Rare earth permanent magnet, manufacturing method thereof and motor

Abstract

The invention discloses a rare earth permanent magnet, a manufacturing method thereof and a motor. The rare earth permanent magnet is of a cuboid structure; the height direction is defined as the H direction, and the H direction is the easy magnetization direction of the rare earth permanent magnet; defining the width direction as a W direction; the cuboid structure is provided with a surface A1 and a surface An which are formed by length and height and are parallel to each other; a plurality of cross sections Ai parallel to the surface A1 are arranged between the surface A1 and the surface An, and the cross section located on the central axis of the cuboid structure is represented as Aj; the coercive force Hcj is reduced from the surface A1 to the surface Aj in the W direction; the coercive force Hcj is reduced from the surface An to the cross section Aj; the coercive force of a certain point D1 on the surface A1 is expressed as H1, an extension line is made from the point D1 in the W direction, and the extension line and the section Aj intersect at a point E1; the coercive force of the point E1 is expressed as H1 ', H1-H1'gt is 80 kA / m, and Hn-Hn' gt is 80 kA / m. The rare earth permanent magnet is good in demagnetization resistance.

Description

Technical Field

[0001] The invention relates to a rare earth permanent magnet and a manufacturing method thereof, and a motor comprising the rare earth permanent magnet. Background Art

[0002] R2Fe 14 R-Fe-B rare earth sintered magnets with B as the main phase are high-performance permanent magnets and are mainly used in voice coil motors for hard disk drives, motors for hybrid vehicles, and various home appliances.

[0003] The anti-demagnetization ability of a motor refers to the ability of the motor to resist the influence of external magnetic fields during operation. Generally speaking, the stronger the anti-demagnetization ability of a motor, the higher its stability and reliability. The strength of the anti-demagnetization ability of a motor is closely related to the materials used. For example, for permanent magnet motors, the coercive force of permanent magnet materials is an important factor affecting the anti-demagnetization ability.

[0004] Generally speaking, in the actual operation of the motor, the corners of the magnet are most likely to demagnetize. Some studies only diffuse heavy rare earths in the corners of the magnet to increase the coercivity, thereby reducing the amount of heavy rare earths used and improving the product cost performance. However, the overall coercivity of the magnet obtained in this way is low, and the anti-demagnetization performance still needs to be improved.

[0005] CN113506665A discloses a method for improving the coercivity of NdFeB magnets by efficient diffusion, comprising: coating the edges of NdFeB magnets with a grain boundary diffuser containing heavy rare earth, light rare earth or no rare earth, and then performing heat treatment. The coercivity of the magnets obtained by this method still needs to be improved.

[0006] CN117497276A discloses a RT-Ga-B rare earth permanent magnet based on optional regional grain boundary diffusion and a preparation method thereof. The preparation method comprises: coating a diffusion source in a selected area on the diffusion surface of a NdFeB magnet substrate, coating the diffusion source in the corner area of ​​the diffusion surface, and not coating the diffusion source in the non-corner area, wherein the diffusion source is a mixed dry powder of heavy rare earth and metal Ga, and then performing diffusion treatment to obtain the RT-Ga-B rare earth permanent magnet based on optional regional grain boundary diffusion.

[0007] CN115602402A discloses a rare earth permanent magnet and a method for preparing the same. The rare earth permanent magnet comprises an outer surface P1 and an adhesive surface P2 opposite to the P1. The coercive force of the central portion a1 of the P1 surface is set to H. a1 , the coercive force of the central part a2 of the bonding surface P2 is set to H a2 , satisfying H a1 >H a2; Establish a rectangular coordinate system with a2 as the origin, take the length direction of P2 surface as the X axis, take the width direction of P2 surface as the Y axis, and set the coercive force at the (0, -Y) position b1 on the edge of P1 surface as H b1 , let the coercive force at position c1 (X, -Y) on the edge of the P1 surface be H c1 , let the coercive force at position d1 (X, 0) on the edge of the P1 surface be H d1 , satisfying: the value of Y is less than the value of X, H a1 ≈H b1 , H a1 <H c1 , H a1 <H d1 The rare earth permanent magnet needs to be coated twice or multiple times, and the preparation method is slightly complicated. Moreover, the coercive force of the obtained rare earth permanent magnet still needs to be improved. Summary of the invention

[0008] One object of the present invention is to provide a rare earth permanent magnet having good anti-demagnetization performance. The magnet is suitable for a permanent magnet motor with 4 poles or more. Another object of the present invention is to provide a method for manufacturing the rare earth permanent magnet as described above. Another object of the present invention is to provide a motor. The present invention adopts the following technical solution to achieve the above objects.

[0009] In one aspect, the present invention provides a rare earth permanent magnet, which is a rectangular parallelepiped structure having a length, a width and a height; the height direction is defined as an H direction, and the H direction is the easy magnetization direction of the rare earth permanent magnet; the width direction is defined as a W direction;

[0010] The rectangular parallelepiped structure has two parallel surfaces A1 and An formed by the length and height; there are a plurality of cross sections Ai parallel to the surface A1 between the surface A1 and the surface An, wherein the cross section located at the central axis of the rectangular parallelepiped structure is denoted as Aj;

[0011] Along the W direction, from surface A1 to surface Aj, the coercive force H cj Decrease; along the W direction, from the surface An to the cross section Aj, the coercive force H cj reduce;

[0012] The coercive force of a point D1 on the surface A1 is represented by H1. From point D1, an extension line is drawn along the W direction. The extension line intersects the cross section Aj at point E1. The coercive force of point E1 is represented by H1'. Then H1-H1'>80kA / m.

[0013] The coercive force of a point Dn on the surface An is expressed as Hn. An extension line is drawn from point Dn along the W direction, and the extension line intersects the cross section Aj at point En. The coercive force of point En is expressed as Hn', then Hn-Hn'>80kA / m.

[0014] According to the rare earth permanent magnet of the present invention, preferably, the rare earth RE content in the rare earth permanent magnet is 28-34wt%, and RE is light rare earth elements and heavy rare earth elements; the light rare earth elements must contain Nd, and the heavy rare earth elements are selected from one or more of Dy, Tb, Gd, Ho and Y.

[0015] According to the rare earth permanent magnet of the present invention, preferably, the light rare earth element is selected from one or more of Pr, Nd, La and Ce, and must contain Nd; the heavy rare earth elements are Dy and Tb.

[0016] According to the rare earth permanent magnet of the present invention, preferably, in the W direction, the relationship between the coercive force y of a certain point of the rare earth permanent magnet and the position x of the point approximately satisfies the parabola y=ax 2 +bx+c, where a>0, b<0, c>0.

