Patent Application
20190255889
The present application benefits by the priority right claimed in Japanese Patent Application No. 2018-028821 filed on Feb. 21, 2018 on the basis of Japanese Patent Application No. 2018-028821. Japanese Patent Application No. 2018-028821 is incorporated herein by reference in its entirety.
The present invention relates to a pneumatic tire.
As disclosed in Patent Documents 1 to 3, a pneumatic tire in which plural polygonal blocks are aligned in a tread has been known. In order for the pneumatic tire to exert a superior traction property in multiple directions, it is advantageous that each of the blocks has a large number of ends (sides) extending in different directions. In particular, in order to improve the traction property in a tire width direction, which is often insufficient, it is advantageous to form a projected section, which extends in a tire circumferential direction, in each of the blocks.
In addition, in order for the pneumatic tire to exert the superior traction property in the multiple directions, it is advantageous to provide two or more types of the blocks in different shapes in a central region of the tread in the width direction. It is advantageous to form the projected section, which extends in the tire circumferential direction, in each of the two or more types of those blocks.
As described in PTL 4, a pneumatic tire in which a tapered surface is formed at an end of each of the blocks has been known.
Patent Document 1: Japanese Patent No. 6097263
Patent Document 2: Japanese Patent No. 6114731
Patent Document 3: Japanese Patent No. 6154834
Patent Document 4: JP-A-2016-222206
In regard to the block having the projected section, which extends in the tire circumferential direction, there is a problem that an end of the projected section is likely to be worn due to low rigidity. In addition, when the block is deformed during braking, the end of the block in the tire circumferential direction comes off a road surface and thus is likely to slip. This is also a cause of facilitating the wear of the end of the projected section.
In view of the above, the present invention has a purpose of providing a pneumatic tire which exerts a favorable traction property and in which local wear of a block is unlikely to occur.
A pneumatic tire according to an embodiment is characterized that a first block and a second block in different shapes are aligned in a tire circumferential direction with a groove being interposed therebetween, the first block has a first projected section extending toward the second block, the second block has a second projected section extending toward the first block, the first projected section and the second projected section overlap each other in a tire width direction, a two-step tapered section is formed at an end of at least one of the first projected section and the second projected section, the two-step tapered section includes: a first tapered surface coupled to a ground contact surface; and a second tapered surface coupled to the first tapered surface and extending toward a bottom of the groove, each of the first tapered surface and the second tapered surface is inclined with respect to a tire radial direction, and an inclination angle of the first tapered surface with respect to the tire radial direction is larger than an inclination angle of the second tapered surface with respect to the tire radial direction.
With the first block and the second block having such projected sections, a favorable traction property is exerted. In addition, since the two-step tapered section is formed in each of the projected sections, local wear of each of the blocks is unlikely to occur.
A pneumatic tire according to an embodiment will be described on the basis of the drawings. Note that features of the pneumatic tire, which will be described below, are features in an unloaded state of the pneumatic tire that is attached to a legitimate rim and is filled with air to have a legitimate inner pressure unless otherwise noted. Here, the legitimate rim is specified as the “Standard Rim” in JATMA standards, the “Design Rim” in TRA standards, or the “Measuring Rim” in ETRTO standards. In addition, the legitimate inner pressure is specified as the “Maximum inflation pressure” in the JATMA standards, a maximum value set in the “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standards, or the “INFLATION PRESSURE” in the ETRTO standards.
In the invention of the present application, a sipe is a narrow groove, and more specifically, is a groove, an opening of which to a ground contact surface is closed under a condition that the pneumatic tire, which is attached to the legitimate rim and is filled with the air to have the legitimate inner pressure, contacts the ground and a legitimate load acts thereon. Here, the legitimate load is specified as the “Maximum load capacity” in the JATMA standards, a maximum value set in the “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standards, or the “LOAD CAPACITY” in the ETRTO standards. In the case where simply the “groove” is referred in the following description, “the groove” means a groove that has a greater width than the sipe and has an opening to the ground contact surface that is not closed even under the above-described condition.
In the following description, the ground contact surface is a surface of the pneumatic tire that comes into contact with a road surface when the legitimate load acts on the pneumatic tire, which is attached to the legitimate rim and is filled with the air to have the legitimate inner pressure.
In the invention of the present application, a block is a land section that is partitioned and formed by the plural grooves. Each of the blocks has the ground contact surface with the road surface.
