Pneumatic radial tires

Abstract: A pneumatic radial tire (1) for passenger cars has good cornering property and either or both of durability and high-speed durability and comprises a circumferential belt layer (7) in addition to a slant belt layer (6), in which specified PET, nylon, PEN or vinylon fiber cords or steel cords as particularly defined are used in the circumferential belt layer.

Description: This invention relates to a pneumatic radial tire having good cornering property and either or both of durability and high-speed durability, and more particularly to a pneumatic radial tire for use in general-purpose passenger cars mainly developed for weight reduction. With the demands of energy saving, it has been attempted to improve the fuel consumption in automobiles by reducing the weight, and in particular by achieving weight reduction in tires, especially in pneumatic radial tires for use in general-purpose passenger cars. In general, a pneumatic radial tire comprises a so-called cross belt formed by laminating at least two slant belt layers on an outer periphery of a carcass crown portion so as to cross cords of these layers with each other. From the viewpoint of tire weight reduction, there have been developed tires comprising a belt composed of a single slant belt layer and a circumferential belt layer(s) containing light-weight organic fiber cords arranged substantially in parallel to the equatorial plane of the tire. Tires of this type are disclosed in, for example, JP-A-62-152904 and JP-A-4-163212. In the tires disclosed in these publications, organic fiber cords having a high tensile rigidity in the circumferential direction such as aromatic polyamide fiber cords (e.g. Kevlar cord) and the like are used as one cord in the circumferential belt layer. Further, there is disclosed that the circumferential belt layer can control the pushing out of the tread portion through centrifugal force during high-speed running to improve the high-speed durability. Moreover, organic fiber cords widely used as carcass ply cords such as polyethylene terephthalate (hereinafter abbreviated as PET) fiber cord, nylon fiber cord, polyethylene naphthalate (hereinafter abbreviated as PEN) fiber cord and vinylon (PVA) fiber cord have considerably low tensile rigidity in the circumferential direction as compared with aromatic polyamide fiber cord, so that they are not applied as the cord for the circumferential belt layer. Also, the use of steel cords for the circumferential belt layer is unfavourable from the viewpoint of weight reduction and the like, so that steel cords are not used in the circumferential belt layer. When aromatic polyamide fiber cords are used in the circumferential belt layer, however, the resistance to compression fatigue is poor, so that it has been confirmed that the belt is apt to create compression breakage accompanied with buckling deformation of the belt generated during severe cornering. The present inventors have made various studies with respect to the use of organic fiber cords in the circumferential belt layer and found that PET, nylon, PEN and vinylon fiber cords, which have not been practically used in circumferential belt layers in the past, can be used in the circumferential belt layer by rationalizing the twisting structure, total denier and twist constant of such a cord, and also high-strength steel cords formed by rationalization of the twisting structure can be used in the circumferential belt layer without so increasing the tire weight. JP-A-06-247105 describes a pneumatic radial tire comprising a carcass 4 toroidally extending between a pair of bead cores 3 and a belt 5,6 superimposed on a crown portion of the carcass and comprised of a slant belt layer 5 (two slant belt layers 5 in the illustrated embodiment) containing a plurality of cords or filaments arranged at a given inclination angle with respect to an equatorial plane of the tire and a circumferential belt edge cover layer 6 laminated on the slant belt layer 5 and containing a plurality of cords arranged substantially in parallel to the equatorial plane, wherein the cord used in the circumferential belt edge cover layer 6 is made from aliphatic polyamide fiber and has a double twisting structure and a total denier D of 1500-4000 and a twist constant N t satisfying N t = T x (0.139 x D/ρ) ½ x 10 -3 of 0.06 to 0.3, wherein T is the twisting number (twists/10 cm) and ρ is the specific gravity (g/cm 3 ). It is an object of the invention to provide pneumatic radial tires having good cornering property and either or both of durability and high-speed