[0017] On the other hand, the present invention also provides a method for manufacturing the rare earth permanent magnet as described above, comprising the following steps:

[0018] 1) providing an initial sintered NdFeB magnet having a rectangular parallelepiped structure; recording the height direction of the initial sintered NdFeB magnet as the H0 direction, and recording the width direction as the W0 direction; making the H0 direction the same as the H direction of the formed rare earth permanent magnet; making the W0 direction the same as the W direction of the formed rare earth permanent magnet;

[0019] 2) covering two opposite surfaces of the initially sintered NdFeB magnet with a heavy rare earth coating containing Dy along a direction perpendicular to the H0 direction, respectively, to obtain a magnet A;

[0020] 3) Covering two opposite sides of magnet A with a heavy rare earth coating containing Tb respectively along a direction perpendicular to W0 to obtain magnet B;

[0021] 4) Heat treating the magnet B to obtain the rare earth permanent magnet.

[0022] According to the manufacturing method of the present invention, preferably, the initial sintered NdFeB magnet is R2Fe 14 B is the main phase.

[0023] According to the manufacturing method of the present invention, preferably, in step (1), the initial sintered NdFeB magnet further contains other elements M, and the other elements M are selected from multiple elements of Cu, Co, Ga, Ti, Zr, Mo and Nb.

[0024] According to the manufacturing method of the present invention, preferably, in step (2), the weight increase of Dy is 0.4-1.5 wt%.

[0025] According to the manufacturing method of the present invention, preferably, in step (3), the weight increase of Tb is 0.05-0.5wt%.

[0026] In another aspect, the present invention further provides a motor, comprising the rare earth permanent magnets as described above; the rare earth permanent magnets are arranged in any of the following ways:

[0027] (1) 2N rare earth permanent magnets are evenly arranged in a circumferential direction along the rotation direction of the motor; the rare earth permanent magnets are located on a regular N-gon, and the angles between two adjacent rare earth permanent magnets are the same; wherein N is a positive integer greater than or equal to 2;

[0028] (2) 2M rare earth permanent magnets are divided into M groups and arranged uniformly in a circumferential direction along the rotation direction of the motor; the connecting line between the end faces of each group of rare earth permanent magnets that are far apart is located on a regular M-gon; in each group of rare earth permanent magnets, the angles between the two rare earth permanent magnets are the same, and they are arranged in a V shape, wherein M is a positive integer greater than or equal to 8;

[0029] (3) 3P rare earth permanent magnets are divided into P groups and arranged uniformly in a circumferential direction along the rotation direction of the motor; in each group of rare earth permanent magnets, three rare earth permanent magnets form an isosceles triangle, and the rare earth permanent magnet serving as the base of the isosceles triangle is located on the regular P-gon; wherein P is a positive integer greater than or equal to 8;

[0030] (4) 4Q rare earth permanent magnets are divided into Q groups and are evenly arranged in a circumferential direction along the rotation direction of the motor; in each group of rare earth permanent magnets, two parallel V-shapes are formed between the four rare earth permanent magnets; in each group of rare earth permanent magnets, the connecting line between the farthest end faces of the two rare earth permanent magnets forming the V-shape is located on a regular Q polygon; wherein Q is a positive integer greater than or equal to 6.

[0031] The rare earth permanent magnet of the present invention has good anti-demagnetization performance and is suitable for permanent magnet motors with more than or equal to 4 poles. The manufacturing method of the present invention can obtain a rare earth permanent magnet with a specific coercive force distribution and good anti-demagnetization performance. The process of the present invention has good repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The diagram is a schematic diagram of a motor formed when the rare earth permanent magnet of the present invention is used.

[0033] Figure 2 The diagram is a schematic diagram of a motor formed when the rare earth permanent magnet of the present invention is used.

[0034] Figure 3 This is a schematic diagram of cutting samples of the rare earth permanent magnet of the present invention in Preparation Example 1.

[0035] Figure 4This is a schematic diagram of preparing Example 1 by cutting the rare earth permanent magnet of the present invention into samples along the W direction and the H direction.

[0036] Figure 5 The graph is a plot of the coercive force of 15 samples (A1 to A15) of the rare earth permanent magnet obtained in Preparation Example 1 at an edge portion cut along the W direction. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0038] The "coercive force" mentioned in the present invention, also known as intrinsic coercive force, refers to the magnetic field intensity when the magnetic field is monotonically reduced to zero and then increased in the opposite direction from the saturated magnetization state of the magnet, so that the magnetization intensity decreases to zero along the saturation hysteresis loop, and the unit is Oersted (Oe) or Ampere / meter (A / m). 1Oe = 79.6A / m.

[0039] The "remanent magnetism" mentioned in the present invention refers to the value of the magnetic flux density corresponding to the point where the magnetic field intensity is zero on the saturation hysteresis loop, and the unit is Tesla (T) or Gauss (Gs).

[0040] In the present invention, the "inert gas" includes helium, neon, argon, krypton and xenon. "Inert atmosphere" refers to an atmosphere formed by inert gas and does not affect the performance of the magnet.

[0041] <Rare earth permanent magnets>

[0042] The rare earth permanent magnet of the present invention is installed in a radial flux motor and is applicable to at least a 4-pole permanent magnet motor. A four-pole motor refers to a motor with two pairs of magnetic poles.

[0043] In the present invention, the rare earth permanent magnet is a rectangular parallelepiped structure having a length, a width and a height; the height direction is defined as the H direction, and the H direction is the easy magnetization direction of the rare earth permanent magnet; the width direction is defined as the W direction;

[0044] The rectangular parallelepiped structure has two parallel surfaces A1 and An formed by the length and height; there are a plurality of cross sections Ai parallel to the surface A1 between the surface A1 and the surface An, wherein the cross section located at the central axis of the rectangular parallelepiped structure is denoted as Aj;

[0045] Along the W direction, from surface A1 to surface Aj, the coercive force H cj Decrease; along the W direction, from the surface An to the cross section Aj, the coercive force H cj reduce;

[0046] The coercive force of a point D1 on the surface A1 is represented by H1. From point D1, an extension line is drawn along the W direction. The extension line intersects the cross section Aj at point E1. The coercive force of point E1 is represented by H1'. Then H1-H1'>80kA / m.

[0047] The coercive force of a point Dn on the surface An is expressed as Hn, and an extension line is drawn from point Dn along the W direction, and the extension line intersects with the cross section Aj at point En; the coercive force of point En is expressed as Hn', then Hn-Hn'>80kA / m. The motor formed by such rare earth permanent magnets has better anti-demagnetization performance.

[0048] According to a specific embodiment of the present invention, point D1, point E1 and point Dn are located on the same straight line in the W direction, and point E1 coincides with point En.

[0049] The difference between H1 and H1' is greater than 80 kA / m, preferably greater than 100 kA / m, and more preferably greater than or equal to 145 kA / m. The difference between Hn and Hn' is greater than 80 kA / m, preferably greater than 100 kA / m, and more preferably greater than or equal to 145 kA / m. The motor formed by such rare earth permanent magnets has better anti-demagnetization performance.

[0050] In the present invention, along the W direction, from surface A1 to surface Aj, the coercive force H cj Gradually decreases; along the W direction, from the surface An to the cross section Aj, the coercive force H cj That is, in the W direction, the coercive force of the rare earth permanent magnet gradually decreases from the two ends to the middle, and the maximum value of the coercive force at the two ends (A1 or An) is greater than 2016 kA / m, preferably greater than or equal to 2019 kA / m; the minimum value of the coercive force in the middle (Aj) is greater than 1700 kA / m, preferably greater than or equal to 1730 kA / m.

[0051] In the present invention, the rare earth permanent magnet is longer than its width.

[0052] In the present invention, the rare earth permanent magnet can be a magnet of an integral structure or a magnet of a spliced ​​structure. According to a specific embodiment of the present invention, the rare earth permanent magnet is a magnet of an integral structure, not a magnet of a spliced ​​structure.

[0053] In the W direction, the relationship between the coercive force y of a certain point of the rare earth permanent magnet and the position x of the point approximately satisfies the parabola y=ax 2 +bx+c, where a>0, b<0, c>0. A point on the surface A1 (or the surface A2) of the rare earth permanent magnet is taken as the origin of the plane rectangular coordinate system, the W direction is the x-axis, the H direction is the y-axis, and the value range of x is 0.1-20, preferably 0.2-19.

[0054] In some embodiments, a is 2 to 5, b is -88 to -38, and c is 2000 to 2070. In some specific embodiments, a is 3 to 5, b is -82 to -50, and c is 2060 to 2070. In other specific embodiments, a is 2 to 4, b is -65 to -38, preferably -65 to -40, and c is 2015 to 2030, preferably 2020 to 2030.

[0055] According to one specific embodiment of the present invention, a=2.3, b=-40.3, c=2029.0. According to another specific embodiment of the present invention, a=3.6, b=-64.0, c=2020.8.

[0056] In the present invention, in the W direction, the remanence of the rare earth permanent magnet basically has a tendency to gradually increase from both ends to the middle.

[0057] The rare earth permanent magnet of the present invention contains light rare earth elements and heavy rare earth elements. The light rare earth elements must contain Nd, and the heavy rare earth elements are selected from one or more of Dy, Tb, Gd, Ho, and Y. According to a specific embodiment of the present invention, the light rare earth elements are selected from one or more of Pr, Nd, La, and Ce, and must contain Nd, and the heavy rare earth elements are Dy and Tb.

[0058] In the present invention, based on the total weight of the rare earth permanent magnet, the content of the rare earth element RE is 28-34 wt %, preferably, the content of the rare earth element RE is 29-34 wt %, more preferably, the content of the rare earth element RE is 31-34 wt %.

[0059] According to a specific embodiment of the present invention, the rare earth permanent magnet has a length of 30 to 45 mm, a width of 10 to 20 mm, and a height of less than 10 mm.

[0060] The present invention finds that such rare earth permanent magnets have good anti-demagnetization performance based on high remanence and high coercive force, and are suitable for permanent magnet motors with more than or equal to 4 poles.

[0061] <Manufacturing method>

[0062] The present invention also provides a method for manufacturing the rare earth permanent magnet as described above, the method comprising the following steps: (1) providing an initial sintered NdFeB magnet; (2) obtaining magnet A; (3) obtaining magnet B; and (4) heat treatment. This is conducive to obtaining the rare earth permanent magnet as described above.

[0063] A detailed description is given below.

[0064] Provide initial sintered NdFeB magnets

[0065] Provided with R2Fe 14The initial sintered NdFeB magnet with B as the main phase has a rectangular parallelepiped structure with length, width and height.

[0066] The height direction of the initial sintered NdFeB magnet is recorded as H0 direction, and the width direction is recorded as W0 direction; the H0 direction is made the same as the H direction of the formed rare earth permanent magnet; the W0 direction is made the same as the W direction of the formed rare earth permanent magnet.

[0067] In the initial sintered NdFeB magnet, R is a rare earth element, including Nd and Pr. Based on the total weight of the sintered NdFeB magnet, the sintered NdFeB magnet includes the following components: PrNd 28-32wt%, B 0.85-0.99wt%, Dy0.01-2wt%, Cu0.01-0.27wt%, Co 0.01-1.95wt%, Ga 0.01-0.5wt%, M 0.01-0.25wt%, Fe balance; wherein M is selected from at least one of Ti, Zr, Mo, and Nb. Wherein, the weight ratio of Pr to Nd is 1:3-1:4. In a preferred embodiment, the sintered NdFeB magnet is composed of the above components.

[0068] Based on the total weight of the initial sintered NdFeB magnet, the PrNd content is preferably 29.0-31wt%, more preferably 29.5-30.5wt%. The B content is preferably 0.87-0.97wt%, more preferably 0.89-0.96wt%. The Dy weight percentage is preferably 0.1-1.9wt%, more preferably 0.4-1.6wt%. The Cu content is preferably 0.05-0.26wt%, more preferably 0.10-0.21wt%. The Co content is preferably 0.1-1.7wt%, more preferably 0.5-1.5wt%, more preferably 1.0-1.25wt%. The Ga content is preferably 0.1-0.44wt%, more preferably 0.15-0.36wt%, such as 0.18wt%, 0.21wt%, 0.34wt%. The M content is preferably 0.05-0.21wt%, more preferably 0.10-0.19wt%, more preferably 0.15-0.18wt%. M is preferably Ti.

[0069] Get Magnet A

[0070] Along the direction perpendicular to H0, two opposite surfaces of the initial sintered NdFeB magnet are respectively covered with a heavy rare earth coating containing Dy to obtain a magnet A. In the initial sintered NdFeB magnet with a rectangular parallelepiped structure, the two opposite surfaces are surfaces of length×width. This is conducive to obtaining a rare earth permanent magnet with a specific coercive force distribution.

[0071] In the present invention, the method of covering the heavy rare earth coating containing Dy is not particularly limited, and those known in the art can be used. In certain embodiments, the method of covering the heavy rare earth coating containing Dy on two opposite surfaces of the initial sintered NdFeB magnet along the direction perpendicular to H0 is selected from one of spraying, screen printing, and magnetron sputtering.

[0072] According to one embodiment of the present invention, the heavy rare earth coating containing Dy is covered by spraying, and a spraying device can be used for the spraying.

[0073] According to one embodiment of the present invention, a Dy-containing material is sprayed to form a Dy-containing heavy rare earth coating. The Dy-containing material can be a Dy-containing substance (e.g., dysprosium hydride, dysprosium powder) mixed with an organic solvent to form a Dy mixture, and the mass concentration of the Dy mixture can be 25 to 50wt%, preferably 25 to 45wt%, and more preferably 25 to 35wt%. The organic solvent can be selected from those known in the art, for example, one selected from acetone, ethanol, isopropanol, and petroleum ether, for example, ethanol, preferably anhydrous ethanol. In this way, Dy can be covered more accurately, with high adhesion and good repeatability.

