JP6786849B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire capable of suppressing uneven wear by reducing the buckling of the belt layer while reducing the weight.

In recent years, it has been strongly desired to reduce the weight of pneumatic tires in order to improve fuel efficiency. Therefore, the present inventor has proposed to reduce the width of the tread portion, which has a large rubber volume and has the highest ratio to the total weight of the tire. Specifically, the tread width is set to 80% or less of the tire cross-sectional width to reduce the rubber weight, and the belt layer width is set to 70% or less of the tire cross-sectional width to reduce the cord weight of the belt layer.

However, in a tire having a reduced tread width or the like in this way, the outer side area of the sidewall portion, which is radially outside the maximum width position of the tire, is wider than that of the conventional tire, and the outer side area is further widened. The rigidity of the tire is excessively small compared to the rigidity of the inner side region that is radially inside the maximum width position of the tire.

Therefore, for example, as shown in an exaggerated manner in FIG. 5, when the outer side region a is grounded, the outer side region a becomes greatly bent and rises, and a so-called buckling c in which the belt layer b is curved in a concave shape is generated. This buckling is also due to the narrow width of the belt layer b. As a result, the contact pressure becomes non-uniform, causing uneven wear, which is a problem peculiar to the tire.

In particular, when the height Hm from the bead baseline to the maximum tire width position is 45% or less of the tire cross-sectional height H0, the range of the bead portion becomes relatively narrow, which is preferable for weight reduction, but the range of the outer side region a. The wider the tire, the greater the deflection and the more pronounced the "buckling" problem.

In Patent Document 1 below, it is proposed that bead apex rubber is formed of an apex main body having a small triangular cross section and a thin plate-shaped wing extending from the apex main body in order to improve road noise. However, it is not expected that the structure of the bead apex rubber suppresses buckling in a tire whose tread width or the like is reduced to reduce the weight.

Japanese Unexamined Patent Publication No. 2004-306742

Therefore, an object of the present invention is to provide a pneumatic tire capable of suppressing buckling in a tire having a reduced tread width or the like and improving uneven wear resistance while reducing the weight.

The present invention includes a carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a belt layer composed of two belt plies arranged radially outside the carcass and inside the tread portion. Pneumatic tires
The width TW of the tread portion is in the range of 65 to 80% of the tire cross-sectional width W0, and the width BW of the belt layer is in the range of 60 to 70% of the tire cross-sectional width.
The bead portion has an apex main portion having a triangular cross section protruding from the radial outer surface of the bead core at a small height, and a thin plate shape that is connected to the apex main portion and extends beyond the apex main portion in the radial direction. Pneumatic tires characterized by having bead apex rubber consisting of parts.

In the pneumatic tire according to the present invention, it is preferable that the radial height H1 of the bead core from the radial outer surface of the apex main portion is 5 to 15% of the tire cross-sectional height H0.

In the pneumatic tire according to the present invention, it is preferable that the outer end in the radial direction of the thin plate-shaped portion is terminated radially inward from the maximum width position of the tire.

In the pneumatic tire according to the present invention, the thin plate-shaped portion overlaps with the radial upper end portion of the apex main portion, and the radial length L of the overlapping portion is the radial outer surface of the bead core of the apex main portion. It is preferable that the height is 0.25 to 0.75 times the height H1 in the radial direction from the above.

In the pneumatic tire according to the present invention, the height Hm from the bead baseline to the maximum width position of the tire is preferably 45% or less of the tire cross-sectional height H0.

In the present specification, unless otherwise specified, the dimensions and the like of each part of the tire are values specified in a no-load state in which the tire is mounted on a regular rim and 5% of the regular internal pressure is filled. The "regular rim" is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, JATTA is a standard rim, TRA is "Design Rim", or ETRTO. If so, it means "Measuring Rim". "Regular internal pressure" is the air pressure specified for each tire by the above standard. For JATMA, the maximum air pressure, for TRA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and at ETRTO. If there is, it means "INFLATION PRESSURE", but in the case of passenger car tires, it is 180 kPa.

In the present invention, as described above, the width TW of the tread portion is reduced to 80% or less of the tire cross-sectional width W0, and the width BW of the belt layer is reduced to 70% or less of the tire cross-sectional width. Therefore, the weight of the rubber of the tread portion and the weight of the belt cord can be reduced, and weight reduction can be achieved.

Further, the bead apex rubber is formed from an apex main portion having a triangular cross section protruding from the outer surface of the bead core at a small height and a thin plate-shaped portion. As a result, the bead apex rubber is easily bent, and it is possible to suppress the rising of the outer side region at the time of touchdown. As a result, it is possible to suppress the buckling peculiar to the tire in which the tread width and the like are reduced to reduce the weight, and the uneven wear resistance can be improved.

