JP2019189038A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire for improving damage resistance by restraining the occurrence of uneven wear, by improving durability of a belt.SOLUTION: A pair of cross belt layers are arranged on the outside of a carcass layer, and an outer diameter side cross belt layer 72 is narrower than an inner diameter side cross belt layer 71, and an auxiliary belt layer 73 is arranged on the outside of the cross belt layer, and the cord inclination direction of the auxiliary belt layer is the same as the cord inclination direction of the outer diameter side cross belt layer, and the auxiliary belt layer is wider width than the outer diameter side cross belt layer, and the auxiliary belt layer contacts with the inner diameter side cross belt layer on the outside in the tire width direction more than the outer diameter side cross belt layer, and a cord angle θcrs-in of the inner diameter side cross belt layer, a cord angle θcrs-out of the outer diameter side cross belt layer and a cord angle θsub of the auxiliary belt layer 73 satisfy (|θcrs-in|+|θcrs-out|)/2>(|θcrs-in|+|θsub|)/2, and |θcrs-in|+|θcrs-out|+|θsub|≤70°.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a pneumatic tire including a plurality of belt layers on the outer peripheral side of a carcass layer. More specifically, the present invention improves the durability of the belt layer, suppresses the occurrence of uneven wear, and further provides damage resistance. The present invention relates to a pneumatic tire that can improve the tire.

  In heavy duty pneumatic tires used for trucks, buses, etc., the outer diameter side of the carcass layer in the tread portion includes a plurality of steel cords inclined with respect to the tire circumferential direction, and the steel cords are interposed between the layers. A plurality of belt layers intersecting each other (for example, a belt layer having a four-layer structure) are arranged. In such a heavy-duty pneumatic tire, outer diameter growth occurs as the vehicle travels, and in particular, the outer diameter growth tends to increase in the shoulder region of the tread portion. When the outer diameter growth occurs, the durability of the belt layer decreases, and when the outer diameter growth in the shoulder region increases, uneven shoulder wear tends to occur. Therefore, in pneumatic tires for low flat heavy loads, it is required to improve the durability of the belt layer by suppressing the outer diameter growth and to suppress the occurrence of uneven wear by making the outer diameter growth uniform. Has been.

  In order to cope with such a demand, it has been proposed to additionally arrange a so-called 0 degree belt layer including a plurality of steel cords oriented in the tire circumferential direction between the belt layers in the tread portion (for example, a patent). References 1 and 2). In this case, it is possible to suppress the outer diameter growth and make the outer diameter growth uniform. However, when a 0-degree belt layer is additionally disposed in the tread portion, the ground pressure increases due to the increase in the number of belt layers, and the envelope characteristics of the tread portion decrease, so the tread portion is cut or chipped. There is a problem that it is easy to be damaged and the damage resistance is deteriorated.

Japanese Patent No. 5186567 Japanese Patent No. 5527003

  An object of the present invention is to provide a pneumatic tire that improves the durability of the belt layer, suppresses the occurrence of uneven wear, and further improves the damage resistance.

In order to achieve the above object, a pneumatic tire according to the present invention includes a tread portion that extends in the tire circumferential direction and has an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and the sidewall portions. And a pair of bead portions arranged on the inner side in the tire outer diameter direction, a carcass layer is mounted between the pair of bead portions, and the carcass layer is wound up around the bead core of each bead portion from the tire inner side to the outer side. In the pneumatic tire having the structure as described above,
The outer diameter side of the carcass layer in the tread portion includes a plurality of steel cords that are inclined with respect to the tire circumferential direction, and a pair of cross belt layers in which the steel cords cross each other are disposed, The cross belt layer on the outer diameter side of the cross belt layer is narrower than the cross belt layer on the inner diameter side,
An auxiliary belt layer including a plurality of steel cords inclined with respect to the tire circumferential direction is disposed on the outer diameter side of the pair of cross belt layers, and the cross belt with the cord inclination direction of the auxiliary belt layer on the outer diameter side. The auxiliary belt layer is wider than the cross belt layer on the outer diameter side, and the auxiliary belt layer is on the outer side in the tire width direction than the cross belt layer on the outer diameter side. In contact with the inner side cross belt layer,
The cord angle θcrs-in with respect to the tire circumferential direction of the inner belt side cross belt layer, the cord angle θcrs-out with respect to the tire circumferential direction of the outer belt side cross belt layer, and the cord angle of the auxiliary belt layer with respect to the tire circumferential direction The average chord angle at the shoulder intersection ((| θcrs-in | + | θsub |) rather than the average chord angle at the center intersection ((| θcrs-in | + | θcrs-out |) / 2) calculated from θsub ) / 2) is smaller,
The cord angle θcrs-in of the inner belt side cross belt layer, the cord angle θcrs-out of the outer belt layer cross belt layer, and the cord angle θsub of the auxiliary belt layer are | θcrs-in | + | θcrs- It is characterized in that the relationship of out | + | θsub | ≦ 70 ° is satisfied.

