JP5519345B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire provided with a block pattern in which a plurality of blocks are defined in a tread portion by a plurality of vertical grooves extending along the tire circumferential direction and a plurality of horizontal grooves intersecting the vertical grooves. The present invention relates to a pneumatic tire having improved wet performance by suppressing water film intrusion to a block tread.

  Intrusion of water film on the block tread when driving on a wet road causes a significant decrease in the coefficient of friction on the wet road (hereinafter referred to as “WETμ”). Therefore, a step is provided on the tread surface of a block defined by a plurality of main grooves extending in the tire circumferential direction and a large number of narrow grooves opening in the main groove on the tread surface before and after the tire circumferential direction. A technique has been proposed in which the wall surface of the narrow groove is formed in a concave bent surface and a widened space is provided between the opposite wall surface facing the bent surface (see Patent Document 1).

JP 2009-51453 A

  However, in the technique described in Patent Document 1, the initial performance can be maintained by providing a step on the block tread surface in the tire circumferential direction, but if the step disappears due to wear, the narrow groove can only function as a normal sipe. Therefore, long-term improvement in WETμ cannot be desired.

  Therefore, an object of the present invention is to provide a pneumatic tire that prevents a water film from entering the block tread surface by a novel method that has not been conventionally used, and exhibits good wet performance over a long period of time.

The present invention has been made to solve the above-described problems, and a pneumatic tire according to the present invention includes a plurality of longitudinal grooves extending along the tire circumferential direction and a plurality of longitudinal grooves intersecting the longitudinal grooves in the tread portion. In a pneumatic tire provided with a block pattern in which a plurality of blocks are partitioned by a lateral groove, at least a part of the blocks has an inclination angle with respect to the tire width direction within a range of −10 ° to 10 ° including 0 °. A width direction edge is provided, and the in-plane density L of the width direction edge calculated from the following formula (1) is set in a range of 2.89 × 10 ⁻⁴ ≦ L ≦ 6.01 × 10 ⁻⁴ , and the width The block aspect ratio, which is the ratio of the length in the width direction of the block to the circumferential length of the block having a direction edge, is in the range of 0.4 to 3.5 ,
The distance from one end to the other end in the tire width direction of the area where the block is arranged is W (mm), the reference pitch length in the area where the block is arranged is PL (mm), and the W and the The number of blocks calculated by the following formula (2), where a (number) is the number of blocks existing in the reference area defined by PL and N (%) is the negative rate in the reference area The density D is in the range of 0.003 to 0.04 (pieces / mm ² ),
The block has no sipes .
L = (Et / S) × (1 / E) (1)
D = a / {PL × W × (1-N / 100)} (2)
However, L is the density in the ground plane at the edge in the width direction (1 / mm ² ), Et is the sum of the length in the width direction edge in the ground plane (mm), and S is the ground area in the tread portion (mm ^2). ), And E is the sum (mm) of the edge length in the width direction per pitch.
The term “landing surface” as used herein refers to the maximum load capacity (applicable to internal pressure and load capacity) in the size and ply rating applicable to JATMA YEAR BOOK when a pneumatic tire is mounted on a standard rim specified in JATMA YEAR BOOK. This is the case where the internal pressure of 100% of the air pressure (maximum air pressure) corresponding to the bold load in the table is filled and the maximum load capacity is applied. When the TRA standard or ETRTO standard is applied at the place of use or manufacturing, the respective standards are followed.

