JP4602806B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire that can improve braking performance without impairing wear performance or rolling resistance performance.

  Conventionally, in a pneumatic tire, as a technique for improving braking performance, it is common to form a tread cap with a rubber compound having high frictional resistance. However, with this method, although the braking performance is improved, it is predicted that the wear performance and the rolling resistance performance are deteriorated.

  Incidentally, in Japanese Patent Laid-Open No. 7-1913 (Patent Document 1), the carcass cord driving density in the carcass layer is changed in the tire circumferential direction in order to reduce noise without impairing the tire performance and riding comfort. Is disclosed.

  Further, in Japanese Patent Laid-Open No. 10-53979 (Patent Document 2), the driving interval of the carcass cord in the carcass layer is set so that the driving interval at the crown center line portion is larger than the driving interval at the bead folding portion. Are disclosed.

Japanese Patent Application Laid-Open No. Hei 6-48113 (Patent Document 3) discloses a cord structure of a belt reinforcing layer disposed on the outer side of the belt layer in order to reduce rolling resistance, and the strength per unit of cord and the hitting force. It is disclosed that the value of the product with the number of inclusions is larger in the central area portion of the belt reinforcing layer than in the side area portion.
Japanese Patent Laid-Open No. 7-1913 JP-A-10-53979 JP-A-6-48113

  Although the technique disclosed in Patent Document 1 discloses changing the cord driving density in the carcass layer, it is a change in the tire circumferential direction, and the cord driving density is varied in the tire width direction. This is not disclosed.

  Moreover, in the technique disclosed in Patent Document 2, although the relationship between the crown center line portion and the bead folding portion is disclosed with respect to the driving density of the carcass cord, the driving force is different between the tread center portion and the shoulder portion. The point of density is not disclosed.

  On the other hand, Patent Document 3 discloses a configuration in which the cord driving density at the tread shoulder portion of the belt reinforcing layer is made smaller than the cord driving density at the tread center portion. However, the technique disclosed in this document reduces the stress generated along with the interlayer strain by reducing the driving density at the tread shoulder portion, thereby reducing the rolling resistance at the shoulder portion. However, nothing is disclosed about improving the braking performance by increasing the loss energy at the tread shoulder portion by the above-described configuration.

  The present invention relates to a cord structure of a belt layer and a carcass layer. By changing the driving density at the tread shoulder portion and the tread center portion, the pneumatic tire can improve the braking performance without causing a decrease in the reverse performance. The purpose is to provide.

  The inventor considered that the energy required for braking, that is, the energy consumed during braking, is almost equivalent to the loss energy due to the hysteresis of the rubber. For this reason, a tire with a large difference between the loss energy during braking and the loss energy during steady load loading consumes a large amount of energy and is considered to improve braking performance. As a result of analyzing the loss energy, the portion where the loss energy is large is the topping rubber between the belt layer having the maximum width and the belt layer superimposed thereon, and the topping rubber of the carcass layer. It was found that the energy loss rate from the tread shoulder portion to the layer and the carcass layer from the tread shoulder portion to the buttress portion contributed greatly. Therefore, if there is a belt layer and a carcass layer and further a belt reinforcement layer so that the loss energy of these parts is increased, if the cord driving density in the reinforcement layer is changed, the wear performance, rolling resistance performance, etc. The present inventors have considered that braking performance can be improved without impairing the reverse performance of the vehicle.

  That is, the pneumatic tire according to the present invention includes a carcass composed of at least one carcass layer that is locked by a bead core of a bead portion through a sidewall portion from a tread portion, and a radially outer side of the carcass in the tread portion. A pneumatic tire including a belt composed of a plurality of belt layers arranged, wherein the belt layer has a belt cord driving density in a tread shoulder portion smaller than a belt cord driving density in a tread center portion, In the carcass layer, the driving density of the carcass cords in the tread shoulder portion and the buttress portion is set smaller than the driving density of the carcass cords in the tread center portion.

  Further, in the case where the belt reinforcing layer arranged on the outer side in the radial direction of the belt is provided, in addition to the setting of the driving density described above, the cord driving density in the tread shoulder portion is further related to the belt reinforcing layer. It is preferable that it is set to be smaller than the cord driving density in the portion.

