Research On Enhancement Test Coefficient For Automobile Proving Ground

The automobile reliability test is one of the important links in the process of finalizing and evaluating the automobile products. Along with the development of automobile industry in China, major domestic automobile proving ground have been built and gradually put into use. The reliability test for exploitation of automobile products has shifted from road test on to proving ground test. Most of the automobile proving grounds have more stringent testing road conditions. When vehicles drive on these roads, their vibration will be stronger than on actual ones, that is to say the stress load and the frequency of the components will increase. Compared to the actual roads, automobile reliability test on proving ground are also named the enhanced test or the accelerated life test. Nowadays, more and more auto manufacturers accelerate the pace of developing and improving the reliability of automobile products by testing on proving grounds. According to proving ground running standards, the automobile reliability test can significantly shorten the test cycle. As the test cost will be greatly reduced, there will be great significance for the development of vehicle products. With these reasons, the research on automobile enhancement test has been an important subject .Based on China's current road conditions, vehicle structure, the use of the environment and working conditions features, there are such practical problems as researches on the rules and methods of enhancement test, designing the proving ground road and establishing enhancement test norms. The various road mileages, the test speed distribution and the composite patterns must be stipulated, particularly in enhancement test norms. It is one of the important contents and the significant basis in drawing up automobile proving ground enhancement test norms, which studies and estimates the enhancement coefficient. The enhancement coefficient is the ratio of injury equivalent in practical road condition and proving condition.This paper takes the model truck as the object, which is researched by the method of calculating enhancement coefficient of motor vehicle reliability on proving ground, according to the equal damage fatigue life principle.By measuring one of the key components, the trucks axles fatigue capability, the fatigue life and the failure probability parameters have been discussed as the method of calculation and the theoretical proof of enhancement coefficient. So this paper could provide an important foundation for constituting the automobile reliability test norms of proving grounds.The research of this thesis can be summarized in the following aspects:(1) In this paper, the author uses an improved PaйTa rule to remove the anomalies of test data, which is followed by the use of the least squares method to eliminate the trend data component, and the inspection of the smooth and normality relations of test data by using rounds test andχ2 method. The results also prove that the test data are consistent with the smooth and normality indicators.(2) The test data are load-time histories, which have been pretreated. In order to analyze the fatigue damage of automobile parts, they must be simplified to a series of the entire circle or semi-circle process, so that we could analysis fatigue life and calculate the enhancement coefficient. In this paper, we have acquired the relationship of the frequency of the mean and amplitude load by using rainflow method. Then we obtain the zero mean equivalent loads by using Goodman experiential fatigue equation.(3) In this paper, we use Basquin relationship to acquire the fatigue characteristic curve of the automobile axles material. Then we employ the least-squares method to acquire the Weibull distributing function of equivalent loads of the rear axle and used the K-S method to inspect the assumption of the distribution function. The results have proved that the equivalent stress amplitude obeys the hypothetical distribution function. We also calculate the max loads by expanded sample method, and acquire eight routine loads spectrum of rear axle by Conover classification method. Meanwhile the author calculates the enhancement coefficient in principle of Miner linear accumulated fatigue damage rule and educes the mathematical model of calculating enhancement coefficient of synthesized roads.(4) We outline the reliability function of automotive products and acquire materials fatigue characteristic indicators of rear axle, and obtain the normal distribution function of the automobile rear axle fatigue limit by parameter estimation method. Then we have educed the failure probability indicators mathematical model of calculating enhancement coefficient by using the stress-strength interference theory and the Weibull distributing function and calculated the enhancement coefficient.In this paper, we have researched the complete determination and calculation method of the enhancement coefficient. Through the fatigue life and the failure probability acquired mathematical model of the enhancement coefficient, this paper compares and evaluates calculated results. Eventually, we give a summary to the research content of this paper, and provide some meaningful suggestions to the next stage research work.