JP2011148361A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire improved in air resistance by reducing rubber flow by optimizing the block size. <P>SOLUTION: In the pneumatic tire including a plurality of blocks 3 partitioned by grooves 2 at a tread 1, at least an area Sb of a block ground contact face for some blocks 3 is 450 mm<SP>2</SP>or less, and the blocks have length Lb in the circumferential direction and length Wb in the width direction, that are 1.5 times or more respectively in respect to the groove depth of the grooves 2 partitioning the blocks 3. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a pneumatic tire provided with a plurality of blocks defined by grooves in a tread portion, and particularly intends to advantageously reduce wear resulting from shear deformation of the blocks at the time of ground contact.

  In recent years, a block pattern is frequently used as a tread pattern formed on a tread portion of a tire. The block pattern includes a large number of blocks (block-shaped land portions) defined by a plurality of vertical grooves extending in the tire circumferential direction and a large number of horizontal grooves extending across the vertical grooves. The block pattern has an all-weather property that exhibits good traction performance not only on a dry road surface but also on a wet road surface and an icy / snow road surface, and therefore the ratio applied to high-performance passenger car tires is increasing (Patent Document 1). reference).

  By the way, since a tire generally has a curvature in a tread portion, a distribution of a diameter difference occurs in the tire width direction. It is known that the shear deformation in the tire circumferential direction that occurs in the block due to the difference in diameter affects the wear resistance of the tire. Conventionally, in order to prevent this shear deformation, measures for mainly increasing shear rigidity (shear direction rigidity) have been taken, for example, increasing the block size.

JP-A-5-169922

  However, if the block size is made too large, the tire circumferential direction of the rubber flow that occurs when the kicking side of the tread is pushed obliquely against the road surface increases shear deformation in the tire circumferential direction, so that sufficient friction resistance performance is achieved. In some cases, it could not be obtained. That is, since the rubber forming the block is incompressible, as shown in FIG. 4A, when the block comes in contact with the road surface, the rubber flows to the side and the shear deformation of the block increases. Conventionally, sufficient studies have not been made on the increase in shear deformation due to such rubber flow, and there has been a limit to improving the friction resistance by increasing the block size.

  Therefore, an object of the present invention is to provide a pneumatic tire having an improved wear resistance by reducing rubber flow by optimizing the block size.

The present invention has been made to solve the above-described problems. A pneumatic tire according to the present invention is a pneumatic tire including a plurality of blocks partitioned by grooves in a tread portion. At least some of the blocks are The area of the block ground plane is 450 mm ² or less, and has a circumferential length and a width length that are 1.5 times or more each of the groove depths of the grooves defining the block. It is what.

  Here, the “area of the contact surface of the block” means the area of the surface region continuously extending on the contact surface of the block. For example, when the block is divided into a plurality of grooves such as sipes and narrow grooves, The area of the surface area in each divided block divided by the groove is indicated. The “circumferential length” of the block refers to a linear distance measured along the tire circumferential direction from one end to the other end of the block in the tire circumferential direction. The “width direction length” of the block refers to a linear distance measured along the tire width direction from one end to the other end of the block in the tire width direction. Furthermore, “the groove depth of the groove defining the block” refers to the groove depth of the groove having the largest groove depth among the grooves defining the block. For example, the block is defined by the vertical groove and the horizontal groove. If the groove depth of the vertical groove is larger than that of the horizontal groove, the groove depth of the vertical groove is used as a reference.

According to the pneumatic tire having such a configuration, the area of the contact surface of the block is set to 450 mm ² or less, and the enlargement of the block size is restricted, thereby suppressing shear deformation due to the rubber flow of the block when the tread portion is kicked out. However, since it becomes possible to increase the shear rigidity against the shear deformation in the tire circumferential direction generated in the block due to the difference in diameter, the wear resistance can be advantageously improved. On the other hand, since the circumferential length and the width direction length of the block are 1.5 times or more the groove depth of the groove defining the block, the required block shear rigidity can be ensured and good A grounding property can be obtained. If the block shear rigidity is low, the block will collapse (buckling), and the contact pressure at the contact end will be very high, that is, the contact pressure at the contact surface will be low, resulting in poor contact and reduced grip. Resulting in.

  In the pneumatic tire of the present invention, the at least some of the blocks have an aspect ratio of 1 or more and 2 or less indicating a ratio of the circumferential length of the block to the width of the block. Is preferred.

