FIELD OF INVENTION
[001] The present invention is relating to a method of configuring a
permanent magnet rotor assembly for a high speed electric motor.
In particular, the present invention relates to a method of mounting
5 a permanent magnet with a supporting ring or sleeve around the
rotor body and adhesion of fibrous material with epoxy resin system.
BACKGROUND OF THE INVENTION
[002] Electrical equipment, such as electric motors or generators,
typically includes a rotor that is installed within a motor and utilized
10 to convert electrical power into mechanical power or vice versa. In
high speed motors, beside the electromagnetic and thermal design,
the mechanical aspects need to be considered. Due to permanent
magnets as source of rotor magnetic field, some advantages as: small
rotor losses, minor thermal rotor expansion and increased efficiency,
15 leads to widespread usage of the permanent magnet synchronous
machines (PMSM) in high speed applications.
[003] In case of PMSM, there are two different rotor configurations,
surface mounted magnets and buried magnets. The rotor with
surface mounted magnets uses a retaining ring or sleeve to withhold
20 the permanent magnets to the lamination stack or to the shaft. The
rotors with buried magnets means that the magnets are placed in a
slot below the outer surface of the rotor or the magnets are placed

in a carrier, which is held by high strength retaining components.
While buried permanent magnet rotor have attractive magnetic
properties, such as increased resistance to demagnetization, they
have been shown to be mechanically weaker compared to rotors with
5 surface mounted magnets, this results in limitations of rotor volume
for the same mechanical speed. The rotors with retaining ring or
sleeves present a very simple design that maximizes the magnetic
field strength and rotor volume by distributing the forces evenly
around the retaining ring or sleeve and avoiding stress
10 concentration. The operating principle of the retainer ring or sleeve
is to generate a compressive force to be applied to the permanent
magnets at all operational speed, allowing the torque transmission
among the magnets and the other rotor parts (mainly to the shaft),
and to prevent significant tensile stresses occurring in the fragile
15 permanent magnets.
[004] To generate the compressive force among the retaining ring or
sleeve and magnets an interference fit is used. Depending on the
materials used for the retaining rings or sleeves the interference fit
can be either done: by thermal shrinkage in case of metal sleeves or
20 by wrapped under tension in case of composite materials. At high
rotational speed, high centrifugal forces are exerted on the
permanent magnets. Thus, when rotors with surface mounted

magnets are used, retaining rings or sleeves must be employed to
reduce the stress in the magnets and to firmly retain the magnets in
their position.
[005] Invention US9219389B2 describes a permanent magnet
5 rotating electrical machine that includes a stator and a rotatable,
approximately cylindrical rotor. The rotor includes a shaft, rotor
cores, radial permanent magnets, and side plates. The shaft
includes projected and depressed engagement portions. The rotor
cores are separated from each other on a magnetic pole basis. The
10 rotor cores constitute circumferentially arranged pole shoes. The
radial permanent magnets are each on a circumferential side of a
pole shoe among the pole shoes. Each of the radial permanent
magnets is engaged with an engagement portion among the
engagement portions of the shaft. The side plates are on axial ends
15 of the rotor. The side plates support the rotor cores and the
permanent magnets in a radial direction of the rotor.
[006] Invention GB2518348 describes the rotor comprising a hub
having a central axis, a plurality of rotor segments and permanent
magnets, retained by lips. The segments are arranged around the
20 hub to define at least two rings, which are adjacent to each other in
the axial direction with a permanent magnet disposed between each
of the segments in each ring. The assembly includes a plurality of

rods which extend in an axial direction to retain the rotor segments,
with an intermediate plate located between each ring of segments
through which the rods pass. The rods are secures in/pass though
cavities in the end plates and pass though bores in each stator
5 segment. The magnets are supported in grooves and may be bonded
in position. The rods may be in the form of bolts threaded into the
cavities or into nuts at the outer side of the end plate. Grooves
encourage air turbulence assisting cooling.
[007] Invention US20150188369A1 describes a rotor of an electric
10 motor including a plurality of magnets arranged in a circumferential
direction. The rotor includes a holding member mounted
concentrically with the rotor and on a radially outside of the magnets
so as to hold the magnets. The holding member includes a plurality
of tubular members having different diameters and being arranged
15 concentrically with one another. The respective tubular members
have expanded diameters, and therefore, compressive holding force
acts on the magnets from the holding member, as a result of elastic
restorative force. The tubular members include tubular members
having different mechanical properties.
20 [008] Invention US8766503B2 describes an accommodating recess
having a magnet accommodating portion for accommodating a
permanent magnet and a cavity, which is located at the q-axis side
5

