Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
s~z
l`his invcntion relates to a rotating electric machine,
and more particularly to a rotating elec-tric machine, such as a
motor and a genera~Lor, comprising an armature core made of magne-
tic material a~d having a plurarity of saliencies and a field
permanent magnet member which is oolarized to a plurarity of N
and S poles alternately and faced to said saliencies of the ar-
mature core. The rotating electric machine of the invention is
characterized by largely reduced cogging torque and reduced
ripple torque according to the intended portion provided to the
salieneies and the auxiliarly salient poles, as described here-
inafter.
A rotating electric rnachine comorising an armature core
of magnetic material having saliencies and a field permanent mag-
net member having magnetized ooles faced to the saliencies is
widely used as it has a high efficieney, but in prior art there
is a problem that a harmful vibration oeeurs owing to an intense
eogging torque generated by the interaetion between the may~et-
ized poles of the permanent magnet and the salieneies of the
armature eore. This eoggirlg torque is harmful for a smooth ro-
tation of the rotating eleetrie maehine, and in order to reduce
the cogging torque, a skewed armature core is used in some cases.
But, it is difficult to make the skewed armature core, and the
eogging torque is not redueed enough sometimes. Use of an ar-
matur~ eore having no~salieney for getting smooth rotation is
unpraetieal beeause of a low effieieney whieh results in a
large size of the maehine.
~ urther, the rotating eleetrie maehine having the
salieneies has another problem, when it is used as a motor,
that a ripple torque due to an amature current is induced and
so smooth rotation of the motor is disturbed by the resultant
lV~5~1~Z
harmful vibration. This ripple torque is generated by an inter-
action between the magnetized poles of the permanent magnet and
the energized saliencies of the armature core. In order to re-
duce the ripple torque, it is possible to vary an armature current
according to the mutual position between the armature core and
the permanent magnet. But, this makes undesirably a driving
circuit of the rotating electric machine complicated, and con-
ventionally it is difficult to reduce both of the cogging torque
and ripple torque.
Therefore, an objects of the present invention is to
provide a novel and improved rotating electric machine of high
efficiency with reduced cogging torque and reduced ripple torque.
Another object of the invention is to provide a rotating
electric machine comprising an armature core of magnetic material
having a plurality of saliencies and a field permanent magnet
member having permanently magnetized N and S poles, and having
reduced cogging torque and reduced ripple torque which are ~elated
to the geometry of the armature core and the magnet.
These objects of the invention are achieved by nroviding
the rotating electric machine according to the invention, which
comprises a field permanent magnet member of a circular form and
an armature core made of a magnetic material, said magnet member
being permanently magnetized to N and S poles alternately around
a ro~ary axis of said rotating electric machine to produce field
a fluxes, the number of said N and S poles is P which is an even
number larger than or equal to 2, i.e. P _ 2, and said armature
core being arranged coaxially with said magnet member and having
a plurality of saliencies faced to said magnet member and a
plurality of winding coils of poly-phase which generate poly-
~18S9~4Z
phase alterna~e voltages according to a relative rotation be-
tween said armature core and said magnet me~ber, at least one
of said saliencies having at least one indented portion at the
face thereof opposed to said magnet member, wherein an angle
between a line from a center of said indented portion to said
rotary axis and a line frol~ a center of a neighbouring indented
portion or from a center of a neighbouring spaced portion be-
tween neighbouring two saliencies to said rotary axis is arrang-
ed not equal to an integer multiple of a quotient of (360)o.
These and other objects and features of the invention
will be apparent from consideration of the detailed description
of the invention together with accompanying with the drawings,
in which:
Fig. 1 is a schematic sectional view of an embodiment
of the rotatina electric machine of the invention;
Figs. 2(a) to (g) are vector diagrams for explain-
ing an operation of reducing a harmful component of the shape
harmonics in the rotating electric machine of the invention;
Figs. 3(a) to (c) are schematic sectional views of
some embodiments of the armature core,used for the rotating
electric machine of the invention;
Figs. 4(a) to (d) show some shapes of indented por-
tions formed at a saliency of the armature core;
Fig. 5 is a schematic sectional view of another em-
bodiment of the rotating electric machine of the invention;
Fig. 6 is a schematic sectional view of a further
another embodiment of the rotating electric machine of the inven-
tion with auxiliary salient poles;
Figs. 7(a) to (d) show waveforms for explaining the
operat,ion of the rotating electric machine of Fig. 5;
1~18~Z
Fig. 8 is a schematic sectional view of a further an-
other embodiment of the rotating electric machine of the inven-
tion;
Figs. 9(a) and (b) are cross-sectional and exploded
views of ~urther another embodiment of the rotating electric
machine of the invention; and
Figs. lO(a) and (b) are developed views of permanent
magnet and the armature core shown in Fig. 9, respectively.
Now, an embodiment of the rotating electric machine
of the invention will be described in detail in the following,
with referring to Fig. 1 which shows a sectional view of a mag-
net yoke designated by a reference numeral 1 and an armature
core 3. The magnet yoke 1 has a permanent magnet 2 mounted on
the inner periphery facing to the armature core 3, and the per-
manent magnet 2 has a pair of permanently magnetized N and S
poles. The field permanent magnet member composed of the per-
manent magnet 2 provides a fixed magnetic field around the ar-
mature core 3.
The armature core 3 has three salient poles 4a, 4b
and 4c projected against the permanent magnet 2. The major
face of each salient pole facing to the permanent magnet is
wider than the bottom part thereof on which an armature coil
is wound. Therefore, the armature winding can be easily pro-
vided~, and further the armature core effectively gathers the
magnetic flux from the permanent magnet 2. That is, three-
phase winding coils 5a, 5b and 5c are wound on the bottom of
the salient poles 4a, 4b and 4c in the spaced portions 6a, 6b
and 6c between the neighbouring two salient poles, respectively.
