JPH06179305A - Pneumatic radial tire for winter season - Google Patents

Abstract

PURPOSE:To ensure high drivability and cornering performance on an ice or snow covered road, high drainage performance on a wet road and high maneuvering stability on a dry road. CONSTITUTION:A pneumatic radial tire 1 has a tread section 6 reinforced with a cord array of belts 5 on the crown 4 of a radial carcass 3 toroidally continuous over a pair of bead cores 2. This tread section 6 has a wide and deep bottomed center recess 7 along a tread circumference at the breadthwise center thereof, and substantially constituted so as to have two divided sections. These divided tread sections have a contour of square shoulder at least outside the tire 1. Furthermore, each divided tread section has a land block 12 formed out of at least one peripheral main groove 10 and a plurality of lateral grooves extended to intersect the groove 10. In this case, the land block 12 has a plurality of sipes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a winter pneumatic radial tire mainly having a flatness of 60% or less, which is mainly used for running on a snowy and snowy road surface. An object of the present invention is to provide a pneumatic radial tire for winter, which has good drivability and cornering property on a snowy and snowy road surface, and has high drainage property on a wet road surface and excellent steering stability on a dry road surface.

[0002]

2. Description of the Related Art As research and development of automobiles for higher speed and higher horsepower progress, the tendency toward flattening tires has become stronger. The flat tire has a smaller percentage of the tire cross-section height with respect to the tire width, that is, the flatness value is smaller than that of a normal tire. When the flatness is small, the tire has a low cross-sectional height, a wide tire width, and the wide tire width tends to widen the tread width. In such a tire, the rigidity of the tire sidewall is increased due to the reduced tire cross-section height, and the vertical deflection of the tire is reduced. As a result, the ground contact shape of the tire is a so-called wide shape that is wide in the axial direction of the tire and short in the circumferential direction. As is well known, such flat tires have excellent steering stability such as high-speed stability and grip on dry road surfaces as compared with ordinary tires, but especially when traveling on ice and snow road surfaces in winter, It is known that driving and braking performance (including climbing performance) are significantly reduced due to the short contact length. Such deterioration in performance can be said to be a drawback in the tire shape that cannot be compensated by the tread pattern and the tread rubber material.

In the flat tire for winter, the tread width is narrowed so as to be unfit for the flat tire in some cases in order to obtain the contact length from the above shape.

[0004]

However, when only the tread width is narrowed with respect to the wide tire width, the angle between the contour of the tread end portion and the contour of the sidewall upper portion (buttless portion) following the tread in the cross section of the tire is narrowed. It becomes remarkably large, that is, it becomes a remarkably large round shoulder, and the edge effect of the tread end portion is reduced during traveling on ice and snow, and the road holding when lateral force such as cornering acts is remarkably deteriorated.

When pneumatic tires having different flatness ratios are compared for the above narrow angles, as shown in Table 1, as the flatness ratio becomes smaller, the inclination angle of the tread shoulder portion with respect to the plane including the tread circumference becomes smaller. It is generally large. This means that a pneumatic tire having a lower flatness ratio has a smaller lateral edge effect due to the tread ground contact end, and in particular has a lower cornering performance on a snowy and snowy road surface.

[0006]

[Table 1]

On the other hand, conventional studless tires usually use a soft material for the tread rubber, so even if ice and snow performance can be expected to some extent, the performance on a dry road surface can be improved by increasing the vehicle speed and horsepower. There are many challenges left to address.

Therefore, an object of the present invention is to provide an air having good drivability and cornering, which are important for traveling on ice and snowy roads, and having high drainage on wet roads and good steering stability on dry roads. It is to provide a radial tire that contains.

[0009]

The present invention has a tread portion reinforced by a belt having an inextensible cord arrangement on the crown portion of a radial carcass extending in a toroidal shape across a pair of bead cores. The tread portion has a wide and deep center recess along the circumference of the tread at the center of the width to form a substantially two-piece configuration, and these tread portions have a square shoulder-shaped contour at least outside the tire. Each divided tread portion has a land block divided by at least one circumferential main groove and a plurality of lateral grooves extending across the groove, and the land block is provided with a plurality of sipes. It is a pneumatic radial tire for winter.

