Patent Application
20200361241
The present invention relates to a tire.
This application is based upon and claims priority to Japanese Patent Application No. 2017-017094, filed on Feb. 1, 2017, the entire contents of which are incorporated herein by reference.
Radial tires are known from Patent Document 1 or the like. The radial tire has a belt layer including a steel cord, and a rubber covering the steel cord. The steel cord is formed by a large number of filaments. Patent Document 1 proposes setting a tenacity per single steel cord, and a ply tenacity to specific values, in order to simultaneously achieve weight saving and strength improvement.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2001-001717
A tire according to the present disclosure includes a plurality of belt layers laminated in a radial direction, wherein the belt layer includes a plurality of steel cords arranged in parallel and aligned in a row, and a rubber covering the plurality of steel cords,
wherein the plurality of steel cords have a 1×4 structure in which 4 filaments are stranded,
wherein a tensile rigidity [N/%] is defined as a value that is obtained when the steel cord is set on a tensile strength tester, the steel cord is pulled at a velocity of 5 mm/minute with a chuck distance of 500 mm, and a stress [N] applied to the steel cord when a distortion of 0.1% is added to the steel cord is divided by the distortion of 0.1% at that time,
wherein a number of ends [-] is defined as a number of the plurality of steel cords existing per width of 5 cm of the belt layer, at a cross section perpendicular to a direction in which the plurality of steel cords extend,
wherein [tensile rigidity]× [number of ends] is 10,000 N/% or greater and 20,000 N/% or less, and
wherein an interface rigidity [Pa] is defined as a ratio of a shear strain [mm] with respect to a shear force [N] when the shear force is caused to act between adjacent belt layers, and
wherein the interface rigidity is 2.5 MPa or higher and 5.0 MPa or lower.
Recently, there are increased demands for weight saving of the tire for the purpose of achieving low fuel consumption. Various methods have been tested for the weight saving of the tire, however, it is necessary to maintain an important performance, which is to provide a comfortable steering stability with the tire.
In order to secure the steering stability, it is regarded important to reduce a bending rigidity of a belt layer of the tire, and it is conceivable to secure the steering stability by increasing the number of filaments, increasing a contact area of the filaments adhered to a rubber, or the like. However, when an attempt is made to secure the steering stability according to these methods, it may be presumed that the cost will increase.
One object of the present disclosure is to provide a tire which is light-weight and has an excellent steering stability, while reducing the cost increase.
According to the present disclosure, it is possible to provide a tire which is light-weight and has an excellent steering stability, while reducing the cost increase.
Summary of embodiments of the present disclosure will be described.
(1) One embodiment of a tire according to the present disclosure provides:
a tire having a plurality of belt layers laminated in a radial direction, wherein the belt layer includes a plurality of steel cords arranged in parallel and aligned in a row, and a rubber covering the plurality of steel cords,
wherein the plurality of steel cords have a 1×4 structure in which 4 filaments are stranded,
wherein a tensile rigidity [N/%] is defined as a value that is obtained when the steel cord is set on a tensile strength tester, the steel cord is pulled at a velocity of 5 mm/minute with a chuck distance of 500 mm, and a stress [N] applied to the steel cord when a distortion of 0.1% is added to the steel cord is divided by the distortion of 0.1% at that time,
wherein a number of ends [-] is defined as a number of the plurality of steel cords existing per width of 5 cm of the belt layer, at a cross section perpendicular to a direction in which the plurality of steel cords extend,
wherein [tensile rigidity]×[number of ends] is 10,000 N/% or greater and 20,000 N/% or less, and
wherein an interface rigidity [Pa] is defined as a ratio of a shear strain [mm] with respect to a shear force [N] when the shear force is caused to act between adjacent belt layers, and
wherein the interface rigidity is 2.5 MPa or higher and 5.0 MPa or lower.
Because the steel cord of the tire (1) has the 1×4 structure in which 4 filaments are stranded, the cost, lightweight properties, and steering stability are well balanced. In addition, because [tensile rigidity]×[number of ends] is 10,000 N/% or greater and 20,000 N/% or less, and the interface rigidity is 2.5 MPa or higher and 5.0 MPa or lower, it is possible to provide a tire which is light-weight and has an excellent steering stability, while reducing the cost increase.
(2) [Tensile rigidity]×[number of ends] may be 13,000 N/% or greater and 16,000 N/% or less. The cost and tire performance of the tire (2) are well balanced.
(3) The interface rigidity may be 3.5 MPa or higher and 4.5 MPa or lower.
The cost and tire performance of the tire (3) are well balanced.
(4) The number of ends may be 20 or greater and 60 or less.
