Motor with brush

Abstract

A brushed motor comprises a rotating shaft, a multi-segment commutator separated by several unequally spaced undercuts, an armature, multiple permanent magnets, a voltage equalization line, a positive electrode brush, and a negative electrode brush. If Pz is the number of permanent magnets and N is the number of segments, then the relationship N = Pz(K - 0.5) is satisfied. Pz is an even number greater than or equal to four. K is a constant and is a natural number greater than or equal to two. The multiple undercuts include at least one set of undercuts spaced at an undercut distance that differs from a reference angle θz. The reference angle θz is given by a comparative expression θz = (360 degrees / Pz) ± (360 degrees / 2N).

Description

The present invention relates to a brush motor. In a conventional brushed motor, the force exerted on a commutator by a brush during rotation generates extraneous noise, which becomes a source of noise, vibration, and the like. This noise can be particularly problematic when the brushed motor is used in a vehicle or onboard motor that is intended to be quiet. A commutator has been proposed in which several segments (commutator parts) arranged on an outer circumferential surface of the commutator have different circumferential widths, so that undercuts (grooves) formed between adjacent elements are not arranged at equal intervals (e.g. Japanese patent JP 3 994 010 B2). In the motor described in Japanese patent JP 3 994 010 B2, a positive electrode brush and a negative electrode brush are arranged facing each other. Thus, during each revolution generated by the motor, the positive and negative electrode brushes run along adjacent segments multiple times simultaneously. Because the positive and negative electrode brushes frequently run along adjacent segments simultaneously during each revolution, this is detrimental to the motor's performance. It increases the fluctuation in the current delivered to a winding and amplifies torque variation, vibration, and extraneous noise. A motor which represents the closest prior art to the motor according to the invention is disclosed in DE 10 2012 212 045 A1. SUMMARY OF THE INVENTION An objective of the present invention is to create a brush motor capable of reducing the level of background noise generated from the positional relationship of a brush and the undercuts of segments formed in irregular angular intervals. This objective is achieved by brush motors with the features of the independent patent claims. To achieve the aforementioned goal, a first aspect of the present invention is a brushed motor with a rotating shaft. A commutator is fixed to the rotating shaft. The commutator comprises several segments that are insulated and separated by multiple undercuts. These undercuts are arranged at irregular angular intervals around a central axis of the rotating shaft. An armature is fixed to the rotating shaft. Several permanent magnets are arranged on an outer surface of the armature. The permanent magnets are arranged at equal intervals such that the directions of the magnetic poles of adjacent permanent magnets are different. A voltage equalization line connects different segments to one another. A positive electrode brush and a negative electrode brush are arranged on an outer circumference of the commutator at positions that do not face each other.If Pz is the number of permanent magnets and N is the number of segments, then the following relationship holds: N = Pz(K - 0.5), where Pz is an even number greater than or equal to four, K is a constant, and K is a natural number greater than or equal to two. The multiple undercuts include at least one set of undercuts spaced at an undercut distance that differs from a reference angle θz, and the reference angle θz is given by a comparative expression θz = (360 degrees / Pz) ± (360 degrees / 2 N). A second aspect of the present invention is a brush motor with a rotating shaft. A commutator is fixed to the rotating shaft. The commutator comprises several segments that are insulated and separated by multiple undercuts. These undercuts are arranged at irregular angular intervals around a central axis of the rotating shaft. An armature is fixed to the rotating shaft. Several permanent magnets are arranged on an outer surface of the armature. The permanent magnets are arranged at equal intervals such that the directions of the magnetic poles of adjacent permanent magnets are different. A voltage equalization line connects different segments to one another. A positive electrode brush and a negative electrode brush are arranged on an outer circumference of the commutator at positions that do not face each other.If Pz is the number of permanent magnets and N is the number of segments, then the relationship N = Pz × K holds, where Pz is an even number greater than or equal to four, K is a constant, and K is a natural number greater than or equal to two. The multiple undercuts include at least one set of undercuts arranged with an undercut spacing that differs from a reference angle θz, and the reference angle θz is given by a comparative expression θz = 360 degrees / Pz. A third aspect of the present invention is a brush motor with a rotating shaft. A commutator is fixed to the rotating shaft. The commutator comprises several segments that are isolated and separated by multiple undercuts. The multiple undercuts are arranged at irregular angular intervals around a central axis of the rotating shaft. An armature is fixed to the rotating shaft. Several permanent magnets are arranged on a radial outer surface of the armature. A brush is arranged on an outer circumference of the commutator. The rotating shaft, the commutator, and the armature are rotatable together in forward and reverse directions. N is the number of segments and the number of multiple undercuts.The mean positions of multiple circumferential undercuts are shifted in both a forward and a reverse direction of rotation from a corresponding mean circumferential position if the multiple undercuts are formed at the same angle. Z1 is the angle of deviation by which the individual undercuts are shifted in the forward direction of rotation. Z2 is the angle of deviation by which the individual undercuts are shifted in the reverse direction of rotation. Z is the sum of the angles of deviation. Z = Z1 + Z2 is satisfied. If P is the number of pole pairs of the magnetic poles of the permanent magnets, then Q = (Z / N) / P represents an index value Q, and the index value Q is -0.5 degrees < Q < +0.5 degrees. BRIEF DESCRIPTION OF THE DRAWINGS The invention, together with its aims and advantages, may best be understood by reference to the following description of the currently preferred embodiments and the accompanying drawings, in which: Fig. 1 is a cross-sectional view of a brush motor with four poles and ten segments according to a first embodiment of the present invention; Fig. 2 is a front view of the individual segments of the motor of Fig. 1 in the axial direction; Fig. 3 is an unfolded diagram showing a winding method for the motor of Fig. 1; Fig. 4 is a front view of each segment of a brush motor with four poles and ten segments of equal spacing, seen in the axial direction; Fig. 5 is an unfolded diagram showing a winding method for the motor of Fig. 4; Fig. 6A is a graph showing an excitation force with respect to each nth-order frequency component of the excitation force of the motor of Fig. 1.6B is a graph showing an excitation force with respect to each nth-order frequency component of the motor of Fig. 4; Fig. 7 is a front view of the individual segments of a four-pole, twelve-segment brush motor according to a second embodiment of the present invention, seen in the axial direction; Fig. 8 is an unfolded diagram showing a winding method for the motor of Fig. 7; Fig. 9 is a front view of the individual segments of a four-pole, twelve-segment brush motor with equal spacing, seen in the axial direction; Fig. 10 is an unfolded diagram showing a winding method for the motor of Fig. 9; Fig. 11 is a front view of each segment of a four-pole, ten-segment brush motor according to a third embodiment of the present invention, seen in the axial direction; Fig. 12A is a front view of the motor of Fig.Fig. 11, seen in the axial direction, shows undercuts formed at unequal angular intervals; Fig. 12B is a graph showing an angle over which the undercuts deviate from the individual reference lines in Fig. 12A; Fig. 13 is a front view of the conventional motor, seen in the axial direction, including undercuts formed at equal angular intervals; Fig. 14 is a graph showing a no-load speed with respect to an index value in the motor of Fig. 11; Fig. 15 is a graph showing a no-load current with respect to an index value in the motor of Fig. 11; Fig. 16 is a graph showing an angle of deviation of each of the undercuts and representing an extreme example of undercuts arranged at unequal angular intervals; Fig.Figure 17 is a front view in the axial direction, showing another example of a brushed motor and the arrangement of the brush and the segments of the motor, where the number of slots is divisible by the number of magnetic poles; Figure 18 is a graph for another example of a brushed motor, showing the angle of deviation from the individual reference lines in the undercuts of the individual inner circumferential surface regions of the motor, where the number of pole pairs is three; and Figure 19 is a front view of the individual segments, seen in the axial direction, in another example of the brushed motor. DETAILED DESCRIPTION OF PREFERRED EXECUTION FORMS First embodiment A first embodiment of a brush motor is now described with reference to Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5 to Fig. 6. As shown in Fig. 1, a brush motor 1 has a motor housing 2. The motor housing 2 has a cylindrical yoke housing 3, an end cover 4 for closing a rear opening of the yoke housing 3, and a front cover 5, formed of an insulating material, for covering a front opening of the yoke housing 3. Several permanent magnets 6 (four in the present embodiment) are arranged and fixed circumferentially on an inner circumferential surface 3a of the yoke housing 3. The four permanent magnets 6 include two permanent magnets 6 in which a radially inner side is magnetized to an N pole and a radially outer side is magnetized to an S pole, and two permanent magnets 6 in which the radially inner side is magnetized to the S pole and the radially outer side is magnetized to the N pole. The permanent magnets are arranged alternately in the circumferential direction. In other words, the permanent magnets 6 in which the direction of the magnetic poles differs in the radial direction are arranged alternately at equal intervals on the inner circumferential surface 3a of the yoke housing 3. Thus, the brushed motor 1 of the present embodiment is a motor in which the number of poles Pz is four (the number of pole pairs P is two). An armature 7 is arranged in the motor housing 2. The armature 7 includes a rotating shaft 8, which is arranged on a central axis line of the yoke housing 3, an armature core 9, which is fixed to the rotating shaft 8, a winding 10, which is wound around the armature core 9, and a commutator 11, which is fixed to the rotating shaft 8 in such a way that it is adjacent to the armature core 9. The rotating shaft 8 is rotatably supported relative to the motor housing 2 by bearings 12 and 13, which are arranged at a central position of the end cover 4 and a central position of the front cover 5, respectively. A distal end of the rotating shaft 8 projects from the front cover 5, so that the rotating shaft 8 serves as a drive shaft that applies a rotational force to a drive mechanism (not shown). The armature core 9 is fixed to the rotating shaft 8 and includes several teeth 9a (ten in the present embodiment) extending radially around a central axis O of the rotating shaft 8 towards its radial outer surface. The ten teeth 9a are formed with a