JP4516342B2 - Heavy duty tire - Google Patents

Description

  The present invention relates to a heavy duty tire that can improve uneven wear resistance, wet grip performance, and the like mainly by specifying a land portion shape on the center side.

  For heavy duty tires used in trucks, buses, etc., in order to stabilize running during rain, etc., the wet grip and the operating conditions are harsh and economical because it is commercialized. Heavy duty tires used for trucks, buses, and the like have a high frequency of starting and stopping that tend to cause uneven wear, and therefore must be able to withstand these.

  Rib lug patterns with zigzag vertical grooves are adopted as heavy duty tires that can improve wet grip and improve driving safety, but the depth of the grooves is deeper than normal tires. Since the width of the land portion between the longitudinal grooves is set wide, the rigidity balance in the land portion is likely to be non-uniform, and the frequency of start and stop is high, and uneven wear is likely to occur.

  For this reason, as illustrated in FIG. 6, a narrow groove extending from the entrance or exit corner of the land portion to the land portion between the tire equator and the three zigzag vertical grooves a passing through both sides thereof, and being interrupted or continuous. A heavy-duty tire provided with b has been proposed (see, for example, Patent Document 1).

JP-A-6-191235

However, in the heavy-duty tire shown in Patent Document 1 or the like, the land portion is divided by a lateral groove, and it is intended to improve wear resistance as well as wet grip properties. It has been found that due to having an inclination angle in the same direction in the vicinity, it causes uneven wear due to slip difference between the center side and the shoulder side of the land.

  The present invention has been completed on the basis of a study on the shape of a lateral groove that divides a land portion into blocks, and an object thereof is to provide a heavy duty tire that can improve wet grip performance and uneven wear resistance performance. .

According to the first aspect of the present invention, the tread surface is provided with at least three longitudinal grooves (3) including the longitudinal grooves 3A on the center side of the zigzag and the longitudinal grooves 3B on the shoulders of the zigzag located on both sides thereof. , Including an inner land portion 6A formed between the central longitudinal groove 3A and the shoulder longitudinal groove 3B, and an outer land portion 6B between the shoulder longitudinal groove 3B and the tread edge E. Forming part (6),
In addition, the inner land portion 6A is traversed starting from the protruding corners 6Ac1 and 6Ac2 on both sides of the inner land portion 6A, and provided with a narrow groove or a siping groove (7) that opens at the longitudinal grooves (3) on both sides. The land portion 6A is a block row (8) in which the blocks 8A are connected,
The groove depth d7 of the horizontal groove (7) is smaller than the average value ((d3A + d3B) / 2) of the groove depths d3A, d3B of the vertical grooves (3) on both sides of the opening, and the groove width w7 of the horizontal groove (7). Is smaller than the average value ((w3A + w3B) / 2) of the groove widths w3A and w3B of the longitudinal grooves on both sides of the opening,
In addition, the lateral groove (7) is composed of an inner lateral groove portion 7a extending from the inner protruding corner 6Ac1 on the inner side in the tire axial direction, an outer lateral groove portion 7b extending from the outer protruding corner 6Ac2, and a central lateral groove portion 7c that connects between the inner lateral groove portions 7a.
In addition, an inclination angle α formed by the inner lateral groove portion 7a with respect to the tire axial direction line, an inclination angle β formed by the outer lateral groove portion 7b with respect to the tire axial direction line, and a central lateral groove portion 7c formed by the tire axial direction line. The inclination angle γ (α, β, γ is an acute angle) is a heavy load tire characterized by the following relationship.
0 ° ≦ β <α < 60 ° ≦ γ

In the invention according to claim 2, in the inner land portion 6A, the intersecting portion where the transverse groove (7) and the longitudinal groove (3) intersect is an intersection line between the transverse groove (7) and the longitudinal groove (3) from the tread surface. c. The invention according to claim 3 is provided with a notch portion (13) formed of a slope notched in a triangular shape extending downward, and the inner land portion 6A includes a transverse groove (7) and a longitudinal groove (3). The crossing portion where the crossing part comprises a cutout part (13) comprising a triangular cutout extending from the tread surface to below the crossing line c between the horizontal groove (7) and the vertical groove (3). In the invention according to No. 4, the outer land portion 6B is provided with a notch portion (14) comprising a slope formed by notching the protruding corner portion 6Bc on the inner side in the tire axial direction from the tread surface to the lower portion of the protruding corner line. In addition, the invention according to claim 5 is a length L7c along the center line of the central lateral groove portion 7c of the lateral groove (7). Is characterized in that a larger than the length L7b of the inner lateral groove portion 7a of the length L7a, and an outer lateral groove 7b.

