U.S. patent application number 11/769930 was filed with the patent office on 2008-01-03 for brush dc motors and ac commutator motor structures with concentrated windings.
This patent application is currently assigned to Quebec Metal Powders Limited. Invention is credited to Jerome Cros, Philippe Viarouge.
Application Number | 20080001492 11/769930 |
Document ID | / |
Family ID | 24631551 |
Filed Date | 2008-01-03 |
United States Patent
Application |
20080001492 |
Kind Code |
A1 |
Cros; Jerome ; et
al. |
January 3, 2008 |
BRUSH DC MOTORS AND AC COMMUTATOR MOTOR STRUCTURES WITH
CONCENTRATED WINDINGS
Abstract
Structures of direct current motors or ac commutator (Universal)
motors which use a concentrated winding on the rotor with coils
wound around the teeth. The number of commutator segments is higher
than the number of rotor teeth. Several coils are wound around the
same tooth. The terminals of the coils are connected to different
segments of the commutator. The parallel paths of the armature
winding are perfectly balanced. An equal current distribution
through the parallel circuits of the armature is maintained and
there is no circulation current between these parallel circuits.
The problems related to commutation are reduced because the value
of the coil inductances is low. The copper volume of the
end-windings, the Joule losses and the axial length of the motor
armature are lower than a lap or a wave winding with interlocked
coils. Two kinds of structures with a concentrated winding are
presented: some with rotor teeth with identical dimensions and some
with rotor teeth with different dimensions.
Inventors: |
Cros; Jerome; (Quebec,
CA) ; Viarouge; Philippe; (Quebec, CA) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
Quebec Metal Powders
Limited
|
Family ID: |
24631551 |
Appl. No.: |
11/769930 |
Filed: |
June 28, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11117356 |
Apr 29, 2005 |
7239060 |
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11769930 |
Jun 28, 2007 |
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09656085 |
Sep 6, 2000 |
6891304 |
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11117356 |
Apr 29, 2005 |
|
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Current U.S.
Class: |
310/233 ;
310/154.01; 310/158 |
Current CPC
Class: |
H02K 1/146 20130101;
H02K 3/18 20130101; Y10T 29/49012 20150115; H02K 3/28 20130101;
H02K 21/16 20130101; H02K 23/30 20130101 |
Class at
Publication: |
310/233 ;
310/154.01; 310/158 |
International
Class: |
H02K 23/00 20060101
H02K023/00; H02K 23/26 20060101 H02K023/26 |
Claims
1-28. (canceled)
29. A direct current (DC) motor comprising: a stator, including a
number of stator poles 2P and a stator core; a concentrated-winding
rotor, including: a rotor core made of ferromagnetic material and
separated from the stator core by an airgap, a number of rotor
slots S, and a number of rotor teeth S, wherein each of the rotor
teeth has same geometrical dimensions, wherein a plurality of
non-overlapping coils of insulated wire is wound around each of the
rotor teeth, and wherein each coil of the plurality of
non-overlapping coils has two ends and is wound around a single
tooth; a commutator with a number of commutator segments Z; and a
number of brushes 2B, with B being equal to or less than P,
wherein, for each coil of the plurality of coils, the two ends are
connected to different commutator segments, wherein each brush of
the number of brushes has a width such that the brush can
simultaneously touch only two commutator segments that are
respectively connected to the two ends of a same coil, and wherein
at least two brushes of the number of brushes are arranged to
respectively touch commutator segments connected to coils wound
around a same tooth.
30. The direct current (DC) motor of claim 29, wherein each stator
pole comprises a permanent magnet mounted on a surface of a core
made of a ferromagnetic material.
31. The direct current motor of claim 29, wherein each stator pole
comprises a coil wound around a tooth made of a ferromagnetic
material.
32. An AC commutator (Universal) motor comprising: a stator,
including a number of stator poles 2P, each pole comprising a coil
wound around a tooth of a stator core made of a ferromagnetic
material; a concentrated-winding rotor, including: a rotor core
made of a ferromagnetic material and separated from the stator core
by an airgap, a number of rotor slots S, and a number of rotor
teeth S, wherein each of the rotor teeth has same geometrical
dimensions, wherein a plurality of non-overlapping insulated wire
coils is wound around each of the rotor teeth, and wherein each
coil of the plurality of non-overlapping coils has two ends and is
wound around a single tooth; a commutator with a number of
commutator segments Z; and a number of brushes 2B, with B being
equal to or less than P, wherein, for each coil of the plurality of
coils, the two ends are connected to different commutator segments,
wherein each brush of the number of brushes has a width such that
the brush can simultaneously touch only two commutator segments
that are respectively connected to the two ends of a same coil, and
wherein at least two brushes of the number of brushes are arranged
to respectively touch commutator segments connected to coils wound
around a same tooth.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to direct current motors or AC
commutator (Universal) motors. More particularly, this invention
relates to such motors which use a concentrated winding on the
rotor with coils wound around the teeth.
[0002] In conventional DC motors or AC commutator (Universal)
motors, there are three types of rotor armature windings: lap
windings, wave windings and frog-legs windings. These windings are
made with simple coil elements which are always interlocked. With
an interlocked winding, the ratio between the axial length of the
end-windings and the axial length of the armature magnetic circuit
is relatively high as it is described by Klein U.S. Pat. No.
4,329,610, Ban et al. U.S. Pat. No. 4,197,475 and Ikeda U.S. Pat.
No. 4,437,028.
[0003] All these windings differ primarily by the method which is
used to connect the terminals of the simple coils to the
commutator. A lap winding is also known as a multiple winding and
for this kind of winding the number of parallel paths are equal to
the number of poles. The wave winding is sometimes called a series
winding and it has only two paths in parallel, regardless of the
number of poles. The frog-leg winding is the association of a lap
winding and a wave winding placed on the same armature, in the same
slots, and connected to the same commutator bars.
