Pneumatic tire

Abstract

The present invention addresses the problem of providing a pneumatic tire capable of reducing cavity resonance sound with a simple configuration. The solution is that the pneumatic tire (1) is provided with a plurality of Helmholtz silencers (9) arranged on the inner cavity surface (1i) of the tire. The plurality of Helmholtz mufflers (9) have a first resonance frequency (f1), which is the maximum resonance frequency (fmax), and a second resonance frequency (f2), which is the minimum resonance frequency (fmin). The difference (f1-f2) between the first resonance frequency f1 and the second resonance frequency f2 is 9-90 Hz.

Description

Technical Field

[0001] The present invention relates to a pneumatic tire capable of reducing cavity resonance sound. Background Art

[0002] Conventionally, pneumatic tires having a device for reducing the resonance sound in the tire cavity generated during driving are known. For example, Patent Document 1 below proposes a pneumatic tire having a plurality of resonators as Helmholtz resonators mounted on the inner circumference of the tire. [Prior art literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Patent No. 6289506 Summary of the invention [Problems to be solved by the invention]

[0004] However, the pneumatic tire of Patent Document 1 needs a plurality of Helmholtz mufflers having different resonance frequencies in order to cope with the cavity resonance sound in the tire that varies with the running speed, and further improvements are required in terms of manufacturing and weight.

[0005] The present invention is proposed in view of the above-mentioned actual situation, and its main purpose is to provide a pneumatic tire capable of reducing cavity resonance sound with a simple structure.

Methods for solving the problem

[0006] The present invention is an inflatable tire having a plurality of Helmholtz mufflers arranged on the inner cavity surface of the tire, wherein the plurality of Helmholtz mufflers have a first resonance frequency as a maximum resonance frequency and a second resonance frequency as a minimum resonance frequency, and the difference between the first resonance frequency and the second resonance frequency is 9 to 90 Hz, preferably 10 to 90 Hz. [Effects of the invention]

[0007] The pneumatic tire of the present invention has the above-mentioned structure, and can reduce the cavity resonance sound with a simple structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

[0009] Hereinafter, embodiments of the present invention will be described in detail based on the drawings. Figure 1 1 is a tire meridian cross-sectional view of the pneumatic tire 1 in a normal state according to the present embodiment. Here, the "normal state" refers to an unloaded state in which the pneumatic tire 1 is mounted on a normal rim and adjusted to a normal internal pressure. Hereinafter, unless otherwise specified, the dimensions of various parts of the pneumatic tire 1 are values ​​measured in the normal state.

[0010] The "regular rim" refers to a rim specified in accordance with each tire when there is a specification system including the specification based on the pneumatic tire 1, such as a "standard rim" in JATMA, a "design rim" in TRA, and a "measuring rim" in ETRTO. When there is no specification system including the specification based on the pneumatic tire 1, the "regular rim" is a rim with the smallest rim diameter and the smallest rim width among the rims that can be mounted on the rim without causing air leakage.

[0011] “Normal internal pressure” refers to the air pressure specified for each tire in each specification when there is a specification system including the specification to which the pneumatic tire 1 is based, and refers to the “maximum air pressure” in JATMA, the maximum value recorded in the table “TIRE LOAD LIMITS ATVARIOUS COLD INFLATION PRESSURES” in TRA, and “INFLATION PRESSURE” in ETRTO. When there is no specification system including the specification to which the pneumatic tire 1 is based, the “Normal internal pressure” is the air pressure specified for each tire by the manufacturer, etc.

[0012] like Figure 1 As shown, the pneumatic tire 1 of this embodiment is suitable for use as a tire for a passenger car. The pneumatic tire 1 is not limited to a tire for a passenger car, but can be applied to various tires such as a heavy-duty tire, a two-wheeled vehicle tire, a racing vehicle tire, and an industrial vehicle tire.

[0013] The pneumatic tire 1 of the present embodiment includes a tread portion 2, a pair of sidewall portions 3, and a pair of bead portions 4. The sidewall portions 3 are, for example, portions extending radially inward from both sides of the tread portion 2 in the tire axial direction. The bead portions 4 are, for example, portions located radially inward of the sidewall portions 3. The bead portions 4 of the present embodiment are portions that come into contact with a regular rim.

[0014] Each of the pair of bead portions 4 has, for example, an annular bead core 5 extending in the tire circumferential direction, and a bead apex rubber 8 extending from the bead core 5 to the outer side of the tire radial direction. The bead core 5 is formed of, for example, a steel wire. The bead apex rubber 8 is formed of, for example, hard rubber. Such a bead portion 4 has high rigidity, so it can suppress deformation during driving, which helps to reduce the cavity resonance sound of the pneumatic tire 1.

[0015] The pneumatic tire 1 of this embodiment includes a carcass 6 extending between a pair of bead portions 4, and a belt layer 7 disposed on the tread portion 2. The belt layer 7 is disposed, for example, on the tire radially outer side of the carcass 6. The pneumatic tire 1 preferably has a tire inner cavity surface 1i defining the tire inner cavity on the inner side of the carcass 6.

[0016] Figure 2 1 is a schematic cross-sectional view of a pneumatic tire 1 viewed from the tire axial direction. Figure 1 and Figure 2 As shown, the pneumatic tire 1 of this embodiment has a plurality of Helmholtz mufflers 9 arranged on the tire inner cavity surface 1i. The plurality of Helmholtz mufflers 9 of this embodiment have a first resonance frequency f1 as the maximum resonance frequency fmax and a second resonance frequency f2 as the minimum resonance frequency fmin. Such a pneumatic tire 1 can reduce the cavity resonance sound in the tire that varies with the running speed by resonating with a plurality of frequencies.

[0017] The difference (f1-f2) between the first resonance frequency f1 and the second resonance frequency f2 is 9 to 90 Hz, preferably 10 to 90 Hz. This pneumatic tire 1 can effectively reduce the cavity resonance sound generated by the driving speed of 10 to 200 km / h, and can suppress the number of Helmholtz mufflers 9. Therefore, the pneumatic tire 1 of this embodiment can reduce the cavity resonance sound by a simple structure. Based on this viewpoint, the difference (f1-f2) between the first resonance frequency f1 and the second resonance frequency f2 is more preferably 9 to 60 Hz, and more preferably 10 to 60 Hz.

[0018] As a more preferred embodiment, the first resonance frequency f1 of the Helmholtz muffler 9 is 130 to 350 Hz. The second resonance frequency f2 of the Helmholtz muffler 9 is preferably 120 to 340 Hz. Such a Helmholtz muffler 9 can cope with the frequency band of the cavity resonance sound generated by the tire for a passenger car, and can effectively reduce the cavity resonance sound of the tire for a passenger car.

[0019] like Figure 1 As shown, the carcass 6 has at least one carcass ply, and in this embodiment, two carcass plies 6A and 6B. The two carcass plies 6A and 6B include, for example, a first carcass ply 6A located radially inward of the tread portion 2, and a second carcass ply 6B located radially outward of the first carcass ply 6A.

[0020] Preferably, at least one of the carcass plies 6A and 6B includes a main body 6a and a folded portion 6b, wherein the main body 6a extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and the folded portion 6b is connected to the main body 6a and folded back from the inner side to the outer side of the tire axial direction around the bead core 5. The first carcass ply 6A and the second carcass ply 6B of this embodiment include a main body 6a and a folded portion 6b, respectively. Such a carcass 6 helps to improve the rigidity of the bead portion 4 and reduce the cavity resonance sound of the pneumatic tire 1.