Further, in the invention according to claim 6, the tread edge E of the outer land portion 6B is such that the width w12 in the tire axial direction is between the protruding corner 6Bc on the inner side in the tire axial direction of the shoulder land portion 6B and the entering corner 6Bs. A hollow groove (12) in the form of a small-width lug groove that is larger than 0.5 times and smaller than 1.5 times the tire axial width wcs between,
The distance L6B1 between the tire axial direction line x1 passing through the corner 6Bs of the outer land portion 6B and the center line x2 of the hollow groove (12) is a zigzag pitch P in the tire circumferential direction between the corners 6Bs. It is characterized by being larger than 0.4 times and smaller than 0.6 times.

  In the invention which concerns on Claim 1, by improving the balance of the rigidity of an inner rib with a lateral groove, uneven wear can be suppressed and wet grip property and abrasion resistance can be ensured. In other words, because it is based on a rib pattern that has a longitudinal groove on the center side of the zigzag and a longitudinal groove on the shoulder, the circumferential rigidity is relatively large, and the lateral rigidity is also excellent. Steering stability, quietness, and wear resistance And the rigidity of the land portion within the ground contact pressure is large. In addition, since the inner land is divided by horizontal grooves whose depth and groove width are smaller than the depth of the vertical grooves on both sides, the depth of the horizontal grooves at the initial stage of wear is prevented from becoming excessive. The wear is prevented, and after the middle stage of wear, the groove depth is shallow or disappears, so that the growth of uneven wear can be prevented and improved. That is, the uneven wear that occurs in the inner land portion is mostly generated in the early stage of wear, and if the uneven wear can be suppressed by the middle of the wear, the possibility of the occurrence of the uneven wear after that becomes small.

  In addition, the horizontal groove that separates the land part by connecting both ends to the vertical groove, compared to the closed type that does not open in the vertical groove and the one side open type (one side closed type) that opens only one side into the vertical groove. It has been found that the land portion is divided into blocks to make it easy to balance the rigidity of the land portion, and by making such a lateral groove, wet grip performance can be improved and uneven wear can be suppressed.

  Further, the lateral groove extends from the corner of the inner land portion as a starting point, so that the groove width is widened by filling the tire with the specified internal pressure, thereby preventing an increase in contact pressure due to a so-called gating phenomenon. Therefore, so-called railway wear (or tram lining wear), which tends to occur from the corners due to the amount of slip between the corners and the road surface, is larger than that at other locations. Therefore, both sides of the lateral groove opening can take independent movements, do not slide on the road surface from the start of contact to the end of contact, and can be in contact with the road surface without being affected by the movement of other parts of the inner rib. Thereby, the wear energy at the protruding corner portion is reduced, and the occurrence of uneven wear can be suppressed.

Moreover, the inclination angle α formed by the inner lateral groove portion 7a with respect to the tire axial direction line, the inclination angle β formed by the outer lateral groove portion 7b with respect to the tire axial direction line, and the central lateral groove portion 7c in the tire axial direction line. By setting the inclination angle γ with respect to the road within the range of the above formula, the ground contact pressure closer to the center side is the outer side in the tire axial direction in the standard state in which the tire filled with the normal internal pressure is pressed against the road surface with the normal load. It becomes larger than the close contact pressure. As a result, in order to reduce the occurrence of slip between the road surface on the center side and the tire surface, the shape of the block partitioned by the inner lateral groove portion 7a has a degree of freedom, but it is partitioned by the outer lateral groove portion 7b on the outer side in the tire axial direction. Since the contact pressure at the edge of the block is smaller than that at the center, the lateral groove angle of the opening is reduced to make the rigidity of the block edges adjacent in the circumferential direction uniform, thereby suppressing H & T wear promoted by uneven rigidity. Further, by setting the inclination angle α formed by the inner lateral groove portion 7a to the tire axial direction line to be 60 ° or less, it is possible to prevent the occurrence of chipping starting from the lateral groove. Further, the water flow inside the block is made smooth by setting the inclination angle γ to 60 ° or more.