[0004] The most significant problem with using a lap winding is
that the voltages induced in the different parallel paths are
unequal. These differences of induced voltages are due to unequal
magnetic circuit reluctances or unequal fluxes under the different
poles, which are created by rotor eccentricity, misalignment of the
poles, and/or differences in permanent magnet magnetization.
Because of the imbalance in induced voltages, circulating currents
appear in the windings and through the brushes. These circulating
currents cause unnecessary heating of the coils and brushes and
tend to produce poor commutation.
[0005] The use of equalizer connections is the common solution to
overcome the undesirable effects of circulating currents. These
connections improve the current commutation and relieve the brushes
of existing circulating currents by providing low resistance paths
which by-pass the brush contacts. In a wave winding, the problem of
the circulating currents due to the unbalanced voltages of the
parallel paths is minimized but it is also impossible to get
perfectly balanced voltages.
[0006] To avoid the interlocking of the coils, it is possible to
directly wind the armature simple coils around each tooth of the
rotor magnetic circuit. This kind of winding is called a
concentrated winding, as described in our scientific papers,
"Permanent Magnet Brushless DC Motor with Soft Metal Powder for
Automotive Applications," IEEE Industry Applications Society, St.
Louis, October 1998, and "Synthesis of High Performance PM Motors
with Concentrated Windings," IEEE IEMDC, Seattle, May 1999. This
kind of winding is also called a non-superposed winding, as
described by Ban et al. U.S. Pat. No. 4,197,475. This kind of
winding reduces the copper volume of the end-winding, the copper
losses and the total axial length of the motor. The efficiency is
improved when compared to the efficiency of classical structures.
This winding structure is also easier to realize than a lap winding
or a wave winding. When the axial length of the motor is small and
the outside diameter of the motor is important, the use of such a
winding structure allows a gain of 70% as compared to the volume of
copper used in an overlapped winding.
[0007] Rotor structures with a concentrated winding have a small
number of slots and the magnetic circuit is easier to realize. The
magnetic circuit can be realized with a conventional soft magnetic
laminated material (a yoke made of a stack of laminations) but it
is also possible to use a soft magnetic composite material made of
metal powder. The permeability of the soft magnetic composite is
usually three times lower than the permeability of the conventional
laminated materials like it is described by Jack et al. W.O. Pat
No. 99,50949. This low value of permeability reduces the value of
the coil inductances in the armature and the commutation process in
both collector and armature is improved. A rotor structure with a
small number of slots is also very well adapted to the realization
of the armature magnetic circuit of direct current motors or ac
commutator (Universal) motors with a soft magnetic composite
material made of metal powder. With a small number of slots having
relatively large dimension, the mechanical constraints on the
direct molding process of the rotor yoke are reduced. It is also
possible to easily insert the end-windings in the active part of
the rotor magnetic circuit. This axial insertion of the
end-windings improves the reduction of the volume of copper and the
total axial length of the motor.
[0008] However, the concentrated winding technique is too often
associated and restricted to windings with a short pitch, i.e.
windings with lower performances than the performances of the
classical winding structures. The concentrated windings with a
short pitch are then limited to sub-fractional power applications
(lower than 100 W) such as used in electrical motors for computer
peripherals or toys. This is the case for the simplest and low cost
brush direct current motor, which is widely used for toys. This
2-pole motor uses permanent magnets on the stator core, and has
three teeth on its rotor core and a concentrated winding with one
coil only wound around each tooth. The armature coil terminals are
connected to a commutator with three segments and two brushes, as
described by Fujisaki et al. U.S. Pat. No. 4,868,433. This
structure has a winding with a short pitch of 120 electrical
degrees. The winding coefficient or the ratio between the
fundamental component of magnetic flux embraced by the winding and
the total magnetic flux per pole is only equal to 0.866.
[0009] The main drawbacks of this motor structure are its low
performance in terms of torque to weight ratio, torque ripple, and
poor commutation performance if the power is increased. With this
structure, the induced voltages in the coil paths between brushes
are not always balanced. This unbalanced condition of operation
produce supplementary losses, torque ripples, mechanical vibrations
and commutation problems. These problems are acceptable for low
power applications only.
SUMMARY OF THE INVENTION
[0010] This invention is an armature winding of a DC or AC
commutator motor, which eliminates the problem of the interlocking
of the coils and the problem of circulating currents. All the path
voltages are perfectly balanced and the current commutation is
improved when compared to the classical structures.
[0011] In this invention, the number of commutator segments is
higher than the number of rotor teeth, and a plurality of simple
coils are wound around the same tooth. The leads of each coil are
connected to different segments of the commutator. Use of the
present invention reduces the number of turns per coil for a same
value of the DC voltage supply and a same speed range of the motor.
The parallel paths of the armature winding can be perfectly
balanced. An equal current distribution through the parallel
circuits of the armature is maintained and there is no circulation
current between these parallel circuits. The inductance value of
each simple coil is reduced and consequently the commutation
problems are minimized when compared to the case of a concentrated
winding with only one coil wound around each tooth. The copper
volume of the end-windings, the Joule losses and the axial length
of the motor armature are lower than in the case of a lap or a wave
winding with interlocking coils. It is also possible to arrange
connections of the leads of each coil to the commutator segments to
obtain balanced emf in the different coil paths between brushes.
These structures can be used efficiently for motors over a wide
range of power, and their cost of realization is lower than the
cost of classical structures.
