JP2011235787A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new pneumatic tire which reduces abrasion resulting from the shearing deformation of a block when grounded and has sufficient drainage.SOLUTION: The pneumatic tire includes in a tread 1, a plurality of circumferential grooves 2 extending circumferentially along the tire and a plurality of rows of ribs 3 partitioned by the circumferential grooves 2, and the ribs 3 include a plurality of blocks 3b partitioned by a plurality of branch grooves 3a continuous to the circumferential grooves 2. The block 3b has an area Sb of a ground surface of the block 3b is 450 mmor smaller, and a length Lb and a length Wb in the direction of a width which are respectively 1.5 times or more as long as the depth of the branch groove 3a. The circumferential groove 2 includes a central side circumferential groove 2a formed in the vicinity of an equator E of the tire and shoulder side circumferential grooves 2b extending with the central side circumferential groove 2a sandwiched between them. The width Wof the centra side circumferential groove 2a is smaller than the width Wof the shoulder side circumferential groove.

Description

  The present invention relates to a pneumatic tire including a plurality of blocks partitioned by grooves in a tread portion, and relates to a pneumatic tire having sufficient drainage while reducing wear due to block deformation at the time of ground contact. is there.

  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).

JP-A-5-169922

  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 generated in the block due to the difference in diameter affects the wear resistance performance of the tire. In order to prevent this shear deformation, for example, it is effective to increase the shear rigidity (rigidity in the shear direction) by increasing the block size. However, if the block size is increased too much, as shown in FIG. When the block touches the road surface, the rubber swells greatly due to the flow and shear deformation of the block increases, and conversely, sufficient wear resistance performance may not be obtained. In addition, the relationship with the circumferential groove for improving drainage has not been sufficiently clarified, and there is still room for improvement in order to achieve both improvement in wear resistance and securing drainage.

  An object of the present invention relates to a pneumatic tire including a plurality of blocks partitioned by grooves in a tread portion, and reduces wear caused by shear deformation of the blocks at the time of ground contact, and has a novel drainage property. It is to provide a pneumatic tire.

The present invention provides a pneumatic tire provided with a plurality of circumferential grooves extending along a circumferential direction of the tire and a plurality of rows of ribs defined by the circumferential grooves in the tread portion.
The rib includes a plurality of blocks defined by a plurality of branch grooves connected to the circumferential groove, and the block has an area of a grounding surface of the block of 450 mm ² or less, and has a groove depth of the branch grooves. In contrast, each has a length in the circumferential direction and a length in the width direction that is 1.5 times or more,
The circumferential groove includes a central circumferential groove provided in the vicinity of the equator of the tire and a shoulder circumferential groove extending across the central circumferential groove. The central circumferential groove is the shoulder circumferential groove. It is a pneumatic tire characterized by having a groove width narrower than the width of.

  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. Further, the “groove depth of the branch groove” refers to the groove depth of the groove having the largest groove depth among the branch grooves defining the block.

  The groove width of the central circumferential groove is preferably 5 mm or less and more than the groove width of the narrowest groove among the branch grooves.

Since the tread portion is provided with a plurality of rows of ribs partitioned by a plurality of circumferential grooves, the ribs are partitioned by branch grooves to form a plurality of blocks, and the area of the ground contact surface of the block is 450 mm ² or less. It is possible to suppress the shear deformation due to the rubber flow of the block at the time of kicking. Also, since the circumferential length and the width direction length are 1.5 times or more of the groove depth of the branch groove, the groove depth becomes deeper than the circumferential length and width direction length of the block. Therefore, the block can be prevented from falling down (buckling), and the wear resistance can be advantageously improved. Further, among the circumferential grooves, the central circumferential groove at the center of the tread portion where the ground pressure increases becomes narrower than the shoulder circumferential groove, so that the distribution of the ground pressure of the block that increases by providing the circumferential groove It is possible to optimize both the wear resistance and ensure drainage.

