JPH0626532A - Power transmission - Google Patents

Abstract

PURPOSE:To decrease noise inside a vehicle by providing an outer plate (drive member), a rubber hub (elastic member), an inner hub (driven member), and frictional plate. CONSTITUTION:When rotational power is transmitted from an outer plate 20 to an inner hub 7 via a rubber hub 8, load torque of the inner hub 7 is varied, and the rubber hub 8 is deformed in rotational direction (shear direction, torsional direction), and thereby a certain extent of torque variation is absorbed by the rubber hub 8. Additionally since the outer plate 20 and the inner hub 7 are relatively rotated by deforming the rubber hub 8 in the rotational direction, a frictional plate 9, and the other side member out of the outer plate 20, and the inner hub 7 are relatively engaged with each other frictionally. Consequently, generation of resonance of the outer plate 20 and the inner hub 7 can be suppressed, and noise inside a vehicle chamber caused by the resonance can be decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving member and a driven member, such as an electromagnetic clutch having a rubber hub or a leaf spring arranged between an armature or an outer plate fixed to the armature and an inner hub. The present invention relates to a power transmission device in which an elastic member is arranged.

[0002]

2. Description of the Related Art Conventionally, for example, JP-A-58-1342
No. 38, there is disclosed an electromagnetic clutch (hereinafter referred to as a conventional technique) for the purpose of reducing the torque fluctuation of the shaft of the compressor to prevent damage to the shaft of the compressor due to torsional resonance between the rotor and the inner hub. Proposed. The conventional technique is that the right end face is fixed to the armature via an elastic member such as a leaf spring and an annular plate between an armature adsorbed to a rotor and an inner hub fixed to a shaft of a compressor.
The left end face is provided with a friction engagement member that frictionally engages with the outer end face of the inner hub.

[0003]

However, in the prior art, when the load torque of the shaft of the compressor fluctuates, some torque fluctuation is absorbed by the elastic member or the friction engagement member. Since the rotational power is transmitted by connecting the members in series, the effect of reducing the torque fluctuation of the compressor shaft is small. Therefore, torque fluctuations of the compressor shaft are transmitted to the inner hub and the annular plate, and the annular plate and the inner hub rotate relative to each other, causing resonance. And
There is a problem in that this resonance is transmitted to the internal combustion engine and the vehicle body, and finally transmitted to the vehicle interior to increase noise in the vehicle interior. It is an object of the present invention to provide a power transmission device that reduces torque fluctuations on the driven member side to reduce noise.

[0004]

According to the present invention, there is provided a driving member which is rotationally driven, one end of which is connected to the driving member, an elastic member which is elastically deformable, and the other end of which is connected. A driven member to which rotational power is transmitted from the drive member via the elastic member, and a member provided on one of the drive member and the driven member and arranged in parallel with the elastic member, among them. The technical means including a friction member that comes into contact with the other member is adopted.

[0005]

According to the present invention, when the rotational power is transmitted from the driving member to the driven member via the elastic member, the load torque of the driven member fluctuates to cause the elastic member to rotate in the rotating direction (shear direction,
The elastic member absorbs a certain amount of torque fluctuation due to the deformation in the twisting direction). Further, since the driving member and the driven member relatively rotate due to the elastic member deforming in the rotation direction, the friction member, the driving member, and the other member of the driven members relatively frictionally engage with each other. Therefore, by converting the energy of the relative rotation between the driving member and the driven member due to the torque fluctuation into the energy of heat generation due to the friction between the friction member and the other member thereof, only the elastic member or the friction with the elastic member is converted. The torque fluctuation reducing effect is improved as compared with the conventional technique in which the engaging member is connected in series.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a power transmission device of the present invention will be described based on the embodiments shown in the drawings. 1 and 2 show a first embodiment of the present invention, and FIG. 1 is a view showing an electromagnetic clutch of a vehicle air conditioner. The electromagnetic clutch 1 is the power transmission device of the present invention, and is a shaft 2 of an engine (not shown) and a compressor (not shown) of a vehicle air conditioner.
The transmission of rotational power with and is intermittent. The engine is arranged in the engine room of the vehicle. Also,
The compressor compresses the sucked refrigerant gas and discharges the high-temperature and high-pressure refrigerant gas. The electromagnetic clutch 1 of this embodiment includes an exciting coil 3, a stator housing 4,
The rotor 5, the armature 6, the inner hub 7, the rubber hub 8 and the friction plate 9 are included.

