Electromagnetic clutch

Electromagnetic clutches operate electrically, but trans- 1.1.2 Disengagement

mit torque mechanically. This is why they used to be re-
ferred to as electro-mechanical clutches. Over the years, When current is removed from the clutch, the armature is
EM became known as electromagnetic versus electro me- free to turn with the shaft. In most designs, springs hold
chanical, referring more about their actuation method the armature away from the rotor surface when power is
versus physical operation. Since the clutches started be- released, creating a small air gap.
coming popular over 60 years ago, the variety of applica-
tions and clutch designs has increased dramatically, but
the basic operation remains the same. 1.1.3 Cycling
Single-face clutches make up approximately 90% of all Cycling is achieved by interrupting the current through
electromagnetic clutch sales. the electromagnet. Slippage normally occurs only during
The electromagnetic clutch is most suitable for remote acceleration. When the clutch is fully engaged, there is
operation since no linkages are required to control its en- no relative slip, assuming the clutch is sized properly, and
gagement. It has fast, smooth operation. However, be- thus torque transfer is 100% efficient.
cause energy dissipates as heat in the electromagnetic ac-
tuator every time the clutch is engaged, there is a risk
of overheating. Consequently, the maximum operating 2 Applications
temperature of the clutch is limited by the temperature
rating of the insulation of the electromagnet. This is a
major limitation. Another disadvantage is higher initial 2.1 Machinery
cost.
This type of clutch is used in some lawnmowers, copy ma-
chines, and conveyor drives. Other applications include
packaging machinery, printing machinery, food process-
ing machinery, and factory automation.
1 Friction-plate clutch

For more and detailed information, please see Friction- 2.2 Automobiles
plate electromagnetic couplings
When the electromagnetic clutch is used in automobiles,
there may be a clutch release switch inside the gear lever.
A friction-plate clutch uses a single plate friction surface
The driver operates the switch by holding the gear lever
to engage the input and output members of the clutch.
to change the gear, thus cutting off current to the elec-
tromagnet and disengaging the clutch. With this mecha-
nism, there is no need to depress the clutch pedal. Alter-
1.1 How it works natively, the switch may be replaced by a touch sensor or
proximity sensor which senses the presence of the hand
near the lever and cuts off the current. The advantages of
1.1.1 Engagement using this type of clutch for automobiles are that compli-
cated linkages are not required to actuate the clutch, and
When the clutch is actuated, current flows through the the driver needs to apply a considerably reduced force to
electromagnet producing a magnetic field. The rotor por- operate the clutch. It is a type of semi-automatic trans-
tion of the clutch becomes magnetized and sets up a mag- mission.
netic loop that attracts the armature. The armature is
pulled against the rotor and a frictional force is gener- Electromagnetic clutches are also often found in AWD
ated at contact. Within a relatively short time, the load is systems, and are used to vary the amount of power sent
accelerated to match the speed of the rotor, thereby en- to individual wheels or axles.
gaging the armature and the output hub of the clutch. In A smaller electromagnetic clutch connects the air condi-
most instances, the rotor is constantly rotating with the tioning compressor to a pulley driven by the crankshaft,
input all the time. allowing the compressor to cycle on only when needed.

1
2 3 OTHER TYPES OF ELECTROMAGNETIC CLUTCHES

2.3 Locomotives 3.2 Electromagnetic tooth clutches

Electromagnetic clutches have been used on diesel loco-
motives, e.g. by Hohenzollern Locomotive Works.

3 Other types of electromagnetic

clutches

3.1 Multiple disk clutches

Electromagnetic tooth clutch

Introduction – Of all the electromagnetic clutches, the

tooth clutches provide the greatest amount of torque in
the smallest overall size. Because torque is transmitted
without any slippage, clutches are ideal for multi stage
machines where timing is critical such as multi stage
Multiple disk clutch
printing presses. Sometimes, exact timing needs to be
Introduction – Multiple disk clutches are used to deliver kept, so tooth clutches can be made with a single position
extremely high torque in a relatively small space. These option which means that they will only engage at a spe-
clutches can be used dry or wet (oil bath). Running the cific degree mark. They can be used in dry or wet (oil
clutches in an oil bath also greatly increases the heat dis- bath) applications, so they are very well suited for gear
sipation capability, which makes them ideally suited for box type drives.
multiple speed gear boxes and machine tool applications. They should not be used in high speed applications or ap-
plications that have engagement speeds over 50 rpm oth-
How it works – Multiple disk clutches operate via an elec-
trical actuation but transmit torque mechanically. When erwise damage to the clutch teeth would occur when try-
ing to engage the clutch.
current is applied through the clutch coil, the coil be-
comes an electromagnet and produces magnetic lines of How it works – Electromagnetic tooth clutches operate
flux. These lines of flux are transferred through the small via an electric actuation but transmit torque mechanically.
air gap between the field and the rotor. The rotor portion When current flows through the clutch coil, the coil be-
of the clutch becomes magnetized and sets up a magnetic comes an electromagnet and produces magnetic lines of
loop, which attracts both the armature and friction disks. flux. This flux is then transferred through the small gap
The attraction of the armature compresses (squeezes) the between the field and the rotor. The rotor portion of the
friction disks, transferring the torque from the in inner clutch becomes magnetized and sets up a magnetic loop,
driver to the out disks. The output disks are connected which attracts the armature teeth to the rotor teeth. In
to a gear, coupling, or pulley via drive cup. The clutch most instances, the rotor is consistently rotating with the
slips until the input and output RPMs are matched. This input (driver). As soon as the clutch armature and rotor
happens relatively quickly typically (0.2 - 2 sec). are engaged, lock up is 100%.
When the current is removed from the clutch, the arma- When current is removed from the clutch field, the ar-
ture is free to turn with the shaft. Springs hold the friction mature is free to turn with the shaft. Springs hold the
disks away from each other, so there is no contact when armature away from the rotor surface when power is re-
the clutch is not engaged, creating a minimal amount of leased, creating a small air gap and providing complete
drag. disengagement from input to output.
 3

