Title of Invention	ARMATURE CORE OF DC MOTOR
Abstract	57) Abstract:- An armature core of a DC motor has axially extended lightening holes provided between a shaft inserting hole and bottom portion of slots, where ratio B/A of distance B between the bottom portion of the slots and the lightening holes to a smallest width A of teeth is set to 1.5 < B/A< 3.0. It is thereby possible to effectively achieve a reduction in weight while preventing a reduction in torque. PRICE: THIRTY RUPEES

Title of Invention

ARMATURE CORE OF DC MOTOR

Abstract

57) Abstract:- An armature core of a DC motor has axially extended lightening holes provided between a shaft inserting hole and bottom portion of slots, where ratio B/A of distance B between the bottom portion of the slots and the lightening holes to a smallest width A of teeth is set to 1.5 < B/A< 3.0. It is thereby possible to effectively achieve a reduction in weight while preventing a reduction in torque. PRICE: THIRTY RUPEES

Full Text	The present invention relates to an annature core of a DC motor which is used, for example, in an engine starter. Fig. 4 is a perspective view showing a conventional armature of a DC motor such as disclosed in Japanese Patent Laid-Open No.6U26454. In this figure, a shaft 2 is press-fitted into a center portion of a cylindrical armature core 1. A number of axially extended slots 4 are provided on the outer periphoal portion of the annature core 1. Inserted into these idots 4 are coils 3. The coils 3 are respectively connected to a commutator 5. Fig. 5 is a front view showing the conventional armature core 1. Teeth 6 are provided respectively between two slots 4 that are next to each other. A shaft inserting hole 7 for inserting the shaft 2 is provided at ^e center portion of the armature core 1. The conventional annature core 1 as described above is heavy because it is constructed by laminating a large number of thin iron plates in ike axial direction. Efforts have been directed toward reducing of its weight as much as possible. To solve the problems as described, it is an object of the present invention to provide an armature core of a DC motor capable of effectively reducing its weight while preventing a reduction in torque. Accordingly the present invention provides an armature core of a DC motor having a plurality of axially extended slots for inserting coils provided radially on the outer peripheral portion thereof teeth respectively formed between the slots that are next to each other, and a shaft inserting hole provided at a center portion thereof said armature core of the DC motor comprising at least one axially extended lightening hole provided between said shaft inserting hole and the bottom portion of said slots, ratio B/A of distance B betweoi the bottom portion of said slots and said lightening hole to the smallest width A of said teeth being 1.5 to 3.0. With reference to the accompanying drawings, in which Fig. 1 is a front view of an armature core of a DC motor according to an embodiment of the present invention. Fig. 2 is a relational graph showing an effect on torque by the extent of tightening holes. Fig. 3 shows a relational graph showing an effect on the weight of the armature core by the extent of lightening holes. Fig. 4 is a perspective view showing an example of conventional armature of a DC motor. Fig. 5 is a front view of the armature core of Fig. 4. An embodiment of the present invention will be described bdow witfi reference to the drawings. Fig. 1 is a front view showing an armature core of a OC motor according to an embodiment of the present invention. Referring to Fig. 1, a number of axialty extended slots 12 are provided radially on the outer peripheral portion of an armature core 11 of this embodiment. Teeth 13 are formed respectively between two - adjacent slots 12. Formed at a center portion of the armature core 11 is a shaft inserting hole 14 into which a shaft 2 (Fig.4) is press-fitted. Provided radially outward of the shaft inserting hole 14, i.e., between the shaft inserting hole 14 and the bottom portion of the slots 12 are four lightening holes 15a to 15d which axially penetrate through the armature core 11. Each lightening hole 15a to 15d has a cross section defined as including concentric circular arcs (substantially a sector). By providing such lightening holes 15a to 15d, the armature core 11 may be reduced in weight. If, however, distance B between the bottom portion of the slots 12 and the lightening holes 15a to 15d is reduced due to an