JP2002307912A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire improvable in wear resistance and dry performance while maintaining ice performance. SOLUTION: In this pneumatic radial tire, the outline of radius of curvature appearing on the surface of a crown part 2 appearing in tire cross section, and the outline of each radius of curvature appearing on the surfaces of both side shoulder parts 3 internally contacting the outline of radius of curvature appearing on the surface of a buttress part 4, are laterally asymmetric with respect to a tire equator line 5. The radius of curvature Rso of the shoulder parts 3 positioned outside of a vehicle when mounting a tire is 5-35 mm, the radius of curvatures Rsi inside of the vehicle is 0-10 mm (Rso >Rsi ), a void ratio near the grounding end of the shoulder parts 3 positioned outside of the vehicle is set to Vo, and a void ratio on the inside is set to Vi, 0.65×Vi<=Vo<=0.98×Vi is to be satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire in which the radius of curvature of the contour of a shoulder portion and the void ratio near the ground contact end of the shoulder portion are asymmetrical with respect to the tire equator line.

[0002]

2. Description of the Related Art Generally, pneumatic tires are designed to prevent uneven wear of a shoulder due to a difference in contact pressure distribution.
The block rigidity of the shoulder part is set larger than that of the center part. In addition, high-roof vehicles such as minivans and one-boxes adopt asymmetric patterns,
In many cases, the shoulder block rigidity outside the vehicle is set higher.

At the time of cornering when a vehicle runs,
The load is moved by the roll, and a large load is applied to the outside of the vehicle. Therefore, the outer portion of the tire pattern is easily reduced quickly, and one-sided wear easily occurs. Also, since a large load is applied to the outside of the tire, if the outside block rigidity is small, sufficient cornering power (C
P) cannot be obtained. In particular, high-roof vehicles such as minivans and one-boxes have a high center of gravity and a large roll.

Therefore, as described above, in a high-roof vehicle, the pattern rigidity is increased by reducing the void (groove area) outside the tire or increasing the block area outside, that is, by adopting an asymmetric pattern. There were many things.

[0005]

However, in the case of an iced road surface, since the road surface mu (friction coefficient) is low, the load change by the roll hardly occurs even on a high-roof vehicle, and the block rigidity in the ground contact surface is uniform (the pattern rigidity is low). The more uniform, the better the performance. Conversely, increasing the rigidity of the shoulder tends to reduce the ice performance.

[0006] In the case of studless tires, the shoulder portion is often shaped like a square (shape with a tread grounded edge) in order to increase the ground contact area, but if the shape is close to a square, a load is applied when the load is applied. The increase in the contact width is small, and a sufficient CP cannot be obtained. For this reason, it is difficult to improve cornering performance on dry road surfaces.

[0007] Japanese Patent Application Laid-Open No. H11-322214 discloses that the radius of curvature of a shoulder portion located on the outside of a vehicle is given by:
A left-right asymmetric pneumatic radial tire that is smaller than the radius of curvature of the shoulder located on the inside is disclosed.However, since the outer radius of curvature is smaller, when a load is moved by a roll at the time of cornering, the contact area is reduced. The effect of increasing it cannot be expected.

Accordingly, an object of the present invention is to provide a pneumatic radial tire capable of improving abrasion resistance and dry performance while maintaining ice performance.

[0009]

The above object can be achieved by the present invention as described below. That is, the pneumatic radial tire of the present invention has a contour of the radius of curvature that appears on the surface of the crown portion of the tire tread, and a surface of both shoulder portions inscribed in the contour of the radius of curvature that appears on the surface of the buttress portion, respectively. In the pneumatic radial tire in which the contours of the respective radii of curvature that appear are asymmetrical with respect to the tire equator, the curvature radii Rso of the contours appearing on the surface of the shoulder portion located outside the vehicle when the tires are mounted are 5 to 5. 35mm
Wherein the radius of curvature Rsi of the contour appearing on the surface of the shoulder portion located inside the vehicle is 0 to 10 mm, and Rso> Rsi, and near the ground contact end of the shoulder portion located outside the vehicle. Is Vo and the void ratio near the ground end of the shoulder portion located inside is Vi, where 0.65 × Vi ≦ Vo ≦ 0.
It is characterized by satisfying 98 × Vi.

