Electric motor

Abstract

This electric motor is provided with: a rotor having a rotating shaft extending in the axial direction; a commutator attached to the rotating shaft; a brush in contact with the commutator; a brush spring for pressing the brush against the commutator; and a holder for holding the brush spring. The brush spring is a constant load spring having a spiral part around which a belt-shaped wire material is wound. The constant load spring applies a pressing force to the brush through the spiral part in contact with the rear end surface of the brush. The holder has a first support part that supports the spiral part when the spiral part moves toward the rotating shaft due to wear of the brush, and the spring load from the brush spring becomes zero when the spiral part abuts on the first support part.

Description

electric motor

[0001] The present disclosure relates to electric motors.

[0002] Electric motors are also widely used in the field of electrical equipment mounted on vehicles such as automobiles. For example, electric motors are used in two-wheeled and four-wheeled vehicles to drive cooling fans that cool the radiator and battery.

[0003] Known electric motors include brushed motors (commutator motors) that use brushes and brushless motors that do not use brushes. Of these, brushed motors include a stator, a rotor that rotates due to the magnetic force of the stator, a commutator attached to the rotating shaft of the rotor, and brushes that contact the commutator.

[0004] In brushed motors, brush springs are used to press the brushes against the commutator. The brush springs apply a pressing force to the brushes by utilizing their spring elasticity. Conventionally, coil springs or torsion springs have been used as brush springs in brushed motors.

[0005] However, when a coil spring or torsion spring is used as the brush spring, the spring load applied to the brush by the brush spring is not constant but gradually decreases as the brush wears, as shown by the dashed line in Figure 20. Figure 20 is a diagram that schematically illustrates the change in brush spring load with respect to brush wear when a coil spring, a torsion spring, and a constant-load spring are used as the brush spring. This results in a large difference between the pressure (initial pressure) before the brush wears and the pressure (final pressure) when the motor reaches the end of its life due to brush wear. Therefore, when using a coil spring or torsion spring, it is considered to set the initial pressure high to ensure a certain level of final pressure. However, this increases friction between the brush and commutator during rotor rotation in the initial stage, resulting in increased brush sliding loss.

[0006] In brushed motors, brush wear determines the motor's lifespan. Specifically, the lifespan of the brushes due to wear determines the motor's lifespan. Brush wear can be broadly divided into two causes: electrical wear caused by sparks (commutation sparks), and mechanical wear caused by the sliding of the brushes against the commutator. The brushes are pressed against the commutator by the pressing force of the brush spring. However, if the pressing force is too high, mechanical wear increases. If the pressing force is too low, the brushes will bounce, inducing sparks and increasing electrical wear.

[0007] Therefore, a conventional technique has been proposed in which a constant force spring, whose spring load does not change with brush wear (stroke), is used as the brush spring. The use of a constant force spring can suppress excessive mechanical and electrical wear. For example, Patent Document 1 discloses an electric motor that uses a spiral spring having a spiral portion formed by winding a strip-shaped wire as a constant force spring, and that can apply a constant spring load to the brush by bringing the spiral portion of the spiral spring into contact with the rear end surface of the brush.

[0008] A constant force spring can apply a constant spring load to the brush, which is effective in suppressing brush wear. However, as shown by the solid line in Figure 20, even with a constant force spring, there is a period during which the load is not constant and the brush cannot be kept constant. In other words, even with a constant force spring, there is a period during which the spring load changes as the brush wears. Specifically, as shown in Figure 20, the spring load applied by the constant force spring is not constant between the initial stage when the brush begins to wear and the final stage when the brush is nearing the end of its life, but gradually decreases as the brush wears.

[0009] Therefore, even if a constant force spring is used as the brush spring, the wear of the brush becomes unstable and the quality of the motor may deteriorate.

[0010] In particular, if the spring load is not constant at the end of the brush's life (the end of the brush's life), not only will electrical wear due to sparks increase at an accelerated rate, but the pressure applied by the constant force spring to the brush will become insufficient or unstable. This will cause uneven contact resistance between the brush and the constant force spring, degrading the motor's performance and causing the motor to behave erratically. This will ultimately result in a deterioration in the quality of the motor.

[0011] Japanese Unexamined Patent Publication No. 118987 / 1987

[0012] The present disclosure has been made to solve such problems, and an object of the present disclosure is to provide an electric motor that can improve the quality of the electric motor at the end of the brush life.

[0013] In order to achieve the above object, one aspect of the electric motor disclosed herein comprises a rotor having a rotating shaft extending in the axial direction, a commutator attached to the rotating shaft, a brush in contact with the commutator, a brush spring for pressing the brush against the commutator, and a holder for holding the brush spring, wherein the brush spring is a constant force spring having a spiral portion around which a strip-shaped wire is wound, and the constant force spring applies a pressing force to the brush by the spiral portion in contact with the rear end surface of the brush, and the holder has a first support portion that supports the spiral portion when the spiral portion moves toward the rotating shaft due to wear of the brush, and the spring load of the brush spring becomes zero when the spiral portion abuts against the first support portion.

[0014] According to the present disclosure, the quality of the electric motor at the end of the brush life can be improved.

[0015] FIG. 1 is an external perspective view of an electric motor according to an embodiment, as viewed from above. FIG. 2 is an external perspective view of an electric motor according to an embodiment, as viewed from below. FIG. 3 is a cross-sectional view of the electric motor according to an embodiment. FIG. 4 is a perspective view showing a brush holder and various components arranged in the brush holder in the electric motor according to an embodiment. FIG. 5 is an exploded perspective view of the brush holder and various components shown in FIG. 4 in the electric motor according to an embodiment. FIG. 6 is a plan view showing a brush and a brush spring arranged in a brush holder in the electric motor according to an embodiment. FIG. 7 is a plan view showing how a spiral portion of a brush spring moves due to wear of the brush in the electric motor according to an embodiment. FIG. 8A is a perspective view showing a configuration of a brush spring before being assembled to a brush holder in the electric motor according to an embodiment. FIG. 8B is a side view showing a configuration of a brush spring before being assembled to a brush holder in the electric motor according to an embodiment. FIG. 9 is a view showing how the brush spring is assembled to the brush holder in the electric motor according to an embodiment. FIG. 10 is a diagram schematically showing changes in the spring load of the brush spring relative to the amount of brush wear in the electric motor according to the embodiment. FIG. 11 is a plan view showing the configuration of a brush holder in an electric motor according to Modification 1. FIG. 12 is a plan view showing the configuration of a brush holder in an electric motor according to Modification 2. FIG. 13 is a plan view showing the configuration of a brush holder in an electric motor according to Modification 3. FIG. 14 is a diagram showing a first modified example of a brush spring that is a constant force spring. FIG. 15 is a diagram showing a second modified example of a brush spring that is a constant force spring. FIG. 16 is a plan view showing the configuration of a brush holder in an electric motor according to Modification 4 when the brush springs shown in FIGS. 14 and 15 are used. FIG. 17 is a plan view showing the configuration of a brush holder in an electric motor according to Modification 5. FIG. 18A is a diagram showing the configuration of another brush spring before being assembled to the brush holder in an electric motor according to Modification 6. FIG. 18B is a side view showing the configuration of another brush spring before being assembled to the brush holder in an electric motor according to Modification 6. FIG. 19 is a diagram showing a state in which the other brush spring shown in FIGS. 18A and 18B is assembled to a brush holder in an electric motor according to the sixth modification.FIG. 20 is a diagram showing a change in the spring load of the brush spring with respect to the amount of brush wear when a coil spring, a torsion spring, and a constant force spring are used as the brush spring.

[0016] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Each of the embodiments described below represents a specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, arrangement positions and connection forms of the components, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Therefore, among the components in the following embodiments, components that are not described in the independent claims that represent the highest concept of the present disclosure will be described as optional components.

[0017] Each figure is a schematic diagram and is not necessarily a precise illustration. In each figure, the same reference numerals are used to designate components that are substantially the same as those in other figures, and redundant explanations will be omitted or simplified.

