GB816948A - Improved unloader device for a hydraulic system - Google Patents

Abstract

816,948. Fluid-pressure servomotor-control systems. GENERAL MOTORS CORPORATION. Jan. 2, 1957 [Feb. 16, 1956], No. 181/57. Class 135. An unloader device for an hydraulic system including a pump 10 (Fig. 1) connected through a check valve 80 to an accumulator 35, comprises a by-pass valve 42 urged by a spring 32 towards the closed position and subjectable to opposed accumulator pressure through a control valve which includes a valve member 52 closable against accumulator pressure by a spring 56, when accumulator pressure falls below a predetermined value, to cut off accumulator pressure from the by-pass valve and permit closure of the by-pass valve, pump discharge pressure being applicable to the control valve member through a pilot valve 31 which opens, when pump discharge pressure exceeds a higher predetermined value, to cause reopening of the by-pass valve. As further shown (see particularly Fig. 2), the control valve member 52 is a ball movable between two seats formed by openings 58 and 60 of different diameters, under the action in one direction of a plunger 50 having a stem slidable in guide sleeve 59 to contact the ball, and the opposed action of a plunger 54 loaded by adjustable control spring 56. Plunger 50 is subject to pump discharge pressure from discharge chamber 36 through spring-adjusted pilot valve 31, accumulator pressure being maintained in seat opening 58 through an open pipe 51 and passage 70 in sleeve 59. The space between seats 58 and 60 communicates with a servo-piston integral with the by-pass valve 30, via passage 66 which has a restriction 66a. Seat opening 60 leads to a tank 20 through a hole in control spring adjuster 92. When the pump discharge pressure exceeds the higher predetermined value, pilot valve 31 opens to admit pressure to plunger 50, causing the stem of the plunger 50 to force ball 52 on to the larger diameter seat 60 and so admit accumulator pressure to bypass valve 30 to open it, loss of accumulator pressure to piston 30 being delayed by restriction 66a. Upon reduction of accumulator pressure below the lower predetermined value, spring 56 returns ball 52 to seat 58 thus venting piston 30 to the tank and allowing the by-pass valve to close and re-load the pump.