Test device and test method for simulating the mechanical properties of permanent magnet motor rotor sleeve

Abstract

The present invention discloses a test device and a test method for simulating the mechanical properties of a permanent magnet motor rotor sleeve. The device includes a rotor support, a first pressing plate, a second pressing plate, a rotating shaft, a permanent magnet, a spring and a guide rod. The first pressing plate and the second pressing plate are respectively installed on both sides of the rotor support. The outer periphery of the first pressing plate is provided with a radial step. The end face of the permanent magnet facing the radial step is provided with an axial guide hole. One end of the guide rod is installed on the radial step, and the other end is located in the axial guide hole. The guide rod is provided with a limiting convex portion. The spring is sleeved on the guide rod and compressed between the limiting convex portion and the end face where the guide hole is located. The outer periphery of the second pressing plate is provided with a positioning portion for axially positioning the permanent magnet. The method includes assembling, sleeved on the outer periphery of the permanent magnet, removing the second pressing plate and testing. The present invention uses elastic force to amplify the relationship between the centrifugal force on the permanent magnet and the limiting effect of the sleeve for easy observation, and can perform a certain analysis on the mechanical relationship between the rotor sleeve and the surface-mounted magnetic steel.

Description

Technical Field

[0001] The invention relates to a permanent magnet motor, and in particular to a test device and a test method for simulating the mechanical properties of a rotor sleeve of a permanent magnet motor. Background Art

[0002] The permanent magnet synchronous motor with a surface-mounted magnetic steel rotor has the characteristics of high power density and high speed. When the motor is running at high speed, the surface-mounted magnetic steel will be subjected to a large centrifugal force. In order to ensure that the rotor can operate normally under high-speed conditions, a sleeve is usually inserted into the permanent magnet of the rotor to enhance the reliability of the rotor. In the design process of the rotor sleeve, the strength of the rotor sleeve is usually calculated by simulation. Due to the characteristics of high-speed rotation of the rotor, there is no method in the prior art that can accurately collect various parameters in the actual operation of the rotor. The present invention can be applied to a rotor rotating at high speed, and can perform a certain analysis of the mechanical relationship between the rotor sleeve and the surface-mounted magnetic steel. Summary of the invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a test device and test method for simulating the mechanical properties of a permanent magnet motor rotor sleeve, which uses a spring to continuously apply elastic force to the permanent magnet when the rotor is in high-speed rotation, amplifies the relationship between the centrifugal force on the permanent magnet and the restrictive effect of the sleeve by means of the elastic force for easy observation, and can perform a certain analysis on the mechanical relationship between the rotor sleeve and the surface-mounted magnetic steel.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A test device for simulating the mechanical properties of a permanent magnet motor rotor sleeve comprises a rotor support, a first pressure plate, a second pressure plate, a rotating shaft, a permanent magnet, a spring and a guide rod, wherein the rotor support is sleeved on the rotating shaft and the two rotate synchronously, the first pressure plate and the second pressure plate are respectively mounted on the two end surfaces of the rotor support, a mounting groove is provided on the circumferential surface of the rotor support, the permanent magnet is arranged in the mounting groove, a radial step is provided on the outer periphery of the first pressure plate, an axial guide hole is provided on the end surface of the permanent magnet facing the radial step, one end of the guide rod is mounted on the radial step, and the other end is located in the axial guide hole, the permanent magnet can move relative to the guide rod, a limiting convex portion is provided on the guide rod, the spring is sleeved on the guide rod and is compressed between the limiting convex portion and the end surface where the guide hole is located, a positioning portion for axially positioning the permanent magnet is provided on the outer periphery of the second pressure plate, and the second pressure plate and the rotor support are detachably connected.

[0006] As a further improvement of the above technical solution, the end face of the permanent magnet facing the positioning portion is provided with an axial step, the circumferential surface of the positioning portion is provided with a radial threaded hole pointing to the axial step, a locking screw is provided in the radial threaded hole, and the locking screw abuts against the axial step.

[0007] As a further improvement of the above technical solution, the second pressing plate is connected to the rotor bracket via a second screw; and the first pressing plate is connected to the rotor bracket via a first screw.

