Plane carbon commutator and its manufacturing method

In a plane carbon commutator which is formed by fixing a plurality of metal segments to a commutator main body made of a resin and by integrally fixing a carbon to each of these segments, engagement projections provided in the carbon are engaged with engagement holes provided in the segments for a mutually fixed integration. Accordingly, it is possible to effectively utilize the characteristics of the carbon which has been burned at a high temperature in advance.

BACKGROUND OF THE INVENTION 
The present invention relates to a plane carbon commutator to be used as a 
commutator for a motor of a fuel pump or the like, for example, and its 
manufacturing method, and relates more particularly to a plane carbon 
commutator and its manufacturing method for ensuring a coupling between a 
segment and a carbon in a commutator. 
A plane carbon commutator has such a structure in which a metal segment is 
fixed to an end surface of a commutator main body made of a mold resin and 
a carbon is fixed to this segment. As methods for manufacturing a plane 
carbon commutator of this type, there are following methods (A) to (D), 
for example. 
(A) When a carbon is molded, a metal base material which becomes a segment 
is inserted into the carbon for integrating these together and these are 
burned. Then, the metal base material integrally molded with carbon is 
molded with a mold resin to form an insulating material section. (For 
example, see Japanese Patent Application Laid-Open No. 95-264812) 
(B) An insulating material and a metal base material are integrated 
together by an integral molding in advance, and thereafter carbon is 
adhered on the surface of the metal base material with solder or with 
conductive adhesive agent. (For example, see International Publication No. 
WO93/01321) 
(C) An insulating material and a metal base material are integrated 
together by an integral molding in advance, and thereafter carbon is 
formed on the surface of the metal base material and burned. (For example, 
see Japanese Utility Model Application Publication No. 951 42223) 
(D) An insulating material and a metal base material are separately 
prepared in advance, and the insulating material and the metal base 
material are inserted into carbon for integrally molding these together at 
the time of molding the carbon. (For example, see Japanese Patent 
Application Laid-Open No. 94-178503) 
According to the above-described method (A), the temperature for burning 
the carbon is as high as at least about 600.degree. C., so that there is a 
problem that the metal base material to be integrally molded is softened 
and this generates difficulties in the product precision and strength 
improvement. To avoid this problem, it is possible to burn the carbon at a 
low temperature of about 200.degree. C. However, in this case, the 
material quality of the carbon itself becomes special with a resultant 
problem in various characteristics such as hardness, electric resistivity, 
gasoline-proof, etc. 
According to the above-described method (B), the carbon can be burned as a 
single in advance and there is no quality problem of the carbon itself. 
However, in the structure of having the carbon soldered on the surface of 
the metal base material, there is a risk of an occurrence of a loosening 
of the solder due to the high temperature at the time of connection fusing 
for assembling the motor. 
Further, in the structure of having the metal base material and the carbon 
adhered together by using a conductive adhesive agent, an adhesive agent 
having both conductivity and gasoline-proof is necessary, which results in 
an expensive structure. Further, even if the adhesive agent has 
conductivity, the electric resistance becomes larger than that of the 
carbon and the metal base material, holding a problem that this portion 
has the risk of heat generation and quality change during the operation of 
the motor. 
According to the above-described method (C), the insulating material made 
of resin is carbonized at a high temperature when the carbon is burned on 
the surface of the metal base material, so that the carbon must be burned 
at a low temperature, which results in a quality problem of the carbon. 
The above-described method (D) has a problem similar to that in the 
above-described method (C). 
SUMMARY OF THE INVENTION 
In the light of the above-described conventional problems, according to the 
present invention, in a plane carbon commutator formed by fixing a 
plurality of metal segments on a commutator main body made of resin and by 
integrally fixing a carbon to each of the segments, an engagement 
projection provided on the carbon is provided in the segments. 
With the above-described structure, the carbon and the segments can be 
integrated together without using a solder or an adhesive agent so that 
the characteristics of the carbon burned at a high temperature in advance 
can be fully utilized. 
Further, by engaging at least a part of the peripheral portion of 
engagement holes provided on the segments with an engagement projection 
provided on the carbon, the integration of the carbon and the segments can 
be achieved with higher security. 
Further, by fastening the engagement projection provided on the carbon with 
the peripheral portion of the engagement holes provided on the segments, 
the integration of the carbon and the segments can be achieved with higher 
security. 
Further, both of the segments and the carbon are plated and bonded together 
by welding the plating on bonding surfaces thereof to each other. This 
reduces contact resistance at the bonding surfaces of the segments and the 
carbon, thereby allowing conductivity at the bonding surfaces to be 
improved. 
