U.S. patent application number 09/788543 was filed with the patent office on 2001-09-27 for motor device having commutator and brush outside yoke.
Invention is credited to Harada, Yoshihiko, Yamamoto, Toshio.
Application Number | 20010024070 09/788543 |
Document ID | / |
Family ID | 18596908 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010024070 |
Kind Code |
A1 |
Yamamoto, Toshio ; et
al. |
September 27, 2001 |
Motor device having commutator and brush outside yoke
Abstract
A motor device comprises a motor unit and a reduction unit. The
motor unit comprises a yoke which is formed in a generally bottomed
cylindrical shape, and a rotor having an armature and a rotary
shaft. The reduction unit comprises a gear housing accommodating a
reduction gear device for producing an output after reducing
rotational speed of the rotor and fixed to the opening of the yoke.
A commutator and brushes for the motor unit are disposed in the
gear housing which is provided outside the opening of the yoke in
the axial direction of the rotary shaft. The gear housing has a
flange formed in a square shape, and the brushes are arranged along
the diagonal lines of the square shape.
Inventors: |
Yamamoto, Toshio;
(Kosai-city, JP) ; Harada, Yoshihiko;
(Hamamatsu-city, JP) |
Correspondence
Address: |
LAW OFFICE OF DAVID G POSZ
2000 L STREET, N.W.
SUITE 200
WASHINGTON
DC
20036
US
|
Family ID: |
18596908 |
Appl. No.: |
09/788543 |
Filed: |
February 21, 2001 |
Current U.S.
Class: |
310/75R |
Current CPC
Class: |
H02K 5/225 20130101;
H02K 7/1166 20130101; H02K 5/148 20130101; H02K 11/024 20130101;
H02K 11/026 20130101 |
Class at
Publication: |
310/75.00R |
International
Class: |
H02K 007/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 2000 |
JP |
2000-79700 |
Claims
What is claimed is:
1. A motor device comprising: a yoke formed generally in a bottomed
cylindrical shape; a rotor in which an armature and a commutator
are fixed to a rotary shaft and which is generally accommodated in
the yoke; brushes force-contacted to the commutator; and a gear
housing accommodating a reduction member which produces output
after reducing a rotation speed of the rotor, and fixed in an
opening of the yoke, wherein the commutator and the brushes are
disposed within the gear housing which is located outside the
opening of the yoke in an axial direction of the rotary shaft.
2. The motor device as in claim 1, wherein: a brush accommodating
recess is formed in the gear housing at an end on a side of the
yoke, the recess being larger at least partly than an inner
periphery of the yoke in a radial direction; and the brushes are
disposed within the brush accommodating recess to extend in a space
which is larger than the inner periphery.
3. The motor device as in claim 2, wherein: the brush accommodating
recess is formed generally in a square shape when viewed in the
axial direction of the rotary shaft; and the brushes are disposed
generally along a diagonal line in the brush accommodating
recess.
4. The motor device as in claim 3, wherein: the yoke is formed with
a flange around the opening of the yoke so that the flange covers
an opening of the brush accommodating recess, the flange being
generally in the square shape when viewed in the axial direction of
the rotary shaft.
5. The motor device as in claim 4, wherein: the brushes are
disposed at two opposing corners of the brush accommodating recess,
respectively; housing-side fitting parts are formed at two corners
of the yoke-side end the gear housing, respectively, where the
brushes are not disposed; yoke-side fitting parts are formed at two
opposing corners of the flange, respectively; and the gear housing
and the yoke are fixed to each other by the housing-side fitting
parts and the yoke-side fitting parts.
6. A motor device comprising: a motor unit having a cylindrical
yoke formed with a flange at one end thereof, a rotary shaft
rotatably supported in the yoke and extending outward through the
flange in an axial direction; a reduction unit having a housing
formed with a flange coupled with the flange of the yoke and
accommodating a reduction device engaged with the rotary shaft, the
flange of the reduction unit providing a generally square-shaped
recess radially inside thereof; a cylindrical commutator fixed to
the rotary shaft in the recess; and a brush disposed in the recess
and biased to contact the commutator along a diagonal line of the
recess.