Each major face of the salient poles 4a, 4b and 4c
has two indented portions 7al, 7a2; 7bl, 7b2; and 7cl and 7c2,
1()8S~4Z
respectively. ~t th~se indented portions, the gap between the
major face of the salient pole and the permanent magnet 2 is
widened. The indented portions are formed parallel to a rotary
axis O, that is vertically to the drawing in Fig. 1, and the
two indented portions of one salient pole are positioned at the
points of about l/3 of an angle between the centers of the spaced
portions at the both side of that salient pole, i.e. about 1/3
of 120, as shown in Fig. 1. Therefore, the nine portions of
the periphery of the armature core 3, i.e. the spaced portions
6a, 6b and 6c, and the indented portions 7al, 7a2, 7bl/ 7b2, 7c
and 7c2, are positioned at the equal or nearly equal angle of
40 facing to the permanent magnet 2. As described hereinbefore,
in this patent, the indented portion is defined that no winding
coil, such as a driving coil of a motor or a generating coil of
a generator, is provided thereon.
The operation of the rotating electric machine of Fig.
1 is described hereinafter. The armature core 3 and the perma-
nent magnet 2 are rotated relatively to each other around the
coaxial rotary axis O. That is, one is a rotor and the other
is a stator. When the rotating electric machine of Fig. 1 is
used as a generator, there are generated three-phase alternate
voltages at the 3-phase winding coils 5a, 5b and 5c according
to rotation o-f the permanent magnet 2 driven by an outer driving
forcQ. When this is used as a motor, there is generated a con-
tinuous driving torque according to the mutual position between
the permanent magnet 2 and the armature core 3 by supplying con-
trolled 3-phase alternate currents to the 3-phase winding coils
5a, 5b and 5c through a mechanical or electronic commutator.
In case of a motor, especially for a motor of an
audio apparatus requiring a high quality, usually an electric
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commutator is employed which comprises a detecting means for
detecting a mutual position between the armature core and the
permanent macJnet, power transis-tors for supplying a current to
each phase winding coils, and a switching means for driving the
power transistors accordins to signals from the detecting means.
Because the commutator is not the subject matter of the inven-
tion, the description thereof is omitted hereinafter. Besides,
although the permanent magnet of Fig. 1 or of other figures is
formed in a continuous circular form, the magnet formed separate-
ly with gap is also possible in the present invention as under-
stood from the description provided hereinafter.
The cogging torque is generated by the interaction
between the field permanent magnet member having permanently
magnetized poles and the armature core made of magnetic material
such as iron, and it changes periodically according to the mutual
position therebetween with a basic period of 360(one revolution).
This is harmful for getting a smooth rotation of the rotating
electric machine. The cogging torque is influenced by the shape
of the armature core facing to the field permanent magnet mem-
ber and by the distribution of the magnetic charge in the per-
manently magnetized poles of the field permanent magnet member.
The shape of the armature core is represented by the shape
harmonics expanded by the Fourier series with the basic period
of 360 (one revolution), and the shape harmonics is proper to
the shape of the armature core. The distribution of the magne-
tic charge is represented by the magnetic distribution harmonics
also expanded by the Fourier series with the basic period 360
(one revolution), and the magnetic distribution harmonics is
proper to the distribution of the magnetic charge in the field
permanent magnet member.
lOBS~Z
Mathematically, the cogging torque is determined by
the convolution between the shape harmonics and the magnetic
distribution harmonics, and is also expanded by the Fourier
series with the basic period 360 (one revolution). The magni-
tude of each component (cycle/revolution~ of the cogging torque
is proportional to the product of the component of the shape
harmonics by the component of the magnetic distribution harmon-
ics of the same degree number as that of the component of the
cogging torque. That is, for example, the degree of the com-
ponent 10 c/r (cycle/revolution) of the cogging tor~ue is pro-
portional to the product of the component 10 cycle/rev of the
shape harmonics by the component 10 cycle/rev of the magnetic
distribution harmonics. Therefore, it is possible to decrease
the magnitude of a component of the cogging torque by reducing
either the magnitude of the component of the shape harmonics or
that of the magnetic distribution harmonics of the same degree
number as that of the component of the cogging torque. Practi-
cally, a cogging torque of a rotating ele~ctric machine has sev-
eral dominant components, and the cogging torque can be de-
creased by reducing one of the dominant comoonents. According
to the present invention, at least one indented portion is form-
ed on the major face of at least one saliency facing to the
magnetized poles of the field permanent magnet member so as to
redu~ce the component of the shape harmonics of the same degree
number as that of the dominant component of the cogging torque,
based on the principle described above. Then, the magnitude of
the component, which is generated in case of having no indented
portion, is reduced and the dominant component can be easily re-
duced.
Now, it is described for the cogging torque of the
~()85~2
rotating electric machine of Fig. 1. ~s the permanent magnet
2 of the field permanent magnet member has two poles, the domi-
nant fundamental component of the magnetic distribution harmo-
nics is 2 c/r (cycles per revolution), and the magnetic distri-
bution harmonics mainly has the harmonic components of 2 c/r
series as of 2 c/r, 4c/r, 6c/r, 8c/r, and so on. If there are
not provided the indented portions 7al to 7c2 to the arma-ture
core 3, the magnetic variation of the armature core 3 is due
to the spaced portions 6a, 6b and 6c. As these spaced portions
6a, 6b and 6c are positioned at the equal or nearly equal angle
(120), the dominant fundamental components of the shape harmo-
nics is 3 c/r, and the shape harmonics mainly has the components
of 3 c/r series as of 3 c/r, 6 c/r, 9 c/r, 12 c/r, and so on.
Therefore, the cogging torque in the case of using the armature
core 3 having no indented portions is mainly composed of the
common components appeared in both of the shape harmonics and
magnetic distribution harmonics, i.e. the components of 6 c/r
series as of 6 c/r, 12 c/r, 18 c/r, and s~o on.
The effect of forming the indented portions according
to the invention is clear from the following description. The
magnetic flux from the permanent magnet 2 is attracted to the
salient poles adjacently faced thereto, and it does not reach
to the deep, distant part of the spaced portions 6a, 6b and
6c. ~Therefore, it is possible to consider that each of the
indented portions 7al to 7c2 has magnetically equal or almost
equal effect to that of the spaced portions 6a, 6b and 6c,
though the gap between the indented portion and the permanent
magnet is much shallower than the depth of the spaced portion.
The indented portions 7al to 7c2 are arranged so that they are
positioned at the equal or nearly equal angle of 40 around
1~)8~
the rotary axis 0. So, the dominant fundamental component of
the shape harmonics of the armature core 3 in case of having
the indentcd portions 7al to 7c2 becomes 9 c/r, which is higher,
by a factor 3, than the dominant fundamental component 3 c/r of
shape harmonics of the armature core 3 in case of having no in-
dented portions. And, the shape harmonics mainly has the com-
ponents of 9 c/r series as of 9 c/r, 18 c/r, 27 c/r and so on.
