Piston and internal combustion engine

Abstract

A piston includes a skirt portion extending downward from a lower end portion of an outer circumference of a piston head, and a coupling portion coupled to a crankshaft that converts reciprocating motion into rotational motion via a connecting rod. The skirt portion includes a convex portion that protrudes toward the coupling portion from a lower portion of an inner peripheral surface opposite to an outer peripheral surface facing the cylinder, the convex portion being capable of retaining the lubricating oil.

What is claimed is: 
     
         1 . A piston that reciprocates within a cylinder, the piston comprising:
 a skirt portion extending downward from a lower end portion of an outer circumference of a piston head; and   a coupling portion coupled to a crankshaft that converts reciprocating motion into rotational motion via a connecting rod, wherein the skirt portion includes a convex portion that protrudes toward the coupling portion from a lower portion of an inner peripheral surface opposite to an outer peripheral surface facing the cylinder, the convex portion being capable of retaining lubricating oil.   
     
     
         2 . The piston according to  claim 1 , wherein the convex portion protrudes from a lower end of the skirt portion toward the coupling portion. 
     
     
         3 . The piston according to  claim 1 , wherein the convex portion protrudes from the inner peripheral surface in a horizontal direction. 
     
     
         4 . The piston according to  claim 1 , wherein the convex portion is formed along a circumferential direction at a lower portion of the inner peripheral surface. 
     
     
         5 . The piston according to  claim 1 , further comprising:
 a cooling portion formed in an annular cavity inside the piston head and through which lubricating oil flows; and   a discharge port that communicates with the cooling portion and discharges lubricating oil from the cooling portion to a lower side of the piston head, wherein the convex portion is located below the discharge port in a vertical direction.   
     
     
         6 . The piston according to  claim 5 , wherein the discharge port is formed in the inner peripheral surface of the skirt portion, and the piston further comprises:
 a discharge path that connects the cooling portion and the discharge port.   
     
     
         7 . The piston according to  claim 1 , wherein a height of the protruding portion in a protruding direction is smaller than a thickness of the skirt portion. 
     
     
         8 . The piston according to  claim 1 , wherein the convex portion retains lubricating oil that, during rotation of the crankshaft, has moved from the crankshaft and adhered to the inner peripheral surface of the skirt portion. 
     
     
         9 . An internal combustion engine comprising:
 a cylinder; and   a piston that reciprocates within the cylinder, wherein the piston includes:
 a skirt portion ( 36 A) extending downward from a lower end portion of an outer circumference of a piston head; and 
 a coupling portion coupled to a crankshaft that converts reciprocating motion into rotational motion via a connecting rod, among which the skirt portion includes a convex portion that protrudes toward the coupling portion from a lower portion of an inner peripheral surface opposite to an outer peripheral surface facing the cylinder, the convex portion being capable of retaining lubricating oil. 
   
     
     
         10 . The internal combustion engine according to  claim 9 , wherein the cylinder includes a thrust region of the inner wall surface against which the skirt portion is pressed, when the piston descends, and
 the convex portion is located in a portion of the inner peripheral surface of the skirt portion corresponding to the thrust region.