JP2007177851A - Viscous damper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively manufacture a viscous damper capable of highly accurately setting a clearance for viscous liquid. <P>SOLUTION: This viscous damper 11 has a case 12 mounted to a rotating shaft and an inertial mass body 20 incorporated in a storage chamber 15 of the case 12, and the clearance formed by the outer face of the inertial mass body 20 and the inner face of the case 12 is filled with the viscous fluid 21. The inertial mass body 20 has a metallic annular inertia ring 22 and a coating layer 24 made of a resin material and provided on the outer face of the inertia ring 22, and the outer face of the inertia ring 22 is coated with the coating layer 24. Since the inertia ring 22 is arranged inside a resin forming mold to form the coating layer 24, a dimension error of the inertia ring 22 can be absorbed by the coating layer 24. As a result, the inexpensive viscous damper 11 having the highly accurate clearance can be obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a viscous damper that is mounted on a rotating shaft such as a crankshaft of an engine and reduces torsional vibration generated on the rotating shaft.

  For example, in the case of rotating shafts that generate large torsional vibrations such as crankshafts and camshafts of large diesel engines, viscous dampers that use the vibration damping characteristics of viscous liquids are often used as torsional dampers to reduce the torsional vibrations. It is done.

  The viscous damper includes a case that is fixed to the rotating shaft and rotates together with the rotating shaft, an annular inertia mass body that is incorporated in an annular accommodating chamber provided in the case so as to be relatively rotatable with respect to the case, an inner surface of the case, and an inertia mass Rotation that occurs in an inertial mass body and an internal combustion engine, etc., that tries to rotate at a constant speed according to the rotation of the rotating shaft, and has a viscous liquid such as silicone oil filled in the clearance formed by the outer surface of the body A differential is generated between the rotating shaft that vibrates due to pulsation, that is, the case, and the torsional vibration of the rotating shaft is reduced by the shearing resistance of the viscous liquid generated at that time.

  The inertia mass body is formed of an inertia ring made of metal such as cast iron or steel. The inertia ring described in Patent Document 1 has a substantially rectangular cross section, and the inertia ring described in Patent Document 2 has a trapezoidal cross section. The inertia ring described in Patent Document 3 is formed by laminating a plurality of annular plates. Normally, in order to prevent direct contact between the inertia ring and the case, journal bearings are provided on the inner peripheral surface of the inertia ring, and thrust bearings are provided on both end surfaces in the axial direction. Is formed. The thrust bearing described in Patent Document 1 is assembled in annular recesses formed on both end faces of the inertia ring, and the thrust bearing described in Patent Document 2 is formed by coating an axially outer portion of the end face with resin. The thrust bearing described in Patent Document 3 is attached to a mounting hole formed in the outer annular plate.

In addition, the torsional vibration preventing viscous dump described in Patent Document 4 is not provided with a thrust bearing. A smooth synthetic resin coating is applied to the outer surface of the annular inertia weight and / or the inner surface of the damper box so that the outer surface and the inner surface of the damper box do not rub against each other by direct contact.
Japanese Utility Model Publication No. 4-75259 Japanese Patent Laid-Open No. 10-54444 JP 2004-53008 A Japanese Utility Model Publication No. 51-65191

  The damping characteristic of such a viscous damper greatly depends on the clearance for the viscous liquid formed between the inner surface of the case and the outer surface of the inertia ring. Therefore, in order to obtain a desired damping characteristic, the clearance must be 1 / It is necessary to adjust with an accuracy of the order of 10 to 1/100 mm.

  For example, when the inertia ring is formed by one member as described in Patent Documents 1 and 2, the dimensional accuracy is increased by cutting the inner surface of the metal case and the outer surface of the inertia ring, respectively. It is necessary to set the clearance to a desired value.

  On the other hand, as described in Patent Document 3, when an inertia ring is formed by laminating a plurality of annular plates, a hot rolled steel plate (SPHC) or a cold rolled steel plate (SPCC) used for a thin plate is used. Since the thickness tolerance of the plate material such as the above is large, the thickness error of the inertia ring after lamination becomes large, and the variation in the thickness increases depending on the circumferential position of the inertia ring. For this reason, in order to manufacture a laminated inertia ring, strict thickness management is required in order to set the clearance to a desired value. Further, since the laminated annular plates are bundled and fixed by caulking or bolting, the number of man-hours for fixing the annular plate is increased in the laminated inertia ring. Furthermore, since the viscous liquid enters the gap between the laminated annular plates, a useless damping liquid that does not contribute to the damping is generated and the manufacturing cost is increased.

