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The door closing sound is one of the important quality of a vehicle, and it is useful to study the improvement method of closing sound. As a step to clarify the relationship between the door structure and closing sound, it is attempted to correlate the formation of closing sound with the vibration, and explained that the effect of structural modification aimed to improve the closing sound from the viewpoint of vibration. First, the formation process of the vibration during the door closing is clarified through the analysis method of transient vibration using the pulse laser holography. And the quality of closing sound are evaluated based on the time historical fluctuation of frequency characteristics. Next, the correlation between the closing vibration and sound are studied, and for the case of that the closing sound are changed by the structural modification, the correlation are confirmed.

The vibration damping composite steel sheet was improved in properties such as dependence on temperature, bending rigidity, press formability and spot weldability and compared with damping materials currently used by reviewing composition and adhesion strength of the resin and the mechanical property of the steel skin sheets. By applying the above-mentioned materials to the floor and wheel-house panels, a reduction in noise and vibration was obtained in the application test, and improvement in door shutting noise was also revealed when applying these materials to the door panels.