JP7288396B2 - pneumatic tire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pneumatic tire (hereinafter also simply referred to as "tire"), and more particularly to a pneumatic tire with an improved bead core.

Generally, a pneumatic tire includes a tread portion, a pair of sidewall portions and a bead portion extending from both sides of the tread portion, and a carcass ply extending like a toroid between the pair of bead portions. Both ends of the carcass ply are locked by being rolled up or wound around a pair of bead cores embedded in the pair of bead portions, or sandwiched between divided bead cores.

As such a bead core, as disclosed in Patent Document 1, one formed by continuously winding a bead wire made of steel around a tire rotating shaft is usually used.

JP 2015-157599 A

As a conventional bead core, bead wires with a wire diameter of about 1.0 mm to 2.0 mm are bundled in a square cross section such as 4 rows and 4 rows, and bead wires with a wire diameter of about 1.3 mm to 1.5 mm are spirally structured. Bundling is the mainstream.

The bead core is responsible for maintaining tire pressure. The number of bead wires is determined by the burst pressure (total strength of the bead core) required for the tire, and the number of bead wires must be increased in order to secure the burst pressure corresponding to the size of the tire, which increases year by year. However, as the number of bead wires increases, the rigidity of the bead core increases proportionately, resulting in deterioration of rim assembly performance and fit of the rim to the tire, as well as the problem of variations in rim fitting performance in the tire circumferential direction. .

If the rim assembling performance deteriorates, problems arise in workability during rim assembling, and the possibility of damage to the rim increases. Also, if the fit pressure is excessively high, there is a problem with the safety of the rim assembly work. Furthermore, if the fit between the tire and the rim becomes uneven, the uniformity of the tire deteriorates, and in addition to lowering ground contact stability while driving, it also affects the stability of the vehicle when going straight or turning. , the effect is particularly large during high-speed running. Therefore, the bead core is required to have a desired breaking pressure and good rim assembly properties.

On the other hand, in recent years, from the viewpoint of reducing environmental load, there is a demand for fuel efficiency of tires, and further weight reduction of tires is desired. Along with this, it is required to reduce the weight of the bead core as well.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pneumatic tire that is lightweight and does not cause problems caused by the bead core by using a bead core that is lightweight and has excellent performance requirements as a bead core such as ease of rim assembly. to do.

As a result of intensive studies, the present inventors have found that, as a bead wire constituting the bead core, a twisted cord made by twisting a plurality of steel filaments is used instead of a single wire cord made of one steel filament, and a bead core unit is The inventors have found that the above problem can be solved by defining a predetermined value of the bead stiffness index, and have completed the present invention.

That is, the pneumatic tire of the present invention is a pneumatic tire comprising a bead core,
The bead core is composed of a twisted cord obtained by twisting 2 to 27 steel filaments containing more than 0.75% by mass of carbon, and
The unit bead stiffness index represented by the ratio of the bead stiffness index to the total bead strength of the bead core (bead stiffness index)/(total bead strength) is expressed by the following formula,
7×10 ⁻⁶ <Unit bead stiffness index (bead stiffness index/total bead strength) <34×10 ⁻⁶
is characterized by satisfying

In the tire of the present invention, the twisted cord preferably has an outer diameter of 2.0 mm or less. Moreover, in the tire of the present invention, it is preferable that the twisted cord is a rubber-coated steel cord. Furthermore, in the tire of the present invention, the wire diameter of the steel filament is preferably 0.3 mm or more and 0.8 mm or less.

Furthermore, in the tire of the present invention, the twisted structure of the twisted cord is preferably a 1×N structure, an M+N structure or an L+M+N structure, more preferably a 1+6 structure. Furthermore, in the tire of the present invention, the steel filaments are preferably brass-plated.

According to the present invention, it is possible to obtain a lightweight bead core which is excellent in the performance required for a bead core such as rim-mountability. I was able to make the tires.

