U.S. patent number 3,818,586 [Application Number 05/181,025] was granted by the patent office on 1974-06-25 for method of making an assembly of alternator magnet blocks with engine flywheel.
This patent grant is currently assigned to Briggs & Stratton Corporation. Invention is credited to Joseph R. Harkness, Leo J. Lechtenberg, John D. Santi.
United States Patent |
3,818,586 |
Harkness , et al. |
June 25, 1974 |
METHOD OF MAKING AN ASSEMBLY OF ALTERNATOR MAGNET BLOCKS WITH
ENGINE FLYWHEEL
Abstract
To secure magnet blocks for an alternator in a cup-shaped
flywheel, the inner surface of the flywheel side wall is coated
with epoxy and an annular cage is axially inserted into the well in
the flywheel. The cage cooperates with inner flywheel surfaces to
define radially inwardly opening pockets, into each of which a
block is inserted. A tool is disclosed for forcing the blocks
radially outwardly to desired positions in which they are held by a
fixture while the epoxy is cured.
Inventors: |
Harkness; Joseph R.
(Germantown, WI), Santi; John D. (West Allis, WI),
Lechtenberg; Leo J. (Elm Grove, WI) |
Assignee: |
Briggs & Stratton
Corporation (Wauwatosa, WI)
|
Family
ID: |
22662590 |
Appl.
No.: |
05/181,025 |
Filed: |
September 16, 1971 |
Current U.S.
Class: |
29/598;
74/572.21; 29/732; 156/293; 156/297; 310/45; 310/153; 310/262 |
Current CPC
Class: |
H02K
15/03 (20130101); Y10T 74/2132 (20150115); Y10T
29/49012 (20150115); Y10T 156/1089 (20150115); Y10T
29/53143 (20150115) |
Current International
Class: |
H02K
15/03 (20060101); H02k 015/02 () |
Field of
Search: |
;29/598,25R
;310/153,156,262,45 ;156/293,297 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lanham; Charles W.
Assistant Examiner: Hall; Carl E.
Claims
The invention is defined by the following claims:
1. The method of assembling a rotor that can serve as the flywheel
of a reciprocating engine and as the moveable element of a
dynamoelectric machine, and which rotor comprises a body having an
annular magnetically permeable wall and a plurality of block-like
permanent magnets fixed to the body in circumferentially spaced
relation to one another and defining a magnet ring adjacent to the
radially inner surface of said wall, which method comprises:
A. forming an annular cage of nonmagnetic material comprising
1. a ring having a diameter to be embraced by said annular wall and
to overlie one axially facing surface of each of the magnets,
and
2. a plurality of spacer portions, equal in number to the number of
magnets, extending in one axial direction from said ring and
circumferentially spaced apart by distances to receive a magnet
between each circumferentially adjacent pair of spacer
portions;
B. coating the inner surface of said annular wall with a hardenable
liquid bonding agent;
C. inserting the cage axially into said annular wall with the cage
in a predetermined rotational orientation relative to the body;
D. inserting the magnets radially into the spaces between said
spacer portions of the cage and bringing them to positions at which
they are within a distance from the annular wall which is small
enough so that there is only a thin, uniform layer of bonding agent
between each magnet and said wall; and
E. maintaining the magnets in said positions while hardening the
bonding agent.
Description
This invention relates to a rotor having a body which can comprise
an engine flywheel and which carries a plurality of block-like
permanent magnets for rotation with the body to cooperate with
stationary elements of a dynamoelectric machine; and the invention
is more particularly concerned with a method and means for securing
permanent magnet blocks to such a rotor body in a predetermined
relationship to it and to one another.