The exciting coil 3 is wound in a cylindrical shape inside a stator housing 4. The exciting coil 3 is electrically connected to an external power source (not shown), and when energized (turned on), magnetic flux is generated in the stator housing 4, the rotor 5 and the armature 6 to resist the elastic force of the rubber hub 8. Then, the armature 6 is attracted to the rotor 5.
The stator housing 4 is made of, for example, low carbon steel (S10C).
It is made of a magnetic material such as and is formed in a substantially cylindrical shape. The stator housing 4 has an annular mounting flange 10
It is fixed to the housing 11 of the compressor via.

The rotor 5 is, for example, low carbon steel (S10C).
It is made of a magnetic material such as and has a U-shaped cross section, and is rotatably fitted to the outer peripheral side of the compressor housing 11 via a bearing 12. This rotor 5
A pulley 13 connected to the engine via a belt (not shown) is joined to the upper part of the engine by means such as welding. An annular friction engagement surface 15 that frictionally engages with the armature 6 is formed on the right end surface of the clutch plate portion 14 of the rotor 5. The clutch plate portion 14 is formed with a plurality of shaft holes 16 for bypassing the magnetic flux generated by the exciting coil 3 so as to penetrate in the axial direction.

The armature 6 is made of, for example, low carbon steel (S1).
(0C) and the like, which are annular plate-shaped clutch plates that are arranged to face the friction engagement surface 15 of the rotor 5 with a narrow gap therebetween. A friction engagement surface 17 that frictionally engages with the friction engagement surface 15 of the rotor 5 is formed on the left end surface of the armature 6. The armature 6 is formed with a plurality of shaft holes 18 for bypassing the magnetic flux generated by the exciting coil 3 so as to penetrate in the axial direction. In addition, the armature 6 of this embodiment has an outer plate 2 which is attached to the right end surface by a rivet 19.
0 and a friction plate 9. That outer plate 2
0 is a drive member of the present invention, and at the inner peripheral side end portion thereof,
A tubular flange portion 21 that faces the inner hub 7 is formed so as to project to the side away from the rotor 5 (right side in the drawing).

The inner hub 7 is a driven member of the present invention and is formed in a substantially annular plate shape, and transmits rotational power to the shaft 2 of the compressor. A flange portion 21 of the outer plate 20 is provided at an outer peripheral side end portion of the inner hub 7.
A cylindrical flange portion 21 facing the flange portion 21 on the inner peripheral side is formed so as to protrude to the right side in the drawing. The rubber hub 8 is the elastic member of the present invention, and is made of butyl rubber or natural rubber having excellent vibration resistance and heat resistance and a large rubber hardness, and absorbs the fluctuating torque of the shaft 2 of the compressor. The rubber hub 8 is arranged between the flange portion 21 of the outer plate 20 and the flange portion 22 of the inner hub 7, and these flange portions 21,
It is joined to the facing surface of 22 by means such as vulcanization adhesion.

The friction plate 9 is the friction member of the present invention,
For example, it is made of a steel plate or a stainless steel plate and is formed into a substantially annular plate shape by means of pressing or the like, and absorbs fluctuating torque of the shaft 2 of the compressor. This friction plate 9
Includes an annular plate portion 23 fixed to the right end surface of the armature 6 with a rivet 19 via an outer plate 20 at one end, and a flange portion 21 of the outer plate 20 from an inner peripheral end of the annular plate portion 23. A cylindrical portion 24 is formed so as to extend in a substantially orthogonal direction along the outer peripheral surface.

Further, the friction plate 9 has an annular projection extending in a substantially orthogonal direction so as to be located on the right side of the rubber hub 8 so as to bypass the rubber hub 8 from the right end of the cylindrical portion 24. A portion 25 and a cylindrical frictional engagement portion 26 extending in a substantially orthogonal direction from the inner peripheral end of the protruding portion 25 are formed. The left end of the friction engagement portion 26 is further frictionally engaged with the inner peripheral surface of the flange portion 22 of the inner hub 7 at all times, that is, both when the armature 6 is rotating and when the rotation is stopped, so that the left end of the friction engaging portion 26 can be elastically deformed. Has been folded back.