The pneumatic tire according to the embodiment is mounted on a vehicle such as a lightweight truck. An overview of a cross-sectional structure of the pneumatic tire according to the embodiment will be described below. A bead is provided on each side in a tire width direction, a carcass ply is folded from an inner side to an outer side in the tire width direction to wrap the beads and defines a framework of the pneumatic tire. A belt is provided on an outer side of the carcass ply in a tire radial direction, and a tread having the ground contact surface is provided on an outer side of the belt in the tire radial direction. A sidewall is provided on each side of the carcass ply in the tire width direction. In addition to these members, plural members that are required to satisfy functions of the tire are provided.
The tread is formed with a tread pattern depicted in
The center region is formed with two block rows, in each of which first blocks 20 and second blocks 30 in different shapes from each other are alternately aligned in the tire circumferential direction. The shoulder region on each of the sides in the tire width direction is formed with a block row, in which third blocks 40 and fourth blocks 45 in different shapes from each other are alternately aligned in the tire circumferential direction. Thus, this tread is formed with the four block rows.
When seen from a tire outer diameter side, each of the first blocks 20 and the second blocks 30 in the center region has a polygonal shape with plural sides. The first block 20 is longer than the second block 30 in the tire width direction. In
As depicted in
As depicted in
The first block 20 and the second block 30 are arranged such that the first projected section 22 and the second projected section 32 respectively approach the cutout sections 31, 21 of the other blocks and overlap each other in the tire width direction. Accordingly, the first projected section 22 of the first block 20 and the second cutout section 31 of the second block 30 oppose each other via a groove, and the first cutout section 21 of the first block 20 and the second projected section 32 of the second block 30 oppose each other via the groove.
The groove that runs from a position between the first projected section 22 and the second cutout section 31 to a position between the first cutout section 21 and the second projected section 32 is a first bent groove 11 that has three bent sections when seen from the tire outer diameter side. The three bent sections of the first bent groove 11 define the shapes of the first projected section 22, the second cutout section 31, the first cutout section 21, and the second projected section 32.
In addition, the first projected section 22 of the first block 20 is located between the two second blocks 30 (that is, the second blocks 30 in the two block rows of the center region). Thus, the two second blocks 30 are arranged on both sides in the tire width direction of the first projected section 22 of the first block 20.
In the center region, the first block 20 in the right block row and the first block 20 in the left block row oppose each other via a second bent groove 12 having a bent section. The second bent groove 12 as a whole extends in an inclined direction with respect to the tire circumferential direction and the tire radial direction. The first cutout section 21 of the one first block 20 and a portion on an opposite side of the first cutout section 21 of the other first block 20 face the second bent groove 12. A distance between the first blocks 20 is longer than a distance between the other blocks in the center region. That is, the second bent groove 12 has a greater width than any of the other grooves, each of which divides the blocks, in the center region. The width of the second bent groove 12 is greater than width of the tire circumferential groove 10.
The first block 20 and the second block 30 are designed to have substantially the equal area (precisely, an area of the ground contact surface of each of the blocks). As a preferred mode, a difference in the area between the first block 20 and the second block 30 falls within 15% of one of the areas. As a further preferred mode, the difference in the area between the first block 20 and the second block 30 falls within 15% of smaller one of the areas.
As depicted in
Each of the first tapered surface 51 and the second tapered surface 52 is inclined with respect to the tire radial direction. An inclination angle 81 of the first tapered surface 51 with respect to the tire radial direction is larger than an inclination angle 82 of the second tapered surface 52 with respect to the tire radial direction. For example, 81 is equal to or larger than 10° and equal to or smaller than 250, and 82 is equal to or larger than 3° and equal to or smaller than 8°.
On the groove bottom side of the second tapered surface 52, an R surface 53 that couples the second tapered surface 52 and the bottom of the first bent groove 11 is formed. Note that a wall surface that extends in the tire radial direction may be formed between the second tapered surface 52 and the R surface 53.
As depicted in
On the groove bottom side of the third tapered surface 54, the R surface 53 that couples the third tapered surface 54 and the bottom of the first bent groove 11 is formed. Note that the wall surface that extends in the tire radial direction may be formed between the third tapered surface 54 and the R surface 53.
