Gleichstrommotor

Abstract

DC motor (2) comprising the following: a cylindrical commutator (9) mounted on a shaft (8a) of an armature (8); Brushes (10, 10a, 10b) arranged on an outer circumference of the commutator (9); Brush springs (11) arranged on an opposite commutator side of the brushes (10, 10a, 10b) to push the brushes (10, 10a, 10b) towards the commutator (9); Brush holders (12) which hold the brushes (10, 10a, 10b) on an inner side in a radial direction perpendicular to a central axis of the commutator (9) and hold the brush springs (11) on the opposite commutator side of the brushes (10, 10a, 10b); a positive connecting plate (13) made of a conductive material and arranged on a core side of the commutator (9) from the brush holders (11) in an axial direction of the commutator (9), wherein the positive connecting plate (13) is electrically connected to positive brushes (10a) of the brushes (10, 10a, 10b) by connecting wires (15); a negative connecting plate (14) made of a conductive material and arranged on a core side of the armature (8) opposite the brush holders (12) in the axial direction, wherein the negative connecting plate (14) is electrically connected to the negative brushes (10b) of the brushes (10, 10a, 10b) by connecting wires (15); and an extension component (16) which is electrically connected to the positive connecting plate (13) at a first end part thereof as a connecting part (16a), wherein a second end part of the extension component (16) extends to an outside of a motor housing (25) of the DC motor (2), wherein one of the brush holders (12) that hold the negative brushes (10b) is a specific brush holder (12A), the positive connecting plate (13) has a mounting groove (13a) to allow the specific brush holder (12A) to be installed in it, the specific brush holder (12A) has a convex part (12c) which is mounted in the mounting groove (130) and a stepped surface (12d) which has a step on a radially outer side of the convex part (12c) and is arranged on the opposite core side from a core-side end surface of the convex part (12c), a space which is present in an axially stepped area which is arranged on the core side of the stepped surface (12d) and in which the step is formed, is a stepped space, and the extension component (16) extends from a position that overlaps in the circumferential direction with the specific brush holder (12A) to the outside of the motor housing (25) and is arranged to overlap with the stepped space in the axial direction.

Description

[0001] The present invention relates to a direct current (DC) motor. Description of the state of the art

[0002] A 6-pole direct current (DC) motor for a starter is known, in which the field pole has permanent magnets. Generally, such a motor uses a wave-winding structure for an armature winding (coil) and a four-brush structure including two positive brushes and two negative brushes. As shown, for example, in JP 2003-189551 A, in such a motor, a lead wire connected to the positive brushes and extending (pulled) from them to the outside of the motor housing is arranged at a substantially central position of the two positive brushes.

[0003] Some starters used for vehicles have an idle stop function and are therefore required to have a long service life. They adopt a 6-brush structure consisting of three positive brushes and three negative brushes. Generally, in such a 6-brush structure, the lead wire is arranged between one of the positive brushes and one of the negative brushes that are adjacent to each other. The power wire extension position (the position where the lead wire is arranged) of the DC motor using the 6-brush structure is different from that of the DC motor using the 4-brush structure. Accordingly, the same motor housing cannot be used for the 4-brush structure and the 6-brush structure.

[0004] In addition, the entire motor length must be increased to set the lead wire extension position of the 6-brush structure to be the same as the lead wire extension position of the 4-brush structure, because the lead wire extension position overlaps with the position of one of the negative brushes in the circumferential direction and accordingly a space for arranging the lead wire thereon on the core side in the axial direction of the negative brushes is required.

[0005] Further DC motors according to the state of the art are known from JP 2014 - 87 102 A, WO 2010 / 125 137 A2 and US 7 256 527 B2. SUMMARY

[0006] It is the object of the present invention to provide a DC motor having a flexible design with regard to an arrangement of different brush structures.

[0007] The object of the present invention is achieved by a DC motor having the features of claim 1.

[0008] Advantageous further developments of the present invention are set out in the subclaims.

[0009] According to an exemplary embodiment of the present invention, a direct current (DC) motor is provided in which the extending position of the lead wire can be set the same for the 6-brush structure and the 4-brush structure without increasing the entire length of the DC motor, thereby enabling the motor housing to have a common design for the 6-brush structure and the 4-brush structure.

