WO2021079508A1

WO2021079508A1 - Electric motor

Info

Publication number: WO2021079508A1
Application number: PCT/JP2019/041996
Authority: WO
Inventors: ザイニアリフ; 友矩佐々木; 亮哉吉村; 裕介坂本; 詠吾十時
Original assignee: 三菱電機株式会社
Priority date: 2019-10-25
Filing date: 2019-10-25
Publication date: 2021-04-29
Also published as: JPWO2021079508A1; TW202118193A

Abstract

An electric motor comprising: a stator (5) having a stator core (3) having a ring-shaped core back (3b) and a plurality of teeth (3a) protruding from the core back (3b) to the inner peripheral side of the core back (3b), and an armature winding (4) that is arranged in a slot (18), which is a space between the two adjacent teeth (3a), and wound around each of the plurality of teeth (3a) in a concentrated winding manner; and a rotor (13) having a permanent magnet (15), the stator (5) being arranged outside the rotor (13), wherein the outer diameter D_out and the inner diameter D_in of the stator (5) satisfy the relationship of D_out/D_in ≥ 2.1, the width T_w of each of the plurality of teeth (3a) and the width C_b of the core back (3b) satisfy the relationship of 2.1 ≥ C_b/T_w ≥ 1.1, and the length L_c of the stator core (3) in the direction along a rotation axis (50) and the inner diameter D_in of the stator (5) satisfy the relationship of L_c/D_in ≥ 1.5.

Description

Electric motor

The present invention relates to an electric motor having a stator core having a plurality of teeth protruding from an annular core bag to the inner peripheral side of the core bag.

The electric motor has an annular stator and a rotor arranged inside the stator. The stator of the electric motor has a stator core and an armature winding wound around the stator core. Generally, the stator core has an annular core back and a plurality of teeth protruding radially from the core back, and the armature winding is wound around the teeth. The space between two adjacent teeth is called a slot.

In the electric motor disclosed in Patent Document 1, the annular stator core is divided into a plurality of iron core pieces having a core back portion and a teeth portion in the circumferential direction, and among the boundary portions of the core back portions of the adjacent iron core pieces. There is a recess in the area facing the slot. The electric motor disclosed in Patent Document 1 has a stator core by making the width of the middle portion of the teeth orthogonal to the radial direction less than twice the radial width of the core back portion which is the thinnest due to the dent. By fitting it into the frame, the compressive stress generated in the stator core is relaxed and iron loss is suppressed.

Japanese Unexamined Patent Publication No. 2010-279126

Electric motors for applications such as shakers or injection molding machines may be required to frequently reverse the direction of rotation or accelerate to a high rotation speed in a short time. In order to satisfy these requirements, it is advantageous that the torque of the electric motor is large, and that the moment of inertia of the rotor is small. The torque of the electric motor is proportional to the square of the diameter of the rotor. On the other hand, the moment of inertia of the rotor is roughly proportional to the fourth power of the diameter of the rotor. Therefore, the moment of inertia of the rotor and the torque of the electric motor are in a relationship that the torque also decreases when the diameter of the rotor is reduced in order to reduce the moment of inertia. Therefore, in order to satisfy the above requirements, it is necessary to suppress a decrease in torque efficiency so that as large a torque as possible can be obtained even when the diameter of the rotor is reduced. Patent Document 1 does not disclose the conditions for suppressing the decrease in torque efficiency when reducing the moment of inertia of the rotor.

The present invention has been made in view of the above, and an object of the present invention is to obtain an electric motor in which the moment of inertia of the rotor is reduced while suppressing the decrease in torque.

In order to solve the above-mentioned problems and achieve the object, the present invention presents a stator core having an annular core back and a plurality of teeth protruding from the core back to the inner peripheral side of the core back, and two adjacent cores. A stator having an armature winding arranged in a slot which is a space between teeth and wound around each of a plurality of teeth in a concentrated winding, and a rotor having a permanent magnet are provided on the outside of the rotor. It is an electric motor in which a stator is placed. The outer diameter D _out and the inner diameter D _{in of the} stator satisfy the relationship of D _out / D _{in ≧ 2.1.} _{The width T w} of each of the plurality of teeth and the width C _{b of the} core back satisfy the relationship of 2.1 ≧ C _b / T _{w ≧ 1.1.} _{The length L c} of the stator core in the direction along the rotation axis of the rotor and the inner diameter D _{in of} the stator satisfy the relationship of 14.3 ≧ L _c / D _{in ≧ 1.5.}

The electric motor according to the present invention has the effect of being able to reduce the moment of inertia of the rotor while suppressing the decrease in torque efficiency.

