JP4950616B2 - Heavy duty tire - Google Patents

Description

  The present invention provides a tire having a tread rubber having a two-layer structure of a cap rubber layer and a base rubber layer, and improves the distribution of the thickness of the base rubber layer, thereby reducing the rolling resistance while maintaining the wear resistance. The present invention relates to a heavy duty tire that can be improved.

  Conventionally, in heavy duty tires used for trucks, buses, etc., in order to achieve both wear resistance and low rolling resistance, the tread rubber is disposed on the inner side in the radial direction of the cap rubber layer that forms the outer surface of the tread. The cap rubber layer is made of rubber having excellent wear resistance, and the base rubber layer is made of low heat-generating rubber with low tangential loss.

  Further, from the viewpoint of reducing fuel consumption in recent years, further improvement in low rolling resistance is strongly desired. However, if the thickness of the cap rubber layer is inadvertently reduced and the proportion of the base rubber layer in the tread rubber is increased, wear resistance and low rolling resistance are reduced. There is a problem that it is difficult to achieve both at a high level.

  Therefore, the present invention has an object to provide a heavy-duty tire capable of achieving both high wear resistance and low rolling resistance on the basis of regulating the thickness distribution of the base rubber layer.

JP-A-2005-35404

In order to achieve the above object, the invention of claim 1 of the present application comprises a carcass extending from a tread portion to a bead core of a bead portion through a sidewall portion, and a plurality of belt plies including a belt ply having a maximum width. A heavy-duty tire comprising a belt layer disposed radially outside and in a tread portion,
The tread rubber disposed in the tread portion is composed of a cap rubber layer forming the outer surface of the tread and a base rubber layer disposed on the inner side in the radial direction, and the outer end portion in the tire axial direction of the tread rubber is Terminate the lateral reference line extending in the tire axial direction from the outer end of the maximum width belt ply in the tire axial direction, inwardly in the radial direction,
The sidewall rubber disposed in the sidewall portion has an outer end in the radial direction that covers the outer end in the tire axial direction of the tread rubber and terminates beyond the lateral reference line radially outward.
On the horizontal reference line, the ratio La / Lt between the thickness La of the base rubber layer and the distance Lt from the tire axially outer end of the maximum width belt ply to the tire outer surface is 0.6 to 0.8, The ratio Lb / Lt between the thickness Lb of the cap rubber layer and the distance Lt is 0.1 to 0.3, and the ratio Ls / Lt between the thickness Ls of the sidewall rubber and the distance Lt is 0.1. -0.2, and on the normal line extending from the outer end in the tire axial direction of the belt ply of the maximum width to the outer surface of the tread, the thickness Ta of the base rubber layer and the outer side of the belt ply of the maximum width in the tire axial direction. The ratio Ta / Tt to the distance Tt from the end to the outer surface of the tread is 0.35 to 0.45,
The ratio Cb / Tb between the thickness Cb of the cap rubber layer in the center region of the tread having a width of 50% of the tread width around the tire equator and the thickness Tb of the cap rubber layer on the normal line is 1. It is characterized by being larger than 0 and smaller than 1.6.

In the invention of claim 2, the tangent loss (tan δa) of the base rubber layer is 0.035 to 0.055, the tangent loss (tan δb) of the cap rubber layer is 0.070 to 0.090, and the The tangent loss (tan δs) of the sidewall rubber is 0.045 to 0.090.
In the invention of claim 3, the rubber hardness (Hsa) of the base rubber layer is 62 to 66 °, the rubber hardness (Hsb) of the cap rubber layer is 64 to 68 °, and the rubber hardness (Hss) of the sidewalls. Is 52 to 56 °, and the rubber hardness (Hsa) is larger than the rubber hardness (Hss) and smaller than the rubber hardness (Hsb).

  In this specification, unless otherwise specified, the dimensions and the like of each part of the tire are values specified in a reference 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 by the standard for each tire in the standard system including the standard on which the tire is based. For example, JAMMA is a standard rim, TRA is “Design Rim”, or ETRTO. Then means "Measuring Rim".

  The tangent loss of the rubber is a value measured by using a viscoelastic spectrometer at a temperature of 70 ° C., a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain of ± 1%. The rubber hardness is a hardness by durometer type A measured in an atmosphere at a temperature of 23 ° C.

