Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-08-29
2003-12-16
Lam, Thanh (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S071000, C310S249000
Reexamination Certificate
active
06664700
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-268959 filed on Sep. 5, 2000.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a brush holding device arranged in a direct current motor.
2. Description of Related Art
A direct current motor includes a commutator and brushes to mechanically commutate direct current supplied from an external direct current source and to supply it to the armature. The brushes are held in a brush holding device in such a manner that the brushes slidably engage against the commutator.
A previously proposed exemplary brush holding device
50
is shown in
FIGS. 13
to
15
. The brush holding device
50
includes a circuit board
51
and brush holders
52
(only one is shown). The circuit board
51
is secured to a motor housing (not shown). Each brush holder
52
is made of a heat-resistant metal material, such as a brass material, that exhibits thermally induced small dimensional change. Furthermore, each brush holder
52
is a hollow casing with a generally rectangular cross-section. A radially inner side (located on commutator
53
side) of the brush holder
52
is open, and a radially outer side (located on side opposite the commutator
53
) of the brush holder
52
is closed.
Each brush holder
52
is secured to the circuit board
51
at its base portion
52
a
. A receiving recess
52
b
is formed in the brush holder
52
and has the open end on the commutator
53
side. A brush
54
and a spring
55
for urging the brush
54
against the commutator
53
are received within the receiving recess
52
b
of each brush holder
52
.
When the commutator
53
rotates, each brush
54
exhibits self-excited vibrations. The self excited vibrations of the brush
54
is induced by fluctuating frictional force between the brush
54
and the commutator
53
and also by collisions between the brush
54
and a respective step formed between each two adjacent segments of the commutator
53
. Because of the self-excited vibrations of the brush
54
, the brush
54
repeatedly hits the corresponding brush holder
52
, causing resonance of the brush holder
52
and generation of noises.
A first possible solution to the above-described disadvantage is to make each brush
54
from a relatively soft material. In this way, a collision force between the brush
54
and the respective step formed between each two adjacent segments of the commutator
53
is reduced, so that the self-excited vibrations of the brush
54
are accordingly reduced.
A second possible solution to the above-described disadvantage is disclosed in Japanese Unexamined Patent Publication No. 10-304625. According to this publication, a notch is formed in a lateral surface of each brush, and a vibration-isolating plate connected to a pig-tail is inserted within and is secured to the notch of the brush. Furthermore, a vibration absorbing material is placed between the vibration-isolating plate and a circuit board. With this arrangement, the self-excited vibrations of the brush are attenuated by the vibration-isolating plate and the vibration absorbing material.
However, in the first solution, there is a disadvantage of accelerated wearing of each brush, resulting in a reduced lifetime of the brush.
In the second solution, the vibration-isolating plate and the vibration absorbing material need to be used, disadvantageously increasing the number of components and the cost.
Furthermore, during rotation of the commutator
53
at a low rotational speed, the brushes
54
and the commutator
53
are placed under a high-friction state that is close to a static friction state. Thus, the self-excited vibrations of the brushes
54
are increased, resulting in generation of relatively large noises.
FIG. 16A
shows levels of noises measured for the brush holder
52
, and
FIG. 16B
shows frequency analysis for these noises. During these measurements, the commutator
53
is rotated at a relatively low rotational speed of 15 [rpm].
As indicated by an arrow B in
FIG. 16A
, it will be understood that the use of the previously proposed brush holders
52
causes relatively large levels of noises. Furthermore, as indicated by an arrow C in
FIG. 16B
, it will be understood that particularly large noises are observed in a range of 6 to 7 [kHz]. Thus, reduction of the noises at the above low rotational speed of the commutator
53
has been demanded.
SUMMARY OF THE INVENTION
The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide a brush holding device that can reduce noises without changing a material of brushes and without increasing the number of components.
To address the above disadvantages, there is provided a brush holding device including a dielectric resin circuit board and at least one metal brush holder secured to the circuit board at its base portion. The circuit board is secured to a motor housing. Each brush holder includes a receiving recess that receives a brush and a spring for urging the brush against a commutator. One of each brush holder and the circuit board or the housing has at least one engaging portion integrally formed therein for achieving resilient engagement between each brush holder and the circuit board or the housing.
REFERENCES:
patent: 4963779 (1990-10-01), Lentino et al.
patent: 5648695 (1997-07-01), Yamaguchi et al.
patent: 5939812 (1999-08-01), Wetzel
patent: 42 41 405 (1994-06-01), None
patent: 2 118 784 (1983-11-01), None
patent: A-9-261914 (1997-10-01), None
patent: A-10-304625 (1998-11-01), None
Ishizuka Toshiyasu
Masui Hisashi
Odagiri Mitsuo
Saito Takashi
Suzuki Noriyuki
Asmo Co. Ltd.
Lam Thanh
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