[0021] Preferably, the outer end 6e of the folded portion 6b of at least one of the carcass plies 6A and 6B in the tire radial direction is located on the outer side in the tire radial direction relative to the tire maximum width position P where the tire cross-sectional width W is the largest. In the carcass 6, for example, the outer end 6e of the folded portion 6b of the first carcass ply 6A is located on the outer side in the tire radial direction relative to the tire maximum width position P, and the outer end 6e of the folded portion 6b of the second carcass ply 6B is located on the inner side in the tire radial direction relative to the tire maximum width position P. Such a carcass 6 can achieve both rigidity and lightness of the sidewall portion 3, and can reduce the cavity resonance sound and rolling resistance of the pneumatic tire 1.

[0022] The carcass cords 6A and 6B include, for example, carcass cords (not shown) made of organic fiber cords. Examples of the organic fiber cords include cords of one or more mixed fibers selected from the group consisting of polyethylene terephthalate fibers, polyethylene naphthalate fibers, nylon fibers, aramid fibers, and rayon fibers.

[0023] The carcass cords are preferably arranged at an angle of 25 to 90° relative to the tire circumferential direction. When the carcass cords are inclined at an angle less than 90° relative to the tire circumferential direction, the carcass cords of the first carcass cord 6A and the carcass cords of the second carcass cord 6B are preferably inclined in opposite directions relative to the tire circumferential direction. For example, the carcass 6 may adopt an offset structure. Here, the angle of the carcass cords is the angle in the pneumatic tire 1 in a normal state, and can be confirmed by, for example, partially peeling off the tread portion 2.

[0024] The belt layer 7 includes at least one, preferably two or more belt layers, and in the present embodiment, includes two belt layers 7A and 7B. The two belt layers 7A and 7B include, for example, a first belt layer 7A located radially inwardly of the tire, and a second belt layer 7B located outside the first belt layer 7A. The outer end 7e of the belt layer 7 in the present embodiment is the outer end 7e of the first belt layer 7A in the tire axial direction. Such a belt layer 7 can improve the rigidity of the tread portion 2 and can reduce the cavity resonance sound of the pneumatic tire 1.

[0025] The belt layers 7A and 7B include belt cords (not shown) composed of, for example, steel cords. The belt cords may be, for example, single steel wires or twisted wires formed by twisting a plurality of steel monofilaments.

[0026] The belt cords are arranged at an angle of 10 to 30 degrees relative to the tire circumferential direction, for example. Preferably, the belt cords of the first belt layer 7A and the belt cords of the second belt layer 7B are inclined in opposite directions relative to the tire circumferential direction. Such a belt layer 7 can improve the rigidity of the tread portion 2 in a balanced manner and can reduce the cavity resonance sound of the pneumatic tire 1. Here, the angle of the belt cords is the angle in the pneumatic tire 1 in a normal state, and can be confirmed, for example, by partially peeling off the tread portion 2.

[0027] The tread portion 2 of the present embodiment has a contact surface 2s extending between a pair of tread ends Te. Here, in the pneumatic tire 1 in a normal state under a load state of 70% of the normal load, the tread end Te is the axially outermost contact position of the tire when the tire contacts the flat surface at a camber angle of 0°. The contact surface 2s has a tire tread width TW, which is the distance between the pair of tread ends Te in the tire axial direction. In addition, the central position between the pair of tread ends Te in the tire axial direction is the tire equator C.

[0028] “Normal load” refers to the load specified for each tire in each specification when there is a specification system including the specification to which the pneumatic tire 1 is based, and in the case of JATMA, it refers to the “maximum load capacity”, in the case of TRA, it refers to the maximum value recorded in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES”, and in the case of ETRTO, it refers to “LOAD CAPACITY”. When there is no specification system including the specification to which the pneumatic tire 1 is based, the “Normal load” is the load specified for each tire by the manufacturer, etc., as the maximum load applicable when the pneumatic tire 1 is used.

