EP1575149A1

EP1575149A1 - Method of manufacturing segment for flat commutator

Info

Publication number: EP1575149A1
Application number: EP03776026A
Authority: EP
Inventors: Shuji Uehara; Hideyuki Minami; Kazuo Iwashita; Hideki Horiuchi; Minoru Isoda; Yasuhiro Takebe; Yoshinori Kojima; Takayuki Ishizeki; Mitsuru Shishido
Original assignee: Mitsuba Corp
Current assignee: Mitsuba Corp
Priority date: 2002-12-10
Filing date: 2003-12-02
Publication date: 2005-09-14
Also published as: AU2003284535A1; CN1723598A; JP4252795B2; CN100342624C; JP2004194396A; EP1575149A4; WO2004054073A1

Abstract

A tator-bar 15 having a similar cross-sectional shape to that of the segments 3 is formed by drawing. Segments 3 for a flat commutator are formed by punching out the segments 3 from the tator-bar 15 in a direction Z perpendicular to a drawing direction X. The drawing direction X of the tator-bar 15 is arranged to be substantially the same as the sliding direction of the brush on the segments 3. Simultaneously, surfaces subjected to drawing are arranged to constitute brush sliding surfaces 4 of the segments 3. Anchor parts 14 which serve as a stopper to prevent falling off of the segments 3 are formed on the tator-bar 15 during the drawing. As a result of this, it is possible to manufacture easily, at low costs, segments capable of preventing leakage of resins during a resin mold process of the flat commutator.

Description

Technical Field

The present invention relates to a method of manufacturing a commutator for use in an electric rotating machine, and particularly to a method of manufacturing segments for a disk-type flat commutator.

Background Art

In recent years, several of motors for use in electric power steering, an engine starter, a fuel pump, and the like have appeared with a flat commutator on demand for downsizing of devices. This flat commutator has a disk-like brush sliding surface extending radially from the rotation axis, unlike a general cylindrical commutator. A metal member called commutator metal is subjected to molding, integrally with synthetic resins. After this integral molding, the commutator metal is divided in radial directions and separated in a circumferential direction, to form plural segments. A brush slides on and contacts, in the axial direction, the brush sliding surface constituted by the commutator metal, to switch an armature current.
A method of manufacturing the commutator metal in this flat commutator adopts a scheme of forming respective segments of commutator metal individually by cold forging, or a scheme of annularly forming chained segments by progressive pressing. However, these schemes involve a problem that the radius of a curved surface (R) is large at a bent corners formed by processing such as press bending, ironing, drawing, or the like. If R at a corner is large, the length of the brush sliding surface is reduced by an amount corresponding to the part of R. This is disadvantageous from the viewpoint of maintaining a certain length of the sliding surface. At the time of resin molding, R at a corner causes a component force to be generated in a direction in which segments are let float in response to resin pressure. Further, the commutator metal is manufactured by a number of complicated processes which require progressive pressing. Therefore, equipment costs increase, and blank areas to maintain feed pilot holes enlarge, so that the yield is reduced.
FIG. 6 is an explanatory view showing influences from R at a corner during resin molding. As shown in FIG. 6, at the corner R, resins supplied from a gate 51 are going to flow around to a brush sliding surface 54 through a corner 53 of a commutator metal 52. Then, the pressure thereof may deform upward the commutator metal 52, thereby making the resins leak to the inner circumferential side of the brush sliding surface 54. Once resins leak, not only deburring of the brush sliding surface 54 is needed but also gaps corresponding to burrs are caused between segments. A further cutting process is needed to eliminate the gaps. Therefore, the number of processing steps after a resin-molding process is increased, leading to a problem of increased costs. Particularly in case of commutator metal for pressed products, there is a possibility that metal deforms by springback. There has been a demand for a countermeasure against leakage of resins.
Meanwhile, there has been an attempt to solve the problem described above by applying a method for manufacturing segments used for a general cylindrical commutator. FIG. 7 is a partially cut-away side view showing the structure of a cylindrical commutator. FIG. 8 is an explanatory view of a method for manufacturing segments used in FIG. 7. In the cylindrical commutator 55, each segment 56 is formed by appropriately cutting a rod-like member called a tator-bar. A tator-bar 57 is a draw member made of copper, and is formed to have a trapezoidal cross-section, as shown in FIG. 8. Each segment 56 is punched out from the tator-bar 57 as indicated by broken lines in the figure, to obtain a shape to be used in the cylindrical commutator 55 shown in FIG. 7.
Hence, if each segment (commutator metal) of the flat commutator is made from the tator-bar 57 as described above, R at corners as shown in pressed products is not caused, and the problem of a springback does not arise. FIG. 9 is an explanatory view showing a state of manufacturing a segment for a flat commutator from a tator-bar. If the segment 58 is cut out as indicated by broken lines shown in FIG. 9, from the tator-bar 57, an end part of the brush sliding surface 59 does not have R. Therefore, if segments 58 are subjected to resin-molding, resins do not flow around toward the brush sliding surface 59. Accordingly, the number of post-process processing steps can be reduced.
However, if the segment 58 is punched out from the tator-bar 57 as shown in FIG. 9, a processed surface forms the brush sliding surface 54. That is, broken-out sections become the brush sliding surface 54. Therefore, surface roughness of the brush sliding surface 54 increases to necessitate a further cutting process after the punch-out process. As a result, although the number of processing steps after molding is reduced, the number of manufacturing processing steps is increased so that an effective cost reduction cannot be achieved. In addition, when forming the segment 58, the portion of the tator-bar 57 to be cut away is relatively large, and therefore, the yield is low disadvantageously for manufacturing costs. Further, an inner portion which is softer than the surface of the tator-bar 57 forms the brush sliding surface 54. Therefore, a problem arises in that the surface hardness lowers, and there has been a demand for an improvement in this point.
The present invention has an object of manufacturing, at low costs, a segment capable of easily preventing leakage of resins in a resin molding process of a flat commutator, to reduce the number of processing steps of manufacturing a flat commutator

