Note: Descriptions are shown in the official language in which they were submitted.
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DYNAMOELECTRIC MACHINE AND METHOD FOR MANUFACTURING SAME
Field of the Invention
This invention relates generally to electrical
apparatus and in particular to a dynamoe:lectric machine and a
method of manufacturing the dynamoelectric machine.
Background of the Invention
Competitive mass production of dynamoelectric
machines in the form of electric motors such as those used in
household appliances and other machines requires in the
design and manufacture of the motor a simultaneous emphasis
on speed and simplicity of manufacture, and the precision of
the final motor construction. Moreover, any design or
manufacturing process must not add costs out of proportion to
the savings achieved through higher production. Thus, the
present invention pertains to a motor which incorporates
design features optimized for speed of manufacture and
precision of the final product.
It is well established that the formation of the
stator core of an electric motor may be most efficiently
carried out by forming the core from a stack of laminations
stamped from a sheet of highly magnetically permeable
material. The laminations are frequently square because this
shape wastes less of the sheet material from which the
laminations are stamped. Each lamination is stamped with a
central opening and radially extending :>lots which typically
open into the central opening. The cent:ral openings of the
stator laminations in the stack form the bore of the stator
core and the slots define the teeth whi<:h extend the length
of the stator bore and receive the wire windings of the
motor. The slots are stamped symmetrically about the center
of the central opening, leaving substantially equal amounts
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of material along each of the four edges of the lamination.
Thus, the amount of magnetic flux which can be carried by the
stator core is substantially the same along all four of its
sides.
It is important that the stator bore be round and
straight so that the rotor may freely rotate in the stator
core bore while maintaining only a minimal separation between
the rotor and the stator core. The straightness of the bore
is adversely affected by the inherent presence of variations
in thickness (called "gamma" variation) of the rolled sheet
material from which the laminations are stamped, so that each
lamination is not truly flat. If the laminations are stacked
one on top of the other in the same orientation as when each
lamination was stamped on the sheet material, the gamma
variations will tend to add together rather than cancel out.
Thus, the stator bore formed may be substantially curved and
unsuitable for mating with the rotor in such a way which will
permit the rotor to freely rotate in th~a stator bore.
Punching the central openings of the laminations from the
sheet material relieves certain stressea in the material;
which tends to cause the material to elastically deform from
the round shape struck by the punch, to an elliptical shape.
Further deviations from round may be introduced by thermal
stress as the stator core is annealed. Again, if the
laminations are stacked together in such a way as to add the
deviations from round, a bore which is too elliptical to
receive the rotor may be produced. In a square lamination
having substantially equal amounts of material remaining
after punching on all four sides, deformations causing
deviation from round can be expected to occur approximately
equally along two perpendicular axes lying in the plane of
the lamination. Accordingly, it is preferred to rotate each
lamination 90° relative to the adjacent lamination in the
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stack so that gamma variations and deviations from round in
the laminations tend to cancel each other out.
However, in the past 90° rotation of each
lamination relative to the adjacent lamination in the stack
has not been practical when constructing stator cores for
certain two speed electric motors having two windings which
have different numbers of poles. In a t:wo speed motor having
a four pole winding and a six pole winding, some of the turns
of wire forming the poles must be placed in the same stator
slots. In order to provide enough room, the slots where the
windings will overlap must be deeper. This requirement
introduces asymmetry in the arrangement of slots about the
center of the central opening of each lamination, and reduces
the amount of material on two of the sides of the lamination
relative to the other sides. Equalizing the amount of
material on all four sides may be accomplished by elongating
the two sides having the deepest slots. However, the
combination of the asymmetry of the slot arrangement and the
rectangular shape of the lamination mak~°s it impossible to
rotate the laminations 90° relative to t:he adjacent
lamination when stacking. The best that can be done
presently is to rotate the laminations 180°, which does not
permit cancellation of manufacturing to:Lerances as
efficiently as 90° rotation, and thus adversely affects the
roundness and straightness of the bore.
It is well known that in order to decouple stator
slot order harmonics the rotor bars in the squirrel cage
rotor of an induction motor should be slcewed. Typically,
skewing is accomplished by turning the rotor laminations
making up the rotor slightly with respect to each other so
that the passages formed by overlapping slots of the rotor
laminations are generally helical in shape. Helical skewing
can be carried out by hand using a jig, or automatically by
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machine. In the former instance, substantial labor costs are
added to the production of the rotor, and in the latter
instance it is difficult to reliably automate the delicate
operation of turning the rotor laminations slightly relative
to each other. Further, the helical passages have a stair-
step configuration which can produce undesirable turbulence
in the molten material poured into the passages to form the
rotor bars. Significant savings can be realized by
implementation of a "straight" skew, in which the rotor bar
passage consists of two smooth, straight: passages which
overlap, but are skewed. The skewed pay>sage is typically
formed by making the rotor slots asymmetrical about a radial
line of the rotor lamination, with the slots in one half of
the stack of laminations forming the rotor being the mirror
image of the slots in the other half. Although decoupling
slot harmonics by using two straight passages which are
skewed relative to one another is known, there is presently a
need for such a straight skew which delivers better motor
performance for single phase motors.
Once the rotor and stator havE: been constructed, it
is necessary to assure that the rotor will be aligned with
the stator core bore when the rotor is inserted into the
bore. The rotor shaft is typically supported for free
rotation at its ends in central openings in metal end frames
which are connected to the stator core. Tolerances inherent
in the formation of the central openings in the end frames
and the stator core bore, and the absence of accurate
location mechanism for the end frames on the stator core
result in many rotor/stator core assemblies being out of
alignment. Present practice calls for the introduction of
shims in the central openings where the rotor shaft is
received to bring the rotor and stator core into alignment.
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This procedure permits only a relatively coarse adjustment,
and requires time and extra labor to ac<:omplish.
The manufacturing step of mounting the rotor shaft
on the end frames also presently requires significant labor
and time to accomplish. The ends of thE: rotor shaft are
mounted by bearings in the central open~_ngs of the end frames
which permit free rotation of the rotor shaft about its
longitudinal axis. Presently, the bearings include many
parts and require substantial time to as>semble and install in
the end frames.
The inner raceways of the bearings held in the
central openings of the end frames are typically fixed to the
rotor shaft at predetermined locations. Thus, the relative
location of the end frames is determined by the predetermined
locations on the rotor shaft. The presence of tolerances in
the dimensions of the rotor shaft, the end frames and the
stator core occasionally results in the stator core and end
frames not fitting together as they should in the assembly of
the machine. A minor misalignment or structural irregularity
of the rotor shaft may cause the shaft to wobble as it
rotates. The wobble causes variations in the air gap (i.e.,
the distance separating the rotor and the stator core) which
results in undesirable noise and vibration.
Another aspect of the assembly of the electric
motor which is labor intensive is the electrical connection
of the windings to a plug and terminal assembly used to
connect the~windings to a source of electricity and to
control operation windings for starting the machine.
Presently, there are at least four connections used to
electrically connect the terminal end of each magnet wire to
the plug and terminal assembly. The magnet wire is first
connected to a terminal having sharp ridges which pierce the
insulation on the wires to make electrical contact as the
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terminals are crimped against the magne~ wire. The ridged
terminal is connected to wire having plastic insulation,
which is in turn connected to a terminal on the plug and
terminal assembly. The terminal on the plug and terminal
assembly is connected to the circuitry _Ln the plug and
terminal assembly. Typically, only two of these connections
are made during assembly of the motor. However, each
terminal connection is a more likely site for failure.
Moreover, connection of the plug and terminal assembly to the
end frames of the motor presently requires separate
fasteners. The use of such fasteners, or alternative joining
methods such as welding or soldering, adds the cost of the
fasteners or joining material, and the cost of labor to
connect the plug and terminal assembly by application of the
fasteners or joining material.
