What is gearbox efficiency. Moscow State Technical University named after

1. The purpose of the work

The study of the efficiency of the gearbox at various modes loading.

2. Installation description

To study the operation of the gearbox, a device of the DP3M brand is used. It consists of the following main units (Fig. 1): the gearbox under test 5, the electric motor 3 with an electronic tachometer 1, the load device 6, the device for measuring moments 8, 9. All units are mounted on the same base 7.

The body of the electric motor is hinged in two supports 2 so that the axis of rotation of the motor shaft coincides with the axis of rotation of the body. The fixation of the motor housing from circular rotation is carried out by a flat spring 4.

The gearbox consists of six identical spur gears with a gear ratio of 1.71 (Fig. 2). The block of gears 19 is mounted on a fixed axle 20 on a ball bearing. The design of blocks 16, 17, 18 is similar to block 19. The transmission of torque from the wheel 22 to the shaft 21 is carried out through the key.

The load device is a magnetic powder brake, the principle of which is based on the property of a magnetized medium to resist the movement of ferromagnetic bodies in it. A liquid mixture of mineral oil and steel powder was used as a magnetizable medium.

Measuring devices torque and braking torques consist of flat springs that create reactive torques for the electric motor and load device, respectively. Strain gauges connected to the amplifier are glued on flat springs.

On the front part of the base of the device there is a control panel: power button of the device "Network" 11; button for powering on the excitation circuit of the load device "Load" 13; button for turning on the electric motor "Engine" 10; knob for regulating the frequency of rotation of the electric motor "Speed ​​control" 12; handle for regulating the excitation current of the load device 14; three ammeters 8, 9, 15 to measure respectively the frequency n, moment M 1 moment M 2 .

Rice. 1. Installation diagram

Rice. 2. Gearbox under test

Technical characteristics of the device DP3M:

3. Calculated dependencies

The determination of the efficiency of the gearbox is based on the simultaneous measurement of the moments on the input and output shafts of the gearbox at a steady value of the speed. In this case, the calculation of the efficiency of the gearbox is carried out according to the formula:

= , (1)

where M 2 is the moment created by the load device, N × m; M 1 - the moment developed by the electric motor, N × m; u is the gear ratio of the gearbox.

4. Order of work

At the first stage, at a given constant frequency of rotation of the electric motor, the efficiency of the gearbox is studied depending on the moment created by the load device.

First, the electric drive is turned on and the set speed is set with the speed control knob. The excitation current adjustment knob of the load device is set to the zero position. The excitation power supply is switched on. By smoothly turning the excitation adjustment knob, the first of the specified values ​​of the load torque on the gearbox shaft is set. The speed control knob maintains the set speed. Using microammeters 8, 9 (Fig. 1), the moments on the motor shaft and load device are recorded. By further adjusting the excitation current, the load torque is increased to the next predetermined value. Keeping the speed unchanged, determine the following values ​​of M 1 and M 2 .

The results of the experiment are entered in Table 1, and a graph of the dependence = f(M 2) is plotted at n = const (Fig. 4).

At the second stage, at a given constant load torque M 2, the efficiency of the gearbox is studied depending on the speed of the electric motor.

The excitation power supply circuit is switched on and the set value of the torque on the output shaft of the gearbox is set by the excitation current adjustment knob. The speed control knob sets a range of speeds (from minimum to maximum). For each speed mode, a constant load torque M 2 is maintained, the moment on the motor shaft M 1 is fixed using a microammeter 8 (Fig. 1).

The results of the experiment are entered in Table 2, and a graph of the dependence = f(n) is plotted at M 2 = const (Fig. 4).

5. Conclusion

It explains what the power losses in the gear train are made up of and how the efficiency of a multi-stage gearbox is determined.

The conditions that allow to increase the efficiency of the gearbox are listed. The theoretical substantiation of the obtained graphs = f(M 2) is given; = f(n).

6. Reporting

– Prepare title page(see sample on page 4).

- Draw the kinematic diagram of the gearbox.

Prepare and complete the table. one.

