Reduction of Driveline Boom Noise and Vibration of 40 Seat Bus through Structural Optimization

In today’s automotive scenario, noise vibration and harshness (NVH) has become a synonym for quality perception. This paper evaluates the problem of vibration and noise experienced in M2 category 40 seat bus and suggests the counter measures. Severe vibration is experienced on the bus floor, predominantly towards rear part of the bus. Vibration along with acoustic boom occurs prominently in 4th gear wide open throttle operating condition between 1300-1600 rpm of the engine. This paper focuses on reducing NVH levels by working on the transfer path with little modifications on power-train. Preliminary torsional measurements conducted on powertrain indicated high torsional excitation in the driveline during the problematic rpm zone. Further, Operational Deflection Shape (ODS) analysis revealed that the transfer path to the cabin is rear differential unit and suspension links. The dominant frequencies were identified along the transfer path and suitable modifications were done. A reduction of ~ 50% in floor vibration level and 3 dB (A) reduction in cabin noise accompanied with improvement in loudness by 4 sones is achieved. These modifications were found to be suitable for future vehicle architecture changes based on power and torque requirements.