JP2015209166A - Pneumatic tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire for heavy load which comprises a belt cushion rubber capable of improving low fuel consumption performance and durability.SOLUTION: A belt cushion rubber disposed between a tire axial outer end part of a belt layer and a carcass is composed of an outer layer, an intermediate layer, and an inner layer which are disposed in the order from the tire axial end of the belt layer to the inner side in a tire radial direction. In a tire meridian cross section, a cross-sectional maximum thickness of the outer layer and the inner layer is in a range of 0.3-1.5 mm, and a cross-sectional area Sm of the intermediate layer is 50% or more of a cross-sectional area S0 of the belt cushion rubber.

Description

  The present invention particularly relates to a heavy-duty pneumatic tire capable of reducing rolling resistance while maintaining durability.

  In recent years, global warming due to the emission of carbon dioxide has progressed, and there is a strong demand to reduce the amount of exhaust gas and carbon dioxide emitted from automobiles. For this reason, there is an increasing demand for lower fuel consumption for automobiles, and there is an urgent need to reduce the rolling resistance of tires as much as possible while reducing the weight.

  Such reduction in rolling resistance is strongly demanded not only for passenger car tires but also for heavy-duty tires such as trucks and buses, especially to reduce the rolling resistance of tires for large trucks traveling at high speed on good roads. Is important.

  On the other hand, in order to reduce the rolling resistance of the tire, a conventionally taken measure is improvement of the tread rubber. However, tread rubber is the member that has the greatest influence on wear resistance and grip performance, so it is no longer technically possible to reduce rolling resistance while maintaining wear resistance and grip performance. It's getting on.

  Thus, there has been a need to pay attention to tire members other than tread rubber that have not been considered as targets for reducing rolling resistance.

  In general, in heavy duty pneumatic tires, a belt cushion rubber having a triangular cross section having a relatively large rubber volume is disposed between the outer end of the belt layer in the tire axial direction and the carcass. Accordingly, the present inventor has proposed to use a rubber composition having a small loss tangent for the belt cushion rubber to reduce the rolling resistance of the tire.

  However, since the outer end portion in the tire axial direction of the belt layer is located at the tire shoulder where the tread portion and the sidewall portion intersect, a large strain is generated at the outer end portion of the belt layer during running. Therefore, when a rubber composition having a small loss tangent is used for the belt cushion rubber, adhesion between the belt layer and the carcass is insufficient, and due to the distortion, between the belt layer and the carcass. There arises a new problem that peeling occurs between the two and the durability of the tire is lowered.

  Patent Document 1 listed below proposes a rubber composition having both reinforcing properties and low fuel consumption by blending a rubber component, carbon black, sulfur, a vulcanization accelerator, and the like at a specific ratio. It is also described that this rubber composition can be used for belt cushion rubber. However, even in this case, there is a limit to further improving the fuel efficiency.

JP 2004-099804 A

  The present invention has been devised in view of the actual situation as described above, and is based on the belt cushion rubber having a multilayer structure of three or more layers, while suppressing the separation between the adjacent belt layer and the carcass. An object of the present invention is to provide a heavy duty pneumatic tire capable of further improving fuel efficiency.

Of the present invention, the invention according to claim 1 is a carcass extending between the bead portions via the tread portion and the sidewall portion,
A belt layer disposed on the outer side in the tire radial direction of the carcass and inside the tread portion,
And a belt cushion rubber disposed between the outer end of the belt layer in the tire axial direction and the carcass,
The belt cushion rubber has at least three layers consisting of an outer layer, an intermediate layer, and an inner layer arranged in order from the outer end in the tire axial direction of the belt layer inward in the tire radial direction,
Moreover, in the tire meridian section,
The maximum cross-sectional thickness of the outer layer and the inner layer is in the range of 0.3 to 1.5 mm,
The cross-sectional area Sm of the intermediate layer is 50% or more of the cross-sectional area S0 of the belt cushion rubber.