In the pneumatic tire of the present invention, the tread portion includes a block group formed by at least one block row in which the blocks are arranged at a predetermined pitch in the tire circumferential direction. The number of the blocks existing in the reference area of the block group defined by the pitch length PL (mm), the width of the block group W (mm), and the reference pitch length PL and the width W. Is the block number density D given by a / {PL × W × (1−N / 100)}, where a (number) is the negative rate in the reference area and N (%) is 0.003 ( Number / mm ² ) or more and 0.04 (number / mm ² ) or less.

  According to the present invention, it is possible to provide a pneumatic tire with improved wear resistance by reducing rubber flow by optimizing the block size.

It is a partial development view of the tread portion of the pneumatic tire of one embodiment according to the present invention. It is the map which showed the relationship between the circumferential direction length and width direction length of a block, and the swelling deformation of a block. It is a figure which shows the relationship between block aspect-ratio BAs and block shear rigidity. It is a figure explaining the bulging deformation | transformation of the block at the time of applying a driving force, (a) showed the block of the conventional pneumatic tire, (b) showed the block of the pneumatic tire to which this invention was applied, respectively. Is. It is a schematic diagram of the block for demonstrating the relationship between the aspect ratio As of a block, and the amount of swelling of a block, (a) is a state of aspect ratio As <1, (b) is a state of aspect ratio As> 1. Respectively. FIG. 6 is a partial development view of a tread portion of a pneumatic tire according to another embodiment according to the present invention. FIG. 6 is a partial development view of a tread portion of a pneumatic tire according to another embodiment according to the present invention. FIG. 6 is a partial development view of a tread portion of a pneumatic tire according to another embodiment according to the present invention. FIG. 6 is a partial development view of a tread portion of a pneumatic tire according to another embodiment according to the present invention. FIG. 6 is a partial development view of a tread portion of a pneumatic tire according to another embodiment according to the present invention. FIG. 6 is a partial development view of a tread portion of a pneumatic tire according to another embodiment according to the present invention. It is a partial expanded view of the tread part of the conventional pneumatic tire.

  The present invention will be described below together with the effects thereof with reference to the drawings. FIG. 1 is a partial development view of a tread portion of a pneumatic tire (hereinafter referred to as “tire”) according to an embodiment of the present invention. In the drawing, the vertical direction is the tire circumferential direction (the direction along the tire equator plane), and the left-right direction (the direction orthogonal to the tire equator plane E) is the tire width direction.

  Although the tire of this embodiment is not illustrated, 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 an outer side in the tire radial direction of the belt It has a tire structure in accordance with the conventional practice including a tread portion 1 disposed, and the tread portion 1 has the block pattern shown in FIG.

As shown in FIG. 1, the tire includes a plurality of blocks 3 defined by grooves 2 in a tread portion 1. The groove 2 includes a vertical groove 2a extending substantially in the tire circumferential direction and a horizontal groove 2b extending substantially in the tire width direction and intersecting the vertical groove 2a. The block 3 is formed in an octagonal prism shape having a substantially regular octagonal contact surface. At least a part of the plurality of blocks 3 formed in the tread portion 1, here, all the blocks 3 except the shoulder land portion 4 straddling the tread grounding end, the area Sb of the block grounding surface is about 450 mm ² or less. (In the example of FIG. 1, it is about 310 mm ² ). Further, the block 3 has a circumferential length Lb and a widthwise length Wb that are 1.5 times or more of the groove depth (block height Hb) of the groove 2 partitioning the block 3. The area Sb of the block ground plane is 450 mm ² or less, and has a circumferential length Lb and a widthwise length Wb that are 1.5 times or more the groove depth of the groove 2 that defines the block 3. In the block 3, the aspect ratio As that is the ratio of the circumferential length Lb of the block 3 to the widthwise length Wb of the block 3 is 1 or more and 2 or less (As = about 1 in the example of FIG. 1). It is preferable to use the shape.

