JP5103069B2 - Pneumatic tire - Google Patents

Description

  The tread portion includes at least one circumferential groove extending substantially in the tire circumferential direction and at least one row of rib-like land portions adjacent to the tread portion tread surface. The present invention relates to a pneumatic tire that is provided with a resonator that branches off from a directional groove and reduces noise generated by resonance in a pipe formed by the circumferential groove and a road surface. Improve wearability.

  In recent years, with the quietness of vehicles, the contribution to automobile noise resulting from load rolling of pneumatic tires has increased, and reduction thereof has been demanded. Above all, tire noise at a high frequency, particularly about 1000 Hz, is a main cause of noise outside the vehicle, and countermeasures for reducing the noise are also required in response to environmental problems.

  The tire noise at a frequency of about 1000 Hz is mainly generated by air column resonance. The air column resonance sound is noise generated by resonance of air in a pipe surrounded by a circumferential groove and a road surface continuously extending in the circumferential direction of the tread surface, and is 800 to 1200 Hz in a general passenger car. It is often observed in the frequency domain. The air column resonance sound occupies most of the noise generated from the pneumatic tire because the sound pressure level at the peak is high and the frequency band is wide.

  In addition, since human hearing is particularly sensitive in the frequency band (A characteristic) around 1000 Hz, the reduction of such air column resonance sound is also effective in improving the quietness of the feeling during running. It is valid.

  Conventionally, for the purpose of reducing such air column resonance noise, the number and volume of circumferential grooves are reduced, or, for example, as described in Patent Document 1, only one end opens into the circumferential groove, and the like. It has been proposed to reduce the air column resonance noise by providing a long horizontal groove whose end terminates in the land and using anti-resonance in the horizontal groove. However, in the pneumatic tire in which the groove volume of the circumferential groove is reduced, the groove volume of the circumferential groove is insufficient, and the drainage performance may be deteriorated. Further, in the pneumatic tire described in Patent Document 1, since it is essential to dispose long lateral grooves, the degree of freedom in designing the tread pattern is impaired, and the rigidity of the land portion is not sufficiently ensured. The handling stability may be reduced.

  As a solution to these problems, as described in Patent Documents 2 to 4, a technique for reducing air column resonance using anti-resonance by arranging a so-called Helmholtz type resonator has been proposed. Yes. By using such a Helmholtz type resonator, the groove volume of the circumferential groove is sufficiently ensured and the drainage performance is ensured, but the design of the tread pattern is higher than that of the pneumatic tire described in Patent Document 1. The degree of freedom can be improved.

International Publication No. 04/103737 Pamphlet Japanese Patent Laid-Open No. 5-338411 JP 2000-118207 A JP 2001-191734 A

  Such a resonator is disposed in a rib-like land portion defined adjacent to the circumferential groove, and the rigidity of the rib-like land portion is greatly affected by the shape of the opening on the tread surface of the resonator. Therefore, the opening shape of the resonator greatly affects not only the reduction of tire noise but also other tire performances, particularly steering stability and uneven wear resistance of land portions. However, in the pneumatic tires described in Patent Documents 2 to 4, two circumferential grooves located on both sides of the rib-like land portion or one circumferential groove and an opening on only one side of the tread grounding end, The rigidity of the land portion on the opening side is greatly reduced compared to that on the opposite side, and the uneven wear and steering stability of the land portion on the opening side are reduced (responses when steering to the left and steering to the right) Difference).

  An object of the present invention is to solve such problems of the prior art, and its purpose is to reduce the resonance noise of the air column by optimizing the aperture shape of the resonator. Another object of the present invention is to provide a pneumatic tire capable of improving steering stability and uneven wear resistance.