In order to ground the motor end frames, a separate
assembly step is required for ground connection. For
instance, a screw may be received through an end frame and
into the plug and terminal assembly, or the connection may be
by insulated wire. The insulated wire is connected to the
end frame by a screw or a clip, which are additional
materials which require additional time to manipulate during
assembly of the motor.
Summary of the Invention
Among the several objects and features of the
present invention may be noted the provision of a
dynamoelectric machine capable of rapid production while
maintaining quality at or above that of existing machines of
the same type; the provision of such a machine which has
fewer parts; the provision of such a machine which is secured
together with fewer fasteners; the provision of such a
machine which makes an economic use of materials in its
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construction; the provision of such a machine which has fewer
internal electrical connections; the provision of such a
machine which is grounded without requiring additional wiring
or special ground connections; the provision of such a
machine which is automatically connected. to a ground remote
from the machine when connected to a source of electrical
power; the provision of such a machine in which the rotor and
stator are accurately aligned; the provision of such a
machine which accommodates misalignment or structural
irregularity of the rotor without introducing substantial
stresses to the machine during operation; and the provision
of such a machine in which stator slot order harmonics are
optimally decoupled.
Further among the objects and features of the
present invention may be noted the provision of a method for
manufacturing a dynamoelectric machine which requires fewer
steps to secure the component parts together; the provision
of such a method in which critical dimensions are held within
closer tolerances to produce more accurate alignment of the
stator and rotor; the provision of such a method which
employs fewer individual fasteners; and the provision of such
a method which can be carried out rapidly and at reasonable
cost.
Generally, a two-speed dynamoelectric machine
constructed according to the principles of the present
invention comprises a stator, at least two windings on the
stator, a rotor received in the stator and means supporting
the rotor for rotation relative to the stator. A first of
the two windings has a first number of poles and a second of
the two windings has a second number of poles different from
the first number of poles. A plurality of stator laminations
stacked one on top of the other form the stator core. Each
stator lamination comprises a sheet of highly magnetically
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permeable material having a generally central opening
therein, and slots opening into the ceni~ral opening and
extending generally radially outwardly therefrom. The slots
are disposed in an arrangement around the periphery of the
central opening and receive turns of wire from the two
windings of the dynarnoelectric machine with at least some of
the slots receiving turns of wire from both of the two
windings. The arrangement of slots on Each stator lamination
is symmetrical about a pair of perpendicular lines lying
generally in the plane of the stator lamination and
intersecting generally at the center of the central opening,
and about a diagonal line lying in the plane of the stator
lamination, passing through the center c>f the central opening
and making an angle of 45° with the perpendicular lines.
Each stator lamination in the stack is rotated 90° relative
to other stator laminations about a longitudinal axis of a
central rotor-receiving bore of the stator core formed by the
central openings of the stator laminations in the stack
thereby forming a central bore which is straighter and mare
nearly cylindrical.
In another aspect of the present invention, a
dynamoelectric machine comprises a stator including a stator
core having a pair of opposing end faces, a bore through the
stator core extending from one end face to the other end
face, and windings including a start winding and at least one
run winding on the stator, each winding having winding leads
extending outwardly from the stator. First and second
opposite end frames mounted on respective end faces of the
stator core each have a generally central opening. A rotor
assembly comprises a shaft received in bearing means
associated with the central openings of the end frames, and a
rotor fixedly mounted on the shaft for conjoint rotation
therewith. The rotor is disposed at least in part in the
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stator core bore, and the rotor and the stator are adapted
for magnetic coupling upon activation of the windings for
rotating the shaft and rotor relative to the stator and end
frames. A plug and germinal assembly includes a casing made
of an insulator material, a plurality of lead terminals
electrically connected to the winding leads and a plurality
of electrical connectors protruding from the casing and
electrically connected to the lead terminals. The electrical
connectors are constructed for connecting the winding leads
to a source of electrical power. A ground tab mounted on and
in electrical contact with the second end frame is received
in an opening in. the casing with the ground tab being
disposed for electrical connection to ground upon connection
of the electrical connectors to ground:
In yet another aspect of the present invention, a
dynamoelectric machine has a stator, windings, end frames,
bearing means and a rotor assembly as described in the
preceding paragraph. The dynamoelectric machine further
comprises a plug and terminal assembly including a casing
made of insulator material. A switch housed in the casing is
operable between a first switch mode in which the start
winding is activated and a second switch mode in which the
start winding is deactivated. A plurality of electrical
connectors are connected to the switch and adapted for
connection to a power supply, and a plurality of magnet wire
terminals are integrally connected to the switch and receive
the terminal ends of the windings thereby providing direct
connection of the windings to the switch.
In still another aspect of the present invention, a
dynamoelectric machine comprises a stator, a rotor assembly,
first and second end frames and first and second bearings.
The first~bearing is disposed in a central opening of the
first end frame and fixedly mounted on a rotor shaft of the
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rotor assembly thereby to prevent axial movement of the rotor
shaft relative to the first bearing. The second bearing,
disposed in a central opening of the second end frame,
comprises a housing and shaft bearing means supported by the
housing in a shaft receiving passage. The shaft bearing
means is constructed and arranged for rolling engagement with
the rotor shaft in the shaft receiving passage for supporting
the rotor shaft and permitting rotation of the rotor shaft
about its longitudinal axis. The shaft bearing means is tree
of connection to the rotor shaft.
Methods of manufacturing a dynamoelectric machine
are also disclosed. In one aspect of th.e method, end frames
are each formed by simultaneously punching from sheet metal
blank a generally central rotor shaft receiving opening and
locator means spaced from the center of the central opening
so as to precisely locate the center of the central opening
relative to the locator means.
Other objects and features of the present invention
will be in part apparent and in part pointed out hereinafter.
Brief Description of the Drawings
FIG. 1 is a front perspective of an electric motor;
FIG. 2 is a longitudinal section of the motor;
FIG. 3 is an exploded front perspective of the
motor;
FIG. 4 is a perspective of the rear end frame of
the motor, with a plug and terminal assembly illustrated as
exploded away from the end frame;
FIG. 5 is an enlarged fragmentary perspective of
the rear end frame showing the plug and terminal assembly as
installed on the end frame;
FIG. 6 is an enlarged fragmentary section taken in
the plane including line 6 - 6 of FIG. 5:
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FIG. 7 is a front elevation of the plug and
terminal assembly showing locating posts of the assembly as
received in a stator slot (shown in phantom ;
FIG. 8 is an end elevation of the plug and terminal
assembly and a fragmentary portion of the stator core
illustrating engagement of the locating posts therewith;
FIG. 9 is a an electrical schematic of the plug and
terminal assembly, shown as plugged into a power source;
FIG. 10 is an enlarged fragmentary cross section of
the motor illustrating the locator nubs of the end frames and
locator openings of the stator core;
FIG. 11 is a section of the rear end frame taken in
the plane including line 11--11 of FIG. 4 and showing a rotor
shaft bearing mounted in the central opening of the rear end
frame;
FIG. 12 is a longitudinal section of the rotor
shaft bearing of FIG. 11;
FIG. 13 is an end elevation of a housing piece of
the housing of the rotor shaft bearing;
FIG. 14 is a fragmentary elevation of the opposite
end of the housing piece of FIG. 13; and
FIG. 15 is a plan of a stator lamination which
forms the stator core;
FIG. 16 is a schematic illustrating the formation
of stator laminations and the stator core;
FIG. 17 is a perspective of a rotor. assembly of the
motor, including a rotor shaft and a rotor core, with parts
of the rotor core brcken away to show details of
construction;
FIG. 18 is a plan view of the rotor core with
portions broken away to two levels to re~Jeal the three
different rotor slot orientations within the rotor core;
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FIG. 19 is an enlarged fragmentary elevation of the
rotor core showing a single rotor slot and illustrating in
hidden lines the orientation of an underlying slot;
FIG.. 20 is an enlarged fragmentary view of a rotor
core having slots which are skewed accordingly to
conventional mathematical prediction; and
FIG. 21 is a diagram illustrating two preferred
windings of the motor and two other windings.
