JP2011143897A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve noise performance while enhancing a water removing effect and a scratching effect on a road surface without sacrificing drainage performance. <P>SOLUTION: A pneumatic tire includes: a plurality of recessed portions 10 dispersed in rib-like land portions 3, 4, 5 and opened toward a tread contact surface; first grooves 12 and second grooves 13 connecting the recessed portions 10 and partitioning a plurality of separated blocks 11 in the rib-like land portions 3, 4, 5; and at least one circumferential main groove 7, 8. A groove width w12 of the first groove 12 is set to have a distance such that the blocks 11 spaced away from each other via the first groove 12 are at least partially brought into contact with each other in a tire grounding state. At least part of the second groove 13 has one end opened toward the recessed portions 10 and the other end opened toward the circumferential main groove 7, 8. The second groove 13 is provided to maintain a communication state between the circumferential main groove 7, 8 and the recess portions 10 even in the tire grounding state. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a pneumatic tire in which a block is defined by a groove in a rib-like land portion extending along the tire circumferential direction. The present invention relates to a pneumatic tire that is improved in noise performance as well as in a water effect and a scratching effect on a road surface.

  Various methods have been proposed in the past to improve the water removal effect to remove the water film on ice and wet road surfaces and the scratching effect by the edge, and some of them have been put to practical use. One of the typical ones is that a relatively large block is partitioned and formed with vertical and horizontal grooves in the tread part, and thousands of fine grooves (sipes) are carved per tire on the surface of the formed block. There is a tire (see Patent Document 1).

  However, in the above method, the water removal performance is improved by increasing the number of narrow grooves, and it can be expected that the scratching effect is increased. However, the fall of the block due to the decrease in the rigidity of the block occurs, and the contact area decreases. There was a problem to do. On the other hand, in order to prevent the reduction of the ground contact area at the time of shear input, a so-called three-dimensional sipe or narrow groove formed by bending the narrow groove in the depth direction is formed in a wave shape or zigzag shape in the extending direction. However, since the narrow groove is formed in the block, for example (see Patent Document 2), this problem has not been solved fundamentally.

Japanese Patent Laid-Open No. 06-320917 JP 2007-015510 A

  Therefore, the inventors have made researches to solve the above problems, and as a result, a large number of blocks are formed by forming narrow grooves such as sipes in a mesh shape in the rib-like land portion extending along the tire circumferential direction. It is found that the same edge length (scratch effect) can be obtained while suppressing a decrease in the rigidity of the block, compared to the case where a narrow groove is cut into the block itself as in the prior art, It has also been found that a desired water removal effect can be obtained by providing a recess opening in the tread ground surface in the rib-like land portion.

  However, in a pneumatic tire adopting such a block pattern, when the rib-like land portion contacts the road surface, the recess functions as a so-called air pocket and is sandwiched between the recess and the road surface to escape. It was newly found that the air that lost the air was compressed and expanded, generating noise called pumping noise. In addition, such a block pattern has a problem that drainage performance is sacrificed because the blocks are arranged relatively densely.

  Therefore, the present invention provides a pneumatic tire with improved noise performance and improved water removal effect and road surface scratching effect without sacrificing drainage by a novel method that has not existed before. Objective.

  In order to solve the above-described problems, a pneumatic tire according to the present invention is arranged in a distributed manner in a rib-like land portion extending along the tire circumferential direction, and a plurality of recesses that open to a tread ground surface and a space between the recesses. A first groove and a second groove that are connected to each other and define a plurality of independent blocks in the rib-shaped land portion, and at least one that is provided adjacent to the rib-shaped land portion and extends in the tire circumferential direction. A circumferential width of the first groove, the groove width of the first groove being a distance at which the blocks separated via the first groove are at least partially in contact with each other in a tire ground contact state. And at least a portion of the second groove of the second groove has one end of the second groove opened in the recess, and the other end of the second groove opened in the circumferential main groove. The second groove is formed in the circumferential direction even in the tire ground contact state. It is characterized in being configured to hold a communication with the main groove and the recess. The “tire contact state” as used herein means that a tire is mounted on an applicable rim described in JATMA or a standard equivalent thereto, the highest air pressure specified in the standard is applied to the tire, and the tire is stationary. A state in which a load corresponding to 80% of the maximum load capacity is applied is set perpendicular to the flat plate. The “circumferential main groove” includes not only a groove extending linearly along the tire circumferential direction but also a groove extending in the tire circumferential direction while being bent or curved.