1 is a cross-sectional view in the width direction showing a preferred example of a pneumatic tire of the present invention; FIG. 1 is a cross-sectional view in a direction perpendicular to the axial direction, showing a preferred example of a twisted cord that constitutes a bead core in the pneumatic tire of the present invention; FIG. 1 is a schematic cross-sectional view showing a bead core of Example 1. FIG. 2 is a schematic cross-sectional view showing a bead core of Comparative Example 1; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings.
FIG. 1 is a cross-sectional view in the width direction showing a passenger car tire as one preferred example of the pneumatic tire of the present invention.

A pneumatic tire 10 as a passenger car tire shown includes a tread portion 11 forming a contact portion, a pair of sidewall portions 12 continuously extending inward in the tire radial direction from both side portions of the tread portion 11, and and a bead portion 13 continuous to the inner peripheral side of the sidewall portion 12 . The tread portion 11 , sidewall portion 12 and bead portion 13 are reinforced by a carcass consisting of one carcass ply 1 extending in a toroidal shape from one bead portion 13 to the other bead portion 13 . In the illustrated passenger car tire 10, the bead cores 2 are embedded in the pair of bead portions 13, respectively, and the carcass ply 1 is folded around the bead cores 2 from the inside to the outside of the tire and locked.

In the present invention, the bead core 2 is composed of a twisted cord obtained by twisting 2 to 27 steel filaments containing more than 0.75% by mass of carbon. As the bead wire that constitutes the bead core, instead of the conventionally used single wire cord consisting of a single steel filament, a twisted cord consisting of multiple steel filaments of the above-mentioned high-carbon steel is used to maintain strength. At the same time, the weight of the bead core can be reduced when the bead wire has the same outer diameter. As a result, the weight of the tire can be reduced while maintaining the strength of the bead core. In addition, while conventionally used single wire cords are made of steel filaments that have been subjected to heat treatment after wire drawing, the above-mentioned twisted cords are made of steel filaments that have not been subjected to heat treatment after wire drawing, so higher strength can be obtained. Therefore, even if the conventional single wire cord is replaced with a twisted cord having the same outer diameter to reduce the amount of steel, the breaking strength of the bead wire itself is improved, so performance as a bead core can be ensured. Also, by using the bead core 2 made of twisted cords, it is possible to improve the fitability to the rim.

In the present invention, the ratio of the bead stiffness index to the total bead strength of the bead core 2 (bead stiffness index)/(total bead strength), and the unit bead stiffness index serving as an index of bending stiffness is expressed by the following formula:
7×10 ⁻⁶ <Unit bead stiffness index (bead stiffness index/total bead strength) <34×10 ⁻⁶
It is important to satisfy By setting the unit bead rigidity index of the bead core 2 to satisfy the above range, it is possible to maintain the rigidity of the bead core while ensuring an improvement in workability during rim assembly. If the unit bead stiffness index is smaller than the above range, the bead core cannot have sufficient stiffness. On the other hand, if the unit bead stiffness index is larger than the above range, workability during rim assembly deteriorates. In the present invention, the unit bead stiffness index is preferably the following formula,
7×10 ⁻⁶ <Unit bead stiffness index <25×10 ⁻⁶
shall be satisfied.

Here, the bead stiffness index can be obtained by multiplying the bead wire stiffness index by n (where n is the number of bead wires forming the bead core). In addition, the bead wire stiffness index is the stiffness index of the bead wire that constitutes the bead core, and is (π/32) × d ⁴ × m (where d is the wire diameter (mm) of the steel filament that constitutes the bead wire. , m is the number of steel filaments constituting the bead wire). Here, in the above formula, “(π/32)×d ⁴ ” means the polar moment of inertia of the steel filament forming the bead wire. Further, when the bead wire is formed using two kinds of steel filaments having different wire diameters d ₁ and d ₂ , for example, m _one steel filament having wire diameter d ₁ and m having wire diameter d ₂ When formed ^from _two steel filaments, ^{the bead strand stiffness index is (π/32)×d 14 ×m 1 +(π/32)×d 24} _{× m 2 ,} where d ₁ and d ₂ are the wire diameters (mm) of the steel filaments forming the bead wires, and m ₁ and m ₂ are the numbers of the steel filaments forming the bead wires).

From the viewpoint of ensuring high strength, the carbon content of the steel filaments used in the present invention must exceed 0.75% by mass, preferably 0.80% by mass or more, and more preferably 0.82% by mass. % by mass or more, preferably 1.10% by mass or less, more preferably 1.02% by mass or less.