Table 1

from the moment created by the load device

– Build a dependency graph

Rice. 4. Dependence graph \u003d f (M 2) at n \u003d const

Prepare and complete the table. 2.

table 2

The results of the study of the efficiency of the gearbox depending on

from the frequency of rotation of the electric motor

– Build a dependency graph.

n, min -1

Rice. 5. Dependence plot = f(n) at M 2 = const

Give a conclusion (see paragraph 5).

Control questions

1. Describe the design of the DPZM device, what main components does it consist of?

2. What power losses take place in the gear and what is its efficiency?

3. How do such gear transmission characteristics as power, torque, rotational speed change from the driving to the driven shaft?

4. How is the gear ratio and efficiency of a multi-stage gearbox determined?

5. List the conditions to improve the efficiency of the gearbox.

6. The procedure for performing work in the study of the efficiency of the gearbox, depending on the moment supplied by the load device.

7. The procedure for performing work in the study of the efficiency of the gearbox, depending on the engine speed.

8. Give a theoretical explanation of the obtained graphs = f(M 2); = f(n).

Bibliographic list

1. Reshetov, D. N. Machine parts: - a textbook for students of engineering and mechanical specialties of universities / D. N. Reshetov. - M.: Mashinostroenie, 1989. - 496 p.

2. Ivanov, M. N. Machine parts: - a textbook for students of higher technical educational institutions/ M. N. Ivanov. – 5th ed., revised. - M .: Higher School, 1991. - 383 p.

LAB #8

Laboratory work

Coefficient research useful action gear reducer

1. The purpose of the work

Analytical determination of the efficiency factor (COP) of a gear reducer.

Experimental determination of the efficiency of a gear reducer.

Comparison and analysis of the obtained results.

2. Theoretical provisions

The energy supplied to the mechanism in the form of workdriving forces and moments for the steady state cycle, is spent on useful workthose. the work of forces and moments of useful resistance, as well as the performance of workassociated with overcoming the forces of friction in kinematic pairs and the forces of resistance of the medium:. Values ​​and are substituted into this and subsequent equations in absolute value. The mechanical efficiency is the ratio

Thus, the efficiency shows what proportion of the mechanical energy supplied to the machine is usefully spent on doing the work for which the machine was created, i.e. is an important characteristic of the mechanism of machines. Since friction losses are inevitable, it is always. In equation (1) instead of works and performed per cycle, we can substitute the average values ​​of the corresponding powers per cycle:

A gearbox is a gear (including a worm) mechanism designed to reduce the angular velocity of the output shaft relative to the input.

The ratio of the angular velocity at the input to the output angular velocity called gear ratio :

For the reducer, equation (2) takes the form

Here T 2 and T 1 - average values ​​of torques on the output (torque of resistance forces) and input (torque of driving forces) shafts of the gearbox.

The experimental determination of the efficiency is based on the measurement of the values T 2 and T 1 and calculation of η by formula (4).

In the study of the efficiency of the gearbox by factors, i.e. system parameters that affect the measured value and can purposefully change during the experiment, are the moment of resistance T 2 on the output shaft and the speed of the input shaft of the gearboxn 1 .

Main way increase efficiency gearboxes is to reduce power losses, such as: the use of more modern lubrication systems that eliminate losses due to mixing and splashing of oil; installation of hydrodynamic bearings; designing gearboxes with the most optimal transmission parameters.

The efficiency of the entire installation is determined from the expression

where - efficiency of the gear reducer;

– efficiency of motor supports,;

– coupling efficiency, ;

– Efficiency of brake mounts,.

The overall efficiency of a gear multi-stage gearbox is determined by the formula:

where – Efficiency of gearing with average workmanship with periodic lubrication,;

- The efficiency of a pair of bearings depends on their design, assembly quality, loading method and is approximately taken(for a pair of rolling bearings) and(for a pair of plain bearings);

– Efficiency taking into account losses due to splashing and mixing of oil is approximately taken= 0,96;

k– number of pairs of bearings;

n- the number of pairs of gears.

