pneumatic tires

Abstract

Pneumatic tires, comprising: an annular tread portion (1) extending in the tire circumferential direction; a pair of sidewall portions (2) provided on both sides of the tread portion (1); a pair of tire bead portions (3) arranged inwardly of the sidewall portions (2) in the tire radial direction; a plurality of lug grooves (30) extending in a shoulder region of the tread portion (1) in a tire width direction up to the sidewall portions (2); a block defined by the lug grooves (30); wherein the block comprises a shoulder block (50) arranged on an inner side in the tire width direction, and a side block (60) arranged outside the shoulder block (50) in the tire width direction, and at a boundary between the shoulder block (50) and the side block (60) is raised higher than a surface of the shoulder block (50); and wherein at least a part of the plurality of lug grooves (30) each includes a closed lug groove (30A) closed by a ridge portion (32) provided therein, the ridge portion (32) being continuous with the side block (60) arranged on both sides of the closed lug groove (30A) in the tire circumferential direction, the ridge portion (32) including a first narrow groove (33) having a smaller groove width and a smaller groove depth than the lug groove (30), the first narrow groove (33) extending in the tire width direction, and wherein the first narrow groove (33) is open to the closed lug groove (30A) and to the sidewall portion (2).

Description

Technical FieldThe present invention relates to a pneumatic tire suitable as a tire for traveling on an unfastened road, and more particularly to a pneumatic tire having highly balanced traveling performance on an unfastened road and cut resistance at a sidewall portion.Prior ArtPneumatic tires generally suitable for traveling on an unpaved road such as uneven terrain, sandy terrain or sandy terrain have a tread pattern mainly consisting of lug grooves with many edge portions or blocks, and also have a large groove area. Such tires are designed to catch mud, sand, stone, rock, etc. on the road to achieve traction performance and prevent the clogging of mud, sand or stone in a groove, so as to improve the running performance on an unfixed road. In addition, a proposal has recently been made to expand a region of a groove or a block up to a side wall portion beyond a shoulder portion to provide a recess and a protrusion in a region from the shoulder portion to the side wall portion (for example, JP 3391692 B). In such tires, the recess and the protrusion (groove or block) ranging from the shoulder portion to the sidewall portion sink into mud or sand on the sandy or sandy background, contacts stone or rock on the sandy background, and catches mud, sand, stone, rock, etc. on the sandy background, whereby high travel performance can be achieved.On an unpaved road (particularly, stoney ground), however, a sidewall portion is easily damaged by the contact with rock, pointed stone, etc., resulting in a problem that a tire having a thin rubber thick portion (groove or recessed portion) with the recess and the protrusion provided over the range from the shoulder portion to the sidewall portion as described above does not ensure sufficient cut resistance. In order to solve this problem, an effective solution is required which can provide both high travel performance on an unpaved road (particularly stoney ground) and high cut resistance at the sidewall portion in a pneumatic tire having a groove or a block over the region from the shoulder portion to the sidewall portion.DE 699 01 908 T2, which is based on WO 99 / 52 720 A1 and U.S. Pat. No. 414 727, discloses a tread for a tire for use on the road and off road. The tread is divided into four rows of block elements, each row being separated by a circumferentially continuous groove. Circumferentially adjacent each long block member is a short block member. Each shoulder block member extends over the tread shoulder and down the sidewall. An adjacent long block member and a short block member are connected by a circumferentially extending portion.US 2010 / 0 147 426 A1 discloses a tire having a circumferentially extending tread and a pair of sidewalls, each sidewall having an upper strip of sidewall block members. The tread is constructed with a first shoulder row of block elements, a first inner row of block elements, a second inner row of block elements and a second shoulder row of block elements. A zigzag shaped circumferential central groove extends between the inner rows and substantially follows the equatorial line of the tread. The first shoulder row is separated from the first inner row by a first circumferential groove. Similarly, the tread comprises a second circumferential groove at the opposite end of the tread, the second circumferential groove separating the second shoulder row from the second inner row.US D 851 580 S discloses a tread pattern in a shoulder region and a sidewall region of a tyre. The tread pattern includes a plurality of blocks separated by a groove, and two adjacent blocks adjacent to each other in