As depicted in
Similar to the case of the two-step tapered section 50, each of the first tapered surface 61 and the second tapered surface 62 is inclined with respect to the tire radial direction. The inclination angle θ1 of the first tapered surface 61 with respect to the tire radial direction is larger than the inclination angle θ2 of the second tapered surface 62 with respect to the tire radial direction. For example, θ1 is equal to or larger than 10° and equal to or smaller than 25°, and θ2 is equal to or larger than 3° and equal to or smaller than 8°.
On the groove bottom side of the second tapered surface 62, an R surface 63 that couples the second tapered surface 62 and the bottom of the first bent groove 11 is formed. Note that a wall surface that extends in the tire radial direction may be formed between the second tapered surface 62 and the R surface 63.
As depicted in
On the groove bottom side of the third tapered surface 64, the R surface 63 that couples the third tapered surface 64 and the bottom of the first bent groove 11 is formed. Note that the wall surface that extends in the tire radial direction may be formed between the third tapered surface 64 and the R surface 63.
As depicted in
As depicted in
Similarly, the second block 30 is divided into two block pieces 30a, 30b by the sipe 33. The sipe 33 is provided such that the block pieces 30a, 30b are divided to have a substantially equal area (precisely, an area of the ground contact surface of each of the block pieces). In a preferred mode, the area of each of the block pieces 30a, 30b is equal to or larger than 35% and equal to or smaller than 65% of the area of the second block 30.
One end of each of these sipes 23, 33 is opened to the tire circumferential groove 10, and the other end thereof is opened to the groove (for example, the first bent groove 11) that divides the first block 20 and the second block 30. Each of these sipes 23, 33 has a bent section that is bent when seen from the tire outer diameter side.
In each of these sipes 23, 33, at least one of the bent section and the end (that is, an opening end to the groove) is shallow. For example, as in the sipe 23 depicted in
A depth of each of the sipes 23, 33 is preferably equal to or greater than 70% and equal to or less than 85% of a depth of the groove surrounding the first block 20 and the second block 30. However, in a shallow portion of each of the sipes 23, 33 as described above, the depth of each of the sipes 23, 33 is preferably equal to or greater than 15% and equal to or less than 25% of the depth of the groove surrounding the first block 20 and the second block 30. Note that the depth of the groove surrounding the first block 20 and the second block 30 is equal to or greater than 12 mm and equal to or less than 14 mm, for example.
As depicted in
As depicted in
The third block 40, which is short in the tire width direction, is aligned with the first block 20, which is long in the tire width direction, in the tire width direction.
The third block 40 and the fourth block 45 are respectively formed with sipes 42, 48. One end of each of these sipes 42, 48 is opened to the tire circumferential groove 10, and the other end thereof is closed in the respective block. Each of these sipes 42, 48 has a bent section when seen from the tire outer diameter side. In each of these sipes 42, 48, at least one of an opening end to the tire circumferential groove 10 (that is, the end of the block) and the bent section may be shallow.
A projection 44 that is lower than the third block 40 and the fourth block 45 is formed on a groove bottom of a lateral groove that divides the third block 40 and the fourth block 45.
The pneumatic tire having the structure that has been described so far exhibits the following effects. The first block 20 and the second block 30 in the different shapes are aligned in the tire circumferential direction, the first block 20 has the first projected section 22 extending toward the second block 30, and the second block 30 has the second projected section 32 extending toward the first block 20. Thus, a traction property is favorably exerted in multiple directions including the tire width direction.
The first projected section 22 and the second projected section 32 overlap each other in the tire width direction. Thus, not only one of the first projected section 22 and the second projected section 32 contacts the ground, but both of these contact the ground simultaneously. Accordingly, an excessive pressure is unlikely to be applied to the first projected section 22 and the second projected section 32, and the first projected section 22 and the second projected section 32 are unlikely to slip significantly on the road surface. As a result, local wear by which the first projected section 22 and the second projected section 32 are significantly worn is unlikely to occur.
The two-step tapered sections 50, 60, which respectively include the first tapered surfaces 51, 61 and the second tapered surfaces 52, 62, are formed at the ends of the first projected section 22 and the second projected section 32. Thus, compared to the case where such two-step tapered sections 50, 60 are not provided, the ends of the first projected section 22 and the second projected section 32 have high rigidity. As a result, the local wear, by which the ends of these are worn, is unlikely to occur.
