tire

Abstract

To provide a tire improved in center wear resistance.SOLUTION: A tire 1 is provided with a plurality of lateral grooves 3 joining tread ends Te at both sides to each other. The lateral groove 3 includes a pair of outer groove parts 8 extending to inside in a tire axial direction, from the tread ends Te toward a tire equator C side and an inner groove part 9 joining the pair of outer groove parts 8 to each other. The pair of outer groove parts 8 are inclined in the same direction with respect to the tire axial direction. The inner groove part 9 is inclined in a direction opposite to the direction of the outer groove parts 8 with respect to the tire axial direction. A groove depth d2 of the inner groove part 9 is smaller than groove depths d1 of the outer groove parts 8.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] The following Patent Document 1 describes a pneumatic tire in which a tread portion is formed with a plurality of lug main grooves extending in the tire width direction on both sides of the tire equator and opening at the tread ends, and a center oblique groove connecting the lug main grooves located on both sides of the tire equator to each other. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-167782 A Summary of the Invention [Problem to be solved by the invention]

[0004] For tires that are often used on rough roads, such as pneumatic truck tires, the ground contact shape of the tread changes significantly depending on the load. In particular, pneumatic tires mounted on drive wheels have a problem in that large ground contact pressure acts on the tread crown when the tire is unloaded, which makes the center wear more likely to occur.

[0005] The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide a tire, particularly an OR (off-the-road) tire, capable of effectively suppressing center wear. [Means for solving the problem]

[0006] The present invention is a tire having a tread portion, in which a plurality of lateral grooves are provided connecting the tread ends on both sides, each of the lateral grooves including a pair of outer groove portions extending axially inward from the tread ends on both sides, and an inner groove portion connecting the pair of outer groove portions, the pair of outer groove portions being inclined in the same direction relative to the tire axial direction, the inner groove portion being inclined in the opposite direction to the outer groove portion relative to the tire axial direction, and the groove depth of the inner groove portion being smaller than the groove depth of each of the pair of outer groove portions.

[0007] In the tire according to the present invention, it is preferable that the groove depth of the inner groove portion is 65% to 85% of the groove depth of the outer groove portion.

[0008] In the tire according to the present invention, it is preferable that the angle of the inner groove portion with respect to the axial direction of the tire is 20 to 50 degrees.

[0009] In the tire according to the present invention, it is desirable that the outer groove portion includes a first portion extending from the tread end toward the tire equator, and a second portion connected to the first portion and inclined at a larger angle relative to the tire axial direction than the first portion.

[0010] In the tire according to the present invention, it is preferable that the groove width of the inner groove portion is smaller than the groove width of the first portion.

[0011] In the tire according to the present invention, it is preferable that the groove width of the inner groove portion is 60% to 80% of the groove width of the first portion.

[0012] In the tire according to the present invention, it is preferable that the length of the first portion in the tire axial direction is 5% to 20% of the tread width.

[0013] In the tire according to the present invention, it is preferable that an angle of the first portion with respect to the tire axial direction is 10 degrees or less.

[0014] In the tire according to the present invention, it is preferable that the angle of the second portion with respect to the tire axial direction is 10 to 30 degrees or less.

[0015] In the tire according to the present invention, it is preferable that the tread portion includes a crown region having an axial width of 40% of the tread width from the tire equator to both sides in the tire axial direction, and the inner groove portion is provided in the crown region.

[0016] In the tire according to the present invention, it is preferable that the tread portion is provided with a first connecting groove connecting the inner groove portions of the lateral grooves adjacent to each other in the tire circumferential direction.

[0017] In the tire according to the present invention, it is preferable that a groove depth of the first connecting groove is smaller than a groove depth of the inner groove portion.

[0018] In the tire according to the present invention, it is preferable that the first connecting groove includes a widened portion in which the groove width increases toward the inner groove portion.

[0019] In the tire according to the present invention, it is preferable that the widened portion is continuous with the inner groove portion.

[0020] In the tire according to the present invention, it is preferable that the length of the widened portion is 10% to 40% of the length of the first connecting groove.

[0021] In the tire according to the present invention, it is preferable that the tread portion is provided with a second connecting groove connecting the outer groove portions of the lateral grooves adjacent to each other in the tire circumferential direction.

