JP2013001319A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire which includes a belt reinforcement layer formed by embedding an N×M steel cord formed of a plurality of twisted wires, in a rubber, and which enables high-speed durability and riding comfort.SOLUTION: In the pneumatic radial tire including the belt reinforcement layer 8 made of the N×M steel cord 10, a diameter dc of the wire 11 in a center areas C is set to be in the range of 0.05 mm≤dc≤0.15 mm, and the ratio de/dc between the diameter dc of the wire 11 in the center area C and a diameter de of the wire 11 in an edge area E is set to be in the range of 1.15≤de/dc≤1.40.

Description

  The present invention relates to a pneumatic radial tire provided with a belt reinforcing layer in which a steel cord having an N × M structure formed by twisting a plurality of strands is embedded in rubber. The present invention relates to a pneumatic radial tire that achieves both comfort.

  In a pneumatic radial tire, generally, a belt reinforcing layer in which a reinforcing cord is spirally wound in the tire circumferential direction is arranged on the outer peripheral side of the belt layer, so that the belt layer can be auctioned to the outer peripheral side during high-speed running. Suppresses and improves high-speed durability. Conventionally, for example, a nylon fiber cord having thermal contractibility, a hybrid cord made of an aramid fiber and a nylon fiber, or the like is used as the reinforcement cord of such a belt reinforcing layer (see, for example, Patent Document 1).

  In contrast, in recent years, instead of organic fiber cords, steel cords are used for belt reinforcement layers in order to improve high-speed durability, high-speed driving stability, flat spot resistance, quietness, and the like. It is being considered. More specifically, in order to follow the diameter growth (lift) of the tire during vulcanization, it has been proposed to use a steel cord having an N × M structure in which ultrafine wires are twisted at a minimum pitch ( For example, see Patent Document 2).

  However, when the steel cord having the N × M structure as described above is used for the belt reinforcing layer, there is a concern that the riding comfort is deteriorated and that the steel cord is likely to be subject to fatigue fracture. That is, when the tread portion is deformed as the tire rotates, tensile deformation or compression deformation is repeatedly generated in the steel cord oriented in the tire circumferential direction, which causes fatigue fracture. Therefore, even if a steel cord is applied to the belt reinforcing layer, it is not always possible to exhibit good high-speed durability.

JP 2009-132324 A JP 2006-232209 A

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and a pneumatic radial provided with a belt reinforcing layer in which a steel cord having an N × M structure formed by twisting a plurality of strands is embedded in rubber. More specifically, the present invention provides a pneumatic radial tire that achieves both high-speed durability and riding comfort.

  In order to achieve the above object, a pneumatic radial tire of the present invention has a plurality of belt layers embedded in the outer peripheral side of the carcass layer in the tread portion, and M strands are twisted together on the outer peripheral side of the belt layer. In a pneumatic radial tire provided with a belt reinforcement layer made of a steel cord having an N × M structure in which N strands are twisted together, a diameter of a steel cord constituting the belt reinforcement layer is set to a center region of the belt layer. And the edge region, the diameter dc of the strand in the center region is in a range of 0.05 mm ≦ dc ≦ 0.15 mm, and the diameter dc of the strand in the center region and the edge region A ratio de / dc with a diameter de of the element wire is in a range of 1.15 ≦ de / dc ≦ 1.40.

  As a result of earnest research on the behavior of the belt reinforcement layer during tire rotation, the inventor of the present invention has a relatively large tensile deformation in the steel cord of the belt reinforcement layer when the tread portion contacts the ground in the edge region of the belt layer, When the tread portion is separated from the road surface, a relatively large compressive deformation is generated in the steel cord of the belt reinforcing layer, and it is found that a large tensile deformation and a large compressive deformation are repeatedly generated as the tire rotates. It has come.

  That is, in the present invention, in the edge region of the belt layer, the diameter de of the wire constituting the steel cord of the belt reinforcing layer is relatively increased, so that the resistance of the portion where the fatigue due to the tensile-compression deformation is feared during traveling is increased. The fatigue property can be improved and the high-speed durability of the pneumatic tire can be improved. On the other hand, in the center region of the belt layer, by making the diameter dc of the wire constituting the steel cord of the belt reinforcing layer relatively small, it is possible to exhibit good riding comfort.

  In the present invention, the width of the center region is preferably 40% or more and 90% or less of the maximum belt width of the belt layer, and the width of the edge region is preferably 5% or more and 30% or less of the maximum belt width of the belt layer. Thereby, both high-speed durability and riding comfort can be achieved at a higher level.

