U.S. patent application number 09/791303 was filed with the patent office on 2001-08-30 for electric rotary machine.
This patent application is currently assigned to Minebea Co., Ltd.. Invention is credited to Fujitani, Sakea, Harada, Naoyuki, Ohyashiki, Taketoshi, Suzuki, Yuzuru.
Application Number | 20010017501 09/791303 |
Document ID | / |
Family ID | 18570236 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010017501 |
Kind Code |
A1 |
Suzuki, Yuzuru ; et
al. |
August 30, 2001 |
Electric rotary machine
Abstract
Electromagnetic conversion efficiency of an electric rotary
machine is enhanced and reduction of leakage flux due to magnetic
discontinuity can be realized without providing holes for
positioning and fixing salient poles in a stator ring. Outer
appearance and decency of the electric rotary machine as a product
are also improved by not allowing lower ends of salient poles of an
armature assembly to be exposed on an outer surface of the electric
rotary machine. For this purpose a radial gap type electric rotary
machine comprises a field magnetic pole consisting of a permanent
magnet which is supported rotatably and an armature assembly
consisting of a plurality of divided salient poles which oppose the
field magnetic pole with a small air gap therebetween and are
radially arranged with respect to a rotation axis. The armature
assembly includes a first ring made of a soft magnetic member for
receiving the plurality of salient poles and a second ring made of
a soft magnet member for receiving the first ring.
Inventors: |
Suzuki, Yuzuru;
(Shizuoka-ken, JP) ; Fujitani, Sakea;
(Shizuoka-ken, JP) ; Ohyashiki, Taketoshi;
(Shizuoka-ken, JP) ; Harada, Naoyuki;
(Shizuoka-ken, JP) |
Correspondence
Address: |
Patent Group
Hutchines, Wheeler & Dittmar
101 Federal Street
Boston
MA
02110
US
|
Assignee: |
Minebea Co., Ltd.
|
Family ID: |
18570236 |
Appl. No.: |
09/791303 |
Filed: |
February 23, 2001 |
Current U.S.
Class: |
310/261.1 |
Current CPC
Class: |
H02K 3/522 20130101;
H02K 1/148 20130101; H02K 2203/12 20130101; H02K 1/185
20130101 |
Class at
Publication: |
310/254 ;
310/218 |
International
Class: |
H02K 001/12; H02K
001/14 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 2000 |
JP |
48099/2000 |
Claims
What is claimed is:
1. A radial gap type electric rotary machine comprising: a field
magnetic pole consisting of a permanent magnet which is supported
rotatably; an armature assembly consisting of a plurality of
separated salient poles which oppose said field magnetic pole with
a small air gap therebetween and are radially arranged with respect
to a rotation axis; wherein said armature assembly includes a first
ring of a soft magnetic member for receiving said plurality of
salient poles and a second ring of a soft magnet member for
receiving said first ring.
2. A radial gap type electric rotary machine as set forth in claim
1, wherein said first ring has rectangular slits or holes for
fixedly holding said salient poles, said slits or holes extending
in parallel to said rotation axis.
3. A radial gap type electric rotary machine as set forth in claim
1, wherein each salient pole of said armature assembly includes a
plurality of soft magnetic material sheets stacked in a
circumferential direction of said armature assembly.
4. A radial gap type electric rotary machine as set forth in claim
1, wherein said first and second rings are fixedly bonded to each
other.
5. A radial gap type electric rotary machine as set forth in claim
1, wherein at least one of said first and second rings comprises a
metallic sheet formed into a ring configuration, and any one of
said salient poles is not located at a joint between a first
rolling end and a second rolling end of said ring.
6. A radial gap type electric rotary machine as set forth in claim
1, wherein each of said first and second rings comprises a metallic
sheet formed into a ring configuration and an angle made by a joint
between a first rolling end and a second rolling end is set to have
an offset in a range of from 30.degree. to 330.degree. inclusive in
terms of a center angle as viewed from the center of the joint.
7. A radial gap type electric rotary machine as set forth in claim
1, wherein a wall thickness of said second ring is equal to or
greater than a wall thickness of said first ring, and an axial
length of said second ring is equal to or greater than an axial
length of said first ring.
8. A radial gap type electric rotary machine as set forth in claim
1, wherein substantially disc shaped flanges each having a bearing
mechanism at its center are fixed to both axial end surfaces of
said second ring.
9. A radial gap type electric rotary machine as set forth in claim
5 or 6, wherein at least one of said first and second rings is
formed of a vibration damping steel sheet.
10. A radial gap type electric rotary machine as set forth in claim
1, being a brushless DC motor.
11. A radial gap type electric rotary machine as set forth in claim
1, having an inner rotor structure.
12. A radial gap type electric rotary machine as set forth in claim
1, having an outer rotor structure.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to an armature
structure of a radial gap type electric rotary machine. More
particularly, the invention relates to an armature structure of a
radial gap type electric rotary machine, in which respective
salient poles of armature are positioned by one of two rings and
reluctance is lowered by the other ring.
