Patent GB-649589-A (GB)
Title: Improvements in or relating to variable-ratio power transmission apparatus
Inventor: HOBBS HOWARD FREDERICK
IPC: F16H61/02
Filed: 1948-02-11
Abstract: 649,589. Change-speed epicyclic gear ; friction clutches. HOBBS TRANSMISSION, Ltd. Feb. 11, 1948, No. 3980. [Class 80(ii)] Three reduced speeds, direct-drive and reverse are provided by a triple stepped-planet train, the largest sun 46 of which is permanently fast to an output shaft 47, whilst its smallest sun 37, fast  on an intermediate sleeve 36, and the planet-carrier 29, fast on an innermost intermediate shaft 28, can be selectively clutched to an input drum 11 by nested hydraulically-applied disc clutches B, A, re- .spectively; and a third sun 43, fast on an outer sleeve 42, the planet-carrier 29 and the smallest sun 37 can be selectively held by nested hydraulically - applied disc-brakes D, E, C respectively, - arranged in front of the gear-train. First speed is by clutch A, driving the carrier 29, and brake D holding the sun 43; second is by clutch B, driving the sun 37, and brake E holding the carrier 29; third is by clutch A driving the carrier 29 and brake C holding the sun 37; fourth (top) is by clutches A and B together for solid drive; and reverse is by clutch B, driving the sun 37 and brake D holding the sun 43. Clutches and brakes. The clutches A, B are each engaged by the pump- and centrifugally-developed pressure of liquid applied to a synthetic-rubber faced diaphragm 23 which acts through an insulatorplate 22 on a spring-released thin metal presser-plate 18, which, like the coacting driving face, carries friction facings, e.g. 16, between which are clamped the unfaced driven plate 26, formed of two thin steel discs with an interposed disc which is slotted to form oil circulation passages. Pumped liquid reaches the diaphragms through drillings 81 and pressure-responsive centrifugally-balanced valves 84, which. in the absence of liquid-pressure, move outwardly under spring-load to exhaust the diaphragms at 87, 88. Both clutches A, B are automatically disengaged at engine idling speeds, to provide automatic clutching on a vehicle both above and below the idle speed range, the latter occurring at very low speeds to permit a towed engine-start. For this purpose each clutch has a spring- loaded centrifugal valve 93, which, in the very low speed position, blanks an exhaust opening 94 in the diaphragm chamber, permitting pressure to build up for clutch engagement; in the idling range moves outwardly to exhaust the diaphragm chamber through a groove 95 for clutch disengagement the exhaust liquid passing into the clutch; and in the normal running range again blanks the opening 94 for clutch engagement. Outward movement of the centrifugal-valve 93 is damped by liquid from the diaphragm-chamber reaching its outer face through a port 103, trapped by a step 104 on the valve 93 and thereafter leaking away past the clearance of an inner piston 105, provided with its own auxiliary loading-spring 99 which is lighter than the main valve .loading-spring 100 and serves to oppose the initial outward movement of the valve 93 to the idle-range position. The friction facings may be carried on driven discs instead of on the driving members. The brakes C. D. E are similar to the clutches A, B but have solid discs slotted for removal of oil. Liquid reaches both clutches A, B and the single brake C for lubricating their friction surfaces. The brakes D, E have heavier torque-loading and are protected from access of the liquid by seals 48, 49, 50. Liquid supply system. Liquid pumped by input and output driven gear-pumps 56, 91, is supplied selectively to the clutches and brakes through a piston distributervalve sliding in a block formed by the body 59 of the input pump 56 which is mounted as a unit between the clutch-group A, B and the brake-group C, D, E, these groups as well as the gear-group being all formed as units to facilitate manufacture and assembly. The Provisional Specification refers to Specifications 628,499, 637,251, 637,269 and 643,499; and states also that the brake D may be a balked positive stop,