JP2010047230A - Tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire capable of certainly reducing an air-column tube resonance sound caused by a circumferential groove extending along a tire circumferential direction without impairing freedom on the design of a tread pattern. <P>SOLUTION: The tire has at least one circumferential groove 6 extending along a tire circumferential direction on a tread 4, and at least one row of rib-like lands 7 adjacent to this, and has a branch groove 8 opened to the circumferential groove 6 of the tread 4 in the rib-like land 7. The branch groove 8 is constituted of: a narrow part 8a opened to the circumferential groove 6 and having a relatively small cross section area; and an air chamber 8b communicating with the circumferential groove 6 through the narrow part 8a at one end side, terminated in the rib-like land 7 at the other end side and having a relatively larger cross section area than the narrow part 8a. The tire is provided with a reinforcement layer 10 in which a plurality of reinforcement cords are arranged at least at an inner side in a tire radial direction of the narrow part 8a of the tread 4 and an outer side in the tire radial direction of a belt 3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a tire that suppresses air column resonance caused by a circumferential groove extending along the tire circumferential direction to reduce noise.

  With air columnar resonance, high-frequency vibration is generated in the groove wall of the circumferential groove as the groove width of the circumferential groove suddenly fluctuates due to the action of external force by stepping on and kicking out during rolling of the tire on the ground, This is a phenomenon in which the air in the pipe formed by the circumferential groove and the road surface is vibrated and the noise is deteriorated by the acoustic resonance action based on the vibration. The frequency is often observed at about 800-1200 Hz for general passenger cars and about 600-1000 Hz for heavy-duty vehicles such as trucks. One. In addition, human hearing is sensitive in this band as shown by the A characteristic, and reducing the air columnar resonance sound greatly contributes to noise reduction.

Conventionally, in order to reduce the air column resonance sound, it has been common to reduce the volume of the circumferential groove, but this is accompanied by a decrease in drainage performance. On the other hand, in the rib-like land portion formed by the circumferential groove, a long branch groove having only one end opened in the circumferential groove and the other end terminated in the land portion is provided, and the groove is a so-called side branch type resonator. Thus, a technique for reducing air column resonance noise by anti-resonance has been proposed (see, for example, Patent Document 1). In addition, in the rib-like land portion formed by the circumferential groove, a branch groove is formed which includes a sipe that opens to the circumferential groove and a resonance chamber that is connected to the sipe and terminates in the rib-like land portion. There has been proposed a technique for absorbing energy in the vicinity of the resonance frequency of air column resonance sound by acting as a resonator of a type (see, for example, Patent Document 2).
International Publication No. 2004/1037737 Pamphlet Japanese Patent Laid-Open No. 5-338411

  However, in the side branch type resonator disclosed in Patent Document 1, it is essential to dispose a long branch groove corresponding to the frequency of the resonance frequency, so that the degree of freedom in designing the tread pattern is impaired. There is. On the other hand, the Helmholtz type resonator disclosed in Patent Document 2 can control the resonance frequency by reducing the cross-sectional area of the sipe, so that the tread pattern design is higher than that of the side branch type resonator. However, there is a problem that the sipe is substantially closed (groove closing) due to the compressive load at the time of rolling of the tire and cannot be sufficiently operated as a resonator. These problems are particularly prominent in heavy load tires that hold relatively heavy loads. This is because, for the side branch type resonator, the circumferential length in the ground contact surface of the heavy duty tire, that is, the pipe length formed by the circumferential groove and the road surface is increased, and accordingly, the length of the branch groove needs to be increased. This is because, for the Helmholtz type resonator, the sipes constituting the resonator are more easily closed due to an increase in the compressive load at the time of tire rolling due to an increase in tire weight.

  Therefore, the present invention proposes a tire that can reliably reduce air columnar resonance noise caused by a circumferential groove extending along the tire circumferential direction without impairing the design freedom of the tread pattern. With the goal.