[0018] In this embodiment, the radial direction of the stator 10 and the rotor 20 is referred to as the "radial direction," and the rotation direction of the rotor 20 is referred to as the "circumferential direction." In other words, the direction spreading from the axis C of the rotating shaft 21 as the center is the "radial direction," and the direction going around the axis C of the rotating shaft 21 as the center is the "circumferential direction." Therefore, the "radial direction" is a direction perpendicular to the direction in which the axis C of the rotating shaft 21 extends (also simply referred to as the "axial direction"). In this specification, the terms "up" and "down" do not necessarily refer to the up direction (vertically upward) and the down direction (vertically downward) in absolute spatial recognition.

[0019] (Embodiment) The overall configuration of an electric motor 1 according to an embodiment will be described with reference to FIGS. 1 to 7. FIG. 1 is an external perspective view of the electric motor 1 according to the embodiment, as viewed from above. FIG. 2 is an external perspective view of the electric motor 1 according to the embodiment, as viewed from below. FIG. 3 is a cross-sectional view of the electric motor 1 according to the embodiment. FIG. 4 is an external perspective view showing a brush holder 60 and various components arranged on the brush holder 60 in the electric motor 1 according to the embodiment. FIG. 5 is an exploded perspective view of the brush holder 60 and various components shown in FIG. 4 in the electric motor 1 according to the embodiment. FIG. 6 is a plan view showing the brush 40 and the brush spring 50 arranged on the brush holder 60 in the electric motor 1 according to the embodiment. FIG. 7 is a diagram showing how the spiral portion 51 of the brush spring 50 moves due to wear of the brush 40 in the electric motor 1 according to the embodiment. The brush 40 is omitted from FIG. 7.

[0020] As shown in Fig. 3, the electric motor 1 includes a stator 10 and a rotor 20 that rotates due to the magnetic force of the stator 10. The electric motor 1 is a brushed electric motor. The electric motor 1 further includes a commutator 30 attached to a rotating shaft 21 of the rotor 20, at least one brush 40 in contact with the commutator 30, a brush spring 50 for pressing the brush 40 against the commutator 30, a brush holder 60 for holding the brush 40, and a cover plate 70 for covering the brush 40. As shown in Figs. 3, 4, and 5, the electric motor 1 further includes a power supply terminal 80 electrically connected to the brush 40, a first bearing 91, a second bearing 92, a first bracket 101, and a second bracket 102.

[0021] The electric motor 1 is a type of direct current motor (DC motor) driven by direct current. The stator 10 of the electric motor 1 is a magnet. The rotor 20 is an armature having a coil 22. The electric motor 1 is a flat-type brushed coreless motor (flat motor) mounted on a vehicle, such as a two-wheeled or four-wheeled vehicle. Therefore, the stator 10 and the rotor 20 do not have cores, and the electric motor 1 is thin and lightweight overall. Specifically, the electric motor 1 is a small motor used in a cooling fan for a vehicle radiator. The outer diameter (diameter) φ of the electric motor 1 is 120 mm or less. For example, the outer diameter φ of the electric motor 1 is 60 mm, 70 mm, or 90 mm. The electric motor 1 is driven by power supplied from an external power source, such as a battery. For example, the electric motor 1 is driven by an input voltage of DC 12 V supplied via a power supply line connected to the external power source.

[0022] Each component of the electric motor 1 will now be described in detail.

[0023] As shown in FIG. 3 , the stator 10 is disposed between the rotor 20 and the stator 10 via a small air gap. The stator 10 generates a magnetic force acting on the rotor 20. The stator 10 is configured to generate magnetic flux on the air gap surface facing the rotor 20 across the air gap. The stator 10, together with the stator 10, which is an armature, forms a magnetic circuit. Specifically, the stator 10 is annular as a whole. The stator 10 is configured so that north and south poles are alternately and evenly distributed on the air gap surface facing the rotor 20 across the air gap along the circumferential direction of the rotating shaft 21. The stator 10 is a field magnet that creates magnetic flux for generating torque. The stator 10 is composed of multiple magnets 11. The magnets 11 constituting the stator 10 are, for example, permanent magnets.

[0024] The multiple magnets 11 that make up the stator 10 are arranged so that north and south poles alternate evenly around the circumferential direction. The direction of the main magnetic flux generated by the stator 10 (magnets) is the direction of the axis C of the rotating shaft 21. The direction of the main magnetic flux is generated in a direction corresponding to the magnetic poles of the magnets 11. The stator 10 (magnets 11) is fixed to a first bracket 101.

[0025] The rotor 20 has a rotating shaft 21 and a coil 22. The rotor 20 is a coreless rotor that does not have a core.

[0026] The rotor 20 rotates around the axis C of the rotating shaft 21 as the center of rotation. The rotor 20 generates a magnetic force that acts on the stator 10. The direction of the main magnetic flux generated by the rotor 20 is the direction of the axis C of the rotating shaft 21. The direction of the main magnetic flux generated by the rotor 20 is generated in a direction corresponding to the direction of the current flowing through the coil 22.

[0027] The rotor 20 is disposed opposite the stator 10. The rotor 20 faces the stator 10 in the direction of the axis C of the rotating shaft 21. Specifically, the coil 22 of the rotor 20 and the stator 10 face each other in the direction of the axis C of the rotating shaft 21. In other words, the coil 22 and the stator 10 are aligned in the direction of the axis C of the rotating shaft 21.

[0028] The rotating shaft 21 is a shaft including an axis C. The rotating shaft 21 is a long, rod-shaped member. As an example, the rotating shaft 21 is a metal rod made of a metal material such as SUS (Stainless Used Steel). The axis C of the rotating shaft 21 serves as the center of rotation when the rotor 20 rotates. The longitudinal direction of the rotating shaft 21, i.e., the direction in which the rotating shaft 21 extends (extension direction), is the direction of the axis C.

[0029] The rotating shaft 21 is supported by a first bearing 91 and a second bearing 92. Specifically, a first end 21a, which is one end of the rotating shaft 21, is supported by the first bearing 91. On the other hand, a second end 21b, which is the other end of the rotating shaft 21, is supported by the second bearing 92. As an example, the first bearing 91 and the second bearing 92 are bearings such as ball bearings.

[0030] The first end 21a of the rotating shaft 21 is the end on the output side (output shaft). The first end 21a of the rotating shaft 21 protrudes from the first bracket 101 and the first bearing 91. A load such as a rotary fan is attached to the first end 21a. The electric motor 1 with a rotary fan attached to the rotating shaft 21 can be used as, for example, a cooling fan or an electric blower. The second end 21b of the rotating shaft 21 is the end on the counter-output side (counter-output shaft). The second end 21b of the rotating shaft 21 does not protrude from the second bracket 102 or the second bearing 92.

[0031] The first bearing 91 is held by the first bracket 101. Specifically, the first bearing 91 is fixed to a recess provided in the first bracket 101. The second bearing 92 is held by the second bracket 102. Specifically, the second bearing 92 is fixed to a recess provided in the second bracket 102.

[0032] The first bracket 101 and the second bracket 102 are made of, for example, a metal material. For example, the first bracket 101 and the second bracket 102 are made of an iron-based material such as cold-rolled steel plate (SPC (Steel Plate Cold) material) or a metal such as aluminum. The first bracket 101 and the second bracket 102 form a housing. The stator 10 and the rotor 20 are arranged in this housing.

[0033] As shown in Figures 1 and 2, the first bracket 101 is an outer shell member of the electric motor 1. The first bracket 101 is formed in a cylindrical shape with a bottom and a cylindrical side wall. The magnets 11 that constitute the stator 10 are fixed to the bottom of the first bracket 101. The coils 22 of the rotor 20 are surrounded by the side wall of the first bracket 101.

[0034] The second bracket 102 is arranged to cover the brush holder 60. Specifically, the second bracket 102 is arranged to cover the opening of the brush holder 60. The second bracket 102 has a flat plate shape. In other words, the second bracket 102 is a flat plate-shaped cover that is arranged to cover the opening of the brush holder 60. The second bracket 102 is arranged between the first bracket 101 and the brush holder 60. Specifically, the second bracket 102 is sandwiched between the first bracket 101 and the brush holder 60.

[0035] The material of the first bracket 101 and the second bracket 102 is not limited to a metal material. The material of the first bracket 101 and the second bracket 102 may be a resin material. From the viewpoint of suppressing noise generated from the electric motor 1, it is preferable that the first bracket 101 and the second bracket 102 are made of a metal material. Specifically, the first bracket 101 and the second bracket 102 are made of a metal plate. The first bracket 101 is formed into a predetermined three-dimensional shape by performing a predetermined press process or the like on the metal plate. The second bracket 102 is a flat, planar metal plate.

