CN115997339A

CN115997339A - Motor with a motor housing having a motor housing with a motor housing

Info

Publication number: CN115997339A
Application number: CN202180053249.7A
Authority: CN
Inventors: 中野圭策; 浅野贵洋; 远矢和雄
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2020-09-01
Filing date: 2021-08-27
Publication date: 2023-04-21
Also published as: WO2022050179A1

Abstract

A motor (1) for detecting the rotational speed of the motor from the waveform of the current flowing through the motor, the motor (1) comprising: a rotation shaft (21); a commutator (30) which is mounted on the rotary shaft (21) and has a plurality of commutator segments (31) arranged along the circumferential direction of the rotary shaft (21); a brush (40) that is in contact with the plurality of segments (31); a rotor core (23) mounted on the rotating shaft (21); and a winding (22) which is wound around the rotor core (23) and is connected to at least one of the plurality of commutator segments (31), wherein the motor (1) is driven with an input voltage of 48V or less, and when detecting the rotational speed of the motor (1), when the impedance of the winding (22) between two adjacent commutator segments (31) among the plurality of commutator segments (31) is Z, and when the contact resistance between the brush (40) and the commutator segment (31) of the contact brush (40) among the plurality of commutator segments (31) is R, 2.ltoreq.Z/R.ltoreq.4.

Description

Motor with a motor housing having a motor housing with a motor housing

Technical Field

The present invention relates to an electric motor.

Background

The motor is typically used widely in the field of household electric appliances such as electric sweepers, and also in the field of electric appliances such as automobiles. For example, in a vehicle such as a motorcycle or a motorcycle, an electric motor is used to drive a cooling fan such as a radiator.

As motors, there are known a commutator motor (commutator motor) using brushes and a brushless motor not using brushes. The commutator motor includes, for example, a stator, a rotor that rotates based on magnetic force of the stator, a commutator mounted on a rotating shaft of the rotor, and a brush that is in sliding contact with the commutator.

The commutator in a commutator motor has a plurality of segments arranged so as to surround the rotation axis of a rotor. Each of the plurality of segments is connected to a winding wound around an iron core of the rotor.

In a commutator motor, a short circuit occurs in windings between two adjacent segments due to brushes contacting the two adjacent segments across, and armature resistance of a rotor as an armature temporarily decreases. As a result, current pulsation occurs in the waveform of the current flowing through the motor. The current ripple is generated due to the number of segments. As described above, in the commutator motor, a current waveform having current ripple with a frequency due to the number of the commutator segments can be obtained by the rotation of the rotor.

Therefore, conventionally, there has been proposed a motor capable of detecting the rotational speed of the motor based on current pulsation of the current waveform. For example, as such a motor, there is proposed a technique of detecting the rotation speed of the motor by increasing the amplitude of current pulsation in order to improve the detection accuracy of the rotation speed (for example, patent documents 1 and 2).

Prior art literature

Patent literature

Patent document 1: japanese patent No. 5026949

Patent document 2: japanese patent No. 6485046

Disclosure of Invention

Problems to be solved by the invention

By detecting the rotational speed of the motor based on the current pulsation of the current waveform in this way, the rotational speed of the motor can be controlled.

However, in the conventional technique, when the motor is made to have a high output, current pulsation of a current waveform is disturbed, and the rotational speed of the motor cannot be accurately detected, so that desired rotational speed control may not be performed.

In addition, when the motor is made high in output, spark is likely to occur between the brush and the commutator segment, and the life of the brush is reduced. That is, the life of the motor is reduced.

The present disclosure has been made to solve the above-described problems, and an object of the present disclosure is to provide a motor capable of precisely controlling the rotational speed of the motor without decreasing the life of the motor even when the motor is increased in output.

Solution for solving the problem

In order to achieve the above object, one embodiment of the motor according to the present disclosure is a motor that detects a rotational speed of the motor from a waveform of a current flowing through the motor, the motor including: a rotation shaft; a commutator mounted on the rotary shaft and having a plurality of commutator segments arranged along a circumferential direction of the rotary shaft; a brush in contact with the plurality of segments; an iron core mounted to the rotating shaft; and a winding wound around the iron core and connected to at least one of the plurality of segments, wherein the motor is driven with an input voltage of 48V or less, and a relationship of 2.ltoreq.z/r.ltoreq.4 is satisfied when detecting the rotational speed of the motor, when the impedance of the winding between two adjacent segments among the plurality of segments is Z and the contact resistance between the brush and a segment among the plurality of segments that contacts the brush is R.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present disclosure, even if the motor is made high-output, the motor life is not reduced, and the motor rotation speed can be controlled with high accuracy.

