pneumatic tires

Abstract

Pneumatic tires, comprising: a tread portion (1) extending in a tire circumferential direction and having a ring shape; a pair of sidewall portions (2) arranged on both sides of the tread portion (1); and a pair of bead portions (3) arranged on an inner side of the sidewall portions (2) in the tire radial direction, wherein a plurality of center blocks are provided in a center region of the tread portion (1), wherein the plurality of center blocks are arranged and form pairs over inclined grooves (20) which are inclined and extend with respect to a tire circumferential direction, wherein center blocks on one side of the pairs of the plurality of center blocks extend across a tire equator (CL) from one side to the other side of the tire equator (CL), and wherein center blocks on the other side extend across the tire equator (CL) from the other side to the one side of the tire equator (CL), wherein each of the plurality of center blocks includes a sipe (11) formed of two wall surfaces connected to each other in a V-shape in a tread contact surface, where in the tread contact surface the two wall surfaces include: a first wall (11a) extending at an angle within ±20° with respect to the tire circumferential direction; and a second wall (11b) extending at an angle within ±10° with respect to the tire transverse direction, and wherein each of wall surface angles of the first wall (11a) and the second wall (11b) is greater than a wall surface angle of a wall surface provided with the notch (11), wherein each of the wall surface angles of the first wall (11a) and the second wall (11b) is set 1.5 times to 4.0 times larger than the wall surface angle of the wall surface provided with the notch (11).

Description

Technical field

[0001] The present invention relates to a pneumatic tire suitable as a tire used for running on unpaved roads, and more particularly relates to a pneumatic tire capable of highly providing unpaved road running performance and block damage resistance performance in a compatible manner. State of the art

[0002] Generally, as a pneumatic tire used for driving on unpaved roads such as uneven ground surfaces, muddy ground surfaces, snow-covered roads, sandy ground surfaces, and rocky ground surfaces, a tire having a tread pattern including mainly lug grooves and blocks including a large number of edge components and having a large groove area is adopted. In such a tire, traction performance is achieved by gripping mud, snow, sand, gravel, stones, and the like (hereinafter collectively referred to as "mud and the like") on road surfaces, and the grooves are prevented from being clogged with mud and the like, thus improving driving performance on unpaved roads (see, for example, Patent Document 1).

[0003] However, such a tire having a large groove area has a problem in that it is difficult to sufficiently ensure block rigidity, and the damage resistance performance of the blocks themselves cannot be sufficiently achieved, and the blocks are likely to be damaged during driving on unpaved roads. Thus, it is necessary to improve driving performance on unpaved roads by making grooves effectively grip mud and the like while maintaining block rigidity and maintaining the damage resistance performance of blocks. A measure for highly providing driving performance on unpaved roads and the damage resistance performance of blocks in a compatible manner is required. Literature listPatent literature

[0004] Patent Document 1: JP 2015-223884 A

[0005] EP 3 162 595 A1 describes a pneumatic tire with good mud and dirt handling properties. This pneumatic tire has a plurality of blocks in the tread pattern, which are arranged along the circumferential direction of the tire on two different sides of the tire equator. Each of these blocks has a first beveled edge and a second beveled edge. Portions of these beveled edges are oriented at different inclinations relative to the radial direction of the tire.

[0006] US 2015 / 0 336 430 A1 describes a pneumatic tire with good performance on muddy terrain. The tread pattern of this pneumatic tire comprises a plurality of paired central blocks, each of which has a cut consisting of two wall surfaces connected in a V-shape to form a tread contact patch. This increases the tire's durability.

[0007] US 772 790 S depicts a tread pattern of a pneumatic tire. This tread pattern comprises four rows of blocks arranged circumferentially of the tire and running parallel to each other. The two middle rows of blocks have a V-shaped cutout.

[0008] WO 2011 / 080 565 A1 describes a pneumatic tire that can be used on and off-road. The tire's tread pattern comprises a plurality of paired center blocks whose longest edges are oriented at an angle to the tire's circumferential and width directions. Brief description of the inventionTechnical problem

[0009] An object of the present invention is to provide a pneumatic tire suitable as a tire used for running on unpaved roads and capable of highly providing unpaved road running performance and damage resistance performance in a compatible manner. Solution to the problem

[0010] To achieve the above-described object, a pneumatic tire according to an embodiment of the present invention includes a tread portion extending in the tire circumferential direction and having an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged on an inner side of the sidewall portions in the tire radial direction. A plurality of center blocks are provided in a central region of the tread portion. The plurality of center blocks are arranged and form pairs via inclined grooves that are inclined and extend with respect to the tire circumferential direction.Center blocks on one side of the pairs of the plurality of center blocks extend across a tire equator from one side to the other side of the tire equator, and center blocks on the other side extend across the tire equator from the other side to one side of the tire equator. Each of the plurality of center blocks includes a sipe formed of two wall surfaces connected to each other in a V-shape in a tread contact surface. In the tread contact surface, the two wall surfaces include a first wall extending at an angle within ±20° with respect to the tire circumferential direction and a second wall extending at an angle within ±10° with respect to a tire transverse direction. Each of the wall surface angles of the first wall and the second wall is larger than a wall surface angle of a wall surface provided with the sipe.Furthermore, each of the wall surface angles of the first wall and the second wall is set 1.5 times to 4.0 times larger than the wall surface angle of the wall surface provided with the notch. Advantageous effects of the invention

[0011] In one embodiment of the present invention, as described above, the center blocks extend across the tire equator. Thus, edge components of the center blocks can be increased in the tire transverse direction, and driving performance on unpaved roads (for example, mud performance and the like) can be improved. In addition, each of the center blocks includes the sipe, and thus the sipe can effectively grip mud and the like in the groove. In this case, the extending directions of the first wall and the second wall are set to the angles described above. Thus, the first wall suppresses tire slippage, and this is advantageous in improving traction performance by the second wall. In addition, the wall surface angles of the first wall and the second wall are relatively large.Thus, even if the sipe is provided, the block rigidity can be sufficiently maintained to a high degree, and this is advantageous in improving the damage resistance performance of the blocks. Note that "wall surface angle" in one embodiment of the present invention refers to an angle formed by a wall surface of a block or groove with respect to a normal of the tread contact surface.

