Pneumatic tire with belt layer overlapping folded portion of carcass

A pneumatic tire includes a carcass folded turned up around a bead core, a belt layer arranged outside of a crown portion of the carcass to have an overlapping portion with the carcass folded portion, a first reinforcing rubber layer arranged between a carcass body portion and the carcass folded portion, and a second reinforcing rubber layer arranged inside the carcass body portion, wherein an overlapping width W1 from an upper end position RE of the first reinforcing rubber layer to an end BE of the belt layer is specified; an overlapping width W2 from an upper end position RF of the second reinforcing rubber layer to the end BE of the belt layer is specified; and thickness RW of the second reinforcing rubber layer on a line TL connecting the end BE of the belt layer and a tread end TE is specified.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pneumatic tire and, more specifically, to a run-flat tire that enables safe drive over a long distance even with a decreased inner pressure at the time of puncture.

2. Description of the Background Art

Generally, at the time of a tire puncture, a side-wall portion31having low rigidity of the tire is folded and protruded in the widthwise direction of the tire as shown inFIG. 6, and a tread portion32moves inward in the radial direction of the tire, so that the tire becomes flat. When running continues, a tire bead portion33falls into a rim well34, possibly causing a hazardous state in which the tire drops off from the rim, disabling steering, or an inner upper end33aof the bead portion is repeatedly subjected to severe friction with the tire inner region32aof the tread portion, damaging the tire.

Conventionally, as a structure of a so-called run-flat tire enabling safe drive even at the time of tire puncture, the following structures have been proposed: a structure in which a crescent shape reinforcing rubber layer is arranged in contact with an inner side of a tire carcass over the bead portion to a shoulder portion, with its thickness gradually reduced toward opposing ends, or a structure in which a reinforcing rubber is arranged from the bead portion to an end of the thread portion between the carcass body and a folded portion thereof (Japanese Patent Laying-Open No. 10-244817); and a structure in which two-layered reinforcing rubber is arranged between a plurality of carcass plies or reinforcing plies (U.S. Pat. No. 5,427,166).

The above described prior art contemplates to reduce tire deformation at the time of puncture to avoid the hazardous state described above, by increasing rigidity of the side-wall portion by the reinforcing rubber. However, the reinforcing rubber layer arranged on an inner peripheral side of the carcass body portion as described above increases local strain at the side-wall portion at the time of tire puncture, and therefore damage to the side-wall portion of the tire cannot be alleviated. In order to further enhance the effect of reinforcement, the thickness of the reinforcing rubber layer must naturally be increased. This, however, increases the weight of the tire, and decreases fuel efficiency of the vehicle.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a pneumatic tire, and particularly a run-flat tire, having tire weight effectively reduced and enabling safe running over a long distance even at a time of tire puncture.

The present invention provides a pneumatic tire, including at least one carcass ply having a steel cord arranged substantially in a radial direction of the tire, folded turned up around a bead core, a belt layer arranged on an outer side of a crown portion of the carcass ply to have an overlapping portion with the folded portion of the carcass, a first reinforcing rubber layer arranged between body portion of the carcass ply and the folded portion of the carcass ply, and a second reinforcing rubber layer arranged inside the body portion of the carcass ply, over a region corresponding to a tire shoulder portion to a bead portion, with its thickness gradually reduced from a central portion to opposing end portions, wherein overlapping width W2from an upper end position RF of the second reinforcing rubber layer to an end BE of the belt layer is 7% to 33% of the width BW of the belt layer, and cross sectional widths G1W, G2W, and G3W representing minimum widths between an inner surface of the tire and respective side-wall outer surface positions G1G2and G3at portions of 1/4GL to 3/4GL corresponding to cross sectional height GL from an upper end of a bead wire to a tire outer peripheral end divided equally by 4 satisfy the following relations:
G3W/G1W=0.85 to 0.95,
and
G2W/G1W=1.0 to 1.05.

In the present invention, preferably, respective cross sectional widths G1W, G2W and G3W at respective side-wall outer surface positions G1G2, and G3corresponding to 1/4GL to 3/4GL, and widths G1a, G2a, and G3a of the second reinforcing rubber layer at respective positions satisfy the following relations:
G1a/G1W=0.30 to 0.55
G2a/G2W=0.38 to 0.48,
and
G3a/G3W=0.20 to 0.30.

