Patent ID: 8069833

Claim:
A reciprocating engine having a piston, comprising: a piston upper body made up of a crown portion for receiving combustion pressure and a land portion having piston rings fitted thereon; and a skirt portion formed on a lower side of said piston upper body, wherein said piston upper body is formed so as to be off-centered toward an anti-thrust side with respect to a center line of a piston, and, on the anti-thrust side an outer peripheral surface of said piston upper body and an outer peripheral surface of a maximum-diameter portion of said skirt portion are formed by being aligned on a vertical line, such that, in a state in which the piston is accommodated in an upright posture in a cylinder, on the anti-thrust side the outer peripheral surface of said piston upper body and the outer peripheral surface of the maximum-diameter portion of said skirt portion are in close abutment against with an inner surface of said cylinder, and on a thrust side a clearance is created between the outer peripheral surface of said piston upper body and an inner surface of said cylinder, an annular gas chamber being formed on a second land portion between a first piston ring fitted on the outer peripheral surface of said piston upper body and a second piston ring, a plurality of recesses being formed in an upper portion on the thrust side of the inner surface of said cylinder, whereby when said piston is located at a top dead center or in a vicinity of the top dead center, high pressure gas above said piston is allowed to flow into said annular gas chamber, said piston is supported from the thrust side by the high pressure gas flowing into the gas chamber, and said piston is lowered such that the outer peripheral surface of said piston upper body and the skirt portion are in abutment with the inner surface of said cylinder on the anti-thrust side.