JPH06286405A - Peneumatic radial tire - Google Patents

Abstract

PURPOSE:To enable adaptation to a heavy load tire, particularly to this kind of tire in a pneumatic radial tire which has a deep and wide annular recessed part almost in the central part of a tread surface and has excellent drainage performance. CONSTITUTION:A hoop material 3 to reduce partially a diameter of a crown part of a carcass 1 of a tire is wound in the circumferential direction, and belt layer 4a and 4b are arranged on the outside in the tire diameter direction of the carcass, and a tread 5 is arranged next, and an annular recessed part 6 formed by recessing a part corresponding to the hoop material of a tread surface to the inside in the tire diameter direction is arranged along a peripheral line of the tread, and the hoop material is composed of a fiber cord of polypara phenylene benzo bistiazole or polypara phenylene benzo bisoxazole having strength of not less than 30g/d.

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 having a deep and wide annular recess in the center of the tread tread surface and having excellent drainage performance. It is a measure.

[0002]

2. Description of the Related Art This annular recess is a groove which is wide and deep by denting the approximately central region of the tread surface in the radial direction, and a pneumatic tire having such an annular recess operates under the action of the annular recess. Therefore, the drainage performance of the tire can be improved.

However, in such a conventional technique, in order to maintain a shape in which an annular recess is provided in the central region of the tread tread, that is, a so-called twin tread shape, the diameter of the carcass is partially inside the recess in the tire radial direction. It is necessary to partially reduce the size of the carcass and so-called ratchet tightening, and it is advantageous to dispose a hoop member that is wound in the circumferential direction of the carcass.

With regard to the tire having the hoop member arranged therein, Japanese Patent Laid-Open No. 232101/1992 discloses that the bending rigidity of the hoop member is reduced so that the annular recess is bent inward in the tire radial direction in the tread tread surface. It is disclosed to prevent the occurrence of separation near the hoop material.

[0005]

However, when this type of tire is applied to a heavy load tire such as a truck / bus tire, which is used under a high internal pressure and a heavy load, its twin tread shape is used. To maintain
It is necessary to increase the rattling force exerted on the carcass of the hoop material, in other words, to increase the circumferential tensile rigidity of the hoop material to counter high internal pressure and heavy load. Therefore, in heavy-duty tires and the like, it is difficult to reduce the bending rigidity of the hoop material according to the proposal of the above publication, that is, to increase the circumferential tensile rigidity of an annular object that extends in the circumferential direction such as the hoop material, The bending rigidity is also increased, and the difference in bending rigidity between the hoop material and the rubber in the vicinity of the hoop material becomes large. Therefore, the problem of separation occurring in the vicinity of the hoop material is still unsolved.

Further, in a tire having an annular concave portion, the opening width of the concave portion is larger than that of a groove of a normal tread, so that the concave portion is apt to be cut and scratched particularly when traveling on a bad road. Since the tire disclosed in the above publication uses a steel cord for the hoop material, when a deep cut scratch is received in the annular recess, the steel cord is corroded by the water entering from the scratch, and as a result, the cord is broken or separated. There is a disadvantage leading to an early failure due to.

[0007] Therefore, an object of the present invention is to propose a new tire structure capable of avoiding the separation which occurs in the vicinity of the hoop material in the tire in which the hoop material is provided inside the annular recess in the tire radial direction. .

[0008]

According to the present invention, a carcass straddling a toroidal shape between a pair of bead cores is circumferentially wound with a hoop member for partially reducing the diameter of its crown portion. A belt layer and then a tread are arranged on the outer side of the carcass in the radial direction of the tire, and an annular recess is formed along the tread circumferential line by recessing a portion of the tread surface of the tread corresponding to the hoop material inward of the tire in the radial direction. The pneumatic hoop material is a pneumatic radial tire characterized in that the hoop material is composed of a fiber cord of polyparaphenylenebenzobisthiazole or polyparaphenylenebenzobisoxazole having a strength of 30 g / d or more. is there.

Further, in carrying out the invention, in the cross section passing through the rotation axis of the tire, the contour line of the carcass divided into two peaks by tightening the hoop member is used as each crown part, and each crown part and the existing side wall. When assuming a single tire each containing, the carcass contour line of each assumed tire adjacent to each other across the annular recess, the shape of intersecting or contact each other on the tire radial inner side of the annular recess, in particular of the annular recess It is advantageous for suppressing separation on the inner side in the tire radial direction.