  In the present invention, a pair of cross belt layers and an auxiliary belt layer are disposed on the outer diameter side of the carcass layer in the tread portion, the cord angle θcrs-in of the inner belt belt and the cord of the outer belt layer When the angle θcrs-out and the cord angle θsub of the auxiliary belt layer satisfy the relationship of | θcrs-in | + | θcrs-out | + | θsub | ≦ 70 °, the outer diameter growth is suppressed and the cross belt The durability of the layer and the auxiliary belt layer can be improved. Also, the average cord angle at the shoulder intersection ((| θcrs-in | + | θsub |) / 2) rather than the average cord angle at the center intersection ((| θcrs-in | + | θcrs-out |) / 2) By making the diameter smaller, the outer diameter growth can be made uniform and the occurrence of uneven wear can be suppressed. In addition, since the above effect is obtained by a laminated structure of a pair of cross belt layers and an auxiliary belt layer, an increase in the contact pressure due to an increase in the number of belt layers is avoided, and the envelope characteristics of the tread portion are improved. Can be maintained. Thereby, generation | occurrence | production of the cut and chipping in a tread part can be suppressed, and damage resistance can be improved.

  In the present invention, the width Wsh of the contact region between the auxiliary belt layer and the inner side crossing belt layer is 15 mm or more, and satisfies the relationship of Wsh ≧ 0.05 × Lc with respect to the maximum width Lc of the carcass layer, It is preferable that the width Lcrs-out of the cross belt layer on the outer diameter side satisfies the relationship of Lcrs-out ≧ 0.54 × Lc with respect to the maximum width Lc of the carcass layer. Thereby, the outer diameter growth in the center region and the shoulder region of the tread portion can be effectively suppressed, the durability of the cross belt layer and the auxiliary belt layer can be improved, and the occurrence of uneven wear can be effectively suppressed. .

  On the outer side in the tire width direction from the contact area between the auxiliary belt layer and the inner diameter side cross belt layer, the auxiliary belt layer and the inner diameter side cross belt layer are separated from each other, and from the edge of the auxiliary belt layer to the inner diameter side cross belt layer The distance te is 2.0 mm or more, and a buffer rubber layer is disposed in the separated portion, the 100% modulus of the buffer rubber layer is 5.5 MPa to 10.0 MPa, and the elongation at break of the buffer rubber layer is 200%. The above is preferable. In this way, by disposing the cushioning rubber layer having predetermined physical properties in the space between the auxiliary belt layer and the inner diameter side crossing belt layer, edge separation of the auxiliary belt layer can be suppressed. The buffer rubber layer also contributes to the suppression of outer diameter growth.

  The average cord angle ((| θcrs-in | + | θcrs-out |) / 2) at the center intersection is 30 ° or less, and the average cord angle at the shoulder intersection ((| θcrs-in | + | θsub |) / 2) is preferably 20 ° or less. By setting the average cord angle of the center intersecting portion and the average cord angle of the shoulder intersecting portion within the above range, the outer diameter growth in the center region and the shoulder region of the tread portion is effectively suppressed, and the intersecting belt layer and the auxiliary belt layer As well as improving the durability, it is possible to effectively suppress the occurrence of uneven wear.

  The 100% modulus of the coat rubber constituting the pair of cross belt layers and the auxiliary belt layer is 5.5 MPa to 10.0 MPa, and the elongation at break of the coat rubber is preferably 200% or more. By using a coat rubber having predetermined physical properties for the cross belt layer and the auxiliary belt layer, it is possible to suppress the outer diameter growth and to suppress the separation due to the interlaminar shear strain.

  The initial elongation of the steel cords constituting the pair of cross belt layers and the auxiliary belt layer is preferably less than 0.8%. Thereby, the circumferential rigidity of the cross belt layer and the auxiliary belt layer can be increased to suppress the outer diameter growth, and the durability of the cross belt layer and the auxiliary belt layer can be improved.

  The cord rubber gauge between the inner diameter side cross belt layer and the outer diameter side cross belt layer and the cord rubber gauge between the outer diameter side cross belt layer and the auxiliary belt layer are 0.3 mm to 1.2 mm, respectively. Preferably there is. Thereby, while suppressing an outer diameter growth, the separation by an interlayer shear strain can be suppressed.