enlargement in the cross section of the lightening holes 15a to 15d, the cross section of magnetic path in the armature core is reduced to result in a lower output, in particular, torque of the DC motor. Fig.2 is a relational graph showing the result of experiments conducted on how the torque is affected by the extent of lightening holes 15a to 15d. B/A on the horizontal axis represents a ratio of distance B between the bottom portion of the slots 12 and the lightening hole 15a to 15d to the smallest width A of the teeth 13, and T/To on the vertical axis represents a ratio of torque T of the motor with the lightening holes 15a to 15d being provided to torque To of the motor without the lightening holes 15a to 15d. As can be seen from Fig.2,in the range where B/A is less than 1.5, the torque is steeply reduced as B/A becomes smaller. For example, for the value of B/A=1, the torque is reduced by 10 % and practicality as a motor is. lost. On the other hand, the values of B/A of 1.5 or more are preferable as a reduction in torque is small. Fig.3 is a relational graph showing the result of experiments on how the weight of the armature core is affected by the extent of the lightening holes 15a to 15d. B/A on the horizontal axis represents the same as in Fig.2, and W/Wo on the vertical axis represents ratio of weight W of the armature core 11 with the lightening holes 15a to 15d being provided to weight Wo of the armature core 1 1 without the lightening holes 15a to 15d. As can be seen from Fig.3, a value of B/A of 3.0 or less is preferred in order to reduce the weight of the armature core 11. If B/A is larger than 3.0, an advantage obtained as a reduction in weight is small. From the above, by cutting B/A to 1.5^B/A^3.0 in providing the lightening holes 15a to 15d, it is possible to effectively reduce the weight while preventing a reduction in torque. In particular, a value of the order of B/A=2.0 is practically most preferable. For example, if the armature core 11 of this embodiment is applied to a DC motor of an engine starter for an automobile, fuel-to-cost efficiency of the automobile may be improved by the reduction in weight of the armature core 11. Further, since the moment of inertia of the armature becomes smaller, it is possible to reduce the impact at the time of meshing of a pinion (not shown) of the starter with a ring gear (not shown) of the engine. It is also possible to prevent wear of bearings, etc., as the vibration of the armature at the time of its rotation is rpdnr-ori While the above embodiment has been described with respect to a DC motor for an engine starter, the armature core of the present invention may also be used in the DC motors for other applications. Further, while the four lightening holes 15a to 15d are provided in the above embodiment, the number of lightening holes is not specifically limited. Furthermore, shape of the cross section of the lightening hole is not limited to those defined as including a circular arc. Moreover, while dimensions in the peripheral direction of the lightening holes are not specifically limited, a sufficient separation in the peripheral direction should be maintained between the adjacent lightening holes 15a to 15d for transmitting the rotation of the shaft 2 to the armature core 11 as a whole and for receiving the press-fitting force of the shaft 2. Further, a similar consideration is required for dimensions between the lightening holes 15a to ISd'and the shaft inserting hole 14. WE CLAIM: 1. An armature core of a DC motor having a plurality of axially extended slots for inserting coils provided radially on the outer peripheral portion thereof teeth respectively formed between the slots that are next to each other, and a shaft inserting hole provided at a center portion thereof, said armature core of the DC motor comprising at least one axially extended lightening hole provided between said shaft inserting hole and the bottom portion of said slots, ratio B/A of distance B between the bottom portion of said slots and said lightening hole to the smallest width A of said teeth being 1.5 to 3.0. 2. The armature core of a DC motor acccording to claim 1, wherrin the plurality of said lightening holes each have a cross section defined to have concentric circular arcs. 3. The armature core of a DC motor according to claim 1, wherein the value of the said ratio B/A is about 2.0. 4. An armature core of a DC motor substantially as hereinabove described with reference to figures 1 - 3 of the accompanying drawings.