durability by using rationalized PET fiber cords, nylon fiber cords, PEN fiber cords, vinylon fiber cords or steel cords in the circumferential belt layer, particularly pneumatic radial tires for use in general-purpose passenger cars developed for attaining a reduction of tire weight. The present invention in one aspect provides a pneumatic radial tire comprising a carcass toroidally extending between a pair of bead cores and a belt superimposed on a crown portion of the carcass and comprised of a single slant belt layer containing a plurality of cords or filaments arranged at a given inclination angle with respect to an equatorial plane of the tire and one or more circumferential belt layers laminated on the slant belt layer and containing a plurality of cords arranged substantially in parallel to the equatorial plane, wherein at least one said circumferential belt layer is a width-wide circumferential belt layer covering approximately the full surface of the slant belt layer, and wherein the cord used in said one or more circumferential belt layers is made from polyethylene terephthalate or nylon fiber and has a layer twisting structure and a total denier D T of 1000d-6000d and a twist constant N t satisfying N t = T x (0.139 x D T /2 x 1/ρ) ½ x 10 -3 ≤ 0.3 wherein T is the twisting number (twist turns/10 cm) and ρ is the specific gravity, and that a coating rubber for the said one or more circumferential belt layers has a modulus of elasticity of not less than 200 kgf/mm 2 . The invention in a second aspect provides a pneumatic radial tire comprising a carcass toroidally extending between a pair of bead cores and a belt superimposed on a crown portion of the carcass and comprised of a single slant belt layer containing a plurality of cords or filaments arranged at a given inclination angle with respect to an equatorial plane of the tire and one or more circumferential belt layers laminated on the slant belt layer and containing a plurality of cords arranged substantially in parallel to the equatorial plane, wherein at least one said circumferential belt layer is a width-wide circumferential belt layer covering approximately the full surface of the slant belt layer, and wherein the cord used in said one or more circumferential belt layers is made from polyethylene naphthalate fiber and has a layer twisting structure and a total denier D T of 1000d-6000d and a twist constant N t satisfying N t = T x (0.139 x D T /2 x 1/ρ) 1/2 x 10 -3 ≤ 0.5 wherein T is the twisting number (twist turns/10 cm) and ρ is the specific gravity, and that a coating rubber for the said one or more circumferential belt layers has a modulus of elasticity of not less than 200 kgf/mm 2 . The invention in a third aspect provides a pneumatic radial tire comprising a carcass toroidally extending between a pair of bead cores and a belt superimposed on a crown portion of the carcass and comprised of a single slant belt layer containing a plurality of cords or filaments arranged at a given inclination angle with respect to an equatorial plane of the tire and one or more circumferential belt layers laminated on the slant belt layer and containing a plurality of cords arranged substantially in parallel to the equatorial plane, wherein at least one said circumferential belt layer is a width-wide circumferential belt layer covering approximately the full surface of the slant belt layer, and wherein the cord used in said one or more circumferential belt layers is made from vinylon fiber and has a layer twisting structure and a total denier D T of 1000d-6000d and a twist constant N t satisfying N t = T x (0.139 x D T /2 x 1/ρ) 1/2 x 10 -3 ≤ 0.6 wherein T is the twisting number (twist turns/10 cm) and ρ is the specific gravity, and that a coating rubber for the said one or more circumferential belt layers has a modulus of elasticity of not less than 200 kgf/mm 2 . The invention in a fourth aspect provides a pneumatic radial tire comprising a carcass toroidally extending between a pair of bead cores and a belt superimposed on a crown portion of the carcass and comprised of a single slant belt layer containing a plurality of cords or filaments arranged at a given inclination angle with respect to an equatorial plane of the tire and one or more circumferential belt layers laminated on the slant belt layer and containing a plurality of cords arranged substantially in parallel to the equatorial plane, wherein at least one said circumferential belt layer is a width-wide circumferential belt layer covering approximately the full surface of the slant belt layer, and wherein the cord used in