Patent GB-602749-A (GB)
Title: Improvements in or relating to power transmission apparatus
IPC: F16H61/02
Filed: 1945-07-09
Abstract: 602,749. Change-speed gear ; friction-clutches. HOBBS, H. F. July 9, 1945, No. 17438. [Class 80 (ii)] [Also in Group XXIX] Change-ratio or other powertransmitting apparatus, for internal - combustion engined or battery-electric vehicles &c., comprises two or more friction plate-clutches 16, 17, each engaged by oil-pressure acting through diaphragms 18, 19 and spring-released pressure-rings 13, 14, carried in a rotating driving-housing 11 and controlled by one or more (two shown) automatic pistonvalves 8, 9, also carried by the driving-housing and moved outwards by centrifugal force in opposition to return-springs 32, and also opposed in each direction by further spring- loaded means such as transverse spring - loaded balldetents 36, 53, which locate the piston valves 8, 9 in extreme positions, and also cause return movement of the valves to occur at a lower speed than their outward movement, the speed-difference between the outward and return movements of the valves being greater than that caused by the change in transmissionratio. The housing has valve-controlled exhaust ports 48, 148 and ducts, e.g. 24, 154, 155, leading thereto from the clutch diaphragmchambers, which ports and ducts are located partly or wholly further from the axis of rotation than the outermost part of the diaphragmchambers to permit rapid draining of the pressure spaces. Oil is also supplied to the friction surfaces of the clutches to render their engagement more progressive. The three-speed gear shown comprises an inner final driven shaft 29, Figs. 1 and 4, to which is secured one side-wheel 26 of a bevel differential gear, the planet-carrier of which is secured to .one driven clutch-disc 16, whilst its other side-wheel 27 is fast on an outer intermediate shaft 30 rotating with the other driven clutch-disc 17 and having at its outer end a fast pinion 35, drivingly connected to the inner driven shaft 29 through countershaft-wheels 37, 41, a wheel 42 and one-way clutch 39. In low-ratio the clutch 17 alone is engaged and drive is through the countershaft train. For second-ratio, the clutch 17 is disengaged and 16 engaged alone, producing a differential drive through the direct and countershaft paths acting simultaneously. For high-ratio, both clutches 16, 17 are engaged together, locking the differential and producing direct-drive, with overrun in the one-way clutch 39. The centrifugal valves 8, 9 control the clutches 16, 17 to produce speed-responsive automatic shift as follows :-In the initial position shown, pressure from a constantlydriven pump 20 reaches the diaphragm 19 of the low-speed clutch 17 through a duct 31, inlet 21 to the interior of the valve-piston 8, a drilling 145, groove 45, duct 46, a groove 47 in the valve 9 and a channel 154 leading to the chamber of the diaphragm 19. A channel 24 leading to the diaphragm 18 of the second-ratio clutch 16 is at this time connected to exhaustports 48 in a plug closing the outer end of the valve-chamber 8. At a predetermined speed, the valve 8 moves centrifugally outwards, exhausting the duct 46, leading to the diaphragm of the clutch 17, through a side port 149 and exhaust opening 150, and at the same time pressurising the channel 24 of the clutch 16 through the groove 45, thus disengaging clutch 17 and engaging 16 to introduce second ratio. At a predetermined higher speed, the second valve 9 moves centrifugally outwards, transferring its groove 47 from the exhausting duct 46 to the pressure-duct 24, and thus supplying pressure to the diaphragm 19 of the clutch 17 through a duct 155, whereby both clutches 16, 17 are engaged together for directdrive. Drift-balls 49 interlock the valves 8, 9 and the spring-loaded ball-detents 36, 53 above referred to engage grooves in the valves to locate them in their extreme positions and to offer additional resistance to movement in either direction so as to ensure that downshifts occur at lower predetermined speeds than the corresponding up-shifts. To provide for automatic declutching at low engine-speeds, the diaphragm-chambers of each clutch 16, 17 communicate through ducts 56, 57 with additional valves 54, 55 also carried by the driving housing 11. At low speeds, these valves are moved inwardly against centrifugal force by springs 59, 60 to exhaust both clutch diaphragm-chambers through ports 58, Fig. 1. The setting speed of the declutch valves 54, 55 may be controlled by the operator through a simple pedal- or lever-operated valve 63 which supplies pressure-oil from the pump 20, through ducts 62 to the inner faces of the valves 54, 55 to supplement centrifugal force to any desired degree. The pistons of the valves 54, 55 may be of differential area at opposite ends. A similar manual control of the operational speed setting of the ratio-shift valves 8, 9 may be provided by connecting the ducts 62 of the operator-controlled valve 63 to the outer or inner faces of the valves 8, 9, the exhaust-ports 48 being replaced by suitable side ports and the exhaust-ports 148 being replaced by a small opening. The Provisional Specification states also that the additional valves may maintain the fluid pressure constant at any speed independent of viscosity change. Specifications 549,988 and 560,379 are referred to.