Further, in a plane carbon commutator formed by fixing a plurality of metal 
segments on a commutator main body made of resin and integrally fixing a 
carbon to each of the segments, both of the segments and the carbon may be 
plated and the plating on the bonding surfaces of the segments and the 
carbon may be welded to improve electrical conduction. 
Such a configuration makes it possible to reduce contact resistance at the 
contact surfaces between the segments and the carbon to further improves 
the conductivity of the contact surfaces. 
Further, the plating layers on both of the segments and the carbon may be 
formed by at least two plating layers, i.e., a first layer which is a 
plating layer compliant to the segments and the cartoon and a second layer 
made of a material which is compliant to the first layer and which 
exhibits mutual affinity when they are welded, to maintain weldability 
when the plating layers on the bonding surfaces of the segments and the 
carbon are welded. 
Further, a plane carbon commutator formed by fixing a plurality of metal 
segments on a commutator main body made of resin and by integrally fixing 
a carbon to each of the segments can also be manufactured by a method 
comprising a step of integrating a metal base material which becomes a 
segment with a carbon, a step of covering an exposed portion of the 
surface of the carbon with the mold resin at the time of molding the metal 
base material and the carbon with a mold resin after the metal base 
material and the carbon have been integrated together, a step of 
disconnecting the carbon at the same time when the metal base material is 
disconnected into segments, and a step of removing the mold resin from the 
surfaces of the carbon. 
According to the above-described manufacturing method, it is possible to 
protect the carbon with the mold resin at each processing step such as, 
for example, a step of bending the connection parts and a step of cutting 
a hole for a motor shaft, and sufficient strength of mechanical coupling 
between the segments and the carbon is maintained. 
Further, a plane carbon commutator formed by fixing a plurality of metal 
segments on a commutator main body made of resin and integrally fixing a 
carbon to each of the segment can be manufactured by a method comprising 
the a step of plating each of a metal base material which becomes a 
segment and a carbon, a step of integrating the metal base material and 
the carbon, a step of heating the integrated metal base material and 
carbon to weld plating on the bonding surfaces of the metal base material 
and the carbon to each other, a step of covering the entire exposed 
portion of a surface of the carbon with mold resin at the time of molding 
the integrated metal base material and the carbon with the mold resin, a 
step of disconnecting the carbon at the same time when the metal base 
material is disconnected into segments, and a step of removing the mold 
resin from the contact surfaces of the carbon and brushes. 
According to such a manufacturing method, it is possible to maintain 
sufficient strength of mechanical coupling between the segments and the 
carbon, to protect the carbon with the mold resin, for example, during a 
cutting process, and to reduce contact resistance at the contact surfaces 
of the segments and the carbon, thereby improving conductivity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIG. 1A and FIG. 1B, a plane carbon commutator 1 relating to 
the present invention is formed by integrally fixing a plurality of 
segments 5 made of a metal such as copper or copper alloy to an end 
surface of a commutator main body 3 made of a mold resin and by integrally 
fixing a carbon 7 to these segments 5. 
The segments 5 include a plurality of anchor nails 9 buried in the 
commutator main body 3 and also include connection parts. 
The commutator 1 is manufactured as follows. At first, as shown in FIG. 2, 
a metal base material 15 having the anchor nails 9 and the connection 
parts 11 is processed by punching. After punching, the metal base material 
15 is disconnected by disconnection lines 13 finally so that the metal 
base material 15 is divided into separated portions. 
Next, as shown in FIG. 3A and FIG. 3B, the anchor nails 9 and the 
connection parts 11 provided in the metal base material 15 are bent to one 
side surface, and a carbon 17 which has been burned at a high temperature 
in a donut shape in advance is integrally fixed to the metal base material 
as shown in FIG. 4A and FIG. 4B. 
As an example of the structure for integrally fixing the metal base 
material 15 with the carbon 17, there is a structure in which a plurality 
of engagement projections 31 are provided in the carbon 17 as shown in 
FIGS. 5A and 5B and then engagement holes 33 are provided at positions 
corresponding to the connection parts 11 of the metal base material 15 and 
the engagement projections 31 are engaged with the engagement holes 33 to 
achieve a fixed integration as shown in FIG. 6. 
As an example of the structure for engaging the engagement projections 31 
with the engagement holes 33 for a fixed integration, there is a structure 
in which the engagement projections 31 are fastened by the peripheral 
portion of the engagement holes 33 by utilizing the thermal compression of 
the material, for example, by shrinkage fit, for achieving a mutual 
fastening integration. 
Further, it is also possible to have such a structure in which the 
engagement projections 31 are compressed into the engagement holes 33. In 
this case, it is also possible to have such a structure in which 
engagement holes 33 are processed by burring and engagement projections 31 
are fastened by the protruding portion formed by burring. 