3. Description of the object of study, devices and tools

This laboratory work is carried out on the DP-3A installation, which makes it possible to experimentally determine the efficiency of the gear reducer. The DP-3A installation (Figure 1) is mounted on a cast metal base 2 and consists of an electric motor assembly 3 (mechanical energy source) with a tachometer 5, a load device 11 (energy consumer), a gearbox under test 8 and flexible couplings 9.

Fig.1. Schematic diagram of the DP-3A installation

The load device 11 is a magnetic powder brake that simulates the working load of the gearbox. The load device stator is an electromagnet, in the magnetic gap of which a hollow cylinder with a roller (load device rotor) is placed. The internal cavity of the loading device is filled with a mass, which is a mixture of carbonyl powder with mineral oil.

Two regulators: potentiometers 15 and 18 allow you to adjust the speed of the motor shaft and the magnitude of the braking torque of the load device, respectively. The speed is controlled by a tachometer5.

The torque values ​​on the motor and brake shafts are determined by means of devices that include a flat spring6 and dial gauges7,12. Supports 1 and 10 on rolling bearings provide the ability to rotate the stator and rotor (for both the motor and the brake) relative to the base.

Thus, when an electric current is applied (turn on the toggle switch 14, the signal lamp 16 lights up) in the stator winding of the electric motor 3, the rotor receives a torque, and the stator receives a reactive torque equal to the torque and directed in the opposite direction. In this case, the stator under the action of the reactive torque deviates (balancing motor) from the initial position depending on the magnitude of the braking torque on the driven shaft of the gearboxT 2 . These angular movements of the stator housing of the electric motor are measured by the number of divisions P 1 , to which the indicator needle deviates7.

Accordingly, when an electric current is applied (turn on the toggle switch 17) to the electromagnet winding, the magnetic mixture resists the rotation of the rotor, i.e. creates a braking torque on the output shaft of the gearbox, recorded by a similar device (indicator 12), showing the amount of deformation (number of divisions P 2) .

Springs of measuring instruments are pre-calibrated. Their deformations are proportional to the torques on the motor shaft T 1 and the output shaft of the reducerT 2 , i.e. the moment of forces driving and the moment of forces of resistance (braking).

The reducer8 consists of six identical pairs of gears mounted on ball bearings in the housing.

The kinematic diagram of the DP 3A installation is shown in Figure 2, a the main parameters of the installation are given in Table 1.

Table 1. Technical characteristics of the installation

Parameter name	Letter designation quantities	Meaning
The number of pairs of spur gears in the gearbox	n
Gear ratio	u
transmission module, mm	m
Rated torque on the motor shaft, Nmm	T 1
Braking torque on the brake shaft, Nmm	T 2	up to 3000
The number of revolutions of the motor shaft, rpm	n 1	1000

Rice. 2. Kinematic diagram of the DP-3A installation

1 - electric motor; 2 - clutch; 3 - reducer; 4 - brake.

4. Research methodology and processing of results

4.1 The experimental value of the efficiency of the gear reducer is determined by the formula:

where T 2 - moment of resistance forces (torque on the brake shaft), Nmm;

T 1 - the moment of driving forces (torque on the motor shaft), Nmm;

u- gear ratio of the gear reducer;

– Efficiency of the elastic coupling;= 0,99;

– Efficiency of the bearings of the supports on which the electric motor and brake are installed;= 0,99.

4.2. Experimental tests involve measuring the torque on the motor shaft at a given rotation speed. At the same time, certain braking torques are sequentially created on the output shaft of the gearbox according to the corresponding indications of the indicator12.

When the electric motor is turned on with toggle switch 14 (Figure 1), the stator of the electric motor support with your hand to prevent hitting the spring.

Turn on the brake with toggle switch 17, after which the indicator arrows are set to zero.

Using potentiometer 15, set the required number of revolutions of the motor shaft on the tachometer, for example - 200 (table 2).

Potentiometer 18 on the output shaft of the gearbox creates braking torques T 2 corresponding to the indications of the indicator12.

Record indicator 7 to determine the torque on the motor shaft T 1 .

After each series of measurements at one speed, potentiometers 15 and 18 are brought to the extreme counterclockwise position.

