JP2019081449A - 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 shoulder lug groove 21 comprises rib-like protruding part 6, formed in a groove bottom of the shoulder lug groove 21, which extends in a groove length direction of the shoulder lug groove 21. The protruding part 6 has a widened part at a connection point P1 between the shoulder lug groove 21 and the center lug groove 22.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 to the groove bottom of the lug groove during traveling should be suppressed.

  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; a plurality of shoulder blocks and a plurality of center blocks defined in the shoulder lug groove and the center lug groove, wherein the shoulder lug groove is A rib-like convex portion is formed in the groove bottom of the shoulder lug groove and extends in the groove length direction of the shoulder lug groove, and the convex portion is formed of the shoulder lug groove and the center lug groove. It is characterized by having a widened part at the connection point.

  In the pneumatic tire according to the present invention, since the convex portion has the widened portion at the connection point between the shoulder lug groove and the center lug groove, the groove bottom of the lug groove is effectively protected by the widened portion of the convex portion. This has the advantage that damage to the groove bottom of the lug groove due to the road stone is suppressed. Further, since the convex portion is formed at the connection point of the lug groove having a large groove volume, there is an advantage that the reduction in the traction property due to the arrangement of the convex portion is suppressed.

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 convex portion described in FIG. FIG. 5 is a cross-sectional view of the convex portion shown in FIG. 6 is a cross-sectional view of the shoulder lug groove shown in FIG. FIG. 7 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).

[Convex part of shoulder lug groove]
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 convex portion described in FIG. The figure extracts and shows a pair of shoulder blocks 31 and 31 and the convex part 6 of the shoulder lug groove 21. FIG. 5 is a cross-sectional view of the convex portion shown in FIG. 6 is a cross-sectional view of the shoulder lug groove shown in FIG.

  As shown in FIG. 3, the shoulder lug groove 21 includes a rib-like convex portion 6 formed at the bottom of the shoulder lug groove. The convex portion 6 protrudes from the groove bottom of the shoulder lug groove 21 and extends in the groove length direction of the shoulder lug groove 21. Further, the convex portion 6 has a widened portion 62 at a connection point P1 between the shoulder lug groove 21 and the center lug groove 22. In such a configuration, the convex portion 6 has the widened portion 62 at the connection point P1 between the shoulder lug groove 21 and the center lug groove 22, so that the groove bottom of the lug grooves 21 and 22 is more effective by the widened portion 62 of the convex portion 6. Protected. Thereby, damage to the groove bottom of the lug grooves 21 and 22 (especially the shoulder lug groove 21) due to the road stone is suppressed.

  For example, in the configuration of FIG. 4, the convex portion 6 includes the main body portion 61 and the widening portion 62. In addition, the main body portion 61 is a rib-like projection having a circumferential width Wp1 (see FIG. 4) and a height Hp (see FIG. 5) of substantially constant (less than 10 [% variation]). It extends in the groove length direction of the shoulder lug groove 21 through it. Further, the end portion on the inner side in the tire width direction of the main body portion 61 is widened in the groove width direction of the shoulder lug groove 21 to form a widened portion 62. Further, the widening portion 62 is formed at the connection point P1 between the shoulder lug groove 21 and the center lug groove 22 described above. Specifically, as described above, the center lug groove 22 is connected in a T shape from the side of the shoulder lug groove 21, and the widened portion 62 of the convex portion 6 is formed by the shoulder lug groove 21 and the center lug groove 22. It arrange | positions including the connection point P1. As a result, the groove bottom region susceptible to road stone damage is effectively protected by the widened portion 62 of the convex portion 6.

  Further, in the configuration of FIG. 3, the circumferential width Wb1 of the shoulder block 31 monotonously decreases in a step or taper form from the tire ground contact end T toward the inside in the tire width direction. Thereby, the traction of the shoulder block 31 is enhanced. At the same time, the groove width Wg1 (not shown) of the shoulder lug groove 21 is expanded in a step-like or tapered manner inward in the tire width direction from the tire ground contact end T. As a result, the groove volume at the connection point P1 between the shoulder lug groove 21 and the center lug groove 22 is increased, and the traction property of the tire is improved. Further, the main body portion 61 extends inward in the tire width direction from the tire ground contact end T side, and is widened in a step-like or taper-like manner from the middle to form a widening portion 62. Further, the convex portion 6 is gently curved along the curve of the groove center line of the shoulder lug groove 21 as a whole. Further, the edge portions of the main body portion 61 of the convex portion 6 and the wide portion 62 are formed such that the edge portion of the convex portion 6 is parallel to one groove wall of the shoulder lug groove 21. Also, the convex portion 6 has a constant height in the tire contact area. Further, the widening portion 62 has a top parallel to the tread surface.

