Title of Invention	DYNAMOELECTRIC MACHINE AND METHOD OF MANUFACTURING A BRUSH THEREOF
Abstract	To provide a low-cost brush in which the extending life of the brush and the shortening of the running processing time or the elimination of the running processing can be compatible with one another, there is provided the brush including: a sliding contact surface which is provided to one end of the brush (4) in a shaft direction, and has a concave-curved surface formed along the outer circumferential surface of the commutator (11) ; and a thickness-reduction portion (15) which has a concave-curved surf ace formed concave to the shaft direction to be gradually away from the outer circumferential surface of the commutator (11) from the sliding contact surface (14) to the other end of the brush (14) in the shaft direction and which has a smooth surface without irregularities on a rotational direction side of the commutator in a radial direction. Also, a method of manufacturing a brush includes the steps of successively cutting the plurality of baked brushes to the rotational direction side of the commutator (11) to form the thickness-reduction portion (15).

Title of Invention

DYNAMOELECTRIC MACHINE AND METHOD OF MANUFACTURING A BRUSH THEREOF

Abstract

To provide a low-cost brush in which the extending life of the brush and the shortening of the running processing time or the elimination of the running processing can be compatible with one another, there is provided the brush including: a sliding contact surface which is provided to one end of the brush (4) in a shaft direction, and has a concave-curved surface formed along the outer circumferential surface of the commutator (11) ; and a thickness-reduction portion (15) which has a concave-curved surf ace formed concave to the shaft direction to be gradually away from the outer circumferential surface of the commutator (11) from the sliding contact surface (14) to the other end of the brush (14) in the shaft direction and which has a smooth surface without irregularities on a rotational direction side of the commutator in a radial direction. Also, a method of manufacturing a brush includes the steps of successively cutting the plurality of baked brushes to the rotational direction side of the commutator (11) to form the thickness-reduction portion (15).