  In the pneumatic tire having such a configuration, at least the first groove is at least partially closed when the tire is in contact with the ground, and the blocks separated by the first groove are in contact with each other. The support effect can increase the rigidity of the block with the same edge length as compared with the conventional case where a narrow groove is cut into the block itself to secure the edge length. The decrease can be effectively prevented. Moreover, since the several recessed part opened to a tread ground surface is provided, the water which penetrate | invaded the tread ground surface can be efficiently discharged | emitted out of a ground surface through a recessed part. On the other hand, the circumferential main groove and the recess are connected by at least a part of the second groove, and the second groove maintains a communication state between the circumferential main groove and the recess even in the tire ground contact state. As a result, the recess is opened to the outside of the ground contact surface even when the tire is in contact with the ground via the second groove, so that an air pocket (sealed space) is not formed, and noise caused by the recess (in the recess) (Noise due to air compression / expansion) can be significantly reduced. Moreover, since the second groove and the recess connected to the circumferential main groove can act as a resonator for the circumferential main groove, noise (so-called air column resonance noise) caused by the circumferential main groove is also effective. It becomes possible to reduce it. Furthermore, since a circumferential main groove extending in the tire circumferential direction is provided adjacent to the rib-like land portion, a good water removal effect and a region in which a block is formed by the first groove and the second groove and the recess and While it is possible to obtain a scratching effect on the road surface and improve noise performance, it is possible to secure drainage in other areas and eliminate the adverse effects on drainage due to the dense arrangement of blocks. .

  Therefore, according to the pneumatic tire of the present invention, the water removal effect and the road surface scratching effect can be improved without sacrificing drainage, and the air pumping sound by the air pockets and the air by the circumferential main groove can be improved. It is possible to effectively reduce the columnar resonance and improve the noise performance.

  In the pneumatic tire according to the present invention, the groove width of the second groove is maintained such that the blocks separated through the second groove are separated from each other even in the tire ground contact state. It is preferable to set the distance.

  Or in the pneumatic tire of this invention, it is preferable that a 2nd groove | channel has a wide part which a width | variety expands locally over the depth direction of this 2nd groove | channel. In this case, it is preferable that the widened portion is disposed closer to the groove bottom in the depth direction of the second groove.

Furthermore, in the pneumatic tire of the present invention, the width of the rib-like land portion is W (mm), the reference pitch length of the block in the rib-like land portion is PL (mm), When the number of blocks existing in the reference area defined by the width W and the reference pitch length PL is a (number) and the negative rate in the reference area is N (%), D = a / { PL × W × (1−N / 100)}, the block number density D (pieces / mm ² ) per unit actual contact area of the rib-like land portion is within a range of 0.003 to 0.04. Preferably there is. Here, “the width of the rib-like land portion” refers to the length of the rib-like land portion along the tire width direction. The “reference pitch length of the block” means the minimum unit or a plurality of units of the repeating pattern in the tire circumferential direction formed by the rib-like land block, for example, one block and this block. When the repeated pattern of the pattern of a tire circumferential direction is prescribed | regulated by the recessed part adjacent to the tire circumferential direction of this, it points to what added each tire circumferential direction length of these blocks and recessed parts. Furthermore, the “block number density” represents the number of blocks existing as a density per actual ground contact area in the reference area (total surface area of all blocks in the reference area).

  According to the present invention, it is possible to provide a pneumatic tire with improved noise performance and improved water removal effect and road surface scratching effect without sacrificing drainage by a novel method that has not been conventionally used. It is.

(A) is the partial expanded view which showed the tread pattern of the tire of one Embodiment (tyre of Example 1) according to this invention, (b) is the cross section in alignment with the AA in FIG. 1 (a). It is a figure, (c) is a sectional view which meets a BB line in Drawing 1 (a), and (d) is a sectional view which follows a CC line in Drawing 1 (a). It is a schematic diagram illustrating a resonator applicable to the present invention, (a) shows a Helmholtz type resonator and (b) shows a stepped tube type resonator. (A) is the partial expanded view which showed the tread pattern of the tire of other embodiment (tire of Example 2) according to this invention, (b) follows the AA line in Fig.3 (a). It is sectional drawing, (c) is sectional drawing in alignment with the BB line in Fig.3 (a), (d) is sectional drawing in alignment with CC line in Fig.3 (a). (A)-(c) is the figure which illustrated other block shapes applicable to this invention, respectively. (A)-(d) is sectional drawing which illustrated the other 2nd groove | channel applicable to this invention, respectively. It is the partial expanded view which showed the tread pattern of the pneumatic tire for comparison (tire of the comparative example 1). It is the partial expanded view which showed the tread pattern of the pneumatic tire for comparison (tire of the comparative example 2). It is the partial expanded view which showed the tread pattern of the pneumatic tire (tire of the prior art example 1) according to a prior art.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a partial development view showing a tread pattern of a pneumatic tire (hereinafter simply referred to as “tire”) according to an embodiment of the present invention.