[0003] 2. Description of the Related Art
[0004] In a conventional electric rotary machine, in which an
armature is constituted by a plurality of ring-shaped plate yokes
made of a soft magnetic plate member such as silicon steel plate or
the like and stacked in an axial direction, each ring-shaped plate
yoke having a plurality of salient poles radially formed, since the
ring-shaped plate yoke is punched out integrally with a plurality
of salient poles, the salient poles are not structurally separated
and therefore a resultant armature will have superior magnetic
efficiency (low reluctance). However, since usually a winding is
wound directly on each salient pole, winding operation is
troublesome. Particularly, in case of an inner rotor type electric
rotary machine, winding operation is quite difficult. As a result,
the winding operation will require a longer time and a space factor
of the winding cannot be increased. Furthermore, because the
winding is done by flyer winding, tensional stress may be applied
to a wire during the winding operation to restrict insulation
reliability of the winding portion.
[0005] However, in recent years, a rare earth magnet having high
energy product has been developed and structure of the electric
rotary machine has been reviewed by analysis of magnetic circuits
using a computer. This results in findings that a divided armature
type electric rotary machine, in which improvement in efficiency in
the winding operation and increase in space factor are expected
while reluctance is slightly increased, can achieve higher
performance and low cost. Therefore, there is a growing demand for
division of an armature.
[0006] As an example of the divided type armature, a conventional
type armature yoke which is constituted by a plurality of
ring-shaped plate yokes stacked in their axial direction is divided
into salient pole portions and a winding is provided on each of the
separated salient pole portions, then the separated salient pole
portions are joined at divided places by laser or the like (welding
or the like) to be reinstated into an armature. This method needs
much labor because the conventional armature is once divided and
then joined again. Moreover, the separated salient pole portions
have to be put back together while maintaining the stacked
condition appropriate, so it is necessary to set the separated
salient pole portions in a die, tooling or the like which ensures
assembling precision satisfactorily and to securely weld them on a
one-by-one basis. Therefore, high precision is required and
workability is low. Furthermore, mechanical and magnetic
characteristics are significantly degraded at the joined (welded)
portions inherently. Thus, the conventional divided type armature
still has a few problems to be solved.
[0007] In order to solve such defects involved in the divided type
armature as set forth above, the inventors have proposed methods to
divide an armature into a structure completely different from the
conventional structure in Japanese Unexamined Patent Publication
No. Heisei 11-355981 and Japanese Unexamined Patent Publication No.
2000-4566. These methods apply an invention in the armature
structure, which is adapted to satisfactorily turn features of the
divided type to advantage for the winding operation and joining the
salient poles. However, a hole for positioning and joining the
salient poles is required on a stator ring (which refers to "outer
casing of the electric rotary machine") which functions as a
magnetic circuit as well. The hole presents discontinuity in the
magnetic circuit to cause outward emission of leakage flux, which
is disadvantageous in view of electromagnetic compatibility (EMC),
etc. to which importance is attached recently. Another problem
resides in lowering of electromagnetic conversion efficiency, which
is caused by increase in reluctance in the ring itself and salient
pole joining portions. And still another problem resides in
degrading external appearance of a product because the lower ends
of the salient poles are exposed through the hole or groove of the
stator ring.
SUMMARY OF THE INVENTION
[0008] It is an object of the present invention to provide a rotary
gap type electric rotary machine with a divided armature comprising
a plurality of separated salient poles and a ring which
magnetically and mechanically couples the salient poles, wherein a
stator ring is provided with no hole for positioning and fixing
separated salient poles whereby leakage flux resulting from
magnetic discontinuity can be reduced and at the same time
electromagnetic conversion efficiency of an electric rotary machine
can be enhanced.
[0009] Another object of the invention is to improve the external
appearance and decency of an electric rotary machine by preventing
the lower ends of the salient poles from being exposed through the
outer surface of the electric rotary machine.
[0010] According to one aspect of the invention, there is provided
a radial gap type electric rotary machine comprising a field
magnetic pole consisting of a permanent magnet which is rotatably
supported and an armature assembly having a plurality of separated
salient poles opposing the field magnetic pole with a small air gap
therebetween and radially arranged with respect to a rotation axis
of the electric rotary machine, wherein the armature assembly
includes a first ring made of a soft magnetic member for receiving
a plurality of salient poles and a second ring made of a soft
magnetic member for receiving the first ring.
[0011] The first ring has substantially rectangular slits or holes
for guiding and fixedly holding the salient poles and the slit or
the hole extends in parallel to the rotation axis.
[0012] Each salient pole of the armature assembly may be formed by
stacking a plurality of soft magnetic plates in a circumferential
direction.
[0013] The first and second rings may be fixedly bonded
together.
