Rotor core

Abstract

To provide a rotor core capable of suppressing the occurrence of an air gap and efficiently rotating.SOLUTION: The rotor core includes an inner core provided with a magnet insertion hole, and an outer core covering an outer peripheral surface of the inner core. A saturation magnetic flux density of the outer core is less than a saturation magnetic flux density of the inner core. Since the outer core is formed of a magnetic material, it is possible to suppress generation of an air gap between the rotor core and the stator. In addition, since the saturation magnetic flux density of the outer core is less than the saturation magnetic flux density of the inner core, a short circuit of the magnetic flux can be suppressed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a rotor core. [Background technology]

[0002] Conventionally, rotors have been known in which the outer periphery of a rotor core having magnet insertion holes is covered with a non-magnetic member (see, for example, Patent Document 1). Patent Document 1 claims that by disposing the non-magnetic member on the outer periphery of the rotor core, the strength of the rotor core can be improved. As the strength of the rotor core improves, it becomes able to withstand centrifugal force. Furthermore, motors using such rotor cores are capable of high-speed rotation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-174899 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the non-magnetic member in Patent Document 1 faces the stator, which is located outside the rotor core. This increases the air gap between the rotor core and the stator. The increased air gap is disadvantageous in terms of improving the motor's output.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a rotor core that can suppress the occurrence of air gaps and can rotate efficiently. [Means for solving the problem]

[0006] The above object is achieved by a rotor core comprising an inner core provided with a magnet insertion hole and an outer core covering the outer surface of the inner core, wherein the saturation magnetic flux density of the outer core is less than the saturation magnetic flux density of the inner core. [Effects of the Invention]

[0007] It is possible to provide a rotor core that can suppress the occurrence of air gaps and rotate efficiently. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing a rotary electric machine equipped with a rotor core according to an embodiment. [Figure 2] Fig. 2A is an explanatory diagram of a rotor including a rotor core according to an embodiment, and Fig. 2B is an enlarged view of a portion of the rotor core according to an embodiment. [Figure 3] Fig. 3A-1 is a perspective view showing an outer core of an embodiment, Fig. 3A-2 is a perspective view showing an outer core of a first modified example, Fig. 3B is a perspective view showing an outer core of a second modified example, and Fig. 3C is a perspective view showing an outer core of a third modified example. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Embodiment) A rotating electric machine 10 shown in FIG. 1 includes a stator 12 and a rotor 14 arranged concentrically inside the stator 12. The rotor 14 is a rotor having a stator 12a.

[0010] The stator 12 has a generally cylindrical stator core 18 with a plurality of teeth (not shown) formed on its inner periphery, and a stator coil 20 wound around each tooth. The stator 12 has three phases: U, V, and W, and the stator coil 20 is wound using distributed winding (not shown). The stator core 18 has 24 slots formed in the circumferential direction, and coils are arranged in the slots. In other words, the rotating electric machine 10 of this embodiment forms an 8-pole, 24-slot motor. However, the motor type is not limited to this, and various conventionally known types can be used.

[0011] A rotating shaft 16 is fixed to the center of the rotor 14. The rotor 14 includes a rotor core 30 and permanent magnets 34 embedded in the rotor core 30. In other words, the rotating electric machine 10 is a permanent magnet synchronous rotating electric machine, a so-called IPM (Interior Permanent Magnet) motor. The rotor 14 has an even number of magnetic poles 2 (eight in FIG. 2 ) arranged at equal intervals in the circumferential direction across the q axis. The polarities of the even number of magnetic poles 2 alternate in the circumferential direction.

[0012] The rotor core 30 includes an inner core 32 and an outer core 38 that covers the outer peripheral surface 32b (see FIGS. 1 and 2).

[0013] The internal core 32 is made of a magnetic material and includes a center bridge 36 for each magnetic pole 2. A d-axis passing through the center of the center bridge 36 extends radially in each magnetic pole 2. Each magnetic pole 2 has a circumferentially symmetrical structure across the d-axis. Therefore, the internal core 32 includes magnet insertion holes 32a for each magnetic pole 2 that are symmetrically arranged with respect to the center bridge 36 and adjacent to each other in the circumferential direction. A pair of adjacent magnet insertion holes 32a have shapes that are inverted relative to each other with respect to the d-axis. Although the pair of magnet insertion holes 32a have inverted shapes, the configuration of each part is common. Therefore, the pair of magnet insertion holes 32a are indicated by the same reference numerals in Figures 2(A) and 2(B).