[0029] The plurality of Helmholtz mufflers 9 of the present embodiment are respectively arranged on the inner side of the tire radial direction of the ground contact surface 2s. That is, the plurality of Helmholtz mufflers 9 are preferably respectively arranged within the range of the tire tread width TW centered on the tire equator C. The plurality of Helmholtz mufflers 9 are respectively arranged in a row, for example, on the tire equator C. Such Helmholtz mufflers 9 are subjected to a force in a pressing direction toward the tire inner cavity surface 1i when subjected to the centrifugal force, thereby reducing the risk of peeling off from the tire inner cavity surface 1i.

[0030] The outer end 7e of the belt layer 7 of this embodiment is located axially outward from the tread end Te. Such a belt layer 7 can improve the rigidity of the entire ground contact surface 2s of the tread portion 2 and contribute to reducing the cavity resonance sound of the pneumatic tire 1.

[0031] The plurality of Helmholtz mufflers 9 of this embodiment are disposed radially inward of the belt layer 7. The Helmholtz mufflers 9 suppress deformation of the tread portion 2 when contacting the ground by the highly rigid belt layer 7, and can suppress resonance sound generated by the Helmholtz mufflers 9 due to impact when contacting the ground.

[0032] like Figure 2 As shown, the plurality of Helmholtz mufflers 9 are preferably arranged separately from each other. The plurality of Helmholtz mufflers 9 are arranged separately from each other in the tire circumferential direction, for example. Such Helmholtz mufflers 9 can reduce the cavity resonance sound in the entire region of the pneumatic tire 1.

[0033] The plurality of Helmholtz mufflers 9 of the present embodiment include: a plurality of first mufflers 9A having a first resonance frequency f1, and a plurality of second mufflers 9B having a second resonance frequency f2. It is preferred to provide an even number of first mufflers 9A and second mufflers 9B in each row arranged along the tire circumferential direction. Such a Helmholtz muffler 9 is easy to adjust the balance when the tire rotates. In addition, although the plurality of Helmholtz mufflers 9 of the present embodiment are illustrated as being arranged in one row, the plurality of Helmholtz mufflers 9 may also be arranged in multiple rows.

[0034] A pair of first mufflers 9A provided in each row are arranged at positions opposite to each other, for example, sandwiching the tire rotation axis. A pair of second mufflers 9B provided in each row are arranged at positions opposite to each other, for example, sandwiching the tire rotation axis. Such Helmholtz mufflers 9 have excellent balance when the tire rotates, and can suppress vibration and noise generated when the pneumatic tire 1 is running.

[0035] Figure 3 : is a perspective view of the Helmholtz type muffler 9 of this embodiment. Figure 3As shown, the Helmholtz muffler 9 includes a sound absorbing chamber 9a having a space inside and a pipe 9b connecting the sound absorbing chamber 9a and the inner cavity of the tire. By adjusting the volume of the sound absorbing chamber 9a and the length of the pipe 9b, the Helmholtz muffler 9 can have different resonance frequencies f.

[0036] The first muffler 9A of the present embodiment includes a first sound absorbing chamber 9a having a first resonance frequency f1. Although not shown in the figure, the second muffler 9B includes a second sound absorbing chamber 9c having a second resonance frequency f2, for example.

[0037] The plurality of Helmholtz mufflers 9 are preferably made of a resin that does not change shape at 120° C. or less. Even when the temperature of the pneumatic tire 1 rises during high-speed running, the Helmholtz mufflers 9 do not change shape and can maintain sound absorption performance.

[0038] As the material of the Helmholtz silencer 9, for example, polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), polyvinylidene chloride (PVDC), polyvinylidene fluoride (PVDF), polyamide (PA), polycarbonate (PC), polyphenylene sulfide (PPS), polyimide (PI), polyetherimide (PEI), polysulfone (PSF), polysulfone (PSU), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyamideimide (PAI), phenolic resin (PF), melamine resin (MF), unsaturated polyester (UP), polyurethane (PU), polydiallyl phthalate (PDAP), silicone resin (SI), epoxy resin (EP), furan formaldehyde resin (FF), cellulose acetate (CA), cellulose nitrate (CN), cellulose propionate (CP), ethyl cellulose (EC), etc.

