PURPOSE: To prevent a piston top part from overheating in time of anything trouble happening in cooling oil feed, by making up the lower wall of a hollow part, cooling a piston by means of feeding and discharging the cooling oil, with a form memory alloy which makes the hollow part open to an empty space beneath the piston as deformed in time of a high temperature.
CONSTITUTION: At the top of a piston body 1, a hollow part 3 to expand inside a cross section except an outer circumferential part of the piston cross section is formed, while its lower wall 4 covers the whole range of the hollow part from the underside, and at the circumferential surface, there are provided with an oil feed hole 5 and an oil drain hole 6. The lower wall 4 is made up of a lower wall plate consisting of a form memory alloy and expands parallely to a top surface 7 of the piston body 1 at the setting temperature of deformation or less, while at the setting temperature or more, a form is stored in memory so as to be bent downward at a right angle at the shifting part from an interval part in a piston pin boss part 8 to the end part. In time of heating at a high temperature, the backside of the top part 2 is cooled by an atmosphere containing an oil splash, and the occurrence of a fusing loss is thus preventable.
NAKANISHI KIYOSHI
MATSUSHITA SOUICHI
KANDA MUTSUMI
