Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2002-04-26
2004-02-03
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S596000, C029S598000, C310S235000
Reexamination Certificate
active
06684485
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a flat commutator with a hub body formed from insulating molding compound, a plurality of conductor segments and an equally large number of carbon segments which form the running surface, comprising the following steps:
The hub body is molded onto a conductor blank provided with radial grooves, whereupon the grooves are filled with molding compound;
the composite part of conductor blank and hub body is then machined by chip-removing tools on the end face of the conductor blank turned away from the hub body, an annular inner fixation ridge being left standing during machining of the end face of the composite pat;
The present invention also relates to a flat commutator produced by this method.
Flat commutators of the most diverse geometries are known and in service. As an example, German Unexamined Specification (DE-OS) 4140475 describes a typical flat commutator.
A typical area of application for flat commutators is as electric motors of fuel pumps (see, for example, German Unexamined Specifications (DE-OS) 19652840 and 197526326). To ensure that the running surface of the commutator will not be attacked by fuel that contains methanol or ethanol, flat commutators with a carbon running surface are widely used for this purpose. The carbon segments thereof are supported on conductor segments of copper, in order that the winding ends of the rotor winding can be brought into contact with the carbon segments without difficulties.
Two fundamentally different procedures are known for the production of flat commutators with a carbon running surface. In one case a carbon ring, which will subsequently be subdivided by separating cuts into carbon segments, can be molded directly onto the conductor blank by sintering of powdered carbon in which the said blank is embedded. In the other case, a prefabricated annular carbon disk is placed on one end face of the conductor blank or of the conductor segments, joined thereto by soldering to achieve an electrically conducting and mechanically robust connection, and subsequently subdivided into the carbon segments by separating cuts, which can also subdivide the conductor blank into the conductor segments if necessary. Both methods are described in, for example, German Unexamined Application (DE-OS) 19652840. Molding of the hub body onto the conductor blank can be accomplished before (see WO 97/03486) or after (see German Unexamined Application (DE-OS) 4028420) the annular carbon disk is soldered onto the conductor blank.
German Patent 4137816 C1 discloses the production of a flat commutator with a carbon running surface, in which a perforated graphite disk is fixed by means of an SMD conductive silver adhesive on a metallic conductor blank which is provided with openings in the region of the subsequent carbon segments. Thereafter the composite part formed in this way is placed in an injection-molding press, where the support member made of insulating material is injection-molded onto it. In the region of the openings of the conductor blank there are formed direct, gap free, inseparable joints between the support member and the graphite disk, in that the material of the support member penetrates into the upper structure of the graphite material. The graphite disk and the conductor blank are then subdivided into the individual carbon segments and conductor segments, for example by abrasive cutting.
A further flat commutator with a carbon running surface, which the carbon segments are bonded to the conductor segments by means of an electronically conductive adhesive, is known from German Utility Model 9211488U1.
A method of the type mentioned in the introduction can be found in the already cited WO 97/03486. The method for producing a flat commutator known from that patent is characterized in that the separating cuts with which the annular carbon disk is subdivided into carbon segments extend into the molding compound of the hub body without cutting through the conductor blank. This is achieved by opening the radial grooves provided on the rear side of the conductor blank, these grooves being broader than the separating cuts and filled with molding compound, before the annular carbon disk is mounted on the composite part of conductor blank and hub body. As a result, the annular carbon disk bears directly against molding compound of the hub body in the region of the opened radial grooves.
In contrast to the situation in the flat commutator made according to German Unexamined Application (DE-OS) 19652840, for example, none of the copper of the conductor segments is exposed in the region of the air gaps separating each two carbon segments in the flat commutator known from WO 97/03486. Similarly, long-term damage to the conductor segments and/or to the solder layer joining them to the copper segments is not ruled out.
In view of this disadvantage, the object underlying the present invention is to provide a method of the class in question that is suitable for producing flat commutators with extremely long useful life.
SUMMARY OF THE INVENTION
This object is achieved according to the present invention in that the annular fixation ridge is produced in such a way that its outside diameter decreases in machining direction, and in that the annular carbon disk is adhesively bonded to the machined end face of the composite part comprising conductor blank and hub body. The adhesive bond between the annular carbon disk and the composite part comprising conductor blank and hub body that is characteristic of the present invention leads in several ways to increased useful life of the inventive flat commutator, compared with such prior an devices. One of the obvious principles of action is that the adhesive bond provided according to the invention does not act merely between the conductor blank, especially the end face thereof, and the corresponding regions of the annular carbon disk as is known for the soldered joint used in the prior art; instead, the adhesive bond also extends to those regions in which the annular carbon disk bears against the molding compound of the hub body. In particular, this is true for the area of contact between the annular carbon disk and a central fixation ridge made of molding compound. An annular pocket suitable for receiving adhesive is formed by the fact that the fixation ridge tapers in the axial direction.
Besides the longer useful life, an advantageous secondary effect resulting from application of the present invention is that the effort associated with production of the flat commutator is less than in application of known methods. The main reason for this is that there is no need for the laborious pretreatment which, in the prior art, must be performed on the annular carbon disk in order to make it amenable to soldering at all. In particular, the annular carbon disk does not have to be metallized, for example by vapor deposition of a thin copper layer.
Finally, the present invention also proves to be advantageous in that, by suitable choice of adhesive, it is possible to reduce the risk which exists in the prior art that, during welding of the winding ends to the conductor segments, the temperature thereof will exceed the softening point of the solder, thus allowing the carbon segments to slip out of position,
Especially when, in a first preferred improvement of the inventive method, the radial grooves are already opened during machining of the end face of the composite part, the adhesive bond provided according to the invention and extending over the entire machined end face of the composite part comprising conductor blank and molded body therefore also acts between the annular carbon disk and the molding compound filling the opened radial grooves. Because of the robust mechanical joint—which is not possible during application of the previously used soldering method—between the annular carbon disk and the molding compound filling the grooves, any bursting of the carbon in the region of the transitions to the molding compound while the separating c
Bachauer Gerhard
Drmota Marjan
Hoell Johann
Kumar Ludvik
Potocnik Jose
Arbes Carl J.
Katten Muchin Zavis & Rosenman
Kolektor D.O.O.
Phan T. D.
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