JP2003319637A - Small and light eddy current speed reducer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small and light eddy current speed reducer by reducing power required for switching to nonbraking and compactifying an apparatus. <P>SOLUTION: This small and light eddy current speed reducer is provided with a braking disc attached to a rotary shaft, a guide cylinder supported by a nonrotating section, a retaining ring capable of shifting back and forth in the direction of the rotary shaft, a plurality of permanent magnets arranged so that their magnetic poles adjoining each other in the circumferential direction are set facing each other, and a ferromagnetic material. A magnet-supporting plate mounted with each permanent magnet is attached tiltably to the retaining ring, or the retaining ring is divided into a plurality of segments in the circumferential direction, and they are tiltably constituted in the direction of the rotary shaft. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current speed reducer which is a disk type for assisting a main brake used in a vehicle such as an automobile and is excellent in mountability in a vehicle. More specifically, the present invention relates to an eddy current reducer having a simple structure design and a simple structure. The present invention relates to an eddy current speed reducer that is compact, lightweight, and excellent in economy.

[0002]

2. Description of the Related Art In addition to a foot brake which is a main brake and an exhaust brake which is an auxiliary brake, a braking device for an automobile such as a truck or a bus is capable of performing stable deceleration on a descending slope of a long slope, and a foot brake. An eddy current speed reducer is used to prevent the vapor lock phenomenon and burnout.

In this eddy current deceleration device, a magnet group in which a large number of permanent magnets are arranged in the circumferential direction is moved, and the permanent magnets are brought closer to a rotating drum (cylindrical type) or a braking disk to rotate them. A method of generating a braking torque on a drum or a braking disc is used.

However, in recent years, the demands on the eddy current speed reducer have become diversified, the manufacturing cost is reduced, and the mountability on the vehicle is improved so that it can be mounted on a small car. ing. In order to improve the mountability, it is required that the size and weight be reduced, the structure be simple, and the economy be excellent.

In response to the above-mentioned demand, it is difficult to reduce the size and weight of the eddy current speed reducer employing the rotary drum because of its structure. First, regarding heat dissipation during braking, when the rotating drum heats up during braking, the outer peripheral portion expands, so in order to absorb this, a complicated drum support design is required and the drum structure becomes complicated. Further, since the rotational weight is concentrated on the outer peripheral side in the radial direction, it becomes difficult to adjust the rotational balance.

Furthermore, the adjustment of the air gap, that is,
The braking torque can be adjusted by adjusting the distance between all permanent magnets and the drum at equal intervals and increasing or decreasing this distance.However, if a rotating drum is adopted, it is necessary to adjust the air gap. Since it is necessary to enlarge or reduce the inner diameter of the rotating drum, it is not possible to sufficiently share the components of the rotating drum.

On the other hand, even when a disc type eddy current reduction device using a braking disc is adopted instead of the drum type using a rotary drum, the method using an electromagnet is suitable for downsizing and weight reduction of the device. Absent. That is, in this method, a current is supplied to the electromagnet provided opposite to the braking disc to generate an eddy current in the braking disc to add a braking torque to the rotating shaft, but a large braking torque is generated. Requires a large number of electromagnets and a device for supplying a large current. For this reason, a space for accommodating a large number of electromagnets is required, and the battery serving as a current supply source becomes large in size, so that the entire configuration of the device becomes large in capacity and heavy in weight.

Therefore, in order to reduce the size and weight of the eddy current speed reducer, a disk type speed reducer is adopted, and the magnetic pole surface of the permanent magnet is made to face the braking disk so as to approach it.
Method to generate braking torque on the disc itself (hereinafter,
It may be called "a magnet pole surface facing method") is effective. With this method, the magnetic force of the permanent magnet can be added to the braking disk with a short magnetic path length, so that the magnetic resistance of the magnetic circuit is reduced, the braking efficiency can be improved, and the overall structure of the device can be simplified. Because.

Further, if the braking efficiency can be improved by adopting the "magnet pole surface facing method" of this simple structure, as a result, a relatively small permanent magnet can be applied, so that the size and weight can be reduced. It becomes even easier.

FIG. 1 and FIG. 2 are cross-sectional views showing an example of the structure of an eddy current reduction device of the "magnet pole surface facing type" using permanent magnets. Figure 1 shows the device configuration during braking,
FIG. 2 shows the device configuration during non-braking.

