The cross-sectional structure of ordinary V-belts includes top rubber (tensile layer), tensile body (strength layer), primer (compression layer) and cloth layer (as shown in Figure 7-4). When the belt goes around the pulley, the top layer is stretched under tension, so it is called the stretched layer; the bottom layer is short when compressed, so it is called the compression layer. The covering layer is made of rubber canvas to protect the V-belt; the tensile layer and the compression layer are both made of rubber; the strength layer is divided into a cord core structure (Figure 7-4(a)) and a rope core structure (Figure 7-4(a)) 7-4(b)) Two kinds. Among them, the V-belt with the cord core structure is convenient to manufacture and has good tensile strength; while the V-belt with the cord core structure has good flexibility and high bending strength, and is suitable for occasions with small pulley diameters and high speeds. Narrow V-belt (Figure 7-4(c)) is a new type of V-belt that uses synthetic fibers such as polyester as a strong layer. Compared with the ordinary V-belt, when the height h is the same, the top width b of the narrow V-belt can be reduced by about 1/3. Its top is arched, and the side surface (working surface) is concavely curved, and its load-bearing capacity is significantly higher than Ordinary V-belt is suitable for occasions that transmit high power and require compact structure.