JP2006160215A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To establish a mild driving stability and an anti-wear performance compatibly. <P>SOLUTION: A pneumatic radial tire is structured so that the grounding length in the tire circumferential direction in the neighborhood of the grounding end 12A of the tread 12 is shortened, the grounding width WS of a train 20A of shoulder region lands is increased, and that the grounding pressure and the wear volume are shifted toward the central region from the grounding end of the tread, whereby the single-sided wear at the time of cornering is prevented without decreasing the cornering power, and the mild driving stability and the anti-wear performance are established compatibly. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pneumatic radial tire capable of achieving both gentle steering stability and wear performance.

  Pneumatic radial tires for automobiles are required to have various performances such as steering stability, riding comfort performance, in-vehicle sound performance and fuel efficiency when mounted on a vehicle. It has become necessary to achieve a high degree of balance.

As techniques for improving these various performances, for example, there are those disclosed in Patent Documents 1 to 3.
JP-A-2-41909 JP-A-3-253409 JP 7-81303 A

  Of the various performances described above, it is necessary to ensure cornering power in order to improve steering stability.

  In order to ensure cornering power, it is necessary to secure land rigidity, to ensure a ground contact area, and to equalize the ground pressure.

  In general, when the vehicle is turning or under a heavy load, the contact pressure on the contact end side of the tread increases compared to the center of the tire, and so-called shoulder drop wear occurs near the contact end. If shoulder drop wear occurs and the land portion near the ground contact end wears to the limit of use, even if the land portion in the center of the tire remains, the tire cannot be used. In other words, the tire life is shortened by shoulder wear.

  Therefore, in order to improve steering stability, it is necessary to consider compatibility with wear performance.

  In recent years, when environmental problems have been highlighted, wear performance has become one of the most important performances. Particularly problematic is the above-mentioned shoulder drop wear, and it is more necessary to prevent shoulder drop wear in a sports car having a large camber angle.

  In addition, from the viewpoint of handling stability, not only sports-oriented ones, but there are an increasing number of cases aiming for calm characteristics that are conscious of safety and versatility, and only ensure the absolute level of cornering power Instead, it is necessary to suppress the sensitivity to load changes (for example, sudden oversteer during turning).

  However, the pneumatic tire described in Patent Document 1 is improved in uneven wear performance and drainage performance in a tire having a directional tread pattern by, for example, using a shoulder land portion as a rib continuous in the tire circumferential direction. The purpose is not to improve the handling stability.

  In addition, the pneumatic tire described in Patent Document 2 is merely intended to improve drainage performance and steering stability without increasing the groove area, and does not consider wear performance.

  Furthermore, the pneumatic tire described in Patent Document 3 is intended to improve wet performance while suppressing deterioration of rolling resistance, and the wear performance is not considered.

  In view of the above facts, the present invention has an object to achieve both gentle handling stability and wear performance.

  The invention of claim 1 comprises a tread having a circumferential main groove formed in the tire circumferential direction, a transverse main groove formed in a direction intersecting the circumferential main groove and arranged in the tire circumferential direction, In a pneumatic radial tire including a main groove and a land portion row formed by connecting land portions defined by the circumferential main grooves in the tire circumferential direction, the number of the circumferential main grooves is four or more. Each of the shoulder region land portion rows adjacent to the end circumferential main groove closest to the ground contact end of the tread on both sides of the tire equatorial plane and positioned on the outer side in the tire width direction than the end circumferential main groove, respectively. The contact width is 15% or more and 25% or less of the total contact width of the tread, and the contact length in the tire circumferential direction at a position of 3 mm from the tire equatorial plane side to the outer side in the tire width direction in the shoulder region land portion row. a and the shoulder region land B / a is 0.4 or more and 0.7 or less, where b is the contact length in the tire circumferential direction at a position 3 mm inward in the tire width direction from the contact end of the tread in the row. Yes.

  The tread contact condition at this time is based on the standard described in STANDARDS MANUAL issued by ETRTO in 2003. The rim used is the standard rim, the internal pressure is the air pressure corresponding to the maximum load capacity in the applicable size and ply rating. 88%, load is 81% of maximum load capacity. The standard may be JATMA or TRA.

