JP2019081448A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire that can make both traction performance and durability performance of the tire compatible.SOLUTION: The pneumatic tire comprises: a plurality of shoulder lug grooves 21 which open to a tire grounding end; center lug grooves 22 which cross a tire equator surface CL and extend obliquely with respect to a tire circumferential direction and communicate with the shoulder lug grooves 21; and a plurality of shoulder blocks 31 and a plurality of center blocks 32 partitioned by the shoulder lug grooves 21 and the center lug grooves 22. Further, the center blocks 32 comprise rectangular notch parts 51 at positions of edge parts outside in a tire width direction thereof, which are opposing to edge parts inside in the tire width direction of the shoulder blocks 31.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire capable of achieving both tire traction performance and durability performance.

  In an off-road tire used for running on a sandy ground, a rocky place, etc., a tread pattern mainly composed of inclined lug grooves and block rows is adopted in order to enhance the tire's traction. The technique described in patent document 1 is known as a conventional pneumatic tire which employ | adopts this structure.

JP, 2015-223884, A

  On the other hand, in the tire for off-road described above, there is a problem that damage such as a block of a block (a so-called chunk) or the like should be suppressed during traveling.

  Then, this invention is made | formed in view of the above, Comprising: It aims at providing the pneumatic tire which can make the traction performance and durability performance of a tire make compatible.

  In order to achieve the above object, a pneumatic tire according to the present invention includes a plurality of shoulder lug grooves opened at the tire ground contact end, and extends while being inclined with respect to the tire circumferential direction while intersecting the tire equatorial plane. A pneumatic tire comprising: a center lug groove communicating with a shoulder lug groove; and a plurality of shoulder blocks and a plurality of center blocks defined in the shoulder lug groove and the center lug groove, wherein the center block is a tire width A rectangular notch portion is provided at a position which is an edge portion on the outer side in the direction and which faces an edge portion on the inner side in the tire width direction of the shoulder block.

  According to the pneumatic tire according to the present invention, the notch portion of the center block is disposed at a position opposite to the edge portion in the tire width direction of the shoulder block, so the groove volume between the center block and the shoulder block is secured. There is an advantage that the traction of the tire is improved. In addition, the rectangular notch has an advantage that the volume of the notch can be increased while securing the width of the block tread compared to, for example, the triangular notch. In addition, since the notch portion is shallower than the lug groove, there is an advantage that the rigidity of the block is secured and the durability performance of the tire is secured.

FIG. 1 is a sectional view in the tire meridian direction showing a pneumatic tire according to an embodiment of the present invention. FIG. 2 is a plan view showing a tread surface of the pneumatic tire described in FIG. FIG. 3 is an enlarged view showing the main part of the tread pattern shown in FIG. FIG. 4 is an explanatory view showing the center block described in FIG. FIG. 5 is an enlarged view showing a cutout of the center block shown in FIG. FIG. 6 is a cross-sectional view taken along line A of FIG. FIG. 7 is an explanatory view showing a shoulder block and a center block described in FIG. FIG. 8 is a chart showing the results of performance tests of the pneumatic tire according to the embodiment of the present invention.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited by the embodiment. Further, constituent elements of this embodiment include substitutable and substitutable ones while maintaining the identity of the invention. In addition, the plurality of modifications described in this embodiment can be arbitrarily combined within the scope of one skilled in the art.

[Pneumatic tire]
FIG. 1 is a sectional view in the tire meridian direction showing a pneumatic tire according to an embodiment of the present invention. The figure shows a cross-sectional view of one side region in the tire radial direction. Moreover, the same figure has shown the radial tire for passenger cars as an example of a pneumatic tire.

  In the figure, the cross section in the tire meridian direction means a cross section when the tire is cut along a plane including a tire rotation axis (not shown). Further, a reference symbol CL is a tire equatorial plane, which means a plane perpendicular to the tire rotation axis passing through the center point of the tire in the tire rotation axis direction. Further, the tire width direction means a direction parallel to the tire rotation axis, and the tire radial direction means a direction perpendicular to the tire rotation axis.

  The pneumatic tire 1 has an annular structure centered on the tire rotation axis, and includes a pair of bead cores 11 and 11, a pair of bead fillers 12 and 12, a carcass layer 13, a belt layer 14, and a tread rubber 15. , A pair of sidewall rubbers 16, 16 and a pair of rim cushion rubbers 17, 17 (see FIG. 1).

  The pair of bead cores 11, 11 is formed by annularly and multiply winding one or a plurality of bead wires made of steel, and is embedded in the bead portion to form a core of the left and right bead portions. The pair of bead fillers 12, 12 are disposed on the outer circumferences of the pair of bead cores 11, 11 in the tire radial direction to reinforce the bead portions.