predetermined, uniform pitch in the circumferential direction. A radial distal end face of each tooth 9a faces the permanent magnet 6, which is arranged on the inner circumferential surface 3a of the yoke housing 3. Since there are ten teeth 9a, there are also ten slots formed between the teeth 9a. The winding 10 is wound around the individual teeth 9a. As shown in Figs. 1 and 2, the commutator 11 is adjacent to the armature core 9 and is fixed to the rotating shaft 8 and arranged in the front cover 5, so that it rotates as a unit with the rotating shaft 8 together with the armature core 9. Several segments SG are formed on the outer circumferential surface of the commutator 11. The number N of segments SG in the present embodiment is ten, to correspond to the number of teeth 9a (the number of slots). Therefore, the brush motor 1 in the present embodiment is a brush motor having four poles and ten segments. The ten segments SG are designated as the first to tenth segments SG1 to SG10 in clockwise order, as shown in Fig. 2, for the sake of simplicity. The clockwise direction in Fig. 2 is referred to as the forward direction of rotation of motor 1. The counterclockwise direction is therefore referred to as the reverse direction of rotation of motor 1. As shown in Fig. 1, a flag 11b, bent towards the radially outer side, is uniformly formed at one end in an axial direction near the armature core 9 of each segment SG (SG1 to SG10). The winding 10, which is wound around the tooth 9a, is held in the flag 11b of each segment. The held section of the winding 10 is fused and fixed to a flag 11b in such a way that it is electrically connected to the segment SG that contains the flag 11b. Fig. 3 is a developed diagram showing the wire connection of winding 10 between segment SG1 to SG10 and teeth 9a. Winding 10 is wound around both adjacent teeth 9a in a loop winding configuration, where the starting end is electrically connected to one segment SG and the ending end is electrically connected to the other segment SG. As shown in Fig. 3, five voltage equalization lines, namely the first to fifth voltage equalization lines WL1 to WL5, connect a pair of segments SG to reduce the number of brushes to two, namely the positive and negative electrode brushes B1 and B2. More precisely, the first voltage equalization line WL1 connects the tenth segment SG10 and the fifth segment SG5. The second voltage equalization line WL2 connects the first segment SG1 and the sixth segment SG6. Furthermore, the third voltage equalization line WL3 connects the second segment SG2 and the seventh segment SG7. The fourth voltage equalization line WL4 connects the third segment SG3 and the eighth segment SG8. The fifth voltage equalization line WL5 connects the fourth segment SG4 and the ninth segment SG9. As shown in Fig. 2, the two brushes, i.e., the positive and negative electrode brushes B1 and B2, are pressed against the first to tenth segments SG1 to SG10, so that they are able to slide in contact from the radially outer side. The positive and negative electrode brushes B1 and B2 are arranged at positions spaced apart by a 90-degree interval (brush arrangement angle θb) in the circumferential direction, so that they do not face each other. More precisely, a base plate 15, as shown in Fig. 1, occupies such an area and is designed to surround the commutator 11 on an inner surface of the front cover 5. Two brush holder boxes 16 (of which only one is shown in Fig. 1), which accommodate the positive and negative electrode brushes B1 and B2 respectively, extend on the base plate 15 in the direction of the central axis O of the rotating shaft 8. The two brush holder boxes 16 are designed such that a circumferentially central position is spaced apart from each other by 90 degrees circumferentially around the central axis O of the rotating shaft 8. The radially inner side of both brush holder boxes 16 is open, and the shape of the opening, viewed from the rotating shaft 8, is square. The positive electrode brush B1 is inserted into one brush holder box 16. The negative electrode brush B2 is inserted into the other brush holder box 16. As shown in Fig. 2, the positive electrode brush B1 and the negative electrode brush B2 are therefore spaced apart by 90 degrees circumferentially around the central axis O of the rotating shaft 8, since the two brush holder boxes 16 are designed with a 90-degree circumferential distance around the central axis O. That is, the circumferentially median positions of the sliding contact surfaces of the positive and negative electrode brushes B1 and B2 are separated by 90 degrees circumferentially around the central axis O of the rotating shaft 8. In other words, the brush arrangement angle θb (=360 / (Pz×K)) is 90 degrees. Pz is the number of poles, and K is a natural number and is one in this case. The two brush holder boxes 16 accommodate a compression helical spring 19, which elastically preloads the corresponding plus and minus electrode brushes B1 and B2 on the radially inner side. As a result, the positive and negative electrode brushes B1 and B2 can each move towards the radially inner side while being guided along the brush holder box 16. The positive and negative electrode brushes B1 and B2 project from the opening on the radially inner side of the respective brush holder boxes 16 and are pressed into sliding contact against the individual segments SG of the commutator 11. Therefore, the current from the positive electrode brush B1 and the negative electrode brush B2 is supplied through the segments SG, which are in sliding contact with the positive electrode brush B1 and the negative electrode brush B2, to the winding 10, which is wound around the armature core 9, so that the brush motor 1 rotates in the forward and reverse directions. As shown in Fig. 2, the first to tenth segments SG1 to SG10 are fixed to an outer circumferential surface of a cylindrical insulating element 11a, which is fixed to the rotating shaft 8, and the adjacent segments SG are insulated by an undercut (groove) C. The ten undercuts C are equidistant in the circumferential direction (across the undercut width G). To facilitate the description of the individual undercuts, the ten undercuts C are designated as the first to tenth undercut C1 to C10 in order of the forward direction of rotation. The first to tenth segments SG1 to SG10 are formed by cutting a cylindrical, conductive metal base material (not shown) in an axial direction. More precisely, the cylindrical, conductive metal base material is fitted and fixed to the outer circumferential surface of the insulating element 11a, which is fixed to the rotating shaft 8. The cylindrical, conductive metal base material, fixed to the outer circumferential surface of the insulating element 11a, is then cut along the axial direction in ten regions that have been predefined in the circumferential direction. This forms the first to tenth segments SG1 to SG10, which are insulated from and spaced apart from each other. The sections cut in the axial direction become the first to tenth undercuts C1 to C10. The first to tenth undercuts C1 to C10 are not arranged at equal angular intervals (equal divisions) around the central axis O of the rotating shaft 8 in the circumferential direction. That is, the first to tenth undercuts C1 to C10 are arranged at predetermined, unequal angular intervals (unequal divisions) in the circumferential direction. Position where the undercut C is formed Now, the positions where the first to tenth undercuts C1 to C10 are formed when the ten segments SG (SG1 to SG10) of commutator 11 are formed are described. Figure 4 shows the positions where the first to tenth undercuts C1 to C10 of the conventional four-pole, ten-segment motor are formed. These undercuts are arranged circumferentially around the central axis O of the rotating shaft 8 with equal spacing (= 36 degrees). Lines extending from the central axis O of the rotating shaft 8 through the circumferentially central positions of each undercut C1 to C10 are designated as the first to tenth reference lines L1 to L10, in order of forward rotation. Fig. 5 is a developed diagram showing a wire connection of winding 10 of the conventional four-pole, ten-segment brush motor shown in Fig. 4. Winding 10 is wound as a loop winding in the same way as in the present embodiment. The brush motor 1 of the present embodiment is a motor in which the number of poles Pz is four and the number of segments N is ten, as in the conventional brush motor with four poles and ten segments shown in Fig. 4, and in which the following comparative expression is true. Here, the number of poles Pz is an even number greater than or equal to four. K is a constant and is a natural number greater than or equal to two. The brush motor for which such a comparative expression is true is a motor for which the number of slots (the number of teeth) cannot be divided by the number of poles Pz. The brush motor 1 of the present embodiment is the motor for which the above-mentioned comparative expression is true when the constant is three. In the case of the brush motor where N=Pz(K-0,5) is true and the positions of each of the undercuts are formed with an equal division, one undercut C is set as a reference and the circumferentially mean positions of the other undercuts C are located at positions of a reference angle θz, which is defined below. If the number of poles Pz is four and the number of segments N is ten, the reference angle θz = (360 degrees / 4) ± (360 degrees / 20) = 90 degrees ± 18 degrees. Furthermore, two reference angles θz are obtained, namely 108 degrees and 72 degrees. These two reference angles θz mean that, viewed from one undercut, the other undercuts are located at the position of 108 degrees and the position of 72 degrees, respectively. Of the two reference angles θz, one of the reference angles θz, namely 72 degrees, is designated as the first reference intersecting distance θz1. The other of the reference angles θz, namely 108 degrees, is designated as the second reference intersecting distance θz2. That is, if, in the case of the motor with four poles and ten segments shown in Fig. 4, for example, the first undercut C1 is used as a reference, then the third undercut C3 is located at the position separated from the first undercut C1 by the first reference undercut distance θz1, and the fourth undercut C4 is located at the position separated from the first undercut C1 by the second reference undercut distance θz2. The positions of the first to tenth undercuts C1 to C10 of the present embodiment are arranged with an unequal division, as shown in Fig. 2. That is, in the present embodiment, at least one set of undercut distances θx1 and θx2 is provided, which differs from the first and second reference undercut distances θz1 and θz2, which are specified by the reference angle θz (=(360 degrees / Pz) ± (360 degrees / 2N). In Fig. 2, the undercut distance θx1 is set to 70 degrees with respect to the first reference undercut distance θz1 (=72 degrees), with the first undercut C1 serving as the reference, and the undercut distance θx2 is set to 110 degrees with respect to the second reference undercut distance θz2 (=108 degrees). Consequently, the third undercut C3, shown in Fig. 2, is configured such that a third reference line L3a is located at a position that deviates counterclockwise by two degrees from the third reference line L3 of the third undercut C3 shown in Fig. 4. Furthermore, the fourth undercut C4, shown in Fig. 2, is configured such that a fourth reference line L4a is located at a position that deviates clockwise by two degrees from the fourth reference line L4 of the fourth undercut C4 shown in Fig. 4. Thus, the division between the third undercut C3 and the fourth undercut C4, shown in Fig. 2, is an unequal division of 40 degrees, which differs from 36 degrees (an equal division). Due to the formation of the unequal division of 40 degrees, the division between the second undercut C2 and the third undercut C3 and the division between the fourth