として表すことができる。この発明では、ブロック個数密度Ｄは、０．００３（個／ｍｍ^２）以上０．０４（個／ｍｍ^２）以下の範囲内とすることが好ましい。図１の例では、ブロック個数密度Ｄは約０．００３２２（個／ｍｍ^２）である。ブロック個数密度Ｄは、ブロック３が配置された部分の実接地面積（溝分を除いた面積）に対して何個のブロック３が存在するかを密度として表現したものであり、上記実接地面積を算出するにあたっては、各ブロック３の接地面の面積Ｓｂを合算して求めても良い。なお、基準区域Ｚ内に在るブロック３の個数ａをカウントするに際して、ブロック３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、ブロック接地面の面積に対する、基準区域内に残ったブロック３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の場合は、１／２個と数えることができる。また、上記数１において、「ブロックの基準ピッチ長さ」とは、ブロック群を構成する任意のブロック列におけるブロック３の繰り返し模様の最小単位（１ピッチ）又は複数単位を指すものとし、例えば１つのブロック３とそのブロック３を区画する横溝２ｂによってパターンの繰り返し模様が規定されている場合は、ブロック３一つ分のタイヤ周方向長さＬｂとこのブロック３を区画する横溝２ｂ１本分のタイヤ周方向長さとを加算したものがブロック３の基準ピッチ長さとなる。 Further, in this tire, a plurality of blocks 3 are provided with a block group G formed by at least one row of block rows arranged here at a predetermined pitch in the tire circumferential direction, here seven rows. In the area of the block group G, the blocks 3 are densely arranged. The block 3 density (block number density D) is defined by the reference pitch length PL (mm) of the block 3, the width of the block group G by W (mm), and the reference pitch length PL and the block group W. When the number of blocks existing in the reference zone Z (region shown by hatching in the figure) is a (number) and the negative rate in the reference zone Z is N (%),

Can be expressed as In the present invention, the block number density D is preferably in the range of 0.003 (pieces / mm ² ) or more and 0.04 (pieces / mm ² ) or less. In the example of FIG. 1, the block number density D is about 0.00322 (pieces / mm ² ). The block number density D expresses how many blocks 3 exist with respect to the actual ground contact area (area excluding the groove) of the portion where the blocks 3 are arranged. May be obtained by adding up the area Sb of the ground contact surface of each block 3. In addition, when counting the number a of the blocks 3 in the reference zone Z, if the block 3 exists across the reference zone Z and cannot be counted as one, the area of the block ground plane is It is counted using the ratio of the remaining area of the block 3 remaining in the reference area. For example, in the case of a block straddling the inside and outside of the reference area Z and only half of the block exists in the reference area Z, it can be counted as 1/2. In the above formula 1, the “reference pitch length of the block” refers to a minimum unit (one pitch) or a plurality of units of the repeated pattern of the block 3 in an arbitrary block row constituting the block group. When the repeating pattern of the pattern is defined by one block 3 and the lateral groove 2b that partitions the block 3, the tire circumferential length Lb for one block 3 and the tire for the lateral groove 2b1 that partitions the block 3 The reference pitch length of the block 3 is obtained by adding the circumferential length.

  Next, the background of the inventor of the present application leading to the invention will be described with reference to the map of FIG. This map shows the bulging amount (rubber flow amount) of the block 3 when a load is applied to the block 3 and the width direction length Wb and the circumferential length Lb of the block 3 are variously changed. is there.

The inventor of the present application has observed in detail the deformation of the block 3 until the block 3 comes in contact with the road surface and leaves, and as a cause of wear of the block 3, the shearing of the block 3 due to the bulging of the side surface of the block due to a load load We found that the contribution of deformation was great. Therefore, the inventor is able to reduce the shear deformation of the block if the rubber flow of the block 3 under load can be reduced, thereby reducing the shear strain of the tread surface, and as a result, the wear of the block can be reduced. As a result of intensive studies on the relationship between the area Sb and the rubber flow of the block 3, the results shown in the map of FIG. 2 were obtained. As apparent from FIG. 2, the smaller the area Sb of the block ground contact surface, the smaller the shear deformation due to rubber flow. Based on this map, the influence on the wear of the block 3 is repeatedly examined, and the wear is advantageously reduced by setting the area S2 to S7, particularly the area Sb of the block contact surface to 450 mm ² or less in the map of FIG. Successful.

  On the other hand, if the area Sb of the ground contact surface of the block 3 becomes too small, the shear rigidity of the block 3 is lowered, the block 3 is collapsed (buckling), and the ground pressure at the block ground end becomes very high. That is, it has been found that since the contact pressure on the block contact surface is reduced, the grip force is reduced, and the amount of slip in the vicinity of the peripheral edge of the block 3 is increased, so that the wear easily proceeds. That is, the block aspect ratio BAs (the ratio of the circumferential length Lb or the width Wb of the block 3 to the height Hb of the block 3) is shown in FIG. It can be seen that the block shear stiffness suddenly decreases when BAs is less than about 1.5. Therefore, by setting each of the circumferential length Lb and the width length Wb of the block 3 to 1.5 times or more of the groove depth (block height Hb) of the groove 2 that defines the block 3, the required block Shear rigidity is ensured and good grounding properties can be obtained.