7. The motor device as in claim 6, wherein: the recess has four
sides each of which is in generally the same length as a diameter
of the yoke.
8. The motor device as in claim 6, wherein: the flange of the yoke
is generally square-shaped in correspondence with the flange of the
housing; and the flange of the yoke and the flange of the housing
are fixed to each other by a screw passing through corners of the
flanges.
9. The motor device as in claim 8, wherein: the brush is disposed
along the diagonal line defined by two corners of each of the
flanges; and the screw is provided in another two corners of each
of the flanges.
10. The motor device as in claim 6, further comprising: a circuit
unit including capacitors and choke coils for electrical noise
suppression and accommodated in the housing at a position adjacent
to the brush in the axial direction and opposite the reduction
device in the radial direction of the rotary shaft.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on and incorporates herein by
reference Japanese patent application No. 2000-79700 filed Mar. 22,
2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a motor device in which a
commutator and brushes are disposed in a reduction unit outside a
yoke.
[0004] 2. Related Art
[0005] In a conventional motor device, an electric motor unit has a
cylindrical yoke and a rotor, and a reduction unit including
reduction gears therein is coupled to the yoke. The rotor is
primarily comprised of a rotary shaft for driving the reduction
gears, an armature, a cylindrical commutator and elongate brushes.
The armature and the commutator are fixed to the rotary shaft and
arranged in the axial direction of the rotary shaft. The brushes
are spring-biased to contact the commutator in the radial direction
of the commucator. The rotor is entirely accommodated within the
yoke. According to this arrangement, the length of the brushes is
restricted by the inner periphery of the yoke. As the brushes wear
during operation of the motor device, the life of the motor device
is limited by the life of brushes.
SUMMARY OF THE INVENTION
[0006] It is therefore an object of the present invention to
provide a motor device which is capable of employing lengthened
brushes.
[0007] According to the present invention, a motor device has a
motor unit and a reduction unit coupled with the motor unit. A
commutator and brushes are disposed within a gear housing of the
reduction unit located outside the opening of a yoke of the motor
unit in an axial direction of the motor unit. Preferably, the gear
housing is formed with a brush accommodating recess, at least a
part of which is larger than an inner periphery of the yoke in a
radial direction. The brushes are disposed within the brush
accommodating recess. The brush accommodating recess is formed in a
generally square shape, each brush is disposed along a diagonal
line of the square shape.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The above and other objects, features and advantages of the
present invention will readily become more apparent from the
following detailed description made with reference to the
accompanying drawings. In the drawings:
[0009] FIG. 1 is a sectional view showing a motor device according
to a first embodiment of the present invention;
[0010] FIG. 2 is a left side view showing the motor device
according to the first embodiment;
[0011] FIG. 3 is a sectional view of the motor device taken along a
line III-III in FIG. 1;
[0012] FIG. 4 is a side view showing a brush arrangement in the
first embodiment;
[0013] FIG. 5 is a left side view showing a circuit unit in the
first embodiment;
[0014] FIG. 6 is a plan view showing the circuit unit in the first
embodiment;
[0015] FIG. 7 is a side view showing a brush arrangement in a
second embodiment of the present invention; and
[0016] FIG. 8 is a side view showing a brush arrangement in a third
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] The present invention will be described below with reference
to various embodiments shown in FIGS. 1 to 7 and modifications
thereof.
[0018] (First Embodiment)
[0019] As shown in FIG. 1, a motor device 1 comprises a motor unit
2 and a reduction unit 3. The motor unit 2 has a yoke 4, which is
generally in a bottomed cylindrical shape having an opening at one
end, a plurality of magnets 5 fixed to the inner peripheral surface
of the yoke 4, and a rotor 6 generally accommodated in the yoke
4.
