pneumatic tires

Abstract

This product provides a pneumatic tire that offers excellent traction performance while effectively suppressing uneven wear of the tire blocks. [Solution] The pneumatic tire 1 has a tread pattern that includes a plurality of ribs demarcated by shoulder main grooves 11 and center main grooves 10. The ribs have axial grooves 30, 40 that extend mainly in the tire axis direction, and the axial grooves 30, 40 include bending points and connect to at least one of the shoulder main grooves 11 and center main grooves 10. The ribs have a triangular notch 70 in the center of the block demarcated by the center main groove 10 and the axial grooves 30 that opens into the center main groove 10. The center main groove 10 has a plurality of groove bottom protrusions 50 that are formed intermittently in the tire circumferential direction, and the groove bottom protrusions 50 are longer in the tire circumferential direction than in the tire axis direction, and all or part of the plurality of groove bottom protrusions 50 are located opposite the notch 70.

Description

Technical Field

[0001] The present disclosure relates to pneumatic tires and to the tread structure of pneumatic tires.

Background Art

[0002] Conventionally, pneumatic tires having a tread pattern including circumferential grooves extending in the tire circumferential direction, axial grooves extending in the tire axial direction, and a plurality of blocks divided by the grooves are widely known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Tires having such a rib pattern may increase traction elements and improve the traction performance of the tire by providing the ribs with notches that open into the main grooves. However, as a result of the inventors' studies, it has been found that when a notch is formed in a rib, the rigidity of the block is locally reduced by the notch, and uneven wear is likely to occur in the block.

Means for Solving the Problems

[0005] The pneumatic tire according to the present invention has a tread pattern comprising shoulder main grooves provided on both ends in the axial direction of the tire, a center main groove provided on the central side in the axial direction of the tire from the shoulder main grooves, and a plurality of ribs partitioned by the shoulder main grooves and the center main groove, wherein the plurality of ribs have axial grooves formed mainly in the axial direction of the tire, the axial grooves include a bending point and are connected to at least one of the shoulder main grooves and the center main groove, and adjacent axial grooves of the plurality of ribs are arranged offset in the circumferential direction of the tire, and the pneumatic tire is The rib comprises shoulder ribs located on both ends in the tire axial direction relative to the shoulder main groove, and a center rib located on the central side in the tire axial direction relative to the shoulder main groove. The center rib has a triangular notch in the center of the block separated by the center main groove and the axial groove, opening into the center main groove. The center main groove has a plurality of groove bottom protrusions formed intermittently in the tire circumferential direction, the groove bottom protrusions are longer in the tire circumferential direction than in the tire axial direction, and all or part of the plurality of groove bottom protrusions are located opposite the notch. [Effects of the Invention]

[0006] The pneumatic tire according to the present invention can effectively suppress uneven wear of the ribs constituting the tread pattern. The present invention provides a pneumatic tire that has excellent traction performance while effectively suppressing uneven wear of the blocks. [Brief explanation of the drawing]

[0007] [Figure 1] This is a plan view showing the tread of a pneumatic tire, which is an example of an embodiment. [Figure 2] This is a cross-sectional view of the area enclosed by oval A in Figure 1. [Figure 3] This is a cross-sectional view of the area enclosed by the oval B in Figure 1. [Figure 4] This is an enlarged schematic diagram showing the area enclosed by the dashed-dotted line frame in Figure 1. [Figure 5]This is a perspective view showing the area enclosed by the dashed-dotted line frame in Figure 1. [Modes for carrying out the invention]

[0008] Hereinafter, an example of an embodiment of the pneumatic tire according to the present invention will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the embodiments described below. Furthermore, forms obtained by selectively combining each component of the embodiments described below are included in the present invention.

[0009] The pneumatic tire 1 of this embodiment has a general configuration for a pneumatic tire, except for the tread 2, which is the part that contacts the road surface. Specifically, bead portions including a bead core and a bead filler are provided on both sides of the tire axial direction, and a carcass ply is provided extending from one bead portion to the other in the tire axial direction. A belt is provided on the outer diameter side of the carcass ply, and the tread 2 is provided on the outer diameter side of the belt. In addition, an inner liner is provided inside the carcass ply, and sidewall rubber is provided on both sides of the carcass ply in the tire axial direction. In addition to the above, several other rubber members are provided to constitute the pneumatic tire 1.

[0010] The tread 2 of the pneumatic tire 1 will be explained using Figures 1 to 3. Figure 1 is a plan view showing the tread 2 of the pneumatic tire 1, which is an example of an embodiment. Figure 2 is a cross-sectional view showing the center main groove 10, shoulder main groove 11, and axial groove 30, etc., enclosed by oval A in Figure 1. Figure 3 is a cross-sectional view showing the shoulder main groove 11, axial groove 40, etc., enclosed by oval B in Figure 1. Note that in Figure 1, only the contact surface including the contact end E is shown. Also, for the sake of explanation, the right side of Figure 1 is the right side of the pneumatic tire 1, and the left side of Figure 1 is the left side of the pneumatic tire 1.

[0011] The contact end E of the pneumatic tire 1 is defined as the axial ends of the area (contact surface) that contacts a flat road surface when a predetermined load is applied to an unused tire mounted on a regular rim and inflated to the normal internal pressure. The predetermined load is equivalent to 88% of the normal load. In this embodiment, the axial outer ends of the contact surface of the shoulder rib 21, which will be described later, become the contact ends E.

[0012] Here, "standard rim" refers to the rim defined by the tire standard, which is "standard rim" for JATMA and "Measuring Rim" for TRA and ETRTO. "Standard internal pressure" refers to "maximum air pressure" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "INFLATION PRESSURE" for ETRTO. "Standard load" refers to "maximum load capacity" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "LOAD CAPACITY" for ETRTO.

[0013] The pneumatic tire 1 is applicable to tires for various vehicles, including passenger cars, trucks, buses, and light trucks (such as SUVs and pickup trucks). Its use is not particularly limited to summer tires, winter tires, or all-season tires.

[0014] The pneumatic tire 1 is a point-symmetric tire in which there is no specified mounting direction on the vehicle, and the tread pattern and sidewall shape remain unchanged regardless of the direction in which it is mounted on the vehicle. The tread pattern and sidewall shape of the pneumatic tire 1 are the same as those obtained by rotating the tire equator CL 180° to the left and right. The tire equator CL is an imaginary line parallel to the circumferential direction of the tire, passing through the center of the tread 2 in the tire axis direction.

[0015] As shown in Figure 1, the pneumatic tire 1 includes a tread 2 comprising a plurality of main grooves provided along the circumferential direction of the tire and a plurality of ribs partitioned by the main grooves. The tread 2 has shoulder main grooves 11 provided on both ends in the axial direction of the tire, and a center main groove 10 provided closer to the center in the axial direction of the tire than the shoulder main grooves 11. In other words, the tread 2 includes shoulder main grooves 11 provided on the contact end E side and a center main groove 10 provided closer to the tire equator CL side than the shoulder main grooves 11.

[0016] The center main groove 10 and the shoulder main groove 11 are formed in a straight shape along the circumferential direction of the tire. The center main groove 10 and the shoulder main groove 11 may have similar axial lengths (groove widths), and the groove width of the center main groove 10 may be greater than that of the shoulder main groove 11. The center main groove 10 and the shoulder main groove 11 may also have similar radial depths. The center main groove 10 and the shoulder main groove 11 are the deepest grooves among the grooves provided in the tread 2, and are the widest grooves among the circumferential grooves provided in the tread 2.

[0017] The tread 2 is divided by a center main groove 10 and shoulder main grooves 11, and includes shoulder ribs 21 located on both ends (contact end E side) in the tire axial direction from the shoulder main grooves 11, and a center rib 20 located on the central side (tire equator CL side) in the tire axial direction from the shoulder main grooves 11. In this embodiment, the tread 2 includes two shoulder main grooves 11, one center main groove 10 provided along the tire equator CL, and includes two center ribs 20 and two shoulder ribs 21, which are divided by the shoulder main grooves 11 and the center main groove 10.

