When selecting the motor bearing support fixed end (hereinafter referred to as the motor fixed end), the following factors should be considered: (1) the precision control requirements of the driven equipment; (2) the nature of the load driven by the motor; (3) the bearing or bearing assembly must be able to withstand a certain axial force. Considering the above three design factors, deep groove ball bearings are more often the first choice for motor fixed end bearings in small and medium-sized motors.

Deep groove ball bearings are the most commonly used rolling bearings. When using deep groove ball bearings, the motor bearing support system structure is very simple, and maintenance is convenient. Deep groove ball bearings are mainly used to bear radial loads, but when the radial clearance is increased, they possess the characteristics of angular contact ball bearings and can bear combined radial and axial loads. They can also be used to bear pure axial loads when the speed is high and thrust ball bearings are not suitable. Compared with other types of bearings of the same dimensions, deep groove ball bearings have the advantages of low friction coefficient and high limiting speed, but the disadvantages of being less impact-resistant and unsuitable for heavy loads.

After a deep groove ball bearing is mounted on a shaft, the radial fit in both directions of the shaft or housing is restricted within the bearing's axial clearance range. Radially, the bearing and shaft use an interference fit, while the bearing and end cover bearing housing or housing use a small interference fit. The ultimate goal of this fit is to ensure that the bearing's operating clearance is zero or slightly negative during motor operation, resulting in better bearing performance. Axially, the axial fit between the locating bearing and related components should be determined based on the specific conditions of the floating end bearing system. The bearing inner ring is limited by the bearing seat limiting step (shaft shoulder) and bearing retaining ring on the shaft, while the bearing outer ring is controlled by the fit tolerance between the bearing and the bearing housing, the height of the inner and outer bearing cover stops, and the length of the bearing housing.

(1) When the floating end selects a bearing with separable inner and outer rings, the outer rings of the bearings at both ends are axially clearance-free.

(2) When a non-separable bearing is selected for the floating end, a certain length of axial clearance is left between the outer ring of the bearing and the bearing cover stop, and the fit between the outer ring and the bearing housing should not be too tight.

(3) When the motor does not have a clearly defined positioning end and floating end, deep groove ball bearings are generally used at both ends, and the fit relationship is that the outer ring of the limit bearing is locked with the inner cover and there is a gap between it and the outer cover in the axial direction; or the fit relationship is that the outer ring of the bearing at both ends has no gap between it and the outer cover in the axial direction, and there is a gap between it and the inner cover in the axial direction.

The above-mentioned fit relationships are all theoretically reasonable. The actual bearing configuration should match the operating conditions of the motor, including specific parameters such as clearance, heat resistance, and precision in the selection of motor bearings, as well as the radial fit relationship between the bearing and the bearing housing.

It should be noted that the above analysis only applies to horizontally mounted motors. For vertically mounted motors, there are specific requirements for both bearing selection and related mating relationships.