Rotation frequencyn 1 shaft electric motor, rpm	Indicator 12, P 2
200, 350, 550, 700	120, 135, 150, 165, 180, 195
850, 1000	100, 105, 120, 135, 150, 160

4.3. By changing the load on the brake with potentiometer 18 and on the engine with potentiometer 15 (see Figure 1), at a constant engine speed, record five indicator readings 7 and 12 ( P 1 and P 2) in table 3.

Table 3. Test results

The number of revolutions of the motor shaft,n 1 , rpm

Indicator 7 readings P 1

Torque on the motor shaft Nmm

Indicator 12 P 2

Torque on the brake shaft Nmm

Efficiency experimental,

In most mechanisms with an electric motor, there is a cylindrical gearbox. It reduces the number of revolutions and increases the power of the unit. The gear mechanism for transmitting torque through cylindrical wheels has the highest efficiency compared to other methods. Different kinds cylindrical gearboxes are widely used in metallurgical and machine-building equipment, electric tools and automobiles.

Design features

The basis of any gearbox is transmitting torque and changing the number of shaft revolutions. Cylindrical gears are characterized by the ability to rotate in both directions. If necessary, the driven shaft with the wheel is connected to the engine and becomes the driving one. They in this design are arranged in parallel, horizontally and vertically. The device of cylindrical gearboxes can be very different, but it necessarily includes in its design:

• leading;
• driven shaft;
• gear;
• wheel;
• bearings;
• frame;
• covers;
• lubrication system.

The body and cover are cast iron or welded from a low-carbon sheet 4-10 mm thick, depending on the dimensions and power of the unit. Small gearboxes are made welded. The rest have a strong cast body.

Characteristics of spur gearboxes

The number of gears, the type of tooth and the relative position of the shafts for all types of equipment are described by GOST Cylindrical gearboxes. It shows the sizes of all parts that can be used in spur gearboxes with different numbers of steps. The maximum of one pair is 6.5. The total multi-stage reducer can be up to 70.

A worm gear can have a gear ratio greater than a cylindrical gearbox, it can reach 80. At the same time, they are compact, but rarely used due to low efficiency. Cylindrical single-stage gearboxes have an efficiency of 99 - 98%, the highest of all types of gears. Worm and cylindrical gearboxes differ in the arrangement of shafts. If they are parallel for cylindrical ones, then the worm is located at an angle to the wheel. Consequently, the driving and driven shafts exit from the perpendicularly located side walls of the housing.

Cylindrical gearboxes are the noisiest, when the teeth come into contact, the surfaces hit one another. This eliminates strong friction and overheating.

For lubrication, it is enough to pour oil into the sump so that the lower gears are partially immersed in it. As the teeth rotate, they grab oil and spray it onto other parts.

Design and calculation procedure

The calculation of the future gearbox begins with the determination of the transmission torque and its selection from normalized pairs. After that, the diameters of the parts and the center distance of the shafts are specified. A kinematic diagram is drawn up, the optimal shape of the body and cover, bearing numbers are determined. The assembly drawing includes a kinematic diagram of a two-stage gearbox, a lubrication system and methods for its control, types of bearings and their installation locations.

GOST 16531-83 describes everything possible types and sizes of gears that can be used in spur gears, indicating the module, number of teeth and diameter. The shaft is selected according to the size of the gear. Its strength is calculated taking into account the twisting and bending torque. The minimum size is determined, multiplied by the strength factor. The nearest larger normalized shaft size is then selected. The key is calculated only for the cut and is selected in the same way.

Download GOST 16531-83

The bearing is selected according to the diameter of the shaft. Its type is determined by the direction of the tooth. With a helical gear, they put stubborn, more expensive ones. The spur gear does not load them in the axial direction, and single row ball bearings operate for several thousand hours.

The assembly scheme is indicated on the drawing below and is detailed in the technological documentation, which is issued for production along with the drawings. On the main drawing general view the table indicates specifications gearbox, which are then transferred to the passport:

• number of steps;
• ratio;
• the number of revolutions of the drive shaft;
• output power;
• dimensions;

Additionally, the vertical arrangement of the engagement, the direction of rotation of the shaft and the installation method can be indicated: flanged or on feet.

