JP2016150665A - Heavy-duty pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heavy-duty pneumatic tire preventing occurrence of crack while securing a wet performance by improving the shape of siping.SOLUTION: In a heavy-duty pneumatic tire 1, the sipings 12 having a cut width W2 of 0.4-1.6 mm and getting across over a total width of a crown rib 8 are separately provided in a tire circumferential direction. The siping 12 has the angle αt of 15 to 50 degrees to the tire circumferential direction in total length range. Besides, the tire includes a first siping 13 tapered from the rib edge 8e of the crown rib 8 toward the intermediate part side of the rib 8 in a tire axial direction, and an intermediate tie bar 14 reducing the depth of the first siping 13 is provided in the whole range of the intermediate area Rc when trisecting a length in the tire circumferential direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a heavy-duty pneumatic tire having improved crack resistance while securing wet performance by improving the shape of siping.

  In recent years, in heavy duty pneumatic tires for trucks, buses, etc., as shown in FIG. It has been proposed to provide a siping s. The siping s includes a pair of end tie bars t1 provided at both ends of the siping s, and one or more intermediate tie bars t2 provided inside the end tie bar t1 and spaced from the end tie bar t1 (described below). Patent Document 1).

  In such a tire, cracks that tend to occur at the bottom of the siping s, rubber chipping starting from siping, and the like are suppressed by the tie bars t1 and t2 that reduce the siping depth. Moreover, wet performance is also ensured by limiting the depth of a tie bar.

  However, Patent Document 1 does not specifically refer to the arrangement position of the intermediate tie bar t2. As a result of various experiments, the inventors have found that by improving the arrangement position of the intermediate tie bar t2, it is possible to increase the rib rigidity in the vicinity of the siping and further improve the generation of cracks while ensuring wet performance. It was.

JP-A-10-151915

  The present invention has been devised in view of the above-described problems, and provides wet performance based on the provision of intermediate tie bars in the entire range of the intermediate region of the specific shape of siping provided on the crown rib. It aims at providing the pneumatic tire which improves crack-proof performance, ensuring.

  The present invention is a heavy duty pneumatic tire having at least one crown rib extending continuously in the tire circumferential direction at the center of the tread portion, wherein the crown rib has a thickness of 0.4 to 1.6 mm. A first siping having an incision width of about 1 to 50 degrees and an angle with respect to the tire axial direction of the siping across the entire width of the crown rib. In the first siping, the angle gradually increases from the rib edge of the crown rib toward the intermediate portion in the tire axial direction of the crown rib, and the first siping divides the tire circumferential length into three equal parts. An intermediate tie bar for reducing the depth of siping is provided over the entire range of the intermediate region.

  In the heavy duty pneumatic tire according to the present invention, the intermediate tie bar preferably has a length along the siping of 6 to 10 mm and a height from the deepest portion of the siping of 2 to 5 mm.

  In the heavy duty pneumatic tire according to the present invention, it is preferable that the first siping has an angle of 30 to 50 degrees in the intermediate region.

  In the heavy duty pneumatic tire according to the present invention, it is preferable that the first siping is provided with an end tie bar extending inward in the tire axial direction from the rib edge and separated from the intermediate tie bar.

  In the heavy duty pneumatic tire according to the present invention, it is preferable that a widened portion having a large cut width is provided at an outer end portion in the tire radial direction of the first siping.

  In the heavy-duty pneumatic tire according to the present invention, the crown rib has the S-shaped first siping extending in the same direction with respect to the tire circumferential direction in the entire length range, and the same direction with respect to the tire circumferential direction. A crank-shaped siping including a pair of extending side portions and a center portion extending in the opposite direction to the tire circumferential direction and connecting between the both side portions is provided alternately in the tire circumferential direction. desirable.

  In the heavy duty pneumatic tire according to the present invention, the crown rib is formed of a pair provided on both sides of the tire equator, and the inner rib edge on the tire equator side of the crown rib extends in a zigzag shape in the tire circumferential direction, It is desirable that the intersection of the S-shaped first siping and the inner rib edge is displaced by 2 to 10 mm in the tire circumferential direction from the end point on the tire equator side of the inner rib edge.