[0010] Further advantages, effects and features of the invention will become apparent from the following description including the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The attached drawings show the following: Fig. 1 is a sectional view of a rear part of a direct current (DC) motor according to a first embodiment of the invention; Fig. 2 is a sectional view showing brush holders included in the DC motor according to the first embodiment of the invention; Fig. 3 is a perspective view of a brush assembly included in the DC motor according to the first embodiment of the invention; Fig. 4 is an enlarged sectional view of one of the brush holders included in the brush assembly of the DC motor according to the first embodiment of the invention; Fig. 5 is a sectional view of a starter including the DC motor according to the first embodiment of the invention; Fig. 6 is a perspective view of a brush assembly of a DC motor according to a second embodiment of the invention; Fig. 7 is a perspective view of a brush assembly of a DC motor according to a third embodiment of the invention; Fig. 8 is a sectional view of a rear part of the DC motor according to the third embodiment of the invention; Fig. 9 is a perspective view showing connections between an extension member and a positive connection plate of the DC motor according to the third embodiment of the invention; Fig. 10 is a perspective view of a brush assembly of a DC motor according to a fourth embodiment of the invention; Fig. 11 is a sectional view of a rear part of the DC motor according to the fourth embodiment of the invention; Fig. 12 is a perspective view showing connections between an extension member and a positive connection plate of the DC motor according to the fourth embodiment of the invention; Fig. 13 is a sectional view of a brush assembly of a DC motor according to a fifth embodiment of the invention; and Fig. 14 is a perspective view showing connections between an extension member and a positive connection plate of the DC motor according to the fifth embodiment of the invention. PREFERRED EMBODIMENTS OF THE INVENTION First Embodiment

[0012] Fig. Fig. 1 is a sectional view of a rear part of a direct current (DC) motor 2 according to a first embodiment of the invention. The DC motor 2 is used in a starter 1, which is shown in Fig. 5 is used. As shown in Fig. 5, the starter 1 comprises an output shaft 3 rotatably driven by the motor 2, a pinion 4 mounted on the output shaft 3, a lever 6, and an electromagnetic switch 5. The starter 1 is a so-called “pinion-winding type” starter in which the lever 6 is driven by the attractive force of the electromagnetic switch 5 to rotate the pinion 4 toward a not-shown ring gear of an internal combustion engine (toward the left side of Fig. 5) to push (pull) outward. Since the structure of the pinion-winding type starter is well known, motor 2 is described in detail below.

[0013] The motor 2 includes a field pole member including a permanent magnet 7, an armature 8 rotatably disposed within the inner periphery of the field pole member, a cylindrical commutator 9 mounted on an armature shaft 8a of the armature 8, and brushes 10 disposed on the outer periphery of the commutator 9. The commutator 9 includes a cylindrical insulating base portion 9a made of, for example, a resin material, and commutator segments 9b held by the insulating base portion 9a to be arranged in a cylindrical shape. The insulating base portion 9a is press-fitted onto the outer periphery of one end of the armature shaft 8a. As shown in Fig. 1, the commutator segments 9b are insulated from each other by the insulating base part 9a, and each armature winding 8c is connected to a riser line 9c arranged at the axial end of the corresponding commutator segment 9b on the armature core 8b side. Hereinafter, the "core side" means the side facing the armature core 8b in the axial direction (the left side in Fig. 1) and the “opposite core side” means the side opposite to the armature core 8b in the axial direction.

[0014] As in Fig. 3, the brushes 10 comprise three positive brushes 10a and negative brushes 10b arranged alternately along the circumference of the commutator 9. The brushes 10 form a brush assembly together with brush springs 11, brush holders 12, and a pair of connecting plates 13 and 14. As shown in Fig. 2, the brush springs 11 are arranged on the opposite commutator side of the brushes 10 and press the brushes 10 against the commutator 9. The axial dimension (spring outer diameter D) of the brush spring 11 is smaller than the axial length L of the brush 10. As shown in Fig. 4, the brush spring 11 accommodated in a specific brush holder 12A explained below (a specific holder of the brush holders 12) is arranged such that the axial center Os thereof is offset to the opposite core side from the axial center Ob of the corresponding brush 10.

