JP2006143135A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of attaining weight reduction without impairing tire strength. <P>SOLUTION: This pneumatic tire 1 includes a carcass 6 having a carcass cord extending in a toroid state in between the bead core 5 embedded in a pair of bead parts 4, a belt layer 7 arranged outside in the tire radial direction and inside a tread part 2. The belt layer 7 includes one cord ply 8 made of a steel cord covered with a topping rubber and arranged in parallel and a reinforced rubber sheet body 9 overlapped with the cord ply 8 and having a complex elastic modulus of 50Mpa or more. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pneumatic tire that can be reduced in weight without impairing tire strength, and is particularly suitable for passenger cars.

  In recent years, there has been a demand for weight reduction of tires for the purpose of realizing low fuel consumption of a vehicle and improving steering stability by reducing unsprung weight in a suspension mechanism. In order to reduce the weight of a tire, for example, the rubber material is thinned, the tire cord is reduced in diameter, and further, the end is reduced. However, the weight reduction effect by such a technique is reaching its limit.

  In the case of a pneumatic radial tire for a passenger car, a belt layer for tagging the carcass is disposed outside the carcass having a radial structure. A general belt layer is formed by superposing two belt plies made of steel cord. Steel cords have a higher specific gravity than rubber, so if you can reduce the number of belt plies by one, you can expect a great weight reduction effect.

  Related prior art documents include the following. In Patent Document 1, a rubber layer is provided between two belt plies, but it is not intended to reduce the weight of the tire.

Japanese Unexamined Patent Publication No. 7-69004 JP-A-7-156612

  The present invention has been devised in view of the above circumstances, and the belt layer is overlapped with one cord ply in which a steel cord is covered with a topping rubber, and this cord ply has a complex elastic modulus of 50 MPa. The object of the present invention is to provide a lightweight pneumatic tire by reducing the number of belt plies of the steel cord while ensuring the tire strength, based on the construction of the reinforced rubber sheet body as described above.

  The invention described in claim 1 is a carcass having a carcass cord extending between a bead core embedded in a pair of bead portions in a toroidal shape, and is arranged outside the tire radial direction and inside the tread portion. A pneumatic tire provided with a belt layer, wherein the belt layer is overlapped on the cord ply with one cord ply in which a parallel steel cord is covered with a topping rubber and has a complex elastic modulus. It is characterized by comprising a reinforced rubber sheet body of 50 MPa or more.

  The invention according to claim 2 is characterized in that the reinforced rubber sheet body is composed of a short fiber reinforced rubber sheet in which short fibers are oriented in a matrix rubber, and its loss tangent tan δ is 0.35 or less. The pneumatic tire according to claim 1.

  The complex elastic modulus and loss tangent tan δ of the reinforced rubber sheet were prepared by preparing a strip-shaped sample of 4 mm width × 30 mm length × 2.0 mm thickness, and using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. It is a value measured under the conditions of 70 ° C., frequency 10 Hz, initial elongation strain 10%, half amplitude 1%.

  According to a third aspect of the present invention, the reinforcing rubber sheet body comprises a central short fiber reinforced rubber sheet piece continuously extending in the tire circumferential direction on the tire equator, and continuously disposed in the tire circumferential direction on both sides thereof. 3. The pneumatic tire according to claim 2, further comprising: an outer short fiber reinforced rubber sheet piece that extends and having different short fiber orientation directions in adjacent short fiber oriented rubber sheet pieces in each tire axial direction. It is.

  The invention according to claim 4 is the pneumatic tire according to any one of claims 1 to 3, wherein the reinforced rubber sheet body has a width at least equal to the cord ply.

  In the pneumatic tire of the present invention, the belt layer is composed of one cord ply and a reinforced rubber sheet body that is stacked on the cord ply and has a complex elastic modulus of 50 MPa or more. The reinforced rubber sheet has a smaller specific gravity than the steel cord belt ply, and therefore can easily provide a lightweight tire. Further, since the complex elastic modulus of the reinforced rubber sheet body is limited to a certain range, the rigidity of the tread portion is not excessively impaired, and a practically necessary strength can be sufficiently secured.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a meridian cross-sectional view (right half cross-sectional view) including the tire rotation axis of the pneumatic tire of the present embodiment, and FIG. 2 is a developed schematic view in which the internal structure including the belt layer is developed. The pneumatic tire 1 includes a carcass 6 including a carcass cord 6C extending in a toroidal shape between bead cores 5 and 5 embedded in a pair of bead portions 4 and 4, and a tread portion on the outer side in the tire radial direction of the carcass 6. 2 is provided, and in this example, a radial tire 1 for a passenger car is illustrated.