  In the invention according to claim 2, the groove depth of the lateral groove is 10 to 60% of the longitudinal groove (3), the groove width is 0.5 mm or more and 50% or less of the groove width of the longitudinal groove (3). If it is less than 10%, uneven wear tends to occur in the initial stage, and if it exceeds 60%, chipping starting from the lateral groove tends to occur. When the groove width is smaller than 0.5 mm, the opposing surfaces separated by the lateral grooves interfere with each other, reducing the rigidity reduction effect of the groove. On the other hand, when it exceeds 50%, a complete block is formed. Toe wear will occur. Further, the inner lateral groove portion 7a, the outer lateral groove portion 7b, and the central lateral groove portion 7c have the same direction inclined in the circumferential direction with respect to the tire axial direction, thereby eliminating a sense of incongruity and stagnation of water flow in the lateral groove. , Prevent stagnation.

  In addition, in the invention according to claim 3, by providing a notch extending from the tread surface to the lower part of the crossing line between the horizontal groove and the vertical groove, the block edge at the initial stage of wear is made obtuse and prevents the chip of the block. The zigzag vertical groove in the early stage of wear can be made closer to the straight groove, the tip portion of small rigidity can be reduced, and the swing width of the zigzag in the early stage of wear that tends to cause an initial phenomenon of uneven wear can be reduced. This also has the same effect in the notch provided in the outer land portion 6B.

  Further, in the invention according to claim 5, the length L7c along the center line of the central lateral groove portion 7c of the lateral groove (7) is the length L7a of the inner lateral groove portion 7a and the length of the outer lateral groove portion 7b. By making it larger than the length L7b, the lateral groove (7) has the largest angle γ with respect to the tire axial direction, that is, the central lateral groove portion 7c that is most inclined in the circumferential direction is set longer. As a result, the circumferential distance D7 between the openings 7ao and 7bo with respect to the vertical grooves (3) on both sides of the lateral groove (7) can be increased, and the openings 7ao and 7bo can be moved away in the circumferential direction. It can be made uniform.

  According to the invention of claim 6, the uniformity of the tire rib circumferential rigidity of the shoulder rib is maintained, the occurrence of uneven wear from the narrow rib portion is prevented, and the tire circumferential rigidity of the shoulder land portion 3 </ b> B is uniform. Traction, can prevent the occurrence of uneven wear from the narrow land (rib) width, reduce the fluctuation of the width of the shoulder side land, while also reducing the wet grip and uneven wear improves.

  An embodiment of the heavy load tire 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing one side of a heavy load tire 1 of the present invention divided on the tire equator plane, FIG. 2 is a plan view showing an example of the tread pattern, and in FIG. The normal internal pressure is filled, and the internal pressure is not loaded.

  Here, the “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based, for example, a standard rim for JATMA, “Design Rim” for TRA, ETRTO Then it becomes "Measuring Rim". In addition, “regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. It is the maximum air pressure for JATMA and the table “TIRE LOAD LIMITS” for TRA. The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES” is “INFLATION PRESSURE” in the case of ETRTO, and the state in which the normal internal pressure is incorporated in the normal rim is referred to as the internal pressure no-load state as described above. When a load is applied to a tire, the “regular load” at that time is a load defined by each standard for each tire, the maximum load capacity specified by JATMA, and the above table of TRA. The maximum value described or “LOAD CAPACITY” defined by ETRTO and when such a load is applied is referred to as the standard state. FIG. 2 shows a tread pattern in a state where no internal pressure is applied, developed on a plane.

  1 and 2, the heavy load tire 1 includes a tread portion 21, a sidewall portion 22 that extends inward in the tire radial direction from both sides thereof, and an inner side in the tire radial direction of the sidewall portion 22. A carcass 26 that folds the bead core 25 of the bead portion 23 from the tread portion 21 through the sidewall portion 22 toward the outside from the inner side in the tire axial direction, and the inside of the tread portion 21 and the carcass 26. A bead apex 29 having a triangular cross section is provided outside the bead core 25 in the tire radial direction.

