JP3930481B2 - Heavy duty tire - Google Patents

Description

  The present invention relates to a heavy-duty tire in which rolling resistance is reduced while maintaining bead durability by increasing the size of a bead apex rubber with a predetermined thickness distribution.

  In heavy-duty tires for trucks and buses, a bead structure as shown in FIG. 3 is generally used, and from the viewpoint of emphasizing durability, a design that does not significantly change the conventional structure with a proven track record in durability is made. In the figure, symbol a represents a carcass ply, symbol b represents a bead apex rubber, and symbol c represents a cord reinforcing layer. Also in this type of tire, reduction of rolling resistance is strongly desired from the viewpoint of protection of environmental resources. For example, it has been proposed to adopt a low heat generation rubber with a small loss tangent for the bead apex rubber b or the like. (For example, refer to Patent Document 1).

JP 2002-178724 A

  However, the ratio of the bead apex rubber b to the entire rubber of the tire is relatively small. Therefore, in the above proposal, in order to sufficiently obtain the effect of reducing rolling resistance, there is a possibility that the basic durability of the bead portion may be impaired, for example, it is necessary to greatly reduce the loss tangent of rubber.

  Therefore, the present inventor studied to reduce the rolling resistance without changing the rubber physical properties of the bead apex rubber b. Here, from the viewpoint that the tire weight is one of the factors that increase the rolling resistance, the height H1 of the bead apex rubber b is conventionally set to about 0.75 times or less the height H0 of the tire maximum width position. Rather, it has been studied to set the height H1 lower. Thus, as a result of confirming the trial production of a tire in which the bead apex rubber b is miniaturized, the inventor has found that the rolling resistance may increase conversely even though the weight is reduced. . This is presumably because the bead apex rubber b is reduced in size, the bead rigidity is reduced, the deflection is spread over the entire tire side region, and the energy loss is increased.

  Therefore, the bead apex rubber b was deliberately increased in size, and the rigidity in the tire side region was increased over a wide range, thereby further researching from the reverse viewpoint of narrowing the bending region and causing energy loss. As a result, when the height H1 of the bead apex rubber b is set in the range of (0.85 to 0.95) × H0 higher than the conventional one and the distribution of the thickness T of the bead apex rubber b is specified, It was found that the rolling resistance can be reduced without degrading the bead durability even when the influence due to the weight increase is subtracted.

  That is, the present invention provides a heavy-duty tire with reduced rolling resistance without impairing bead durability by setting the height of the bead apex rubber to a higher range than before and specifying the thickness distribution thereof. The purpose is to do.

In order to achieve the above object, the invention of claim 1 of the present application is folded back from the inner side in the tire axial direction around the bead core to the ply body part extending from the tread part through the sidewall part to the bead core of the bead part. A heavy duty tire comprising a carcass ply having a ply turn-up portion, and a bead apex rubber extending between the bead core and the ply turn-up portion and extending radially outward from the bead core;
The ply turn-up portion is interrupted at the tire axial direction outer surface of the bead apex rubber,
And the radial height H1 from the bead base line at the tip of the bead apex rubber is 0.85 to 0.95 times the radial height H0 from the bead base line at the tire maximum width position, and
The bead apex rubber has a thickness Ta of the bead apex rubber at a position Pa where the outer surface is the height of the tip of the ply turn-up portion, and the outer surface is a radial direction from the bead base line of the tip of the ply turn-up portion. 0.85 to 1.10 times the thickness Tb of the bead apex rubber at a position Pb that is 2/5 of the height H2, and the outer side surface is the tip of the ply turn-up portion and the tip of the bead apex rubber The thickness Tc of the bead apex rubber at a position Pc that is an intermediate height is 0.35 to 0.45 times the thickness Ta.

  According to a second aspect of the present invention, the bead apex rubber has a loss tangent tan δ at 70 ° C. of 0.05 to 0.11.

  In the present specification, the dimensions and the like of the tires such as the heights H0 and H1 are values specified in a 50 kPa internal pressure state in which the tire is assembled on a regular rim and filled with an internal pressure of 50 kPa. 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".