  Although not shown in the drawings, the tire of this embodiment includes a tread portion that forms a tread surface of the tire, a pair of sidewall portions that are connected to the outer side in the width direction of the tread portion via a shoulder portion, and tires of these sidewall portions. Conventionally provided with a pair of bead portions disposed radially inside, a carcass extending in a toroidal shape between the pair of bead portions inside the tire, and a belt layer disposed on the outer side in the tire radial direction of the crown region of the carcass The tire has a tire structure according to the above.

  As shown in FIG. 1, the tire includes at least one, in this case, three rib-like land portions 3, 4, 5 extending on the tread contact surface 1 in the tire circumferential direction. Between four and five, two circumferential main grooves 7 and 8 extending in the tire circumferential direction are provided. The circumferential main grooves 7 and 8 are preferably arranged at positions corresponding to within 35% of the tread contact width (the length in the tire width direction between the tread contact ends TW) with the tire equatorial plane E as the center. This is because if the width of the block row between the ground contact TE and the circumferential grooves 7 and 8 is reduced, the wear performance may be reduced. The groove widths of the circumferential grooves 7 and 8 are preferably 10 to 40% of the tread ground contact width in order to ensure sufficient drainage. Here, for convenience, both regions outside the circumferential main grooves 7 and 8 in the tire width direction are shoulder regions, and when three or more circumferential main grooves are provided, the tire among the plurality of circumferential main grooves. Both regions on the outer side in the tire width direction than the circumferential main groove located on the outermost side in the width direction are defined as shoulder regions.

In each of the rib-like land portions 3, 4, and 5, a plurality of recessed portions 10 that are open to the tread ground contact surface 1 (surface in contact with the road surface) are arranged in a distributed manner. The recess 10 takes in water, ice or snow interposed between the tread contact surface 1 and the road surface, and the water, ice or snow taken into the recess 10 is exposed to the outside by centrifugal force accompanying rotation of the tire. Discharged. The depth, volume, number, shape, disposition position, etc. of the recess 10 can be appropriately set according to the water removal capability required for the tire, for example, the depth of the recess 10 is 3 mm to 8 mm, volume preferably set to the 30mm ² ~400mm ^2. A cross-sectional area S10 (a cross-sectional area in a plane orthogonal to the longitudinal direction) of the recess 10 is larger than a cross-sectional area S13 (a cross-sectional area in a plane orthogonal to the longitudinal direction) of a second groove 13 described later.

  The rib-like land portions 3, 4, 5 are connected to each other between the adjacent recesses 10, and a plurality of independent blocks 11 are defined in the rib-like land portions 3, 4, 5. The groove 12 and the second groove 13 are provided. That is, the block 11 is formed by arranging the first groove 12 and the second groove 13 in a mesh pattern. As a result, a plurality of blocks 11 are densely formed in the rib-like land portions 3, 4, and 5. In FIG. 1A, the second groove 13 is a line thicker than the first groove 12 for the sake of convenience so that the first groove 12 and the second groove 13 can be distinguished on the drawing. It is shown in figure.

  Further, the blocks 11 in the rib-like land portions 3, 4 and 5 are arranged in a staggered manner. That is, the blocks 11 are arranged side by side in the tire circumferential direction to form a plurality of block rows, and the blocks 11 in one block row and the blocks 11 in another block row adjacent to the block row in the tire width direction. Is arranged so that the phase is different in the tire circumferential direction. Here, “the phases are different in the tire circumferential direction” means, for example, in the example of FIG. 1, a state in which each block 11 is shifted by half a pitch in the tire circumferential direction between adjacent block rows. . By adopting such a staggered arrangement, the ground contact timing of the recess 10 can be shifted, which is advantageous in reducing pattern noise. Further, pattern noise can be further reduced by shifting the positions of the recesses 10 in the tire circumferential direction between all the block rows.

  Here, the groove width w12 of the first groove 12 is set to a distance at which the blocks 11 separated via the first groove 12 are at least partially in contact with each other in the tire ground contact state. The groove width w13 of the second groove 13 is set to a distance at which the blocks 11 separated via the second groove 13 are held apart from each other even in the tire ground contact state. Here, the adjacent blocks “partially contact” means that the block 11 is deformed by being pressed against the road surface, and the side wall surfaces 11 a of the adjacent blocks 11 are partially in contact with each other. In this embodiment, the groove widths w12 and w13 of the first and second grooves 12 and 13 are constant in the depth direction, but the groove widths w12 and w13 gradually increase or decrease in the depth direction. You may comprise as follows.

