The planetary gear mechanism of an automobile is composed of a sun gear, three planetary gears, a gear ring and a planet carrier. The gear ring is fixed, and the sun gear is the driving gear.
The specific parameters of the planetary gear unit are shown in the table.
| Name | Number of teeth (Z) | Modulus (m/mm) | Pressure angle（α） | Tooth width (b/mm) |
| Planetary gear | 27 | 2 | 20° | 30 |
| Sun wheel | 18 | 2 | 20° | 30 |
| Ring gear | 72 | 2 | 20° | 30 |
In order to carry out the follow-up rigid flexible coupling dynamics simulation research on the crack of the planetary gear of the gearbox and the characteristic frequency analysis of the actual fault vibration signal, the author has established the three-dimensional models of the planetary gear mechanism under normal working conditions and under the fault conditions of the planetary gear crack in SolidWorks software.
According to the solid model of a certain type of automobile planetary gear mechanism, the three-dimensional models of the sun gear, planet gear, planet carrier and gear ring are established by using SolidWorks software; According to the actual assembly relationship of each component, the assembly body of planetary gear mechanism under normal working conditions is established.
The planetary gear mechanism of an automobile under normal working conditions is shown in the figure.