Further, the number of steel filaments constituting the twisted cord in the present invention can be 2 to 27, preferably 3 to 12.

In the present invention, as long as the steel filament satisfies the range of carbon content, specific physical properties can be appropriately selected according to the desired bead core shape and performance. not. For example, the tensile strength of the steel filament is preferably 2150 MPa or more, more preferably 2940 MPa or more, and preferably 4300 MPa or less, more preferably 4000 MPa or less. The breaking strength of the twisted cord as a bead wire is preferably 2300N or more, more preferably 2420N or more, and preferably 3500N or less, more preferably 3400N or less, though it depends on the tire type.

In the present invention, the wire diameter of the steel filament is preferably 0.3 mm or more and 0.8 mm or less, and more preferably more than 0.4 mm and 0.7 mm or less. By setting the wire diameter of the steel filament within the above range, both strength and flexibility can be achieved, which is preferable.

Furthermore, the steel filaments are preferably plated in order to improve adhesion to rubber. The type of plating is not particularly limited, and includes brass (copper-zinc (Cu-Zn)) plating, zinc (Zn) plating, tin (Sn) plating, bronze (copper-tin (Cu-Sn)) plating, and the like. In addition, ternary plating such as copper-zinc-tin (Cu--Zn--Sn) plating and copper-zinc-cobalt (Cu--Zn--Co) plating can be used. In particular, the use of brass-plated steel filaments is preferred because the adhesiveness to rubber is further improved. In the case of bronze plating, etc., it is necessary to fill the gaps between the steel filaments in the twisted cord with an insulation rubber compound that has excellent adhesion to the bronze plating. Even if general-purpose coating rubbers similar to those used for other members are used, there is an advantage that adhesion can be ensured.

In the present invention, the specific twisted structure of the twisted cord used for the bead core 2 can be a 1×N structure, an M+N structure, or an L+M+N structure. Examples of the 1×N structure include those in which N is an integer of 2 to 12, particularly those in which N is an integer of 2 to 5. Specifically, examples include a 1×3 structure and a 1×4 structure. structure, 1×5 structure, 1×6 structure, 1×9 structure, 1×12 structure, and the like. Further, examples of the M+N structure include those in which M is an integer of 1 to 3 and N is an integer of 2 to 12, particularly N is an integer of 2 to 9. Specific examples of the M+N structure include a 1+6 structure, a 3+9 structure, a 3+8 structure, etc., when the M core portions and the N sheath portions are made of steel filaments having the same wire diameter. When the portion and the N sheath portions are made of steel filaments with different wire diameters, 1+3 structure, 1+5 structure, 1+7 structure, 1+9 structure, 1+12 structure and the like can be mentioned. Furthermore, examples of the L+M+N structure include those in which L is an integer of 1 to 4, M is an integer of 3 to 9, and N is an integer of 9 to 15. Specific examples of the L+M+N structure include 1+6+9, 3+9+15, and the like. In the present invention, it is preferable to use a 1+6 twisted cord 22 composed of seven steel filaments 21 having the same wire diameter, as shown in FIG. 2, from the viewpoint of excellent durability and cord strength.

In the present invention, the outer diameter of the twisted cord is preferably 2.0 mm or less, more preferably 0.96 mm or more and 1.9 mm or less. By setting the outer diameter of the twisted cord within the above range, the desired rigidity can be obtained, which is preferable.

In the present invention, the steel cord as the twisted cord can be coated with rubber and used to manufacture the bead core 2 . Also, the twisted cord according to the present invention shall not be coated with a matrix such as a resin material prior to rubber coating. Furthermore, the elongation percentage at break of the twisted cord according to the present invention is preferably 0.5% or more and 8% or less. Furthermore, although the cross-sectional shape of the steel cord as the twisted cord is not particularly limited, it is preferably circular.

The bead core according to the present invention can be formed by circularly winding the bead wire as the twisted cord a plurality of times. The cross-sectional structure of the bead core according to the present invention is not particularly limited as long as it has a generally known structure as a bead core. A cross-sectional structure having a substantially rectangular cross section is preferable.

The bead core using the twisted cord according to the present invention has a torsional rigidity of preferably 50% or less, more preferably 20%, compared to a bead core using a conventional single wire cord that can maintain the same burst pressure of the tire. It is more than 40%, and by this, it is possible to improve the rim fit while maintaining the tire performance.

The tire of the present invention is not particularly limited except that the bead core is made of the above twisted cord made of steel filaments, and can be made according to a conventional method. In addition, although the illustrated tire is a passenger car tire, the type of tire is not particularly limited in the present invention, such as truck and bus tires, construction vehicle tires, motorcycle tires, aircraft tires, agricultural tires, and the like. It can also be suitably applied to any tire, and the intended effect of the present invention can be obtained regardless of the application to any tire.

The carcass ply 1 is a member that forms the frame of the tire, and is arranged in at least one, for example, one to three. In the illustrated tire 10, bead cores 2 are embedded in a pair of bead portions 13, respectively, and the carcass ply 1 is folded back around the bead cores 2 from the inside of the tire to the outside. The stopping method is not limited to this. As the reinforcing cords of the carcass ply 1, for example, organic fiber cords such as polyester such as polyethylene naphthalate (PEN) and polyethylene terephthalate (PET), nylon, and semi-aromatic fibers can be used.

In the illustrated tire, a belt layer 3 made up of two belts 3a and 3b whose cord direction is inclined with respect to the tire circumferential direction is arranged on the radially outer side of the crown portion of the carcass ply 1. As shown in FIG. At least one belt layer, for example, two to four belt layers 3 are arranged. As reinforcing cords for the belt layer 3, organic fiber cords can be used in addition to steel cords.

Further, in the illustrated tire, a cap layer 4 arranged over the entire width or more of the belt layer 3 on the outer side of the belt layer 3 in the tire radial direction, and a layer layer 5 arranged in a region covering both ends of the belt layer 3 Either one or both of can be provided. The cap layer 4 and the layer layer 5 are generally formed by spirally winding a strip of constant width, which is made by arranging a large number of cords and covering them with rubber, in the tire circumferential direction. The cap layer 4 and the layer layer 5 may be provided alone or in combination. Also, a combination of two or more cap layers 4 or two or more layer layers 5 may be used.

Further, in the illustrated tire, a bead filler 6 having a tapered cross-section is arranged outside the bead core 2 in the tire radial direction. Furthermore, although not shown, an inner liner made of a rubber material or a resin material is usually arranged as the innermost layer of the tire. As the gas to be filled in the tire, in addition to normal air or air with adjusted oxygen partial pressure, an inert gas such as nitrogen, argon, or helium can be used.

The present invention will now be described in more detail using examples.
In accordance with the conditions shown in Tables 1 and 2 below, a study was conducted on bead cores in which each bead wire was looped and bundled. The steel filaments used for each bead wire were plated as shown in the table, and the bead wire was coated with rubber.

FIG. 3 shows a schematic cross-sectional view of the bead core of Example 1, and FIG. 4 shows a schematic cross-sectional view of the bead core of Comparative Example 1. As shown in FIG. The illustrated bead core 30 of Example 1 is composed of a twisted cord 32 in which steel filaments 31 are twisted together, and the bead core 40 of Comparative Example 1 is composed of a single wire cord 42 composed of steel filaments 41 .

It is the product of the bead wire strength (N) and the total number of bead wires from the bead wire strength (N), which is the strength of the bead wires that make up the bead core, based on the specifications of each bead core for each example and comparative example. The total bead strength (N) is calculated, and the bead stiffness index, which is the product of the bead wire stiffness index and the number of bead wires that make up the bead core, is calculated from the bead wire stiffness index, which is the stiffness index of the bead wires that make up the bead core. Calculated.

<Unit bead stiffness index>
Based on the values calculated above, the unit bead stiffness index represented by the ratio of the bead stiffness index to the total bead strength (bead stiffness index)/(total bead strength) was determined for each example and comparative example.

<Rim assembleability index>
Regarding the bead cores of Examples 2 and 5 and Comparative Examples 1 to 3 and 5 according to the conditions shown in the table below, the easiness of rim fitting during rim assembly was comparatively evaluated by fitting internal pressure. The results were expressed as an index by P1/P×100, where P1 is the rim fit pressure of the control tire of Comparative Example 1 and P is the actually measured rim fit pressure.

