The drive axle assembly of electric vehicle is one of the main components of the vehicle and transmission system. Its quality determines the running stability and service life of the vehicle to a certain extent. At present, the damage of the drive axle assembly is mainly manifested in the fatigue damage of the main reducer spur gear under long-term random load. However, the drive axle assembly produced by most enterprises only uses the static strength design method for design, This method ignores the effect of random load on the spur gear of the drive axle main reducer in the process of vehicle operation, and considers that it is under the continuous and stable load, which will inevitably lead to a large error in the estimation of the fatigue life of the spur gear of the main reducer. Therefore, in order to calculate the fatigue life of the spur gear of the main reducer more accurately, this paper studies the fatigue life of the spur gear of the main reducer under long-term random load based on a certain road driving condition.
(1) Through consulting relevant literature and materials, understand the relevant theories of fatigue and fatigue life calculation, and determine to use the nominal stress method and fatigue cumulative damage theory to calculate the fatigue life of the spur gear of the main reducer; The inapplicability of the rain flow counting method to the random fatigue load counting of spur gears is analyzed with a simple calculation example. According to the contact stress characteristics of spur gear meshing, a suitable random load counting method of spur gears is used to count the random load received in the process of spur gear meshing of the main reducer.
(2) According to the vehicle driving equation, the torque transmitted by the spur gear of the main reducer is calculated by taking the driving condition of the Chinese passenger car (CLTC-P) as the speed input. The contact stress of the spur gear mesh is obtained by using the formula for calculating the contact fatigue strength of the spur gear tooth surface. The random load counting method of the spur gear is used to process, and the fatigue load spectrum of the spur gear that can be used for theoretical calculation is obtained. Then, according to the S-N curve of the material contact fatigue of the spur gear, Considering various factors affecting the fatigue strength of mechanical parts, it is modified to the contact fatigue S-N curve of spur gear parts. Finally, the fatigue life of spur gear of main reducer is calculated using the nominal stress method and the fatigue cumulative damage theory.
(3) Use a test vehicle to do the actual road following test, collect the actual driving speed of the vehicle, and calculate the input torque of the spur gear of the main reducer according to the vehicle driving equation; Then use CATIA to carry out 3D modeling on the spur gear of the main reducer, get the gear mesh assembly of the main reducer, and then import it into ANSYS/Workbench to carry out static simulation on the spur gear, and get the contact stress generated by the spur gear to the mesh; Finally, the contact fatigue life of spur gear is analyzed and calculated by using the finite element calculation and analysis software ANSYS Code DesignLife, and the contact fatigue life of spur gear of main reducer is obtained. The comparison and analysis with the theoretical calculation results verify the feasibility of the method of calculating the fatigue life of spur gear of main reducer based on CLTC-P road conditions.