Patent ID: 7624574

Claim:
An external combustion engine comprising: a piston apparatus; and a cylinder, wherein the piston apparatus includes a piston main body, a pressure-accumulating chamber formed inside the piston main body, an introduction portion that is arranged in a first portion corresponding to a predetermined height position in a circumferential portion of the piston main body, and that serves to introduce a working medium compressed in a working space of the external combustion engine into the pressure-accumulating chamber, and a hole that is arranged in a second portion corresponding to a position lower than the predetermined height position in the circumferential portion of the piston main body, and that runs from the pressure-accumulating chamber to a clearance between the piston main body and the cylinder, and a size of the clearance between the first portion in the circumferential portion of the piston main body and the cylinder is configured to be larger when the piston apparatus is at a top dead center than when the piston apparatus is at a bottom dead center.