FIG. 1 illustrates a concrete example of a pneumatic radial tire according to the present invention, in which 1 is a bead core 2a and 2b.
In this example, a carcass consisting of a single carcass ply extending over the space is shown, and a hoop material 3 for reducing the diameter of the center of the crown portion of the carcass 1 in the width direction is wound in the circumferential direction. The crown portion is divided into two peaks 1a and 1b. Further, on the mountains 1a and 1b of the carcass 1, belt layers 4a and 4b each composed of four belt plies are arranged, and a tread 5 is provided on the outside thereof.
The tread 5 is provided with an annular recess 6 formed by denting the widthwise central portion of the tread surface inward in the tire radial direction, and a circumferential groove 7 and the like as required. Note that reference numerals 8a and 8b
Is a bead portion reinforcing layer.

In the present invention, the hoop material 3 is
A fiber cord of polyparaphenylene benzobisthiazole (hereinafter referred to as PBT) or polyparaphenylene benzobisoxazole (hereinafter referred to as PBO) having a strength of 30 g / d or more is used. That is, in order to reduce the bending rigidity of the hoop material 3 in order to suppress the separation of the hoop material 3 in the tire radial direction, it is necessary to reduce the bending rigidity of the cord itself and the cross-sectional area of the hoop material. It is valid. Therefore, it is of course possible to use a cord having low bending rigidity, but it is also possible to use a cord that can maintain the strength required for the hoop material even if the hoop material has a small cross-sectional area, that is, a cord having high strength. , Becomes essential. Such a requirement is 30g /
Advantageously achieved by a fiber cord of PBT or PBO having a strength of d or more.

Further, the rotation shaft of the tire having the above structure is
In the section through which the carcass 1 passes, as shown in FIG.
Crown the mountains 1a and 1b of carcass 1, respectively
The crown part and the existing side wall.
Including single tire T₁And T ₂Assuming that
And the assumed tires T that are adjacent to each other with the annular recess 6 interposed therebetween.₁And
And T₂Carcass contour line is the tire radial direction of the annular recess 6
Intersecting or touching each other inside, intersection P₁And P₂Well
Or contact points, by restricting the shape,
Suppression of separation on the inner side of tire 3 in the radial direction of the tire
Can be encouraged.

Next, the contour line shape of the carcass 1 according to the present invention will be more specifically shown. First, an assumed tire assumed for determining the contour line shape of the carcass 1 will be described by taking an assumed tire T ₁ having a crown 1 a on one side of the carcass ₁ as an example. That is, the straight line L ₁ parallel to the tire rotation axis drawn from the inflection point A in the central portion of the carcass 1 reduced in diameter by the hoop material 3 to the sidewall and the carcass 1
Let B be the point of intersection with and a straight line L ₂ passing through the midpoint of the line segment AB on the straight line L ₁ and perpendicular to the tire rotation axis. On the other hand, a straight line L ₃ that passes through the point C where the carcass 1 has the maximum width and is perpendicular to the tire rotation axis is determined, and the shortest distance w between the straight line L ₃ and the straight line L ₂ is obtained. Then, a straight line L ₄ perpendicular to the tire rotation axis is drawn at a position away from the straight line L ₂ on the side opposite to the straight line L ₃ by a distance w. Furthermore, starting from the inflection point A of the above and tangent to the straight line L ₄ extends in the shape forming the sidewall portion over the shape axisymmetrical existing carcass 1 from the point B, and assume a virtual carcass line CL1 . Then, the line from the virtual carcass line CL1 to the sidewall portion of the existing carcass 1 through the mountain 1a is defined as the carcass contour line of the assumed tire T ₁ .

Similarly, a carcass contour line can also be obtained for the assumed tire T ₂ (the items having the same meanings as those shown in FIG. 2 are indicated by adding “′”), and the obtained virtual carcass line CL 2 is assumed. The contour line of the carcass 1 is regulated so that the virtual carcass line CL ₁ of the tire T ₁ intersects or contacts each other inside the annular recess 6 in the tire radial direction.

[0015]

[Function] In order to reduce the bending rigidity of the hoop material conventionally made of steel cords, it is necessary to use organic fiber cords such as nylon, polyester or aramid, which have a smaller filament diameter than steel cords. However, since these organic fiber cords have lower strength per unit cross-sectional area than steel cords, the number of cords increases in order to provide the hoop material with the required strength. Then, naturally the cross-sectional area of the hoop material increases and the bending rigidity of the hoop material does not decrease,
As a result, it becomes difficult to suppress the separation.

