JP2009092082A - Electromagnetic brake and electromagnetic clutch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic brake which can reduce noise such as a collision sound generated by a collision between an armature and a yoke or a disk, or a sliding sound and a squeaky sound between the armature and the disk, and an electronic clutch. <P>SOLUTION: An electromagnetic brake 20A comprises a disk 22 rotating integrally with a braked rotary shaft 2, a yoke 23 arranged at one side of the disk 22, an armature 24 arranged movably in the axial direction and unrotatably between the disk 22 and the yoke 23, and a plate 25 fixed to the yoke 23 by sandwiching the disk 22 and the armature 24 between a space with the yoke 23. Furthermore, in the disk 22, a resonance structure 30 reducing a sound generated when the disk 22 collides with the armature 24 is formed. Additionally, the resonance structure 30 is composed of a small-diameter hole 31 having an opening connected to an external space at the armature 24 side, and a large-diameter hole 32 having an opening at only the small-diameter hole side. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electromagnetic brake that switches braking and release with respect to a rotating shaft by electromagnetic force, and an electromagnetic clutch that switches transmission and disconnection of rotation of an input-side rotating body to an output-side rotating body by electromagnetic force. The present invention relates to noise reduction technology for electromagnetic brakes and electromagnetic clutches.

  Electromagnetic brakes and electromagnetic clutches used in combination with motors are important control elements for various industrial machinery. An example of a conventional electromagnetic brake is shown in FIGS. 9 and 10 are both cross-sectional views in a plane parallel to the braked rotating shaft of the electromagnetic brake. FIG. 9 shows a state at the time of braking and FIG. 10 shows a state at the time of releasing the brake.

  As shown in the drawing, a conventional electromagnetic brake 10 includes a disk 12 fixed so as to rotate integrally with a braked rotating shaft 1 via a spline 11, and a yoke 13 disposed on one side of the disk 12. An armature 14 that is axially movable and non-rotatable between the disk 12 and the yoke 13, and a plate 15 that is fixed to the yoke 13 with the disk 12 and the armature 14 interposed between the arm 13 and the yoke 13. I have. Note that linings 12 a and 12 a that are friction materials are attached to both surfaces of the disk 12.

  The yoke 13 is provided with a ring-shaped exciting coil 13a around the axis facing the armature 14, and a coil spring 13b for urging the armature 14 toward the disk 12 side. On the other hand, spacers 15a are attached between the plate 15 and the yoke 13 at three places (only one place is shown in the figure) at intervals of 120 degrees. The plate 15 is fixed to the yoke 13 at a predetermined interval by the spacer 15a.

  When the energizing coil 13a is not energized, as shown in FIG. 9, the armature 14 is pressed against the disk 12 by the urging force of the coil spring 13b, so that the braked rotating shaft 1 is braked. On the other hand, when the excitation coil 13a is energized, as shown in FIG. 10, the armature 14 is moved toward the yoke 13 against the biasing force of the coil spring 13b by the electromagnetic force generated in the excitation coil 13a, and braking is performed. To release. For example, Patent Documents 1 and 2 disclose electromagnetic brakes having such a structure.

  The electromagnetic clutch is provided with two rotating bodies that are coaxially and relatively rotatable. One armature is provided on one rotating body, and a disk is provided on the other rotating body. By switching the contact and separation between the armature and the disk, this switches the transmission and disconnection of the rotational force between the two rotating bodies, and the operating principle is the same as that of the electromagnetic brake. Description is omitted.

JP 2001-280375 A Japanese Patent Laid-Open No. 11-063049

  However, in the conventional electromagnetic brake described above, when the energization to the exciting coil 13a is cut off, the armature 14 is pushed by the repulsive force of the coil spring 13b and collides with the disk 12, so that an irritating collision sound is generated. If the disk 12 is rotating at this time, a squealing sound is generated due to friction with the armature 14.