In this eddy current speed reducer, a braking disk 2 made of a ferromagnetic material is attached to the rotating shaft 1, and a guide cylinder 3 made of a non-magnetic material is arranged on the side of the braking disk 2. . The guide cylinder 3 is supported by a non-rotating portion of a vehicle or the like, and inside thereof, a holding ring 4 made of a ferromagnetic material capable of moving forward and backward in a direction perpendicular to the braking surface of the braking disk 2 is accommodated. The guide cylinder 3 is provided with a cylinder 5 for moving the holding ring 4 forward and backward. On the other hand, a ferromagnetic material (pole piece) 8 is arranged on the end surface of the guide cylinder 3 facing the braking disk.

On the side surface of the holding ring 4 facing the braking disc 2, a plurality of permanent magnets 7 are arranged at equal intervals in the circumferential direction. The direction of the magnetic poles of the magnet 7 faces the braking surface of the braking disk 2, and the adjacent permanent magnetic poles are arranged in opposite directions. A plurality of ferromagnetic materials 8 facing the magnetic pole surface of each permanent magnet 7 are arranged so as to form a pair with the permanent magnet 7 in the circumferential direction. The thickness of the ferromagnetic material 8 is not particularly limited, but it is desirable that it be thin. For example, when the guide tube 3 made of aluminum is cast,
The ferromagnetic material can be cast as one piece.

As a drive mechanism for the permanent magnet 7, a guide tube 3 is used.
A cylinder 5 is disposed on the outer end wall of the guide cylinder 3, and a piston rod 6 fitted into the cylinder 5 penetrates the outer end wall of the guide cylinder 3 and is connected to the holding ring 4. With this configuration, the holding ring 4 can be moved forward and backward in the direction orthogonal to the braking disc 2 by the operation of the cylinder 5.

Next, the operation of the above eddy current speed reducer will be described. During braking, as shown by the white arrow in FIG. 1, the piston 6 of the cylinder 5 moves to the right, the retaining ring advances in the direction perpendicular to the braking disc 2, and the permanent magnet 7 faces the braking disc. approach.

At this time, when the rotating braking disc 2 traverses the magnetic field lines exerted by the permanent magnets 7 through the ferromagnetic material 8 perpendicularly to the braking surface of the braking disc 2, the change in the magnetic flux in the braking causes the braking disc 2 to move to the braking disc 2. Eddy current flows and braking torque is generated.

When switching to non-braking, the cylinder 5
2 to switch the operation, as shown by the white arrow in FIG.
Since the holding ring 4 directly connected to the piston rod 6 is moved to the left, the permanent magnet 7 is made of a ferromagnetic material (pole piece).
8, the magnetic force exerted by the permanent magnet 7 on the braking disk 2 becomes weak.

[0017]

As described above, in the "magnet pole surface facing type" eddy current reduction device in which the permanent magnets are arranged so as to face the braking disk, during braking, as shown in FIG. The ring is advanced in a direction orthogonal to the braking disc so that the permanent magnets face and approach the braking disc. On the other hand, at the time of non-braking, it is necessary to retract the holding ring to separate the permanent magnet and the braking disc by a predetermined stroke as shown in FIG.

In the above braking and non-braking operations, since the permanent magnet is attracted to the braking disc which is a ferromagnetic body during braking, the holding ring on which the permanent magnet is arranged is moved forward in the direction orthogonal to the braking disc. Requires almost no power for On the other hand, when the holding ring is retracted in order to pull the permanent magnet away from the braking disk during non-braking, it is necessary to overcome the magnetic attraction force from the braking disk, which requires a large amount of power.

Particularly, in a retarder which requires a high braking torque, a magnet having a strong magnetic force is used to secure the braking torque, or the volume of the magnet is increased to increase the magnetic flux density acting on the braking disk. The magnetic attraction between the magnet and the braking disc becomes stronger. Therefore, a large amount of power is required to pull the permanent magnet away from the braking disk against the magnetic attraction force and switch to the non-braking state.

If the power required for switching is to be covered by a device such as an actuator, it is necessary to increase the required cylinder diameter and increase the number of installations, resulting in a large device and a complicated structure. If these devices are incorporated into an eddy current reduction gear, the overall structure of the device will increase in size and the weight thereof will increase, which significantly deteriorates the mountability on a vehicle.

