| 摘要 |
PURPOSE:To prevent a skirt portion from local deformation by forming smoothly a cooling cavity over the whole periphery of the upper portion of a piston and the skirt portion of an integrally formed wall only in a portion of which a thrust force acts in the direction perpendicular to the axial direction of the piston pin. CONSTITUTION:A cooling cavity 22 is formed of a ring land portion (outer wall) 16 consecutive to a piston crown portion 10 and an inner wall 18 inside said portion 16. The cooling cavity 22 is formed annularly over the whole periph ery of the upper portion of piston to reach the upper edge of a portion in which a piston pin boss portion 24 is disposed. Also, in a portion on which thrust forces act in the direction perpendicular to the axial direction of a piston pin is formed a skirt portion 28 integrally with a boss portion 24 by a wall 30 consecutive to the outer peripheral surface of the boss portion 24. Thus, the piston can be prevented from local deformation and seizure. Also, the pin boss portion 24 can be sufficiently cooled. |