  Further, in FIG. 3, a distance Dp1 from the tire ground contact end T to an end on the inner side in the tire width direction of the convex portion 6 and a ground contact width Wbc of the shoulder block 31 satisfy 0.65 ≦ Dp1 / Wbc ≦ 0.95. It is preferable to have a relation, and it is more preferable to have a relation of 0.70 ≦ Dp1 / Wbc ≦ 0.90. Thereby, the extension range of convex part 6 is rationalized.

  Further, as shown in FIG. 3, it is preferable that an end on the inner side in the tire width direction of the convex portion 6 is on the outer side in the tire width direction than an end on the outer side in the tire width direction of the center block 32.

  Further, in FIG. 4, it is preferable that the maximum circumferential width Wp2 of the widened portion 62 and the circumferential width Wp1 of the convex portion 6 at the tire ground contact end T have a relationship of 1.5 ≦ Wp2 / Wp1. It is more preferable to have the relationship of 0 ≦ Wp2 / Wp1. Thereby, the amount of widening of the wide part 62 is appropriately secured. The upper limit of the ratio Wp2 / Wp1 is not particularly limited, but is restricted by the relationship with the groove width Wg1 of the shoulder lug groove 21.

  Further, at least the shoulder block 31 is grounded in a region (codes omitted in the figure) inside the tire width direction from the position at which the widening portion 62 extends from the tire ground contact end T to 50% of the tread width Wbc of the shoulder block 31. It is preferable that the above condition of the ratio Wp2 / Wp1 be satisfied in a region of 10% of the width Wbc, preferably a region of 15% or more. Thereby, the extension range of the widthwise part 62 in the tire width direction is appropriately secured.

  The circumferential widths Wp1 and Wp2 are measured as widths in the tire circumferential direction in a plan view of the tread.

  Further, in FIG. 4, the maximum circumferential width Wp2 of the widened portion 62 and the circumferential width Wg1 ′ of the shoulder lug groove 21 at the measurement point of the maximum circumferential width Wp2 satisfy 0.20 ≦ Wp2 / Wg1 ′ ≦ 0. It is preferable to have a relationship of 60, and it is more preferable to have a relationship of 0.30 ≦ Wp2 / Wg1 ′ ≦ 0.50. As a result, the maximum circumferential width Wp2 of the widened portion 62 is made appropriate.

  The circumferential width Wg1 'of the shoulder lug groove is measured as the opening width of the lug groove in the tire circumferential direction when the tire is attached to the prescribed rim and a prescribed internal pressure is applied and no load is applied.

  Further, as shown in FIG. 4, the convex portion 6 is formed apart from the groove wall of the shoulder lug groove 21. Specifically, it is required that the edge portion of the top surface of the convex portion 6 and the groove wall of the shoulder lug groove 21 be separated from each other. The distance between the convex portion 6 and the left and right groove walls of the shoulder lug groove 21 is not particularly limited, but is preferably 10% or more of the circumferential width Wg1 'of the shoulder lug groove 21.

  Further, in FIG. 5, it is preferable that the height Hp of the convex portion 6 and the maximum groove depth Hg1 of the shoulder lug groove 21 have a relationship of 0.15 ≦ Hp / Hg1 ≦ 0.45. It is more preferable to have the relationship of ≦ Hp / Hg1 ≦ 0.40. Thereby, the height Hp of the convex portion 6 is made appropriate.

  Moreover, it is preferable that the height Hp of the convex part 6 is uniform in a tire contact surface. Specifically, the ratio of the maximum value to the minimum value of the height Hp of the convex portion 6 (including the main body portion 61 and the wide portion 62) in the tire contact surface is preferably 10% or less.

  The height Hp of the protrusion is measured as the maximum distance from the maximum groove depth position of the shoulder lug groove to the top surface of the protrusion.

