JP6615266B2 - Permanent magnet rotating electric machine - Google Patents

Description

  The present invention relates to a rotating electrical machine having a permanent magnet rotor such as an electric motor or a generator.

  Rotating electrical machines such as electric motors and generators are more demanding to be lighter, thinner and smaller than the market, and recently, demands for energy saving and higher efficiency are increasing as a countermeasure against global warming. In order to realize this, it is necessary to increase the magnetic flux density of the air gap between the stator and the rotor. For this purpose, high magnetic energy magnets such as rare earth magnets tend to be used by being embedded in the rotor core. Furthermore, it is a strong demand to be inexpensive. However, the price of rare earth magnets is increasing year by year, and there is a problem in dealing with low costs. On the other hand, a rotating electrical machine forms a stator and a rotor by laminating silicon steel plates in the axial direction in order to reduce iron loss and increase efficiency. In that case, a silicon steel sheet laminated stator or rotor generally has a two-dimensional shape in which the cross-sectional shape perpendicular to the shaft is the same cross-sectional shape at any position along the axial direction. It is also known that the core of the stator or rotor is a so-called dust core that is compression-molded in a state in which a soft magnetic iron powder is coated with a resin film from a lamination method of silicon steel plates. The dust core is used in some high-speed rotating electrical machines because the eddy current loss in the iron loss can be smaller than that of the silicon steel plate. However, the dust core is inferior in magnetic permeability as compared with a silicon steel plate, and generally hinders high torque in a low speed region.

Basics and application of electric motor drive, author: Hideo Hyakume, P131 Fig. 6-12, P134 Fig. 6-15, Technical Review. On the other hand, there is the above-mentioned reference as related art.

Rotating electric machines are roughly classified into radial gap type and axial gap type.
A brushless DC (hereinafter referred to as BLDC) motor which uses a permanent magnet as a rotor in a conventional general radial gap type rotating electric machine always has a field generated by a permanent magnet orthogonal to a rotating magnetic field generated by an armature current. Since the maximum torque according to the so-called IBL law can be obtained, the quantity used has increased in recent years. BLDC motors are classified into SPM (Surface Permanent Magnet) type in which the magnet is exposed on the rotor surface and IPM (Internal Permanent Magnet) type in which the magnet is embedded inside the rotor core, and the latter is based on the IBL. Since reluctance torque can be obtained in addition to the torque according to the law, it is further used for applications that require high torque. The reluctance torque is generated by a force that attracts iron with an electromagnet. In the IPM type, iron is exposed on the rotor surface in addition to the permanent magnet, and this torque can be utilized. A BLDC motor is generally constructed by laminating a stator core with a silicon steel plate, and a concentrated winding method is adopted for winding when low cost and efficiency are important. The reason for this is that in the radial distributed winding method, the coil end portion that does not contribute to torque generation becomes larger and the copper loss increases, the efficiency decreases, and in concentrated winding, the winding is simple and it is possible to wind directly into the slot. This is because the winding becomes inexpensive. In the case of the concentrated winding method, the number of slots of the stator is limited to 4 to 12 mainly from the viewpoint of the cost of the rotating electrical machine if configured practically. However, the concentrated winding method has a drawback that harmonic magnetic flux is easily generated and vibration noise is increased. The distributed winding method is also employed for applications that particularly require low vibration and low noise.
On the other hand, there is an axial gap type rotating electrical machine that has an air gap in the axial direction. However, because the air gap is opposed to the plane, there are problems such as surface blurring. Compared to the gap type, it is inferior in efficiency and torque. For this reason, there is a problem that is less prevalent than the radial gap type except for special uses such as a flat-shaped electric motor and an electric motor that emphasizes constant speed rotation without much start and stop.
The axial height of the coil end of the concentrated winding method is smaller than that of distributed winding, so the copper loss is reduced and the efficiency is increased, but in order to further increase the efficiency, it does not become the area facing the rotor, contributing to torque generation The area occupied by the coil ends that are not used is also required to generate torque. As one of the solutions, there is a technique in which a so-called overhang shape in which the pole shape of the stator winding portion is protruded in the axial direction or the rotation circumferential direction is formed of a dust core. Since this overhang structure is generally difficult or expensive in a silicon steel sheet laminated type, a dust core that can be molded in three dimensions is advantageous. The compacted iron core is obtained by compression-molding soft magnetic iron powder with a small amount of resin coated with a binder and iron powder, and mixing them for insulation of eddy current. The compacted iron core has the advantage that it has a three-dimensional complicated shape compared to the two-dimensional simple shape of the silicon steel sheet laminated type, and further has a small eddy current loss of iron loss. Although the above-described dust core has the disadvantage that the magnetic flux density is smaller than that of the silicon steel plate, it can be said that the overhang shape is suitable for increasing the efficiency because the area facing the rotor increases.
It is known that high torque can be achieved by adopting an overhang structure for the portion of the stator magnetic pole portion facing the rotor so as to increase the facing area of the rotor. However, there is a problem that the winding of the stator becomes difficult because the stator winding is obstructed by the overhang portion.
Therefore, the rotating electrical machine according to the present invention makes winding work as easy as before, and increases the magnetic flux density of the air gap by using an inexpensive magnet to generate high torque. The dust core is used for an embedded magnet type rotor.

The present invention is realized by the following means.
"Means 1"
A rotating electrical machine having a stator and a rotor, wherein the rotor includes a rotor core made of soft magnetic iron powder and a permanent magnet that is substantially parallel to the shaft inside the rotor core. The iron core is formed such that an axial length in a portion facing the stator is shorter than an axial length in a contact portion of the permanent magnet with the rotor core in the rotor core, and the fixing from the contact portion is performed. The axial length is gradually reduced to the portion facing the child, and is integrally formed with the soft magnetic iron powder along the axial direction . It is a radial gap type rotating electric machine according to means Rukoto.

1) The axial height of the coil end of the stator winding is a space that does not contribute to torque generation. The space is used to expand the rotor in the axial direction, and the rotor core faces the stator. By extracting the magnetic flux from the permanent magnet that is larger than the axial length, the magnetic flux can be condensed up to the length of the stator facing part with the rotor core, so the magnetic flux density of the air gap is increased, and high torque and miniaturization are easily realized. it can.
2) If a rotor core with a saturation magnetic flux density of 2 (T) is used and a neodymium rare earth magnet with a residual magnetic flux density of 1.3 (T) is used, the gap magnetic flux density is 1.3 at the maximum in the SPM system. (T) cannot be exceeded, but in the present invention of the IPM type, the axial magnetic flux density is increased to nearly 2 (T) by expanding the axial direction of the rotor to about 2 / 1.3 = 1.54 times. Can be increased. In the radial gap type, the space of 1.54 times is easily obtained as the shape becomes thinner in the axial direction. Since the generated torque of the BLDC motor is proportional to the gap magnetic flux density, in this case, a torque increase of more than 50% can be expected.
3) In a radial rotating electric machine, if not only the axial length of the magnet but also the radial thickness is appropriately increased, for example, a neodymium magnet can be substituted with a ferrite magnet, and the cost of the rotating electric machine can be reduced.
4) The present invention is effective for both the radial gap type and the axial gap type.

Sectional drawing including the axis | shaft of the radial gap type rotary electric machine of an example of this invention AA sectional view of the rotating electrical machine of FIG. 1 (however, the rotor portion is seen from the axial direction) Sectional view including the axial gap type shaft of the present invention AA sectional view of the rotating electrical machine of FIG. Sectional view including the shaft of a conventional radial gap type rotating electrical machine AA sectional view of the rotating electrical machine of FIG. Explanatory drawing of conventional IPM type rotating electrical machine

  This will be described below with reference to the drawings.

