JP5129855B2 - Heavy duty tire - Google Patents

Description

  The present invention relates to a heavy duty tire in which a tread pattern having a shoulder rib extending along a tread ground contact edge is provided, and distortion of a buttress portion is reduced and crack resistance is improved.

  High traction performance is required for tires mounted on the drive shaft side of heavy-duty vehicles such as trucks and buses. Therefore, a block pattern in which a plurality of circumferential land portions divided by longitudinal main grooves extending in the tire circumferential direction are arranged in a block row is desired for the tread portion of the tire on the drive shaft side.

  On the other hand, in a heavy-duty vehicle, the load change is large, for example, the load of the tire on the drive shaft side during so-called idle when no load is loaded is reduced to about 40% of the load at the maximum loading. Therefore, when the vehicle is idle, the contact pressure of the outer circumferential land portion arranged on the outermost side in the tire axial direction is significantly lower than the contact pressure of the inner circumferential land portion. As a result, there is a problem in that the amount of slip with the road surface increases in the outer circumferential land portion, and uneven wear such as so-called shoulder drop wear, in which the outer circumferential land portion wears quickly, is likely to occur.

  Therefore, in a tire with a large load change, for example, as shown in FIG. 7, only the outer circumferential land portion a is increased not as a block row b but as a rib body c continuous in the circumferential direction, thereby increasing the rigidity. It is intended to suppress the uneven wear by increasing the wear resistance of the circumferential land portion a.

  However, in the tire t2 in which the outer circumferential land portion a is the rib body c, the distortion of the buttress portion d tends to be larger at the time of load rolling than the tire t1 in which the block row b is formed. As a result, by repeating this distortion, cracks are likely to occur in the buttress portion d, resulting in a new problem of reducing durability.

  In order to suppress the occurrence of cracks, the weather resistance is increased by adding an anti-aging agent to the sidewall rubber forming the outer surface of the buttress part d, or the rubber gauge thickness at the position of the buttress part d where cracks are likely to occur is increased. It can be considered to increase and suppress distortion.

  However, in the former, an increase in the amount of anti-aging agent causes an increase in material cost, and when manufacturing tires t1 and t2, the rubber composition of the side wall rubber cannot be made common, and the production efficiency is lowered. Occurs. In the latter case, when the tires t1 and t2 are manufactured, it is necessary to change the side mold for sidewall molding in addition to the tread mold for tread molding among the vulcanization molds. There is a problem that the molds cannot be shared, leading to an increase in mold costs and a decrease in production efficiency.

  Therefore, the present invention can reduce the distortion of the buttress portion in a tire having a rib body on the outer circumferential land portion while making the rubber composition of the side wall rubber and the side mold in common. An object of the present invention is to provide a heavy-duty tire that can improve both wear and wear.

Japanese Patent Laid-Open No. 10-100706 JP 2005-289122 A

In order to achieve the above object, according to the first aspect of the present invention, the tread portion is provided with a plurality of longitudinal main grooves extending in the circumferential direction so that the tread portion is grounded between the longitudinal main grooves and the longitudinal main grooves and the tread. A heavy-duty tire divided into a plurality of circumferential land portions between the ends,
Out of the circumferential land portion, the outer circumferential land portion arranged on the most tread grounding end side is formed as a shoulder rib extending substantially continuously in the circumferential direction without being divided by a lateral groove,
And the shoulder rib comprises a plurality of hollow grooves spaced in the circumferential direction at the tread grounding end, forming a hollow shape recessed inward in the radial direction from the tread surface,
In the hollow groove, the hollow groove length Lh in the circumferential direction on the tread surface is 0.003 to 0.01 times the tire outer circumferential length LT at the position of the tread grounding end, and the hollow groove in the tire axial direction on the tread surface. The width Wh is 0.03 to 0.20 times the tread contact width WT,
Moreover, the hollow groove depth Hh in the radial direction from the tread contact end at the radially inner end of the hollow groove is set to 0.08 to 0.12 times the tire cross-section height HT ,
The main tread rubber portion constituting the tread surface has a rubber hardness Hs of 66 ° or more .

