What is a gearbox? Characteristics and types

Advantages of helical gearboxes

The group is the most common due to a number of advantages.

1. High efficiency of 95-98%.
   As the number of steps increases, its value decreases slightly. Low energy losses are caused by low friction forces during operation.
2. High load capacity.
   With suitable dimensions, a cylindrical gearbox is capable of passing through itself and transmitting significant power over a distance. The design features of the mechanisms do not create jamming in the gears. In most applications, losses are neglected, but in large and high-speed units they must be taken into account.
3. Insignificant play of the shaft
   at the output allows achieving high kinematic accuracy of the mechanism.
4. The absence of large energy losses
   does not lead to overheating of the unit. The main power is transferred from the drive to the consumer. A small proportion of energy is used for heating, which does not cause strong heating of the parts. Most gears do not require cooling systems.
5. Reliable operation under dynamic influences (frequent starts, uneven loads).
   In this regard, spur gearboxes are widely used in equipment where the working parts are subject to significant impulse loads: crushers, shredders, shredders, etc. The advantage is provided by the small amount of sliding friction, due to which the parts wear out little. High service life of shafts, gears and bearings.
6. Large selection of devices with different gear ratios.

Gearbox layout diagram

The gearbox layout diagram (Fig. 4.10) should be drawn on A1 graph paper on a scale of 1:1 with thin lines so that necessary changes can be made if necessary.

The sequence of drawing the gearbox layout diagram:

1) place the shaft axes at a distance aw from each other;

2) draw the shafts in accordance with the found dimensions (clauses 4.3.1, 4.3.2);

3) using the previously obtained dimensions bi and di (section 4.5) draw gears;

4) stepping back from the outer ends of the wheels to a distance a, draw lines outlining the inner wall of the gearbox housing;

5) take the gap between the pitch diameter of the wheel and the inner wall of the gearbox equal to a1;

6) draw a dotted line corresponding to the outer wall of the gearbox, retreating a distance dк (section 4.7) from the inner wall of the gearbox;

Rice. 4.9, sheet 1

Rice. 4.9, sheet 2

7) stepping back at a distance K2 from the dotted line, draw lines describing the mating planes for the rolling bearing caps;

at a distance K3 from the dotted line, draw lines limiting the end dimensions of the housing flanges;

9) depict the rolling bearing in overall dimensions (section 4.4);

10) close the holes for the bearings with covers (see Fig. 4.8).

When executing the layout diagram presented in Fig. 4.10, dimensions can be taken from table. 4.4.

Table 4.4

Dimensions for the gearbox layout diagram

Rice. 4.10

Calculation of shafts for the combined action of bending and torsion

The gearbox shafts are loaded with forces acting in the transmission mesh and experience bending and torsion deformations. To simplify the calculations, it is assumed that the forces are concentrated, applied in the middle of the gear rims and directed along the normals to the tooth profiles in the meshing poles. When calculating, they are decomposed into components acting along the coordinate axes. The diagram of the gearbox and the forces acting in the transmission is shown in Fig. 4.11.

Rice. 4.11

Forces acting in gears:

district –

radial –

axial –

where a = 20º – pitch angle of the profile;

b - angle of inclination of the tooth line.

Let's consider the calculation sequence using the example of an output shaft exposed to the greatest forces.

Reactions in the shaft supports (bearings) from forces acting in the XOZ plane along the Z axis (Fig. 4.12):

Reactions to forces acting in the XOY plane along the X and Y axes:

Total reactions:

Bending moments and diagrams caused by forces acting in the XOZ plane:

shaft section AB –

shaft section BC –

Based on the found values ​​of bending moments, diagrams are constructed.

Rice. 4.12

Bending moments and diagrams caused by forces acting in the XOY plane:

shaft section AB –

shaft section BC –

Total bending moments:

Equivalent moment according to the third theory of strength

Shaft diameter in dangerous section

The permissible stress [si] is chosen low so that the shafts have sufficient rigidity to ensure normal operation of the gearing and bearings. It is recommended that the shafts be made from steels 35,40,45, St 5, St 6, for which MPa.

Compare the calculated values ​​of the shaft diameter d in the dangerous section with the diameter dк under the wheel found during the approximate calculation (clause 4.3.2). The following condition must be met: . If this condition is not met, the dimensions of the shaft should be accepted and determined again (clause 4.3.2).

