Patent Application
20190210407
The present disclosure relates to tires, particularly to high performance tires having high drainage performance, braking performance and turning performance.
Conventionally, particularly in the field of high performance tires, it is known to enlarge blocks in order to improve the block rigidity during load rolling. For example; PTL 1 discloses a tire in which blocks are enlarged to improve the block rigidity, and thereby the cornering force (CF) characteristics are improved.
PTL 1: JPH 10-297216 A
When the blocks of a tire tread are enlarged as described above; the block rigidity is improved; however, there is a problem that the grounding property in the blocks deteriorates especially during high speed rolling of the tire. That is, during rolling of the tire, when a load is applied to the tread surface, the force concentrates on the boundaries between the groove bottom and the groove walls of each width direction groove, such that a stress is generated toward the inside of each block from the side walls of the block, causing deformation that the end portions in the width direction of each block are pushed up. As a result, the ground contact pressure at the central portion of each block becomes lower than the surroundings. Particularly, at the time of high speed rotation, the ground contact pressure of the tire tread surface is higher than that at the time of low speed rotation, such that deterioration of the grounding property inside each block becomes remarkable. As described above, the grounding property in each block becomes non-uniform, such that the drainage performance, braking performance and turning performance might have not been sufficiently improved. In other words, the larger the blocks, the greater the difference in ground contact pressure between the central portion and the end portions of each block, such that the problem remains in that the effect of enlarging the blocks cannot be sufficiently enjoyed.
It is an object of the present disclosure to provide a high performance tire that improves the grounding property of blocks, and thereby further improving the drainage performance, braking performance and turning performance.
The inventor conducted a diligent investigation in order to solve the above problem. Through this investigation, the inventor discovered that in order to increase the ground contact pressure at the central portion of a block, it is effective to adopt a shape that protrudes toward the central portion. On the other hand, since the rubber of the protruding portion swells toward the sides of the block at the time of grounding, it was found that a protruding shape is not such useful for increasing the ground contact pressure at the central portion. Then, it was found that by forming a part of each width direction groove like a sipe having a very narrow opening width, the rubber of the protruding portion can be prevented from swelling toward the sides of the block, and the adjacent blocks protrude in a manner supported by each other, enabling an increase in ground contact pressure at the central portion. That is, the inventor discovered that in order to avoid deterioration in grounding property of a block, it is effective to adopt a shape that protrudes toward the central portion of the block and suppress swelling of the protruding rubber toward width direction grooves by forming a part of each width direction groove to be a sipe, and thereby completed the present disclosure.
The subject of this disclosure is as follows.
(1) A tire, comprising a tread surface divided into a plurality of land portions by at least one circumferential groove extending along a tire equator and tread edges, wherein at least one of the land portions divided by the at least one circumferential groove and the tread edges comprises a plurality of blocks divided by a plurality of width direction grooves; each of the blocks has a shape that protrudes from four sides toward a central portion; and each of the width direction grooves comprises a sipe portion.
Here, a “ground contact width” in the present disclosure refers to the maximum straight line distance in the tread width direction on a contact surface with a flat plate, when the tire is mounted on an applicable rim and placed perpendicularly to the flat plate in a stationary state with the air pressure set to be a prescribed value, and a load corresponding to a prescribed mass is applied thereto. Further, a “ground contact length” refers to the maximum straight line distance in the tread circumferential direction on the same contact surface.
Furthermore, an “applicable rim” refers to a rim prescribed by an industrial standard which is valid in an area where the tire is manufactured and used, and examples of the industrial standard include: “JATMA (The Japan Automobile Tyre Manufacturers Association, Inc.) YEAR BOOK” of Japan; “STANDARDS MANUAL” of ETRTO (The European Tyre and Rim Technical Organisation) of Europe; and “TRA (THE TIRE AND RIM ASSOCIATION INC.) Year Book” of the United States.
According to the present disclosure, a high performance tire having high drainage performance, braking performance and turning performance can be provided.
In the accompanying drawings:
Hereinafter, a pneumatic tire of the present disclosure (hereinafter also referred to as “the tire”) is described in details with reference to the accompanying drawings by exemplifying embodiments thereof.
Although it is omitted in the drawings, a regular tire structure comprising a pair of sidewall portions respectively extending from a pair of bead portions in a radially outward direction; a carcass composed of an organic fiber cord or a steel cord ply extending from one bead portion to the other bead portion through a crown portion including a tread portion formed to extend between the sidewall portions; and a belt composed of a steel cord layer disposed between the carcass and the tread.