Drawings

Fig. 1 is a sectional view of an electric motor according to an embodiment.

Fig. 2 is a sectional view of the motor according to the embodiment on line II-II in fig. 1.

Fig. 3 is a diagram showing a state in which windings between the segments are energized and a state in which windings between the segments are shorted in the motor according to the embodiment.

Fig. 4 is a diagram showing an example of a current waveform of the motor according to the embodiment.

Fig. 5 is a graph showing the relationship between the impedance of the windings between the segments, the rotation speed controllability of the motor, and the life of the motor, with respect to the multiple of the contact resistance between the brushes and the segments.

Detailed Description

Embodiments of the present disclosure are described below with reference to the accompanying drawings. The embodiment described below represents a specific example of the present disclosure. Accordingly, the numerical values, shapes, materials, components, arrangement positions of components, connection modes, and the like shown in the following embodiments are examples, and the gist of the present invention is not limited to the present disclosure. Therefore, among the components in the following embodiments, the components not described in the independent claims are described as arbitrary components.

The drawings are schematic and are not necessarily strictly illustrated. In the drawings, substantially the same structures are denoted by the same reference numerals, and overlapping description is omitted or simplified.

(embodiment)

First, the overall configuration of the motor 1 according to the embodiment will be described with reference to fig. 1 and 2. Fig. 1 is a sectional view of a motor 1 according to an embodiment. Fig. 2 is a sectional view of the motor 1 on the line II-II of fig. 1. In fig. 2, the frame 50 is not shown. In fig. 2, black arrows indicate the flow of current.

The motor 1 is a brush-equipped commutator motor, and includes a stator 10 (stator), a rotor 20 (rotor) that rotates based on the magnetic force of the stator 10, a commutator 30 that is attached to a rotary shaft 21 of the rotor 20, brushes 40 that contact the commutator 30, and a frame 50 that houses the stator 10 and the rotor 20.

The motor 1 in the present embodiment is a type of direct current motor (DC motor) driven by direct current, and uses a magnet 11 as a stator 10 and an armature having a winding 22 as a rotor 20.

In the present embodiment, the motor 1 is driven with an input voltage of 48V or less. Specifically, the motor 1 is a low-voltage high-output motor (large-current motor) having an input voltage of 12V or more and 25V or less and a maximum output of 200W or more. Such an electric motor 1 is used for a vehicle such as a motorcycle or a four-wheeled motor vehicle, for example. As an example, the motor 1 is a motor for a vehicle having an input voltage of 13V. The motor 1 is not limited to a vehicle, and may be used for an electric blower or the like mounted on an electric cleaner or the like. The constituent elements of the motor 1 will be described in detail below.

The stator 10 generates a magnetic force acting on the rotor 20. The stator 10 constitutes a magnetic circuit together with the rotor 20 as an armature. The stator 10 is configured such that N poles and S poles alternately exist in the circumferential direction on the air gap surface with the rotor 20. In the present embodiment, the stator 10 is constituted by a plurality of magnets 11. The magnet 11 is a magnetic field that generates magnetic flux for generating torque, and is, for example, a permanent magnet (magnet) having an S-pole and an N-pole. Each of the plurality of magnets 11 has a circular arc shape with a substantially constant thickness in a plan view. A plurality of magnets 11 are fixed to the frame 50.

The plurality of magnets 11 are arranged so that N poles and S poles alternately and uniformly exist along the circumferential direction of the rotary shaft 21. Thus, the main magnetic flux generated by the stator 10 (the magnet 11) is directed in a direction intersecting the direction of the axial center C of the rotary shaft 21. In the present embodiment, the plurality of magnets 11 are arranged at equal intervals in the circumferential direction so as to surround the rotor 20, and are located on the radially outer peripheral side of the rotor core 23 in the rotor 20. Specifically, the plurality of magnets 11 magnetized into N and S poles are arranged such that the magnetic pole center of the N pole and the magnetic pole center of the S pole are equally spaced in the circumferential direction.

The rotor 20 has a rotation shaft 21, and rotates around an axial center C of the rotation shaft 21. The rotor 20 generates a magnetic force acting on the stator 10. In the present embodiment, the main magnetic flux generated by the rotor 20 is directed in a direction perpendicular to the direction of the axial center C of the rotary shaft 21.

The rotor 20 is an armature, and includes a winding 22 and a rotor core 23. In the present embodiment, the rotor 20 is an inner rotor, and is disposed inside the stator 10. Specifically, the rotor core 23 of the rotor 20 is surrounded by the plurality of magnets 11 constituting the stator 10. The rotor 20 and the stator 10 are disposed with an air gap therebetween. Specifically, a minute air gap exists between the outer peripheral surface of the rotor core 23 and the inner surface of each magnet 11.

