JP5193549B2 - Pneumatic tire - Google Patents

Description

  The present invention includes a tread portion including at least one circumferential groove extending along the tire circumferential direction and at least one row of rib-shaped land portions adjacent to the tread portion, and the circumferential direction in the rib-shaped land portion. Resonance comprising a branch groove opening in the groove, and an air chamber portion communicating with the circumferential groove through the branch groove and having a larger cross-sectional area than the branch groove, and reducing noise caused by the circumferential groove. In particular, the present invention relates to a pneumatic tire in which a rib is provided, and in particular, to reduce uneven wear of a rib-like land portion resulting from the arrangement of the resonator and to improve steering stability.

  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. Among them, tire noise at a high frequency, particularly around 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 around 1000 Hz is a so-called air column resonance sound generated by resonance of air in the pipe mainly formed by a circumferential groove extending along the tire circumferential direction and a road surface in a contact area of the tread portion. In general passenger cars, it is often observed at about 800 to 1200 Hz, and since the peak sound pressure level is high and the frequency band is wide, it occupies most of the noise generated from pneumatic tires. It becomes. 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.

  In order to reduce such air column resonance noise, it is effective to reduce the number of circumferential grooves and the volume of the grooves, but in this case, the drainage performance is a result of insufficient groove volume of the circumferential grooves. May decrease. In order to reduce air column resonance without reducing the number of circumferential grooves and the volume of grooves, Patent Document 1 discloses that one end of the circumferential groove is opened in the rib-like land portion formed by the circumferential grooves. In addition, a pneumatic tire is disclosed in which a long horizontal groove (air column resonator) whose other end terminates in a land portion is provided, and air column resonance noise can be reduced by using anti-resonance in the horizontal groove. . However, in the pneumatic tire disclosed in Patent Document 1, since it is essential to dispose long lateral grooves corresponding to the magnitude of the amplitude, the degree of freedom in designing the tread pattern is impaired.

  As a solution to these problems, as disclosed in Patent Document 2, a so-called sipe (branch groove) that opens to a circumferential groove and a resonance chamber (air chamber part) that is connected to the branch groove is a so-called one. Techniques have been proposed in which energy in the vicinity of the resonance frequency of air column resonance is absorbed by a Helmholtz resonator. As a result, the degree of freedom in designing the tread pattern is improved as compared with the pneumatic tire described in Patent Document 1, while ensuring sufficient groove volume of the circumferential groove and ensuring drainage performance and the like. Is possible.

International Publication No. 04/103737 Pamphlet Japanese Patent Laid-Open No. 5-338411

  However, in the pneumatic tire described in Patent Document 2, since the branch groove extends linearly from the air chamber portion, the size of the air chamber portion is increased or the length of the branch groove is increased. As a result, there is a problem that the frequency band of the air column resonance sound that can be reduced is limited. Further, as shown in FIG. 7, in order to secure a sufficient length of the branch groove 107, if the branch groove 107 is inclined and extended with respect to the tire circumferential direction 103, it is sandwiched between the branch groove 107 and the circumferential groove 103. The sharpened portion 110 is formed at the portion, and the rigidity of the portion is lowered. As a result, when the road surface touches down, the part falls down and escapes from contact with the road surface, so that only the pinched part is locally slowed down, causing uneven wear problems, and the steering stability is also lowered due to reduced rigidity. There is also a concern that

  Accordingly, it is an object of the present invention to solve these problems, and an object of the present invention is to make it possible to reduce air column resonance by the resonator by optimizing the shape of the resonator. Accordingly, it is an object of the present invention to provide a pneumatic tire capable of improving uneven wear resistance and steering stability.