undercut C4 and the fifth undercut C5 are unequal divisions of 34 degrees, in order to compensate for the 4 degrees with each of the other divisions. Therefore, the circumferential widths of the second and fourth segments SG2 and SG4, which are located at positions corresponding to the unequal division of 34 degrees, are designed to be short relative to the circumferential width of segment SG located at the position corresponding to the equal division of 36 degrees. In contrast, the circumferential width of the third segment SG3, which is located at the position corresponding to the unequal division of 40 degrees, is designed to be long relative to the circumferential width of segment SG located at the position corresponding to the equal division of 36 degrees. Furthermore, in the present embodiment, the eighth undercut C8, shown in Fig. 2, is also configured such that an eighth reference line L8a is located at a position that deviates counterclockwise by two degrees from the eighth reference line L8 of the eighth undercut C8 shown in Fig. 4. Moreover, the ninth undercut C9, shown in Fig. 2, is configured such that a ninth reference line L9a is located at a position that deviates clockwise by two degrees from the ninth reference line L3 of the ninth undercut C9 shown in Fig. 4. Thus, the division between the eighth undercut C8 and the ninth undercut C9, shown in Fig. 2, is an unequal division of 40 degrees, which differs from 36 degrees (an equal division). Similarly, the division between the seventh undercut C7 and the eighth undercut C8, and the division between the ninth undercut C9 and the tenth undercut C10, are formed with an unequal division of 34 degrees due to the formation of the 40-degree unequal division, in order to compensate for the 4 degrees difference with each of the other divisions. Therefore, the circumferential widths of the seventh and ninth segments SG7 and SG9, which are located at positions corresponding to the unequal division of 34 degrees, are designed to be short relative to the circumferential width of segment SG located at the position corresponding to the equal division of 36 degrees. In contrast, the circumferential width of the eighth segment SG8, ​​which is located at the position corresponding to the unequal division of 40 degrees, is designed to be long relative to the circumferential width of segment SG located at the position corresponding to the equal division of 36 degrees. In the present embodiment, the first to fifth undercuts C1 to C5 comprise a set of three undercuts, two of which are arranged at an unequal division of 34 degrees and one at an unequal division of 40 degrees. The segments SG, which have different circumferential widths, are formed corresponding to the two unequal divisions of 34 degrees and the one unequal division of 40 degrees on the right half of the first to fifth undercuts C1 to C5. Furthermore, the sixth to tenth undercuts C6 to C10 also comprise a set of three undercuts, two of which are arranged at the unequal division of 34 degrees and one at the unequal division of 40 degrees.The segments SG, which have different circumferential widths, are also formed according to the two unequal divisions of 34 degrees and the one unequal division of 40 degrees on the left half of the sixth to tenth undercuts C6 to C10. In the present embodiment, two unequal divisions of 34 degrees are used to compensate for the 4-degree circumferential width generated when the unequal division is formed by each of the other divisions. Alternatively, the 4-degree circumferential width can be compensated, for example, by a single unequal division of 32 degrees. In this case as well, a segment SG corresponding to an unequal division of 32 degrees and a segment SG corresponding to an unequal division of 40 degrees can be formed on the right half of the first to fifth undercuts C1 to C5. In the present embodiment, the undercut distances θx1 and θx2, which differ from the first and second reference undercut distances θz1 and θz2 (the reference angle θz), are 70 degrees and 110 degrees, respectively. In other words, the third undercut C3 is formed at the location of the third reference line L3a, which deviates counterclockwise from the third reference line L3 by two degrees, and the fourth undercut C4 is formed at the location of the fourth reference line L4a, which deviates clockwise from the fourth reference line L4 by two degrees. However, the different undercut distances θx1 and θx2 are not limited to 70 degrees and 110 degrees. This means that, in the case mentioned above, neither the angle that deviates counterclockwise from the third reference line L3, nor the angle that deviates clockwise from the fourth reference line L4, is limited to two degrees. However, the circumference of the second segment SG2 is limited in such a way that it cannot be smaller than the pre-specified value if the deviation angle is too large and the third reference line L3a approaches the second reference line L2 (the same applies to the fourth segment SG4). This means that the positive electrode brush B1 and the negative electrode brush B2 do not simultaneously touch the three segments, namely the second segment SG2 and the first and third segments SG1 and SG3 adjacent to the second segment SG2 (the same applies to the fourth segment SG4). The angle of deviation is limited within a predefined range such that the circumference of the second segment SG2 is adjusted so that the positive electrode brush B1 and the negative electrode brush B2 do not simultaneously touch the three segments (the same applies to the fourth segment SG4). The functionality of brush motor 1 will now be described. In brush motor 1, the brush arrangement angle θb, formed by the positive electrode brush B1 and the negative electrode brush B2, is 90 degrees. Therefore, the positive and negative electrode brushes B1 and B2 do not run along the adjacent segment SG simultaneously. This means that the contact time during which the positive electrode brush B1 runs along the adjacent segment SG and the separation time during which the positive electrode brush B1 is separated from it differ from the contact time during which the negative electrode brush B2 runs along the adjacent segment SG and the separation time during which the negative electrode brush B2 is separated from it. Therefore, the fluctuation range of the current value supplied to winding 10 can be reduced compared to when the positive electrode brush B1 and the negative electrode brush B2 run simultaneously along the adjacent segments SG. This allows the excitation force of the brush motor 1 to be distributed, and vibration and background noise can be reduced. Furthermore, in the first to twelfth segments SG1 to SG12, two sets of undercut distances θx1 and θx2 are set, which differ from the reference angle θz, that is, from the first and second reference undercut distances θz1 and θz2, which are defined for the brush motor 1, which has four poles and ten segments. This means that, of the first to twelfth segments SG1 to SG12, the circumferential widths of the second, fourth, seventh, and ninth segments SG2, SG4, SG7, and SG9, which are located at positions corresponding to an unequal division of 32 degrees, are shorter than the circumferential width of the segment SG located at the position corresponding to an equal division of 36 degrees. Furthermore, the circumferential widths of the third and eighth segments SG3 and SG8, ​​which are located at positions corresponding to an unequal division of 40 degrees, are longer than the circumferential width of the segment SG located at the position corresponding to an equal division of 36 degrees. Therefore, the background noise generated by the force with which the individual segments SG1 to SG10 are subjected to the plus and minus electrode brushes B1 and B2 during rotation is not maximized, but averaged, so that the background noise level can be reduced. Fig. 6A is a graph showing the absolute value of the excitation force with respect to the nth-order component of each excitation force in the brush motor 1 shown in Fig. 2, which has four poles and ten segments and unequal spacing between the undercuts, obtained experimentally at a speed of 6500 rpm. Fig. 6B is a graph showing the absolute value of the excitation force with respect to the nth-order component of each excitation force in the brush motor 1 shown in Fig. 4, which has four poles and ten segments and equal spacing between the undercuts, obtained experimentally at a speed of 6500 rpm. As can be seen from Fig. 6A and Fig. 6B, the excitation force in the case of the brush motor 1 with four poles and ten segments, which has the undercuts with unequal spacing, can be greatly reduced compared to the brush motor with four poles and ten segments, which has the undercuts all having the same spacing. The first embodiment has the following advantages. (1) In the embodiment described above, the brush arrangement angle θb formed by the positive electrode brush B1 and the negative electrode brush B2 in the four-pole, ten-segment brush motor 1 is 90 degrees. Thus, the fluctuation range of the current value supplied to the winding 10 is reduced compared to when the positive electrode brush B1 and the negative electrode brush B2 simultaneously travel along the adjacent segments SG. As a result, the brush motor 1 distributes the excitation force and reduces vibration and extraneous noise.(2) In the embodiment described above, the first to twelfth segments SG1 to SG12 include two sets of undercut distances θx1 and θx2 that differ from the reference angle θz, that is, from the first and second reference undercut distances θz1 and θz2 defined for the brush motor 1, which has four poles and ten segments. Therefore, the background noise generated by the force applied to each segment SG1 to SG10 by the positive and negative electrode brushes B1 and B2 during rotation is not maximized but averaged, and the background noise level is reduced. (3) In the present embodiment, the voltage equalization lines WL1 to WL2, which connect different segments SG, are used such that the number of positive electrode brushes B1 and the number of negative electrode brushes B2 is one each.This reduces the likelihood of contact failure caused by brush vibration, and reliably maintains the desired contact across unequal pitches. The first embodiment can be modified as described below. In the first embodiment, the brush arrangement angle θb, formed by the positive electrode brush B1 and the negative electrode brush B2, is 90 degrees. As shown in Fig. 2, the positive electrode brush B1, represented by the solid line, can be arranged differently, as indicated by the double dashed line. In this case, the deviation angle θy is preferably changed within a range of θy < (360 degrees / 2Pz). In other words, the positive electrode brush B1 and the negative electrode brush B2 can be arranged at the positions indicated by θb+θy. The reference angle θz is expressed using the following comparison expression when the deviation angle is shifted only by θy. In this case, at least one set of undercuts is used, arranged at an undercut distance that differs from the reference undercut distance obtained from the comparison expression given above. Again, in this case, the fluctuation range of the current value supplied to winding 10 can be reduced. As a result, the brushed motor 1 can distribute the excitation force and reduce vibration and extraneous noise. In the first embodiment described above, the present invention is implemented in the brush motor 1, which has four poles and ten segments. However, the present invention can be applied to a brush motor other than the brush motor 1 with four poles and ten segments, where N=Pz(K-0.5) is satisfied. K is a natural number of two or greater than or equal to four. Second embodiment A second embodiment will now be described with reference to Fig. 7, Fig. 8, Fig. 9 to Fig. 10. The brush motor 1 described in the above first embodiment is a motor for which a comparison expression N=Pz (K-0,5) is true, where Pz is the number of poles and N is the number of segments. The brush motor 1 of the second embodiment is a motor in which the following comparative expression is true, where Pz is the number of poles and N is the number of segments. Here, the number of poles Pz is an even number greater than or equal to four. K is a constant and is a natural number greater than or equal to two. The brush motor for which such a comparative expression is true is a motor where the number of slots (the number of teeth) can be divided by the number of poles Pz. This differs from the first embodiment. In the second embodiment, the brush motor 1 of a so-called four-pole, twelve-segment motor, where the number of poles Pz is four, the constant K is three, and the number of segments N is twelve, is described for the sake of brevity. The characteristic features of the second embodiment are that the number N of segments SG is 12 (the number of teeth 9a is 12) and the positions of the 12 undercuts for the 12 segments SG in the circumferential direction are formed at a predetermined unequal angular interval (an unequal pitch). Therefore, for the sake of brevity, only the positions where the undercut is formed will be described. Position where the undercut C is formed Now the positions are described where the first to twelfth undercuts C1 to C12 are formed, which form the twelve segments SG (SG1 to SG12) of the commutator 11. Figure 9 shows the position where the first to twelfth undercuts C1 to C12 of the conventional four-pole, twelve-segment brushed motor are formed. These undercuts are arranged circumferentially around the central axis O of the rotating shaft 8 with equal spacing (= 30 degrees). In this case, lines extending from the central axis O of the rotating shaft 8 through the circumferentially central position of each of the undercuts C1 to C12 are designated as the first to twelfth reference lines L1 to L12, in order of the forward direction of rotation. Fig. 10 is a developed diagram showing a wire connection of the winding 10 of the conventional four-pole, twelve-segment brush motor shown in Fig. 9, in which the winding 10 is wound as a loop winding. To reduce the number of brushes to two, the positive and negative electrode brushes B1 and B2, six voltage equalization lines, the first through sixth WL1 to WL2, are connected between the pairs of segments SG. Specifically, the first WL1 connects the twelfth segment SG12 and the sixth segment SG6. The second WL2 connects the first segment SG1 and the seventh segment SG7. The third WL3 connects the second segment SG2 and the eighth segment SG8. The fourth WL4 connects the third segment SG3 and the ninth segment SG9. The fifth WL5 connects the fourth segment SG4 and the tenth segment SG10. The sixth WL6 connects the fifth segment SG5 and the eleventh segment SG11. The brush motor 1 of the second embodiment shown in Fig. 7 is a motor belonging to a motor in which the number of poles Pz is four and the number of segments N is twelve, as in the brush motor with four poles and twelve segments having an equal division shown in Fig. 9, and in which the following comparative expression is true. If N=Pz×K is satisfied and the position of each of the undercuts is formed at an equal division, an undercut C is used as a reference and the circumferentially mean positions of the other undercuts C are located at positions of the reference angle θz, which is defined below. If the number of poles Pz is four and the number of segments N is twelve, the reference angle θz is 90 degrees. A reference angle θz (= 90 degrees) means that, viewed from one undercut, the other undercuts are located at 90-degree angles. That is, in the brush motor with four poles and twelve segments with equal spacing, shown in Fig. 9, in which, for example, the first undercut C1 is used as a reference, the fourth undercut C4 is located at a point that is spaced from the first undercut C1 by the reference angle θz. The first to twelfth undercuts C1 to C12 of the second embodiment are arranged with an unequal division, as shown in Fig. 7. That is, in the second embodiment, at least one set of undercut distances θx is set which differ from the angle specified by the reference angle θz (=360 degrees / Pz). In Fig. 7, the undercut distance θx, which differs from the reference angle θz, which has the first undercut C1 as its reference, is 88 degrees. As a result, the fourth undercut C4, shown in Fig. 7, is designed such that a fourth reference line L4a is located at a position that deviates counterclockwise by two degrees from the fourth reference line L4 of the fourth undercut C4 shown in Fig. 9. Thus, the division between the third undercut C3 and the fourth undercut C4, shown in Fig. 7, becomes an unequal division of 28 degrees, which differs from 30 degrees (an equal division). Due to the formation of the unequal division of 28 degrees, the division between the fourth undercut C4 and the fifth undercut C5 is formed with an unequal division of 32 degrees to compensate for the two degrees difference with each of the other divisions. Therefore, the circumferential width of the third segment SG3, which is located at the position corresponding to the unequal division of 28 degrees, is designed to be short relative to the circumferential width of segment SG, which is located at the position corresponding to the equal division of 30 degrees. In contrast, the circumferential width of the fourth segment SG4, which is located at a position corresponding to the unequal division of 32 degrees, is designed to be long relative to the circumferential width of segment SG, which is located at the position corresponding to the equal division of 30 degrees. In the present embodiment, the tenth undercut C10, shown in Fig. 7, is also designed such that a tenth reference line L10a is located at a position that deviates counterclockwise by two degrees from the tenth reference line L10 of the tenth undercut C10 shown in Fig. 9. Thus, the division between the ninth undercut C3 and the tenth undercut C10, shown in Fig. 7, is an unequal division of 28 degrees, which differs from 36 degrees (an equal division). Due to the formation of the unequal division of 28 degrees, the division between the tenth undercut C10 and the eleventh undercut C11 is formed as an unequal division of 32 degrees to compensate for the two degrees difference with each of the other divisions. Therefore, the circumferential width of the ninth segment SG9, located at the position corresponding to the unequal division of 28 degrees, is designed to be short relative to the circumferential width of segment SG, located at the position corresponding to the equal division of 30 degrees. Conversely, the circumferential width of the tenth segment SG10, located at the position corresponding to the unequal division of 32 degrees, is designed to be long relative to the circumferential width of segment SG, located at the position corresponding to the equal division of 30 degrees. In the present embodiment, the first to sixth undercuts C1 to C6 comprise a set of undercuts, including two undercuts, one of which is arranged at the unequal division of 28 degrees and the other at the unequal division of 32 degrees. The segments SG, which have different circumferential widths, are formed according to the one unequal division of 28 degrees and the one unequal division of 32 degrees on the right half of the first to sixth undercuts C1 to C6. Furthermore, the seventh to twelfth undercuts C7 to C12 also comprise a set of undercuts, including two undercuts, one of which is arranged at the unequal division of 28 degrees and the other at the unequal division of 32 degrees.The segments SG, which have different circumference widths, are also formed according to the one unequal division of 28 degrees and the one unequal division of 32 degrees on the left half of the seventh to twelfth undercuts C7 to C12. In the second embodiment, the undercut distance θx, which differs from the reference angle θz, is 88 degrees. In other words, the fourth undercut C4 is formed at the position of the fourth reference line L4a, which deviates counterclockwise from the fourth reference line L4 by two degrees. However, the undercut distance θx, which differs from the reference angle θz, is not limited to 88 degrees. That is, in the above case, the angle that deviates counterclockwise from the fourth reference line L4 is not limited to two degrees. The circumference width of the third segment SG3 is limited in such a way that it must not be smaller than the pre-specified value if the deviation angle is too large and the fourth reference line L4a approaches the third reference line L3. This means that the positive electrode brush B1 and the negative electrode brush B2 do not simultaneously touch the three segments of the third segment SG3 and the second and fourth segments SG2 and SG4, which are adjacent to the third segment SG3. The angle of deviation is limited within a predefined range such that the circumference of the third segment SG3 is adjusted so that the positive electrode brush B1 and the negative electrode brush B2 do not simultaneously touch the three segments. As shown in Fig. 8, the winding 10 of the brush motor 1 of the second embodiment is also wound in a loop winding. The functionality of brush motor 1 will now be described. In the brush motor 1, the brush arrangement angle θb, formed by the positive electrode brush B1 and the negative electrode brush B2, is 90 degrees. Therefore, the positive and negative electrode brushes B1 and B2 do not run simultaneously along the adjacent segment SG every time the rotating shaft 8 is turned by 30 degrees. That is, there are cases where the positive and negative electrode brushes B1 and B2 run simultaneously along the adjacent segment SG, and cases where they do not. Thus, it is rare for the positive and negative electrode brushes B1 and B2 to run simultaneously along the adjacent segment SG on every rotation of the rotating shaft 8. Therefore, the fluctuation range of the current value supplied to winding 10 can be reduced compared to when the brushes often run along simultaneously. As a result, the excitation force of the brush motor 1 can be distributed, and the vibration and background noise can be reduced. Furthermore, in the first to twelfth segments SG1 to SG12, two sets of distinction distances θx are set, which differ from the reference angle θz (=90 degrees) defined in the brush motor 1 with the four poles and 12 segments. This means that, of the first to twelfth segments SG1 to SG12, the circumferential widths of the third and ninth segments SG3 and SG9, which are located at positions corresponding to an unequal division of 28 degrees, are shorter than the circumferential width of segment SG located at a position corresponding to an equal division of 30 degrees. Furthermore, the circumferential widths of the fourth and tenth segments SG4 and SG10, which are located at positions corresponding to an unequal division of 32 degrees, are longer than the circumferential width of segment SG located at a position corresponding to an equal division of 30 degrees. Therefore, background noise generated by the force with which the individual segments SG1 to SG12 are subjected to rotation by the plus and minus electrode brushes B1 and B2 cannot be maximized, but averaged, and the background noise level can be reduced. The second embodiment has the following advantages. (1) In the embodiment described above, in the brush motor 1, which has four poles and twelve segments, the brush arrangement angle θb formed by the positive electrode brush B1 and the negative electrode brush B2 is 90 degrees. Thus, the positive and negative electrode brushes B1 and B2 less frequently run along the adjacent segments SG simultaneously during each rotation of the brush motor 1, thereby reducing the fluctuation range of the current value supplied to the winding 10. As a result, the brush motor 1 distributes the excitation force and reduces vibration and extraneous noise. (2) In