pneumatic tires

Abstract

To provide a pneumatic tire equipped with a belt reinforcement layer comprising an organic fiber cord that can improve operation stability during normal travel and circuit travel while maintaining durability.SOLUTION: A belt layer 7 of two layers, which is located on an outer peripheral side of a carcass layer at a tread part, is configured from a single wire having a wire diameter of 0.30 mm or more and 0.45 mm or less, and a belt reinforcement layer 8 located on an outer peripheral side of the belt layer 7 is configured from an organic fiber cord which comprises polyethylene terephthalate fibers and of which an intermediate elongation at 2.0 cN / dtex load is 2.0% to 4.0%. A terminal Ec of the belt reinforcement layer 8 in a tire width direction is located between a terminal Eb1 of an inner belt layer 7A in the tire width direction and a terminal Eb2 of an outer belt layer 7B in the tire width direction.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a pneumatic tire provided with a belt reinforcing layer made of organic fiber cords, and more particularly to a pneumatic tire that enables improvement of handling stability during normal driving and circuit driving while maintaining durability.

Background Art

[0002] In a pneumatic tire, a carcass layer is mounted between a pair of bead portions, a plurality of belt layers are arranged on the outer peripheral side of the carcass layer in the tread portion, and further, a belt reinforcing layer including a plurality of organic fiber cords spirally wound along the tire circumferential direction is arranged on the outer peripheral side of the belt layer. Such a belt reinforcing layer suppresses the lifting of the belt end portion during high-speed driving, and thus contributes to the improvement of high-speed durability.

[0003] As the organic fiber cords used for such a belt reinforcing layer, nylon fiber cords are the mainstream, but it has been proposed to use polyethylene terephthalate fiber cords (hereinafter referred to as PET fiber cords) which are highly elastic and inexpensive compared to nylon fiber cords (see, for example, Patent Document 1). However, the elastic modulus (rigidity) of PET fiber cords has temperature dependence, and there is a risk that the elastic modulus (rigidity) decreases and the handling stability decreases during ultra-high-speed driving such as circuit driving. Therefore, in a pneumatic tire provided with a belt reinforcing layer made of PET fiber cords, countermeasures for improving durability and handling stability during normal driving and circuit driving are required.

[0004] Furthermore, in a pneumatic tire provided with a plurality of belt layers and a belt reinforcing layer made of PET fiber cords, at the end portion in the tire width direction of the belt layer located at the innermost side in the tire radial direction, the potential strain during driving is large, and there is a problem that separation is likely to occur between the belt layer and the belt reinforcing layer.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2001-63312 [Overview of the project] [Problems that the invention aims to solve]

[0006] The object of the present invention is to provide a pneumatic tire equipped with a belt reinforcement layer made of organic fiber cords, which improves handling stability during normal driving and circuit driving while maintaining durability. [Means for solving the problem]

[0007] To achieve the above objective, the pneumatic tire of the present invention comprises a tread portion extending in the circumferential direction of the tire and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged radially inward of these sidewall portions. along Between the pair of bead portions The carcass layer is mounted In a pneumatic tire having two belt layers arranged on the outer periphery of the carcass layer in the tread portion, and a belt reinforcing layer arranged on the outer periphery of the belt layers, the belt cord constituting the belt layer is a single wire with a strand diameter of 0.30 mm or more and 0.45 mm or less. The amount of wire, which is the product of the unit mass [g / m] of the single-strand wire and the number of single-strand wires driven in [wires / 50mm], is in the range of 50 to 280. The belt reinforcing cord constituting the belt reinforcing layer is an organic fiber cord made of polyethylene terephthalate fibers, the intermediate elongation of the belt reinforcing cord under a 2.0 cN / dtex load is 2.0% to 4.0%, and the end of the belt reinforcing layer in the tire width direction is positioned between the end of the inner belt layer located on the inner side in the tire radial direction and the end of the outer belt layer located on the outer side in the tire radial direction. , the width W between the two ends of the belt reinforcement layer in the tire width direction c and the width W between the two ends of the inner belt layer in the tire width direction. b1 and the width W between the two ends of the outer belt layer in the tire width direction. b2 The value of 0.40 ≤ (W c -W b2 ) / (Wb1 -W b2 The relationship ) ≤ 0.60 is satisfied, the belt reinforcement layer includes a full cover layer that covers the entire area of ​​the outer belt layer, the full cover layer extends parallel to the outer belt layer, and the ends of the protrusions in the full cover layer that project outward in the tire width direction from the end of the outer belt layer extend parallel to the inner belt layer. It is characterized by the following: [Effects of the Invention]