  Since the present invention is configured as described above, it is possible to reduce rolling resistance without impairing the bead durability in a heavy duty tire.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing an internal pressure state of 50 kPa when the heavy load tire of the present invention is a tubeless tire for trucks and buses, and FIG. 2 is an enlarged cross-sectional view of the bead portion.

  In FIG. 1, a heavy load tire 1 is disposed on a carcass 6 that extends from a tread portion 2 to a bead core 5 of a bead portion 4 through a sidewall portion 3, and on the radially outer side of the carcass 6 and on the inner side of the tread portion 2. Belt layer 7.

  The belt layer 7 is formed of three or more belt plies using a belt cord. In this example, the belt layer 7 includes a first belt ply 7A on the innermost side in the radial direction in which steel cords are arranged at an angle of 60 ± 15 ° with respect to the tire circumferential direction, and 10 to 10 with respect to the tire circumferential direction. A case of a four-sheet structure with second to fourth belt plies 7B to 7D arranged at a small angle of 35 ° is illustrated. The belt layer 7 has one or more portions where the belt cords cross each other between the plies, thereby increasing belt rigidity and reinforcing the tread portion 2 with a tagging effect.

  The carcass 6 is formed of a single carcass ply 6A in which carcass cords are arranged at an angle of 70 to 90 ° with respect to the tire circumferential direction. A steel cord is suitable as the carcass cord, but an organic fiber cord such as nylon, rayon, polyester, aromatic polyamide or the like is also used if necessary. The carcass ply 6A includes a series of ply folding portions 6b that are folded from the inner side to the outer side in the tire axial direction around the bead core 5 on both sides of the ply body portion 6a straddling the bead cores 5 and 5. A bead apex rubber 8 extending from the bead core 5 outward in the tire radial direction is disposed between the main body 6a and the ply turn-up portion 6b. The ply turn-up portion 6b has a so-called low turn-up structure (1-0 LTU) that is interrupted by the tire axial direction outer surface S of the bead apex rubber 8.

  In the present invention, as shown in FIG. 2, the radial height H1 from the bead base line BL of the tip 8e of the bead apex rubber 8 is set to the radial height from the bead base line BL at the tire maximum width position M. It is set to 0.85 to 0.95 times as large as H0 compared to a conventional tire. Thereby, the rigidity of the tire side region is increased over a wide range, and the bending region at the time of tire deformation is narrowed. As a result, the energy loss of the entire tire can be kept low, and the rolling resistance can be reduced even when the increase in weight accompanying the increase in the height H1 is taken into account.

And in order to demonstrate such an effect, in the bead apex rubber 8,
The thickness of the bead apex rubber 8 at the position Pa where the outer surface S is at the height of the tip 6e of the ply turn-up portion 6b is Ta;
The position Pb at which the outer surface S is 2/5 of the radial height H2 from the bead base line BL of the tip 6e of the ply turn-up portion 6b, in other words, a distance of 2/5 of the height H2. The thickness of the bead apex rubber 8 at the position Pb on the outer surface S that separates Kb radially outward from the bead base line BL is Tb;
The distance Kc corresponding to the position Pc at which the outer side surface S is at an intermediate height between the front end 6e of the ply folded portion 6b and the front end 8e of the bead apex rubber 8, in other words, is equivalent to (H1-H2) / 2. The thickness of the bead apex rubber at the position Pc on the outer side surface S spaced radially outward from the tip 6e; Tc;
When
(1) The thickness Ta is 0.85 to 1.10 times the thickness Tb, and (2) the thickness Tc is 0.35 to 0.45 times the thickness Ta,
Is important.

  The “bead base line BL” means a tire axial line passing through the rim diameter position of the regular rim J, and the “tire maximum width position M” means irregularities such as patterns and characters from the sidewall surface. This means the position of the so-called tire cross-sectional width at which the width of the tire contour shape excluding is maximized. The thicknesses Ta to Tc are the thicknesses T measured from the positions Pa to Pc in the direction perpendicular to the ply main body 6a as is well known, and the thickness T varies smoothly between the positions. Yes.

