Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-09-24
2003-09-09
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S235000, C029S597000
Reexamination Certificate
active
06617743
ABSTRACT:
The present invention relates to a flat commutator for an electrical machine, comprising a support body made of an insulating molding compound, a plurality of conductor segments and an equal number of carbon segments, which are disposed at the ends and are connected in electrically conductive relationship to the conductor segments. The present invention also relates to a production method as well as to a conductor blank and a carbon disk for use in production of such a flat commutator.
Flat commutators of the type cited in the foregoing are found in many different versions in the prior art. Examples in this connection are published in U.S. Pat. No. 5,175,463 A1, German Utility Model 98007045 U1, German Patent 19752626 A1, U.S. Pat. No. 5,255,426 A1, German Patent 19652840 A1, International Patent WO 97/03486, German Patent 19601863 A1, German Patent 4028420 A1, European Patent 0667657 A1, U.S. Pat. No. 5,442,849 A1, International Patent WO 92/01321, German Patent 19713936 A1, U.S. Pat. No. 5,637,944 A1 and German Patent 19713936 A1. Further pertinent prior art can be found in U.S. Pat. No. 5,629,576 A1, German Patent 19903921 A1 and European Patent 0935331 A1. The large number of protective rights relating to flat commutators with carbon running surfaces proves the great need for practical commutators of this design, which are used in particular to drive fuel pumps in motor vehicles. At the same time, it can be inferred from the large number of publications that there exists a large number of problems, which have not yet been solved satisfactorily.
One of the reasons for this situation is that different and partly conflicting requirements exist for known flat commutators of the class in question; they include in particular the objectives of small dimensions, low manufacturing costs and long commutator life. A particularly serious conflicting relationship among those cited above exists between reducing the dimensions and lengthening the life of the flat commutator, since the wires of the rotor winding are generally welded to the conductor segments. If the dimensions of the flat commutator are too small, the electrically conductive connections of the conductor segments to the carbon segments can easily be damaged by overheating, in turn leading to reduced life of the flat commutator. The reality is that, if the known flat commutators described in the documents cited above are based on a soft-soldered electrically conductive connection between the carbon segments and the conductor segments, they are not used in practice because of the aforesaid problems and the resulting unsatisfactory life. This is the background for proposals such as using a silver solder having resistance to high temperature to connect the carbon segments to the conductor segments (see European Patent 0935331 A1) or to position the contact points between conductor segments and carbon segments relatively far from the leads of the rotor winding (see German Patent 19903921 A1). The first of these proposals is burdened with additional costs, however, and the second proposal involves larger dimensions of the commutator.
The object of the present invention is to provide a flat commutator of the type cited in the introduction that can be produced relatively inexpensively and at the same time has a long life despite relatively small dimensions. Another object of the present invention is to provide a method for production of such a flat commutator as well as particularly expedient intermediate products used in such a production method.
The object stated in the foregoing is achieved according to the present invention by the fact that, in a flat commutator of the type mentioned in the introduction, the conductor segments are each provided with a thick-walled terminal region disposed on the periphery of the support body, a contact region, which is also thick-walled, disposed between the support body and the associated carbon segment, and a thin-walled transition region disposed between the terminal region and the contact region. In other words, what is of substantial importance for the inventive flat commutator is that the conductor segments are no longer constructed with more or less constant wall thickness throughout, but instead the wall thicknesses of different regions of the conductor segments differ significantly from one another, specifically in that a relatively thin-walled transition region is provided between the terminal region used as the terminal of the rotor winding and the contact region via which the electrically conductive connection of the conductor segment is established to the associated carbon segment. In each case the wall thickness—determined perpendicular to the heat-flow direction—of the transition region is smaller than the wall thickness—measured in radial direction—of the terminal region and the wall thickness—measured in axial direction—of the contact region of the conductor segment in question, in addition to which the terminal region also has relatively large dimensions in axial and in peripheral direction (see below). Such a configuration of the conductor segments ensures in particular that welding of the winding wires to the terminal regions of the conductor segments does not cause overheating damage to the electrically conductive connections of the conductor segments to the carbon segments even in extremely compact flat commutators having the smallest dimensions, since the thick-walled terminal regions of the conductor segments represent, by virtue of their high heat capacity, a first heat sink for the heat developed during the welding process. In contrast, by virtue of its small cross-sectional area—normally aligned with the heat flow—for heat conduction from the terminal region to the contact region of the conductor segments, the thin-walled transition region from the terminal region to the contact region forms a considerable resistance. And, in turn, the thick-walled contact region forms an excellent heat sink for the thermal energy (which in any case is reduced) conducted through the transition region. The outcome is that the contact region of the conductor segments is not heated nearly as severely during welding of the wires of the rotor winding to the conductor segments as is known from the prior art. When conventional welding techniques are used in combination with the present invention, the maximum temperatures occurring at the connection of the conductor segments to the carbon segments can be lowered by 50° C. or even more compared with known flat commutators belonging to the class in question. Consequently, the danger that the electrically conductive connections of the carbon segments to the conductor segments will be damaged during welding of the rotor winding to the flat commutator is decisively reduced. By application of the present invention, it is even possible permanently to connect the carbon segments electrically to the conductor segments by soft soldering, since the temperatures occurring at the contact point remain reliably under the softening point for soft solder. This is true even for extremely compact flat commutators. In this connection, another benefit of the application of the present invention is that the need no longer exists to position the electrically conductive connection of the carbon segments to the conductor segments as far as possible from the terminal regions of the conductor segments, which heretofore has frequently led to relatively small contact areas, disposed in radially inner position, between the carbon segments and the conductor segments. To the contrary, by application of the present invention, it is entirely possible to establish large-size contact areas between the conductor segments and the carbon segments, with favorable consequences for the life of the connection in question.
Incidentally, the resistance to thermal conduction (see above) of the thin-walled transition region explained in the foregoing and provided according to the invention between the terminal region and the contact region of each conductor segment is not its only advan
Drmota Marjan
Potocnik Joze
Katten Muchin Zavis & Rosenman
Kolektor D.O.O.
Tamai Karl
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