An eddy current brake magnet

Abstract

The application discloses a kind of eddy current brake magnets, the eddy current brake magnets are used for the braking system of rail transit vehicle on steel rail or rail;The eddy current brake magnet includes: magnetic yoke, by the support arm of both sides is arranged at the bottom of the rail transit vehicle;Multiple magnetic poles are arranged below the magnetic yoke;In the case where the rail transit vehicle brakes, the vertical suction force generated by the magnetic pole close to the midpoint of the magnetic yoke is less than the vertical suction force generated by the magnetic pole away from the midpoint of the magnetic yoke;Wherein, the midpoint of the magnetic yoke is located at the midpoint of the distance of both sides support arm.This scheme is designed into different suction force level by magnetic pole, optimizes the distribution of magnetic pole suction force on the magnetic yoke, and higher eddy current braking force is obtained under the premise of installation space and magnetic yoke deflection limit.

Description

Technical Field

[0001] This invention relates to the field of rail vehicle braking technology, and in particular to an eddy current braking magnet. Background Technology

[0002] Track linear eddy current braking uses an eddy current braking magnet as the primary and the rail as the secondary pole. It generates braking force through electromagnetic induction and directly transmits this force to the bogie. This is a non-adhesive braking technology that does not rely on wheel-rail adhesion. An eddy current braking magnet typically consists of a yoke and several magnetic poles. When eddy current braking is applied, a braking force parallel to the track direction and an attractive force perpendicular to the track direction are generated between the eddy current braking magnet and the rail. The vertical attractive force causes the yoke to bend and deform; if the deformation is too large, the bottom surface of the magnetic poles may collide with the rail. To avoid this, the design limit for the vertical deformation of the yoke under the product's own weight and the vertical attractive force is generally no more than 2mm.

[0003] To achieve the above design goals, the longitudinal section of the magnetic yoke is usually designed as stepped, and the cross section as I-shaped, in order to obtain high bending stiffness within a suitable weight range. When the bogie installation space is limited, and the commonly used measures to improve the bending stiffness of the magnetic yoke cannot meet the deflection requirements, the attraction force of the magnetic poles must be limited. Since the braking force is positively correlated with the attraction force, the eddy current braking force will also be limited to a certain extent.

[0004] Therefore, given the limitations of installation space and yoke deflection, how to rationally design the magnet to obtain the maximum braking force is a problem that urgently needs to be solved in eddy current braking devices. Summary of the Invention

[0005] The purpose of this specification is to provide an eddy current braking magnet to solve the problem of how to rationally design a magnet to obtain the maximum braking force under the constraints of installation space and yoke deflection.

[0006] This invention provides an eddy current braking magnet for use in the braking system of a rail transit vehicle traveling on steel rails or railway tracks. The eddy current braking magnet includes: a magnetic yoke, which is disposed at the bottom of the rail transit vehicle via support arms on both sides; and a plurality of magnetic poles disposed below the magnetic yoke. When the rail transit vehicle is braking, the vertical attraction force generated by the magnetic poles near the midpoint of the magnetic yoke is less than the vertical attraction force generated by the magnetic poles far from the midpoint of the magnetic yoke. The midpoint of the magnetic yoke is located at the midpoint of the distance between the two support arms.

[0007] In some embodiments, among any two adjacent magnetic poles, the vertical attraction force generated by the magnetic pole closer to the midpoint of the yoke is less than or equal to the vertical attraction force generated by the magnetic pole farther from the midpoint of the yoke.

[0008] In some embodiments, the plurality of magnetic poles employ two or three different specifications.

[0009] In some embodiments, the plurality of magnetic poles are all permanent magnet poles; the magnetic poles near the midpoint of the yoke and the magnetic poles away from the midpoint of the yoke are different in at least one of the following aspects, so that the vertical attraction force generated by the magnetic poles near the midpoint of the yoke is less than the vertical attraction force generated by the magnetic poles away from the midpoint of the yoke: the space in which the permanent magnet is located, and the magnetic energy product of the permanent magnet.

