| The transmission efficiency and dynamic performance will be improved when the Blade Electric Vehicles(BEV) carry on two speed automatic transmission(2 AMT), which provides the BEV with two speed transmission huge marketing prospects, but brings reliability and security problems of BEV two speed transmission. Currently the research of BEV transmission mainly focuses on ratio optimization and structural design of transmission, the contact-stress fatigue life of the gears of the two speed transmission is rare. But the gear is the key component of transmission, the contact-stress fatigue life of gears determined the reliability of the transmission. The acquisition and analysis of contact stress and the use of fatigue life calculation theory are the two most important steps for calculation of contact-stress fatigue life of transmission gears. The BEV two speed transmission working conditions and fatigue load spectrum couldn’t be acquired by road test because of none BEV carried on two speed transmission. Because the rain flow counting method is not suited to contact stress process of gears, the method of rain flow counting method couldn’t be applied here. The problems above lead to the final problem that the fatigue life of currently designed BEV 2 AMT couldn’t be estimated accurately.For these problems, firstly this paper proposed a method to acquire the contact stress of a 2 AMT gears based on the instantaneous road condition UDDS condition. The steps of application of the method is as follows:firstly based on the UDDS condition, using the two-parameter shift schedule and driving equation, this paper set up a simulation modeling of the 2 AMT in MATLAB/Simulink and obtained the working condition of the 2 AMT, including the shift information, speed information and torque information. Then this paper calculated the contact stress of gears by formula. And then this paper proposed an improved calculation method of cycles of load for gears, using the new method to calculate the stress amplitude-mean value frequency. Finally this paper calculated the contact-stress fatigue life of the transmission gear through nominal stress method S-N Method and cumulative damage theory. For proving the feasibility of this progress, this paper took the measured vehicle speed condition instead of the UDDS condition, using the established Simulink modeling to obtain the working conditions of the two speed transmission based on the measured vehicle speed and driving equation, then used several software co-simulation method to calculate the two speed transmission gear contact fatigue life, compared with the fatigue life based on the first method, verifying feasibility of the first method. |
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