  The carcass layer 13 has a single layer structure of one carcass ply or a multilayer structure of laminating a plurality of carcass plies, and is toroidally bridged between the left and right bead cores 11 to form a tire skeleton. Configure Further, both ends of the carcass layer 13 are wound and locked outward in the tire width direction so as to wrap around the bead core 11 and the bead filler 12. The carcass ply of the carcass layer 13 is formed by coating a plurality of carcass cords made of steel or an organic fiber material (for example, aramid, nylon, polyester, rayon, etc.) with a coated rubber and rolling it. It has a carcass angle (defined as an inclination angle in the longitudinal direction of the carcass cord with respect to the tire circumferential direction) of not less than [deg] and not more than 95 [deg]. In the configuration of FIG. 1, the carcass layer 13 has a single-layer structure consisting of a single carcass ply, but not limited to this, it has a multilayer structure in which the carcass layer 13 is formed by laminating a plurality of carcass plies. Also good (not shown).

  The belt layer 14 is formed by laminating a pair of cross belts 141 and 142, a belt cover 143 and a pair of belt edge covers 144, and is disposed so as to be wound around the outer periphery of the carcass layer 13. The pair of cross belts 141 and 142 is formed by coating a plurality of belt cords made of steel or organic fiber material with a coating rubber and rolling it, and the belt angle of 20 [deg] or more and 55 [deg] or less in absolute value Have. In addition, the pair of cross belts 141 and 142 have mutually opposite belt angles (defined as inclination angles in the longitudinal direction of the belt cord with respect to the tire circumferential direction), and cross the longitudinal directions of the belt cords Laminated (so-called cross-ply structure). The belt cover 143 and the pair of belt edge covers 144 are configured by coating a belt cord made of steel or an organic fiber material with a coat rubber, and have a belt angle of 0 [deg] or more and 10 [deg] or less in absolute value. Further, the belt cover 143 and the pair of belt edge covers 144 are, for example, strip materials formed by coating one or a plurality of belt cords with a coat rubber, and the strip materials are applied to the outer peripheral surfaces of the cross belts 141 and 142. And a plurality of helical windings in the circumferential direction of the tire.

  The tread rubber 15 is disposed on the outer periphery of the carcass layer 13 and the belt layer 14 in the tire radial direction to form a tread portion of the tire. The pair of sidewall rubbers 16, 16 are respectively disposed on the outer side in the tire width direction of the carcass layer 13 to constitute left and right sidewall portions. The pair of rim cushion rubbers 17, 17 are disposed on the inner side in the tire radial direction of the left and right bead cores 11, 11 and the wound portion of the carcass layer 13, respectively, to form a rim fitting surface of the bead portion.

[Tread pattern]
FIG. 2 is a plan view showing a tread surface of the pneumatic tire described in FIG. The figure shows a tread pattern of an off-road tire. In the figure, the tire circumferential direction refers to a direction around the tire rotation axis. Further, reference symbol T is a tire ground contact end, and dimension symbol TW is a tire contact width. Moreover, in the same figure, the groove center line of the shoulder lug groove 21 and the center lug groove 22 which are mentioned later is shown by an imaginary line.

  As shown in FIG. 2, the pneumatic tire 1 includes a shoulder lug groove 21, a center lug groove 22 and a communication groove 23, and a plurality of shoulder blocks 31 and a plurality of center blocks defined by the lug grooves 21 to 23. And 32.

  The shoulder lug groove 21 is a lug groove that opens at the tire ground contact end T, and particularly in an off-road tire, has a groove width of 20 mm or more and a groove depth of 10 mm or more. Further, the plurality of shoulder lug grooves 21 are arranged at a predetermined pitch in the tire circumferential direction.

  The center lug groove 22 is a lug groove extending across the tire equatorial plane CL and inclining with respect to the circumferential direction of the tire and communicating with the shoulder lug groove 21. In particular, in an off-road tire, 8 [mm] It has the above groove width and the groove depth of 10 [mm] or more. Further, a plurality of center lug grooves 22 are arranged at a predetermined pitch in the tire circumferential direction.

  The communication groove 23 is a groove connecting the pair of center lug grooves 22 adjacent in the tire circumferential direction, and has a groove width of 8 mm or more and a groove depth of 10 mm or more.

  The tire ground contact end T is a contact surface between the tire and the flat plate when the tire is mounted on a prescribed rim to apply a prescribed internal pressure and is placed perpendicular to the flat plate in a stationary state and a load corresponding to the prescribed load is applied. It is defined as the maximum width position in the tire axial direction at.

  The groove width is measured as the maximum value of the distance between the left and right groove walls at the groove opening in a no-load state where the tire is mounted on a specified rim and filled with a specified internal pressure. In the configuration in which the land portion has the notch portion and the chamfered portion at the edge portion, the groove width is determined with the intersection point of the tread surface and the extended line of the groove wall as a measurement point in cross section view with the groove length direction as the normal direction. Is measured. Further, in the configuration in which the grooves extend in a zigzag or wave shape in the tire circumferential direction, the groove width is measured with the center line of the groove wall amplitude as a measurement point.