Full Text

The present invention relates to an annature core of a DC motor which is used, for example, in an engine starter.
Fig. 4 is a perspective view showing a conventional armature of a DC motor such as disclosed in Japanese Patent Laid-Open No.6U26454. In this figure, a shaft 2 is press-fitted into a center portion of a cylindrical armature core 1. A number of axially extended slots 4 are provided on the outer periphoal portion of the annature core 1. Inserted into these idots 4 are coils 3. The coils 3 are respectively connected to a commutator 5.
Fig. 5 is a front view showing the conventional armature core 1. Teeth 6 are provided respectively between two slots 4 that are next to each other. A shaft inserting hole 7 for inserting the shaft 2 is provided at ^e center portion of the armature core 1.
The conventional annature core 1 as described above is heavy because it is constructed by laminating a large number of thin iron plates in ike axial direction. Efforts have been directed toward reducing of its weight as much as possible.
To solve the problems as described, it is an object of the present invention to provide an armature core of a DC motor capable of effectively reducing its weight while preventing a reduction in torque.

Accordingly the present invention provides an armature core of a DC motor having a plurality of axially extended slots for inserting coils provided radially on the outer peripheral portion thereof teeth respectively formed between the slots that are next to each other, and a shaft inserting hole provided at a center portion thereof said armature core of the DC motor comprising at least one axially extended lightening hole provided between said shaft inserting hole and the bottom portion of said slots, ratio B/A of distance B betweoi the bottom portion of said slots and said lightening hole to the smallest width A of said teeth being 1.5 to 3.0.
With reference to the accompanying drawings, in which
Fig. 1 is a front view of an armature core of a DC motor according to an embodiment of the present invention.
Fig. 2 is a relational graph showing an effect on torque by the extent of tightening holes.
Fig. 3 shows a relational graph showing an effect on the weight of the armature core by the extent of lightening holes.
Fig. 4 is a perspective view showing an example of conventional armature of a DC motor.
Fig. 5 is a front view of the armature core of Fig. 4.
An embodiment of the present invention will be described bdow witfi reference to the drawings. Fig. 1 is a front view showing an armature core

of a OC motor according to an embodiment of the present invention. Referring to Fig. 1, a number of axialty extended slots 12 are provided radially on the outer peripheral portion of an armature core 11 of this embodiment. Teeth 13 are formed respectively between two -

adjacent slots 12. Formed at a center portion of the armature core 11 is a shaft inserting hole 14 into which a shaft 2 (Fig.4) is press-fitted.
Provided radially outward of the shaft inserting hole 14, i.e., between the shaft inserting hole 14 and the bottom portion of the slots 12 are four lightening holes 15a to 15d which axially penetrate through the armature core 11. Each lightening hole 15a to 15d has a cross section defined as including concentric circular arcs (substantially a sector). By providing such lightening holes 15a to 15d, the armature core 11 may be reduced in weight. If, however, distance B between the bottom portion of the slots 12 and the lightening holes 15a to 15d is reduced due to an enlargement in the cross section of the lightening holes 15a to 15d, the cross section of magnetic path in the armature core is reduced to result in a lower output, in particular, torque of the DC motor.
Fig.2 is a relational graph showing the result of experiments conducted on how the torque is affected by the extent of lightening holes 15a to 15d. B/A on the horizontal axis represents a ratio of distance B between the bottom portion of the slots 12 and the lightening hole 15a to 15d to the smallest width A of the teeth 13, and T/To on the vertical axis represents a ratio of torque T of the motor with the lightening holes 15a to 15d being provided to torque To of the motor without the lightening holes 15a to 15d.
As can be seen from Fig.2,in the range where B/A is less than 1.5, the torque is steeply reduced as B/A becomes smaller. For example, for the value of B/A=1, the torque is