In the invention of claim 2, the circumferential distance La between the hollow grooves adjacent in the circumferential direction is 50 to 80 mm.
In the invention of claim 3, the main tread rubber part is characterized in that the rubber hardness Hs is 70 ° or less.

  In this specification, unless otherwise specified, the dimensions and the like of each part of the tire are values specified in a normal internal pressure state in which a normal rim is assembled and a normal internal pressure is filled. The tread grounding end means the outermost end in the tire axial direction of the tread grounding surface that is grounded when a normal load is applied to the tire in the normal internal pressure state, and the tire axial distance between the tread grounding ends is defined as the tread grounding end. This is defined as the tread ground contact width WT.

  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, or ETRTO means "Measuring Rim". The “regular internal pressure” is the air pressure defined by the standard for each tire. If JATMA, the maximum air pressure, if TRA, the maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” If so, it means "INFLATION PRESSURE". The “regular load” is the load specified by the standard for each tire. If it is JATMA, it is the maximum load capacity. If it is ETRTO, it is "LOAD CAPACITY".

  In the heavy-duty tire of the present invention, first, the outer circumferential land portion is a shoulder rib that extends substantially continuously in the circumferential direction, thereby increasing the rigidity of the outer circumferential land portion and reducing shoulder wear. To prevent uneven wear.

  Further, a plurality of hollow hollow grooves are provided in the circumferential direction at the tread grounding end of the shoulder rib. Since this hollow groove also opens on the buttress surface, this hollow groove can be deformed to disperse the stress when grounded, and the overall surface distortion on the radially inner side of this hollow groove can be reduced. It becomes. As a result, it is possible to suppress the occurrence of cracks in the buttress portion due to the repeated distortion.

  However, if the hollow groove is too small, the stress dispersion effect is too small and the crack generation suppressing effect is not activated. On the other hand, if the hollow groove is too large, it is impossible to suppress the initial uneven wear due to a reduction in rigidity of the shoulder rib. Therefore, in order to improve both crack resistance and uneven wear resistance, it is important to specify the hollow groove within a predetermined size range that is larger than the conventional size.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a heavy duty tire according to the present invention in a normal internal pressure state, and FIG. 2 is a developed view of the tread pattern developed on a plane.

  In FIG. 1, a heavy load tire 1 includes a carcass 6 extending from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, and a belt disposed inside the tread portion 2 and radially outside the carcass 6. With layer 7.

  The carcass 6 is formed of one or more carcass plies 6A in this example, in which carcass cords are arranged at an angle of, for example, 75 ° to 90 ° with respect to the tire circumferential direction. The carcass ply 6 </ b> A has ply folding portions 6 b that are folded from the inner side to the outer side in the tire axial direction around the bead core 5 at both ends of the toroidal ply main body portion 6 a straddling the bead cores 5 and 5. The bead portion 4 is provided with a bead apex rubber 8 having a triangular shape in a sectional view extending radially outward from the bead core 5, and is reinforced from the bead portion 4 to the sidewall portion 3.

  The belt layer 7 is composed of at least two belt plies. In this example, the belt layer 7 is formed of a total of four belt plies 7A to 7D, which are arranged in order from the carcass side toward the tread surface. The case is illustrated. For example, the first belt ply 7A has a belt cord arranged at an angle of about 45 to 70 degrees with respect to the tire circumferential direction, and the second to fourth belt plies 7B to 7D have an angle of about 10 to 35 degrees. The belt cord is arranged. In addition, the inclination direction of the cord with respect to the tire circumferential direction is different between the second and third belt plies 7B and 7C, thereby increasing the belt rigidity and reinforcing the tread portion 2 firmly.

  Next, a plurality of longitudinal main grooves 10 extending in the circumferential direction are formed in the tread portion 2, thereby dividing the tread portion 2 into a plurality of circumferential land portions 11.

  In this example, as shown in FIG. 2, the tread portion 2 includes a central longitudinal main groove 10c extending on the tire equator C and a pair of outer longitudinal main grooves 10o arranged on both outer sides thereof. A longitudinal main groove 10 is formed. As a result, the tread portion 2 can be connected to the outer circumferential land portion 11i between the central vertical main groove 10c and the outer vertical main groove 10o and between the outer vertical main groove 10o and the tread grounding end Te. It is divided into the circumferential direction land portion 11o.