Therefore, the cogging torque in using the armature core 3 with
the indented portions 7al to 7c2 is mainly composed of the com-
ponents of 18 c/r series as of 18 c/r, 36 c/r, 54 c/r and so on.
Comparing this result with the former, it is under-
stood that the rotating electric machine of the invention using
the armature core having the indented portions has much less
cogging components than that of the conventional machine using
the armature core having noindented portions,Moreover, the dominant
fundamental component of the cogging torque of the former is
much higher as 18 c/r than that of the latter, as 6 c/r. Usual-
ly, the magnitude-of the component decreases in accordance with
increase of the degree nu~ber thereof for both the shape harmo-
nics and the magnetic distribution harmonics. Further, the
dominant fundamental component becomes the dominant component
of the cogging torque. Accordingly, the cogging torque of the
rotating electric machine of Fig.l using the armature core 3
with~the indented portions 7al to 7c2 becomes much less than
that of the conventional rotating electric machine using the
armature core 3 without the indented portions 7al to 7c2j as
described above.
There are many arrangements of the indented portions
to reduce the harmful component of the shape harmonics. Fig.
2 is the vector diagrams for explaining the basic conception
1~)859~;~
of the arrangements of the indented portions for reducing the
harmful component of the cogging torque. In Fig. 2, the period
of the harmful component i5 expressed as 2~ radian, and the
vector of the solid line shows the harmful component of the
shape harmonics derived from the spaced portions of the armature
core having no indented portions. The length of the vector
means the magni~ude of the harmful component. When other vectors
expressed by the dotted line are ~dded to the harrnful vec-
tor of the solid line as sh~ in Fi~. 2(b) to (g~, each of the
compound vectors is reduced to zero vector. That is, the harm-
ful component is reduced to zero. The dotted vectors are ob-
tained by arranging the indented portions at the position of
different phases from the spaced portions which causes the harm-
ful component.
The vector diagrams of FigS,2(b) to (e) show examples
of the vectors of the equal length which are positioned at the
equal or nearly equal angle of the phase, and the vector dia-
grams of Fig~.2(f) and (g) show examples of the vectors of the
unequal lengths which are positioned at the unequal angles of
the phase. Thus, there are many arrangements of the indented
portions for reducing a harmful component of the shape harmo-
nics of the armature core.
Based on the above idea, now it will be described for
some~embodiments of the armature core with reduced harmful 6
c/r component of the shape harmonics, hereinafter. Because
40 of 1 c/r is equal to 240 of 6 c/r and each of the indent-
ed portions 7al to 7c2 has magnetically equal effect to each
of the spaced portions 6a, 6b and 6c, the armature core 3 shown
in the rotating electric machine of Fig. 1 is equivalent to the
vector diagram of Fig. 2(c) for the harmful 6 c/r component of
-- 10 --
- ., ~,
i~5~'~2
the shape harmonics.
Fig~, 3 (a) to (c) are schematic view of the other em-
bodiments of the armature cores with reduced harmful 6 e/r com-
ponent. The armature core of Yig. 3(a) has 3 spaced portions
6a, 6b and 6c, whlch are identical to those of Fig. 1, and 3
indented porti~ns 8a, 8b and 8c. Each of these indented por-
tions is 30 away from the center of the adjacent spaced portion
and has magnetically equal effect to that of the spaced portion.
So, this armature core is equivalent to the vector diagram of
Fig. 2(b) for the 6 c/r, eomponent, because 30 of 1 e/r is
equal to 180 of 6 e~r. As 360 of 6 c/r is equal to 60 of 1
e/r, it is easily noticed that the harmful 6 c/r eomponent of
the shape harmonics is not reduced even if the position of an
indented portion, for example 8a, is arranged at the angle 60,
120, 180, 240 and 300. And, as the 3 indented portions 8a,
8b and 8e are at the same phase for the 6 e/r eomponent, these
indented portions can be replaeed by one wider and deeper in-
dented portion than 8a sp2eed at the same phase of 8a for the
6 e/r eomponent.
The armature eore of Fig. 3(b) has 12 indented por-
tions 9al to 9a4, 9bl to 9b4, and 9el to 9C4, eaeh of whieh
has magnetieally equal effeet to that of the spaced portion 6a,
6b and 6e, and the eenter of whieh is 24 (144 of 6 e/r) away
from~the eenter of the neighbouring indented portion or spaeed
portion, as shown in Fig. 3(b). So, the armature eore of Fig.
3(b) is equivalent to the veetor diagram of Fig. 2(e) for the
6 e/r eomponent.
Another embodiment of the armature eore of Fig. 3(e)
is equivalent to the veetor diagram of Fig. 2(f) for the 6 e/r
eomponent, beeause eaeh eenter of 6 indented portions lOa1 to
-- 11 --
s~z
lOc2 arranged on the armat~re core is 37.5 (225 of 6 c/r) away
from the center o~ -the neighbouring spaced portion, and has mag~
netically smaller effect than that the spaced por~ions 6a to 6c
for the harmful 6 c/r component. The component distribution of
the shape harmonics derived from the indented portion changes
according to the width and dep-th thereof, and so the optimum
shape of the indented portion is achieved by changing the width
and/or depth thereof.
Although the shapes of the indented portions shown in
Fig. 1 and Fig. 3 are all cylindrical, the effect of the in-
dented portion of reducing the cogging torque is not limited to
a particular shape of the indented portion. The indented por-
tion of any shape can achieve the effect of reducing the cogg-
ing torque to a certain extent, whenever the indented portions
are positioned at the opposite phase with the harmful component
of the shape harmonics derived from the spaced portions.
Some examples of the shapes of the indented portions
suitable for the projected saliencies, such as the salient
poles 4a, 4b and 4c shown in Fig. 1, are shown in Figs. 4(a) to
4(d), which are front and top/section views of a projected
saliency with 2 indented portions. The shape of the indented
portions shown in Fig. 4(a) is cylindrical and parallel to the
rotary axis, which is identical to the indented portions shown
in F~g. 1. The sectional shape of the indented portions shown
in Fig. 4(b) is a square, and the indented portions and both
sides of the saliency are obliquely parallel to the rotary axis.
