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

This paper presents a new method for identifying the stiffness of engine mounts under the condition of being built in a structural system as in practical use. A conventionally standard method is to use a dynamic stiffness measurement equipment that can deal with only an individual mount. 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 in an operational condition can make it possible to consider preload effect caused by the gravitational and driving force, such as thrust force, applied to the structural system. Additionally, vibration testing using an impact hammer is widely available so that the new method can make it much easier to identify the stiffness of mounts in various situations than the conventional method. In this paper, the validity of the method is demonstrated using both a simulation study using a finite element model and an actual trial for an actual outboard engine. The result shows the dependence of the mount stiffness on the gravitational force and the thrust force at the propeller of the outboard engine.