  Among them, the inner circumferential land portion 11i is formed as a block row 13R in which a plurality of blocks 13 divided by the transverse grooves 12 crossing the circumferential land portion 11i are arranged in the circumferential direction.

  Here, in the vertical main groove 10, the groove width Wg on the tread surface S and the groove depth Hg (shown in FIG. 1) from the tread surface S are the groove widths of the vertical main grooves of the conventional heavy duty tire. The same depth as the groove depth can be used. In this example, the groove width Wg is set to a range of 4.0 to 10.0% of the tread ground contact width WT, and the groove depth Hg is set to a range of 15 to 30 mm. In the lateral groove 12, the groove width Wy on the tread surface S is preferably in the range of 3.0 to 7.0% of the tread grounding width WT from the viewpoint of securing traction performance. The depth Hy (shown in FIG. 1) is preferably not more than 1.0 times the groove depth Hg of the longitudinal main groove 10 from the viewpoint of securing block rigidity.

  In this example, each vertical main groove 10 is formed as a zigzag groove in order to improve the traction performance. The vertical main grooves 10 have the same number of zigzag pitches, and the longitudinal main grooves 10 are shifted in the circumferential direction between the adjacent vertical main grooves 10. The lateral grooves 12 connect zigzag corners Ka between adjacent vertical main grooves 10 so that each block 13 has a maximum width portion 14 having a maximum block width at the center in the circumferential direction. Is forming. Further, in this example, for the purpose of improving the traction performance, the transverse grooves 12 are formed between the gently inclined groove portions 12a and 12a extending from the respective longitudinal main grooves 10 at an angle of 60 ° or less with respect to the tire axial direction. It is formed in a bent shape that is joined by a steeply inclined groove portion 12b that is inclined at a large angle.

  Next, the outer circumferential land portion 11o is formed as a shoulder rib 15 that extends substantially continuously in the circumferential direction without being divided by a lateral groove. Thereby, the rigidity of the outer circumferential land portion 11o is increased, and uneven wear such as shoulder drop wear is suppressed in a tire having a large load change. The lateral groove means a groove having a groove width Wy of 3.0% or more, preferably 4.0% or more of the tread ground contact width WT. Accordingly, the outer circumferential land portion 11o can be divided by a narrow groove having a groove width of less than 2.0% of the tread grounding width WT or by siping. More preferably, they are not separated by siping.

  As shown in FIGS. 1 and 2, a plurality of hollow grooves 16 having a hollow shape recessed radially inward from the tread surface S are provided in the circumferential direction in the tread contact end Te of the shoulder rib 15. . The hollow groove 16 is opened at the buttress surface Bs and the tread surface S, which are surfaces in the vicinity of the tread grounding end Te, of the outer surface of the sidewall portion 3 (hereinafter referred to as the sidewall surface 3S). The sidewall surface 3S has a contour shape that is a main portion 3S1 curved in a convex arc shape from the tire maximum width position M toward the outer side in the radial direction, and a straight line extending toward the tread grounding end Te that continues to the main portion 3S1. And the sub-part 3S2 extending in the shape of a circular arc or a concave arc, and this sub-part 3S2 is normally called a buttress surface Bs. Moreover, the crack of the side wall portion 3 is likely to occur at a position near the inflection point P where the main portion 3S1 and the sub portion 3S2 intersect.

  As shown in FIG. 2, the opening shape J1 in the tread surface S of the hollow groove 16 has an inner side j1a on the inner side in the tire axial direction extending substantially parallel to the tread ground contact Te and treads from both ends in the circumferential direction of the inner side j1a. A quadrangular shape having a side j1b extending to the ground contact Te is formed. As the opening shape J1, as in this example, each side j1b has a trapezoidal shape that spreads on both sides in the circumferential direction toward the outside in the tire axial direction at an angle α of 15 to 55 ° with respect to the tire axial direction. It is particularly preferable from the viewpoint of crack resistance and uneven wear resistance.