Disclosure of the Invention

According to an aspect of the present invention, a method of manufacturing segments for a flat commutator which has a holder part formed of synthetic resins in a disk-like shape, and a plurality of segments arranged along a circumferential direction of the holder part on an end surface thereof in an axial direction, the method characterized by comprising: a step of forming a base metal having a portion whose cross-sectional shape is similar to cross-sectional shapes of the segments by drawing; and a step of forming the segments by cutting the base metal.
In the present invention, segments are manufactured by cutting a base metal having a cross-sectional shape similar to that of the segments. Therefore, the segments can be formed by, for example, performing punching one time, and punching need not be performed plural times. Accordingly, segments can be formed with good precision without dimensional variants due to errors in matching and feeding in each process. In addition, since processing of the base metal is only punching and it does not require precise feeding, equipments for manufacturing segments may be general-purpose equipments available at low prices. Thus, the segments can be processed at low costs.
In the method of manufacturing segments for a flat commutator described above, the segments may be arranged radially on the one end surface of the holder part in the axial direction, and the base metal may have a portion whose cross-sectional shape is similar to the cross-sectional shape of each of the segment along a diameter direction thereof.
Also, in the method of manufacturing segments for a flat commutator described above, a drawing direction of the base metal may be substantially the same direction as a brush sliding direction of the segments. As a result of this, the processing direction of the brush sliding surfaces substantially coincides with the brush sliding direction of the segments. Without carrying out cutting finish work after punching, surfaces subjected to drawing can be directly used as the brush sliding surfaces.
Also, in the method of manufacturing segments for a flat commutator described above, surfaces of the base metal subjected to the drawing may form brush sliding surfaces in the segments. As a result of this, portions which have produced work hardening by processing of drawing constitute the brush sliding surfaces, and improve the hardness of the brush sliding surfaces. Thus, durability of the commutator can be improved.
Further, in the method of manufacturing segments for a flat commutator described above, anchor parts of the segments that serve as a stopper to prevent the segments from falling off of the holder part in the axial direction may be formed on the base metal by the drawing. As a result of this, work for forming anchor-part, such as tapering, deburring, and the like, is unnecessary after the drawing so that the number of processing steps can be reduced.
Alternatively, in the method of manufacturing segments for a flat commutator described above, the segments may be formed by punching out the segments from the base metal in a direction perpendicular to the drawing direction. In this case, the segments may be punched out with the inner circumferential and outer circumferential sides of adjacent segments inverted to each other. As a result of this, unnecessary parts of the base metal are reduced, and so, the segments can be punched out efficiently. Accordingly, the yield of the segments can be improved, and the manufacturing costs can be reduced. Besides, waste material can be reduced.