[0014] The magnet insertion hole 32a includes a magnet insertion portion 32a1 into which a permanent magnet 34 is inserted.

[0015] The magnet insertion hole 32a includes a first air hole 32a2 on the side of the magnet insertion section 32a1 that is farther from the center bridge 36, i.e., closer to the q axis. The first air hole 32a2 is open on the outer circumferential side of the internal core 32. However, the internal core 32 may have a closed first air hole 32a2 and an outer circumferential bridge formed radially outward of the first air hole 32a2. The magnet insertion hole 32a includes a second air hole 32a3 on the side closer to the center bridge 36 than the magnet insertion section 32a1, i.e., closer to the d axis. The first air hole 32a2 and the second air hole 32a3 may be voids or may be filled with resin. Filling the first air hole 32a2 and the second air hole 32a3 with resin secures the permanent magnet 34. This also improves the strength of the internal core 32.

[0016] The outer core 38 may be formed of any suitable material as long as it can cover the outer peripheral surface 32b of the inner core 32. For example, as shown in FIG. 3A-1 , a first cylindrical member 38a may be prepared and placed on the outside of the inner core 32. The first cylindrical member 38a is formed of a magnetic material. The axial dimension of the first cylindrical member 38a corresponds to the axial dimension of the inner core 32. In other words, the first cylindrical member 38a has no axial seams and can cover the entire outer peripheral surface 32b of the inner core 32 by itself. The first cylindrical member 38a is integrated with the inner core 32 by press fitting or shrink fitting to form the outer core 38.

[0017] The outer core 38 is made of a magnetic material. This makes it difficult for an air gap to occur between the rotor 14 and the stator 12 disposed around the rotor 14. By suppressing the occurrence of an air gap, the rotor 14 can be rotated efficiently. As a result, the efficiency of the rotating electric machine 10 can be improved. This allows the rotation speed of the rotating electric machine 10 to be increased and the rotating electric machine 10 to be made smaller.

[0018] Here, the saturation magnetic flux density of the outer core 38 will be described. Both the inner core 32 and the outer core 38 are formed of magnetic materials. However, the saturation magnetic flux density of the outer core 38 is lower than that of the inner core 32. In other words, the outer core 38 has a lower magnetic flux density than the inner core 32. This makes it possible to suppress short-circuiting of magnetic flux in the outer core 38. As a result, the rotor 14 can be rotated efficiently, and the efficiency of the rotating electric machine 10 can be improved. This makes it possible to increase the rotation speed of the rotating electric machine 10 and reduce the amount of magnets required to make the rotating electric machine 10 more compact.

[0019] Next, the strength of the outer core 38 will be described. The outer core 38 is made of a magnetic material. The mechanical strength of the outer core 38 is greater than the mechanical strength of the inner core 32, which is also made of a magnetic material. This improves the overall strength of the rotor core 30. The improved strength of the rotor core 30 allows the rotating electric machine 10 to operate at a higher rotational speed. Furthermore, providing the outer core 38 supplements the strength of the rotor core 30. Therefore, the width of the center bridge 36 can be narrowed or eliminated, or, as in this embodiment, the first air hole 32a2 can be formed with an open shape. As a result, short-circuiting of magnetic flux can be suppressed, which in turn allows the rotor 14 to rotate efficiently and improves the efficiency of the rotating electric machine 10.

[0020] The inner core 32 and the outer core 38 can be made of a combination of magnetic materials that satisfies the relationship between mechanical strength and saturation magnetic flux density.

[0021] Although the rotating electrical machine 10 of this embodiment is an IPM motor, it may be based on an SPM (Surface Permanent Magnet) motor and have an outer core provided on the outer periphery of the SPM motor.