of the magnet accommodating portion. The cavity opens through a
rotor outer circumferential surface. A starting point of an outer
cavity forming surface is located on the rotor outer circumferential
surface. The outer cavity forming surface intersects either a
5 magnetic pole surface or an imaginary extended plane of a magnetic
pole facing surface. The rotor outer circumferential surface includes
portions of an imaginary annular line. A starting point of the outer
cavity forming surface is located between the d-axis and an
intersection point between the imaginary annular line and the
10 imaginary extended plan of the magnetic pole facing surface.
[009] The present invention differs from the practices disclosed in
the prior art. The present disclosure does not use any conventional
materials, like metal side plates. Instead, it uses fibrous sheet
material with opening/hole at certain positions to allow proper
15 wetting of epoxy resin composite and act as proper adhesive material
from one fibrous sheet to another sheet, thereby acting as single
composite body with higher mechanical strength more than the
compressive and/or centrifugal forces exerted by permanent
magnets during high speed operation of permanent magnet motor.
20 [010] In order to promote the proper adhesion between outer
surfaces of the metallic rotor body to the fibrous sheet having
openings at certain positions, the outer surface of the rotor body is
6

chemically etched with silane coupling agent. The prior art fails to
disclose a less expensive resin system for the manufacture of high
speed permanent magnet rotor with high thermal conductivity
and/or thermal expansion, which are mechanically strong and
5 which also meet the depicted high voltage insulation requirements.
OBJECTIVE OF THE INVENTION
[011] It is therefore an object of the present invention to provide a
method for manufacturing a permanent magnet excited rotor
avoiding use of any conventional materials, like metal side plates.
10 [012] Another object of the present invention is to configure a fibrous
material having multiple holes for easy penetration of epoxy resin
matrix material and to provide the good adhesion between different
adhesion layers.
[013] Another object of the present invention is to propose a method
15 of expanding retaining ring or sleeve by a liquid and applying the
liquid between the retaining ring or sleeve and the rotor body after
chemical etching with silane coupling agent to promote the proper
adhesion between outer surface of the metallic rotor body to the
fibrous sheet having openings at certain positions.
20 [014] Yet another object of the present invention is to provide a quick
and simple manufacturing, requiring less severe conditions for the
7

magnets and resulting in a rotor with better characteristics,
permitting amongst others a higher rotational speed.
[015] Further object of the present invention is to prevent the
permanent magnet from scattering by fitting a retaining ring or
5 sleeve made of a nonmagnetic material into the outer peripheral
surface of the permanent magnet fixed to the rotor core.
SUMMARY OF THIS INVENTION
[016] The present invention provides a method for manufacturing a
permanent magnet type rotating electric machine, there is one in
10 which a permanent magnet is bonded to an outer peripheral surface
of a rotor iron core (rotor core). If the permanent magnet is simply
bonded to the outer peripheral surface of the rotor core, the adhesive
cannot withstand the tensile force and/or centrifugal force during
high-speed rotation, and the permanent magnet may be scattered.
15 In order to prevent the permanent magnets from scattering, a
retaining ring/sleeve made of a nonmagnetic material is fitted into
the outer peripheral surface of the permanent magnet to fix the
permanent magnet to the rotor core. Layers of fibrous material
having multiple holes for easy penetration of epoxy resin matrix
20 material provides the good adhesion between different adhesion
layers.
8