  Here, the reason why the contact width of the shoulder region land row is set to 15% or more and 25% or less of the total contact width of the tread is that if it falls below this, shoulder fall wear is likely to occur in the shoulder region land row. This is because when the number of circumferential main grooves is four or more, the width of the other land portion rows cannot be sufficiently secured.

  In addition, the lower limit of b / a is set to 0.4. It is physically difficult to lower b / a while widening the shoulder region land portion row, and 0.4 is considered to be the limit. The reason why the upper limit is set to 0.7 is that the smaller the numerical value, the more likely it is that the increase in the contact pressure at the contact end can be suppressed against the increase in load. It is because it becomes difficult to suppress the rise of the.

  In the pneumatic radial tire according to claim 1, since the contact length in the tire circumferential direction in the vicinity of the contact end of the tread is shortened, the contact pressure in the shoulder region land portion row near the contact end of the tread decreases. The contact pressure in the center area of the tread increases, and the contact pressure is made uniform.

  If the contact length in the tire circumferential direction in the vicinity of the contact end of the tread is simply shortened, the contact area of the tread becomes small and the cornering power is insufficient. However, in the pneumatic radial tire according to claim 1, By increasing the contact width of the area land part row to 15% or more and 25% or less of the total contact width of the tread, the wear volume is increased, and the decrease in the cornering power due to the shortened contact length is compensated. .

  In this way, by shifting the ground pressure and wear volume from the grounded end side of the tread to the center region side, shoulder wear during turning is prevented without reducing cornering power, and gentle steering stability is achieved. And wear performance.

  According to a second aspect of the present invention, in the pneumatic radial tire according to the first aspect, the intermediate region land portion row located on the inner side in the tire width direction than the end circumferential main groove on at least one side of the tire equatorial plane is provided. The first horizontal main grooves and the second horizontal main grooves having different groove shapes are alternately arranged in the tire circumferential direction, and the first horizontal main grooves have inner sides that open to the circumferential main grooves on the inner side in the tire width direction. The groove width of the opening is formed narrower than the groove width of the outer opening that opens in the circumferential main groove on the outer side in the tire width direction.

  In the pneumatic radial tire according to claim 2, since the first horizontal main grooves and the second horizontal main grooves having different groove shapes are alternately arranged in the intermediate region land portion row in the tire circumferential direction, the shoulder region land portion The width in the tire circumferential direction of each land portion in the intermediate region land portion row, which is narrowed because the width of the row is secured, is increased by the amount by which the groove width of the first horizontal main groove is reduced. The hydroplaning performance and the land rigidity can be balanced.

  According to a third aspect of the present invention, in the pneumatic radial tire of the first or second aspect, a lug groove that does not penetrate the shoulder region land portion row in the tire width direction is formed in the shoulder region land portion row. It is characterized by being.

  In the pneumatic radial tire according to claim 3, since the rigidity of the shoulder region land portion row is moderately reduced by the lug groove, even if the ground contact pressure at the ground contact end becomes high under heavy load, Steering stability is not impaired by the generation of force.

  As described above, according to the pneumatic radial tire of the present invention, there is an excellent effect that both gentle steering stability and wear performance can be achieved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The pneumatic radial tire 10 according to the present embodiment is a land divided into a tread 12 by a circumferential main groove 14, a transverse main groove 16, and the transverse main groove 16 and the circumferential main groove 14 in FIG. The portion 18 includes a land portion row 20 formed continuously in the tire circumferential direction.

  The circumferential main grooves 14 are grooves formed on the tread 12 in the tire circumferential direction, and for example, four or more are formed.

  The horizontal main grooves 16 are grooves formed in a direction intersecting with the circumferential main grooves 14 and arranged in the tire circumferential direction.

  In the land portion row 20, a shoulder region land portion row 20 </ b> A adjacent to the end circumferential main groove 14 </ b> A closest to the ground contact end 12 </ b> A of the tread 12 and positioned on the outer side in the tire width direction than the end circumferential main groove 14 </ b> A. And an intermediate region land row 20B located on the inner side in the tire width direction from the end circumferential main groove 14A, and a center land portion row 20C as a center rib located on the tire equatorial plane CL, for example.

  On both sides of the tire equatorial plane CL, each ground contact width WS of the shoulder region land row 20A is 15% or more and 25% or less of the total ground contact width W of the tread 12.

