Abstract:
Addressed herein are commutators and methods of manufacturing them. The methods permit the carbonaceous material and core of a commutator to be molded simultaneously, rather than in a two-step process, and can eliminate one of two curing procedures used in connection with other manufacturing techniques. The necessity of machining the inner surface of the commutator shell to remove undesired excess phenolic or other material additionally is avoided by use of the techniques detailed herein. Commutators formed according to these methods may have increased useful lives and provide better performance than others presently available.

Description:
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&#39; 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 shell, but also to provide electrical continuity between the shell and carbonaceous material. Whereas the core of the Aupac commutator is already cured (and nonreactive) when the carbonaceous material is molded and thus no chemical bonding of the two substances occurs, the core and carbon pre-forms of the commutators of the present invention bond, or interlock, both chemically and mechanically as their simultaneous molding transpires. The result is increased mooring of the carbonaceous material to the core within the shell without the need to form additional anchors in the shell itself. 
     Avoiding projections  116  of the Aupac commutator enhances the useful lives of commutators of the present invention. By permitting use of essentially the entirety of their electrically-conductive segments, commutators according to the present invention likewise reduce waste of carbonaceous material. These commutators further are formed so that the molding of the carbonaceous material produces higher density, more uniform material, advantageous properties for many of their intended uses. 
     Commutators of the invention also may have shells of extended height during part or all of the manufacturing process. Increasing the height of the shell protects the integrity of the carbonaceous (or other) face material of each device, reducing its exposure to being chipped, scratched, or otherwise damaged during manufacture. The shell can be sheared at the end of the manufacturing process if desired so as not to protrude, or to protrude only a selected amount, beyond the commutator face. 
     It is therefore an object of the invention to provide an anchoring system for one or more conductive segments of a rotary switch or commutator. 
     It is also an object of the present invention to provide such a system which permits use of the commutator until the segments are substantially completely worn. 
     It further is an object of the present invention to provide methods of forming commutators in which either or both of the processes of molding and curing the core and carbonaceous material can occur simultaneously. 
     It additionally is an object of the present invention to provide methods of forming commutators in which unwanted insulating material of the core (i.e. flash) is either not deposited, or deposited in reduced amounts, on the interior surface of the shell. 
     It is, moreover, an object of the present invention to provide commutators having improved characteristics and longer useful lives than at least certain other commutators discussed herein. 
     It is an additional object of the present invention to provide a commutator whose expense and difficulty of manufacture is decreased and whose shell may extend beyond the face of the segments during at least part of the manufacturing process. 
     Other objects, features, and advantages of the present invention will be apparent with reference to the remainder of the text and to the drawings of this application. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of, essentially, the shell of the Aupac commutator. 
     FIG. 2 is an elevational view of the shell of the Aupac commutator of FIG.  1 . 
     FIG. 3 is a cross-sectional view of the shell of the Aupac commutator taken along lines A—A of FIG.  1 . 
     FIGS. 4-5 are cross-sectional views of the Aupac commutator of FIG. 6 illustrating aspects of its formation. 
     FIG. 6 is a cross-sectional view of the Aupac commutator incorporating the shell of FIG.  1 . 
     FIG. 7 is a cross-sectional view of a commutator of the present invention. 
     FIGS. 8-10 are cross-sectional views of the commutator of FIG. 7 illustrating aspects of its formation. 
     FIGS. 11-12 are cross-sectional view of an alternative, barrel-style commutator made consistent with techniques of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 7 provides a cross-sectional view of an exemplary commutator  10  of the present invention. Commutator  10  includes multiple conductive segments  14 , whose exposed surfaces  18  are intended to contact one or more conductive brushes in use. Intermediate adjacent segments  14  are gaps or slots (not illustrated), which isolate the adjacent segments  14  and permit commutator  10  to operate as a high-speed rotary switch. 
     Also shown in FIG. 7 are core  26  and “blank” or shell  30 . Core  26  is made of electrically-insulating material, typically (although not necessarily) phenolic, and defines a central aperture  34  for receiving a spindle or shaft in use. Core  26  additionally defines collar  38 , which circumscribes aperture  34  in the area of segments  14 . 
     Usually manufactured from a curled strip of copper or other suitable metal, shell  30  constitutes the outer diameter of commutator  10 . Formed into shell  30  are multiple tangs  42 , which may be bent into hooks. Additionally included in shell  30  are internal anchors  46 . As shown in FIG. 8, both tangs  42  and anchors  46  typically are formed following the blanking of shell  30 . 