  On the other hand, when the energization to the exciting coil 13a is started, the armature 14 collides with the yoke 13, so that a collision sound is also generated in this case. Further, when the armature is not completely separated from the disk, a rubbing sound is generated between the armature and the disk. For this reason, when using an electromagnetic brake in a quiet environment where people are present, such as an elevator brake in an office building, noise countermeasures such as attaching a cushioning material such as rubber to the collision part are required. There is a problem that the score and cost increase.

  The present invention has been made in view of the above-described problems of the prior art, and reduces noise such as a collision sound generated by an armature colliding with a yoke or a disk, a rubbing sound between an armature and a disk, and a squealing sound. It is an object (problem) to provide an electromagnetic brake and an electromagnetic clutch.

  First, in order to solve the above-mentioned problem, an electromagnetic brake according to a first aspect of the present invention includes a disk provided so as to rotate integrally with a braked rotating shaft, a yoke incorporating an exciting coil, and the yoke. The armature made of a magnetic material that is axially movable and non-rotatable is arranged in the axial direction, and the armature is brought into contact with the disk by switching between energization and de-energization, and the position away from the disk In this configuration, switching between braking and releasing with respect to the braked rotating shaft is performed, and at least one member that collides with another member by the switching operation is resonated to reduce the sound generated by the collision of the member. The resonance structure has a large-diameter hole and a small-diameter hole that are continuous in the axial direction, and the small-diameter hole opens on the other member side that collides. Includes, large-diameter hole is characterized in that it comprises an opening only in the small-diameter hole side. In this case, it is desirable that the armature is disposed between the yoke and the disk, and is fixed to the yoke so that the disk is sandwiched between the armature and the plate is provided.

According to the first aspect of the present invention, by providing a resonance structure including a large-diameter hole and a small-diameter hole that are continuous with each other, sound waves generated by collision or friction can be generated by air between the small-diameter hole and the large-diameter hole. Since the one-degree-of-freedom system is resonated and converted into thermal energy, noise can be reduced.
Further, the resonance structure composed of the large-diameter hole and the small-diameter hole can be processed relatively easily, and the number of parts can be reduced and the cost required for manufacturing and assembly can be reduced as compared with the case where the cushioning material is provided.

The resonance structure may include a plurality of types of structures in which the diameter and length of the small diameter hole are different from each other and the diameter and length of the corresponding large diameter hole are different from each other.
According to the configuration of the second aspect, the resonance structures having different natural frequencies are mixed, so that noise including a plurality of frequencies can be effectively reduced.

Further, as described in claim 3, when a plurality of resonance structures are formed on members that collide with other members on both sides in the axial direction, some of the resonance structures have small diameter holes on one side in the axial direction. It opens to the other member side which collides, and another resonance structure may open to the other member side which a small diameter hole collides on the other side of an axial direction.
According to the configuration of the third aspect, by forming the resonance structure in one member, it is possible to obtain an effect of reducing noise generated by collision and friction with the members on both sides.

Furthermore, the resonance structure is formed in at least one member of an armature, a yoke, a disk, and a plate as described in claim 4.
If it is set as the structure of Claim 4, the resonance structure can reduce the noise by the collision and friction of each member in the site | part in which each resonance structure was formed.

Next, an electromagnetic clutch according to the present invention includes a first rotating body, a second rotating body that is coaxial with the first rotating body and capable of rotating relative to the first rotating body, and a shaft relative to the first rotating body. An armature made of a magnetic body that is movable in the direction and rotates integrally, a disk that faces the armature so as to rotate integrally with the second rotating body, and a yoke that incorporates an excitation coil By switching between energizing and de-energizing the exciting coil, the armature is switched between a position where it contacts the disk and a position away from the disk, thereby connecting and disconnecting the first rotating body and the second rotating body. In the switching configuration, a resonance structure for reducing sound generated by the collision of the member is formed on at least one member that collides with another member by the switching operation. Has a large-diameter hole and the small-diameter hole continuous in the axial direction, the small-diameter hole is provided with an opening in the other member side collision, the large-diameter hole is characterized in that it comprises an opening only in the small-diameter hole side.
According to the fifth aspect of the present invention, by providing a resonance structure having a large-diameter hole and a small-diameter hole that are continuous with each other, sound waves generated by collision and friction can be generated by air between the small-diameter hole and the large-diameter hole. Since the one-degree-of-freedom system is resonated and converted into thermal energy, noise can be reduced.
Further, the resonance structure composed of the large-diameter hole and the small-diameter hole can be processed relatively easily, and the number of parts can be reduced and the cost required for manufacturing and assembly can be reduced as compared with the case where the cushioning material is provided.