[0014] One of the first and second rings may be made of a flat
metal plate and formed into a ring configuration, and the salient
pole is not positioned at a joint between a first rolling end and a
second rolling end of the ring.
[0015] Both the first and second rings may be made of a metallic
flat plate and formed into a ring configuration, and an angle
formed by the joint between the first rolling end and the second
rolling end of the ring may be set to have an offset in a range of
from 30.degree. to 330.degree. inclusive in terms of a center
angle.
[0016] The second ring may have a wall thickness equal to or
greater than a wall thickness of the first ring, and the second
ring may have an axial length equal to or greater than an axial
length of the first ring.
[0017] Substantially disc shaped flanges having bearing mechanism
at the center portions thereof may be fixed by welding on both
axial end surfaces of second ring.
[0018] At least one of the first and second rings may be formed of
vibration damping steel sheet which is made by integrating a
synthetic resin made of a high polymeric material with a metal and
has a damping effect.
[0019] The electric rotary machine may be a brushless DC motor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The present invention will be understood more fully from the
detailed description given hereinafter and from the accompanying
drawings of the preferred embodiment of the present invention,
which, however, should not be taken to be limitative to the
invention, but are for explanation and understanding only.
[0021] In the drawings:
[0022] FIG. 1 is an axial section of a radial gap type brushless DC
motor as one embodiment of an electric rotary machine according to
the present invention;
[0023] FIG. 2. is a partially sectioned front elevation of the DC
brushless motor of FIG. 1 as viewed in axial direction;
[0024] FIG. 3A is a perspective view of a bobbin of a salient
pole;
[0025] FIG. 3B is a perspective view of polar teeth of the salient
pole;
[0026] FIG. 4 is a perspective view of the salient pole in
assembled condition;
[0027] FIG. 5 is a perspective view showing another embodiment of a
salient pole in assembled condition;
[0028] FIG. 6A is a perspective view of a salient pole assembly of
an armature assembly of a brushless DC motor as another embodiment
of the electric rotary machine according to the invention;
[0029] FIG. 6B is a perspective view of a pole tooth ring;
[0030] FIG. 6C is a perspective view of a stator ring;
[0031] FIG. 7 is a perspective view of another embodiment of a pole
tooth ring;
[0032] FIG. 8 is a perspective view showing the brushless DC motor
of FIG. 1 with one flange removed;
[0033] FIGS. 9A and 9B are diagrammatic illustration for explaining
two different joining conditions of the salient poles, the pole
tooth ring and the stator ring;
[0034] FIG. 10A is a perspective view of a sheet member for
fabricating a pole tooth ring as a second embodiment;
[0035] FIG. 10B is a perspective view of the pole tooth ring
fabricated of the sheet member;
[0036] FIG. 11A is a perspective view of a sheet member for
fabricating a pole tooth ring as a third embodiment;
[0037] FIG. 11B is a perspective view of the pole tooth ring
fabricated of the sheet member.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0038] The present invention will be discussed hereinafter in
detail in connection with preferred embodiments of the present
invention by reference to the accompanying drawings. In the
following description, numerous specific details are set forth in
order to provide a thorough understanding of the present invention.
It will be obvious, however, to those skilled in the art that the
present invention may be practiced without these specific
details.
[0039] FIGS. 1 and 2 show a structure of a three-phase inner rotor
type brushless DC motor which has six salient poles and eight
magnetic poles, as an example of an electric rotary machine of the
present invention. The embodiment here shows a so-called integrally
resin-molded armature assembly, in which a resin is filled for
integral molding inside an armature assembly except a portion where
a rotor field magnet is received.
[0040] A feature of the present invention resides in a magnetic
circuit construction of an armature assembly constituted by a
plurality of salient poles and two soft magnetic rings. The
armature assembly is constituted in such a manner that the
plurality of salient poles which are formed by concentrically
winding a coil on a resin bobbin and inserting a substantially pole
tooth stacked into a rectangular hole located at a center of the
bobbin are radially fixed inside a pole tooth ring and that a
stator ring is fitted over the pole tooth ring.
[0041] The present invention will now be discussed with reference
to the drawings.
[0042] FIG. 1 is a section of a brushless DC motor as taken along a
longitudinal axis thereof, and FIG. 2 is a half-sectioned front end
of the brushless DC motor as viewed along the axial direction. The
brushless DC motor is constructed with an armature assembly 10,
flanges 12 and 13 arranged at both axial ends of the armature
assembly 10 and a rotor assembly 20 rotatably arranged within the
armature assembly 10.
[0043] The armature assembly 10 has a cylindrical stator ring 100
on the outer periphery thereof. A pole tooth ring 50 is fitted on
the inner surface of the stator ring 100. Within the pole tooth
ring 50, six salient poles 6 are arranged radially at an
equiangular position of 60.degree..