The present invention was developed in view of the problems involved in the above-mentioned "magnet pole surface facing type" eddy current reduction device using a permanent magnet, and switches from braking to non-braking. In this case, the power required to separate the permanent magnet from the braking disk is reduced, and the actuators, cylinders, and other equipment required for this are made compact.
It is an object of the present invention to provide a small-sized and light-weight current reducer.

[0022]

Means for Solving the Problems The present invention includes the following (1) to
The gist is the small and lightweight eddy current reduction gear of (3). (1) A braking disc mounted on a rotating shaft, a guide cylinder supported by a non-rotating portion and arranged on the side of the braking disc, and housed inside the guide cylinder and movable in the rotating shaft direction. A retaining ring, a plurality of permanent magnets that are arranged in the circumferential direction of the retaining ring and face each other in the circumferential direction of the retaining ring, and adjacent magnetic poles are arranged in opposite directions. On the end face of the guide tube so as to face the permanent magnets. An eddy current speed reducer provided with a ferromagnetic material provided, wherein the permanent magnet is provided so as to be tiltable with respect to a braking disc, and when braking, the magnetic pole surface of the permanent magnet is made to face and approach the braking disc. A small and lightweight eddy current reduction device characterized by tilting the permanent magnet during non-braking to move the permanent magnet away from a braking disc to a non-braking position. (2) A braking disc attached to the rotating shaft, a guide cylinder supported by a non-rotating portion and arranged on the side of the braking disc, and housed inside the guide cylinder and movable in the rotating shaft direction. A retaining ring, a plurality of permanent magnets that are arranged in the circumferential direction of the retaining ring and face each other in the circumferential direction of the retaining ring, and adjacent magnetic poles are arranged in opposite directions. On the end face of the guide tube so as to face the permanent magnet. An eddy current reduction device provided with a ferromagnetic material provided, wherein a magnet support plate on which the permanent magnets are individually mounted is provided on a holding ring so as to cover a surface of the holding ring facing the braking disk. It is mounted so that it can be tilted, and when braking, the permanent magnet is made to face and come close to the positioned braking possible position, and when not braking, the magnet support plate is tilted to separate the permanent magnet from the braking disk. It is a small and lightweight eddy current speed reducer characterized by moving to a braking position.

In the eddy current speed reducer of the above (2), the case where the magnet support plate is tilted along the radial direction of the holding ring,
The device configuration can be divided into the case where the holding ring is formed along the circumferential direction. (3) A braking disc mounted on the rotating shaft, a guide cylinder supported by a non-rotating portion and arranged on the side of the braking disc, and housed inside the guide cylinder and movable in the rotating shaft direction. A retaining ring, a plurality of permanent magnets that are arranged in the circumferential direction of the retaining ring and face each other in the circumferential direction of the retaining ring, and adjacent magnetic poles are arranged in opposite directions. On the end face of the guide tube so as to face the permanent magnet. An eddy current reduction device provided with a ferromagnetic material disposed, wherein the retaining ring is divided into a plurality of portions in the circumferential direction, and each of the retaining rings is configured to be movable in the rotation axis direction for braking. Occasionally, the support ring is brought close to the braking disc positioned in the fixing groove so as to face the braking disc, and when not braking, the supporting ring is tilted in the fixing groove and separated from the braking disc to move to the non-braking position. It is a small and lightweight eddy current reduction device characterized by being made possible.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION A large amount of power is required to vertically separate a permanent magnet with the magnetic pole surface of the permanent magnet facing the braking surface of a braking disk made of a ferromagnetic material.
This is because in order to separate the entire magnetic pole surface of the permanent magnet from the braking disk surface at the same time, a power equivalent to the magnetic attraction force acting between the magnet and the braking disk surface is required.

From the state in which the magnetic pole surface of the permanent magnet faces the braking disk surface, a part of the permanent magnet is separated from the braking disk surface so that the magnetic pole surface is inclined with respect to the braking disk surface. If the permanent magnet is separated vertically from the braking disk, the power required for the separation can be reduced.

That is, when the eddy current speed reducer is switched from braking to non-braking, the permanent magnet is tilted and separated from the braking disk, so that the power required for this is reduced.