It is preferred that each of the tensile stiffness Am of the pair of cross belt layers and the auxiliary belt layer is ^{1.5 × 10 6 N / 50mm~4.0 ×} 10 6 N / 50mm. Thereby, outer diameter growth can be suppressed and durability of a cross belt layer and an auxiliary belt layer can be improved effectively.

1 is a meridian cross-sectional view showing a heavy duty pneumatic tire according to an embodiment of the present invention. It is sectional drawing which shows the principal part of the pneumatic tire of FIG. FIG. 2 is a development view showing an extracted cross belt layer and an auxiliary belt layer of the pneumatic tire of FIG. 1. It is a graph which shows the relationship between the sum total of the cord angle of a cross belt layer and an auxiliary | assistant belt layer, and an outer diameter growth amount.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a heavy-duty pneumatic tire according to an embodiment of the present invention, and FIGS. 2 and 3 show an extracted main part thereof.

  As shown in FIG. 1, the pneumatic tire of the present embodiment includes a tread portion 1 that extends in the tire circumferential direction and has an annular shape, and a pair of sidewall portions 2, 2 disposed on both sides of the tread portion 1. And a pair of bead portions 3 and 3 disposed inside the sidewall portion 2 in the tire radial direction.

  A carcass layer 4 is mounted between the pair of bead portions 3 and 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and has a structure wound around the bead core 5 disposed in each bead portion 3 from the tire inner side to the outer side. A bead filler 6 made of a rubber composition having a triangular cross-section is disposed on the outer periphery of the bead core 5.

  In the pneumatic tire, as shown in FIGS. 1 to 3, three belt layers 7 are embedded on the outer diameter side of the carcass layer 4 in the tread portion 1. The belt layer 7 includes a pair of cross belt layers 71 and 72 and an auxiliary belt layer 73. The pair of intersecting belt layers 71 and 72 include a plurality of steel cords inclined with respect to the tire circumferential direction, and are disposed so that the steel cords intersect each other between the layers. The cross belt layer 71 on the inner diameter side is inclined to one side with respect to the tire equator CL, whereas the cross belt layer 72 on the outer diameter side is inclined to the other side with respect to the tire equator CL. Further, the cross belt layer 72 on the outer diameter side is narrower than the cross belt layer 71 on the inner diameter side. That is, the width Lcrs-out of the outer diameter side cross belt layer 72 is set smaller than the width Lcrs-in of the inner diameter side cross belt layer 71.

  The auxiliary belt layer 73 includes a plurality of steel cords that are inclined with respect to the tire circumferential direction, and is disposed on the outer diameter side of the pair of cross belt layers 71 and 72. The cord inclination direction of the auxiliary belt layer 73 is the same as the cord inclination direction of the cross belt layer 72 on the outer diameter side. The auxiliary belt layer 73 is wider than the cross belt layer 72 on the outer diameter side. That is, the width Lsub of the auxiliary belt layer 73 is set larger than the width Lcrs-out of the cross belt layer 72 on the outer diameter side. The auxiliary belt layer 73 is in contact with the inner belt side cross belt layer 71 on the outer side in the tire width direction than the outer belt side cross belt layer 72 (see FIG. 2). Here, the contact state is the distance between the steel cord of the auxiliary belt layer 73 and the steel cord of the outer diameter side cross belt layer 72, and the distance measured in the thickness direction of the cross belt layer 72 is 1 mm or less. Means the case.

  In the pneumatic tire, the cord angle θcrs-in with respect to the tire circumferential direction of the inner diameter side cross belt layer 71, the cord angle θcrs-out with respect to the tire circumferential direction of the outer diameter side cross belt layer 72, and the auxiliary belt layer 73 Average cord angle ((| θcrs-in | + | θcrs-out |) / 2) and average cord angle ((| θcrs-in) of the shoulder intersection calculated from the cord angle θsub with respect to the tire circumferential direction | + | Θsub |) / 2) satisfies the relationship of (| θcrs-in | + | θcrs-out |) / 2> (| θcrs-in | + | θsub |) / 2.

  The cord angle θcrs-in of the inner diameter side cross belt layer 71, the cord angle θcrs-out of the outer diameter side cross belt layer 72, and the cord angle θsub of the auxiliary belt layer 73 are | θcrs-in | + | Θcrs-out | + | θsub | ≦ 70 ° is satisfied. The cord angle | θcrs-in | of the cross belt layer 71 on the inner diameter side, the cord angle | θcrs-out | of the cross belt layer 72 on the outer diameter side, and the cord angle | θsub of the auxiliary belt layer 73 are all 10 ° to It is desirable to set in the range of 30 °.

  According to the pneumatic tire described above, the pair of cross belt layers 71 and 72 and the auxiliary belt layer 73 are arranged on the outer diameter side of the carcass layer 4 in the tread portion 1, and the cord angle θcrs− of the cross belt layer 71 on the inner diameter side is arranged. in, the cord angle θcrs-out of the cross belt layer 72 on the outer diameter side, and the cord angle θsub of the auxiliary belt layer 73 have a relationship of | θcrs-in | + | θcrs-out | + | θsub | ≦ 70 ° When satisfied, the outer diameter growth can be suppressed and the durability of the belt layer 7 including the cross belt layers 71 and 72 and the auxiliary belt layer 73 can be improved.

  FIG. 4 shows the relationship between the sum of the cord angles of the cross belt layer and the auxiliary belt layer and the outer diameter growth amount in the center region of the tread portion. According to the knowledge of the present inventor, as shown in FIG. 4, when the cord angles of the pair of cross belt layers 71 and 72 and the auxiliary belt layer 73 are changed, | θcrs-in | + | θcrs-out | + When the value of | θsub | is 70 ° or less, the outer diameter growth amount is small, but when the value exceeds 70 °, the outer diameter growth amount increases rapidly. Therefore, it is necessary to satisfy | θcrs-in | + | θcrs-out | + | θsub | ≦ 70 °.

  Further, according to the pneumatic tire described above, the average cord angle ((| θcrs-in) of the shoulder intersection is larger than the average cord angle ((| θcrs-in | + | θcrs-out |) / 2) of the center intersection. By reducing | + | θsub |) / 2), the outer diameter growth can be made uniform. That is, the average cord angle ((| θcrs-in | + | θsub |) / 2) of the shoulder crossing portion is relatively reduced to increase the circumferential rigidity in the shoulder region, thereby increasing the outer cord in the shoulder region. The diameter growth is suppressed, and the outer diameter growth in the tread portion 1 is made uniform. Thereby, generation | occurrence | production of uneven wear can be suppressed.

  In addition, since the above-described effect can be obtained by the laminated structure of the pair of cross belt layers 71 and 72 and the auxiliary belt layer 73, the number of layers of the belt layer 7 is different from the conventional structure in which, for example, a 0 degree belt layer is added. As a result, it is possible to avoid the increase in the contact pressure due to the increase in the pressure and maintain the envelope characteristics of the tread portion 1 well. Thereby, generation | occurrence | production of the cut and chipping in the tread part 1 can be suppressed, and damage resistance can be improved.

  In the auxiliary belt layer 73, a portion that contacts the inner belt side cross belt layer 71 functions as a cross belt layer, but a portion that overlaps the outer belt side cross belt layer 72 is a protective belt for the cross belt layers 71 and 72. Acts as a layer. The protective belt layer is usually provided to protect the cross belt layers 71 and 72 in preparation for a case where a nail is pierced into a center region where the surface pressure is high. Works well as a protective belt layer. Therefore, it is possible to eliminate the protective belt layer conventionally used. In this case, the envelope characteristics can be improved as compared with a pneumatic tire provided with a belt layer having a four-layer structure. However, in the pneumatic tire, it is possible to add a protective belt layer as necessary in addition to the pair of cross belt layers 71 and 72 and the auxiliary belt layer 73.

  In the pneumatic tire described above, the width Wsh of the contact region between the auxiliary belt layer 73 and the cross belt layer 71 on the inner diameter side is 15 mm or more and Wsh ≧ 0.05 × Lc with respect to the maximum width Lc of the carcass layer 4 And the width Lcrs-out of the cross belt layer 72 on the outer diameter side preferably satisfies the relationship Lcrs-out ≧ 0.54 × Lc with respect to the maximum width Lc of the carcass layer 1. Thereby, the outer diameter growth in the center region and the shoulder region of the tread portion 1 is effectively suppressed, the durability of the belt layer 7 including the cross belt layers 71 and 72 and the auxiliary belt layer 73 is improved, and uneven wear is reduced. Generation | occurrence | production can be suppressed effectively.

  Here, if the width Wsh of the contact region between the auxiliary belt layer 73 and the inner diameter side cross belt layer 71 is less than 15 mm or less than 0.05 × Lc, the outer diameter growth in the shoulder region becomes excessive, and therefore, Uniform outer diameter growth occurs, and the effect of improving the durability of the belt layer 7 also decreases. Further, if the width Lcrs-out of the cross belt layer 72 on the outer diameter side is less than 0.54 × Lc, the outer diameter growth in the center region becomes excessive, resulting in uneven outer diameter growth and the belt. The effect of improving the durability of the layer 7 is also reduced. The maximum width Lc of the carcass layer 4 is a distance between the cords in the tire width direction at the maximum width position of the carcass layer 4 when no tire is loaded with the tire mounted on the specified rim (see FIG. 1). . When there are a plurality of carcass layers 4, the maximum width Lc is specified based on the carcass layer 4 closest to the tire inner surface.