In many small gasoline engine applications it is desired to have an
alternator that is powered by the engine to provide a source of
current for charging a starter battery or for energizing headlights
or the like. In such installations the alternator often comprises a
ring of block-like permanent magnets carried by the engine flywheel
for cooperation with a core and windings that are stationary on the
engine body at a location adjacent to the flywheel. The flywheel in
such cases is made of cast-iron, so that it not only has sufficient
mass for its flywheel function but is also magnetically permeable
to provide flux paths between the permanent magnets that it
carries. Usually, too, the flywheel body is cup-shaped, with a
front end wall and a generally cylindrical side wall that enclose
the stationary elements of the alternator, and the permanent
magnets are mounted in a ring around the inner surface of its side
wall.
Various methods and means have heretofore been proposed for
securing the several permanent magnet blocks to a flywheel body to
provide a rotor assembly of the above described character, but all
of these prior expedients have had the disadvantage of being
relatively costly.
For example, U.S. Pat. No. 3,390,291, to Eberline et al., discloses
a procedure in which a multiple-member die or mold is used to form
a cast ring in which the magnet blocks are embedded to hold them in
a desired circumferentially spaced relationship to one another. The
cast ring is inserted into the flywheel body after the latter has
been heated to expand it. Then, after the flywheel body has cooled
to shrink into tight engagement with the ring, the inner surface of
the ring is machined to expose magnet shoes associated with the
magnets. This procedure, involving a multiplicity of operations and
relatively expensive molding equipment, as well as waste of metal
that is machined away, is obviously expensive.
U.S. Pat. No. 3,265,913, to I. J. Irwin, discloses an assembly
procedure involving a substantially larger number of parts than
that of the Eberline et al patent, and wherein the magnets are held
assembled with one another and with the flywheel body by means of
an arrangement of clamping rings, screws and other fasteners. While
the expedient of the Irwin patent avoids the need for casting and
machining operations, the multiplicity of parts involved and the
complexity of the assembly are such that the Irwin rotor is in the
same cost area as that of Eberline et al.
By contrast with these prior expedients, it is the general object
of this invention to provide a rotor comprising a flywheel body or
the like and a plurality of block-like permanent magnets that are
secured to the body in a ring at circumferentially spaced intervals
therearound, which rotor can be manufactured at substantially lower
cost than any heretofore available.
More specifically, it is an object of this invention to provide a
rotor of the character described that is very low in cost by reason
of the fact that it incorporates a very minimum number of
relatively simple parts and requires for its manufacture a very
small number of operations, all of which can be performed very
quickly and easily by relatively unskilled labor and with the use
of simple and inexpensive tools and equipment.
Another object of this invention is to provide a method and means
for assembling individual block-like permanent magnets directly
into a cup-shaped rotor body such as an engine flywheel, to dispose
the magnets in the proper relationship to the body in the very act
of assembling them into a ring, thus avoiding the necessity for
first assembling the magnets with one or more other components to
provide a magnet ring that must subsequently be installed in the
body.
Another object of this invention is to provide very simple and
inexpensive means for properly locating magnet blocks in a desired
relationship to one another and to a rotor body during an easily
performed assembly operation, and for holding them in that
relationship during the curing of an adhesive material by which the
blocks are directly bonded to the rotor body.
It is also an object of this invention to provide a method and
means for assembling permanent magnet blocks into an annular or
cup-shaped rotor body, and for securing them therein, whereby such
assembly can be accomplished in operations that are so simple and
small in number as to be well adapted to being performed in whole
or in substantial part with automated equipment.
With these observations and objectives in mind, the manner in which
the invention achieves its purpose will be appreciated from the
following description and the accompanying drawings, which
exemplify the invention, it being understood that changes may be
made in the specific apparatus disclosed herein without departing
from the essentials of the invention set forth in the appended
claims.
The accompanying drawings illustrate two complete examples of
embodiments of the invention constructed according to the best
modes so far devised for the practical application of the
principles thereof, and in which:
FIG. 1 is a disassembled perspective view of a rotor embodying the
principles of this invention;
FIG. 2 is a plan view of the rotor in partially assembled
condition;
FIG. 3 is a view, partially in side elevation and partially in
axial section, showing the rotor assembled with a tool that is
employed for forcing the magnet blocks to their desired
positions;
FIG. 4 is a sectional view taken on the plane of the line 4--4 in
FIG. 3;
FIG. 5 is a perspective view of a fixture that is installed in the
rotor during the epoxy curing operation;
FIG. 6 is a plan view of a finished rotor embodying a modified form
of the invention;
FIG. 7 is a sectional view taken on the plane of the line 7--7 in
FIG. 6;
FIG. 8 is a fragmentary plan view of another modified form of
magnet cage, with a portion shown broken away;
FIG. 9 is a fragmentary side view of the magnet cage shown in FIG.
