Patent GB-637251-A (GB)
Title: Improvements in or relating to friction clutches
IPC: F16D43/284
Filed: 1947-06-20
Abstract: 637,251. Fluid-pressure servomotor-control systems. HOBBS TRANSMISSION, Ltd., THOMPSON, J. A., and HOBBS, H. F. June 20, 1947, No. 16369. [Class 135] [Also in Group XXIV] To provide clutch-engagement for a towed engine-start on a motor-vehicle having a friction-clutch controlled automatically by a spring-loaded centrifugal valve 5, slidable radially in the rotary driving housing 1 of the clutch and controlling release of clutch-engaging oil-pressure, supplied to the chamber 14 of a diaphragm 11 through a manually-operated valve 30 and a pressure-responsive localexhausting-valve 36, the centrifugal valve 5 is so arranged that : (1) in its radially innermost positions over a low-speed range (i.e. for a towed start), it seals the diaphragm chamber 14, permitting build-up of pressure for clutch engagement ; (2) over a higher speed range corresponding to engine-idle, it slides outwards to an intermediate position exhausting pressure from, but not draining, the diaphragm chamber 14 at its inner periphery through ports 15, 8, 10, giving automatic clutch-release ; and (3) over a still higher speed range, corresponding to normal running, it slides to its outermost position, blanking the diaphragm exhaust port 15 and again permitting clutch engagement. To prevent hunting and also to assist the valve-loading springs in maintaining the centrifugal valve 5 closed up to an appreciable speed below the idle-range, the valve 5 also controls an outer port 44 leading from the diaphragm chamber 14 past a piston clearance 45, or a groove and drilling, to the outer end of the valve 5, this port 44 being closed by the valve 5 before it closes the inner exhaust port 15 during its outward travel for clutch engagement. Oil thus trapped at the outer end of the valve leaks slowly away either past an inner abutment 49 and through the inside of the valve, or back through the port 44 to the diaphragm chamber, this leak serving to damp movement of the centrifugal valve 5 and also to provide suitable take-up characteristics. Outward movement of the valve 5 may be resisted by a single spring or, as shown, by two springs, one, 7, slightly resisting alone the first range of movement and arranged between a cap 47 and a sliding cup 46, tied to the valve 5 by a central slidable pin 48, loaded in tension by a second and heavier spring 6 which resists further outward movement after the cup 46 abuts the cap 47. Grooves 52, 53 in the valve 5 permit the pressure to act completely round it to prevent sticking. Oil pressure is supplied by a duplex pump 24, driven by the input and output shafts of the clutch, and passes to the manual valve 30 which can effect clutchrelease at any time, and when opened for clutch engagement, supplies pressure through a radial duct 34 to the outer face of the pressureresponsive valve 36, moving it radially inwards against spring-resistance 37 to open a port 40 connecting the pressure-duct 34 with the diaphragm chamber. Opening the manual rotary valve 30 thus produces clutch engagement, providing the centrifugal valve 5 is not exhausting the diaphragm chamber in the engineidle speed range ; whilst closing the valve 30 closes the pressure-responsive valve 36, exhausting the diaphragm chamber at 38, causing declutching at any time. The mass of the pressure-responsive valve 36 and its spring- load balance the centrifugal force in the liquid supply duct 34. Additional centrifugal valves in the same rotary housing may control additional clutches in the housing or other clutches and/or brakes in a change-speed gear.