Cross-sectional view along the rotation axis of the electric motor according to the first embodiment of the present invention. Cross-sectional view perpendicular to the rotation axis of the rotor and stator of the electric motor according to the first embodiment. The figure which shows the shape of the iron core piece of the electric motor which concerns on Embodiment 1. The figure which shows the relationship between the ratio of the width of the core back of the electric motor which concerns on Embodiment 1 and the width of a tooth, and torque efficiency. The figure which shows the relationship between the ratio of the core width of the electric motor which concerns on Embodiment 1 and the inner diameter of a stator, and torque efficiency. The figure which shows the relationship between the amount of deflection of the rotor of the electric motor which concerns on Embodiment 1 and the size of an air gap part. The figure which shows the definition of the slot opening angle of the electric motor which concerns on Embodiment 1. The figure which shows the relationship between the ratio of the slot opening angle of the electric motor which concerns on Embodiment 1 and the angle per tooth, and torque efficiency. Cross-sectional view perpendicular to the rotation axis of the rotor and stator of the electric motor according to the second embodiment of the present invention. The figure which shows the shape of the tooth of the electric motor which concerns on the modification of Embodiment 1 or Embodiment 2 of this invention.

The electric motor according to the embodiment of the present invention will be described in detail below with reference to the drawings. The present invention is not limited to this embodiment.

Embodiment 1.
FIG. 1 is a cross-sectional view taken along the rotation axis of the electric motor according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view perpendicular to the rotation axis of the rotor and stator of the electric motor according to the first embodiment. The electric motor 1 has a stator 5, a frame 6, a housing 7, and a rotor 13. The frame 6 has a cylindrical shape, and a stator 5 is press-fitted into the inner wall surface. One end 6a of the frame 6 is covered with a housing 7. The housing 7 is fixed to one end 6a of the frame 6 by a bolt 8. The other end 6b of the frame 6 is covered with an end cover 19. A gap called an air gap portion 20 is formed between the rotor 13 and the stator 5.

The stator 5 has a stator core 3 and an armature winding 4 that is wound around the stator core 3 via an insulator (not shown). The rotor 13 includes a shaft 11 supported by the first bearing 9 and a second bearing 10, a rotor core 14 through which the shaft 11 penetrates, and a rotor at equal pitches along the circumferential direction of the rotor core 14. It has a plurality of permanent magnets 15 attached to the outer periphery of the iron core 14. The first bearing 9 is fitted in the housing 7. The second bearing 10 is fitted in the wall portion 12 of the frame 6. The central axis of the shaft 11 coincides with the rotating shaft 50 of the rotor 13. In the electric motor 1 according to the first embodiment, the rotor 13 has 10 permanent magnets 15 installed on the outer circumference of the rotor core 14. The permanent magnet 15 is a rare earth magnet or a ferrite magnet. For the purpose of protecting the permanent magnet 15 and preventing scattering, a cover made of a non-magnetic material such as stainless steel or aluminum in a cylindrical shape may be installed on the outer peripheral side of the permanent magnet 15.

Further, the stator 5 includes a connection portion 16 connected to the armature winding 4. When a U-phase, V-phase, and W-phase three-phase alternating current is supplied to the armature winding 4 through the connection portion 16, the rotor 13 rotates.

A pulley 17 is attached to one end of the shaft 11. A rotation transmission member (not shown) such as a V-belt is hung on the pulley 17, and the rotation of the shaft 11 is transmitted to a load (not shown) through the rotation transmission member.

The stator core 3 and the rotor core 14 are formed by laminating a magnetic core material such as an electromagnetic steel plate. In the assembled state of the electric motor 1, the stacking direction of the magnetic core material is the direction along the rotation shaft 50. _{The length L c} of the stator core 3 in the direction along the rotation axis 50 is the same as the length of the rotor core 14 in the direction along the rotation axis 50. _{Hereinafter, the length L c} of the stator core 3 in the direction along the rotation axis 50 is referred to as a core width L _c .

