Optimization Of Transmission Based On Vibration And Noise

Vibration and noise radiation of transmission are important factors that affects auto harshness(NVH) performance. Since the gear transmission system is not only producing noise radiation itself, it can also causes the vibration of transmission box to generate noise radiation. The optimization of dynamic response of gear transmission system becomes one of the most efficient paths to control the noise level of transmission. Based on gear dynamics and the theory of mechanical optimization design, gear geometric parameters of a transmission are optimized in this paper and references for reducing vibration and noise of the transmission are provided. Specific works are provided as follows.Calculation methods of gear time-varying meshing stiffness are summed up in this paper. Considering the effects of modification coefficient, modified Y.Cai method to calculate gear meshing stiffness is developed. Programs are written using MATLAB to analyze the differences of gear stiffness calculated by different methods to decide the methods used in this paper.Based on gear dynamics, a dynamic model of 2-level gear transmission system is built considering the effects of time-varying mesh stiffness, mesh error, the torsional vibration of the shaft, and gear radial vibration. Differences of the system dynamic response under different gear parameters are analyzed considering the dimensionless displacement, natural frequency of gear transmission system and acceleration of the gearbox as index. According to the analysis, static displacement of gear pairs is reduced with the increase of gear modulus, tooth number, tooth width, helix angle. Average meshing stiffness of gear pair is not sensitive to the changing of module and the helix angle and it is increased with the increase the value of gear teeth number and tooth width. As the value of gear module, teeth number, tooth width and helix angle increase, the natural frequency of gear pair and system natural frequency decreased. Amplitude of dimensionless displacement varies when the system excitation frequency, system natural frequency and ratio of system mass changes. Acceleration depends on the size of the system meshing force. And positive correlation has been shown between acceleration and the value of dimensionless distance.Based on the theory of mechanical optimization design, the transmission ratio, center distance and indicators of gear strength are taken as the constraint mechanism, and an empirical formula to calculate transmission noise level, the volume of a gear pairs are introduced as the objective function, a nonlinear programing problem can be constructed to optimize macroscopic geometric parameters of gear, a case in literature is utilized to validate the feasibility of the proposed optimization procedure, the computed results indicate that the noise of transmission can be suppressed, and vibration of transmission can be reduced by means of the optimized geometric dimension parameters of transmission gear.