Magnets, rotors, electric motors, and vacuum cleaners

Abstract

This prevents the situation where the magnetic force of a magnet is weaker in the center of a given direction compared to the ends. [Solution] A magnet for use in an electric motor, comprising a compound made of a mixture of magnetic powder and a binder, and including both ends in a predetermined direction, the end portion made of a first compound having a first magnetic flux density, and a central portion sandwiched between the end portions, made of a second compound having a second magnetic flux density higher than the first magnetic flux density.

Description

Technical Field

[0001] The present invention relates to a magnet, a rotor, an electric motor, and a vacuum cleaner.

Background Art

[0002] Patent Document 1 describes a rotating electric machine. This rotating electric machine includes a stator having a stator core provided with slots over the entire circumference and a stator winding wound around the stator core, and a rotor provided rotatably with respect to the stator. The rotor includes a rotor core including electromagnetic steel sheets laminated in a direction along the rotation axis of the rotor and having a plurality of magnetic poles arranged in the circumferential direction, and a plurality of first permanent magnets and a plurality of second permanent magnets for forming each of the plurality of magnetic poles. Further, the first permanent magnet and the second permanent magnet for forming each magnetic pole of the rotor have different recoil permeabilities from each other.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a magnet obtained by, for example, compression molding general magnetic powder in a predetermined direction, the compression density at the central portion in the predetermined direction is lower than the compression density at both end portions. As a result, the magnetic force at the central portion in the predetermined direction of the magnet becomes weaker than that at both end portions.

[0005] An object of the present invention is to suppress a situation where the magnetic force at the central portion in a predetermined direction of a magnet becomes weaker than that at both end portions.

Means for Solving the Problems

[0006] To this end, the present invention provides a magnet for use in an electric motor, comprising a compound made of a mixture of magnetic powder and a binder, and including both ends in a predetermined direction, the magnet comprising two end portions made of a first compound having a first magnetic flux density, and a central portion sandwiched between the end portions, made of a second compound having a second magnetic flux density higher than the first magnetic flux density. In this case, the magnet may be formed by compression molding the compound in a predetermined direction.

[0007] In the above-described magnet, the length of the central part in a predetermined direction may be 5% to 50% of the total length of the magnet in that predetermined direction.

[0008] In the magnet described above, the magnetic powder may contain neodymium. In that case, the magnetic powder may further contain niobium.

[0009] In the magnet described above, the average crystal grain size of the magnetic powder contained in the second compound may be larger than the average crystal grain size of the magnetic powder contained in the first compound.

[0010] In the magnet described above, the amount of binder contained in the second compound may be less than the amount of binder contained in the first compound.

[0011] In the magnet described above, the magnetic powder contained in the second compound may contain a substance that increases the magnetic flux density. In that case, the substance that increases the magnetic flux density may be aluminum, copper, or cobalt.

[0012] In the magnet described above, the magnetic powder contained in the first compound may contain a substance that increases coercivity. In that case, the substance that increases coercivity may be either gallium or zirconium.

[0013] Furthermore, the present invention also provides a rotor using the above-mentioned magnet.

[0014] Furthermore, the present invention also provides an electric motor equipped with the above-described rotor.

[0015] Furthermore, the present invention also provides a vacuum cleaner equipped with the above-described electric motor.

Advantages of the Invention

[0016] According to the present invention, it is possible to suppress a situation where the magnetic force at the central portion in a predetermined direction of the magnet is weaker than that at both end portions.

Brief Description of the Drawings

[0017] [Figure 1] It is a diagram showing a configuration example of a stick-type vacuum cleaner to which the present embodiment is applied. [Figure 2] It is a diagram showing a configuration example of a rotor assembly of a fan motor in a stick-type vacuum cleaner to which the present embodiment is applied. [Figure 3] It is a diagram illustrating a method of forming a magnet by compression molding. [Figure 4] It is a diagram showing a configuration example of the magnet in the present embodiment. [Figure 5] It is a diagram showing the result of examining the ratio of the length in the axial direction of the central portion to the length in the axial direction of the entire magnet.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0019] [Vacuum Cleaner] FIG. 1 is a diagram showing a configuration example of a stick-type vacuum cleaner 1 to which the present embodiment is applied. This vacuum cleaner 1 is a cordless type and is configured to be driven by the power of a built-in battery 8.

[0020] As shown in the drawing, the vacuum cleaner 1 includes a suction part 2, a tube part 3, a main body part 4, a handle part 5, and a dust case 6.

[0021] The suction part 2 has a suction port 2a on its lower surface and is configured to be slidable along the floor surface by a rotatable roller 2b. The pipe part 3 is composed of an elongated cylindrical member that can be expanded and contracted. The lower end of the pipe part 3 is connected to the suction part 2, and the upper end thereof is connected to the main body part 4. The pipe part 3 communicates the suction port 2a and the main body part 4.

[0022] The main body part 4 is formed to be slightly larger in size than the pipe part 3. The main body part 4 houses a fan motor 7, a battery 8, a control part 9, etc. The control part 9 controls the driving of the fan motor 7. The battery 8 is a rechargeable secondary battery and supplies electric power to the fan motor 7.

[0023] The handle part 5 is a part that the user grips and is provided integrally with the main body part 4. The handle part 5 is provided so as to protrude rearward from the rear side of the main body part 4. The cleaner 1 is configured to be handled with the user holding the handle part 5 with one hand.

[0024] The dust case 6 is installed below the handle part 5. The dust case 6 is configured to be detachable from the main body part 4. The fan motor 7 is disposed at a position adjacent to the dust case 6. The fan motor 7 is driven by the electric power supplied from the battery 8 according to the control of the control part 9. When the fan motor 7 is driven, a strong suction force is formed. Thereby, the dust sucked from the suction port 2a is accumulated in the dust case 6 through the pipe part 3.

[0025] [Fan motor] The fan motor 7 is a small device in which a fan and a motor (electric motor) are integrally configured. The fan is a so-called centrifugal fan. As the impeller (not shown) rotates around the rotation axis, air is sucked in from the intake port (not shown) and discharged outward in the radial direction. The outer diameter and the overall height of the fan motor 7 are designed to be very small so that it can be accommodated in the main body part 4.

[0026] Figure 2 shows an example of the configuration of the rotor assembly 10 of the fan motor 7 in the vacuum cleaner 1 shown in Figure 1. As shown in the figure, the rotor assembly 10 comprises a rotating shaft 20 and a magnet 30. The magnet 30 is directly fixed to the rotating shaft 20 by adhesive. Here, the magnet 30 is assumed to have a cylindrical shape.

[0027] The fan motor 7 also includes a stator assembly, which is not shown in the diagram, positioned to surround the magnet 30 via an air gap. The stator assembly rotates the rotor assembly 10 by the magnetic force generated when current flows through the winding coils.

[0028] [magnet] Now, let's consider the case where the magnet 30 is formed by compression molding in the axial direction of the cylinder. Figure 3 illustrates a method for forming the magnet 30 by compression molding. As shown in the diagram, in compression molding, first, a compound made by mixing magnetic powder and a binder is fixed to the die 90. Then, as indicated by arrow A1, this compound is pressed from above by the upper punch 91 and as indicated by arrow A2, as pressed from below by the lower punch 92, thereby forming the magnet 30. Furthermore, compression molding can be performed either while heating or without heating, followed by firing. In either case, when compression molding is performed, the compression density in the center of the magnet 30 in the compression direction tends to be lower than that in the compression density at both ends of the magnet 30 in the compression direction. In the figure, areas with high compression density are shown with cross-hatching, and areas with low compression density are shown with diagonal hatching. This is because pressure is not uniformly distributed during the compression molding process, and the pressure decreases particularly in the center in the compression direction. This results in a decrease in the magnetic force of the magnet 30, leading to a decrease in performance.