  The crown rib of the heavy duty pneumatic tire of the present invention is provided with sipings having a cut width of 0.4 to 1.6 mm and across the entire width of the crown rib in the tire circumferential direction. Accordingly, since the water film on the road surface is sucked up and removed in the siping, the wet performance is ensured. Further, the siping includes a first siping having an angle with respect to the tire axial direction of 15 to 50 degrees in the entire length range, and the first siping is an intermediate portion in the tire axial direction of the crown rib from the rib edge of the crown rib. In the first siping, an intermediate tie bar that reduces the depth of siping is provided in the entire range of the intermediate region when the tire circumferential length is equally divided into three. A tire having such a siping can increase the rigidity of an intermediate region of the siping and reliably suppress the opening of the siping, thereby preventing the occurrence of cracks more effectively.

It is sectional drawing (XX cross section of FIG. 2) of the heavy duty pneumatic tire which shows embodiment of this invention. It is a partial expanded view of the tread part. It is an enlarged view of the tread part of FIG. It is an enlarged view of the crown rib of FIG. It is ZZ sectional drawing of FIG. It is a fragmentary perspective view of a crown rib. (A) is Y1-Y1 sectional drawing of FIG. 2, (b) is Y2-Y2 sectional drawing of FIG. It is sectional drawing equivalent to the ZZ cross section of FIG. 4 explaining a comparative example. It is sectional drawing which shows the conventional siping.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a right half sectional view of a normal state of the heavy duty pneumatic tire 1 of the present embodiment. In the present specification, the “normal state” means that the tire is in a no-load state in which a rim is assembled on a normal rim (not shown) and is filled with a normal internal pressure, and unless otherwise specified, dimensions of each part of the tire, etc. Is a value measured in this normal state.

  The “regular rim” is a rim defined for each tire in the standard system including the standard on which the tire is based. “Standard Rim” for JATMA, “Design Rim” for TRA For ETRTO, "Measuring Rim". In addition, the “regular internal pressure” is an air pressure determined by each standard for each tire in the standard system including the standard on which the tire is based. TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES "Maximum value", ETRTO, "INFLATION PRESSURE".

  A heavy-duty pneumatic tire (hereinafter, simply referred to as “tire”) 1 according to the present embodiment includes a carcass 6 that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and the carcass. 6 and a belt layer 7 composed of a plurality of belt plies arranged radially outside and inside the tread portion 2.

  The carcass 6 includes a main body portion 6a straddling a pair of bead cores 5 and 5 in a toroidal manner, and a folded portion 6b that is continuous from both sides of the main body portion 6a and is folded around from the inner side in the tire axial direction around the bead core 5. And at least one carcass ply 6A (in the present embodiment). In the carcass ply 6A, carcass cords made of, for example, steel are arranged at an angle of, for example, 75 to 90 ° with respect to the tire equator C direction.

  In the present embodiment, the belt layer 7 is composed of a total of four belt plies 7A to 7D stacked in the tire radial direction. For example, the belt ply 7B having the largest width in the tire axial direction has two belt plies 7B from the inner side in the tire radial direction. Arranged in the layer. The belt plies 7A to 7D are made of steel cords, and include at least two belt plies that are inclined at 15 to 45 ° with respect to the tire equator C and intersect each other.

  As shown in FIGS. 1 and 2, the tread portion 2 of the present embodiment includes a crown circumferential groove 10 extending continuously on the tire equator C, and a tire shaft at both outer sides in the tire axial direction and at the tread end Te. A pair of shoulder circumferential grooves 11 extending continuously in the direction inside are formed. Accordingly, the tread portion 2 includes a pair of crown ribs that are divided by the crown circumferential groove 10 and the shoulder circumferential groove 11 on the center portion of the tread portion 2 and on both sides of the tire equator C and extend continuously in the tire circumferential direction. 8 and a pair of shoulder ribs 9 that are divided by the shoulder circumferential groove 11 and the tread end Te and extend continuously in the tire circumferential direction.