The stator core 3 has an annular core back 3b in a cross section perpendicular to the rotation axis 50, and twelve teeth 3a protruding toward the inner diameter side from the core back 3b. A slot 18 is formed between two adjacent teeth 3a, which is a space in which the armature winding 4 is arranged. The rotor 13 has 12 slots 18 formed in the same number as the teeth 3a. Since the electric motor 1 according to the first embodiment includes 10 permanent magnets 15 arranged on the outer periphery of the

rotor core

14 and 12 slots 18, a surface permanent magnet motor having 10 poles and 12 slots is used. is there. _{In the electric motor 1, the number of magnetic poles N p} formed by the permanent magnet 15 on the outer peripheral side of the rotor 13 _{and the number N t} of teeth of the stator 5 have a relationship of N _p / N _{t = 5/6.}

An armature winding 4 is wound around each of the teeth 3a. The armature winding 4 wound around each of the teeth 3a is assigned to either the U phase, the V phase, or the W phase. The armature winding 4 assigned to the U phase is called the U phase winding, the armature winding 4 assigned to the V phase is called the V phase wiring, and the armature winding 4 assigned to the W phase is called the W phase wiring. .. U-phase wiring, V-phase wiring, and W-phase wiring are arranged for each set of two adjacent teeth 3a as a set. That is, the 12 teeth 3a include U-phase wiring, U-phase wiring, V-phase wiring, V-phase wiring, W-phase wiring, W-phase wiring, U-phase wiring, U-phase wiring, V-phase wiring, and V-phase wiring. The armature winding 4 is arranged in the order of the W-phase wiring and the W-phase wiring. The stator 5 has a so-called centralized winding structure in which a single phase armature winding 4 is wound around one tooth 3a.

A brim portion 32 is provided at the tip portion 311a on the inner diameter side of the teeth 3a facing the rotor 13. By providing the brim portion 32 on the teeth 3a, cogging torque and torque ripple are suppressed. Further, by providing the brim portion 32 on the teeth 3a, the magnetic flux generated by the permanent magnet 15 can be efficiently received by the stator 5.

FIG. 3 is a diagram showing the shape of the iron core piece of the electric motor according to the first embodiment. The stator core 3 is configured by arranging a plurality of iron core pieces 31 divided in the circumferential direction in an annular shape. The plurality of iron core pieces 31 are fixed to the inner peripheral surface of the frame 6 in a state of being arranged in the circumferential direction, so that they are connected to each other to form an annular stator core 3. The iron core piece 31 is fixed to the inner peripheral surface of the frame 6 by press fitting or adhesion.

Each of the iron core pieces 31 includes a teeth 3a and a core back 3b. In the teeth 3a, the main direction of the magnetic flux is the radial direction at the center of the circumferential direction indicated by the arrow A in FIG. In the core back 3b, the main direction of the magnetic flux is the circumferential direction indicated by the arrow B in FIG. The teeth 3a has a so-called straight teeth shape, and the width, which is the dimension of the teeth 3a in the circumferential direction of the rotating shaft 50, is constant regardless of the position in the radial direction. In the following description, the length which is the dimension of the teeth 3a in the radial direction of the circle centered on the rotation shaft 50 is T _l , the width of the teeth 3a is T _w , and the width of the core back 3 _b is C b. The width T _{w of the} teeth 3a and the width C _b of the core back 3b are dimensions in a direction orthogonal to the main direction of the magnetic flux. Further, in the following description, the diameter of the circle connecting the tip portion 311a of the teeth 3a, that is, the inner diameter of the stator 5 is defined as D _in , and the diameter of the circle formed by the outer peripheral portion 311b of the core back 3b, that is, the outer diameter of the stator 5. _Let it be D out.

Since the torque of the electric motor 1 is proportional to the product of the side area of the rotor 13 and the radius, it is known to be proportional to the square of the diameter of the rotor 13. Further, the diameter of the rotor 13 can be regarded as substantially equal to the inner diameter of the stator 5 if the size of the air gap portion 20 can be ignored. Further, when the size of the entire motor 1 is specified, the outer diameter of the stator 5 is determined by subtracting the thickness of the frame 6 from the size of the entire motor 1. Therefore, when the size of the entire electric motor 1 is specified, it is desirable that the value of _{D out} / D _{in is small in order to increase the torque generated by the electric motor 1.} On the other hand, since the moment of inertia I of a cylinder having a diameter D is ^{calculated by I = ρπD 4} h / 32 g, it is known that the moment of inertia of the rotor 13 is proportional to the fourth power of the diameter of the rotor 13. .. Note that ρ is the density of the rotor, π is the pi, and g is the gravitational acceleration. Therefore, when the size of the entire motor 1 is specified, it is desirable that the value of _{D out} / D _{in is large in order to reduce the moment of inertia of the rotor 13.} As described above, the torque generated by the electric motor 1 and the moment of inertia of the rotor 13 are in a trade-off relationship.

