Variable displacement pump

A variable displacement pump comprising:

• a pump housing having a pump accommodating portion, a suction portion and a discharge portion wherein the suction portion and the discharge portion are open at the pump accommodating portion;
• an adjustment ring movably provided in the pump accommodating portion;
• a pump structure provided inside the adjustment ring and discharging oil, which is sucked from the suction portion, from the discharge portion by being driven and rotated, wherein a flow amount of the oil discharged from the discharge portion by the pump structure is changed when the adjustment ring moves;
• a control hydraulic chamber provided between the pump accommodating portion and the adjustment ring in a radial direction of the pump structure with respect to a rotation axis of the pump structure and forcing the adjustment ring in a direction in which the flow amount of the oil discharged from the discharge portion decreases when a control pressure is introduced into the control hydraulic chamber;
• a control valve controlling pressure of oil in the control hydraulic chamber;
• and
• a first low pressure chamber provided at a position that overlaps with the discharge portion between the pump accommodating portion and the adjustment ring in the radial direction of the pump structure with respect to the rotation axis of the pump structure and always communicating with an oil pan having atmospheric pressure that is equal to or less than a hydraulic pressure of the oil discharged from the discharge portion,
• wherein the first low pressure chamber is provided with a drain hole that directly communicates with the oil pan, and
• wherein the first low pressure chamber is configured such that the atmospheric pressure of the oil pan is introduced into the first low pressure chamber through the drain hole, and the oil discharged from the discharge portion flows into, through a gap between the adjustment ring and the pump housing, the first low pressure chamber by a pressure difference between the discharge portion and the low pressure chamber, and the oil flowing into the first low pressure chamber is drained to the oil pan through the drain hole.