  In order to achieve the above object, the first invention comprises, in the tread portion, at least one circumferential groove extending along the tire circumferential direction, and at least one row of rib-shaped land portions adjacent thereto. The rib-shaped land portion includes a branch groove that opens to the circumferential groove, and an air chamber portion that communicates with the circumferential groove through the branch groove and has a larger cross-sectional area than the branch groove. In a pneumatic tire provided with a resonator that reduces noise caused by a directional groove, the branch groove has at least one bent portion, and the branch groove has an opening end that opens to the circumferential groove. The pneumatic tire is characterized in that an angle formed between the center line of the branch groove and the tire circumferential direction is in a range of 45 degrees or more and 90 degrees or less. Here, the “circumferential groove” means not only a groove extending linearly along the tire circumferential direction, but also a groove extending in a zigzag shape or a wave shape and making one round in the circumferential direction as a whole tire. The “angle between the center line of the branch groove and the tire circumferential direction” means an angle measured from an acute angle side among the intersection angles formed by the intersection of the center line of the branch groove and the tire circumferential direction. To do. By adopting such a configuration, it is possible to increase the length of the branch groove as compared with the case where the branch groove is extended linearly as in the conventional case, and therefore the frequency of the resonance frequency that can correspond to the frequency of tire noise. The bandwidth can be expanded and the tread pattern design freedom can be improved. Furthermore, at the opening end where the branch groove opens into the circumferential groove, the angle between the center line of the branch groove and the tire circumferential direction is within a range of 45 degrees or more and 90 degrees or less, so that the branch groove and the circumferential direction are A sharp portion is not formed in the portion sandwiched between the grooves, and the rigidity of the portion can be increased. Therefore, even when the road surface is in contact with the road surface, the portion reliably contacts the road surface without falling down, and the contact pressure is kept uniform, so that steering stability and uneven wear resistance are improved.

According to another invention, the tread portion includes at least one circumferential groove extending along the tire circumferential direction, and at least one row of rib-shaped land portions adjacent to the tread portion, and the rib-shaped land portion includes the circumferential groove. Resonance that is composed of a branch groove that opens to the directional groove and an air chamber portion that communicates with the circumferential groove through the branch groove and has a larger cross-sectional area than the branch groove to reduce noise caused by the circumferential groove. In the pneumatic tire formed by arranging the vessel, the branch groove has at least one curved portion, and the opening of the branch groove to the circumferential groove has a center line of the branch groove. The pneumatic tire is characterized in that an angle formed with a tire circumferential direction is in a range of 45 degrees to 90 degrees. Here, when the center line of the branch groove is a curve, the “angle formed between the center line of the branch groove and the tire circumferential direction” refers to the angle formed between the tangent line of the center line of the branch groove and the tire circumferential direction. To do. By adopting such a configuration, it is possible to increase the length of the branch groove as compared with the case where the branch groove is extended linearly as in the conventional case, and therefore the frequency of the resonance frequency that can correspond to the frequency of tire noise. The bandwidth can be expanded and the tread pattern design freedom can be improved. Furthermore, at the opening end where the branch groove opens into the circumferential groove, the angle between the center line of the branch groove and the tire circumferential direction is within a range of 45 degrees or more and 90 degrees or less, so that the branch groove and the circumferential direction are A sharp portion is not formed in the portion sandwiched between the grooves, and the rigidity of the portion can be increased. Therefore, even when the road surface is in contact with the road surface, the portion reliably contacts the road surface without falling down, and the contact pressure is kept uniform, so that steering stability and uneven wear resistance are improved.

  Further, the branch groove is at the end of the rib-shaped land portion in the tire width direction and within a region at a distance of at least 0.8 times the depth of the branch groove from the side having the opening end of the branch groove toward the other side. The angle formed by the center line and the tire circumferential direction is preferably in the range of 45 degrees to 90 degrees.

  Furthermore, the angle formed by the center line of the branch groove at the opening end and the tire circumferential direction is preferably 60 degrees or more.

  According to these inventions, it is possible to provide a pneumatic tire capable of improving uneven wear resistance and steering stability on the assumption that air column resonance noise can be reduced by a resonator.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an enlarged plan view showing an enlarged main part of a tread portion of a pneumatic tire (hereinafter referred to as “tire”) according to the present invention.

  The tire shown in FIG. 1 includes a tread portion 1 having a circumferential groove 3 extending along the tire circumferential direction and a rib-like land portion 5 adjacent thereto. Furthermore, this tire is comprised in the rib-like land part 5 by the branch groove 7 opened to the circumferential groove 3, and the air chamber part 9 communicating with the circumferential groove 3 through the branch groove 7, and in the circumferential direction. A resonator 11 is provided for reducing noise generated by resonance in the pipe formed by the groove 3 and the road surface. The air chamber portion 9 is formed such that a cross-sectional area in a plane perpendicular to the center line C1 is larger than a cross-sectional area in the plane perpendicular to the center line C2 of the branch groove 7.

