Rotor for electric motors

A rotor for an electric motor includes a plurality of annularly disposed rotor magnets, a frame made of a steel plate and having an annular wall disposed outside the annularly disposed rotor magnets so as to be located at a side opposed to the stator with respect to the rotor magnets, the annular wall having an open end, a ring member made of a magnetic material and disposed along the annular wall of the frame at an inner or outer circumferential side of the annular wall, and a resin molded member comprising a resin for integrating the rotor magnets, the frame and the ring member together.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to electric motors, and more particularly 
to a rotor for electric motors in which rotor magnets and a rotor frame 
are integrated by a resin and a method of making the rotor. 
2. Description of the Prior Art 
The prior art has provided outer rotor type electric motors in which a 
bottomed short cylindrical rotor having a relatively large diameter is 
used. The rotor comprises a bottomed short cylindrical frame having a 
large diameter and made of a steel plate and a number of rotor magnets 
mounted on an inner circumferential surface of an annular wall of the 
frame. With regard to mounting the rotor magnets on the inner 
circumferential surface of the frame wall, the prior art has proposed a 
method of integrating the rotor magnets and frame by means of a resin. 
More specifically, the rotor magnets and frame are accommodated in a 
cavity of a forming mold. Subsequently, a molten resin is poured into the 
cavity to be hardened so that the rotor magnets and frame are enclosed in 
the hardened resin to be integrated together. 
The thickness of the annular wall of the frame needs to be increased in the 
above-described rotor so that magnetic paths are sufficiently secured for 
the rotor magnets. However, the increase in the thickness of the annular 
wall results in an increase in the thickness of a bottom wall of the 
frame. That is, the bottomed short cylindrical frame is formed by pressing 
a steel plate and accordingly, the thickness of the steel plate needs to 
be increased so that the thickness of the annular wall of the frame is 
increased. This also increases the thickness of the bottom wall of the 
frame. Thus, the entire thickness of the frame is increased. This 
disadvantageously increases the entire weight of the rotor. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to provide a rotor for the 
electric motor wherein the magnetic paths can sufficiently be secured for 
the rotor magnets without an increase in the entire thickness of the frame 
and with an increase in the weight of the rotor being restrained. 
The present invention provides a rotor for an electric motor including a 
stator, the rotor comprising a plurality of annularly disposed rotor 
magnets, a frame made of a steel plate generally having an overall cup 
shape and having an annular wall disposed outside the annularly disposed 
rotor magnets so as to be located at a side opposed to the stator with 
respect to the rotor magnets, the annular wall having an open end, a ring 
member made of a magnetic material and disposed along the annular wall of 
the frame at an inner or outer circumferential side of the annular wall, 
and a resin molded member comprising a resin for integrating the rotor 
magnets, frame and ring member together. 
According to the above-described rotor, the ring member made of the 
magnetic material is disposed along the annular wall of the frame. The 
magnetic paths are sufficiently secured by the annular wall and the ring 
member. Consequently, the thickness of the annular wall of the frame need 
not be increased and accordingly, the entire thickness of the frame need 
not be increased. 
The resin molded member preferably includes a covering portion integrally 
formed therewith so as to cover axial ends of the rotor magnets at an open 
end side of the annular wall of the frame. The covering portion preferably 
has a plurality of windows each for exposing both a part of the axial end 
of each rotor magnet at the open end side of the annular wall of the frame 
and a part of the frame at the open end side of the annular wall. Since 
the axial end of each rotor magnet is covered by the cover, each rotor 
magnet can be prevented from falling off and protected. Furthermore, the 
axial ends of the rotor magnets and the open end of the frame are viewed 
through the windows formed in the covers so that the positional relation 
between each rotor magnet and the annular wall can readily be confirmed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of the present invention will be described with 
reference to FIGS. 1 to 4B. The invention is applied to the rotor for an 
outer rotor type electric motor. FIGS. 1 and 2 each illustrate the 
construction of a rotor 1 manufactured in accordance with the invention. 
FIG. 3 illustrates the construction of the motor incorporating the rotor 1 
shown in FIGS. 1 and 2. FIGS. 4A and 4B illustrate manufacturing steps for 
the rotor 1. 