  In addition, the crown rib 8 formed in the center portion of the tread portion 2 means a rib provided closest to the tire equator C. In the present embodiment, the crown ribs 8 are provided on both sides of the tire equator C. However, the crown ribs 8 may be composed of only one provided on the tire equator C.

  In the present embodiment, each of the circumferential grooves 10 and 11 extends while being bent in a zigzag shape in the tire circumferential direction. Such circumferential grooves 10 and 11 can collect and drain water from a wide range of the ground contact surface, which is useful for ensuring large wet performance.

  The crown circumferential groove 10 has a first inclined portion 10a that inclines toward one side at a relatively small angle with respect to the tire circumferential direction, and a first inclined portion 10a that extends in an opposite direction to the first inclined portion 10a. Two inclined portions 10b are alternately provided. In the present embodiment, a wide portion 10c having a substantially triangular shape in plan view for increasing the groove width is provided on the valley side of the corner portion of the zigzag where the first and second inclined portions 10a and 10b intersect. Such zigzag grooves effectively collect the water film on the ground contact surface in the first inclined portion 10a and the second inclined portion 10b, and the drainage resistance can be reduced in the wide portion 10c, so that the wet performance is improved. . As shown in FIGS. 1 and 2, the groove bottom surface 10U of the crown circumferential groove 10 of the present embodiment is provided with raised portions H for preventing stone biting that are raised in a substantially prismatic shape in the tire circumferential direction. ing.

  The shoulder circumferential groove 11 has the same configuration as the crown circumferential groove 10, and the first inclined portion 11a, the second inclined portion 11b, and the first and second inclined portions 11a, 11b intersect. And a wide portion 11c provided on the valley side of the corner portion of the zigzag.

  The zigzag pitch Ps of the shoulder circumferential groove 11 of the present embodiment is 45 to 55% of the zigzag pitch Pc of the crown circumferential groove 10. As a result, the crown circumferential groove 10 is relatively straighter than the shoulder circumferential groove 11. Since such a crown circumferential groove 10 has a drainage resistance smaller than that of the shoulder circumferential groove 11, wet performance is improved by utilizing a high ground pressure on the tire equator side. Further, the circumferential rigidity of the crown rib 8 is also increased, which helps to improve the steering stability.

  Each of the circumferential grooves 10 and 11 has a groove width (a groove width perpendicular to the longitudinal direction of the groove) W1 between the tread ends Te and Te in order to ensure a good balance between wet performance and steering stability performance. A range of 4.0 to 8.0% of the tread width TW, which is a tire axial distance, is desirable. Similarly, the groove depth D1 (shown in FIG. 3) of the circumferential grooves 10, 11 is desirably in the range of 12 to 16 mm.

  The “tread end Te” is defined as the outermost contact end in the tire axial direction when a normal load is applied to the tire in the normal state and the tread portion 2 is grounded to a plane with a camber angle of 0 degree. The “regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum value described in “LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES”, or “LOAD CAPACITY” in the case of ETRTO.

  The inclination angle θ of the circumferential grooves 10 and 11 with respect to the tire circumferential direction is not particularly limited, but is in the range of 5 to 25 degrees from the viewpoint of ensuring a good balance between the wet performance and the rigidity of the ribs 8 and 9. Is desirable.

  Furthermore, in the case of the 4-rib pattern as in the present embodiment, it is desirable that the crown circumferential groove 10 extends on the tire equator C. The tire axial distance L1 between the center line 11G of the shoulder circumferential groove 11 (amplitude center line in the case of zigzag) and the tread end Te is desirably about 17 to 25% of the tread width TW. However, the arrangement positions of the circumferential grooves 10 and 11 are not limited to such a mode and can be changed as appropriate.