3.3 Electromagnetic particle clutches

Main article: magnetic particle clutch
Introduction – Magnetic particle clutches are unique in

Hysteresis powered clutch

transmitted magnetically, there is no contact, so no wear

occurs to any of the torque transfer components providing
Electromagnetic particle clutch
for extremely long life.
When the current is applied, it creates magnetic flux. This
their design, from other electro-mechanical clutches be- passes into the rotor portion of the field. The hysteresis
cause of the wide operating torque range available. Like disk physically passes through the rotor, without touch-
a standard, single face clutch, torque to voltage is almost ing it. These disks have the ability to become magnetized
linear. However, in a magnetic particle clutch torque can depending upon the strength of the flux (this dissipates as
be controlled very accurately. This makes these units ide- flux is removed). This means, as the rotor rotates, mag-
ally suited for tension control applications, such as wire netic drag between the rotor and the hysteresis disk takes
winding, foil, film, and tape tension control. Because of place causing rotation. In a sense, the hysteresis disk is
their fast response, they can also be used in high cycle pulled after the rotor. Depending upon the output torque
application, such as card readers, sorting machines, and required, this pull eventually can match the input speed,
labeling equipment. giving a 100% lockup.
How it works – Magnetic particles (very similar to iron When current is removed from the clutch, the armature is
filings) are located in the powder cavity. When current free to turn and no relative force is transmitted between
flows through the coil, the magnetic flux that is created either member. Therefore, the only torque seen between
tries to bind the particles together, almost like a mag- the input and the output is bearing drag.
netic particle slush. As the current is increased, the mag-
netic field builds, strengthening the binding of the parti-
cles. The clutch rotor passes through the bound particles, 4 See also
causing drag between the input and the output during ro-
tation. Depending upon the output torque requirement,
• Electromagnetic brake
the output and input may lock at 100% transfer.
When current is removed from the clutch, the input is • Magnetic coupling
almost free to turn with the shaft. Because the mag-
netic particles remain in the cavity, all magnetic particle
clutches have some minimum drag. 5 References
W. Pelczewski: SPRZEGLA ELEKTROMAGNETY-
3.4 Hysteresis-powered clutch CZNE (Polisch original edition); German Edition: Elek-
tromagnetische Kupplung, Kapitel: Elektromagnetische
Electrical hysteresis units have an extremely high torque Induktionskuppling; Vieweg 1971, ISBN 3 528 04906 5
range. Since these units can be controlled remotely, they
are ideal for testing applications where varying torque is
required. Since drag torque is minimal, these units offer
the widest available torque range of any electromagnetic
6 External links
product. Most applications involving powered hysteresis
units are in test stand requirements. Since all torque is
4 7 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

7 Text and image sources, contributors, and licenses

7.1 Text
• Electromagnetic clutch Source: https://en.wikipedia.org/wiki/Electromagnetic_clutch?oldid=680456208 Contributors: Hooperbloob, Dr-
breznjev, Woohookitty, Mindmatrix, MZMcBride, RussBot, Dspradau, Mdwyer, Ma8thew, Gilliam, Fletcher, Cydebot, Alaibot, AnAj,
Destynova, Choppingmall, CommonsDelinker, The Discoverer, Inwind, Funandtrvl, Andy Dingley, Typ932, Neparis, Biscuittin, Dwandelt,
Wdwd, Mild Bill Hiccup, Skarebo, Addbot, Magus732, Gail, Yobot, FEAR6655, LilHelpa, Jackshotton, Prari, Oguraclutch, BenzolBot,
Denzil Simoes, Vrenator, OIC1998, Dotoree, TyA, ClueBot NG, Strike Eagle, Sensenschmied, Hebert Peró, The Quixotic Potato and
Anonymous: 22

7.2 Images
• File:B-1_electromagnetic-clutch1.gif Source: https://upload.wikimedia.org/wikipedia/commons/7/7b/B-1_electromagnetic-clutch1.
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Clutch.png License: Public domain Contributors: Own work Original artist: Oguraclutch
• File:Electromagnetic_Tooth_Clutch.png Source: https://upload.wikimedia.org/wikipedia/commons/0/06/Electromagnetic_Tooth_
Clutch.png License: Public domain Contributors: Own work Original artist: Oguraclutch
• File:Hysteresis_Clutch.gif Source: https://upload.wikimedia.org/wikipedia/commons/9/90/Hysteresis_Clutch.gif License: Public do-
main Contributors: Own work Original artist: Oguraclutch
• File:Multiple_Disk_Clutch.gif Source: https://upload.wikimedia.org/wikipedia/commons/6/60/Multiple_Disk_Clutch.gif License:
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