JP5116449B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire excellent in belt durability, and more particularly to a radial tire for trucks and buses.

  In recent years, tires mounted on vehicles have been flattened due to demands for speeding up and flooring of vehicles, and along with this, the amount of tire tread growth in the tire radial direction when standard internal pressure is applied tends to increase further. It is known that this increase in the amount of radial growth of the tread increases the stress concentration at the end of the belt in the width direction, which in turn induces belt end separation, leading to a decrease in tire durability.

Therefore, Patent Document 1 has at least two layers of intersecting belts, each of which includes a plurality of cords or filaments that cross each other across the tire equator plane at an inclination angle of 10 to 40 ° with respect to the tire equator plane, In addition, under the cross belt, there is provided at least one crown reinforcing layer with strips in which a number of corrugated or zigzag cord or filament reinforcing elements are oriented along the tire equator, to increase the radial growth of the tire. Suppression techniques have been proposed.
JP-A-2-208101

  However, the flattening of tires accompanying the increase in the speed of vehicles has been further promoted. Specifically, tires having a flatness ratio of less than 0.70, which is the ratio of the cross-sectional height to the cross-sectional width, have become widespread. In such a tire having a small flatness ratio, it is difficult to suppress the radial growth amount unless the width of the circumferential belt layer is further increased.

  However, if the width of the circumferential belt layer is increased, circumferential bending deformation occurs at the end of the circumferential belt layer in the width direction in the tire ground contact area, so that the belt is repeatedly input to the cord constituting the belt. The tensile force will be greatly increased. As a result, the cord tends to be fatigued and fractured particularly at the end in the width direction of the circumferential belt layer. If the cord of the circumferential belt layer is broken, the circumferential belt layer cannot bear the circumferential tension of the tire, and it becomes difficult to maintain the normal shape of the tire.

  Incidentally, in order to improve the fatigue fracture of the cord of the circumferential belt layer described above, it is conceivable to use a low elastic cord for the cord of the circumferential belt layer as a technique for suppressing the tensile input applied to the cord. That is, by using the low elastic cord, the stress applied to the tire cord during running is reduced, and the fatigue rupture property of the cord can be improved.

  However, if a low elastic cord is used, when the tire steps on the projection in the ground plane, the tire deforms greatly under the load, and a very large tensile force is generated in the carcass, thereby forming the carcass. The use of a low elastic cord is not practical because the cord is likely to break.

  Accordingly, an object of the present invention is to improve the fatigue rupture resistance of the cord of the circumferential belt layer and the fatigue rupture resistance of the carcass cord while suppressing the tire diameter growth amount, so that the tire having high belt durability. Is to provide.

  As described above, due to recent demands for higher speed and lower flooring of vehicles, tires mounted on vehicles have become more flat, and along with this, the amount of growth in the tire radial direction of the tread when standard internal pressure is applied tends to increase further. It is in. This increase in the radial growth amount of the tread portion amplifies the stress concentration at the belt and causes a decrease in the durability of the tire due to belt end separation.For tires with a small flatness ratio, the width of the circumferential belt layer is reduced. It is necessary to widen and suppress the amount of growth in the tire radial direction. At this time, if the width of the circumferential belt layer is increased, there is a problem that the cord tends to be fatigued and broken particularly at the end portion in the width direction of the circumferential belt layer, and thus this problem needs to be solved.

In order to avoid the fatigue fracture of the cord of the circumferential belt layer, it is necessary to suppress the tensile input applied to the cord. For that purpose, it is effective to use a cord having a low elasticity for the cord of the circumferential belt layer. is there. That is, by using a low elastic cord, the stress applied to the cord during running of the tire is relaxed, and the fatigue rupture resistance of the cord is improved.
Here, the elastic modulus of the cord means that a tensile test is performed on a rubber-covered cord taken out by disassembling a pneumatic tire, and a stress-strain diagram is created from the result. The tangent slope (slope) at a strain of 1.8% is calculated, and the value is divided by the cross-sectional area of the cord.

However, as described above, the tire using the low elastic cord for the circumferential belt layer has a new problem that the circumferential rigidity is lowered.
Therefore, when the method for solving this problem was intensively studied, a circumferential belt auxiliary layer made of a high elastic cord having a narrower belt width than a circumferential belt layer made of a low elastic cord was arranged particularly in the central region in the tire width direction. Thus, the present inventors have found that the circumferential rigidity of the tire can be reinforced and have completed the present invention.