  In order to achieve the above object, the present invention provides a carcass extending in a toroidal shape between a pair of left and right bead cores, a belt disposed on the outer side in the tire radial direction of the crown portion of the carcass, and disposed on the outer side in the tire radial direction of the belt. A tire having at least one circumferential groove extending along the tire circumferential direction in the tread portion and at least one row of rib-shaped land portions adjacent to the tread portion. A branch groove that opens to the circumferential groove is provided in the rib-like land portion, and the branch groove is opened to the circumferential groove and has a comparatively small cross-sectional area. In a tire configured to communicate with a groove and terminate in the rib-like land portion at the other end side and having a relatively large cross-sectional area than the narrowed portion, at least the narrowed portion of the tread portion. Department of parts The outer side in the tire radial direction of the Ya radially inward a and the belt, a tire, characterized in that is embedded a reinforcing layer formed by arranging a plurality of reinforcing cords. Here, the “circumferential groove” includes not only a groove that extends linearly along the tire circumferential direction but also a groove that extends in a zigzag shape or a wave shape and makes one round in the circumferential direction as a whole tire.

  By adopting such a configuration, a Helmholtz-type resonator consisting of a constriction and an air chamber is used as a resonator to reduce air columnar resonance caused by circumferential grooves. It is not necessary to provide a long branch groove unlike a vessel, and the tread pattern design freedom is not impaired. In addition, the reinforcement layer embedded on the inner peripheral side of the narrowed portion can increase the rigidity of the portion around the narrowed portion of the tread portion and can suppress the closing of the narrowed portion due to compressive deformation of the tread portion due to ground contact. Thus, the branch groove can be reliably acted as a resonator.

  Therefore, according to the tire of the present invention, air columnar resonance noise caused by the circumferential groove extending along the tire circumferential direction can be surely reduced without impairing the design freedom of the tread pattern. it can.

  For example, in the case of a tire in which the compression deformation in the tire circumferential direction of the red portion due to depression and kicking is larger than the compression deformation in the tire width direction during cornering or the like, the extending direction of the narrowed portion of the branch groove is the tire circumferential direction. In contrast, when it is inclined at 45 degrees or more, it is effective to increase the rigidity of the reinforcing layer in the tire circumferential direction in order to suppress the groove closing of the narrowed portion due to the compression deformation of the tread portion. For this purpose, it is effective to arrange the reinforcing cords constituting the reinforcing layer at an inclination angle of 10 degrees or less with respect to the tire circumferential direction, and further, 2 GPa against the tensile force in the tire circumferential direction on the reinforcing layer. It is more effective to give the above rigidity.

  Further, when the tire is compressed in the tire circumferential direction, the tire width direction elongation (Poisson deformation) occurs at the same time. For example, the tread portion compressive deformation in the tire width direction during cornering or the like is depressed and kicked. In the case of a tire that is larger than the compression deformation in the tire circumferential direction due to protrusion, or when the extending direction of the narrowed portion of the branch groove is inclined at 45 degrees or less with respect to the tire circumferential direction, the tread portion is compressed and deformed. It is effective to increase the rigidity of the reinforcing layer in the tire width direction in order to suppress the closing of the narrowed portion due to the groove. For this purpose, the reinforcing cords constituting the reinforcing layer are arranged on the acute angle side with respect to the tire circumferential direction. It is effective to arrange with an inclination angle of 80 degrees or more as measured by the above, and it is more effective to give the reinforcement layer a rigidity of 40 GPa or more against the tensile force in the tire width direction.

  And this invention is suitably applicable to the tire for heavy loads.

  According to the present invention, it is possible to reliably reduce air columnar resonance noise caused by a circumferential groove extending along the tire circumferential direction without impairing the design freedom of the tread pattern.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a view showing a pneumatic tire (hereinafter referred to as “tire”) according to an embodiment of the present invention, (a) is a cross-sectional view showing a cross section in the tire width direction, and (b) is a cross-sectional view. It is an expanded view which shows the tread pattern in a tread surface.

  As shown in FIG. 1 (a), this tire includes a carcass 2 extending in a toroidal shape between a pair of left and right bead cores 1 and 1, and two layers of, for example, two layers disposed on the outer side in the tire radial direction of the crown portion of the carcass 2. The belt 3 includes a belt layer 3a and a cap belt layer 3b, and a tread portion 4 disposed on the outer side in the tire radial direction of the cap belt layer 3b. Moreover, as shown in FIG.1 (b), this tire is provided with the four circumferential groove | channel 6 extended along a tire circumferential direction in the tread part 4, and the rib-shaped land part 7 adjacent to this. A branch groove 8 that opens to the circumferential groove 6 is provided in the two rib-like land portions 7 adjacent to the outer side in the tire width direction of the two circumferential grooves 6 positioned on the inner side in the tire width direction. The branch groove 8 is open to the circumferential groove 6 and has a narrow section 8a having a relatively small cross-sectional area. The branch groove 8 communicates with the circumferential groove 6 through the narrow section 8a on one end side and the rib on the other end side. An air chamber portion 8b that terminates in the land portion 7 and has a relatively larger cross-sectional area than the narrow portion 8a. Here, the cross-sectional area of the narrowed portion 8a indicates the cross-sectional area of the groove in the plane orthogonal to the center line C1 in the extending direction, and the cross-sectional area of the air chamber portion 8b is orthogonal to the center line C2 in the extending direction. It refers to the cross-sectional area of the groove on the surface to be cut.

