JP2004222405A - Ferromagnetic plate and eddy current type reduction gear - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ferromagnetic plate and an eddy current type reduction gear in which a brake torque can be enhanced especially at the time of braking. <P>SOLUTION: The ferromagnetic plate has pole pieces 4 arranged oppositely to the permanent magnets 5, 5a and 5b of an eddy current type reduction gear. Among end faces 4b and 4c directed in the forward rotational direction, a recess 4a continuous to the inner circumferential surface 4d is provided in the end face 4b on the backward rotational direction. The pole piece 4 is extended such that the remaining part of the recess 4a is located on the backward rotational side as compared with the facing permanent magnets 5, 5a and 5b. The plate section of the side faces 4f and 4f' at the recess 4a forming section along the rotational direction has a thickness t set to cause magnetic saturation when a short circuit magnetic circuit is formed at the time of non-braking. Brake torque can be enhanced at the time of braking by reducing the density of magnetic lines of force directed from the permanent magnet through the pole piece toward the rotor. Furthermore, loss torque can be reduced at time of non-braking because magnetic leakage directed from the permanent magnet through the support toward the rotor is absorbed on the upper surface at the part of the recess. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a ferromagnetic plate of an eddy current type speed reducer which is attached to a large vehicle such as a bus or a truck as a braking auxiliary device and which can improve braking torque, and an eddy current type speed reducer employing the ferromagnetic plate. It is about.
[0002]
[Prior art]
In recent years, stable deceleration during long downhills, etc., reduce the number of times the foot brake is used, prevent abnormal wear of the lining and fade phenomenon, and shorten the stopping distance of buses and trucks. Eddy current type reduction gears have come to be attached to large automobiles in addition to foot brakes and exhaust brakes.
[0003]
At present, the eddy current type reduction gear is mainly of a permanent magnet type which does not need to be energized at the time of braking, and there are the following four types.
{Circle around (1)} As shown in FIG. 15, for example, a non-magnetic member is provided on the inner peripheral surface side of a drum type member (hereinafter referred to as “rotor”) 2a which is attached to the rotating shaft 1 and generates an eddy current inside during braking. N poles and S poles at the same interval as the pole pieces 4 via a group of ferromagnetic plates (hereinafter referred to as "pole pieces") 4 arranged at predetermined intervals in the circumferential direction between the supports 3 A ferromagnetic magnet support ring 6 having permanent magnets 5 arranged alternately in the circumferential direction attached to the outer peripheral surface thereof is arranged, and the permanent magnets 5 are entirely opposed to the pole pieces 4 by the magnet support ring 6. (See, for example, Patent Document 1).
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 1-234043 (page 1, FIG. 1)
[0005]
{Circle around (2)} As shown in FIG. 16, for example, a permanent magnet 5 in which a magnet supporting ring 6 disposed on the inner peripheral surface side of the rotor 2a and opposed thereto is attached to the outer peripheral surfaces of the pole piece 4 and the magnet supporting ring 6 is used. And a position where one permanent magnet 5 overlaps an adjacent pole piece 4 by half so as to be able to select a position in which the permanent magnet 5 overlaps (see, for example, Patent Document 2). .
[0006]
[Patent Document 2]
JP-A 1-298948 (page 1, FIG. 1)
[0007]
{Circle around (3)} As shown in FIG. 17, for example, two magnet support rings each having a permanent magnet group in which N poles and S poles are alternately arranged on the outer peripheral surface at predetermined intervals along the circumferential direction are arranged in parallel, One of the magnet support rings is fixed (hereinafter, referred to as a “fixed support ring 6a”), and the other magnet support ring is configured to be rotatable by a predetermined angle (hereinafter, referred to as a “movable support ring 6b”). Due to the turning movement of the ring 6b, the position where the permanent magnet 5b of the movable support ring 6b and the permanent magnet 5a of the fixed support ring 6a adjacent to each other have the same polarity, and the position of the permanent magnet 5b of the adjacent movable support ring 6b and the fixed support ring 6a. A double-row turning system configured to be able to select a position where the permanent magnet 5a has a different polarity (for example, see Patent Document 3).
