Patent Application
20160009140
This disclosure relates to a heavy load pneumatic tire, and in particular to a heavy load pneumatic tire that improves uneven wear resistance without a decrease in durability.
In heavy load pneumatic tires, used for example in heavy load vehicles such as buses and trucks, uneven wear tends to occur on the shoulder portion of the tire tread. A variety of techniques have been proposed to reduce the uneven wear occurring in the shoulder portion and improve the uneven wear resistance (for example, see JP 2009-18629 A (PTL 1)).
In a heavy load pneumatic tire based on such a conventional technique, however, the uneven wear occurring in the shoulder portion of the tread may not be sufficiently reduced. Also, improving the uneven wear resistance may worsen another property, for example by reducing durability due to separation at the belt edge, thus making it difficult to achieve both uneven wear resistance and other properties.
It could therefore be helpful to provide a heavy load pneumatic tire that improves uneven wear resistance without a decrease in durability.
In my heavy load pneumatic tire, 10°<θ1<25° and 15°<θ2−θ1<25°, where θ1 is the angle, with respect to the tire equatorial plane, of the belt cords in the belt plies forming the intersecting belt layer, and θ2 is the angle, with respect to the tire equatorial plane, of a belt cord in the belt ply forming the angled belt layer,
in a cross-section in a tire width direction, the carcass has a shape, from an outermost position of the carcass in the tire radial direction to an outermost position of the carcass in the tire width direction, formed by connecting two arcs with a center of curvature towards an inside of the tire and with different radii of curvature, and R1>R2, where R1 is a radius of curvature of an inner arc positioned inward in the tire width direction and R2 is a radius of curvature of an outer arc positioned outward in the tire width direction, and
the distance, measured along the tire width direction from the tire equatorial plane, to the intersection of the inner arc and the outer arc is 80% or more of the distance, measured along the tire width direction from the tire equatorial plane, of the range of overlap between the belt plies in the intersecting belt layer.
It is thus possible to improve uneven wear resistance while preventing separation at the outer edges of the belt in the tire width direction and preventing a reduction in durability.
The “range of overlap between the belt plies in the intersecting belt layer” (overlapping range) refers to the range in which the belt plies in the intersecting belt layer overlap when viewed in the tire radial direction.
In my heavy load pneumatic tire, the radii of curvature R1 and R2 are preferably such that R1/R2≧9.5. With this structure, the amount of radial growth in the tire radial direction near the shoulder portion of the carcass can be further reduced, thereby more reliably suppressing a reduction in tire durability.
In this disclosure, the angles and dimensions, such as the angle of the belt cords in the belt with respect to the tire equatorial plane, the distance of the overlapping range from the tire equatorial plane, and the like, refer to the angles and dimensions for a tire mounted on an applicable rim, with specified air pressure and no load applied, unless otherwise specified. An “applicable rim” refers to a standard rim (“approved rim” or “recommended rim”) of applicable size specified in accordance with valid industrial standards for the region in which the tire is produced and used, such as the “JATMA (Japan Automobile Tyre Manufacturers Association) Year Book” in Japan, the “ETRTO (European Tyre and Rim Technical Organisation) Standard Manual” in Europe, and the “TRA (Tire and Rim Association, Inc.) Year Book” in the United States of America. The “tire mounted on an applicable rim, with specified air pressure and no load applied” refers to a state in which the tire is mounted on the above applicable rim and filled to the air pressure (maximum air pressure) corresponding to the maximum load capability for a single wheel of the applicable size/ply rating listed by JATMA or the like. Note that the air referred to here can be substituted with, for example, an inert gas such as nitrogen gas.
It is thus possible to provide a heavy load pneumatic tire that improves uneven wear resistance without a decrease in durability.
In the accompanying drawings:
Embodiments will be described below with reference to the drawings.
The heavy load pneumatic tire 1 illustrated in
In the tread portion 2, tread rubber 21 is provided outward from the carcass 3 in the tire radial direction, and circumferential grooves 22 extending in the tire circumferential direction are formed on the surface of the tread rubber 21. The figures show circumferential grooves 22, yet other grooves such as width direction grooves extending in the tire width direction may instead be formed, as may any tread pattern such as a ribbed pattern, block pattern, or the like.