[0008] As a further improvement of the above technical solution, the guide rod is a guide bolt, the radial step is provided with an axial threaded hole cooperating with the guide bolt, and the limiting protrusion is a nut cooperating with the guide bolt or a nut fixed on the guide bolt.

[0009] As a further improvement of the above technical solution, the permanent magnet is made of structural steel.

[0010] As a further improvement of the above technical solution, the rotor bracket and the rotating shaft are connected by a key, there is a clearance fit between the rotor bracket and the rotating shaft, and the two are connected by welding after assembly.

[0011] As a further improvement of the above technical solution, the pressure plate 1 and the rotor bracket as well as the pressure plate 2 and the rotor bracket are positioned by a stop structure.

[0012] A test method based on the above-mentioned test device for simulating the mechanical properties of a permanent magnet motor rotor sleeve comprises the following steps:

[0013] S1. Assembly: install the rotor bracket on the rotating shaft, install the first and second pressing plates on the two end surfaces of the rotor bracket respectively, install the permanent magnets, adjust the permanent magnets to make them abut against the positioning part of the second pressing plate, and ensure that the end surfaces of all permanent magnets abutting against the positioning part are aligned, install the guide rod and the spring, and make the spring compressed between the limiting protrusion and the end surface where the guide hole is located;

[0014] S2, putting a sheath on the periphery of the permanent magnet;

[0015] S3, remove the second pressing plate;

[0016] S4. Test: Apply rotational force to the shaft. During the rotation, the centrifugal force on the permanent magnet and the radial force of the sleeve cancel each other out to a balance. The elastic force of the spring will cause the permanent magnet to undergo axial displacement, thereby deriving the relationship between the rotational speed, centrifugal force and sleeve strength.

[0017] A test device for simulating the mechanical properties of a permanent magnet motor rotor sleeve comprises a rotor support, a first pressure plate, a second pressure plate, a rotating shaft, a permanent magnet, a spring and a guide rod, wherein the rotor support is sleeved on the rotating shaft and the two rotate synchronously, the first pressure plate and the second pressure plate are respectively mounted on the two end surfaces of the rotor support, a mounting groove is provided on the circumferential surface of the rotor support, the permanent magnet is arranged in the mounting groove, a radial step is provided on the outer periphery of the first pressure plate, an axial guide hole is provided on the end surface of the permanent magnet facing the radial step, one end of the guide rod is mounted on the radial step, and the other end is located in the axial guide hole, the permanent magnet can move relative to the guide rod, the spring is sleeved on the guide rod and is compressed between the radial step and the end surface where the guide hole is located, a positioning portion is provided on the outer periphery of the second pressure plate for axially positioning the permanent magnet, and the second pressure plate and the rotor support are detachably connected.

[0018] A test method for a test device for simulating the mechanical properties of a permanent magnet motor rotor sleeve based on the above-mentioned claim, comprising the following steps:

[0019] S1. Assembly: Install the rotor bracket on the rotating shaft, install the pressure plate 1 and the pressure plate 2 on the two end surfaces of the rotor bracket respectively, install the permanent magnet, adjust the permanent magnet so that it abuts against the positioning part of the pressure plate 2, and ensure that the end surfaces of all permanent magnets abutting against the positioning part are aligned, install the guide rod and the spring, and compress the spring between the radial step and the end surface where the guide hole is located.

[0020] S2, putting a sheath on the periphery of the permanent magnet;

[0021] S3, remove the second pressing plate;

[0022] S4. Test: Apply rotational force to the shaft. During the rotation, the centrifugal force on the permanent magnet and the radial force of the sleeve cancel each other out to a balance. The elastic force of the spring will cause the permanent magnet to undergo axial displacement, thereby deriving the relationship between the rotational speed, centrifugal force and sleeve strength.

[0023] Compared with the prior art, the advantages of the present invention are:

[0024] The present invention specially manufactures a set of test equipment for simulating the mechanical properties of the permanent magnet motor rotor sleeve. When the rotor is in high-speed rotation, a spring is used to continuously apply elastic force to the permanent magnet. With the help of the elastic force, the relationship between the centrifugal force on the permanent magnet and the restrictive effect of the sleeve is amplified for easy observation. The mechanical relationship between the rotor sleeve and the surface-mounted magnetic steel can be analyzed to a certain extent, filling the gap in the industry that high-speed rotating rotors cannot be directly detected. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the structure of the test device of Example 1 of the present invention.