[0010] Here, the grounding end of the shoulder portion means that after the tire is mounted on the applicable rim, the internal pressure is set to 180 kPa,
When a mass equivalent to 88% of the indicated maximum load capacity of the tire is loaded, it indicates the outermost positions on both sides that touch the flat road surface. The void ratio in the vicinity of the ground end is, as shown in FIG. 3, the center line G of the groove defining the blocks B3o and B4i where the ground end lines To and Ti intersect.
It indicates the percentage (%) of the groove area surrounded by the center lines Go and Gi in the pitch area of one pitch surrounded by o and Gi and the ground end lines To and Ti. In the case where the land portion where the ground end lines To and Ti intersect is continuous over the entire circumference without passing through the groove, the ground end lines To and Ti for one pitch are provided.
The percentage (%) of the groove area in the area between Ti and the center line Go, Gi of the circumferential groove adjacent to the land portion is defined.

According to the present invention, the radius of curvature R
Since so and the radius of curvature Rsi have the above-described relationship, when the void ratios of the shoulder portions on both sides are the same, when cornering on an ice road surface, the contact area outside the vehicle (the contact width from the equator line) ) Is reduced, the present invention changes the void ratio on both sides to increase the block area ratio in proportion to the decrease in the ground contact area. Can be maintained. On the other hand, when cornering on a dry road surface, the larger radius of curvature Rso increases the contact area on the outside of the vehicle, so that the block rigidity on the outside of the vehicle is higher than on the inside, thereby preventing one-sided abrasion and sufficient cornering power. Obtainable. as a result,
It is possible to improve the wear resistance and dry performance while maintaining the ice performance.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view showing an outline of a cross section of a pneumatic tire showing an example of the present invention.
Is an enlarged view of the main part.

In FIG. 1, 1 is a tire tread, 2 is a crown portion of the tire tread 1, 3 is a shoulder portion,
Is a buttress part. 5 is a tire equator line running in the center of the tire tread 1, and 6 is an imaginary line indicating the tire maximum width.

As shown in the figure, the contours 71 and 72 of the radius of curvature Rso and Rsi of the tire outer peripheral surface in the shoulder portion 3 are the contours 81 and 82 of the radius of curvature Rt appearing on the surface of the crown portion 2 and the buttress. It is inscribed in the contours 91 and 92 of the radius of curvature Rb appearing on the surface of the portion 4, respectively.
In FIG. 2, a dashed line 83 represents a contour 81 of the radius of curvature Rt.
The dashed line 93 is a virtual extension of the contour 91 having the radius of curvature Rb.

The contours 71 and 72 of the radii of curvature Rso and Rsi appearing on the surface of the shoulder portion 3 are as shown in FIG.
It is left-right asymmetric with respect to the tire equator line 5. That is,
A contour 71 that appears on the surface of the shoulder portion located outside the vehicle when the tire is mounted, and a contour 72 that appears on the surface of the shoulder portion located inside the vehicle have asymmetrical radii of curvature.

Further, Rso> Rsi, and the radius of curvature Rso of the contour 71 of the shoulder located outside the vehicle is:
The radius of curvature Rsi of the contour 72 of the shoulder portion located inside the vehicle is larger than that of the shoulder portion.

A shoulder portion 3 located outside the vehicle
As a specific numerical value of the radius of curvature Rso of the contour 72 and the radius of curvature Rsi of the contour 72 located inside the vehicle, the radius of curvature Rso is 5
And the radius of curvature Rsi of the contour appearing on the surface of the shoulder portion located inside the vehicle is 0 to 10 mm.
It is. Preferably, the radius of curvature Rso is 15 to 30 mm, and the radius of curvature Rsi of the contour appearing on the surface of the shoulder portion located inside the vehicle is 0 to 5 mm. Contour 7
If the radius of curvature Rso of No. 1 is smaller than 5 mm, the increase in the contact area during cornering on a dry road surface is so small that the dry performance cannot be sufficiently improved, and the radius of curvature Rso of the contour 71 is 35 m.
If it is larger than m, it is not possible to secure a sufficient contact area on the outer side of the shoulder portion 3 during straight running or on an ice road surface. If the radius of curvature Rsi of the contour 72 is larger than 10 mm, the contact area of the shoulder portion 3 located inside cannot be sufficiently secured.