the tire circumferential direction are formed in the shoulder region and separated from each other by a groove. Adjacent to and separate from the two adjacent blocks, a third block is formed in the sidewall region. The third block extends circumferentially along the two adjacent blocks and includes a small groove open to the sidewall of the tire and terminating within the third block.US 2010 / 0 043 934 A1 discloses a pneumatic tire having a tread and sidewalls. The sidewalls are disposed axially outward and radially inward from the tread edge. A first edge portion of the tread extends axially inward from the first tread edge. Beginning at a circumferential groove, adjacent blocks are formed in the circumferential direction. An axially outer edge of each block connects to a radially outwardly curved surface that merges with the tire sidewall. The blocks have an axially outer edge disposed axially inward of the tread edge and merging with a surface that is curved radially inward. The surface merges into a radially outwardly curved surface. Between two blocks is disposed a relatively wide lateral groove. The second edge portion of the tread extends axially inward from the second tread edge. Beginning at a circumferential groove, adjacent blocks are formed in the circumferential direction. An axially outer edge of each block connects to a radially outwardly curved surface that merges with the tire sidewall. The blocks have an axially outer edge disposed axially inward of the tread edge and merging into a surface. The surface is connected to a radially outwardly curved surface which merges with the side wall. Along the radially outer portion of each side wall, a sequence of elongated blocks is formed. A block is formed between circumferentially adjacent elongated blocks. At a radially inner end of the block, a triangular extension block is formed which extends radially below the adjacent elongated block and forms a triangular surface.SUMMARY OF THE INVENTION

[0005] Technical ProblemAn object of the present invention is to provide a pneumatic tire that ensures highly balanced traveling performance on an unfastened road and cut resistance at a sidewall portion.

[0006] Solution of the ProblemIn order to achieve the above-described object, a pneumatic tire according to the present invention includes an annular tread portion extending in the tire circumferential direction, a pair of sidewall portions provided on both sides of the tread portion, a pair of bead portions provided inward of the sidewall portions in the tire radial direction, a plurality of lug grooves extending to the sidewall portions in a shoulder region of the tread portion in the tire width direction, and a block defined by the lug grooves. The block includes a shoulder block disposed on an inner side in the tire width direction and a side block disposed outside the shoulder block in the tire width direction and raised higher than a surface of the shoulder block at a boundary between the shoulder block and the side block. At least a part of the plurality of lug grooves each include a closed lug groove closed by a ridge portion provided therein, the ridge portion continuous to the side block disposed on both sides of the closed lug groove in the tire circumferential direction, the ridge portion includes a first narrow groove having a smaller groove width and a smaller groove depth than the lug groove, the first narrow groove extends in the tire width direction, and the first narrow groove is open to the closed lug groove and the sidewall portion.

[0007] Advantageous Effects of the InventionAccording to the present invention, as described above, the lug groove or the block extends to the side wall portion beyond the shoulder area, whereby the running performance (stone performance) on stoney ground can be improved. Specifically, a higher raised side block forms a sufficient recess and a protrusion on an outer side (sidewall portion side) in the tire width direction, so that when the sidewall portion comes into contact with rock, etc., the sidewall portion can catch the rock, etc., and can exhibit high stone performance. On the other hand, a ridge portion provided in the lug groove and continuous to the side block can prevent occurrence of side cuts caused by contact with rock, etc., and in turn can increase the cut strength. At this time, the first narrow groove formed in the ridge portion can equalize an edge reduced by the formation of the ridge portion, so that high stone performance can be achieved.According to the present invention, it is preferable that the lug grooves that do not include the ridge portion and the closed lug grooves are provided alternately in the tire circumferential direction. Such an alternating arrangement of the closed lug grooves ensures both stone performance and cut resistance in a balanced manner.According to the present invention, it is preferable that the side blocks are provided in a position covering a range of 30% to 45% of a tire cross-sectional height SH from an outer diameter position at a tire equator to an inner side in the tire radial