[0026] Figure 2 It is an end view of the rotor bracket in Example 1 of the present invention.

[0027] Figure 3 It is a front view of the permanent magnet in Example 1 of the present invention.

[0028] Figure 4 It is a front view of the pressing plate 2 in embodiment 1 of the present invention.

[0029] Figure 5 This is an end view of the pressure plate 2 in Example 1 of the present invention.

[0030] Figure 6 It is an end view of the pressure plate 1 in Example 1 of the present invention.

[0031] The symbols in the figure represent:

[0032] 1. Rotor bracket; 11. Mounting groove; 2. Pressure plate 1; 21. Radial step; 22. Screw 1; 23. Axial threaded hole; 3. Pressure plate 2; 31. Positioning part; 32. Radial threaded hole; 33. Set screw; 34. Screw 2; 4. Rotating shaft; 5. Permanent magnet; 51. Guide hole; 52. Axial step; 6. Spring; 7. Guide rod; 71. Limiting protrusion. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] Example 1

[0035] like Figures 1 to 6 As shown, the test device for simulating the mechanical properties of the rotor sleeve of a permanent magnet motor in this embodiment comprises a rotor support 1, a pressure plate 1 2, a pressure plate 2 3, a rotating shaft 4, a permanent magnet 5, a spring 6 and a guide rod 7. The rotor support 1 is sleeved on the rotating shaft 4 and the two rotate synchronously. The pressure plate 1 2 and the pressure plate 2 3 are respectively mounted on the two end faces of the rotor support 1. A mounting groove 11 is provided on the circumferential surface of the rotor support 1. The permanent magnet 5 is arranged in the mounting groove 11. A radial step 21 is provided on the outer periphery of the pressure plate 1 2. An axial guide hole 51 is provided on the end face of the permanent magnet 5 facing the radial step 21. One end of the guide rod 7 is mounted on the radial step 21, and the other end is located in the axial guide hole 51. The permanent magnet 5 can move relative to the guide rod 7. A limiting protrusion 71 is provided on the guide rod 7. The spring 6 is sleeved on the guide rod 7 and is compressed between the limiting protrusion 71 and the end face where the guide hole 51 is located ( Figure 1 and Figure 3 The outer periphery of the pressure plate 2 is provided with a positioning portion 31 for axially positioning the permanent magnet 5. The pressure plate 2 is detachably connected to the rotor support 1. There is a certain distance between the radial step 21 and the end face M, so that the spring 6 has a certain activity space.

[0036] All structures of the test device are individually made test samples, not finished products for actual use. During assembly, first install the rotor bracket 1, the pressure plate 1 2, the pressure plate 2 3, and the rotating shaft 4, and then install the permanent magnet 5. The installation groove 11 is preferably a dovetail groove. After the permanent magnet 5 is installed in the dovetail groove, it needs to be aligned with the positioning portion 31 of the pressure plate 2 3 along the axial direction, so as to ensure that the initial positions of the permanent magnet 5 used in the circumferential direction are aligned, that is, in Figure 1 In the figure, the right end face of the permanent magnet 5 ( Figure 1 and Figure 3 The guide rod 7 and the spring 6 are then installed, and the position of the spring 6 is adjusted to be in a compressed state, giving the permanent magnet 5 an elastic force to the right. During the simulation test, the sheath is first tied on the permanent magnet 5, and then the pressure plate 2 is removed. Finally, power is applied to the shaft 4, and the device is installed to rotate. During the rotation process, the permanent magnet 5 is not separated from the rotor bracket 1 at first due to the small centrifugal force. At this time, the elastic force of the spring 6 on the permanent magnet 5 is not enough to make the permanent magnet 5 move axially; when the speed increases, the permanent magnet 5 is offset by the centrifugal force and the radial force of the sheath to a balance, and the permanent magnet 5 is separated from the rotor bracket 1. At this time, the elastic force of the spring 6 will cause the permanent magnet 5 to undergo axial displacement ( Figure 1 The axial displacement of the permanent magnet 5 amplifies the relationship between the centrifugal force on the permanent magnet and the limiting effect of the sheath, making it easier to observe and analyze.