[0036] The coils 22 of the rotor 20 shown in Fig. 3 are wound coils. The rotor 20 has a plurality of coils 22. Each of the plurality of coils 22 is an armature winding made of electric wire. Each of the plurality of coils 22 is wound so as to generate a magnetic force acting on the stator 10 when a current flows through it. The direction of the main magnetic flux generated by each of the plurality of coils 22 is the direction of the axis C of the rotating shaft 21. Specifically, each of the plurality of coils 22 is wound in a flat shape. The coil surface of each of the plurality of coils 22 is arranged in a position facing the direction of the axis C of the rotating shaft 21.

[0037] Each of the multiple coils 22 is configured from an insulating-coated wire having a core wire made of a metal such as copper or aluminum and an insulating film coating the core wire. Each of the multiple coils 22 is a thin wound coil having a coil layer in which the insulating-coated wire is wound in a planar shape. Specifically, each of the multiple coils 22 is configured, for example, from one layer or multiple coil layers in which the insulating-coated wire is wound in a substantially fan-like shape in a planar view. The multiple coils 22 configured in this manner are arranged to surround the rotating shaft 21 when viewed from the direction of the axis C of the rotating shaft 21.

[0038] Each of the plurality of coils 22 is electrically connected to the commutator 30. Specifically, each of the plurality of coils 22 is electrically connected to one of the plurality of commutator segments 31 of the commutator 30. Therefore, a current flows through each of the plurality of coils 22 via the commutator segment 31 with which the brush 40 is in contact.

[0039] The multiple coils 22 are covered with molded resin 23. That is, the multiple coils 22 are resin-molded. Therefore, the multiple coils 22 are molded integrally with the molded resin 23 by being covered with the molded resin 23. The planar external shape of the molded resin 23 after molding the multiple coils 22 is circular. The molded resin 23 may be made of an insulating resin material such as phenolic resin or unsaturated polyester resin (BMC (Bulk Molding Compound)). The molded resin 23 may be made of either a thermosetting resin or a thermoplastic resin.

[0040] In this way, the electric motor 1 is a coreless motor in which the rotor 20 does not have a core. In the electric motor 1, the rotor 20 has a plurality of thin coils 22 molded from resin. This makes it possible to realize a flat, thin electric motor 1 with low inductance.

[0041] 3 , the commutator 30 is attached to the rotating shaft 21. Therefore, the commutator 30 rotates together with the rotating shaft 21 as the rotor 20 rotates. The commutator 30 is attached to the second end 21b of the rotating shaft 21. The commutator 30 attached to the rotating shaft 21 may be a part of the rotor 20.

[0042] The commutator 30 has a plurality of commutator bars 31 (commutator segments) arranged along the rotation direction of the rotating shaft 21. Specifically, the plurality of commutator bars 31 are arranged in an annular shape along the rotation direction of the rotating shaft 21 so as to surround the rotating shaft 21. Each commutator bar 31 is shaped as an elongated member extending in the longitudinal direction of the rotating shaft 21.

[0043] Each of the plurality of commutator segments 31 is a conductive terminal made of a metal material such as copper. Each of the plurality of commutator segments 31 is electrically connected to a coil 22 of the rotor 20. The plurality of commutator segments 31 are arranged insulated and separated from one another. However, the plurality of commutator segments 31 are electrically connected by the coil 22 of the rotor 20.

[0044] As an example, the commutator 30 is a molded commutator. The commutator 30 has a configuration in which a plurality of commutator segments 31 are molded in the molded resin 23. In this case, the plurality of commutator segments 31 are embedded in the molded resin 23 so that their surfaces are exposed. The molded resin 23 is the commutator body. The molded resin 23 is a substantially cylindrical member having a through hole into which the rotating shaft 21 is inserted. The molded resin 23 is a resin molded body made of an insulating resin material such as a thermosetting resin.

[0045] 3, at least one brush 40 is in contact with the commutator 30. Specifically, the front end of the brush 40 is in contact with the commutator segments 31 of the commutator 30. As the commutator 30 rotates with the rotation of the rotary shaft 21, the brush 40 continues to come into contact with all of the commutator segments 31 in sequence.

[0046] As shown in FIGS. 3 and 5, the brush 40 includes a front end surface 40a that contacts the commutator 30 and a rear end surface 40b that is the surface opposite to the front end surface 40a.

[0047] The front end surface 40a of the brush 40 is an end surface of the front end portion, which is one longitudinal end of the brush 40. The front end surface 40a is a tip surface of the brush 40 on the rotating shaft 21 side (radially inner side). The front end surface 40a is a contact surface that comes into contact with the commutator segments 31 of the commutator 30.

[0048] The rear end surface 40b of the brush 40 is the end surface of the rear end, which is the other longitudinal end of the brush 40. The rear end surface 40b is the tip surface of the brush 40 on the opposite side (radially outward) from the rotary shaft 21 side. The rear end surface 40b is a contact surface that comes into contact with the brush spring 50. Specifically, the spiral portion 51 of the brush spring 50 comes into contact with the rear end surface 40b.

[0049] The brushes 40 are power supply brushes for supplying power to the coils 22. Specifically, the brushes 40 contact the commutator segments 31 of the commutator 30 to supply power to the coils 22. When the brushes 40 contact the commutator segments 31, the armature current supplied to the brushes 40 from the power supply terminals 80 flows through the commutator segments 31 to the coils 22.

[0050] As an example, the brush 40 is a conductive carbon brush made of carbon. The brush 40 is a long, substantially rectangular parallelepiped. In this case, the brush 40 is preferably a carbon brush containing a metal such as copper. This reduces the contact resistance between the brush 40 and the commutator segments 31. The brush 40 can be produced, for example, by crushing a mixture of graphite powder, copper powder, a binder resin, and a hardener, compression-molding the mixture into a rectangular parallelepiped, and then firing the mixture.

[0051] In this embodiment, a plurality of brushes 40 are provided. Specifically, as shown in FIGS. 3 to 5, two brushes 40 are provided in the electric motor 1. The two brushes 40 are arranged opposite each other with the commutator 30 therebetween. In other words, the two brushes 40 are arranged at 180° intervals along the rotation direction of the rotor 20. Therefore, the two brushes 40 are arranged so as to be positioned on a single straight line. The angle formed by the longitudinal directions of the two brushes 40 is 180°. Therefore, the commutator 30 is pressed in a uniaxial direction by the two brushes 40 arranged in a straight line. However, the number of brushes 40 is not limited to two.

[0052] The brushes 40 are subjected to a pressing force from the brush springs 50 and are constantly in contact with the commutator segments 31 of the commutator 30. In other words, the brushes 40 are pressed against the commutator 30 by the brush springs 50. In this way, the brushes 40 are in sliding contact with the commutator 30 due to the pressing force from the brush springs 50, and are arranged so as to be movable in a direction (radial direction) intersecting the direction of the axis C of the rotating shaft 21 due to wear with the commutator 30.

[0053] 5 and 6, the two brushes 40 are arranged in a brush holder 60. Specifically, each of the two brushes 40 is arranged in the brush holder 60 so that its longitudinal direction is perpendicular to the axis C of the rotating shaft 21 (i.e., the radial direction of the rotation of the rotating shaft 21).

[0054] The number of brush springs 50 provided corresponds to the number of brushes 40. In this embodiment, the electric motor 1 is provided with two brushes 40, and therefore, two brush springs 50 are also provided. The brushes 40 and the brush springs 50 are housed in a brush holder 60 and covered with a cover plate 70.

[0055] The brush spring 50 applies a pressing force (spring pressure) to the brush 40 by means of its spring elastic force (spring restoring force), urging the brush 40 toward the commutator 30. The brush spring 50 is a constant force spring. Therefore, the brush spring 50 applies a uniform load to the brush 40. In other words, the brush spring 50, which is a constant force spring, applies a uniform pressing force to the brush 40.

