JP4453435B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire suitable for use in a passenger car, and more particularly to a pneumatic tire that can achieve both high handling stability and hydroplaning prevention performance.

  In recent years, a vehicle such as a sports utility vehicle (SUV) is also required to have high-dimensional steering stability on a dry road surface or a wet road surface, and at the same time, excellent hydroplaning prevention performance is also required.

  Conventionally, in order to ensure steering stability, it has been proposed to arrange a rib in the center region of the tread portion and increase the inclination angle of the side wall of the center rib to increase the rib rigidity (for example, Patent Documents). 1 and Patent Document 2).

  However, when the inclination angle of the side wall of the center rib is increased, the ground contact shape of the entire tread becomes a substantially elliptical shape, whereas the ground contact front end line formed by the center rib is a reverse radius recessed in the ground contact surface. There is a tendency to end up. In such a ground contact shape, the center rib reduces the action of scraping the water on the road surface outward in the tire axial direction, so the drainage performance in the center region where the contact length is long is reduced and the hydroplaning prevention performance is significantly impaired. There is a fear.

The following points can be considered as the cause of the reverse radius. First, since the restraining force in the tire circumferential direction at the time of internal pressure filling is smaller in the main groove portions on both sides of the center rib than in the center rib portion, the main groove portion is in the tire radial direction during the internal pressure filling. The tread profile changes so as to bulge outward. Secondly, when the inclination angle of the side wall of the center rib is increased, the deformation of the edge portion of the center rib is increased when a load is applied. In any case, if the ground contact front end line formed by the center rib forms a reverse radius, it is disadvantageous in terms of drainage.
Japanese Patent Laid-Open No. 7-186628 JP-A-7-195911

  An object of the present invention is to provide a pneumatic tire capable of achieving both steering stability and hydroplaning prevention performance at a high level.

The pneumatic tire of the present invention for solving the above-described object is provided with a pair of main grooves continuously extending in the tire circumferential direction on both sides of the tire equator in the tread portion, and continuous in the tire circumferential direction between the main grooves. A pneumatic tire having a center rib defined therein, wherein a cross-sectional profile line of a tread surface of the center rib intersects a virtual tread profile line that smoothly connects a tread surface including both ground contact edges except for the center rib, The center portion in the tire axial direction has a smooth convex shape toward the outer side in the tire radial direction and bulges outward from the virtual tread profile line in the tire radial direction, and the bulge amount A from the virtual tread profile line of the center rib There while a 0.5 mm to 3.0 mm, the tread and the side wall of the center rib forms a ridge, It is characterized in that the ridge line in the edge portions of both of the serial center rib is depressed in the tire radial direction inner side than the virtual tread profile line.

  Here, the cross-sectional profile line of the tread of the center rib is an arc shape formed by the tread of the center rib in the tire meridian cross section in a state where the pneumatic tire is filled with air pressure corresponding to the maximum load capacity specified by JATMA. It is a contour line. On the other hand, a virtual tread profile line is a state in which a pneumatic tire is filled with air pressure corresponding to the maximum load capacity specified by JATMA, and the tread surface including the ground contact edges on both sides excluding the center rib in the tire meridian section is smooth. It is an arcuate virtual contour line to be connected. The term “grounding end” as used herein refers to a tire shaft in a grounding region formed when a pneumatic tire is filled with air pressure corresponding to the maximum load capacity defined by JATMA and a load of 80% of the maximum load capacity is applied. It is an end portion on the outside in the direction.

In the present invention, in the pneumatic tire provided with the center rib, the ground contact shape in the center rib can be improved by defining the cross-sectional profile line of the tread surface of the center rib as described above. That is, bulging from the center rib in the tire axial direction of the central portion the virtual tread profile line forms a smooth convex shape toward the outer side in the tire radial direction to the outer side in the tire radial direction, ridges virtual in the edge portions of both of the center rib Since the structure that falls inward in the tire radial direction than the tread profile line is adopted, even if the inclination angle of the side wall of the center rib is increased in order to improve steering stability, the ground contact front line formed by the center rib Can be prevented from becoming reverse radius. This makes it possible to achieve both steering stability and hydroplaning prevention performance at a high level.

In the present invention, the inclination angle θ of the side wall of the center rib with respect to the tread normal is preferably 25 ° to 45 °. It is necessary to form an edge line between the tread surface and the side wall of the center rib. The bulging amount A from the virtual tread profile line of the center rib needs to be 0.5 mm to 3.0 mm. The maximum height difference B of the tread surface of the center rib preferably satisfies the relationship of A <B ≦ 2A with respect to the bulging amount A. The center rib width CRW is preferably 10% to 20% of the ground contact width GCW. By satisfying these conditions, it is possible to more reliably obtain the effect of improving the steering stability and the hydroplaning prevention performance.

