JP2003262243A - Power transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power transmission, which has a long life and a small size by increasing frictional force and reducing wear of friction pads. <P>SOLUTION: A braking device 1 has a rotary surface 20 formed along a peripheral direction of a rotary shaft 2, a rotary disk 3 fixed to the rotary shaft 2, a pressure contact surface 10 facing the rotary surface 20, and a friction pad 5 for generating frictional force by bringing the pressure contact surface 10 into contact with the rotary surface 20 under pressure. Further, the braking device 1 is provided with a driving section 6 having an armature 11, compression springs 12, and an electromagnet 13 for reciprocating the friction pad 5. The rotary surface 20 is a flat surface having surface roughness of a maximum of 0.1 μm in maximum center line average height Ra. Accordingly, when the pressure surface 10 comes into contact with the rotary surface 20 under pressure, a frictional coefficient increases due to the increase of a contact area, and also the amount of worn mass of the friction pad 5 reduces. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power transmission device such as a clutch or a brake, and more particularly to a power transmission device that transmits power by friction.

[0002]

2. Description of the Related Art FIG. 5 is a schematic diagram showing a structure of a braking device which is a conventional power transmission device. In FIG. 5, a braking device 100 is fixed to a rotary shaft 2 that is a shaft that rotates about an axis, and a rotary disc 3 that is a disk-shaped moving unit that rotates together with the rotary shaft 2 and the rotary disc 3
And a friction pad 5 which is a press-contact portion having a press-contact surface 10 which is arranged so as to face the side surface 4 and moves toward the rotary disk 3 to press-contact the side surface 4. The braking device 100 also includes a drive unit 6 that supports and fixes the friction pad 5, and drives the friction pad 5 to reciprocate to press or separate the rotary disc 3 from the rotary disc 3.

At the center of the rotary disk 3, a rotary shaft 2 is vertically penetrated and fixed. Therefore, even if the rotary shaft 2 rotates about the axis, the side surface 4 of the rotary disk 3 smoothly rotates without meandering. The material of the rotating disk 3 is, for example, Rockwell hardness HRC20.
It is an iron-based material that is cast iron. The side surface 4 of the rotary disk 3 has a surface roughness of about 1 to 5 μm in order to secure a predetermined friction coefficient. This is because when the pressure contact surface 10 of the friction pad 5 is pressed against the side surface 4, a plurality of convex portions 4a formed on the side surface 4 come into contact with the pressure contact surface 10 and bite a little to generate a resistance force. The side 4
This is because it acts as a frictional force generated between the contact surface 10 and the pressure contact surface 10. Therefore, when the side surface 4 of the rotating disk 3 is pressed against the pressure contact surface 10, a frictional force is generated between the side surface 4 and the pressure contact surface 10, and the rotational force of the rotating disk 3 is transmitted to the friction pad 5. It has become.

The friction pad 5 is made of an organic friction material which is softer than the rotary disc 3 and is, for example, a phenol resin mold having a Rockwell hardness of HRM15. It is adapted to be slightly deformed along the shape of 4a.

The drive unit 6 is connected to the armature 11 which is a magnetic body to which the friction pad 5 is fixed, and is connected to the armature 11 so as to press the friction pad 5 fixed to the armature 11 against the rotating disk 3. It has a pressing spring 12 that urges it, and an electromagnetic magnet 13 that generates an electromagnetic force that attracts the armature 11 against the direction in which the pressing spring 12 is biased by energization. Therefore, the friction pad 5 is pressed against the side surface 4 by the biasing force of the pressing spring 12 when the electromagnetic magnet 13 is not energized and no electromagnetic force is generated, and when the electromagnetic magnet 13 is energized, the friction pad 5 is It is designed to be separated from the side surface 4. The drive unit 6 is fixed to the structure 14 so that the friction pad 5 does not move in the rotation direction of the rotary disk 3.

[0006] The power transmission device 100 configured as described above.
Operates as follows. That is, when the electromagnetic force is generated in the electromagnetic magnet 13 by energization, the armature 11 is attracted to the electromagnetic magnet 13 against the urging force of the pressing spring 12, so that the pressure contact surface 1 of the friction pad 5 is
0 is separated from the rotating disk 3. At this time, when a rotating force is applied to the rotary shaft 2, the rotary shaft 2 rotates together with the rotary disk 3.