[0056] The brush spring 50 is made of a strip-shaped wire material. The brush spring 50 is a spiral spring. As shown in Figures 5 and 6, the brush spring 50 has a spiral portion 51 (coil portion) in which the strip-shaped wire material is wound in a spiral shape. The brush spring 50 is made of a single strip-shaped wire material made of a metal material such as a steel plate.

[0057] Specifically, brush spring 50 is made of a long, strip-shaped metal plate. Therefore, spiral portion 51 is a portion of brush spring 50 in which the long, strip-shaped metal plate is wound in a spiral shape multiple times in only one direction. When one end of the wire is stretched from spiral portion 51, brush spring 50 generates a force (spring restoring force) that tries to return to its original spiral shape.

[0058] 3 and 5 , the brush spring 50 applies a pressing force (load) to the brush 40 by the spiral portion 51 that contacts the rear end surface 40b of the brush 40. In other words, the brush spring 50 presses the brush 40 against the commutator 30 by the spiral portion 51. Specifically, the brush spring 50 applies a pressing force to the brush 40 by the spring restoring force of the spiral portion 51, as the spiral portion 51, to which a spring restoring force is applied, contacts the rear end surface 40b of the brush 40. As a result, the brush 40 is urged toward the commutator 30.

[0059] Electric power is supplied to the brushes 40 from an external power supply located outside the electric motor 1 via a power supply terminal 80 shown in FIG. 2. The external power supply is a power supply that exists outside the electric motor 1. The external power supply supplies a predetermined input voltage to the electric motor 1. The external power supply is a DC power supply that supplies an input voltage of DC 12 V to the electric motor 1.

[0060] The power supply terminal 80 receives power from an external power supply to be supplied to the brush 40. Therefore, the power supply terminal 80 is electrically connected to the brush 40. The power supply power supplied to the brush 40 is supplied to the coil 22 of the rotor 20. As shown in FIGS. 4 and 6 , the power supply terminal 80 and the brush 40 are electrically connected by a pigtail wire 41. The pigtail wire 41 is fixed to the brush 40. Specifically, one end of the pigtail wire 41 is fixed to the brush 40. The other end of the pigtail wire 41 is connected to the power supply terminal 80. The pigtail wire 41 is fixed to the brush 40 so as to be drawn out from the side surface of the brush 40, for example. The pigtail wire 41 and the power supply terminal 80 are joined by, for example, soldering or the like.

[0061] 4 and 6, the power supply terminal 80 is fixed to the brush holder 60. Specifically, a portion of the power supply terminal 80 is press-fitted into an insertion hole provided in the brush holder 60, thereby fixing the power supply terminal 80 to the brush holder 60. The power supply terminal 80 and the external power supply are electrically connected by a power supply line.

[0062] The electric motor 1 is provided with two power supply terminals 80. The two power supply terminals 80 receive DC power from an external power supply. In this case, one of the two power supply terminals 80 is a positive power supply terminal (high-voltage terminal) connected to the positive side of the DC power supply. The other of the two power supply terminals 80 is a negative power supply terminal (low-voltage terminal) connected to the negative side of the DC power supply.

[0063] Noise-reducing capacitors may be connected to the two power supply terminals 80. In this case, the capacitors are connected to the two power supply terminals 80 so as to be connected in parallel with the two power supply terminals 80. This makes it possible to suppress noise generated by the electric motor 1.

[0064] As shown in Figures 3 and 4, the brushes 40 are disposed in a brush holder 60. The brush holder 60 is a holding member that holds the brushes 40. The brush holder 60 holds not only the brushes 40, but also the brush springs 50, the cover plate 70, and the power terminals 80. As shown in Figures 1 to 3, the brush holder 60 is also an outer shell member that constitutes the outer shell of the electric motor 1. The brush holder 60 covers the main surface of the second bracket 102 from the outside.

[0065] The brush holder 60 is made of an insulating resin material. The brush holder 60 is a resin-molded product integrally formed from the insulating resin material. As an example, the resin material constituting the brush holder 60 is phenolic resin. However, the present invention is not limited to this.

[0066] As shown in Figures 3 to 6, the brush holder 60 has a brush storage section 60a, which is a spatial region in which the brushes 40 are stored. The brush storage section 60a is a recessed portion formed in a concave shape. The brush storage sections 60a are formed in accordance with the number of brushes 40. Two brush storage sections 60a are formed in the brush holder 60. The two brush storage sections 60a are elongated in a direction perpendicular to the direction of the axis C of the rotary shaft 21 (i.e., in the radial direction), and are formed in a concave shape with a rectangular cross section.

[0067] 3 and 6, the brush storage section 60a stores the brush spring 50 together with the brush 40. Therefore, the longitudinal length of the brush storage section 60a is longer than the length of the brush 40. Specifically, the spiral portion 51 of the brush spring 50 is disposed rearward of the rear end surface 40b of the brush 40. In other words, the brush spring 50 is disposed in the brush storage section 60a so that the spiral portion 51 is located on the opposite side of the brush 40 from the side on which the commutator 30 is located within the brush storage section 60a.

[0068] The brush spring 50 is arranged so that the spiral axis of the spiral portion 51 is oriented along the direction of the axis C of the rotary shaft 21. In other words, the spiral surface (coil surface) of the spiral portion 51 is substantially perpendicular to the axis C of the rotary shaft 21. The brush spring 50 is stored in the brush storage portion 60a so that the spiral portion 51 is oriented horizontally.

[0069] 5 and 6 , the brush spring 50 has a lead wire 52, which is a wire drawn out from the spiral portion 51. The brush spring 50 is fixed to the brush spring 50 by a portion of the lead wire 52 being supported by the brush holder 60.

[0070] The brush 40 stored in the brush storage section 60a is pressed by the brush spring 50, causing it to slide within the brush storage section 60a. As the front end surface 40a of the brush 40 pressed against the brush spring 50 wears due to friction with the commutator segments 31, the brush 40 moves within the brush storage section 60a toward the commutator 30 due to the pressing force from the brush spring 50. In other words, as the brush 40 wears, the rear end surface 40b of the brush 40 moves in a direction (radial direction) toward the axis C of the rotating shaft 21. As a result, as shown in FIG. 7 , the spiral portion 51 of the brush spring 50 in contact with the rear end surface 40b of the brush 40 also moves in a direction (radial direction) toward the axis C of the rotating shaft 21.

[0071] As shown in Figures 3 and 4, a cover plate 70 is provided to cover the brushes 40 stored in the brush storage section 60a. The cover plate 70 covers not only the brushes 40 but also the brush springs 50. The cover plate 70 is fixed to the brush holder 60 by press-fitting a portion of the cover plate 70 into the brush holder 60. The cover plate 70 is made of a metal material such as brass or stainless steel (SUS). The cover plate 70 is made of a plate-shaped metal plate. The cover plate 70 is formed by performing sheet metal processing such as bending or pressing on a single metal plate that has been punched into a predetermined shape.

[0072] 5 to 7, the brush holder 60 has three support parts, a first support part 61, a second support part 62, and a third support part 63, which serve as support points for supporting the brush spring 50. The first support part 61, the second support part 62, and the third support part 63 are wall parts of the brush holder 60.

[0073] As shown in FIG. 7 , the first support portion 61 is located on the movement path of the spiral portion 51 of the brush spring 50. The first support portion 61 supports the spiral portion 51 when the spiral portion 51 of the brush spring 50 moves toward the rotation shaft 21 due to wear of the brush 40. In other words, as shown in FIG. 6 , the first support portion 61 is not in contact with the spiral portion 51 before the brush 40 is worn. As shown in FIG. 7 , when the brush 40 is worn and the spiral portion 51 slides together with the brush 40, the spiral portion 51 abuts against the first support portion 61, thereby supporting the spiral portion 51. When the spiral portion 51 abuts against the first support portion 61, the spring load of the brush spring 50 becomes zero. In other words, the pressing force of the brush spring 50 on the brush 40 becomes zero, and the sliding of the brush 40 stops. The spring load being zero may include a state in which the brush spring 50 has a pressure force pressing the brush 40, but the brush 40 does not move in the direction of the rotary shaft 21.