said one or more circumferential belt layers is a steel cord having a modulus of elasticity of not less than 3000 kgf/mm 2 and a twisting structure of 1 x N or 1 + N in which N is the number of steel filaments, and that a coating rubber for said one or more circumferential belt layers has a modulus of elasticity of not less than 200 kgf/mm 2 . The term "layer twisting structure" used herein means that one or more fibers are twisted in a certain direction (cable twist) and two or more fibers are twisted in a direction opposite thereto (ply twist). The term "total denier" used herein means a product of fiber denier and number of fibers to be twisted. It is preferable that the cord for the circumferential belt layer has a loss tangent (tan δ) of not more than 0.3 under conditions that initial tension is 1 kgf/cord, strain amplitude is 0,1%, frequency is 20 Hz and atmospheric temperature is 25°C. In case of requiring further circumferential rigidity in the circumferential belt layer as compared with the case of using the PET, nylon, PEN or vinylon fiber cords, the cord in the circumferential belt layer is a steel cord having a modulus of elasticity of not less than 3000 kgf/mm 2 and a twisting structure of 1 x N or 1 + N in which N is the number of steel filaments. In preferred embodiments of the invention, the cord for the circumferential belt layer is spirally wound around the slant belt layer; and the slant belt layer contains steel cords or steel filaments therein; and the slant belt layer has a cord inclination angle of 15-45° with respect to the equatorial plane; and a gauge of rubber located between the cord of the slant belt layer and the cord of an innermost circumferential belt layer in a radial direction of the tire is made larger in a side end region of the tire than in a central region thereof in the widthwise direction at a radial section of the tire; and further a gauge of rubber located between the cord of an outermost circumferential belt layer in the radial direction and an inner periphery of a tread rubber is made larger in the central region of the tire than in the side end region thereof in the widthwise direction at a radial section of the tire; and at least two circumferential belt layers are disposed in the central region in the widthwise direction of the tire; and at least two circumferential belt layers are disposed in the side end region in the widthwise direction of the tire. Moreover, the modulus of elasticity of the coating rubber for the circumferential belt layer is calculated from a relationship between load and displacement by compactly filling a rubber specimen 9 in a cylindrical cavity of a steel jig 8 having a diameter d of 14 mm and a height h of 28 mm as shown in Fig. 7a of the accompanying drawings, setting the jig 8 into a compression testing machine 10 as shown in Fig. 7b and applying a load W onto upper and bottom faces of the rubber specimen 9 at a rate of 0.6 mm/min to measure displacement by means of a laser displacement meter 11. The invention will be further described with reference to the accompanying drawings, wherein: Fig. 1 is a diagrammatic sectional view of a first embodiment of a pneumatic radial tire according to the invention; Fig. 2 is a diagrammatic sectional view of a second embodiment of a pneumatic radial tire according to the invention; Fig. 3 is a diagrammatic view illustrating a gauge of rubber located between cord of a slant belt layer and cord of an innermost circumferential belt layer in the radial direction of the tire; Fig. 4 is a diagrammatic view illustrating a gauge of rubber located between cord of an outermost circumferential belt layer in the radial direction of the tire and an inner peripheral face of a tread rubber; Fig. 5 is a diagrammatic sectional view of a third embodiment of a pneumatic radial tire according to the invention; Fig. 6 is a diagrammatic sectional view of a fourth embodiment of a pneumatic radial tire according to the invention; and Figs. 7a and 7b are diagrammatic views illustrating a method for measuring a modulus of elasticity of a coating rubber for a circumferential belt layer. In Fig. 1 is diagrammatically shown a radial section of a first embodiment of a pneumatic radial tire according to the invention, in which numeral 1 is a pneumatic radial tire, numeral 2 a bead core, numeral 3 a carcass, numeral 4 a crown portion of the carcass, numeral 5 the equatorial plane of the tire, numeral 6 a slant belt layer, and numeral 7 a circumferential belt layer. In this tire 1, the slant belt layer 6 containing a plurality of cords or filaments arranged at a certain inclination angle with respect to the equatorial plane 5 is superimposed around the crown portion 4 of the carcass 3 toroidally extending between at least a pair of the bead cores 2, and further at least one circumferential belt layer 7 containing a plurality of cords arranged substantially in parallel to the equatorial plane 5 is disposed on the slant belt layer 6. As the cord for the circumferential belt layer 7 are used PET fiber cords, nylon fiber cords, PEN fiber cords, vinylon fiber cords or steel cords. When PET, nylon, PEN or vinylon fiber cord is used in the circumferential belt layer 7, if the cord has a layer twisting structure, a total denier D T of 1000d - 6000d and a twist constant (twisting coefficient) N t of not more than 0.3 in the case of PET or nylon fiber, not more than 0.5 in the case of PEN fiber or not more than 0.6 in the case of vinylon fiber, sufficient cornering power is obtained. Moreover, the formation of the layer twisting structure is based on the improvement of resistance to compression fatigue of the cord itself and the operability. When the total denier is less than 1000d, the cords can not physically be arranged in the circumferential belt layer, while when the total denier exceeds 6000d, the cord becomes too thick and hence the amount of rubber used undesirably increases to bring about an increase of tire weight. If the twist constant N t is too small, there is danger of loosening the cord to degrade the operability, so that the lower limit of the twist constant is preferably 0.1 for all of these organic fiber cords. In the case of using the PET, nylon, PEN or vinylon fiber cords in the circumferential belt layer, cord braking-up through compression fatigue hardly occurs as compared with the conventionally used aromatic polyamide fiber cord. Since the organic fibers such as PET, nylon, PEN and vinylon fibers exhibit large work loss and are apt to generate heat, when these fiber cords are used in the belt layer, there is a possibility that they are fused to bring about tire burst as a result of a test for high-speed durability. For this end, it is preferably to prevent the fusion of these fiber cords by rendering the loss tangent (tan δ) of each of these fiber cords used in the circumferential belt layer 7 to be not more than 0.3 under conditions that initial tension is 1 kgf/cord, strain amplitude is 0,1%, frequency is 20 Hz and atmospheric temperature is 25°C. When steel cord is used in the circumferential belt layer 7, if the steel cord has a modulus of elasticity of not less than 3000 kgf/mm 2 and a twisting structure of 1 x N or 1 + N, the rigidity in the circumferential direction can be more enhanced while somewhat increasing the tire weight as compared with the case of using the above organic fiber cords, whereby more satisfactory cornering power can be obtained. When the modulus of elasticity is less than 3000 kgf/mm 2 , the rigidity can not effectively be enhanced. Further, when the twisting structure is not 1 x N or 1 + N, the reductions of weight and cost can not be attained. Moreover, the end count of steel cords in the circumferential belt layer is preferably within a range of 15-50 cords/50 mm from the viewpoint of maintenance of circumferential rigidity and weight reduction. As seen from the above, the cord to be used in the circumferential belt layer 7 can properly be selected from the group consisting of PET fiber cord, nylon fiber cord, PEN fiber cord, vinylon fiber cord and steel cord in accordance with the use purpose. On the other hand, even when the cord used in the circumferential belt layer 7 satisfies the above requirements, if the modulus of elasticity of a coating rubber for the circumferential belt layer 7 is too low, the cords are easily moved in the belt layer to cause local buckling of the cord and hence there is a danger of creating cord break-up. For this end, the modulus of elasticity of the coating rubber for the circumferential belt layer 7 is restricted to not less than 200 kgf/mm 2 , whereby cord break-up can be prevented. Moreover, the circumferential belt layer is formed by spirally winding the cord around the slant belt layer, whereby the uniformity of the tire can be improved. The number of the circumferential belt layers is preferably 1 or 2 from the viewpoint of weight reduction. Furthermore, sufficient tire casing strength is obtained by using steel cords or steel filaments in the slant belt layer 6. In this case, the inclination cord angle with respect to the equatorial plane 5 in the slant belt layer is within a range of 15-45° for providing sufficient in-plane shearing rigidity. As shown in Fig. 3, a gauge tl of rubber located between the cord of the slant belt layer 6 and the cord of an innermost circumferential belt layer 7 in the radial direction is made larger in a side end region 13 of the tire than in a central region 12 thereof in the widthwise direction at a radial section of the tire. Specifically, the rubber gauge in the side end region 13 is 2 times or more the rubber gauge in the central region 12. On the other hand, a range L2 maintaining the rubber gauge in the central region 12 is 50-90% of a width L1 of the slant belt layer 6 centering around the equatorial plane 5. Thus, there is created a so-called sandwich beam effect (T. W. Chou and F. K. Ko, "Textile Structural Composite", Elsevir, 1989) and hence the bending rigidity in the circumferential direction becomes relatively lower in the central region 12 than in the side end region 13. Consequently, the ground contacting length of the tire becomes long in the central zone of the tread and short in the shoulder region thereof to put the ground contacting shape of the tire close to a chipped round shape, whereby water existing ahead of the tire during running on a wet road surface can rapidly be discharged sideward from the tire to control the occurrence of hydroplaning. Since the total thickness T of the slant belt layer 6 and the circumferential belt layer 7 becomes small at a position corresponding to the central region 12 of the tire in the widthwise direction thereof, there may be caused a phenomenon that ruggedness corresponding to the cords in the circumferential belt layer appears in an inner peripheral surface of the tire after the vulcanization at the widthwise central region 12 (cord-exposing phenomenon). In the latter case, a gauge t2 of rubber located between the cord of an outermost circumferential belt layer 7 in the radial direction and an inner peripheral surface of a tread rubber is made larger in the central region 12 of the tire than in the side end region 13 thereof in the widthwise direction as shown in Fig. 4, whereby the total thickness T of the slant belt layer 6 and the circumferential belt layer 7 can be made uniform in the widthwise direction of the tire to prevent the cord-exposing phenomenon. If it is required to further control the pushing out of the widthwise central region of the tire during running at high speed, the circumferential belt layer 7 preferably comprises at least two layers in the widthwise central region 12 of the tire. As shown in Fig. 2, two or more belt layers 7-1, 7-2 having a relatively wide width may be arranged as the circumferential belt layer 7. Although the widths of the two belt layers 7-1 and 7-2 are different in the embodiment of Fig. 2, two or more circumferential belt layers having a width approximately equal to that of the slant belt layer may be used. Alternatively, as shown in Fig. 5, the circumferential belt layer 7 may comprise a width-wide circumferential belt layer 7-1 covering approximately the full surface of the slant belt layer 6 and a narrow-width circumferential belt layer 7-2 covering only a central region of the width-wide circumferential belt layer 7-1. If it is required to further control separation failure at the belt ends, the circumferential belt layer 7 preferably comprises at least two layers in the side end region of the tire in the widthwise direction. In this case, the full surface of the slant belt layer may be covered with two or more width-wide circumferential belt layers, or the circumferential belt layer 7 may comprise a width-wide circumferential belt layer 7-1 covering approximately the full surface of the slant belt layer 6 and a pair of narrow-width circumferential belt layers 7-2 covering only the side end regions of he width-wide circumferential belt layer 7-1 or width-narrow circumferential belt layers 7-2 covering only the side end regions and central region of the width-wide circumferential belt layer 7-1 (Fig. 6). In any case, the width, number and the like of the circumferential belt layer 7 may properly be changed in accordance with the use purpose. The following examples are given in illustration of the invention and are not intended as limitations thereof. A pneumatic radial tire to be tested has a tire size of 195/65R14 and a construction as shown in Fig. 1, which comprises a carcass 3 toroidally extending between a pair of bead cores 2, one slant belt layer 6 superimposed about a crown portion 4 of the carcass 3 and containing a plurality of steel cords arranged at a given cord angle with respect to an equatorial plane 5 of the tire, and a circumferential belt layer 7 arranged on the slant belt layer 6 and containing a plurality of cords arranged at a cord angle of approximately 0° with respect to the equatorial plane 5. In this case, the circumferential belt layer 7 is formed by spirally winding the cord on the slant belt layer. Moreover, the number of the circumferential belt layers 7 (at central region and side end region), the material, twisting structure, total denier, twist constant, loss tangent and end count of the cord used in the circumferential belt layer 7, the modulus of elasticity of the coating rubber for the circumferential belt layer 7, the material and inclination angle with respect to the equatorial plane 5 in the cord of the slant belt layer 6, the gauge tl of rubber located between the cord of the slant belt layer 6 and the cord of the innermost circumferential belt layer 7 in the radial direction (at central region and side end region) and the gauge t2 of rubber located between the cord of the outermost circumferential belt layer 7 in the radial direction and the inner peripheral surface of the tread rubber (at central region and side end region) are summarized in Table 1. In Table 1, tire Nos. 1-15 are examples, and tire Nos. 16-18 are comparative examples, and tire Nos. 19-20 are conventional examples. The other construction of the above tires is the same as in conventional pneumatic radial tires for passenger cars. It is noted that tire No. 10 is not an example of the invention because the elastic modulus of the coating rubber of the circumferential belt layer is less than 200 kgf/mm 2 . Test Method The following tests for evaluating the cornering property, high-speed durability and durability are carried out with respect to these test tires. (1) Test for the evaluation of cornering property The cornering property is evaluated by measuring the cornering power. The test tire subjected to an internal pressure of 1.7 kgf/cm 2 is set on a drum of 3000 mm in outer diameter and trained at a speed of 30 km/h under a load defined from the tire size and internal pressure according to JATMA or JIS for 30 minutes. After the internal pressure is adjusted to 1.7 kgf/cm 2 under no load, the tire is run on the drum at the same speed under the same load as mentioned above while varying a slip angle with respect to the circumferential line of the urum within a range of ±1° to ±4°, during which an average value of cornering force (CF) at each slip angle is measured. Then, the cornering power (CP value) is calculated by substituting these average values into the following equation: CP (kgf/deg) = [CF(kgf/1°) + CF(kgf/2°)/2 + CF(kgf/3°)/3 + CF(kgf/4°)/4] ÷ 4 The test results are shown in Table 2. In this case, the CP value is represented by an index value on the basis that Conventional Example 19 is 100, in which the larger the index value, the better the cornering property. (2) Test for the evaluation of high-speed durability The high-speed durability is evaluated by increasing the running speed of the test tire on a drum every 30 minutes according to a step-speed system test defined in FMVSS No. 109 until the occurrence of tire damage to measure the speed (km/h) at the occurrence of tire damage. The test results are also shown in Table 2. The high-speed durability is represented by an index value on the basis that Conventional Example 19 is 100. The larger the index value, the better the high-speed durability. (3) Test for the evaluation of durability. The test tire subjected to an inner pressure of 1.0 kgf/cm 2 is run on a drum at a slip angle of 8° under a maximum load defined in JATMA for 16 hours, and thereafter the tire is cut to measure the presence or absence of cord break-up in the circumferential belt layer, whereby the durability is evaluated. The test results are also shown in Table 2, in which the occurrence of cord break-up is described as "presence" and no occurrence is described as "absence". Tire No. Test results Cornering property High-speed durability Durability Example 1 108 115 absence 2 108 117 absence 3 101 90 absence 4 105 95 absence 5 108 115 absence 6 110 115 absence 7 108 115 absence 8 102 112 absence 9 121 120 absence 10 108 110 presence 11 108 115 absence 12 108 105 absence 13 102 100 absence 14 104 105 absence 15 109 110 absence Comparative Example 16 95 95 absence 17 95 90 absence 18 94 93 presence Conventional Example 19 100 100 absence 20 97 90 absence As seen from the test results of Table 2, the tire Nos. 1-15 of the examples exhibit good cornering property as compared with the tire No. 19 of the conventional example. Furthermore, the tires of the examples other than the tire Nos. 3, 4 and 10 exhibit good durability and high-speed durability. Moreover, the tire Nos. 3 and 4, in which the loss tangent of the cord in the circumferential belt layer is somewhat outside the preferable range, exhibit poor high-speed durability as compared with the tire No. 19 of the conventional example, while the occurrence of cord break-up is observed in the tire No. 10 in which the modulus of elasticity of the coating rubber for the circumferential belt layer is less than the required range. Moreover, the cornering property is relatively poor in the tire No. 13 in which the inclination cord angle of the slant belt layer is somewhat larger than the preferable range as compared with the tire No. 1. In the tire Nos. 16-18 of the comparative examples, the twist constant of the cord in the circumferential belt layer is larger than the range defined in the invention, so that the cornering property is poor as compared with the tire Nos. 1-15. The tire No. 20 of the conventional example exhibits poor cornering property and high-speed durability as compared with the tire Nos. 1-15, while the tire No. 19 of the conventional example has a belt comprised of cross belt layers and circumferential belt layer and has fairly large tire weight as compared with the tire No. 1. For reference, the drainage property and cord-exposing phenomenon are measured with respect to these test tires. As a result, the drainage property is somewhat poor in the tire No. 11 and the occurrence of cord exposing phenomenon is observed in the tire No. 12 among the tire Nos. 1-15 of the examples, while the tire Nos. 1-10 and 13-15 have good drainage property and have no cord exposing phenomenon. According to the invention, the rationalized PET, nylon, PEN or vinylon fiber cords or high-strength steel cords as previously mentioned are used in the circumferential belt layer, so that it is possible to provide pneumatic radial tires for use in the general-purpose passenger cars having improved cornering property, satisfactory durability and/or high-speed durability and light weight.

Claims: A pneumatic radial tire (1) comprising a carcass (3) toroidally extending between a pair of bead cores (2) and a belt (6,7) superimposed on a crown portion (4) of the carcass and comprised of a single slant belt layer (6) containing a plurality of cords or filaments arranged at a given inclination angle with respect to an equatorial plane (5) of the tire and one or more circumferential belt layers (7) laminated on the slant belt layer (6) and containing a plurality of cords arranged substantially in parallel to the equatorial plane, wherein at least one said circumferential belt layer is a width-wide circumferential belt layer (7-1) covering approximately the full surface of the slant belt layer (6), and wherein the cord used in said one or more circumferential belt layers (7) is made from polyethylene terephthalate or nylon fiber and has a layer twisting structure and a total denier D T of 1000d-6000d and a twist constant N t satisfying N t = T x (0.139 x D T /2 x 1/ρ) 1/2 x 10 -3 ≤ 0.3 wherein T is the twisting number (twist turns/10 cm) and ρ is the specific gravity, and that a coating rubber for the said one or more circumferential belt layers (7) has a modulus of elasticity of not less than 200 kgf/mm 2 . A pneumatic radial tire (1) comprising a carcass (3) toroidally extending between a pair of bead cores (2) and a belt (6,7) superimposed on a crown portion (4) of the carcass and comprised of a single slant belt layer (6) containing a plurality of cords or filaments arranged at a given inclination angle with respect to an equatorial plane (5) of the tire and one or more circumferential belt layers (7) laminated on the slant belt layer (6) and containing a plurality of cords arranged substantially in parallel to the equatorial plane, wherein at least one said circumferential belt layer is a width-wide circumferential belt layer (7-1) covering approximately the full surface of the slant belt layer (6), and wherein the cord used in said one or more circumferential belt layers (7) is made from polyethylene naphthalate fiber and has a layer twisting structure and a total denier D T of 1000d-6000d and a twist constant N t satisfying N t = T x (0.139 x D T /2 x 1/ρ) 1/2 x 10 -3 ≤ 0.5 wherein T is the twisting number (twist turns/10 cm) and ρ is the specific gravity, and that a coating rubber for the said one or more circumferential belt layers (7) has a modulus of elasticity of not less than 200 kgf/mm 2 . A