Vane oil pump with different back pressure supplied to vanes

A vane oil pump comprising:

• a rotor including a plurality of slits open on an outer circumferential surface of the rotor;
• a housing having an inner circumferential cam surface and accommodating the rotor inside the housing such that the outer circumferential surface of the rotor faces the inner circumferential cam surface, the housing being configured to allow rotation of the rotor with respect to the housing, the inner circumferential cam surface of the housing being configured to have a diameter dimension from a rotational axis of the rotor, and the diameter dimension being configured to increase or decrease in a rotational direction of the rotor such that a first pump unit and a second pump unit taking in and discharging oil in accordance with rotation of the rotor are separately disposed in the rotational direction of the rotor;
• a plurality of vanes respectively fitted in the plurality of slits of the rotor, a tip end portion of each of the plurality of vanes being radially disposed to protrude from the opening of each of the plurality of slits of the rotor, and the plurality of vanes being configured to advance or retract with respect to the plurality of slits in a radial direction of the rotor;
• and
• a pressure adjusting device configured to adjust a second discharge pressure of the second pump unit to a lower pressure than a first discharge pressure of the first pump unit,
• wherein a back pressure groove is disposed on the housing, the back pressure groove is provided to supply back pressure oil to a bottom portion of each of the plurality of slits such that the tip end portion of each of the plurality of vanes is pressed to the inner circumferential cam surface, and the back pressure groove is provided such that the back pressure oil supplied to the bottom portion of each of the plurality of slits corresponding to an oil discharge part of the second pump unit has a lower pressure than the back pressure oil supplied to the bottom portion of each of the plurality of slits corresponding to an oil discharge part of the first pump unit when the second discharge pressure is adjusted to a lower pressure than the first discharge pressure.