rubber composition

Abstract

The problem addressed by the present application is to provide a rubber composition having excellent vibration-proofing and sound-deadening properties. The rubber composition disclosed by the present application is a crosslinked rubber composition containing ethylene propylene diene rubber (EPDM), 110–190 parts by mass of carbon black per 100 parts by mass of the ethylene propylene diene rubber, 10–35 parts by mass of an aromatic modified terpene resin per 100 parts by mass of the ethylene propylene diene rubber, a crosslinking agent, and oil. The nitrogen adsorption specific surface area of the carbon black is 70–120 m2 / g, the iodine adsorption capacity is 70–125 mg / g, and the DBP oil absorption capacity is 50–100 cm3 / 100 g.

Description

[Technical Field]

[0001] This invention relates to a rubber composition. [Background technology]

[0002] Rubber compositions have been used in a variety of applications for a long time. Depending on the application, rubber compositions require various properties. When used as a material with excellent vibration damping properties, rubber compositions are required to have excellent sound-dampening properties against radiated noise caused by vibration.

[0003] Figure 1 of Patent Document 1 (Japanese Patent Publication No. 2020-41684) discloses a torsional damper as a technology to enhance noise reduction, comprising a boss portion attached to the front end of the crankshaft, a vibrating ring positioned outside the boss portion with a belt wrapped around its outer circumference, and a cavity formed along the outer edge of the front of the boss portion, which uses sound wave interference to reduce radiated sound emitted from the center of the front of the boss portion through the crankshaft (

[0017] ). However, it is necessary to appropriately set the volume and opening area of ​​the cavity portion according to the radiated sound from the crankshaft, and there was room for further improvement in terms of versatility. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-41684 [Overview of the project] [Problems that the invention aims to solve]

[0005] This invention was made in view of the above circumstances, and the inventors have found a rubber composition in which rubber hardness Hs and sound pressure level have a specific relationship, and which can reduce sound pressure level and has excellent vibration damping properties, thus completing the present invention. In other words, the present invention provides a rubber composition with excellent vibration damping and sound absorption properties. [Means for solving the problem]

[0006] The gist of the present invention is as follows: [1] A rubber composition whose sound pressure level and rubber hardness, measured under the vibration conditions described below, satisfy the following formula (1). (Sound pressure level) (dB) ≤ 0.045x 2 -6.63x + 351.33 (1) (In equation (1) above, x represents the rubber hardness Hs°, and 45 ≤ x ≤ 85) [Excitation conditions] A sweep test is performed on rubber compositions at 55-65°C with an excitation amplitude of ±10G and a sweep frequency of 200-3000Hz. [2] The rubber composition, Ethylene propylene diene rubber (EPDM) and To 100 parts by mass of the ethylene propylene diene rubber, 110 to 190 parts by mass of carbon black are added. To 100 parts by mass of the ethylene propylene diene rubber, 10 to 35 parts by mass of aromatic modified terpene resin, Crosslinking agent and oil and A crosslinked rubber composition containing, The nitrogen adsorption specific surface area of ​​the carbon black is 70-120 m². 2 / g, iodine adsorption capacity 70-125 mg / g, DBP oil absorption capacity 50-100 cm 3 The rubber composition described in [1] above, wherein the weight is / 100g. [3] The rubber composition according to [1] or [2] above, which is a rubber composition for a torsional damper. [4] Ethylene propylene diene rubber (EPDM) and To 100 parts by mass of the ethylene propylene diene rubber, 110 to 190 parts by mass of carbon black are added. To 100 parts by mass of the ethylene propylene diene rubber, 10 to 35 parts by mass of aromatic modified terpene resin, Crosslinking agent and oil and A crosslinked rubber composition containing, The nitrogen adsorption specific surface area of the carbon black is 70 to 120 m 2 / g, the iodine adsorption amount is 70 to 125 mg / g, and the DBP oil absorption amount is 50 to 100 cm 3 / 100 g, a rubber composition. [5] The rubber composition according to [4] above, which is a rubber composition for a torsional damper. [Advantages of the Invention]

[0007] It is possible to provide a rubber composition excellent in vibration damping properties and sound absorption properties. [Brief Description of the Drawings]