  At least one second groove 13 is connected to each recess 10. One end of at least a part of the second groove, specifically, the second groove 13 adjacent to the circumferential main grooves 7, 8 opens into the recess 10, and the second groove The other end of 13 is open to the circumferential main grooves 7 and 8, whereby the recess 10 is connected to the circumferential main grooves 7 and 8. The other second groove 13, here the second groove 13 disposed on the outer side in the tire width direction in the rib-like land portions 3, 5, is not opened in the circumferential main grooves 7, 8 but is adjacent to the recessed portion 10. They are connected to each other. Thereby, in the rib-like land portions 3 and 5, the two second grooves 13 and the two concave portions 10 are alternately connected. Of course, three or more second grooves 13 and three or more recesses 10 may be alternately connected.

The groove width w12 of the first groove 12 is preferably less than 0.7 mm, and the groove width w13 of the second groove 13 is preferably 0.7 mm or more. When the groove width w12 of the first groove 12 is 0.7 mm or more, the blocks 11 separated via the first groove 12 may not come into contact with each other in the tire ground contact state. If the groove width w13 of the groove 13 is less than 0.7 mm, the blocks 11 separated via the second groove 13 may not be maintained in a state of being separated from each other even in the tire ground contact state. Because.
When the groove widths w12 and w13 of the first and second grooves 12 and 13 are changed, it can be easily realized by adjusting the thickness of the blade applied to the tire vulcanization mold. is there.

  According to the tire employing such a configuration, at least the first groove 12 is at least partially closed in the tire ground contact state, and the blocks 11 separated by the first groove 12 are in contact with each other. Due to the mutual support effect, the rigidity of the block 11 having the same edge length comparison can be increased as compared with the conventional case where the edge length is ensured by engraving a narrow groove in the block itself. It is possible to effectively prevent a decrease in the ground contact area. Further, by providing the recess 10 on the tread ground surface 1, water that has entered the tread ground surface 1 can be efficiently discharged out of the ground surface via the recess 10. On the other hand, the circumferential main grooves 7 and 8 and the recess 10 are connected by at least a part of the second groove 13, and the second groove 13 is connected to the circumferential main grooves 7 and 8 even in the tire ground contact state. The communication state with the recess 10 is maintained. As a result, the recess 10 is opened to the outside of the ground contact surface even in the tire ground contact state through the second groove 13 and the circumferential main grooves 7 and 8, so that no air pocket (sealed space) is formed. The noise caused by the recess 10 (noise due to air compression / expansion in the recess 10) can be significantly reduced. In addition, since the second groove 13 and the recess 10 connected to the circumferential main grooves 7 and 8 can act as a resonator to be described later with respect to the circumferential main grooves 7 and 8, this is caused by the circumferential main grooves 7 and 8. Noise (so-called air column resonance) can also be effectively reduced. Furthermore, since the circumferential main grooves 7 and 8 extending in the tire circumferential direction are provided adjacent to the rib-like land portions 3, 4, and 5 on the tread contact surface 1, the first groove 12 and the second groove 13, In the region where the block 11 is formed by the recess 10 (rib-shaped land portions 3, 4, 5), it is possible to obtain a good water removal effect and a scratching effect on the road surface, and to improve the noise performance, while other regions ( In the circumferential main grooves 7, 8), drainage can be ensured, and adverse effects on drainage due to the dense arrangement of the blocks 11 can be eliminated.

  In order to make the second groove 13 opened in the circumferential main grooves 7 and 8 and the concave portion 10 connected thereto function as a resonator, the number of connections between the second groove 13 and the concave portion 10 is increased or decreased. Thus, the level of the resonance frequency with respect to the air column resonance sound can be easily adjusted. For example, in the rib-like land portions 3 and 5, since the two second grooves 13 and the two concave portions 10 are alternately connected per resonator, the corresponding resonance frequency is higher than that of the resonator of the rib-like land portion 4. Can be lowered.