  The tread portion 21 is provided with a tread rubber that forms the tread surface 21A on the outer side in the tire radial direction of the belt layer 27. The carcass 26 is composed of a single carcass ply in a radial arrangement inclined at an angle of about 90 ° with respect to the tire equator C in the present embodiment. Therefore, the heavy duty tire of the present invention is formed as a heavy duty radial tire. ing. In addition, a steel cord is used as a carcass cord, and the belt layer 27 is composed of a belt ply using three to four steel cords, in this embodiment, first to fourth steel cords from the carcass 26 side. The second and third belt plies are arranged so that their belt cords cross each other.

The tread surface 21A has 3 to 4 zigzag center longitudinal grooves 3A and zigzag shoulder longitudinal grooves 3B located on both sides of the tread surface 21A. In this embodiment, the center longitudinal groove 3A is the tire equator. By passing on C, three vertical grooves 3 are provided. Accordingly, the inner land portion 6A formed between the central vertical groove 3A and the shoulder vertical groove 3B, and the outer land portion 6B between the shoulder vertical groove 3B and the tread edge E are formed. A land portion 6 is formed.

  Also, the zigzag pitch between the central longitudinal groove 3A and the shoulder longitudinal groove 3B is the same in the circumferential direction, and the phases of the peaks (protruding corners) and the valleys (entrance corners) are also aligned in the tire axial direction. As a result, the inner land portion 3A is substantially the same width and zigzag continuously in the tire circumferential direction, and the circumferential rigidity is constant. The outer land portion 6B has a zigzag wall on the tire equator side. When the central longitudinal groove 3A is arranged on both sides of the tire equator C, the land portion between the longitudinal grooves 3A forms a land portion (not shown) of the center, The land portion 6A in the present invention is formed in the region between the vertical groove 3A and the shoulder vertical groove 3B. Note that the land portion of the center can be configured in the same manner as the land portion 6A.

  Further, the groove depth d3 of the longitudinal groove 3 varies depending on the tire size and is usually set to about 70 to 90% of the thickness t of the tread rubber. However, the longitudinal groove 3A on the center side and the longitudinal groove 3B on the shoulder are set. In FIG. 5, a difference can be given to the groove depths d3A and d3B. In this embodiment, the groove depth d3B of the shoulder vertical groove 3B is set to a small ratio with respect to the thickness t of the tread rubber at the groove depth d3A groove position of the central vertical groove 3A. The rigidity of the part is relatively improved.

  Furthermore, the inner land portion 6A is provided with a lateral groove 7 that starts from the corners 6Ac1 and 6Ac2 on both sides of the inner land portion 6A and opens at the vertical grooves 3 on both sides of the inner land portion 6A. A block row 8 is formed in which the blocks 8A divided by the horizontal grooves 7 are continuous. This prevents so-called railway wear (or tram lining wear) at the exit corners 6Ac1 and 6Ac2 due to the amount of slip between the exit corner portion and the road surface being larger than at other locations. By connecting the transverse groove 7 between the longitudinal grooves 3 at this place, both sides of the opening of the transverse groove can take independent movements. It is possible to contact the road surface without being affected by the movement of the location, thereby reducing the wear energy at the protruding corner portion and suppressing the occurrence of uneven wear. In addition, it is preferable not to provide siping in entrance corner part 6As1 and 6As2 from the viewpoint regarding the exit corners 6Ac1 and 6Ac2.

  Further, the lateral groove 7 can be configured using a narrow groove or siping. Here, the narrow groove means a small groove having a groove depth d7 of 10 to 60% of the longitudinal groove 3, a groove width w7 of 0.5 mm or more and 50% or less of the groove width w3 of the longitudinal groove 3, and the other siping means In the case of non-grounding, it has no substantial groove width, or is a cut smaller than a maximum of 0.5 mm, and has the same depth. In FIG. 2, the lateral groove 7 is illustrated as a narrow groove. Yes. This is because the effect of the lateral groove is small if it is less than 10%. Further, if it exceeds 60%, the rigidity of the end portion becomes too small, and chipping tends to occur. Further, the reason why the groove width w7 is set to 0.5 mm or more is that if the width is less than 0.5 mm, the lateral groove 7 has a rigidity balance and the effect of suppressing uneven wear is reduced. On the other hand, if it exceeds 50%, the adverse effect on the wear resistance cannot easily be ignored, and heel and toe wear tends to occur on both sides of the lateral groove in the tire circumferential direction.