Further, it is desired that the first reinforcing rubber layer consists of two layers including a hard rubber layer extending in a direction from an upper side of the bead core to the side-wall portion, having JISA hardness of 80 to 95, and a soft rubber layer extending from an upper side of the hard rubber layer to a vicinity of an end portion of the belt layer, having JISA hardness of 65 to 80.

Further, overlapping width W1of the upper end RE of the first reinforcing rubber layer and the end BE of the belt layer is in the range of 3% to 20% of the width BW of the belt width.

According to another aspect, the present invention provides a pneumatic tire, including at least one carcass ply having a steel cord arranged substantially in a radial direction of the tire, folded turned up around a bead core, a belt layer arranged on an outer side of a crown portion of the carcass ply to have an overlapping portion with the folded portion of the carcass, a first reinforcing rubber layer arranged between body portion of the carcass ply and the folded portion of the carcass ply, and a second reinforcing rubber layer arranged inside the body portion of the carcass ply, over a region corresponding to a tire shoulder portion to a bead portion, with its thickness gradually reduced from a central portion to opposing end portions, wherein overlapping width W1of an upper end position RE of the first reinforcing rubber layer and an end BE of the belt layer is in the range of 3% to 20% of the width BW of the belt layer, an overlapping width W2of an upper end position RF of the second reinforcing rubber layer and the end BE of the belt layer is 7% to 33% of the width BW of the belt layer, and thickness RW of the second reinforcing rubber layer on a line TL connecting the end BE of the belt layer and a tread end TE is 5% to 25% of the total thickness SW of the tire. Preferably, the first reinforcing rubber layer consists of two layers including a hard rubber layer extending in a direction from an upper side of the bead core to the side-wall portion, having JISA hardness of 80 to 95, and a soft rubber layer extending from an upper side of the hard rubber layer to a vicinity of an end portion of the belt layer, having JISA hardness of 65 to 80. Further, preferably, JISA hardness of the second reinforcing rubber layer is in the range of 65 to 80.

Further, in the pneumatic tire of the present invention, the width Ga of the second reinforcing rubber layer, the width Gb of the soft rubber layer and the width Gc of the hard rubber layer of the first reinforcing rubber layer and the width Gd of the side-wall on the lines of minimum cross sectional widths G11W, G12W, G13W and G14W representing minimum widths from respective inner liner positions G11, G12, G13and G14to a tire outer contour line at positions 1/6GL to 4/6GL corresponding to the cross sectional height GL from a lower end of the bead wire to a tire outer peripheral end divided equally by 6 satisfy the following relations:
AtG11W, G11a≦G11d<G11c,
AtG12W, G12b<G12a≦G12c<G2d,
AtG13W, G13a≈G13b≈G13d,
and
AtG14W, G14a≈G14b<G14d.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention will be described with reference to the figures.

FIG. 1shows the right half of a cross section of a pneumatic tire representing an embodiment of the present invention.

Here, the pneumatic tire1in accordance with the present invention has at least one carcass ply3with cords arranged substantially in the radial direction of the tire, folded turned up around a bead core6from the inside to the outside. A folded end3E is fixed below a belt layer7arranged outside a crown portion of the carcass ply, to be partially overlapped with an end portion of the belt layer. Carcass ply3has its folded end3E pulled to the direction of the bead portion as it is repeatedly subjected to deformation as the tire runs, and the rubber deforms near the end portion BE of the belt layer. Therefore, stress concentration tends to generate here. Therefore, by fixing the folded end3E at a lower side of the belt layer, the effect of reducing stress concentration and improving rigidity of the side-wall portion can be attained. Here, the width of overlapping between the folded portion3aof the carcass ply and the belt layer7should preferably be 5 to 20% of the width BW of the belt layer.

A steel cord of (1×n) structure such as 1×2, 1×3, 1×4 and 1×5, or (2×n) structure may be used as a carcass cord. The diameter of the steel filament constituting the cord is preferably in the range of 0.10 to 0.30 mm and more preferably, 0.15 to 0.27 mm. A steel cord having tensile strength per one cord of 100N to 480N, and more particularly 150N to 450N is preferably used. Use of such a steel cord improves lateral rigidity of the side-wall portion of the tire, further enhancing steering stability and durability in the run-flat situation.

Further, carcass strength (cord number in the width of 5 cm×cord strength) for the width of 5 cm of the carcass ply is in the range of 3500N to 15800N and more preferably, 4500N to 11000N. When the carcass strength is smaller than 3500N, rigidity would be insufficient, degrading durability in the run-flat situation. When the strength exceeds 15800N, heat tends to build up while the tire is running, degrading durability.

The steel cord is arranged in the range of 800 to 90° and more particularly 86° to 90° with respect to the peripheral direction of the tire.

Next, in the present invention, a first reinforcing rubber layer4is arranged between carcass ply body3and the folded portion3athereof, extending from an upper end of bead core6to the vicinity of an end portion of the belt layer. Here, the overlapping width W1between the upper end position RE of the first reinforcing rubber layer and the belt layer should preferably in the range of 3% to 20% of the width BW of the belt layer. When the overlapping width W1is smaller than 3%, the upper end position RE of the first reinforcing rubber layer would be positioned near or below the end BE of the belt layer, generating an abrupt change in rigidity in this region, which tends to produce stress concentration.

By contrast, when the width exceeds 20%, the volume of the rubber layer not contributing to the run-flat property increases, which is disadvantageous in reducing the weight of the tire. Preferably, the first reinforcing rubber layer4consists of two layers, including a hard rubber layer4aextending from an upper side of the bead core to the direction of the side-wall portion with its thickness gradually reduced and having JISA hardness of 80 to 95 and more preferably 85 to 95, and a soft rubber layer4bextending from an upper side of the hard rubber layer4ato the vicinity of the end portion of the belt layer and having JISA hardness of 65 to 80 and preferably 65 to 70.

Hard rubber layer4areinforces the bead portion and enhances lateral rigidity of the tire at the time of tire puncture, while soft rubber layer4breinforces the tire side-wall portion, relaxes stress concentration near opposing ends of the belt layer at the shoulder portion and alleviates damages. When the first reinforcing rubber layer4is to be formed of one layer, a material having JISA hardness of 65 to 90, and more preferably 65 to 85, is used. As the first reinforcing rubber layer4is surrounded by the carcass ply with the upper end of the folded portion of the carcass ply fixed at the lower side of the end portion of the belt layer, the effect of reinforcement can further be enhanced by the volume effect.

Next, in the pneumatic tire in accordance with the present invention, a second reinforcing rubber layer2is arranged on the inner side of carcass ply body3over a region from a portion corresponding to the tire shoulder portion to the bead portion. The second reinforcing rubber layer2is of a rubber composition having small oil content and superior heat resistance, and a relatively soft rubber having JISA hardness of 65 to 80 is used. At the time of tire puncture, the side-wall portion is folded protruding outward, and the second reinforcing rubber layer2inside the tire is subjected to severe flexion deformation. Therefore, the second reinforcing rubber layer is formed by using rubber with low heat build up property, for example, rubber having the resilience of at least 50%, so that heat build-up associated with the flexion deformation can be suppressed. As to the cross sectional shape of the second reinforcing rubber layer2, it has substantially the maximum width in the side-wall region, the thickness is gradually reduced toward opposing ends, and the upper end portion RF extends inward, over the end BE of the belt layer. The overlapping width W2with the belt layer is in the range of 7 to 33% of the width BW of the belt layer. When the overlapping width is smaller than 7%, a bead portion and a shoulder portion of the second reinforcing rubber, layer would not be in contact with each other, and hence the effect of reducing friction heat cannot be attained. When the width exceeds 33%, unnecessary rubber that does not have the function of reducing heat build-up would be arranged, undesirably increasing the weight of the tire.

When the each space between the upper end RE of the first reinforcing layer and the upper end RF of the second reinforcing layer, between the upper end RE of the first reinforcing layer and the folded end3E of the carcass is set to be in the range of 2% to 20% of the width BW of the belt layer, origins of stress concentration can be dispersed, and hence durability can further be enhanced.