[0015] The brush holders 12 are made of an insulating material such as resin and are formed in a box shape. As shown in Fig. As shown in Figure 2, each brush holder 12 includes a brush accommodating chamber 12a located inside in the radial direction perpendicular to the axial center of the commutator 9 and accommodating the brush 10 therein, and a spring accommodating chamber 12b located outside in the radial direction and accommodating the brush spring 11 therein. Each brush holder 12 is formed with an insertion hole to allow the insertion of the brush spring 11 and the brush on its inner circumference. Each brush holder 12 is formed with a wall surface that closes the outer circumference of the spring accommodating chamber 12b and regulates the radial position of the brush spring 11. The brush accommodating chamber 12a and the spring accommodating chamber 12b of the specific brush holder 12A are configured to satisfy the above-described positional relationship between the axial center Ob of the brush and the axial center Os of the brush spring 11.That is, the spring receiving chamber 12b is formed smaller (shorter) in its axial length than the brush receiving chamber 12a, and the axial center of the spring receiving chamber 12b is offset to the opposite core side from the axial center of the brush receiving chamber 12a.

[0016] The connecting plates 13 and 14, which are made of steel in this embodiment, are formed in a ring shape, the diameter in its center hole (inner diameter) being larger than the outer diameter of the commutator 9. The connecting plates 13 and 14 are arranged along the direction perpendicular to the axial center of the commutator 9. As shown in Fig. As shown in Figure 3, the connecting plate 13 is electrically connected to three positive brushes 10a by connecting wires 15, and the connecting plate 14 is electrically connected to the three negative brushes 10b by connecting wires 15. Hereinafter, the connecting plate 13 and the connecting plate 14 may also be referred to as the positive connecting plate 13 and the negative connecting plate 14, respectively. The positive connecting plate 13 and the negative connecting plate 14 are electrically insulated from each other and are arranged side by side (side by side) with the six brush holders 12 therebetween. As shown in Fig. As shown in Figure 5, the positive connection plate 13 is arranged on the core side relative to the brush holders 12 and is electrically connected to an M-terminal screw 18 of the electromagnetic switch 5 through an extension member 16 and a motor lead 17. The negative connection plate 14 is arranged on the opposite core side relative to the brush holders 12 and is fixed and electrically connected to an end frame 20 by screws 19.

[0017] As in Fig. 3, the positive connecting plate 13 is formed with six mounting grooves 13a on its periphery for installing the brush holders 12. The positive connecting plate 13 is further formed with transition parts 22, each connecting two corresponding plate parts of six plate parts 21 arranged circumferentially adjacent to each other opposite the mounting groove 13a. Each mounting groove 13a is open to the radially inner periphery of the positive connecting plate 13 and extends toward the radially outer periphery of the positive connecting plate 13. Of the six plate parts 21, three plate parts 21 are each connected to the lead wires 15 of the positive brushes 10a at their surfaces on the opposite core side, respectively. The transition parts 22 are flush with the plate parts 21 and extend to surround the outer peripheries of the mounting grooves 13a.Each transition part 22 is connected to the outer peripheries of the adjacent plate parts 21 at both circumferential ends thereof.

[0018] The core-side shape of the brush holders 12, which are installed in the positive plate 13, is explained below. As shown in Fig. 3, the brush holder 12 has a convex part 12c formed on its core side, which is mounted in the mounting groove 13a of the positive plate 13. The convex part 12c is inserted from the inner circumference of the positive connecting plate 13 and is mounted (fitted, received) in the mounting groove 13a when the brush holder 12 is mounted on the positive connecting plate 13. As shown in Fig. As shown in Fig. 4, the brush holder 12 has a stepped surface (step surface) 12d formed radially outward of the convex part 12c at both circumferential ends. The stepped surface 12d is stepped in the axial direction and is located on the opposite core side from the core-side end surface of the convex part 12c. The opposite core-side shape of the brush holder 12 may be the same as the core-side shape explained above. That is, the brush holder 12 may have a convex part formed on the opposite core side thereof, which is mounted in a mounting groove formed in the negative connection plate from the inner periphery of the negative connection plate.