[0020] As shown in FIG. 2, the yoke 4 is formed at its opening with
a flange 4a, which extends in the radial direction into a generally
square shape when viewed in the axial direction. The length of each
side of this flange 4a is set to be a little longer than a diameter
of the cylindrical part 4b of the yoke 4. The flange 4a is formed
with a screw hole 4c at its each corner.
[0021] Referring back to FIG. 7, the rotor 6 has a rotary shaft 7,
an armature 8 and a commutator 9. The rotary shaft 7 has a base end
supported rotatably by a bearing 10 disposed at the bottom side
(left side end in FIG. 1) of the yoke 4. The armature 8 is fixedly
disposed at the base end side of the rotary shaft 7 in a manner to
face the magnets 5. The commutator 9 is formed in a cylindrical
shape and fixedly disposed around the rotary shaft 7 on a side of
the reduction unit 3. The commutator 9 is disposed to protrudes
from the opening of the yoke 4, that is, it is disposed in the
reduction unit 3 which is outside the opening of the yoke 4 in the
axial direction of the rotary shaft 7. The rotary shaft 7 is formed
with a worm 11 at its end side.
[0022] The reduction unit 3 has a gear housing 20, a cover 21 (FIG.
3), and a reduction gear device 22, an electric circuit unit 23 and
a brush holder unit 24. The side end of the gear housing 20 fixedly
coupled to the yoke 4 is formed in generally a square shape in
correspondence with the square shape of the flange 4a of the yoke 4
when viewed in the axial direction of the rotary shaft 7. The side
end of the gear housing 20 is recessed to provide a brush
accommodating recess 20a in generally a square shape when viewed in
the axial direction of the rotary shaft 7. Further, as shown in
FIG. 4, female threads 20n are formed in the corners of the side
end. Here, the length of each side of the brush accommodating
recess 20a is sized to be generally equal to the diameter of the
cylindrical part 4b of the yoke 4.
[0023] The gear housing 20 is formed with a worm accommodating
chamber 20b, which extends from the bottom center of the brush
accommodating recess 20a to accommodate the top end side (worm 11)
of the rotary shaft 7. Further, the gear housing 20 is formed with
a wheel accommodating chamber 20c, which communicates with the worm
accommodating chamber 20b, in a direction (downward direction in
FIG. 1) orthogonal to the axial direction at the central part of
the worm accommodating chamber 20b. The wheel accommodating chamber
20c is formed in a generally circular shape when viewed in a
direction orthogonal to the axis of the rotary shaft 7. As shown in
FIG. 3, its one end side (left side in the figure) is open. An
output shaft central hole 20d, which passes to the outside, is
formed in the center of the other side of the wheel accommodating
chamber 20c.
[0024] Further, the gear housing 20 is formed with a circuit
accommodating chamber 20e, which extends from the bottom of the
brush accommodating recess 20a in parallel with the worm
accommodating chamber 20b. Further, the gear housing 20 is formed
with a connector body 20f at the top end side (right side in FIG.
1) of the circuit accommodating chamber 20e. The connector body 20f
is formed in a generally cylindrical shape, which is open at the
side opposite the opening of the brush accommodating recess 20a.
The connector body 20f is formed in its bottom with a through hole
20g, which passes to the circuit accommodating chamber 20e.
[0025] The gear housing 20 is fixed to the yoke 4, as shown in FIG.
2, by screws N which are threaded into the female threads 20n
passing through the screw holes 4c. The opening of the brush
accommodating recess 20a is covered by the flange 4a under this
condition. A bearing 25 is disposed in the opening of the worm
accommodating chamber 20b to rotatbly support the intermediate part
of the rotary shaft 7.