[0012] In one embodiment of the present invention, preferably, the second wall has a length in the tread contact surface that is from 0.5 times to 2.0 times greater than a length in the tread contact surface of the first wall. An aspect ratio of the first wall and the second wall is specified as described above, and thus, skid suppression due to the first wall and traction performance improvement due to the second wall can be provided in a well-balanced and compatible manner.

[0013] In one embodiment of the present invention, preferably, in the tread contact surface, the area of a sipe region surrounded by the first wall, the second wall, and an extension line of the sipe-provided wall surface is from 5% to 20% of the ground contact area of the center block. The size of the sipe is set to the appropriate range with respect to the center block as described above, and an effect due to the sipe (improving driving performance on unpaved roads) can be effectively exerted while maintaining satisfactory block rigidity.Note that, in one embodiment of the present invention, “ground contact area of the center block” refers to the area of a portion that actually comes into contact with a ground in the contact surface of the center block (the area obtained by excluding a portion such as a chamfered portion that does not actually come into contact with a ground).

[0014] In one embodiment of the present invention, a facing block including a sipe-facing wall surface is preferably provided in the tread portion. The facing block is provided as described above, and thus, mud and the like in a region surrounded by the first wall, the second wall, and the facing block (the sipe-facing wall surface) are compressed during running, and a high shear force is achieved. Thus, this is advantageous in improving driving performance on unpaved roads (for example, mud performance and the like).

[0015] In this case, preferably, in a region surrounded by the first wall, the second wall, and the sipe-facing wall surface of the facing block, a distance in the tread contact surface from an edge point P1 on the facing block side of the first wall to an edge point p1 on the first wall side of the facing block is smaller than a length in the tread contact surface of the second wall, and a distance from an edge point P2 on the facing block side of the second wall to an edge point p2 on the second wall side of the facing block is smaller than a length in the tread contact surface of the first wall. Accordingly, a positional relationship between the facing block and the sipe is satisfactory, and an opening portion of the region surrounded by the first wall, the second wall, and the sipe-facing wall surface of the facing block is narrow.Thus, mud and the like in the area surrounded by the first wall, the second wall and the facing block (the wall surface facing the cut) are effectively compressed during running, and this is advantageous in improving running performance on unpaved roads (for example, mud performance and the like).

[0016] In one embodiment of the present invention, inclined shoulder grooves that are inclined and extend with respect to the tire circumferential direction are preferably provided in shoulder regions in the tread portion, and an inclination direction of the inclined shoulder grooves is opposite to an inclination direction of the inclined grooves. The inclined shoulder grooves are provided as described above, and thus, a part of mud and the like in the inclined center grooves and a part of mud and the like in the inclined shoulder grooves are likely to flow into the sipes. Accordingly, mud and the like in the sipes are compressed, and a shear force is likely to be obtained, and thus this is advantageous in improving driving performance on unpaved roads (for example, mud performance and the like).

[0017] In this case, preferably, a shoulder block is provided between the inclined shoulder grooves adjacent in the tire circumferential direction. The shoulder block includes at least one wall surface with a wall surface angle larger than a wall surface angle of the center block, and the inclined shoulder grooves have a groove width increased toward a tire equator side. The shoulder block is provided as described above, and thus, when driving performance on unpaved roads (for example, mud performance and the like) is improved by the shoulder block, the rigidity of the shoulder block is improved to achieve damage resistance performance, and mud and the like in the grooves can also be likely to be expelled.

[0018] In this case, preferably, a groove bottom protrusion is formed in each of the inclined shoulder grooves, and the groove bottom protrusion extends outward in the tire transverse direction beyond an outer edge of the shoulder block. The groove bottom protrusion is provided as described above, and thus mud and the like can be likely to be separated in the inclined shoulder grooves. Note that the outer edge of the shoulder block refers to an edge portion of the shoulder block on the outer side in the tire transverse direction in the road contact surface, and refers to an edge formed by the road contact surface of the shoulder block and the side surface of the shoulder block on the outer side in the tire transverse direction.

[0019] In one embodiment of the present invention, a connecting groove is preferably provided in the center region of the tread portion, connecting the inclined grooves adjacent in the tire circumferential direction, and the connecting groove extends at an angle within ±10° with respect to the tire transverse direction in the tread contact surface. Accordingly, the traction performance can be further improved by the connecting groove.

[0020] In one embodiment of the present invention, preferably, a sipe is formed in each of the blocks provided in the tread portion, including at least one end coupled to a groove, and a sipe depth at the end of the sipe coupled to the groove is shallow. Accordingly, an edge effect due to the sipe is achieved, and traction performance is improved. Furthermore, a reduction in rigidity caused by providing the sipe can be suppressed, and the damage resistance performance of the blocks can be maintained.It should be noted that in one embodiment of the present invention, “sipe” refers to a fine groove having a groove width and a groove depth smaller than a groove width and a groove depth of each of various grooves (the inclined groove, the connecting groove, the inclined shoulder groove, and the like described above), and having a groove width of, for example, from 0.5 mm to 1.5 mm and a groove depth of, for example, from 1.5 mm to 14.0 mm.