At least one of the land portions 3a and 3b, specifically, both of the land portions 3a and 3b in the illustrated example; are divided into a plurality of blocks 5 by a plurality of width direction grooves 4 communicating with the circumferential groove 2 and the tread edges TE. The circumferential groove 2 and the width direction grooves 4 are provided in the tread to ensure drainage performance.
Here, each width direction groove 4 is constituted by a sipe portion 4a extending from the circumferential groove 2 to a tread edge TE side and a groove portion 4b extending from the sipe portion 4a to the tread edge TE side. A sipe portion is a groove having an extremely narrow width such that it closes in the tread footprint during rolling of the tire, and a groove portion is a groove having a width such that it remains open in the tread footprint.
Each block 5 has a shape that protrudes from the four sides of the block 5 toward the central portion. Regarding this protruding shape, cross-sectional views taken from line A-A, line B-B and line C-C in
As described above, in the case that the block 5 defined by the circumferential groove 2 and the width direction grooves 4 is a conventional one whose surface is substantially flat, the ground contact pressure at the end portions of the block is higher than that at the central portion. On the contrary, according to the present disclosure, since the ground contact pressure of the central portion when the block grounds can be increased by adopting a shape that protrudes from the four sides of the block toward the central portion, the ground contact pressure difference between the central portion and the end portions becomes extremely small. Here, during rolling of the tire, if the rubber of the central portion which preferentially contacts the road surface swells and deforms toward the width direction groove sides of the block, it becomes difficult to enjoy the effect of increase in ground contact pressure due to the aforementioned protrusion of the central portion, and therefore it is essential to provide a sipe portion 4a in each width direction groove 4. Provided with the sipe portion 4a, swelling deformation of the block rubber toward the width direction groove 4 sides is suppressed, and therefore an increase in ground contact pressure due to the protrusion of the block central portion is realized.
As illustrated in
Here, each width direction groove 4 includes a sipe portion 4a. The sipe portion 4a may be disposed at a tire tread edge side, or at the central portion of the width direction groove 4; however, is preferably disposed at the tire equator side. Since the ground contact pressure distribution on the tread surface during straight running becomes higher at the central portion than at the tread edges; by suppressing swelling deformation of the block portion at the tire equator side having a higher ground contact pressure in the block, equalization of the ground contact pressure distribution of the entire block 5 can be reliably achieved.
In the present disclosure, as illustrated in
In the present disclosure; it is preferable that the sipe portion 4a of the width direction groove 4 has an opening width of 0.05 mm to 0.5 mm. By defining the opening width of the sipe portion 4a as described above, it is possible to more effectively suppress swelling deformation of the block 5 toward the side surface, and suppress the grounding property difference between the end portions and the central portion of the block 5. Further, it is possible to minimize reduction in rigidity due to formation of the width direction groove 4.
The opening width of the sipe portion 4a is more preferably 0.05 mm to 0.4 mm, and further preferably 0.05 mm to 0.3 mm. With such a configuration, it is possible to prevent reduction in rigidity of the block 5, while more effectively equalizing the ground contact pressure distribution of the block. Further, in order to ensure sufficient drainage performance by the width direction groove 4, it is preferable that the groove portion 4b has an opening width of 0.1 mm to 0.5 mm.
In the present disclosure, as illustrated in
Also, it is preferable that, the apex 6 has a tread width direction maximum length w1 that is 30% to 40% of the width direction length W of the block; and the apex 6 has a tread circumferential direction maximum length 11 that is 30% to 40% of the circumferential direction length L of the block. With such a configuration, it is possible to suppress decrease in footprint area of the block even if the load applied to the tread surface is relatively low.
In the protrusion of the block, it is preferable that the apex 6 is located within the overlapping region between the intermediate portion when the width direction length W of the block 5 is equally divided into three and the intermediate portion when the circumferential direction length L of the block 5 is equally divided into three. With such a configuration, the ground contact pressure distribution of the block 5 can be further equalized. In the case that the block 5 is not rectangular, it is preferable that the overlapping region has a shape along the sides constituting the block 5 and substantially similar to the block 5. Further, as illustrated in
It is preferable that the presently disclosed block 5 protrudes from the opening edge 40 of each width direction groove 4 and the opening edge 20 of the circumferential groove 2 toward the central portion. In
Regarding the protrusion of the block, it is preferable that the block 5 has a tire radial direction height h up to the apex 6 and a width direction length W that satisfy the following equation:
0.01≤h/W≤0.023.
When h/W is less than the lower limit, the grounding property cannot be improved. On the other hand, when h/W exceeds the upper limit, the footprint area decreases.