[0016] Therefore, the inventors diligently studied a method of reducing the bending rigidity of the hoop material. As a result, the bending rigidity of the cord itself used for the hoop material is reduced, and further, the cord is reduced in order to reduce the cross-sectional area of the hoop material. It has been found that increasing the strength of itself is effective. That is,
For hoop material, PBT or PBO with a strength of 30g / d or more
By using this fiber cord, the strength comparable to that of steel cord can be obtained, and the diameter of the filaments that make up the cord is significantly smaller than that of steel cord, and the bending rigidity of the hoop material is reduced and separation is suppressed. It will be possible. Furthermore, even if the annular recess receives a cut damage and water enters from the cut damage, it does not corrode, so it is possible to avoid cord breakage and separation due to corrosion.

Here, in using the fiber cord of PBT or PBO, the twist coefficient Nt defined by the following formula (1) is
The range of 0.28 <Nt <0.60 is preferable.

## EQU1 ## Nt = N × (0.139Td / 2ρ) ^1/2 × 10 ^-3 Here, N is the number of twists per 10 cm of cord, Td is the total number of denier of cord, and ρ is the density of PBT and PBO (g / cm). ³ ) Because, when Nt is 0.28 or less, the angle formed by the cord axis and the filament is too small, and the filament is likely to be excessively strained when the cord is bent, and the fatigue resistance as a hoop material cannot be maintained. On the other hand, when Nt exceeds 0.60, the angle formed by the cord axis and the filament becomes too large, and the strength and elastic modulus of the cord decrease, making it difficult to maintain the carcass shape.

Further, in order to produce the above-mentioned high-density PBT or PBO fibers, PBT or PBO is dissolved in polyphosphoric acid or methanesulfonic acid and the solution is spun out, and then the solution is spun in an aqueous coagulation liquid via an air layer. The so-called gel-spinning method of preparation is advantageously adapted. After spinning, wash and dry,
Then, a treatment under tension is applied to adjust the elastic modulus and strength to a target.

Further, according to the present invention, as shown in FIG. 2, the carcass contour lines are formed such that the carcass contour lines of the respective assumed tires cross each other inside the annular recess in the tire radial direction. Conventionally, the circumferential tensile stress applied to the hoop material and its vicinity, which was conventionally borne by the hoop material, can now be carried by the belt layers on both sides of the hoop material, and the hoop material and the vicinity thereof are effectively covered. This will reduce the tensile stress in the direction. This is because in order to keep the virtual carcass line in a flatter shape, it is necessary to strengthen the restraining force of the crown portion of each carcass line, which increases the tensile stress load on the belt layers on both sides. Then, in the carcass line near the hoop material of the crown part, the inclination of the tangent line at the inflection point becomes closer to the tire rotation axis (horizontal line), so that the tire radial component of the tension acting on the carcass decreases and the hoop material is reduced. Since the force that tends to expand outward in the tire radial direction is reduced, the circumferential tensile stress applied to the hoop material is reduced. Therefore, even if the circumferential rigidity of the hoop material is not so high,
This kind of tire can be used for heavy loads, and the separation in the vicinity of the hoop material that occurs with the increase in the circumferential rigidity of the hoop material can be avoided.

[0020] Here, when crossing a virtual carcass line CL2 virtual carcass line CL1 and assume the tire T ₂ of the assumed tire T _1, both the amount of overlap, the straight line L ₄ are specifically shown in FIG. 2 and The distance between L ₄ ′ is 1/4 of the maximum width of the carcass 1 (distance between the straight lines L ₃ and L ₃ ′)
The following is desirable. This is because when the amount of overlap exceeds 1/4 of the maximum width of carcass 1, the curvature of the crown of each carcass peak becomes too small and the diameter of the carcass is reduced from the top of each peak. The amount of diameter becomes small, it becomes impossible to give a sufficient depth for drainage to the annular concave portion on the outer side of the hoop material, and particularly the wet property at the end of wear of the tread tread is significantly deteriorated,
There is a risk.

Next, as the hoop material, a fiber cord of PBT or PBO is wound in a spiral shape in the circumferential direction, or a bias laminated structure in which cords arranged so as to be inclined at a small angle in the circumferential direction are stacked in a direction intersecting with each other. It is preferable to use a reinforcing material.

Further, it is preferable that the belt layer is not continuous over the entire width of the tread as in a normal tire, but is divided and arranged with the annular recess as a boundary. That is, in tires used at high internal pressure such as truck and bus tires, the number of belt layers is large and the tire outer diameter is large compared to passenger car tires. The difference is very large. Therefore, when the belt layer is made continuous over the entire width of the tread, the belt layer is arranged in a largely undulating state, and at the time of tire manufacturing, the reinforcing cords are likely to be disordered in the vicinity of the annular recess, and this portion of the tire is May be the core of separation in long-term use. When a multi-layer belt is arranged, it is possible to make one of the layers continuous over the entire width of the tread as a protection layer against external damage received from the road surface.

