JP2001112235A - Eddy current reduction gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eddy current reduction gear having a fan for introducing the outer air into a brake drum in order to cool the inside thereof. SOLUTION: This eddy current reduction gear comprises a drake drum 13 coupled with a rotary shaft 4 through a supporting arm 14, a nonmagnetic guide tube 18 having an inner cavity 16 of rectangular cross-section fixed to the nonrotational part, e.g. the chassis, while facing the inside of the brake drum 13, magnet supporting cylinders 19, 59 contained in the inner cavity 16 of the guide tube 18 such that at least one of them is rotatable, a large number of magnets 20, 60 bonded to the outer circumferential surface of the magnet supporting cylinders 19, 59 at a constant interval in the circumferential direction, and a ferromagnetic plate 21 cast at a part facing each magnet 20, 60 of the guide tube 18. A brake force is generated in the brake drum 13 by the fields from the magnets 20, 60 based on the eddy current. A fan 44 is formed by providing blades 45, 46 on the supporting arm 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current reduction device for assisting a friction brake of a large vehicle or the like, and more particularly to an eddy current reduction device in which a fan is provided in a rotating portion to enhance a cooling performance.

[0002]

2. Description of the Related Art In an eddy current reduction device such as disclosed in Japanese Patent Publication No. Hei 7-118901, a rotating braking drum moves a magnet of a magnet support cylinder from a ferromagnetic plate of a guide cylinder containing the magnet support cylinder. When traversing the magnetic field that reaches the brake drum via the brake drum, the brake drum generates a braking force based on eddy currents. Eddy currents turn into heat to heat the braking drum. Cooling fins are provided on the outer peripheral surface of the braking drum so that the braking drum is cooled by the outside air, but the gap between the inner peripheral surface of the braking drum and the guide cylinder is preferably as narrow as possible in terms of braking performance. On the other hand, the amount of air that the outside air passes in the axial direction along the inner peripheral surface of the braking drum is limited. In particular, during braking during high-speed operation of the vehicle, heat due to the eddy current is transmitted not only to the braking drum but also to the guide cylinder, causing a reduction in braking capability.

[0003]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide an eddy current reduction device provided with a fan for introducing outside air into the inside of a brake drum in order to cool the inside of the brake drum. Is to do.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention comprises a brake drum connected to a rotating shaft via a support arm, and a non-rotating portion of a vehicle body or the like facing the inside of the brake drum. A guide tube made of a non-magnetic material having an inner space with a rectangular cross section attached to the magnet, at least one movable magnet support tube housed in the inner space of the guide tube, and an outer peripheral surface of the magnet support tube. An eddy current reduction device having a large number of magnets connected at equal intervals in a circumferential direction, and a ferromagnetic plate cast in the guide cylinder, wherein an eddy current reduction device generates a braking force based on an eddy current on the braking drum by a magnetic field from the magnet. , Wherein a fan is formed on the support arm.

According to another aspect of the present invention, there is provided a brake drum coupled to a rotating shaft via a support arm, and an inner space disposed so as to face the brake drum and having a rectangular cross section. A guide tube made of a non-magnetic material and a ferromagnetic plate cast at equal intervals, and an inner tube portion not facing the inner peripheral surface of the braking drum is made of a ferromagnetic material; A magnet support cylinder which is axially movably supported by the inner space of the cylinder and couples a large number of magnets on the outer peripheral surface at equal intervals in the circumferential direction, and the braking force based on eddy current is generated by a magnetic field from the magnet. In the eddy current reduction device generated on the braking drum,
A fan is formed on the support arm.