[0021] In one embodiment of the present invention, various dimensions (a length and an angle) are values measured when a tire is mounted on a regular rim and inflated to a regular internal pressure and placed vertically on a flat surface with a regular load applied. Note that the "road contact surface" of each block refers to a surface portion of each block that actually comes into contact with a flat surface on which a tire is placed in this state, and excludes, for example, a chamfered portion that does not actually come into contact. In addition, "ground contact edges" in this state are both edge portions in the tire axial direction."Regular rim" refers to a rim defined by a standard for each tire according to a system of standards that includes standards on which tires are based, and refers to a "standard rim" in the case of JATMA, a "design rim" in the case of TRA, and a "measuring rim" in the case of ETRTO. "Regular internal pressure" refers to an air pressure defined by standards for each tire according to a system of standards that includes standards on which tires are based, and refers to a "maximum air pressure" in the case of JATMA, the maximum value according to the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "INFLATION PRESSURE" in the case of ETRTO. A “regular internal pressure” is 180 kPa for a tire on a passenger car.“Regular load” means a load defined by a standard for each tire according to a system of standards that includes standards on which tires are based and refers to a “maximum load capacity” in the case of JATMA, to the maximum value according to the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the case of TRA and to “LOAD CAPACITY” in the case of ETRTO. Brief description of the drawings Fig. 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 a pneumatic tire according to an embodiment of the present invention. Fig. 3 is an enlarged front view of a center block of Fig. 2. Fig. 4A and Fig. 4B are explanatory views illustrating the area of a center block. Fig. 5 is an enlarged front view of the vicinity of the center block of Fig. 2. Description of embodiments

[0022] Configurations of embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] As in Fig. 1, a pneumatic tire of one embodiment of the present invention includes a tread portion 1 extending in the tire circumferential direction and having a ring shape, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged on an inner side of the sidewall portions 2 in the tire radial direction. It should be noted that in Fig.1 the reference symbol CL indicates a tire equator and the reference symbol E indicates a ground contact edge.

[0024] A carcass layer 4 is disposed between the pair of left and right bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction and is folded back from a vehicle inner side to a vehicle outer side around a bead core 5 disposed in each of the bead portions 3. In addition, bead fillers 6 are disposed on an outer periphery of the bead cores 5, and each bead filler 6 is enclosed by a main body part and a folded-back portion of the carcass layer 4. Meanwhile, in the tread portion 1, a plurality of belt layers 7 (two layers in Fig.1) embedded on the outer peripheral side of the carcass layer 4. The belt layers 7 each include a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and the reinforcing cords of the different layers are arranged and overlap each other. In these belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set, for example, in the range of 10° to 40°. Further, a belt reinforcing layer 8 is provided on the outer peripheral 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, for example, to 0° to 5°.

[0025] The embodiment of the present invention is applied to such a general pneumatic tire; however, the cross-sectional structure of the pneumatic tire is not limited to the basic structure described above.

[0026] As in Fig. 1 and Fig.As illustrated in FIG. 2, a plurality of center blocks 10 are provided in a central region in an outer surface of the tread portion 1. The center blocks 10 are arranged and paired (block pairs 10') via inclined grooves 20 that are inclined and extend with respect to the tire circumferential direction. Then, the center blocks 10 on one side of the block pairs 10' (the left side of the tire equator in the figure) extend across the tire equator from one side (the left side of the tire equator in the figure) to the other side (the right side of the tire equator in the figure) of the tire equator, and the center blocks 10 on the other side (the right side of the tire equator in the figure) extend across the tire equator from the other side (the right side of the tire equator in the figure) to the one side (the left side of the tire equator in the figure) of the tire equator.

[0027] As in Fig.As illustrated in an enlarged manner in FIG. 3, in a wall surface of each of the center blocks 10 on the outer side in the tire transverse direction (the wall surface on a side opposite to the inclined groove 20), a sipe 11 including two wall surfaces (a first wall 11a and a second wall 11b) connected to each other in a V-shape in the tread contact surface is provided. In the tread contact surface, the first wall 11a extends at an angle within ±20° with respect to the tire circumferential direction, and the second wall 11b extends at an angle within ±10° with respect to the tire transverse direction. That is, in the tread contact surface, an angle θa formed by the first wall 11a with respect to the tire circumferential direction is within ±20°, and an angle θb formed by the second wall 11b with respect to the tire circumferential direction is within ±10°.In addition, each of the wall surface angles of the first wall 11a and the second wall 11b is larger than the wall surface angle of the wall surface provided with the notch 11.

[0028] As described above, the center blocks 10 are provided and form the block pairs 10', and the center blocks 10 extend across the tire equator. Thus, edge components of the center blocks 10 can be increased in the tire transverse direction, and driving performance on unpaved roads (for example, mud performance and the like) can be improved. In addition, each of the center blocks 10 includes the sipe 11, and thus the sipe 11 can effectively grip mud and the like in the groove. In this case, the extending directions of the first wall 11a and the second wall 11b are set to the angles described above. Thus, the first wall 11a can suppress tire slippage, and the second wall 11b can improve traction performance, and this is advantageous in improving driving performance.In addition, each of the wall surface angles of the first wall 11a and the second wall 11b is relatively larger than each of the wall surface angles of other portions of the center blocks 10. Thus, even if the sipe 11 is provided, the block rigidity can be sufficiently maintained to a high degree, and this is advantageous in improving the damage resistance performance of the blocks.