  In the present invention, it is preferable that the inflection point in the load-elongation curve with the horizontal axis as elongation (%) and the vertical axis as load (N) is located in the range of 2.5% to 5%. As a result, the belt reinforcing layer can follow the lift during vulcanization, so that the cord interlayer gauge between the belt layer and the belt reinforcing layer can be maintained and the durability can be improved. In addition, it is possible to improve the handling stability by increasing the tensile rigidity of the cord.

  In the present invention, the strand twist pitch is preferably 1.0 mm to 2.0 mm, and the steel cord twist pitch is preferably 2.0 mm to 5.0 mm. As a result, the belt reinforcing layer can follow the lift during vulcanization, so that the cord interlayer gauge between the belt layer and the belt reinforcing layer can be maintained, and the high-speed durability can be improved.

1 is a meridian cross-sectional view showing a pneumatic radial tire according to an embodiment of the present invention. It is principal part meridian sectional drawing which shows the belt reinforcement layer of the pneumatic radial tire of this invention. It is sectional drawing which shows an example of the steel cord which comprises a belt reinforcement layer by this invention. It is a graph which shows the load-elongation curve of the steel cord of this invention.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. 1 shows a pneumatic radial tire according to an embodiment of the present invention, FIG. 2 shows an enlarged view of a tread portion of the pneumatic radial tire of the present invention, and FIG. 3 shows a steel cord constituting a belt reinforcing layer according to the present invention. Is shown.

  In FIG. 1, 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. A carcass layer 4 is mounted between the pair of left and right bead portions 3 and 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded from the tire inner side to the outer side around the bead core 5 disposed in each bead portion 3. A bead filler 6 is disposed on the outer periphery of the bead core 5, and the bead filler 6 is wrapped by the main body portion and the folded portion of the carcass layer 4.

  On the other hand, a plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 7 include a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between the layers. In the belt layer 7, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in a range of, for example, 10 ° to 40 °.

  Further, a belt reinforcing layer 8 is provided on the outer peripheral side of the belt layer 7. The cord angle of the belt reinforcing layer 8 with respect to the tire circumferential direction is 5 ° or less, more preferably 3 ° or less. In FIG. 1, the belt reinforcing layer 8 is provided so as to cover the entire area on the outer peripheral side of the belt layer 7b having the maximum width. A full cover layer 8a covering the entire belt layer 7b having a large area and an edge cover layer 8b covering only the edge region E of the belt layer 7 can be used. Further, as shown in FIG. 2B, the belt reinforcing layer 8 is not continuous between the center region C and the edge region E of the belt layer 7 and is divided into a center region portion 8c and an edge region portion 8e. It doesn't matter.

  In the pneumatic radial tire, an N × M steel cord 10 formed by twisting a plurality of strands 11 is used as a reinforcing cord constituting the belt reinforcing layer 8 (see FIG. 3). In FIG. 3, the steel cord 10 is formed in a 5 × 4 structure formed by twisting five strands 12 formed by twisting four strands 11. In the present invention, the twisted structure is not limited to the illustrated 5 × 4 structure, and may be an N × M structure configured by twisting N strands 12 in which M strands 11 are twisted. . Here, the number M of strands is preferably 3 to 4, and the number N of strands is preferably 3 to 5 from the viewpoint of the stability of the cord structure.

  The direction in which the strands 11 are twisted and the direction in which the strands 12 are twisted may be the same or different.

  The diameter of the strand 11 of the steel cord 10 is different between the center region C and the edge region E of the belt layer 7, and the diameter dc of the strand 11 of the steel cord 10 in the center region C is 0.05 mm ≦ dc ≦ The range is set to 0.15 mm. Further, the ratio de / dc between the diameter dc of the strand 11 of the steel cord 10 in the center region C and the diameter de of the strand 11 of the steel cord 10 in the edge region E is 1.15 ≦ de / dc ≦ 1.40. Set to range.

  As described above, during tire rotation, in the edge region E of the belt layer 7, when the tread portion 1 contacts the ground, tensile deformation occurs in the steel cord 10 of the belt reinforcing layer 8, and when the tread portion 1 moves away from the road surface. The steel cord 10 of the belt reinforcing layer 8 is compressed and deformed, and a large tensile deformation and a large compressive deformation are repeatedly generated as the tire rotates. Therefore, in the edge region E, by increasing the diameter de of the wire 11 constituting the steel cord 10 of the belt reinforcing layer 8, the fatigue resistance of a portion where fatigue due to tensile-compressive deformation is a concern during traveling can be improved. The high-speed durability of the pneumatic tire can be improved. On the other hand, in the center region C, by making the diameter dc of the wire 11 constituting the steel cord 10 of the belt reinforcing layer 8 relatively small, it is possible to exhibit good riding comfort.