When the electromagnetic magnet 13 is de-energized, the armature 11 loses its attractive force by the electromagnetic magnet 13, so that the urging force of the pressing spring 12 causes the armature 11 to move to the rotary disk 3 and the friction pad 5 to move.
The pressure-contact surface 10 of the above-mentioned pressure-contacts the side surface 4 of the rotating disk 3.

When the pressure contact surface 10 of the friction pad 5 is pressed against the side surface 4 of the rotary disk 3, the plurality of convex portions 4a of the side surface 4 bite slightly into the pressure contact surface 10, and the pressure force of the rotary disk 3 causes the pressure contact surface 10 to move. It is scraped off little by little. The resistance force generated at this time acts as a frictional force between the side surface 4 and the pressure contact surface 10, and the rotational force of the rotary disk 3 is transmitted to the friction pad 5. Since the friction pad 5 is fixed to the drive unit 6 fixed to the structure 14, the friction pad 5 does not rotate together with the rotary disc 3, and as a result, the friction pad 5 applies a braking force to the rotary disc 3.

[0009]

In this way, the braking device 100 has a structure in which the plurality of convex portions 4a on the side surface 4 of the rotary disk 3 scrape off the pressure contact surface 10 of the friction pad 5 to cause friction with the rotary disk 3. Since the frictional force with the pad 5 is secured, the friction pad 5 is inevitably worn in a short time. Since the thickness of the friction pad 5 decreases when the friction pad 5 is greatly worn, the side surface 4 and the pressure contact surface 10 when the armature 11 is attracted to the electromagnetic magnet 13 are attached.
The distance between and becomes large. From this, the pressing spring 1
2 moves the friction pad 5 toward the side surface 4 by a larger distance, and the pressing force becomes smaller accordingly. When the pressing force of the pressure contact surface 10 is reduced, the force of the plurality of convex portions 4a biting into the pressure contact surface 10 is reduced, and the frictional force generated by scraping off the pressure contact surface 10 is also reduced. Therefore, in the braking device 100, the friction pad 5 is greatly worn at the beginning of use, and as a result, the friction pad 5 is worn out in a short time and the frictional force between the rotating disk 3 and the friction pad 5 is reduced. Therefore, it is necessary to replace the friction pad 5 frequently, resulting in a high running cost. Further, due to the abrasion of the friction pad 5, the reciprocating movement distance of the armature 11 also increases, so the pressing spring 12 and the electromagnetic magnet 13
However, there is a problem that the life of the drive unit 6 and the like is shortened due to the burden on the drive unit and the like.

Further, in order to further increase the frictional force between the side surface 4 and the pressure contact surface 10 to make power transmission efficient, it is necessary to increase the pressing force applied to the pressure contact surface 10 by the drive portion 6.
The pressure spring 12 and the electromagnetic magnet 13 are increased in size. On the contrary, increasing the arithmetic mean roughness Ra of the side surface 4 to increase the frictional force while keeping the pressing force applied to the pressure contact surface 10 as it is increases the amount of the convex portion 4a scraping off the pressure contact surface 10. There is also a problem that the running cost becomes higher and the life becomes shorter.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above problems, and to provide a power transmission device having a long life and a small size by increasing the frictional force and reducing the wear of the friction pad. The purpose is to get.

[0012]

A power transmission device according to the present invention has a contact surface, is provided so as to be movable with a movable portion, and is provided so as to face the contact surface. A contact surface and a pressure contact surface having a pressure contact surface for generating a friction force between the contact surface and the contact surface, the pressure contact portion transmitting the moving force of the moving portion by the friction force. One surface of the hard side is a range of the surface roughness in which the pressure contact surface has a large friction coefficient in a state of being pressed against the contact surface in relation to the surface roughness of the one surface,
In addition, it is a smooth surface that can reduce wear on the other surface.

The other surface is a smooth surface which is substantially the same as the one surface.

Of the moving part and the pressure contact part,
The material on one side is an iron-based metal and the material on the other side is an organic friction material, and the surface roughness of the smooth surface on the one side is 0.1 μm at maximum in terms of calculated average roughness.