8; and
FIG. 10 is a greatly enlarged axial sectional view through a
portion of a flywheel rotor incorporating the magnet cage of FIGS.
8 and 9, illustrating in exaggerated form the effects thereon of
the heat used in curing the epoxy.
Referring now more particularly to the accompanying drawings, the
numeral 5 designates generally a rotor body member which carries a
ring of permanent magnet blocks 6, and which is here shown as a
flywheel of the type commonly used on single-cylinder gasoline
engines. The blocks 6, when magnetized, cooperate with the
stationary elements of an alternator (not shown) which can be
mounted on the body of an engine upon which the flywheel is
installed. As is conventional, the flywheel or rotor body 5 is
generally cup-shaped, having an end wall 7 and a generally
cylindrical or annular side wall 8, which walls cooperate to define
an axially shallow rearwardly opening well 9. A coaxial bore 10 in
the end wall is adapted to receive the crankshaft of an engine (not
shown) on which the flywheel is mounted.
As is usual with flywheels for small engines, the rotor body member
5 here illustrated has vanes 11 projecting forwardly from the
exterior surface of its end wall to blow cooling air across the
engine on which it is mounted. As is also conventional, a permanent
magnet 12 is embedded in the flywheel body and is exposed at its
outer peripheral surface for cooperation with stationary elements
of an ignition magneto (not shown) that is mounted on the engine
body outwardly adjacent to the flywheel.
The block-like permanent magnets 6 are secured to the flywheel in
circumferentially spaced relation to one another in a ring adjacent
to the inner surface of the side wall 8. The blocks are so
magnetized that adjacent ones have opposite polarity, and the rotor
body is preferably made of cast iron to provide magnetic flux paths
between them. The stationary alternator components with which the
magnets 6 cooperate are mounted on the engine body within the
embrace of the ring that the blocks define, where said alternator
components are covered and protected by the flywheel.
The magnet blocks 6 are of arcuate shape, to conform to the
curvature of the body side wall 8, and accordingly each has an
arcuately convex radially outer surface 14 that is curved on the
same radius as the inner surface of the side wall 8, a concave
radially inner surface 15 that provides a pole face, flat, slightly
arch-shaped front and rear surfaces 16 and 17, respectively, and
rectangular flat side surfaces 18. The rectangular side surfaces
lie in parallel planes, for reasons which will appear as the
description proceeds, and hence lie only approximately on radials
to the axis of the finished rotor.
In the finished rotor the magnet blocks are held in place by being
bonded to the inner surface of the side wall 8 with an adhesive
bonding agent such as epoxy resin. There is no substantial force
upon the blocks that tends to break their bond to the body since
they are magnetically attracted to it and are urged against it by
centrifugal force.
An annular cage 19 of nonmagnetic material, preferably cast or
molded in one piece, serves to establish the magnet blocks in their
proper positions during the assembly operation, retains them in
those positions while the bonding agent is curing, and protects
them in the finished rotor. The cage can be molded of a plastic
material such as nylon, but because the coefficient of thermal
expansion of most plastics is substantially different from that of
the cast iron of the rotor body, it is considered preferable to
make the cage as a die casting of zinc or the like.
For assembly of the rotor body, a coating of epoxy resin is first
applied to the inner surface of the rotor body side wall, all
around the same, and then the cage is inserted axially into the
well in the rotor body, in a predetermined rotational position. The
cage cooperates with inner surface portions of the rotor body to
define a plurality of radially inwardly opening pockets 20, one for
each magnet block, and the magnet blocks are inserted radially into
these pockets. The pockets are of such size that the magnet blocks
fit them loosely enough to be quickly and easily installed by hand.