[0008] [Figure 1] It is a broken perspective view showing an example of a torsional damper having the rubber composition of the present invention. [Figure 2] It is a diagram showing the relationship between the hardness of the rubber composition in formulas (1) to (3) and the sound pressure level. [Figure 3] It is a diagram showing a method of measuring the sound pressure level of the rubber composition of one embodiment. [Figure 4] It is a diagram showing a torsional damper used for measuring the sound pressure level. [Modes for Carrying Out the Invention]

[0009] The rubber composition of the present invention satisfies the following formula (1) for the sound pressure level and rubber hardness measured in a state of being vibrated according to the following vibration conditions. (Sound pressure level) (dB) ≤ 0.045x 2 -6.63x + 351.33 (1) (In the above formula (1), x represents the rubber hardness Hs° (unit), and 45 ≤ x ≤ 85) [Vibration conditions] For the rubber composition at 55 to 65 °C, a sweep test is performed with a vibration amplitude of ±10 G and a sweep frequency of 200 to 3000 Hz.

[0010] The above excitation conditions are achieved by exciting the rubber composition with a vibration exciter. The rubber composition is integrated with the vibrating body to dampen its vibrations and reduce the sound radiated from the vibrating body. Therefore, the sound pressure level of the rubber composition is measured when the structure, which integrates the rubber composition and the vibrating body, is fixed to the vibration exciter, and the structure is excited by the vibration exciter, thereby exciting the rubber composition within the structure. For example, when using a torsional damper having the rubber composition of the present invention as the structure, the center of the torsional damper 1 is fixed to the vibration exciter 10 with a bolt 12, as will be described later with reference to Figure 3. Next, a sweep test is performed on the torsional damper and the rubber composition contained in the torsional damper to excite them under the above excitation conditions, and the sound pressure level of the rubber composition is measured using a microphone 11 positioned at a distance D in the axial direction of the fixing bolt 12 of 70 mm, for the sound radiated from the torsional damper. A free-field type 378A06 manufactured by PCB can be used as the microphone. Furthermore, for measuring the sound pressure level of the rubber composition, a torsional damper with the shape and dimensions shown in Figure 4 is used. The material of the hub 2 and vibration ring 4 of the torsional damper 1 in Figure 4 is FC250 (cast iron), and the projected area of ​​the hub 2 is 6236 mm². 2 The dimensions are as follows: d1 (outer diameter of torsional damper 1) = 147 mm, d2 (stay width) = 32 mm, d3 (outer diameter of casting window) = 95 mm, d4 (inner diameter of casting window) = 57 mm, d5 (width of boss portion) = 29.5 mm, and d6 (inner diameter of hub) = 105 mm. The torsional damper 1 in Figure 4 has the rubber composition of the present invention as a rubber ring 3.

[0011] The rubber composition of the present invention has a high tanδ (loss coefficient) and, by satisfying the relationship in formula (1) above, can achieve excellent vibration damping and noise reduction. The rubber hardness Hs° can be measured using a Type A durometer hardness tester under the conditions of JIS K6253. Formula (1) is represented by the line shown as standard 3 in Figure 2, which will be described later.

[0012] The tanδ of the rubber composition is preferably 0.29 or more. By the tanδ of the rubber composition being within these ranges, it is possible to have excellent vibration damping properties and sound absorption properties.

[0013] The rubber hardness Hs of the rubber composition can be adjusted according to the component composition of the rubber composition. The rubber composition preferably contains ethylene propylene diene rubber (EPDM), carbon black, an aromatic-modified terpene resin, a crosslinking agent, and oil, and is a thermosetting rubber composition crosslinked by the crosslinking agent. Further, the rubber composition is a crosslinked rubber composition containing ethylene propylene diene rubber (EPDM), 110 to 190 parts by mass of carbon black with respect to 100 parts by mass of ethylene propylene diene rubber, 10 to 35 parts by mass of an aromatic-modified terpene resin with respect to 100 parts by mass of ethylene propylene diene rubber, a crosslinking agent, and oil, and the nitrogen adsorption specific surface area of the carbon black is 70 to 120 m 2 / g, the iodine adsorption amount is 70 to 125 mg / g, and the DBP oil absorption amount is 50 to 100 cm 3 / 100 g is more preferable.

