The present disclosure relates to a pneumatic tire.
To improve the drainage performance when wear progresses, it has been proposed to arrange a sipe, provided with a wide-diameter portion having a larger groove width, in the innermost tread rubber layer in the tire radial direction, which is a different rubber layer from the tread rubber layer forming the tread surface of the tread portion. For example, see Patent Literature (PTL) 1.
PTL 1: JP 2001-130227 A
However, when the aforementioned grooves with a large groove width in the aforementioned technology are exposed as wear progresses, the rigidity of the land portions is reduced. This may result in reduced wear resistance, particularly when, for example, rubber that wears easily is used in the aforementioned innermost tread rubber layer in the tire radial direction.
The present disclosure aims to provide a pneumatic tire capable of improving the drainage performance without sacrificing wear resistance when wear progresses.
A summary of the present disclosure is as follows.
A pneumatic tire according to the present disclosure includes:
a tread portion; and
at least one sipe on a tread surface of the tread portion, wherein
the sipe includes a first sipe portion on the tread surface side, a second sipe portion on a sipe bottom side, and a wide-diameter portion, between the first sipe portion and the second sipe portion, having a sipe width larger than a sipe width of the first sipe portion and a sipe width of the second sipe portion, and
at least a bottom portion of the wide-diameter portion is included in an intermediate tread rubber layer located at an intermediate position in a tire radial direction between a tread rubber layer forming the tread surface and a tread rubber layer on an innermost side of the tread portion in the tire radial direction.
Here, the “tread surface” refers to the entire tread surface in the tread circumferential direction that comes into contact with the road surface when the pneumatic tire is mounted on an applicable rim, filled to a prescribed internal pressure, and subjected to the maximum load.
The “sipe” refers to a sipe having an opening width of 2.5 mm or less at the tread surface when the pneumatic tire is mounted on an applicable rim, filled to a prescribed internal pressure, and under no load.
In the present specification, the “applicable rim” refers to a standard rim of an applicable size, such as the Measuring Rim in the STANDARDS MANUAL of the European Tyre and Rim Technological Organisation (ETRTO) in Europe or the Design Rim in the YEAR BOOK of the Tire and Rim Association, Inc. (TRA) in the USA, that is described, or will be described in the future, in industrial standards effective in the region where the tire is manufactured and used, such as the YEAR BOOK published by the Japan Automobile Tyre Manufacturers Association (JATMA) in Japan, the STANDARDS MANUAL of the ETRTO, and the YEAR BOOK of the TRA. (In other words, the “rim” encompasses not only current sizes but also sizes that may be included in industrial standards in the future. An example of the “size that will be described in the future” is the size described under “future developments” in the ETRTO Standards Manual 2013). In the case of a size not specified in the aforementioned industrial standards, the “rim” refers to a rim whose width corresponds to the bead width of the tire.
The “prescribed internal pressure” represents the air pressure (maximum air pressure) corresponding to the maximum load capability of a single wheel in an applicable size/ply rating described by the aforementioned JATMA or the like. In the case of a size not listed in the industrial standards, the “prescribed internal pressure” refers to the air pressure (maximum air pressure) corresponding to the maximum load capability prescribed for each vehicle on which the tire is mounted.
The “maximum load” refers to the load corresponding to the aforementioned maximum load capability.
In the present specification, the “loss tangent” refers to the ratio (E″/E′) of the dynamic loss modulus (E″) to the dynamic storage modulus (E′) and is the value measured on a test piece of tread rubber having a thickness of 2 mm, a width of 5 mm, and a length of 20 mm under the conditions of an initial load of 160 g, an initial strain of 1%, a vibration frequency of 50 Hz, and a temperature of 30° C.
In the present specification, the “circumferential main groove” refers to a groove extending in the tread circumferential direction, having an opening width of 2 mm or more at the tread surface when the pneumatic tire is mounted on an applicable rim, filled to a prescribed internal pressure, and under no load, and having a wear indicator affixed thereto.
According to the present disclosure, a pneumatic tire capable of improving the drainage performance without sacrificing wear resistance when wear progresses can be provided.
In the accompanying drawings:
Embodiments of the present disclosure are described below in detail with reference to the drawings.
The internal structure and the like of the pneumatic tire (hereinafter referred to simply as the tire) can be the same as those of a conventional tire that has a tread portion. As an example, the tire can have a pair of bead portions, a pair of sidewall portions connected to the pair of bead portions, and a tread portion disposed between the pair of sidewall portions. The tire can also have a carcass extending toroidally between the pair of bead portions and a belt disposed on the radially outward side of a crown portion of the carcass.
Unless otherwise specified, the dimensions and the like refer to the dimensions and the like when the tire is mounted on an applicable rim, filled to a prescribed internal pressure, and under no load (referred to as the “reference state” in the present specification).