Corresponding reference characters indicate
corresponding parts throughout the several views of the
drawings.
Detailed Description of the Preferred E~~odiment
Referring now to the drawings, and in particular to
FIGS. 1, 3 and 15, a dynarnoelectric machine in the form of a
single phase, two speed induction motor 20 is shown to
include a stator 22 having a core 24 made up of a stack of
thin stator laminations 26, and windings 27 on the stator
core including a four pole start winding 28, a four pole run
winding 30 and a six pole run winding 32. The stator 20,
stator core 24, stator laminations 26 and windings 27 are
indicated generally by their respective reference numerals.
The windings illustrated are exemplary only, as the invention
is applicable to dynamoelectric machines of other winding
configurations. A rotor assembly indicated generally at 36
includes a rotor 38 received in a bore 40 of the stator core
24 and a rotor shaft 42 fixedly connected to the rotor.
Opposite end portions of the rotor shaft 42 are received in a
first bearing 44 and a second bearing (g~anerally indicated at
46), respectively, for free rotation of 'the rotor assembly 36
about the longitudinal axis of the rotor shaft. As may be
seen in FIG. 2, the first and second bearings 44, 46 are held
in central openings 48 of first and second end frames
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(designated generally by reference numbers 50 and 52,
respectively) which support the rotor assembly 36. A plug
and terminal assembly, generally indicated at 56 is located
on the second end frame 52, and a centrifugal mechanism 58 of
the type well known in the art is mounted on the rotor shaft
42 adjacent the second end frame. The end frames 50, 52
engage opposite end faces of the stator core 24 where they
are positively located by locator nubs 60 associated with
each end frame, which locator nubs are received in
corresponding locator holes 62 in the en.d faces. The motor
20 is held together by keys 64 which are received in
preformed channels 66 in the stator core 24 and bent over at
their ends 68 (shown in phantom in FIG. 3) to hold the motor
components together as shown in FIG. 1.
One of the stator laminations 26 which is stacked
together with a plurality of other stator laminations of
identical construction to form the stator core 24 is shown in
FIG. 15. The lamination 26 has a generally central opening
72, and a plurality of stator teeth 74 defining slots 76
therebetween opening into the central opening and extending
generally radially outwardly from the central opening.
Notches 78 at the four corners of the lamination 26 define
the channel 66 of the stator core 24 (FI:G. 3). As shown in
FIG. 16, the laminations 26 are stamped fram a strip W (from
a roll R) of highly magnetically permeable material in a die
D. All stator laminations 26 are preferably square in shape
to permit maximum usage (and corresponds.ngly less waste) of
the material in the strip W. The slots 76 are shaped and
arranged around the periphery of the central opening 72 so
that the arrangement of slots is symmetrical about a pair of
perpendicular lines L1 and L2 lying generally in the plane of
the stator lamination 26 and intersecting generally at the
center C of the central opening. The arrangement of slots 76
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is also symmetrical about a diagonal line L3 lying in the
plane of the stator lamination 26, passing through the center
C of the central opening 72 and making an angle of 45° with
the perpendicular lines L1, L2.
Stated another way, the size and arrangement of
slots 76 of the stator laminations 26 are "90° symmetrical",
i.e., any stator lamination superposed with another stator
lamination may be rotated relat°ive to tree other stator
lamination 90°, or any multiple thereof, about an axis
perpendicular to the plane of the laminations and passing
through the center C of the laminations, and the slots 76
will be substantially superposed and coextensive. However,
it is to be understood that the rotational symmetry of the
slots 76 could be other than 90° and still fall within the
scope of the present invention. Generally speaking,
rotational symmetry of the slots 76 of N°, where N is less
than 180, will permit at least incremental improvement in the
roundness and straightness of the stator bore 40.
As is known, the 90° symmetry of the stator
laminations 26 permits the construction of a stator core 24
having a straighter and more nearly cylindrical bore 40. In
the final assembly of the motor 20, the rotor_ 38 and the
periphery of the stator core bore 40 should preferably have
the minimum possible separation, while permitting free
rotation of the rotor in the bore. Deviations of the stator
core bore 40 from being straight and cylindrical typically
occur because of non-uniform thickness of individual stator
laminations 26 ("gamma variations"), and elliptical
deformation of the central openings 72 caused by stress
relief in the material after punching the central opening.
It has been found that these errors tencL to occur equally
along the lines L1, L2 shown in FIG. 15. All of the stator
laminations 26 have the same original orientation when they
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are stamped from the highly magnetically permeable material
and fed one after another in a forward direction to a
stacking station. Rotation of each stator lamination 26 from
its original orientation 90° relative to the adjacent stator
lamination in the stack forming the stator core 24 results in
the aforementioned errors tending to car.~cel each other out.
As shown in FIG. 16, rotation of the stator laminations 26 is
carried out in a revolving barrel B (the: "stacking station°'j
into which the stator laminations are received after they are
stamped. Prior to each stator laminatic>n being driven into
the barrel B, it rotates 90° so that adjacent stator
laminations 26 in the stack forming the stator core 24 are
rotated relative to each other 90° from their original
orientations. The stacking and rotating of the stator
laminations 26 continues until the stack: reaches a
predetermined height corresponding to the size of the stator
core 24.
The four pole start winding 28, four pole run
winding 30 and six pole run winding 32 are schematically
illustrated on the stator lamination 26 shown in Fig. 15.
Each winding 27 has a pair of magnet wire leads 80 at
opposite ends of the winding which are connected to a source
of power as described in detail hereinafter. It is to be
understood that the precise arrangement of the windings 27
may be other than shown in FIG. 15 and still fall within the
scope of the present invention. As may be seen from the
winding diagram, turns of magnet wire from different windings
will lie in the same slots 76.
Difficulty in exploiting the advantage derived from
90° rotation of each stator lamination 26 arises when the
stator core 24 is wound for a two speed motor of the type
disclosed herein having two windings each with a different
number of poles (e. g., a four pole winding 30 and a six pole
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winding 32). More specifically, the difficulty occurs when
one of the windings has a rotational sy~runetry which differs
from and is not a whole number factor of the rotational
symmetry of the stator laminations 26. Rotational symmetry
of a winding is equal to the angular spa~,cing of the poles of
the winding around the periphery of the stator core bore 40.
In the six pole winding 32, the poles are spaced at 60°
intervals around the stator core bore 40, and no two poles of
the six poles are spaced apart by 90°. If the six pole
winding 32 is rotated 90° from an initial position, its
appearance is not the same as it was in the initial position.
Difficulty in winding a 90° symmetric stator occurs generally
when two of the windings have a different number of poles,
and the number of one of the poles is an even number which is
greater than two and not a multiple of four.
Accordingly, when the six pole winding 32 and four
pole winding 30 (or four pole start winciing 28) are wound on
the stator 22, some of the slots 76 adjacent two sides of the
lamination will be required to receive ~;ubstantially more
turns of magnet wire than others. In the past, accommodation
has been made by making the lamination t>lots which receive
extra turns of wire deeper. However, this introduces
asymmetry in the arrangement of slots, making them no longer
90° symmetric. Moreover, the amount of :material to carry the
magnetic flux produced by the windings s.s reduced along two
of the edges of the lamination. The amc>unt of material along
each side of the lamination 26 is referred to as the "yoke"'
of the lamination. Preferably, the yokE: should be nearly the
same along all four edges of the lamination 26. The decrease
in material caused by the depth of the t>lots can be remedied
by making the lamination with an elongated rectangular shape.
