Basic introduction
The role of mechanical transmission: the role of mechanical transmission is to transmit movement and force. Common types of mechanical transmission systems include gear transmission, worm gear transmission, belt transmission, and chain transmission , Gear train, etc.
Belt drive
According to the different cross-sectional shape of the belt, the belt is divided into flat belts, V-belts and special belts (V-ribbed belts, round belts, etc.). Belt drive structure It is simple, stable in transmission, capable of buffering and absorbing vibration, can transmit power between large shaft spacing and multiple shafts, and is low in cost, does not require lubrication, and is easy to maintain. However, the precise transmission ratio cannot be guaranteed, and the transmission efficiency is low. Belt drive is mainly used for medium and small power transmission occasions with smooth transmission and less stringent transmission ratio requirements.
Chain drive
Chain drive is a meshing drive that uses a chain as a flexible pulling element between two or more sprockets. Compared with belt drive, the main advantages of chain drive are: no sliding; higher efficiency, η≈98%; no great tensioning force is required, and the load acting on the shaft is smaller; Use in large environments, etc. The main disadvantages are: it can only be used for the transmission between parallel shafts; the instantaneous speed is uneven, and it is not as smooth as the belt transmission at high speed; it is not suitable for the application in the transmission with large load changes and rapid reverse; there is noise during work. Compared with gear transmission, chain drive has its main features: lower manufacturing and installation accuracy requirements; when the center distance is large, its transmission structure is simple; the instantaneous chain speed and instantaneous transmission ratio are not constant, and the transmission stability is poor. In addition to being widely used as a transmission with a fixed transmission ratio, the chain drive can also be made into a stepped chain transmission and a continuously variable chain transmission.
Worm drive
Worm drive is used to transmit the rotary motion between the interleaved shafts. In most cases, the two axes are perpendicular to each other in space. The main advantages of the worm drive are compact structure, stable operation, no noise, low impact and vibration and a large single-stage transmission ratio. The disadvantage is that under the same manufacturing accuracy and transmission ratio, the efficiency of worm transmission is lower than that of gear transmission. In addition, worm gears generally need to be made of expensive anti-friction materials (such as bronze). Worm drive is widely used in machinery and related industries, such as driving axle transmission of automobiles; transmission of intersecting central axes of machine tools, automobiles, tractors and other machinery; used in rolling machinery, mining machinery, lifting and transporting machinery, etc.
Gear drive
Gear drive has a wide range of applications, transmission power can reach tens of thousands of kilowatts, single-stage transmission ratio can reach 8 or more, so it is widely used in machines . Compared with other mechanical transmissions, the advantages of gear transmission are: reliable work and long service life; instantaneous transmission ratio is constant; transmission efficiency is high; compact structure; power and application range are very wide. The disadvantages are: gear manufacturing requires special machine tools and equipment, and the cost is relatively high; when the accuracy is low, the vibration and noise are large; it is not suitable for transmission with large distance between shafts. There are many types of gear transmission. According to the relative motion of the two gears, the relative motion is plane motion or space motion, which can be divided into plane gear transmission and space gear transmission.
Gear train
The transmission system consisting of a series of gears is collectively called the gear train, which is widely used in various mechanical equipment. The gear train is divided into two types: fixed-axis gear train and epicyclic gear train. The main features of the gear train: It is suitable for transmission between two shafts far apart; it can be used as a transmission to realize variable speed transmission; it can obtain a larger transmission ratio; it can realize the synthesis and decomposition of motion.
Introduction to typical applications of mechanical transmission system
Reducer
The reducer is a gear drive, worm drive or gear-worm enclosed in a rigid housing The independent components composed of the transmission are often used as the transmission device for deceleration between the power machine and the working machine; in a few occasions, it is also used as the transmission device for increasing the speed, at this time it is called a speed increaser. The reducer is widely used in modern machines because of its compact structure, high efficiency, accurate transmission movement, reliable use and simple maintenance, and mass production. There are many types of reducers, mainly gear reducers, worm reducers, gear-worm reducers and planetary gear reducers.
Differential
An automobile differential is a mechanism that enables the left and right (or front and rear) drive wheels to rotate at different speeds. It is mainly composed of left and right half shaft gears, two planetary gears and a gear carrier. The function is to make the left and right wheels roll at different speeds when the car is turning or driving on uneven roads, that is, to ensure the pure rolling motion of the driving wheels on both sides. The differential is installed to adjust the difference in the rotational speed of the left and right wheels. In four-wheel drive, in order to drive the four wheels, all the wheels must be connected. If the four wheels are mechanically connected, the car cannot rotate at the same speed when driving in a curve, in order to allow the car to travel in a curve. The rotation speed is basically the same. At this time, a middle differential needs to be added to adjust the speed difference between the front and rear wheels.
Characteristics of mechanical transmission system
(1) Main characteristics of meshing transmission
Advantages: reliable operation, long life, accurate transmission ratio, high transmission power, High efficiency (except worm drive) and wide speed range.
Disadvantages: higher precision requirements for manufacturing and installation.
(2) The main features of friction transmission
Advantages: stable operation, low noise, simple structure, low cost, and overload protection.
Disadvantages: large outline size, inaccurate transmission ratio, low transmission efficiency, and short component life.
Classification introduction
1. The classification of gear transmission:
(1) According to the relative motion during transmission, it is divided into plane motion or space motion: ①Plane gear transmission (Common spur gear transmission, helical cylindrical gear transmission, herringbone gear transmission, according to the tooth direction, it is also divided into external meshing, internal meshing and gear and rack meshing) ②Space gear transmission (bevel gear transmission, Cross-shaft gear drive).
(2) According to the working conditions of gear transmission: closed transmission (enclosed in a rigid box), open transmission (gears are exposed).
2. Classification of worm gear drives:
(1) According to the worm spiral surface, it is divided into Archimedes spiral worm, involute spiral worm, and extended involute. Helical worm;
(2) According to the number of the worm spiral, it is divided into single-head, double-head and multi-head worm;
(3) According to the rotation direction of the spiral, it is divided into There are two kinds of left-handed and right-handed.
3. Classification of chain drives:
(1) Active chain
(2) Follower chain
(3) Ring The chain transfers movement and force by the meshing between the chain and the teeth of the sprocket. According to the structure, it is divided into roller chain and toothed chain. Toothed chain is used for high-speed or high-precision transmission. The transmission ratio of the chain drive is not more than 8, the center distance is not more than 5-6M, the transmission power is not more than 100KW, and the circumferential speed is not more than 15M/s.
4. Classification of the gear train (consisting of a series of gears):
(1) The gear train is divided into fixed-axis gear trains (the geometric axis of each gear is fixed) And epicyclic gear train (the geometric axis of at least one gear rotates around the geometric axis of another gear) two types.
(2) The ratio of the angular velocity (or rotational speed) of the input shaft to the output shaft in the gear train is called the gear train transmission ratio. The transmission ratio of the fixed-axis gear train is equal to the ratio of the product of the number of teeth of all driven gears in each pair of meshing gears and the product of the number of teeth of all driving gears.
(3) In the epicyclic gear system, the gears whose axis position changes, that is, the gears that both rotate and revolve, are called planetary gears, and the gears with fixed axis positions are called sun gears or suns. Round.
(4) The transmission ratio of the epicyclic gear train cannot be directly calculated by the method of solving the fixed-axis gear train transmission ratio. The principle of relative motion must be used, and the relative speed method (or reversal method) must be used. Convert the epicyclic gear train into an imaginary fixed-axis gear train for calculation.