[0044] The salient pole 6 is constructed in such a manner that a
pole tooth 34 shown in FIG. 3B which is formed by stacking nine
pieces of electromagnetic steel sheets each having a thickness of
0.35 mm and shaped into substantially T configuration is inserted
into a rectangular hole 36a (width T1) of a resin bobbin 36 shown
in FIG. 3A, and that a magnet wire 38 is wound between flange
portions 36b and 36c of the bobbin 36 shown in FIG. 3A. The pole
tooth 34 is formed in such a manner as to have its lower end (a
left side thereof in FIG. 3B) projecting from the surface of the
flange portion 36b by a prescribed height (height T3) across the
entire length (length T2) thereof. One end of the magnet wire 38 is
bound around a terminal 40 inserted at the lower end of the flange
36c of the bobbin 36. The salient pole 6 thus formed is shown in
FIG. 4. Two recesses 36d are formed apart from each other on each
side of the flange 36c of the bobbin 36 to form ports for injecting
resin.
[0045] It should be noted that the pole tooth 34 may be, in
addition to the electromagnetic magnetic steel sheets, of soft
magnetic materials, such as ceramic moldings formed of sintered
soft magnetic material powder, and so-called powder metallurgic
moldings formed of sintered soft magnetic material consisting of
micro-powder of pure iron or the like with its outer surface
treated for insulation. Other soft magnetic metallic plates
containing metallic materials of Fe--Cr type may not only maintain
high reluctance but also has relatively high electric resistance
thereby reducing eddy current loss, and at the same time, may be
free of corrosion even without providing rust preventive treatment
on the surface of respective plate components, which enables
effective usage in a severe environment (such as automotive
application).
[0046] FIG. 5 shows another embodiment of a salient pole.
[0047] In the embodiment, when the pole tooth 34 is inserted in the
bobbin 36, only projection 34a formed at substantially central
portion of the lower end, instead of the entire lower end of the
pole tooth 34 as shown in FIG. 4, projects from the surface of the
flange 36b of the bobbin 36 by height T3.
[0048] When the salient pole 6 is formed of an electromagnetic
steel sheet, a plurality of plate sheets are stacked in
circumferential direction to form the pole tooth 34 as shown in
FIG. 3B. This is not necessarily the case, when the salient pole 6
is formed of a soft magnetic material such as a ceramic molding of
sintered soft mangetic material powder or a metallurgic
molding.
[0049] FIGS. 6A, 6B and 6C are exploded perspective views showing
the armature assembly, wherein FIG. 6A shows a salient pole
assembly formed of six salient poles radially arranged at an
equiangular position of 60.degree. in such a manner that flanges
36c contact with each other. FIG. 6B shows a pole tooth ring 50 and
FIG. 6C shows a stator ring 100.
[0050] As can be seen from FIG. 6A, resin injecting ports 37 are
formed by the recesses 36d which mate with each other on the side
edge of the flanges 36c of the bobbins 36 of two adjacent salient
poles 6.
[0051] FIG. 6B shows the pole tooth ring 50 which is adapted to
receive the salient pole assembly shown in FIG. 6A. The pole tooth
ring 50 is made of a metallic cylinder and formed by drawing
process. Six slits 50a are formed at an equiangular position in
circumferential direction extending in the longitudinal direction
(parallel to the rotary axis of the rotor field magnet) up to a
substantially center portion. The shape of the slit 50a is
rectangular. The slits 50a may be positioned not necessarily
equidistantly from each other but arbitrarily attempting to enable
adjustment of cogging torque. The slit 50a has a function to guide
each salient pole 6 inside the pole tooth ring 50 when the salient
pole assembly shown in FIG. 6A is inserted into the pole tooth ring
50 and to fix the salient pole 6 in the pole tooth ring 50 when the
salient pole 6 is guided all the way in position. By setting the
width of the slit 50a to be slightly smaller than the thickness of
the projection 34a as viewed in a circumferential direction of the
salient pole 6 shown in FIG. 5, the salient pole 6 may be press
fitted into the pole tooth ring 50. In order to secure a greater
press fitting force and magnetic coupling force, it is preferable
that the salient pole 6 should be structured in such a manner that
the projection 34a projecting from the flange 36b as shown in FIG.
4 has as long axial length T2 as possible. The inventors found in
the experiments that it is effective when the length T2 of the
projection 34a of the salient pole 6 is three to ten times as large
as the circumferential thickness T1 of the projection 34a, and
particularly effective when it is seven times as large.
[0052] On the other hand, the height T3 of the projection 34a of
the salient pole 6 may be set to be equal to or slightly smaller
than the wall thickness of the pole tooth ring 50 so that the
projection 34a does not project from the peripheral surface of the
pole tooth ring 50 when the salient pole assembly is assembled into
the pole tooth ring 50 thereby permitting the pole tooth 50 to fit
smoothly into the stator ring 100. Thus, the stator ring 100 will
suffer no deformation. If tapers 51 are provided at the inlet
portion of the slit 50a as shown in FIG. 7, workability in
assembling will be improved.