direction. Such arrangement of the side block provides a sufficient recess and a protrusion in an area that tends to contact rock, etc. when driving on a stoney ground, etc. This is advantageous in improving stone performance.According to the present invention, it is preferable that an edge of the rib portion on the stud groove closed side is provided in a range of 35% to 45% of a tire cross-sectional height SH from an outer diameter position at a tire equator to an inner side in the tire radial direction. Such a configuration of the comb portion can increase the cut resistance by using the comb portion while maintaining sufficient stone performance. This is advantageously effective for securing both stone performance and cut resistance in a balanced manner.According to the present invention, it is preferable that the side block includes a second narrow groove having a smaller groove width and a smaller groove depth than the lug groove, the second narrow groove extending in the tire width direction, and the second narrow groove being open at least at an inner end in the tire width direction. Such a formation of the second narrow groove provides more edges in the side block. This is advantageously effective in improving stone performance.According to the present invention, it is preferable that the shoulder block includes a third narrow groove having a smaller groove width and a smaller groove depth than the lug groove, the third narrow groove extending in the tire width direction, the third narrow groove being open at least at an outer end in the tire width direction, and the second narrow groove and the third narrow groove being continuous with each other. Such a formation of the third narrow groove provides more edges in the shoulder block. This is advantageously effective in improving stone performance. In particular, the second and third continuous narrow grooves function as a groove and catch rock, etc., and again ensure high stone performance.Brief Description of the DrawingsFIG. 1 is a meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is a front view illustrating a tread surface of the pneumatic tire according to the embodiment of the present invention. FIG. 3 is an enlarged front view illustrating a part of a shoulder block and a side block according to the present invention. FIG. 4 is an enlarged meridian cross-sectional view illustrating a part of a shoulder block and a side block according to the present invention.DESCRIPTION OF EMBODIMENTSConfigurations of embodiments of the present invention will be described below in detail with reference to the accompanying drawings.As illustrated in FIG. 1, the pneumatic tire of the present invention includes a tire circumferential direction annular tread portion 1, a pair of sidewall portions 2 disposed on both sides of the tread portion 1, and a pair of bead portions 3 disposed inward of the sidewall portions 2 in the tire radial direction. Reference symbol CL in FIG. 1 denotes the tire equator, and reference symbol E denotes a ground contact edge.A carcass layer 4 is disposed between a pair of left-right tire bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction and is folded back around a bead core 5 disposed in each of the bead portions 3 from a vehicle inner side toward a vehicle outer side. In addition, bead fillers 6 are disposed on the outer periphery of the tire bead cores 5, and each bead filler 6 is enclosed by a main body portion and a folded-back portion of the carcass layer 4. On the other hand, in the tread portion 1, a plurality of belt layers 7 (two layers in FIGS. 1 to 3 ) are embedded on the outer circumferential side of the carcass layer 4. These belt layers 7 each include a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and the directions of the reinforcing cords of the different layers intersect each other. In these belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set in the range of, for example, 10° to 40°. In addition, a belt reinforcing layer 8 is provided on the outer circumferential side of the belt layers 7. The belt reinforcing layer 8 includes organic fiber cords oriented in the tire circumferential direction. In the belt reinforcing layer 8, the angle of the organic fiber cords with respect to the tire circumferential direction is set to, for example, 0° to 5°.The present invention can be applied to such a typical pneumatic tire; however, the cross-sectional structure thereof is not limited to the above-described basic structure.As illustrated in FIG. 2, a circumferential groove 10 is formed in a center region (on the tire equator CL in FIG. 2 ) of the tread portion 1 extending in the tire circumferential direction. In addition, a plurality of inner lug grooves 20 and a plurality of outer lug grooves 30 are formed on both sides of the circumferential groove 10 at a certain interval in the tire circumferential direction. The circumferential groove 10, the inner lug grooves 20, and the outer lug grooves 30 define a center block 40, a shoulder block 50, and a side block 60.The circumferential groove 10 has a varying groove width