That is, the gist configuration of the present invention is as follows.
(1) At least one layer in which a carcass extending in a toroidal shape between a pair of bead portions is used as a skeleton, and a plurality of low elastic cords extending along the tire equatorial plane are coated with rubber on the radially outer side of the crown portion of the carcass A pneumatic tire in which a tire circumferential belt layer and at least one inclined belt layer in which a plurality of cords extending in a direction inclined with respect to the equator plane of the tire are covered with rubber are arranged in order,
The pneumatic tire further comprises at least one circumferential belt auxiliary layer having a width smaller than that of the circumferential belt layer and covering a large number of highly elastic cords with rubber.

(2) The pneumatic tire according to (1), wherein the circumferential belt auxiliary layer is disposed in a central region in a tire width direction including a tire equatorial plane.

(3) The cord of the circumferential belt layer has an elastic modulus of 30 to 100 GPa at a tensile strain of 1.8%, and the cord of the circumferential belt auxiliary layer has an elastic modulus of 80 to 210 GPa at a tensile strain of 1.8%. The pneumatic tire according to (1) or (2), characterized in that:

(4) The pneumatic tire according to (1), (2), or (3), wherein the cord of the circumferential belt auxiliary layer is formed in a wave shape or a zigzag shape.

(5) In the crown portion of the carcass, a circumferential belt layer, a circumferential belt auxiliary layer, and an inclined belt layer are sequentially arranged from the inner side to the outer side in the tire radial direction. The pneumatic tire according to any one of the above.

(6) The tire circumferential belt layer and the circumferential belt auxiliary layer are formed by spirally winding a strip material in which one or more cords are covered with rubber around the crown portion of the carcass. The pneumatic tire according to any one of (1) to (6).

  According to the present invention, it is possible to improve the fatigue rupture resistance of the cord of the circumferential belt layer and the fatigue rupture resistance of the carcass cord while suppressing the tire diameter growth amount. Can be provided.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a cross section in the width direction of a crown portion of a tire according to the present invention. In the figure, reference numeral 1 denotes a carcass that forms a skeleton of a tire straddling a pair of bead cores (not shown), and a circumferential belt layer 2 and an inclined belt layer are disposed radially outside the crown portion of the carcass 1. 3 are arranged in order, and a tread 4 is arranged on the radially outer side of the inclined belt layer 3.
As shown in FIG. 2, the circumferential belt layer 2 is made of a rubberized cloth in which a plurality of low elastic cords 2 a extending along the tire equatorial plane O are covered with rubber. At least one layer, in the illustrated example, one layer. Deploy. Two or more circumferential belt layers 2 may be disposed, but it is desirable that the circumferential belt layer 2 be one layer in consideration of an increase in tire weight.

  On the other hand, the inclined belt layer 3 is made of a rubberized cloth in which a plurality of cords 3a extending in a direction inclined with respect to the equator plane O of the tire are covered with rubber, and at least one layer, in the illustrated example, one layer is arranged. The inclined belt layer 3 may have two or more layers, but if it becomes three or more layers, the tire weight increases, and therefore it is preferably two or less layers.

It is important for the circumferential belt layer 2 that the arrangement cord 2a is a low elastic cord to avoid fatigue fracture of the cord of the circumferential belt layer. This is because by using a low elastic cord, the stress applied to the cord during running of the tire is relaxed, and the fatigue rupture resistance of the cord is improved.
In particular, in order to ensure the fatigue rupture resistance of the cord while suppressing the amount of growth in the tire radial direction, it is preferable to use a low elastic cord having an elastic modulus of 30 to 100 GPa at a tensile strain of 1.8%. That is, if the elastic modulus of the cord is less than 30 GPa, it is difficult to suppress the radial growth of the tire. On the other hand, if it exceeds 100 GPa, the tensile input applied to the cord increases and the cord may be broken. Such cords can include extensible metal cords and organic fiber cords.

