Pump device

Abstract

A fixed capacity pump (P) sucks working oil from a reservoir (R) through a conduit (Rp) and a suction passage ( 1 ), and discharges the pressurized working oil into a discharge passage ( 2 ) connected to an actuator (A). A choke ( 21 ) is disposed in the discharge passage ( 2 ), and a flow control valve (F) recirculates a part of the working oil in the discharge passage ( 2 ) upstream of the choke ( 21 ) to the suction passage ( 1 ) according to a pressure loss generated by the choke ( 21 ). The characteristic of the choke ( 21 ) which significantly increases the flow resistance in a low temperature state makes the flow rate of the recirculated working oil increase, thereby preventing cavitation/noise from occurring in the pump (P) when operated at high speed and in a low temperature state.

1 . A pump device for supplying oil to an actuator, comprising: 
 a fixed capacity pump;    a choke through which working oil discharged by the pump flows; and    a flow control valve which recirculates a part of the working oil discharged by the pump to a suction side of the pump, according to a pressure loss generated by the choke.    
   
   
       2 . The pump device as defined in  claim 1 , further comprising a casing in which the pump, the choke and the flow control valve are enclosed.  
   
   
       3 . The pump device as defined in  claim 2 , further comprising a suction passage which supplies working oil to the suction side of the pump, a discharge passage which supplies a part of the working oil discharged by the pump to the actuator, the choke being disposed in the discharge passage, and a recirculation passage which supplies the working oil recirculated by the flow control valve to the suction passage.  
   
   
       4 . The pump device as defined in  claim 3 , wherein the flow control valve comprises a spool which regulates a flow rate of the working oil recirculated by the flow control valve according to a difference in pressure between an upstream side of the choke and a downstream side of the choke.  
   
   
       5 . The pump device as defined in  claim 1 , wherein a diameter of the choke is set within a range of two to eight millimeters, and a ratio of the diameter to a length of the choke is set to be equal to or less than unity.