[0023]

EXAMPLE Size 385/65 R2 according to the structure shown in FIG.
A 2.5 pneumatic radial tire (invention tire 1) was prototyped. For the hoop material, a 6.9 mm wide ribbon-like rubberized cloth with 29 d / 50 mm of 1500 d / 3 PBO fiber cord (twist number: 32 x 32, cord strength: 145 kg / strand) was struck. It was provided by spirally winding 9 layers.

As a comparison, a ribbon-shaped rubberized cloth obtained by similarly striking steel cords having a cord strength of 145 kg / piece was wound around the hoop material of the same tire in a spiral shape in 9 layers. The tires that were installed as a trial were also manufactured as comparative tires.

Further, the hoop material of the tire according to the structure shown in FIG. 2 is provided with a ribbon-shaped rubberized cloth made of the same PBO fiber cord as the above, wound in a spiral shape in six layers. Inventive tire 2 was prototyped.

The contour of the carcass 1 of the tire having the structure shown in FIG. 1 in a state where the tire is assembled in a specified rim and filled with an internal pressure of 0.5 kgf / cm ² is line segment AB: 152 mm and w: 87 mm. Similarly, in the tire having the structure shown in FIG. 2, the contour line of the carcass 1 is line segments AB: 155 mm and w: 97 mm, and the assumed amount of overlap between tires is 24.
mm (carcass maximum width: 363 mm). In each case, the annular recess 6 has an opening width of 43 mm and a depth of 27 mm.
So, it was provided at the center of the tread tread in the width direction.

The test tire thus obtained had an internal pressure of 9.
After filling with 0 kgf / cm ³ , the drum test was performed while applying a load of 5400 kg, and the drum was run at a speed of 60 km / h, and the running distance until separation occurred near the hoop material was measured. Here, internal pressure: 9.0 kgf / cm ² the carcass line after filling, the internal pressure: 0.5 kgf / cm ² is equivalent to the filling state, the annular recess was maintained after high internal pressure to a predetermined shape. These measurement results are indexed when the traveling distance of the comparative tire was 100, and as shown in Table 1, it was confirmed that the invention tire severely suppressed the occurrence of separation.

[0028]

[Table 1]

In addition, in the above-mentioned invention tire 2, in the low internal pressure state before use and the high internal pressure state during use,
Although the carcass shapes were the same, if the carcass shapes change, it is essential that at least the carcass shape under high internal pressure during use complies with the present invention. Further, although the invention is directed to the tire in which the crown portion of the carcass is divided into two peaks, if the tire in which the crown portion is divided into three or more peaks can be technically or performanceally produced. In that case, the carcass contour line of the present invention is also meaningful in that case.

[0030]

According to the present invention, it is possible to advantageously avoid the separation in the tire radial direction inner side of the annular recess, which has prevented the application of the pneumatic tire having the annular recess having excellent drainage performance to the heavy-duty tire. Therefore, the drainage performance of the heavy duty tire can be remarkably improved.

[Brief description of drawings]

FIG. 1 is a sectional view in the tread width direction of a tire according to the present invention.

FIG. 2 is a sectional view in the tread width direction of the tire according to the present invention.

[Explanation of symbols]

 1 Carcass 1a, 1b Mountain 2a, 2b Bead core 3 Hoop material 4a, 4b Belt layer 5 Tread 6 Annular recess 7 Circumferential groove 8a, 8b Bead reinforcement layer

Claims (2)

[Claims] 1. A carcass that straddles a toroidal shape between a pair of bead cores is circumferentially wound with a hoop material that partially reduces the diameter of the crown portion of the carcass. Place the belt layer, then the tread,
A pneumatic radial tire provided with an annular recess formed along the tread circumferential line by recessing a portion of the tread surface corresponding to the hoop material inward in the tire radial direction, wherein the hoop material is 30 g / d. A pneumatic radial tire comprising a fiber cord of polyparaphenylenebenzobisthiazole or polyparaphenylenebenzobisoxazole having the above strength. 2. A carcass contour line divided into two peaks by tightening the hoop material in a cross section passing through the rotation axis of the tire has each peak as a crown portion, and includes the crown portion and existing sidewalls. The pneumatic tire according to claim 1, wherein when assuming a single tire, the carcass contour lines of the respective assumed tires that are adjacent to each other with the annular recess interposed therebetween have a shape intersecting or contacting each other on the tire radial direction inner side of the annular recess. Radial tires.