It is sectional drawing which shows one Example of the pneumatic tire of this invention. It is sectional drawing which shows the bead part enlarged. (A) and (B) are schematic cross-sectional views showing the width of the tread portion. It is a schematic cross-sectional view explaining the buckling amount of Table 1. FIG. It is a schematic cross-sectional view which exaggeratedly shows the buckling of a belt layer.

Hereinafter, embodiments of the present invention will be described in detail.
As shown in FIG. 1, the pneumatic tire 1 of the present embodiment has a carcass 6 extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and a tread portion outside the carcass 6 in the radial direction. It includes a belt layer 7 arranged inside the 2.

The carcass 6 includes a carcass ply 6A in which the carcass cords are arranged at an angle of, for example, 75 to 90 ° with respect to the tire circumferential direction. The carcass ply 6A has folded portions 6b that are folded back from the inside to the outside in the tire axial direction around the bead core 5 on both sides of the main body portion 6a that straddles between the bead cores 5 and 5.

The belt layer 7 is formed of two belt plies 7A and 7B in which belt cords are arranged at an angle of, for example, 10 to 40 ° with respect to the tire circumferential direction. The belt cords of the belt plies 7A and 7B are arranged in different directions so that the plies intersect with each other. One belt ply (for example, the inner belt ply 7A in the radial direction) is formed to be about 10 to 15 mm wider than the other belt ply (for example, the outer belt ply 7B in the radial direction). As the carcass cord and the belt cord, the same tire cord as the conventional one can be preferably adopted.

In the pneumatic tire 1, the width of the tread portion 2 (hereinafter sometimes referred to as the tread width) TW is 80% or less of the tire cross-sectional width W0 and the width of the belt layer 7 (hereinafter referred to as the belt width) in order to reduce the weight. In some cases, BW is set to 70% or less of the tire cross-sectional width W0.

As shown in FIG. 3A, the tread width TW is the distance between the intersection points P and P in the tire axial direction when the tread contour line Kt and the sidewall contour line Ks intersect in a bending line. Defined. As shown in FIG. 3B, when the tread contour line Kt and the sidewall contour line Ks are smoothly connected via the arc portion R, the extension line of the tread contour line Kt and the sidewall contour line Ks It is defined by the distance between the intersection points P and P with the extension line of P in the tire axial direction. When the intersection P is unclear, the tread width TW is replaced by the tread grounding width. The tread ground contact width means the maximum width in the tire axial direction of the ground contact surface that touches the ground when a normal load is applied to a tire in a state where the rim is assembled on a regular rim and the tire is filled with a regular internal pressure. The "regular rim" is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, JATTA is a standard rim, TRA is "Design Rim", or ETRTO. If so, it means "Measuring Rim". The "regular internal pressure" is the air pressure defined for each tire by the standard, the maximum air pressure for JATTA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and ETRTO. If so, it means "INFLATION PRESSURE", but in the case of passenger car tires, it is 180 kPa. The "regular load" is the load defined by the standard for each tire, and is the maximum load capacity for JATMA and the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA. If it is ETRTO, it is "LOAD CAPACITY".

Further, the belt width BW is defined as the width of the widest belt ply among the two belt plies 7A and 7B, and in this example, the width of the inner belt ply 7A.

By narrowly defining the tread width TW and the belt width BW in this way, the rubber weight of the tread portion 2 and the cord weight of the belt layer 7 can be reduced, and the weight of the tire can be reduced. From such a viewpoint, the tread width TW is more preferably 75% or less of the tire cross-sectional width W0. Further, the belt width BW is more preferably 65% or less of the tire cross-sectional width W0.

On the other hand, the tread width TW needs to be 65% or more of the tire cross-sectional width W0, and if it is less than 65%, the ground contact width and the ground contact area become too small, resulting in a decrease in steering stability. Further, the belt width BW needs to be 60% or more of the tire cross-sectional width W0, and if it is less than 60%, the tread rigidity becomes excessive and the steering stability is deteriorated.

A tire in which the tire cross-sectional height H0 is reduced so that the tire flatness W0 / H0 is 70% or less is preferable for weight reduction. Further, in order to reduce the weight, it is preferable to set the radial height Hm from the bead baseline BL to the tire maximum width position Pm to 45% or less of the tire cross-sectional height H0, and further to 40% or less. As a result, the range of the bead portion 4 becomes relatively narrow, which can contribute to weight reduction. However, since the range of the outer side region Yo (the region on the outer side in the radial direction from the maximum width position Pm of the tire in the sidewall portion 3) becomes wider, the deflection at the time of touchdown becomes large, which is disadvantageous to the buckling.

