JP2006232012A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of suppressing the generation of uneven wear while keeping original performance such as drainability, driveability, and riding comfort. <P>SOLUTION: Multiple lines of land parts 21 to 24 are divided by vertical grooves 11 to 13 provided on a tread portion 1, and the width W3 of the land part 23 on a shoulder side is made to be smaller than the width W2 of the land part 22 on a tread center side. A plurality of lateral grooves 4 opening to at least the vertical groove 12 on the shoulder side while tilting in a tire width direction is provided on the land part 22. An acute-angled block 22a is divided at a part on the shoulder side of the land part 22 by the lateral grooves 4. In the pneumatic tire, curved portions are respectively formed between a groove bottom and both groove walls of the vertical groove 12. A radius R3 of curvature of the curved portion on the shoulder side is made to be larger than a radius R2 of curvature of the curved portion on the tread center side, and an end portion of the curved portion on the shoulder side is disposed on the shoulder side rather than a groove width direction center position. A tilting angle to a tread normal direction of the groove wall on the acute-angled block 22a side of the lateral groove 4 is made to be not less than 5° and less than 45°. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pneumatic tire in which a plurality of vertical grooves extending in the tire circumferential direction are provided in a tread portion and a plurality of rows of land portions are partitioned by the vertical grooves, and more specifically, uneven wear while maintaining original performance. The present invention relates to a pneumatic tire that can suppress the occurrence of tire.

  In a pneumatic tire, a plurality of vertical grooves extending in the tire circumferential direction are provided in a tread portion, a plurality of rows of land portions are defined by the vertical grooves, and a land on a shoulder side of a pair of land portions adjacent to each other in the tire width direction. The width of the portion is made smaller than the width of the land portion on the tread center side, and a plurality of horizontal grooves are provided in the land portion on the tread center side and open to at least the vertical grooves on the shoulder side while being inclined with respect to the tire width direction. There is one in which an acute angle block is defined at the shoulder side portion of the land portion on the tread center side by a horizontal groove.

  In a pneumatic tire having such a tread pattern, when running in a harsh environment, a load is applied to the shoulder side edge of the land portion on the tread center side, and uneven wear tends to occur on the land portion on the tread center side. . This phenomenon remarkably appears in a tread pattern in which the lateral grooves are narrow and the lateral groove pitch is small and emphasizes low noise.

  As a countermeasure against the above-mentioned uneven wear, it is effective to avoid the concentration of the ground energy on the land portion on the tread center side. More specifically, it is effective to reduce the difference in rigidity between the land portion on the tread center side and the land portion on the shoulder side to avoid stress concentration at the shoulder side edge of the land portion on the tread center side.

  As a method of reducing the rigidity difference between the land portion on the tread center side and the land portion on the shoulder side, for example, widening the width of the land portion on the shoulder side, thinning out the lateral grooves that divide the land portion on the shoulder side, or It has been proposed that the inclination angle of the groove wall on the shoulder side of the vertical groove separating the pair of land portions with respect to the normal direction of the tread is larger than the inclination angle of the groove wall on the tread center side (for example, Patent Document 1 and Patent Document 2).

  Further, as a technique for avoiding stress concentration at the shoulder side edge of the land portion on the tread center side, for example, it is proposed to chamfer the shoulder side edge of the land portion on the tread center side (for example, Patent Documents). 3).

However, when the width of the shoulder-side land portion is widened or the lateral groove that divides the shoulder-side land portion is thinned out, noise performance and riding comfort performance are deteriorated. Also, if the inclination angle of the groove wall on the shoulder side of the vertical groove that separates a pair of adjacent land parts is increased, or if the shoulder side edge of the land part on the tread center side is chamfered, the ground contact area will be reduced as a result. As a result, the braking performance on the dry road surface and the steering stability are adversely affected. Therefore, it is difficult for the conventional measures described above to suppress the occurrence of uneven wear while maintaining the original tire performance.
Japanese Patent Laid-Open No. 9-132009 JP-A-11-310010 JP 2000-225811 A

  An object of the present invention is to provide a pneumatic tire capable of suppressing the occurrence of uneven wear while maintaining the original performance with respect to drainage performance, steering stability, and riding comfort performance.

  In order to achieve the above object, the pneumatic tire of the present invention is provided with a plurality of longitudinal grooves extending in the tire circumferential direction in the tread portion, and a plurality of rows of land portions are defined by these longitudinal grooves, and are adjacent in the tire width direction. The width of the land portion on the shoulder side of the pair of land portions is smaller than the width of the land portion on the tread center side, and at least the vertical groove on the shoulder side is inclined with respect to the tire width direction in the land portion on the tread center side. In a pneumatic tire in which a plurality of horizontal grooves are formed in the tire, and an acute angle block is defined on the shoulder side portion of the land portion on the tread center side by these horizontal grooves, the groove bottom and both sides of the vertical groove dividing the pair of land portions are provided. A curved part is formed at the boundary with the groove wall, the curvature radius of the curved part on the shoulder side is made larger than that of the curved part on the tread center side, and the end of the curved part on the shoulder side is grooved. With placing the shoulder side from direction central position, and characterized in that the inclination angle with respect to the tread normal line direction of the groove wall of the acute angle block side of the lateral grooves below 5 ° or 45 °.

  The present inventor has provided a plurality of vertical grooves extending in the tire circumferential direction in the tread portion, and a plurality of rows of land portions are defined by the vertical grooves, and a shoulder-side land among a pair of land portions adjacent in the tire width direction. The width of the portion is made smaller than the width of the land portion on the tread center side, and a plurality of horizontal grooves are provided in the land portion on the tread center side and open to at least the vertical grooves on the shoulder side while being inclined with respect to the tire width direction. In order to suppress the occurrence of uneven wear while maintaining the original performance of a pneumatic tire with a sharp angle block at the shoulder side part of the land portion on the tread center side by a lateral groove, if the following two conditions are satisfied at the same time: I found out that it was good.

  The first condition is that a curved portion is formed at the boundary between the groove bottom and both groove walls separating the pair of land portions, and the curvature radius of the curved portion on the shoulder side is set to the curvature radius of the curved portion on the tread center side. The end of the curved portion on the shoulder side is arranged closer to the shoulder side than the center position in the groove width direction. If the first condition is satisfied, the difference in rigidity between the land portion on the tread center side and the land portion on the shoulder side is reduced without impairing the original performance in terms of drainage performance, steering stability, and riding comfort performance. It can contribute to suppression.

  The second condition is that the inclination angle of the groove wall on the acute angle block side of the lateral groove with respect to the normal direction of the tread is 5 ° or more and less than 45 °. If the second condition is satisfied, the stress in the land portion on the tread center side is reinforced by reinforcing the portion of the land portion on the tread center side with low rigidity without impairing the original performance in terms of drainage performance, steering stability, and riding comfort performance. Concentration can be avoided and it can contribute to suppression of uneven wear.

  That is, the first condition is a structural change that does not impair the original performance with respect to the land portion on the shoulder side, and the second condition does not impair the original performance with respect to the land portion on the tread center side. Although it is a structural change of the extent, by satisfying these two conditions at the same time, it is possible to effectively suppress the occurrence of uneven wear without impairing the original performance.

  In the present invention, as a more specific configuration, it is preferable that the number of longitudinal grooves provided in the tread portion is at least five. Moreover, it is preferable that the horizontal groove provided in the land portion on the tread center side is not in communication with the vertical groove on the tread center side. Furthermore, it is preferable to gradually increase the inclination angle of the groove wall on the acute block side of the lateral groove with respect to the tread normal direction from the tread center side portion of the lateral groove toward the shoulder side portion. Moreover, it is preferable that the tread pattern including the vertical groove and the horizontal groove has directivity.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows a tread pattern of a pneumatic tire according to an embodiment of the present invention, and FIG. 2 shows an enlarged main portion thereof. This tread pattern is a directional tread pattern which is formed substantially symmetrically on both sides of the crown center CL and whose rotation direction is designated.

  As shown in FIG. 1, the tread portion 1 includes two longitudinal grooves 11 extending in the tire circumferential direction in the tread center region, two longitudinal grooves 12 extending in the tire circumferential direction in the left and right shoulder regions, Two longitudinal grooves 13 that are narrower than the grooves 12 and extend in the tire circumferential direction outside the longitudinal grooves 12 in the tire width direction are formed. By these vertical grooves 11 to 13, four types of land portions 21, 22, 23, and 24 are sequentially partitioned from the tread center side to the shoulder side in the tread portion 1. These land portions 21 to 24 may be either ribs continuously connected in the tire circumferential direction or a block row including a plurality of blocks divided in the tire circumferential direction, but here, the land portion on the most shoulder side A tread pattern in which 24 is a block row and the other land portions 21 to 23 are ribs is formed. That is, a plurality of lug grooves 3 extending in the tire width direction are formed in the most shoulder side land portion 24 at a predetermined interval in the tire circumferential direction. Further, the land portions 21 to 24 may be appropriately provided with sipes and shallow grooves for improving noise performance.

  When the contact width of the tread portion 1 is TCW, the vertical groove 12 in the shoulder region is in the range of (TCW / 2) × 0.2 to (TCW / 2) × 0.9 from the tread center position to the outer side in the tire width direction. Has been placed. However, the ground contact width is when the air pressure corresponding to the maximum load capacity is filled and the load of 80% of the maximum load capacity is applied in the air pressure-load capacity correspondence table specified in the JATMA Yearbook (2004 edition). Is the ground contact width.