[0029] In this case, if the center blocks 10 each have a shape that does not extend beyond the tire equator, edge components of the center blocks 10 in the tire transverse direction cannot be sufficiently secured, and driving performance on unpaved roads cannot be improved. If the angle θa of the first wall 11a is not within the range of ±20° with respect to the tire circumferential direction, the extending direction in the tread contact surface of the first wall 11a is excessively inclined with respect to the tire circumferential direction. Thus, an edge effect due to the first wall 11a cannot be sufficiently achieved, and tire slippage cannot be sufficiently suppressed. If the angle θb of the second wall 11b is not within the range of ±10° with respect to the tire transverse direction, the extending direction in the tread contact surface of the second wall 11b is excessively inclined with respect to the tire transverse direction.Thus, the edge effect due to the first wall 11b cannot be sufficiently achieved, and the traction performance cannot be sufficiently improved. When each of the wall surface angles of the first wall 11a and the second wall 11b is smaller than the wall surface angle of the wall surface provided with the sipe 11, it is difficult to sufficiently ensure the block rigidity.

[0030] Note that it is only necessary that the wall surface angles of the first wall 11a and the second wall 11b satisfy the above-described size relationship with respect to the wall surface angle of the wall surface provided with the notch 11. However, a groove wall angle of the first wall 11a may be set to, for example, from 5° to 20°, a groove wall angle of the second wall 11b may be set to, for example, from 5° to 20°, and the wall surface angle of the wall surface provided with the notch 11 may be set to, for example, from 2° to 10°. Then, preferably, each of the wall surface angles of the first wall 11a and the second wall 11b is set to be from 1.5 times to 4.0 times larger than the wall surface angle of the wall surface provided with the notch 11.

[0031] In such a center block 10, it is preferable that a length Lb in the tread contact surface of the second wall 11b is 0.5 times to 2.0 times longer than a length La in the tread contact surface of the first wall 11a. An aspect ratio of the first wall 11a and the second wall 11b is specified as described above, and thus, suppression of slippage due to the first wall 11a and improvement of traction performance due to the second wall 11b can be provided in a well-balanced and compatible manner. In this case, if the length Lb of the second wall 11b is less than 0.5 times the length La of the first wall 11a, edge traction decreases, and the balance of a V-shape of the sipe 11 is lost. Thus, the shear force due to the sipe 11 decreases.When the length Lb of the second wall 11b is greater than 2.0 times the length La of the first wall 11a, slippage cannot be sufficiently suppressed, and a balance of a V-shape of the sipe 11 is lost. Thus, the shear force due to the sipe 11 decreases. More preferably, the length Lb in the tread contact surface of the second wall 11b is greater than the length La in the tread contact surface of the first wall 11a, and the length Lb can be set to be from 1.1 times to 2.0 times greater than the length La.

[0032] Further, in the center block 10 in an embodiment of the present invention, preferably in the tread contact surface, the area of a cut portion (a hatched portion of Fig.4A) from 5% to 20% of the ground contact area of the center block 10 (a hatched section of Fig.4B). The size of the sipe 11 is set to the appropriate range with respect to the center block 10 as described above, and thus an effect (improvement of driving performance on dirt roads) due to the sipe 11 can be effectively exerted while maintaining satisfactory block rigidity. In this case, if the area of the sipe portion is less than 5% of the ground contact area of the center block 10, the sipe 11 is excessively small. Thus, a shear force due to the sipe 11 cannot be sufficiently achieved. If the area of the sipe portion is larger than 20% of the ground contact area of the center block 10, the sipe 11 is excessively large with respect to the center block 10. Thus, it is difficult to maintain satisfactory block rigidity.It should be noted that, as in the illustrated example, in a case where extending directions in the tread contact surface of the wall surface provided with the sipe 11 on both sides of the sipe 11 are different from each other, as the extension line of the wall surface provided with the sipe 11, a connecting point of the first wall 11a and the wall surface provided with the sipe 11 in the tread contact surface (an edge point p1 on the wall surface side of the first wall 11a provided with the sipe 11) and a connecting point of the second wall 11b and the wall surface provided with the sipe 11 (an edge point p2 on the wall surface side of the second wall 11b provided with the sipe 11) are used.

[0033] The inclined groove 20 between the two center blocks 10 constituting the block pair 10' may extend with a constant width. However, as in the illustrated example, a wide-width portion 21 having a larger groove width than groove widths of other portions of the inclined groove 20 may be provided in the center of the extending direction of the inclined groove 20 (a portion overlapping with the tire equator CL in the illustrated example) by bending, in the tread contact surface, the wall surface on the inclined groove 20 side of the center block 10. The wide-width portion 21 is provided as described above, and thus mud and the like are pressed into the wide-width portion 21 during running, and a shearing force is achieved. Thus, this is advantageous in improving driving performance on unpaved roads.

[0034] In the central region, a plurality of block pairs 10' are arranged at a distance in the tire circumferential direction, and thus, grooves are formed between the block pairs 10' adjacent to each other in the tire circumferential direction. As such grooves, as illustrated in the figure, a connecting groove 30 is preferably provided that connects the inclined grooves 20 adjacent to each other in the tire circumferential direction. Specifically, it is preferable that the connecting groove 30 extends at an angle within ±10° with respect to the tire transverse direction in the tread contact surface. Furthermore, it is preferable that the connecting groove 30 is provided at a position intersecting the tire equator CL. The connecting groove 30 is provided as described above, and thus, the traction performance can be further improved by the connecting groove 30.In this case, if the angle of the connecting groove 30 is not within the range of ±10° with respect to the tire transverse direction, the extending direction in the tread contact surface of the connecting groove 30 is excessively inclined with respect to the tire transverse direction. Thus, an edge effect due to the connecting groove 30 cannot be sufficiently achieved, and the traction performance cannot be sufficiently improved.

