Abstract: The method for determining the zero clearance of back-to-back paired single-row tapered roller bearings is described. Three methods for measuring the width of the inner spacer under zero clearance are introduced and compared. The results show that: Method 3 is an accurate method. Appropriate measurement method, and the error in the measurement process of method 3 are analyzed, and corresponding solutions are given to improve the assembly quality.
The back-to-back paired structure of single-row tapered roller bearings not only has good rigidity, but also has good guiding accuracy, and can also bear the overturning moment, so it has been more and more widely used in wind power gearboxes. This bearing arrangement is mainly used in planetary gears, including traditional planetary gear structures  and planetary gear structures using flexible pin technology. The planetary gear structure using flexible pin technology is shown in Figure 1.
The adjustment of the axial clearance of the single-row tapered roller bearing after pairing is completed by grinding the inner spacer. If the inner spacer is processed and adjusted by the bearing manufacturer, the cost is high and the installation clearance changes greatly. Therefore, the inner spacer The processing and adjustment of the axial clearance are completed by the gearbox manufacturer. At present, the planetary gears of wind turbine gearboxes using this bearing structure all adopt negative clearance, and the axial clearance is generally -0. 1 to 0 mm. Although this bearing configuration has the characteristics of simple structure and flexible assembly , its installation process is complicated, and the installation accuracy will affect the running stiffness and service life of the bearing.
For workshop mass production, the adjustment of axial clearance is a key factor affecting production efficiency and product quality, and the adjustment of axial clearance is achieved by grinding the inner spacer ring, so it is necessary to find a convenient and quick way to determine the inner spacer. How to measure circle width. At present, various wind turbine gearbox manufacturers have different measurement and installation methods for this bearing structure configuration. Here, we will compare and analyze several measurement methods for the width of the inner spacer, determine an accurate and fast measurement and installation method, and give Suggestions for optimization of planetary gear structure.
2 Zero clearance determination
When adjusting the installation of a pair of back-to-back tapered roller bearings, the bearings must be rotated so that the rollers are in the correct position, that is, the large end face of the inner assembly roller is tightly pressed against the large rib of the inner ring, and the outer ring raceway is tightly pressed Relying on the tapered surface of the roller , this is the zero clearance state of the tapered roller bearing.
As shown in Figure 2, install the A and B bearings in place, and put the entire planetary gear on the platform, and rotate the planetary gear until it runs smoothly. At this time, the large end face of the roller of bearing B is tightly pressed against the large rib of the inner ring, while there is a gap between the large end face of the roller of bearing A and the large rib of the inner ring, use 0. 1 to 0. The 15 mm feeler gauge fits easily, so you can be sure that Bearing B is now at zero clearance and Bearing A is at non-zero clearance.
3 Determine the width of the inner spacer
The key to adjusting the axial clearance is to determine the width of the inner spacer in the zero-clearance state. Let the width of the inner spacer in the zero-clearance state be L0, and the required clearance is δ0, then the width of the inner spacer after installation L is L = L0 + δ0. If the width of the inner spacer is L1 in the initial state, the wear distribution ΔL of the inner spacer is ΔL = L1 – L. For the measurement of the width L0 of the inner spacer in the state of zero clearance, each gearbox manufacturer adopts 3 different measurement methods.
1 method 1
The measurement principle is shown in Figure 3. Put the planetary wheel on the platform, remove the inner spacer, add a load block to the bearing A (the mass and structural design of the load block will not be introduced here), rotate the planet When the wheel is in a stable state, directly measure the height H between the upper and lower bearings, and H is the width L0 of the inner spacer in the zero clearance state.
Bearing B is in a state of zero clearance under the action of the planetary gear, load block and bearing gravity, but bearing A is in a state of zero clearance due to the self-locking effect of the inner component cone, the base surface of the roller ball and the inner ring rib cannot be completely contacted, and there is a certain The gap is in a non-zero clearance state, at this time, the height H is taken as the width L0 of the inner spacer in the zero clearance state, and there will be a large error in the measurement result.