[0074] According to a specific embodiment of the present invention, during spraying, the initial sintered NdFeB magnet is preheated, and the preheating temperature can be 120-240°C, preferably 150-200°C, and more preferably 180-200°C. A material containing Dy is sprayed on one surface of the initial sintered NdFeB magnet perpendicular to the H0 direction, so that a heavy rare earth coating containing Dy is covered on the surface. The weight increase of Dy on a single surface is controlled to be 0.2-1wt%, preferably 0.25-0.8wt%, and more preferably 0.3-0.55wt%. The weight increase of Dy on a single surface = (the weight of the initial sintered NdFeB magnet covered with a heavy rare earth coating containing Dy on one side - the weight of the initial sintered NdFeB magnet) / the weight of the initial sintered NdFeB magnet × 100%.

[0075] After spraying on one surface, the magnet is turned over, and a material containing Dy is sprayed on the other surface of the initial sintered NdFeB magnet perpendicular to the H0 direction, thereby forming a magnet A. The weight increase of Dy on a single surface is controlled to be 0.2-1wt%, preferably 0.25-0.8wt%, and more preferably 0.3-0.55wt%.

[0076] During spraying, the total Dy weight gain is controlled to be 0.4-1.5wt%, preferably 0.5-1.2wt%, more preferably 0.6-1.0wt%. The total Dy weight gain = (weight of magnet A - weight of initial sintered NdFeB magnet) / weight of initial sintered NdFeB magnet × 100%.

[0077] Magnet B

[0078] Along the direction perpendicular to W0, two opposite sides of magnet A are respectively covered with heavy rare earth coatings containing Tb to obtain magnet B. In magnet A having a rectangular parallelepiped structure, the two opposite sides are surfaces of length × height (or thickness). This is conducive to obtaining a rare earth permanent magnet with a specific coercive force.

[0079] In the present invention, there is no particular limitation on the manner of covering two opposite sides of the magnet A with a heavy rare earth coating perpendicular to the W0 direction, and those known in the art may be used, for example, one selected from spraying, screen printing, and magnetron sputtering.

[0080] According to one embodiment of the present invention, a Tb-containing material is sprayed to form a Tb-containing heavy rare earth coating. The Tb-containing material can be a Tb-containing substance (such as terbium powder) mixed with an organic solvent to form a Tb mixture, and the mass concentration of the Tb mixture can be 25 to 50wt%, preferably 25 to 40wt%, and more preferably 25 to 30wt%. The organic solvent can be those known in the art, for example, it can be selected from one of acetone, ethanol, isopropanol and petroleum ether, preferably ethanol. In this way, Tb can be covered more accurately, with high adhesion and good repeatability. In the present invention, a spraying device can be used during spraying.

[0081] According to a specific embodiment of the present invention, during spraying, magnet A is preheated at 120-240°C, preferably 150-200°C, and more preferably 180-200°C. A material containing Tb is sprayed on one side of magnet A perpendicular to the W0 direction, so that a heavy rare earth coating containing Tb is covered on the side. The weight increase of Tb on a single side is controlled to be 0.02-0.2wt%, preferably 0.03-0.15wt%, and more preferably 0.05-0.1wt%. The weight increase of Tb on a single side = (the weight of magnet A covered with a heavy rare earth coating containing Tb on a single side - the weight of magnet A) / the weight of magnet A × 100%.

[0082] After spraying on one side, the magnet is turned over, and a material containing Tb is sprayed on the other side of the magnet A perpendicular to the W0 direction, thereby forming a magnet B. The weight increase of Tb on a single side is controlled to be 0.02-0.2wt%, preferably 0.03-0.15wt%, and more preferably 0.05-0.1wt%.

[0083] During spraying, the total Tb weight gain is controlled to be 0.05-0.5wt%, preferably 0.1-0.5wt%, more preferably 0.15-0.35wt%. The total Tb weight gain = (weight of magnet B - weight of magnet A) / weight of magnet A × 100%.

[0084] Heat Treatment

[0085] The magnet B is subjected to heat treatment to obtain the rare earth permanent magnet.

[0086] In the present invention, the heat treatment may be performed under vacuum conditions, with a vacuum degree of less than or equal to 0.1 Pa, preferably less than or equal to 0.01 Pa, and more preferably less than or equal to 0.001 Pa.

[0087] The magnet B may be subjected to heat treatment at multiple gradient temperatures to obtain a rare earth permanent magnet. Preferably, the magnet B is subjected to heat treatment at a first temperature, a second temperature, a third temperature, and a fourth temperature, and then cooled; and then subjected to heat treatment at a fifth temperature and cooled to obtain a rare earth permanent magnet.

[0088] The magnet B is heated to a first temperature and heat treated at the first temperature for 1 to 1.5 hours. The first temperature is 100 to 140°C, preferably 100 to 130°C, and more preferably 100 to 120°C. Then the temperature is raised to a second temperature and heat treated at the second temperature for 1 to 1.5 hours. The second temperature can be 180 to 250°C, preferably 200 to 230°C, and more preferably 200 to 220°C. Then the temperature is raised to a third temperature and heat treated at the third temperature for 1 to 1.5 hours; the third temperature can be 450 to 550°C, preferably 500 to 550°C, and more preferably 500 to 530°C. Then the temperature is raised to a fourth temperature and heat treated at the fourth temperature for 8 to 24 hours. The fourth temperature can be 860 to 950°C, preferably 880 to 920°C, and more preferably 900 to 920°C. The heat treatment time at the fourth temperature is preferably 10 to 11 hours.

[0089] In the present invention, the cooling may be performed using an inert gas, preferably an argon gas, and the temperature may be 50° C. or lower.

[0090] Then the temperature is raised to the fifth temperature, and heat treated at the fifth temperature for 4 to 7 hours. The fifth temperature can be 450 to 550°C, preferably 490 to 530°C, and more preferably 500 to 530°C. The heat treatment time is preferably 5 to 6 hours. After the heat treatment at the fifth temperature is completed, the rare earth permanent magnet is obtained by cooling to below 50°C. This is conducive to obtaining a rare earth permanent magnet with stable performance.

[0091] According to a specific embodiment of the present invention, magnet B is heated to a first temperature of 100-140°C and heat treated at the first temperature for 1-1.5h; then the temperature is raised to a second temperature of 180-250°C and heat treated at the second temperature for 1-1.5h. Then the temperature is raised to a third temperature of 450-550°C and heat treated at the third temperature for 1-1.5h. Continue to raise the temperature to a fourth temperature of 850-950°C and heat treat at the fourth temperature for 8-24h. Then, stop heating and cool to below 50°C using an inert gas. Then, raise the temperature to a fifth temperature of 450-520°C, heat treat at the fifth temperature for 4-7h, and stop heating. Cool to below 50°C using an inert gas to obtain a rare earth permanent magnet. This is conducive to obtaining a rare earth permanent magnet with stable performance.

[0092] <Motor>

[0093] The present invention also provides a motor, comprising the above-mentioned rare earth permanent magnet; the rare earth permanent magnet is arranged in any of the following ways:

[0094] (1) 2N rare earth permanent magnets are evenly arranged in a circumferential direction along the rotation direction of the motor; the rare earth permanent magnets are located on a regular N-gon, and the angles between two adjacent rare earth permanent magnets are the same; wherein N is a positive integer greater than or equal to 3;

[0095] (2) 2M rare earth permanent magnets are divided into M groups and arranged uniformly in a circumferential direction along the rotation direction of the motor; the connecting line between the end faces of each group of rare earth permanent magnets that are far apart is located on a regular M-gon; in each group of rare earth permanent magnets, the angles between the two rare earth permanent magnets are the same, and they are arranged in a V shape, wherein M is a positive integer greater than or equal to 8;

[0096] (3) 3P rare earth permanent magnets are divided into P groups and arranged uniformly in a circumferential direction along the rotation direction of the motor; in each group of rare earth permanent magnets, three rare earth permanent magnets form an isosceles triangle, and the rare earth permanent magnet serving as the base of the isosceles triangle is located on the regular P-gon; wherein P is a positive integer greater than or equal to 8;

[0097] (4) 4Q rare earth permanent magnets are divided into Q groups and are evenly arranged in a circumferential direction along the rotation direction of the motor; in each group of rare earth permanent magnets, two parallel V-shapes are formed between the four rare earth permanent magnets; in each group of rare earth permanent magnets, the connecting line between the farthest end faces of the two rare earth permanent magnets forming the V-shape is located on a regular Q polygon; wherein Q is a positive integer greater than or equal to 6.

[0098] The motor is a motor with 4 poles or more and has good anti-demagnetization performance.

[0099] According to a specific embodiment of the present invention, 8 rare earth permanent magnets are evenly arranged in a circumferential direction along the rotation direction of the motor; the rare earth permanent magnets are located on a regular octagon, and the angles between two adjacent rare earth permanent magnets are the same. According to another specific embodiment of the present invention, 16 rare earth permanent magnets are divided into 8 groups and evenly arranged in a circumferential direction along the rotation direction of the motor; the line between the end faces of each group of rare earth permanent magnets that are far apart is located on a regular octagon; in each group of rare earth permanent magnets, the angles between the two rare earth permanent magnets are the same, and they are arranged in a V-shape.

[0100] <Test Method>

[0101] Determination of magnetic properties: The magnetic properties were measured at room temperature using a magnetic tester produced by Belgium's Metis.

[0102] <Ingredients>

[0103] During spraying, the material containing Dy is a Dy mixture with a Dy mass concentration of 30 wt% formed by dysprosium powder and anhydrous ethanol. The material containing Tb is a Tb mixture with a Tb mass concentration of 30 wt% formed by terbium powder and anhydrous ethanol.

[0104] Preparation Example 1-Rare Earth Permanent Magnet

[0105] This embodiment provides a rare earth permanent magnet, which is installed on a radial flux motor.

[0106] The rare earth permanent magnet is a rectangular parallelepiped structure having a length, a width and a height. The height direction is defined as an H direction, which is the easy magnetization direction of the rare earth permanent magnet. The width direction is defined as a W direction.

[0107] The rectangular parallelepiped structure has two parallel surfaces A1 and An consisting of a length and a height; there are several sections Ai parallel to the surface A1 between the surface A1 and the surface An, among which the section located at the central axis of the rectangular parallelepiped structure is denoted as Aj.

[0108] Along the W direction, from surface A1 to surface Aj, the coercive force H cj Decrease; along the W direction, from the surface An to the cross section Aj, the coercive force H cj Reduced. Let the coercive force of a point D1 on the surface A1 be H1, and an extension line is drawn from point D1 along the W direction, and the extension line intersects with the section Aj at point E1; let the coercive force of point E1 be H1', ​​then H1-H1'>80kA / m. Let the coercive force of a point Dn on the surface An be Hn, and an extension line is drawn from point Dn along the W direction, and the extension line intersects with the section Aj at point En; let the coercive force of point En be Hn', then Hn-Hn'>80kA / m. And D1, E1 and Dn are on the same straight line in the W direction, and E1 and En coincide.

[0109] In the W direction, the relationship between the coercive force y of a certain point of the rare earth permanent magnet and the position x of the point approximately satisfies the parabola y=ax 2 +bx+c, where a>0, b<0, c>0. A point on the surface A1 of the rare earth permanent magnet is taken as the origin of the plane rectangular coordinate system, the W direction is the x-axis, the value range of x is 0.1-20, and the H direction is the y-axis.

[0110] The manufacturing method of the rare earth permanent magnet is introduced below, comprising the following steps:

[0111] An initial sintered NdFeB magnet was provided, with a size of 39 mm (length) × 17.8 mm (width) × 4 mm (height, ie, orientation direction), and the surface of the magnet was polished. The composition of the initial sintered NdFeB magnet is shown in Table 1 below.

[0112] Table 1

[0113] Components PcqI B Dy Cu Co Ga Ti Fe wt% 29.97 0.95 0.54 0.19 1.08 0.21 0.15 margin

[0114] Note: The weight ratio of Pr to Nd is 1:3.

[0115] The height direction of the initial sintered NdFeB magnet is recorded as H0 direction, and the width direction is recorded as W0 direction; the H0 direction is made the same as the H direction of the formed rare earth permanent magnet; the W0 direction is made the same as the W direction of the formed rare earth permanent magnet.

[0116] Along the direction perpendicular to H0, two opposite surfaces of the initial sintered NdFeB magnet are respectively covered with a heavy rare earth coating containing Dy to obtain a magnet A. Specifically, the following steps are included: the initial sintered NdFeB magnet is placed in a spraying device, one surface (the surface of 39mm×17.8mm) of the magnet faces upward, and is preheated at 180°C, and then the heavy rare earth coating containing Dy is covered on the surface by spraying. The single-sided weight gain of Dy is 0.325wt%. The magnet is turned over. The other surface (the opposite side of the surface of 39mm×17.8mm) is covered with a heavy rare earth coating containing Dy by spraying to obtain a magnet A. The single-sided weight gain of Dy is 0.325wt%.

[0117] Along the direction perpendicular to W0, two opposite sides of magnet A are respectively covered with a heavy rare earth coating containing Tb to obtain magnet B. Specifically, the following steps are included: one side (39mm×4mm side) of magnet A is facing upward, preheated at 180°C, and the heavy rare earth coating containing Tb is covered on the side by spraying. The single-side weight gain of Tb is 0.075%. Turn the magnet over, and cover the other side (the opposite side of the 39mm×4mm side) with a heavy rare earth coating containing Tb by spraying to obtain magnet B. The single-side weight gain of Tb is 0.075%.