[0014] The rubber hardness Hs of the rubber composition can be set to a desired range of 45° to 85° by adjusting the content and type of carbon black, which has properties that harden the rubber composition, and the content and type of oil, which has properties that soften the rubber composition. The oil may be incorporated into the ethylene propylene diene rubber in advance to form an oil-expanding polymer type ethylene propylene diene rubber. The ethylene propylene diene rubber may be a non-oil-expanding polymer type ethylene propylene diene rubber that does not contain oil, and the rubber composition may contain both the non-oil-expanding polymer type ethylene propylene diene rubber and oil. Alternatively, the rubber composition may contain both the oil-expanding polymer type ethylene propylene diene rubber and oil. In the case of oil-expanding polymer type ethylene propylene diene rubber, the content of ethylene propylene diene rubber in the rubber composition is the total content of oil-expanding polymer type ethylene propylene diene rubber minus the content of oil. The Mooney viscosity ML1+4 (125°C) of the oil-expanding polymer type ethylene propylene diene rubber (before crosslinking) is preferably 50 or higher.

[0015] When the ethylene propylene diene rubber contains ENB (5-ethylidene-2-norbornene) as a diene unit, the ENB content in the ethylene propylene diene rubber is preferably 4.0 to 9.0% by mass, and more preferably 4.5 to 8.5% by mass. Commercially available ethylene propylene diene rubber can be used. Examples of commercially available oil-expanding polymer type ethylene propylene diene rubber include ENEOS EP98 (trade name) and ARLANXEO KELTAN4869C (trade name). Examples of commercially available non-oil-expanding polymer type ethylene propylene diene rubber include ENEOS EP35 (trade name) and ARLANXEO KELTAN2750 (trade name).

[0016] Regarding the carbon black content in the rubber composition, it is preferable that the carbon black content be 110 to 190 parts by mass, and more preferably 120 to 180 parts by mass, per 100 parts by mass of ethylene propylene diene rubber. By having a carbon black content within the above range, the rubber composition can have excellent processability. The nitrogen adsorption specific surface area of ​​carbon black is 70 to 120 m². 2 It is preferable that the value be / g, and 80-110m 2 It is more preferable that the amount is / g. Nitrogen adsorption specific surface area represents the specific surface area per unit weight of carbon black and can be measured according to JIS K6217-2:2001. The amount of iodine adsorbed by carbon black is preferably 70-125 mg / g, and more preferably 80-120 mg / g. The amount of iodine adsorbed can be measured according to JIS K6217-1:2008. The amount of DBP oil absorbed by carbon black is 50-100 cm³. 3 It is preferable that the weight be 100g, and the length is 60-90cm. 3 It is more preferable that the amount is / 100g. The amount of DBP oil absorbed can be measured according to JIS K6217-4:2017. Specifically, examples of carbon black include HAF-LS carbon black and ISAF-LS carbon black. By having the nitrogen adsorption specific surface area, iodine adsorption amount, and DBP oil absorbed amount of the carbon black within the above range, it is possible to increase the internal friction of the rubber composition while maintaining excellent processability. As a result, the tanδ of the rubber composition can be improved, and the sound-absorbing properties of the rubber composition can be improved.

[0017] Regarding the content of aromatically modified terpene resin in the rubber composition, it is preferable that the aromatically modified terpene resin is 10 to 35 parts by mass, more preferably 15 to 35 parts by mass, and even more preferably 15 to 30 parts by mass, per 100 parts by mass of ethylene propylene diene rubber. By having the aromatically modified terpene resin content within the above range, the rubber composition has excellent tackiness and good compatibility with ethylene propylene diene rubber. Therefore, by shifting the glass transition temperature of ethylene propylene diene rubber to the high-temperature side, the tanδ of the rubber composition can be improved, thereby improving the sound-absorbing properties of the rubber composition. As an example of aromatically modified terpene resin, it is obtained by copolymerizing a terpene monomer such as α-pinene, β-pinene, or dipentene (limonene) with an aromatic monomer such as substituted styrene or unsubstituted styrene, and can be an oligomer with a molecular weight of several hundred to several thousand.

[0018] The crosslinking agent content in the rubber composition is preferably 3 to 5 parts by mass, and more preferably 3.3 to 4.5 parts by mass, per 100 parts by mass of ethylene propylene diene rubber. At least an organic peroxide-based crosslinking agent is preferably used, and examples of such organic peroxide-based crosslinking agents include dicumyl peroxide (DCP). Furthermore, sulfur can be used together with the organic peroxide-based crosslinking agent.