[0019] The connection structure between the extension member 16 and the positive connection plate 13 is explained below. One of the three brush holders 12, each holding the negative brushes 10b, is referred to as the specific brush holder 12A (see Fig. 3). The space with a step along the axial direction on the core side formed by the stepped surface 12a of the specific brush holder 12A is referred to as the stepped space (step space). As shown in Fig. 3, the transition part 22 is arranged in the stepped space in the state where the convex part 12c of the specific brush holder 12A is mounted in the mounting groove 13a. That is, in the specific brush holder 12A, the convex part 12c is mounted in the mounting groove 13a in a state where the core-side end surface of the convex part 12c protrudes from the positive connection plate 13 toward the core. The positive connection plate 13 is provided with a fusible part 23 explained below at the transition part 22. The cross-sectional area of ​​the transition part 22 is a minimum at this fusible part 23.

[0020] The extension member 16 is a plate-like member made of a material (e.g., copper) whose resistance is smaller (lower) than that of the positive connection plate 13. The extension member 16 is arranged such that its two main surfaces are perpendicular to the axial center of the commutator 9. The extension member 16 has a connecting part 16a at one end thereof. The connecting part 16a is connected (attached) to the opposite core-side surface of the transition part 22. The other end of the extension member 16 extends to the outside of the motor housing 25 through a bushing 24.That is, the extension member 16 extends from a position circumferentially overlapping with the specific brush holder 12A to the outside of the motor housing 25, and is arranged to axially overlap with the stepped space. As shown in FIG. Fig. 5, the extension member 16 is connected to one end of the motor cable 17, which is fixed to the M-terminal screw 18 of the electromagnetic switch 5. As shown in Fig. 1 and Fig. 2, the bushing 24 as an insulating member made of rubber is mounted on an extension groove 25a formed in the motor housing 25 to hold the outer periphery of the extension member 16 for insulation to a motor housing 25. As shown in Fig. As shown in Figure 3, the bushing 24 is formed with a core-side projection 24a that projects radially inward. The core-side projection 24a essentially covers the entire core side of the transition part 22.

[0021] The part on the other end side of the connecting part 16a of the extension member 16 is referred to as a plate-like extension part 16b. The circumferential width of the connecting part 16a is larger than that of the plate-like extension part 16b. That is, the connecting part 16a is formed such that its end part on the one end side of the extension member 16 extends toward both circumferential ends above the plate-like extension part 16b, and its circumferential width is larger than that of the mounting groove 13a. Therefore, the connecting part 16a is connected to the transition part 22 at a region whose circumferential width is larger than that of the mounting groove 13a. The melting part 23 of the positive connection plate 13 is provided at two different positions on the side where its voltage is smaller (lower, less) than the voltage of the connecting portion between the transition part 22 and the connecting part 16a. In particular, as shown in Fig. 3, the melting part 23 is provided between a portion connecting the plate part 21 and the connecting portion between the transition part 22 and the connecting part 16a.