  The operation of the present invention will be described together with the background to the invention. The inventor has made a detailed study on removing the water film interposed between the road surface and the tire by the edge of the block, and as a result, the entrainment of the force (for example, braking force) near the entrance edge becomes large. (That is, when the non-contact area immediately after the edge becomes large), the load concentrates on the edge and the contact pressure of the edge (hereinafter referred to as “edge pressure”) increases, and as a result, the water film is cut by the edge. We were able to obtain knowledge that water would not easily enter the ground plane. Hereinafter, the effect of water film cutting by such an edge is referred to as a wiper effect. However, when the inventors conducted experiments by simply increasing the edges based on such knowledge, there were cases where the expected WETμ could not be obtained. In other words, as a method of increasing the edge amount in the ground plane, (A) a method of increasing the number of edges in the circumferential direction by reducing the pitch between edges, and (B) providing an inclination at each edge to increase the edge length. Although there is a method of increasing, in the case of the above (A), as the pitch between the edges is reduced, the block becomes relatively small, and it becomes difficult to secure an appropriate edge pressure for exerting the wiper effect. . In particular, when the aspect ratio of the block (the ratio of the length in the width direction of the block to the length in the circumferential direction of the block) increases, the block itself undergoes bending deformation, which further promotes a decrease in edge pressure. On the other hand, in the case of the above (B), depending on the size of the inclination angle of the edge, the entrainment of the force entry side edge becomes small and the edge pressure is lowered. Therefore, the inventor has determined the optimum edge amount as a result of intensive studies, and by defining the appropriate values for the aspect ratio of the block and the angle of the edge, while ensuring the number of edges in the ground plane, The inventors have newly found that the wiper effect can be surely exhibited while suppressing the decrease in edge pressure, and the present invention has been completed.

  Therefore, according to the pneumatic tire of the present invention, it is possible to increase the area where the wiper effect is exhibited by securing the edge amount with the in-plane density of the width direction edge, and the inclination angle and block of the width direction edge Since the edge pressure can be increased by setting the aspect ratio to an appropriate value, the wiper effect can be reliably increased to prevent the water film from entering the block tread surface. Further, since the wiper effect continues as long as the lateral groove forming the width direction edge exists, a good wet performance is provided over a long period of time as compared with the above-described known technique.

  In the pneumatic tire of the present invention, the width direction edge is formed in a region of 25% or more of the width direction length of the block from the width direction center position of the block to both sides of the width direction center position. Is preferred.

  In the pneumatic tire of the present invention, the block preferably has an octagonal shape on the tread surface.

  According to the present invention, it is possible to provide a pneumatic tire that prevents water film from entering the block tread surface and exhibits good wet performance over a long period of time.

It is a partial development view showing a tread pattern of a pneumatic tire according to an embodiment of the present invention. (A) is the side view which showed the adhesion area | region and the sliding area | region in the contact surface of a tread part, (b) is the figure which showed the water film thickness at the time of using the pneumatic tire of FIG. 1, and the change of WETμ. It is. It is the figure which showed the relationship between the inclination angle of an edge, and edge pressure. It is the figure which showed the change of the water film thickness at the time of using the pneumatic tire of a comparative example, and WETmicro. It is the figure which showed the change of the water film thickness at the time of using the pneumatic tire of a comparative example, and WETmicro. It is the figure which showed the relationship between the aspect ratio of a block, and edge pressure. It is an enlarged view of a tread part showing an example of other block tread shape applicable to this invention. It is a figure which shows the evaluation result in a test example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a typical tread pattern of a pneumatic tire according to the present invention, in which 1 is a tread portion, 2 is a vertical groove, 3 is a horizontal groove, 4 is a block, 5 is a block row, and C is a tire equatorial plane. It is. The pneumatic tire includes a block 4 formed in the tread portion 1 by a plurality of, here six, longitudinal grooves 2 extending along the tire circumferential direction and a plurality of lateral grooves 3 extending across the circumferential grooves 2. Have