[0022] In the tire according to the present invention, it is preferable that the outer groove portion is provided with a projection for preventing stone trapping at a groove bottom where the second connecting groove is continuous.

[0023] The tyre according to the invention is preferably for heavy loads. Effect of the Invention

[0024] By employing the above-mentioned configuration, the tire of the present invention can suppress center wear. [Brief description of the drawings]

[0025] [Figure 1] 1 is a plan view of a tread portion showing one embodiment of the present invention. [Diagram 2] 2 is a cross-sectional view taken along line AA in FIG. 1. [Diagram 3] FIG. [Figure 4] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 is a plan view of a tread portion 2 of a tire 1 showing one embodiment of the present invention. The present invention is applied to, for example, heavy-duty OR tires that are often used on rough roads such as dirt roads. However, the present invention can also be applied to pneumatic tires for passenger cars and light trucks, or non-pneumatic tires that are not filled with compressed air.

[0027] 1, a tire 1 of this embodiment is provided with a plurality of lateral grooves 3 connecting both tread ends Te in a tread portion 2. As a result, the tread portion 2 is provided with a plurality of land portions 4 arranged between the lateral grooves 3 adjacent to each other in the tire circumferential direction.

[0028] In this specification, the "tread end Te" refers to the axially outermost contact position when the tire 1 in a normal state is placed on a flat surface with a normal load and a camber angle of 0 degrees. The axial distance between the tread ends Te on both sides is the tread width TW.

[0029] In the case of a pneumatic tire for which various standards are established, the "normal state" refers to a state in which the tire is mounted on a normal rim (not shown), inflated to the normal internal pressure, and no load is applied. In this specification, unless otherwise specified, the dimensions of each part of the tire are values ​​measured in the normal state.

[0030] A "genuine rim" is a rim that is defined for each tire by the standard system that includes the standard on which the tire is based. For example, in the case of JATMA, it is called a "standard rim," in the case of TRA, it is called a "Design Rim," and in the case of ETRTO, it is called a "Measuring Rim."

[0031] "Normal internal pressure" is the air pressure set for each tire by each standard in the standard system on which the tire is based. In the case of JATMA, it is the "maximum air pressure." In the case of TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." In the case of ETRTO, it is the "INFLATION PRESSURE."

[0032] In the case of pneumatic tires for which various standards are established, the "normal load" is the load that is established for each tire under the system of standards including the standards on which the tire is based. In the case of JATMA, it is the "maximum load capacity," in the case of TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and in the case of ETRTO, it is the "LOAD CAPACITY."

[0033] Each of the lateral grooves 3 includes a pair of outer groove portions 8 extending axially inward from both tread ends Te, and an inner groove portion 9 connecting the pair of outer groove portions 8. The pair of outer groove portions 8 are inclined in the same direction relative to the tire axial direction (upward to the right in the figure). The inner groove portion 9 is inclined in the opposite direction to the outer groove portion 8 relative to the tire axial direction (downward to the right in the figure). Such lateral grooves 3 distribute the load during running in multiple directions, suppress sliding deformation of the tread portion 2, and suppress wear of the land portion 4.

[0034] FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. As shown in FIG. 2, the groove depth d2 of the inner groove portion 9 is smaller than the groove depth d1 of each of the pair of outer groove portions 8. As a result, the rigidity of the land portion 4 on the tire equator C side, which is subjected to a relatively larger ground pressure than the land portion 4 on the tread end Te side during straight running, is maintained high, and center wear can be particularly suppressed. In this specification, such tire performance is referred to as "center wear resistance performance." In addition, the land portion 4 on the tire equator C side comes into contact with the road surface even under a low load load condition, compared to the land portion 4 on the tread end Te side. In this regard, in this embodiment, since the groove depth d2 of the inner groove portion 9 is small, stone bite into the inner groove portion 9 is suppressed, and excellent stone bite resistance performance is exhibited, particularly under a low load load condition. The "low load load condition" refers to a state in which a load of 30% or less of the normal load is applied to the tire 1 in a normal state.

