tire

Abstract

To provide a tire capable of effectively suppressing a cut chip at the end part of a shoulder block of a tread in particular, and maintaining favorable traction performance over a long period, even in the case of travelling on an off-road surface, for example.SOLUTION: A tire 1 according to the present invention includes a pair of shoulder areas 12 in a tread 4. In each shoulder area 12, the tire 1 includes a plurality of shoulder transverse grooves 13 arranged, and a shoulder block row 15 formed by arranging a plurality of shoulder blocks 14 in a tire circumferential direction C. In the shoulder transverse groove 13, an angle θ1 of a groove wall 13a with respect to a perpendicular line P1 drawn from a groove opening end position 20a to a tread surface 21a of the shoulder block 14 is within the range of 10 to 20 degrees, and a groove corner part 13d1 connecting the groove wall 13a and a groove bottom 13c is formed in a concave curved surface shape with a curvature radius R1 of 6 mm or more and 15 mm or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a tire suitable for running on, for example, off-road surfaces. [Background technology]

[0002] Tires intended for running on off-road surfaces usually have the land portion that makes up the tread surface divided into multiple blocks by arranging main grooves that extend along the tire circumferential direction, and lateral grooves that extend between the main grooves and between the main grooves and the tread edge, etc., to form a block pattern on the tread surface.

[0003] When such tires are driven off-road, they are prone to chipping, a phenomenon known as cut chipping, in which the rubber at the ends of the blocks in the tread, particularly in the shoulder area of ​​the tread, breaks off due to collisions or contact with uneven surfaces such as stones of various shapes scattered on the road surface or sharp rocks.

[0004] When cut chips occur in multiple blocks, the tire's contact area decreases, which can lead to a decline in traction and other steering stability performance. It also makes the tread more susceptible to premature wear, resulting in a shorter tire lifespan and the need for earlier tire replacement.

[0005] As an example of a conventional tire having a block pattern, Patent Document 1 discloses an off-road tire having a block pattern row on the shoulder side of the tread, in which the groove walls on the leading side of each block constituting the block pattern row have an inclination angle with respect to the tread normal that is within the range of 5 to 10 degrees on the center side and within the range of 10 to 30 degrees on the shoulder side, and in which all or part of the groove walls have an angle decreasing portion where the inclination angle gradually decreases from the shoulder side to the center side.

[0006] However, Patent Document 1 only discloses that durability and handling stability have been improved under relatively gentle driving conditions when the running surface is a loose gravel road surface made up of gravel (rounded stones with a uniform particle size). Patent Document 1 also does not disclose any evaluation of performance on off-road surfaces under harsh driving conditions, such as when the stones scattered on the road surface are angular or when there are sharp rocks, particularly when running on harsh desert racing roads such as undulating desert areas or mountainous areas where vehicles must overcome rocky terrain. Furthermore, Patent Document 1 does not consider at all how to prevent cut chips that tend to occur at the ends of blocks located in the shoulder region of the tread when a vehicle is running on an off-road road surface under such harsh driving conditions. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-247153 Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to provide a tire that can effectively suppress cut chips that tend to occur particularly at the ends of shoulder blocks located in the shoulder region of the tread, even when traveling on off-road surfaces under severe driving conditions, and that can maintain good traction performance for a long period of time. [Means for solving the problem]

[0009] The inventors discovered that even when driving on off-road surfaces under severe driving conditions, cut chips, which are particularly likely to occur at the ends of shoulder blocks, can be effectively suppressed by optimizing the angle of the groove walls of the shoulder lateral grooves that define the shoulder blocks located in the shoulder region of the tread and the shape of the groove corners that connect the groove walls to the groove bottom of the shoulder lateral grooves, and thus completed the present invention.

[0010] That is, the tire of the present invention has a pair of shoulder regions defined in the tread by a pair of tread edges and a pair of shoulder main grooves arranged at a distance from each other across the tire equatorial plane and extending circumferentially of the tire, and each shoulder region has a plurality of shoulder lateral grooves extending from the shoulder main grooves toward the tread edge toward the outside in the tire width direction, and the tire has a shoulder block row formed by arranging a plurality of shoulder blocks defined by the tread edge, shoulder main groove, and plurality of shoulder lateral grooves in the tire circumferential direction, and the shoulder lateral groove is characterized in that, when viewed in circumferential cross section, the angle of the groove wall with respect to a perpendicular line drawn from the groove opening end position to the tread surface of the shoulder block is in the range of 10 to 20 degrees, and the shoulder lateral groove has groove corners connecting the groove wall and the groove bottom, and the groove corners are formed into a concave curved surface with a radius of curvature of 6 mm or more and 15 mm or less.