However, these rectangular laminations (not shown) are only
symmetrical when rotated 180° relative to each Other. Less
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effective cancellation of gamma deviations and elliptical
deformations of the central openings 72 occurs with 180°
rotation of the stator laminations 26 when forming the stator
core 24.
The stator lamination 26 of the present invention
has been constructed to receive magnet wire from the four and
six poles windings 28, 30, 32 of a two speed motor in a 90°
symmetrical arrangement of the slots 76. The yoke along the
four peripheral edges of the lamination 26 is substantially
the same, with the minimum distance y sE:parating the bottom
of any of the slots 76 and the nearest edge of the stator
lamination 26 being approximately equal along all four edges
of the lamination. However, a sinusoidal distribution of the
turns of magnet wire at each pole of each winding 27 would
result in certain slots 76 being overfi~_led and other slots
being under-filled. The amount a slot 76 is filled with wire
is commonly expressed in terms of "slot fill percentage°',
which corresponds to a ratio of the cross sectional area of
the magnet wire times the number of turns in the slot,
divided by the area of the slot. The slot fill percentage of
each slot 76 should be greater than about 30o and less than
about 700, and more preferably be greater than about 40o and
less than about 60o. To achieve slot f~_11 percentages in
this range in a stator 22 made up of 90° symmetrical stator
laminations 26, the spatial distribution of turns of magnet
wire among the slots 76 at least some of. the poles of some of
the windings is distorted from an ideal sinusoidal
distribution of turns for the particular number of slots of
the stator. More turns of wire are placed in some slots 76
and fewer in others than would be called for in an ideal
sinusoidal distribution of turns. Further, the distortion of
the turns from the sinusoidal distribution is dissimilar at
least two of the pales of one of the windings 27 resulting in
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the introduction of a controlled amount of even harmonics
upon energizing the winding. Preferably, the distortion
should occur in the run winding (i.e., t:he four pole winding
30 or six pole winding 32) which is used least in ordinary
operation of the motor 20. Distortion i.s carried out so as
to bring the slot fill percentages within the preferred
ranges. Another, lesser preferred way of bringing slot fill
percentages within an acceptable range~i.s to remove turns
from one or more of the poles of one of the windings 27. The
precise arrangement of the turns will depend upon the size of
the stator 22, the number of windings 27 and poles in each
winding, as well as the desired operating characteristics of
the motor 20.
Two preferred winding configurations for the motor
20 of the present invention, having a stator 22 with 36 slots
wound with a four pole start winding (designated °°4P START"),
four pole main winding (designated "4P MAIN") and six pole
winding (designated '°6P") are diagrammatically illustrated in
FIG. 21, and compared with a sinusoidal winding and another
winding. The lettered columns represent. slots in the stator
22, as indicated on the stator lamination 26 shown in
Fig. 15, and the lines between the columns represent the
teeth 74 of the stator. The numbers in the columns are the
number of turns received in the slot for a particular
winding, and each row of numbers represents the distribution
of turns for the winding designated at the right hand side of
the. row. The rows are arranged in four vertically spaced
groups of three rows, each group representing all windings on
a given stator. At the bottom of FIG. 21, the location and
span of the coils of each pole for each of the windings are
schematically indicated by nested brackets. The brackets
illustrate generally the possible spans of the coils, but in
fact the designer may chose not to include one of the spans
18
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shown by the brackets. In winding groups where it has been
chosen not to include particular spans, the number "0°' has
been placed in the slots where turns of wire making up that
span would ordinarily be received. The instance where a
particular slot or slots 76 lie at the interior of the pole,
and no wire is placed there, the absencE: of wire is indicated
by dashed lines '°--" .
The top group of windings is a sinusoidal
distribution of turns for the 36 slot stator 22 illustrated
herein. A sinusoidal winding configuration is ordinarily
preferred for best motor performance. Ffowever, in this
instance, some of the slots are too full. and others
relatively empty, making it completely impractical to
manufacture. The winding group second from the top in the
diagram of FIG. 21 is a first attempt to reduce the disparity
in the number of turns received in respE:ctive slots 76.
Although this second winding configuration makes better use
of the slots by distorting the turns from the sinusoidal
configuration, it is also impractical to manufacture. The
third and fourth groups from the top are manufacturable
winding configurations and are believed to operate within
acceptable parameters.
The completed stator 22 is supported together with
the rotor assembly 36 in the final assembly of the motor 20
by the first and second end frames 50, 'i2. The rotor 38 is
received inside the stator bore 40 and is in a closely spaced
relation with the stator core 24 in the stator core bore.
The end frames 50, 52 are each formed from sheet metal blank
which is formed into a cup-shaped configuration including
generally square, flat interior and extE:rior faces
(designated 90 and 92, respectively) and a skirt 94
projecting outwardly from the interior face 90 of the end
frame. Four feet 96 extend laterally outwardly from the
19
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outer edges of the skirt 94 at the corners of the end frames
50, 52. The central opening 48 of each end frame is
generally tubular in shape, and an inwardly projecting
retaining lip 98 narrowing the central opening at its axially
outer end is disposed for engaging the bearing (44 or 46)
received in the opening. Referring now to FIGS. 4 and 5,
material is removed from the end frames 50, _'i2 at
circumferentially spaced locations around their respective
central openings 48 leaving vents 100 permitting circulation
of cooling air through the motor. However, not all of the
material at the location of the vents 100 is removed from the
end frames 50, 52. At each vent 100, maa erial is left
forming a retaining tab 102 which extends axially inwardly
from the inner end of the central opening 48 at the periphery
of the opening.
The first bearing 44 includes an inner race 106, an
outer race 108 and ball bearings 109 received in the races
(FIGS. 1 and 3). The inner race 106 is fixedly connected to
the rotor shaft 42 of. the rotor assembly 36 adjacent one end,
and the shaft and first bearing 44 are located in the central
opening 48 in the first end frame 50 with the outer race of
the first bearing engaging the retaining lip 98. The
retaining tabs 102 are deformed inwardly against the outer
ring 108 of the first bearing 44 so that: the first bearing is
captured in the central opening 48 betwE:en the retaining lip
98 and retaining tabs (FIG. 2). Thus, t;he first end frame 50
is positively located relative to the first bearing 44 and
the rotor 38. The second bearing 46, described in more
detail below, and the opposite end of the rotor shaft 42 are
located in the central opening 48 of thE: second end frame 52.
The second bearing 46 is captured in thE: central opening 48
between the retaining tabs 102 and reta~_ning lip 98 of the
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second end frame 52 in the same way as the first bearing 44
(Fig. 5).
The relative radial position of the stator 22 and
rotor assembly 36 is controlled by the locator nubs 60 and
locator holes 62 associated with the first and second end
frames 50, 52 and the stator core 24. Z'he end frames 50, 52
each include four of the locator nubs 60, one on each of the
four feet 96 of the end frame. As best seen in FIG. 10, each
locator nub 60 is received in a corresponding locator hole 62
formed in the end face of the stator core 24, thereby
positively radially locating the stator core and the end
frames 50, 52. The nubs 60 are preferably formed by punching
through the end frames 50, 52 at the feEa 96 so that the nubs
extend outwardly from the feet a substantial distance into
the holes 60 upon assembly of the end frames with the stator
22. Positive location of the end frame~> 50, 52 and stator
core 24 also produces positive location of the rotor assembly
36 and stator core 24 by virtue of the first and second
bearings 44, 46 being captured in the cE:ntral openings 48 of
respective end frames. In the preferred embodiment, the
locator nubs 60 and the central opening:> 48 of the end frames
50, 52 are punched from the sheet metal blank during the same
stroke of the die, which permits a closE: tolerance to be
maintained on the distance from the center of the central
openings 48 and the center of the locator nubs 60.
