ROTATING ELECTRICAL MACHINE

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rotating electrical machine including a commutator having a hook.

2. Description of the Related Art

As one conventional rotating electrical machine, there is known a rotating electrical machine in which a plurality of projections are formed on a hook portion on a side on which the hook portion is brought into contact with a winding so that the projection part breaks through a coating of the winding at the time of fusing, to thereby electrically connect a commutator segment and the winding to each other (see, for example, Japanese Patent Application Laid-open No. Hei 10-257736).

In the conventional rotating electrical machine, the plurality of projections are formed on the hook portion on the side on which the hook portion is brought into contact with the winding (coil) , and hence it is difficult to form the projections . Further, in such cases where the wire diameter of the coil is increased and the volume of the commutator segment in the vicinity of the hook portion is increased, the thermal capacities of the coil and the hook portion increase, which causes insufficient heating in the vicinity of the hook portion at the time of fusing. Thus, the fusing becomes insufficient, which may lead to unstable electrical connection between the coil and the commutator segment and deterioration in motor performance.

When the energization amount or the pressurization is increased at the time of fusing in order to avoid this situation, excess coil deformation occurs, which may cause coil disconnection or the like.

Further, when the heating in the vicinity of the hook portion is insufficient at the time of fusing, close-contacting strength between the surface of the hook portion on the coil side, which is brought into contact with the coil, and the commutator segment opposed to the surface becomes insufficient. In this case, due to the centrifugal force at the time of motor rotation or the like, the hook portion may be separated from the surface of the commutator segment, which may lead to deterioration of electrical connection between the coil and the commutator segment, reduction in motor performance, and the like.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-mentioned problems, and therefore has an object to obtain a high-performance rotating electrical machine which is capable of securing heating in the vicinity of the hook at the time of fusing, establishing stable electrical connection between the coil and the commutator segment, and preventing coil disconnection even when the wire diameter of the coil is increased or when the volume of the commutator segment in the vicinity of the hook is increased.

According to an exemplary embodiment of the present invention, there is provided a rotating electrical machine, including: a commutator; and a coil, the commutator including a commutator segment integrally including, on one axial end side thereof, a hook connected to the coil, and, on another end side thereof, a sliding-contact portionwhich is brought into sliding contact withabrush, aplurality of the commutator segments being arranged in a circumferential direction, the coil being electrically connected to the hook by fusing, in which the commutator segment includes a thinned portion between a leading end portion of the hook and the sliding-contact portion in an axial direction and in vicinity of the leading end portion.

According to the exemplary embodiment of the present invention, it is possible to obtain the high-performance rotating electrical machine which is capable of securing heating in the vicinity of the hook at the time of fusing, establishing stable electrical connection between the coil and the commutator segment, and preventing coil disconnection.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a sectional view of a rotating electrical machine according to a first embodiment of the present invention;

FIG. 2 is an explanatory view of a main part in the vicinity of a commutator of FIG. 1;

FIG. 3 is an explanatory view before fusing of FIG. 2;

FIG. 4 is an explanatory view illustrating a connection relationship of equalizers;

FIG. 5 is an explanatory view of a main part in the vicinity of a commutator according to a second embodiment of the present invention;

FIG. 6 is an explanatory view of a main part in the vicinity of a commutator according to a third embodiment of the present invention;

FIG. 7 is an explanatory view of a main part in the vicinity of a commutator according to a fourth embodiment of the present invention; and

FIG. 8 is an explanatory view of a main part of a commutator segment according to a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment.

Description is made of a first embodiment of the present invention with reference to FIGS. 1 to 4 . Note that, in the following drawings, the same or corresponding parts are denoted by the same reference symbols for description.

FIG. 1 is a sectional view of a brush motor serving as a rotating electrical machine, which is used for a motor for an electric power steering device or the like. FIG. 2 is an explanatory view of a main part in the vicinity of a commutator of FIG. 1, FIG. 3 is an
explanatory view before fusing of FIG. 2, and FIG. 4 is an explanatory-view illustrating a connection relationship of equalizers.

