US3034006A

US3034006A - Shockproof brush holder assembly

Info

Publication number: US3034006A
Application number: US796430A
Authority: US
Inventors: Harold O Short
Original assignee: Black and Decker Manufacturing Co
Current assignee: Black and Decker Corp
Priority date: 1959-03-02
Filing date: 1959-03-02
Publication date: 1962-05-08
Anticipated expiration: 1979-05-08

Description

y 8, 1962 H. 0. SHORT 3,034,006

SHOCKPROOF BRUSH HOLDER ASSEMBLY Filed March 2, 1959 2 Sheets-Sheet l INVENTOR. HAROLD 0. SHORT May 8, 1962 Filed March 2, 1959 H. 0. SHORT SHOCKPROOF BRUSH HOLDER ASSEMBLY FlG-3 2 Sheets-Sheet 2 INVENTOR. HAROLD 0- SHORT United States Patent 3,034,006 SHOCKPROOF BRUS HOLDER ASSEMBLY Harold 0. fihort, Towson, Mi, assignor to The Black and Decker Manufacturing Company, Towson, Md, a corporation of Maryland Filed Mar. 2, 1959, Ser. No. 796,430 2 Claims. (Cl. 310247) The present invention relates to a brush holder assembly for an electric motor, and more particularly, to a shockproof brush holder assembly capable of withstanding extreme environments of shock and vibration.

The present invention will be described with refer ence to an electric tool of the percussive type; but it is to be understood that the essenceof the present invention is not to be limited thereby, but is to be adaptable to any application wherein the brush holder assemblies are subjected to extreme and unusual conditions of impact shock, vibrations, and various mechanical forces.

In a high-capacity portable electric hammer, for example, of the type capable of drilling a two inch cylindrical hole in solid concrete four inches deep in one minute, the shock and mechanical recoil forces operating upon the tool are necessarily tremendous; and the result is such that the tool is self-destructive and breaks down after continuous usage of approximately 50 hours. A habitual cause of tool failure are the brush holder assemblies for the electric motor, which heretofore, had to be replaced or repaired in about every 50 hours. For example, the brush cap (no matter how tightly threaded) would soon become loosened, or the brush spring would soon buckle and thus fail to force the brush firmly against the motor commutator, or in general, the various parts would soon become loose and quickly disengage. The relative movement between the loose parts would rapidly precipitate an early failure, or quite often, the entire brush holder assembly would simply pop out of the motor casing.

Accordingly, it is the general object of the present invention to provide a rugged, reliable brush holder assembly capable of withstanding extreme shocks and vibra- 3,034,906 Patented May 8, 1962 inder is lightly press-fitted into the motor casing to allow the protruding brush to make sliding contact with the motor armature in the conventional manner. A suitable roll-pin is lodged between the outer cylinder and the motor casing, transversely to the axis of the cylinder, so as to lock the cylinder within the casing; and an outer continuous steel band is secured directly to the motor casing and is positioned over the cylinders to preclude their escape from the motor casing. Means are then provided to make a suitable electric contact with the protruding lower portion of the inner conducting cylinder.

The present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is an exploded view of the brush holder assembly, showing in pictorial view all of the parts, with tions and yet render full performance for at least 500 hours.

It is a specific object of the present invention to provide a simple, but rugged, brush holder assembly capable of being manufactured easily and economically.

In accordance with the teachings of the present invention, two concentric hollow cylinders are nested and firm- 1y press-fitted within each other in such a manner whereby the inner cylinder is recessed below and protrudes below the outer cylinder. The inner cylinder is made of a conductive material, such as brass, and functions as a brush holder insert; while the outer cylinder is made of a suitable insulation material, such as fibre, and acts as an insulated outer sleeve. The lower portion of the inner conducting cylinder has an axial rectangular slot machined therein so as to snugly and slidably house a rectangular carbon brush which protrudes therefrom; while the upper portion of the inner conducting cylinder has an axial counterbore, which communicates with the axial rectangular slot and which is internally-threaded. Each cylinder has a suitable cap secured thereto, and each cap is provided with external threads adapted to engage the internal threads of the respective cylinders. The cap for the inner cylinder is known as the brush cap, and it is made of a suitable conducting material. Lock washer means are provided to hold the brush cap securely in place. The brush cap is provided with a blind axial bore, which is adapted to fully guide the conventional brush spring and shunt. The cap for the outer cylinder is made of a suitable insulating material, such as hard fibre, and engages the inner threads of the outer cylinder. The outer cylthe exception of the outer steel band;

FIGURE 2' is a view of the type of electric tool in which the present invention is used; and

FIGURE 3 is a view taken at line 33' of FIGURE 2.