  The crown rib 8 is provided with sipings 12 across the entire width of the crown rib 8 in the tire circumferential direction. Such a siping 12 can suck up the water film on the wet road surface and drain it into the circumferential grooves 10 and 11. Therefore, the wet performance of the rib pattern is improved. On the other hand, the shoulder rib 9 of the present embodiment is not provided with siping that crosses the rib across its full width.

  The siping 12 needs to be formed with a cut width W2 (shown in FIG. 4) of 0.4 to 1.6 mm, which is a width perpendicular to the longitudinal direction of the siping. If the cut width W2 exceeds 1.6 mm, the rib rigidity in the vicinity of the siping 12 becomes small, and there is a possibility that cracks, chips or the like starting from that portion may occur. Conversely, if the cut width W2 is less than 0.4 mm, smooth drainage cannot be performed, and wet performance deteriorates. From such a viewpoint, the cut width W2 is preferably 0.6 mm or more, preferably 1.4 mm or less, more preferably 1.2 mm or less. From the same viewpoint, the maximum depth D2 (shown in FIG. 3) from the rib tread surface of the siping 12 is preferably 30% or more, more preferably 40% or more of the groove depth D1 of the circumferential groove. Further, it is preferably 90% or less, more preferably 80% or less.

  Moreover, as FIG. 4 shows, the siping 12 contains the 1st siping 13 whose angle (alpha) with respect to a tire axial direction is 15-50 degrees. The first siping 13 of the present embodiment extends in the same direction with respect to the tire circumferential direction in the entire length range, and is displayed as an S-shaped first siping 16 (hereinafter simply referred to as “S-shaped siping 16”). May be included.)

  In the first siping 13, the angle α is satisfied in the entire length range of the siping. When the angle α exceeds 50 degrees, the lateral rigidity of the crown rib 8 is lowered and steering stability is deteriorated, and damage such as cracks and rubber chips is likely to occur near the first siping 13. From such a viewpoint, the angle α is more preferably 45 degrees or less. Conversely, when the angle α is less than 15 degrees, drainage resistance increases and wet performance deteriorates. From such a viewpoint, the angle α is more preferably 20 degrees or more. When the first siping 13 is curved as in the present embodiment, the angle α is an angle of a tangent to the siping center line.

  In the first siping 13, the angle α with respect to the tire axial direction gradually increases from the rib edge 8 e of the crown rib 8 toward the intermediate portion of the crown rib 8 in the tire axial direction. Such a 1st siping 13 can perform the drainage by the middle part side smoothly. Further, the edge component in the axial direction can be effectively used on the rib edge 8e side of the crown rib 8 where the braking force and the driving force during the straight traveling are relatively large. Therefore, the first siping 13 can maintain high wet performance and steering stability performance. Further, by reducing the angle α of the first siping 13 in the vicinity of the rib edge 8e having relatively low rigidity, the rib rigidity in the vicinity of the rib edge 8e is secured and the crown rib 8 having relatively high rigidity is also provided. By increasing the angle α of the first siping 13 at the intermediate portion in the tire axial direction, the circumferential component length of the first siping 13 can be increased and wet performance can be improved.

  As shown in FIG. 5 which is a ZZ cross-section of FIG. 4 and FIG. 4, the first siping 13 is formed in at least the entire range of the intermediate region Rc when the tire circumferential direction length Ls is divided into three equal parts. An intermediate tie bar 14 is provided to reduce the depth. The intermediate region Rc of the first siping 13 has a large tire circumferential direction component, and is easily opened largely by a lateral force during turning. However, by providing the intermediate tie bar 14, the siping depth is reduced in the entire range of the intermediate region Rc, and as a result, large opening of the siping in the intermediate region Rc is reliably suppressed even during turning. Thereby, generation | occurrence | production of the crack in the vicinity of siping, rubber | gum missing, etc. is prevented.

  Further, if the length Lc in the tire circumferential direction of the intermediate tie bar 14 is too large, the drainage resistance is increased and the wet performance may be deteriorated. From such a viewpoint, the ratio Lc / Ls between the tire circumferential length Lc of the intermediate tie bar 14 and the tire circumferential length Ls of the first siping 13 is preferably 40% or more, and preferably 50%. The following is desirable.

