Magnet assembly for a rotational speed sensor and method for producing a magnet assembly

Abstract

The application discloses a magnet assembly for a rotating speed sensor and a preparation method thereof, and relates to the field of rotating speed sensors.The magnet assembly comprises a magnet structure, a copper sleeve structure and a cladding structure.The copper sleeve structure is located at the bottom of the magnet structure and is used to be connected with the magnet structure so that the magnet structure is assembled with a fine rotating shaft of a motor.The cladding structure is located outside the magnet structure and the copper sleeve structure and is used to claddingly fix the magnet structure and the copper sleeve structure and to protect the magnet structure from being broken.The magnet structure, the copper sleeve structure and the cladding structure are cooperatively arranged.The cladding shell is cladded outside the magnet main body and the copper sleeve main body.The anti-rotation claw part and the anti-rotation groove are used to protect the magnet main body and the copper sleeve main body from rotating, which is beneficial to enhancing the bonding strength of the copper sleeve main body and the magnet main body and solving the problem of the interference of the eddy current effect of the traditional copper sleeve inner injection molding magnet scheme during overall magnetization.

Description

Technical Field

[0001] This invention relates to the field of speed sensors, and in particular to a magnet assembly for a speed sensor and its fabrication method. Background Technology

[0002] In motor speed sensor applications, a magnet assembly is typically installed at the end of the motor shaft. The speed and rotor position are measured by detecting the changes in the magnetic field generated by the rotation of the magnet.

[0003] In the prior art, for thin rotating shafts, the diameter of the thin rotating shaft is usually less than 10mm. The existing magnet assembly usually uses neodymium iron boron magnets injected into the top part inside the copper sleeve, and then the entire assembly is magnetized.

[0004] However, this method of fixing the injection-molded magnet directly into the copper sleeve usually results in insufficient fixing strength between the magnet and the metal sleeve. Furthermore, when the entire magnet assembly is pulse-magnetized, eddy currents will occur in the copper sleeve, generating an interfering magnetic field that affects the magnetization accuracy and consequently the stability of the sensor signal. Therefore, it is necessary to use a prefabricated magnet assembly for the speed sensor. Summary of the Invention

[0005] The purpose of this invention is to provide a magnet assembly for a speed sensor and a method for manufacturing the same, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a magnet assembly for a speed sensor, comprising: Magnet structure; A copper sleeve structure is located at the bottom of the magnet structure and is used to connect with the magnet structure so that the magnet structure can be assembled with the thin rotating shaft of the motor. An encapsulation structure is located outside the magnet structure and the copper sleeve structure. The encapsulation structure is used to encapsulate and fix the magnet structure and the copper sleeve structure, and to protect the magnet structure from breakage.

[0007] Preferably, the magnet structure includes: The main body of the magnet; Multiple anti-rotation claws are located at the bottom of the magnet body and are arranged in a ring array.

[0008] Preferably, the magnet structure further includes a circular groove, which is formed on the top of the magnet body. The circular groove is used to reduce the angular error and total harmonic distortion in the central region above the magnet body.

[0009] Preferably, the copper sleeve structure includes: A copper sleeve body, the copper sleeve body being located at the bottom of the magnet body, and the top of the copper sleeve body being positioned between multiple anti-rotation claws; The cavity is located in the middle of the copper sleeve body, and the inner diameter of the cavity is used to match the outer diameter of the end of the motor's thin rotating shaft; Multiple anti-rotation grooves are arranged in a ring array on the outside of the copper sleeve body.

[0010] Preferably, the covering structure includes: A casing is provided, which covers the exterior of the magnet structure and the copper sleeve structure; A protrusion is formed inside the housing and engages with the inner cavity of the anti-rotation groove.

[0011] A method for fabricating a magnet assembly for a speed sensor includes the following specific steps: S1: The magnet structure is injection molded using a mixture of magnetic powder and PPS resin. The injection molded magnet body has a circular groove on the top and an anti-rotation claw on the bottom. S2: Select a copper sleeve body. The inner diameter of the cavity on the copper sleeve body is adapted to the outer diameter of the end of the motor shaft. Then, open an anti-rotation groove on the outside of the copper sleeve. Then, place the magnet structure and copper sleeve structure prepared in step S1 on the rear mold side and front mold side of the injection mold cavity respectively, so that the two are in the preset assembly position. S3: Inject molten material into the cavity of the injection mold, and control the injection temperature at 280-300℃ and the injection pressure at 80-120MPa; S4: Perform pressure holding and cooling treatment on the injection mold. The pressure holding pressure is controlled at 50-80MPa and the pressure holding time is controlled at 15-30 seconds, so that the molten material can be fully filled and solidified in the cavity to form a covering structure that encapsulates the magnet structure and the copper sleeve structure. The covering structure forms a mechanical interlocking structure in the contact area between the magnet structure and the copper sleeve structure. S5: After the material has completely solidified, open the mold and remove the formed magnet assembly.

[0012] Preferably, the magnetic powder in step S1 is neodymium iron boron magnetic powder or samarium iron nitrogen magnetic powder, and the injection molding temperature of the magnet structure is 260-280℃ and the injection pressure is 70-90MPa.

[0013] Preferably, in step S2, the rear mold side of the injection mold cavity is provided with a positioning boss that matches the circular groove on the top of the magnet body, the front mold side is provided with a positioning groove that matches the outer wall contour of the copper sleeve body, and the anti-rotation groove on the copper sleeve body faces the inside of the cavity, and the anti-rotation claw on the magnet body and the anti-rotation groove on the copper sleeve body form a misaligned fit in the axial direction.

[0014] Preferably, in step S3, the molten material is a molten composite material modified by blending polyhexamethylene adipamide with 30% glass fiber by mass. The injection of the molten material adopts a segmented temperature control method, wherein the temperature of the front section of the barrel is 280-290℃, the temperature of the middle section is 290-295℃, and the temperature of the rear section is 295-300℃, and the injection rate is 50-80mm / s. The pressure holding and cooling treatment in step S4 adopts a combination of water cooling and air cooling, and after the pressure holding stage, air cooling continues for 5-15 seconds to reduce the surface temperature of the magnet assembly to below 80℃. The thickness of the injection molding coating layer in step S4 is 1.5-3mm, and a protrusion is formed in the anti-rotation groove on the copper sleeve body.

[0015] Preferred options also include: Subsequent processing involves deburring and cleaning the removed magnet components to remove injection molding overflow and surface impurities. The magnet assembly is then magnetized radially with a magnetic field strength of 1.2-1.5T to form uniformly distributed N and S poles. After magnetization, the magnetic properties of the magnet assembly are tested. If the magnetic properties meet the set requirements, the preparation of the magnet assembly is complete. If the magnetic properties do not meet the set requirements, adjustments are required.

[0016] The technical effects and advantages of this invention are as follows: This invention utilizes a combination of a magnet structure, a copper sleeve structure, and a covering structure. The magnet structure is connected to the copper sleeve structure, and the covering shell covers the exterior of the magnet body and the copper sleeve body. Anti-rotation claws and anti-rotation grooves protect the magnet body and the copper sleeve body from rotation. The covering shell wraps and locks the connection between the copper sleeve body and the magnet body and cooperates with the anti-rotation groove to form an integral structure of the magnet assembly. The cavity on the copper sleeve body is assembled with the thin rotating shaft of the motor, which helps to enhance the bonding strength between the copper sleeve body and the magnet body. This solves the problems of difficult assembly of thin rotating shaft magnets and eddy current interference during overall magnetization in traditional copper sleeve injection-molded magnet solutions. It improves the bonding strength and signal stability of the magnet assembly and is suitable for mass production. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the structure of the casing of the present invention; Figure 3 This is a schematic diagram of the structure of the magnet body of the present invention; Figure 4 This is a schematic diagram of the structure of the copper sleeve body of the present invention.

[0018] In the diagram: 1. Magnet structure; 11. Magnet body; 12. Anti-rotation claw; 13. Circular groove; 2. Copper sleeve structure; 21. Copper sleeve body; 22. Cavity; 23. Anti-rotation groove; 3. Covering structure; 31. Covering shell; 32. Protrusion. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] This invention provides, for example Figures 1-4 The illustrated magnet assembly for a speed sensor includes a magnet structure 1, a copper sleeve structure 2, and a covering structure 3. The copper sleeve structure 2 is located at the bottom of the magnet structure 1 and is used to connect with the magnet structure 1 so that the magnet structure 1 can be assembled with the thin rotating shaft of the motor. The covering structure 3 is located outside the magnet structure 1 and the copper sleeve structure 2. The covering structure 3 is used to cover and fix the magnet structure 1 and the copper sleeve structure 2 and to protect the magnet structure 1 from breakage. The assembly and fixing of the magnet structure 1, the copper sleeve structure 2, and the covering structure 3 solves the problem of difficult assembly of the thin rotating shaft magnet. The copper sleeve transition enables convenient assembly, improves the bonding strength between the magnet and the metal sleeve, and prevents loosening under high-speed rotation. The anti-rotation claw 12 at the bottom of the magnet body 11, away from the sensor side, can effectively prevent the magnet body 11 from rotating in the finished assembly without affecting the magnetic field accuracy. The design of the covering structure 3 covering the magnet body 11 can effectively prevent the magnet body 11 from breaking under long-term high-speed rotation and thermal shock, making it suitable for mass production.

[0021] Furthermore, the magnet structure 1 includes a magnet body 11 and multiple anti-rotation claws 12. The magnet body 11 is preferably manufactured by injection molding and is easy to assemble with the copper sleeve body 21. The anti-rotation claws 12 are useful for protecting the magnet body 11 from rotation and improving the stability of the magnet body 11 in use. The multiple anti-rotation claws 12 are all located at the bottom of the magnet body 11 and are arranged in a ring array.

[0022] Furthermore, the magnet structure 1 also includes a circular groove 13, which is located on the top of the magnet body 11. The circular groove 13 is used to reduce the angular error and total harmonic distortion in the central area above the magnet body 11, improve the sensor accuracy, and avoid the eddy current effect in the copper part from negatively affecting the magnetic field accuracy during magnetization.

[0023] Specifically, the copper sleeve structure 2 includes a copper sleeve body 21, a cavity 22, and multiple anti-rotation grooves 23. The copper sleeve body 21 is convenient for connecting with the thin rotating shaft of the motor, and the cavity 22 is convenient for inserting into the thin rotating shaft of the motor to achieve assembly operation. The anti-rotation grooves 23 are convenient for cooperating with the covering shell 31, thereby providing anti-rotation protection for the copper sleeve body 21 and improving the stability of the copper sleeve body 21 in use. The copper sleeve body 21 is located at the bottom of the magnet body 11, and the top of the copper sleeve body 21 is placed between multiple anti-rotation claws 12. The cavity 22 is located in the middle of the copper sleeve body 21, and the inner diameter of the cavity 22 is used to cooperate with the outer diameter of the end of the thin rotating shaft of the motor. Multiple anti-rotation grooves 23 are arranged in a ring array on the outside of the copper sleeve body 21.

[0024] Specifically, the covering structure 3 includes a covering shell 31 and a protrusion 32. The covering shell 31 is beneficial for wrapping and fixing the connection between the copper sleeve body 21 and the magnet body 11, and can effectively prevent the magnet body 11 from breaking during long-term high-speed rotation and thermal shock, thus protecting the magnet body 11. The protrusion 32 is beneficial for cooperating with the inner cavity of the anti-rotation groove 23, thus facilitating anti-rotation protection for the copper sleeve body 21. The covering shell 31 covers the outside of the magnet structure 1 and the copper sleeve structure 2, and the protrusion 32 is formed inside the covering shell 31, and the protrusion 32 cooperates with the inner cavity of the anti-rotation groove 23.

[0025] A method for fabricating a magnet assembly for a speed sensor includes the following specific steps: S1: The magnet structure 1 is injection molded by mixing magnetic powder and PPS resin, and the magnet body 11 is injection molded with a circular groove 13 on the top and an anti-rotation claw part 12 on the bottom; S2: Select the copper sleeve body 21. The inner diameter of the cavity 22 on the copper sleeve body 21 is adapted to the outer diameter of the end of the motor shaft. Then, open the anti-rotation groove 23 on the outside of the copper sleeve. Then, place the magnet structure 1 and the copper sleeve structure 2 prepared in step S1 on the rear mold side and the front mold side of the injection mold cavity respectively, so that the two are in the preset assembly position. S3: Inject molten material into the cavity of the injection mold, and control the injection temperature at 280-300℃ and the injection pressure at 80-120MPa; S4: Perform pressure holding and cooling treatment on the injection mold. The pressure holding pressure is controlled at 50-80MPa and the pressure holding time is controlled at 15-30 seconds, so that the molten material can be fully filled and solidified in the cavity to form a covering structure 3 that wraps the magnet structure 1 and the copper sleeve structure 2. The covering structure 3 forms a mechanical interlocking structure in the contact area between the magnet structure 1 and the copper sleeve structure 2. S5: After the material has completely solidified, open the mold and remove the formed magnet assembly.

[0026] Furthermore, the magnetic powder in step S1 is neodymium iron boron magnetic powder or samarium iron nitrogen magnetic powder, and the injection molding temperature of the magnet structure 1 is 260-280℃ and the injection molding pressure is 70-90MPa.

[0027] Furthermore, in step S2, the rear mold side of the injection mold cavity is provided with a positioning boss that matches the circular groove 13 on the top of the magnet body 11, and the front mold side is provided with a positioning groove that matches the outer wall contour of the copper sleeve body 21. The anti-rotation groove 23 on the copper sleeve body 21 faces the inside of the cavity, and the anti-rotation claw 12 on the magnet body 11 and the anti-rotation groove 23 on the copper sleeve body 21 form a misaligned fit in the axial direction to ensure the molding accuracy of the mechanical interlocking structure.

[0028] Specifically, in step S3, the molten material is a molten composite material modified by blending polyhexamethylene adipamide with 30% glass fiber by mass. The injection of the molten material adopts a segmented temperature control method, wherein the temperature of the front section of the barrel is 280-290℃, the middle section is 290-295℃, and the rear section is 295-300℃, and the injection rate is 50-80mm / s to ensure material flowability and filling uniformity. The pressure holding and cooling treatment in step S4 adopts a combination of water cooling and air cooling, and after the pressure holding stage, air cooling continues for 5-15 seconds to reduce the surface temperature of the magnet assembly to below 80℃. The thickness of the injection molding coating layer in step S4 is 1.5-3mm, and a protrusion 32 is formed in the anti-rotation groove 23 on the copper sleeve body 21 to enhance the mechanical interlocking strength.

