Patent Application
20250074120
The present technology relates to a pneumatic tire in which a carcass layer is turned up around a bead core of each bead portion from a tire inner side to a tire outer side, and particularly relates to a pneumatic tire that can effectively suppress separation starting from a radially outer end portion of an organic fiber reinforced layer embedded in the bead portion while suppressing separation starting from a turned-up end portion of the carcass layer.
In some heavy duty pneumatic tires used for trucks, buses, and the like, a carcass layer is mounted between a pair of bead portions and turned up around a bead core of each bead portion from a tire inner side to a tire outer side, and a steel reinforced layer including a plurality of steel cords is disposed in each bead portion to wrap the carcass layer. In such a pneumatic tire, for the purpose of preventing separation starting from the turned-up end portion of the carcass layer, two organic fiber reinforced layers including a plurality of organic fiber cords arranged in one direction and disposed so that the organic fiber cords intersect with each other between the layers are embedded on the outer side of the steel reinforced layer in the tire width direction (for example, see Japan Patent No. 65549857 B).
However, when the two organic fiber reinforced layers that are cross-layered are disposed in the bead portion, there is a problem in that separation starting from the radially outer end portion is likely to occur. Specifically, since the two organic fiber reinforced layers are disposed so that the end positions thereof are shifted from each other, one of the organic fiber reinforced layers becomes a single layer at the radially outer end portion. When the two cross-layered organic fiber reinforced layers are lifted up to the outer side in the tire radial direction in the tire molding step, the angle of the organic fiber reinforced layer tends to increase in the single layer region outside the layered region. As a result, a tension generated in the organic fiber cords constituting the organic fiber reinforced layer is increased, and separation starting from the radially outer end portion is likely to occur.
The present technology provides a pneumatic tire that can effectively suppress separation starting from a radially outer end portion of an organic fiber reinforced layer embedded in a bead portion while suppressing separation starting from a turned-up end portion of the carcass layer.
A pneumatic tire according to an embodiment of the present technology includes: a tread portion extending in a tire circumferential direction and having an annular shape; a pair of sidewall portions disposed on both sides of the tread portion; and a pair of bead portions disposed on inner sides of the sidewall portions in a tire outer diameter direction, a carcass layer being mounted between the pair of bead portions, the carcass layer being turned up around a bead core of each of the bead portions from a tire inner side to a tire outer side, and a steel reinforced layer including a plurality of steel cords being disposed in each of the bead portions so as to wrap the carcass layer,
As a result of diligent research on a tire structure in which an organic fiber reinforced layer is disposed in a bead portion, the present inventor has found that cross-layered organic fiber reinforced layers suppress rubber flow in the bead portion during vulcanization, thereby bringing a carcass layer closer to an equilibrium carcass line and suppressing separation starting from a turned-up end portion of the carcass layer, in other words, has found that there is no need to cross-layer the organic fiber reinforced layers at or near the turned-up end portion of the carcass layer, and has made the present technology.
That is, in the present technology, cross-laminated first and second organic fiber reinforced layers are disposed on the outer side of the steel reinforced layer in the tire width direction, and both of the first and second organic fiber reinforced layers are extended to at least below the bead core with reference to a line segment composed of a normal line drawn from the apex of the bead core protruding farthest to the inner side in the tire radial direction to the surface of a bead base, and thus rubber flow in the bead portion is suppressed during vulcanization, the position of the bead core is shifted to a toe side, and the carcass layer can be brought closer to the equilibrium carcass line. This allows suppression of separation starting from the turned-up end portion of the carcass layer. The radially outer end portion of the first organic fiber reinforced layer is disposed more on the outer side in the tire radial direction than the turned-up end portion of the carcass layer, while the radially outer end portion of the second organic fiber reinforced layer is disposed more on the inner side in the tire radial direction than the turned-up end portion of the carcass layer and more on the outer side in the tire radial direction than a line segment formed by a horizontal line drawn in the tire width direction from the apex of the bead core protruding farthest to the outer side in the tire radial direction, thereby reducing a lift rate when the cross-layered first and second organic fiber reinforced layers are lifted on the outer side in the tire radial direction in the tire molding step, and preventing the first organic fiber reinforced layer from increasing in angle at or near the radially outer end portion. As a result, a cord angle θA of the first organic fiber reinforced layer with respect to the tire circumferential direction and a cord angle θB of the second organic fiber reinforced layer with respect to the tire circumferential direction can be set in a range in which the tension generated in the organic fiber cords becomes small, and separation starting from the radially outer end portions of the first and second organic fiber reinforced layers can be effectively suppressed.