として表される。よって、周方向溝６に発生する気柱管共鳴音の周波数との関連の下で、狭窄部８ａの長さＬ、狭窄部８ａの断面積Ｓ及び気室部８ｂの容積Ｖの大きさを適宜設定することで、所望に応じた共鳴周波数ｆを得ることができる。 As a result, the branch groove 8 forms a Helmholtz resonator as schematically shown in FIG. 2 (a) when both the constriction 8a and the air chamber 8b are sealed by the road surface. The resonance frequency f is such that the length in the extending direction of the constriction 8a is L, the cross-sectional area of the constriction 8a in the plane perpendicular to the center line C1 is S, the volume of the air chamber 8b is V, and the sound velocity is When C

Represented as: Therefore, in relation to the frequency of the air column resonance sound generated in the circumferential groove 6, the length L of the constriction 8a, the cross-sectional area S of the constriction 8a, and the volume V of the air chamber 8b are set as follows. By appropriately setting the resonance frequency f as desired, it can be obtained.

  As shown in FIG. 1 (b), a plurality of reinforcing cords are provided on the inner side (inner circumference side) of the narrowed portion 8a of the tread portion 4 and on the outer side (outer circumference side) in the tire radial direction of the belt. An array of reinforcing layers 10 is embedded over the entire circumference. An organic fiber cord having an elastic modulus at 30 ° C. of 3.2 GPa to 47.0 GPa is used for the reinforcing cord constituting the reinforcing layer 10. Examples of such an organic fiber cord include nylon fiber and aramid fiber.

  In the tire of the embodiment shown in FIG. 1, a Helmholtz type resonator composed of a constricted portion 8 a and an air chamber portion 8 b is employed as a resonator that reduces air column resonance noise caused by the circumferential groove 6. Therefore, it is not necessary to provide a long branch groove unlike a side branch type resonator, and the design freedom of the tread pattern is not impaired. Further, the reinforcing layer 10 embedded on the inner peripheral side of the narrowed portion 8a increases the rigidity of the peripheral portion of the narrowed portion 8a of the tread portion 4, and the narrowed portion 8a resulting from the compressive deformation of the tread portion 4 due to tire load rolling. Therefore, the branch groove 8 can be reliably acted as a resonator.

  Therefore, according to the tire of this embodiment, air columnar resonance noise caused by the circumferential groove 6 extending along the tire circumferential direction is reliably reduced without impairing the design freedom of the tread pattern. be able to.

  By the way, in the case of a tire in which the compression deformation in the tire circumferential direction of the tread portion 4 due to depression and kicking is larger than the compression deformation in the tire width direction at the time of cornering or the like, or the extending direction of the narrowed portion 8a of the branch groove 8 is When inclined at 45 degrees or more with respect to the direction, it is effective to increase the rigidity of the reinforcing layer 10 in the tire circumferential direction in order to suppress the closing of the narrowed portion 8a due to the compression deformation of the tread portion 4. Is. For that purpose, it is effective to arrange the reinforcing cords constituting the reinforcing layer 10 along the tire circumferential direction, more specifically, with an inclination angle of 10 degrees or less with respect to the tire circumferential direction. It is more effective to give the reinforcing layer 10 a rigidity of 2 GPa or more against the tensile force in the tire circumferential direction. Here, the rigidity with respect to the tensile force in the tire circumferential direction is the unit width of the reinforcing layer 10 when 1% of the tire circumferential tensile strain is applied at room temperature with the reinforcing layer 10 taken out of the tire. It is defined by Young's modulus.