として表される、各リブ状陸部３、４、５の単位実接地面積当りのブロック個数密度Ｄ（Ｄ１、Ｄ２、Ｄ３）はそれぞれ、０．００３（個／ｍｍ^２）以上０．０４（個／ｍｍ^２）以下である。ここで、リブ状陸部３、４、５の幅Ｗは、タイヤ幅方向の一側縁及び他側縁間のタイヤ幅方向距離を指し、一側縁又は他側縁がトレッド接地端ＴＷを越える場合には、一側縁又は他側縁とトレッド接地端ＴＷとの相互間のタイヤ幅方向距離を指すものとする。ブロック個数密度Ｄは、各リブ状陸部の実接地面積（溝分を除いた面積）の単位面積当りに何個のブロック１１が存在するかということを密度として表現したものである。ちなみに、例えば通常のスタッドレスタイヤの場合には、この密度Ｄは概ね０．００２以下となる。なお、基準区域Ｚ内のブロックの個数ａをカウントするに際して、ブロック１１が基準区域Ｚの内外に跨って存在し、１個として数えることができない場合は、基準区域Ｚを跨るブロック１１の表面積に対する、基準区域内に残った同ブロック１１の残存面積の比率を用いて数えることとする。例えば、基準区域Ｚの内外に跨り、基準区域Ｚ内にその半分しか存在しないブロック１１の場合は、１／２個と数えることができる。 By the way, in order to increase the total edge length of the block 11 (the total length of the peripheral edges of each block 11), it is necessary to reduce the size of each block to form more blocks 11. However, the proper range is as follows. That is, the width of each rib-like land portion 3, 4, 5 is W (W3, W4, W5) (mm), and the reference pitch length of the block 11 in the rib-like land portions 3, 4, 5 is PL (PL3 , PL4, PL5) (mm), a reference zone Z (Z3, Z4, Z5) defined by the width W of the rib-like land portions 3, 4, 5 and the reference pitch length PL (indicated by diagonal lines in the figure) When the number of blocks 11 existing in (area) is a (a3, a4, a5) (pieces) and the negative rate in the reference area Z is N (N3, N4, N5) (%),

The block number density D (D1, D2, D3) per unit actual ground contact area of each of the rib-like land portions 3, 4, 5 is expressed as 0.003 (pieces / mm ² ) or more and 0.04 ( Pieces / mm ² ) or less. Here, the width W of the rib-like land portions 3, 4 and 5 indicates the distance in the tire width direction between the one side edge and the other side edge in the tire width direction, and the one side edge or the other side edge defines the tread grounding end TW. When exceeding, it shall refer to the distance in the tire width direction between the one side edge or the other side edge and the tread ground contact edge TW. The block number density D represents the number of blocks 11 per unit area of the actual ground contact area (area excluding the groove) of each rib-like land portion as a density. Incidentally, for example, in the case of a normal studless tire, this density D is approximately 0.002 or less. When counting the number a of blocks a in the reference zone Z, if the block 11 exists over the inside and outside of the reference zone Z and cannot be counted as one, it corresponds to the surface area of the block 11 across the reference zone Z. Counting is performed using the ratio of the remaining area of the block 11 remaining in the reference area. For example, in the case of the block 11 straddling the inside and outside of the reference zone Z and having only half of the block in the reference zone Z, it can be counted as 1/2.

When the block number density D in the rib-like land portions 3, 4 and 5 is less than 0.003 (pieces / mm ² ), the total edge length should be increased without forming sipes in the block 11. On the other hand, if the block number density D exceeds 0.04 (pieces / mm ² ), the size of the block 11 becomes too small and it becomes difficult to achieve the required block rigidity. Further, if the block number density D in the rib-like land portions 3, 4 and 5 is within the range of 0.0035 to 0.03 / mm ² , both ensuring block rigidity and increasing the total edge length are achieved. Can be achieved in higher dimensions.

  The negative rate N in the rib-like land portions 3, 4, 5 is preferably 5% to 50%. When the negative rate N in the rib-like land portions 3, 4 and 5 is less than 5%, the groove area is too small and the drainage is insufficient, and the size of each block is too large and the present invention is aimed. This is because it is difficult to increase the edge length. On the other hand, if it exceeds 50%, the contact area becomes too small and the steering stability may be lowered.

  Here, various resonators constituted by the recess 10 and the second groove 13 connected to the recess 10 and opening in the circumferential main grooves 7 and 8 and applicable to the present invention will be described with reference to FIG. To do. 2A and 2B are schematic views illustrating a resonator applicable to the present invention. FIG. 2A is a so-called Helmholtz resonator, and FIG. 2B is a so-called stepped tube resonator.

として表すことができるので、この共鳴周波数ｆは、周方向主溝７、８の気柱共鳴周波数との関連の下で、第２の溝１３の長さｌ_ｈ、第２の溝１３の断面積Ｓ１３（半径ｒ）及び凹部１０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。 As described above, in order for the second groove 13 and the concave portion 10 to act as a resonator, the second groove 13 is opened in the circumferential main grooves 7 and 8 and the concave portion connected to the second groove 13. 10 is required to be larger than the cross-sectional area S13 of the second groove 13. Such a resonator forms a Helmholtz resonator as schematically shown in FIG. 2 (a) under the condition that the second groove 13 and the recess 10 are both sealed by the road surface. The resonance frequency f of the resonator is such that the length of the second groove 13 is l _h , the radius of the second groove 13 is r, the cross-sectional area of the second groove 13 is S13, and the volume of the recess 10 is When V and sound speed are c,

This resonance frequency f is related to the air column resonance frequency of the circumferential main grooves 7 and 8, and the length l _h of the second groove 13 and the breakage of the second groove 13. By selectively changing the area S13 (radius r) and the size of the volume V of the recess 10, it can be changed as required.