  The lateral grooves 7 open to the vertical grooves 3 at the outer protruding corners 6Ac1 on the inner side in the tire axial direction and at the outer protruding corners 6Ac2, respectively, and from the inner lateral groove portions 7a on the protruding corner 6Ac1 side and the outer protruding corners 6Ac2. The outer lateral groove portion 7b extends and the central lateral groove portion 7c that connects the outer lateral groove portion 7b. Here, the length L7c along the center line of the central lateral groove portion 7c is larger than the length L7a of the inner lateral groove portion 7a and the length L7b of the outer lateral groove portion 7b. Moreover, the length L7a of the inner lateral groove portion 7a along the groove center line is 10 to 30% of the total length L7 of the inner lateral groove portion 7a, the outer lateral groove portion 7b, and the central lateral groove portion 7c. The length L7b of the lateral groove portion 7b is about 10 to 30%, and the length L7c of the central lateral groove portion 7c is about 40 to 75% (the total is naturally 100%).

  When the length L7c along the center line of the central lateral groove portion 7c is smaller than the length L7a of the inner lateral groove portion 7a or the length L7b of the outer lateral groove portion 7b, the lateral groove (7) The angles α and β with respect to the axial direction are small, that is, the inner lateral groove portion 7a and the outer lateral groove portion 7b that are greatly inclined in the tire axial direction are set longer. As a result, the circumferential distance D7 between the openings 7ao and 7bo with respect to the vertical grooves (3) on both sides of the lateral groove (7) is shortened, and the openings 7ao and 7bo approach the circumferential direction, so the circumferential rigidity is not uniform. It becomes.

In addition, assuming that the depth of the groove 7 is not constant, the groove depth w7 of the lateral groove 7 is an average value d7m represented by the following equation from one end to the other end. In the following formula, “0” is one lateral groove end, L7 is the total length along the lateral groove center line, and di is the distance from the zero point.
_L7
d7m = (∫di · d (di) / L7
⁰

  The horizontal groove 7 has a groove depth d7 (d7m) set to be smaller than the groove depth d3 of the vertical groove 3, and the groove depth d3B of the shoulder vertical groove 3B and the central vertical groove 3A. When the groove depth d3A is different, the groove depth d7 of the lateral groove 7 is made smaller than the average value ((d3A + d3B) / 2) of the groove depths d3A and d3B of the longitudinal grooves 3 on both sides of the opening. Preferably, it is about 10 to 60% of the groove depth d7 of the longitudinal groove 3, and further 30 to 60%. This prevents uneven wear by preventing the lateral groove depth from becoming excessive at the initial stage of wear, and prevents the growth of uneven wear by making the groove depth shallower or disappearing after the middle stage of wear. It can be improved. That is, the uneven wear that occurs in the inner land portion 6A is mostly generated in the early stage of wear, and if the uneven wear can be suppressed by the middle of the wear, the possibility of occurrence of the uneven wear after that becomes small.

  Further, as shown in detail in FIG. 5, the groove depth d6c of the central lateral groove portion 7c can be made smaller than the groove depths d7a and d7b of the inner lateral groove portion 7a and the outer lateral groove portion 7b, so as to form a raised tie bar shape. .

  Further, the lateral groove 7 prevents the increase in the contact pressure due to the so-called gating phenomenon that the groove width is widened by extending the tire 6Ac1 of the inner land portion 6A as a starting point and filling the tire with the specified internal pressure. By connecting the lateral groove 7 to the longitudinal groove 3, both sides of the lateral groove opening can take independent movements, and it can move to other parts of the inner rib without sliding with the road surface from the start to the end of contact. It is not affected and can contact with the road surface, whereby the wear energy at the protruding corner portion is reduced and the occurrence of uneven wear can be suppressed.

  Further, the lateral groove 7 has a groove width w 7 smaller than the groove width W 3 of the vertical groove 5. When the groove width w3B of the shoulder vertical groove 3B is different from the groove width w3A of the central vertical groove 3A, the average value ((w3A + w3B) / 2) is made smaller. Preferably, it is 0.5 mm or more and 50% or less of the groove width w3 of the longitudinal groove (3). Thereby, the function as a rib of the land part 6 is exhibited, and the fall of abrasion resistance by the reduction | decrease of a contact area is prevented.