[0053] The stator ring 100 shown in FIG. 6C is designed to receive
the pole tooth ring 50 with the salient pole assembly inserted.
Unlike the pole tooth ring 50, the stator ring 100 has no
positioning mechanism and no fixing mechanism on its outer or inner
surface. Therefore, the internal diameter SR4 of the stator ring
100 is set to be equal to or slightly greater than the external
diameter TR4 of the pole tooth ring 50 so that they may fit with
each other upon insertion. In case of an outer rotor type motor,
the stator ring 100 is disposed inside the pole tooth ring 50.
[0054] On the other hand, the axial length SR1 of the stator ring
100 is set to be equal to or larger than the length TR1 of the pole
tooth ring 50, so that the pole tooth ring 50 can be completely
received within the stator ring 100. Therefore, no mechanism for
positioning and fixing the pole tooth ring 50 relative to the
stator ring 100 will appear on the outer peripheral surface of the
motor so that the magnetic discontinuity can be completely
compensated by the stator ring 100 which covers the outside of the
pole tooth ring 50. Thus, leakage flux can be significantly
reduced. Of course, external appearance and decency of the motor as
a product is greatly improved. On the other hand, in the
embodiment, the wall thickness SR2 (1.0 t in the embodiment) of the
stator ring 100 is set to be larger than the wall thickness TR2
(0.8 t in the embodiment) of the pole tooth ring 50 for the
convenience of resistance welding flanges 12 and 13 to the stator
ring 100(see FIG. 1). However, it is preferred to minimize the wall
thickness SR2 as long as the resistance welding is applicable. It
should be noted that a cutout 100a is provided on the lower end of
the stator ring 100 for clearance of a connector 57 (see FIG.
1).
[0055] Here, explanation will be given on mechanical and magnetical
connection between the pole tooth 34 of the salient pole 6, the
pole tooth ring 50 and the stator ring 100.
[0056] In the embodiment, connection between the salient pole 6 and
the pole tooth ring 50 is established by inserting the projection
34a of the pole tooth 34 into the slit 50a of the pole tooth ring
50. This is the important element of the present invention.
However, the connecting structure should not be limited to the way
examplified in the embodiment, but can be another way in which the
projection of the salient pole loosely fits in the slit 50a of the
pole tooth ring 50 and then the joint portion is welded for
reinforcement.
[0057] In the present invention, the connection between the
projection on the lower end of the salient pole and the stator ring
100 is critical from a standpoint of motor characteristics.
Particularly, it is preferable in economical viewpoint that
respective pole teeth inserted in one and the same bobbin have the
same shape. In case of an inner rotor, it is preferable that the
projections of each sheet of the pole teeth 34 are arranged along
the inner surface of the stator ring 100 and contact therewith
continuously and uniformly as shown in FIG. 9A.
[0058] On the other hand, the projections of each sheet of the pole
tooth 34 may also be arranged on a straight line to partially form
a gap g as shown in FIG. 9B instead of being arranged along the
inner surface of the stator ring 100. In comparison with the case
shown in FIG. 9A, no significant degradation of characteristics was
found in the experiment. This is because the larger the outer
diameter is the smaller the gap is due to curvature.
[0059] The pole tooth ring 50 is preferably inserted into the
stator ring 100 by press fitting or close fitting in consideration
of magnetic characteristics. However no substantial degradation of
characteristics was recognized when stop fitting was applied in
consideration of workability. It will be effective in reducing
vibration and/or noise if bonding is jointly employed depending
upon the amount of gap between the pole tooth ring and the stator
ring.
[0060] In more detail, FIGS. 9A and 9B show particular examples of
connection condition between the lower end of the salient pole 6
and the inner surface of the stator ring 100. Each of FIGS. 9A and
9B shows a section of one sixth (for 60.degree.) taken in a
direction perpendicular to the rotary axis for a three-phase
brushless DC motor having an outer diameter of 42 mm and including
eight rotor field magnetic poles and six salient poles which are
constituted by stacking seven electromagnetic steel sheets each
having a thickness of 0.5 mm. FIG. 9A shows an example of the
connection condition in which the projections 34a on the lower end
of the salient pole 6 are arranged along the arc-shaped inner
surface of the stator ring 100 and contact therewith continuously
and uniformly. FIG. 9B shows another example of the connection
condition in which the projections 34 or the lower end of the
salient pole 6 (as well as the upper end line opposing the magnetic
pole surface of the rotor field magnet 23) are arranged on a
straight line instead of along and in contact with the arc-shaped
inner surface of the stator ring 100. In FIGS. 9A and 9B, like
reference numerals identify like components to those of FIGS. 1 and
2, and explanation is omitted.
