JP5727161B2 - Pneumatic radial tire - Google Patents

Description

  The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire with improved ride comfort performance and noise performance while maintaining flat spot performance.

  Generally, a pneumatic radial tire has a cross belt composed of at least two cord rubber coating layers as a reinforcing layer on the outer periphery of a crown portion of a carcass extending in a toroidal shape, and further on the outer side in the tire radial direction of the cross belt. And at least one belt reinforcing layer covering the entire width of the cross belt.

  In recent years, flat spot performance is a performance required for pneumatic radial tires. A flat spot refers to a phenomenon in which, after a tire generates heat by running and is cooled in a state where a load is applied, the roundness of the tire collapses, and vibration is generated when the running starts again. As a technique for reducing the flat spot, a highly elastic fiber (for example, a cord of a belt reinforcing layer having a so-called cap / layer structure including a cap covering the entire belt layer and a layer covering only the vicinity of the end of the belt layer is used. A technique of applying a cord in which an aromatic polyamide fiber) and a low elastic fiber (nylon fiber) are twisted together is known (see Patent Document 1).

JP 2008-6875 A

  However, when high-elasticity fibers such as aromatic polyamide fibers are used as the cord material for the belt reinforcement layer, the entire circumference of the belt reinforcement layer is centrally and laterally compared to the case where only nylon fiber is used as the cord material. Directional rigidity increases. As a result, the vertical spring constant of the pneumatic tire increases, and there is a concern that the riding comfort and noise performance are deteriorated. Thus, conventionally, it has been difficult to achieve both flat spot performance, ride comfort performance and noise performance.

  In view of the above problems, an object of the present invention is to provide a novel pneumatic radial tire that can improve ride comfort performance and noise performance while maintaining flat spot performance.

  The present inventor uses a flat spot performance, a ride comfort performance and a noise performance when a cord composed of a plurality of kinds of organic fibers having different elastic moduli (hereinafter referred to as “composite cord”) is used for a belt reinforcing layer. We studied diligently to achieve both. As a result, in order to maintain flat spot performance, the circumferential rigidity should be high mainly at both width ends of the belt reinforcement layer, and the circumferential rigidity is not necessarily increased to the center of the width of the belt reinforcement layer. Found that it is not necessary.

  In addition, pneumatic radial tires have a process in which a cross belt and a belt reinforcing layer are attached to a BT drum and inflated with air pressure to form the tread part tread into a tire crown shape. In the previous zero internal pressure state), the composite cord located at the center of the width of the belt reinforcing layer is usually in a state where a tensile tension is applied as compared with the composite cord located at the width end. However, it has also been found that such a state in which the circumferential rigidity is particularly high at the center of the tire causes a decrease in riding comfort performance and noise performance.

  Based on the above knowledge, the present inventor can reduce the tensile stress applied to the composite cord located at the center of the width of the belt reinforcing layer in a tire product state after vulcanization (internal pressure zero state before assembling the rim). The inventors have obtained the idea that the ride performance and noise performance can be improved while maintaining the flat spot performance, and the present invention has been completed.

That is, in view of the above problems, the gist of the present invention is as follows.
(1) A cross belt comprising at least two cord rubber coating layers formed by laminating cords on the outer periphery of a crown portion of a carcass extending in a toroid shape so as to cross each other across the tire equator, and the cross belt An outer side of the tire in the radial direction of the tire has at least one belt reinforcing layer disposed so as to cover the entire width of the crossing belt and rubber-coated with a plurality of cords arranged parallel to the tire equator,
The cord constituting the belt reinforcing layer is a composite cord formed by twisting a plurality of types of organic fibers having different elastic moduli,
The tensile residual stress of the composite cord located at the center of the width of the belt reinforcing layer is σ1,
When the tensile residual stress of the composite cord located at the width end of the belt reinforcing layer is σ2,
σ1 / σ2 is in the range of 1.0 to 1.7,
The pneumatic radial tire characterized in that the σ1 is in a range of 17.5 to 29.75 N and the σ2 is in a range of 17.5 to 26.25 N.

  (2) The pneumatic radial tire according to (1), wherein the σ1 / σ2 is 1.2 or more.

(3) The above (1) or (2) , wherein the composite cord includes an aramid fiber and a nylon fiber.
The pneumatic radial tire according to any one of the above.

(4) The pneumatic radial tire according to (3) , wherein the composite cord includes two aramid fibers and one nylon fiber.

  According to the present invention, in the conventional radial tire, σ1 / σ2 is usually a value larger than 2.0, and is set to 1.7 or less. It was possible to provide a pneumatic radial tire capable of improving noise performance.

