Background of the Invention

1 . Field of the Invention

The invention relates to electric motors and is directed more particularly

to an electric motor having brush tubes fixed in an endframe portion of the

motor.

2. Description of the Prior Art

In electric motors, brushes are commonly retained in brush tubes which usually are molded integrally with a plastic endframe portion of the motor. The endframe and brush tubes typically are of a plastic material. The brush tubes

are square in cross-section and hollow, somewhat like elevator shafts, in which spring-biased brushes are slidably moveable into engagement with the commutator of the motor.

In assembly of such motors, it is common that a coil spring is inserted in a brush tube and, thereafter, a brush, with a shunt attached thereto, is inserted in the brush tube on top of the spring. In shipment and handling prior to

assembly, it is sometimes the case that the brush and spring fall out of the open end of the tube. At the final assembly point, it is on occasion overlooked that the spring is missing. It is usually apparent when the brush is missing, but sometimes the brush is replaced without the absence of the spring having been

noticed. In some instances, the shunt may, for a limited time, exercise spring¬ like properties and hold the brush in a commutator-engaging position. However,

the shunt usually cannot maintain its spring-like performance and, in due

course, the brush falls away from commutator engagement, terminating proper

operation of the motor.

Accordingly, there exists a need for a motor having brush spring retention

means.

Summary of the Invention

It is, therefore, an object of the invention to provide an electric motor

having an endframe and brush tube arrangement, wherein the brush tubes are

provided with means for retaining the coil springs therein while permitting the

coil springs to flex as needed to urge their respective brushes into engagement

with a commutator.

With the above and other objects in view, as will hereinafter appear, a

feature of the present invention is the provision of an electric motor comprising

a drive shaft, an armature and commutator assembly fixed on the drive shaft, a

housing disposed around the armature and commutator assembly, magnet

means disposed between the armature and commutator assembly and the

housing, and an endframe fixed to the housing. The endframe has therein

means for retaining the drive shaft, brush means in contact with a commutator

portion of the armature and commutator assembly, shunt and terminal means

connected to the brush means, and brush tubes for slidably retaining the brush

means, and for retaining a coil spring for urging the brush means into engagement with the commutator portion of the armature and commutator

assembly. Each of the brush tubes retains one of the coil springs therein, and is

provided with an outer end, side, front and rear walls sufficiently closed to

prevent egress of the coil spring means, and an open inner end through which

one of the brush means slidably engages the commutator portion. At least one

of the side, front and rear walls of the brush tube is provided with an integral

barb extending inwardly of the brush tube to overlie a portion of the coil spring

proximate the brush tube closed end. The barb is configured to permit passage

of the coil spring toward the brush tube closed end, but prevent passage of the coil spring toward the brush tube open inner end, thereby to prevent egress of the coil spring through the brush tube inner end.

In accordance with a further feature of the invention, there is provided a

brush tube for an electric motor, the brush tube being configured to slidably

retain a brush, and to retain a coil spring for urging the brush into engagement with a commutator of the motor, the brush tube comprising an outer end wall

sufficiently closed to prevent egress of the spring therethrough, side, front and

rear walls sufficiently closed to prevent egress of the spring therethrough, and

an open inner end through which the brush may protrude to engage the motor

commutator. The brush tube further comprises a barb integral with at least one

of the side, front and rear walls and extending inwardly of the brush tube to

overlie a portion of the coil spring proximate the brush tube closed end. The

barb is configured to permit passage of the coil spring toward the brush tube

closed end, but prevent passage of the coil spring towards the brush tube open

inner end, to prevent egress of the coil spring through the brush tube inner end.

The above and other features of the invention, including various novel

details of construction and combinations of parts, will now be more particularly

described with reference to the accompanying drawings and pointed out in the

claims. It will be understood that the particular devices embodying the

invention are shown by way of illustration only and not as limitations of the

invention. The principles and features of this invention may be employed in

various and numerous embodiments without departing from the scope of the

invention.

Brief Description of the Drawings

Reference is made to the accompanying drawings in which is shown an

illustrative embodiment of the invention, from which its novel features and advantages will be apparent.

In the drawings:

Fig. 1 is a partly side elevational, partly sectional, view of one form of motor illustrative of an embodiment of the invention;

Fig. 2 is an end view of an endframe portion of the motor shown in Fig.

1 , taken from the open end of the endframe;

Fig. 3 is a front elevational view of an illustrative brush tube assembly;

Fig. 4 is a rear elevational view of the brush tube assembly of Fig. 3;

Fig. 5 is a side elevational view of the brush tube assembly of Figs. 3 and

4;

Fig. 6 is similar to Fig. 3, but shows the brush tube assembly with

brushes and brush springs in place; and

Fig. 7 is an enlarged sectional view of a brush tube assembly, showing

means for retaining an end of the brush spring in place.

Description of the Preferred Embodiment

Referring to Fig. 1 , it will be seen that the illustrative motor includes a

drive shaft 10. Fixed to the drive shaft 10 is an armature and commutator assembly 1 2, including an armature 14, a commutator 1 6, and appropriate

windings 18.

A metal housing shell 20, preferably of steel, is disposed around the

armature 14. Permanent magnets 22 are disposed between the housing shell 20 and the armature 14 and are secured to the housing shell.

An endframe 30, of plastic material, is fixed to the housing shell 20. The endframe 30 has formed in a substantially closed end 32 a journal 34 for

retaining a bearing 36 which, in turn, supports the drive shaft 10.

Disposed in the endframe 30 is a brush tube assembly 40 (Figs. 1 and 2)

which comprises a cylindrically-shaped central portion 42 configured to retain

the commutator 1 6. Extending radially from the central portion 42 are opposed

brush tubes 44 (Figs. 2-5). The central portion 42 and the brush tubes 44 are

of plastic and may be formed integrally with each other. Each of the brush

tubes 44 has disposed therein a coil spring 46 and a brush 48 (Fig. 2), the spring 46 biasing the brush 48 into engagement with the commutator 1 6 in the

brush tube assembly central portion 42. Each brush 48 has attached thereto a

conductive wire lead, or shunt 50, the other end of which is connected to a

terminal 52 fixed in a terminal housing portion 54 (Fig. 2).

As may be seen in Figs. 3-6, the brush tube assembly 40 may be a

discrete member which is mounted in the endframe 30. Alternatively, the brush

tube assembly may be molded integrally with the endframe.

Referring to Figs. 3-7, it will be seen that each brush tube 44 is provided

with a closed outer end 80, and closed side walls 82 (Fig. 5). Front and rear

walls 84, 86 (Figs. 3 and 4) are sufficiently closed to prevent egress of the coil spring 46 therethrough. Though the outer end 80 and side walls 82 are shown

as completely closed, it is necessary only that they be sufficiently closed to

prevent movement of the spring therethrough. At least one wall, and preferably

opposed walls, as for example, the side walls 82, are provided with barbs 90

integral therewith and extending inwardly of the brush tube 44 to overlie a

portion of the coil spring 46 proximate the brush tube closed end 80. The barb is configured (Fig. 7) to permit passage of the coil spring toward the brush tube

closed end 80, but prevent passage of the coil spring toward the brush tube open end. Thus, in assembly, the spring 46 easily may be inserted into the

brush tube 44, readily override the barb 90, and snap thereunder, to anchor the

spring in the brush tube.

It is to be understood that the present invention is by no means limited to the particular construction herein disclosed and/or shown in the drawings, but

also comprises any modifications or equivalents within the scope of the claims.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States is: