JP2006298060A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate large cornering power and improve braking performance. <P>SOLUTION: Four circumferential grooves 2, 3 continuously extending to the circumferential direction are provided on a tread surface 1, and the number of pitches over whole circumference of the shoulder block rows 12 which are partitioned further outside from respective shoulder circumferential grooves 3 positioned at the most outside in the width direction is made to be not more than 80. The number of sipes 13, 14 provided on the land row partitioned at the tread surface part 1 is made to be 1 to 5 per one pitch of the shoulder block rows 12. The length of sipe per one pitch length of the shoulder block row 12 is made to be longer than that of the shoulder block row 12 at the center rib 4 and the second block row 8, and the ratio of the curvature radius (CR<SB>1</SB>) of the center rib 4 at the area sandwiching tire equatorial plane EP relative to the curvature radius (CR<SB>2</SB>) of the same at the area straddling the shoulder block row 12 from the second block row 8 is made to be less than 1 in the cross section in the width direction of the tire. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire, in particular, a radial tire for a light vehicle, which is used as a summer tire and generates a large cornering power and still has an improved braking performance.

Conventionally, in order to improve the braking performance of a tire, it has been common to increase the circumferential rigidity of the tread land portion in order to increase the maximum frictional force of the tread surface against the road surface.
However, in recent vehicles with an ABS device, in order to improve the braking performance, rather than increasing the maximum frictional force of the tread surface, the road surface frictional force in the sliding region of the tread surface within the ground surface is increased. Was found to be more effective.

  Therefore, in this type of tire used as a summer tire, in order to ensure a large cornering power and to improve the braking performance, the tread tread surface is required rather than increasing the circumferential rigidity of the tread land portion unnecessarily. It is effective to increase the frictional force in the sliding area under moderate contact with the road surface. To this end, the number of pitches is determined in relation to the ground contact form of the tread surface. It is necessary to appropriately select the distribution of sipe and the number and length of sipe without impairing the basic performance of the tire.

By the way, as a conventional tire in which the arrangement density of sipes is devised for the purpose of improving the running performance of the tire on snow and ice, there are, for example, those described below.
Japanese Patent Application Laid-Open No. 63-275406 discloses a block pattern all-season tire whose main purpose is to improve performance on snow without impairing steering stability. The kerf density provided in the block is set to be lower as the block arranged in the shoulder portion is higher, and as the block arranged in the center portion is higher, JP-A-10-181314 discloses a tread band. As a vehicle tire recommended as a winter tire with uniform wear and improved grip over the axial length, the tread band softening action in the shoulder range is weaker than the center range. Has been.
JP-A-63-275406 JP-A-10-181314

  However, the conventional tires disclosed in these publications originally set a large negative rate of the tread surface and a relatively large sipe arrangement density on the premise that the tires run on ice and snow. Even if it is possible to use the tread pattern of those tires for summer tires because the rigidity in the circumferential direction and the width direction of the tread land portion is both too low compared to summer tires. As a result, there was no way to achieve great cornering power and to ensure excellent braking performance.

  According to the present invention, in the case of load rolling of a general tire, the contact pressure distribution of the tread tread surface is higher than the center region in the shoulder region of the tread surface due to the so-called buckling tendency of the tread surface portion. The uneven distribution prevents the tread tread from touching properly and contributes to the deterioration of braking performance. This is particularly important in small-sized tires for small vehicles with low belt tension. The purpose of this is to provide a pneumatic radial tire that is capable of generating large cornering power and ensuring sufficient steering stability while advantageously improving braking performance. It is in.

In the pneumatic radial tire according to the present invention, two or more circumferential grooves continuously extending in the tread circumferential direction are provided on the tread tread surface portion, and further outward from the respective shoulder circumferential grooves positioned on the outermost side in the tread width direction. The number of pitches of the shoulder land sections to be divided is 80 or less over the entire circumference of the tread tread section, and the number of sipes provided in each land section section to be divided into the tread tread sections is set as one of the shoulder land sections. 1 to 5 per pitch, and the sipe length per pitch length of the shoulder land portion row is sandwiched between the shoulder land portion rows, for example, two or more center side land portion rows, for example, those Large, medium and small pitch lengths of the land section row are longer than those of the shoulder land section under the condition corresponding to that of the shoulder land section row. air pressure 10% of the air pressure in the widthwise cross section of the filled tires, the radius of curvature of the tread surface in areas which sandwich the tire equatorial plane (CR _1), extends over the area from the land row on the center side in the shoulder land row The ratio to the same radius of curvature (CR ₂ ) is less than 1, more preferably 0.4 to 0.7.

