US3714481A

US3714481A - Brush construction for a small electrodynamic machine

Info

Publication number: US3714481A
Application number: US00142398A
Authority: US
Inventors: H Dijkstra
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1968-10-09
Filing date: 1971-05-11
Publication date: 1973-01-30
Anticipated expiration: 1990-01-30
Also published as: NL6814414A; DE1950584A1; FR2020226A1; CA919238A; GB1239010A

Abstract

A brush-holder assembly for an electrodynamic machine such as an electric motor, with the brush-holder arm urged by a separate leaf spring both axially and laterally.

Description

[ 1 Jan.30,1973

United States Patent [191 Dijkstra [54] BRUSH CONSTRUCTION FOR A [56] References Cited [TED STATES PATENTS SMALL ELECTRODYNAMIC MACHINE [75] Inventor:

Homme Dijkstra, Drachten, Netherlands Schultz................ Van Dijk et al. Mabuchi lll] Edmundson.....

[73] Assignee: Philips Corporation, New

York,N.Y.

22 Filed: Mayl1,l97l 21 Appl.No.: 142,398

FOREIGN PATENTS OR APPLICATIONS Related US. Application Data Continuation of Ser. No. 864,380, Oct. 7, I969,

v abandoned.

8/l966 Great Britain.......................310/239 Primary Examiner-D. F. Duggan Att0rneyFrank R. Trlfari ABSTRACT [30] Foreign Application Priority Data PAIENIED'JAHO I975 3,714,481

INVENTOR.

HOMME DIJKSTRA BY A ENT

one end presses against a rigid point of support of the machine and with its other end resiliently loads the brush-holder arm.

Such a brush construction is known from British Patent Specification l.0l0,244, in which two brushholder arms are arranged one on each side of a commutator in an end shield, each brush holder arm being at a point intermediate the brush and one end of the brushholder arm by a bent leaf spring arranged in the respective end shield, one end of each brush-holder arm pressing pivotably, by means of an arcuate portion,against a pivot pin rigidly secured to the end shield. The force exerted on the commutator by the brush depends on several factors, such as the manufacturing tolerances in the dimensions of the leaf spring and in its location in the end shield, the tolerances with respect to the point at which the leaf spring exerts pressure on the brush-holder arm and finally the angular position occupied by the brush-holder arm, in view of the spring characteristic of the leaf spring. The latter angular position is itself dependent on several manufacturing tolerances in the dimensions and disposition of various component parts and in addition depends on the degree ofwear of the brush.

It is an object of the invention to provide a brush construction of the above-mentioned kind in which the brush pressure is less dependent upon manufacturing tolerances and upon brush wear, and the invention is characterized in that the said resilient load is mainly due to buckling of the leaf spring. While retaining the leaf spring, which is attractive for use in small electrodynamic machines, because of its simplicity and cheapness, the arrangement according to the invention provides a spring characteristic within a comparatively wide range and a brush pressure which only slightly depends on manufacturing and assembling tolerances.

An embodiment of the invention is characterized in that the pivotable attachement comprises a knife-edge bearing and that the leaf spring exerts a force on the brush-holder arm acting in the direction from the knife edge to the supporting surface of the knife-edge bearing. This permits a very simple bearing construction.

A further embodiment of the invention is characterized in that the brush-holder arm is brought out through an aperture provided in the machine and in that the part thus protruding from the machine is extended so as to be capable of being pivoted by hand. This embodiment is of particular importance for the assembly and for the prevention of damage to the frequently small and hence vulnerable brush constructions which are used in the small electrodynamic machines to which the invention relates.

A still further embodiment of the invention for use in combination with one of the two last-mentioned embodiments is characterized in that the bearing surface of the knife-edge bearing and the brush rocker of the machine are an integral unit made of a synthetic material. In such an embodiment the entire brush construction may be mounted on the said brush rocker and only at a later stage of the assembly, the brush rocker with the brush construction mounted on it is mounted in the machine as an integral unit.

The invention will be described more fully with reference to the accompanying drawing, the single FIGURE of which shows an embodiment of the invention.

in the Figure, pivotably secured brush-holderarms 1 form part of a brush construction of a small direct-voltage commutator motor for use in an electric dry-shaving apparatus. The brush-holder arms I carry gauze brushes 2 which are pressed against the commutator 3 of the motor. Each of two leaf springs 4, pressed with one end against a fixed support 5 of the motor at reference point 14, and with its other end against one of the brush-holder arms 1 at reference point 15, so

that these arms are resiliently loaded. The two leaf springs 4 in their unmounted condition are flat having an initial length L defined by a straight line between the ends of the spring and during assembly are given the buckled shape shown in the drawing whereby the spring has a loaded length L defined by a straight line between the ends of the spring, L being obvioisly less than L So that the resilient loading of the brushholder arms 1 is mainly due to the buckling or column loading of the leaf springs, for owing to their elastic properties these springs tend to stretch to regain their flat state. As is obvious from the drawing, the length L of the buckled spring is the same as the distance between reference pointsl4 and 15 established by the frame and the arm 1. It thus follows, that this distance L is less than the initial, unloaded length L of the spring.

