GB/T 17855-2017Calculation of load capacity of spline (English PDF)

5.1 Use factor K1

The use factor K1 is mainly a factor that considers the influence of power overload caused by external factors of the transmission system. The impact of this overload depends on factors such as the characteristics of the prime mover (input) and the working machine (output), the mass ratio, the mating nature and accuracy of the spline pair, the operating status, etc.

The coefficient can be obtained by precise measurement, or it can be determined after analyzing the whole system. When the above method cannot be realized, it can refer to Table 2 for values.

5.2 Tooth side clearance factor K2

When the stressing state of the spline pair is as shown in Figure 4, the load on the teeth of the involute spline or rectangular spline depends on the elastic deformation of the key teeth; it also depends on the size of the side clearance of spline pair. Under the action of the shaft load, as the backlash changes (half of the circumferential gap increases, the other half of the circumferential gap decreases), there will be a relative displacement e0 between the two axes of the inner spline and the outer spline, as shown in Figures 4 and 9. The magnitude of the displacement e0 is related to factors such as the size of the backlash (clearance) of the spline and the level of manufacturing accuracy.

After the displacement occurs, the load is distributed on fewer key teeth (the self-centering effect is lost for the involute spline), which affects the load-bearing capacity of the spline. The side clearance factor K2 considers of this impact, usually K2 = 1.1 ~ 3.0.

When the shaft load is small and the accuracy of the spline pair is high, it may take K2 = 1.1 ~ 1.5; when the shaft load is large and the accuracy of the spline pair is low, it may take K2 = 2.0 ~ 3.0; when the shaft load is zero and only bearing the rotational moment (see Figure 2), K2 = 1.0.

5.3 Distribution factor K3

When the two axes of the inner spline and the outer spline of the spline pair are coaxial, the theoretical backlash (single tooth backlash) of the spline pair is different due to the influence of cumulative error of the tooth pitch (indexing error); the load on each key tooth is also different.

The distribution factor K3 considers this influence. For the spline pair before running-in, when the accuracy is high (the precision rectangular spline according to the GB/T 1144 standard or the accuracy level according to the GB/T 3478.1-2008 standard is level 5 or higher), K3 = 1.1 ~ 1.2. When the accuracy is low (the general use rectangular splines according to the GB/T 1144 standard or the accuracy level according to the GB/T 3478.1-2008 standard is lower than level 5), K3 = 1.3 ~ 1.6. For the spline pair after running-in, when each key tooth is involved in the work, and the load is basically the same, take K3 = 1.0.

5.4 Axial eccentric load factor K4

Due to the tooth orientation error produced during the manufacture of the spline pair and the concentricity error after installation, as well as the torsional deformation after being loaded, the load on each key tooth along the axial direction is uneven. The axial eccentric load factor K4 is used to consider this. Its value can be selected from Table 3.

For the spline pair after running-in, when the axial load distribution of each key tooth is basically the same, it takes K4 = 1.0.

When the accuracy of the spline is high and the indexing circle diameter D or the average circle diameter dm is small, the axial eccentric load factor K4 in Table 3 shall be the smaller value, and vice versa. […]