Lubrication structure in engine

1. A lubrication structure for a splash lubrication in an engine having a cylinder, a piston provided in the cylinder, a crank case, a crank shaft having a crank pin, the crank shaft being rotatably supported in the crank case, and a connecting rod for connecting the piston and the crank shaft so as to allow the piston to reciprocatingly move in the cylinder, the connecting rod having a small end and a big end, the small end being linked with the piston, the big end receiving the crank pin with an inner peripheral surface of the big end in contact with an outer peripheral surface of the crank pin so as to rotate with respect to each other, the lubrication structure comprising:

an oil collector formed as a depression in the outer peripheral surface of the crank pin approximately at the center of the crank pin in an axial direction, the oil collector being displaced from an explosive force in an expansion cycle of the engine, transmitted from the piston via the connecting rod; and

an oil groove provided on the big end of the connecting rod, the oil groove having a first and a second end, the first end being open in the inner peripheral surface approximately at the center thereof in an axial direction, the second end being open into the crank case, the oil collector receiving oil stored in the crank case and the oil being transferred to the oil groove;

wherein the connecting rod comprises a rod portion which integrally connects the small end with the big end, the big end being divided into a first half extending from the rod portion and second half along a diameter line of the inner peripheral surface of the big end, and the oil groove being formed in the second half.

2. A lubrication structure for a splash lubrication in an engine having a cylinder, a piston provided to the cylinder, a crank case, a crank shaft having a crank pin, the crank shaft being rotatably supported in the crank case, and a connecting rod for connecting the piston and the crank shaft so as to allow the piston to reciprocatingly move in the cylinder, the connecting rod having a small-end and a big end, the small end being linked with the piston, the big end receiving the crank pin with an inner peripheral surface of the big end in contact with an outer peripheral surface of the crank pin so as to rotate with respect to each other, the lubrication structure comprising:

an oil collector formed as a depression in the outer peripheral surface of the crank pin approximately at the center of the crank pin in an axial direction, the oil collector being formed within an area at a part of the crank pin, which is opposite to the piston when the piston is situated at the top dead center in the expansion cycle; and

an oil groove provided on the big end of the connecting rod, the oil groove having a first end and a second end, the first end being open in the inner peripheral surface approximately at the center thereof in an axial direction, the second end being open into the crank case, the oil collector receiving oil stored in the crank case and the oil being transferred to the oil groove.

3. The lubrication structure as claimed in claim 2 , wherein the oil groove has a tapered surface which increases in diameter from the first end of the oil groove to the second end of the oil groove.

4. The lubrication structure as claimed n claim 2 , wherein the connecting rod comprises a rod portion which integrally connects the small end with the big end, the big end being divided into a first half extending from the rod portion and a second half along a diameter line of the inner peripheral surface of the big end, and the oil groove being formed in the second half.

5. The lubrication structure as claimed in claim 2 , wherein said area is adapted to extend from a point of 135° in the anti-rotational direction of the connecting rod with respect to the center line of the cylinder bore to a point of 45° in the rotational direction of the connecting rod with respect to the center line of the cylinder bore.