JP5399718B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire provided with a block formed by a groove in a tread portion, and more specifically, proposes a technique that brings about a dramatic improvement in performance on ice.

  Conventionally, in a pneumatic tire, for the purpose of improving the performance on ice by enhancing the edge effect, as shown in FIG. 3, the tread portion 100 has a longitudinal groove 101 extending in the tread circumferential direction and a tread width direction. In general, it is widely performed that the block 103 is partitioned by the extending lateral groove 102 and a plurality of sipes 104 are added to the formed block 103. In such a conventional pneumatic tire, a large number of sipes 104 are arranged in the block 103 under the requirements of higher driving, braking and turning performance, and in particular, on-ice performance is ensured for a large ground contact area. Therefore, the number of block rows in the tread surface is reduced to 3 to 9 rows, and each block 103 has a vertically long shape in the tread circumferential direction (see, for example, Patent Document 1).

JP 2002-192914 A

  However, in the conventional pneumatic tire as described above, the divided block portion 103a partitioned by the sipe 104 becomes horizontally long and the rigidity becomes too low, and the divided block portion 103a falls down at the time of ground contact, and the grounding property is deteriorated. Therefore, it is difficult to obtain sufficient on-ice performance commensurate with recent improvements in vehicle performance. In addition, the size of each block 103 is large, and in the central area of the block 103, it is not possible to sufficiently remove the water film between the ice surface and the tire when braking on ice only by forming the sipe 104. Therefore, it has been difficult to dramatically improve the performance on ice.

  Therefore, an object of the present invention is to solve these problems, and an object thereof is to dramatically improve the performance on ice by optimizing the tread pattern.

In order to achieve the above object, the pneumatic tire of the present invention is provided with a small block group in which a plurality of independent small blocks partitioned by grooves are densely arranged with each other in at least a part of the tread portion. A pneumatic tire in which a block row or a land portion row is formed by small blocks of the small block group, wherein the small blocks include a first small block having a first tread surface contour shape, and the first small block. A second small block having a second tread surface contour shape different from the tread surface contour shape, and the first small blocks have the tread surface contour shape congruent with each other, and small block between the 2 Ri joint der mutually their tread surface contour,
The first tread surface contour shape is a pentagon, and the second tread surface contour shape is a circle;
Two first small blocks adjacent in the tread circumferential direction, two first small blocks adjacent in the tread width direction, and at least one second small block are defined as one small block unit, and the same small In the block unit, the two first small blocks adjacent to each other in the tread circumferential direction are arranged symmetrically with respect to each other about a straight line parallel to the tread width direction and are adjacent to each other in the tread width direction. The first small blocks are arranged symmetrically with respect to each other about a straight line parallel to the tread circumferential direction,
The small block units are arranged in a staggered manner with respect to the tread circumferential direction,
The second small block is arranged near the center of the small block unit .

  In the pneumatic tire according to the present invention, since the small blocks partitioned by the grooves are densely arranged with each other, the total edge length of the land portion is increased, and an edge effect higher than that of the sipe is obtained. Moreover, since the surface area per small block is small, the grounding property of each block is improved. In addition, since the distance from the central area of the small block to the periphery of the block is small, the water film in the central area of the small block is efficiently removed when the block is grounded. In the pneumatic tire of the present invention, since the tread surface contour shape is congruent between the first small blocks and between the second small blocks, the contact pressure in the arrangement range of the small blocks is made uniform. To improve the ground contact. Further, in the pneumatic tire of the present invention, since the small block is composed of two kinds of small blocks having different tread surface contour shapes, it is possible to reduce waste of grooves (area where the small blocks are not arranged). And small blocks can be arranged efficiently. This is particularly advantageous when a shape that is difficult to arrange efficiently as a tread pattern due to the nature of the shape, such as a pentagon or heptagon, is adopted as the tread surface contour shape of the small block. This is because, in the case of a square, hexagon, or octagon, it is possible to place the sides facing each other between all adjacent small blocks. Can be arranged. On the other hand, pentagons, heptagons, and the like are shapes that cannot be uniformly arranged with the sides facing each other between all adjacent small blocks, so they can be efficiently arranged as a tread pattern. This is because it is very difficult and a wasteful space (groove) is easily generated. In the present invention, by arranging small blocks having different shapes and sizes in such a useless space, the number density of small blocks can be increased, that is, the edge component length can be further increased. Also, by using two types of small blocks of shape and size, the direction in which edges act can be diversified compared to the case where a small block group is composed of small blocks of a single shape and size. Therefore, the handling performance especially on ice and snow can be improved.