[0008] The inventors of the present invention have discovered that by employing a belt layer made of single-strand wire having a predetermined wire diameter and a belt reinforcement layer made of a highly rigid organic fiber cord in a pneumatic tire, it is possible to improve handling stability during normal driving and circuit driving while maintaining durability. Furthermore, they have found that the improvement effect of the above tire performance can be enhanced by devising the terminal position of the belt reinforcement layer in the tire width direction, leading to the present invention.

[0009] In other words, as described above, the present invention uses an organic fiber cord made of highly rigid polyethylene terephthalate fiber (PET fiber) with an elongation of 2.0% to 4.0% under a 2.0 cN / dtex load in the belt reinforcement layer, thereby improving handling stability during normal driving. Furthermore, this belt reinforcement layer effectively suppresses the lifting of the belt end during high-speed driving, thus improving high-speed durability. On the other hand, since a single wire is used in the belt layer, the elongation of the belt cord can be suppressed, and the belt layer can be made thinner, so heat generation can be suppressed even during ultra-high-speed driving such as on a circuit. Therefore, a decrease in the elastic modulus (rigidity) of the belt reinforcement layer (PET fiber cord) can be prevented, and good handling stability during ultra-high-speed driving can be ensured. Furthermore, by positioning the end of the belt reinforcement layer in the tire width direction between the end of the inner belt layer, which is located on the inside of the belt layer in the tire radial direction, and the end of the outer belt layer, which is located on the outside of the belt layer in the tire radial direction, stress concentration at the end of the outer belt layer in the tire width direction can be suppressed, and shear stress between the belt reinforcement layer and the inner belt layer can be suppressed, thereby improving durability against belt edge separation.

[0010] In the pneumatic tire of the present invention, the width W between the two ends of the belt reinforcement layer in the tire width direction.c and the width W between both ends in the tire width direction of the inner belt layer b1 and the width W between both ends in the tire width direction of the outer belt layer b2 satisfies the relationship of 0.20 ≦ (W c - W b2 ) / (W b1 - W b2 ) ≦ 0.80, and preferably satisfies the relationship of 0.40 ≦ (W c - W b2 ) / (W b1 - W b2 ) ≦ 0.60. Thereby, stress concentration at the end in the tire width direction of the outer belt layer can be suppressed, and shear stress between the belt reinforcing layer and the inner belt layer can be suppressed, so that belt edge separation can be more effectively prevented.

Brief Description of the Drawings

[0011] [Figure 1] It is a meridian cross-sectional view showing a pneumatic radial tire according to an embodiment of the present invention. [Figure 2] It is an explanatory view schematically showing the arrangement of the belt layer (single wire). [Figure 3] It is an explanatory view schematically showing the arrangement of each end of the belt layer and the belt reinforcing layer.

Modes for Carrying Out the Invention

[0012] Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

[0013] As shown in Figure 1, the pneumatic tire of the present invention comprises a tread portion 1, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged radially inward of the sidewall portions 2. In Figure 1, the symbol CL indicates the tire equator. Although not depicted in Figure 1 because it is a meridian cross-sectional view, the tread portion 1, sidewall portions 2, and bead portions 3 each extend in the circumferential direction of the tire and form an annular shape, thereby forming the toroidal basic structure of the pneumatic tire. The following explanation using Figure 1 is basically based on the illustrated meridian cross-sectional shape, but each tire component extends in the circumferential direction of the tire and forms an annular shape.