An example of the pneumatic radial tire of the present invention is shown in FIG. 1, in which 1 is a pneumatic radial tire, 2 is a bead core, 3 is a radial carcass, 4 is a crown portion, 5 is a belt, 6 is a tread portion, 7 is a tire. Is a central recess, 8 is a cap layer, 9 is an auxiliary layer, 10 is a circumferential main groove, 11 is a lateral groove, 1
2 is a land block and 13 is a sipe. The pneumatic radial tire 1 of the present invention has a tread portion 6 reinforced by a belt 5 in a cord arrangement on a crown portion 4 of a radial carcass 3 extending in a toroidal shape across a pair of bead cores 2. 6 is substantially divided into two by providing a wide and deep bottom central depression 7 along the circumference of the tread at the center of its width.

The radial carcass 3 is composed of a rubberized sheet in which fiber cords represented by nylon, polyester, rayon, aramid, etc. are arranged in a direction orthogonal to the tire equatorial plane. The number is 1 to 2, but the number may be increased to 3 if necessary.

The belt 5 is made of a non-stretchable cord typified by steel, aramid, etc. with respect to the equatorial plane of the tire in an amount of 15-3.
It has a structure in which at least two rubberized sheets arranged at an inclination angle of 0 ° are overlapped so that the cords intersect each other. Further, in order to reinforce both outer ends of the belt 5, a cap layer 8 may be provided at a position covering at least the outer ends of the belt 5, and an auxiliary layer 9 may be provided at a position corresponding to the central recess 7. . Cap layer 8 and auxiliary layer 9
Is made of a cord rubberized sheet in which the cords are arranged substantially parallel to the equatorial plane of the tire, and the cords are made of heat-shrinkable fibers typified by nylon for both the cap layer 8 and the auxiliary layer 9. The auxiliary layer 9 may be formed by spirally laminating a ribbon-shaped sheet in which about 3 to 15 cords are arranged and rubberized, and spirally wound along the circumference of the tread. The belt 5 of the invention tire shown in FIG. 1 is dented at a position corresponding to the central depression 7, and the inclination angle of the reinforcing cord of the belt with respect to the equatorial plane at this position is between the equatorial plane position of the belt and the belt side end. It is larger than the code at the center position of the distance.

The tread portion 6 is substantially divided into two parts having a wide and deep central depression 7 along the circumference of the tread at the center of the width thereof, and the width cross-sectional shape is a twin-hump shape. The treads of these divided tread portions have independent curvatures in the tread width direction, and have a considerably large curvature (small curvature radius) as compared with the curvature of the tread of a normal tire. The tread is designed so that the cross-sectional shape of the twin hump does not change significantly due to the load applied to the tire, and in order to maintain an appropriate tread curvature, the radial carcass or the tire inner peripheral surface is made to correspond to the central depression of the tread portion. Although it is preferable that the shape is a shape, a normal radial carcass or a tire inner peripheral surface may be used as long as the above tread shape can be maintained. The tread width of the tread portion 6 is in the range of 85 to 100% of the tire width, preferably 90 to 98%, and a normal studless tire (tread width / tire width × 100 = 75).
~ 85%).

The central recess 7 is provided substantially in the center of the tread portion 6. The central recess 7 has a U-shaped cross section, and both side walls of the central recess 7 are inclined in a direction diverging outward, and the inclination angle is 5 to 30 with respect to the circumferential surface of the tread. The angle is preferably in the range of 10 ° to 25 °, preferably 10 to 25 ° (the cross-sectional shape is linear), and the corners formed by the side walls and the tread are preferably angled in order to exert the edge effect. In addition, you may chamfer in order to make this corner part square. The width of the central depression 7 is in the range of 10 to 25% of the tread width, preferably 12 to 20%. If this range is less than 10%, the ground contact length cannot be effectively increased, and the lateral edge effect due to the groove wall of the center thick groove cannot be exhibited, so sufficient ice and snow performance cannot be obtained. If it exceeds 25%, the contact area with the ground cannot be secured.