[0039] For example, the plurality of Helmholtz mufflers 9 may have at least one resonance frequency f different from the first resonance frequency f1 and the second resonance frequency f2. Such a Helmholtz muffler 9 can resonate with a wide frequency band of the cavity resonance sound, and can more reliably reduce the cavity resonance sound.

[0040] In the plurality of Helmholtz mufflers 9, it is preferred that the unit width df is substantially equal, and the unit width df is the difference between the resonance frequencies of a group of adjacent ones in the frequency band. Here, the unit width df being substantially equal means that the difference between the unit widths df is less than 10% of the unit width df. Such a Helmholtz muffler 9 can absorb sound uniformly in the entire frequency band.

[0041] The unit width df of the plurality of Helmholtz mufflers 9 is preferably 3 to 10 Hz. Such Helmholtz mufflers 9 can uniformly absorb sound in the entire frequency band without excessively increasing the number of types thereof.

[0042] Figure 4 2 is a perspective view of a Helmholtz muffler 10 according to the second embodiment. Figure 4 As shown, each of the plurality of Helmholtz mufflers 10 may include, for example, a hemispherical sound absorbing chamber 10a and a pipe portion 10b extending along the sound absorbing chamber 10a. Such a Helmholtz muffler 10 can evenly absorb the cavity resonance sound of the tire cavity by adjusting the direction of the pipe portion 10b.

[0043] Figure 5 3 is a perspective view of the Helmholtz muffler 11 according to the third embodiment. Figure 5 As shown, each of the plurality of Helmholtz mufflers 11 may include, for example, at least one first sound absorbing chamber 11a having a first resonance frequency f1, and at least one second sound absorbing chamber 11c having a second resonance frequency f2. Such a Helmholtz muffler 11 may have a plurality of resonance frequencies f in one Helmholtz muffler 11. Therefore, the Helmholtz muffler 11 of the third embodiment can reduce cavity resonance sound with a simple structure.

[0044] It is preferable that the first muffler 11A having the first sound absorbing chamber 11a and the second muffler 11B having the second sound absorbing chamber 11c are formed integrally with each other. Such a Helmholtz muffler 11 can reduce the number of components and reduce the cavity resonance sound in a wide frequency band.

[0045] Figure 6 FIG. 2 is a tire meridian cross-sectional view of a pneumatic tire 21 in a normal state according to another embodiment. Figure 6 As shown, the pneumatic tire 21 of this embodiment, like the pneumatic tire 1 described above, includes a tread portion 2, a pair of sidewall portions 3, and a pair of bead portions 4. The bead portion 4 has, for example, an annular bead core 5 extending in the tire circumferential direction, and a bead apex 8 extending from the bead core 5 in the tire radial direction outward.

[0046] The pneumatic tire 21 of this embodiment includes a carcass 6 extending between a pair of bead portions 4, and a belt layer 7 arranged on the tire radially outer side of the carcass 6 in the tread portion 2. The carcass 6 includes, for example, two carcass plies 6A and 6B having a main body portion 6a and a folded portion 6b. The belt layer 7 includes, for example, two belt layers 7A and 7B. Similar to the above-mentioned pneumatic tire 1, the pneumatic tire 21 preferably has a tire inner cavity surface 21i defining the tire inner cavity on the inner side of the carcass 6.

[0047] The pneumatic tire 21 of this embodiment is the same as the pneumatic tire 1, and includes a plurality of Helmholtz mufflers 9 arranged on the tire inner cavity surface 21i. The plurality of Helmholtz mufflers 9 of this embodiment are respectively arranged on the tire axial inner side of at least one of the sidewall portion 3 and the bead portion 4. Such a Helmholtz muffler 9 can suppress the change of the Helmholtz muffler 9 itself even when the tread 2 is deformed when contacting the ground, and can suppress the resonance sound generated by the Helmholtz muffler 9 due to the impact when contacting the ground.

