Variable displacement pump having throttled control passages

A variable displacement pump comprising:

• a rotor having vanes and rotatably arranged within a pump body;
• a cam ring fitted on an outer periphery of the rotor and movably arranged within the pump body for forming a variable pump chamber, the cam ring being urged in a direction to increase the pump chamber in volume;
• a discharge-side passage through which fluid discharged from the pump chamber flows;
• a metering orifice provided at a midway in the discharge-side passage;
• first and second fluid-pressure chambers formed between an outer periphery of the cam ring and the pump body and sealingly divided from each other with sealing means;
• a control valve having a spool, said control valve being controlled by pressure difference between upstream and downstream sides of the metering orifice for selectively introducing fluid pressure on a suction side of the pump and the upstream and downstream sides of the metering orifice into the first and second fluid-pressure chambers to operatively move the cam ring in accordance with flow rate of the pressure fluid discharged from the pump chamber;
• a first fluid passage for communicating the upstream side of the metering orifice in the discharge-side passage with a first valve chamber of the control valve;
• a second fluid passage for communicating the downstream side of the metering orifice with a second valve chamber of the control valve;
• a third valve chamber of the control valve, located axially between the first and second valve chambers and communicated with the suction side of the pump;
• a third fluid passage for selectively communicating one of the first and third valve chambers with the first fluid-pressure chamber in response to the movement of the spool;
• and
• at least one throttle portion provided in at least one of the first and third fluid passages.