JP5013522B2 - Pneumatic radial tire - Google Patents

Description

  The present invention relates to a pneumatic radial tire (hereinafter, also simply referred to as “tire”), and more specifically, in an ultra-high performance tire that is used for long-time high-speed running, while reducing rolling resistance and improving fuel efficiency, The present invention relates to a pneumatic radial tire with improved high-speed durability, road noise, and steering stability.

  Conventionally, in a passenger car radial tire in which a belt layer is embedded on the outer peripheral side of the carcass layer in the tread portion, by providing a belt cover layer whose cord angle with respect to the tire circumferential direction is substantially 0 ° on the outer peripheral side of the belt layer, It is known that the tagging effect on the belt layer can be enhanced. As a result, it is possible to prevent the edge separation phenomenon caused by the rising of both ends of the belt layer due to the centrifugal force at the time of tire rotation, and at the same time, the high-frequency road noise characteristics of the tire are improved by increasing the tire circumferential rigidity. become.

  When such a belt cover layer is provided, an organic fiber cord such as a nylon cord is generally used as the cord, but it cannot be said that the belt cover layer made of the organic fiber cord has a sufficient tagging effect, and the tire When the cord is continuously rotated at a high speed for a long time, the cord is continuously subjected to centrifugal force at a high temperature, and permanent deformation due to creep growth specific to the organic fiber cord is inevitable. Therefore, it has been difficult for the belt cover layer using the organic fiber cord to further improve the high-speed durability and high-frequency road noise characteristics of the tire.

  In order to overcome such difficulties, a radial tire using a steel cord as a cord for the belt cover layer has been proposed. For example, Patent Document 1 discloses that a HE (High Elongation) steel cord having a breaking elongation of 4 to 8% and a double twist structure is used as a reinforcement cord for a belt cover layer (annular reinforcing structure). .

Patent Document 2 discloses that in the circumferential belt layer as the belt cover layer, the product of the cross-sectional area of the steel cord per 50 mm width and the number of cords to be driven is 3.0 mm ² or more, so that high speed durability is achieved. A radial tire with improved road noise and steering stability is disclosed.
JP-A-56-82609 (Claims etc.) JP 2006-69338 A (Claims etc.)

  However, in the radial tire described in Patent Document 1, the tension load acts on the normal belt and the belt cover layer so as to resist the stress at 2/3 and 1/3, respectively. The code will cause significant disruption to the power distribution. In addition, it is difficult to ensure sufficient rigidity as a tire effect of the tire, and there is a problem in terms of durability.

  On the other hand, in the radial tire to which the circumferential belt layer described in Patent Document 2 is applied, a sufficient tagging effect can be obtained, so that it is possible to obtain good performance with respect to high-speed durability, road noise, and steering stability. It is. However, on the other hand, there has been a new problem such as an increase in weight and the like, an increase in rolling resistance, and a reduction in fuel consumption of the automobile.

  Accordingly, an object of the present invention is to solve the above problems, improve high-speed durability, road noise, and steering stability, suppress an increase in weight, and prevent an increase in rolling resistance. The object is to provide an improved pneumatic radial tire.

  As a result of diligent studies to solve the above problems, the present inventors have found that in the circumferential belt layer made of steel cords arranged on the outer circumferential side of a normal crossing belt layer, the cross-sectional area of the steel cord and the number of cords to be driven The present invention has been completed by finding that the above-mentioned object can be achieved by changing the product of the above to a predetermined value in the belt width direction.

That is, the pneumatic radial tire of the present invention includes a radial carcass made of one or more carcass plies, and a belt made of three or more belt layers disposed on the outer peripheral side of the crown portion of the radial carcass, The belt has two layers of crossing belt layers arranged so as to cross each other, and at least one steel cord arranged on the outer peripheral side of the two layers of crossing belt layers substantially parallel to the tire equatorial plane. In a radial tire having a circumferential belt layer of layers,
The product of the cross-sectional area of the steel cord and the number of cords driven per 50 mm in the circumferential belt layer is 20 mm ≦ a ≦ L / 4 from the end of the circumferential belt layer (L is the circumferential belt layer) It is 3 to 6 mm ² in the region A up to the width a that satisfies the total width (mm), and is smaller than the region A in the other regions.

In the present invention, it is preferable to use a steel cord obtained by twisting steel strands having a tensile strength of 2700 N / mm ² or more as the steel cord.

  According to the present invention, the above configuration makes it possible to suppress the increase in rolling resistance while ensuring high-speed durability, road noise, and steering stability, and is particularly suitable for ultra-high performance tires used for long-time high-speed running. As a result, it is possible to realize a pneumatic radial tire suitable for the above.

DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional perspective view showing a pneumatic radial tire according to an embodiment of the present invention with a part thereof removed by breaking. The illustrated pneumatic radial tire is continuous with a tread portion 1, a pair of sidewall portions 2 extending inward in the tire radial direction continuously on both sides of the tread portion 1, and an inner peripheral side of each sidewall portion 2. And a bead portion 3 for performing.