[0008]
[Patent Document 3]
JP-A-4-12659 (page 1, FIG. 1)
[0009]
{Circle around (4)} As shown in FIG. 18, for example, at a position facing the disk-shaped rotor 2 b attached to the rotating shaft 1, a predetermined interval is provided between the non-magnetic supports 3 in the circumferential direction thereof. Through the group of pole pieces 4, a ferromagnetic magnet support ring 6 having permanent magnets 5 in which N poles and S poles are alternately arranged in the circumferential direction at the same intervals as the pole pieces 4 is attached to the side face, A shaft-sliding method using a disk-type rotor provided with the magnet support ring 6 so as to be able to move forward and backward in the case by an actuator 7 from a position where the group of permanent magnets 5 is entirely opposed to a group of pole pieces 4 to a position where the permanent magnet is completely separated.
[0010]
In any of the above-described eddy current type speed reducers, the magnet support ring 6 is adjacent to the pole support 4 and the permanent magnets 5, 5a, 5b during braking in which the entire surface is opposed. A magnetic circuit is formed between the permanent magnets 5, 5a, 5b and the adjacent pole pieces 4, and the rotors 2a, 2b. Lines of magnetic force from the permanent magnets 5, 5a, 5b act on the rotors 2a, 2b to generate eddy currents. And a braking torque is generated.
[0011]
[Problems to be solved by the invention]
However, conventionally, the shape of the pole piece 4 is substantially a rectangular parallelepiped, and the length in the rotation (circumferential) direction on the inner circumferential side is substantially the same as the outer circumferential surface length of the permanent magnets 5, 5a, 5b, as shown in FIG. Since the magnetic lines of force from the permanent magnets 5, 5a, 5b cannot be increased in magnetic flux density because they are the same, if the generation of braking torque is weak or the rotation speed of the rotors 2a, 2b increases, the thin line in FIG. As shown in FIG. 5, the magnetic lines of force are dragged in the rotation direction of the rotors 2a and 2b, which are members that generate eddy currents, and the lines of magnetic force are directed forward (in the direction of rotation of the rotors 2a and 2b of the pole piece 4) during braking. There is a drawback that magnetic saturation occurs at the "rotation front side"), the magnetic flux reaching the rotors 2a and 2b decreases, and the braking torque decreases.
[0012]
The present invention has been made in view of the above-mentioned conventional problems, and in particular, a pole piece of an eddy current type reduction device capable of improving braking torque during braking, and an eddy current type deceleration employing the pole piece. It is intended to provide a device.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a pole piece, which is disposed to face a permanent magnet of an eddy current type reduction gear, and has a front end face, a rear end face, or a rear end face in a rotation advancing direction of a rotor during braking. Both end faces (hereinafter, simply referred to as “rotation front end face”, “rotation rear end face”, or “rotation front / rear end face”, respectively) have depressions. Further, the present invention also provides a pole piece disposed opposite to a permanent magnet of an eddy current type reduction gear, on the right side surface, the left side surface, or both side surfaces (hereinafter, referred to as the direction of rotation of the rotor during braking). Each of them simply has a depression on the “right side of rotation”, “left side of rotation”, and “both sides of right and left sides of rotation”. This makes it possible to improve the braking torque particularly during braking.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
The eddy current type speed reducer according to the present invention is a pole piece arranged opposite to the permanent magnet of the eddy current type speed reducer, the rotation front end surface, the rotation rear end surface, the rotation front and rear end surfaces, the rotation right side surface, the rotation left side. The pole piece according to the present invention, which has a depression on the side surface or on both the right and left sides of the rotation, is employed.
[0015]
In the present invention, the depression 4a in the pole piece 4 is formed as a rotation rear end face 4b as illustrated in FIG. 1A, or as a rotation front end face 4c as illustrated in FIG. As illustrated in (c), either the rotation rear end face 4b or the rotation front end face 4c may be used. The end faces 4b and 4c are not limited to those parallel to the rotation axis 1 as illustrated in FIG. 2A, but have an angle α with respect to the rotation axis 1 as illustrated in FIG. Including those that did. In the present invention, the term “dent” refers to a case where a surrounding wall surrounding a dent portion is continuously closed at an end face where the dent exists, and a case where at least one of four sides of the end face is the wall. Including the case where is broken. In addition, the “dent” may be provided at a plurality of positions in one end surface.