[0011] In this way, in the tire of the present invention, the shoulder lateral grooves have groove wall angles in the range of 10 to 20 degrees relative to a perpendicular line drawn from the groove opening end position to the tread surface of the shoulder block when viewed in a circumferential cross section of the tire. This effectively increases the land portion rigidity of the shoulder blocks located in the shoulder region of the tread, particularly the ends of the shoulder blocks, even when traveling on off-road surfaces.

[0012] Furthermore, the tire of the present invention has groove corners connecting the groove wall and groove bottom, and the groove corners are formed as concave curves with a radius of curvature of 6 mm or more and 15 mm or less. This ensures a groove volume in the shoulder lateral grooves that is sufficient to scrape away mud, soil, sand, etc. and provide traction performance, while the groove corners, which are the connecting parts between the shoulder lateral groove groove wall and the shoulder lateral groove bottom, are formed as smooth concave curves without any angular edges, making it less likely that rubber cracks will occur or progress due to stress concentration at the groove corners, and as a result, rubber chipping in the shoulder blocks is less likely to occur.

[0013] As a result, even when driving on off-road surfaces, cut chips that tend to occur particularly at the ends of the shoulder blocks can be effectively suppressed, and good traction performance can be maintained for a long period of time.

[0014] In the tire of the present invention, the circumferential dimension of the shoulder blocks is preferably 2.2 to 3.8 times the groove depth of the shoulder lateral grooves.

[0015] This makes it possible to more reliably increase the rigidity of the land portions at the ends of the blocks while ensuring the groove volume of the shoulder lateral grooves.

[0016] Furthermore, in the tire of the present invention, the groove width of the shoulder lateral groove is preferably 15 mm or more and 30 mm or less at the opening position and 5 mm or more and 15 mm or less at the groove bottom position.Furthermore, in the tire of the present invention, the shoulder lateral groove is preferably 11 mm or more in depth.

[0017] As a result, the shoulder lateral grooves can have a sufficient groove volume, which makes it possible to more reliably achieve good traction performance.

[0018] Additionally, in the tire of the present invention, the shoulder lateral groove preferably has a protrusion at the groove bottom that partially protrudes toward the groove opening side.

[0019] This prevents foreign matter such as mud and stones from clogging the shoulder lateral grooves, making it possible to maintain good traction performance for an even longer period of time.

[0020] In addition, in the tire of the present invention, it is preferable that the tread has a center region defined by the pair of shoulder main grooves, a center main groove extending along the tire circumferential direction is arranged in the center region, and the center main groove and the pair of shoulder main grooves are arranged in a generally zigzag extending shape that communicates with each other, thereby providing two center block rows formed by arranging a plurality of defined center blocks in the tire circumferential direction.

[0021] This allows the tire to fully demonstrate good traction performance over a wide range of driving surfaces, including normal paved roads and unpaved off-road surfaces. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a tire that can effectively suppress cut chips that are particularly likely to occur at the ends of shoulder blocks, even when driving on off-road surfaces, and that can maintain good traction performance for a long period of time. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a development view of a portion from the tread to (a part of) the sidewall of a tire according to one embodiment of the present invention. [Figure 2] FIG. 2 is a half cross-sectional view in the width direction of the tire shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line II in FIG. [Figure 4] FIG. 4 is a photograph taken at 1:1 magnification of the condition of the tread of the tire of Example A after it had been driven on a test course simulating a severe off-road road surface. [Figure 5]FIG. 5 is a photograph taken at 1:1 magnification of the condition of the tread of the tire of Comparative Example A after it had been driven on a test course simulating a severe off-road road surface. DETAILED DESCRIPTION OF THE INVENTION

[0024] Next, embodiments of a tire according to the present invention will be described below with reference to the drawings. Fig. 1 is a developed view of a portion from the tread to (a part of) the sidewall of a tire according to one embodiment of the present invention, and Fig. 2 is a half cross-sectional view in the width direction of the tire shown in Fig. 1. Note that hatching of the cross section is omitted in Fig. 2 to make the cross-sectional structure easier to understand.

[0025] The tire 1 of the present invention is a pneumatic tire (hereinafter, sometimes simply referred to as "tire") that is suitable for use on vehicles that are expected to run not only on paved roads but also on off-road surfaces. However, the tire 1 of the present invention is not limited to only these modes and uses. Note that the "off-road surface" referred to here means a road surface including any terrain that a vehicle can enter, such as unpaved grassland, gravel, sand, muddy ground, or rocky area.

[0026] 2, the tire 1 of this embodiment includes a pair of beads 2 (only one bead is shown), a pair of sidewalls 3 (only one sidewall is shown) extending radially outward from each of the pair of beads 2, and a tread 4 (only half of which is shown) continuing to both radially outer ends of the pair of sidewalls 3. The bead 2 includes an annular bead core 5 made of a rubber-coated steel cord or the like, and a bead filler 6 arranged radially outward of the bead core 5.

[0027] The tire 1 also includes a carcass 7 that is secured to the pair of bead cores 5 and extends in a toroidal shape as a whole, a belt 8 and a reinforcing belt 9 that are provided between the tread 4 and the outer periphery of the carcass 7, and an inner liner 10 that is provided on the inner side of the carcass 7 to maintain air pressure.

[0028] 1 shows a case where the carcass 7 is configured from at least one carcass ply, for example, two carcass plies 7a and 7c which are turn-up plies wound up so as to sandwich the bead core 5 and the bead filler 6, and one carcass ply 7b which is a down ply located between the carcass plies 7a and 7c and has a width dimension such that both ends do not reach the bead core 5. These carcass plies 7a to 7c are configured from carcass cords arranged at an angle of 75 to 90 degrees with respect to the tire circumferential direction C, for example.

[0029] The belt 8 is disposed between the tread 4 and the outer periphery of the carcass 7 to reinforce the carcass 7. The belt 8 is composed of at least two belt plies, two belt plies 8a and 8b in this embodiment, in which belt cords made of, for example, steel or organic fiber are layered and arranged in an inclined orientation. The belt plies 8a and 8b are desirably layered and arranged in a positional relationship such that the belt cords are arranged inclined in different directions relative to the tire circumferential direction C. In the tire of this embodiment, the belt cords of the belt plies 8a and 8b are desirably arranged in an inclined orientation at an angle of 10 to 45° relative to the tire circumferential direction C.

[0030] The tire of this embodiment is also provided with a reinforcing belt 9 disposed so as to cover a part or the entire outer surface of the belt 8. The reinforcing belt 9 is typically a rubberized cord ply in which cords are arranged substantially parallel (0 to 5°) to the tire circumferential direction C. In the tire of this embodiment, the reinforcing belt 9 is shown to be composed of two wide reinforcing plies 9a, 9b disposed so as to cover the entire outer surface of the belt 8, but it may also be composed of one or three or more wide reinforcing plies. The reinforcing belt 9 may also be composed of a pair of narrow reinforcing plies (not shown) covering only both ends of the belt, or may be composed of a combination of both a wide reinforcing ply and a pair of narrow reinforcing plies.

[0031] As shown in Fig. 1, the tread 4 has a pair of shoulder regions 12, 12 defined by a pair of tread edges Te, Te and a pair of shoulder main grooves 11, 11. The pair of shoulder main grooves 11, 11 are arranged spaced apart across the tire equatorial plane EL and extend along the tire circumferential direction C.

[0032] Each shoulder region 12 is provided with a plurality of shoulder lateral grooves 13 extending outward in the tire width direction W from the shoulder main groove 11 to the tread edge Te. The shoulder block row 15 is formed by arranging a plurality of shoulder blocks 14 defined by the tread edge Te, the shoulder main groove 11, and the plurality of shoulder lateral grooves 13 in the tire circumferential direction C. In the tire 1 of the embodiment shown in FIG. 1 , the shoulder block row 15 is formed by alternatingly arranging two types of shoulder blocks 14a, 14b with different block tread surface sizes in the tire circumferential direction C. In this tire 1, the tire widthwise outer end of the first shoulder block 14a is located at the same position as the tread edge Te, and the tire widthwise outer end of the second shoulder block 14b is located more inward in the tire width direction W than the tire widthwise outer end of the first shoulder block 14a. However, the tire of the present invention is not limited to such a configuration. For example, the multiple shoulder blocks that make up the shoulder block row 15 can be composed of only one type of shoulder block with the same block tread size, or they can be composed of three or more types of shoulder blocks with different block tread sizes.

