Automatic bearing pre-tightening mechanism

The invention discloses an automatic bearing pre-tightening mechanism which comprises a box body, a sliding seat assembly, a stopping assembly, a differential assembly and a driving assembly, the differential assembly comprises a high-speed gear and a low-speed gear, the high-speed gear is in transmission with a locking nut, the low-speed gear is in transmission with a mandrel, and the stopping assembly comprises a torque disc, a pull rope and a heavy hammer. The driving assembly drives the high-speed gear and the low-speed gear to rotate in the same direction at a differential speed, the locking nut is gradually screwed, when the pre-tightening force is larger than or equal to a preset value, the outer ring of the bearing assembly starts to drive the clamping base and the torque disc to rotate, the heavy hammer is lifted through the pull rope, and after the heavy hammer is disengaged from the contact, the driving assembly is powered off and stops rotating. The friction torque of the pre-tightened bearing ass