[0035] In order to exert the above-mentioned effect, the groove depth d2 of the inner groove portion 9 is preferably 85% or less of the groove depth d1 of the outer groove portion 8, and more preferably 80% or less. If the groove depth d2 of the inner groove portion 9 is excessively small, the driving performance (traction) on rough roads may decrease. For this reason, the groove depth d2 of the inner groove portion 9 is preferably 65% ​​or more of the groove depth d1 of the outer groove portion 8, and more preferably 70% or more. Although not particularly limited, the groove depth d2 of the inner groove portion 9 is preferably 17 mm or more, more preferably 19 mm or more, and more preferably 25 mm or less, and more preferably 23 mm or less.

[0036] 1, the tread portion 2 includes a crown region Cr having an axial width of 40% of the tread width TW on both sides of the tire equator C in the tire axial direction, and a pair of shoulder regions Sh disposed between the crown region Cr and the tread end Te. The crown region Cr is subjected to a relatively larger ground pressure than the shoulder regions Sh during straight running.

[0037] The tread portion 2 of this embodiment further includes a first connecting groove 6 connecting the inner groove portions 9 adjacent to each other in the tire circumferential direction, and a second connecting groove 7 connecting the outer groove portions 8 adjacent to each other in the tire circumferential direction. In this embodiment, the second connecting groove 7 is arranged on both sides of the tire equator C. As a result, the land portion 4 of this embodiment is divided into a pair of inner blocks 4A sandwiched between the first connecting groove 6 and the second connecting groove 7, and a pair of outer blocks 4B sandwiched between the second connecting groove 7 and the tread edge Te.

[0038] The circumferential pitch P1 of the lateral grooves 3 is preferably 20% or more of the tread width TW, more preferably 25% or more, more preferably 40% or less, and even more preferably 35% or less. Since the pitch P1 of the lateral grooves 3 is 20% or more of the tread width TW, the rigidity of the tread portion 2 is maintained high and wear is suppressed, thereby improving center wear resistance and life performance. Since the pitch P1 of the lateral grooves 3 is 40% or less of the tread width TW, large traction can be exerted and driving performance on rough roads is improved.

[0039] Fig. 3 is a plan view of the tread portion 2 of this embodiment. As shown in Fig. 3, the outer groove portion 8 includes a first portion 10 extending from the tread edge Te toward the tire equator C, and a second portion 11 continuing to the first portion 10 and inclining at an angle θ1b with respect to the tire axial direction larger than that of the first portion 10. In this specification, the groove angle is measured at the groove width center line.

[0040] In the present embodiment, the groove width W1 of the outer groove portion 8 decreases from the tread end Te toward the tire equator C. The groove width W1 of the outer groove portion 8 decreases continuously from the axially outer end 8e to the axially inner end 8i. Such an outer groove portion 8 maintains high rigidity of the tread portion 2 on the tire equator C side, improving center wear resistance. In addition, even if stone trapping occurs, the outer groove portion 8 can use the rolling motion of the tire 1 to expel stones from the tread end Te where the groove width W1 is large, improving stone trapping resistance.

[0041] In this embodiment, the first portion 10 and the second portion 11 are connected via a bent portion 8k. Such a bent portion 8k not only distributes the load during running to improve uneven wear resistance, but also suppresses block chipping that is likely to occur at the tread end Te. The first portion 10 and the second portion 11 extend, for example, in a straight line. In this embodiment, the bent portion 8k is disposed in the shoulder region Sh (shown in FIG. 1). This effectively exerts the above-mentioned effect. Note that the outer groove portion 8 may have the first portion 10 and the second portion 11 connected in an arc shape (not shown).

[0042] The axial length La of the first portion 10 is preferably 5% or more of the tread width TW, more preferably 10% or more, more preferably 20% or less, and even more preferably 15% or less. Since the length La of the first portion 10 is 5% or more of the tread width TW, the effect of discharging stones from the tread end Te is enhanced. Stones caught in the outer groove portion 8 are smoothly discharged by using the first portion 10. Since the length La of the first portion 10 is 20% or less of the tread width TW, excessive decrease in rigidity of the crown region Cr is suppressed.

[0043] In this embodiment, the first portion 10 is inclined with respect to the tire axial direction. Such a first portion 10 distributes the load in the tire circumferential direction during straight running, improving the life performance. If the angle θ1a of the first portion 10 with respect to the tire axial direction is excessively large, the rigidity in the tire axial direction of the land portion 4 near the first portion 10 decreases, and block chipping is likely to occur, which may actually deteriorate the life performance. From this viewpoint, the angle θ1a of the first portion 10 is preferably larger than 0 degrees, preferably 10 degrees or less, and more preferably 5 degrees or less.