The condition is met: dк=50>d=45

Calculation of rolling bearings

The calculation of rolling bearings is based on two criteria: residual deformation and fatigue spalling. At a ring rotation speed of n£ 10 rpm, the criterion is residual deformation, the calculation is performed using the static load capacity Cor; at n> 10 rpm, the criterion is fatigue spalling of the raceways, the calculation is performed using the dynamic load capacity Cr. A judgment about the suitability of a bearing is made from a comparison of the required and basic load capacities (Str < Cr) or durability (L10h³ [L10h]).

Calculation of rolling bearings is given in [1, p. 85; 3, p. 239: 5, p. 372].

Let us consider the sequence of calculation of rolling bearings using the example of an output shaft.

Shaft rotation speed n2 = 67 rpm. Basic bearing life [L10h] = 18200 hours. The diameter of the shaft seating surfaces dп = 45 mm. Acting forces: radial – N and N; axial – Fa = 1000 N.

Taking into account the diameter of the shaft seating surfaces and the nature of the acting load, we will choose an angular contact ball bearing 33209 (section 4.4), for which the static load capacity Cor = 25100 N; dynamic Сr = 41200 N.

The installation diagram of bearings and acting forces is shown in Fig. 4.13.

Rice. 4.13

Define relation:

Based on the relation from the appendix, table A.12, find the axial loading parameter

Axial components from radial loads:

Total axial loads on the bearing:

since S2>S1, Fa>S2 – S1, then from the appendix, table. Item 13 follows:

For a support loaded with a greater axial force, determine the ratio:

Specify the value of the axial loading parameter (Appendix, Table P. 12):

Determine the ratio for the right, more loaded support:

where V is the rotation coefficient of the inner ring of the bearing.

Since > e2, then from the appendix, table. Item 12, for e2 find the values ​​of the coefficients of radial X and axial Y loads:

Equivalent dynamic load of the right support

where Kb = 1.3 – safety factor;

Kt = 1 – temperature coefficient;

P2 = (1 × 0.45 × 13563 + 1.00 × 4835) × 1.3 × 1 = 14219 (N).

Specify coefficient e1 for the left support (Appendix, Table P. 12):

Find relation:

Determine the coefficients X and Y from the appendix, table. P. 12:

Equivalent dynamic load of the left support

P1 = (1 × 0.45 × 10897 + 1.03 × 1658) × 1.3 × 1 = 8594 (N).

For a more loaded support (right), determine the durability of the selected bearing 36209:

(h).

Since the calculated (required) durability is greater than the basic one [ ] (59701>18200), the selected bearing is suitable for the given operating conditions.

If < [ ], then it is necessary to select an angular contact bearing of a heavier series, having a higher load capacity, or a tapered roller bearing.

Disadvantages of spur gearboxes

Along with advantages, the cylindrical type of gears has disadvantages.

1. One stage does not provide a large gear ratio.
   The minimum number of wheel teeth is 17. This requires a significant increase in dimensions with the highest possible gear ratios (up to 1:12.5).
2. High level of noise created when pairs of teeth alternately enter into contact.
   The simplest design is when they are straight. Contact here occurs along the entire length of the tooth. This allows for high power transmission, but also significant wear and increased rotational noise. In helical gearing, each subsequent link is engaged gradually, which reduces vibration and shock. This requires less effort to rotate the shaft.
3. No self-braking.
   An external load may rotate the output shaft, which is not always practical. In one case this is a disadvantage, in another it is an advantage.
4. Gears have high rigidity and do not provide the ability to compensate for dynamic loads.

Front and rear gearboxes - what's the difference?

If we consider the elements of both gearboxes in isolation from the overall system, then it will not be possible to determine whether it belongs to the drive. But upon comparative analysis, it turns out that the driven gears of the rear mechanism will be larger. Otherwise, only the configuration of the location of the combined nodes changes. In particular, the rear axle gearbox is located along the longitudinal line of the automobile body together with the gearbox and engine. The cardan shaft is responsible for the flexibility of the coupling. The front-wheel drive system uses ball-type angular velocity reducers. Otherwise, the mechanics of work remain the same.

