Electromagnetic clutch designed to transmit torque of the engine to the working mechanism. The principle of their operation is based on electromagnetic properties bind the elements. The coupling consists of two parts: leading and driven, which form a closed magnetic system.

Below we consider three types of electromagnetic clutches, received the greatest application to ACS: friction (contact and contactless), powder and asynchronous (the slip clutch).

Incontact electromagnetic friction clutch the transmission of torque from the leading half coupling on output occurs due to the friction forces between the contacting surfaces of the friction discs, one of which is located at the leading coupling half, and the other on slave.  These discs are made of a material with a high coefficient of friction.

 The device of the electromagnetic clutch shown in figure 1 via slip rings2 and brushes4 tension control clutchU_in is supplied to the coil5. The resulting current in the coil induces in the magnetic system of the coupling flux f. Closed in the anchor, serving as a leading hub9, this thread will create it traction. Fastening anchors (leading coupling half) on the shaft is, it allows a small axial movement. As a result, the anchor9, overcoming the resistance of the return spring7, resting in the ring6, will gravitate to the core1(leading coupling half) and surface friction discs10 grasp. In this case, the rotation from the drive shaft8 is transmitted to the driven shaft3 due to friction forces between the friction discs.

 

Figure 1 Electromagnetic friction clutches

If you need to disconnect the coupling, remove the voltage from contact brushes. Under the action of the spring7 anchor to shift to the right, and the surface of the friction discs will open and the rotation of the driven shaft be stopped. To increase the transmitted torque in some designs use multiple pairs of friction disks, a number of the more, the more torque.

The main drawback of the considered coupling – the presence of sliding contact "brushes – slip rings", which reduces the reliability of the coupling.

Contactless electromagnetic friction clutch consists of three main elements, figure 2. Fixed element2 with coil3 seated on the output shaft through the bearing1. With this design in the transmission of rotation to the driven shaft, this part of the coupling remains stationary, allowing the coil3 directly to include in the network, without using sliding contacts, as in contact the friction clutch, figure 1 Item5 is a leading hub, planted on the drive shaft by a key6. The design of this element is similar to the leading tooth clutch slip clutch contact, ie. it has the possibility of a small axial movement, overcoming the resistance of the return spring. Item4 consider the intermediate clutch is able thanks to the key7 to transmit rotation to the driven shaft, ie. this element is a driven coupling half. When you turn the coil3 in the network of the magnetic system of the coupling, composed of three elements, excited by a magnetic flux f, closing the contour of f that creates the master hub5, which is the anchor of the electromagnet, traction, which shifts the coupling to the left along drive shaft. Friction discs are closed, and the rotating moment from the drive shaft is transmitted to the driven shaft. So that the magnetic flux is not confined in the intermediate element4, that would break the clutch, this item has a "window" around the perimeter of the cylindrical coil3. When removing the voltage coil3 the pulling force disappears and under the action of the return spring (not shown in the figure) item5 moves to the right, friction discs opens.

To reduce magnetic losses in rotating parts of the contactless coupling these parts sometimes make laminated. Contactless electromagnetic coupling more difficult and expensive contact, but the absence of sliding contact makes it more reliable.

Industry produces the electromagnetic clutches series Э1ТМ. Couplings are intended for inclusion in the network DC voltage 24 In and has degree of protection IP00.

Key features of electromagnetic clutches: Torque - the torque transmitted by; n_nom – rated speed; n_max – the maximum allowable rotational speed; P₂₀ – power, consumed by the solenoid coil in a cold state (at a temperature of 20° C).

 

Figure 2 Contactless electromagnetic friction clutch

Power consumption contactless couplers more, than contact, due to the presence of two air gaps in the non-contact couplings.

The operating principle of magnetic powder clutch based on a property of liquid or powdered ferromagnetic substances (filler coupling) under the action of the magnetic field to increase its viscosity and stick to the walls of magnetized elements. In Khakimov principle of powder clutch is a friction. However, unlike last, the transmission of torque from the drive part to the driven clutch powder clutch is not at the expense of friction forces of the compressed surfaces, but at the expense of increasing the viscosity of the ferromagnetic filler coupling.  

Figure 3 shows the device pin powder clutch.

 

Figure 3 Electromagnetic powder clutch

The leading part of the clutch consists of gear wheel1, a hollow ferromagnetic steel cylinder3 and covers7. Driven part of the clutch consists of a driven shaft9, which is rigidly secured ferromagnetic core2 with coil4. Power to the coil is supplied through slip rings8 and brushes. Wire, connecting ring8 with coil4, laid on the surface of the shaft9. When voltage is applied to the coil magnetic flux f, confined in the magnetic core, passes through the air gap, separating driver and driven parts of the coupling. This gap is filled with a mixture of, containing powdered ferromagnetic material5 .When you turn off the coil4this mixture creates almost no connection between leading and driven parts of the clutch. When the coil current appears in the magnetic circuit, a magnetic flux f, ferromagnetic particles5, filling the gap, magnetized and create a rigid connection between the parts of the clutch. As a result, the rotation of the leading part of the coupling is transmitted to the driven shaft9. Seals6 to hold the filler in the working volume.

With its high performance (ferromagnetic mixture is practically instantaneous), what is the advantage of powder clutch, these couplers have the disadvantage, due to the complexity of the design: the need to protect bearings from the ingress of powder and periodic replacement of ferromagnetic filler due to its gradual "aging" and loss of ferromagnetic properties.

Asynchronous electromagnetic clutch consists of inductor6 with the excitation coil3 on the driven shaft5 and anchors2 the drive shaft 1, figure 4,and. Coil is powered from a DC source via slip rings (insulated from the shaft and from each other) and brushes4. anchor2 rotates with the driving shaft1 in the magnetic field of the inductor. When this magnetic field induces in a robust anchor2 eddy currents. As a result of the interaction of these currents with the field of the inductor on the inductor occurs torque, directed in the direction of rotation of the armature. By this point, the inductor comes into rotation, ie. the rotation of the armature is transmitted to the inductor. Torque, transferred thus from the armature to the inductor, is asynchronous, ie. in the clutch is slipping, and therefore, the rotational speed of the driven shaftn₂ is always less than the frequency of rotation of the drive shaftn₁, since only under this condition the armature induced eddy currents.

The properties of the described electromagnetic coupling is largely similar to the properties of the induction motor and define its mechanical characteristics figure 5.10,b. With increase in static load torqueM_with on the driven shaft speed is reduced. The mechanical characteristic of the coupling is soft and the dependence of the frequency of rotation of the load in the asynchronous coupling is more significant, than the asynchronous motor.

 

Figure 4 Asynchronous electromagnetic clutch

Changing the current in the inductorI_in you can change the frequency of rotation of the driven shaft. If the load torque of the drive mechanism is greater than the maximum torque of the coupling, there is a roll – rotation of the driven part is stopped. Thanks to the ability to rollover the coupling can protect the drive motor from overloading large. The advantages of such a drive with a clutch are the simplicity of the device and operation, low cost, high reliability. But with the increase in slip losses is increasing the capacity and efficiency of the drive decreases.

In order to increase efficiency in some designs anchored asynchronous couplings comprise a short-circuited coil2, similar to the rotor winding of the induction motor, and the cores of the inductor1 and anchors make laminated, figure 5.

Dignity clutch: the smoothness of the transmission Khakimov torque moment on output shaft; simple design, the possibility of regulation of frequency of rotation of the driven shaft, the lack of wear parts.

Disadvantages clutch: low efficiency due to significant losses on eddy currents, low mass-dimension indicators.

Figure 5 Asynchronous coupling with a short-circuited winding