[0118] The magnet B is heat treated to obtain the rare earth permanent magnet. Specifically comprising the following steps: heating the magnet B to a first temperature of 100°C and keeping it at 100°C for 1 hour. Then, heating it to a second temperature of 200°C and keeping it at 200°C for 1 hour. Then, heating it to a third temperature of 500°C and keeping it at 500°C for 1 hour. Continue heating it to a fourth temperature of 920°C and keep it at 920°C for 12 hours. Stop heating, cool it to below 50°C with argon, then heat it to a fifth temperature of 490°C and keep it at 490°C for 5 hours. Stop heating, cool it to below 50°C with argon, and obtain a rare earth permanent magnet.

[0119] Reference Figure 3 , three samples with the size of 17.8mm×4mm×1mm were cut along the length and width direction of the rare earth permanent magnet (length is 39mm, width is 17.8mm). The cutting parts are located at two end positions and one center position in the length direction of the magnet (length is 39mm), namely position 1, position 2, and position 3.

[0120] Reference Figure 4 , cut the 17.8mm×4mm×1mm sample along the center line position and two edge positions in the H direction (height is 4mm) to obtain samples with a size of 1mm×1mm×1mm, 15 samples per layer, and the serial numbers are shown in the following table. The room temperature properties of the samples were measured respectively, as shown in Table 2. Since positions 1 and 3 are symmetrical, only the properties of the samples cut from position 1 were measured. The coercivity curves of the samples from A1 to A15 at position 1 are formed, as shown in Table 2. Figure 5 .

[0121] Table 2

[0122] Sampling No. Br(T) Hcj(kA / m) Sample 1 (A1) 1.332 2030 Sample 2 (A2) 1.344 1951 Sample 3 (A3) 1.339 1918 Sample 4 (A4) 1.338 1910 Sample 5 (A5) 1.401 1880 Sample 6 (A6) 1.403 1865 Sample 7 (A7) 1.411 1857 Sample 8 (A8) 1.41 1843 Sample 9 (A9) 1.405 1861 Sample 10 (A10) 1.402 1878 Sample 11 (A11) 1.403 1893 Sample 12 (A12) 1.339 1905 Sample 13 (A13) 1.338 1934 Sample 14 (A14) 1.341 1963 Sample 15 (A15) 1.338 2019 Sample 1'(B1) 1.335 2013 Sample 2'(B2) 1.341 1941 Sample 3'(B3) 1.345 1820 Sample 4'(B4) 1.344 1805 Sample 5'(B5) 1.409 1783 Sample 6'(B6) 1.41 1753 Sample 7'(B7) 1.414 1751 Sample 8'(B8) 1.41 1738 Sample 9'(B9) 1.405 1759 Sample 10'(B10) 1.402 1788 Sample 11'(B11) 1.403 1791 Sample 12'(B12) 1.339 1803 Sample 13'(B13) 1.338 1841 Sample 14'(B14) 1.341 1929 Sample 15'(B15) 1.338 1988

[0123] It can be seen that in the rare earth permanent magnet of the present invention, in the W direction, the coercive force of the rare earth permanent magnet has a tendency to decrease from both ends to the middle. And the difference between the coercive force H1 of a certain point D1 on the surface A1 of the rare earth permanent magnet (for example, the coercive force of the A1 sample is 2030 kA / m) and the coercive force H1' of the point E1 where the extension line from point D1 along the W direction intersects the cross section Aj (for example, the coercive force of the A8 sample is 1843 kA / m) is greater than 80 kA / m, for example, 187 kA / m.

[0124] Similarly, the difference between the coercive force of the A15 sample (2019 kA / m) and the coercive force of the A8 sample (1843 kA / m) is greater than 80 kA / m, for example, 176 kA / m.

[0125] Likewise, the difference between the coercive force of the B1 sample (2013 kA / m) and the coercive force of the B8 sample (1738 kA / m) is greater than 80 kA / m, for example, 275 kA / m.

[0126] Likewise, the difference between the coercive force of the B15 sample (1988 kA / m) and the coercive force of the B8 sample (1738 kA / m) is greater than 80 kA / m, for example, 250 kA / m.

[0127] In the W direction, the relationship between the coercive force y of a certain point of the rare earth permanent magnet and the position x of the point approximately satisfies the parabola y=ax 2 +bx+c, where a>0, b<0, c>0. A point on the surface A1 of the rare earth permanent magnet is taken as the origin of the plane rectangular coordinate system, the W direction is the x-axis, the value range of x is 0.1-20, and the H direction is the y-axis.

[0128] At the edge (A1 to A15), the parabola is a = 2.3, b = -40.3, c = 2029.0; R 2 =0.9691.

[0129] In the center (B1-B15), the parabola is a=3.6, b=-64.0, c=2020.8; R 2 =0.9515.

[0130] for Figure 3 Continue sampling at position 2: Figure 4 As shown, the sample at position 2 is sampled and tested in the same manner as the sample at position 1, and the samples are A1' to A15'.

[0131] (i.e. the same sampling positions as A1 to A15 respectively), B1” to B15” (i.e. the same sampling positions as B1 to B15 respectively), the detected coercive forces are shown in Table 3.

[0132] Table 3

[0133] Sampling No. Br(T) Hcj(kA / m) Sample 1" (A1') 1.333 2035 Sample 2" (A2') 1.341 1958 Sample 3" (A3') 1.336 1921 Sample 4" (A4') 1.335 1913 Sample 5" (A5') 1.405 1885 Sample 6" (A6') 1.402 1859 Sample 7" (A7') 1.41 1861 Sample 8" (A8') 1.409 1848 Sample 9" (A9') 1.403 1869 Sample 10" (A10') 1.4 1875 Sample 11" (A11') 1.401 1897 Sample 12" (A12') 1.337 1910 Sample 13" (A13') 1.336 1939 Sample 14" (A14') 1.342 1961 Sample 15" (A15') 1.336 2026 Sample 1"'(B1') 1.337 2009 Sample 2"'(B2") 1.342 1936 Sample 3"' (B3) 1.343 1823 Sample 4"' (B4') 1.346 1811 Sample 5"' (B5') 1.406 1785 Sample 6"' (B6') 1.413 1751 Sample 7”' (B7') 1.411 1748 Sample 8"' (B8') 1.412 1741 Sample 9"' (B9') 1.408 1756 Sample 10"' (B10') 1.405 1786 Sample 11"' (B11') 1.401 1797 Sample 12"' (B12') 1.337 1805 Sample 13"' (B13') 1.339 1839 Sample 14"' (B14') 1.34 1926 Sample 15"' (B15') 1.336 1991

[0134] It can be seen from this that in the rare earth permanent magnet of the present invention, in the W direction, the coercive force of the rare earth permanent magnet tends to decrease from both ends to the middle.

[0135] Moreover, the difference between the coercive force H1 of a certain point D1 on the surface A1 of the rare earth permanent magnet (for example, the coercive force of the A1' sample is 2035 kA / m) and the coercive force H1' of the point E1 where the extension line from point D1 along the W direction intersects the cross section Aj (for example, the coercive force of the A8' sample is 1848 kA / m) is greater than 80 kA / m, for example, it can be greater than or equal to 187 kA / m.