  Further, from the same viewpoint, the intermediate tie bar 14 has a length L2 along the first siping 13 of preferably 5 mm or more, more preferably 6 mm or more, as shown in FIG. On the other hand, if the length L2 of the intermediate tie bar 14 is too large, the drainage resistance tends to increase and the wet performance tends to decrease. From the same viewpoint, the height h1 of the intermediate tie bar 14 from the deepest portion 13s of the first siping 13 is preferably 2 mm or more, and preferably 5 mm or less. The deepest portion 13s extends parallel to the rib tread surface.

  As described above, in the present embodiment, the angle of the first siping 13 formed on the crown rib 8 is defined, and the intermediate tie bar 14 is provided in the entire range of the intermediate region Rc, so that drainage is performed smoothly. The rigidity of the crown rib 8 is maintained with a good balance. Thereby, the tire 1 of this invention improves wet performance and crack-proof performance with a good balance.

  In order to further enhance the above action, the angle α in the intermediate region Rc of the first siping 13 is preferably 30 degrees or more, more preferably 35 degrees or more, and preferably 50 degrees or less, more preferably 45 degrees or less is desirable. In order to further enhance the above action, the difference between the maximum value and the minimum value of the angle α of the first siping 13 is preferably determined in the range of 20 to 30 degrees.

  As shown in FIGS. 3 and 5, the first siping 13 of the present embodiment is provided with a pair of end tie bars 15, 15 extending inward in the tire axial direction from the rib edges 8 e, 8 e on both sides. Such an end tie bar 15 can increase the rigidity of the bottom part of the siping on the rib edge 8e side, which has a particularly low rigidity, and can prevent the occurrence of cracks by suppressing a large opening. Moreover, the end tie bar 15 is provided away from the intermediate tie bar 14. Such an end tie bar 15 can secure a drainage space and prevent deterioration of wet performance.

  When the length L3 and the height h2 of the end tie bar 15 are excessively increased, the wet performance tends to be deteriorated. Conversely, when the length L3 and the height h2 are decreased, wear on the rib edge side or rubber There is a risk of chipping. From such a viewpoint, the length L3 along the siping of the end tie bar 15 is preferably 2 mm or more, and preferably 7 mm or less. Similarly, the height h2 from the deepest portion 13s of the first siping 13 of the end tie bar 15 is preferably 2 mm or more, and preferably 5 mm or less.

  As shown in FIGS. 7A and 7B which are Y1 and Y2 cross sections of FIGS. 6 and 2, the widened portion 18 having a large cut width is formed at the outer end portion 13U in the tire radial direction of the first siping 13. Is provided. Since such a 1st siping 13 can ensure the amount of drainage largely, wet performance improves. Moreover, since the load due to the driving force or the braking force is reduced at the deepest portion 13s of the first siping 13 by providing the widened portion 18, it is possible to effectively suppress cracks and the like generated in this portion. Even if the widened portion 18 disappears due to wear, a sharp edge of the first siping 13 can newly appear on the tread. Therefore, excellent wet performance can be exhibited over a long period of time. In the present embodiment, the widened portion 18 is provided at all outer end portions 13U of the siping 12. Thereby, the above-mentioned operation is effectively enhanced.

  As shown in FIG. 7, the widened portion 18 of the present embodiment includes a pair of inwardly facing surfaces 18a extending inward in the tire radial direction from the rib tread surface in a cross-sectional view perpendicular to the longitudinal direction of the first siping 13. It is formed in a rectangular shape including bottom surfaces 18b, 18b extending from the inner ends of the inward surfaces 18a, 18a to the first siping 13. In the present embodiment, the pair of inwardly facing surfaces 18a extends in the normal direction of the tread surface, and is separated from the first siping 13 by an equal distance. The bottom surface 18b is formed by a surface parallel to the rib tread surface. However, the widened portion 18 is not limited to such an aspect. For example, the intersection of the inward surface 18a and the outward surface 18b may be chamfered, or the inward surface 18a and the outward surface 18b may be formed as a smooth arc surface.