  Since the width of the central side circumferential groove is 5 mm or less and not less than the width of the narrowest groove among the branching grooves, the wear resistance can be improved more advantageously.

It is the figure which showed the relationship between block size and the shear deformation of a block, (b) is a figure which shows the state of the shear deformation when block size is small with respect to (a). (A) is a plan development view showing a tread pattern of the tire according to an embodiment of a pneumatic tire according to the present invention, and (b) is a diagram showing a width direction length Wb and a block height Hb. is there. It is the figure which showed the relationship between the circumferential direction length and width direction length of a block, and the bulging deformation | transformation of a block. It is a figure which shows the relationship between block aspect-ratio BAs and block shear rigidity. It is a block schematic diagram for demonstrating the relationship between the aspect ratio As of a block, and the amount of swelling of a block, (a) is the state of aspect ratio As <1, (b) is the state of aspect ratio As> 1. Each is shown. It is a plane development view showing a tread pattern of a conventional pneumatic tire.

Hereinafter, the present invention will be described more specifically with reference to the drawings.
FIG. 2 is a developed plan view showing a tread pattern of a tire according to an embodiment of a pneumatic tire according to the present invention, and (b) shows a width Wb and a block height Hb of the block. FIG. 2A, 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 according to the present invention 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 The tread portion 1 has a tire structure according to a customary manner, and the tread portion 1 has the block pattern shown in FIG.

  As shown in FIG. 2A, the tread portion 1 has a plurality of circumferential grooves 2 extending in the tire circumferential direction, and includes a plurality of rows of ribs 3 partitioned by the circumferential grooves 2.

The circumferential groove 2 includes a central circumferential groove 2a provided in the vicinity of the equator E of the tire and a shoulder side circumferential groove 2b extending across the central circumferential groove 2a. In the illustrated example, one central circumferential groove 2a extends on the equator E of the tire, but may be plural. Further, one shoulder side circumferential groove 2b is disposed outside the central side circumferential groove 2a, but a plurality of shoulder side circumferential grooves 2b may be disposed. The width W ₁ of the center-side circumferential groove 2a is narrower than the width W ₂ of the shoulder-side circumferential groove 2b.

The rib 3 includes a plurality of blocks 3b partitioned by a plurality of branch grooves 3a. The branch groove 3 a is configured by a vertical groove 3 a ₁ extending substantially in the tire circumferential direction and a lateral groove 3 a ₂ extending substantially in the tire width direction and intersecting the vertical groove 3 a _1, and is connected to the circumferential groove 2. As the shape of the block 3b, a polygon, a circle, an ellipse, or the like can be adopted. However, in the example shown in FIG. 2A, a basic block (hereinafter, referred to as a tread portion 1) is arranged over the entire tread portion 1. The shape of the basic block is an octagonal column having a substantially regular octagonal contact surface. Since the shape of the grounding surface of the basic block is a substantially regular octagon, the anisotropy of the so-called edge effect can be reduced and the uniform grounding property of the block 3 can be enhanced. In the example shown in the figure, the basic blocks are arranged at equal intervals in the tire circumferential direction to form a row, and a basic block group having a staggered arrangement with a half pitch shift in the tire circumferential direction between adjacent rows is formed. The block group is cut out by the circumferential groove 2 to form the rib 3. With the staggered arrangement, the ground contact timing of the block 3 can be shifted in the tire width direction, which is advantageous for reducing pattern noise. The area Sb of the ground contact surface of the block 3b is about 450 mm ² or less (in the example of FIG. 2A, the basic block is about 310 mm ² ). Of the blocks 3b, the basic block has a circumferential length Lb and a width direction length Wb shown in FIGS. 2A and 2B that are 1 with respect to the groove depth (block height Hb) of the branch groove 3a. More than 5 times.