[0012] In accordance to this invention, two kinds of structures are
presented: structures with a regular distribution of rotor teeth
with identical dimensions, and structures with a regular
distribution of rotor teeth with different dimensions. Both
structures are efficient in terms of performance and cost of
realization. The values of the winding coefficients of these
structures (i.e. the ratio between the fundamental component of
magnetic flux embraced by the winding and the total magnetic flux
per pole) are high.
[0013] The performance of the structures proposed in accordance
with the present invention is similar to the performance of the
classical structures in terms of current commutation. But the
performance of the structures proposed in accordance with the
present invention in terms of torque to winding volume ratio is
higher than the performance of the classical structures. With the
proposed structures, the volume of copper is reduced, the Joules
losses (copper losses) and the weight are minimized. The total
axial length of the motor is reduced. The efficiency is improved
and is higher than in the case of classical structures. The
structures of the winding and the magnetic circuit, which are
proposed in accordance with the present invention, are also easier
to realize. The total cost of the motor is then minimized.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a cross-sectional view of an example of a direct
current motor with a concentrated winding and permanent magnets in
accordance with the present invention.
[0015] FIG. 2 is a diagram of a developed surface of a drum
armature, made by unrolling the periphery of the armature and
commutator into a plane.
[0016] FIG. 3 is a diagram of construction of a machine equivalent
to the machine of FIG. 2 with a rotor winding made of concentrated
windings wound around the teeth.
[0017] FIG. 4 is a developed diagram of a machine with 3 rotor
slots, 2 stator poles, 6 commutator segments and 2 brushes with a
rotor winding made of concentrated windings wound around the
teeth.
[0018] FIG. 5 is a developed diagram of a machine with 6 rotor
slots, 4 stator poles, 12 commutator segments and 4 brushes with a
rotor winding made of concentrated windings wound around the
teeth.
[0019] FIG. 6 is a developed diagram of a machine with 6 rotor
slots, 4 stator poles, 12 commutator segments and 2 brushes with a
rotor winding made of concentrated windings wound around the
teeth.
[0020] FIG. 7 is a diagram of a machine with 20 rotor slots, 4
stator poles, 20 commutator segments, 4 brushes with a simplex lap
winding and a short pitch from 1 to 5.
[0021] FIG. 8 is a diagram of construction of a machine equivalent
to the machine of FIG. 7 with a rotor winding made of concentrated
windings wound around the teeth.
[0022] FIG. 9 is the diagram of a machine with 5 rotor slots, 4
stator poles, 20 commutator segments and 4 brushes with a rotor
winding made of concentrated windings wound around the teeth.
[0023] FIG. 10 is a diagram of the parallel coils paths of the
machines presented in FIG. 7 and FIG. 9.
[0024] FIG. 11 is a developed diagram of a machine with 5 rotor
slots, 4 stator poles, 20 commutator segments and 2 brushes with a
rotor winding made of concentrated windings wound around the
teeth.
[0025] FIG. 12 is a developed diagram of a machine with 5 rotor
slots, 4 stator poles, 40 commutator segments and 4 brushes with a
rotor winding made of concentrated windings wound around the
teeth.
[0026] FIG. 13 is a developed diagram of a machine with 5 rotor
slots, 4 stator poles, 40 commutator segments and 2 brushes with a
rotor winding made of concentrated windings wound around the
teeth.
[0027] FIG. 14 is a developed diagram of a machine with 10 rotor
slots, 8 stator poles, 40 commutator segments and 8 brushes with a
rotor winding made of concentrated windings wound around the
teeth.
[0028] FIG. 15 is a developed diagram of a machine with 12 rotor
slots, 4 stator poles, 12 commutator segments, 4 brushes with a
simplex lap winding and a diametral pitch.
[0029] FIG. 16 is a diagram of construction of an equivalent
machine of FIG. 15 with a rotor winding made of concentrated
windings wound around the teeth.
[0030] FIG. 17 is a developed diagram of a machine with 6 rotor
slots, 4 stator poles, 12 commutator segments and 4 brushes with a
rotor winding made of concentrated windings wound around the
teeth.
[0031] FIG. 18 is a developed diagram of a machine with 6 rotor
slots, 4 stator poles, 12 commutator segments, 2 brushes with a
rotor winding made of concentrated windings and a regular
distribution of rotor teeth with two different dimensions.
[0032] FIG. 19 is a developed diagram of a machine with 10 rotor
slots, 8 stator poles, 40 commutator segments, 4 brushes with a
rotor winding made of concentrated windings and a regular
distribution of rotor teeth with two different dimensions.
[0033] FIG. 20 is the axial sectional view of a permanent magnet
motor with a rotor magnetic circuit realized with a laminated steel
material.
[0034] FIG. 21 is the axial sectional view of a permanent magnet
motor with a rotor magnetic circuit realized with an isotropic soft
magnetic composite material.
[0035] FIG. 22 is the axial sectional view of a motor with a rotor
magnetic circuit realized with an isotropic soft magnetic composite
material.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] In one embodiment of the present invention, the rotor has a
regular distribution of rotor teeth with identical dimensions, and
there are 2P poles, magnetized alternatively North and South in the
stator. These poles can be constructed with segments of permanent
magnet mounted on the surface of a core made of soft magnetic
material or with coils wound around teeth made of soft magnetic
material and fed by a DC or AC current. The rotor core has S slots.