the embodiment described above, two sets of undercut distances θx are used, which differ from the reference distance θz defined for the brush motor 1 with four poles and twelve segments.Therefore, background noise generated by the force exerted on the individual segments SG1 to SG12 by the positive and negative electrode brushes B1 and B2 during rotation is not maximized but averaged, and the background noise level is reduced. (3) In the present embodiment, the voltage equalization lines WL1 to WL6, which are connected between different segments SG, are used such that one positive electrode brush B1 and one negative electrode brush B2 are provided in each case. This reduces the frequency of contact failures caused by brush vibration and reliably maintains the desired contact across the unequal segments. The second embodiment can be modified as described below. In the second embodiment, the brush arrangement angle θb, formed by the positive electrode brush B1 and the negative electrode brush B2, is 90 degrees. As shown in Fig. 7, the positive electrode brush B1, represented by the solid line, can be offset as indicated by the double-dashed line. In this case, the deviation angle θy is preferably changed within a range of θy < (360 degrees / 2Pz). In other words, the positive electrode brush B1 and the negative electrode brush B2 can be arranged at the positions indicated by θb+θy. The reference angle θz is expressed using the following comparison expression when the deviation angle deviates by θy. In this case, at least one set of undercuts is used, positioned at an undercut distance that differs from the reference undercut distance obtained from the comparison expression given above. Again, in this case, the fluctuation range of the current value supplied to winding 10 can be reduced. As a result, the brushed motor 1 can distribute the excitation force and reduce vibration and extraneous noise. In the second embodiment described above, the present invention is implemented in the brush motor having four poles and twelve segments. However, the present invention need not be applied to the brush motor 1 with four poles and twelve segments, and it can be applied to a brush motor for which N = Pz × K. K is a natural number that is either two or four or greater. Third embodiment A third embodiment is now described with reference to Fig. 11, Fig. 12, Fig. 13, Fig. 14, Fig. 15 to Fig. 16. The brush motor 1 according to the third embodiment is the same as the four-pole, ten-segment brush motor described in the first embodiment. However, the method for forming the ten undercuts for the ten segments SG differs from that of the first embodiment. Therefore, for the sake of brevity, the position where the undercuts are formed will be described. As shown in Fig. 11, the first to tenth segments SG1 to SG10 are fixed to the outer circumferential surface of the cylindrical insulating element 11a, which is fixed to the rotating shaft 8. The positive electrode brush B1 and the negative electrode brush B2 are spaced apart from each other by 90 degrees in the circumferential direction around the central axis O of the rotating shaft 8. Those segments SG1 to SG10 that are adjacent to each other are isolated from one another by an undercut (groove). The ten undercuts, that is, the first to tenth undercuts C1 to C10, have the same circumferential spacing (the same undercut width G). The first to tenth undercuts C1 to C10 are not arranged at equal angular intervals (equal divisions) around the circumferential direction around the central axis O of the rotating shaft 8. That is, the first to tenth undercuts C1 to C10 are arranged at predetermined, unequal angular intervals around the circumferential direction. The positions where the first to tenth undercuts, C1 to C10, are formed are set based on the following two objectives. The first objective is to reduce the extraneous noise generated by the force exerted by the positive and negative electrode brushes B1 and B2 during rotation on the individual segments SG, which slide in contact along the positive and negative electrode brushes B1 and B2. The second objective is to reduce changes in motor characteristics based on differences in the pitch pattern of the undercut C (the transit time of the brushes B1 and B2) during forward and reverse rotation. The positions where the first to tenth undercuts, C1 to C10, are formed are described below. Since the first to tenth undercuts C1 to C10, which have the same undercut widths G, are formed with unequal angular spacings, the first to tenth segments SG1 to SG10 do not all have the same circumferential width (segment width W). Therefore, the first to tenth segments SG1 to SG10 include the segment SG with the smallest segment width W (minimum segment width Wmin). Thus, the circumferential width (brush width) F of the sliding contact surface, which slides in contact along the segment SG of the positive and negative electrode brushes B1 and B2, is set with a constant relationship between the minimum segment width Wmin and the undercut width G, as described below. The brush widths F of the positive and negative electrode brushes B1 and B2 are the same. Position where the undercut C is formed Now, the positions where the first to tenth undercuts C1 to C10 are formed when the ten segments SG of commutator 11 are formed are described. Fig. 13 shows the positions of the first to tenth undercuts C1 to C10 of the prior art. The first to tenth undercuts C1 to C10 are formed circumferentially around the central axis O of the rotating shaft 8 at a distance (for a standard pitch) at an equal angle (= 36 degrees). In this case, lines passing through the circumferentially medial positions of each of the undercuts C1 to C10 from the central axis O of the rotating shaft 8 are designated, in order of the forward direction of rotation, as the first to tenth reference lines L1 to L10. Fig. 12A shows the positions of the first to tenth undercuts C1 to C10 of the third embodiment. The first to tenth undercuts C1 to C10 are formed circumferentially around the central axis O of the rotating shaft 8 at unequal angular intervals. In this case, lines passing through the circumferentially medial positions of each of the undercuts C1 to C10 from the central axis O of the rotating shaft 8 are designated, in order of the forward direction of rotation, as the first to tenth reference lines L1a to L10a. As shown in Fig. 12A, the circumferentially mean position (the first reference line L1a) of the first undercut C1 deviates by one degree (= -1 degree) from the first reference line L1 in the reverse direction of rotation. The circumferentially mean position (the second reference line L2a) of the second undercut C2 deviates by one degree (= -1 degree) from the second reference line L2 in the reverse direction of rotation. The circumferentially mean position (the third reference line L3a) of the third undercut C3 deviates by one degree (= +1 degree) in the forward direction of rotation from the third reference line L3. The circumferentially mean position (the fourth reference line L4a) of the fourth undercut C4 deviates by one degree (= -1 degree) from the fourth reference line L4 in the reverse direction of rotation. The circumferentially mean position (the fifth reference line L5a) of the fifth undercut C5 deviates by one degree (= +1 degree) in the forward direction of rotation from the fifth reference line L5. The circumferentially central position (the sixth reference line L6a) of the sixth undercut C6 deviates by one degree (= -1 degree) from the sixth reference line L6 in the reverse direction of rotation. The circumferentially central position (the seventh reference line L7a) of the seventh undercut C7 deviates by one degree (= -1 degree) from the seventh reference line L7 in the reverse direction of rotation. The circumferentially central position (the eighth reference line L8a) of the eighth undercut C8 deviates by one degree (= +1 degree) in the forward direction of rotation from the eighth reference line L8. The circumferentially central position (the ninth reference line L9a) of the ninth undercut C9 deviates by one degree (= -1 degree) from the ninth reference line L9 in the reverse direction of rotation. The circumferentially central position (the tenth reference line L10a) of the tenth undercut C10 deviates by one degree (= +1 degree) in the forward direction of rotation from the tenth reference line L10. The first to tenth undercuts C1 to C10 are thus formed at unequal angular intervals. As a result, extraneous noises generated by the force with which the individual segments SG, which slide in contact along the positive and negative electrode brushes B1 and B2, are acted upon by the positive and negative electrode brushes B1 and B2 during forward and reverse rotation, are not maximized but averaged. Fig. 12B is a graph showing the angle of deviation from each reference line L1 to L10 at each undercut C1 to C10. The horizontal axis indicates the individual undercuts C1 to C10, and the vertical axis shows the angle of deviation in the forward direction of rotation with a positive value and the angle of deviation in the reverse direction of rotation with a negative value, assuming each reference line L1 to L10 is at zero degrees. The motor characteristics were tested based on the fact that the pitch pattern (passage time) of the undercuts passing the brush differs depending on the direction of rotation. First, the total amount Z1 (hereinafter referred to as the forward-rotation total amount) of the deviation angles of those undercuts C that assume a positive value is determined. Next, the total amount Z1 (hereinafter referred to as the backward-rotation total amount) of the deviation angles of those undercuts C that assume a negative value is determined. Then, a sum Z (=Z1 + Z2) of the forward-rotation total amount Z1 and the backward-rotation total amount Z2 is calculated. As shown in Figs. 12A and 12B, the present embodiment has four undercuts C, the third, fifth, eighth, and tenth undercuts C3, C5, C8, and C10, which are shifted by one degree (= +1 degree) in the forward direction of rotation. The total forward-rotation-side amount Z1 of the deviation angles of the undercuts C3, C5, C8, and C10 in the forward direction of rotation is +4 degrees. In contrast, there are six undercuts C, the first, second, fourth, sixth, seventh, and ninth undercuts C1, C2, C4, C6, C7, and C9, which are shifted by one degree (= -1 degree) in the reverse direction of rotation. The total amount Z2 of the deviation angles of the undercuts C1, C2, C4, C6, C7, and C9 in the reverse direction of rotation is -6 degrees. Consequently, the sum Z (=Z1 + Z2) in the case of the present embodiment is -2 degrees. An index value Q, with which the engine characteristics of the engine can be determined, is defined as described below. Through experiments, the value of the index value Q is changed, a zero-load speed is determined with respect to the index value Q, and a zero-load current is determined with respect to the index value Q. In this case, the value of the index Q is changed by modifying the sum Z with the number of segments N and fixing the number of pole pairs P. That is, if the number of segments N is ten and the number of pole pairs is two, then the sum Z (=Z1 + Z2) is modified to change the index Q. Therefore, the unit of the index value Q is an angle. The index value Q is a + (positive) value if the sum Z is in the forward direction of rotation, and the index value Q is a - (negative) value if the sum Z is in the reverse direction of rotation. Fig. 14 is a graph showing the zero-load speed for the index value Q, which is determined by experiments, where the horizontal axis represents the index value Q and the vertical axis represents the zero-load speed (RPM). Fig. 14 is a graph obtained by rotating the brushed motor 1 in the forward direction. When the brushed motor 1 is rotated backward, the speed characteristic of the index value Q has a shape that is symmetrical to the speed characteristic