Application of helical gearboxes

Due to their high efficiency, spur gearboxes are the most common. They are used in drives of rolling rolls, metalworking machines, mixers, etc. The load can be uniform, variable, reversible, unidirectional. Other types of gears are used when it is necessary to ensure special conditions: smooth running, high gear ratio with small dimensions, angular drive layout.

Gearboxes are used for the following purposes:

• stepwise reduction in rotation speed - gearbox;
• stepless change in angular speed - variator;
• conversion of low speed to high speed - multiplier;
• combination with the engine in one unit - gear motor.

Main types of gearmotors

According to the type of transmission, the following types of gearboxes are distinguished:

• Planetary gearboxes, operating through a gear system, are the most reliable today. Their disadvantage is the lack of acceleration and braking;
• Worm-type, operating using the clutch of a worm wheel and a special screw (worm). They have smooth acceleration and good braking, but have low efficiency;
• Cylindrical, having two main types: coaxial and flat. They have a high efficiency coefficient, but are very complex in design and, as a result, quite expensive;
• Wave, set in motion with the help of deformation waves in a flexible element of the device. It can be used in the most extreme conditions, as it has high performance and is insensitive to contamination.

Gearboxes are classified according to the number of stages:

• single stage;
• two-stage;
• multi-stage.

According to the scope of application, gearboxes are:

• general machine-building purposes;
• special.

The first type of gearboxes is the most universal. Special gearboxes are used in a narrower area (shipbuilding, aviation, etc.)

Single stage gearbox

The most common is a single-stage horizontal cylindrical gearbox.

Vertical models are also used. This or that design is associated with the convenience of the drive layout. Wheels are made with straight, oblique or chevron teeth. The helical gear housing is made of cast iron or welded steel.

Rolling bearings and, less frequently, sliding bearings are used (for heavily loaded gears).

The horizontal cylindrical gearbox has a gear ratio of no higher than 6.3. A further increase in the gear ratio (it can be increased to 12.5) irrationally increases the dimensions of the unit. If a single-stage cylindrical gearbox exceeds the permissible dimensions, use a smaller device with 2 stages.

Two-stage gearbox

Horizontal type mechanisms are common. The two-stage cylindrical gearbox contains drive, intermediate and driven shafts. The first stage is called high-speed, and the second is called low-speed.

The rational two-stage design of the helical gearbox has a gear ratio of no more than 50. With its further increase, the weight and dimensions of the device increase significantly. For large gear ratios, a three-stage type is recommended.

The two-stage cylindrical gearbox can be made with a bifurcated, pine or deployed design. The latter is the most common due to its simplicity of design. Asymmetrical placement of wheels leads to uneven load on bearings and teeth.

With a bifurcated high-speed stage with oppositely inclined teeth on the wheels, the axial forces are balanced, and the circumferential forces are leveled due to the self-alignment of the drive shaft.

Design specifics of the rear axle gearbox

Wheels with meshing teeth that transmit torque to the driven shafts from the drive shaft are called gears. Due to the fact that the shafts are located at different angles, the teeth of the wheels are made of a special shape - this is the so-called. bevel gears.

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The cone shape, in addition to its main purpose of transmitting torque, also provides a low noise level, which is an advantage in terms of ease of operation of a passenger car.

The drive wheel must be of a different size than the driven ones - only in this case will a reduction in gear be ensured. If this requirement is met, several full rotations of the driven shaft will correspond to one full revolution of the driving shaft - in other words, there is a decrease (reduction) in the rotation speed. There are a number of vehicles (all-terrain vehicles, for example), where a serious reduction in rotation speed is applied in the gearbox - thus ensuring a very low pace of movement so as not to get bogged down.

Gearbox layout

The high-speed stage is often made with a helical tooth, and the low-speed stage is often made with a straight tooth. For mass production of helical gears, it is customary to produce gears with the tooth directed to the left, and wheels with the tooth directed to the right. In small-batch production, the first stage gears are made as usual, and the second stage is made in the right direction. Due to this, the axial forces on the intermediate shaft are balanced.

If it is necessary to transmit torque that does not depend on the angle of supply, bevel-cylindrical gears are used. Vertical devices are made of a worm-cylindrical type. They have lower efficiency, so gearboxes are used mainly for short-term operating conditions.