[0136] Likewise, the difference between the coercivity of the A15' sample (2026 kA / m) and the coercivity of the A8' sample (1848 kA / m) is greater than 80 kA / m, for example, 178 kA / m.

[0137] Similarly, the difference between the coercive force of the B1' sample (2009 kA / m) and the coercive force of the B8' sample (1741 kA / m) is greater than 80 kA / m, for example, 268 kA / m.

[0138] Likewise, the difference between the coercive force of the B15' sample (1991 kA / m) and the coercive force of the B8' sample (1741 kA / m) is greater than 80 kA / m, for example, 250 kA / m.

[0139] In the W direction, the relationship between the coercive force y of a certain point of the rare earth permanent magnet and the position x of the point approximately satisfies the parabola y=ax 2 +bx+c, where a>0, b<0, c>0. A point on the surface A1 of the rare earth permanent magnet is taken as the origin of the plane rectangular coordinate system, the W direction is the x-axis, the value range of x is 0.1-20, and the H direction is the y-axis.

[0140] At the edge (A1' to A15'), the parabola is a = 3.3, b = -52.5, c = 2064.0; R 2 =0.9669.

[0141] In the center (B1'-B15'), the parabola is a = 5.0, b = -81.1, c = 2063.9; R 2 =0.9579.

[0142] Example 1 - Motor

[0143] like Figure 1 As shown, eight rare earth permanent magnets of Example 1 are evenly arranged in a circumferential direction along the rotation direction of the motor. The rare earth permanent magnets are located on a regular octagon, and the angles between two adjacent rare earth permanent magnets are the same.

[0144] Example 2 - Motor

[0145] like Figure 2 As shown, 16 rare earth permanent magnets of Example 1 are divided into 8 groups and evenly arranged in a circumferential direction along the rotation direction of the motor. The connecting line between the end faces of each group of rare earth permanent magnets that are far apart is located on a regular octagon. In each group of rare earth permanent magnets, the angles between the two rare earth permanent magnets are the same, and they are arranged in a V shape.

[0146] Comparative Preparation Example 1

[0147] The difference from Preparation Example 1 is that the terbium Tb attached in the direction perpendicular to W0 is replaced by dysprosium Dy. The details are as follows:

[0148] The orientation direction of the initial sintered NdFeB magnet is recorded as H0 direction, and the width direction is recorded as W0 direction; the H0 direction is made the same as the H direction of the formed rare earth permanent magnet; the W0 direction is made the same as the W direction of the formed rare earth permanent magnet.

[0149] Along the direction perpendicular to H0, two opposite surfaces of the initial sintered NdFeB magnet are respectively covered with a heavy rare earth coating containing Dy to obtain a magnet A. Specifically, the following steps are included: the initial sintered NdFeB magnet is placed in a spraying device, one surface (the surface of 39mm×17.8mm) of the magnet faces upward, and is preheated at 180°C, and then the heavy rare earth coating containing Dy is covered on the surface by spraying. The single-sided weight gain of Dy is 0.325wt%. The magnet is turned over. The other surface (the opposite side of the surface of 39mm×17.8mm) is covered with a heavy rare earth coating containing Dy by spraying to obtain a magnet A. The single-sided weight gain of Dy is 0.325wt%.

[0150] Along the direction perpendicular to W0, two opposite sides of magnet A are respectively covered with a heavy rare earth coating containing Dy to obtain magnet B". The specific steps include: facing one side (the 39mm×4mm side) of magnet A upward, preheating at 180°C, and covering the side with a heavy rare earth coating containing Dy by spraying. The single-sided weight gain of Tb is 0.4%. Turn the magnet over and cover the other side (the opposite side of the 39mm×4mm side) with a heavy rare earth coating containing Dy by spraying to obtain magnet B". The single-sided weight gain of Dy is 0.4%.

[0151] The magnet B" is heat-treated to obtain the rare earth permanent magnet. Specifically, the following steps are included: the magnet B" is heated to a first temperature of 100°C, and kept at 100°C for 1 hour. Then, the temperature is raised to a second temperature of 200°C, and kept at 200°C for 1 hour. Then, the temperature is raised to a third temperature of 500°C, and kept at 500°C for 1 hour. The temperature is continued to be raised to a fourth temperature of 920°C, and kept at 920°C for 12 hours. Stop heating, cool to below 50°C with argon gas, then raise the temperature to a fifth temperature of 490°C, and keep at 490°C for 5 hours. Stop heating, cool to below 50°C with argon gas, and obtain a rare earth permanent magnet.

[0152] The rare earth permanent magnet is Figure 3 and Figure 4 Sampling tests were performed, and only sampling position 1 was sampled. The sampling numbers were A1” to A15” and B1” to B15”. Only one end position 1 was analyzed. The test and analysis results are shown in Table 4.

[0153] Table 4

[0154] Sampling No. Br(T) Hcj(kA / m) A1” 1.388 1785 A2” 1.384 1782 A3” 1.389 1791 A4” 1.391 1783 A5” 1.385 1788 A6” 1.388 1789 A7” 1.39 1779 A8” 1.383 1781 A9” 1.386 1773 A10” 1.381 1789 A11” 1.386 1773 A12” 1.389 1782 A13” 1.385 1793 A14” 1.391 1781 A15” 1.388 1788 B1” 1.403 1688 B2” 1.411 1681 B3” 1.408 1669 B4” 1.41 1681 B5” 1.399 1671 B6” 1.413 1665 B7” 1.411 1678 B8” 1.407 1677 B9” 1.409 1679 B10” 1.41 1682 B11” 1.415 1673 B12” 1.393 1681 B13” 1.408 1678 B14” 1.413 1684 B15” 1.405 1679

[0155] In Table 4, in the W direction, the coercive force of the rare earth permanent magnet does not gradually decrease from the two ends to the middle. Moreover, the difference H1-H1' between the coercive force of A1" 1785kA / m and the coercive force of A8" 1781kA / m is less than 80kA / m, and the difference Hn-Hn' between the coercive force of A15" 1788kA / m and the coercive force of A8" 1781kA / m is less than 80kA / m. The difference between the coercive force of B1" 1688kA / m and the coercive force of B8" 1677kA / m is less than 80kA / m. The difference between the coercive force of B15" 1679kA / m and the coercive force of B8" 1677kA / m is less than 80kA / m.

[0156] The coercive force distribution of the rare earth permanent magnet is different from that of Preparation Example 1.

[0157] Comparative Example 1 - Motor

[0158] like Figure 1 As shown, eight rare earth permanent magnets of Comparative Preparation Example 1 are evenly arranged in a circumferential direction along the rotation direction of the motor. The rare earth permanent magnets are located on a regular octagon, and the angles between two adjacent rare earth permanent magnets are the same.

