JPH08175108A - Pneumatic tire - Google Patents

Abstract

PURPOSE: To compatibly realize the riding comfort and the braking performance by making the ratio of the modulus in the width direction of a base rubber layer arranged on a carcass side of a cap rubber layer to the modulus in the circumferential direction larger at the equatorial part of the tire than that of the tread shoulder part. CONSTITUTION: A belt layer 18 is provided on the outer side in the radial direction of a crown part of a carcass 14 across beads 12, a tread 20 is provided on the outer side thereof, and the tread is of double-layered structure of a cap rubber 20A on the tread side and a base rubber 20B on the carcass 14 side. The ratio η of the modulus in the circumferential direction to the modulus in the width direction at the base rubber 20B is made larger at the equatorial part of the tire than at the tread shoulder part. Thus, the shearing rigidity in the circumferential direction on the equatorial part side where the contribution to the braking performance is high becomes higher while the bending rigidity on the shoulder part side where the contribution to the riding comfort is high becomes lower, and the braking performance and the riding comfort are compatibly realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire having a tread having a cap-base structure and having both ride comfort and braking performance.

[0002]

2. Description of the Related Art Tread rubber has been improved in order to improve the riding comfort of pneumatic tires.

For example, conventionally, a tire having a tread with a cap-base structure has been known, but a method of using a soft rubber as a base rubber is adopted in order to improve riding comfort performance. Here, a soft rubber such as a base rubber is not used on the cap side, but a rubber having excellent wear resistance and cut resistance is used.

[0004]

However, when a soft base rubber is used, the amount of deformation of the tread in the circumferential direction during braking becomes large, resulting in a delay in transmission of force, which leads to a reduction in braking performance and a reduction in braking performance. If a hard rubber is used to improve the ride quality, the riding comfort will be reduced.

In view of the above facts, an object of the present invention is to provide a pneumatic tire capable of satisfying both ride comfort performance and braking performance.

[0006]

As a result of an in-depth analysis of the braking performance and the riding comfort performance, the inventor has found that the higher the shear rigidity in the circumferential direction of the tread portion, the better the braking performance, particularly the equator portion (center portion). It turned out that the contribution of

Further, it has been found that the ride comfort is better when the bending rigidity of the tread portion in the circumferential direction is softer, and the contribution of the shoulder portion is particularly high.

Therefore, it has been found that the ride comfort performance and the braking performance can be made compatible by increasing the shear rigidity in the circumferential direction of the equator while reducing the flexural rigidity on the shoulder side of the tread.

The invention according to claim 1 is made in view of the above facts, and a tread rubber is arranged in a crown portion of a carcass extending in a toroidal shape, and the tread rubber is a cap rubber layer on the tread surface side. In a pneumatic tire having a laminated structure of at least two layers with a base rubber layer disposed on the carcass side of the cap rubber layer, a ratio η of a circumferential modulus to a widthwise modulus of the base rubber layer is tread shoulder portion. It is characterized by being larger at the equator of the tire.

The invention according to claim 2 is the pneumatic tire according to claim 1, characterized in that the ratio η gradually increases from the tread shoulder portion toward the tire equator portion.

The invention described in claim 3 is the same as claim 1.
Alternatively, in the pneumatic tire according to claim 2, the base rubber layer is characterized in that the ratio η in the tire equator portion is larger than 1 and the ratio η in the tread shoulder portion is smaller than 1.

[0012]

According to the pneumatic tire of the first aspect, the ratio η of the modulus in the circumferential direction to the modulus in the width direction in the base rubber layer is larger at the tire equator than at the tread shoulder. Therefore, in the base rubber layer, the shear rigidity in the circumferential direction is large at the tire equator and the bending rigidity is small at the shoulder.

Since the shear rigidity in the circumferential direction on the side of the equator where the contribution of braking performance is high is increased and the bending rigidity on the side of the shoulder where the contribution of riding comfort is high is lowered, the braking performance and the riding comfort performance are improved. It can be compatible.

In the pneumatic tire according to the second aspect, since the ratio η of the modulus in the circumferential direction gradually increases from the tire shoulder portion toward the tire equator portion, the circumferential shear rigidity of the base rubber layer has a tire shoulder portion. To the tire equator, the flexural rigidity gradually decreases from the tire equator to the tire shoulder.

Further, according to the pneumatic tire of claim 3, the circumferential modulus ratio η in the tire equatorial portion of the base rubber layer is larger than 1, and the circumferential modulus ratio η in the tread shoulder portion is larger than 1. By making it smaller, it is possible to further increase the shear rigidity in the circumferential direction on the side of the equator where the contribution of braking performance is high, and to lower the bending rigidity on the side of the shoulder where contribution of ride comfort performance is high.