Further, for each bead core of Examples 1, 3, 4 and Comparative Examples 4, 6 according to the conditions shown in the table below, the fit internal pressure was determined based on the results of Examples 2, 5 and Comparative Examples 1 to 3, 5. values were estimated. The larger the numerical value, the better the rim assembly property.

<Hydraulic breakdown index>
Using the bead cores of Examples 2 and 5 and Comparative Examples 1 to 3 and 5 according to the conditions shown in the table below, test tires having a tire size of 205/55R16 were produced, and a water pressure rupture test was carried out. asked for pressure.

Further, for the bead cores of Examples 1, 3, 4 and Comparative Examples 4, 6 according to the conditions shown in the table below, the breaking pressure was calculated based on the results of Examples 2, 5 and Comparative Examples 1 to 3, 5. values were estimated. The obtained rupture pressure was shown as an index with Comparative Example 1 being 100. The larger the numerical value, the higher the breaking pressure and the better.

<Steering stability index>
Using the bead cores of Examples 2 and 5 and Comparative Examples 1 to 3 and 5 according to the conditions shown in the table below, test tires having a tire size of 205/55R16 were produced, and four of these test tires were mounted. The vehicle was tested by a test driver, and the actual vehicle feeling was evaluated at low speed (up to 60 km/h) and high speed (60 km/h to 120 km/h). The results were compared by averaging the evaluation results of two drivers, and shown as an index, with the index of the control tire of Comparative Example 1 being 100. A numerical value of 110 or more indicates a clear performance improvement, a numerical value of 120 or more indicates a large performance improvement, a numerical value of 90 or less indicates a clear performance deterioration, and a numerical value of 80 or less indicates a large performance deterioration.

Further, for each bead core of Examples 1, 3, 4 and Comparative Examples 4, 6 according to the conditions shown in the table below, the actual vehicle feeling was evaluated based on the results of Examples 2, 5 and Comparative Examples 1 to 3, 5. The value of was predicted and evaluated.

These results are shown together in the table below.

*1) Shows the number of rows on the 1st stage + the number of rows on the 2nd stage + the number of rows on the 3rd stage + the number of rows on the 4th stage from the bead side.

As shown in the above table, according to the present invention, in the bead core, it is possible to maintain the steering stability as before while ensuring the rim assembly performance, and furthermore, it is possible to reduce the weight. It was confirmed that a lightweight pneumatic tire could be obtained without the problems caused by the bead core.

1 carcass plies 2, 30, 40 bead core 3 belt layers 3a, 3b belt 4 cap layer 5 layer layer 6 bead filler 10 tire 11 tread portion 12 sidewall portion 13 bead portion 21, 31, 41 steel filaments 22, 32 twisted cord 42 single wire cord

Claims (7)

In a pneumatic tire with a bead core,
The bead core is composed of a twisted cord obtained by twisting 2 to 27 steel filaments containing more than 0.75% by mass of carbon, and
The unit bead stiffness index represented by the ratio of the bead stiffness index to the total bead strength of the bead core (bead stiffness index)/(total bead strength) is expressed by the following formula,
7×10 ⁻⁶ <Unit bead stiffness index (bead stiffness index/total bead strength) <34×10 ⁻⁶
A pneumatic tire characterized by satisfying The pneumatic tire according to claim 1, wherein the twisted cord has an outer diameter of 2.0 mm or less. 3. The pneumatic tire according to claim 1, wherein said twisted cord is a steel cord covered with rubber. The pneumatic tire according to any one of claims 1 to 3, wherein the steel filament has a wire diameter of 0.3 mm or more and 0.8 mm or less. The pneumatic tire according to any one of claims 1 to 4, wherein the twisted structure of said twisted cord is a 1xN structure, an M+N structure or an L+M+N structure. 6. The pneumatic tire according to claim 5, wherein the twisted structure of said twisted cord is a 1+6 structure. The pneumatic tire according to any one of claims 1 to 6, wherein said steel filaments are brass-plated.

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