JP2005271654A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire capable of improving high speed durability without lowering steering stability. <P>SOLUTION: A tread part 1 is made of at least three kinds of rubber materials of an A layer of a center part, a B layer at the inside of a shoulder part and a C layer for covering an outer surface of the shoulder part in a crescent shape in cross section. The rubber material in the A layer has JIS-A hardness of 65 to 80. In the rubber material in the B layer, tanδis 5 to 60% of tanδ of the A layer, and a cross sectional area ratio occupying in the tread part 1 is 10 to 40%. In the rubber material in the C layer, JIS-A hardness is 65 to 80 and Lambourn abrasion amount is 2 to 5 times as much as that in the A layer, and a cross sectional area ratio occupying in the tread part 1 is 1 to 10%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pneumatic radial tire, and more particularly, to a pneumatic radial tire that has improved high-speed durability without reducing steering stability.

  In recent years, due to an increase in the load on pneumatic tires and an increase in the camber angle set in the vehicle, the tread rubber near the end of the belt layer generates excessive heat during high-speed running and peels off at the interface with the belt layer end. There is a problem of causing failure.

  As a countermeasure against failure due to excessive heat generation of the rubber near the end of the belt layer as described above, a low heat generation rubber with a low hysteresis loss is arranged on the shoulder portion of the tread, that is, a low tan δ rubber is arranged. I think it would be good. Conventionally, although not intended to suppress the heat generation in the shoulder portion, there has been a proposal that low tan δ rubber is disposed in the shoulder portion for the purpose of reducing tire rolling resistance and reducing fuel consumption (patent) Reference 1).

However, as described above, if the low tan δ rubber is simply disposed on the shoulder portion of the tread, the low tan δ rubber has low rigidity, so that the shoulder portion rigidity is lowered and steering stability is deteriorated. There was a problem.
JP-A-11-208216

  An object of the present invention is to provide a pneumatic radial tire that solves the above-described problems and can improve high-speed durability without deteriorating steering stability.

In the pneumatic radial tire of the present invention that achieves the above object, a carcass layer is mounted between a pair of left and right bead portions, and at least two belt layers are disposed between an outer peripheral side of the carcass layer and a tread portion. In pneumatic radial tires,
The tread portion is composed of at least three kinds of rubber materials, that is, the A layer in the center portion, the B layer inside the shoulder portion, and the C layer covering the outer surface of the shoulder portion in a crescent shape, and the rubber material of the A layer is JIS- A hardness is 65 to 80, the rubber material of the B layer is tan δ is 5 to 60% of the tan δ of the A layer, and the cross-sectional area ratio in the tread portion is 10 to 40%, and the C layer The rubber material has a JIS-A hardness of 65 to 80, a lamborn wear amount of 2 to 5 times that of the A layer, and a cross-sectional area ratio in the tread portion of 1 to 10%.

  According to the present invention, as described above, the tread portion is composed of at least three kinds of rubber materials of the A layer at the center portion, the B layer inside the shoulder portion, and the C layer on the outer surface of the shoulder portion, and the rubber material of the B layer. Tan δ is made of a low tan δ rubber corresponding to 5 to 60% of the tan δ of the A layer, so that heat generation of the rubber near the end of the belt layer during high speed running can be suppressed and high speed durability can be improved. In addition, by making the rubber material of the C layer on the outer surface of the shoulder portion high rigidity with a JIS-A hardness of 65 to 80, in order to compensate for the decrease in rigidity of the B layer made of the low tan δ rubber material, Even if a low tan δ rubber material is provided, it is possible to prevent the steering stability at the initial stage of wear from being lowered.

  In addition, the groove cross-sectional area decreases during the middle wear phase of the tread, and the wet braking performance decreases due to the reduced drainage. However, the C layer disappears during the middle wear phase by increasing the amount of lamborn wear of the C layer. Since the tread contact pressure is improved and the contact length is extended, it is possible to suppress a decrease in wet braking performance. In addition, the rigidity of the center part increases due to the thickness reduction in the middle period of wear of the tread part, but the rigidity of the shoulder part decreases due to the disappearance of the C layer, so the tread body is balanced so that the rigidity does not increase too much, Steering stability can be suppressed so as not to cause a large fluctuation over time.