Brief Description of the Drawings

FIG. 1 is a partially cut-away perspective view showing an example of a flat commutator using segments manufactured in a manufacturing method according to the present invention;
FIG. 2 is a perspective view showing the structure of segments for a flat commutator;
FIG. 3 is an explanatory view showing a method of manufacturing segments, according to the first embodiment of the present invention;
FIG. 4 is also an explanatory view showing the method of manufacturing segments, according to the first embodiment of the present invention;
FIG. 5 is an explanatory view showing a method of manufacturing segments, according to the second embodiment of the present invention;
FIG. 6 is an explanatory view showing influences from R at a corner during resin molding;
FIG. 7 is a partially cut-away side view showing the structure of a cylindrical commutator;
FIG. 8 is an explanatory view of a method of manufacturing segments used in FIG. 7; and
FIG. 9 is an explanatory view showing a state of manufacturing a segment of a flat commutator from a tator-bar.

Best Mode for Carrying Out the Invention

(First Embodiment)

Hereinafter, an embodiment of the present invention will be described in detail by referring to the accompanying drawings. FIG. 1 is a partially cut-away perspective view showing an example of a flat commutator using segments manufactured according to a manufacturing method of the present invention.
A commutator 1 is constructed in a flat structure as shown in FIG. 1, and is used in a starter motor, ink-tank-type fuel feed pump, and the like. The commutator 1 has a holder part 2 made of synthetic resins, and plural segments 3 made of metal. The segments 3 are molded integrally with the holder part 2. Surfaces of the segments 3 (upper surfaces in FIG. 1) constitute brush sliding surfaces 4 which a brush (not shown) contacts from an axial direction.
In this commutator 1, the respective segments 3 are placed in a circular cartridge. Kept in this state, the whole segments are subjected to molding to form the commutator 1. The commutator 1 thus molded is assembled together with a rotation shaft (not shown), an armature core, a coil wire, and the like. Thereafter, a coating of synthetic resins is provided thereon to complete an armature assembly.
The holder part 2 is formed in a thick and substantially disk-like shape. A shaft hole 5 to fix a motor rotation shaft is formed in the center part of the holder part 2. On one end surface in the axial direction of the holder part 2, plural segments 3 are provided at equal intervals. The segments 3 each are formed in a substantially sector shape, and are arranged radially on the surface of the holder part 2. Slits 6 are formed between the segments 3, to electrically insulate adjacent segments 3 from each other.
FIG. 2 is a perspective view showing the structure of one of the segments 3. As shown in FIG. 2, each segment 3 has a body part 7 where a brush sliding surface 4 is formed, and an outer circumferential part 8 formed outside the body part 7, stepped therefrom. A U-shaped coil mount groove 9 is provided in the outer circumferential part 8. To the coil mount groove 9, an armature coil (not shown) is fixed by fusing or the like.
A boss part 11 is provided in the inner circumferential side of the body part 7. A tapered part 12a is formed on the inner surface side. The boundary between the body part 7 and the outer circumferential part 8 forms a step part 13. The inner surface side of the step part 13 also forms a tapered part 12b. The tapered parts 12a and 12b widen toward the body part 7, forming an anchor part 14 which serves as a fall stopper to prevent the segment 3 from axially slipping off from the holder part 2.
The segments 3 as described above are formed in a manner as follows. FIGS. 3 and 4 are explanatory views showing a method of manufacturing the segments 3, as the first embodiment of the present invention. As shown in FIG. 3, each segment 3 is also cut out from a copper-made tator-bar (base metal) 15. The tator-bar 15 is formed by a drawing process of drawing the copper material in the direction X indicated by an arrow. Also as shown in FIGS. 3 and 4, the tator-bar 15 is formed to have a cross-section which is the same as the A-A cross-section (a cross-section in the diameter direction) of the segment 3 in FIG. 2. That is, the tator-bar 15 has a form in which a body forming part 17 to form a body part 7, an outer circumference forming part 18 to form an outer circumferential part 8, and a boss forming part 21 to form a boss part 11 are formed integrally.