It is a tire width direction sectional view of a pneumatic radial tire according to the present invention. It is an expanded sectional view of the crown part of the tire shown in FIG. It is the figure which showed the stress-strain curve (SS curve) of the composite cord located in the width center part and width end part of a belt reinforcement layer, respectively, (a) is about a conventional radial tire, (b) is this It is about a pneumatic radial tire according to the invention. It is a schematic diagram for demonstrating the length of the cord taken out from the product tire when measuring the SS curve shown in FIG.3 (b).

  Hereinafter, the present invention will be described in more detail with reference to the drawings. In principle, the same components are denoted by the same reference numerals, and description thereof is omitted.

  As shown in FIG. 1, a typical pneumatic tire 10 according to the present invention has a carcass 1 extending in a toroidal shape between a pair of bead portions 11 as a skeleton, and on the outer side in the tire radial direction of the crown portion on the inner layer side. The belt layers 2a and 2b (intersecting belts), a wide cap layer 3 as a belt reinforcing layer, and a pair of narrow layer layers 4 are sequentially provided. Reference numeral 12 denotes a tread portion, and 13 denotes a sidewall portion.

  The carcass 1 includes at least one carcass ply extending in a toroidal shape between a pair of bead cores 5 embedded in the bead portion 11. The carcass ply is a cord rubber coating layer, and examples of the cord material include steel and organic fibers. In the case of a radial carcass, the cords are arranged at an angle of 70 ° to 90 ° with respect to the tire circumferential direction. In FIG. 1, the carcass ply has a shape in which each side portion is folded around the pair of bead cores 2. However, the present invention is not limited to this.

  The belt layers 2a and 2b are cross belts 2 formed of a cord rubber coating layer formed by laminating cords on the outer periphery of the crown portion of the carcass 1 so that the cords cross each other across the tire equator. Examples of the cord include a steel cord and an organic fiber cord. The cord rubber coating layer may be at least two layers.

  The cap layer 3 is disposed on the outer side in the tire radial direction of the cross belt 2 so as to cover the entire width of the cross belt 2, and is a belt reinforcing layer formed by rubber coating a plurality of cords arranged substantially parallel to the tire equator It is. Although one wide belt reinforcing layer is shown as the cap layer in FIG. 1, the present invention is not limited to this, and a plurality of layers may be arranged.

  In the present invention, a composite cord formed by twisting a plurality of types of organic fibers having different elastic moduli is used as the cord constituting the cap layer 3. Preferably, an organic fiber composite cord formed by twisting low elastic fibers and high elastic fibers is used.

  Specific examples of the low elastic fiber constituting the composite cord include nylon fiber, polyester fiber (excluding wholly aromatic polyester fiber), such as polyethylene terephthalate (PET) fiber, polyethylene naphthalate (PEN) fiber. Polytrimethylene terephthalate (PTT) fiber, polyvinyl alcohol fiber, aliphatic polyketone (PK) fiber, and the like.

  On the other hand, specific examples of highly elastic fibers include aromatic polyamide fibers (aramid fibers), wholly aromatic polyester fibers such as polyarylate fibers, polyvinyl alcohol fibers, carbon fibers, and polyparaphenylene benzoxazole (PBO) fibers. And lyocell fiber. The lyocell fiber is a cellulose fiber obtained from a raw material cellulose by a solvent spinning method. For example, as described in Japanese Patent Publication No. 60-28848 and Japanese Patent Publication No. 11-504995, A solution containing cellulose and a non-solvent such as water is spun into air or a non-precipitating medium, and at that time, the fiber-forming solution exiting from the spinneret is pulled at a speed higher than the speed at which it is fed. It can obtain by extending | stretching by the draw ratio more than double, and processing with a non-solvent.

  In addition, since the polyvinyl alcohol fiber can be used as either a low elastic fiber or a high elastic fiber, when a polyvinyl alcohol fiber is selected as one of the fibers, the elastic modulus is higher or lower than this as the combined fiber. It is necessary to select and use fibers appropriately.

  In the present invention, in particular, a composite cord obtained by twisting together aromatic polyamide fibers (aramid fibers) as high elastic fibers and nylon fibers as low elastic fibers is particularly suitable. Thus, by using the composite cord containing the high elastic fiber, the circumferential rigidity of the tire is increased, and the flat spot performance can be improved.

  Moreover, it is preferable to form a composite cord with two aramid fibers and one nylon fiber. Aramid fiber is a fiber that contributes to improved flat spot performance, and nylon fiber is a fiber that contributes to ride comfort performance. Is also advantageous.

