GB1003605A - Improvements in or relating to fluid-pressure operated power transmission systems - Google Patents

Abstract

1,003,605. Hydrostatic transmissions. C. VAN DER LELY N.V. June 21, 1962 [July 18, 1961], No. 3443/65. Divided out of 1,003,604. Heading F2C. An hydrostatic transmission for a vehicle comprises pump and motor units 66, 67 of the swash-plate type controlled by a selector valve 82, and an auxiliary make-up pump 58 discharging through a cooler 59 and non-return valve 63 to the low-pressure circuit 65 of the transmission, the circuit 65 being connected to the pump reservoir 57 by a line 71, one-way valve 70 and relief valve 80. The valve unit 70 has end ports 111, 112 connected to the transmission high and low pressure lines 69, 71 respectively, a central port 113 connected to the low pressure relief valve 80, and opposed identical valve closure elements 94, 95 with spring-loaded centering plungers 101, 102. Normally the valve elements are moved to the right by the higher pressure prevailing in line 69 and port 111 to close valve element 94 and establish an open communication between ports 112, 113 whereby a continuous flow of cooled liquid is fed from pump 58 to the transmission. The valve 80 is set to open at a predetermined pressure in the low pressure line 71. As shown the high and low pressure lines 69, 71 are interconnected through relief and check valves 73, 75 which are preferably of the form described in Specification 1,003,604. In a modified system, Fig. 5 (not shown), the relief valve 73 is omitted and the pipeline 84 from the selector valve 82 replaced by one connected directly to the non-return valve 89.