  As shown in FIG. 2, the width W3 of the land portion 23 on the shoulder side is the width of the land portion 22 on the tread center side with respect to a pair of land portions 22 and 23 adjacent to each other in the tire width direction across the longitudinal groove 12 in the shoulder region. It is smaller than W2. The land portion 22 on the tread center side is formed with a plurality of lateral grooves 4 that are inclined with respect to the tire width direction and open to the longitudinal grooves 12 on the shoulder side. The lateral groove 4 is not in communication with the longitudinal groove 11 on the tread center side. A plurality of acute angle blocks 22a are defined by the lateral grooves 4 at the shoulder side portion of the land portion 22 on the tread center side.

  In a pneumatic tire having such a tread pattern, when running in a harsh environment, uneven wear tends to occur in the land portion 22 on the tread center side due to the tread pattern. That is, since the width W3 of the land portion 23 on the shoulder side is smaller than the width W2 of the land portion 22 on the tread center side, the load during cornering is concentrated on the land portion 22 on the tread center side, and the acute angle block 22a is Since it is easy to displace, stress concentration is likely to occur in other portions of the land portion 22 on the tread center side. Therefore, in order to reduce the difference in rigidity between the land portion 22 on the red center side and the land portion 23 on the shoulder side, and to avoid stress concentration on the shoulder side edge of the land portion 22 on the tread center side, the above pneumatic tire is used. The following structure is adopted.

  3 is a cross-sectional view taken along the line A1-A2 of FIG. As shown in FIG. 3, curved portions are respectively formed at the boundary between the groove bottom of the longitudinal groove 12 that separates the pair of land portions 22 and 23 and both groove walls. The curvature radius R3 of the curved portion on the shoulder side is set larger than the curvature radius R2 of the curved portion on the tread center side. Here, the curvature radii R2 and R3 are curvature radii measured in the cross section of the longitudinal groove. Further, the end portion of the shoulder side curved portion (the portion defined by the curvature radius R3) is disposed on the shoulder side from the center position in the groove width direction (center position on the tread surface). By making the curvature radius R3 of the curved portion on the shoulder side larger than the curvature radius R2 of the curved portion on the tread center side, the land on the tread center side is not impaired in terms of drainage performance, steering stability, and ride performance. The difference in rigidity between the portion 22 and the land portion 23 on the shoulder side can be reduced, and the occurrence of uneven wear can be suppressed. However, if the end portion of the curved portion on the shoulder side is closer to the center side than the center position in the groove width direction, the drainage performance is impaired.

  4 is a cross-sectional view taken along the line B1-B2 of FIG. 2, and FIG. 5 is a perspective view showing a land portion on the tread center side provided with a lateral groove. As shown in FIGS. 4 and 5, the inclination angle θ of the groove wall on the acute angle block 22a side of the horizontal groove 4 with respect to the normal direction of the tread is set to 5 ° or more and less than 45 °. By setting the inclination angle θ of the groove wall on the acute block 22a side of the lateral groove 4 within the above range, the rigidity of the land portion 22 on the tread center side without impairing the original performance in terms of drainage performance, steering stability, and riding comfort performance. Therefore, it is possible to reinforce the low-part, avoid stress concentration at the edge of the land portion 22 on the tread center side, and suppress the occurrence of uneven wear. Here, if the inclination angle θ is less than 5 °, the effect of suppressing uneven wear is insufficient, and conversely if it is 45 ° or more, the riding comfort performance deteriorates. In particular, the inclination angle θ is preferably 7 ° or more. Moreover, it is preferable that the inclination angle θ gradually increases from the tread center side portion of the lateral groove 4 toward the shoulder side portion. Thus, by increasing the inclination angle θ toward the shoulder, the effect of suppressing uneven wear can be enhanced.

  The tire size is 235 / 50R17 96W, the tread portion is provided with six longitudinal grooves extending in the tire circumferential direction, the vertical grooves define seven rows of land portions, and the shoulder region is adjacent to the tire width direction. The width of the land portion on the shoulder side is smaller than the width of the land portion on the tread center side, and the land portion on the tread center side is inclined with respect to the tire width direction and opens into the vertical groove on the shoulder side. In a pneumatic tire in which a plurality of lateral grooves are provided, and an acute angle block is defined at a shoulder side portion of the land portion on the tread center side by these lateral grooves, the tread center side curved portion provided in the longitudinal groove separating the pair of land portions. The curvature radius R2 of the shoulder and the curvature radius R3 of the curved portion on the shoulder side and the inclination angle θ of the groove wall on the acute angle block side of the lateral groove with respect to the normal direction of the tread are varied. Conventional tires, Comparative Examples 1 to 4 and Examples 1 to 2 were manufactured.

