Research About Gear Modification And Housing Noise Reduction Of A Six-speed Manual Transmission In Medium-sized Truck

The NVH characteristic of the transmission is one of important factors affecting the ride comfort of the whole vehicle.Consumers and automakers increasingly attach importance to vibration and noise of the transmission.Therefore,the research about mechanism and method of transmission vibration and noise reduction has important theoretical significance and practical engineering value.To reduce vibration and noise of the transmission,this paper takes such transmission as object of study as well as confirms gear optimization scheme and housing improvement design scheme of the transmission by simulation、 optimization and experimental verification.Finally,this paper verifys the effectiveness of these schemes by comparison.Firstly,the gear system of the transmission is subject to modeling and simulation in the RomaxDESIGNER.Transmission error curve,transmission error peak-to-peak value and loading of the gear are known by simulation.Reducing the gear transmission error peak-to-peak value、the maximum contact stress、improving the transmission error curve and the gear loading are regarded as optimization objectives.The gear modification is used as optimization means and the gear optimization of the transmission is completed by setting modification parameter as optimization variable.The gears before and after optimization are compared to verify the scheme proposed in this paper.Secondly,after the gear system is simulated and optimized,by modal analysis it’s found that the transmission housing resonates at the time of 718 Hz by comparing the inherent frequency and gear engagement frequency.After modal analysis the frequency response of the housing is analyzed.Surface velocity and acceleration are extracted at the moment of 718 hz.And then the harmonic response characteristics of the transmission are analyzed.The vibration velocity on the housing surface is used as output.The analysis result is used as input document of transmission acoustic analysis and the radiation noise analysis(including housing surface sound pressure level analysis,hexahedral analysis of external sound pressure level,independent measuring point analysis and sound pressure level panel analysis)of the housing which is accomplished by direct boundary element method.finally,the improvement scheme for the housing side wall thickening is confirmed based on modal analysis,frequency response analysis and acoustic analysis results.The housing before and after the improvement design is subject to simulation and test with effectiveness of the improvement scheme verified.