How to connect 2 shafts of different diameters. Couplings

General information. Drive couplings are devices that connect the shafts of jointly operating units and transmit torque. The need for connecting shafts is due to the fact that most machines are assembled from a number of separate parts with input and output shafts. These parts are the engine. M, reducer R and working machine RM(Fig. 23.1).

The main purpose of couplings is to connect shafts and transmit torque. Couplings can perform a number of important additional functions. On this basis, couplings are classified.

There is a class permanent(non-disengaging) couplings that ensure a constant connection of the shafts during the entire operation of the machine.

Some machines use clutches. clutch, providing connection of units or their separation during machine operation. In turn, clutches are divided into managed and self-managed.

Controlled clutches connect machine units according to some command. Self-controlled clutches are switched on automatically, connecting or disconnecting the shafts, depending on the operating conditions of the machine and the principle of operation of the clutch.

The main characteristic of the clutch load is the torque T.

Usually the rated torque T on the clutch is approximately determined depending on the dynamic properties of the machine, characterized by the degree of uneven rotation and the magnitude of the accelerated masses, i.e. the value of the dynamic component of the torque on the clutch:

T = T n + T d = T n (1+ T d / T n) = T n,

where T n - the rated torque is usually approximately determined by the power consumption of the engine and by the speed;

T e – dynamic moment;

dynamic factor.

Silent couplings. Long shafts, according to the conditions of manufacture, assembly and transportation, are sometimes made composite. In this case, the individual parts of the shaft are connected by blind couplings. In some cases, these couplings are also used to connect strictly coaxial shafts of units. Deaf couplings include sleeve couplings, which are a sleeve put on with a gap on the ends of the shafts, and flange couplings (Fig. 23.2), consisting of two identical coupling halves, made in the form of a hub with a flange. The flanges are bolted together.

Compensating clutches. For economic and technological reasons, machines are usually made from separate units, which are connected by couplings. However, the exact installation of the shafts of such units is impossible due to manufacturing and installation errors; installation of units on a deformable base; and also due to elastic deformations of the shafts under load.

Possible types of shaft displacements (axial, radial and angular) and the resulting additional loads at the ends of the shafts are shown in fig. 23.3.

To connect shafts with mismatched axes, compensating couplings are used. Due to their design, these couplings ensure machine performance even with mutual shaft misalignments. In this case, shafts and supports are additionally loaded with axial, radial forces and bending moments, depending on the magnitude and type of misalignment of the shafts.

It should be emphasized that with an increase in shaft displacements, the performance of the coupling decreases.

Compensating clutches include gear (Fig. 23.4), chain cam-disc and other clutches.

The gear coupling consists of two bushings 1 and 4 with external teeth and two clips 2 and 3 with internal teeth. Clips are rigidly connected with bolts.

Elastic couplings. Elastic couplings are distinguished by the presence of an elastic element and are universal in the sense that, having some torsional compliance, these couplings are also compensating. Elastic couplings are capable of:

1) To soften shocks and torque shocks caused by the process or gap selection when starting and stopping the machine. In this case, the kinetic energy of impact is accumulated by the coupling during the deformation of the elastic element, turning into potential energy of deformation;

2) Protect the drive of the machine from harmful torsional vibrations;

3) Connect shafts with mutual displacements. In this case, the elastic element of the coupling is deformed, and the coupling functions as a compensating one.

According to the material of the elastic elements, these couplings are divided into couplings with non-metallic elastic elements and couplings with metallic elastic elements.

The most widely used in mechanical engineering has received an elastic sleeve-pin coupling (Fig. 23.5). It consists of two coupling halves 1 and 5. Coupling half 1 has conical holes, and coupling half 5 has cylindrical holes. Pins 4 are inserted into these holes, on which elastic elements 3 are put on. Screwing the nut 2, fingers 4 enter the conical holes, as a result of which the coupling halves 1 and 5 are connected. The torque is transmitted through the elastic elements 3.

