Patent GB-637269-A (GB)
Title: Improvements in or relating to friction clutches
IPC: F16D25/04
Filed: 1947-11-26
Abstract: 637,269. Fluid-pressure servomotor-control systems. HOBBS TRANSMISSION, Ltd., HOBBS, H. F., and THOMPSON, J. A. Nov. 26, 1947, No. 31320. [Class 135] [Also in Group XXIV] Gradual engagement of a friction clutch comprising a driven friction disc 17, clamped between a driving flywheel 10 and a presserplate 18 by liquid- (e.g. oil-) pressure acting on the presser-plate through an insulator plate 19 and flexible diaphragm 20 or piston enclosing a liquid pressure-space 22 in a rotating cover plate 9 attached to the member 10, is ensured by one or more air-cavities 8 in the cover plate 9, which are always in communication at their outer periphery 11 with the liquid pressure-space 22 so as to trap air which is gradually compressed as an increasing volume of liquid is supplied to cause gradual increase of clutch-loading pressure. Pressure in the liquid-space 22 is derived from a pump 25 and is supplemented by centrifugal force. Control is by three valves : one, a main manual valve 26 shuts off the supply to cause disengagement at any speed : the second valve is a centrifugally-balanced pressure-responsive local exhausting valve 40 in the rotating cover-plate 9, which also carries the third valve, a speedresponsive centrifugal valve 46 causing automatic declutch at idle speeds. The outwardly spring-loaded pressure-responsive valve 40 is forced inwards by liquid-pressure supplied to an outer port 32 when the manual valve 26 is opened, thus cutting off communication between the outer periphery of the pressurespace 22 and an exhaust opening 41, and supplying pressure thereto from the supply port 32 to engage the clutch. At idle-speeds the centrifugal valve 46 is moved inwards by a spring 47 in opposition to centrifugal force, to open communication between an exhaust-port 51 and a port 44 at the inner periphery of the pressure space 22 to cause automatic declutch.- Speed increase moves the centrifugal valve 46 outwards in opposition to the spring and to liquid-pressure in the pressure-space 22, which pressure reaches the outer face of the valve through a port 59, which, during outward movement of the valve, is sealed off by the stepped valve-skirt so that further outward movement of the valve is opposed by liquid trapped in the outer sealed space 43, which liquid leaks slowly past the piston-valve clearance, so as to render speed-responsive clutch-engagement progressive. Manual disengagement of the clutch by closing the valve 26 to release the pressure-responsive valve 40, exhausts the pressure-space 22 at its outer periphery so that it drains completely and also communicates the air cavities 8 with the atmosphere for replenishing any lost air. Speed-responsive disengagement by the centrifugal-valve 46 exhausts the pressure-space 22 at its inner periphery, leaving the pressurespace still liquid-filled, but subject to centrifugal pressure only, the air remaining trapped in the cavities 8. The pressure-responsive and centrifugal valves 40, 26 are arranged diametrically opposite in the cover-plate 9 with two diametrically opposite air-cavities 8 equispaced between them. The clutch may be used in a change-speed gear.