[0074] In the present embodiment, the first support portion 61 is inclined with respect to the movement direction of the spiral portion 51 of the brush spring 50 (the sliding direction of the brush 40). Specifically, the first support portion 61 is a curved surface that is concave with respect to the spiral portion 51 of the brush spring 50. As an example, the first support portion 61 is a curved surface having a curvature similar to that of the curved surface that constitutes the outer surface of the spiral portion 51. Note that the first support portion 61 is not limited to a curved surface, and may be a flat inclined surface that is inclined with respect to the movement direction of the spiral portion 51 of the brush spring 50. For example, the first support portion 61 may be a chamfered surface.

[0075] 6 and 7 , the second support portion 62 and the third support portion 63 support a portion of the lead wire 52 drawn out from the spiral portion 51 of the brush spring 50. With the lead wire 52 supported by the second support portion 62 and the third support portion 63, the brush spring 50 is held and fixed in the brush holder 60. Note that even if the brush 40 wears and slides toward the commutator 30, the portion of the lead wire 52 supported by the second support portion 62 and the third support portion 63 does not rewind onto the spiral portion 51, but remains held by the second support portion 62 and the third support portion 63.

[0076] 5, the lead wire 52 drawn out from the spiral portion 51 of the brush spring 50 is bent at two locations, a first bent portion 50a and a second bent portion 50b. The second bent portion 50b is located closer to the spiral portion 51 than the first bent portion 50a.

[0077] By bending the lead wire 52 in this manner, the brush spring 50 has a first portion 52a, which is a portion of the lead wire 52 located closer to the tip (outer end) than the first bent portion 50a, and a second portion 52b, which is a portion of the lead wire 52 between the first bent portion 50a and the second bent portion 50b. The plate-shaped wire material that forms the first portion 52a stands upright on the plate-shaped wire material that forms the second portion 52b.

[0078] In this embodiment, the lead wire 52 is bent at the first bent portion 50a so that the first portion 52a faces the rotating shaft 21 (the commutator 30). Specifically, the lead wire 52 is bent at the first bent portion 50a at an acute angle of less than 90°. The lead wire 52 is bent at the second bent portion 50b at a right angle of 90°. Therefore, the first portion 52a and the second portion 52b have a substantially V-shaped cross section.

[0079] As shown in Figure 7, the second support portion 62 of the brush holder 60 supports the lead-out wire 52 by engaging the first portion 52a of the lead-out wire 52. The second support portion 62 and the first portion 52a of the lead-out wire 52 are in line contact (point contact in the plan view of Figure 7). The second support portion 62 has a planar support surface that is in line contact with the lead-out wire 52. Specifically, a bent piece 52a1 is formed at the tip of the first portion 52a of the lead-out wire 52. The planar second support portion 62 supports the base portion (bent portion) of the bent piece 52a1.

[0080] As shown in Fig. 7 , the third support portion 63 supports the lead-out wire 52 by engaging the second portion 52b of the lead-out wire 52. The third support portion 63 and the second portion 52b of the lead-out wire 52 are in surface contact (line contact in the plan view of Fig. 7 ). The third support portion 63 has a planar support surface that is in surface contact with the lead-out wire 52. Specifically, the planar second support portion 62 supports the planar second portion 52b of the lead-out wire 52.

[0081] The second support portion 62 is located on the opposite side (outside) of the rotation shaft 21 than the first support portion 61 in the sliding direction of the brush 40. In other words, the first support portion 61 is located closer to the rotation shaft 21 (inside) than the second support portion 62 in the sliding direction of the brush 40. The third support portion 63 is located closer to the rotation shaft 21 than the first support portion 61 in the sliding direction of the brush 40. In other words, the first support portion 61 is located between the second support portion 62 and the third support portion 63 in the sliding direction of the brush 40.

[0082] The brush holder 60 has a groove into which the lead wire 52 is inserted. Specifically, the brush holder 60 has a first groove 60b into which the first portion 52a of the lead wire 52 is inserted, and a second groove 60c into which the second portion 52b of the lead wire 52 is inserted. In other words, the first groove 60b and the second groove 60c are storage portions that store the wire that constitutes the brush spring 50.

[0083] The first groove 60b and the second groove 60c are connected to each other to form a single groove. Specifically, the single groove formed by the first groove 60b and the second groove 60c is bent at a right angle so that the angle between the first groove 60b and the second groove 60c is 90°.

[0084] The first groove 60b has a pair of opposing inner surfaces (inner wall surfaces). The first portion 52a of the lead wire 52 is sandwiched between the pair of inner surfaces that make up the first groove 60b. The first portion 52a is inserted into the first groove 60b in an orientation that is inclined with respect to the longitudinal direction of the first groove 60b. Therefore, the second support portion 62, which serves as a support surface, is one of the pair of inner surfaces that make up the first groove 60b. As described above, the second support portion 62 is in line contact with the base portion of the bent piece 52a1 of the first portion 52a of the lead wire 52.

[0085] A bent piece 52a1 formed at the tip of the first portion 52a is fitted into the first groove 60b. Specifically, the bent piece 52a1 is fitted into the first groove 60b in the groove width direction of the first groove 60b. At this time, before the brush 40 is worn, the bent piece 52a1 may be in contact with each of the pair of inner surfaces that make up the first groove 60b, or may be in contact with only one of the pair of inner surfaces that make up the first groove 60b (the second support portion 62). In other words, the tip of the bent piece 52a1 does not have to be in contact with the other of the pair of inner surfaces that make up the first groove 60b (the surface facing the second support portion 62).

[0086] The second groove 60c has a pair of opposing inner surfaces (inner wall surfaces). The second portion 52b of the lead wire 52 is sandwiched between the pair of inner surfaces that make up the second groove 60c. Specifically, the third support portion 63, which serves as a support surface, is one of the pair of inner surfaces that make up the second groove 60c. The third support portion 63 is in surface contact with the second portion 52b of the lead wire 52.

[0087] The other of the pair of inner surfaces constituting the second groove 60c does not, but may, be in contact with the lead wire 52. A protrusion 64 that protrudes toward the lead wire 52 inserted into the second groove 60c is provided on the other of the pair of inner surfaces constituting the second groove 60c. By providing the protrusion 64, the second portion 52b of the lead wire 52 inserted into the second groove 60c can be supported in a state where it is sandwiched between the third support portion 63.

[0088] A method for setting the brush 40 and the brush spring 50 in the brush holder 60 will be described with reference to Fig. 7 and Figs. 8A, 8B, and 9. Figs. 8A and 8B are diagrams showing the configuration of the brush spring 50 before it is assembled to the brush holder 60 in the electric motor 1 according to the embodiment. Fig. 8A is a perspective view of the brush spring 50, and Fig. 8B is a side view of the brush spring 50. Fig. 9 is a diagram showing the state when the brush spring 50 is assembled to the brush holder 60 in the electric motor 1 according to the embodiment. In Fig. 9, the dashed circle indicates the state of the spiral portion 51 of the brush spring 50 shown in Figs. 8A and 8B.

[0089] 8A and 8B show the brush spring 50 in a state where no stress is applied to the brush spring 50. The brush spring 50 in the state shown in Figures 8A and 8B is set in the brush storage portion 60a of the brush holder 60.

[0090] 9 , the lead wire 52 of the brush spring 50 is supported by the second support portion 62 and the third support portion 63 of the brush holder 60, thereby fixing the brush spring 50 to the brush holder 60. That is, the first portion 52a and the second portion 52b of the lead wire 52 are hooked onto the second support portion 62 and the third support portion 63, respectively, thereby fixing the brush spring 50 to the brush holder 60. In this case, the first portion 52a of the lead wire 52 is inserted into the first groove 60b and engaged with the second support portion 62, and the second portion 52b of the lead wire 52 is inserted into the second groove 60c and engaged with the third support portion 63.

[0091] At this time, the spiral portion 51 of the brush spring 50 abuts against the first support portion 61 and is slightly pushed out by the first support portion 61. In other words, the spiral portion 51 abutting against the first support portion 61 is slightly moved toward the opposite side of the rotary shaft 21 (commutator 30) from the state before the brush spring 50 was assembled to the brush holder 60 (the dashed circle in FIG. 9 ). In other words, the spiral portion 51 is pushed toward the opposite side (outward) of the rotary shaft 21.

