L u f t r e i f e n

Abstract

Pneumatic tires, including: a tread section(1) extending in a circumferential direction of the tire and having a ring shape; a pair of sidewall sections (2) which are arranged on both sides of the running surface section (1); a pair of bead sections (3) which are each arranged on an inside sidewall section (2) in a tire radial direction; a carcass layer (4) arranged between the pair of bead sections (3); a plurality of belt layers (7) arranged on an outer circumferential side of the carcass layer (4) in the tread section (1); and a belt reinforcement layer (8) arranged on an outer circumferential side of the belt layers (7), wherein the belt cover layer (8) is formed by spirally winding an organic fiber cord thread covered with coating rubber along the circumferential direction of the tire, wherein the organic fiber cord thread is a polyethylene terephthalate fiber cord thread whose modulus of elasticity at a load of 2.0 cN / dtex at 100 °C is in the range of 3.5 cN / (tex·%) to 5.5 cN / (tex·%), wherein the belt cover layer (7) includes at least one complete cover layer (8a) covering an entire width direction of the belt layer (7), wherein the number of layers of the belt cover layer (8) in a shoulder area (B) located on both sides in the tire width direction is 2 or less, and a Sh / Ce ratio of an increase in Sh in the shoulder area (B) and The increase Ce at a tire equator position (CL) during driving at 240 km / h is 0.85 to 1.15.

Description

Technical field

[0001] The present invention relates to a pneumatic tire which uses polyethylene terephthalate (PET) fiber cord threads in a belt cover layer. State of the art

[0002] Pneumatic tires for passenger cars or light trucks typically include a structure in which a carcass ply is mounted between a pair of bead sections, multiple belt plies arranged on an outer circumferential side of the carcass ply within a tread section, and a belt cover ply arranged on an outer circumferential side of the belt ply, the belt cover ply comprising multiple organic fiber cord threads wound helically along a circumference of the tire. In this structure, the belt cover ply contributes to improved durability at high speeds and a reduction in mid-frequency road noise.

[0003] In the prior art, nylon fiber cord threads are mainly applied to the organic fiber cord threads used in the belt's outer layer; however, it has been proposed to use polyethylene terephthalate fiber cord threads (hereinafter referred to as PET fiber cord threads), which are very elastic and cost-effective compared to nylon fiber cord threads (see, for example, Patent Document 1). Unfortunately, PET fiber cord thread tends to generate heat more readily than conventional nylon fiber cord thread. To reduce road noise using PET fiber cord thread, heat generation must be reduced and resistance to humid heat conditions improved. List of literature on patent literature

[0004] Patent Document 1: JP 2001-63312 A

[0005] DE 11 2020 003 164 T5 discloses a pneumatic tire. On the outer circumferential side of a belt layer in a tread section, a belt cover layer made of an organic fiber cord wound spirally in the tire's circumferential direction is provided, and the organic fiber cord used is a polyethylene terephthalate fiber cord whose modulus of elasticity at a load of 2.0 cN / dtex at 100°C is in the range of 3.5 cN / (tex·%) to 5.5 cN / (tex·%).

[0006] EP 1 671 813 A1 relates to a radial pneumatic tire with low road noise and low flattening as well as high high-speed durability and in particular a radial pneumatic tire with a radial carcass, a belt which is arranged in the radial direction outside a crown section of the carcass and consists of at least two belt layers, and a belt reinforcement layer which is arranged in the radial direction outside the belt, characterized in that the belt reinforcement layer is formed by continuous and spiral winding of one or more polyethylene terephthalate cords in the circumferential direction of the tire and this cord has a modulus of elasticity of not less than 2.5 mN / dtex·% at a load of 29.4 N, measured at 160 °C. Brief description of the invention: Technical problem

[0007] One object of the present invention is to provide a pneumatic tire that is able to improve resistance under humid heat conditions in order to reduce road noise by using PET fiber cord threads for a belt cover layer. Solution to the problem