The rotary shaft 21 is a shaft (shaft) having an axis C, and is a bar-like member such as a metal bar. The axial center C of the rotary shaft 21 becomes the center of the rotor 20 when rotating. The longitudinal direction (extending direction) of the rotary shaft 21 is the direction (axial direction) of the axial center C.

The rotation shaft 21 is rotatably supported by a bearing such as a ball bearing. The first end 21a, which is one end of the rotation shaft 21, is supported by a first bearing, which is held by a bracket fixed to the frame 50 or directly by the frame 50, for example, though not shown in detail. The second end 21b, which is the other end of the rotation shaft 21, is supported by a second bearing that is held by a bracket fixed to the frame 50 or is directly held by the frame 50. The bracket is fixed to the frame 50 so as to cover an opening of the frame 50, for example.

The rotation shaft 21 and the rotor 20 are fixed to each other. That is, the rotary shaft 21 is attached to the rotor 20, and the rotor core 23 is attached to the rotary shaft 21. Specifically, the rotary shaft 21 is fixed to the rotor core 23 in a state of penetrating the rotor core 23. For example, the rotary shaft 21 is fixed to the rotor core 23 by press-fitting or shrink-fitting the rotary shaft 21 into the center hole of the rotor core 23.

The winding 22 is an armature winding of the rotor 20 serving as an armature, and is wound around the rotor core 23. Specifically, the winding 22 is wound around the rotor core 23 so that a magnetic force acting on the stator 10 is generated by a current flowing therethrough.

The winding 22 is a winding coil having a coil portion 22a (rotor coil). Specifically, a part of the electric wire constituting the winding 22 is wound around the rotor core 23 as the coil portion 22a. In the present embodiment, the coil portion 22a of the winding 22 is a portion where the electric wire constituting the winding 22 is wound around the teeth of the rotor core 23 via the insulator 24. The electric wire constituting the winding 22 is, for example, an insulated coated wire, and includes a conductive wire (core wire) made of a conductive material such as copper and an insulating film coating the conductive wire. The winding 22 may be a molded coil. The insulator 24 is made of an insulating resin material or the like. The insulator 24 is provided in plurality so as to cover each of the plurality of teeth of the rotor core 23.

In addition, the winding 22 is electrically connected to the commutator 30. Specifically, the winding 22 is connected to at least one of the plurality of segments 31 of the commutator 30. Current flows to the winding 22 via the commutator segments 31 contacted by the brushes 40. As an example, the winding 22 is locked by a hook formed on the commutator segment 31 or buried in a groove provided in the commutator segment 31, and welded to the commutator segment 31 by welding or the like. The winding 22 may be constituted by one continuous electric wire having a plurality of coil portions 22a formed continuously over the entire plurality of segments 31, or may be constituted by a plurality of electric wires each having a coil portion 22a provided between two of the plurality of segments 31. That is, one winding 22 has one or more coil portions 22a.

The rotor core 23 is an armature core around which the winding 22 is wound. In the present embodiment, the rotor core 23 is a laminated body in which a plurality of electromagnetic steel plates are laminated in the direction of the axis C of the rotary shaft 21. The rotor core 23 is not limited to a laminate of electromagnetic steel plates, and may be a block made of a magnetic material.

The rotor core 23 has a plurality of teeth. The plurality of teeth are magnetic poles, and a magnetic force is generated by passing a current through the windings 22 wound around the teeth. The plurality of teeth protrude radially outward of the rotary shaft 21, and are present at equal intervals in the entire rotation direction of the rotary shaft 21. That is, the plurality of teeth extend radially in a direction orthogonal to the axial center C of the rotary shaft 21. Coil portions 22a of the winding 22 are disposed in the slots between two adjacent teeth.

The commutator 30 is mounted on the rotary shaft 21. Thus, the commutator 30 rotates together with the rotation shaft 21 based on the rotation of the rotor 20. In the present embodiment, the commutator 30 is mounted on the first end 21a of the rotary shaft 21. The commutator 30 mounted on the rotary shaft 21 may be a part of the rotor 20.

As shown in fig. 2, the commutator 30 has a plurality of segments 31 (segments) provided along the circumferential direction of the rotary shaft 21. Specifically, the plurality of segments 31 are annularly arranged along the rotation direction of the rotation shaft 21 so as to surround the rotation shaft 21. In the present embodiment, the commutator 30 has 24 segments 31. The shape of each segment 31 is an elongated member extending in the longitudinal direction of the rotary shaft 21.