  As described above, according to the present invention, the ratio La of the thickness La of the base rubber layer to the distance Lt from the outer end to the tire outer surface on the horizontal reference line extending from the outer end of the belt ply of the maximum width in the tire axial direction. / Lt is 0.6 to 0.8, the ratio Lb / Lt of the cap rubber layer thickness Lb is 0.1 to 0.3, and the ratio Ls / Lt of the sidewall rubber thickness Ls is 0.1 The ratio Ta / Tt of the thickness Ta of the base rubber layer to the distance Tt from the outer end to the outer surface of the tread on the normal extending from the outer end to the outer surface of the tread is 0.35. 0.45.

  That is, the proportion of the low heat-generating base rubber layer is increased while optimizing the distribution of each rubber in the shoulder portion where the heat generation is largest and the energy loss is large in the tread portion. This can effectively improve the low rolling resistance performance.

  On the other hand, in the center region of the tread, the thickness Cb of the cap rubber layer is higher than the thickness Tb of the cap rubber layer on the normal line. That is, the ratio of the cap rubber layer in the center region of the tread having a high contact pressure and a large influence on the wear life is increased, and excellent wear resistance is ensured. In addition, in the tread central region, the increase in the cap rubber layer increases the rigidity and suppresses the movement thereof, so that the increase in energy loss due to the decrease in the base rubber layer in the tread central region can be suppressed to a low level. As a result, the rolling resistance can be lowered comprehensively, and it is possible to achieve both wear resistance and low rolling resistance at a high level.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a reference state in which an internal pressure of 50 kPa is filled in a heavy load tire of the present invention, and FIG. 2 is an enlarged cross-sectional view showing a tread portion thereof.
In FIG. 1, a heavy load tire 1 includes a carcass 6 that extends from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, and a belt disposed radially outside the carcass 6 and in the tread portion 2. And at least a layer 7.

  The carcass 6 is formed of at least one carcass ply 6A, in this example, one carcass ply 6A in which carcass cords are arranged at an angle of, for example, 80 to 90 ° with respect to the tire equator. As the carcass cord, a steel cord is preferably used, but an organic fiber cord such as nylon, rayon, polyester, aromatic polyamide or the like may be used as necessary. The carcass ply 6A has ply folding portions 6b that are folded and locked from the inner side to the outer side in the tire axial direction around the bead core 5 on both sides of the toroidal ply main body portion 6a straddling the bead cores 5 and 5. Have. In this example, a bead apex rubber 8 which is tapered from the bead core 5 toward the radially outer side is disposed between the ply main body portion 6a and the ply turn-up portion 6b. ing. It is also possible to adopt a wind bead structure in which the ply folded portion 6b is wound around the bead core 5 and the tip end portion is sandwiched between the bead core 5 and the bead apex rubber 8.

  The belt layer 7 is formed of a plurality of belt plies using steel cords as belt cords, usually 3 to 4 belt plies. In this example, the belt layer 7 includes a first belt ply 7A on the innermost side in the radial direction in which belt cords are arranged at an angle of, for example, 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.

  Among the belt plies 7A to 7D, the second belt ply 7B has the maximum width, and the width is, for example, 0.80 to 0.95 times the tread width TW, and the first and third belts The width of the plies 7A and 7C is set to, for example, 85 to 95% of the width of the second belt ply 7B. As a result, the substantially full width of the tread portion 2 is reinforced with a tagging effect, and the concentration of stress generated at the outer end in the tire axial direction of each belt ply is reduced. At least the outer end in the tire axial direction of the second belt ply 7A, in this example, the outer end in the tire axial direction of the first to third belt plies 7A to 7C is covered and protected in a U shape by a thin covering rubber 13, and the belt Prevents damage from the end of the cord. The rubber hardness of the covering rubber 13 is preferably in the range of 60 to 70 °, and the thickness thereof is in the range of 0.1 to 1.5 mm, preferably 0.3 to 0.6 mm.

  The belt layer 7 is gradually separated from the carcass 6 at both ends, and a belt cushion rubber 10 having a triangular cross section is disposed in the separated portion. The belt cushion rubber 10 has a maximum thickness at the position of the outer end 7Be of the second belt ply 7B. From the position of the outer end 7Be, the belt cushion rubber 10 extends along the outer surface of the carcass 6 while gradually decreasing the thickness. Extend. The radial distance h1 from the lower surface of the outer end 7Be to the radially inner end of the belt cushion rubber 10 is 1/3 of the radial distance H1 from the lower surface of the outer end 7Be to the tire maximum width position Pm. It is the range of ~ 3/4 times. As the belt cushion rubber 10, as in the case of the covering rubber 13, one having a rubber hardness of 60 to 70 ° is preferably employed. As a result, it is possible to maintain the tread effect of the belt layer 7 and maintain the tread shape while relaxing the shearing force between the belt cord and the carcass cord. Further, by extending from the outer end 7Be of the second belt ply 7B having the maximum width, it is possible to protect the outer end of the inner belt ply 7A that is likely to be a starting point of structural damage.

