Methods and results of manufacturing commutators

Details Methods and results of manufacturing commutators Methods and results of manufacturing commutators

1999-02-26

2001-05-22

Ramirez, Nestor (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S235000, C310S236000, C310S237000, C029S597000

Reexamination Certificate

active

06236136

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to rotary switches and more particularly, although not exclusively, to “flat” or “face-style” commutators for use with electric motors and methods of manufacturing such commutators.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,491,373 to Cooper, et al., incorporated herein in its entirety by this reference, discloses an exemplary high-speed rotary switch or commutator. Denoted a “barrel-style” device, the commutator illustrated in the Cooper, et al. patent includes multiple electrically-conductive segments arranged into a cylinder on the outer diameter of a non-conductive core. An electrical brush passes along the outer diameter of the core to form a conductive path with the one or more segments in contact with it at any given instant.
Described in U.S. Pat. Nos. 5,760,518 and 5,826,324 to Abe, et al. (also incorporated herein in their entireties by this reference) is a commutator whose face, rather than outer diameter or edge, conducts electricity. This face-style commutator is an alternative to a barrel-style device and is often used in devices exposed to corrosive environments or immersed in fuel.
FIGS. 1 and 2
of the Abe, et al. patents illustrate aspects of such a commutator, with electrically-conductive segments
3
consisting principally of graphite.
Also shown in
FIG. 2
of the Abe, et al. patents is metal shell or plate
5
, whose terminal
6
admits connection to windings of a motor, and an electrically-insulating support
1
. Plate
5
includes on its inner surface “small projections
7
,” which function to anchor the graphite segments
3
from displacement as the commutator operates. According to the Abe, et al. patents, a separate, unillustrated “part of . . . metal plate
5
is embedded in the electrically insulating support
1
” to retain the relative positions of the plate and support.
Listed on the faces of the Abe, et al. patents as their assignee is Aupac Co., Ltd. (“Aupac”). A commutator made by Aupac includes two sets of anchors in the plate or shell. One set, analogous to the unshown portions of metal plate
5
discussed in the Abe, et al. patents, retains the position of the insulating support or core of the commutator, while the other (analogous to “small projections
7
”) assists in anchoring the conductive segments relative to the plate or shell. However, unlike projections
7
of the Abe, et al. patents, which extend radially inward from an inner surface of the plate or shell, the analogous anchors of the Aupac commutator are formed by bending radially inward axially-extending protrusions on an edge of the plate or shell (rather than as protrusions from its side).
FIGS. 1-6
illustrate, essentially identically, aspects of the Aupac commutator
100
. Detailed in
FIGS. 1-3
is metal shell
104
in which anchors
108
are formed. Such anchors
108
extend radially inward from shell
104
and are used to moor an electrically-insulating core
110
(see FIG.
4
). Also shown in
FIGS. 1-3
are terminals
112
(which ultimately will be bent into tangs or hooks) and projections
116
. As noted in the preceding paragraph, projections
116
are not formed in inner surface
120
of shell
104
but rather extend from its edge
124
before being bent inward.
Manufacture of the Aupac commutator
100
is relatively complex. Initially, shell
104
must be blanked and formed in the manner of
FIGS. 1-3
so as to create anchors
108
, terminals
112
, and projections
116
. Core
110
must then be molded into shell
104
, as shown in
FIG. 4
, so that its phenolic material surrounds anchors
108
. Molding core
110
in this manner effectively embeds anchors
108
therein, helping fix the position of core
110
relative to shell
104
.
After the phenolic material of core
110
is molded and cured, excess material (typically denoted “flash”) must be removed from inner surface
120
. Failure to remove such excess material can be problematic, as it can adversely affect the electrical continuity between shell
104
and the electrically-conductive graphite segments
126
(see
FIG. 6
) ultimately forming the face of the Aupac commutator
100
. Machining, furthermore, is required to delete flash from inner surface
120
once core
110
has been molded and cured.
After the material of core
110
is cured and the flash is removed from inner surface
120
of shell
104
, projections
116
must be bent radially inward as illustrated in FIG.
5
. Concurrently terminals
112
may be formed into tangs or hooks
128
for subsequent attachment to the windings of a motor. Only then are conductive segments
126
created as shown in FIG.
6
.
Included in
FIG. 6
are the segments
126
, which initially consist of graphite powder or material. The material is molded, or pressed, into recess
132
(see
FIG. 5
) so that it abuts core
110
and projections
116
are embedded within. Doing so anchors the material of segments
126
to shell
104
, after which the material is cured and slotted to form the segments
126
.
Surface
136
contacts electrical brushes, and thereby wears, in use. As is readily visible in
FIG. 6
, a substantial portion of each segment
126
lies further from surface
136
than projections
116
(and thus is not within the depth D
2
shown in that figure). It hence is unavailable as a contact surface, resulting in significant waste of the graphite material.
Moreover, to applicants' knowledge, at no time does shell
104
of the Aupac commutator
100
extend beyond surface
136
. Shell
104
indeed cannot readily do so, as projections
116
must be bent inward in order to be embedded within segments
126
. Similarly, neither commutator of the Abe, et al. patents contemplates having a plate
5
extending at any time above the exposed face of the carbonaceous material. Even though theoretically not impossible to extend plates
5
(upward as oriented in
FIGS. 2 and 3
of the Abe, et al. patents) beyond pieces
3
, no basis for such extension appears in the Abe, et al. patents.
SUMMARY OF THE INVENTION
Manufacturing methods of the present invention are substantially simpler than those used to produce both the Aupac commutator and those of the Abe, et al. patents. Unlike those utilized to create the Aupac commutator, for example, the methods employed with the present invention reverse the sequence of inserting a carbonaceous (typically at least slightly deformable) pre-form and (phenolic or other) insulating core into the commutator shell. As a consequence, the carbonaceous material and core can be molded simultaneously rather than in the two-step process described in the preceding section.
Methods of the present invention likewise eliminate one of two curing procedures involved in manufacturing the Aupac commutator. Because the insulating core of the Aupac commutator forms a base against which the carbonaceous material is forced under pressure, the core must be cured prior to molding of the carbonaceous material. Otherwise, the core will lack sufficient strength and rigidity to admit proper molding of the carbon segments as it encounters such pressure. With the present invention, however, curing of the carbonaceous material and core can occur simultaneously.
The necessity of machining the inner surface of the commutator shell to remove flash additionally is avoided by use of the present techniques. By having the annular (or otherwise-shaped) carbonaceous pre-form inserted into the shell prior to molding the insulating core, these techniques allow the pressure caused by the molding of the core to force the material of the pre-form outward so that it abuts the inner surface of the shell. This action prevents the core material from migrating to the inner surface of the shell and becoming undesired flash.
Noted in the preceding section are the two sets of anchors required for making the Aupac commutator. Although commutators of the present invention similarly may be made with two (or more) sets of anchors, only one set is necessary, as such set is adapted not only to secure both the core and carbonaceous material to the sh

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