This is used for a skewed armature core. Fig. 4(c) shows an-
other example of the shape of the indented portions which is
formed not through the projected saliency but only at a part
thereof, and the sectional shape of it is a trapezoid. The
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1~8S~2
shape of the indented portion sho~n in Fig. 4(d) is a hemisphere.
Further, it is not necessari1y required that each shape of the
indented portions is all the same. Practically, it is desirable
that all of the indented portions are parallel or obliquely par-
allel to the rotary axis, as the armature core is usually made
by laminating stamped out sheet cores.
Now, it is described for the effective arrangements
of the indented portions on the armature core, relating to the
pole number of the field permanent magnet member for reducing
the cogging torque. When the field permanent magnet member has
P poles composed of permanently and alternately magnetized N
and S poles facing to the armature core, the dominant fundamental
number of the magnetic distribution harmonics is P, and the mag-
netic distribution harmonics mainlyhave the harmonic components
of P c/r series as of P c/r, 2P c/r, 3P c/r and so on. As de-
scrived hereinbefore, an arbitrary component of the cogging
torque is proportional to the product of the component of the
magnetic distribution harmonics and the component of the shape
harmonics of the same degree number, it is desiable to arrange
the indented portions so that each angle between a center of
an indented portion and a center of the other indented or spaced
portion neighbouring to said indented portion is not equal to
an integer multiple of (360/P), for reducing the COgging tor-
que~effectively. Besides, there are the effective arrangements
of the indented portions so as to increase the dominant funda-
mental number of the shape harmonics, relating to the pole
number P, as described hereinafter.
Now, it is arranged that the dominant fundamental
degree number of the shape harmonics of the armature core with
the indented portions is C and the dominant fundamental degree
1085~4Z
number of the shape harmonics of the armature core without the
indented portions is C'~ and these numbers have the following
relatlon;
C = K-C' (l)
where K is an integer larger than l (K>l). That is, the shape
harmonics of the armature core with the indented portions main-
ly has the harmonic components of C c/r series as of C c/r, 2C
c/r, 3C c/r, and so on, and the shape harmonics of the armature
core without the indented portions mainly has the harmonic com-
ponents of C' c/r series as of C' c/r, 2C' c/r, 3C' c/r, and so
on. As the cogging torque has the components which exist in
both of the shape harmonics and the magnetic distribution harmo-
nics, the dominant fundamental degree number of the cogging tor-
que is L.C.M.t the least common multiple) between these two
harmonics. So, the dominant fundamental numbers G and G' of
the cogging torque at using the armature core with the indented
portions and without the indented portions are expressed as
follows;
G = L.C.M. (C,P) ---(2)
G' = L.C.M. (C', P) ---(3)
where P is the nu~ber of the poles of the permanent magnet,
that is the dominant fundamental degree number of the magnetic
distribution harmonics of the field permanent magnet member,
as d~escribed above. When G.C.M. (the greatest common mesure)
between C' and P is Q and G.C.M. between P/Q and K is R, G' and
G are represented by the next equations;
G' = PQC ....(4)
G = (R)-G' ---(5)
From the above equations ~4) and (5), in order to in-
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1~35~
crease the dominant foundamental numbcr G of the cogging torque
than G', R should be smaller than K. Therefore, the effect of
the indented portions for reducing the cogging torque is obtain-
ed under the following condition;
R<K, (6)
and the effect is larges-t under the following condition;
R=l. ....(7)
It is noticed that the larger value of K is better
for reducing the cogging torque. Practically, in most cases,
the condition as K/R- 3 is sufficient for reducing the cogging
torque. For the embodiment of Fig. 1 each values described above
are calculated as follows;
P = 2
C' = 3
C = 9
K = C/C~ = 3
Q = G.C.M. (P,C~) = 1
R = G.C.M. (P/Q,K) = 1
G' = (PCI)/Q = 6
G = (K/R)GI = 1~
For the arrangement of C = KC' and R<K as described
above, it is desirable to make the number of the indented por-
tions more than or equal to the number of the spaced portions.
This~is also effective for reducing the magnetic permeance
variation at each indented portion, as each of the indented
portions can be made narrow and shallow according to increase
of the number of the indented portions. Also, it is better
that each of the salient poles has the same number of the in-
dented portions so as to gather flux equally. Different shapes
of the salient poles result in variation of the electrical or
108544;~
mechanical output of the rotating eLectric machine at the poly-
phase winding coils wound to these salient poles. Practically,
in many cases, the total number of the spaced portions and the
indented portions is an integer larger than 1 multiple of the
number of the spaced portions.
As described hereinbefore, the effect of the indented
portions according to the invention of reducing the cogging tor-
que is obtained for arranging at least one indented portions at
a major face of at least one saliency of the armature core.
That is, the effect is not based on the other factors such as
pole number of the field permanent magnet member, number of the
saliencies of the armature core, and phase number and winding
types of the poly-phase winding coils. Also, it is not necessary
that the field permanent magnet member is composed of a single
permanent magnet. It may be composed of a plurality of separate
magnet arranged on the magnet yoke through a gap. Further, it
is understood that the effect of the indented portions of the
invention is also possible for various cases such as even when
the saliencies of the armature core are bent poles of stamped
out sheet discs made of soft steel, when the armature core exists
partially around the rotary axis, and further when the actual
angle of each magnetized pole of the field permanent magnet mem-
ber is different from the value of (360/P). Further, the features
of the invention described hereinbefore for reducing the cogging
torque are also applicable to the rotating electric machine with
an axial gap in which the armature core is placed with an-axial
gap against the field permanent magnet member of a circular form.
Fig. 5 shows another embodiment of the invention, in
which each of three salient poles has a major face which is wider
than one pole angle of the field permanent magnet member. A per-
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i~85'~9L~
manent mac3net 12 is mounted on a magnet yoke 11 at the inner pe-
riphery facing to an armature core 13, and the magnet 12 is per-
manently magneti%ed ~o 8 pairs of N and S-poles, that i5 16 poles
in alternate and circular arrangement so as to make a fixed mag-
netic field around the armature core 13. The armature core 13
has 3 salient poles 14a, 14b and 14c projected against the per-
manent magnet 12. The major face of each of the salient poles
facing to the permanent magnet is made wider than the bottom
part thereof, so that the armature coil can be wound easily
thereon and also the armature core effectively gathers the mag-
netic flux from the permanent magnet. That is, three-phase wind-
ing coils 15a, 15b and 15c are wound at spaced portions 16a, 16b
and 16c between the neighbouring two salient poles.
