PURPOSE: To reduce a friction force at the skirt part of a piston by casting a reinforcement part respectively into the back of the skirt parts at a height equivalent to the axial line of a piston pin near a direction orthogonal with the axial line, and at a piston grade point where piston diameter is maximum.
CONSTITUTION: A piston 1 has a body formed with material other than iron, for example, an Al alloy, and constituted with a crown part 3 subjected to combustion pressure, a ring land part 5 jointed to the crown part 3 and retaining a piston ring, a pin boss part connected to the back of the crown part 3 with a pin boss rib and coupled with a piston pin, and a skirt part 11 jointed to the underside of the ring land part 5. In this case, upper iron skirt reinforcement parts 13 and 14, and a lower iron skirt part 15 are respectively cast into the back of the skirt part 11. Furthermore, the skirt part 11 is made in contact with a cylinder only at each of the skirt reinforcement parts 13 to 15 of high rigidity, thereby reducing the contact area and a friction force at the skirt parts.
GOTO TAKAHARU
USUKU HISAFUMI
HAMAI KYUGO