Each of the plurality of segments 31 is a conductive terminal made of a metal material such as copper, and is electrically connected to the winding 22 included in the rotor 20. The plurality of commutator segments 31 are insulated from each other, but the plurality of commutator segments 31 are electrically connected through the windings 22 of the rotor 20. For example, two adjacent segments 31 are electrically connected by winding 22. The coil portion 22a of the winding 22 is present in the current path between the two commutator segments 31 connected by the winding 22.

As an example, the commutator 30 is a molded commutator, and is formed by molding a plurality of commutator segments 31 with resin. In this case, the plurality of segments 31 are embedded in the molding resin 32 with the surfaces exposed.

The commutator 30 contacts the brushes 40. Specifically, the brushes 40 are in contact with the plurality of segments 31 of the commutator 30. The commutator 30 rotates based on the rotation of the rotation shaft 21, so that the brushes 40 continuously contact all the segments 31 in sequence. In addition, the brush 40 contacts one or both of the segments 31 at the instant in the rotation of the commutator 30.

Although not shown, a brush spring such as a coil spring or a torsion spring for pressing the brush 40 against the commutator 30 is disposed in the motor 1. The brush spring applies a pressing force to the brush 40 by using spring elasticity. The brushes 40 are always brought into a state in which the surfaces of the tip portions are in contact with the segments 31 of the commutator 30 by receiving the pressing force from the brush springs. That is, the brush 40 is in sliding contact with the commutator segments 31 by the brush springs, and the surface of the brush 40 where the commutator segments 31 slide with each other is a sliding surface.

The brush 40 is a power supply brush that supplies electric power to the rotor 20 by contacting the commutator segments 31. Thus, the brush 40 is connected to an electric wire through which an electric current supplied from the power supply flows. For example, the brush 40 is electrically connected to an electrode terminal that receives an input voltage from a power source via an electric wire such as a pigtail. Specifically, the other end of the pigtail, one end of which is connected to the electrode terminal, is connected to the rear end of the brush 40, and the brush 40 contacts the commutator segment 31, so that the armature current supplied to the brush 40 via the pigtail flows to the winding 22 of the rotor 20 via the commutator segment 31. The power supply is an external power supply that is external to the motor 1, and supplies a predetermined input voltage to the motor 1. For example, the power supply supplies an input voltage of 13V to the motor 1.

The brush 40 is an electrically conductive body having conductivity. As an example, the brush 40 is a long, substantially rectangular parallelepiped carbon brush made of carbon. Specifically, the brush 40 is a metal graphite brush containing a metal such as copper and carbon. In the present embodiment, the brush 40 is a copper-containing carbon brush. In this case, the content of copper in the brush 40 may be 50 wt% or more and 60 wt% or less. By setting the copper content in the brush 40 to 50 wt% or more, the contact resistance between the brush 40 and the commutator segment 31 can be reduced. On the other hand, when the copper content in the brush 40 exceeds 60 wt%, sparks generated between the brush 40 and the commutator segments 31 become large and the life of the brush 40 becomes short. That is, the life of the motor 1 becomes short. The brush 40 may contain 0.1 wt% or more and 3 wt% or less of SiO ₂ Or an additive to SiC.

Such brushes 40 can be produced by pulverizing a kneaded product obtained by kneading graphite powder, copper powder, a binder resin, and a curing agent, compression-molding the pulverized product into a rectangular parallelepiped, and firing the resultant. In this case, the brush 40 may be a metallic graphite brush produced by low-temperature firing at 500 ℃. By reducing the firing temperature at the time of manufacturing the brush 40 to 500 ℃ or lower in this way, the brush 40 can be made soft and elastic as compared with the case of manufacturing by firing at a temperature exceeding 500 ℃. As a result, the brush 40 has good contact with the commutator segments 31, and can suppress spark generation even when the copper content is increased as described above. Thus, the lifetime of the motor 1 can be prolonged.

The length of the brush 40 in the direction of the axis C of the rotary shaft 21 may be 2 times or more and 4 times or less than the length of the brush 40 in the sliding direction. Specifically, the height of the front end surface of the brush 40 on the commutator segment 31 side may be 2 times or more and 4 times or less the length of the brush 40 in the direction (radial direction) orthogonal to the axial center C of the rotary shaft 21.

In the present embodiment, the brushes 40 are provided in a pair. The pair of brushes 40 are disposed so as to face each other with the commutator 30 interposed therebetween. That is, the pair of brushes 40 are arranged in line symmetry about the axial center C of the rotary shaft 21. Each brush 40 of the pair of brushes 40 contacts the segment 31 of the commutator 30 in a direction (radial direction) orthogonal to the axial center C of the rotary shaft 21. That is, the armature current is supplied from each brush 40 of the pair of brushes 40 to the segment 31 via the sliding surface between the brush 40 and the segment 31.

