1. Establish the precise modification model of cylindrical gear
Among the components of electric vehicles, cylindrical gear is the most widely used type of automotive components in the transmission mechanism. Its own composition has a more special design concept and processing technology. In the process of production and processing, the manufacturing accuracy value has a far-reaching impact on the transmission accuracy, stability and noise formation of cylindrical gear components in vehicle operation. Therefore, it is very necessary to establish a parametric model of wheel removal for electric vehicle gearbox. According to the working principle of standard involute cylindrical gear, a three-dimensional model of applied cylindrical gear is established by using the parametric modeling and modification technology pro/e. The basic parameters are shown in Table 1.
| Name | Driving wheel Z1 | Driven wheel Z2 | Modulus mn/mm | Pressure angle αn（/ °） | Helix angle β （/ °） | Tooth type b/mm |
| Corresponding angle | 11 | 34 | 2.5 | 20 | 26.7 | 12 |
2. Finite element contact analysis
The parameterized model of helical gear established by using pro/e software is introduced into ANSYS Workbench for corresponding settings. The setting program mainly includes the following points:
① The material property of driving wheel and driven wheel is defined as 20CrMnTi, and the elastic modulus is set as 2.2 × 1011pa, Poisson’s ratio is set to 0.289, and the density value is set to 7860kg/m3.
② The models of driving and driven wheels use 8-node 6-hedral elements to complete the discrete work, forming a network with a size of 0.4mm, a driving wheel with a speed of 1800r/ min and a driving torque of 90N · M.
③ In the study of gearbox gears, it was found that the contact problem was a linear problem, and it was decided to solve it through the simulation scheme. Newton Raphson calculation method was applied in ANSYS Workbench software to calculate, and finally the contact stiffness value was 0.01 and the friction coefficient was 0.1.
④ According to the above, after the finite element contact analysis using ANSYS Workbench software, the real contact pressure between the driving gear and the driven gear inside the electric vehicle transmission can be obtained.
⑤ After using the finite element contact analysis method to complete the research work, we can know from it that when selecting the best modification scheme from the modification methods of different types of transmission cylindrical gears, it is mainly through the comparison of the size of contact stress that the scheme with the maximum contact stress is the best modification scheme. Three schemes will be compared.
As shown in Table 2, three contact finite element models are established by using the software, and the corresponding analysis process is carried out to summarize the maximum contact force in the practice program.
| Programme | Wheel | Shaping amount /mm | Modification curve |
| A | Driving wheel | 0.2 | Fillet |
| A | Driven wheel | 0.5 | Fillet |
| B | Driving wheel | 0.27 | Straight line |
| B | Driven wheel | 0.26 | Straight line |
| C | Driving wheel | 0.2 | Parabola |
| C | Driven wheel | 0.2 | Parabola |
Through the research on three kinds of cylindrical gear repair technology of electric vehicle gearbox, the maximum contact stress in the three schemes is the best method of shaping. According to table 2, the maximum contact stress of scheme a is 1010.58mpa, and that of scheme C is 820.64mpa. During this period, compared with the other two maintenance schemes, scheme C has the least impact on the overall stability of the vehicle. It is concluded that scheme C is the most reasonable and applicable cylindrical gear modification scheme of electric vehicle transmission among the three schemes.