At the shoulder portion of the pneumatic tire shown inFIG. 1, the thickness t of the second reinforcing rubber layer on a line TL connecting the end BE of the belt layer and a tread end TE should desirably be within the range of 18% to 50% of the entire tire thickness T.

Here, the tread end TE is defined as an intersecting point of an extension of curvature arc of the tread portion and an extension of curvature arc of the shoulder portion.

In the run-flat situation, the pneumatic tire has its side-wall portion deformed to protrude outward, as shown in FIG.6. In this situation, stress-strain tends to generate at the end portion of the belt layer. Therefore, by arranging a rubber layer of a prescribed thickness in this region, stress concentration can effectively be dispersed and relaxed. Thus, when the thickness t is smaller than 18%, the above-described effect is not expected. When the thickness t exceeds 50%, the effect associated with the increase in thickness is not recognized, and rather the weight of the tire is increased undesirably. More preferable range is 20% to 40%.

In the pneumatic tire in accordance with the present invention, cross sectional widths G1W, G2W and G3W, respectively representing minimum width between an inner surface of the tire and positions G1, G2and G3on the outer surface of the side-wall at portions 1/4GL to 3/4GL corresponding to the cross sectional height GL from an upper end of the bead wire6to a tire outer peripheral end divided equally by 4 shown inFIG. 1, satisfy prescribed relations.

More specifically, G3W/G1W is in the range of 0.85 to 0.95, and G2W/G1W is in the range of 1.0 to 1.05. By maximizing the thickness at the central portion of the side-wall and minimizing it near the shoulder portion, the amount of deflection in the run-flat situation can be suppressed and, in addition, the amount of deflection can be made uniform from the bead portion to the shoulder portion. Thus, stress concentration can effectively be reduced.

Further, in the present invention, respective ratios of the widths G1a, G2a and G3a of the second reinforcing rubber layer at respective positions G1G2and G3to the cross sectional widths G1W, G2W and G3W are in the range of G1a/G1W=0.30 to 0.55, G2a/G2W=0.38 to 0.48 and G3a/G3W=0.20 to 0.30. By this arrangement, the ratio of load shared by the second reinforcing rubber layer can gradually be reduced in the direction from the bead portion to the shoulder portion, enabling effective stress relaxation in the run-flat situation.

FIG. 2shows the right half of a cross section of a pneumatic tire representing an embodiment of the present invention.

Here, the pneumatic tire11in accordance with the present invention has at least one carcass ply13with cords arranged substantially in the radial direction of the tire, folded turned up around a bead core16from the inside to the outside. A folded end13E is fixed below a belt layer17arranged outside a crown portion of the carcass ply, to be partially overlapped with an end portion of the belt layer. Carcass ply13has its folded end13E pulled to the direction of the bead portion as it is repeatedly subjected to deformation as the tire runs, and the rubber deforms near the end portion BE of the belt layer. Therefore, stress concentration tends to generate here. Therefore, by fixing the folded end13E at a lower side of the belt layer, the effect of reducing stress concentration and improving rigidity of the side-wall portion can be attained. Here, the width of overlapping between the folded portion13aof the carcass ply and the belt layer17should preferably be 5 to 20% of the width BW of the belt layer.

Next, in the present invention, a first reinforcing rubber layer14is arranged between carcass ply body13and the folded portion13athereof, extending from an upper end of bead core16to the vicinity of an end portion of the belt layer. Here, the overlapping width W1between the upper end position RE of the first reinforcing rubber layer and the end BE of the belt layer is in the range of 3% to 20% of the width BW of the belt layer. When the overlapping width W1is smaller than 3%, the upper end position RE of the first reinforcing rubber layer would be positioned near or below the end BE of the belt layer, generating an abrupt change in rigidity in this region, which tends to produce stress concentration. As a result, peeling of the rubber results near the opposing ends of the belt layer.

By contrast, when the width exceeds 20%, the volume of the rubber layer not contributing to the run-flat property increases, which hinders reduction of the tire weight. Preferably, the first reinforcing rubber layer14consists of two layers, including a hard rubber layer14aextending from an upper side of the bead core to the direction of the side-wall portion with its thickness gradually reduced and having JISA hardness of 80 to 90 and more preferably 85 to 95, and a soft rubber layer14bextending from an upper side of the hard rubber layer14ato the vicinity of the end portion of the belt layer and having JISA hardness of 65 to 80 and preferably 65 to 70.