  The groove depth is measured as the maximum value of the distance from the tread surface to the groove bottom in an unloaded state where the tire is mounted on a prescribed rim and filled with a prescribed internal pressure. Moreover, in the structure which a groove | channel has a partial uneven part and sipe in a groove bottom, these are excluded and groove depth is measured.

  The prescribed rim means the “application rim” defined in JATMA, the “Design Rim” defined in TRA, or the “Measuring Rim” defined in ETRTO. Further, the specified internal pressure means the "maximum air pressure" defined in JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFlation PRESSURES" defined in TRA, or "INFLATION PRESSURES" defined in ETRTO. The specified load means the "maximum load capacity" defined in JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" defined in TRA, or "LOAD CAPACITY" defined in ETRTO. However, in the case of a passenger car tire in JATMA, the prescribed internal pressure is the air pressure of 180 [kPa], and the prescribed load is 88 [%] of the maximum load capacity.

  Shoulder block 31 is defined as a block which constitutes a block sequence which is the outermost part in the tire width direction. The center block 32 is defined as a block that constitutes a block row that is on the inner side in the tire width direction than the block row of the shoulder blocks 31.

  For example, in the configuration of FIG. 2, in one region bounded by the tire equatorial plane CL, the shoulder lug groove 21 opens at the tire ground contact end T at one end, and is curved in the tire circumferential direction while the tire It extends in the width direction and terminates at the other end without exceeding the tire equatorial plane CL. Further, a plurality of shoulder lug grooves 21 are arranged at a predetermined pitch. The center lug groove 22 is an inclined main groove and has a wear indicator (not shown) defined in JATMA. The center lug groove 22 has a gentle S-shaped curved shape, and is inclined in the opposite direction of the tire circumferential direction with respect to the shoulder lug groove 21 so as to cross the tread portion center region. Connected to Further, the inclination angle of the center lug groove 22 with respect to the tire circumferential direction is in the range of not less than 30 [deg] and not more than 60 [deg]. Further, the plurality of center lug grooves 22 are arranged at the same pitch as the pitch of the shoulder lug grooves 21. Further, the communication groove 23 is disposed so as to intersect with the tire equatorial plane CL, and extends substantially parallel to the tire width direction. Further, the communication groove 23 is connected to the pair of center lug grooves 22 adjacent to each other in the tire circumferential direction, and the center lug grooves 22 are communicated with each other. Further, a single communication groove 23 is disposed in each of the center lug grooves 22 and 22 adjacent to each other.

  More specifically, in the right side area of FIG. 2, the first center lug groove 22 (22A) extends from the side of the first shoulder lug groove 21 (21A) to the first shoulder lug groove 21 (21A). The second shoulder lug groove 21 (21B) is connected in a T shape and terminates in a T shape from the side of the first center lug groove 22 (22A) to the first center lug groove 22 (22A) Connect and terminate, and the second center lug groove 22 (22B) connects to the second shoulder lug groove 21 (21B) from the side of the second shoulder lug groove 21 (21B) in a T shape to terminate Do. A plurality of sets of shoulder lug grooves 21 and center lug grooves 22 are repeatedly arranged in the tire circumferential direction. Thus, one shoulder lug groove 21 connects to two center lug grooves 22 and one center lug groove 22 connects to two shoulder lug grooves 21. Further, the communication groove 23 is disposed on the tire equatorial plane CL and connected to the adjacent center lug grooves 22, 22. The pneumatic tire 1 also has a substantially point-symmetrical tread pattern centered on a point on the tire equatorial plane CL. Thus, a mesh-like groove pattern is formed on the entire tread.

  Also, focusing on the block row, four block rows consisting of the shoulder block 31 and the center block 32 are formed. In addition, a row of left and right shoulder blocks 31 is on the tire ground contact end T, and two center block rows are disposed in the tread center region. In addition, the shoulder blocks 31 and the center blocks 32 are arranged in a zigzag in the circumferential direction of the tire, and the center blocks 32 are arranged in two rows in parallel. Further, each center block 32 is disposed to intersect the tire equatorial plane CL.

  Further, in the configuration of FIG. 2, the shoulder lug grooves 21 and the center lug grooves 22 are alternately connected by alternately connecting the plurality of sets of shoulder lug grooves 21 and the center lug grooves 22 in the T shape and the tire circumferential direction as described above. A zig-zag circumferential groove (not shown in the figure) is formed. Here, a connection point between the shoulder lug groove 21 and the center lug groove 22, that is, a bending point of the zigzag circumferential groove is defined as points P1 and P2.

  The connection points P1 and P2 are defined as the intersections of the groove center lines of the shoulder lug groove 21 and the center lug groove 22.