[0061] In FIG. 9A, the pole tooth 34 consists of plate sheets each
hearing the same shape and dimension. As the projections 34a on the
lower end of the salient pole 6 are arranged along and in contact
with the inner surface of the stator ring 100, an air gap defined
between the upper end portion of the salient pole 6 and the rotor
field magnet 23 is not uniform in the circumferential direction as
shown. This is because each plate sheet of the pole tooth 34 has
the same length and the inner surface of the stator ring 100 and
the magnetic pole surface of the rotor field magnet 23 have
different curvatures from each other. It may be possible to prepare
respective plate sheets of the pole tooth 34 having different
lengths (to make the pole tooth plate sheet at outer side longer
and to make the pole tooth plate sheet at inner side shorter) to
avoid the problem set forth above. For this purpose, however, a
plurality of punching dies are required for the pole tooth plate
sheets of slightly different dimensions, which is uneconomical in
viewpoint of cost and management. It should be noted, however,
that, in the example of the air gap shown in FIG. 9A (which is
narrow at the center portion of the salient pole and increases as a
distance increases from the center portion), cogging torque can be
decreased in comparison with the case of a uniform air gap length,
which is advantageous in view of motor characteristics.
[0062] FIG. 9B shows another example where the projections 34a at
the lower end portion of respective plate sheets of the pole tooth
34 are arranged on a straight line instead of being arranged along
and in contact with the inner surface of the stator ring 100. In
this example, there may be undesired possibility that an air gap of
maximum g (mm) (see FIG. 9B) is formed between the projection 34a
of the pole teeth 34 and the inner surface of the stator ring 100.
However, in the embodiment shown here, where the external diameter
of the stator ring 100 is 42 mm and the pole tooth 34 consists of
seven sheets of electromagnetic steel plates each having a
thickness of 0.5 mm, the gap length g (mm) will be about 76 .mu.m.
This value is at most one third of 250 .mu.m which is the average
length of air gap between the rotor field magnet 23 and the upper
end of the salient pole 6 and does not constitute a serious problem
in practical use. In the embodiment of FIG. 9B, since only thing
required is to align respective plate sheets of the pole tooth 34
on a straight line, stacking and crimping operation can be
performed immediately after punching out the plate sheets of the
pole tooth 34. If the plate sheets of the pole tooth 34 are crimped
in advance, the pole tooth 34 can be inserted into the bobbin
significantly more easily in comparison with when not crimped.
There is another advantage that vibration caused by excitation in
motor operation can be reduced.
[0063] Hitherto, discussion has been given on the armature assembly
10. Hereafter, discussion will be given on the rotor assembly 20
with reference to FIG. 1.
[0064] The construction of the rotor assembly 20 of the brushless
DC motor in the embodiment is the same as the conventional one and
therefore only brief explanation will be given. The rotor assembly
20 has a sleeve 22 fixed on a shaft 21 as a center of rotation and
a rotor field magnet 23 is fixedly arranged on the sleeve 22. In
the embodiment, the rotor field magnet 23 is a plastic magnet
formed by molding a resin matrix (e.g. 6-6 nylon) made of high
polymeric material and containing ferrite powder which is
inexpensive and has high moldability. A flange 23a integrally
formed on the right end of the rotor field magnet 23 is a rotor
position detecting magnet portion which can accurately detect the
position of the rotor assembly 20 in cooperation with a Hall sensor
52 arranged on a printed circuit board 51. On one axial end of the
rotor assembly 20 (the left end in the drawing), a spacer 24 and a
ball bearing 25 are provided on a flange 12. On a flange 13 at the
opposite end of the rotor assembly 20, a sleeve bearing 26 is
provided. Between the sleeve bearing 26 and the sleeve 22, a
preload spring holder 27 and a preload spring 28 are arranged. An
appropriate preload is applied to the ball bearing 25 by the
preload spring 28. The shaft 21 is rotatably supported by the ball
bearing 25 and the sleeve bearing 26.
[0065] FIG. 8 shows the motor with the flange 12 removed. As can be
seen in FIG. 8, a plurality (six in the embodiment) of tiny
projections 12a (having a height of 0.3 mm, for example) are formed
on the inner surface of the flange 12 at places which are to
contact the end face of the stator ring 100. The flange 12 is
welded to the stator ring 100 by way of projection welding, in
which pressure and electric power are applied while the tiny
projections 12a are kept in contact with the end face of the stator
ring 100. The flange 13 is earlier welded to the stator ring 100 in
the same manner.
[0066] By using this welding method, a plurality of places can be
welded simultaneously and with high finish quality. Therefore, the
method set forth above is quite suitably applicable to the electric
rotary machine of the present invention with regard to
productivity, quality, external appearance and decency.
[0067] In the embodiment, the inside of the armature assembly 10 is
entirely molded including the ball bearing 25 except a space for
receiving the rotor assembly 20, with a resin 60 of high polymer
material. The resin 60 is filled in a space between the salient
poles 6, particularly around a magnet wire 38, also in the resin
injecting ports 37 formed between adjacent salient poles 6 (see
FIG. 6A) and in the slits 50a of the pole ring 50. Therefore, not
only the salient poles are integrated between themselves but also
the salient pole assembly, the pole tooth ring 50 and the stator
ring 100 are integrated as a whole.