Further, the structure of the present invention has a brake drum connected to a rotating shaft via a support arm, and an inner space arranged so as to face the brake drum and having a rectangular cross section. The outer cylinder portion facing the surface is made of a thin plate of a non-magnetic material, and the inner space not facing the inner peripheral surface of the braking drum is made of a ferromagnetic material. An eddy current reduction device that has a magnet support cylinder that supports a large number of magnets at equal intervals in the circumferential direction and that generates a braking force based on an eddy current on the braking drum by a magnetic field from the magnets , Wherein a fan is formed on the support arm.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, blades are integrally formed on a rotating portion of a braking drum, particularly on a support arm (spoke) for connecting a boss portion and a drum body, so that the blade is integrated into a braking drum and a guide cylinder. Construct a fan for introducing outside air.
The fan sucks in the outside air from a gap between the distal end portion of the brake drum and the outer cylinder portion of the guide cylinder, cools the inner peripheral surface of the brake drum having the highest temperature, and discharges it to the outside through the opening of the support arm. In addition, at the same time as cooling the inner peripheral surface of the braking drum, outside air is sucked in from the tip of the guide cylinder by the fan,
The inner cylinder portion of the guide cylinder can also be cooled and can be discharged to the outside through the opening of the support arm. This allows
This prevents overheating of the brake drum and the guide cylinder, and suppresses a decrease in the braking capacity due to overheating, especially during braking during high-speed running of the vehicle.

[0008]

FIG. 1 is a front sectional view of an eddy current reduction device according to the present invention, and FIG. 2 is a side sectional view of the eddy current reduction device. The eddy current reduction device includes a braking drum 13 made of a conductor, a stationary guide cylinder 18 made of a non-magnetic material, and an inner space 1 of the guide cylinder 18.
6 is a movable magnet support cylinder 19 supported by a bearing 15
And a stationary magnet support cylinder 59 fixed to the guide cylinder 18 by the pins 30. A large number of cooling fins 13a are provided on the outer peripheral surface of the braking drum 13 at equal intervals in the circumferential direction. The distal ends of a plurality of support arms 14 extending in the radial direction from the boss 9 are joined to the base end of the braking drum 13 by welding or the like. Guide tube 18 having inner space 16 having a rectangular cross section
Is supported by a non-rotating portion of the vehicle body so as to face the inside of the braking drum 13. Mounting flange 9a integral with boss 9
Is attached to the rotating shaft 4 via a spline 5 a by a bolt 10 and a nut together with an end wall of a braking drum 7 of a parking brake, and is fastened by a nut 6.
Is combined with The magnets 20, 60 are respectively opposed to the respective ferromagnetic plates 21 of the outer tube 18 a of the guide tube 18 in the magnet support tubes 19, 59 housed in the inner space 16 of the guide tube 18, respectively.
In addition, the ferromagnetic plates 21 are coupled so that their polarities alternately differ in the circumferential direction.

The guide cylinder 18 has annular end walls 18c and 18d integrally connected to both ends of an outer cylinder 18a and an inner cylinder 18b made of a non-magnetic material such as aluminum. Many ferromagnetic plates 21 are connected at equal intervals in the circumferential direction. Actually, the ferromagnetic plate 21 is cast when the outer cylindrical portion 18a is cast from aluminum. End wall 1 of guide tube 18
Actuator 51 integrally formed with 8c has a piston 52 inserted into cylinder 52 to define oil chambers at both ends.
The rod connected to the piston 53 projects from the cylinder 52 to the outside, and is connected to the arm 54 projecting from the magnet support cylinder 19 through the slit 50 of the end wall 18c, thereby reversing the magnet support cylinder 19 by the arrangement pitch of the magnets 20. It is configured to be rotatable. By attaching an annular baffle plate 41 to the annular end wall 18d in the radial direction, the inner cylindrical portion 1 of the guide cylinder 18 is formed.
It is possible to cool the inner peripheral surface 13b of the braking drum 13, which becomes higher in temperature, without introducing outside air into the 8b.