The lateral grooves 3 extend linearly along the tire width direction, whereby all the blocks 4 are adjacent to the lateral grooves 3 and have an inclination angle of 0 ° to 10 ° including 0 ° with respect to the tire width direction. A width direction edge 4e within the range is formed. In addition, by extending the lateral groove 3 in the tire width direction while bending or curving, the width direction edge 4e is formed in a part of the blocks 4, or the width direction edge 4e is formed in a part of the blocks 4. You may do it. The width direction edge 4e is provided so that the in-plane density L of the width direction edge 4e calculated from the following formula (1) is 2.89 × 10 ⁻⁴ or more and 6.01 × 10 ⁻⁴ or less. Yes.
L = (Et / S) × (1 / E) (1)
However, L is the density in the ground plane of the width direction edge (1 / mm ² ), Et is the sum of the width direction edge lengths in the ground plane (mm), and S is the ground area (mm) of the tread portion 1 ² ), and E is the sum (mm) of edge lengths in the width direction per pitch. Here, “one pitch” is a distance between adjacent lateral grooves in the tire circumferential direction. The density L in the ground plane of the width direction edge is the density of the width direction edge 4e in the circumferential direction by normalizing the sum of the width direction edge lengths in the ground plane by the ground area and dividing by the width direction edge length per pitch. It represents.

Block 4, the tread shape is rectangular, block aspect ratio is the ratio of the width direction length W ₄ of the block with respect to the circumferential length L ₄ of the block 4 having a width direction edge 4e is 0.4 or more 3. Within 5 or less. Further, in order to ensure the required block rigidity, the circumferential length L ₄ and the width direction length W ₄ of the block 4, (deeper the depth of the longitudinal grooves and transverse grooves defining a block of) the block height Is preferably 1.5 times or more.

  According to the pneumatic tire of this embodiment, the area where the wiper effect is exhibited can be increased by securing the edge amount with the in-plane density L of the width direction edge 4e, and the inclination angle of the width direction edge 4e. Since the edge pressure can be increased by setting the aspect ratio of the block 4 to an appropriate value, the wiper effect can be surely exhibited and the water film can be prevented from entering the block tread. That is, as shown in FIG. 2, in the sliding region (the region after the frictional force gradually increases after reaching the ground and reaches the maximum static frictional force), the water film is gradually reduced in the circumferential direction by the wiper effect, Along with this, WETμ increases. Further, since the wiper effect continues as long as the lateral groove 3 forming the width direction edge 4e exists, a good wet performance is provided over a long period of time compared to the known technique.

  In the following, the process leading to the completion of the present invention will be described together with the explanation of the operation.

  The inventor made a detailed study on removing the water film interposed between the road surface and the tire by the edge 4e of the block 4 and found that the entrainment of the force (for example, the braking force) near the entrance edge was not performed. When it becomes large (that is, when the non-grounding area immediately after the edge becomes large), the load concentrates on the edge and the edge pressure increases. As a result, the water film is cut (wiped) by the edge, and water enters the grounding surface. As described above, the knowledge that it is difficult to enter is obtained.

  Therefore, the inventor considers such a wiper effect and sets the inclination angle of the edge formed at the periphery of the block 4 with respect to the tire width direction to −10 ° to 10 ° in the width direction edge. 4e can surely exert the wiper effect, and by securing the edge amount with the in-plane density of the width direction edge 4e, the area where the wiper effect is exhibited is increased, and the inclination angle of the width direction edge 4e is further increased. The inventors have found that by setting the aspect ratio of the block 4 to an appropriate value, the edge pressure can be increased and the water film can be effectively prevented from entering the block tread, and the present invention has been completed. .

  The reason why the width direction edge 4e is set to −10 ° to 10 ° including 0 ° with respect to the tire width direction is that the relationship between the edge inclination angle (lateral groove inclination angle) and the edge pressure (average value). As shown in FIG. 3, when the inclination angle of the edge exceeds 10 °, the edge pressure is suddenly reduced, and a sufficient wiper effect by the edge is not exhibited.

Moreover, the reason why the density L in the ground plane of the width direction edge 4e is 2.89 × 10 ⁻⁴ or more and 6.01 × 10 ⁻⁴ or less is that the density L in the ground plane of the width direction edge 4e is 2.89 × 10. ^If it is less than ⁻⁴ , as shown in FIG. 4 as a comparison, the number of edges decreases in the circumferential direction, so that water film removal is insufficient and the expected WETμ cannot be obtained. On the other hand, when the in-plane density L at the edge in the width direction exceeds 6.01 × 10 ⁻⁴ , the block rigidity is reduced as the size of the block 4 is reduced. This is because the edge pressure is insufficient, and as shown in FIG. 5 for comparison, water film removal is insufficient and the expected WETμ cannot be obtained.

