Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-10-19
2001-05-01
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S256000, C310S254100, C310S089000
Reexamination Certificate
active
06225714
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric motor, and, more particularly, to a permanently excited direct current electric motor comprising a housing carrying a magnetic pole and a grounding ring arranged on it.
2. Prior Art
Grounding or short-circuiting rings made from magnetically conducting material, e.g. from steel, are used in permanently excited direct current motors, in order to conduct the magnetic flux of the permanent magnet to the stator. Furthermore, the motor housing itself, or an additional steel ring, may be employed for this purpose.
A motor housing of a small electric motor is known from German Patent Document DE 28 10 21 5 A1, in which a housing carrying a permanent magnetic sector of a stator is made from corrosion-resistant galvanized steel plate. A grounding ring that is similarly made from corrosion-resistant steel plate is arranged on the housing in order to provide a sufficiently large grounding cross-section for conducting the magnetic flux in a motor of greater power.
In another known small motor described in German Patent Document DE 42 24 628 A1 the pole housing carrying the magnetic pole is made from a corrosion-resistant sheet metal, for example from galvanized steel plate, and has a grounding ring made from a similar corrosion-resistant sheet metal material on its outer side. Fins that are folded around the wall of the pole housing without play are cut into the end faces of the cylindrical grounding ring, so that the grounding ring is at least secured axially on the pole housing.
In operation of this sort of motor the vibrational modes of the housing itself or of the grounding ring-housing system may be easily excited, so that the housing and/or the grounding ring-housing system generates sound transmitted by the surrounding air at the eigenfrequencies of the housing or the grounding-ring housing system. Additional damping devices and/or damping measures are usually required to take care of this undesirable situation.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved electric motor, especially an improved direct current motor, having reduced noise or sound generation.
These objects, and others that will be made more apparent hereinafter, are attained in a permanently excited direct current electric motor comprising a housing carrying a magnetic pole and a grounding ring arranged on the housing.
According to the invention the grounding ring is made from a thread-form or wire-form magnetically conductive material.
The electric motor according to the invention has the advantage that the additional damping devices and/or damping measures mentioned hereinabove are not needed or included, since the grounding ring is made from a thread-form or wire-form magnetically conductive material, preferably from a woven or knitted article consisting of the magnetically conductive material, which acts both to conduct the magnetic flux and also to damp the vibrations of the housing. The grounding ring thus acts as a vibration quenching device so that secondary sound damping and/or sound absorbing measures can be avoided.
The term “wire-form” means that the magnetically conductive material consists of wires made of the magnetically conductive material and the term “thread-form” means that the magnetic conductive material consists of threads of the magnetically conductive material.
Further features and improvements are part of preferred embodiments described in the following description and claimed in the following dependent claims.
It is particularly advantageous when the grounding ring is made from a ferromagnetic material, preferably knitted from steel wire. The preferred embodiment of the grounding ring using the steel wire simultaneously provides good sound insulating and good sound absorbing properties, since, on the one hand, vibrations of the housing are damped by the mass of the grounding ring and, on the other hand, vibrations are hardly conducted at all by the knitted structure, which thus has a sound insulting effect, while the magnetic properties in contrast are not impaired.
In another embodiment of the invention the grounding ring is connected under tension or tensionally connected to the housing. A good mechanical and magnetic coupling may be attained in this way, so that the grounding ring may reliably fulfill is its dual purpose.
Although it is possible to wind a knit article made from thread-form or wireform magnetically conductive material in one or more layers around the electric motor housing carrying the magnetic pole, according to a preferred embodiment of the invention the grounding ring is made from a seamless circular or round knit article. Because of the structure of this embodiment it is especially simple to mount the grounding ring on the housing, because the grounding ring only needs to be pushed on the housing like a tightly fitting stocking. The knit article usually has some elasticity in the direction of the row of knitted loops, thus in the circumferential direction around the circular or round knit article, so that it will just fit around the housing when it is suitably designed according to the dimensions of the housing in order to achieve the required fit around the housing.
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patent: 2667591 (1954-01-01), Gindroz
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patent: 4385251 (1983-05-01), Mallick et al.
patent: 4528473 (1985-07-01), Tezuka
patent: 4619588 (1986-10-01), Moore, III
patent: 5391954 (1995-02-01), Takehara et al.
patent: 5698918 (1997-12-01), Shinoda et al.
patent: 5903083 (1999-05-01), Mukai et al.
patent: 28 10 215 (1979-09-01), None
patent: 42 24 628 A1 (1994-01-01), None
Agnon Reuben
Allgeier Christian
Brass Otto
Lehnert Walter
Dinh Le Dang
Ramirez Nestor
Robert & Bosch GmbH
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