[0010] In some embodiments, the plurality of magnetic poles are all electromagnetic poles; the magnetic poles near the midpoint of the yoke and the magnetic poles away from the midpoint of the yoke are different in at least one of the following aspects, so that the vertical attraction force generated by the magnetic poles near the midpoint of the yoke is less than the vertical attraction force generated by the magnetic poles away from the midpoint of the yoke: number of winding turns, core cross-sectional area, core material, and core height.

[0011] In some embodiments, the excitation circuits of each electromagnetic pole are connected in series.

[0012] In some embodiments, the bottom surface of the magnetic yoke is a plane.

[0013] In some embodiments, the center of the bottom surface of the magnetic yoke bulges downward.

[0014] In some embodiments, the middle portion above the yoke protrudes upward.

[0015] The technical solution of this invention has the following significant advantages: by designing each magnetic pole with a different vertical attraction level, the vertical attraction of the middle magnetic pole is relatively small, while the vertical attraction of the magnetic poles at both ends is relatively large, making the vertical attraction distribution more reasonable. This allows for controllable vertical deflection of the yoke while simultaneously achieving a larger eddy current braking force. By designing the magnetic poles with different attraction levels and optimizing the distribution of magnetic pole attraction on the yoke, a high eddy current braking force can be obtained under the constraints of installation space and yoke deflection.

[0016] Specific embodiments of the invention are disclosed in detail below with reference to the description and accompanying drawings, indicating how the principles of the invention can be employed. It should be understood that the embodiments of the invention are not therefore limited in scope. Features described and / or shown for one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments. Attached Figure Description

[0017] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely illustrative to aid in understanding the invention and do not specifically limit the shapes and proportions of the components. Those skilled in the art, guided by the teachings of this invention, can select various possible shapes and proportions to implement the invention according to specific circumstances.

[0018] Figure 1 A schematic diagram of the structure of an eddy current braking magnet used in rail transit vehicles is shown.

[0019] Figure 2 A schematic diagram of the force analysis of the magnetic yoke is shown;

[0020] Figure 3 The relative values ​​of deflection corresponding to each magnetic pole are shown;

[0021] Figure 4 A schematic diagram of one embodiment of the eddy current braking magnet provided in this specification is shown;

[0022] Figure 5 A schematic diagram of the structure of a common electromagnetic pole is shown;

[0023] Figures 6 to 8 Schematic diagrams of three types of small-force electromagnetic poles are shown;

[0024] Figure 9 A schematic diagram of the structure of a common permanent magnet pole is shown;

[0025] Figures 10 to 11 Schematic diagrams of two types of small-force permanent magnet poles are shown;

[0026] Figure 12 A schematic diagram of another embodiment of the eddy current braking magnet provided in this specification is shown;

[0027] Figure 13 A schematic diagram of the cross-section of the magnetic yoke is shown;

[0028] Figure 14 A schematic diagram of an electromagnetic pole that is shorter than a conventional electromagnetic pole is shown.

[0029] Figure 15 A schematic diagram of a permanent magnet pole that is shorter than that of a conventional permanent magnet pole is shown.

[0030] The reference numerals in the above figures are as follows: eddy current brake magnet-1, yoke-11, magnetic pole-12, support arm-2, support roller-3; 121 to 128 represent 8 magnetic poles respectively, 9 represents one end plate, 10 represents another end plate, 11 represents the yoke; 51 represents the terminal, 52 represents the winding, 53 represents the outer shell, 54 represents the iron core; 71 represents the outer shell, 72 represents the permanent magnet, and 73 represents the soft magnetic material. Detailed Implementation

[0031] The details of the present invention can be more clearly understood by referring to the accompanying drawings and the description of specific embodiments. However, the specific embodiments of the present invention described herein are for illustrative purposes only and should not be construed as limiting the invention in any way. Under the teachings of this invention, those skilled in the art can conceive of any possible modifications based on the invention, all of which should be considered within the scope of the invention. It should be noted that when an element is referred to as being "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or there may be an intervening element. The terms "mounted," "connected," and "connected" should be interpreted broadly, for example, they can refer to mechanical or electrical connections, or internal communication between two elements, and can be direct or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only embodiments.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0033] A track-mounted linear eddy current braking magnet assembly typically consists of an eddy current braking magnet 1, a support arm 2, and a support roller 3. The eddy current braking magnet 1 includes a magnetic yoke 11 and magnetic poles 12, such as... Figure 1 As shown. When eddy current braking is applied, a braking force parallel to the track direction and an attractive force perpendicular to the track direction are generated between the eddy current braking magnet and the rail. The vertical attractive force causes the magnetic yoke to bend and deform.

