pneumatic tires

Abstract

The pneumatic tire 1 has a tread band 2 for engaging the road surface in the tire's footprint area, shoulder blocks 20A, 21A arranged along shoulder circumferential ribs 20, 21, and central blocks 25A, 26A, 27A arranged along central circumferential ribs 25, 26, 27. Four circumferential grooves 30, 31, 32, 33 separate the shoulder ribs (20, 21) and the central ribs 25, 26, 27 from one another. The central blocks 25A, 26A, 27A are separated along their entire axial width by transverse sipes 50, 51, 52, which define two end points at their respective axially outer ends where they intersect with the circumferential grooves 30, 31, 32, 33.

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire.

[0002] In recent years, there has been an increasing demand for reduced tire noise as part of the demand for overall vehicle quietness. Furthermore, with the increasing uptake of electric vehicles, which typically have quieter propulsion systems compared to vehicles propelled by internal combustion engines, tire noise is becoming a more dominant component of overall vehicle noise. At the same time, there is a demand for tires with improved wear resistance to extend tire life, as well as improved cornering, traction, and braking performance.

[0003] The present invention aims to provide a tire that alleviates at least one of the problems associated with existing tires.

[0004] The present invention relates to a pneumatic tire having a tread band for engaging a road surface in a footprint area of ​​the tire, the tread band comprising: two shoulder regions at the axially outer ends of the tread band; a central region identified between the shoulder regions; a row of shoulder elements disposed along the first circumferential rib in each of the shoulder regions; at least two rows of central elements disposed along the second circumferential rib in a central region; at least three circumferential grooves separating the first and second circumferential ribs from one another; The central elements are separated along their entire axial width by transverse sipes which define two endpoints at their respective axially outer ends where they intersect with the circumferential grooves.

[0005] In this specification, the term "footprint area" refers to the entire outer surface of the tire that comes into contact with the road surface when the tire is mounted on a rim, inflated to a predetermined internal pressure, and rolled under maximum load.

[0006] The above-mentioned "rim" refers to the approved rim (measurement rim in the ETRTO (European Tire and Rim Technical Organization) Standards Manual, and design rim in the TRA (Tire and Rim Association) Yearbook) for the applicable size that is described or to be described in the industrial standards valid in the region where the tire is produced and used, such as the JATMA Yearbook of the Japan Automobile Tire Manufacturers Association (JATMA) in Japan, the ETRTO Standards Manual in Europe, or the TRA Yearbook in the United States (i.e., the above-mentioned "rim" includes not only existing sizes but also sizes that may be included in the above-mentioned industrial standards in the future. Examples of "sizes to be described in the future" include the sizes described as "future developments" in the 2013 edition of the ETRTO Standards Manual).

[0007] The term "predetermined internal pressure" refers to the air pressure (maximum air pressure) that corresponds to the maximum load capacity of a single wheel for the applicable size and ply rating described in the above-mentioned standard manuals such as ETRTO. Furthermore, the term "maximum load" refers to the load that corresponds to the above-mentioned maximum load capacity.

[0008] According to the present invention, the central elements are separated along their entire axial width by transverse sipes that define two endpoints at their respective axially outer ends where they intersect with the circumferential grooves. The separation of the central elements by transverse sipes improves the lateral and circumferential connectivity of the central elements compared to when the central elements are separated by lugs that extend substantially in the axial direction of the tire, resulting in improved cornering performance and circumferential stiffness (and thus traction and braking performance).

[0009] Preferably, an imaginary linear extension between the two end points defines an inclination angle of the transverse sipe relative to the axial direction of the tire, the absolute value of which is in the range of 25° to 50°, more preferably in the range of 25° to 45°, and even more preferably in the range of 30° to 40°. The absolute value may be approximately 35°. The sipes are thus positioned to improve the lateral and circumferential connection of the central element, resulting in improved cornering performance and circumferential stiffness. Furthermore, because the sipes are inclined, they move gradually and progressively into the tire's contact patch without simultaneously moving along the entire length of the sipe. This reduces noise emissions.

[0010] Preferably, the imaginary linear extensions of the transverse sipes of the two rows of central elements are inclined in opposite directions to balance the direction and magnitude of the lateral force.

