**2. Basic nature of the rolling bearing**

#### **2.1 Structure and failure forms**

#### *2.1.1 Basic structure and parameters*

The most basic structure of the rolling bearing is the outer ring in the outside, and the inner ring inside, and in the middle through the rolling body like the ball or the column, so as to transform the sliding friction into the rolling friction. In general, the outer ring is fixed, and the inner ring is connected with the matched axis, and the holder is also a common structure of the rolling bearing, which can avoid the friction seen by the rolling body.

The quality of the rolling body is quite critical, and a good rolling body can well reduce the friction coefficient, reduce the friction, loss, and the bearing rotation will become smooth and efficient. The smoother the inner circle is, the less the friction is in contact with the axis, and the smoother the rotation will be. The outer ring plays a supporting role, hardness must be high, otherwise easy to wear, cause bearing off. The role of the holder is to fix the rolling body; the size must fit with the rolling body, too large and too small will cause adverse effects.

As shown in **Figure 1**, we can clearly see the structure of the rolling bearing through the 3-dimensional diagram, and the main parameters are marked in the plane structure diagram, including: inner circle radius *r*<sup>1</sup> , outer circle radius *r*<sup>2</sup> , rolling body diameter d, bearing joint diameter D, rolling body number Z, bearing contact angle θ.

**Figure 1.** *Drawing and plane structure of the rolling bearing.*