The resonance structure may include a plurality of types of structures in which the diameter and length of the small-diameter hole are different from each other and the diameter and length of the corresponding large-diameter hole are different from each other.
If it is set as the structure of Claim 6, the resonant structure from which a natural frequency differs will coexist, and the noise which a several frequency coexists can be reduced effectively.

Further, as described in claim 7, when a plurality of resonance structures are formed on members that collide with other members on both sides in the axial direction, some of the resonance structures have small diameter holes on one side in the axial direction. It opens to the other member side which collides, and another resonance structure may open to the other member side which a small diameter hole collides on the other side of an axial direction.
According to the configuration of the seventh aspect, by forming the resonance structure in one member, an effect of reducing noise generated by collision and friction with the members on both sides can be obtained.

Each resonance structure may be formed on at least one member of a disk, a yoke, and an armature as described in claim 8.
According to the configuration of the eighth aspect, the resonance structure can reduce noise caused by the collision and friction of each member at the site where each resonance structure is formed.

  According to the electromagnetic brake and the electromagnetic clutch of the configuration of the present invention, by providing a characteristic resonance structure, a noise such as a collision sound generated when the armature collides with a yoke or a disk, a friction sound between the armature and the disk, and a noise. It is possible to provide an electromagnetic brake and an electromagnetic clutch that can reduce the noise.

  Embodiments of an electromagnetic brake according to the present invention will be described below with reference to the drawings. In the following description, six examples are shown.

1 to 3 show an electromagnetic brake 20A according to a first embodiment of the present invention. 1 is a cross-sectional view in a plane parallel to the braked rotating shaft showing the braking state of the electromagnetic brake 20A, the left side of FIG. 2 is an enlarged view of the main part of FIG. 1, and the right side is a spring equivalent to the resonance structure of FIG. FIG. 3 is an explanatory view of the mass model, and FIG. 3 is a cross-sectional view in a plane parallel to the braked rotating shaft, showing a braking release state of the electromagnetic brake 20A.

  As shown in FIG. 1, the electromagnetic brake 20 </ b> A according to the first embodiment is disposed on a disk 22 provided to rotate integrally with the braked rotating shaft 2 via a spline 21, and on one side of the disk 22. The yoke 23, the armature 24 that is axially movable and non-rotatable between the disk 22 and the yoke 23, and the yoke 23 are fixed to the yoke 23 with the disk 22 and the armature 24 interposed therebetween. Plate 25.

  The yoke 23 is provided with a ring-shaped exciting coil 23a around the axis facing the armature 24, and a coil spring 23b for urging the armature 24 toward the disk 22 side. On the other hand, spacers 25a are attached between the plate 25 and the yoke 23 at, for example, three locations (only one location is shown in the figure) at intervals of 120 degrees. The plate 25 is fixed to the yoke 23 at a predetermined interval by the spacer 25a.

  A lining 22 a that is a friction material is attached to the disk 22 on the outer peripheral side of the surface facing the armature 24 and the surface facing the plate 25. Further, a resonance structure 30 is formed at the position where the lining 22a is affixed to reduce the sound generated when the disk 22 collides with the armature 24. In addition, although the case where the resonance structure 30 was arrange | positioned in two places was shown in FIG. 1, you may form in more places than this.