The expanded scheme is more common, since the components of the mechanism (shafts, wheels, gears) are used to manufacture several standard sizes of gearboxes. The disadvantage is the increased stress concentration on the working area of ​​the tooth, which requires the use of rigid shafts.

Gearboxes with a split circuit have a weight of 20% less, due to their greater compactness.

What is a gearbox?

No mechanical engine can function without a gearbox. The performance of a machine or device depends on this part. How to correctly determine what a gearbox is?

Rotary mechanism

A gearbox is, first of all, a mechanism that converts and transmits the frequency of rotating torque to other devices and tools. This is a transmission link between the rotational devices of an internal combustion engine or electric motor to the final operating unit. The main indicators that characterize it are the number of driven and driven rotary shafts, efficiency and transmitted power. On the rotating devices of this mechanism, worm or gear drives are fixedly fixed, with the help of which movement from one to another is transmitted and regulated. The housing holes contain bearings on which the shafts are located.

We briefly looked at what a gearbox is. Now let’s find out what they are.

Classification of devices

Today the following types of gearboxes are used:

- cylindrical, has high efficiency and can withstand heavy loads;

— bevel gearbox;

— conical-cylindrical, used in engines with an orthogonal arrangement of low-speed and high-speed shafts;

— planetary gearbox, used in the location of the engine and working unit and characterized by a large gear ratio, as well as compact dimensions and lightness;

- a reducer for a gas cylinder, designed to regulate the pressure of gas (oxygen, propane, carbon dioxide, nitrous oxide, gas mixture), which comes from a closed container or directly from a gas pipeline.

Application

What is a gearbox? This is an irreplaceable and diligent assistant in all areas of human activity.

The use of gearboxes in industry is very extensive. What is a gearbox? It is a rotary transmission part in various processing machines. Here these mechanisms are used to increase the speed of revolutions.

And in automobile gearboxes, gearboxes are used, on the contrary, to reduce engine speed. The softness and smoothness of transport depends on their properly adjusted adjustment.

Electrical equipment and household appliances that contain electric motors also use these very important speed-reducing and speed-regulating devices. It is impossible to imagine the design of mixers, food processors, washing machines, grinders, and drills without these mechanisms.

Gearboxes are a necessary and irreplaceable part of pumping systems, treatment facilities, and ventilation equipment. They are used to maintain optimal gas pressure in gas flame installations for soldering, cutting, welding and other processing.

The gas production industry also cannot do without gearboxes. After all, storing and transporting gases classified as explosive substances is quite a troublesome matter. And here the rotation mechanism comes to the rescue. With its use, you can block the access of gas or, conversely, open its exit by adjusting the pressure.

For example, gas coming from a gas pipeline distributor comes out at very high pressure, which needs to be reduced. Using a network reducer, you can ensure automatic maintenance of pressure in a given operating mode.

The pharmaceutical and food industries also use similar pressure-reducing valves, which are necessary to maintain constant pressure and regulate it in oxygen cushions, devices for measuring blood pressure, cooking and blending containers, and cylinders for storing gas mixtures.

Lubrication of gearboxes

Liquid oil is supplied to the gearbox engagement. The following lubrication methods are used.

1. Crankcase
   - immersion in an oil bath if the speed is not higher than 10 m/s. With its further increase, energy losses due to oil splashing increase significantly. The lower part of the gear wheel is located at a depth of two to three tooth heights.
2. Crankcase flow-through:
   oil is supplied to the unit bath on one side, and removed from the other. This cools the oil.
3. Centralized (jet).
   The method is used at a maximum peripheral transmission speed of more than 10 m/s. Oil is supplied by a pump to the gearing and bearings. At the same time, it is cleaned in mesh or plate filters and cooled with water through the walls of tubular refrigerators.
4. Combined:
   one stage can be lubricated centrally, and the other - by crankcase method.

Where and for what are single-stage horizontal gearboxes used?

They find their use:

• where constant or variable load, reversible and one direction is required;
• to ensure continuous work or with short breaks;
• to ensure rotation of the shafts in different directions.

This is interesting: Instructions for tuning the cylinder head

They cannot or are dangerous to use if the shaft rotation speed exceeds 1800 revolutions per minute, as well as when the air dust content is higher than 10 mg per cubic meter. meter and atmosphere of the first and second types in accordance with GOST 15150-69.

