Patent ID: 7534100

Claim:
A rotary fluid machine comprising: a cylinder having an annular cylinder chamber formed as a space between a cylindrical inner periphery and a cylindrical outer periphery of the annular cylinder chamber; an annular piston disposed in the cylinder chamber to be eccentric to the cylinder, the annular piston dividing the cylinder chamber into an outer working chamber and an inner working chamber, the annular piston having a cylindrical inner piston surface facing the inner periphery of the cylinder chamber and a cylindrical outer piston surface facing the outer periphery of the cylinder chamber; and a blade arranged in the cylinder chamber, the blade extending in a radius direction from the outer periphery to the inner periphery of the cylinder chamber to divide each of the outer and inner working chambers into a high pressure region and a low pressure region, the cylinder and the piston making relative rotations, the cylinder chamber having a radial width measured between the inner and outer peripheries of the cylinder chamber that is varied about a circumference of the cylinder chamber such that a gap between the inner periphery of the cylinder chamber and the inner piston surface of the piston and a gap between the outer periphery of the cylinder chamber and the outer piston surface of the piston are kept substantially smallest during a full rotation, with a difference in fluid pressure between the outer working chamber and the inner working chamber taking place in the full rotation.