Here, FIG. 2 is a graph showing the relationship between the one-sided amplitude torque and the frequency of torque fluctuation, and the frequency of torque fluctuation has a 1: 1 relationship with the rotational speed of the compressor. Further, the solid line shows the case of the electromagnetic clutch 1 of the present invention, the broken line shows the case of the conventional electromagnetic clutch, and ΔT represents the oscillating piece amplitude torque of the compressor. The friction torque generated by the friction engagement between the friction engagement portion 26 of the friction plate 9 and the flange portion 22 of the inner hub 7 is 50% to 100% of the vibration piece amplitude torque (ΔT) of the compressor. Is set to. That is, the electromagnetic clutch 1
The friction engagement portion 2 of the friction plate 9 generated when the inner hub 7 is relatively rotated with respect to the outer plate 20 and the armature 6 with the rubber hub 8 removed further.
The friction plate 9 is designed so that the friction torque between the shaft 6 and the flange portion 22 of the inner hub 7 is 50% to 100% of the above-described vibration piece amplitude torque (ΔT) of the compressor.

Next, the operation of the electromagnetic clutch 1 will be described with reference to FIG.
A brief description will be given with reference to FIG. When the exciting coil 3 is energized by starting the engine and turning on an air conditioner switch (not shown), magnetic flux is generated in the stator housing 4, the rotor 5 and the armature 6, and the force attracted to the rotor 5 is applied to the armature 6. Join.
Therefore, the rubber hub 8 is elastically deformed in the axial direction, whereby the armature 6 moves axially toward the rotor 5 side together with the outer plate 20 and the friction plate 9, and the friction engagement surface 17 of the armature 6 moves toward the rotor 5. Friction engagement surface 1
5 is strongly adsorbed.

Since the rotor 5 is rotationally driven by the engine via the belt and the pulley 13, the rotational power of the engine is transmitted to the armature 6 via the rotor 5. When the armature 6 starts rotating in the same direction as the rotation direction of the rotor 5, the rotational power transmitted to the armature 6 is transmitted to the outer plate 20 via the rivet 19. Therefore, the rotational power is transmitted from the outer plate 20 to the shaft 2 via the rubber hub 8 and the inner hub 7, the compressor starts compressing the refrigerant, and the vehicle air conditioner is activated to air-condition the vehicle interior. To be done.

At this time, if the load torque of the shaft 2 of the compressor fluctuates due to the compression action of the refrigerant, the torque fluctuation is transmitted from the shaft 2 to the rubber hub 8 via the inner hub 7. For this reason, the rubber hub 8 is attached to the armature 6
The torque fluctuations are absorbed to some extent by elastically deforming in the rotation direction, that is, in the shearing direction. However, due to the elastic deformation of the rubber hub 8 in the shearing direction, the flange portion 21 of the outer plate 20 and the flange portion 22 of the inner hub 7 rotate relative to each other, so that the rubber hub 8 is arranged in parallel with the inner hub 7 and is attached to the inner hub 7. The friction engagement portion 26 of the friction plate 9 pressed by a predetermined pressing force.
Slides relative to the flange portion 22 of the inner hub 7, so that the friction engagement portion 26 of the friction plate 9 and the flange portion 22 of the inner hub 7 frictionally engage with each other.

That is, the energy of the relative rotational motion between the outer plate 20 and the inner hub 7 due to the torque fluctuation of the compressor is generated by the friction engagement between the friction engagement portion 26 of the friction plate 9 and the flange portion 22 of the inner hub 7. By converting into heat generation energy, as shown by the solid line in the graph of FIG. 2, a conventional technique in which only a rubber hub or an elastic member and a friction engagement member are arranged in series (shown by a broken line in the graph of FIG. 2) The effect of further reducing the torque fluctuation can be achieved only by adding a simple friction plate 9 as compared with the above-mentioned method. Therefore, the resonance between the rotor 5 and the inner hub 7 can be completely prevented, and the vibration due to the resonance is not transmitted to the engine or the vehicle body. Therefore, noise in the vehicle compartment can be reduced.

