Belt transmission is a kind of mechanical transmission that uses the flexible belt tensioned on the pulley to carry out movement or power transmission.According to the different transmission principles, there are friction belt transmission driven by the friction between the belt and the pulley, and synchronous belt transmission driven by the meshing between the belt and the teeth on the pulley.
Chinese name
Belt drive
Foreign name
belt drive
Features
Transmission movement composed of flexible belt and pulley
Classification
Friction transmission and meshing transmission
Disadvantages
Inaccurate transmission ratio, low service life, low efficiency, etc
Discipline
Mechanical engineering, transmission, belt transmission
Belt transmission has the characteristics of simple structure, smooth transmission, shock absorption, power transmission between large axle spacing and multiple axles, low cost, no lubrication, easy maintenance, etc. It is widely used in modern mechanical transmission.The friction type belt transmission energy is overloaded and skids, and the running noise is low, but the transmission ratio is inaccurate (the sliding rate is below 2%);Synchronous belt transmission can ensure transmission synchronization, but the absorption capacity of load variation is slightly poor, and there is noise during high-speed operation.In addition to power transmission, belt transmission is sometimes used to transport materials and complete the train of parts.
Structure composition
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Belt transmission is usually composed of driving wheel, driven wheel and annular belt tensioned on two wheels.
Stress composition
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The stress of belt transmission during operation includes:
1. Stress caused by tension of tight and loose edges;
2. Stress caused by centrifugal force;
3. Bending stress caused by belt bending on pulley.
classification
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According to different uses, belt transmission can be divided into general industrial belt, automobile belt, agricultural machinery belt and household appliance belt.Friction type transmission belt is divided into flat belt, V-belt and special belt (multi wedge belt, round belt) according to its different section shape.
The type of transmission belt is generally selected according to the type, purpose, use environment and characteristics of various belts of the working machine.If there are multiple transmission belts to meet the transmission needs, the optimal scheme can be comprehensively selected according to the factors such as the compactness of the transmission structure, production costs, operating costs, and market supply.
Flat belt drive
When the flat belt drive works, the belt is sleeved on the smooth wheel surface and driven by the friction between the belt and the wheel surface.The transmission types include open transmission, cross transmission and half cross transmission, which respectively meet the needs of different relative positions and different rotation directions of the driving shaft and driven shaft.Flat belt transmission is simple in structure, but easy to slip. It is usually used for transmission with a transmission ratio of about 3.
Flat belt drive
Flat belt, braided belt, strong nylon belt and high-speed annular belt.Tape is the most commonly used type of flat belt.It has high strength and wide power transmission range.The braided tape is flexible, but easy to relax.The strong nylon belt has high strength and is not easy to relax.The cross section size of the flat belt has standard specifications. Any length can be selected and connected into a ring by gluing, sewing or metal joints.The high-speed annular belt is thin and soft, flexible, and wear-resistant. It can be made into endless rings, and the transmission is stable. It is specially used for high-speed transmission.
V-belt drive
V-belt drive
When V-belt transmission works, the belt is placed in the corresponding groove on the pulley, and the transmission is realized by friction between the belt and the two walls of the groove.V-belts are usually used in combination, and the pulley has a corresponding number of grooves.When driving with V-belt, the belt and wheel contact is good, the slip is small, the transmission ratio is relatively stable, and the operation is stable.V-belt transmission is suitable for the occasions with short center distance and large transmission ratio (about 7), and can also work well in vertical and inclined transmission.In addition, because several V-belts are used together, one of them will not be damaged, and no accident will occur.
V-belt is one of the most widely used V-belts. It is an endless annular tape made of strong layer, stretch layer, compression layer and wrapping layer.The strength layer is mainly used to bear the tension. The tension layer and compression layer play the role of tension and compression when bending, and the role of the blanket layer is mainly to enhance the strength of the belt.The cross section size and length of the V-belt have standard specifications.In addition, there is also a flexible V-belt, whose section size standard is the same as that of V-belt, but the length specification is not limited, which is easy to install and tighten, and can be replaced locally if it is damaged locally, but its strength and stability are not as good as those of V-belt.V-belts are often used side by side. In design, the belt type, number and pulley structure size can be determined according to the transmitted power and the rotating speed of the small wheel.
1) Standard V-belt
It is used for household facilities, agricultural machinery and heavy machinery.The ratio of top width to height is 1.6:1.The belt structure with cord and fiber bundle as the pulling element is much smaller than the power transmitted by the equal width narrow V-belt.Due to their high tensile strength and lateral stiffness, these belts are suitable for severe working conditions with sudden load changes.The belt speed is allowed to reach 30m/s, and the bending frequency can reach 40Hz.
2) Narrow V-belt
Used for automobile and machine structures in the 1960s and 1970s.The ratio of top width to height is 1.2:1.The narrow V-belt is an improved version of the standard V-belt, which eliminates the central part that has little effect on power transmission.It transmits higher power than the standard V-belt of the same width.A toothed belt variant that rarely slips when used on small pulleys.The belt speed is allowed to reach 42 m/s, and the bending frequency can reach 100Hz.