As shown in the enlarged view on the left side of FIG. 2, the resonance structure 30 includes a small-diameter hole 31 having a length t and a diameter φ ₁ formed in the disk 22, and a length L and a diameter φ formed continuously therewith. It is configured in combination with _two large-diameter holes 32. The large-diameter hole 32 is formed before the lining 22a is attached, and one end is sealed by attaching the lining 22a. As a result, an opening is provided only on the small-diameter hole 31 side. On the other hand, the small-diameter hole 31 communicates with the large-diameter hole 32 and has an opening that penetrates the disk 22 and the lining 22a and is connected to the external space on the armature 24 side.

  The resonance structure 30 configured as described above constitutes a one-degree-of-freedom system in which sound waves generated by collision and friction are made of air between the small-diameter hole 31 and the large-diameter hole 32, which is shown in FIG. This is equivalent to a spring-mass model in which an object of mass m shown on the right is supported by a spring having a spring constant k.

  In the electromagnetic brake 20A of the first embodiment, when the excitation coil 23a is not energized, the armature 24 is pressed against the disk 22 by the urging force of the coil spring 23b as shown in FIG. Apply braking. On the other hand, when the energizing coil 23a is energized, the armature 24 is moved to the yoke 23 side against the urging force of the coil spring 23b by the electromagnetic force generated in the exciting coil 23a, as shown in FIG. To release.

  When such energization is switched, the armature 24 collides with the disk 22 or the yoke 23 to generate a collision sound. However, since the resonance structure 30 formed on the disk 22 absorbs sound such as a collision sound and converts it into thermal energy, the generated noise can be reduced. In the configuration of the first embodiment, since the small-diameter hole 31 of the resonance structure 30 formed in the disk 22 is opened toward the armature 24 side, the energization to the exciting coil 23a is particularly cut off, and the armature 24 is applied to the disk 22. It is possible to reduce a collision sound generated when a collision occurs. Hereinafter, the noise reduction mechanism will be described with reference to FIG. 2 shows an enlarged view of a portion of the upper resonance structure in FIG. 1 taken out and rotated 90 degrees clockwise.

  When noise such as a collision sound, a rubbing sound, and a squealing sound is generated by switching the energization, the sound wave generated on the surface of the disk 22 pushes the air in the small diameter hole 31 to the large diameter hole 32 side. Thereby, since the air in the large diameter hole 32 is compressed, it is pushed back to the small diameter hole 31 again, and the air in the small diameter hole 31 shown in the left side of FIG. 2 is pushed back to the upper side of the lining 22a. By repeating this, resonance is generated, and sound energy is converted into heat energy to reduce noise. The air in the small-diameter hole 31 and the large-diameter hole 32 can be considered equivalent to a one-degree-of-freedom spring-mass model as shown in the right side of FIG. Then, the natural frequency f of this spring-mass model is given by the following equation (1) expressed by equation (1).

In the above equation, c is the velocity of sound (340 m / s), and P is the hole area ratio obtained by φ ₁ ² / φ ₂ ² . If φ ₁ , φ ₂ , t, and L are adjusted so that the frequency of the sound wave having the highest intensity among the sound waves constituting the noise is equal to the natural frequency f obtained by Equation (1), the disk The sound wave generated on the surface of 22 is incident on a system represented by a spring-mass model, and greatly vibrates the air corresponding to the mass by resonance.
Therefore, the energy of the sound incident on this system is converted into thermal energy by the frictional resistance around the small-diameter hole 31, and noise during braking operation can be reduced.

In the first embodiment, a specific design example of the resonance structure 30 is shown.
Lining thickness: t = 1mm
Disc thickness: L = 14mm
Opening ratio: P = 0.1
Diameter of small-diameter hole 31: φ ₁ = 1mm
Diameter of large-diameter hole 32: φ ₂ = √ (φ ₁ ² /P)≒3.2mm
Speed of sound: C = 340m / s
Then, the natural frequency f can be obtained by the following equation shown in Equation 2 when the unit of length is obtained in the MKS unit system.