According to the present invention, the boss 9 and the brake drum 1 are provided in order to enhance the cooling of the brake drum 13 and the guide cylinder 18.
The fan 45 is formed by connecting the blades 45 and 46 to the support arm 14 that connects the fan 3 to the fan 3. As shown in FIGS. 3 and 4, the support arm 14 is preferably configured as an annular plate 47 from which the blades 45 are cut and raised inward and project obliquely in the direction of rotation indicated by the arrow y. 47 from feather 46
Are outwardly protruded and obliquely project in a direction opposite to the rotation direction indicated by the arrow y, and a large number of blades 45 and 46 are provided on the support arm 14 at equal intervals in the circumferential direction. When the brake drum 13 rotates in the direction of the arrow y, the outside air is released by the fan 44 from the front end (the left end in FIG. 1) of the brake drum 13.
Is introduced into the gap between the inner peripheral surface 13b of the brake drum 13 and the outer cylindrical portion 18a of the guide cylinder 18, cools the inner peripheral surface 13b of the brake drum 13, and is discharged to the outside through the openings 48 and 49 of the annular plate 47. Further, by removing the baffle plate 41, the outside air is introduced from the left end side of the guide tube 18 into the gap between the inner tube portion 18 b and the braking drum 7 by the fan 44, and cools the inner tube portion 18 b and the annular plate 47. Can be discharged to the outside through the openings 48 and 49 of the first embodiment.

Next, the operation of the eddy current reduction device according to the present invention will be described. When the brake is not applied, as shown in FIG. 1, the polarities of the magnets 20 and 60 facing the ferromagnetic plate 21 are different.
A short-circuit magnetic circuit w is formed between the magnet support cylinders 19 and 59 and the ferromagnetic plate 21, and does not apply a magnetic field to the braking drum 13. At the time of braking, as shown in FIG. 2, when the magnet support cylinder 19 is rotated by the pitch of the arrangement of the magnets 20, each of the magnets 20 and 60 is rotated.
Have the same polarity with respect to the ferromagnetic plate 21, and each magnet 2
A magnetic field of 0,60 reaches the braking drum 13 via the ferromagnetic plate 21. When the rotating brake drum 13 crosses the magnetic field, a braking torque is generated based on the eddy current flowing through the brake drum 13. At this time, the magnet support cylinders 19 and 59 and the braking drum 1
3, a magnetic circuit z is generated.

The heat based on the eddy current during braking is applied to the braking drum 1
3 is transmitted to the guide cylinder 18 as well as being heated.
The braking drum 13 is cooled by the cooling air 13 a by the outside air, and the inner peripheral surface 13 b is cooled by the outside air sucked by the fan 44 from the tip end of the braking drum 13.
Similarly, the outer cylinder portion 18a of the guide cylinder 18 is cooled by the outside air sucked from the tip side of the braking drum 13. At the same time, the guide cylinder 18 is cooled in the inner cylinder portion 18b by the outside air sucked from the left end side in FIG. The outside air that has cooled the braking drum 13 and the guide cylinder 18 is supplied to the support arm 14.
Are blown to the right through the openings 48 and 49 of FIG.

The embodiment shown in FIG. 5 includes a clutch 73 and a gear speed increaser 57 between the rotating shaft and the braking drum 13,
In particular, when the vehicle is running at a low speed, the number of revolutions of the braking drum 13 is made higher than that of the rotating shaft to enhance the braking effect. Further, a fan 44 is formed by providing a large number of blades 45 and 46 at intervals in the circumferential direction on the boss portion 9 supporting the braking drum 13 with a large number of supporting arms 14, and the fan 44 constitutes a left end of the braking drum 13. After the outside air is introduced into the gap between the inner peripheral surface 13b of the braking drum 13 and the outer cylindrical portion 18a of the guide cylinder 18 from the portion to cool the braking drum 13 and the outer cylindrical portion 18a, the openings 48, 4 of the support arm 14 are cooled.
9 (see FIG. 3).

