1. Field of the Invention
The present invention relates to a brush holder device for use in a small-size motor used for driving, for example, a power tool.
2. Description of the Related Art
The brush holder device of the present invention can be used in ordinary small-size motors. An example of such a small-size motor is described below with reference to
The shaft 17 carries a laminated core 18, windings 19 wound onto the laminated core 18, and a commutator 10, thus forming a rotor of the small-size motor. Brushes in contact with the commutator 10 are connected to brush arms. Input terminals 11 connected to the brush arms extend through the end cover 15 and project outward from the end cover 15 for electric connection.
As described above, a brush holder device of the small-size motor is composed of a brush, and a brush arm for supporting the brush. The brush arm is mechanically and electrically connected to an input terminal supported by an end bell 14. Such a conventional brush holding technique will next be described with reference to
An end of a brush 7 that is opposite an end for contact with a commutator is attached to a brush arm 1. In order to enhance longitudinal rigidity, the brush arm 1 is bent along laterally opposite edges (see
As shown in
However, the brush holder device involves high cost in assembly, since the electrically conductive adhesive 8 is expensive. Additionally, use of the electrically conductive adhesive 8 impairs work efficiency, since, for example, the adhesive 8 requires drying. Particularly, in view of the brush arm 1 serving not only as a current path to the brush 7 but also as a heat radiator for releasing heat generated from sliding contact between the brush 7 and a commutator, a thicker brush arm 1 is advantageous. However, the thickness of the brush arm 1 is limited, since the brush arm 1 must cause the brush 7 to be in contact with the rotating commutator at constant brush tension while absorbing vibration induced by the brush 7 being in contact with the surface of the commutator, which is not smooth due to gaps between commutator segments. As a result, the conventional brush arm 1 fails to exhibit sufficient heat radiation effect.
An object of the present invention is to solve the above-mentioned problems and to provide a brush holder device for use in a small-size motor, allowing use of inexpensive members to thereby reduce manufacturing cost and exhibiting enhanced heat radiation effect for releasing heat generated in a brush.
Another object of the present invention is to provide a brush holder device for use in a small-size motor in which a brush arm supports a brush while reliably maintaining mechanical, electrical, and thermal contact with the brush.
A brush holder device for use in a small-size motor of the present invention includes a brush arm connected at one end to an input terminal for external electrical connection and supporting at an opposite end a brush. The brush holder device comprises a brush including an integrally formed engagement portion; a brush arm having an engagement hole formed therein, the engagement hole assuming substantially the same shape as that of the engagement portion of the brush, and including brush contact portions located at laterally opposite edges of the engagement hole; and a holder. The holder has an engagement hole formed therein, the engagement hole assuming substantially the same shape as that of the engagement portion of the brush, and is fixedly attached to the brush arm such that the engagement hole is aligned with that of the brush arm. The engagement portion of the brush is press-fitted into the engagement holes of the holder and the brush arm, which are fixedly attached to each other, to thereby be fixed in place.
Brush contact portions may be formed on the holder through bending along longitudinally opposite edges of the engagement hole of the holder. Further, the holder may include fins formed through bending along longitudinally opposite ends thereof.
A brush holder device for use in a small-size motor of the present invention includes a brush, and a brush arm for supporting the brush, which brush arm is mechanically and electrically connected, through known means such as crimping, to an input terminal supported by an end bell. Since the present invention is similar to the conventional technique described previously except for a manner in which the brush is supported by the brush arm, the following description merely encompasses a brush holding configuration.
The brush 7 itself can be made of a conventionally employed material (e.g., carbon) and can assume a conventionally employed shape. As shown in
According to the present invention, the brush 7 is not directly attached to the thus-configured brush arm 1; i.e., first, a holder 2 shown in
As shown in
Next, the brush 7 is attached to the thus-joined unit of the holder 2 and the brush arm 1. As mentioned previously, since the holder 2 does not need to assume intensive spring properties, the holder 2 can be formed of a rather thick sheet to thereby impart rigidity thereto. For example, the brush arm 1 assume a thickness of not greater than 0.15 mm, whereas the holder 2 can assume a thickness of 0.3 mm. According to the present invention, the brush arm 1 is bent along laterally opposite edges thereof to thereby be enhanced in rigidity along the longitudinal direction. Further, the brush contact portion 5 and the cooling fins 6 provided on the holder 2 can function to enhance the rigidity of the completed brush holder device along the lateral direction.
As a result of the holder 2 being fixedly attached to the brush arm 1, the engagement hole is surrounded entirely by the brush contact portions 4 and 5. Additionally, the brush contact portions 5 of the holder 2 assume high rigidity. Thus, when the brush 7 is press-fitted into the engagement hole, the brush 7 is fixed rigidly in place by means of the elasticity of the brush contact portions 4 and 5. Not only does the holder 2 itself serve as a heat radiator, but also the holder 2 has the fins 6, which are formed through bending along longitudinally opposite ends thereof, thereby yielding high heat radiation effect.
The table below compares durability among a conventional brush holder device employing electrically conductive adhesive, a conventional brush holder device employing no electrically conductive adhesive, and a brush holder device of the present invention. Three or five respective brush holder device samples were incorporated into small-size motors of the same configuration. The samples were compared in life as measured until the brush attachment portion of a brush arm suffers any fault, such as cracking. The life is represented by the number of cycles, each cycle consisting of one-second operation of motor and 19-second halt.
As shown in Table 1, the present invention can provide a brush holder device of lengthened life for the following reason. As a result of a rigid holder being fixedly attached to an elastic brush arm, strength is enhanced, thereby preventing torsion of a brush-holding portion of the brush arm.
According to the configuration of the present invention, a holder is fixedly attached to a brush arm, and an engagement portion of a brush is press-fitted into engagement holes of the united holder and brush arm, thereby allowing use of inexpensive members to thereby reduce manufacturing cost and exhibiting enhanced heat radiation effect for releasing heat generated in the brush.
The present invention enables a brush arm to support a brush while reliably maintaining mechanical, electrical, and thermal contact with the brush.
Number | Date | Country | Kind |
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2001-029124 | Feb 2001 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
4085346 | Yoshida | Apr 1978 | A |
4088912 | Yoshida | May 1978 | A |
4157483 | Frimley | Jun 1979 | A |
4238703 | Yoshida | Dec 1980 | A |
4431933 | Mabuchi | Feb 1984 | A |
4574215 | Mabuchi | Mar 1986 | A |
4746829 | Strobl | May 1988 | A |
5103131 | Sekine | Apr 1992 | A |
Number | Date | Country |
---|---|---|
51-13503 | Jan 1976 | JP |
58058848 | Apr 1983 | JP |
63-66054 | May 1988 | JP |
11-252869 | Sep 1999 | JP |
Number | Date | Country | |
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20020135261 A1 | Sep 2002 | US |