[0035] With regard to the above-described structure of the center region (the structure of the center block 10 and the like), tread patterns of other regions (structures of land portions and grooves other than the center block 10) are not particularly limited. However, as shown in Fig. 2 and Fig.5, preferably a facing block 40 including a wall surface facing the notch 11 is provided. It is only necessary that the facing block 40 encloses the wall surface facing the notches 11. Thus, as in Fig. 2 and Fig. 5, a shoulder block 50 provided in a shoulder region may function as the facing block 40. Alternatively, in addition to the center block 10 provided in the center region and the shoulder block 50 provided in the shoulder region, the facing block 40 may be provided including the wall surface facing the recess 11. In any case, such a facing block 40 is provided, and thus mud and the like are collected in a region (a hatched portion of Fig.5), which is formed by the first wall 11a, the second wall 11b and the wall surface of the facing block 40 (the shoulder block 50 in Fig. 5) is compressed during driving, achieving high shear force. Thus, this is beneficial for improving driving performance on unpaved roads (e.g., mud performance, etc.).

[0036] In this case, in the area (the hatched section of Fig.5) surrounded by the first wall 11a, the second wall 11b, and the wall surface of the facing block 40 (the shoulder block 50) facing the notch 11, preferably, a distance Da in the tread contact surface from an edge point P1 on the facing block 40 side (the shoulder block 50 side) of the first wall 11a to an edge point p1 on the first wall 11a side of the facing block 40 (the shoulder block 50) is smaller than a length Lb in the tread contact surface of the second wall 11b, and a distance Db from an edge point P2 on the facing block 40 side (the shoulder block 50 side) of the second wall 11b to an edge point p2 on the second wall 11b side of the facing block 40 (the shoulder block 50) is smaller than the length La in the tread contact surface of the first wall 11a.A positional relationship of the facing block 40 (the shoulder block 50) and the sipe 11 is optimized as described above, and thus an opening portion of the area (the hatched portion in . Fig.5) surrounded by the first wall 11a, the second wall 11b, and the wall surface of the facing block 40 (the shoulder block 50) facing the notch 11 is narrow. Thus, mud and the like in the area surrounded by the first wall 11a, the second wall 11b, and the wall surface of the facing block 40 (the shoulder block 50) facing the notch 11 are effectively compressed during running, and this is advantageous in improving running performance on unpaved roads (for example, mud performance and the like). Specifically, in order to achieve the above-described effect, it is preferable that the distance Da is set to be from 0.4 times to 0.8 times greater than the length Lb, and the distance Db is set to be from 0.4 times to 0.8 times greater than the length La.

[0037] In one embodiment of the present invention, a plurality of shoulder blocks 50 are preferably provided in the shoulder regions in addition to the above-described center blocks 10, as in the illustrated example. In this case, inclined shoulder grooves 60 that are inclined and extend with respect to the tire transverse direction are formed between the shoulder blocks 50 adjacent in the tire circumferential direction. The shoulder block 50 may function as the above-described facing block 40 or may be provided separately from the facing block 40. The shape of the shoulder block 50 does not have to be particularly limited and may be a shape that extends along the tire transverse direction to have many edge components in the tire transverse direction, as illustrated in the figure.Furthermore, to ensure block rigidity, it is preferable that the wall surface angle of at least one wall surface of the shoulder block 50 be larger than the wall surface angle of the center block 10. Specifically, among the wall surfaces constituting the shoulder block 50, the wall surface angle of the wall surface forming the inclined shoulder groove 60 is set to be larger than the wall surface angle of the center block 10, and this is effective for ensuring block rigidity. The wall surface angles of the other wall surfaces may be identical to the wall surface angle of the center block 10. The wall surface angle of the wall surface with the large wall surface angle may be set, for example, from 10° to 20° larger than the above-described wall surface angle of the center block 10 (from 2° to 10°).

[0038] In the case of providing the shoulder block 50 as described above, the inclined shoulder groove 60 preferably has an inclination direction opposite to an inclination direction of the inclined groove 20 provided in the central region. The inclined shoulder groove 60 is provided as described above, and part of mud and the like in the inclined groove 20 in the central region and part of mud and the like in the inclined shoulder groove 60 are likely to flow into the sipe 11. Accordingly, mud and the like in the sipe 11 are compressed, and shearing force is likely to be achieved. Thus, this is advantageous in improving driving performance on unpaved roads (for example, mud performance and the like).In this case, when the inclination directions of the inclined groove 20 in the central region and the inclined shoulder groove 60 are aligned in the same direction, sludge and the like are likely to flow in a single direction from the inclined groove 20 in the central region to the inclined shoulder groove 60, and the discharge performance of sludge and the like is improved. However, an effect is difficult to achieve due to the recess 11.

[0039] The groove width of the inclined shoulder groove 60 may be constant throughout the length of the inclined shoulder groove 60. However, in order to improve the discharge performance of sludge and the like in the grooves, the groove width is preferably larger toward the tire equator CL side, as illustrated in the figure. Specifically, when the wall surface angle of the shoulder block 50 is larger than the wall surface angle of the center block 10, in order to achieve block rigidity as described above, the groove width of the inclined shoulder groove 60 is relatively small. Thus, the groove width is set to be larger toward the tire equator CL side, and thus, ensuring block rigidity and improving the discharge performance of sludge and the like can be provided in a well-balanced and compatible manner.

