GB996537A - Valves for use in hydraulic transmission systems - Google Patents

Abstract

996,537. Valves. JOSEPH LUCAS (INDUSTRIES) Ltd. June 1, 1964 [May 31, 1963], No. 21839/63. Heading F2V. A valve for use in an hydraulic transmission system of the type in which a pump drives a motor, comprises a housing 10 provided with a bore 12 having chambers 13, 14 at opposite ends of the bore in which are provided spring-loaded pistons 15, 16. A valve spool, formed by two parts 19a, 19b is located in the bore 12 and is loaded by springs 20 to a central position. The housing is provided with a series of ports opening into the bore of which ports 21, 22 are connected to the two lines connecting the pump and the motor, ports 25, 26 are connected respectively to a boost or make-up pump and to a non-return valve 28 in a drain line, ports 30, 31 which are connected by an external pipe and ports from the transmission lines which lead to spaces 32, 33 at the outer end of the bore. The port 25 is connected through a non-return valve 39 to a groove 37 in the bore which is also connected through a restriction 38 to a passage 37 which connects chambers 13, 14. The passage 37 is connected through a pressure relief valve 39a to port 25. In operation, assuming that the port 22 and space 33 is connected to the high pressure line and port 21 and space 32 is connected to the low pressure line, the spool 19a, 19b moves to the left to abut piston 16. In this position, the port 25 is connected to the port 21 through groove 40b to supply fluid from the boost pump to the low pressure line. The space 32 is also connected through groove 41b, port 30, pipe (not shown), port 31, groove 41a, and port 26 to drain thus providing a circulation for cooling. The high pressure line is connected through port 22, groove 40a, recess 37 and restriction 38 to passage 37 and thus acts on both pistons 15, 16. If the high pressure exceeds a predetermined value, the relief valve 39a opens and the pressure in space 33 is then able to move the spool 19a, 19b and piston 16 further to the left and connect ports 22, 21 to relieve pressure from the high to the low pressure line. When the high and low pressure lines are reversed, the valve acts in the opposite direction in a similar manner. Before starting the pump of the transmission the boost pump 27 is started to supply fluid past non-return valve 39 to recess 37 and the two parts of the piston valve move outwards to allow flow to the transmission lines.