[0019] Regarding the oil content in the rubber composition, it is preferable that the oil is 45 to 80 parts by mass, and more preferably 55 to 70 parts by mass, per 100 parts by mass of ethylene propylene diene rubber. Mineral oil is preferably used as the oil, and paraffin oil is an example of such mineral oil. In addition to ethylene propylene diene rubber, carbon black, aromatic modified terpene resin, crosslinking agent, and oil, the rubber composition may also contain components such as zinc oxide, stearic acid, antioxidant, and co-crosslinking agent.

[0020] One embodiment is, Ethylene propylene diene rubber (EPDM) and To 100 parts by mass of the ethylene propylene diene rubber, 110 to 190 parts by mass of carbon black are added. To 100 parts by mass of the ethylene propylene diene rubber, 10 to 35 parts by mass of aromatic modified terpene resin, Crosslinking agent and oil and A crosslinked rubber composition containing, The nitrogen adsorption specific surface area of ​​the carbon black is 70-120 m². 2 / g, iodine adsorption capacity 70-125 mg / g, DBP oil absorption capacity 50-100 cm 3 This invention relates to a rubber composition in a quantity of / 100g. The rubber composition of this embodiment contains specific components in a specific composition, and due to the synergistic effect of these specific components, excellent vibration damping and sound insulation can be achieved.

[0021] The rubber composition of the present invention is preferably a rubber composition for torsional dampers. The rubber composition can effectively dampen noise radiated from the hub when the torsional damper is in use. Figure 1 is a cutaway perspective view showing a part of a torsional damper having the rubber composition of the present invention. As shown in Figure 1, the torsional damper 1 is mounted on the tip of the crankshaft of an automobile engine and transmits the rotation of the crankshaft to the alternator, power steering, etc. The torsional damper 1 comprises a hub 2 having a boss portion 2a, a stay 2b and an outer circumference portion 2c, a rubber ring 3 made of the rubber composition of the present invention, and a vibration ring 4. The boss portion 2a is fastened to the tip of the crankshaft and rotated around its central axis. A pulley groove 4a on the outer circumference of the vibration ring 4 is provided, which constitutes a pulley for power transmission, on which a belt is attached.

[0022] The torsional damper 1 suppresses (absorbs) the torsional resonance of the crankshaft by causing the vibrating ring 4 to resonate in the rotational direction and by damping vibrations with the rubber ring 3. The rotational resonance frequency of the vibrating ring 4 is generally around 300-600 Hz. On the other hand, the vibrating ring 4 also resonates in the axial direction, and its frequency is several hundred Hz, similar to the torsional vibration. Since the local resonance of the hub 2 is the largest, radiated sound is emitted from the hub 2.

[0023] In the torsional damper 1, the radiated sound associated with the local resonance of the hub 2 originates from the stay 2b and outer circumference 2c of the hub 2. Therefore, as shown below, tanδ is increased. This can reduce the amount of radiated noise.

[0024] (i) The equation representing (hub axial vibration velocity) is shown as equation (4) below. As shown in equation (4) below, (hub axial vibration velocity) depends on (hub axial acceleration) and (hub axial frequency). (Hub axis vibration velocity) = (Hub axis acceleration) / (2 × π × Hub axis frequency) (4) (ii) Increasing tanδ reduces the (acceleration in the hub axis direction). (iii) By increasing tanδ, the local frequency of the hub, which is the hub axis frequency, The vibration frequency shifts to the higher frequency side.

[0025] Therefore, by increasing the tanδ of the rubber composition constituting the rubber ring 3, the hub axis direction This allows for a reduction in the vibration velocity in the direction, thereby reducing radiated noise. [Examples]

[0026] (Examples 1-3, Comparative Examples 1-3) The materials with the compositions shown in Table 1 below were kneaded using a mixer such as an intermixer, kneader, Banbury mixer, or open roll. Then, rubber compositions for measuring rubber hardness Hs and tanδ were prepared by press crosslinking at 180°C for 6.0 minutes. Separately, an annular rubber composition was prepared, and this annular rubber composition was press-fitted as a rubber ring 3 between the boss portion 2a and the metal members of the vibrating ring 4 to create a torsional damper 1 for measuring sound pressure level, as shown in Figure 4. In the torsional damper 1 in Figure 4, the material of the hub 2 and vibrating ring 4 is FC250 (cast iron), and the projected area of ​​the hub 2 is 6236 mm². 2 d1 (outer diameter of torsional damper 1) = 147 mm, d2 (stay width) = 32 mm, d3 (outer diameter of casting window) = 95 mm, d4 (inner diameter of casting window) = 57 mm, d5 (width of boss section) = 29.5 mm, and d6 (inner diameter of hub) = 105 mm. In each example, the rubber hardness Hs was set to 55°, 65°, or 75° by adjusting the material composition.

