Variable displacement type gear pump

Abstract

In a variable displacement type gear pump, each of a main gear pump portion and a sub gear pump portion has a drive gear, a driven gear engaging with the drive gear, and an urging portion applying radial load to the drive and driven gears. A bypass passage returns fluid in a discharge-side space of the sub gear pump portion to a suction passage. An opening and closing valve opens the bypass passage in a small displacement operational state. A drive shaft supports the main drive gear and the sub drive gear. A driven shaft supports the main driven gear and the sub driven gear. The drive gears and the driven gears are rotated in accordance with a rotation of the drive shaft. The drive and driven shafts transmit the radial load in the main gear pump portion to the sub gear pump portion in the small displacement operational state.

1 . A variable displacement type gear pump for introducing and discharging fluid, comprising:
 a main gear pump portion having a main drive gear, a main driven gear, and a main urging portion, wherein the main drive gear and the main driven gear are engaged with each other and applied a radial load by the main urging portion;   a sub gear pump portion having a sub drive gear, a sub driven gear, and a sub urging portion, wherein the sub drive gear and the sub driven gear are engaged with each other and applied a radial load by the sub urging portion;   a suction-side space formed in the main gear pump portion and the sub gear pump portion, respectively;   a suction passage communicating with the suction-side spaces;   a discharge-side space formed in the main gear pump portion and the sub gear pump portion, respectively;   an outlet passage communicating with the discharge-side spaces;   a bypass passage returning the fluid in the discharge-side space of the sub gear pump portion to the suction passage;   an opening and closing valve formed in the bypass passage and opening the bypass passage in a small displacement operational state;   a check valve located between the discharge-side space of the sub gear pump portion and the outlet passage for preventing the fluid discharged from the main gear pump portion from flowing into the discharge-side space of the sub gear pump portion in the small displacement operational state;   a drive shaft supporting the main drive gear and the sub drive gear; and   a driven shaft supporting the main driven gear and the sub driven gear, wherein the main and sub drive gears and the main and sub driven gears are rotated in accordance with a rotation of the drive shaft, wherein the drive and driven shafts transmit the radial load in the main gear pump portion to the sub gear pump portion in the small displacement operational state.   
   
   
       2 . The variable displacement type gear pump according to  claim 1 , wherein the main drive gear is formed integrally with the drive shaft. 
   
   
       3 . The variable displacement type gear pump according to  claim 2 , wherein the sub drive gear is connected to the drive shaft through a rotational force transmitting device so that the rotational force transmitting device transmits the rotation of the drive shaft to the sub drive gear. 
   
   
       4 . The variable displacement type gear pump according to  claim 3 , wherein the sub drive gear has a through hole with a spline groove formed therein, wherein the drive shaft has a spline formed therein so that the sub drive gear is connected to the drive shaft by spline coupling, wherein the rotational force transmitting device includes the spline formed in the drive shaft and the spline groove formed in the through hole of the sub drive gear. 
   
   
       5 . The variable displacement type gear pump according to  claim 2 , wherein the main driven gear is formed integrally with the driven shaft. 
   
   
       6 . The variable displacement type gear pump according to  claim 5 , wherein the driven shaft and the sub driven gear are relatively rotatable. 
   
   
       7 . The variable displacement type gear pump according to  claim 6 , wherein the sub driven gear has a through hole with a circular cross section in which the driven shaft is rotatably inserted. 
   
   
       8 . The variable displacement type gear pump according to  claim 7 , wherein clearance between the through hole of the sub driven gear and the driven shaft is set smaller than the clearance between the driven shaft and a bearing for the driven shaft. 
   
   
       9 . The variable displacement type gear pump according to  claim 1 ,
 wherein the main drive gear is formed integrally with the drive shaft, wherein the sub drive gear has a through hole in which the drive shaft is inserted, wherein rotational force of the drive shaft is transmitted to the sub drive gear through a rotational force transmitting device,   wherein the main driven gear is formed integrally with the driven shaft, wherein the sub driven gear has a through hole with a circular cross section, wherein the driven shaft is rotatably inserted in the through hole.   
   
   
       10 . The variable displacement type gear pump according to  claim 1 , the main gear pump portion further comprising:
 a main gear chamber;   a main gear mechanism formed in the main gear chamber; and   a side plate formed adjacent to the main gear chamber, wherein the side plate has a groove as the main urging portion for introducing the fluid of the discharge-side space and generating a gear approaching force as the radial load in the main gear pump portion to move the main drive gear and the main driven gear close to each other, and wherein the gear approaching force in the main gear pump portion is transmitted to the sub gear pump portion through the drive and driven shafts in the small displacement operational state.