     Thereafter, pre-form  50  (which may, but need not necessarily, be deformable) for segments  14  may be placed within shell  30 . Consistent with FIG. 9, pre-form  50  may be inserted so that its inner face  54  is penetrated by anchors  46 , thereby at least partially securing it in position within shell  30 . Contact between anchors  46  and inner face  54  additionally provides further electrical connection between shell  30  and the pre-form  50 . As shown in FIG. 9, shell  30  may extend beyond outer face  58  of pre-form  50 , thereby protecting it to some extent during the remainder of the manufacturing process. 
     Although anchors  46  are shown as extending at an acute angle from shell  30 , those skilled in the art will recognize that anchors  46  may be shaped or positioned differently if appropriate or desired. Anchors  46  additionally need not necessarily penetrate pre-form  50  if other securing mechanisms are adequate, but rather may instead merely abut or otherwise contact it. Likewise, shell  30  is not required to extend beyond outer faces  58 , notwithstanding the advantages obtained when such extension exists. 
     Following placement of pre-form  50  within shell  30 , the material of core  26  is injected and molded onto pre-form  50 . The act of such molding, illustrated in FIG. 10, embeds portions of anchors  46  within core  26 , thereby securing its position relative to shell  30 . The high pressures and temperatures used to mold core  26  likewise concurrently mold pre-form  50 , bonding core  26  to inner face  54  (typically via bonding of resins contained in both core  26  and pre-form  50 ) and mechanically interlocking features (i.e. protrusions and cavities represented diagrammatically in FIG. 10) on their adjoining surfaces (or possibly created by at least slight deformation of either or both components during the molding process). This chemical bonding and mechanical interlock between core  26  and pre-form  50  functions further to anchor pre-form  50  within shell  30 . 
     FIGS. 9-10 additionally illustrate the flash-avoidance aspects of the present invention. Because pre-form  50  is inserted into shell  30  before core  26  is molded, the pressure used to mold core  26  forces the material of pre-form  50  to expand outward against the inner surface  62  of shell  30 . This expansion prevents excess material of core  26  from coming between pre-form  50  and inner surface  62 , thus both preventing flash within shell  30  and avoiding any need to remove it. Further anchoring of preform  50  conceivably could occur if inner surface  62  contains a recess into which a portion of pre-form  50  could be fitted (or protrude when deformed). 
     To the extent any flash exists on outer surface  66  of shell  30 , it can be removed using conventional mechanical-abrasion (or other) methods. As denoted in FIG. 10, height A 1  is greater than the sum of the depth A 2  to which core  26  is positioned within shell  30  and the height A 3  of pre-form  50 . If shell  30  is abraded mechanically, its added height can advantageously protect outer face  58  from certain types of damage associated with such abrasion. Thereafter the material of both core  26  and pre-form  50  can be cured together and any added height of shell  30  (as well as the outermost layer of outer face  58 ) removed. Slotting additionally can occur to create segments  14 , with contact surfaces  18 , from pre-form  50 . 
     As shown in FIG. 7, most or all of the depth D 1  of segments  14  is available as a contact surface for the electrical brushes used in conjunction with commutator  10 . The useful life of commutator  10  is thus increased over that of the Aupac commutator, as the commutator  10  can continue to operate until surface  18  of each segment  14  is worn substantially the entirety of depth D 1 . By contrast, only the portions of segments  124  within depth D 2  of FIG. 6 are available for contact and wear. 
     Certain performance aspects of commutator  10  additionally are enhanced through use of the present techniques, as they permit more consistent and higher density molding of preform  50 . Because the present invention reduces the likelihood of damage to core  26  as commutator  10  is formed, greater pressure can be used to mold core  26  and pre-form  50 . The greater pressure increases the ability of the core  26  to conform to the shape of pre-form  50  and for the two to link together. Greater uniformity of temperature conditioning also is achieved, because the material of core  26  being molded is at approximately the same temperature as the tooling being used and the portion of shell  30  surrounding pre-form  50 . 
     FIGS. 11-12 illustrate a barrel-style commutator  200  according to the present invention. Commutator  200  includes shell  204  from which tangs  208  and anchors  212  are formed. Carbonaceous pre-form  216  can be placed so that shell  204  penetrates it, thereby partially (directly) securing pre-form  216  to shell  204 . Core  220  can then be injected within shell  204  and molded onto pre-form  216 , with the joint molding of core  220  and pre-form  216  chemically and mechanically interlocking them. 
     As shown in FIGS. 11-12, anchors  212  are embedded within core  220 . If other fixing mechanisms are adequate, anchors  212  need not necessarily be used. Alternatively, anchors  212  (if present) could be repositioned so as to contact pre-form  216  as well. 
     The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of the present invention. Further modifications and adaptation to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope of spirit of the invention.