ISSN 1068-798X, Russian Engineering Research, 2017, Vol. 37, No. 7, pp. 565–567. © Allerton Press, Inc., 2017.
Original Russian Text © A.Ya. Krasil’nikov, 2017, published in Vestnik Mashinostroeniya, 2017, No. 4, pp. 3–5.
Magnetic Clutches Based on Highly Coercive Permanent Magnets
with a Small Active Length
A. Ya. Krasil’nikov
Yeltsin Ural Federal University, Yekaterinburg, Russia
Abstract—Cylindrical magnetic clutches based on highly coercive permanent magnets whose active length is
less than their width are considered. On the basis of the results, correction factors may be introduced in cal-
culating the torques transmitted by the clutches.
Keywords: magnetic clutch, half-clutch, highly coercive permanent magnet, torques, calculation methods
In the present work, methods employed for sealed
machines in radiochemistry and the chemical industry
are applied to the design of magnetic clutches based on
thin highly coercive permanent magnets whose active
length (the length of the magnet along the axis of
clutch rotation) is less than their width. In general,
magnetic clutches are used to transmit torques from an
electric motor to some mechanism through an immo-
bile barrier (screen), which is positioned in the air gap
between the magnetic half-clutches.
At present, the magnetic clutches for sealed
machines are used to transmit small torques from an
electric motor to some mechanism.
At Rosatom factories, sealed screw compressors of
special design have been developed and manufac-
tured. For one such compressor, a magnetic clutch
capable of transmitting a torque of 1.5 N m is required.
The magnetic clutch (shown in the Fig. 1) must be as
small as possible. The diameter of the seating hole in
the internal magnetic half-clutch must correspond to
the diameter of the motor shaft used in the compressor
Available experience in the development of mag-
netic clutches with highly coercive permanent mag-
nets for various sealed systems relates to standard val-
ues of the external diameter of the internal half-clutch
(the distance over the magnets): D
= 71, 90, 120, 133,
158, 180, or 233 mm .
For the clutch in the Fig. 1, however, the external
diameter of the internal half-clutch 2 is D
= 49 mm
[2, 3], while the diameter d = 50 mm [1, Table 5].
In addition, the length B of the magnet is less than
its width A. Previous calculations assumed that B is
greater than or equal to A.
Finally, the thickness of the magnet H = 7 mm,
whereas H = 10 mm in standard magnetic clutches. In
practice, such clutches have not previously been devel-
oped and manufactured.
The design of magnetic clutches involves compari-
son of the torques that they transmit with the torques
transmitted by magnetic clutches with the standard
external diameter D
of the internal half-clutch [2, 3].
Their torques are 10–15% greater than those of the
The torque transmitted by the magnetic clutch is
calculated from the formula
Here N = 4 is the number of magnets in the half-
clutch; m(x, z) is the maximum torque transmitted by
two magnets 3 opposite one another in the internal
and external half-clutches, N m;
Finally, δ is the air gap between the magnets of the
internal and external half-clutches; δ
is the grinding
depth of the magnet; and ϕ is the angle of rotation of
the external half-clutch relative to the internal half-
δ= − −
arctan 2 .