JP3175027B2 - Pneumatic radial tire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightweight pneumatic radial tire using a belt layer made of steel cord.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for lower fuel consumption of vehicles due to the problem of global environmental pollution. As one of the measures, weight reduction of pneumatic radial tires has been attracting attention as one of the major technical issues. I have. For the belt layer of the pneumatic radial tire, a steel cord having excellent tensile strength and tensile modulus is used, but its specific gravity is extremely large, which has been an obstacle to the above-mentioned weight reduction. On the other hand, organic fiber cords, which have a lower specific gravity than steel cords, have low tensile strength and tensile modulus and cannot exhibit the same tire performance as steel cords, so for the time being it is necessary to rely on steel cords for the time being. .

Therefore, as a measure for achieving weight reduction on the premise of using the above-mentioned steel cord, it is conceivable to reduce the amount of wire used and the rubber gauge. As one of the concrete means, it is proposed to use a steel cord as a single wire, instead of using a plurality of wires as stranded wires. This single wire cord has a smaller cord diameter at the same wire cross-section than a stranded cord, thereby reducing the tread under-groove gauge (rubber gauge) and the belt layer cord gauge (rubber gauge). As a result, the amount of rubber can be reduced and the weight can be reduced. In addition, since the single wire can be completely covered with rubber, the corrosion fatigue due to water absorption and the decrease in adhesiveness can be reduced, and the durability can be improved.

[0004] However, a single wire cord having such features is also rigid because it has no twist. Therefore, there is a drawback that durability against bending deformation and compression deformation due to repeated load is small. The lack of durability causes wire breakage more frequently than tires using a stranded wire cord, causing a reduction in belt durability.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to use a single wire cord to reduce the weight compared to the use of a twisted cord and to improve the tire performance such as belt durability to the same level as using a twisted cord. It is an object of the present invention to provide a pneumatic radial tire having a larger size.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a pneumatic radial tire in which a belt layer disposed on the outer peripheral side of a carcass layer of a tread is made of a steel cord. 0.90 to 1.10% by weight, the chromium content is 0.1% by weight or more, and the tensile strength is at least 320 kgf / mm ^2.
This is a configuration in which a single wire having a diameter d of 0.28 to 0.60 mm is shaped with a two-dimensional waveform along the longitudinal direction, and the diameter d of the single wire and the height h of the waveform are formed. The parameter F = (h−d) / P specified from the pitch length P of the waveform is set to 0.01 ≦ F ≦ 0.06, and the steel cord is connected to the tread surface by the two-dimensional surface of the waveform. It is characterized by being arranged so as to be parallel.

[0007] By using a single wire having a specific tensile strength and a specific diameter having a specific carbon content and a specific chromium content as the steel cord of the belt layer, it is possible to reduce the weight and to reduce the length thereof. By shaping the two-dimensional waveform along the direction, the rigidity of the single wire itself can be reduced, and wire break resistance (belt durability) can be imparted. In addition, by setting the parameter F specified from the diameter d of the single wire, the height h of the corrugation and the pitch length P in the range of 0.01 to 0.06, the rigidity is reduced and the steering stability based on the relaxation is improved. The effect of suppressing the decrease can be harmonized. Moreover, by arranging the single wire so that the two-dimensional surface of the waveform is parallel to the tread surface, the gauge under the groove of the tread and the gauge between the plies of the belt layer can be reduced, and the amount of rubber can be reduced. Therefore, the weight can be further reduced.

Hereinafter, the configuration of the present invention will be specifically described with reference to the drawings. In FIG. 1, 1 is a tread portion,
Numeral 2 denotes a carcass layer whose both ends are wound around a pair of left and right bead cores 5 from the inside to the outside of the tire. The cord angle of the carcass layer 2 with respect to the tire circumferential directions E and E 'is substantially 90 degrees. On the outer peripheral side of the carcass layer 2 of the tread portion 1, two inner belt layers 4 having a cord angle of 5 to 40 degrees with respect to the tire circumferential directions E and E ', and reinforced with steel cords 40 crossing each other, and an outer side Each of the belt layers 4 'is arranged over the entire circumference of the tire. On the surface of the tread portion 1, a main groove 6 extending in the tire circumferential direction E, E 'and a sub groove 7 intersecting the main groove 6 are provided.

