Piston ring set

The utility model relates to a piston ring assembly, which comprises piston rings which are respectively arranged in three ring grooves which are processed on a piston, wherein the cross section of the first piston ring (2) has a rectangular structure, and the working surface of the outer side of the piston ring, which is matched with a cylinder wall has a convex arc-shaped surface structure; the second piston ring is a combined ring which is formed by that an upper and a lower rings are overlapped, wherein the upper ring (3) is a reverse torsion ring, and the lower ring (4) is a front torsion ring; the contact surfaces of the upper and the lower rings are mutually matched to form a conic ring surface structure, and the upper and the lower rings are overlapped and combined together in the mode that openings thereof are staggered at the angle of 180 DEG; the working surface of the outer side of the upper ring, which is matched with the cylinder wall, has an inverted cone structure, and the working surface of the outer side of the lower ring, which is matched with the cylinder wall, has a convex arc surface structure; the third piston ring (5) is an integral type oil ring or a sheet steel combined type oil ring.