  Patent Document 4 describes that a synthetic resin film is applied to the outer surface of the inertia ring for the purpose of protection when contacting the inner surface of the case, but this does not contribute to the maintenance of the clearance.

  An object of the present invention is to make it possible to manufacture a viscous damper capable of setting a clearance for a viscous liquid with high accuracy at a low cost.

  The viscous damper of the present invention is a viscous damper that is mounted on a rotating shaft and attenuates torsional vibration of the rotating shaft, and has a cylindrical wall portion on the radially inner side and a radially outer side, and end wall portions on both axial sides. And a case in which an annular storage chamber is formed and attached to the rotating shaft, a metal annular inertia ring, and a resin material coating layer provided on the outer surface of the inertia ring, the storage chamber An annular inertial mass incorporated in the cylinder, a thrust bearing for slidably supporting the inertial mass with a desired clearance from the end wall, and the inertial mass rotatable with a desired clearance from the cylindrical wall A journal bearing that is supported on the inner surface of the body, and a viscous liquid filled in a clearance formed by an outer surface of the inertia mass body and an inner surface of the case. To.

  The viscous damper of the present invention is characterized in that the inertia ring is formed by laminating a plurality of thin plates.

  The viscous damper according to the present invention is characterized in that a bonding layer made of a resin material connected to the coating layer is provided between the thin plates.

  The viscous damper of the present invention is characterized in that an axial through-hole is formed in the inertia ring, and a plurality of the thin plates are fixed to each other by a resin-made fixing portion filled in the through-hole. .

  The viscous damper of the present invention is characterized in that a journal bearing that contacts the cylindrical wall portion of the case and / or a thrust bearing that contacts the end wall portion is formed of a resin material integrally with the coating layer.

  The viscous damper of the present invention is characterized in that the resin material is a lubricating resin such as polyethylene terephthalate, polyamide, and fluorine resin.

  The viscous damper of the present invention is characterized in that a fine uneven surface is formed on the surface of the thin plate.

  The viscous damper of the present invention is characterized in that three or more odd-numbered low-rigidity portions are formed in the inertia ring at predetermined intervals in the circumferential direction.

  The viscous damper of the present invention is characterized in that the low-rigidity part is formed by an opening hole provided in the inertia ring.

  According to the present invention, since the inertia mass body is formed by the metal inertia ring and the resin coating layer provided on the outer surface, the outer dimensions of the inertia mass body can be set with the molding accuracy of resin molding. A highly accurate viscous damper can be manufactured at low cost. The inertia mass body is supported in the case with a clearance with respect to the end wall portion by the thrust bearing and is supported in the case with a clearance with respect to the cylindrical wall portion by the journal bearing, so that the covering layer is directly applied to the inner surface of the case. Sliding contact is avoided. When the inertia ring is cast from cast iron or cast steel, it is not necessary to perform surface processing on the inertia ring formed by casting, and the inertia mass body can be manufactured as it is. Even if the inertia ring is manufactured from a thin laminate having a large thickness error, the outer dimension of the inertia mass body can be set with high accuracy by absorbing the error of the inertia ring by the coating layer. When a fine uneven surface is formed on the surface of the inertia ring, the adhesion between the inertia ring and the coating layer can be increased.

  When an inertia ring is manufactured by laminating thin plates, by providing a resin-made bonding layer between the thin plates, the bonding strength between the thin plates can be increased and the gap between the thin plates can be adjusted. . The bonding layer and the coating layer can be integrally formed when the coating layer is formed. In addition, the thin plates can be firmly fixed to each other by forming a through hole in the inertia ring in which the thin plates are stacked and filling the through hole with a resin material to form a fixing portion.

  By providing at least one of the journal bearing and the thrust bearing integrally with the covering layer, an inertial mass body having one bearing or both bearings can be formed integrally with the covering layer at the time of forming the covering layer. When the bearing and the covering layer are formed integrally, it is preferable to use a lubricious resin as the resin material.

