Patent GB-1053892-A (GB)
IPC: F16H61/46
Abstract: 1,053,892. Hydrostatic transmissions. JOSEPH LUCAS (INDUSTRIES) Ltd. March 25, 1965 [Jan. 29, 1964], No. 3863/64. Heading F2D. In a hydrostatic transmission having an electric motor driving a variable displacement swash-plate pump which supplies liquid to a swash-plate motor, the pump swash-plate is adjusted by a hydraulic servomotor under the control of a solenoid-operated valve which is adjusted in accordance with the load on the electric motor. The pump swash-plate is connected mechanically to a piston 18 slidable in a stepped cylinder 17 having a passage 24 connectable to passages 22, 23 under the control of a valve 19. The passage 22 is connected to a selector valve 35 which is manually adjustable to forward, reverse and neutral (shown) positions. In the forward position the passage 22 is connected to a passage 34 which is connected to the high pressure transmission line. In the reverse position the passage 22 is connected to a passage 36 providing exhaust of fluid to a reservoir through the space between the heads of the piston 18 and a passage 37. In the neutral position the passage 22 is connected to a line 33 connected to the other transmission line and permanently connected to the passage 23. When the selector valve 35 is in its forward position, and a demand for power (decreasing current in the electric motor) results in a solenoid 27 being operated, the valve 19 is moved to the left by a spring 26 so that pressure fluid from the line 34 is admitted through a passage 48, the valve 35 and passages 22, 24 to the cylinder 17 to increase the stroke of the pump. Increasing current in the electric motor circuit causes solenoid 27 to move the valve 19 to the right to permit escape of liquid from the cylinder 17 through the passage 23 to the lower pressure line 33 to decrease the stroke of the pump. In reverse, decreasing motor current causes movement of the valve 19 to the left to permit escape of liquid from cylinder 17 to the reservoir through passages 36, 37. This causes an increase in the stroke of the pump in the reverse direction. Increasing electric motor current causes admission of high pressure fluid, through the line 33 and passage 23 to reduce the stroke of the pump. In order to modify the movement of the solenoid so that the displacement of the armature is proportional to the voltage, the armature instead of acting directly on the valve 19, actuates a valve 29 (Fig. 3, not shown) which closes an exhaust passage 30 through a piston 25 fast with the valve 19, the left-hand side of the piston being supplied with pressure fluid from the line 34 through a relief valve 44 and with fluid from a make-up pump through a line 40 and restriction 43. The valve member 29 is supported by a spring diaphragm and movement of the armature with decreased voltage causes the valve member 29 to open the exhaust passage 30 so that the spring shifts the valve 19 and piston 25 until the valve 29 again closes passage 30. An adjustable resistance in the solenoid circuit may be set to permit a required proportion of the available current to pass through the solenoid or it may be used to vary the horse power of the motor by controlling the servo piston position.