Heavy duty pneumatic tires

Abstract

To provide a pneumatic tire for heavy load that can suppress chipping of a sacrifice rib.SOLUTION: A shoulder rib 42 provided on a tread 16 comprises: a sub groove 60 extending along a tire circumferential direction on a tire width direction inner side Wi of a ground contact end E; a sacrifice rib 422 formed on a tire width direction outer side Wo of the sub groove 60; and an inclined part 48 which is provided on the tire width direction outer side Wo of the sacrifice rib 422, and expands to the tire width direction outer side Wo in a direction of a tire radial inward direction Ri beyond the ground contact end E. A groove bottom 64B of the sub groove 60 passes a tire radial direction inside end of the inclined part 48, and is provided within a range of 1 mm from a surface S0 parallel to a tread surface 422a of the sacrifice rib 422 to both sides respectively in the tire radial direction.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a heavy duty pneumatic tire. [Background technology]

[0002] Heavy-duty pneumatic tires mounted on trucks, buses, etc., usually have a tendency to have higher ground pressure near the ground-contact ends of the shoulder ribs of the tread during driving. As a result, uneven wear can become a problem, in which the amount of wear near the ground-contact ends of the shoulder ribs is greater than the other land portions of the tread.

[0003] As a method of suppressing such uneven wear, a tire has been proposed in which a secondary groove extending circumferentially along the tire near the ground contact end of the shoulder rib is provided to divide the shoulder rib into a main rib on the inner side in the tire width direction and a sacrificial rib on the outer side in the tire width direction, thereby reducing uneven wear of the main rib, which makes a large contribution to actual tire performance (for example, Patent Documents 1 and 2 listed below).

[0004] However, in Patent Documents 1 and 2, when a relatively large frictional force acts on the sacrificial rib, cracks originating from the groove bottom of the sub-groove occur in the sacrificial rib, which tends to cause partial chipping of the sacrificial rib. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2001-97006 [Patent Document 2] Patent Publication No. 2001-260612 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a heavy-duty pneumatic tire that has a secondary groove extending circumferentially around the tire near the ground-contact end of the shoulder rib and a sacrificial rib provided on the outer side of the secondary groove in the tire width direction, and that can reduce damage to the sacrificial rib. [Means for solving the problem]

[0007] The heavy-duty pneumatic tire of this embodiment includes a pair of left and right beads, a pair of left and right sidewalls provided on the tire radial outer side of the pair of left and right beads, and a tread provided between the pair of left and right sidewalls so as to connect the radial outer ends of the pair of left and right sidewalls to each other. The tread includes a plurality of main grooves extending in the tire circumferential direction and a plurality of ribs partitioned by the main grooves. The main groove includes a shoulder main groove provided on the outer side in the tire width direction. The rib includes a shoulder rib formed on the outer side in the tire width direction of the shoulder main groove. The shoulder rib includes a sub-groove extending along the tire circumferential direction on the tire width inner side of the ground contact edge, a sacrificial rib formed on the outer side in the tire width direction of the sub-groove, and an inclined portion provided on the outer side in the tire width direction of the sacrificial rib and expanding outward in the tire width direction as it moves inward in the tire radial direction from the ground contact edge. The groove bottom of the sub-groove passes through the tire radial inner end of the inclined portion and is provided within a range of 1 mm on both sides in the tire radial direction from a plane parallel to the tread surface of the sacrificial rib. Effect of the Invention

[0008] The above-described heavy-duty pneumatic tire can suppress the occurrence of cracks originating from the bottom of the auxiliary groove, and can suppress damage to the sacrificial rib. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a half cross-sectional view of a heavy-duty pneumatic tire according to a first embodiment of the present invention; [Diagram 2] Enlarged view of the main part of Figure 1 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, a heavy-duty pneumatic tire (hereinafter, sometimes referred to as a pneumatic tire) according to one embodiment of the present invention will be described with reference to the drawings. In this specification, the dimensions of each part of the pneumatic tire and the maximum tire width position are values ​​measured in an unloaded state in which the pneumatic tire is mounted on a regular rim and inflated to a regular internal pressure. The regular rim is a rim that is determined for each tire by a standard system including the standard on which the tire is based, for example, a standard rim for JATMA, and a "Measuring Rim" for TRA and ETRTO. The regular internal pressure is an air pressure that is determined for each tire by each standard in a standard system including the standard on which the tire is based, and in the case of truck and bus tires and light truck tires, it is the 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.

[0011] 1 is a right half cross-sectional view of a pneumatic tire 10 according to an embodiment, taken along a meridian cross section including the tire axis. Note that since the pneumatic tire 10 is a symmetrical tire, the left half is not shown.