In the present technology, when the cord inclination directions of the first and second organic fiber reinforced layers with respect to the tire circumferential direction are opposite to each other, the cord angle θA of the first organic fiber reinforced layer with respect to the tire circumferential direction is preferably in a range 20°≤|θA|≤45°. By setting the cord angle θA of the first organic fiber reinforced layer whose radially outer end portion is a single layer to be small as described above, the separation starting from the radially outer end portion of the first organic fiber reinforced layer can be effectively suppressed. Since the cord inclination directions of the first and second organic fiber reinforced layers with respect to the tire circumferential direction are opposite to each other, the rubber flow of the bead portion during vulcanization can be effectively suppressed.
In the present technology, when the cord inclination directions of the first and second organic fiber reinforced layers with respect to the tire circumferential direction are the same, it is preferable that the cord angle θA of the first organic fiber reinforced layer with respect to the tire circumferential direction be in the range 20°≤|θA|≤45°, and the cord angle θB of the second organic fiber reinforced layer with respect to the tire circumferential direction be in the range |θA|+20≤|θB|. By setting the cord angle θA of the first organic fiber reinforced layer whose radially outer end portion is a single layer to be small as described above, the separation starting from the radially outer end portion of the first organic fiber reinforced layer can be effectively suppressed. By making the cord angle θB of the second organic fiber reinforced layer sufficiently larger than the cord angle θA of the first organic fiber reinforced layer, the rubber flow of the bead portion during vulcanization can be effectively suppressed.
It is preferable that a distance Ah from a bead heel apex of the bead portion to the radially outer end portion of the first organic fiber reinforced layer and a distance Ph from the bead heel apex of the bead portion to a turned-up end portion of the carcass layer satisfy the relationship Ah−Ph≥5.0 mm. This mitigates stress concentration at the turned-up end portion of the carcass layer, allowing effective suppression of separation starting from the turned-up end portion.
It is preferable that a crack suppression layer be embedded at a position adjacent to the turned-up end portion of the carcass layer, an end portion of the steel reinforced layer on the outer side in the tire width direction, the radially outer end portion of the first organic fiber reinforced layer, and the radially outer end portion of the second organic fiber reinforced layer, 100% modulus KcM100 of the crack suppression layer be in the range 4.5 MPa≤KcM100≤10.0 MPa, and elongation at break KcEB of the crack suppression layer be in the range 300%≤KcEB. This allows effective suppression of separation starting from the turned-up end portion of the carcass layer, the radially outer end portion of the first organic fiber reinforced layer, and the radially outer end portion of the second organic fiber reinforced layer. Note that the 100% modulus and the elongation at break are measured in accordance with JIS (Japanese Industrial Standard) K 6251.
It is preferable that one of the first and second organic fiber reinforced layers be an inner organic fiber reinforced layer positioned on the inner side in the tire width direction, and the other of the first and second organic fiber reinforced layers be an outer organic fiber reinforced layer positioned on the outer side in the tire width direction, the outer organic fiber reinforced layer be disposed so as to cover a radially inner end portion of the inner organic fiber reinforced layer, and a radially inner end portion of the outer organic fiber reinforced layer be separated from the radially inner end portion of the inner organic fiber reinforced layer by 5 mm or more and be positioned more on the inner side in the tire radial direction than a line segment formed by a horizontal line drawn in the tire width direction from an end portion of the steel reinforced layer on the outer side in the tire width direction. In this case, even if the toe of the bead portion is deformed when removing the rim, separation starting from the radially inner end portion of the outer organic fiber reinforced layer and the radially inner end portion of the inner organic fiber reinforced layer is less likely to occur.
Each of the fiber structures of organic fiber cords constituting the first and second organic fiber reinforced layers is preferably in a range from 800 dtex/2 to 1500 dtex/2. By making the organic fiber cords constituting the first and second organic fiber reinforced layers thin in this way, a step portion formed when one of the first and second organic fiber reinforced layers is disposed so as to cover the radially inner end portion of the other of the first and second organic fiber reinforced layers can be made small, stress concentration on the step portion can be reduced, and separation starting from the step portion of the first or second organic fiber reinforced layer can be suppressed. Since the organic fiber cords constituting the first and second organic fiber reinforced layers have a necessary minimum thickness, an effect of suppressing the rubber flow can also be exhibited.
