Brush device for miniature electric motor

A brush device for a miniature electric motor constructed with a brush holder made of a leaf spring having a pair of flaps for holding a commutator brush, which are opposed each other along the longitudinal direction of a flat surface part, and which are formed in an inwardly bent shape, a guide member for insertion of the commutator brush formed at a corner of each of the pair of flaps, and a fitting member for the brush holder onto the main body of the motor; and a commutator brush having a head part to be inserted and held between said pair of flaps provided along the side edges of the flat surface part of the brush holder.

BACKGROUND OF THE INVENTION 
This invention is concerned with a brush device for a miniature electric 
motor. 
It has so far been a general practice that the brush device for the 
miniature electric motors is made as simple a construction as possible by 
causing the brush made by powder-forming on a leaf spring of 
beryllium-copper alloy having a thickness of 0.15 mm or so, for example, 
to be held on the commutator portion of the motor, thereby utilizing the 
leaf spring as a brush holder, an electrically conductive body, and a 
contact-pressure holding body. 
In the brush device of the above-described construction, the brush per se 
is made of such materials having a high metal content, and also it is made 
of such other materials having a high graphite content. When the 
metal-graphite brush of high metal content is to be mounted on the leaf 
spring, it is done in such a manner that a head part of the brush in a 
rectangular form is fitted into a hole or opening perforated in the leaf 
spring serving as a brush holder, and the rectangular head part of the 
brush protruded from the perforated hole or opening in the brush holder 
made of the leaf spring is caulked so as to fixedly secure the brush to 
the brush holder. In this case, an electrically conductive adhesive agent 
may also be applied to the caulked part of the brush as an additional 
reinforcing expedient to ensure rigid fixation of the brush to the leaf 
spring holder. 
On the other hand, when the metal-graphite brush of high graphite content 
is to be mounted on the brush holder made of the leaf spring, the 
afore-mentioned caulking expedient cannot be adopted, because the brush 
per se is very brittle. In this case, therefore, the brush is mounted on 
the brush holder in such a manner that a resilient lining member is first 
fitted onto and along a pair of opposing sides of the opening perforated 
in the leaf spring holder, and then the rectangular head part of the brush 
is intromitted into the opening, and, while holding the brush by the 
abovementioned resilient lining member, an electrically conductive 
adhesive agent is applied to the fitted part between the brush and the 
perforated opening, to which the brush contacts, thereby fixedly securing 
the brush to the leaf spring holder. It goes without saying that this 
reinforcing expedient may be applied to the first-mentioned case where the 
brush to be mounted on the leaf spring holder is made of the material of 
high metal content. 
The brush device manufactured in accordance with the abovementioned 
conventional technique, however, has been replete with various problems 
mainly in respect of its industrialized mass-production, hence expected 
reduction in cost of manufacture of the miniature electric motor for 
controlling purposes in various kinds of automatically operated 
apparatuses and appliances, the demand for which in the market has been, 
and is, extremely high, cannot be realized. The source of such problem 
resides in its necessity for considerable number of manufacturing steps in 
assembling the brush and the leaf spring holder by caulking as well as in 
mounting the resilient lining member on the leaf spring holder. 
SUMMARY OF THE INVENTION 
In view of such problems existing in the known type of brush device for the 
miniature electric motors, it is a principal object of the present 
invention to provide an improved brush device for miniature electric 
motors, in which the assembly structure of the brush and its holder is 
simplified so as to enable an automatic assembly work to be carried out, 
to improve mass-production in an industrialized scale, and to promote 
decrease in the manufacturing cost thereof. 
It is another object of the present invention to provide a brush device for 
a miniature electric motor, in which the assembly of the brush and the 
holder is rigid and strong, and yet electric conductivity from the brush 
to the holder is highly stable. 