  In the present invention, as shown in FIG. 1, at least one pair of narrow widths formed by rubber-drawing organic fiber cords arranged in both end regions of the cap layer 3 and arranged substantially parallel to the tire equator. A layer layer 4 may be provided. The composite code as described above can also be used as the code of the layer layer 4.

  The main structural features of the present invention are that the tensile residual stress of the composite cord located at the width center portion 3a (see FIG. 2) of the belt reinforcing layer 3 is σ1, and the tensile residual stress of the composite cord located at the width end portion 3b. When σ2 is σ2, σ1 / σ2 is 1.7 or less. Here, “tensile residual stress” in this specification means the tensile stress applied to the composite cord of the belt reinforcing layer in a tire product state after vulcanization (internal pressure zero state before rim assembly). .

  The technical significance will be described below. When the belt reinforcing layer 3 is formed of a cord including a high elastic fiber such as an aromatic polyamide fiber, the flat spot performance is improved as described above, but the circumferential rigidity is provided over the entire central portion and side portions of the belt reinforcing layer. As a result, the longitudinal spring constant of the tire increases, and there is a concern that the riding comfort and noise performance deteriorate. Pneumatic radial tires have a process in which a cross belt and a belt reinforcement layer are attached to a BT drum and inflated with air pressure to form the tread surface in a tire crown shape. The composite cord to be applied is in a state where tensile tension is applied as compared with the composite cord located at the width end. Therefore, usually σ1 / σ2 is a value larger than 2.0.

  Here, when σ1 / σ2 is 1.7 or less, the tensile residual stress σ1 of the composite cord located at the width center portion 3a of the belt reinforcing layer 3 is significantly reduced as compared with the conventional case. The circumferential rigidity of the width central portion 3a can be reduced. As a result, the vertical spring constant of the tire is greatly reduced, and the riding comfort performance and noise performance can be improved.

  Here, in order to improve the riding comfort performance and noise performance, not only the tensile residual stress σ1 of the composite cord located in the central portion 3a but also the tensile residual stress σ2 of the composite cord located in the width end portion 3b is reduced. The flat spot performance cannot be maintained. For this reason, in the present invention, it is important that σ1 / σ2 that is usually larger than 2.0 is set to 1.7 or less by reducing only σ1 without changing the value of σ2. Here, if σ1 / σ2 is larger than 1.7, it is not possible to sufficiently obtain the effect of improving the riding comfort performance and the noise performance.

  The absolute value of σ1 is preferably in the range of 17 to 51N, and σ2 is preferably in the range of 10 to 30N. This is because if σ2 is less than 10N, high-speed durability and flat spot performance may not be sufficiently obtained, which is not preferable. On the other hand, if it exceeds 30N, ride comfort may be deteriorated. A preferable range of σ1 is obtained by multiplying σ2 by 1.7.

  σ1 / σ2 is preferably 1.2 or more. When σ1 / σ2 is less than 1.2, there is no problem from the viewpoint of compatibility between flat spot performance, ride comfort performance, and noise performance, but the rigidity of the composite cord in the width central portion 3a is made too low to stabilize operation. This is because there is a risk of damaging the sex.

  In the present specification, the “composite cord located at the center of the width” refers to an arbitrary cord within a 7 mm width centering on the tire equator, and preferably means a composite cord located closest to the tire equator. . The “composite cord located at the width end” refers to an arbitrary cord in a region 7 mm wide from the end of the belt reinforcing layer 3 in the tire width direction.

  A method of measuring “tensile residual stress” in the present invention will be described. First, a predetermined portion of the composite cord is taken out from the vulcanized product tire by a predetermined length L1, and a stress-strain curve (SS curve) is measured for the cord. The SS curve is measured by the method defined in JIS-L-1013. Since the taken out composite cord is released from the product tire, it has a length shorter than L1 (described later in FIG. 4). The tensile stress when the cord is tensioned and extended to the length L1 when taken out is the “tensile residual stress” in the present invention. This is because the state extended to L1 indicates the distortion state of the composite cord at each position of the product tire.

  In FIG. 3, the outline of the stress-strain curve (SS curve) of the composite cord located in the width | variety center part and width | variety edge part of a belt reinforcement layer, respectively is shown. The case where both the composite cord at the center of the width and the composite cord at the width end are composite cords in which two aramid fibers and one nylon fiber are twisted together is illustrated.

  First, a conventional radial tire in which σ1 / σ2 is greater than 2.0 will be described with reference to FIG. x1 is a distortion of the tire product state after vulcanization of the composite cord located at the width end portion of the belt reinforcing layer, and x2 is that of the composite cord located at the width center portion of the belt reinforcing layer. Each SS curve is as shown. The tensile tension at the strain x2 in the SS curve of the composite cord at the width end portion is σ2, and the tensile tension at the strain x1 in the SS curve of the composite cord at the width center portion is σ1.