[0029] Furthermore, it also includes: Subsequent processing involves deburring and cleaning the removed magnet components to remove injection molding overflow and surface impurities. The deburring process uses ultrasonic deburring equipment with diamond polishing paste to refine the injection molding overflow, parting surface burrs, and sharp angles at the copper sleeve ports of the magnet components. This process takes 3-5 minutes to ensure the component surface is free of sharp protrusions or residual burrs, preventing scratches to the motor shaft during assembly. The cleaning process includes three sequential cleaning steps. The first step involves ultrasonic cleaning for 5 minutes with a neutral cleaning agent at 60-80℃ to remove... The first step is to remove surface oil and grinding impurities; the second step is to ultrasonically rinse with deionized water for 3 minutes to remove residual cleaning agent; the third step is to use hot air circulation drying at a temperature of 80-100℃ for 10-15 minutes to ensure that there is no moisture residue on the component surface and the moisture content is ≤0.1%. The magnetization pretreatment specifically includes fixing the cleaned and dried magnet components in a special magnetization fixture with a positioning accuracy of ≤±0.02mm, ensuring that the radial magnetization direction of the magnet is perpendicular to the central axis of the motor shaft, and avoiding magnetization offset that would lead to uneven magnetic field distribution. The magnetization process has specific... The magnet assembly undergoes radial magnetization using a pulse magnetizer. The magnetization magnetic field strength is gradually increased to 1.2-1.5T, maintained for 3-5 seconds, and then slowly demagnetized to zero. During magnetization, the magnet assembly temperature is monitored in real-time and controlled below 60℃ using water cooling to prevent high temperatures from affecting magnetic properties. Magnetic performance testing involves using a high-precision gaussmeter to uniformly select eight detection points on the outer circumference of the magnet assembly. Each detection point can be set at a 45-degree angle. The surface magnetic field strength at each point is measured, and the average and maximum deviation values ​​are calculated to ensure the deviation does not exceed [a certain value]. The tolerance is within ±5%; at the same time, the remanence and coercivity of the magnet are tested by a hysteresis loop tester. The remanence must be ≥1.2T and the coercivity must be ≥800kA / m. Products that fail the test are directly rejected. The appearance and size re-inspection specifically includes using an optical image measuring instrument to re-inspect the key dimensions of the component, such as the outer diameter, length, and inner diameter of the copper sleeve. The dimensional tolerance is controlled within ±0.03mm. The visual inspection system is used to check for appearance problems such as surface scratches, cracks, and injection molding defects. Qualified products are vacuum packaged to avoid moisture or impact during transportation. Subsequently, the magnet assembly is magnetized radially with a magnetic field strength of 1.2-1.5T to form uniformly distributed N and S poles. After magnetization, the magnetic properties of the magnet assembly are tested. If the magnetic properties meet the set requirements, the preparation of the magnet assembly is completed. If the magnetic properties do not meet the set requirements, adjustments are required to ensure that the deviation of the surface magnetic field strength does not exceed ±5%.

[0030] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A magnet assembly for a speed sensor, characterized in that: include: Magnet structure (1); A copper sleeve structure (2) is located at the bottom of the magnet structure (1). The copper sleeve structure (2) is used to connect with the magnet structure (1) so that the magnet structure (1) can be assembled with the motor shaft. The covering structure (3) is located outside the magnet structure (1) and the copper sleeve structure (2). The covering structure (3) is used to cover and fix the magnet structure (1) and the copper sleeve structure (2) and to protect the magnet structure (1) from breakage.

2. The magnet assembly for a speed sensor according to claim 1, characterized in that: The magnet structure (1) includes: Magnet body (11); Multiple anti-rotation claws (12) are located at the bottom of the magnet body (11) and are arranged in a ring array.

3. The magnet assembly for a speed sensor according to claim 2, characterized in that: The magnet structure (1) also includes a circular groove (13), which is opened on the top of the magnet body (11). The circular groove (13) is used to reduce the angular error and total harmonic distortion in the central area above the magnet body (11).

4. The magnet assembly for a speed sensor according to claim 3, characterized in that: The copper sleeve structure (2) includes: The copper sleeve body (21) is located at the bottom of the magnet body (11), and the top of the copper sleeve body (21) is placed between multiple anti-rotation claws (12); Cavity (22), the cavity (22) is located in the middle of the copper sleeve body (21), and the inner diameter of the cavity (22) is used to match the outer diameter of the end of the motor thin shaft; Multiple anti-rotation grooves (23) are arranged in a ring array on the outside of the copper sleeve body (21).

