Patent GB-652560-A (GB)
Title: Improvements in or relating to power transmission apparatus
IPC: B64C27/20
Filed: 1948-09-28
Abstract: 652,560. Friction clutches; couplings. HOBBS TRANSMISSION, Ltd., and HOBBS H. F. Sept. 28, 1948, No. 25245. [Class 80(ii)] In a friction clutch engaged by oil pressure, for driving a sustaining rotor of an aircraft from an engine shaft 9, the driving housing 27 of the clutch is connected to the shaft 9 through relatively-movable elements including centrifugal weights operatively associated with a rotary valve A controlling the oil pressure in the clutch. An axially-movable control valve 47 is also provided. Main centrifugal weights 22, 23 and auxiliary weights 24, 25 extend from spindles 20 journalled in the housing 27 and geared to a disc 11 secured to the shaft 9, the gear pinions for the weights 22, 23 being twice the size of those for the weights 24, 25, so that, over part of their travel, which is limited by studs 29 on the housing 27 engaging slots in the disc 11 the auxiliary weights act in opposition to the main weights while over the remaining travel they act with the main weights. The spindle 20 of the weight'23 forms the rotary valve A. Oil is supplied by two pumps, one 44 driven from the housing 27 and the other 78 driven from the output shaft 41 geared to the rotor, to a conduit 84 fitted with a relief valve 79 and leading to the valve 47 which is associated with an exhaust port 85 and with conduits 59a, 60a leading through passages in the shaft 41 and housing 27 to the valve A, as shown diagrammatically in Fig. 5, the valve A controlling a port 64 leading to a chamber 66 containing a spring-loaded valve 68 controlling ports 71, 72 leading to the clutch diaphragm chamber 31 and an exhaust port 73. With the valve 47 in the normal middle position shown in Fig. 5, pressure oil passes from conduit 84 to conduit 59a, the conduit 60a being open to exhaust 85. The weights normally maintain the valve A in such a position that conduit 59a connects with port 64, so that oil passes into chamber 66 and depresses valve 68 to open port 71, whereby oil enters the chamber 31 and holds the clutch engaged. Under excessive torque, however, valve A moves to put both conduits 59a, 60a into communication with port 64 so that the clutch pressure is reduced, allowing slip, while if the shaft 41 over-runs the shaft 9, valve A moves to close conduit 59a and open port 64 to conduit 60a, so that valve 68 moves to open port 72 to exhaust 83 and the clutch disengages. By moving valve 47 to the right in Fig. 5 (free-engine position), conduits 59a, 60a are both cut off from conduit 84 and opened to exhaust 85, whereby the clutch is disengaged. By moving valve 47 to its other extreme position, conduits 59a, 60a are both opened to conduit 84, so that the clutch is held engaged whatever the position of the weights, so allowing the engine to be re-started by the rotor or allowing the engine to be used as a brake. In an aircraft with two rotors, each has a separate engine and clutch, but the rotors are geared together by idler pinions so that both may be driven from one engine or one or both engines can be restarted by the rotors. Springs may be provided tending to maintain valve A in predetermined position. Specification 673,737 is referred to in the Provisional Specification.