Further, regarding the protrusion of the block, it is preferable that the tire radial direction height h from the opening edge 40 of the width direction groove 4 to the apex 6 is 0.5 mm to 1.5 mm. This is because, by providing a sufficient height difference between the end portions and the central portion of the block, it becomes easy for the rubber at the central portion to preferentially contact the road surface during rolling of the tire. When it is 0.5 mm or more, equalization of the ground contact pressure distribution can be achieved; however, when it exceeds 1.5 mm, the footprint area decreases, which may result in deterioration in grounding property. It is more preferably 0.8 mm to 1.0 mm. Thereby, the ground contact pressure can be further equalized.
It is preferable that the width direction length W of the block 5 is 28% to 70% with respect to the ground contact width TW of the tire. With such a configuration, it is possible to ensure block rigidity that is enough to compete with side forces during high speed turning, which leads to improvement in movement performance.
It is more preferably 33% to 42%, and further preferably 36% to 40%. By setting this numerical range, it is possible to equalize the ground contact pressure distribution at a high level while maintaining sufficient block rigidity.
It is preferable that the circumferential direction length L of the block 5 is 35% to 49% with respect to the ground contact length TL of the tire. That is, during acceleration and deceleration of the vehicle, an input acting in the circumferential direction is generated in the tire; however, by having such a configuration, it is possible to ensure block rigidity that is enough to compete with such an input and improve the movement performance.
It is more preferably 38% to 46%, and further preferably 41% to 44%. By setting this numerical range, it is possible to equalize the ground contact pressure distribution at a high level while maintaining sufficient block rigidity.
Next, a tire according to a second embodiment of the present disclosure is described with reference to
The shoulder land portions 9a and 9b are divided into a plurality of blocks 12 by a plurality of width direction grooves 10. The width direction grooves 10 and the blocks 12 have the same configuration as that of the width direction grooves 4 and the blocks 5 in
On the other hand, the central land portion 8, as illustrated, is divided into a plurality of blocks 13 by a plurality of sipes 11 extending in the tread width direction.
Like the blocks 5 in the first embodiment, the blocks 13 preferably have a shape that protrudes toward the central portion. Thereby, even in the vicinity of the tire equator, the ground contact pressure distribution of each block can be equalized, and the drainage performance can be improved. Further, during rolling of the tire, if the rubber of each central portion which preferentially contacts the road surface swells and deforms, it becomes difficult to enjoy the effect of increase in ground contact pressure due to protrusion of the central portions. Therefore; by dividing the blocks 13 by the sipes 11, swelling deformation of the block rubbers toward the sipe 11 sides is suppressed, and as a result, an increase in ground contact pressure due to protrusion of the central portion of each block is realized.
As illustrated, each sipe 11 has a certain opening width, and similarly to the width direction grooves 4 in
Here, since the central land portion 8 is divided into a plurality of blocks 13 by a plurality of sipes 11, and the blocks 13 have a protruding shape, it is possible to increase the ground contact pressure at the central portions and improve the drainage performance when the blocks 13 ground.
Additionally, the sipe portion 10a and groove portion 10b of each width direction groove 10 may have chamfers 10c and 10d applied to the opening edges, and each sipe 11 may have chamfers 11c and 11d applied to the opening edges. With such a configuration, the drainage performance can be improved.
The following describes Examples of the disclosure; however, the disclosure is in no way limited thereto.
Tires of size 205/55R16 according to the tread patterns illustrated in
After attaching each obtained Sample Tire to a rim (having a size of 7.0 J) with an internal pressure of 240 kPa, it was assembled to a rear wheel drive vehicle of 2000 cc displacement, and thereafter, the drainage performance, braking performance and turning performance were evaluated when the vehicle runs on a test course (dry road surface and wet road surface included) with a driver riding.
[Turning Performance] [Braking Performance]
For each of the above tires, the turning performance and braking performance when running on a dry road surface were evaluated by sensory evaluation by the driver. The results were indicated as a relative value taking the evaluation results of Sample Tire 1 as 100. Note that the larger the value, the better the performance.
For each of the above tires, the running performance during running on a wet road surface (having a water depth of 1 mm) was evaluated by sensory evaluation by the driver. The result was evaluated as a relative value taking the evaluation result of Sample Tire 1 as 100. Note that the larger the value, the better the drainage performance.
As can be seen from Table 1, the tires according to Examples are all better in drainage performance, braking performance and turning performance than those of Sample Tire 1.
Therefore, Examples of the present disclosure is capable of providing a tire with equalized ground contact pressure distribution and improved drainage performance, braking performance and turning performance.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-117229 | Jun 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/021861 | 6/13/2017 | WO | 00 |