As described above, since the inner diameter of the stator 5 can be regarded as equal to the outer diameter of the rotor 13, the torque of the motor 1 is approximately proportional to the square of the inner diameter of the stator 5, and the moment of inertia is approximately the inner diameter of the stator 5. Is proportional to the fourth power of. Since the rotational acceleration of the electric motor 1 is obtained by dividing the torque by the moment of inertia, it is advantageous to reduce the inner diameter of the stator 5 if the electric motor 1 is designed with an emphasis on the rotational acceleration. Therefore, in the first embodiment, _{the value of D out} / D _in is limited to 2.1 or more.

The _{reason for limiting the D out} / D _in value to 2.1 or more will be described below. The magnetic resistance per tooth 3a is represented by the following formula (1).

Here, R _g is the reluctance of the air gap portion 20, and R _c is the reluctance of the teeth 3a. R _g is represented by the following formula (2). R _c is represented by the following equation (3).

Here, _gl is the length of the air gap portion 20, and g _w is the width of the air gap portion 20. Further, T _l is the length of the teeth 3a, and T _w is the width of the teeth 3a. Further, μ ₀ is the magnetic permeability of the vacuum, and μ is the magnetic permeability of the stator core 3. However, in the above equations (2) and (3), in consideration of the resistance of the magnetic circuit, the length _gl of the air gap portion 20 includes the length of the permanent magnet 15 in addition to the length of the physical void. .. According to Hopkinson's law, the magnetomotive force F _m and the magnetic flux Φ of the magnetic circuit satisfy the following equation (4).

By differentiating the above equation (4) with Φ, the following equation (5) is obtained.

The left side of the above equation (5) means the amount of increase in electromotive force required to increase the magnetic flux by one unit, and it is necessary to make this value as small as possible in order not to reduce the torque linearity described later. is there. When the second term on the right side of the above equation (5) is decomposed, among the components of _{R m} _{, R g} does not change with respect to the magnetic flux and the derivative becomes 0, so that the following equation (6) holds.

Therefore, since it is only necessary to consider the differentiation of the stator core 3, the above equation (5) can be rewritten to the following equation (7).

Assuming that the magnetic flux density in the stator core 3 is B, the following equations (8) and (9) hold.

Further, assuming that the magnetic field in the stator core 3 is H, the magnetic field H and the magnetic flux density B have the relationship of the following equation (10).

Substituting the above equation (10) into the above equation (3) and partially differentiating it with respect to the magnetic flux density B gives the following equation (11).

Substituting the above equations (9) and (11) into the above equation (7), the amount of increase in the magnetomotive force required to increase the magnetic flux by one unit is expressed by the following equation (12).

Here, the first term on the right side of the above equation (12) is represented by the following equation (13), and the second term on the right side is represented by the following equation (14).

_{If R'g} <_R'c , it means that the stator core 3 has a larger contribution to the amount of increase in the magnetomotive force required to increase the magnetic flux by one unit than the air gap portion 20. A motor in which the stator core 3 contributes more to the amount of increase in the magnetomotive force required to increase the magnetic flux by one unit than the air gap portion 20 suppresses the magnetic resistance of the stator core 3. The magnetic flux can be increased efficiently.

Normally, as shown in the following formula (15), the length _gl of the air gap portion 20 is set to about 1/10 of the inner diameter D _{in of the stator 5.}

As shown in the following equation (16), the width g _w of the air gap portion 20 can be approximated by dividing the circumference length of the inner diameter D _in of the stator 5 by the number of slots N _s.

The length T _l of the teeth 3a and the width T _{w of the} teeth 3a have a physically set upper limit. The length T _l of the teeth 3a can be secured up to only half of the difference between the inner diameter D _in of the stator 5 and the outer diameter D _{out of the stator 5.} Further, the width T _{w of the} teeth 3a can be secured only up to the same length as the width of the air gap portion 20 at the maximum. Therefore, the following equation (17) and the following equation (18) hold.

Here, k ₁ and k ₂ are constants larger than 0 and smaller than 1. The values of k ₁ and k ₂ differ depending on the design, but since they are set so as to maintain the aspect ratio from the maximum value, they can be approximated by the following equation (19).