  The contact length in the tire circumferential direction at a position of 3 mm on the outer side in the tire width direction from the tire equatorial plane CL side in the shoulder region land portion row 20A is a, and the tire width direction from the contact end 12A of the tread 12 in the shoulder region land portion row 20A. When the contact length in the tire circumferential direction at a position of 3 mm inside is b, b / a is 0.4 or more and 0.7 or less.

  The tread contact condition at this time is based on the standard described in STANDARDS MANUAL issued by ETRTO in 2003. The rim used is the standard rim, the internal pressure is the air pressure corresponding to the maximum load capacity in the applicable size and ply rating. 88%, load is 81% of maximum load capacity. The standard may be JATMA or TRA.

  In the intermediate region land row 20B on at least one side of the tire equatorial plane CL, first lateral main grooves 16A and second lateral main grooves 16B having different groove shapes are alternately arranged in the tire circumferential direction.

  In the first lateral main groove 16A, the groove width of the inner opening 22 that opens to the circumferential main groove 14 on the inner side in the tire width direction is the circumferential main groove (end portion circumferential main groove 14A) on the outer side in the tire width direction. It is formed narrower than the groove width of the outer opening 24 that opens.

  A lug groove 26 that does not penetrate the shoulder region land portion row 20A in the tire width direction is formed in the shoulder region land portion row 20A. Instead of the lug grooves 26, land rigidity may be reduced by forming sipes or holes.

  Here, considering the mechanism of shoulder drop wear, it is considered that the shoulder drop wear is caused by an increase in input to the tire due to securing of lateral force (cornering power) or the like as a whole tire. In particular, the shoulder drop wear is caused by a large energy burden on the shoulder region land portion row 20A with respect to the central region (for example, the intermediate region land portion row 20B and the central land portion row 20C) of the land portion row 20. To do.

  Since the wear itself occurs due to the dominant influence of the occurrence of slip in the land portion row 20, the shoulder drop wear is caused by the concentration of contact pressure on the shoulder region land portion row 20A and the amount of slip in the shoulder region land portion row 20A. Can be considered as a combined phenomenon.

  Also, considering the energy loss, the energy loss is the contact pressure at the contact end 12A × the amount of slip. Therefore, in order to reduce the energy loss, the tire turning angle and the ground contact when the tire lateral force is to be secured. The key is to suppress the contact pressure at the end 12A.

  Next, considering the steering stability mechanism, the rigidity balance between the tire case part and the top part is important for steering stability, but as a characteristic, by ensuring the absolute level of cornering power, It is necessary to suppress the turning angle and improve responsiveness. For that purpose, it is necessary to increase the lateral rigidity in the land portion of the tread, which can be realized by widening the land portion in the tire width direction, and in particular, it is effective to widen the width of the shoulder region land portion row 20A. It is.

  On the other hand, it is also important to make the grounding load change characteristic gentle so that the cornering power changes linearly so as not to cause a sudden lateral force change with respect to the load change.

  Considering the above-described shoulder drop wear and steering stability mechanism, as a countermeasure for the land portion row 20, first, the shoulder region land portion row 20A is set wide in the width direction to increase the wear volume, and the cornering power is absolute. As one means for improving the land portion rigidity of the central land portion row 20C and the intermediate region land portion row 20B and suppressing the load dependency in order to secure the level, the land portion rigidity of the shoulder region land portion row 20A. Can be set to a moderately low value (particularly, the rigidity of the ground contact end 12A under high load can be reduced).

  Basically, it is desirable to set the rigidity of the land portion row 20 to be higher, but for the shoulder region land portion row 20A in which the ground pressure is increased at high loads, the rigidity is moderately lowered to increase the load. The contact pressure at the time is suppressed. In the central land row 20C and the intermediate region land row 20B, it is desirable to have a balance between high rigidity and drainage, and the ground pressure is applied from the ground end 12A to the central land row 20C and the intermediate region land row 20B. In view of the shifting, it is effective to increase the rigidity of these land rows.

  Further, as a countermeasure for the cross-sectional shape of the tread 12, as the amount of change in the radius of curvature in the shoulder region land portion row 20A is set large, the contact length of the shoulder region land portion row 20A on the inner side in the tire width direction is set. It is possible to shorten the contact length of the portion near the contact end 12A.