The depth of the central depression 7 is the depression depth D measured along the tire equatorial plane from the straight line m connecting the outer edges of both side walls of the central depression 7 in the tire width direction to the maximum depth in the tire width section. This depth D is 80 to 1 of the tread thickness (thickness at the maximum cross-section height position of the tire).
20%, preferably 90 to 110%. 80%
If it is less than the above, the effect of providing the central depression is small, and drainage performance, snow column shearing force, and contact length increase cannot be expected, and if it exceeds 120%, the rigidity of the land part decreases significantly, so steering stability on ice and snow roads and dry roads Is worse. In addition, a raised object having a trapezoidal cross section may be provided intermittently or continuously at the bottom of the central recess 7 in order to prevent the inclusion of foreign matter or the like.

Each of the divided tread portions has a square shoulder shape in which at least the outer portion of the tire is angular. The shoulder portion forming the outer portion of the tire has an inclination angle α inward of the tread width in the range of 5 to 30 ° with respect to the circumferential surface of the tread, preferably 10 to 25 ° (the cross-sectional shape is linear). To do. This is because if it is less than 5 °, the steering stability on a dry road surface deteriorates, and if it exceeds 30 °, an effective edge effect cannot be obtained on an icy and snowy road surface.

Further, each divided tread portion is provided with a land block 12 defined by at least one circumferential main groove 10 and a plurality of lateral grooves 11 extending across the main groove 10, and the land block 12 is provided with a plurality of sipes. Equipped with 13. It is preferable that each divided tread has about 1 to 3 circumferential main grooves 10 (two arranged in FIG. 2), and the groove shape is preferably a straight shape, a crank shape, a zigzag shape, or a combination thereof. The groove width is in the range of 20 to 40% of the central depression 7, preferably 25 to 35%, and the groove depth is 50 to 9 of the depression depth D of the central depression 7.
The range is 0%, preferably 65 to 75%.

The lateral grooves 11 are arranged at substantially equal intervals along the circumference of the tread so as to traverse straight between the tread edge and the circumferential main groove 10 and between the circumferential main groove 10 and the central recess 7, respectively. Further, the arrangement angle of the lateral groove 11 is set in the range of 0 to 45 ° with respect to the tread width direction, and the arrangement angle can be appropriately changed in consideration of the balance between the driving performance and the cornering performance. The width of the lateral groove 11 is in the range of 15 to 35% of the central recess 7, preferably 20 to 30.
%, And the groove depth is in the range of 50 to 90% of the recess depth D of the central recess, preferably in the range of 65 to 75%, and may be shallower than the groove depth of the circumferential main groove 10. preferable.

Further, the land block 12 is provided with a plurality of sipes 13 in order to enhance the edge effect. The number of sipes is at least two, preferably three.
It is preferable that the number of the sipe is 6 to 6, and the sipe arrangement angle corresponds to the lateral groove as shown in FIG. 2, but it can be appropriately changed in consideration of the balance of the driving performance and the cornering performance.

When the sectional height positions i and o of the inner end and the outer end of each divided tread portion are defined by the deviation from the plane passing through the maximum sectional height position t of both divided treads, these deviations are 15 to 30 at the inner end i with respect to the central recess depth D
%, 30 to 60% at the outer end, and the ratio (deviation of inner end / deviation of outer end) is preferably in the range of 0.4 to 0.6.

The rubber structure of the tread portion 6 may be composed of only a single layer rubber, but a two-layer structure of cap / base is preferable, and in that case, the cap rubber is fragile. Temperature is in the range of -45 to -65 ° C, rubber hardness is in the range of 40 to 60 °, preferably 45 to
It is more preferably in the range of 55 °, and more preferably made of foamed rubber excellent in ice and snow performance, and the base rubber is preferably made of non-foamed rubber harder than the cap rubber. The present invention is
In particular, it is preferable that the flatness of the tire when assembled on the applicable rim and filled with a predetermined internal pressure is 60% or less.