The value of (∂H / ∂B) in the stator core 3 differs depending on the magnitude of the magnetic flux density B, but most of the iron-based core materials used for the stator 5 are around 2T. It is known to saturate with magnetic flux density. In the first embodiment, since the motor having a low moment of inertia and a high torque is to be realized, the stator core 3 is almost saturated. In the case of an iron-based core material, the value of (∂H / ∂B) near 2T is about 1.5 × 10 5 m / H, which is ^{1/5 based on} _{the magnetic permeability μ 0 of the vacuum.} . Corresponds to 3μ _0.

The results, towards the stator core 3 than the air gap portion 20, a condition for contribution to increase amount of required magnetomotive force to increase one unit of magnetic flux is increased R _{'g <R'} _c Substituting into, the following equation (20) is obtained.

By rearranging the above formula (20), the following formula (21) can be obtained.

From the above, if D _out / D _in is approximately 2.1 or more, the reluctance of the stator core 3 has a greater effect on the decrease in torque linearity than the reluctance of the air gap portion 20, and therefore the core shape It can be seen that the effect of improving linearity by devising is particularly large.

When _{the value of D out} / D _in is approximately 2.1 or more, the radial length of the iron core piece 31 becomes larger than the outer diameter of the rotor 13. Therefore, the teeth 3a has a shape in which _{the length T l} is larger than the width T _w. Since the magnetic reluctance of the teeth 3a with respect to the magnetic flux passing through the teeth 3a in the radial direction is proportional to the radial length of the teeth 3a and inversely proportional to the width in the circumferential direction, the length T _l of the teeth 3a is larger than the width T _w. In the case of the iron core piece 31 having a shape, the magnetic resistance of the teeth 3a becomes extremely large. Therefore, the magnetic flux generated from the permanent magnet 15 of the rotor 13 and interlinking with the armature winding 4 of the stator 5 is reduced, and the torque tends to be reduced as compared with the case where the width of the teeth 3a can be secured widely. .. Further, in the case of the iron core piece 31 in which the length T _l of the teeth 3a is larger than the width T _w , the teeth 3a are likely to be magnetically saturated, so that the amount of torque increase is proportional to the amount of current supplied to the armature winding 4. A phenomenon occurs in which the torque is less likely to increase as the amount of current increases without increasing. The phenomenon in which the torque is less likely to increase as the amount of current increases is called "decrease in torque linearity".

When the torque linearity decreases, the amount of current required to output the target torque increases, so the Joule loss generated by the electrical resistance of the armature winding 4 increases.

In the electric motor 1 according to the first embodiment, the _{moment of inertia is reduced by setting the D out} / D _in value to 2.1 or more, and the width C _b of the core back 3b is increased to increase the magnetic resistance of the magnetic path. Is reduced to prevent a decrease in torque linearity. FIG. 4 is a diagram showing the relationship between the ratio between the width of the core back and the width of the teeth of the electric motor according to the first embodiment and the torque efficiency. In order to obtain a relational expression that does not depend on the size of the entire motor 1, the width C _b of the core back 3b is standardized by dividing by the width T _w of the teeth 3a, and the torque is standardized by dividing by the Joule loss. ing. The magnitude of torque per joule loss is called torque efficiency. In FIG. 4, the torque efficiency is shown normalized with the maximum value set to "1".

The torque efficiency of the electric motor 1 is maximized when the value of the ratio C _b / T _w _{of the width C b} of the core back 3b and the width T _{w of the} teeth 3a is between 1.5 and 1.7. The torque efficiency does not change significantly even if the _{C b} / T _w value changes slightly near the peak, but the slope with respect to the _{C b} / T _{w value increases at a distance from the peak.} In the electric motor 1 according to the first embodiment, the torque efficiency is set to 90% or more by setting the value of _{C b} / T _{w to 1.1 or more.}

Even if the width C _b of the core back 3 b is made too large, the torque efficiency tends to decrease. _{This is because increasing the width C b} of the core back 3b reduces the cross-sectional area of the armature winding 4, increases the electrical resistance, and increases the Joule loss. That is, if the effect of the increase in Joule loss due to the decrease in the cross-sectional area of the armature winding 4 exceeds the effect of improving the torque linearity due to the decrease in the magnetic resistance, the torque efficiency decreases even if _{the width C b of the core back 3b increases.} To do. As shown in FIG. 4, the electric motor 1 according to the first embodiment has a torque efficiency of 90% or more by setting the value of _{C b} / T _{w to 2.1 or less.}