Here, the specified rim and the specified air pressure refer to the rim specified in the following standards and the air pressure specified corresponding to the maximum load capacity, respectively. The maximum load capacity is the following standards, The maximum mass allowed to be applied to the tire.
In addition, instead of air, the tire may be filled with an inert gas or the like with air pressure and equal pressure.

  The standard is determined by an industrial standard effective in the region where the tire is produced or used. For example, in the United States, “THE TIRE AND RIM ASSOCIATION INC. YEAR BOOK”, in Europe, “The It is “STANDARDS MANUAL” of European Tire and Rim Technical Organization, and “JATMA YEAR BOOK” of Japan Automobile Tire Association in Japan.

  Here, in specifying the radius of curvature of the tread surface, the filling state of “10% of the prescribed air pressure” is used as a reference as close as possible to the shape of the product tire in the vulcanization mold. The purpose is to specify the radius of curvature based on the shape.

  The tire configured as described above is sufficient to be used as a summer tire because the number of sipes provided in each land section row is a small number of 1 to 5 per pitch per shoulder land section row. In this case, the extension length of the sipe formed in the land portion row on the center side existing in the tread center region, where the contact pressure is relatively low, can be obtained. The land-side rigidity of the center-side land section row is made smaller than that of the shoulder-land section row so that the contact pressure at the center-side land section row is reduced, but the actual ground contact area is sufficiently large. Realizing excellent braking performance can be ensured by making it possible to ensure.

And this means that the radius of curvature (CR ₁ ) of the tread tread near the tire equator surface is made smaller than the radius of curvature (CR ₂ ) extending to the shoulder land section row, resulting in the occurrence of buckling. It can be made more effective by suppressing a decrease in the contact pressure in the sub-row.
The ratio of the radii of curvature is
_{0.4 <CR 1 / CR 2 <} 0.7
More preferably.

  These are particularly effective when the tire is of a small size with a small belt tension for a light vehicle.

  On the other hand, the land portion of the shoulder land portion row can be grounded in a large area under high rigidity due to a large ground pressure, so that high cornering power can be generated when the vehicle is steered, Thereby, excellent steering stability can be realized.

As is apparent from the above description, according to the present invention, in particular, a large cornering power is generated by the high-rigid shoulder land row, and the braking performance under the action of the land portion row on the center side. Can be effectively improved.

Embodiments of the present invention will be described below based on the drawings.
FIG. 1 is a developed view of a tread pattern showing an embodiment of the present invention. In addition, since the internal complementary layer structure of a tire is the same as that of a general radial tire, illustration is abbreviate | omitted.

  Here, the tread tread surface portion is provided symmetrically with the tire equatorial plane EP and is provided with two pairs of circumferential main grooves 2 and 3 that continuously extend linearly in the tread circumferential direction. A center rib 4 as a center land portion row is defined between a pair of center main grooves 2 and 2 that are located close to each other, and a narrow groove 5 that extends linearly at the center of the center rib 4 so as to overlap the tire equatorial plane EP. Further, a second block row 8 as a second land portion row is provided between each of the circumferential main grooves 2 and 3 and each block 7 is divided by an inclined groove 6 extending downward in the figure. In addition, each circumferential main groove 3 positioned on the outermost side in the tread width direction, that is, a shoulder land portion row partitioned further outside than the shoulder circumferential groove, is divided into a shoulder circumferential groove 3 and a linearly extending bar. The shoulder block row 12 of each block 11 obtained by dividing by lateral grooves 10 provided by extending substantially "to" shape or reverse "to" shape between the Torres circumferential groove 9.

  Further, here, each block 11 of the shoulder block row 12 is arranged under, for example, three pitch variations in which the pitch length is changed to three types of large, medium and small, and the shoulder block row 12 The number of pitches over the entire circumference of the tread surface 1 is 80 or less, for example 66. In the figure, the number of pitches of each of the center rib 4 and the second block row 8 is 33 under the three-pitch variation.

  Further, 1 to 5 sipes per pitch P of the shoulder block row 12 are formed in each of the center rib 4, the second block row 8 and the shoulder block row 12. As shown in the drawing, one center rib 4 has two sipes 13 per pitch, and each of the two second block rows 8 has a total of six sipes 13 per pitch. When the number of sipes is converted per one pitch P of the shoulder block row 12, the center rib 4 and the second block row 8 both equal the two pitches of the shoulder block row 12. The pitch is 8/2, that is, four.

