Piston type variable displacement fluid machine

摘要

A piston type variable displacement fluid machine includes a drive shaft and a cylinder bore. A piston reciprocates along a line of movement in the cylinder bore in accordance with the rotation of the drive shaft. The stroke of the piston is varied between the maximum stroke and the minimum stroke, which is greater than zero. The displacement of the fluid machine is changed in accordance with the stroke of the piston. A ring groove is formed on the outer circumferential surface of the piston. A piston ring is fitted in the ring groove and moves with respect to the piston in the line of movement of the piston. An allowable movement amount of the piston ring with respect to the piston is greater than or equal to the minimum stroke of the piston.