Variable-flow rate oil pump

A variable-flow rate oil pump, comprising:

• a main oil pump;
• a subsidiary oil pump;
• a control valve provided with a spool valve body;
• a main discharge oil passage extending from the main oil pump;
• a subsidiary discharge oil passage extending from the subsidiary oil pump and merging with the main discharge oil passage;
• a main relief oil passage branching from the main discharge oil passage;
• a subsidiary relief oil passage branching from the subsidiary discharge oil passage;
• and a check valve permitting a flow only in one direction from an upstream side to a downstream side of the subsidiary discharge oil passage, wherein
• the control valve is positioned at respective intermediate points of the main relief oil passage and the subsidiary relief oil passage;
• the control valve is positioned on the upstream side of the check valve in the subsidiary discharge oil passage;
• the subsidiary discharge oil passage is shut off by the check valve before the subsidiary discharge oil passage is shut off due to movement of the spool valve body to the rear side;
• and relief of oil in the subsidiary relief oil passage is performed before the subsidiary discharge oil passage is shut off by the check valve.