However, by adopting the following bead structure, it is possible to suppress the buckling peculiar to the tire, which has been made lighter as described above. Specifically, the bead portion 4 is provided with a bead apex rubber 8 including an apex main portion 8A and a thin plate-shaped portion 8B.

As shown in FIG. 2, the apex main portion 8A has a triangular cross section protruding from the radial outer surface (hereinafter, may be referred to as the core outer surface) 5S of the bead core 5 at a small height. The radial height H1 of the apex main portion 8A from the core outer surface 5S is preferably in the range of 5 to 15% of the tire cross-sectional height H0 (shown in FIG. 1). The height H1 is defined as the height in the radial direction from the point located on the outermost radial direction on the outer surface 5S of the core when the outer surface 5S of the core is inclined or curved.

Further, the thin plate-shaped portion 8B is connected to the apex main portion 8A and extends beyond the apex main portion 8A in the radial direction. The thin plate-shaped portion 8B has a thickness T of 0.8 to 2.0 mm, and its radial outer end ends radially inside the tire maximum width position Pm. The radial height H3 from the core outer surface 5S at the radial outer end of the thin plate-shaped portion 8B is preferably in the range of 20 to 40% of the tire cross-sectional height H0 (shown in FIG. 1).

The thin plate-shaped portion 8B has an overlapping portion 20 that overlaps with the radial upper end portion of the apex main portion 8A. The radial length L of the overlapping portion 20 is 0.25 to 0.75 times the height H1 of the apex main portion 8A. By forming the overlapping portion 20, it is possible to prevent the thin plate-shaped portion 8B and the apex main portion 8A from peeling off when the tire is formed, and a reliable joint is guaranteed.
It is preferable that the thin plate-shaped portion 8B overlaps with the inner surface surface of the apex main portion 8A in the tire axial direction.

The apex main portion 8A and the thin plate-shaped portion 8B are formed of hard rubber having a rubber hardness Hs (durometer A hardness) of, for example, 80 to 95 °. In this example, the apex main portion 8A and the thin plate-shaped portion 8B are formed of rubber having the same composition. However, when the rubber composition is different, it is preferable that the rubber hardness HsA of the apex main portion 8A is smaller than the rubber hardness HsB of the thin plate-shaped portion 8B in order to suppress buckling.

In such a bead apex rubber 8, the thin plate-shaped portion 8B reduces the vertical rigidity of the inner side region Yi (the region radially inside the maximum tire width position Pm in the sidewall portion 3), and the inner side region Yi at the time of touchdown. The deflection of the tire can be increased. As a result, the rise in the outer side region Yo at the time of touchdown is reduced, and the buckling of the belt layer 7 can be reduced.

Here, when the height H1 of the apex main portion 8A exceeds 15% of the tire cross-sectional height H0, or when the thin plate-shaped portion 8B exceeds the tire maximum width position Pm in the radial direction, the inside is inside. The bending at the time of touchdown in the side region Yi is insufficient, and the buckling suppressing effect is reduced.

On the contrary, when the height H1 of the apex main portion 8A is less than 5% of the tire cross-sectional height H0, and when the height H3 of the thin plate-shaped portion 8B is less than 20% of the tire cross-sectional height H0. In addition, the steering stability tends to decrease.

Further, in order to reduce the deflection in the outer side region Yo, the thickness Tm of the sidewall rubber 3G at the maximum tire width position Pm is preferably in the range of 2.0 to 3.0 mm. The rubber hardness Hs (durometer A hardness) of the sidewall rubber 3G is preferably 50 to 60 ° as in the conventional tire.

Further, it is preferable that the folded-back portion 6b of the carcass 6 is terminated at a position equal to or lower than the radial outer end of the apex main portion 8A in order to suppress buckling. Reference numeral 21 in FIG. 2 is a chafer rubber, and 22 is a clinch rubber, which prevent damage such as rim misalignment and crushing (sagging) of the rubber due to compression. The chafer rubber 21 and the clinch rubber 22 are preferably terminated while being in contact with the outer surface of the thin plate-shaped portion 8B in the tire axial direction.

In the pneumatic tire 1, the cord reinforcing ply is not formed from the bead portion 4 to the sidewall portion 3 from the viewpoint of ensuring the deflection of the inner side region Yi.