Full Text	DYNAMOELECTRIC MACHINE AND METHOD OF MANUFACTURING A BRUSH THEREOF BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynaxnoelectric machine including a brush, and to a method of manufacturing the brush, 2. Description of the Related Art There have been known, as conventional dynamoelectricmachines attempting to reduce noises caused by sliding contact between a brush and a commutator and as manufacturing methods for the brush, one that employs a brush including a sliding contact surface formed in an inner diameter side surface of the brush so as to be curved in a concave shape along an outer circumferential surface of the commutator and a tilt surface tilted so that the sliding contact surface is gradually away from the outer circumferential surface of the commutator, the tilt surface is curved in a concave shape along with the curved surface of the sliding contact surface to maintain a slide contact width of the slide contact surface in a motor shaft direction at a substantially constant value. Further, there was one in which the concave-curved surface of the tilt surface and the concave-curved surface of the sliding contact surface are formed at the same curvature. In addition, there has been known one, in which after the assembly of the dynamoelectric machine, the commutator is rotated to slightly wear the slide contact surface of the brush so that the slide contact surface conforms along the outer circumferential surface of the commutator, and running/conditioning of the dynamoelectric machine is performed so as to stabilize a slide contact state between the brush and the commutator, thereby reducing noises caused by the sliding contact in the dynamoelectric machine immediately after the assembly, (refer to JP 2003-259607 A, paragraph [0004] and FIG, 4, and refer to JP 2005-102412 A, paragraph [0002] ) The conventional dynamoelectric machines aimed to reduce the noises caused by sliding contact by providing the sliding contact surface to an end of the brush in the shaft direction, However, the tilt surface of the brush provided in the shaft direction is linearly tilted relative to the shift direction so that the sliding contact surface is gradually away from the outer circumferential surface of the commutator in the shaft direction. Therefore, in a case of a brush whose tilt angle is small, in other words, in a case where the tilt surface is close to be parallel to the outer circumferential surface of the commutator, a volume of the brush is increased by a small tilt, so the wear-resistance life of the brush can be extended to a relatively long life. However, there is a problem in that the dynamoelectric machine to which the brush is installed requires an addition of running processing, or the running processing takes a relatively long time. On the other hand, in a case of a brush whose tilt angle is large, in other words, in a case where the tilt surface is relatively widely spaced apart from the outer circumferential surface of the commutator, a volume of the brush is reduced by a large tilt, so the dynamoelectric machine to which the brush is installed can eliminate the addition of the running processing or the running processing can be shortened relatively to a short time. However, there is a problem in that the wear-resistance life of the brush becomes a relatively short life. Therefore, there is a problem in that an improvement of the wear-resistance life of the brush and shortening of the running processing time or an elimination of the running processing cannot be compatible with each other, Further, the conventional dynamoelectric machines have a structure in which the concave-curved surface along the curved sliding contact surface is formed on the commutator rotational direction side of the tilt surface which is linearly tilted relative to the shift direction to be gradually away from the outer circumferential surface of the commutator in the shaft direction. The surface (inner diameter side surface) in which the tilt surface is opposed to the commutator has the concave-curved surface whose center on the rotational direction side is recessed to the outside in the radial direction, so it is difficult to successively cutting a plurality of stacked brushes to the rotational direction side of the commutator to form the tilt surface having the concave-curved surface. Therefore, for example, when a grind stone rotating about a rotating shaft of the dynamoelectric machine or a shaft substantially parallel to the tilt surface is pressed to each of the brushes to form the concave-curved surface by cut processing, the formation of the tilt surface takes a relatively long processing time. Thus, when the brush having the conventional shape is to be obtained, there is a problem in that the cost of the brush becomes relatively higher. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. It is an object of the present invention to provide a dynamoelectric machine including a low-cost brush in which an increase in life of the brush and the shortening of the running processing time or the elimination of the running processing can be compatible with one another and a method of manufacturing the brush. According to the present invention, there is provided a dynamoelectric machine, including: a cylindrical commutator fixed to a rotating shaft; and a brush which is in sliding contact with an outer circumferential surface of the commutator, wherein; the brush includes: a sliding contact surface which is provided to a side surface located on a commutator side and one end of the brush in a shaft direction, and has a concave-curved surface formed along the outer circumferential surface of the commutator; and a thickness-reduction portion which has a concave-curved surface formed concave to the shaft direction to be gradually away from the outer circumferential surface of the commutator from the sliding contact surface to the other end of the brush in the shaft direction, and the thickness-reduction portion has a smooth surface without irregularities on a rotational direction side of the commutator in the radial direction. According to the present invention, there is provided a method of manufacturing a brush of a dynamoelectric machine, the brush being in sliding contact with an outer circumferential surface of a cylindrical commutator of the dynamoelectric machine the brush including: a sliding contact surface which is provided to a side surface located on a commutator side and one end of the brush in a shaft direction, and has a concave-curved surface formed along the outer circumferential surface of the commutator; and a thickness-reduction portion which has a concave-curved surface formed concave to the shaft direction to be gradually away from the outer circumferential surface of the commutator from the sliding contact surface to the other end of the brush in the shaft direction, and which has a smooth surface without irregularities on a rotational direction side of the commutator in a radial direction, the method of manufacturing the brush of a dynamoelectric machine including the steps of: compression-molding material powder filled in a forming mold of the brushy-baking the compression-molded material powder; and successively cut processing a plurality of the baked brushes to the rotational direction side of the commutator to form the thickness-reduction portion. According to the present invention, it is possible to obtain the dynamoelectric machine including the low-cost brush in which the extending life of the brush and the shortening of the running processing time or the elimination of the running processing can be compatible with one another and the method of manufacturing the brush. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 is a cross sectional view showing a motor according to Embodiment 1 of the present invention; Figs. 2(a) to 2(c) are explanatory views showing shapes of a brush according to Embodiment 1 of the present inventions-Fig. 3 is an explanatory view showing a comparison between a thickness-reduction portion of the brush according to Embodiment 1 of the present invention and a tilt surface of a conventional brush; Fig. 4 is an explanatory view showing the formation of the thickness-reduction portion of the brush according to Embodiment 1 of the present inventions- Fig. 5 is a front view showing a brush according to Embodiment 2 of the present invention; and Fig. 6 is a front view showing a brush according to Embodiment 3 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Embodiment 1 will be described with reference to Figs. 1 to 4. In each of the drawings, the same or corresponding parts are expressed by the same reference numerals for description. Fig. 1 is a cross sectional view showing a motor for electric power steering device . Figs. 2(a) to2(c) are explanatory views showing brush shapes of the motor of Fig. 1. Fig, 3 is an explanatory view showing a comparison between a thickness-reduction portion of the brush of Figs. 2 (a) to 2 (c) and a tilt surface of a conventional brush. Fig. 4 is an explanatory view showing the formation of the thickness-reduction portion of the brush of Figs. 2 (a) to 2 (c) • In Fig, 1, a motor 1 for electric power steering device which is a dynamoelectric machine includes a cylindrical yoke 2 which serves as a stator and has a closed end, an armature 3 which serves as a rotator and provided inside the yoke 2, a brushes 4 for supplying power to the armature 3, a bracket 5 which is fitted into an opening portion of the yoke 2 to fix to the yoke 2, and a boss 7 fixed to an end of a rotating shaft 6 of the armature 3 to couple to a steering side of a vehicle. Two pairs of N-S magnetic poles 8^ each of which is made of a permanent magnet, are fixed to an inner circumferential surface of the yoke 2 . The armature 3 is located inside the magnetic poles 8 through a gap. The rotating shaft 6 is rotatably supported by bearings 9 and 10. The brushes 4 are in sliding contact with an outer circumferential surface of a cylindrical commutator 11 fixed to the rotating shaft 6 to supply power to armature coils 12 connected with the cylindrical commutator 11. The brushes 4 including two positive brushes and two negative brushes are radially provided around the commutator 11. Each of the brushes 4 is pressed by a spring 13 to the outer circumferential surface of a cylindrical commutator 11 in a shaft center direction of the rotating shift 6. The brush 4 has a substantially cuboid shape. The brush 4 includes: a sliding contact surface 14 which is included in a side surface (inner diameter side surface) located on the commutator side and provided to an end of the corresponding brush 4 in a shaft direction (side opposed to the armature 3 in Fig. 1); and a thickness-reduction portion 15 which has a concave-curved surface formed concave to the shaft direction so as to be gradually away from the outer circumferential surface of the commutator 11 from the sliding contact surface 14 to the other end of the brush 4 in the shaft direction (armature 3 side in Fig. 1). The brush 4 which is the substantial cuboid includes a pigtail 16 led from a shaft direction end surface opposed to a shaft direction end surface located on the sliding contact surface 14 side (end surface on the armature 3 side in Fig, 1). The pigtail 16 is electrically connected with a lead wire 27 joined to a control device for electric power steering device. Figs. 2(a) to 2(c) are explanatory views showing the shapes of the brush 4, in which Fig. 2(a) shows a side surface thereof as viewed from the commutator side, Fig. 2(b) shows a side surface thereof when it is viewed from the shaft direction end surface opposed to the shaft direction end surface located on the sliding contact surface 14 side, that is, when Fig. 2(a) is a side surface view viewed from the armature side, and Fig. 2(c) shows the same view as the brush 4 of Fig. 1 and is a front view showing a rotational direction side end surface of the brush 4 as viewed from a rotational direction side of the commutator 11. A longitudinal direction of a space including the brush 4 of Figs. 1 and 2(c) is referred to as the rotational direction side of the commutator. A direction from the sliding contact surface side of the brush 4 which is the substantial cuboid to an end surface opposed to the sliding contact surface side is referred to as a radial direction. The brush 4 includes: the sliding contact surface 14 which is formed to an end thereof in the shaft direction and curved in a concave shape along the outer circumferential surface of the commutator 11; and the thickness-reduction portion 15 which has the concave-curved surface formed concave to the shaft direction so as to be gradually away from the outer circumferential surface of the commutator 11 from the sliding contact surface 14 to the other end of the brush 4 in the shaft direction. The thickness-reduction portion 15 has a smooth surface without irregularities on the rotational direction side of the commutator 11 in the radial direction. That is, the concave-curved surface of the thickness-reduction portion 15 is formed by extending a curve indicating the thickness-reduction portion 15 of Figs. 1 and 2(c) perpendicular to the space in a downward direction of the space of Figs . 