[0034] The term "vertical" as used in this specification refers to the direction perpendicular to the plane of the rail or the rail itself.

[0035] According to the theory of mechanics of materials, the bending moment and deflection are greatest in the middle part of the magnetic yoke, and the deflection value is most sensitive to the attraction force of the middle magnetic pole. Therefore, the key to controlling bending deformation lies in improving the bending stiffness of the middle part of the magnetic yoke and controlling the distribution of the vertical attraction force of each magnetic pole.

[0036] The inventors studied the relationship between the vertical attractive force of each magnetic pole and the deflection of the middle part of the yoke. The specific research process is as follows: Figure 1 The eddy current brake magnet shown is simplified as follows: Figure 2 The simply supported beam stress model shown is given, where F ai (i = 1, 2, ..., 8) represents the vertical attraction force generated on each magnetic pole. Then, the superposition method is applied to analyze the influence of the attraction force of each magnetic pole on the deflection at the middle position of the yoke. The deflection generated at the middle position when a vertical attraction force of 1 kN is applied to each magnetic pole is calculated, and the deflection corresponding to each magnetic pole is normalized (i.e., the deflection corresponding to each magnetic pole / the maximum deflection among the deflections corresponding to each magnetic pole). The relative ratio of the deflection generated by each magnetic pole is observed, and the results are as follows. Figure 3 As shown.

[0037] from Figure 3 As can be seen from this, the deflection value of the middle part of the magnetic yoke exerts a vertical attractive force F on the middle magnetic pole. a3 F a4 F a5 F a6 It is quite sensitive, for example, to vertical suction force F. a4 The resulting deflection is approximately F a1 The resulting deflection is 1.3 times the vertical suction force F. a3 The resulting deflection is approximately F a1 The resulting deflection is 1.1 times that of the magnetic field. Therefore, theoretically, by coordinating the distribution of the attractive forces of each magnetic pole, the vertical deformation of the eddy current braking magnet can be controlled and the overall attractive force of the eddy current braking magnet can be maximized. Since the attractive force is positively correlated with the braking force, the maximum eddy current braking force can ultimately be achieved.

[0038] Based on the above analysis, this specification provides an eddy current braking magnet for use in the braking system of rail transit vehicles traveling on steel rails or railway tracks. For example... Figure 1 , Figure 4 and Figure 12 As shown, the eddy current braking magnet includes a yoke 11 and a plurality of magnetic poles 12 disposed below the yoke 11.

[0039] The magnetic yoke 11 is mounted on the bottom of the rail transit vehicle via support arms on both sides.

[0040] When a rail transit vehicle is braking, the vertical attraction force generated by the magnetic pole near the midpoint of the yoke is less than that generated by the magnetic pole far from the midpoint of the yoke; the midpoint of the yoke is located at the midpoint of the distance between the two support arms.

[0041] In some embodiments, among any two adjacent magnetic poles, the vertical attraction force generated by the magnetic pole closer to the midpoint of the yoke is less than or equal to the vertical attraction force generated by the magnetic pole farther from the midpoint of the yoke.

[0042] exist Figure 4 and Figure 12 In the diagram, 121 to 128 represent 8 magnetic poles, 9 represents one end plate, 10 represents the other end plate, and 11 represents the yoke.

[0043] When the rail vehicle is braking, the vertical attraction generated by magnetic poles 124 and 125 can be less than that generated by magnetic poles 121, 122, 123, 126, 127, and 128; alternatively, starting from the boundary between magnetic poles 124 and 125, the vertical attraction generated by each magnetic pole can increase sequentially from the starting point to end plate 9 or 10. For ease of explanation, the magnetic pole closer to the midpoint of the yoke will be referred to as the middle magnetic pole, and the magnetic pole farther from the midpoint of the yoke will be referred to as the two end magnetic poles.