Preferably, a distance A measured along a straight line extending through an apex of the bead core protruding farthest to the outer side in the width direction and being parallel to a longest side of the bead core, the distance A being from the apex to the bead heel position, is in the range 2.5 mm≤A≤5.5 mm. By sufficiently securing the distance A in this way, the position of the bead core is shifted to the toe side, and the angle formed by the toe of the bead portion can be increased. As a result, the rigidity of the toe of the bead portion is increased, and separation starting from the radially inner end portion of the first organic fiber reinforced layer and the radially inner end portion of the second organic fiber reinforced layer is less likely to occur.
Configurations of embodiments of the present technology will be described in detail below with reference to the accompanying drawings.
As illustrated in
A carcass layer 4 is mounted between the pair of bead portions 3, 3. The carcass layer 4 includes a plurality of steel cords extending in the tire radial direction and is turned up around a bead core 5 disposed in each of the bead portions 3 from a tire inner side to a tire outer side. A bead filler 6 having a triangular cross-sectional shape and formed of a rubber composition is disposed on the outer circumference of the bead core 5.
Four belt layers 7 are embedded on the radially outer side of the carcass layer 4 in the tread portion 1. Each of the belt layers 7 includes a plurality of belt cords (steel cords) inclined with respect to the tire circumferential direction. The belt layers 7 include two central main belt layers 72 and 73 with belt cords intersecting with each other, and auxiliary belt layers 71 and 74 disposed on the radially inner side and the radially outer side of the main belt layers 72 and 73. The inclination angle of the belt cords constituting the main belt layers 72 and 73 with respect to the tire circumferential direction is set to range from 15° to 35°, for example, and the inclination angle of the belt cords constituting the auxiliary belt layers 71 and 74 with respect to the tire circumferential direction is set to range from 15° to 75°, for example.
In the pneumatic tire described above, a steel reinforced layer 10 including a plurality of steel cords is disposed in each of the bead portions 3 so as to wrap around the carcass layer 4, the bead core 5, and the bead filler 6. First and second organic fiber reinforced layers 11 and 12 are disposed on the outer side of the steel reinforced layer 10 in the tire width direction. Each of the first and second organic fiber reinforced layers 11 and 12 includes a plurality of organic fiber cords that are arranged in one direction, and the organic fiber cords constituting the first and second organic fiber reinforced layers 11 and 12 are oriented so as to cross each other between the layers.
As illustrated in
Radially inner end portions 11i and 12i of the first and second organic fiber reinforced layers 11 and 12 are both positioned more on the inner side in the tire width direction than a line segment J formed by a normal line drawn from the apex of the bead core 5 protruding farthest to the inner side in the tire radial direction to the surface of a bead base 3b. That is, the first and second organic fiber reinforced layers 11 and 12 extend to below the bead core 5.
As illustrated in
According to the pneumatic tire described above, since the cross-layered first and second organic fiber reinforced layers 11 and 12 are disposed on the outer side of the steel reinforced layer 10 in the tire width direction and both the first and second organic fiber reinforced layers 11 and 12 extend to at least below the bead core 5 with reference to the line segment J formed by the normal line drawn from the apex of the bead core 5 protruding farthest to the inner side in the tire radial direction to the surface of the bead base 3b, the rubber flow of the bead portion 3 during vulcanizing is suppressed, the position of the bead core 5 is shifted to a toe 3t side, and the carcass layer 4 can be brought closer to the equilibrium carcass line. This allows suppression of separation starting from the turned-up end portion 4e of the carcass layer 4.
The radially outer end portion 11o of the first organic fiber reinforced layer 11 is disposed more on the outer side in the tire radial direction than the turned-up end portion 4e of the carcass layer 4, while the radially outer end portion 12o of the second organic fiber reinforced layer 12 is disposed more on the inner side in the tire radial direction than the turned-up end portion 4e of the carcass layer 4 and more on the outer side in the tire radial direction than the line segment K formed by a horizontal line drawn in the tire width direction from the apex of the bead core 5 protruding farthest to the outer side in the tire radial direction, thereby reducing a lift rate when the cross-layered first and second organic fiber reinforced layers 11 and 12 are lifted on the outer side in the tire radial direction in the tire molding step, and preventing the first organic fiber reinforced layer 11 from increasing in angle at or near the radially outer end portion 11o. Note that, since the first organic fiber reinforced layer 11 extends more to the outer side in the tire radial direction than the turned-up end portion 4e of the carcass layer 4, the effect of suppressing the rubber flow of the bead portion 3 during vulcanizing is sufficiently secured.