[0044] The groove width W1b of the second portion 11 is preferably 70% or more, more preferably 75% or more, and more preferably 90% or less, and even more preferably 85% or less of the groove width W1a of the first portion 10. This maintains a good balance between the rigidity of the tread portion 2 on the tire equator C side and the rigidity of the tread portion 2 on the tread end Te side, improving the life performance. The groove width W1a of the first portion 10 and the groove width W1b of the second portion 11 are each an average value of the maximum groove width and the minimum groove width.

[0045] The angle θ1b of the second portion 11 with respect to the tire axial direction is preferably 10 degrees or more, and more preferably 15 degrees or more. This allows the load in the tire circumferential direction during straight running to be more dispersed. The angle θ1b of the second portion 11 is preferably 30 degrees or less, and more preferably 25 degrees or less. This maintains the tire axial rigidity of the land portion 4 near the second portion 11, and suppresses chipping or chipping of the tread portion 2 due to cornering. Although not particularly limited, the difference (θ1b-θ1a) between the angle θ1b of the second portion 11 and the angle θ1a of the first portion 10 is preferably 5 degrees or more, more preferably 10 degrees or more, more preferably 25 degrees or less, and more preferably 20 degrees or less.

[0046] The outer groove portion 8 is provided with a protrusion 12 for preventing stone trapping at a groove bottom 8s where the second connecting groove 7 is continuous. The protrusion 12 extends, for example, away from the groove wall of the outer groove portion 8 and outward in the tire radial direction.

[0047] In this embodiment, the protrusions 12 are provided at the groove bottom 11s of the second portion 11. This suppresses stone trapping in the second portion 11, where stones are less easily discharged than in the first portion 10. For example, the protrusions 12 are not provided in the first portion 10 extending from the tread end Te. Moreover, in this embodiment, the protrusions 12 are not provided in the inner groove portion 9 having a narrow groove depth.

[0048] The projection 12 includes a pair of outer projections 13 arranged on both sides in the longitudinal direction, and an inner projection 14 connecting the pair of outer projections 13. In this embodiment, the inner projection 14 is formed with a narrower width than the outer projection 13. In this type of projection 12, the inner projection 14 increases the rigidity of the outer projection 13 to suppress a decrease in stone-trapping resistance, and is also useful for improving traction when driving on rough roads.

[0049] The outer protrusions 13 in this embodiment are arranged on an imaginary straight line 7k that is a smooth extension of the groove center line 7c of the second joint groove 7 in the longitudinal direction. This prevents a decrease in the rigidity of the land portion 4 near the second joint groove 7 (rigidity in the groove width direction of the second joint groove 7), and suppresses deformation of the second joint groove 7, thereby reducing the amount of stones getting caught in the second joint groove 7. In this embodiment, the outer protrusions 13 are arranged on both sides of the second joint groove 7 in the longitudinal direction.

[0050] Although not particularly limited, the width Wb of the inner protrusion 14 is desirably 20% or more, more desirably 30% or more, desirably 50% or less, and more desirably 40% or less of the width Wa of the outer protrusion 13. Moreover, the width Wa of the outer protrusion 13 is desirably 10% or more, more desirably 15% or more, desirably 30% or less, and more desirably 25% or less of the maximum groove width W1m of the second portion 11.

[0051] To improve stone trapping resistance, the axial length L2 of the protrusion 12 is preferably 35% or more, and more preferably 40% or more, of the axial length Lb of the second portion 11. To maintain traction performance when traveling on rough roads, the length L2 of the protrusion 12 is preferably 55% or less, and more preferably 50% or less, of the length Lb of the second portion 11.

[0052] In order to effectively exert the above-mentioned effect, the protrusion height h of the protrusion 12 is desirably 10% or more of the groove depth d1 (shown in FIG. 2) of the outer groove portion 8, more desirably 12% or more, preferably 20% or less, and even more desirably 18% or less.

[0053] The inner groove portion 9 of this embodiment is provided in the crown region Cr (shown in FIG. 1). The inner groove portion 9 is arranged, for example, so as to straddle the tire equator C. This further improves stone trapping resistance and center wear resistance. The axial length Lc of such an inner groove portion 9 is preferably 10% or more of the tread width TW, more preferably 15% or more, more preferably 35% or less, and even more preferably 30% or less.