[0011] Preferably, the extension of the transverse sipe along the axial direction between the two end points of the transverse sipe is non-linear, and the sipe is thus positioned to improve the lateral and circumferential connection of the central element, resulting in improved cornering performance and circumferential stiffness.

[0012] Preferably, the axial extension between the two end points of the transverse sipe is substantially S-shaped. The sipes are thus arranged to improve the lateral and circumferential connection of the central element, resulting in improved cornering performance and circumferential stiffness. This arrangement can also reduce tire noise by providing a more gradual block impact with the road surface.

[0013] Preferably, the wavy profile is superimposed on an S-shaped extension along the axial direction of the transverse sipe, resulting in a three-dimensional shape of the transverse sipe. (The wavy profile can be visible on the tread surface, or it can terminate at a certain distance below the tread surface on the inside of the tread.) This results in a local increase in contact area, which leads to improved braking, and may also lead to localized wear reduction.

[0014] Preferably, the transverse sipes have a total length along their extension between two endpoints, and the total length of the transverse sipes having a wavy profile superimposed on the S-shaped extension is at least 20% greater than a transverse sipe extending along a straight line between the two endpoints, such that the sipes have minimal performance improvement compared to sipes that follow a straight line between the endpoints.

[0015] As the axially wavy profile extends radially (i.e., in the depth direction of the sipe), another wavy profile may be superimposed on the radial extension. In this way, the profile undulates in two directions. Therefore, as a first block moves radially, it contacts an adjacent second block on the other side of the sipe, limiting the first block's radial movement. This further enhances the above-mentioned effect of the axially wavy profile.

[0016] Preferably, each end point of the transverse sipes in each row of the central element is offset circumferentially relative to each circumferentially closest end point of the transverse sipes in one or more adjacent rows. In this manner, the end points of adjacent rows are not aligned along the tire axial direction. This results in reduced tire noise. The impacts of the different end points with the road surface are arranged so that they do not all occur simultaneously; if all the end points impact simultaneously, the result would be interference with noise generation.

[0017] Preferably, each of the end points is circumferentially offset relative to a respective circumferentially closest end point of each transverse sipe in the row.

[0018] Preferably, the transverse sipes have a radial extension inward of the tread band along a radial profile which becomes wavy or zigzag as the sipe extends axially.

[0019] Preferably, in the footprint region, the axial width of each shoulder element is greater than the axial width of each central element, and the total number of shoulder elements in each row is greater than the total number of central elements in each row around the tire. This helps balance the stiffness of the tire's shoulders and center, avoid rib "bumps," and reduce tire wear. This arrangement can also reduce tire noise by reducing the synchronization of impacts of the center and shoulder elements with the road surface.

[0020] Preferably, the total number of shoulder elements in each row is at most 125%, preferably at most 120%, more preferably about 115% of the total number of central elements in each row.

[0021] Preferably, the total number of shoulder elements in each row is at least 110% of the total number of central elements in each row.

[0022] In one preferred form, the central elements are free of cuts and are preferably separated only by transverse sipes.

[0023] Preferably, the shoulder elements are separated by lugs extending substantially in the axial direction of the tire, the lugs having a width in the circumferential direction and along their longitudinal extension having a first portion intersecting the circumferential groove and a second portion extending outward in the axial direction of the tire.

[0024] Preferably, the width of the lug at the first portion intersecting the circumferential groove is smaller than the width of the lug at the second portion. This helps to reduce noise caused by the impact of the shoulder element or block on the road surface. More specifically, this helps to reduce so-called air pumping within the lug, which generates noise emissions. Tire noise can be measured using a pass-by noise test. Conversely, the fact that the lug intersects the circumferential groove means that adjacent blocks can move relative to each other as they exit the tire's contact patch with the road surface, which leads to improved wear performance.

[0025] Preferably, the width of the first portion is in the range of 1 / 12 to 1 / 8 of the width of the second portion, which helps to reduce so-called air pumping within the lug, which generates noise emissions.

[0026] The width of the first portion may be about 0.4 mm.

[0027] Preferably, the sidewalls of the first portion are configured to contact each other as the first portion passes through the tire's contact patch with the road surface. In this way, the first portion is closed when it is within the contact patch, which helps reduce noise caused by the block's impact on the road surface. Conversely, when the block leaves the contact patch, the first portion allows adjacent blocks to move relative to each other, which leads to improved wear performance.