[0037] The present invention specially manufactures a set of test equipment for simulating the mechanical properties of the permanent magnet motor rotor sleeve. When the rotor is in high-speed rotation, a spring is used to continuously apply elastic force to the permanent magnet. With the help of the elastic force, the relationship between the centrifugal force on the permanent magnet and the restrictive effect of the sleeve is amplified for easy observation. The mechanical relationship between the rotor sleeve and the surface-mounted magnetic steel can be analyzed to a certain extent, filling the gap in the industry that high-speed rotating rotors cannot be directly detected.

[0038] In this embodiment, the end face (end face N) of the permanent magnet 5 facing the positioning portion 31 is provided with an axial step 52, and the circumferential surface of the positioning portion 31 is provided with a radial threaded hole 32 pointing to the axial step 52, and a set screw 33 is provided in the radial threaded hole 32, and the set screw 33 is abutted against the axial step 52. The set screw 33 is pressed against the axial step 52 on the permanent magnet 5, so that the positioning between the permanent magnet 5 and the pressure plate 2 3 is more accurately achieved, the positioning accuracy of the permanent magnet 5 is ensured, and the permanent magnet 5 is prevented from being offset.

[0039] In this embodiment, the second pressing plate 3 is connected to the rotor support 1 by the second screw 34. The first pressing plate 2 is connected to the rotor support 1 by the first screw 22. The first pressing plate 2 and the rotor support 1 and the second pressing plate 3 and the rotor support 1 are positioned by a stopper structure, and the stopper structure is a concave-convex part, and the concave part and the convex part are arranged on the pressing plate and the rotor support 1, respectively. Multiple screws 34 and screws 22 are provided.

[0040] In this embodiment, the guide rod 7 is a guide bolt, the radial step 21 is provided with an axial threaded hole 23 matched with the guide bolt, and the limiting protrusion 71 is a nut matched with the guide bolt, and the elastic force of the spring 6 can be realized by rotating the nut. It should be noted that, in addition to this embodiment, in other embodiments, the limiting protrusion 71 can also be a nut fixed on the guide bolt.

[0041] In this embodiment, the permanent magnet 5 is made of structural steel. Since it is necessary to drill holes in the permanent magnet 5 in the test, and the permanent magnets of the actual permanent magnet synchronous motor are made of rare earth sintered materials with poor machinability, the material of the test permanent magnet 5 in this embodiment is changed to structural steel, which can be processed and will not have a significant impact on the verification effect.

[0042] In this embodiment, the rotor bracket 1 and the rotating shaft 4 are connected by a key, and the key is used to transmit torque. There is a clearance fit between the rotor bracket 1 and the rotating shaft 4. After the two are assembled, they are connected by welding to ensure that the rotor bracket 1 and the rotating shaft 4 rotate synchronously.

[0043] The test method of the test device of this embodiment includes the following steps:

[0044] S1. Assembly: Install the rotor support 1 on the rotating shaft 4, install the pressure plate 1 2 and the pressure plate 2 3 on the two end surfaces of the rotor support 1 respectively, install the permanent magnet 5, adjust the permanent magnet 5 so that it abuts against the positioning portion 31 of the pressure plate 2 3, and ensure that all the end surfaces of the permanent magnet 5 abutting against the positioning portion 31 are aligned, install the guide rod 7 and the spring 6, and make the spring 6 be compressed between the limiting protrusion 71 and the end surface where the guide hole 51 is located;

[0045] S2, putting a sheath on the outer periphery of the permanent magnet 5;

[0046] S3, remove the pressure plate 23;

[0047] S4. Test: Apply rotational force to the rotating shaft 4. During the rotation, when the centrifugal force on the permanent magnet 5 and the radial force of the sheath cancel each other out to a balance, the elastic force of the spring 6 causes the permanent magnet 5 to undergo axial displacement, thereby obtaining the relationship between the rotational speed, centrifugal force and sheath strength.

[0048] During this test method, the elastic coefficient of the spring 6 should be adjusted according to the sheath fitting interference or the tension of the carbon fiber sheath binding.