The cause of the above is that a part of the magnetic pole surface of the permanent magnet is separated from the braking disk surface.
The power required for this is smaller than when the entire magnetic pole surface is pulled away from the braking disk surface at the same time, and since the magnetic flux applied from the permanent magnet is straight, it acts when the magnetic pole surface tilts with respect to the braking disk surface. The magnetic flux generated is reduced, and the magnetic attraction between the permanent magnet and the braking disk surface is drastically reduced.

As described above, if the permanent magnet is tilted and pulled apart, its power can be reduced. Therefore, when these motive power is covered by devices such as actuators and cylinders, the required cylinder diameter can be made small, and the devices can be made compact. As a result, large vehicles with eddy current reduction gears,
Alternatively, regardless of whether it is a small vehicle or not, it is possible to significantly improve the mountability of the vehicle.

The specific structure of the eddy current speed reducer of the present invention and its effects will be described below with reference to specific embodiments. It should be noted that the following embodiments merely show an example of the configuration of the device, and do not limit the content of the eddy current reduction device of the present invention.

[0030]

(Embodiment 1) FIG. 3 is a diagram showing a cross-sectional configuration example of an eddy current reduction gear device according to Embodiment 1 of the present invention. The eddy current reduction device of the first embodiment includes a braking disk 2 made of a ferromagnetic material attached to the rotating shaft 1 and a guide cylinder 3 made of a non-magnetic material. The guide cylinder 3 is provided in a non-rotating portion of a vehicle or the like. The holding ring 4 is supported and accommodated therein so that it can be moved back and forth in the direction of the rotation axis in a direction perpendicular to the braking surface of the braking disc 2. Further, the guide ring 3 moves the holding ring 4 back and forth. A cylinder 5 is provided. On the other hand, the guide tube 3
A ferromagnetic material (pole piece) 8 is disposed on the end surface of the braking disc 2 facing the braking disc 2 to suppress the attenuation of the magnetic force acting on the braking disc 2.

FIG. 4 is a plan view showing a retaining ring used in the eddy current speed reducer of the first embodiment of the present invention. On the surface of the holding ring 4 facing the braking disc 2, permanent magnets 7 are arranged at equal intervals in the circumferential direction with a groove 4a therebetween. The magnetic pole direction of the permanent magnet 7 faces the braking surface of the braking disk 2, and adjacent magnetic poles are arranged in opposite directions. The plurality of permanent magnets 7 are individually mounted on the magnet supporting plate, and the fixing pin 10 is used to attach the magnet supporting plate to the holding ring 4.

As shown in FIG. 3, the magnet support plate 9 on which the permanent magnets 7 are mounted has the fixing pin 10 on the outer peripheral side of the holding ring 4 so as to cover the surface of the holding ring 4 facing the braking disk 2. It is mounted by pivoting. Thereby, the magnet support plate 9 can be tilted along the radial direction of the holding ring 4 with the fixing pin 10 as a reference. The tilting direction of the magnet support plate 9 is shown by a white arrow in FIG.

Further, a magnet stopper 3a is provided on the inner peripheral portion of the guide cylinder 3 on the side of the end of the ferromagnetic material 8 and positioned so that the permanent magnet 7 can be braked during braking.

FIG. 5 is a diagram for explaining the configuration when switching from braking to non-braking in the eddy current speed reducer of the first embodiment of the present invention. When switching from braking to non-braking, the permanent magnet 7 is separated from the braking disk 2 and retracted to a non-braking position. However, since the initial operation of separation is an instantaneous operation, inertia acting on the magnet support plate 9 Due to the force and the magnetic attraction force between the permanent magnet 7 and the braking disk 2, the magnet support plate 9 tilts with the fixed pin 10 axially supported as a reference,
The permanent magnet 7 is tilted with respect to the surface of the braking disk 2.

Further, by retracting the permanent magnet 7, it is possible to switch to the non-braking state while reducing the power required for separation. In the eddy current speed reducer of the first embodiment, as shown in FIG. 5, a rotation stopper 4b may be provided at the end of the holding ring 4 in order to adjust the tilt amounts of the magnet support plate 9 and the permanent magnet 7. (Embodiment 2) The eddy current speed reducer of the second embodiment of the present invention is, like the device of the first embodiment, a method in which a magnet support plate on which permanent magnets are individually mounted is tiltably attached to a holding ring. The difference from the device of the first embodiment is that the magnet support plate is tilted along the circumferential direction of the retaining ring.