[017] The present invention proposes a method of fixing magnet on
the surface of rotor core with the retaining ring or sleeve thereupon
and by adhesion of the liquid between the retaining ring or sleeve
and the rotor body after chemical etching with silane coupling agent
5 to promote the proper adhesion between outer surfaces of the
metallic rotor body to the fibrous sheet having openings at certain
positions.
DETAIL DESCRIPTION OF THE PRESENT INVENTION
[018] While the embodiments of the disclosure are subject to various
10 modifications and alternative forms, specific embodiment thereof is
shown by way of example in the figures and is described below. It
should be understood, however, that it is not intended to limit the
disclosure to the particular forms disclosed, but on the contrary, the
disclosure is to cover all modifications, equivalents, and alternative
15 falling within the scope of the disclosure.
[019] The terms “comprises”, “comprising”, or any other variations
thereof used in the disclosure, are intended to cover a non-exclusive
inclusion, such that a device, system, assembly that comprises a list
of components does not include only those components but may
20 include other components not expressly listed or inherent to such
system, or assembly, or device. In other words, one or more elements
in a system or device proceeded by “comprises… a” does not, without
9

more constraints, preclude the existence of other elements or
additional elements in the system or device.
[020] The present invention provides a method of providing the
retaining ring or sleeve on the outer periphery of the rotor body for
5 manufacturing a permanent magnet type rotating electric machine.
The permanent magnet is embedded to an outer peripheral surface
of a rotor iron core (rotor core). In order to prevent the permanent
magnets from scattering, a retaining ring or sleeve made of a
nonmagnetic material is fitted into the outer peripheral surface of
10 the permanent magnet to secure the fixing of the
permanent magnet to the rotor core.
[021] An outer peripheral surface of a rotor iron core is prepared by
chemical etching and/or mechanically for promoting the adhesion
between rotor iron core and the fibrous non-magnetic material. An
15 “emulsion of adhesion material” (AM) is prepared by mixing and
maintaining a weight ratio of (90-100%): (30-50%) for epoxy resin
system as di-glycidyl ether of bisphenol-A (DGEBA) and hardener
system as carboxylic acid anhydride. The said “emulsion of adhesion
material” (AM) is applied on an outer peripheral surface of a rotor
20 iron core for a thickness of about 5-20-micron size for making or
promoting the adhesion between rotor core and fibrous material.
10

[022] An “emulsion of additive or filler material” (FM) is prepared
thereafter comprising alumina. Similarly, other emulsion of additive
or filler materials can be prepared by mixing and treating the
additive or filler materials, with a functionalization agent or
5 flexibilizer for example liquid silane and a hardener for example,
carboxylic acid based anhydride, wherein a 3D mixer for mixing of
additive or filler material with functionalization agent, hardener in a
commercial Epoxy Resin system is adapted. The predetermined
weight ratio (90-100%): (5-10%): (1-5%) for hardener: flexibilizer:
10 additive/filler material in each of the additive or filler material
including the silane and hardener is applied.
[023] A “mixed liquid” (ML) is prepared containing conventional
Epoxy Resin for example bisphenol-a Epoxy Resin, flexibilizer for
example polyglycol liquid, and accelerator for example tertiary amine
15 liquid in a pre-defined ratio using a high shear mixer. The ‘mixed
liquid’ (ML) is prepared by maintaining a weight ratio of (90-100%):
(5-10%): (1-5%) for epoxy: flexibilizer: accelerator. The said
“emulsion of additive or filler material” (FM) is mixed with the “mixed
liquid” (ML) under a vacuum with pre-determined weight ratio of 1:1
20 to produce an “additive or filler-modified Epoxy Resin” emulsion
(FMER).
11