The range in which the circumferential modulus ratio η is 1 or more is 0.about. The tread width centered on the tire equatorial plane.
The range of 3 to 0.7 times is preferable.

If the range in which the circumferential modulus ratio η is 1 or more is less than 0.3 times the tread width, sufficient braking performance cannot be obtained.

On the other hand, when the range in which the circumferential modulus ratio η is 1 or more exceeds 0.7 times the tread width, the riding comfort performance is deteriorated.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

As shown in FIG. 1, a pneumatic tire (tire size 205 / 65R15) 10 is composed of a carcass 14 that straddles between beads 12, and a plurality of layers provided radially outside the crown portion of the carcass 14. The belt 18 and a tread 20 provided outside the belt 18 are provided. The internal structure of the pneumatic tire 10 of this embodiment is the same as that of a normal radial structure tire except for the tread 20.

The tread 20 has a so-called cap-base structure and has a two-layer structure including a tread side cap rubber 20A and a carcass 14 side base rubber 20B. A predetermined pattern (not shown) is formed on the tread surface of the tread 20.

Here, in the rubber member constituting the tire, D
The IN test piece was punched in the circumferential direction and width direction, and
300% modulus is measured according to K6301,
The modulus in the direction along the tire circumferential direction is the circumferential modulus M _T , and the modulus in the tire width direction of the rubber member forming the tire is the lateral modulus M _W , and the circumferential modulus M _T and the lateral modulus M _W are Assuming that the modulus ratio M _T / M _W is η, the base rubber 20B of this embodiment is
The modulus ratio η of is the largest at the equator CL, and gradually decreases toward both shoulders (conversely, it is the smallest on the shoulder side and gradually increases toward the equator CL). ).

The base rubber 20B of this embodiment has an equator C
Circumferential modulus M _T in L is 111 kg / cm ^2, the width direction modulus M _W is 102 kg / cm ^2, the modulus ratio η at the equator CL is approximately 1.09. On the other hand, the circumferential modulus M _T at the shoulder end of the base rubber 20B is 98 kg / cm ² , and the transverse modulus M _{W is}
Is 108 kg / cm ² and the modulus ratio η at the shoulder end is about 0.91. Therefore, the modulus ratio distribution (maximum modulus ratio η _max / minimum modulus ratio η _min ) is about 1.2.

Further, as shown in FIG. 2, the tread width TW of the tread 20 is 167 mm and the modulus ratio η is 1
From the position P to the position P'where the modulus ratio η is 1 (that is, the range where the modulus ratio η is 1 or more)
Is 67 mm (≈0.4 TW).

On the other hand, in the cap rubber 20A, the circumferential direction modulus M _T and the width direction modulus M _W are the same (that is, the modulus ratio η is 1) at any part, and there is no anisotropy. The cap rubber 20A
The rubber has a modulus of 103 kg / cm ² .

The tread 20 has an average rubber gauge of about 9.0 mm, and the base rubber 20B has an average rubber gauge of about 3.1 mm.

Next, the details and the manufacturing method of the base rubber 20B in which the circumferential modulus M _T and the transverse modulus M _W are partially different will be described.

The base rubber 20B may be a single rubber or a rubber containing a filler. No filler is added to the base rubber 20B of this embodiment.

The base rubber 20B is controlled so that the orientation of the rubber molecules (and the filler) is different depending on the position in the width direction when the rubber (or the rubber containing the filler) is extruded by the extruder.

As shown in FIGS. 3 and 7, the extruder (not shown) for extruding the base rubber 20B has a flow passage cross-sectional shape between the tip of the cylindrical extruder barrel 32 and the die 34. A head 38 having a flow path 36 gradually changing from a circular shape to a horizontally long flat shape wider than the base rubber 20B is provided, and a part of the head 38 and a mouthpiece 34 are provided with a flow of rubber. It is provided with a horizontally long flat orientation control flow channel 40 that changes orientation and has a distribution in orientation.

As shown in FIGS. 3 and 4, the orientation control channel
40 is provided with a narrowing flow passage 42 in the central horizontal direction,
The splayed channels 44 are provided on both sides of the leak channel 42. Figure
As shown in FIG. 3, the narrowed flow path 42 has a horizontal inlet width.
W₁, Exit width W₂Is W₁> W ₂Have a relationship of
The channel 44 has a horizontal inlet width W.₃, Exit width W_FourIs W₃<
W_FourHave a relationship.