In FIG. 1, on an inner peripheral surface of a yoke 10 having a bottomed cylindrical shape, four permanent magnets 11 are fixed together with a holder 12 made of a resin. An armature 20 includes a commutator 22 and a core 24, which are fixed to a shaft 21.

Through twenty-two slots provided in the core 24 , amulti-wound coil (winding) 23 is provided. The coil 23 is connected to the commutator 22 (commutator segment 40). On one end side (core 24 side) of the commutator 22, an equalizer 50 is arranged. The equalizer 50 is connected to the commutator 22 (commutator segment 40).

A brush holder is fixed to a housing 3 0 fitted to the yoke 10, and four brushes 33 held by the brush holder are biased by a spring 32 so as to be arranged in a sliding-contactable manner with respect to an outer peripheral surface of the commutator 22. The brushes 33 are connected to a power supply via an external lead wire 34. In the vicinity of both ends of the shaft 21, a bearing 13 and a bearing 31 are provided, respectively, thereby supporting the armature 2 0 rotatably via an air gap provided between the armature 20 and inner peripheral surfaces of the permanent magnets 11. In this manner, a brush motor 1 (rotating electrical machine) is constructed.

The commutator 22 is a mold commutator in which a plurality of commutator segments 40 are integrally formed with a base resin 41 by resin molding, and is integrally constructed of twenty-two commutator segments 4 0 arranged in a circumferential direction, and the base resin 41 for holding (fixing) the respective commutator segments 4 0 and insulating the respective commutator segments 4 0 from each other.

Each of the commutator segments 4 0 integrally includes, on one axial end side (core 24 side) thereof, a hook 42 connected to the coil 23 and the equalizer 50, and, on the other end side thereof, a sliding-contact portion 43 which is brought into sliding contact with the brush 33. The commutator segment 4 0 is made of a copper alloy material, and is formed by cold forging in an initial step.

The sliding-contact portion 43 is provided in an axial range in which the brush 33 is brought into sliding contact with the outer peripheral surface of the commutator segment 4 0 (brush width dimension) . The sliding-contact portion 43 is formed by subjecting the outer peripheral surface of the commutator segment 4 0 to cutting with use of a lathing machine or the like.

The coil 23 and the equalizer 50 are electrically connected to the commutator segment 4 0 via the hook 42.

As illustrated in FIG. 2, between a leading end portion 42a of the hook 42 after fusing and the sliding-contact portion 43 in the axial direction, and in the vicinity of the leading end portion 42a, there is provided a thinned portion 46 formed on the outer peripheral side of the commutator segment 40 from the outer peripheral side, for reducing the sectional area of the commutator segment 40.

In this first embodiment, the thinned portion 46 is a groove portion 44 provided by annularly and radially inwardly recessing the outer peripheral surface of the commutator segment 40.

The groove portion 44 is formed by subjecting the mold commutator 22 to cutting with use of a lathing machine or the like, and has a concave shape recessed inwardly from the outer peripheral side. The groove portion 44 is formed at the same time of roughing the sliding-contact portion 43 . The groove portion 44 includes fine irregular processing marks formed by a cutting tool during cutting.

An outer diameter dimension D of the commutator segment 4 0 opposed to a surface 42b of the leading end portion 42a of the hook 42 on the coil side is formed larger in diameter than an outer diameter dimension d of the commutator segment 40 in the sliding-contact portion 43.

A dimension of the commutator segment 40 on the inner diameter side (boundarypart with respect to thebase resin41) is substantially the same over the axial direction, and is formed linearly.

When the outer diameter dimension D is formed larger than the outer diameter dimension d, the volume of the commutator segment 40 in the part of the outer diameter dimension D (vicinity of the hook portion) is increased, and hence the thermal capacity of the commutator segment 4 0 in this part is increased.

Note that, when the outer diameter dimension D is formed larger than the outer diameter dimension d, a circumferential length of a root part of the hook 42 is increased, and hence a gap dimension between the hooks 42 adjacent to each other in the circumferential direction can be increased. Therefore, it becomes possible to increase a motor output by increasing (thickening) a wire diameter of the coil 23. Even when the wire diameter is increased, a gap dimension between the adjacent parts of the coil 23 can be secured.

