Abstract: This paper is to study the variation law of engine excitation torque fluctuation coefficient under different driving conditions of the vehicle, and analyze the influence of the key parameters of the transmission system on torsional vibration of the system. Firstly, a simplified lumped mass model of the transmission system and a longitudinal dynamic model of the vehicle are established. Then, the order analysis of the measured torsional vibration data is conducted to determine the main torque excitation order of the transmission system. Furthermore, two intelligent algorithms are introduced to estimate the excitation torque fluctuation coefficient under each gear with the aim to minimize the acceleration time squared error between the measured and simulated values of each WOT condition, and the convergence curves of the two intelligent parameter estimation methods are compared. Finally, with the time domain average speed fluctuation as the evaluation index, the adjustment effect of each main parameter on the torsional vibration is analyzed. The results show that within the test speed, the engine excitation torque fluctuation coefficient decreases with the increase of the speed and load, indicting that the engine runs more smoothly. The conclusion is drawn that proper reduction of clutch stiffness, increase of clutch damping, increase of half-shaft stiffness and damping, increase of flywheel inertia are beneficial to reduce the torsional vibration of the transmission system, thus improving the comfort of the vehicle.

Key words: transmission system, parameter estimation, torque fluctuation, torsional vibration test, order analysis