[0022] The first embodiment described above provides the following advantages. 1) In the motor of the first embodiment, a step is formed between the stepped surface 12d and the core-side end surface of the convex part 12c provided on the core side of the specific brush holder 12A. The extension member 16 is arranged in the space formed in the axial direction by this step (stepped space, step space). That is, since the extension member 16 extends from the position overlapping with the specific brush holder 12A in the circumferential direction to the outside of the motor housing 25, the extension position can be set the same for the 6-brush structure and the 4-brush structure, and accordingly, the motor housing 25 can be made common (the same) for the 6-brush structure and the 4-brush structure. 2) The extension member 16 is a plate-like member and is arranged such that its two major surfaces are perpendicular to the axial center of the commutator 9 and is housed within the stepped space in the axial direction (hereinafter, this may be referred to as the "axial stepped portion"). That is, the extension member 16 is arranged within the axial stepped portion without protruding toward the core side from the convex part 12c. Accordingly, if the extension position for the 6-brush structure is set the same as that for the 4-brush structure, the motor 2 can be made compact in the axial direction because it is not necessary to secure a space for arranging the extension member 16 therein on the core side of the specific brush holder 12A. 3) The brush spring 11 is housed in the specific brush holder 12A such that its axial center Os is offset toward the opposite core side from the axial center Ob of the brush 10. Accordingly, the step formed between the core-side end surface of the convex part 12c and the stepped surface 12d can be made sufficiently large. As a result, since the axial stepped area can be set large and accordingly the degree of freedom for disposing the extension member 16 can be increased, the motor 2 can be made compact in the axial direction. 4) The connecting portion 16a is larger in its circumferential width than the plate-like extension portion 16c and the mounting groove 13a formed in the positive connecting plate 13. Accordingly, the connecting portion 16a can be connected to the transition portion 22 at a region that is sufficiently large in circumferential width. As a result, since the sufficiently large connection area can be ensured without increasing the radial dimensions of the connecting portion 16a and the transition portion 22, the motor 2 can be made compact in the radial direction. 5) Since the brush holders 12 are made of an insulating material, it is not necessary to arrange any insulating component between the extension member 16 and the specific brush holder 12A. Accordingly, the manufacturing cost can be reduced. 6) The extension member 16 is made of a material whose resistance is smaller (lower, lower) than that of the positive connection plate 13. Accordingly, since the heat generated during operation (use, use) can be reduced, the size (size) of the extension member 16 can be made compact. 7) The transition part 22 of the positive connection plate 13 is formed with the fusible part 23 where the cross-sectional area is minimal. Accordingly, when an unexpectedly large current occurs in the motor 2, the motor 2 can be protected because the fusible part 23 is fused. When the fusible part 23 is fused, its temperature is extremely high (high). Accordingly, the distance between the fusible part 23 and the bushing 24 must be extremely large. In the first embodiment, the fusible part 23 is provided between the portion connected to the plate part 21 and the connecting portion between the transition part 22 and the connecting part 16a. That is, since the fusible part 23 is provided radially inward from the radial position of the connecting part 16a, the distance between the fusible part 23 and the bushing 24 can be set large.Accordingly, since a space for reducing the effect of the high temperature that occurs when the melting part 23 is melted can be made small, the motor 2 can be formed in the radial direction. 8) The core-side protrusion 24a provided in the bushing 24 protrudes radially inward to cover substantially the entire core side of the transition part 22. Accordingly, even if a part of the conductive material enters the interior of the motor 2, it is possible to prevent the part from contacting a part whose voltage is higher than that of the fusible part 23. Accordingly, when an unexpectedly large current occurs in the motor 2 due to the part, the motor 2 can be protected because the fusible part 23 is immediately melted.

[0023] Further embodiments of the invention are described below.

[0024] In the embodiments described below, the parts or components that are the same as or equivalent to those described in the first embodiment are indicated or designated by the same reference numerals. Second embodiment

[0025] A second embodiment of the invention is described in relation to Fig. 6. As described in Fig. 6, in the second embodiment, the axial center Os of the brush spring 11 accommodated in the specific brush holder 12A is not offset to the opposite core side from the axial center Ob of the brush 10, and the connecting part 16a is connected to the core-side surface of the transition part 22. Accordingly, since the connecting part 16a does not protrude to the core side from the stepped surface and therefore the connecting part 16a can be arranged within the axial stepped region, the same or similar advantages as those provided by the first embodiment can be obtained. Third embodiment

[0026] A third embodiment of the invention is described below. In the third embodiment, the transition part 22 of the positive connection plate 13 is connected to the connecting part 16a of the extension member 16 such that they are radially opposite to each other. As shown in Fig. 7, in this embodiment, the transition part 22, which is arranged at a position circumferentially overlapping with the specific brush holder 12A, is bent at a substantially right angle to the core side of the plate part 21. As shown in Fig. 8, the extension member 16 is arranged such that the two main surfaces of the plate-like extension part 16b are perpendicular to the center axis of the commutator 9 as in the case of the first embodiment, and that the connecting part 16b is bent to the core side from the plate-like extension part 16b and joined (connected) to the radially outer surface of the transition part 22.