  Further, in FIG. 6, the groove wall angle φg1 of the shoulder lug groove 21 and the groove wall angle φg2 of the center lug groove 22 have a relationship 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, the rigidity of the center block 32 can be secured, and the burrs of the blocks 31 and 32 can be suppressed.

  The groove wall angles φg1 and φg2 are straight lines passing through the edge of the land and perpendicular to the tread of the land with a tire mounted on the specified rim and filled with the specified internal pressure in a cross-sectional view in the tire meridian direction in the unloaded condition. And the angle formed by the groove wall surface.

[effect]
Further, in the pneumatic tire 1, the shoulder lug grooves 21 opened at the tire ground contact end T and the tire lug surface 21 intersect with the tire equatorial plane CL and extend while being inclined with respect to the tire circumferential direction. A center lug groove 22 communicating with each other, and a plurality of shoulder blocks 31 and a plurality of center blocks 32 partitioned into the shoulder lug grooves 21 and the center lug grooves 22 are provided (see FIG. 2). Further, the shoulder lug groove 21 is provided with a rib-like convex portion 6 which is formed at the bottom of the shoulder lug groove 21 and extends in the groove length direction of the shoulder lug groove 21 (see FIG. 3). Further, the convex portion 6 has a widened portion 62 at a connection point P1 between the shoulder lug groove 21 and the center lug groove 22.

  In this configuration, (1) the convex portion 6 has the widened portion 62 at the connection point P1 between the shoulder lug groove 21 and the center lug groove 22, so the groove bottom of the lug grooves 21 and 22 is formed by the widened portion 62 of the convex portion 6 Effectively protected. Thereby, there is an advantage that damage to the groove bottom of the lug grooves 21 and 22 (especially, the shoulder lug groove 21) due to the road stone can be suppressed. (2) Since the convex portion 6 is formed at the connection point P1 of the lug groove having a large groove volume, there is an advantage that the reduction in the traction property due to the arrangement of the convex portion 6 is suppressed.

  Moreover, in the pneumatic tire 1 according to the present invention, the center lug groove 22 is connected in a T-shape from the side of the shoulder lug groove 21 and the widened portion 62 (see FIG. 4) of the convex portion 6 is the center lug. It arrange | positions including the connection point P1 of the groove | channel 22 and the shoulder lug groove 21 (refer FIG. 3). As a result, there is an advantage that the groove bottom area susceptible to road stone damage is effectively protected by the widening portion 62 of the convex portion 6.

  Further, in the pneumatic tire 1, the convex portion 6 is expanded in a step shape or a tapered shape inward in the tire width direction from the tire ground contact end T side to form the expanded portion 62. Thereby, there is an advantage that damage to the groove bottom due to the road stone can be effectively suppressed by the convex portion 6.

  Further, in the pneumatic tire 1, the groove width (not shown) of the shoulder lug groove 21 is expanded in a step or taper shape from the tire ground contact end T toward the tire equatorial plane CL (see FIG. 3). As a result, the groove volume at the connection point P1 between the shoulder lug groove 21 and the center lug groove 22 is increased, and there is an advantage that the traction property of the tire is improved.

  Further, in the pneumatic tire 1, the distance Dp 1 from the tire ground contact end T to the end on the inner side in the tire width direction of the convex portion 6 and the ground contact width Wbc of the shoulder block 31 satisfy 0.65 ≦ Dp1 / Wbc ≦ 0. It has the relationship of .95 (see FIG. 3). Thereby, there is an advantage that the extension range of convex part 6 is rationalized.

  Further, in the pneumatic tire 1, the maximum circumferential width Wp2 of the widened portion 62 and the circumferential width Wp1 of the convex portion 6 at the tire ground contact end T have a relationship of 1.5 ≦ Wp2 / Wp1 (FIG. 4) reference). Thereby, there is an advantage that the widening amount of the widening portion 62 is properly secured.

  Further, in the pneumatic tire 1, the maximum circumferential width Wp2 of the widened portion 62 and the circumferential width Wg1 'of the shoulder lug groove 21 at the measurement point of the maximum circumferential width Wp2 satisfy 0.20 ≦ Wp2 / Wg1'. It has a relation of ≦ 0.60 (see FIG. 4). As a result, there is an advantage that the maximum circumferential width Wp2 of the widened portion 62 is optimized.