The major faces of the salient poles 14a, 14b and 14c
facing to the permanent magnet 12 have two indented portions 17al,
17a2; 17bl, 17b2; and 17Cl and 17c2, respectively. At these
intended portions, the gap between the major face of the salient
pole and the permanent magnet 12 is widened. The indented por-
tions are arranged parallel to the rotary axis O, vertically
to the drawing, and they are positioned at about 1/3 points of
the angle 120 between the centers of the spaced portions at the
both sides of the salient poles. Therefore, the spaced portions
16a, 16b and 16c, and the indented portions 17al, 17a2, 17bl, 17b2,
17c, and 17C2 are positioned at the equal or nearly equal angle
of 40 on the outer periphery of the armature core 13 facing to
the permanent magnet 12.
The armature core 13 and the permanent magnet 12 rotate
relatively to each other around the coaxial rotary axis O, and
so one is a rotor and the other is a stator. The angle of the
major face of each salient pole is approximately equal to 112.5,
- 17 -
~08S~Z
5 multiple of the 1 pole angle 22 5 of the permanent magnet
12, so the flux entering the salient pole and passing through
the coil changes alternately according to rotation with the
maximum of the 1 pole flux. ~hen the rotating electric ma-
chine of Fig. 5 is used as a generator, 3-phase atternate
voltages are generated at the 3-phase winding coils 15a, 15b
and 15c according to the relative rotation of the permanent
magnet 12 to the armature core 13. When this is used as a
motor, continuous driving torque is provided by supplying
controlled 3-phase atternate currents to the 3-phase winding
coils l5a, 15b and 15c through a mechanical or electronic
commutator~according to the mutual position between the per-
manent magnet 12 and the armature core 13.
The cogging torque of the rotating electric machine
of Fig. 5 can be also reduced by the indented portions, as
described in the following. Each of the indented portions
17al to 17C2 has magnetically equal or almost equal effect
to that of the spaced portions 16a, 16b and 16c, and the
spaced portions and the indented portions are positioned at
the equal or nearly equal angle, 40 which is not equal to
an integer multiple of the 1 pole angle, that is (360/16)=22.5,
of the permanent magnet 12. In this case, the values relating
to the cogging torque described in the former embodiment are
cal~culated as follows: -
p = 16
C' = 3
C = 9 ' .
K = C/C~ = 3
Q = G.C.M. (P,C') = 1
R = G.C.M. (P/Q,K) = 1
- 18 -
: ~ .
4~:
G' = Pn - = ~8
G = (R)G' = 144
It is understood that G is 3 multiple of G' and the cogging
torque is reduced by the indented portions.
In this case, an angle between the centers of the
two neighbouring indented portions or between the center of
the indented portion and the center of the neighbouring spaced
portion is larger than the 1 pole angle of the permanent mag-
net 12 as shown in the drawing. But, the effect of the in-
dented portions of reducing the cogging torque is also pro-
vided even when such the angle is not equal to an integer
multiple of the 1 pole angle of the permanent magnet. It is
desirable that a width of the indented portion is smaller than
the 1 pole angle of the permanent magnet, because magnetic
variation of the armature core due to the indented portion and
variation of the flux dencity at the gap are reduced according
to decrease of the width of the indented portion. The effect
of the indented portions of reducing the cogging torque does
not depend on a width of the saliency of the armature core, and
the effect can be also provided when the major face of the
saliency of the armature core is almost equal to an odd integer
multiple of the 1 pole angle of the permanent magnet and when
it has a different width.
~ Fig. 6 shows further another e~bodiment of the in-
vention. ~ rotating electric machine of Fig. 6 is especially
suitable to a motor with less ripple torque as well as less
cogging torque. A permanent magnet 22 is mounted on a magnet
yoke 21 at the inner periphery facing to an armature core 23,
and it is permanently magnetized to two pairs of N and S poles,
that is 4 poles, in alternate and circular arrangement, so as
-- 19 --
lO~S~4Z
to make a fixed maqnetic field around the armature core 23.
The armature core 23 has 3 main salient poles 24a, 24b and 24c,
and 3 auxiliary salient poles 25a, 25b and 25c projected
against the permanent magnet 22. The major face of each of the
main salient poles facing to the permanent magnet is wider than
the bottom part thereof, so that an armature coi] can be e~ily wound
thereon and also the armature core effectively gathers the
magnetic flux from the 2ermanent magnet. That is, three-phase
winding coils 26a, 26b and 26c are wound at spaced portions
27a, 27b; 27c, 27d; and 27e and 27f between the neighbouring
two salient poles.
The major faces of the main salient ,ooles 24a, 24b
and 24c facing to the permanent magnet 22 have 3 indented por-
tions 28al, 28a2 and 28a3; 28bl, 28b2 and 28b3; and 28cl, 28C2
and 28c3, respectively. At these indented portions, the gap
between the major face of the main salient pole and the perma-
nent magnet 22 is widened. The indented portions are arranged
parallel to the rotary axis O, vertically to the drawing sheet.
The angle between the centers of the two spaced portions at
the both sides of the main salient pole is 96 which is equal
to 4 multiple of the angle 24 between the centers of the two
spaced portions at the both sides of the auxiliary salient
poles. The spaced portions 27a to 27f and the indented por-
tio~s 28al to 28c3 are positioned at the angle 24 on the
outer periphery of the armature core 23 facing to the perma-
nent magnet 22. Each of the indented portions 28al to 28c3
has magnetically equal or almost equal effect to that the
spaced portions 27a to 27f.
Similarly to the embodiments presented hereinbefore,
the armature core 23 and the permanent magnet 22 rotate re-
- 20 -
~6)8~t~2
latively to each o~her around the coaxial rotary axis O, that
is one is rotor and the other stator. There is provided con-
tinuous driving torque by supplying controlled 3-phase alter-
nate currents to the 3-phase winding coils 26a, 26b and ~6c
through a mechanical or electronic commutator, according to
the mutual position between the permanent magnet 22 and the
armature core 23. As the permanent magnet 22 has 4 permanently
magnetized poles, the dominan-t fundamental number P of the
magnetic distribution harmonics is 4. The dominant fundamental
number C' of the shape harmonics of the armature core without
the indented portions is 3. The dominant fundamental number
C of the compound shape harmonics of the armature core with
the indented portions is 15, as each of the 15 portions of the
spaced portions and the indented portions positioned at the
equal angle 24 has magnetically equal or almost equal effect.