As illustrated in
As illustrated in
In the illustrated example, the circumferential main grooves 2 all extend along the tread circumferential direction (without inclination) in plan view of the tread surface 1, but at least one of the circumferential main grooves 2 may extend at an inclination relative to the tread circumferential direction. In this case, the circumferential main groove 2 may be inclined at an angle of, for example, 5° or less relative to the tread circumferential direction. In the illustrated example, all of the circumferential main grooves 2 extend straight in the tread circumferential direction, but at least one of the circumferential main grooves 2 may have a shape such as a zigzag shape or a curved shape.
In the illustrated example, all of the widthwise grooves 4 extend along the tread width direction (without inclination), but at least one of the widthwise grooves 4 may extend at an inclination relative to the tread width direction. In this case, the widthwise grooves 4 are preferably inclined relative to the tread width direction at an inclination angle of 45° or less, and are more preferably inclined at an inclination angle of 30° or less. In the illustrated example, all of the widthwise grooves 4 extend straight in the tread width direction, but at least one of the widthwise grooves 4 may have a bent portion.
In the illustrated example, the widthwise grooves 4 of the land portion 3a adjacent to the tread edge TE of one half in the tread width direction and the widthwise grooves 4 of the land portion 3d adjacent to the tread edge TE of the other half in the tread width direction are arranged at matching positions in the tread circumferential direction so as to overlap when projected in the tread width direction. The widthwise grooves 4 of the land portions 3 can, however, be arranged at positions shifted with respect to each other in the tread circumferential direction so as not to overlap when projected in the tread width direction.
As illustrated in
In the present example, each block 5 has only one sipe 6 in the land portions 3a, 3d adjacent to the tread edges TE. Each block 5 may, however, have two or more sipes 6, or some blocks may have no sipe 6.
In the illustrated example, the sipe 6 provided in each block 5 of the land portions 3a, 3d adjacent to the tread edges TE is a widthwise sipe 6a extending in the tread width direction. The widthwise sipe 6a extends along the tread width direction in the illustrated example but may extend at an inclination relative to the tread width direction, in which case the widthwise sipe 6a is preferably inclined relative to the tread width direction at an inclination angle of 45° or less, and more preferably inclined at an inclination angle of 30° or less.
On the other hand, when the sipe 6 is provided in the block 5, the sipe 6 can be a circumferential sipe extending in the tread circumferential direction. In this case, the sipe may be a circumferential sipe extending along the tread circumferential direction or may extend at an inclination to the tread circumferential direction. In the case in which the circumferential sipe extends at an inclination relative to the tread circumferential direction, the circumferential sipe is preferably inclined relative to the tread circumferential direction at an inclination angle of 45° or less, more preferably an inclination angle of 30° or less.
Alternatively, when sipes 6 are provided on the block 5, both widthwise sipes and circumferential sipes may be provided.
In the present example, the land portions 3b, 3c by the center in the tread width direction each include four sipes 6 within the illustrated range. Specifically, widthwise sipes 6a extending in the tread width direction and circumferential sipes 6b extending in the tread circumferential direction are connected in a substantial T-shape and arranged at intervals in the tread circumferential direction. On the other hand, when the land portions 3b, 3c by the center in the tread width direction include sipes 6, the land portions 3b, 3c can include only the widthwise sipes 6a or only the circumferential sipes 6b. In this case, the number of sipes 6 (the number of widthwise sipes 6a and the number of the circumferential sipes 6b) is not particularly limited and can be set appropriately. When both the widthwise sipes 6a and the circumferential sipes 6b are provided, the combination of the number of the widthwise sipes 6a and the number of the circumferential sipes 6b is not particularly limited and can be set appropriately. The widthwise sipe 6a and the circumferential sipe 6b may intersect, as in the present example, or may be configured not to intersect.
In the illustrated example, the widthwise sipe 6a extends along the tread width direction, but the widthwise sipe 6a may also extend at an inclination relative to the tread width direction. The circumferential sipe 6b extends along the tread circumferential direction in the illustrated example but may extend at an inclination relative to the tread circumferential direction, in which case the circumferential sipe 6b is preferably inclined relative to the tread circumferential direction at an inclination angle of 45° or less, and more preferably inclined at an inclination angle of 30° or less.
In the illustrated example, the widthwise sipes 6a of the land portion 3a adjacent to the tread edge TE in one half, in the tread width direction, bounded by the tire equatorial plane CL and the widthwise sipes 6a of the land portion 3d adjacent to the tread edge TE in the other half, in the tread width direction, bounded by the tire equatorial plane CL are aligned in phase in the tread circumferential direction so as to overlap when projected in the tread width direction but may instead be arranged at different phases in the tread circumferential direction.