of Fig. 14, with a line that is orthogonal to the zero-degree position on the horizontal axis, which serves as the axis of symmetry. That is, if the tests are carried out by rotating the brushed motor 1 in reverse, then the test result obtained is one in which the index value Q of the horizontal axis of Fig. 14 is positively / negatively inverted. As shown in Fig. 14, the no-load speed increases relative to the index value Q (= (sum Z / number of segments N) / number of pole pairs P). In other words, the no-load speed increases as the sum Z becomes larger from a negative to a positive value. When the brush motor 1 is rotated backwards, the no-load speed increases as the sum Z decreases from the positive value to the negative value. In this case, taking into account individual differences, for example manufacturing deviations of the permanent magnet 6 and the armature core 9, the change in the characteristic value between forward rotation and reverse rotation at zero load speeds is limited to a maximum of ±0.2%, which represents the acceptable range when the index value Q is zero, i.e., the sum Z is zero, the central value. The change in the characteristic value can be limited to a maximum of ±0.2% if the index value Q lies within the range of -0.5 degrees < Q < +0.5 degrees, where zero degrees is the central value. In other words, the change in the characteristic value can be limited to a maximum of ±0.2% even when the brush motor 1 is rotated forwards or backwards, as long as the index value Q remains within the range of -0.5 degrees < Q < +0.5 degrees. Figure 15 is a graph showing the no-load current in relation to the index value Q, which was determined experimentally. The horizontal axis shows the index value Q and the vertical axis shows the no-load current (amperes). Fig. 15 is a graph obtained by rotating the brush motor 1 in the forward direction. When the brush motor 1 is rotated backward, the current characteristic of the index value Q has a shape that is symmetrical to the current characteristic of Fig. 15, with a line that is orthogonal to the zero-degree position on the horizontal axis, which serves as the axis of symmetry. That is, if the experiments are carried out by rotating the brush motor 1 in reverse, then the experimental result is obtained in which the index value Q of the horizontal axis of Fig. 15 is positively / negatively inverted. As shown in Fig. 15, the no-load current increases relative to the index value Q (= (sum Z / number of segments N) / number of pole pairs P). In other words, the no-load current increases towards the negative side and towards the positive side, with the minimum value occurring when the sum Z is zero. Similarly, when the brush motor 1 is rotated in reverse, the no-load current increases towards the negative side and towards the positive side, when the minimum value is reached when the sum Z is zero degrees. As long as the index value Q lies within the range of -0.5 degrees < Q < +0.5 degrees, with zero degrees being the central value, the change in the no-load current is small (at most ±0.2%). In other words, even when rotating the brushed motor 1 in both forward and reverse directions, the change in the characteristic value in the no-load current is small as long as the index value Q lies within the range of -0.5 degrees < Q < +0.5 degrees. Therefore, the change in the no-load current is small, and the change in the no-load speed can be limited to a maximum of ±0.2% by setting the index Q within the range of -0.5 degrees < Q < +0.5 degrees, even when the brushed motor 1 is rotated in forward and reverse directions. Thus, in the brush motor 1 of the present embodiment, the sum Z is -2 degrees, the number of segments N is ten, and the number of pole pairs is two. Therefore, the index value Q (= (Z / N) / P) is -0.1 degrees. Consequently, the change in the no-load current is small and the no-load speed is at most ±0.2%, even when the brushed motor 1 is rotated in forward and reverse directions. The ten undercuts C (C1 to C10) are determined in total for the sum Z (=Z1 + Z2) under the above conditions of the index value Q. Instead, the 360-degree inner circumferential area formed by four (=2P) permanent magnets 6 is divided by the number of pole pairs P (=2) to define P (=2) inner circumferential area regions. The sum Z is determined for a group of successive undercuts belonging to each inner circumferential area region. In other words, the sum Z of the successive undercuts C arranged relative to the inner circumferential area region facing each of the inner circumferential areas is obtained. The motor 1 is preferably designed such that the index value Q for each inner circumferential area region, using the sum Z determined for each inner circumferential area region, is at most ±0.5 degrees, that is, in the undercuts C belonging to the group and the number of segments N and the number of pole pairs P of the brushed motor 1. That is, as shown by the double-dashed line in Fig. 12B, in the present embodiment the inner circumferential area of ​​360 degrees in the circumferential direction, which includes the four permanent magnets 6, is divided by the number of pole pairs P (=2) into two inner circumferential regions, first and second inner circumferential regions Da and Db, of 180 degrees in the circumferential direction. The sums Za and Zb are determined for the five undercuts C belonging to the first inner circumferential region Da and the second inner circumferential region Db. Then, using the sums Za and Zb obtained for each of the first and second inner circumferential regions Da and Db, an index value Qa (=(Za / N) / P) is determined for the first inner circumferential region Da, and an index value Qb (=(Zb / N) / P) for the second inner circumferential region Db. The motor 1 is preferably designed such that the index values ​​Qa and Qb for each of the first and second inner circumferential regions Da and Db are within ±0.5 degrees. Although this is an extreme example, its aim is to exclude the formation of the undercut C if the deviation angles of the five successive undercuts C, arranged so that they face the first inner circumferential region Da, are all in the forward direction of rotation, and the deviation angles of the five successive undercuts C, arranged so that they face the second inner circumferential surface region Db, are all in the backward direction of rotation. Fig. 16 shows an extreme example using the four-pole, twenty-two-segment motor. With the 22 sub-intersections C as the first to twenty-second sub-intersections C1 to C22, these sub-intersections C are represented on the horizontal axis of the graph in Fig. 16. In this case, the index value Q satisfies the condition -0.5 degrees < Q < +0.5 degrees. However, the index values ​​Qa and Qb in each of the inner circumferential surface regions Da and Db are less than or equal to -0.5 degrees or greater than or equal to +0.5 degrees. In such a case, the timing of the current switching (rectification) in brushes B1 and B2 and segments SG differs at each 360-degree position equal to the number of pole pairs P. This shifts the timing of the magnetic excitation force of brush motor 1, causing it to become unbalanced. This leads to an undesirable condition that generates vibration and noise. To prevent such a situation from occurring, the index values ​​Qa and Qb for the first and second inner circumference regions Da and Db are preferably set within ±0.5 degrees. In the case of the brush motor 1 of the present embodiment, the inner circumferential surface of 360 degrees in the circumferential direction, formed by four permanent magnets 6, is divided by the number of pole pairs P (=2) to be divided into two inner circumferential regions, namely first and second inner circumferential regions Da and Db, each of 180 degrees in the circumferential direction. In this case, in the ten undercuts C1 to C10, the five consecutive undercuts C are each arranged in the circumferential direction such that they face the first and second inner circumferential surface regions Da and Db, respectively. In other words, the five consecutive undercuts C each belong to the first inner circumferential surface region Da and to the second inner circumferential surface region Db. The five undercuts C arranged in the first inner circumferential surface region Da are radially oriented towards the five undercuts C arranged in the second inner circumferential surface region Db. As shown by the double-dashed line in Fig. 12B, the first to fifth undercuts C1 to C5 are arranged so that they face the first inner circumferential surface region Da, and the sixth to tenth undercuts C6 to C10 are arranged so that they face the second inner circumferential surface region Db. In this case, the index value Qa (=Za / N) / P) is obtained using the first to fifth undercuts C1 to C5 in the first inner perimeter region Da. In this case, there are two undercuts C, as shown in Fig. 12B, namely the third and fifth undercuts C3 and C5, where the angle of deviation deviates by one degree (= +1 degree) in the forward direction of rotation in the first inner circumferential surface region Da. The total forward-rotation-side amount Z1a of the angle of deviation of the undercuts C3, C5 in the forward direction of rotation is +2 degrees. In contrast, there are three undercuts C, namely the first, second, and fourth undercuts C1, C2, and C4, where the deviation angle deviates by one degree (= -1 degree) in the reverse direction of rotation. The total reverse-rotation-side deviation angle Z2a of the undercuts C1, C2, and C4 in the reverse direction of rotation is -3 degrees. Consequently, the sum Za (= Z1a + Z2a) in the first inner circumferential region Da is -1 degree. The index Qa = ((Za / N) / P) in the first inner circumferential region Da is -0.05 degrees. The index value Qb (=Zb / N) / P) is obtained using the sixth to tenth undercuts C6 to C10 in the second inner perimeter area region Db. In this case, there are two undercuts C, as shown in Fig. 12B, namely the eighth and tenth undercuts C8 and C10, where the angle of deviation deviates by one degree (= +1 degree) in the forward direction of rotation, in the second inner circumferential surface region Da. The total forward-rotation-side amount Z1b of the angle of deviation of the undercuts C8 and C10 in the forward direction of rotation is +2 degrees. In contrast, there are three undercuts C, namely the sixth, seventh, and ninth undercuts C6, C7, and C9, where the deviation angle deviates by one degree (= -1 degree) in the reverse direction of rotation. The total reverse-rotation-side deviation angle Z2b of the undercuts C6, C7, and C9 in the reverse direction of rotation is -3 degrees. Consequently, the sum Zb (= Z1b + Z2b) in the second inner circumferential surface region Db is -1 degree. The index Qb = ((Zb / N) / P) in the second inner circumferential region Db is -0.05 degrees. Therefore, the brush motor 1 of the present embodiment reduces the generation of vibration and noise that would be caused by an unevenness resulting from a deviation in the timing of the magnetic excitation force of the brush motor 1 through the time at which the switching (rectification) of the current carried out in the brushes B1 and B2 and the segments SG is performed. Setting the brush width F, the minimum segment width Wmin and the undercut width G However, since the undercuts C1 to C10 are arranged at unequal angular intervals, the following problems can occur. The first problem is that the positive electrode brush B1 and the negative electrode brush B2, which are spaced 90 degrees apart, run along the undercut C simultaneously, thus negatively affecting the motor characteristics. The second problem is that the positive electrode brush B1 and the negative electrode brush B2, which are spaced 90 degrees apart, touch three segments simultaneously, namely the segment SG with the minimum segment width Wmin and the segments SG that are adjacent to the segment SG, thus negatively affecting the motor characteristics. The