  In the pneumatic tire, as shown in FIG. 2, the auxiliary belt layer 73 and the inner belt side cross belt layer 71 are located outside the contact region between the auxiliary belt layer 73 and the inner belt side cross belt layer 71 in the tire width direction. They are separated from each other. A distance te from the edge of the auxiliary belt layer 73 to the cross belt layer 71 on the inner diameter side is set to 2.0 mm or more. The distance te is the shortest distance from the edge of the auxiliary belt layer 73 to the cross belt layer 71 on the inner diameter side, and is the mutual distance between both steel cords. A shock absorbing rubber layer 8 is disposed in a separation portion between the auxiliary belt layer 73 and the cross belt layer 71 on the inner diameter side. The 100% modulus of the buffer rubber layer 8 is 5.5 MPa to 10.0 MPa, and the breaking elongation of the buffer rubber layer 8 is preferably 200% or more. 100% modulus and elongation at break are measured according to JIS-K6251. In this way, by arranging the shock-absorbing rubber layer 8 having predetermined physical properties at the separation portion between the auxiliary belt layer 73 and the inner belt side crossing belt layer 71, edge separation of the auxiliary belt layer 73 can be suppressed. The buffer rubber layer 8 also contributes to the suppression of outer diameter growth.

  Here, if the distance te from the edge of the auxiliary belt layer 73 to the cross belt layer 71 on the inner diameter side is less than 2.0 mm, the effect of suppressing the edge separation of the auxiliary belt layer 73 cannot be obtained. If the 100% modulus of the buffer rubber layer 8 is less than 5.5 MPa, the rigidity in the circumferential direction is reduced, so the effect of suppressing the growth of the outer diameter is reduced. Conversely, if it exceeds 10.0 MPa, the elongation at break is 200% or more. It becomes difficult to secure. In particular, the 100% modulus of the buffer rubber layer 8 is preferably 6.5 MPa to 9.0 MPa. Further, if the breaking elongation of the buffer rubber layer 8 is less than 200%, the effect of suppressing separation due to interlayer shear strain cannot be obtained.

  In the pneumatic tire, the average cord angle Cc (Cc = (| θcrs-in | + | θcrs-out |) / 2) at the center intersection is 30 ° or less, and the average cord angle Cs (Cs at the shoulder intersection). = (| Θcrs-in | + | θsub |) / 2) is preferably 20 ° or less. By setting the average cord angle Cc of the center crossing portion and the average cord angle Cs of the shoulder crossing portion within the above ranges, the outer diameter growth in the center region and the shoulder region of the tread portion 1 is effectively suppressed, and the belt layer 7 While improving durability, generation | occurrence | production of uneven wear can be suppressed effectively.

  Here, when the average cord angle Cc at the center crossing portion is more than 30 °, the outer diameter growth in the center region becomes excessive, so that the deterioration rate of the coated rubber of the belt layer 7 is increased, and the durability of the belt layer 7 is increased. Tends to decrease. Further, if the average chord angle Cs at the shoulder intersection exceeds 20 °, the outer diameter growth in the shoulder region becomes excessive, and it is difficult to achieve uniform outer diameter growth.

  In the pneumatic tire, the 100% modulus of the coated rubber constituting the pair of cross belt layers 71 and 72 and the auxiliary belt layer 73 is 5.5 MPa to 10.0 MPa, and the elongation at break of the coated rubber is 200% or more. good. By using coated rubber having predetermined physical properties for the cross belt layers 71 and 72 and the auxiliary belt layer 73, it is possible to increase circumferential rigidity and suppress outer diameter growth, and to suppress separation due to interlayer shear strain.

  Here, when the 100% modulus of the coating rubber constituting the cross belt layers 71 and 72 and the auxiliary belt layer 73 is less than 5.5 MPa, the circumferential rigidity is reduced, so the effect of suppressing the outer diameter growth is reduced. If it exceeds 10.0 MPa, it will be difficult to ensure a break elongation of 200% or more. In particular, the 100% modulus of the coated rubber is preferably 6.5 MPa to 9.0 MPa. Further, if the breaking elongation of the coated rubber is less than 200%, the effect of suppressing separation due to interlayer shear strain cannot be obtained.

