Research On Prediction And Optimization Of Radiated Noise Of Automobile 2×4 Drive Switching Control Mechanism

With the improvement of sales for four-wheel-drive SUV and the need for comfort to the passengers,it is of great importance to analyze the dynamics and noise of the shift mechanism for 4WD transfer case and to improve the design of the mechanism.As the key component of the four-wheel drive-vehicle,both the dynamic performance and vibration noise of the Shift Mechanism for 4WD Transfer Case would affect the power output and the quality of the vehicle.The main research work of this thesis is as follows:(1)A purely torsional model with nonlinear dynamics of the shift mechanism for 4WD transfer case is established.The noise transfer process of the shift mechanism for 4WD transfer case is studied,and the excitation of the gear transmission system is analyzed.At the same time,both the analysis of the relative displacement of each component in the system and the establishment of the pure torsional dynamic model of the system provide the theoretical foundation for analyzing the vibration noise of the Shift Mechanism for 4WD Transfer Case gear transmission system.(2)The multi-body dynamics is analyzed which is based on the shift mechanism for 4WD transfer case of torsional vibration method.A multi-body dynamic simulation model is established on LMS Virtual.Lab Motion.The analytical method is used to analyze the torque equivalence of the gear transmission.Internal accelerations such as time-varying meshing stiffness and flank clearance are taken into consideration to obtain the output of shaft rotational speed and the dynamic engagement force of gear.And the result is compared to the theoretical value to ensure the accuracy of the simulation model.(3)Analysis of vibration characteristics of the shift mechanism for 4WD transfer shell was performed based on modal superposition method.The ANSYS software is used to establish the finite element model of the shift mechanism for 4WD transfer shell and to perform modal analysis.The vibration mode and natural frequency of the shell are obtained.And the vibration mode is mainly based on the bending and torsion.Under this condition,the vibration of the upper shell is obvious.The modal superposition method was used to solve the vibration response of the mechanism shell,and the vibration displacements of the surface nodes of the mechanism shell are obtained.(4)The direct boundary element method is used to analyze the radiation noise of the shift mechanism to obtained the sound pressure cloud diagram and frequency response curve of the sound field outside the mechanism.Later,the noise test is conducted.The sound pressure level at each simulation test point is similar to the experimental test value of 70 d B which ensures the accuracy of prediction method.And the ATV method is used to solve the contributions of different parts of the mechanism to the noise.(5)Analysis of the noise reduction on the shift mechanism for 4WD Transfer Case was performed.Three noise reduction optimization schemes were proposed to achieve this aim.Romax software is used to shape the tooth form and tooth orientation.Then the transmission error corresponding to the gear profile modification was obtained.The secondorder response surface method is used to solve the optimal gear profile modification.And the structure of the upper housing is optimized.A method of covering a layer of soundabsorbing material on the surface is adopted.The sound pressure values of the three schemes after optimization are lower than before,and the effect of noise reduction is achieved.