The Investigation On Helical Gear Modification Of Electric Vehicle Gearbox And Reduction Of Vibration And Noise

At present,there is a huge demand for new energy vehicles in China.Taking electric vehicles as an example,the number of charging piles or related equipment has reached 1.68 million.Due to the fact that the gearbox noise accounts for a large proportion of the whole vehicle noise of electric vehicles,and the gear noise accounts for the vast majority,how to achieve the goal of reducing gear vibration and noise to improve the NVH performance of electric vehicles has been widely concerned.Taking the helical gear pair of an electric vehicle gearbox as an example,this paper aims to improve the vibration and noise characteristics of the gear and increase its service life by using gear modification technology.Therefore,a series of systematic studies are carried out,the determination process of the optimal gear modification scheme is described in detail,and the influence law of gear parameters on gear performance is explored and summarized.Firstly,the vibration and noise mechanism of electric vehicle gearbox and helical gear pair is described,the corresponding nonlinear vibration mathematical model is established,and the gear vibration excitation,especially the internal excitation,is deeply analyzed.Secondly,according to the actual working conditions,the modification scheme is formulated.With the goal of reducing the error excitation and improving the tooth strength(service life),the KISSsoft software is used to preliminarily optimize all the schemes.Thirdly,the multi-body dynamics of the electric vehicle gearbox is simulated by LMS Virtual Lab Motion software,and the modification schemes are optimized again to reduce the time-varying meshing force and time-varying meshing stiffness of the gear.At the same time,LMS Virtual Lab Acoustic software is used to carry out acoustic analysis on each secondary optimization modification scheme,in order to screen out the gear modification scheme with the lowest noise.Finally,through meshing contact and multi-body dynamics simulation,and combined with gear contact spot and noise bench test,the reason why the vibration and noise characteristics and service life of helical gear after empirical modification in an enterprise are decreased is explained.The main research work and achievements are summarized as follows:(1)The influence of parameters of helical gear on its meshing performance and dynamic characteristics is summarized.Appropriately increasing the pressure angle of helical gear can improve the transmission efficiency,Hertz contact stress and meshing stiffness,but it will increase the transmission error.Appropriate helix angle can reduce the transmission error,Hertz contact stress and time-varying meshing force of helical gear pair,but the larger helix angle is,the larger time-varying meshing stiffness is,and the lower transmission efficiency is.The timevarying meshing force at low speed(2000r/min)can be reduced by appropriately increasing the tooth width,but the larger the tooth width is,the greater the time-varying meshing stiffness is.The backlash has no effect on the time-varying meshing stiffness,but the smaller the backlash is,the smaller time-varying meshing force is,generally 0.05 mm.(2)According to the results of KISSsoft numerical simulation,the main functions of tooth profile modification and tooth direction modification are systematically explored.The main function of tooth profile modification is to reduce the Hertz contact stress on the tooth surface,that is,to improve the strength(service life)of the gear,but also to reduce the transmission error.The main function of tooth direction modification is to reduce the transmission error,that is,to reduce the internal dynamic excitation of the gear,but also to reduce the Hertz contact stress.(3)At high speed(10000r / min),the vibration noise of helical gear mainly depends on the time-varying meshing stiffness and transmission error,but it is not significant affected by the tooth shape and the time-varying meshing force.(4)Taking the gear pair as an example,the selection suggestions of modified gears are given.From the perspective of vibration reduction and noise reduction,it is suggested to modify the big and small gears at the same time.If only modify the big gear can reduce the transmission error of the gear and improve the strength of the gear teeth,but it is recommended to modify both the big and the small gears.In addition,except for drum profile modification,only the pinion modification can not play a role in reducing vibration,noise and increasing life.(5)In the long tooth profile addendum optimization modification schemes of all transmission error,Hertz contact stress,time-varying meshing force and time-varying meshing stiffness of the helical gear pair of an electric vehicle reducer(linear,progressive,arc-like,linear with transition radius): in order to reduce the gear error excitation and improve the tooth strength,the modification(linear)of the tooth tips of big and small gears at the same time with long tooth profile is the best;from the perspective of reducing the time-varying meshing force,the time-varying meshing stiffness and the vibration and noise of the gear pair,it is better to modify the tooth tips(progressive,arc-like)of the big and small gears at the same time.(6)In the optimization modification schemes of all transmission error,Hertz contact stress,time-varying meshing force and time-varying meshing stiffness of the helical gear pair of an electric vehicle reducer: the tooth profile drum(simultaneous modification of big and small gears)has the best vibration and noise reduction effect.Because the overall noise reduction effect of the optimization scheme of tooth profile drum(modify the big gear only)is close to that of the most quadratic optimization modification schemes,the optimization modification scheme of tooth profile drum only for big gear can be used in engineering practice for the sake of production cost.(7)According to the simulation results,it is deduced that the vibration and noise of the helical gear will be reduced only when the dynamic excitations(time-varying meshing stiffness,time-varying meshing force and transmission error)are simultaneously reduced by gear modification,and the shape of the tooth is suitable,which overturns some conclusions that the lower the transmission error of the gear,the lower the meshing noise must be.(8)Blind experience modification of gear pair can only increase the production cost,shorten the service life and aggravate the vibration and noise.