When using NSK angular contact ball bearings and requiring a large axial load, as shown in the figure, a combination of 3 sets of single-row bearings is used. There are 3 combination methods, which are represented by the assembly codes DBD, DFD and DTD respectively. . When calculating the fatigue life of this kind of precision combined bearing, the equivalent dynamic load obtained from the radial load and axial load borne by the bearing is also used for calculation, just like the single-row bearing or double-row bearing. Assuming that the equivalent dynamic load is Pr, the radial load is Fr, and the axial load is Fa, the relationship between the radial equivalent dynamic load and the bearing load will be approximated by the following formula. Pr u003d XFr＋YFa(1) In the formula, : X Radial load factor: Y Axial load factor is shown in Table 1. The axial load factor varies with the contact angle. Angular contact ball bearings with smaller contact angles will increase the contact angle when the axial load increases. This change in the contact angle can be expressed as the ratio of the basic static load rating Cor to the axial load Fa. Therefore, an angular contact ball bearing with a contact angle of 15 represents the axial load factor of the contact angle corresponding to this ratio. Angular contact ball bearings with contact angles of 25, 30, and 40 have a negligible effect on the axial load coefficient due to the change of the contact angle, so the axial load coefficient is regarded as a constant value. Among the three rows, 2 sets of bearings bear axial load type code or DFD In three rows, 1 set of bearings bear axial load type code DBD or DFD.