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Crank train torsional vibration is an important aspect for design and development of Powertrain for NVH refinement and durability. Crank train torsional vibration parameters like angular acceleration of flywheel or twist, depends upon various design parameters like geometry of crankshaft, mass of flywheel, stiffness of clutch, mass of pulley etc. It also depends upon engine operating conditions like engine speed, engine load, combustion peak pressure and combustion pressure variation etc. Most of these parameters are decided by engine power, torque, engine architecture and packaging constraints. Addition of torsional vibration damper (TVD), which works on the principle of tuned dynamic absorber, is commonly deployed design solution to control the torsional vibrations as well as stresses (to improve durability of crank train) induced in crank train assembly at specified modal frequency.

As automotive technology has evolved, gear rattle has become a prominent contributor for cabin noise as the masking from the engine noise has decreased. The market and customer expectation make the rattle noise a question to be addressed as early as possible in the vehicle development process. However, to simulate rattle, it calls for a detailed modeling of different complex subsystems of driveline to represent their true characteristics. Thus, the paper adopts an FE based elastic multi body dynamics model to predict gear rattle. The approach involves modeling of a complete flexible driveline using condensed FE models from Nastran in AVL Excite Powerunit/Transmission module. It includes combustion pressure as input excitations to crankshaft and then predicts parameters like gear teeth impacts, gear normal meshing force, dynamic mesh stiffness & overall contact state in transient and frequency domain. The output parameters are then analyzed to evaluate the rattle index.