With reference to FIGURES l and 3, an insulated outer sleeve 1 (in the form of a hollow cylinder) has counterbored portion 2 that is provided with suitable internal threads 3. Outer sleeve 1 is made of a suitable insulation, such as hard fibre. A brush holder insert 4, made of brass or other suitably conducting material, is likewise made in the general form of a hollow cylinder. Brush holder insert 4 is adapted to be nested and firmly pressfitted within outer sleeve 1 in such a manner whereby brush holder insert 4 is recessed below and protrudes below outer sleeve 1, as shown more particularly in FIG- URE 3. Other means of securing brush holder insert 4 within outer sleeve 1 may also be used, but a tight press-fit is recommended for ease and economy of manufacture. An axial rectangular slot 5 is broached or otherwise machined within the lower portion of brush holder insert 4, while the upper portion of brush holder insert 4 has an axial counterbore communicating with the axial rectangular slot 5 and being provided with suitable internal threads 6.

The axial rectangular slot 5 is adapted to snugly and slidably house brush 7, which is a rectangular block of carbon or other suitably conducting material. Brush 7 has a cylindrical collar 8 integrally-fashioned thereon; and the lower portion of helical, coiled spring 9 seats upon collar 8 and extends longitudinally therefrom. The opposite end of spring 9 seats upon an annular shoulder on conducting slug 10. A twisted, stranded copper wire is secured to collar 8 of brush 7 and extends therefrom within spring 9 to be secured at its opposite end to conducting slug 16, thus forming a suitable shunt 11 that provides a low-resistance electrical path to brush 7. Brush 7, collar 8, spring 9, slug 10, and shunt 11 thus comprise the brush, spring, and shunt subassembly 12.

A brush cap 13, made or brass or other suitably conducting material, has a generally cylindrical surface on which external threads 14 are fashioned so as to mate with the internal threads 6 in brush holder insert 4. Brush cap 13 has a blind axial bore 15 (shown more particularly in FIGURE 3), which is adapted to house and fully-guide spring 9. Slug 10 seats upon and makes finm electrical contact with the closed end 16 of blind axial bore 15, as shown in FIGURE 3. Brush cap 13 is seated and engaged within brush holder insert 4 and is securely locked therein by means of an intervening cone lock washer 17. A flanged slotted head 18 is provided to enable brush cap 13 to become easily engaged with brush holder insert 4; and when so engaged, the flanged slotted head 18 of brush cap 13 is recessed below the top of the enlarged upper portion of outer sleeve 1, thus allowing sufilcient room for insulated cap 19 to become seated within the enlarged upper portion of aesspoe 3 outer sleeve 1. It will be appreciated from an examination of the drawings, particularly FIGURE 3, that the counter-bored internally-threaded portion 2 of outer sleeve 1 constitutes an internal annular shoulder, that the counterbored internally-threaded portion 6 of inner sleeve 4 has an outwardly-projecting annular flange seated upon the internal annular shoulder, and finally, that the conducting brush cap 13 has an outwardly-projecting annular flange seating upon the annular flange of the inner sleeve, thus aiiording not only good electrical contact, but also, an additional mechanical support by means of the cone lock washer 17 disposed therebetween. Insulated cap 19 is suitably slotted and provided with external threads to allow it to be readily seated and engaged within the internally-threaded enlarged upper portion of outer sleeve 1.