[0044] It should be noted that, according to Figure 3 Each magnetic pole has a different effect on deflection. Theoretically, all magnetic poles could be configured with different specifications. However, for ease of production and assembly, it is not recommended to design too many specifications. Generally, using 2 to 3 different specifications is sufficient. Based on the degree of influence of the vertical attraction force generated by each magnetic pole on deflection, the vertical attraction force generated by the middle magnetic pole can be reduced first. If the deflection requirement is not met, the attraction force generated by its adjacent magnetic poles can be reduced. For example, magnetic poles 124 and 125 can be designed as low-attraction magnetic poles first. If the deflection requirement is not met, magnetic poles 123 and 126 can also be designed as low-attraction magnetic poles, and so on.

[0045] In some embodiments, the multiple magnetic poles are all electromagnetic poles, and all magnetic poles must be connected in series to ensure braking safety; therefore, the excitation current of all magnetic poles is the same. In order to make the magnetic poles generate different attractive forces, the magnetic poles near the midpoint of the yoke and the magnetic poles far from the midpoint of the yoke differ in at least one of the following aspects, so that the vertical attractive force generated by the magnetic poles near the midpoint of the yoke is less than that generated by the magnetic poles far from the midpoint of the yoke: number of winding turns, core cross-sectional area, and core material.

[0046] Figure 5 A schematic diagram of a common electromagnetic pole is shown, where 51 represents a terminal, 52 represents a winding, 53 represents the outer casing, and 54 represents the iron core. A common electromagnetic pole can serve as the aforementioned two poles. Figures 6 to 8 The diagram shows the structure of three types of small attractive magnetic poles. Figures 6 to 8 The electromagnetic poles in the middle can serve as the intermediate magnetic poles mentioned above.

[0047] Figure 6 and Figure 5 The difference between the electromagnetic poles shown is that the number of winding turns is reduced, so the excitation magnetomotive force is smaller than that of ordinary poles. The empty winding space is filled by the outer shell while the overall volume of the electromagnetic pole remains unchanged. Figure 7 and Figure 5 The difference between the electromagnetic poles shown is that: the cross-sectional area of ​​the iron core is increased, so the number of winding turns is reduced accordingly while the overall volume of the electromagnetic pole remains unchanged; there is an optimal combination between the cross-sectional area of ​​the iron core and the number of winding turns to maximize the attraction force, and by adjusting the parameters of the two, the attraction force of the middle pole can be made smaller than that of the ordinary pole. Figure 8 and Figure 5 The difference between the electromagnetic poles shown lies in the magnetic permeability of the core material compared to... Figure 5 The magnetic permeability of the core material is slightly poor. For example, if medium-high carbon steel is used, the air gap magnetic flux density corresponding to the middle magnetic pole is smaller, resulting in a smaller attraction force. The winding and outer shell are the same as those of ordinary magnetic poles.

[0048] In other embodiments, the multiple magnetic poles are all permanent magnets, and the magnetic poles near the midpoint of the yoke are different from the magnetic poles far from the midpoint of the yoke in at least one of the following aspects, so that the vertical attraction generated by the magnetic poles near the midpoint of the yoke is less than the vertical attraction generated by the magnetic poles far from the midpoint of the yoke: the space in which the permanent magnets are located, and the magnetic energy product of the permanent magnets.

[0049] For eddy current braking magnets with permanent magnet excitation, the permanent magnet must be encased in a protective shell. The volume of the permanent magnet can be changed by adjusting its grade (i.e., magnetic energy product) or volume, thereby changing the vertical attraction force generated by the magnetic poles.

[0050] Figure 9 A schematic diagram of the structure of a common permanent magnet pole is shown, in which 71 represents the outer shell, 72 represents the permanent magnet, and 73 represents the soft magnetic material. Figure 10 and Figure 11 Schematic diagrams of two types of small-force permanent magnet poles are shown. Figure 9 The permanent magnet poles shown can serve as the two magnetic poles mentioned above. Figure 10 and Figure 11 The permanent magnet poles shown can serve as the intermediate magnets mentioned above.