  According to a second aspect of the present invention, the maximum cross-sectional thickness of the outer layer is 1.0 mm or less.

  According to a third aspect of the present invention, the cross-sectional area Sm of the intermediate layer is 80% or more of the cross-sectional area S0 of the belt cushion rubber.

  According to a fourth aspect of the present invention, the belt cushion rubber is formed by winding a rubber strip having a width of 20 to 25 mm and a thickness of 1.0 to 1.5 mm in the tire circumferential direction.

Further, in claim 5, the outer layer and the inner layer are made of a rubber composition B having a complex elastic modulus E ^* b and a loss tangent tan δb, and the intermediate layer has a complex complex substantially the same as the complex elastic modulus E ^* b. It is characterized by comprising a rubber composition C having an elastic modulus E ^* c and a loss tangent tan δc smaller than the loss tangent tan δb.

In the present specification and claims, unless otherwise specified, the loss tangent tan δ and complex elastic modulus E ^* of the rubber member are measured using a viscoelastic spectrometer at a temperature of 70 ° C., a frequency of 10 Hz, and an initial tensile strain of 10 %, Dynamic strain amplitude ± 2%.

  Further, in this specification, unless otherwise specified, the dimensions of each part of the tire are values specified in a no-load normal internal pressure state in which the tire is assembled on a normal rim and filled with a normal internal pressure. 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 it is ETRTO, it will be "INFLATION PRESSURE".

  In the present invention, as described above, the belt cushion rubber is formed of a plurality of layers having an outer layer, an intermediate layer, and an inner layer that are sequentially arranged from the outer end in the tire axial direction of the belt layer toward the inner side in the tire radial direction. Therefore, even when a rubber composition having a small loss tangent is used for the intermediate layer and the rolling resistance of the tire is reduced, sufficient adhesion between the belt layer and the carcass can be ensured by the outer layer and the inner layer. Thus, the durability of the tire can be maintained.

  It is difficult to extrude the belt cushion rubber having the multilayer structure with an extruder. However, the belt cushion rubber having the multilayer structure can be easily formed by using a so-called strip wind method in which a tape-shaped rubber strip is wound in the tire circumferential direction.

It is sectional drawing which shows one Embodiment of the pneumatic tire for heavy loads of this invention. It is sectional drawing which expands and shows the tire shoulder. It is a conceptual diagram which shows the arrangement | sequence state of a belt cord. It is sectional drawing which shows the other example of belt cushion rubber. (A) is sectional drawing which shows the formation method of belt cushion rubber, (B) is sectional drawing of the rubber strip used for it.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the heavy-duty pneumatic tire 1 of the present embodiment includes a carcass 6 extending between the bead portions 4 and 4 on both sides via the tread portion 2 and the sidewall portion 3, and the tire of the carcass 6. A belt layer 7 disposed radially outside and inside the tread portion 2, and a belt cushion rubber 8 disposed between each outer end portion in the tire axial direction of the belt layer 7 and the carcass 6 are provided. In this example, the case where the heavy-duty pneumatic tire 1 is formed as a radial tire for a large truck / bus is shown.

  The carcass 6 includes a toroidal main body portion 6a extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4 and is connected to the main body portion 6a and around the bead core 5 from the inner side in the tire axial direction to the outer side. In this example, it is formed of one carcass ply 6A having one or more folded portions 6b that are folded back.

  As the turn-up portion 6b of the carcass ply 6A, a so-called winding type (shown in FIG. 1) extending outward in the tire radial direction along the outer surface in the tire axial direction of the bead apex rubber 9 and winding around the bead core 5 for approximately one turn. A type (not shown) or the like can be adopted as appropriate. The bead apex rubber 9 is disposed on the outer side in the tire radial direction of the bead core 5 and extends in a tapered shape from the bead portion 4 to the lower portion of the sidewall portion 3 to reinforce this region and increase its bending rigidity.

  The carcass ply 6A is made of a carcass cord rubberized with a topping rubber, and the carcass cord is arranged at an angle of 75 to 90 degrees with respect to the tire equator C, for example. As the carcass cord, a steel cord, or an organic fiber cord such as aromatic polyamide, nylon, rayon, or polyester can be used. When an organic fiber cord is used as the carcass cord, the carcass 6 is constituted by a plurality of carcass plies 6A. However, when a steel cord is used as in this example, the carcass 6 can be formed by one carcass ply 6A. it can.

  Next, the belt layer 7 is formed of at least two belt plies. In this example, as shown in FIGS. 1 to 3, the belt layer 7 is formed of first, second, and third belt plies 7 </ b> A, 7 </ b> B, and 7 </ b> C that overlap sequentially from the carcass side toward the radially outer side. Is shown. As shown in FIG. 3, the first, second, and third belt plies 7A, 7B, and 7C of this example are rubbers that are inclinedly arranged at angles θ1, θ2, and θ3 of 15 to 23 ° with respect to the tire equator C, respectively. It consists of a drawn belt cord, and a steel cord is adopted as the belt cord.

  The belt cord 11A of the first belt ply 7A is inclined upward at an angle θ1 with respect to the tire equator C, for example, and the belt cords 11B and 11C of the second and third belt plies 7B and 7C are These are both leftward and inclined at angles θ2 and θ3, and are opposite to those of the first belt ply 7A.

  Thus, the belt layer 7 forms a strong truss structure in which the belt cords 11A and 11B intersect each other while the angles θ1, θ2, and θ3 of the cords of the belt plies 7A to 7C are set to low angles. The belt rigidity is increased, and the necessary tagging effect (restraint force on the tire) is secured. As a result, it is possible to maintain the steering stability while reducing the weight as a three-sheet structure. In the three-sheet structure, when the angles θ1, θ2, and θ3 are less than 15 °, the lateral stiffness of the ply is lowered, and conversely, when it exceeds 23 °, the stiffness in the tire circumferential direction is lowered. This reduces the steering stability.

  Further, as shown in FIG. 1, the ply widths W1 to W3 in the tire axial direction of the belt plies 7A to 7C of this example satisfy the relationship of W1> W2> W3. The ply width W1 of the first belt ply 7A which is the widest is preferably 0.7 times or more, more preferably 0.8 times or more of the tread grounding width TW. It has a strong reinforcement. When the ply width W1 is less than 0.7 times the tread contact width TW, the restraining force on the tire shoulder side is insufficient, and the steering stability and uneven wear resistance tend to be reduced. Conversely, if the ply width W1 is too large, it is difficult to regenerate the tread. From such a viewpoint, the upper limit of the ply width W1 is preferably 0.97 times or less, more preferably 0.95 times or less of the tread ground contact width TW.

  The tread ground contact width TW means the maximum width in the tire axial direction of the tread ground contact surface that is grounded when a normal load is applied to the tire in the normal internal pressure state. 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 load capacity is specified for JATMA, and the table “TIRE LOAD LIMITS” is set for TRA. The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES”. If ETRTO, it means “LOAD CAPACITY”.

  The ply width W2 of the second belt ply 7B is preferably 0.8 times or more, more preferably 0.9 times or more the ply width W1 of the first belt ply 7A. When the ply width W2 is less than 0.8 times the ply width W1, the restraining force on the tire shoulder side is similarly insufficient, and steering stability and uneven wear resistance are reduced. On the other hand, if the ply width W2 is too large, the end portion thereof approaches the end portion of the first belt ply 7A and stress concentrates, which tends to induce ply end peeling. From such a viewpoint, it is preferable to secure a tire axial distance K of 5 mm or more between the tire axial direction outer end e1 of the first belt ply 7A and the tire axial direction outer end e2 of the second belt ply 7B. The ply width W3 of the third belt ply 7C is preferably 0.4 times or more, more preferably 0.5 times or more of the ply width W2 of the second belt ply 7B from the viewpoint of tire strength.