In the present invention, the radius of curvature Rt of the arcs 81 and 82 appearing on the surface of the crown portion and the radius of curvature Rb of the arcs 91 and 92 appearing on the surface of the buttress portion 4 are not particularly limited. The shape of the tire of the present invention is all specified on the basis of the standard internal pressure.

In the present invention, when the void ratio near the ground contact end of the shoulder located outside the vehicle is Vo and the void ratio near the ground contact of the shoulder located inside is Vi, 0.65 × Vi ≦ Vo ≦ 0.9
8 × Vi, preferably 0.75 × Vi ≦ Vo
Satisfies ≦ 0.9 × Vi. The void ratio Vo is 0.65 × V
If it is smaller than i, the void ratio Vo becomes too small, and it becomes difficult to keep the ice rigidity close to the block rigidity between the outer shoulder portion 3 and the inner shoulder portion 3. On the other hand, if the void ratio Vo is larger than 0.98 × Vi, the void ratio Vo becomes too large, and similarly, it is difficult to maintain the ice performance by approaching the block rigidity of the outer shoulder portion 3 and the inner shoulder portion 3. become.

In the present invention, the shape of the tread pattern is not particularly limited. For example, a tread pattern having asymmetry with respect to the equator line 5 of the tire as shown in FIG. In this example, the ground end lines To, Ti
Crosses blocks B3o and B4i, and block B
Inside blocks 3o and B4i, there are provided blocks B1o and B1i arranged near the tire equator line 5, and blocks B2o, B2i and B3i arranged on both sides thereof.

Each of the blocks B1o to B4i has a circumferential groove 1
1 and a zigzag oblique groove 12 and a lateral groove 13. Each of the blocks B1o to B4i has a plurality of wavy sipes.

In the present invention, any block may have a rib shape, and the rib may have a lug (lateral groove).

In the present embodiment, the center line Go of the pitch area of one pitch surrounded by the center line Go of the groove defining the block B3o intersecting the ground end line To and the ground end line To. The void ratio Vo, which is a percentage of the groove area, is smaller than the similarly defined void ratio Vi. In other words, when the block area ratio of the block B3o inside the ground end lines To and Ti is larger than the block area ratio of the block B4i, and thus the void ratio of the shoulder portions on both sides is the same, when cornering on an ice road surface. Where the contact area on the outside of the vehicle (the contact width from the equator line) is reduced, the present invention increases the block area ratio as much as the decrease in the contact area,
On an ice road surface, the block rigidities on both sides are equalized, and ice performance can be maintained.

In the present invention, when the rubber composition or the rigidity of the rubber itself in the tread pattern is the same, the effect of improving the abrasion resistance and the dry performance while maintaining the ice performance can be exhibited in a well-balanced manner. The rubber composition and the like in the tread pattern may be different. However, it is preferable that the rigidity of the rubber itself in the tread pattern be similar.

Since the tire of the present invention has an asymmetric tread pattern, the mounting direction or the rotation direction is specified. The present invention is a pneumatic radial tire having an asymmetric tread pattern, and can be suitably used particularly for a pneumatic radial tire for high-roof vehicles such as minivans and one-box vehicles.
This means that even if it is a pneumatic radial tire having the above-described asymmetric tread pattern, when applied to a high-roof vehicle such as a minivan or a one-box vehicle, the center of gravity of the vehicle is higher than that of a normal passenger car tire. This is because a large force acts on the shoulder portion located outside the vehicle during traveling, particularly when turning, and the problems of uneven wear and cornering performance on a dry road surface as described above are large. Further, since the ice performance can be maintained, it is useful as a studless tire.

However, the tire of the present invention is not limited to these, and can be used for a tire for a passenger car which satisfies a nominal sectional width of 135 to 325 (mm) and a flatness of 30 to 80 (%). Further, the tire of the present invention can be easily manufactured by vulcanizing and molding using a mold or the like in which the curvature radius of the shoulder portion is left-right asymmetric.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments and the like specifically showing the configuration and effects of the present invention will be described below.

According to the above-described embodiment shown in FIGS. 1 to 3, the tire size 2 is determined by the curvature radius Rso, the curvature radius Rsi, and the void ratio ratio Vo / Vi of the shoulder portion shown in Table 1.
Example tires and comparative example tires of 15 / 60R16 were prototyped. With respect to these, ice performance, dry performance, and abrasion resistance were respectively evaluated by the following evaluation methods. The results are shown in Table 1.