Types of cylindrical gearboxes

Helical gearboxes are diverse in design, size and power, they are divided into types according to several characteristics:

• fastening type;
• shaft arrangement;
• number of steps;
• tooth cutting.

Characteristics may include types of bearings and type of shaft connection.

Single-stage cylindrical gearboxes can be attached to the engine and the body of the working unit with flanges. The design is compact, with minimal cost materials. They are mainly installed on a sole with protrusions around the perimeter or on paws with holes for. Small units can be installed on a welded frame. For overall units, a special foundation is made.

Shaft arrangement

The input and output shafts can be located horizontally, vertically, parallel to each other, but in different planes for multi-stage units. If there is only one engagement, the shafts are in the same plane, strictly vertical or horizontal. They are rarely displayed in one direction, only with the possibility of a compact arrangement of the engine and the working unit. In a two-stage spur gearbox, the center distance is greater and it is possible to mount the motor from the side of the actuator.

Cylindrical gearboxes can be produced with a vertical shaft arrangement. They are convenient to install on machines, but the upper gearing and bearings are poorly lubricated. For long work they are not suitable for heavy loads.

The case of a reducer of cylindrical horizontal dimensional, occupies a lot of place. It heats up less, withstands loads and vibrations, and is stable. In models with 3 or more stages, the shafts are located horizontally. Grease reaches all bearings. In multi-row structures, additional irrigation is done from above, from an oil pipeline installed in the cover.

Gear boxes

A kind of spur gearbox with a movable intermediate shaft is a well-known gearbox. When the position of the shaft changes, some pairs disengage, others begin to interact. As a result, the gear ratio changes, the rotation speed at the output.

Gearboxes are made with a straight tooth. Helical teeth are rare when there is a large load on the actuator.

Application of spur gearboxes

- lowering the engine speed and increasing the power on the output shaft. The assembly of a cylindrical gearbox is not difficult. In the center of the holes there is a connector for the body and cover. Bearings are mounted on shafts, installed in prepared sockets and supported from the outside by covers.

Wheels and gears are attached to the shafts with keys.

To adjust the center distance, it is necessary to bore the body with great accuracy.

Gearbox maintenance is easy. It is necessary to add oil regularly, change it periodically. The parts located inside are designed for continuous operation for at least 10 years.

Gearboxes are used in various industries. Some types of large equipment are able to withstand any weather conditions. They are installed in quarries and open areas, on gantry cranes.

Rolling and forging and pressing equipment will not be able to work without gearboxes. There are many types of gearboxes in demand in this industry. Spurs stand on cranes. Powerful herringbones rotate crank presses, rollers, manipulators that feed metal.

Rolling t-straightening mills operate solely thanks to the stands that transmit the rotation of the engine to the rolls and work units.

Under each hood hides a gearbox. Each machine has a gearbox or several. Small gears are installed in the power tool and regulate the speed of rotation of the drill spindle, grinder and router.

Advantages and disadvantages

The cylindrical transmission mechanism has been widely used in various fields. It has undeniable advantages compared to the worm:

• high efficiency;
• does not heat up;
• works both ways.

The advantages and disadvantages of a spur gearbox depend on the characteristics of the gearing and other structural elements.

Advantages

Main positive moment is a high efficiency. It significantly exceeds the output power with the same engines, all gears and other types of gears.

node can work long time without interruption, switch endless times from one mode to another and even change the direction of rotation.

Heat generation is minimal. There is no need to install a cooling system. Lubrication is sprayed on the lower wheels, lubricates the upper gears, bearings and collects down into the sump, all the dirt, chipped metal particles. It is enough to periodically add oil and change it every 3 to 6 months. The frequency of preventive measures depends on the mode of operation.

The output shaft is mounted in rolling bearings and has virtually no play. Its movement is accurate enough to use the gear mechanism as a drive for precision devices and instruments. Axial and radial runout of mating parts does not affect the operation of the mechanism.

Efficiency does not depend on voltage drops. The gear ratio is stable. If the engine speed drops, the rotation of the driven wheel slows down proportionally. The power stays the same.