Further, it is also possible to achieve a fixed integration of the metal 
base material 15 with the carbon 17 in the following manner. As shown in 
FIG. 7A, the engagement projections 31 of the carbon 17 are engaged with 
the engagement holes 33 of the metal base material 15, and then cut-open 
pieces 21 are formed at one portion of the peripheral edge of the 
engagement holes 33 in the metal base material 15 and the engagement 
projections 31 are fastened with these cut-open pieces 21 and the cut-open 
pieces 21 are filled into the peripheral surface of the engagement 
projections 31 so that the metal base material 15 is fixed with the carbon 
for integration, as shown in FIGS. 7B and 7C. 
After the metal base material 15 and the carbon 17 have been integrated 
together, this integrated unit is set to a mold (not shown) and a mold 
resin 23 is molded to form the commutator main body 3. The mold resin 23 
is molded in such a way that the exposed portion of the surface of the 
carbon 17 is fully covered, as shown in FIGS. 8A and 8B. 
After the mold resin 23 has been molded, as shown in FIGS. 1A and 1B, a 
desired bending is formed at the connection parts 11, a hole 25 is 
provided by cutting for engaging with a motor shaft, slits 27 are 
processed and the carbon 17 and the metal base material 15 are divided to 
each segment, then the mold resin 23 is removed by cutting from the 
sliding surface of the carbon 17 which slides with a brush (not shown), so 
that the plane carbon commutator 1 of the structure as shown in FIG. 1 can 
be obtained. 
As is clear from the above explanation, according to the present 
embodiment, necessary processings are carried out in the state that the 
exposed portion of the surface of the carbon 17 is covered with the mold 
resin 23, and the mold resin is removed from the sliding surface of the 
carbon in the final step. Therefore, in the various processing steps, the 
mold resin protects the carbon, with a result that there occurs no damage 
to the carbon such as a crack or a recess in the process of bending the 
connection parts 11 and the process of providing the hole 25, for example. 
Further, according to the above-described embodiment, the carbon which has 
been burned at a high temperature in advance can be engaged with the metal 
main material by engaging the engagement projections with the engagement 
holes, to thereby achieve a fixed integration. Therefore, it is possible 
to utilize the characteristics of the carbon which has been burned at a 
high temperature and there is no problem which will otherwise occur when a 
solder or an adhesive agent is used. 
As a structure for integrating the carbon 15 with the metal base material 
15, it is also possible to have such a structure as shown in FIG. 9 in 
which large diameter parts 17a and small diameter parts 17b are formed at 
the front end portions of the engagement projections 31 of the carbon 17 
which is engaged with and piercing through the engagement holes 33 of the 
metal base material 15, and these large diameter parts 17a and small 
diameter parts 17b are buried within the mold resin 3. 
A second embodiment of the present invention will now be described. 
As shown in FIG. 10, according to the present embodiment, plating layers 31 
and 33 are respectively provided on a carbon 17 and a metal base material 
15; the metal base material 15 and the carbon 17 having the plating layers 
31 and 33 are integrally fixed as described above; and the plating layers 
31 and 33 on the bonding surfaces of the metal base material 15 and the 
carbon 17 are welded to each other by heating to improve electrical 
conduction therebetween. Subsequent manufacturing steps are similar to 
those described above. and will not be described here to avoid 
duplication. 
The plating layers 31 and 33 are made of nickel, tin, chromium, gold, 
silver, copper, or an alloy of such materials and are preferably formed 
into two or more layers. In this case, a first layer is preferably made of 
a material compliant to each of the metal base material 15 and the carbon 
17, and a second layer is preferably made of a material which is compliant 
to the first layer and which exhibits mutual affinity when they are welded 
together by heating. The plating layers are not limited two layers and may 
have a multiplicity of layers. 
In a configuration wherein the metal base material 15 and the carbon 17 
respectively have the plating layers 31 and 33 provided thereon and the 
plating layers on the bonding surfaces thereof are welded to each other by 
heating after they are integrally fixed to each other as described above, 
sufficient strength of mechanical coupling is maintained by a 
configuration wherein an engagement projection 17P provided on the carbon 
17 is engaged with an engagement hole H in the metal base material 15. 
Further, conductivity is improved by reduction in contact resistance 
between the bonding surfaces compared to simple surface contact. 
The effect of improving conductivity can be achieved by plating the carbon 
17 and the metal base material 15 with the plating layers 31 and 33, 
respectively, and by bonding the bonding surfaces of the metal base 
material 15 and the carbon 17 through welding of the plating layers 31 and 
33 to each other even if the metal base material 15 and the carbon 17 are 
fixed together using methods other than that described above.