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Within an angular area where each vane of a vane pump having backpressure grooves is moved radially inwardly as the rotor rotates, the outer circumferential edge of the backpressure groove is indented toward the rotational axis of the rotor along a locus drawn by the radial innermost end of each van

Within an angular area where each vane of a vane pump having backpressure grooves is moved radially inwardly as the rotor rotates, the outer circumferential edge of the backpressure groove is indented toward the rotational axis of the rotor along a locus drawn by the radial innermost end of each vane so that the radial innermost end of each vane does not protrude radially inwardly beyond a predetermined distance from the indented part of the outer circumferential edge of the backpressure groove.

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1. A vane pump comprising:a vane pump section composed of a cam ring contained in a pump housing, a rotor rotatably provided in said cain ring with a plurality of slits formed in radial direction, and a plurality of vanes guided to be radially slidable respectively in said slits and brought at radia

1. A vane pump comprising:a vane pump section composed of a cam ring contained in a pump housing, a rotor rotatably provided in said cain ring with a plurality of slits formed in radial direction, and a plurality of vanes guided to be radially slidable respectively in said slits and brought at radial outermost ends into sliding engagement with a cam surface formed at the internal surface of said cam ring for partitioning a space between the outer circumferential surface of said rotor and said cam surface into plural pump chambers each of which is varied in volume as said rotor rotates; at least one side wall member closing at least one side surface of said vane pump section and enabling said rotor and said vanes to be slidable thereon; and an annular backpressure groove formed on an inside end surface of said side wall member to encircle the rotational axis of said rotor to communicate with innermost end portions of said slits and supplied with pressurized fluid ejected from said pump, wherein within an angular area where each vane is moved radially inwardly while being rotated together with said rotor, the outer circumferential edge of said backpressure groove is deflected to be indented toward the rotational axis of said rotor along a locus on which the radial innermost end of each vane moves so that the radial innermost end of each vane does not protrude radially inwardly beyond a predetermined distance from the indented part of the outer circumferential edge of said backpressure groove,wherein within at least a part of another angular area where each vane is moved radially inwardly from the radial outermost position, a recess portion for preventing a radial innermost part of one side surface of each vane from contacting the inside end surface of said side wall member is further provided on the inside end surface of said side wall member which slidably contacts said rotor and each vane; and the outer circumferential edge of said recess portion is deflected at its rotationally preceding part to be indented toward the rotational axis of said rotor along said locus so that the radial innermost end of each vane does not protrude radially inwardly beyond a predetermined distance from the rotationally preceding part of the outer circumferential edge of said recess portion. 2. The vane pump as set forth in claim 1, wherein said backpressure groove comprising:at least one suction backpressure groove arranged to be circumferentially close to at least one suction port which opens to said pump chambers within an angular area where each of said pump chambers increases its volume as said rotor rotates; at least one ejection backpressure groove arranged to be circumferentially close to at least one ejection port which opens to said pump chambers within another angular area where each of said pump chambers decreases its volume as said rotor rotates; and communication grooves of an arc shape having a center on the rotational axis of said rotor and connecting said at least one suction backpressure groove with said at least one ejection backpressure groove; and wherein the outer circumferential edge of said ejection backpressure groove is deflected at its rotationally preceding part to be indented toward the rotational axis of said rotor along said locus so that the radial innermost end of each vane does not protrude radially inwardly beyond said predetermined distance from the rotationally preceding part of the outer circumferential edge of said ejection backpressure groove. 3. The vane pump as set forth in claim 2, wherein the rotationally preceding part of the outer circumferential edge of said ejection backpressure groove is in parallel to said locus.4. The vane pump as set forth in claim 1, wherein the rotationally preceding part of the outer circumferential edge of said recess portion is in parallel to said locus.5. A vane pump comprising:a vane pump section composed of a cam ring contained in a pump housing, a rotor rotatably provided in said cam ring with a plurality of slits formed in radial direction, and a plurality of vanes guided to be radially slidable respectively in said slits and brought at radial outermost ends into sliding engagement with a cam surface formed at the internal surface of said cam ring for partitioning a space between the outer circumferential surface of said rotor and said cam surface into plural pump chambers each of which is varied in volume as said rotor rotates; at least one side wall member closing at least one side surface of said vane pump section and enabling said rotor and said vanes to be slidable thereon; and an annular backpressure groove formed on an inside end surface of said side wall member to encircle the rotational axis of said rotor to communicate with innermost end portions of said slits and supplied with pressurized fluid ejected from said pump, wherein within an angular area where each vane is moved radially inwardly while being rotated together with said rotor, the outer circumferential edge of said backpressure groove is deflected to be indented toward the rotational axis of said rotor along a locus on which the radial innermost end of each vane moves so that the radial innermost end of each vane does not protrude radially inwardly beyond a predetermined distance from the indented part of the outer circumferential edge of said backpressure groove,wherein said backpressure groove comprises at least one suction backpressure groove arranged to be circumferentially close to at least one suction port which opens to said pump chambers within an angular area where each of said pump chambers increases its volume as said rotor rotates; at least one ejection backpressure groove arranged to be circumferentially close to at least one ejection port which opens to said pump chambers within another angular area where each of said pump chambers decreases its volume as said rotor rotates; and communication grooves of an arc shape having a center on the rotational axis of said rotor and connecting said at least one suction backpressure groove with said at least one ejection backpressure groove; and wherein the outer circumferential edge of said ejection backpressure groove is deflected at its rotationally preceding part to be indented toward the rotational axis of said rotor along said locus so that the radial innermost end of each vane does not protrude radially inwardly beyond said predetermined distance from the rotationally preceding part of the outer circumferential edge of said ejection backpressure groove, wherein: within at least a part of another angular area where each vane is moved radially inwardly from the radial outermost position, a recess portion for preventing a radial innermost part of one side surface of each vane from contacting the inside end surface of said side wall member is further provided on the inside end surface of said side wall member which slidably contacts said rotor and each vane; and the outer circumferential edge of said recess portion is deflected at its rotationally preceding part to be indented toward the rotational axis of said rotor along said locus so that the radial innermost end of each vane does not protrude radially inwardly beyond a predetermined distance from the rotationally preceding part of the outer circumferential edge of said recess portion. 6. The vane pump as set forth in claim 5, wherein the rotationally preceding part of the outer circumferential edge of said recess portion is in parallel to said locus.