CAE Based Benchmarking of Shaft Deflection for Transmission Gear Rattle Noise

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 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. Subjective and objective evaluation shows that one is better than the other for rattle noise. Paper focuses on simulation and comparison transmission shaft deflection as a measure of transmission rattle. FEA based nonlinear static simulations are carried out by applying torque induced forces at each of the gear contacts for all the gear engaged conditions. Simulated shaft deflections, for identical loading and boundary conditions, are compared for the two transmission designs. Their rattle behavior is correctly reflected in the simulated shaft deflection results. Further, the design features causing this difference in behavior are identified and their sensitivity towards rattle improvement is established thru NVH simulations for shaft deflection and gear impact power at loose gears.