[0029] Therefore, in this embodiment, we propose a magnet 30 to improve this situation. Figure 4 shows an example of the configuration of the magnet 30 in this embodiment. In this embodiment, when supplying powder during compression molding, first, ordinary magnetic powder is put into the portion corresponding to the lower end portion 31b after compression molding. Next, magnetic powder with a higher magnetic flux density than ordinary is put into the portion corresponding to the central portion 32 after compression molding. Then, ordinary magnetic powder is put into the portion corresponding to the upper end portion 31a after compression molding again.

[0030] In other words, in this embodiment, the magnetic flux density of the compound forming the central portion 32 is made higher than the magnetic flux density of the compound forming the upper portion 31a and the lower portion 31b. As described above, the compound is a mixture of magnetic powder and a binder. As the magnetic powder, for example, one containing neodymium may be used. Furthermore, as the magnetic powder, one that further contains niobium may be used to increase its strength.

[0031] Here, the upper end portion 31a is the portion that includes the upper end in the axial direction of the cylinder, and the lower end portion 31b is the portion that includes the lower end in the axial direction of the cylinder. The portion that combines the upper end portion 31a and the lower end portion 31b is sometimes called the end portions 31. In other words, the end portions 31 are the portions that include both ends in the axial direction of the cylinder. The central portion 32 is the portion sandwiched between the end portions 31. In this embodiment, it is assumed that the magnet 30 is formed by compression molding in the axial direction of the cylinder. Therefore, the portions that include both ends in the axial direction of the cylinder are called the end portions 31, and the portion sandwiched between the end portions 31 is called the central portion 32. However, if it is not limited to compression molding in the axial direction of the cylinder, the axial direction of the cylinder can be generally considered as a predetermined direction.

[0032] Hereinafter, the compound forming both ends 31 will be referred to as the "first compound," and its magnetic flux density will be referred to as the "first magnetic flux density." The compound forming the central part 32 will be referred to as the "second compound," and its magnetic flux density will be referred to as the "second magnetic flux density." In this embodiment, for example, it is preferable to make the second magnetic flux density of the second compound higher than the first magnetic flux density of the first compound by the following method.

[0033] The first method involves making the average crystal grain size of the magnetic powder in the second compound larger than the average crystal grain size of the magnetic powder in the first compound. The crystal grain size contributes to the magnitude of the remanent magnetic flux density. A larger crystal grain size results in a higher remanent magnetic flux density and lower coercivity. On the other hand, a grain size distribution of aggregated crystal grains with a higher proportion of fine grains results in a higher compressive density. Even if the compressive density is high, the remanent magnetic flux density will also be high. The grain size distribution of aggregated crystal grains differs between the central part 32 and both ends 31, with the central part 32 having a higher proportion of fine grains. This first method can be implemented, for example, by selecting a magnetic powder with an appropriate average crystal grain size from among magnetic powders with a large average crystal grain size and magnetic powders with a small average crystal grain size. The second method involves using a smaller amount of binder in the second compound than in the first compound. The third method involves incorporating a substance that increases magnetic flux density into the magnetic powder contained in the second compound. Examples of substances that increase magnetic flux density include aluminum, copper, and cobalt.

[0034] Furthermore, the magnetic powder contained in the first compound may contain a substance that increases coercivity. Examples of such substances include gallium and zirconium. While the ends 31 tend to have high compressive density and magnetic flux density, they are also prone to demagnetization. Therefore, the ends 31 are sometimes infused with substances such as gallium and zirconium to increase their demagnetization resistance.

[0035] In other words, the magnet 30 in this embodiment can be understood as consisting of a first magnet, a second magnet, and a third magnet. The first magnet may be a neodibond magnet, the second magnet may be a neodibond magnet with a higher magnetic flux density than the first magnet, and the third magnet may be the same neodibond magnet as the first magnet. The magnet 30 may be a bond magnet in which these magnets are arranged in the axial direction of a cylinder and integrally molded in a mold.

[0036] By using the method described above, the decrease in magnetic force in the central part 32 is suppressed, making it possible to improve the performance of the rotor.

[0037] Furthermore, the inventors investigated the ratio of the axial length of the central portion 32 to the overall axial length of the magnet 30.

[0038] Figures 5(a) and 5(b) show the results of an examination of these proportions. First, as shown in Figure 5(a), the inventors divided the compression-molded magnet 30 into five parts 300, 311, 312, 321, and 322. In Figure 5(a), the scale placed below the magnet 30 indicates the positions of parts 300, 311, 312, 321, and 322. Specifically, the position of magnet 30 is set to 0 [mm] to 20 [mm]. The position of part 312 is set to 3 [mm], and the position of part 311 is set to 6.5 [mm]. The position of part 300 is set to 10 [mm]. The position of part 321 is set to 13.5 [mm], and the position of part 322 is set to 17 [mm].

[0039] The inventors then measured the compressive density of each of the sections 300, 311, 312, 321, and 322. Figure 5(b) shows the results of the compressive density measurements. From the graph in Figure 5(b), it can be seen that in the range where the position is less than 10 [mm], the compression density of section 312 is the highest. It can also be seen that the compression density of section 311 is lower than that of section 312. Furthermore, it can be seen that the compression density of section 300 is the lowest. From the graph in Figure 5(b), it can be seen that even in the range where the position is greater than 10 [mm], the compression density decreases in the order of parts 322, 321, and 300.

[0040] Based on the graph in Figure 5(b), the inventors considered what proportion of the overall axial length of the magnet 30 should be filled with magnetic powder that has a high magnetic flux density. The inventors found that the compressed density is 5.83 g / cm³. 3We considered that magnetic powder with a high magnetic flux density should be added to the range where the magnetic flux density is less than or equal to 20 mm. In this case, such a range is 9.75 mm to 10.75 mm. Therefore, it is approximately 5% of the total axial length of the magnet 30 (= (10.75 mm - 9.75 mm) / 20 mm).

[0041] Furthermore, based on the graph in Figure 5(b), the inventors investigated what proportion of the overall axial length of the magnet 30 should be filled with magnetic powder that has a high magnetic flux density. The inventors found that the compressed density is 5.91 g / cm³. 3 It was considered sufficient to introduce magnetic powder with a high magnetic flux density into the range where the magnetic flux density is less than or equal to 6.5 mm. In this case, such a range is 6.5 mm to 16.5 mm. Therefore, it is approximately 50% of the total axial length of the magnet 30 (= (16.5 mm - 6.5 mm) / 20 mm).

[0042] In other words, it is preferable that the axial length of the central portion 32 relative to the overall axial length of the magnet 30 be 5% to 50%.

[0043] Furthermore, the graph in Figure 5(b) is not symmetrical. Therefore, it is only stated that it is preferable for the axial length of the central portion 32 to be 5% to 50% of the overall axial length of the magnet 30. In other words, the position of the central portion 32 in the axial direction of the magnet 30 is not specified. However, the graph in Figure 5(b) should be symmetrical if measured under ideal conditions. In this case, the position of the central part 32 of the magnet 30 in the axial direction should be symmetrical around position 10 [mm]. Specifically, the position of the smallest central part 32 should be from a position shifted 2.5% to the left of position 10 [mm] to a position shifted 2.5% to the right of position 10 [mm]. The position of the largest central part 32 should be from a position shifted 25% to the left of position 10 [mm] to a position shifted 25% to the right of position 10 [mm].

[0044] In the above description, the magnet 30 in this embodiment was explained as being used in a rotary motor, but it is not limited to this. The magnet 30 in this embodiment may also be used in motors other than rotary motors, such as vibration motors or linear motors.

[0045] This embodiment can be understood as follows: The first embodiment of the magnet is a magnet used in an electric motor, comprising a compound made of a mixture of magnetic powder and a binder, and including both ends in a predetermined direction, the compound comprising both ends and a first compound having a first magnetic flux density, and a central part sandwiched between the two ends and comprising a second compound having a second magnetic flux density higher than the first magnetic flux density. The magnet of the second embodiment is a magnet formed by compressing and molding a compound in a predetermined direction, as in the magnet of the first embodiment. A magnet of the third embodiment is a magnet of the first or second embodiment in which the length of the central part in a predetermined direction is 5% to 50% of the total length of the magnet in that predetermined direction. The fourth embodiment of the magnet is a magnet in which the magnetic powder contains neodymium, in any of the first to third embodiments. The fifth embodiment of the magnet is a magnet in which the magnetic powder further contains niobium, in the case of the fourth embodiment of the magnet. The sixth embodiment of the magnet is a magnet in which, in any of the first to fifth embodiments, the average crystal grain size of the magnetic powder contained in the second compound is larger than the average crystal grain size of the magnetic powder contained in the first compound. The seventh embodiment of the magnet is a magnet in which, in any of the first to sixth embodiments, the amount of binder contained in the second compound is less than the amount of binder contained in the first compound. The eighth embodiment of the magnet is a magnet of any of the first to seventh embodiments, wherein the magnetic powder contained in the second compound contains a substance that increases the magnetic flux density. The magnet of the ninth embodiment is a magnet in which, in the magnet of the eighth embodiment, the substance that increases the magnetic flux density is one of aluminum, copper, and cobalt. The magnet of the tenth embodiment is a magnet of any of the first to ninth embodiments, wherein the magnetic powder contained in the first compound contains a substance that increases coercivity. The magnet of the eleventh embodiment is a magnet in which, in the magnet of the tenth embodiment, the substance that increases the coercivity is either gallium or zirconium. The rotor of the first embodiment is a rotor using a magnet of any of the first to eleventh embodiments. The electric motor of the first embodiment is an electric motor equipped with a rotor of the first embodiment. The vacuum cleaner of the first embodiment is a vacuum cleaner equipped with an electric motor of the first embodiment. [Explanation of Symbols]

[0046] 1...Vacuum cleaner, 2...Suction part, 3...Pipe part, 4...Main body part, 5...Handle part, 6...Dust case, 7...Fan motor, 8...Battery, 9...Control unit, 10...Rotor assembly, 20...Rotating shaft, 30...Magnet, 31...Both ends, 31a...Upper end, 31b...Lower end, 32...Center part, 300, 311, 312, 321, 322...Parts

Claims

1. A magnet used in an electric motor, It consists of a compound made by mixing magnetic powder and a binder. Both ends, including both ends in a predetermined direction, are made of the first compound which is the compound having a first magnetic flux density, A central portion consisting of a second compound, which is the compound having a second magnetic flux density higher than the first magnetic flux density, sandwiched between the two ends of the aforementioned compound. Magnets, including

2. The magnet according to claim 1, formed by compressing the compound in the predetermined direction.

3. The magnet according to claim 1 or claim 2, wherein the length of the central portion in the predetermined direction is 5% to 50% of the total length of the magnet in the predetermined direction.

4. The magnetic powder contains neodymium, as described in claim 1 or claim 2.

5. The magnet according to claim 4, wherein the magnetic powder further contains niobium.

6. The magnet according to claim 1 or claim 2, wherein the average crystal grain size of the magnetic powder contained in the second compound is larger than the average crystal grain size of the magnetic powder contained in the first compound.

7. The magnet according to claim 1 or claim 2, wherein the amount of the binder contained in the second compound is less than the amount of the binder contained in the first compound.

8. The magnet according to claim 1 or claim 2, wherein the magnetic powder contained in the second compound contains a substance that increases the magnetic flux density.

9. The magnet according to claim 8, wherein the substance that increases the magnetic flux density is any of aluminum, copper, and cobalt.

10. The magnet according to claim 1 or claim 2, wherein the magnetic powder contained in the first compound contains a substance that increases coercivity.

11. The magnet according to claim 10, wherein the substance that increases the coercivity is either gallium or zirconium.

12. A rotor using the magnet described in claim 1 or claim 2.

13. An electric motor equipped with the rotor described in claim 12.

14. A vacuum cleaner equipped with the electric motor described in claim 13.

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