Rotating electric machine with ferrite magnet in rotor

Abstract

To achieve temperature rise of a ferrite magnet with a simple configuration in a permanent magnet type rotating electric machine employing a ferrite magnet 14 in a rotor 10.SOLUTION: In a permanent magnet rotating electric machine in which a ferrite magnet is incorporated into a rotor core to give the rotor magnetic poles, a member 16 made of a soft magnetic material capable of generating eddy currents within the surface of the ferrite magnet is disposed on the surface facing stator poles while the rotor is rotating. When the rotor rotates, the magnetic flux density from the stator poles penetrating the soft magnetic material changes, generating eddy currents in the soft magnetic material, which then heats the ferrite magnet due to Joule heat, increasing its coercive force and suppressing demagnetization.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a permanent magnet type rotating electric machine, and more particularly to a rotating electric machine that uses ferrite magnets as permanent magnets. [Background technology]

[0002] Permanent magnet rotating electric machines are primarily used in motors for electric vehicles. The permanent magnets used in their rotors are typically neodymium magnets, which have high magnetic flux density. However, because neodymium magnets have a lower coercivity at high temperatures, the use of ferrite magnets, whose coercivity is positively correlated with temperature, has been considered. Because ferrite magnets have low coercivity and are prone to demagnetization at low temperatures, for example, Patent Document 1 proposes controlling the coil current in a brushless motor for an electric power steering system that uses ferrite magnets to maintain the temperature of the ferrite magnet above a certain level by increasing the flow of current through the stator coil to further increase the temperature. While not an example of using ferrite magnets, Patent Document 2 proposes placing soft magnetic material with a higher electrical resistivity than the rotor core on the radially outer pole faces of the neodymium magnets in a rotating electric machine that uses neodymium magnets in its rotor to suppress the generation of eddy currents on the pole faces. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2016-86502 [Patent Document 2] Patent Publication No. 2021-136860 Summary of the Invention [Problem to be solved by the invention]

[0004] As mentioned above, the coercive force of ferrite magnets increases with increasing temperature, but because their coercive force is low at low temperatures, they are demagnetized when a rotating electric machine is operated at low temperatures, impairing the functionality (torque and output) of the rotating electric machine. Therefore, when using ferrite magnets, it is preferable to be able to increase their temperature and prevent demagnetization. In this regard, it would be advantageous if the temperature of ferrite magnets could be increased with a simple configuration without requiring special electrical system control, additional hardware, or complex software integration.

[0005] In view of the above circumstances, a main object of the present invention is to make it possible to raise the temperature of a ferrite magnet with a simple configuration in a rotating electrical machine that employs a ferrite magnet in the rotor. [Means for solving the problem]

[0006] According to the present invention, the above object is achieved by a permanent magnet type rotating electric machine in which a ferrite magnet is incorporated into a rotor core to provide magnetic poles in the rotor, and in which a member made of a soft magnetic material capable of generating eddy currents is arranged on the surface of the ferrite magnet facing the poles of the stator during rotation of the rotor.

[0007] In the above configuration, the "rotor core" may be formed in a conventional manner, typically made of electromagnetic steel sheets stacked with insulating layers sandwiched in the direction of the rotation axis. The ferrite magnets are arranged in any manner in the rotor core to form the magnetic poles of the rotor, as will be described later with reference to the drawings. The stator of the rotating electric machine may be formed in a conventional manner. The "surface facing the stator poles during rotor rotation" of the ferrite magnet refers to a surface that intersects with the magnetic flux lines generated from the stator coil during rotor rotation, and is a surface where the magnetic flux density passing through the surface from the stator poles changes during rotor rotation (hereinafter referred to as the "stator-facing surface"). The "member made of a soft magnetic material in which eddy currents can be generated within the surface" (hereinafter referred to as the "soft magnetic material member") may be a member of any shape, such as a thin plate or a conductor arranged in a ring or spiral shape, as long as it is configured to allow continuous current to flow within the surface. The soft magnetic material constituting the soft magnetic member has physical properties of relative permeability >1 (air) and electrical resistivity <10 Ωm, and may be, specifically, iron, silicon iron, permalloy, sendust, permendur, amorphous magnetic alloy, nanocrystalline magnetic alloy, etc.

[0008] With the above configuration, when the rotating electric machine is operated and the rotor rotates, the magnetic flux density from the stator poles on the ferrite magnet's surface facing the stator changes, causing eddy currents to be generated in the soft magnetic material arranged on the surface facing the stator poles. This in turn generates Joule heat that heats the ferrite magnet, thus increasing the coercive force of the ferrite magnet and suppressing demagnetization.

[0009] In the above configuration, the stator-facing surface on which the soft magnetic material is placed can be any surface of the ferrite magnet parallel to the rotor's rotational axis. However, if the ferrite magnet has a rectangular cross section perpendicular to the rotor's rotational axis, placing the soft magnetic material on the long side increases the heat generation area due to eddy currents, which allows the ferrite magnet to heat up more quickly. In this case, placing the soft magnetic material so that it covers the entire long side of the ferrite magnet allows the ferrite magnet to heat up more quickly. The thickness of the soft magnetic material (perpendicular to the rotor's rotational axis) can be determined based on suitability. [The magnetic steel sheets of the rotor core are also soft magnetic, but an insulating layer is sandwiched between the magnetic steel sheets perpendicular to the rotor's rotational axis, preventing current flow in a plane parallel to the rotor's rotational axis and preventing eddy currents from being generated.] [Effects of the Invention]

[0010] Thus, according to the present invention, it is possible to achieve temperature rise of a ferrite magnet with a simple configuration by simply placing a soft magnetic material member on the surface of the ferrite magnet facing the stator poles while the rotor is rotating, without requiring special electrical system control, additional hardware, or complex software implementation. The configuration of the present invention may be adopted in rotating electric machines for driving electric vehicles or other rotating electric machines for any other machinery and equipment.