Each brush 40 is configured to contact two adjacent segments 31 across. That is, the length of the brush 40 in the rotation direction of the rotor 20 is wider than the length of the interval between the adjacent two segments 31. Thus, since each brush 40 transversely contacts the adjacent two segments 31, the winding 22 existing on the current path between the two segments 31 is short-circuited.

Although not shown, the brush 40 may be housed in a brush holder. In this case, the brush 40 becomes slid within the brush holder.

The frame 50 is a case (housing) that houses components constituting the motor 1, such as the stator 10 and the rotor 20. The frame 50 has, for example, a cylindrical portion having a cylindrical shape. The frame 50 is made of a metal material such as aluminum. The stator 10 (magnet 11) is mounted to the frame 50 along the inner peripheral surface of the frame 50. In addition, the frame 50 may be a bottomed cylinder shape having a bottom.

In the motor 1 configured as described above, the current supplied to the brushes 40 flows as an armature current (driving current) to the windings 22 of the rotor 20 via the commutator 30, and the rotor 20 generates magnetic flux. The magnetic force generated by the interaction between the magnetic flux generated by the rotor 20 and the magnetic flux generated by the stator 10 becomes torque for rotating the rotor 20. At this time, the direction of current flow is switched according to the positional relationship when the commutator segments 31 are in contact with the brushes 40. That is to say commutation takes place. The rotational force in a fixed direction is generated by repulsive force and attractive force of magnetic force generated between the stator 10 and the rotor 20 due to the switching of the direction in which such current flows. Thereby, the rotor 20 rotates about the rotation shaft 21 as a rotation center.

When the rotor 20 rotates, the commutator 30 attached to the rotary shaft 21 also rotates. As a result, the state (one-piece contact state) in which only one of the segments 31 contacts the brush 40 as shown in fig. 3 (a) and the state (two-piece contact state) in which the segments 31 contact the brush 40 as shown in fig. 3 (b) are alternately repeated. In fig. 3, black arrows indicate the flow of current.

Specifically, in the case where only one of the segments 31 is in contact with the brush 40 (in the case of fig. 3 (a)), the winding 22 existing in the current path between the segment 31 in contact with the brush 40 and the segment 31 adjacent to the segment 31 is not short-circuited and is in the energized state.

On the other hand, in the case where the commutator segments 31 in contact with the brushes 40 are brought into two states (in the case of (b) of fig. 3), the brushes 40 are brought into a state of being in contact with the adjacent two commutator segments 31 across. In this case, the winding 22 existing on the current path between the two commutating segments 31 contacted by the brush 40 is short-circuited to become a short-circuited state. In this case, no current flows through the coil portion 22a of the winding 22 existing in the current path between the adjacent two segments 31. When the winding 22 existing on the current path between the adjacent two segments 31 is shorted as described above, the armature resistance of the rotor 20 temporarily decreases.

As a result, the energization state shown in fig. 3 a and the short-circuit state shown in fig. 3 b are repeated, and as shown in fig. 4, current pulsation (ripple) is generated at a frequency that is caused by the number of the commutating segments 31 in the waveform (current waveform) of the current flowing through the motor 1. In fig. 4, the top of the peak of the current waveform corresponds to the energized state shown in fig. 3 (a), and the bottom of the valley of the current waveform corresponds to the short-circuited state shown in fig. 3 (b).

In the present embodiment, since the commutator 30 has 24 segments 31, the short circuit and energization of the winding 22 are repeated to obtain 24 current waveforms. That is, each 24 times the valley of the current waveform appears, it means that the rotation shaft 21 rotates once (rotates 360 °).

The motor 1 also has a function of detecting the rotation speed of the motor 1 from the waveform of the current flowing through the motor 1. Specifically, the motor 1 can detect the rotation speed of the motor 1 based on the current pulsation of the waveform of the current.

Here, the characteristics of the motor 1 according to the present embodiment and the process including the technology that will be considered in the present disclosure will be described.

In a commutator motor, the rotational speed of the motor can be detected based on current ripple of the current waveform of the motor. This enables the rotational speed control of the motor. That is, by accurately detecting the rotational speed of the motor, the rotational speed control of the motor can be accurately performed.

However, when the inventors actually manufactured the motor and tried to control the rotational speed of the motor, the inventors of the present application know that the accuracy of the rotational speed control is low. It is apparent that, particularly when a motor driven with a low voltage of 12V or more and 25V or less is increased in output (for example, the maximum output is 200W or more) and the driving (operation) of the motor is continued, the current pulsation of the current waveform is disturbed, and it becomes difficult to perform the rotation speed control.