[0068] Following advantages are expected by integrally molding the
entire armature assembly with a resin:
[0069] (1) Since the coils, the pole teeth, the bobbins, the pole
tooth ring and the stator ring are all integrated with resin,
vibration and noise generated by the motor can be reduced.
[0070] (2) Since the coils, the pole teeth, the bobbins, the pole
tooth ring and the stator ring are all integrated completely with
resin, heat conduction higher than that of air can be achieved to
suppress increase in coil temperature at the same output for the
same efficiency.
[0071] (3) Since an air gap surface between the salient pole of the
armature assembly and the rotor field magnet can be as a reference
surface when designing a molding die, high precision of the air gap
surface finish which requires high dimensional precision can be
ensured. Accordingly, an air gap with a shorter length in the
radial direction of the motor causes no problem of possible touch
with the rotor field magnet.
[0072] (4) Integration of even the bearing housing with the
armature assembly secures a center of rotation with high precision
at the same time. This is also effective in removing a fear of
touch of the armature assembly with the rotor field magnet, which
may be caused by setting an air gap length shorter.
[0073] While no problem will be raised if the overall armature
assembly is integrally molded with a high polymer resin as in the
embodiment, a fine gap is apt to be formed between the pole tooth
ring 50 and the stator ring 100 if the armature assembly is not
integrated. The gap thus formed can be a cause of noise generation
during operation. In such a case, noise can be prevented by filling
bonding material in the gap. Particularly, to fill bonding material
of low viscosity in the fine gap is effective in ensuring
electrical insulation between both of the rings and mechanical
strength, whereby eddy current loss at the rings decreases possibly
improving efficiency and whereby vibration and noise are
reduced.
[0074] FIGS. 10A and 10B show the second embodiment of the pole
tooth ring.
[0075] A pole tooth ring 70 shown in FIG. 10B is produced in such a
way that slits 70a are punched out at a predetermined interval in a
soft magnetic sheet member A (such as galvanized steel sheet,
nickel plated steel sheet, pure iron sheet or the like), and that
thereafter the sheet member A is rolled into a ring configuration.
Thus, the pole tooth ring can be produced without using high level
drawing process.
[0076] When the salient pole is assembled into the pole tooth ring
70 thus produced, it is preferred to arrange the slits 70a such
that the joint between a first rolling end and a second rolling end
of the sheet member A does not coincide with the lower end of the
salient pole. In the embodiment, the joint is arranged to be
positioned in the middle between the salient poles. Thus,
respective salient poles can be uniformly, firmly and stably
engaged with the slits 70a of the pole tooth ring 70.
[0077] In the embodiment shown in FIG. 10A, a recess 65a and a
protrusion 65b are formed on the first rolling end (the leftmost
end of the sheet member A in the drawing) of the sheet member A,
and a protrusion 66b and a recess 66a are formed on the second
rolling end (the rightmost end of the sheet member A in the
drawing) thereof. The recess 65a on the first rolling end and the
protrusion 66b on the second rolling end are mated with each other
and the protrusion 65b on the first rolling end and the recess 66a
on the second rolling end are mated with each other to form the
ring 70 with high precision. Therefore, even when some or less
external force is applied to the ring 70 during assembly process,
diametrical dimension will never suffer a change. The shapes of the
recesses and the protrusions are not limited to those as shown. It
will do if both the first and second rolling ends are made straight
and made to simply abut each other. It is to be noted that the
suggestion that the salient pole should not be positioned at the
joint between the first rolling end and the second rolling end
means that a mechanism for inserting the salient pole, that is a
slit or hole, should not be provided in a region identified by 2a
(see FIGS. 10A and 10B) which is necessary for formation of the
recesses and the protrusions.
[0078] The stator ring 100 may also be made of a soft magnetic
plate and formed into a ring configuration. As described above, the
stator ring 100 does not require a mechanism for inserting the
salient pole.
[0079] When the pole tooth ring 50 and the stator ring 100 are made
of a sheet member, the positional relation between the joints of
both of the rings is critical. It is essential that the joints do
not overlap with each other at regions which include the recesses
and the protrusions (namely, the region identified by 2a in FIG.
10B). The shape and size of the recesses 65a and 66a and the
protrusions 65b and 66b jointing the first rolling end and the
second rolling end of the sheet member A are determined depending
on the ring diameter, and in case of small size electric rotary
machines having a diameter of 100 mm or less, an angle formed by
the joints of the rings should necessarily be set between
30.degree. and 330.degree. inclusive in terms of a center angle
with each other as viewed at the center of the joints. In the
experiment, it was confirmed that sufficient effect could be
obtained by setting the angle at 90.degree.. It was mentioned above
that vibration and noise can be reduced if the armature assembly is
integrally molded with a resin. It should be noted that vibration
and noise can also be reduced if the pole tooth ring and the stator
ring are made of a vibration damping steel sheet.