[0011] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view taken along the direction of the rotation axis of a rotor of a rotating electrical machine to which this embodiment is applied. [Figure 2] FIG. 2(A) is a schematic partial cross-sectional view of a rotor of a rotating electric machine according to one aspect of this embodiment, viewed along the rotational axis direction of the rotor, and FIG. 2(B) is a partial cross-sectional view of a rotor of a rotating electric machine according to this embodiment, viewed from a direction perpendicular to the rotational axis of the rotor. [Figure 3]3(A) to 3(D) are schematic partial cross-sectional views taken along the rotation axis direction of a rotor of a rotating electric machine according to another aspect of the present embodiment. [Figure 4] 4(A) and 4(B) are schematic partial cross-sectional views taken along the rotation axis direction of a rotor of a rotating electric machine according to still another aspect of the present embodiment. [Explanation of symbols]

[0013] 10... rotor, 12... rotor core, 14... ferrite magnet, 16... soft magnetic member BEST MODE FOR CARRYING OUT THE INVENTION

[0014] Rotor configuration 1, a permanent magnet rotor 10 for a rotating electric machine according to this embodiment may have a configuration in which magnets 14 are incorporated into a rotor core 12 so that north and south poles are arranged alternately along the circumferential direction, as in a conventional configuration. The rotor core 12 is typically formed by laminating thin plates cut from electromagnetic steel sheets with insulating layers sandwiched between them in the direction of the rotation axis C of the rotor 10 (see FIG. 2(B)). The magnets 14 extend over substantially the same length as the entire length of the rotor core 12 along the rotation axis C and are permanent magnets magnetized as shown. In particular, in this embodiment, a ferrite magnet is used for the magnets 14, which has a coercive force that increases with increasing temperature.

[0015] Temperature rise mechanism of ferrite magnets In this embodiment, as shown in FIGS. 2A and 2B, a configuration for raising the temperature of the ferrite magnet 14 is provided. A soft magnetic member 16 is disposed on the surface of the magnet 14 that faces the stator poles during rotor rotation, i.e., on a surface parallel to the rotor's rotation axis c. The soft magnetic member 16 may be formed in a shape that allows eddy currents to be generated on a surface parallel to the surface of the magnet 14, such as a thin plate or a conductor arranged in a ring or spiral shape. With this configuration, as can be seen from the figure, during operation of the rotating electric machine, magnetic flux Φs from the stator poles penetrates the soft magnetic member 16. The magnetic flux density of the magnetic flux Φs changes with the rotation of the rotor 10, generating eddy current Iw in the soft magnetic member 16, as shown in FIG. 2B. The flow of the eddy current Iw generates Joule heat, which heats the magnet 14 and raises its temperature.

[0016] In the above configuration, the length of the soft magnetic material member 16 in the direction of the rotor's rotation axis c and the length in the circumferential direction may be long enough to cover the entire surface of the magnet 14. The thicker the soft magnetic material member 16, the greater the heat generation, but the greater the loss. Therefore, the radial thickness of the soft magnetic material member 16 may be determined appropriately so that the loss is within an acceptable range. Note that, to prevent a deterioration in magnetic permeability, it is preferable to use the soft magnetic material member 16 so that no gap is formed between the magnet 14 and the rotor core 12. As already mentioned, the material selected for the soft magnetic material member 16 is iron, silicon iron, permalloy, sendust, permendur, amorphous magnetic alloy, nanocrystalline magnetic alloy, etc., and has a relative magnetic permeability > 1 (air) and an electrical resistivity < 10 Ω-m.

[0017] 3 and 4, the soft magnetic material member 16 may be placed anywhere on a plane parallel to the rotor's rotation axis c, that is, on a plane where the magnetic flux density of the stator magnetic flux Φs passing through it changes while the rotor is rotating. If the ferrite magnet 14 has a rectangular cross section, placing the soft magnetic material member 16 on the long side of the plane increases the heat generation area due to eddy currents, which is preferable because it allows the ferrite magnet to heat up quickly.

[0018] Thus, according to the configuration of the present embodiment described above, the temperature of the ferrite magnet can be raised with a simple configuration in which the soft magnetic material member 16 is simply placed on the surface of the ferrite magnet 14 facing the stator poles while the rotor 10 is rotating.

[0019] The above description has been made in relation to the embodiments of the present invention, but it will be apparent that many modifications and changes will be readily apparent to those skilled in the art, and the present invention is not limited to the above-described exemplary embodiments, but can be applied to various devices without departing from the concept of the present invention.

Claims

[Claim 1] A permanent magnet type rotating electric machine in which a ferrite magnet is incorporated into a rotor core to provide magnetic poles in the rotor, and in which a member made of a soft magnetic material capable of generating eddy currents is arranged on the surface of the ferrite magnet facing the poles of the stator while the rotor is rotating.

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