  Next, tread rubber 2G is disposed on the outer side of the belt layer 7 in the tire radial direction. As shown in FIG. 2, the tread rubber 2G has a two-layer structure including a cap rubber layer 2Gb that forms a tread outer surface 2S that comes in contact with the road surface, and a base rubber layer 2Ga that is arranged on the inner side in the radial direction. The outer end 2Ge in the tire axial direction of the tread rubber 2G extends radially inward from the lateral reference line X extending in the tire axial direction from the outer end 7Be in the tire axial direction of the belt ply 7B having the maximum width. It terminates in contact with the cushion rubber 10. The sidewall rubber 3G disposed outside the carcass 6 and on the sidewall portion 3 has a radially outer end portion 3Ge covering a tire axial direction outer end portion 2Ge of the tread rubber 2G, and the horizontal reference line. Terminate beyond X outward in the radial direction.

  Here, from the viewpoint of wear resistance, the cap rubber layer 2Gb is highly elastic with excellent wear resistance in which the network bond between rubber molecules is reinforced and the rubber hardness (Hsb) is increased to a range of 64 to 68 °. Rubber is used. In the cap rubber layer 2Gb, the wet grip performance is also important. For this reason, the cap rubber layer 2Gb having a large hysteresis friction with a tangent loss (tan δb) increased to a range of 0.070 to 0.090 is used. On the other hand, in the base rubber layer 2Ga, from the viewpoint of reducing the rolling resistance, a low heat-generating rubber with a small energy loss obtained by reducing the tangent loss (tan δa) to a range of 0.035 to 0.055 is used. Is done. The rubber hardness (Hsa) of the base rubber layer 2Ga is smaller than the rubber hardness (Hsb) of the cap rubber layer 2Gb. In this example, the rubber hardness (Hsb) is 62 to 66 ° in order to obtain necessary steering stability. The range is set.

  When the rubber hardness (Hsb) of the cap rubber layer 2Gb is less than the above range, the wear resistance is lowered. Further, when the tangent loss (tan δb) of the cap rubber layer 2Gb is less than the above range, the wet grip performance is insufficient, and conversely when it exceeds, the rolling resistance is disadvantageous. In the base rubber layer 2Ga, if the tangent loss (tan δa) is less than the above range, it is difficult to ensure sufficient rubber strength, and if it exceeds the tangent loss (tan δa), the effect of improving the rolling resistance becomes insufficient. On the other hand, if the rubber hardness (Hsa) of the base rubber layer 2Ga is less than the above range, the steering stability is disadvantageous, and if it exceeds, the tangent loss (tan δa) is difficult to reduce to the above range.

  Further, the side wall rubber 3G can be flexibly bent following the deformation of the tire, and in order to suppress the occurrence of cracks on the outer surface of the tire, the rubber hardness (Hss) is in the range of 52 to 56 °, and the base rubber layer A rubber having a low elasticity, which is further reduced from the rubber hardness (Hsa), is used. If it is below the range, the cut resistance is insufficient, and if it exceeds the range, the crack resistance is not sufficiently exhibited. The tangent loss (tan δs) of the sidewall rubber 3G is not particularly limited, but is preferably set in the range of 0.045 to 0.090 in order to obtain the cut resistance and crack resistance.

  In the present invention, in order to make the wear resistance and the low rolling resistance compatible at a higher level, first, in the shoulder portion Ye where the heat generation is largest and the energy loss is large in the tread portion 2, each rubber 2Ga, 2Gb While optimizing the distribution of 3G, the proportion of the base rubber layer 2Ga made of low heat-generating rubber is increased. On the other hand, in the tread central region Yc having a high contact pressure and a large influence on the wear life, the ratio of the cap rubber layer 2Gb is increased to ensure excellent wear resistance. In addition, in the tread central region Yc, the increase in the cap rubber layer 2Gb increases the rigidity and suppresses the movement thereof, so that an increase in energy loss due to the decrease in the base rubber layer 2Ga in the tread central region Yc can be suppressed to a low level. . As a result, the rolling resistance can be lowered comprehensively, and it is possible to achieve both wear resistance and low rolling resistance at a high level.