として表すことができるので、この共鳴周波数ｆは、周方向溝３の気柱共鳴周波数との関連の下で、枝溝７の長さにｌ_ｈ、枝溝７の断面積をＳ（半径ｒ）及び気室部９の容積Ｖの大きさを選択的に変えることによって、所要に応じて変化させることができる。 The resonator 11 forms a Helmholtz resonator as schematically shown in FIG. 2 (a) under the condition that both the air chamber 9 and the branch groove 7 are sealed by the road surface. The resonance frequency f is expressed as follows: the length of the branch groove 7 is l _h , the radius of the branch groove 7 is r, the cross-sectional area of the branch groove 7 is S, the volume of the air chamber 9 is V, and the sound velocity is c.

This resonance frequency f can be expressed as follows: in relation to the air column resonance frequency of the circumferential groove 3, the length of the branch groove 7 is l _h , and the sectional area of the branch groove 7 is S (radius r ) And the volume V of the air chamber portion 9 can be selectively changed as required.

  In addition, when the cross-sectional shape of the branch groove 7 is not circular, the radius r in the above formula is obtained by calculating backward based on the cross-sectional area of the branch groove 7. The coefficient “1.3” in the equation has a different value depending on the literature, but it can be generally obtained from an empirical equation and is used as one coefficient in the present invention.

  Further, the air chamber portion 9 can be applied with the same cross-sectional area as the opening area over the entire depth direction, but the cross-sectional area gradually increases or decreases in the depth direction. Things may apply. In addition, the bottom wall of the air chamber portion 9 may be a substantially flat surface, or may be a convex or concave curved surface toward the opening side.

  Furthermore, in the tire of the illustrated example, the opening shape of the air chamber portion 9 to the surface of the rib-like land portion 5 is a rectangle, but this opening shape is not limited to this, but a polygon, a circle, an ellipse, Other closed curve shapes, irregular closed shapes, etc. can be applied.

  As shown in FIG. 1, the main feature of the configuration of the present invention is that the branch groove 7 has a bent portion 15 between the air chamber portion 9 and the opening end 13 opened in the circumferential groove 3. Furthermore, the angle θ formed by the center line C2 of the branch groove 7 and the tire circumferential direction at the opening end 13 is in the range of 45 degrees or more and 90 degrees or less. There should be at least one bent portion 15 in the branch groove 7, and the resonance frequency can be appropriately increased or decreased to correspond to the frequency of tire noise. Further, the angle of the bent portion 15 is not particularly specified, and can be set as appropriate for convenience of design.

  According to the tire of the embodiment shown in FIG. 1, the branch groove 7 does not extend linearly from the air chamber portion and open to the circumferential groove as in the prior art, but instead extends from the air chamber portion 9 through the bent portion 15. Since it opens to the direction groove | channel 3, it becomes possible to lengthen the length of the branch groove 7 compared with the past. As a result, the frequency band of the resonance frequency that can correspond to the frequency of tire noise can be expanded, and the degree of freedom in designing the tread pattern can be improved. Furthermore, at the opening end 13 where the branch groove 7 opens into the circumferential groove 3, the angle θ formed by the center line C2 of the branch groove 7 and the tire circumferential direction is within a range of 45 degrees or more and 90 degrees or less. A sharp portion is not formed in the portion sandwiched between the branch groove 7 and the circumferential groove 3, and the rigidity of the portion can be increased. Therefore, even when the road surface is in contact with the road surface, the portion reliably contacts the road surface without falling down, and the contact pressure is kept uniform, so that steering stability and uneven wear resistance are improved.

Next, another embodiment will be described. Here, FIG. 3 is an enlarged plan view showing an essential part of a tread portion of another tire. In addition, the same code | symbol is attached | subjected and demonstrated to the member similar to the tire of embodiment shown in FIG.

  The tire shown in FIG. 3 comprises a tread portion 1 having a circumferential groove 3 extending along the tire circumferential direction and a rib-like land portion 5 adjacent thereto. Furthermore, this tire is comprised in the rib-shaped land part 5 by the branch groove 17 opened to the circumferential groove 3, and the air chamber part 9 communicating with the circumferential groove 3 through the branch groove 17, and in the circumferential direction. A resonator 19 is provided to reduce noise generated by resonance in the pipe formed by the groove 3 and the road surface. The air chamber portion 9 is formed so that a cross-sectional area in a plane perpendicular to the center line C1 is larger than a cross-sectional area in the plane perpendicular to the center line C2 of the branch groove 17.

  The resonator 19 in the illustrated example is a Helmholtz resonator similar to that of the tire of the previous embodiment, and description thereof is omitted.