In order to achieve the above object, the present invention comprises, on the tread portion tread surface, at least one circumferential groove extending substantially in the tire circumferential direction and at least one row of rib-shaped land portions adjacent to the groove. A pneumatic tire (hereinafter referred to as “tire”) is provided with a resonator for reducing noise generated by resonance in a pipe formed by the circumferential groove and a road surface in the rib-shaped land portion. The resonator includes an air chamber portion having a relatively large cross-sectional area orthogonal to the extending direction, a branch from the air chamber portion, extending toward the circumferential groove, and orthogonal to the extending direction. At least two branch groove portions having a cross-sectional area smaller than that of the air chamber portion, and the opening shape to the tread portion tread surface of the resonator is substantially a line with respect to at least one of the tire circumferential direction and the tire width direction. symmetry der is, tread of the gas chamber The opening shape to the tread surface is substantially line symmetric with respect to at least one of the tire circumferential direction and the tire width direction, and the opening shape to the tread portion tread of the air chamber portion has at least one bent portion, those resonators, characterized by opening to isosamples through the branch groove into two circumferential grooves or a single circumferential groove and a tread ground contact end to define this in disposed a rib-like land portion It is. Alternatively, the present invention comprises, on the tread portion tread surface, at least one circumferential groove extending substantially in the tire circumferential direction, and at least one row of rib-shaped land portions adjacent to the groove, and in the rib-shaped land portion, A pneumatic tire comprising a resonator that branches off from the circumferential groove and that reduces noise generated by resonance in a pipe formed by the circumferential groove and a road surface. An air chamber portion having a relatively large cross-sectional area orthogonal to the air chamber portion, and extending from the air chamber portion toward the circumferential groove and having a cross-sectional area perpendicular to the extending direction smaller than that of the air chamber portion. The opening shape to the tread portion tread surface of the resonator is substantially line symmetric with respect to both the tire circumferential direction and the tire width direction, and the air chamber portion has an opening to the tread portion tread surface. Shape is tire circumferential direction and tire width direction Is substantially axisymmetric with respect to at least one, opening shape of the tread surface of the air chamber portion is characterized in that it has at least one bent portion. By adopting such a configuration, the land portion rigidity and the force borne by the land portion are substantially uniform on both sides around the axis of symmetry. The term “substantially line symmetric” as used herein means to allow such a small asymmetry that does not affect the rigidity of the land portion and the uniformity of the force borne by the land portion. Yes, for example, the width of air chambers and branch grooves of air column resonators, and the presence or absence of communication with circumferential grooves due to slight differences in the length of the ends of branch grooves, etc. It is assumed that the asymmetry within a range that does not give the above is included in the “substantially line symmetry”. Further, the “substantially tire circumferential direction” means not only a groove extending linearly in the tire circumferential direction but also a groove extending in a zigzag shape or a wave shape and making a round in the tire circumferential direction as a whole tire.

として表すことができる。このとき、Ｌの値は文献によって相違するが、ここでは、枝溝部２の半径をｒ、長さをＬ_０として、Ｌ＝１．３ｒ＋Ｌ_０として考えるものとする。したがって、上式において、枝溝部２の断面積Ｓ、枝溝部２の長さと枝溝部２の開口端の補正長さとの和Ｌ、気室部３の容積Ｖを適宜に選択することで、所望の共鳴周波数ｆ_０を得ることができる。 The type of the resonator is not particularly limited as long as the air column resonance can be effectively reduced. For example, a Helmholtz type resonator can be used. In this case, the resonator can be modeled as a shape as shown in FIG. 1, and the resonance frequency f ₀ is the sum of the distance between the length of the branch groove portion 2 and the corrected length of the open end of the branch groove portion 2. L, the cross-sectional area of the branch groove portion is S, the volume of the air chamber portion 3 is V, the sound speed is c,

Can be expressed as At this time, although the value of L differs depending on the literature, it is assumed here that L = 1.3r + L ₀ where r is the radius of the branch groove portion 2 and L ₀ is the length. Accordingly, in the above equation, the cross-sectional area S of the branch groove portion 2, the sum L of the length of the branch groove portion 2 and the corrected length of the open end of the branch groove portion 2, and the volume V of the air chamber portion 3 are appropriately selected. it is possible to obtain the resonant frequency f ₀ of the.

Further, as shown in FIG. 2, the air chamber portion 3 and the branch groove portion 2 of the resonator 1 are regarded as the first conduit 4 and the second conduit 5, respectively, and are connected to each other. It is also possible to use an attached type resonator, and the resonance frequency f _{0 in} this case can be obtained as follows.