  The carcass 6 is composed of one or more radial structures in which the carcass cord 6C is arranged at an angle of, for example, 80 ° to 90 ° with respect to the tire equator C, in this example, one carcass ply 6A. As the carcass cord 6C, for example, an organic fiber cord such as polyester, nylon, rayon, or aramid is employed. In this example, a polyester cord is used. In addition, the carcass ply 6A includes a main body portion 6a extending between the bead cores 5 and 5 in a toroidal shape, and a folded portion 6b that is connected to the main body portion 6a and is folded around the bead core 5 from the inner side to the outer side in the tire axial direction. . A bead apex 8 made of hard rubber extending from the bead core 5 to the outer side in the tire radial direction is disposed between the main body portion 6a and the folded portion 6b, and the bead portion 4 is appropriately reinforced.

  The belt layer 7 is composed of one cord ply 8 and a reinforced rubber sheet body 9 that is stacked on the cord ply 8 and has a complex elastic modulus of 50 MPa or more. In the belt layer 7 of this embodiment, a cord ply 8 is disposed on the inner side in the tire radial direction, and a reinforced rubber sheet body 9 having a width BW substantially equal to the cord ply 8 is overlapped on the outer side.

  In such a pneumatic tire 1, the number of cord plies included in the belt layer 7 is reduced by one compared to a general radial tire for passenger cars. In order to supplement the reinforcing ability, a reinforced rubber sheet body 9 having a specific gravity smaller than that of the cord ply is incorporated instead of the reduced cord ply. For this reason, the pneumatic tire 1 of the present invention can reduce the weight of the belt layer.

  The cord ply 8 is constituted by a steel cord ply in which a plurality of parallel steel cords 8C are covered with a topping rubber. The cord ply 8 is exemplified by a steel cord 8C that is inclined with respect to the tire equator C at a small angle, for example, an angle of about 15 to 40 °. Although there is no particular limitation, if the angle is less than 15 °, the in-plane rigidity when the slip angle is given tends to be lowered, and there is a tendency that sufficient cornering force cannot be obtained. If it exceeds, the hoop effect on the carcass 6 is lowered, the expansion deformation of the tread portion 2 is increased, and the wear resistance of the tread portion 2 tends to be deteriorated.

  Although not particularly limited, the cord ply 8 has an end number of 15 to 60 (lines / 5 cm), more preferably 20 to 50 (lines / 5 cm), which is the number of steel cords 8C driven per 5 cm of ply width. It is desirable that When the ending is less than 15 (lines / 5 cm), the ply rigidity of the cord ply 8 tends to decrease, and the tire strength necessary for the belt layer 7 tends not to be obtained, and conversely exceeds 60 (lines / 5 cm). The topping rubber does not sufficiently permeate between the steel cords 8C and 8C, and the rubber tends to be peeled between the cords. The steel cord 8C of this embodiment is formed by twisting four strands having a wire diameter of 0.3 mm, and its end is 40 (lines / 5 cm).

  In the present embodiment, the reinforced rubber sheet body 9 is configured by a short fiber reinforced rubber sheet 11 in which short fibers f are oriented in a matrix rubber r. Such a short fiber reinforced rubber sheet 11 can give a high complex elastic modulus in the orientation direction of the short fibers, for example, and is particularly effective as a rubber material for reinforcing the tread portion 2.

  The complex elastic modulus of the short fiber reinforced rubber sheet 11 is at least 50 MPa or more, preferably 70 MPa or more. Since only one cord ply 8 is used as the belt layer 7, if the complex elastic modulus is less than 50 MPa, the performance required for the belt layer 7 to tighten the carcass 6 and increase the rigidity of the tread portion 2 Cannot be demonstrated. On the other hand, when the complex elastic modulus is too large, the rigidity becomes too high, the envelope performance of the tread portion 2 is lowered, and the riding comfort tends to be deteriorated. From such a viewpoint, the upper limit of the complex elastic modulus is preferably 1000 MPa or less, more preferably 500 MPa or less, and still more preferably 100 MPa or less. When the reinforced rubber sheet body 9 exhibits anisotropy due to the orientation of the short fibers f, it is sufficient that the maximum value of the complex elastic modulus of the reinforced rubber sheet body satisfies the above-mentioned numerical limitation.