Heat-resistant class F windings specified in JIS C 4003 are widely used for motors. The permissible temperature of the heat resistant class F winding is 155 ° C. Since the ambient temperature of the motor during operation is 40 ° C., the temperature rise of the winding that can be tolerated due to the loss is 115 ° C. Further, since a margin of 15 ° C. is required to absorb the influence of variations in motor characteristics due to manufacturing variations, the actual allowable increase in winding temperature is 100 ° C. The motor 1 according to the first embodiment is designed so that a larger current is applied in order to maximize the motor output, but the winding temperature rise is 90 ° C., which is slightly lower than the permissible rise temperature of 100 ° C. There is. Therefore, when the torque efficiency shown in FIG. 4 decreases by 10% and falls below 90%, the winding temperature rises by 10% and exceeds the allowable temperature of the winding. Therefore, the electric motor 1 according to the first embodiment is designed so that the torque efficiency is 90% or more.

Further, the torque of the electric motor 1 is basically proportional to the core widths L _c, the core width L _c is significantly shortened, torque is smaller than the value proportional to the core widths L _c. This is because the interlinkage magnetic flux leaks in the direction along the rotation shaft 50 at both ends of the stator core 3 in the direction along the rotation shaft 50. On the other hand, when the core width L _c is long, the Joule loss in the armature winding 4 is substantially proportional to the _{core width L c} as well as the torque. On the other hand, when the core width L _c is extremely shortened, the influence of the resistance of the coil end portion, which is a portion of the armature winding 4 that does not face the permanent magnet 15 at both ends of the stator 5 in the direction along the rotation axis 50. Cannot be ignored, so _{that it does not decrease in proportion to the core width L c} , and a certain amount of Joule loss remains.

Consequently, the torque obtained by dividing the torque in joules loss efficiency, although not less than a certain value core width L _c can be regarded as substantially constant value without depending on the core width L _c, the core width L _c is It decreases when it becomes shorter than a certain value. FIG. 5 is a diagram showing the relationship between the ratio of the core width of the electric motor according to the first embodiment to the inner diameter of the stator and the torque efficiency. As shown in FIG. 5 _{, if the value of L c} / D _in , which is the ratio of _{the core width L c} of the motor 1 to the inner diameter D _{in of the} stator 5, is 1.5 or more, the torque efficiency is 100%. ing. Therefore, in the electric motor 1, the torque efficiency is set to 100% by setting the value of _{L c} / D _{in to 1.5 or more.}

On the other hand, _{if the value of L c} / D _in is too large, the rotor 13 bends and the rotor 13 and the stator 5 come into contact with each other. Therefore, the amount of deflection δ is set smaller than that of the air gap portion 20. There is a need to. FIG. 6 is a diagram showing the relationship between the amount of deflection of the rotor of the electric motor according to the first embodiment and the size of the air gap portion. Normally, the size of the air gap portion 20 _{is set to about 1/10 of the diameter D in} , so the amount of deflection δ must be smaller than _{D in / 10.} The Young's modulus E of the shaft 11 made of steel is generally 20.6 Gpa. When the value of L _c / D _in is 14.3, δ / (D _in / 10), that is, the amount of deflection of the shaft 11 with respect to the size of the air gap portion 20 is the same, and the rotor 13 is the stator 5 Contact. Therefore, in the first embodiment, _{the upper limit of L c} / D _in is set to 14.3.

FIG. 7 is a diagram showing a definition of a slot opening angle of the electric motor according to the first embodiment. As shown in FIG. 7, the central angle of the arc 62 connecting the corners 61 of the two teeth 3a sandwiching the slot 18 is the slot opening angle _So. If the slot opening angle _So is too small, the arc 62 becomes short and the distance between the two corners 61 becomes short, so that the magnetic flux generated by the armature winding 4 does not pass through the rotor 13 and the adjacent teeth 3a A phenomenon called magnetic flux leakage occurs, which leads to a decrease in torque linearity. Therefore, the electric motor 1 according to the first embodiment, the slot opening angle S _o is sized to decrease the torque linearity does not occur.