A flange 55a of a support cylinder 55 is fastened to a mounting flange 5 fitted and fixed to a rotating shaft (not shown) via a spline 5a with a bolt 10 and a nut 10a. The cylindrical boss 9 is rotatably supported on the support cylinder 55 by a bearing 56. The base end (the right end in FIG. 5) of the brake drum 13 having the cooling fin 13a is connected to the base end of the boss 9 via a support arm 14 formed of an annular plate. Immobile guide tube 1 housed inside braking drum 13
8 has an annular left end wall 18c and a right end wall 18d on an outer cylindrical portion 18a facing the inner peripheral surface 13b of the braking drum 13 and an inner cylindrical portion 18b not facing the inner peripheral surface 13b of the braking drum 13.
To form an inner space having a rectangular cross section. A large number of ferromagnetic plates 21 are cast at equal intervals in the circumferential direction in the outer cylindrical portion 18a made of a nonmagnetic material such as aluminum.

A movable magnet support tube 19 and an immovable magnet support tube 59 are accommodated in the inner space of the guide tube 18, and the magnet support tube 19 is supported by the inner cylinder portion 18b by the bearing 15, and the magnet support tube 59 is fixed to the end wall 18d by the pin 30.
Each ferromagnetic plate 21 is provided on the outer peripheral surface of each magnet support cylinder 19, 59.
A large number of magnets 20 and 60 facing each other are connected at equal intervals in the circumferential direction so that the polarities to the ferromagnetic plate 21 are alternately different in the circumferential direction. A roller 62 is supported on the left end wall of the magnet support cylinder 19 via a support plate 63. Although not shown, the roller 6
2 is engaged with a groove formed at an end of a rod 61 extending from an actuator formed by inserting a piston into a cylinder. When the rod 61 is reciprocated by the actuator in a direction substantially perpendicular to the plane of the drawing, the magnet support cylinder 19 is rotated forward and backward by the pitch of the magnets 20. Rod 61 and roller 6
The second engaging portion is covered by the cover 68. An annular support frame 71 integral with the inner cylinder portion 18b of the guide cylinder 18 is fitted to the cylindrical wall portion 42a of the end wall of the gear box 42 of the vehicle transmission, and a bolt (not shown) together with the support cylinder 69. Is fixed by

The gear speed increaser 57 includes a ring gear 9b formed on the inner peripheral surface of the left end of the boss portion 9 and a sun gear 7 formed on an inner cylinder 76 rotatably supported by a bearing 77 on a support cylinder 69.
A planetary gear 75 meshes with the support shaft 6a, and the planetary gear 75 is supported on a support shaft 74 fixed to the left end flange of the support cylinder 55.
It is supported rotatably. The clutch 73 for fixing the inner cylinder 76 includes a plurality of annular friction plates spline-supported on the inner peripheral wall of the outer cylinder 72 integrated with the support frame 71 and a plurality of annular friction plates spline-supported on the outer peripheral wall of the inner cylinder 76. With the friction plate,
If both friction plates are pressed by the actuator 64 and frictionally engaged with each other, the inner cylinder 76
Is fixed. The actuator 64 is formed by inserting a piston 67 into a cylinder 65 integrated with the support frame 71, and supplies a pressurized fluid from the entrance 66 to the end chamber of the cylinder 65.
The piston 67 moves to the right, the frictional engagement between the friction plate of the outer cylinder 72 and the friction plate of the inner cylinder 76 is achieved, and the braking drum 13
Is rotated at a higher speed than the rotating shaft, and the braking effect is enhanced. Accordingly, when the brake drum 13 rotates at a higher speed than the rotary shaft together with the boss portion 9, the fan 44 also rotates at a high speed equally, and the inner peripheral surface 13b of the brake drum 13 and the guide cylinder extend from the left end of the brake drum 13. Outside air is introduced into the gap between the outer cylinder portions 18a of the support 18 and cools the braking drum 13 and the outer cylinder portion 18a, and then is discharged to the outside through the openings 48 and 49 (see FIG. 3) of the support arm 14. . When the outside air intake 71a as shown in FIG.
The outside air is introduced into the gap 35 between the inner cylindrical portion 18b and the boss portion 9 from the position a, cools the inner cylindrical portion 18b, and is discharged to the outside through the openings 48 and 49 of the support arm 14.

