GB836690A - Improvements in or relating to vehicles having hydraulic transmissions and hydrauliccontrol systems for the hydraulic transmissions - Google Patents

Abstract

836,690. Hydraulic transmissions. MASCHINENFABRIK ESSLINGEN. Aug. 8, 1958 [Aug. 8, 1957], No. 25625/58. Class 69 (2). A vehicle transmission comprises a swash plate pump 1 connected to a motor 3, or motors, by lines 18, 19. The swash-plate is adjusted by pistons 4, 5 in cylinders 34, 35 connected, through a reversing valve 6 with a control cylinder 11 and a reservoir 12. The upper ends of cylinders 34, 35 are connected by passages 16, 17 to the lines 18, 19. In operation a motor driving the pump is started with the swash-plate in its neutral position, a foot pedal 10 is then depressed to move a controlpiston 8 against a spring 9 to draw liquid from the reservoir 12 through a non-return valve 13 into the control cylinder. On releasing pedal 10 the piston is urged by its spring to the right, expelling liquid from the cylinder 11 through valve 6 to cylinder 34 or 35 to tilt the swash-plate. Under heavy load conditions, such as hill climbing, the pressure in the high-pressure line 18 or 19 rises and acts on the associated piston 4 or 5 to reduce the tilt of the swashplate, spring 9 yielding to allow the movement. The maximum pressure is limited by a relief valve, 20 between lines- 18, 19. Valve 6 is actuable to reverse the angle of the swash-plate to reverse the motor 3, and has another position in which the lower ends of the cylinders 34, 35 are interconnected and the control cylinder is connected to the reservoir. In this position the pump swash-plate is returned to neutral by springs 14, 15 acting on the pistons 4, 5 and the motor 3 is thus braked. Valve 20 may be manually operable to short-circuit the motor when desired, and a valve 24 short-circuits the control cylinder 11 whenever an operator is not in position on the vehicle.