In the present invention, as shown in FIG. 3, the steel cord 40 for reinforcing the belt layers 4, 4 'is formed of a two-dimensional corrugated single wire, and the single wire has at least a tensile strength. Is 320 kgf / mm ² or more, and the diameter d is 0.28 mm to 0.60 mm, so that a sufficient reinforcing effect equal to or more than that of the stranded cord can be exerted. To enable such high tensile strength, the carbon content of the wire must be between 0.90 and 1.10.
Manufactured from high carbon steel with a chromium content of 0.1% by weight or more by weight. By setting the content of carbon and chromium in the above range, not only the tensile strength of the single wire but also the toughness and the fatigue resistance can be improved. The upper limit of the chromium content is not particularly limited, but if it is too large, heat treatment at the time of wire production becomes difficult, and the production cost becomes high. Good.

The diameter d of the single wire is 0.28 mm.
With less than the above-mentioned carbon content and chromium content,
Even if the tensile strength is high, the bending stiffness of the belt layer is too low, so it is difficult to suppress wire breakage. On the other hand, if the diameter d exceeds 0.60 mm, the single wire becomes too rigid and the surface distortion accompanying the compression deformation increases, so that the belt durability deteriorates.

As shown in FIG. 3, the single wire has a two-dimensional waveform having a height h larger than a diameter d and a pitch length P along its longitudinal direction. By shaping the single wire in this manner, the tensile modulus is reduced and the rigidity is reduced as compared with a straight single wire. Therefore, even with a single wire that is not twisted, the durability against repeated bending load and compression load (fatigue resistance) is improved, and the durability when used for the belt layer is the same as that of using a stranded wire cord, or It can be further improved. However, if the degree of molding of the single wire is too large, the tensile modulus is significantly reduced, the lateral rigidity of the belt layer is reduced, and the cornering power is reduced. It will be difficult to secure.

The above-described characteristic of a single wire is based on the difference (h−h) between the height h of the shaped two-dimensional waveform and the wire diameter d.
d) and the pitch length P. That is, associating with the parameter F = (hd) / P defined by the difference (h−d) and the pitch length P, as described below with reference to Table 1 and FIG. Correlation with fatigue and tensile modulus can be further clarified, and furthermore, correlation with belt layer durability and cornering power (steering stability) can be clarified. In the present invention, this parameter F is 0.01
≦ F ≦ 0.06.

Table 1 shows the relationship between the two-dimensional waveform parameter F of the single wire and the fatigue resistance against repeated bending loads performed under the following measurement conditions. From the results in Table 1, the parameter F =
It can be seen that, when a waveform of 0.01 is formed, a fatigue resistance effect can be exhibited as compared with a straight single wire (F = 0). Further, it can be seen that if F = 0.04 or more, almost no break in the belt wire is recognized. Fatigue resistance measurement method : As shown in FIG. 5, a diameter of 0.40 mm
12.5 mm x 12.5 mm
Embedded in a rubber block 60 with a size of × 20.0 mm,
12.5mm x 12.5mm x 15.0m at both ends
The measurement sample S is prepared by bonding a brass support block 70 of m m so that both ends of the single wire 40 are connected to the support block 70. As shown in FIG. 6, ten samples S were prepared and mounted between a pair of rotating plates T and T ′, and set so that the extension lines of both rotating shafts U and U ′ made an angle θ. A maximum 1.5% expansion and a maximum 1.5% compression strain is applied to the rubber block 60 per rotation. After rotating the two rotating plates T and T 'thus set four million times, the presence or absence of breakage of the single wire 40 in each sample S was examined, and the number of breaks was displayed as a percentage.

[0014]

On the other hand, FIG. 4 shows the relationship between the two-dimensional waveform parameter F and the tensile modulus of a single wire having a diameter of 0.30 mm and a pitch of waveform P = 0.4 mm. FIG. 4 shows that the tensile modulus decreases as the parameter F increases. The tensile elastic modulus that the single wire should have is at least about 1.3 × from the relationship with the cornering power based on the belt layer.
Since it is necessary to set to 10 ⁴ kgf / mm ² , it can be seen that the upper limit of the parameter F is 0.06.

In the present invention, when such a single wire is used as a reinforcing cord of the belt layer, the two-dimensional waveform is arranged so as to be parallel to the tread surface. With such an arrangement, the under-groove gauge t from the groove bottom of the main groove 6 formed on the tread to the single wire 40 of the outermost belt layer 4 'can be reduced (see FIG. 2), thereby reducing the amount of rubber. It is possible to reduce the weight and weight.
Further, the weight can be reduced by reducing the distance a (gauge between plies) between the single wires 40 constituting the inner belt layer 4 and the outer belt layer 4 ', and the cornering power is increased to increase the interlayer shear force. It is possible. Moreover, since the wire is a single wire, the cord diameter can be reduced when the wire has the same cross-sectional area as compared with the stranded wire cord. Further, the periphery thereof can be completely covered with the coating rubber, so that it can have excellent water resistance and rust resistance.

