In the process of power transmission, vibration and noise are generated, which have a great effect on vehicle NVH performance. Automobile power transmission system is an important part of automobile, which mainly includes engine, clutch, gearbox, drive shaft, main reducer, half axle and driving wheel. The torque of engine transfers to driving wheel through clutch, gearbox, drive shaft and rear axle. During the operation of vehicles, it is found that dramatic vibration occurs when the engine rotation speed reaches a certain value.This phenomenon has been investigated experimentally. A torsional vibration test rig was developed to investigate the torsional vibration caused by engine excitation, including the torsional vibration responses of flywheel end of engine and gearbox input shaft (Yang et al., 2017). The torsional vibration signals of transmission system were collected and the results show that increasing the flywheel mass can effectively reduce the effect of engine excitation on the torsional vibration of transmission system. For the investigation of torsional vibration of drive shafts, a field test of torsional vibration of automobile drive shaft shows that the reasonable arrangement of universal joints can reduce the torsional vibration of drive shafts (Wu et al., 2013). The fluctuation of input torque induced by internal-combustion engines is an AbstractDuring the operation of vehicles, it is found that dramatic vibration occurs when the engine rotation speed reaches a certain value. In order to study this phenomenon, a theoretical model of automobile transmission system is developed in this paper. This model includes four sub-models of gearbox, drive shafts, main reducer and rear axle, which take into account the inhomogeneous transmission speed of universal joint of drive shafts as well as the effect of time-varying and nonlinear factors of main reducer gears. In this model, the transmission system is an elastic system characterized by mass, stiffness and damping. The torsional vibration responses of transmission system are simulated, and the natural frequencies of transmission system and corresponding mode shapes are calculated using this model. Simulation results indicate that the maximum amplitude of torsional vibration response appears at a certain speed. On the other hand, experimental investigation on the effect of rotation speed on torsional vibration is conducted to verify the theoretical model. Experimental results also show there is the maximum amplitude of torsional vibration response appearing at a certain speed. The results of FEA indicate that the excitation frequencies of drive shaft are quite close to the first order natural frequency of drive shaft, and the resonant vibration of drive shaft would induce the resonant vibration of transmission system, given that the first order natural frequency of drive shaft is quite close to the third order natural frequency of transmission system. In particular, it is discovered that deviations between the rotation speeds corresponding to the maximum...

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In the operating process, it is found the vibration of main reducer reaches a maximum value when certain types of vehicles are running at a speed around 4000 RPM. However, how the rotation speed of engine affects the vibration responses to automobile transmission system has not been investigated theoretically in details. To investigate this problem, the transmission system of automobile is simplified to a drive-final shaft system in this research, and a coupled vibration model of drive-final shaft system is developed. This model is used to simulate the vibration response to transmission system at different rotation speeds. Simulation results show that the torsional vibration responses reach the maximum when the rotation speeds are 3800 RPM and 4200 RPM and the vibration responses of pinion reach the maximum value when the rotation speeds are 4000 RPM and 4200 RPM. Moreover, finite element analysis is conducted to investigate the reason for this phenomenon. It is found that the torsional vibration responses reach the maximum value when the excitation frequency of engine is close to the resonance frequency of drive shafts. This research provides an effective method to analyse the vibration characteristics of automobile transmission system.

The drive shaft arrangement has a considerable influence on the vibration responses of the shaft-final drive system. In this research, a coupled vibration model is developed based on force analysis of hypoid gear and lumped mass method. The effect of time-varying mesh stiffness, gear backlash and transfer error are included to investigate the effect of the angle between drive shafts on vibration responses of main reducer. The vibration responses of main reducer are acquired using this model. The results show that the vibration amplitude of the gears of main reducer increase with the angle between drive shafts. This paper presents an analytical method to determine the value of the angle between drive shafts, so as to control the vibration of main reducer.

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