[0016]
In the present invention, the position of the depression 4a provided in the end surfaces 4b and 4c of the pole piece 4 is limited to a portion between the inner and outer peripheral surfaces 4d and 4e of the pole piece 4, as exemplified in FIG. Instead, as illustrated in FIG. 3B, the wall around the dent 4a is cut off at one of the four sides of the end face 4c of the pole piece 4 on the side of the inner peripheral surface 4d, and the dent 4a becomes the inner peripheral surface. As shown in FIG. 3 (c), one of the four sides of the end face 4c of the pole piece 4 on the outer peripheral surface 4e side cuts the wall around the recess 4a, and 4a may open to the outer peripheral surface 4e.
[0017]
In the eddy current type speed reducer according to the present invention, as an example, the pole piece 4 according to the present invention having the depressions 4a in the end faces 4b and 4c is used. Therefore, as shown in FIG. The density of the lines of magnetic force from the magnets 5, 5a, 5b via the pole piece 4 to the rotors 2a, 2b is such that the conventional pole piece 4 (see FIG. 4 (b)) having no depressions 4a in the end faces 4b, 4c was used. Higher than the ones. Note that the thin line from the permanent magnets 5, 5a, 5b shown in FIG. 4 to the rotors 2a, 2b via the pole piece 4 indicates the lines of magnetic force.
[0018]
When the magnetic flux lines having the increased density reach the rotors 2a and 2b, a large eddy current is generated, and a large Lorentz force is obtained. Therefore, as described above, for example, the magnetic flux lines are dragged by the rotation of the rotors 2a and 2b and moved forward in the rotation direction. Even when the vehicle is concentrated, the overall braking force is improved.
[0019]
In the above-described eddy current type reduction gear according to the present invention, the area of the inner peripheral surface 4d of the pole piece 4 is, as illustrated in FIGS. If the pole piece 4 according to the present invention is equal to or larger than the area of the outer peripheral surface 5c of the permanent magnets 5a, 5b, or is larger than the area of the outer peripheral surface 5c of the permanent magnets 5, 5a, 5b, the permanent magnet Since more magnetic lines of force coming out of 5, 5a, 5b are input to pole piece 4, a braking force can be obtained effectively.
[0020]
The operation of the depression 4a is provided by providing the depression 4a on the left and / or right side surface 4f in the traveling direction of the rotation direction during braking of the rotors 2a and 2b as illustrated in FIG. Is also obtained. As shown in FIG. 13B, these depressions 4a become more remarkable when they are grooves 4g provided between the inner and outer peripheral surfaces 4d and 4e of the pole piece 4. In addition, it can be said that this groove 4g is a case where the “dent” wall is cut on two of the four sides of the end face where the groove is provided. When these depressions and grooves are located at the central portion between the inner and outer peripheral surfaces 4d and 4e of the pole piece 4, the effects of these actions can be further obtained.
[0021]
Although not shown, the depression 4a provided on the side surface 4f of the pole piece 4 is also provided between the inner and outer peripheral surfaces 4d and 4e of the pole piece 4, similarly to the depression 4a provided on the rotation front end surface 4c and the rotation rear end surface 4b. Not only the portion but also an opening on the inner peripheral surface 4d of the pole piece 4 or an opening on the outer peripheral surface 4e of the pole piece 4 may be used.
[0022]
Further, in the eddy current type reduction gear according to the present invention described above, the projection shape as viewed from above the main surface of the pole piece 4 as illustrated in FIG. 6A, or as illustrated in FIG. In the eddy current type reduction gear transmission according to the present invention employing the pole piece 4 according to the present invention in which the shape of the outer peripheral surface 4e is widened toward the rear side of rotation, the line of magnetic force from the rotor easily enters the pole piece during braking. The braking force is further improved. In this case, as compared with the case where only the outer peripheral surface shape is used as illustrated in FIG. 7A, the book in which the entire thickness of the pole piece 4 spreads toward the rotation rear side as illustrated in FIGS. 6B and 6C. It is considered that the use of the pole piece according to the present invention further improves the braking force. The main surface of the pole piece 4 refers to a surface having the largest surface area among the surfaces of the pole piece 4, and for example, in the case of a kamaboko type, one curved surface is the main surface. The term “above the main surface” refers to an axial direction that extends vertically from the center of the main surface based on this definition.