Controlled couplings. Couplings connect and disconnect stationary or rotating shafts on a control command. These couplings are divided into couplings with profile closure (cam) and friction. The latter are widely used when it is necessary to change the operating mode of the machine without stopping the engine.

Cam clutches are used to transmit large torques with infrequent switching. They have significantly smaller overall dimensions and weight than friction clutches. However, they connect shafts whose angular velocities are equal or slightly different. This requires precise alignment of the coupling halves.

b

On fig. 23.6 shows clutches with end cone cams (Fig. 23.6, a) and with rectangular ones (Fig. 23.6, b). The choice of the shape of the cams is determined mainly by the conditions for switching on the clutch.

Friction couplings. These clutches can be engaged on the move and transmit torque due to friction forces on the working surfaces, created by smooth pressing of the working surfaces. By changing the pressing force, it is possible to adjust the moment of friction forces. During the inclusion of the friction clutch, the working surfaces slip. After the clutch is engaged, there is no slip.

The design of these clutches can be made with one or more disks, with cylindrical or conical friction surfaces, with mechanical, pneumatic, hydraulic or electromagnetic control. The group of couplings with force closing by electromechanical coupling consists of couplings with a liquid or powdered ferromagnetic mixture, in which, when an electric current passes in the excitation coil, a magnetic flux arises, as a result, the ferromagnetic mixture filling the gap between the coupling halves is magnetized, which ensures the adhesion of the mixture to the surfaces of the coupling halves.

A friction layer is applied to the working surfaces of the disks or pads made of a friction material that increases the friction force are attached.

Depending on the operating conditions, friction clutches are divided: into clutches without lubrication of rubbing surfaces and into clutches with lubrication of rubbing surfaces. The latter transmit less torque, but they are more durable, since the wear rate of the working surfaces is less than that of dry couplings.

Self-controlled or automatic clutches are switched on and off depending on the change in the operating mode of the machine. These include: overrunning clutches or freewheels that transmit torque only in one direction of rotation of the drive half-coupling relative to the driven one and rotate with the opposite direction of rotation, centrifugal clutches that turn on and off depending on the speed of rotation of the drive half-coupling, limit torque clutches that turn off the machine when dangerous increase in torque.

Safety couplings. The safety clutch serves to disconnect the shafts or the shaft from the part sitting on it in case of overload or unacceptable rotation speed, i.e., protecting the machine from breakage in the event of a violation of normal operation. Safety couplings with a collapsing element are small in size and high precision triggering. When overloaded, the safety element is sheared and the coupling halves open. To restore the machine to working capacity, it must be stopped and the safety element replaced.

Cam safety clutches are held in place by springs until the increasing torque generates a force that can overcome the force of the spring.

Friction safety clutches automatically restore the machine's performance after the overload has ceased, however, their operation accuracy is not high due to the variability of the friction coefficient on the rubbing surfaces of the disks.

Literature

1. Applied mechanics: Proc. allowance / A.T. Skoybeda, A.A. Miklashevich, E.N. Levkovsky and others; Under total ed. A.T. Skoybedy.- Mn.: Vysh. school, 1997. - 552 p.

2. Feodosiev V.I. Resistance of materials. - M.: Mashinostroyeniye, 1979. - 560 p.

3. Lyuboschits M.I., Itskovich G.M. Handbook of the strength of materials.- Mn.: Vysh. school, 1969.- 464 p.

4. Arkusha A.I. Technical mechanics: Theoretical mechanics and strength of materials: Proc. for machine building specialist. Tekhnikumov.- 2nd ed., add. - M .: Higher. school, 1989. - 352 p.

Similar information.

Possible ways of connecting the motor and cylindrical, bevel-helical, and worm gearboxes are shown in fig. 2.1, where a, d, and - shaft-to-shaft connections, b, e, k - compensating clutch connections, c, g, l - gear connections, g, h, m - V-belt transmission connection.