The simple coils of the rotor are wound around S teeth or in some
case around S/2 teeth only. There are Z segments on the commutator
which are connected to the terminals of the coils. 2B brushes are
sliding on the commutator surface when the rotor is rotating. The
characteristics of these machines respect the following conditions:
TABLE-US-00001 P is an integer and 0 < P < 10 S = 2P + A A is
an integer equal to -1 or 1 or 2 or 3 S > 2 Z = k*LCM(S, 2P)
.+-. n k is an integer greater than 0 LCM is the Least Common
Multiple of S and 2P n is equal to 0 or k B = P or less
[0037] Table 1 hereto presents some structures which respect these
conditions with k equal to 1 and n equal to 0. The number of coils
per path is equal to mph (mph=Z/2P). The number of brushes 2B is
normally equal to the number of stator poles 2P. Several concentric
coils are wound around each rotor tooth and are connected on
different commutator segments. In this case, the number N of
concentric coils per tooth is equal to: N=Z/S
[0038] With this winding configuration, a reduction of the number
of turns per simple coil is obtained. The same reduction of the
number of turns is usually obtained in a classical machine
structure with the same number of stator poles by employing a
higher number of rotor slots. Because the inductance value of each
simple coil is reduced, commutation problems are minimized.
[0039] It is also possible to arrange the connections of each coil
to the commutator segments to obtain balanced emf's in the
different coil paths between brushes. Such structures can have a
value of winding coefficient Kb (ratio between the fundamental
component of magnetic flux embraced by the winding and the total
magnetic flux per pole) near to 1 (table 1) and consequently a high
torque-weight ratio. All these machines can be used efficiently for
motors and generators over a wide range of power and for high
levels of armature current. TABLE-US-00002 TABLE 1 2P 2 4 4 6 6 6 8
8 8 10 12 S 3 5 6 5 7 8 7 9 10 12 15 Z = LCM(S, 2) 6 20 12 30 42 24
56 72 40 60 60 Mph = Z/2P 3 5 3 5 7 4 7 9 5 6 5 2B 2 4 4 6 6 6 8 8
8 10 12 N 2 4 2 6 6 3 8 8 4 5 4 Kb 0.866 0.951 0.866 0.951 0.975
0.924 0.975 0.984 0.951 0.965 0.951
[0040] It is additionally possible to reduce the number of brushes
2B and also the number N of concentric coils which are wound around
the same rotor tooth to minimize the cost of the motor. Motors
having such a structure are presented in table 2. The structures
listed in column 2 to 11 of table 1 present this characteristic. It
is then necessary to add some equalizer connections on the
commutator segments (wires which directly connect segments without
lying in the slots, see for example wire conecting segment 3 to 9
in FIG. 6). It should be noted that this modification decreases the
performance of the commutation process, while increasing the level
of current in the remaining brushes. This kind of modification is
preferably utilized in sub-fractional and fractional power
machines. TABLE-US-00003 TABLE 2 2P 2 4 4 6 6 6 8 8 8 10 S 3 5 6 5
7 8 7 9 10 12 Z = LCM(S, 2P) 6 20 12 30 42 24 56 72 40 60 mph =
Z/2P 3 5 3 5 7 4 7 9 5 6 2B 2 2 2 2 2 2 2 or 4 2 or 4 2 2 N 2 2, 4
1, 2 2, 6 2, 6 1, 3 2, 4, 8 2, 4, 8 2, 4 1, 5 Kb 0.866 0.951 0.866
0.951 0.975 0.924 0.975 0.984 0.951 0.965
[0041] It is also possible to reduce the number of commutator
segments Z by two and to apply the following relations to determine
the number of segments: Z=LCM(S,2P)/2 and Z/2P>3
[0042] With this reduction of the number of segments, as in the
structures presented in table 3, one obtains an unbalanced emf in
the different coil paths between brushes, with the level of this
unbalance being inversely proportional to the number of coils in
each parallel path. TABLE-US-00004 TABLE 3 2P 4 6 6 8 8 8 10 12 12
S 5 5 7 7 9 10 11 11 15 Z = LCM(S, 2P)/2 10 15 21 28 36 20 55 66 30
2 mph = Z/2P 5 5 7 7 9 5 11 11 5 2B 4 6 6 8 8 8 10 12 12 N 2 3 3 4
4 2 5 6 2 Kb 0.951 0.951 0.975 0.975 0.984 0.951 0.990 0.990
0.951
[0043] In a second embodiment of the present invention, the rotor
of these structures presents a regular distribution of rotor teeth
with different dimensions.
[0044] In particular, the stator of these machines have 2P poles
magnetized alternatively North and South. These poles can be
realized with permanent magnet segments mounted on the surface of a
core made of soft magnetic material, or with coils wound around
teeth made of soft magnetic material and fed by a DC or AC current.
The rotor core has S slots and rotor teeth of two different
geometrical dimensions, which alternate around the circumference of
the core. The rotor coils are wound around S/2 teeth. There are Z
segments on the commutator which are connected to the terminals of
the coils. 2B brushes slide on the commutator surface when the
rotor is rotating. The characteristics of these machines respect
the following conditions: TABLE-US-00005 P is an integer and 1 <
P < 10 S = 2P + 2A A is an integer and 1 < A < P Z =
k*LCM(S/2, 2P) .+-. n k is an integer greater than 0 LCM is the
least Common 1 Multiple of S/2 and 2P n is equal to 0 or k B = P or
less
[0045] Table 4 herein provides exemplary structures which respect
these conditions, with k equal to 1 and n equal to 0. The number of
coils per path is equal to mph (mph=Z/2P). The number of brushes 2B
is normally equal to the number of stator poles 2P. Several
concentric coils are wound around each rotor tooth and are
connected on different commutator segments. In this case, the
number N of concentric coils wound around each rotor tooth is equal
to: N=2Z/S
[0046] TABLE-US-00006 TABLE 4 2P 4 6 6 8 8 8 10 10 10 10 S 6 8 10
10 12 14 12 14 16 18 Z = LCM(S/2, 2P) 12 12 30 40 24 56 60 70 40 90
mph = Z/2P 3 4 5 5 3 7 3 7 4 9 2B 4 6 6 8 8 8 10 10 10 10 N 4 3 6 8
4 8 10 10 5 10 Kb 1 1 1 1 1 1 1 1 1 1
[0047] These motor structures offer the same advantages of the
previous ones listed in table 1 in terms of current commutation
performance and balanced parallel coils path. But it is also
possible to get a higher winding coefficient Kb (equal to unity,
Kb=1), and to maximize the torque per unit of volume of copper.