[0027] As in Fig. As shown in Fig. 9, the fusible part 23 is provided at both circumferential ends of the connecting portion (joining portion) between the transition part 22 and the bonding part 16a. The specific brush holder 12A has an inner protrusion 12f protruding toward the core side from the outer circumferential end of the convex part 12c. The inner protrusion 12f is formed to overlap with the transition part 22 in the axial direction, the stress of which is higher than that of the fusible part 23. Preferably, the axial height of the inner protrusion 12f is slightly larger than the axial height of the transition part 22 from the plate part 21. In this configuration, since the axial length of the bonding part 16a can be made sufficiently large, the joining area with the transition part 22 can be made sufficiently large to increase the reliability of the bonding portion.

[0028] As in Fig. 8, the connection part 16a to the core side (to the left side in Fig. 8) is bent on the outside of the rising line 9c connected to the armature winding 8c. Accordingly, since the connecting part 16a can be prevented from interfering with the rising line 9c, the space available radially outside the rising line 9c can be effectively utilized for arranging the connecting part 16a. Furthermore, the inner protrusion 12f provided on one of the specific brush holders 12A is arranged to axially overlap with the transition part 22 whose voltage is higher than that of the fusible part 23. Accordingly, even if a part of a conductive material enters the interior of the motor 2, the inner protrusion 12f, in conjunction with the core-side protrusion 24a provided in the bushing 24, can prevent the part from contacting a part whose voltage is higher than that of the fusible part 23.Accordingly, when an unexpectedly large current occurs in the motor 2, the motor 2 can be protected because the melting part 23 immediately melts (is melted, is melted). Fourth embodiment

[0029] A fourth embodiment of the invention will be described below. In the fourth embodiment, the transition part 22 of the positive connection plate 23 is connected to the connecting part 16a of the extension member 16 such that they are radially opposite to each other, as in the case of the third embodiment. The fourth embodiment differs from the third embodiment with respect to the direction of the extension member 16. As shown in Fig. 10 and Fig. 12, in the fourth embodiment, the extension member 16 is arranged such that both main surfaces of the plate-like extension part 16b are perpendicular to the circumference of the commutator 9 and the connecting part 16a is bent at a substantially right angle in the circumferential direction from the plate-like extension part 16b and is connected to the radially outer surface of the transition part 22. As shown in Fig. 11 and Fig. As shown in FIG. 12, the positive connection plate 23 may be provided with two connection parts 23 formed in the transition part 22, and may be provided with an extension plate part 26 axially overlapping the stepped surface by extending a part between the two connection parts 23 to the opposite core side. According to this configuration, since the axial width of the combination of the transition part 22 and the axial width of the extension plate part 23 can be made equal to each other, the joining area can be made sufficiently large to increase the reliability of the joining portion. Fifth embodiment

[0030] A fifth embodiment of the invention is described below. Fig. 5, the transition part 22 is provided separately from the positive connecting plate 13 for the specific brush holder 12A. As shown in Fig. 13, in this embodiment, only the transition part 22, which is arranged at a position overlapping with the specific brush holder 12A in the circumferential direction, is provided separately from the positive connection plate 13 and is connected to the plate part 21. As shown in Fig. 14, this separate transition part 22 includes a main body part 22a formed with two connecting parts 23, and a pair of leg parts 22b formed in both circumferential ends of the main body part 22a. The leg parts 22b are connected to the core-side surface of the plate part 21. The main body part 22a is bent substantially at a right angle to the core side from the leg parts 22b. The plate-like extension part 26 described in the fourth embodiment may be provided integrally with the main body part 22a.

[0031] The extension member 16 is arranged such that both main surfaces of the plate-like extension part 16b are perpendicular to the circumference of the commutator 9, and the connecting part 16a is bent substantially at a right angle in the circumferential direction from the plate-like extension part 16b and connected to the main body part 22a of the transition part 22 and the plate-like extension part 26. According to this configuration, the joining area between the transition part 22 and the connecting part 16a can be made sufficiently large to increase the reliability of the joining portion. The extension member 16 can be arranged such that both main surfaces of the plate-like extension part 16b are perpendicular to the central axis of the commutator 9, and the connecting part 16a is bent substantially at a right angle to the core side of the plate-like extension part 16b. Modifications

[0032] In the first embodiment, the brush spring 11 is housed in the specific brush holder 12A such that its axial center Os is offset to the opposite core side from the axial center Ob of the brush 10. However, the axial center Os of the brush spring 11 and the axial center Ob of the brush 10 may coincide with each other. In the first embodiment, the convex part 12c is inserted from the inner periphery of the positive connection plate 13 and is mounted in the mounting groove 13a when the brush holder 12 is installed in the positive connection plate 13. However, the convex part 12c may be inserted along the axial direction and may be press-fitted into the mounting groove 13a.