Likewise, the locator holes 62 in each .stator lamination 26
are formed during the same stroke of the press which forms
the central opening 72 of the lamination so that the distance
between the center of the stator bore 40 formed by the
stacked stator laminations 26 and the center of the locator
holes 62 is maintained within a close tolerance. The
maintenance of these close tolerances in turn allows the
relative radial position of the rotor assembly 36 and stator
21
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core 24 to be maintained within a tight range for each motor
20 manufactured.
The locator nubs 60 of the end frames 50, 52 are
disposed on an embossment 112 formed on each foot 96 of the
end frames and protruding inwardly from an inwardly facing
surface 114 of the foot (FIG. 4}. As shown in FIG. 10, the
embossments 112 are the portions of the feet 96 of each end
frame 50, 52 which engage a respective end face of the stator
core 24. All of the embossments 112 on each end frame 50, 52
are formed at the same time in the die ~so that their relative
location is very precise, more so particularly than the
relative location of the inwardly facing surfaces 114 of the
feet 96. The embossments 112 on each end frame 50, 52 are
generally located in a plane so that when they engage the
stator core 24 the end frame is not undesirably pitched or
cocked with respect to the stator core. As a direct
consequence, the longitudinal axis of the rotor shaft 42 is
better aligned with the centerline of the stator core bore
40.
Referring now to FIGS. 3 and 11-14, the second
bearing 46 includes a plastic, tubular housing formed from
first and second pieces (generally indicated at 116 and 118,
respectively) and having a shaft receiv_Lng passage 120. An
annular raceway defining member 122 is disposed in the shaft
receiving passage 120 and extends around the shaft receiving
passage. A plurality of long, thin needle bearings 124
(broadly, "shaft bearing means") are disposed in the raceway
of the raceway defining member 122 and engage the rotor shaft
42 in the shaft receiving passage 120. The rotor shaft 42 is
received through the shaft receiving passage 120 of the
second bearing 46 and is supported for .rotation by engagement
with the needle bearings 124, but is free of any fixed
connection to the second bearing. Thus, the shaft 42 and
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second bearing 46 are free to slide lengthwise of each other
such that the location of the second bearing on the rotor
shaft is determined by the engagement of the second end frame
52 with the stator core 24.
The first and second pieces 116, 118 of the second
bearing housing are substantially identical, each having a
cylindrical outer wall 126 sized for close fitting reception
in the central opening 48 of the second end frame 52 and a
generally cylindrical inner wall 128 wh_ch is concentric with
and spaced radially inwardly of the outer wall. As shown in
FIG. 13, the outer and inner walls 126, 128 are joined by
three generally thin, arcuate diaphragm portions 130
extending between the inner and outer walls. The arcuate
diaphragm portions 130 are spaced angularly of each other
around the shaft receiving passage 120 by arcuate voids 132.
The arrangement of arcuate diaphragm portions 130 and voids
132 is such that the relative location c>f diaphragm pardons
and voids is exactly reversed about a transverse line Z4.
Thus, when the second piece 118 is rotated about the line L4
and brought into engagement with the first piece 116, the
diaphragm portions 130 of the first piece are received in the
voids 132 of the second piece and vice versa. The diaphragm
portions 130 of the first and second pieces 116, 118 form a
continuous annular diaphragm 134 when the first and second
pieces are mated together.
Preassembly of the second bearing 46 is carried out
by installing the raceway defining member 122 in the first
piece 116 of the housing. The raceway defining member 122
engages a locating shoulder 136 formed in the first piece 116
and projects out of the first piece. The second piece 118
slides over the exposed portion of the raceway defining
member 122 and into engagement with the first piece 116. The
raceway defining member engages another locating shoulder 138
23
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in the second piece 118, arid the diaphragm portions 130 of
the first and second pieces mate in the way described above
to form the continuous diaphragm 134. The first and second
pieces 116, 118 are temporarily held on the raceway defining
member 122 by friction fits, and there is preferably no
separate connection of the pieces to one another. Upon
installation of the second bearing 46 in the central opening
48 of the second end frame 52, and bending of the retaining
tabs 102 against the second piece 118, t:he first and second
pieces are held together by engagement with the retaining
tabs and the retaining lip 98 of the central opening 48. It
is to be understood that the second bearing 46 may be formed
as one piece or otherwise than precisely described herein and
still fall within the scope of the presE:nt invention.
The rotor shaft 42 may extend through the shaft
receiving passage 120 of the second bearing 46 at an angle to
the longitudinal axis L5 of the shaft receiving passage in
the undeformed configuration of the second bearing housing.
In that event, the diaphragm 134 deforms by deflecting out of
its plane to permit the shaft receiving passage 120 to be
pivoted to generally align itself with the longitudinal axis
LA of the rotor shaft 42. However, the diaphragm 134 has
sufficient strength of resist translational movement of the
rotor shaft 42 in directions perpendicular to its
longitudinal axis LA so that the shaft does not wobble as it
rotates in operation. The plastic material of the second
bearing housing pieces 116, 118 has a preferred modulus of
elasticity in the range of 400,000 to 800,000 psi. It is
believed that a modulus of elasticity of the plastic as high
as 2,500,000 would still permit the second bearing 46 to
function properly. Steel and other materials having far
greater moduli of elasticity could be used if made
sufficiently thin.
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To reduce noise in operation, the clearance between
the needle bearings 124 and the rotor shaft 42 is taken up by
intentionally canting the second bearing 46 relative to the
longitudinal axis L5 of the rotor shaft 42. Canting is
accomplished by an asymmetrical formation (broadly "canting
means") on the housing, which in the illustrated embodiment
comprises a pair of longitudinally and radially opposite
bumps 140 on the outer walls 126 of the first and second
housing pieces 116, 118 (see FIGS. 12 and 14). The bump 140
associated with the first housing piece 116 engages the
retaining lip 98 in the central opening 48 of the second end
frame 52, causing the second bearing 46 to be tilted relative
to the second end frame in the central opening. As
illustrated in FIG. 2, the bump 140 is sized so that the
longitudinal axis L5 of the shaft receiving passage 120 makes
an angle of approximately 1° with the longitudinal axis LA of
the rotor shaft 42. The angle shown in FIG. 2 has been
greatly exaggerated for purposes of illustration. The
intentional misalignment of the axes of the shaft receiving
opening 120 and the rotor shaft 42 causes the shaft to bear
against the needle bearings 124 and to elastically deform the
diaphragm 134. The elasticity of the diaphragm material
provides a reaction force against the rotor shaft 42 so that
the needle bearings 124 are held against the shaft. This
constant, forced engagement of the rotor shaft 42 and the
needle bearings 124 significantly reduces noise during
operation.
The bump 140 on the second housing piece 118 is not
necessary to produce the desired cant of the second bearing
46 relative to the longitudinal axis of the rotor shaft 42.
Of course, the bump 140 is present on the second piece 118
because it is identical to the first piece 116. To do away
with the bump 140 on one of the housing pieces would require
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completely separate molds for the two pieces 116, 118 which
is undesirable from the stand-point of cost and simplicity of
assembly. However, the bump 140 on thf~ second piece 118
also facilitates installation of the second bearing 46 in the
central opening 48 of the second end frame 52 with the
desired cant. More specifically, the bump on the second
piece is constructed for engagement with an .installing tool
(not shown) having a flat face which engages the radially
inner end of the second piece 118 for pushing the second
bearing 46 into the central opening 48 of the second end
frame 52. The bump 140 on the second piece 118 causes the
second piece, and hence the entire second bearing 46 to be
canted in the same direction as the engagement of the bump
140 on the first piece 116 with the retaining lip 98. Thus,
the desired misalignment is achieved evE~n when, as will occur
from time to time, the bump 140 on the first piece 116 is not
fully seated against the retaining lip 98 in the central
opening 48.