The tire according to the present invention having the above configuration is excellent in wear resistance and has sufficient drainage properties. This point will be described with reference to FIGS. 3 and 4 show basic blocks having a substantially regular octagonal tread pattern, which are evenly arranged on the entire surface of the tread portion 1, and are not provided with the circumferential groove 2 (from the tread pattern to the circumferential groove shown in FIG. 2A). 2 shows a result of examination on a tread pattern excluding 2). As a result of intensive studies by the inventor on wear resistance performance, the cause of wear of the block 3b is that the block 3b has a large contribution of shear deformation due to the bulging of the block 3b until the block 3b contacts the road surface and leaves. I found. As a result of further studies, a certain relationship was found between the area Sb of the ground contact surface of the block 3b and the bulging deformation (rubber outflow amount) of the rubber. The results are shown in FIG. The horizontal axis in FIG. 3 is the block width direction length Wb, the vertical axis is the block circumferential direction length Lb, and the area where the two lengths intersect is the area Sb. Further, the magnitude of the bulging deformation of the rubber corresponding to the area Sb is shown separately by dots or diagonal lines. As is apparent from FIG. 3, the smaller the area Sb of the contact surface of the block 3b, the smaller the rubber bulge deformation. The wear can be advantageously reduced when the area of S2 to S7 in FIG. 3, especially the area Sb of the ground contact surface of the block 3b is 450 mm ² or less.

  On the other hand, if the area Sb of the ground contact surface of the block 3b becomes too small, the shear rigidity of the block 3b decreases and collapses (buckling) occurs, and the ground pressure at the ground contact end of the block 3b becomes very high. Since the ground contact pressure on the ground is low, it has been found that the gripping force is reduced and the wear proceeds easily. This point will be described with reference to FIG. 4. The relationship between the block aspect ratio BAs (the ratio of the circumferential length Lb or width Wb of the block 3b to the height Hb of the block 3b) and the block shear rigidity is as follows. When the block aspect ratio BAs is a relatively large numerical value, the block shear rigidity does not change greatly, but rapidly decreases when the block aspect ratio BAs is less than about 1.5. That is, when the circumferential length Lb and the width direction length Wb of the block 3b are 1.5 times or more with respect to the groove depth (block height Hb) of the branch groove 3a, the required block shear rigidity is It is ensured and good grounding property can be obtained.

Investigation of the tire that becomes the tread pattern in FIG. 2A in which the circumferential groove 2 is formed on the tire that becomes the tread pattern described above has proceeded. As a result, the contact surface of the tread portion 1 is reduced by adding the circumferential groove 2. Therefore, the compressive force is more strongly applied to each block 3b, the deformation amount increases, and the wear resistance performance tends to decrease. In particular, at the center of the tread portion 1 of the tire, since the contact pressure is higher than the portion near the shoulder portion, the wear resistance performance is greatly reduced. If the width W ₁ of the center-side circumferential groove 2a is narrower than the width W ₂ of the shoulder-side circumferential groove 2b, the distribution of ground pressure on the block 3b is optimized, improved and drainage of wear resistance It has been clarified that it is possible to achieve both of these.

The width W ₁ of the center-side circumferential groove 2a is preferably set to 5mm or less from consideration of the area Sb of the ground contact surface of the block 3b. Thereby, the deformation | transformation of the block 3b of the center of the tread 1 is suppressed more, and it becomes possible to aim at the improvement of abrasion resistance performance. The width W ₁ of the center-side circumferential grooves 2a, it is preferable that the narrowest become grooves of the groove width or more of the branch grooves 3a. This ensures drainage and facilitates tire manufacture.