[0014] In the illustrated example, multiple main grooves (four in the illustrated example) extending in the circumferential direction of the tire are formed on the outer surface of the tread portion 1, but the number of main grooves is not particularly limited. In addition to the main grooves, various grooves and sipes, including lug grooves extending in the width direction of the tire, can also be formed.

[0015] Between the pair of left and right bead sections 3, at least one carcass layer 4 (one layer in the illustrated example) is mounted, which includes multiple reinforcing cords extending in the radial direction of the tire. A bead core 5 is embedded in each bead section 3, and a bead filler 6 with a roughly triangular cross-section is placed on the outer circumference of the bead core 5. The carcass layer 4 is folded back around the bead core 5 from the inside to the outside in the tire width direction. As a result, the bead core 5 and bead filler 6 are enclosed by the main body portion of the carcass layer 4 (the portion extending from the tread section 1 through each sidewall section 2 to each bead section 3) and the folded portion (the portion that is folded back around the bead core 5 in each bead section 3 and extends toward each sidewall section 2).

[0016] On the other hand, two belt layers 7 are embedded on the outer circumference of the carcass layer 4 in the tread portion 1. Specifically, the belt layers 7 consist of an inner belt layer 7A located on the inside in the tire radial direction and an outer belt layer 7B located on the outside in the tire radial direction. The width of the inner belt layer 7A is greater than that of the outer belt layer 7B. Each belt layer 7 includes multiple belt cords 7c that are inclined with respect to the tire circumferential direction, and the belt cords 7c are arranged to intersect each other between layers. In these belt layers 7, the inclination angle of the belt cords 7c with respect to the tire circumferential direction is set to, for example, in the range of 10° to 40°.

[0017] A belt reinforcement layer 8 is provided on the outer circumference of the belt layer 7 for the purpose of improving high-speed durability and reducing road noise. The belt reinforcement layer 8 includes belt reinforcement cords oriented in the circumferential direction of the tire. In the belt reinforcement layer 8, the angle of the belt reinforcement cords with respect to the circumferential direction of the tire is set to, for example, 0° to 5°. In the present invention, the belt reinforcement layer 8 always includes a full cover layer that covers the entire area of ​​the outer belt layer 7B that constitutes the belt layer 7. Optionally, the belt reinforcement layer 8 may also be configured to include a pair of edge cover layers that locally cover both ends of the full cover layer in the tire width direction. The belt reinforcement layer 8 is preferably constructed by winding a strip material, which is made by aligning at least one belt reinforcement cord and covering it with coated rubber, spirally in the circumferential direction of the tire, and a jointless structure is particularly desirable.

[0018] Since this invention relates to the belt cords constituting the belt layer 7 and the belt reinforcing cords constituting the belt reinforcing layer 8 described above, the basic structure of the entire tire is not limited to those described above.

[0019] In the present invention, as shown in Figures 2(a) and (b), the belt cord 7c constituting the belt layer 7 is not a twisted cord made by twisting together multiple strands, but is made of a single steel wire. The diameter of the strands of this single wire is 0.30 mm or more, preferably 0.32 mm or more. By using a single wire in the belt layer 7 in this way, the elongation of the belt cord 7c can be suppressed, and the belt layer 7 can be made thinner, so that heat generation can be suppressed even during ultra-high-speed driving such as on a race track. From the viewpoint of making the belt layer 7 thinner, the diameter of the strands of the single wire should be 0.45 mm or less, preferably 0.40 mm or less.

[0020] When constructing the belt layer 7 with single wires, as shown in Figure 2(a), the single wires may be arranged individually with spacing between them, or as shown in Figure 2(b), multiple single wires (two in the figure) may be aligned and then arranged with spacing between each set of aligned wires. In this case, it is preferable to set the spacing between the single wires (the spacing between each set of aligned wires) to, for example, 0.30 mm to 1.80 mm.

[0021] As long as the wire diameter described above is met, the specific structure of the single-strand wire is not particularly limited. For example, various types of single-strand wires that can be used in pneumatic tires can be employed, such as single-strand wires with a twist around the wire axis (twisted single-strand wire), single-strand wires with a flattened cross-section (flattened single-strand wire), single-strand wires shaped into a spiral (spiral single-strand wire), and single-strand wires shaped into a planar corrugated shape (two-dimensional corrugated single-strand wire).

