The rotor part of the motor product usually needs to be supported by two sets of bearings, and the rotor is radially and axially positioned relative to the stator. According to different use requirements, such as: load, required rotation accuracy, and manufacturing cost requirements, the bearing configuration of the motor generally adopts: one end fixed and one end floating configuration; two ends fixed pre-adjustment configuration; two ends floating "floating" configuration, etc.

01 One end fixed, one end floating configuration

The fixed end bearing is fixed by the shaft and the end cover bearing chamber at the same time, and radially supports one end of the shaft, and plays an axial positioning role in both axial directions. The bearing at the fixed end must be a radial bearing that can withstand combined radial and axial loads. The most commonly used in motor products are deep groove ball bearings. In some other equipment and machinery, double-row or paired single-row angular contact ball bearings and other bearings that can withstand combined loads are also used. For motors with three bearing structures, positioning is performed by a bearing combination, that is, a radial bearing that can only withstand pure radial loads (cylindrical roller bearings with rings without flanges) is combined with a deep groove ball bearing that can withstand combined loads. In this configuration, the other bearing, a deep groove ball bearing, is only used for axial positioning in two directions, and a certain radial degree of freedom must be left in the bearing chamber, that is, a clearance fit with the diameter direction of the bearing chamber.

The floating end bearing of the motor is at the other end of the shaft, and only provides radial support. Therefore, the floating end bearing can be a deep groove ball bearing or a cylindrical bearing. For motors with large loads and impact loads, cylindrical roller bearings are used in most cases. In this configuration, a certain axial displacement of the shaft must be allowed so that there is no mutual force between the bearings. During the operation of the motor, when the shaft expands due to heat, axial displacement can be achieved inside certain types of bearings (cylindrical roller bearings). Axial displacement can also occur between one of the bearing rings and the component connected to it, preferably between the outer ring of the bearing and the bearing chamber. In view of this, the choice of N-type or NU-type bearings requires comparative analysis and demonstration by the designer. There are many different combinations of bearing configurations for the fixed and floating ends. The following are some of the more commonly used combinations. For rigid bearing configurations, combinations that can achieve axial displacement in the bearing should be used, such as deep groove ball bearings and cylindrical roller bearings; double row angular contact ball bearings and cylindrical roller bearings; paired single row tapered roller bearings and cylindrical roller bearings, etc. There are certainly other combinations. For this design, it is recommended to conduct joint analysis and selection with the bearing manufacturer.

In the above combinations, the angular error between the shaft and the bearing seat must be minimized. If the application does not allow, it is recommended to use a combination of self-aligning bearings that can withstand larger angular errors. These configurations can withstand certain angular errors and axial displacements, and can avoid generating internal axial forces in the shaft system. For bearing configurations where the inner ring bears rotating loads, the length change of the shaft needs to be adjusted between the bearing and its mating surface, and the axial displacement should be between the outer ring and the bearing chamber. The most commonly used combinations are deep groove ball bearings and deep groove ball bearings; paired single row angular contact ball bearings and deep groove ball bearings.

02 Floating bearing configuration

Floating bearing configurations are also a cross-positioning method, which is suitable for applications where only moderate axial positioning is required or there are other components on the shaft for axial positioning. In this configuration, it is important that each bearing can be displaced axially. This can be between one of the bearing rings and its mating surface, but preferably between the outer ring of the bearing and the bearing chamber.

03 Pre-adjusted bearing arrangement

In a pre-adjusted bearing arrangement, the shaft is axially located in one direction by one bearing and fixed in the other direction by another bearing. This arrangement is called "cross" positioning and is usually used for shafting with shorter lengths. All radial bearings that can withstand axial loads (in one or two directions) are suitable for this arrangement. In some cases, single-row angular contact ball bearings or tapered roller bearings are used in a cross-positioned configuration, but some preload may be required.

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