FIG. 3 shows a second embodiment of the present invention and is a view showing an electromagnetic clutch of a vehicle air conditioner. In this embodiment, an annular friction plate 9 is joined to the left end surface of the inner hub 7 by means such as welding. The friction plate 9
Has a substantially L-shaped cross section, and has an annular plate portion 27 fixed to the inner hub 7 and a cylindrical friction member bent in a substantially orthogonal direction from the outer peripheral end of the annular plate portion 27. The joint 28 is provided. The frictional engagement portion 28 is arranged so as to be frictionally engaged with the inner peripheral surface of the armature 6 at all times, that is, when the armature 6 is rotated and stopped.
In the case of this embodiment, the armature 6 constitutes the driving member of the present invention.

FIG. 4 shows a third embodiment of the present invention and is a view showing an electromagnetic clutch of a vehicle air conditioner. In this embodiment, the armature 6 and the inner hub 7 are connected by a leaf spring 29 as an elastic member. The outer peripheral side end portion of the leaf spring 29 is fixed to the left end surface of the armature 6 by the rivet 19, and the inner peripheral side end portion is formed by the rivet 19.
Is fixed to the right end surface of the inner hub 7. Further, the pulley 13 is integrally formed on the outer peripheral side portion of the rotor 5. In the case of this embodiment, the armature 6 constitutes the driving member of the present invention.

Further, an annular friction plate 9 is joined to the left end surface of the inner hub 7 by means such as welding. The friction plate 9 has a substantially U-shaped cross section, and has a cylindrical portion 31 fixed to the inner hub 7, and the cylindrical portion 31.
The annular plate portion 3 extending from the left end of the armature 6 to the armature 6 side
2 and a cylindrical frictional engagement portion 33 that is bent in a substantially orthogonal direction from the outer peripheral end of the annular plate portion 32. This friction engagement portion 33 is always in contact with the armature 6.
Is arranged so as to be frictionally engaged with the inner peripheral surface of the armature 6 both during rotation and during rotation stop. Here, the leaf spring 29
An elastically deformable bush may be interposed between the rivet 19 and the rivet 19.

FIG. 5 shows a fourth embodiment of the present invention and is a view showing an electromagnetic clutch of a vehicle air conditioner. In this embodiment, the holder 41, the O-rings 42a and 42b, and the viscous fluid 43 form a friction member. The holder 41 has an outer annular plate portion 44 fixed to the left end portion of the armature 6 with a rivet 19 via an outer plate 20 at one end, and a rubber hub 8 bypassing the inner peripheral end of the outer annular plate portion 44. Thus, an annular protrusion 45 is formed so as to be located on the left side of the rubber hub 8. Further, the holder 41 includes an inner annular plate portion 47 extending from the inner peripheral end of the protruding portion 45 to the center side along the annular plate portion 46 of the inner hub 7, and the inner annular plate portion 47. A cylindrical portion 48 is formed so as to extend from the peripheral end toward the inner peripheral side of the inner hub 7. This cylindrical portion 48 is always in contact with the inner hub 7 through the O-ring 42b, that is, when the armature 6 is rotating and when the rotation is stopped.
Is arranged so as to be frictionally engaged with the inner peripheral surface of the.

The O-ring 42a and the outer plate 20 and the outer periphery of the protruding portion 45 of the holder 41 prevent the viscous fluid 43 from leaking from the space formed between the holder 41 and the inner hub 7, the rubber hub 8 and the outer plate 20. It is mounted between the inner circumference of the flange portion 21 and the inner circumference of the flange portion 21. The O-ring 42b is provided on the cylindrical portion 4 of the holder 41 so that the viscous fluid 43 does not leak from the space formed between the holder 41 and the inner hub 7, the rubber hub 8 and the outer plate 20.
It is mounted between the outer circumference of the inner hub 7 and the inner circumference of the flange portion 22 of the inner hub 7. The viscous fluid 43 is the sealing member of the present invention, and is made of, for example, silicone oil, a grease-like fluid, gel, or the like, and is in a space formed between the holder 41 and the inner hub 7, the rubber hub 8, and the outer plate 20. It is sealed by O-rings 42a and 42b.

In this embodiment, when the load torque of the shaft 2 of the compressor fluctuates due to the compression action of the refrigerant and the torque fluctuation is transmitted from the shaft 2 to the rubber hub 8 via the inner hub 7, the rubber hub 8 is deformed in the shearing direction. However, the outer plate 20 and the inner hub 7 relatively twist and vibrate. Therefore, the shearing force of the sealed viscous fluid 43 acts as a damping force and the energy of torque fluctuation is absorbed, so that noise in the vehicle interior can be prevented.