  In the present invention, the tread portion is composed of at least three kinds of rubber materials including an A layer in the center portion, a B layer inside the shoulder portion, and a C layer covering the shoulder portion outer surface in a crescent shape. Of these, the A layer located in the center portion of the tread is made of a highly rigid rubber material having a JIS-A hardness of 65 to 80 in order to ensure steering stability. When the JIS-A hardness of the rubber material constituting the A layer is lower than 65, it becomes difficult to maintain good steering stability. On the other hand, when the JIS-A hardness is greater than 80, the ride comfort is deteriorated and the noise / vibration performance is deteriorated.

  A low tan δ rubber material having a small hysteresis loss is used for the B layer disposed inside the shoulder portion. Specifically, a rubber material having a low tan δ corresponding to 5 to 60% of the tan δ of the A layer is used. The B layer is disposed on the inner side of the shoulder portion so as to be in contact with the end portion of the belt layer or, if a belt cover layer is provided, in contact with the belt cover layer.

  If the tan δ of the rubber material constituting the B layer is larger than 60% of the tan δ of the rubber material of the A layer, it becomes difficult to suppress the heat generation of the rubber in the vicinity of the belt layer end, and the high speed durability is improved. Can not be. On the other hand, if it is smaller than 5% of tan δ of the rubber material of the A layer, the steering stability is lowered due to the reduction in rigidity.

  In general, the rubber material of the A layer is one having a tan δ in the range of 0.12 to 0.5, but the tan δ of the B layer that exhibits the above effects can be 0.2 or less. preferable. Although a minimum is not specifically limited, 0.01 is preferable.

  In addition, since the B layer is a low tan δ rubber, it is possible to reduce the rolling resistance of the tire in addition to the effect of suppressing heat generation, and to achieve low fuel consumption.

  Here, tan δ is a value measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho under conditions of an initial strain of 10%, a dynamic strain of ± 2%, a frequency of 20 Hz, and a temperature of 60 ° C.

  In order to ensure the high-speed durability and low rolling property obtained based on the B layer as described above, it is important that the cross-sectional area ratio of the B layer in the entire tread portion is 10 to 40%. When the cross-sectional area ratio is less than 10%, the effect of suppressing the heat generation of the rubber is small, so that the effect of improving the high-speed durability cannot be obtained. On the other hand, when the cross-sectional area ratio is more than 40%, the volume occupied by the A layer in the center portion is reduced, so that the rigidity is lowered and the steering stability is lowered. In addition, wet braking performance after the middle stage of wear is also reduced. More preferably, the distance Wb from the tire equator CL to the inner end of the B layer in the tire width direction may be 0.7 to 0.95 times the distance W from the tire equator to the belt layer maximum width end.

  The C layer is formed so that the cross section has a crescent shape and covers the outer surface of the shoulder portion in a thin shape. As the rubber material constituting the C layer, a rubber material having a JIS-A hardness of 65 to 80 and a lamborn wear amount of 2 to 5 times the lamborn wear amount of the A layer is used. Since the C layer has the same rigidity as the A layer, the C layer has the same rigidity, so that the lowering of the rigidity of the B layer, which is a low tan δ, is compensated for and steering stability in the initial stage of wear is ensured. .

  Here, the amount of lamborn wear refers to the amount of wear measured by a lamborn wear test in accordance with the provisions of JIS-K6264.

  Since the wear characteristics of the lamborn wear amount are 2 to 5 times the lamborn wear amount of the A layer, the C layer disappears by the middle stage of wear of the tread portion, and the shoulder portion has a round shape. The C layer wears and disappears in this way, and the shoulder portion has a round shape, whereby the tread contact pressure is increased and the contact length is increased. Accordingly, the braking performance on the wet road surface can be maintained even if the groove cross-sectional area is reduced.

  In addition, when the wear of the tread portion is in the middle period or later, the center portion of the A layer increases in rigidity due to a decrease in thickness. On the other hand, the rigidity of the shoulder portion is lowered after the middle stage of wear because the highly rigid C layer disappears and the B layer is exposed. Therefore, the rigidity of the tread as a whole can be balanced by the rigidity change of the center part and the shoulder part in the opposite directions, and the fluctuation of the steering stability can be suppressed to be small.

  In order to obtain the effect of the C layer as described above, the C layer needs to have a cross-sectional area ratio of 1 to 10% in the entire tread portion. When the cross-sectional area ratio of the C layer is less than 1% of the entire tread portion, it is not possible to obtain stable steering stability in the early stage of wear. If the cross-sectional area ratio of the C layer is greater than 10%, the C layer may not disappear even when the tread portion is in the middle of wear, and good wet braking performance cannot be obtained. More preferably, the distance Wc from the tire equator CL to the inner end of the C layer in the tire width direction may be 0.7 to 0.95 times the distance W from the tire equator to the end of the belt layer maximum width.