[0092] In this way, when the brush spring 50 is assembled to the brush holder 60, the brush spring 50 is supported by the brush holder 60 at three points: the first support portion 61, the second support portion 62, and the third support portion 63. In other words, the brush spring 50 is supported by the brush holder 60 at three points. As a result, when the brush spring 50 is assembled, it is held in the brush holder 60 by the spring force of the brush spring 50 itself. Therefore, the assembly of the brush spring 50 can be improved.

[0093] In this case, as shown in Figure 8B, the length (spring leg length) of the first portion 52a of the lead wire 52 of the brush spring 50 before assembly to the brush holder 60 is defined as L, and as shown in Figure 9, the length of the first groove 60b in the brush holder 60 into which the first portion 52a is inserted is defined as W, so that W < L.

[0094] By doing so, when the brush spring 50 is assembled to the brush holder 60, the second portion 52b inserted into the second groove 60c can be prevented from tilting toward the inner surface of the commutator 30 (rotary shaft 21). In other words, the second portion 52b can be prevented from separating from the third support portion 63. As a result, as shown in FIG. 9 , when the brush spring 50 is assembled to the brush holder 60, the brush spring 50 can be maintained in a three-point support state by the first support portion 61, the second support portion 62, and the third support portion 63.

[0095] As shown in Fig. 8B , before the brush spring 50 is assembled to the brush holder 60, the angle (return angle) between the first portion 52a and the second portion 52b of the lead wire 52 of the brush spring 50 is denoted as α. The angle α should be an acute angle. In other words, the angle α should be less than 90°. As shown in Fig. 9 , after the brush spring 50 is assembled to the brush holder 60, the angle (return angle) between the first portion 52a and the second portion 52b of the lead wire 52 of the brush spring 50 is denoted as β. The angle α should satisfy the relationship α≦β≦90°.

[0096] This prevents the lead wire 52 of the brush spring 50 inserted into the first groove 60b and the second groove 60c from coming loose from the first groove 60b and the second groove 60c. In other words, before the spiral portion 51 of the brush spring 50 abuts the first support portion 61 (i.e., the lead wire 52 of the brush spring 50 is stretched), a tensile force acts on the lead wire 52 inserted into the first groove 60b and the second groove 60c in the direction toward the brush 40 (downward in the plane of FIG. 9 ), causing the brush spring 50 to try to come loose from the first groove 60b and the second groove 60c. However, by satisfying the relationship α≦β≦90°, a repulsive force acts against the brush spring 50 coming loose. This prevents the lead wire 52 inserted into the first groove 60b and the second groove 60c from coming loose from the first groove 60b and the second groove 60c.

[0097] In particular, in this embodiment, a bent piece 52a1 is formed at the tip of the first portion 52a. Therefore, when a tensile force acts on the lead wire 52 in the direction toward the brush 40 before the spiral portion 51 abuts against the first support portion 61, the bent piece 52a1 fitted in the first groove 60b is stretched within the first groove 60b. This more reliably prevents the lead wire 52 from coming out of the first groove 60b and the second groove 60c.

[0098] Next, after the brush spring 50 is held in the brush holder 60, the rear end surface 40b of the brush 40, to which the pigtail wire 41 is connected, is brought into contact with the spiral portion 51 of the brush spring 50, and the brush 40 is set in the brush storage portion 60a. At this time, the front end of the brush 40 protrudes from the brush storage portion 60a and is present in the area where the commutator 30 is disposed. At this time, the pigtail wire 41 connected to the brush 40 may be joined to the power terminal 80.

[0099] Next, from the state shown in Fig. 9, the brush 40 is moved in a direction (outward) away from the rotary shaft 21. Specifically, the brush 40 is moved toward the rear until the front end surface 40a of the brush 40 is positioned at the front end of the brush storage section 60a.

[0100] At this time, the spiral portion 51 of the brush spring 50, which abuts against the rear end surface 40b of the brush 40, moves toward the back of the brush storage section 60a as the brush 40 moves. At this time, because the lead wire 52 of the brush spring 50 is engaged with the second support portion 62 and the third support portion 63 of the brush holder 60, the strip-shaped wire material constituting the brush spring 50 is pulled out from the spiral portion 51 along the inner surface of the brush storage section 60a as the brush 40 moves. In other words, the brush 40 moves toward the back while receiving a gradually increasing spring elastic force from the spiral portion 51 of the brush spring 50.

[0101] Thereafter, the rotor 20 with the commutator 30 attached to the rotating shaft 21 is set in the brush holder 60. As a result, as shown in Figure 6, the front end surfaces 40a of the brushes 40 come into contact with the commutator 30, and the brushes 40 are held in place. In other words, the brushes 40 are set in the brush holder 60 while receiving a pressing force from the brush springs 50.

[0102] In the electric motor 1 configured as described above, when power is supplied to the power supply terminals 80, the power supplied to the power supply terminals 80 is supplied to the brushes 40. As a result, an armature current (drive current) flows through the coils 22 via the commutator 30, which is in contact with the brushes 40, generating magnetic flux in the rotor 20 (coils 22). The magnetic flux generated in the rotor 20 interacts with the magnetic flux generated by the stator 10, generating a magnetic force that serves as torque to rotate the rotor 20. At this time, the direction of the current flowing through the coils 22 is switched depending on the positional relationship between the commutator segments 31 and the brushes 40 when they come into contact. As the direction of the current flow is switched in this way, a rotational force in a fixed direction is generated by the magnetic repulsive and attractive forces generated between the stator 10 and the rotor 20, causing the rotor 20 to rotate about the axis C of the rotating shaft 21.

[0103] At this time, the brush 40 held by the brush holder 60 is pressed against the commutator 30 by the brush spring 50. Therefore, as the rotor 20 rotates, the front end surface 40a of the brush 40 is worn due to friction with the commutator segments 31 of the commutator 30. In other words, the brush 40 shortens due to wear with the commutator segments 31. Therefore, as the brush 40 wears, the rear end surface 40b of the brush 40 moves toward the commutator 30 within the brush storage section 60a. At this time, the wire constituting the brush spring 50 is wound into a spiral portion 51 as the brush 40 shortens due to wear. In other words, the lead wire 52 pulled out from the spiral portion 51 shortens, and as shown in FIG. 7, the spiral portion 51 moves toward the commutator 30. In FIG. 7, the dashed line indicates the trajectory of the center O of the spiral portion 51 as the spiral portion 51 moves due to wear of the brush 40.

[0104] As shown by the dashed line in Figure 7 , in the middle stage (between the middle two spiral portions 51 of the four spiral portions 51 in Figure 7 ) between the initial stage when the brush 40 begins to wear and the final stage when the brush 40 is nearing the end of its life, the spiral portions 51 of the brush spring 50 move linearly toward the rotation shaft 21. Therefore, as shown in Figure 10 , in this middle stage, the spring load of the brush spring 50 remains constant even as the brush 40 wears. Figure 10 is a diagram schematically showing the change in the spring load of the brush spring 50 relative to the amount of brush wear in the electric motor 1 according to the embodiment.

[0105] On the other hand, as shown by the dashed line in Figure 7 , in the initial stage when the brush 40 begins to wear (between the two leftmost spiral portions 51 of the four spiral portions 51 in Figure 7 ) and in the final stage when the brush 40 is nearing the end of its life (between the two rightmost spiral portions 51 of the four spiral portions 51 in Figure 7 ), the spiral portions 51 of the brush spring 50 do not move in a straight line but move in a curved manner. In other words, the spiral portions 51 are shifted left and right relative to the center line along the longitudinal direction of the brush 40. Therefore, as shown in Figure 10 , the spring load applied to the brush 40 by the brush spring 50 is not constant between the initial stage and the final stage, but gradually decreases as the brush 40 wears.

[0106] Thus, even when a constant-force spring is used as the brush spring 50, the spring load does not remain constant at the end of the brush 40's life (the end of the brush's life). As a result, not only does electrical wear due to sparks increase at an accelerated rate at the end of the brush's life, but the pressing force of the brush spring 50 on the brush 40 may become insufficient or unstable, resulting in a deterioration in the quality of the motor. Furthermore, this deterioration in the quality of the motor cannot be visually confirmed from the outside of the motor. Therefore, motor users have called for improvements in ease of use, as it is difficult to tell when it is time to replace the motor.