  When an odd number of low-rigidity portions are provided in the circumferential direction in the inertia ring, the amplitude of the inertia mass body during vibration can be reduced, and the generation of vibration and noise during the operation of the viscous damper can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing an appearance of a viscous damper according to an embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view taken along line AA in FIG. 1, and FIG. 3 (A) is shown in FIG. 3 (B) is a cross-sectional view taken along line BB in FIG. 3 (A), and FIG. 4 is an enlarged cross-sectional view taken along line CC in FIG. 3 (A). .

  As shown in FIG. 1, the viscous damper 11 is used by being attached to the rotary shaft 10 in order to reduce torsional vibration in the rotary shaft 10 such as a crankshaft of an internal combustion engine. The viscous damper 11 has an annular case 12 attached to the rotary shaft 10, and as shown in FIG. 2, the case 12 includes an inner cylindrical wall portion 13a having a substantially cylindrical shape and an inner cylindrical wall portion 13a. A case body 13 having a substantially cylindrical outer cylindrical wall portion 13b having a large diameter and an end wall portion 13c integrated with the outer cylindrical wall portion 13b on one end side in the axial direction. ing.

  A cover 14 that closes the opening end 13 d is attached to the case body 13, and the cover 14 constitutes an end wall portion that faces the end wall portion 13 c of the case body 13. A case 12 is constituted by the case body 13 and the cover 14, and an annular storage chamber 15 is formed inside the case 12. A flange 16 is provided integrally with the inner cylindrical wall 13 a of the case body 13, and a plurality of attachment holes 17 through which bolts for attaching the viscous damper 11 to the rotary shaft 10 pass are formed in the flange 16. . The case body 13 is formed by cutting after casting using a metal material such as an aluminum alloy or an iron alloy, and the cover 14 is made of an annular plate formed of the same metal material as the case body 13.

  An annular inertia mass body 20 is incorporated in the storage chamber 15 so as to be rotatable relative to the case 12. Silicone oil is provided in the clearance formed by the outer surface of the inertia mass body 20 and the inner surface of the case 12. A viscous liquid 21 such as is filled. In order to fill the case 12 with the viscous liquid 21, the cover 14 is formed with an inlet to which the plug member 18 is attached as shown in FIG. 1, and after the case 12 is filled with the viscous liquid 21, The injection port is closed by the plug member 18.

  When the rotating shaft 10 rotates with the viscous damper 11 mounted, the case 12 rotates with the rotating shaft 10, and the inertia mass body 20 in the storage chamber 15 follows the case 12 due to the viscosity of the viscous liquid 21. Rotate. When the torsional vibration of the engine occurs on the rotating shaft 10, the inertial mass body 20 that rotates at a constant speed according to the rotation of the rotating shaft 10 and the rotating shaft 10 that vibrates due to the rotational pulsation generated by the engine, that is, the case 12. A differential occurs, and the torsional vibration of the rotating shaft 10 is reduced by the shear resistance of the viscous liquid 21 generated by the differential.

  The inertia mass body 20 has a metal annular core member, that is, an inertia ring 22 and a resin coating layer 24 provided on the outer surface thereof, and both the inner and outer peripheral surfaces of the inertia ring 22 and both ends in the axial direction. The entire outer surface with the surface is covered with the covering layer 24. The inertia ring 22 is formed by laminating a plurality of thin plates 23, and each thin plate 23 is processed into an annular shape by pressing using a plate material such as a hot rolled steel plate or a cold rolled steel plate. In order to manufacture the inertial mass body 20, a predetermined number of laminated thin plates 23 are placed in a resin molding die and injected into the resin molding die to form a laminate. The inertia mass body 20 having the inertia ring 22 and the covering layer 24 covering the outer surface thereof is manufactured.

  The outer surface of the inertia ring 22 is subjected to surface treatment in advance by shot peening, sand blasting, or the like, and a fine uneven surface is formed on the outer surface of the inertia ring 22, and the inertia ring 22 when the coating layer 24 is resin-molded. And the covering layer 24 are enhanced in adhesion. The surface treatment may be performed only on the outer surface of the outermost thin plate 23 in the axial direction of the laminated body, or may be performed on the entire outer surface of the inertial ring 22 in a laminated state. Alternatively, a surface punch may be applied by pressing a press punch having an unevenness on the tip surface against the end surface of the inertia ring, and a large number of traces may be formed on the surface of the inertia ring 22 by a cutter or the like. May be formed.

  As described above, by manufacturing the inertia ring 22 from the laminate of the thin plates 23, even if the thickness tolerance of the steel plate is large and the thickness error of the inertia ring after lamination becomes large, the covering layer 24 covered on the surface of the inertia layer 22 Since the error can be absorbed by the thickness, the outer dimensions of the inertial mass body 20, that is, the inner and outer diameter dimensions and the axial thickness dimension can be set with high accuracy by the resin molding die. Therefore, the dimensional accuracy of the inertial mass body 20 can be increased without increasing the dimensional accuracy of the inertia ring 22. Since the resin material as the coating layer 24 has a lower specific gravity than iron or the like that is the material of the inertia ring 22, even if the resin filling amount increases, the vibration system is hardly affected.

  As shown in FIG. 3, the inertia ring 22 is formed with three through holes 25 with a phase of 120 degrees in the circumferential direction. Each through hole 25 penetrates the inertia ring 22 in the axial direction and is circumferential. It has an oval shape extending in the direction. The through hole 25 is filled with a fixing portion 26 made of a resin material, and the plurality of thin plates 23 are fixed by the fixing portion 26. The fixing portion 26 is formed integrally with the covering layer 24 when the inertia ring 22 is disposed in the resin mold and the covering layer 24 is formed.

  As shown in FIG. 4, a part of the coating layer 24 covering the inner peripheral surface of the inertia ring 22 is formed with a large thickness to form a journal bearing 27. The journal bearing 27 is formed as shown in FIG. In addition, when the inertia mass body 20 is incorporated in the case 12, it comes into contact with the inner surface of the inner cylindrical wall portion 13 a of the case 12. Further, thrust bearings 28 and 29 are formed on a part of the covering layer 24 covering the left and right end faces in FIG. 4 of the inertia ring 22 so as to be thicker than the other parts. As shown in FIG. 3A, the thrust bearing 28 is provided so as to protrude from one surface of the covering layer 24 at intervals of 120 degrees in the circumferential direction, and the thrust bearing 29 is similarly formed of the three covering layers 24. It protrudes from the other surface.

  As shown in FIG. 2, in a state where the inertia mass body 20 is incorporated in the case 12, the thrust bearing 28 contacts the cover 14 as the end wall portion of the case 12, and the thrust bearing 29 is connected to the end of the case body 13. It will contact the wall 13c. The bearings 27 to 29 are formed integrally with the bearing layer 24, the fixing portion 26, and the bearing 27 when the inertia ring 22 is disposed in the resin mold and the covering layer 24 and the fixing portion 26 are formed. ... To 29 are integrally connected to each other in a resinous manner, and the dimensional accuracy of the inertial mass body 20 including the bearings 27 to 29 can be increased by resin molding. The number of the thrust bearings 28 and 29 is not limited to three as shown in the figure, and may be provided more than that. The thrust bearing 28 is provided so as to project annularly on one surface of the coating layer 24, and the thrust bearing 29 is provided. The other surface of the coating layer 24 may be provided so as to project in an annular shape.

  As a resin material constituting the coating layer 24, the fixed portion 26, and the bearings 27 to 29, a lubricating resin such as polyethylene terephthalate, polyamide, and fluororesin is used, and the bearing is in sliding contact with the inner surface of the case 12. The slidability of 27 to 29 is enhanced. However, when the covering layer 24 and the fixing portion 26 are integrally molded with resin and the bearings 27 to 29 are separated, only the bearings 27 to 29 are made of a lubricating resin, and the covering layer 24 and the fixing portion 26 are formed. Other resin materials may be used.

  FIG. 5 is an enlarged sectional view showing a part of a viscous damper according to another embodiment of the present invention, and FIG. 5 shows a portion corresponding to FIG. 4 in the above-described embodiment.