Accordingly, it is possible to prevent short-circuit failure between the adjacent parts of the coil 23 and the like.

In addition, the outer diameter dimension d is formed smaller than the outer diameter dimension D, and hence it is possible to prevent upsizing of the radial dimension of the part of the brush 33 (upsizing of the motor), and further prevent increase in loss (loss torque) due to friction of the brush 33.

Even when the outer diameter dimension D is increased, when the outer diameter dimension d is not changed, parts in the vicinity of the brush 33, parts in the vicinity of the housing 30, or the like can be used without being changed.

In particular, in a motor for an electric power steering device, the returning of the steering wheel deteriorates when the loss torque increases, and hence the structure without increase of the outer diameter dimension d is suitable for the motor for an electric power steering device.

As illustrated in FIG. 2, the groove portion 44 is formed in a part (stepped part) at a boundary between a large diameter portion (outer diameter dimension D) and a small diameter portion (outer diameter dimension d) in an axial direction. As illustrated in FIG.
2, a left side surface (core 24 side) of the groove portion 44 is formed substantially at a right angle from a bottom surface of the groove portion 44 on the inner diameter side, and is communicated to the large diameter portion.

The left side surface of the groove portion 44 is formed at substantially the same axial position as an end surface of the leading end portion 42a of the hook 42 on the brush 33 side.

An axial right side surface (brush side) of the groove portion 44 includes a tapered portion 44a, and the tapered portion 44a is formed at the same time of cutting the groove portion 44.

In the commutator segment 40 of the mold commutator 22 on the inner peripheral side of the hook 42, a reduced thickness portion 45 is formed on one axial end side (core 24 side) by axially and annularly recessing the mold commutator 22 by cutting with use of
a lathing machine or the like. The reduced thickness portion 45 includes fine irregular processing marks formed by a cutting tool during cutting.

The reduced thickness portion 45 is formed by cutting over a range from the commutator segment 4 0 to the base resin 41 on the inner periphery side thereof. Therefore, a surface of the reduced thickness portion 45 on the inner periphery side is the base resin 41 (insulator). The surface of the reduced thickness portion 45 on the inner periphery side is formed so that the commutator segment 40 (conductor) does not remain thereon.

FIG. 3 illustrates a state in which the coil 23 and the equalizer 50 are locked by the claw-like hook 42 included in the mold commutator 22, and is an explanatory view illustrating a state before fusing.

The commutator segment 4 0 includes, in a part opposed to the surface 42b of the hook 42 on the coil side, a coil groove 47 in which the coil 23 and the equalizer 50 are accommodated after fusing.

The thinned portion 46 (groove portion 44) is formed at a position different from the coil groove 47 in the axial direction.

The coil groove 47, the thinned portion 46 (groove portion 44) , and the reduced thickness portion 45 are formed in advance in the mold commutator 22 in a unit state.
Reference symbols A and B in FIG. 3 represent examples of positions at which electrodes for fusing are arranged, and the electrodes are arranged in the vicinity of the leading end portion 42a of the hook 42 and in the vicinity of the sliding-contact portion 43, respectively.

With the electrodes arranged as illustrated in FIG. 3, a large current is applied between the vicinity of the leading end portion 42a and the vicinity of the sliding-contact portion 43 . In addition, in the vicinity of the leading end portion 42a, a pressure is applied in an axis center direction (shaft 21 direction) by the electrode. In this manner, the fusing is performed.

Through heat generation by energization (heating) and pressurization, as illustrated in FIG. 2, the hook 42 is bent, and insulating coatings of the coil 23 and the equalizer 50 are removed. Further, the coil 23 and the equalizer 50 are deformed, thereby being brought into close contact (fused) between the coil groove 47 and the surface 42b of the hook 42 on the coil side. Accordingly, the coil 23 and the equalizer 50 are electrically connected to the commutator segment 40.

At this time, a close-contact state is established between the surface 42b of the hook 42 on the coil side in the vicinity of the leading end portion 42a and the commutator segment 4 0 opposed thereto (outer diameter dimension D) by the above-mentioned heat generation (heating) and pressurization.

