| As an important part of the traction drive system,the transmission gear of EMU is mainly used to transmit the motion and torque generated by the motor to drive the train.In this process,due to the long-term service of the train in the complex random load environment,the transmission gear is very easy to produce failure,and ultimately has a certain impact on its safe and reliable operation.Moreover,various failure modes and their reliability are considered in the current design and analysis of transmission gears,but only the direct consequences caused by failure are analyzed,such as the increase of contact stress and gear vibration,the reduction of transmission efficiency,etc.The influence of failure mode and its correlation on reliability is less studied,therefore the change of reliability caused by failure is not well understood.For that reason,this work study the main failure modes of transmission gears and the influence of their correlation on the reliability from the two point of view that is the static reliability under multiple failure modes and the dynamic reliability under failure correlation,so as to further understand the change trend of static/dynamic reliability.A gear shape modification optimization design method under multi-load cases are proposed considering the influence of the multi-load cases characteristics of the transmission gear on its failure mode,which further improves the reliability of the transmission gear.The main work is as follows.Firstly,in order to explore the structural performance of transmission gear in multiple failure modes,a static reliability analysis method based on multiple failure modes is proposed.Through the analysis of the failure modes of the transmission gears,the failure modes which are harmful to them are determined.On this basis,the corresponding structure function is established and the probability distribution is obtained by Monte Carlo sampling.The correlation matrix between failure modes is calculated based on MATLAB,the reliability model related to multiple failure modes is constructed,the reliability of transmission gears is calculated,and the sensitivity analysis of failure modes and their random variables is further carried out.The results show that the failure mode correlation has an important influence on the reliability of the transmission gear,and the tooth surface contact fatigue and its related random variables have the greatest influence on the reliability of the transmission gear.Secondly,the dynamic reliability of transmission gear based on failure correlation is studied considering the correlation between failure modes and the influence of time on reliability.According to the actual load case,the dynamic simulation model of the transmission gear is established,the contact stress time history of the gear is calculated,and the rain flow counting method is used for statistical processing.The equivalent load under multiple random loads is calculated,and the probability density distribution is compared and analyzed based on the 12 level load spectrum.In addition,Frank copula function is used to describe the correlation between contact fatigue and bending fatigue failure modes.Based on the above analysis,the dynamic reliability analysis model of transmission gear is established and solved.The results show that under the single failure mode,the decrease degree of reliability caused by the change of contact fatigue with time is higher than that of bending fatigue;the change of reliability value with time under the consideration of failure correlation is higher than that without consideration of relevant failure,which shows that the reliability analysis results without consideration of failure correlation are more conservative.Finally,to reduce the probability of failure,the shape modification optimization design of the transmission gear under multiple working conditions is carried out.Taking torque as load index,the actual operation load case of transmission gear is transformed into multi load cases.The tooth contact stress,tooth load distribution and transmission error are analyzed.In this paper,a comprehensive method of parallel modification of tooth profile and direction is selected,and the modification parameters and torque are taken as test factors.16 groups of test schemes are obtained through orthogonal test.The response surface function between the modification parameters and contact stress is constructed,and the optimal value of each modification parameter is obtained by genetic algorithm.Through the comparative analysis of the meshing performance of the gear before and after the modification optimization,the rationality of the optimization scheme is verified.The results show that the modification optimization reduces the contact stress and transmission error on the tooth surface of the transmission gear,and the load distribution on the tooth surface is also improved synchronously,which means the probability of failure is reduced. |
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