U.S. patent application number 10/002786 was filed with the patent office on 2003-05-08 for permanent magnet retaining arrangement for high speed rotors.
Invention is credited to Franco, Alberto, Gheorghiu, Michael, Pappas, Spyro, Van Dine, Pieter.
Application Number | 20030085629 10/002786 |
Document ID | / |
Family ID | 21702506 |
Filed Date | 2003-05-08 |
United States Patent
Application |
20030085629 |
Kind Code |
A1 |
Van Dine, Pieter ; et
al. |
May 8, 2003 |
Permanent magnet retaining arrangement for high speed rotors
Abstract
In the embodiments described in the specification, permanent
magnets are retained on a permanent magnet rotor rim by inverted
U-shaped retainers and in one embodiment the outer surfaces of the
retainers converge inwardly in the radially outward direction and
engage corresponding surfaces of adjacent pole pieces which
converge inwardly in the radially outward direction. In another
embodiment the U-shaped retainers are affixed to the rotor rim by
screws accessible through openings in the radially outer wall of
the retainers and a further embodiment each retainer has outwardly
projecting flanges which are affixed to the rotor rim by
screws.
Inventors: |
Van Dine, Pieter; (Mystic,
CT) ; Franco, Alberto; (Hazlet, NJ) ; Pappas,
Spyro; (Fort Lee, NJ) ; Gheorghiu, Michael;
(Forest Hills, NY) |
Correspondence
Address: |
BAKER & BOTTS
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
|
Family ID: |
21702506 |
Appl. No.: |
10/002786 |
Filed: |
November 2, 2001 |
Current U.S.
Class: |
310/156.08 |
Current CPC
Class: |
H02K 1/2773
20130101 |
Class at
Publication: |
310/156.08 |
International
Class: |
H02K 021/12 |
Claims
We claim:
1. A permanent magnet rotor arrangement comprising: a rotor having
a rim; a circumferential array of pole pieces made of magnetic
material affixed to the rotor rim; an inverted U-shaped magnet
retainer made of nonmagnetic material and formed with a channel
mounted between each adjacent pair of pole pieces; and at least one
permanent magnet inserted into the channel formed in each U-shaped
retainer.
2. A permanent magnet rotor arrangement according to claim 1
wherein each adjacent pair of pole pieces has surfaces facing the
U-shaped magnet retainer which converge inwardly in the radially
outward direction and the U-shaped retainer has corresponding outer
surfaces which converge inwardly in the radially outward direction
and engage the inwardly converging surfaces of the pole pieces.
3. A permanent magnet rotor arrangement according to claim 1
wherein the U-shaped permanent magnet retainer is affixed to the
rotor rim by a mechanical attachment.
4. A permanent magnet rotor arrangement according to claim 3
wherein the mechanical attachment comprises screws.
5. A permanent magnet rotor arrangement according to claim 4
wherein the U-shaped magnet retainer has projecting flanges
engaging a rim portion and the adjacent pole pieces extend in the
angular direction over the projecting flanges.
6. A permanent magnet rotor arrangement according to claim 1
including an outer wrap of fiber-reinforced polymer material
surrounding the rotor.
7. A permanent magnet rotor arrangement according to claim 1
wherein the pole pieces are mechanically connected to corresponding
rim portions by bolts.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to arrangements for retaining
permanent magnets radially in position in permanent magnet rotors
for electric machines operating at high speed.
[0002] Conventional arrangements for retaining magnets in position
in rotors for electric machines include slot wedges which span the
distance between adjacent pole pieces across the radially outer
surface of the magnets. Such arrangements have limited centrifugal
load carrying capability.
[0003] The Burson U.S. Pat. No. 4,179,634 discloses a magneto rotor
having permanent magnets which are retained in a cavity formed in
the rotor by pole pieces disposed on opposite sides of the magnet
and retained by retaining pins received in axially extending slots
in the pole pieces.
[0004] The U.S. Pat. No. 2,516,901 to Morill discloses a permanent
magnet rotor having a hub to which permanent magnets are affixed by
screws engaging shoulders on the magnets. In addition, rings may be
cast around the shoulders of the magnets and the screws to assist
in retaining the magnets on the hub.
[0005] In the magneto shown in the Iwata et al. U.S. Pat. No.
5,811,908, U-shaped permanent magnet retention channels made of
magnetic material have projections at the outer ends of the walls
which are received in corresponding grooves in adjacent pole
pieces.
[0006] According to the Tomite et al. U.S. Pat. No. 4,745,319,
permanent magnets are secured to the inner surface of a surrounding
yoke by attaching one surface of a U-shaped elastic retainer member
to the inner surface of the yoke and attaching the ends of the
U-shaped retainer to edges of adjacent magnets which are to be
retained in the yoke.
SUMMARY OF THE INVENTION
[0007] Accordingly, it is an object of the present invention to
provide a retaining arrangement for permanent magnets in a rotor
for an electric machine which overcomes disadvantages of the prior
art.
[0008] Another object of the invention is to provide a retaining
arrangement for permanent magnets by which they are secured
effectively in the radial direction during high speed operation of
a rotor.