Referring to FIG. 3, the construction of the outer rotor type motor 101 
will be described in brief. The motor 101 is a three-phase brushless dc 
motor, for example. The motor 101 comprises a generally annular stator 102 
and the rotor 1 covering the entire stator 102 and mounted for rotation. 
The stator 102 comprises a generally annular stator core 103 and a winding 
104 wound on the stator core 103. The stator 102 is mounted on a motor 
mounting plate 105 by a plurality of screws 106 one of which is shown. A 
shaft 107 fixed to a central portion of the rotor 1 extends through a 
central portion of the stator 102 and is rotatably mounted on bearing 
means (not shown). 
The construction of the rotor 1 will now be described with reference to 
FIGS. 1 and 2. The rotor 1 comprises a bottomed short cylindrical frame 3 
and a number of rotor magnets 2 mounted on an inner circumferential 
surface of an annular wall 5 of the frame 3. The rotor magnets 2 are each 
made of a slender plate-shaped member and disposed annularly. The frame 3 
is formed by pressing a steel plate and includes a disc-like main plate 4, 
a short cylindrical annular wall 5 extending downward from an outer 
circumferential end of the main plate 4 as viewed in FIG. 1, and a holder 
portion 6 extending from a lower outer circumferential end of the annular 
wall 5 and having a generally L-shaped section, all of which are formed 
integrally with the frame 3. The annular wall 5 of the frame 3 is disposed 
outside the rotor magnets 2 so as to be located at a side opposed to the 
stator 102 with respect to the rotor magnets 2. The holder portion 6 has a 
concave portion in which a short cylindrical ring member 7 made of a 
magnetic material is disposed along an outer circumferential surface of 
the annular wall 5. The rotor magnets 2, frame 3 and ring member 7 are 
enclosed in a resin molded member 8 formed around the annular wall 5 so as 
to be integrated together as will be described later. Lower ends of the 
rotor magnets 2 as viewed in FIG. 1 or one of axial ends of the rotor 
magnets project downward from a lower end or an open end of the frame 3. 
The manufacture of the above-described rotor 1 will be described with 
reference to FIGS. 4A and 4B. A forming mold 10 includes a lower mold 10a 
and an upper mold 10b to be put on the lower mold 10a. First, a number of 
rotor magnets 2 are accommodated in a recess 11 defined in the lower mold 
10a so to be arranged annularly, as shown in FIG. 4A. The recess 11 is 
formed in the lower mold 10a so that the axial ends of the rotor magnets 2 
projecting outward (downward as viewed in FIGS. 4A and 4B) from the lower 
open end of the annular wall 5 of the frame 3 are fitted into the recess 
11. The frame 3 is disposed on the lower mold 10a so that the annular wall 
5 thereof is positioned outside the rotor magnets 2. With this, the ring 
member 7 is placed in the concave portion of the holder portion 6 of the 
frame 3, being fitted with the outer circumference of the annular wall 5. 
Subsequently, the upper mold 10b is put on the lower mold 10a from above so 
that the forming mold 10 is closed, as shown in FIG. 4B. A predetermined 
amount of molten resin is poured through gates (not shown) into a cavity 
12 defined between the lower and upper molds 10a and 10b and then 
hardened. The amount of resin is determined so that the resin spreads over 
both outer and inner circumferential sides of the annular wall 5. The 
resin molded member 8 is formed by the resin poured into the cavity 12 and 
then hardened. The rotor magnets 2, frame 3 and ring member 7 are enclosed 
by the hardened resin molded member 8 to thereby be integrated by the 
resin molded member 8. Subsequently, the forming mold 10 is opened so that 
the rotor 1 is taken out. 
According to the first embodiment, the ring member 7 made of the magnetic 
material is disposed along the annular wall of the frame 3 made of the 
steel plate. As a result, magnetic paths for the rotor magnets 2 can 
sufficiently be secured by the annular wall 5 and the ring member 7. 
Moreover, the thickness of the annular wall 5 and accordingly, the entire 
thickness of the frame 3 need not be increased even though the magnetic 
paths are secured for the rotor magnets 2. Furthermore, the entire weight 
of the rotor 1 is increased by the ring member 7. However, the increase in 
the weight of the rotor 1 can be restrained to a smaller extent as 
compared with the case where the entire thickness of the frame 3 is 
increased. 