[0033] In the present invention, when viewed in a tire circumferential cross section (cross section II shown in FIG. 1) as shown in FIG. 3, the angles θ1 and θ2 of the groove walls 13a and 13b with respect to perpendicular lines P1 and P2 drawn from the groove opening end positions 20a and 20b to the tread surfaces 21a and 21b of the shoulder blocks 14a and 14b must both be in the range of 10 to 20 degrees. In addition, in the present invention, the shoulder lateral groove 13 has groove corners 13d1 and 13d2 connecting the groove walls 13a and 13b of the shoulder lateral groove 13 to the groove bottom 13c, respectively, and the groove corners 13d1 and 13d2 are formed into concave curves with a curvature radius of 6 mm or more and 15 mm or less. The groove opening end positions 20a, 20b are clear when, in a circumferential cross section of the tire, the corners connecting the tread surfaces 21a, 21b of the shoulder blocks 14a, 14b and the groove walls 13a, 13b of the shoulder lateral groove 13 have a vertex (intersection) as shown in Figure 3. However, the groove opening end positions 20a, 20b may have corners that are curved without a vertex. In such cases, the groove opening end positions 20a, 20b are defined as the intersections of extensions of the tread surfaces 21a, 21b of the shoulder blocks 14a, 14b and the groove walls 13a, 13b of the shoulder lateral groove 13. Furthermore, "perpendicular lines P1, P2 drawn from each of the groove opening end positions 20a, 20b to the tread surfaces 21a, 21b of the shoulder blocks 14a, 14b" shall be read as "perpendicular lines intersecting with extension lines drawn from each of the intersection positions from the tread surfaces 21a, 21b of the shoulder blocks 14a, 14b."

[0034] In the tire 1 of this embodiment, by setting the angles θ1 and θ2 of the groove walls 13a and 13b of the shoulder lateral grooves 13 to a range of 10 to 20 degrees, in other words, by setting the angles between the tread surface of the shoulder block 14 and both side walls (the same portions as the groove walls 13a and 13b) to a range of 100 to 110 degrees, the land portion rigidity of the shoulder block 14 located in the shoulder region 12 of the tread 4, particularly the ends of the shoulder block 14 (on both the leading and trailing sides when the tire is in contact with the ground), can be effectively increased even when traveling on off-road surfaces. If the angles θ1 and θ2 of the groove walls 13a and 13b are less than 10 degrees, the land portion rigidity of the shoulder block 14 cannot be sufficiently increased. Furthermore, if the angles θ1 and θ2 of the groove walls 13a and 13b are greater than 20 degrees, the land portion rigidity of the shoulder block 14 can be increased, but the groove volume of the shoulder lateral groove 13 is reduced by a large percentage. This reduces the ability of the shoulder lateral groove 13 to plow through water, soil, sand, mud, etc., particularly on off-road surfaces such as sandy or muddy ground, and as a result, sufficient traction performance (cross-country ability) cannot be obtained.

[0035] Furthermore, the shoulder lateral grooves 13 have groove corners 13d1, 13d2 formed as concave curves with curvature radii R1, R2 of 6 mm or more and 15 mm or less, thereby ensuring a groove volume sufficient for the shoulder lateral grooves 13 to exhibit traction performance by plowing through water, soil, sand, mud, etc. Furthermore, the groove corners 13d1, 13d2, which are the connecting portions between the groove walls 13a, 13b of the shoulder lateral grooves 13 and the groove bottoms 13c of the shoulder lateral grooves 13, are formed as smooth concave curves without any angular edges, making them less susceptible to the occurrence and propagation of rubber cracks due to stress concentration at the groove corners 13d1, 13d2, and therefore less susceptible to cut chips in the shoulder blocks 14. If the curvature radii R1, R2 of the groove corners 13d1, 13d2 were less than 6 mm, the occurrence of rubber cracks at the groove corners 13d1, 13d2 would not be sufficiently suppressed. Furthermore, if the curvature radii R1 and R2 of the groove corners 13d1 and 13d2 are greater than 15 mm, the area of ​​the flat groove bottom 13c of the shoulder lateral groove 13 cannot be sufficiently secured, and if the area ratio of the flat groove bottom 13c is small, stress tends to concentrate, making cracks more likely to occur.