  Next, FIG. 3 (b) shows an outline of the stress-strain curve (SS curve) of the composite cord positioned at the width center portion 3a and the width end portion 3b of the belt reinforcing layer 3 in the present invention. x1 is the distortion of the tire product state after vulcanization of the composite cord located at the width end portion 3b of the belt reinforcing layer 3, and x2 is that of the composite cord located at the width center portion 3a of the belt reinforcing layer 3. . Each SS curve is as shown. The tensile tension at the time of strain x2 in the SS curve of the composite cord at the width end portion 3b is σ2, and the tensile tension at the time of strain x1 in the SS curve of the composite cord at the width center portion is σ1. Here, in FIG. 3B, compared with FIG. 3A, the slope of the SS curve of the composite code at the center of the width becomes gentler and σ1 becomes smaller.

  Here, in FIG. 3, although the composite cord of the width center portion 3a and the composite cord of the width end portion 3b are composite cords formed by twisting two aramid fibers and one nylon fiber, they are the same material. The reason why the SS curves are different will be described. The composite cord of the width center portion 3a is vulcanized in a state where a larger tensile tension is applied than the composite cord of the width end portion 3b. Thus, when the tensile tension during vulcanization is different, the tensile properties of the composite cord after vulcanization are also different.

  This will be described in more detail with reference to FIG. When both the composite cord of the width center portion 3a and the composite cord of the width end portion 3b are taken out from the product tire by a predetermined length L1, the taken-out composite cord is released from the product tire and thus has a length shorter than L1. Here, the composite code of the width end portion 3b is L2 smaller than L1, and the composite code of the width center portion 3a is L3 smaller than L1 but larger than L2. This is because the composite cord of the width center portion 3a is vulcanized in a state where a larger tensile tension is applied than the composite cord of the width end portion 3b, and the degree of plastic deformation is advanced. .

  Next, an example of the manufacturing method of the pneumatic radial tire 10 of the present invention will be described. Normally, a cylindrical BT drum having the same circumference is used regardless of the position in the width direction. In order to manufacture the pneumatic radial tire 10 of the present invention, the center portion of the width is larger than the circumference of the width end portion. A cross belt and a belt reinforcing layer are pasted on a BT drum having a long circumference and are inflated with air pressure to form a tire shape. In this way, when the product is completed, the tension applied to the composite cord at the center of the width can be made smaller than before, and σ1 / σ2 can be made smaller. In order to set σ1 / σ2 to 1.7 or less, it is necessary to make the circumferential length of the width center part 1.005 times or more than the width end part.

  The pneumatic tire of the present invention is particularly effective for an ultra flat tire having an aspect ratio of 45% or less. Such super flat tires tend to have high overall belt tension and good flat spot performance, but tend to deteriorate riding comfort, but according to the present invention, the riding comfort is also sacrificed. Because there is no.

  Next, in order to further clarify the effects of the present invention, a comparative evaluation performed using pneumatic tires according to the following examples and comparative examples will be described. In accordance with the conditions shown in Table 1 below, a pneumatic radial tire having a cap / layer structure as shown in FIG. 1 was prepared. The tire size was 305 / 30ZR20. The composite cord was formed by twisting one 900 dtex nylon and two 1100 dtex aramids. The present invention is characterized by optimizing the tensile residual stress of the composite cord constituting the belt reinforcing layer, and other tire structures are not required to be modified. Therefore, the present invention is the same as the conventional pneumatic radial tire.

<Evaluation of ride comfort and noise performance>
Each tire was assembled on a rim having a rim size of 20 × 11 J, filled with an internal pressure of 250 kPa, and mounted on an actual vehicle. The test course was run under the condition of one occupant, and a feeling evaluation was performed on ride comfort and noise performance. The evaluation results were all expressed as an index with Comparative Example 1 as 100. For both ride quality and noise performance, the higher the value, the better the result.

<Flat spot test>
Each tire was assembled on a rim having a rim size of 20 × 11 J, filled with an internal pressure of 250 kPa, a load of 4.0 kN was added, and a flat spot test was performed in the following procedure. The results were displayed as an index with the flat spot value of Comparative Example 1 as 100. The larger the numerical value, the better the result, which means that flat spots are reduced.

