Development of a Nonlinear Shock Absorber Model for Low-Frequency NVH Applications

This paper dis cusses the development of a nonlinear shock absorber model for low-frequency CAE-NVH applications of body-on-frame vehicles. In CAE simulations, the shock absorber is represented by a linear damper model and is found to be inadequate in capturing the dynamics of shock absorbers. In particular, this model neither captures nonlinear behavior of shock absorbers nor distinguishes between compression and rebound motions of the suspension. Such an inadequacy limits the utility of CAE simulations in understanding the influence of shock absorbers on shake performance of body-on-frame vehicles in the low frequency range where shock absorbers play a significant role. Given this background, it becomes imperative to develop a shock absorber model that is not only sophisticated to describe shock absorber dynamics adequately but also simple enough to implement in full-vehicle simulations. This investigation addresses just that. The developed model is nonlinear and is constructed using control-force data of shock absorbers. While the model maintains simplicity without increasing vehicle model size, it describes shock absorber behavior both in compression and rebound. The shock absorber model is implemented in full-vehicle simulation of a full-size pickup truck, and the vehicle shake and impact harshness performances are evaluated. Numerical results show the influence of using a nonlinear model in lieu of a linear model. Moreover, a parametric study with respect to input excitation level shows that for large displacements of suspension, nonlinear damping plays a significant role in controlling the response. The nonlinear model also captures the frequency dependency of shock absorber characteristics; this offers considerable promise in analytically tuning shock absorber characteristics for different frequencies of operation.