[0049] Example 2

[0050] The test device for simulating the mechanical properties of the permanent magnet motor rotor sleeve of this embodiment is different from that of Embodiment 1 in that:

[0051] In this embodiment, the guide rod 7 does not need to be provided with the limiting protrusion 71 , and the spring 6 is sleeved on the guide rod 7 and compressed between the radial step 21 and the end surface where the guide hole 51 is located.

[0052] The test method of the test device of this embodiment includes the following steps:

[0053] S1. Assembly: install the rotor support 1 on the rotating shaft 4, install the pressure plate 1 2 and the pressure plate 2 3 on the two end surfaces of the rotor support 1 respectively, install the permanent magnet 5, adjust the permanent magnet 5 to make it abut against the positioning part 31 of the pressure plate 2 3, and ensure that all the end surfaces of the permanent magnet 5 abutting against the positioning part 31 are aligned, install the guide rod 7 and the spring 6, and make the spring 6 be compressed between the radial step 21 and the end surface where the guide hole 51 is located;

[0054] S2, putting a sheath on the outer periphery of the permanent magnet 5;

[0055] S3, remove the pressure plate 23;

[0056] S4. Test: Apply rotational force to the rotating shaft 4. During the rotation, when the centrifugal force on the permanent magnet 5 and the radial force of the sheath cancel each other out to a balance, the elastic force of the spring 6 causes the permanent magnet 5 to undergo axial displacement, thereby obtaining the relationship between the rotational speed, centrifugal force and sheath strength.

[0057] The remaining details are basically the same as those in Example 1 and will not be described again.

[0058] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the technical content disclosed above without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should fall within the scope of protection of the technical solution of the present invention.

Claims

1. A test device for simulating the mechanical properties of a permanent magnet motor rotor sleeve, characterized in that: The invention comprises a rotor support (1), a first pressure plate (2), a second pressure plate (3), a rotating shaft (4), a permanent magnet (5), a spring (6) and a guide rod (7); the rotor support (1) is sleeved on the rotating shaft (4) and the two rotate synchronously; the first pressure plate (2) and the second pressure plate (3) are respectively mounted on two end surfaces of the rotor support (1); a mounting groove (11) is provided on the circumferential surface of the rotor support (1); the permanent magnet (5) is arranged in the mounting groove (11); the outer circumference of the first pressure plate (2) is provided with a radial step (21); the end surface of the permanent magnet (5) facing the radial step (21) An axial guide hole (51) is provided, one end of the guide rod (7) is mounted on the radial step (21), and the other end is located in the axial guide hole (51), the permanent magnet (5) can move relative to the guide rod (7), the guide rod (7) is provided with a limiting convex portion (71), the spring (6) is sleeved on the guide rod (7) and is compressed between the limiting convex portion (71) and the end surface where the guide hole (51) is located, the outer periphery of the second pressure plate (3) is provided with a positioning portion (31) for axially positioning the permanent magnet (5), and the second pressure plate (3) and the rotor bracket (1) are detachably connected.

2. The test device for simulating the mechanical properties of a permanent magnet motor rotor sleeve according to claim 1, characterized in that: The end surface of the permanent magnet (5) facing the positioning portion (31) is provided with an axial step (52), the circumferential surface of the positioning portion (31) is provided with a radial threaded hole (32) pointing to the axial step (52), a set screw (33) is provided in the radial threaded hole (32), and the set screw (33) abuts against the axial step (52).

3. The test device for simulating the mechanical properties of a permanent magnet motor rotor sleeve according to claim 1, characterized in that: The second pressing plate (3) is connected to the rotor bracket (1) via a second screw (34); the first pressing plate (2) is connected to the rotor bracket (1) via a first screw (22).

4. The test device for simulating the mechanical properties of a permanent magnet motor rotor sleeve according to any one of claims 1 to 3, characterized in that: The guide rod (7) is a guide bolt, the radial step (21) is provided with an axial threaded hole (23) matched with the guide bolt, and the limiting protrusion (71) is a nut matched with the guide bolt or a nut fixed on the guide bolt.

5. The test device for simulating the mechanical properties of a permanent magnet motor rotor sleeve according to any one of claims 1 to 3, characterized in that: The permanent magnet (5) is made of structural steel.