  About these test tires, rib edge uneven wear, steering stability, riding comfort performance, and braking performance were evaluated by the following test methods, and the results are also shown in Table 1.

Rib edge uneven wear:
The test tire was assembled to a JATMA standard rim, mounted on a large sedan with a displacement of 3000 cc, the air pressure was set to 220 kPa, limit running was performed on the test course, and the wear state after running was visually evaluated. The evaluation results are divided into three stages. In a relative comparison, the occurrence of uneven rib edge wear is indicated by “XX”, and the occurrence of rib edge uneven wear is indicated by “X”. A case where almost no occurrence was observed was indicated by “◯”.

Steering stability:
The test tire was assembled on a JATMA standard rim, mounted on a large sedan with a displacement of 3000 cc, and the air pressure was 220 kPa. The evaluation results are shown as relative scores with the conventional example being 7 points. The larger this score, the better the steering stability.

Ride comfort performance:
The test tires were assembled on a JATMA standard rim, mounted on a large sedan with a displacement of 3000 cc, and the air pressure was 220 kPa. The evaluation results are shown as relative ratings with 7 points for the conventional example. The larger this score, the better the riding comfort performance.

Braking performance:
The test tire was mounted on a JATMA standard rim, mounted on a large sedan with a displacement of 3000 cc, air pressure was 220 kPa, ABS braking was performed on a wet road surface at a speed of 100 km / h, and the braking distance was measured. The evaluation results are shown as an index with the conventional example being 100, using the reciprocal of the measured value. A larger index value means better braking performance.

  As shown in Table 1, in the tire of the conventional example, the rib edge uneven wear was remarkable in the land portion on the tread center side. In the tires of Comparative Examples 1 and 2, although a slight improvement effect was observed for the rib edge uneven wear, it was not always sufficient. In the tires of Examples 1 and 2, by taking the measures of Comparative Examples 1 and 2 at the same time, the rib edge uneven wear suppression effect could be sufficiently obtained without impairing the handling stability, riding comfort performance, and braking performance. . In the tire of Comparative Example 3, the riding performance was deteriorated because the inclination angle θ of the lateral groove provided in the land portion on the tread center side was 45 °. In the tire of Comparative Example 4, the curvature radius R3 of the curved portion on the shoulder side of the longitudinal groove in the shoulder region was increased. As a result, the end of the curved portion reached the center position in the groove width direction, and the braking performance was adversely affected.

It is a top view which shows the tread pattern of the pneumatic tire which consists of embodiment of this invention. It is a top view which expands and shows the principal part of FIG. It is A1-A2 arrow sectional drawing of FIG. It is B1-B2 arrow sectional drawing of FIG. It is a perspective view which shows the land part by the side of the tread center provided with the horizontal groove.

Explanation of symbols

1 Tread part 3 Lug groove 4 Horizontal groove 11, 12, 13 Vertical groove 21, 22, 23, 24 Land part 22a Acute angle block CL Crown center TCW Grounding width

Claims (5)

A plurality of longitudinal grooves extending in the tire circumferential direction are provided in the tread portion, and a plurality of rows of land portions are partitioned by these longitudinal grooves, and the width of the land portion on the shoulder side of the pair of land portions adjacent in the tire width direction is treaded. A width of the land portion on the center side is smaller than the width of the land portion on the tread center side. In a pneumatic tire in which an acute angle block is defined on a shoulder side portion of a land portion on the center side, a curved portion is formed at the boundary between the groove bottom of the longitudinal groove that separates the pair of land portions and both groove walls, and the shoulder side The radius of curvature of the curved portion is larger than the radius of curvature of the curved portion on the tread center side, and the end of the curved portion on the shoulder side is arranged on the shoulder side from the center position in the groove width direction. Serial The acute angle block-side pneumatic tire the angle of inclination with respect to the tread normal line direction of the groove wall was less than 45 ° 5 ° or more lateral grooves. The pneumatic tire according to claim 1, wherein the number of longitudinal grooves provided in the tread portion is at least five. The pneumatic tire according to claim 1 or 2, wherein a lateral groove provided in a land portion on the tread center side is not communicated with a longitudinal groove on the tread center side. The air according to any one of claims 1 to 3, wherein an inclination angle of a groove wall of the horizontal groove on the acute angle block side with respect to a tread normal direction is gradually increased from a tread center side portion to a shoulder side portion of the horizontal groove. Enter tire. The pneumatic tire according to any one of claims 1 to 4, wherein a tread pattern including the vertical grooves and the horizontal grooves has directionality.

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