As a result of intensive studies on the cause of this, the inventors of the present application have found that one of the causes is disturbance of current pulsation of the current waveform due to the influence of contact resistance between the brushes 40 and the commutator segments 31. This point will be described below.

The magnitude of the current ripple of the current waveform of the motor shown in fig. 4 is determined by the impedance (Z) of the winding present on the current path between two adjacent segments. Specifically, the impedance of the winding is the impedance value of the coil portion of the winding. The higher the resistance value of the winding, the higher the impedance of the winding, the higher the inductance of the coil portion of the winding, and the higher the impedance of the winding, the more turns of the coil portion of the winding.

The impedance of this winding is the signal component of the current waveform of the motor, affecting the difference between the top of the peak and the bottom of the valley of the current waveform shown in fig. 4. That is, the impedance of the winding has an effect on the magnitude of the current ripple.

Therefore, in order to improve the detection accuracy of the rotation speed of the motor, it is conceivable to increase the current ripple of the current waveform, but to increase the current ripple, it is conceivable to thin the winding to increase the resistance value of the winding, to increase the inductance of the coil portion of the winding, and to increase the number of turns of the coil portion of the winding.

However, when the motor is to be increased in output without changing the input voltage, it is necessary to increase the current flowing through the winding, and therefore, it is necessary to thicken the winding to reduce the resistance value and to reduce the number of turns of the coil portion of the winding. In this case, the impedance (single-coil impedance) of the coil portion of the winding existing in the current path between the two adjacent segments becomes small, and the amplitude of the current ripple of the current waveform becomes small.

In particular, according to experiments by the inventors of the present application, it was found that, in a motor having an input voltage of 25V or less (for example, 13V), when an attempt is made to increase the output to 200W or more, the current waveform is disturbed and cannot be recognized as peaks or valleys of the current ripple.

After the motor is analyzed to find the cause, it is known that there is a contact resistance between the brushes and the segments, but in the motor in which the output is increased without changing the input voltage, the contact resistance (contact resistance value) becomes a larger value than the impedance (single-coil impedance) of the coil portion of the winding existing on the current path between the adjacent two segments.

In actual measurement, the contact resistance between the brushes and the commutator segments was 27mΩ when the current flowing through the winding was 10A, and the single-coil impedance was 41mΩ when the rotational speed of the motor was 7000 r/min.

The contact resistance between the brushes and the segments (contact resistance of the brushes) varies greatly depending on wear of the segments, a height difference, or a coating state. In fact, the inventors of the present application have conducted a durability test, and found that minute irregularities and level differences are formed on the surfaces of the segments, and that the contact area between the brushes and the segments is drastically reduced, and that the contact resistance (R) between the brushes and the segments is larger than an initial value, and that there is a deviation for each segment. Specifically, the surface of the commutator segment after the temperature endurance test was roughened by the presence of irregularities of about 10 μm and a height difference, and the contact resistance between the brush and the commutator segment was 54mΩ (measured) when the current flowing through the winding was 10A. That is, the contact resistance between the brushes and the commutator segments is increased by about 2 times the initial value (27 mΩ). Moreover, the contact resistance between the brushes and the segments also varies greatly for each segment.

As described above, it is understood that the contact resistance (R) between the brushes and the segments is larger than the value of the single-coil impedance, and the value varies for each segment.

When the motor is made high in output, spark is likely to occur between the brush and the commutator segment, and the life of the brush is reduced. That is, the life of the motor is reduced. Therefore, when the motor is to be high in output, a brush having a high contact resistance is selected to suppress spark generated between the brush and the commutator segment. When the motor is designed in this way, the contact resistance (R) between the brushes and the commutator segments further increases.

As described above, in the case of the conventional motor, when an attempt is made to increase the output without changing the input voltage, the impedance Z (single-coil impedance) of the coil portion of the winding existing in the current path between the two adjacent segments becomes small, and the contact resistance (R) between the brushes and the segments becomes large. As a result, the current waveform of the motor is disturbed, the amplitude of the current ripple is reduced, and it becomes difficult to detect the rotational speed of the motor and control the rotational speed. That is, it is understood that the higher the output, the more difficult it becomes to control the rotation speed. This is an insight discovered by the inventors of the present application as a new fact.

Based on this finding, the inventors of the present application have made experiments to index the relationship between the impedance (Z) of the winding between the segments, with respect to the contact resistance (R) between the brushes and the segments, the rotation speed controllability of the motor, and the life of the motor. The results of this experiment are shown in fig. 5. Fig. 5 is a graph showing the relationship between the impedance of the windings between the segments, the rotation speed controllability of the motor, and the life of the motor, with respect to the multiple of the contact resistance between the brushes and the segments. In fig. 5, the rotational speed controllability of the motor is determined based on whether rotational speed control is possible in both the initial case and the case where the motor is continuously driven.