Hard rubber layer14areinforces the bead portion and enhances lateral rigidity of the tire at the time of tire puncture, while soft rubber layer14breinforces the tire side-wall portion, relaxes stress concentration near opposing ends of the belt layer at the shoulder portion and alleviates damages. When the first reinforcing rubber layer14is to be formed of one layer, a material having JISA hardness of 65 to 90, and more preferably, 65 to 85 is used. As the first reinforcing rubber layer14is surrounded by the carcass ply with the upper end of the folded portion of the carcass ply fixed at the lower side of the end portion of the belt layer, the effect of reinforcement can further be enhanced by the volume effect.

Next, in the pneumatic tire in accordance with the present invention, a second reinforcing rubber layer12is arranged on the inner side of carcass ply body13over a region from a portion corresponding to the tire shoulder portion to the bead portion, with its thickness gradually reduced from the central portion toward opposing ends. The second reinforcing rubber layer12is of a rubber composition having small oil content and superior heat resistance, and a relatively soft rubber having JISA hardness of 65 to 80 is used. At the time of tire puncture, the side-wall portion is folded protruding outward, and a bead portion and a shoulder portion of the second reinforcing rubber layer12inside the tire come to be in contact with each other, causing friction. Therefore, the second reinforcing rubber layer is formed by using rubber with low heat build up property, for example, rubber having the resilience of at least 50%, so that damages associated with the friction can be suppressed. As to the cross sectional shape of the second reinforcing rubber layer12, it has the maximum width in the side-wall region, the thickness is gradually reduced toward opposing ends, and the upper end portion RF extends inward, over the end BE of the belt layer. The overlapping width W2with the belt layer is in the range of 7 to 33% of the width BW of the belt layer.

InFIG. 3showing, in enlargement, the shoulder portion of the pneumatic tire shown inFIG. 2, the thickness RW of the second reinforcing rubber layer12on the line TL connecting the end BE of the belt layer and the tread end TE is in the range of 5 to 25% of the entire thickness of the tire.

Here, the tread end TE is defined as an intersecting point of an extension of curvature arc of the tread portion and an extension of curvature arc of the shoulder portion.

In the run-flat situation, the tire deforms significantly as shown in FIG.6. In this situation, stress-strain tends to generate at the end portion of the belt layer. Therefore, by arranging a rubber layer of a prescribed thickness in this region, stress concentration can effectively be dispersed and relaxed. Thus, when the thickness RW is smaller than 5%, the above-described effect is not expected. When the thickness RW exceeds 25%, the effect associated with the increase in thickness is not recognized, and rather the weight of the tire is increased undesirably. More preferable range is 7% to 15%.

Next, in the pneumatic tire in accordance with the present invention, the width Ga of the second reinforcing rubber layer, the width Gb of the soft rubber layer and the width Gc of the hard rubber layer of the first reinforcing rubber layer, and the width Gd of the side-wall23should desirably satisfy the following relations, on the cross sectional minimum width lines G11W, G12W, G13W and G14W, representing minimum width between the tire outer contour line and respective inner liner positions G11, G12, G13and G14at positions 1/6GL to 4/6GL corresponding to cross sectional height GL from a lower end of the bead wire16to a tire outer peripheral end divided equally by 6 inFIGS. 2to4. Here, the outer contour line of the tire is defined as a contour line of an outer surface of the tire from the bead portion to the side-wall23, while the rim protector portion22is defined by a smooth extension22L of the contour of the bead portion and the side-wall.
atG11W, G11a≦G11d<G11c,
atG12W, G12b≦G12a≦G12c≦G12d,
atG13W, G13a≈G13b∓G13d,
and
at G14W, G14a≈G14b<G14d.

Further, in the present invention, it is desired that the following relations are satisfied at respective positions G11to G14.

Position G11G11ais 0% to 20% with respect to the width G11W,G11cis 50% to 67% with respect to the width G11W, andG11dis 10% to 30% with respect to the width G11W

Position G12: G12ais 10% to 20% with respect to the width G12W,G12bis 0% to 20% with respect to the width of G12W,G12cis 10% to 25% with respect to the width of G12W, andG12dis 25 to 34% with respect to the width of G12W.