FIG. 6 is a plan view showing a retaining ring used in the eddy current speed reducer of the second embodiment of the present invention. The plurality of permanent magnets 7 are individually mounted on the magnet support plate, and the surface of the holding ring 4 facing the braking disk 2 is covered by the magnet support plate so as to cover the surface.
It is attached so that it can be tilted using a fixing pin 10. The tilting direction of the magnet support plate is along the circumferential direction of the holding ring 4, as indicated by the white arrow.

FIG. 7 is a perspective view showing a situation in which the magnet support plate is attached to the holding ring in the eddy current speed reducer of the second embodiment of the present invention. Magnet support plate 9 on which the permanent magnet 7 is mounted
Is provided so as to cover the surface of the holding ring 4 and to be tiltable in the circumferential direction of the holding ring 4 while pivotally supporting the fixing pin 10.

In the eddy current speed reducer of the second embodiment, as shown in FIG.
As shown in FIG. 7, the magnet support plate 9 may be attached at one end in the circumferential direction of the retaining ring 4 so as to be tiltable with respect to the attachment point. Further, as shown in FIG. A slide hole through which the fixing pin 10 is inserted may be provided at the other end so that the tilt amount of the magnet support plate 9 can be adjusted.

The configuration and operation when switching from braking to non-braking in the eddy current speed reducer of the second embodiment of the present invention are the same as those of the eddy current speed reducer of the first embodiment shown in FIG. (Embodiment 3) FIG. 8 is a diagram showing an example of a sectional configuration of an eddy current reduction gear device of Embodiment 3 of the present invention. In the eddy current reduction device of the third embodiment, the permanent magnets 7 are arranged in the circumferential direction of the retaining ring 4 so as to face the braking disc 2 so that the polarities of the adjacent permanent magnets are opposite to each other. The retaining ring 4
It is connected to a piston rod 6 that fits in the cylinder 5, and the actuation of the cylinder 5 enables the permanent magnet group 7 to move forward and backward in the direction of the rotation axis.

At this time, the piston rod 6 pivotally supports the connecting pin 10 provided on the outer peripheral side of the central portion of the radial width of the holding ring 4, and is tiltably connected based on this. Further, a fixing groove 3b is provided in the inner peripheral portion of the guide cylinder 3 on the side of the ferromagnetic material 8 end, and one end of the retaining ring 4 is inserted during braking, and the permanent magnet 7 is positioned so that braking is possible. There is.

FIG. 9 is a plan view showing a retaining ring used in an eddy current speed reducer according to a third embodiment of the present invention. The entire holding ring 4 has an annular shape (ring shape), and a plurality of permanent magnets 7 are arranged so as to face the braking disk in the circumferential direction and have adjacent magnetic poles in opposite directions. . In the eddy current speed reducer of the third embodiment, the retaining ring 4 having an annular shape is divided into four to form the retaining ring 4 having an arc shape. Each arcuate retaining ring 4 is connected to a piston rod 6 so that it can move in the rotation axis direction.

FIG. 10 is a diagram for explaining the configuration when switching from braking to non-braking in the eddy current speed reducer of the third embodiment of the present invention. When the permanent magnet 7 is separated from the braking disc 2 due to the switching to the non-braking state, the permanent magnet 7 tilts with respect to the surface of the braking disc 2 because one end of the retaining ring 4 is in the fixing groove 3b. When the holding ring 4 is further retracted, the inclination of the permanent magnet 7 increases,
One end of the retaining ring 4 is disengaged from the fixed groove 3b, and the permanent magnet 7 is pulled away from the braking disc, and the non-braking state is set.

[0043]

According to the eddy current speed reducer of the present invention, since the "magnet pole surface facing method" is adopted for the disk type speed reducer, the braking efficiency is excellent and the time from braking to non-braking is excellent. Reduces the power required to disconnect the permanent magnets from the braking discs during switching,
Equipment such as an actuator required for this can be made compact, and the size and weight can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a configuration example during braking of an “magnet pole surface facing type” eddy current reduction device that uses a permanent magnet.

FIG. 2 is a diagram illustrating a configuration example of a “magnet pole surface facing type” eddy current reduction device using a permanent magnet when not braking.

FIG. 3 is a diagram illustrating a cross-sectional configuration example of an eddy current reduction gear device according to a first embodiment of the present invention.