5. The magnet assembly for a speed sensor according to claim 4, characterized in that: The covering structure (3) includes: A casing (31) is used to cover the exterior of the magnet structure (1) and the copper sleeve structure (2); A protrusion (32) is formed inside the housing (31) and the protrusion (32) engages with the inner cavity of the anti-rotation groove (23).

6. A method for manufacturing a magnet assembly for a speed sensor, applied to the magnet assembly for a speed sensor as described in any one of claims 1-5, characterized in that: The specific steps include the following: S1: The magnet structure (1) is injection molded by mixing magnetic powder and PPS resin, and the magnet body (11) is injection molded with a round groove (13) on the top and an anti-rotation claw (12) on the bottom. S2: Select the copper sleeve body (21), the inner diameter of the cavity (22) on the copper sleeve body (21) is adapted to the outer diameter of the end of the motor shaft, and then open the anti-rotation groove (23) on the outside of the copper sleeve. Then place the magnet structure (1) and the copper sleeve structure (2) prepared in step S1 on the back mold side and front mold side of the injection mold cavity respectively, so that the two are in the preset assembly position. S3: Inject molten material into the cavity of the injection mold, and control the injection temperature at 280-300℃ and the injection pressure at 80-120MPa; S4: Perform pressure holding and cooling treatment on the injection mold. The pressure holding pressure is controlled at 50-80MPa and the pressure holding time is controlled at 15-30 seconds, so that the molten material is fully filled and solidified in the cavity to form a covering structure (3) that wraps the magnet structure (1) and the copper sleeve structure (2). The covering structure (3) forms a mechanical interlocking structure in the contact area between the magnet structure (1) and the copper sleeve structure (2). S5: After the material has completely solidified, open the mold and remove the formed magnet assembly.

7. The method for preparing a magnet assembly for a speed sensor according to claim 1, characterized in that: The magnetic powder in step S1 is neodymium iron boron magnetic powder or samarium iron nitrogen magnetic powder, and the injection molding temperature of the magnet structure (1) is 260-280℃ and the injection molding pressure is 70-90MPa.

8. The method for preparing a magnet assembly for a speed sensor according to claim 1, characterized in that: In step S2, the rear mold side of the injection mold cavity is provided with a positioning boss that matches the circular groove (13) on the top of the magnet body (11), and the front mold side is provided with a positioning groove that matches the outer wall contour of the copper sleeve body (21). The anti-rotation groove (23) on the copper sleeve body (21) faces the inside of the cavity, and the anti-rotation claw (12) on the magnet body (11) and the anti-rotation groove (23) on the copper sleeve body (21) form a misaligned fit in the axial direction.

9. The method for preparing a magnet assembly for a speed sensor according to claim 1, characterized in that: In step S3, the molten material is a molten composite material modified by blending polyhexamethylene adipamide with 30% glass fiber by mass. The injection of the molten material adopts a segmented temperature control method, wherein the temperature of the front section of the barrel is 280-290℃, the temperature of the middle section is 290-295℃ and the temperature of the rear section is 295-300℃, and the injection rate is 50-80mm / s. The pressure holding and cooling treatment in step S4 adopts a combination of water cooling and air cooling, and after the pressure holding stage, air cooling continues for 5-15 seconds to reduce the surface temperature of the magnet assembly to below 80℃. The thickness of the injection molding coating layer in step S4 is 1.5-3mm, and a protrusion (32) is formed in the anti-rotation groove (23) on the copper sleeve body (21).

10. The method for preparing a magnet assembly for a speed sensor according to claim 1, characterized in that: Also includes: Subsequent processing involves deburring and cleaning the removed magnet components to remove injection molding overflow and surface impurities. The magnet assembly is then magnetized radially with a magnetic field strength of 1.2-1.5T to form uniformly distributed N and S poles. After magnetization, the magnetic properties of the magnet assembly are tested. If the magnetic properties meet the set requirements, the preparation of the magnet assembly is complete. If the magnetic properties do not meet the set requirements, adjustments are required.

Images