6. The test device for simulating the mechanical properties of a permanent magnet motor rotor sleeve according to any one of claims 1 to 3, characterized in that: The rotor bracket (1) and the rotating shaft (4) are connected via a key, the rotor bracket (1) and the rotating shaft (4) are clearance-fitted, and the two are connected via welding after being assembled.

7. The test device for simulating the mechanical properties of a permanent magnet motor rotor sleeve according to any one of claims 1 to 3, characterized in that: The first pressing plate (2) and the rotor support (1) as well as the second pressing plate (3) and the rotor support (1) are positioned by means of stop structures.

8. A test method based on the test device for simulating the mechanical properties of a permanent magnet motor rotor sleeve according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Assembly: Install the rotor support (1) on the rotating shaft (4), install the first pressing plate (2) and the second pressing plate (3) on the two end surfaces of the rotor support (1), install the permanent magnet (5), adjust the permanent magnet (5) so that it abuts against the positioning portion (31) of the second pressing plate (3), and ensure that the end surfaces of all the permanent magnets (5) abutting against the positioning portion (31) are aligned, install the guide rod (7) and the spring (6), and make the spring (6) be compressed between the end surface where the limiting protrusion (71) and the guide hole (51) are located; S2, putting a sheath on the outer periphery of the permanent magnet (5); S3, remove the second pressure plate (3); S4. Test: A rotational force is applied to the rotating shaft (4). During the rotation, when the centrifugal force on the permanent magnet (5) and the radial force of the sleeve cancel each other out to a balance, the elastic force of the spring (6) causes the permanent magnet (5) to undergo axial displacement, thereby obtaining the relationship between the rotational speed, the centrifugal force and the sleeve strength.

9. A test device for simulating the mechanical properties of a permanent magnet motor rotor sleeve, characterized in that: The invention comprises a rotor support (1), a pressure plate 1 (2), a pressure plate 2 (3), a rotating shaft (4), a permanent magnet (5), a spring (6) and a guide rod (7), wherein the rotor support (1) is sleeved on the rotating shaft (4) and the two rotate synchronously, the pressure plate 1 (2) and the pressure plate 2 (3) are respectively mounted on the two end surfaces of the rotor support (1), a mounting groove (11) is provided on the circumferential surface of the rotor support (1), the permanent magnet (5) is arranged in the mounting groove (11), the outer circumference of the pressure plate 1 (2) is provided with a radial step (21), and the permanent magnet (5) is directed toward the radial direction. An axial guide hole (51) is provided on the end face of the radial step (21); one end of the guide rod (7) is mounted on the radial step (21) and the other end is located in the axial guide hole (51); the permanent magnet (5) can move relative to the guide rod (7); the spring (6) is sleeved on the guide rod (7) and compressed between the radial step (21) and the end face where the guide hole (51) is located; a positioning portion (31) for axially positioning the permanent magnet (5) is provided on the outer periphery of the second pressure plate (3); the second pressure plate (3) and the rotor bracket (1) are detachably connected.

10. A test method based on the test device for simulating the mechanical properties of a permanent magnet motor rotor sleeve according to claim 9, characterized in that: The following steps are involved: S1. Assembly: Install the rotor support (1) on the rotating shaft (4), install the first pressure plate (2) and the second pressure plate (3) on the two end surfaces of the rotor support (1), install the permanent magnet (5), adjust the permanent magnet (5) so that it abuts against the positioning portion (31) of the second pressure plate (3), and ensure that the end surfaces of all the permanent magnets (5) abutting against the positioning portion (31) are aligned, install the guide rod (7) and the spring (6), and make the spring (6) be compressed between the radial step (21) and the end surface where the guide hole (51) is located; S2, putting a sheath on the outer periphery of the permanent magnet (5); S3, remove the second pressure plate (3); S4. Test: A rotational force is applied to the rotating shaft (4). During the rotation, when the centrifugal force on the permanent magnet (5) and the radial force of the sleeve cancel each other out to a balance, the elastic force of the spring (6) causes the permanent magnet (5) to undergo axial displacement, thereby obtaining the relationship between the rotational speed, the centrifugal force and the sleeve strength.

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