  In the pneumatic tire, the initial elongation of the steel cord constituting the belt layer 7 including the pair of cross belt layers 71 and 72 and the auxiliary belt layer 73 is preferably less than 0.8%. Thereby, the circumferential rigidity of the belt layer 7 can be increased to suppress the outer diameter growth, and the durability of the belt layer 7 can be improved. Here, when the initial elongation of the steel cord is 0.8% or more, the outer diameter growth increases and the durability of the belt layer 7 decreases. In particular, the initial elongation of the steel cord constituting the belt layer 7 is desirably less than 0.6%. The initial elongation of the steel cord is the initial elongation when the steel cord is covered with rubber. The initial elongation is an elongation rate (%) when a load corresponding to 10% of the breaking load is applied with reference to the length of the steel cord in an unloaded state.

  In the pneumatic tire, an intercord rubber gauge between the inner diameter side cross belt layer 71 and the outer diameter side cross belt layer 72 and an inter cord rubber gauge between the outer diameter side cross belt layer 72 and the auxiliary belt layer 73. Is preferably 0.3 mm to 1.2 mm. Thereby, the circumferential rigidity can be increased to suppress the outer diameter growth, and the separation due to the interlayer shear strain can be suppressed.

  Here, if the rubber gauge between the cords of the belt layer 7 is less than 0.3 mm, the interlaminar shear strain becomes excessive, so that separation is likely to occur. Conversely, if it exceeds 1.2 mm, the outer diameter growth increases, and the belt The effect of improving the durability of the layer 7 is reduced. In particular, the rubber gauge between cords of the belt layer 7 is desirably 0.5 mm to 1.0 mm.

In the pneumatic tire, each of the tensile stiffness Am of the pair of cross belt layers 71, 72 and the auxiliary belt layer 73 may is ^{1.5 × 10 6 N / 50mm~4.0 ×} 10 6 N / 50mm. Thereby, outer diameter growth can be suppressed and the durability of the belt layer 7 including the cross belt layers 71 and 72 and the auxiliary belt layer 73 can be effectively improved. The tensile stiffness Am is obtained by the following formula (1). In the following formula (1), A is the cross-sectional area [mm ² ] of each steel cord, E is the elastic modulus [Pa] of the steel cord, and C is each of the cross belt layers 71 and 72 and the auxiliary belt layer 73. The number of steel cords driven in [number / 50 mm].
Am [N / 50 mm] = A [mm ² ] × E [Pa] × C [lines / 50 mm] (1)

Here, when the tensile rigidity Am of each of the cross belt layers 71 and 72 and the auxiliary belt layer 73 is less than 1.5 × 10 ⁶ N / 50 mm, the circumferential rigidity of the belt layer 7 is lowered, and the outer diameter growth is increased. As a result, the deterioration rate of the coated rubber increases, and as a result, the durability of the belt layer 7 including the cross belt layers 71 and 72 and the auxiliary belt layer 73 decreases. On the contrary, if the tensile rigidity Am is more than 4.0 × 10 ⁶ N / 50 mm, it is necessary to increase the number of steel cords to be driven. As a result, the distance between the steel cords is narrowed, and separation is likely to occur. In particular, it is desirable that each of the tensile stiffness Am cross belt layers 71, 72 and the auxiliary belt layer 73 is ^{2.0 × 10 6 N / 50mm~3.5 ×} 10 6 N / 50mm.

  The tire size is 315 / 60R22.5, and includes a tread portion, a pair of sidewall portions, and a pair of bead portions, a carcass layer is mounted between the pair of bead portions, and the carcass layer is a bead core of each bead portion. Conventional tires 1 to 4 having four belt layers on the outer diameter side of the carcass layer in the tread portion of the pneumatic tire having a structure wound around from the tire inner side to the outer side were manufactured. In the tires of the conventional examples 1 to 4, the cord angle of the first to fourth belt layers (1B to 4B) counted from the inner side in the tire radial direction, the presence or absence of the 0 degree belt layer, the average cord angle Cc at the center intersection, the shoulder The average code angle Cs at the intersection and the difference (Cc−Cs) in the average code angle were set as shown in Table 1. The average chord angle Cc at the center intersection and the average chord angle Cs at the shoulder intersection are average chord angles of portions corresponding to Examples 1 to 8 and Comparative Examples 1 to 6 described later.

