According to practical experience, contact fatigue often occurs in helical cylindrical gears of transmission. The basic parameters of the high-speed helical cylindrical gear pair of the electric vehicle studied are shown in the table below. During the meshing process of helical cylindrical gears, the maximum contact stress on the tooth surface of helical cylindrical gears σ H occurs on the pinion, and the dangerous position of contact fatigue usually first appears in the single tooth meshing area near the pitch line, so the node is taken as the dangerous position of tooth contact fatigue. Based on Hertz contact theory, the maximum contact stress is taken as the basic value of contact stress of helical cylindrical gear on the tooth surface, and the calculation formula of contact stress is as follows:
Where: σ H refers to contact stress; T refers to pinion torque; B refers to tooth width; D1 refers to the pinion indexing circle diameter; α N represents the normal pressure angle; β Represents the helix angle; E1 and E2 respectively represent the elastic modulus of two helical cylindrical gears; ν １ 、 ν 2 is the Poisson’s ratio of two helical cylindrical gears respectively; The curvature radii R1 and R2 of the two tooth profile contact points are calculated according to the following formula:
Where: the base circle radius of RB1 and Rb2 helical cylindrical gears respectively; α Represents the meshing angle of two helical cylindrical gears.
| Parameters | Numerical value |
| Radius of base circle Rb1, Rb2 / M | 0.02，0.084 |
| Normal pressure angle α ｔ／ （°） | 20 |
| End pressure angle α ｎ／ （°） | 21.88 |
| Pitch circle helix angle β／ （°） | 25 |
| Normal modulus Mn | 2.25 |
| Tooth width B / M | 0.027 |
| Poisson’s ratio ν １ ， ν ２ | 0.3 |
| Elastic modulus E / GPa | 206 |
The dynamic torque of the drive motor obtained from the simulation is substituted into the formula, and the contact stress spectrum of the driving gear of the electric vehicle transmission under the cyclic condition is calculated based on the quasi-static method, as shown in the figure.