[0027] [Table 1]

[0028] Note that each value in Table 1 represents parts by mass. Furthermore, the parts by mass of Oil-Spread EPDM1 and Oil-Spread EPDM2 represent the total parts by mass of EPDM and oil, and "Oil in Oil-Spread EPDM1" and "Oil in Oil-Spread EPDM2" represent the parts by mass of oil in Oil-Spread EPDM1 and Oil-Spread EPDM2, respectively. Therefore, the parts by mass of EPDM in Oil-Spread EPDM1 is (Oil-Spread EPDM1) - (Oil in Oil-Spread EPDM1). Similarly, the parts by mass of EPDM in Oil-Spread EPDM2 is (Oil-Spread EPDM2) - (Oil in Oil-Spread EPDM2).

[0029] The names of the materials used in each example are listed below. Oil-extended EPDM1:ML1+4(125℃)=48, ENB content 8.7% by mass, C2 content 62% by mass Oil-extended EPDM2:ML1+4(125℃)=52, ENB content 4.5% by mass, C2 content 58% by mass Non-oil extended EPDM1:ML1+4(125℃)=65, ENB content 9.0% by mass, C2 content 44% by mass Non-oil extended EPDM2: ML1+4(100℃)=38, ENB content 5.8% by mass, C2 content 61% by mass Non-oil extended EPDM3: ML1+4(125℃)=87, ENB content 4.5% by mass, C2 content 59% by mass Carbon Black A: SRF-HS carbon black, nitrogen adsorption specific surface area 32 m² 2 / g, iodine adsorption amount 30mg / g, DBP oil absorption amount 140cm 3 / 100g Carbon Black B: HAF carbon black, nitrogen adsorption specific surface area 79 m² 2 / g, iodine adsorption amount 80mg / g, DBP oil absorption amount 101cm 3 / 100g Carbon Black C: HAF-LS Carbon Black, Nitrogen Adsorption Specific Surface Area 84 m² 2 / g, iodine adsorption amount 86mg / g, DBP oil absorption amount 75cm 3 / 100g Aromatic-modified terpene resin: YS Resin TO-115 (product name); ethylene vinyl acetate copolymer (compound name) Resin B: UltraSen 750 (product name) DCP: Dicumyl Peroxide Oil A: Diana Process Oil PW-380 (product name)

[0030] For the rubber compositions obtained in each example, the rubber hardness Hs, tanδ, and o were determined by the following method. The sound pressure level was also measured.

[0031] (Rubber hardness Hs) For each example of rubber composition, a Type A durometer hardness tester was used, according to JIS standards. The rubber hardness Hs was measured under the K6253 conditions.

[0032] (tanδ) Using a viscoelastic spectrometer (trade name) and a rheometer manufactured by UBM, the tanδ of the rubber compositions obtained in each example was measured under the conditions of 60°C, excitation frequency of 100 Hz, and dynamic strain of 1%. It was measured.

[0033] (Sound pressure level) For measuring the sound pressure level, a torsional damper having the rubber composition obtained in each example as a rubber ring was used. As shown in Figure 3, the center of the torsional damper 1 for sound pressure level measurement, which was prepared as described above, was fixed to the exciter 10 via a bolt 12. A high-frequency dynamic characteristics tester (product name), manufactured by Sagimiya Seisakusho Co., Ltd., was used as the exciter. Using this tester, the torsional damper 1 and the rubber composition, which is the rubber ring 3 contained in the torsional damper 1, were heated to 55-65°C, and a sweep test was performed with an excitation amplitude of ±10G and a sweep frequency of 200-3000Hz. During the sweep test, the sound pressure level of the sound radiated from the torsional damper 1 having the rubber composition (rubber ring 3) was measured using a microphone 11 (manufactured by PCB; free-field type 378A06) positioned at a distance D in the axial direction of the bolt from the bolt 12 of 70 mm.

