Patent ID: 8794933

Claim:
A hermetic compressor comprising: a closed vessel storing lubricating oil; an electric-driving element; and a compressing element, the compressing element including: a shaft having a main shaft rotated by the electric-driving element, and an eccentric shaft that integrally moves with the main shaft; a cylinder block having a cylindrical hole portion for forming a compression chamber, and a bearing for supporting the main shaft; a piston inserted in the cylindrical hole portion in a reciprocating manner; and a connecting device connecting the eccentric shaft and the piston; wherein the cylindrical hole portion encircles a top end of the piston when the piston is at a top dead point, the cylindrical hole portion having: a uniform clearance portion where an inner diameter is constant in an axial direction of the piston, and an expanded clearance portion formed such that an inner diameter thereof broadens from the top dead point to a bottom dead point of the piston, the expanded clearance portion being adjacent to the uniform clearance portion, wherein the cylinder block is formed such that a bottom end of the piston is exposed when the piston is at the bottom dead point, and the piston includes a concave portion recessed inward in a radial direction of the piston on its outer circumferential face, wherein at least a part of the concave portion is exposed from the cylinder block when the piston is at the bottom dead point, and an end of the concave portion faces the uniform clearance portion when the piston is at the top dead point.