REDUCTION OF TIME DOMAIN VIBRATION OF A STRUCTURE SUPPORTED BY MECHANICS USING SENSITIVITIES WITH RESPECT TO NONLINEAR STIFFNESS

With the increasing popularity of the electric and hybrid vehicle which are quiet than the conventional internal combustion engine vehicle, th e importance of the NVH performance is increasing. Upon the NVH performance, the suspension plays important role for both road noise and harshness. On the suspension design, the geometry configuration and the stiffness of the suspension bush are considered as design par ameters. The design parameters often shows trade-off relationship between the road noise and the harshness, so that achieving the compatibility between the two is difficult task in the vehicle development. In this paper, one of the way to achieve the compatibility is proposed focusing on the difference of the assumptions of each analysis. The road noise is usually m odeled linearized equation of motion due to the small displacement of the system, whereas no nlinearity has to be taken into account for the harshness due to the large displacement of the system. Therefore, harshness could be improved by the modifying nonlinearity characterist ics of the stiffness of the suspension bushes after linear part of design parameters are f ixed for the road noise. For simplicity, 2dimensional model that consists of rigid links and simply supported beam which are connected by the nonlinear spring is considered. In th is model, the rigid links suppose suspension assembly and the beam supposes vehicle body. The equation of motion is described following the manner of multi body dynamics. Time history of the model is computed by the numerical integration. Then optimized nonlinear cha racteristics of the springs, which reduces the peak value of the beam vibration, are found by the use of the sensitivity analysis with respect to coefficient of nonlinearity. Finally, the mechanism of the vibration reduction is discussed.