  Further, as shown in FIG. 2, the outer ends of the first and second belt plies 7A and 7B in the tire axial direction are folded back in a U-shape so as to cover and protect the outer ends e1 and e2. Edge covers 12 and 13 are arranged. As a result, an inclined deformation portion that is inclined so as to be gradually separated from the first belt ply 7A is formed at the outer end in the tire axial direction of the second belt ply 7B. The edge covers 12 and 13 are made of a rubber composition A sheet.

  The rubber composition A contains a filler (carbon black) at a relatively high ratio, and in order to improve the adhesion with the end of the belt cord, which is a steel cord, the rubber component is mainly composed of natural rubber or isoprene rubber. Furthermore, it is preferable to contain cobalt. Thereby, the edge covers 12 and 13 can cover the steel cord end, relieve the stress generated between the adjacent rubber layers, and increase the adhesive force. Cobalt is preferably included in an amount of 0.5 to 5.0 parts by mass with respect to 100 parts by mass of the rubber component.

  Further, while the carcass 6 is curved and extends, the first belt ply 7A extends substantially parallel to the tread profile over the entire width thereof. Therefore, the outer end side of the first belt ply 7A is gradually separated from the carcass 6 as it goes outward in the tire axial direction, and the belt cushion rubber 8 is disposed in this space.

  The belt cushion rubber 8 has a maximum thickness at a position of an outer end of the belt layer 7 (corresponding to the outer end e1 in the present example), and from the maximum thickness position toward the inside and outside in the tire axial direction. The section has a triangular shape with a gradually reduced thickness. That is, the belt cushion rubber 8 is a cross section that surrounds the bottom side 20a along the radially outer surface of the carcass 6 and the oblique sides 20b and 20c in the tire axial direction extending from both ends of the bottom side 20a to the top at the position of the outer end e1. The inner hypotenuse 20b is adjacent to the inner surface of the belt layer 7 in the radial direction, and the outer hypotenuse 20c is adjacent to the tread rubber 2G.

  The belt cushion rubber 8 has a multilayer structure of three or more layers at the outer end of the belt layer 7 in the tire axial direction. Specifically, when viewed along the normal line N drawn from the outer end e1 of the belt layer 7 in the tire axial direction with respect to the carcass 6, the belt cushion rubber 8 includes at least the outer layer 8o, the intermediate layer 8m, and the inner layer 8i. Consists of three layers. In this example, the case of having a three-layer structure is shown.

  The outer layer 8o includes at least a main portion 8o1 extending along the inner hypotenuse 20b over the entire length of the inner hypotenuse 20b. In this example, the outer layer 8o is connected to the main portion 8o1 and near an intermediate position of the outer hypotenuse 20c. The case where the sub part 8o2 which interrupts by is further provided is shown. The outer layer 8o of this example has a substantially constant thickness at the main portion 8o1, and the thickness at the sub portion 8o2 gradually decreases toward the outer side in the tire axial direction. The sub-portion 8o2 can be formed with a substantially constant thickness over the entire length of the outer hypotenuse 20c, and the outer layer 8o is formed only by the main portion 8o1 without providing the sub-portion 8o2. You can also.

  The inner layer 8i extends over the entire length of the bottom 20a along the bottom 20a with a substantially constant thickness. The inner end of the inner layer 8i in the tire axial direction and the inner end of the outer layer 8o in the tire axial direction Connected to each other. The intermediate layer 8m is interposed in a wedge shape between the outer layer 8o and the inner layer 8i.

  Here, in the outer layer 8o and the inner layer 8i, the maximum cross-sectional thicknesses to and ti are in the range of 0.3 to 1.5 mm, and the cross-sectional area Sm of the intermediate layer 8m is the same as that of the belt cushion rubber 8. It is 50% or more of the cross-sectional area S0.