[0051] Figure 10 and Figure 9 The difference between the permanent magnet poles shown is: Figure 10 Permanent magnet ratio Figure 9 The permanent magnet is small in size, in order to make Figure 10 and Figure 9 The outer dimensions of the middle magnetic poles are the same. Figure 10 A layer of soft magnetic material is superimposed on a permanent magnet; Figure 11 and Figure 9 The difference between the permanent magnet poles shown is: Figure 11 permanent magnets and Figure 9 The permanent magnets are the same size, but different grades, and the permanent magnets with smaller energy products were selected.

[0052] In some embodiments, such as Figure 4 As shown, the bottom surface of the magnetic yoke is a plane.

[0053] In other embodiments, such as Figure 12 As shown, the bottom surface of the magnetic yoke bulges downwards in the middle. In this case, the top of the magnetic yoke can be flat or bulge upwards in the middle, depending on the bogie mounting space.

[0054] The cross-section of the magnetic yoke is I-shaped, such as... Figure 13 As shown, the cross-section refers to the section perpendicular to the length of the rail. According to mechanics of materials, increasing the cross-sectional height of the yoke can improve its bending stiffness. The cross-sectional height refers to... Figure 4 and Figure 12 The dimension H is shown. (As shown in the image) Figure 4 and Figure 12 As shown, if the installation space is limited, the vertical cross-sectional height that can be increased in the middle of the yoke is limited. Therefore, the middle of the yoke can be designed to increase the cross-sectional height in both the upward and downward directions, forming a fish-belly shape, thereby maximizing the bending stiffness of the yoke's middle section. The length L and height H of the fish-belly protrusion can be designed and adjusted according to the specific requirements of the bogie installation space and bending stiffness.

[0055] To ensure that the bottom surfaces of all magnetic poles are flush, the height of the middle magnetic pole needs to be reduced accordingly due to the downward increase in height at the center of the yoke.

[0056] For electrically excited magnetic poles, the intermediate magnetic pole is like... Figure 14 As shown, the cross-section of the iron core is... Figure 5 The ordinary magnetic poles shown are the same, but the iron core height is relatively small, so the winding space is smaller and the number of winding turns is less.

[0057] For the magnetic poles of a permanent magnet excitation system, the intermediate magnetic pole is like... Figure 15 As shown, the volume ratio of permanent magnets Figure 7 The ordinary magnetic poles shown are small. Therefore, regardless of whether the eddy current braking magnet is an electromagnet or a permanent magnet, the magnetomotive force of the middle magnetic pole is smaller than that of the two end magnetic poles, resulting in a smaller vertical attraction force of the middle magnetic pole compared to the two end magnetic poles.

[0058] The following is based on Figure 4Taking the eddy current braking magnet shown as an example, we will illustrate the technical effect of this solution. Since the eddy current braking force is positively correlated with the generated vertical attraction force, and the vertical attraction force is the main cause of vertical deformation of the yoke, the vertical attraction force is used as the optimization target. Under the constraint that the yoke deflection does not exceed 2mm, the attraction force is optimized to the maximum. If all magnetic poles have the same specifications, the vertical attraction force of each magnetic pole needs to be controlled below 3.57kN, that is, the overall vertical attraction force of each magnetic pole needs to be controlled below 28.56kN. If the magnetic poles are designed with two specifications, the vertical attraction force of magnetic poles 123 to 126 shall not exceed 2.70 kN per pole, and the vertical attraction force of magnetic poles 121, 122, 127, and 128 shall not exceed 4.70 kN per pole. That is, the total vertical attraction force of all magnetic poles shall be controlled below 29.60 kN. Then the deflection of the yoke shall also meet the requirement of not exceeding 2 mm. However, the total vertical attraction force of the eddy current braking magnet of this invention is about 3.6% higher than that of the single-pole specification eddy current braking magnet. Based on the positive correlation between vertical attraction force and eddy current braking force, and the design experience of the ratio of vertical attraction force to braking force improvement, it can be predicted that the average braking force of the eddy current braking magnet in this scheme will be more than 3.6% higher than that of the single-pole specification eddy current braking magnet.