reduced by 10 % and practicality as a motor is. lost. On the other hand, the values of B/A of 1.5 or more are preferable as a reduction in torque is small.
Fig.3 is a relational graph showing the result of experiments on how the weight of the armature core is affected by the extent of the lightening holes 15a to 15d. B/A on the horizontal axis represents the same as in Fig.2, and W/Wo on the vertical axis represents ratio of weight W of the armature core 11 with the lightening holes 15a to 15d being provided to weight Wo of the armature core 1 1 without the lightening holes 15a to 15d.
As can be seen from Fig.3, a value of B/A of 3.0 or less is preferred in order to reduce the weight of the armature core 11. If B/A is larger than 3.0, an advantage obtained as a reduction in weight is small.
From the above, by cutting B/A to 1.5^B/A^3.0 in providing the lightening holes 15a to 15d, it is possible to effectively reduce the weight while preventing a reduction in torque. In particular, a value of the order of B/A=2.0 is practically most preferable.
For example, if the armature core 11 of this embodiment is applied to a DC motor of an engine starter for an automobile, fuel-to-cost efficiency of the automobile may be improved by the reduction in weight of the armature core 11. Further, since the moment of inertia of the armature becomes smaller, it is possible to reduce the impact at the time of meshing of a pinion (not shown) of the starter with a ring gear (not shown) of the engine. It is also possible to prevent wear of bearings, etc., as the vibration of the armature at the time of its rotation is rpdnr-ori

While the above embodiment has been described with respect to a DC motor for an engine starter, the armature core of the present invention may also be used in the DC motors for other applications.
Further, while the four lightening holes 15a to 15d are provided in the above embodiment, the number of lightening holes is not specifically limited.
Furthermore, shape of the cross section of the lightening hole is not limited to those defined as including a circular arc.
Moreover, while dimensions in the peripheral direction of the lightening holes are not specifically limited, a sufficient separation in the peripheral direction should be maintained between the adjacent lightening holes 15a to 15d for transmitting the rotation of the shaft 2 to the armature core 11 as a whole and for receiving the press-fitting force of the shaft 2. Further, a similar consideration is required for dimensions between the lightening holes 15a to ISd'and the shaft inserting hole 14.

WE CLAIM:
1. An armature core of a DC motor having a plurality of axially
extended slots for inserting coils provided radially on the outer peripheral
portion thereof teeth respectively formed between the slots that are next to
each other, and a shaft inserting hole provided at a center portion thereof,
said armature core of the DC motor comprising at least one axially extended
lightening hole provided between said shaft inserting hole and the bottom
portion of said slots, ratio B/A of distance B between the bottom portion of
said slots and said lightening hole to the smallest width A of said teeth being
1.5 to 3.0.
2. The armature core of a DC motor acccording to claim 1, wherrin the
plurality of said lightening holes each have a cross section defined to have
concentric circular arcs.
3. The armature core of a DC motor according to claim 1, wherein the
value of the said ratio B/A is about 2.0.
4. An armature core of a DC motor substantially as hereinabove
described with reference to figures 1 - 3 of the accompanying drawings.

Documents:

967-mas-1995 abstract.jpg

967-mas-1995 abstract.pdf

967-mas-1995 claims.pdf

967-mas-1995 correspondence others.pdf

967-mas-1995 correspondence po.pdf

967-mas-1995 description (complete).pdf

967-mas-1995 drawings.pdf

967-mas-1995 form-1.pdf

967-mas-1995 form-26.pdf

967-mas-1995 form-4.pdf

967-mas-1995 petition.pdf

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Patent Number

190310

Indian Patent Application Number

967/MAS/1995

PG Journal Number

30/2009

Publication Date

24-Jul-2009

Grant Date

10-Mar-2004

Date of Filing

28-Jul-1995

Name of Patentee

M/S. MITSUBISHI DENKI KABUSHIKI KAISHA

Applicant Address

2-3 MARUNOUCHI 2-CHOME CHIYODA-KU, TOKYO 100

Inventors:

#	Inventor's Name	Inventor's Address
1	KEIICHI KONISHI	M/S. MITSUBISHI DENKI KABUSHIKI KAISHA 2-3 MARUNOUCHI 2-CHOME CHIYODA-KU, TOKYO 100

PCT International Classification Number

H02K15/16

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA