JP2000295804A - Rare earth sintered magnet and permanent magnet type synchronous motor - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] To provide a permanent magnet synchronous motor in which generation of eddy current is reduced. SOLUTION: In a permanent magnet type synchronous motor in which a rare earth sintered magnet is incorporated in a rotor, a plurality of slits are provided on an armature side surface of the rare earth sintered magnet. By this slit, the vortex flow generated in the magnet of the rotor is reduced, and as a result, a highly versatile permanent magnet type synchronous motor that does not cause demagnetization of the magnet even at high speed rotation can be provided in a simple process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a permanent magnet type synchronous motor which is most suitable for an electric vehicle motor or an FA motor which rotates at a high speed.

[0002]

2. Description of the Related Art Rare earth magnets are mainly used as materials for small motors used in electric and electronic equipment in the audio and video fields. The reason is that the use of rare earth magnets with a large coercive force and residual magnetic flux density greatly increases the degree of freedom in motor design.Therefore, small, flat and highly efficient motors can be manufactured and incorporated into electric and electronic devices. It is possible. Since such a small motor generally has a rating of 100 W or less, an eddy current generated in the rare-earth magnet and the accompanying heat generated as an element for reducing the motor efficiency have an effect on the motor efficiency as compared with other motor efficiency loss elements. The impact was so small that it didn't matter.

However, in recent years, rare-earth magnets have been used in large-capacity motors of several hundred W to several tens kW rated as AC servomotors and 10 kW to several tens kW as electric motor driving motors. Rare earth magnets used for rotors of large-capacity AC servomotors and electric vehicle driving motors are much larger than those used for rotors (rotors) of small motors and have higher rotation speeds (for example, 500 rpm).
Above) is often required. Therefore, there is a problem of loss of motor efficiency due to eddy current generated in the rare earth magnet and accompanying heat generation. Similarly, eddy currents are a serious problem from the viewpoint of motor control, such as application of a reverse magnetic field to the rotor magnet and control involving a sudden change in the armature magnetic field. This is a problem that small motors did not have.

The electric resistance of a rare earth magnet is 10 ⁻⁴ Ω · cm.
It has a relatively high resistance as compared with the iron-based material of the order of 10 ⁻⁶ Ω · cm. However, since the rare earth magnet is used in a bulk shape, it is not possible to increase the resistance by thinning and punching / insulating and laminating like a ferrous material. Since a ferrite magnet is essentially an insulator, in a conventional synchronous motor using a ferrite magnet, the eddy current generated in the magnet did not cause any problem. However, since a ferrite magnet has low magnetic properties, a large synchronous motor using a ferrite magnet has not been put to practical use. On the other hand, rare earth magnets can be said to be metallic materials although there is a problem in the resistance value. Therefore, under the above-mentioned fields of use and conditions, eddy currents generated in the rare-earth magnet cause a decrease in motor efficiency, and demagnetization of the magnet due to heat generation of the rare-earth magnet is serious. Since the rotor core is a laminate of iron-based thin plates or an iron-based bulk core, the loss (eddy current loss, iron loss) generated in this portion is the same as in the related art.

In order to reduce the eddy current generated in the rare-earth magnet, the electric resistance of the magnet material is increased like a ferrite magnet, or a segment magnet obtained by dividing the magnet is adhered and solidified to obtain a magnet of a required size. The method is effective. However, since the former method is extremely difficult to be compatible with the magnet characteristics, there is almost no prospect of practical use at present. On the other hand, although the latter method is a practical method, the number of manufacturing steps of the magnet increases, which leads to an increase in manufacturing cost and a decrease in the weight yield of the magnet. In addition, in the step of magnet surface treatment, a good coating cannot be applied to the bonded portion of the segment magnet, and there is a risk that corrosion resistance may be reduced. Although it is conceivable to use the segment magnet as a small magnet without bonding and solidifying it, it is difficult to incorporate and fix the small magnet in the rotor against the repulsive force between the magnets.
Also, the dimensional accuracy when combined is reduced.

As a method for solving the problem caused by eddy current generated in the magnet, it is possible to use the magnet at a high temperature for the time being by improving the heat resistance of the rare-earth magnet so that the magnet is not demagnetized even when the temperature rises. Is also conceivable. For example, in an NdFeB-based sintered magnet, it is known that by adding an additive such as Dy to an alloy composition, heat resistance can be improved and coercive force can be increased. By increasing the coercive force at room temperature, a coercive force that does not cause demagnetization even when the magnet is exposed to a high temperature can be secured. In addition, as the electric motor, the NdFeB magnet is required to have heat resistance of about 150 ° C., and the electric vehicle driving motor is required to have heat resistance up to 200 ° C. However, all the additional elements for increasing the coercive force are accompanied by a decrease in the remanent magnetization.
The magnetic flux that can be extracted from the magnet decreases. Further, magnets with improved heat resistance cause a greater decrease in magnetic properties and an increase in raw material costs, so that the fields in which they can be used are limited.

[0007]

As described above, in a permanent magnet type synchronous motor having a capacity of kW class or more, a serious problem is that the motor efficiency is reduced due to an eddy current generated in the rare earth magnet of the rotor during high-speed rotation. Accordingly, an object of the present invention is to provide a permanent magnet type synchronous motor in which the occurrence of eddy current generated in a rare earth magnet is reduced by using the rare earth magnet having eddy current resistance and the rotor as the magnet.

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies on improving the effective electric resistance of rare earth sintered magnets, and as a result, have completed the present invention. That is, the present invention is characterized in that a rare earth sintered magnet provided with a plurality of slits on at least one surface thereof and the rare earth sintered magnet provided with a plurality of slits on at least the armature side surface are incorporated in a rotor. This is a permanent magnet type synchronous motor.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A feature of the present invention is that in a rare earth sintered magnet having a plurality of slits on at least one surface thereof and a permanent magnet type synchronous motor in which the rare earth sintered magnet is incorporated in a rotor, an eddy current is mainly generated. The eddy current is suppressed by providing a fine slit in the magnet surface generated in the above, that is, the magnet surface on the armature side to reduce the effective area where the eddy current is generated. Eddy current is a current generated on a conductor in a direction that impedes a change in magnetic flux. One cause of the eddy current in the motor is that the relative position between the rotor and the stator (armature) changes due to the rotation of the rotor, and the magnetic flux changes particularly at the slot portion. One of the causes of the eddy current is that the rotating magnetic flux created by the armature is not a smooth sine wave. Therefore, the eddy current is not generated only in the magnet portion, but the magnet is thermally demagnetized by the heat generated by the eddy current, so that the influence of the eddy current is more serious than other members.

Since the eddy current is generated at the portion where the magnetic flux changes, the portion of the magnet incorporated in the rotor where the eddy current is particularly problematic is the magnet surface on the armature side. The penetration depth of an eddy current in a conductor is expressed by the formula δ = √2 / μσω (μ is magnetic permeability, σ is electric conductivity, ω is each frequency of magnetic flux change), and δ is skin depth (eddy current Is the depth at which 1 / e is reached). Although the skin depth varies depending on the magnetic permeability and electric conductivity of the metal, eddy current generally does not flow except in the vicinity of the surface. For example, if μ = 1, σ = 10 ⁴ , ω = 10 ³ Hz in the above equation,
The skin depth δ is on the order of μm. Therefore, if the effective resistance near the surface where the eddy current flows can be increased, the influence of the eddy current can be avoided. In addition, it is most certain that the substantial surface area through which eddy currents flow is reduced by cutting the entire area in the thickness direction of the magnet and fixing and integrating the same with a non-conductive agent. There are problems such as an increase and a decrease in yield.
Therefore, in the present invention, the eddy current can be reduced by forming a slit sufficiently deeper than the skin depth of the eddy current on the surface of the magnet. By using this magnet for the rotor, the motor can be turned at high rotation. In the present invention, it is generally sufficient to form the slit only on the surface on the armature side, which is the surface where the magnetic flux changes mainly occur, and the other surfaces need not be slit.

The width of the slit is preferably as narrow as 1 mm or less so that the effect of disturbing the magnetic flux distribution is reduced. When the width of the slit exceeds 1 mm, the influence of the magnet loss on the surface on the magnetic flux density distribution becomes too large, which is not preferable. Since the slit is formed by processing the groove with an inner or outer peripheral cutting machine or a wire saw and the like, and taking into account the thickness of the cutting teeth, it is preferably 0.8 mm or less,
On the other hand, the lower limit of the slit width may be any value, but is practically 0.05 mm or more due to the restriction of the wire saw of the processing machine. It is desirable that the depth of the slit is deeper from the viewpoint of reducing the eddy current, but if it is too deep, the bending strength of the magnet decreases. Although the skin depth changes depending on the conditions, the skin depth is 1
A value of 0 or more is practically sufficient. Therefore,
The thickness is preferably 0.5 mm or more, and may be 1/3 or less of the magnet thickness in the slit direction.

In order to form a slit on the surface of the rare earth sintered magnet, an advantageous method may be selected in consideration of the size and shape of the magnet. For example, when a wire saw is used, a plurality of slits can be cut at one time and the width of the slit can be reduced to near the wire diameter, but the groove cutting speed is slow. In the case of a cutting machine, the grooving speed is high, and in the case of a peripheral cutting machine, a plurality of slits can be cut, but the width of the slit is larger than that of a wire saw. At the time of compacting magnetic powder, a method of forming a slit in a molded body by providing a projection on a punch may be considered, but in such a method, the width of the slit is 0.8 mm.
It is relatively difficult to provide the following narrow slits.

Although the eddy current is reduced by providing the slit, the bending strength is reduced as described above. In particular, in the case of a surface magnet type rotor (SPM type), a large centrifugal force acts on the magnet at a high speed rotation, and if the mechanical properties are not good, the magnet is broken and scattered. In the case of an internal magnet type rotor (IPM type), since a magnet is inserted into a cavity in the rotor and is mechanically held, a problem in mechanical characteristics due to the slit is reduced. In order to solve such a problem, it is preferable to fill the slit with a non-conductive substance such as an adhesive or a resin to compensate for the decrease in mechanical strength. It is possible to compensate for the decrease in force.

