Rotor insulating core for miniature motors

A rotor insulating core for miniature motors comprising a stator having a field-forming permanent magnet, a rotor having a rotor winding wound on a rotor core fixedly fitted to a motor shaft; an insulating core being disposed on the surface of the rotor core; and the rotor winding being wound on the rotor core via the insulating core, in which the insulating core consists of an insulating end-face portion covering the end face of the rotor core and an insulating rib covering the side of the rotor core; both being integrally formed; the insulating rib is formed in such a fashion as to have a thickness smaller than the insulating end-face portion and a predetermined length, and disposed in such a manner as to cover the rotor core on which the rotor winding is wound.

BACKGROUND OF THE INVENTION 
This invention relates generally to a rotor insulating core for miniature 
motors, and more particularly to a rotor insulating core for miniature 
motors adapted to improve the winding space factor and insulating 
performance of the rotor winding. 
DESCRIPTION OF THE PRIOR ART 
FIG. 6 illustrates a miniature motor, to which this invention is applied, 
having essentially the same construction as conventional miniature motors. 
That is, a brush 13 is integrally formed with a terminal 12 supported by a 
small case 11. The brush 13 makes contact with a commutator 17. A motor 
shaft 16 is supported by bearings 14 and 15. The commutator 17 and a rotor 
core 18 are mounted on the motor shaft 16. Current is fed to a rotor 
winding 19 wound on the rotor core 18 via the terminal 12, the brush 13 
and the commutator 17. A miniature motor rotor 22 is caused to rotate by 
the current flowing in the rotor winding 19 and a permanent magnet 21 
fixedly fitted to the inner circumferential surface of a large case 20. 
In a miniature motor as shown in FIG. 6, an iron core comprising the rotor 
core 18 is made of laminated silicon steel sheets, for example. 
Consequently, an insulating core 23 is interposed between the rotor core 
18 and the rotor winding 19, as shown in FIG. 7. FIG. 7(A) is a front view 
of the rotor 22, as viewed in the direction shown by an arrow in FIG. 6, 
and FIG. 7(B) is a cross-sectional view taken along line A--A in FIG. 7 
(A). 
In the conventional miniature motor shown in FIG. 7, the insulating core 23 
has a shape corresponding to the shape of the end face of the rotor core 
18 in the direction of the motor shaft 16, with the side edge 23-1 thereof 
bent by stamping, for example, in such a direction as to extend along the 
side of the rotor core 18. The rotor winding 19 is wound on the rotor 22 
in such a state where the insulating core 23 is disposed at both ends of 
the rotor core 18, as shown in FIG. 7(B). That is, the rotor 22 has such a 
construction that electrical insulation between the rotor core 18 and the 
rotor winding 19 is ensured by preventing the rotor winding 19 from coming 
in direct contact with the rotor core 18. 
As described above, the side edge 23-1 of the insulating core 23 in the 
conventional miniature motor shown in FIG. 7 is bent at essentially right 
angles by stamping. The side edge 23-1 of the insulating core 23 should 
preferably be kept in close contact with the rotor core. In press working 
the insulating core, however, the clearance between the die and punch (not 
shown) is set to the same size as the thickness of the material of the 
insulating core 23. This causes the bending angle of the side edge 23-1 of 
the insulating core 23 to be larger than the right angle due to the 
springback of the material. As a result, the winding space factor of the 
rotor winding 19 wound on the insulating core 23 tends to be unwantedly 
lowered due to a space 24 existing between the rotor winding 19 and the 
rotor core 18, as shown in FIG. 7(B). The lowered winding space factor 
leads to the limited number of winding turns. 
In the conventional miniature motor shown in FIG. 7, the force exerted on 
the side edge 23-1 of the insulating core 23 varies from the beginning of 
winding to the state where the force caused at one turn of winding is 
accumulated as the winding of the rotor winding 19 proceeds. Consequently, 
as winding operation proceeds from the initial state, the bending angle of 
the side edge 23-1 of the insulating core 23 becomes gradually smaller. 