[0022] If the wire quantity is defined as the product of the unit mass of the single-strand wire (g / m) and the number of single-strand wires driven in per 50 mm width in the direction perpendicular to the longitudinal direction of the single-strand wire (wires / 50 mm), then this wire quantity is preferably in the range of 50 to 280. This results in a good structure for the belt layer 7, which is advantageous for improving handling stability while maintaining durability. If the wire quantity is less than 50, the proportion of single-strand wires in the belt layer 7 decreases, which may reduce handling stability. If the wire quantity exceeds 280, there is a risk of belt edge separation occurring.

[0023] In this invention, a polyester fiber cord having an elongation of 2.0% to 4.0%, preferably 2.6% to 3.4%, under a 2.0 cN / dtex load is used as the belt reinforcing cord constituting the belt reinforcing layer 8. Polyethylene terephthalate fiber (PET fiber) can be used as an example of polyester fiber. In this invention, the elongation under a 2.0 cN / dtex load is the elongation rate (%) of the sample cord measured under a 2.0 cN / dtex load by conducting a tensile test in accordance with the "Test Method for Chemical Fiber Tire Cords" of JIS-L1017, with a gripping distance of 250 mm and a tensile speed of 300 ± 20 mm / min.

[0024] In the above-mentioned pneumatic tire, as shown in Figure 3, the end E of the belt reinforcement layer 8 in the tire width direction c On both sides of the tire equator CL, the terminals E in the tire width direction of the inner belt layer 7A b1 and the end E in the tire width direction of the outer belt layer 7B b2 It is positioned between them. That is, the end E in the tire width direction of the belt reinforcement layer 8 c This is the terminal E of the outer belt layer 7B. b2 It is positioned to protrude outward in the tire width direction, and the end E of the inner belt layer 7A b1 It is positioned inside the tire width direction from the terminal without reaching it. At that time, both terminals E of the inner belt layer 7A b1 Width W b1 The widest part is the belt reinforcement layer 8, followed by both ends E c Width W cThe outer belt layer 7B is wide, and both ends E b2 Width W b2 This is the narrowest point. In particular, the terminal E of the belt reinforcement layer 8 c On both sides of the tire equator CL, the terminal E of the inner belt layer 7A b1 and the terminal E of the outer belt layer 7B b2 It is preferable that it be located near the intermediate position of the outer belt layer 7B. b2 The protruding portion of the belt reinforcement layer 8, which extends outward in the tire width direction, is bent along the tire diameter direction and is adjacent to the inner belt layer 7A.

[0025] Thus, by combining a belt layer 7 made of single-strand wire of a specific wire diameter with a belt reinforcement layer 8 made of organic fiber cord having specific physical properties, the pneumatic tire of the present invention can improve handling stability during normal driving and circuit driving while maintaining durability. Specifically, by using polyethylene terephthalate fiber (PET fiber) with the above-mentioned physical properties and high rigidity in the belt reinforcement layer 8, handling stability during normal driving can be improved. Furthermore, since the belt reinforcement layer 8 can effectively suppress the lifting of the belt end during high-speed driving, high-speed durability can also be improved. On the other hand, by using the above-mentioned single-strand wire in the belt layer 7, the elongation of the belt cord 7c is suppressed, and the belt layer 7 can be made thinner, so that heat generation can be suppressed even during ultra-high-speed driving such as circuit driving. Therefore, a decrease in the elastic modulus (rigidity) of the belt reinforcement layer 8 (PET fiber cord) can be prevented, and good handling stability during ultra-high-speed driving can be ensured. Furthermore, the terminal E of the belt reinforcement layer 8 c The terminal E of the inner belt layer 7A b1 and the terminal E of the outer belt layer 7B b2 By being positioned between them, stress concentration at the tire width direction end of the outer belt layer 7B can be suppressed, and shear stress between the belt reinforcement layer 8 and the inner belt layer 7A can be suppressed, thereby improving durability against belt edge separation.