The windings 27 may be connected to a source of
electrical power via the plug arid termir..al assembly 56
mounted on the second end frame 52 of the motor 20. As shown
in FIG. 7, the plug and terminal assembly 56 includes a two-
piece casing, generally indicated at 150, made of insulator
material, and a plurality of lead terminals 152 which receive
the magnet wire leads 80 extending from the windings 27. The
lead terminals 152 each have a serrated formation 154
including a plurality of sharpened ridges so that when the
lead terminals 152 are crimped onto the magnet wire leads (as
shown for the top terminal in FIG. 7), the insulation of the
magnet wire is penetrated by the ridges to provide electrical
connection. In the preferred embodiment, the lead terminals
152 are Amplivar~ terminals manufactured by Amp, Inc. of
Harrisburg, Pennsylvania. Referring to Fig. 9, a switch 157
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forming part of a switch circuit (generally indicated at 155)
housed in the casing 150 is operable between a first switch
mode (shown in solid lines) in which the start winding 28 is
activated and a second switch mode (shown in phantom) in
which the start winding is deactivated. The switch 154 is
operated by the centrifugal mechanism 58 in a way which is
well known in the art. Generally, the centrifugal mechanism
58 rotates with the rotor shaft 42, and extends as the
revolutions of the shaft reach a predetermined level to
actuate a lever arm 159 which opens the switch 157. As shown
in FIG. 5, a plurality of electrical connectors (designated
sequentially by reference numerals 156a--156f) protruding from
casing 150 are electrically connected to lead terminals 152
through the switch circuit. The electrical connectors 156a-
156f are constructed as plugs for plug-in connection to a
source of electrical power.
The switch circuit 155 is of conventional
construction and is schematically shown in Fig. 9 as part of
the electrical circuit including the windings 27, a plug 160
from the power source and contral switches associated with
the power source. A pair of leads 162, 164 are respectively
interposed between electrical connectors 156b and 156c and a
pair of terminal posts 166, 168 of a single pole double throw
speed selector switch 170. Speed selector switch 170 has a
movable arm 172 for selective circuit making engagement with
its cooperating posts 166, 168, and the switch arm 172 is
connected in circuit relation with a line terminal LT1. A
switch 173 located in the circuit between the electrical
connector 156a and the six pole (low speed) winding 32 is
shown in its motor start position in which the four pole
(high speed) winding 30 will be activated even of the arm 172
of the selector switch 170 has been moved to post 168 for low
speed operation of the motor 20. The switch 173 is moved as
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a result of actuation of the lever arm 159 by the centrifugal
mechanism 58 to de-energize the four pole winding 30 and
energize the six pole winding 32 when the motor reaches the
predetermined speed. Of course, when high speed (i.e., the
four pole winding 30; is selected by moving the arm 172 into
engagement with post 166, movement of 'the switch 173 out of
electrical contact with the four pole winding does not result
in energization of the six pole winding 32 or de-energization
of the four pole winding 30.
Another line terminal LT2 is connected by a lead
174 with electrical connector 156f, the line terminals LTl,
LT2 defining the power source. A double pole double throw
reversing switch 176 of the type well known in the art is
used for controlling the direction of current through start
winding 28 and, consequently, the direction of rotation of
the motor.20. A lead 178 connects the reversing switch 176
to a terminal post 1~6 of speed selector switch 170. Other
leads, designated 180a-180c, connect the reversing switch 176
to electric connectors 156d, 156e and 156a, respectively. A
ground lead 182 connects the second end frame 52 to ground,
as described in more detail below.
The casing 150 of the plug and terminal assembly 56'
is formed with an integral stall 186 for receiving a thermal
protector indicated generally at 188 (sh.own exploded from the
stall in FIG. 3) which protects the motor 20 from overloads.
The thermal protector 188 has a housing 189 and two contacts
190 projecting from it for connection to the switch circuit
155. The thermal protector 188 may be inserted into the
stall 186 with the contacts 190 extending further into the
casing 150 generally in registration with contacts 192 of the
switch circuit 155 (FIG. 9). As shown in FIG. 7, two
openings 194 on each side of the casing 150 are located at
the junction of the thermal protector contacts 190 and switch
28
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circuit contacts 192 (not seen in FIG. 7). A joining tool
(not shown) is extended through the openings 194 to join (as
by soldering) the thermal protector contacts 190 to the
switch circuit contacts 192.
As shown in FIGS. 4 and 5, the plug and terminal
assembly 56 is supported in a cutout 200 formed in the skirt
94 of the second end frame 52 without fixed connection to the
end frame or other part of the motor 20. Slot defining
formations, generally indicated at 202, on each side of the
plug and terminal casing 150 define slots 204 which receive
respective edge margins 2OC of the second end frame 52
bounding the cutout 200. The slots 204 are sized so that the
slot defining formations Z02 grip the second end frame edge
margins 206 in the slots to facilitate holding the plug and
terminal assembly 56 in position. However, the slot defining
formations 202 do not grip the edge margins 206 of the second
end frame 52 so tightly as to prevent the plug and terminal
assembly 56 from being manually slid into and out of the
cutout 200. The plug and terminal assembly 56 is further
secured in position in the cutout 200 by locating post means
comprising in this embodiment a single generally triangular
locating post 208 generally adjacent one end of the plug and
terminal assembly, and a pair of flat en.d surfaces 210 of the
slot defining formations 202 located adjacent the opposite
end of the plug and terminal assembly. The locating post 208
and the flat end surfaces 210 are formed as one piece with
the casing 150. As shown in FIG. 8, the locating post 208
and flat end surfaces 210 engage one end face of the stator
core 24 and urge the plug and terminal assembly 56 against
the second end frame 52 at the closed end of the cutout 200.
A cylindrical projection 212 at the axially inner end of the
locating post 208 is received in one of the slots 76 of the
stator. Thus, it may be seen that the plug and terminal
29
CA 02485937 1994-10-13
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assembly 56 is mounted on the motor 20 without welding and
without any nuts, bolts or other fastening devices.
The first and second end frames 50, 52 of the motor
are grounded by connection to the ground associated with the
power source (e.g., the frame of a washing machine) by a
ground tab (designated generally by reference numeral 218)
formed as one piece with the second end frame. As shown in
FIGS. 4 and 5, the ground tab 218 is located at the bottom of
the cutout 200 in the second end frame 52. The cutout 200 is
formed in the sheet metal blank at a location corresponding
to one side of the skirt 94 of the second end frame 52.
However, the metal is not completely removed and a portion
remains as a flap 220 extending laterally outwardly from the
second end frame 52 at the bottom of the cutout 200. The
ground tab 218 is stamped out of the material in the flap 220
and bent to project axially inwardly from the flap. An
electrical connector portion 222 of the ground tab 218
projects radially outwardly of the remainder of the tab, and
a stabilizing finger 224 extends axially inwardly of the
electrical connector portion.
The plug and terminal assembly casing 150 is formed
with an opening 228 which receives the ground tab 218 upon
insertion of the plug and terminal assembly 56 into the
cutout 200. As shown in FIG. 5, the electrical connector
portion 222 of ground tab 218 as received in casing 150 is
aligned with the other electrical connectors 156a-156f which
are adapted to be connected to the plug 160 associated with
the power source (FIG. 9). The stabilizing finger 224 is
received in a recess 230 at the end of the opening 228
defined in part by an overhang portion 232 of the casing 150
(FIG. 6). In the recess 230, the stabilizing finger 224 is
held by engagement with the overhang portion 232 and the
portion of the casing 150 opposite the overhang portion from
CA 02485937 1994-10-13
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substantial movement transverse to the 7_engthwise extension
of the finger as shown in FIG. 6. Thus, the stabilizing
finger 224 aids in holding the plug and terminal assembly 56
in place in the cutout 200 in the second end frame 52 by
resisting tilting movement of the plug and terminal assembly
casing 150.