As the blocks are inserted, the cage establishes them in desired
positions relative to one another and the rotor body.
By means of a tool 21 (see FIGS. 3 and 4) that is described
hereinafter, all of the blocks are simultaneously forced radially
outwardly to displace so much of the bonding material as is
necessary to bring their radially outer surfaces 14 to within a
predetermined distance from the inner surface of the side wall 8,
and then they are held in that position by means of a fixture 22
while the bonding material is cured.
As shown in FIG. 1, the cage comprises front and rear rings 24 and
25 and spacer portions 27 which extend axially between the rings
and connect them. The rear ring 24 flatwise overlies the rear faces
17 of the magnet blocks. The front ring 25, which can be relatively
narrow radially, overlies the front faces 16 of the blocks and
extends axially forwardly to hold the blocks axially spaced from
the end wall and to seal off the space between them and the end
wall. The spacer portions 27, which are equal in number to the
magnet blocks, space the blocks apart circumferentially. Each of
the spacer portions is generally channel shaped, having a pair of
circumferentially spaced legs 28 that extend lengthwise axially and
project radially outwardly from a web 29.
As may be seen by reference to the magnet blocks 6' in FIG. 2,
which are shown in the positions they occupy in the finished rotor,
the radially inner surfaces of the webs 29 of the spacer portions
are substantially flush with the inner surfaces 15 of the magnet
blocks; and the radially inner surface of the front ring 25 on the
cage, at the portion thereof that is axially adjacent to the magnet
blocks, is likewise flush with said magnet surfaces and said web
surfaces, as best seen in FIG. 3. Hence the cage cooperates with
the magnets to provide a magnet ring in the rotor that has a
relatively smooth inner surface. As a result, the cage affords
protection to the magnets during assembly of the rotor onto an
engine, and also protects the magnets from being dislodged by
flying stones and the like that might enter through the space
between the engine body and the rear edge of the rotor when the
engine is in use.
The adjacent legs 28 of circumferentially adjacent spacer portions
define opposing pocket surfaces which are parallel to one another
and which overlie the parallel side surfaces 18 on a magnet block.
By reason of the parallelism of these surfaces of the blocks and
pockets, the blocks can have a relatively simple shape that
facilitates their production, and they can be easily inserted
radially into the pockets 20.
Note that no particular reliance is placed upon an adhesive bond
between the cage and the rotor body to hold the cage of the FIG. 1
embodiment of the invention against displacement relative to the
body. Instead, the magnet blocks are mainly relied upon to hold the
cage in place by their engagement with the pocket defining surfaces
of the cage. Since many plastics do not make a good bond with epoxy
resin, the embodiment illustrated in FIG. 1 therefore lends itself
well to rotor assemblies in which the cage is formed of plastic, in
cases where the coefficient of expansion of the plastic presents no
particular problem.
The modified form of cage 19' illustrated in FIGS. 6 and 7 is
especially suitable for die casting in zinc or other nonmagnetic
metal and thus makes for a rotor assembly that is satisfactory even
though subjected to moderately varying temperature conditions. The
metal cage also has the advantage of affording more protection to
the magnet blocks than does the plastic cage. In the FIGS. 6 and 7
embodiment the rotor body 5 is provided with a circumferential
ledge or shoulder 32 that extends radially inwardly from its side
wall and is spaced a distance rearwardly from its end wall proper.
The front surfaces 16 of the magnets seat on this ledge.
Since there is no space between the magnets and the front wall of
the rotor body, the modified cage 19' comprises only a rear ring 24
that overlies the rear faces 17 of the magnet blocks and a
plurality of box-like spacer portions 27' that are formed
integrally with the rear ring and project forwardly from it. Each
of the spacer portions is preferably cored to form a forwardly
opening well 33 therein that saves both weight and material. The
opposing pocket-defining surfaces on circumferentially adjacent
spacer portions are again parallel to one another, as above
described, rather than lying on true radials, to provide for radial
insertion of the blocks 6 into the pockets 20 that are conjointly
defined by the cage and the inner surface of the side wall 8.