along the tire circumferential direction in which a plurality of wide portions 11 and a plurality of narrow portions 12 are alternately formed. Specifically, in the illustrated example of FIG. 2, the alternately arranged wide portions 11 and narrow portions 12 make the circumferential groove 10 apparently zigzag along the tire circumferential direction. A portion (corresponding to the wide portion 11) inclined in one direction with respect to the tire circumferential direction has a relatively large groove width, while a portion (corresponding to the narrow portion 12) inclined in the other direction has a relatively small groove width.The inner lug grooves 20 extend with a certain inclination in a direction with respect to the tire circumferential direction. One end (tire width direction inner end) of each inner lug groove 20 communicates with the wide portion 11 of the circumferential groove 10, and the other end (tire width direction outer end) communicates with the outer lug groove 30, as described later. In the illustrated example of FIG. 2, the inner lug groove 20 is inclined in a direction with respect to the tire circumferential direction, while the inclination angle is changed accordingly by bending at a certain center. In the illustrated example, the inner lug grooves 20 are formed in both sides of the circumferential groove 10, and thus a wide portion 11 communicates with a pair of inner lug grooves 20.The outer lug grooves 30 extend with a certain inclination in the other direction (opposite to the direction of the inner lug grooves 20) with respect to the tire circumferential direction. One end (inner end in the tire width direction) of each outer lug groove 30 communicates with the inner lug groove 20, and the other end (outer end in the tire width direction) extends to the outer side in the tire width direction and reaches the sidewall portion 2 beyond a shoulder region. In the illustrated example of FIG. 2, the outer lug groove 30 crosses the inner lug groove 20, and the one end thereof, as described later, terminates inside the center block 40. Also, in the illustrated example of FIG. 2, the outer lug groove 30 is inclined in the other direction with respect to the tire circumferential direction while the inclination angle is changed accordingly by bending at a certain center. In the illustrated example of FIG. 1, the outer lug groove 30 includes a protrusion portion 31 that protrudes from a groove bottom at the center of the groove bottom near the other end and extends along the outer lug groove 30. Note that the outer lug groove 30 includes a closed lug groove 30A provided therein with a ridge portion 32 as described later and an open lug groove 30B that does not include the ridge portion 32 and that is open to the side wall portion. In the illustrated example of FIG. 1, the open lug groove 30B is bent at a position corresponding to the ridge portion 32 in the closed lug groove 30A.The center block 40 is defined by the circumferential groove 10, the inner lug groove 20, and the outer lug groove 30, and is provided in a position adjacent to the circumferential groove 10. As described above, since the one end of the outer lug groove 30 terminates within the center block 40, the center block 40 appears to have a substantially triangular recess in the illustrated example of FIG. 2. The center blocks 40 each include a sipe 41 whose one end communicates with the circumferential groove 10, curves inside the center block 40, then crosses one end (recess) of the outer lug groove 30, and extends along the extending direction of the inner lug groove 20; and whose other end communicates with the outer lug groove 30. A sharp edge portion adjacent to the circumferential groove 10 and the inner lug groove 20, and a sharp edge portion adjacent to the inner lug groove 20 and the outer lug groove 30 each include a chamfer 42.As illustrated in FIGS. 2 and 3, the shoulder block 50 is defined by the outer lug groove 30 and the inner lug groove 20, and is disposed between the outer lug grooves 30 adjacent to each other in the tire circumferential direction. The shoulder blocks 50 each include a sipe 51 whose one end communicates with the outer lug groove 30, curves inside the shoulder block 50, and then extends along the extending direction of the outer lug groove 30; whose other end terminates inside the shoulder block 50; and a narrow shoulder groove 52 extending from the end portion of the sipe 51 along the extending direction of the outer lug groove 30. Note that the sipe 51 and the shoulder narrow groove 52 are spaced apart from each other and are not continuous to each other. A corner portion in contact with the outer lug groove 30 and the inner lug groove 20 includes a chamfer 53.As illustrated in FIGS. 2 and 3, the respective side blocks 60 are defined between the outer lug grooves 30 adjacent to each other in the tire circumferential direction and are disposed outside the shoulder block 50 in the tire width direction. The side block 60 provided continuously with the shoulder block 50 to form a row of blocks is raised higher