Moreover, the inclination angle α formed by the inner lateral groove portion 7a with respect to the tire axial direction line, the inclination angle β formed by the outer lateral groove portion 7b with respect to the tire axial direction line, and the central lateral groove portion 7c formed by the tire axial direction line. The inclination angle γ has the following relationship.
0 ° ≦ β <α < 60 ° ≦ γ
Here, each angle refers to an acute angle among the angles formed by the center line of the lateral groove and the tire axis. When γ is less than 60 °, the effect of balancing the rigidity of the inner ribs by the lateral grooves becomes poor. Preferably, 60 ° ≦ γ ≦ 85 °, more preferably 65 ° ≦ γ ≦ 80 °. This is because if β and α are 60 ° or more, chipping near the end of the lateral groove is likely to occur. Preferably, it is set to 45 ° or less, more preferably 30 ° or less.

  In addition, 0 ° ≦ β ≦ α is defined as the road surface and the tire surface at the center side where the ground contact pressure in the standard state in which the tire filled with the normal internal pressure is pressed against the road surface with the normal load is larger than the outside in the tire axial direction. There is little slippage between the two. Therefore, the shape of the block delimited by the inner lateral groove portion 7a has a degree of freedom, but the edge of the block delimited by the outer lateral groove portion 7b on the outer side in the tire axial direction has a smaller ground pressure than the center side, so the opening portion This is to reduce the horizontal groove angle of the block to make the rigidity of the block edges adjacent in the circumferential direction uniform, and to suppress H & T wear promoted by the non-uniform rigidity.

  Preferably, the lateral groove (7) has the inner lateral groove portion 7a, the outer lateral groove portion 7b, and the central lateral groove portion 7c that have the same inclination in the circumferential direction with respect to the tire axial direction, thereby eliminating the uncomfortable appearance. At the same time, it prevents water flow stagnation and retention in the lateral groove.

  The inner land portion 6A is formed from a slope that is notched in a triangular shape extending from the tread surface 21A to a position below the intersection line c between the horizontal groove 7 and the vertical groove 3 at each intersection where the horizontal groove 7 and the vertical groove 3 intersect. The notch part 13 is provided. As shown in FIGS. 3 and 4, the notch 13 has a notch line f on the tread surface 21A at an inclination angle δ with respect to the tire circumferential direction starting from the edge of the longitudinal groove 3 and the tread surface 21A. The notch line f extends to the end point where the edge of the lateral groove 7 and the tread surface 21A intersects with the center side of the block 8A.

The inclination angle δ is set to about 0 to 45 °, preferably about 10 to 35 °. Further, the lower end of the notch 13 is about 30 to 100% of the groove depth d3B of the vertical groove 3B of the shoulder on the intersecting line c of the horizontal groove 7 and the vertical groove 3 and the height h12 from the tread surface 21A, Preferably it is about 40 to 80%. The length Lf of the notch line f in the tire circumferential direction is set to 1 to 10 mm, preferably about 2 to 6 mm. Such a notch 13 can be curved as well as confronted, and by forming it symmetrically on both sides of the lateral groove 7, the difference due to the tire rotation direction can be reduced. Such a notch 13 makes the block edge at the initial stage of wear an obtuse angle and prevents the block from being chipped. In addition, zigzag vertical grooves in the early stage of wear can be brought closer to straight grooves, and the tip of the small rigidity is reduced, and the zigzag swing width in the early stage of wear, which tends to cause initial phenomena, is reduced to prevent uneven wear. it can. If the height h12 is too small, the notch shape disappears in the early stage of wear, and the effect of preventing chipping is not in the middle stage of wear. In the late stage of wear exceeding 100%, the depth of the longitudinal groove becomes shallow and the rigidity of the rib edge becomes high, so that a notch shape is not necessary.

  The outer land portion 6B is a continuous rib without the lateral groove 7, and only the inner side surface in the tire axial direction facing the shoulder longitudinal groove 3B is zigzag tired by the shoulder longitudinal groove 3B. The direction with respect to the circumferential direction is changing. A notch portion 14 is formed in the zigzag protruding corner portion 6Bc on the inner side in the tire axial direction of the outer land portion 6B, and the notched portion 14 is formed at the notch portion of the inner land portion 6A. The portion 13 is formed in substantially the same shape as the plane, with the same inclination and depth.