  Furthermore, the reason why the aspect ratio of the block 4 having the width direction edge 4e is 0.4 to 3.5 is that the relationship between the aspect ratio obtained by FEM analysis and the edge pressure is as shown in FIG. This is because the edge pressure decreases when the aspect ratio is outside the range of 0.4 to 3.5. In order to exhibit the wiper effect effectively, the edge pressure needs to be 99 or more when the maximum value of the edge pressure is 100.

Note that, in the above embodiment, the width direction edge 4e are provided to match the entire width of the block 4, the width direction edge 4e has a width direction of the respective blocks on both sides from the width direction center of the block 4 length W ₄ Preferably, it is provided in an area of 25% or more. The reason why the width direction edge 4e is provided in the center region in the width direction of the block 4 in this way is that when the braking force is input, the end portion in the width direction of the input side bulges outward in the width direction and This is because the edge pressure tends to concentrate on the region.

  Moreover, in the said embodiment, although the block 4 is formed in the rectangle, it is preferable to make it a polygon more than a pentagon, and it is preferable to make it an octagon so that a part of tread part may be expanded and shown in FIG. . According to this, since the blocks 4 can be densely arranged while securing the groove volume of the entire tread portion, it is possible to enhance the effect of the dense arrangement of the blocks 4 described later. In addition, by making the tread shape of the block 4 octagonal in this way, the corners of the block 4 can be obtused to ensure rigidity, and the tire circumferential direction, the tire width direction, and the directions that incline in both directions. In other words, the edges that function effectively during traction, braking, and cornering can be efficiently arranged, and the wet performance can be improved as a whole.

Furthermore, in this invention, it is preferable that the block number density D calculated by the following formula (2) is in the range of 0.003 to 0.04 (pieces / mm ² ).
D = a / {PL × W × (1-N / 100)} (2)
However, W (mm) is the distance from one end to the other end in the tire width direction of the area where the block is arranged (block arrangement area), and PL (mm) is the reference pitch length (tire of the block arrangement area) (Distance between the lateral grooves 3 and 3 adjacent in the circumferential direction), a (piece) is the number of blocks 4 present in the reference zone Z partitioned by W and PL, and N (%) is the reference Negative rate in zone Z. The block number density D represents the number of blocks per unit area of the actual ground contact area (area excluding the groove) of the tread portion 1 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 of blocks a in the reference zone Z, if the block exists inside and outside the reference zone Z and cannot be counted as one, the reference to the surface area of the block across the reference zone Z It is counted using the ratio of the remaining area of the same block remaining in the 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.

  The negative rate N in the block arrangement region is preferably 5% to 50%. When the negative rate N in the block arrangement area is less than 5%, the groove volume becomes too small and the drainage becomes insufficient, and the size of the block 4 becomes too large and the effect of the block dense arrangement becomes small. It is. On the other hand, if it exceeds 50%, the total area of the block tread becomes too small, and the steering stability may be lowered.

Thus, by setting the block number density D within the range of 0.003 to 0.04 (pieces / mm ² ), the total edge length of the block increases, and the edge length is gained by forming sipes in the block. Compared to the case, a high edge effect can be obtained while ensuring the block rigidity. Further, the block rigidity is increased by the support of the blocks, and it is possible to ensure steering stability and wear resistance while increasing the total edge length.

<Test example>
In order to confirm the effect of the present invention, the pneumatic tire (the tires of Examples 1 to 7) included in the scope of the present invention and the pneumatic tire (Comparative Examples 1 to 3) as a comparison outside the scope of the present invention. Tires and a pneumatic tire (reference tire) having a width direction edge density of 2.05 × 10 ⁻⁴ (1 / mm ² ) as a reference for evaluation, WETμ was measured for each, and the reference tire was Each tire was evaluated with an index of 100.