[0159] Comparative Example 2 - Motor

[0160] like Figure 2 As shown, 16 rare earth permanent magnets of comparative preparation example 1 are divided into 8 groups and evenly arranged in a circumferential direction along the rotation direction of the motor. The connecting line between the end faces far apart of each group of rare earth permanent magnets is located on a regular octagon. In each group of rare earth permanent magnets, the angles between the two rare earth permanent magnets are the same, and they are arranged in a V shape.

[0161] The rare earth permanent magnets obtained in Example 1-2 and Comparative Example 1-2 were installed in the motor, and the back electromotive force V0 was measured at room temperature. High temperature load tests at 120°C, 140°C, and 160°C were performed, and then the back electromotive force V was measured after returning to room temperature. t , use the following formula to calculate the corresponding attenuation ratio α:

[0162] α=(V0-V t ) / V0×100%.

[0163] The calculation results are shown in Table 5.

[0164] Table 5

[0165] serial number α(120℃) α(140℃) α(160℃) Example 1 0.21 0.33 0.38 Example 2 0.24 0.31 0.35 Comparative Example 1 0.33 0.48 3.37 Comparative Example 2 0.27 0.38 3.18

[0166] It can be seen from the table that in the W direction, the coercive force of the rare earth permanent magnet has a tendency to gradually decrease from both ends to the middle (that is, along the W direction, from surface A1 to surface Aj, the coercive force Hcj Decrease; along the W direction, from the surface An to the cross section Aj, the coercive force H cj When H1-H1' is greater than 80kA / m and Hn-Hn' is greater than 80kA / m, the motor has smaller high-temperature attenuation and stronger anti-demagnetization ability.

[0167] The present invention is not limited to the above-mentioned embodiments. Without departing from the essential content of the present invention, any deformation, improvement and substitution that can be conceived by those skilled in the art shall fall within the scope of the present invention.

Claims

1. A rare earth permanent magnet, characterized in that: It is a rectangular parallelepiped structure having a length, a width and a height; the height direction is defined as an H direction, and the H direction is the easy magnetization direction of the rare earth permanent magnet; The width direction is defined as W direction; The rectangular parallelepiped structure has two parallel surfaces A1 and An formed by the length and height; there are a plurality of cross sections Ai parallel to the surface A1 between the surface A1 and the surface An, wherein the cross section located at the central axis of the rectangular parallelepiped structure is denoted as Aj; Along the W direction, from surface A1 to surface Aj, the coercive force H cj Decrease; along the W direction, from the surface An to the cross section Aj, the coercive force H cj reduce; The coercive force of a point D1 on the surface A1 is represented by H1. From point D1, an extension line is drawn along the W direction. The extension line intersects the cross section Aj at point E1. The coercive force of point E1 is represented by H1'. Then H1-H1'>80kA / m. The coercive force of a point Dn on the surface An is expressed as Hn. An extension line is drawn from point Dn along the W direction, and the extension line intersects the cross section Aj at point En. The coercive force of point En is expressed as Hn', then Hn-Hn'>80kA / m.

2. The rare earth permanent magnet according to claim 1, characterized in that: The rare earth RE content in the rare earth permanent magnet is 28-34wt%, and RE is a light rare earth element and a heavy rare earth element; the light rare earth element must contain Nd, and the heavy rare earth element is selected from one or more of Dy, Tb, Gd, Ho and Y.

3. The rare earth permanent magnet according to claim 2, characterized in that: The light rare earth elements are selected from one or more of Pr, Nd, La and Ce, and must contain Nd; the heavy rare earth elements are Dy and Tb.

4. The rare earth permanent magnet according to claim 1, characterized in that: In the W direction, the relationship between the coercive force y of a certain point of the rare earth permanent magnet and the position x of the point approximately satisfies the parabola y=ax 2 +bx+c, where a>0, b<0, c>0.

5. A method for manufacturing a rare earth permanent magnet according to any one of claims 1 to 4, characterized in that: The following steps are involved: 1) providing an initial sintered NdFeB magnet having a rectangular parallelepiped structure; recording the height direction of the initial sintered NdFeB magnet as the H0 direction, and recording the width direction as the W0 direction; making the H0 direction the same as the H direction of the formed rare earth permanent magnet; making the W0 direction the same as the W direction of the formed rare earth permanent magnet; 2) covering two opposite surfaces of the initially sintered NdFeB magnet with a heavy rare earth coating containing Dy along a direction perpendicular to the H0 direction, respectively, to obtain a magnet A; 3) Covering two opposite sides of magnet A with a heavy rare earth coating containing Tb respectively along a direction perpendicular to W0 to obtain magnet B; 4) Heat treating the magnet B to obtain the rare earth permanent magnet.

6. The manufacturing method according to claim 5, characterized in that: The initial sintered NdFeB magnet is R2Fe 14 B is the main phase.

7. The manufacturing method according to claim 6, characterized in that: In step (1), the initial sintered NdFeB magnet further contains other elements M, and the other elements M are selected from multiple elements of Cu, Co, Ga, Ti, Zr, Mo and Nb.

8. The manufacturing method according to claim 6, characterized in that: In step (2), the weight gain of Dy is 0.4 to 1.5 wt%.

9. The manufacturing method according to claim 6, characterized in that: In step (3), the weight increase of Tb is 0.05 to 0.5 wt%.

10. A motor, characterized in that: The method comprises the rare earth permanent magnet according to any one of claims 1 to 4; wherein the rare earth permanent magnet is arranged in any of the following ways: (1) 2N rare earth permanent magnets are evenly arranged in a circumferential direction along the rotation direction of the motor; the rare earth permanent magnets are located on a regular N-gon, and the angles between two adjacent rare earth permanent magnets are the same; wherein N is a positive integer greater than or equal to 2; (2) 2M rare earth permanent magnets are divided into M groups and arranged uniformly in a circumferential direction along the rotation direction of the motor; the connecting line between the end faces of each group of rare earth permanent magnets that are far apart is located on a regular M-gon; in each group of rare earth permanent magnets, the angles between the two rare earth permanent magnets are the same, and they are arranged in a V shape, wherein M is a positive integer greater than or equal to 8; (3) 3P rare earth permanent magnets are divided into P groups and arranged uniformly in a circumferential direction along the rotation direction of the motor; in each group of rare earth permanent magnets, three rare earth permanent magnets form an isosceles triangle, and the rare earth permanent magnet serving as the base of the isosceles triangle is located on the regular P-gon; wherein P is a positive integer greater than or equal to 8; (4) 4Q rare earth permanent magnets are divided into Q groups and are evenly arranged in a circumferential direction along the rotation direction of the motor; in each group of rare earth permanent magnets, two parallel V-shapes are formed between the four rare earth permanent magnets; in each group of rare earth permanent magnets, the connecting line between the farthest end faces of the two rare earth permanent magnets forming the V-shape is located on a regular Q polygon; wherein Q is a positive integer greater than or equal to 6.

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