| 摘要 |
An automatic clutch comprises an actuator 25, eg an electric motor, driving a crank drive 74 which operates a piston rod 72 of master piston 60. The master piston 60 contains a non-return valve 70 that allows hydraulic fluid to overflow from compensating chamber 62 into work chamber 58 of master cylinder 27. Movement of the master piston 60 is hydraulically transferred, via pipe 56, to slave piston 50 which extends to disengage the clutch and retracts, under an influence of a clutch spring, to engage the clutch. When engaging the clutch at low temperatures, eg -10‹C to -20‹C, the viscosity of the fluid prevents it moving quickly through pipe 56 so that under pressure occurs in the work chamber 58 which leads to an opening of the valve 70, thereby increasing the volume of fluid in chambers 52, 58. So that this increase in volume, eg pumping up, does not occur the speed of the electric motor 25 is altered, by an electronic controller, in dependence on the fluid temperature. For example, at low temperatures the speed of the motor 25 when engaging is slower than when disengaging, hence the retraction speed of the master piston 60 is matched to that of the fluid through pipe 56 so that no under pressure occurs and the valve 70 does not open. In another embodiment at low temperature a stroke of the piston 60 is controlled such that it passes snifting bore 64. The temperature maybe sensed, eg by temperature sensors in actuator 25, or it may be calculated. A method of checking the temperature sensors is also disclosed. |