[0048] The plurality of Helmholtz mufflers 9 are preferably disposed axially inward of the bead portion 4. Such a Helmholtz muffler 9 does not generate resonance sound due to impact at the time of ground contact, and can more reliably reduce cavity resonance sound.

[0049] The plurality of Helmholtz mufflers 9 are respectively arranged on the inner side of the tire axial direction, for example, from the inner end 5e of the bead core 5 in the tire radial direction to the outer end 8e of the bead apex 8 in the tire radial direction. That is, the plurality of Helmholtz mufflers 9 are preferably respectively arranged in the range of the height H from the inner end 5e of the bead core 5 to the outer end 8e of the bead apex 8. Since such a Helmholtz muffler 9 is arranged in a range having high rigidity, it is possible to more reliably reduce the cavity resonance sound.

[0050] Even when a plurality of Helmholtz mufflers 9 are disposed on the inner side of the tire axial direction of the sidewall portion 3, they are preferably disposed on the inner side of the tire radial direction than the outer ends 6e of the carcass plies 6A and 6B. Such a Helmholtz muffler 9 helps suppress the resonance sound generated by the Helmholtz muffler 9 due to the impact at the time of ground contact.

[0051] Although particularly preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments and can be implemented in various modified forms. [Example]

[0052] based on Figure 1 to Figure 3 and Figure 6 A pneumatic tire of the embodiment with a tire size of 215 / 55R17 was trial-produced according to the specifications in Table 1. As a comparative example, a pneumatic tire of the same size without a Helmholtz muffler was trial-produced. The noise performance at different driving speeds was tested using the trial-produced pneumatic tire.

[0053] <Noise Performance> The trial pneumatic tire was installed on the test bench, and the axial force was measured when the tire was running at 20 km / h, 60 km / h and 150 km / h, and the low-frequency side sound pressure and high-frequency side sound pressure of the cavity resonance sound were obtained. The results were expressed as an index with the comparison example as 100. The smaller the value, the smaller the sound pressure and the better the noise performance.

[0054] The test results are shown in Table 1.

Table 1

[0055] The test results confirmed that the pneumatic tire of the example was superior to the comparative example in noise performance at any running speed, and that the cavity resonance sound could be reduced by simply attaching a Helmholtz muffler.

[0056] [Notes] The present invention is as follows.

[0057] [Present invention 1] A pneumatic tire, characterized in that: A plurality of Helmholtz-type mufflers are arranged on the inner cavity surface of the tire. The plurality of Helmholtz mufflers have a first resonance frequency as a maximum resonance frequency and a second resonance frequency as a minimum resonance frequency, The difference between the first resonance frequency and the second resonance frequency is 9 to 90 Hz, preferably 10 to 90 Hz.

[0058] [Present invention 2] According to the pneumatic tire of the first aspect of the present invention, the first resonance frequency is 130 to 350 Hz. The second resonance frequency is 120 to 340 Hz.

[0059] [Present invention 3] In the pneumatic tire according to Invention 1 or 2, the plurality of Helmholtz mufflers are arranged separately from each other.

[0060] [Present invention 4] According to the pneumatic tire of any one of Inventions 1 to 3, the plurality of Helmholtz mufflers are made of a resin that does not change shape at 120° C. or lower.

[0061] [Present invention 5] In the pneumatic tire according to any one of Inventions 1 to 4, the plurality of Helmholtz mufflers have at least one resonance frequency different from the first resonance frequency and the second resonance frequency.

[0062] [Present invention 6] In the pneumatic tire according to the fifth aspect of the present invention, the unit widths of the plurality of Helmholtz mufflers are substantially equal, and the unit width is a difference between a set of the resonance frequencies adjacent to each other in a frequency band.