  The groove center line of the lug groove is defined as a line obtained by approximating a curve connecting middle points of the groove width measurement points with a smooth arc or a straight line in the tread plan view. For this reason, as shown in FIG. 2, even when the block has a bent edge, the groove center line is approximated as a smooth arc or straight line.

  In addition, the distances Dp1 and Dp2 from the tire ground contact end T to the connection points P1 and P2 are 0.10 ≦ Dp1 / TW, Dp2 / TW ≦ 0.40 and 0.10 ≦ Dp2 with respect to the tire ground contact width TW. It is preferable to satisfy the condition Dp1 ≦ 0.30. As a result, the lug groove pattern is optimized, and the traction of the tire during off-road traveling is improved.

  The tire contact width TW is the contact surface between the flat plate and the tire when the tire is mounted on a prescribed rim to apply a prescribed internal pressure and is placed perpendicular to the flat plate in a stationary state and a load corresponding to the prescribed load is applied. Measured as the maximum linear distance in the tire axial direction at

  The distances Dp1 and Dp2 are measured as a no-load state while mounting the tire on a prescribed rim to apply a prescribed internal pressure.

  In the configuration of FIG. 2, as described above, the pneumatic tire 1 has a substantially point-symmetrical tread pattern centered on a point on the tire equatorial plane CL. However, the present invention is not limited to this, and the pneumatic tire 1 may have, for example, a tread pattern symmetrical about the tire equatorial plane CL or a tread pattern symmetrical about the left or right. It may have a tread pattern (not shown).

  Moreover, in the structure of FIG. 2, the pneumatic tire 1 is provided with the center block row | line of 2 rows as mentioned above. However, the pneumatic tire 1 may have three or more center block rows (not shown).

[Notch of center block]
FIG. 3 is an enlarged view showing the main part of the tread pattern shown in FIG. FIG. 4 is an explanatory view showing the center block described in FIG. The figure extracts and shows a single center block 32.

  As shown in FIG. 3, the center block 32 includes a cutout 51 having a rectangular shape in a plan view of the tread. The rectangular notch portion 51 increases the edge component of the block and improves the traction of the tire. In addition, since the notch 51 is shallower than the lug grooves 21 and 22, the rigidity of the block 32 is secured, and the flaking of the block 32 is suppressed.

  The notch portion 51 is a step-like recess (i.e., a step portion) having a bottom surface parallel to the tread surface of the center block 32, and is distinguished from the chamfered portion connecting the block tread surface and the groove wall surface. The rectangular shape includes, for example, a square, a rectangle, a trapezoid, a parallelogram, and a rhombus.

  In addition, a notch 51 is formed in an edge portion of the center block 32 on the outer side in the tire width direction. For example, in the configuration of FIG. 3, the center block 32 has a shape elongated in the groove length direction of the center lug groove 22, and the longitudinal direction is inclined in the tire circumferential direction. Moreover, the traction property of the tire is enhanced by the center block 32 having a polygonal shape. And the center block 32 is provided with the notch 51 in the edge part facing the center lug groove 22 of the tire width direction outer side, ie, a long edge part.

  Further, the notch 51 is disposed at a position facing the edge portion on the inner side in the tire width direction of the shoulder block 31. For example, in the configuration of FIG. 3, as described above, the shoulder blocks 31 and the center blocks 32 are arranged in a staggered manner in the tire circumferential direction in one side region of the tire equatorial plane CL (see FIG. 2). Further, the shoulder lug groove 21 is connected to the center lug groove 22 from the side of the center lug groove 22 to form a T-shaped three-forked path. The center block 32 is provided with a notch 51 at an edge facing the connection point P2 between the shoulder lug groove 21 and the center lug groove 22.

  In the configuration of FIG. 3, as shown in FIG. 4, the center block 32 extends from the end on the inner side in the tire width direction to a region of 10% to 30% of the block width Lc2. It crosses to CL. Further, the center block 32 has a sharp corner at the end of the tire equatorial plane CL, and is provided with a chamfer 52 at this corner. Further, the center block 32 is provided with a step portion 53 at an edge portion facing the center lug groove 22 on the tire equatorial plane CL side. Then, the width of the center block 32 is narrowed on the tire equatorial plane CL side by the step portion 53, and the center block 32 has a shape that widens from the tire equatorial plane CL side toward the tire width direction outer side as a whole. There is. Also, the center block 32 does not have sipes and therefore has continuous treads.

  Further, in FIG. 4, the maximum opening width Wn in the tire width direction of the notch 51 and the length Lc2 in the tire width direction of the center block 32 have a relationship of 0.10 ≦ Wn / Lc2 ≦ 0.40. Is preferable, and it is more preferable to have the relationship of 0.15 ≦ Wn / Lc2 ≦ 0.35. Thereby, the maximum opening width Wn of the notch 51 is made appropriate.

  Further, in FIG. 4, the maximum thickness Tn of the notch 51 and the maximum width Wc1 of the tread surface of the center block 32 in the normal direction of the back wall 511 of the notch 51 satisfy 0.10 ≦ Tn / Wc1 ≦ 0. It is preferable to have the relationship of 40, and it is more preferable to have the relationship of 0.15 ≦ Tn / Wc1 ≦ 0.35. Thereby, the maximum thickness Tn of the notch 51 is optimized.

  The maximum thickness Tn of the notch is measured as the maximum distance from the edge of the block having the notch to the back wall of the notch in a plan view of the tread.

  The maximum width Wc1 of the center block is measured as the maximum width of the tread from the back wall of the notch in the normal direction of the back wall of the notch to the edge on the opposite side.

  In addition, in FIG. 4, it is preferable that the opening area Sn of the notch 51 and the area Sb of the tread surface of the center block 32 have a relationship of 0.05 ≦ Sn / Sb ≦ 0.10. Thereby, opening area Sn of the notch part 51 is rationalized.

  FIG. 5 is an enlarged view showing a cutout of the center block shown in FIG. FIG. 6 is a cross-sectional view taken along line A of FIG.

  As shown in FIG. 5, it is preferable that the notch 51 have a trapezoidal shape in which the back wall 511 side is narrowed. This can increase the edge component of the block while securing the rigidity of the block.

  Further, in FIG. 5, it is preferable that an angle θn1 between the first sidewall 512 of the notch 51 and the circumferential direction of the tire be in the range of −20 deg ≦ θ n1 ≦ 20 deg, −15 deg. It is more preferable to be in the range of ≦ θ n1 ≦ 15 [deg]. In addition, it is preferable that an angle θn2 formed by the second side wall 513 of the notch 51 and the tire width direction be in a range of −10 deg ≦ θ n2 ≦ 10 deg, −5 deg ≦ θ n2 ≦ It is more preferable to be in the range of 5 [deg]. As a result, the orientations of the side walls 512 and 513 of the notch 51 are optimized, and the traction of the tire is improved.

  The first side wall 512 is defined as a side wall that faces the wall surface outward in the tire width direction, and the second side wall 513 is defined as a side wall that points the wall surface in the tire circumferential direction. Further, the angles θn1 and θn2 approximate the wall surfaces of the side walls 512 and 513 with straight lines in tread plan view, and are measured as angles formed by the straight lines and the tire circumferential direction and the tire width direction.

  Further, in FIG. 5, the lengths Ln2 and Ln3 of the first and second side walls 512 and 513 of the notch 51 have a relationship of 0.5 ≦ Ln3 / Ln2 ≦ 2.0. Therefore, the lengths Ln2 and Ln3 of the first and second side walls 512 and 513 are set to be substantially the same. Further, the ratio Ln3 / Ln2 preferably has a relationship of 1.1 ≦ Ln3 / Ln2 ≦ 2.0, and preferably has a relationship of 1.2 ≦ Ln3 / Ln2 ≦ 1.8. That is, it is preferable that the length Ln3 of the second side wall 513 which directs the wall surface in the tire circumferential direction be larger than the length Ln2 of the first side wall 512. Thereby, the lengths of the side walls 512 and 513 of the notch 51 are made appropriate, and the traction property of the tire is improved.

  Further, as shown in FIG. 5, it is preferable that the length Ln1 of the back wall 511 of the notch 51 is larger than the lengths Ln2 and Ln3 of the first and second side walls 512 and 513.

  Further, in FIG. 6, it is preferable that the maximum step amount Hn of the notch 51 and the maximum groove depth Hg2 of the center lug groove 22 have a relationship of 0.30 ≦ Hn / Hg2 ≦ 0.70, and 0.40. It is more preferable to have the relationship of ≦ Hn / Hg2 ≦ 0.60. As a result, the maximum step amount Hn of the notch 51 is made appropriate, and the traction of the tire is improved. In addition, in the structure of FIG. 6, the notch part 51 has fixed level | step difference amount Hn by having a flat bottom face.

  The maximum step amount Hn of the notch portion is measured as the maximum value of the distance from the tread surface of the block to the bottom surface of the notch portion.

  Further, in FIG. 6, it is preferable that the wall angle φn of the wall surface of the notch 51 be in the range of 5 [deg] ≦ φn ≦ 20 [deg]. Thereby, while securing the volume of the notch part 51, the baldness of the blocks 31 and 32 can be suppressed.

  A groove wall angle φg1 (not shown) of the shoulder lug groove 21 and a groove wall angle φg2 of the center lug groove 22 at the arrangement position of the notch 51 have a relation of φg2 <φg1. Specifically, it is preferable that the groove wall angles φg1 and φg2 be in the range of 3 [deg] ≦ φg1−φg2 ≦ 10 [deg]. Further, it is preferable that the groove wall angle φg2 of the center lug groove 22 particularly on the center block 32 side be in the range of 2 [deg] ≦ φg2 ≦ 10 [deg]. Thereby, while securing the volume of the notch part 51, the baldness of the blocks 31 and 32 can be suppressed.

  The groove wall angles φ n, φ g 1 and φ g 2 are perpendicular to the tread surface of the land portion through the edge portion of the land portion in a cross-sectional view in the tire meridian direction in a no load state where the tire is mounted on a specified rim and filled with a specified internal pressure. It is measured as the angle between the straight line and the groove wall surface.

  FIG. 7 is an explanatory view showing a shoulder block and a center block described in FIG. This figure shows the relationship between one center block 32 and a pair of shoulder blocks 31, 31 facing the center block 32.

  In the configuration of FIG. 3, as described above, the two shoulder blocks 31, 31 face one center block 32. Specifically, as shown in FIG. 7, the edge portion on the inner side in the tire width direction of the first shoulder block 31 (31 A) is a short edge portion of the center block 32 (that is, an edge portion not having the cutout portion 51) ) Are opposed to each other with the shoulder lug groove 21 interposed therebetween. Further, the edge portion on the inner side in the tire width direction of the second shoulder block 31 (31B) sandwiches the center lug groove 22 with respect to the long edge portion of the center block 32 (that is, the edge portion having the notch 51). Are facing each other.

  At this time, as shown in FIG. 7, the distances D1 to D3 from the edge of the second shoulder block 31 (31B) to the wall surface of the notch 51 are the center from the edge of the first shoulder block 31 (31A) The distance D4 to the wall surface of the block 32 is preferably in the range of ± 20 [%], and more preferably in the range of ± 15 [%]. In this configuration, the distances D1 to D3 from the wall surface of notch 51 of center block 32 to the edge portion of one shoulder block 31 (31B) are the other wall surface of center block 32 and the other shoulder block 31 (31A). Is equalized to the distance D4 of Thereby, the groove volume around the center block 32 is equalized, and the traction property of the tire is improved.

[effect]
As described above, the pneumatic tire 1 includes the plurality of shoulder lug grooves 21 opened at the tire ground contact end T, and the tire equatorial plane CL intersecting with the tire circumferential direction and extending while being inclined. A center lug groove 22 communicating with the lug groove 21 and a plurality of shoulder blocks 31 and a plurality of center blocks 32 sectioned into the shoulder lug groove 21 and the center lug groove 22 are provided (see FIG. 2). In addition, the center block 32 is provided with a rectangular notch 51 at a position opposite to the edge in the tire width direction and facing the edge in the tire width direction of the shoulder block 31.

  In such a configuration, (1) the center block 32 having the cutout portion 51 has an advantage that the traction property of the tire is improved as compared with, for example, the configuration in which the block has a chamfered portion. (2) The notch 51 of the center block 32 is disposed at a position opposite to the edge of the shoulder block 31 in the tire width direction, so the groove volume between the center block 32 and the shoulder block 31 is secured. There is an advantage that the traction of the tire is improved. Further, (3) the rectangular notch 51 has an advantage that the volume of the notch 51 can be increased while securing the width of the block tread compared to, for example, the triangular notch. (4) Since the notch 51 is shallower than the lug grooves 21 and 22, the rigidity of the block 32 is secured. Thereby, there is an advantage that the flaking of the block 32 is suppressed and the durability performance of the tire is secured.

  Moreover, in this pneumatic tire 1, the notch 51 has a trapezoidal shape in which the back wall 511 side is narrowed (see FIG. 4). In this configuration, as compared with, for example, a triangular notch, there is an advantage that the volume of the notch 51 can be increased while securing the width of the block tread surface.

  In the pneumatic tire 1, the relationship between the maximum opening width Wn in the tire width direction of the notch 51 and the length Lc2 in the tire width direction of the center block 32 satisfies 0.10 ≦ Wn / Lc2 ≦ 0.40. (See FIG. 4). As a result, there is an advantage that the maximum opening width Wn of the notch 51 is optimized. That is, by the above lower limit, the maximum opening width Wn of the notch 51 is secured, and the traction property of the tire is improved. Further, the rigidity of the block 32 is secured by the upper limit, and the haze of the block 32 is suppressed.

  Further, in the pneumatic tire 1, the maximum thickness Tn of the notch 51 and the maximum width Wc1 of the tread surface of the center block 32 in the normal direction of the back wall 511 of the notch 51 satisfy 0.10 ≦ Tn / Wc1. It has a relation of ≦ 0.40 (see FIG. 4). As a result, there is an advantage that the maximum thickness Tn of the notch 51 is optimized. That is, by the above lower limit, the maximum thickness Tn of the notch 51 is secured, and the traction property of the tire is improved. Moreover, the rigidity and the contact area of the block 32 are secured by the upper limit.

