Brush having inclined grooved contact surface

Details Brush having inclined grooved contact surface Brush having inclined grooved contact surface

1997-10-21

1999-06-01

Ramirez, Nestor

Electrical generator or motor structure

Dynamoelectric

Rotary

310248, 310252, 310 51, H02K 1300

Patent

active

059090774

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The invention pertains to a carbon brush for an electrical machine having a collector.


BACKGROUND OF THE INVENTION

Numerous brushes of this type have been disclosed, e.g., in DE 31 48996.
One problem in the construction of such brushes can be seen in the fact that the unit consisting of the brush and the collector generates noise during the operation. This noise is caused by the contact surface of the brush sliding along the surface of the collector such that the lamellar structure of the collector surface induces vibrations that cause airborne sound that are perceived as noise. Numerous proposals pertaining to the reduction of this noise have been disclosed. In all new proposals, it must be observed that the contact resistance between the brush and the collector cannot be excessively small. In addition, the brush should have a sufficient resistance to abrasion, i.e., the brush cannot be excessively soft.
According to one proposal, the contact surface is inclined relative to the axis of the collector or the outer surface of the collector. In this case, the contact surface is correspondingly beveled. However, this results in a sharp-edged transition between the contact surface and the lower lateral edge of the brush, i.e., the brush merely adjoins the collector with one edge during the initial phase of operation.
In brushes of this type, the hard surface produced during the pressing of the graphite mixture is usually not removed and the attainable noise reduction is quite low. If the surface skin of the brush is removed after the pressing, it is possible that the edge will break.
It is also known to provide the contact surface of the brush with longitudinal grooves over the entire surface. These grooves extend in the transverse direction, i.e., in the circumferential direction of the collector. However, this measure results in an insignificant reduction in the noise level.
According to the invention, it is proposed to incline the contact surface relative to the axial direction of the collector, and to provide the contact surface with one or more grooves that extend in the transverse direction within the lower region, with said grooves being machined into the surface while the hard surface skin is simultaneously removed.
It was established that two or three grooves are sufficient, with the lowest groove being open toward the bottom. The contact surface is curved in accordance with the cylindrical surface of the collector. The incline of the contact surface relative to the outer surface of the collector lies on the order of 6-10 degrees, preferably at approximately 8 degrees. The ideal incline depends on the fact that electric currents should be transmitted by the brush, as well as other factors.
For example, ideal inclination decreases proportionally with the intensity of the electric currents to be transmitted.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a , 1b and 1c show a carbon brush viewed from different directions, and
FIG. 2 shows a portion of the carbon brush illustrated in FIG. 1a in greater detail.


DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The carbon brush 1 shown in the figures consists of an oblong cuboid body that has an approximately square shape if viewed from a cross section (FIG. 1b) and an approximately rectangular shape if viewed from a longitudinal section (FIG. 1a).
Such a carbon brush is provided with a shunt 2 that serves as the conductor for delivering electrical current to brush 1. The brushes are guided in cartridge-type brush holders that are arranged on a brush carrier plate.
One surface of the brush, namely, the contact surface 3, is in contact with the outer surface of a collector 4 after the assembly of the motor.
The embodiment comprises a cylindrical collector, with the contact surface of the collector being arranged on its outer surface. The contact surface 3 of the brush 1 is in contact with the outer surface/contact surface of the collector 4.
The contact surface 3 of the brush 1 is realized by curving the contact surface 3 in the transverse d

REFERENCES:
patent: 2296366 (1942-10-01), Redmond
patent: 3467846 (1969-09-01), Reille
patent: 5019741 (1991-05-01), Fukui et al.
patent: 5414319 (1995-05-01), Nowicki et al.
German Search Report for Application No. 195 33 031.5 dated Dec. 27, 1995.
English translation of the International Preliminary Examination Report of Application No. PCT/EP96/00001 filed Jan. 2, 1996.

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