[0022]

The pneumatic radial tire of the present invention can provide a wide tread width commensurate with a wide tire width by providing a wide central depression on an icy and snowy road surface.
Thereby, the ground contact length can be sufficiently increased. Also, in order to obtain sufficient ice and snow performance, at least the outer ends of the split tread parts divided into two by the central recess have a proper square shoulder-shaped contour, so that lateral force can be applied when running on ice and snow roads. Since a strong edge component is obtained, cornering performance is improved. Further, by providing the tread with a block pattern (including a plurality of sipes in the land block) suitable for an ice and snow road surface, sufficient drivability and cornering can be obtained.

In addition, by disposing the central depression, both high drainage performance on a wet road surface and excellent steering stability on a dry road surface can be improved.

[0024]

EXAMPLES The width section and the tread pattern of the inventive tire used in the examples are shown in FIGS. 1 and 2, respectively.
This tire has a tread portion reinforced by a belt on the crown portion of a radial carcass that extends in a toroidal shape across a pair of bead cores. The radial carcass 3 is composed of a single rubberized sheet in which polyester cords are arranged in a direction orthogonal to the tire equatorial plane. The belt 5 has a steel cord attached to the equatorial plane of the tire 24
It has a structure in which two rubberized sheets arranged at an inclination angle of ° are overlapped so that the cords intersect each other.

In order to reinforce the belt 5, the belt 5
Has a cap layer 8 consisting of one cord rubberized sheet for covering the entire outer peripheral surface of the belt and one narrow rubber cord sheet for reinforcing the outer end of the belt 5, and also has a cap layer 8 at the center. One narrow auxiliary layer 9 was provided at a position corresponding to the depression 7. The cords used for the cap layer 8 and the auxiliary layer 9 were arranged parallel to the tire equatorial plane, and nylon was used for the cap layer and the auxiliary layer 9, respectively.

The tread portion 6 is provided with a wide and deep bottom central depression 7 along the circumference of the tread at the center of its width, and is substantially divided into two parts, and the width cross-sectional shape is a twin-hump shape. The treads of these divided tread portions had independent curvatures in the tread width direction, and the radial carcass or the tire inner peripheral surface had a shape corresponding to the central depression of the tread portion. The tread width of the tread portion 6 is 208 mm, the tire width is 218 mm, and the percentage ((tread width / tire width) × 100) is 95.4.
%Met.

The central recess 7 is provided substantially in the center of the tread portion 6. The central depression 7 has a U-shaped cross-section, and both side walls of the central depression 7 are inclined in the direction of divergence, and the inclination angle is 17 ° with respect to the circumferential surface of the tread. The width of the central recess 7 was 34 mm, and the percentage of the tread width was 16.3%. The depth D of the central depression 7 is 15 mm, and the tread thickness T
Since the (thickness at the maximum cross-section height position of the tire) is 15 mm, the percentage ((D / T) × 100) of these is 10
It is 0%.

The shoulder portion of each divided tread portion has an inclination angle α of 17 ° inward from the circumferential surface of the tread. Further, each divided tread portion is provided with a land block 12 which is divided by two circumferential main grooves 10 and a plurality of lateral grooves 11 which extend across the main groove.
2 has a plurality of sipes 13.

Two circumferential main grooves 10 of the divided tread portion
, The circumferential main groove on the shoulder side is straight,
The circumferential main groove located on the center side of the tread has a zigzag shape. The groove width of the circumferential main groove was set to 10 mm, and the percentage of the central recess 7 with respect to the groove width was set to 29.4%.
The circumferential main groove has a groove depth of 11 mm and a central recess 7
The percentage of the depression depth D was 73.3%.

The lateral groove 11 has a groove width of 8 mm and a groove depth of 11
mm, and the percentage for the central depression is 24
%, 73.3%, and the arrangement angle was 0 ° with respect to the tread width direction. Five sipes were placed in each land block in parallel with the lateral grooves.