That is, the cross-sectional area perpendicular to the extending direction of the first pipe line is S ₁ , the cross-sectional area perpendicular to the extending direction of the second pipe line is S ₂ , and the acoustic impedance on the first pipe line 4 side at the boundary is Z _12. When the acoustic impedance of the second conduit 5 side at the boundary and Z _21, the following expression is derived from a continuous condition.
Z ₂₁ = (S ₂ / S ₁ ) · Z ₁₂
Further, the sound pressure P _{2 at} the point of the distance x from the portion of the second pipe 5 that is open to the circumferential groove of the second pipe is defined by the boundary condition x = 0 and V ₂ = V ₀ e ^jwt. Where x = L ₂ and P ₂ / V ₂ = Z ₂ ,
_{P 2 = Z s · {Z} 21 cos (k (L 2 -x)) + jZ c sin (k (L 2 -x)) / Z c cos (kL 2) + jZ 21 sin (kL 2)} · V ₀ e ^jwt , where k = 2πf ₀ / c
V ₂ represents the particle velocity distribution in the second pipe line 5, V ₀ represents the particle velocity at the input point, j represents the imaginary unit, and Zc represents ρc (ρ: air density, c: sound velocity).
Moreover, the sound pressure _{P 1} of the first conduit 4, the boundary condition, and V ₁ = 0 at x = L _1, as _P 2 _/ V 2 _{= Z 21} in x = _{L 2,} are guided by the following equation.
_{P 1 = Z s · [Z} 21 cos (k (L 2 -x)) / cos (kL 1) · {Z c co (kL 2) + jZ 21 sin (kL 2)}] · V 0 e jwt

Therefore, the conditional expression of the resonance frequency f ₀ is derived as the following expression when the resonance condition is x = 0 and P ₂ = 0.
tan (kL ₁ ) tan (kL ₂ ) − (S ₂ / S ₁ ) = 0
A desired resonance frequency f ₀ can be obtained by appropriately selecting k, L ₁ , L ₂ , S ₂ , S ₁ , and c based on this resonance conditional expression.

  In addition, the shape of the opening to the tread part tread surface of the resonator is substantially line symmetric with respect to the tire circumferential direction when there is no designation on the tire mounting side (inside or outside), but there is a designation of the rotation direction. Preferably, there is a designation of the tire mounting side, but when there is no designation of the rotational direction, it is preferable that the tire is substantially line symmetric with respect to the tire width direction.

Furthermore, the opening shape of the tread surface of the air chamber portion, but can also be a circular shape, in the present invention shall have at least one bent portion.

In addition, when the rib-like land portion in which the resonator is disposed is defined by two circumferential grooves, the resonator opens to each of the two circumferential grooves via a branch groove portion, and the rib When the land portion is defined by a single circumferential groove and a tread ground end, both the circumferential groove and the tread ground end open through branch grooves.

Alternatively, the opening shape of the resonator of the tread surface is Ri substantially axisymmetric der respect to both the tire circumferential direction and the tire widthwise direction, such a configuration, in particular, specify any of the mounting side and the rotational direction of the tire It is preferable when there is no.

  According to the present invention, the rigidity of the land portion is substantially uniform on both sides around the axis of symmetry, so that the steering stability can be greatly improved, and the force borne by the land portion is substantially uniform, so that uneven wear is caused. It is possible to provide a tire that can effectively suppress the occurrence of the above.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a plan view of a part of a tread portion of a typical tire according to the present invention.

  In the tire of this embodiment, a rib-like land portion 8 is defined on the tread portion tread 6 by two circumferential grooves 7a and 7b extending substantially in the tire circumferential direction. In this rib-shaped land portion 8, a resonator is branched from the circumferential grooves 7a and 7b and reduces noise generated by resonance in a tube (air column) formed by the circumferential grooves 7a and 7b and the road surface. 9 is provided. The resonator 9 includes an air chamber portion 10 and two branch groove portions 11 and 11 that branch from the air chamber portion 10 and extend toward the circumferential grooves 7a and 7b and communicate with the circumferential grooves 7a and 7b. Become. As shown in the figure, the air chamber portion 10 has a relatively large cross-sectional area perpendicular to the extending direction, that is, the branch groove portion 11 is also larger than the cross-sectional area perpendicular to the extending direction. Is formed. Therefore, in this tire, the resonator 9 plays a role of reducing air column resonance generated in the two circumferential grooves 7a and 7b.

  In general, in the tread portion of a tire, a portion with relatively high land rigidity bears more braking / driving force and cornering force, and a portion with low land rigidity has the braking / driving force and cornering force on the contrary. Less burden. In order to increase the sum of the load that can be borne and the cornering force with a certain contact area, it is desirable to make the rigidity distribution in the tread portion uniform, thereby improving steering stability. In addition, the wear of the land portion is made uniform by making the burdening force uniform within the tread portion. On the contrary, in the resonator opening shape as shown in FIG. 15, the distribution of the rigidity of the land portion is uneven and asymmetrical. For example, there is a difference between the responsiveness when steering to the right and the responsiveness when steering to the left. For example, the stability is reduced. Therefore, in the present invention, the opening shape to the tread portion tread surface of the resonator is made substantially line symmetric, thereby maintaining the uniformity of the block rigidity and improving the steering stability and the uneven wear resistance.