Then, the following values are calculated;
K = C/C' = 5
Q = G.C.M. (P,C') = 1
R = G.C.M. (P/Q,K) = 1
G' = PQ = 12
G = (R)G' = 60
The value of G is increased as 5 multiple of G', and the cogg-
ing torque is much reduced by the indented portions.
~ Now, it is described for reduction of a ripple tor-
que which is defined as torque variation due to geometry of
armature saliencies, armature winding coils and magnetized
poles of the field permanent magnet member, and generated by
the interaction between the excited winding coils on the ar-
mature core and the permanently magnetized poles of the field
permanent magnet member. As the mutual position between the
- 21 -
1~8~42
excited winding coils and the magnetized poles changes accord-
ing to rotation, the driving torque generated by the armature
current varies according to the angular displacement.
The permanent magnet 22 is magnetized usually as a
trape~oid waveform as shown in Fig. 7(a) with the angle ~ in
Fig. 6, where the flux density of an N pole is shown positive.
As the spaced por-tions and the indented portions are small and
the magnetic variation thereat is negligible with the flux
density waveform, the flux density waveform on the surface of
the permanent magnet is approximately the same as the magnetiz-
ed waveform. When one coil eg. 26a is excided by a constant
current, the generated torque is theoretically proportional
to the product between the current value and the derivative
of the flux passing through said excited coil from the perma-
nent magnet 22 by the rotational angle ~, which is defined as
a mutual angle between a reference point Ao of the permanent
magnet 22 and a reference point Bo of the armature core 23.
A flux passing through a coil is the flux entering to the main
salient pole, on which said coil is wound, from the permanent
magnet. As a flux from a part of the permanent magnet facing
to a spaced portion goes into the neighbouring salient poles
at the both sides of said spaced portion, a substantial angle
of a main salient pole gathering flux from the permanent magnet
bec~omes a little wider than the actual geometric angle of the
major face of said main salient pole. This is almost equal to
the angle between the centers of the spaced portions at the
both sides of said main salient pole~ that is 96 in the case
in Fig. 6. When the magnetic variation of the armature core
derived from the indented portions and the spaced portions
are negligibly small, that is considered approximately true,
- 22 -
l~S~9L;2
the derivative of the flux passing through the excited coil is
a~proximately ~roportional to the difference between the flux
densities at the ~oth sides of the substantial angle of the
main salient pole on which said excited coil is wound.
When the macJnetized waveform of the permanent magnet
22 is tra~ezoid as of Fig. 7(a), that is an ordinary case, the
derivatives of the fluxes passing through the 3-phase winding
coils 26a, 26b and 26c become 3~phase waveforms, as shown in
Fig. 7(b). The 3-phase winding coils 26a, 26b and 26c are ex-
cited sequentially by the constant armature current which is
composed of 3-phase alternate currents ia, ib and ic shown in
Fig. 7(c) and controlled by a mechanical or electronic commuta-
tors according to the rotational angle ~. Then, there is gen-
erated a torque of Fig. 7(d) with less ripple torque. Therefore,
the rotating electric machine of Fig. 6 generates the nearly
constant driving torque with less ripple torque and less cogg-
ing torque. Such the rotating electric machine of Fig. 6 can
be used as a motor particularly suitable to an audio apparatus
because of its high quali~y.
From the above description, it is understood that a
ripple torque can be reduced by widening the flat part of the
derivative of the flux passing through the winding coils. There-
fore, the conditions for reducing the ripple torque are to widen
the flat part of the magnetized waveform of the field permanent
magnet member, and to get the substantial angle of the coil near
to an odd integer multiple of the 1 pole angle (360/P) of the
field permanent magnet member. Because the field permanent
magnet member is magnetized with a charging yoke and the flat
part of the ma~netized waveform is proportional to the width of
the charging face of the charging yoke, the former condition is
achieved by the charging yoke having the pole number of the sa-
- 23 -
~()85~Z
lient poles each of which has a charging face wide enough to
achieve that cond~tion. The latter condition is also easily
achieved by se],ecting the number of the main salient poles
smaller than the pole number P, and at the same time by ar-
ranging the auxiliary salient poles among the main salient poles.
The flat part of the magnetized waveform of the field
permanent magnet member also relates to the cogging torque of
the rotating electric machine, as the spectrum distribution of
the magnetic distribution harmonics varies according to the
flat part of the magnetized waveform. That is, as higher com-
ponent of the magnetic distribution harmonics usually becomes
larger in accordance with increase o the width of the flat
part of the magnetized waveform, the cogging torque in case of
without indented portions becomes large at widening the flat
part of the magnetized waveform. The indented portion of the
invention is also effective for this case for reducing the cogg-
ing torque, and at forming the indented portion the cogging
torque becomes small even when the flat part of the magnetized
waveform is made wider. Therefore, it is capable to provide
a rotating electric machine with reduced cogging torque and re-
duced ripple torque by arranging both the indented portions and
auxiliary poles on the armature core. Moreover, the rotating
electric machine of Fig. 6 h~as another advantages of high ef-
ficiency and easiness of constructing.
The auxiliary salient poles are also useful to reduce
the cogging torque as well as to reduce the ripple torque, as
described below. If all of the auxiliary salient poles 25a, 25b
and 25c shown in Fig. 6 are deleted from the armature core 23,
the spaced portions between two of the main salient poles 24a,
24b and 24c become much wider. Then, it becomes very difficult
to arrange the indented portions having magnetically equal effect
to that of these spaced portions because it should be much larg-
- 24 -
~ 9tZ
er according to ~he large spaced portion. There~ore, the aux-
iliary salient poles are also effective for reducing the cogg-
ing torque, when ~he spaced portions are too large. Further,
it is possible and eEfectiJe to arrange the indented portions
also at the auxiliary salient poles, as easily understood.