[0012] 1 includes a pair of left and right beads 12, a pair of left and right sidewalls 14 extending radially outward from the beads 12, a tread 16 that constitutes the tread surface, and a pair of left and right buttresses 18 arranged on the tire radially inner side of the tread 16. Here, the buttresses 18 are boundary regions between the tread 16 and the sidewalls 14, and are provided so as to connect between the tread 16 and the sidewalls 14.

[0013] The pneumatic tire 10 includes a carcass ply 20 that is toroidally disposed between a pair of beads 12. A ring-shaped bead core 22 is embedded in each of the pair of beads 12.

[0014] The carcass ply 20 runs from the tread 16 through the buttresses 18 and sidewalls 14, and is anchored by bead cores 22 at the beads 12, reinforcing the beads 12, sidewalls 14, buttresses 18, and tread 16. In this example, the carcass ply 20 is anchored by folding back both ends around the bead cores 22 from the inside to the outside in the tire width direction. An inner liner 24 for retaining air pressure is disposed on the inside of the carcass ply 20.

[0015] The carcass ply 20 is made of at least one ply in which reinforcing cords such as steel cords are arranged at a predetermined angle (for example, 70° to 90°) with respect to the circumferential direction of the tire and covered with topping rubber, and in this example, it is composed of one ply.

[0016] In the bead 12, a bead filler 34 made of a hard rubber material is disposed on the outer circumferential side of the bead core 22 and extends in a tapered shape toward the outer side Ro in the tire radial direction.

[0017] A sidewall rubber 32 is provided on the sidewall 14 outside the carcass ply 20 (i.e., on the tire outer surface side). The sidewall rubber 32 extends from the vicinity of the bead 12 toward the tire radially outward Ro, and is provided so as to straddle the bead 12 and the tread rubber 28. An outer end 32A in the tire radial direction of the sidewall rubber 32 overlaps an end 28A of the tread rubber 28 (on the tire outer surface side) and is disposed on the tire outer surface.

[0018] A belt 26 is disposed on the outer circumferential side of the carcass ply 20 in the tread 16. That is, the belt 26 is provided between the carcass ply 20 and the tread rubber 28 in the tread 16. The belt 26 is made up of a plurality of crossed belt plies in which belt cords are arranged at a predetermined angle (for example, 10° to 35°) with respect to the tire circumferential direction. As the belt cords, steel cords or organic fiber cords having high tensile strength are used.

[0019] In this example, the belt 26 has a four-layer structure including a first belt 26A located at the innermost side Ri in the tire radial direction, and a second belt 26B, a third belt 26C, and a fourth belt 26D layered in that order on the outer circumferential side of the first belt 26A.

[0020] A plurality of main grooves 36, preferably three or more (four in this embodiment), extending in the tire circumferential direction are provided on the surface of the tread 16. Specifically, the main grooves 36 are composed of a pair of center main grooves 36A arranged on both sides of the tire equatorial plane CL, and a pair of shoulder main grooves 36B provided on the outer side Wo in the tire width direction of the pair of center main grooves 36A. The outer side Wo in the tire width direction refers to the side away from the tire equatorial plane CL in the tire width direction W.

[0021] Due to the four main grooves 36, a central rib 38 is formed between the two center main grooves 36A, an intermediate rib 40 is formed between the center main groove 36A and the shoulder main grooves 36B, and a shoulder rib 42 is formed on the outer side Wo in the tire width direction of the two shoulder main grooves 36B in the tread 16. The groove width at the opening end of each main groove 36 is, for example, 9 mm or more and 12 mm or less.

[0022] The main grooves 36 may be zigzag grooves extending in the tire circumferential direction while bending in the tire width direction W, or may be linear grooves extending straight in the tire circumferential direction. In the present embodiment, the central rib 38, intermediate rib 40 and shoulder ribs 42 are described as ribs that are continuous in the tire circumferential direction, but the central rib 38 and intermediate rib 40 may be block rows divided in the tire circumferential direction by lateral grooves.

[0023] The outer end in the tire width direction of the tread surface (outer surface) 42a of the shoulder rib 42 forms a tread ground contact edge E, and is connected to a buttress 18 that extends radially inward and constitutes an upper part of the tire side surface.

[0024] 1 and 2, an inclined portion 48 extending from the ground contact end E to the inside Ri in the tire radial direction is formed on the outer surface of the buttress 18. The inclined portion 48 is inclined so as to widen toward the outside Wo in the tire width direction as it moves from the ground contact end E to the inside Ri in the tire radial direction. In this embodiment, the cross-sectional shape of the inclined portion 48 as shown in Fig. 2 has a curved shape that bulges gently outward in the tire radial direction.

