Modern industry, engineering and other industries use a variety of mechanisms in their work. They provide the operation of units, vehicles, motors, etc. One of the popular, often used devices is V-belt transmission .
The presented mechanism includes several categories of designs. They differ in geometric parameters, purpose, approach to the implementation of tasks assigned to the mechanism. What are the presented devices will be discussed further.
general characteristics
A V-belt transmission device involves the use of a special method of actuating the entire mechanism. In this case, the energy produced in the process of torque is applied. This provides a belt drive. It uses mechanical energy, which subsequently transfers to another mechanism.
This design consists of a belt and a minimum of two pulleys. The first of these structural elements is most often made of rubber. The V-belt transmission belt is made of material that has undergone special processing. This allows the presented element to be resistant to medium and small mechanical stresses, elevated temperatures.
Among belt drives, V-belt is the most demanded. This design is often used today in the manufacture of automobiles, as well as other varieties of vehicles.
Design features
The design of the presented type of transmission of mechanical energy includes V-belt pulleys and a belt. The last of these elements has a wedge-shaped shape. Pulleys are made in the form of metal discs. They have branches evenly distributed around the circumference. They hold the belt in position on the surface of the pulleys.
The tape can be of two types. It can have teeth or has an absolutely smooth surface. The choice depends on the purpose of the mechanism. Previously, the design presented was used in many systems of various categories of vehicles.
Today, the presented type of mechanical energy transmission is used in water pumps and machine generators. In heavy automotive vehicles, a similar system is installed with the aim of driving the power steering. This system has a hydraulic pump. It is in it that a similar design is used. V-belt drives are also installed in air-type compressors. They are intended for vehicle brake system amplifiers.
Requirements for structural elements
V-belts are relatively thin. This allows you to significantly reduce the size occupied by the system. However, this fact requires a special approach to the organization of pulley geometry. To prevent the tape from jumping off, the outer surface of the disks has special grooves. They hold the belt in the grooves.
The size of the pulley itself is selected in accordance with the gear ratio. If it is necessary to create a reduction gear, the driven pulley will be larger than the leading structural member. There is an inverse relationship.
In the manufacture of belt belts, special soft materials are used, which should not lose their performance under any weather conditions. In frost and heat, the belt remains flexible. For this reason, it is not allowed to install other material instead of a special tape. This will damage the unit.
Varieties
V-belt transmission can be performed in several configurations. There are several popular types of mechanisms presented. One of the simplest is an open system. In this case, the pulleys rotate in one direction, the axes move in parallel.
If the disks move in opposite directions while maintaining the parallelism of the strips, a cross-section of the system appears. If the axes cross, it will be a semi-cross variety.
If the axes intersect, angular transmission occurs. She uses stepped pulleys. This design allows you to influence the speed at an angle of the driven shaft. The speed of the drive pulley remains constant.
The idle gear transmission allows the driven pulley to stop moving while the drive shaft continues to rotate. The transmission with a tension roller facilitates independent belt tensioning.
Belt
V-belts belong to the category of traction structural elements. It must ensure the return of the required energy without slipping. The tape should have increased strength, wear resistance. The blade should adhere well to the outer surface of the discs.
The width of the belts can vary significantly. In the manufacture of rubberized cotton, woolen materials, leather. The choice depends on the operating conditions of the equipment.
The tape may be made of cord fabric or cord. These are the most reliable, flexible and high-speed varieties.
Modern engineering today often uses timing belts. They are also called polyamide. On their surface 4 protrusions are provided. They engage with the corresponding elements on the pulleys. They have proven themselves in high-speed gears, mechanisms with a small distance between the pulleys.
Estimated Pulley Diameter
The calculation of the V-belt drive begins with the determination of the diameter of the pulley. To do this, take two cylindrical rollers. Their diameter is D. The value is set for each size of the groove section. In this case, the contact of the rollers passes at the diameter level.
Two rollers of the presented type must be placed in the groove. Surfaces must touch. Between the tangent planes that form the rollers, it is necessary to measure the distance. They should run parallel to the pulley.
A special formula is used to calculate the diameter of the disk. It looks like this:
D = RK - 2X, where RK is the distance that is measured between the rollers, mm; X is the distance from the diameter of the disk to the tangent suitable to the roller (runs parallel to the axis of the disk).
Transfer calculation
Calculation of V-belt transmission is carried out according to the established methodology. In this case, the indicator of the transmitted power of the mechanism is determined. It is calculated using the following formula:
M = Mnom. * K, where is Mnom. - rated power that the drive consumes during operation, kW; K is the dynamic load coefficient.