  As shown in FIG. 3, the main feature of the configuration of the present invention is that the branch groove 17 has a curved portion 21 between the air chamber portion 9 and the opening end opened in the circumferential groove 3. Furthermore, the angle θ formed by the center line C2 of the branch groove 17 and the tire circumferential direction at the opening end 13 is in the range of 45 degrees or more and 90 degrees or less. There should be at least one bending portion 21 in the branch groove 17, and the resonance frequency can be appropriately increased or decreased to correspond to the frequency of tire noise. Further, the radius of curvature of the curved portion 21 is not particularly specified, and can be appropriately set depending on the design convenience.

  According to the tire of the embodiment shown in FIG. 3, the branch groove 17 does not extend linearly from the air chamber portion and open to the circumferential groove as in the prior art, but instead extends from the air chamber portion 9 through the curved portion 21. Since it opens to the direction groove | channel 3, compared with the past, the length of the branch groove 17 can be lengthened. As a result, the frequency band of the resonance frequency that can correspond to the frequency of tire noise can be expanded, and the degree of freedom in designing the tread pattern can be improved. Furthermore, by making the angle between the center line C2 of the branch groove 17 and the tire circumferential direction at the opening end 13 where the branch groove 17 opens into the circumferential groove 3, it is within a range of 45 degrees or more and 90 degrees or less. A sharp portion is not formed in a portion sandwiched between the branch groove 17 and the circumferential groove 3, and the rigidity of the portion can be increased. Therefore, even when the road surface is in contact with the road surface, the portion reliably contacts the road surface without falling down, and the contact pressure is kept uniform, so that steering stability and uneven wear resistance are improved.

  As shown in FIGS. 1 and 3, the branch grooves 7 and 17 are the ends in the tire width direction of the rib-like land portion 5 and are directed from the side 23 having the opening ends 13 of the branch grooves 7 and 17 toward the other side. The angle between the center line C2 and the tire circumferential direction is within a range of 45 degrees or more and 90 degrees or less in a region at a distance of at least 0.8 times the depth of the branch grooves 7 and 17. preferable. In general, the rigidity of a rubber block formed of tread rubber as shown in FIG. 4 (a) is shown in FIG. 4 (b) as W / H increases when the width is W and the height is H. ) And increases gradually when W / H reaches about 0.8, and W / H almost reaches saturation around 1.0. Therefore, at least 0.8 times the depth of the branch groove 7 from the side 23 having the opening end 13 of the branch grooves 7 and 17 toward the other side at the end in the tire width direction of the rib-like land portion 5 in this way. The angle θ formed by the center line C2 and the tire circumferential direction is within the range of 45 degrees or more and 90 degrees or less, so that the branch grooves 7 and 17 and the circumferential groove 3 are sandwiched. It is possible to more effectively secure the rigidity of the portion.

  In addition, the angle θ formed by the center line C2 of the branch grooves 7 and 17 at the opening end 13 and the tire circumferential direction is preferably 60 degrees or more. According to this, the rigidity of the portion sandwiched between the branch grooves 7 and 17 and the circumferential groove 3 can be further increased, and steering stability and uneven wear resistance can be further improved.

Further, the region Z _{in where the} angle θ formed by the center line C2 of the branch grooves 7 and 17 and the tire circumferential direction is within the range of 45 degrees or more and 90 degrees or less is the end of the rib-like land portion 5 in the tire width direction. It is preferable that the distance is not more than twice the depth of the branch grooves 7 and 17 from the side 23 having the open ends 13 of the branch grooves 7 and 17 toward the other side. Even if the region Z _in is larger than twice the depth of the branch grooves 7 and 17, the rigidity of the portion sandwiched between the branch grooves 7 and 17 and the circumferential groove 3 as described above with reference to FIG. This is because the effect on the increase is small, and it may be difficult to secure the length of the branch grooves 7 and 17 while ensuring the tire performance.

Further, as shown in FIGS. 1 and 3, the angle formed between the center line C2 of the branch grooves 7 and 17 and the tire circumferential direction including the open ends 13 of the branch grooves 7 and 17 is within a range of 45 degrees or more and 90 degrees or less. the angle theta _out of the center line C2 and the tire circumferential direction of the Edamizo 7, 17 in the area _{Z in} the area outside the _{Z OUT} that is, the center line C2 of Edamizo 7 in the area _{Z in} the tire circumferential direction It is preferable to make it smaller than the angle θ formed by In this way, it is possible to easily secure the length of the branch grooves 7 and 17 required in the design, and the groove edges of the branch grooves 7 and 17 do not simultaneously contact the road surface when the road surface is grounded. Pitch noise caused by the groove edges of the branch grooves 7 and 17 hitting the road surface can be reduced while ensuring steering stability and uneven wear resistance.