  As shown in the perspective view of the hollow groove 16 in FIG. 3, the inner surface of the hollow groove 16 has a back surface portion 17 extending radially inward from the inner side j1a and a side surface portion 18 extending radially inward from the side j1b. , And a bottom surface portion 19 connecting the inner ends in the radial direction of the back surface portion 17 and the side surface portion 18. 4A and 4B, a plan view and a side view of the hollow groove 16 are shown. In FIGS. 3 and 4, for the sake of convenience, the intersecting portions of the surface portions 17, 18, and 19 are illustrated in an edge shape. However, in order to suppress cracks, the intersecting portions are formed into circles having a curvature radius of, for example, 1 to 5 mm. It is preferable to form it in an arc shape.

  In this example, the opening shape J2 of the hollow groove 16 in the buttress surface Bs is such that the side edge 18e where the side surface portion 18 and the buttress surface Bs intersect extends in the radial direction, and the bottom surface portion 19 and the buttress surface Bs intersect. The bottom edge 19e forms a substantially rectangular shape (including a square) extending in parallel with the tread grounding end Te. In particular, in this example, the cross-sectional shape of the hollow groove 16 parallel to the tread surface S is such that the back surface portion 17 is parallel to the inner side jia and the side surface portion 18 is the side at the free radial height position. The preferable thing formed in the trapezoid shape which makes a parallel with the edge | side j1b is illustrated.

In the present invention, in the hollow groove 16,
(1) The hollow groove length Lh (shown in FIG. 3) in the circumferential direction on the tread surface S is 0.003 to 0.01 times the tire outer circumferential length LT (not shown) at the position of the tread ground contact Te. (2) The hollow groove width Wh (shown in FIG. 3) in the tire axial direction on the tread surface S is in the range of 0.03 to 0.20 times the tread contact width WT (shown in FIG. 1), and ( 3) The hollow groove depth Hh (shown in FIG. 3) in the radial direction from the tread contact end Te at the radially inner end of the hollow groove 16 is set to 0.08 to 0.08 to the tire cross-section height HT (shown in FIG. 1). The range is restricted to 0.12 times.

  As described above, the hollow groove 16 of the present embodiment, in which the hollow groove length Lh, the hollow groove width Wh, and the hollow groove depth Hh are larger than the conventional hollow groove, 16 can be deformed to disperse the stress. As a result, it is possible to reduce the overall surface distortion in the radially inner portion of the hollow groove 16, and to suppress the occurrence of cracks in the buttress surface Bs due to the repetition of the distortion.

  However, the hollow groove length Lh is less than 0.003 times the tire outer peripheral length LT, the hollow groove width Wh is less than 0.03 times the tread contact width WT, and the hollow groove depth Hh is the tire cross-sectional height HT. In the case of less than 0.08 times, the hollow groove 16 is too small, and the stress dispersion effect becomes too small, and the crack generation suppressing effect cannot be activated. Conversely, the hollow groove length Lh is greater than 0.01 times the tire outer peripheral length LT, the hollow groove width Wh is greater than 0.20 times the tread contact width WT, and the hollow groove depth Hh is the tire cross-sectional height. When the height HT is larger than 0.12 times, the hollow groove 16 is too large. As a result, the rigidity of the shoulder rib 15 is lowered, and it is impossible to suppress uneven wear such as initial shoulder drop wear.

  The hollow groove 16 is formed by embedding a hollow groove forming projection provided in a vulcanization mold in a tire during vulcanization molding. However, when the hollow groove depth Hh is greater than 0.12 times the tire cross-sectional height HT, the carcass 6 is pushed into the tire lumen by embedding the protrusions, so that the internal pressure is applied to the vulcanized tire. When filled, the pushed-in portion swells, causing a risk of deforming the tire shape.