Referring now to FIGS. 17-19, the rotor assembly 36
of the present invention is made up of a stack of generally
thin, circular rotor laminations 240 made of highly
magnetically permeable material. Slots 242 in the rotor
laminations 240 are spaced circumferenti.ally around the
periphery of the rotor laminations. As shown in Fig. 19,
each slot 242 includes a radially inner portion 244 and a
radially outer skew portion 246 extending outwardly and
laterally (e. g., circumferentially), frc>m the radially inner
portion toward the circumference of the rotor_ lamination 240.
The radially inner portion 244 of each ;lot 242 at least
partially overlies corresponding radially inner portions of
slots on the other rotor laminations in the stack forming the
rotor 38. The overlying slots 242 define axially extending
passages in which rotor bars 248 are disposed. The rotor
bars 248 are formed by pouring molten aluminum or another
suitable conductor into the passages formed by the overlying
slots (FIG. 17). However, it is to be understood that rotor
bars may be placed in the rotor 38 by other methods, such as
press fitting, and still fall within the: scope of the present
invention. The rotor bars 248 are not shown in FIGS. 18 and
19 for clarity, but are connected at the ends thereof by end
rings (not shown) to form a squirrel cage rotor conductor
arrangement as will be understood by persons skilled in the
art.
The rotor laminations 240 in the stack defining the
rotor 28 are arranged in three adjacent sets, designated 250,
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CA 02485937 1994-10-13
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252 and 254, respectively. The slots 242 in the first set of
laminations 250 have their skew portions 246 extending
laterally in a first direction, the slogs in the second set
of laminations 252 have their skew portions extending
laterally in a second direction opposite the first, and the
slots in the third set of laminations 2-'i4 have their skew
portions extending laterally in the firs>t dir_ection. All of
the rotor laminations 240 are virtually identical. Thus, the
slots 242 are of substantially the same size and shape, and
thus the slots in the second set of laminations 252 (as
arranged in the stack) appear to be mirror images of the
slots. in the first set 250 and third set 254 of laminations.
As shown in FIG. 19, the radially inner portions 244 of
partially overlying slots of the first ~>et 250 and second set
252 of laminations generally overlie each other. However,
the skew portions 246 of the first set 250 and second set 252
of laminations have no portions which are overlying. The
skewed condition of the skew portions 29:6 of the slots 242 of
the second set 252 of laminations relative to the skew
portions of the first set 250 and third set 254 of
laminations facilitates decoupling from the rotor bars 248 of
stator slot order winding harmonics and stator slot opening
permeance harmonics. The first set 250 and third set 254 of
rotor laminations have slots 242 which are oriented the same
way, and the second set of laminations 252 is interposed
between the first and third sets. The dimension of each of
the first set 250 and third set 254 of rotor laminations
parallel to the longitudinal axis LA of the rotor shaft 42 is
preferably approximately equal to 1/4 the total axial dimension
of the rotor, and the dimension of the second set of
laminations 252 is preferably approximately equal to 1/2 the
total axial dimension of the rotor. The arrangement of the
sets 250, 252, 254 of rotor laminations produces a more
32
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balanced rotor which reduces mechanical noise in operation of
the motor 20. Moreover, the arrangement of laminations 240
into the three sets 250, 252 and 254 reduces current loss due
to leakage from the rotor bars into tYie laminations 240. It
is to be understood that the rotor 38 may be formed from two
sets of rotor laminations 240 having slots 242 which are
skewed, or more than three sets of rotor laminations and
still fall within the scope of the present invention. The
skew of the present design is easily manufactured and
provides particularly good performance for single phase
motors.
Referring to FIGS. 17 and 1~~, the laterally
outermost points L of the skew portions 246 of the overlying
slots 242 in said first set of rotor laminations 250 lie
generally along a first axially extending line A1 and the
laterally outermost points of said skew portions of the
corresponding slots in said second set of rotor laminations
252 lie generally along a second axially extending line A2.
The skew of the slots 242 in the first and second sets may be
represented by the distance d between whe first line A1 and
the second line A2. In the preferred embodiment, the
distance d falls within a range expressed by the following
equation,
(2~tr) / (2S - P) < d <_. (2~r) / (2S - P) + 8 + p (1)
The variable r is the radial distance between the center of
the rotor lamination 240 and the either line A1 or A2
(Fig. 18). S is the number of slots in the stator core, and
P is the number of poles of a selected one of the windings
(the harmonics of which are to be decoupled from the rotor).
As explained in more detail below, p/2 corresponds to the
distance between the laterally outermost point L of the slot
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242 and its radially outermost point R (FIG. 19), and 8/2
generally corresponds to the distance ~/2 between a first
magnetic saturation region M1 and a second magnetic
saturation region M2 (FIG. 20).
More specifically, p/2 is the distance between
first and second parallel planes (which are seen on edge in
FIG. 19 and appear as lines A3 and A4, respectively) in a
third plane (which is also seen on edge in Fig. 19 and
appears as line A5) which includes the lines A1 and A2. The
first plane A3 includes the radially outermost point R of the
skew portion 246 of the slot, and the second plane A4
includes the line Al or A2. The first plane A3 and second
plane A4 intersect the third plane A5 at right angles, and
all three planes (A3, A4, A5) are perpendicular to the plane
in which FIG. 19 lies.
The distance 8/2 is explained with reference to
FIG. 20 showing two sets of rotor laminations 258 having
slots 260 with skew portions 246 which extend laterally in
opposite directions. The illustrated skewed slots 260 do not
have the same shape as the slots 242 shown in Fig. 19.
Generally, the rotor laminations 240 having slots 242 have
more material between the slot and the circumference of the
rotor lamination 240 than the rotor laminations 258 having
slots 260. The configuration of the s7_ats 260 is an initial
configuration chosen on the assumption that, for each slot
260, the sole location of magnetic saturation is region M1
adjacent the radially outermost point P, of each slot which
corresponds to the slot bridge (i.e., the narrowest strip of
material surrounding the slot). However, as explained below,
we have found an unexpected result that. a second saturation
region M2 occurs at a location spaced from the first
saturation region MI. The distance 8/2 corresponds to the
distance between parallel lines, designated A6 and A7,
34
CA 02485937 1994-10-13
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respectively. Line A6 is perpendicular to the plane A5 and
intersects the first saturation region M1 (and radially
outermost point R). Line A7 is also perpendicular to plane
A5 and intersects the second saturation region M2.
The stator slot order harmonics which are decoupled by
the skew of the rotor bars 248 are represented by:
n = 2mS/P ~ 1 (2)
where n is the harmanic order number, m is the mode number
(typically m=1), S is the number of slots in the stator
core 24, and P is the fundamental number of magnetic poles of
the motor 20. In order to decouple a particular stator slot
order harmonic, the mutual reactance X of the slot should go
to zero. Mutual reactance X may be expressed by the
following equation for the skew geometry of the rotor bars
248 of rotors embodying the present invention:
X = XmXa, where Xa = cos (nc~/4) (3)
Xa is the component of mutual reactance attributable to the
angle tx of skew of the rotombar in "e:Lectrical" degrees. In
order to decouple a particular harmonic X~,:
anl4 = n/2 (4)
Substituting for n in equation (2), the angle of skew a
needed to decouple the stator slot order harmonics can be
expressed as:
a/2 = n (2S/P ~ 1) (5)
The conversion to mechanical degrees of. skew is made by
substituting ex = e~echP/2. or:
~nech/2 = 2n/ (2S ~ P)
Thus, the predicted distance d° in plane A5 between
the lines A1 and A2, defined above, may be found by
substituting for c~,e~h in equation (6)
amech = 2nd' / ( 2nr )
or, after simplification:
d' - (2nr) / (2S ~ P) (8)
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It is apparent from equation (7) that distance d' is the
length of an arcuate segment of a circle having a radius r.
