Optimization of crank angles to reduce excitation forces and moments in engines

The forces from the engine firings and the rotational motion of a crankshaft cause excitations in vehicle engines. In conventional in-line engines, crank angles might be evenly assigned by dividing 360 degrees by the number of cylinders. In this paper, allocation of crank angles was carried out in two different ways, (1) to minimize the moments excited in an engine and (2) to minimize the forces transmitted to the engine mounts. The forces and moments due to gas pressure and reciprocating parts in the engine were formulated, and a computer program to predict the excitation forces and moments was developed. The developed program was applied to a four-stroke seven-cylinder engine to reduce the first- and the second- order moments produced by the engine. Then, it was also applied to minimize the forces transmitted to the engine mounts. The optimized crank angles, in contrast to those of conventional engines, were not evenly distributed. The moments and forces were reduced with the optimized crank angles.