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

The Applicant's earlier patent GB2 088 007 describes a clutch control system in which the clutch is progressively engaged as the torque demand issued by the driver increases to temporarily limit the engine speed to a set value. This provides a smooth take up from rest.

The Applicant has also developed the clutch control system described in PCT application WO 92/08065 for a vehicle having a clutch, a gearbox and an engine, the system comprising a vehicle speed sensor for generating a vehicle speed variable with the speed of the vehicle, an engine speed sensor for generating an engine speed signal variable with the speed of the engine, a reference signal generator for generating a reference signal, comparator means for comparing the engine and vehicle speed signals and the reference signal, and clutch actuation means for increasing engagement of the clutch if either one of the engine or vehicle speed signals exceeds the reference siσnal.

This further development allows the vehicle clutch to engage when vehicle is running at a predetermined minimum speed, independent of engine speed, to facilitate tow starting, or prevent runaway if the vehicle begins to move down an incline.

In a further development described in the Applicant's co-pending PCT application No. PCT/GB93/01896 the vehicle starter circuit is provided with a starter inhibit relay which prevents operation of the vehicle starter when the clutch control system is in certain operative modes .

The present invention provides a means of operating the vehicle starter in emergency situations, wherein the clutch control system may have failed or when the clutch control system is in said certain modes in order to prevent complete immobilization of the vehicle.

According to > the present invention there is provided a clutch control system for a vehicle having a clutch, a gearbox having a plurality of gear ratios, an engine, and an engine starter

circuit including a starter inhibitor which is normally in a condition to allow engine starting, the control system comprising at least one vehicle operating condition sensor for sensing a vehicle condition and generating a vehicle condition signal in response to a detected condition, a control unit including a clutch engagement command signal generator for generating a command signal, a clutch actuation means for controlling the state of engagement of the clutch, and an actuation control responsive to the command signal to operate said actuation means, and a starter circuit state sensor for detecting activation of the starter circuit, the control unit being connected to said sensors and on detecting initial activation of the starter circuit, and on sensing said vehicle condition, switches the starter inhibitor to deactivate the starter circuit, wherein the control unit is disconnectable from the starter inhibitor and a driver warning device is provided to indicate when said vehicle condition is detected, and/or when said control unit is disconnected.

Preferably the warning device is a warning light, and conveniently the control unit is disconnectable from the remainder of the system through a plug connector.

The invention will now be described by way of example only with reference to the accompanying drawing in which:-

Fig 1 is a schematic of a control system according to a first embodiment of the present invention;

Fig 2 is a circuit diagram of the details relating to the starter inhibitor circuit and warning light circuit .

Referring to Fig 1 a motor vehicle has an engine 10 and a gearbox 12 coupled through a clutch 14 via a gearbox input shaft 15. Fuel is supplied to the engine by a throttle 16 which includes a throttle valve 18 operated by accelerator pedal 19. The clutch 14 is actuated by a release fork 20 which is operated by an hydraulic slave cylinder 22 which is powered by an hydraulic control 38 under the control of a gear lever 24 having a load sensor 25 which senses a load on the gear lever.

The clutch control system includes a series of vehicle condition sensors for sensing respective particular vehicle operating conditions. The engine speed is monitored by an engine speed sensor

26 including a transducer which produces an engine speed signal Ve. The state of the throttle valve 18 is monitored by a throttle valve position sensor 30. The state of the gearbox 12 is monitored by a gear position sensor 32. The position of the slave cylinder 22 is monitored by an actuation sensor 34. The speed of the gearbox input shaft 15, which is equal to that of a driven plate 40 of the clutch 14, is monitored by a driven plate speed sensor 42. Since the speed of the vehicle depends on the driven plate speed and the gear engaged, the driven plate speed sensor 42 acts in effect as a vehicle speed sensor to produce a vehicle speed signal Vs. Signals from the sensors are transmitted to a microprocessor control unit 36 which generates a clutch position signal Vp to control the actuation of the clutch via the hydraulic control 38. Such a system is described in detail in the applicants published application WO 92/08065.

The clutch control system also includes a reference signal generator 31 which generates a reference signal Vr. On clutch take-up from a vehicle "at-rest" position the degree of clutch engagement is determined by the difference between the reference signal Vr and the engine speed Ve, so that when the engine speed signal Ve is less than

the reference signal Vr the control unit 36 demands clutch disengagement and when the engine speed signal Ve exceeds the reference signal Vr the control unit 36 demands clutch engagement. Such a control system is described in British Patent GB2 088 007. The reference signal generator 31 and the above signal comparisons may be software based being generated by and carried out by a microprocessor.

The vehicle ^' has an engine starter circuit which includes a driver operable ignition switch 50 which acts as a sensor of the state of the starter circuit. The switch 50 is typically a key operated switch, but could be operated by coded card, or a push button digital input. The starter circuit further includes a starter inhibitor in the form of an inhibit relay 51 and a starter motor 52 which has a starter solenoid 53. The switch 50 and inhibit relay 51 are connected to the control unit 36, so that the control unit can sense when a "start inhibit" condition is asserted.

The inhibit relay 51 normally has closed contacts and when the relay is energised by the control unit 36 the current to the starter motor solenoid 53 is interrupted to prevent the starter motor from operating.

The control unit 36 is also connected to a driver

warning device, for example a warning light 61 located on the vehicle dash board, but other warning devices such as audible sound generators could be utilised. The warning light is again connected through a relay 62 having normally closed contacts, and the light will be illuminated by the control unit 36 on detection of a particular vehicle condition, ceasing to energise the relay 62, allowing the relay contacts to close.

In order to start the engine when the inhibit relay is effective to disable the solenoid 53 in response to the sensed condition(s) the control unit 36 must be disconnected from the starter inhibit relay 51. This can be easily achieved by removing the entire control unit 36 from the vehicle wiring loom by unplugging the unit at connectors 63. It will be appreciated that connectors 63 may be incorporated into one or more multi-wire connectors or plugs or may comprise individual wire connectors or plugs.

An alternative means of disconnecting the starter relay would be to place an on/off switch or a single disconnectable plug or connector in the wire connecting the control unit 36 to the inhibit relay 51 so that the relay 51 can be easily de-energised.

Details of the electrical circuit for the start inhibit relay 51 and warning light 61 are shown in Fig 2. Switch 50 has an off position "0", a cranking position "C" and a running position "R" . The relays 51 and 62 have their solenoids 51A, 62A connected between the 12 volt power source and the control unit 36 so that when the control unit 36 energises the solenoids 51A and 62A, the solenoid contacts 51C and 62C are opened. The contacts 51C when open interrupt the connection between the starter/ignition switch 50 and the starter solenoid 53. The control unit 36 is arranged to keep the solenoid 62A in an energised state so that the solenoid contacts Θ2C are open and interrupt the connection between the 12 volt power source and earth. If the control unit 36 detects undesired vehicle conditions and/or the control unit 36 is removed, then the solenoid will cease to be energised and the contacts 62C close to illuminate the light.

The invention thus provides a simple and efficient means for re-activating the engine starter circuit following its de-activation in response to the sensing of a predetermined vehicle operating condition. By providing this ability to re-activate or override the deactivation of the

starter circuit the inconvenient immobilization of the vehicle can be avoided.