pneumatic radial tire (1) comprising a carcass (3) toroidally extending between a pair of bead cores (2) and a belt (6,7) superimposed on a crown portion (4) of the carcass and comprised of a single slant belt layer (6) containing a plurality of cords or filaments arranged at a given inclination angle with respect to an equatorial plane (5) of the tire and one or more circumferential belt layers (7) laminated on the slant belt layer (6) and containing a plurality of cords arranged substantially in parallel to the equatorial plane, wherein at least one said circumferential belt layer is a width-wide circumferential belt layer (7-1) covering approximately the full surface of the slant belt layer (6), and wherein the cord used in said one or more circumferential belt layers (7) is made from vinylon fiber and has a layer twisting structure and a total denier D T of 1000d-6000d and a twist constant N t satisfying N t = T x (0.139 x D T /2 x 1/ρ) 1/2 x 10 -3 ≤ 0.6 wherein T is the twisting number (twist turns/10 cm) and ρ is the specific gravity, and that a coating rubber for the said one or more circumferential belt layers (7) has a modulus of elasticity of not less than 200 kgf/mm 2 . A pneumatic radial tire as claimed in any of claims 1 to 3, characterized in that the cord for the circumferential belt layer (7) has a loss tangent (tan δ) of not more than 0.3 under conditions that initial tension is 1 kgf/cord, strain amplitude is 0.1%, frequency is 20 Hz and atmospheric temperature is 25°C. A pneumatic radial tire (1) comprising a carcass (3) toroidally extending between a pair of bead cores (2) and a belt (6,7) superimposed on a crown portion (4) of the carcass and comprised of a single slant belt layer (6) containing a plurality of cords or filaments arranged at a given inclination angle with respect to an equatorial plane (5) of the tire and one or more circumferential belt layers (7) laminated on the slant belt layer (6) and containing a plurality of cords arranged substantially in parallel to the equatorial plane, wherein at least one said circumferential belt layer is a width-wide circumferential belt layer (7-1) covering approximately the full surface of the slant belt layer (6), and wherein the cord used in said one or more circumferential belt layers (7) is a steel cord having a modulus of elasticity of not less than 3000 kgf/mm 2 and a twisting structure of 1 x N or 1 + N in which N is the number of steel filaments, and that a coating rubber for said one or more circumferential belt layers (7) has a modulus of elasticity of not less than 200 kgf/mm 2 . A pneumatic radial tire as claimed in any of claims 1 to 5, characterized in that the cord for the circumferential belt layer (7) is spirally wound around the slant belt layer (6). A pneumatic radial tire as claimed in any of claims 1 to 6, characterized in that the slant belt layer (6) contains steel cords or steel filaments therein. A pneumatic radial tire as claimed in any of claims 1 to 7, characterized in that the slant belt layer (6) has a cord inclination angle of 15-45° with respect to the equatorial plane (5). A pneumatic radial tire as claimed in any of claims 1 to 8, characterized in that a gauge (t1) of rubber located between the cord of the slant belt layer (6) and the cord of an innermost circumferential belt layer (7) in a radial direction of the tire is made larger in a side end region (13) of the tire than in a central region (12) thereof in the widthwise direction at a radial section of the tire. A pneumatic radial tire as claimed in any of claims 1 to 9, characterized in that a gauge (t2) of rubber located between the cord of an outermost circumferential belt layer (7) in the radial direction and an inner periphery of a tread rubber is made larger in the central region (12) of the tire than in the side end region (13) thereof in the widthwise direction at a radial section of the tire. A pneumatic radial tire as claimed in any of claims 1 to 10, characterized in that at least two circumferential belt layers (7-1,7-2) are disposed in the central region (12) in the widthwise direction of the tire. A pneumatic radial tire as claimed in any of claims 1 to 11, characterized in that at least two circumferential belt layers (7-1,7-2) are disposed in the side end region (13) in the widthwise direction of the tire.

Inventors: KOBAYASHI TOSHINOBU, KOHNO YOSHIHIDE, SATO TAKAYUKI, YAMANAKA EIJI, KOBAYASHI, TOSHINOBU, KOHNO, YOSHIHIDE, SATO, TAKAYUKI, YAMANAKA, EIJI
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1995
Main classification: B60C9
IPC codes: B60C9, D07B1, D02G3