FIG. 4 is a plan view showing a retaining ring used in the eddy current speed reducer of the first embodiment of the present invention.

FIG. 5 is a diagram illustrating a configuration when switching from braking to non-braking in the eddy current speed reducer according to the first embodiment of the present invention.

FIG. 6 is a plan view showing a retaining ring used in an eddy current speed reducer according to a second embodiment of the present invention.

FIG. 7 is a perspective view showing a situation in which a magnet support plate is attached to a retaining ring in an eddy current reduction gear system of Embodiment 2 of the present invention.

FIG. 8 is a diagram showing an example of a cross-sectional configuration of an eddy current speed reducer according to a third embodiment of the present invention.

FIG. 9 is a plan view showing a retaining ring used in an eddy current speed reducer according to a third embodiment of the present invention.

FIG. 10 is a diagram illustrating a configuration when switching from braking to non-braking in an eddy current reduction gear system according to a third embodiment of the present invention.

[Explanation of symbols]

1: rotating shaft 2: braking disc 3: Guide tube, 3a: Magnet stop 3b: fixing groove, 4: retaining ring 4a: groove, 4b: rotation stopper 5: Cylinder, 6: Piston rod 7: Permanent magnet, 8: Ferromagnetic material 9: Magnet support plate, 10: Fixed pin, connection pin

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasunori Tani             4-53 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture             Sumitomo Metal Industries, Ltd. F-term (reference) 5H649 AA02 BB03 GG09 GG13 GG18                       HH10 HH18 JK03

Claims (5)

[Claims] 1. A braking disc mounted on a rotating shaft,
A guide tube supported by a non-rotating portion and arranged laterally of the braking disc, a holding ring housed inside the guide tube and movable in the rotation axis direction, and the holding ring in the circumferential direction of the holding ring. Eddy current provided with a plurality of permanent magnets facing the braking disk, with adjacent magnetic poles arranged in opposite directions, and a ferromagnetic material disposed on the end surface of the guide cylinder so as to face the permanent magnets. In the speed reducer, the permanent magnet is provided so as to be tiltable with respect to the braking disc, the magnetic pole surface of the permanent magnet is made to face and approach the braking disc when braking, and the permanent magnet is tilted when not braking to make the permanent magnet. A small and lightweight eddy current speed reducer characterized by moving a magnet away from a braking disk to a non-braking position. 2. A braking disc mounted on a rotating shaft,
A guide tube supported by a non-rotating portion and arranged laterally of the braking disc, a holding ring housed inside the guide tube and movable in the rotation axis direction, and the holding ring in the circumferential direction of the holding ring. Eddy current provided with a plurality of permanent magnets facing the braking disk, with adjacent magnetic poles arranged in opposite directions, and a ferromagnetic material disposed on the end surface of the guide cylinder so as to face the permanent magnets. In the speed reducer, a magnet support plate on which the permanent magnets are individually mounted is tiltably attached to the holding ring so as to cover a surface of the holding ring facing the braking disc, and the permanent magnet is positioned during braking. To the position where the braking is possible, and the magnet support plate is tilted when not braking to move the permanent magnet away from the braking disc to a non-braking position. That small, lightweight eddy current reduction apparatus. 3. The small and lightweight eddy current speed reducer according to claim 2, wherein the magnet support plate is tilted along the radial direction of the retaining ring. 4. The small and lightweight eddy current speed reducer according to claim 2, wherein the magnet support plate is tilted along the circumferential direction of the retaining ring. 5. A braking disc mounted on a rotating shaft,
A guide tube supported by a non-rotating portion and arranged laterally of the braking disc, a holding ring housed inside the guide tube and movable in the rotation axis direction, and the holding ring in the circumferential direction of the holding ring. Eddy current provided with a plurality of permanent magnets facing the braking disk, with adjacent magnetic poles arranged in opposite directions, and a ferromagnetic material disposed on the end surface of the guide cylinder so as to face the permanent magnets. In the speed reducer, the retaining ring is divided into a plurality of portions in the circumferential direction, and each of the retaining rings is configured to be movable in the rotation axis direction, and at the time of braking, the support ring can be positioned by a fixing groove for braking. Eddy current of small size and light weight, characterized in that the support ring is moved to a position where the braking disc is opposed to the braking disc, and when not braking, the support ring is tilted by a fixed groove to be separated from the braking disc and moved to a non-braking position. Speed devices.