In this example, the outer layer 8o and the inner layer 8i are made of a rubber composition B having a complex elastic modulus E ^* b and a loss tangent tan δb, and the intermediate layer 8m has a complex elasticity substantially the same as the complex elastic modulus E ^* b. It is formed from a rubber composition C having a rate E ^* c and a loss tangent tan δc smaller than the loss tangent tan δb.

  Thus, in the belt cushion rubber 8, the outer layer 8o, the intermediate layer 8m, and the inner layer 8i have substantially the same complex elastic modulus. Therefore, the belt cushion rubber 8 can be elastically deformed as a single rubber elastic body in spite of having a multilayer structure, reinforces a space sandwiched between the belt layer 7 and the carcass 6 and generates the belt layer 7 generated during traveling. Large distortion at the outer end can be alleviated.

  Further, in the belt cushion rubber 8, since the intermediate layer 8m has a relatively low loss tangent, the rolling resistance of the tire can be reduced. Moreover, since the outer layer 8o and the inner layer 8i have a relatively high loss tangent, it is possible to ensure adhesion between the belt layer 7 and the carcass 6, and between the belt layer 7 and The peeling damage between the carcass 6 can be suppressed, and the durability can be maintained at the same level as before.

  In particular, when the belt layer 7 has a three-layer structure as described above, the amount of strain at the outer end of the belt layer tends to be larger and more easily peeled than the conventional four-layer belt layer. The belt cushion rubber 8 of this embodiment can be more preferably employed.

The complex elastic modulus E ^* b and the complex elastic modulus E ^* c are “substantially the same” as the ratio between the complex elastic modulus E ^* b and the complex elastic modulus E ^* c (E ^* b / E ^* c). Means a range of 0.8 to 1.2, and in this range, it is preferably closer to 1.0.

  Further, the loss tangent tan δb between the outer layer 8o and the inner layer 8i is preferably 0.035 or more, which is the same as the conventional one, from the viewpoint of securing the adhesion between the belt layer 7 and the carcass 6. However, if the loss tangent tan δb is too large, it is disadvantageous for the rolling resistance performance. Therefore, the upper limit is preferably 0.045 or less, more preferably 0.042 or less.

  Further, the loss tangent tan δc of the intermediate layer 82 is preferably smaller than 0.035, more preferably 0.030 or less, from the viewpoint of reducing rolling resistance. However, if the loss tangent tan δc is too small, the rubber strength is insufficient and conversely the durability is lowered. Therefore, the lower limit of the loss tangent tan δc is preferably 0.020 or more, and more preferably 0.025 or more.

  In order to set the loss tangent to a different value as described above while making the complex elastic modulus substantially the same, the rubber composition C has a rubber reinforcing filler (carbon black) compared to the rubber composition B. This can be achieved by reducing the blending amount of silica and silica) and increasing the blending amount of sulfur.

  In order to exert the effect, as described above, the maximum cross-sectional thickness to of the outer layer 8o and the maximum cross-sectional thickness ti of the inner layer 8i are each in the range of 0.3 to 1.5 mm, and the intermediate layer. It is important that the cross-sectional area Sm of 8 m is 50% or more of the cross-sectional area S0 of the belt cushion rubber 8. When the cross-sectional maximum thickness to, ti exceeds 1.5 mm, and the cross-sectional area Sm of the intermediate layer 8m is less than 50% of the cross-sectional area S0 of the belt cushion rubber 8, the rolling resistance is reduced by the intermediate layer 8m. The effect is not fully exhibited. From such a viewpoint, the upper limit of the cross-sectional maximum thickness to, ti is preferably 1.0 mm or less, and the lower limit of the cross-sectional area Sm of the intermediate layer 8m is preferably 80% or more of the cross-sectional area S0 of the belt cushion rubber 8. . On the other hand, if the maximum cross-sectional thicknesses to and ti are less than 0.3 mm, the outer layer 8o and the inner layer 8i do not function sufficiently, and it becomes difficult to ensure the adhesion between the belt layer 7 and the carcass 6.

