GB1249235A - A regulating device for hydraulic circuits, such as dan drives - Google Patents

Abstract

1,249,235. Hydrostatic transmission. M. BEHR, [trading as SUDDEUTSCHE KUHLERFABRIK JULIUS FR. BEHR]. 19 March, 1969 [20 March, 1968], No. 14398/69. Addition to 1,186,401. Heading F2D. In a hydrostatic drive for a vehicle engine cooling fan comprising a pump (1), Fig. la (not shown), and a motor (2), a pressure limiting valve 6 is arranged to by-pass motor (2), the response pressure of the valve 6 being automatically adjusted by motor return pressure 19 and the return pressure being delivered via a restrictor 42 to a chamber 40 to load a piston 35 acting on a pilot valve 38 controlling throughflow of an orifice 14 in the pressure-limiting valve piston 13, the chamber 40 being vented through a thermostatically controlled pilot valve 28. As shown, the pilot valve 28 is closed by a thermostat 3 when the temperature exceeds a predetermined value. Below this value, the valve 28 opens to vent chamber 40 to unload piston 35 and open valve 38 allowing flow through orifice 14. Such flow forms a pressure differential across the piston 13 to move the piston down and directly connect delivery and return lines 11, 19, and the motor does not rotate. With rising temperature, valve 28 closes to load piston 35 and close valve 38, decreasing flow through the orifice 14. Piston 13 moves up to restrict flow between lines 11, 19, and the motor rotates the fan. A manual screw 43 blocks a leak line 33 from the pilot valve 28 to provide fan drive if the thermostat fails. Again, Fig. 3, (not shown), valves 3 and 28 are mounted separate from valves 6 and 38, and are connected to chamber 40 by a conduit (49). Also, Fig. 4 (not shown), the orifice 14 is formed as an insert in the valve 6 piston, and valve 38 is loaded by a servo piston (51) in which slides a throttle edge (52) on a piston-rod (50) connected to the thermostat 3.