[0026] As shown in FIG. 3 (not shown in FIG. 1), an internal wheel
gear 26 is disposed in the inner periphery of the wheel
accommodating chamber 20c. This internal wheel gear 26 is disposed
in a manner offset from the worm 11 in the axial direction of the
wheel accommodating chamber 20c, that is, in the direction
orthogonal to the drawing sheet in FIG. 1 and in the leftward
direction in FIG. 3.
[0027] The reduction gear device 22 is accommodated within the
wheel accommodating chamber 20c. Specifically, as shown in FIG. 3,
the reduction gear device 22 has a wheel 27, a sun gear 28, a
carrier 29, three (only two are shown in FIG. 3) planetary gears 30
and an output shaft 31. The wheel 27 has a ring-shaped worm wheel
27a having teeth on its outer periphery for engagement with the
worm 11, and a tubular part 27b protruding from the inner periphery
of the worm wheel 27a in the axial direction (leftward direction in
FIG. 3).
[0028] The sun gear 28 is fit on the tubular part 27b to be
rotatable therewith. The carrier 29 has a circular disk 29a and a
plurality of support pins 29b extending from the surface of the
disk 29a in the axial direction (rightward direction in FIG. 3) in
equi-angularly (120.degree.) spaced relation from each other. A
fitting pin 32 is fixed to the opposite side of the disk 29a at a
position corresponding to one support pin 29b. Each planetary gear
30 is supported rotatably about the support pin 29b and meshed with
the internal wheel gear 26 and the sun gear 28. The output shaft 31
has an intermediate part which passes through the tubular part 27b,
and is rotatable relative to the inner peripheral surface of the
tubular part 27b. Its base end is insert-fit in the disk 29a of the
carrier 29 to be rotatable therewith.
[0029] That is, the reduction gear device 22 is accommodated within
the wheel accommodating chamber 20c in such a manner that the top
end side of the output shaft 31 is insert-supported by a pair of
sliding bearing 33 fixed to the output shaft central hole 20d, the
teeth of the worm wheel 27a meshes with the worm 11 and each
planetary gear 30 meshes with the internal wheel gear 26. Thus,
when the rotary shaft 7 (worm 11) rotates, the wheel 27 rotates,
the planetary gears 30 revolve around the sun gear 28 while
rotating themselves based on the rotation of the wheel 27, and the
carrier 29 and the output shaft 31 rotate in response to the
revolution of the planetary gears 30. That is, the reduction unit
of this motor device 1 produces output while reducing the rotation
speed of the rotary shaft 7 (rotor 6) in two stages by the worm
gear and the planetary gears 30.
[0030] The circuit unit 23 is accommodated within the circuit
accommodating chamber 20e. Specifically, as shown in FIGS. 1, 5 and
6, the circuit unit 23 has a main body 41, three brush wiring
terminals 42-44, five external terminals 45-49, two choke coils 50,
51, two capacitors 52, 53, and a circuit breaker 54 as a burn-out
protection device. FIGS. 5 and 6 are a left side view and a plan
view of the circuit unit 23. In this embodiment, two choke coils
50, 51 and two capacitors 52, 53 form a noise- suppressing
device.
[0031] The main body 41 is made of resin, and has an annular disk
41a and an insertion plate 41b extending in the axial direction
from a part of the disk 41a and formed in a generally rectangular
shape. As shown in FIG. 5, the brush wiring terminals 42-44 and the
capacitors 52, 53 are mounted on the surface of the disk 41a. The
capacitors 52, 53 are provided in such a manner to protrude from
the surface of the disk 41a. The brush wiring terminal 42 is for
common connection to the ground, the brush wiring terminal 43 is
for connection to a high voltage power source for high speed
operation, and the brush wiring terminal 44 is for connection to a
high voltage power source for low speed operation. The capacitor 52
is connected between the brush wiring terminals 42 and 43, which
are for common connection to the ground and for connection to the
high voltage power source for high speed operation,
respectively.