The embodiment shown in FIG. 7 is an eddy current deceleration type in which the magnet support cylinder 19 is switched between a braking position where the magnet support cylinder 19 is inserted into the inside of the brake drum 13 and a non-braking position where the magnet support cylinder 19 is pulled out from the brake drum 13. It concerns the device. The braking drum 13 is provided with a cooling fin 13a on the outer peripheral surface,
The base end of the braking drum 13 is connected to a support arm 14 that projects radially from the boss 9. Flange 9a of boss 9
The bolt 10 and the nut 1 are attached to the mounting flange 5 fitted together with the end wall of the braking drum 7 of the parking brake by the spline 5a to the rotary shaft 4 and fastened by the nut 6.
0a. In the illustrated embodiment, a thin annular body 39 made of a good conductor such as copper is connected to the inner peripheral surface of the braking drum 13 in order to spread the flow of the eddy current in the axial direction. The support arm 14 has a blade 45 projecting inward from the support arm 14 and a blade 4 projecting outward from the support arm 14.
6 are integrally formed to constitute the fan 44, as in the case shown in FIG.

The guide cylinder 18 whose right half portion projects into the brake drum 13 has a C-shaped cross section integrally including a thick outer cylinder 28 made of a magnetic material, a left end wall 18c, and an inner cylinder 18b. A cylindrical portion having an inverted L-shaped cross section integrally provided with an outer cylindrical portion 18a made of a non-magnetic material and a right end wall 18d integrally facing the inner peripheral surface of the braking drum 13 is connected to a plurality of bolts 12. An inner space 16 having a rectangular cross section is formed. Outer cylinder 18
A large number of ferromagnetic plates 21 are cast at equal intervals in the circumferential direction.

The rotary shaft 4 and the mounting flange 5 are rotatably supported by the gear box 42 of the vehicle transmission via the bearing 3, and the cylindrical wall 42 a surrounding the rotary shaft 4 is reinforced by the reinforcing rib 31 a. The frame 31 is fitted outside and fastened by bolts (not shown). The support frame 31 is superimposed on the left end wall 18c of the guide tube 18, and fixes the guide tube 18 concentrically with the brake drum 13 by a plurality of axial bolts 33 and radial bolts 32. A magnet support tube 19 is accommodated in the inner space 16 of the guide tube 18 so as to be able to reciprocate in the axial direction.
Therefore, the magnet support cylinder 19 is connected to a rod 17 projecting from the actuator (not shown) supported on the left end wall 18c to the inner space 16. On the outer peripheral surface of the magnet support cylinder 19, a large number of magnets 20 are arranged at regular intervals in the circumferential direction and the ferromagnetic plate 2 is provided.
The polarities for 1 are coupled so as to be alternately different in the circumferential direction. In order to enhance the cooling performance of the guide tube 18, the support arm 14 is integrally formed with a blade 45 protruding inward from the support arm 14 and a blade 46 protruding outward from the support arm 14 to form a fan 44. Is similar to that shown in FIG.

At the time of braking, when the magnet support cylinder 19 projects into the braking drum 13 as shown in the figure, the rotating braking drum 13 is moved from the magnet 20 via the ferromagnetic plate 21 to the braking drum 13.
, A braking torque based on the eddy current is generated in the braking drum 13. The fan 44 is rotated together with the brake drum 13, and the fan 44 allows the outside air to flow from the front end side of the brake drum 3 to the inner peripheral surface of the brake drum 13 and the outer cylinder 18.
a into the gap between the brake drum 13 and the outer cylinder 18
After cooling a, it is discharged to the right through the openings 48 and 49 (see FIG. 3) of the support arm 14. When the outside air intake 31b as shown in FIG. 8 is opened in the support frame 31, outside air is sucked into the inside of the guide cylinder 18 from the outside air intake 31b.
After cooling the inner cylindrical portion 18b, the openings 48, 4
It is discharged from 9 to the right. At the time of non-braking, when the magnet support tube 19 is pulled out to the left from the brake drum 13 by the actuator, the magnet 20 is opposed to the outer tube portion 28 made of a magnetic material. A short-circuited magnetic circuit is generated at this time, and the magnet 20 does not exert a magnetic field on the braking drum 13.