[0022] (Modifications) Here, modifications of the outer core will be described. First, a first modification will be described with reference to FIG. 3A-2. In the first modification, the outer core 38 is formed by a plurality of second cylindrical members 38b instead of the first cylindrical member 38a. The first cylindrical member 38a has an axial dimension that allows it to cover the entire outer peripheral surface 32b of the inner core 32 by itself. The axial dimension of the second cylindrical members 38b is shorter than that of the first cylindrical member 38a. In the example shown in FIG. 3A-2, three second cylindrical members 38b are stacked to cover the outer peripheral surface 32b of the inner core 32. The magnetic material for forming the second cylindrical members 38b is selected in the same manner as the magnetic material for forming the first cylindrical member 38a. In other words, a magnetic material is selected for the material of the second cylindrical members 38b such that the saturation magnetic flux density of the outer core 38 is lower than that of the inner core 32. The stacked second cylindrical members 38b are integrated with the inner core 32 by press-fitting or shrink-fitting, similar to the first cylindrical member 38a. This allows the outer core 38 to be formed in the same manner as the first cylindrical member 38a. The number of layers of the second cylindrical member 38b can be selected appropriately.

[0023] Next, with reference to FIG. 3B , a second modified outer core 48 will be described. The second modified outer core 48 is configured by winding a thin plate member 48a having a width W around the outer peripheral surface 32b of the internal core 32 while applying tension. The thin plate member 48a is formed from the same magnetic material as the first cylindrical member 38a. The thin plate member 48a is positioned so that the width W coincides with the axial direction of the internal core 32. The thin plate member 48a may be wound in a single layer or in multiple layers in the radial direction. The longitudinal ends of the thin plate member 48a are joined using an adhesive or by welding. The longitudinal ends of the thin plate member 48a may also be joined by caulking. The thin plate member 48a does not require shrink fitting, which requires heating during assembly. This reduces manufacturing costs. The second modified outer core 48 can achieve the same effects as the external core 38.

[0024] Next, with reference to FIG. 3C , an outer core 58 according to a third modification will be described. The outer core 58 according to the third modification is formed by winding a strip-shaped or linear winding member 58a around the outer peripheral surface 32b of the inner core 32 while applying tension. The winding member 58a is formed from the same magnetic material as the first cylindrical member 38a. The winding member 58a is wound around the outer peripheral surface 321b of the inner core 32 so as to move along the axial direction of the inner core 32. The winding member 58a may be wound in a single layer or in multiple radial layers. The longitudinal ends of the winding member 58a are joined using an adhesive or by welding. The longitudinal ends of the winding member 58a may also be joined by caulking. The winding member 58a does not require shrink fitting, which requires heating during assembly. This reduces manufacturing costs. The outer core 58 according to the third modification can achieve the same effects as the outer core 38.

[0025] [Effects] The rotor core 30 of the embodiment includes an internal core 32 provided with a magnet insertion hole 32a, and an external core 38 (48, 58) covering the outer peripheral surface 32b of the internal core 32. The saturation magnetic flux density of the external core 38 (48, 58) is less than the saturation magnetic flux density of the internal core 32. By forming the external core 38 (48, 58) from a magnetic material, it is possible to suppress the occurrence of an air gap between the external core 38 (48, 58) and the stator 12. Furthermore, by making the saturation magnetic flux density of the external core 38 (48, 58) less than the saturation magnetic flux density of the internal core 32, it is possible to suppress short-circuiting of magnetic flux in the external core 38 (48, 58). This allows the rotor 14 to rotate efficiently.

[0026] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0027] 2...magnetic pole, 10...rotating electric machine, 12...stator, 14...rotor, 18...stator core, 20...stator coil, 30...stator core, 32...inner core, 32a...magnet insertion hole, 32a1...magnet insertion portion, 32a2...first air hole, 32a3...second air hole, 32b...outer peripheral surface, 34...permanent magnet, 36...center bridge, 38, 48, 58...outer core, 38a...first annular member, 38b...second annular member, 48a...thin plate member, 58a...wound member

Claims

[Claim 1] A rotor core including an inner core provided with a magnet insertion hole and an outer core covering an outer peripheral surface of the inner core, The saturation magnetic flux density of the outer core is less than the saturation magnetic flux density of the inner core. Rotor core.

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