  In general, a tire for a passenger car has a high ground pressure in the shoulder region land portion row 20A, particularly in the ground contact end 12A under a high load, in terms of size and size. This is largely due to the setting of the cross-sectional shape at the time of air filling. The ground pressure increases in the convex portion outward in the tire radial direction, and the ground pressure decreases in the concave portion.

  Therefore, as the setting of the cross-sectional shape of the tread 12, the distribution of the contact pressure is changed by partially changing the radius of curvature of the tread 12 in the cross section in the width direction so that the entire contact pressure becomes more uniform. be able to. In particular, since the influence of the radius of curvature of the shoulder region land row 20A is large, the load dependency of the cornering power is suppressed by moderating the pressure change at the ground contact end 12A with respect to the load change under actual use conditions. It becomes possible to suppress wear of the ground contact end 12A.

  By taking these measures, the ground contact shape with uniform contact pressure concentration at the contact end 12A as shown in FIG. 1 can be obtained while increasing the wear volume of the shoulder region land row 20A. In addition, by increasing the rigidity of the middle region land portion row 20B and appropriately lowering the rigidity of the shoulder region land portion row 20A (particularly, by lowering the rigidity of the ground contact end 12A under high load), the absolute level of cornering power can be reduced. It is possible to achieve both ensuring (steering stability) and reduction of wear due to shoulder fall (wear performance) by suppressing load dependency.

  In addition, as described above, when a difference in ground contact is provided between the portion closer to the inner side in the tire width direction and the portion closer to the contact end 12A in the shoulder region land portion row 20A having a higher contact pressure, the depression pattern of the land portion row 20 is provided. Since the impact component in noise is reduced, there is also a merit in noise.

  In the pneumatic radial tire 10 according to the present embodiment, since the contact length b in the tire circumferential direction in the vicinity of the contact end 12A of the tread 12 is shortened, the shoulder region land portion row 20A in the vicinity of the contact end 12A of the tread 12 is used. As the ground pressure decreases, the ground pressure in the central region of the tread 12 increases, and the ground pressure becomes uniform.

  If the contact length b in the tire circumferential direction in the vicinity of the contact end 12A of the tread 12 is simply shortened, the contact area of the tread 12 becomes small and the cornering power becomes insufficient. However, the contact width of the shoulder region land row 20A By increasing WS to 15% or more and 25% or less of the total contact width W of the tread 12, the wear volume is increased, and the decrease in the cornering power due to the decrease in the contact length b is compensated.

In this way, by shifting the ground pressure and wear volume from the ground end 12A side of the tread 12 to the center region side, shoulder wear during turning is prevented without reducing cornering power, and gentle maneuvering is performed. Both stability and wear performance can be achieved.
(Test example)
Under the conditions shown in Table 1, pneumatic radial tires according to the conventional example 1, the conventional example 2, the comparative example 1, the comparative example 2, the comparative example 3 and the example are manufactured, respectively, and the cornering power, the ground shape, the rolling resistance, and the steering are manufactured. Tests were conducted for stability, ride comfort, road noise and shoulder wear.

  The tire size is 205 / 60R16.

  In Table 1, the tread pattern of the series B means that the first horizontal main groove and the second horizontal main groove are alternately arranged in the intermediate region land portion row and does not penetrate the land portion in the shoulder region land portion row. The lug groove is formed, and the series A tread pattern does not have any of them.

  In FIG. 2, R1 in the shape setting is a curvature radius in the tire cross section of the central land portion row 20C and the middle region land portion row 20B, and R2 is a curvature radius in the tire cross section of the shoulder region land portion row 20A. . R1 / R2 is indicated by an index when the conventional example is set to 100, and the larger the numerical value, the greater the difference between R1 and R2.

  The evaluation of the cornering power is indicated by an index when the conventional example 1 is set to 100. The absolute level is better as the numerical value is larger, and the load dependency is better as the numerical value is smaller. Show.

  As for the ground contact shape, the smaller b / a is, the smaller the contact pressure concentration near the ground contact end is.

  The rolling resistance is a value measured by a drum testing machine and is indicated by an index when the conventional example 1 is set to 100. The smaller the numerical value, the lower the rolling resistance.

  Regarding the driving stability and ride comfort, the driver's feeling evaluation is performed, and the larger the value, the better the result.