As a result, as shown in fig. 5, it is apparent that when the impedance of the coil portion of the winding existing on the current path between two adjacent segments is Z and the contact resistance between the brushes and the segments is R, the magnitude of the impedance Z as a signal component is 2 times or more the magnitude of the contact resistance R as a noise component, and thus the rotational speed of the motor can be controlled. This is because, when the rotational speed of the motor is detected, the impedance Z is 2 times or more (2. Ltoreq.z/R) the contact resistance R, whereby stable current ripple can be obtained, and stable rotational speed control can be performed. Thus, from the standpoint of motor rotation speed control, the impedance Z may be 2 times or more the contact resistance R. In order to more accurately control the rotation speed, the impedance Z may be 2.5 times or more the contact resistance R. Further, the impedance Z is the magnitude (|z|) of the absolute value of the impedance of the coil portion of the winding existing on the current path between the adjacent two segments.

In addition, as shown in fig. 5, it is understood that when the magnitude of the impedance Z exceeds 4 times the magnitude of the contact resistance R, the life of the motor is drastically reduced. This is because, when the resistance Z exceeds 4 times the contact resistance R (Z/R > 4) at the time of detecting the rotation speed of the motor, the spark generated between the brush and the commutator segment becomes excessively large and the life of the brush is drastically reduced. Further, the life of the brushes is the life of the commutator motor. Thus, from the viewpoint of the life of the motor, the impedance Z may be 4 times or less (Z/R.ltoreq.4) with respect to the contact resistance R. In addition, from the viewpoint of further suppressing the reduction in the lifetime of the motor, the impedance Z may be 3.5 times or less (Z/r.ltoreq.3.5) with respect to the contact resistance R.

As described above, the motor 1 according to the present embodiment is a motor driven at a low voltage by an input voltage of 48V or less, and when the impedance of the winding 22 between two adjacent segments 31 among the plurality of segments 31 is Z and the contact resistance between the brush 40 and the segment 31 of the contact brush 40 among the plurality of segments 31 is R, the relationship of 2.ltoreq.z/r.ltoreq.4 is satisfied when the rotational speed of the motor 1 is detected.

Accordingly, even if the motor 1 is made high-output, the lifetime of the motor is not reduced, and the rotational speed of the motor can be detected with high accuracy because the current pulsation of the current waveform is not disturbed. Therefore, the rotational speed of the motor can be controlled with high accuracy without reducing the life of the motor.

In the motor 1 according to the present embodiment, the ratio of Z/R may be 2.5 or less and 3.5 or less.

This makes it possible to control the rotational speed of the motor with higher accuracy without further decreasing the life of the motor.

In the motor 1 according to the present embodiment, the motor is driven with a low voltage having an input voltage of 25V or less and a maximum output of 200W or more.

In the motor 1 driven by the low voltage of 25V or less as described above, when the maximum output is increased to 200W or more, it becomes difficult to perform the rotation speed control, but by setting 2.ltoreq.z/r.ltoreq.4, the lifetime of the motor 1 is not reduced, and the rotation speed control of the motor 1 can be performed with high accuracy.

In the motor 1 according to the present embodiment, the brush 40 is a copper-containing carbon brush, and the copper content in the brush 40 is 50 wt% or more.

By setting the copper content in the brush 40 to 50 wt% or more in this way, the contact resistance R between the brush 40 and the commutator segment 31 can be reduced. Accordingly, even if the impedance Z of the winding 22 between two adjacent segments 31 becomes small due to the high output of the motor 1, the relational expression of 2.ltoreq.z/r.ltoreq.4 can be easily satisfied.

Further, when the copper content in the brush 40 exceeds 60%, spark becomes much and the life of the brush 40 decreases, and the life of the motor 1 decreases. Accordingly, the copper content in the brush 40 may be 60 wt% or less.

In the motor 1 according to the present embodiment, the length of the brush 40 in the direction along the axial center C of the rotary shaft 21 may be 2 times or more the length of the brush 40 in the sliding direction.

This can increase the contact area between the brush 40 and the commutator segment 31, and therefore, the contact resistance between the brush 40 and the commutator segment 31 can be reduced. Thus, even if the impedance Z of the winding 22 between two adjacent segments 31 becomes small due to the high output of the motor 1, the motor 1 can be designed so that the relational expression of 2.ltoreq.z/r.ltoreq.4 is easily satisfied.

