Torsion damper

Abstract

The vibration suppression unit suppresses the emission of sound waves in the axial direction. [Solution] The torsional damper comprises a vibration-suppressing section and an elastic layer. The vibration-suppressing section includes a hub fixed to a shaft member, an annular vibration ring surrounding the hub, and an annular damper section interposed between the hub and the vibration ring. The elastic layer is in close contact with at least a portion of one axial end face of the vibration-suppressing section.

Description

Technical Field

[0004] , ,

[0005] , ,

[0001] The present disclosure relates to a torsional damper.

Background Art

[0002] For example, torsional dampers have been conventionally proposed to reduce vibrations generated in shaft members such as crankshafts in internal combustion engines. For example, Patent Document 1 discloses a configuration for adjusting the natural frequency of a torsional damper by means of an embedded portion provided at a specific location in the circumferential direction of a vibration ring.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When vibrations are propagated from a shaft member to a torsional damper, the vibrations are imparted from one end face of the torsional damper in the axial direction to the surrounding air. Therefore, sound waves are radiated axially from the torsional damper. From the viewpoint of reducing noise and the like, the radiation of sound waves caused by the vibrations of the torsional damper should be reduced. In view of the above circumstances, one aspect of the present disclosure aims to suppress the radiation of sound waves directed axially from the torsional damper.

Means for Solving the Problems

[0005] To solve the above problems, a torsional damper according to one aspect of the present disclosure is a torsional damper comprising a vibration suppression portion and an elastic layer, wherein the vibration suppression portion includes a hub fixed to a shaft member, an annular vibration ring surrounding the hub, and an annular damper portion interposed between the hub and the vibration ring, and the elastic layer is in close contact with at least a portion of one axial end face of the vibration suppression portion. [Brief explanation of the drawing]

[0006] [Figure 1] These are a plan view and a cross-sectional view of the torsional damper in the first embodiment. [Figure 2] This graph shows the vibration propagation characteristics from the vibration suppression section to the elastic layer. [Figure 3] These are a plan view and a cross-sectional view of the torsional damper in the second embodiment. [Figure 4] These are a plan view and a cross-sectional view of a torsional damper in a modified example. [Modes for carrying out the invention]

[0007] The embodiments for implementing this disclosure will be described with reference to the drawings. Note that the dimensions and scale of the elements in each drawing may differ from those of the actual product. Furthermore, the embodiments described below are illustrative examples of embodiments that may be envisioned when implementing this disclosure. Therefore, the scope of this disclosure is not limited to the embodiments exemplified below.

[0008] A: First Embodiment Figure 1 is a plan view and a cross-sectional view of a torsional vibration damper (TVD) 100 in the first embodiment. The torsional damper 100 of the first embodiment is used, for example, as a damper pulley in an internal combustion engine such as an engine. An internal combustion engine is equipped with a shaft member 200 (crankshaft) that rotates around a rotation axis C. The torsional damper 100 is a dynamic vibration absorber that reduces vibrations (specifically torsional vibrations) generated in the shaft member 200.

[0009] In the following explanation, the direction of the rotation axis C will be referred to as the "axial direction." The axial direction is distinguished into the Z1 direction and the Z2 direction. The Z1 direction is one direction along the rotation axis C, and the Z2 direction is the opposite direction to the Z1 direction. For example, the internal combustion engine is located in the Z2 direction of the torsional damper 100. That is, the Z1 direction is the opposite direction from the internal combustion engine when viewed from the torsional damper 100.

[0010] Furthermore, the direction of the circumference of a virtual circle of arbitrary diameter centered on the axis of rotation C is referred to as the "circumferential direction," and the direction of the radius of the virtual circle is referred to as the "radial direction." In the radial direction, the direction opposite to the axis of rotation C is sometimes referred to as the "outside," and the direction toward the axis of rotation C in the radial direction is sometimes referred to as the "inside."

[0011] As illustrated in Figure 1, the torsional damper 100 of the first embodiment comprises a vibration suppression section 11 and an elastic layer 12a. The vibration suppression section 11 functions as a dynamic vibration absorber that reduces vibration (specifically torsional vibration) of the shaft member 200. Specifically, the vibration suppression section 11 comprises a hub 20, a vibration ring 30, and a damper section 40.