According to the above design example, the natural frequency f is about 3.4 kHz, which has a significant reduction effect on noise at this frequency.
In other words, the noise generated can be effectively reduced by frequency analysis of collision sound, friction sound, and the like, and designing the resonance structure 30 according to the frequency having the highest intensity.
In addition, by including a plurality of types of resonance structures in which the diameter and length of the small-diameter hole 31 are different from each other and the diameter and length of the corresponding large-diameter hole 32 are different from each other, it is possible to reduce sound having a plurality of high frequencies. You can also.

FIG. 4 is a cross-sectional view in a plane parallel to the braked rotating shaft showing the braking state of the electromagnetic brake 20B according to the second embodiment of the present invention.
In the electromagnetic brake 20B of the second embodiment, the direction of the resonance structure 30 formed on the disk 22 is different from that of the first embodiment.

That is, in the first embodiment, the large-diameter hole 32 of the resonance structure 30 is arranged on the plate 25 side, and the small-diameter hole 31 communicating with the large-diameter hole 32 opens toward the armature 24 side. Then, the large-diameter hole 32 of the resonance structure 30 is disposed on the armature 24 side, and the small-diameter hole 31 communicating with the large-diameter hole 32 opens toward the plate 25 side.
Therefore, in the configuration of the second embodiment, it is possible to effectively reduce the collision sound generated when the disk 22 pushed by the armature 24 collides with the plate 25 by cutting off the energization to the exciting coil 23a.

  Since other configurations are the same as those of the first embodiment, the same reference numerals are given to the same members, and duplicate descriptions are omitted.

FIG. 5 is a cross-sectional view in a plane parallel to the braked rotating shaft showing the braking state of the electromagnetic brake 20C according to the third embodiment of the present invention.
In the electromagnetic brake 20C of the third embodiment, the resonance structure 30 is composed of the small-diameter hole 31 and the large-diameter hole 32, which is the same as the first and second embodiments, but the resonance structure formed in the disk 22 The direction of 30 is different from the first and second embodiments as follows.

That is, in the first and second embodiments, the resonance structure 30 has the small-diameter hole 31 opened toward either the armature 24 side or the plate 25 side, but in the third embodiment, some of the resonance structures 30 have a small diameter. The hole 31 opens toward the armature 24 side, and the other resonance structure 30 has the small-diameter hole 31 opened toward the plate 25 side.
Therefore, in the configuration of the third embodiment, the energization to the exciting coil 23 a is cut off, and the collision sound generated when the armature 24 collides with the disk 22 and the disk 22 pushed by the armature 24 collides with the plate 25. Any of the collision sounds generated in the above can be effectively reduced at the site of the collision.

  Since other configurations are the same as those of the first embodiment, the same reference numerals are given to the same members, and duplicate descriptions are omitted.

  FIG. 6 is a partial cross-sectional view in a plane parallel to the braked rotating shaft showing the braking state of the electromagnetic brake 20D according to the fourth embodiment of the present invention. Since the basic structure is common to the first to third embodiments, only the upper side from the central axis is shown in FIG.

In each of the first to third embodiments, the resonance structure 30 is formed on the disk 22. However, the fourth embodiment is different from the first to third embodiments in that the resonance structure 30 is formed on the yoke 23. That is, in the electromagnetic brake 20D according to the fourth embodiment, a hole penetrating a part of the yoke 23 in the axial direction is formed, a small diameter hole 31 is formed on the side opened to the armature 24 side, and a large diameter is continuously formed on the left side in the drawing. A hole 32 is formed.
Further, the length of the large-diameter hole 32 is secured by inserting a rod-shaped plug member 23c having a predetermined length from the left side in the drawing.
Therefore, in the configuration of the fourth embodiment, it is possible to effectively reduce the collision sound generated when the energization of the exciting coil 23 a is started and the armature 24 collides with the yoke 23.