The deviation from the sectional height positions i and o at the inner and outer ends of each divided tread portion to the plane passing through the maximum sectional height position t of both divided treads is 3.5 m.
m, 7.0 mm, and the percentage with respect to the central recess depth D is 23.3% at the inner end i and 46.6% at the outer end, and these ratios (deviation of inner end / deviation of outer end) ) Was set to 0.5.

The tread portion 6 has a two-layer structure of cap / base, the cap rubber is made of foamed rubber having a rubber hardness of 49 °, and the base rubber is non-foamed rubber having a rubber hardness of 59 °.

The internal structure of the conventional tire used in the conventional example is the same as that of the inventive tire shown in FIG.

The test shows that the tire internal pressure is 2.0 kgf / cm.
^2. Under the condition that the tire load is equivalent to two passengers, the steering stability on dry road surface, high-speed drainage on wet road surface, driveability on ice and snowy road surface, braking performance and cornering performance were investigated. In addition, in order to examine the ground contact characteristics, the ground contact width, contact length and actual contact area of the tread contact surface were measured. The driving stability on a dry road surface was evaluated by a driver's feeling evaluation. The high-speed drainage property on a wet road surface was evaluated by the ratio of the remaining contact area of the tire when running on a test course with a water depth of 6 mm at a speed of 100 km / h. The drivability was evaluated by the passage time index during running on the section of 0 to 30 m on the road surface on freezing and snow. The braking property was evaluated by an index of a stopping distance of 40 km / h. The cornering property was evaluated by a driver's feeling evaluation.

Table 2 shows the results of the above performance test, and Table 3 shows the results of examining the grounding characteristics. All the numerical values in the table are shown by index comparison with the conventional example being 100, and the larger the value, the better. The values in parentheses in Table 3 represent actual measured values.

[0036]

[Table 2]

[0037]

[Table 3]

From the test results shown in Table 2, the invention tire is superior to the conventional tire in any performance. Further, from the results of Table 3, the inventive tire has an actual contact area substantially the same as that of the conventional tire, and the contact length can be increased.

[0039]

According to the present invention, by providing the central depression in the width center of the tread, the ground contact property of the tire on the ice and snow road surface is increased and the actual tire contact area spreads in the circumferential direction of the tire. Therefore, it is possible to eliminate the shortcomings of conventional flat tires, which had a short ground contact length.
As a result, sufficient driving performance and cornering performance can be obtained. Further, by making at least the outer side of the tread portion a square shoulder-shaped contour shape having a small inclination angle, a remarkable edge effect can be exerted particularly on the lateral force generated at the time of cornering on an icy and snowy road surface. Further, the tire of the present invention has a larger ratio of the tread width to the tire width than that of a normal flat tire, and thus is excellent in steering stability on a dry road surface. Further, even on a wet road surface, the water that has entered the tread contact surface can be quickly stored in the central recess and eliminated, so that the contact surface can be secured and sufficient steering stability can be obtained. From the above, the tire of the present invention not only has excellent performance on icy and snowy road surfaces, but also exhibits excellent performance on dry road surfaces and wet road surfaces, even when these road surfaces are mixed, there is no problem. Can be used.

[Brief description of drawings]

FIG. 1 is a width sectional view of an inventive tire used in an example.

FIG. 2 is a tread pattern of the inventive tire shown in FIG.

[Explanation of symbols]

 1 Pneumatic radial tire 2 Bead core 3 Radial carcass 4 Crown part 5 Belt 6 Tread part 7 Central depression 8 Cap layer 9 Auxiliary layer 10 Circumferential main groove 11 Lateral groove 12 Land block 13 Sipe

Claims (1)

[Claims] 1. A tread portion reinforced by a belt having an inextensible cord arrangement is provided on a crown portion of a radial carcass extending in a toroidal shape across a pair of bead cores, and the tread portion has a width center in its width. A wide, deep center recess along the circumference of the tread results in a substantially bisection configuration.These tread sections have a square shoulder profile at least outside the tire and each tread section is Is at least one circumferential main groove,
A winter pneumatic radial tire comprising a land block which is divided by a plurality of lateral grooves extending across the land block, and the land block having a plurality of sipes.