  The inertia ring 22 shown in FIG. 5 is formed by laminating a plurality of thin plates 23 as in the case described above, and a resin bonding layer 31 is provided between the thin plates 23. Each bonding layer 31 is formed integrally with the coating layer 24 by placing the inertia ring 22 in a resin mold for forming the coating layer and molding the resin in a state where a gap is formed between the thin plates 23. Is done. However, after the thin plates 23 are bonded to each other by the bonding layer 31, the coating layer 24 may be molded in a resin molding die.

  Thus, by interposing the bonding layer 31 between the thin plates 23, the bonding strength of the thin plates 23 can be increased, the gap between the thin plates 23 can be adjusted, and further the gap can be reduced. By changing, it is possible to adjust and tune the inertia moment of the inertia mass body 20 while using the same case.

  FIG. 6 is an enlarged sectional view showing a part of a viscous damper according to another embodiment of the present invention, and FIG. 6 shows a portion corresponding to FIG. 4 in the above-described embodiment.

  The inertia ring 22 shown in FIG. 6 is formed by laminating a plurality of thin plates 23 as in the case described above, but has a plurality of types of thin plates 23 having different inner diameters, and has a small inner diameter. Is embedded with the same resin as that of the coating layer 24. As described above, the inertial ring 22 is formed by laminating a plurality of types of thin plates 23 having different diameters, so that the inertial mass body tuned to a desired inertial mass while maintaining the necessary clearance from the inner surface of the case 12. 20 is possible.

  FIG. 7 is an enlarged sectional view showing a part of a viscous damper according to another embodiment of the present invention, and FIG. 6 shows a portion corresponding to FIG. 4 in the above-described embodiment.

  The inertia ring 22 shown in FIG. 7 is formed of one annular member, different from each of the inertia rings 22 described above, and the inertia ring 22 can be formed by casting. Moreover, since the inner and outer diameter dimensions and the axial thickness dimension of the inertial mass body 20 can be set with high accuracy by resin molding, the annular member formed by casting is directly put into the resin molding die without surface treatment. Thus, the inertia mass body 20 having a predetermined moment of inertia can be manufactured. As described above, even when the inertia ring 22 is manufactured by one annular member, the journal bearing 27 and the thrust bearings 28 and 29 can be formed integrally with the coating layer 24. When the inertia ring 22 is formed of one annular member as shown in FIG. 7, the cross-sectional shape of the inertia ring 22 is not limited to a rectangle as shown in the figure, and may be a trapezoid.

  FIG. 8 is a schematic view showing a state in which the annular member having a shape corresponding to the inertial mass body is resonated by applying vibration. FIG. 8A shows the front of the annular member, and FIG. The cross section of is shown. When vibration is applied to an annular member having an inner peripheral surface and an outer peripheral surface having a circular shape, the portion indicated by + in FIG. 8 is bent and deformed by resonance so that the portion is displaced to one side in the axial direction.

  FIG. 9 shows an experimental result of a bending deformation state at a resonance point by performing an experimental mode analysis on a single annular member made of a steel plate.

  As shown in FIG. 9, in the annular member, at each resonance frequency, a portion indicated by a broken line is displaced as a deformed bent portion, a portion attached with + is displaced to one side in the axial direction, and a portion attached with − is indicated in the axial direction. It can be seen that the annular member is bent and deformed so as to be displaced to the other side. The circular member is bent and deformed in this way. The circular annular member is not only point-symmetric with respect to the rotation center point, but also formed of the same material as a whole, and the strength is also point-symmetric. Therefore, displacement in the + direction and − direction occurs, and the amplitude at the time of resonance increases. On the other hand, it has been found that when three through holes are formed at equal intervals in the circumferential direction of the annular member, the amplitude at the time of resonance is greatly reduced.

  As shown in FIG. 3, when three through holes 25 are formed in the inertia ring 22 with a phase of 120 degrees in the circumferential direction, and a fixing portion 26 is formed by embedding a resin material in each of them, the through holes 25 are formed. Since the portion is a low-rigidity portion that is weaker than the portion that is not formed, that is, a weak bending portion, if the resin material is embedded in the through-hole 25 formed in the inertia ring 22 as described above, the thin plate 23 Not only can the fixing strength be increased, but also the inertia ring 22 shown in FIG. 3 is not formed with a through-hole as in the above-described test with the annular member in which the through-hole 25 is a low-rigidity portion. It was possible to reduce the amplitude during vibration.