[0028] Preferably, the intersections between the lugs and the circumferential grooves are circumferentially offset relative to the circumferentially closest end points of the transverse sipes in each row of the center element, which arrangement can reduce tire noise by reducing synchronization of the center element and shoulder elements with the road surface.

[0029] Preferably, the lugs in each shoulder region are so arranged.

[0030] In one preferred form, the shoulder elements are free of notches and are preferably separated only by lugs.

[0031] Preferred embodiments of the present invention will now be described, purely by way of example, with reference to the drawings, in which: [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a perspective view of a tire according to a preferred embodiment of the present invention. [Figure 2] FIG. 2 is a front view of the tire of FIG. 1. [Figure 3] FIG. 2 is a partial front view of the tire of FIG. 1. [Figure 4]FIG. 2 is a schematic view of a transverse sipe forming portion of a mold for the tire of FIG. 1.

[0033] 1 to 3, there is shown a pneumatic tire 1. The tire 1 has a tread band 2 for engaging the road surface in the footprint area of ​​the tire 1.

[0034] As best seen in Figure 2, the tread band 2 has two shoulder regions 10, 11 at the axially outer ends of the tread band 2 and a central region 15 identified between the shoulder regions 10, 11. The central region includes the tire equatorial plane.

[0035] Each of the shoulder regions 10, 11 has a shoulder (first) circumferential rib 20, 21 extending along the circumferential direction of the tire 1. Also, each of the shoulder regions 10, 11 has a row of shoulder elements or blocks 20A, 21A arranged along the shoulder circumferential rib 20, 21.

[0036] In this embodiment, the central region 15 has three central (second) circumferential ribs 25, 26, 27 that extend circumferentially around the tire 1. Also in this embodiment, the central region 15 has three rows of central elements or blocks 25A, 26A, 27A arranged along the central circumferential ribs 25, 26, 27.

[0037] In this embodiment, the tire equatorial plane passes through the central circumferential rib 26, which is a circumferential rib located between the other two central circumferential ribs 25,27.

[0038] In this embodiment, the tread band 2 has four circumferential grooves 30, 31, 32, 33 separating the shoulder ribs 20, 21 and the central rib 25, 26, 27 from the other circumferential ribs 20, 21, 25, 26, 27.

[0039] In the footprint region, the axial width of each of the shoulder blocks 20A, 21A is greater than the axial width of each of the central blocks 25A, 26A, 27A.

[0040] Additionally, the total number of shoulder blocks 20A, 21A in each row is greater than the total number of center blocks 25A, 26A, 27A in each row around the tire 1. This helps balance the stiffness of the tire's shoulders and center, avoiding rib "bumps" and reducing tire wear. This arrangement also reduces tire noise by reducing the synchronization of center and shoulder elements with the road.

[0041] In this embodiment, the tire 1 has 80 shoulder blocks 20A, 21A in each row and 70 center blocks 25A, 26A, 27A in each row, although this is not required.

[0042] The shoulder blocks 20A, 21A are separated by a lug 40 that extends substantially in the axial direction of the tire 1.

[0043] As best shown in FIG. 3 , the lug 40 has a width in the circumferential direction and, along its longitudinal extension, a first portion 40A that intersects the circumferential groove 33 and a second portion 40B that extends axially outward from the first portion 40A. The width of the lug 40 at the first portion 40A is smaller than the width of the lug 40 at the second portion 40B. In particular, the width of the first portion 40A is small enough so that the sidewalls of the first portion 40A contact each other when the first portion 40A passes through the tire's contact patch with the road surface. In this manner, the first portion 40A is closed when it is within the contact patch, which helps reduce noise generated by the impact of the blocks 20A, 21A on the road surface.

[0044] The central blocks 25A, 26A, 27A are separated along their entire axial width by transverse sipes 50, 51, 52. The transverse sipes 50, 51, 52 each define two endpoints at their respective axially outer ends where they intersect with the circumferential grooves 30, 31, 32, 33.