[0040] In the illustrated example, groove bottom protrusions 61 are formed in the groove bottoms of the inclined shoulder grooves 60. The groove bottom protrusion 61 protrudes from the groove bottom in the center portion in the groove width direction of the inclined shoulder groove 60 and has a protrusion height set to be, for example, from 10% to 25% of the groove depth of the inclined shoulder groove 60 and a groove width set to be from 5% to 20% of the groove width of the inclined shoulder groove 60. The groove bottom protrusion 61 prevents mud and the like from being accumulated on the groove bottom of the inclined shoulder groove 60 and plays a role in promoting the separation of mud and the like by vibration of the groove bottom protrusion 61 during traveling.Preferably, the groove bottom protrusion 61 extends outward in the tire width direction beyond an outer edge of the shoulder block 50, that is, an edge of the shoulder block 50 on the outer side in the tire width direction in the road contact surface (an edge formed by the road contact surface of the shoulder block 50 and the side surface of the shoulder block 50 on the outer side in the tire width direction). The groove bottom protrusion 61 is provided as described above, mud and the like in the inclined shoulder groove 60 can likely be effectively discharged.

[0041] As described above, the tread portion 1 of one embodiment of the present invention necessarily includes the center blocks 10 and optionally includes the facing blocks 40 and the shoulder blocks 50. Preferably, any of the blocks includes a sipe 70 having at least one end coupled to the groove (the inclined groove 20, the connecting groove 30, the inclined shoulder groove 60, and the like). Then, at the end of the sipe 70 coupled to the groove, a sipe depth can be shallow.For example, in the illustrated example, the center block 10 is provided with a sipe 71 including one end connected to the connecting groove 30 and the other end connected to the inclined groove 20 (the sipe 11), and a sipe 72 including one end connected to the inclined groove 20 (the sipe 11) and the other end connected to the inclined shoulder groove 60. Furthermore, the shoulder block 50 is provided with a sipe 73 including one end connected to the inclined shoulder groove 60 and the other end connected to a depressed portion having a zigzag shape formed from the road contact surface to the side surface of the shoulder block 50. With respect to the slats 71, 72 and 73, both ends of the slat 71, both ends of the slat 72 and one end of the slat 73 are connected to the grooves.Thus, one end and / or the other end of the sipe 71, one end and / or the other end of the sipe 72, and one end of the sipe 73 each have a shallow sipe depth. The sipes 70 (the sipes 71, 72, and 73) are provided as described above, and thus, an edge effect due to the sipes 70 is achieved, and traction performance is improved. In addition, a reduction in rigidity caused by providing the sipes 70 can be suppressed, and the damage resistance performance of the blocks can be maintained. Note that, in the case of varying the depth of each of the sipes 70, a sipe depth of a relatively shallower portion can be set to be from 0.1 times to 0.4 times greater than a sipe depth of a relatively deep portion in each of the sipes 70. Example

[0042] Twenty-two types of pneumatic tires of Prior Art Example 1, Comparative Examples 1 to 4 and Examples 1 to 17 were tested with a tire size of LT265 / 70R17, Fig. 1 illustrated basic structure and the tread pattern of Fig.2 as a basic pattern and with the setting of the angle θa of the first wall with respect to the tire circumferential direction, the angle θb of the second wall with respect to the tire transverse direction, the wall surface angles of the first wall and the second wall, a ratio Lb / La of the length La of the first wall and the length Lb of the second wall, a sipe area of the center block with respect to the ground contact surface, the angle of the connecting groove with respect to the tire transverse direction, a size ratio between the length La of the first wall and the distance Db, a size ratio between the length Lb of the second wall and the distance Da, an inclination direction of the inclined groove, the wall surface angle of the shoulder block, the groove width variation of the inclined shoulder groove, the position of the outer edge of the groove bottom protrusion and the variation of the sipe depth as shown in Table 1 and Table 2.

[0043] It should be noted that with regard to the item "Wall surface angles of the first and second walls" in Table 1 and Table 2, the cases where each of the wall surface angles is greater than, equal to, and smaller than the angle of the wall surface provided with the notch are indicated as "Large", "Equal", and "Small", respectively. With regard to the item "Inclination direction of the inclined shoulder groove" in Table 1 and Table 2, the cases where the inclination direction of the inclined shoulder groove is opposite to and equal to the inclination direction of the inclined groove in the central region are indicated as "Opposite" and "Equal", respectively. With regard to the item "Wall surface angle of the shoulder block" in Table 1 and Table 2, the cases where the wall surface angle of the shoulder block is greater than and smaller than the wall surface angle of the central block are indicated as "Large" and "Small", respectively.Regarding the item "Groove width variation of the inclined shoulder groove" in Table 1 and Table 2, the cases where the groove width of the inclined shoulder groove is larger toward the tire equator side and is completely constant along the length of the inclined shoulder groove are indicated as "Yes" and "No" respectively. Regarding the item "Position of the outer edge of the groove bottom protrusion" in Table 1 and Table 2, the cases where the groove bottom protrusion extends beyond the outer edge of the shoulder block and ends blindly before the outer edge of the shoulder block are indicated as "Outside" and "Inside" respectively. Regarding the item "Variation of sipe depth" in Table 1 and Table 2, the cases where the sipe depth is shallow and constant at the end of the sipe coupled to the groove are indicated as "Yes" and "No" respectively.

