Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to induction motors, and
in particular it relates to rotor punchings for an
induction motor.
In the manufacture of induction motors, a
number of generally circular, similar punchings from
sheet metal are stacked together to form a rotor core.
Each punching or lamination has a plurality of slots
spaced apart around the periphery and when the
punchings are stacked with the slots aligned the slots
are ready to receive a conductor. When the conductor
is placed in the slot, the fit must be such that there
is no vibration or rattling.
One way of ensuring a good fit is disclosed in
~anadian Patent No. 251 776 - Lindquist, issued July 14,
1925. This patent describes a corrugated strip of
resilient or elastic material that is placed in the
bottom of the slot usually after the conductor has
been inserted. This strip acts as a spring which
presses the conductor outwardly to prevent rattling
and vibration.
The installation of a separate spring at the
bottom of each slot complicates the assembly of the
rotor. It involves additional steps and is not always
easy to plac:e in position. In addition, it is not
particularly suitable for squirrel cage induction
motors.
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In a squirrel cage type motor the slots are
frequently closed at the outer periphery of the
punchings, that is, the slot frequently terminates
just inside the periphery. The conductor bar is
driven through the slot from an end of the s-tack of
laminations or punchings. The bar and the slot must
be dimensioned to provide a correct fit. If the bar
is of a size that makes a fit that is not tight enough,
the bar will rattle or some means must be provided
to take up the extra space. If the bar is of a size
that makes a fit that is too tight, the bar cannot be
driven into the slot with reasonable assembly forces.
In the assembly of squirrel cage rotors, it is known
to adjust the ~it of a particular bar or bars by
broaching the slot or by machining the bars. This
complicates and slows the assembly operation.
The present invention is concerned with
simplifying the construction of a squirrel cage rotor
for an induction motor and for providing for easier
assembly. The invention permits more clearance between
the slot walls and the conductor bar during assembly,
and prevents rattling by the use of a spring force.
The spring force is not applied by a separate spring
which requires individual installation in each slot.
According to the invention, the spring force is
provided by a special punching which has a spring
element projecting into the space to be occupied by
the bar. That is, the spring is an integral part of
~he punching. The special punching is interleaved
with the regular punchings at intervals in the stack.
When the conductor bar is driven through the slot it
deflects these spring elements or spring tabs which
then exert an outwardly directed force on the bar.
Assembly using the special punchings is faster, it
avoids any final broaching or machining steps, and it
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requires no additional steps.
It is therefore a feature of the invention to
provide a punching ~o be used in assembly which provides
a spring force on each conductor extruding through the
aligned openings or slots.
Accordingly the present invention provides a
rotor for an induction motor, comprising a stack of
punchings including first and second punchings, forming
the body of said rotor, said first punchings having a
plurality of conductor-receiving openings spaced
around said rotor, and being arranged with said
conductor-receiving openings in alignment, said first
punchings including at each set of aligned openings
means to restrain conductors against radially outward
movement, said second punchings being spaced apart in
said stack by at least several first punchings, said
second punchings having the same numbex of conductor-
receiving openings as said first punchings and being
arranged in said stack with the openings in alignment,
and a conductor extending through each set of aligned
; openings, said openings of said second punchings
having a portion extending radially inwardly farther
than necessary to receive a respective conductor and
having at the inward extent an outwardly projecting
integral tab engaging said respective conductor, said
tab being deflected when said conductor is inserted
through said aligned openings to provide on the
conductor an outwardly directed spring force, said
stack of punchings being provided with means to permit
deflection of said tabs.
The invention will be described with reference
to the acco]mpanying drawings, in which
Figure 1 is a plan view of a part of a punching
which is usl_d to form the body of a rotor according to
the invention, and
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Case 2661
Figure 2 is a plan v:iew of part of a special
punching incorporating a spring according to one form
of the invention,
Figure 3 is an elevat:ion in section of part of
a rotor showing a stack of punchings including those
of Figure 1 and 2.
Referring to Figure 1, a portion of a punching
10 is shown. Punchings are normally made from sheet
steel in a manner well known :in the art. The punching
10 has a main portion 11 with projeeting arms or
spokes 12 which define the edges 14 of a slot 15. The
slot 15 is enelosed, that is the edges 1~ defining the
outermost point 16 are very slightly spaeed from the
periphery 17 of punehing 10. This is eertainly not
essential but it is common for a squirrel cage rotor.
If punchings 11 are used where the slot is not
closed but is open, then some means, sueh as eaps or
wedges engaging grooves in the edges 14 at the
periphery, or sueh as conduetor-retaining peripheral
projeetions, must be provided to restrain eonduetors
in the slot against radially outward movement.
A broken line 18 indicates generally the
position in slot 15 the bar will oeeupy after it is
installed. The slot 15 is shown as having a portion
slightly deeper than the bar whieh it reeeives. Th~s
is to provide an open region 19 to accommodate movement
of a spring as will beeome elear in the following
description~ The slot 15 preferab~y has lips 27
whieh engage the bottom edges of a conduetor to
restrain it against inward movement, and to serve as
a guide during installation.
Referring now to Figure 2, a portion of
punehing 20 is shown. This punehing would normally
be made from the same material as punehing 10 but it
may be made from other materials as it oeeupies only
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Case 2661
a small volume of total rotor volume. For example, it
may be desirable to make punching 20 ~rom a m~terial
with better spring quali-ties.
Punching 20 has a main portion 21 with projec-
ting arms or spokes 22 which define lateral edges 23of slot 24. The slot 24 is also punched deeper than
necessary to accommodate a conductor bar, but it has
an integral tab or projection 25 which acts as a
spring. A broken line 26 inclicates generally the
position in slot 24 the bar will occupy after it is
installed. It will be seen that the projecting tab
or spring projection 25 extends into the region the
bar will occupy after it is installed.
It will be apparent that punching 21, which
is shown with an open slot 24 (i.e. open at its
outer ena~, could have a closed slot similar to slot
15 of punching 11.
Referring now to Figure 3, a sectional view of
part of a rotor is shown with punchings 10 stacked
together, and at intervals in the stack a punching
20. A conductor bar 28 is installed and the projecting
integral tab 25 of each punching 20 is deformed by the
bar 28 during installation of the bar. The spring
tabs 25 are bent into the open region 19. The deformed
spring tabs 25 apply an outwardly directed force to
keep the bar 28 firmly in the slot comprising slots
15 and 24 of punchings 10 and 20 respectively.
The spacing between punchings 20 is not
critical and can be determined for a particular design
of squirrel cage motor. If more spring force is
reguired, th~ spacing between adjacent punchings 20
can be decreased.
If ithe rotor is provided with ventilating
passages at intervals therethrough, it may be
convenient to position a punching 20 adjacent the
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ventilating passage. In such an arrangement the
projecting spring tab 25 can be deflected into the
ventilating passage as the conductor bar is installed
and the slots 15 in punchings 10 need not be any
deeper than the bar. That is, there is no need to
provide space at the hottom of slot 15 to provide
room for deflection of spring tab 25 as the room is
available in the ventilating passage.
It will be apparent that in the absence of
ventilating passages, space must be provided at the
bottom of slot 15 for deflection of spring projection
25, but this space is only required for several
punchings adjacent to each spring tab 25, that is
adjacent to each punching 20. Consequently an
alternative arrangement might have several punchings
10 adjacent each punching 20 with intermediate space
filled with normal punchings where slot 15 is only
deep enough to accommodate a bar.
Other variations and alternatives may become
apparent to those s~illed in the art.
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