[0045] An imaginary straight extension 60 between the two end points defines the inclination angle θ of the transverse sipe 52 relative to the axial direction of the tire 1. The absolute value of the angle θ ranges from 25° to 50°, and in this embodiment is 35°. The sipes are thus positioned to improve the lateral and circumferential connection of the central elements, resulting in improved cornering performance and circumferential stiffness.

[0046] In Figure 3, an imaginary linear extension line 60 is shown for sipe 52 separating central blocks 27A. It can be seen that sipe 51 separating central blocks 26A is angled in the same direction as sipe 52. However, it can be seen that sipe 50 separating central blocks 25A is angled in the opposite direction to sipes 51 and 52.

[0047] The sipes 50, 51, 52 do not extend in a straight line, this is done to improve the lateral and circumferential connection of the central elements, resulting in improved cornering performance and circumferential stiffness.

[0048] The axial extension between the two end points of the transverse sipes 50, 51, 52 is substantially S-shaped in plan view. The sipes are thus arranged to improve the lateral and circumferential connection of the central element, resulting in improved cornering performance and circumferential stiffness. This arrangement can also reduce tire noise by providing a more gradual block impact with the road surface.

[0049] Furthermore, a wave-like profile (a zigzag profile in this embodiment) is superimposed on the S-shaped extension of the transverse sipes 50, 51, 52 in the axial direction in a plan view.

[0050] In this embodiment, each end point of the transverse sipes 50, 51, 52 in the central blocks 25A, 26A, 27A of each row is offset circumferentially from the circumferentially closest end point of each of the transverse sipes 50, 51, 52 in one or more adjacent rows. Taking the lower transverse sipe 51 of block 26A as an example, it can be seen in FIG. 3 that its end point is offset from the nearest end point of the sipe 50 in block 25A and also from the nearest end point of the sipe 52 in block 27A. This is indicated by dashed lines. Taking the lower transverse sipe 52 of block 27A as another example, it can be seen in FIG. 3 that its end point is offset from the nearest end point of the sipe 51 in an adjacent row. Furthermore, one end point of the lower sipe 52 (i.e., its upper end point) is offset from the nearest end point of the upper sipe 50 in a non-adjacent row.

[0051] The transverse sipes 50, 51, 52 have a radial extension inside the tread band 2 along a radial profile that takes on a wavy or zigzag shape as the sipes 50, 51, 52 extend axially.

[0052] In this embodiment, the central blocks 25A, 26A, 27A are not notched and are separated only by transverse sipes 50, 51, 52. The central blocks 25A, 26A, 27A also have smooth radially outer surfaces.

[0053] In this embodiment, the intersections of the lugs 40 with the circumferential grooves 30, 33 are offset circumferentially relative to the circumferentially closest end points of the transverse sipes 50, 51, 52 in each row of the center blocks 25A, 26A, 27A. This arrangement can reduce tire noise by reducing the synchronization of impact between the center and shoulder blocks 25A, 26A, 27A, 20A, 21A and the road surface. Taking the lower lug 40 shown in FIG. 3 as an example, it can be seen that its intersection with the circumferential groove 33 is offset from the end point of the upper sipe 51 in block 26A. The intersections of the lower lugs 40 are also offset from the end points of the sipes 50, 52 in the other blocks 25A, 27A. In this embodiment, this is the case for at least some of the lugs 40 in the right shoulder region shown in FIG. 3. This is also the case for at least some of the lugs 40 in the left shoulder region shown in FIG. 3.

[0054] As shown in Figure 3, the lower lugs 40 extend in a substantially straight line. Furthermore, in this embodiment, although not required, the inclination angle of the lugs 40 relative to the tire axial direction is less than the inclination angle of an imaginary straight line extension between the two end points of the transverse sipes 50, 51, 52. However, it is not required that all of the lugs 40 and all of the transverse sipes 50, 51, 52 have this relationship; it is also possible that only some of the lugs 40 and the transverse sipes 50, 51, 52 have this relationship. In this embodiment, although not required, the inclination angle of the lugs 40 relative to the tire axial direction is approximately 15°.

[0055] In this embodiment, there are three central circumferential ribs 25, 26, 27, three rows of central blocks 25A, 26A, 27A, and four circumferential grooves 30, 31, 32, 33. However, this is not required and the number of ribs, rows, and circumferential grooves may be different.