  Therefore, according to the pneumatic tire of the present invention, the above-mentioned actions can be combined to ensure excellent grounding performance and edge effect and to efficiently remove the water film with a small block, and dramatically improve the performance on ice. Can be improved.

  In addition, although the small block group is more effective for the performance on ice when it is provided on the entire tread, it can be applied to a limited area to balance with other performance such as steering stability and uneven wear resistance. it can.

Further, in the pneumatic tire of the present invention, the reference pitch length of the small blocks in the small block group is PL (mm), the width of the small block group is W (mm), the reference pitch length PL and the When the number of small blocks existing in the reference area of the small block group divided by the width W is a (number) and the negative rate in the reference area is N (%), a / (PL × W × (1−N / 100)), the small block number density D per unit actual contact area of the small block group is 0.003 (pieces / mm ² ) to 0.04 (pieces / mm ² ). It is preferable to be within the range.

  Here, “the reference pitch length of a small block” refers to the minimum unit of the repeated pattern of small blocks in one block row constituting the small block group. For example, one small block and the small block are partitioned. When the repeating pattern of the pattern is defined by the groove to be added, the tread circumferential length of one small block and the tread circumferential length of one groove adjacent to the tread circumferential direction of this small block are added. Becomes the reference pitch length of the small block. The “small block group width W” refers to the length in the tread width direction of the small block group formed by densely arranging the small blocks. For example, when the small block group exists in the entire tread, the tread grounding width is set. Shall point to. Furthermore, the “actual ground contact area” of the small block group means the total surface area of all the small blocks in the reference area of the small block group, in other words, the product of the reference pitch length PL and the width W. It refers to the area defined by subtracting the area of the groove defining each small block from the area of the reference area defined above.

  Moreover, in the pneumatic tire of the present invention, it is preferable that a sipe is formed on at least one of the first small block and the second small block. Here, “sipe” refers to a thin notch that can divide at least the surface of a small block into two or more block pieces that can be closed when grounded.

  According to the pneumatic tire of the present invention, it is possible to remarkably improve the performance on ice by ensuring excellent grounding property and edge effect and efficiently removing the water film with a small block.

It is the partial expanded view which showed the tread pattern of the pneumatic tire (tire of Example 1) of one Embodiment according to this invention. It is the partial expanded view which showed the tread pattern of the pneumatic tire (tire of Example 2) of other embodiment according to this invention. It is the partial expanded view which showed the tread pattern of the pneumatic tire of the prior art (tire of the prior art example 1). It is the partial expanded view which showed the tread pattern of the pneumatic tire (tire of the comparative example 1) as a comparison. It is the partial expanded view which showed the tread pattern of the pneumatic tire (tire of the comparative example 2) as a comparison. It is the partial expanded view which showed the tread pattern of the pneumatic tire (tire of the comparative example 3) as a comparison. It is the partial expanded view which showed the tread pattern of the pneumatic tire (tire of the comparative example 4) as a comparison.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a partial development view showing a tread pattern of a pneumatic tire (hereinafter referred to as “tire”) according to an embodiment of the present invention. In the drawing, the vertical direction indicates the tread circumferential direction, and the horizontal direction (direction perpendicular to the equator plane E) indicates the tread 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 arranged, and has the tread pattern shown in FIG. 1 in the tread portion.

This tire, as shown in FIG. 1 has a tread portion 1, and defined by grooves 2, the small block group G _B formed by each other is densely plurality of small blocks 3 independent. Small block group G _B is present throughout the tread portion 1.