  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 resonators 11 and 19 include the branch grooves 7 and 17 and the air chamber portion 9 that communicates with the circumferential groove 3 through the branch grooves 7 and 17 and has a larger cross-sectional area than the branch grooves 7 and 17. In place of the Helmholtz resonators 11 and 19 described above, the air chamber 9 and the branch grooves 7 and 17 are respectively connected to the first duct 9 ′ and the second duct 17 as shown in FIG. It is also possible to apply a stepped tube type resonator comprising connecting pipes that are regarded as pipes 7 'and 17' and connected to each other. In this case, the resonance frequency f is used as described below. Can be requested.

For the stepped tube type resonator, the acoustic impedance on the first pipeline 9 ′ side at the boundary is Z ₁₂ , the acoustic impedance on the second pipeline 7 ′, 17 ′ side in the boundary is Z ₂₁ , and the first pipeline 9 ′. Where S _{1 is} the cross-sectional area, and S ₂ is the cross-sectional area of the second pipes 7 ′ and 17 ′,
Z ₂₁ = (S ₂ / S ₁ ) · Z ₁₂
The relationship is established.

For the second pipes 7 ′ and 17 ′, 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 second pipe 7 ′, The sound pressure P _{2 at} a distance x from the opening 17 ′ is
_{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 pipelines 7 ′ and 17 ′, V ₂ is the particle velocity distribution of the second pipelines 7 ′ and 17 ′, V ₀ is the particle velocity of the input point, and j is , Imaginary unit, Z _c is ρc (ρ is the density of air, c is the speed of sound), and k is 2πf / c.

In addition, regarding the first pipeline 9 ′, 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 9 ′ 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 pipe line 9 ′.

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 each of the second pipes 7 ′ and 17 ′ is opened by the groove wall of the circumferential groove 3, but the first pipe 9 ′ and the second pipes 7 ′ and 17 ′ Since the closed space is formed by contact with the road surface in the ground contact surface of the tread surface, the upper end of the tread surface 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.

  In the performance evaluation, the effect of the difference in resonator shape on steering stability and uneven wear resistance was investigated. Each of the tires of Examples 1 to 6 is a tire according to the first invention, and is a radial tire for a passenger car having a tire size of 225 / 55R17. As shown in FIG. 5, the tire 4 extends in the tire circumferential direction on the tread portion. A circumferential groove of the book and a rib-like land portion adjacent to the groove are provided. The circumferential groove has a width of 10 mm and a depth of 8 mm. Each of these tires has 60 resonators having the shape shown in FIG. 1 in each rib-like land portion, and the dimensions of each resonator are the same as the length of the air chamber portion in the longitudinal direction. 18 mm, air chamber width 6 mm, air chamber depth 7 mm, branch groove length 6 mm, branch groove width 1 mm, branch groove depth 2 mm, and the resonance frequency of the resonator is 1061 Hz. The branch groove has one bent portion. Table 1 shows the angle between the center line of the branch groove and the tire circumferential direction at the opening end where the branch groove opens into the circumferential groove, and the distance from the opening end of the branch groove portion extending inclined at such an angle. Show.

The tires of Reference Examples 7 to 12 are all radial tires for passenger cars having a tire size of 225 / 55R17. As shown in FIG. 6, the tread portion has four circumferential grooves extending in the tire circumferential direction, and these tires. And a rib-like land portion adjacent to. The circumferential groove has a width of 10 mm and a depth of 8 mm. Further, these tires have 60 resonators each having a shape shown in FIG. 3 in each rib-like land portion, and the dimensions of each resonator are the lengths of the air chambers in the longitudinal direction. Is 18 mm, the width of the air chamber is 6 mm, the depth of the air chamber is 7 mm, the length of the branch is 6 mm, the width of the branch is 1 mm, the depth of the branch is 2 mm, and the resonance frequency of the resonator Is 1061 Hz. The branch groove has one curved portion. The angle range between the center line of the branch groove and the tire circumferential direction at the opening end where the branch groove opens into the circumferential groove, and the distance from the opening end of the branch groove portion extending incline in such an angle range. It is shown in 1.