Therefore, according to the tire having the above-described configuration, the contact surface area Sb of the block 3 is set to 450 mm ² or less (preferably 310 mm ² ), so that the conventional block and the present invention are shown in FIGS. 4 (a) and 4 (b). In comparison with the applied block, the bulging deformation amount ΔX of the block side surface, particularly the kicking side block side surface at the time of tire load rolling (when the load F is applied) is reduced as the rubber flow decreases. As a result, shear deformation is reduced. As a result, frictional force and slip acting on the block 3 from the road surface are suppressed, and wear is reduced. Moreover, the circumferential length Lb and the width length Wb of the block 3 are both 1.5 times or more of the groove depth of the groove 2 (vertical groove 2a, horizontal groove 2b) adjacent to the block 3, and therefore required. The block rigidity can be secured, that is, the block 3 is buckled due to the decrease in the block rigidity due to the downsizing of the block 3, and the displacement near the peripheral edge of the block 3 is increased to increase the slip amount. There is no risk of lowering stability.

In this embodiment, the block number density D is set to 0.003 to 0.04 (pieces / mm ² ), and the blocks are densely arranged, so that the total edge length of the blocks 3 (the edge length of each block 3) Sum) can be increased, which is very advantageous for improving the performance on ice. When the block number density D is less than 0.003 (pieces / mm ² ), it is difficult to increase the total edge length without forming sipes in the block 3, while the block number density D is If it exceeds 0.04 (pieces / mm ² ), the block size becomes too small and it becomes difficult to achieve the required block rigidity. Further, if the block number density D is in the range of 0.0035 to 0.03 (pieces / mm ² ), both the block rigidity and the increase in the total edge length can be achieved at a higher level. .

  Furthermore, the negative rate N in the block group G region is preferably 5% to 50%. When the negative rate N is less than 5%, the groove area is too small and the drainage performance is insufficient, and the block size becomes too large to increase the total edge length, while it exceeds 50%. This is because the ground contact area becomes too small and the steering stability may be lowered.

In the tire of this embodiment, the area Sb of the block contact surface is 450 mm ² or less, and the circumferential length Lb that is 1.5 times or more the groove depth of the groove 2 defining the block 3 and In the block 3 having the width direction length Wb, it has been described that the aspect ratio As indicating the ratio of the circumferential direction length Lb of the block 3 to the width direction length Wb of the block 3 is 1. However, other blocks shown in FIG. As in the tire of the embodiment, it is preferable that the aspect ratio As is 1 or more and 2 or less, and the block 3 is formed in a vertically long shape elongated in the circumferential direction. According to this, as shown in FIG. 5, in the side surface of the block 3, the area of the surface P (free surface P) facing the tire circumferential direction is made larger than the area of the surface Q (free surface Q) facing the tire width direction. As a result, the ratio of the bulging amount in the tire width direction can be increased compared to the bulging amount in the tire circumferential direction when the load F is applied, and the wear on the kick-out side of the block 3 is more efficient. Can be reduced. When the aspect ratio As is less than 1, the block 3 has a horizontally long shape in the tire width direction, which may reduce the shear rigidity of the block 3 against load input in the tire circumferential direction, and the aspect ratio As is 2. In the case of exceeding the block contact surface area Sb of 450 mm ² or less, the width direction length Wb of the block 3 becomes too small, and the steering stability may be lowered.

  Further, in the present invention, as in the tire of still another embodiment shown in FIG. 8, the circumferential direction in which the groove width is larger than the longitudinal groove 2 a extending along the tire circumferential direction and defining the block 3 in the tread portion 1. The main groove 5 may be provided, and according to this, good drainage performance can be ensured even when the blocks 3 are arranged relatively densely. The number of circumferential main grooves 5 is not limited to two, and may be one or three or more.

  Further, in the present invention, like the tires of other embodiments shown in FIGS. 10 and 11, the shape of the ground contact surface of the blocks 3 formed in the tread portion 1 may be rectangular, and although not shown, A rectangular shape, a circular shape, an elliptical shape, or the like may be adopted. However, as shown in FIGS. 1, 6, 7, and 8, a substantially octagonal contact surface shape is preferable. The anisotropy of the so-called edge effect can be reduced, and the uniform grounding property of the block 3 can be improved.

  Further, in the present invention, the blocks 3 are preferably arranged in a staggered manner. That is, it is preferable that the phase of the block 3 is shifted by a half pitch in the tire circumferential direction between adjacent block rows. By adopting such a staggered arrangement, the density (block number density D) of the blocks 3 can be increased, and the total age length included in the block group G can be increased. Further, the ground contact timing of the block 3 can be shifted in the tire width direction, which is advantageous in reducing pattern noise.