Since the first organic fiber reinforced layer 11 is prevented from increasing in angle at or near the radially outer end portion 11o as described above, the cord angle θA of the first organic fiber reinforced layer 11 with respect to the tire circumferential direction and the cord angle θB of the second organic fiber reinforced layer with respect to the tire circumferential direction can be set in a range in which the tension generated in the organic fiber cords becomes small, and the separation starting from the radially outer end portions 11o and 12o of the first and second organic fiber reinforced layers 11 and 12 can be effectively suppressed.
Here, when the cord angle θA of the first organic fiber reinforced layer 11 is in the range 45°<|θA|<70°, separation starting from the radially outer end portion 11o of the first organic fiber reinforced layer 11 is likely to occur. Similarly, when the cord angle θB of the second organic fiber reinforced layer 12 is in the range 45°<|θB|<70°, separation starting from the radially outer end portion 12o of the second organic fiber reinforced layer 12 is likely to occur. When the cord angles |θA| and |θB| are less than 20°, it is difficult to lift up the cross-layered first and second organic fiber reinforced layers 11 and 12 on the outer side in the tire radial direction in the tire molding step. In particular, it is preferable that the cord angle θA of the first organic fiber reinforced layer 11 with respect to the tire circumferential direction be set in the range 25°≤|θA|≤40° or 75°≤|θA|≤85°, and the cord angle θB of the second organic fiber reinforced layer 12 with respect to the tire circumferential direction be set in the range 25°≤|θ|≤40° or 75°≤|θB|≤85°.
As illustrated in
As illustrated in
As illustrated in
Here, if the 100% modulus KcM100 of the crack suppression layer 15 is less than 4.5 MPa, the stress concentration at the turned-up end portion 4e of the carcass layer 4, the radially outer end portion 11o of the first organic fiber reinforced layer 11, and the radially outer end portion 12o of the second organic fiber reinforced layer 12 is promoted, and there is a concern about the generation of separation starting therefrom. If the 100% modulus KcM100 of the crack suppression layer 15 exceeds 10.0 MPa, it is difficult to set the elongation at break KcEB of the crack suppression layer 15 to 300% or more. When the elongation at break KcEB of the crack suppression layer 15 is less than 300%, the effect of suppressing the separation starting from the turned-up end portion 4e of the carcass layer 4, the radially outer end portion 11o of the first organic fiber reinforced layer 11, and the radially outer end portion 12o of the second organic fiber reinforced layer 12 is decreased. The upper limit value of the elongation at break KcEB of the crack suppression layer 15 may be 500%.
When the above-described structure is adopted, the radially inner end portion 11i of the inner organic fiber reinforced layer 11 is covered with the outer organic fiber reinforced layer 12, and thus a rigid step portion (stress concentratedportion) is not formed at or near the toe 3t of the bead portion 3.
Therefore, even if the toe 3t of the bead portion 3 is deformed when removing the rim, separation starting from the radially inner end portion 11i of the inner organic fiber reinforced layer 11 is less likely to occur. Since the radially inner end portion 12i of the outer organic fiber reinforced layer 12 is also disposed at an appropriate position, separation starting from the radially inner end portion 12i of the outer organic fiber reinforced layer 12 is less likely to occur.
Here, if the separation distance between the radially inner end portion 12i of the outer organic fiber reinforced layer 12 and the radially inner end portion 11i of the inner organic fiber reinforced layer 11 is less than 5 mm, the radially inner end portion 12i of the outer organic fiber reinforced layer 12 is positioned in the vicinity of the toe 3t of the bead portion 3, so that separation starting from the radially inner end portion 12i of the outer organic fiber reinforced layer 12 is likely to occur. A region R more on the inner side in the tire radial direction than a line segment L formed by a horizontal line drawn in the tire width direction from the end portion 10e of the steel reinforced layer 10 on the outer side in the tire width direction is a region with little motion during tire rolling, but when the radially inner end portion 12i of the outer organic fiber reinforced layer 12 is positioned more on the outer side in the tire radial direction than the line segment L, motion during tire rolling becomes large, so that separation is likely to occur from the radially inner end portion 12i of the outer organic fiber reinforced layer 12.