  The small block 3 includes a first small block 3A having a first tread surface contour shape and a second small block 3B having a second tread surface contour shape different from the first tread surface contour shape. Become. The tread surface contour shape of the first small block 3A is a pentagon, and the tread surface contour shape of the second small block 3B is a circle.

  The two first small blocks 3A, 3A adjacent in the tread circumferential direction are arranged symmetrically with respect to each other about a straight line m parallel to the tread width direction. More specifically, the corner portion c1 of one first small block 3A and the corner portion c2 of the other first small block 3A are arranged to face each other. The two first small blocks 3A, 3A adjacent in the tread width direction are arranged symmetrically with respect to each other about a straight line n parallel to the tread circumferential direction. That is, between the first small blocks 3A adjacent in the tread width direction, the corner portion c3 of one first small block 3A and the corner portion c4 of the other first small block 3A face each other. Has been placed.

  Further, a gap (groove 2) formed between the two first small blocks 3A and 3A adjacent in the tread circumferential direction and between the two first small blocks 3A and 3A adjacent in the tread width direction. ), The second small block 3B having a surface area smaller than that of the first small block 3A is arranged so as to reduce the gap. In other words, the four first small blocks 3A are arranged close to each other so as to surround the second small block 3B.

  With such an arrangement, two first small blocks 3A and 3A adjacent in the tread circumferential direction, two first small blocks 3A and 3A adjacent in the tread width direction, and these four first small blocks are arranged. One small block unit U is formed by the second small blocks 3B arranged between 3A. The small block units U are arranged in a staggered manner with respect to the tread circumferential direction. The distance d between the first small block 3A and the second small block 3B in the unit U is a distance that can contact each other during tire load rolling (including acceleration / deceleration, cornering, etc.). Is set.

として表される、小ブロック群Ｇ_Ｂの単位実接地面積当りの小ブロック個数密度Ｄ（個／ｍｍ^２）が、０．００３（個／ｍｍ^２）以上０．０４（個／ｍｍ^２）以下である。なお、小ブロック群Ｇ_Ｂの基準区域Ｚ内の小ブロック３の個数ａをカウントするに際して、小ブロック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、小ブロック３の表面積に対する、基準区域内に残った小ブロック３の残存面積の比率を用いて数えることとする。例えば、図１に符号Ｂ１で示すブロックのように、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。 Here, the sizes of the first small block 3A and the second small block 3B are set smaller than the conventional pattern shown in FIG. 3, and the first small block 3A and the second small block 3B have the same size. The density is set higher than the conventional pattern shown in FIG. The edge effect and the water removal effect can be enhanced as the size of the first small block 3A and the second small block 3B is reduced and the density is increased. Street. That is, the reference pitch length of the small block 3 in the small block group G _B PL (mm), the width W (mm) (this embodiment of the small block group G _B, the small block 3 on the entire tread portion 1 since There are arranged equal to the tread width TW.), it is defined by the said reference pitch length PL and the width W, reference zone Z of the small block group G _B (region shown in FIG hatching) The number of small blocks 3 existing in the frame (the total number of first small blocks 3A and the number of second small blocks 3B) is a (number), and the negative rate in the reference zone Z is N (%). When

Expressed as the small block number density D per unit actual ground contact area of the small block group _{G B} (number / mm ²⁾ is 0.003 (pieces / mm ²⁾ 0.04 (pieces / mm ²⁾ or less It is. Note that when counting the number a of the small block 3 in the reference zone Z of the small block group G _B, if the small block 3 is present across the inside and outside of the reference zone Z, can not be counted as one is small Counting is performed using the ratio of the remaining area of the small block 3 remaining in the reference area to the surface area of the block 3. For example, in the case of a block that spans the inside and outside of the reference zone Z and only half of the block exists in the reference zone Z, such as a block indicated by reference numeral B1 in FIG.

If the number density D of the small block 3 in the small block group G _B is less than 0.003 (pieces / mm ^2), without the formation of sipes, it is difficult to realize a high edge effect, whereas, the number of small blocks 3 When the density D exceeds 0.04 (pieces / mm ² ), the small block 3 becomes too small and it is difficult to achieve the required block rigidity. Further, the number density D of the small block 3 in the small block group _{G B,} if within the range of 0.0035 to 0.03 piece / mm ^2, higher level of compatibility between rigidity and the edge effect of the small block 3 Can be achieved.

In the tire of this embodiment, since the small blocks 3 partitioned by the grooves 2 are densely arranged with each other, the total edge length of the land portion is increased, and the edge effect is higher than that of the conventional sipe. can get. Moreover, since the surface area per one small block 3 is small, the grounding property of each block improves. Further, since the distance from the central area of the small block 3 to the block periphery is small, the water film in the central area of the small block 3 is efficiently removed when the block is grounded. In the tire of this embodiment, since the tread surface contour shape is congruent between the first small blocks 3A and between the second small blocks 3B, the contact pressure in the arrangement range of the small blocks is uniform. To improve the ground contact. Further, in the tire of this embodiment, since the small block 3 is configured by two kinds of small blocks 3A and 3B having different tread surface contour shapes, the waste of the groove 2 (the small blocks are not disposed). Area) can be reduced and the small blocks 3 can be arranged efficiently, so that the number density of the small blocks 3 can be increased, that is, the edge component length can be further increased. Further, two kinds of shape and size of the small block 3A, by using 3B, as compared with the case where the small block group G _B in small blocks of a single shape and size, the direction of action of the edge Since it can be diversified, the handling performance especially on ice and snow can be improved.

  Therefore, according to the tire of this embodiment, the above-mentioned action is combined, and it is possible to secure excellent grounding property and edge effect and to efficiently remove the water film by the small block 3, so that the performance on ice is leap. Can be improved.

  In this embodiment, since the small block 3A having a pentagonal surface contour shape and the small block 3B having a circular surface contour shape are used in combination, the ground contact area is reduced due to difficulty in arrangement. Compared to the square blocks that have been widely used in the past, the angle of the corners can be made obtuse to increase the block rigidity, and the edge action direction can be diversified to effectively improve the performance on ice and snow. Can be made. Moreover, by using the circular small block 3B, it can be made to act equally as an edge with respect to all directions, and the cornering property on ice and snow can also be improved effectively.

  Further, in this embodiment, in one small block unit U, a straight line m parallel to the tread width direction is symmetrical between the two first small blocks 3A and 3A adjacent in the tread circumferential direction. Since it is arranged line-symmetrically as an axis and is arranged line-symmetrically using a straight line parallel to the tread circumferential direction between the two first small blocks 3A, 3A adjacent in the red width direction as a symmetry axis, Since the arrangement directions of the four first small blocks 3A are all different to further diversify the direction in which the edge acts, the handling property on ice and snow can be further improved. Further, since such units U are arranged in a zigzag pattern, further dense arrangement of the small blocks 3 is possible.

  Furthermore, in this embodiment, since the second small block 3B having a circular surface contour shape is disposed near the center of the small block unit U, the groove volume near the center of the small block unit U is reduced. Nevertheless, smooth drainage can be promoted by the circular small block 3B. That is, at least one of the first small block 3A and the second small block 3B has a smooth curved surface so that the small blocks 3 are highly dense without sacrificing drainage. An increase in the edge effect due to the arrangement can be easily realized.

  Further, since a plurality of first small blocks 3A are arranged so as to surround the second small block 3B, the second small block is relatively low in rigidity because of its relatively small surface area, and is easy to fall down when rolling on a tire load. 3B can be supported by the first small block 3A having a relatively large surface area and high rigidity, and the rigidity of the small block 3 can be enhanced as a whole to achieve further improvement in performance on ice.

  Next, another embodiment of the present invention will be described with reference to FIG.

  In the tire shown in FIG. 2, each of the first small blocks 3A is provided with two sipes 4 each extending in an arc shape. Two first small blocks 3A and 3A adjacent in the tread circumferential direction so that the respective corners c1 and c2 face each other, and two adjacent small blocks 3A and 3A in the tread width direction so that the respective corners c3 and c4 face each other. When the first small blocks 3A and 3A and the second small block 3B arranged therebetween are regarded as one small block unit U, the sipe 4 formed in the first small block 3A is A double substantially annular sipe is formed in cooperation with the sipe 4 formed in the other first small block 3A in the same unit U.

  Thus, by providing the sipe 4 in the first small block 3A, the edge effect and the water removal effect can be further improved, so that higher performance on ice and snow can be obtained, and for example, other than performance on ice and snow From the viewpoint of achieving adjustment with other performances, the present invention aims at reducing the small block number density D compared to the case where the sipe 4 is not formed (that is, even if the size of the small block 3 is increased to some extent). The excellent performance on ice can be obtained.

  In addition, since the shape of the sipe 4 is to diversify the direction of the sipe edge so that an effective edge effect can be exerted against the input of force from all directions, as shown in FIG. The sipe 4 is not limited to the illustrated example, but can be linear, or a so-called three-dimensional sipe that refracts in the tire radial direction. You can also. Further, in the illustrated example, the sipe 4 is opened in the groove 2 that partitions the first small block 3A at both ends thereof, but is not limited thereto, and one end or both ends are terminated in the block. A so-called blind sipe can also be used, which can suppress a decrease in block rigidity, which is particularly advantageous when a plurality of sipes 4 are provided in the small block 3. The sipes 4 are not necessarily provided in all the first small blocks 3A, and can be provided in the plurality of first small blocks 3A or in the second small blocks 3B. When a high edge effect or the like is required, the sipes 4 may be provided in the small blocks 3 that are approximately half or more of each block group.

Further, the number of sipes 4 provided for each small block 3 is not limited to two, but may be three or one by adjusting the rigidity of the small block 3 and the required edge component length (edge effect). Can be. More specifically, for example, when the small blocks 3 are required to be formed relatively large for the purpose of balancing with other performances such as steering stability and wear resistance, the small block number density D is set. It is preferable that the number of sipes 4 provided in the small blocks 3 is ^two or more within a range of 0.003 pieces / mm ² or more and 0.01 pieces / mm ² or less. In this way, the required edge effect can be obtained while balancing with other performances. When a plurality of sipes 4 are arranged in the small block 3 in this way, it is preferable that the sipes 4 in the same small block 3 are arranged in parallel to each other. Thus, by arranging the sipes 4 in the same small block 3 in parallel, the shape of the divided block portion between the sipes can be made uniform, and the partial strength of the block rigidity can be eliminated or reduced. This is because the performance can be further improved. Further, reducing the partial strength of the block rigidity is also advantageous for uneven wear resistance. In addition, under the demand for higher block rigidity, the small block number density D is more preferably 0.003 / mm ² or more and 0.008 / mm ² or less.

On the other hand, when it is required to make the small blocks 3 relatively small for the purpose of balancing with other performances such as steering stability and wear resistance, the small block number density D is set to 0.005. It is preferable that the number of sipes 4 provided in each small block 3 is one in the range of / mm ² or more and 0.02 pieces / mm ² or less. In this way, the required edge effect can be obtained while balancing with other performances. In addition, it is more preferable to set the small block number density D to 0.007 / mm ² or more and 0.015 / mm ² or less under the requirement of a higher edge effect.

  Further, the extending direction of the sipe 4 is not limited to that in FIG. 2 and can be arbitrarily set in relation to the required performance. For example, when importance is attached to traction performance and braking performance, it can be set along the tread width direction. On the other hand, when importance is attached to lateral input (cornering performance), it is inclined with respect to the tread width direction. Can be set. Moreover, although illustration is abbreviate | omitted, performance can be adjusted more effectively by changing the direction of the sipe 4 partially in a block unit within a tread. If it does in this way, these can be improved efficiently, aiming at the good balance of traction performance, brake performance, and cornering performance.