[0018] The tire axial length (width) of the shoulder rib 21 is the same as or greater than the tire axial length of the center rib 20. Specifically, it is preferable that the tire axial length of the shoulder rib 21 is 100% or more and 135% or less of the tire axial length of the center rib 20. For example, the tire axial length of the shoulder rib 21 is 103% of the tire axial length of the center rib 20. By providing such a configuration, the width of the shoulder rib 21 can be ensured, and the occurrence of uneven wear can be suppressed.

[0019] Axial grooves extending mainly in the tire axial direction are formed in the plurality of ribs. The axial grooves include bending points and are connected to at least one of the shoulder main groove 11 and the center main groove 10. Specifically, axial grooves 30 and 40 extending mainly in the tire axial direction are formed in the center rib 20 and the shoulder rib 21. The axial grooves 30 and 40 include bending points and are connected to at least one of the center main groove 10 and the shoulder main groove 11. Incidentally, it is preferable that the axial groove 30 is provided so as to communicate the center main groove 10 and the shoulder main groove 11. Further, when a plurality of center main grooves 10 are formed, it is preferable that the axial groove 30 is provided so as to communicate the center main grooves 10 with each other. More specifically, a plurality of axial grooves 30 are provided at intervals in the center rib 20, and similarly, a plurality of axial grooves 40 are provided at intervals in the shoulder rib 21. By providing the axial grooves 30 and 40 in the center rib 20 and the shoulder rib 21, the pneumatic tire 1 can increase the traction elements and improve the traction performance.

[0020] The axial groove 30 has one or more bending points, and the shoulder main groove 11, the center main groove 10, and the bending points are formed in a straight line. In this embodiment, the axial groove 30 is formed by two bending points 31, 32 and three straight portions 33. The axial groove 30 includes a first straight portion 33A parallel to the tire axial direction and opening to the shoulder main groove 11, a second straight portion 33B formed between the bending points 31 and 32, and a third straight portion 33C extending obliquely from the bending point 32 in the tire axial direction and opening to the center main groove 10. Note that the second straight portion 33B including the tire circumferential direction component can ensure the lateral slip resistance.

[0021] The depth of the axial groove 30 is 10% or more and 30% or less of the depth of the center main groove 10, and preferably 15% or more and 25% or less. For example, the depth of the axial groove 30 is 15% of the depth of the center main groove 10. By providing such a configuration, the traction performance can be improved more effectively.

[0022] The axial groove 30 may be provided with sipes 34 at the groove bottom, with both ends connected to at least one of the center main groove 10 and the shoulder main groove 11. The sipes 34 are preferably provided to communicate the center main groove 10 and the shoulder main groove 11. Also, when a plurality of center main grooves 10 are formed, the sipes 34 are preferably provided to communicate the center main grooves 10 with each other. The sipes 34 are grooves narrower than the axial groove 30, provided at the center in the groove width direction of the axial groove 30, and bent at the same position as the axial groove 30. In this embodiment, the sipes 34 open to the center main groove 10 and the shoulder main groove 11 and are formed over the entire length of the axial groove 30. By providing such a configuration for the pneumatic tire 1, the sipes 34 remain even at the end of friction, so that the traction performance at the end of friction can be ensured and the uneven wear resistance can be ensured.

[0023] The combined depth of the axial groove 30 and the sipe 34 (i.e., the length from the contact surface to the bottom of the sipe 34) is preferably 50% to 90% of the depth of the center main groove 10. For example, the combined depth of the axial groove 30 and the sipe 34 is 70% of the depth of the center main groove 10. By having such a configuration, the pneumatic tire 1 can more effectively ensure traction performance and resistance to uneven wear at the end of its lifespan.

[0024] The axial groove 40 has one or more inflection points, and the space between the shoulder main groove 11, the center main groove 10, and the inflection points is formed in a straight line. Furthermore, as shown in Figure 3, the axial groove 40 is formed to connect to the shoulder main groove 11 and to close within the shoulder rib 21. In this embodiment, the axial groove 40 is formed from two inflection points 41 and 42 and three straight sections 43. The axial groove 40 is formed from a first straight section 43A parallel to the tire axis direction that opens into the shoulder main groove 11, a second straight section 43B formed between inflection point 41 and inflection point 42, and a third straight section 43C that extends parallel to the tire axis direction from inflection point 42 and closes within the shoulder rib 21. The second straight section 43B, which includes a tire circumferential component, ensures resistance to skidding.

[0025] The depth of the axial groove 40 is 5% to 30% of the depth of the shoulder main groove 11, and more preferably 10% to 25%. For example, the depth of the axial groove 40 is 15% of the depth of the shoulder main groove 11. By having such a configuration, traction performance can be improved more effectively.

[0026] It is preferable that the axial grooves 30 and 40, which are provided at adjacent positions on the center rib 20 and shoulder rib 21, are arranged so as to be offset in the circumferential direction of the tire. For example, in the tread 2, the axial grooves 30 and 40 are arranged such that adjacent axial grooves 30 and 40 do not overlap in the axial direction of the tire. Non-adjacent axial grooves 30 and 40 may have overlapping areas in the axial direction of the tire, but preferably, all axial grooves 30 and 40 formed on the tread 2 are arranged so as not to overlap in the axial direction of the tire.

[0027] It is preferable that the axial grooves 30 and 40 are arranged such that the amount of axial displacement in the tire axial direction of adjacent axial grooves 30 that straddle the center main groove 10 is smaller than the amount of axial displacement in the tire axial direction of adjacent axial grooves 30 and 40 that straddle the shoulder main groove 11. By having such a configuration, the traction performance of the center rib 20 can be further improved, and the resistance to uneven wear of the shoulder rib 21 can be further improved.

[0028] The amount of circumferential displacement in the tire direction of adjacent axial grooves 30 that straddle the center main groove 10 is 5% to 20% of the tire circumferential length (pitch length) of one pitch, for example, 9% of the tire circumferential length (pitch length) of one pitch. Here, in this specification, the tire circumferential length (pitch length) of one pitch refers to the tire circumferential length of one repeating unit of the tread pattern, for example, the distance P in the tire circumferential direction between the closed ends of two adjacent axial grooves 40 in the tire circumferential direction (see the shoulder rib 21 on the right side of Figure 1). Note that the tire circumferential length (pitch length) of one pitch may be equal in all pitches in the tread 2, but from the viewpoint of improving quietness, a variable pitch (unequal length) in which the pitch length changes in the tire circumferential direction is preferred.

[0029] Preferably, the center rib 20 is provided with narrow grooves 60 that connect the axial grooves 30 and are inclined in the direction of the tire axis. The narrow grooves 60 open only into the axial grooves 30 and not into the center main groove 10. In this embodiment, the narrow grooves 60 connect the bending point 32 of the axial grooves 30 to the third straight section 33C of the adjacent axial grooves 30 in the tire circumferential direction. By having such a configuration, the pneumatic tire 1 can ensure resistance to skidding through the narrow grooves 60 having a tire circumferential component.

[0030] The narrow groove 60 is preferably inclined at an angle of 5° to 30° relative to a straight line, assuming a straight line parallel to the circumferential direction of the tire. The straight line parallel to the circumferential direction of the tire is, for example, the tire equator CL. In this embodiment, the narrow groove 60 is inclined at 10° relative to the tire equator CL. The narrow groove 60 may also be inclined perpendicular to the axial groove 30. That is, in this embodiment, it may be inclined perpendicular to the third straight section 33C. It is preferable that the inclination direction of the narrow groove 60 is the same for all narrow grooves 60 formed in the center rib 20. It is even more preferable that the inclination direction and inclination angle of the narrow groove 60 are the same.

[0031] The depth of the narrow groove 60 is 10% to 30% of the depth of the center main groove 10, for example, it is formed to a depth of 15% of the depth of the center main groove 10. The narrow groove 60 may also be formed to the same depth as the axial groove 30, or to a different depth.

[0032] As shown in Figure 2, the center main groove 10 may include, in order from the groove bottom, a groove bottom surface 10A parallel to the tire axis direction, a curved surface 10B that curves so as to be convex toward the inside of the center rib 20, a flat surface 10C parallel to the tire radial direction, and an inclined surface 10D formed at an angle from the tire radial direction. By providing the curved surface 10B between the groove bottom surface 10A and the center rib 20, the pneumatic tire 1 makes it easier to distribute the stress acting on the center rib 20.