1 and 2 (c) . Therefore, unlike the conventional brush, the concave-curved surface whose center is recessed to the outside in the radial direction is not provided and the smooth surface without irregularities in the radial direction is formed perpendicular to the rotational direction side end surface of the brush 4. The brush 4 includes the pigtail 16 led from the shaft direction end surface opposed to the shaft direction end surface located on the sliding contact surface 14 side. The brush 4 includes a chamfered portion 17 which is provided on the other end side (pigtail 16 side) of the brush 4 in the shaft direction, connected with the thickness-reduction portion 15 having the concave-curved surface concave to the shaft direction, and formed with a forming die of the brush 4 so as to be gradually away from the outer circumferential surface of the commutator 11 in the shaft direction. The sliding contact surface 14, the thickness-reduction portion 15, and the chamfered portion 17 are successively connected from the one end side to the other end side in the shaft direction and constructed so as to be gradually away from the outer circumferential surface of the commutator 11 to the other end side in the shaft direction. As shown in Figs, 2(a) to 2(c), a chamfered portion of approximately 0,5 (mm) to 1 (mm) is formed with the forming die of the brush of the brush 4 in each of corner portions extending in the radial direction, of both end surfaces of the brush 4 which are located on the shaft direction side and in each of corner portions extending in the shaft direction, of both end surfaces of the sliding contact surface 14 which are located on the rotational direction side. The chamfered portions are provided to prevent the corner portions of the brush 4 from being damaged. The chamfered portions are formed with the forming die of the brush 4 in low cost. The concave-curved surface of the sliding contact surface 14 is formed such that a radius thereof is slightly larger than a radius of the outer circumferential surface of the commutator 11. For example, the radius of the concave-curved surface of the sliding contact surface 14 is 12,5 (mm) and the radius of the outer circumferential surface of the commutator 11 is 12.3 (mm), so at the early stage of assembly of the motor 1^ the vicinity of the center of the sliding contact surface 14 which is located on the rotational direction side is first in sliding contact with the outer circumferential surface of the commutator 11 and wears along the outer circumferential surface of the commutator 11 from an early stage. Therefore, a sliding contact sound can be reduced from an early stage to eliminate a running processing or shorten the running processing time. At the early stage of assembly of the motor 1, undercuts of the outer circumferential surface of the commutator 11 which are provided between adjacent commutator pieces do not interfere with corner portions or the like which are close to both end surfaces of the sliding contact surface 14 which are located on the rotational direction side, so the sliding contact sound can be reduced. Note that, when the radius of the concave-curved surface of the sliding contact surface 14 becomes larger than the radius of the outer circumferential surface of the commutator 11, the sliding contact is made in a thin linear shape in the vicinity of the center of the sliding contact surface 14, with the result that a sliding contact area reduces to increase the heat of the brush 4 which is generated by a supplied current. Thus, the concave-curved surface of the sliding contact surface 14 is desirably formed such that the radius thereof is larger than the radius of the outer circumferential surface of the commutator 11 by a value substantially equal to or smaller than 10%, desirably a value substantially equal to approximately 5%. Fig. 3 is an explanatory view showing a comparison between the thickness-reduction port ion 15 having the concave-curved surface formed concave to the shaft direction, of the brush 4 of Figs, 2(a) to 2(c) and a tilt surface linearly formed in the shaft direction, of a conventional brush. The thickness-reduction portion 15 is connected with a portion of the sliding contact surface 14 formed in the one end in the shaft direction and has a curved surface formed so as to gradually increase a gap size in the radial direction from (gradually increase a distance from) the outer circumferential surface of the commutator 11 toward the other end in the shaft direction. Because the curved surface is concave to the shaft direction, the distance from the outer circumferential surface of the commutator 11 relatively rapidly increases in the vicinity of the sliding contact surface 14, but the distance can be relatively slowly increased in the vicinity of the other end of the brush 4 in the shaft direction. Therefore, the extending life of the brush and the shortening of the running processing time or the elimination of the running processing can be compatible with one another. The sliding contact surface 14 can be continuously brought into sliding contact from the one end to the other end in the shaft direction with the wearing of the brush 4 to reduce noises caused by sliding contact. When the curved surface is convex to the shaft direction, as in the caseofatiltsur face 18a whose tilt angle is small as described later, the addition of running processing is necessary or the running processing takes a relatively long time. In addition, a problem occurs in which, for example, the convex-curved surface cannot be formed by a normal circular grind stone. The brush 4 has the curved surface concave to the shaft direction, so the concave-curved surface can be easily formed by the grind stone. In contrast to this, tilt surfaces 18a and 18b of conventional brushes are linear to the shaft direction. In the case of the tilt surface 18 whose tilt angle is small, in other words, in the case where the tilt surface 18a is close to be parallel to the outer circumferential surface of the commutator 11, a brush volume to brush wearing is relatively increased by a small tilt, so the wear-resistance life of the brush can be extended to a relatively long life. However, because of the increase in volume, in running processing of the dynamoelectric machine to which the brush is installed requires the addition of running processing or the running processing takes a relatively long time. On the other hand, in the case of the tilt surface 18b whose tilt angle is large, in other words, in the case where the tilt surface 18b is relatively widely spaced apart from the outer circumferential surface of the commutator 11, the brush volume to brush wearing is relatively reduced by a large tilt, so in the running processing of the dynamoelectric machine can eliminate the running processing or the running processing, it is possible to be shortened to a relative short time. However, the wear-resistance life of the brush becomes a relatively short life. Each of the thickness-reduction portion 15 and the tilt surfaces 18a and 18b is constructed such that the sliding contact surface 14 is continuously in sliding contact from the one end side to the other end side in the shaft direction with the wearing. However, in the case of the tilt surfaces 18a and 18b, the extending life of the brush and the shortening of the running processing time or the elimination of the running processing cannot be compatible with one another. The brush 4 is a metal graphite brush. The forming die of the brush 4 is filled with material powder such as graphite powder or copper powder, compression-molded, and baked at high temperature to produce a brush main body. The material powder filled in the forming die and the pigtail 16 whose end portion is embedded in the material powder are pressurized in an A-direction and a B-direction of Fig. 2(c) to be integrally compression-molded. After the compression molding, a resultant is pressed in the A-direction of Fig, 2(c) to be taken out from the forming die and then baked to produce the brush main body. Of the shapes of the brush 4 of Figs. 2(a) to 2(c), each shape other than the thickness-reduction portion 15 is formed with the forming die. For example, the concave-curved surface of the sliding contact surface 14 is formed with the forming die. The chamfered portion 17 is also formed with the forming die. The pigtail 16 is embedded in the brush main body to be integrally formed. Fig. 4 is an explanatory view showing the formation of the thickness-reduction portion 15 of the brush 4 of Figs, 2 (a) to 2 (c) , The baked brush main body is shaped to have an excess thickness portion 19 as indicated by a dashed line of Fig. 4, This reason is as follows. In the case where compression molding is performed without the excess thickness portion 19, when the brush 4 is pressed in the A-direction of Fig. 2(c) (direction to the pigtail 16) to be taken out from the forming die, the protruded sliding contact surface 14 interferes with the forming die, so the brush 4 is not easily taken out from the forming die. Therefore, in order to press the brush 4 in the A-direction to be easily taken out from the forming die, the compression molding is performed with the shape in which the excess thickness portion 19 is provided, thereby forming the brush main body. Therefore, even when the pigtail 16 led from the shaft direction end surface opposed to the shaft direction end surface located on the sliding contact surface 14 side is integrally formed with the brush main body by compression molding, the brush main body can be formed with the forming die because the excess thickness portion 19 is provided and the curved surface concave to the shaft direction is formed by cut processing* As shown in Fig. 4, the baked brush main body and a grind stone 20 for forming the thickness-reduction portion 15 by cut processing (grinding) are located. When the excess thickness portion 19 is removed to form the thickness-reduction portion 15, the brush 4 can be obtained. The grind stone 20 rotates about a shaft orthogonal to the shaft center of the rotating shift 6 of the motor 1 in a C-direction of Fig, 4 and the shaft is decentered on the other end side (pigtail 16 side) relative to the center position of the brush in the shaft direction. The grind stone 20 has a substantially cone shape convex to a downward direction of the space of Fig, 4, When a plurality of brush main bodies stacked in the downward direction of the space of Fig, 4 are moved (slide) up relative to the grind stone 20 on the space of Fig. 4 to be subjected to continuous cut processing on the rotational direction side (in the longitudinal direction of the space of Fig. 4) of the commutator 11, it is possible to successively produce the brushes 4, each of which has the thickness-reduction portion 15 in which the concave-curved surface corresponding to a maximum of a diameter of the grind stone 20 is formed in the shaft direction and a smooth surface which is orthogonal to the longitudinal direction of the space of Fig. 4 and does not include irregularities in the radial direction is formed in the rotational direction side, The grind stone 20 has the substantially cone shape, so a processing margin can be gradually increased with a good processability and a plurality of brushes can be successively processed. Because the thickness-reduction portion 15 orthogonal to the end surface of the brush 4 located on the rotational direction side is formed on the rotational direction side, the thickness-reduction portion 15 is symmetrical with respect to the rotational direction of the commutator 11. Therefore-, a difference between sounds generated by sliding contact in rotational directions does not easily occur, so a dynamoelectric machine suitable for the motor 1 for electric power steering device which rotates in both directions can be obtained. In Fig, 4, a step size S between the one end side (sliding contact surface 14 side) of the thickness-reduction portion 15 and the other end side (pigtail 16 side) thereof in the radial direction is set to 20% or less of a radial direction size H of the brush 4. For example, the radial direction size H between the sliding contact surface 14 and a radial direction end surface opposed thereto is 10 (mm) and the step size S between the sliding contact surface 14 and the other end side of the thickness-reduction portion 15 in the radial direction is 1.7 (mm). Therefore, the step size S is 17% of the radial direction size H. When the step size S increases, the processing margin becomes larger. When a ratio between S and H (S/H) increases, the fixation ofthebrush4 becomes insufficient, so it is difficult to successively form the thickness-reduction portions 15. Therefore, a problem occurs in which a cost of the brush 4 increases and the life of the brush shortens. Thus, it is important to set the step size S to 20% or less of the radial direction size H. It is desirable to set the step size S to 2 (mm) or less. Next, the operation of the above-mentioned structure in Embodiment 1 will be described. A control device for controlling the motor 1 for electric power steering device based on a signal from a steering torque sensor provided on a steering side of a vehicle or a signal indicating a vehicle speed or the like is provided. Power is supplied to the brush 4 through the pigtail 16 connected with the lead wire 27 joined to the control device. A current is supplied from the commutator 11 with which the brush 4 is in sliding contact to the armature coil 12. The rotating shaft 6 is rotated by an electromagnetic action between the armature 3 to which the current is supplied and the magnetic pole 8. A rotating force is transferred to the steering side through the boss 7 to aid a steering force of a steering wheel of the vehicle. Therefore, a steering force of a driver can be reduced. The electric power steering device is increasingly applied to even a vehicle whose displacement is large because of energy saving. The motor 1 is required in which, for example, a reduction in noises caused by sliding contact with the brush is realized, a size is small, and a cost is low, As described above, according to Embodiment 1, the brush 4 includes: the sliding contact surface 14 which is included in the side surface located on the commutator side, provided to the end of the brush 4 in the shaft direction, and has the concave-curved surface formed along the outer circumferential surface of the commutator 11; and the thickness-reduction portion 15 which has the curved surface formed concave to the shaft direction so as to be gradually away from the outer circumferential surface of the commutator 11 from the sliding contact surface 14 to the other end of the brush 4 in the shaft direction. Therefore, it is possible to obtain a dynamoelectric machine in which an extending life of the brush and the shortening of the running processing time or the elimination of the running processing can be compatible with one another. At the same time, in the brush 4, the thickness-reduction portion 15 has the smooth surface without irregularities on the rotational direction side of the commutator 11 in the radial direction, so the thickness-reduction portion can be formed in low cost. Thus, a dynamoelectric machine including a low-cost brush can be obtained. The brush 4 includes the pigtail 16 led from the shaft direction end surface opposed to the shaft direction end surface located on the sliding contact surface 14 side, the sliding contact surface 14 whose concave-curved surface along the outer circumferential surface of the commutator 11 is formed with the forming die of the brush 4, and the thickness-reduction portion 15 whose curved surface concave to the shaft direction is f ormed by cut processing . Therefore, for example, the concave-curved surface along the outer circumferential surface of the commutator 11 can be formed with the forming die in low cost and the curved surface concave to the shaft direction can be formed by cut processing in low cost. Thus, a dynamoelectric machine including the low-cost brush 4 can be obtained. The chamfered portion 17 is located on the other end side of the brush 4 in the shaft direction, connected in the shaft direction with the thickness-reduction portion 15 having the concave-curved surface concave to the shaft direction, and formed with the forming die of the brush 4 so as to be .gradually away from the outer circumferential