In automobile transmission, traditional systems mostly use rolling bearings to support the rotating axle to ensure stable rotation of the rotating axle. Here, cylindrical roller bearings are used to support the stable transmission of the rotating axle. During use, it is found that the cylindrical roller bearing The circle appeared to be out of sight. What causes the inner ring of cylindrical roller bearing to fall out?

1. Failure phenomenon and influence of inner ring of cylindrical roller bearing

The faulty parts were removed from the whole box for inspection, and it was found that the inner ring of the cylindrical roller bearing of the driving wheel shaft was 3mm away from the plane position of the internal measurement. If the inner ring of a cylindrical roller bearing is out of a certain distance, the roller does not make full-length contact with the raceway surface of the inner ring of the bearing, the bearing will experience abnormal vibration under load, and this vibration will directly affect the operation of the gearbox and cause undesirable noise , Thereby affecting normal use.

2. Cause analysis of the failure of inner ring of cylindrical roller bearing

a. System structure analysis: According to the structural design, the two ends of the drive axle are bearings, the fixed end adopts deep groove ball bearings, and the free end adopts cylindrical roller bearings. The deep groove ball bearing is subjected to the radial force generated by the steel belt and the axial force generated by the spindle oil pressure. Cylindrical roller bearings are only subjected to the pulling force of the steel belt transmitted from the axle, and no axial force is applied to the bearing, that is, the cylindrical roller bearing will not be pulled out by the axial force.

b. Reason analysis: It can be known from the mechanical principle that the parts of the two interference fits are separated during the use process, or the parts are manufactured out of tolerance, which reduces the tightening force insufficiently, or the designed fit interference is too small. The resulting tightening force is insufficient, and the thrust generated during the work of the parts is greater than the tightening force, which causes the parts to move and move away. The reason for the bearing out is explored based on this idea.

1) Size inspection:

If the part size is not qualified, there is a risk that the inner ring of the bearing will fall out. The bearing mating parts of the two prototypes were measured. The results are shown in Table 1. The dimensions of the parts meet the design requirements, and the influence of this factor can be excluded.

2) Calculation of binding force:

The inner ring of the bearing and the axle have an interference fit, and the reason for the inner ring to come out may be insufficient interference in the design. Check the dimensional design of the axle and the bearing, and found that the minimum interference between the two in the limit state is 0.002mm. At this time, the combination of the inner ring of the bearing and the axle can be calculated by the following formula (1):

among them:

P-Bonding force between inner ring and shaft, N

d1-the diameter of the shaft, mm

d2-bearing inner diameter, mm

B-Bearing and inner ring contact width, mm

E-The elastic modulus of the shaft, Mpa

According to the calculation, when the interference between the bearing and the axle is 0.002mm, the combined tightening force P is 23.73N. If this value is too small, it is easy to cause insufficient tightening and fixing of the driving axle to the inner ring of the bearing and cause the bearing to fall out. However, in the previous structural analysis, cylindrical roller bearings are not subject to axial force. It does not seem to be able to explain that a small binding force will cause a problem of separation. The problem needs to be further explored.

3) The CAE analysis structure model of the force on the axle and the bearing is established, and the computer software is used for CAE analysis. According to the CAE calculation and analysis results, a certain amount of bending deformation will occur when the wheel axle is stressed, which will then generate axial force on the bearing.

At the same time, the CAE analysis results of the driving axle showed that the tapered flange contacting the steel belt also deformed, and the bearing position deformation caused by the maximum steel belt tension was 0.084mm. The deformation of the tapered flange also produces axial force on the bearing.

3.Reason confirmation

According to the above analysis, under the action of the steel belt tension, the axial force between the wheel axle and the cylindrical roller bearing will not be completely absent. In addition, the error of product manufacturing and assembly will increase the axial force. When the total axial force caused by the forced operation of the axle and the manufacturing error is greater than the combined fastening force of the bearing, the bearing will slip at the original position on the axle.

The numerical calculation of the axial force generated by the deformation of the wheel axle is more complicated, and no specific deduction is made here. From the results of CAE analysis—the tapered flange bearing of the drive wheel shaft has a 0.084mm deformation at the bearing position, it can be seen that the axial force will not be too small, and the minimum interference between the bearing and the shaft combined with the fastening force of 23.73N must be minimal.

From this, it can be confirmed that the reason for the failure of the cylindrical roller bearing inner ring of the driving axle in the bench test of this CVT product is that the matching interference between the bearing and the axle given by the part design is insufficient, and there is no structural design. The bearing is on the axle of the limited anti-off structure.

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