[0059] The eddy current braking magnet provided in this manual is designed with different vertical attraction levels for each magnetic pole. The vertical attraction of the middle pole is relatively small, while the vertical attraction of the poles at both ends is relatively large, making the vertical attraction distribution more reasonable. This allows for controllable vertical deflection of the yoke while simultaneously achieving a large eddy current braking force. By designing the magnetic poles with different attraction levels and optimizing the distribution of the magnetic pole attraction on the yoke, a high eddy current braking force can be obtained within the constraints of installation space and yoke deflection.

[0060] The various embodiments described in this specification are presented in a progressive manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0061] All articles and references disclosed herein, including patent applications and publications, are incorporated herein by reference for various purposes. The term “substantially constitutes…” used to describe a combination should include the identified elements, components, parts, or steps, as well as other elements, components, parts, or steps that do not substantially affect the essential novelty of the combination. The use of the terms “comprising” or “including” to describe combinations of elements, components, parts, or steps herein also contemplates embodiments substantially constituted by such elements, components, parts, or steps. The use of the term “may” herein is intended to indicate that any described attribute included by “may” is optional.

[0062] Multiple elements, components, parts, or steps can be provided by a single integrated element, component, part, or step. Alternatively, a single integrated element, component, part, or step can be divided into multiple separate elements, components, parts, or steps. The use of "a" or "an" to describe an element, component, part, or step does not imply the exclusion of other elements, components, parts, or steps.

[0063] The above are merely a few embodiments of the present invention. Although the embodiments disclosed in the present invention are as described above, the content is only for the purpose of facilitating understanding of the present invention and is not intended to limit the present invention. Any person skilled in the art to which this invention pertains may make any modifications and changes in the form and details of the embodiments without departing from the spirit and scope disclosed in the present invention. However, the patent protection scope of the present invention shall still be determined by the scope defined in the appended claims.

Claims

1. An eddy current braking magnet, characterized in that, The eddy current braking magnet is used in the braking system of rail transit vehicles running on steel rails or railway tracks; the eddy current braking magnet includes: The magnetic yoke is mounted on the bottom of the rail transit vehicle via support arms on both sides; Multiple magnetic poles are arranged below the magnetic yoke; when the rail transit vehicle is braking, the vertical attraction force generated by the magnetic pole near the midpoint of the magnetic yoke is less than the vertical attraction force generated by the magnetic pole far from the midpoint of the magnetic yoke; wherein, the midpoint of the magnetic yoke is located at the midpoint of the distance between the two support arms. In any two adjacent magnetic poles, the vertical attraction force generated by the magnetic pole closer to the midpoint of the yoke is less than or equal to the vertical attraction force generated by the magnetic pole farther from the midpoint of the yoke.

2. The eddy current braking magnet according to claim 1, characterized in that, The multiple magnetic poles adopt two or three different specifications.

3. The eddy current braking magnet according to claim 1, characterized in that, All of the aforementioned magnetic poles are permanent magnet poles; The magnetic poles near the midpoint of the yoke and the magnetic poles away from the midpoint of the yoke differ in at least one of the following aspects, such that the vertical attraction generated by the magnetic poles near the midpoint of the yoke is less than the vertical attraction generated by the magnetic poles away from the midpoint of the yoke: the space in which the permanent magnet is located, and the magnetic energy product of the permanent magnet.

4. The eddy current braking magnet according to claim 1, characterized in that, All of the aforementioned magnetic poles are electromagnetic poles; The magnetic poles near the midpoint of the yoke and the magnetic poles away from the midpoint of the yoke differ in at least one of the following aspects, such that the vertical attraction force generated by the magnetic poles near the midpoint of the yoke is less than that generated by the magnetic poles away from the midpoint of the yoke: number of winding turns, core cross-sectional area, core material, and core height.

5. The eddy current braking magnet according to claim 4, characterized in that, The excitation circuits for each electromagnetic pole are connected in series.

6. The eddy current braking magnet according to claim 1, characterized in that, The bottom surface of the magnetic yoke is a plane.

7. The eddy current braking magnet according to claim 1, characterized in that, The bottom surface of the magnetic yoke bulges downward in the middle.

8. The eddy current braking magnet according to claim 7, characterized in that, The middle part above the magnetic yoke bulges upward.

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