Incidentally, in the present invention, negative ratio N of the small block group _{G B} is preferably 5% to 50%. If negative ratio N is less than 5% in the small block group G _B, except that the insufficient drainage groove area is too small, the present invention is to aim too large one size one small block However, it is difficult to realize the edge effect. On the other hand, if it exceeds 50%, the ground contact area becomes too small, and the steering stability may be lowered.

The above description shows only some of the embodiments of the present invention, and these configurations can be combined with each other or various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, the small block group G _B formed by densely arranging the small blocks 3 has been described as extending across the tread portion 1, it may be provided only in a part of the tread portion 1. In the above-described embodiment, the small block is composed of a pentagonal tread surface contour shape and a circular tread surface contour shape. However, the present invention is not limited to this. It may be composed of a square shape, may be composed of a trapezoidal shape and a triangular shape, and other shapes may be employed.

  Next, the tires of Examples 1 and 2 according to the present invention, the tire of Conventional Example 1 according to the prior art, and the tires of Comparative Examples 1 to 4 were respectively prototyped and evaluated for performance on ice and snow.

  The tire of Example 1 is a 205 / 55R16 size passenger car radial tire having the tread pattern shown in FIG. 1 in the tread portion. This tire has a small block group in which a plurality of independent small blocks are formed densely on the entire tread portion and formed by grooves. The small block is a first small block whose tread surface contour shape is a regular pentagon. And the tread surface contour shape is a second small block having a perfect circle. Other specifications of the tire of Example 1 are as shown in Table 1.

  The tire of Example 2 is a 205 / 55R16 size passenger car radial tire having the tread pattern shown in FIG. 2 in the tread portion. This tire is substantially the same as the tire of Example 1 except that two sipes are provided for each first small block. Other specifications of the tire of Example 2 are as shown in Table 1.

  For comparison, a 205 / 55R16 size radial tire for passenger cars, the negative rate of the tread portion shown in FIG. 3 having a negative rate of 31.9% in the entire tread portion, and the negative rate of the entire tread portion is shown in FIG. A tire of Comparative Example 1 having a tread pattern shown in FIG. In the tire of Conventional Example 1, a plurality of rectangular small blocks are defined in the tread portion by vertical grooves extending in the tread circumferential direction and horizontal grooves extending orthogonally to the vertical grooves. The longitudinal groove has a width of 3 mm and a depth of 8.5 mm, and the transverse groove has a width of 7.9 mm and a depth of 8.5 mm. Each small block has three sipes extending linearly. In the tire of Comparative Example 1, a plurality of rectangular small blocks are defined in the tread portion by vertical grooves extending in the tread circumferential direction and horizontal grooves extending orthogonally to the vertical grooves. The longitudinal groove has a width of 1.2 mm and a depth of 8.5 mm, and the transverse groove has a width of 4.5 mm and a depth of 8.5 mm. Each small block has two sipes extending linearly. Other specifications are shown in Table 2.

For comparison, a tire of Comparative Examples 2 and 3 which is a 205 / 55R16 size passenger car radial tire and has a tread pattern shown in FIGS. Comparative Examples 2 and 3 differ from the tire of Example 1 in that the small block number density D is outside the range of 0.003 / mm ^{2 to} 0.04 / mm ² . Other specifications are shown in Table 2.

  Further, for comparison, a tire of Comparative Example 4 which is a 205 / 55R16 size passenger car radial tire having a tread pattern shown in FIG. In this tire, the tread surface contours of the small blocks are all regular pentagons. Other specifications are shown in Table 2.

(Performance evaluation)
About each said test tire, it assembled | attached to the rim of size 6.5Jx16, it mounted on the vehicle as internal pressure 220kPa (relative pressure), the following test was done, and the performance was evaluated.