  In particular, when a tire with no designation on the mounting side and with a designation for the direction of rotation is fitted to the vehicle, the tread part of each tire of the four wheels is in the same direction with respect to the tire circumferential force (mainly braking / driving force) However, the direction of the input in the tire width direction (mainly cornering force) is reversed between the left wheel and the right wheel. In such a case, as in the tire shown in FIG. 3, the opening shape to the tread portion tread surface 6 of the resonator 9 is formed symmetrically with respect to the tire circumferential direction C, and the resonator 9 substantially ribs. By equalizing the rigidity in the tire width direction of the block formed by dividing the left and right wheels irrespective of the input direction, it becomes possible to equalize the steering stability and uneven wear resistance of the left and right wheels. In particular, from the viewpoint of uniform rigidity, it is preferable to make the resonator 9 line-symmetric with respect to a straight line passing through the center position of the rib-like land portion 8 and extending along the tire circumferential direction C as in the embodiment of FIG. .

  Further, as shown in FIG. 4, one of the two branch grooves 11a is terminated in the land as long as it hardly affects the rigidity of the land on both sides with respect to the tire circumferential direction C as the axis of symmetry. Only the other branch groove portion 11b may communicate with the circumferential groove 7b. In this case, the resonator 9 reduces only the air column resonance generated in the circumferential groove 7b. Further, as shown in FIG. 5, with respect to the tire circumferential direction C, which is the axis of symmetry, an air chamber 10 and a relatively narrow branch groove portion 11b are disposed on one side (left side in the figure) and the other side (FIG. 5). Then, a branch groove portion 11c wider than the branch groove portion 11b may be disposed on the right side. However, the volume occupied by the air chamber in the resonator is large, and thus making the opening shape of the air chamber different on both sides with respect to the axis of symmetry can restrict the resonance frequency and design of the resonator. There is. In such a case, as shown in FIGS. 3 and 4, the opening shape of the air chamber portion 10 to the tread portion tread surface is substantially line symmetric with respect to the axis of symmetry (the tire circumferential direction C in the illustrated embodiment). It is preferable to do.

  As is clear from the above description, the volume of the air chamber 10 needs to be increased in order to obtain a low resonance frequency. In order to increase the volume of the air chamber portion 10, it is only necessary to increase the depth, width, or length. However, increasing the depth is naturally limited in terms of the manufacturing method and strength, and the width If the value of is increased, the rigidity of the land portion is lowered, which leads to a reduction in steering stability, which is not preferable from the viewpoint of the overall performance of the tire. Therefore, it is effective to increase the length of the air chamber portion 10, but in the straight air chamber portion, the length is restricted by the width of the rib-like land portion 8, but as shown in FIG. If the air chamber portion 10 is provided with at least one bent portion, a low resonance frequency can be obtained without increasing the width of the air chamber portion 10 and thus without significantly reducing the rigidity of the land portion.

  In addition, as described above, even when there is no designation of the mounting side of the tire and the designation of the rotation direction, input from various directions is applied when the tire rolls. Therefore, as shown in FIG. 6, if the opening shape of the air chamber portion 10 having a large influence on the land portion rigidity to the tread portion tread surface 6 is circular, uneven wear of the land portion can be more effectively suppressed. .

  FIGS. 7 to 14 show other embodiments of the present invention. The same reference numerals are used for the same parts as those of the tire of the embodiment shown in FIG.

  When a tire with a designation on the mounting side and no designation of the direction of rotation is fitted to the vehicle, the tread part of each tire of the four wheels is the left and right wheels for the tire circumferential force (mainly braking / driving force) However, the input direction is reversed, but the force in the tire width direction (mainly cornering force) is input in the same direction. In such a case, like the tire shown in FIGS. 7 to 10, the opening shape to the tread portion tread surface 6 of the resonator 9 is formed symmetrically with respect to the tire width direction W, and the resonator 9 substantially By equalizing the tire circumferential rigidity of the block formed by dividing the ribs independently of the direction of input, it is possible to make the steering stability and uneven wear resistance of the left and right wheels uniform.