[0023]
Further, in the eddy current type reduction gear according to the present invention described above, the projected shape as viewed from above the pole piece main surface as illustrated in FIG. 8A, or the outer peripheral surface as illustrated in FIG. In the eddy current type speed reducer according to the present invention, which employs the pole piece 4 according to the present invention, the shape of which spreads toward the rotation front side, the line of magnetic force from the permanent magnet easily enters the rotor via the pole piece during braking. The braking force is further improved. Also in this case, according to the present invention, the entire thickness of the pole piece extends toward the rotation front side as illustrated in FIG. 8A, compared with the case of only the outer peripheral surface shape as illustrated in FIG. 9A. As with the previous case, it is considered that the use of the pole piece improves the braking force.
[0024]
In the above-described present invention, the rotation front side or the rotation rear side means the rotation front side or the rotation rear side from the center of the circumferential length of the pole piece. As shown in FIG. 10 (a), not only the rotation front end or the rotation rear end only extends in the rotation axis direction, but also the rotation rear side expands with respect to the rotation front side. On the contrary, as illustrated in FIG. 10B, an example in which the rotation front side is wider than the rotation rear side is also included.
[0025]
Although not shown in the drawings, in the eddy current type speed reducer according to the present invention, the shape of the projection or the outer peripheral surface viewed from above the main surface of the pole piece extends to both the rotation front side and the rotation rear side. In the eddy current type speed reducer according to the present invention employing the pole piece according to the present invention, the braking force is further improved by the above synergistic effect.
[0026]
FIG. 11 shows an example in which the pole piece 4 is extended in the direction of rotation of the rotor. The remaining portion of the recess 4a in the end surface 4b on the rotation rear side of the pole piece 4 forms the right side surface 4f, the left side surface 4f ', and the outer peripheral surface in the rotation advancing direction at the time of braking of the member generating the eddy current therein. It is configured to include. In the eddy current type speed reducer according to the present invention employing the pole piece 4 according to the present invention, at least the thickness t of either the right side surface 4f or the left side surface 4f 'is set at the time of forming the short-circuit magnetic circuit during braking. Even when the thickness is magnetically saturated, the magnetic leakage from the permanent magnets 5, 5a, 5b to the rotors 2a, 2b via the support 3 during non-braking is much smaller than that during braking. And the torque loss can be reduced.
[0027]
FIG. 12 is a diagram illustrating a pole piece 4 according to the present invention. In this example, the pole piece 4 is disposed so as to face the permanent magnets 5, 5a, 5b of the eddy current type speed reducer in a state where the pole piece 4 is extended in the rotation direction of the rotor. A recess 4a is provided in the rotation rear end face 4b of the pole piece 4 having an area of the inner peripheral surface 4d equal to or greater than the area of the outer peripheral surface 5c of the permanent magnets 5, 5a, 5b. . The remaining portion of the depression 4a is configured to include the right side surface 4f, the left side surface 4f ', and the outer peripheral surface 4e in the direction of rotation of the rotor during braking.
[0028]
A thickness of one of the plate portions of the pole piece 4 including at least the right side surface 4f of the remainder of the recess 4a and a thickness t of any of the plate portions including the left side surface 4f ′ is such that the thickness is magnetically saturated when the short-circuit magnetic circuit is formed during braking. Have been. Note that the magnetically saturated state is a state in which magnetic flux cannot enter any more, and the magnetically saturated state is always below a thickness at which the magnetic flux does not enter.
[0029]
In this example, a part of the depression 4a corresponding to the permanent magnets 5, 5a, 5b has a semi-cylindrical groove shape formed substantially in the center, and the remaining depression 4a has a rectangular parallelepiped shape. Is shown.
[0030]
In the eddy current type speed reducer according to the present invention using the pole piece 4 having such a shape, at the time of braking, the braking force is improved by the following operation.
{Circle around (1)} The density of the lines of magnetic force from the permanent magnets 5, 5a, 5b to the rotors 2a, 2b via the pole piece 4 is narrowed and increased in the depressions 4a, and when they reach the rotors 2a, 2b, a large eddy current is generated. Large Lorentz force is obtained.
[0031]
Also, when not braking,
{Circle around (2)} Magnetic leakage from the permanent magnets 5, 5a, 5b to the rotors 2a, 2b via the support 3 is absorbed by the upper surface of the recess 4a (including the outer peripheral surface 4e), thereby reducing loss torque. You can do it.