Furthermore, in
The belt 4 includes an intersecting belt layer 41 formed by layering a pair of belt plies 4a, belt cords in the belt plies 4a intersecting each other with the tire equatorial plane E therebetween, and an angled belt layer 42 formed by at least one belt ply 4a. In the figures, the angled belt layer 42 is formed by one belt ply 4a. The belt cords of the belt plies 4a forming the intersecting belt layer 41 are inclined at an angle θ1 with respect to the tire equatorial plane E and are arranged to be substantially symmetrical. As long as the belt cords intersect each other with the tire equatorial plane E therebetween, they need not be symmetrical (θ1 may differ). The belt cords of the belt ply 4a forming the angled belt layer 42 are inclined at an angle θ2 with respect to the tire equatorial plane E.
As illustrated in
In a conventional heavy load pneumatic tire, when the tire is rolling, the tension of the belt provided in the tread portion is typically largest in the central portion of the tread portion and decreases towards the shoulder portion of the tread portion outward in the tire width direction. Therefore, the ground contact pressure on the road surface reduces in the shoulder portion, and when the tire rolls and kicks off the road surface, the shoulder portion may slip on the road surface, resulting in uneven wear in the shoulder portion.
Therefore, in the heavy load pneumatic tire 1, the relationships 10°<θ1<25° and 15°<θ2−θ1<25° hold, where θ1 is the angle, with respect to the tire equatorial plane E, of the belt cords in the belt plies 4a forming the intersecting belt layer 41, and θ2 is the angle, with respect to the tire equatorial plane E, of the belt cords in the belt ply 4a forming the angled belt layer 42.
By thus setting the angle θ1 of the intersecting belt layer 41 to be within the above range, when the tire is rolling, the tension of the belt 4 at the shoulder portion increases relatively as compared to the tension of the belt 4 at the central portion. Therefore, when the tire is rolling, the tension of the belt 4 at the shoulder portion can be improved. Setting the angle θ1 of the intersecting belt layer 41 to be within the above range, however, causes the tension of the belt 4 at the central portion to be insufficient. To address this point, the angle θ2 of the angled belt layer 42 is set to be within the above range, which is greater than that of the intersecting belt layer 41, so that when the tire is rolling, the angled belt layer 42 can compensate for the tension of the belt 4 at the central portion without reducing the tension of the belt 4 at the shoulder portion. Therefore, in the belt width direction, the tension of the belt 4 increases overall from the central portion to the shoulder portion, or the tension of the belt 4 becomes uniform in the tire width direction. As a result, it is possible to guarantee the ground contact pressure on the road surface in the central portion while increasing the ground contact pressure on the road surface in the shoulder portion, thereby improving uneven wear resistance.
If the angle θ of the intersecting belt layer 41 is set to be 10° or less, the tension of the belt 4 at the central portion when the tire is rolling is greatly reduced, which may cause uneven wear at the central portion. Conversely, even if the angle θ1 of the intersecting belt layer 41 is set to be 25° or more, the tension of the belt 4 at the shoulder portion when the tire is rolling does not increase enough to contribute further to improving uneven wear resistance.
If the relationship between the angles θ1 and θ2 is such that θ2−θ1≦15°, then the tension of the belt 4 at the shoulder portion when the tire is rolling decreases dramatically, whereas if 25°≦θ2−θ1, then although the tension of the belt 4 at the central portion increases, the tension of the belt 4 at the shoulder portion, which was increased by setting the angle θ1 of the intersecting belt layer 41 to be within the above range, decreases.
Furthermore, from the perspective of making an increase in uneven wear resistance compatible with the below-described tire durability, the relationships 14°<θ1<20° and 15°<θ2−θ1<20° are more preferable.
As illustrated in
While only half of the tire is illustrated in
As described above, the uneven wear resistance can be improved by setting the angle θ1 of the intersecting belt layer 41 and the angle θ2 of the angled belt layer 42 to be within prescribed ranges. On the other hand, upon applying internal pressure to the tire 1, separation occurs more easily due to strain on the tread rubber 21 caused by the increased tension of the belt 4 at the shoulder portion near the outer edge of the belt 4 in the tire width direction, specifically near the outer edge of the intersecting belt layer 41 in the tire width direction. Hence, the durability of the tire 1 tends to worsen.
To address this issue, in the heavy load pneumatic tire 1, the radii of curvature R1 and R2 of the inner arc and the outer arc are set so that R1>R2, and the distance Di, measured along the tire width direction from the tire equatorial plane E, to the intersection I of the arcs is 80% or more of the distance D, measured along the tire width direction from the tire equatorial plane E, of the range of overlap between the belt plies 4a in the intersecting belt layer 41.