  Further, when the tire is compressed in the tire circumferential direction, the tire width direction elongation (Poisson deformation) occurs simultaneously. For example, when the cornering or the like, the tread portion 4 is compressed and deformed in the tire width direction. In the case of a tire that is larger than the compressive deformation in the tire circumferential direction due to kicking out or when the extending direction of the narrowed portion 8a of the branch groove 8 is inclined at 45 degrees or less with respect to the tire circumferential direction, the tread portion 4 It is effective to increase the rigidity of the reinforcing layer 10 in the tire width direction in order to suppress the closing of the narrowed portion 8a due to compressive deformation. For this purpose, the reinforcing cord constituting the reinforcing layer 10 is attached to the tire circumference. It is effective to arrange at an inclination angle of 80 degrees or more when measured at an acute angle side with respect to the direction, and the reinforcing layer 10 has a rigidity of 40 GPa or more with respect to the tensile force in the tire width direction. Rukoto is more effective. Here, the rigidity with respect to the tensile force in the tire width direction is determined by the unit width of the reinforcing layer 10 when a tensile strain of 1% in the tire width direction is applied at room temperature with the reinforcing layer 10 taken out of the tire. It is defined by Young's modulus.

  Note that the above description shows only a part of the embodiment of the present invention, and these configurations can be combined with each other or various modifications can be made without departing from the gist of the present invention. . For example, the reinforcing layer 10 can also be provided on the inner side in the tire radial direction of the air chamber portion 8, and in this way, the volume V of the air chamber portion 8 at the time of tire rolling can be reliably ensured. . In the above-described embodiment, the air chamber portion 8b is such that the shape of the opening to the tread surface (that is, the cross-sectional area) does not change in the depth direction, but the air chamber portion 8b in the depth direction. Of course, the cross-sectional area of each of them may be gradually increased or decreased. Further, the groove bottom of the air chamber portion 8b may be substantially flat or an uneven curved surface. In this embodiment, the opening shape to the tread surface of the air chamber portion 8b is rectangular, but the present invention is not limited to this, and various shapes such as a polygon, a circle, an ellipse, and an irregular closed shape can be applied. Further, the branch groove 8 is constituted by a narrowed portion 8a that opens to the circumferential groove 6 and an air chamber portion 8b that communicates with the circumferential groove 6 through the narrowed portion 8a and has a larger cross-sectional area than the narrowed portion 8a. In place of the Helmholtz type resonator described above (see FIG. 2A), as shown in FIG. 2B, the air chamber portion 8b and the narrowed portion 8a are respectively connected to the first duct and the second duct. It can also be used as a stepped tube type resonator comprising connecting pipes connecting them to each other. In this case, the resonance frequency f ′ can be obtained as shown below.

For the stepped tube resonator, the acoustic impedance on the first pipeline 8b ′ side at the boundary is Z ₁₂ , the acoustic impedance on the second pipeline 8a ′ side in the boundary is Z ₂₁ , and the sectional area of the first pipeline 8b ′. Is S ₁ , and the cross-sectional area of the second pipe line 8a ′ is S ₂ ,
Z ₂₁ = (S ₂ / S ₁ ) · Z ₁₂
The relationship is established.

With respect to the second pipe line 8a ′, when the boundary conditions are x = 0 and V ₂ = V ₀ e ^jwt , x = l ₂ and P ₂ / V ₂ = Z ₂₁ , the boundary condition from the opening of the second pipe line 8a ′ distance the sound pressure P ₂ which definitive position of x,
_{P 2 = Z c · {(} 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
It is expressed. Here, l ₂ is the length of the second conduit 8a ′, V ₂ is the particle velocity distribution of the second conduit 8a ′, V ₀ is the particle velocity at the input point, j is the imaginary unit, Z _c Is ρc (ρ is the density of air, c is the speed of sound), and k is 2πf / c.

Further, regarding the first pipeline 8b ′, when the boundary conditions are V = ₁ = 0 when x = l ₁ and P ₂ = P ₁ when x = 0, the position of the distance x from the opening of the first pipeline 8b ′ Sound pressure P ₁
P ₁ = Z _c · [Z ₂₁ cos (k (l ₁ −x)) / (cos (kl ₁ ) · {Z _c cos (kl ₂ ) + jZ ₂₁ sin (kl ₂ )})] · e ^jwt
It is expressed. Here, l ₁ is the length of the first pipeline 8b ′.

Here, since the resonance condition x = 0 and P ₂ = 0,
tan (kl ₁ ) tan (kl ₂ ) − (S ₂ / S ₁ ) = 0, and k, l ₁ , l ₂ , S ₂ , S ₁ , c are determined based on the conditional expression of this resonance. The resonance frequency f ′ can be obtained.