 Further, as shown in FIG. 4, an adhesive layer 15 can be added between the belt cushion rubber 8 and the carcass 6 to enhance the adhesiveness between the inner layer 8 i and the carcass 6. The adhesive layer 15 is a layer that is thinner than the inner and outer layers 8i, 8o and has a substantially constant thickness, and is made of a sheet of the rubber composition D. The rubber composition D has a rubber component mainly composed of natural rubber or isoprene rubber excellent in adhesiveness, similar to the edge covers 12 and 13, and further for adhesiveness to a carcass cord (steel cord). Cobalt is preferably contained. Cobalt is preferably included in an amount of 0.5 to 5.0 parts by mass with respect to 100 parts by mass of the rubber component.

  Further, as shown in FIG. 2, the tread rubber 2G of this example is formed in a two-layer structure of a cap rubber 2GC forming the tread surface 2S and a base rubber 2GB inside in the radial direction. In order to reduce rolling resistance, the loss tangent of the base rubber 2GB is set to be smaller than the loss tangent of the cap rubber 2GC (for example, 0.030 to 0.050), and in terms of wear resistance and cut resistance. Therefore, the complex elastic modulus of the cap rubber 2GC is set to be larger (for example, 4.5 to 5.5 MPa) than the complex elastic modulus of the base rubber 2GB. From the viewpoint of adhesiveness, the base rubber 2GB is terminated in contact with the outer layer 8o of the belt cushion rubber 8, and the cap rubber 2GC is terminated in contact with the intermediate layer 8m.

  Next, the multilayered belt cushion rubber 8 has a complicated cross-sectional shape, and the outer layer 8o and the inner layer 8i are very thin with a thickness of 1.5 mm or less. There is difficulty. Therefore, in the tire 1 of the present embodiment, as shown in FIGS. 5A and 5B, the tire 1 is composed of unvulcanized rubber compositions B and C, the width W is 20 to 25 mm, and the thickness T is 1. Using a so-called strip wind method in which two types of rubber strips Pb and Pc in the form of a long tape of 0 to 1.5 mm are used and the rubber strips Pb and Pc are wound on the carcass 6 in the tire circumferential direction, A belt cushion rubber 8 is formed.

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

A heavy-duty pneumatic tie (11R22.514PR) having the basic structure shown in FIG. 1 and the belt cushion rubber shown in Table 1 was prototyped, and the rolling resistance and durability of each sample tire were tested. For comparison, a tire in which a belt cushion rubber has a one-layer structure was manufactured as Comparative Example 1. The specifications other than those listed in Table 1 are substantially the same, and the common specifications are as follows.
<Carcass>
Number of plies: 1 carcass cord: Steel cord (cord diameter 0.85mm)
<Belt layer>
Belt cord: Steel cord (cord diameter 1.15mm)
First belt ply:
Cord angle θ1: 19 ° (upward)
Second belt ply:
Cord angle θ2: 19 ° (upward to the left)
Third belt ply:
Cord angle θ3: 19 ° (upward to the left)

The outer and inner layers are based on Formulation 1 shown in Table 2, and the intermediate layer is based on Formulation 2, and the amount of carbon, sulfur, and vulcanization accelerator is adjusted to adjust the complex elastic modulus E ^* b. , E ^* c, tan δb, and tan δc are adjusted. Further, the composition of the edge cover is the composition 3. Details are as follows.
Natural rubber (NR): RSS # 3
Butadiene rubber (BR): BR150B manufactured by Ube Industries, Ltd.
Carbon: Show Black N220 manufactured by Cabot Japan
Process oil: Mineral oil PW-380 manufactured by Idemitsu Kosan Co., Ltd.
Anti-aging agent 6C: Antigen 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Paraffin wax: Sannox wax from Ouchi Shinsei Chemical Co., Ltd. Stearic acid: Agate made by Nippon Oil & Fats Co., Ltd. Zinc flower: Zinc flower No. 1 made by Mitsui Mining & Smelting Co., Ltd. Sulfur: Made by Karuizawa Sulfur Co., Ltd. Powdered sulfur Vulcanization accelerator: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
The test method is as follows.