FIG. 4 is an explanatory view illustrating a connection relationship of the equalizers 50, and illustrates that the equalizer 50 is used to electrically connect between the first and twelfth commutator segments 4 0 (hooks 42) radially opposed to each other of the twenty-two commutator segments 4 0 (twenty-two hooks 42) as illustrated in FIG. 4.
Similarly, connection is established between the commutator segments 40 (hooks 42) radially opposed to each other as the second and thirteenth commutator segments 40 (hooks 42), the third and fourteenth commutator segments 40 (hooks 42), •••. As described above, the commutator segments 4 0 which are supposed to have the same potential are connected to each other by the equalizer 50. In this manner, it is possible to prevent a circulation current from flowing into the brush 33 and the like. Thus, the high-performance brush motor 1 can be achieved.

The operation of the brush motor 1 constructed as described above is described. The external lead wire 34 included in the brush motor 1 is connected to the power supply (drive device) , and the coil 23 is energized via the commutator segment 40 which is brought into sliding contact with the brush 33 connected to the external lead wire 34 .
With the electromagnetic action between the permanent magnets 11 and the armature 20 energized by the coil 23, the shaft 21 is rotated. With this rotational force, a steering force for steering a vehicle can be supported.

The motor 1 for an electric power steering device is increasingly mounted onto a vehicle having a larger displacement for the purpose of energy saving in recent years, and hence a motor having a larger output has been desired.

A small, high-performance motor has been desired at low cost, which can establish stable electrical connection between the coil 23 and the commutator segment 40 even when a coil 23 having a large wire diameter is applied in order to increase the motor output.

As described above, according to the first embodiment, the rotating electrical machine is provided, which includes: the commutator 22 including the plurality of commutator segments 4 0 arranged in the circumferential direction, the commutator segments 40 each integrally including, on the one axial end side thereof, the hook 42 connected to the coil 23, and, on the other end side thereof, the sliding-contact portion 43 which is brought into sliding contact with the brush 33; and the coil 23 electrically connected to the hook 42 (commutator segment 40) by fusing. The commutator segment 4 0 includes the thinned portion 46 between the leading end portion 42a of the hook 42 and the sliding-contact portion 43 in the axial direction and in the vicinity of the leading end portion 42a. In this manner, it is possible to reduce the thermal capacity of the commutator segment 4 0 in the vicinity of the hook 42 even when the wire diameter of the coil 23 is increased or

when the volume of the commutator segment 40 in the vicinity of the hook 42 is increased. Thus, it is possible to obtain the high-performance brush motor 1 (rotating electrical machine) which is capable of securing heating (heat generation) in the vicinity of the hook 42 at the time of fusing, establishing stable electrical connection between the coil 23 and the commutator segment 40, and preventing disconnection of the coil 23.

Through adjustment of the size of the thinned portion 46, the thermal capacity can be adjusted. Even when the wire diameter of the coil 23 is changed, the main body of the commutator 22 can be used without being changed. Therefore, it is possible to prevent increase in the number of parts, to increase the degree of freedom for setting the fusing condition, and to improve the connection reliability.

Even when the commutator is changed to a commutator 22 including a commutator segment 40 having a large volume in the vicinity of the hook 42, through adjustment of the size of the thinned portion 46, the thermal capacity can be adjusted. Accordingly, it is possible to increase the degree of freedom for setting the fusing condition and improve the connection reliability.

The thinnedportion46isprovidedinthevicinityof the leading end portion 42a, and hence the thermal capacity of the commutator segment 40 in the fusing part can be adjusted effectively. Further, the thinned portion 46 can be downsized, and it is possible to prevent increase in axial length of the brush motor 1.

A firm close-contact state can be established between the surface 42b of the hook 42 on the coil side in the vicinity of the leading end portion 42a and the commutator segment 40 opposed thereto.

The thinned portion 4 6 is the groove portion 44 provided on the outer peripheral surface of the commutator segment 40 . Therefore, the formation thereof is easy, and the groove portion 44 can be formed at the time of processing the sliding-contact portion 43. Thus, the groove portion 44 can be formed at low cost.

