Possibilities of the Counterbalanced Connecting-Rod 270017
IN considering the possibilities of the counterbalanced connecting-rod, the author points out that (a) every automobile engine is dynamically unbalanced; (b) inertia unbalance of two, four and eight-cylinder engines can be eliminated by counterbalancing the connecting-rods; (c) such engines so balanced have a better balance than the conventional six-cylinder engine; (d) the design of counterbalanced connecting-rods is practicable and adds little to the cost of the engine; and (e) if a counterbalanced connecting-rod is used, the single-cylinder engine can be as well balanced as the conventional six-cylinder engine by using the geared-balancer that is described. The fundamentals relating to the foregoing statements are analyzed mathematically.
The geared-balancer proposed by the author consists of a pair of small shafts geared to run at crankshaft speed in opposite directions, each shaft carrying a pair of weights that produce a rotating centrifugal-couple. The center lines of the shafts must lie in the same plane, which must also pass through the center line of the crankshaft. One weight on each shaft rotates in one plane and the other weights rotate in a plane that is parallel to and a short distance away from the first plane. In the instance cited, the piston center-line is vertical, the balancer-shafts lie in a horizontal plane and the weights lie in the plane of the shafts when the piston is on head-end dead-center. The resultant forces on the weights are then equal in magnitude and each is proportional to the square of the angular velocity of the crank, which is assumed to be constant.
Because of the arrangement of the shafts, the horizontal components of the forces neutralize each other; the vertical components are unbalanced and are proportional to the square of the angular velocity of the crank times the sine of the angle of the displacement of the crank from the vertical. The centrifugal couple produced by the balancer, which is the product of the vertical components by the distance between the planes of rotation of the weights, is therefore also proportional to the unbalance of the vertical components and approximately proportional to the angular acceleration of the connecting-rod. Hence, the inertia couple of the single-cylinder engine can be balanced equally as well as the one that is present in the conventional six-cylinder engine.