A part between the body forming part 17 and the outer circumference forming part 18 of the tator-bar 15 forms a step part 23. Tapered surfaces 22a and 22b are respectively formed inside these parts. Since the cross-sectional shape of the tator-bar 15 is defined by a drawing die, the degree of freedom of the cross-sectional shape is greater compared with bending. Accordingly, the tapered surfaces 22a and 22b can be formed inside the boss part 11 and inside the step part 23. Commutator metal 52 based on press working, as shown in FIG. 6, requires a step of processing a boss part 61 into a tapered shape to prevent falling off or a deburring step of forming an engagement piece 62. In contrast, in case of the segment 3 in the present embodiment, an anchor shape is formed at the same time in a drawing process. Therefore, neither tapering nor deburring is needed, and so, the number of processing steps can be reduced.
As shown in FIG. 4, the segments 3 arranged laterally in line are punched out from the tator-bar 15. The punching is carried out in a direction at right angles to the drawing direction X (i.e., the direction Y in FIG. 3). Segment forming from the tator-bar 15 can be completed by one time of punching. Compared with a case of performing punching plural times, less dimensional variants are caused due to errors in matching and feeding in each process, and so, the segments 3 can be formed with higher precision. Equipments at this time are used only for the punching with respect to pressing. Precision is not particularly required for the equipments. Therefore, general-purpose equipments of low prices are satisfactory to cover this pressing, so that the segments 3 can be processed at low costs.
Also, as shown in FIG. 4, in the case of punching out the segments 3, the area to be removed can be reduced more than in another case shown in FIG. 9. Therefore, materials can be utilized efficiently to improve the yield. Further, since no bending is performed when forming the segments 3, R at corners can be reduced to the minimum. Accordingly, resins do not flow around toward the brush sliding surfaces 4 due to resin molding, so that the number of post-processing steps can be reduced.
On the other side, in the segments 3, outer surfaces 17a of the body forming parts 17 constitute the brush sliding surfaces 4. That is, surfaces subjected to drawing form the brush sliding surfaces 4. Surfaces subjected to drawing have higher surface roughness and flatness compared with a broken-out section formed by punching, and can be directly used as the brush sliding surfaces 4. In conventional segments shown in FIGS. 8 and 9, surfaces subjected to drawing are embedded in a resin mold, and broken-out sections form the brush sliding surfaces 4. Although there are excellent surfaces, those surfaces are not utilized effectively. In contrast, the segments 3 in the present embodiment are arranged such that surfaces subjected to drawing constitute the brush sliding surfaces 4. These excellent surfaces are utilized actively. Therefore, if the segments 3 are used, no finish work for the brush sliding surfaces 4 is needed after resin molding. The number of processing steps of manufacturing the commutator 1 can be reduced. Note that the outer surface 17a of each body forming part 17 has so high hardness due to work hardening based on drawing that durability of the brush sliding surfaces 4 can be improved.
In general, the drawing direction X of the tator-bar is perpendicular to the brush sliding direction (rotation direction) Z, as shown in FIGS. 8 and 9. From the viewpoint of orientations of materials on the surface of the brush sliding surfaces 4, the processing direction and the brush sliding direction are preferably the same. However, in the case of FIGS. 8 and 9, the brush sliding surfaces of the segments are subjected to cutting finish work after punching. Therefore, there is no significant influence even if both directions are different. In contrast, of the brush sliding surfaces 4 of the segments 3, the drawing direction (the direction X in FIG. 3) of the tator-bar 15 is substantially the same as the brush sliding direction (the direction Z in FIG. 2). In the present embodiment, the tangential projection of the brush sliding direction Z on the center line (the line A-A in FIG. 2) in the circumferential direction of each segment 3 coincides with the drawing direction X of the tator-bar 15. Therefore, it is possible for the segments 3 to omit post processes necessitated by the difference between the processing direction and the brush sliding direction. In addition, owing to the excellence of the surfaces subjected to drawing and the surface hardness, parts punched out from the tator-bar 15 can be directly used as products.

(Second embodiment)