  When the cross-sectional shape of the second groove 13 constituting the resonator is not circular (rectangular in this embodiment), the radius r in the above formula is calculated backward from the cross-sectional area S13 of the second groove 13. Is required. 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.

  In addition, as the recess 10 constituting the resonator, one having the same cross-sectional area as the opening area (cross-sectional area along the tread grounding surface) can be applied over the entire depth direction. Alternatively, a conical shape in which the cross-sectional area gradually increases or decreases in the depth direction may be employed. Moreover, the bottom part of the recessed part 10 may be made into a substantially flat surface, and is good also as a convex or concave curved surface toward the opening side.

  Furthermore, in the said embodiment, although the opening shape to the tread ground surface 1 of the recessed part 10 which comprises a resonator is a rectangle, this opening shape is good also as polygons other than this, circular, and an ellipse.

  Alternatively, instead of the Helmholtz resonator as described above, the recess 10 and the second groove 13 are regarded as the first conduit 10 ′ and the second conduit 13 ′, respectively, as shown in FIG. A stepped tube type resonator comprising connecting pipes interconnecting them can also be applied. In this case, the resonance frequency f can be obtained as described below.

For the stepped tube type resonator, the acoustic impedance on the first pipeline 10 ′ side at the boundary is Z ₁₂ , the acoustic impedance on the second pipeline 13 ′ side in the boundary is Z ₂₁ , and the sectional area of the first pipeline 10 ′. Is S ₁ (S ₁ = S10), and the cross-sectional area of the second conduit 13 ′ is S ₂ (S ₂ = S13),
Z ₂₁ = (S ₂ / S ₁ ) · Z ₁₂
The relationship is established.

'For the boundary condition, x = 0 at _V 2 _{= V} ⁰ e jwt, when at x = _{l 2} and _{P 2 / V 2 = Z 21} , second conduit 13' second conduit 13 from the opening of The sound pressure P _{2 at} the position of the distance x 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 conduit 13 ′, V ₂ is the particle velocity distribution of the second conduit 13 ′, 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 10 ′, if 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 10 ′ 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 )})] · V ₀ e ^jwt
It is expressed. Here, l ₁ is the length of the first pipeline 10 ′.

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 13 ′ is opened by the groove walls of the circumferential main grooves 7 and 8, but the first pipe line 10 ′ and the second pipe line 13 ′ are in contact with the tread. Since the closed space is formed by the contact between the ground and the road surface, the upper end of the closed space can be opened at the surface of the rib-like land portions 3, 4, and 5, and this point is also limited. There is no.

  Next, another embodiment of the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the component same as the component in the tire demonstrated in FIG. 1, and the description is abbreviate | omitted.

  In the tire illustrated in FIG. 3, the groove width w <b> 13 of the second groove 13 is a distance at which the blocks 11 separated via the second groove 13 are at least partially in contact with each other in the tire ground contact state. Is set. Further, as shown in FIG. 3C, the second groove 13 has a widened portion 14 whose width is locally expanded in the depth direction (the radial direction of the tire). Therefore, the wide groove portion 14 and the narrow width portion 15 having a groove width smaller than that of the wide width portion 14 are formed in the second groove 13. Here, the widened portion 14 is formed by locally denting the side wall surfaces 11a of both blocks 11 separated by the second groove 13 into a dome shape, whereby the widened portion 14 has a substantially spherical shape. The widened portion 14 does not close even in the tire ground contact state. That is, the side wall portion of the block 11 provided with the widened portion 14 is held in a state of being separated from the side wall portion of the block 11 opposed to the side wall portion across the widened portion 14 even in the tire ground contact state. The widened portion 14 is disposed closer to the groove bottom in the depth direction of the second groove 13, more specifically, in contact with the groove bottom. Here, “close to the groove bottom” means that the widened portion 14 is disposed below the central position in the depth direction of the second groove 13.

  The groove width w14 (maximum value) in the widened portion 14 of the second groove 13 is preferably 0.7 mm or more and 3 mm or less. This is because if the groove width w14 in the widened portion 14 of the second groove 13 is less than 0.7 mm, the widened portion 14 may be closed in the tire ground contact state, while if it exceeds 3 mm, the widened portion 14 is exceeded. This is because the volume of the block 11 is reduced by a small amount, and sufficient block rigidity may not be ensured.