When carrying out calculations, an indicator is taken into account, the probability of distribution of which in the stationary mode is no more than 80%. The load factor and mode are presented in special tables. In this case, you can determine the speed for the belt. It will be:
= π * 1 * 1 / 6000 = π * 2 * 2 / 6000, where 1, 2 - diameter of the smaller and larger pulley (respectively); 1, 2 - rotational speed of a smaller and a larger disk. The diameter of the smaller pulley must not exceed the calculated maximum permissible belt speed. It is 30 m / s.
Calculation Example
In order to delve into the calculation methodology, it is necessary to consider the technology for conducting this process using a specific example. Suppose you want to determine the gear ratio of a V-belt transmission. It is known that the power of the drive disk is 4 kW, and its speed (angular) is 97 rad./s. In this case, the driven pulley has this indicator at the level of 47.5 rad./s. The diameter of the smaller pulley is 20 mm, and the larger is 25 mm.
To determine the gear ratio, it is necessary to take into account belts with a normal cross-sectional index made of cord fabric (size A). The calculation looks like this:
IF = 97 / 47.5 = 2.04
Having determined the diameter of the pulleys from the table, it was found that the smaller shaft has a recommended size of 125 mm. A larger shaft with a belt slip of 0.02 will be equal to:
D2 = 2.04 * 1.25 (1-0.02) = 250 mm
The result obtained fully complies with the requirements of GOST.
Belt Length Calculation Example
The length of the V-belt transmission belt can also be determined using the presented calculation. First you need to calculate the distance between the axes of the disks. For this, the formula is used:
P = C * D2
C = 1.2
From here you can find the distance between the shafts:
P = 1.2 * 250 = 300 mm
Next, you can determine the length of the belt:
D = (2 * 300 + (250-125) ² + 1.57 (250 + 125)) / 4 * 300 = 120.5 cm
The internal length of the belt with size A according to GOST is 118 cm. In this case, the estimated length of the tape should be 121.3 cm.
Calculation of system operation
Determining the size of the V-belt drive, it is necessary to calculate the main indicators of its operation. First you need to set the speed at which the tape will rotate. For this, a certain calculation is applied. The data for it were given above.
C = 97 * 0.125 / 2 = 6.06 m / s
In this case, the pulleys will rotate at different speeds. A smaller shaft will turn around with this indicator:
CBM = 30 * 97 / 3.14 = 916 min - ¹
Based on the presented calculations in the respective reference books, the maximum power that can be transmitted using the presented belt is determined. This figure is 1.5 kW.
To check the material for durability, you need to make a simple calculation:
E = 6.06 / 1.213 = 5.
The obtained indicator is acceptable by GOST, according to which the presented belt is manufactured. Its operation will be quite long.
Design flaws
V-belt drive is used in many mechanisms and assemblies. This design has many advantages. However, she has a whole list of shortcomings. They are large in size. Therefore, the presented system is not suitable for all units.
Moreover, the belt drive is marked by low bearing capacity. This affects the performance of the entire system. When using even the most modern materials, the life of the belt leaves much to be desired. It is erased, torn.
The gear ratio is variable. This is due to the slip of the flat belt. On the shafts when using the presented design is a high mechanical impact. Also, the load acts on their supports. This is due to the need to pretension the belt. In this case, additional elements are used in the design. They dampen line vibrations by holding a strip on the surface of the pulleys.
Positive sides
V-belt transmission has a lot of advantages, so today it is used in various units quite often. The similar design provides high smoothness of work. The system functions almost silently.
With inaccuracies in the installation of pulleys, this deviation is compensated. This is especially noticeable by the angle of intersection, which is determined between the disks. The load is compensated during belt slippage. This allows you to slightly extend the life of the system.
Belt-type transmission compensates for pulsations that occur during engine operation. Therefore, you can do without installing an elastic coupling. The simpler the design, the better.
Lubricate the presented mechanism is not required. Savings are manifested in the absence of the need to purchase supplies. Pulleys and belt can be easily replaced. The cost of the items presented remains acceptable. Mounting the system is easy.
When using this system, it turns out to create an adjustable gear ratio. The mechanism has the ability to work at high speeds. Even if the tape breaks, the remaining elements of the system remain intact. The shafts can be located at a considerable distance from each other.
Having considered what a V-belt drive is, its high performance characteristics can be noted. Due to this, the presented system is used today in many units.