The influence of the bearing stiffness of the central component of the system on the dynamic characteristics of planetary gears is studied. The central component in the gear transmission system of hybrid electric vehicle refers to the large sun gear, small sun gear, planet carrier and ring gear in the composite planetary gear mechanism. Assuming that all support stiffness K of each central member is equal, in order to analyze the influence of bearing stiffness on the system, change the bearing stiffness. The simulation analysis stiffness is: (1) 5x107n / M; (2)5x108N/m； (3)5x109N/m. According to the change of natural frequency (critical angular velocity) of the system, the results of the first ten natural frequencies are summarized in the table below.
| Situation | f1 | f2 | f3 | f4 | f5 | f6 | f7 | f8 | f9 | f10 |
| 5e7 | 0 | 11.3 | 112.5 | 141.3 | 201.6 | 207.8 | 316.3 | 380.2 | 853.4 | 5532.7 |
| 5e8 | 0 | 11.6 | 158.39 | 160.39 | 362.61 | 410.3 | 2782.3 | 2783.4 | 5565.1 | 5565.1 |
| 5e9 | 0 | 11.6 | 160.96 | 160.96 | 416.28 | 416.28 | 2783.4 | 2783.4 | 5565.7 | 5565.7 |
By analyzing the natural frequencies under these three support stiffness, it can be found that the natural frequency increases with the increase of support stiffness When the support stiffness is 5x107n / m, there are many low-frequency frequencies, which is likely to cover the angular frequency of system operation, which means that it will have a great impact on the stability of the system. Especially when hybrid electric vehicles drive at low speed, it will attract more attention. When the support stiffness is 5x108n / M and 5x109n / m, the support stiffness has little effect on the high-order natural frequency. The high-order natural frequency has little impact on the research object of this paper. Through analysis, select the support stiffness of the central component as large as possible within the appropriate range. In this way, within the normal speed range, the natural frequency becomes less, the speed to be avoided is reduced, and the dynamic characteristics of the gear transmission system of hybrid electric vehicle are improved. The analysis results of the support stiffness of planetary gears and parallel shaft gears are similar to those of the central member, which will not be described in detail here.