Conditions of the desired slot opening angle S _o varies depending the number of teeth. When there are many number of teeth is fewer magnetic flux responsible is per one tooth 3a, since each also reduced the stator magnetomotive force with the armature winding 4 of the teeth 3a, necessary to so large a slot opening angle S _o Will disappear. Therefore, when defines a desired slot opening angle S _o, at an angle T _o per one tooth 3a shown in FIG. 7, it is necessary to standardize by dividing the slot opening angle S _o. The angle T _o per one tooth 3a, the central circumferential each of the two slots 18 adjacent to each, it can be said that the center angle formed on the rotational center located on the rotating shaft 50. FIG. 8 is a diagram showing the relationship between the ratio of the slot opening angle of the electric motor according to the first embodiment to the angle per tooth and the torque efficiency. If the value of the slot which is the ratio of the aperture angle _{S o} and the angle _{T o} per one tooth 3a _S _o / _T o of 0.2 or more, the torque efficiency is above 90%. Therefore, the motor _1, by the values of S o / _{T o} and 0.2 or more, and a torque efficiency to 90% or more.

On the other hand, if the teeth tip width T _s to increase the S _{o /} T _o until narrower than the tooth width T _w, torque linearity rather small. At this time, since the cross-sectional area at the tip of the teeth 3a through which the magnetic flux passes is smaller than the cross-sectional area at the tip of the teeth 3a, the magnetic saturation of the tip of the teeth becomes remarkable. Therefore, it is necessary to set the tooth tip width T _s to the tooth width T _{w or more.}

As a secondary effect, the electric motor 1 according to the first embodiment _{has a larger width C b} of the core back 3b than that of a general electric motor, so that the mechanical strength is improved, and vibration due to electromagnetic vibration and vibration and vibration due to electromagnetic vibration force are generated. Noise is reduced. Further, in the electric motor 1 according to the first embodiment, since the inductance of the armature winding 4 is low, the voltage between terminals is particularly low when the rotor 13 is rotated at high speed, and the voltage of the drive system is limited. For example, high torque can be maintained up to higher speeds.

In the electric motor 1 according to the first embodiment, the rotor 1 has a D _out / D _in value of 2.1 or more so that the length Tl of each of the plurality of teeth 3a becomes larger than the _{width T w.} 13 aims to reduce the moment of inertia, and the torque efficiency is to set the value of the value of C _{b /} T _w and S _{o /} T _o to prevent lower than 90%, reducing the moment of inertia Even so, torque can be obtained efficiently.

Embodiment 2.
The electric motor 1 according to the second embodiment of the present invention is different from the electric motor 1 according to the first embodiment in the structures of the stator 5 and the rotor 13. FIG. 9 is a cross-sectional view perpendicular to the rotation axis of the rotor and stator of the electric motor according to the second embodiment of the present invention. The number of teeth 3a included in the stator 5 is 6, and the number of slots 18 formed between two adjacent teeth 3a is 6. Further, in the rotor 13, a permanent magnet 15 is embedded in the rotor core 14. In the rotor 13 according to the second embodiment, a total of eight permanent magnets 15 are embedded in the rotor core 14. Each of the permanent magnets 15 is arranged so that the direction in which the N-pole magnetic flux is concentrated and the direction in which the S-pole magnetic flux is concentrated are orthogonal to each other in the air gap portion 20 between the rotor 13 and the stator 5. In FIG. 9, the magnetization direction of each permanent magnet 15 is indicated by an arrow. Since the permanent magnet 15 is arranged so that the direction in which the N-pole magnetic flux is concentrated and the direction in which the S-pole magnetic flux is concentrated are orthogonal to each other, the permanent magnet 15 is placed on the surface of the rotor 13 facing the air gap portion 20. It forms four magnetic poles. The electric motor 1 according to the second embodiment has four magnetic poles formed by eight permanent magnets 15 embedded in the rotor core 14, and six slots 18, so that the surface permanent magnets have four poles and six slots. It is a motor.

The electric motor 1 according to the second embodiment has a so-called Halbach structure in which magnetic fluxes from a plurality of permanent magnets 15 are concentrated on one magnetic pole of the rotor 13, and is a surface magnet type as in the first embodiment. A larger torque can be obtained than a motor.

In embodiments 1 and 2 above, the number of magnetic poles N _p of the permanent magnet 15 is formed on the surface of the rotor 13 facing the air gap portion 20, the number of teeth N _t of the stator 5 is not limited to the combination of the above .. For example, the same effect can be obtained with an electric motor having 20 poles and 24 slots, 8 poles and 6 slots, or 8 poles and 12 slots. _{That is, the number of magnetic poles N p} formed on the surface of the rotor 13 facing the air gap portion 20 by the permanent magnet 15 _{and the number N t} of teeth of the stator 5 are N _p / N _t = 5/6, N _p. / _N t = 2/3 or should satisfy a relation of _{_{N p / N t = 4/}} 3.