  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, FIG. 2 shows an enlarged center rib, and FIG. 3 shows a virtual tread profile line. As shown in FIG. 1, the tread portion 1 includes two straight main grooves 2 extending continuously in the tire circumferential direction on both sides of the tire equator, and obliquely extending outward from the main grooves 2 in the tire axial direction. A plurality of inclined grooves 3, a plurality of lug grooves 4 extending obliquely outward in the tire axial direction from the inclined grooves 3 and communicating to the tread end, and lug grooves 5 extending between the lug grooves 4 Is formed. Accordingly, the center rib 6 positioned in the center region between the main grooves 2, the plurality of blocks 7 positioned on the outer side in the tire axial direction of the center rib, and the shoulder region on the outer side in the tire axial direction of these blocks 7 are positioned. A plurality of blocks 8 are partitioned.

  In the pneumatic tire, as shown in FIG. 2, the cross-sectional profile line L1 of the tread surface of the center rib 6 is a virtual tread profile line L2 (FIG. 3) that smoothly connects the tread surface including both ground contact edges except for the center rib 6. ), The center portion of the center rib 6 in the tire axial direction forms a smooth convex shape outward in the tire radial direction, and bulges outward from the virtual tread profile line L2 in the tire radial direction. The edge portions on both sides are falling inward in the tire radial direction from the virtual tread profile line L2.

  The tread surface and the side wall of the center rib 6 form a ridgeline. That is, in the tire meridian cross section, the tread surface and the side wall of the center rib 6 are connected via the bending point X. If this ridgeline (bending point X) does not exist, the edge component is insufficient, and the steering stability on the wet road surface is deteriorated.

  The inclination angle θ of the side wall of the center rib 6 with respect to the tread normal is set in the range of 25 ° to 45 °. The inclination angle θ is an angle formed by the tangent to the side wall and the tread normal at the upper end position (bending point X) of the side wall of the center rib 6. When the inclination angle θ is less than 25 °, the rigidity of the center rib 6 is insufficient and steering stability is deteriorated. Conversely, when it exceeds 45 °, the groove volume is reduced and the hydroplaning prevention performance is deteriorated.

  The bulging amount A from the virtual tread profile line L2 of the center rib 6 is set in a range of 0.5 mm to 3.0 mm. If the bulging amount A is less than 0.5 mm, the effect of improving the hydroplaning prevention performance becomes insufficient. Conversely, if it exceeds 3.0 mm, the contact pressure of the center rib 6 becomes excessive and the steering stability deteriorates. In addition, the wear of the center rib 6 is promoted and the wear life is shortened.

The maximum height difference B of the tread surface of the center rib 6 is set so as to satisfy the relationship of A <B ≦ 2A with respect to the bulging amount A. If this maximum height difference B is smaller than the bulging amount A, the ground pressure of the center rib 6 becomes excessive, and conversely if it is larger than twice the bulging amount A, the contact pressure drop at the edge of the center rib 6 becomes large. Steering stability on wet roads deteriorates.

  The width CRW of the center rib 6 is set in a range of 10% to 20% of the ground contact width GCW. The width CRW is a distance between points P and P where the tangent of the side wall at the upper end position (bending point X) of the center rib 6 intersects the virtual tread profile line L2. If the width CRW is less than 10% of the ground contact width GCW, it becomes difficult to ensure excellent steering stability. Conversely, if the width CRW exceeds 20%, the groove volume in the center region is insufficient and the hydroplaning prevention performance deteriorates. To do.

  The width GW of the main groove 2 adjacent to the center rib 6 is set in a range of 50% to 150% of the width CRW of the center rib 6. When the width GW is less than 50% of the width CRW, the hydroplaning prevention performance is deteriorated. Conversely, when the width GW exceeds 150%, the tread rigidity is insufficient and the steering stability is lowered.

  As described above, the cross-sectional profile line L1 of the tread surface of the center rib 6 intersects the virtual tread profile line L2, and the center portion of the center rib 6 that bulges smoothly bulges outward from the virtual tread profile line L2 in the tire radial direction. Since the edge portions on both sides of the center rib 6 have fallen inward in the tire radial direction from the virtual tread profile line L2, the inclination angle θ of the side wall of the center rib 6 is increased in order to improve steering stability. However, it is possible to avoid reverse grounding of the grounding front end line formed by the center rib 6.

  Here, FIG. 4 shows a footprint of the pneumatic tire having the tread pattern when running on a wet road surface. However, the tire size is 255 / 55R18, the air pressure is 260 kPa, and the load is 6.5 kPa. As shown in part C of FIG. 4, the grounding front end line formed by the center rib 6 is rounded outward. For comparison, the grounding front end line which has become a reverse radius is indicated by a broken line.

  According to the pneumatic tire, an ideal ground contact shape can be obtained even when the inclination angle θ of the side wall of the center rib 6 is increased. Therefore, the steering stability and the hydroplaning prevention performance can be achieved at a high level.