  As shown in the figure, the tread portion 1, the sidewall portion 2, and the bead portion 3 are reinforced by a radial carcass 4 including a single carcass ply extending from one bead portion 3 to the other bead portion 3 in a toroidal shape. . Further, the tread portion 1 includes two layers of intersecting belt layers 5a and 5b disposed on the outer peripheral side of the crown portion of the radial carcass 4, and a single circumferential belt disposed on the outer peripheral side of these belt layers. Reinforced by a belt 5 comprising the layer 5c.

  Here, the carcass ply of the radial carcass 4 may be plural, and an organic fiber cord extending in a direction substantially orthogonal to the tire circumferential direction, for example, an angle of 70 to 90 °, can be preferably used.

  Further, the two intersecting belt layers 5a and 5b, which are the belt layers on the radial carcass 4 side, are arranged so that the cord driving angle is preferably 10 ° to 30 ° with respect to the tire circumferential direction and intersect with each other. To do. As the cords of these crossing belt layers 5a and 5b, organic fiber cords such as polyamide fibers can be suitably used.

  Furthermore, the circumferential belt layer 5c which is the belt layer on the tread portion 1 side has a cord driving angle of substantially 0 ° with respect to the tire circumferential direction. That is, the cords of the circumferential belt layer 5c are arranged substantially parallel to the tire equatorial plane. The circumferential belt layer 5c is one layer in the illustrated example, but may be a plurality of layers.

  In the present invention, the product of the cross-sectional area of the steel cord constituting the circumferential belt layer 5c and the number of cords driven per 50 mm width in the circumferential belt layer 5c, that is, the steel per 50 mm width in the circumferential belt layer 5c. It is important that the total cross-sectional area of the cord is different between the belt end and the belt center.

Specifically, in the present invention, the product of the cord cross-sectional area and the number of cords to be driven is set to 20 mm ≦ a ≦ L / 4 from the end of the circumferential belt layer 5c (L is the total width of the circumferential belt layer ( mm) in the region A up to the width a satisfying ² ). If the width a of the region A in which the product of the cord cross-sectional area and the number of cords to be driven is 3 to 6 mm ² is less than 20 mm, the hoop effect at the belt end portion is reduced, and as a result, high-speed durability is reduced. On the other hand, if it exceeds L / 4, the amount of steel becomes more than necessary, resulting in an increase in weight and rolling resistance deteriorates. Further, if the steel amount in the region A at the end of the circumferential belt layer 5c is smaller than 3 mm ² , the tagging effect is reduced, and as a result, the high-speed durability is lowered. On the other hand, if it exceeds 6 mm ² , the weight is increased, and the rolling resistance is deteriorated.

In the present invention, the product of the cord cross-sectional area and the number of cords to be driven is smaller than the region A in a region other than the region A at the end of the circumferential belt layer 5c. The value of the product of the cord cross-sectional area and the number of cords driven in the region other than the region A, that is, in the center portion of the circumferential belt layer 5c is preferably 1 to 3 mm ² , more preferably 1 to ² mm ^2. It is. If the product of the cord cross-sectional area and the number of cords to be driven is less than 1 mm ² , the required strength is insufficient, and various performances as a tire may be reduced. On the other hand, if it exceeds 3 mm ² , the weight is increased and the rolling resistance may be deteriorated.

In the present invention, the steel cord constituting the circumferential belt layer 5c is preferably a steel cord formed by twisting steel strands having a tensile strength of 2700 N / mm ² or more, preferably 3200 to 4000 N / mm ^2. Can be used. If the tensile strength of the steel strand to be used is less than 2700 N / mm ² , the belt strength may be reduced, and durability such as plunger energy may be deteriorated.

  In the present invention, as a method for changing the value of the product of the cord cross-sectional area and the number of cords to be driven in the region A at the end of the circumferential belt layer 5c and the region other than the center portion, There are a method of using a steel cord having a different cross-sectional area, that is, a different cord diameter in each region, and a method of changing the number of cords to be driven in each region. Specifically, for example, in the region A at the end of the circumferential belt layer 5c, a steel cord having a cord diameter of 0.15 to 0.80 mm can be used at a driving number of 30 to 170 pieces / 50 mm. In the other region of the belt layer 5c center portion, a steel cord having a cord diameter of 0.15 to 0.80 mm can be driven and used at a number of 15 to 150 pieces / 50 mm.

  In the present invention, as shown in the drawing, the circumferential belt layer 5c is preferably in the form of a full cover that covers substantially the entire crossing belt layers 5a and 5b. The circumferential belt layer 5a is, for example, It can be easily formed by winding one or a plurality of steel cords in a spiral manner in the tire circumferential direction in a state where the steel cords are aligned and covered with rubber.

  In the tire of the present invention, only the point that satisfies the condition relating to the product of the cord cross-sectional area and the number of cords to be driven is important, and other details of the tire structure, materials of each member, etc. The known structures and materials can be appropriately selected and used without any particular limitation.