[024] The fibrous nonmagnetic material sheets are placed on outer
peripheral surface of a rotor iron core over which “emulsion of
adhesion material” (AM) is applied. The obtained “additive or filler-
modified Epoxy Resin emulsion” (FMER) is casted over the layers of
5 fibrous nonmagnetic material sheets till the required thickness of
layer of fibrous material is achieved as per the dimension or shape
of the components or specimens. During casting process, air bubble
in the composite body is removed through de-gassing.
[025] The fibrous sheets have multiple holes at certain positions to
10 allow proper wetting of epoxy resin composite by penetration
through the said holes and act as proper adhesive material from one
fibrous sheet to another sheet, thereby acting as single composite
body with higher mechanical strength more than the compressive
and/or centrifugal forces exerted by permanent magnets during
15 high speed operation of permanent magnet motor.
[026] To produce a “pre-cured additive-modified” resin body, heat
treatment of the wounded fibrous nonmagnetic material with rotor
iron core is performed in an air circulated oven in a temperature
range of 80-90oC preferably at 80oC for a period of 6-8 hours. A
20 further heat treatment is performed on the “pre-cured additive-
modified” resin body with air in an oven at a temperature range of
140o – 150oC preferably at 140oC for a period of 6 – 8 hours, which
12

produces a “fully-cured additive-modified Epoxy Resin” composite
body.
[027] In the present invention, a validation of the process is made
by testing of “additive/filler-modified Epoxy Resin” (FMER)
5 composite body obtained therefrom, for measurement of
withstanding or withholding of magnets due to exerted high tensile
or compressive or centrifugal forces under high speed operation of
rotor.
[028] The derived ‘pre-cured additive-modified’ epoxy body
10 according to the present invention, can be used as a superior
electrical insulation material in the field of high voltage insulation
system for producing numerous insulation components for indoor
and outdoor use.
[029] The retaining ring or sleeve made of a nonmagnetic material is
15 fitted into the outer peripheral surface of the permanent magnet to
fix the permanent magnet to the rotor core. The said rotor core is
configured with a fibrous material having multiple holes on its outer
surface for easy penetration of epoxy resin matrix material. It
provides the good adhesion between one layer to another fibrous
20 material layer, with the number of layers depending on the thickness
of retaining ring or sleeve made of a nonmagnetic material and also
on the design of rotor.
13

[030] It should be noted that the description and figures merely
illustrate the principles of the present subject matter. It should be
appreciated by those skilled in the art that conception and specific
embodiment disclosed may be readily utilized as a basis for
5 modifying or designing other structures for carrying out the same
purposes of the present subject matter. It should also be appreciated
by those skilled in the art that by devising various arrangements
that, although not explicitly described or shown herein, embody the
principles of the present subject matter. Furthermore, all examples
10 recited herein are principally intended expressly to be for
pedagogical purposes to aid the reader in understanding the
principles of the present subject matter and the concepts
contributed by the inventor(s) to furthering the art and are to be
construed as being without limitation to such specifically recited
15 examples and conditions. The novel features which are believed to
be characteristic of the present subject matter, both as to its
organization and method of operation, together with further objects
and advantages will be better understood from the following
description when considered in connection with the accompanying
20 figures.
[031] These and other advantages of the present subject matter
would be described in greater detail with reference to the following
figures. It should be noted that the description merely illustrates the
14

principles of the present subject matter. It will thus be appreciated
that those skilled in the art will be able to devise various
arrangements that, although not explicitly described herein, embody
the principles of the present subject matter and are included within
5 its scope. The present invention will now be described more
specifically with reference to the following specification.
[032] It should be noted that the description and figures merely
illustrate the principles of the present subject matter. It should be
appreciated by those skilled in the art that conception and specific
10 embodiment disclosed may be readily utilized as a basis for
modifying or designing other structures for carrying out the same
purposes of the present subject matter. It should also be appreciated
by those skilled in the art that by devising various arrangements
that, although not explicitly described or shown herein, embody the
15 principles of the present subject matter and are included within its
spirit and scope. Furthermore, all examples recited herein are
principally intended expressly to be for pedagogical purposes to aid
the reader in understanding the principles of the present subject
matter and the concepts contributed by the inventor(s) to furthering
20 the art and are to be construed as being without limitation to such
specifically recited examples and conditions. The novel features
which are believed to be characteristic of the present subject matter,
both as to its organization and method of operation, together with
15