  The road noise was measured three times using a microphone installed on the window side near the driver's ear position, and the average value (overall value (OA value)) was calculated. Table 1 shows the relative difference in noise when Conventional Example 1 is used as a reference. Traveling conditions are an internal pressure of 220 kPa, a speed of 60 km / h, and a load equivalent to two passengers.

  The shoulder fall wear is the ratio of the average wear amount of the shoulder region land portion to the average wear amount of the central land portion row, and is indicated by an index with the conventional example 1 being 100, and the smaller the value, the better the result. It is shown that.

  According to this test example, in Comparative Example 1 having the series A tread pattern, the shoulder drop wear is reduced and the absolute level of cornering power is improved, but the load dependency is not improved so much. The degree of pressure concentration remains slightly good (based on Conventional Example 1). In addition, the rolling resistance increases conversely, and the evaluations of the handling stability and the riding comfort are only the same as those of the conventional example 1, and the road noise is also reduced by 0.1 dB.

  Conventional example 2 having a series B tread pattern has R1 / R2 of 100, and WS / W and b / a do not satisfy the conditions of the present invention. As in Example 1, the evaluation of steering stability and riding comfort is only slightly improved. The degree of contact pressure concentration is the same as in Conventional Example 1.

  In Comparative Example 2, R1 / R2 is 200, and b / a satisfies the conditions of the present invention, but WS / W does not satisfy the conditions of the present invention, so cornering power, ground pressure concentration, and road noise. However, the steering stability and ride comfort have not improved so much, and the reduction in shoulder wear is only 3%.

  In Comparative Example 3, R1 / R2 is 150 and WS / W satisfies the conditions of the present invention, but b / a does not satisfy the conditions of the present invention, so that cornering power and steering stability are improved. However, load dependency, contact pressure concentration, riding comfort and road noise are not improved so much. On the other hand, the rolling resistance increases, and the shoulder wear is only reduced by 2%.

  In the examples according to the present invention, all items are improved in a well-balanced manner, and particularly the shoulder drop wear is greatly reduced to 5%.

It is a figure which shows the tread pattern and grounding state in a pneumatic radial tire. It is sectional drawing of a pneumatic radial tire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Pneumatic radial tire 12 Tread 12A Grounding end 14 Circumferential main groove 14A End circumferential main groove 16 Horizontal main groove 16A First horizontal main groove 16B Second horizontal main groove 18 Land portion 20 Land portion row 20A Shoulder region land portion Row 20B Middle region land portion row 22 Inner opening 24 Outer opening 26 Lug groove W Total ground width WS Shoulder region ground width

Claims (3)

The tread has a circumferential main groove formed in the tire circumferential direction, a transverse main groove formed in a direction intersecting the circumferential main groove and arranged in the tire circumferential direction, the transverse main groove and the circumferential main groove. In a pneumatic radial tire provided with a land portion row formed by connecting land portions divided by grooves in the tire circumferential direction,
The number of the circumferential main grooves is 4 or more,
The ground contact width of each shoulder region land portion row adjacent to the end circumferential main groove closest to the ground contact edge of the tread on both sides of the tire equatorial plane and positioned on the outer side in the tire width direction than the end circumferential main groove, respectively. Is not less than 15% and not more than 25% of the total contact width of the tread,
The contact length in the tire circumferential direction at a position of 3 mm from the tire equatorial plane side to the tire width direction outer side in the shoulder region land portion row is a, and the tire width direction from the contact end of the tread in the shoulder region land portion row B / a is 0.4 or more and 0.7 or less, where b is the contact length in the tire circumferential direction at a position of 3 mm inside,
Pneumatic radial tire characterized by. A first horizontal main groove and a second horizontal main groove having different groove shapes from each other are arranged in the middle region land portion row located on the inner side in the tire width direction than the end circumferential main groove on at least one side of the tire equator plane. Alternately arranged in the circumferential direction,
In the first horizontal main groove, the groove width of the inner opening that opens in the circumferential main groove on the inner side in the tire width direction is larger than the groove width of the outer opening that opens in the circumferential main groove on the outer side in the tire width direction. Is also narrowly formed,
The pneumatic radial tire according to claim 1.   The pneumatic radial tire according to claim 1 or 2, wherein a lug groove that does not penetrate the shoulder region land portion row in the tire width direction is formed in the shoulder region land portion row.

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