[0032] The capacitor 53 is connected between the brush wiring
terminals 42 and 44, which are for common connection to the ground
and for connection to the high voltage power source for low speed
operation, respectively. The brush wiring terminals 42-44 are
formed with brush connecting pieces 42a-44a, respectively. The ends
of the brush wiring terminals 44 are bent and placed on the top
surface of the insertion plate 41b.
[0033] As shown in FIG. 6, three terminals 45-47, two choke coils
50, 51 and the circuit breaker 54 are arranged in parallel on the
central part of the insertion plate 41b in such a manner that the
choke coils 50, 51 sandwiches the circuit breaker 54. The external
terminals 45-47 are arranged so that the respective terminals
thereof protrude from top ends. The brush wiring terminal 42 for
common connection to the ground is connected to the external
terminal 45 through the circuit breaker 54. The brush wiring
terminal 43 for connection to the high voltage power source for
high speed operation is connected to the external terminal 46
through the choke coil 50. The brush wiring terminal 44 for
connection to the high voltage power source for high speed
operation is connected to the external terminal 47 through the
choke coil 51.
[0034] Two external terminals 48, 49 are mounted on the bottom
surface of the insertion plate 41b. The external terminals 48, 49
are arranged in parallel so that respective ends at one side
protrude from the top end of the insertion plate 41b. The external
terminals 48, 49 are provided to output detection signals of a
rotation sensor (not shown).
[0035] As shown in FIG. 1, the circuit unit 23 is fixed in such a
manner that the insertion plate 41b is inserted into the circuit
accommodating chamber 20e and the disk 41a is inserted into the
brush accommodating recess 20a. The top ends of the external
terminals 45-49 passe through the communication hole 20g and
protrude into the connector body 20f, thus forming pins of the
connector.
[0036] The brush accommodating recess 20a accommodates therein a
brush holding unit 24. Specifically, as shown in FIG. 4, the brush
holding unit 24 has a plate 61, three brush holders 62-64, three
brushes 65-67 and three helical torsion springs 68-70.
[0037] The plate 61 is formed in a generally square shape to be
accommodated within the brush accommodating recess 20a. The plate
61 formed with a central hole 61a in its center and cut-outs 61b,
61c at its outer peripheral ends while avoiding the capacitors 52,
53. Three brush holders 62-64 are fixed on the top surface of the
plate 61. Each brush holder 62-64 supports respective brushes
65-67. The brush holders 62-64 and the brushes 65-67 are arranged
generally along diagonal lines of the generally square-shaped plate
61.
[0038] In this embodiment, the brushes 65, 67 are arranged to
oppose each other with respect to the center of the plate 61, and
the brush 66 is disposed at a location which is 70.degree. spaced
apart from the brush 67. The brush holder 62 and the brush 65 are
for connection to the common ground, the brush holder 63 and the
brush 66 are for connection to the high voltage power source for
high speed operation, and the brush holder 64 and the brush 67 are
for connection to the high voltage power source for low speed
operation. Pins P are provided on the plate 61 near brush holders
62-64 in the counter-clockwise direction, respectively. The brushes
65-67 are biased towards the commutator 9 (shown with two-dot chain
line in FIG. 4) by the helical torsion springs 68-70,
respectively.
[0039] The brush holder unit 24 is accommodated in the brush
accommodating recess 20a in parallel with the disk 41a of the
circuit unit 23. Pig tails 65a-67a of the brushes 65-67 are
connected to corresponding connecting terminals 42a-44a,
respectively. Each brush 65-67 is located outside the opening of
the yoke 4 in the axial direction of the rotary shaft 7 together
with the commutator 9.
[0040] As shown in FIG. 4, each brush 65-67 extends closely to the
inner periphery (shown with two-dot chain line in FIG. 4) 4d of the
yoke 4. The helical torsion springs 68-70 are partly disposed
outside the inner periphery 4d in the radial direction. The
capacitors 52, 53 are not in contact with the plate 61 under this
condition due to the cut-outs 61b, 61c, and protrude above the
plate 61. The capacitors 52, 53 are partly disposed outside the
inner periphery 4d of the yoke 4 in the radial direction.
