Research On Nonlinear Dynamic Characteristics Of Vehicle Transmission Gears

Noise and vibration characteristics of vehicle transmissions have a significant influence on the NVH performance of the vehicle. As the main carrier of transmitting power, the transmission gear system dynamics largely determines the performance of the vibration of transmission. With the improvement of people’s vehicle NVH performance requirements, the study on the characteristics of dynamics of vehicle transmission gear has an increasingly important engineering significance.The main contents are as follows:(1) In this paper, a single pair of helical gears was taken as the research object,internal dynamic excitation of gear meshing was studied, including time-varying meshing stiffness excitation and error excitation. Time-varying meshing stiffness was theoretically solved, and the correctness of the theory of solving methods was verified using KISSsoft software. Influences on time-varying meshing stiffness from different helix angles and different input torques were studied, and different pitch error’s influence on transmission error was analyzed. The results show,1) there is an optimal helix angle to make time-varying meshing stiffness amplitude gentle; when the helix angle changes, the angle causes time-varying meshing stiffness volatility increases, the system vibrations also change severely. 2) When the input torque becomes larger, time-varying meshing stiffness amplitude increases accordingly. However, the magnitude of the increase decreases at each time. 3) The introduce of pitch error makes the degree of transmission errors’ fluctuations and values larger. If pitch error increases with same percentage each time, the corresponding transmission error increase by equal amplitude.(2) Combined with an internal dynamic excitations, six degrees of freedom nonlinear dynamic model and nonlinear dynamical equations of helical gears pair were established. Using two methods of simulation in finite element software and theoretical method in Matlab to obtain a helical gear system undamped free vibration inherentcharacteristics of system,Subsequently, natural frequencies were compared and analyzed.(3) Nonlinear dynamical equations were solved using fourth-order Runge-Kutta method to obtain the time-domain responses of system. The corresponding frequency responses were obtained by FFT transform. Influence on dynamic characteristics of helical gears with different time-varying meshing stiffness and different pitch errors were studied respectively.The results show,1) when the time-varying meshing stiffness decreases,vibration accelerations of helical gear system in all directions correspondingly increase,and the increase speed itself get higher. 2) When the pitch errors increases at the same rate,the response of the system also increases accordingly, and the increase steps almost keep unchanged.(4) Gear modification methods were analyzed. Modification program of the pinion was identified.The effect of transmission error and tooth surface contact stress with different amounts of crowning modification. It was found that, only the amount of crowning be controlled within a reasonable range, a smooth and little change in the magnitude of transmission error can be obtained, and the tooth surface phenomenon of partial load get improved meanwhile.