than the shoulder block 50, as shown in FIG. 4. In other words, a higher raised portion of the block defined by the outer lug grooves 30 corresponds to the side block 60, and the other portion corresponds to the shoulder block 50. That is, in the side block 60 in the illustrated example, a portion inward of the broken line is raised higher than the shoulder block 50, and a portion outward of the broken line is flush with the shoulder block 50 (corresponding to a portion where the shoulder block 50 and the side block 60 are connected) or is recessed below the shoulder block 50 (corresponding to a groove wall of the outer lug groove 40 adjacent to the side block 60).Some (closed lug groove 30A) of the plurality of outer lug grooves 30 include a ridge portion 32 between the side blocks 60 adjacent to each other in the tire circumferential direction. The ridge portion 32 continuous with the ridge portion 32 to the side blocks 60 of the outer lug groove 30 (lug groove 30A) provided on both sides in the tire circumferential direction closes the outer lug groove 30 (lug groove 30A) closed. On the other hand, the ridge portion 32 includes a first narrow groove 33 having a groove width and depth smaller than the outer lug groove 30 extending in the tire width direction on the extension of the outer lug groove 30. At least one end of the first narrow groove 33 penetrates toward the outer lug groove 30 (closed lug groove 30A) or the side wall portion 2. Note that, in the illustrated example, one end of the first narrow groove 33 penetrates toward the outer lug groove 30 (closed lug groove 30A) and bends at a certain midpoint in the extending direction, and the other end penetrates toward the side wall portion 2.According to the present invention, the outer lug groove 30, the shoulder block 40, the side block 50, etc. have a particular configuration in the shoulder region, so that the side wall portion 2 can catch rock, etc. when contacting rock, etc. when driving on stoney ground, etc., thereby improving stone performance, as well as suppressing side cuts, etc., and thereby increasing cut strength. Thus, the configuration of the center portion is not limited to the above-described configuration.In the tire configured as described above, first, the outer lug grooves 30 are formed to the sidewall portion 2 beyond the shoulder region, and the outer lug grooves 30 define the blocks (shoulder block 50 and side block 60) by which a sufficient recess and a sufficient protrusion are formed over a region from the shoulder region to the sidewall portion 2 to achieve high stone performance. Specifically, the side block 60 is raised higher than the shoulder block 50 to form a sufficient recess and a protrusion on an outer side (sidewall portion 2 side) in the tire width direction, so that the sidewall portion 2 can catch rock upon contact with the rock etc., and high stone performance is achieved again. On the other hand, the ridge portion 32 is formed inside the outer lug groove 30 and is continuous to the side block 60, whereby occurrence of the side cuts can be suppressed and, in turn, cut strength can be increased. In addition, the first narrow groove 33 formed in the ridge portion 32 can equalize an edge reduced according to the formation of the ridge portion 32 to achieve high stone performance.In this case, provided that the side block 60 is not raised higher, an adequate recess and projection cannot be formed, and thus stone performance cannot be improved. The outer lug groove 30 not including the ridge portion 32 is easily susceptible to damage such as side cuts in contacting rock, etc., and has reduced cut resistance. Unless the first narrow groove 33 is provided, the margin is reduced and rocks, etc. may not be properly caught due to the continuous side block 60 and the ridge portion 32, resulting in insufficient stone performance.The ridge portion 32 may be formed in all the outer lug grooves 30, but it is preferable to alternately arrange the closed lug groove 30A including the ridge portion 32 and the open lug grooves 30B without the ridge portion 32 in the tire circumferential direction as illustrated in the figure. Such an alternating arrangement of the stud closed grooves 30A ensures that the stud closed groove 30A and the stud open groove 30B are necessarily included in a grounded region. As a result, both stone performance and cutting resistance can be realized in a balanced manner.As illustrated in the figure, the side block 60 may include a second narrow groove (side narrow groove 61) having a groove width and depth smaller than the outer lug groove 30 extending in the tire width direction. It is preferable that the second narrow groove (lateral narrow groove 61) is open at least at an inner end in the tire width direction. In the illustrated example, the second narrow groove is open to the shoulder block 50 side at an inner end in the tire width direction, bent at a midpoint in the extending direction, and is open to the sidewall portion 2 side at the outer end in the tire width direction. In other words, since the side block 60 and