  From such a viewpoint, the lower limit value of the hollow groove length Lh is preferably 0.003 times or more, more preferably 0.005 times or more of the tire outer peripheral length LT, and the upper limit value is 0 of the tire outer peripheral length LT. It is preferably 0.01 times or less, more preferably 0.008 times or less. The lower limit value of the hollow groove width Wh is preferably 0.03 times or more, more preferably 0.05 times or more of the tread ground contact width WT, and the upper limit value is 0.2 times or less of the tread ground contact width WT, and more preferably 0. 15 times or less is preferable. The lower limit of the hollow groove depth Hh is preferably 0.08 times or more, more preferably 0.09 times or more of the tire cross-section height HT.

  In the hollow groove 16, from the viewpoint of crack suppression, the circumferential distance La (shown in FIG. 2) between the hollow grooves 16 and 16 adjacent in the circumferential direction is preferably in the range of 50 to 80 mm. The stress dispersion effect is exhibited over the entire tire circumference, and the generation of cracks can be suppressed over the entire tire circumference. If the distance La exceeds 80 mm, the stress dispersion effect becomes too small, and it becomes difficult to sufficiently suppress the occurrence of cracks. On the contrary, if the distance La is less than 50 mm, the rigidity of the shoulder rib 15 is greatly reduced, and uneven wear tends to occur.

  Further, in this example, in order to enhance the stress dispersion effect in the hollow groove 16, as shown in FIG. 5, the hollow groove 16 has a hollow groove width W in the tire axial direction from the buttress surface Bs to the back surface portion 17, and the tread surface. A groove width gradually increasing region 16a that gradually increases inward in the radial direction from S and reaches the maximum groove width position Q where the hollow groove width W is maximum, and a hollow groove width from the maximum groove width position Q inward in the radial direction And a groove width gradually decreasing region 16b in which W gradually decreases.

  Such a hollow groove 16 can be easily deformed in the vicinity of the maximum groove width position Q, such as being easily deformed in the vicinity of the maximum groove width position Q at the time of grounding, and as a result, in the vicinity of the inflection point P. It is possible to more uniformly reduce the distortion and suppress the occurrence of cracks.

  At this time, the maximum groove width position Q is preferably such that the radial distance Ha from the tread ground contact Te is 0.08 to 0.13 times the tire cross-section height HT. If the distance Ha is less than 0.08 times the tire cross-section height HT, deformation occurs too much on the upper side, adversely affecting uneven wear resistance. Conversely, if the distance Ha exceeds 0.13 times, the deformation position changes. Since it approaches the bending point P, it is disadvantageous for suppressing cracks. The radial distance Ha of the maximum groove width position Q is preferably in a range of 0.5 to 0.8 times the hollow groove depth Hh. If the distance is outside the range, formation of the maximum groove width position Q is performed. The improvement of the stress dispersion effect due to is not sufficiently achieved. The maximum value Wmax of the hollow groove width W at the maximum groove width position Q is preferably in the range of 1.0 to 1.2 times the hollow groove width Wh on the tread surface S.

  As shown in FIG. 1, among the tread rubber 2G arranged on the outer side in the radial direction of the belt layer 7, at least the main tread rubber portion 2Ga constituting the tread surface S has a rubber hardness Hs (durometer A hardness). Is preferably made of rubber of 66 ° or more. When the rubber hardness Hs is less than 66 °, even when the hollow groove 16 of the present embodiment is formed, the wear resistance is insufficient, and the effect of suppressing uneven wear cannot be fully exhibited. The upper limit of the rubber hardness Hs is preferably 70 ° or less from the viewpoint of crack resistance. In addition, the code | symbol 3G in a figure means side wall rubber.

  FIG. 6 shows another embodiment of the hollow groove 16. In FIG. 6 (A), there is a case where the hollow groove width W in the tire axial direction from the buttress surface Bs to the back surface portion 17 is substantially constant as the hollow groove 16 from the tread surface S to the bottom surface portion 19. FIG. 6B shows a case where the hollow groove width W gradually decreases inward in the radial direction from the tread surface S to the bottom surface portion 19. In any case, although it is inferior to the case where the maximum groove width position Q is provided on the back surface portion 17, the stress dispersion effect can be sufficiently exhibited.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  A heavy-duty tire (TL295 / 75R22.5) in which the tread pattern shown in FIG. 2 was used as a basic pattern and the hollow groove 16 was formed on the tread ground contact Te according to the specifications shown in Table 1 was prototyped. Each sample tire was tested for crack resistance and uneven wear resistance, and the results were compared. In each tire, the opening shape J1 in the tread surface S of the hollow groove 16 and the cross-sectional shape parallel to the tread surface S are trapezoidal, and the angle α of the side j1b (or side surface portion 18) with respect to the tire axial direction is 50 °. is there. Moreover, each surface part 17-19 cross | intersects via the circular arc part with a curvature radius of 4 mm. Also, in the table, the symbol LT is the tire outer peripheral length (3235 mm) at the tread contact end Te, the symbol WT is the tread contact width (212 mm), and the symbol HT is the tire cross-sectional height (229 mm), which is constant for each tire. .