  Since other configurations are the same as those of the first embodiment, the same reference numerals are given to the same members, and duplicate descriptions are omitted.

  FIG. 7 is a partial cross-sectional view in a plane parallel to the braked rotating shaft, showing a braking state of the electromagnetic brake 20E according to the fifth embodiment of the present invention. Since the basic structure is common to the first to third embodiments, only the upper side from the central axis is shown in FIG.

In the fifth embodiment, the resonance structure 30 is formed in the armature 24. That is, in the electromagnetic brake 20 </ b> E according to the fifth embodiment, the resonance structure 30 having two different directions is formed in a part of the armature 24.
Since the lining is not attached to the armature 24, one end of the large-diameter hole cannot be closed with the lining as in the first embodiment. Therefore, the thick plate 24a around the armature 24 and the thin plates 24b on both sides, 24c is divided into three parts.
That is, the large-diameter hole 32 is first formed in the thick plate 24a, and then the thin plates 24b and 24c are pasted to form the small-diameter hole 31 from different sides.

  In this configuration, since the small-diameter hole 31 of one resonance structure 30 opens to the yoke 23 side and the small-diameter hole 31 of the other resonance structure 30 opens to the disk 22 side, energization to the excitation coil 23a is started. Both the collision sound generated when the armature 24 collides with the yoke 23 and the collision sound generated when the armature 24 collides with the disk 22 by cutting off the current can be effectively reduced.

  Since other configurations are the same as those of the first embodiment, the same reference numerals are given to the same members, and duplicate descriptions are omitted.

  FIG. 8 is a partial cross-sectional view in a plane parallel to the braked rotating shaft showing the braking state of the electromagnetic brake 20F according to the sixth embodiment of the present invention. Since the basic structure is common to the first to third embodiments, only the upper side from the central axis is shown in FIG.

In the sixth embodiment, the resonance structure 30 is formed on the plate 25.
That is, in the electromagnetic brake 20F according to the sixth embodiment, the resonance structure 30 in which the small diameter hole 31 is opened to the disk 22 side is formed in a part of the plate 25. In the sixth embodiment, the plate 25 is divided into a thick plate 25b and a thin plate 25c. First, the large-diameter hole 32 and the small-diameter hole 31 are formed in the thick plate 25 b, and then the thin plate 25 c is attached to close one end of the large-diameter hole 32.

  In this configuration, since the small-diameter hole 31 of the resonance structure 30 is open to the disk 22 side, it is generated when the disk 22 pressed by the armature 24 with the energization to the excitation coil 23 a collides with the plate 25. The collision sound can be effectively reduced.

  Since other configurations are the same as those of the first embodiment, the same reference numerals are given to the same members, and duplicate descriptions are omitted.

Although only the electromagnetic brake has been described in the above embodiments, the present invention can also be applied to an electromagnetic clutch that operates on the same operation principle that performs a clutch operation instead of a brake operation.
What is necessary is just to comprise as a structure for this in Claims 5-8.

It is sectional drawing in the surface parallel to a to-be-brake rotation axis | shaft which shows the braking state of the electromagnetic brake concerning Example 1 of this invention. The left side is an enlarged view of the main part of FIG. 1, and the right side is an explanatory view of a spring-mass model equivalent to the resonance structure of FIG. It is sectional drawing in the surface parallel to a to-be-brake rotation axis | shaft which shows the braking cancellation | release state of the electromagnetic brake concerning Example 1. FIG. It is sectional drawing in the surface parallel to a to-be-brake rotation axis | shaft which shows the braking state of the electromagnetic brake concerning Example 2 of this invention. It is sectional drawing in the surface parallel to a to-be-brake rotation axis | shaft which shows the braking state of the electromagnetic brake concerning Example 3 of this invention. It is half sectional drawing in the surface parallel to a to-be-brake rotation axis | shaft which shows the braking state of the electromagnetic brake concerning Example 4 of this invention. It is half sectional drawing in the surface parallel to the to-be-brake rotation axis | shaft which shows the braking state of the electromagnetic brake concerning Example 5 of this invention. It is half sectional drawing in the surface parallel to a to-be-brake rotation axis | shaft which shows the braking state of the electromagnetic brake concerning Example 6 of this invention. It is sectional drawing in the surface parallel to a to-be-brake rotation axis | shaft which shows the braking state of the conventional electromagnetic brake. It is sectional drawing in the surface parallel to a to-be-brake rotation axis | shaft which shows the braking cancellation | release state of the conventional electromagnetic brake.