  In the pneumatic tire of the present invention, the driving density of the belt cord at the tread shoulder portion in the belt layer is set smaller than the driving density at the tread center portion. In the carcass layer, the driving density of the carcass cord at the tread shoulder portion and the buttress portion on the outer side in the width direction is set smaller than the driving density at the tread center portion. By adopting such a configuration, the restraining force in the circumferential direction of the shoulder portion can be reduced. Accordingly, when a large force acts on the tire in the front-rear direction as in braking, the loss energy is also increased by increasing the distortion energy of the shoulder portion compared to the center portion. Therefore, energy required for braking can be earned, and braking performance can be improved.

  In particular, since the shear strain increases from the shoulder portion of the belt layer and the shoulder portion of the carcass layer to the buttress portion, which greatly contributes to the energy loss rate, the braking performance is effectively improved without impairing other performance. can do. In addition, since it is not necessary to change the composition of the tread cap rubber in order to improve the braking performance, it is possible to suppress a decrease in the contradiction performance such as wear performance and rolling resistance performance.

  Also, if there is a belt reinforcement layer, by setting the cord driving density at the tread shoulder portion to be smaller than the driving density at the tread center portion, the circumferential restraint at the tread shoulder portion is also provided. The force is reduced, the shear strain of the rubber between the cords at this portion can be increased, the loss energy can be effectively increased, and the braking performance can be improved.

  Hereinafter, a pneumatic tire according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view in the tread width direction of a pneumatic tire 10 according to a first embodiment of the present invention. The tire 10 includes a pair of left and right bead portions 12 and sidewall portions 14, and a tread portion 16 that extends between the sidewall portions 14.

  The bead portion 12 is provided with an annular bead core 18 formed by winding a bead wire in the tire circumferential direction, and a rubber bead filler 20 is disposed on the outer periphery in the radial direction of the bead core 18.

  A carcass 22 is provided between the pair of left and right bead cores 18. The carcass 22 passes through the sidewall portion 14 from the tread portion 16, and is locked by being folded back by the bead core 18 in the bead portion 12. The carcass 22 includes at least one carcass layer in which carcass cords made of organic fiber cords and the like are arranged at right angles to the tire circumferential direction. In this embodiment, the carcass layer 24 includes one carcass layer 24. The carcass layer 24 is configured by covering the carcass cord with a topping rubber.

  A belt 26 is disposed on the outer side in the radial direction of the carcass 22 in the tread portion 16. The belt 26 is provided so as to overlap the radial outer peripheral surface of the crown portion of the carcass 22, and at least a belt layer formed by inclining and arranging a non-extensible belt cord such as a steel cord at a shallow angle with respect to the tire circumferential direction. Two layers are overlapped so that the belt cords intersect each other, and in this embodiment, the belt cord is composed of two layers of an inner first belt layer 28 and an outer second belt layer 30. Among them, the inner first belt layer 28 adjacent to the carcass 22 is wider, that is, the first belt layer 28 is the maximum width belt layer. These belt layers 28 and 30 are formed by covering the belt cord with a topping rubber.

  In this embodiment, the belt layers 28 and 30 are configured to satisfy the following formula (1) in the present embodiment.

EB (CE)> EB (SH) (1)
In the formula, EB (CE) is a belt cord driving density (book / 25.4 mm) in the tread center portion CE, and EB (SH) is a belt cord driving density (book / book) in the tread shoulder portion SH. 25.4 mm).

  Here, the driving density is the number of drivings per predetermined width (25.4 mm) in the direction orthogonal to the longitudinal direction of the cord (the same applies to the carcass cord and the belt reinforcing layer cord). Further, the tread shoulder portion SH is a side portion in the range of 15 to 35% of the width W from each width direction end 28A of the first belt layer (maximum width belt layer) 28 in the tire 10 after vulcanization molding. It is an area portion, more preferably a side area portion within a range of 20 to 30% of the width W. In this embodiment, 25% of the width W, that is, the width W is set in the tread width direction. It is the outer side section when divided into four equal parts. The tread center portion CE is a remaining central area portion of the tread shoulder portion SH in the width W of the first belt layer 28. In this embodiment, the center when the width W is equally divided into four in the tread width direction. It is a central area part consisting of two sections.

