Vane pump

1. A vane pump comprising:

a rotor that is coupled with a rotation shaft to rotate;

a plurality of vanes that are slidably held by a plurality of vane grooves which are disposed in a radiation direction in an outer circumferential portion of the rotor;

a cam ring that is arranged to surround the rotor and the plurality of vanes;

a side plate that covers the cam ring and includes a suction port which is configured to supply a working fluid to the cam ring and is formed on an outer circumference of the side plate as a portion being recessed to a radially inner side of the rotation shaft to form the supply unit; and

wherein the suction port has an inner end portion, which extends along and is spaced from an inner circumference of the cam ring by a constant distance in a radial direction of the rotation shaft.

2. The vane pump according to claim 1 , further comprising:

another side plate that is arranged on a side opposite to the side plate across the cam ring to cover the cam ring and includes another suction port which is configured to supply the working fluid to the cam ring and is formed on an outer circumference of the other side plate as a portion being recessed to the radially inner side of the rotation shaft, and

wherein the other suction port has another inner end portion, which extends along and is spaced from the inner circumference of the cam ring by another constant distance in a radial direction of the rotation shaft.

3. The vane pump according to claim 2 , wherein

the side plate includes a through-hole, on the radially inner side of the rotation shaft compared to the other suction portion, which supplies the working fluid pressing the plurality of vanes to allow the plurality of vanes to protrude from the rotor into the cam ring, and

the through-hole is formed in such a manner that an outer end portion thereof extends and is spaced from the inner circumference of the cam ring by another constant distance in the radial direction.

4. The vane pump according to claim 1 , wherein

the side plate includes a through-hole, on the radially inner side of the rotation shaft compared to the suction portion, which supplies the working fluid pressing the plurality of vanes to allow the plurality of vanes to protrude from the rotor into the cam ring, and

the through-hole is formed in such a manner that an outer end portion thereof extends and is spaced from the inner circumference of the cam ring by a constant distance in the radial direction.

5. The vane pump according to claim 1 , wherein the inner end portion of the suction portion has an arc shape, which is smaller in radius than an outer circumferential circle of the side plate.

6. The vane pump according to claim 5 , wherein the arc shape of the inner end portion is a part of an elliptical shape.

7. The vane pump according to claim 1 , wherein

an opening with the constant distance in the radial direction is formed between the inner end portion and the inner circumference of the cam ring.

8. The vane pump according to claim 7 , wherein in the opening, the vane is configured to protrude by the constant distance to a radially outer side of the rotation shaft when the vane is in operation.

9. The vane pump according to claim 1 , wherein a position of the inner end portion is determined such that the vane protrudes from the inner side plate by less than half of the length thereof in the radial direction.