The acceptable noise and vibration performance is one of the most important requirements in a passenger bus as it is intended for widest spectrum of passengers covering all age groups. Gear rattle, being one of the critical factors for NVH and durability, plays a vital role in passenger comfort inside vehicle. The phenomenon of gear rattle happens due to irregularity in engine torque, causing impacts between the teeth of unloaded gear pairs of a gearbox which produce vibrations giving rise to this unacceptable acoustic response. In depth assessment of the dynamic behavior of systems and related components required to eliminate gear rattle.
During normal running conditions, abnormal in-cab noise was perceived in a bus. Initial subjective evaluation revealed that the intensity was high during acceleration and deceleration. Objective measurements and analysis of the in-cab noise and vibration measurements had indicated that the noise is mainly due to gear rattling. Further analysis led to the identification of coincidence of this abnormal noise encountered with a driveline mode. Root cause analysis indicated that the clutch had a major influence on gear rattle. As it was initiated by driveline mode, it was pertinent to change either the driveline mode or to reduce the energy being transferred to the gearbox to eliminate the noise encountered. Elimination of gear rattle was achieved by maximizing the hysteresis of clutch thereby absorbing the energy being transferred. This paper explains in detail the various steps followed during the initial investigation, analysis and solving the problem.