[0032]
FIG. 13 also illustrates a pole piece 4 according to the present invention. In the example shown in FIG. 13, the rotation front and rear end surfaces 4b of the pole piece 4 whose inner peripheral surface 4d has the same area as the outer peripheral surface 5c of the permanent magnets 5, 5a, 5b. , 4c, and both sides 4f, 4f ', a groove 4g is provided at the center between the inner and outer peripheral surfaces 4d, 4e.
[0033]
In the example of such a configuration, although the operation of (2) at the time of non-braking in the example illustrated in FIG. 12 is not performed, the operation of (1) at the time of braking becomes more remarkable. Compared with the eddy current type speed reducer used, a large improvement in braking torque can be achieved.
[0034]
FIG. 14 also illustrates a pole piece 4 according to the present invention. In the example shown in FIG. 14, in the example shown in FIG. 13, the projection shape viewed from above the main surface of the pole piece is made to spread to both the rotation front side and the rotation rear side.
[0035]
In the example of such a configuration, in addition to the operation of the one illustrated in FIG. 13, the following operation is performed at the time of braking, so that a greater improvement in braking torque can be achieved.
{Circle around (3)} The lines of magnetic force from the permanent magnets easily enter the rotor via the pole piece.
(4) Magnetic lines of force from the rotor easily enter the pole piece.
[0036]
It goes without saying that the present invention is not limited to the above-described embodiment, but can be applied to only the claims to improve the braking torque.
Further, when the pole piece 4 according to the present invention is manufactured by forging, the pole piece 4 which is inexpensive and has excellent magnetic properties can be obtained as compared with the case where the pole piece 4 is manufactured by casting.
As described above, the embodiments of the present invention have been described, but the present invention is not limited to these exemplifications, and can be modified within the scope of the technical idea shown in the claims.
[0037]
【The invention's effect】
As described above, according to the present invention,
(1) To reduce the density of magnetic lines of force from the permanent magnet to the rotor via the pole piece,
(2) To make it easy for the line of magnetic force from the permanent magnet to enter the rotor via the pole piece,
(3) To make it easy for the magnetic field lines from the rotor to enter the pole piece,
In particular, the braking torque during braking can be improved.
[Brief description of the drawings]
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of a depression provided on an end face of a pole piece according to the present invention, wherein (a) is an example provided on an end face on the rotation rear side, (b) is an example provided on an end face on the rotation front side, (c) () Is a diagram showing an example in which both the rotation rear side end face and the rotation front side end face are provided.
FIGS. 2A and 2B are explanatory views of a depression provided on an end face of a pole piece according to the present invention, wherein FIG. 2A is an example parallel to a rotation axis and FIG. 2B is an example having an angle with respect to the rotation axis.
3A and 3B are explanatory views of a dent provided on an end face of a pole piece according to the present invention, wherein FIG. 3A is an example provided in a portion between inner and outer peripheral faces, and FIG. An example in which the surrounding wall is cut and the dent is opened on the inner peripheral surface, and FIG. 2C is an example in which the dent is also opened on the outer peripheral surface.
FIG. 4A is an explanatory view of the flow of the magnetic force lines when the pole piece according to the present invention has a depression, which is an essential component of the pole piece according to the present invention, and FIG. 4B is a diagram illustrating the flow of the magnetic force lines of a conventional pole piece having no depression. FIG.
FIG. 5 is an explanatory view of a dent provided in the pole piece according to the present invention, showing an example in which the dent is provided on a left side and / or a right side in a rotation direction.
FIGS. 6A and 6B are views showing an example of a pole piece according to the present invention in which a projected shape as viewed from above the main surface of the pole piece spreads backward in rotation, wherein FIG. 6A is a view as viewed from a plane, and FIG. (C) is a view from the left side.
FIGS. 7A and 7B are views showing an example of a pole piece according to the present invention, in which the outer peripheral surface shape extends rearward in rotation, wherein FIG. 7A is a plan view, FIG. 7B is a front view, and FIG. It is the figure seen from the left side.
8A and 8B are diagrams illustrating an example of a pole piece according to the present invention in which a projection shape as viewed from above a main surface of the pole piece spreads forward in a rotation direction, wherein FIG. 8A is a diagram viewed from a plane, and FIG. (C) is a view from the left side.