Position G13: G13ais 20% to 34% with respect to the width G13W,G13bis 20% to 35% with respect to the width G13W, andG13dis 20% to 36% with respect to the width G13W

Position G14: G14ais 10% to 20% with respect to the width G14WG14bis 10% to 20% with respect to the width G14W, andG14dis 33% to 67% with respect to the width G14W.

By such an arrangement, it becomes possible to minimize the thickness of the first reinforcing rubber layer14, the second reinforcing rubber layer12and side-wall23, and to improve running stability and durability in the run-flat situation.

In the bead core6of the present invention as shown inFIG. 5, the ratio CW/CH of the cross sectional height CH to the cross sectional width CW should preferably be 1.0 or higher, and preferably in the range of 1.2 to 2.0.

In the present invention, as the first and second reinforcing rubber layers are arranged, the cross sectional width COW of the bead portion is made thicker than in a common pneumatic tire. In order to reinforce such a bead portion, a bead portion of a prescribed width is necessary. On the other hand, wide cross sectional shape at the bead portion is advantageous to meet the demand of a light weight tire.

In the present invention, it is possible to arrange an inner liner L entirely over the inside of the second reinforcing rubber layers2and12shown inFIGS. 1 and 2. For the inner liner L, a rubber composition mainly consisting of butyl rubber, halogenated butyl rubber or the like may be used.

Comparative Example 1

In accordance with the specification shown in Table 1, tires of the tire size 195/45R15 and having the basic structure shown inFIG. 1were manufactured as Example 1 and Comparative Example 1, where Example 1 satisfy the relations shown in Table 2, and Comparative Example 1 satisfy the relations of Table 3. Performances of the tires were evaluated in the following manner, in 4 grades of excellent (⊚), good (◯) fair (Δ) and failed (X).

The tire was subjected to running under the load of 262 kg with the air pressure of 0, and the distance until a crack was observed on the outer surface of the tire was measured.

(2) Deflection Amount in the Run-flat Situation

The tires were mounted on a vehicle, and the air pressure was reduced to 0 to realize the run-flat state. In this state, deflection amount of the tire was measured in terms of the ratio of cross sectional height to the height when the tire was filled with the normal inner pressure, and the result is given as an index using Comparative Example 1 as a reference.

(3) Steering Performance

The tires were mounted on a vehicle, only one front tire was set to the run-flat state, the vehicle was driven at 60 km/h, and the feeling of steering stability was evaluated.

From the results of evaluation shown in Tables 2 and 3, it can be understood that a drum durability, deflection amount in the run-flat situation and the steering performance of Example 1 in accordance with the present invention are all improved as compared with Comparative Example 1.

EXAMPLES 2 TO 5

Comparative Examples 2 to 4

Tires of the tire size 195/45R15 and having the basic structure ofFIG. 2were manufactured, in accordance with the specifications of Tables 4 and 5. The performances of the tires were evaluated in the following manner. The evaluation was in 4 grades of excellent (⊚), good (◯), fair (Δ) and failed (X).

The drum durability and the steering performance were evaluated in the similar manner as described above.

Actual On-board Test of Rim Holding

The tires were mounted on a vehicle, and the air pressure was reduced to 0 to realize the run flat state. In this state, the vehicle was driven to run rotating on a circle of 7.5R at 27 km/h, and the number of rotation until the tire was folded into the rim well was measured.

From the result of evaluation shown in Table 5, it can be understood that the drum durability, rim holding performance and steering performance of the examples in accordance with the present invention are all improved as compared with the Comparative Examples.

As described above, in the present invention, the strain experienced at the side-wall portion when the inner pressure lowers at the time of tire puncture, for example, can be dispersed sufficiently, while the rigidity of the side-wall portion is enhanced. Therefore, the amount of deflection in the run-flat situation can be reduced to 6 to 8% in terms of the ratio of cross sectional height (which was conventionally about 20%), which means that the run-flat running distance can be ensured while maintaining steering stability. Further, as the hardness and the thickness of the first and second reinforcing rubber layers arranged at the side-wall portion are in prescribed ranges, the weight of the tire can be reduced.