FIG. 1 shows an example of the configuration of a rotating electrical machine to which the present invention is applied, and is a cross-sectional view including a shaft of a radial gap type rotating electrical machine. 2 is a cross-sectional view of the rotary electric machine of FIG. 1 taken along the line AA. However, the rotor part is shown in the figure seen from the axial direction.
1 and 2, reference numeral 1 denotes the rotor core of the present invention. The rotor core 1 is provided with a groove in the axial direction, and a plate-like permanent magnet 7 is embedded therein. In the drawing, four permanent magnets 7 are provided, and N poles and S poles are alternately magnetized to be arranged as a four pole rotor. Reference numeral 2 denotes a stator, which is configured by laminating silicon steel plates. Reference numeral 3 denotes a winding portion. In this figure, since there are 6 slots, there are 6 winding portions, and an example of concentrated winding is shown. Reference numeral 4 denotes a rotating shaft, reference numeral 5 denotes a bearing such as a ball bearing, and reference numeral 6 denotes brackets provided on the left and right sides of the stator 2, and holds the bearing 5 to rotate the rotor core 1 with the stator 2. Maintain an air gap between them.
Referring to FIG. 1, the configuration of the present invention includes a rotor core 1 made of soft magnetic iron powder and a permanent magnet 7 that is substantially parallel to the axis inside the rotor core 1. The axial length of the portion facing the stator 2 is shorter than the axial length of the contact portion with the permanent magnet 7 in which the rotor core 1 is embedded. That is, the coil portion 3 has a protruding axial height of the coil end, and this space portion does not directly contribute to torque generation. Therefore, the rotor space length and the magnet length are increased in the axial direction using the space in the axial direction, and the magnetic flux is taken out from the permanent magnet 7 where the rotor core 1 is opposed to the stator 2 and is larger than the axial length. The length in the axial direction is gradually reduced from the contact portion between the radially outer portion of the magnet 7 and the rotor core 1 to the length of the stator facing portion. According to such a shape, since the magnetic flux can be condensed at the portion of the rotor core 1 facing the stator 2, the magnetic flux density in the air gap is increased, and high torque and downsizing can be easily realized. The rotor core 1 can be formed easily and inexpensively if it is a sintered iron core made of soft magnetic iron or a powder iron core coated with a soft magnetic iron with a resin powder and subjected to a compression heat treatment. However, if this is to be realized by a silicon steel sheet laminating system, it will be expensive and complicated, including a punching die. Furthermore, in the case of the soft magnetic iron composition, the magnetic flux permeability has no directivity but is uniform, but in the lamination type, the magnetic flux tends to pass in the rolling direction but difficult to pass in the lamination direction. The configuration is inappropriate. 1 and 2 show the inner rotor type, the present invention also applies to the outer rotor type as it is. The above applies not only to electric motors but also to generators.

  For example, if a rotor core having a saturation magnetic flux density of 2 (T) is used and a neodymium rare earth magnet having a residual magnetic flux density of 1.3 (T) is used, the permanent magnet is exposed on the air gap surface in the SPM type. Therefore, the gap magnetic flux density cannot exceed 1.3 (T) at the maximum, but in the present invention of the IPM type, the axial direction of the rotor is expanded to about 2 / 1.3 = 1.54 times. Thus, the gap magnetic flux density can be increased to nearly 2 (T). In the radial gap type, this 1.54 times space can be obtained more easily in a thin shape in the axial direction. This is because the axial height of the coil end is constant regardless of the opposing length of the stator and rotor, and the torque generated by the BLDC motor is proportional to the air gap magnetic flux density. In this case, a torque increase of more than 50% is expected. it can. That is, the torque can be increased by 50% without increasing the size of the motor and by a very simple and easy to implement method.

The permanent magnet 7 in FIGS. 1 and 2 does not necessarily have a plate shape. The permanent magnet shape seen from the axial direction in FIG. 2 may be a U-shape or a V-shape that opens outward in the radius direction. Alternatively, it may be an inverted square shape that opens in the radially outward direction. However, it must be parallel to the axis.
The magnetization of the embedded magnet is magnetized in the radial direction. In this case, if the magnet thickness in the radial direction is increased, the magnetomotive force of the magnet is proportional to the magnet thickness length and can be increased.
When a neodymium magnet is replaced with a ferrite magnet in its original shape, the torque decreases by about 50% to 70%. However, if the present invention is applied, and if the thickness of the magnet in the radial direction is increased as necessary, the ferrite magnet However, torque values close to those of neodymium magnets can be expected. Even if the ferrite magnet is 1.5 times the axial length and twice the thickness of the radial magnet, so even if the volume is three times the volume of the neodymium magnet, the magnet cost is the ferrite magnet. Is cheap enough.