[0063] [Present invention 7] According to the pneumatic tire of the sixth aspect of the present invention, the unit width is 3 to 10 Hz.

[0064] [Present invention 8] In the pneumatic tire according to any one of Inventions 1 to 7, each of the plurality of Helmholtz mufflers includes at least one first sound absorbing chamber having the first resonance frequency and at least one second sound absorbing chamber having the second resonance frequency.

[0065] [Present invention 9] In the pneumatic tire according to the eighth aspect of the present invention, the first muffler having the first sound absorbing chamber and the second muffler having the second sound absorbing chamber are formed integrally with each other.

[0066] [Present invention 10] In the pneumatic tire according to any one of Inventions 1 to 9, the difference between the first resonance frequency and the second resonance frequency is 9 to 60 Hz, preferably 10 to 60 Hz.

[0067] [Present invention 11] According to any one of the present inventions 1 to 10, the pneumatic tire comprises: a tread portion, a pair of sidewall portions extending radially inward from both sides of the tread portion in the tire axial direction, and a pair of bead portions located radially inward of the pair of sidewall portions. The plurality of Helmholtz mufflers are respectively arranged on the inner side of at least one of the pair of sidewall portions and the pair of bead portions in the tire axial direction.

Claims

1. A pneumatic tire, characterized in that: A plurality of Helmholtz-type mufflers are arranged on the inner cavity surface of the tire. The plurality of Helmholtz mufflers have a first resonance frequency as a maximum resonance frequency and a second resonance frequency as a minimum resonance frequency, The difference between the first resonance frequency and the second resonance frequency is 9 to 90 Hz.

2. A pneumatic tire, characterized in that: A plurality of Helmholtz-type mufflers are arranged on the inner cavity surface of the tire. The plurality of Helmholtz mufflers have a first resonance frequency as a maximum resonance frequency and a second resonance frequency as a minimum resonance frequency, The difference between the first resonance frequency and the second resonance frequency is 10 to 90 Hz.

3. The pneumatic tire according to claim 1 or 2, wherein: The first resonance frequency is 130 to 350 Hz, The second resonance frequency is 120 to 340 Hz.

4. The pneumatic tire according to claim 1 or 2, wherein: The plurality of Helmholtz mufflers are arranged separately from each other.

5. The pneumatic tire according to claim 1 or 2, wherein: The plurality of Helmholtz mufflers are made of a resin that does not change shape at 120° C. or less.

6. The pneumatic tire according to claim 1 or 2, wherein: The plurality of Helmholtz mufflers have at least one resonance frequency different from the first resonance frequency and the second resonance frequency.

7. The pneumatic tire according to claim 6, wherein: The unit widths of the plurality of Helmholtz mufflers are substantially equal, and the unit width is a difference between a set of the resonance frequencies adjacent to each other in a frequency band.

8. The pneumatic tire according to claim 7, wherein: The unit width is 3 to 10 Hz.

9. The pneumatic tire according to claim 1 or 2, wherein: Each of the plurality of Helmholtz mufflers includes at least one first sound absorbing chamber having the first resonance frequency and at least one second sound absorbing chamber having the second resonance frequency.

10. The pneumatic tire according to claim 9, wherein: The first muffler having the first sound absorbing chamber and the second muffler having the second sound absorbing chamber are formed integrally with each other.

11. The pneumatic tire according to claim 1, wherein: The difference between the first resonance frequency and the second resonance frequency is 9 to 60 Hz.

12. The pneumatic tire according to claim 2, wherein: The difference between the first resonance frequency and the second resonance frequency is 10 to 60 Hz.

13. The pneumatic tire according to claim 1 or 2, comprising: a tread portion, a pair of sidewall portions extending radially inward from both sides of the tread portion in the tire axial direction, and a pair of bead portions located radially inward of the pair of sidewall portions. The plurality of Helmholtz mufflers are respectively arranged on the inner side of at least one of the pair of sidewall portions and the pair of bead portions in the tire axial direction.

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