[0008] A pneumatic tire according to an embodiment of the present invention for solving the aforementioned problem is a pneumatic tire comprising: a tread section extending in the circumferential direction of the tire and having a ring shape; a pair of sidewall sections arranged on both sides of the tread section; a pair of bead sections arranged on an inner side of the sidewall sections in a tire radial direction; a carcass layer arranged between the pair of bead sections; a plurality of belt layers arranged on an outer circumferential side of the carcass layer in the tread section;and a belt cover layer arranged on an outer circumferential side of the belt layers, wherein the belt cover layer is formed by spiral winding of an organic fiber cord yarn coated with coating rubber along the tire circumferential direction, wherein the organic fiber cord yarn is a polyethylene terephthalate fiber cord having a modulus of elasticity at a load of 2.0 cN / dtex at 100 °C in the range of 3.5 cN / (tex·%) to 5.5 cN / (tex·%), wherein the belt cover layer includes at least one complete cover layer covering an entire width direction of the belt layer, wherein the number of layers of the belt cover layers in a shoulder area arranged on both sides in the tire width direction is 2 or less, and a Sh / Ce ratio of a rise Sh in the shoulder area and a rise Ce at a tire equator position during driving at 240 km / h is 0.85 to 1.15. Advantageous effects of the invention

[0009] As a result of thorough research on a pneumatic tire equipped with a belt cover made of PET fiber cord, the inventor arrived at the present invention by finding that the fatigue resistance and ring action of the cord suitable for the belt cover can be achieved by properly dipping a PET fiber cord and adjusting the modulus of elasticity under a load of 2.0 cN / dtex at 100 °C within a predetermined range. That is to say, in one embodiment of the present invention, a PET fiber cord with a modulus of elasticity under a load of 2.0 cN / dtex at 100 °C in the range of 3.5 cN / (tex·%) to 5.5 cN / (tex·%) is used as the organic fiber cord forming the belt cover. Thus, road noise can be effectively reduced while satisfactorily maintaining the durability of the pneumatic tire.

[0010] Furthermore, as described above, the belt cover layer using this PET fiber cord yarn has a structure in which the belt cover layer includes at least one complete cover layer that covers the entire width of the belt layer, and the number of belt cover layer layers in the shoulder area is two or fewer. This prevents excessive stiffness in the shoulder area while sufficiently suppressing belt vibration across its entire width to reduce road noise, thereby preventing belt edge separation and advantageously ensuring tire durability.

[0011] In addition, due to the properties of the PET fiber cord threads and the structure of the belt cover layer described above, the Sh / Ce ratio of the Sh slope in the shoulder area and the Ce slope at the tire's equator is adjusted to between 0.85 and 1.15 during driving at 240 km / h. This prevents the belt cover layer from becoming excessively tensile in the shoulder area, thus preventing belt edge separation and ensuring tire durability, while simultaneously suppressing belt layer vibration to effectively reduce road noise.

[0012] In one embodiment of the present invention, the internal tension of the organic fiber cord threads in the tire is preferably 0.9 cN / dtex or more. This has the advantage of suppressing heat generation and improving the tire's durability.

[0013] In the present invention, a region comprising 70% of the ground contact width, centered on the tire's equator, is defined as a central region, and a region on the outside of the central region in the tire width direction is defined as a shoulder region. Here, the "ground contact width" is the distance between the ground contact edges on both sides in the tire width direction. "Ground contact edge" refers to end sections of a ground contact region in the tire's axial direction. The ground contact region is formed when a regular load is applied to the tire, which is mounted on a regular rim, inflated to a regular internal pressure, and placed vertically on a flat surface.A "regular rim" is a rim that is defined for each tire by a standard according to a system of standards that includes standards which the tires meet, and refers, for example, to a "standard rim" as defined by the Japan Automobile Tyre Manufacturers Association (JATMA), a "design rim" as defined by the Tire and Rim Association Inc. (TRA), or a "measurement rim" as defined by the European Tire and Rim Technical Organization (ETRTO).In the system of standards, including standards that tires meet, "regular inflation pressure" is an air pressure defined by each standard for each tire. It refers to "maximum air pressure" in the case of JATMA, with the maximum value listed in the "Tire Load Limits at Various Cold Inflation Pressures" table in the case of TRA, and to "inflation pressure" in the case of ETRTO. The "regular inflation pressure" for a passenger car tire is 180 kPa.“Regular load” is a load defined by a standard for each tire according to a system of standards that includes standards tires meet and refers to “maximum load capacity” in the case of JATMA, to the maximum value in the “Tire Load Limits at Various Cold Inflation Pressures” table in the case of TRA, and to “load capacity” in the case of ETRTO. “Regular load” is equivalent to 88% of the loads described above in a case where a tire is a passenger car tire. Brief description of the drawings Fig. Figure 1 is a meridian cross-sectional view illustrating a pneumatic tire according to an embodiment of the present invention. Fig.Figure 2 is an explanatory view that schematically illustrates a multilayer structure of a belt cover layer according to an embodiment of the present invention. Description of embodiments

[0014] Configurations according to embodiments of the present invention are described in detail below with reference to the drawings.