In this case, since the cage has no front ring, the epoxy is relied
upon to bond the cage 19' to the side wall 8 of the rotor body and
prevent rearward displacement of the cage relative to it, and for
this reason the box-like spacer portions 27' are formed with
radially outer surfaces that are curved to mate with the inner
surface of the side wall and are chamfered at their front edge
portions, as at 34. As the cage is inserted axially into the rotor
body, the chamfers 34 wipingly distribute an even coating of epoxy
between the spacer portions of the cage and the inner surface of
the body side wall.
The junction of the side wall 8 of the rotor body with its end wall
9 should be at a rounded corner, to insure structural strength to
the rotor body and to avoid problems in machining it. However, the
adjacent surfaces of the magnet blocks meet at a square corner. For
this reason, as best seen in FIG. 10, the rearwardly offset ledge
32 upon which the blocks are seated has a surface 85 that is
inclined forwardly and radially outwardly, so that the blocks rest
on only the radially inner portion of that surface. When set in
place, the blocks are of course held in their proper orientations
by their flatwise engagement against the inner surface of the side
wall.
FIGS. 8 and 9 illustrate another form of cage 19" that is suitable
for die casting in zinc or other metal, and which is well adapted
for use where the epoxy resin that secures the cage and the magnet
blocks to the rotor body is cured at a relatively high temperature.
Like that illustrated in FIGS. 6 and 7, the cage of FIGS. 8 and 9
comprises a rear ring 24 that overlies the rear faces of the magnet
blocks and a plurality of spacer portions 27" that are formed
integrally with the rear ring and project forwardly from it between
circumferentially adjacent magnet blocks.
In this case, however, each of the spacer portions comprises a
radially inner finger 71 and a radially outer finger 72, each of
the fingers being in the nature of a circumferentially extending
wall portion. The radially inner finger 71 has axially extending
ribs or flutings 73 that reinforce and stiffen it. The radially
outer finger 72, however, is relatively thin, so that it has a
slight degree of radial flexibility. Each radially outer finger has
its front edge portion chamfered, as at 34, so that epoxy is
wipingly distributed evenly across the radially outer surface of
the finger 72 as the cage is inserted into the rotor.
During curing of the epoxy, the cage tends to expand slightly more
than the rotor body, owing to the high temperature used in the
curing operation and the fact that zinc has a higher coefficient of
expansion than cast iron. As the assembly cools after the curing
operation, the ring portion of the magnet cage shrinks away from
the adjacent surface of the rotor body and tends to break the epoxy
bond between the cage and the rotor body as indicated at 75 in FIG.
10. But because of the above mentioned slight flexibility of the
radially outer finger 72, that finger can assume a slight
S-curvature that allows its front end portion to remain well bonded
to the rotor body, as at 76. It will be understood that in FIG. 10
the S-curve that is imparted to the finger is greatly exaggerated,
as is the separation in the epoxy at 75.
It will be seen that the circumferential side edges of the front
and rear fingers cooperate to define side surfaces of the block
receiving pockets 20, as at 76, and have sufficient area to insure
that the blocks will be properly located as they are installed in
the cage.
For assembly of any of the above described cages into the rotor
body, the latter will normally be oriented with its axis vertical
and its end wall 7 lowermost, and it can remain in that orientation
through the curing operation. The blocks 6 can be manually inserted
into the pockets 20 just to the extent necessary to assure that
they will not drop out of the pockets. However, the permanent
magnets 6 are intended to be in a magnetic circuit with the
permeable side wall 8 of the rotor body, and therefore in the
finished rotor the distance between the inner surface of that side
wall and the radially outer surface 14 of each magnet block should
be as small as possible consistent with the presence of a thin
bonding layer of epoxy between them. Hence when all of the blocks
have been inserted, the above mentioned tool 21 is placed in the
rotor body cavity and is actuated to force the blocks radially
outwardly to their desired positions, exerting enough force upon
the blocks to squeeze all excess epoxy out from between them and
the rotor body side wall.
