Sectional magnet array and brushless permanent magnet synchronous motor

Abstract

The invention relates to a segmented magnet array and a brushless permanent magnet synchronous motor. The segmented magnet array includes first magnet segments and second magnet segments, the two magnet segments are alternately arranged in a circumferential direction to form a magnet ring, the first magnet segments and the second magnet segments are configured as rare earth element-free magnets, and the first magnet segments and the second magnet segments have magnetization directions perpendicular to each other. The brushless permanent magnet synchronous motor comprises a stator and a rotor, and the rotor is constructed into the segmented magnet array. According to the motor disclosed by the invention, the cogging torque and the torque pulsation can be obviously reduced under the condition that a rare earth element magnet is not used, and the performance which is approximately equivalent to that of a rare earth permanent magnet motor is obtained under the same excitation condition and volume.

Description

Technical Field

[0001] The present invention relates to the field of motors, and more particularly to brushless permanent magnet synchronous motors. Specifically, in a first aspect, the present invention relates to a segmented magnet array for a motor rotor. In a second aspect, the present invention relates to a brushless permanent magnet synchronous motor including the segmented magnet array. Background Art

[0002] Conventional brushless permanent magnet synchronous motors require high-performance permanent magnets made of sintered rare earth elements due to the requirement for high power density. Since the reserves of rare earth elements in nature are gradually decreasing as the amount used increases, and the price is increasing year by year, the manufacturing cost of motors is also gradually increasing. Therefore, there is a need to eliminate the dependence on rare earth elements.

[0003] Ferrite and alnico magnets are inexpensive. However, the remanence of pure ferrite is only 1 / 3 of that of rare earth element magnets, so it is difficult to achieve performance comparable to that of rare earth element magnets. The remanence of alnico magnets can reach 1.05 Tesla, which is about 70% of the remanence of rare earth element magnets. However, at room temperature, its coercivity is only 10% of that of rare earth element magnets. Therefore, alnico magnets are generally considered not suitable for use in motors. Summary of the Invention

[0004] The object of the present invention is to overcome the above-mentioned disadvantages existing in the prior art. Therefore, the object of the present invention is to provide a permanent magnet motor, such as a brushless permanent magnet synchronous motor, in which the permanent magnet does not contain rare earth elements and still can achieve performance comparable to that of rare earth element magnets.

[0005] On the one hand, the present invention provides a segmented magnet array for a motor rotor, which includes a first magnet segment and a second magnet segment. The two magnet segments are arranged alternately in the circumferential direction to form a magnetic ring. According to the present invention, the first magnet segment and the second magnet segment are configured not to contain rare earth element magnets, and the first magnet segment and the second magnet segment have magnetization directions perpendicular to each other.

[0006] According to an embodiment, the first magnet segment is an alnico magnet, and the second magnet segment is a ferrite. The alnico magnet can also be replaced by a ferrite.

[0007] According to an embodiment, the magnetization direction of the first magnet segment is the radial direction, and the magnetization direction of the second magnet segment is the tangential direction or the circumferential direction.

[0008] According to an embodiment, the magnetization directions of adjacent first magnet segments in the circumferential direction are opposite to each other, and the magnetization directions of adjacent second magnet segments in the circumferential direction are opposite to each other.

[0009] According to an embodiment, the first magnet segment is configured as a sector cross-section segment, and the second magnet segment is configured as a rectangular cross-section segment.

[0010] Under the above configuration, preferably, the first magnet segment and the second magnet segment are configured according to at least one of the following parameters:

[0011] The ratio of the maximum pole arc (i.e., the outer arc length of the first magnet segment) to the maximum pole pitch (i.e., the outer ring radius of the magnetic ring*2π / number of poles) is 0.7-0.8;

[0012] The ratio of the maximum pole pitch to the radial length of the second magnet segment is 1.3-2.0;

[0013] The ratio of the radial length of the second magnet segment to the width of the second magnet segment, that is, the thickness of the second magnet segment, is 2-3;

[0014] A ratio of a maximum thickness of the first magnet segment in a radial direction to a radial length of the second magnet segment is 1-1.5;

[0015] The first magnet segment has a Hcj of >110 kA / m at room temperature;

[0016] The second magnet segment has a Hcj of >300 kA / m at room temperature.

[0017] The temperature coefficient of coercivity of rare earth magnets is about -0.6%, while that of AlNiCo magnets is about 0.04%. Therefore, although the coercivity of the two magnets differs by 10 times at room temperature, at high temperatures, such as 130 degrees Celsius, the coercivity of the two magnets differs by only 3-4 times. By selecting the above parameters, the thickness of the AlNiCo magnet in the magnetization direction is increased, for example, by about 3-4 times the thickness of the rare earth magnet in the magnetization direction, and the present invention avoids demagnetization of the AlNiCo magnet.

[0018] According to an embodiment, the third harmonic or the fifth harmonic is injected into the first magnet segment.

[0019] According to embodiments, the magnet segments of a segmented magnet array may be assembled together in a variety of ways, such as by overmolding with a plastic holder or held together by gluing.

[0020] In another aspect, the present invention provides a brushless permanent magnet synchronous motor, which includes a stator and a rotor configured with the segmented magnet array as described above.

[0021] According to an embodiment, the rotor is an inner rotor, and the motor is an 18-slot 16-pole, 12-slot 14-pole, 12-slot 10-pole or 12-slot 8-pole motor or an 18-slot 12-pole or 9-slot 6-pole motor. The rotor structure can also be extended to an outer rotor.

[0022] According to the configuration of the present invention, the need for relying on rare earth elements is eliminated, while under the same excitation conditions and volume, the motor can still obtain performance substantially equivalent to that of a rare earth permanent magnet motor, such as in terms of torque density. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Embodiments of the invention will be explained in more detail in the accompanying drawings, in which:

[0024] Figure 1 is a schematic diagram of the arrangement of a rotor and a stator of a brushless permanent magnet synchronous motor according to an embodiment of the present invention, wherein the permanent magnets constituting the rotor do not contain rare earth elements;

[0025] Figure 2 yes Figure 1 Schematic diagram of the magnetization of the rotor in FIG.

[0026] Figure 3 yes Figure 1 A schematic diagram of an alternating arrangement of magnet segments of a rotor in FIG.

[0027] Figure 4 Is adopted Figure 1 A schematic diagram of the magnetic field strength of the arrangement in , where for clarity, only the magnetic field strength of one quarter of the model is shown, and the magnetic field strength of the remaining parts is similar; and

[0028] Figure 5 Is adopted Figure 1 Schematic diagram of the magnetic flux of the arrangement in , where for clarity, only the magnetic flux of one quarter of the model is shown, and the magnetic flux of the remaining parts is similar.

[0029] In the drawings, embodiments of the present invention are shown in a simplified manner for the sake of clarity. Furthermore, the drawings are not drawn to scale. DETAILED DESCRIPTION

[0030] The embodiments of the present invention are described in detail below.

[0031] Figure 1 The arrangement of the rotor 10 and the stator 20 of the brushless permanent magnet synchronous motor 1 according to an embodiment of the present invention is shown. In this example, the motor is a 12-slot 8-pole motor, that is, the rotor 10 has 8 poles, the stator 20 has 12 stator slots and corresponding stator teeth, and the rotor 10 is an inner rotor, and the stator 20 is located outside the rotor 10. The motor can also be selected as an 18-slot 16-pole, 12-slot 14-pole or 12-slot 10-pole motor or an 18-slot 12-pole or 9-slot 6-pole motor.

[0032] Figure 2 The magnetization of the rotor 10 is shown. Figure 2As shown, the rotor 10 is a segmented structure, which includes a first magnet segment 11 and a second magnet segment 12. The two magnet segments are alternately arranged along the circumferential direction to form a magnetic ring, and the magnetization directions of the first magnet segment 11 and the second magnet segment 12 are perpendicular to each other, wherein the magnetization direction of the first magnet segment 11 is the radial direction of the rotor 10, and the magnetization direction of the second magnet segment 12 is the tangential direction or circumferential direction of the rotor 10. The first magnet segment 11 is configured as a fan-shaped cross-section segment, and the second magnet segment 12 is configured as a rectangular cross-section segment. Each first magnet segment 11 has the same structure, and each second magnet segment 12 has the same structure.

[0033] Figure 2 It is also shown that the magnetization directions of the first magnet segments 11 adjacent in the circumferential direction are opposite to each other, and the magnetization directions of the second magnet segments 12 adjacent in the circumferential direction are opposite to each other.

[0034] The first magnet segment 11 and the second magnet segment 12 do not contain rare earth elements. In an embodiment, the first magnet segment 11 is an Alnico magnet and the second magnet segment 12 is a ferrite. In another embodiment, the first magnet segment is also a ferrite.

[0035] Figure 3 The dimensional relationship between the first magnet segment 11 and the second magnet segment 12 of the rotor 10 is shown. Figure 3 As shown, the first magnet segment 11 and the second magnet segment 12 are constructed according to the following parameters:

[0036] The ratio of the maximum pole arc PA (i.e., the outer arc length of the first magnet segment 11) to the maximum pole pitch PP (i.e., the outer ring radius Rad1*2π / number of poles of the magnetic ring) is 0.7-0.8;

[0037] The ratio of the maximum pole pitch PP to the radial length Lm1 of the second magnet segment 12 is 1.3-2.0;

[0038] The ratio of the radial length Lm1 of the second magnet segment 12 to the width Wid of the second magnet segment 12, that is, the thickness of the second magnet segment, is 2-3;

[0039] The ratio of the maximum thickness Lm2 of the first magnet segment 11 in the radial direction to the radial length Lm1 of the second magnet segment 12 is 1-1.5;

[0040] The first magnet segment 11 has a Hcj of >110 kA / m at room temperature;

[0041] The second magnet segment 12 has a Hcj of >300 kA / m at room temperature.

[0042] The temperature coefficient of coercivity of rare earth magnets is about -0.6%, while that of AlNiCo magnets is about 0.04%. Therefore, although the coercivity of the two magnets differs by 10 times at room temperature, at high temperatures, such as 130 degrees Celsius, the coercivity of the two magnets differs by only 3-4 times. By selecting the above parameters, the thickness of the AlNiCo magnet in the magnetization direction is increased, for example, by about 3-4 times the thickness of the rare earth magnet in the magnetization direction, and the present invention avoids demagnetization of the AlNiCo magnet.

[0043] Furthermore, the third harmonic or the fifth harmonic is injected into the first magnet segment, and the magnet segments are held together by overmolding with a plastic holder.

[0044] Figure 4 and Figure 5 Schematic diagrams showing the magnetic field strength and magnetic flux using the above arrangement are shown respectively.

[0045] In some cases, features disclosed in the present invention may be used independently of other features. On the other hand, when necessary, features disclosed in the present invention may be combined to provide various combinations.

[0046] The words and expressions used in the present invention are illustrative rather than restrictive, and therefore the use of these words and expressions is not intended to exclude any equivalents of the features illustrated and described from the scope of the present invention. Various modifications, variations and alternatives may exist within the scope of the claims. The claims are intended to cover all such equivalents.

Claims

1. A segmented magnet array for a motor rotor, comprising a first magnet segment and a second magnet segment, wherein the two magnet segments are alternately arranged along a circumferential direction to form a magnetic ring, It is characterized in that The first magnet segment and the second magnet segment are configured to contain no rare earth element magnets, and the first magnet segment and the second magnet segment have magnetization directions perpendicular to each other.

2. The segmented magnet array according to claim 1, It is characterized in that The first magnet segment is an Alnico magnet or a ferrite, and the second magnet segment is a ferrite.

3. The segmented magnet array according to claim 2, It is characterized in that The magnetization direction of the first magnet segment is a radial direction, and the magnetization direction of the second magnet segment is a tangential direction or a circumferential direction.

4. The segmented magnet array according to claim 3, It is characterized in that The magnetization directions of the first magnet segments adjacent to each other in the circumferential direction are opposite to each other, and the magnetization directions of the second magnet segments adjacent to each other in the circumferential direction are opposite to each other.

5. The segmented magnet array according to any one of claims 1 to 4, It is characterized in that The first magnet segment is configured as a sector-shaped cross-section segment, and the second magnet segment is configured as a rectangular cross-section segment.

6. The segmented magnet array according to claim 5, It is characterized in that The first magnet segment and the second magnet segment are configured according to at least one of the following parameters: The ratio of the maximum pole arc, i.e. the length of the outer arc of the first magnet segment, to the maximum pole pitch is 0.7-0.8; The ratio of the maximum pole pitch to the radial length of the second magnet segment is 1.3-2.0; The ratio of the radial length of the second magnet segment to the width of the second magnet segment, that is, the thickness of the second magnet segment, is 2-3; A ratio of a maximum thickness of the first magnet segment in a radial direction to a radial length of the second magnet segment is 1-1.5; The first magnet segment has a Hcj of >110 kA / m at room temperature; The second magnet segment has a Hcj > 300 kA / m at room temperature.

7. The segmented magnet array according to claim 5, It is characterized in that The third harmonic or the fifth harmonic is injected into the first magnet segment.

8. The segmented magnet array according to any one of claims 1 to 4, It is characterized in that The magnet segments of the segmented magnet array are held together by overmolding with plastic holders or by gluing.

9. A brushless permanent magnet synchronous motor, comprising a stator and a rotor, It is characterized in that The rotor is constructed as a segmented magnet array according to any one of claims 1-8.

10. The brushless permanent magnet synchronous motor according to claim 9, It is characterized in that The rotor is either an inner rotor or an outer rotor.

11. The brushless permanent magnet synchronous motor according to claim 9 or 10, It is characterized in that The motor is an 18-slot 16-pole motor, a 12-slot 14-pole motor, a 12-slot 10-pole motor or a 12-slot 8-pole motor, or an 18-slot 12-pole motor or a 9-slot 6-pole motor.

Images