In the illustrated example, the widthwise sipes 6a of the land portion 3b by the center in the tread width direction in one half, in the tread width direction, bounded by the tire equatorial plane CL and the widthwise sipes 6a of the land portion 3c by the center in the tread width direction in the other half, in the tread width direction, bounded by the tire equatorial plane CL are aligned in phase in the tread circumferential direction so as to overlap when projected in the tread width direction but may instead be arranged at different phases in the tread circumferential direction. In the illustrated example, the circumferential sipes 6b of the land portion 3b by the center in the tread width direction in one half, in the tread width direction, bounded by the tire equatorial plane CL and the circumferential sipes 6b of the land portion 3c by the center in the tread width direction in the other half, in the tread width direction, bounded by the tire equatorial plane CL are aligned in phase in the tread circumferential direction so as to overlap when projected in the tread width direction but may instead be arranged at different phases in the tread circumferential direction.
In the illustrated example, the widthwise sipes 6a of the land portions 3a, 3d adjacent to the tread edges TE and the widthwise sipes 6a and circumferential sipes 6b of the land portions 3b, 3c by the center in the tread width direction are arranged with shifted phases in the tread circumferential direction so as not to overlap when projected in the tread width direction but may be arranged so as to overlap at least partially when projected in the tread width direction.
In the example illustrated in
As illustrated in
As described above, the sipe 6 includes the first sipe portion 7 on the tread surface 1 side. The first sipe portion 7 can achieve the same function as an ordinary sipe from when the tire is new to the early stage of wear.
As illustrated in
As described above, the sipe 6 includes the second sipe portion 8 on the sipe bottom side.
In contrast, as illustrated in
When the wide-diameter portion 9 is exposed as wear progresses, the wide-diameter portion 9 can be used to improve the drainage performance, and the above configuration enables use of the intermediate tread rubber layer 12 at this time.
As illustrated in
The sipe 6 most preferably extends while bending in the extending direction in plan view, the first sipe portion 7 most preferably extends in the depth direction of the sipe while bending, and the second sipe portion 8 most preferably extends straight in the depth direction of the sipe.
When the tread surface 1 has one or more circumferential main grooves 2 extending in the tire circumferential direction, as in the example illustrated in
In the present example, the sipe width of the second sipe portion 8 is 2.0 mm or less, and the ratio of the extension length of the second sipe portion 8 in the sipe depth direction to the sipe width of the second sipe portion 8 is 2 or more. This can further suppress the above-described flow of the tread rubber during vulcanization, thereby further improving the manufacturability of the tire.
As in the present example, the extension length of the first sipe portion 7 in the sipe depth direction is preferably longer than the extension length of the second sipe portion 8 in the sipe depth direction. The extension length of the first sipe portion 7 in the sipe depth direction can, however, be shorter than or the same as the extension length of the second sipe portion 8 in the sipe depth direction.
As described above, the sipe 6 includes the wide-diameter portion 9. As a result, the wide-diameter portion 9 with a large sipe width appears when wear progresses, thereby improving the drainage performance.
As illustrated in
Here, as illustrated in
The thicknesses of the tread rubber layers 10, 11, and 12 in
As illustrated in
As illustrated in
In the present example, the tread portion includes a cap rubber layer and a base rubber layer positioned farther inward in the tire radial direction than the cap rubber layer. In the present example, the cap rubber layer includes an outer cap rubber layer and an inner cap rubber located farther inward in the tire radial direction than the outer cap rubber layer.
That is, in the present example, the tread rubber layer 10 forming the aforementioned tread surface 1 is the outer cap rubber layer. In the present example, the tread rubber layer 11 on the innermost side of the tread portion in the tire radial direction is the base rubber layer. The intermediate tread rubber layer 12 is the inner cap rubber layer.
Accordingly, in the present example, at least the bottom portion (all in the illustrated example) of the wide-diameter portion 9 is included in the inner cap rubber layer.
As a result, the drainage performance can be improved without sacrificing wear resistance when wear progress in the case in which the tread portion has a laminated rubber structure.
The tread portion is not, however, limited to a laminated rubber structure.
At this time, the loss tangent tan δCi of the intermediate cap rubber layer 12 is preferably larger than the loss tangent tan δB of the base rubber layer 11.
The aforementioned sipes 6 can, for example, be manufactured by machining with metal sheets, casting, or laminate molding (3D printing).
While embodiments of the present disclosure have been described above, the present disclosure is in no way limited to the above embodiments. For example, the tread rubber layer 10 forming the tread surface and the tread rubber layer 11 on the innermost side of the tread portion in the tire radial direction are each one layer in the above examples but may instead be two or more layers. The intermediate tread rubber layer 12 is also one layer in the above examples but may be two or more layers.
Number | Date | Country | Kind |
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2019-110824 | Jun 2019 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2020/021004 | 5/27/2020 | WO | 00 |