The “shaft to shaft” connection is used: when striving to reduce overall dimensions and weight; if you need a rigid connection to obtain accurate positioning and accurate speed of movement; when striving to reduce the reduced moment of inertia

drive. This connection is compact, but extremely sensitive to errors in the manufacture and assembly of the drive. With an increase in these errors, the forces in the supports of the connected motor and gearbox shafts increase, and the possibility of fretting in the connection also arises. As you know, the fretting of fixed joints

- This is a type of damage that occurs when two surfaces that are in contact and nominally stationary with respect to each other experience local small periodic relative displacements.

When connecting the shafts of the motor and the gearbox using a compensating clutch, it is possible to compensate for rather large errors in the assembly of the drive. This slightly increases the size of the drive in length. Cantilever radial load on the connected shafts is approximately 0.2 of the circumferential force on the coupling.

If the motor and gearbox shafts are connected by a gear, then overall size worm or bevel gear motor-reducer slightly increases in length. In this case, the motor-reducer becomes, respectively, a helical-worm or helical-bevel-cylindrical. The connected shafts are loaded with forces acting on the gear teeth.

The connection using a V-belt drive increases the overall height of the gearmotor. The load on the shafts to be connected is determined by the cantilevered radial pretensioning force of the belts.

Comparative analysis ( fig. 2.2) of the prevalence of various connections of the engine shafts and

Ivanov A.S., Murkin S.V. "Designing modern geared motors"

of a reducer in geared motors for general industrial use of 72 companies from 17 countries showed that three types of connections: “shaft to shaft” (white fill), compensating clutch (black fill), using a gear train (gray fill) are quite common in modern motor- gearboxes manufactured both in Western countries and in Russia. Belt drive connections are not included in this analysis as they are used only by some geared motor manufacturers.

Shaft-to-shaft connection is used by Bockwoldt (Germany) in a cylindrical-bevel-cylindrical gearmotor. Firms Rotor (Netherlands), Renold (Great Britain), Innovari (Italy) use such a connection in one-, two- and three-stage helical gear motors. Coupling is typical

Ivanov A.S., Murkin S.V. "Designing modern geared motors"

for geared motors manufactured by Stöber, Bauer (Germany), etc. It is performed using a gear coupling, an asterisk coupling, MUVP, etc. Gear connection is common in Germany (SEW, Bauer, Nord), Great Britain (Renold), USA (firm Baldor Dodge), Italy (firms Innovari, Rossi) and other countries.

2.1 Shaft to shaft connection

AT gearmotors three types of shaft-to-shaft connections are used: 1) both the motor shaft and the gearbox shaft are mounted on two supports, the torque is transmitted by a keyed connection; 2) both the motor shaft and the gearbox shaft are mounted on two supports, the torque is transmitted by short splines; 3) the motor shaft is mounted on two supports, and the input shaft of the gearbox is on one, the torque is transmitted by the connection with an interference fit created by tightening the screws of the terminal connection.

On fig. 2.3 shows these types of connections in relation to a helical-bevel-helical gear motor: the first (a) is a gear motor from Pujol Muntala (Spain); the second (b) is a gear motor from ZAE (Germany); the third (c) is a Bauer gear motor (Germany). The first type of connection is also used by firms

GFC and Bockwoldt (Germany), Renold (UK), Rossi

(Italy), Mozhga-reductor LLC, Reduktor OJSC, Barysh, Reduktor OJSC, Izhevsk (Russia), etc. The second type of compound is also common among Swedrive (Sweden), Bonfiglioli (Italy ) and others. The third type of connection is also used by KEB (Great Britain) and others.

Ivanov A.S., Murkin S.V. "Designing modern geared motors"

Ivanov A.S., Murkin S.V. "Designing modern geared motors"

An example of a connection of the third type in relation to a planetary gear motor manufactured by ZF (Germany) is shown in fig. 2.4 (the engine is not shown in the figure).