FIG. 5 is an explanatory view showing a method of manufacturing segments, as a second embodiment of the present invention. Those parts and members that are identical to those of the first embodiment are denoted at the identical reference symbols. Detailed descriptions thereof will be omitted herefrom.
In the manufacturing method according to the second embodiment, as shown in FIG. 5, zig-zag punching is performed on a tator-bar (base metal) 25 in order to improve more the yield of the segments 3. In the tator-bar 25, a portion having a similar cross-sectional shape to the segment 3 is formed such that adjacent segments 3 are punched out in opposite directions, i.e., upward and downward directions. Thus, the tator-bar 25 has a vertically symmetrical form. That is, the tator-bar 25 has a shape in which parts corresponding to the outer circumferential parts 18 shown in the tator-bar 15 which has as a whole a similar cross-sectional shape to that of the segments 3 are arranged at both ends. Outer end parts 26 are formed also at both ends.
Adjacent segments 3 are punched out up-side-down, i.e., with the inner circumferential and outer circumferential sides inverted between the adjacent segments 3. From the tator-bar 25, each outer end parts 26 as the inner circumferential side (tapered end) is punched out at an intermediate position, thereby forming a boss part 11. As is apparent from comparison between FIGS. 4 and 5, in the present manufacturing method, unnecessary parts of the tator-bar 25 are so small that the segments 3 can be punched out very efficiently. Accordingly, the yield of the segments 3 can be improved, and the manufacturing costs can be reduced. Besides, waste material can be reduced.
It goes without saying that the present invention is not limited to the above embodiment, and various changes may be made without departing from the scope of the invention.
For example, in the commutator 1 described previously, cutting finish work to clean the brush sliding surfaces 4 can be omitted. However, finish work may be carried out by cutting to attain flatness and surface roughness corresponding to precision required for a complete product. Therefore, the tator- bars 15 and 25 each may have not only the same cross-sectional shape as the segments 3 but also a shape which can be easily processed into the segments 3 by a post process. The term of the similar cross-sectional shape to that of the segments may include a cross-sectional shape which is not perfectly the same. In case of performing a post process, it is possible to reduce the number of processing steps, such as a grinding step and the like, compared with a conventional method.
According to the method of manufacturing segments for a flat commutator, base metal which has a portion having a similar cross-sectional shape to the cross-sectional shape of segments is formed by drawing. This base metal is cut to form the segments. Therefore, the segments can be shaped by cutting the base metal, and so, a large number of processing steps are not necessary. Accordingly, segments can be formed with good precision without dimensional variants due to errors in matching and feeding in each process. In addition, since processing of the base metal does not require precise feeding, equipments for manufacturing segments may be general-purpose equipments available at low prices. Thus, the segments can be processed at low costs.
In addition, the drawing direction of the base metal is substantially the same as the brush sliding direction of the segments. Therefore, the processing direction of the brush sliding surfaces can be substantially the same as the brush sliding direction. Without carrying out cutting finish work after punching, surfaces subjected to drawing can be directly used as the brush sliding surfaces.
Further, surfaces of the base metal subjected to drawing are used as the brush sliding surfaces. Therefore, portions which are hardened by processing of the drawing constitute the brush sliding surfaces, and improve the hardness of the brush sliding surfaces. Thus, durability of the commutator can be improved.
In addition, anchor parts are formed on the base metal by drawing. Therefore, work for forming anchor-part, such as tapering, deburring, and the like, is unnecessary so that the number of processing steps can be reduced.
On the other side, if adjacent segments are punched out from the base metal, with their inner and outer circumferential sides inverted to each other, unnecessary parts of the base metal can be reduced, and so, the segments can be punched out efficiently. Accordingly, the yield of the segments can be improved, and the manufacturing costs can be reduced. Besides, waste material can be reduced.

Claims

A method of manufacturing segments for a flat commutator which has a holder part formed of synthetic resins in a disk-like shape, and a plurality of segments arranged along a circumferential direction of the holder part on an end surface thereof in an axial direction, the method characterized by comprising:

a step of forming a base metal having a portion whose cross-sectional shape is similar to cross-sectional shapes of the segments by drawing; and

a step of forming the segments by cutting the base metal.
The method according to claim 1, characterized in that the segments are arranged radially on the one end surface of the holder part in the axial direction, and the base metal has a portion whose cross-sectional shape is similar to the cross-sectional shape of each of the segment along a diameter direction thereof.
The method according to claim 1 or 2, characterized in that a drawing direction from the base metal is substantially the same direction as a brush sliding direction of the segment.
The method according to any one of claims 1 to 3, characterized in that surfaces of the base metal subjected to the drawing form brush sliding surfaces in the segments.
The method according to any one of claims 1 to 4, characterized in that anchor parts of the segments that serve as a stopper to prevent the segments from falling off of the holder part in the axial direction is formed on the base metal by the drawing.
The method according to any one of claims 1 to 5, characterized in that the segments are formed by punching out the segments from the base metal in a direction perpendicular to the drawing direction.
The method according to claim 6, characterized in that the segments are punched out with the inner circumferential and outer circumferential sides of adjacent segments inverted to each other.