Patent GB-896400-A (GB)
Title: Hydraulic transmission mechanism for vehicles
Inventor: SKINNER ROBERT THOMAS JOHN
IPC: F16H61/42
Filed: 1959-11-11
Abstract: 896,400. Hydraulic transmission of gears. LUCAS (INDUSTRIES) Ltd., JOSEPH. Nov. 8, 1960 [Nov. 11,1959], No. 38189/59. Class 69 (2). [Also in Group XXXI] In an hydraulic transmission mechanism for a motor vehicle in which an engine-driven pump supplies motive fluid to an hydraulic motor which drives the vehicle, the stroke of the pump and/or the motor being variable to provide a change speed ratio between the engine and the motor, there is provided a control means comprising a valve, the setting of which is varied with the setting of the engine throttle, a pump for supplying hydraulic fluid to the valve at a rate dependent upon the engine speed and means responsive to the pressure drop across the valve for varying the speed ratio between the engine and the motor whereby the speed of the engine will be adjusted within the capacity of the mechanism to accord with the engine setting. The transmission system may be as described in Specification 896,399, wherein an engine 3 drives a pump 2 which drives a motor 1 from which the vehicle wheels are driven, and the strokes of the motor and pump may be varied by the positioning of a member 10 which is operated hydraulically by pistons working in cylinders 11 and 12, the latter being larger so that with equal pressures in the cylinders, the control-member 10 is biased towards a position determined by an hydraulic stop-member 13, normally the position of zero output of pump 2. Another hydraulic stop 14 is provided in cylinder 12, both stops comprising stepped pistons the movements of which are limited by shoulders in the cylinders. The stop 13 is held against its abutment by fluid pressure from pump 2 by way of non-return valves 14 and reversing valve 15 which, when set to open cylinder 11 to exhaust, allows stop 13 to move past the zero output position to the reversing position of member 10. The stop 13 is perforated by a passage 13a, the movements of the stop being accounted for by the different sizes of the areas subjected to pressure. Between the reversing valve 15 and the non-return valves 14, a branch passage 18 incorporating a restriction 19 leads to a valve 20 and to the cylinder 12 through a valve 23 operated by the brake pedal 24. This latter line holds stop 14 normally open and when the brake pedal is depressed, valve 23 opens the stop 14 to exhaust so that the pressure in line 21 moves the stop to a position preventing the member 10 from being moved to the " overdrive " position. With the reversing valve 15 in the position shown, fluid from the ends of cylinders 11 and 12 can escape to valve 20 which comprises a diaphragm 28 subjected to the pressure difference across a throttle valve 25, the setting of which is determined by the position of the throttle pedal 26 of the engine 3 and which is supplied with fluid from an enginedriven pump 27. Pressure differences in valve 25 are proportional to the engine speed; when the engine throttle is opened and the load on the engine is constant, the engine speed will rise increasing the rate of flow through 25. The pressure differential will increase, moving diaphragm 28 and thus opening the valve member 29. Since the fluid can escape from cylinder 11 at a slower rate than from cylinder 12 due to restriction 19, the member 10 will move to a position to give a higher speed ratio. A line 16 is connected between stop 13 and exhaust to reservoir 17.