In the above-described embodiment, the tread pattern shown in FIG. 1 has been described, but the tread pattern is not particularly limited in the present invention .

  The circumferential main groove and the center rib preferably have no point height. If there is a point height, the force at the time of load application is dispersed, and it is difficult for the front end of the ground wire to stick out, so the hydroplaning prevention performance decreases. Further, it is preferable that the center rib has no notches. If there is a notch, the force at the time of load application will be dispersed and it will be difficult for the front contact end line to stick out, so the hydroplaning prevention performance will deteriorate.

  In the pneumatic tire having the tread pattern shown in FIG. 1 with the tire size 255 / 55R18, the bulging amount A from the virtual tread profile line of the center rib, the maximum height difference B of the tread of the center rib, and the tread on the side wall of the center rib Inclination angle θ with respect to normal, ratio of center rib width CRW to ground width GCW (CRW / GCW × 100%), ratio of main groove width GW to center rib width CRW (GW / CRW × 100%) As shown in Fig. 1, 13 types of tires (conventional examples, Examples 1 to 9 and Comparative Examples 1 to 3) were manufactured. In the tires of the conventional example, Examples 1 to 9 and Comparative Examples 1 to 3, the tread surface and the side wall of the center rib have ridge lines.

  These test tires are assembled on a wheel with a rim size of 18 × 8 JJ, mounted on an SUV vehicle with a displacement of 4500 cc at a front wheel pressure of 260 kPa and a rear wheel pressure of 290 kPa, and under the conditions of a vehicle weight of 2500 kg (equivalent to two passengers), the following method Thus, the steering stability on the dry road surface, the steering stability on the wet road surface, and the hydroplaning prevention performance were evaluated. The results are also shown in Table 1.

Steering stability on dry roads:
Feeling evaluation by skilled panelists was performed on dry road surface. The evaluation results are shown as an index with the conventional example being 100. The larger the index value, the better the steering stability on the dry road surface.

Steering stability on wet surfaces:
Feeling evaluation by an experienced panelist was performed on the wet road surface. The evaluation results are shown as an index with the conventional example being 100. The larger the index value, the better the steering stability on the wet road surface.

Hydroplaning prevention performance:
In a straight path provided with a pool with a water depth of 10 mm, the speed when entering the pool was changed, and the speed when the tire slip rate reached 10% was evaluated as the hydroplaning generation speed. The evaluation results are shown as an index with the conventional example being 100. The larger the index value, the better the hydroplaning prevention performance when going straight.

  As shown in Table 1, the tires of Examples 1 to 9 were improved in a well-balanced manner in terms of steering stability on a dry road surface, steering stability on a wet road surface, and hydroplaning prevention performance as compared with the conventional tires. . On the other hand, since the cross-sectional profile line of the tread surface of the center rib does not intersect the virtual tread profile line, the tires of Comparative Examples 1 to 3 can achieve both steering stability and hydroplaning prevention performance at a high level. could not.

It is an expanded view which shows the tread pattern of the pneumatic tire which consists of embodiment of this invention. It is an expanded sectional view which shows the center rib of the tread pattern of FIG. It is explanatory drawing which shows the virtual tread profile line of the tread pattern of FIG. It is a top view which shows the footprint at the time of wet road running of the pneumatic tire which has a tread pattern of FIG.

Explanation of symbols

1 tread portion 2 main groove 3 inclined groove 4,5 lug groove 6 center rib 7,8 block L1 cross-sectional profile line L2 virtual tread profile line

Claims (4)

In a pneumatic tire in which a tread portion is provided with a pair of main grooves continuously extending in the tire circumferential direction on both sides of the tire equator, and a center rib continuous in the tire circumferential direction is defined between the main grooves, the tread surface of the center rib The cross-sectional profile line of the center rib intersects a virtual tread profile line that smoothly connects the tread surfaces including the ground contact edges on both sides except for the center rib, and the center portion of the center rib in the tire axial direction faces outward in the tire radial direction. While forming a smooth convex shape and bulging outward from the virtual tread profile line in the tire radial direction , the bulging amount A from the virtual tread profile line of the center rib is 0.5 mm to 3.0 mm, while the center forming a ridge and a tread and a sidewall of the rib, said ridge at the edge portions of both of the center rib A pneumatic tire, characterized in that depressed on the inner side in the tire radial direction than the serial virtual tread profile line.   2. The pneumatic tire according to claim 1, wherein an inclination angle θ of the side wall of the center rib with respect to a tread normal is 25 ° to 45 °. 2. The pneumatic tire according to claim 1 , wherein a maximum height difference B of a tread surface of the center rib satisfies a relationship of A <B ≦ 2A with respect to the bulging amount A. 3. The pneumatic tire according to any one of claims 1 to 3 , wherein a width CRW of the center rib is 10% to 20% of a ground contact width GCW.

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