The pivotable attachment consists of a knife-edge bearing, and to the leaf springs 4 exert a force on the brush-holder arms which acts in the direction from the knife edge to the bearing surface of the knife-edge bearing. The resilient load imposed on the brush-holder arms 1 by the leaf-springs 4 thus serves-a double pur pose, namely firstly resiliently pressing the gauze brushes 2 to the commutator, and secondly thrusting and fixing the knife edge in the bearing recess which is the supporting surface of the knife-edge bearing.

The brush-holder arms 1 are brought out through a slit-shaped aperture 6 and the part protruding from the machine is extended so as to enable it to be pivoted by hand. By pressing the two ends 7 together between thumb and first finger, the brush-holder arms can readily be lifted from the commutator, simplifying assembly and protecting the comparatively vulnerable and small brush-constructions during assembly.

The bearing surface of the knife-edge bearing is integral with a plastics brush rocker 8 of the motor and forms part of the upper surface of the said brush rocker on either side of the slit-shaped aperture 6, in conjunction with a number of bosses 9. The brush-rocker 8 may previously be provided with the complete brush construction and at a later stage of the assembly may be secured to the end shield 11 of the motor by, means of tapping screws 10. Current is supplied to the brushes consecutively through soldering lugs 12 located under the tapping screws 10, short lengths of stranded wire 13 connected to the brush-holder arms 1 by spot-welding, brush-holder arms 1 and gauze brushes 2.

What is claimed is:

1. In an electrodynamic machine including a frame having a spring-engaging first reference point, an assembly for holding a brush against a commutator, the assembly comprising at least one arm having a first end part pivotally secured to the frame, a remote part holding the brush, and a second reference point along the length of said arm, the assembly further comprising a leaf spring which is generally flat in its unloaded condition defining an initial length between its ends, this spring when assembled being bowed under a buckling load whereby the spring has a first end secured to the frame at said first reference point and the spring has a remote part engaging the arm at said second reference point, the distance between said two points being less than said initial spring length, the spring so loaded exerting a force on the arm both axially along the length thereof and laterally relative to said pivot and thereby resiliently positioning and urging the brush against the commutator, said spring having a spring characteristic which is very level within a comparatively wide range of spring deflection.

2 Apparatus according to claim 1 wherein the frame defines an aperture through which the first part of the arm extends externally, whereby said first end is manually removable from the frame.

3. In an electric motor including a frame having a spring-engaging first reference point, and commutator and brush elements, the improvement in combination therewith of an assembly for holding each brush against the commutator, comprising for each brush an arm having a first end-part pivotally secured to the frame, a remote part holding the brush, and a second reference point along the length of said arm, and-a leaf spring which is generally flat in its unloaded condition defining an initial length between its ends, this spring when the spring has a first end secured to the frame at said first reference point and the spring has a remote part engaging the arm at said second reference point, the distance between said two points being less than said initial spring length, the spring exerting a force on the arm both axially along the length thereof and laterally relative to said pivot and thereby resiliently positioning and urging the brush against the commutator, said spring having a spring characteristic which is very level within a comparatively wide range of spring deflection.

4. Apparatus according to claim 3 wherein said spring has a spring characteristic which is very level within a comparatively wide range of spring deflection.

5. Apparatus according to claim 3 wherein said pivoted engagement of said first end part comprises a knife-edge bearing.

6. Apparatus according to claim 3 wherein the frame defines an aperture through which the first part of the arm extends externally, whereby said first end is manually removable from the frame.

7. In an electric motor including a frame, a commutator rotatable about its axis, and at least two separate brushes engaging the commutator, the improvement in combination therewith of an assembly for positioning each brush comprising an arm having a first end secured to the frame and pivotable about an axis generally parallel to the commutator axis, and a second part remote from the first part and to which the brush is secured, a leaf spring having a first end engaged to the frame and a second end which is remote from the first end and engages the arm, the spring being flexed m columnar loading whereby the spring resiliently urges assembled being bowed under a buckling load whereby the arm axially along its length and laterally relative to its pivot point and the brush is resiliently urged against the commutator. v

Claims

2. Apparatus according to claim 1 wherein the frame defines an aperture through which the first part of the arm extends externally, whereby said first end is manually removable from the frame.

3. In an electric motor including a frame having a spring-engaging first reference point, and commutator and brush elements, the improvement in combination therewith of an assembly for holding each brush against the commutator, comprising for each brush an arm having a first end-part pivotally secured to the frame, a remote part holding the brush, and a second reference point along the length of said arm, and a leaf spring which is generally flat in its unloaded condition defining an initial length between its ends, this spring when assembled being bowed under a buckling load whereby the spring has a first end secured to the frame at said first reference point and the spring has a remote part engaging the arm at said second reference point, the distance between said two points being less than said initial spring length, the spring exerting a force on the arm both axially along the length thereof and laterally relative to said pivot and thereby resiliently positioning and urging the brush against the commutator, said spring having a spring characteristic which is very level within a comparatively wide range of spring deflection.