FIG. 6 shows a fifth embodiment of the present invention and is a view showing an electromagnetic clutch of a vehicle air conditioner. In this embodiment, the holder 51, the two O-rings 52a, 52b
And the magnetic powder 53 constitutes a friction member.
The holder 51 has a circular plate portion 54 fixed to the left end portion of the armature 6 by the rivet 19 via the outer plate 20 at one end, and the rubber hub 8 is detoured from the inner peripheral end of the circular plate portion 54. An annular projecting portion 55 is formed on the left side of the rubber hub 8. In addition, the outer plate 20 is provided on the protrusion 55.
Outer tubular portion 56 that abuts the flange portion 21 of the inner tubular portion 5 and the inner tubular portion 5 that extends along the flange portion 22 of the inner hub 7.
7 are formed. The inner tubular portion 57 is always connected to the flange portion 2 of the inner hub 7 via the O-rings 52a and 52b, that is, when the armature 6 is rotated and stopped.
It is arranged so as to be frictionally engaged with the inner peripheral surface of 2.

The magnetic powder 53 is sealed in a space formed between the two O-rings 52a and 52b, the flange portion 22 and the inner cylindrical portion 57 so as not to leak. Magnetic powder 5
Reference numeral 3 denotes the sealing member of the present invention, which is made of magnetic material particles such as iron.

In this embodiment, when the exciting coil 3 is energized, a part of the magnetic circuit is rotor 5 → armature 6 → holder 51 → inner hub 7 → armature 6 → rotor 5
By forming a magnetic circuit so as to pass through, the magnetic powder 53 is attracted in the space between the inner tubular portion 57 and the flange portion 22. Therefore, the shearing force of the magnetic powder 53 increases. Then, when the load torque of the shaft 2 of the compressor fluctuates due to the compression action of the refrigerant and the torque fluctuation is transmitted from the shaft 2 to the rubber hub 8 via the inner hub 7, the rubber hub 8 is deformed in the shearing direction and the outer plate 20 and Since the inner hub 7 and the inner hub 7 generate torsional vibrations relative to each other, the magnetic powder 53 is magnetized and has a large shearing force.
A large friction force can be obtained. As a result, the magnetic powder 5
Since a shearing force acts on 3 to absorb the energy of torque fluctuation, noise in the vehicle interior can be prevented.

FIGS. 7 and 8 show the sixth embodiment of the present invention, and are views showing the electromagnetic clutch of the vehicle air conditioner. In this embodiment, the flange portion 22 of the inner hub 7 is
A friction material 61 is fixed to the inner peripheral side of the. Friction material 61
Is made by molding metal powder or the like into a cylindrical shape from a phenolic resin. The rivet 19 is attached to the left end of the armature 6 via the outer plate 20.
The holder 62 is fixed by. The inner peripheral side end of the holder 62 is extended so as to be located on the left side of the rubber hub 8 so as to bypass the rubber hub 8, and the inner peripheral side end of the leaf spring 64 by the rivet 63. One end is fixed. At the other end of the leaf spring 64, the friction material 6
A brake shoe 65 made of cast iron, hardened steel or the like is fixed by a rivet 66 so as to face the inner peripheral surface of 1. The brake shoe 65 is arranged to frictionally engage the friction member 61 only when the armature 6 rotates, that is, only when the rotor 5 and the armature 6 frictionally engage.

When the rotor 5 and the armature 6 are engaged with each other, the brake shoe 65 is radially displaced by centrifugal force as the outer plate 20 rotates and frictionally contacts the friction material 61 to act as a friction brake. Further, the brake shoe 65 is arranged with a predetermined gap from the friction material 61 when the rotor 5 and the armature 6 are separated from each other, that is, when the rotation of the outer plate 20 is stopped.

In this embodiment, when the exciting coil 3 is energized, the armature 6 is engaged with the rotor 5,
The compressor is started by transmitting the rotational power of the engine to the shaft 2 through the rotor 5, the armature 6, the outer plate 20, the rubber hub 8, and the inner hub 7. At this time, when the brake shoe 65 fixed to the outer plate 20 via the leaf spring 64 rotates, the centrifugal force overcomes the urging force of the leaf spring 64 and displaces in the radial direction. It is pressed against the friction material 61 fixed to the inner circumference of the. As a result, the torque fluctuation caused by the load torque of the shaft 2 of the compressor generated by the compression action of the refrigerant is attenuated by the elastic deformation of the rubber hub 8 and the frictional force between the brake shoe 65 and the friction material 61. For this reason, it is possible to prevent vibration transmission to the vehicle compartment due to torque fluctuations, and thus to prevent noise in the vehicle compartment.