In addition, the sipe length per sipe length of the shoulder block row 12 of the sipe 13, 14 formed in this way in each land portion row, in other words, under the three pitch variation of the shoulder block row 12 Sipes in large, medium and small length pitches in the center rib 4 and the second block row 8 respectively corresponding to the large, medium and small pitch lengths P ₃ , P ₂ and P ₁ in FIG. Is made longer than the sipe length in the shoulder block row 12.

Further, in this tire, as shown in the cross-sectional view in the width direction of the tread portion in FIG. 2, the tread surface in the region sandwiching the tire equatorial plane EP under the tire posture that is assembled to the specified rim and filled with the specified air pressure. radius of curvature, in the figure, the center rib 4, at least the curvature radius CR ₁ of the central partial surface, the radius of curvature of the tread surface at straddles area from the land row shoulder land row of the center side, which in FIG. where indicated, the ratios from the second block row 8 for the curvature radius CR ₂ portions of the surface over the shoulder block rows 12 as less than 1, even if buckling occurs in the tread portion hitting the load rolling of the tire, the center rib 4 and Lifting of the surface of both second block rows 8 from the road surface is effectively suppressed.

Here, in many cases, the respective arc portions specified by the respective curvature radii CR ₁ and CR ₂ are smoothly continued by one or more types of relaxation curves and other curves, The same applies to the buttress side portion of the shoulder block row 12.

  1, in addition to the above, the center rib 4 is provided with a notch groove 15 that rises to the right and ends in the center main groove 2 and ends in the rib, and the second block row 8 Each block 7 is provided with one notch groove 16 that is opened to the shoulder circumferential groove 3 and ends in the block and ends in the block, and one end of each block 11 of the shoulder block row 12 has a buttress. Each short lateral groove 17 is provided in the circumferential groove 9 and the other end ends in the block.

  It is a tire for a light vehicle having a size of 165/55 R14, and the conventional tire having the basic tread pattern shown in FIG. 3 and the center rib and the blocks of the second block row as shown in FIG. As shown in FIG. 4, each of the blocks in the second block row has two bowl-shaped sipes, and each block in the shoulder block row has a straight line in the circumferential direction. When the specifications shown in Table 1 were given to each of the comparative tires each having one sipe extending in a shape, the braking performance and the cornering power of each tire were determined. The result shown in 2 was obtained.

Here, the braking performance is obtained by measuring the distance from the initial speed of 100 km / h to the stoppage of braking under the action of the ABS device after running an actual vehicle on a wet road surface. The power was measured by an indoor drum test and indexed.
The larger the index value, the better the result.

  According to Table 2, it is clear that the example tire can generate cornering power equivalent to that of the conventional tire, and can exhibit wet braking performance superior to that of the comparative tire, regardless of the sipe.

  Although the case where the tire according to the present invention is used for a light vehicle has been described above, the present invention can also be applied to a tire for a normal passenger car.

It is an expanded view of the tread pattern which shows embodiment of this invention. FIG. 2 is a cross-sectional view in the width direction showing a tread portion of the tire shown in FIG. 1. It is a development view of a tread pattern of a conventional tire. It is an expanded view of the tread pattern of a comparative tire.

Explanation of symbols

1 tread portion 2 center main groove 3 shoulder main groove 4 center rib 5 narrow grooves 6 inclined grooves 7,11 block 8 second block row 9 buttress circumferential groove 10 lateral groove 12 shoulder block row 13, 14 sipe _{P 1,} P 2, _{P 3} Pitch length EP Tire equatorial plane

Claims (2)

The tread of the shoulder land portion row provided with two or more circumferential grooves continuously extending in the tread circumferential direction on the tread surface portion and partitioned further outward than the respective shoulder circumferential grooves positioned on the outermost side in the tread width direction. The number of pitches over the entire circumference of the tread surface is set to 80 or less, and the number of sipes provided in the land portion row partitioned by the tread tread portion is set to 1 to 5 per pitch in the shoulder land portion row. The sipe length per pitch length of the partial row is longer than that of the shoulder land portion row at the center side land portion row sandwiched by the shoulder land portion row, and is attached to the prescribed rim to 10% of the prescribed air pressure. In the cross section in the width direction of the tire filled with the air pressure of the tire, the radius of curvature (CR ₁ ) of the tread surface in the region sandwiching the tire equatorial plane, in the region extending from the land side row on the center side to the shoulder land portion row Similar radius of curvature ( A pneumatic radial tire according to the ratio R ₂₎ as less than 1. The pneumatic radial tire according to claim 1, wherein the size of the pneumatic radial tire is for a light vehicle.

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