2 method 2
The measurement principle is shown in Figure 4. First, take out any bearing from the paired 2 sets of bearings and make a mark, measure the assembly widths T1 and T2 of the bearing in the forward and reverse states, and calculate the difference between the two, δ1, that is, δ1 = T1 – T2, δ1 is the error value produced by measuring the axial clearance of the paired bearing in the non-zero clearance state of bearing A in Fig. 4b (a load block should be added when measuring T1 and T2).
Take out the inner spacer, add a load block to the bearing A, make the probe hit the center of the load block, rotate the planetary wheel to a stable state, and the bearing B is in a state of zero clearance. The wheel sleeve moves out of the measurement area. Then put the unground inner spacer ring, add the load block again, put the measuring instrument probe in the center of the load block , rotate the planetary wheel to a stable state, record the reading δ2 of the measuring instrument, at this time it can be calculated If the axial clearance Δδ of the paired tapered roller bearing is obtained, that is, Δδ = δ1 + δ2, the width of the inner spacer in the zero clearance state is L0 = L1 + Δδ.
3 methods 3
The measurement principle is shown in Figure 5. Put the planetary wheel on the platform, remove the inner spacer, with bearing A at the top, rotate the planetary wheel to a stable state, and measure the height H1 from the upper end face of the planetary wheel to the end face of the inner ring of bearing B ; Then turn over the planetary gear so that the bearing B is at the top, rotate the planetary gear to a stable state, and measure the height H2 from the end face of the planetary gear to the end face of the inner ring of bearing A. Assuming that the width of the planetary gear is K, the width L0 of the inner spacer in the zero clearance state is
L0 = H1 + H2 – K.
Comparing the above three measurement methods, it is found that although method 1 has a simple measurement process, there is a large measurement error, and the difference in the mass of the load block has a great influence on the measurement results. Method 2 eliminates the error of the axial clearance when the upper bearing is measured in a non-zero clearance state, but needs to measure δ1, the whole measurement process is long, and the error generated by the instrument during the two measurements before and after cannot be ignored. Compared with the first two methods, measurement method 3 has less measurement data, and the error generated in the whole measurement process is smaller, which is more suitable for workshop mass production applications.
4 Error analysis and countermeasures
Compared with the above measurement methods and combined with the installation process of the planetary gear components, the errors generated in the measurement process of method 3 are analyzed and countermeasures are given. Method 3 During the measurement process, when measuring the data K, H1 and H2, due to the end face runout and parallelism tolerance on the two end faces of the planetary wheel and the end face of the bearing inner ring, a certain error will occur during the measurement process. Generally, the end face runout of the planetary wheel is less than 0. . 03mm, the verticality of the bearing end face relative to the inner hole is smaller, so the method of multi-point measurement and average value can be used for measurement. In order to improve production efficiency and ensure the accuracy of measurement during installation, 4 to 6 points can be taken for measurement, and the average value can be taken as the final measurement value of K, H1 and H2.
In addition, in order to facilitate the measurement of H1 and H2, when designing the planetary gear, it is necessary to ensure that the end face of the bearing inner ring is lower than the end face of the planetary wheel, that is, there is a certain height difference γ between the end face of the bearing and the end face of the planetary wheel, as shown in Figure 6.
Due to the interference fit between the outer ring of the bearing and the inner hole of the planetary wheel, the planetary wheel is heated during installation for hot fitting. During the cooling process of the planetary wheel, there will be a certain gap between the end face of the outer ring of the bearing and the inner hole of the planetary wheel. The measured gap value is about 0. 02 to 0. 05mm, the existence of this clearance will affect the axial clearance value of the matched bearing. During the slow cooling process when the bearing outer ring is installed in place, the end face of the bearing outer ring can be brought into close contact with the end face of the inner hole rib of the planet gear by applying pressure, as shown in Figure 7. Applying a heavy object to a single planetary gear or stacking two or more planetary gears together can ensure that the end face of the bearing outer ring is in close contact with the rib of the inner hole of the planetary gear during the cooling process of the planetary gear, which improves the installation quality.
Taking two sets of 32040 tapered roller bearings composed of back-to-back paired bearings as an example, the bearing installation process and the determination process of the inner spacer width are described.