[0012] The hub 20 is a structure fixed to the shaft member 200 and is made of a material with higher rigidity than the elastic layer 12a. Specifically, the hub 20 is made of a metal material, for example. Examples of metal materials used for the hub 20 include gray cast iron, spheroidal graphite cast iron, stainless steel, SPCC (Steel Plate Cold Commercial), or SPHC (Steel Plate Hot Commercial). In the first embodiment, the hub 20 is a structure in which the boss portion 21, the rim portion 22, and the connecting portion 23 are integrally formed.

[0013] The boss portion 21 is a cylindrical part fixed to the shaft member 200. A keyway 27 is formed on the inner circumferential surface of the boss portion 21, running in the axial direction. The keyway 27 is a groove of a predetermined width that fits onto a key protruding from the outer circumferential surface of the shaft member 200. The rim portion 22 is an annular part that surrounds the boss portion 21 and is installed coaxially with the boss portion 21.

[0014] The connecting portion 23 is the part that connects the boss portion 21 and the rim portion 22. In the first embodiment, the connecting portion 23 is composed of a plurality of stay portions 24. The plurality of stay portions 24 are arranged at equal intervals along the circumferential direction. Each stay portion 24 is a spoke that extends radially from the outer circumferential surface of the boss portion 21 to the inner circumferential surface of the rim portion 22. Each stay portion 24 is a flat plate-like portion that includes a first surface Sa1 and a second surface Sa2. The first surface Sa1 is an end face that faces the Z1 direction in the axial direction. The first surface Sa1 can also be described as the surface that faces away from the internal combustion engine. The second surface Sa2 is an end face that faces the Z2 direction in the axial direction. The second surface Sa2 can also be described as the surface that faces the internal combustion engine. The connecting portion 23 can also be described as a plate-like member in which a plurality of openings 25 corresponding to the spacing between adjacent stay portions 24 in the circumferential direction are formed.

[0015] The vibrating ring 30 is an annular mass that surrounds the hub 20 and is installed coaxially with the hub 20. The outer circumferential surface of the rim portion 22 and the inner circumferential surface of the vibrating ring 30 face each other with an annular gap between them. Multiple pulley grooves 31 are formed on the outer circumferential surface of the vibrating ring 30. The multiple pulley grooves 31 are V-shaped grooves for winding an endless belt that transmits the rotational torque of the shaft member 200 to an external mechanism. Note that the multiple pulley grooves 31 may be omitted.

[0016] The damper portion 40 is an annular elastic body interposed between the hub 20 and the vibration ring 30. Specifically, the inner circumferential surface of the damper portion 40 is in close contact with the outer circumferential surface of the rim portion 22, and the outer circumferential surface of the damper portion 40 is in close contact with the inner circumferential surface of the vibration ring 30. In other words, the damper portion 40 is fitted into the gap between the hub 20 and the vibration ring 30. As can be understood from the above explanation, the hub 20 and the vibration ring 30 are elastically connected via the damper portion 40.

[0017] The damper portion 40 is formed of an elastic material such as a rubber material. Examples of the rubber material used for the damper portion 40 include various rubber materials such as chloroprene rubber (CR), silicone rubber (SR), acrylic rubber (ACM), urethane rubber (U), polyurethane rubber (PUR), vinyl methyl silicone rubber (VMQ), ethylene propylene diene rubber (EPDM), or fluororubber (FKM).

[0018] The elastic layer 12a is a film body that covers the first surface Sa1 of each stay portion 24 (i.e., the connecting portion 23) of the vibration suppressing portion 11. The elastic layer 12a adheres to the first surface Sa1 of each stay portion 24. Specifically, the elastic layer 12a of the first embodiment covers the entire area of the first surface Sa1 of each stay portion 24. The thickness of the elastic layer 12a is less than the thickness of the damper portion 40. On the other hand, the elastic layer 12a is not formed on the second surface Sa2 of each stay portion 24.

[0019] The elastic layer 12a is formed of an elastic material such as a rubber material that is more flexible than the connecting portion 23, for example. Examples of the rubber material used for the damper portion 40 include various rubber materials such as chloroprene rubber (CR), silicone rubber (SR), acrylic rubber (ACM), urethane rubber (U), polyurethane rubber (PUR), vinyl methyl silicone rubber (VMQ), ethylene propylene diene rubber (EPDM), or fluororubber (FKM). Note that the damper portion 40 and the elastic layer 12a may be formed of the same type of material or different types of materials.