[0033] Similarly, the shoulder main groove 11 may include, in order from the groove bottom as shown in Figure 3, a groove bottom surface 11A parallel to the tire axis direction, a curved surface 11B that curves so as to be convex toward the inside of the center rib 20 or shoulder rib 21, and an inclined surface 11C formed at an angle from the tire radial direction. By providing the curved surface 11B between the groove bottom surface 11A and the center rib 20 and between the groove bottom surface 11A and the shoulder rib 21, the pneumatic tire 1 makes it easier to distribute the stress on the center rib 20 and the shoulder rib 21.

[0034] The center rib 20 is provided with a triangular notch 70 in the center of the block separated by the center main groove 10 and the axial groove 30, which opens into the center main groove 10. The notch 70 is formed, for example, at the center of the circumferential distance between two adjacent axial grooves 30 of the center rib 20 in the tire circumferential direction. Furthermore, it is preferable that opposing notches 70 that straddle the center main groove 10 are offset in the tire circumferential direction. By providing the notch 70 to the center rib 20, traction performance can be further improved. In addition, by offsetting the notches 70 in the tire circumferential direction, resistance to uneven wear can be improved.

[0035] As shown in Figure 5, the notch 70 is formed to cut out the center main groove 10 from the contact surface of the center rib 20 to the groove bottom surface 10A, following the shape of the center main groove 10. More specifically, the triangular notch 70 is formed to cut out the inclined surface 10D, the flat surface 10C, and the curved surface 10B in order from the contact surface. It is preferable that the notch 70 is formed to follow each surface. When the notch 70 is formed, the curved surface 10B of the center main groove 10 extends in the circumferential direction of the tire along the notch 70.

[0036] With further reference to Figures 4 and 5, a tread 2, which is an example of an embodiment, will be described in detail. Figure 4 is an enlarged schematic diagram showing the portion enclosed by the dashed line in Figure 1. Figure 5 is a perspective view showing the portion enclosed by the dashed line in Figure 1. Note that in Figure 4, for clarity of the drawing, the curved surface 10B of the center main groove 10, etc., has been omitted. The dashed line in Figure 4 is a virtual line showing the extension of the center line of the axial groove 30. The double-dashed line in Figure 4 is a virtual line showing the extension of the outer shape of the axial groove 30.

[0037] The center main groove 10 has a plurality of groove bottom protrusions 50 that are intermittently formed in the circumferential direction of the tire. The groove bottom protrusions 50 have a shape that is longer in the circumferential direction of the tire than in the axial direction of the tire. The groove bottom protrusions 50 are protrusions formed to protrude from the bottom of the groove of the center main groove 10, and in this embodiment, their shape in plan view is formed to be approximately square. In detail, when the groove bottom protrusions 50 are viewed in plan view, they are formed to be chamfered at each corner of the square. Note that the shape of the groove bottom protrusions 50 is not limited to an approximately square shape in plan view, and any shape such as an elliptical shape or a polygonal shape can be adopted. By having such a configuration, the pneumatic tire 1 can suppress stone jamming, increase the rigidity of the part whose rigidity has decreased due to the formation of the axial groove 30, and maintain rigidity balance, thereby improving resistance to uneven wear.

[0038] All or part of the multiple groove bottom protrusions 50 are located on the extension of the axial groove 30. When the tread 2 is viewed from above, the groove bottom protrusions 50 are located on the extension of the center line of the axial groove 30 (the dashed line in Figure 4). In other words, the groove bottom protrusions 50 are located so as to overlap the extension of the center line of the axial groove 30 in the radial direction of the tire. If the sipe 34 is located in the center of the axial groove 30 in the groove width direction, the groove bottom protrusions 50 may be located on the extension of the sipe 34. Alternatively, the groove bottom protrusions 50 may be located so as to overlap the extension of the center line of the axial groove 30 in the radial direction of the tire.

[0039] The groove bottom projection 50 is preferably provided on the center line of the center main groove 10. That is, the groove bottom projection 50 is preferably provided within the center main groove 10 so as not to be biased toward either center rib 20. In this embodiment, it is preferable that the groove bottom projection 50 is formed on the tire equator CL. Also, the groove bottom projection 50 is provided, for example, within the groove bottom surface 10A of the center main groove 10.