From the description presented hereinbefore, it is
understood that for the easy and effective method for reducing
the cogging torque and/or xi~ple torque, there are four kinds
of conditions as follows;
(1) The number of the main salient poles is smaller
than the pole number of the field permanent magnet member.
(2) The auxilia~ salient poles are arranged~among
the main salient poles so that the substantial angle of the
each main salient pole becomes near to an odd integer multiple
of the 1 pole angle of the field permanent magnet member.
(3) The ratio of the angle between the centers of
the spaced portions at the both sides of an arbitrary main
salient pole to the angle between the centers of the spaced
portions at the both sides of an arbitrary auxiliary salient
pole is an integer.
(4) The indented portions have magnetically equal
or almost equal effect to that of the spaced portions and they
are arranged so that the spaced portions and the indented por-
tions~are arranged at the e~ual or nearly equal angle which is
not equal to an integer multiple of the 1 pole angle. The ro-
tating electric machine of Fig. 6, which has the same number
of the alternately arranged main salient poles and the auxiliary
salient poles, satisfies these four conditions. E~owever, it is
noted that a rotating electxic machine with reduced cogging tor-
que and reduced ripp]e torque is not limited to these conditions.
- 25 -
- ~ ~
l()~S~Z
As apparentlv from the description presented hereinbefore, there
can be provided the other rotating electric machines with re-
duced cogging tor~ue and reduced ripple torque, according to
the invention. Further, although t:he embodiments presented
hereinbefore use the 3-phase winding coils, a rotating electric
machine of any phase winding coil is oossible.
For making the armature core, laminated sheet cores
each haviny the same shape are used to form both the main sa-
lient poles and auxiliary salient poles, and in this case the
cogging torque and the ripple torque of the rotating electric
machine will be stable during the mass production as the shape
of the armature core scarcely vary. But, for the convenience
of winding the coils, the armature core is separated to a main
salient pole set and an auxiliary salient pole set. For exam-
ple, the main salient pole set is made by laminating the stamp-
ed out sheet cores, and the auxiliary salient pole set is made
of a soft steel disk having bent auxiliary salient poles. In
this case, after winding the poly-phase winding coils on the
bottom parts of the main salient poles; the auxiliary salient
pole set is connected mechanically and magnetically to the main
salient pole set so as to arrange the auxiliary salient poles
among the main salient poles.
For reducing the ripple torque, it is desirable that
the n~umber of the indented nortions is larger than or equal to
the number of the spaced portions, so that the indented portions
are narrower and shallower and magnetic variation at each in-
dented portions is smaller. It is also desirable, for reducing
the ripple torque, to arrange the same number of the indented
portions on each main salient pole, and to make each main sa-
lient pole magnetically symmetric with the center thereof.
- 26 -
4Z
The rotating electric machine of Fig. 6 can be also
used as a aenerator. It generates 3-Phase alternate voltages
whose wave~orms are the same as shown in Fig. 7(b) in rotating
at a constant anyular speed, as each of the generated voltages
is also proportional to the product between the angular speed
and the derivative of the flux passing through each phase wind-
ing coils. So, a D.C. voltage having little ripple voltage is
easily obtained from the 3-phase alternate voltages just by
rectifying them with 3 diodes, negative poles of which are con-
nected in common, or with a mechanical commtator. This D.C.
voltage is often used as a detected signal varied according to
the angular speed in controlling the speed of the rotating elec-
tric machine.
Fig. 8 shows further another embodiment of the inven-
tion which uses lap wound poly-phase winding coils. A permanent
magnet 32 is mounted on a magnet yoke 31 at the inner periphery
facing to an armature core 33, and it has permanently magne,tized
two pairs of N and S poles, that is 4 poles, in alternate and
circular arrangement, so as to make a fixed magnetic field around
the armature core 33. The armature core 33 has 12 salient teeth
34a to 34~ projected against the permanent magnet 32. The major
face of each of the salient tooth 34 facing to the permanent
magnet 32 is wider than the bottom part thereof, so that the
armature winding can be easily wound thereon, and also the ar-
mature core effectively gathers the magnetic flux from the per-
manent magnet 32. That is, armature coils 35al to 35c4 are
wound at spaced portions 36a to 36~ between neighbouring two of
the twelve salient teeth facing to the permanent magnet 32.
Each major face of the salient teeth 34a to 34~ has
one indented portion of 37a to 37, respectively. At these in-
lV8~9 ~
dented portions, the gao between the major face of the salienttooth and the perm~nent magnet 32 is widened. The indented
portions are arranged parallel to the rotary axis 0, vertically
to the drawing, and they are positioned at about a half point
of 30, an angle between the centers of the spaced ~ortions at
the both sides of the salient tooth. Therefore, the spaced por-
;tions 36a to 36R and the indented portions 37a to 37~ are posi-
tioned at the equal or nearly equal angle 15 on the outer pe-
riphery of the armature core 33 facing to the permanent magnet
32. Each of the indented portions 37a to 37~ has magnetically
equal or almost equal effect to that of the spaced portions 36a
to 36~, though the depth of the indented portion is much shallow-
er than the deoth of the spaced portion.
The armature core 33 and the permanent magnet 32 ro-
tat~s relatively to each other around the coaxial rotary axis 0,
i that is one is rotor and the other stator. As the armature coils
35al to 35c4 form 3-phase winding coil groups 35ai, 35bi and 35ci
(i =1,2,3,4), in case of usiny the rotating electric machine of
Fig. 7 as a motor, a continuous driving torque is obtained by
supplying controlled 3-phase alternate currents to the 3-phase
winding coil groups 35ai, 35bi and 35ci through a mechanical or
electronic commutator, according to the mutual position between
the permanent magnet 32 and the armature core 33.
For the rotating electric machine of Fig. 8, the values
of the factors for the dominant fundamental number of the cogging
torque is calculated as follows;
P = 4
C' = 12
C = 24
K = C/C' = 2
- 28 -
~V~3549LZ
Q = G.C.M. (P, C') = 4
R = G.c.r~l. (P/Q,K) = 1
G' = QC_ _ 12
G = (R)Gl = 24
As G is increased to 2 multi~le of ~', the co~ging torque i5 re-
duced.