In particular,
(1) On the horizontal reference line X,
(1-1) The ratio La / Lt between the thickness La of the base rubber layer 2Ga and the distance Lt from the outer end 7Be of the belt ply 7B having the maximum width to the tire outer surface 1S (so-called buttress surface 1S), 0.6 to 0.8,
(1-2) The ratio Lb / Lt between the thickness Lb of the cap rubber layer 2Gb and the distance Lt is 0.1 to 0.3, and (1-3) the thickness Ls of the sidewall rubber 3G. And the ratio Ls / Lt to the distance Lt is 0.1 to 0.2; and
(2) On the normal line N extending from the outer end 7Be of the maximum width belt ply 7B to the outer surface 2S of the tread,
(2-1) The ratio Ta / Tt between the thickness Ta of the base rubber layer 2Ga and the distance Tt from the outer end 7Be of the belt ply 7B having the maximum width to the outer surface 2S of the tread is 0.35 to .0. 45; and (3) the ratio Cb / Tb between the thickness Cb of the cap rubber layer 2Gb in the tread central region Yc and the thickness Tb of the cap rubber layer 2Gb on the normal line N from 1.0 Large and smaller than 1.6.

  The “tread central region Yc” means a region having a width of 50% of the tread width TW with the tire equator C as the center. The tread portion 2 is formed with tread grooves g in various patterns in order to ensure wet grip performance. Under the grooves, the thickness of the cap rubber layer 2Gb is affected by the influence when the tread grooves g are formed. Will vary partially. Therefore, the “thickness Cb” is the thickness of the cap rubber layer 2Gb at a position not affected by the tread groove g in the tread central region Yc, and even at a position not particularly affected by the tread groove g. When the thickness of the cap rubber layer 2Gb changes, the average value of the maximum thickness and the minimum thickness is set. The shoulder portion Ye means a land portion (shoulder land portion) on the outer side in the tire axial direction than the longitudinal main groove ge in the tire circumferential direction arranged on the outermost side in the tire axial direction. The “lateral reference line X” means a straight line extending in the tire axial direction from the thickness center of the outer end 7Be.

  Here, by satisfying the conditions (1-1) to (1-3), the thickness of each rubber 2Ga, 2Gb, 3G in the shoulder portion Ye, particularly in the portion outside the belt end in the tire axial direction. While optimizing the thickness, the proportion of the base rubber layer 2Ga is greatly increased. When the ratio La / Lt is less than 0.6, the proportion of the base rubber layer 2Ga is small, and the rolling resistance cannot be sufficiently reduced. The cap rubber layer 2Gb has a high hardness and has a reinforcing effect at the shoulder portion Ye. Therefore, if the ratio Lb / Lt is less than 0.1, this reinforcing effect cannot be exhibited, resulting in a decrease in durability. Further, the sidewall rubber 3G functions as a protective layer. Therefore, if the ratio Ls / Lt is less than 0.1, crack damage such as cracks is likely to occur on the buttress surface 1S (tire outer surface 1S). When Lb / Lt is greater than 0.3 and Ls / Lt is greater than 0.2, the low rolling resistance is insufficient, and the balance between durability and crack resistance is reduced.

  Further, by satisfying the condition (2-1), the effect of improving the low rolling resistance can be ensured while ensuring the balance between the durability and the cracking damage. If the ratio Ta / Tt is less than 0.35, the low rolling resistance cannot be exhibited sufficiently. Conversely, if it exceeds 0.45, the wear resistance is lowered.

  Moreover, by satisfying the condition (3), the rigidity of the tread central region Yc, which has a great influence on the wear life, can be appropriately increased, and the wear resistance can be improved while ensuring the above-described excellent low rolling resistance. . When the ratio Cb / Tb is 1.0 or less, the wear resistance cannot be improved. Conversely, when the ratio Cb / Tb is 1.6 or more, the low rolling resistance is inhibited. Accordingly, the lower limit value of the ratio Cb / Tb is preferably 1.1 or more, and the upper limit value is preferably 1.5 or less.

  From the viewpoint of low rolling resistance, when a point on the horizontal reference line X separating a distance 0.3 times the distance Lt from the outer end 7Be is Px, the point Px is applied to the tread outer surface 2S. The thickness Tbx of the cap rubber layer 2Gb on the extending normal line Nx is preferably 1.2 times or less, more preferably 1.1 times or less of the thickness Tb on the normal line N.