(1) Crack resistance:
A sample tire is mounted on a vehicle (drive shaft of a tractor head vehicle with two drive shafts) with a rim (8.25 × 22.5) and internal pressure (760 kPa), and the trailer vehicle is loaded with a load of 20 tons. Ran on a regular road 53km. Then, the occurrence of cracks on the buttress surface after running was evaluated in five stages by visual inspection. The evaluation is as follows. Level 4 or higher is an NG level in the market.
Level 1 --- No cracking:
Level 2 --- Slight cracking:
Level 3 --- Moderate occurrence of cracks:
Level 4 --- Cracks are very small:
Level 5 --- Big cracking:

(2) Abrasion resistance:
After running the actual vehicle of 53 km, the amount of wear around the hollow groove was measured and evaluated in three stages. The evaluation is as follows. Level 3 or higher is an NG level in the market.
Level 1 --- Abrasion amount is 0 or more and less than 1.0 mm:
Level 2 --- Abrasion amount is 1.0 mm or more and less than 2.0 mm:
Level 3 --- Abrasion amount is 2.0 mm or more:

  As shown in Table 1, it can be confirmed that the tires of the examples can improve both crack resistance and uneven wear resistance.

It is sectional drawing which shows one Example of the tire for heavy loads of this invention. It is an expanded view developed and shown on the plane which shows the tread pattern. It is a perspective view which shows a hollow groove. (A) and (B) are the top view and side view of a hollow groove. It is AA sectional drawing of the hollow groove | channel in FIG. (A), (B) is sectional drawing which shows the other Example of a hollow groove | channel. It is a fragmentary perspective view of the tire explaining a prior art.

2 tread portion 10 longitudinal main groove 11 circumferential land portion 11o outer circumferential land portion 15 shoulder rib 16 hollow groove 16a groove width gradually increasing region 16b groove width gradually decreasing region Bs buttress surface Q maximum groove width position S tread surface Te tread grounding end

Claims (3)

By providing a plurality of longitudinal main grooves extending in the circumferential direction on the tread portion, the load is divided into a plurality of circumferential land portions between the longitudinal main grooves and between the longitudinal main grooves and the tread grounding end. A heavy duty tire,
Out of the circumferential land portion, the outer circumferential land portion arranged on the most tread grounding end side is formed as a shoulder rib extending substantially continuously in the circumferential direction without being divided by a lateral groove,
And the shoulder rib comprises a plurality of hollow grooves spaced in the circumferential direction at the tread grounding end, forming a hollow shape recessed inward in the radial direction from the tread surface,
In the hollow groove, the hollow groove length Lh in the circumferential direction on the tread surface is 0.003 to 0.01 times the tire outer circumferential length LT at the position of the tread grounding end, and the hollow groove in the tire axial direction on the tread surface. The width Wh is 0.03 to 0.20 times the tread contact width WT,
Moreover, the hollow groove depth Hh in the radial direction from the tread contact end at the radially inner end of the hollow groove is set to 0.08 to 0.12 times the tire cross-section height HT ,
The main tread rubber portion constituting the tread surface has a rubber hardness Hs of 66 ° or more, and is a heavy duty tire.   The heavy load tire according to claim 1, wherein a circumferential distance La between hollow grooves adjacent to each other in the circumferential direction is 50 to 80 mm. The heavy duty tire according to claim 1, wherein the main tread rubber portion has the rubber hardness Hs of 70 ° or less.

Images