[0080] FIGS. 11A and 11B show a third embodiment of a pole tooth
ring.
[0081] This embodiment is different from the second embodiment
shown in FIGS. 10A and 10B regarding means for fixing and
maintaining salient poles to be provided in the pole tooth ring. As
shown in FIG. 11A, rectangular or square holes 80a are formed at
substantially central (as viewed widthwise) portions of a sheet
member B formed of a soft magnetic material. A recess 85a and a
protrusion 85b are formed on the first rolling end (the leftmost
end of the sheet member B in the drawing) and a protrusion 86b and
a recess 86a are formed on the second rolling end (the right end of
the sheet member B). FIG. 11b shows an unfinished state of a pole
tooth ring 80 manufactured of the sheet member B thus worked.
[0082] The salient pole assembly shown in FIG. 6A which has been
fabricated in a separate process is rolled up by the sheet member B
already worked in such a manner that the projections of respective
salient poles of the salient pole assembly fit in respective holes
80a of the sheet member B. Then, the protrusion on the first
rolling end and the recess on the second rolling end are engaged
with each other, and vice versa, to complete the pole tooth ring
80.
[0083] Finally, applying the present invention to a three phase
brushless DC motor which uses a low-cost plastic ferrite magnet as
rotor field magnet 23 and has an external diameter of 42 mm, an
axial length of 60 mm and which has six salient poles and eight
rotor magnetic poles, it was confirmed in the experiment that a
maximum efficiency for electromechanical conversion in the motor of
the present invention having a double ring structure comprising the
pole tooth ring and the stator ring was increased from 50% to 60%
showing improvement by 10% in comparison with a conventional motor
having a single ring structure. This is because of reduction in the
current value under no load condition and it is considered that
magnetic efficiency has been improved and resultingly
electromagnetic conversion efficiency has been improved.
[0084] Accordingly, it should be easily inferred that a still
higher efficiency can be achieved by employing a high performance
magnet such as Nd--Fe--B or Sm--Co type magnet.
[0085] With the present invention, since the salient poles are
magnetically coupled to each other with the double ring structure,
reluctance in the armature can be reduced. Further, the hole,
groove or the like for positioning and fixing the salient poles
will never be exposed on the external surface of the electric
rotary machine.
[0086] As a result, the reluctance of the armature can be reduced
with the result that the electromagnetic conversion efficiency of
the electric rotary machine is improved. Furthermore, as there is
no magnetic discontinuity on the surface of the electric rotary
machine, leakage flux can be reduced and at the same time pop-up of
discontinuous increase in leakage flux can be eliminated. Namely, a
kind of magnetic shield effect can be provided on the stator ring.
Furthermore, as the lower end of the salient pole will never be
exposed at the outer surface of the electric rotary machine, the
product may provide superior external appearance which enhances
value of products.
[0087] Furthermore, core loss or eddy current loss can be reduced
for improvement in efficiency if the pole tooth is formed by
stacking sheet members such as electromagnetic steel sheets whose
surfaces are electrically insulated.
[0088] Vibration and noise can be reduced by bonding and fixing a
gap between the pole tooth ring and the stator ring or, in some
cases, a gap between respective plate sheets of the pole tooth.
Core loss or eddy current loss of the ring can also be reduced.
[0089] The pole tooth ring or the stator ring or both can be
manufactured without using a high level drawing technology if made
using the soft magnetic sheet member and processing it into a ring
configuration. Reliability of fixing the salient poles can be
improved and outward emission of the leakage flux can be held down
by appropriately setting the shape and/or the positional
relationship of the first rolling end and the second rolling end of
the sheet member.
[0090] The respective flanges can be easily welded at each of both
ends of the stator ring by resistance welding and sufficient
welding margin can be provided by making the thickness of the
stator ring larger than the thickness of the pole tooth ring and at
the same time by making the axial length of the stator ring larger
than the axial length of the pole tooth ring. As a result, even if
the sheet member processed into a ring shape is employed,
sufficient welding strength can be certainly obtained and
sufficient strength against external mechanical stress or external
force can be provided.
[0091] Furthermore, in case of an inner rotor type brushless DC
motor, winding operation can be significantly facilitated and space
factor can be improved. As a result, it is possible to obtain a
motor having small leakage flux and superior electromagnetic
conversion efficiency as well.
[0092] Although the present invention has been illustrated and
described with respect to exemplary embodiments, it should be
understood by those skilled in the art that the foregoing and
various other changes, omission and additions may be made therein
and thereto, without departing from the spirit and scope of the
present invention. Therefore, the present invention should not be
understood as limited to the specific embodiments set out above but
to include all possible embodiments which can be embodied within a
scope encompassed and equivalent thereof with respect to the
feature set out in the appended claims.
* * * * *