  If the lamborn wear amount of the C layer is less than twice the lamborn wear amount of the A layer, the C layer remains even in the middle stage of the tread wear, so that it is difficult to obtain the above-described effect. On the other hand, if it is more than 5 times, steering stability at the beginning of tread wear cannot be obtained.

  Further, it is preferable that the inner end of the C layer in the tire width direction and the inner end of the B layer in the tire width direction are arranged so that the distance from the tire equator CL is substantially the same. Preferably, the relative positional deviation in the tire width direction between the inner end of the C layer in the tire width direction and the inner end of the B layer in the tire width direction may be within ± 5 mm.

  The C layer having a crescent-shaped cross section preferably has a maximum thickness t in the range of 0.5 to 3 mm. When the maximum thickness t is less than 0.5 mm, the above-described rigidity complementation capability at the initial stage of wear is insufficient, so that good steering stability cannot be obtained. On the other hand, if it is larger than 3 mm, it may remain without disappearing even when the tread portion is worn about 50%.

  FIG. 1 shows a half section of a pneumatic radial tire according to an embodiment of the present invention.

  In the figure, only one side from the tire center CL (tire equator) is shown. 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. A carcass layer 4 is provided inside the tire. The carcass layer 4 extends from the both sides of the tread portion 1 to the pair of left and right sidewall portions 2 and 2 and the bead portions 3 and 3, and then the bead cores 5 and 5 are folded back from the tire inner side to the outer side, respectively. Further, on the outer peripheral side of the carcass layer 4, two inner and outer belt layers 6, 6 are provided so as to cross the reinforcing cord between the tread portion 1, and a belt cover is provided outside the outer belt layer 6. The layer 7 is provided so as to cover the whole.

  The tread portion 1 is composed of an A layer in the center portion, a B layer inside the shoulder portion, and a C layer covering the outer surface of the shoulder portion, and these A layer, B layer, and C layer are composed of different rubber materials. ing. The B layer is disposed so as to be in contact with the surface of the belt cover layer 7, and the C layer is formed so that the cross section has a crescent shape.

  The rubber material of the A layer is made of rubber having a JIS-A hardness of 65 to 80 and high rigidity, and ensures the steering stability of the tire. The rubber material of the B layer has a low tan δ, corresponds to 5 to 60% of the tan δ of the A layer, and the cross-sectional area ratio in the tread portion 1 is 10 to 40%. By disposing the low tan δ B layer in the vicinity of the end of the belt layer 6, heat generation during high speed running is suppressed and high speed durability is improved.

  The rubber material of the C layer has a JIS-A hardness of 65 to 80, which is the same level as that of the A layer, and is highly rigid. However, the wear characteristics are lower than that of the A layer. ~ 5 times more. Moreover, the cross-sectional area ratio which occupies for the tread part 1 is 1 to 10%. By disposing the C layer having such characteristics on the outer surface of the shoulder portion, the low rigidity of the B layer is compensated, and the steering stability in the initial stage of tread wear is favorably maintained. Further, the C layer disappears in the middle stage of wear and increases the tread contact pressure, so that the wet braking performance is maintained so as not to be different from that in the early stage of wear.

  The distance Wb from the tire equator CL to the inner end of the B layer in the tire width direction and the distance Wc from the tire equator CL to the inner end of the C layer in the tire width direction are respectively the maximum width end of the belt layer 6 from the tire equator CL. It is set to be 0.7 to 0.95 times the distance W to the portion (the end of the belt layer on the inner layer side in the figure). The C layer having a crescent cross section has a maximum thickness t set to 0.5 to 3 mm.

  2 to 4 each illustrate another embodiment of the present invention.

  The B layer and the C layer occupying the shoulder portion of the tread portion 1 do not need to be in a laminated state in which the B layer and the C layer overlap each other with the same width as in the embodiment of FIG. As illustrated in FIG. 5, the A layer in the center portion may be extended and interposed between the B layer and the C layer. In any case, the B layer is in contact with the belt cover layer 7, and in the absence of the belt cover layer 7, the B layer directly contacts the belt layer 6, and the C layer covers the outer surface of the shoulder portion. It is in a state of covering.