the ridge portion 32 are continuous as described above, three narrow grooves (a first narrow groove 33 and two second narrow grooves (side narrow grooves 61)) having a groove width and depth smaller than that of the outer lug groove 30 are formed in a series of blocks defined by the two side blocks 60 and the ridge portion 32 interposed therebetween. As such, the formation of the second narrow groove (side narrow groove 61) contributes to enlarging the margin in the side block 60. This is advantageously effective in improving stone performance.As described above, in forming the second narrow groove (side narrow groove 61), it is preferable to form, in the shoulder block 50, the third narrow groove (shoulder narrow groove 52) continuous to the second narrow groove (side narrow groove 61). It is preferable that the third narrow groove (shoulder narrow groove 52) has a groove width and depth smaller than the outer lug groove 30, extends in the tire width direction, and is open at least at the outer end in the tire width direction. As such, the formation of the third narrow groove (shoulder narrow groove 52) also helps to enlarge the margin within the shoulder block 50. This is advantageously effective in increasing stone performance. In particular, the second narrow groove (side narrow groove 61) and the third narrow groove (shoulder narrow groove 52) continuous like a single groove can catch rock, etc., and provide high stone performance. Since the side block 60 is raised higher than the shoulder block 50, the second narrow groove (narrow side groove 61) and the third narrow groove (narrow shoulder groove 52) need not be completely connected. As long as the third narrow groove (shoulder narrow groove 52) is formed in the extension line, on the shoulder block 21 side, the second narrow groove (side narrow groove 61) as shown in the figure, the second narrow groove (side narrow groove 61) and the third narrow groove (shoulder narrow groove 52) may be referred to as continuous.On the side of the side wall portion 2 of the comb portion 32, a recess portion 34 may be formed as shown in the figure. In the case of forming the recess portion 34 as described above, it is preferable that an outer end in the tire width direction of the first narrow groove 33 is continuous to the recess portion 34. In addition, it is also preferable that the second narrow groove (side narrow groove 61) is continuous to the recess portion 34 formed in the ridge portion 32 as shown in the figure. In other words, it is preferable that, of three narrow grooves (a first narrow groove 33 and two second narrow grooves (shoulder narrow grooves 52)) formed in a series of blocks defined by the side block 50 and the ridge portion 32, two (a first narrow groove 33 and one of the two second narrow grooves (shoulder narrow grooves 52)) continuously extend to the recess portion as described above. Such a configuration of the recess portion reinforces the engagement with a road surface at more positions when driving on a stoney ground, etc., and thus provides higher stone performance.At the boundary between the shoulder block 50 and the side block 60, a series of step portions 70 may also be provided across the outer lug groove 30, the shoulder block 50, and the side block 60 extending in the tire circumferential direction as in the illustrated example. Such a configuration of the step portions 70 contributes to making it difficult to configure a recess and a protrusion in a range from the shoulder portion to the side wall portion 2, and provides more edges. This is advantageously effective in improving stone performance.According to the present invention, it is preferable to provide the side blocks 60 at positions covering a range of 30% to 45% of a tire cross-sectional height SH from an outer diameter position at the tire equator CL to the inner side in the tire radial direction. In other words, it is preferable that a distance A from the outer diameter position on the tire equator CL to the edge of the side block 60 on the shoulder block 50 side is less than 30% of the tire cross-sectional height SH, and a distance B from the outer diameter position on the tire equator CL to the edge of the side block 60 on the side wall portion 2 side is greater than 45% of the tire cross-sectional height SH. Such arrangement of the side blocks 60 provides a sufficient recess and protrusion in an area that easily comes into contact with rock, etc. when driving on a stoney ground, etc. This is advantageous in improving stone performance.According to the present invention, it is preferable that the edge of the ridge portion 32 on the side of the closed lug groove 30A is located in a range of 35% to 45% of the tire cross-sectional height SH from the outer diameter position at the tire equator CL to the inner side in the tire radial direction. In other words, it is preferable that a distance C from the outer diameter position at the tire equator CL to the edge of the ridge portion 32 on the stud groove 30A closed side be in a range of 35% to 45% of the tire cross-sectional height SH. Such arrangement