Belt drives are a type of mechanical transmission that uses a flexible belt tensioned on pulleys to transmit motion or power. Depending on the transmission principle, there are friction belt drives, which rely on the friction between the belt and pulleys, and synchronous belt drives, which rely on the meshing of teeth on the belt and pulleys.
▲ Friction type belt drive
▲Meshing type belt drive
1. Classification of belt drives
Depending on their application, transmission belts can be categorized into general industrial transmission belts, automotive transmission belts, agricultural machinery transmission belts, and household appliance transmission belts. Friction type transmission belts are further classified according to their cross-sectional shape into flat belts, V-belts, and special belts (multi-ribbed belts, round belts), etc.
Flat belt drive
There are open belt drives, cross belt drives, and semi-cross belt drives, which are adapted to different relative positions and rotation directions of the driving and driven shafts, respectively. Flat belt drives have a simple structure but are prone to slippage and are usually used for transmissions with a transmission ratio of around 3.
V-belt drive
When a V-belt drive is in operation, the belt is placed in the corresponding groove on the pulley, and transmission is achieved through friction between the belt and the two walls of the groove. V-belts are usually used in combination, with a corresponding number of grooves on the pulley. With V-belt drives, the belt and pulley have good contact, minimal slippage, a relatively stable transmission ratio, and smooth operation. V-belt drives are suitable for applications with short center distances and large transmission ratios (around 7), and also work well in vertical and inclined transmissions. Furthermore, because multiple V-belts are used in combination, the failure of one will not cause an accident.
Multi-ribbed belt drives offer excellent flexibility, and the back of the belt can also be used to transmit power. If the containment angle around each driven pulley is large enough, a single belt can drive several vehicle accessories (alternator, fan, water pump, air conditioning compressor, power steering pump, etc.). It is available in five cross-sections: PH, PJ, PK, PL, and PM, with the PK type becoming increasingly common in automobiles in recent years. This type of belt allows the use of pulleys narrower than narrow V-belts (diameter dmin ≈ 45mm). To transmit the same power, the preload of this belt should ideally be about 20% greater than that of a narrow V-belt.
Applications of friction-type transmission belts:
Belt drives are suitable for applications where the power transmission is not high or where a precise transmission ratio is not required. In multi-stage reduction gears, belt drives are typically located in the high-speed stage. Ordinary V-belts generally transmit power not exceeding 50–100 kW, with operating speeds ranging from 5–35 m/s.
In general machinery, V-belt drives are the most widely used. A V-belt has an isosceles trapezoidal cross-section, and the pulleys also have corresponding grooves. During transmission, the V-belt only contacts two sides of the grooves; that is, the two sides of the V-belt are the working surfaces, while the bottom surface of the belt does not contact the pulleys. According to the principle of groove friction, under the same tension, V-belt drives can generate greater frictional force than flat belt drives. Therefore, V-belt drives have stronger capacity and a more compact structure, making them far more widely used than flat belt drives.
2. V-belt and V-belt pulley
V-belts are a general term for annular transmission belts with a trapezoidal cross-section, and are divided into two main categories: special core V-belts and ordinary V-belts. Compared with flat transmission belts, they have advantages such as easy installation, small footprint, high transmission efficiency, and low noise, and occupy an important position in the entire transmission field. They are mainly used for power transmission in mechanical equipment driven by electric motors and internal combustion engines.
▲Standard V-belt
V-belt pulley
V-belt pulleys consist of a rim, spokes, and a hub. Based on the spoke structure, they are classified into three types: solid pulleys, spoked pulleys, and spoked pulleys. Common materials for V-belt pulleys include gray cast iron, steel, aluminum alloy, or engineering plastics, with gray cast iron being the most widely used.
▲Solid pulley
▲Spoke-type pulley
3. Meshing type synchronous belt drive
Meshing belt drives, also known as synchronous belt drives, transmit motion through the meshing of equidistant transverse teeth on the inner surface of the belt and corresponding grooves on the pulleys. Compared to friction belt drives, synchronous belt drives eliminate relative slippage between the pulleys and the belt, ensuring a precise transmission ratio. However, synchronous belt drives require high precision in center distance and dimensional stability.
Synchronous belt drives transmit motion and power through meshing between the belt and pulleys, eliminating relative slippage and ensuring an accurate transmission ratio. Synchronous belts typically use steel wire rope or fiberglass rope as the tensile strength and neoprene or polyurethane as the matrix. These belts are thin and lightweight, making them suitable for high speeds. Linear speeds during transmission can reach 50 m/s, transmission ratios can reach 10, and efficiency can reach 98%.
Advantages and disadvantages of synchronous belt drives:
Synchronous belts have lower transmission noise than belt drives, chain drives, and gear drives, better wear resistance, require no oil lubrication, and have a longer lifespan than friction belts. Their main disadvantages are the higher precision requirements for manufacturing and installation, and the stricter requirements for center distance. Therefore, synchronous belts are widely used in medium and low power transmissions requiring accurate transmission ratios.
For more information, please visit the Mechanical Transmission channel.