  In the example shown in the figure, the stepped tube type resonator is a combination of pipes that are rectangular parallelepiped. However, to obtain the resonance frequency using the above conditional expression, the cross-sectional area and length of each pipe are determined. Therefore, the shape of the pipe line is not limited to a rectangular parallelepiped, and various shapes can be applied.

  In addition, it is indispensable that one end of the second pipe line 8 a ′ is opened by the groove wall of the circumferential groove 6, but the first pipe line 8 b ′ and the second pipe line 8 a ′ are in contact with the tread portion 4. Since the closed space is formed by contact with the road surface in the ground, the upper end thereof can be opened at the surface of the rib, and this point is not limited.

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

The tire of Example 1 is a 225 / 55R17 size radial tire for a passenger car having a 1-ply carcass, 2-belt ply, and 1-cap belt structure having the structure and tread pattern shown in FIGS. 1 (a) and 1 (b). This tire includes four circumferential grooves extending in the tire circumferential direction and a rib-like land portion adjacent to the circumferential groove in the tread portion. The circumferential groove has a width of 8.0 mm and a depth of 8.0 mm. Further, this tire has 60 branch grooves as resonators having a constricted portion and an air chamber portion in the rib-like land portion over the circumference. The dimensions of each branch groove are as follows: the volume of the air chamber portion is 950 mm ³ , the longitudinal length of the narrowed portion is 34.0 mm, the cross-sectional area of the narrowed portion is 13.0 mm ² , and the resonance frequency is 1070 Hz. Further, on the inner peripheral side of the narrowed portion of the branch groove of this tire and on the outer peripheral side of the belt, a reinforcing layer having the specifications shown in Table 1 below is provided, and the axial direction of the reinforcing cord constituting the tire is in the tire circumferential direction. It was applied in an arrangement with an inclination angle of 5 degrees.

The tire of Example 2 includes a 315 / 80R22.5 size truck having a 3.5B structure (one ply carcass and 3.5 belt ply structure) having a structure and a tread pattern shown in FIGS. This is a radial tire for buses. This tire includes four circumferential grooves extending in the tire circumferential direction and a rib-like land portion adjacent to the circumferential groove in the tread portion. The circumferential groove has a width of 12.0 mm and a depth of 17.0 mm. Further, this tire has 60 branch grooves as resonators having a constricted portion and an air chamber portion in the rib-like land portion over the circumference. The dimensions of each branch groove are as follows: the volume of the air chamber portion is 8210 mm ³ , the longitudinal length of the constriction portion is 20 mm, the cross-sectional area of the constriction portion is 39 mm ² , and its resonance frequency is 840 Hz. Further, on the inner peripheral side of the narrowed portion of the branch groove of this tire and on the outer peripheral side of the belt, a reinforcing layer having the specifications shown in Table 1 below is provided, and the axial direction of the reinforcing cord constituting the tire is in the tire circumferential direction. It applied with the arrangement | positioning used as the inclination-angle of 84 degree | times.

  For comparison, the tire of Comparative Example 1 having the same configuration as the tire of Example 1 except that the reinforcing layer is not provided on the inner peripheral side of the narrowed portion of the branch groove and on the outer peripheral side of the belt, A tire of Comparative Example 2 having the same configuration as the tire of Example 2 was also prototyped except that the reinforcing layer was not provided on the inner peripheral side of the constricted portion and on the outer peripheral side of the belt.

  Each test tire thus obtained was applied to the tire of Example 1 and the tire of Comparative Example 1 on a rim of size 7.50 × 17, and then an internal pressure of 250 kPa (relative pressure) was applied. For the tire of Example 2 and the tire of Comparative Example 2, an internal pressure of 800 kPa (relative pressure) was applied after being mounted on a rim of size 9.00 × 22.5, and the noise reduction effect and the narrowing of the narrow portion were closed for each tire. The inhibitory effect was tested as follows.

(Noise reduction effect)
Using an indoor drum testing machine, these tires were subjected to a predetermined load (load of 7.2 kN for the tire of Example 1 and Comparative Example 1 and 33.1 kN for the tire of Example 2 and Comparative Example 2). Under the action of load rolling at a predetermined speed (80 km / h for the tire of Example 1 and Comparative Example 1 and 70 km / h for the tire of Example 2 and Comparative Example 2), The side sound of the tire was measured according to the conditions defined in JASO C606, and the overall value of the 1/3 octave band center frequency 800 Hz-1000 Hz-1250 Hz band was measured. The evaluation results are shown in Table 2. The evaluation results in Table 2 show the relative values with respect to the measurement results of the tire of Comparative Example 1 for the tire of Example 1, and the measurement results of the tire of Comparative Example 2 for the tire of Example 2. The relative value is shown. The larger the negative value, the lower the noise level.