These structures can be used efficiently for motors and generators
over a wide power range and for high levels of armature current. It
is also possible, as in the case of the previous structures of
table 1, to apply different simplifications for the choice of the
number of brushes, the number commutator segments and the number of
concentric coils per tooth to reduce the cost of the motor and
simplify the realization.
[0048] It must be noticed that all the proposed solutions which are
in accordance with the present invention can be used with different
brush widths.
[0049] According to the present invention, a DC or AC commutator
motor can be manufactured with a magnetic circuit made of laminated
steel or made of a soft magnetic composite material.
[0050] In particular, when an isotropic soft magnetic composite is
used, a portion of the magnetic flux can also circulate in the
axial direction. For this reason, it is possible to expand the
tooth tips in the axial direction, and thus maximize the axial
length of the active air-gap area for a given total axial length of
the motor as fixed by the specifications of the application. In
such structures, the air-gap flux is concentrated into the center
part of the rotor teeth under the coils and the yoke. Because the
axial length of the center part of the rotor teeth under the coils
and the axial length of the yoke is smaller than the axial length
of the tooth tips, the end-windings, the commutator and the brushes
are now axially inserted and the total axial length of the motor is
reduced. With this method, the isotropic properties of the soft
magnetic composites are used to minimize the axial length of a
motor without reducing the torque performance.
[0051] When an isotropic soft magnetic composite is used, the
cross-section profile of the center part of the rotor and stator
teeth under the coils can be made round, oval, or circular. These
profiles can reduce the risk of destruction of the insulation by a
sharp bending of the winding coils, and maximize the copper filling
factor.
[0052] It is also possible to skew the permanent magnets or the
teeth of the stator to reduce the variations of the air-gap
reluctance or the cogging torque. The same result can be obtained
by skewing the teeth of the rotor. When an isotropic soft magnetic
composite is used, it is possible to skew only the tooth tips.
[0053] FIG. 1 shows a cross-sectional view of an example of a
direct current motor with a concentrated winding and permanent
magnets in accordance with the present invention. Part 1 is the
yoke of the stator. Part 2 is one of the stator poles, which are
magnetized alternatively North and South, and which is made of a
segment of permanent magnet. Part 3 is the tip of a rotor tooth.
Part 4 is the center part of the rotor tooth under the coils. Part
5 is the yoke of the rotor. Part 6 is the concentrated winding,
wound around a stator tooth. Part 7 is one of the segments or bars
of the commutator. Part 8 is one of the brushes in contact with the
segments of the commutator and which is used to feed the supply
current to the armature winding.
[0054] FIGS. 2, 3 and 4 each illustrates a method to derive the
structure of a machine with a rotor winding made of concentrated
windings wound around the teeth from the structure of a classical
machine. Each of these structures presents the same number of
stator poles, and a commutator segment number equal to the rotor
slot number.
[0055] More particularly, FIG. 2 shows a classical structure with 6
rotor slots, 2 stator poles, 6 segments on the commutator and 2
brushes. The winding of the rotor is a simplex lap winding,
overlapped with a short pitch of 120 electric degrees. The
connections of the terminals of each simple coil to the segments of
the commutator are arranged to get coils paths perfectly balanced
in the armature winding.
[0056] In FIG. 2, the 6 simple coils of the armature winding are
denoted 1.1, 1.2, 2.1,2.2,3.1,3.2. Coils 1.1 and 1.2 denote simple
coils which have the same phase of emf, because their positions
relative to the stator poles are identical. The same is the case
with coils 2.1, 2.2, and with coils 3.1, 3.2. The dots in FIG. 2
are polarity marks and indicate the polarity of the winding, in
accordance with standard notation in the art. The teeth defining
the 6 rotor slots are defined by T1 through T6, respectively. The
commutator segments are labeled 1 through 6 respectively, and as
can be seen, a voltage V is applied to the brushes B1, B2. The
north and south stator poles are labeled N and S, respectively.
Similar nomenclature is used in the balance of the figures.
[0057] In comparison with FIG. 2, by regrouping simple coils which
have the same phase of emf on the same tooth of the rotor, one
avoids the interlocking of the end-windings, as is shown on FIG. 3.
More particularly, FIG. 3 is a diagram of construction of a machine
equivalent to the machine of FIG. 2 in terms of torque and emf
characteristics, magnetic flux and current density, where the rotor
winding in FIG. 3 is made of concentrated windings around the
teeth. The simple coils having emf's which are in phase as coils
1.1 and 1.2 in FIG. 2 are regrouped on a same tooth. To increase
the size of the slots filled with conductors and to preserve the
same total copper section of the whole rotor armature in the
original machine of FIG. 2 and in the equivalent machine of FIG. 3
(i.e. the sum of the copper section of each slot), the teeth around
the empty slots are regrouped to form the new distribution of teeth
presented in FIG. 3. As compared to FIG. 2, the position of the
tooth tips in FIG. 3 are not modified at the level of the airgap;
however the center parts of the teeth of the machine of FIG. 2
between the tooth tips and the inner rotor yoke have been shifted
in FIG. 3 to form a single big tooth. With this method, the pattern
of the no-load magnetic flux spatial distribution in the airgap is
not modified and the total section of the soft magnetic material in
the teeth from the original machine of FIG. 2 to the equivalent
machine of FIG. 3 is also preserved to avoid a saturation of the
magnetic flux. Therefore the total amounts of soft magnetic
material in the yoke and copper in the slots are modified as well.
