle is left parked in gear, for example when left parked on a hill, and the hydraulic circuit accumulator discharges, then the driver may experience unacceptable delay as the accumulator charges before he is able to select 'neutral' in the gear box before starting the engine.

This is particularly true where the clutch control system is of the type disclosed in GB application 92 19101.4 in which the engine start-up is prevented when the vehicle is in gear.

The present invention seeks to overcome this problem.

Accordingly there is provided a motor vehicle clutch control system for a motor vehicle having an electrical system including an ignition switch, the control system comprising a hydraulic power circuit including an electrically driven pump, an accumulator and a clutch actuator, at least one sensor for sensing a predetermined vehicle condition and a control unit which controls the actuator in response to sensed vehicle conditions to operate an associated clutch, wherein the control unit causes the pump to charge the accumulator for subsequent operation of the actuator when the imminent starting of the vehicle is sensed by said at least one sensor but prior to operation of the ignition switch.

Preferably said at least one sensor senses either the presence of the driver in the vehicle, or the entry of the driver into the vehicle.

Preferably the power hydraulic circuit has four operating conditions, an inert mode, a wake up-mode, a normal operating mode and a waiting mode, and the control unit selects the operating mode in response to sensed vehicle conditions .

Conveniently wherein the power circuit is inert, when the ignition switch is off, the circuit goes to wake up mode when the "imminent starting" condition is sensed, and the circuit enters its normal operating mode when the ignition switch is turned-on.

The invention will be described by way of example and with reference to the accompanying drawings in which:

Fig 1 is a diagrammatic illustration of a motor vehicle having a clutch control system according to the present invention;

Fig 2 is a diagrammatic representation of a hydraulic power circuit for a clutch control system according to the invention;

Fig 3 is a diagrammatic representation of a clutch control system according to the invention and which includes a hydraulic power circuit as shown in Fig 2, and

Fig 4 is a state transition diagram for the control system of Fig 3.

Figure 1 shows a motor vehicle 2 having rear road wheels 4 driven via a propeller shaft 6 connected with an outpur shaft 8 of a change speed gearbox 10 in which a plurality

of gear ratios are each respectively engaged, or disengaged in response to manual operation, by the vehicle's driver, of a gear ratio selector device 12, in this example in the form of a gear lever. Signals from gear lever 12, in this example in the form of movement, are transmitted via a connection or linkage 14 to gear ratio change means (known per se) in the gearbox.

On the other hand any other form of gear selector device may be used from which gear ratio disengage and engage signals can be transmitted to gear ratio change means in the gearbox. For example, the gear ratio change means may be hydraulically operated controlled by push buttons.

Driving torque is input to the gearbox 10 through a clutch 18, by an internal combustion engine 22. As an alternative the transmission 10, 18 may drive front road wheels 24 or the front and rear road wheels 24 and 4 of the vehicle.

A hydraulic power circuit 30 for operation of the clutch 18 is shown in Fig 2. The hydraulic power circuit comprises a fluid reservoir 31, a fluid supply pipe 32 leading from the reservoir 31, via a pump 33 (driven by an electric motor 33a) which forms a source of fluid pressure, a non-return valve 34 and an accumulator 35, to a control valve 36. A drain 37 runs from the control valve 36 back to the reservoir 31. A service pipe 38 runs from the control

valve 36 to a fluid pressure actuator 39 for the clutch 18. The clutch 18 has a diaphragm spring 41 which provides a spring force to engage a clutch driven plate 51 which is splined onto a gearbox input shaft 16. The actuator 39, controlled by operation of the control valve 36, operates the clutch 18 via the lever 42, and release bearing 43.

The valve 36 is a spool valve, having an inlet port 44, a service port 46 and an outlet port 48. The inlet port 44 is connected to the fluid supply pipe 32, the service port

46 is connected to the service pipe 38, and the outlet port

48 is connected to the drain 37. The valve 36 is controlled by a solenoid 45.

With reference to Figure 3, the clutch 18 in this example is a push type diaphragm spring clutch known per se having a cover 26 secured to a flywheel or other counter pressure plate 28 rotated by the engine 22. The clutch 18 includes a pressure plate 40 acted on by diaphragm spring 41 and a driven plate 51 with an internally splined central hub engaging splines on the gearbox input shaft 16. The clutch release bearing 43 acted on by the release fork or lever 42 is pivoted at 58 to the clutch housing 20 and is connected at the other end to a thrust rod 39b of the hydraulic actuator 39 (see Figure 2) in the power hydraulic circuit 30.

Operation of the hydraulic circuit 30 is under control of an electronic control unit 49 comprising computer means connected by signal paths 50, 52, 33b and 35b to the hydraulic control 30. One path 50 instructs operation of the hydraulic control 30 via solenoid 45 to cause disengagements and re-engagements of the clutch 18, path 52 supplies electronic control unit 49 with information on the extent of clutch engagement and disengagement from actuator sensor 39a, path 33b connects motor 33a to the control unit, and path 35b connects accumulator pressure sensor 35a to the control unit.