Through adjustment of the size of the groove portion 44, the thermal capacity can be adjusted, and effects similar to those in the case of the thinned portion 4 6 can be obtained.

The commutator 22 is the mold commutator 22 including the base resin 41 for holding the respective commutator segments 4 0 and insulating the respective commutator segments 40 from each other, and includes the groove portion 44 formed in the mold commutator 22 by cutting. Therefore, the groove portion 44 is formed in the mold commutator 22 in which the commutator segments 40 are integrally formed with the base resin 41 in advance, and there is no need to perform resin molding after the groove portion 44 is formed.

Therefore, resin adhesion due to resin molding, dropping of an adhered resin, and the like do not occur. Thus, productivity and reliability are improved.

The groove portion 44 can be formed at the time of cutting of the sliding-contact portion 43. Therefore, the groove portion 44 can be formed easily at low cost.
The outer diameter dimension D of the commutator segment 4 0 opposed to the surface 42b of the leading end portion 42a of the hook 42 on the coil side is formed larger than the outer diameter dimension d of the commutator segment 4 0 in the sliding-contact portion 43, and hence a circumferential length of the commutator segment 40 in the fusing part is increased, and a gap dimension between the hooks 42 adjacent to each other in the circumferential direction is increased. Therefore, it becomes possible to increase the motor output by increasing (thickening) the wire diameter of the coil 23, and even when the wire diameter is increased, a gap dimension between the adjacent parts of the coil 23 can be secured. Accordingly, it is possible to prevent short-circuit failure between the parts of the coil 23, and the reliability is improved. When the outer diameter dimension D is formed larger than the outer diameter dimension d, the above-mentioned effects of the thinned portion 46 (groove portion 44) can be exerted more effectively.

The groove portion 44 is formed at a boundary between the large diameter portion D and the small diameter portion d in the axial direction. Therefore, the thermal capacity of the commutator segment 40 in the fusing part can be effectively adjusted. In addition, the groove portion 44 can be easily formed, and it is possible to prevent increase in axial length of the brush motor 1.

A firm close-contact state can be established between the surface 42b of the hook 42 on the coil side in the vicinity of the leading endportion42a and the commutator segment 40 opposed thereto.

The axial side surface of the groove portion 44 includes the tapered portion 44a, and hence the groove portion 44 can be easily formed. The groove portion 44 can be formed at the time of cutting the sliding-contact portion 43, and hence processing is possible with use of the same cutting tool. Thus, the productivity is improved.

The commutator 22 is the mold commutator 22 including the base resin 41 for holding the respective commutator segments 40 and insulating the respective commutator segments 40 from each other, and the commutator segment 40 of the mold commutator 22 includes, on the inner peripheral side of the hook 42, the reduced thickness portion 45 formed on the one axial end side by reducing the thickness by cutting. Therefore, the effects of the thinned portion 46 and the groove portion 44 can be achieved more effectively. In addition, even when the wire diameter of the coil 2 3 is increased or when the volume of the commutator segment 40 in the vicinity of the hook 42 is increased, the degree of freedom for adjusting the thermal capacity can be enlarged. Accordingly, it is possible to establish stable electrical connection between the coil 23 and the commutator segment 40, and prevent disconnection of the coil 23.

A firmer close-contact state can be established between the surface 42b of the hook 42 on the coil side in the vicinity of the leading endportion 42a and the commutator segment 40 opposed thereto.

The reduced thickness portion 45 is formed over the range from the commutator segment 40 to the base resin 41 on the inner periphery-side thereof . Therefore, on the inner periphery side of the reduced thickness portion 45, there is no thinned part of the commutator segment 4 0 as a conductor. Therefore, for example, short-circuit or rotation failure of a rotor due to dropping of the thinned part does not occur, and hence the
reliability is further improved.

The equalizer 50 which is electrically connected to the hook 42 by fusing is provided. Therefore, it is possible to prevent a circulation current from flowing into the brush 33.