[0034] The tanδ and sound pressure levels measured for each example are shown in Table 2 below.

[0035] [Table 2]

[0036] Also, for rubber hardness Hs from 45° to 85°, formula (3); 0.057x 2 -7.88x+387.38, Formula (2);0.0593x 2 -8.2668x+399.46, formula (1); 0.045x 2 -6.63x + 351.33, according to Figure 2 shows the relationship between the sound pressure level and the given values. In Figure 2, equations (3), (2), and (1) are shown as standards 1, 2, and 3, respectively. Figure 2 also shows the sound pressure levels as points for rubber hardness Hs of 55°, 65°, and 75° in standards 1, 2, and 3. Table 3 below shows the sound pressure level values ​​for rubber hardness Hs of 55°, 65°, and 75° in standards 1, 2, and 3.

[0037] [Table 3]

[0038] The rubber compositions of Examples 1 to 3 all have sound pressure levels below those expressed in Standard 3, indicating that the rubber compositions of the present invention exhibit excellent sound-dampening properties. Furthermore, the rubber compositions of Examples 1 to 3 have a tanδ of 0.29 or higher compared to Comparative Examples 1 to 3, indicating excellent vibration damping properties.

[0039] On the other hand, although the rubber compositions of Comparative Examples 1 to 3 have sound pressure levels below those expressed in Standard 1, they exceed the sound pressure levels expressed in Standards 2 and 3, and do not exhibit sufficient sound dampening. Furthermore, the rubber compositions of Comparative Examples 1 to 3 have low tanδ values ​​of 0.22 or less, indicating poor vibration damping properties. [Explanation of symbols]

[0040] 1 Torsional damper 2 hubs 2a Boss section 2b Stay 2c outer periphery 3 rubber rings 4. Vibration Ring 4a Pulley groove

Claims

[Claim 1] The sound pressure level and rubber hardness measured under the vibration conditions described below satisfy the following formula (1) for a rubber composition for torsional dampers, The aforementioned rubber composition, Ethylene propylene diene rubber (EPDM) and Amount to 100 parts by mass of ethylene propylene diene rubber is mixed with 160 to 190 parts by mass of carbon black, Amount of 100 parts by mass of ethylene propylene diene rubber is mixed with 10 to 35 parts by mass of aromatic modified terpene resin, Crosslinking agent and Amount to 100 parts by mass of ethylene propylene diene rubber is mixed with 45 to 80 parts by mass of oil, A crosslinked rubber composition containing, The nitrogen adsorption specific surface area of ​​the carbon black is 70 to 120 m². ２ / g, iodine adsorption capacity 70-125 mg / g, DBP oil absorption capacity 50-100 cm ３ A rubber composition for torsional dampers, weighing 100g. (Sound pressure level) (dB) ≤ 0.045x ２ -6.63x + 351.33 (1) (In equation (1) above, x represents the rubber hardness Hs°, and 45 ≤ x ≤ 85) [Excitation conditions] A sweep test is performed on rubber compositions at 55-65°C with an excitation amplitude of ±10G and a sweep frequency of 200-3000Hz. The sweep test described above will be performed under the following conditions. First, an annular rubber composition is prepared, and the annular rubber composition is press-fitted as a rubber ring between each metal member of the boss portion and the vibration ring to produce a torsional damper for sound pressure level measurement. In the torsional damper, the materials of the hub and the vibration ring are FC250 (cast iron), and the projected area of the hub is 6236 mm ２ , d １ (outer diameter of the torsional damper 1) = 147 mm, d ２ (stay width) = 32 mm, d ３ (outer diameter of the cast window) = 95 mm, d ４ (inner diameter of the cast window) = 57 mm, d ５ (width of the boss portion) = 29.5 mm, d ６ (inner diameter of the hub) = 105 mm. Next, the center of the torsional damper is fixed to a high-frequency dynamic characteristics tester manufactured by Sagimiya Seisakusho Co., Ltd. via a bolt, and the sweep test is performed. During the sweep test, the sound pressure level of the sound radiated from the torsional damper is measured using a PCB Corporation free-field type 378A06 microphone positioned at a distance of 70 mm in the axial direction from the bolt.

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