The rotor magnets 2 are placed in the recess 11 of the lower mold 10a so as 
to be axially positioned. Consequently, the rotor magnets 2 can readily be 
positioned relative to the forming mold 10 and moreover, the positioning 
work can accurately be performed. 
FIGS. 5 and 6 illustrate a second embodiment of the invention. The 
identical parts are labeled by the same reference symbols in the second 
embodiment as in the first embodiment. The differences between the first 
and second embodiments will be described. In the second embodiment, an 
intermediate mold 15 is used together with the forming mold 10. The 
intermediate mold 15 is attached to and detached from the forming mold 10. 
As shown in FIG. 5, the intermediate mold 15 has a generally L-shaped 
section and is generally annular. The intermediate mold 15 is adapted to 
hold on its outer circumference the rotor magnets 2 and the frame 3 with 
the ring member 7 being attached thereto. 
In manufacture of the rotor 1, the rotor magnets 2 are fitted into a recess 
16 of the intermediate mold 15 to be held in position, as shown in FIG. 5. 
The recess 16 is formed in the intermediate mold 15 so that the axial ends 
of the rotor magnets 2 projecting outward (downward as viewed in FIG. 5) 
from the lower open end of the annular wall 5 of the frame 3 are fitted 
into the recess 16. The frame 3 is then placed on an upper surface of the 
intermediate mold 15 to be held thereon and the ring member 7 is placed on 
the holder portion 6 of the frame 3 to be held thereon. The intermediate 
mold 15 holding these parts is accommodated in an accommodating section 17 
formed in the lower mold 10a of the forming mold 10 as shown in FIG. 6. 
Subsequently, the upper mold 10b is put on the lower mold 10a so that the 
forming mold 10 is closed. The resin is then poured into the cavity 12 to 
be hardened. Consequently, the same rotor 1 is formed in the second 
embodiment as in the first embodiment. The intermediate mold 15 is removed 
from the formed rotor 1. 
The construction of the rotor 1 other than described above in the second 
embodiment is the same as that in the first embodiment. Accordingly, the 
same effect can be achieved in the second embodiment as in the first 
embodiment. In the second embodiment, particularly, the rotor magnets 2, 
frame 3 and ring member 7 are held by the intermediate mold 15. The 
intermediate mold 15 is then accommodated in the forming mold 10 so that 
the rotor 1 is formed. Consequently, the work for accommodating the rotor 
magnets 2, frame 3 and ring member 7 in the forming mold 10 can be 
rendered easier. Furthermore, the contact of intermediate mold 15 with the 
rotor magnets 2 sometimes wears the intermediate mold when the rotor 
magnets 2 are fitted into the intermediate mold. Since only the 
intermediate mold 15 among the molds is worn, it needs to be replaced by a 
new one. Consequently, the maintenance of molds is rendered easier and the 
cost for replacement of the molds is reduced. Since the rotor magnets 2 
are directly attracted to the lower mold when the intermediate mold is not 
used, the lower mold is worn. In this case, the lower mold needs to be 
replaced by a new one. In the above-described embodiment, however, the 
replacement of the lower mold 10a is not required. 
Furthermore, the rotor magnets 2 are fitted in the recess 16 of the 
intermediate mold 15 constituting the forming mold 10. The intermediate 
mold 15 is then accommodated in the accommodating section 17 of the lower 
mold 10a so that the rotor magnets 2 are radially positioned. 
Consequently, the rotor magnets 2 can readily and reliably be positioned 
relative to the forming mold 10. 
FIGS. 7 to 9 illustrate a third embodiment of the invention. The identical 
parts are labeled by the same reference symbols in the third embodiment as 
in the first embodiment. The annular wall 5 of the frame 3 has a number of 
notch-like mounting holes 20 constituting mounting sections and formed in 
the upper end (open end) thereof to be circumferentially disposed at 
regular intervals, as viewed in FIG. 7. Positioning members 21 have 
protrusions 21a which are inserted in the mounting holes 20 of the annular 
wall 5 so that the positioning members 21 are mounted on the annular wall 
5, respectively. Each rotor magnet 2 is placed between the adjacent 
positioning members 21. An axial length L1 of a magnetic path forming 
section 22 between the lower end of the mounting hole 20 as viewed in FIG. 
