Patent GB-671215-A (GB)
Title: Improvements in or relating to gear changing mechanisms
Filed: 1948-11-15
Abstract: 671,215. Operating clutches; variable-speed gearing. SCHUELER, P., and ANSDALE, R. F. K. Nov. 15, 1949 [Nov. 15, 1948No. 29648/48. Class 80 (ii). In a pre-selector motor-vehicle transmission system, the main clutch is disengaged under predetermined torque conditions in the gear box-output, and a pre-selected gear automatically engages when the clutch is fully disengaged. In the arrangement shown in Fig, 4, wherein a torque-sensitive element comprises a spring-loaded coupling sleeve 11 helically splined on the gear-box output and propeller shafts so as to move axially on reversal of torque, a spring- loaded shaft 20 having an arm 19 carrying a shoe 18 is normally held retracted by a catch 24. On preselecting a gear, the catch is released and the shoe 18 engages a groove in the sleeve 11. On now releasing the accelerator, so that the vehicle over-runs the engine, the sleeve 11 moves axially, turning the shaft 20 whereby a cam 23 thereon lifts a ball valve 27. Pressure oil from an engine-driven pump now passes via a port 39, groove 40 on a valve 34, ports 32, 31, 30, 49, groove 50 and ports 48, 43b to depress a plunger 46 which closes an exhaust port 45 and allows the oil to pass via a port 44 to a servomotor which disengages the clutch. Selector mechanism now operates to engage the preselected gear, e.g. by servomotors controlled by valves operated by the clutch mechanism. At the same time, the engine decelerates and a pump 8, driven differentially from the driving and driven sides of the clutch, supplies pressure oil at 36 to depress the valve 34, closing the ports 32, 49 but putting the port 39 into communication with the port 43b, so as to maintain the clutch disengaged, via a groove 41 and port 42. Depression of the valve 34 also allows the differential oil pressure at 36 to act via port 52 on a piston 21 to retract the shaft 20 with its shoe 18 and cam 23, whereby the catch 24 re-engages and the valve 27 closes.. The clutch re-engages only when the engine is speeded up sufficiently to allow the valve 34 to be returned to the normal position shown by a spring. A bell-crank lever 38 connected to the, valve 34 is linked to a foot pedal so that by depressing the latter the valve 34 may be lifted beyond its normal position to enable oil to pass from port 39 to port 42 via a groove 41a and thus effect clutch disengagement at any time. In the alternative arrangement shown in Fig. 5, the clutch servomotor 4 is controlled by a valve 43 operated by a solenoid 79. The latter is normally in circuit, via a normallyclosed switch 80, with a switch 83 controlled by. the torque-sensitive element. On reversal of torque, the switch 83 closes and the clutch is disengaged. An arm 78 of the clutch mechanism now closes a switch 77 to energise a solenoid 75 whereby the preselected gear is engaged. The arm 8 also opens the switch 80 and closes a switch 81 whereby a circuit for the solenoid 79 is completed via a differential-speed switch 84, 85 to maintain the clutch disengaged until the engine is speeded up sufficiently to open the switch 84, 85. The clutch may be disengaged at any time by depression of a pedal 89, which at the same time breaks the circuits of the solenoid 79. The torque-sensitive element may operate when the transmitted torque falls below a predetermined amount instead of on reversal of torque.