In automobile transmissions, most traditional systems use rolling bearings to support the rotating axle to ensure stable rotation of the rotating axle. The following example illustrates the use of NSK cylindrical roller bearings to support the stable transmission of the rotating axle. During use, NSK cylinders are found The inner ring of the roller bearing has come out. What causes the inner ring of cylindrical roller bearing to fall out? If the solution is the best solution? Below, Eric Bearing Limited will share relevant content based on the understanding of bearing knowledge.
NSK cylindrical roller bearing inner ring detachment failure phenomenon and its influence
Example: The faulty part was 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 the NSK cylindrical roller bearing is out of a certain distance, and the roller does not make full-length contact with the raceway surface of the inner ring of the bearing, abnormal vibration of the bearing will occur under load, and this vibration will directly affect the operation of the gearbox and cause defects Noise, which affects normal use.
Analysis of the Causes of the Breakout of the Inner Ring of NSK Cylindrical Roller Bearings
1. 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 subject to the tensile force of the steel belt transmitted from the axle, and no axial force is applied to the bearing, that is, the NSK cylindrical roller bearing will not be released by the axial force.
2. Reason analysis
From the mechanical principle, it can be known that the two parts of the interference fit have been separated during the use process, or the parts are manufactured out of tolerance, which reduces the tightening force insufficiently, or the tightening force generated by the designed fit interference is too small. Insufficient, the thrust generated in the work of the part is greater than the tightening force, so that the part is sent and moved. The reason for the bearing out is explored based on this idea. NSK 6207VVNRC3 bearings online , pls click here :
(1) Size detection:
If the part size is not qualified, there is a risk that the inner ring of the bearing will fall out. Measure the bearing mating parts of the two prototypes. If the dimensions of the parts meet the design requirements, the influence of this factor can be excluded.
(2) Calculation of binding force:
The inner ring of the NSK bearing has an interference fit with the axle, 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 find 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:
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
The example we have given can be seen from calculations. When the interference between the NSK bearing and the axle is 0.002mm, the combined tightening force P is 23.73N. This value is too small, which will easily cause insufficient tightening and fixing of the drive axle to the inner ring of the bearing. 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.
The CAE analysis of the force on the axle and the bearing establishes the model according to the structure, and uses the computer software for the 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 an 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 an axial force on the NSK bearing.
(3) Reason confirmation
According to the above analysis, under the action of the steel belt tension, the axial force between the axle and the NSK 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, so specific derivation and calculation will not be made here. From the result of CAE analysis—the tapered flange bearing of the driving wheel shaft has a deformation of 0.084mm, it can be seen that the axial force will not be too small. The minimum interference between the NSK bearing and the shaft combined with the fastening force of 23.73N must be very small compared to it.
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 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.
In response to the two reasons identified above, two measures to solve the problem have been formulated:
(1) Increase the interference between the inner ring of the NSK bearing and the axle. Adjusting the diameter tolerance of the axle-to-bearing fit will increase the minimum fit between the axle and the NSK cylindrical roller bearing from 0.002mm to 0.011mm.
(2) A limit anti-drop structure is added to the inner ring of NSK bearing. A retaining ring groove is added to the outer position of the NSK bearing on the axle, and the retaining ring is installed to limit the inner ring of the bearing to prevent the inner ring from falling out.
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