7 and the main plate 4 is set so that the magnetic path forming section 22 
is not saturated with the magnetic flux due to the rotor magnets 2. The 
rotor magnets 2, frame 3 and ring member 7 are accommodated in the forming 
mold 10 and then, the resin is poured into the forming mold to be hardened 
in the same manner as in the first embodiment, so that the resin molded 
member 8 for integrating these parts is formed. The construction of the 
rotor 1 other than described above in the third embodiment is the same as 
that in the first embodiment. Accordingly, the same effect can be achieved 
in the third embodiment as in the first embodiment. In the third 
embodiment, particularly, the rotor magnets 2 can readily be positioned by 
the positioning members 21 mounted on the annular wall 5 of the frame 3. 
Furthermore, the rotor magnets 2 can be prevented from being displaced by 
an injection pressure of the resin during the forming. 
FIGS. 10 to 12 illustrate a fourth embodiment of the invention. The 
identical parts are labeled by the same reference symbols in the fourth 
embodiment as in the third embodiment. The annular wall 5 of the frame 3 
has a number of protrusions 25 formed thereon to be circumferentially 
disposed at regular intervals and project toward the inner circumferential 
side. Each rotor magnet 2 is inserted into a space between the adjacent 
protrusions 25 so as to be mounted on the annular wall 5. The construction 
of the rotor 1 other than described above in the fourth embodiment is the 
same as that in the third embodiment. Accordingly, the same effect can be 
achieved in the fourth embodiment as in the third embodiment. 
FIGS. 13 and 14 illustrate a fifth embodiment of the invention. The 
identical parts are labeled by the same reference symbols in the fifth 
embodiment as in the first embodiment. The main plate 31 of the frame 30 
has a number of resin flow-through holes 32 formed therein to correspond 
to upper portions of the rotor magnets 2 respectively. After the frame 30, 
rotor magnets 2 and ring member 7 are accommodated in the forming mold 10, 
the resin is poured through runners 33 and gates 34 into the cavity 12. 
Flowing through the resin flow-though holes 32, the resin further flows as 
shown by arrows A in FIG. 14, thereby pressing the corresponding rotor 
magnets 2 toward the recess 11 of the lower mold 10a as shown by arrows B 
and toward the axial center as shown by arrow C in FIG. 13. Consequently, 
the rotor magnets 2 are desirably positioned and the inner side surface of 
each rotor magnet 2 is closely attached to the wall surface 11a of the 
recess 11. 
Furthermore, the gates 34 and the resin flow-through holes 32 are provided 
in the vicinity of portions of the frame 30 spaced from the rotor magnets 
2 longitudinally (vertically in FIG. 13) with respect to the rotor magnets 
2 accommodated in the forming mold 10 or above the rotor magnets 2. In 
this disposition of the gates 34, the resin is injected through the resin 
flow-through holes 32 lengthwise with respect to the rotor magnets. 
Accordingly, since an injection pressure of the resin acts on (or toward) 
the portions of the rotor magnets 2 having a sufficiently high strength, 
the rotor magnets 2 are prevented from being split or broken. 
The resin is injected from the gates perpendicularly to the surfaces of the 
rotor magnets if the gates are provided at the left or right hand of the 
rotor magnet. In this construction, the rotor magnets are sometimes broken 
when subjected to the injection pressure of the resin, which results in 
occurrence of defective. In the fifth embodiment, however, the rotor 
magnets 2 can reliably be prevented from being broken. The construction of 
the rotor 1 other than described above in the fifth embodiment is the same 
as that in the first embodiment. Accordingly, the same effect can be 
achieved in the fifth embodiment as in the first embodiment. 