Here, when the low elastic cord is used for the circumferential belt layer, the circumferential rigidity of the tire is already lowered. However, as shown in FIGS. A countermeasure is provided by providing a circumferential belt auxiliary layer 5 between the belt layer 2 and the inclined belt layer 3, which is narrower than the circumferential belt layer 2 and covered with a plurality of high elastic cords with rubber.
That is, by providing the circumferential belt auxiliary layer 5 reinforced with the high elastic cord, the circumferential rigidity of the tire is increased. For example, when the tire steps on a protrusion, the entire tire circumferential direction is deformed and shock is applied. Can be absorbed, and local deformation directly under the tire protrusion can be suppressed. As a result, for example, the tensile input to the carcass due to the projection input can be suppressed, and the breakage of the carcass cord can be significantly suppressed.

  In particular, the circumferential belt auxiliary layer 5 is preferably disposed in the center region in the tire width direction including the tire equatorial plane O. This is because if the end portion of the circumferential belt auxiliary layer 5 is in the tire width direction side region, the cord of the circumferential belt auxiliary layer 5 is easily broken.

The circumferential belt auxiliary layer 5 is
Width of circumferential belt layer 2 / width of circumferential belt auxiliary layer 5> 1.1
It is preferable that the center of the width overlaps with the tire equator plane O under a width satisfying the above relationship.

  Here, the high elastic cord applied to the circumferential belt auxiliary layer 5 has an elastic modulus at a tensile strain of 1.8% in order to improve the circumferential rigidity of the tire and reduce the tensile input to the carcass at the time of projection input. It is preferably in the range of 80 to 210 GPa. That is, if the elastic modulus of the cord is less than 80 GPa, it becomes difficult to suppress the input to the carcass due to the projection input, whereas if it exceeds 210 GPa, the tensile input applied to the cord of the circumferential belt auxiliary layer 5 increases. May break. Examples of such cords include non-extensible metal cords.

  Two or more circumferential belt auxiliary layers 5 may be disposed, but one layer is preferable in order to avoid an increase in tire weight.

Further, the high elastic cord 5a applied to the circumferential belt auxiliary layer 5 is not limited to a general linear one, but is shaped into a wave shape shown in FIG. 3A or a zigzag shape shown in FIG. 3B. You may have done. The cord thus molded is effective in further reducing the tensile input to the carcass when the tire steps on the protrusion.
That is, by shaping the high elastic cord into a wave shape or a zigzag shape, the shear rigidity in the tire width direction of the circumferential belt auxiliary layer is increased, and can be deformed in the entire tire width direction with respect to the input of the protrusion, Local deformation directly below the tire protrusion can be further suppressed. Accordingly, the tensile input to the carcass due to the projection input is further suppressed, and the carcass cord can be prevented from breaking.

  Here, it is preferable that the wave pattern or zigzag wavelength λ and wave height d shown in FIGS. 3A and 3B are λ / d: 1.5 to 4 for the molding to be applied to the highly elastic cord 5a. If both are within this range, it is effective to suppress deformation applied to the circumferential belt auxiliary layer 5.

  From the above, in addition to suppressing the radial growth of the tire by disposing a highly elastic circumferential belt auxiliary layer between the low elastic circumferential belt layer 2 and the inclined belt layer 3, The cord fatigue rupture of the circumferential belt layer and the rupture of the carcass cord with respect to the protrusion input can be suppressed, and a tire with greatly improved tire belt durability can be obtained.

  Here, the belt structure is preferably arranged in the order of the circumferential belt layer, the circumferential belt auxiliary layer, and the inclined belt layer on the radially outer side from the carcass side. In other words, it is not preferable to dispose the circumferential belt layer having the function of maintaining the internal pressure of the tire on the outermost radial direction, and in order to protect the circumferential belt layer from projection input, the inclined belt layer is disposed in the circumferential direction. By disposing the belt layer and the circumferential belt auxiliary layer on the outer side in the tire radial direction, durability against protrusion input is further improved. Considering the deformation during running of the tire, the circumferential belt layer on the inner side in the tire radial direction is further extended, and there is a possibility that fatigue breakage may occur in the cord. Therefore, a low-elasticity circumferential belt layer is disposed on the innermost side in the tire radial direction, and a high-elasticity circumferential belt auxiliary layer and an inclined belt layer are disposed on the outer side in the tire radial direction. It is possible to further improve the property.