[0020] The method of forming the elastic layer 12a on each stay portion 24 is arbitrary. For example, an elastic layer 12a is formed by joining an elastic sheet formed in the same planar shape as the stay portion 24 to the first surface Sa1 of the stay portion 24 with an adhesive. The elastic layer 12a is composed of a laminate of the elastic sheet and the adhesive. Also, the elastic layer 12a may be formed by vulcanizing adhesion (rubber baking) of a rubber material. Specifically, a fluid elastic material is injected into a mold in which the hub 20 and the vibration ring 30 are installed, heated and pressurized, and after the elastic material is cured, the mold is removed to form the elastic layer 12a.

[0021] As described above, in the first embodiment, the elastic layer 12a is formed on the first surface Sa1 of each stay portion 24 in the vibration suppression portion 11. Since the vibration propagated from the shaft member 200 to the stay portion 24 is absorbed by the elastic layer 12a, the vibration propagated from the first surface Sa1 of each stay portion 24 to the air is reduced. Therefore, according to the first embodiment, the radiation of the sound wave in the Z1 direction from the first surface Sa1 of the connecting portion 23 (each stay portion 24) can be suppressed. That is, it is possible to reduce the noise caused by the vibration of the shaft member 200.

[0022] FIG. 2 is a graph showing the propagation characteristics of the vibration generated in the vibration suppression portion 11. The horizontal axis in FIG. 2 is the vibration frequency ratio R. The vibration frequency ratio R (hereinafter referred to as "vibration frequency ratio Ra") in the first embodiment is the ratio of the resonance frequency (excitation frequency) of the excitation source to the resonance frequency Fa2 of the elastic layer 12a. The excitation source is an element that imparts vibration to the elastic layer 12a. In the first embodiment, the excitation source that imparts vibration to the elastic layer 12a is the hub 20. That is, the vibration frequency ratio Ra in the first embodiment is the ratio of the resonance frequency Fa1 of the hub 20 in the axial direction to the resonance frequency Fa2 of the elastic layer 12a in the axial direction (Ra = Fa1 / Fa2).

[0023] The vertical axis in FIG. 2 is the vibration transmission rate Q. The vibration transmission rate Q is the ratio of the intensity (for example, amplitude) of the vibration at the vibration transmission destination to the intensity (for example, amplitude) of the vibration at the excitation source. When the vibration transmission rate Q exceeds 1, the vibration at the vibration transmission destination is amplified compared to the vibration of the excitation source (that is, resonance), and when the vibration transmission rate Q is less than 1, the vibration at the vibration transmission destination is attenuated compared to the vibration of the excitation source.

[0024] As understood from FIG. 2, when the vibration frequency ratio Ra is √2 or more, the vibration transmission rate Q tends to be less than 1. In consideration of the above tendency, in the first embodiment, the vibration frequency ratio Ra (Ra = Fa1 / Fa2), which is the ratio of the resonance frequency Fa1 of the hub 20 to the resonance frequency Fa2 of the elastic layer 12a, is √2 or more. That is, the resonance frequency Fa2 of the elastic layer 12a and the resonance frequency Fa1 of the hub 20 are selected so that the vibration frequency ratio Ra is √2 or more.

[0025] For example, consider a case where the resonant frequency Fa1 of the hub 20 in the axial direction is between 2kHz and 6kHz. The resonant frequency Fa2 of the elastic layer 12a is set to 1.41kHz (=2 / √2) or less so that the frequency ratio Ra is √2 or more with respect to the resonant frequency Fa1. That is, the material or dimensions (e.g., thickness) of the elastic layer 12a are selected so that the resonant frequency Fa2 is 1.41kHz or less.

[0026] As illustrated above, in the first embodiment, the vibration transmission coefficient Q in the axial direction from the connecting portion 23 of the vibration suppression unit 11 is suppressed to 1 or less. Therefore, sound waves radiated from the connecting portion 23 in the Z1 direction can be effectively suppressed.

[0027] B: Second Embodiment A second embodiment will now be described. For elements whose function is the same as in the first embodiment, the same reference numerals as in the first embodiment will be used, and detailed descriptions of each will be omitted as appropriate.

[0028] Figure 3 is a plan view and a cross-sectional view of the torsional damper 100 in the second embodiment. As illustrated in Figure 3, the torsional damper 100 of the second embodiment comprises a vibration suppression section 11 and an elastic layer 12b. The configuration of the vibration suppression section 11 in the second embodiment is the same as in the first embodiment. That is, the second embodiment is a configuration in which the elastic layer 12a in the first embodiment is replaced with an elastic layer 12b.

[0029] As illustrated in Figure 3, the vibrating ring 30 includes a first surface Sb1 and a second surface Sb2. The first surface Sb1 is an end face facing the Z1 direction in the axial direction. The first surface Sb1 can also be described as the surface facing away from the internal combustion engine. The second surface Sb2 is an end face facing the Z2 direction in the axial direction. The second surface Sb2 can also be described as the surface facing the internal combustion engine.

[0030] The elastic layer 12b of the second embodiment is a film that covers the first surface Sb1 of the vibration ring 30 within the vibration damping section 11. The elastic layer 12b adheres closely to the first surface Sb1 of the vibration ring 30. Specifically, the elastic layer 12b of the second embodiment is formed in an annular shape that covers the entire area of ​​the first surface Sb1 of the vibration ring 30. The thickness of the elastic layer 12b is less than the thickness of the damper section 40. The elastic layer 12b is formed from an elastic material such as a rubber material that is more flexible than the vibration ring 30. The material and manufacturing method of the elastic layer 12b are the same as those of the elastic layer 12a of the first embodiment. On the other hand, the elastic layer 12b is not formed on the second surface Sb2 of the vibration ring 30.

[0031] As described above, in the second embodiment, an elastic layer 12b is formed on the first surface Sb1 of the vibration ring 30 within the vibration suppression section 11. Since vibrations propagated from the shaft member 200 to the vibration ring 30 are absorbed by the elastic layer 12b, vibrations propagated from the first surface Sb1 of the vibration ring 30 into the air are reduced. Therefore, according to the second embodiment, the radiation of sound waves directed in the Z1 direction from the first surface Sb1 of the vibration ring 30 can be suppressed. In other words, in the second embodiment as in the first embodiment, it is possible to reduce noise caused by vibrations of the shaft member 200.

[0032] In the second embodiment, the vibration propagation characteristics from the vibration suppression unit 11 to the elastic layer 12b will be explained with reference to Figure 2. In the second embodiment, the frequency ratio R (hereinafter referred to as "frequency ratio Rb") is the ratio of the resonance frequency (excitation frequency) of the excitation source to the resonance frequency Fb2 of the elastic layer 12b. In the second embodiment, the excitation source that imparts vibration to the elastic layer 12b is the vibration ring 30. That is, in the second embodiment, the frequency ratio Rb is the ratio of the resonance frequency Fb1 of the vibration ring 30 in the axial direction to the resonance frequency Fb2 of the elastic layer 12b in the axial direction (Rb = Fb1 / Fb2).

[0033] As mentioned above with reference to Figure 2, when the frequency ratio Rb is √2 or greater, the vibration transmittance Q tends to be less than 1. Taking this tendency into consideration, in the second embodiment, the frequency ratio Rb (Rb = Fb1 / Fb2), which is the ratio of the resonance frequency Fb1 of the vibrating ring 30 to the resonance frequency Fb2 of the elastic layer 12b, is √2 or greater. That is, the resonance frequency Fb2 of the elastic layer 12b and the resonance frequency Fb1 of the vibrating ring 30 are selected so that the frequency ratio Rb is √2 or greater.

[0034] For example, consider a case where the resonant frequency Fa1 of the hub 20 in the axial direction is between 400 Hz and 800 Hz. The resonant frequency Fb2 of the elastic layer 12b is set to 280 Hz (= 400 / √2) or less so that the frequency ratio Rb is √2 or more with respect to the resonant frequency Fb1. That is, the material or dimensions (e.g., thickness) of the elastic layer 12b are selected so that the resonant frequency Fb2 is 280 Hz or less.

[0035] As illustrated above, in the second embodiment, the vibration transmission coefficient Q in the axial direction from the vibration ring 30 of the vibration suppression unit 11 is suppressed to 1 or less. Therefore, sound waves radiated from the vibration ring 30 in the Z1 direction can be effectively suppressed.