  According to the tire of this embodiment, the groove width w13 of the second groove 13 is set to a distance at which the blocks 11 separated via the second groove 13 are at least partially in contact with each other in the tire ground contact state. Since the setting is made, the blocks 11 separated by the second groove 13 are in contact with each other as in the case of the first groove 12, so that the support effect between the adjacent blocks 11 is exhibited. Therefore, the rigidity of the block 11 having the same edge length comparison can be further increased.

  Further, the rigidity of the block 11 increases as the widened portion 14 is closer to the groove bottom in the depth direction of the second groove 13. In this embodiment, since the widened portion 14 is disposed closer to the groove bottom, the block 11 Since the rigidity is high, the steering stability is excellent, and even if the block 11 is worn away by wear, the widened portion 14 can remain, and the noise reduction effect can be maintained for a long period of time.

  The present invention has been described based on the illustrated examples. However, the present invention is not limited to the above-described embodiment, and can be appropriately changed within the scope of the claims. For example, the first and first embodiments The shape of the block 11 defined by the two grooves 12 and 13 and the recess 10 may be a square, a pentagon, or a hexagon as illustrated in FIGS. 4A to 4C. The shape of the concave portion 10 surrounded by a rectangular shape may be various shapes other than a rectangle, such as a triangle or a circle (not shown). Further, the arrangement position of the widened portion 14 in the depth direction of the second groove 13 is not limited to the above-described embodiment, and the widened portion 14 is tread-contacted as shown in FIGS. 5A and 5B, for example. It can be provided so as to open to the ground or can be provided at a central position in the depth direction. Further, the shape of the widened portion 14 is not limited to the above-described embodiment. For example, as shown in FIGS. 5C and 5D, the maximum width is taken at the groove bottom and the width from the narrow portion 15 toward the narrowed portion 15 is increased. Is gradually reduced, or only the side wall surface 11a of one block 11 of the opposing blocks 11 separated by the second groove 13 is locally recessed into a dome shape to have a substantially half-moon shape. Can be. Moreover, two or more widened portions 14 may be provided for each second groove 13.

  Next, the tires of Examples 1 and 2 according to the present invention, the tires of Comparative Examples 1 and 2 for comparison, and the tire of Conventional Example 1 according to the prior art are respectively prototyped, noise reduction effect, dry steering stability performance, wet Since the performance evaluation about the steering stability performance was performed, it demonstrates below. Each of these tires is a radial tire for passenger cars having a tire size of 195 / 65R15, and the tread contact width is 140 mm.

The tire of Example 1 has the tread pattern shown in FIG.
The circumferential main groove 7 is disposed at a position corresponding to 20% of the tread contact width centered on the tire equator plane E, and the circumferential main groove 8 is set to 20% of the tread contact width centered on the tire equator plane E. It is arranged at the corresponding position. The groove width of the circumferential main groove 7 is 14 mm, and the groove depth is 8.3 mm. The groove width of the circumferential main groove 8 is 17 mm, and the groove depth is 8.3 mm. The volume of the recess 10 is 145 mm ³ , the cross-sectional area S 10 is 18.0 mm ² , and 236 tires are provided in each rib-like land portion around the tire. The groove width w12 of the first groove 12 is 0.5 mm, and the groove depth is 6.0 mm. The groove width w13 of the second groove 13 is 0.7 mm, the groove depth is 6.0 mm, and the cross-sectional area S13 is 4.2 mm ² . In the rib-like land portions 3, 4, 5, the length of the second groove 13 opening to the circumferential main grooves 7, 8 is 16.5 mm, and the length of the other second grooves 13 is It is 6.6 mm.

The tire of Example 2 has the tread pattern shown in FIG. 3 in the tread portion. The tire of Example 2 differs from the tire of Example 1 in that the second groove 13 has a widened portion 14. The groove width (groove width of the narrow portion) w13 of the second groove 13 is 0.5 mm, the groove depth is 6.0 mm, and the cross-sectional area S13 is 2.0 mm ² . The widened portion 14 is provided in contact with the groove bottom. The width w14 of the widened portion 14 is 1.2 mm. The negative ratio of the entire tread portion including the circumferential main grooves 7 and 8 is 28%. Other specifications are shown in Table 1.

  The tire of Comparative Example 1 has the tread pattern shown in FIG. 6 in the tread portion, and all the grooves that define the block 11 in the rib-like land portions 3, 4, and 5 are configured by the first grooves 12. Except for the above, the tire has substantially the same configuration as that of the tire of Example 1. The groove width w12 of the first groove 12 is 0.5 mm, and the groove depth is 6.4 mm. The negative ratio of the entire tread portion including the circumferential main grooves 7 and 8 is 28%. Other specifications are shown in Table 1.