Further, in the above-described first and second embodiments, the teeth 3a of the iron core piece 31 constituting the stator core 3 are straight teeth, but the teeth 3a have the width of the teeth 3a on the inner diameter side and the outer diameter side. It may be different, tapered teeth. FIG. 10 is a diagram showing the shape of the teeth of the electric motor according to the modified example of the first embodiment or the second embodiment of the present invention. In the case of tapered teeth, the same effect can be obtained by defining the average width of the entire teeth 3a as the width T _{w of the teeth 3a.} For example, in the case of FIG. 10, since the portion having the largest width of the teeth 3a is T _w1 and the portion having the smallest width is T _w2 , the average value of the widths of the entire teeth 3a (T _w1 + T _w2 ) / 2 is set. The width T _{w of the} teeth 3a may be set, and the design may be performed in the same manner as in the first and second embodiments.

Further, in the first and second embodiments, the iron core piece 31 forms a three-dimensional stator core 3 by laminating electromagnetic steel sheets, but the present invention is not limited to this. For example, a stator core 3 made of a so-called compressed iron core, which is formed by compacting a magnetic powder, may be used.

Further, in the first and second embodiments, one iron core piece 31 has one tooth 3a, but the present invention is not limited to this. For example, the stator core 3 may be configured by combining a plurality of iron core pieces 31 having a plurality of teeth 3a. Further, a part of the plurality of iron core pieces 31, for example, only the core back 3b may be integrally formed with each other to form the core back 3b of the stator core 3 as a single component.

Further, in the above-described first and second embodiments, the core width L _c is the same as the length of the rotor core 14 in the direction along the rotation axis 50, but is not limited thereto. _{For example, an electric motor having a core width L c} shorter than the length of the rotor core 14 in the direction along the rotation shaft 50, that is, a rotor overhang may be used. _{Further, an electric motor having a core width L c} longer than the length of the rotor core 14 in the direction along the rotation shaft 50, that is, a rotor underhang may be used.

The configuration shown in the above-described embodiment shows an example of the content of the present invention, can be combined with another known technique, and is one of the configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

1 motor, 3 rotor core, 3a teeth, 3b core back, 4 armature winding, 5 stator, 6 frame, 6a one end, 6b other end, 7 housing, 8 bolts, 9 first bearing, 10 2nd bearing, 11 shaft, 12 wall part, 13 rotor, 14 rotor core, 15 permanent magnet, 16 connection part, 17 pulley, 18 slot, 19 end cover, 20 air gap part, 31 iron core piece, 32 brim Part, 50 rotation shaft, 61 corner, 62 arc, 311a tip, 311b outer circumference.

Claims

A plurality of the stator cores having an annular core back and a plurality of teeth protruding from the core back to the inner peripheral side of the core back, and a plurality of the said ones arranged in a slot which is a space between two adjacent teeth. An electric motor having a stator having an armature winding wound around each of the teeth in a concentrated winding and a rotor having a permanent magnet, and the stator being arranged outside the rotor.
The outer diameter D out and the inner diameter D in of the stator satisfy the relationship of D out / D in ≧ 2.1.
The width T w of each of the plurality of teeth and the width C b of the core back satisfy the relationship of 2.1 ≧ C b / T w ≧ 1.1.
The length L c of the stator core in the direction along the rotation axis of the rotor and the inner diameter D in of the stator satisfy the relationship of 14.3 ≧ L c / D in ≧ 1.5. An electric motor featuring.
The electric motor according to claim 1, wherein each of the plurality of the teeth is a straight tooth having a constant width T w.
The number of magnetic poles N p formed by the permanent magnet on the surface of the rotor facing the air gap portion which is the gap between the rotor and the stator and the number N t of the plurality of teeth are N p / N t = 5/6, N p / N t = 2/3 or motor according to claim 1 or 2, characterized by satisfying the relation of N p / N t = 4/ 3.
The electric motor according to any one of claims 1 to 3, wherein the armature winding supplies at least one set of adjacent teeth with a current of the same phase among three-phase alternating currents.
In the cross section perpendicular to the rotation axis, the tip width T s of the tooth and the width T w of the tooth satisfy the relationship of T s ≧ T w , and an arc connecting the corners of the two teeth sandwiching the slot. a slot opening angle S o is the central angle, the angle T o per one said tooth is either one of claims 1 to satisfy the relationship of S o / T o ≧ 0.2 4 of The electric motor according to item 1.
The electric motor according to any one of claims 1 to 5, wherein the stator core is formed by laminating magnetic core materials.