Patent ID: 8210832

Claim:
A hermetic compressor storing oil in a hermetic container and accommodating a compression mechanism for compressing refrigerant gas, wherein the compression mechanism comprises: a crank shaft disposed in vertical direction, and having a main shaft and an eccentric shaft, a block forming a cylinder, a piston making a reciprocating motion in the cylinder, and having a top surface and a skirt surface, both vertical to a direction of the reciprocating motion, a connecting rod for coupling the eccentric shaft and the piston, and an oil supply system for supplying the oil to an outer circumference of the piston, grooves are provided at an upper side and a lower side of the outer circumference of the piston, and an outer shape of the grooves communicating with a space in the hermetic container at least when the piston is in a bottom dead center is a shape not forming a parallel line to an axial center of the piston when the grooves are developed in a plane, wherein the outer shape of the grooves is a closed semicircular shape extending toward a skirt side of the piston, and the semicircular shape includes a first outer shape extending toward the skirt side of the piston, a second outer shape parallel to the top surface of the piston, and a third outer shape linking the first outer shape and the second outer shape, and a curvature of the first outer shape is smaller than that of the third outer shape, a width of the grooves being greater at an upper portion thereof, and the groove enclosed by the first outer shape communicates at least with the space in the hermetic container when the piston is in the bottom dead center.