[0041] As shown in FIG. 3, the cover 21 is fixed to the opening of
the wheel accommodating chamber 20c of the gear housing 20. A
connector of an electronic motor control circuit device (not shown)
is connected to the connector of the motor device 1, that is, the
connector body 20f and the top ends of the external terminals
45-49.
[0042] In the motor device 1 constructed as above, the armature 8
generates magnetic field to rotate the rotor 6, when a direct
current voltage is applied from the control circuit device to the
external terminal 45, 47. The rotor 6 rotates at high speeds, when
the direct current voltage is applied from the control circuit
device to the external terminals 45, 46.
[0043] Electrical noises occur during this rotation, because the
brushes 65, 67 (65, 66) slidingly contact the commutator 9.
[0044] These electrical noises are suppressed by the inductance of
the choke coil 51 (50) and the capacitance of the capacitor 53
(52). As a result, transmission of the electrical noises to the
external control circuit device is suppressed, and radiation of
electromagnetic noises arising from the electrical noises is
restricted.
[0045] Further, the choke coil 51 (50) generates heat, when the
winding of the armature 8 generates heat due to excessive current
during rotation of the rotor 6, for instance, when a heavy load is
applied to the side of the output shaft 31. The circuit breaker 54
is turned into a disconnection condition in accordance with the
generated heat of the choke coil 51 (50), so that no more excessive
current is supplied. Thus, burnout due to heat generation is
prevented.
[0046] The first embodiment provides the following advantages.
[0047] (1) The commutator 9 and the brushes 65-67 are disposed
outside the opening of the yoke 4, which is formed in a bottomed,
generally cylindrical shape, in the axial direction of the rotary
shaft 7. Thereby, the brushes 65-67 can be disposed without being
restricted by the inner periphery 4d of the yoke 4. As a result,
the length of the brushes can be increased to prolong life of the
brushes. Further, members which are disposed on the same plane in
the axial direction as the brushes 65-67, for instance, the helical
torsion springs 67-70 which bias the brushes 65-67 towards the
central axis side of the yoke 4, can also be disposed without being
restricted by the inner periphery 4d of the yoke 4.
[0048] (2) The brushes 65-67 are arranged generally along the
diagonal lines in the brush accommodating chamber 20a which is
formed at the side end of the yoke 4 of the gear housing 20 and
formed in a generally square shape when viewed in the axial
direction of the rotary shaft 7. As a result, the length of the
brushes can be maximized within the brush accommodating chamber
20a.
[0049] (3) The length of each side of the brush accommodating
recess 20a is set to be generally equal to the diameter of the
cylindrical part 4b of the yoke 4. As a result, the length of the
brushes can be increased without sizing entirety of the motor
device large.
[0050] (4) The opening of the brush accommodating chamber 20a is
covered with the flange 4a which is formed at the opening side of
the yoke and in a generally square shape when viewed in the axial
direction of the rotary shaft. As a result, no additional member is
required to cover the opening of the brush accommodating chamber
20a formed in a generally square shape when viewed in the axial
direction of the rotary shaft 7.
[0051] (5) The capacitors 52, 53 are accommodated in the brush
accommodating chamber 20a with parts thereof being disposed outside
the inner periphery 4d of the yoke 4. As a result, space required
for accommodating the capacitors 52, 53 is provided sufficiently,
and no space is required at other locations.
[0052] (Second Embodiment)
[0053] In this embodiment, the motor device 1 has two brushes 81,
82 as shown in FIG. 7. Specifically, the yoke-side end of a gear
housing 83 is formed in a generally square shape when viewed in the
axial direction of the rotary shaft 7 in the same manner as in the
gear housing 20. This end is formed with a brush accommodating
recess 83a formed in a generally square shape when viewed in the
axial direction of the rotary shaft 7. Further, as the housing-side
engagement parts, female threads 83b are formed in the two opposing
corners at the yoke-side end of the gear housing 83.