In the two-step tapered sections 50, 60, the inclination angles of the first tapered surfaces 51, 61 on the ground contact surface side with respect to the tire radial direction are larger than those of the second tapered surfaces 52, 62 on the groove bottom side. Thus, even when the blocks are deformed during braking, the ends of the first projected section 22 and the second projected section 32 are unlikely to come off the road surface. As a result, the local wear, by which the ends of these are worn, is unlikely to occur. This will be described with reference to
As depicted in
As depicted in
Meanwhile, in the case where the two-step tapered sections 50, 60, which respectively include the first tapered surfaces 51, 61 and the second tapered surfaces 52, 62, are formed, and the inclination angles of the second tapered surfaces 52, 62 with respect to the tire radial direction are reduced, the inclination angles of the first tapered surfaces 51, 62 with respect to the tire radial direction can be increased while the areas of the ground contact surfaces of the blocks 20, 30 and the width of the groove (the first bent groove 11) are secured. As depicted in
Here, in the case where the inclination angles θ1 of the first tapered surfaces 51, 61 with respect to the tire radial direction are equal to or larger than 10° and equal to or smaller than 25°, a superior local wear prevention effect is exerted. Also, in the case where the inclination angles θ2 of the second tapered surfaces 52, 62 with respect to the tire radial direction are equal to or larger than 30 and equal to or smaller than 80, the superior local wear prevention effect is exerted. Due to a combination of θ1, which is equal to or larger than 100 and equal to or smaller than 25, and θ2, which is equal to or larger than 3° and equal to or smaller than 8°, the local wear prevention effect becomes particularly prominent.
Since each of the two-step tapered sections 50, 60 includes the two tapered surfaces at the different angles, the corner section (a bent section) is formed in a portion where the two tapered surfaces are coupled. Due to the formation of such a corner section in addition to the polygonal shape of each of the blocks, the tread pattern can exhibit rugged design.
The third tapered surfaces 54, 64 are formed at the adjacent positions to the two-step tapered sections 50, 60 at the ends of the blocks 20, 30 on the groove side (the first bent groove 11 side). Thus, such positions are also unlikely to be worn.
The first block 20 and the second block 30 are respectively formed with the sipes 23, 33, each of which penetrates the respective block. Accordingly, the sipes 23, 33 cancel slippage of the blocks 20, 30 on the road surface, and thus the local wear is suppressed. In addition, a ground contact pressure is uniformized in each of the blocks 20, 30.
Here, the first block 20 is divided by the sipe 23 into the two block pieces 20a, 20b. The area of each of the block pieces 20a, 20b falls within the range that is equal to or larger than 35% and equal to or smaller than 65% of the area of the first block 20, and thus the difference in the area between the two block pieces 20a, 20b is small. Accordingly, the ground contact pressure between the two block pieces 20a, 20b is unlikely to be unequal, and both of the block pieces 20a, 20b are worn substantially equally. The same can be said for the second block 30, which is divided into the two block pieces 30a, 30b.
The difference between the area of the first block 20 and the area of the second block 30 is equal to or smaller than 15% of one of the areas. Thus, the ground contact pressure between the first block 20 and the second block 30 is unlikely to be unequal, and both of the blocks 20, 30 are worn substantially equally. These effects are further increased when the difference between the area of the first block 20 and the area of the second block 30 falls within 15% of smaller one of the areas.
Each of the sipes 23, 33 is formed to be shallower than other portion in the bent section or the ends thereof. Thus, a decrease in the rigidity of each of the blocks 20, 30 in the bent section or the ends is suppressed.
The first bent groove 11, which separates the first block 20 and the second block 30, has three bent sections. Thus, the first bent groove 11 is unlikely to resonate therein, and generation of noise is suppressed.
In the case where each of the first block 20 and the second block 30 has the polygonal shape when seen from the tire outer diameter side, each of these blocks has the plural sides extending in the multiple directions. Thus, the pneumatic tire has the superior traction property.
The embodiment that has been described so far is merely illustrative, and the scope of the invention is not limited thereto. Various types of modifications, replacement, elimination, and the like can be made to the embodiment that has been described so far within the scope that does not depart from the gist of the invention. For example, the above effects can be exerted even when the two-step tapered section is formed in only one of the first projected section 22 and the second projected section 32.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-028821 | Feb 2018 | JP | national |