FIGS. 15 to 30 illustrate a sixth embodiment of the invention. Referring to 
FIGS. 15 to 19, a number of rotor magnets 42 constituting the rotor 41 are 
annularly disposed. The frame 43 is formed by pressing the steel plate as 
the magnetic material, for example. The frame 43 includes a disc-like main 
plate 44, an annular wall 45 formed along the outer circumference of the 
main plate 44, and a flange 46 formed along the outer circumference of the 
annular wall 45, all of which are formed integrally with the frame 43. The 
annular wall 45 is disposed outside the rotor magnets 42 so as to be 
located at the side opposed to the stator 47 (see FIG. 20) with respect to 
the rotor magnets 42. The ring member 48 made of a magnetic material is 
disposed along the outer circumferential surface of the annular wall 45. 
A boss 50 is disposed at a central portion of the main plate 44 of the 
frame 43. The boss 50 has an axially extending fitting hole 49. A number 
of axially extending grooves 49a and teeth 49b are formed on an inner 
circumferential surface of the fitting hole 49 of the boss 50, as shown in 
FIG. 19. A shaft (not shown) is fitted into the fitting hole 49 to be 
fixed in position. The rotor magnets 42, frame 43, ring member 48 and boss 
50 are integrated by the resin molded member 51. 
One of axial ends of each rotor magnet 42 or the lower end thereof as 
viewed in FIG. 16 projects downward from the open end of the annular wall 
45 of the frame 43. The resin molded member 51 includes a covering portion 
52 formed integrally therewith and covering the axial ends of the rotor 
magnets 42 projecting from the annular wall 45. More specifically, the 
covering portion 52 covers a part of an end face 42a of the axial end of 
each rotor magnet 42 and a part of an outer peripheral face 42b of the 
axial end of each rotor magnet 42 at the annular wall 45 side. The resin 
molded member 51 includes convex portions 53 formed integrally therewith. 
Each convex portion 53 is located between the adjacent rotor magnets 42 
and has a radial distal end projecting toward the side of the stator 47 or 
toward the inner circumferential side. The radial distal ends of the 
convex portions 53 project so as to assume the same positions as the 
distal ends of the rotor magnets 42 projecting nearest to the stator 47 or 
so as to be located nearer to the stator 47 than the distal ends of the 
rotor magnets 42. 
The covering portion 52 has a number of first windows 54 formed therein to 
correspond to outer circumferential central portions of the rotor magnets 
42 respectively. The covering portion 52 further has a number of second 
windows 55 formed to correspond to both ends of the rotor magnets 42. 
Axial end faces 42a (each including an inclined face) and outer peripheral 
faces 42b of the rotor magnets 42 and a flange 46 or the open end of the 
annular wall 45 are exposed through the first windows 54, as shown in 
FIGS. 16 and 20. Furthermore, the axial end faces 42a of the adjacent 
rotor magnets 42 are exposed through the second windows 55, as shown in 
FIGS. 15 and 22. 
The ring member 48 has holes 57 located between gates 56 (shown by two-dot 
chain line in FIG. 18) for guiding the resin into the cavity during the 
forming. The holes 57 constitute resin penetration sections. During the 
forming, the resin penetrates the holes 57 to be formed into the resin 
molded member 51. As shown in FIG. 23, the main plate 44 of the frame 43 
has a plurality of air-gap confirming windows 59 formed therein to 
correspond to an air gap 58 between the rotor magnets 42 and the stator 
47. 
An axially outer end face of the boss 50 has a mark 60 (see FIG. 19) 
comprising a recess and provided to correspond to one of the teeth 49b of 
the fitting hole 49. Furthermore, an outer face of the main plate 44 of 
the frame 43 has another mark 61 (see FIG. 18) comprising a convex portion 
provided to correspond to the one of the teeth 49b and accordingly, to the 
mark 60. These marks 60 and 61 are exposed so that assembling personnel 
can view them. 
The manufacture of the rotor 41 will now be described with reference to 
FIGS. 24 to 30. The forming mold 65 includes a lower mold 66, intermediate 
mold 68 which can be attached to and detached from the accommodating 
section 67 of the lower mold 66, and an upper mold 69 covering the lower 
and intermediate molds 66 and 68. As shown in FIGS. 24 to 26, one ends of 
the rotor magnets 42 are inserted into the positioning recess 70 formed in 
the intermediate mold 68. Each rotor magnet 42 is radially positioned by a 
stepped portion 71 (see FIG. 24) for forming the first windows 54, a 
stepped portion 72 (see FIG. 26) for forming the second windows 55, and an 
outer circumferential surface of a cylindrical portion 73. 
