GB733937A - Improvements in semi-automatic hydraulic gear change mechanisms - Google Patents

Abstract

733,937. Controlling change-speed gearing. AUSTIN MOTOR CO., Ltd., and HARRIS, D. P. Dec. 16, 1953 [Dec. 18, 1952], No. 32054/52. Class 80 (2). A control system for the change-speed gear and main clutch of a motor vehicle comprises a primary hydraulic circuit including in sequence an engine-driven pump 10 with accumulator 11, a check valve 13, an operating cylinder 14 for the spring-engaged clutch, a restriction valve 17 with by-pass valve 18, and parallel branches 19, 20, 21 controlled jointly by a manually-operated selector valve 22 and a valve 23, and a secondary hydraulic circuit controlled by a valve 24 and leading from the pump 10 to a valve 25 connected to valve 22 and controlling supply of the fluid to opposite ends of a doubleacting gear-shift servo 26 to which valve 23 is connected. Valve 17 is closed at engine idling speed and opens as the speed is increased. Valve 18 is connected to valve 22 so as to be open only when the latter is in neutral position. Valve 24 is opened by a diaphragm 16 subject to the pressure in cylinder 14, or by the movement of the clutch piston. In the neutral position shown, servo 26 is in mid-position, valve 17 is closed but valve 18 is open, and valves 22, 23 allow free flow through branch 19 so that pressure in cylinder 14 is relieved and the clutch is engaged and valve 24 closed. On moving valve 22 to the left (or right), flow through branch 19 is prevented by valve 22 and flow through branch 21 (or 20) is prevented by valve 23, so that pressure builds up in cylinder 14, causing disengagement of the clutch and opening of valve 24. Since valve 25 has moved with valve 22, fluid now passes to the right-hand (or lefthand) end of servo 26, causing the latter and valve 23 to move left (or right) to engage the selected gear and open branch 21 (or 20), so that free flow through that branch is allowed, pressure in cylinder 14 is relieved, valve 24 closes and the clutch re-engages. If, however, the engine is idling, valve 17 is closed so that pressure in cylinder 14 is not relieved and the clutch remains disengaged until the engine is speeded up sufficiently to open valve 17. On returning valve 22 to neutral position, branch 21 (or 20) is closed by valve 22 and branch 19 remains closed by valve 23, so that clutch disengagement results. A conduit 27 branching from branch 19 between the valves 22, 23 and leading to a mid-port of the servo cylinder is controlled by a valve 28 which is opened with the valve 24. The servo piston has oppositelyinclined ports 29, 30 such that, after the clutch disengagement, the servo is returned to midposition, a central exhaust port being controlled by a valve 31 connected to valve 22 so as to be open only when the latter is in neutral position.