  For example, a tread pattern is appropriately formed on the surface of the tread portion 1, and an inner liner (not shown) is disposed on the innermost layer of the tire. Further, in the tire of the present invention, as the gas filled in the tire, it is possible to use normal or air having a changed oxygen partial pressure, or an inert gas such as nitrogen.

Hereinafter, the present invention will be described in more detail with reference to examples.
A pneumatic radial tire of tire size 225 / 45R17 having the belt structure shown in FIG. 1 was manufactured according to the following.

  One radial carcass 4 was used and a rayon fiber cord was used. The two intersecting belt layers 5a and 5b were the same, and the cord driving angles were + 62 ° and −62 ° with respect to the tire circumferential direction, and nylon fiber cords were used. Further, the circumferential belt layer 5c is a single layer, and steel cords (nylon cords for conventional examples 1 to 3) according to the conditions shown in Tables 1 and 2 below were used. In the table, the end region A indicates a range from the end of the circumferential belt layer 5c to the width a, and the center region indicates a range other than the end region A of the circumferential belt layer 5c.

  The following evaluation tests were carried out for each manufactured tire. The results are also shown in Tables 1 and 2 below. Table 1 shows a comparison when the belt width a from the end portion is changed, and Table 2 shows a comparison when the cord cross-sectional area per 50 mm width in the end region A is changed.

<High-speed durability test>
Each test tire was mounted on a rim having a rim size of 7J × 17, the air pressure was set to 300 kPa, and a high speed durability test was performed by a speed step method according to the test method of JATMA standard. The results are indicated by an index with the speed at the time of tire failure in Conventional Example 1 being 100. The higher the number, the better the result.

<Cornering power (CP) test>
The cornering power was measured according to the following test method, and the index was displayed with the tire of Conventional Example 1 as 100. The higher the number, the better the result.
In the cornering power test, each test tire was loaded with a normal internal pressure and load of JIS standard, pressed onto a drum with an outer diameter of 3000 mm, pre-run for 30 minutes at a speed of 30 km / h, and then the internal pressure was returned to the normal value again. Adjust and run at the same speed. At this time, an angle (slip angle) with a maximum of 14 degrees is added between the rolling direction of the tire and the circumferential direction of the drum. This was done by measuring the force (CF). From this result, an average cornering power value was calculated and evaluated by the following formula.
CP = {CF (1 °) + CF (2 °) / 2 + CF (3 °) / 3 + CF (4 °) / 4} / 4

<Running diameter growth test>
Each test tire was mounted on a rim having a rim size of 7 J × 17, the air pressure was set to 220 kPa, the circumference after running 500 km at 160 km / h was measured, and the difference in circumference from the new one was calculated. The results are shown as an index with the tire of Conventional Example 1 as 100. The smaller the numerical value, the smaller the circumference difference, and the better the result.

<Road noise test>
Road noise was measured in accordance with the following test method, and displayed as an index when the tire of Conventional Example 1 was taken as 100. The smaller the value, the lower the road noise and the better.
In the road noise test, each test tire is assembled on a rim of 7J × 17, mounted on a passenger car with a displacement of 2000 cc with an air pressure of 220 kPa, and the sound when driving on a specific road noise test road with a road noise measuring instrument. This was done by measuring the pressure.

<Rolling resistance test>
The rolling resistance was measured in accordance with the following test method, and displayed as an index when the tire of Conventional Example 1 was taken as 100. The smaller the value, the smaller the rolling resistance and the better.
The rolling resistance test was measured using a rotating drum with a steel smooth surface with an outer diameter of 1707.6 mm and a width of 350 mm, and rotating at a speed of 0 to 180 km / h under the action of JIS standard normal pressure and a load of 450 kgf. This method was carried out by the so-called coasting method.

  As shown in Tables 1 and 2 above, in the tires of the examples using steel cords in the circumferential belt layer in accordance with the conditions according to the present invention, compared to the tires using nylon cords of the conventional example, high-speed durability It was confirmed that the performance, cornering power, running diameter growth, road noise and rolling resistance were all excellent.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional perspective view showing a radial tire according to an embodiment of the present invention with a part thereof removed by breaking.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Radial carcass 5 Belt 5a, 5b Crossing belt layer 5c Circumferential belt layer

Claims (2)

A radial carcass composed of one or more carcass plies, and a belt composed of three or more belt layers disposed on the outer peripheral side of the crown portion of the radial carcass, wherein the belts are arranged so as to cross each other. A radial tire having two intersecting belt layers and at least one circumferential belt layer in which a plurality of steel cords are arranged substantially parallel to the tire equatorial plane on the outer peripheral side of the two intersecting belt layers In
The product of the cross-sectional area of the steel cord and the number of cords driven per 50 mm in the circumferential belt layer is 20 mm ≦ a ≦ L / 4 from the end of the circumferential belt layer (L is the circumferential belt layer) A pneumatic radial tire characterized by being 3 to 6 mm ² in a region A up to a width a that satisfies the total width (mm) and smaller than the region A in other regions. The pneumatic radial tire according to claim 1, wherein the steel cord is a steel cord formed by twisting steel strands having a tensile strength of 2700 N / mm ² or more.

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