Patent GB-707313-A (GB)
Title: Improvements in or relating to friction clutches
Inventor: HOBBS HOWARD FREDERICK
IPC: F16D43/284
Filed: 1951-10-16
Abstract: 707,313. Friction clutches. HOBBS TRANSMISSION, Ltd. Sept. 29, 1952 [Oct. 16, 1951], No. 24088/51. Class 80 (2) Relates to a centrifugal valve 17 carried in a radial bore in a rotary input housing 10 of a fricton clutch wherein a single output disc (not shown) is clamped against a wall of the housing 10 by a presser plate 12 moved axially by liquid (e.g. oil) pressure applied in a housing space 15 to a flexible diaphragm 13 acting through a heatinsulator plate 14, said valve 17 exhausting the pressure-space 15 over an idle speed range for automatic clutch release, and sealing the space for clutch re-engagement above and below such range, the latter for a towed or downhill engine-start on a vehicle. Pumped liquidpressure is supplied to the pressure-space 15 through further valves as in Specification 628,499. The centrifugal valve 17, which may replace the corresponding valve in Specification 637,251, controls inner and outer ports 24, 20 of the pressure-space 15, together with co-operating exhaust ports 25, 30 in the housing 10, the outer ports functioning, as described below, to stabilize clutch-release speed in relation to centrifugal force only, in spite of variation in viscosity of the liquid. Slight idle drag when disengaged is also provided. At the lower end of the idle-speed range, as shown in Fig. 4, the valve-piston 17 is in an intermediate position. Above idle range the piston 17 is held outwards by centrifugal force opposed by a spring 19 and by liquid pressure in the diaphragm space 15, permanently reaching a space 26 above the valve-piston 17 through the outer space-port 20 and the reduced outer end of the piston. Clutch-engaging pressure is thus maintained in the diaphragm-space 15 and increases with speed. With reduction in speed into the idle range, the valve-piston 17 moves inwards, Fig. 4 position, and a lower groove 23 therein uncovers the lower port 24, to exhaust the diaphragm-space 15 through the lower port 24, groove 23, drilling 21, lower valve-space 34 and exhaust port 25, thus disengaging the clutch. Below idle range and to zero speed, the valvepiston moves further inwards and the pistongroove 23 moves below the port 24, again cutting off the exhaust connection and causing clutch engagement. To prevent this re-engaged condition being reached during normal running due to excess viscosity building up back-pressure and delaying release at idle speed, an outer groove 29 in the valve-piston 17 registers with the outer exhaust port 30 just before the lower groove 23 cuts off the lower port 24, which releases pressure from the diaphragm-space 15 and upper piston space 26, through the upper port 20, space 26, drilling 27, groove 29 and exhaust port 30, thus reducing the inward loading on the valve-piston 17 and checking its further inward movement. The designed mass of the valve-piston 17 is such that in the clutchreleased idle-speed condition a residual pressure is maintained in'the diaphragm space 15 to provide a clutch-engaging pressure slightly exceeding that of the usual disengaging springs, providing a light clutch-drag, increasing with speed, which transmits overrun torque and also ensures minimum delay on re-engagement. Should this function require an inconveniently great mass of the piston 17, there is provided an additional piston-valve 31, outwardly spring- pressed and of mass low enough to be only slightly affected by centrifugal force, which only uncovers the inner exhaust port 25 when diaphragm-space pressure, introduced into the lower valve-space 34 through the inner exhaust groove 23 of the main piston 17 in the idle-range position, rises above a predetermined minimum.