[0054] The angle θ2 of the inner groove portion 9 with respect to the tire axial direction is preferably larger than the angle θ1b of the second portion 11. Such an inner groove portion 9 can further distribute the load during driving in the crown region Cr where a relatively large ground pressure acts, thereby further improving the center wear resistance. If the angle θ2 of the inner groove portion 9 is large, the traction may be reduced, and the driving performance on rough roads may be deteriorated. For this reason, the angle θ2 of the inner groove portion 9 is preferably 20 degrees or more, more preferably 30 degrees or more, more preferably 50 degrees or less, and even more preferably 40 degrees or less.

[0055] The groove width W2 of the inner groove portion 9 is formed to be smaller than, for example, the groove width W1a of the first portion 10. Such an inner groove portion 9 maintains the rigidity of the land portion 4 (inner block 4A) of the crown region Cr higher, improving the center wear resistance. In this embodiment, the inner groove portion 9 extends in the longitudinal direction with the same groove width W2.

[0056] In order to effectively exert the above-mentioned effect, the groove width W2 of the inner groove portion 9 is preferably 80% or less, more preferably 75% or less, of the groove width W1a of the first portion 10. If the groove width W2 of the inner groove portion 9 is excessively small, the running performance on rough roads may be deteriorated. For this reason, the groove width W2 of the inner groove portion 9 is preferably 60% or more, more preferably 65% ​​or more, of the groove width W1a of the first portion 10.

[0057] Fig. 4 is a plan view of the tread portion 2 of this embodiment. As shown in Fig. 4, the first connecting groove 6 is disposed so as to straddle the tire equator C, for example.

[0058] The first connecting groove 6 is formed to include a constant width portion 15 extending in the longitudinal direction with the same groove width W3a, and a pair of widened width portions 16 arranged on both sides of the constant width portion 15 and having a groove width W3b that increases toward the inner groove portion 9 (in the direction away from the constant width portion 15). In this embodiment, the widened width portions 16 have a groove width W3b that increases continuously toward the inner groove portion 9.

[0059] The widened portion 16 is continuous with, for example, the inner groove portion 9. This reduces the chance that a stone or the like will be caught between the widened portion 16 and the inner groove portion 9.

[0060] The length Le of the widened portion 16 is preferably 10% or more of the length Ld of the first connecting groove 6, more preferably 20% or more, more preferably 40% or less, and even more preferably 30% or less. Since the length Le of the widened portion 16 is 10% or more of the length Ld of the first connecting groove 6, the rigidity step of the portion where the widened portion 16 and the uniform width portion 15 are connected is suppressed. Since the length Le of the widened portion 16 is 40% or less of the length Ld of the first connecting groove 6, the length of the uniform width portion 15 is secured, and the center wear resistance performance is maintained. The length Le of the widened portion 16 and the length Ld of the first connecting groove 6 are lengths along the groove center line 15c of the uniform width portion 15.

[0061] The first connecting groove 6 is continuously inclined toward one side with respect to the tire circumferential direction. Such a first connecting groove 6 suppresses a decrease in rigidity of the crown region Cr (shown in FIG. 1) and improves center wear resistance.

[0062] The angle θ3 of the first connecting groove 6 with respect to the tire circumferential direction is preferably 45 degrees or less, more preferably 40 degrees or less, and even more preferably 35 degrees or less. Such a first connecting groove 6 helps to reduce stone bite and improve stone bite resistance. The angle θ3 of the first connecting groove 6 is preferably 15 degrees or more, and more preferably 20 degrees or more. This increases the traction provided by the first connecting groove 6, improving driving performance on rough roads. The angle θ3 of the first connecting groove 6 is measured at the groove center line 15c of the equal width portion 15, which has a longer longitudinal length than the widened portion 16.

[0063] The groove width W3a of the constant width portion 15 of the first connecting groove 6 is smaller than the groove width W2 of the inner groove portion 9, for example. Such a first connecting groove 6 has high stone trapping resistance. If the groove width W3a of the constant width portion 15 of the first connecting groove 6 is excessively smaller than the groove width W2 of the inner groove portion 9, there is a risk that the running performance due to traction on rough roads may deteriorate. For this reason, the groove width W3a of the constant width portion 15 of the first connecting groove 6 is preferably 55% or more of the groove width W2 of the inner groove portion 9, more preferably 60% or more, more preferably 75% or less, and even more preferably 70% or less.