As you know, a rod fixed in one support (Fig. 2.5, a) forms a mechanism. To fix the rod in space, it is enough to install it on two supports (Fig. 2.5, b). If the number of supports is increased, then the system becomes statically indeterminate, and in order to determine the reactions in the supports, it is necessary, in addition to the equilibrium equations, to draw up conditions for the compatibility of displacements. When the shafts are misaligned or misaligned, the bearings located near the joint are loaded with forces that can exceed the reactions in the bearings from the working process. A four-bearing shaft without a hinge (Fig. 2.5, c) is a design scheme for the “shaft-to-shaft” connection of the first type, a four-bearing shaft with a hinge

Ivanov A.S., Murkin S.V. "Designing modern geared motors"

(Fig. 2.5, d) - the design scheme of the “shaft to shaft” connection of the second type, the three-bearing shaft (Fig. 2.5, d) is the design scheme of the “shaft to shaft” connection of the third type.

Since the shaft-to-shaft connection forms a statically indeterminate design scheme of the connected shafts, manufacturing and assembly errors can lead to significant forces in the supports. To limit the magnitude of these forces, it is necessary to take into account the relationship of reactions in the supports with the location errors of the surfaces of the parts, the bending stiffness of the shafts, the contact stiffness of the bearings, the radial clearances in the bearings, and to assign location tolerances based on the considered statically indeterminate system.

In addition to an increase in reactions in the supports, which reduces the life of the bearings, in the shaft-to-shaft connection, fretting may occur in the interface between the contact surfaces of the output end of the motor shaft and the hole in the gearbox shaft. To exclude the appearance of fretting, SEW (Germany) recommends applying NOCO anti-seize paste to the contact surfaces during assembly, Italian companies - Klűberpaste-46MR401 paste, firm

Ivanov A.S., Murkin S.V. "Designing modern geared motors"

Shafts and axles

Rotating machine parts are mounted on axles or shafts. Shafts always rotate with the parts and transmit torque; the axes, whether they rotate with the parts or remain stationary, do not transmit momentum and only support the parts. Therefore, the axles are loaded only with bending forces, and the shafts, in addition to them, with torques.

Shafts are straight, cranked and flexible (Figure 3.8). When the diameter of the worm or gear is close to the diameter of the shaft, they are made as a whole, for example, a shaft with a worm, a shaft with a gear.

Shafts

a - straight lines; b - cranked; c - flexible.

Figure 3.8.

Shafts and rotating axles are mounted by supports (trunnions) in bearings. The trunnions that perceive the axial load are called heels.

Bearings

Shafts and parts rotating around them are supported on bearings. Distinguish between plain and rolling bearings.

Plain bearings(Figure 3.9). Depending on the magnitude and direction of the loads that occur on the shafts supported by plain bearings, there are radial bearings, which can take radial loads, and thrust bearings, which can take both axial and radial forces.

The trunnion surface in radial bearings slides relative to its inner surface. The reduction of friction forces between the rubbing surfaces is created by a layer of lubricant. During operation, the trunnion occupies an eccentric position in the bearing, and therefore the lubricant between the surfaces of the bearing and the trunnion takes the form of a wedge. An oil layer separating the journal and bearing is also created if oil is supplied to the gap using an oil pump.

Plain bearings are installed for heavy shafts when disassembly of the bearing is required, or when the latter operates in aggressive environments or with heavy contamination.

Sleeve bearing with split housing

1 - cover; 2 - bolts; 3 - liners; 4 - body; 5 - cap oiler.

Figure 3.9.

Friction bearing(Figure 3.10) consists of outer and inner rings with raceways. Between the rings in the raceways are balls or rollers that roll along the tracks. In order for the rollers or balls to be at the same distance from one another, the bearings are provided with separators, which are stamped rings with holes for the rollers or balls.

Main types of rolling bearings

Figure 3.10.

Roller bearings are widely used (with small roller diameters they are called needle bearings).

Rolling bearings can be divided into three types: radial, perceiving radial loads and allowing small axial loads; radial-thrust, perceiving both radial and axial loads, but the value of the latter should not exceed 0.7 of the difference between the allowable and effective radial loads; persistent, perceiving only axial loads.

