Patent ID: 7661395

Claim:
A stroke-variable engine comprising: a main connecting rod connected at one end to a piston through a piston pin; a subsidiary connecting rod which is connected to a crankpin of a crankshaft rotatably supported in a crankcase of an engine body and which is connected to the other end of the main connecting rod; a control rod connected at one end to the subsidiary connecting rod at a position offset from a connected position of the main connecting rod; and a pivot shaft which is rotated about an eccentric axis by a power transmitted at a reduction ratio of 1/2 from the crankshaft and to which the other end of the control rod is connected, wherein a position of a center of gravity of the subsidiary connecting rod is determined so that a distance between the position of the center of gravity of the subsidiary connecting rod and an axis of the crankpin is smaller than a distance between a point of connection of the main connecting rod to the subsidiary connecting rod and the position of the center of gravity as well as a distance between a point of connection of the control rod to the subsidiary connecting rod and the position of the center of gravity, wherein the subsidiary connecting rod comprises: a subsidiary connecting rod body to which the main connecting rod and the control rod are connected, a cap mounted to the subsidiary connecting rod body with the crankpin interposed therebetween, and a weight member mounted on a side of the cap opposite from the subsidiary connecting rod body, wherein the cap is disposed completely between the weight member and the subsidiary connecting rod body, and wherein a density of a material forming the weight member is greater than a density of a material forming the subsidiary connecting rod body to reduce a vibration generated in the subsidiary connecting rod by an order of 0.5.