  Here, the thickness distribution can be achieved by increasing the thickness T from the position Pb to the position Pc as compared with the prior art. In particular, in the present invention, the bead apex rubber 8 has its root portion. To the position Pa, while maintaining a substantially constant thickness without reducing the thickness T as much as possible. As a result, in combination with the increase in the height H1, the rigidity of the tire side region can be improved in a well-balanced manner over a wide range, the flexion region when the tire is deformed is narrowed, and energy loss is reduced throughout the tire. It becomes possible to suppress. In addition, stress concentration at the tip 6e is alleviated, which is advantageous for durability.

  Here, when the thickness Ta at the position Pa is less than 0.85 times the thickness Tb, the rigidity of the whole bead apex rubber becomes insufficient, and the height H1 of the bead apex rubber is increased to the above range. However, it is difficult to reduce the flexure region narrowly, and the effect of suppressing the energy loss cannot be sufficiently exhibited. Moreover, even if it exceeds 1.10 times, the further reduction | decrease of a bending area | region is not anticipated, conversely, it will become a weight increase and will be disadvantageous for rolling resistance, fuel consumption, and durability. From such a viewpoint, the lower limit value of the thickness Ta is preferably 0.90 or more, more preferably 0.95 times or more of the thickness Tb, and the upper limit value is 1.05 or less. preferable.

  When the thickness Tc at the position Pc is less than 0.35 times the thickness Ta, the rigidity from the position Pa to the tip 8e, in particular, the rigidity from Pc to the tip 8e becomes insufficient. The rolling resistance cannot be reduced without narrowing the flexure region. On the other hand, if it exceeds 0.45 times, the state of the carcass line inside the tire becomes far away from the single R, causing a problem that the durability performance is lowered. From such a viewpoint, the lower limit value of the thickness Tc is preferably 0.375 times or more the thickness Ta, and the upper limit value is preferably 0.425 times or less. At this time, the inner surface in the tire axial direction of the bead apex rubber 8 is curved with a convex arc surface from the position Pa to the vicinity area Y of the position Pc, and is curved with a concave arc surface from the vicinity area Y to the tip 8e. . The “neighboring area Y” means a radial height area of 30% of the distance Kc with the position Pc as the center.

  In addition, even when the height H1 exceeds 0.95 times the height H0, no further reduction of the flexure region can be expected, and conversely, the weight increases, which is disadvantageous for rolling resistance, fuel efficiency, and durability. In addition, the ride comfort is reduced.

  The H2 is preferably 0.35 to 0.55 times, more preferably 0.40 to 0.50 times the height H1, from the viewpoint of rigidity balance.

  Next, in order to ensure the durability of the bead part 4, the loss tangent tan δ at 70 ° C. of the bead apex rubber 8 is 0.05 to 0.11 as in the case of a conventional heavy duty tire. It is preferable to stay within the range, and if it is less than 0.05, the durability tends to be lowered, such as cracks occurring in the bead portion 4. Moreover, when it exceeds 0.11, it will be disadvantageous for rolling resistance. This loss tangent tan δ is a value measured using a viscoelastic spectrometer under the conditions of a temperature of 70 ° C., a frequency of 10 Hz, and a dynamic strain rate of 2%.

  Further, in this example, the bead apex rubber 8 includes an inner apex portion 8A having a small cross-sectional shape having a slope X inclined inwardly from the outer side in the tire axial direction toward the outer side in the tire radial direction, as shown in FIG. The case where a two-layer structure is formed by the outer apex portion 8B extending outward in the tire radial direction from the slope X is illustrated. The outer apex portion 8B is made of rubber having a rubber hardness HsB (durometer A hardness) of 50 to 70 °, and is smaller than the rubber hardness HsA of the inner apex portion 8A, thereby ensuring the bead rigidity. Stress concentration at the tips 6e and 8e can be relaxed. The difference in rubber hardness (HsA-HsB) is preferably in the range of 20 to 40 °. Further, the height H3 of the inner apex portion 8A from the bead base line BL is preferably 55% or less, more preferably 50% or less of the height H1, and the lower limit thereof is preferably 35% or more, more preferably 40% or more. .