[0107] Therefore, in the electric motor 1, a first support portion 61 is provided on the brush holder 60 to support the spiral portion 51 of the brush spring 50 when the spiral portion 51 moves toward the rotating shaft 21 (commutator 30) due to wear of the brush 40. The electric motor 1 is configured so that the spring load of the brush spring 50 becomes zero when the spiral portion 51 abuts against the first support portion 61. In other words, when the amount of wear of the brush 40 reaches a specified amount, the pressing force of the brush spring 50 on the brush 40 is immediately made zero, forcing the sliding of the brush 40 to stop.

[0108] This configuration shortens the period during which the spring load of the brush spring 50 is not constant, even if the brush spring 50 is a constant-load spring. This prevents the wear of the brush 40 from becoming unstable at the end of its life, thereby improving the quality of the electric motor 1 at the end of its life.

[0109] In this embodiment, as shown in Figure 10, the point at which the spiral portion 51 abuts against the first support portion 61 of the brush holder 60 and the spring load of the brush spring becomes zero is in the middle of a period (final stage period) in which the spring load of the brush spring 50 is not constant, following a period (middle period) in which the spring load of the brush spring 50 is constant.

[0110] This shortens the period of the final stage of the motor 1, which is the end of the brush life, and thus prevents the wear of the brush 40 from becoming unstable at the end of the brush life, thereby improving the quality of the motor 1 at the end of the brush life.

[0111] By changing the position of the first support portion 61 on the brush holder 60, the time when the spiral portion 51 contacts the first support portion 61 (i.e., the life of the electric motor 1) can be changed. The time when the spiral portion 51 contacts the first support portion 61 may be changed depending on the type of electric motor 1. In this case, the time when the spiral portion 51 contacts the first support portion 61 may be changed within the terminal stage shown in FIG. 10 . However, this is not limited to this. For example, the time when the spiral portion 51 contacts the first support portion 61 may be during the middle period shown in FIG. 10 . This shortens the life of the electric motor 1, but it is possible to completely eliminate the terminal stage period in which the spring load of the brush spring 50 is not constant. This further improves the quality of the electric motor 1 at the end of its brush life.

[0112] (Modifications) The electric motor 1 according to the present disclosure has been described above based on the embodiment. However, the present disclosure is not limited to the above embodiment. FIG. 11 is a plan view showing the configuration of a brush holder 60A in an electric motor 1 according to Modification 1. FIG. 12 is a plan view showing the configuration of a brush holder 60B in an electric motor 1 according to Modification 2. FIG. 13 is a plan view showing the configuration of a brush holder 60C in an electric motor 1 according to Modification 3. FIG. 14 is a diagram showing a brush spring 50A as a first modification of the brush spring 50, which is a constant force spring. FIG. 15 is a diagram showing a brush spring 50B as a second modification of the brush spring 50, which is a constant force spring. FIG. 16 is a plan view showing the configuration of a brush holder 60D in an electric motor 1 according to Modification 4 when the brush springs 50A and 50B shown in FIGS. 14 and 15 are used, respectively. FIG. 17 is a plan view showing the configuration of a brush holder 60E in an electric motor 1 according to Modification 5. 18A and 18B are diagrams showing the configuration of another brush spring 50C before being assembled to a brush holder in an electric motor 1 according to Modification 6. Fig. 18A is a perspective view of the brush spring 50C, and Fig. 18B is a side view of the brush spring 50C. Fig. 19 is a diagram showing the state when another brush spring 50C is assembled to a brush holder 60 in an electric motor 1 according to Modification 6.

[0113] For example, in the present embodiment, the first support portion 61 of the brush holder 60 is a curved surface that is concave with respect to the spiral portion 51 of the brush spring 50. However, this is not limited to this. Specifically, as in the brush holder 60A shown in Fig. 11, the first support portion 61A may be a curved surface that is convex with respect to the spiral portion 51 of the brush spring 50. Furthermore, as in the brush holder 60B shown in Fig. 12, the first support portion 61B may be a right-angled corner portion (pin corner).

[0114] Furthermore, in this embodiment, the first support portion 61 of the brush holder 60 is located closer to the rotating shaft 21 (commutator 30) than the second support portion 62 in the sliding direction of the brush 40. However, this is not limited to this. For example, as in the brush holder 60C shown in FIG. 13 , the first support portion 61C may be located on the opposite side of the rotating shaft 21 than the second support portion 62 in the sliding direction of the brush 40. This configuration shortens the life of the electric motor 1 compared to the above embodiment, but also suppresses unstable behavior of the electric motor 1. Therefore, the quality of the electric motor 1 can be further improved.

[0115] Furthermore, in the present embodiment, the lead wire 52 of the brush spring 50 is bent at two locations, the first bent portion 50a and the second bent portion 50b. However, this is not limited to this. For example, as in the brush spring 50A shown in FIG. 14 and the brush spring 50B shown in FIG. 15, the lead wire 52 may be bent at three locations, the first bent portion 50a, the second bent portion 50b, and the third bent portion 50c. In this case, the third bent portion 50c is located between the first bent portion 50a and the second bent portion 50b. The lead wire 52 has a third portion 52c between the first portion 52a and the second portion 52b. The lead wire 52 is bent at the first bent portion 50a so that the first portion 52a faces away from the rotary shaft 21.

[0116] 14, the lead wire 52 is bent so that the first portion 52a and the second portion 52b form an acute angle or a right angle, and the second portion 52b and the third portion 52c form a right angle. In the brush spring 50A shown in FIG. 14, the angle α (return angle) formed between the first portion 52a and the third portion 52c is α≦90°.

[0117] In the brush spring 50B shown in Fig. 15, the lead wire 52 is bent so that the first portion 52a and the third portion 52c form an acute angle or a right angle, and the third portion 52c and the second portion 52b form an acute angle or a right angle. In the brush spring 50B shown in Fig. 15, the angle γ (return angle) formed by the second portion 52b and the third portion 52c is γ≦90°.

[0118] The brush spring 50A shown in FIG. 14 or the brush spring 50B shown in FIG. 15 can be assembled to a brush holder 60D shown in FIG.

[0119] At this time, the lead wires 52 of the brush springs 50A and 50B are bent at the first bent portions 50a so that the first portions 52a face away from the rotary shaft 21. The lead wires 52 have a third portion 52c in addition to the first portion 52a and the second portion 52b. Therefore, in the brush holder 60D shown in FIG. 16 , the second support portion 62D is located on the opposite side (outside) from the rotary shaft 21 than the third support portion 63 in the sliding direction of the brush 40. The brush holder 60D has a fourth support portion 65 that supports the third portion 52c of the lead wire 52.

[0120] As shown in Fig. 14, before the brush spring 50A is assembled to the brush holder 60D, the angle (return angle) between the first portion 52a and the third portion 52c of the lead wire 52 of the brush spring 50A is α, and as shown in Fig. 16, after the brush spring 50A is assembled to the brush holder 60D, the angle (return angle) between the first portion 52a and the third portion 52c of the lead wire 52 of the brush spring 50A is β. This preferably satisfies the relationship α≦β≦90°. This makes it possible to prevent the lead wire 52 of the brush spring 50A from coming loose from the brush holder 60D.

[0121] Furthermore, as shown in Fig. 15, when the angle (return angle) between the second portion 52b and the third portion 52c of the lead wire 52 of the brush spring 50B before assembly into the brush holder 60D is γ, and as shown in Fig. 16, when the angle (return angle) between the second portion 52b and the third portion 52c of the lead wire 52 of the brush spring 50B after assembly into the brush holder 60D is δ, it is preferable that the relationship γ≦δ≦90° is satisfied. This makes it possible to prevent the lead wire 52 of the brush spring 50B from coming off the brush holder 60D.

[0122] In the above embodiment, the third support portion 63 of the brush holder 60D is in surface contact with the lead wire 52 of the brush spring 50. However, this is not limited to this. For example, as in the brush holder 60E shown in Fig. 17, a protrusion 63a may be provided on the third support portion 63, so that the third support portion 63 and the lead wire 52 of the brush spring 50 are in line contact.

[0123] Furthermore, in the above embodiment, the brush holder 60 that holds the brush 40 is used as the holder that holds the brush spring 50. However, this is not limited to this. Specifically, the holder that holds the brush spring 50 may be a separate part from the brush holder 60 that holds the brush 40. In other words, instead of using a single holder that serves as both the holder that holds the brush 40 and the holder that holds the brush spring 50, the holder that holds the brush 40 and the holder that holds the brush spring 50 may be separate.