[0040] All or some of the multiple groove bottom protrusions 50 are located opposite the notches 70. Specifically, the center main groove 10 has groove bottom protrusions 50 located opposite the notches 70 in the tire axial direction. Alternatively, they may be positioned between two notches 70 provided on different center ribs 20. By having such a configuration, the pneumatic tire 1 can suppress stone jamming and improve resistance to uneven wear by increasing the rigidity of the parts where rigidity is reduced due to the formation of the notches 70 and maintaining rigidity balance.

[0041] The groove bottom projection 50 may be provided so as to face the entire length of the notch 70 in the tire circumferential direction in the tire axial direction, or it may be provided so as to face a part of the length of the notch 70 in the tire circumferential direction in the tire axial direction. That is, the groove bottom projection 50 may be provided so as to completely overlap with the notch 70 in the tire axial direction, or it may be provided so as to overlap a part of the notch 70 in the tire axial direction. In this case, the groove bottom projection 50 may be provided so as to overlap with multiple notches 70 in the tire axial direction, or it may be provided so as to overlap with one notch 70 in the tire axial direction.

[0042] The center main groove 10 of the tread 2 may have groove bottom protrusions 50 only on the extension of the axial groove 30, or groove bottom protrusions 50 only at positions facing the notches 70. Alternatively, one groove bottom protrusion 50 may be provided so as to overlap the extension of multiple axial grooves 30 in the tire radial direction. On the other hand, one groove bottom protrusion 50 may be provided on the extension of the axial groove 30 and facing the notches 70. It is preferable that the center main groove 10 has groove bottom protrusions 50 both on the extension of the axial groove 30 and at positions facing the notches 70. Note that some of the multiple groove bottom protrusions 50 may be located at positions other than those on the extension of the axial groove 30 and positions facing the notches 70. Furthermore, it is preferable that the multiple groove bottom protrusions 50 formed in the center main groove 10 consist of only two types: groove bottom protrusions 50 located on the extension of the axial groove 30 and groove bottom protrusions 50 located at positions facing the notches 70.

[0043] As shown in Figure 5, the groove bottom projection 50 may include a flat surface 51 formed parallel to the tire radial direction and a curved surface 52 formed at the base end of the center main groove 10. The curved surface 52 is a surface that is curved so as to be convex toward the inside of the groove bottom projection 50 and is provided along the entire side of the base end of the groove bottom projection 50. With this configuration, it is easier to distribute the stress on the groove bottom projection 50. As a result, the rigidity near the groove bottom projection 50 can be increased, and the rigidity balance of the entire tread 2 can be maintained and uneven wear can be suppressed.

[0044] The groove bottom projection 50 has a length (height) in the tire radial direction of 1.5 mm or more and 5.0 mm or less, and is more preferably 2.0 mm or more and 4.0 mm or less. The height of the groove bottom projection 50 is, for example, 2.5 mm. The height of the groove bottom projection 50 is the length in the tire radial direction from the bottom of the center main groove 10 (groove bottom surface 10A) to the highest point of the groove bottom projection 50.

[0045] Preferably, two to six groove bottom protrusions 50 are provided within one pitch. For example, three groove bottom protrusions 50 are provided within one pitch. The tire circumferential length of the groove bottom protrusions 50 is determined, for example, based on the number of groove bottom protrusions 50 provided within one pitch. Preferably, the tire circumferential length of the groove bottom protrusions 50 is 15% to 40% of the tire circumferential length of one pitch. For example, the tire circumferential length of the groove bottom protrusions 50 is 27% of the tire circumferential length of one pitch. Furthermore, the tire circumferential lengths of multiple groove bottom protrusions 50 may be different.

[0046] The axial length of the groove bottom projection 50 is preferably 15% to 40% of the axial length of the center main groove 10. Alternatively, the axial length of the groove bottom projection 50 may be the same as or less than the axial length of the groove bottom surface 10A. Here, the axial length of the groove bottom projection 50 includes the curved surface 52.

