Patent ID: 6682078
Filing Date: 2004-01-27
Classification: F05C,F16J

Abstract:
(Amended) A ring groove of a piston for an oil ring, comprising:an upper inner surface and a lower inner surface, both said upper and said lower inner surfaces being orthogonal to an axial direction of said piston; a ring body equipped with a coil expander, said ring body having an upper outer surface and a lower outer surface, both said upper and said lower outer surface being orthogonal to the axial direction of said piston, wherein said upper and lower inner surfaces have radially inward ends located radially inwardly separated by a first predetermined distance from a radially inwards ends of said upper and lower outer surfaces of said ring body when said oil ring is mounted within said ring groove so that an outer circumferential surface of said ring body is in contact with an inner circumferential surface of a cylinder which is engaged with said piston, and said ring groove has a very small cavity space behind said ring body; a radially inward-most bottom surface connecting said upper and lower inner surfaces, said radially inward-most bottom surface having a concave surface formed by a generating line drawn on a cross-sectional plane of said ring groove along a centerline of said piston, said generating line having an upper and lower ends coinciding with said radially inward ends of said upper and lower inner surfaces of said ring groove, said generating line surrounding said coil expander projecting from said radially inward ends of said ring body so that the generating line is separate from a surface of a projecting portion of said coil expander by a certain predetermined distance, not only when said oil ring stays on a lower side of said ring groove but also when said oil ring moves towards an upper side of said ring groove; and oil drain holes, each of said oil drain holes having an opening located in said radially inward-most bottom surface, wherein said oil ring groove is slightly greater in axial width than said ring body.