[0044] These twenty-two types of pneumatic tires were evaluated for mud performance and damage resistance performance using the evaluation methods described below, and the results are also shown in Table 1 and Table 2. Sludge performance

[0045] The test tires were mounted on 17 × 8.0-inch wheels, inflated to an air pressure of 450 kPa, and mounted on a test vehicle (light truck). A sensory evaluation of traction performance and starting performance was conducted by a test driver on a muddy road surface. The evaluation results are expressed as an index value, with the prior art example 1 assigned a value of 100. Higher index values indicate superior mud performance. Damage resistance performance

[0046] After evaluating mud performance, a weight of each tire was measured, and the difference (weight loss) between the measured weight and the original weight was determined. The evaluation results are expressed as an index value, with a multiplicative inverse of the prior art example 1 assigned a value of 100. Larger index values indicate lower weight loss and superior damage resistance performance. [Table 1-I] Example of the prior art 1 Comparison example 1 Comparison example 2 Comparison example 3 Angle θa of the first wall ° 30 30 15 15 Angle θb of the second wall ° 20 5 20 5 Wall surface angle of the first wall and the second wall Same Same Same Same Ratio Lb / La 3,0 3,0 3,0 3,0 incision area % 3 3 3 3 Angle of the connecting groove ° 30 30 30 30 Relationship between length La and distance Db La < Db La < Db La < Db La < Db Relationship between length Lb and distance Da Lb < Da Lb < Da Lb < Da Lb < Da Inclination direction of the inclined shoulder groove Opposite Opposite Opposite Opposite Wall surface angle of the shoulder block Same Same Same Same Groove width variation of the inclined shoulder groove No No No No Position of the outer edge of the groove bottom projection Within Within Within Within Variation of slat depth No No No No Sludge performance Index value 100 102 101 103 Damage resistance performance Index value 100 98 98 98 [Table 1-II] Comparison example 4 Example 1 Example 2 Example 3 Angle θa of the first wall ° 15 15 0 20 Angle θb of the second wall ° 5 5 0 10 Wall surface angle of the first wall and the second wall Small Large Large Large Ratio Lb / La 3,0 3,0 3,0 3,0 incision area % 3 3 3 3 Angle of the connecting groove ° 30 30 30 30 Relationship between length La and distance Db La < Db La < Db La < Db La < Db Relationship between length Lb and distance Da Lb < Da Lb < Da Lb < Da Lb < Da Inclination direction of the inclined shoulder groove Opposite Opposite Opposite Opposite Wall surface angle of the shoulder block Same Same Same Same Groove width variation of the inclined shoulder groove No No No No Position of the outer edge of the groove bottom projection Within Within Within Within Variation of slat depth No No No No Sludge performance Index value 103 105 106 104 Damage resistance performance Index value 95 104 102 104 [Table 1-III] Example 4 Example 5 Example 6 Angle θa of the first wall ° 15 15 15 Angle θb of the second wall ° 5 5 5 Wall surface angle of the first wall and the second wall Large Large Large Ratio Lb / La 1,3 0,5 2,0 incision area % 3 3 3 Angle of the connecting groove ° 30 30 30 Relationship between length La and distance Db La < Db La < Db La < Db Relationship between length Lb and distance Da Lb < Da Lb < Da Lb < Da Inclination direction of the inclined shoulder groove Opposite Opposite Opposite Wall surface angle of the shoulder block Same Same Same Groove width variation of the inclined shoulder groove No No No Position of the outer edge of the groove bottom projection Within Within Within Variation of slat depth No No No Sludge performance Index value 107 105 106 Damage resistance performance Index value 104 103 104 [Table 2-I] Example 7 Example 8 Example 9 Example 10 Angle θa of the first wall ° 15 15 15 15 Angle θb of the second wall ° 5 5 5 5 Wall surface angle of the first wall and the second wall Large Large Large Large Ratio Lb / La 1,3 1,3 1,3 1,3 incision area % 12 5 20 12 Angle of the connecting groove ° 30 30 30 30 Relationship between length La and distance Db La < Db La < Db La < Db La > Db Relationship between length Lb and distance Da Lb < Da Lb < Da Lb < Da Lb > Da Inclination direction of the inclined shoulder groove Opposite Opposite Opposite Opposite Wall surface angle of the shoulder block Same Same Same Same Groove width variation of the inclined shoulder groove No No No No Position of the outer edge of the groove bottom projection Within Within Within Within Variation of slat depth No No No No Sludge performance Index value 109 108 110 114 Damage resistance performance Index value 103 104 102 104 [Table 2-II] Example 11 Example 12 Example 13 Example 14 Angle θa of the first wall ° 15 15 15 15 Angle θb of the second wall ° 5 5 5 5 Wall surface angle of the first wall and the second wall Large Large Large Large Ratio Lb / La 1,3 1,3 1,3 1,3 incision area % 12 12 12 12 Angle of the connecting groove ° 30 5 0 10 Relationship between length La and distance Db La > Db La > Db La > Db La > Db Relationship between length Lb and distance Da Lb > Da Lb > Da Lb > Da Lb > Da Inclination direction of the inclined shoulder groove Same Opposite Opposite Opposite Wall surface angle of the shoulder block Same Same Same Same Groove width variation of the inclined shoulder groove No No No No Position of the outer edge of the groove bottom projection Within Within Within Within Variation of slat depth No No No No Sludge performance Index value 107 117 117 116 Damage resistance performance Index value 104 104 104 104 [Table 2-III] Example 15 Example 16 Example 17 Angle θa of the first wall ° 15 15 15 Angle θb of the second wall ° 5 5 5 Wall surface angle of the first wall and the second wall Large Large Large Ratio Lb / La 1,3 1,3 1,3 incision area % 12 12 12 Angle of the connecting groove ° 5 5 5 Relationship between length La and distance Db La > Db La > Db La > Db Relationship between length Lb and distance Da Lb > Da Lb > Da Lb > Da Inclination direction of the inclined shoulder groove Opposite Opposite Opposite Wall surface angle of the shoulder block Large Large Large Groove width variation of the inclined shoulder groove Yes Yes Yes Position of the outer edge of the groove bottom projection Within Within Outside Variation of slat depth No Yes Yes Sludge performance Index value 120 120 122 Damage resistance performance Index value 106 108 108

[0047] As can be seen from Table 1 and Table 2, each of Examples 1 to 17 improved the mud performance and damage resistance performance compared to Prior Art Example 1. Note that the evaluation was conducted only on mud performance on muddy road surfaces. However, even in the case of running on other unpaved roads (snow-covered roads, sandy ground surfaces, rocky ground surfaces, and the like), the tire of one embodiment of the present invention exerts the similar function with respect to snow, sand, gravel, stones, and the like on road surfaces as in the case of running on muddy roads. Thus, excellent running performance on unpaved roads can be exerted, and excellent damage resistance performance can also be achieved.