<Rolling resistance>
Using a drum type tire rolling resistance tester, each tire was tested at the speed (50 km / h) under the conditions of the rim (7.50X22.5), internal pressure (750 kPa), and longitudinal load (24.51 kN). The rolling resistance at that time was displayed as an index with Comparative Example 1 as 100. A smaller value means less rolling resistance and less fuel consumption.

<Durability (adhesiveness)>
Each test tire is mounted on a 2D4 type track with the rim (7.50X22.5) and internal pressure (750 kPa), and the actual driving conditions are the same for 6 months. did. Thereafter, the tire was disassembled, and the adhesive force between the belt cushion rubber and the carcass ply and the adhesive force between the belt layer and the belt cushion rubber were measured. The larger the value, the greater the adhesive strength and the higher the durability. In addition, the measuring method of the adhesive force measured the drag when it peeled on the conditions of 20 degreeC of room temperature, 65% of humidity, and the tension | pulling speed of 50 mm / min using the tensile tester (INTESCO2005 type).
The test results are shown in Table 1.

  As a result of the test, it was confirmed that the tire of the example could reduce rolling resistance while maintaining durability. As shown in Comparative Example 2, when the thickness to and ti are less than 0.3 mm, it can be confirmed that the durability (adhesiveness) sharply decreases.

DESCRIPTION OF SYMBOLS 1 Heavy load pneumatic tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A Carcass ply 7 Belt layer 7A, 7B, 7C, 7D Belt ply 8 Belt cushion rubber 81 Outer layer 82 Middle layer 83 Inner layer

Claims (5)

A carcass extending between the bead portions via the tread portion and the sidewall portion,
A belt layer disposed on the outer side in the tire radial direction of the carcass and inside the tread portion,
And a belt cushion rubber disposed between the outer end of the belt layer in the tire axial direction and the carcass,
The belt cushion rubber has at least three layers consisting of an outer layer, an intermediate layer, and an inner layer arranged in order from the outer end in the tire axial direction of the belt layer inward in the tire radial direction,
Moreover, in the tire meridian section,
The maximum cross-sectional thickness of the outer layer and the inner layer is in the range of 0.3 to 1.5 mm,
And the cross-sectional area Sm of the said intermediate | middle layer is 50% or more of the cross-sectional area S0 of the said belt cushion rubber, The heavy duty pneumatic tire characterized by the above-mentioned.   The heavy duty pneumatic tire according to claim 1, wherein the outer layer has a maximum cross-sectional thickness of 1.0 mm or less.   The heavy duty pneumatic tire according to claim 1 or 2, wherein a cross-sectional area Sm of the intermediate layer is 80% or more of a cross-sectional area S0 of the belt cushion rubber.   The belt cushion rubber is formed by winding a rubber strip having a width of 20 to 25 mm and a thickness of 1.0 to 1.5 mm in the tire circumferential direction. The heavy-duty pneumatic tire described. The outer layer and the inner layer are composed of a rubber composition B having a complex elastic modulus E ^* b and a loss tangent tan δb,
The intermediate layer, according to claim 1, characterized in that comprising the rubber composition has a complex elastic modulus E ^{* b} substantially the same complex elastic modulus E ^{* c} and the loss tangent tanδb consisting small loss tangent Tanderutashi C The heavy duty pneumatic tire according to any one of 4.

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