| In respect of the squeak about the MF510E01 on its 5th step, we will have further investigation in this article. Based on the vibration and noise analyses by FEA and test analysis, we will introduce the ways of noise reduction, and reach the final destination of vibration and noise reduction by improving the 5th gear.Several concepts will be introduced at the first, which will pave a way for analysis and evaluation of the transmission's radiated noise. Noise production mechanism analysis showed that the main factors which caused transmission gear noising were the mesh stiffness change, the transmission error, and the mesh impact. Among those noises, the auto-noise was the main transmitting pathway. All of these provided theory suggestions for vibration and noise reduction of transmission.For the theory modal analysis and the acquirement of its most vibrative part, which would provide theory guide for the NVH test, we established the 3D model of gearbox, gear and axis according to the 2D papers. We also carried out the finite element modeling analysis after model simplification. Characteristic analyses led us to find the sensitive part of the transmission that causes vibration.The NVH test of MF510E01 was carried out in semi-anechoic rooms. The maximal surface of radiated noise was determined, and the relationship of the radiated noise with the speed and torque was concluded. Coherence function analysis showed the main part of the radiated noise owed to the air born sound. Eigen-frequency and eigen-order were found. After structure analysis, interactive filtering analysis, the main noise source was determined to be the gear pair. By analyzing the dynamic power of gear system, it was certain the mesh impact was the main power source. Then, reducing backlash, increasing contact radio and micro-geometry were used to optimize the gears. By comparing, the result showed an evident roaring reduction of the 5th step and a whole reduction by 3dB(A) on average after the optimization.
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