An Equivalent Model for Modal Analysis of Engine Mounting System

Abstract

An equivalent analysis model for engine powertrain mounting system is built with the FEA software ANSYS, in which the engine powertrain is equivalent to a composite body of one inertial body and one elastic body, every mounting component is simplified as one spring along its three principal elastic axes and the powertrain mass and rotational inertia are accurately embodied. With this equivalent model, vibration modes and energy decoupling degrees can be calculated. The result of an example in ANSYS shows that this equivalent modeling method is validity and feasibility for engine powertrain mounting systems. Introduction An engine powertrain mounting system refers to a system comprising of an engine powertrain and elastic connecting components between the engine powertrain and the vehicle frame or vehicle body, shown in Fig.1, where the red circled parts are mounting components. A mounting system shall have good effect of vibration isolation: it is to prevent the engine from transferring vibration forces to the vehicle frame, and to prevent the vibrations due to the excitation of uneven road surface from being passed to the engine. Meanwhile, it should be able to limit effectively the engine’s maximum displacement to avoid collision and interference with adjacent parts, and thus to guarantee the normal running of the engine. Fig.2 shows a schematic diagram of equivalent mode of an engine powertrain mounting system, where the circled parts are the simplified mounting components. Fig.1 An engine mounting system Fig.2 equivalent mode The purpose of analysis and optimization for an engine mounting system [1-3] is to find the optimum design parameters such as angle of each principal elastic axis of every mounting component, location of elastic center and stiffness in various directions of each mounting component, so as to maximize the vibration isolation effect. At present, optimization methods for mounting systems [4-7] are mostly to treat the engine powertrain as a six-degree-of-freedom rigid body described by mass center, mass, moments of inertia, and products of inertia, mounting components as undamped springs, and the vehicle frame as a rigid foundation, and to establish an undamped free vibration equation: 2 ( ) 0 ω φ − = K M (1) where, the mass matrix M is composed of the mass, the moments of inertia and the products of inertia of the engine powertrain; the stiffness matrix K depends on the location, the direction of elastic axis and the stiffness in various directions of mounting components; ω is the resonant angular 1128 2nd International Conference on Electronic & Mechanical Engineering and Information Technology (EMEIT-2012) Published by Atlantis Press, Paris, France. © the authors frequency and φ is the corresponding mode shape vector. By solving the generalized eigenvalues of Eq. (1), the six-natural frequencies and corresponding mode shapes can be obtained. Then, through the following equation, the energy decoupling degrees in various directions of each mode shape can be solved, 6