Conventionally, there is known a vane pump which includes: a housing having an approximately circular pump room; a rotor which rotates at an eccentric position relative to the center of the pump room; and a vane rotated by the rotor for dividing the pump room full-time into a plurality of spaces.
Then, in order to lubricate such a vane pump, there is known a vane pump configured in a manner that an oil supply passage which intermittently communicates with the pump room owing to rotation of the rotor described above is formed in the rotor, and a lubricating oil is intermittently fed from the oil supply passage into the pump room (Patent Document 1).
However, in the case of the vane pump having such oil supply passage, when the rotor stops with the oil supply passage being in communication with the pump room, then owing to a negative pressure in the pump room, the lubricating oil in the oil supply passage is sucked down into the pump room, and when the vane pump, subsequently, gets started, the vane may be damaged by an excessive load which is applied to the vane to discharge this lubricating oil.
To address such a problem, there is known a technology that an air passage constantly communicating with an atmospheric air is formed in the oil supply passage, and when the rotor stops, a negative pressure in the pump room is eliminated by sucking an atmospheric air into the pump room through the air passage, thereby a large amount of the lubricating oil is prevented from flowing into the pump room (Patent Document 2).
Patent Document 1: Japanese Patent No. 3107906 (particularly see paragraph 0022)
Patent Document 2: Japanese Patent Laid-Open No. 2003-239882 (particularly see paragraph 0012)