[0025] A bent portion 49 bent toward the inner side Ri in the tire radial direction is provided on the outer side Wo in the tire width direction of the inclined portion 48. The inclined portion 48 is inclined such that the ground contact end E is the outer end in the tire radial direction of the inclined portion 48, the bent portion 49 is the inner end in the tire radial direction of the inclined portion 48, and the diameter decreases from the ground contact end E to the bent portion 49 toward the outer side Wo in the tire width direction.

[0026] The length of the inclined portion 48 in the tire radial direction R, i.e., the length H in the tire radial direction R from the ground contact end E to the bent portion 49, is, for example, 5 mm or more and 20 mm or less. The length of the inclined portion 48 in the tire width direction W, i.e., the length L in the tire width direction W from the ground contact end E to the bent portion 49, is, for example, 5 mm or more and 15 mm or less.

[0027] Such an inclined portion 48 appropriately weakens the rigidity of the shoulder rib 42 on the side of the ground contact end E, thereby improving wandering performance when going over bumps in the road surface such as ruts.

[0028] The shoulder rib 42 is provided with a sub groove 60 along the tire circumferential direction on the inner side Wi in the tire width direction of the ground contact edge E. The sub groove 60 divides the shoulder rib 42 into a main body rib 421 on the inner side Wi in the tire width direction and a sacrificial rib 422 on the outer side Wo in the tire width direction.

[0029] The sub groove 60 is a recessed groove that extends linearly along the tire circumferential direction, and has a groove width M at an opening end that is set narrower than the groove width at an opening end of the shoulder main groove 36B. The groove width M at the opening end of the sub groove 60 is, for example, 2.0 mm or more and 2.5 mm or less.

[0030] The sub groove 60 is recessed from the tread surface 42a toward the tire radially inward side Ri, and the groove wall 62 of the sub groove 60 is preferably parallel to the tire equatorial plane CL. The bottom 64 of the sub groove 60 is preferably curved so as to bulge radially inward. In the sub groove 60, the flat groove wall 62 is connected to a tire radially outer end 64A of the bottom 64 provided in a curved shape.

[0031] The deepest portion 64B of the secondary groove 60 (hereinafter, this portion may be referred to as the groove bottom of the secondary groove 60) passes through the tire radially inner end (i.e., the bent portion 49) of the inclined portion 48, and is provided within a range of 1 mm on each side in the tire radial direction from a plane (hereinafter, this plane may be referred to as the reference plane) S0 parallel to the tread surface 422a of the sacrificial rib 422. In other words, the secondary groove 60 is recessed from the tread surface 42a to the tire radially inner side Ri so that the groove bottom 64B of the secondary groove 60 is located in an area sandwiched between a first surface S1 1 mm away from the reference plane S0 toward the tire radially inner side and a second surface S2 1 mm away from the reference plane S0 toward the tire radially outer side, and the distance P from the reference plane S0 to the groove bottom 64B of the secondary groove 60 is within 1 mm.

[0032] The tire radial outer end 32A of the sidewall rubber 32 is preferably located at a position Ro outward in the tire radial direction from the bent portion 49 so as to be located at the inclined portion 48. The tire radial outer end 32A of the sidewall rubber 32 passes through the tire radial outer end 64A of the bottom 64 of the sub groove 60 and is preferably located at a position Ri inward in the tire radial direction from the third surface S3 parallel to the reference surface S0. In other words, the tire radial outer end 32A of the sidewall rubber 32 is preferably located between the reference surface S0 and the above-mentioned third surface S3.

[0033] In addition, it is preferable that the maximum thickness T of the sacrificial rib 422 (the length from the groove bottom 64B of the secondary groove 60 to the outer surface of the buttress 18 along a plane parallel to the above-mentioned reference plane S0) is 80% or more and 100% or less of the maximum protruding height D of the sacrificial rib 422 (the length from the groove bottom 64B of the secondary groove 60 to the tread surface 422a of the sacrificial rib 422).

[0034] The secondary groove 60 is preferably located on the outer side Wo in the tire width direction of 7.5% of the tire cross-sectional width from the ground contact edge E, and is preferably located on the inner side Wi in the tire width direction of 2.5% of the tread contact width (distance between the left and right ground contact edges E) L from the ground contact edge E. The tire cross-sectional width is the outermost position on the surface of the sidewall 14 in the tire width direction W, and is the position on the sidewall surface at the maximum tire width.

[0035] In the pneumatic tire 10 configured as described above, the groove bottom 64B of the sub groove 60 is provided within a range of 1 mm from the reference plane S0 to the tire radially inward Ri, so that the maximum protruding height D of the sacrificial rib 422 defined by the sub groove 60 does not become too large, and damage to the sacrificial rib 422 can be suppressed. In addition, since the groove bottom 64B of the sub groove 60 is provided within a range of 1 mm from the reference plane S0 to the tire radially outward Ro, even if the sacrificial rib 422 is provided with an inclined portion 48, the maximum thickness T of the sacrificial rib 422 can be ensured, and damage to the sacrificial rib 422 can be suppressed.