In the pneumatic tire described above, the fiber structures of the organic fiber cords constituting the first and second organic fiber reinforced layers 11 and 12 are preferably in the range 800 dtex/2 to 1500 dtex/2, respectively. By making the organic fiber cords constituting the first and second organic fiber reinforced layers 11 and 12 thin in this way, as illustrated in
Here, if the fiber structure of the organic fiber cord is smaller than 800 dtex/2, the rubber flow in the bead portion 3 cannot be suppressed. Conversely, if the fiber structure of the organic fiber cord is larger than 1500 dtex/2, a step portion formed when one of the first and second organic fiber reinforced layers 11 and 12 is disposed so as to cover the radially inner end portion 11i, 12i of the other of the first and second organic fiber reinforced layer 11 becomes large, and suppression of separation caused by the stress concentration on the step portion is likely to occur.
In the pneumatic tire described above, as illustrated in
Note that a specific determination of the distance A is as follows. The bead core 5 has a multilayer structure in which a plurality of wires are arranged in a tire meridian cross-section. The apex E is a point where a straight line D extending through the center of gravity of a wire positioned on the outermost side of the bead core 5 in the width direction and being parallel to the longest side of the bead core 5 meets the contour of the wire positioned on the outermost side in the width direction. Here, when a straight line D, a virtual intersection point H, a straight line M, and a straight line F are determined, the straight line D extending through the apex E of the bead core 5 protruding farthest to the outer side in the width direction and being parallel to the longest side of the bead core 5, the virtual intersection point H being a point where an extension line of a side forming the profile of a bead bottom surface meets an extension line of a curve forming the profile of a bead back surface, the straight line M extending through the virtual intersection point H and being orthogonal to the straight line D, and the straight line F extending through the apex E and being orthogonal to the straight line D, the distance A is the length of a line segment on the straight line D defined between the straight line M and the straight line F.
Here, when the distance A is less than 2.5 mm, the position of the bead core 5 is not sufficiently shifted to the toe 3t side, and an increase in rigidity of the toe 3t is small, and thus the effect of suppressing the separation is reduced. On the other hand, when the distance A is more than 5.5 mm, an excessive cost increase occurs.
The pneumatic tire according to the embodiment described above may have a load index of 121 or more on a single wheel or a ply rating of 10 PR or more. In pneumatic tires having such a load index or ply rating, improving the durability of the bead portions is extremely meaningful.
Pneumatic tires according to Conventional Examples 1 and 2, Comparative Examples 1 to 3, and Examples 1 to 12 were manufactured. The tires had a tire size of 275/70R22.5, included a tread portion, a pair of sidewall portions, and a pair of bead portions, and included a carcass layer mounted between the pair of bead portions and including a plurality of steel cords, the carcass layer being turned up around a bead core of each of the bead portions from a tire inner side to a tire outer side, and a steel reinforced layer that includes a plurality of steel cords being disposed in each of the bead portions so as to wrap the carcass layer, the tires having first and second organic fiber reinforced layers (see
In the tires of Conventional Examples 1 and 2, Comparative Examples 1 to 3, and Examples 1 to 12, a distance Ph from the bead heel apex to the turned-up end portion of the carcass layer, a distance Ah from the bead heel apex to the radially outer end portion of the first organic fiber reinforced layer, a distance Bh from the bead heel apex to the radially outer end portion of the second organic fiber reinforced layer, a position of the radially inner end portion of the first organic fiber reinforced layer, a position of the radially inner end portion of the second organic fiber reinforced layer, a cord angle θA of the first organic fiber reinforced layer in the tire, a cord angle θA′ of the first organic fiber reinforced layer in the molding step, a cord angle θB of the second organic fiber reinforced layer in the tire, a cord angle θB′ of the second organic fiber reinforced layer in the molding step, |θB|−|θA|, Ah−Ph, 100% modulus KcM100 of the crack suppression layer, and elongation at break KcEB of the crack suppression layer were set as shown in Tables 1 and 2. The fiber structures of the organic fiber cords constituting the first organic fiber reinforced layer and the second organic fiber reinforced layer are both 1400 dtex/2.
Regarding the positions of the radially inner end portions of the first organic fiber reinforced layer and the second organic fiber reinforced layer, a case where the radially inner end portion is positioned more on the inner side in the tire width direction than the line segment J is referred to as “inner side”, and a case where the radially inner end portion is positioned more on the outer side in the tire width direction than the line segment J is referred to as “outer side”. When Ah>Ph, the radially outer end portion of the first organic fiber reinforced layer is positioned more on the outer side in the tire radial direction than the turned-up end portion of the carcass layer, and when Bh<Ph, the radially outer end portion of the second organic fiber reinforced layer is positioned more on the inner side in the tire radial direction than the turned-up end portion of the carcass layer.