One gets a machine with a concentrated winding presented in FIG. 3
which is equivalent to the initial machine of FIG. 2, as explained
above. The shape and the emf amplitude in each coil are not
modified.
[0058] As shown in FIG. 3, some slots are empty and it is possible
to group teeth around each empty slot. The position of the tooth
tips are not modified at the level of the airgap, only the center
parts of the teeth between the tooth tips and the inner rotor yoke
are shifted to form a single big tooth. The pattern of the no-load
magnetic flux spatial distribution in the airgap is not modified,
as is shown in FIG. 3. One can then concentrate the simple coils
around each tooth. The total section of soft magnetic material in
the teeth and the total copper section of the whole rotor armature
are preserved and are identical to the corresponding sections in
the initial machine with a classical structure.
[0059] FIG. 4 is a developed diagram of a machine with 3 rotor
slots, 2 stator poles, 6 commutator segments and 2 brushes with a
rotor winding made of concentrated windings wound around the teeth.
Two simple coils, like coils 1.1 and 1.2, are wound around the same
tooth and are connected to different segments of the commutator.
The connections to the commutator segments are identical to the
connections used in the machine shown in FIG. 2.
[0060] One can notice on the diagram on the right that the coils
paths are not modified. Each simple coil wound around a same tooth
like coil 1.1 and coil 1.2 has an identical emf. The total emf's
across each parallel coil path are now perfectly balanced, even if
the airgap reluctances or the magnetization of the permanent
magnets under each pole of the stator are not perfectly identical.
This machine is equivalent to the machine presented in FIG. 2 in
terms of torque and emf characteristics, magnetic flux density and
current density.
[0061] The machine presented on the FIG. 4 has a concentrated
winding, which is equivalent to the initial machine of FIG. 2, in
terms of torque and emf characteristics, magnetic flux and current
density. The connections of the terminals of the simple coils to
the commutator are identical in both machines (i.e. machines on
FIG. 2 and FIG. 4). The coil paths in the armature winding are
always balanced: i.e. the total emf's across each parallel coil
path are balanced, even if the airgap reluctances or the
magnetization of the permanent magnets under each pole of the
stator are not perfectly identical.
[0062] FIG. 5 is a developed diagram of a machine with 6 rotor
slots, 4 stator poles, 12 commutator segments and 4 brushes with a
rotor winding made of concentrated windings wound around the teeth.
This machine is derived from the machine presented in the FIG. 4 by
doubling the periodicity of its structure.
[0063] In addition, several modifications can be realized to
simplify these structures in the case of a sub-fractional power
machine made in accordance to the present invention. In particular,
it is possible to reduce the number of brushes while adding
equalizer connections on the commutator. This is shown in FIG. 6,
which is a developed diagram of a machine with 6 rotor slots, 4
stator poles, 12 commutator segments and 2 brushes with a rotor
winding made of concentrated windings wound around the teeth. This
machine is an evolution of the machine presented in FIG. 5 with a
reduced number of brushes and with equalizer connections added on
the commutator. It can be seen in FIG. 6 that the two coils wound
around each tooth are connected in parallel by equalizer
connections. Optionally, one could reduce the number of simple
coils around each tooth to one, with several of the commutator
segments not being directly connected to coil terminals.
[0064] The same method is applied on FIGS. 8 and 9 for another
example, in accordance to the present invention. Initially FIG. 7
depicts a classical machine having 20 rotor slots, 4 stator poles,
20 segments on the commutator and 4 brushes. The winding of the
rotor is overlapped with a short pitch of 1 to 5. The coil paths in
the armature winding are presented on FIG. 10.
[0065] FIG. 8 is a diagram of the construction of a machine
equivalent to the machine of FIG. 7 in terms of torque and emf
characteristics, magnetic flux and current density, with the rotor
winding in FIG. 8 made of concentrated windings wound around the
teeth. The coils having emf's which are in phase as coils 1.1, 1.2,
1.3, 1.4 are regrouped on a same tooth. To increase the size of the
slots filled with conductors and to preserve the same total copper
section of the whole rotor armature in the original machine of FIG.
7 and in the equivalent machine of FIG. 8 (i.e. the sum of the
copper section of each slot), the teeth around the empty slots are
regrouped to form the new distribution of teeth presented in FIG.
8. The position of the tooth tips are not modified at the level of
the airgap, only the center parts of the teeth of the machine of
FIG. 7 between the tooth tips and the inner rotor yoke have been
shifted to form a single big tooth. With this method, the pattern
of the no-load magnetic flux spatial distribution in the airgap is
not modified. The total section of soft magnetic material in the
teeth from the original machine of FIG. 7 to the equivalent machine
of FIG. 8 is also preserved to avoid saturation of the magnetic
flux. Therefore the total amounts of soft magnetic material in the
yoke and copper in the slots are not modified as well. One gets a
machine with a concentrated winding presented in FIG. 8 which is
equivalent to the initial machine of FIG. 7, as explained above.
The shape and the emf amplitude in each coil are not modified.
[0066] FIG. 9 is the diagram of a machine with 5 rotor slots, 4
stator poles, 20 commutator segments and 4 brushes with a rotor
winding made of concentrated windings wound around the teeth. Four
simple coils are wound around a same tooth and are connected to
different segments of the commutator. Connections to the commutator
segments are identical to the connections used in the machine
presented on the FIG. 7. Each simple coil wound around a same
tooth, like coils 1.1 and 1.2 and 1.3 and 1.4, has an identical
emf. The total emf's across each parallel coil path (FIG. 10) are
now perfectly balanced, even if the airgap reluctances or the
magnetization of the permanent magnets under each pole of the
stator are not perfectly identical. This machine is equivalent to
the machine presented in FIG. 7 in terms of torque and emf
characteristics, magnetic flux density and current density.
[0067] FIG. 10 is a diagram of the parallel coils paths of the
machines presented in FIG. 7 and FIG. 9.
[0068] Several modifications can be realized to simplify these
structures in the case of a sub-fractional power machine in
accordance to the present invention. It is possible to reduce the
number of brushes while adding equalizer connections on the
commutator. One can also reduce the number of simple coils as it is
presented on the FIG. 11. In accordance to the present invention,
FIG. 12 shows the same kind of motor as is depicted in FIG. 9 with
a higher periodicity of structure.
[0069] More particularly, FIG. 11 is a developed diagram of a
machine with 5 rotor slots, 4 stator poles, 20 commutator segments
and 2 brushes with a rotor winding made of concentrated windings
wound around the teeth. This machine is an evolution of the machine
presented in the FIG. 9 with a reduced number of brushes and
equalizer connections are added on the commutator. In this machine,
it is also possible to reduce the number of simple coils on each
tooth to 2 as is shown in FIG. 11. Likewise, FIG. 12 is a developed
diagram of a machine with 5 rotor slots, 4 stator poles, 40
commutator segments and 4 brushes with a rotor winding made of
concentrated windings wound around the teeth. This machine is an
evolution of the machine presented in the FIG. 9 with a higher
number of simple coils and number of commutator segments.
[0070] FIG. 13 shows the same structure of motor presented on FIG.
9 with a higher number of commutator segments and a higher simple
coil number wound around a tooth, in accordance with the present
invention.
[0071] More particularly, FIG. 13 is a developed diagram of a
machine with 5 rotor slots, 4 stator poles, 40 commutator segments
and 2 brushes with a rotor winding made of concentrated windings
wound around the teeth. This machine is an evolution of the machine
presented in the FIG. 12 with a reduced number of brushes and
equalizer connections added on the commutator. The number of
segments between 2 brushes of inverse polarity (+ and -) is
increased according to the solution presented with respect to FIG.
9 (10 segments vs. 5 segments). Therefore, the voltage between 2
successive segments is lower. This kind of solution is of utility
when the supply voltage is high and it permits limiting the
amplitude of the voltage between 2 successive segments. It is
possible to reduce the number of simple coils on each tooth to 2 in
this figure.
[0072] FIG. 14 is an evolution of the solution presented on FIG. 9,
in accordance to the present invention, with a higher periodicity
of the structure.
[0073] More particularly, FIG. 14 is a developed diagram of a
machine with 10 rotor slots, 8 stator poles, 40 commutator segments
and 8 brushes with a rotor winding made of concentrated windings
wound around the teeth. This machine is derived from the machine
presented in the FIG. 9 by doubling the periodicity of its
structure.
[0074] The present invention is applied on FIGS. 16 and 17, which
depict a machine with a rotor winding made of concentrated windings
and a regular distribution of rotor teeth with two different
dimensions. The classical machine for reference presented in FIG.
15 has 12 rotor slots, 4 stator poles, 12 segments on the
commutator and 4 brushes. The winding of the rotor is overlapped
with a diametral pitch.
[0075] FIG. 16 is a diagram of construction of an equivalent
machine of FIG. 15, in terms of torque and emf characteristics,
magnetic flux and current density, with the rotor winding in FIG.
16 made of concentrated windings wound around the teeth. The coils
having emf's which are in phase as coils 1.1, 1.2, 1.3, 1.4 are
regrouped on a same tooth. To increase the size of the slots filled
with conductors and to preserve the same total copper section of
the whole rotor armature in the classical machine of FIG. 15 and in
the equivalent machine of FIG. 16 (i.e. the sum of the copper
section of each slot), the teeth around the empty slots are
regrouped to form the new distribution of teeth presented in FIG.
16. The position of the tooth tips are not modified at the level of
the airgap, only the center parts of the teeth of the machine of
FIG. 15 between the tooth tips and the inner rotor yoke have been
shifted to form a single big tooth. With this method, the pattern
of the no-load magnetic flux spatial distribution in the airgap is
not modified. The total section of soft magnetic material in the
teeth from the original machine of FIG. 15 to the equivalent
machine of FIG. 16 is also preserved to avoid a saturation of the
magnetic flux. Therefore the total amounts of soft magnetic
material in the yoke and copper in the slots are not modified as
well. One can notice that all the coils are wound around 3 teeth
only. One gets a machine with a concentrated winding presented in
FIG. 16 which is equivalent to the initial machine of FIG. 15, as
explained above. The shape and the emf amplitude in each coil are
not modified.
[0076] FIG. 17 is a developed diagram of a machine with 6 rotor
slots, 4 stator poles, 12 commutator segments and 4 brushes with a
rotor winding made of concentrated windings wound around 3 teeth.
There is a regular distribution of rotor teeth of two different
dimensions, with teeth T1, T2 and T3 of one dimension, and teeth
T4, T5 and T6 of a second dimension. Four simple coils are wound
around each tooth and are connected to different segments of the
commutator. The connections to the commutator segments are
identical to the connections used in the machine presented on the
FIG. 15. The coils paths are perfectly balanced. This machine is
equivalent to the machine presented in FIG. 15 in terms of torque
and emf characteristics, magnetic flux density and current density,
with a winding coefficient equal to 1. The performance of this kind
of concentrated winding machine is high.
[0077] In the case of a sub-fractional power machine constructed in
accordance with this invention, several modifications can be made
to simplify the structure. For example, it is possible to reduce
the number of brushes while adding equalizer connections on the
commutator. FIG. 18 is a developed diagram of a machine with 6
rotor slots, 4 stator poles, 12 commutator segments, 2 brushes with
a rotor winding made of concentrated windings and a regular
distribution of rotor teeth with two different dimensions. This
machine is an evolution of the machine presented in the FIG. 17
with a reduced number of brushes and equalizer connections added on
the commutator. In this machine, it is also possible to reduce the
number of simple coils on each tooth to 2 as is shown in FIG.
18.
[0078] FIG. 19 presents the result of another example of a machine
with a rotor winding made of concentrated windings and a regular
distribution of rotor teeth with two different dimensions. The
initial machine has 40 rotor slots, 8 stator poles, 40 segments on
the commutator and 8 brushes. The equivalent machine, in accordance
to the present invention, has 10 rotor slots with rotor teeth of
two different geometrical dimensions (teeth T1 through T5 being of
one dimension, and T6 through T10 being of a second dimension), 8
stator poles, 40 segments on the commutator and 4 brushes. There
are 8 simple coils per tooth. Connections of the simple coils on
the commutator are the same as the initial machine. It is possible
to reduce the number of brushes while adding equalizer connections
on the commutator.
[0079] FIG. 20 is an axial sectional view of a permanent magnet
motor with a rotor magnetic circuit realized with a laminated steel
material. Usually, the axial dimension of the magnetic circuit of
the rotor (parts 3, 4, 5) is lower than the axial length of the
permanent magnet. The flux of the permanent magnets is thus
concentrated axially into the rotor and it is possible to insert,
partially, the end-winding under the permanent magnets axial
length. This modification of the axial dimension of the rotor
reduces the total axial length of the motor.
[0080] FIG. 21 is the axial sectional view of a permanent magnet
motor with a rotor magnetic circuit realized with an isotropic soft
magnetic composite material. In an isotropic magnetic material, a
portion of the magnetic flux can also circulate in the axial
direction. It is therefore possible to increase the flux
concentration without decreasing the performance of the motor. The
center part of the rotor teeth under the coils (part 4) and the
rotor yoke (part 5) have the same axial dimension and the tips of
the teeth (part 3) have an axial dimension nearly identical to the
axial length of the permanent magnets. The total axial length of
the motor is reduced when compared to a rotor with a laminated
steel (FIG. 20). It is then possible with this structure to
maximize the axial length of the active air-gap area for a total
axial length fixed by the specifications of the application.
[0081] FIG. 22 is the axial sectional view of a motor with a rotor
magnetic circuit realized with an isotropic soft magnetic composite
material. The structure presented on FIG. 22 is an evolution of the
structure of the FIG. 21. The center part of the rotor teeth under
the coils (part 4) and the rotor yoke (part 5) have the same axial
dimension and the tips of the teeth (part 3) have an axial
dimension nearly identical to the axial length of the permanent
magnets. Part 4 and part 5 are shifted axially. The end-windings,
commutator and brushes are inserted partially or totally in the
axial direction for a further minimization of the total axial
length of the motor.
[0082] The proposed motor structures of this invention are very
well adapted to the realization of the rotor magnetic circuit with
a soft magnetic composite material made of metal powder. With a
small number of slots with relatively large dimensions, the
mechanical constraints on the direct molding process of the rotor
yoke are reduced. An isotropic soft magnetic composite is also well
adapted to realize an axial air-gap flux concentration in the rotor
or the stator magnetic circuit and to reduce the total axial length
of the motor without decreasing the performances of motor. The tips
of the teeth can be expanded axially and used to concentrate the
magnetic flux in the airgap, axially, into the teeth and the yoke
of the rotor or the stator (FIG. 21 & 22). The axial length of
the tips of the rotor teeth can have an axial dimension nearly
identical to the axial length of the permanent or the axial length
of the tooth tips of the stator. The axial dimension of the teeth
and the yoke are the same and can be lower than the axial dimension
of the tooth tips (FIG. 21 & 22). The center part of the rotor
teeth under the coils and the rotor yoke can also be decentered and
shifted axially (FIG. 22). It is also possible to axially insert
the end-windings inside the tooth tips (FIG. 21 & 22). The
commutator and the brushes can also be inserted partially or
totally in the axial direction under the rotor tooth tips (FIG.
22). This kind of structure has utility in reducing the total axial
length of the motor.
[0083] When an isotropic soft magnetic material is used, it is also
useful to make the cross-section profile of the center part of the
rotor and stator teeth under the coils, round, oval, or circular to
get a reduction of the risk of destruction of the insulation by a
sharp bending of the winding coils, and to maximize the copper
filling factor.
[0084] All the embodiments of this invention can be used with
different brush widths. The rotor slots and/or the stator slots can
be skewed to reduce the variations of the magnetic reluctance. In
the case of a stator with permanent magnets, it is also possible to
skew the rotor slots and/or the permanent magnets to reduce the
cogging torque. When an isotropic soft magnetic composite is used,
it is possible to skew only the tips of the rotor teeth and/or the
tips of the stator teeth.
[0085] The new structures of DC and AC commutator motor of the
present invention can be used in a large variety of applications
(automotive applications, electrodomestic appliances, corded
electric tools, electric vehicles, fractional and sub-fractional DC
and AC commutator motors, etc.). The improved efficiency and the
simplifications realized on the rotor winding will provide a lower
realization cost and higher performances than classical
structures.
[0086] While only some embodiments of the present invention are
described above, it is obvious that several modifications or
simplifications are possible without departing from the spirit of
the present invention. Thus, the invention may be applied to motors
with a radial airgap or tranversal airgap. Also, the invention can
be used in machines having an inner rotor or an outer rotor
structure. It is also understood that various further changes and
modifications can be made without departing from the spirit and
scope of the invention.
* * * * *