surface of the commutator 11 in the shaft direction. Therefore, the chamfered portion 17 can be formed with the forming die in low cost. The chamfered portion 17 is gradually spaced apart in the shaft direction, so the sliding contact surface 14 can be continuously brought into sliding contact from the one end to the other end in the shaft direction with the wearing of the brush 4 to stably reduce noises caused by sliding contact. Even in the case where, for example, an upper limit of a diameter size of the grind stone 20 for obtaining the thickness-reduction portion 15 by grinding is limited, when the chamfered portion 17 is provided, the thickness-reduction portion 15 can be formed by the grind stone 20, so a device for processing the thickness-reduction portion 15 can be also used. Therefore, the low-cost brush 4 can be obtained. The concave-curved surface of the sliding contact surface 14 is formed such that the radius thereof is slightly larger than the radius of the outer circumferential surface of the commutator 11. Therefore, the sliding contact sound can be reduced from an early stage to eliminate the running processing or shorten the running processing time, The step size S between the one end side of the thickness-reduction portion 15 and the other end side thereof in the radial direction is set to 20% or less of the radial direction size H of the brush. Therefore, the low-cost brush 4 can be obtained and the life of the brush can be extended to a relatively long life, A method of manufacturing the brush 4 according to Embodiment 1 includes a step of compression-molding material powder with which forming dies of the brushes 4 are filled, a step of baking the brushes obtained by the compression molding, and a step of successively cutting the plurality of baked brushes 4 to the rotational direction side of the commutator 11 to form the thickness-reduction portions 15, Therefore, a low-cost brush manufacturing method can be obtained. Embodiment 2 Embodiment 2 will be described with reference to Fig, 5. The same or corresponding parts as those in Embodiment 1 are expressed by the same references and thus the description will be omitted. Fig, 5 is a view corresponding to Fig. 2(C), which is a front view showing the rotational direction side end surface of the brush 4 as viewed from the rotational direction side of the commutator 11. The brush 4 includes: the pigtail 16 led from the end surface located on the rotational direction side of the commutator 11 (pigtail 16 is led perpendicular to the space of Fig, 5); the sliding contact surface 14 having the concave-^curved surface formed along the outer circumferential surface of the commutator 11 by cut processing (which is indicated by a broken line of Fig, 5) ; and the thickness-reduction portion 15 having the curved surface formed concave to the shaft direction with the forming die of the brush 4. Each of the sliding contact surface 14, the thickness-reduction portion 15, and the chamfered portion 17 are the same as that of Embodiment 1, The material powder filled in the forming die and the pigtail 16 whose end portion is embedded in the material powder are pressurized in the longitudinal direction of the space of Fig. 5 to be integrally compression-molded. After the compression molding, the brush main body is pressed in an upward direction of the space of Fig, 5 to be taken out from the forming die and then baked to produce the brush main body* In this embodiment;- the thickness-reduction portion 15 is formed with the forming die, but the concave-curved surface of the sliding contact surface portion is formed by cut processing. The chamfered portion 17 is formed with the forming die. The sliding contact surface 14 is formed to have the concave-curved surface along the outer circumferential surface of the commutator 11, Therefore, when the sliding contact surface 14 is formed with the forming die, the concave-curved surface recessed to the inner portion (outside in the radial direction) of the brush 4 interferes with the forming die at the time of taking out after compression molding, so the brush 4 is not easily taken out from the forming die . Therefore, compression molding is performed using the smooth surface located on the rotational direction (longitudinal direction of the space of Fig. 5) side which does not include the concave-curved surface . After baking, a skin of the sliding contact surface portion corresponding to the position of the sliding contact surface 14 formed with the forming die is removed by cut processing to form the sliding contact surface 14 having the concave-curved surface along the outer circumferential surface of the commutator 11. At the time of compression molding, the material powder is drown by a wall surface of the forming die and is made dense to thereby relatively cure the surface of the brush, so there is the case where a sliding contact sound generated at the beginning of operation of the dynamoelectric machine becomes larger. However, the skin of the sliding contact surface portion is removed by the cut processing. Therefore, it is possible to obtain the sliding contact surface 14 including the concave-curved surface whose hardness is relatively low and material tissue is relatively uniform and to reduce the sliding contact sound from an early stage-As described above, according to Embodiment 2, the brush 4 includes the pigtail 16 led from the end surface located on the rotational direction side of the commutator 11, the sliding contact surface 14 whose concave-curved surface along the outer circumferential surface of the commutator 11 is formed by the cut processing, and the thickness-reduction portion 15 whose curved surface concave to the shaft direction is formed with the forming die of the brush 4, Therefore, for example, the sliding contact sound can be reduced and from an early stage and the curved surface concave to the shaft direction can be formed with the forming die in low cost. Thus, a low-cost dynamoelectric machine can be obtained. The skin of the sliding contact surface portion which is formed with the forming die is removed by the cut processing to form the sliding contact surface 14. Therefore, the sliding contact surface 14 wears along the outer circumferential surface of the commutator 11 from an early stage, so the sliding contact sound can be reduced from an early stage to eliminate the running processing or shorten the running processing time. Embodiment 3 Embodiment 3 will be described with reference to Fig, 6. The same or corresponding parts as those in Embodiment 1 or 2 are expressed by the same references and thus the description will be omitted. Fig. 6 is a view corresponding to Fig. 2(C) and Fig. 5, which is a front view showing the rotational direction side end surface of the brush 4 as viewed from the rotational direction side of the commutator 11. The brush 4 includes : the pigtail 16 led from the shaft direction end surface located on the sliding contact surface 14 side; the sliding contact surface 14 having the concave-curved surface formed along the outer circumferential surface of the commutator 11 with the forming die of the brush 4; and the thickness-reduction portion 15 having the curved surface formed concave to the shaft direction with the forming die thereof* Each of the sliding contact surface 14 and the thickness-reduction portion 15 are the same as that of Embodiment 1 or 2, The material powder filled in the forming die and the pigtail 16 whose end portion is embedded in the material powder are pressurized in the lateral direction of the space of the Fig, 6 as the case of the A-di rection and the B-direction in Embodiment 1, to be integrally compression-molded. After the compression molding, a resultant is pressed from the right to the left of the space of the Fig, 6 to be taken out from the forming die and then baked to produce the brush 4, In this embodiment, both the sliding contact surface 14 and the thickness-reduction portion 15 are formed with the forming die, The sliding contact surface 14 protruding relative to the thickness-reduction portion 15 is located on the pigtail 16 side and the brush 4 is pressed from the right to the left (pigtail 16 side) of the space of the Fig. 6 to be taken out after the compression molding. Therefore, the brush 4 is taken out without the interference of the sliding contact surface 14 with the forming die, so the sliding contact surface 14 and the thickness-reduction portion 15 can be formed with the forming die, In this embodiment, the sliding contact surface 14 can be formed with the forming die. A sliding contact surface portion having a concave-curved surface in which a processing margin is added to the concave-curved surface of the sliding contact surface 14 may be formed with a forming die and then the skin of the sliding contact surface portion formed with the forming die may be removed by cut processing after baking, thereby forming the concave-curved surface of the sliding contact surface 14 of the brush 4. In this case, as in Embodiment 2, the sliding contact surface 14 wears along the outer circumferential surface of the commutator 11 from an early stage, so it is possible to eliminate the running processing or shorten the running processing time. As described above, according to Embodiment 3, the brush 4 includes the pigtail 16 led from the shaft direction end surface located on the sliding contact surface 14 side, the sliding contact surface 14 having the concave-curved surface formed along the outer circumferential surface of the commutator 11 with the forming die of the brush 4, and the thickness-reduction portion 15 having the curved surface formed concave to the shaft direction with the forming die thereof. Therefore, both the sliding contact surface 14 and the thickness-reduction portion 15 can be formed with the forming die to obtain the low-cost brush 4. In the above-mentioned embodiments, the motor 1 for electric power steering device is described as the dynamoelectric machine. However, the dynamoelectric machine is not limited to this. WHAT IS CLAIMED IS: 1. A dynamoelectric machine, comprising: a cylindrical commutator fixed to a rotating shaft; and a brush which is in sliding contact with an outer circumferential surface of the commutator, the brush comprising: a sliding contact surface which is provided to a side surface located on a commutator side and one end of the brush in a shaft direction, and has a concave-curved surface formed along the outer circumferential surface of the commutator; and a thickness-reduction portion which has a concave-curved surface formed concave to the shaft direction to be gradually away from the outer circumferential surface of the commutator from the sliding contact surface to the other end of the brush in the shaft direction, wherein the thickness-reduction portion has a smooth surface without irregularities on a rotational direction side of the commutator in a radial direction. 2. A dynamoelectric machine according to claim 1, wherein the brush comprises: a pigtail led from a shaft direction end surface opposed to a shaft direction end surface located on the sliding contact surface side; a sliding contact surface which has a concave-curved surface formed along the outer circumferential surface of the commutator by using a forming die of the brush; and a thickness-reduction portion which has a concave-curved surface formed concave to the shaft direction by cut processing. 3. A dynamoelectric machine according to claim 1, wherein the brush comprises: a pigtail led from an end surface located on the rotational direction side of the commutator; a sliding contact surface has a concave-curved surface formed along the outer circumferential surface of the commutator by cut processing; and a thickness-reduction portion which has a concave-curved surface formed concave to the shaft direction by using a forming die of the brush. 4. A dynamoelectric machine according to claim 1^ wherein the brush comprises: a pigtail led from a shaft direction end surface located on a sliding contact surface side, a sliding contact surface has a concave-curved surface formed along the outer circumferential surface of the commutator by using a forming die of the brush; and the thickness-reduction portion which has a concave-curved surface formed concave to the shaft direction by using the forming die of the brush. 5. A dynamoelectric machine according to claim 2 or 4, wherein the concave-curved surface of the sliding contact surface of the brush is formed by removing, by cut processing, a skin of the sliding contact surface portion formed by using the forming die of the brush. 6. A dynamoelectric machine according to any one of claims 1 to 5, wherein the brush comprises a chamfered portion which is provided to another end of the brush in the shaft direction, connected in the shaft direction with the thickness-reduction portion having the concave-curved surface concave to the shaft direction, and formed by using a forming die of the brush to be gradually away from the outer circumferential surface of the commutator in the shaft direction. 7. A dynamoelectric machine according to any one of claims 1 to 6, wherein the concave-curved surface of the sliding contact surface is formed so that a radius thereof is slightly larger than a radius of the outer circumferential surface of the commutator. 8. A dynamoelectric machine according to any one of claims 1 to 1, wherein a step size between one end side of the thickness-reduction portion and another end side in the radial direction is set to a value equal to or smaller than 20% of a step size of the radial direction of the brush. 9. A method of manufacturing a brush of a dynamoelectric machine. the brush being in sliding contact with an outer circumferential surface of a cylindrical commutator of the dynamoelectric machine the brush including: a sliding contact surface which is provided to a side surface located on a commutator side and one end of the brush in a shaft direction, and has a concave-curved surface formed along the outer circumferential surface of the commutator; and a thickness-reduction portion which has a concave-curved surface formed concave to the shaft direction to be gradually away from the outer circumferential surface of the commutator from the sliding contact surface to the other end of the brush in the shaft direction, and which has a smooth surface without irregularities on a rotational direction side of the commutator in a radial direction, the method of manufacturing the brush of a dynamoelectric machine comprising the steps of: compression-moldingmaterial powder filled in a forming mold of the brush; baking the compression-molded material powder; and successively cut processing a plurality of the baked brushes to the rotational direction side of the commutator to form the thickness-reduction portion.