The separation resistance (organic fiber reinforced layer, carcass layer) of these test tires was evaluated by the following test methods, and the results are shown in Tables 1 and 2.
Each of the test tires was mounted on a rim specified by JATMA (The Japan Automobile Tyre Manufacturers Association Inc.), inflated to 75% of the air pressure specified by JATMA, and subjected to a load 1.4 times as heavy as the load specified by JATMA, and running tests were performed on a drum testing machine at a running speed of 49 km/h. After running 40,000 km, each test tire was cut at eight locations at equal intervals in the tire circumferential direction along the tire meridian, and the cross-sectional direction lengths of cracks starting from the end portion of the organic fiber reinforced layer and the turned-up end portion of the carcass layer were measured in cut sections at the eight locations of both bead portions (a total of 16 locations), respectively. The sum of the cross-sectional direction lengths of the cracks starting from the end portion of the organic fiber reinforced layer and the turned-up end portion of the carcass layer was obtained, respectively. Evaluation results are expressed as index values using the reciprocals of the measurement values, with Conventional Example 2 expressed as an index value of 100, for each of the organic fiber reinforced layer and the carcass layer. Larger index values indicate superior separation resistance.
As can be seen from Tables 1 and 2, in comparison with Conventional Example 2, the tires of Examples 1 to 12 were able to significantly improve the separation resistance related to the organic fiber reinforced layer while satisfactorily maintaining the separation resistance related to the carcass layer. Note that, in Conventional Example 1, a tire could not be obtained due to a failure during manufacturing. On the other hand, in the tires of Comparative Examples 1 to 3, since the cord angle of the second organic fiber reinforced layer was not appropriate, separation starting from the radially outer end portion of the second organic fiber reinforced layer was likely to occur.
Next, tires of Examples 13 to 17 in which a part of the tire structure of Example 1 was changed were manufactured. In the tires of Examples 13 to 17, the first organic fiber reinforced layer is an inner organic fiber reinforced layer, and the second organic fiber reinforced layer is an outer organic fiber reinforced layer. The fiber structure of the inner organic fiber reinforced layer, the position of the radially inner end portion of the inner fiber reinforced layer, the fiber structure of the outer organic fiber reinforced layer, the position of the radially inner end portion of the outer fiber reinforced layer, the presence of covering of the radially inner end portion of the inner fiber reinforced layer with the outer organic fiber reinforced layer, the distance between the radially inner end portion of the outer organic fiber reinforced layer and the radially inner end portion of the inner organic fiber reinforced layer, the bead core distance A, and the toe angle θ were set as shown in Table 3.
Regarding the position of the radially inner end portion of the inner organic fiber reinforced layer, a case where the radially inner end portion is positioned more on the inner side in the tire width direction than the line segment J is referred to as “inner side”, and a case where the radially inner end portion is positioned more on the outer side in the tire width direction than the line segment J is referred to as “outer side”. Regarding the position of the radially inner end portion of the outer organic fiber reinforced layer, a case where the radially inner end portion is positioned more on the inner side in the tire radial direction than the line segment L is referred to as “lower side”, and a case where the radially inner end portion is positioned more on the outer side in the tire radial direction than the line segment L is referred to as “upper side”.
The separation resistance (organic fiber reinforced layer) of these test tires was evaluated by the following test methods, and the results are shown in Table 3.
Each of the test tires was mounted on a rim specified by JATMA, inflated to 75% of the air pressure specified by JATMA, and subjected to a load 1.4 times as heavy as the load specified by JATMA, and running tests were performed on a drum testing machine at a running speed of 49 km/h. After running 40,000 km, each test tire was cut at eight locations at equal intervals in the tire circumferential direction along the tire meridian, and the cross-sectional direction lengths of cracks starting from the end portion of the organic fiber reinforced layer were measured in cut sections at the eight locations of both bead portions (a total of 16 locations). Then, the sum of the cross-sectional direction lengths of the cracks starting from the end portion of the organic fiber reinforced layer was obtained. Evaluation results are expressed as index values using the reciprocals of the measurement values, with Conventional Example 2 expressed as an index value of 100. Larger index values indicate superior separation resistance.
As can be seen from Table 3, in the tires of Examples 13 to 17, similarly to Examples 1 to 12, the separation resistance related to the organic fiber reinforced layer was good.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-108832 | Jun 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/014789 | 3/28/2022 | WO |