Setting the radius of curvature R1 to be larger than R2 and bringing the intersection I of the arcs closer to the distance D allows for a reduction in the radial growth, outward in the tire radial direction, of the outer edge of the belt 4 in the tire width direction when internal pressure is applied to the tire. Setting the distance of the intersection I to be 80% or more of the distance D reduces the amount of radial growth at the outer edge of the belt 4 in the tire width direction and sufficiently suppresses strain within the tread rubber 21, allowing for prevention of separation at the outer edges of the belt 4 in the tire width direction and for prevention of a reduction in durability.
In the heavy load pneumatic tire 1, the radii of curvature R1 and R2 are preferably such that R1/R2≧9.5. With this structure, when internal pressure is applied to the tire, the amount of radial growth outward in the tire radial direction at the outer edge of the belt 4 in the tire width direction is further reduced. Therefore, strain on the tread rubber 21 can be better suppressed, thus more effectively allowing for prevention of separation at the outer edges of the belt 4 in the tire width direction and prevention of a reduction in durability.
The upper limit on the distance Di is not restricted, since setting the distance Di to be 80% or more of the distance D can prevent a reduction in durability, yet from a manufacturing perspective, an upper limit of 105% of the distance D is preferable (i.e. 80% Di/D×100≦105%).
In
As illustrated in
The aspect ratio of the heavy load pneumatic tire 1 is preferably from 60% to 100%. In a tire with an aspect ratio of less than 60%, the tension acting on the belt when the tire is rolling tends to increase as compared to a tire with an aspect ratio of 60% to 100%. Such increased tension may place a burden on the angled belt layer. Therefore, the structure in this disclosure is preferably applied to a tire with an aspect ratio of 60% to 100%.
When the carcass is formed from two or more plies, the shape of the carcass in a cross-section in the tire width direction refers to the neutral axis line of tension-compression in the carcass when the tire 1 is mounted on an applicable rim, with specified air pressure and no load applied.
While an embodiment has been described as an example with reference to the drawings, the heavy load pneumatic tire of the present disclosure is not limited to the above embodiment, and modifications may be made freely to the above embodiment.
The following provides further details by way of examples, yet the following examples are in no way limiting.
The tire of Example 1 has a size of 295/75R22.5 and is structured so that the radii of curvature R1 and R2 of two arcs forming the shape of the carcass satisfy the relationship R1>R2, as illustrated in
The tires of Examples 2 to 6 and of Comparative Examples 1 to 8 have the same structure as that of the tire in Example 1, except for the structural changes indicated by the specifications in Table 1.
The below-described uneven wear resistance test and durability test were performed on each of the above sample tires. Table 1 shows the test results.
For the uneven wear resistance test, each sample tire was mounted on an 8.25×22.5 sized rim, and an internal pressure of 690 kPa was applied. The sample tire was then placed in an indoor drum test machine, a load of 27 kN was applied, and the tire was run a distance of 10000 km at a speed of 80 km/h. The amount of uneven wear at the shoulder portion of the tread portion in the sample tire after test running was then measured. Table 1 lists the amount of uneven wear, expressed as an index with the value for the tire of Comparative Example 1 as 100, calculated by taking the inverse of the value yielded by multiplying the uneven wear depth (mm) from the tread surface edge by the length of the uneven wear in the tire width direction and dividing by two. A larger index indicates better uneven wear resistance.
For the durability test, each sample tire was mounted on an 8.25×22.5 sized rim, and an internal pressure of 690 kPa was applied. The sample tire was then placed in an indoor drum test machine, a load of 30 kN was applied, and the tire was run a distance of 10000 km at a speed of 60 km/h. For each sample tire after test running, the separation length at the edge of the intersecting belt layer in the tire width direction was then measured. The inverse of the length of each test tire was then taken and expressed as an index, with the separation length of the tire of Comparative Example 1 as 100. Table 1 lists the resulting separation length. A larger index indicates shorter separation length and better durability.
Table 1 shows that as compared to the tires of Comparative Examples 1 to 4 and 7 to 8, uneven wear resistance was improved for the tires of Examples 1 to 6 and Comparative Examples 5 to 6, since the relationships
It is thus possible to provide a heavy load pneumatic tire that improves uneven wear resistance without a decrease in durability.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-069008 | Mar 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/001855 | 3/28/2014 | WO | 00 |