[0064] In this embodiment, the groove depth d3 (shown in FIG. 2) of the first connecting groove 6 is smaller than the groove depth d2 of the inner groove portion 9. Such a first connecting groove 6 improves the center wear resistance and the stone trapping resistance.

[0065] In order to effectively exert the above-mentioned effect, the groove depth d3 of the first connecting groove 6 is preferably 60% or less of the groove depth d1 of the outer groove portion 8, and more preferably 55% or less. If the groove depth d3 of the first connecting groove 6 is too small, the running performance on rough roads may be deteriorated. For this reason, the groove depth d3 of the first connecting groove 6 is preferably 40% or more of the groove depth d1 of the outer groove portion 8, and more preferably 45% or more.

[0066] In this embodiment, the second connecting groove 7 is formed as a uniform width groove extending in the longitudinal direction with the same groove width W4. The second connecting groove 7 is continuously inclined in the opposite direction to the first connecting groove 6 with respect to the tire circumferential direction, for example.

[0067] In this embodiment, the second connecting groove 7 is disposed across the shoulder region Sh and the crown region Cr (as shown in FIG. 1). This maintains a good balance between the rigidity of the shoulder region Sh and the crown region Cr, improving driving performance on rough roads. For example, the second connecting groove 7 is disposed larger in the shoulder region Sh than in the crown region Cr. This maintains a high rigidity of the land portion 4 of the crown region Cr, improving center wear resistance. Note that the second connecting groove 7 may be provided only in the shoulder region Sh (not shown), for example, in order to ensure the rigidity of the land portion 4 of the crown region Cr.

[0068] In this embodiment, the groove width W4 of the second connecting groove 7 is smaller than the groove width W2 of the inner groove portion 9. Such a second connecting groove 7 improves running performance on rough roads and maintains high center wear resistance and life performance. Although not particularly limited, the groove width W4 of the second connecting groove 7 is preferably 55% or more of the groove width W2 of the inner groove portion 9, more preferably 60% or more, more preferably 75% or less, and even more preferably 70% or less.

[0069] The angle θ4 of the second connecting groove 7 with respect to the tire circumferential direction is preferably smaller than the angle θ3 of the first connecting groove 6. Such a second connecting groove 7 has excellent stone trapping resistance because, even if a stone gets caught in the groove, the stone can be smoothly removed by utilizing the rolling of the tire 1. From this viewpoint, the angle θ4 of the second connecting groove 7 is preferably 45 degrees or less, more preferably 35 degrees or less, and even more preferably 30 degrees or less. In addition, in order to improve driving performance on rough roads, the angle θ4 of the second connecting groove 7 is preferably 5 degrees or more, and even more preferably 10 degrees or more.

[0070] The groove depth d4 (shown in FIG. 2) of the second connecting groove 7 is smaller than, for example, the groove depth d1 of the outer groove portion 8. Such a second connecting groove 7 maintains high center wear resistance, life performance, and stone trapping resistance. In order to effectively exert such functions while improving driving performance on rough roads, the groove depth d4 of the second connecting groove 7 is preferably 40% or more of the groove depth d1 of the outer groove portion 8, more preferably 45% or more, more preferably 60% or less, and even more preferably 55% or less. The groove depth d4 of the second connecting groove 7 is preferably the same as, for example, the groove depth d3 of the first connecting groove 6.

[0071] Although a particularly preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the illustrated embodiment and can be modified and carried out in various forms. EXAMPLES

[0072] A pneumatic tire having the basic pattern shown in FIG. 1 was prototyped based on the specifications in Table 1, and tested for center wear resistance and stone trapping resistance. The test method was as follows.