Flaws

Positive quality - the absence of friction and braking, in certain conditions creates problems. In hoisting mechanisms, when installing a cylindrical gearbox, it is necessary to put a strong brake in order to keep heavy objects in weight and prevent them from lowering themselves. In worm gears, only a worm can be the leader, and due to the high friction, a self-braking effect occurs.

The problem with all gears is the lack of a safety mechanism.

When overloaded or abruptly turned on, the belt slips along the pulley. The tooth can only break, and the part will have to be changed. Keys are used as additional fuses. They are calculated on a cut without a margin of safety. Replacing a simple part cut off by a coupling is much easier.

The cost of working parts is high. The manufacturing technology is long and complicated. At the same time, the tooth is gradually erased, the gap between the working surfaces increases. It is impossible to change the center distance, as in rack and pinion and worm gears in a gearbox. You have to periodically replace gears, wheels, bearings.

The more the involute is erased, the more the teeth knock against each other, and the gearbox makes noise.

Veselova E. V., Narykova N. I.

Study of instrument reducers

Guidelines for laboratory work No. 4, 5, 6 on the course "Fundamentals of instrument design"

Original: 1999

Digitization: 2005

Digital layout based on the original was compiled by: Alexander A. Efremov, gr. IU1-51

Purpose of work

Acquaintance with the designs of installations for determining the efficiency of gearboxes.

Experimental and analytical determination of the efficiency of a given type of gearbox depending on the load on the output shaft.

In various kinds of devices, devices called drives have found wide application. They consist of an energy source (motor), a gearbox and control equipment.

A gearbox is a mechanism consisting of a system of gear, worm or planetary gears that reduce the speed of rotation of the driven link compared to the speed of rotation of the drive link.

A similar device that serves to increase the speed of rotation of the driven link compared to the speed of rotation of the leading link is called a multiplier.

The following types of gearboxes are explored in these labs: helical multi-stage gearbox, planetary gearbox, and single-stage worm gearbox.

The concept of efficiency

With the steady movement of the mechanism, the power of the driving forces is spent completely on overcoming useful and harmful resistances:

Here P g- power of driving forces; P c- the power expended to overcome the frictional resistance; P n is the power expended to overcome useful resistances.

The efficiency is the ratio of the power of the forces of useful resistance to the power of the driving forces:

(2)

Index 1-2 indicates that the movement is transmitted from link 1, to which the driving force is applied, to link 2, to which the useful resistance force is applied.

Value
is called the transmission loss ratio. Obviously:

(3)

In the case of lightly loaded gears (they are typical in instrumentation), the efficiency depends significantly on the intrinsic friction losses and on the degree of power loading of the mechanism. In this case, formula (3) takes the form:

(4)

where c- coefficient taking into account the influence of own losses on friction and load F,

Components a and b depends on the type of transmission.

At
coefficient
reflects the influence of own losses on friction in lightly loaded gears. With increasing F coefficient c(F) decreases, approaching the value
with a large amount F.

When connected in series m mechanisms with efficiency The efficiency of the entire connection of mechanisms:

(5)

where P g- power supplied to the first mechanism; P n- the power removed from the last mechanism.

The gearbox can be considered as a device with a series connection of gears and supports. Then the efficiency is determined by the expression:

(6)

where - efficiency i- oh pairs of gearing;
- efficiency of one pair of supports; - number of pairs of supports.

Support efficiency

The efficiency of the support is determined by the formula

(7)

since the ratio of the powers at the output and input of the support is equal to the ratio of the corresponding moments due to the constancy of the rotation speed. Here M- torque on the shaft; M tr- moment of friction in the support.

The moment of friction in a rolling bearing can be determined by the formula:

(8)

where M 1 - friction moment, depending on the load on the support; M 0 - friction torque, depending on the design of the bearing, the speed and viscosity of the lubricant.

In instrument gearboxes, the component M 1 much less component M 0 . Thus, we can assume that the moment of friction of the supports is practically independent of the load. Consequently, the efficiency of the support does not depend on the load. When calculating the efficiency of the gearbox, you can take the efficiency of one pair of bearings equal to 0.99.