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 a discrete plastic brush card mounted in an

endframe but isolated from the endframe.

2. Description of the Prior Art

In electric motors, brushes are commonly retained in brush tubes which

usually are molded integrally with the endframe 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.

Noise usually is generated at the commutator-brush interface, the surface

of the rotating commutators being continuously engaged by the relatively

stationary brushes. The noise is exacerbated by the hollow elongated brush

tubes, acting as echo-chambers, which, being integral with the endframe,

transmit the noise to the endframe, which is exposed.

In some applications, the noise generated at the commutator-brush interface is unacceptable. For example, in D.C. motors used in automobiles for

operation of power seats, it is most desirable that the motors operate silently.

Accordingly, there exists a need for a motor having a quieter arrangement

of endframe and brush tubes.

Summary of the Invention

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

having an endframe and brush tube arrangement given to relatively silent

running.

A further object of the invention is to provide an electric motor having a

discrete brush card which includes brush tubes, the brush card being mounted in the endframe but isolated from the endframe so as not to transmit noise

thereto.

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

metal housing disposed around an armature portion of the armature and

commutator assembly, permanent magnet means disposed between the

armature portion and the housing, and an endframe fixed to the housing. The

motor further includes a discrete brush card mounted in the endframe. The

brush card is provided with a cylindrical portion for retaining a commutator

portion of the armature and commutator assembly, and brush tubes extending

radially outwardly from the cylindrical portion. Each of the brush tubes is

adapted to retain a brush for engaging the commutator portion, and a brush

spring for urging the brush into engagement with the commutator. The brush

card is provided with tab portions having orifices therethrough. Elastomeric

grommets are mounted on the tab portions and have openings therethrough and

aligned with the tab orifices. The endframe is provided with posts extending

from an end wall of the endframe. The grommet openings are configured to

receive the posts to lock the grommets onto the posts. The grommets are

disposed at least in part between the brush card and the endframe end wall to

isolate the brush card from the endframe end wall.

In accordance with a further feature of the invention, there is provided a brush card for connection to an endframe of an electric motor, the card comprising a cylindrically-shaped central portion for retaining a commutator portion of the motor, brush tubes extending radially outwardly from the central

portion, the brush tubes being configured each to retain a brush, and a brush

spring for urging the brush into engagement with the commutator portion. The

brush card is provided with tab portions with orifices therethrough, and

grommets are mounted on the tab portions, the grommets having openings

therethrough aligned, respectively, with the tab orifices. At least a portion of

each of the grommets is disposed on a surface of the tab portion adapted to be

adjacent a wall of the endframe, whereby to separate the brush card from the

endframe wall upon the connection of the brush card to the endframe.

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 card;

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

Fig. 5 is a side elevational view of the brush card of Figs. 3 and 4;

Fig. 6 is similar to Fig. 3, but shows the brush card with grommets,

brushes and brush springs in place;

Fig. 7 is a sectional view of the endframe of Figs. 1 and 2, showing one

of the posts extending from the endframe closed end;

Fig. 8 is an enlarged elevational view of the post of Fig. 7;

Fig. 9 is similar to Fig. 5, but shows the grommets in place on the brush

card; and

Fig. 10 is an enlarged elevational view of the brush card grommet and

endframe post interlock.

Description of the Preferred Embodiment

Referring to Fig. 1 , it will be seen that the illustrative motor includes a drive shaft 1 0. 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 1 8.

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 noise-absorbing 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 discrete brush card 40 (Figs. 1 and 2)

which comprises a cylindrically-shaped central portion 42 (Fig. 2) 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. Each of the brush tubes 44 has

disposed therein a coil spring 46 and a brush 48, the spring 46 biasing the

brush 48 into engagement with the commutator 1 6 in the brush card central

portion 42 (Fig. 1 ). 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).

Referring again to Fig. 1 , it will be seen that the endframe 30 extends

axially of the motor a sufficient distance to provide a plastic shell housing 56,

comprising a side wall portion 58 of the endframe 30, around the commutator

1 6. The side wall portion 58 of the endframe 30 extends towards the armature

14 such that the commutator 1 6 is disposed fully within the plastic endframe

30 and is axially spaced from an open end 60 of the endframe 30 and from the

metal shell 20. Thus, the noise-absorbing plastic shell housing 56 extends well

beyond either end of the commutator to absorb radiated noise generated by the commutator-brush interface.

As may be seen in Figs. 3-6 and 9, the brush card 40 is provided with

flat tabs 62 having orifices 64 therethrough. Elastomeric grommets 66 (Figs. 6

and 9) are mounted on the tabs 62 and in and around the orifices 64, the

grommets 66 having openings 68 therein which are aligned, respectively, with

the orifices 64.

In Fig. 7, there is shown, in a sectional view of the endframe 30, a post

70 extending from the closed end 32 of the endframe. In Fig. 8, there is shown

an enlarged elevational view of the post 70, which includes a barrel portion 72,

a probe portion 74, and therebetween, a winged portion 76. The endframe

preferably is provided with a plurality of such posts 70, as shown in Fig. 2.

In assembly of the endframe 30 and brush card 40, the grommets 66 of

the brush card 40 are aligned with the posts 70 and pushed onto the posts.

The probe portions 74 of the posts 70 pass through the grommet openings 68

and the brush card orifices 64 from one side thereof, followed by the winged

portions 76 which emerge from the other side and overlie the other side of the

grommets 66 (Fig. 10) to securely lock the brush card 40 to the endframe 30,

but with the brush card separated from the end 32 of the endframe by the

elastomeric grommets. As shown in Fig. 1 , the outer ends of the brush tubes

44 are spaced from the endframe side wall portion 58. Thus, the noise generated at the interface of the brushes 48 and commutator 1 6 is not transmitted to the endframe, but, instead, is radiated from the commutator and,

to a large degree, absorbed by the endframe side wall 58 and endframe end

wall 32. There is thereby provided a motor which is quieter in operation and

still easy and inexpensive to assemble.

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: