Variable displacement type gear pump

Abstract

A variable displacement type gear pump has gear chambers, one of which is a specific gear chamber. A suction passage is formed in the housing so as to communicate with suction-side spaces. An outlet passage communicates with discharge-side spaces. A return passage returns the fluid discharged to the discharge-side space of the specific gear chamber to the suction passage. The return passage communicates with the suction passage at a confluence portion located upstream side of the suction-side space. An opening and closing valve opens the return passage in a small displacement operational state. A check valve is located between the discharge-side space of the specific gear chamber and the outlet passage for preventing the fluid discharged from the gear chamber other than the specific gear chamber from flowing into the discharge-side space of the specific gear chamber in the small displacement operational state.

1  . A variable displacement type gear pump for introducing and discharging fluid, comprising:
 a housing;   plural gear chambers formed in the housing, one of which is a specific gear chamber;   a gear mechanism accommodated in the respective gear chamber;   a suction-side space formed in the respective gear chamber;   a suction passage formed in the housing so as to communicate with the suction-side spaces;   a discharge-side space formed in the respective gear chamber;   an outlet passage communicating with the discharge-side spaces;   a return passage returning the fluid discharged to the discharge-side space of the specific gear chamber to the suction passage, the return passage communicating with the suction passage at a confluence portion located upstream side of the suction side space;   an opening and closing valve provided in the return passage and opening the return passage in a small displacement operational state; and   a check valve located between the discharge-side space of the specific gear chamber and the outlet passage for preventing the fluid discharged from the gear chamber other than the specific gear chamber from flowing into the discharge-side space of the specific gear chamber in the small displacement operational state.   
   
   
       2 . The variable displacement type gear pump according to  claim 1 , wherein the gear mechanism includes a drive shaft, wherein the suction passage is formed along a rotational axis of the drive shaft, wherein the suction passage has an inlet, wherein the inlet is open at an end face of the housing so as to face in the direction of the rotational axis. 
   
   
       3 . The variable displacement type gear pump according to  claim 1 , wherein the return passage, the outlet passage, and the check valve are formed in the housing. 
   
   
       4 . The variable displacement type gear pump according to  claim 1 , wherein the suction passage has a circular cross-sectional surface, wherein the return passage communicates with the suction passage in a tangent direction with respect to the circular cross-sectional surface at the confluence portion. 
   
   
       5 . The variable displacement type gear pump according to  claim 1 , wherein the return passage communicates with the suction passage at the confluence portion in an inclined manner with respect to a flow direction of the suction passage, wherein the inclination is in a direction to increase the speed of the fluid in the suction passage. 
   
   
       6 . The variable displacement type gear pump according to  claim 1 , wherein the confluence portion has a guide portion at an end of the return passage adjacent to the suction passage, wherein a flow direction of the outflow from the return passage is coincident with a flow direction of the suction passage.