In the present invention, the under-groove gauge t obtained by the above-described effect is preferably set in the range of 1.5 to 3.5 mm. By setting the under-groove gauge t to 1.5 mm or more, corrosion fatigue due to moisture absorption can be prevented and belt wire breakage can be prevented. On the other hand, by setting the thickness to 3.5 mm or less, the effect of reducing the weight can be secured. Further, the gauge a between the plies is preferably set in a range of 0.15 to 0.8 mm in a radial tire for a passenger car. By setting the gauge a between plies to 0.15 mm or more, it is possible to suppress the interlayer shear strain from becoming too large, and to suppress separation and belt wire breakage. On the other hand, 0.
When the thickness is 80 mm or less, sufficient interlayer shear strain can be imparted, and good cornering power and high-speed durability can be secured. The present invention is suitable mainly for application to pneumatic radial tires for passenger cars, but is also applicable to pneumatic tires for other uses such as trucks and buses.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Tire size, carcass cord, width of inner and outer belt layers and cord angle with respect to the circumferential direction of tire, pitch length P of waveform of single wire, gauge a between belt plies and gauge t under groove are common as described below. Except for the size, the comparative tires 1 to 7 differing in the carbon content, the chromium content, the tensile strength, the diameter d and the parameter F of the single wire, and the tires of the present invention 1 to 6 as shown in Table 2. Thirteen kinds of radial tires were manufactured.

Tire size: 175 / 70R13 Carcass cord: Polyester fiber cord 1500D /
2 Cord structure of belt layer: single line Width of inner belt layer = 120 mm Width of outer belt layer = 110 mm Belt cord angle with respect to tire circumferential direction = 20 ° Pitch length of waveform of single wire P = 4.0 mm Ply gauge a = 0 .64 mm Under-groove gauge t = 3.5 mm For comparison, 49 strands / 50 mm of steel cord in which two strand wires having a diameter d = 0.28 mm were converted into a stranded wire having a cord structure of 1 × 2 and a twist pitch of 14 were used. A comparative tire having the same configuration as that of the tire 2 of the present invention except that the belt layer was configured with the number of ends of the width was manufactured.

For these 14 types of radial tires, the weight reduction index, cornering power,
High-speed durability and slalom belt wire breakability (belt durability) were evaluated by a drum test after moisture absorption. The results are shown in Table 2. Weight reduction index : based on tire weight of comparison tire (100)
The ratio of the weight reduction of each tire is expressed in%. The index was indicated by using the measured value of the comparative tire as a reference (100). The smaller the index value, the lighter the weight. Cornering power (hereinafter abbreviated as CP): The test tire was tested at an air pressure of 200 kPa (2.0 kgf / cm ² ).
The rim is assembled on a rim of × 5-J, and runs on a drum having a diameter of 1707.6 mm at a speed of 10 km / hr under a load of 2942 N (300 kgf / cm ² ) at a slip angle of 1 ° to the right. The average of the absolute values of the lateral force and the lateral force when the slip angle was 1 ° to the left was measured. The index was indicated by using the measured value of the comparative tire as a reference (100). The larger the index value is, the larger the CP is, and the more excellent the steering stability is. High-speed durability : The test tire was subjected to an air pressure of 220 kPa (2.2
kgf / cm ² ) and assembled to the rim of 13 × 5-J,
After the humidity was adjusted by leaving the substrate in an atmosphere of 70 ° C. × 98% RH for 30 days, a load of 4119 N (420 kgf / cm ² ) was applied on a drum having a diameter of 1707.6 mm at a speed of 81 km / hr. After running for 121 hours
When the running speed was increased to km / hr and thereafter the running speed was increased by 8 km / hr every 30 minutes and the running was continued, the running speed at the time when the tire failed was evaluated. The speed reached 185 km / hr,
If no failure occurred even after continuing for 0 minutes, the test was terminated with this. Based on the measured value of the comparison tire (1
00). The higher the index value, the better the high-speed durability. Slalom belt wire breakability : pneumatic test tire 1
At 70 kPa (1.7 kgf / cm ² ), the rim was assembled to a 13 × 5-J rim, and the humidity was adjusted in the same manner as in high-speed durability.
5 °, load 3432N (350kgf) ± 2157N
Under a fluctuation condition of (220 kgf), the vehicle ran for 300 km while changing the load and the slip angle with a rectangular wave of 0.067 Hz. After running, the test tire was incised to evaluate whether the belt wire was broken or not.