  The low-rigidity part may be a bottomed hole as long as the strength of each part in the circumferential direction of the inertia ring 22 does not become point-symmetric, and a resin or the like for reducing the filling amount of the viscous liquid 21 Since it is necessary to embed the hole, the through hole may not be used as long as it is an opening hole opened in the end face. A similar low rigidity portion, that is, a weak bending portion can also be formed when the inertia ring 22 is formed of one annular member as shown in FIG.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. For example, the viscous damper 11 can be mounted not only on the crankshaft of the engine but also on various rotating shafts such as a camshaft of a diesel engine as long as it is a rotating shaft that generates torsional vibration. Further, the case 12 is formed by the case body 13 and the cover 14 having a U-shaped cross section, but the case 12 may be configured by abutting two case bodies each having a U-shaped cross section. Although the case 12 shown in the figure has a flange 16 attached to the rotating shaft by a bolt, the inner cylindrical wall portion 13a may be directly press-fitted into the rotating shaft. The journal bearing 27 may be provided outside the inertia mass body.

It is a perspective view which shows the external appearance of the viscous damper which is one embodiment of this invention. It is an AA line expanded sectional view in FIG. (A) is a front view which shows the inertial mass body shown by FIG. 2, (B) is the BB sectional drawing in (A). FIG. 4 is an enlarged sectional view taken along line CC in FIG. It is an expanded sectional view showing a part of viscous damper which is other embodiments of the present invention. It is an expanded sectional view showing a part of viscous damper which is other embodiments of the present invention. It is an expanded sectional view showing a part of viscous damper which is other embodiments of the present invention. (A), (B) is a schematic diagram which shows the state which this resonated by applying a vibration to the cyclic | annular member of the shape corresponding to an inertial mass body. It is an experimental result which shows the bending deformation state in a resonance point by performing an experimental mode analysis on the annular member alone.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Rotating shaft 11 Viscous damper 12 Case 13 Case main body 13a Inner cylindrical wall part 13b Outer cylindrical wall part 13c End wall part 14 Cover (end wall part)
15 Containment chamber 20 Inertial mass body 21 Viscous liquid 22 Inertial ring 23 Thin plate 24 Cover layer 25 Through hole 26 Fixing portion 27 Journal bearings 28 and 29 Thrust bearing 31 Coupling layer

Claims (9)

A viscous damper that is mounted on a rotating shaft to attenuate torsional vibration of the rotating shaft,
A case having a cylindrical wall portion on the radially inner side and a radially outer side and end wall portions on both sides in the axial direction, in which an annular storage chamber is formed and attached to the rotating shaft;
An annular inertial ring made of metal, and a resin-made coating layer provided on the outer surface of the inertial ring;
A thrust bearing that slidably supports the inertial mass body from the end wall portion with a desired clearance;
A journal bearing that rotatably supports the inertial mass body from the cylindrical wall portion with a desired clearance;
A viscous damper having a viscous liquid filled in a clearance formed by an outer surface of the inertia mass body and an inner surface of the case.   The viscous damper according to claim 1, wherein the inertia ring is formed by laminating a plurality of thin plates.   3. The viscous damper according to claim 2, wherein a bonding layer made of a resin material connected to the coating layer is provided between the thin plates.   4. The viscous damper according to claim 2, wherein an axial through hole is formed in the inertia ring, and a plurality of the thin plates are fixed to each other by a fixing portion made of a resin material filled in the through hole. This is a viscous damper.   5. The viscous damper according to claim 1, wherein a journal bearing that contacts the cylindrical wall portion of the case and / or a thrust bearing that contacts the end wall portion is integrally formed with the covering layer as a resin material. A viscous damper, characterized in that it is formed by:   The viscous damper according to any one of claims 1 to 5, wherein the resin material is a lubricating resin such as polyethylene terephthalate, polyamide, and fluororesin.   The viscous damper according to any one of claims 2 to 6, wherein a fine uneven surface is formed on a surface of the thin plate.   The viscous damper according to any one of claims 1 to 7, wherein three or more odd-numbered low-rigidity portions are formed in the inertia ring at predetermined intervals in the circumferential direction. .   9. The viscous damper according to claim 8, wherein the low rigidity portion is formed by an opening hole provided in the inertia ring.

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