According to the present invention, in one aspect thereof, there is 
provided a brush device for miniature electric motor which comprises in 
combination: a brush holder of a leaf spring having a pair of flaps for 
holding a commutator brush, which are opposed each other along the 
longitudinal direction of a flat surface part, and which are formed in an 
inwardly bent shape, a guide member for insertion of the brush, and a 
fitting part to secure the holder to the main body of the motor; and a 
brush member having a head part to be inserted between a pair of flaps of 
the brush holder of a leaf spring. 
According to the present invention, in another aspect thereof, there is 
provided a brush device for a miniature electric motor which comprises in 
combination: a brush holder of a leaf spring having an opening part along 
the longitudinal direction of a flat surface part, a pair of flaps for 
holding the brush which are formed on both sides of the opening part and 
in an inwardly bent shape, a brush insertion guide formed at a corner of 
each of the flaps, and a fitting part to secure the spring holder to the 
main body of the motor; and a brush member in a cross-sectional shape of a 
letter "T" having an enlarged, or horizontally extended head part and a 
foot part, in which the foot part of the brush member is inserted and 
passed through the opening part of the holder, and the horizontally 
extended head part of the brush is press-contacted to the flat surface 
part of both edges of the opening part by the pair of flaps. 
The foregoing objects, other objects, as well as the specific construction 
and function of the brush device contemplated and realized by the present 
invention will become more apparent and understandable from the following 
detailed description thereof, when read in connection with the 
accompanying drawing.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The present invention will now be described in detail in reference to a few 
preferred embodiments thereof shown in the accompanying drawing. 
FIG. 1 shows an inter-relationship between a commutator 1 and brushes 2, in 
which each of the brushes 2 is held by a brush holder 3 made of a leaf 
spring. 
In the first embodiment shown in FIGS. 2 to 5, the brush holder 3 of the 
leaf spring is formed in the shape of an alphabetical letter "L", one flat 
surface part 31 of which serves as a brush holding member, and the other 
flat surface part 32 of which serves as a fitting part to secure the brush 
holder per se to the main body of the brush. When a lead wire is to be 
fitted, it may be directly soldered to the leaf spring holder, or it may 
be soldred to a tab formed on the leaf spring holder. Any other 
appropriate expedient may be adopted depending on the circumstances. 
On both side edges of the flat surface part 31 of the brush holder 3, there 
are provided upwardly extending reinforcing ribs 4 and 5 along the 
lengthwise direction thereof and up to approximately half way of the 
length. A pair of flaps 6 and 7 are also provided along the same 
direction, i.e., the lengthwise direction of the brush holder 3, as the 
ribs 4 and 5, but extending in the opposite direction, i.e., downward 
direction, to that of the ribs. These flaps are formed by cutting a 
portion of the flat surface part 31 of the brush holder 3 in the vicinity 
of each rib in three sides, and the cut portion is bent at the uncut side 
thereof to the opposite direction from the ribs at an angle of 30.degree. 
to 40.degree. with respect to the flat surface portion so that they may be 
opposed each other and bent inwardly to form a dovetail groove together 
with the flat surface part. 
A tab 8 is also provided on the flat surface part 31 near the front end 
thereof which functions as a stopper to restrict the insertion of the 
brush as will be described hereinafter. The tab 8 is also formed in the 
same manner as the flaps, i.e., by cutting a portion of the flat surface 
part 31 near the end thereof in three sides, and the cut portion is bent 
at the uncut side thereof at the right angle. 
As shown in FIG. 5, the brush 2 has a dovetail 9 at its head part, the 
width of which is made slightly larger than the width of the dovetail 
groove formed by the abovementioned flaps 6 and 7. Or, the angle of 
inclination of the dovetail 9 may be made slightly greater than the angle 
of inclination of the flaps 6 and 7. 