Further, when the length of the brush 40 in the sliding direction is increased, the current value flowing through the brush 40 and the winding 22 increases, and the motor performance changes, but by increasing only the length of the brush 40 in the direction of the axial center C of the rotary shaft 21, the current value can be prevented from increasing.

Further, although the length of the brush 40 in the direction of the axial center C of the rotary shaft 21 is not particularly limited, if the length of the brush 40 in the direction of the axial center C of the rotary shaft 21 becomes excessively large, the size (particularly the height) of the motor 1 as a whole becomes excessively large, the area of the sliding contact surface between the brush 40 and the commutator segments 31 becomes large, and the sliding loss increases, so that the efficiency of the motor 1 is lowered. Therefore, the length of the brush 40 in the direction of the shaft center C of the rotary shaft 21 may be 4 times or less the length of the brush 40 in the sliding direction.

In the motor 1 according to the present embodiment, the brush 40 may contain SiO in an amount of 0.1 wt% or more and 3 wt% or less ₂ Or an additive to SiC.

SiO ₂ Or SiC functions as a grinding agent for cleaning the surface of the segment 31. Thus, the brush 40 contains SiO ₂ Or SiC, it is possible to suppress the formation of irregularities and level differences on the surface of the commutator segments 31 due to sliding contact between the brushes 40 and the commutator segments 31. This can suppress a decrease in the contact area between the brush 40 and the commutator segment 31, and thus an increase in the contact resistance between the brush 40 and the commutator segment 31 can be suppressed. As a result, the current ripple of the current waveform is stable, and thus the accuracy of the rotational speed control is improved.

(modification)

The motor 1 according to the present disclosure has been described above based on the embodiments, but the present disclosure is not limited to the above embodiments.

For example, in the above embodiment, the brushes 40 are provided in two, but not limited thereto. For example, the number of brushes 40 may be one or three or more. The motor 1 may have an auxiliary brush in addition to the brush 40 serving as the energizing brush.

In the above embodiment, the stator 10 is constituted by the magnet 11, but is not limited thereto. For example, the stator 10 may be composed of a stator core and a winding wound around the stator core.

In the above embodiment, the rotor 20 has the iron core, but is not limited thereto. That is, the motor 1 in the above embodiment can also be applied to a coreless motor having no iron core. For example, the motor 1 according to the above embodiment can be applied to a flat motor as a coreless motor in which magnetic fluxes of the stator 10 and the rotor 20 are generated in the direction of the axial center C of the rotary shaft 21.

Other modes of applying various modifications to the above-described embodiments and modifications that can be conceived by those skilled in the art, and modes of implementing any combination of components and functions in the embodiments and modifications without departing from the gist of the present disclosure, are also included in the present disclosure.

Industrial applicability

The present disclosure can be applied to various products including a motor that detects a rotational speed to perform rotational speed control.

Description of the reference numerals

1: a motor; 10: a stator; 11: a magnet; 20: a rotor; 21: a rotation shaft; 21a: a first end; 21b: a second end; 22: a winding; 22a: a coil section; 23: a rotor core; 24: an insulator; 30: a commutator; 31: a reversing sheet; 32: molding a resin; 40: a brush; 50: and a frame.

Claims

1. A motor that detects a rotational speed of the motor from a waveform of a current flowing in the motor, the motor comprising:

a rotation shaft;

a commutator mounted on the rotary shaft and having a plurality of commutator segments arranged along a circumferential direction of the rotary shaft;

a brush in contact with the plurality of segments;

an iron core mounted to the rotating shaft; and

a winding wound around the core and connected to at least one of the plurality of segments,

wherein the motor is driven with an input voltage of 48V or less,

when the impedance of the winding between two adjacent segments among the plurality of segments is set to Z and the contact resistance between the brush and the segment of the plurality of segments contacting the brush is set to R,

when the rotating speed of the motor is detected, the relation of Z/R being more than or equal to 2 and less than or equal to 4 is satisfied.

2. The motor according to claim 1, wherein,

2.5≤Z/R≤3.5。

3. the motor according to claim 1 or 2, wherein,

the input voltage is below 25V,

the maximum output of the motor is 200W or more.

4. The motor according to any one of claims 1 to 3, wherein,

the brush is a copper-containing carbon brush,

the copper content in the brush is 50 wt% or more.

5. The motor according to any one of claims 1 to 4, wherein,

the length of the brush in the axial direction of the rotating shaft is 2 times or more the length of the brush in the sliding direction.

6. The motor according to any one of claims 1 to 5, wherein,

the brush contains 0.1 to 3 wt% of SiO ₂ Or SiC.