first problem arises when the number of slots in the motor is not divisible by the number of magnetic poles, that is, when the slots cannot be evenly distributed across each magnetic pole. A motor in which the slots cannot be equally distributed across each magnetic pole has a superior effect in terms of reducing torque fluctuations or increasing rectification. In contrast, a second problem arises when the number of slots in the motor is divisible by the number of magnetic poles; in other words, in the case of a motor where the slots can be evenly distributed across each magnetic pole. The motor in which the slots can be evenly distributed across each magnetic pole has the superior effect in terms of delivering high torque. The brushed motor 1 of the present embodiment is a motor in which the number of slots is ten and the number of magnetic poles Pz is four (the number of pole pairs P is four (=2P)). Dividing the number of slots by the number of magnetic poles yields the value 2.5. Therefore, the slots cannot be evenly distributed across the individual magnetic poles. This can cause the first problem. In the present embodiment, the brush width F is adjusted so that it satisfies the following conditions for the relationship between the minimum segment width Wmin and the undercutting width G, so that the first problem does not occur. The brush width F is 0.8 times the actual circumferential contact width of the positive and negative electrode brushes B1 and B2 of the brush motor 1, which rotates forwards and backwards. Furthermore, the segments SG with the minimum segment width Wmin are four segments, that is, the third, fifth, eighth and tenth segments SG3, SG5, SG8 and SG10, as shown in Fig. 11 and Fig. 12. If the brush width F is set to a width that meets the above condition, the positive electrode brush B1 and the negative electrode brush Bq do not run along the undercut C simultaneously, and the motor characteristics are therefore not negatively affected. The functionality of brush motor 1 will now be described. Since each of the undercuts C1 to C10, formed between adjacent segments SG, is created at uneven angular intervals, background noise caused by the force received from the positive and negative electrode brushes B1 and B2 during rotation is not maximized but averaged. This reduces the background noise level. Furthermore, in brushed motor 1, where the number of segments N is ten and the number of pole pairs P is two, the motor 1 is designed such that the sum Z (=Z1+Z2) is -2 degrees and the index value Q (= (Z / N) / P) is -0.1 degrees. Thus, the index value Q lies in the range of -0.5 degrees < Q < +0.5 degrees, the change in the no-load current is small (at most ±0.2%), and the change in the no-load speed is at most ±0.2% when brushed motor 1 is rotated forwards and backwards. Furthermore, the inner circumferential area of ​​360 degrees in the circumferential direction, formed by the four permanent magnets 6, is divided by the number of pole pairs P (=2) into two inner circumferential regions Da and Db of 180 degrees in the circumferential direction. The five successive undercuts C during rotation are arranged such that they face the two inner circumferential regions Da and Db. The sums Z of the five undercuts C facing the two inner circumferential regions Da and Db are set to a maximum of ±0.5. Thus, the timing of the magnetic excitation force of brush motor 1 does not deviate based on the time at which the switching (rectification) of the current in brushes B1 and B2 and segments SG is performed. This reduces the vibration and noise generated by the imbalance in the timing of the magnetic excitation force of brush motor 1. Furthermore, brush motor 1 is a motor with ten slots and four magnetic poles (=2P), and the slots cannot be evenly distributed across each magnetic pole. Therefore, the brush width F is adjusted so that, in relation to the minimum segment width Wmin and the undercut width G, (Wmin+2×G) / 2>0.8×F is satisfied. Consequently, the positive electrode brush B1 and the negative electrode brush B2 do not travel along the undercut C simultaneously. The third embodiment has the following advantages. (1) In the present embodiment, the undercuts C1 to C10, which are formed in the ten segments, i.e., in the first to tenth segments SG1 to SG10, are formed at unequal angular intervals. This reduces the level of background noise generated by the force received from the positive and negative electrode brushes B1 and B2 during rotation. (2) In the brush motor 1 of the present embodiment, the number of segments N is ten, and the number of pole pairs P is two. The sum Z (=Z1 + Z2) is -2 degrees, and the index value Q is -0.1, which is in the range of -0.5 degrees < Q < +0.5 degrees. Therefore, when the brush motor 1 is rotated forwards and backwards, the change in the no-load current is small (at most ±0.2%), and the change in the no-load speed is at most ±0.2%.(3) In the present embodiment, the 360-degree inner circumferential surface formed by four permanent magnets 6 is divided by the number of pole pairs P (=2) into two inner circumferential regions Da and Db, each with a circumference of 180 degrees. Since the sum Za of the five undercuts C facing inner circumferential region Da is set to -1 degree and the sum Zb is set to +1 degree, the respective index values ​​Qa and Qb are set within a range of at most ±0.5 degrees. Therefore, the timing of the magnetic excitation force of the brush motor 1, based on the time at which the switching (rectification) of the current in brushes B1 and B2 and segment Sg is performed, does not deviate. This reduces the vibration and noise generated by imbalances in the timing of the magnetic excitation force of the brush motor 1.(4) In the present embodiment, the brush motor 1 is a motor in which the number of slots is ten and the number of magnetic poles is four (=2P), and the slots cannot be distributed across each magnetic pole simultaneously. The brush width F is set such that, in relation to the minimum segment width Wmin and the undercut width G, (Wmin+2×G) / 2>0.8×F. Thus, the positive and negative electrode brushes B1 and B2 do not run along the undercut C simultaneously. Therefore, the motor characteristics are not adversely affected when the positive electrode brush B1 and the negative electrode brush B2 run along the adjacent segments SG simultaneously. The third embodiment can be modified as described below. In the third embodiment described above, the number of slots is not divisible by the number of magnetic poles in the motor (motor in which the slots cannot be evenly distributed across each magnetic pole), and the brush width F is set such that the relationship with the minimum segment width Wmin and the undercut width G is (Wmin+2×G) / 2>0.8×F. In this respect, the brush F can be adjusted as described below if the number of slots can be divided by the number of magnetic poles in a motor (motor in which the slots can be evenly distributed across each magnetic pole). As an example, Fig. 17 shows a motor having twelve segments SG, twelve slots, and four magnetic poles. In this case, the number of slots (=12) is divisible by the number of magnetic poles (=4), and the slots can be evenly distributed across each magnetic pole. In the case of brushed motor 1, the positive electrode brush B1 and the negative electrode brush B2 cannot simultaneously touch three segments, that is, the segment with the minimum segment width Wmin and two segments SG adjacent to it. In this case, the brush width F is set such that the following relationship is satisfied in relation to the minimum segment width Wmin and the undercutting width G. Therefore, the positive electrode brush B1 and the negative electrode brush B2 do not simultaneously touch the three segments SG, namely the segment SG with the minimum segment width Wmin and the two segments SG adjacent to segment SG. Thus, the motor characteristics are not negatively affected by simultaneous contact. In the third embodiment described above, the present invention is implemented in the brush motor 1, in which the number of pole pairs P is two. However, the present invention can, for example, be applied to a brush motor with six poles and twenty-one segments (21 slots), in which the number of pole pairs P is three. As shown in the graph of Fig. 18, in this case the inner circumferential area of ​​360 degrees in the circumferential direction, formed by six permanent magnets 6, is divided by the number of pole pairs P (=3) into three inner circumferential regions, namely the first to third inner circumferential area regions Da, Db and Dc of 120 degrees in the circumferential direction. The 21 undercuts C are designated as the first to twenty-first undercuts C1 to C21, and the undercuts C are shown on the horizontal axis of the graph of Fig. 18. The sums Da, Db, and Dc were determined for the seven consecutive intersections C, each facing the inner perimeter regions Da, Db, and Dc, respectively. Then, an index value Qa (=(Za / N) / P) was calculated for the first inner perimeter region Da. An index value Qb (=(Zb / N) / P) was calculated for the second inner perimeter region Db. An index value Qc (=(Zc / N) / P) was calculated for the third inner perimeter region Dc. Motor 1 is designed such that the index values ​​Qa and Qb for each of the first to third inner circumferential surface regions Da, Db and Dc are within ±0.5 degrees. The brush motor 1 is a motor in which the number of slots is not divisible by the number of magnetic poles and the brush width F must therefore be set so that in the relationship with the minimum segment width Wmin and the undercut width G (Wmin+2×G) / 2>0.8×F is satisfied. In the first to third embodiments, the positive electrode brush B1 and the negative electrode brush B2, as shown in Fig. 1, are forced towards the radially inner side by the compression helical spring 19, which is arranged in the brush holder housing 16. Alternatively, the positive and negative electrode brushes B1 and B2, as shown in Fig. 19, can be pushed forward using first and second torsion springs SP1 and SP2, respectively. In this case, the first torsion spring SP1 is inserted into and supported by a supporting column R1, which projects from the base plate 15 and is arranged clockwise in the circumferential direction of the positive electrode brush B1. When the clockwise rotation of one end of the first torsion spring SP1 is restrained by an engagement pin T1, the rear surface of the positive electrode brush B1 is forced towards the radially inner side by the other end of the first torsion spring SP1. The second torsion spring SP2 is inserted into and supported by a supporting column R2 projecting from the base plate 15, which is arranged counterclockwise in the circumferential direction of the negative electrode brush B2. When the counterclockwise rotation of one end of the second torsion spring SP2 is inhibited by an engagement pin T2, the rear surface of the positive electrode brush B1 is forced radially inward by the other end of the second torsion spring SP2. In this case, the first torsion spring SP1 and the second torsion spring SP2 are arranged symmetrically with respect to a center line that runs circumferentially through the midpoint between springs SP1 and SP2. Therefore, when the commutator 11 is rotated clockwise, the direction of the radial center axis of the negative electrode brush B2 is shifted clockwise by the pressure exerted by the second torsion spring SP2. This reduces the pressure with which the negative electrode brush B2 slides in contact with the individual segments SG, thus reducing brush vibration. Conversely, when the commutator 11 is rotated counterclockwise, the direction of the radial center axis of the positive electrode brush B1 is shifted counterclockwise by the pressure exerted by the first torsion spring SP1.Therefore, the pressure with which the positive electrode brush B1 glides along the individual segments SG in contact can be reduced, and the brush vibration can be reduced.