[0036] Therefore, in the tire 1 of this embodiment, the angles θ1, θ2 of the groove walls 13a, 13b relative to perpendicular lines P1, P2 drawn from the groove opening end positions 20a, 20b to the tread surfaces 21a, 21b of the shoulder blocks 14a, 14b are in the range of 10 to 20 degrees, and the shoulder lateral grooves 13 have groove corners 13d1, 13d2 connecting the groove walls 13a, 13b to the groove bottom 13c. The groove corners 13d1, 13d2 are formed as concave curves with radii of curvature R1, R2 of 6 mm or more and 15 mm or less. This makes it possible to effectively suppress cut chips that are likely to occur, particularly at the ends of the shoulder blocks 14, even when driving on off-road surfaces, and to maintain good traction performance for a long period of time.

[0037] In the tire of this embodiment, the circumferential dimensions a1 and a2 of the shoulder blocks 14a and 14b are preferably 2.2 to 3.8 times the groove depth d of the shoulder lateral groove 13. This ensures a sufficient groove volume for the shoulder lateral grooves 13 while improving the land portion rigidity at the ends of the shoulder blocks 14a and 14b in a balanced manner. The tread shapes of the shoulder blocks 14a and 14b include, but are not limited to, various shapes such as a rectangle or a parallelepiped. The circumferential dimensions a1 and a2 of the shoulder blocks 14a and 14b are measured at a position shifted 3 mm in the tire width direction W toward the tire equatorial plane EL from the outer end position of the shoulder block 14 located on the tread edge Te side.

[0038] Furthermore, in the tire of this embodiment, the shoulder lateral grooves 13 preferably have a groove width w1 at the opening position 20a of 15 mm or more and 30 mm or less, and a groove width w2 at the groove bottom position 13c of 5 mm or more and 15 mm or less. Furthermore, in the tire of this embodiment, the shoulder lateral grooves 13 preferably have a groove depth d of 11 mm or more. By adopting these configurations, the groove volume of the shoulder lateral grooves 13 can be effectively secured, thereby more reliably realizing good traction performance. The groove width of the shoulder lateral grooves 13 is measured using a normal ruler at both the opening position 20a and the groove bottom position 13c.

[0039] Additionally, in the tire 1 of this embodiment, the shoulder lateral grooves 13 preferably have raised portions 22 at the groove bottoms 13c that partially protrude toward the groove openings 20a, 20b. This prevents foreign matter such as mud and stones from clogging the shoulder lateral grooves 13, further maintaining good traction performance over a long period of time. The raised portions 22 may be provided at the widthwise center of the groove bottoms 13c so as to extend continuously or intermittently (FIG. 1) along the extension direction of the shoulder lateral grooves 13. Although the cross-sectional shape of the raised portions 22 is rectangular in FIG. 3, various shapes such as circular, elliptical, and triangular may be used, and there is no particular limitation.

[0040] The tire 1 of this embodiment also has a center region 16 defined by a pair of shoulder main grooves 11, 11 in the tread 4. The center region 16 is provided with a center main groove 17 extending along the tire circumferential direction C, and the center main groove 17 and the pair of shoulder main grooves 11, 11 are configured to extend in a generally zigzag pattern that connects them to define a plurality of defined center blocks 18a, 18a, ... and a plurality of defined center blocks 18b, 18b, .... Two center block rows 19a, 19b are provided on both sides of the tire equatorial plane EL.

[0041] In addition, the tire 1 of this embodiment has a tread pattern in which the shoulder blocks 14, 14 located in different shoulder block rows 15, 15, and the center blocks 18a, 18b located in different center block rows 19a, 19b, respectively, are formed in a point-symmetric pattern.