  When the width W3 or the depth D3 of the widened portion 18 is reduced, the drainage space may be reduced. Conversely, when the width W3 or the depth D3 is increased, the rigidity of the crown rib 8 may be reduced. From this point of view, the width W3 is preferably 2 mm or more, and preferably 3 mm or less. Similarly, the depth D3 of the widened portion 18 is preferably 1 mm or more, and preferably 4 mm or less.

  As shown in FIG. 4, the crown rib 8 is provided with a crank-shaped siping 17 in addition to the S-shaped siping 16.

  The crank-shaped siping 17 has a pair of both side portions 17a extending in the same direction with respect to the tire circumferential direction, and the both side portions 17a extend in the opposite direction with respect to the tire circumferential direction and connects between the both side portions 17a and 17a. And a central portion 17b. In such a crank-shaped siping 17, even when a large shearing force in the tire circumferential direction is applied during driving or braking, the land portions facing each other through the central portion 17b mesh with each other, and a large opening of siping is suppressed. For this reason, generation | occurrence | production of a crack, a chip, etc. is prevented effectively.

  In the present embodiment, S-shaped sipings 16 and crank-shaped sipings 17 are alternately provided in the tire circumferential direction. For example, when the arrangement pitches of the S-shaped siping 16 and the crank-shaped siping 17 are set equal to the zigzag pitch of the crown circumferential groove 10, the rigidity of the rib is maintained in a well-balanced manner. In such an embodiment, the wet performance and the crack resistance performance are further improved in a balanced manner.

  As shown in FIG. 4, the S-shaped siping 16 has an intersection 16t between the S-shaped siping 16 and the inner rib edge 8i in the tire circumferential direction from the end point 8it of the inner rib edge 8i closest to the tire equator. It is desirable to be provided with a positional deviation of 2 to 10 mm. As a result of various experiments, when the distance L4 in the tire circumferential direction between the intersecting portion 16t and the end point 8it is less than 2 mm, an opening of the S-shaped siping 16 is provided in the vicinity of the end point 8it having a large contact pressure. Damage to the part is likely to occur. On the other hand, if the distance L4 exceeds 10 mm, the length of the siping in the tire axial direction cannot be sufficiently secured, and the wet performance tends to be lowered.

  In the crank-shaped siping 17, as in the S-shaped siping 16, the intersection 17 t with the inner rib edge 8 i is displaced from the end point 8 it on the tire equator side.

  Further, in the S-shaped siping 16 and the crank-shaped siping 17 of the present embodiment, the intersecting portions 16u and 17u with the outer rib edge 8s are provided at the end point 8st closest to the tire equator of the outer rib edge 8s. Such an S-shaped siping 16 and a crank-shaped siping 17 are useful for eliminating a rigidity step near the end point 8st and preventing the occurrence of cracks and chips.

  Further, as shown in FIG. 2, the shoulder rib 9 has a small length of shoulder siping that extends from the outer edge 9i on the tire equator side of the shoulder rib 9 to the tread end Te side and breaks without reaching the tread end Te. 19 are spaced apart in the tire circumferential direction. The shoulder siping 19 of the present embodiment faces the opening edge portion 13k on the outer side in the tire axial direction of the first siping 13. Thus, by not providing the first siping on the shoulder rib 9, it is possible to ensure a large rigidity of the shoulder rib 9 to which a large load acts during turning, and to improve the turning performance.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the illustrated embodiments, and can be implemented in various forms.

  In order to confirm the effects of the present invention, a heavy duty tire for trucks and buses having a tire size of 10.00R20 having the internal structure of FIG. 1 and the basic pattern of FIG. These were tested for crack resistance and wet performance. The main common specifications are as follows, and all parameters other than those shown in Table 1 are the same.

