Analytical Investigation of Light Truck Low Frequency Vibration Issues

After-shake vibrations can be defined as unpleasant low frequency vibrations (8--15 Hz) felt by the driver and passengers of a vehicle, which are excited by road irregularities. These vibrations typically have high vertical and lateral components, and may also involve fore-aft vibrations. Traditionally, experimental testing has been used in the automotive industry in order to find a way to cure the after shake vibrations, similarly to solving other vehicle vibration problems. This approach may provide information necessary to characterize the vibrations, but it cannot explain their origin, the nature of couplings among various vehicle subsystems, and the system sensitivity to its parameters and design modifications. In the paper, an analytical approach to identify the root cause of light truck after-shake vibrations is presented. The approach relies on building and correlating a mathematical model of the vehicle. This model is then used to assess system sensitivity and suggest modifications which would lead to improved vehicle after-shake behavior. The root causes of the after-shake vibrations are identified, and the effects of the assessed modifications are described. The paper concludes with a series of changes that are predicted by the model to reduce vehicle after-shake to an acceptable level. The results of experimental validation of the proposed modifications are also included.