Tubular brush holder

Details Tubular brush holder Tubular brush holder

2002-04-30

2004-10-05

Nguyen, Tran (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S242000, C310S245000, C310S251000

Reexamination Certificate

active

06800981

ABSTRACT:

DESCRIPTION OF THE INVENTION
The present invention proposes a new brush holder for metal fiber and metal foil brushes. It is designed to guide the brush in axial direction as it wears even while a constant light brush pressure is exerted and a large current is conducted to or from the brush at very low electrical resistance. The invention is depicted in
FIGS. 1A
to
1
E and is called the “tubular brush holder.”
In the version of
FIGS. 1A and 1B
, fiber brush
27
is conductively fastened to metal baseplate
28
and is pushed forward in electrically conductive brush box
29
by constant force spring
37
so as to load brush
27
against rotor
2
with the desired brush force. At least one of the four long sides of the inside of brush box
29
is lined in an electrically conductive manner with resilient multi-contact metal material
47
, i.e., in the form of metal velvet, metal felt, strands of fine metal fibers, metal fibers combined in the manner of textiles, e.g., through weaving or knitting or any other. At least one metal guide
38
is rigidly, electrically conductive attached to base plate
28
in such a manner that it is parallel to at least one side of the brush box that is lined with resilient multi-contact metal material
47
and is disposed so that it guides fiber brush
27
along the inside of brush box
29
while the brush wears.
Low-resistance electrical contact is established between the at least one guide
38
and at least one multi-contact metal material by means of at least one compression spring
54
(in this case depicted as helical springs
54
(
1
) and
54
(
2
) extending between guide
38
and a thin low-friction plate
39
that is flexibly hinged to baseplate
28
disposed so that it is parallel to the at least one metal guide
38
. Teflon may be a particularly suitable material for hinged low-friction plate
39
. For further stabilization of the brush motion, the remaining inner surfaces of the brush box may be provided with low-friction liner or the edges of base plate
28
may be lined with a low-friction material such as Teflon. Such a liner is indicated by number
56
.
The spring action between guide
38
and hinged low-friction plate may be provided by at least one conventional spring, e.g., a helical spring, or by at least one constant force spring. The spring force is adjusted to compare with the brush force exerted on fiber brush
27
by means of constant force spring
37
. The friction force due to the described elastic compression of the multi-contact metal material
47
and metal guide
38
will reduce the brush force on fiber brush
27
by about 30% of the force imposed by constant force spring
37
, for the reason that the coefficient of friction between multi-contact metal material and smooth metals is in the range of 0.2 to 0.3.
The contact resistance between brush box
29
and fiber brush
27
via the resilient multi-metal material
47
will be about one half of the electrical resistance between the brush and rotor
2
since static multi contacts have about one half of the resistance of similar sliding contacts under same pressure (compare C. M. Adkins III and D. Kuhlmann-Wilsdorf, “Devleopment of high-performance Metal Fiber Brushes II—Testing and Properties”, Electrical Contacts—1979 (Proc. Twenty-Fifth Holm Conf. On Electrical Contacts, III. Inst. Techn., Chicago, Ill., 1979), pp. 171-184, the entire contents of which is incorporated by reference herein.), provided that the surfaces are clean. This is a requirement that must be fulfilled, either by operating in a protective atmosphere such as humidified CO
2
or making the contact surface between multi contact metal material and slider of noble metal or plating with a noble metal.
In cases of high packing density of brush holders, e.g., as may be the case in homopolar motors, the outside of the brush box should be coated with a nonconductive paint or lacquer, e.g., red stop-off lacquer.
For a particular application, the tubular brush holder designed in
FIGS. 1A and 1B
may be too costly or requires too much space. In fact restricted space for bushes is a perennial problem for homopolar motors since their appeal derives from their potentially large power to weight ratio and, due to the typically low voltage per current turns, they require large numbers of brushes.
FIGS. 1C
to
1
E therefore show simplifications of the concept of the tubular brush holder according to the present invention that are designed both to save space and cost.


REFERENCES:
patent: 3308321 (1967-03-01), Provost, Jr.
patent: 4246508 (1981-01-01), Zimmer
patent: 4267912 (1981-05-01), Bauer et al.
patent: 5114351 (1992-05-01), Hoffmann
patent: 5621262 (1997-04-01), Han
patent: 5631513 (1997-05-01), Coles et al.

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