Full Text

DYNAMOELECTRIC MACHINE AND METHOD OF MANUFACTURING A BRUSH THEREOF
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dynaxnoelectric machine including a brush, and to a method of manufacturing the brush,
2. Description of the Related Art
There have been known, as conventional dynamoelectricmachines attempting to reduce noises caused by sliding contact between a brush and a commutator and as manufacturing methods for the brush, one that employs a brush including a sliding contact surface formed in an inner diameter side surface of the brush so as to be curved in a concave shape along an outer circumferential surface of the commutator and a tilt surface tilted so that the sliding contact surface is gradually away from the outer circumferential surface of the commutator, the tilt surface is curved in a concave shape along with the curved surface of the sliding contact surface to maintain a slide contact width of the slide contact surface in a motor shaft direction at a substantially constant value. Further, there was one in which the concave-curved surface of the tilt surface and the concave-curved surface of the sliding contact surface are formed at the same curvature.
In addition, there has been known one, in which after the

assembly of the dynamoelectric machine, the commutator is rotated
to slightly wear the slide contact surface of the brush so that
the slide contact surface conforms along the outer circumferential
surface of the commutator, and running/conditioning of the
dynamoelectric machine is performed so as to stabilize a slide contact
state between the brush and the commutator, thereby reducing noises
caused by the sliding contact in the dynamoelectric machine
immediately after the assembly, (refer to JP 2003-259607 A, paragraph
[0004] and FIG, 4, and refer to JP 2005-102412 A, paragraph [0002] )
The conventional dynamoelectric machines aimed to reduce the
noises caused by sliding contact by providing the sliding contact
surface to an end of the brush in the shaft direction, However,
the tilt surface of the brush provided in the shaft direction is
linearly tilted relative to the shift direction so that the sliding
contact surface is gradually away from the outer circumferential
surface of the commutator in the shaft direction. Therefore, in
a case of a brush whose tilt angle is small, in other words, in
a case where the tilt surface is close to be parallel to the outer
circumferential surface of the commutator, a volume of the brush
is increased by a small tilt, so the wear-resistance life of the
brush can be extended to a relatively long life. However, there
is a problem in that the dynamoelectric machine to which the brush
is installed requires an addition of running processing, or the
running processing takes a relatively long time.

On the other hand, in a case of a brush whose tilt angle is large, in other words, in a case where the tilt surface is relatively widely spaced apart from the outer circumferential surface of the commutator, a volume of the brush is reduced by a large tilt, so the dynamoelectric machine to which the brush is installed can eliminate the addition of the running processing or the running processing can be shortened relatively to a short time. However, there is a problem in that the wear-resistance life of the brush becomes a relatively short life. Therefore, there is a problem in that an improvement of the wear-resistance life of the brush and shortening of the running processing time or an elimination of the running processing cannot be compatible with each other,
Further, the conventional dynamoelectric machines have a structure in which the concave-curved surface along the curved sliding contact surface is formed on the commutator rotational direction side of the tilt surface which is linearly tilted relative to the shift direction to be gradually away from the outer circumferential surface of the commutator in the shaft direction. The surface (inner diameter side surface) in which the tilt surface is opposed to the commutator has the concave-curved surface whose center on the rotational direction side is recessed to the outside in the radial direction, so it is difficult to successively cutting a plurality of stacked brushes to the rotational direction side of the commutator to form the tilt surface having the concave-curved

surface. Therefore, for example, when a grind stone rotating about a rotating shaft of the dynamoelectric machine or a shaft substantially parallel to the tilt surface is pressed to each of the brushes to form the concave-curved surface by cut processing, the formation of the tilt surface takes a relatively long processing time. Thus, when the brush having the conventional shape is to be obtained, there is a problem in that the cost of the brush becomes relatively higher.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-mentioned problems. It is an object of the present invention to provide a dynamoelectric machine including a low-cost brush in which an increase in life of the brush and the shortening of the running processing time or the elimination of the running processing can be compatible with one another and a method of manufacturing the brush.
According to the present invention, there is provided a dynamoelectric machine, including:
a cylindrical commutator fixed to a rotating shaft; and
a brush which is in sliding contact with an outer circumferential surface of the commutator, wherein;
the brush includes:
a sliding contact surface which is provided to a side

surface located on a commutator side and one end of the brush in a shaft direction, and has a concave-curved surface formed along the outer circumferential surface of the commutator; and
a thickness-reduction portion which has a concave-curved surface formed concave to the shaft direction to be gradually away from the outer circumferential surface of the commutator from the sliding contact surface to the other end of the brush in the shaft direction, and
the thickness-reduction portion has a smooth surface without irregularities on a rotational direction side of the commutator in the radial direction.
According to the present invention, there is provided a method of manufacturing a brush of a dynamoelectric machine,
the brush being in sliding contact with an outer circumferential surface of a cylindrical commutator of the dynamoelectric machine
the brush including:
a sliding contact surface which is provided to a side surface located on a commutator side and one end of the brush in a shaft direction, and has a concave-curved surface formed along the outer circumferential surface of the commutator; and
a thickness-reduction portion which has a concave-curved surface formed concave to the shaft direction to be gradually away from the outer circumferential surface of the

commutator from the sliding contact surface to the other end of the brush in the shaft direction, and which has a smooth surface without irregularities on a rotational direction side of the commutator in a radial direction,
the method of manufacturing the brush of a dynamoelectric machine including the steps of:
compression-molding material powder filled in a forming mold of the brushy-baking the compression-molded material powder; and successively cut processing a plurality of the baked brushes to the rotational direction side of the commutator to form the thickness-reduction portion.
According to the present invention, it is possible to obtain the dynamoelectric machine including the low-cost brush in which the extending life of the brush and the shortening of the running processing time or the elimination of the running processing can be compatible with one another and the method of manufacturing the brush.
BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:
Fig. 1 is a cross sectional view showing a motor according to Embodiment 1 of the present invention;
Figs. 2(a) to 2(c) are explanatory views showing shapes of

a brush according to Embodiment 1 of the present inventions-Fig. 3 is an explanatory view showing a comparison between
a thickness-reduction portion of the brush according to Embodiment
1 of the present invention and a tilt surface of a conventional
brush;
Fig. 4 is an explanatory view showing the formation of the
thickness-reduction portion of the brush according to Embodiment
1 of the present inventions-
Fig. 5 is a front view showing a brush according to Embodiment
2 of the present invention; and
Fig. 6 is a front view showing a brush according to Embodiment
3 of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1
Embodiment 1 will be described with reference to Figs. 1 to 4. In each of the drawings, the same or corresponding parts are expressed by the same reference numerals for description. Fig. 1 is a cross sectional view showing a motor for electric power steering device . Figs. 2(a) to2(c) are explanatory views showing brush shapes of the motor of Fig. 1. Fig, 3 is an explanatory view showing a comparison between a thickness-reduction portion of the brush of Figs. 2 (a) to 2 (c) and a tilt surface of a conventional brush. Fig. 4 is an explanatory view showing the formation of the

thickness-reduction portion of the brush of Figs. 2 (a) to 2 (c) • In Fig, 1, a motor 1 for electric power steering device which is a dynamoelectric machine includes a cylindrical yoke 2 which serves as a stator and has a closed end, an armature 3 which serves as a rotator and provided inside the yoke 2, a brushes 4 for supplying power to the armature 3, a bracket 5 which is fitted into an opening portion of the yoke 2 to fix to the yoke 2, and a boss 7 fixed to an end of a rotating shaft 6 of the armature 3 to couple to a steering side of a vehicle. Two pairs of N-S magnetic poles 8^ each of which is made of a permanent magnet, are fixed to an inner circumferential surface of the yoke 2 . The armature 3 is located inside the magnetic poles 8 through a gap. The rotating shaft 6 is rotatably supported by bearings 9 and 10. The brushes 4 are in sliding contact with an outer circumferential surface of a cylindrical commutator 11 fixed to the rotating shaft 6 to supply power to armature coils 12 connected with the cylindrical commutator 11.
The brushes 4 including two positive brushes and two negative brushes are radially provided around the commutator 11. Each of the brushes 4 is pressed by a spring 13 to the outer circumferential surface of a cylindrical commutator 11 in a shaft center direction of the rotating shift 6. The brush 4 has a substantially cuboid shape. The brush 4 includes: a sliding contact surface 14 which is included in a side surface (inner diameter side surface) located on the commutator side and provided to an end of the corresponding

brush 4 in a shaft direction (side opposed to the armature 3 in Fig. 1); and a thickness-reduction portion 15 which has a concave-curved surface formed concave to the shaft direction so as to be gradually away from the outer circumferential surface of the commutator 11 from the sliding contact surface 14 to the other end of the brush 4 in the shaft direction (armature 3 side in Fig. 1). The brush 4 which is the substantial cuboid includes a pigtail 16 led from a shaft direction end surface opposed to a shaft direction end surface located on the sliding contact surface 14 side (end surface on the armature 3 side in Fig, 1). The pigtail 16 is electrically connected with a lead wire 27 joined to a control device for electric power steering device.
Figs. 2(a) to 2(c) are explanatory views showing the shapes of the brush 4, in which Fig. 2(a) shows a side surface thereof as viewed from the commutator side, Fig. 2(b) shows a side surface thereof when it is viewed from the shaft direction end surface opposed to the shaft direction end surface located on the sliding contact surface 14 side, that is, when Fig. 2(a) is a side surface view viewed from the armature side, and Fig. 2(c) shows the same view as the brush 4 of Fig. 1 and is a front view showing a rotational direction side end surface of the brush 4 as viewed from a rotational direction side of the commutator 11. A longitudinal direction of a space including the brush 4 of Figs. 1 and 2(c) is referred to as the rotational direction side of the commutator. A direction