  As shown in FIG. 8 and FIG. 9, even when the opening shape of the resonator 9 is formed line-symmetrically with respect to the tire width direction W, as shown in FIGS. The shape of the branch groove portion can be changed. Moreover, as shown in FIGS. 7 and 8, the opening shape to the tread portion tread surface of the air chamber portion 10 is substantially line-symmetric with respect to the symmetry axis (tire width direction W), as shown in FIGS. It is preferable that at least one bent portion is provided in the air chamber portion 10 and that the opening shape of the air chamber portion 10 is circular as shown in FIG. These reasons are the same as those described in the embodiment in which the opening shape of the resonator 9 is formed in line symmetry with respect to the tire circumferential direction C, and the description thereof is omitted.

  When a tire with no designation on the mounting side or a direction of rotation is fitted to the vehicle, the tread part of each tire of the four wheels also has a tire circumferential direction force (mainly braking / driving force), in the tire width direction. As for force (mainly cornering force), each wheel may receive input from different directions. In such a case, as in the tire shown in FIGS. 11 to 14, the opening shape of the resonator 9 to the tread portion tread surface 6 is formed symmetrically with respect to both the tire circumferential direction C and the tire width direction W. In addition, the tire circumferential direction rigidity and the tire width direction rigidity of the block formed by the ribs being substantially divided by the resonator 9 are made uniform regardless of the input direction, so that the steering stability and uneven wear resistance of each wheel are uniformed. Can be made uniform.

  In this way, even when the opening shape of the resonator 9 is formed line-symmetrically with respect to the tire circumferential direction C and the tire width direction W, as long as it does not substantially affect the rigidity of the land portions on both sides with respect to both symmetry axes, FIG. As shown in FIG. 13, the shape of the branch groove part 11 can be changed. Further, as shown in FIGS. 11 and 12, the shape of the opening to the tread surface of the air chamber 10 is substantially line-symmetric with respect to both symmetry axes (tire circumferential direction C and tire width direction W), FIG. As shown in FIG. 2, it is preferable that the opening shape of the air chamber 10 is circular. These reasons are the same as those described in the embodiment in which the opening shape of the resonator 9 is formed in line symmetry with respect to the tire circumferential direction C, and the description thereof is omitted.

  The above description shows only a part of the embodiment of the present invention, and these configurations can be combined alternately or various changes can be made without departing from the gist of the present invention. For example, in the above description, only the embodiment in which the rib-like land portion is defined by the two circumferential grooves is shown. However, although not shown, one circumferential groove and the tread ground contact end adjacent to the circumferential groove are shown. A resonator having the same configuration as that described above can also be applied to the rib-like land portion defined by the above.

  Next, tires according to the present invention were prototyped and performance evaluations were performed, which will be described below.

The tires of Examples 1 and 2 are radial tires for passenger cars having a tire size of 225 / 55R17, and the resonance frequency is 1000 Hz, which is the air column resonance sound frequency of a tire having no resonator, respectively. 66 resonators having the opening shape shown in (Example 1) and FIG. 11 (Example 2 ) are provided on the circumference of the rib-like land portion.

For comparison, the tires of Comparative Examples 1 and 2 configured in the same manner as in Examples 1 and 2 except that the resonator opening shapes are as shown in FIGS. 15 and 7, respectively . Prototype.

  Each of the test tires was mounted on a rim having a size of 7.5 × 17 to form a tire wheel, an air pressure of 220 kPa (relative pressure) was applied to the tire wheel, and each of the following tests was performed.

(Silence effect)
The sound pressure level when running on a drum tester under a tire load of 5.25 kN and increasing the running speed from 40 km / h to 100 km / h in increments of 10 km / h is based on the conditions specified in JASO C606. The noise reduction effect of the resonator was evaluated based on the Partial Overall value of the 1/3 Octave Band center frequency 800-1000-1250 Hz band. As a result, it was found that the silencing effect of the tire of each example is equivalent to the silencing effect of the tire of the conventional example.

(Maneuvering stability)
Each tire wheel is mounted on a test vehicle, and under a load condition equivalent to two passengers, a test course consisting of a peripheral circuit including a long straight portion and a handling evaluation road with many gentle curves, from low speed to about 100 km / h The car was run at a speed range experienced by general drivers on public roads, and the driving stability on dry roads was evaluated by a professional driver on a 10-point scale. At this time, the tire of Example 1 was mounted so that the upper direction of FIG. 3 was the rotational direction, and the tire of Comparative Example 2 was mounted so that the right side of FIG. The evaluation results are shown in Table 1.