As for the ripple torque of the rotating electric ma-
chine of Fig. 8, the substantial angle of each winding coil ga-
thering flux from the nermanent magnet 32 is equal or almost
equal to the angle between the centers of two spaced portions
where said winding coil is arranged, that is to one pole angle
90 of the permanent magne. 32. And, the flat part of the mag-
netized waveform of the permanent magnet 32 is widened enough
within an approvable small cogging torque by means of the in-
dented portions. Accordingly, the rotating electric machine of
Fig. 8 can have reduced ripple torque and reduced cogging torque.
The rotating electric machine of Fig. 8 can be also used as a
generator, and a DC voltage with reduced ripple voltage is gen-
erated, similarly to the rotating electric machine of Fig. 6.
Figs. 9 and 10 show further another embodiment of the
invention using bent salient poles. Fig 9(a) is a cross-sec-
tional view of the rotating electric machine using the bent sa-
lient poles, and in exploded view of Fig. 9(b) the parts of the
machin~e are separated along the axis to clarify their relation-
ship with each other.
The armature elements are mounted on a base 41. A
bearing core 43 made of soft steel is firmly gripped at a center
aperture 42, and it has two bearings 44 and 45 at both sides so
as to support a rotor shaft 59. The bearing core 43 forms a
support for a soft steel disc 46 having two bent salient poles
_ zg _
~ 5~Z
46a and 46b facing to a permanent magnet 57. A center aperture 47
o~ the disc 46 has a diameter fitting the bearing core 43. A
short and hollow cylinder 48 made of soft steel is a connecting
core 48, which is mounted to the bearing core 43 and stand at
the back surface of the disc 46. The connecting core 48 serves
as a low reluctance support for a cylindrical coil 50 wound on
a coil form 49, and also as a spacer to separate a second disc
51 from the first disc 46.
The second disc 51 has two ~ent salient poles 51a and
51b which are positioned between the bent salient poles 46a and
46b of the first disc 46 without touching to them. A third soft
steel disc 52 having two bent salient poles 52a and 52b is mount-
ed to the bearing core 43 onto the opposite side of the second
disc 51. Another connecting core 53 of soft steel and another
cylindrical coil 55 wound on another coil form 54 are also in-
serted to the bearing core 43. A forth soft steel disc 56 having
two bent salient poles 56a and 56b is mounted to the connecting
core 53. The bent salient poles 56a and 56b are positioned be-
tween the bent salient poles 52a and 52b of the third disc 52
without touching to them. These four discs 46, 51, 52 and 56
are firmly fixed to the base 41. So, the armature core is com-
posed of the two identical basic blocks axially laminated, each
of which is composed of two soft steel discs, magnetically con-
necting mean between said two discs, and at least one cylindri-
cal coil wound around the rotary axis.
A cylindrical permanent magnet 57 is mounted to the
inner periphery of a magnet yoke 58 and positioned at the outer
~eriphery of the armature core. The magnet yoke 58 has a rotary
axis 59 inserted to the bearings 45 and 44 in order to rotate
relatively to the armature core. The permanent magnet 57 is
- 30 -
lO~S~Z
magnetized to two pole pairs of N and s ~oles, that is 4 poles,
in alternate and ~ircular arrangement so as to make a fixed
magnetic field around the armature core.
Figs. lO(a) and (b) are developed views of the per-
manent magnet 57 and the bent salient poles of the ~our soft
steel discs 46, 51, 52 and 56 facing to the magnetized poles
of the permanent magnet 57, respectively. The steel discs 46,
51, 52 and 56 has two ~ent salient poles of 46a, 46b; 51a, 51b;
52a, 52b; and 56a, 56b, respectively, each of which has the
major face facing to the permanent magnet 57. The substantial
angle of each bent salient pole is equal or almost equal to the
one pole angle 90. The bent salient poles 46a to 56b have two
indented portions 60Cl to C4, 60dl to d4, 60el to e4, and 60fl
to f4, respectivel~ at about 1/3 points of the substantial angle
90 of each bent salient pole. Each of the indented portions
has magnetically equal or almost equal effect to that of the
spaced portions 60al to a4, and 60hl to b4 between neighbouring
two of the bent salient poles, and these spaced portions and
indented portions are positioned at the equal or nearly equal
angle 15.
The flux passing through the winding coil 50 comes
from the permanent magnel: 57 to the bent salient poles 46a and
46b of the soft steel disc 46, and the flux passing through the
winding coil 55 to the bent salient poles 56a and 56b of the
soft steel disc 56. ~he flux of the winding coil SO has delay
of 45, a half of the one pole angle, from the flux of the wind-
ing coil 55. So, at using this rotating electric machine as a
motor, continuous driving torque is obtained by sup~lying con-
trolled currents to the coils 50 and 55 through a mechanical
or electronic commutator, according to the mutual position be-
- 31 -
1~8~4Z
tween the permanen-t magnet 57 and the armature core.
As for the cogging torque of the rotating electric
machine shown in Fig. 9, ~he ualues of the factors related to
the cogging torque are calculated as follows;
P = 4
C' = 8
C = 24
K = C/C' = 3
Q = G.C.M. (P,C'~ = 4
R = G.C.M. (P/Q,R) = 1
G' = PC' = 8
G = ~KR)G' = 24
G is increased 3 multiple of G', and it is understood that the
cogging torque is reduced by arranging the indented portions.
This rotating electric machine has also reduced rip-
ple torque when it is used as a motor, because the substantial
angle of each bent salient pole gathering flux from the per-
manent magnet to the winding coils is equal or almost equal to
the one pole angle 90 of the permanent magnet, and because
the flat part of the magnetized waveform of the permanent mag-
net is widened within an approvable small cogging torque by
the indented portions. Thus, the rotating electric machine
shown in Fig. 9 can have reduced ripple torque as well as re-
duced;cogging torque.
As each of the soft steel discs 46, 51, 52 and 56 is
the same shape, they can be treated as one part at production.
The effect of the indented portions does not depend on the other
factors such as way of making the salient poles, types of outer
rotor or inner rotor, winding way, and so on, and an actual
shape of the indented portion may be changed whenever it has
- 32 -
lV85'~4Z
magnetically equal effect. For example, -the indented portion
60c, may be replaced by a straight slit from the upside to the
downside of the bent salient pole. The substantial angle of
each bent sal;.ent pole can be made equal to an odd integer
multiple of the one pole angle of the field permanent magnet
member by increasing the pole number of the field permanent
magnet member, for further reducing the cogging torque.
