GB1292922A - Improvements in rotary positive displacement pumps - Google Patents

Abstract

1292922 Rotary pumps ROBERT BOSCH GmbH 6 March 1970 10808/70 Heading F1F In a rotary positive-displacement pump of the two-abutment sliding vane kind driven at varying speed to supply a load, e.g., vehicle power steering gear, wherein at low speeds the liquid supplier to the load is returned therefrom through a return bore to the suction side of the pump and at higher speeds residual flow of liquid in excess of that required is diverted by way of a flow regulating valve to the suction side of the pump, the residual flow is throttled to increase its velocity to produce a partial vacuum for indicating liquid through the bore into the suction side of the pump and a control valve spool of the flow regulating valve acts as a diffuser to lower the velocity of the liquid and increase its pressure to ensure satisfactorily charging of the pump even at maximum pump speed, In one embodiment, a control valve spool 14, Fig.2, slidable in a bore 13 and urged by a spring 23 into end engagement with a fixed insert 12 is formed with a recess 29, Fig.3, which faces a passage 24 leading to the inlet zones of the pump and controls a return bore 26 connected to a reservoir 28 which receives the returned liquid from the load being operated. The insert 12 is connected to pump delivery by a passage 10 and formed with a wall 18<SP>1</SP> having a throttling orifice 25, Fig.1, through which pump delivery passes to pump discharge passage 20. A part 21 connects the discharge passage 20 with a chamber 22 behind the valve spool 14 so besides being acted upon by the spring, the spool is subjected to the pressure difference on the two sides of the orifice 25. At low pump speeds this pressure difference is small so that the spring 23 holds the spool 14 in abutment with the insert 12. At high speeds as the pressure difference increases the spool 14 is moved rightwardly and the return bore 26 is connected via a tapered recess 27 with the passage 24 leading to the inlet zones of the pump. A flow-off flank 30 from the recess 29 and diffuser passages 24' leading to the two suction zones of the pump produce or partial vacuum, to decrease the velocity of the liquid sucked from the bore 24 and increase its pressure to ensure full filling of the pump inlet zones even at high pump speeds. For other embodiments reference should be made to the Specification.