That is, the space 24 between the rotor winding 19 and the rotor core 18 
is gradually changed from the state shown in FIG. 7(B) at the initial 
stage of winding to the state shown in FIG. 8 as the rotor winding 19 is 
forced toward the rotor core 18 to the extent that the rotor winding 19 
eventually comes in contact with the rotor core 18. As a result, the 
vibration caused by the rotation of the rotor 22 causes the rotor winding 
19 and the rotor core 18 to be in constant friction with each other, 
causing damage to the insulation coating of the rotor winding 19. This 
could lead to an unwanted problem of leakage. 
SUMMARY OF THE INVENTION 
This invention is intended to overcome the aforementioned problems. To 
achieve this objective, the rotor insulating core for miniature motors of 
this invention comprises a stator having a field-forming permanent magnet, 
a rotor having a rotor winding wound on a rotor core fixedly fitted to a 
motor and an insulating core being disposed on the surface of the rotor 
core. The rotor winding being wound on the rotor core via the insulating 
core. The insulating core consists of an insulating end-face portion 
covering the end face of the rotor core and an insulating rib covering the 
side of the rotor core; both being integrally formed. The insulating rib 
is formed by ironing, for example, a substantially flat section of 
insulating material in such a fashion as to have a thickness smaller than 
the insulating end-face portion and a predetermined length, and disposed 
in such a manner as to cover the rotor core on which the rotor winding is 
wound. 
These and other objects of this invention will become more apparent by 
reference to the description, taken in connection with the accompanying 
FIGS. 1 through 5.

DETAILED DESCRIPTION OF THE EMBODIMENT 
In the following, an embodiment of this invention will be described, 
referring to FIGS. 1(A) and (B). 
In FIG. 1, (A) is a plan view of an insulating core in a rotor, and (B) is 
a cross-sectional view taken along line A--A in (A). Reference numeral 1 
in the figure refers to an insulating core; 1-1 to an insulating end-face 
portion; and 1-2 to an insulating rib, respectively. 
The insulating core 1 shown in FIG. 1 consists of the insulating end-face 
portion 1-1 and the insulating rib 1-2. The insulating end-face portion 
1-1 has a shape essentially corresponding to the shape of the end face or 
axial end, in the direction of the motor shaft 16 of the rotor core 18 of 
the miniature motor (shown in FIG. 6) to which this invention is applied. 
The insulating rib 1-2 is formed by ironing, which will be described later 
in connection with FIG. 2. The thickness t.sub.1 of the insulating 
end-face portion 1-1 is essentially the same as the thickness of the 
original insulating material. The insulating rib 1-2 is formed by ironing 
so that the thicknesses t.sub.2 and t.sub.3 of the insulating rib 1-2 
become about 20 to 85% of t.sub.1. The reason why the thicknesses t.sub.2 
and t.sub.3 are made 20 to 85% of t.sub.1 is as follows: Making t.sub.2 
and t.sub.3 smaller than 20% of t.sub.1 would reduce the mechanical 
strength, deteriorating insulating performance, while making t.sub.2 and 
t.sub.3 larger than 80% of t.sub.1 would cause springback, deteriorating 
winding space factor. The groove width W between the insulating ribs 1-2 
corresponds to the width W (as shown in FIG. 3) of the axial end the rotor 
core 18, and the length 1 of the insulating rib 1-2 may be an appropriate 
length and need not be a length sufficient to cover the overall or 
longitudinal side surface of the rotor core 18. 
Next, ironing for forming the insulating rib 1-2 of the insulating core 1 
will be described with reference to FIG. 2. Ironing is accomplished using 
a punch 3 having a thickness W, that is, the same size as the groove width 
W of the insulating ribs 1-2, and a die 4 having a groove width W', that 
is substantially equal to W'=W+T2+T3. The insulating core 1 shown in FIG. 
1 is formed by the aforementioned ironing. 
The rotor core 18 is covered from both sides thereof with the insulating 
core 1 formed in the aforementioned manner, on which the rotor winding 19 
is wound. 
In the foregoing, the embodiment shown in FIG. 1 has been described. The 
rotor of a miniature motor to which the embodiment shown in FIG. 1 is 
applied is shown in FIG. 3. FIG. 3(A) is a front view of the rotor viewed 
in the direction of the motor shaft, and FIG. 3(B) is a cross-sectional 
view taken along line A--A in FIG. 3(A). 