In addition, in the present invention, the area Sb of the block ground plane is 450 mm ² or less, and the circumferential length Lb and the width direction length are 1.5 times or more the groove depth of the groove 2 defining the block 3. The block 3 having the width Wb may be a part of the plurality of blocks provided in the tread portion 1, and the block 3 may occupy an area of 50% or more of the land portion area in contact with the road surface. Preferably, 70% or more of the land area in contact with the road surface is occupied by the block 3 in order to further enhance the effect of the present invention.

  Next, tires of Examples 1 to 7 and a tire of Conventional Example 1 according to the present invention were respectively prototyped and evaluated for wear resistance, and will be described below. All of these tires are radial tires for passenger cars having a tire size of 195/65 / R15, and the tread contact width is 135 mm.

The tires of Examples 1 to 7 are each provided with a tread portion having a configuration corresponding to FIGS. 1 and 6 to 11, and a plurality of blocks are arranged on the tread portion. In each of the tires of Examples 1 to 7, each block has an area of the block grounding surface of 450 mm ² or less (excluding the shoulder land portion), and each has a groove depth of 1. It has a circumferential direction length and a width direction length of 5 times or more. The tire of Example 4 has two straight circumferential main grooves extending in the tire circumferential direction in the tread portion. The circumferential main groove located on the inner side (left side in the figure) in the mounting posture to the vehicle is disposed at a position corresponding to 22% of the tread contact width with the tire equator plane E as the center, and the outer side in the mounting posture to the vehicle. The circumferential main groove located on the right side in the figure is disposed at a position corresponding to 18% of the tread contact width with the tire equatorial plane as the center. The groove width of the left circumferential main groove is 7.0 mm, and the groove depth is 7.0 mm. The right circumferential main groove has a groove width of 12.0 mm and a groove depth of 7.0 mm. The tires of Examples 1 to 7 have the specifications shown in Table 1.

  The tire of Conventional Example 1 has the tread pattern shown in FIG. 12 in the tread portion and the specifications shown in Table 1.

  Each of these test tires is attached to a rim of size 6J × 15 to be a tire wheel, and is attached to a driving wheel of a passenger car used for the test, and an air pressure of 210 kPa (relative pressure) and a tire load load of 4.41 kN are applied. The wear amount of the block after traveling 5000 km on the course was measured. The results of the amount of wear are shown in Table 2. The results in Table 2 are expressed as an index with the wear amount of the conventional example being 100, and the larger the value, the higher the wear resistance performance. The evaluation results are also plotted in the map of FIG. 2 (points A1 to 7: Examples 1 to 7, point B: conventional example).

  As is clear from the results in Table 2, the tires of Examples 1 to 7 have a smaller wear amount and improved wear resistance performance than the tire of Conventional Example 1 by optimizing the block size. I understand that Moreover, when the tire of Example 6 and the tire of Example 7 are compared, it can be seen that the wear resistance performance is further improved by setting the aspect ratio As to 1 or more and 2 or less.

  Thus, according to the present invention, it is possible to provide a pneumatic tire with improved wear resistance by reducing rubber flow by optimizing the block size.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Groove 2a Vertical groove 2b Horizontal groove 3 Block 4 Shoulder land part 5 Circumferential main groove

Claims (3)

In the pneumatic tire provided with a plurality of blocks partitioned by grooves in the tread portion,
At least some of the blocks have an area of the block ground plane of 450 mm ² or less, and a circumferential length and a width direction length that are 1.5 times or more each of the groove depths defining the blocks. A pneumatic tire characterized by having a thickness.   2. The pneumatic tire according to claim 1, wherein the at least some of the blocks have an aspect ratio of 1 or more and 2 or less indicating a ratio of a circumferential length of the block to a length of the block in the width direction. The pneumatic tire includes, in a tread portion, a block group formed by at least one row of block rows in which the blocks are arranged at a predetermined pitch in the tire circumferential direction.
In the block group, a reference pitch length of the block group is defined by PL (mm), a width of the block group is W (mm), and is divided by the reference pitch length PL and the width W. A block given by a / {PL × W × (1−N / 100)} where a is the number of the blocks existing in the area and N is the negative rate in the reference area. The pneumatic tire according to claim 1 or 2, wherein the number density D is 0.003 (pieces / mm ² ) or more and 0.04 (pieces / mm ² ) or less.

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