  Further, in the pneumatic tire 1, the opening area Sn of the notch 51 and the area Sb of the tread surface of the center block 32 have a relationship of 0.05 ≦ Sn / Sb ≦ 0.10 (see FIG. 4). Thereby, there is an advantage that opening area Sn of notch 51 is rationalized. That is, the opening area Sn of the notch part 51 is ensured by the said minimum, and the traction property of a tire improves. Moreover, the rigidity and the contact area of the block 32 are secured by the upper limit.

  Further, in the pneumatic tire 1, an angle θn1 formed by the first side wall 512 of the notch 51 and the circumferential direction of the tire is in the range of −20 [deg] ≦ θn1 ≦ 20 [deg], and the second The angle θn2 formed between the side wall 513 of the tire and the tire width direction is in the range of −10 deg ≦ θ n2 ≦ 10 deg (see FIG. 5). As a result, the direction of the side walls 512 and 513 of the notch 51 is made appropriate, and there is an advantage that the traction property of the tire is improved.

  Further, in this pneumatic tire 1, the lengths Ln2 and Ln3 of the first and second side walls 512 and 513 of the notch 51 have a relationship of 0.5 ≦ Ln3 / Ln2 ≦ 2.0 (see FIG. 5). ). As a result, the lengths of the side walls 512 and 513 of the notch 51 are made appropriate, and there is an advantage that the traction property of the tire is improved.

  Further, in the pneumatic tire 1, the maximum step amount Hn of the notch 51 and the maximum groove depth Hg of the center lug groove 32 have a relationship of 0.30 ≦ Hn / Hg2 ≦ 0.70 (see FIG. 6). ). As a result, there is an advantage that the maximum step amount Hn of the notch 51 is optimized. That is, the rigidity of the center block 32 is secured by the above lower limit, and the haze of the center block 32 is suppressed. Moreover, the volume of the notch part 51 is ensured by the said upper limit, and the traction property of a tire improves.

  Further, in the pneumatic tire 1, the wall angle φ n of the wall surface of the notch 51 is in the range of 5 [deg] ≦ φ n ≦ 20 [deg] (see FIG. 6). Thereby, there is an advantage that it is possible to suppress the burrs of the blocks 31 and 32 while securing the volume of the notch 51.

  Further, in the pneumatic tire 1, the groove wall angle φg1 (not shown) of the shoulder lug groove 21 (not shown) and the groove wall angle φg2 of the center lug groove 22 (see FIG. 6) at the arrangement position of the notch 51 are φg2 <φg1. Have a relationship of Thereby, there is an advantage that it is possible to suppress the burrs of the blocks 31, 32 while securing the volume of the notch 51.

  Further, in the pneumatic tire 1, the edge portion on the inner side in the tire width direction of the first shoulder block 31 (31 A) faces the edge portion having no notch 51 of one center block 32, and The edge portion on the inner side in the tire width direction of the shoulder block 31 (31B) faces the edge portion having the cutout portion 51 of the center block 32 (see FIG. 7). Further, distances D1 to D3 from the edge of the second shoulder block 31 (31B) to the wall surface of the notch 51 of the center block 32 are the edges of the first shoulder block 31 (31A) to the edge of the center block 32 For the distance D4 to the part, it is in the range of ± 20 [%]. In this configuration, the distances D1 to D3 from the wall surface of notch 51 of center block 32 to the edge portion of one shoulder block 31 (31B) are the other wall surface of center block 32 and the other shoulder block 31 (31A). Is equalized to the distance D4 of As a result, the groove volume around the center block 32 is made uniform, and there is an advantage that the traction property of the tire is improved.

  The pneumatic tire 1 further includes a pair of shoulder block rows including the shoulder blocks 31 and two or more center block rows including the center blocks 32 (see FIG. 2). The shoulder blocks 31 of the adjacent shoulder block rows and the center blocks 32 of the center block rows are arranged in a staggered manner in the tire circumferential direction. Further, center blocks 32 of adjacent center block rows are arranged in parallel in the tire circumferential direction. Such a block pattern has an advantage that the traction property of the tire is effectively secured.

  Further, in the pneumatic tire 1, the center block 32 has a continuous tread surface which is not divided by sipes (see FIG. 4). Thereby, the rigidity of the center block 32 is secured, and there is an advantage that the haze of the block 32 is suppressed.

  FIG. 8 is a chart showing the results of performance tests of the pneumatic tire according to the embodiment of the present invention.

  In this performance test, evaluations on (1) traction performance and (2) durability performance were performed on a plurality of test tires. In addition, a test tire having a tire size of 39 × 13.50R17 × 1265 is assembled to a prescribed rim of JATMA, and an internal pressure of 280 [kPa] and a prescribed load of JATMA are applied to the test tire. In addition, a test tire is mounted on all the wheels of the test vehicle for off-road with vehicle weight of 2580 [kg] and 875 [HP].

  (1) In the evaluation related to the traction performance, the test vehicle takes four laps of the evaluation course of 40 [mile], and the lap time is measured. Then, based on the measurement result, index evaluation is performed using the conventional example as a reference (100). In this evaluation, the larger the numerical value, the faster the lap time, and the better.