[0047] As shown in Figures 1 and 3, the shoulder rib 21 is provided with a one-sided closed sipe 80 that opens into the shoulder main groove 11 and closes within the shoulder rib 21. The one-sided closed sipe 80 is a groove that has a smaller axial length and groove width in the tire than the axial groove 40. With this configuration, slippage at the edge portion of the shoulder rib 21 can be suppressed, thereby improving resistance to uneven wear.

[0048] The axial length of the single-sided closed sipe 80 is 1% to 10% of the axial length of the shoulder rib 21, and more preferably 3% to 6%. For example, the axial length of the single-sided closed sipe 80 is 4% of the axial length of the shoulder rib 21.

[0049] The depth of the one-sided closed sipe 80 is 50% to 90% of the depth of the shoulder main groove 11, and more preferably 60% to 80%. For example, the depth of the one-sided closed sipe 80 is 70% of the depth of the shoulder main groove 11.

[0050] It is preferable that the one-sided closed sipes 80 are arranged at tire circumferential intervals of 10% to 30% of the tire circumferential length of one pitch. For example, the one-sided closed sipes 80 are arranged at tire circumferential intervals of 14% of the tire circumferential length of one pitch. It is also preferable that the one-sided closed sipes 80 are formed within the axial grooves 40.

[0051] The center rib 20 is provided with a single-sided closed sipe 81 that opens into the shoulder main groove 11 and closes within the center rib 20. The single-sided closed sipe 81 is a groove that has a smaller axial length and groove width than the axial groove 30. With this configuration, slippage at the edge portion of the center rib 20 can be suppressed, thereby improving resistance to uneven wear.

[0052] The axial length of the single-sided closed sipe 81 is 1% to 10% of the axial length of the center rib 20, and more preferably 3% to 6%. For example, the axial length of the single-sided closed sipe 81 is 4% of the axial length of the center rib 20. Alternatively, the axial length of the single-sided closed sipe 81 may have dimensions of 1.5 mm to 3.5 mm.

[0053] The depth of the one-sided closed sipe 81 is 50% to 90% of the depth of the center main groove 10, and more preferably 60% to 80%. For example, the depth of the one-sided closed sipe 81 is 70% of the depth of the center main groove 10.

[0054] It is preferable that the one-sided closed sipes 81 are arranged at tire circumferential intervals of 10% to 30% of the tire circumferential length of one pitch. For example, the one-sided closed sipes 81 are arranged at tire circumferential intervals of 14% of the tire circumferential length of one pitch. Furthermore, if sipes 34 are formed in the axial groove 30, it is preferable that the one-sided closed sipes 81 are not formed within the axial groove 30.

[0055] The single-sided closed sipes 80 and 81 may be formed at similar circumferential tire spacings, or they may be formed at different circumferential tire spacings. Furthermore, when they are formed at similar circumferential tire spacings, it is preferable that the single-sided closed sipes 80 and 81 are formed to face each other in the axial direction of the tire.

[0056] The above embodiments can be modified as appropriate without impairing the objectives of the present invention. For example, the center main groove 10 and the shoulder main groove 11 may be main grooves that extend in a zigzag pattern in the circumferential direction of the tire. Also, the number of center main grooves 10 does not have to be one, but may be multiple, and the number of center ribs 20 will change accordingly. For example, if two center main grooves 10 are provided, three center ribs 20 will be formed. In this case, it is preferable that groove bottom protrusions 50 are provided in each of the two center main grooves 10. [Explanation of Symbols]

[0057] 1 Pneumatic tire, 2 Tread, 10 Center main groove, 10A Groove bottom, 10B Curved surface, 10C Flat surface, 10D Inclined surface, 11 Shoulder main groove, 11A Groove bottom, 11B Curved surface, 11C Inclined surface, 20 Center rib, 21 Shoulder rib, 30, 40 Axial groove, 31, 32, 41, 42 Bending point, 33, 43 Straight section, 34 Sipe, 50 Groove bottom projection, 51 Curved surface, 52 Flat surface, 60 Narrow groove, 70 Notch, 80, 81 One-sided closed sipe, CL Tire equator, E Contact edge

