Balancer structure for three-cylinder engines

A balancer structure for a three-cylinder in-line engine having three cylinders, a first and third cylinder, and a second cylinder between said first and third cylinders, a crankshaft having crank arms disposed at angles of 120.degree. with respect to each other and operatively connected to said cylinders, respectively, consisting of:

• a single countershaft adjacent and parallel to and rotated at the same speed as the crankshaft but in the opposite direction;
• means comprising first counterweights securely mounted on said crankshaft only at positions thereof corresponding to the first and third cylinders for balancing a part of inertia force of reciprocating masses and the entire inertia force of rotating masses;
• means comprising at least one second counterweight securely mounted on said crankshaft substantially opposite to the crank arm corresponding to the second cylinder for balancing another part of the inertia force of the reciprocating masses;
• at least two balancers securely mounted on said countershaft at both ends thereof for the balancing of the remainder of the inertia force of the reciprocating masses and a couple of inertia of the crankshaft about an axis perpendicular to the crankshaft.