from the sliding contact surface side of the brush 4 which is the substantial cuboid to an end surface opposed to the sliding contact surface side is referred to as a radial direction.
The brush 4 includes: the sliding contact surface 14 which is formed to an end thereof in the shaft direction and curved in a concave shape along the outer circumferential surface of the commutator 11; and the thickness-reduction portion 15 which has the concave-curved surface formed concave to the shaft direction so as to be gradually away from the outer circumferential surface of the commutator 11 from the sliding contact surface 14 to the other end of the brush 4 in the shaft direction. The thickness-reduction portion 15 has a smooth surface without irregularities on the rotational direction side of the commutator 11 in the radial direction. That is, the concave-curved surface of the thickness-reduction portion 15 is formed by extending a curve indicating the thickness-reduction portion 15 of Figs. 1 and 2(c) perpendicular to the space in a downward direction of the space of Figs . 1 and 2 (c) . Therefore, unlike the conventional brush, the concave-curved surface whose center is recessed to the outside in the radial direction is not provided and the smooth surface without irregularities in the radial direction is formed perpendicular to the rotational direction side end surface of the brush 4.
The brush 4 includes the pigtail 16 led from the shaft direction end surface opposed to the shaft direction end surface located on

the sliding contact surface 14 side.
The brush 4 includes a chamfered portion 17 which is provided on the other end side (pigtail 16 side) of the brush 4 in the shaft direction, connected with the thickness-reduction portion 15 having the concave-curved surface concave to the shaft direction, and formed with a forming die of the brush 4 so as to be gradually away from the outer circumferential surface of the commutator 11 in the shaft direction. The sliding contact surface 14, the thickness-reduction portion 15, and the chamfered portion 17 are successively connected from the one end side to the other end side in the shaft direction and constructed so as to be gradually away from the outer circumferential surface of the commutator 11 to the other end side in the shaft direction.
As shown in Figs, 2(a) to 2(c), a chamfered portion of approximately 0,5 (mm) to 1 (mm) is formed with the forming die of the brush of the brush 4 in each of corner portions extending in the radial direction, of both end surfaces of the brush 4 which are located on the shaft direction side and in each of corner portions extending in the shaft direction, of both end surfaces of the sliding contact surface 14 which are located on the rotational direction side. The chamfered portions are provided to prevent the corner portions of the brush 4 from being damaged. The chamfered portions are formed with the forming die of the brush 4 in low cost.
The concave-curved surface of the sliding contact surface 14

is formed such that a radius thereof is slightly larger than a radius of the outer circumferential surface of the commutator 11. For example, the radius of the concave-curved surface of the sliding contact surface 14 is 12,5 (mm) and the radius of the outer circumferential surface of the commutator 11 is 12.3 (mm), so at the early stage of assembly of the motor 1^ the vicinity of the center of the sliding contact surface 14 which is located on the rotational direction side is first in sliding contact with the outer circumferential surface of the commutator 11 and wears along the outer circumferential surface of the commutator 11 from an early stage. Therefore, a sliding contact sound can be reduced from an early stage to eliminate a running processing or shorten the running processing time. At the early stage of assembly of the motor 1, undercuts of the outer circumferential surface of the commutator 11 which are provided between adjacent commutator pieces do not interfere with corner portions or the like which are close to both end surfaces of the sliding contact surface 14 which are located on the rotational direction side, so the sliding contact sound can be reduced. Note that, when the radius of the concave-curved surface of the sliding contact surface 14 becomes larger than the radius of the outer circumferential surface of the commutator 11, the sliding contact is made in a thin linear shape in the vicinity of the center of the sliding contact surface 14, with the result that a sliding contact area reduces to increase the heat of the brush 4 which is

generated by a supplied current. Thus, the concave-curved surface of the sliding contact surface 14 is desirably formed such that the radius thereof is larger than the radius of the outer circumferential surface of the commutator 11 by a value substantially equal to or smaller than 10%, desirably a value substantially equal to approximately 5%.
Fig. 3 is an explanatory view showing a comparison between the thickness-reduction port ion 15 having the concave-curved surface formed concave to the shaft direction, of the brush 4 of Figs, 2(a) to 2(c) and a tilt surface linearly formed in the shaft direction, of a conventional brush.
The thickness-reduction portion 15 is connected with a portion of the sliding contact surface 14 formed in the one end in the shaft direction and has a curved surface formed so as to gradually increase a gap size in the radial direction from (gradually increase a distance from) the outer circumferential surface of the commutator 11 toward the other end in the shaft direction. Because the curved surface is concave to the shaft direction, the distance from the outer circumferential surface of the commutator 11 relatively rapidly increases in the vicinity of the sliding contact surface 14, but the distance can be relatively slowly increased in the vicinity of the other end of the brush 4 in the shaft direction. Therefore, the extending life of the brush and the shortening of the running processing time or the elimination of the running processing can

be compatible with one another. The sliding contact surface 14 can be continuously brought into sliding contact from the one end to the other end in the shaft direction with the wearing of the brush 4 to reduce noises caused by sliding contact.
When the curved surface is convex to the shaft direction, as in the caseofatiltsur face 18a whose tilt angle is small as described later, the addition of running processing is necessary or the running processing takes a relatively long time. In addition, a problem occurs in which, for example, the convex-curved surface cannot be formed by a normal circular grind stone.
The brush 4 has the curved surface concave to the shaft direction, so the concave-curved surface can be easily formed by the grind stone.
In contrast to this, tilt surfaces 18a and 18b of conventional brushes are linear to the shaft direction. In the case of the tilt surface 18 whose tilt angle is small, in other words, in the case where the tilt surface 18a is close to be parallel to the outer circumferential surface of the commutator 11, a brush volume to brush wearing is relatively increased by a small tilt, so the wear-resistance life of the brush can be extended to a relatively long life. However, because of the increase in volume, in running processing of the dynamoelectric machine to which the brush is installed requires the addition of running processing or the running processing takes a relatively long time.

On the other hand, in the case of the tilt surface 18b whose tilt angle is large, in other words, in the case where the tilt surface 18b is relatively widely spaced apart from the outer circumferential surface of the commutator 11, the brush volume to brush wearing is relatively reduced by a large tilt, so in the running processing of the dynamoelectric machine can eliminate the running processing or the running processing, it is possible to be shortened to a relative short time. However, the wear-resistance life of the brush becomes a relatively short life.
Each of the thickness-reduction portion 15 and the tilt surfaces 18a and 18b is constructed such that the sliding contact surface 14 is continuously in sliding contact from the one end side to the other end side in the shaft direction with the wearing. However, in the case of the tilt surfaces 18a and 18b, the extending life of the brush and the shortening of the running processing time or the elimination of the running processing cannot be compatible with one another.
The brush 4 is a metal graphite brush. The forming die of the brush 4 is filled with material powder such as graphite powder or copper powder, compression-molded, and baked at high temperature to produce a brush main body. The material powder filled in the forming die and the pigtail 16 whose end portion is embedded in the material powder are pressurized in an A-direction and a B-direction of Fig. 2(c) to be integrally compression-molded. After

the compression molding, a resultant is pressed in the A-direction of Fig, 2(c) to be taken out from the forming die and then baked to produce the brush main body. Of the shapes of the brush 4 of Figs. 2(a) to 2(c), each shape other than the thickness-reduction portion 15 is formed with the forming die. For example, the concave-curved surface of the sliding contact surface 14 is formed with the forming die. The chamfered portion 17 is also formed with the forming die. The pigtail 16 is embedded in the brush main body to be integrally formed.
Fig. 4 is an explanatory view showing the formation of the thickness-reduction portion 15 of the brush 4 of Figs, 2 (a) to 2 (c) , The baked brush main body is shaped to have an excess thickness portion 19 as indicated by a dashed line of Fig. 4, This reason is as follows. In the case where compression molding is performed without the excess thickness portion 19, when the brush 4 is pressed in the A-direction of Fig. 2(c) (direction to the pigtail 16) to be taken out from the forming die, the protruded sliding contact surface 14 interferes with the forming die, so the brush 4 is not easily taken out from the forming die. Therefore, in order to press the brush 4 in the A-direction to be easily taken out from the forming die, the compression molding is performed with the shape in which the excess thickness portion 19 is provided, thereby forming the brush main body. Therefore, even when the pigtail 16 led from the shaft direction end surface opposed to the shaft direction end surface