Claims

1. Shoulder main grooves are provided on both ends in the axial direction of the tire, A center main groove is provided on the central side in the tire axial direction from the aforementioned shoulder main groove, The tread pattern includes a plurality of ribs partitioned by the shoulder main groove and the center main groove, Multiple of the aforementioned ribs have axial grooves formed in them, which mainly extend in the direction of the tire axis. The axial groove includes a bending point and connects to at least one of the shoulder main groove and the center main groove. The adjacent axial grooves of the multiple ribs are arranged offset in the circumferential direction of the tire, in a pneumatic tire. The rib comprises shoulder ribs located on both ends in the tire axial direction of the shoulder main groove, and a center rib located on the central side in the tire axial direction of the shoulder main groove. The center rib is provided with a triangular notch in the center of the block separated by the center main groove and the axial groove, which opens into the center main groove. The aforementioned center main groove has a plurality of groove bottom protrusions that are intermittently formed in the circumferential direction of the tire, The groove bottom projection is longer in the tire circumferential direction than in the tire axial direction. A pneumatic tire in which all or some of the multiple groove bottom protrusions are located opposite the notches.

2. The pneumatic tire according to claim 1, wherein some of the multiple groove bottom protrusions are located on the extension of the axial groove.

3. The pneumatic tire according to claim 1, wherein the amount of displacement of adjacent axial grooves that straddle the center main groove is smaller than the amount of displacement of adjacent axial grooves that straddle the shoulder main groove.

4. The pneumatic tire according to claim 1, wherein the amount of circumferential displacement of adjacent axial grooves that straddle the center main groove is 5% to 20% of the circumferential length of one pitch of the tire.

5. The pneumatic tire according to claim 1, wherein the depth of the axial groove formed in the center rib is 10% or more and 30% or less of the depth of the center main groove.

6. The pneumatic tire according to claim 1, wherein sipes are provided at the bottom of the axial groove formed in the center rib, with both ends connected to at least one of the center main groove and the shoulder main groove.

7. The pneumatic tire according to claim 6, wherein the sum of the axial groove and the sipe formed at the bottom of the axial groove is 50% or more and 90% or less of the depth of the center main groove.

8. The pneumatic tire according to claim 1, wherein the center rib is provided with a narrow groove that connects the axial groove and is inclined in the direction of the tire axis.

9. The pneumatic tire according to claim 8, wherein the narrow groove is inclined at an angle of 5° to 30° with respect to a straight line, assuming that the straight line is parallel to the circumferential direction of the tire.

10. The pneumatic tire according to claim 8, wherein the depth of the fine groove is 10% or more and 30% or less of the depth of the center main groove.

11. The pneumatic tire according to claim 1, wherein the axial groove formed in the shoulder rib connects to the main shoulder groove and closes within the shoulder rib.

12. The pneumatic tire according to claim 1, wherein the depth of the axial groove formed in the shoulder rib is 5% or more and 30% or less of the depth of the shoulder main groove.

13. The pneumatic tire according to claim 1, wherein the axial length of the shoulder rib is the same as or greater than the axial length of the center rib.

14. The pneumatic tire according to claim 1, wherein the shoulder rib is provided with a one-sided closed sipe that opens into the shoulder main groove and closes within the shoulder rib.

15. The pneumatic tire according to claim 14, wherein the tire circumferential spacing of the one-sided closed sipes is 10% or more and 30% or less of the tire circumferential length of one pitch.

16. The pneumatic tire according to claim 14, wherein the axial length of the one-sided closed sipe is 1% or more and 10% or less of the axial length of the shoulder rib.

17. The pneumatic tire according to claim 14, wherein the depth of the one-sided closed sipe is 50% or more and 90% or less of the depth of the shoulder main groove.

18. The pneumatic tire according to claim 1, wherein the center rib is provided with a one-sided closed sipe that opens into the shoulder main groove and closes within the center rib.

19. The pneumatic tire according to claim 1, wherein the height of the groove bottom projection is 1.5 mm or more and 5.0 mm or less.

20. The pneumatic tire according to claim 1, wherein the groove bottom protrusions are provided in a number of two to six within one pitch.

21. The pneumatic tire according to any one of claims 1 to 20, wherein the axial length of the groove bottom projection is 15% or more and 40% or less of the axial length of the center main groove.

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