  Further, the loss tangent tan δ of the short fiber reinforced rubber sheet 11 is preferably 0.35 or less, more preferably 0.30 or less, and further preferably 0.25 or less. When the loss tangent tan δ exceeds 0.35, most of the elastic energy stored in the short fiber reinforced rubber sheet 11 deformed during turning travel is converted into heat energy, which tends to inhibit the generation of a large cornering force. In addition, the internal heat generation of the tread portion 2 tends to increase and the durability tends to deteriorate. The lower limit value of the loss tangent tan δ is not particularly limited, but for example, 0.05 or more is practical.

  Further, the matrix rubber r of the short fiber reinforced rubber sheet 11 is preferably a diene rubber, for example, specifically, one or two of natural rubber, isoprene rubber, styrene butadiene rubber, butadiene rubber, chloroprene rubber, acrylonitrile butadiene rubber, or the like. More than one species can be blended and used. Further, the short fiber f is preferably non-metallic having a low specific gravity and excellent adhesion to rubber, and specifically, nylon, polyester, aramid, rayon, vinylon, aromatic polyamide, cotton, cellulose resin, In addition to organic substances such as crystalline polybutadiene, boron, glass fiber, carbon fiber, or the like is desirable, and these can be used alone or in combination of two or more. Particularly preferably, the fiber has a tensile modulus of elasticity of 50 to 1000 GPa, more preferably 100 to 800 GPa, measured according to JIS R7601 “Carbon Fiber Test Method”.

  The short fiber f preferably has an average fiber diameter of 1 to 100 μm and an average length of 0.1 to 5 mm, for example. When the average fiber diameter is less than 1 μm or the length is less than 0.1 mm, the rubber reinforcing effect due to the short fiber itself tends to decrease, and conversely, the average fiber diameter is greater than 100 μm or the length is 5 mm. If it is larger than that, the short fiber f becomes too large, the adhesion to rubber is lowered, and the wear resistance and crack resistance are lowered. From this viewpoint, it is particularly desirable that the average fiber diameter of the short fibers is 3 to 50 μm and the length thereof is 0.1 to 3 mm.

  The short fiber reinforced rubber sheet 11 is preferably prepared by blending, for example, 5 to 70 parts by weight, and more preferably 10 to 60 parts by weight of the short fiber f with respect to 100 parts by weight of the matrix rubber. If the short fiber f is less than 5 parts by weight, the reinforcing effect is not sufficient. Conversely, if the short fiber f exceeds 70 parts by weight, the interface between the matrix rubber and the short fiber is increased and the tear resistance, crack resistance, etc. are reduced. Tend. Needless to say, the total weight of the short fiber reinforced rubber sheet 11 is smaller than the total weight of the cord ply 8. Table 1 shows some examples of blending of such short fiber reinforced rubber sheet 11.

  In the embodiment shown in FIG. 2, the short fibers f of the short fiber reinforced rubber sheet 11 are oriented substantially along the tire axial direction (the longitudinal direction of the short fibers f is substantially along the tire axial direction). ). In such a short fiber reinforced rubber sheet 11, the complex elastic modulus E * a in the tire axial direction is larger than the complex elastic modulus E * c in the tire circumferential direction. In the embodiment shown in FIG. 3, the short fibers f of the short fiber reinforced rubber sheet 11 are oriented substantially along the tire circumferential direction (the longitudinal direction of the short fibers f is substantially along the tire circumferential direction). ). In such a short fiber reinforced rubber sheet 11, the complex elastic modulus E * c in the tire circumferential direction is larger than the complex elastic modulus E * a in the tire axial direction.

  When a slip angle is given to the tire during traveling of the vehicle, the reinforced rubber sheet body 9 (short fiber reinforced rubber sheet 11) included in the ground plane has a ground plane as shown by an arrow A in FIGS. An in-plane bending moment in a plane parallel to the surface (however, the direction may be reversed) acts on each short fiber reinforced rubber sheet 11 with a tensile stress in the arrow B direction and a compressive stress in the arrow C direction. Works. In the aspect of FIG. 2, there is an effect of suppressing the compressive deformation in the axial direction of the short fiber reinforced rubber sheet 11. However, since the complex elastic modulus E * c in the tire circumferential direction of the short fiber reinforced rubber sheet 11 is relatively smaller than the complex elastic modulus E * a in the tire axial direction, in the direction of tensile or compressive stress B, C. Is relatively easy to stretch. Therefore, the amount of deformation of the short fiber reinforced rubber sheet 11 tends to be slightly increased during turning.