3) Thick edged V-belt
According to Part 3 of DIN7753, the fiber under the surface layer is perpendicular to the movement direction of the belt, which makes the belt highly flexible and has excellent lateral stiffness and high wear resistance.These fibers can also provide good support for specially treated tension elements.Especially when used on small diameter pulleys, this structure can improve the belt transmission capacity and have a longer service life than the wrapped narrow V-belt.
4) Further development
The latest development of V-belt is the fiber tension element made of Kevlar.Kevlar has high tensile strength, low elongation and can withstand high temperature.
Multi wedge belt (multi groove belt)
Very flexible, and the back of the belt can also be used to transmit power.If the containment angle around each driven pulley is large enough, one such belt can drive several accessories of the vehicle (alternator, fan, water pump, air conditioning compressor, power steering pump, etc.) at the same time.It has five types of sections for selection, including PH, PJ, PK, PL and PM, among which the PK type section has been widely used in automobiles in recent years.This type of belt allows a narrower pulley (diameter d) than a narrow V-beltmin≈45mm)。In order to transmit the same power, the preload of this belt is better to increase about 20% than that of narrow V-belt.
Synchronous belt
Synchronous belt
This is a special belt drive.The working surface of the belt is made into a tooth shape, and the rim surface of the pulley is also made into a corresponding tooth shape. The belt and pulley are mainly driven by meshing.The synchronous toothed belt generally uses thin steel wire rope as the strength layer, and is covered with polychloroprene or neoprene.The center line of the strength layer is the pitch line of the belt, and the perimeter of the belt line is the nominal length.The basic parameters of the band are circumferential pitch p and modulus m.The circumferential pitch p is equal to the dimension measured along the pitch line between the corresponding points of two adjacent teeth, and the modulus m=p/π.The synchronous toothed belt in China adopts the module system, and its specification is expressed by module × bandwidth × number of teeth.
Compared with ordinary belt drive, the characteristics of synchronous toothed belt drive are:
The strength layer made of steel wire rope has little deformation after being loaded, the circumferential pitch of the toothed belt is basically unchanged, there is no relative sliding between the belt and the pulley, and the transmission ratio is constant and accurate;
The toothed belt is thin and light, which can be used in high speed situations. When driving, the linear speed can reach 40 m/s, the transmission ratio can reach 10, and the transmission efficiency can reach 98%;
Compact structure, good wear resistance;
Due to the small pre tension, the bearing capacity is also small;The manufacturing and installation precision is required to be very high, and strict center distance is required, so the cost is high.Synchronous toothed belt drive is mainly used for occasions requiring accurate transmission ratio, such as external equipment in computers, movie projectors, video recorders and textile machinery.
efficiency
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The power loss of belt transmission includes:
(1) When the sliding loss friction type belt drive works, it is caused by the tension difference on both sides of the pulley and the corresponding deformation differenceElastic sliding, resulting in speed loss of belt and driven wheel.The elastic slip rate is usually between 1% and 2%.Serious sliding, especially overload sliding, will make the movement of the belt in an unstable state, sharply reduce the efficiency, increase wear, and seriously affect the life of the belt.The sliding loss increases with the increase of tension difference between tight and loose edges, and decreases with the increase of elastic modulus of belt body.
(2) The repeated expansion and contraction of the internal friction loss belt in operation and the deflection on the pulley will cause friction inside the belt body and cause power loss.Internal friction lossPreloadThe ratio of belt thickness to pulley diameter increases.Reducing the tension change of the belt can reduce its internal friction loss.
(3) The adhesion between the belt and the working surface of the pulley, as well as the side friction loss of V-belt wedging and exiting the pulley groove.(4) Air resistance loss The power loss caused by operating wind resistance at high speed.The loss is proportional to the square of the speed.Therefore, when designing high-speed belt drives, the surface area of the belt should be reduced, and thick and narrow belts should be used as far as possible;The spoke surface of the belt wheel shall be smooth (such as elliptical spoke) or the spoke plate shall be used to reduce wind resistance.
(5) Bearing friction loss The effect of bearing bearing tension is one of the important factors that cause power loss.To sum up the above losses, the efficiency of belt transmission is about 80%~98%. When designing the transmission, select according to the type of belt.
characteristic
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(1) Advantages: stable transmission, shock absorption, simple structure, low cost, convenient use and maintenance, good flexibility and elasticity, overload and slip.
(2) Disadvantages: inaccurate transmission ratio, low belt life, large axle load, large external size of transmission device, and low efficiency.
Therefore, belt drive is usually suitable for large center distance, medium and small power, and belt speed v=5~25m/s,
I ≤ 7.
Use and maintenance
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matters needing attention
(1) Installation: reduce the center distance, loosen the tensioner, and adjust it after installation.
Belt drive
(2) Pay attention to the model and reference length of V-belt.(3) The centerlines of the two pulleys are parallel, and the pulley section is perpendicular to the centerline
The grooved wheel of the moving wheel is in the same plane, and the deformation of the shaft and the shaft end is small.
(4) Regular inspection.Different belt types, different manufacturers, different degrees of novelty
V-belt of shall not be used in the same group.
(5) Keep clean and avoid aging caused by acid, alkali or oil contamination.[1]
