The invention relates to friction clutches of the kind in which a fluid such as oil is used to lubricate and/or cool the inter-engaging friction faces and which are generally known as wet clutches.
One type of wet friction clutch incorporates a driving member which is normally the engine flywheel and a pressure member which is normally referred to as a pressure plate and which is urged towards the flywheel. A driven member normally referred to as a driven plate is arranged between the flywheel and pressure plate. These members have inter-engaging friction faces which constitute one friction interface between the flywheel and driven plate and another friction interface between the driven plate and pressure plate. Torque is applied to the driven plate through both friction interfaces. In a wet clutch oil or a similar fluid is supplied, normally by centrifugal force, to the region of the friction faces of the driven plate and some of this oil finds its way to both the friction interfaces.
It has been appreciated in the past that a sufficient oil flow must be provided to the driven plate to prevent over-heating and to ensure that the friction faces are appropriately lubricated to provide consistent friction qualities and it has previously been proposed to control the total flow of oil to the driven plate in accordance with its operating conditions. However, despite a sufficient supply of oil to the driven plate, wet clutches do not always operate satisfactorily.
It is also known, for example from Deere & Company U.K. Patent Specification No. 1,389,515 and from General Motors U.K. Patent Specification No. 694,385 to control the oil flow to individual friction interfaces in a multi-plate clutch of the kind in which two or more plates are supported for longitudinal sliding movement along the outside of a generally cylindrical carrier for these plates. With such a clutch construction, internal lips or other barriers are provided at the ends of the cylinder to provide a reservoir into which oil is held by centrifugal force while the clutch is rotating. The oil is supplied to the interior of the cylinder by any suitable feed. Bleed holes are provided at suitable positions in the cylinder to allow oil to pass out through the cylinder under centrifugal force to the friction interfaces. Suitable positioning of the bleed holes gives even distribution among the interfaces.
This kind of arrangement for dividing oil flow between two interfaces of a clutch is not suitable for the kind of clutch in which the driven member incorporated a friction facing carrier plate rivetted or similarly secured to a splined hub. This kind of driven member is frequently used in single plate clutches intended for installation in a limited axial space and intended for use in situations where a low moment of inertia for the driven member is required. The limited space and low inertia requirements preclude the use of the known types of oil distribution system discussed above. Another disadvantage of the known oil distribution systems is that they require a high flow rate of oil to fill the reservoir and sufficient speed of the driven member to provide an adequate centrifugal force before even distribution of the oil can be achieved. With many clutches it is particularly important to achieve good oil distribution at low speeds or even when the driven member is stationary and when the rate of oil supply is low.
An object of the present invention is to provide an improved fluid supply to a wet clutch which overcomes the above mentioned disadvantages.