Cut-out brush for electric hand tool

Details Cut-out brush for electric hand tool Cut-out brush for electric hand tool

1999-04-20

2000-07-11

Ramirez, Nestor

Electrical generator or motor structure

Dynamoelectric

Rotary

310248, 310251, H02K 1310, H01R 3958, H01R 3938

Patent

active

060877545

DESCRIPTION:

BRIEF SUMMARY
PRIOR ART

The invention is based on a manual electric machine tool as generically defined by the preamble to claim 1.
From German Published, Non-Examined Patent Application DE-OS 43 21 475, a carbon brush for direct current electric motors is known, which in the region of its head part has two axial, stepped continuations that each act as a socket for one current-carrying pigtail lead. Between the continuations, a bearing face of fabric-base laminate for a pressure element and a damping overlay located beneath it is provided; the pressure element is intended to press the carbon brush against the commutator. The continuations protrude axially past the bearing face for the pressure element by only approximately 5% of the total length of the carbon brush. As a result, the known carbon brush has the disadvantage that it does not extend even nearly as far as the structural height of the pressure element or contact-pressure spring, or in other words as far as the axially farthest outward region thereof. Thus the region of the carbon brush that determines the service life of the carbon brush is relatively short, and thus the service life of the carbon brush is also relatively short. The outer diameter, determined by the position and size of the contact-pressure spring, of the electric motor equipped with the corresponding carbon brushes, and the corresponding housing region of the manual electric machine tool equipped with such a motor, is relatively large and is in no way optimal for a handle of the tool if the motor housing acts as a handle. An optimal, that is, the smallest possible, handle circumference of the manual electric machine tool is feasible only at relatively great difficulty, because there are limits to miniaturizing the collector diameter and the carbon brush length. The length of the carbon brush is determined by the difference between the collector radius and the outer radius of the housing, minus the spring protrusion (structural height) relative to the housing.
The known carbon brush is therefore too short for power tools whose handle is formed by the motor housing.
The known carbon brush also has no turn-off device that improves the safety of the power tool and that further reduces the usable carbon brush lengths, and so if the turnoff device were built into the known carbon brush, its running time would be even shorter than without the turn-off device.


ADVANTAGES OF THE INVENTION

The power tool of the invention having the characteristics of the body of claim 1 has the advantage over the prior art that with the turn-off device installed it is longer by 2 to 3 mm, so that the running time of the power tool until the next time the carbon brush has to be changed is lengthened by approximately 20 to 30 hours.
Because the spring means are embodied as a spiral spring, minimal installation space in the motor housing can be fully utilized for the maximum length of the carbon brush.
Because the spiral leaf spring is secured with its support arm region in a groove of the carbon brush position, it is assured that the carbon brush will be securely pressed in the direction of the carbon brush until the turn-off device responds, so that sparking and fire damage to the commutator can be precluded.
Because the head of the carbon brush is lengthened, the guidance performance with increasing wear and shortening of the carbon brush is better than in the earlier carbon brushes, because its guide faces are longer.
Because the flat side of the spiral spring is disposed substantially parallel and close to the narrow side of the carbon brush, an especially compact design of the brush holder is possible.


DRAWING

Exemplary embodiments of the invention are described in further detail in the description below in conjunction with the associated drawing.
Shown are
FIG. 1, a power tool embodied as a right angle grinder, having the carbon brushes of the invention, in fragmentary longitudinal section;
FIG. 2, the right angle grinder of FIG. 1 in a view from above with the motor housing partly cut away;
FIG. 3, the cro

REFERENCES:
patent: 2016173 (1935-10-01), McNeil
patent: 2454562 (1948-11-01), Linke
patent: 2813208 (1957-11-01), Ritter
patent: 3681635 (1972-08-01), Bayer
patent: 3908142 (1975-09-01), Gaudry
patent: 5648706 (1997-07-01), Polk et al.

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