[0015] As in Fig. As illustrated in Figure 1, a pneumatic tire of an embodiment of the present invention includes a tread section 1, a pair of sidewall sections 2 arranged on both sides of the tread section 1, and a pair of bead sections 3 arranged in the sidewall sections 2 on the inside in the tire radial direction. Fig. 1. The reference symbol CL indicates a tire equator, the reference symbol E indicates a ground contact edge, and the reference symbol W indicates a ground contact width. Furthermore, as in Fig.As shown in Figure 1, an area of ​​70% of the ground contact width W, centered on the tire equator CL, is defined as a central area A, and the areas on the outside in the tire width direction are defined as shoulder areas B. Although in Fig. 1 not shown, because Fig. Figure 1 shows a cross-sectional meridian view. The tread section 1, the sidewall sections 2, and the bead sections 3 each extend in the tire's circumferential direction to form a ring-shaped form. This configures a torus-shaped basic structure of the pneumatic tire. Although the description uses Fig. 1. Essentially based on the illustrated meridian cross-section, all tire components extend in the direction of the tire's circumference and form the ring shape.

[0016] In the illustrated example, a plurality of main grooves (four main grooves in the illustrated example), extending in the circumferential direction of the tire, are formed in the outer surface of tread section 1; however, the number of main grooves is not subject to any specific restrictions. Furthermore, in addition to the main grooves, various grooves and sipes can be formed, including lug grooves, which extend in the width direction of the tire.

[0017] A carcass layer 4, enclosing a plurality of reinforcing cord threads extending radially in the tire, is mounted between a pair of left and right bead sections 3. A bead core 5 is embedded in each of the bead sections, and a bead filler 6 with an approximately triangular cross-sectional shape is arranged on an outer circumference of the bead core 5. The carcass layer 4 is folded back around the bead core 5 from an inside to an outside in the tire width direction. Accordingly, the bead core 5 and the bead filler 6 are encased by a body section (a section extending from the tread section 1 through each of the sidewall sections 2 to each of the bead sections 3) and a folded-back section (a section folded back around the bead core 5 of each bead section 3 to extend to each sidewall section 2) of the carcass layer 4.For example, polyester cord threads are preferably used as the reinforcing cord threads of carcass layer 4.

[0018] A plurality (in the illustrated example, two layers) of belt layers 7 are embedded on an outer circumferential side of the carcass layer 4 in the tread section 1. Each belt layer 7 encloses a plurality of reinforcing cord threads that are inclined with respect to the tire's circumferential direction and are arranged such that the reinforcing cord threads of the different layers intersect each other. In each belt layer 7, the angle of inclination of the reinforcing cord threads with respect to the tire's circumferential direction is set within a range of, for example, 10° to 40°. For example, steel cords are preferably used as the reinforcing cord threads of the belt layers 7.

[0019] A belt reinforcement layer 8 is provided on an outer circumferential side of the belt layers 7 to improve high-speed durability and reduce road noise. The belt reinforcement layer 8 includes organic fiber cord threads oriented in the tire's circumferential direction. In the belt reinforcement layer 8, the angle of the organic fiber cord threads relative to the tire's circumferential direction is, for example, set to 0° to 5°. The belt reinforcement layer 8 is preferably configured such that a strip material consisting of at least one single organic fiber cord thread, bundled and covered with coating rubber, is wound spirally in the tire's circumferential direction and, desirablely, has a seamless structure.

