Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1996-05-06
1998-09-15
Stephan, Steven L.
Electrical generator or motor structure
Dynamoelectric
Rotary
310251, 310252, 310245, 310242, H02K 1300
Patent
active
058083944
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to carbon brushes for an electric motor and more particularly relates to carbon brushes having a bar-shaped design and feature an essentially rectangular cross-section.
BACKGROUND OF THE INVENTION
In brush designs, typically one of the ends of the bar has a front frontal surface which is abutted against a commutator. On the other end of the bar, there is a rear frontal surface which supports a spring which presses the front frontal surface against the commutator.
The carbon brush is typically guided in a tubular brush holder the inside cross-section of which is the same as that of the carbon brush itself, with a relatively large play being provided in the regular case. Too small a play would imply excessive precision demands on the manufacture of the brush holder. Generally, the brush holder is mounted on a carbon-brush holder plate extending perpendicularly to the axis of the commutator. The brush holder itself, on its part, stands perpendicularly on the carbon-brush holder plate so that the side surfaces of the carbon brushes extend parallel to the axis of the commutator.
Usually, the circumference of the commutator features several commutator bars separated from one another by slits. The commutator bars and slits extend parallel to the commutator axis. As a result of this arrangement the edge between the front frontal surface of the carbon brush and the side surface of the carbon brush is passed over its entire length over a slit at the same time. With the commutator revolving, this action will be repeated in quick succession. It is easy to see that, like in the case of a ratchet, noises result from this action. At the same time, fluttering movements of the carbon brush will be induced within the brush holder which will likewise produce noises.
It is thus an object of this invention to design the carbon brushes so that as few noises as possible will form when the brushes are used in an electric motor. Thus, the electric motor will become particularly suitable for applications in the automotive industry, e.g., for driving wipers or other independently operating vehicle systems.
In order to accomplish this object, this invention suggests that the outer contour of a cross-section near the front frontal surface be trapezoidal. As a result, the edge between the front frontal surface and the side surface will slope so that, over the major part of its length, the edge will be supported by the respective adjacent commutator bars when overriding a slit. Only a small portion of the edge will actually be over a slit. It is easy to see that the rathet effect known from prior art cannot come up here.
It has been found out that it will be completely sufficient to give only the front part of the carbon brush this design. In the rear part, it is possible to maintain a rectangular cross-section which will ensure that the carbon brush is guided in the brush holder. In general, it will be completely sufficient if about 10% of the length of the carbon brush has a trapezoidal cross-section, with the slope of the side edges becoming less and less towards the rear so that there will be a slow transition from the trapezoidal into the rectangular area.
As already explained, on the one hand, the noise reduction is based on avoiding the ratchet effect as the carbon brush slides over the commutator surface. On the other hand, in this way, the fluttering movements of the carbon brush within the brush holder will be induced only in a more reduced manner. A measure for stopping the remaining fluttering movements and vibrations consists in tilting the carbon brush within the brush holder. This can be done in different ways. One way is to incline the rear frontal surface towards the top and bottom surfaces of the carbon brush, on the one hand, and towards the side surfaces, on the other hand. The force of the spring will then no longer act in a straight line but rather with a slight skew so that a lateral force will be applied which will press the carbon brush against the side walls, or rather
REFERENCES:
patent: 2206366 (1940-07-01), Redmond
patent: 3075111 (1963-01-01), Starre
patent: 3791331 (1974-02-01), Dilley
patent: 4800313 (1989-01-01), Warner et al.
patent: 4924129 (1990-05-01), Copus
Search Report of the German Patent Office for Application No. P4329753.6.
English Translation of the International Preliminary Examination Report for Application PCT/EP94/02865.
ITT Automotive Europe GmbH
Lewis J. Gordon
Stephan Steven L.
Twomey Thomas N.
Williams Timothy A.
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