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Today’s competitive market demands for low cost passenger cars with lighter, smaller size, peppy response and fuel efficient engines and having world class NVH refinement levels. For such requirements, it is essential to optimize the product starting from the design conceptual stage, considering all performance aspects. Generally, three cylinder engines, due to less reciprocating masses, compared to four-cylinder engine, are said to be fuel efficient for the same capacity. Nevertheless, NVH problems caused by inherent imbalance forces and couples remain as drawback of the three-cylinder engine. However, through optimal design of the crank train, control of cylinder to cylinder pressure variation, stiffening of the engine structure, optimizing the integration with a vehicle through proper design of mounts, NVH refinement levels can be improved.

Vehicle transmission gear rattle is one of the most critical NVH irritants for refined vehicles. It is perceived more dominantly in lower gears of vehicle running. It depends on various design parameters like engine input torque amplitude & fluctuations, driveline torsional vibrations, gear micro & macro geometry, shaft flexibility, etc. Establishing exact contribution of each of these parameters to transmission rattle, thru experimental or simulation technique, is very challenging. Current paper explains the NVH CAE benchmark approach deployed to understand difference in rattle behavior of two transmission designs. Paper focuses on simulation of gear impact power and its sensitivity to transmission shaft deflections.