  On the other hand, in the embodiment of FIG. 3, the complex elastic modulus E * c in the tire circumferential direction of the short fiber reinforced rubber sheet 11 is relatively larger than the complex elastic modulus E * a in the tire axial direction. It is difficult to extend in both the B and C directions. Therefore, when turning, for example, the short fiber reinforced rubber sheet 11 can have a small deformation amount to prevent buckling of the belt layer 7 and exhibit high in-plane bending rigidity. This makes it possible to generate a large cornering force on the tire.

  FIG. 4 and FIG. 5 show still another embodiment of the short fiber reinforced rubber sheet 11. The short fiber reinforced rubber sheet of this embodiment includes a central short fiber reinforced rubber sheet piece 11A continuously extending in the tire circumferential direction on the tire equator C, and an outer side extending on both sides and continuously extending in the tire circumferential direction. Short fiber reinforced rubber sheet pieces 11B and 11B are included. The sheet pieces 11A and 11B are arranged with their side edges in contact with each other. In this example, the center short fiber reinforced rubber sheet 11A is the widest width of about 0.5 times the entire width, and is substantially bilaterally symmetrical. It is composed of

  As shown in FIG. 5, the direction of the acting stress during cornering is different between the central region in the vicinity of the tire equator C and its side region. For this reason, in this embodiment, the orientation directions of the short fibers of the short fiber oriented rubber sheet pieces 11A and 11B adjacent in the tire axial direction are different. In this example, the short fibers f of the central short fiber reinforced rubber sheet piece 11A are oriented along the tire axial direction, and the short fibers f of the outer short fiber reinforced rubber sheet pieces 11B and 11B are along the tire circumferential direction. Oriented. Therefore, as shown in FIG. 5, when the tensile stress B and the compressive stress C due to the in-plane bending moment A during turning are applied to the short fiber reinforced rubber sheet 11, the outer short fiber reinforced rubber sheet pieces 11B and 11B Since the complex elastic modulus E * c in the tire circumferential direction is large as in the embodiment of FIG. Further, the short fiber reinforced rubber sheet 11A at the center increases resistance to compressive stress D from the outer short fiber reinforced rubber sheet pieces 11B and 11B. Therefore, in such an embodiment, the in-plane rigidity of the reinforced rubber sheet body 9 is further improved, and a much larger cornering force is generated to help improve the steering stability.

  Further, the thickness t of the short fiber reinforced rubber sheet 11 is not particularly limited, but if it is too small, the reinforcing effect of the tread portion 2 is lowered, and conversely, if it is too large, the tire weight is likely to increase. From such a viewpoint, the thickness t of the short fiber reinforced rubber sheet 11 is preferably 0.3 mm or more, more preferably 0.5 mm or more, and the upper limit is preferably 30 mm or less, more preferably 20 mm or less. .

  Moreover, the belt layer of each said embodiment has illustrated the thing which has arrange | positioned the reinforced rubber sheet | seat body 9 in the tire radial direction outer side of the cord ply 8. FIG. Such an aspect is preferable in terms of good productivity.

FIG. 6 shows another embodiment of the belt layer 7.
In this embodiment, an example in which a reinforced rubber sheet body 9 is disposed on the inner side in the tire radial direction of the cord ply 8 is illustrated. Such an aspect is advantageous in that the tire expansion rate can be kept low and the dimensional change can be made smaller than that in which the reinforced rubber sheet body 9 is disposed outside the cord ply 8 in the tire radial direction.

  Further, the reinforced rubber sheet body 9 shown in FIG. 6 includes a first short fiber reinforced rubber sheet piece 11a in which the short fibers f are oriented along the first direction, and the short fibers f that are overlapped on the outer side in the tire radial direction. Includes at least a second short fiber reinforced rubber sheet piece 11b oriented in a second direction different from the first direction. That is, an example in which at least two short fiber reinforced rubber sheets with different orientation directions of the short fibers f are stacked in the tire radial direction is exemplified. Crossing the short fibers f exhibits a stronger reinforcing effect and helps the belt layer 7 exhibit high in-plane bending rigidity. The angle α formed by the first direction and the second direction is preferably 30 to 150 °, more preferably 70 to 110 °.