Further, even when the thermal capacity increases due to the addition of the equalizer 50, stable electrical connection can be established among the coil 23, the equalizer 50, and the commutator segment 40. Still further, it is possible to prevent disconnection of the coil 23 and the equalizer 50.

Second Embodiment.

Description is made of a second embodiment of the present invention with reference to FIG. 5. FIG. 5 is an explanatory view of a main part in the vicinity of the commutator.

The second embodiment mainly differs from the first embodiment in the following points.

The size of the groove portion 44 as the thinned portion 46 is increased with respect to the commutator segment 40 . In contrast, the reduced thickness portion 45 is formed smaller.

Through adjustment of the sizes of the thinned portion 46 (groove portion 44) and the reduced thickness portion 45, the thermal capacity can be effectively adjusted. Therefore, it is possible to increase the degree of freedom for setting the fusing condition and improve the connection reliability.

The reduced thickness portion 45 is formed, but in the second embodiment, the reduced thickness portion 45 is not formed over the range from the commutator segment 40 to the base resin 41 on the inner periphery side thereof. The reduced thickness portion 45 is formed in a part of the commutator segment 40, and is formed so that, on the inner periphery side of the reduced thickness portion 45, the part of the commutator segment 40 as a conductor remains.

The left side surface of the thinned portion 46 (groove portion 44) formed in the vicinity of the leading end portion 42a of the hook 42 is provided slightly on the core 24 side (left side) with respect to the end surface of the leading end portion 42a of the hook 42 on the brush side. The thinned portion 46 (groove portion 44) is formed on the core 24 side (left side) , and hence the axial length of the brush motor 1 can be reduced.

Third Embodiment.

Description is made of a third embodiment of the present invention with reference to FIG. 6. FIG. 6 is an explanatory view of a main part in the vicinity of the commutator.

In the third embodiment, the tapered portion 44a and a tapered portion 44b are provided on both axial side surfaces of the thinned portion 46 (groove portion 46) , respectively. Although the axial length increases, the degree of freedom in selection of a processing method, a processing tool, and the like increases.

Further, a joining auxiliary material 48 is provided between the surface 42b of the leading end portion 42a of the hook 42 on the coil side and the commutator segment 40 which abuts against the surface 42b.

The joining auxiliary material 48 is formed by subjecting the surface of the commutator segment 40 to plating of tin (Sn) or the like. Before the coil 23 is locked by the hook 42 as illustrated in FIG. 3, the joining auxiliary material 48 is formed in advance in the unit state of the mold commutator 22.

After fusing, the joining auxiliary material 4 8 is provided between the surface 42b of the leading end portion 42a of the hook 42 on the coil side and the commutator segment 40 which abuts against the surface 42b, and hence the close-contacting strength therebetween is further increased. Thus, it is possible to prevent the hook 42 from being separated from the surface of the commutator segment 4 0 due to the centrifugal force at the time of motor rotation and the like. Accordingly, a stable electrical connection is established between the coil 23 and the commutator segment 40, and the motor performance is improved.

The joining auxiliary material 48 is formed in advance in the unit state of the mold commutator 22. Therefore, it is unnecessary to add the joining auxiliary material 48 after winding and before fusing. Accordingly, the productivity is improved.

Note that, the joining auxiliary material 48 is applicable in the respective embodiments.

Fourth Embodiment.

Description is made of a fourth embodiment of the present invention with reference to FIG. 7. FIG. 7 is an explanatory view of a main part in the vicinity of the commutator.

In the fourth embodiment, the outer diameter dimension of the commutator segment 4 0 opposed to the surface of the leading end portion 42a of the hook 42 on the coil side and the outer diameter dimension of the commutator segment 40 in the sliding-contact portion 43 are formed to be the same outer diameter dimension d.

Also in the commutator 22 of the fourth embodiment, the thinned portion 46 (groove portion 44) , the reduced thickness portion 45, and the like are provided, and thus effects similar to those described above can be obtained. However, greater effects can be obtained in the case where, as in the first embodiment, the outer diameter dimension D is formed larger than the outer diameter dimension d.

Fifth Embodiment.