  (2) In the evaluation regarding the durability performance, the test vehicle travels a predetermined evaluation course, and thereafter, the number of occurrences of 20 [mm] square or more of baldness generated on the block of the test tire is measured. In this evaluation, it is preferable that the number of occurrence of block bales be smaller.

  The test tires of Examples 1 to 10 have the configurations of FIG. 1 and FIG. 2, and the center block 32 has a trapezoidal cutout 51. The circumferential length Lc1 (not shown) and the width direction length Lc2 (see FIG. 4) of the center block 32 are Lc1 = 75 [mm] and Lc2 = 80 [mm]. Further, the maximum groove depth Hg2 of the center lug groove 22 is Hg2 = 13.4 [mm].

  The test tire of the conventional example does not have the notch 51 in the test tire of the first embodiment.

  As the test results show, in the test tires of Examples 1 to 10, it can be seen that the traction performance of the tire can be improved while maintaining the block durability.

  1: Pneumatic tire, 11: bead core, 12: bead filler, 13: carcass layer, 14: belt layer, 141, 142: cross belt, 143: belt cover, 144: belt edge cover, 15: tread rubber, 16: Side wall rubber, 17: rim cushion rubber, 21: shoulder lug groove, 22: center lug groove, 23: communicating groove, 31: shoulder block, 32: center block, 51: notch, 52: chamfer, 53: Step

Claims (13)

A plurality of shoulder lug grooves open at the tire ground contact end, a center lug groove extending across the tire equatorial plane and inclining with respect to the tire circumferential direction and communicating with the shoulder lug groove, the shoulder lug groove and A pneumatic tire comprising: a plurality of shoulder blocks and a plurality of center blocks partitioned in the center lug groove;
A pneumatic tire characterized in that the center block is provided with a rectangular notch at a position opposite to an edge portion in the tire width direction and facing an edge portion in the tire width direction of the shoulder block.   The pneumatic tire according to claim 1, wherein the notch portion has a trapezoidal shape in which a back wall side is narrowed.   The maximum opening width Wn in the tire width direction of the cutout portion and the length Lc2 in the tire width direction of the center block have a relationship of 0.10 ≦ Wn / Lc2 ≦ 0.40. Pneumatic tire.   The maximum thickness Tn of the notch and the maximum width Wc1 of the tread surface of the center block in the normal direction of the back wall of the notch have a relationship of 0.10 ≦ Tn / Wc1 ≦ 0.40. The pneumatic tire as described in any one of 1-3.   The air-filled according to any one of claims 1 to 4, wherein the opening area Sn of the notch and the area Sb of the tread surface of the center block have a relationship of 0.05? Sn / Sb? 0.10. tire.   The angle θn1 between the first sidewall of the notch and the circumferential direction of the tire is in the range of −20 deg ≦ θ n1 ≦ 20 deg, and the angle between the second sidewall and the tire width direction The pneumatic tire according to any one of claims 1 to 5, wherein θ n2 is in a range of -10 [deg] θ θ n2 10 10 [deg].   The pneumatic tire according to any one of claims 1 to 6, wherein the lengths Ln2 and Ln3 of the first and second side walls of the notch have a relationship of 0.5 ≦ Ln3 / Ln2 ≦ 2.0. .   The maximum step amount Hn of the notch and the maximum groove depth Hg of the center lug groove have a relationship of 0.300.30Hn / Hg2 ≦ 0.70 according to any one of claims 1 to 7. Pneumatic tire.   The pneumatic tire according to any one of claims 1 to 8, wherein a wall angle nn of the wall surface of the notch portion is in a range of 5 [deg] φ ≦ n 20 20 [deg].   The air according to any one of claims 1 to 9, wherein the groove wall angle φg1 of the shoulder lug groove and the groove wall angle φg2 of the center lug groove at the arrangement position of the notch have a relation of φg2 <φg1. Containing tire. The inner edge portion of the first shoulder block in the tire width direction faces the edge portion of the one center block not having the cutout portion, and the inner edge portion of the second shoulder block in the tire width direction Facing an edge portion having the cutout portion of the center block, and
The distance from the edge of the second shoulder block to the wall surface of the notch of the center block is relative to the distance from the edge of the first shoulder block to the edge of the center block, The pneumatic tire according to claim 1, which is in the range of ± 20 [%].   The shoulder block of the adjacent shoulder block row and the center block of the center block row are provided with a pair of shoulder block rows of the shoulder blocks and two or more center block rows of the center blocks. The pneumatic tire according to any one of claims 1 to 11, wherein the center blocks of the adjacent center block rows arranged in a staggered manner in the tire circumferential direction are arranged in parallel in the tire circumferential direction.   The pneumatic tire according to any one of claims 1 to 12, wherein the center block has a continuous tread not divided by sipes.

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