[0026] In this case, if a stranded cord is used instead of a single wire as the belt cord constituting the belt layer 7, elongation may occur in the belt cord due to the twisted structure, and the thinning of the belt layer 7 cannot be achieved, thus preventing the above-mentioned effects from being obtained. If the strand diameter of the single wire is less than 0.30 mm, the single wire is too thin, and the durability of the wire itself cannot be sufficiently ensured, which tends to reduce handling stability. If the strand diameter of the single wire exceeds 0.45 mm, the belt layer 7 cannot be made sufficiently thin compared to when a conventional stranded cord is used, and separation is more likely to occur. Furthermore, if the elongation of the organic fiber cord constituting the belt reinforcement layer 8 under a 2.0 cN / dtex load is less than 2.0%, the rigidity is too high, resulting in large shear stresses between the belt layer 7 and the belt reinforcement layer 8, and reduced resistance to separation. If the elongation of the organic fiber cord constituting the belt reinforcement layer 8 under a 2.0 cN / dtex load exceeds 4.0%, the rigidity of the belt reinforcement layer 8 becomes low, making it difficult to obtain good handling stability.

[0027] Also, the terminal E of the belt reinforcement layer 8 c The terminal E of the inner belt layer 7A b1 If it is located further outward in the tire width direction than the belt reinforcement layer 8, shear stress will occur between the belt reinforcement layer 8 and the inner belt layer 7A, making separation more likely. On the other hand, the end E of the belt reinforcement layer 8 c The outer belt layer 7B is at terminal E b2 If it is located further inward in the tire width direction, stress will concentrate at the end of the outer belt layer 7B in the tire width direction, making it easier for separation to occur between the inner belt layer 7A and the outer belt layer 7B.

[0028] In the above-mentioned pneumatic tire, the width W of the belt reinforcement layer 8 c and the width W of the inner belt layer 7A b1 and the width W of the outer belt layer 7B b2 This means 0.20 ≤ (W c -W b2 ) / (W b1 -W b2 It is preferable that the relationship )≦0.80 is satisfied, and 0.40≦(W c -W b2 ) / (Wb1 -W b2 It is more preferable that the relationship ) ≤ 0.60 is satisfied. The closer the value calculated using the above relationship is to zero, the better the terminal E of the belt reinforcement layer 8. c The outer belt layer 7B is at terminal E b2 This means that it is close to the terminal E of the belt reinforcement layer 8, and the closer the value calculated by the above relation is to 1.0, the closer the terminal E of the belt reinforcement layer 8 is to 1.0. c The terminal E of the inner belt layer 7A b1 This means that they are in close proximity. By setting the belt reinforcement layer 8, the inner belt layer 7A, and the outer belt layer 7B to satisfy the above relationship, stress concentration at the end of the outer belt layer 7B in the tire width direction can be suppressed, and shear stress between the belt reinforcement layer 8 and the inner belt layer 7A can be suppressed, thereby more effectively preventing belt edge separation.

[0029] Furthermore, both ends E in the tire width direction of the inner belt layer 7A b1 Width W b1 , both ends E in the tire width direction of the outer belt layer 7B b2 Width W b2 and both ends E in the tire width direction of the belt reinforcement layer 8 c Width W c This is the average value of the width [mm] of each component measured at three points, each of which is obtained by removing the tire tread and dividing the tire circumference into three equal parts.

[0030] Here, the end E of the belt reinforcement layer 8 c The terminal E of the inner belt layer 7A b1 When the value is close to 0.20, that is, when the value calculated using the above relation is less than 0.20, shear stress tends to occur between the belt reinforcement layer 8 and the inner belt layer 7A, causing separation. On the other hand, at the end E of the belt reinforcement layer 8 c The outer belt layer 7B is at terminal E b2 When the value is close to 0.80, that is, when the value calculated using the above relation is greater than 0.80, stress tends to concentrate at the end of the outer belt layer 7B in the tire width direction, causing separation between the inner belt layer 7A and the outer belt layer 7B.

