How the overrunning clutch works

1. Development and application of wedge overrunning clutch

The overrunning clutch is one of the basic parts of mechanical transmission. It is a kind of clutch with self-clutching function using the speed change or rotation direction of the main and driven parts and is widely used. The roller type overrunning clutch has a long history. According to literature reports, it was included in the German DRP2804.47h5 patent in 1878 under the title of "reversing motor" and used in the reversing mechanism. In the following hundred years, the roller overrunning clutch has been continuously developed and improved, the structure type has increased, and the application has become more common.

The sprag overrunning clutch is a new type of clutch developed after the roller overrunning clutch. Since its inception, it has been widely used in mechanical transmission due to its large carrying capacity, reliable self-locking, light reverse release, compact structure and convenient operation. First of all, the United States has been developed and popularized in automobiles and airplanes. For example, the United States uses it on Boeing 707 aircraft and F4-C bombers and M102-105 light howitzers. It has also been widely used in Japan and Germany.

In recent years, with the development of new products and the need for localization of imported products, the wedge block overrunning clutch has developed rapidly, and its structure, performance and reliability have become more and more perfect, and the types and specifications of the clutch have become more complete, and product quality has gradually improved . The wedge overrunning clutch produced by Luoyang Best Precision Machinery Manufacturing Co., Ltd. can not only meet the needs of domestic scientific research and production, but also replace the overrunning clutch imported from Japan, the United States, Italy and other countries on corrugated paper production lines and oxygen-free copper production lines. good.

The wedge overrunning clutch is often matched with a ball screw pair or other components. It can also be used alone as a mechanism to prevent reverse rotation. It can be used as a precise positioning between the driving shaft and the driven shaft to transmit or cut off torque. It has the function of self-clutching of a clutch. Therefore, it is called a backstop or a one-way bearing. It is widely used in packaging machinery, printing machinery, food machinery, light industrial machinery, agricultural machinery, metallurgy and mining, petrochemical, machine tools, automobiles, weapons, aviation, power stations and other mechanical equipment.

 2. Characteristics of wedge block overrunning clutch

The wedge overrunning clutch is to place the wedge element (wedge) between the inner ring and the outer ring (raceway), so that when it rotates, one can transmit torque, while the other has relative idling performance. Only when the inner and outer rings have the same steering and the same rotational speed, the torque can be transmitted, otherwise it is a relative slip. This slip state that does not transmit torque is called overtaking.

1) The shape of the raceway The raceway of the wedge overrunning clutch has two forms: the inner and outer ring raceways are round and the inner ring is machined with a number of concave grooves.

(1) The inner ring is a full circle. The inner and outer rings of the clutch are all smooth cylindrical surfaces. In order to ensure no slippage during operation, the wedge angle of the wedge should not exceed the minimum friction angle between the wedge and the inner and outer rings. In design, it is generally 3°-4°. In practice, when the wedge angle begins, the wedge angle is about 2°-2.5°. When the inner and outer rings are elastically deformed by force, the wedge angle increases accordingly.

(2) The inner ring has a concave groove shape. The wedge has the same radius as the circular arc groove of the inner ring, so that the two are in surface contact, which improves the stress state and increases the bearing capacity and service life of the wedge. But the number of wedges is reduced by the structure.

2) The shape of the wedge block The shape of the wedge block used in the wedge block overrunning clutch is mostly special shape, such as fist shape, shoe shape, etc. When designing the clutch, different shapes of wedge blocks can be selected according to the function requirements.

3) Wedge block and roller type overrunning clutch have their own characteristics due to the different wedge elements placed between the inner and outer rings.

 3. Selection and calculation of wedge overrunning clutch

In order to ensure the reliable operation of the clutch, usually when designing and selecting the clutch, the comprehensive function of the clutch in the transmission system is clarified, and the variety and type of the clutch are selected from the overall design of the transmission system. The selection of specifications is mainly based on the calculated torque.

1) The relationship between the torques of the clutch The main parameter of the clutch is the nominal torque. When selecting a clutch, the torques should meet the following relationship: T

2) Calculated torque of the clutch The calculated torque of the clutch is calculated according to the power, working speed, reserve coefficient and related factors of the transmission system. Tc=βT where Tc—calculated torque, N·m; β—reserve coefficient (generally 1.2-3.2); T—theoretical torque, N·m. The value of the reserve coefficient β is related to factors such as the performance of the prime mover and the working machine, and the structural type of the clutch. Generally, the working conditions are good, the load is light, and the β value is small; the working conditions are bad, the load is large, and the β value is large.

 4. Structural form of wedge block overrunning clutch and its scope of application

According to GB10043-1988 "Clutch Classification" standard, wedge block overrunning clutch can be divided into contact type, non-contact type and two-way type. The first two types are actually one-way type. Table 2 lists the structure and application scope of various types of sprag overrunning clutches.