| Summary: | The number of speed changes of stepped automatic transmissions (ATs) for vehicles is increased in order to optimize the operating points of internal combustion engines. As a result, the mechanical structure of ATs has become increasingly complex. This advanced complexity leads to torsional vibration in ATs. Computational simulations are carried out utilizing the one-dimensional model of the powertrain of the vehicle. The simulation results show that the torsional vibration level does not decrease proportionally with the acceleration of engine speed; the reason for this remains unknown. From the detailed investigation of the simulation results, it was observed that the idle parts and clearances in the AT caused the nonlinear torsional vibration in the powertrain. The idle parts periodically collide with the main geartrain in the AT synchronizing with the engine torque, and work as the active damping. As a result, the torsional vibration in the powertrain is suppressed. On the other hand, when the idle parts do not collide with the main geartrain in the AT, the torsional vibration level in the powertrain becomes equal to that of the model which originally did not contain idle parts. From the relationship between the period of the engine torque and the clearances in the AT, the angular velocities of the idle parts are derived for the periodic collision between the idle parts and main geartrain in the AT. The experimental results of the motor bench show that the nonlinear torsional vibration occurs in the experimental AT.
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