The moving part has a base material provided on the shaft and a protective film having a higher corrosion resistance than the base material for coating the surface of the base material, and the protective film comprises: The surface forms at least the smooth surface.

The moving portion is provided on a shaft rotatable about the axis, and the contact surface is formed around the shaft rotatable about the axis along the circumferential direction of the axis. By being provided on the shaft, the moving unit is adapted to rotate together with the contact surface by the rotation of the shaft.

Further, it is a braking device for an elevator that brakes the lifting and lowering of a car.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. The same or equivalent members and parts as those of the conventional example are designated by the same reference numerals. Embodiment 1. 1 is a schematic diagram showing the configuration of a power transmission device according to a first embodiment of the present invention. In FIG. 1, a braking device 1 which is a power transmission device includes a rotating disk 3 having a rotating surface 20 which is a contact surface formed along the axis of the rotating shaft 2. The rotation surface 20 is the side surface 4.
Is formed in a part of. The rotating surface 20 is arranged so as to face the pressure contact surface 10 of the friction pad 5, and the pressure contact surface 10 is disposed.
Is in pressure contact with the rotating surface 20. Surface 20
Is a smooth surface having a surface roughness of 0.1 μm when expressed by, for example, arithmetic average roughness Ra. This rotating surface 20
Is formed by a machining method such as grinding, buffing or lapping, or chemical polishing such as etching or electric field polishing. Other configurations and operations are similar to those of the conventional example.

FIG. 2 is a graph showing the relationship between the arithmetic mean roughness Ra of the rotating surface 20 and the static friction coefficient or dynamic friction coefficient when the pressing surface 10 is pressed against the rotating surface 20.
Here, the static friction coefficient is the maximum from the state in which the pressing surface 10 presses the rotating surface 20 to make the rotating disk 3 stand still until the rotational force of the rotating disk 3 overcomes the frictional force in that state and starts rotating. The friction coefficient is a value, and the dynamic friction coefficient is a coefficient of friction when the rotating disk 3 is rotating while being pressed against the pressure contact surface 10. Further, the friction coefficient is a value obtained by dividing the frictional force in the rotation direction of the rotary disk 3 between the rotating surface 20 and the pressure contact surface 10 by the pressing force applied to the pressure contact surface 10. The condition of the pressure contact surface 10, the pressing force with which the pressure contact surface 10 is in pressure contact with the rotating surface 20, and the rotation speed of the rotating disk 3 are all the same conditions. In FIG. 2, the static friction coefficient and the dynamic friction coefficient are shown as the friction coefficient increase rate, respectively. This friction coefficient increase rate is such that the arithmetic mean roughness Ra of the rotating surface 20 is 2.7 μ.
When the value of the static friction coefficient and the value of the dynamic friction coefficient when m are 1 respectively, the value of the static friction coefficient and the value of the dynamic friction coefficient at each arithmetic mean roughness Ra are shown as their relative values. The rotating disk 3 having the arithmetic average roughness Ra of 2.7 μm is one of the rotating disks of the conventional example, and the static friction coefficient and the dynamic friction coefficient at this time are used as a reference to compare with the conventional example. It can be performed.

As shown in FIG. 2, although there is an error as an experimental value, as the arithmetic mean roughness Ra of the rotating surface 20 becomes smaller, either the coefficient of increase in the coefficient of static friction or the coefficient of increase in the coefficient of dynamic friction is increased. Thighs tend to grow.
In particular, when the arithmetic average roughness Ra is 0.025 μm, both the static friction coefficient and the dynamic friction coefficient have a friction coefficient increase rate that is completely larger than the reference friction coefficient increase rate 1. Therefore, from the tendency of the change of the friction coefficient increase rate in FIG. 2, if the arithmetic mean roughness Ra of the rotating surface 20 is 0.1 μm at the maximum, the static friction coefficient and the dynamic friction coefficient larger than those of the conventional example can be obtained. This is because the surface roughness of the rotating surface 20 that comes into contact with the pressure contact surface 10 is reduced, so
This is because the number of parts that contact each other between and increases and the contact area increases.