For assembly of the brush 2 and the brush holder 3, the dovetail 9 formed 
at the head part of the brush 2 may be simply inserted into the dovetail 
groove formed by the flaps 6 and 7 from the direction of an arrow mark a 
shown in FIG. 2 until the forward end of the brush head part collides with 
the tab, or stopper, 8. Insertion of of dovetail 9 into the dovetail 
groove, at the time of the assembly, is greatly facilitated by guide 
portions 10 and 11 formed by outwardly bending a corner of each of the 
flaps 6 and 7. 
The embodiment shown in FIGS. 6 to 8 inclusive is such that a dovetail 
groove is formed by downwardly bending a pair of flaps 12 and 13 along 
both side edges of the flat surface part 31 of the brush holder 3. In this 
embodiment, the flaps 12 and 13 also possess the function of the 
reinforcing ribs. On both side edges of the flat surface part 31 of the 
brush holder 3, there are further formed another pair of flaps 14 and 15 
adjacent to flaps 12 and 13 and in the same direction therewith so that 
the brush inserting position may be readily determined when the brush is 
to be inserted between them. These flaps 14 and 15 are also formed by 
bending both side edges of the flat surface part 31 of the brush holder 3. 
Between the pair of flaps 14 and 15, the dovetail 9 of the brush 2 shown 
in FIG. 5 is positioned, after which it is inserted in between the flaps 
12 and 13. 
The embodiment shown in FIGS. 9 to 12 inclusive is such that the dovetail 
part is formed by a pair of upwardly bent flaps 16 and 17 along both side 
edges of the flat surface part 31 of the brush holder 3, while the 
dovetail groove 18 is formed on the head part of the brush 2a as shown in 
FIG. 12. In this case, the brush insertion guides 19 and 20 are formed by 
bending the corner of each of the flaps 16 and 17 mutually inwardly. 
The embodiment shown in FIGS. 13 to 16 inclusive is such that an opening 21 
to guide the brush is cut out in the flat surface part 31 of the brush 
holder 3 in the longitudinal direction thereof, and a pair of upwardly 
directing flaps 22 and 23 are provided at both side edges of the flat 
surface part 31. These flaps 22 and 23 form the dovetail groove. On the 
other hand the brush 2b has a crosssectional shape of a letter "T" as 
shown in FIG. 16. 
The assembly of the brush holder and the brush is so performed that the 
foot part 24 of the brush 2b is inserted into the opening 21 of the brush 
holder 3 from the top of the opening 21 as shown in FIG. 14, thereby 
causing the lower surface of the horizontally extended head part or 
flanged part 25 of the brush 2b to be engaged with the brim of the opening 
21. Subsequently, with the opening 21 and the brush guide parts 10 and 11 
of the flaps 22 and 23 being made as the guide for the brush insertion, 
the horizontally extended or flanged part of the brush head 25 is pushed 
into the pair of inwardly bent flaps 22 and 23 so that the brush head 25 
may be press-contacted at its lower surface to both brims of the opening 
21 in the flat surface part of the brush holder 3. In this case, one end 
brim 26 at the front end part of the brush holder 3 functions as the 
stopper. 
In the above described construction of the device, the brush member can be 
manufactured in a single process step by molding. Also, the brush holder 
can be easily manufactured in a series of steps comprising cutting of a 
sheet material, bending and uprighting the cutout portion in the brush 
holder. 
Since the present invention is to assemble the brush member with the brush 
holder through the dovetail, or any other effective expedient similar to 
it in a single process, no auxiliary process step such as welding, 
soldering, gluing, and so forth is required whatsoever, whereby the 
abovementioned purpose can be attained. Also, the brush and the holder are 
rigidly joined in a manner to be closely adhered to the meeting surfaces 
of both members, so that contact electric resistance can be ignored. 
Although the present invention has been described in the foregoing in 
reference to a preferred embodiment thereof, it should be borne in mind 
that the embodiment is merely illustrative and not so restrictive, and 
that any change and modification may be made by those persons skilled in 
the art within the spirit and scope of the present invention as set forth 
in the appended claims.