A Method to Identify the Stiffness of Engine Mounts Using Experimental Modal Analysis

This paper presents a new method for identifying the stiffness of mounts under the condition of being built in a structural system as in practical use. A conventionally standard method is to identify an individual mount using a dynamic stiffness measurement equipment. In the new method, the stiffness values of mounts built in a structural system are identified using the modal parameters of the system which are obtained by experimental modal analysis. Vibration testing of the structural system with a posture in an operational condition can make it possible to consider preload effect that is caused by the gravitational and thrust force applying to the structural system in practical conditions. Additionally, vibration testing using impact hammer is often made available so that the new method can make it much easier to identify the stiffness of mounts than the conventional measurement of dynamic stiffness. In this paper, the validity of the method is demonstrated using both a simulation study using a finite element model and an experimental identification of an actual outboard engine. The experimental result shows a dependence of the mount stiffness on the gravitational force and the thrust force at the propeller of the outboard engine.