As shown in FIG. 5, at the outlet of the narrowed flow path 42, the upper surface is separated from the upper surface of the mouth opening 34A of the mouthpiece 34 and joined to the upper side thereof, and the lower surface is the same as the lower surface of the mouth opening 34A of the mouthpiece 34. Or it is joined below that. This forms a damming portion of the base rubber 20B by the mouthpiece 34 at the outlet in the narrowed flow path 42.

As shown in FIG. 6, at the outlet in the divergent flow passage 44, the upper surface is joined to the upper surface of the opening 34A of the mouthpiece 34, and the lower surface is joined at the same height as the lower surface of the die 34 and above. ing. As a result, the end widening channel 44
A part without a damming part is formed at the outlet part in A and 44B.

Normally, the orientation of rubber molecules (and filler) is formed by the stretching deformation of a polymer material in flow, and when the rubber suddenly enters a narrow channel from a wide channel,
The one having a low average flow velocity is accelerated toward the narrow channel and largely extends in the flow direction, and at this time, the rubber molecules (and the filler) are oriented in the extrusion direction.

Therefore, the rubber flowing in the narrowed flow channel 42, which has a narrow width in the horizontal direction in the orientation control flow channel 40, is narrowed in the horizontal direction in the flow channel. Since the (and the filler) are oriented in the extrusion direction and the flow path is sharply reduced on the surface of the die 34, the rubber molecules (and the filler) are extruded with the orientation in the extrusion direction further strengthened. On the other hand, the rubber flowing in the divergent flow passage 44 having a wider width in the horizontal direction has a wider width in the flow passage in the horizontal direction, so that the rubber is stretched in the direction perpendicular to the flow, and the rubber molecules (and the filler) are in that direction. Since there is no abrupt contraction of the flow path on the surface of the die 34, it is extruded while maintaining that state as much as possible.

The rubber flowing through the orientation control flow path 40 having the narrowing flow path 42 and the end widening flow path 44 is extruded from the mouthpiece 34 as one flat extrudate, that is, the base rubber 20B.

Therefore, as shown in FIG. 7, in the extruded base rubber 20B, in the same rubber layer, the rubber molecules 21 (and the filler) are oriented at the center in the extruding direction (tire circumferential direction), and both sides thereof are arranged. In this case, the rubber molecules (and the filler) are oriented in the width direction, the orientation changes depending on the position in the width direction, and the orientation has a distribution.

As the filler, for example, calcium carbonate, hydrous basic magnesium carbonate, viscosity, silicate mineral, natural silicic acid, alumina hydrate, barium sulfate, calcium sulfate, metal powder, wood powder, fruit. Inorganic or organic fillers such as shell powder and cellulosics can be used.

Furthermore, short fibers can also be used as a filler,
For example, aromatic polyamide, vinylon, polyester,
Cut organic fibers such as nylon and rayon, oblique crystals such as cis-1,2-polybutadiene, organic substances such as whiskers of polyoxymethylene and glass, carbon,
Examples include inorganic substances such as graphite, cut inorganic fibers such as metals, silicon carbide whiskers, tungsten carbide whiskers, alumina whiskers, and the like. Needless to say, the filler may be other than these. These fillers may be used alone or in combination of two or more. Among these materials, all materials having an aspect ratio (ratio of vertical and horizontal lengths) of not 1 are oriented. (Test Example) In order to examine the effect of the present invention, a brake performance test and a riding comfort performance test were performed.

In the test, one type of conventional tire and three types of example tires to which the present invention was applied were used, and these tires were used as actual vehicles (front wheel drive domestic vehicle with displacement of 2000 CC).
It was attached to and tested. In addition, each test evaluated the feeling by the test driver.

FIG. 2 shows the relationship between the base rubber position of each of the conventional tire and the example tire and the modulus ratio.

The embodiment tire 1 of FIG. 2 is the tire of the embodiment described above, and the modulus ratio η at the equator CL of the base rubber is about 1.09, and the modulus ratio η at the shoulder end is about 0.91. And the modulus ratio η is 1
The width of the above portion is set to 67 mm (≈0.4 TW).

The tire 2 of the example has the equator C of the base rubber.
The modulus ratio η at L is about 1.09, the modulus ratio η at the shoulder end is about 0.91, and the width of the portion where the modulus ratio η is 1 or more is 100 mm (≈
It is a tire set to 0.6 TW).

In the example tire 3, the modulus ratio η at the equator CL of the base rubber is about 1.2, the modulus ratio η at the shoulder end is about 0.8, and the modulus ratio η is 1 or more. The width of the cut part is 100mm (≒
It is a tire set to 0.6 TW).