[0056] Figure 4 shows a transverse sipe forming portion 100 of a mold for tire 1. The shape of the transverse sipe forming portion 100 corresponds to the sipes to be formed, such as sipes 50, 51, and 52. As can be seen in Figure 4, as the axially oriented wavy profile extends radially (i.e., in the direction of the sipe depth), another wavy profile is superimposed on the radial extension. In this way, the profile undulates in two directions.

[0057] Preferred embodiments of the present invention have been described purely by way of example and various modifications, additions and / or omissions may be suggested to those skilled in the art, all of which form part of the present invention.

Claims

1. 1. A pneumatic tire having a tread band for engaging a road surface in a footprint area of ​​the tire, said tread band comprising: two shoulder regions at the axially outer ends of the tread band; a central region identified between the shoulder regions; a row of shoulder elements disposed along a first circumferential rib in each of the shoulder regions; at least two rows of central elements disposed along the second circumferential rib in the central region; at least three circumferential grooves separating the first circumferential rib and the second circumferential rib from another circumferential rib; the central elements are separated along their entire axial width by transverse sipes, the transverse sipes defining two end points at their respective axially outer ends where they intersect with circumferential grooves.

2. 2. The tire of claim 1, wherein an imaginary straight extension of the two end points defines an inclination angle of the transverse sipe relative to the axial direction of the tire, the absolute value of which is in the range of 25° to 50°.

3. 3. The tire of claim 2, wherein the imaginary linear extensions of the transverse sipes in the two rows of central elements are inclined in opposite directions.

4. 4. A tire according to claim 2 or 3, wherein the extension of the transverse sipe along the axial direction between the two end points of the transverse sipe is non-linear.

5. 5. A tire according to claim 2, wherein the axial extension between the two end points of the transverse sipe is substantially S-shaped.

6. 6. The tire of claim 5, wherein a wave profile is superimposed on said S-shaped extension along said axial direction of said transverse sipe.

7. 7. The tire of claim 6, wherein the transverse sipes have a total length along their extension between the two end points, the total length of the transverse sipes having a wavy profile superimposed on the S-shaped extension being at least 20% greater than a transverse sipe extending along a straight line between the two end points.

8. 8. The tire of claim 1, wherein each end point of the transverse sipes in each row of the central element is circumferentially offset relative to each circumferentially closest end point of the transverse sipes in the adjacent row or rows.

9. 9. A tire according to any one of claims 1 to 8, wherein the transverse sipes have a radial extension inward of the tread band along a radial profile which becomes wavy or zigzag as the sipes extend in the axial direction.

10. 10. A tire according to claim 1, wherein in the footprint area, the axial width of each of the shoulder elements is greater than the axial width of each of the central elements, and wherein the total number of shoulder elements in each row is greater than the total number of central elements in each row around the circumference of the tire.

11. 11. A tire according to claim 10, wherein the total number of said shoulder elements in each row is at most 125%, preferably at most 120%, more preferably about 115% of the total number of said central elements in each row.

12. 12. A tire according to any one of claims 1 to 11, wherein said central elements are unscored and are separated only by said transverse sipes.

13. the shoulder elements are separated by lugs extending substantially in the axial direction of the tire; 13. A tire according to any one of claims 1 to 12, wherein the lug has a width in the circumferential direction and has, along its longitudinal extension, a first portion that intersects a circumferential groove and a second portion that extends outward in the axial direction of the tire.

14. The tire of claim 13 , wherein a width of the lug at the first portion intersecting the circumferential groove is smaller than a width of the lug at the second portion.

15. 15. The tire of claim 14, wherein the width of said first portion is in the range of one-twelfth to one-eighth the width of said second portion.

16. 16. A tire according to any one of claims 13 to 15, wherein the sidewalls of the first portion are configured to contact each other as the first portion passes through the contact patch of the tire with the road surface.

17. 17. The tire of claim 13, wherein the intersections between lugs and circumferential grooves are offset in the circumferential direction relative to each circumferentially nearest end point of a transverse sipe in each row of the central element.

18. 18. A tire according to any one of the preceding claims, wherein the shoulder elements are free of cuts and are separated only by the lugs.

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