(1) Measure the RFV (Radial Force Variation; load fluctuation when the tire is pressed against a drum testing machine and rolled) of the test tire of the above size.
(2) Runs at 150 km / h for 30 minutes on the drum under the above load and internal pressure, and immediately after that, the RFV primary bottom (the waveform of the primary component extracted from the RFV waveform by Fourier series expansion (RFV primary component, vibration) Search for the smallest value).
(3) Press the position of the RFV primary bottom on the drum for 1 hour.
(4) Run at 100 km / h on the drum under the above load and internal pressure, measure the primary bottom value of RFV for every 2 km of travel distance, and in the measured RFV primary bottom value and test procedure (1) A difference between the measured RFV and the primary bottom value is calculated as a flat spot value by using an area value of a graph drawn with the travel distance of 0 to 10 km as the horizontal axis.

<High speed durability>
Each tire is assembled with a rim, adjusted to an internal pressure of 250 kPa, and then starts running at a speed of 220 km / h. The speed is gradually increased by 10 km / h every 20 minutes, and the speed when a failure occurs is measured and compared. The index was displayed with the failure occurrence rate of Example 1 as 100. The larger the index value, the higher the endurance limit speed and the higher the durability at high speed.

<Steering stability>
Each tire was attached to the vehicle, and the driving stability such as turning ability and lane changeability when running on the test course was evaluated by a professional driver. The evaluation results were displayed as an index with Comparative Example 1 as 100. The larger the index, the better the steering stability.

  If only σ2 is made smaller than Comparative Example 1 as in Comparative Example 2, the circumferential rigidity of the entire tire is somewhat reduced, so that the ride performance and noise performance are improved, but the flat spot performance cannot be maintained. In addition, it is inferior in high-speed durability and handling stability. On the other hand, when σ1 is increased as compared with Comparative Example 1 as in Comparative Example 3, riding comfort performance and noise performance deteriorate. Further, as in Comparative Example 4, when not only σ1 but also σ2 is reduced and the value of σ1 / σ2 is maintained at 2.0 as compared with Comparative Example 1, the riding comfort performance is the same as in Comparative Example 2.・ Although noise performance improves, flat spot performance cannot be maintained.

  On the other hand, as in Examples 1 to 4, when only σ1 is smaller than that of Comparative Example 1 and the value of σ1 / σ2 is 1.7 or less, the ride performance and noise are maintained while maintaining flat spot performance. The performance could be improved. Moreover, high-speed durability could be maintained. On the other hand, in Example 4, σ1 / σ2 is less than 1.2, and in this case, the steering stability is deteriorated. In the tire of this example, steering stability is a particularly important factor, and it is not preferable that the index is less than 100. Therefore, σ1 / σ2 is preferably 1.2 or more.

  In Example 5, the value of σ1 / σ2 was set to 1.0 while increasing σ2 compared to Comparative Example 1, but the overall performance increased, but the noise performance deteriorated somewhat, but the other performance was large. Improved.

  According to the present invention, when σ1 / σ2 is usually larger than 2.0, the value of 1.7 or less can improve the riding comfort performance and the noise performance while maintaining the flat spot performance. It was possible to provide a pneumatic radial tire that can be used.

DESCRIPTION OF SYMBOLS 1 Carcass 2 Crossing belt 2a, 2b Belt layer 3 Cap layer (belt reinforcement layer)
3a Width center portion of belt reinforcing layer 3b Width end portion of belt reinforcing layer 4 Layer layer 10 Pneumatic radial tire

Claims (4)

A cross belt composed of at least two cord rubber coating layers formed by laminating cords on the outer periphery of a crown portion of a carcass extending in a toroid shape so as to cross the tire equator, and a tire diameter of the cross belt And at least one belt reinforcing layer formed by covering a plurality of cords arranged in parallel to the tire equator and covered with rubber on the outer side in the direction so as to cover the entire width of the cross belt,
The cord constituting the belt reinforcing layer is a composite cord formed by twisting a plurality of types of organic fibers having different elastic moduli,
The tensile residual stress of the composite cord located at the center of the width of the belt reinforcing layer is σ1,
When the tensile residual stress of the composite cord located at the width end of the belt reinforcing layer is σ2,
σ1 / σ2 is in the range of 1.0 to 1.7,
The pneumatic radial tire characterized in that the σ1 is in a range of 17.5 to 29.75 N and the σ2 is in a range of 17.5 to 26.25 N.   The pneumatic radial tire according to claim 1, wherein the σ1 / σ2 is 1.2 or more.   The pneumatic radial tire according to claim 1 or 2, wherein the composite cord includes an aramid fiber and a nylon fiber.   The pneumatic radial tire according to claim 3, wherein the composite cord includes two of the aramid fibers and one of the nylon fibers.

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