  At this time, if the diameter dc of the strand 11 in the center region C is smaller than 0.05 mm, the high-pressure durability of the pneumatic tire is deteriorated because the compression fatigue resistance against compression that the center region C receives during high-speed running deteriorates. If the diameter dc of the wire 11 in the center region C is larger than 0.15 mm, the bending rigidity becomes too high, and the riding comfort deteriorates. Further, if the diameter ratio de / dc of the wire 11 is smaller than 1.15, the fatigue resistance of the edge region E cannot be sufficiently improved, and the high-speed durability of the pneumatic tire is deteriorated. If the ratio de / dc of the diameters of the strands 11 is greater than 1.40, the bending rigidity becomes excessively high in the edge region E, and the riding comfort deteriorates.

  The center region C is a region on the center side in the tire width direction having a width of 40% to 90% of the width (maximum belt width W) of the belt layer 7b having the maximum width among the belt layers 7. The edge region E is a region located on both outer sides in the tire width direction of the center region C and having a width of 5% or more and 30% or less of the maximum belt width W. If the width of the center region C is smaller than 40% of the maximum belt width W and the width of the edge region E is larger than 30% of the maximum belt width W, the portion where the diameter of the strand 11 is relatively small is reduced. Comfort is reduced. If the width of the center region C is larger than 90% of the maximum belt width W and the width of the edge region E is smaller than 5% of the maximum belt width W, the portion where the diameter of the strand 11 becomes relatively large decreases. The fatigue resistance of the edge region E cannot be sufficiently improved, and the high-speed durability of the pneumatic tire is lowered.

  In the present invention, as shown in FIG. 4, when a load-elongation curve is created with the horizontal axis representing elongation (%) and the vertical axis representing load (N), the inflection point of the load-elongation curve is elongated. It is preferably located in the range of 5% to 5%. Thus, since the inflection point is provided in the load-elongation curve, the belt reinforcing layer 8 can be made to follow the lift during vulcanization. That is, up to the inflection point of the load-elongation curve, it is possible to follow the lift during vulcanization by the elongation resulting from the twist of the cord. Further, after the elongation due to the twist of the cord disappears, that is, after the elongation increases from the inflection point, the elastic modulus due to the material itself is exhibited. In this way, the high-speed durability of the pneumatic tire can be improved and the steering stability can be improved. The variable curve in the load-elongation curve is a load-elongation curve in which the horizontal axis indicates elongation (%) and the vertical axis indicates load (N). This is an intersection of a straight line connecting the points and a straight line connecting the point at 6.0% elongation and the point at 6.5% elongation.

  If the position of the inflection point is smaller than 2.5%, it is impossible to follow the lift during vulcanization, and the cord interlayer gauge between the belt layer 7 and the belt reinforcing layer 8 becomes thin. As a result, the gauge is thin. The point becomes the starting point of separation between codes, and high-speed durability deteriorates. When the position of the inflection point is larger than 5%, the tensile rigidity of the cord is lowered and the steering stability is lowered.

  In the present invention, the strand 12 preferably has a twist pitch of 1.0 mm to 2.0 mm, and the steel cord 10 has a twist pitch of 2.0 mm to 5.0 mm. By setting the twist pitch of the strands 12 and the steel cord 10 in this way, even if the steel cord 10 extends with respect to tire specifications having different lift rates, the vulcanized rubber surrounding the vulcanized coating covers the tire specifications. Since the elongation is suppressed and it becomes difficult to stretch, the high rigidity exhibited by the steel cord 10 can further improve the high-speed durability.

  When the twist pitch of the strand 12 is smaller than 1.0 mm, or when the twist pitch of the steel cord 10 is smaller than 2.0 mm, the steel cord 10 becomes too easy to be stretched and the stretch is suppressed by the surrounding vulcanized rubber to be coated. Cannot be obtained, and the effect of improving high-speed durability cannot be obtained sufficiently. When the twist pitch of the strand 12 is larger than 2.0 mm, or when the twist pitch of the steel cord 10 is larger than 5.0 mm, it is not possible to cope with tire specifications having different lift rates. It may become difficult to stretch.