Although the particularly preferable embodiments of the present invention have been described in detail above, the present invention is not limited to the illustrated embodiments and can be modified into various embodiments.

Pneumatic tires (155 / 65R14) having the tire structure shown in FIG. 1 were prototyped based on the specifications shown in Table 1, and the bucklings of the sample tires were measured and compared. Each tire has been reduced in weight by reducing the tread width TW and belt width BW, and is substantially the same except for the structure of the bead apex. The common specifications are as follows.
Tire cross-sectional height H0 = 101 mm.
Tread width TW = 120 mm.
Tire cross-section width W0 = 162 mm.
Belt layer width BW = 106 mm.
Height of maximum tire width position Hm = 38.0 mm.
The length of the overlapping part L = 3.8 mm.
Number of carcass ply: 1 piece.
The folded part of the carcass is about the same height as the main part of Apex.
The rubber hardness of the sidewall rubber is 56.

For reference, the vertical spring constant, horizontal spring constant, sidewall rigidity, and rolling resistance are measured for each tire.

(1) Buckling:
The tire was grounded on a flat surface under the conditions of a rim (14 × 4.5J), an internal pressure of 230kPa), and a vertical load (2.66kN), and the cross section of the tire at that time was photographed with a CT scan tester. Then, on the shooting screen, the amount of buckling on the outer surface of the belt layer was evaluated by the ratio x / y (unit%) of the buckling height x and the buckling width y, as shown in FIG. The smaller the value, the better.

(2) Vertical spring constant:
Using a static tester, the ratio of vertical load / vertical deflection under the conditions of rim (14 × 4.5J), internal pressure 230kPa), and vertical load (3.04kN) was measured as the vertical spring constant.

(3) Lateral spring constant:
Using a static tester, the ratio of lateral load / lateral deflection under the conditions of rim (14 x 4.5J), internal pressure 230kPa), longitudinal load (2.66kN), and lateral load (0.5kN) is the lateral spring constant. Was measured as.

(4) Sidewall rigidity:
The torsional rigidity of the sidewall portion was measured under the conditions of rim (14 × 4.5J) and internal pressure (230 kPa) using a sidewall rigidity tester.

(5) Rolling resistance:
Using a rolling resistance tester, the rolling resistance was measured under the conditions of rim (14 × 4.5J), internal pressure 230kPa), vertical load (2.66kN), and speed (80km / h).

As shown in Table 1, it can be confirmed that in the examples, the buckling of the belt layer can be suppressed for the tire in which the tread width TW and the belt width BW are reduced to reduce the weight.

1 Pneumatic tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 7 Belt layer 7A, 7B Belt ply 8 Bead apex rubber 8A Apex main part 8B Thin plate 20 Overlapping part BL bead baseline

Claims (5)

A pneumatic tire equipped with a carcass that extends from the tread portion through the sidewall portion to the bead core of the bead portion, and a belt layer consisting of two belt plies arranged on the radial outside of the carcass and inside the tread portion. There,
The width TW of the tread portion is in the range of 65 to 80% of the tire cross-sectional width W0, and the width BW of the belt layer is in the range of 60 to 70% of the tire cross-sectional width.
The bead portion has an apex main portion having a triangular cross section protruding from the radial outer surface of the bead core at a small height, and a thin plate shape that is connected to the apex main portion and extends beyond the apex main portion in the radial direction. With a bead apex rubber consisting of a part,
In the apex main portion, the radial height H1 from the radial outer surface of the bead core is 5 to 15% of the tire cross-sectional height H0.
The thin plate portion, the radially outer end, a pneumatic tire, wherein end to Rukoto radially inward from the tire maximum width position. The pneumatic tire according to claim 1 , wherein the radial height H3 of the bead core from the radial outer surface of the radial outer end of the thin plate-shaped portion is 20 to 40% of the tire cross-sectional height H0. .. The carcass comprises a carcass ply having a fold back around the bead core from the inside to the outside in the tire axial direction.
The pneumatic tire according to claim 1 or 2 , wherein the folded-back portion is terminated at a position equal to or lower than the radial outer end of the apex main portion . The thin plate-like portion overlaps with the radial upper end portion of the apex main portion, and the radial length L of the overlapping portion is 0 of the radial height H1 from the radial outer surface of the bead core of the apex main portion. The pneumatic tire according to any one of claims 1 to 3, wherein the tire is .25 to 0.75 times. The pneumatic tire according to any one of claims 1 to 4, wherein the height Hm from the bead baseline to the maximum tire width position is 45% or less of the tire cross-sectional height H0.

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