Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-11-27
2004-09-07
Le, Dang (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S249000, C310S251000, C310S252000, C310S253000
Reexamination Certificate
active
06787963
ABSTRACT:
This application is based on Application No. 2001-139731, filed in Japan on May 10, 2001, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a brush assembly incorporated in a motorized power steering apparatus for example.
2. Description of the Related Art
FIG. 6
is a cross sectional side view of a known motorized power steering apparatus, and
FIG. 7
is a front elevation of a brush assembly
40
incorporated in the motorized power steering apparatus.
This motorized power steering apparatus includes an electric motor
30
for generating a rotating force or torque and an electromagnetic clutch
2
connected with the electric motor
30
for controlling the transmission of the rotating force or torque thereof.
The electric motor
30
includes: a cylindrical yoke
3
; four field permanent magnets
4
housed in and fixedly secured to the yoke
3
in an opposed relation with respect to each other; a shaft
7
rotatably supported by a first bearing
5
and a second bearing
6
in the yoke
3
; an armature
8
fixedly mounted on the shaft
7
; a commutator
9
having a plurality of segments
9
a
(see
FIG. 10
) fixed to the shaft
7
near one end thereof; a brush assembly
40
having brushes
32
, which are urged into abutting engagement with a surface of the commutator
9
under the action of elastic forces of corresponding springs
10
, and brush holders
31
holding the corresponding brushes
32
, respectively; a housing
14
to which the brush holder
31
is fixedly attached through a magnetic shield plate
41
, the housing being made of a non-magnetic material in the form of aluminum and connected with the yoke
3
by means of fastening screws
19
, and a grommet
16
through which a line or conductor
15
extends. The magnetic shield plate
41
comprises a flat plate which is made, for example, by punching a rolled steel sheet of a thickness of 1 mm by press working to form a doughnut-shaped configuration.
The armature
8
is provided with a core
17
which has a plurality of slots extending in an axial direction, and a winding
18
which is formed of a conductor fitted in and wound around the slots of the core
17
in a plurality of turns.
The electromagnetic clutch
2
includes a clutch stator
20
fixed to the housing
14
by clutch fastening screws
21
, a clutch coil
22
disposed in the clutch stator
20
, a boss
23
rotatably mounted on one end of the shaft
7
through a third bearing
6
a
, a drive rotor
24
fixedly mounted on the shaft
7
, and a doughnut-shaped disk
25
fixedly secured to the boss
23
through a spring member
26
.
The brush assembly
40
includes a base
35
with a plurality of conductors
36
embedded therein by insert molding, four metal brush holders
31
fixed to the base
35
, four brushes
32
held in the corresponding brush holders
31
and being urged to abut against the commutator
9
under the action of the elastic forces of the corresponding springs
10
, and a plurality of lead wires
33
each having one end thereof connected with a corresponding brush
32
and the other end thereof connected with a connecting portion
34
of a corresponding conductor
36
. The brushes
32
and the connecting portions
34
of the conductors
36
are arranged in line symmetry with respect to center lines A and B, which extend in diametrical directions passing through the center of the shaft
7
, and which are perpendicular with respect to each other.
In the motorized power steering apparatus as constructed above, current is supplied to the winding
18
through the brushes
32
which are in abutment with the segments
9
a
of the commutator
9
, so that the armature
8
is driven to rotate together with the shaft
7
under the action of an electromagnetic force.
On the other hand, by energizing the clutch coil
22
, a magnetic circuit MC is formed by the clutch stator
20
, the drive rotor
24
and the disk
25
, all of which are made of magnetic materials. The spring member
26
is caused to flex or deform toward the clutch stator
20
under the action of the magnetic circuit MC thus formed, whereby the disk
25
is magnetically attracted and fixed to the drive rotor
24
, which is thereby made integral with the boss
23
.
Thus, the rotating force of the shaft
7
is transmitted to the drive rotor
24
, which is fixed to the shaft
7
, and thence to the boss
23
, from which the rotating force is further transmitted to a warm shaft (not shown) splined with the boss
23
, thereby assisting the steering force of a steering wheel of a vehicle (not shown).
FIG.
8
and
FIG. 9
are explanatory views for explaining the conductivity orientation of each brush
32
of the brush assembly
40
.
Electroconductive particles
41
(for instance, copper powder) contained in each brush
32
are turned into the powder particles (for instance, copper powder) deformed into tabular or flattened configurations in a direction perpendicular to the direction of pressing by a compressive stress generated upon press molding of each brush
32
. Therefore, an orientation is created in the electroconductivity of each brush
32
. A Z direction of each brush
32
in
FIG. 9
is the direction of the press molding (i.e., pressing direction). The electric resistance of each brush
32
in the Z direction indicated by arrow Z exhibits a value greater than that in an X direction indicated by arrow X (i.e., in the direction of rotation of the shaft
7
), or in a Y direction indicated by arrow Y (i.e., in a diametrical direction of the shaft
9
). Generally, the ratio of the Z-direction resistance to the X-direction or Y-direction resistance is about 4 to 5.
FIG. 10
is a view illustrating the appearance in which a brush
32
press-molded in the Z direction is in abutment against the commutator
9
. In this figure, the brush
32
is formed at its opposite edges with tapered contact portions
32
a
and
32
b
extending in parallel with the direction of rotation of the commutator
9
, the tapered contact portions
32
a
and
32
b
being in abutment with the surface of a segment
9
a
of the commutator
9
. A tip end of a lead wire
33
is embedded in the corresponding brush
32
in such a manner that it extends up to about the middle (i.e., half) of the length L of the brush
32
.
In the brush assembly
40
of the above construction, when a comparison is made between current paths, indicated at arrows m
0
and m
2
, respectively, passing through the brush
32
in
FIG. 10
, the current path indicated at arrow m
2
is inclined in a direction of arrow Z in comparison with the current path indicated at arrow m
0
, and hence has an accordingly larger electric resistance, so that there takes place a greater temperature rise in the brush
32
when the electric motor
30
is energized. As a result, for example, the base
35
made of synthetic resin or plastic would be melted, causing a defective sliding of the brush
32
.
Though in relatively infrequent cases such as, for example, when a car with the motorized power steering apparatus is put into a garage, large current is supplied to the electric motor
30
thereby to abnormally raise the temperature of the brush
32
. Thus, there arises a problem in that certain measures have to be taken in order to prevent such situations. That is, for example, a maximum current to be supplied to the electric motor
30
or the time during which current is continuously supplied to the electric motor
30
is limited; or the sizes or dimensions of the respective component parts such as the brushes
32
, etc., of the brush assembly
40
are enlarged in order to increase the thermal capacity and the effect of heat radiation.
SUMMARY OF THE INVENTION
The present invention is intended to obviate the problems as referred to above, and has for its object to provide a brush assembly in which electric power losses in brushes can be reduced to effectively suppress an abnormal rise in temperature of the brushes and hence the entire brush assembly.
Bearing the above object in min
Fukazawa Keiichi
Matsui Yusuke
Tanaka Toshinori
Yamamoto Kyouhei
Yonemori Kei
Le Dang
Mitsubishi Denki & Kabushiki Kaisha
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