Optimal mounting system of a variable displacement engine

Abstract

The need for the variable displacement engine which can greatly improve fuel economy has become strong all over the world in recent years, and some of them have aleady reached production. Reducing the number of operating cylinders brings about significant inherent engine vibration. Because of this defect, it is necessary to redesign and refine the engine``s mounting system to isolate vibrations effectively. In the present study, the three degrees-of-freedom dynamic model of an inline four-cylinder engine which has a three point mounting system is developed, and its excitation forces are analyzed at normal and misfiring conditions. Mount locations, inclined angles, and isolator shapes are selected as the design variable to minimize the vibration of the variable displacement engine. This optimization problem is solved by the gradient projection method. Simulation studies using the developed program show that by adjusting the engine``s mounting system, the vibration level is reduced significantly, and thus, at the idling speed, the rms displacement of the engine under the misfiring condition is reduced by about thirty percent.