[0042] A tire having such a tread pattern is suitable for use on a vehicle without limiting the wheels (left and right wheels) on which the tire is mounted, but as with tires in which the wheels on a vehicle are limited, the tread pattern may be linearly symmetrical with respect to the tire equatorial plane, or the tread patterns on both sides of the tire equatorial plane EL may be formed in different patterns rather than being symmetrical, and there are no particular limitations.

[0043] In the tire of this embodiment, the center blocks 18a, 18b located in the center region 16 are not limited to the above configuration, and may have any shape that can exhibit steering stability performance, including traction performance, on off-road surfaces.

[0044] Furthermore, in the tire of this embodiment, as shown in Figures 1 and 2, it is preferable that the outer surface of the sidewall 3 is provided with a side block row 25 consisting of a plurality of side blocks 24, 24, ... that protrude outward from the outer surface of the sidewall 3 along the tire circumferential direction C.

[0045] Furthermore, the side blocks 24 are preferably arranged in the tire circumferential direction C in a positional relationship corresponding to each circumferential range 23 in which one shoulder block 14 (14-1) and two shoulder lateral grooves 13, 13 that define one shoulder block 14 (14-1) are located, on the outer surface of the sidewall 3 located on the side of at least one of the pair of shoulder regions (in Figure 1, the side of both shoulder regions 12, 12), and have a circumferential dimension Lb that is equal to or greater than the circumferential range 23.

[0046] By adopting this configuration, especially when traveling on soft surfaces such as sand or mud, the tire sinks due to the weight of the vehicle, allowing the side block rows 25 located on the tire sidewall to virtually touch the ground. As a result, the grooves 26 located between the side blocks 24, 24, increase the tire's ability to push away water, soil, sand, and mud, thereby improving traction performance (traversability) particularly on such off-road surfaces. Furthermore, by adopting this configuration, obstacles such as sharp rocks that could collide with or come into contact with the tire's outer surface from the side are more likely to come into contact with the side blocks 24, while also reducing the likelihood of collision or contact with the ends of the shoulder blocks 14 (14-1). As a result, chipping, which is prone to occur at the ends of the shoulder blocks 14, can be further reduced.

[0047] 1 also shows, for convenience of explanation, three of the shoulder blocks 14 of the tread 4 that are aligned in the tire circumferential direction C, denoted by reference numerals 14-1, 14-2, and 14-3, in order to explain the relative positional relationship in the tire circumferential direction C between the shoulder blocks 14 and the side blocks 24 of the sidewall 3. In this case, it is preferable that the side blocks 24 be arranged in a circumferential range that includes one shoulder block 14-1 and two shoulder blocks 14-2 and 14-3 located on both sides of the shoulder block 14-1 in the tire circumferential direction, that is, a total of three shoulder blocks 14-1, 14-2, and 14-3.

[0048] This configuration makes it less likely that the two shoulder lateral grooves 13, 13 that define one shoulder block 14-1 (at both ends thereof) will be damaged by sharp stones or rocks scattered on the road surface from the side of the tire, further reducing chips and cuts. In this case, it is more preferable that the circumferential overlap dimension of the side block 24 with the two shoulder blocks 14-2, 14-3 be in the range of 5% to 20% of the circumferential dimension a1 of the shoulder blocks 14-2, 14-3.

[0049] The side blocks 24 that protrude outward in the tire width direction preferably have a maximum height h in the range of 4 mm to 15 mm. By adopting this configuration, the cut-chip resistance of the tire can be effectively improved while minimizing the increase in tire weight.

[0050] The maximum height dimension h of the side block 24 is the maximum value of the dimension measured vertically along the profile line of the tire T from the outer surface 3a of the sidewall 3 to the outer surface 24a of the side block.

[0051] Furthermore, in the tire 1 of this embodiment, by providing such a plurality of side blocks 24, 24, ..., when traveling on rough roads such as muddy ground or rocky areas, the shear resistance of the side blocks 24 provides a traction effect, improving rough-road driving performance. In addition, the provision of the side blocks 24 provides a protection effect by keeping traumatic factors such as angular rock faces away from the outer surface 3a of the sidewall 3, thereby improving the resistance of the sidewalls of the tire 1 to trauma.