Couplings

Couplings are used to connect shafts that are a continuation of one another, or located at an angle, as well as to transmit torque between the shaft and the parts sitting on it.

According to their purpose, they are divided into permanent clutches (uncontrolled) and coupling clutches (controlled).

Couplings connecting the shafts rigidly, distinguish the following types:

- Sleeve couplings simple in design, small in size (Figure 3.11). Their disadvantage is that in order to connect the shafts, the latter must be moved apart. Couplings are used for shaft diameters not exceeding 120 mm.

Sleeve couplings:

a - with prismatic keys; b - with segment keys; in - with pins; g - with slots.

Figure 3.11.

- Flange Couplings(figure 3.12) usually consist of two coupling halves and come in two types. In one type of coupling, the bolts are installed without clearance, while the bolts work in shear. In another type of coupling, the bolts are installed with a gap. In this case, the torque is transmitted under the action of the frictional moment created by tightening the bolts.

Couplings connecting the shafts with some mutual displacement or misalignment as a result of inaccuracies in manufacturing, installation or deformation during operation are called compensatory.

There are several types of compensating couplings:

The simplest coupling consists of two half-couplings, the same as for rigid couplings, only the bolt in one of the half-couplings rests against rubber gaskets, which makes it possible to compensate for inaccuracies in the position of the shafts.

- Cross couplings are used to connect shafts when there can be large misalignments of the axes. They consist of two coupling halves, at the ends of which there are grooves. A disc is placed between the coupling halves, on the ends of which there are protrusions located perpendicular to one another. The disadvantage of these couplings is the high wear of the grooves, since during operation the middle disk moves relative to the coupling halves. Friction forces arise between the disc and the coupling halves, causing radial forces that are transmitted to the shaft.

- Articulated Couplings(Figure 3.13) is used to transfer motion between shafts located at an angle. The possibility of transmitting rotation at an angle of up to 45° is ensured by the fact that the coupling has two hinges located mutually perpendicular.

Couplings for connecting two shafts. Silly clutch.

Clutch. Cam clutch. Friction clutch. Cross cam-disc clutch ("Oldtema" clutch).

Connection of two shafts may be deaf when a long shaft, according to the conditions of manufacture and operation of the machine, is made composite, and the composite shaft must work as a whole. Such a connection is shown in Fig. 234. This is a sleeve fitted with an interference fit on the ends of the connected shafts. The bushing is mounted on the shafts and transmits the torque by means of feather keys, segment keys or taper pins.

Rice. 234 : 1 - coupling, 2 - key, 3 - shaft

clutches designed to connect and disconnect shafts. These include cam and friction clutches.

dog clutch(Fig. 235) consists of two parts mounted on the connected ends of the shafts. One coupling half is fitted tightly, the second can move along the shaft along the guide key using a special lever. When moving, the cams interlock, which ensures the transmission of torque.

Rice. 235. Cam clutch

Friction clutches(Fig. 236) provide more smooth start(due to slippage) of the driven shaft. The moment is transmitted due to the friction force between the driving and driven parts of the clutch. Friction clutches are divided into disc, conical, drum (with pads, expandable rings, tight bands or springs).

Rice. 236 friction clutch

The types of movable couplings are flexible couplings. These couplings are used to compensate for errors in the relative position of the connected shafts: center displacement, mutual inclination of the axes, axial displacement. The ability to compensate for one or another type of error depends on the design of the couplings. For example, a cam expansion clutch compensates only for axial movement, which occurs, for example, as a result of thermal deformation.

To compensate for the displacement of the shaft axes in the direction perpendicular to the axis, as well as small axial displacements, a cross coupling (Oldhem coupling) is used (Fig. 237). It consists of two half-couplings with a groove on the end surface and a middle disk with two mutually perpendicular ledges included in the grooves of the half-couplings. When rotating shafts connected by a coupling, the axes of which are offset but parallel, the protrusions of the middle disk slide along the depressions of the coupling halves. The middle disk, in addition to rotation, moves in a plane perpendicular to the axis (“floats”).