Patent ID: 8156914
Filing Date: 2012-04-17
Classification: F02B,F16C,F16F,Y10T

Abstract:
1. A balancer for an engine including a crankshaft arranged to rotatably driven by reciprocal motion of a drive piston, the balancer comprising: a rod including a first end portion and a second end portion, the first end portion including a joining portion arranged to be joined to the crankshaft at a position that is eccentric relative to a rotation axis of the crankshaft, the second end portion arranged to reciprocate inside a cylinder including a cylindrical inner wall surface according to a rotation of the crankshaft; and a balancer piston fixed to the second end portion of the rod, the balancer piston arranged to reciprocate inside the cylinder so as to reduce vibrations caused by reciprocal motion of the drive piston, while rocking between a contact state in which the balancer piston is in contact with the inner wall surface and a non-contact state in which the balancer piston is separated from the inner wall surface according to the rotation of the crankshaft; wherein the balancer piston includes a cylindrical outer peripheral portion that is curved so as to expand towards the inner wall surface, the outer peripheral portion arranged such that lines of intersection with planes perpendicular or substantially perpendicular to a central axis of the balancer piston define circles, and such that there is a maximum outer diameter circle having a largest radius among the circles; the outer peripheral portion includes a contact portion which is arranged to come into contact with the inner wall surface, and the contact portion includes a contact start portion which is arranged to come into contact first with the inner wall surface when the balancer piston switches from the non-contact state to the contact state; and a distance from a center of the maximum outer diameter circle to the contact start portion is larger than the radius of the maximum outer diameter circle.