Mode decoupling concepts of an engine mount system for practical application

Abstract

In recent years, appropriate engine mount system design has become increasingly important due to a consistent trend towards lighter car bodies combined with more power-intensive engines and often lower idle speed. Decoupling dominant vibration directions of the engine-gearbox assembly (EGA) from input excitation direction, in particular based on elastic axis decoupling and torque roll axis decoupling concepts, are often referred to in literature. However, their practical application remains scarce. Hence, multi-body system dynamics simulation and numerical optimization is used in order to introduce an easily applicable implementation of the referred concepts. Therefore, the modal kinetic energy distribution of the EGA with respect to physical directions is considered. Effects of coupling or decoupling of EGA eigenmodes regarding engine-excited (e.g. from engine run-up or idling) as well as road-induced vibrations (e.g. from rough road or cobblestones) are addressed in an engine mount system parameter design study for a small-sized engine. Decoupling modal kinetic energy fractions of all rigid body modes considerably reduces effects from engine-excited vibrations, while strong coupling might offer benefits for road-induced vibrations. As modal kinetic energy fractions can easily be varied by means of optimization and/or by using findings from correlation coefficients derived with design of experiment methods, the adaptation of design parameters (mount positions and inclinations, stiffnesses, and loss angles) is possible in a quite straightforward manner for an effective compromise.