[0033] The preferred embodiments explained above are exemplary of the present invention, the scope of which is defined by the following claims.

[0034] A positive connection plate of a direct current (DC) motor has a mounting groove for installing a specific brush holder therein. The specific brush holder has a convex part mounted in the mounting groove and a stepped surface having a step on a radially outer side of the convex part and located on the opposite core side of an armature from a core-side end surface of the convex part. A space existing in an axial stepped portion located on the core side of the stepped surface and in which the step is formed is a stepped space. An extension member extends from a position overlapping with the specific brush holder in the circumferential direction to the outside of a motor housing and is arranged to overlap with the stepped space in the axial direction.

Claims

[1] DC motor (2) comprising: a cylindrical commutator (9) mounted on a shaft (8a) of an armature (8); Brushes (10, 10a, 10b) arranged on an outer circumference of the commutator (9); Brush springs (11) arranged on an opposite commutator side of the brushes (10, 10a, 10b) for pressing the brushes (10, 10a, 10b) towards the commutator (9); Brush holders (12) which hold the brushes (10, 10a, 10b) on an inner side in a radial direction perpendicular to a central axis of the commutator (9) and hold the brush springs (11) on the opposite commutator side of the brushes (10, 10a, 10b); a positive connection plate (13) made of a conductive material and arranged on a core side of the commutator (9) of the brush holders (11) in an axial direction of the commutator (9), the positive connection plate (13) being electrically connected to positive brushes (10a) of the brushes (10, 10a, 10b) by connecting wires (15); a negative connection plate (14) made of a conductive material and arranged on an opposite core side of the armature (8) from the brush holders (12) in the axial direction, the negative connection plate (14) being electrically connected to negative brushes (10b) of the brushes (10, 10a, 10b) by connecting wires (15); and an extension member (16) electrically connected to the positive connection plate (13) at a first end portion thereof as a connection portion (16a), wherein a second end portion of the extension member (16) extends to an outside of a motor housing (25) of the DC motor (2), wherein one of the brush holders (12) holding the negative brushes (10b) is a specific brush holder (12A), the positive connecting plate (13) has a mounting groove (13a) to allow the specific brush holder (12A) to be installed therein, the specific brush holder (12A) has a convex part (12c) mounted in the mounting groove (130) and a stepped surface (12d) having a step on a radially outer side of the convex part (12c) and arranged on the opposite core side from a core-side end surface of the convex part (12c), a space present in an axial stepped portion located on the core side of the stepped surface (12d) and in which the step is formed is a stepped space, and the extension member (16) extends from a position circumferentially overlapping with the specific brush holder (12A) to the outside of the motor housing (25) and is arranged to overlap with the stepped space in the axial direction. [2] DC motor (2) according to claim 1, wherein an axial length (D) of the brush springs (11) is smaller than an axial length (L) of the brushes (10, 10a, 10b), and the specific brush holder (12A) is formed such that the step is arranged at a position between the core-side end surface of the convex part (12c) and the stepped surface (12d) depending on an axial distance between a core-side axial end of the brush (10, 10a, 10b) and a core-side axial end of the brush spring (11). [3] The DC motor (2) according to claim 2, wherein the specific brush holder (12A) is formed such that an axial center of a spring accommodating chamber (12b) accommodating the brush spring (11) is offset to the opposite core side from an axial center of a brush accommodating chamber (12a) accommodating the brush (10, 10a, 10b). [4] A DC motor (2) according to claim 1, wherein the specific brush holder (12A) is made of an insulating material. [5] DC motor (2) according to claim 1, wherein a resistance of the material of the extension member (16) is smaller than a resistance of the material of the positive connection plate (13). [6] DC motor (2) according to claim 1, wherein the positive connection plate (13) comprises plate parts (21) arranged to be located at both circumferential ends of each of the mounting grooves (13a), and transition parts (22) each connecting two circumferentially adjacent plate parts of the plate parts (21) to each other, one of the transition parts (22) is arranged in the stepped space, the connecting part (16a) is joined to the transition part (22), a circumferential width of the connecting part (16a) is greater than a circumferential