[0073] <Center wear resistance and stone bite resistance> The test tires were mounted on each of the eight wheels (drive wheels and driven wheels) of a two-axle trailer towed by a 2DD vehicle under the following conditions, and driven on a dirt road surface. After that, the groove depth of each groove and the number of stones trapped in the groove were measured. Center wear resistance was calculated by calculating the average groove depth of each groove in the crown region, and expressed as an index with the value of Example 1 set to 100. Stone trapping resistance was also expressed as an index with the reciprocal of the number of stones in Example 1 set to 100. In each test, the higher the value, the better, and a value of 90 or more is a pass. Tire size: 295 / 75R22.5 Rim: 22.5 x 8.25 Internal pressure: 850kPa Load: 10.44kN (mileage: 5000km) Load: 34.81kN (mileage: 5000km) Traveling speed: 40~80km / h Total mileage: 10,000km In Table 1, "A" means that the inner groove is angled in the opposite direction to the outer groove, and "B" means that the inner groove is angled in the same direction as the outer groove. The test results are shown in Table 1.

[0074] [Table 1]

[0075] As shown in the table, the tires of the examples have high center wear resistance. The tires of the examples also have excellent stone trapping resistance. Furthermore, the tires of the examples were highly evaluated by the test drivers for their running performance on rough roads. [Explanation of symbols]

[0076] 1 Tire 3 Yokomizo 8 Outer groove 9 Inner groove C Tire Equator Te tread edge

Claims

1. A tire having a tread portion, The tread portion is provided with a plurality of lateral grooves connecting the tread ends on both sides, Each of the lateral grooves includes a pair of outer groove portions extending axially inward from the tread ends on both sides, and an inner groove portion connecting the pair of outer groove portions, The pair of outer groove portions are inclined in the same direction with respect to the tire axial direction, The inner groove portion is inclined in an opposite direction to the outer groove portion with respect to the tire axial direction, a groove depth of the inner groove portion is smaller than a groove depth of each of the pair of outer groove portions, A first connecting groove is provided in the tread portion to connect the inner groove portions of the lateral grooves adjacent to each other in the tire circumferential direction, The first connecting groove includes a widening portion in which the groove width increases toward the inner groove portion. tire.

2. 2. The tire according to claim 1, wherein the groove depth of the inner groove portion is 65% to 85% of the groove depth of the outer groove portion.

3. The tire according to claim 1 or 2, wherein an angle of the inner groove portion with respect to the tire axial direction is 20 to 50 degrees.

4. 4. The tire according to claim 1, wherein the outer groove portion includes a first portion extending from the tread edge toward the tire equator, and a second portion connected to the first portion and inclined at an angle larger than that of the first portion with respect to the tire axial direction.

5. The tire of claim 4 , wherein the groove width of the inner groove portion is smaller than the groove width of the first portion.

6. The tire according to claim 4 or 5, wherein the groove width of the inner groove portion is 60% to 80% of the groove width of the first portion.

7. The tire according to any one of claims 4 to 6, wherein the length of the first portion in the tire axial direction is 5% to 20% of the tread width.

8. The tire according to claim 4 , wherein an angle of the first portion with respect to the tire axial direction is equal to or smaller than 10 degrees.

9. The tire according to any one of claims 4 to 8, wherein an angle of the second portion with respect to the tire axial direction is 10 to 30 degrees or less.

10. The tread portion includes a crown region having an axial width of 40% of the tread width from the tire equator to both sides in the tire axial direction, 10. The tire of claim 1, wherein the inner groove is provided in the crown area.

11. A tire as described in any one of claims 1 to 10, wherein the groove depth of the first connecting groove is smaller than the groove depth of the inner groove portion.

12. A tire as described in any one of claims 1 to 11, wherein the widening portion is connected to the inner groove portion.

13. A tire as described in any one of claims 1 to 12, wherein the length of the widened portion is 10% to 40% of the length of the first connecting groove.

14. A tire having a tread portion, The tread portion is provided with a plurality of lateral grooves connecting the tread ends on both sides, Each of the lateral grooves includes a pair of outer groove portions extending axially inward from the tread ends on both sides, and an inner groove portion connecting the pair of outer groove portions, The pair of outer groove portions are inclined in the same direction with respect to the tire axial direction, The inner groove portion is inclined in an opposite direction to the outer groove portion with respect to the tire axial direction, a groove depth of the inner groove portion is smaller than a groove depth of each of the pair of outer groove portions, A second connecting groove is provided in the tread portion to connect the outer groove portions of the lateral grooves adjacent to each other in the tire circumferential direction, The outer groove portion has a protrusion for preventing stone trapping at a groove bottom where the second connecting groove is connected. tire.

15. A tire as described in any one of claims 1 to 14, wherein the tire is for heavy loads.

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