Sensitivity Analysis of a Lightweight Rear Differential Unit on Ride Comfort of a Sport Utility Vehicle

Lightweight is an important measure to the fuel efficiency and the cost reduction in development of contemporary vehicles. However, how the lightweight structure could affect the NVH performance or ride comfort of a vehicle needs to be carefully investigated. In this paper, the effect of a lightweight rear differential unit of a sport utility vehicle on ride comfort was studied. A multi-body dynamic model of the vehicle was developed which includes powertrain and driveline, tyres, suspensions, steering system, and a flexible car body. The baseline model was correlated with the accelerations measured at the seat rail in a field test. Using the correlated model, a factorial analysis of Design of Experiment was conducted to study the sensitivity of the masses and the moments of inertia of rear differential components on the vibration at the seat rails in terms of accelerations r.m.s. values. Results showed that the seat rail vibration energy was centred at two frequency ranges: 1-2 Hz and 6-15 Hz. The vibration in these two frequency bands in different directions had different sensitivities to the variation of the mass properties of the rear differential unit. It was found that the vertical vibration of the seat rail was most sensitive (in descending order) to: the mass of the rear differential housing, the moment of inertia of the inner constant velocity joint about the longitudinal direction, and the mass of the driveshaft. In the context of this study, they are three most significant contributors to the ride comfort that need to be considered when designing a lightweight structure for the rear differential unit.