[0009] These and other objects of the invention are attained by
providing a retaining arrangement in which permanent magnets are
retained in a permanent magnet rotor by U-shaped retainers
supported from a rotor rim, the retainers being made of nonmagnetic
material and having a smooth channel to receive magnets and provide
radial support. In one embodiment the U-shaped retainers have
laterally outer surfaces which converge inwardly in the radially
outward direction and the adjacent opposed pole pieces, which are
affixed to the rotor rim, have corresponding lateral surfaces which
converge inwardly in the radially outward direction. In another
embodiment, the U-shaped retainer is connected to the rotor rim by
fasteners such as screws.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Further objects and advantages of the invention will be
apparent from a reading of the following description in conjunction
with the accompanying drawings in which:
[0011] FIG. 1 is a schematic perspective view illustrating a
representative embodiment of a permanent magnet rotor for an
electric machine having a magnet retaining arrangement in
accordance with the invention;
[0012] FIG. 2 is an enlarged fragmentary view of the magnet
retaining arrangement shown in FIG. 1.;
[0013] FIG. 3 is a cross sectional view showing the shape of the
magnet retainer used in the arrangement shown in FIGS. 1 and 2;
[0014] FIG. 4 is a fragmentary cross sectional view illustrating a
permanent magnet rotor having an alternative magnet retaining
arrangement in accordance with the invention; and
[0015] FIG. 5 is a fragmentary cross sectional view showing a
permanent magnet rotor having still another embodiment of a magnet
retaining arrangement in accordance with the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0016] In the representative embodiment of the invention
illustrated in FIGS. 1-3, a rotor 10 has a shaft 12 connected to an
outer rim 14 by an array of angularly spaced inclined blades 16
forming a rim-driven propeller which may be used, for example, in a
propulsion pod. A spaced circumferential array of pole pieces 18,
made of laminated magnetic material in the conventional manner is
mechanically attached to the rim by key members 20 held by screws
22.
[0017] Between each adjacent pair of pole pieces 18 a magnet 24 is
held in position by a slot wedge 26 made of nonmagnetic material
and having grooves 28 in its opposite edges to receive projections
30 of the adjacent pole pieces 18.
[0018] In order to facilitate radial retention of the magnets 24
during high speed rotation of the rotor 10, an inverted U-shaped
retainer 32, also made of nonmagnetic material, is located in the
space between each magnet 24 and the adjacent surfaces of the pole
pieces 18 and the slot wedge 26. As best seen in FIG. 3, the
U-shaped retainer 32 has rectangularly arranged inner surfaces 34
and 36 to conform to the rectangular periphery of the magnet 24 and
is formed with a radially outer surface 38 which engages the
radially inner surface 40 of the adjacent slot wedge 26 and with
circumferentially outer surfaces 44 which converge inwardly in the
radially outward direction to conform to corresponding inwardly
converging surfaces 46 of the adjacent pole pieces 18 to facilitate
retention of the U-shaped retainer 32 and the magnet 24 enclosed
therein during high speed rotation of the rotor 10.
[0019] In addition, a circumferential outer wrap 50 of
fiber-reinforced polymer material surrounds the entire peripheral
surface of the entire rotor structure. With this arrangement, the
magnet retention is facilitated by the engaging angled surfaces 44
and 46 of the U-shaped retainer and the pole pieces as well as the
fiber-reinforced polymer wrap 50.
[0020] In the alternative embodiment illustrated in the fragmentary
view of FIG. 4, a rotor 60 has an outer rim 62 to which nonmagnetic
U-shaped magnet retainers 66 are affixed by screws 68 accessible
through holes 70 formed in the top wall 72 of the retainers.
Permanent magnets 76 are inserted longitudinally into the channels
formed in the U-shaped retainers. Pole pieces 80 between each
adjacent pair of magnet retainers 66 are secured to the rim 62 by
opposed jaws 82 projecting from the rim 62 to receive a
correspondingly shaped portion 84 of the pole piece 80 which may be
retained securely in position by a bolt 86 extending through the
jaws and the portion 84.
[0021] In the further embodiment schematically shown in FIG. 5, a
rotor 90 has a peripheral rim 94 to which pole pieces 96 are
secured by opposed jaws 98 and a bolt 100 in the manner described
with respect to FIG. 4. In this case, nonmagnetic U-shaped magnet
retainers 104 have angularly projecting flanges 106 which are
fastened to corresponding surfaces 108 of the rim 94 by screws 110
before the pole pieces are mounted on the rim. The U-shaped
retainers have access openings 112 through which the bolts 100 can
be inserted to retain the pole pieces after the retainers 104 have
been secured to the rim 94. Thereafter, permanent magnets 116 are
inserted into channels 118 formed by the retainers 104. With this
arrangement, the magnets 116 and their retainers 104 are securely
held in position during high speed rotation by the screws 110 as
well as by the pole pieces 96 and their retaining bolts 100. The
outer surface of the rotor may be enclosed by a fiber-reinforced
polymer wrap 120 as in the other embodiments.
[0022] Although the invention has been described herein with
reference to specific embodiments, many modifications and
variations therein will readily occur to those skilled in the art.
Accordingly, all such variations and modifications are included
within the intended scope of the invention.
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