[0036] C: Variant The following are examples of specific modifications that may be added to the embodiments exemplified above. Two or more embodiments may be arbitrarily selected from the following examples and merged as appropriate, provided they do not contradict each other.

[0037] (1) In the first embodiment, an elastic layer 12a is formed on the first surface Sa1 of the connecting portion 23, and in the second embodiment, an elastic layer 12b is formed on the first surface Sb1 of the vibration ring 30. A configuration in which an elastic layer 12a is formed on the first surface Sa1 of the connecting portion 23 and an elastic layer 12b is formed on the first surface Sb1 of the vibration ring 30 is also conceivable. That is, multiple elastic layers 12 (12a, 12b) may be formed at different positions on the vibration suppression portion 11.

[0038] The elastic layer 12a may be formed on only a portion of the first surface Sa1 of each stay portion 24. That is, the elastic layer 12a is formed so as to be in close contact with at least a portion of the end face in the Z1 direction of the connecting portion 23. Alternatively, the elastic layer 12b may be formed on only a portion of the first surface Sb1 of the vibrating ring 30. That is, the elastic layer 12b is formed so as to be in close contact with at least a portion of the end face in the Z1 direction of the vibrating ring 30.

[0039] The region in the vibration-dampening section 11 where the elastic layer 12 is formed is not limited to the examples above. For example, the elastic layer 12 may be formed on at least a portion of the end face in the Z1 direction of the vibration-dampening section 11. The end face in the Z1 direction of the vibration-dampening section 11 is a surface of the vibration-dampening section 11 that faces the Z1 direction, and includes, for example, the surface in the Z1 direction of the hub 20 (boss section 21, rim section 22, connecting section 23), the surface in the Z1 direction of the vibration ring 30, and the surface in the Z1 direction of the damper section 40. For example, the elastic layer 12 may be formed on the surface in the Z1 direction of the boss section 21 or the rim section 22.

[0040] Furthermore, in the above-described embodiments, an example was given in which the elastic layer 12 is formed on the end face in the Z1 direction of the vibration suppression part 11. However, the elastic layer 12 may also be formed on the end face in the Z2 direction of the vibration suppression part 11. For example, a configuration in which the elastic layer 12 is formed on the end face in the Z2 direction of the vibration suppression part 11, or a configuration in which the elastic layer 12 is formed on both the end face in the Z1 direction and the end face in the Z2 direction of the vibration suppression part 11.

[0041] (2) In the embodiments described above, the connecting portion 23 is shown as being composed of a plurality of stay portions 24, but the shape of the connecting portion 23 is not limited to the above embodiments. For example, as illustrated in Figure 4, the connecting portion 23 may be formed in an annular shape. That is, the opening 25 illustrated in the first embodiment may be omitted. In the embodiment in which the connecting portion 23 is formed in an annular shape, an annular elastic layer 12a may be formed that covers the entire area of ​​the first surface Sa1 of the connecting portion 23, as illustrated in Figure 4, or an elastic layer 12a of any shape may be formed that covers a part of the first surface Sa1 of the connecting portion 23.

[0042] D: Note From the forms exemplified above, the following configuration can be understood, for example.

[0043] A torsional damper according to one aspect of the present disclosure (Aspect 1) is a torsional damper comprising a vibration suppression portion and an elastic layer, wherein the vibration suppression portion includes a hub fixed to a shaft member, an annular vibration ring surrounding the hub, and an annular damper portion interposed between the hub and the vibration ring, and the elastic layer is in close contact with at least a portion of one axial end face of the vibration suppression portion. In the above aspect, since the vibration of one axial end face of the vibration suppression portion is absorbed by the elastic layer, vibrations propagated from the vibration suppression portion into the air are reduced. Therefore, the radiation of sound waves axially from the vibration suppression portion can be suppressed.

[0044] In a specific example of Embodiment 1 (Embodiment 2), the hub includes a boss portion fixed to the shaft member, a rim portion surrounding the boss portion, and a connecting portion connecting the boss portion and the rim portion, and the elastic layer is in close contact with at least a portion of one end face of the connecting portion in the axial direction. According to the above embodiment, the vibration suppression portion can suppress the emission of sound waves in the axial direction from the end face of the connecting portion constituting the hub by the elastic layer.