  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 of size 11R22.5R having the structure shown in FIG. 1 was prototyped based on the specifications in Table 1, and tested for its low rolling resistance, crack resistance, durability, and wear resistance. Each tire has the same specifications except for the ratio of the thicknesses of the cap rubber layer, the base rubber layer, and the sidewall rubber. The cap rubber layer has a tangent loss (tan δb) of 0.08 and a rubber hardness (Hsb) of 66. A rubber having a tangent loss (tan δa) of 0.04 and a rubber hardness (Hsa) of 64 ° is used for the base rubber layer, and a tangent loss (tan δs) of 0 is used for the side wall rubber. .05 and rubber having a rubber hardness (Hss) of 54 ° is used.

(1) Low rolling resistance:
Using a rolling resistance tester, measure rolling resistance under conditions of rim (7.50 × 22.5), internal pressure (700 kPa), longitudinal load (24.52 kN), and speed (80 km / h). Example 1 was evaluated with an index of 100. The smaller the value, the lower the rolling resistance and the better.

(2) Crack resistance:
Running on the drum under the conditions of rim (7.50 × 22.5), internal pressure (700 kPa), longitudinal load (36 kN), speed (40 km / h) while emitting ozone, cracks on the buttress surface The running time until it occurred was measured.

(3) Durability:
Running time from running on the drum under the conditions of rim (7.50 × 22.5), internal pressure (700 kPa), longitudinal load (36 kN), speed (20 km / h) until the tread is damaged Was evaluated by an index with Example 1 as 100. The larger the value, the better the durability.

(4) Abrasion resistance:
The rim (7.50 × 22.5) and internal pressure (700 kPa) were used, and the load per tire was set to 24.5 kPa so that the load was loaded on a truck loaded 200,000 km. . Then, the depth of wear was measured by measuring the groove depth in the outermost longitudinal main groove in the tire axial direction and the innermost longitudinal main groove in the tire axial direction, and the average value was evaluated by an index with Example 1 as 100. The smaller the value, the better the wear resistance.

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 the tread part.

Explanation of symbols

1S Tire outer surface 2 Tread portion 2S Tread outer surface 2G Tread rubber 2Ga Base rubber layer 2Gb Cap rubber layer 3 Side wall portion 3G Side wall rubber 4 Bead portion 5 Bead core 6 Carcass 7 Belt layer 7B Maximum width belt ply 7Be Outer end X Horizontal reference line Yc Tread center area

Claims (3)

A carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a belt layer comprising a plurality of belt plies including a belt ply having a maximum width and disposed on the outer side in the radial direction of the carcass and in the tread portion. A heavy duty tire,
The tread rubber disposed in the tread portion is composed of a cap rubber layer forming the outer surface of the tread and a base rubber layer disposed on the inner side in the radial direction, and the outer end portion in the tire axial direction of the tread rubber is Terminate the lateral reference line extending in the tire axial direction from the outer end of the maximum width belt ply in the tire axial direction, inwardly in the radial direction,
The sidewall rubber disposed in the sidewall portion has an outer end in the radial direction that covers the outer end in the tire axial direction of the tread rubber and terminates beyond the lateral reference line radially outward.
On the horizontal reference line, the ratio La / Lt between the thickness La of the base rubber layer and the distance Lt from the tire axially outer end of the maximum width belt ply to the tire outer surface is 0.6 to 0.8, The ratio Lb / Lt between the thickness Lb of the cap rubber layer and the distance Lt is 0.1 to 0.3, and the ratio Ls / Lt between the thickness Ls of the sidewall rubber and the distance Lt is 0.1. ~ 0.2,
Moreover, on the normal line extending from the outer end in the tire axial direction of the maximum width belt ply to the outer surface of the tread, the thickness Ta of the base rubber layer and the outer end in the tire axial direction of the maximum width belt ply The ratio Ta / Tt to the distance Tt to the surface is 0.35 to 0.45,
The ratio Cb / Tb between the thickness Cb of the cap rubber layer in the center region of the tread having a width of 50% of the tread width around the tire equator and the thickness Tb of the cap rubber layer on the normal line is 1. A heavy-duty tire characterized by being larger than 0 and smaller than 1.6.   The tangent loss (tan δa) of the base rubber layer is 0.035 to 0.055, the tangent loss (tan δb) of the cap rubber layer is 0.070 to 0.090, and the tangent loss (tan tan of the sidewall rubber) 2. The heavy duty tire according to claim 1, wherein [delta] s) is 0.045 to 0.090.   The rubber hardness (Hsa) of the base rubber layer is 62 to 66 °, the rubber hardness (Hsb) of the cap rubber layer is 64 to 68 °, and the rubber hardness (Hss) of the sidewall is 52 to 56 °, The heavy duty tire according to claim 1, wherein the rubber hardness (Hsa) is larger than the rubber hardness (Hss) and smaller than the rubber hardness (Hsb).

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