located on the sliding contact surface 14 side is integrally formed with the brush main body by compression molding, the brush main body can be formed with the forming die because the excess thickness portion 19 is provided and the curved surface concave to the shaft direction is formed by cut processing*
As shown in Fig. 4, the baked brush main body and a grind stone 20 for forming the thickness-reduction portion 15 by cut processing (grinding) are located. When the excess thickness portion 19 is removed to form the thickness-reduction portion 15, the brush 4 can be obtained. The grind stone 20 rotates about a shaft orthogonal to the shaft center of the rotating shift 6 of the motor 1 in a C-direction of Fig, 4 and the shaft is decentered on the other end side (pigtail 16 side) relative to the center position of the brush in the shaft direction. The grind stone 20 has a substantially cone shape convex to a downward direction of the space of Fig, 4, When a plurality of brush main bodies stacked in the downward direction of the space of Fig, 4 are moved (slide) up relative to the grind stone 20 on the space of Fig. 4 to be subjected to continuous cut processing on the rotational direction side (in the longitudinal direction of the space of Fig. 4) of the commutator 11, it is possible to successively produce the brushes 4, each of which has the thickness-reduction portion 15 in which the concave-curved surface corresponding to a maximum of a diameter of the grind stone 20 is formed in the shaft direction and a smooth surface which is orthogonal

to the longitudinal direction of the space of Fig. 4 and does not include irregularities in the radial direction is formed in the rotational direction side,
The grind stone 20 has the substantially cone shape, so a processing margin can be gradually increased with a good processability and a plurality of brushes can be successively processed.
Because the thickness-reduction portion 15 orthogonal to the end surface of the brush 4 located on the rotational direction side is formed on the rotational direction side, the thickness-reduction portion 15 is symmetrical with respect to the rotational direction of the commutator 11. Therefore-, a difference between sounds generated by sliding contact in rotational directions does not easily occur, so a dynamoelectric machine suitable for the motor 1 for electric power steering device which rotates in both directions can be obtained.
In Fig, 4, a step size S between the one end side (sliding contact surface 14 side) of the thickness-reduction portion 15 and the other end side (pigtail 16 side) thereof in the radial direction is set to 20% or less of a radial direction size H of the brush 4. For example, the radial direction size H between the sliding contact surface 14 and a radial direction end surface opposed thereto is 10 (mm) and the step size S between the sliding contact surface 14 and the other end side of the thickness-reduction portion 15

in the radial direction is 1.7 (mm). Therefore, the step size S is 17% of the radial direction size H.
When the step size S increases, the processing margin becomes larger. When a ratio between S and H (S/H) increases, the fixation ofthebrush4 becomes insufficient, so it is difficult to successively form the thickness-reduction portions 15. Therefore, a problem occurs in which a cost of the brush 4 increases and the life of the brush shortens. Thus, it is important to set the step size S to 20% or less of the radial direction size H. It is desirable to set the step size S to 2 (mm) or less.
Next, the operation of the above-mentioned structure in Embodiment 1 will be described. A control device for controlling the motor 1 for electric power steering device based on a signal from a steering torque sensor provided on a steering side of a vehicle or a signal indicating a vehicle speed or the like is provided. Power is supplied to the brush 4 through the pigtail 16 connected with the lead wire 27 joined to the control device. A current is supplied from the commutator 11 with which the brush 4 is in sliding contact to the armature coil 12. The rotating shaft 6 is rotated by an electromagnetic action between the armature 3 to which the current is supplied and the magnetic pole 8. A rotating force is transferred to the steering side through the boss 7 to aid a steering force of a steering wheel of the vehicle. Therefore, a steering force of a driver can be reduced.

The electric power steering device is increasingly applied to even a vehicle whose displacement is large because of energy saving. The motor 1 is required in which, for example, a reduction in noises caused by sliding contact with the brush is realized, a size is small, and a cost is low,
As described above, according to Embodiment 1, the brush 4 includes: the sliding contact surface 14 which is included in the side surface located on the commutator side, provided to the end of the brush 4 in the shaft direction, and has the concave-curved surface formed along the outer circumferential surface of the commutator 11; and the thickness-reduction portion 15 which has the curved surface formed concave to the shaft direction so as to be gradually away from the outer circumferential surface of the commutator 11 from the sliding contact surface 14 to the other end of the brush 4 in the shaft direction. Therefore, it is possible to obtain a dynamoelectric machine in which an extending life of the brush and the shortening of the running processing time or the elimination of the running processing can be compatible with one another. At the same time, in the brush 4, the thickness-reduction portion 15 has the smooth surface without irregularities on the rotational direction side of the commutator 11 in the radial direction, so the thickness-reduction portion can be formed in low cost. Thus, a dynamoelectric machine including a low-cost brush can be obtained.
The brush 4 includes the pigtail 16 led from the shaft direction

end surface opposed to the shaft direction end surface located on the sliding contact surface 14 side, the sliding contact surface 14 whose concave-curved surface along the outer circumferential surface of the commutator 11 is formed with the forming die of the brush 4, and the thickness-reduction portion 15 whose curved surface concave to the shaft direction is f ormed by cut processing . Therefore, for example, the concave-curved surface along the outer circumferential surface of the commutator 11 can be formed with the forming die in low cost and the curved surface concave to the shaft direction can be formed by cut processing in low cost. Thus, a dynamoelectric machine including the low-cost brush 4 can be obtained.
The chamfered portion 17 is located on the other end side of the brush 4 in the shaft direction, connected in the shaft direction with the thickness-reduction portion 15 having the concave-curved surface concave to the shaft direction, and formed with the forming die of the brush 4 so as to be .gradually away from the outer circumferential surface of the commutator 11 in the shaft direction. Therefore, the chamfered portion 17 can be formed with the forming die in low cost. The chamfered portion 17 is gradually spaced apart in the shaft direction, so the sliding contact surface 14 can be continuously brought into sliding contact from the one end to the other end in the shaft direction with the wearing of the brush 4 to stably reduce noises caused by sliding contact. Even in the case

where, for example, an upper limit of a diameter size of the grind stone 20 for obtaining the thickness-reduction portion 15 by grinding is limited, when the chamfered portion 17 is provided, the thickness-reduction portion 15 can be formed by the grind stone 20, so a device for processing the thickness-reduction portion 15 can be also used. Therefore, the low-cost brush 4 can be obtained.
The concave-curved surface of the sliding contact surface 14 is formed such that the radius thereof is slightly larger than the radius of the outer circumferential surface of the commutator 11. Therefore, the sliding contact sound can be reduced from an early stage to eliminate the running processing or shorten the running processing time,
The step size S between the one end side of the thickness-reduction portion 15 and the other end side thereof in the radial direction is set to 20% or less of the radial direction size H of the brush. Therefore, the low-cost brush 4 can be obtained and the life of the brush can be extended to a relatively long life,
A method of manufacturing the brush 4 according to Embodiment 1 includes a step of compression-molding material powder with which forming dies of the brushes 4 are filled, a step of baking the brushes obtained by the compression molding, and a step of successively cutting the plurality of baked brushes 4 to the rotational direction side of the commutator 11 to form the thickness-reduction portions 15, Therefore, a low-cost brush manufacturing method can be

obtained. Embodiment 2
Embodiment 2 will be described with reference to Fig, 5. The same or corresponding parts as those in Embodiment 1 are expressed
by the same references and thus the description will be omitted. Fig, 5 is a view corresponding to Fig. 2(C), which is a front view showing the rotational direction side end surface of the brush 4 as viewed from the rotational direction side of the commutator 11. The brush 4 includes: the pigtail 16 led from the end surface located on the rotational direction side of the commutator 11 (pigtail 16 is led perpendicular to the space of Fig, 5); the sliding contact surface 14 having the concave-^curved surface formed along the outer circumferential surface of the commutator 11 by cut processing (which is indicated by a broken line of Fig, 5) ; and the thickness-reduction portion 15 having the curved surface formed concave to the shaft direction with the forming die of the brush 4. Each of the sliding contact surface 14, the thickness-reduction portion 15, and the chamfered portion 17 are the same as that of Embodiment 1,
The material powder filled in the forming die and the pigtail 16 whose end portion is embedded in the material powder are pressurized in the longitudinal direction of the space of Fig. 5 to be integrally compression-molded. After the compression molding, the brush main body is pressed in an upward direction of the space of Fig, 5 to be taken out from the forming die and then baked to produce the

brush main body* In this embodiment;- the thickness-reduction portion 15 is formed with the forming die, but the concave-curved surface of the sliding contact surface portion is formed by cut processing. The chamfered portion 17 is formed with the forming die.
The sliding contact surface 14 is formed to have the concave-curved surface along the outer circumferential surface of the commutator 11, Therefore, when the sliding contact surface 14 is formed with the forming die, the concave-curved surface recessed to the inner portion (outside in the radial direction) of the brush 4 interferes with the forming die at the time of taking out after compression molding, so the brush 4 is not easily taken out from the forming die . Therefore, compression molding is performed using the smooth surface located on the rotational direction (longitudinal direction of the space of Fig. 5) side which does not include the concave-curved surface . After baking, a skin of the sliding contact surface portion corresponding to the position of the sliding contact surface 14 formed with the forming die is removed by cut processing to form the sliding contact surface 14 having the concave-curved surface along the outer circumferential surface of the commutator 11.
At the time of compression molding, the material powder is drown by a wall surface of the forming die and is made dense to thereby relatively cure the surface of the brush, so there is the