[0124] In the above embodiment, the rear end surface 40b of the brush 40 is a flat surface perpendicular to the sliding direction of the brush 40. However, this is not limiting. For example, the rear end surface 40b of the brush 40 may be an inclined surface that is inclined with respect to the sliding direction of the brush 40. A recess may be formed in the portion of the rear end surface 40b of the brush 40 where the spiral portion 51 of the brush spring 50 abuts. This allows a portion of the spiral portion 51 to fit into the recess, so that the spiral portion 51 is stably held on the rear end surface 40b of the brush 40 when the brush 40 slides.

[0125] In the above embodiment, the rotating shaft 21 is supported by two bearings, the first bearing 91 and the second bearing 92. However, this is not limiting. Specifically, the rotating shaft 21 may be supported by a single bearing.

[0126] Furthermore, in the above embodiment, the electric motor 1 is a coreless motor in which the stator 10 and the rotor 20 do not have cores. However, this is not limiting. For example, the electric motor 1 may be an electric motor in which the stator 10 and the rotor 20 have cores. However, by using a coreless motor as in the above embodiment, it is possible to realize an electric motor 1 that has low inductance and is thin.

[0127] In the above embodiment, the stator 10 is composed of only permanent magnets. However, this is not limiting. For example, the stator 10 may be a stator composed of permanent magnets and an iron core, or an armature composed of a stator winding and an iron core without using permanent magnets.

[0128] In the above embodiment, the electric motor 1 is a flat motor having an outer size in which the thickness is smaller than the outer diameter. However, this is not limited to this. The technology of the present disclosure can also be applied to, for example, a cylindrical electric motor having a cylindrical housing having an outer size in which the thickness is larger than the outer diameter.

[0129] In the above embodiment, the direction of the main magnetic flux generated by the stator 10 and the rotor 20 is the direction of the axis C of the rotating shaft 21. However, this is not limited to this. Specifically, the direction of the main magnetic flux generated by the stator 10 and the rotor 20 may be a direction perpendicular to the direction of the axis C of the rotating shaft 21 (the radial direction of the rotation of the rotating shaft 21). For example, the technology disclosed herein may be applied to an inner rotor type motor in which the rotor 20 is arranged inside the stator 10.

[0130] In the above embodiment, the brush spring 50 has a bent piece 52a1 at the tip of the lead wire 52. However, the brush spring 50 is not limited to this configuration. Specifically, as shown in FIGS. 18A, 18B, and 19, the brush spring 50C may have a configuration in which the lead wire 52B does not have a bent piece at the tip. When using the brush spring 50C of this modification, the first portion 52a is attached to the second support portion 62 so that the angle α1 formed between the first portion 52a and the second portion 52b shown in FIG. 18B widens to the angle β1 formed between the first portion 52a and the second portion 52b shown in FIG. 19. In this case, the angle formed between the first portion 52a and the second portion 52b satisfies the relationship α1 < β1. As a result, the first portion 52a exerts an elastic force that tends to return toward the second portion 52b. The first portion 52 a is held by the second support portion 62 by utilizing this elastic force.

[0131] In the above embodiment, the electric motor 1 is a vehicle motor used in a vehicle. However, the present disclosure is not limited to this. The technology of the present disclosure can also be applied to electric motors used in various other electrical devices, such as electric motors used in electric blowers mounted on electric vacuum cleaners.

[0132] In addition, the present disclosure also includes forms obtained by applying various modifications to the above-described embodiments and variations that would occur to a person skilled in the art, or forms realized by arbitrarily combining the components and functions of the embodiments within the scope of the present disclosure. The present disclosure also includes any combination of two or more claims from the multiple claims set forth in the claims at the time of filing, provided that there is no technical contradiction. For example, when a dependent claim set forth in the claims at the time of filing is made into a multiple claim or multiple multiple claims that cite all of the superordinate claims within the scope of the technical contradiction, the present disclosure also includes any combination of all claims included in that multiple claim or multiple multiple claims.

[0133] The technology disclosed herein can be widely used in a variety of products equipped with electric motors, including products in the electrical equipment field of automobiles and the like and in the field of household electrical appliances.

[0134] REFERENCE SIGNS LIST 1 Electric motor 10 Stator 11 Magnet 20 Rotor 21 Rotating shaft 21a First end 21b Second end 22 Coil 23 Molded resin 30 Commutator 31 Commutator segment 40 Brush 40a Front end surface 40b Rear end surface 41 Pigtail wire 50, 50A, 50B, 50C Brush spring 50a First bent portion 50b Second bent portion 50c Third bent portion 51 Spiral portion 52, 52B Lead wire 52a First portion 52a1 Bent piece 52b Second portion 52c Third portion 60, 60A, 60B, 60C, 60D, 60E Brush holder 60a Brush storage portion 60b First groove 60c Second groove 61, 61A, 61B, 61C First support portion 62, 62D Second support portion 63 Third support portion 64, 63a Protrusion 65 Fourth support portion 70 Cover plate 80 Power terminal 91 First bearing 92 Second bearing 101 First bracket 102 Second bracket

Claims

1. An electric motor comprising: a rotor having a rotating shaft extending in the axial direction; a commutator attached to the rotating shaft; brushes in contact with the commutator; brush springs for pressing the brushes against the commutator; and a holder for holding the brush springs, wherein the brush springs are constant-force springs having a spiral portion around which a strip-shaped wire is wound, and the constant-force springs apply a pressing force to the brushes by means of the spiral portion in contact with a rear end surface of the brush, and the holder has a first support portion that supports the spiral portion when the brush wears and moves toward the rotating shaft, and the spring load of the brush spring becomes zero when the spiral portion abuts against the first support portion.

2. The electric motor as set forth in claim 1, wherein the point at which the spiral portion comes into contact with the first support portion and the spring load of the brush spring becomes zero is midway through a period in which the spring load of the brush spring is not constant following a period in which the spring load of the brush spring is constant.

3. The electric motor according to claim 1, wherein the spring load being zero includes a state in which the brush spring has a pressure force pressing against the brush, but the brush does not move in the direction of the rotation shaft.

4. An electric motor as claimed in any one of claims 1 to 3, wherein the constant force spring has a lead wire which is the wire material drawn out from the spiral portion, and the holder has a second support portion which supports a part of the lead wire.

5. An electric motor as set forth in claim 4, wherein the lead wire is bent at a first bent portion, and the second support portion supports the lead wire by engaging a first portion, which is a portion of the lead wire that is located further towards the tip side than the first bent portion.

6. The electric motor according to claim 5, wherein the lead wire is bent at the first bent portion so that the first portion faces the rotating shaft.

7. The electric motor according to claim 5, wherein the lead wire is bent at the first bent portion so that the first portion faces away from the rotating shaft.

8. The electric motor according to claim 5, wherein the holder has a first groove into which the first portion is inserted.

9. The electric motor according to claim 8, wherein a bent piece is formed at a tip end of said first portion, said bent piece being fitted into said first groove.

10. The electric motor according to claim 8, wherein, assuming that the length of the first portion of the brush spring before being attached to the holder is L and the length of the first groove is W, W<L.

11. An electric motor as described in claim 5, wherein the pull-out wire is further bent at a second bend portion which is located closer to the spiral portion than the first bend portion, and the holder further has a third support portion which supports a portion of the pull-out wire, and the third support portion supports a second portion of the pull-out wire which is a portion between the first bend portion and the second bend portion.

12. The electric motor according to claim 11, wherein the third support portion has a support surface that is in surface contact with the second portion.

13. The electric motor according to claim 12, wherein the holder has a second groove into which the second portion is inserted, the second groove has a pair of opposing inner surfaces, and the support surface is one of the pair of inner surfaces.

14. The electric motor according to claim 13, wherein the other of the pair of inner surfaces is provided with a protrusion protruding toward the lead wire inserted in the second groove.

15. An electric motor as described in claim 11, wherein an angle between the first portion and the second portion of the brush spring before being assembled into the holder is α, and an angle between the first portion and the second portion after the brush spring is assembled into the holder is β, satisfying the relationship α≦β≦90°.

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