As shown in FIGURE 3, outer sleeve It (when assembled to brush holder insert 4, brush, spring, and shunt subassernbly 12, cone lock washer 17, brush cap 13, and insulated cap 1'9) is lightly press-fitted within casing 20 of motor 21; and a roll-pin 22 made of. spring steel or other suitable material is lodged within the transverse notch 23 so as to lock outer sleeve 1 against casing 20. Smooth-surfaced transverse roll-pin 22 is more desirable than a locking screw or bolt having external threads. Otherwise, the inherent vibrations (however minute) would cause the external threads of the screw or bolt to cut and dig into and scrape against the fibre surface of outer sleeve 1; and thus, within a relatively short period of time, such a locking means would be ineffectual to hold outer sleeve 1 within casing 20'. As shown in FIGURE 3, outer sleeve 1 is directed radially inward in such a manner whereby the lower edge of protruding brush 7 makes sliding contact with com mutator 24 of motor 21, with sufiicient pressure being exerted on brush 7 by means of spring 9.

As shown in FIGURES 1 and 3, electrical connection to brush 7 is made by means of a conventional brush lead terminal spring 25, which comprises a helical coiled spring folded back upon itself so as to form a circular, flexible terminal conductor capable of being enlarged and snapped over the protruding bottom portion of brush holder insert 4. An annular recess 26 is formed on brushholder insert 4 so as to accommodate brush lead terminal spring 25. When brush lead terminal spring 25 is folded back upon itself (as shown in FIGURE 1) two extended portions thereof mesh within each other at 27, and the end of an electrical connector is inserted therein and soldered in place to hold brush lead terminal spring 25 together and keep the extended portions 27 from separating. The electrical connection is thus made from electrical connector 23 to brush lead terminal spring 25 and via brush holder insert 4, brush cap 13, conducting slug 10, and shunt 11 to brush 7. A hard fibre washer 29 is predisposed between the end of outer sleeve 1 and brush lead terminal spring 25 to prevent any dirt or conducting foreign substances from providing an electrical path from brush spring terminal spring 25 to casing 20.

Finally, a continuous steel band 30 is placed around the casing of motor 21 and is positioned over cap 19 as shown in FIGURES 2 and 3, Band 291 is secured to casing 20 by means of four screws 31, each being provided with suitable lock washers 32; and band 29 thus provides an additional means of maintaining the brushes within casing 20, i i i A v To recapitulate briefly on some of the advantageous features of the present invention, spring 9 is fully-guided (not merely partially guided) within blind axial bore 15 of brush cap 13 so that it cannot buckle and cannot fail to provide the necessary continuous pressure on brush 7. Brush cap 13 is locked to brush holder insert by means of cone lock Washer 17. An additional cap 19 (made of hard fibre insulation) is secured within outer sleeve 1. A smooth-surfaced transverse spring-steel rollpin 22 (not an externally threaded screw) prevents outer sleeve 1 from becoming dislodged from casing 20. Finally, should the previous components become loose and disengaged from each other, steel band will prevent the overall assembly, or any of the components thereof, from flying out of casing 26. The result is a muchneeded shockproof brush holder assembly fully-capable of rendering at least 500 hours of trouble-free service (rather than merely 50 hours) under extreme conditions of shock and vibration, such as those encountered in a portable electric hammer.

Obviously, minor modifications and improvements may be made without departing from the basic spirit of the present invention. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described.

I claim:

1. A shockproof brush holder assembly for an electric motor having a motor casing, comprising, an outer insulated sleeve including an internally-threaded counterbored upper portion having an internal annular shoulder, an inner conducting sleeve firmly press-fitted within said outer sleeve and having a lower portion protruding below said outer sleeve, said inner sleeve including an internally threaded counterbored upper portion having an outwardly-projecting annular flange seated upon said internal annular shoulder of said inner sleeve, an externallythreaded conducting cap seated within said counterbored portion of said inner sleeve, said conducting cap having a blind axial bore and further having an outwardly-projecting annular flange seated upon said annular flange of said inner sleeve, whereby a brush, spring, and shunt subassembly may be housed within said bore of said cap and said inner sleeve, and an externally-threaded insulated cap seated within said counterbored portion of said outer sleeve.

2. A shockproof brush holder assembly according to claim 1, wherein means, including an outer continuous band secured to the motor casing directly above he brush holder assembly, are provided to preclude the brush holder assembly from movement outwardly of the motor casing. I I l References fired in the file of this patent