  Further, a hollow groove 12 having a small-width lug groove is provided on the tread edge E of the outer land portion 6B. The hollow groove 12 is formed by notching the tread surface 21 </ b> A in the vicinity of the projecting corner 6 </ b> Bc of the shoulder land portion 3 </ b> B facing outward in the tire axial direction. “The vicinity of the outer corner 6Bc of the shoulder land portion 3B facing the outer side in the tire axial direction” in FIG. 2 is the tire axial direction line x1 passing through the center of the corner 6Bs of the outer land portion 6B, and A distance L6B1 between the hollow groove 12 and the center line x2 that equally bisects the tire circumferential direction 12 is larger than the tire circumferential pitch P0.4 times between the corners 6Bs and 6Bs and smaller than 0z6 times. Therefore, it means that it is arranged in the widest region in the tire axial direction width of the land portion 3B of the shoulder. Thereby, the uniformity of the tire rib direction rigidity of a shoulder rib is maintained, and generation | occurrence | production of the partial wear from a part with a narrow rib width | variety is prevented.

  Further, the hollow groove 12 has a width w12 in the tire axial direction that is 0.5 times the width wcs in the tire axial direction between the protruding corner 6Bc on the inner side in the tire axial direction of the land portion 3B of the shoulder and the entering corner 6Bs. Is set to be larger and smaller than 1.5 times. By being in this range, as described above, the uniformity of the rigidity in the tire circumferential direction of the land portion 3B of the shoulder is maintained, and the occurrence of uneven wear from the narrow portion of the land portion (rib) is prevented. Further, in this example, the hollow groove 12 has a planar trapezoidal shape on the tread surface 21S, and the length Le12 on the tread edge E corresponding to the lower side thereof is 20 of the circumferential pitch P between the protruding corner 6Bc and the entering corner 6Bs. % Or more and 65% or less is preferable. If it is less than 20%, the uniformity of the circumferential rigidity of the shoulder rib cannot be maintained, and if it exceeds 65%, the uniformity cannot be maintained and uneven wear occurs, and the portion other than the hollow groove 12 on the shoulder decreases. There is a concern about the lack of tread edges. Further, the length Lb12 at the bottom is preferably 10% or more and 55% or less of the half pitch length P. If it is less than 10% or exceeds 55%, the relationship with the length Le12 on the tread edge E becomes worse, and an appropriate trapezoidal shape cannot be obtained. That is, there is a concern that the prevention of uneven wear due to the function of rigidity uniformity may be prevented, or the tread portion may be chipped.

It is preferable that the edge portion of the inner rib 5 formed by the lateral groove 6, the central longitudinal groove 3, and the shoulder longitudinal groove 4, that is, both end portions of the lateral groove 6 have a notch shape. Thereby, the chipping at both ends of the lateral groove can be prevented. Here, “notch shape” means so-called “taper cut”, and “taper cut” means that the end of a rib or block is cut off obliquely with respect to the tread surface to create an inclined plane or curved surface. Say.
Also,

The inventor conducted experiments in various patterns and obtained the results shown in Table 1.
The test conditions are as follows.
(1) Driving conditions Vehicle: Domestic truck 2D vehicle (2) Evaluation method Wet grip performance: Entering a course with a puddle on a circular asphalt surface while increasing the speed stepwise, the lateral acceleration (lateral G) The measurement was made and evaluated by the average lateral G at a speed of 70 to 90 km / h, and the result was indexed.
Uneven wear resistance performance: Comparative Example 4 is mounted on the control shaft, and each test specimen is mounted on the drive shaft. About 3 months (30,000 km) after traveling users on highway 80% and general road 20% After traveling, the partial wear state was compared and indexed.
Block chipping resistance: Mounted on drive shaft, climbed on rough road, intentionally slipped tire, and indexed “number of chips × depth” of block based on tire mounted on control shaft. The larger the index, the better.