  Although the embodiment of the present invention has been described above, it is needless to say that the present invention is not limited to the illustrated embodiment but is modified in various forms. For example, a jointless band in which an organic fiber cord is spirally wound in the tire circumferential direction can be disposed outside the belt layer 7 in the tire radial direction.

  In order to confirm the effect of the present invention, a radial tire for passenger cars having a tire size of “195 / 65R15 91S” based on the specifications in Table 1 was prototyped and tested for tire weight, cornering force, and tire strength. As described above, the steel cord of the cord ply was formed by twisting four steel strands having a wire diameter of 0.3 mm, and the end was 40 (pieces / 5 cm). The test method is as follows.

<Tire weight>
The weight of each test tire was measured and displayed as an index with the tire weight of Comparative Example 1 being 100. The smaller the value, the smaller the tire weight.

<Tire expansion coefficient>
As shown in FIG. 7, the maximum outer diameter R1 obtained from the tire cross-sectional profile when each test tire is assembled on a regular rim (15 × 6JJ) and filled with 10 kPa, and the profile when filled with 200 kPa. The tire expansion coefficient was measured by the following formula from the maximum outer diameter R2 obtained.
Tire expansion coefficient = (R2-R1) / R1 × 100
If the tire expansion rate becomes excessively large, the distortion of the tread portion is localized during filling with internal pressure, which is not preferable.

<Cornering Force>
Using a laboratory tester, the cornering force of each test tire was measured under the following conditions.
Rims: 15x6JJ
Internal pressure: 200 kPa
Slip angle: 12 ° Longitudinal load: 4.35kN
Speed: 10km / H
The results were expressed as an index with the cornering force of Comparative Example 1 as 100. The larger the value, the better.

<Tire strength>
The tire was assembled on a rim (15 × 6JJ), and water was injected from the tire valve into the tire lumen to adjust the water pressure to 500 kPa. And it was allowed to stand for 24 hours and the undestructed one was regarded as acceptable. Table 1 shows the test results.

  As a result of the test, it can be confirmed that the tire of the example is lighter than the comparative example. As for the cornering force, a value comparable to the comparative example is obtained, and practical steering stability can be sufficiently expected. Moreover, it passed the severe water pressure destruction test, and it was confirmed that there was no problem with the tire strength. Furthermore, if the tire expansion rate is too large, the cornering force tends to be small and the steering stability tends to decrease. Therefore, the tire expansion rate is preferably -5 to 20%, more preferably 0 to 10%. It is desirable to set the rigidity of the belt layer 7 so that it can be suppressed to%. Therefore, the tire of the present invention can be reduced in weight and can be provided at low cost. For example, it is also suitable as a spare tire.

It is sectional drawing of the tire which shows embodiment of this invention. It is an expanded view which expand | deploys and shows a belt layer. It is an expanded view of the belt layer which shows other embodiment. It is an expanded view of the belt layer which shows other embodiment. It is a fragmentary perspective view of a belt layer. It is an expanded view of the belt layer which shows other embodiment. The cross-sectional profile of the tire explaining a tire expansion rate is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 7 Belt layer 8 Cord ply 9 Reinforced rubber sheet body r Matrix rubber f Short fiber

Claims (4)

A carcass having a carcass cord extending in a toroidal shape between bead cores embedded in a pair of bead portions;
A pneumatic tire provided with a belt layer disposed outside the tire radial direction and inside the tread portion,
The belt layer is composed of one cord ply in which parallel steel cords are covered with a topping rubber, and a reinforced rubber sheet body that is superimposed on the cord ply and has a complex elastic modulus of 50 MPa or more. A featured pneumatic tire.   2. The pneumatic tire according to claim 1, wherein the reinforced rubber sheet body is made of a short fiber reinforced rubber sheet in which short fibers are oriented in a matrix rubber, and the loss tangent tan δ is 0.35 or less. . The reinforced rubber sheet body includes a central short fiber reinforced rubber sheet piece continuously extending in the tire circumferential direction on the tire equator, and an outer short fiber reinforced rubber sheet piece arranged on both sides and continuously extending in the tire circumferential direction. Including
3. The pneumatic tire according to claim 2, wherein the orientation directions of the short fibers of the short fiber oriented rubber sheet pieces adjacent in the tire axial direction are different.   The pneumatic tire according to claim 1, wherein the reinforced rubber sheet body has at least a width of the cord ply.

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