  Further, in the pneumatic tire 1, the convex portion 6 is formed apart from the groove wall of the shoulder lug groove 21 (see FIG. 4). This has the advantage that the traction of the block is ensured.

  Further, in the pneumatic tire 1, the height Hp of the convex portion 6 and the maximum groove depth Hg1 of the shoulder lug groove 21 have a relationship of 0.15 ≦ Hp / Hg1 ≦ 0.45 (see FIG. 5). ). Thereby, there is an advantage that height Hp of convex part 6 is rationalized.

  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 groove wall angle φg1 of the shoulder lug groove 21 and the groove wall angle φg2 of the center lug groove 22 have a relationship of φg2 <φg1 (see FIG. 6). As a result, there is an advantage that the volume of the lug grooves 21 and 22 can be secured and the burrs of the blocks 31 and 32 can be suppressed.

  Moreover, in this pneumatic tire 1, the shoulder block 31 has a continuous tread surface which is not divided by sipes (see FIG. 4). Thereby, the rigidity of the shoulder block 31 is secured, and there is an advantage that the block of the block is suppressed.

  FIG. 7 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. Also, if the numerical value is 98 or more, it can be said that the traction performance is properly maintained.

  (2) In the evaluation on durability performance, the test vehicle travels on a predetermined evaluation course, and thereafter, the number of groove bottom cracks generated in 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 tire of Examples 1 to 10 has the configuration of FIGS. 1 and 2, and the shoulder lug groove 21 includes the convex portion 6 having the widening portion 62. The contact width Wbc of the shoulder block 31 is Wbc = 80 [mm], and the circumferential width Wp1 of the convex portion 6 at the tire contact end T is Wp1 = 6.5 [mm]. Further, the maximum groove depth Hg1 of the shoulder lug groove 21 is Hg1 = 13.4 [mm].

  The test tire of the conventional example is the test tire of Example 1, and does not include the widening portion 62 of the convex portion 6.

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

  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, 6: convex portion, 61: main body portion, 62: widening Department

Claims (12)

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;
The shoulder lug groove includes a rib-like convex portion which is formed in the bottom of the shoulder lug groove and extends in the groove length direction of the shoulder lug groove, and
The pneumatic tire characterized in that the convex portion has a widened portion at a connection point between the shoulder lug groove and the center lug groove. The center lug groove is connected in a T-shape from the side of the shoulder lug groove;
The pneumatic tire according to claim 1, wherein the widening portion of the convex portion is disposed including a connection point between the center lug groove and the shoulder lug groove.   The pneumatic tire according to claim 1 or 2, wherein the convex portion is expanded in a step-like shape or a tapered shape inward in the tire width direction from the tire ground contact end side to form the widening portion.   The pneumatic tire according to any one of claims 1 to 3, wherein the groove width of the shoulder lug groove increases in a step-like or tapered manner from the tire ground contact end toward the tire equatorial plane side.   The distance Dp1 from the tire ground contact end to the end on the inner side in the tire width direction of the convex portion and the ground contact width Wbc of the shoulder block have a relationship of 0.65 ≦ Dp1 / Wbc ≦ 0.95. The pneumatic tire as described in any one of 4.   The maximum circumferential width Wp2 of the widening portion and the circumferential width Wp1 of the convex portion at the tire ground contact end have a relationship of 1.5 ≦ Wp2 / Wp1 according to any one of claims 1 to 5. Pneumatic tire.   The maximum circumferential width Wp2 of the widening portion and the circumferential width Wg1 ′ of the shoulder lug groove at the measurement point of the maximum circumferential width Wp2 have a relationship of 0.20 ≦ Wp2 / Wg1 ′ ≦ 0.60. The pneumatic tire as described in any one of claim | item 1 -6.   The pneumatic tire according to any one of claims 1 to 7, wherein the convex portion is formed apart from the groove wall of the shoulder lug groove.   The height Hp of the convex portion and the maximum groove depth Hg1 of the shoulder lug groove have a relationship of 0.15 ≦ Hp / Hg1 ≦ 0.45. Pneumatic tire.   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 9, 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 10, wherein the groove wall angle φg1 of the shoulder lug groove and the groove wall angle φg2 of the center lug groove have a relationship of φg2 <φg1.   The pneumatic tire according to any one of claims 1 to 11, wherein the shoulder block has a continuous tread not divided by sipes.

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