Patent ID: 7191741

Claim:
A link mechanism comprising: a first link including a cylindrical first pin boss portion; a second link including a cylindrical second pin boss portion; and a connecting pin passing through the first and second pin boss portions so as to allow a relative rotational movement between the first and second links within a limited range; the first pin boss portion including a first narrow section extending in a circumferential direction of the first pin boss portion, and having an axial wall thickness as measured in an axial direction of the connecting pin; the first pin boss portion further including a first wide section extending in the circumferential direction of the first pin boss portion, and having an axial wall thickness greater than the axial wall thickness of the first narrow section; the second pin boss portion including a second narrow section extending in a circumferential direction of the second pin boss portion, and having an axial wall thickness as measured in the axial direction; the second pin boss portion including a second wide section extending in the circumferential direction of the second pin boss portion, and having an axial wall thickness greater than the axial wall thickness of the second narrow section; the first wide section of the first pin boss portion and the second wide section of the second pin boss portion overlap each other in the axial direction; wherein the link mechanism further comprises a third link linked with one of the first and second links, to form a linkage of the first, second and third links connected with a piston of an internal combustion engine; wherein one of the first and second links is a lower link rotatably mounted on a crank pin of a crankshaft for the engine; wherein the first wide section of the first link includes a short subsection extending circumferentially from a link center line of the first link in a first rotational direction, and a long subsection extending from the link center line of the first link in a second rotational direction opposite to the first rotational direction, and having a circumferential length greater than a circumferential length of the short subsection.