[0031] To obtain a belt reinforcement cord (PET fiber cord) with the physical properties described above, it is advisable to optimize the dipping process, for example. In other words, prior to the calendering process, the belt reinforcement cord (PET fiber cord) is dipped in adhesive, but in the normalization process after the two-bath treatment, the ambient temperature should be set within the range of 210°C to 250°C, and the cord tension should be 2.2 × 10⁻⁶. -2 N / tex~6.7×10 -2 It is preferable to set the N / tex range. This makes it possible to impart the desired physical properties described above to the belt reinforcement cord (PET fiber cord). The cord tension in the normalization process is 2.2 × 10⁻⁶. -2 If it is smaller than N / tex, the code modulus of elasticity will be low, reducing handling stability, while conversely, 6.7 × 10 -2 If the ratio is greater than N / tex, the cord modulus becomes higher, making separation more likely.

[0032] In the above-described example of a pneumatic tire, the belt reinforcement layer 8 is shown as a single layer, but it is not limited to this, and the belt reinforcement layer 8 can also be composed of multiple layers. In that case, the widest layer of the belt reinforcement layer 8 that covers the entire outer belt layer 7B is targeted, and the terminal E in the tire width direction of that layer is targeted. c The structure of the present invention described above shall be applied to the above. [Examples]

[0033] Conventional Example 1, Comparative Examples 1-4, and Examples 1-4 were manufactured with a tire size of 235 / 40R18 and the basic structure illustrated in Figure 1. The structure of the belt cords constituting the belt layer, the wire diameter (cord diameter), the type of organic fiber used in the organic fiber cords constituting the belt reinforcement layer, the elongation of the organic fiber cords under a 2.0 cN / dtex load, and the relationship between the width of the belt layer and the belt reinforcement layer were varied as shown in Table 1.

[0034] In all examples, the belt reinforcement layer has a jointless structure in which a strip made of a single organic fiber cord (nylon 66 fiber cord or PET fiber cord) is aligned and coated with rubber is wound spirally in the circumferential direction of the tire. The cord density in the strip is 50 cords / 50 mm. Furthermore, the organic fiber cord (nylon 66 fiber cord or PET fiber cord) has a structure of 1400 dtex / 2 in Conventional Example 1, and a structure of 1100 dtex / 2 in the other examples. In addition, in Comparative Examples 1 to 4 and Examples 1 to 4, the width of the belt layer (W b1 ,W b2 ) are the same, while the width of the belt reinforcement layer (W c ) is different.

[0035] In Table 1, the "Type of Organic Fiber" column is indicated as "N66" for nylon 66 fiber cords and "PET" for PET fiber cords. Also, in the "Relationship between the width of the belt layer and the belt reinforcement layer" column of Table 1, the formula (W c -W b2 ) / (W b1 -W b2 The calculated values ​​are shown. The calculated value for Comparative Example 1 (1.10) means that the terminal position of the belt reinforcement layer is located further outward in the tire width direction than the terminal position of the inner belt layer, and the calculated value for Comparative Example 2 (-0.10) means that the terminal position of the belt reinforcement layer is located further inward in the tire width direction than the terminal position of the outer belt layer.

[0036] For these test tires, the handling stability during normal driving, handling stability during circuit driving, and tire durability were evaluated using the evaluation method described below, and the results are shown in Table 1.

[0037] Handling stability (during normal driving and on a circuit): Each test tire was mounted on an 18x8J rim wheel and fitted to a test vehicle (3000cc engine). The air pressure was set to 230kPa, and the handling stability was evaluated subjectively by five test drivers on a paved test course under two conditions: speeds of 30km / h to 100km / h (normal driving) and speeds of 100km / h to 270km / h (circuit driving). The evaluation results were scored on a 5-point scale, with the result of Conventional Example 1 being 3 points (base), and the average score of the five test drivers is shown. A higher score indicates better handling stability at high speeds.