Vertical gearboxes

Vertical circuits are required for mechanisms that cannot operate using conventional horizontal gears. A vertical cylindrical gearbox from one to three stages is most often used in mechanisms operating in crane modes. It can also be used in an inclined position.

The steps are usually made with helical gears. Wheels and gears are made of forged alloy steels with heat treatment. Single-row tapered roller bearings are used as supports.

Gear housings

The main requirements for the gearbox housing are rigidity and strength, eliminating the possibility of shaft misalignment. In modern gearbox production, two types of housings are produced - split and one-piece.

The split housing design includes a base and a removable cover. Some models of vertical helical gearboxes have connectors along 2-3 planes. To prevent oil leakage, the gear housing connectors are treated with sealant. It is not recommended to install gaskets between the cover and the base, since they are deformed when fixing the mounting bolts. As a result, the bearings may not fit properly.

The one-piece housing is more often used for worm gearboxes and other types of equipment that are lightweight. This design includes a removable lid.

For the production of gearbox housings, mainly cast iron grades SCh 10-15 are used. Sheet steel is used less frequently, as a rule, when completing large-scale drive equipment for individual orders. The welded steel housing has a wall thickness that is approximately one third less than that of cast iron gearboxes. Recently, aluminum alloys have been increasingly used for the production of housings.

Manufacturers

Domestic production noticeably lags behind foreign production. Imported models enter the Russian market without adaptation to local conditions. Traditional Russian gearboxes are extremely simplified designs, which gives them the opportunity to somehow reduce prices and maintain demand. The consumer is increasingly convinced of their low reliability, preferring to purchase imported products. The domestic cylindrical gearbox has the following disadvantages:

• absence of finishing and finishing operations for processing the surface of the teeth;
• low power and torque, fragility and lack of reliability;
• a significant limitation in the variety of designs, which does not make it possible to use them in modern machines and mechanisms with multifunctional drives.

Very few enterprises are engaged in improving domestic products, improving their performance to foreign levels. Among them, the Scientific and Technical Center "Reductor" stands out, the main focus of which is the modernization of standard products through the application of advances in the science of gearboxes and the introduction of foreign innovations.

Types of gearmotors and their application in the industrial sector.

gear motors

A geared motor is a mechanism whose operation is based on the interaction of a gearbox and an electric motor. Such gearboxes are actively used in a variety of industrial fields and in construction. They are included in the design of concrete mixers, winches and all kinds of conveyors.

With their help, if necessary, you can control the speed of electric motors or change the power of torque. A fairly large number of firms and companies are currently engaged in the production of geared motors. However, regardless of this, units of this type are divided into five types:

1) Helical gearboxes are characterized by a high level of reliability and a huge resource of operating power. As a rule, such mechanisms are part of the design of large machines operating at high speeds. In turn, cylindrical gearmotors are divided into spur, chevron and helical. They are used in metal-cutting equipment, woodworking and many other industrial fields. 2) Worm gearboxes - mechanisms of this type are characterized by a high gear ratio, high heat generation and low efficiency. They are the basis for the operation of various industrial conveyors, conveyors and lifts, as well as pumps and concrete mixers. 3) Bevel gearboxes - unlike other types of units, bevel gearboxes are equipped with intersecting axes. This is what allows you to change the direction of kinetic transmissions. In other gearboxes, the input and output shaft axes are mounted parallel to each other. They are used to operate freight elevators, production conveyors and all kinds of shredders. 4) Planetary gearboxes - despite their small size and weight, they can withstand enormous loads, which allows you to set a decent gear ratio. Such devices are part of the design of drilling machines, mixers, winches and many other tools. 5) Mixed type gearboxes - such multifunctional units have a whole set of gears. Recently, they have been especially actively used in modern construction. Most often, a bevel-cylindrical gear motor is used on construction sites. Geared motors remain particularly relevant devices in construction for a reason. The fact is that almost all modern construction equipment operates on the basis of electric motors, which transmit their energy to the required devices through a gearbox. A key feature of these units is the self-locking function, which ensures efficient and safe operation. As you know, it is worm gearboxes that are included in the design of tower cranes.

Go to the catalog of geared motors