Further, FIG. 3 shows that when the friction pad 5 is brought into pressure contact with a rotating surface having a standard surface roughness, the wear mass of the friction pad 5 and the rotating pad having an arithmetic average roughness Ra of 0.025 μm show the friction pad 5 It is a graph which shows a comparison with the abrasion mass of the friction pad 5 when pressed. Here, the reference surface roughness is an arithmetic average roughness Ra of 2.7 μm which is a conventional example. The conditions such as the pressing force applied to the rotating surface by the pressure contact surface 10 are the same as the conditions applied in FIG. 2, and the time during which the pressure contact surface 10 is pressed against the rotating surface is the same. Also,
The wear mass of the friction pad 5 when it comes into pressure contact with a rotating surface having an arithmetic average roughness Ra of 0.025 μm is as follows: It is represented by a relative value, that is, a friction pad wear mass ratio.

As is apparent from FIG. 3, when the pressure contact surface 10 is pressure-contacted to the rotating surface having the arithmetic mean roughness Ra of 0.025 μm, the pressure contact surface 10 is pressure-contacted to the rotating surface having the standard surface roughness. The wear mass of the friction pad 5 is smaller than that. This is because the surface roughness of the rotating surface is reduced and the depth of scraping off the pressure contact surface 10 is reduced. That is, the height of the plurality of convex portions formed on the rotating surface becomes low due to the reduction of the surface roughness, and the depth of the bite into the pressure contact surface 10 becomes small due to the reduction of the plurality of convex portions. From such a tendency, as a matter of course, the arithmetic average roughness Ra in this embodiment is 0.1.
When the pressure contact surface 10 is pressed against the rotating surface 20 of μm, the abrasion mass of the friction pad 5 generated is smaller than when the pressure contact surface 10 is pressed against the rotating surface having the standard surface roughness which is the conventional example.

Therefore, if the arithmetic mean roughness Ra of the rotating surface 20 of the rotating disk 3 is 0.1 μm or less, the static friction coefficient and the dynamic friction coefficient in the state where the pressure contact surface 10 is in pressure contact with each other will be described with reference to FIG. Both of them are larger than those in the conventional example, and the wear mass of the friction pad 5 generated in this state is smaller than that in the conventional example due to the description of FIG.

From this fact, the pressing force applied to the pressure contact surface 10 in order to generate the predetermined frictional force necessary for braking the rotating disk 3 can be reduced, so that the braking device 1 is provided with the mechanism portion 6.
The pressing spring 12, the electromagnetic magnet 13 and the like can be downsized, the installation space of the mechanism portion 6 can be reduced, and the downsizing can reduce the cost.

At the same time, since the wear mass of the friction pad 5 is also reduced, the frequency of exchanging the friction pad 5 is reduced, the running cost is reduced, and the drive unit 6 is used.
The life of the braking device 1 is extended due to the reduction of the load of the braking device 1.

In the above-mentioned embodiment, the material of the rotary disk 3 is cast iron, but the material is not limited to this, as long as it is harder than the friction pad 5.
A ferrous metal such as stainless steel, a non-ferrous metal such as aluminum or copper, or a ceramic may be used.

In the above embodiment, the material of the friction pad 5 is a phenol resin mold organic friction material, but any friction material softer than the rotating disk 3 and capable of generating a certain amount of resistance may be used. However, it is not limited to this, and for example, a metallic friction material containing a large amount of metal may be used.

Further, not only the rotating surface 20 but also the surface roughness of the friction pad 5 may be reduced. By doing so, the contact area between the rotating surface 20 and the pressure contact surface 10 is further increased,
The friction coefficient is further increased when the pressure contact surface 10 is in pressure contact with the rotating surface 20.

Further, the rotary disk and the friction pad may be made of different materials for the rotary disk and the friction pad. In this case, the pressure contact surface of the hard side friction pad is a smooth surface having an arithmetic average roughness Ra of 0.1 μm at the maximum.