Each tire had the same structure except for the "radius of curvature of the shoulder portion" and the "magnification of void ratio", and the void ratio of the entire pattern was constant. Also,
The radius of curvature of the shoulder portion of 0 mm means that the shape of the shoulder portion is a square shape.

(Ice Performance Test) The ice road surface was changed to a domestic minivan (3) equipped with the prototype tires of Examples and Comparative Examples.
The vehicle was run at 000 cc) and evaluated by a feeling test by two drivers. The evaluation was performed by giving each driver a type of a prototype tire, running the vehicle, and giving scores on a scale of 10 out of 10 points, and performing an index evaluation when the average value of the tire of Comparative Example 1 was set to 100. Table 1 shows the results. Each numerical value in the table indicates that the larger the value, the better the riding comfort.

(Dry Performance Test) A dry mini-van was mounted on a domestic minivan (3) equipped with each of the prototype tires of Examples and Comparative Examples.
The vehicle was run at 000 cc) and evaluated by a feeling test by two drivers. The evaluation was performed by giving each driver a type of a prototype tire, running the vehicle, and giving scores on a scale of 10 out of 10 points, and performing an index evaluation when the average value of the tire of Comparative Example 1 was set to 100. Table 1 shows the results. Each numerical value in the table indicates that the larger the value, the better the riding comfort.

(Uneven wear resistance test) A domestic minivan (3000 cc) equipped with each of the prototype tires of the examples and comparative examples was run on our test course for 6000 km, and the four tires were positioned outside the vehicle. The difference in the amount of wear between the shoulder portion and the tire center portion was measured, and the reciprocal of the measured value was evaluated as an index with the tire of Comparative Example 1 taken as 100. The running conditions in each of the examples and the comparative examples were five people, without tire rotation until completion. Table 1 shows the results of the uneven wear resistance test. The larger the value, the better the uneven wear resistance.

[0033]

[Table 1] As is clear from Table 1, the tires according to the examples can significantly improve the dry performance and the uneven wear resistance while maintaining the ice performance as compared with the tire of the comparative example 1 (conventional example). it can. On the other hand, in Comparative Example 2 in which the curvature radius Rso was too large, the ice performance could not be maintained. In Comparative Example 3 in which the ratio of the void ratio is too small, the groove area of the outer shoulder portion is too small, and the ice performance is reduced. In Comparative Example 4, in which the ratio of the void ratio is too large (Vo / Vi = 1), There was almost no improvement in the dry performance and uneven wear resistance, and the ice performance also tended to decrease.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an outline of a cross section showing an example of a pneumatic tire of the present invention.

FIG. 2 is an enlarged view of a main part showing an outline of a cross section showing an example of the pneumatic tire of the present invention.

FIG. 3 is a developed view showing an example of a tread pattern of the pneumatic tire of the present invention.

[Explanation of symbols]

 Reference Signs List 1 tire tread 2 crown portion 3 shoulder portion 4 buttress portion 5 tire equator line 71 contour of radius of curvature Rso (outer shoulder portion) 72 contour of radius of curvature Rsi (inner shoulder portion) Rso radius of curvature (outer shoulder portion) Rsi radius of curvature ( Center line of Go groove (outer shoulder portion) Center line of Gi groove (inner shoulder portion) B1o-B4i block

Claims (1)

[Claims] 1. A radius of curvature appearing on a surface of a crown portion of a tire tread, and respective radii of curvature appearing on surfaces of shoulder portions on both sides inscribed in a contour of a radius of curvature appearing on a surface of a buttress portion, respectively. In the pneumatic radial tire whose contour is asymmetrical with respect to the tire equator line, the curvature radius Rso of the contour appearing on the surface of the shoulder portion located outside the vehicle when the tire is mounted is 5 to 35 mm, The radius of curvature Rsi of the contour appearing on the surface of the shoulder portion located inside is 0 to 10 mm, and R
When so> Rsi and the void ratio near the ground end of the shoulder portion located outside the vehicle is Vo, and the void ratio near the ground end of the shoulder portion located inside is Vi,
A pneumatic radial tire which satisfies 0.65 × Vi ≦ Vo ≦ 0.98 × Vi.