Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to electric motors
and in particular to multi-rotor electric motors having
a common startor.
Prior Art
.,
The concept of using a plurality of rotors
and common starter in the single electric motor housing
is well known. In prior art motors of this type, the
rotors are usually located for rotation one within the
other on concentric shafts within an electrical field
by a stator exterior to both.
Each of the rotors conventionally has a
commutator and stationary brushes and rotate independ- ~ -
ently of each other.
SUMMARY OF THE INVENTION
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~5 The present invention provides a dual-rotor
electric motor having a stator sandwiched between the
two rotors so as to take advantage of full flux and
which is so arranged that only one of the rotors need
be provided with a commutator and brushes.
The rotors of the present motor are, further-
more, independently rotat~ble yet are automatically
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connectçd for mutual rotation to obtain increased
torque when one of the rotors attempts to slow down
under over-load conditions, thus reducing likelihood
of motor damage.
A detailed description following, related to
the drawings, gives exemplification of apparatus and
method according to the invention which, however, is
capable of expression in method and means other than ~ -
those particularly described and illustrated. ~ ~
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DESCRIPTION OF THE DRAWINGS
Fig. 1 is a central sectional view through the upper
half of the dual-rotor electric motor, ~-
Fig. 2 is an end view of the same with the casing
partially removed,
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Fig. 3 is a view taken on Line 3-3 of Fig. 1
DETAILEE) DESCRIPTION
Referring to the drawings, and in particular
to Fig; 1, the upper half of the motor is shown only,
it being understood that the lower is symmetrical
therewith. r
The motor includes a housing 10 having a cir-
cumferential wall 11 and end shields 12 and 13 connected
thereto by machine screws 14.
The motor, generally, has a wound rotor 16
rotatable within a cup-shaped stator 17, windings
of which when connected to a polyphase source of power ~-
provides a rotating magnetic field. The rotor and ~ ;
stator act as components of an induction motor. The
motor also includes a second rotor 19 carrying perm-
anent magnets disposed about the stator in concentricity
therewith, which is normally connected by a clutch
assembly 21 to the first rotor 16. Said clutch
assembly being arranged to link the rotor 16 and 19 for
mutual rotation from starting speed to rated speed of
the first rotor 16 which is fractionally less than
synchronous speed. The clutch said rated speed dis-
engages the rotors for independent rotation.
'
As seen in Fig. 1 the rotor 16, which has a
core and windings, generally 23, is keyed on a main
drive shaft 24, one end 25 of which is supported for
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rotation in bearings 26 in the end shield 13 of the
housing. The drive shaft 24 extends at its opposite
end 31 through a tubular drive shaft 32, the latter
being mounted for rotation in bearings 33 secured by
a retaining plate 34 in the end shield 12 of the housing
10. Bearings 35 support the drive shaft 34 for rotation
within and co-axially of the tubular drive shaft.
. . .
The stator 17 has a cup-shaped support 36,
bearing field windings 37 and has an annular tubular
support 38 provided with an end flange 39 which is
secured to the end wall 13 by bolts 41. Power leads - :
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43, shown in broken outline, extend through suitable
passages, now shown, in the tubular support 38 and are
lS connected to brushes 44 mounted on the tubular support
which are in wiping engagement with commutator 45 of
the rotor 16.
The second rotor 19 has a pair of annular
end plates 51 and 52 between which a cylindrical carrier
~3 is secured by cap screws, severally 54. The carrier
is formed of a dielectric material and carries a
plurality of permanent magnets, severally 55, secured
thereto by bolts 56. The end plate 51 is secured by
bolts 58 to a flange 59 on the inner end of the tubular
drive shaft and the end plate 52 is supported for
rotation on the tubular support 38 by bearings 61.
The permanent magnets are arranged so that their re- `
action with magnetic lines of force developed in the
rotating magnetic field develops torque tending to ~ -
turn the second rotor in the same direction
as the main rotor. A second stator 63 having ~-
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windings 64 similar to the windings of the first stator
17, is secured by machine screws 65 to the circumferential
wall 11 of the housing and are connected through leads
not sho~n to the same source of polyphase power.
c
The end plates 51 of the rotor 19 has an
inner frustoconical projection 67 to which a wear plate
68 is secured. The clutch assembly 21 includes an
annular carrier 72 which is secured by bolts 73 to the
end of the rotor 16 confronting the end shield 51.
The carrier has a radially extending clyindrical socket ~ -
76 over which an annular retaining plate77 having-an
annular sleeve78, is bolted. The socket slideably
receives the upset end 81 of a shaft 82 ~hich slideably
extends outwards through the sleeve 78. The outer end
of the shaft carries a clutch shoe 84 and a weight 85
which are secured against sliding relative to the shaft
between a stop 86 and a nut 87 threaded on the outer -
end of the shaft. The clutch shoe 84 extends over the
wear plate and has an inner face provided with clutch
lining 88 which matches the shape of the wear plate 68.
A compression spring 91 fits over the shaft between
the retaining plate 77 and the upset end 81 of the
shaft normally urging the clutch shoe into engagement
with the wear plate 68 so as to link both rotors for
mutual rotation. The strength of the compression spring
is such that when the first rotor reaches a speed
fractionally less than that of rated speed the centri-
fical force of the clutch shoe and the weight acting
outwards against the outer end of the shoe result in
slight compression of the spring and thus will effect-
ively result in disengagement of the clutch lining
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and wear plate so that both rotors are free to rotate
independently of each other.
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Between speeds from start to fractionally -
less than rated speed of the rotor 16, both rotors ~ ;
are engaged for mutual rotation. The torque of the
rotor 16, common in induction motors, decreases
as speed increases whereas the torque of the -
rotor 19, common in synchronous motors,
increases as speed increases so as to result in a
high combined torque from 0 speed to rated speed. When
the speed of the rotor 16 reaches a speed fractionally
less than rated speed, disengagement of the clutch
allows the speed of the rotor 19 to increase until rotor
19 reaches the speed synchronous with the rotating field.
If the speed of the rotor 16 due to increase in torque
demand, should fall below clutch release speed the clutch ~ -~
will re-engage to link both rotors and thus increase
the torque output and enable the rotor 16 to regain
rated speed, thus greatly reducing chances of damage which
are normally suffered by electric motors occasioned by
slow down under heavy loading.
.
Under normal operating conditions the clutch
will always be disengaged so th~t the rotor 19 under
such normal conditions can be connected by way of the
tubular drive shaft to drive components other than '~
those driven by the rotor 16.
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It is to be understood that although the
rotor 1~ has been shown and described as an induction
rotor it can also be a synchronous motor in which case
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rated speed thereof will be synchronous speed. The
clutch assembly would be arranged to release at speeds
fractionally less than synchronous speed.