[0021]

From Table 2, it can be seen that both Comparative Tire 1 using a single wire having a carbon content of less than 0.90% and Comparative Tire 2 using a single wire having a carbon content of more than 1.10% had a broken belt wire. And the belt durability was poor. Further, the comparative tire 3 using a single wire having a chromium content of less than 0.1% also suffered a break in the belt wire. The tire 1 of the present invention is an example in which a single wire having a particularly high chromium content (0.50% by weight) is used,
While maintaining the same CP and high-speed durability as the comparison tire,
Lightweight and belt durability are improved. However, when the chromium content is large, heat treatment at the time of manufacturing a wire is difficult, which is not practical.

The comparative tire 4 using a single wire having a diameter d smaller than that specified in the present invention has the same CP as the comparative tire.
However, the high-speed durability and the breakability of the belt wire are significantly reduced. On the other hand, the comparative tire 5 using a single-wire wire having an excessively large diameter d also has a remarkably reduced high-speed durability and belt wire breakability, and has a lighter weight index than the comparative tire. On the other hand, the tire 2 of the present invention using a single wire whose diameter d is close to the lower limit specified in the present invention is reduced in weight while having the same CP, high-speed durability and belt wire breakability as the comparative tire. I have. In addition, the tire 3 of the present invention using a single-wire wire having a diameter d close to the upper limit has a slightly lower high-speed durability,
P, belt wire breakability, and weight reduction index are the same as the comparative tire.

The comparative tire 6 using a single wire having a parameter F smaller than the lower limit of the present invention has the same CP and high-speed durability as the comparative tire, and is lighter, but breaks the belt wire. ing. The comparative tire 7 using a single wire having the parameter F exceeding the upper limit has the same high-speed durability as the comparative tire and does not break the belt wire, but has a reduced CP and a small weight-reducing effect. On the other hand, the tires 4, 5 and 6 of the present invention in which the parameter F is within the specified range of the present invention have the same CP, high-speed durability and slalom durability as the comparative tire, although the CP of the tire 6 of the present invention is slightly lower. It can be seen that the weight is reduced while holding.

[0025]

According to the present invention, the steel cord of the belt layer is formed of a single wire having a specific carbon content and a high tensile strength having a chromium content and having a specific diameter. In addition, since the two-dimensional waveform is typed on the single wire and the parameter F for specifying the waveform is within a certain range, the rigidity inherent in the single wire is relaxed, and good fatigue resistance is maintained. While suppressing excessive softening, it is possible to maintain good steering stability. Moreover, by arranging the single-wire so that its waveform is parallel to the tread surface, the under-groove gauge t of the tread and the gauge a between the plies of the belt layer can be reduced, and the amount of rubber can be reduced. It is possible to further reduce the weight, to impart an interlayer shear strain, and to further improve the steering stability.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a main part of a pneumatic radial tire for a passenger car according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a main part of the tire of FIG. 1;

FIG. 3 is a side view showing an example of a two-dimensional corrugated single wire used in the present invention.

FIG. 4 is a graph showing a relationship between a parameter F of a single wire and a tensile modulus.

FIG. 5 is a perspective view showing a shape of a sample for measuring fatigue resistance of a single wire.

FIG. 6 is a diagram schematically illustrating an apparatus for measuring fatigue resistance of a single wire.

[Explanation of symbols]

Reference Signs List 1 tread portion 4 inner belt layer 4 'outer (outermost) belt layer 6 main groove 40 steel cord (single wire) d wire diameter h waveform height P waveform pitch length

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-51-47702 (JP, A) JP-A-48-63961 (JP, A) JP-A-4-84395 (JP, U) 5294 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60C 9/00 B60C 9/18-9/20 D07B 1/06

Claims (1)

(57) [Claims] 1. A pneumatic radial tire in which a belt layer disposed on the outer side of a carcass layer of a tread is formed of a steel cord, wherein the steel cord has a carbon content of 0.90 to 1.10% by weight, a chromium content. Is 0.1% by weight or more and at least a tensile strength of 320 kgf / mm
A single wire with a diameter of at least ² and a diameter d of 0.28 to 0.60 mm is shaped into a two-dimensional waveform along its longitudinal direction, and the diameter d of the single wire and the height of the waveform h, the parameter F = (h−d) / P specified from the pitch length P of the waveform is set to 0.01 ≦ F ≦ 0.06, and the steel cord is placed on the tread surface by the two-dimensional surface of the waveform. Pneumatic radial tires arranged in parallel to.