The frame 43 is then disposed on the intermediate mold 68 so that the 
annular wall 45 thereof is located outside the rotor magnets 42. Fitted 
with the outer circumference of the annular wall 45, the ring member 48 is 
placed on the flange 46 of the frame 43 to be held in position. The 
underside of the flange 46 of the frame 43 is abutted against the upper 
face of a support 68a of the intermediate mold 68. Alternatively, the 
frame 43 may be disposed on the intermediate mold 68 after the ring member 
48 is previously held on the frame 43. 
The intermediate mold 68 on which the frame 43 and the ring member 48 are 
mounted as described above is accommodated in the accommodating section 67 
of the lower mold 66, as shown in FIGS. 27 to 29. The upper mold 69 is 
then placed on the lower and intermediate molds 66 and 68 so that the 
forming mold 65 is closed. The resin is poured through the gates 66 into 
the cavity 74 defined by the upper, lower and intermediate molds 69, 66 
and 68 to be hardened. The resin is formed into the resin molded member 51 
for integrating the rotor magnets 42, frame 43, ring member 48 and boss 
50. Thereafter, the forming mold 65 is opened so that the rotor 41 is 
taken out of the mold. The rotor magnets 42 of the rotor 41 are magnetized 
by a suitable magnetizer (not shown). Furthermore, the shaft (not shown) 
is fitted into the fitting hole 49 of the boss 50 to be fixed in position. 
The rotor 41 manufactured as described above is assembled into an electric 
motor with the rotor magnets 42 being disposed outside the stator 47. 
According to the sixth embodiment, the ring member 48 made of the magnetic 
material is disposed along the annular wall 45 of the steel plate frame 43 
as in the first embodiment. As a result, the magnetic paths can 
sufficiently be secured for the rotor magnets 42 without an increase in 
the entire thickness of the frame 43 and with the entire weight of the 
rotor being rendered as small as possible. Furthermore, the rotor magnets 
42 are inserted in the recess 70 of the intermediate mold 68 so as to be 
radially positioned. Thus, the rotor magnets 42 can readily and reliably 
be positioned relative to the forming mold 65. Consequently, the rotor 41 
of high performance can be manufactured. 
The rotor magnets 42, frame 43 and ring member 48 are held on the 
intermediate mold 68. The intermediate mold 68 holding these parts is 
accommodated in the forming mold 65. Accordingly, the rotor magnets 42 
etc. can readily be accommodated in the forming mold 65. The resin molded 
member 51 for integrating the rotor magnets 42 etc. includes the 
integrally formed covering portion 52 for covering the axial end faces of 
the rotor magnets 42 projecting from the open end of the frame 43 and the 
outer peripheral faces 42b of the rotor magnets 42 at the annular wall 45 
side. The covering portion 52 can prevent the rotor magnets 42 from 
falling off and protect them. Consequently, the rotor magnets 42 can be 
prevented from being chipped or broken. Furthermore, iron powder etc. can 
be prevented from adhering to the rotor magnets 42. 
The rotor magnets 42, frame 43 and ring member 48 are enclosed by the resin 
molded member and thereafter, the molding is pushed by a knock pin 75 so 
as to be released from the forming mold 65, as shown in FIG. 30. In this 
case, the covering portion 52 is pushed by the knock pin 75. Since the 
rotor magnets 42 can be protected as compared with the case where the 
rotor magnets are directly pushed by the knock pin, the rotor magnets 42 
can be prevented from being chipped or broken. Furthermore, the open end 
of the annular wall 5 of the frame 43 or the flange 46 is exposed and the 
flange 46 is pushed by a knock pin 76 when the molding is released from 
the forming mold 65. Since the frame 43 has a mechanical strength higher 
than the other portions and hard to deform, the flange 46 can strongly be 
pushed by the knock pin 75. Consequently, since the pushing force of the 
knock pin 75 pushing the other portion can be reduced, the deformation of 
the molding or rotor 41 can be prevented during the mold release. 