[0048] Meanwhile, in Comparative Examples 1 and 2, the angle of the first wall or the second wall (θa or θb) was excessively large, and thus, an effect of improving sludge performance could not be sufficiently achieved. In addition, each of the wall surface angles of the first wall and the second wall was the same as the angle of the incised wall surface of the center block, and thus the damage resistance performance was deteriorated. In Comparative Examples 3 and 4, each of the wall surface angles of the first wall and the second wall was the same as the angle of the incised wall surface of the center block, and thus the damage resistance performance was deteriorated. List of reference symbols 1 tread section 2 side wall section 3 bead section 4 carcass layers 5 bead core 6 bead fillers 7 belt layer 8 Belt reinforcement layer 10 Middle block 11 incision 11a First Wall 11b Second Wall 20 Inclined groove 30 connecting groove 40 Facing Block 50 shoulder block 60 Inclined shoulder groove 61 Groove bottom projection 70 (71, 72, 73) slat CL Tire Equator E Ground contact edge

Claims

[1] Pneumatic tire, comprising: a tread portion (1) extending in a tire circumferential direction and having a ring shape; a pair of sidewall portions (2) arranged on both sides of the tread portion (1); and a pair of bead portions (3) arranged on an inner side of the sidewall portions (2) in the tire radial direction, wherein a plurality of center blocks are provided in a center region of the tread portion (1), wherein the plurality of center blocks are arranged and form pairs over inclined grooves (20) which are inclined and extend with respect to a tire circumferential direction, wherein center blocks on one side of the pairs of the plurality of center blocks extend across a tire equator (CL) from one side to the other side of the tire equator (CL), and wherein center blocks on the other side extend across the tire equator (CL) from the other side to the one side of the tire equator (CL), wherein each of the plurality of center blocks includes a sipe (11) formed of two wall surfaces connected to each other in a V-shape in a tread contact surface, where in the tread contact surface the two wall surfaces include: a first wall (11a) extending at an angle within ±20° with respect to the tire circumferential direction; and a second wall (11b) extending at an angle within ±10° with respect to the tire transverse direction, and wherein each of wall surface angles of the first wall (11a) and the second wall (11b) is greater than a wall surface angle of a wall surface provided with the notch (11), wherein each of the wall surface angles of the first wall (11a) and the second wall (11b) is set 1.5 times to 4.0 times larger than the wall surface angle of the wall surface provided with the notch (11). [2] A pneumatic tire according to claim 1, wherein the second wall (11b) has a length in the tread contact surface that is from 0.5 times to 2.0 times greater than a length in the tread contact surface of the first wall. [3] A pneumatic tire according to claim 1 or 2, wherein in the tread contact surface, the area of a sipe portion surrounded by the first wall, the second wall (11b) and an extension line of the wall surface provided with the sipe (11) is from 5% to 20% of the ground contact area of the center block (10). [4] A pneumatic tire according to any one of claims 1 to 3, wherein a facing block (40) including a wall surface facing the sipe (11) is provided in the tread portion (1). [5] A pneumatic tire according to claim 4, wherein, in a region surrounded by the first wall, the second wall (11b), and the wall surface of the facing block (40) facing the sipe (11), a distance in the tread contact surface from an edge point P1 on the facing block (40) side of the first wall (11a) to an edge point p1 on the first wall (11a) side of the facing block (40) is smaller than a length in the tread contact surface of the second wall (11b), and a distance from an edge point P2 on the facing block (40) side of the second wall (11b) to an edge point p2 on the second wall (11b) side of the facing block (40) is smaller than a length in the tread contact surface of the first wall. [6] A pneumatic tire according to any one of claims 1 to 5, wherein inclined shoulder grooves (60) inclined and extending with respect to the tire circumferential direction are provided in shoulder regions in the tread portion, and an inclination direction of the inclined shoulder grooves (60) is opposite to an inclination direction of the inclined grooves (20). [7] A pneumatic tire according to claim 6, wherein a shoulder block (50) is provided between the inclined shoulder grooves (60) adjacent in the tire circumferential direction, the shoulder block (50) includes at least one wall surface with a wall surface angle that is greater than the wall surface angle of the center block (10), and the inclined shoulder grooves (60) have a groove width which is increased towards a tire equator side. [8] A pneumatic tire according to claim 7, wherein a groove bottom projection (61) is formed in each of the inclined shoulder grooves (60), and the groove bottom projection (61) extends outward in the tire transverse direction beyond an outer edge of the shoulder block (50). [9] Pneumatic tire according to one of claims 1 to 8, wherein in the central region of the tread portion, a connecting groove (30) connecting the inclined grooves (20) adjacent in the tire circumferential direction is provided, and the connecting groove (30) extends at an angle within ±10° with respect to the tire transverse direction in the tread contact surface. [10] A pneumatic tire according to any one of claims 1 to 9, wherein in each of the blocks provided in the tread portion, a sipe (70) including at least one end coupled to a groove is formed, and a sipe depth at the end of the sipe (70) coupled to the groove is shallow.

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