case where a sliding contact sound generated at the beginning of operation of the dynamoelectric machine becomes larger. However, the skin of the sliding contact surface portion is removed by the cut processing. Therefore, it is possible to obtain the sliding contact surface 14 including the concave-curved surface whose hardness is relatively low and material tissue is relatively uniform and to reduce the sliding contact sound from an early stage-As described above, according to Embodiment 2, the brush 4 includes the pigtail 16 led from the end surface located on the rotational direction side of the commutator 11, the sliding contact surface 14 whose concave-curved surface along the outer circumferential surface of the commutator 11 is formed by the cut processing, and the thickness-reduction portion 15 whose curved surface concave to the shaft direction is formed with the forming die of the brush 4, Therefore, for example, the sliding contact sound can be reduced and from an early stage and the curved surface concave to the shaft direction can be formed with the forming die in low cost. Thus, a low-cost dynamoelectric machine can be obtained. The skin of the sliding contact surface portion which is formed with the forming die is removed by the cut processing to form the sliding contact surface 14. Therefore, the sliding contact surface 14 wears along the outer circumferential surface of the commutator 11 from an early stage, so the sliding contact sound can be reduced from an early stage to eliminate the running processing or shorten

the running processing time. Embodiment 3
Embodiment 3 will be described with reference to Fig, 6. The same or corresponding parts as those in Embodiment 1 or 2 are expressed by the same references and thus the description will be omitted. Fig. 6 is a view corresponding to Fig. 2(C) and Fig. 5, which is a front view showing the rotational direction side end surface of the brush 4 as viewed from the rotational direction side of the commutator 11.
The brush 4 includes : the pigtail 16 led from the shaft direction end surface located on the sliding contact surface 14 side; the sliding contact surface 14 having the concave-curved surface formed along the outer circumferential surface of the commutator 11 with the forming die of the brush 4; and the thickness-reduction portion
15 having the curved surface formed concave to the shaft direction
with the forming die thereof* Each of the sliding contact surface
14 and the thickness-reduction portion 15 are the same as that of
Embodiment 1 or 2,
The material powder filled in the forming die and the pigtail
16 whose end portion is embedded in the material powder are pressurized
in the lateral direction of the space of the Fig, 6 as the case
of the A-di rection and the B-direction in Embodiment 1, to be
integrally compression-molded. After the compression molding, a
resultant is pressed from the right to the left of the space of

the Fig, 6 to be taken out from the forming die and then baked to produce the brush 4, In this embodiment, both the sliding contact surface 14 and the thickness-reduction portion 15 are formed with the forming die,
The sliding contact surface 14 protruding relative to the thickness-reduction portion 15 is located on the pigtail 16 side and the brush 4 is pressed from the right to the left (pigtail 16 side) of the space of the Fig. 6 to be taken out after the compression molding. Therefore, the brush 4 is taken out without the interference of the sliding contact surface 14 with the forming die, so the sliding contact surface 14 and the thickness-reduction portion 15 can be formed with the forming die,
In this embodiment, the sliding contact surface 14 can be formed with the forming die. A sliding contact surface portion having a concave-curved surface in which a processing margin is added to the concave-curved surface of the sliding contact surface 14 may be formed with a forming die and then the skin of the sliding contact surface portion formed with the forming die may be removed by cut processing after baking, thereby forming the concave-curved surface of the sliding contact surface 14 of the brush 4. In this case, as in Embodiment 2, the sliding contact surface 14 wears along the outer circumferential surface of the commutator 11 from an early stage, so it is possible to eliminate the running processing or shorten the running processing time.

As described above, according to Embodiment 3, the brush 4 includes the pigtail 16 led from the shaft direction end surface located on the sliding contact surface 14 side, the sliding contact surface 14 having the concave-curved surface formed along the outer circumferential surface of the commutator 11 with the forming die of the brush 4, and the thickness-reduction portion 15 having the curved surface formed concave to the shaft direction with the forming die thereof. Therefore, both the sliding contact surface 14 and the thickness-reduction portion 15 can be formed with the forming die to obtain the low-cost brush 4.
In the above-mentioned embodiments, the motor 1 for electric power steering device is described as the dynamoelectric machine. However, the dynamoelectric machine is not limited to this.

WHAT IS CLAIMED IS:
1. A dynamoelectric machine, comprising:
a cylindrical commutator fixed to a rotating shaft; and a brush which is in sliding contact with an outer circumferential surface of the commutator,
the brush comprising:
a sliding contact surface which is provided to a side surface located on a commutator side and one end of the brush in a shaft direction, and has a concave-curved surface formed along the outer circumferential surface of the commutator; and
a thickness-reduction portion which has a concave-curved surface formed concave to the shaft direction to be gradually away from the outer circumferential surface of the commutator from the sliding contact surface to the other end of the brush in the shaft direction,
wherein the thickness-reduction portion has a smooth surface without irregularities on a rotational direction side of the commutator in a radial direction.
2. A dynamoelectric machine according to claim 1, wherein the brush comprises:
a pigtail led from a shaft direction end surface opposed to a shaft direction end surface located on the sliding contact surface side;

a sliding contact surface which has a concave-curved surface formed along the outer circumferential surface of the commutator by using a forming die of the brush; and
a thickness-reduction portion which has a concave-curved surface formed concave to the shaft direction by cut processing.
3. A dynamoelectric machine according to claim 1, wherein the brush comprises:
a pigtail led from an end surface located on the rotational direction side of the commutator;
a sliding contact surface has a concave-curved surface formed along the outer circumferential surface of the commutator by cut processing; and
a thickness-reduction portion which has a concave-curved surface formed concave to the shaft direction by using a forming die of the brush.
4. A dynamoelectric machine according to claim 1^ wherein the brush comprises:
a pigtail led from a shaft direction end surface located on a sliding contact surface side,
a sliding contact surface has a concave-curved surface formed along the outer circumferential surface of the commutator

by using a forming die of the brush; and
the thickness-reduction portion which has a concave-curved surface formed concave to the shaft direction by using the forming die of the brush.
5. A dynamoelectric machine according to claim 2 or 4, wherein the concave-curved surface of the sliding contact surface of the brush is formed by removing, by cut processing, a skin of the sliding contact surface portion formed by using the forming die of the brush.
6. A dynamoelectric machine according to any one of claims 1 to 5, wherein the brush comprises a chamfered portion which is provided to another end of the brush in the shaft direction, connected in the shaft direction with the thickness-reduction portion having the concave-curved surface concave to the shaft direction, and formed by using a forming die of the brush to be gradually away from the outer circumferential surface of the commutator in the shaft direction.
7. A dynamoelectric machine according to any one of claims 1 to 6, wherein the concave-curved surface of the sliding contact surface is formed so that a radius thereof is slightly larger than a radius of the outer circumferential surface of the commutator.

8. A dynamoelectric machine according to any one of claims 1 to 1, wherein a step size between one end side of the thickness-reduction portion and another end side in the radial direction is set to a value equal to or smaller than 20% of a step size of the radial direction of the brush.
9. A method of manufacturing a brush of a dynamoelectric machine.
the brush being in sliding contact with an outer circumferential surface of a cylindrical commutator of the dynamoelectric machine
the brush including:
a sliding contact surface which is provided to a side surface located on a commutator side and one end of the brush in a shaft direction, and has a concave-curved surface formed along the outer circumferential surface of the commutator; and
a thickness-reduction portion which has a concave-curved surface formed concave to the shaft direction to be gradually away from the outer circumferential surface of the commutator from the sliding contact surface to the other end of the brush in the shaft direction, and which has a smooth surface without irregularities on a rotational direction side of the commutator in a radial direction,
the method of manufacturing the brush of a dynamoelectric

machine comprising the steps of:
compression-moldingmaterial powder filled in a forming
mold of the brush;
baking the compression-molded material powder; and successively cut processing a plurality of the baked
brushes to the rotational direction side of the commutator to form
the thickness-reduction portion.

Documents:

673-CHE-2008 AMENDED CLAIMS 23-04-2012.pdf

673-CHE-2008 CORRESPONDENCE OTHERS 04-06-2012.pdf

673-CHE-2008 FORM-3 23-04-2012.pdf

673-CHE-2008 POWER OF ATTORNEY 23-04-2012.pdf

673-CHE-2008 CORRESPONDENCE OTHERS 23-04-2012.pdf

673-CHE-2008 CORRESPONDENCE OTHERS.pdf

673-CHE-2008 FORM-18.pdf

673-che-2008-abstract.pdf

673-che-2008-claims.pdf

673-che-2008-correspondnece-others.pdf

673-che-2008-description(complete).pdf

673-che-2008-drawings.pdf

673-che-2008-form 1.pdf

673-che-2008-form 3.pdf

673-che-2008-form 5.pdf

673-che-2008-other document.pdf

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Patent Number

252349

Indian Patent Application Number

673/CHE/2008

PG Journal Number

19/2012

Publication Date

11-May-2012

Grant Date

09-May-2012

Date of Filing

18-Mar-2008

Name of Patentee

MITSUBISHI ELECTRONIC CORPORATION

Applicant Address

7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN.

Inventors:

#	Inventor's Name	Inventor's Address
1	WAKU, OSAMU	MITSUBISHI ELECTRONIC CORPORATION, 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN.
2	YAMAMOTO, KYOHEI	MITSUBISHI ELECTRONIC CORPORATION, 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN.
3	YAMAMOTO, MASAYOSHI	MITSUBISHI ELECTRONIC CORPORATION, 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN.
4	OKAZAKI, MASAFUMI	MITSUBISHI ELECTRONIC CORPORATION, 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN.

PCT International Classification Number

H 02 K 3/28

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2007-219645	2007-08-27	Japan