further objects and advantages will be better understood from the
following description when considered in connection with the
accompanying figures.
[033] It will be understood by those within the art that, in general,
5 terms used herein, and especially in the appended claims (e.g.,
bodies of the appended claims) are generally intended as “open”
terms (e.g., the term “including” should be interpreted as “including
but not limited to,” the term “having” should be interpreted as
“having at least,” the term “includes” should be interpreted as
10 “includes but is not limited to,” etc.). It will be further understood by
those within the art that if a specific number of an introduced claim
recitation is intended, such an intent will be explicitly recited in the
claim, and in the absence of such recitation no such intent is
present. For example, as an aid to understanding, the following
15 appended claims may contain usage of the introductory phrases “at
least one” and “one or more” to introduce claim recitations. However,
the use of such phrases should not be construed to imply that the
introduction of a claim recitation by the indefinite articles “a” or “an”
limits any particular claim containing such introduced claim
20 recitation to inventions containing only one such recitation, even
when the same claim includes the introductory phrases “one or
more” or “at least one” and indefinite articles such as “a” or “an”
(e.g., “a” and/or “an” should typically be interpreted to mean “at
16

least one” or “one or more”); the same holds true for the use of
definite articles used to introduce claim recitations. In addition, even
if a specific number of an introduced claim recitation is explicitly
recited, those skilled in the art will recognize that such recitation
5 should typically be interpreted to mean at least the recited number
(e.g., the bare recitation of “two recitations,” without other modifiers,
typically means at least two recitations, or two or more recitations).
Furthermore, in those instances where a convention analogous to
“at least one of A, B, and C, etc.” is used, in general such a
10 construction is intended in the sense one having skill in the art
would understand the convention (e.g., “a system having at least one
of A, B, and C” would include but not be limited to systems that have
A alone, B alone, C alone, A and B together, A and C together, B and
C together, and/or A, B, and C together, etc.). In those instances
15 where a convention analogous to “at least one of A, B, or C, etc.” is
used, in general such a construction is intended in the sense one
having skill in the art would understand the convention (e.g., “a
system having at least one of A, B, or C” would include but not be
limited to systems that have A alone, B alone, C alone, A and B
20 together, A and C together, B and C together, and/or A, B, and C
together, etc.). It will be further understood by those within the art
that virtually any disjunctive word and/or phrase presenting two or
more alternative terms, whether in the description, claims, or
17

drawings, should be understood to contemplate the possibilities of
including one of the terms, either of the terms, or both terms. For
example, the phrase “A or B” will be understood to include the
possibilities of “A” or “B” or “A and B.”
5 [034] It will be further appreciated that functions or structures of a
plurality of components or steps may be combined into a single
component or step, or the functions or structures of one-step or
component may be split among plural steps or components. The
present invention contemplates all of these combinations. Unless
10 stated otherwise, dimensions and geometries of the various
structures depicted herein are not intended to be restrictive of the
invention, and other dimensions or geometries are possible. In
addition, while a feature of the present invention may have been
described in the context of only one of the illustrated embodiments,
15 such feature may be combined with one or more other features of
other embodiments, for any given application. It will also be
appreciated from the above that the fabrication of the unique
structures herein and the operation thereof also constitute methods
in accordance with the present invention. The present invention also
20 encompasses intermediate and end products resulting from the
practice of the methods herein. The use of “comprising” or
“including” also contemplates embodiments that “consist essentially
of” or “consist of” the recited feature.
18

[035] Although embodiments for the present subject matter have
been described in language specific to package features, it is to be
understood that the present subject matter is not necessarily limited
to the specific features described. Rather, the specific features and
5 methods are disclosed as embodiments for the present subject
matter. Numerous modifications and adaptations of the
system/device of the present invention will be apparent to those
skilled in the art, and thus it is intended by the appended claims to
cover all such modifications and adaptations which fall within the
10 scope of the present subject matter.
ADVANTAGE OF THE INVENTION
[036] The advantage of the present invention is that it provides a
method for manufacturing a permanent magnet excited rotor
without using any conventional materials, like metal side plates.
15 [037] Another advantage of the present invention is that it
configures a fibrous material having multiple holes for easy
penetration of epoxy resin matrix material and provides the good
adhesion between different adhesion layers.
[038] Another advantage of the present invention is that it proposes
20 a method of expanding retaining ring or sleeve by a liquid and
applying the liquid between the retaining ring or sleeve and the rotor
19