The cost and tire performance of the tire (4) are well balanced. When the number of ends is less than 20, the number of steel cords with respect to the tire becomes too small, and it is difficult to obtain a sufficient tire strength. When the number of ends is greater than 60, a large number of steel cords becomes required, and a productivity of the tire greatly deteriorates.
(5) A diameter of the filaments may be 0.18 mm or greater and 0.42 mm or less.
The cost and tire performance of the tire (5) are well balanced. When the diameter of the filament is less than 0.18 mm, a large number of filaments becomes required to obtain the required tensile strength, and the cost becomes high. When the diameter of the filament is greater than 0.42 mm, processes become difficult when stranding the filaments, or the like, and the production cost of the tire becomes high.
(6) The tensile strength of the filaments may be 100 N or greater and 450 N or less.
The cost and tire performance of the tire (6) are well balanced. When the tensile strength of the filaments is less than 100 N, the number of ends for obtaining the required tire strength becomes large, and the productivity of the tire deteriorates. When the tensile strength of the filaments is greater than 450 N, it becomes difficult to process the filaments, and the productivity of the tire deteriorates.
(7) When a center distance of the steel cords in at least two adjacent belt layers along the radial direction is denoted by T, and an average diameter of a virtual circumscribed circle of the steel cords in the 1×4 structure is denoted by D,
T/D may be 1.25 or greater and 2.25 or less.
Because T/D is 1.25 or greater and 2.25 or less, the tire (7) can maintain light-weight, and the steering stability is further improved. A preferable range for T/D is 1.3 or greater and 2.0 or less, and a more preferable range for T/D is 1.35 or greater and 1.80 or less.
(8) The average diameter D may be 0.2 mm or greater and 1.5 mm or less.
According to the tire (8), it is possible to simultaneously achieve the required strength of the steel cords and the excellent tire performance. When the average diameter D is less than 0.2 mm, it is difficult to sufficiently secure the strength of the steel cords. When the average diameter D is greater than 1.5 mm, the rigidity of the steel cords becomes too high and the tire performance deteriorates. A preferable range for the average diameter D is 0.3 mm or greater and 1.2 mm or less.
(9) The center distance T may be 0.4 mm or greater and 1.6 mm or less.
The tire (9) is light weight and has an excellent durability. When the center distance T is less than 0.4 mm, the amount of rubber filled inbetween the cords is small, and the durability deteriorates. When the center distance T is greater than 1.6 mm, the weight of the tire increases. A preferable range for the center distance T is 0.5 mm or greater and 1.3 mm or less.
(10) The rubber elastic modulus E* of the tire may be 5 MPa or higher and 20 MPa or lower. The tire performance and the productivity of the tire (10) are well balanced. When the rubber elastic modulus E* is less than 5 MPa, the required rigidity for the tire cannot be secured. When the rubber elastic modulus E* is greater than 20 MPa, the productivity deteriorates. A preferable range for the rubber elastic modulus E* of the tire is 7 MPa or higher and 20 MPa or lower, and a more preferable range for the rubber elastic modulus E* of the tire is 8 MPa or higher and 12 MPa or lower.
(11) [Cord breaking load]×[number of ends] may be 15,000 N or greater and 40,000 N or less. According to the tire (11), the cord weight of the tire can be reduced while securing the required strength. When [cord breaking load]×[number of ends] is less than 15,000 N, the strength becomes insufficient, and the durability deteriorates. When [cord breaking load]×[number of ends] is greater than 40,000 N, the possibility that the steering stability will deteriorate becomes high.
(12) In a cross sectional view on a plane perpendicular to a longitudinal direction of the steel cords, the rubber may be filled into a center part surrounded by the 4 filaments. According to the tire (12), because gaps among the filaments are also filled by the rubber, the filaments uneasily contact moisture, and rusting of the filaments can be reduced. In addition, because a large contact area can be secured between the filaments and the rubber, a sufficient adhesion can be secured.
(13) Among the 4 filaments, at least 1 filament may be formed with a bent part and a non-bent part repeatedly along the longitudinal direction of the 1 filament. According to the tire (13), gaps can be formed between the filaments by the bent part and the non-bent part. It is possible to cause the rubber to enter the center part surrounded by the filaments through these gaps, and the rubber can easily be filled into the center part surrounded by the filaments.
(14) A repetition pitch of the bent part and the non-bent part of the filament may be 2.2 mm or greater and 7.0 mm or less. According to the tire (14), the bent part and the non-bent part can easily be formed, and the rubber can easily be caused to enter the gaps between the filaments. When an attempt is made to make the repetition pitch less than 2.2 mm, it becomes difficult to form the bent part and the non-bent part, and the effect of causing the rubber to enter the gaps between the filaments deteriorates. When an attempt is made to make the repetition pitch greater than 7.0 mm, a large-scale machine becomes required to form the bent part and the non-bent part, and the production cost increases.
(15) When the filament is placed on a plane, and a height of the filament from this plane to the bent part on a far end of this plane is defined as a bent height, the bent height may be 0.2 times or more and 0.8 times or less with respect to the diameter of the filament. According to the tire (15), the rubber can easily be caused to enter the gaps between the filaments, and the steel cords can easily be manufactured. When the bent height is less than 0.2 times the filament diameter, it is difficult to secure the gaps by the bent part, and the effect of causing the rubber to enter the gaps between the filaments deteriorates. When an attempt is made to make the bent height more than 0.8 times the filament diameter, the bent part may damage other filaments when the filaments are stranded, and breaking of the filament may occur.
Examples of embodiments of the tire according to the present invention will be described in the following, by referring to the drawings. The present invention is not limited to these examples of the embodiments, and is intended to include all modifications within the meaning and scope of the claims presented and equivalents thereof.
The tread part 2 is a part that makes contact with a road surface. The bead part 4 is provided on an inner diameter side of the tread part 2. The bead part 4 is a part that contacts a rim of a wheel of a vehicle. The sidewall part 3 connects the tread part 2 and the bead part 4. When the tread part 2 receives shock from the road surface, the sidewall part 3 undergoes elastic deformation, and absorbs the shock.
The tire 1 includes an inner liner 5, a carcass 6, a belt layer 7, and a bead wire 8.
The inner liner 5 is made of rubber, and seals a space between the tire 1 and the wheel.
The carcass 6 forms a framework of the tire 1. The carcass is made of an organic fiber, such as polyester, nylon, rayon, or the like, and rubber.
The bead wire 8 is provided in the bead part 4. The bead wire 8 receives a tensile force acting on the carcass 6.
The belt layer 7 clamps the carcass 6, and increases the rigidity of the tread part 2. In the illustrated example, the tire 1 includes 2 belt layers 7. The 2 belt layers 7 are laminated in a radial direction of the tire 1.
As illustrated in
In
A diameter of this virtual circumscribed circle of the steel cord 10 may have values that are respectively different at a plurality of positions along the longitudinal direction of the steel cord 10. When the cross section illustrated in
For example, a value that is measured by pinching the 4 filaments 20 by a micrometer, may be regarded as the diameter of the virtual circumscribed circle. In this specification, the diameter of the virtual circumscribed circle is measured by the micrometer at 5 positions along the longitudinal direction, and the average value of the measured diameters is regarded to as the average diameter D of the virtual circumscribed circle of the steel cord 10.
The average diameter D of the virtual circumscribed circle of the steel cord 10 having the 1×4 structure is preferably 0.2 mm or greater and 1.5 mm or less. When the average diameter D is less than 0.2 mm, it is difficult to sufficiently secure the strength of the steel cord 10. When the average diameter D is greater than 1.5 mm, the rigidity of the steel cord 10 becomes too high, and the performance of the tire 10 deteriorates.
The average diameter D is preferably 0.3 mm or greater and 1.2 or less.
As illustrated in
In addition to portions of the filaments 20 positioned on the outer peripheral side of the steel cord 10, because the gaps among the filaments 20 are also filled by the rubber 11, the filaments 20 uneasily contact moisture, and rusting of the filaments 20 can be reduced. In addition, because a large contact area can be secured between the filaments 20 and the rubber, a sufficient adhesion can be secured.
Gaps can be formed between the filaments 20 by the bent part 21 and the non-bent part 22. The rubber 11 can easily be caused to enter the center part surrounded by the filaments 20 through these gaps, and the rubber 11 can easily be filled into the center part surrounded by the filaments 20.
As illustrated in
The repetition pitch P of the filament 20 is preferably 3.0 mm or greater and 7.0 mm or less. The repetition pitch P of the filament 20 is more preferably 3.0 mm or greater and 5.0 mm or less.
As illustrated in
When the bent height h is less than 0.2 times the filament diameter, it is difficult to secure the gaps by the bent part 21 and the non-bent part 22, and the effect of causing the rubber 11 to enter the mutual gaps between the plurality of filaments 20 deteriorates. When an attempt is made to make the bent height h more than 0.8 times the filament diameter, the bent part 21 may damage other filaments 20 when the filaments 20 are mutually stranded, and breaking of the filament may occur.
The bent height h of the filament 20 is preferably 0.25 times or more and 0.5 times or less with respect to the filament diameter. The bent height h of the filament 20 is more preferably 0.3 times or more and 0.5 times or less with respect to the filament diameter.
For the purpose of achieving weight saving and cost reduction, the smaller the number of filaments 20 forming the steel cord 10, the better. However, when the number of filaments 20 is small, the cord strength or the like becomes insufficient, and it becomes difficult to secure a satisfactory steering stability. For example, it is not realistic to form the steel cord 10 using 1 or 2 filaments 20.
Accordingly, the present inventors examined forming the steel cord using 3 or more filaments 20 for the purpose of securing the cord strength, and using 5 or less filaments 20 for the purpose of weight saving and cost reduction. When forming the steel cord using 3 or more and 5 or less filaments 20, steel cords having 1×3, 1×4, 1×5, 2+1, and 2+2 structures are conceivable.
The present inventors repeated further examinations of the steel cords having these structures.
The steel cord having the 1×3 structure includes 3 filaments, and the steel cord can easily be formed at a low cost. However, compared to the structure using 4 or 5 filaments, a bending rigidity becomes high, and a satisfactory steering stability is difficult to obtain. For this reason, it is conceivable to increase the cord strength using thin filaments, however, as a result of the machining ratio of the filaments becoming high, it becomes difficult to manufacture the steel cord by stranding the filaments.
Furthermore, in the cross section perpendicular to the longitudinal direction of the steel cord 110, the filaments 20 may be unevenly arranged. Conceivably, even if the steel cord 110 can be manufactured so that the filaments 20 are evenly distributed, it is difficult to maintain the positions of the filaments 20 as they are. For example, as illustrated in
In addition, as illustrated in
In addition, as illustrated in
The cord strength and the cost of the steel cord 10 having the 1×4 structure are well balanced, and it is possible to easily reduce the weight while maintaining the required strength of the steel cord. Moreover, as illustrated in
As a result of considering the above, the present inventors discovered that the low cost, weight saving, and steering stability are well balanced for the steel cord 10 having the 1×4 structure.
In addition, a CP (Cornering Power) value is known as an index of the tire performance. As a result of various research, the present inventors discovered that the tensile rigidity of the steel cord 10, and the interface rigidity between the adjacent belt layers 7, have a strong correlation to the CP value. Hence, the present inventors obtained an even better balance between the tire performance and the cost of the tire 1 using the steel cord 10 having the 1×4 structure.
<Tensile Rigidity>
When the steel cord 10 is set on the tensile strength tester, and the steel cord 10 is pulled at a velocity of 5 mm/minute with a chuck distance of 500 mm, a value which is obtained by dividing a stress [N] applied to the steel cord 10 when a distortion of 0.1% is added to the steel cord, by the distortion of 0.1% at that time, is defined as a tensile rigidity [N/%]. When a tensile test of the steel cord 10 is performed, and a stress-strain diagram is obtained, a slope in the stress-strain diagram at a time when the distortion of 0.1% is obtained corresponds to the tensile rigidity.
In other words, the tensile rigidity of the steel cord 10 is an index indicating an inelasticity of the steel cord 10 when the steel cord 10 is pulled. In the case of the tire 1, the tensile rigidity may be regarded as an index related to the inelasticity of the tire 1 in the circumferential direction thereof.
The diameter of the filament 20 forming the steel cord 10, the repetition pitch P of the filament 20, an elongation of the filament 20 when applied with a low load, or the like may be regarded as main influencing factors of the tensile rigidity. Hence, by varying each of the influencing factors, samples 1-4 of the steel cord 10 having mutually different tensile rigidities were obtained, and as illustrated in Table 1, the tensile rigidity and the CP value were obtained. The tires 1 having the same specification except for the steel cord 10 were manufactured, and the CP values of these tires 1 were compared.
The CP value that is obtained when the tire 1 is manufactured using the steel cord 10 of the sample 2, is set to 100, and the CP values of the samples 1, 3, and 4 were indicated using relative indexes. It is known that the steel cord 10 of the sample 2 can obtain a high CP value by using a large number of thin filaments 20, however, the cost is high.
In Table 1, a structure name is the name of the stranded structure of the steel cord 10.
1×12 refers to a structure in which 12 filaments 20 are stranded altogether.
2+7 refers to a structure in which a total of 9 filaments 20 are stranded, so that 2 filaments 20 are positioned at the center, and 7 filaments are positioned around the 2 filaments 20.
1×5 refers to a structure in which 5 filaments 20 are stranded altogether.
2+2 refers to a structure in which a total of 4 filaments 20 are stranded, so that 2 filaments 20 are positioned at the center, and 2 filaments 20 are positioned around the 2 filaments positioned at the center.
The sample 1 has the 1×12 structure, and is a steel cord in which 12 filaments having a diameter of 0.15 mm are stranded at a repetition pitch P of 10.0 mm. A low-load elongation of each filament is 0.5%. The low-load elongation refers to an elongation (distortion) [%] when 1 filament is pulled to a load of 49 N.
When the tensile test is performed on the steel cord of the sample 1 that is formed in this manner, the tensile rigidity was 325 N/%.
In addition, when a tire is manufactured using the steel cord of the sample 1, it was confirmed that the CP value is 99 when the CP value of the sample 2 is 100.
The sample 2 has the 2+7 structure, and is a steel cord in which 9 filaments having a diameter of 0.18 mm are stranded at a repetition pitch P of 15.0 mm. The low-load elongation of each filament is 0.3%.
When the tensile test is performed on the steel cord of the sample 2 that is formed in this manner, the tensile rigidity was 341 N/%.
The sample 3 has the 1×5 structure, and is a steel cord in which 5 filaments having a diameter of 0.20 mm are stranded at a repetition pitch P of 9.0 mm. The low-load elongation of each filament is 0.2%.
When the tensile test is performed on the steel cord of the sample 3 that is formed in this manner, the tensile rigidity was 316 N/%.
In addition, when a tire is manufactured using the steel cord of the sample 3, it was confirmed that the CP value is 98 when the CP value of the sample 2 is 100.
The sample 4 has the 2+2 structure, and is a steel cord in which 4 filaments having a diameter of 0.23 mm are stranded at a repetition pitch P of 13.0 mm. The low-load elongation of each filament is 0.2%.
When the tensile test is performed on the steel cord of the sample 4 that is formed in this manner, the tensile rigidity was 315 N/%.
In addition, when a tire is manufactured using the steel cord of the sample 4, it was confirmed that the CP value is 98 when the CP value of the sample 2 is 100.
<Interface Rigidity>
A ratio of a shear strain [mm] with respect to a shear force [N] when the shear force is caused to act between the adjacent belt layers 7, is defined as the interface rigidity [Pa]. The shear strain is measured using a portion that is cut out to a size of 5 cm square when viewed in a plan view of the two laminated belt layers 7.
For example, in
The interface rigidity in the case of the tire 1 may be regarded as an index related to the difficulty of causing strain to the belt layers 7 in an axle direction of the tire 1.
The rubber elastic modulus S* of the belt layer 7, and the center distance T (also referred to as a gauge thickness) of the steel cord 10 in the adjacent belt layers 7 may be regarded as main influencing factors of the interface rigidity.
The center distance T, as illustrated in
In addition, the rubber elastic modulus E* is an index indicating a viscoelasticity of rubber. The rubber elastic modulus may also be referred to as a complex modulus of elasticity or a dynamic viscoelasticity. In the following description, the rubber elastic modulus E* of the tire 1 refers to a numerical value that is measured using a spectrometer manufactured by Toyo Seiki Seisaku-sho, Ltd., for a small piece (test piece) of the tire 1, having a width of 5 mm, a thickness of 2 mm, and a length of 20 mm, at an initial load of 150 g, a frequency of 50 Hz, a dynamic strain of 1%, and a temperature of 70° C.
The manufacturing cost of the steel cord 10 having the 1×12 structure and the 2+7 structure of the samples 1 and 2 in Table 1 becomes high. In addition, as described above, the lightweight properties and the steering stability are well-balanced for the steel cord 10 having the 1×4 structure. Hence, in the following, a relationship between the interface rigidity and the CP value was verified with respect to the steel cord 10 having the 1×4 structure.
Samples 5-8 of the tire, that use belt layers having mutually different interface rigidities, were obtained by manufacturing the belt layers with different types of rubber and gauge thicknesses T, using a steel cord having the 1×4 structure in which filaments having a low-load elongation of 0.13% and a diameter of 0.27 mm are stranded at a repetition pitch P of 15.5 mm, to obtain the interface rigidities and the CP values as illustrated in Table 2. The CP values are the values that are obtained when the tires are manufactured with the same specifications except for the belt layer and the steel cord. The CP values of the samples 5-7 in Table 2 indicate relative indexes when the CP value of the sample 8 is 100.
A rubber elastic modulus E* of 5.5 MPa, and a gauge thickness T of 1.10 mm were used for the tire of the sample 5. The tire of the sample 5 had an interface rigidity of 2.4 MPa/mm, and a CP value of the tire of the sample 5 was 97 when the CP value of the sample 8 is 100.
A rubber elastic modulus E* of 8.5 MPa, and a gauge thickness T of 1.10 mm were used for the tire of the sample 6. The tire of the sample 6 had an interface rigidity of 3.4 MPa/mm, and a CP value of the tire of the sample 6 was 98 when the CP value of the sample 8 is 100.
A rubber elastic modulus E* of 8.5 MPa, and a gauge thickness T of 0.86 mm were used for the tire of the sample 7. The tire of the sample 7 had an interface rigidity of 4.1 MPa/mm, and a CP value of the tire of the sample 7 was 99.5 when the CP value of the sample 8 is 100.
A rubber elastic modulus E* of 8.5 MPa, and a gauge thickness T of 0.60 mm were used for the tire of the sample 8. The tire of the sample 8 had an interface rigidity of 4.4 MPa/mm.
The present inventors discovered from the results of
[Tensile rigidity]×[number of ends], the interface rigidity, and the CP value were examined for the samples 9-13. The CP value was represented as an index using the CP value of 100 for a reference tire. The reference tire used a steel cord having the 2+7 structure in which 9 filaments having a low-load elongation of 0.14% and a diameter of 0.18 mm are stranded at a repetition pitch P of 13.0 mm, and a T/D value, obtained by dividing the gauge thickness T (mm) by the average diameter D (mm) of the virtual circumscribed circle of the steel cord, was set to 2.00. When the tire is manufactured using the steel cord that uses a large number of such thin filaments, a high CP value is obtained, however, the cost is high. Hence, the samples 10-13 were manufactured to realize high-performance tires at a low cost.
The tire of the sample 9 that is the reference example was manufactured using a steel cord having the 2×7 structure in which 9 filaments having a low-load elongation of 0.14% and a diameter of 0.18 mm are stranded at a repetition pitch P of 8.0 mm. In addition, a rubber elastic modulus E* of 5.5 MPa was used for the tire of the sample 9, and a T/D value, obtained by dividing the gauge thickness T (mm) by the average diameter D (mm) of the virtual circumscribed circle of the steel cord, was set to 2.00.
The tire of the sample 9 had a [tensile rigidity]×[number of ends] of 15500 [N/%], and an interface rigidity of 3.50 [MPa], and the CP value was 101.
The tire of the sample 10 that is an exemplary implementation was manufactured using a steel cord having the 1×4 structure in which 4 filaments having a low-load elongation of 0.13% and a diameter of 0.27 mm are stranded at a repetition pitch P of 15.5 mm. In addition, a rubber elastic modulus E* of 5.5 MPa was used for the tire of the sample 10, and a T/D value, obtained by dividing the gauge thickness T (mm) by the average diameter D (mm) of the virtual circumscribed circle of the steel cord, was set to 1.90.
The tire of the sample 10 had a [tensile rigidity]×[number of ends] of 16000 [N/%], and an interface rigidity of 2.70 [MPa], and the CP value was 100.
The tire of the sample 11 that is an exemplary implementation was manufactured using a steel cord having the 1×4 structure in which 4 filaments having a low-load elongation of 0.13% and a diameter of 0.27 mm are stranded at a repetition pitch P of 15.5 mm. In addition, a rubber elastic modulus E* of 8.5 MPa was used for the tire of the sample 11, and a T/D value, obtained by dividing the gauge thickness T (mm) by the average diameter D (mm) of the virtual circumscribed circle of the steel cord, was set to 1.85.
The tire of the sample 11 had a [tensile rigidity]×[number of ends] of 16000 [N/%], and an interface rigidity of 3.10 [MPa], and the CP value was 101.
The tire of the sample 12 that is an exemplary implementation was manufactured using a steel cord having the 1×4 structure in which 4 filaments having a low-load elongation of 0.16% and a diameter of 0.22 mm are stranded at a repetition pitch P of 14.5 mm. In addition, a rubber elastic modulus E* of 8.5 MPa was used for the tire of the sample 12, and a T/D value, obtained by dividing the gauge thickness T (mm) by the average diameter D (mm) of the virtual circumscribed circle of the steel cord, was set to 2.10.
The tire of the sample 12 had a [tensile rigidity]×[number of ends] of 13000 [N/%], and an interface rigidity of 3.72 [MPa], and the CP value was 101.
The tire of the sample 13 that is an exemplary implementation was manufactured using a steel cord having the 1×4 structure in which 4 filaments having a low-load elongation of 0.16% and a diameter of 0.22 mm are stranded at a repetition pitch P of 14.5 mm. In addition, a rubber elastic modulus E* of 8.5 MPa was used for the tire of the sample 13, and a T/D value, obtained by dividing the gauge thickness T (mm) by the average diameter D (mm) of the virtual circumscribed circle of the steel cord, was set to 1.70.
The tire of the sample 13 had a [tensile rigidity]×[number of ends] of 13000 [N/%], and an interface rigidity of 4.1 [MPa], and the CP value was 102.
Based on the result of Table 3,
Contour lines of the CP values may be drawn in
From the above results, it was confirmed that a tire having a high tire performance can be manufactured using the low-cost steel cord 10 having the 1×4 structure, when [tensile rigidity]×[number of ends] is 10,000 N/% or greater and 20,000 N/% or less, and the interface rigidity is 2.5 MPa or greater and 5.0 MPa or less, as in the case of the samples 10-13. The tire in accordance with the present invention has a performance that is the same or higher than those of the high-cost high-performance tires.
When [tensile rigidity]×[number of ends] is less than 10,000 N/%, the CP value that is obtained is low, and a sufficient tire performance cannot be obtained. When [tensile rigidity]×[number of ends] is greater than 20,000 N/%, the manufacturing cost becomes too high and unrealistic. The tire performance and the cost are well-balanced and preferable when [tensile rigidity]×[number of ends] is 13,000 N/% or greater and 16,000 N/% or less.
When the interface rigidity is lower than 2.5 MPa, the CP value that is obtained is low, and a sufficient tire performance cannot be obtained. When the interface rigidity is higher than 5.0 MPa, the manufacturing cost becomes too high and unrealistic. The tire performance and the cost are well-balanced and preferable when the interface rigidity is 3.5 MPa or higher and 4.5 MPa or lower.
The number of ends is preferably 20 or greater and 60 or less. When the number of ends is less than 20, the number of steel cords 10 with respect to the tire 1 becomes too small, and a sufficient tire strength is difficult to obtain. When the number of ends is greater than 60, a large number steel cords 10 is required, and the productivity of the tire 10 greatly deteriorates.
The diameter of the filament 20 is preferably 0.18 mm or greater and 0.42 mm or less.
When the diameter of the filament 20 is less than 0.18 mm, a large number of steel cords 10 is required in order to obtain the required tensile rigidity, and the cost becomes high. When the diameter of the filament 20 is greater than 0.42 mm, the processes become difficult when stranding the filaments 20, and the production cost of the tire 1 becomes high.
The tensile strength of the filament 20 is preferably 100 N or greater and 450 N or less. The tensile strength of the filament 20 is more preferably 130 N or greater and 420 N or less. The tensile strength of the filament 20 is a ratio of a tensile force [N] with respect to a distortion [%.] when a tensile test is performed on the filament 20.
When the tensile strength of the filament 20 is less than 100 N, the number of ends for obtaining the required tire strength becomes large, and the productivity of the tire 1 deteriorates. When the tensile strength of the filament 20 is greater than 450 N, it becomes difficult to process the filament 20, and the productivity of the tire 1 deteriorates.
Further, in the embodiment described above, the present inventors discovered that the steering stability can be improved further when the T/D value is 1.2 or greater and 2.25 or less, where the center distance of the steel cords 10 in the two belt layers 7 that are adjacent along the radial direction is denoted by T, and the average diameter of the virtual circumscribed circle of the steel cord 10 having the 1×4 structure is denoted by D. Details of the discovery are described below.
Steel cords having the 1×4 structure were manufactured using filaments having the same diameter and formed with the bent part and the non-bent part in the same way, and the T/D value that is a ratio of the center distance T of the steel cords 10 in the two belt layers 7 that are adjacent along the radial direction, and the average diameter D of the virtual circumscribed circle of the steel cord 10 having the 1×4 structure, were set to various values, to manufacture and evaluate tires of the following exemplary implementations 21-27 and comparison examples 21 and 22.
Exemplary Implementation 21:
The steel cord having the 1×4 structure was manufactured using filaments having the diameter of 0.30 mm. The bent part and the non-bent part were formed in 1 of the 4 filaments, so that the repetition pitch is 3.0 mm and the bent height is 0.5 times the diameter of the filament. The average diameter D of the virtual circumscribed circle of the steel cord having the 1×4 structure was 0.72 mm.
The belt layer was formed using this steel cord, to manufacture a tire of the exemplary implementation 21. The center distance T of the cords was set to 1.47 mm. The T/D value of the exemplary implementation 21 was 2.04.
Exemplary Implementation 22:
The belt layer was formed using the steel cord manufactured for the exemplary implementation 21, to manufacture a tire of the exemplary implementation 22. The center distance T of the cords was set to 1.30 mm. The T/D value of the exemplary implementation 22 was 1.81.
Exemplary Implementation 23:
The belt layer was formed using the steel cord manufactured for the exemplary implementation 21, to manufacture a tire of the exemplary implementation 23. The center distance T of the cords was set to 1.27 mm. The T/D value of the exemplary implementation 23 was 1.77.
Exemplary Implementation 24:
The belt layer was formed using the steel cord manufactured for the exemplary implementation 21, to manufacture a tire of the exemplary implementation 24. The center distance T of the cords was set to 1.13 mm. The T/D value of the exemplary implementation 24 was 1.57.
Exemplary Implementation 25:
The belt layer was formed using the steel cord manufactured for the exemplary implementation 21, to manufacture a tire of the exemplary implementation 25. The center distance T of the cords was set to 1.12 mm. The T/D value of the exemplary implementation 25 was 1.55.
Exemplary Implementation 26:
The belt layer was formed using the steel cord manufactured for the exemplary implementation 21, to manufacture a tire of the exemplary implementation 26. The center distance T of the cords was set to 0.99 mm. The T/D value of the exemplary implementation 26 was 1.38.
Exemplary Implementation 27:
The belt layer was formed using the steel cord manufactured for the exemplary implementation 21, to manufacture a tire of the exemplary implementation 27. The center distance T of the cords was set to 0.96 mm. The T/D value of the exemplary implementation 21 was 1.34.
The belt layer was formed using the steel cord manufactured for the exemplary implementation 21, to manufacture a tire of the comparison example 21. The center distance T of the cords was set to 1.67 mm. The T/D value of the comparison example 21 was 2.32.
The belt layer was formed using the steel cord manufactured for the exemplary implementation 21, to manufacture a tire of the comparison example 22. The center distance T of the cords was set to 0.83 mm. The T/D value of the comparison example 22 was 1.15.
The CP (Cornering Power) values were measured for the ties of the exemplary implementations 21-27 and the comparison examples 21 and 22. Table 4 tabulates the average diameter D of the virtual circumscribed circle of the steel cord, the center distance T of the cords, the T/D value, and the CP value.
As illustrated in
In a case where the average diameter D of the virtual circumscribed circle of the steel cords is constant, the T/D value becomes smaller as the center distance T of the cords becomes smaller. When the center distance T of the cords is small, it is possible to reduce the amount of rubber filled inbetween the steel cords adjacent along the radial direction. For this reason, the tire in accordance with the present invention can secure a comfortable steering stability, while reducing the amount of rubber and achieving weight saving. On the other hand, in a case where the center distance T of the cords is too small, there is a possibility that the steel cords will not be covered by the rubber, and thus, the durability deteriorates. Hence, the T/D value is set to 1.25 or greater.
As illustrated in
A more preferable range for the rubber elastic modulus E* is 7 MPa or greater and 20 MPa or less, and a further preferable range is 8 MPa or greater and 12 MPa or less.
As illustrated in
In addition, in a case where a tire having an index of the cord weight that is 2.50 is desired, for example, [cord breaking strength]×[number of ends] can be made the largest when the cord having the 1×4 structure is used. The cords having the 1×4 structure, the 2+2 structure, and the 1×2 structure provide tires, in this descending order of [cord breaking strength]×[number of ends].
For example, in a case where the required [cord breaking strength]×[number of ends] is the same, using the 1×4 structure can reduce the weight by approximately 10% compared to using the 1×2 structure, and by approximately 5% compared to using the 2+2 structure.
Accordingly, when cord having the 1×4 structure is used, it is possible to easily secure the required strength, while easily making a light-weight tire.
[Cord breaking strength]×[number of ends] is preferably 15,000 N or greater and 40,000 N or less. When [cord breaking strength]×[number of ends] is less than 15,000 N, the strength becomes insufficient, and the durability greatly deteriorates. When [cord breaking strength]×[number of ends] is greater than 40,000 N, the possibility that the steering stability will deteriorate becomes high. Desirably, [cord breaking strength]×[number of ends] is 18,000 N or greater and 37,000 N or less.
In the embodiments described above, the described tire has 2 belt layers, however, the present invention is not limited to such. The tire may have 3 belt layers, and at least 2 adjacent belt layers along the radial direction among the 3 belt layers may satisfy a relationship 1.25<=T/D<=2.25.
The tire in accordance with the present invention is applicable to automobile tires for passenger cars, ultralight trucks, light trucks, trucks, buses, or the like, aircraft tires, or the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-017094 | Feb 2017 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/038709 | 10/26/2017 | WO | 00 |