Claims

Brushed motor (1) comprising: a rotating shaft (8); a commutator (11) fixed to the rotating shaft (8), the commutator (11) having several segments (SG) insulated and separated from one another by several undercuts (C1, C2, ..., C12), the several undercuts (C1, C2, ..., C12) being arranged at unequal angular intervals around a central axis (O) of the rotating shaft (8); an armature (7) fixed to the rotating shaft (8); several permanent magnets (6) arranged on an outer surface of the armature (7), the several permanent magnets (6) being arranged at equal intervals such that the directions of magnetic poles in adjacent permanent magnets (6) differ; a voltage equalization line (WL1, WL2, ...,WL6), which connects various segments (SG) together; and a positive electrode brush (B1) and a negative electrode brush (B2) arranged on an outer circumference of the commutator (11) at positions not facing each other; wherein, where Pz is the number of permanent magnets (6) and N is the number of segments (SG), a relationship N=Pz(K-0.5) is satisfied, where Pz is an even number greater than or equal to four, K is a constant and a natural number greater than or equal to two, and the multiple undercuts (C1,C2,...C12) include undercuts arranged at an undercutting distance corresponding to a reference angle θz and at least one set of undercuts arranged at an undercutting distance different from the reference angle θz, and the reference angle θz is specified by a comparative expression θz = (360 degrees / Pz) ± (360 degrees / 2N). Brushed motor (1) comprising: a rotating shaft (8); a commutator (11) fixed to the rotating shaft (8), the commutator (11) having several segments (SG) insulated and separated from one another by several undercuts (C1, C2, ..., C12), the several undercuts (C1, C2, ..., C12) being arranged at unequal angular intervals around a central axis (O) of the rotating shaft (8); an armature (7) fixed to the rotating shaft (8); several permanent magnets (6) arranged on an outer surface of the armature (7), the several permanent magnets (6) being arranged at equal intervals such that the directions of magnetic poles in adjacent permanent magnets (6) differ; a voltage equalization line (WL1, WL2, ...,WL6), which connects various segments (SG); and a positive electrode brush (B1) and a negative electrode brush (B2) arranged on an outer circumference of the commutator (11) at positions not facing each other; wherein, where Pz is the number of permanent magnets (6) and N is the number of segments (SG), a relationship N=Pz×K is satisfied, where Pz is an even number greater than or equal to four, and K is a constant and a natural number greater than or equal to two, comprising several undercuts (C1,C2,...,C12) arranged at an undercutting distance corresponding to a reference angle θz and at least one set of undercuts arranged at an undercutting distance different from the reference angle θz, and the reference angle θz is specified by a comparative expression θz=(360 degrees / Pz). Brushed motor (1) comprising: a rotating shaft (8); a commutator (11) fixed to the rotating shaft (8), the commutator (11) having several segments (SG) insulated and separated from one another by several undercuts (C1, C2, ..., C12), the several undercuts (C1, C2, ..., C12) being arranged at unequal angular intervals around a central axis (O) of the rotating shaft (8); an armature (7) fixed to the rotating shaft (8); several permanent magnets (6) arranged on an outer surface of the armature (7), the several permanent magnets (6) being arranged at equal intervals such that the directions of magnetic poles in adjacent permanent magnets (6) differ; a voltage equalization line (WL1, WL2, ...,WL6), which connects various segments (SG); and a positive electrode brush (B1) and a negative electrode brush arranged on an outer circumference of the commutator (11) at positions not facing each other; wherein, if Pz is the number of permanent magnets (6) and N is the number of segments (SG), a relationship N=Pz(K-0.5) is satisfied, where Pz is an even number greater than or equal to four, K is a constant and a natural number greater than or equal to two, and the multiple undercuts (C1,C2,...,C12) include at least one set of undercuts arranged with an undercut distance that differs from a reference angle θz, and the reference angle θz is specified by a comparison expression θz = (360 degrees / Pz) ± (360 degrees / 2N), where if θb is a brush arrangement angle and θy is a deviation angle, the positive electrode brush (B1) and the negative electrode brush (B2) are arranged at positions specified by θb+θy, θb = 360 degrees / (Pz×K) is satisfied, where K is a constant and a natural number, θy < 360 degrees / 2Pz is satisfied, and the reference angle θz is specified by a comparison expression θz=(360 degrees / Pz)±(360 / 2N)±θy. Brushed motor (1) comprising: a rotating shaft (8); a commutator (11) fixed to the rotating shaft (8), the commutator (11) having several segments (SG) insulated and separated from one another by several undercuts (C1, C2, ..., C12), the several undercuts (C1, C2, ..., C12) being arranged at unequal angular intervals around a central axis (O) of the rotating shaft (8); an armature (7) fixed to the rotating shaft (8); several permanent magnets (6) arranged on an outer surface of the armature (7), the several permanent magnets (6) being arranged at equal intervals such that the directions of magnetic poles in adjacent permanent magnets (6) differ; a voltage equalization line (WL1, WL2, ...,WL6), which connects various segments (SG); and a positive electrode brush (B1) and a negative electrode brush (B2) arranged on an outer circumference of the commutator (11) at positions not facing each other; wherein, where Pz is the number of permanent magnets (6) and N is the number of segments (SG), a relationship N=Pz×K is satisfied, where Pz is an even number greater than or equal to four, and K is a constant and a natural number greater than or equal to two, the multiple undercuts (C1,C2,...,C12) include at least one set of undercuts arranged with an undercut distance that differs from a reference angle θz, and the reference angle θz is specified by a comparison expression θz=(360 degrees / Pz), where if θb is a brush arrangement angle and θy is a deviation angle, the positive electrode brush (B1) and the negative electrode brush (B2) are arranged at positions specified by θb+θy, θb = 360 degrees / (Pz×K) is satisfied, where K is a constant and a natural number, θy < 360 degrees / 2Pz is satisfied; and the reference angle θz is specified by a comparison expression θz=(360 degrees / Pz)±θy. Brushed motor (1) comprising: a rotating shaft (8); a commutator (11) fixed to the rotating shaft (8), the commutator (11) having several segments (SG) insulated and separated from each other by several undercuts (C1, C2, ..., C12), the several undercuts (C1, C2, ..., C12) being arranged at unequal angular intervals around a central axis (O) of the rotating shaft (8); an armature (7) fixed to the rotating shaft (8); several permanent magnets (6) arranged on a radial outer side of the armature (7); and a brush arranged on an outer circumference of the commutator (11), wherein the rotating shaft (8), the commutator (11) and the armature (7) are rotatable together in forward and reverse directions; N is the number of segments (SG) and the number of multiple undercuts (C1, C2, ..., C12), middle positions of the multiple undercuts (C1, C2, ...,C12) deviate circumferentially in a forward and a reverse direction of rotation from a corresponding mean position circumferentially if the multiple undercuts (C1,C2,...,C12) are formed at the same angle, Z1 is the total angle of deviation of the individual undercuts (C1,C2,...,C12) that deviate in the forward direction of rotation, Z2 is the total angle of deviation of the individual undercuts (C1,C2,...,C12) that deviate in the reverse direction of rotation, Z is the sum of the angles of deviation, Z=Z1+Z2 is satisfied if P is the number of pole pairs of the magnetic poles of the permanent magnets, Q=(Z / N) / P represents an index value Q and the index value Q is -0.5 degrees < Q < +0.5 degrees. Brush motor (1) according to claim 5, wherein the multiple undercuts (C1,C2,...,C12) are divided by the number of pole pairs, and a sum of the deviation angles of the undercuts (C1, C2, ..., C12) belonging to the individual groups is obtained for each divided group, and the index value Q for each group is -0.5 degrees < Q < +0.5 degrees. Brush motor (1) according to claim 5 or 6, wherein the armature (7) has multiple slots, the number of slots is a number that is not divisible by the number of multiple magnetic poles, and (Wmin+2×G) / 2>0.8×F is satisfied if F is a circumferential width of the brush, wherein the multiple segments (SG) each have a segment width (W) which is a circumferential width, Wmin is a minimum segment width in the multiple segments (SG), and G is a circumferential width of the individual undercuts. Brush motor (1) according to claim 7, wherein the number of pole pairs is two and the number of segments (SG) and the number of slots are each ten. Brush motor (1) according to claim 5 or 6, wherein the armature (7) has multiple slots, the number of slots is a number divisible by the number of multiple magnetic poles, and (Wmin+2×G) / >0.8×F is satisfied when F is a circumferential width of the brush, wherein the multiple segments (SG) each have a segment width (W) which is a circumferential width, Wmin is a minimum segment width in the multiple segments (SG), and G is a circumferential width of the individual undercuts. Brush motor (1) according to claim 9, wherein the number of pole pairs is two and the number of segments (SG) and the number of slots are each twelve.

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