The electronic control unit 49 is also connected by two signal paths 54 and 56 to the gearbox 10 and the lever 12 respectively. The information in the signal on line 54 indicates when a gear ratio is engaged and when no gear ratio is engaged. Information in the signal on line 56 indicates when the driver desires or does not desire to change gear. Gear lever 12 comprises a shaft 57 arranged to pivot universally at 60. A tube 62 surmounted by a hand knob 64 is pivotally mounted at 66 on the shaft 57 so that the tube can move slightly relatively to the shaft. Such knob movements caused by the driver pushing or pulling the knob 64 cause switch or transducer means 68 to initiate a signal on line 56 indicating the driver's wish to change gear. In response the control unit 49 causes the hydraulic power circuit 30 to function causing clutch 18 to disengage

automatically. Further manual movement of the knob 64 causes the shaft 57 to move to cause operation of the gear ratio change means to cause disengagement of the hitherto engaged gear ratio and the engagement of another gear ratio. That engagement produces a signal on line 54 causing the control unit 49 and hydraulic power circuit 30 to function so that the clutch 18 is re-engaged automatically.

A more detailed disclosure of the control unit 49 can be found in GB-A-2088007 and in PCT WO92/08065.

The control unit 49 is also connected to the vehicle ignition switch 70 and to a sensor 71 which senses when likely vehicle start-up is imminent.

The sensor 71 can be arranged to detect change of condition to the vehicle locking system or a door switch detecting opening of the vehicle driver door.

Alternatively the sensor 71 could be connected with a pressure switch in the driver seat, or a seat belt switch.

The control unit 49 can be arranged to operate a vehicle alarm 73 if it senses the presence of the driver through the sensor 71 or the activation of the ignition circuit, while the vehicle locking system is sensed to be in a

locked condition by second sensor 71A. The control unit 49 then causes the hydraulic system to be disabled.

On activation of the sensor 71 the control unit 49 causes the pump 33 to charge the accumulator 35 for operation of the actuator 39.

The hydraulic circuit 30 and control unit 49 have four modes of operation and transitions between these four modes are made in response to various events. These four modes are an inert mode, a wake-up mode, a normal operation mode and a waiting mode. Fig 4 shows the state transition diagram which defines the modes and the triggers for transitions between them.

The inert mode, indicated in Fig 4 by box 80, is the mode occupied when the vehicle is locked and not in use.

Unlocking of the vehicle indicated by line 81 (sensed by sensor 71) places the system in wake-up mode, indicated by box 82. When wake-up mode is entered a time-out sequence is initiated and the hydraulic pressure sensor 35a is checked and if a low pressure is indicated in accumulator 35 the pump 33 is started and the accumulator charged.

Turning on of the ignition switch whilst in wake-up mode causes transition, indicated by line 83, to normal

operation mode, indicated by box 84. Locking of the vehicle or a completion of the timeout sequence, indicated by line 89, causes transition to the inert mode. The time-out sequence is initiated on entry to the wake-up mode and if during a predetermined time period, the ignition switch is not operated, the time-out sequence is considered to be completed.

On entry into the normal mode pressure sensor 35a is again checked and, if a low pressure level is indicated, the accumulator is charged. The output from sensor 35a is then monitored and any fall in pressure below a predetermined level is reacted to by further charging of the accumulator so that an adequate level of pressure is maintained in the accumulator. A transition from normal operating mode to the waiting mode, indicated by box 85, is made if the ignition is turned-off (see line 86).

On entry to the waiting mode a timeout sequence is started (which looks for turning off the ignition switch on again) and the pump 33 is turned off. If the ignition switch is operated before the end of the time-out sequence, see line 87, then the normal operating mode is re-entered. Completion of the time-out sequence or locking of the vehicle, see line 88, returns the system to its inert mode.

The system also includes line 90 which allows a direct transition from the inert mode 80 to the normal operation mode 84. This line is needed to cater, for example, with the situation when the vehicle comes to rest and the driver turns off the ignition thus entering the waiting mode 85 but remains sealed in the vehicle until after the time-out sequence has been completed so that the system returns to its inert mode via line 80. If the driver now turns-on the ignition the system can make the transition to the normal operation mode 84 via line 90 but would not be capable of leaving the inert mode 80 via line 81 since no operation of the locking system would occur.

Also the requirement to make the transition direct from inert mode 80 to normal operation mode 84 is necessary if the vehicle is unlocked and enters wake-up mode 82 but the timeout sequence is completed before the ignition is turned on so that the system returns to its inert mode 80 via line 89. Line 90 allows the driver to remain seated in the vehicle and subsequently turn-on the ignition and go directly to the normal operation mode from the inert mode.

Whilst the system has been described working with a lock condition sensor 71, this could be replaced with any other suitable sensor, as previously described such as a door switch detecting opening of the vehicle drivers door.

The sensor 71 could also be made to cause the control unit 49 to energise a display module 72 to display information relating to the gear engaged.