It is sectional drawing which illustrates embodiment of the tire for heavy loads of this invention in the right half of a tire equator. It is a top view which illustrates the tread pattern of the present invention. It is a top view which expands and illustrates an inner land part. It is sectional drawing which illustrates a horizontal groove along the centerline. It is a perspective view which illustrates the notch part of a lateral groove end part. It is a top view which illustrates the tread pattern of the conventional tire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heavy load tire 3 Vertical groove 3A Center side vertical groove 3B Shoulder vertical groove 6A Inner land 6B Outer land part 7 Horizontal groove 7a Inner horizontal groove part 7b Outer horizontal groove part 7c Central horizontal groove part 8 Block row 8A Block 9 Tolerance part 12 Hollow groove 13 Notch 21A Tread surface c Intersection line

Claims (6)

On the tread surface, by providing at least three vertical grooves (3) including a vertical groove 3A on the center side of the zigzag and a vertical groove 3B on the shoulder of the zigzag on both sides, the vertical groove 3A on the central side is provided. A land portion (6) including an inner land portion 6A formed between the shoulder longitudinal groove 3B and an outer land portion 6B between the shoulder longitudinal groove 3B and the tread edge E,
In addition, the inner land portion 6A is traversed starting from the protruding corners 6Ac1 and 6Ac2 on both sides of the inner land portion 6A, and provided with a narrow groove or a siping groove (7) that opens at the longitudinal grooves (3) on both sides. The land portion 6A is a block row (8) in which the blocks 8A are connected,
The groove depth d7 of the horizontal groove (7) is smaller than the average value ((d3A + d3B) / 2) of the groove depths d3A, d3B of the vertical grooves (3) on both sides of the opening, and the groove width w7 of the horizontal groove (7). Is smaller than the average value ((w3A + w3B) / 2) of the groove widths w3A and w3B of the longitudinal grooves on both sides of the opening,
In addition, the lateral groove (7) is composed of an inner lateral groove portion 7a extending from the inner protruding corner 6Ac1 on the inner side in the tire axial direction, an outer lateral groove portion 7b extending from the outer protruding corner 6Ac2, and a central lateral groove portion 7c that connects between the inner lateral groove portions 7a.
In addition, an inclination angle α formed by the inner lateral groove portion 7a with respect to the tire axial direction line, an inclination angle β formed by the outer lateral groove portion 7b with respect to the tire axial direction line, and a central lateral groove portion 7c formed by the tire axial direction line. A heavy-duty tire having the following relationship with an inclination angle γ (α, β, and γ are acute angles):
0 ° ≦ β <α < 60 ° ≦ γ
  The central longitudinal groove 3A passes over the tire equator C, and the lateral groove (7) has a groove depth d7 of 10 to 60% of the groove depth d3 of the longitudinal groove (3) and a groove width of 0.5 mm. The inner lateral groove portion 7a, the outer lateral groove portion 7b, and the central lateral groove portion 7c of the lateral groove (7) are 50% or less of the groove width w3 of the longitudinal groove (3). The heavy-duty tire according to claim 1, wherein the directions inclined in the circumferential direction are the same. It said inner land portion 6A includes lateral grooves (7) and longitudinal groove (3) and intersect intersection is cut from the tread surface to the lateral grooves (7) and longitudinal groove (3) and the intersection line c triangular leading downward The heavy-duty pneumatic tire according to claim 1 or 2, further comprising a notch (13) formed of a notched slope.   The outer land portion 6B is provided with a notch portion (14) comprising a slope formed by notching the protruding corner portion 6Bc on the inner side in the tire axial direction from the tread surface to the lower portion of the protruding corner line. Item 4. The heavy duty pneumatic tire according to any one of Items 1 to 3.   The length L7c along the center line of the central lateral groove portion 7c of the lateral groove (7) is larger than the length L7a of the inner lateral groove portion 7a and the length L7b of the outer lateral groove portion 7b. The heavy-duty tire according to any one of claims 1 to 4. The tread edge E of the outer land portion 6B has a width w12 in the tire axial direction that is 0 of the width wcs in the tire axial direction between the protruding corner 6Bc inside the tire axial direction of the land portion 6B of the shoulder and the corner 6Bs. A hollow groove (12) having a small width lug groove that is larger than 5 times and smaller than 1.5 times,
The distance L6B1 between the tire axial direction line x1 passing through the corner 6Bs of the outer land portion 6B and the center line x2 of the hollow groove (12) is a zigzag pitch P in the tire circumferential direction between the corners 6Bs. The heavy-duty tire according to claim 1, wherein the tire is larger than 0.4 times and smaller than 0.6 times.

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