The adhesive is desirably one having both heat resistance and adhesive strength, and examples thereof include epoxy-based and acrylic-based adhesives. The epoxy resin includes, for example, Scotch (registered trademark) Weld EW-2 (Sumitomo 3M), and these can be used for both SPM type and IPM type. However, the silicone resin is excellent in heat resistance and elasticity, but does not have high adhesive strength. Therefore, it is desirable to use the silicone resin for the IPM type. Further, as the non-conductive substance to be filled in the slit, a composite resin obtained by kneading a resin with a permanent magnet powder for a bonded magnet or the like can be used. Since the composite resin has magnet properties, it is possible to compensate for the decrease in magnet properties due to the formation of the slits to some extent. However, since almost no adhesive strength can be expected, it is desirable to use the IPM type. Examples of the permanent magnet powder include NdFeB-based quenched ribbons and 2-17-based Sm.
Co magnet magnetic powder or the like can be used. In order to fill the slit with the various non-conductive substances, the non-conductive substance may be embedded in the slit and solidified.

In the present invention, the magnet to be incorporated in the rotor is a rare earth sintered magnet having a rectangular or tiled shape, and more specifically, an NdFeB-based sintered magnet, an SmCo-based sintered magnet, or the like.
Rare-earth bonded magnets are composite magnets mixed with resin.They are considered to be candidates for large synchronous motor magnets because of their original high electrical resistance, little influence of eddy current, and low resin heat resistance and low magnetic properties. Not been. Therefore, the bonded magnet is not an object of the present invention.

In the rare earth sintered magnet used in the present invention, the step of providing slits on the magnet surface is increased as compared with the powder metallurgy method for manufacturing a normal magnet without a slit, but a magnet in which segment magnets are bonded and solidified is manufactured. Is simpler than that of the split bonding method, and yet an eddy current reduction effect substantially equal to that of the magnet can be produced. Further, since the magnet volume reduced by providing the slit on the magnet surface is small and the magnetic flux is reduced only slightly, the reduction in the electromagnetic torque is small. Therefore, unlike a conventional permanent magnet type synchronous motor, it is not necessary to apply a large coercive force to the magnet in advance on the premise of heat generation and temperature rise due to eddy current. A great effect can be expected. In addition, the magnet used in the present invention can perform coating well even in a state where a slit is provided, so that there is no problem in terms of corrosion resistance.

[0017]

[Examples] (Examples and Comparative Examples) The dimensions are 40 mm x 60 m.
mx 3 mm, 4 MGOe grade NdFeB sintered magnets (N42H manufactured by Shin-Etsu Chemical Co., Ltd.)
The magnet was inserted into a 0 mm, 62 mm long silicon steel sheet laminated (0.5 mm thick silicon steel sheet) rotor to produce an IPM type rotor. On the armature side surface of the magnet,
Eleven slits having a width of 0.5 mm and a depth of 1 mm were inserted at intervals of 5 mm. The direction is parallel to the width direction of 40 mm, 0.4
11 teeth were multi-assembled and chopped by a peripheral cutting machine having a thickness of mm. After the magnet was coated with electric Ni plating, when it was inserted into the rotor, it was sealed together with an epoxy-based one-part cold curing adhesive (Scotchweld EW-2), and the slit was sealed with the adhesive. Then, the rotor is incorporated into a stator having an armature of 12 slots, and 3
A phase alternating current was supplied, and rotation was performed at 6000 rpm for 1 hour. Immediately after the stop, the rotor was disassembled and the temperature of the magnet at the end of the rotor was measured. For comparison, a similar rotor was manufactured using the same dimensions and material as above using a magnet without a slit, and rotated under the same conditions to measure the temperature rise. As a result, the temperature of the magnet portion at the rotor end was 145 ° C.
There was a difference in temperature rise over ℃. That is, the temperature rise of the magnet was suppressed by providing the slit in the magnet.

[0018]

According to the present invention, an eddy current generated in a magnet of a rotor is reduced, and as a result, a highly versatile permanent magnet type synchronous motor which does not cause demagnetization of the magnet even at a high rotation speed can be provided in a simple process. Therefore, its utility value is extremely high in industry.

Claims (4)

[Claims] 1. A rare earth sintered magnet, wherein a plurality of slits are provided on at least one or more surfaces of the rare earth sintered magnet. 2. The permanent magnet type synchronous motor according to claim 1, wherein a plurality of slits are provided on the armature side surface of the rare earth sintered magnet. Type synchronous motor. 3. The permanent magnet according to claim 2, wherein the slit provided on the surface of the rare earth sintered magnet has a width of 1 mm or less and a depth of 0.5 mm or more, and the slit is filled with a non-conductive substance. Type synchronous motor. 4. The permanent magnet type synchronous motor according to claim 3, wherein the non-conductive substance filled in the slit is an adhesive, a resin or a composite resin obtained by kneading a resin with a permanent magnet powder.