FIGS. 9A and 9B are views showing an example of a pole piece according to the present invention in which the outer peripheral surface shape spreads forward in the rotation, wherein FIG. 9A is a plan view, FIG. 9B is a front view, and FIG. It is the figure seen from the left side.
FIG. 10 (a) is a diagram illustrating the meaning of “spread backward in rotation” in the present invention, and FIG. 10 (b) is a diagram illustrating the meaning of “spread forward in rotation” in the present invention.
11A and 11B are views showing a pole piece according to the present invention, which is extended in the direction of rotation of the rotor, wherein FIG. 11A is a plan view, FIG. 11B is a front view, and FIG. ) Is a view from the right side.
12A and 12B are diagrams showing an example of a pole piece according to the present invention, wherein FIG. 12A is a perspective view, FIG. 12B is a view along arrow A of FIG. FIG. 6B is a diagram viewed from the arrow B, and FIG. 5D is a diagram viewed from the arrow C in FIG.
13A and 13B are diagrams showing an example of a pole piece according to the present invention, wherein FIG. 13A is a perspective view, and FIG. 13B is an A view of FIG.
FIG. 14 is a perspective view showing an example of a pole piece according to the present invention.
FIG. 15 is a cross-sectional view of a shaft slide type eddy current type speed reducer in the direction of the rotation axis.
FIG. 16 is a cross-sectional view of a single-row turning type eddy current type reduction gear in a rotation axis direction.
FIG. 17 is a sectional view of a double-row turning type eddy current type speed reducer in a rotation axis direction.
FIG. 18 is a cross-sectional view of a shaft-sliding eddy current type reduction gear transmission using a disk rotor in the direction of the rotation axis.
FIG. 19 is an explanatory diagram of a magnetic circuit formed at the time of braking in a conventional eddy current type speed reducer.
[Explanation of symbols]
2a, 2b Rotor 4 Pole piece 4a Depression 4b Rotation rear end surface 4c Rotation front end surface 4d Inner peripheral surface 4e Outer peripheral surface 4f Right side surface 4f 'Left side surface 4g Grooves 5, 5a, 5b Permanent magnet 5c Outer peripheral surface

Claims (9)

A ferromagnetic plate arranged opposite to a permanent magnet of an eddy current type reduction gear, wherein a recess is formed in a front end face and / or a rear end face in a direction in which rotation of a member generating an eddy current occurs during braking. A ferromagnetic plate comprising: A ferromagnetic plate arranged opposite to a permanent magnet of an eddy current type reduction gear, wherein a depression is formed on a left side surface and / or a right side surface in a traveling direction of rotation of a member that generates an eddy current during braking. A ferromagnetic plate comprising: 3. The ferromagnetic plate according to claim 1, wherein the area of the inner peripheral surface of the ferromagnetic plate is equal to the area of the outer peripheral surface of the permanent magnet facing the inner peripheral surface, or the area of the outer peripheral surface of the permanent magnet. A ferromagnetic plate characterized by being wider than the area. The ferromagnetic plate according to any one of claims 1 to 3, wherein the depression is a groove provided between inner and outer peripheral surfaces of the ferromagnetic plate. The ferromagnetic plate according to any one of claims 1 to 4, wherein the depression is provided at a central portion between inner and outer peripheral surfaces of the ferromagnetic plate. The ferromagnetic plate according to any one of claims 1 to 5, wherein the shape of the projection or the outer peripheral surface of the ferromagnetic plate viewed from above the main surface is such that the rotation of a member that generates an eddy current inside during braking is advanced. A ferromagnetic plate that extends rearward and / or forward in a direction. The ferromagnetic plate is extended in the rotation direction of the member that generates the eddy current therein, and the remainder of the dent on the rear end surface of the ferromagnetic plate is directed toward the rotation direction of the member that generates the eddy current during braking. 7. The ferromagnetic plate according to claim 1, comprising a right side surface, a left side surface and an outer peripheral surface. The thickness of the plate portion including at least the right side surface and / or the plate portion including the left side surface of the remaining portion of the recess of the ferromagnetic plate is a thickness that is magnetically saturated when the short-circuit magnetic circuit is formed during non-braking. The ferromagnetic plate according to claim 1. An eddy current type reduction gear comprising the ferromagnetic plate according to claim 1.

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