Embodiment 2. FIG. 4 is a schematic diagram showing the configuration of the power transmission device according to the second embodiment of the present invention.
In FIG. 4, a braking device 30 which is a power transmission device has a rotating disk 3 having a rotating disk 31 which is a base material provided on the rotating shaft 2 and a protective film 32 which coats the surface of the rotating disk 31. Is equipped with. The material of the rotary disc 31 is cast iron. The rotating disk 31 has the rotating shaft 2 at its center.
Is fixed vertically. The rotary disc 31 has a film forming surface 33 on the friction pad 5 side.
A protective film 32 is formed on the surface 3. The material of the protective film 32 is a material having higher corrosion resistance than the rotating disc 31 against corrosion due to oxidation or the like. The material of the protective film 32 is harder than the friction pad 5, and preferably harder than the rotary disc 31. Therefore, this protective film 32 is formed, for example, by electroless nickel plating, chrome plating,
Any ceramic spray coating or nitride film may be used. The protective film 32 has a rotating surface 34 which is a contact surface with which the pressure contact surface 10 is in pressure contact with the friction pad 5 side. Surface of revolution 34
Are formed along the axis of the rotary shaft 2 and have a smooth surface with an arithmetic average roughness Ra of 0.1 μm. Other configurations and operations are the same as those in the first embodiment.

After the protective film 32 is formed on the film forming surface 33 of the rotary disk 31, the surface of the friction pad 5 facing the pressure contact surface 10 is machined, for example, by grinding, buffing or lapping. Alternatively, it is smoothed by a processing method such as etching or chemical polishing such as electric field polishing, and finished as the rotating surface 34. At this time, the surface facing the pressure contact surface 10 is cut too much so that the film forming surface 33 of the rotary disc 31 is not exposed. Before forming the protective film 32, the film forming surface 33 is finished to be smooth by the above processing method,
After that, the protective film 32 may be formed to have a uniform thickness.

The braking device 30 constructed in this way has the same effect as that of the first embodiment, and the rotary disk 3 has the protective film 32 having excellent corrosion resistance.
Since the rotating surface 34 is formed on the surface of 2, the rotating surface 3
It is possible to suppress an increase in the surface roughness due to corrosion of No. 4 and to prevent the static friction coefficient and the dynamic friction coefficient between the pressure contact surface 10 and the rotating surface 34 from decreasing. In particular, the above effect is remarkably exhibited in an atmosphere containing a large amount of humid or corrosive gas such as hydrogen sulfide, such as a factory area or a hot spring area.

The braking device in each of the above embodiments may be used in an elevator in which a car moves up and down. In this case, the rotary shaft 2 is fixed with its axis aligned with the central axis of the sheave around which the rope connected to the car is wound or the main shaft of the hoisting machine. It is designed to rotate. In this case, for example, the pressing force of the pressure contact surface 10 for holding the stopped state of the car is reduced, so that the braking device itself is downsized and the installation space can be reduced. At the same time, the wear mass of the friction pad 5 is also reduced, so that the burden of maintaining and managing the braking device is reduced.

In each of the above embodiments, the power transmission device is a disc type braking device having the rotating disc 3. However, friction force is generated by pressing the friction pad against the rotating surface. As long as the power can be transmitted, the above effect can be obtained. Therefore, for example, a drum-type braking device having a drum, a part of which is a rotating surface, may be used, and the braking device need not be limited. It doesn't matter. Furthermore, the contact surface does not have to be limited to the rotating surface, as long as the power of the moving portion is transmitted by the frictional force generated by the pressure contact surface being pressed against the contact surface, for example, a surface along a straight line, A power transmission device that transmits the power of the reciprocating moving unit may be used.

[0035]

As is apparent from the above description, the power transmission device according to the present invention has a contact surface, is provided with a movable portion which is movable, and is opposed to the contact surface. A power transmission device comprising: a pressure contact surface that is in pressure contact with the contact surface to generate a friction force, and a pressure contact portion to which the moving force of the moving portion is transmitted by the friction force. One of the surfaces and the one of the press contact surfaces on the hard side is a range of the surface roughness in which the friction coefficient in the state where the press contact surface is pressed against the contact surface is large in relation to the surface roughness of the one surface. And, since it is a smooth surface that can reduce the wear of the other surface, the pressing force for pressing the pressure contact surface against the contact surface to obtain a predetermined frictional force becomes small and the other surface Has a longer life,
The replacement frequency of the member can be reduced.

Since the other surface is substantially the same smooth surface as the one surface, the contact area between the one surface and the other surface is further increased, and the friction coefficient is further increased. As the size increases, the wear of the other surface decreases further.

