Interior Noise Refinement in an ICV Bus through Driveline Torsional Vibration Analysis 2018-01-1472

With a push for urbanization across cities, there is an increased demand for mobility in public transportation especially buses which are provided through state transport undertakings. Hence, the expectations of this class of vehicles will be high in terms of quality and comfort to the passengers. The noise inside the passenger area of the bus becomes an important parameter, which sets apart a bus manufacturer from its competitors. The driveline of the bus is the system responsible for the transfer of power from engine to the wheels. The noise and vibration problems associated with it are detected only in the late stages of the design chain, when all its elements are tested together over a wide range of conditions. Since, calibration of engine and the selection of transmission is freezed in early stages, satisfying power and torque requirements, the only viable option left to address the problem is by optimizing the clutch parameters. Combustion in multi-cylinder four stroke diesel engine produces periodically changing gas and inertia forces associated with reciprocating pistons. This leads to fluctuation in the engine speed and the torque transmitted by the engine, inducing torsional vibrations into the system. These torsional vibrations make the unloaded gear pairs of the gearbox to impact against each other generating Gear rattle noise. In the present work, an abnormal noise was observed in an ICV (Intermediate Commercial Vehicle) bus at both idling and driving conditions. Near source noise measurements and interior noise measurements were carried out to determine the source of the noise. Torsional vibration levels were also measured at engine and gearbox. Upon identification of the source, the clutch parameters including the clutch torsion spring stiffness was scrutinized and modified. This gave improvement in the interior noise levels inside the passenger area of the bus.