width of the mounting groove (13a). [7] DC motor (2) according to claim 1, wherein the commutator (9) has commutator segments (9b) which are arranged in a cylindrical shape and are insulated from one another, core-side ends of the commutator segments (9b) being connected to armature windings (8c), and the positive connecting plate (13) comprises plate parts (21) arranged to be located at both circumferential ends of each of the mounting grooves (13a), and transition parts (22) each connecting two circumferentially adjacent plate parts of the plate parts (21) to each other, wherein the transition part (22) is arranged at a position circumferentially overlapping with the specific brush holder (12A) which is bent to the core side from the plate part (21) at a circumferentially outer position of a core-side end of the commutator segment (9b), the extension component (16) is joined to a radially outer surface of the transition part (22). [8] DC motor (2) according to claim 1, wherein the commutator (9) has commutator segments (9b) which are arranged in a cylindrical shape and are insulated from one another, core-side ends of the commutator segments (9b) being connected to armature windings (8c), and the positive connecting plate (13) has plate parts (21) arranged to be located at both circumferential ends of each of the mounting grooves (13a), and transition parts (22) each connecting two circumferentially adjacent plate parts of the plate parts (21) to each other, the transition part (22) which is arranged at a position overlapping with the specific brush holder (12A) in the circumferential direction, is provided separately from the positive connection plate (13) and is bent toward the core side from the plate part (21) at a circumferentially outer position of a core-side end of the commutator segment (9b), the extension component (16) is joined to a radially outer surface of the transition part (22). [9] DC motor (2) according to claim 7, wherein the extension component (16) is formed from a plate-like component, the second end part of the extension member (16) is a plate-like extension member (16b), the plate-like extension member (16b) is arranged such that both main surfaces thereof are perpendicular to the axial center of the commutator (9), and the connecting part (16a) is bent towards the core side of the plate-like extension component (16b). [10] DC motor (2) according to claim 7, wherein the extension component (16) is formed from a plate-like component, the second end part of the extension member (16) is a plate-like extension member (16b), the plate-like extension member (16b) is arranged such that both main surfaces thereof are perpendicular to a circumferential direction of the commutator (9), and the connecting part (16a) is bent in the circumferential direction of the plate-like extension member (16b). [11] The DC motor (2) according to claim 6, wherein the positive connection plate (13) is formed with a fusible part (23) between a connecting portion at which the connecting portion (16a) is connected to the transition part (22) and a portion at which the transition part (22) is connected to the plate part (21), a cross-sectional area of ​​the positive connection plate (13) at the fusible part (23) being a minimum. [12] The DC motor (2) according to claim 7, wherein the positive connection plate (13) is formed with a fusible part (23) between a connecting portion at which the connecting portion (16a) is connected to the transition part (22) and a portion at which the transition part (22) is bent to the core side from the plate part (21), a cross-sectional area of ​​the positive connection plate (13) at the fusible part being a minimum (23). [13] A DC motor (2) according to claim 7, wherein the transition part (22) has an extension plate part (26) extending to the opposite core side and axially overlapping with the stepped space. [14] The DC motor (2) according to claim 11, further comprising an insulating member (24) for insulating between the extension member (16) and the motor housing (25), the insulating member (24) being mounted on the motor housing (25) to hold a periphery of the extension member (16), the insulating member (24) having a core-side projection (24a) projecting radially inwardly of the motor housing (25) from a joining portion where the transition part (22) is joined to the joining part (16a) and radially overlapping with a portion whose voltage is higher than that of the fusible part (23). [15] The DC motor (2) according to claim 11, wherein the specific brush holder (12A) has an inner projection (12f) projecting toward the core side from an outer peripheral end of the convex part (12c) and axially overlapping with a portion whose voltage is higher than that of the fusible part (23). [16] DC motor (2) according to claim 1, wherein a field pole component of the DC motor (2) comprises permanent magnets (7).

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