  The tires of Examples 1 to 7, the tires of Comparative Examples 1 to 3 and the reference tire are all tire sizes of 195 / 65R15, intersect the longitudinal grooves and longitudinal grooves extending in the tire circumferential direction at the tread portion, and in the tire width direction. The blocks are partitioned by the extending lateral grooves. In the tires of Examples 1 and 2, the tread shape of the block is an octagon as shown in FIG. 7, and the sizes of the blocks are different from each other. In the tires of Examples 3 to 6, the shapes of the treads of the blocks are all rectangular, and the aspect ratios of the blocks are different from each other. In the tire of Example 7, the tread shape of the block is rectangular. In the tires of Comparative Examples 1 to 3, the shape of the tread surface of the block is rectangular, and the sizes of the blocks are different from each other. In the reference tire, the tread shape of the block is an octagon. Table 1 shows other specifications of each tire.

  The WETμ was evaluated from a speed of 64 km / h on an asphalt surface with a depth of 0.6 mm with each test tire assembled on a rim of size 6JJ and mounted on a vehicle (panel truck) with an internal pressure of 210 kPa (relative pressure). The friction coefficient until full lock was measured, and the peak value (average value of 3 times) was indexed. The evaluation results are shown in Table 2 and FIG. 8, and the evaluation in the table is represented by an index for the tires of Examples 1 to 7 and Comparative Examples 1 to 3, where the result of the reference tire is 100, and the numerical value is A larger value indicates better WETμ.

As is apparent from the evaluation results shown in Table 2 and FIG. 8, by setting the in-plane density L of the edge in the width direction within the range of 2.89 × 10 ⁻⁴ ≦ L ≦ 6.01 × 10 ^−4. The result that WETμ becomes high was obtained.

  Thus, according to the present invention, it is possible to provide a pneumatic tire that prevents water film from entering the block tread and exhibits good wet performance over a long period of time.

1 tread part 2 vertical groove 3 horizontal groove 4 block 4e width direction edge 5 block row

Claims (3)

In the pneumatic tire provided with a block pattern in which a plurality of blocks are defined by a plurality of vertical grooves extending along the tire circumferential direction and a plurality of horizontal grooves intersecting the vertical grooves in the tread portion,
At least a part of the blocks is provided with a width direction edge within a range of −10 ° to 10 ° including an inclination angle of 0 ° with respect to the tire width direction,
The in-ground surface density L of the width direction edge calculated from the following formula (1) is in the range of 2.89 × 10 ⁻⁴ ≦ L ≦ 6.01 × 10 ⁻⁴ ,
The block aspect ratio, which is the ratio of the length in the width direction of the block to the circumferential length of the block having the width direction edge, is in the range of 0.4 to 3.5 ,
The distance from one end to the other end in the tire width direction of the area where the block is arranged is W (mm), the reference pitch length in the area where the block is arranged is PL (mm), and the W and the The number of blocks calculated by the following formula (2), where a (number) is the number of blocks existing in the reference area defined by PL and N (%) is the negative rate in the reference area The density D is in the range of 0.003 to 0.04 (pieces / mm ² ),
The pneumatic tire according to claim 1, wherein the block does not have sipes .
L = (Et / S) × (1 / E) (1)
D = a / {PL × W × (1-N / 100)} (2)
However, L is the density in the ground plane at the edge in the width direction (1 / mm ² ), Et is the sum of the lengths in the width direction edge in the ground plane (mm), and S is the ground area in the tread (mm) ² ), and E is the sum (mm) of edge lengths in the width direction per pitch.   2. The pneumatic tire according to claim 1, wherein the width direction edge is formed in a region of 25% or more of the width direction length of the block on both sides of the width direction center position from the width direction center position of the block. .   The pneumatic tire according to claim 1 or 2, wherein the block has an octagonal shape on a tread surface.

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