body after chemical etching with silane coupling agent to promote
the proper adhesion between outer surface of the metallic rotor body
to the fibrous sheet having openings at certain positions.
[039] Yet another advantage of the present invention is that it
5 provides a quick and simple manufacturing, requiring less severe
conditions for the magnets and resulting in a rotor with better
characteristics, permitting amongst others a higher rotational
speed.
[040] Further advantage of the present invention is that it prevents
10 the permanent magnet from scattering by fitting a retaining ring or
sleeve made of a nonmagnetic material into the outer peripheral
surface of the permanent magnet fixed to the rotor core.
20

We Claim :
1. A method for fixing permanent magnet on the surface of rotor
core with the adhesion of fibrous material with epoxy resin
system and retaining ring thereupon, said method comprising
5 the steps of:
applying an “emulsion of adhesion material” (AM) comprising
of an epoxy resin and a hardener system on an etched outer
peripheral surface of a rotor iron core for a thickness of (5-20)
micron;
10 performing multiple layering of a plurality of fibrous
nonmagnetic material sheets on outer peripheral surface of the
rotor iron core with applying the (AM) thereupon;
preparing an “emulsion of additive/filler material” (FM)
comprising filler/additives treated with a functionalization agent
15 or flexibilizer as liquid silane and a hardener, wherein a 3D mixer
mixes the components in a predetermined weight ratio including
the silane and the hardener;
preparing a “mixed liquid” (ML) comprising an Epoxy Resin, a
flexibilizer and an accelerator in a pre-defined ratio using a mixer;
20 casting an “additive/filler-modified Epoxy Resin emulsion”
(FMER) prepared by mixing the (FM) and the (ML) together under
a vacuum with pre-determined ratio of the two components, over
21

the layers of the fibrous nonmagnetic material sheets achieving
required thickness of layers of said fibrous materials as per the
dimension or shape of the components or specimens;
performing a heat treatment of the wounded fibrous
5 nonmagnetic material sheets with the rotor iron core in an air
circulated oven in a temperature range of 80-90oC for 6-8 hours
to produce a “pre-cured additive-modified” resin body;
performing a heat treatment of the “pre-cured additive-
modified” resin body with air in an oven at a temperature range
10 of 140_150oC for 6 – 8 hours to produce a “fully-cured additive-
modified” Epoxy Resin composite body; and
fitting a retaining ring made of a nonmagnetic material onto
the outer peripheral surface of the permanent magnet rotor
assembly for fixing the permanent magnet to the rotor core.
15 2. The method as claimed in claim 1, wherein the fully-cured epoxy
resin composite secures holding of the permanent magnets upon
the rotor body against the centrifugal forces during rotational
operation of the rotor.
3. The method as claimed in claim 1, wherein a plurality of holes on
20 the fibrous material sheet allow penetration of epoxy resin
22

composite through said holes for combining multiple layers of
said fibrous material sheets into single composite body.
4. The method as claimed in claim 1, wherein the ‘emulsion of
adhesion material’ (AM) is prepared by mixing and maintaining a
5 weight ratio of (90-100%): (30-50%) for the epoxy resin system
and the hardener system.
5. The method as claimed in claim 1, wherein the “emulsion of
additive/filler material” (FM) comprises of the hardener, the
flexibilizer and the additive/filler material in a weight ratio of (90-
10 100%): (5-10%): (1-5%).
6. The method as claimed in claim 1, wherein the ‘mixed liquid’ (ML)
comprises of the Epoxy Resin, the flexibilizer and the accelerator
in a weight ratio of (90-100%): (5-10%): (1-5%).
7. The method as claimed in claim 1, wherein the “filler-modified
15 Epoxy Resin emulsion” (FMER) comprises of the (ML) mixed with
the (FM) in a weight ratio of 1:1.
8. The method as claimed in claim 1, wherein the performance of
casting an “additive/filler-modified Epoxy Resin emulsion”
(FMER) over the layers of the fibrous nonmagnetic material
20 sheets ensures removal of an air bubble in the composite body
through de-gassing.