On the other hand, the conventional tire is a tire in which the modulus ratio η of the base rubber is made uniform.

The riding comfort was evaluated by a 10-point perfect score method by running an actual vehicle on a good road and a bad road of a test course at a speed of 40 to 80 km / h. It should be noted that the greater the comfort value, the better the riding comfort.

On the other hand, the braking performance was evaluated by measuring the braking distance from a speed of 40 km / h and 80 km / h on a test course and evaluating the braking distance. The evaluation is expressed as an index with the braking distance of the conventional tire (control) as 100, and the smaller the value, the shorter the braking distance and the better the braking performance.

[0048]

[Table 1]

From the test results shown in Table 1 above, the tires of the examples to which the present invention is applied have both improved riding comfort performance and braking performance than conventional tires, and both riding comfort performance and braking performance are compatible. It is clear that

The above-mentioned value of the modulus ratio η is just the value of one embodiment, and it goes without saying that it may be appropriately changed.

In order to affect the orientation-controlled base rubber 20B, the rubber gauge of the base rubber 20B is preferably at least 20% or more of the rubber gauge of the tread 20. In addition, the rubber gauge of the base rubber 20B is approximately 50% of the rubber gauge of the tread 20.
The above is not preferable because the base rubber 20B is exposed on the tread surface at the end of wear.

Further, the present invention can of course be applied to a pneumatic tire having a bias structure or another structure.

Further, although it is preferable to gradually change the modulus ratio η in the width direction, a plurality of belt-shaped rubber members each having a different modulus ratio η can be arranged in the width direction to form the base rubber. In this case, it goes without saying that the modulus ratio η of the belt-shaped rubber member arranged on the tire equator side is made larger than the modulus ratio of the belt-shaped rubber member arranged on the shoulder side. Further, even when a plurality of belt-shaped rubber members are arranged in the width direction to form the base rubber, the modulus ratio η of each belt-shaped rubber member is gradually increased from the tread shoulder portion side toward the tire equator portion side. Is preferred.

Although the tread is composed of two layers in the above embodiment, the tread may be composed of three layers or more.

[0055]

As described above, the pneumatic tire according to claim 1 has a high shear rigidity in the circumferential direction on the side of the equator, which has a high contribution to the braking performance, and a shoulder, which has a high contribution to the riding comfort performance. Since the bending rigidity on the part side is lowered, it has an excellent effect that both braking performance and riding comfort performance can be achieved.

In the pneumatic tire according to claim 2, the circumferential shearing rigidity of the base rubber layer is gradually increased from the tire shoulder portion toward the tire equator portion, and the bending rigidity is increased from the tire equator portion toward the tire shoulder portion. Since it is gradually decreasing,
While ensuring sufficient braking performance in the tread center section, it is possible to obtain good ride comfort performance due to the flexibility of the shoulder section.

Further, the pneumatic tire according to claim 3 has a higher shear rigidity in the circumferential direction on the side of the equator where the contribution of braking performance is high, and a bending rigidity on the side of the shoulder where contribution of ride comfort is high. By lowering, the braking performance and the riding comfort performance can be further improved.

[Brief description of drawings]

FIG. 1 is a sectional view taken along the axis of a pneumatic tire according to an embodiment of the present invention.

FIG. 2 is a graph showing a modulus ratio η at each position of the tread.

FIG. 3 is a plan view of the vicinity of the head of the extruder.

FIG. 4 is a perspective view of a head.

5 is a sectional view taken along line 5-5 of the head shown in FIG.

FIG. 6 is a sectional view taken along line 6-6 of the head shown in FIG.

FIG. 7 is a perspective view of a base rubber extruded from a base.

[Explanation of symbols]

 10 Pneumatic tire 14 Carcass 20 Tread 20A Cap rubber 20B Base rubber CL Tire equator

Claims (3)

[Claims] 1. A tread rubber is arranged on a crown portion of a carcass extending in a toroidal shape, and the tread rubber includes at least a cap rubber layer on a tread surface side and a base rubber layer disposed on a carcass side of the cap rubber layer. A pneumatic tire having a laminated structure of layers, wherein the ratio η of the modulus in the circumferential direction to the modulus in the width direction in the base rubber layer is larger in the tire equator than in the tread shoulder. 2. The pneumatic tire according to claim 1, wherein the ratio η gradually increases from the tread shoulder portion toward the tire equator portion. 3. The base rubber layer according to claim 1, wherein the ratio η at the tire equator is greater than 1 and the ratio η at the tread shoulder is less than 1. Pneumatic tire.