  On the other hand, the tire size is 315 / 60R22.5, and includes a tread portion, a pair of sidewall portions, and a pair of bead portions, and a carcass layer is mounted between the pair of bead portions, and the carcass layer is attached to each bead portion. In a pneumatic structure having a structure wound around the bead core from the inside to the outside of the tire, a pair of cross belt layers and an auxiliary belt layer are arranged on the outer diameter side of the carcass layer in the tread portion, and the cross belt layer on the outer diameter side is arranged. The inner belt is narrower than the cross belt layer on the inner diameter side, the auxiliary belt layer is wider than the cross belt layer on the outer diameter side, and the auxiliary belt layer is crossed on the inner diameter side outside the cross belt layer on the outer diameter side in the tire width direction. It is structured so as to be in contact with the belt layer, the cord angle θcrs-in of the cross belt layer on the inner diameter side, the cord angle θcrs-out of the cross belt layer on the outer diameter side, the cord angle θsub of the auxiliary belt layer, Average cord angle Cc (Cc = (| θcrs-in | + | θcrs-out |) / 2), average cord angle Cs at the shoulder intersection (Cs = (| θcrs-in | + | θsub |) / 2), Tires of Examples 1 to 8 and Comparative Examples 1 to 6 in which the difference in average cord angle (Cc−Cs) and | θcrs-in | + | θcrs-out | + | θsub | were set as shown in Tables 2 and 3 Was made.

In Tables 1 to 3, the cord angle is shown as a positive value when tilted to one side with respect to the tire equator, and as a negative value when tilted to the other side with respect to the tire equator. Further, in the tires of Examples 1 to 8 and Comparative Examples 1 to 6, the width Wsh of the contact region between the auxiliary belt layer and the inner diameter side intersecting belt layer is set to 22 mm (0.073 × Lc), and the outer diameter side intersecting is performed. The width Lcrs-out of the belt layer was 180 mm (0.60 × Lc). Further, a separation portion is formed between the auxiliary belt layer and the inner diameter side crossing belt layer outside the contact region between the auxiliary belt layer and the inner diameter side crossing belt layer in the tire width direction, and the buffer rubber layer is formed in the separation portion. The 100% modulus of the buffer rubber layer was 7.0 MPa, and the elongation at break of the buffer rubber layer was 350%. Further, the 100% modulus of the coated rubber of the belt layer was 8.0 MPa, and the elongation at break of the coated rubber was 250%. The initial elongation of the steel cord of the belt layer was 0.45%, the rubber gauge between cords of the belt layer was 0.8 mm, and the tensile stiffness Am of the belt layer was 2.9 × 10 ⁶ N / 50 mm.

  About these test tires, the durability, damage resistance, and uneven wear resistance of the belt layer were evaluated by the following test methods, and the results are shown in Tables 1 to 3.

Durability of belt layer:
Each test tire is mounted on a specified rim of ETRTO, set to 75% of the specified pressure of ETRTO, loaded 1.4 times the specified load of ETRTO, and run on a drum tester at a running speed of 49 km / h. The test was conducted. The tire was run until separation occurred in the tread portion of the tire, and the running distance was measured. The evaluation results are shown as an index with the conventional example being 100. It means that durability of a belt layer is excellent, so that this index value is large.

Damage resistance:
Each test tire is assembled to a specified rim of ETRTO and mounted on the test vehicle, filled with the specified air pressure of ETRTO, and after running to the end of wear at the quarry, the degree of cut scratches and chipping received on the tread part Indexed. The evaluation results are shown as an index with the conventional example being 100. A larger index value means better damage resistance.

Uneven wear resistance:
Each test tire is assembled to a specified rim of ETRTO, mounted on a test vehicle, filled with the specified air pressure of ETRTO, traveled 100,000 km on a paved road, and then the groove depth after traveling from the groove depth before traveling The amount of wear in each circumferential main groove is calculated by subtracting the length, and the amount of wear in the circumferential main groove located in the center of the tire width direction is calculated from the amount of wear in the circumferential main groove located on the outermost side in the tire width direction. The amount of uneven wear was calculated by subtracting. The evaluation results are shown as an index with the conventional example being 100, using the reciprocal of the measured value. The larger the index value, the better the uneven wear resistance.

  As can be seen from Table 1, in the tires of Conventional Examples 2 and 3 in which the difference (Cc−Cs) between the average cord angle Cc at the center intersection and the average cord angle Cs at the shoulder intersection is larger than that in Conventional Example 1, Although the damage resistance and uneven wear resistance were improved, the durability of the belt layer was deteriorated. On the other hand, in the tire of Conventional Example 4 in which the 0-degree belt layer is added to the tread portion, although the durability of the belt layer is improved, the damage resistance is deteriorated.