In accordance with the belt structure shown in FIG. 1, truck / bus tires of size 435/45 R22.5 were manufactured under the specifications shown in Table 1.
Here, (1 + 6) x 0.32mm layer twist cord is applied to the inclined belt layer at 24.5 / 50mm, and the circumferential belt layer is 4 x (l x 0.28mm + 6 x 0.25mm). ) With an elastic modulus of 70 GPa applied at a driving speed of 20/50 mm, and a circumferential belt auxiliary layer with a structure of (3 + 9 + 15) × 0.23 mm and an elastic modulus of 140 GPa with a driving speed of 22.5 Applied at / 50mm. In Invention Examples 3 and 4, the cord of the circumferential belt auxiliary layer has an amplitude d ratio of 2d / λ = 4 as shown in FIG.
I was typed.

Next, each prototype tire was incorporated into a 14.00 × 22.5 rim, the internal pressure was adjusted to 900 kPa, and the following evaluation was performed.
First, in the evaluation of the tire radial growth amount, the tire radial growth amount when the internal pressure was changed from 0 kPa to 900 kPa was confirmed after assembling each prototype tire with a rim. Table 1 shows the index of the tire radial growth amount at the width end position of the inclined belt layer where belt edge separation occurs due to the increase in the radial growth amount, with the conventional radial growth amount being 100. Show. In addition, it shows that the amount of growth in the tire radial direction is smaller and the durability is better as the index is smaller.

  Fatigue fracture resistance of the circumferential belt layer cord was evaluated by running the tire 30000km on the drum under the conditions of drum load: 63.7kN and drum rotation speed: 60km / h, and then dissecting the tire and tire circumferential belt layer The number of cords with fatigue fracture was confirmed. The results are shown in Table 1 in terms of an index when the number of fractures in the conventional example is 100. In addition, it shows that there are few fatigue fracture | rupture numbers, so that durability is favorable, so that a numerical value is small.

In the evaluation of carcass cord rupture resistance, a hemispherical projection with a diameter of 38 mm was pushed into the center in the tire width direction, and the energy was calculated from the pushing amount of the projection and the reaction force from the tire when the tire broke down. Table 1 shows the results of indexing the energy values. In addition, the larger the value, the greater the energy until the tire breaks down, and the carcass cord is less likely to break, indicating that the durability is better.
Here, the elastic modulus of the cord is the elastic modulus of the cord at a tensile strain of 1.8% as described above by performing a tensile test on the cord with an Instron type tensile tester. The cord shown in the conventional example is indexed with an elastic modulus of 100. The smaller this value is, the lower the elastic modulus is.

It is sectional drawing of the width direction centering on the crown part of the tire according to this invention. It is a figure which shows the laminated structure of a belt. It is a figure which shows the code arrangement | sequence of a week direction bell auxiliary | assistant layer.

Explanation of symbols

1 carcass 2 circumferential belt layer 3 inclined belt layer 4 tread 5 circumferential belt auxiliary layer 2a, 3a, 5a cord

Claims (6)

A carcass extending in a toroidal shape between a pair of bead portions, and at least one layer of a tire circumference in which a large number of low elastic cords extending along the tire equatorial plane are coated with rubber on the radially outer side of the crown portion of the carcass A pneumatic tire in which a directional belt layer and at least one inclined belt layer in which a plurality of cords extending in a direction inclined with respect to the equator plane of the tire are covered with rubber are sequentially arranged,
The pneumatic tire further comprises at least one circumferential belt auxiliary layer having a width smaller than that of the circumferential belt layer and covering a large number of highly elastic cords with rubber.   The pneumatic tire according to claim 1, wherein the circumferential belt auxiliary layer is disposed in a central region in a tire width direction including a tire equatorial plane.   The cord of the circumferential belt layer has an elastic modulus of 30 to 100 GPa at a tensile strain of 1.8%, and the cord of the circumferential belt auxiliary layer has an elastic modulus of 80 to 210 GPa at a tensile strain of 1.8%. The pneumatic tire according to claim 1 or 2.   The pneumatic tire according to claim 1, 2, or 3, wherein the cord of the circumferential belt auxiliary layer is formed into a wave shape or a zigzag shape.   The air according to any one of claims 1 to 4, wherein a circumferential belt layer, a circumferential belt auxiliary layer, and an inclined belt layer are arranged in this order from the inner side to the outer side in the tire radial direction on the crown portion of the carcass. Enter tire.   The tire circumferential belt layer and the circumferential belt auxiliary layer are formed by spirally winding a strip material in which one or a plurality of cords are covered with rubber around a crown portion of the carcass. Item 7. The pneumatic tire according to any one of Items 1 to 6.

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