When the rotor 41 is enclosed by the resin, flows of resin collide with 
each other between the gates 56 through which the resin is poured into the 
cavity 74 (see FIGS. 27-29) so that weld lines 77 are formed as shown in 
FIG. 18. Cracks tend to occur in the portions of the resin molded member 
51 where the weld lines 77 are formed. The reason for this is that a 
coefficient of thermal expansion differs among the resin molded member 51, 
frame 43 and ring member 48 to a large extent. The differences in 
shrinkage among the resin molded member 51, frame 43 and ring member 48 
cause tensile forces as shown by arrows P in FIG. 18 on the portions of 
the resin molded member 52 in the vicinity of the weld lines 77. 
In view of the foregoing problem, the holes 57 are formed in the portions 
of the ring member 48 corresponding to the weld lines 77 in the sixth 
embodiment. The resin is penetrated into the holes 57. Accordingly, when 
the resin molded member 51 is subjected to the tensile forces as shown by 
arrows P, the tensile forces are received by the resin in the holes 57 to 
be dispersed. As a result, the tensile forces can be restrained from 
concentrating on the portions of the member 51 in the vicinity of the weld 
lines 77. Furthermore, the resin molded member 51 at the outer 
circumferential side is connected to that at the inner circumferential 
side via the holes 57. Consequently, occurrence of cracks can further be 
prevented in the resin molded member 51. The same effect can be achieved 
when the holes 57 serving as the resin penetration sections are formed in 
the annular wall 45 of the frame 43. The resin penetration sections should 
not be limited to the holes 57. The resin penetration sections may be 
catches formed on the resin molded member 57 such as notches or grooves. 
The covering portion 52 formed integrally with the resin molded member 51 
has the first windows 54 through which the axial end faces 42a and the 
outer peripheral faces 42b of the rotor magnets 42 are exposed. 
Consequently, the covering portion 52 prevents the rotor magnets 42 from 
falling off and protects them. Moreover, the end faces 42a of the rotor 
magnets 42 and the end of the annular wall 45 are viewed through the first 
windows 54 so that the positional relation between the rotor magnets and 
the annular wall can visually be confirmed. Furthermore, the resin molded 
member 51 has the integrally formed convex portions 53 each located 
between the adjacent rotor magnets 42 and each having the radial distal 
end projecting toward the side of the stator 47 or toward the inner 
circumferential side. The convex portions 53 can prevent the rotor magnets 
42 from striking against the stator 47 side when the rotor 41 and the 
stator 47 are assembled together. As a result, the rotor magnets 42 can be 
prevented from being chipped or broken. Additionally, the main plate 44 of 
the frame 43 has the air-gap confirming windows 59 formed therein to 
correspond to the air gap 58 between the rotor magnets 42 and the stator 
47. 
The marks 60 and 61 are formed on the boss 50 and the main plate 44 of the 
frame 43 so as to correspond to one of the teeth 49b of the fitting hole 
49 respectively when the shaft is fitted into the fitting hole 49. Teeth 
formed on the shaft are engaged with the teeth 49b of the fitting hole 49 
on the basis of the marks 60 and 61. As a result, the shaft can readily be 
fitted into the fitting hole 49. The marks 60 and 61 are further effective 
in automatically fitting the shaft into the fitting hole 49. The marks 60 
and 61 may be provided so as to correspond to one of the grooves 49a. 
Either one of the marks 60 and 61 may be provided. 
The present invention should not be limited by the description of the 
foregoing embodiments. Although the invention is applied to the outer 
rotor type motor in the foregoing embodiments, the invention may be 
applied to inner rotor type electric motors in which the rotor is located 
inside the stator. In the inner rotor type motor, the rotor magnets are 
disposed along the outer circumference of the annular wall of the frame. 
The ring member may be disposed along the inner circumference of the 
annular wall. The frame may be formed of a magnetic material into the 
shape of a plate. 
The foregoing description and drawings are merely illustrative of the 
principles of the present invention and are not to be construed in a 
limiting sense. Various changes and modifications will become apparent to 
those of ordinary skill in the art. All such changes and modifications are 
seen to fall within the true spirit and scope of the invention as defined 
by the appended claims.