[0052] The above-mentioned dimensional values ​​were measured under normal conditions with the tire mounted on a standard rim and inflated to the standard internal pressure without load. A standard rim is a rim specified for each tire by the standard system, including the standard on which the tire is based. For example, this is a standard rim for JATMA, a "Design Rim" for TRA, or a "Measuring Rim" for ETRTO. Furthermore, the standard internal pressure is the air pressure specified for each tire by the standard system, including the standard on which the tire is based. For JATMA, this is the maximum air pressure, for TRA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table, and for ETRTO, this is the "INFLATION PRESSURE."

[0053] The tire according to the present invention can be constructed in the same manner as a normal pneumatic tire, except that the shoulder region 12 of the tread 4 is constructed as described above. Therefore, any of the conventionally known materials, shapes, structures, manufacturing methods, etc. can be applied to the tire according to the present invention.

[0054] While the above describes an embodiment of the present invention, the present invention is not limited to the above embodiment and includes all aspects encompassed by the concept and scope of the claims. Various modifications can be made within the scope of the present invention. For example, the tire 1 shown in FIG. 1 is formed with a tread pattern having so-called pitch variations, in which the shoulder blocks 14a, 14b arranged in the tire circumferential direction C are arranged at different pitches Pc in the tire circumferential direction C to reduce pattern noise, etc. However, the present invention is not limited to such a configuration, and various modifications are possible. Furthermore, the tire shown in FIG. 1 is shown with sipes and narrow grooves 27 (FIG. 1) arranged on the tread surfaces of the shoulder blocks 14a, 14b, center blocks 18a, 18b, and side blocks 24 for reasons such as providing an edge effect. However, such configurations can be appropriately arranged or the number of sipes and narrow grooves can be increased as needed. [Example]

[0055] Next, in order to further clarify the effects of the present invention, examples and comparative examples will be described, but the present invention is not limited to these examples.

[0056] (Examples 1 to 3, Comparative Examples 1 to 5) The tires of Examples 1 to 3 and Comparative Examples 1 to 5 all had a tread pattern similar to that shown in FIG. 1, except that the shoulder regions had no pitch variation and only one type of shoulder blocks 14a were arranged at a constant pitch along the tire circumferential direction. They also had the tire half cross section shown in FIG. 2, a size of LT285 / 70R17, and were prototyped based on the specifications in Table 1. Each prototype tire had a substantially similar tire structure except for the configuration of the shoulder regions of the tread. Vehicles fitted with each prototype tire were driven on off-road surfaces under the conditions shown below to evaluate traction performance and cut / chip resistance. The evaluation method was as follows.

[0057] <Traction performance> Traction performance was evaluated by a professional driver at an average speed of 60 km / h on a dry-rider test course designed to simulate the harsh conditions of desert racing, including undulating desert terrain and rocky mountain terrain. The test course included roads with rough rocks, hills, and terrain that required sudden braking and sharp turns. The vehicles were driven around the course at an average speed of 60 km / h for a total distance of 50 km. The results were evaluated by a professional driver based on their feel at the beginning and end of the test. A good feeling was assigned a "good" rating, indicating excellent traction performance, while a poor feeling was assigned a "poor" rating, indicating poor traction performance. The results are shown in Table 1. Rim size: 17 x 7.5 Tire pressure: 200kPa Vehicle: Toyota Land Cruiser with a 4608cc engine Wheels with tires: All wheels

[0058] <Cut and chip resistance> After the traction performance test, the tire was visually inspected for damage such as chips on the outer surface of the tire, including the tread, to determine whether or not damage such as chips had occurred at the ends of the shoulder blocks. The evaluation results are shown in Table 1. A tire with no chips or other damage was rated as excellent in cut and chip resistance, a tire with slight chips or other damage was rated as slightly poor in cut and chip resistance, and a tire with significant chips or other damage was rated as extremely poor in cut and chip resistance.

[0059] [Table 1]

[0060] The evaluation results in Table 1 show that the tires of Examples 1 to 3, in which the shoulder groove wall angles θ1, θ2 and the groove corner curvature radii R1, R2 are within the appropriate ranges of the present invention, are all excellent in both traction performance and cut / chip resistance.On the other hand, the tires of Comparative Examples 1 to 5, in which at least one of the shoulder groove wall angles θ1, θ2 and the groove corner curvature radii R1, R2 is outside the appropriate ranges of the present invention, are inferior in both traction performance and cut / chip resistance.