The tire of Comparative Example 2 has the tread pattern shown in FIG. 7 in the tread portion, and unlike the tire of Comparative Example 1, the tread portion is filled with the block 11 instead of providing the circumferential main groove. The groove width w12 of the first groove 12 is 0.5 mm, and the groove depth is 6.4 mm. The negative rate of the entire tread portion is 7.5%. In the tire of Comparative Example 1, the number of blocks in the reference area is 12, the negative rate in the reference area is 7.5%, and the block number density is 0.0053 / mm ² .

The tire of Conventional Example 1 has the tread pattern shown in FIG. This tire has circumferential main grooves 21 and 22 on both sides of the tire equatorial plane. The groove width of the circumferential main groove 21 is 14 mm, the groove depth is 8.3 mm, the groove width of the circumferential main groove 22 is 17 mm, and the groove depth is 8.3 mm. A block land portion 23 is formed between the circumferential main grooves 21 and 22, and a sipe 25 is formed in each block 24. Similarly, block land portions 26 and 27 are formed outside the circumferential main grooves 21 and 22 in the tire width direction, and sipes 25 are formed in the blocks 28 and 29. In the tire of Conventional Example 1, the number of blocks in the reference area is 2, the negative rate excluding the circumferential main grooves in the reference area is 7.5%, and the block number density is 0.0016. / Mm ² .

  Regarding the noise reduction effect, after mounting the tire on a rim of size 6J × 15 and applying air pressure of 210 kPa (relative pressure) inside, an indoor noise tester (drum: speed 60 km / hour) was used. Measured by placing a microphone at a position 50 cm away from the tire, and compared with the overall value of all bands. The measured value of noise is an overall value, and the greater the negative value with reference to the tire of Comparative Example 1, the greater the noise reduction effect. The measurement results are shown in Table 2. For the tire of Conventional Example 1 and the tire of Comparative Example 2, a test for confirming the noise reduction effect was not performed.

  In addition, the wet steering stability performance test is carried out by incorporating each test tire into the above rim, mounting it on a test vehicle (vehicle type: Volkswagen Golf, displacement: 2000 cc), and at a Bridgestone Proving Ground under a water depth of 2 mm. It was done by feeling by a test driver. The evaluation is in 0.5 point increments, and the point difference of 0.5 points is a significant difference. The evaluation results are shown in Table 2.

  Furthermore, the dry steering stability performance test was conducted by incorporating each test tire into the above rim and mounting it on a test vehicle (model: Volkswagen Golf, displacement: 2000 cc) under the dry road surface at the Bridgestone Proving Ground. It was done by feeling by a test driver. The evaluation is in 0.5 point increments, and the point difference of 0.5 points is a significant difference. The evaluation results are shown in Table 2.

  From the results shown in Table 2, it can be seen that application of the present invention improved the noise performance while ensuring wet steering stability.

  Thus, according to the present invention, the water removal effect and the road surface scratching effect can be improved without sacrificing the drainage, and the noise performance can be improved.

DESCRIPTION OF SYMBOLS 1 Tread ground surface 3, 4, 5 Rib-shaped land part 7, 8 Circumferential main groove 10 Recess 11 Block 12 1st groove 13 2nd groove 14 Wide part 15 Narrow part

Claims (5)

A plurality of recesses disposed in a distributed manner in a rib-like land extending along the tire circumferential direction, and opening in the tread ground surface;
A first groove and a second groove for connecting the recesses to each other and defining a plurality of independent blocks in the rib-like land portion;
At least one circumferential main groove provided adjacent to the rib-shaped land portion and extending in the tire circumferential direction;
The groove width of the first groove is set to a distance at which the blocks separated via the first groove are at least partially in contact with each other in a tire ground contact state.
At least a part of the second groove of the second groove has one end of the second groove opened in the recess, and the other end of the second groove opened in the circumferential main groove.
The pneumatic tire according to claim 2, wherein the second groove is configured to maintain a communication state between the circumferential main groove and the recess even in the tire contact state.   The groove width of the second groove is set to a distance at which the blocks separated through the second groove are held apart from each other even in a tire ground contact state. Pneumatic tires.   2. The pneumatic tire according to claim 1, wherein the second groove has a widened portion whose width locally expands in a depth direction of the second groove.   The pneumatic tire according to claim 3, wherein the widened portion is disposed closer to the groove bottom in the depth direction of the second groove. The rib-shaped land portion has a width W (mm), a reference pitch length of a block in the rib-shaped land portion is PL (mm), and the rib-shaped land portion width W and the reference pitch length PL are partitioned. D = a / {PL × W × (1−N / 100)} where a is the number of blocks existing in the reference area and N is the negative rate in the reference area. The block number density D (piece / mm ² ) per unit actual ground contact area of the rib-like land portion to be given is within a range of 0.003 to 0.04, according to any one of claims 1 to 4. The described pneumatic tire.

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