(Uneven wear resistance)
Each tire wheel is mounted on a test vehicle and travels 10,000 km on a course including ordinary roads, expressways and mountain roads under a load condition equivalent to two passengers, and then the most in the rib-like land portion where the resonator is disposed. The difference in the amount of wear (step amount) between the portion with the largest wear and the portion with the least wear was measured, and the difference in the step amount between the left and right wheels was calculated to evaluate the uneven wear resistance. The difference in level difference is shown in Table 1. The smaller the difference in level difference between the left and right wheels, the better the uneven wear resistance.

As is clear from the results shown in FIG. 1, the tires of Examples 1 and 2 have improved steering stability and uneven wear resistance compared to the tires of the comparative examples.

  As is apparent from the above description, according to the present invention, it is possible to provide a pneumatic tire that can improve steering stability and uneven wear resistance while maintaining the silencing effect of the air column resonance sound. It was.

It is a figure which shows typically a Helmholtz type resonator. It is a figure which shows a stepped type resonator typically. 1 is a plan view of a part of a tread portion of a typical tire according to the present invention. It is a top view of a part of tread part of a basic tire. It is a top view of a part of tread part of a basic tire. It is a top view of a part of tread part of a basic tire. 6 is a plan view of a part of a tread portion of a tire of Comparative Example 2. FIG. It is a top view of a part of tread part of a basic tire. It is a top view of a part of tread part of a basic tire. It is a top view of a part of tread part of a basic tire. FIG. 6 is a plan view of a part of a tread portion of another tire according to the present invention. FIG. 6 is a plan view of a part of a tread portion of another tire according to the present invention. It is a top view of a part of tread part of a basic tire. It is a top view of a part of tread part of a basic tire. 4 is a plan view of a part of a tread portion of a tire of Comparative Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Resonator 2 Branch groove part 3 Air chamber part 4 1st pipe line 5 2nd pipe line 6 Tread part tread 7a, 7b Circumferential groove 8 Rib-shaped land part 9 Resonator 10 Air chamber 11, 11a, 11b, 11c Branch groove part

Claims (4)

The tread portion has at least one circumferential groove extending substantially in the tire circumferential direction and at least one row of rib-shaped land portions adjacent to the tread portion, and branches into the rib-shaped land portion from the circumferential groove. In a pneumatic tire provided with a resonator that reduces noise generated by resonance in the pipe formed by the circumferential groove and the road surface,
The resonator has an air chamber portion having a relatively large cross-sectional area perpendicular to the extending direction, and extends from the air chamber portion toward the circumferential groove, and has a cross-sectional area perpendicular to the extending direction. Comprising at least two branch grooves smaller than that of the chamber,
Opening shape to the resonator of the tread surface of the tread portion is Ri substantially axisymmetric der respect to at least one of the tire circumferential direction and the tire width direction,
The opening shape to the tread portion tread of the air chamber portion is substantially line symmetric with respect to at least one of the tire circumferential direction and the tire width direction,
The opening shape to the tread part tread of the air chamber part has at least one bent part,
The resonator has two circumferential grooves or one circumferential groove that defines a rib-like land portion on which the resonator is disposed, and a tread grounding end that opens through the branch groove portion. Enter tire. The pneumatic tire according to claim 1 , wherein an opening shape of the resonator to the tread portion tread surface is substantially line symmetric with respect to both the tire circumferential direction and the tire width direction. The tread portion has at least one circumferential groove extending substantially in the tire circumferential direction and at least one row of rib-shaped land portions adjacent to the tread portion, and branches into the rib-shaped land portion from the circumferential groove. In a pneumatic tire provided with a resonator that reduces noise generated by resonance in the pipe formed by the circumferential groove and the road surface,
The resonator has an air chamber portion having a relatively large cross-sectional area perpendicular to the extending direction, and extends from the air chamber portion toward the circumferential groove, and has a cross-sectional area perpendicular to the extending direction. Comprising at least two branch grooves smaller than that of the chamber,
Opening shape to the resonator of the tread surface of the tread portion is Ri substantially axisymmetric der respect to both the tire circumferential direction and the tire width direction,
The opening shape to the tread portion tread of the air chamber portion is substantially line symmetric with respect to at least one of the tire circumferential direction and the tire width direction,
A pneumatic tire characterized in that an opening shape of the air chamber portion to the tread portion tread has at least one bent portion . 4. The resonator according to claim 3 , wherein the resonator opens to two circumferential grooves or one circumferential groove and a tread grounding end that define a rib-like land portion on which the resonator is disposed via the branch groove portion. Pneumatic tires.

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