In the embodiment shown in FIG. 9, annular bodies 39 and 39a made of a good conductor such as copper are connected to the inner peripheral surface of the braking drum 13 at both end portions not opposed to the magnet 20, so that eddy currents are reduced. Improve flow and increase braking capacity. Brake drum 1
The guide cylinder 18 whose right half part projects into the inside of the cylinder 3 has an outer cylinder part 18a facing the inner peripheral surface of the braking drum 13 formed of a thin plate made of a non-magnetic material such as stainless steel, and is conically expanded. The left end thus formed is fitted to the conical surface 28a of the outer cylinder portion 28, and the right end of the outer cylinder 18a is bent radially inward and overlapped on the end wall 18d, and each is joined by a plurality of bolts 40. . Outer cylindrical portion 28 made of magnetic material and left end wall 18
c and the inner cylindrical portion 18b are configured as a cylindrical body having a C-shaped cross section, and the right end wall 18d is preferably formed of a non-magnetic material. A magnet support tube 19 is accommodated in the inner space 16 of the guide tube 18 so as to be able to reciprocate in the axial direction. On the outer peripheral surface of the magnet support cylinder 19, a large number of magnets 20 are arranged at regular intervals in the circumferential direction and the outer cylinder portion 1
8a are coupled so that the polarity with respect to the circumferential direction is alternately different.

The actuator 26 connected to the left end wall 18c is provided with a piston
The magnet support tube 19 is coupled to a rod 17 which is divided into sections 9 and 29 a and protrudes from the piston 25 to the inner space 16. In the illustrated braking state, the magnetic field from the magnet 20 exerts a magnetic field on the braking drum 7 via the extremely thin outer cylindrical portion 18a to generate a braking torque on the braking drum 13. When the brake is not applied, the pressurized fluid is supplied to the chamber 29a of the actuator 26, and the pressurized fluid in the chamber 29 is released.
The magnet support cylinder 19 is pulled out of the brake drum 13 to the left via the. At this time, a short-circuit magnetic circuit is generated between the magnet support cylinder 19 and the outer cylinder 28. A number of blades 45 and 46 are connected to the support arm 14 to form a fan 44. The outside air introduced into the outer cylinder 18a and the inner cylinder 18b from the left end side of the guide cylinder 18 by the fan 44 is applied to the braking drum 1
3 and the guide cylinder 18 are cooled and discharged to the right through the opening of the support arm 14. In order to enhance the cooling effect on the inner peripheral surface of the braking drum 13 where the temperature becomes highest, a baffle plate 41 as shown in FIG. 1 may be attached to the right end wall 18d.

In each of the above embodiments, the blades 54 and 55 provided on the support arm 14 are not limited to those shown in the drawings, but may be of various shapes.

[0024]

As described above, according to the present invention, a fan is formed by connecting a large number of blades to a supporting arm for connecting a braking drum and a boss at a circumferential interval. Therefore, always, the fan is rotated together with the brake drum, and after the outside air is sucked into the inner peripheral surface of the brake drum and the inner cylinder portion of the guide cylinder to cool the brake drum and the guide cylinder,
It is discharged outside through a gap or opening between the support arms.
In other words, the braking drum is cooled from the inner peripheral side, and the guide cylinder is cooled from the inner and outer peripheral sides, and together with the braking drum being cooled from the outer peripheral side by the cooling fins, the eddy current due to the heat of the eddy current is reduced. Since overheating of the speed reducer is suppressed, it is possible to suppress a decrease in the braking capacity due to overheating, particularly during braking during high-speed running of the vehicle.