  Moreover, it is preferable that the block 3b has a vertically long shape in the circumferential direction. This point will be described with reference to FIGS. 5A and 5B. In the case of a vertically long shape in the circumferential direction, the area of the surface P (free surface P) facing the tire circumferential direction on the side surface of the block 3b. Is smaller than the area of the surface Q (free surface Q) facing the tire width direction, and when the load F is applied, the ratio of the bulge amount in the tire width direction is increased compared to the bulge amount in the tire circumferential direction. Therefore, the wear on the kick-out side of the block 3b can be reduced more efficiently. In particular, the aspect ratio As, which is the ratio of the circumferential length Lb to the width length Wb, is preferably 1 or more and 2 or less. When the aspect ratio As is less than 1, the block 3b becomes a long and narrow shape in the tire width direction, which may reduce the shear rigidity of the block 3b against the load input in the tire circumferential direction. If the value exceeds 2, the width Wb of the block 3b in the width direction may become too small due to the relationship with the area Sb of the ground contact surface of the block 3b, and the steering stability may be lowered. Thus, excellent wear resistance performance can be obtained while maintaining the tire performance.

  Prototype tires with a size of 195 / 65R15 with the combinations shown in Table 1, assembled in a rim with a size of 6J-15, mounted on a passenger car, run on a test course, wear resistance and drainage We investigated about. The air pressure at this time was 210 kPa, and the tire load was 4.41 kPa. The results are also shown in Table 1.

  The anti-wear performance was measured by measuring the amount of wear of a block after running a passenger car on a test course and running 10,000 km. The index was displayed with the wear amount of the reference tire as a conventional example as 100. A larger value indicates higher wear resistance.

  The drainage was confirmed by feeling evaluation by a test driver after mounting the passenger car on a wet road surface with a water depth of 10 mm. The results are shown in Table 1 with the reference tire as 100. The larger the value, the higher the drainage.

As a result, a tire (comparative tire 1) that has an appropriate block size but no circumferential groove has improved wear resistance but cannot obtain sufficient drainage. Also if the groove width W ₁ of the center-side circumferential groove while optimizing the block size is larger than the groove width W ₂ of the shoulder-side circumferential groove 2b, or equivalent to the tire (Comparative Tire 2, 3), the wear performance I can't be satisfied. On the other hand, the tire (adapted tires 1, 2) which is narrower than the groove width W ₂ of the shoulder-side circumferential groove 2b and a groove width W ₁ of the center-side circumferential groove while optimizing the block size, both drainage and wear resistance Can be satisfied. In particular the groove width W ₁ of the center-side circumferential groove and 5mm or less, and the tire (adapted tires 2) which is the most narrow and becomes the groove of the groove width or more of the branch groove, the result was particularly good.

  ADVANTAGE OF THE INVENTION According to this invention, while reducing the abrasion resulting from the shear deformation of the block at the time of grounding, a pneumatic tire provided with sufficient drainage can be supplied stably.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Circumferential groove 2a Center side circumferential groove 2b Shoulder side circumferential groove 3 Rib 3a Branching groove 3a ₁ Vertical groove 3a ₂ Horizontal groove 3b Block Sb The area of the ground contact surface of the block W ₁ The width of the central side circumferential groove W _{2 The} shoulder side circumference Groove width

Claims (2)

In the pneumatic tire provided with a plurality of circumferential grooves extending along the circumferential direction of the tire in the tread portion and a plurality of rows of ribs partitioned by the circumferential grooves,
The rib includes a plurality of blocks defined by a plurality of branch grooves connected to the circumferential groove, and the block has an area of a grounding surface of the block of 450 mm ² or less, and has a groove depth of the branch grooves. In contrast, each has a length in the circumferential direction and a length in the width direction that is 1.5 times or more,
The circumferential groove includes a central circumferential groove provided in the vicinity of the equator of the tire and a shoulder circumferential groove extending across the central circumferential groove. The central circumferential groove is the shoulder circumferential groove. A pneumatic tire having a groove width narrower than the width of the tire.   The pneumatic tire according to claim 1, wherein a groove width of the central circumferential groove is 5 mm or less and is equal to or greater than a groove width of the narrowest groove among the branch grooves.

Images