[0054] The two brushes 81, 82 are arranged at the other corners
where the female threads 83b are not formed along the generally
diagonal lines in the brush accommodating chamber 83a. In this
instance, the screw holes 4c of the yoke 4 need to be provided only
in the two corners which correspond to the female threads 83b. The
screw holes 4c function as the yoke-side engagement parts in this
modification. Thus, the gear housing 83 is fixed to the yoke 4 by
threading screws into the female threads 83b through the thread
holes 4c.
[0055] In this second embodiment, the advantages (1)-(4) of the
first embodiment can be provided similarly. In addition, because
the gear housing 83 and the yoke 4 are fixed to each other at the
part of the female threads 83b formed in the two corners of the
gear housing 83 where the brushes 81, 82 are not disposed, the gear
housing 83 and the yoke 4 can be fixed with ease while ensuring a
sufficient space for arranging the brushes 81, 82.
[0056] (Third Embodiment)
[0057] In this embodiment, the motor device 1 has four brushes
84-87 as shown in FIG. 8. Specifically, the yoke-side end of a gear
housing 88 is formed in a generally square shape when viewed in the
axial direction of the rotary shaft 7 in the same manner as in the
gear housing 20. This end is formed with a brush accommodating
recess 88a formed in a generally square shape when viewed in the
axial direction of the rotary shaft 7. The four brushes 84-87 are
arranged at the corners along the generally diagonal lines in the
brush accommodating chamber 83a.
[0058] In this third embodiment, the advantages (1)-(4) of the
first embodiment can be provided similarly.
[0059] The above embodiments may be modified or altered as
follows.
[0060] The number of the brushes may be only one, as long as it is
arranged along the generally diagonal line in the brush
accommodating recess 20a. According to this modification, the life
of brush can be increased as well by increasing the length of the
at least one of the brushes.
[0061] The length of each side of the brush accommodating recess
20a need not be generally the same as the diameter of the
cylindrical part of the yoke 4. For instance, the length of the
brush can be made further longer by sizing the length of each side
of the brush accommodating recess 20a to be longer than the
diameter of the cylindrical part 4b of the yoke 4. Even if the
length of each side of the brush accommodating recess 20a to be
shorter than the diameter of the cylindrical part 4b of the yoke 4,
the entire size of the motor can be reduced while maintaining the
same brush length as in the conventional one.
[0062] The brush accommodating recess 20a may be formed in other
shapes as long as it is at least partially larger than the inner
periphery of the yoke 4 in the radial direction. For instance, the
brush accommodating recess 20a may be formed in a shape which is
generally circular but extends in the radial direction only at
locations where the brushes are arranged when viewed in the
direction of the rotary shaft 7. In this modification as well, the
length of the brush can be increased to prolong the life of the
brush.
[0063] The capacitors 52, 53 may be positioned at different
locations. In this modification as well, the advantages (1)-(4) of
the first embodiment can be provided similarly.
[0064] Noise-suppressing circuit elements other than the capacitors
52, 53, that is, choke coils 50, 51, may be disposed outside the
inner periphery 4d of the yoke 4 in the radial direction while
being disposed at least partially in the brush accommodating
chamber 20a. Further, the circuit breaker 54 may be disposed
outside the inner periphery of the yoke 4 in the radial direction
while being disposed at least partially in the brush accommodating
recess 20a. This arrangement ensures a sufficient space for the
circuit breaker 54, and no additional space need be provided at
other locations.
[0065] The helical torsion springs 68-70 in the above embodiment
may be modified to compression coil springs 89 as shown in FIGS. 7
and 8. In this modification, the brushes 81, 82, 84-87, and the
compression coil springs 89 can be disposed without being
restricted by the inner periphery 4d of the yoke 4.
* * * * *