  In a pneumatic radial tire having a belt reinforcing layer in which a tire cord is made common to 205 / 55R16 and a steel cord having an N × M twist structure formed by twisting a plurality of strands is embedded in rubber, the reinforcement cord Table 1, the reinforcement cord structure, the center region and edge region strand diameters dc and de, the strand diameter ratio de / dc, and the inflection point position in the load-elongation curve are set as shown in Table 1. Eight types of test tires of Conventional Example 1, Examples 1 to 3, and Comparative Examples 1 to 4 were produced. In the first conventional example, the belt reinforcing layer is not a steel cord but a hybrid cord made of aramid fiber and nylon fiber. Moreover, in all the steel cords of Examples 1 to 3 and Comparative Examples 1 to 4, the strand twist pitch is 1.5 mm, and the steel cord twist pitch is 3 mm.

  These eight types of test tires were evaluated for high speed durability, riding comfort, and steering stability by the following evaluation methods, and the results are also shown in Table 1.

High-speed durability Each test tire is attached to a drum testing machine, filled with an air pressure of 230 kPa, and at a speed of 81 km / h, 120% at a speed of 81 km / h at 88% of the load corresponding to the pneumatic conditions specified by JATMA. I traveled for a while. Next, after allowing to cool for more than 3 hours, adjust the air pressure, start the test from a speed of 121 km / h, gradually increase the speed by 8 km / h every 30 minutes, and the distance traveled until the failure occurs Was measured. The evaluation result is indicated by an index value with the conventional example 1 being 100. The higher this value, the better the high speed durability.

Riding comfort Each test tire is mounted on a rim with a rim size of 16 x 6 1/2 JJ, filled with air pressure of 200 kPa, mounted on a FR vehicle with a displacement of 1500 cc, and a test course consisting of an asphalt road surface at an average speed of 80 km / h. It was run and sensory evaluation was performed by a test driver. The evaluation results are shown as an index with Conventional Example 1 as 100. It means that riding comfort is excellent, so that this index value is large.

Steering stability Each test tire is mounted on a rim with a rim size of 16 x 6 1/2 JJ, filled with air pressure of 200 kPa, mounted on a FR vehicle with a displacement of 1500 cc, and an asphalt road test course with an average speed of 80 km / h. It was run and sensory evaluation was performed by a test driver. The evaluation results are shown as an index value in which Conventional Example 1 is 100. The larger the index value, the better the steering stability.

  As can be seen from Table 1, each of Examples 1 to 3 improved riding comfort, high-speed durability, and steering stability in comparison with Conventional Example 1. On the other hand, in Comparative Examples 1 to 4 in which the wire diameter deviated from the definition of the present invention, the riding comfort or high-speed durability deteriorated.

  Specifically, Comparative Example 1 in which the diameter of the strands in the center region is too small has decreased high-speed durability, and Comparative Example 2 in which the diameter of the strands in the center region is too large has decreased riding comfort. The ratio of the edge region strand diameter to the center region strand diameter is too small in Comparative Example 3 because the high-speed durability is reduced, and the ratio of the edge region strand diameter to the center region strand diameter is low. In Comparative Example 4, which is too large, the ride comfort is reduced.

  Further, Example 2 in which the position of the inflection point in the load-elongation curve was set in an appropriate range highly achieved high speed durability, riding comfort, and steering stability.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Belt reinforcement layer 10 Steel cord 11 Strand 12 Strand

Claims (4)

From an N × M steel cord in which a plurality of belt layers are embedded on the outer peripheral side of the carcass layer in the tread portion, and N strands in which M strands are twisted are twisted on the outer peripheral side of the belt layer. In a pneumatic radial tire provided with a belt reinforcing layer,
The diameter of the strands of the steel cord constituting the belt reinforcing layer is made different between the center region and the edge region of the belt layer, and the diameter dc of the strands in the center region is 0.05 mm ≦ dc ≦ 0.15 mm. And the ratio de / dc of the diameter dc of the wire in the center region and the diameter de of the wire in the edge region is in the range of 1.15 ≦ de / dc ≦ 1.40. Pneumatic radial tire characterized by.   The width of the center region is 40% or more and 90% or less of the maximum belt width of the belt layer, and the width of the edge region is 5% or more and 30% or less of the maximum belt width of the belt layer. The pneumatic radial tire according to claim 1.   The inflection point in the load-elongation curve with the horizontal axis as elongation (%) and the vertical axis as load (N) is located in the range of 2.5% to 5% elongation. The described pneumatic radial tire.   4. The pneumatic radial according to claim 1, wherein the strand has a twist pitch of 1.0 mm to 2.0 mm, and the steel cord has a twist pitch of 2.0 mm to 5.0 mm. tire.

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