One problem associated with such clutch actuating systems is that vibration generated in the clutch or in the associated engine or driveline may be transmitted through the clutch actuation system to the occupants of the vehicle with unpleasant/annoying consequences.

It is an object of the present invention to provide an improved form of clutch actuating system which at least mitigates the above problem.

Thus according to the present invention there is provided a clutch actuating system which includes a clutch actuator, sensing means associated with the actuator which generates a signal representative of the vibration of the actuator, processing means for receiving said vibration signal and providing an output signal which is phased shifted relative to said vibration signal, and vibrating means for vibrating said actuator in accordance with said phase shifted output signal to tend to nullify the effect of said sensed vibration.

The actuating system may be hydraulically actuated in which, for example a master cylinder is connected with a slave cylinder by conduit means and the sensing means generates a signal representative of the vibration of the slave cylinder, in such an arrangement a diaphragm or piston exposed to the hydraulic pressure of the system may be vibrated in accordance with the phase shifting output signal of the processing means.

Alternatively, for example, the actuator may be a cable actuator or an electrical actuator (for example electric motor operated screw device) and the phase shifted output signal from the processing means may be applied electrically to the actuator.

The invention is equally applicable to clutch actuating systems which are operated by a vehicle driver through, for example, a conventional pedal or to systems which are automatically operated and which, for example, form part of an automated manual transmission.

The present invention also provides a clutch actuating system which includes a clutch actuator, sensing means associated with the actuator which generates a signal representative of the axial position of the actuator relative to an actuating member of the associated clutch, processing means for receiving said position signal and calculating from said position of the actuator when the actuator is in a non-operational (i. e. in its rest or clutch engaged position) diagnostic parameters such as the wear condition of the clutch.

The above diagnostic feature can easily be incorporated in the vibration damping form of the present invention by appropriate software programming and without the need for additional hardware.

The invention also provides a method of damping vibrations in a clutch actuating system comprising : - - sensing the vibrations of a clutch actuator; - providing a signal representative of said vibrations; - applying a phase shift to said vibration signal to generate a damping signal, and - oscillating parts of said system in accordance with said damping signal to tend to nullify the effect of the sensed vibrations.

The present invention will now be described, by way of example only, with reference to the accompanying drawing which shows schematically a clutch actuating system in accordance with the present invention.

The clutch actuating system comprises a master cylinder 10 operated by a pedal 11 and connected with a concentric slave cylinder 12 via a conduit 13. The concentric slave cylinder includes a piston 14 which moves an associated clutch release bearing 15 to displace a clutch clamping diaphragm spring 16 in a conventional manner to release the contact pressure between the clutch pressure plate 17 and the clutch driven plate 18. As is conventional to disengage the clutch the pedal 11 is depressed which operates master cylinder 10 to actuate concentric slave cylinder 12 and unclamp the clutch. hi accordance with the present invention the concentric slave cylinder 12 is provided with a position sensing means 19 which may be of any suitable form. A Hall Effect type sensor is particularly suitable since it provides a convenient electrical output signal. In the arrangement shown the sensor comprises a stationary sensor part 20 which forms part of the housing of the concentric slave cylinder and a movable part 21 which comprises, for example, a magnet which is either mounted on the piston 14 or the associated release bearing 15. The Hall Effect sensor arrangement described in the Applicant's co-pending UK Patent Application No 03 00514.7 is particularly suitable for use with the present invention.

Thus axial movement of the release bearing 15 relative to the housing of the concentric slave cylinder is sensed by sensing means 19 and the output of sensing means 19 is shown diagrammatically at A in the drawing. This output is fed via a connection 23 to a processing means 24 having an output connection 25 which is connected with an electrical oscillator 26 which oscillates a diaphragm or piston 27 which is connected with conduit 13.

The output signal from processing means 24 present in output connection 25 is arranged to be 180° out of phase with the input signal into processing means 24 from the connection 23. The oscillator 26 oscillates diaphragm/piston 27 in accordance with output signal in line 25 thus producing an oscillation in the conduit 13 which is 180° out of phase with any hydraulic oscillation coming from vibration of the release bearing 15 caused by vibrations applied thereto by the clutch, engine or driveline etc. This phase shifted signal arrangement is shown diagrammatically at B in the drawing.

Thus the pulsations in conduit 13 caused by vibration of release bearing 15 are nullified to provide a relatively vibration free column of fluid in conduit 13 as indicated diagrammatically at C in the drawing.

As will be appreciated, since the sensing means 19 measures the position of the release bearing relative to the housing of the concentric slave cylinder in a continuous manner the position signals from sensing means 19 can be processed within processing means 24 to provide an indication as to the rest position of release bearing 15 when the actuator 12 is not operated. Thus processing means 24 can provide diagnostic information indicative of the wear condition of the clutch based on the rest (non-actuated) position of release bearing 15.

This diagnostic infonnation can be obtained by connecting a suitable monitor to an output port of processing means 24 shown diagrammatically at 28 in the drawing.

Although the invention has been described above in relation to a hydraulically operated clutch actuating system it will be appreciated that the invention is equally applicable to all types of clutch actuating system whether the clutch is actuated by a cable or by, for example, an electric motor. If the clutch is actuated mechanically or electrically the actuating system may be oscillated electrically in accordance with the output signal of processing means 24 to nullify any vibration applied to pedal 11 by the actuator.