[0045] In a specific example of Embodiment 2 (Embodiment 3), the frequency ratio R (R=Fa1 / Fa2), which is the ratio of the resonant frequency Fa1 of the hub in the axial direction to the resonant frequency Fa2 of the elastic layer in the axial direction, is √2 or greater. According to the above embodiment, by setting the frequency ratio R to √2 or greater, the axial vibration transmission coefficient from the connecting portion of the vibration suppression unit to the elastic layer is suppressed to 1 or less. Therefore, sound waves radiated from the connecting portion can be effectively suppressed.

[0046] In a specific example of Embodiment 2 or Embodiment 3 (Embodiment 3), the resonant frequency Fa1 is 2 kHz or higher, and the resonant frequency Fa2 is 1.41 kHz or lower. According to the above embodiment, the axial vibration transmission coefficient from the connecting portion of the vibration suppression unit to the elastic layer is suppressed to 1 or less. Therefore, sound waves radiated from the connecting portion can be effectively suppressed.

[0047] In any specific example of Embodiments 1 to 4 (Embodiment 5), the elastic layer is in close contact with at least a portion of one end face of the vibration ring in the axial direction. According to the above embodiments, the vibration suppression portion can suppress the radiation of sound waves in the axial direction from the end face of the vibration ring by the elastic layer.

[0048] In a specific example of Embodiment 5 (Embodiment 6), the frequency ratio Rb (Rb = Fb1 / Fb2), which is the ratio of the resonant frequency Fb1 of the vibrating ring in the axial direction to the resonant frequency Fb2 of the elastic layer in the axial direction, is √2 or greater. According to the above embodiment, by setting the frequency ratio R to √2 or greater, the vibration transmission coefficient from the vibrating ring in the axial direction is suppressed to 1 or less. Therefore, sound waves radiated from the vibrating ring can be effectively suppressed.

[0049] In a specific example of Embodiment 5 or Embodiment 6 (Embodiment 7), the resonant frequency Fb1 is 400 Hz or higher, and the resonant frequency Fb2 is 280 Hz or lower. According to the above embodiments, the vibration transmission coefficient from the vibrating ring in the axial direction is suppressed to 1 or less, so that sound waves radiated from the vibrating ring can be effectively suppressed. [Explanation of Symbols]

[0050] 100... Torsional damper, 200... Shaft member, 11... Vibration suppression part, 12a, 12b... Elastic layer, 20... Hub, 21... Boss part, 22... Rim part, 23... Connecting part, 24... Stay part, 25... Opening, 27... Keyway, 30... Vibration ring, 31... Pulley groove, 40... Damper part.

Claims

1. A torsional damper comprising a vibration suppression section and an elastic layer, The vibration suppression unit is A hub fixed to the shaft member, The annular vibrating ring surrounding the hub, It includes an annular damper portion interposed between the hub and the vibration ring, The aforementioned elastic layer is The vibration suppression portion is in close contact with at least a portion of one end face in the axial direction. Torsional damper.

2. The aforementioned hub is A boss portion fixed to the shaft member, The rim portion surrounding the boss portion, It includes a connecting portion that connects the boss portion and the rim portion, The aforementioned elastic layer is At least a portion of one end face in the axial direction of the aforementioned connecting portion is in close contact with it. A torsional damper according to claim 1.

3. The frequency ratio R (R = Fa1 / Fa2), which is the ratio of the resonant frequency Fa1 of the hub in the axial direction to the resonant frequency Fa2 of the elastic layer in the axial direction, is √2 or greater. A torsional damper according to claim 2.

4. The aforementioned resonant frequency Fa1 is 2 kHz or higher. The aforementioned resonant frequency Fa2 is 1.41 kHz or less. A torsional damper according to claim 2.

5. The aforementioned elastic layer is At least a portion of one end face in the axial direction of the aforementioned vibrating ring is in close contact with A torsional damper according to claim 1.

6. The frequency ratio Rb (Rb = Fb1 / Fb2), which is the ratio of the resonant frequency Fb1 of the vibrating ring in the axial direction to the resonant frequency Fb2 of the elastic layer in the axial direction, is √2 or greater. A torsional damper according to claim 5.

7. The aforementioned resonant frequency Fb1 is 400 Hz or higher. The aforementioned resonant frequency Fb2 is 280 Hz or less. A torsional damper according to claim 5.

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