[0038] Tire durability: Each test tire was mounted on a wheel with a rim size of 18×8J, filled with oxygen at an internal pressure of 230kPa, and kept in a chamber maintained at room temperature of 60°C for two weeks. After that, the internal oxygen was released and the tire was filled with air at an internal pressure of 160kPa. The pre-treated test tires were then driven for 100 hours (5000km) using a steel drum testing machine with a smooth drum surface and a diameter of 1707mm, under conditions of ambient temperature of 38±3°C, running speed of 50km / hr, slip angle of 0±3°, and variation of 70±40% of the maximum load, with the load and slip angle varied by a 0.083Hz square wave. After the run, the tire was cut open and the widthwise separation length [mm] at the end in the belt width direction was measured. The evaluation results are shown as an index using the reciprocal of the measured value, with Conventional Example 1 set to 100. A larger index value indicates a smaller separation length and superior durability against belt edge separation.

[0039] [Table 1]

[0040] As can be seen from Table 1, the tires of Examples 1 to 4, compared to the standard conventional example 1, maintain tire durability while improving handling stability during normal driving and handling stability during circuit driving, achieving a high level of balance between these performance characteristics.

[0041] On the other hand, in Comparative Example 1, the terminal position of the belt reinforcement layer was located further outward in the tire width direction than the terminal position of the inner belt layer, which caused shear stress to occur between the belt reinforcement layer and the inner belt layer, resulting in separation and reduced tire durability. In Comparative Example 2, the terminal position of the belt reinforcement layer was located further inward in the tire width direction than the terminal position of the outer belt layer, which caused stress to concentrate at the end of the outer belt layer in the tire width direction, resulting in separation between the inner and outer belt layers and reduced tire durability. In Comparative Example 3, the elongation under a 2.0 cN / dtex load was small and the rigidity of the belt reinforcement layer was too high, resulting in separation between the belt layer and the belt reinforcement layer and reduced tire durability. In Comparative Example 4, the elongation under a 2.0 cN / dtex load was large and the rigidity of the belt reinforcement layer was too low, resulting in reduced handling stability during normal driving and during circuit driving. [Explanation of symbols]

[0042] 1. Tread section 2 Sidewall section 3. Bead section 4. Carcass layer 5 Bead core 6. Bead Filler 7 Belt layer 7A Inner belt layer 7B Outer belt layer 7c belt cord 8 Belt reinforcement layer CL Tire Equator E terminal W width

Claims

[Claim 1] A pneumatic tire comprising a tread portion extending in the circumferential direction of the tire and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged radially inward of these sidewall portions, wherein a carcass layer is mounted between the pair of bead portions, and the tread portion comprises two belt layers arranged on the outer periphery side of the carcass layer and a belt reinforcing layer arranged on the outer periphery side of the belt layers, The belt cord constituting the belt layer is a single-strand wire with a strand diameter of 0.30 mm or more and 0.45 mm or less, and the amount of wire, which is the product of the unit mass [g / m] of the single-strand wire and the number of single-strand wires driven in [wires / 50 mm], is in the range of 50 to 280. The belt reinforcing cord constituting the belt reinforcing layer is an organic fiber cord made of polyethylene terephthalate fibers, and the intermediate elongation of the belt reinforcing cord under a 2.0 cN / dtex load is 2.0% to 4.0%. The end of the belt reinforcement layer in the tire width direction is positioned between the end of the inner belt layer located on the inner side in the tire radial direction and the end of the outer belt layer located on the outer side in the tire radial direction, with a width W between the two ends of the belt reinforcement layer in the tire width direction. c and the width W between the two ends of the inner belt layer in the tire width direction. b1 and the width W between the two ends of the outer belt layer in the tire width direction. b2 0.40 ≤ (W c -W b2 ) / (W b1 -W b2 The relationship ) ≤ 0.60 is satisfied, A pneumatic tire characterized in that the belt reinforcing layer includes a full cover layer that covers the entire area of ​​the outer belt layer, the full cover layer extends parallel to the outer belt layer, and the ends of the protrusions in the full cover layer that project outward in the tire width direction from the end of the outer belt layer extend parallel to the inner belt layer.

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