of the comb portion 32 makes it possible to maintain sufficient stone performance as well as to improve the cut resistance by using the comb portion 32. This is advantageously effective for realizing both in a balanced manner.ExamplesEleven types of pneumatic tires in total, i.e., Conventional Example 1, Comparative Examples 1 and 2, and Examples 1 to 8, were manufactured under the same conditions. A tire size was LT265 / 70R17, the basic configuration of FIG. 1 was adopted, and the tread pattern of FIG. 2 was used as the basic pattern and under different conditions set as shown in Table 1: presence of the ridge portion in the lug groove; presence of the narrow groove in the ridge portion, the side block, and the shoulder block; the depth of the narrow groove; a relationship between the side narrow groove and the shoulder narrow groove (continuous or non-continuous); a ratio A / SH between the distance A from the outer diameter position at the tire equator to the outer end of the side block in the tire radial direction and the tire cross-sectional height SH; a ratio B / SH of the distance B from the outer diameter position on the tire equator to the inner end of the side block in the tire radial direction and the tire cross-sectional height SH; and a ratio A / SH between a distance C from the outer diameter position on the tire equator and the outer end of the ridge portion in the tire radial direction and the tire cross-sectional height SH;In the example having the narrow groove as shown in the figure, the narrow groove formed in the ridge portion is open to the outer lug groove and, according to the invention, to the side wall portion, the narrow groove formed in the side block is open to the shoulder block and the side wall portion, the narrow groove formed in the shoulder block is open to the side block at one end and terminates within the block at the other end.Regarding the "presence of the narrow groove" in Table 1, for each of the narrow grooves in the ridge portion (array of the "ridge portion" in Table 1), the narrow groove (narrow side groove) in the side block (array of the "side block" in Table 1), and the narrow groove (narrow shoulder groove) in the shoulder block (array of the "shoulder block" in Table 1), an array indicating "presence of the narrow groove" is set. Here, since no ridge portion was provided in Comparative Example 1, "-" is entered into the field "presence of a narrow groove" for the field "ridge portion" in Table 1.Regarding the "depth of the narrow groove" in Table 1, a case where the narrow groove has a greater depth than the outer lug groove is indicated as "large", and a case where the narrow groove has a smaller depth than the outer lug groove is indicated as "small". Here, an array of the "depth of the narrow groove" in Table 1 to which "large" is input means that all formed narrow grooves have a greater depth than the outer lug groove, and the array to which "small" is input means that all formed narrow grooves have a lesser depth than the outer lug groove.These eleven types of pneumatic tires were evaluated for stone performance and cut resistance by the following evaluation method, and the evaluation results are also shown in Table 1.Stone performanceThe test tires were mounted on wheels having a rim size of 17.times.8.0JJ, inflated to an air pressure of 450 kPa, and mounted on a pickup truck (test vehicle). Sensory evaluation by a test driver was performed on a stonegy test lane. The evaluation results were expressed as index values, and the Conventional Example 1 was assigned an index value of 100. Larger index values indicate better stone performance.Cut StrengthThe test tires were mounted on wheels having a rim size of 17.times.8.0JJ, inflated to an air pressure of 450 kPa, and mounted on a pickup truck (test vehicle). After traveling on a stone test track, the total cut length in the side portion was measured. The evaluation results were expressed as index values, with the inverse of the measurement value of Conventional Example 1 being assigned the index value 100. Larger index values indicate a shorter total length of a side cut and a greater cut resistance. [Table 1-I] [Table 1-I]Presence of the comb portionYesNo. NOYesYesPresence of the narrow grooveComb PortionNo. NO-YesYesPage BlockNo. NONo. NONo. NOYesShoulder BlockNo. NONo. NONo. NOYesGroove Depth of Narrow Grooves--Large-size is largeSmall size is smallRelationship between lateral narrow groove and shoulder narrow groove---Continuously, continuously, the continuous process is performedA / SH x 100%20202020B / SH x 100%50505050C / SH x 100%40-4040StoneLe GIndex value index value100105103112Resistance to CuttingIndex value index value1009598109[Table 1-II][Table 1-II]Presence of the comb portionYesYesYesYesPresence of the narrow grooveComb PortionYesYesYesYesPage BlockYesYesYesYesShoulder BlockYesYesYesYesGroove Depth of Narrow GroovesSmall size is smallSmall size is smallSmall size is smallSmall size is smallRelationship between lateral narrow groove and shoulder narrow grooveContinuously, continuously, the continuous process