Of the moving part and the pressure contact part,
The material on one side is an iron-based metal, the material on the other side is an organic friction material, and the surface roughness of the smooth surface on the one side is 0.1 μm at the maximum in the calculated average roughness. The pressing force for pressing the pressure contact surface against the contact surface in order to obtain a predetermined frictional force is reduced, the life of the member having the other surface is extended, and the replacement frequency of the member can be reduced. .

The moving part has a base material provided on the shaft and a protective film having a higher corrosion resistance than the base material coating the surface of the base material, and the protective film comprises: Since the surface forms at least the smooth surface, it is possible to suppress corrosion of the contact surface and suppress increase in surface roughness of the contact surface.

The moving portion is provided on a shaft rotatable about the axis, and the contact surface is formed around the shaft rotatable about the axis along the circumferential direction of the axis. Since the moving portion is provided on the shaft to rotate together with the contact surface by the rotation of the shaft, power can be easily and continuously transmitted.

Further, since it is an elevator braking device that brakes the lifting and lowering of the car, the pressing force of the pressure contact portion necessary for maintaining the stopped state of the car can be reduced and downsized, and the wear of the pressure contact portion can be reduced. The reduced mass reduces the burden of maintenance and management, and also reduces running costs.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a power transmission device according to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between an arithmetic mean roughness Ra of a rotating surface and a static friction coefficient or a dynamic friction coefficient when the pressing surface is brought into pressure contact with the rotating surface.

FIG. 3 is a wear amount of the friction pad when the friction pad is brought into pressure contact with a rotating surface having a surface roughness of 2.7 μm in arithmetic mean roughness Ra and a rotating surface having a surface roughness of 0.025 μm in arithmetic mean roughness Ra. 5 is a graph showing a comparison with the wear mass of the friction pad when the friction pad is pressed against the surface.

FIG. 4 is a schematic diagram showing a configuration of a power transmission device according to a second embodiment of the present invention.

FIG. 5 is a schematic diagram showing a configuration of a braking device that is a conventional power transmission device.

[Explanation of symbols]

1,30 Braking device (power transmission device), 2 rotating shaft (shaft), 3 rotating disk (moving part), 5 friction pad (press contact part), 20,34 rotating surface (contact surface), 31 rotating disk (mother) Material), 32 protective film.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoyuki Maruyama             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. F-term (reference) 3F306 AA07 BA09                 3J056 AA58 AA62 BA02 BC02 CA04                       CA16 EA03 FA05 GA01                 3J058 AA47 AA57 AA78 AA88 BA41                       BA67 BA68 CA42 CB27 EA12                       EA32 FA37 GA04 GA92 GA93

Claims (6)

[Claims] 1. A movable portion having a contact surface, which is movable, and a pressure contact surface which is provided so as to face the contact surface and is in pressure contact with the contact surface to generate a frictional force between the contact surface. A power transmission device having a pressure contact portion to which the moving force of the moving portion is transmitted by the friction force, wherein one surface on a hard side of the contact surface and the pressure contact surface is
A smooth surface in which the friction coefficient in the state where the pressure contact surface is in pressure contact with the contact surface is in the range of the surface roughness that is large in relation to the surface roughness of the one surface, and the wear of the other surface can be reduced. The power transmission device is characterized in that. 2. The power transmission device according to claim 1, wherein the other surface is a smooth surface substantially the same as the one surface. 3. A material of one side of the moving portion and the pressure contact portion is an iron-based metal, and a material of the other side is an organic friction material, and the surface roughness of the smooth surface on the one side is: 2. The maximum average roughness calculated is 0.1 μm.
Alternatively, the power transmission device according to claim 2. 4. The moving section has a base material provided on the shaft, and a protective film having a higher corrosion resistance than the base material coating the surface of the base material, and the protective film comprises: The power transmission device according to any one of claims 1 to 3, wherein the surface forms at least the smooth surface. 5. The moving section is provided on a shaft rotatable about an axis, and the contact surface is formed around a shaft rotatable about the axis along a circumferential direction of the axis. The power transmission device according to any one of claims 1 to 4, wherein the moving portion is provided on the shaft to rotate together with the contact surface by the rotation of the shaft. . 6. The power transmission device according to claim 5, wherein the power transmission device is an elevator braking device that brakes the lifting and lowering of a car.