GB1289883A - - Google Patents

Abstract

1289883 Hydraulic motor control circuits R BERINGER K STERL K GOGAL F LEUTENEGGER and W OLDANI [trading as BERINGER-HYDRAULIK R BERINGE CO] 24 April 1970 [25 April 1969] 19845/79 Heading F1P [Also in Division B8] A hydraulic circuit for maintaining constant the speed of a lift motor 102 independently of the load comprises a two-part block having pump and return connections 1, 8 Fig. 1b a chamber 3 connectable by means of volume flow control valve 20 Fig. 1α to motor 102 and having a pressure difference balancing piston valve 5 which serves to maintain the pressure in chamber 3 a constant amount above that in the motor 102 during lifting and a constant amount below motor pressure during descent under gravity, the block also having a spring-biased piston 39 responsive to pump pressure transmitted through a duct 40 and serving to vary the thrust exerted by a spring 34 on a control piston 33 which in turn controls fluidpressure in a duct 37 leading to a spring space above valve 5; the control valve 20 being adjusted indirectly by means of a solenoid-actuated slider member 11 and the balancing valve 5 being adjusted indirectly by a further solenoid-actuated slider 22. To move the lift upwardly magnets 9, 10 are simultaneously energized. Slide 11 moves down and so connects chamber 3 and a conduit 12 with a conduit 14 leading to the underside of a piston 16 which unseats valve 20 so that pressure fluid flows to the underside of cylinder 102. The simultaneous upward movement of slider 22 unseats a ball 24 and connects a duct 25 leading from the lower end of cylinder 102 with a duct 27 and a branch duct 30 thereof with an annular recess 36 of control piston 33 and hence with the duct 37 leading to the spring space of valve 5. Near the end of ascent, magnet 10 is de-energized so that conduct 12 is blocked by slider 11 and the motor decelerates and is stopped on de-energizing magnet 9 whereon valve 20 is closed by its spring 21. Fluid-pressure in ducts 27, 30, 37 is exhausted through ducts 55, 17 and the pump pressure in chamber 3 acting through a base 4 in valve 5 lifts the latter and thus connects the pump to return. During descent under gravity and with both magnets 9, 10 energized and the pump inoperative, piston 39 is subjected to the full downward pressure of its spring 41 thereby compressing the spring 34 to displace control piston 33 to a position determined by an adjustable stop 59 thereby regulating the pressure drop between ducts 30, 37. Pressure in duct 37 is opposed by a greater pressure in chamber 3 which unseats piston 5 and connects the underside of motor 102 to exhaust.