is performedContinuously, continuously, the continuous process is performedContinuously, continuously, the continuous process is performedContinuously, continuously, the continuous process is performedA / SH x 100%30402020B / SH x 100%50504540C / SH x 100%40454035StoneLe GIndex value index value110103109107Resistance to CuttingIndex value index value109107105103[Table 1-III][Table 1-III]Presence of the comb portionYesYesYesPresence of the Narrow GrooveComb PortionYesYesYesPage BlockNo. NOYesYesShoulder BlockYesNo. NOYesGroove Depth of Narrow GroovesSmall size is smallSmall size is smallSmall size is smallRelationship between lateral narrow groove and shoulder narrow grooveContinuously, continuously, the continuous process is performedContinuously, continuously, the continuous process is performedNot ContinuousA / SH x 100%202020B / SH x 100%505050C / SH x 100%404040StoneLe GIndex value index value109107109Resistance to CuttingIndex value index value109109109As is apparent from Table 1, compared with Conventional Example 1, stone performance and cut resistance were improved, and both were achieved in balance in all Examples 1 to 8. In Comparative Example 1, on the other hand, the absence of a ridge portion within the outer lug groove resulted in lower cut resistance. In Comparative Example 2, although the ridge portion was formed and had the narrow groove, the depth of the narrow groove was larger than the lug groove. This decreased the cut resistance.List of Reference Numerals1 Tread portion 2 Sidewall portion 3 Tire bead portion 4 Carcass layer 5 Tire bead core 6 Bead filler 7 Belt layer 8 Belt reinforcing layer 10 Circumferential groove 11 Wide portion 12 Narrow portion 20 Inner lug groove 30 Outer lug groove 31 Protrusion portion 32 Ridge portion 33 First narrow groove 34 Recess portion 40 Center block 41 Sipe 42 Chamfer 50 Shoulder block 51 Sipe 52 Shoulder narrow groove (third narrow groove) 53 Chamfer 60 Side block 61 Side narrow groove (second narrow groove) 70 Step portion CL Tire equator

Claims

A pneumatic tire comprising: an annular tread portion (1) extending in the tire circumferential direction; a pair of sidewall portions (2) provided on both sides of the tread portion (1); a pair of tire bead portions (3) disposed inward of the sidewall portions (2) in the tire radial direction; a plurality of lug grooves (30) extending in a shoulder region of the tread portion (1) in a tire width direction to the sidewall portions (2); a block defined by the lug grooves (30); wherein the block includes a shoulder block (50) disposed on an inner side in the tire width direction and a side block (60) disposed outside the shoulder block (50) in the tire width direction and raised higher than a surface of the shoulder block (50) at a boundary between the shoulder block (50) and the side block (60); and wherein at least a part of the plurality of lug grooves (30) each includes a closed lug groove (30A) closed by a ridge portion (32) provided therein, the ridge portion (32) continuous to the side block (60) disposed on both sides of the closed lug groove (30A) in the tire circumferential direction, the ridge portion (32) includes a first narrow groove (33) having a smaller groove width and a smaller groove depth than the lug groove (30), the first narrow groove (33) extends in the tire width direction, and the first narrow groove (33) is open to the closed lug groove (30A) and the sidewall portion (2).The pneumatic tire according to claim 1, wherein the lug groove (30B) that does not include the ridge portion (32) and the closed lug groove (30A) is provided alternately in the tire circumferential direction.The pneumatic tire according to claim 1 or 2, wherein the side block (60) is provided in a position covering a range of 30% to 45% of a tire cross-sectional height SH from an outer diameter position on a tire equator (CL) to an inner side in the tire radial direction.The pneumatic tire according to any one of claims 1 to 3, wherein an edge of the rib portion (32) on the stud groove closed side (30A) is provided in a range of 35% to 45% of a tire cross-sectional height SH from an outer diameter position on a tire equator (CL) to an inner side in the tire radial direction.The pneumatic tire according to any one of claims 1 to 4, wherein the side block (60) includes a second narrow groove (61) having a smaller groove width and a smaller groove depth than the lug groove (30), the second narrow groove (61) extending in the tire width direction, and the second narrow groove (61) being open at least at an inner end in the tire width direction.The pneumatic tire according to claim 5, wherein the shoulder block (50) includes a third narrow groove (52) having a smaller groove width and a smaller groove depth than the lug groove (30), the third narrow groove (52) extending in the tire width direction, the third narrow groove (52) being open at least at an outer end in the tire width direction, and the second narrow groove (61) and the third narrow groove (52) being continuous with each other.

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