The tool 21 comprises, in general, a circular body 36 that has a
diameter to be received within the cage annulus with a substantial
radial clearance, a plurality of plungers 37 -- one for each magnet
block 6 -- that are slidably guided in the body 36 for radially in
and out motion, and a coaxial driver 38 which is slidable in the
body 36 for up and down motion and which comprises an upper stem
portion 39 and a lower frustoconical cam portion 40 that slidingly
engages the inner ends of the plungers 37.
The body 36 of the tool can comprise two parts, namely, an upper
part 41 that provides a boss 42 in which the stem portion of the
driver is slidably guided, and a lower part 43 that has a plurality
of radial slots 44, in each of which one of the plungers 37 is
slidable. The cam portion 40 of the driver 38 is received in a
counterbore 45 which extends axially through the lower body part
and to which the slots 44 open at their radially inner ends, and
which also extends partway up into the upper part of the body,
where it communicates with a smaller diameter bore 46 that
continues up through the boss and slidably guides the stem portion
of the driver.
Each of the plungers 37 has a slot 48 therethrough, intermediate
its ends and elongated lengthwise of the plunger, and has a
radially outwardly facing shoulder 49. The plunger is biased
radially inwardly by means of a coiled compression spring 50 which
reacts between the shoulder 49 on the plunger and a pin 51 that is
fixed in the tool body and extends through the slot 48 in the
plunger. The radially inner end surface 52 of each plunger is
inclined to correspond with the taper of the downwardly convergent
frustoconical cam portion 40 of the driver, so that downward motion
of the driver cams all of the plungers radially outwardly against
the bias of their springs 50. A pad 53 of rubber or similar
resilient material on the radially outer end of each plunger
protects the magnet blocks from damage by the plunger and
accommodates slight differences in the combined radial dimensions
of the several blocks and plungers.
The driver 38 is preferably constrained to axial up and down motion
by means of a pin 55 that is fixed in the boss portion of the body
and extends transversely across the bore 46 through axially
elongated slots in the driver stem portion. The upper end of the
driver stem is preferably provided with an enlarged head 56
suitable for engagement by the ram of a hydraulic press or the
like, by which the tool 21 can be actuated.
FIG. 5 illustrates an inexpensive fixture 57 which can be placed in
the cage annulus immediately after the tool 21 is removed
therefrom, and which can remain in the well 9 in the rotor all
through the curing operation to maintain the magnet blocks in the
positions in which the tool 21 has established them. The fixture 57
comprises a central disc or plate 58 from which spring fingers 59
project radially outwardly and upwardly. There is of course a
spring finger 59 for each of the magnet blocks 6, and each spring
finger can be secured to the plate 58 by means of rivets 60 or the
like. The fixture is merely inserted axially, plate lowermost, into
the well 9 in the flywheel body, with its fingers substantially
aligned with the magnet blocks, and the spring fingers, in engaging
the magnet blocks under resilient bias, hold the fixture centered
in the well.
The flywheel is preferably balanced after the bonding agent has
been cured. Since balancing is accomplished by removing cast iron
from its body, the blocks 6 are preferably installed in
unmagnetized conditions so that they will not attract and collect
chips produced during the balancing operation. The magnet blocks
are magnetized in a known manner after the flywheel is
balanced.
From the foregoing description taken with the accompanying drawings
it will be apparent that this invention provides an extremely
inexpensive method and means for securing magnet blocks to the
inner side wall surface of a cup-shaped rotor body such as an
engine flywheel, and for establishing the blocks in a predetermined
relationship to one another and to the rotor body as they are being
quickly and easily assembled with the flywheel.
Those skilled in the art will appreciate that the invention can be
embodied in forms other than as herein disclosed for purposes of
illustration.
* * * * *