  Further, in this example, a case where a reinforcing cord layer 9 surrounding the bead core 5 in a U-shape is disposed on the bead portion 4 via the carcass 6 is illustrated. The reinforcing cord layer 9 is made of a cord ply in which steel reinforcing cords are arranged at an angle of 10 to 60 ° with respect to the tire circumferential direction, and an inner piece 9i extending along the inner surface of the ply main body portion 6a; It is formed in a U-shaped cross section having an outer piece 9o that continues to the inner piece 9i and passes radially inward of the bead core 5 and rises radially outward along the outer surface of the ply turn-up portion 6b.

  The height Di of the inner piece 9i in the radial direction from the bead base line BL is preferably in the range of 20 to 50% of the height H0, and is particularly used under a heavy load and frequently travels on a rough road. In the case of reinforced specifications such as for dump trucks, the range is preferably 30 to 50%, and in the case of general-purpose specifications, the range is preferably 20 to 30%. If the height Di is less than 20% of the height H0, the reinforcing effect by the inner piece 9i cannot be sufficiently expected. Conversely, if the height Di exceeds 50%, the maximum width position M of the tire is severely bent. Edge peeling tends to occur. Further, since the outer piece 9o is arranged close to the rim flange, the reinforcing effect is inferior to that of the inner piece 9i. Therefore, the radial height Do is limited to 30% or less of H0 and the height Di of the inner piece 9i, and the difference Di-Do from the height Di is set to 2 mm or more, further 10 mm or more. It is preferable to secure the cord end and suppress the cord end peeling.

  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 tire having the structure shown in FIG. 1 and having a tire size of 11R22.5 was made on the basis of the specifications shown in Table 1, and the rolling resistance and bead durability of each sample tire were tested and compared. Specifications other than those listed in Table 1 are substantially the same for each tire.

(1) Rolling resistance:
Using a rolling resistance tester, the rolling resistance was measured under the conditions of a rim (7.50 × 22.5), an internal pressure (700 kPa), and a load (24.52 kN). Indicated by an index. The smaller the value, the smaller the rolling resistance and the better.

(2) Bead durability:
Using a drum tester, the tire was run at a speed of 20 km / h under the conditions of a rim (7.50 × 22.5), internal pressure (1000 kPa), and load (76.53 kN). The running time until this is shown as an index with Comparative Example 1 taken as 100. The greater the value, the better the durability.

  As shown in the table, it can be confirmed that the tires of the examples can reduce rolling resistance while maintaining bead durability.

It is sectional drawing which shows one Example of the tire for heavy loads of this invention. It is sectional drawing which expands and shows a bead part. It is sectional drawing explaining the conventional bead structure.

Explanation of symbols

2 Tread portion 3 Side wall portion 4 Bead portion 5 Bead core 6A Carcass ply 6a Ply main body portion 6b Ply folded portion 6e Tip end of ply folded portion 8 Bead apex rubber 8e Tip of bead apex rubber Bead base line M Tire maximum width position S Bead Apex rubber outer surface

Claims (2)

A carcass ply having a ply folded portion that is folded from the inner side to the outer side in the tire axial direction around the bead core in the ply main body portion extending from the tread portion to the bead core through the sidewall portion, and the ply main body portion and the ply folding portion. A heavy-duty tire comprising a bead apex rubber extending radially outward from the bead core between the parts,
The ply turn-up portion is interrupted at the tire axial direction outer surface of the bead apex rubber,
And the radial height H1 from the bead base line at the tip of the bead apex rubber is 0.85 to 0.95 times the radial height H0 from the bead base line at the tire maximum width position, and
The bead apex rubber has a thickness Ta of the bead apex rubber at a position Pa where the outer surface is the height of the tip of the ply turn-up portion, and the outer surface is a radial direction from the bead base line of the tip of the ply turn-up portion. 0.85 to 1.10 times the thickness Tb of the bead apex rubber at a position Pb that is 2/5 of the height H2, and the outer side surface is the tip of the ply turn-up portion and the tip of the bead apex rubber A heavy load tire, wherein a thickness Tc of the bead apex rubber at a position Pc at an intermediate height is 0.35 to 0.45 times the thickness Ta.   The heavy load tire according to claim 1, wherein the bead apex rubber has a loss tangent tan δ at 70 ° C of 0.05 to 0.11.

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