Tread width TW: 188mm
Number of carcass plies: 1 carcass cord angle: 90 °
Carcass cord material: Steel Number of belt plies: 4 Belt cord material: Steel Rim: 7.00
Crown and shoulder circumferential groove width W1: 12-15 mm
Groove depth D1: 15 mm of the circumferential groove
Tire axial distance L1 / TW between shoulder circumferential groove and tread edge: 21%
Tire circumferential direction angle α in the range of the total length of the first siping: 15 to 40 degrees Tire circumferential direction angle α in the middle area of the first siping: 40 degrees Maximum depth of siping of the crown rib D2: 7 mm
End tie bar height from the deepest part: 3.0mm
Ratio of tire circumferential length of end tie bar to tire circumferential length of first siping: 10%
Land ratio: 77%
The test method is as follows.

<Crack resistance>
Each sample tire fitted with a rim under the following conditions was run for 8000 km on a drum having a diameter of 1.7 m, and the damaged state near the rib siping was observed with the naked eye. The results were scored with the damage state of Comparative Example 1 taken as 100. The larger the value, the better.
Tire longitudinal load: 26.97kN
Internal pressure: 750 kPa
Speed: 50km / h

<Wet performance>
The test tire was mounted on the front wheel of the test vehicle under the above conditions, and the running time was measured when the test course under the following conditions was run fully open for 5 laps. The result was an index with the reciprocal of the running time value of Comparative Example 1 as 100. The larger the value, the better.
Test vehicle: 10-carried 2DD vehicle Test course: Asphalt road with a radius of 60m, water depth of 1-2mm
The test results are shown in Table 1.

  As a result of the test, the tire of the example was excellent in both crack resistance and wet performance, and a significant effect was confirmed.

DESCRIPTION OF SYMBOLS 1 Heavy load pneumatic tire 2 Tread part 8 Crown rib 8e Crown rib rib edge 12 Siping 13 First siping 14 Intermediate tie bar Rc Middle area

Claims (7)

A heavy-duty pneumatic tire having at least one crown rib extending continuously in the tire circumferential direction at the center of the tread portion,
In the crown rib, siping having a cutting width of 0.6 to 1.4 mm and across the entire width of the crown rib is provided in the tire circumferential direction,
The siping includes a first siping having an angle with respect to the tire axial direction of 15 to 50 degrees in the entire length range,
In the first siping, the angle gradually increases from the rib edge of the crown rib toward the intermediate portion of the crown rib in the tire axial direction.
The first siping is a heavy duty pneumatic tire characterized in that an intermediate tie bar for reducing the depth of siping is provided in the entire range of the intermediate area when the tire circumferential length is divided into three equal parts. .   2. The heavy duty pneumatic tire according to claim 1, wherein the intermediate tie bar has a length along the siping of 6 to 10 mm and a height from the deepest portion of the siping of 2 to 5 mm.   3. The heavy duty pneumatic tire according to claim 1, wherein in the first siping, the angle in the intermediate region is 30 to 50 degrees.   4. The heavy duty pneumatic tire according to claim 1, wherein the first siping is provided with an end tie bar extending inward in the tire axial direction from the rib edge and spaced apart from the intermediate tie bar. 5.   The pneumatic tire for heavy loads according to any one of claims 1 to 4, wherein a widened portion having a large cut width is provided at an outer end portion in the tire radial direction of the first siping.   In the crown rib, the S-shaped first siping extending in the same direction with respect to the tire circumferential direction in the entire length range, a pair of both side portions extending in the same direction with respect to the tire circumferential direction, and the both side portions 6. The heavy duty load according to claim 1, wherein crank-shaped sipings including a central portion extending in a direction opposite to the tire circumferential direction and connecting between both side portions are alternately provided in the tire circumferential direction. Pneumatic tire. The crown rib comprises a pair provided on both sides of the tire equator, and the inner rib edge on the tire equator side of the crown rib extends in a zigzag shape in the tire circumferential direction,
The heavy load pneumatic according to claim 6, wherein the intersection of the S-shaped first siping and the inner rib edge is displaced by 2 to 10 mm in the tire circumferential direction from an end point on the tire equator side of the inner rib edge. tire.

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