[0001]The present invention is an automotive engine, marine engine, to a crank shaft mounted in a reciprocating engine such as a general-purpose engine of the generator or the like.
Background technique
[0002]
　Reciprocating engine, for extracting power by converting the piston reciprocating in the cylinder (cylinder) into a rotary motion requires crankshaft. Crankshaft, and those produced by die forging, are roughly classified into those which are produced by casting. In particular, the number of cylinders in the two or more multi-cylinder engine, die forging crankshaft dominant former strength and stiffness are often used.

WE CLAIM

[Claim 1]And a journal portion as a rotation center axis, and a pin portion which is eccentric with respect to the journal portion, and a plurality of crank arm portion connecting the pin portion and the journal portion, a crank shaft mounted on a reciprocating engine Te,
　all or part of the plurality of crank arm portion has a counterweight portion integrally,
　wherein all or some of the plurality of crank arm portion having a counterweight portion, said of the crank arm comprising a lightening portion on the surface of the pin portion,
　wherein at least one of the two sides of the thin portion, the rib portion along the contour of the crank arm portion is provided, a crank shaft of the reciprocating engine.
[Claim 2]
　A crankshaft of a reciprocating engine according to claim 1,
　wherein the rib portion is provided on each of the two sides of the thin portion, the crank shaft of the reciprocating engine.
[Claim 3]
　A crankshaft of a reciprocating engine according to claim 1 or 2,
　wherein the rib portion is from the end of the pin portion of the lightening portion, the position of the counterweight unit nearer the center of rotation of the crankshaft extends to,
　when viewed the crank arm from the side, the ends of the counterweight side of the rib portion from the position of the axis of the journal portion, the outer periphery and the crank arm portion of said journal portion present in a range up to the position of the point closest to the counterweight unit among the intersection points, the crank shaft of the reciprocating engine.
[Claim 4]
　A crankshaft of a reciprocating engine according to claim 3,
　the crank arm when viewed from the side, the top surface of the rib portion, of the intersection of the outer periphery and the crank arm portion of the pin portion wherein the point closest to the counterweight unit is parallel to the straight line connecting a point closest to the counterweight unit among the intersection of the outer periphery and the crank arm portion of the journal portion, a crank shaft of the reciprocating engine.