[0036] In this embodiment, when the maximum thickness T of the sacrificial rib 422 is 80% or more and 100% or less of the maximum protruding height D of the sacrificial rib 422, the shear strain applied to the root portion of the sacrificial rib 422 can be suppressed.

[0037] Furthermore, in this embodiment, by positioning the tire radially outer end 32A of the sidewall rubber 32 on the tire radially outer side Ro of the reference plane S0, the end of the sidewall rubber 32 can be positioned in a position that is less susceptible to distortion in the sacrificial rib 422, and tire damage originating from the tire radially outer end 32A of the sidewall rubber 32 can be suppressed.

[0038] Furthermore, by positioning the tire radially outer end 32A of the sidewall rubber 32 radially inward Ri of the third surface S3 described above, the tire radially outer end 32A can be positioned to avoid positions on the sacrificial rib 422 that are prone to movement, further reducing tire damage. EXAMPLES

[0039] Examples and comparative examples were carried out for heavy-duty pneumatic radial tires with tire sizes of 11R22.5 14PR. The basic configuration of each tire of the examples and comparative examples is as described in the above embodiment, and tire models were created by setting each parameter as shown in Table 1 below. In Table 1 below, the distance P from the reference plane S0 to the groove bottom 64B of the sub-groove 60 is expressed as a positive amount for the amount of movement from the reference plane S0 toward the tire radial outward Ro, and a negative amount for the amount of movement from the reference plane S0 toward the tire radial inward Ri. The crack resistance of each prototype tire was evaluated. The evaluation method is as follows.

[0040] Crack resistance: For the tire models produced, the amount of shear strain acting on the root of the sacrificial rib in a static contact state under maximum air pressure and maximum load was calculated by analysis using the finite element method. The calculated strain was evaluated using an index with the strain in Example 1 set at 100. The smaller the index, the smaller the amount of strain acting on the root of the sacrificial rib and the better the crack resistance.

[0041] [Table 1]

[0042] The results are shown in Table 1. In the example, the shear strain applied to the root portion of the sacrificial rib could be suppressed compared to Comparative Examples 1 to 4, and the crack resistance could be improved.

[0043] Although several embodiments have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. [Explanation of symbols]

[0044] 10...pneumatic tire, 12...bead, 14...sidewall, 16...tread, 18...buttress, 20...carcass ply, 22...bead core, 24...inner liner, 26...belt, 28...tread rubber, 32...sidewall rubber, 36...main groove, 36A...center main groove, 36B...shoulder main groove, 38...center rib, 40...intermediate rib, 42...shoulder rib, 48...inclined portion, 49...bent portion, 60...secondary groove, 62...groove wall, 64...bottom, 64A...outer end, 64B...groove bottom, 421...main rib, 422...sacrificial rib

Claims

1. The tire has a pair of left and right beads, a pair of left and right sidewalls provided on radially outer sides of the pair of left and right beads, and a tread provided between the two sidewalls so as to connect radially outer ends of the pair of left and right sidewalls to each other, The tread includes a plurality of main grooves extending in a tire circumferential direction and a plurality of ribs defined by the main grooves, The main groove includes a shoulder main groove provided on the outer side in the tire width direction, The rib includes a shoulder rib formed on an outer side of the shoulder main groove in the tire width direction, The shoulder rib includes a sub-groove extending along the tire circumferential direction on the inner side in the tire width direction of the ground contact end, a sacrificial rib formed on the outer side in the tire width direction of the sub-groove, and an inclined portion provided on the outer side in the tire width direction of the sacrificial rib and expanding outward in the tire width direction as it moves inward in the tire radial direction from the ground contact end, The inclined portion has a cross-sectional shape that is curved and bulges outward in the tire radial direction, A groove bottom of the sub-groove passes through the radially inner end of the inclined portion and is provided within a range of 1 mm on both sides in the radial direction of the tire from a plane parallel to the tread surface of the sacrificial rib, A heavy-duty pneumatic tire in which a radially outer end of a sidewall rubber provided on the sidewall is located radially outward from a radially inner end of the inclined portion, and is located radially inward from a plane that passes through the radially outer end of a bottom of the auxiliary groove and is parallel to the tread surface of the sacrificial rib.

2. 2. The heavy-duty pneumatic tire according to claim 1, wherein the maximum thickness of the sacrificial rib is 80% or more and 100% or less of the length from the bottom of the auxiliary groove to the tread surface of the sacrificial rib.

3. 3. The heavy duty pneumatic tire according to claim 1, wherein a groove wall of the auxiliary groove is provided parallel to the tire equatorial plane.

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