  FIG. 3 is a diagram in which the present invention is applied to an axial gap type rotating electrical machine, and includes a shaft. 4 is a cross-sectional view of the rotary electric machine of FIG. 3 taken along the line AA. Referring to FIGS. 3 and 4, the rotating electric machine includes a stator 11, a winding portion 12 thereof, and a rotor. The rotor has a rotor core 9 made of soft magnetic iron powder, and a permanent magnet 8 that exists between the rotor core 9 and the back yoke 10 in the axial direction. The back yoke 10 is made of a magnetic material and is supported on the rotating shaft 4 via a bearing 13. In the rotor core 9, the area of the portion facing the stator 11 is smaller than the area of the contact portion with the permanent magnet 8 in the axial direction, and the permanent magnet has a larger area than the air gap facing portion. 8 is an axial gap type rotating electrical machine in which the magnetic flux collected from 8 is condensed in a rotor core 9 whose area is gradually reduced in the axial direction to increase the magnetic flux density of the air gap. Also in this case, without increasing the motor size, as shown in FIG. 3, a possible guide for the degree of magnetic flux condensation is to increase the radial length of the permanent magnet 8 up to the radial length of the winding portion 12 in the radial direction. Yes, it is the ratio to the radial length of the air gap facing portion. This ratio in FIG. 3 is 1.5 times, and a torque increase of nearly 50% is possible. In FIG. 4, the stator is an example of concentrated winding of 6 slots and 6 coils. Although illustration of the configuration of the rotor is omitted, there are four poles in which N poles and S poles are alternately arranged, and the rotor configuration in FIG. 2 is developed in an axial gap.

  FIG. 5 shows an example of the prior art, and FIG. 6 is a cross-sectional view taken along line AA of FIG. The configuration of the stator and the bracket is the same as in FIG. The rotor core is a laminated type of silicon steel plates, and permanent magnets 15 shorter in the axial direction than the permanent magnets 7 of the present invention are embedded in the grooves. Comparing FIG. 5 and FIG. 1, it can be easily understood whether the present invention is an effective means capable of increasing the torque with a simple configuration. The illustration of the prior art of the axial gap is omitted. Non-patent document 1 (corresponding to FIG. 7 attached to this specification) is shown as a reference. FIGS. 7A and 7B show the magnetic circuit configuration of an embedded magnet type IPM type rotating electrical machine. A four pole example is shown. The center line of the magnet width is the d axis, and an IBL law torque is generated on this axis. It is shown that the axis separated by 45 ° from the d-axis is the q-axis. That is, in the IPM system, the non-magnet portion formed on the rotor surface with a slight width becomes a magnetic flux passage opening from the stator winding q-axis, and reluctance torque is added. FIG. 7C shows a torque comparison between the SPM type and the IPM type, and it is stated that the IPM is advantageous in increasing the torque. The present invention aims to improve the IPM system.

  Although the rotor core of the present invention is described as an iron core made of soft magnetic iron, the actual manufacturing method is to compress and secure the strength by heat treatment or sintering at an appropriate temperature. Furthermore, after coating with soft magnetic iron powder and insulation and resin powder as binder, heat treatment at an appropriate temperature, so-called powder iron core can reduce eddy current loss and reduce iron loss. Is obtained. Furthermore, by adding an appropriate amount of silicon powder, it is possible to reduce hysteresis loss due to silicon powder in addition to reduction of eddy current loss due to resin powder, and further improve the efficiency of the rotating electrical machine. The same effect can be obtained even in the case of a dust core due to the iron loss mitigation principle of a silicon steel plate that reduces iron loss by adding about 3% silicon to a cold or hot rolled steel plate. .

  The rotating electrical machine according to the present invention can be used for an electric motor or a generator, and is extremely practical, inexpensive, robust, light and thin, suitable for high torque and high efficiency. Therefore, it is expected to make a significant industrial contribution.

1, 9, 14, rotor cores 2, 11, stator cores 3, 12, winding 4, rotating shafts 5, 13, bearing 6, brackets 7, 8, 15, permanent magnet 10, back yoke

Claims (1)

A rotating electric machine having a stator and a rotor,
The rotor has a rotor core made of soft magnetic iron powder, and a permanent magnet that exists substantially in parallel with the shaft inside the rotor core;
The rotor core, the axial length of the stator and facing portions, the formed shorter than the axial length of the contact portion between the rotor core of the permanent magnet in the rotor core, wherein the contact portion The axial length of the portion facing the stator is gradually reduced and formed integrally with the soft magnetic iron powder along the axial direction ,
The stator is a radial gap type rotary electric machine winding portion is characterized Rukoto wound.

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