In the figures, like numerals correspond to like parts in FIGS. 1 and 7. 
In the embodiment shown in FIG. 3, a rotor 22 in which the insulating core 
1 described with reference to FIG. 1 is disposed on both end faces of the 
rotor core 18, and the rotor winding 19 is wound on the insulating core is 
shown. 
As shown in FIG. 3(B), the springback as described at the beginning of this 
Specification does not occur in the state where the rotor winding 19 is 
wound on the rotor core 18 because the insulating end-face portion 1-1 and 
the insulating rib 1-2 of the insulating core 1 come in close contact with 
the rotor core 18 and the thickness t.sub.2 of the insulating rib 1-2 is 
made smaller than the thickness t.sub.1. Furthermore, electrical 
insulating performance is not deteriorated since the thickness t.sub.2 of 
the insulating rib 1-2 is made smaller than the thickness t.sub.1 of the 
insulating end-face portion 1-1 by ironing. Thus, the winding space factor 
and insulating performance of the rotor winding 19 can be improved. If the 
gap G between the tips of the rotor core 18 is reduced by appropriately 
setting the length 1 of the insulating rib 1-2 as described in connection 
with FIG. 1(B), the rotor core 18 can be substantially covered by the 
insulating core 1, making the insulation between the rotor winding 19 and 
the rotor core 18 more positive. 
FIG. 4 is a diagram of assistance in explaining another embodiment of this 
invention. 
FIG. 4(A) is a plan view, and FIG. 4(B) is a cross-sectional view taken 
along line A--A shown in FIG. 4(A). Numeral 2 in the figures refers to an 
insulating core; 2-1 to an insulating end-face portion; 2-2 to an 
insulating rib; and 2-3 to a rib tip, respectively. 
The insulating core shown in FIG. 4 has a rib tip 2-3 formed at the tip of 
the insulating rib 2-2. The embodiment shown in FIG. 4 has essentially the 
same construction as the embodiment shown in FIG. 1, and is formed in the 
same machining method. That is, the insulating core 2 is formed by ironing 
as in the case of the embodiment shown in FIG. 1, with the rib tip 2-3 2-3 
left intact. As a result, the thickness of the rib tip 2-3 is formed into 
the same thickness as the thickness t.sub.1 (the thickness of the 
material) of the insulating end-face portion 1-1. 
FIG. 5 shows the rotor of a miniature motor to which the embodiment shown 
in FIG. 4 is applied. FIG. 5(A) is a front view of the rotor viewed from 
the direction of the motor shaft, and FIG. 5(B) is a cross-sectional view 
taken along line A--A in FIG. 5(A). Like numerals in the figures 
correspond to like parts shown in FIGS. 3 and 4. 
In the embodiment shown in FIG. 5, the aforementioned insulating core 2 
shown in FIG. 4 is disposed on both end faces of the rotor core 18, as in 
the case of the embodiment shown in FIG. 3, and then the rotor winding 19 
is wound on the rotor core 18. The state in which the rotor winding 19 is 
wound on the rotor core 18 is shown in FIG. 5(B). That is, the springback 
as described at the beginning of this Specification does not occur because 
the insulating end-face portion 2-1, insulating rib 2-2 and rib tip 2-3 of 
the insulating core 2 come in close contact with the rotor core 18, and 
the thickness t.sub.2 of the insulating rib 2-2 is made smaller than the 
thickness t.sub.1 of the insulating end-face portion. 
Thus, the winding space factor and insulating performance of the rotor 
winding 19 can be improved. 
Furthermore, a groove can be provided at the bent portion of the insulating 
core 1 on the opposite side to the bending direction, though not shown in 
the figure. The groove helps prevent the springback of the insulating core 
1, improve the winding space factor of the rotor winding 19, and prevent 
the insulating performance of the insulating core 1 from deteriorating. 
In the above embodiments, the insulating core is formed by ironing, but the 
insulating core may be formed by integral molding using an injection 
molding machine. 
As described above, this invention makes it possible to improve the winding 
space factor and insulating performance of the rotor winding since the 
insulating rib of the insulating core is ironed to reduce the thickness 
thereof, and the portion of the rotor core on which the rotor winding is 
wound is covered with the insulating rib.