Since the fan is simply provided by providing a blade on the support arm of the conventional eddy current reduction device, manufacturing costs can be minimized.

[Brief description of the drawings]

FIG. 1 is a front sectional view of an eddy current reduction device to which the present invention is applied.

FIG. 2 is a side sectional view of the eddy current reduction device.

FIG. 3 is a plan sectional view showing a support arm of the eddy current reduction device in a developed state.

FIG. 4 is a left side view of a support arm of the eddy current reduction device.

FIG. 5 is a front sectional view of another eddy current reduction device to which the present invention is applied.

FIG. 6 is a front sectional view of the eddy current reduction device to which the modified embodiment of the present invention is applied;

FIG. 7 is a front sectional view of another eddy current reduction device to which the present invention is applied.

FIG. 8 is a front sectional view of the eddy current reduction device to which the modified embodiment of the present invention is applied;

FIG. 9 is a front sectional view of another eddy current reduction device to which the present invention is applied.

[Explanation of Signs] 4: Rotating shaft 9: Boss 9b: Ring gear 13: Brake drum 14: Support arm 16: Inner space 18: Guide cylinder 18a: Outer cylinder 18
b: Inner cylinder part 19: Magnet support cylinder 20: Magnet 21: Ferromagnetic plate 26: Actuator 31: Support frame 31b: Outside air intake 42: Gear box 44: Fan 4
5: Blade 46: Blade 48: Opening 49: Opening 51: Actuator 5
7: Gearbox 59: Magnet support cylinder 60: Magnet 6
4: actuator 73: clutch 75: planetary gear 76a: sun gear

Claims (3)

[Claims] 1. A brake drum connected to a rotating shaft via a support arm, and a non-magnetic material having a rectangular hollow section attached to a non-rotating portion such as a vehicle body so as to face the inside of the brake drum. A guide cylinder, at least one movable magnet support cylinder housed in the inner space of the guide cylinder, a large number of magnets coupled to the outer peripheral surface of the magnet support cylinder at equal circumferential intervals, and An eddy current reduction device for generating a braking force based on an eddy current on the braking drum by a magnetic field from the magnet, wherein a fan is formed on the support arm. Reduction gear. 2. A brake drum coupled to a rotation shaft via a support arm, and an outer space disposed so as to face the brake drum and having an inner space having a rectangular cross section and facing an inner peripheral surface of the brake drum. A guide cylinder whose cylindrical portion is made of a non-magnetic material and a ferromagnetic plate is cast at equal intervals, and whose inner cylindrical portion not facing the inner peripheral surface of the braking drum is made of a ferromagnetic material; A magnet support cylinder which is supported movably in the axial direction and has a plurality of magnets connected to the outer circumferential surface at equal intervals in a circumferential direction, and a braking force based on an eddy current is generated in the braking drum by a magnetic field from the magnets. An eddy current reduction device, wherein a fan is formed in the support arm. 3. A brake drum coupled to a rotation shaft via a support arm, and an outer space disposed to face the brake drum and having an inner space with a rectangular cross section and facing an inner peripheral surface of the brake drum. The cylindrical portion is made of a non-magnetic thin plate, and the inner space not facing the inner peripheral surface of the braking drum is a guide tube made of a ferromagnetic material, and is supported by the inner space of the guide tube so as to be movable in the axial direction, and An eddy current reduction device having, on an outer peripheral surface thereof, a magnet support cylinder for coupling a large number of magnets at equal intervals in a circumferential direction, wherein the braking arm generates a braking force based on an eddy current on the braking drum by a magnetic field from the magnet; An eddy current reduction device characterized in that a fan is formed in the eddy current reduction device.