The arcuate segment corresponding to d' would be defined by
the intersection of radial lines (not shown) passing through
the laterally outermost points L of the skew portions 246
with the circle of radius r. However, the difference between
the linear distance between end points of the arcuate segment
of length d' and the length d' is so small that it has been
represented as a linear distance in the drawings. Likewise,
the distances b and p, which are actually lengths of arcuate
segments of a circle having a radius r, are shown for
simplicity as linear distances in a plane A5. The distances
8/2 and p/2 are large relative to the difference between the
arcuate distance and the linear distance between end points
of the corresponding arcuate segments. The arcuate segment
of length b 2 would be defined by the intersection of radial
lines (not shown) passing through the first and second
saturation regions M1 and M2, respectively, with the circle
of radius r. The arcuate segment of length p/2 would be
defined by the intersection of radial .Lines (not shown)
passing through the radially outermost point R and laterally
outermost point L of a slot 242 with the circle of radius r.
The predicted distance d' (which is actually a
range due to the presence of ~P) does not in fact equate to
the distance d between laterally outermost points of the skew
portions 246 of the slots 242 of the rotor laminations of the
first set 250 and second set 252. The predicted distance d'
must be first corrected by adding p/2 for both the slots of
the first set 250 of rotor laminations and the slots of the
second set 252 of rotor laminations to account for the
distance (p/2) in the plane line A5 between the radially
outermost point R and the laterally outermost point L
intersecting line A1 of the first set slot, and the distance
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(p/2) in the plane A5 between the radially outermost point R
and the laterally outermost point L intersecting line A2 of
the second set slot. Ideally, p would equal zero and the
radially outermost point R would coincide with the laterally
outermost point L. However, the slot 242 should preferably
have a finite radius of curvature at the radially outermost
point R to accommodate manufacture so the two points L and R
do not actually coincide.
However, even when the distance d' has been
modified to account for the noncoincid~~nce of the radially
outermost point R and the laterally outermost point L, the
optimum skewing for single phase motors has not been
achieved. The equations (3)-(8), used to predict the
necessary skew distance d', clearly assume that the location
of magnetic flux saturation (M1) will be in the narrowest
strip of rotor lamination material bettaeen the slot 260 and
the outer circumference of the lamination 258 (i.e.,
generally at the radially outermost point R of the slot).
Referring to FIG. 20, the predicted distance between
laterally outermost points L of the slots 260 having
oppositely extending skew portions is d' + p. In Fig. 20,
p/2 is the distance between a first plane (seen on edge in
FIG. 20 and represented by line A6) and a second plane (also
seen on edge in FIG. 20 and represented by line A8). The
fi-rst plane A6 intersects the radially outermost point R and
is perpendicular to a third plane seen on edge in FIG. 20 and
represented by line A5. The second plane A9 is parallel to
the first plane A6 and intersects a line including the
laterally outermost points L of the axially aligned slots of
a respective set of rotor laminations 258.
However, we have surprisingly found that for single
phase motors there is a second saturation region M2 spaced
from the first region Ml, as discussed above (Fig. 20). In
37
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order to compensate for this unexpected anomaly, the skew
distance d is further increased from the predicted distance
d' + p by 8, where cS/2 corresponds to the distance between
the narrow strip (i.e., first magnetic saturation region M1)
and the second saturation region M2, as stated above. The
skew distance d will always be greater than the predicted
distance d'. Accordingly, the lower limit for the skew
distance d will be greater than the upper predicted distance
d' (i.e., d > ~D/(2S-P) + p). The amount 8 varies from slot-
to-slot and with the rotational position of the rotor 38
relative to the stator 22. Therefore, b is actually an
averaged value of the actual 8 associated with each slot 242.
Presently, we have determined b both experimentally, and by
use of a finite element analysis of the rotor 38. In view of
the foregoing, d would preferably be chosen as:
d = ~D/2S + p + 8 (9)
where the quantity p + 8 is sufficiently large so that the
distance d still exceeds the predicted distance d°, or:
p + 8 > ~D/(2S-P) - nD/(2S) ,(10)
The dynamoelectric machine (induction motor 20) of
the present invention is constructed for ease, speed and
precision of assembly. The component parts of the motor
shown in FIG. 3 may be assembled without the use of fasteners
other than the keys 64. Nut and bolt fasteners may be
completely eliminated. As discussed above, many of the
component parts, in particular the stator 22 and the end
frames 50, 52, have been constructed to achieve greater
precision and to facilitate the final assembly of the motor
20. The following is an example of one way in which the
motor components shown in FIG. 3 might be assembled together.
However, this example is not exclusive of other possible
methods of assembly, particularly in the order of assembly.
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The first bearing 44 is press fit onto the rotor
shaft 42 of the rotor assembly 36 at a predetermined
location. The centrifugal mechanism 58 is fixed to the rotor
shaft 42 on the opposite side of the rotor 38 from the first
bearing 44. The end of the rotor shaft 42 mounting the first
bearing 44 is inserted into the central opening 48 of the
first end frame 50 with the first bearing engaging the
retaining lip 98 of the central opening to terminate further
movement of the rotor shaft and first bearing through the
opening. The retaining tabs 102 are bent over against the
first bearing 44 to capture the first bearing in the central
opening 48 of the first end frame 50.
The stator 22 is placed over the rotor assembly 36
with the rotor 38 being received in the stator core bore 40.
One end face of the stator core 24 engages the embossments
112 on the feet 96 of the first end frame 50, and the locator
hubs 60 are received in corresponding locator holes 62 of the
stator core 24. The stator windings 2'7 are connected to the
plug and terminal assembly 56 by placing the magnet wire
leads 80 into respective lead terminals 152 and crimping the
terminals against the magnet wire (FIG. 7). The ridges of
the serrated formation 154 of the lead terminals 152
penetrate the magnet wire insulation and bring the lead
terminals into electrical connection with the magnet wires.
The second bearing 46, assembled as previously
described, is secured in the central opening 48 of the second
end frame 52 by bending over the retaining tabs 102 against
the bearing. The second end frame 52 is placed over the end
of the rotor shaft 42 opposite the first end frame 50 and the
rotor~shaft is received in the shaft receiving passage 120 of
the second bearing 46. The plug and terminal assembly 56 is
mounted on the second end frame 52 by pushing it into the
cutout 200. The slots 204 of the slot defining formations
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202 have flared mouths 234 at one end to facilitate entry of
the edge margins 206 bordering the cutout 200 into the slots
(FIGS. 4 and 5). The ground tab 218 is received into the
opening 228 in the casing 150 as the plug and terminal
assembly 56 is pushed into the cutout 200, and the
stabilizing Linger 224 enters the recess 230. The electrical
connector portion 222 of the ground tab 218 is aligned with
the electrical connectors 156a-156f of the plug and terminal
assembly 56 so that it is prepared to be plugged into the
ground lead 182 when the motor 20 is connected to a source of
electrical power.
The second end frame 52 is pushed toward the end
face of the stator core 24 with the rotor shaft 42 sliding
through the shaft receiving passage 120 until the embossments
112 on the feet 96 of the second end frame 52 engage the end
face of the stator core with the locator nubs 60 received in
the locator holes 62 in the stator core. The motor
components are secured together by placing the keys 64 into
the channels 66 in the stator core 24 and deforming the ends
68 of the keys over onto the feet 96 of respective end frames
50, 52. The intentional misalignment of the axis L5 of the
shaft receiving passage 120 of the second bearing 46 with the
longitudinal axis LA of the rotor shafts 42 causes the
diaphragm 134 of the second bearing to be elastically
deformed and hold the needle bearings 124 against the rotor
shaft.
In view of the above, it will be seen that the
several objects of the invention are achieved and other
advantageous results attained.
As various changes could be made in the above
constructions without departing from the scope of the
invention, it is intended that all matter contained in the
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above description or shown in the accompanying drawings shall
be interpreted as illustrative and not in a limiting sense.
4~