Further, in this embodiment, since the brake shoe 65 and the friction material 61 are separated from each other before the compressor is started, and they are not operated as a friction brake, the spring characteristics of the rubber hub 8 in the axial direction are affected. Instead, it has the advantage of improving the spring properties in the shear direction. In addition,
When the energization of the exciting coil 3 is stopped during the operation of the compressor, the friction surface of the brake shoe 65 is slightly displaced in the shearing direction due to the torque fluctuation, which causes dynamic friction. Therefore, even the electromagnetic clutch 1 provided with the brake shoe 65 and the friction material 61 has little influence on the spring characteristic of the rubber hub 8 in the axial direction, and does not deteriorate the release characteristic of the armature 6 from the rotor 5. .

[Modification] In the present embodiment, the present invention is used for the electromagnetic clutch of the vehicle air conditioner, but the present invention may be used for the electromagnetic clutch that connects and disconnects the supercharger and the internal combustion engine. It may be used for an electromagnetic clutch that connects and disconnects a drive source such as an electric motor and a rotating machine. Further, it may be used in any power transmission device in which an elastic member is arranged between a drive member such as a drive shaft and a driven member such as a driven shaft. In this embodiment, one end of the friction plate (friction member) is fixed to the inner hub or the outer plate. However, one end of the friction member may be fixed to the armature, and the friction member may be a drive member or a driven member. It may be formed integrally with one of the members.

[0032]

According to the present invention, since the effect of reducing the torque fluctuation can be improved as compared with the prior art in which only the elastic member or the elastic member and the friction engagement member are connected in series, the driving member and the driven member can be improved. It is possible to suppress the occurrence of resonance. Therefore, it is possible to suppress the generation of noise due to those resonances.

[Brief description of drawings]

FIG. 1 is a sectional view showing an electromagnetic clutch of a vehicle air conditioner applied to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a one-sided amplitude torque and a frequency of torque fluctuation.

FIG. 3 is a sectional view showing an electromagnetic clutch of a vehicle air conditioner applied to a second embodiment of the present invention.

FIG. 4 is a sectional view showing an electromagnetic clutch of a vehicle air conditioner applied to a third embodiment of the present invention.

FIG. 5 is a sectional view showing an electromagnetic clutch of a vehicle air conditioner applied to a fourth embodiment of the present invention.

FIG. 6 is a cross-sectional view showing an electromagnetic clutch of a vehicle air conditioner applied to a fifth embodiment of the present invention.

FIG. 7 is a sectional view showing an electromagnetic clutch of a vehicle air conditioner applied to a sixth embodiment of the present invention.

8 is a cross-sectional view taken along the line AA of FIG.

[Explanation of symbols]

 1 Electromagnetic clutch (power transmission device) 6 Armature (driving member) 7 Inner hub (following member) 8 Rubber hub (elastic member) 9 Friction plate (friction member) 20 Outer plate (driving member)

Claims (4)

[Claims] 1. A driving member that is rotationally driven; (b) one end portion of which is connected to the driving member; and an elastic member that is elastically deformable; and (c) that is connected to the other end portion of the elastic member. A driven member to which rotational power is transmitted from the drive member via the elastic member; (d) provided on one member of the drive member and the driven member and arranged in parallel with the elastic member; And a friction member that contacts the other member of them. 2. The friction member is a friction member fixed to the one member and being in contact with the other member when the other member is rotated and stopped. The power transmission device described. 3. The friction member is fixed to the one member and is surrounded by a holder that comes into contact with the other member when the other member is rotated and stopped, and is surrounded by the other member and the holder. The power transmission device according to claim 1, wherein the power transmission device comprises an encapsulating member such as a viscous fluid or magnetic powder enclosed in a closed space. 4. The power transmission according to claim 1, wherein the friction member is a friction material that is fixed to the one member and comes into contact with the other member only when the other member rotates. apparatus.