Patent ID: 7290507

Claim:
A lower link for a piston crank mechanism of an internal combustion engine, comprising: a first half member which includes, a first half of a crankpin bearing portion defining a central hole adapted to receive a crankpin of a crankshaft, a first pin boss portion located on a first side of the crankpin bearing portion and adapted to receive a first pin to connect the lower link with a first link which is one of an upper link having a first end connected with a piston of the engine and a second end connected with the lower link, and a control link having a first end connected with the lower link and a second end mounted swingably on the engine, and a bolt through hole extending through the first half member; and a second half member which is joined with the first half member by a first bolt located on one side of the crankpin bearing portion and a second bolt located on the other side of the crankpin bearing portion, and which includes, a second half of the crankpin bearing portion which is joined with the first half of the crankpin bearing portion to make up a whole of the crankpin bearing portion, a second pin boss portion formed on a second side of the crankpin bearing portion opposite to the first side and adapted to receive a second pin to connect the lower link with a second link which is the other of the upper link and the control link, an internally threaded portion defining a threaded through hole which extends, through the second half member, from a first open end to a second open end and arranged to receive the second bolt inserted through the bolt through hole of the first half member and screwed into the threaded through hole from the first open end to the second open end, to join a joint surface of the first half member and a joint surface of the second half member together, and a load transfer portion which is made greater in rigidity than the internally threaded portion so as to separate, from the internally threaded portion, a stress transfer path transmitting stress acting in the lower link among the first pin boss portion, the crankpin bearing portion and the second pin boss portion.