Patent GB-632498-A (GB)
Title: Improvements in and relating to automatic fluid pressure actuated transmission for aself-propelled vehicle
IPC: F16H61/688
Filed: 1945-06-22
Abstract: 632,498. Fluid-pressure servomotor-control systems. LIVERMORE, W. T. June 22, 1945, No. 16008. Convention date, June 8, 1944. [Class 135] [Also in Group XXIV] An automatic fluid-pressure-actuated transmission for a self-propelled vehicle includes a pair of fluid-pressure-actuated clutches and change-speed gearing interposed between an engine-driven shaft and a propeller shaft, a one-way drive connection, e.g. a free-wheeling clutch, arranged so that shifts from a low-speed drive through one of said clutches to an intermediate or second-speed drive may be effected by engagement of the second clutch, while the first clutch remains engaged, and a shiftable synchronizer unit to permit said first clutch to establish a high-speed drive byepassing said one-way drive connection, said synchronizer unit being adapted to be set for high-speed drive while power is being transmitted through the second clutch in said second-speed drive. The engine shaft 10 drives the vehicle through either of two clutches 12, 13 connected respectively to a shaft 14 and to a sleeve 21. For low-speed drive, the clutch 12 is engaged, partly by pressure-fluid admitted to a chamber 40 where it acts on a diaphragm 44 moving a plate 45 and rods 47 to the right, and partly by centrifugal force exerted by weights 60 rotating with the engine and pivotally connected to the plate 45 and to the rods 47, the drive being transmitted through gear-wheels 18, 33, a free-wheel unit 34, a sleeve 26, gear-wheels 27, 28, the latter of which is rotatably mounted on a shaft 29, and a free-wheel unit 32, to the main drive coupling 30. The second-speed drive is established through the clutch 13, which is engaged by pressure-fluid acting on a diaphragm 50, gearwheels 22, 23 and gear-wheels 27, 28, irrespective of whether or not the clutch 12 is disengaged, on account of the free-wheel unit 34, whilst high-speed drive is established by direct drive to the shaft 29 through the clutch 12 and a dogclutch 18a, 20 having synchronizing-mechanism. An engine-driven pump 65 delivers pressure-fluid through a conduit 75 to an accumulator 76 comprising a spring-loaded piston 77, and thence through a conduit 79 to a control valve 85 comprising a pair of spring- loaded lift-valves 87, 88 loosely mounted on a spindle 89 bearing at its lower end against a spring-loaded plunger 91 and abutting at its upper end against a plunger 90 adaped to be depressed by an accelerator pedal 100. Pressure-fluid in the conduit 79 opens the valve 88 against its spring and passes through a restriction 91a, a conduit 101 and a selector valve 83 to one or other of the clutch-actuating diaphragms 44, 50 and since depression of the accelerator pedal 100 reduces the spring-loading on the valve 88, the pressure applied to the clutches will be proportional to the throttle opening. A vehicle-driven pump 66 delivers pressure-fluid to a spring-loaded piston 71, working in a ported cylinder 70, and connected by a rod 72 to a floating lever 73, to which is connected by lost-motion connections, a pair of pilot valves 81, 82. In operation, when the engine is accelerated from idling speed, pressurefluid from the pump 65 opens the valve 88, and passes through a conduit 35, to the diaphragm 44 to engage low-speed drive. As the vehicle starts moving the pump 66 delivers fluid to the cylinder 70 causing the piston 71 to rock the lever 73 clockwise about an adjustable stop 120, thus causing the pilot valve 81 to connect the conduit7 9 with a conduit 115 to apply pressurefluid to a piston 113, thereby moving the piston 113, together with the selector valve 83, to the right, until the piston 113 reaches the end of its bore and a pin 121 on a valve-rod 83a of the selector valve engages a pivoted stop 122. In this position of the selector valve the supply of pressure-fluid to the clutch 12 is cut off and the conduit 35 is vented through a restricted passage 140, whilst the clutch 13 is engaged by the admission of pressure-fluid through a conduit 36 to the diaphragm 50, thus engaging secondspeed drive. As the vehicle speed increases further, a point is reached. when the pilot valve 82 places a conduit 116 in communication with the conduit 79 and pressure-fluid then acts on the left-hand end of the selector valve, which is prevented from moving by the stop 122, and also on the left-hand end of a synchronizer valve 103 which is moved against a spring 103b to permit pressure-fluid to flow from a conduit 79a, through a conduit 79e and a valve 104 to the right-hand end of a cylinder 105 containing a piston 106 for engaging the dog-clutch 18a, 20, the actual engagement being delayed whilst synchronization takes place, by a restricted inlet 111a to the cylinder 105 and by a spring- connection between the piston 106 and a rod 107 carrying a striker fork 109 for moving the member 20. As the piston 106 moves, a collar 125a on the rod 107 engages a lever 125 which rocks the lever 122 to permit the selector valve 83 to move further to the right and cause the clutch 12 to be engaged and the clutch 13 to be disengaged, high-speed drive then being established. In order that the engine may be used as a brake, a pedal 126 is provided whereby second-speed may be engaged when desired, one end of this pedal also serving as a stop to prevent movement of the rod 107 under the influence of pressure-fluid admitted to the left-hand end of the cylinder 105 during normal operation. When depressed, the pedal acts through aseries of bellcrank levers and links 131 to 135 to depress a plunger 136 which bears upon the lever 73, causing the pilot valve 82 to interrupt communication between the conduits 79, 116, whereby the selector valve returns to the position in which the clutch 13 is engaged and the clutch 12 is disengaged. At the same time the synchronizer valve 103 is moved to the left to permit pressure-fluid to act on the left-hand side of the piston 106 to engage a dog-clutch 20, 28a, thus rendering the free-wheel unit 32 ineffective. To start the engine by towing the vehicle, the pedal 126 is depressed and pressurefluid for engaging second-speed will be delivered by the vehicle-driven pump through a checkvalve 77c. Specifications 515,001 and 632,562 are referred to.