  On the other hand, as can be seen from Tables 2 and 3, in the tires of Examples 1 to 8, in comparison with Conventional Example 1, while improving the durability of the belt layer, suppressing the occurrence of uneven wear, Furthermore, the damage resistance could be improved. In the tires of Comparative Examples 1 to 3, since the average cord angle Cs at the shoulder intersection was not smaller than the average cord angle Cc at the center intersection, the effect of improving uneven wear resistance could not be obtained. In the tires of Comparative Examples 4 to 6, since the value of | θcrs-in | + | θcrs-out | + | θsub | exceeded 70 °, the durability of the belt layer was deteriorated.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Buffer rubber layer 71,72 Cross belt layer 73 Auxiliary belt layer

Claims (8)

An annular tread portion extending in the tire circumferential direction, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the tire radially outer side of the sidewall portions; In a pneumatic tire having a structure in which a carcass layer is mounted between the pair of bead portions, and the carcass layer is wound around the bead core of each bead portion from the inside of the tire to the outside.
The outer diameter side of the carcass layer in the tread portion includes a plurality of steel cords that are inclined with respect to the tire circumferential direction, and a pair of cross belt layers in which the steel cords cross each other are disposed, The cross belt layer on the outer diameter side of the cross belt layer is narrower than the cross belt layer on the inner diameter side,
An auxiliary belt layer including a plurality of steel cords inclined with respect to the tire circumferential direction is disposed on the outer diameter side of the pair of cross belt layers, and the cross belt with the cord inclination direction of the auxiliary belt layer on the outer diameter side. The auxiliary belt layer is wider than the cross belt layer on the outer diameter side, and the auxiliary belt layer is on the outer side in the tire width direction than the cross belt layer on the outer diameter side. In contact with the inner side cross belt layer,
The cord angle θcrs-in with respect to the tire circumferential direction of the inner belt side cross belt layer, the cord angle θcrs-out with respect to the tire circumferential direction of the outer belt side cross belt layer, and the cord angle of the auxiliary belt layer with respect to the tire circumferential direction The average chord angle at the shoulder intersection ((| θcrs-in | + | θsub |) rather than the average chord angle at the center intersection ((| θcrs-in | + | θcrs-out |) / 2) calculated from θsub ) / 2) is smaller,
The cord angle θcrs-in of the inner belt side cross belt layer, the cord angle θcrs-out of the outer belt layer cross belt layer, and the cord angle θsub of the auxiliary belt layer are | θcrs-in | + | θcrs- A pneumatic tire characterized by satisfying a relationship of out | + | θsub | ≦ 70 °.   A width Wsh of a contact region between the auxiliary belt layer and the inner belt side cross belt layer is 15 mm or more and satisfies a relationship of Wsh ≧ 0.05 × Lc with respect to the maximum width Lc of the carcass layer, 2. The pneumatic tire according to claim 1, wherein the width Lcrs-out of the cross belt layer on the radial side satisfies a relationship of Lcrs-out ≧ 0.54 × Lc with respect to the maximum width Lc of the carcass layer. .   The auxiliary belt layer and the inner diameter side crossing belt layer are separated from each other on the outer side in the tire width direction from the contact region between the auxiliary belt layer and the inner diameter side crossing belt layer, and the inner diameter from the edge of the auxiliary belt layer The distance te to the cross belt layer on the side is 2.0 mm or more, and a buffer rubber layer is disposed in the separated portion, and the 100% modulus of the buffer rubber layer is 5.5 MPa to 10.0 MPa. The pneumatic tire according to claim 1 or 2, wherein the rubber layer has an elongation at break of 200% or more.   The average chord angle ((| θcrs-in | + | θcrs-out |) / 2) of the center intersection is 30 ° or less, and the average chord angle ((| θcrs-in | + | θsub) of the shoulder intersection The pneumatic tire according to claim 1, wherein |) / 2) is 20 ° or less.   The 100% modulus of the coated rubber constituting the pair of cross belt layers and the auxiliary belt layer is 5.5 MPa to 10.0 MPa, and the elongation at break of the coated rubber is 200% or more. 4. The pneumatic tire according to any one of 4 above.   The pneumatic tire according to any one of claims 1 to 5, wherein an initial elongation of steel cords constituting the pair of cross belt layers and the auxiliary belt layer is less than 0.8%.   An intercord rubber gauge between the inner diameter side cross belt layer and the outer diameter side cross belt layer and an inter cord rubber gauge between the outer diameter side cross belt layer and the auxiliary belt layer are each 0.3 mm to The pneumatic tire according to claim 1, wherein the pneumatic tire is 1.2 mm. Of claim 1, wherein the tensile rigidity Am of each of the pair of cross belt layer and the auxiliary belt layer is ^{1.5 × 10 6 N / 50mm~4.0 ×} 10 6 N / 50mm The pneumatic tire according to any one of the above.

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