Driveline Vibration Reduction in Light Weight all Wheel Drive Vehicle

The test vehicle is All Wheel Drive (AWD) vehicle which is powered by four-cylinder engine. The power is transferred from the powertrain to the wheel through power transfer unit (PTU), propeller shaft, flexible rubber coupling and Integrated Rear Differential Assembly (IRDA) . Higher boom noise and vibration levels are observed when driving the vehicle in 4^th gear WOT conditions. NVH levels are dominant between 1150 rpm to 2100 rpm and at 2200 rpm in 2^nd order and 4^th order respectively. Operational deflection shape (ODS) analysis is carried out on entire vehicle to identify the location where maximum deflection is observed at the problematic frequency. It is identified that higher torsional excitation from the powertrain is exciting the IRDA pitching mode and the propeller shaft bending mode which is the reason for higher 2^nd order and 4^th order NVH levels. The driveline forces are entering the body through the IRDA and rear cradle bushes. The dynamic stiffness of IRDA bushes is reduced which resulted in reduction of 2^nd order vibration levels by ~ 7 dB at 2100 rpm. Further reduction of vibration is achieved by using mass dampers on IRDA and by reducing the stiffness of rear cradle bushes. Modal analysis is done on the propeller shaft to identify the mode shape at the problematic frequency. Various solutions like increasing the propeller shaft dynamic stiffness and tuned mass dampers on propeller shaft are investigated and the optimum solution which provides the best performance is selected. Stiffness of the rubber coupling used in driveline is modified to reduce the torsional excitation on the IRDA and various methods of reducing torsional excitation in driveline are discussed. With all the countermeasures, the boom noise is eliminated and vibration levels are reduced by ~ 10 dB.