  From the results in Table 2, the tires of Example 1 and Example 2 have lower noise levels than the tires of Comparative Example 1 and Comparative Example 2 in which the reinforcing layer is not provided on the inner peripheral side of the narrowed portion. It was. Further, the tire of Example 2 for trucks and buses was more excellent in noise reduction effect than the tire of Example 1 for passenger cars.

(Groove closing suppression effect)
Using an indoor drum tester, the tire was subjected to a predetermined load (load 7.2 kN for the tire of Example 1 and Comparative Example 1; 33.1 kN for the tire of Example 2 and Comparative Example 2). Under the action, the rolling was performed at a very low speed, the groove shape of the narrowed portion at that time was modeled, and the remaining groove cross-sectional area (minimum value) was measured. The evaluation results are shown in Table 3. The evaluation results in Table 3 show the ratio of the groove cross-sectional area reduction to the groove cross-sectional area before rolling the tire (initial groove cross-sectional area) as the groove cross-sectional area reduction rate (%). Indicates that the groove closing is small. The groove shape was formed by filling the groove with curable silicon, and the change in the cross-sectional area was examined by rotating at a low speed in this state, and the remaining groove cross-sectional area was measured.

  From the results of Table 3, the tire of Example 1 and the tire of Example 2 have a larger remaining groove area than the tire of Comparative Example 1 and the tire of Comparative Example 2 that do not have a reinforcing layer on the inner peripheral side of the narrowed portion. The groove closing was small. In addition, the tire of Example 2 for trucks and buses had a greater effect of suppressing groove closing than the tire of Example 1 for passenger cars.

  According to the present invention, it is possible to reliably reduce air columnar resonance noise caused by the circumferential groove extending along the tire circumferential direction without impairing the design freedom of the tread pattern.

It is a figure which shows the pneumatic tire of one Embodiment according to this invention, (a) is sectional drawing of a tire width direction, (b) is a development view of a tread pattern. It is a schematic diagram which shows each resonator applicable to this invention, (a) is a Helmholtz type resonator, (b) is a stepped tube type resonator. It is a figure which shows the pneumatic tire of other embodiment according to this invention, (a) is sectional drawing of a tire width direction, (b) is a development view of a tread pattern.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bead core 2 Carcass 3 Belt 3a Belt layer 3b Cap belt layer 4 Tread part 6 Circumferential groove 7 Rib-like land part 8 Branch groove 8a Narrow part 8b Air chamber part 10 Reinforcement layer

Claims (6)

A carcass extending in a toroidal shape between a pair of left and right bead cores, a belt disposed on the outer side in the tire radial direction of the crown portion of the carcass, and a tread portion disposed on the outer side in the tire radial direction of the belt. A tire provided with at least one circumferential groove extending in the direction and at least one row of rib-like land portions adjacent to the groove and opening in the circumferential groove in the rib-like land portion of the tread portion A branch groove is provided, and the branch groove is opened to the circumferential groove and has a relatively small cross-sectional area. The narrow groove communicates with the circumferential groove through the narrow portion on one end side and on the other end side. In a tire configured with an air chamber portion terminating in the rib-like land portion and having a relatively large cross-sectional area than the narrowed portion,
A tire characterized in that a reinforcing layer formed by arranging a plurality of reinforcing cords is embedded at least inside the tire tread portion in the tire radial direction and outside the belt in the tire radial direction.   The tire according to claim 1, wherein the reinforcing cords constituting the reinforcing layer are arranged at an inclination angle of 10 degrees or less with respect to the tire circumferential direction.   The tire according to claim 2, wherein the reinforcing layer has a rigidity of 2 GPa or more with respect to a tensile force in a tire circumferential direction.   The tire according to claim 1, wherein the reinforcing cords constituting the reinforcing layer are arranged at an inclination angle of 80 degrees or more measured from an acute angle side with respect to the tire circumferential direction.   The tire according to claim 4, wherein the reinforcing layer has a rigidity of 40 GPa or more with respect to a tensile force in a tire width direction.   The tire according to any one of claims 1 to 5, wherein the tire is a heavy load tire.

Images