Explanation of symbols

2: Braked rotating shaft 20A, 20B, 20C, 20D, 20E, 20F: Electromagnetic brake 21: Spline 22: Disc 23: Yoke 23a: Excitation coil 23b: Coil spring 24: Armature 25: Plate 30: Resonant structure 31: Small diameter Hole 32: Large diameter hole

Claims (8)

A disk provided to rotate integrally with the braked rotating shaft, a yoke containing an exciting coil, and an armature made of a magnetic material that is movable in the axial direction and cannot rotate with respect to the yoke are provided in the axial direction. By switching between energization and non-energization for the exciting coil, the armature is switched between a position in contact with the disk and a position away from the disk, thereby braking and releasing the braked rotating shaft. In switching electromagnetic brake,
At least one member that collides with another member by the switching operation is formed with a resonance structure for reducing sound generated by the collision of the member, and the resonance structure includes a large-diameter hole and a small-diameter hole that are continuous in the axial direction. The small-diameter hole has an opening on the other member side that collides, and the large-diameter hole has an opening only on the small-diameter hole side.   2. The electromagnetic brake according to claim 1, wherein the resonance structure includes a plurality of types of structures in which a diameter and a length of the small-diameter hole are different from each other, and a diameter and a length of the corresponding large-diameter hole are different from each other. .   A plurality of the resonance structures are formed on members that collide with other members on both sides in the axial direction, and some of the resonance structures open on the other member side where the small-diameter holes collide on one side in the axial direction. The electromagnetic brake according to claim 1, wherein the small-diameter hole is opened on the other member side that collides with the other side in the axial direction.   4. The electromagnetic brake according to claim 1, wherein the resonance structure is formed on at least one of the armature, the yoke, the disk, and the plate. 5. A first rotating body, a second rotating body that is coaxially rotatable relative to the first rotating body, and a magnetic body that is movable in the axial direction and rotates integrally with the first rotating body. An armature, a disk provided facing the armature so as to rotate integrally with the second rotating body, and a yoke containing an excitation coil; and switching the energization and de-energization to the excitation coil In an electromagnetic clutch that switches between a position where the armature contacts the disk and a position away from the disk, thereby switching between connection and disconnection of the first rotating body and the second rotating body,
At least one member that collides with another member by the switching operation is formed with a resonance structure for reducing sound generated by the collision of the member, and the resonance structure includes a large-diameter hole and a small-diameter hole that are continuous in the axial direction. The small diameter hole has an opening on the side of the other member that collides, and the large diameter hole has an opening only on the small diameter hole side.   6. The electromagnetic clutch according to claim 5, wherein the resonance structure includes a plurality of types of structures in which the diameter and length of the small diameter hole are different from each other and the diameter and length of the corresponding large diameter hole are different from each other. .   A plurality of the resonance structures are formed on members that collide with other members on both sides in the axial direction, and some of the resonance structures open on the other member side where the small-diameter holes collide on one side in the axial direction. The electromagnetic clutch according to claim 5, wherein the small-diameter hole is opened on the other member side that collides with the other side in the axial direction.   The electromagnetic clutch according to claim 5, wherein the resonance structure is formed on at least one member of the disk, the yoke, and the armature.

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