  In the present embodiment, the carcass layer 24 is also configured to satisfy the following formula (2).

EP (CE)> EP (SH) ≧ EP (BAT) (2)
In the formula, EP (CE) is the driving density of the carcass cord (book / 25.4 mm) in the tread center portion CE, and EP (SH) is the driving density of the carcass cord in the tread shoulder portion SH (book / 25.4 mm), and EP (BAT) is the driving density of the carcass cord in the buttress portion BAT (pieces / 25.4 mm). Here, the buttress portion BAT is a region outside the width direction end 28A of the first belt layer 28 in the width direction. In this embodiment, the largest tire extends from the width direction end 28A along the tire outer periphery. It is an area up to a cross-sectional width position 32 (a position where the width is maximum in a cross section obtained by cutting the tire in the tread width direction).

Regarding the driving density of the belt cord and the carcass cord, the ratio of the tread shoulder portion SH to the center portion CE is preferably as follows.
EB (SH) / EB (CE) = 0.4-0.9
EP (SH) / EP (CE) = 0.4-0.9
When the ratio between the shoulder portion and the center portion is larger than the above upper limit, the effect margin of the target performance is small. Conversely, when the ratio is smaller than the above lower limit, there is a concern that the durability performance is deteriorated.

  As described above, specific means for changing the cord driving density is not particularly limited, but in the present embodiment, as shown in FIG. 2, the arrangement width of each cord is changed.

  As shown in FIG. 2, since the belt cords of the belt layers 28 and 30 are inclined and arranged at a predetermined angle (usually 15 to 25 °) with respect to the tire circumferential direction, the wide belt cords extending over the entire width in the width direction. By combining the belt cords 36 and 40 having narrow widths extending between both ends in the width direction of the tread center portion CE, the tread center portion CE and the tread shoulder portion SH can be made dense. The arrangement of the wide belt cords 34 and 38 and the narrow belt cords 36 and 40 may be alternated as shown in FIG. The ratio between the center portion and the center portion can be appropriately provided so as to be within the above range.

  Further, since the carcass cords of the carcass layer 24 are arranged substantially at right angles (usually 90 to 70 °) with respect to the tire circumferential direction, the wide carcass cord 42 and the tread center portion CE spanned between the left and right bead portions 12. By combining the narrow carcass cords 44 extending between both ends in the width direction, the tread center portion CE and the tread shoulder portion SH can be roughened. About arrangement | positioning structure of both, like a belt cord, it can provide suitably so that ratio of a shoulder part and a center part may become in the said range.

  In the pneumatic tire 10 of the present embodiment configured as described above, the belt cord driving density in both the belt layers 28 and 30 and the carcass cord driving density in the carcass layer 24 are given specific roughness as described above. Since the belt 26 is configured, the circumferential restraining force is reduced in the shoulder portion SH, and the carcass 22 is reduced in the circumferential direction from the shoulder portion SH to the buttress portion BAT. For this reason, the shear strain of the rubber (topping rubber) between the cords at these parts increases, so that the loss energy at these parts can be effectively increased. Therefore, energy required for braking can be effectively earned, and braking performance can be improved.

  FIG. 3 is a cross-sectional view in the tread width direction of a pneumatic tire 50 according to the second embodiment of the present invention. This embodiment is different from the first embodiment in that a belt reinforcing layer 52 is provided on the outer side in the radial direction of the belt 26.

  The belt reinforcing layer 52 has a width substantially equal to the width W of the first belt layer 28, and is overlapped on the outer peripheral surface of the belt 26 so as to cover the entire width of the belt 26, and is substantially parallel to the tire circumferential direction (normal tires). It is comprised from organic fiber cords, such as nylon arranged in 0-5 degrees with respect to the circumferential direction.

  In this case, in addition to the above formulas (1) and (2), the belt reinforcing layer 52 is configured to satisfy the following formula (3).

EC (CE)> EC (SH) (3)
In the formula, EC (CE) is the cord driving density (25.4 mm) of the reinforcing layer 52 in the tread center portion CE, and EC (SH) is the cord density of the reinforcing layer 52 in the tread shoulder portion SH. The driving density (book / 25.4 mm).