(1) Brake performance evaluation test on ice Brake performance on ice was evaluated from the measured distance by measuring the braking distance when fully braking from 20 km / h on an ice plate road surface. The evaluation results are shown in Table 3. The evaluation in Table 3 is the index of the tires of Examples 1 and 2 and the tires of Comparative Examples 1 to 4 with the result of Conventional Example 1 being 100. The larger the value, the better the braking performance on ice. Indicates that

(2) Traction performance evaluation test on ice The traction performance on ice was evaluated from the measured time by fully accelerating the road surface on ice and measuring the time to reach a distance of 20 m. The evaluation results are shown in Table 3. The evaluation in Table 3 is the index of the tires of Examples 1 and 2 and the tires of Comparative Examples 1 to 4 with the result of Conventional Example 1 being 100. The larger the value, the better the traction performance on ice. Indicates that

(3) Feeling evaluation test on ice Feeling evaluation on ice comprehensively includes braking performance, acceleration performance, straight travel performance and cornering performance by a test driver when traveling on a test course on an ice sheet in various driving modes. It was done by evaluating the feeling. The evaluation results are shown in Table 3. The evaluation in Table 3 is the index of the tires of Examples 1 and 2 and the tires of Comparative Examples 1 to 4 with the result of Conventional Example 1 being 100. The larger the numerical value, the better the feeling on ice. Indicates that

(4) Feeling evaluation test on snow Feeling evaluation on snow is based on the comprehensive braking performance, acceleration performance, straight travel performance and cornering performance by the test driver when traveling on the test course on the snowy road surface in various driving modes. This was done by evaluating the feeling. The evaluation results are shown in Table 3. The evaluation in Table 3 is the index of the tires of Examples 1 and 2 and Comparative Examples 1 to 4 with the result of Conventional Example 1 being 100. The larger the value, the better the feeling on snow. Indicates that

  From the evaluation results shown in Table 3, the tires of Examples 1 and 2 show superior performance in all of the brake performance on ice, the traction performance on ice, the feeling on ice, and the feeling on snow. In addition, the tire of Example 2 in which the sipe is formed in the first small block shows superior results compared to the tire of Example 1 in terms of performance on ice.

  According to the present invention, it is possible to drastically improve the performance on ice and snow by ensuring excellent grounding property and edge effect and efficiently removing the water film with a small block.

1 tread portion 2 grooves 3 small blocks 3A first small block 3B the second small blocks c1, c2, c3, c4 tread circumferential direction of the first small block corners 4 sipe G _B small block group PL small block group Reference pitch length PW Small block group pitch length in the tread width direction BL Small block circumferential length BW Small block width direction length U Small block unit W Small block group width Z Reference area

Claims (3)

A small block group in which a plurality of independent small blocks partitioned by grooves are densely arranged mutually is provided in at least a part of the tread portion, and a block row or a land portion row is formed by the small blocks of the small block group A pneumatic tire,
The small block includes a first small block having a first tread surface contour shape and a second small block having a second tread surface contour shape different from the first tread surface contour shape. ,
Said first small block each other with their tread surface contour which is congruent to each other, said second small block each other Ri congruent der mutually their tread surface contour,
The first tread surface contour shape is a pentagon, and the second tread surface contour shape is a circle;
Two first small blocks adjacent in the tread circumferential direction, two first small blocks adjacent in the tread width direction, and at least one second small block are defined as one small block unit, and the same small In the block unit, the two first small blocks adjacent to each other in the tread circumferential direction are arranged symmetrically with respect to each other about a straight line parallel to the tread width direction and are adjacent to each other in the tread width direction. The first small blocks are arranged symmetrically with respect to each other about a straight line parallel to the tread circumferential direction,
The small block units are arranged in a staggered manner with respect to the tread circumferential direction,
A pneumatic tire characterized in that the second small block is arranged near the center of the small block unit . The small block group defined by PL (mm) as the reference pitch length of the small blocks in the small block group, W (mm) as the width of the small block group, and the reference pitch length PL and the width W. A / (PL × W × (1−N / 100)) where a is the number of small blocks existing in the reference area and N is the negative rate in the reference area. The small block number density D per unit actual ground contact area of the small block group is within a range of 0.003 (pieces / mm ² ) to 0.04 (pieces / mm ² ). Pneumatic tires. The pneumatic tire according to claim 1 or 2, wherein a sipe is formed on at least one of the first small block and the second small block.

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