  The tire size is 225 / 45ZR17 and the tire basic structure is the same as in FIG. 1, and the JIS-A hardness of the A layer constituting the tread portion, the ratio of the tan δ of the B layer to the A layer, and the T layer portion of the B layer The cross-sectional area ratio, the JIS-A hardness of the C layer, the multiple of the lamborn wear amount of the C layer to the lamborn wear amount of the A layer, and the cross-sectional area ratio in the tread portion of the C layer are varied as shown in Table 1, respectively. Seven types of pneumatic tires (Examples 1 to 3, Comparative Examples 1 to 4) were manufactured. In addition, the comparative example 1 was taken as the pneumatic tire comprised only by A layer and B layer, without providing C layer.

  For these seven types of tires, the following test methods were used to measure high-speed durability, steering stability Si at the beginning of wear, steering stability Sm at the middle stage of wear, wet braking property Bi at the beginning of wear, and wet braking property Bm at the middle stage of wear, respectively. The results are shown in Table 1.

[High-speed durability]
After mounting the test tire on a drum testing machine having a drum diameter of 1707 mm and completing the high-speed durability test specified in JIS D4230, the speed is increased every 30 minutes until the tire breaks by 10 km / h. The speed at which the breaks was measured.

  Evaluation was shown by the index | exponent which sets the measured value of the comparative example 1 to 100. FIG. The larger the index value, the better the high speed durability.

[Maneuvering stability Si, Sm]
The test tire was mounted on a 2.5-liter passenger car, and the driving stability when five test drivers circulated around the test course was measured using the five-point method, and the average score of the five persons was evaluated. . The steering stability Si is a test value of the tire when it is new, and the steering stability Sm is a test value of the tire after traveling 10,000 m.

  Evaluation was shown by the index | exponent which makes the score of the comparative example 1 100. FIG. The larger the index value, the better the steering stability.

[Wet braking Bi, Bm]
The test tire was mounted on a passenger car with a displacement of 2.5 liters, traveled on an asphalt road surface sprinkled with water at an initial speed of 40 km / h, and the braking distance when sudden braking was measured. The wet braking performance Bi is a test value of a tire when new, and the wet braking performance Bm is a test value of a tire after traveling 10,000 m.

  The evaluation was performed by using the reciprocal of the measured value, and indicated by an index with the reciprocal of the measured value of Comparative Example 1 being 100. A larger index value means better wet braking performance.

1 is a half sectional view showing a pneumatic radial tire according to an embodiment of the present invention. It is a half sectional view showing the important section of a pneumatic radial tire according to another embodiment of the present invention. FIG. 6 is a half cross-sectional view showing a main part of a pneumatic radial tire according to still another embodiment of the present invention. FIG. 6 is a half cross-sectional view showing a main part of a pneumatic radial tire according to still another embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Belt layer 7 Belt cover layer

Claims (5)

In a pneumatic radial tire in which a carcass layer is mounted between a pair of left and right bead portions, and at least two belt layers are disposed between the outer peripheral side of the carcass layer and a tread portion,
The tread portion is composed of at least three kinds of rubber materials, that is, the A layer in the center portion, the B layer inside the shoulder portion, and the C layer covering the outer surface of the shoulder portion in a crescent shape, and the rubber material of the A layer is JIS- A hardness is 65 to 80, the rubber material of the B layer is tan δ is 5 to 60% of the tan δ of the A layer, and the cross-sectional area ratio in the tread portion is 10 to 40%, and the C layer This rubber material is a pneumatic radial tire having a JIS-A hardness of 65 to 80, a lamborn wear amount of 2 to 5 times that of the A layer, and a cross-sectional area ratio of 1 to 10% in the tread portion.   The pneumatic radial tire according to claim 1, wherein tan δ of the rubber material of the B layer is 0.2 or less.   The pneumatic radial tire according to claim 1 or 2, wherein a maximum thickness of the C layer having a crescent-shaped cross section is 0.5 to 3 mm.   The distance Wb from the tire equator to the inner end of the B layer in the tire width direction and the distance Wc from the tire equator to the inner end of the C layer in the tire width direction are distances from the tire equator to the maximum width end of the belt layer, respectively. The pneumatic radial tire according to any one of claims 1 to 3, wherein the range is 0.7 to 0.95 times W. The pneumatic radial tire according to claim 4, wherein a relative positional deviation between the inner end of the B layer in the tire width direction and the inner end of the C layer in the tire width direction is within ± 5 mm.

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