Regarding the cord driving density of the belt reinforcing layer 52, the ratio of the tread shoulder portion SH to the center portion CE is preferably as follows.
EC (SH) / EC (CE) = 0.3-0.9
When this ratio is larger than the upper limit, the effect margin of the target performance is small. Conversely, when the ratio is smaller than the lower limit, there is a concern that the durability performance is deteriorated.

  Although the specific means for changing the cord driving density of the belt reinforcing layer 52 is not particularly limited, in this embodiment, as shown in FIG. 4, the driving interval of the cord 54 extending in the tire circumferential direction is changed. Yes. That is, by reducing the cord 54 driving interval in the tread center portion CE and increasing the cord 54 driving interval in the tread shoulder portion SH, the cord 54 driving density in the tread shoulder portion SH is reduced. Yes.

  In the case where the belt reinforcing layer 52 is provided in this way, the belt 54 also has the belt 54 by setting the driving density of the cord 54 in the tread shoulder portion SH to be smaller than the driving density in the tread center portion CE. The restraining force in the circumferential direction at the shoulder portion SH of the reinforcing layer 52 can be reduced, and the shear strain of rubber at this portion can be increased. Therefore, the loss energy can be effectively increased and the braking performance can be improved. Can do.

  Other configurations of the second embodiment are the same as those of the first embodiment described above, and the same operational effects are achieved.

  FIG. 5 shows an example of a modification for increasing the density of belt cord driving. That is, as shown in FIG. 5, in the belt layer 28, the angle of the belt cord 60 with respect to the tire circumferential direction is changed between the tread center portion CE and the tread shoulder portion SH, and the angle of the cord 60A at the tread shoulder portion SH. θ1 is set to be larger than the angle θ2 of the cord 60B at the center portion CE, so that the driving density at the tread shoulder portion SH of the belt cord 60 is smaller than the driving density at the tread center portion CE. ing. The belt cord driving density can also be changed by such a method. When the belt cord 60 is refracted in this way, the driving density of the tread center portion CE and the tread shoulder portion SH is the number of driving per unit length in the direction orthogonal to the longitudinal direction of the cord in each region. It is obtained by measuring.

  In the first and second embodiments, an edge ply that covers only the end area in the width direction of the belt 26 may be provided. The edge ply, like the belt reinforcing layer 52, is made of an organic fiber cord such as nylon that is arranged substantially parallel to the tire circumferential direction. When the edge ply is provided, the cord driving density of the edge ply may be constant in the tread width direction.

(Example 1 and Comparative Examples 1 and 2)
As the tires of Example 1 and Comparative Examples 1 and 2, pneumatic radial tires having a cross-sectional structure shown in FIG. 1 were produced with a tire size of 225 / 45ZR17. The configurations of the belt layers 28 and 30 and the carcass layer 24 in each tire are as shown in Table 1 below (the driving density in the table is a value after vulcanization). Here, Comparative Example 1 is a control tire, and Comparative Example 2 is a tire whose braking performance is improved by the conventional method. Compared with Comparative Example 1, the rubber composition of the tread cap improves the braking performance. The tire has the same configuration as that of Comparative Example 1 except that the composition of resistance is changed. Further, Example 1 is a tire having the same configuration as Comparative Example 1 except that the cord configurations of the belt layer and the carcass layer are changed as shown in Table 1 with respect to Comparative Example 1.

  For each tire of Example 1 and Comparative Examples 1 and 2, braking performance and wear performance were evaluated. The evaluation method is as follows.

-Braking performance: Rim used: 17 x 7.5 JJ, air pressure: 220 kPa, and each tire is mounted on a 2500 cc passenger car. After accelerating the passenger car to 100 km / h in the run-up section and maintaining the test speed of 100 km / h in the initial speed adjustment section, at the same time as passing through the braking start point, the brake pedal is quickly stepped on and maintained until it stops. Read the stop distance. The result is an inverse exponential display with the stopping distance of Comparative Example 1 being 100, and the larger the value, the better the braking performance.

Wear performance: Rim used: 17 x 7.5 JJ, air pressure: 220 kPa, each tire is mounted on a 2500 cc passenger car and travels 10,000 km on a test course (mixed urban area and highway). The amount of wear of the tread center portion CE and the tread shoulder portion SH is measured, and the average of both is calculated. The results are indexed with the wear amount of Comparative Example 1 being 100, and the larger the value, the better the wear performance.