For comparison, the tire of Comparative Example 1 having the same configuration as the tires of Examples 1 to 6 and Reference Examples 7 to 12 except for the shape of the resonator was also prototyped. The resonator has the shape shown in FIG. 7, and the dimensions of each resonator are 18 mm in the longitudinal direction of the air chamber, 6 mm in the width of the air chamber, and the depth of the air chamber. The length of the branch groove is 7 mm, the width of the branch groove is 1 mm, the depth of the branch groove is 2 mm, and the resonance frequency of the resonator is 1061 Hz.

  Each test tire is mounted on a rim of size 7.5J × 17, and after applying an air pressure of 220 kPa (relative pressure), the test tire is assembled in a passenger car for each test tire under the load load conditions equivalent to two passengers. The experiment and evaluation were performed.

(Maneuvering stability)
Drive the actual vehicle in the speed range experienced by general drivers on public roads, from low speeds to around 100 km / h, on the test course with a long circuit including a long straight line and a gentle evaluation curve. A professional driver evaluated the feeling of driving on a dry road with a 10-point scale. The evaluation results are shown in Table 2. The larger this value, the better the steering stability.

(Uneven wear resistance)
After traveling 10,000 km on a course including a general road, an expressway, and a mountain road, the level difference between the most worn portion and the least worn portion is measured in each rib-like land portion where the resonator is disposed. The average value of this step amount is calculated, and the smaller the value, the better the uneven wear resistance. The evaluation results are shown in Table 2.

  As is apparent from the results shown in Table 2, a bent portion or a curved portion is provided in the branch groove of the resonator, and at the opening end where the branch groove opens into the circumferential groove, the center line of the branch groove and the tire circumferential direction are It was confirmed that the steering stability and uneven wear resistance can be improved by setting the angle to be in the range of not less than 45 degrees and not more than 90 degrees. In addition, the greater the angle formed between the center line of the branch groove and the tire circumferential direction, or the greater the distance from the opening end of the branch groove portion that is inclined at such an angle, the greater the steering stability and uneven wear resistance. It is confirmed to improve.

  As is apparent from the above description, according to the present invention, it is possible to provide a pneumatic tire capable of improving uneven wear resistance and steering stability on the assumption that air column resonance noise can be reduced by a resonator. It became.

FIG. 3 is an enlarged plan view showing an enlarged main part of a tread portion of a pneumatic tire according to the present invention. It is the figure which showed the resonator applicable to this invention typically, (a) is a Helmholtz type resonator, (b) is a stepped tube type resonator. It is an enlarged plan view which expands and shows the principal part of the tread part of another pneumatic tire. (A) is a schematic diagram of the rubber block formed with tread rubber, (b) is a graph which shows the relationship between the width | variety and depth of a rubber block, and rigidity. It is a figure which shows the tread pattern of the tire of the Example according to 1st invention. It is a figure which shows the tread pattern of the tire of a reference example. FIG. 3 is an enlarged plan view showing an enlarged main part of a tread portion of a tire of Comparative Example 1.

Explanation of symbols

3 Circumferential groove 5 Rib-shaped land portion 7, 17 Branch groove 9 Air chamber portion 11, 19 Resonator 13 Open end 15 Bending portion 21 Bending portion

Claims (3)

The tread portion includes at least one circumferential groove extending along the tire circumferential direction and at least one row of rib-shaped land portions adjacent to the tread portion, and the rib-shaped land portion opens into the circumferential groove. A resonator configured to reduce the noise caused by the circumferential groove is formed by a branch groove and an air chamber portion communicating with the circumferential groove through the branch groove and having a larger cross-sectional area than the branch groove. In the pneumatic tire
The branch groove has at least one bent portion, and an angle formed between the center line of the branch groove and the tire circumferential direction is 45 degrees or more at an opening end where the branch groove opens into the circumferential groove. A pneumatic tire characterized by being within a range of 90 degrees or less. The branch groove is an end of the rib-shaped land portion in the tire width direction and is a region having a distance of at least 0.8 times the depth of the branch groove from the side having the opening end of the branch groove toward the other side. The pneumatic tire according to claim 1 , wherein an angle formed between the center line and the tire circumferential direction is within a range of 45 degrees or more and 90 degrees or less. The pneumatic tire according to claim 1 or 2, wherein an angle formed by a center line of the branch groove at the opening end and a tire circumferential direction is 60 degrees or more.

Images