Variable displacement vane pump

1. A variable displacement vane pump comprising:

a pump housing including a first housing having a cylindrical portion and a bottom located on one end side of the cylindrical portion, and a second housing located on an opposite end side of the cylindrical portion to close the opposite end side of the cylindrical portion;

a drive shaft rotatably provided in the pump housing;

a rotor rotated by the drive shaft and provided with slits;

vanes projectably or retractably provided in the slits of the rotor;

a cam ring disposed within the cylindrical portion, provided to be movable relative to a rotational axis of the drive shaft, formed into a cylindrical shape, and forming a plurality of pumping chambers together with the rotor and the vanes, the cam ring being provided with a suction area in which volumes of the pumping chambers increase as the rotor rotates and a discharge area in which volumes of the pumping chambers decrease as the rotor rotates;

an inlet port formed in the pump housing so as to open into the suction area;

a high pressure chamber provided in the first housing, the high pressure chamber being located opposite to the inlet port relative to the drive shaft, and the high pressure chamber being formed into a substantially annular shape so as to open into the discharge area;

a discharge passage disposed in the first housing and configured to discharge hydraulic fluid to the outside of the pump housing, the discharge passage being formed so that one end-side opening of the discharge passage opens into the high pressure chamber;

a pressure plate disposed between the rotor and the high pressure chamber in a direction of the rotational axis of the drive shaft, the pressure plate being provided with a communication hole which connects the pumping chambers and the high pressure chamber to each other and being biased toward the rotor by pressure of the hydraulic fluid in the high pressure chamber;

an orifice provided in the discharge passage;

a control valve which is provided in the pump housing and controllable according to differential pressure between upstream and downstream sides of the orifice, and configured to control displacement of the cam ring; and

a plurality of ribs provided within the high pressure chamber and formed so as to connect parts of an inner peripheral surface and an outer peripheral surface of the high pressure chamber, the parts being arranged opposite to each other in a radial direction of the rotational axis of the drive shaft,

the plurality of ribs including:

a first rib located on a closest side to the one end-side opening of the discharge passage in a direction around the rotational axis of the drive shaft, a top portion of the first rib being provided so as not to face the communication hole in a direction of the rotational axis of the drive shaft, and

a second rib, the second rib being located at a position adjacent the first rib in a direction away from the one end-side opening of the discharge passage,

wherein the communication hole of the pressure plate includes a first communication hole portion formed on a closest side to the one end-side opening of the discharge passage in the direction around the rotational axis of the drive shaft, and a second communication hole portion, the second communication hole portion being located at a position adjacent the first communication hole portion in the direction away from the one end-side opening of the discharge passage.

2. The variable displacement vane pump described in claim 1 , wherein

the first communication hole portion is located farther from the one end-side opening of the discharge passage than the first rib in the direction around the rotational axis of the drive shaft.

3. The variable displacement vane pump described in claim 2 , wherein

the first communication hole portion is located between the first and second ribs in the direction around the rotational axis of the drive shaft.

4. The variable displacement vane pump described in claim 1 , wherein

the second rib is located so as not to face the communication hole in a direction of the rotational axis of the drive shaft.

5. The variable displacement vane pump described in claim 4 , comprising:

a third rib provided within the high pressure chamber, the third rib and the first rib being located on the opposite sides relative to the second rib in the direction around the rotational axis of the drive shaft, wherein

the third rib is located so as not to face the communication hole in the direction around the rotational axis of the drive shaft.

6. The variable displacement vane pump described in claim 1 , comprising:

a third rib disposed in the high pressure chamber, the third rib and the first rib being located on the opposite sides relative to the second rib in the direction around the rotational axis of the drive shaft, wherein

the first and third ribs are arranged so that a gap between the first rib and the pressure plate in the direction around the rotational axis of the drive shaft and a gap between the third rib and the pressure plate in the direction around the rotational axis of the drive shaft is smaller than a gap between the second rib and the pressure plate.

7. The variable displacement vane pump described in claim 6 , wherein

the first rib is formed so that the gap between the pressure plate and the first rib in the direction of the rotational axis of the drive shaft is equal to or smaller than the gap between the pressure plate and the third rib.

8. The variable displacement vane pump described in claim 1 , wherein

the high pressure chamber includes a chamber section;

the chamber section is provided between the first rib and the one end-side opening of the discharge passage; and

a flow channel sectional area of the chamber section is larger than a sectional area of a gap between the first rib and the pressure plate and larger than a sectional area of the one end-side opening of the discharge passage.

9. The variable displacement vane pump described in claim 8 , wherein

the one end-side opening of the discharge passage is offset from the gap between the first rib and the pressure plate in the direction of the rotational axis of the drive shaft.

10. The variable displacement vane pump described in claim 8 , wherein

the orifice is provided adjacent to the one end-side opening of the discharge passage;

the chamber section includes a machined surface grinded by machining; and

the machined surface is located in a region which is part of an inner peripheral surface of the chamber section, the region being provided with the one end-side opening of the discharge passage.