  As shown in Table 1, in Comparative Example 2 according to the conventional method, although the braking performance was improved as compared with Comparative Example 1, the wear performance was deteriorated. On the other hand, in Example 1, the braking performance was improved without impairing the wear performance.

(Example 2 and Comparative Examples 3 to 5)
As the tires of Example 2 and Comparative Examples 3 to 5, pneumatic radial tires having a cross-sectional structure shown in FIG. 3 were produced with a tire size of 225 / 45ZR17. The configurations of the belt layers 28 and 30, the carcass layer 24, and the belt reinforcing layer 52 in each tire are as shown in Table 2 below (the driving density in the table is a value after vulcanization). Here, Comparative Example 3 is a control tire, and Comparative Example 4 is a tire whose braking performance is improved by a conventional method. Compared to Comparative Example 3, the rubber composition of the tread cap improves the braking performance. The tire has the same configuration as that of Comparative Example 3 except that the composition of resistance is changed. Further, in Comparative Example 5 and Example 2, the cord configurations of the belt layer, the carcass layer, and the belt reinforcing layer were changed as shown in Table 2 with respect to Comparative Example 3, and the other configurations were the same as those in Comparative Example 3. Tire.

About each tire of Example 2 and Comparative Examples 3-5, braking performance and wear performance were evaluated. The evaluation method is as described above.

  The results are as shown in Table 2. In Comparative Example 4 using the conventional method, the braking performance was improved compared to Comparative Example 3, but the wear performance was deteriorated. Further, in Comparative Example 5 in which only the cord configuration of the belt reinforcing layer is provided, the shoulder portion of the belt layer and the carcass layer is not reduced in the circumferential restraining force similarly to the center portion, or the braking performance is improved. Was not recognized. On the other hand, in Example 2, the braking performance was improved without impairing the wear performance.

It is a tread width direction sectional view of the pneumatic tire concerning a 1st embodiment. It is a development top view of the belt and carcass in a 1st embodiment. It is a tread width direction sectional view of the pneumatic tire concerning a 2nd embodiment. It is a development top view of a belt, a carcass, and a belt reinforcement layer in a 2nd embodiment. It is a top view of the belt layer which concerns on the example of a change.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10,50 ... Pneumatic tire, 12 ... Bead part, 14 ... Side wall part, 16 ... Tread part, 18 ... Bead core, 22 ... Carcass, 24 ... Carcass layer, 26 ... Belt, 28 ... 1st belt layer (maximum width) Belt layer), 30 ... second belt layer, 34, 36, 38, 40, 60 ... belt cord, 42, 44 ... carcass cord, 52 ... belt reinforcing layer, 54 ... cord of belt reinforcing layer, CE ... tread center portion , SH ... tread shoulder, BAT ... buttress

Claims (2)

A carcass composed of at least one carcass layer locked from a tread portion through a sidewall portion by a bead core of a bead portion, and a belt composed of a plurality of belt layers arranged radially outside the carcass in the tread portion. A pneumatic tire comprising:
The belt layer has a belt cord driving density in the tread shoulder portion smaller than a belt cord driving density in the tread center portion,
The pneumatic tire according to claim 1, wherein the carcass layer has a carcass cord driving density at a tread shoulder portion and a buttress portion set smaller than a carcass cord driving density at a tread center portion. A carcass composed of at least one carcass layer locked from a tread portion through a sidewall portion by a bead core of a bead portion, and a belt composed of a plurality of belt layers arranged radially outward of the carcass in the tread portion. A pneumatic tire comprising a belt reinforcing layer disposed radially outward of the belt,
The belt layer has a belt cord driving density in the tread shoulder portion smaller than a belt cord driving density in the tread center portion,
In the carcass layer, the driving density of the carcass cord in the tread shoulder portion and the buttress portion is smaller than the driving density of the carcass cord in the tread center portion,
The pneumatic tire according to claim 1, wherein the belt reinforcing layer has a cord driving density at a tread shoulder portion set smaller than a cord driving density at a tread center portion.

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