[0061] 4 is a photograph taken at 1:1 magnification of the tread condition of Example A tire, in which shoulder groove wall angles θ1 and θ2 are both 10 degrees and groove corner curvature radii R1 and R2 are both 6 mm, both of which are within the appropriate range of the present invention, after 50 km of driving on the road surface of the above-mentioned dry tartar test course. On the other hand, Fig. 5 is a photograph taken at 1:1 magnification of the tread condition of Comparative Example A tire, in which shoulder groove wall angles θ1 and θ2 are both 5 degrees and groove corner curvature radii R1 and R2 are both 3.5 mm, both of which are outside the appropriate range of the present invention, after 50 km of driving on the road surface of the above-mentioned dry tartar test course.

[0062] 4 and 5, after traveling 50 km on the road surface of the dry-rider test course, the tire of Example A showed some wear at the ends of the shoulder blocks of the tread, but no cut chips were observed, whereas the tire of Comparative Example A showed cut chips at the ends of the shoulder blocks of the tread (the area surrounded by the ellipse X in FIG. 5). [Explanation of symbols]

[0063] 1. Tires (pneumatic tires) 2 beads 3 Sidewall 4 Tread 5 bead core 6 Bead filler 7. Carcass 8. Belt 9 Reinforcement belt 10 Inner liner 11 Shoulder main groove 12 Shoulder area 13 Shoulder groove 13a, 13b Shoulder lateral groove wall 13c Shoulder groove bottom 13d1, 13d2 Shoulder lateral groove corners 14 Shoulder Block 15 Shoulder Block Row 16 Center Area 17 Center main groove 18a, 18b Center Block 19a, 19b Center Block Row 20a, 20b Position of the groove opening end of the shoulder lateral groove 21a, 21b Shoulder block tread 22 Ridge 23 Circumferential Range 24 Side Block 25 Side Block Row 26 Groove 27 Narrow groove C Circumferential direction of tire D Tire radial direction d Depth of shoulder lateral groove EL Tire Equatorial Plane h Maximum height of side block Lb Circumferential dimension of side block P1, P2 Perpendicular lines drawn on shoulder block treads R1, R2 Radius of curvature of groove corner Te tread edge W Tire width direction w1 Shoulder lateral groove width (opening position) w2 Shoulder lateral groove width (groove bottom position) θ1, θ2 groove wall angles

Claims

1. a tire having a tread including a pair of shoulder regions defined by a pair of tread edges and a pair of shoulder main grooves spaced apart across the tire equatorial plane and extending along the tire circumferential direction, wherein each shoulder region is provided with a plurality of shoulder lateral grooves extending from the shoulder main grooves toward the tread edges toward the outside in the tire width direction, and a shoulder block row formed by arranging a plurality of shoulder blocks defined by the tread edges, the shoulder main grooves, and the plurality of shoulder lateral grooves in the tire circumferential direction, The shoulder lateral grooves, when viewed in a cross section in the tire circumferential direction, the groove wall has an angle of 10 to 20 degrees with respect to a perpendicular line drawn from the groove opening end position to the tread surface of the shoulder block, and the groove has a groove corner portion connecting the groove wall and the groove bottom, the groove corner portion being formed into a concave curved surface with a curvature radius of 6 mm or more and 15 mm or less, a circumferential dimension of the shoulder block is 2.2 times or more and 3.8 times or less the groove depth of the shoulder lateral groove, The tire is characterized in that the groove width of the shoulder lateral groove is 15 mm or more and 30 mm or less at an opening position, and 5 mm or more and 15 mm or less at a groove bottom position.

2. The tire according to claim 1 , wherein the shoulder lateral grooves have a groove depth of 11 mm or more.

3. The tire according to claim 1 or 2, wherein the shoulder lateral groove has a protrusion at the groove bottom that partially protrudes toward the groove opening side.

4. 4. The tire according to claim 1, wherein the tread includes a center region defined by the pair of shoulder main grooves, a center main groove extending circumferentially of the tire is disposed in the center region, and the center main groove and the pair of shoulder main grooves are arranged in a generally zigzag extending shape that communicates with each other, thereby defining two center block rows formed by arranging a plurality of defined center blocks in the tire circumferential direction.

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