Description is made of a fifth embodiment of the present invention with reference to FIG. 8. FIG. 8 is an explanatory view of a main part of the commutator segment, and is a front view of a single commutator segment when viewed from a radially outer side. The fifth embodiment describes a different mode of the thinned port ion 46.

The thinned portion 46 has a circumferential width reduced with respect to a width dimension Wl in the circumferential direction (motor rotation direction) of the single commutator segment 40. The part of the thinned portion 46 is formed to have a width dimension W2 in the circumferential direction. A plurality of the commutator segments 4 0 are arranged in the circumferential direction.

The thinned portion 46 is formed by pressing the commutator segment 4 0 in a unit state, and the commutator segments 4 0 thus formed are integrated with the base resin 41 to obtain the mold commutator 22.

The thinned portion 46 is provided, and hence, similarly to the above, the thermal capacity of the commutator segment 4 0 in the vicinity of the hook 42 can be reduced.

The commutator segments 40 each having the thinned portion 46 formed in advance are integrated with the base resin 41 to obtain the mold commutator 22, and hence as compared with the thinned portion 46 (groove portion 44) of other embodiments, the size change of the thinned portion 46 is more difficult. However, it is unnecessary to form the thinned portion 4 6 by cut ting and the like in the subsequent step, and the thinned portion 46 can be formed by pressing at low cost.

Note that, the thinned portion 46 is provided on each of both circumferential sides of the single commutator segment 40, but the thinned port ion 4 6 maybe provided on one side thereof. Alternatively, a hole portion or the like may be provided in the commutator segment 40.

In each of the above-mentioned embodiments, the parts having the same configuration produce the same effects.

Further, the present invention is not limited to the above-mentioned embodiments, and may be appropriately modified without departing from the spirit of the present invention.

WHAT IS CLAIMED IS:

1. A rotating electrical machine, comprising:

a commutator; and

a coil, the commutator including a commutator segment integrally including, on one axial end side thereof, a hook connected to the coil, and, on another end side thereof, a sliding-contact port ion which is brought into sliding contact with a brush, a plurality of the commutator segments being arranged in a circumferential direction,

the coil being electrically connected to the hook by fusing,

wherein the commutator segment includes a thinned portion between a leading end portion of the hook and the sliding-contact portion in an axial direction and in vicinity of the leading end portion.

2 . A rotating electrical machine according to claim 1, wherein the thinned portion comprises a groove portion provided on an outer peripheral surface of the commutator segment.

3. A rotating electrical machine according to claim 1 or 2, wherein the commutator comprises a mold commutator including a base resin for holding the respective plurality of the commutator segments and insulating the respective plurality of the commutator segments from each other, and includes a groove portion formed in the mold commutator by cutting.

4. A rotating electrical machine according to any one of claims 1 to 3 , wherein an outer diameter dimension of the commutator segment opposed to a surface of the leading end portion of the hook on the coil side is formed larger than an outer diameter dimension of the commutator segment in the sliding-contact portion.

5. A rotating electrical machine according to claim 2, wherein the groove portion is formed at a boundary between a large diameter portion and a small diameter portion in the axial direction.

6. A rotating electrical machine according to claim 2, wherein the groove portion has a tapered portion on an axial side surface thereof.

7. A rotating electrical machine according to any one of claims 1 to 6, further comprising a joining auxiliary material between a surface of the leading end portion of the hook on the coil side and the commutator segment which abuts against the surface.

8 . A rotating electrical machine according to any one of claims 1 to 7, wherein the commutator comprises a mold commutator including a base resin for holding the respective plurality of the commutator segments and insulating the respective plurality of the commutator segments from each other, and

wherein the commutator segment of the mold commutator includes, on an inner peripheral side of the hook, a reduced thickness portion formed on the one axial end side
by reducing a thickness by cutting.

9. A rotating electrical machine according to claim 8 , wherein the reduced thickness portion is formed over a range from the commutator segment to the base resin on an inner peripheral side of the commutator segment.

10. A rotating electrical machine according to anyone of claims 1 to 9, further comprising an equalizer which is electrically connected to the hook by the fusing.