Analysis On Enhancement Coefficient And Accelerate Life Test Design For Automotive Gears

Road test is an effect way to investigate and evaluate the reliability of vehicles.In order to shorten the design and test period,road test is conducted on proving ground roads.Enhancement coefficient is necessary to compare proving ground roads with ordinary roads.The manual transmission is known as an important assembly and widely used in a variety of vehicles.Nevertheless,technical difficulty emerges during the calculation of enhancement coefficient of gears for its stress history is complex and hard to collect.Firstly,the manual transmission of a certain SUV is employed as research object,and a method of enhancement coefficient calculation based on road load and virtual prototype simulation is presented.The load spectrums of manual transmission exposed to ordinary road,enhanced road,mountain road and high way road are sampled.The distribution format of load spectrums is obtained by means of rain-flow counting method and statistical theory.The mean of torque is found to obey normal distribution,but the amplitude of torque is not distributed as normal or Weibull distribution like other automotive parts.The distribution function of mean of torque is evaluated via parameter estimation.On the basis of the extrapolated load spectrum,Conover method is applied to convert torque spectrum to one-dimensional load spectrum.At the second stage,a multi-body dynamic model of transmission is established in ADAMS and the stress history of key nodes based on one-dimensional load spectrum is computed.Transient dynamic analysis in ANSYS is used to compare the stress history of same node and the result turns out to be fit well with ADAMS.The damage of gears under all sampled load spectrums is calculated using Miner linear accumulated fatigue damage theory.Enhancement coefficients of proving ground roads are obtained by comparing damage with ordinary road.Finally,bench test condition based on occupation standard is lead to enhancement coefficient calculation and accelerate life test schedule is presented based on the enhancement coefficient between bench test condition and ordinary road.This dissertation provides a theoretical evidence for automotive reliability testing and proving ground designing.