[0020] In one embodiment of the present invention, the belt cover layer 8 necessarily includes a full cover layer 8a that covers the entire area of ​​the belt layers 7 and can be configured to include a pair of edge cover layers 8b that locally cover both end sections of the belt layers 7 as required (in the illustrated example, both with the full cover layer 8a and the edge cover layers 8b). However, when the edge cover layer 8b is included, the number of layers of the belt cover layer 8 in the shoulder region B is limited to two or fewer. In the case of the tire of Fig. 1 (see also) Fig. 2A, which is the belt layer 7 and the belt cover layer 8 of the tire. Fig.Figure 1, extracted in a simplified manner and shown), provides a complete top layer 8a and a pair of edge top layers 8b, which are provided separately from this complete top layer 8a, to cover the end sections of the belt layer 7. Therefore, the maximum number of layers of the belt top layer 8 in the shoulder region is two, which is a structure that corresponds to the present invention. Furthermore, in the example of Fig. 2B by continuously spirally winding the strip material in the circumferential direction of the tire, a structure is obtained in which a complete top layer 8a and the pair of edge top layers 8b are continuous at the end sections on the outside in the tire width direction. In this case as well, the maximum number of layers of the belt top layer 8 in the shoulder region B is two, which corresponds to the present invention. In contrast, in the example of Fig.2C provides a complete cover layer 8a and a pair of edge cover layers 8b separately from the complete cover layer 8a to cover the end sections of the belt layer 7. However, since each edge cover layer 8b is folded back to essentially form two layers, the shoulder region B includes a section where the number of layers of the belt cover layer 8 is three. Therefore, the structure corresponds to, as shown in Fig. Figure 2C is not part of the present invention. When two complete cover layers 8a are provided, the number of layers of the belt cover layer 8 is two in both the central region A and the shoulder region B. However, since the number of layers in the shoulder region B is two or less, this structure corresponds to the present invention.

[0021] If the belt cover layer 8 is configured using organic fiber cord threads with the physical properties described later, by adjusting the multilayer structure of the belt cover layer 8 as described above, excessive stiffness in the shoulder region B can be prevented, while vibrations of the belt layer 7 are sufficiently suppressed across its entire width to reduce road noise. This makes it possible to prevent belt edge separation and ensure good tire durability. If the number of layers in the shoulder region B exceeds two, as described in Fig.As shown in Figure 2C, the stiffness in the shoulder region B becomes excessively high, and belt edge separation can occur. Furthermore, if the complete surface course 8a is not provided and only the edge surface course 8b is provided (not illustrated), the vibration of the belt course 7 cannot be suppressed in the entire width direction of the belt course 7, and the road noise reduction effect cannot be expected.

[0022] In one embodiment of the present invention, a polyethylene terephthalate fiber cord (PET fiber cord) is used as the organic fiber cord thread of which the belt cover layer 8 consists. The modulus of elasticity of this PET fiber cord thread, under a load of 2.0 cN / dtex at 100 °C, is in the range of 3.5 cN / (tex·%) to 5.5 cN / (tex·%). By using a specific PET fiber cord thread as the organic fiber cord thread forming the belt cover layer 8, it is possible to effectively reduce road noise while simultaneously maintaining the durability of the pneumatic tire. If the modulus of elasticity of this PET fiber cord thread is less than 3.5 cN / (tex·%) under a load of 2.0 cN / dtex at 100 °C, the road noise in the mid-frequency range cannot be sufficiently reduced.If the modulus of elasticity of the PET fiber cord exceeds 5.5 cN / (tex·%) at a load of 2.0 cN / dtex at 100 °C, the fatigue resistance of the cord decreases and the durability of the tire diminishes. In one embodiment of the present invention, the modulus of elasticity [N / (tex·%)] at a load of 2.0 cN / dtex at 100 °C is calculated by performing a tensile test under the conditions of a gripping interval of 250 mm and a tensile speed of 300 ± 20 mm / min according to the "Test methods for tire cords made of synthetic fibers" of JIS L1017 and converting the slope of the tangent at the point corresponding to the load of 2.0 cN / dtex of the load-strain curve into the value per tex.

[0023] When this organic fiber cord thread (PET fiber cord thread) is used as the belt cover layer 8, the internal tension of the cord thread within the tire is preferably 0.9 cN / dtex or higher, more preferably 1.5 cN / dtex to 2.0 cN / dtex. By adjusting the tension of the cord thread within the tire, heat generation can be suppressed and the tire's durability improved. If the cord thread tension of this organic fiber cord thread (PET fiber cord thread) within the tire is less than 0.9 cN / dtex, the peak value of tanδ increases, and the improvement in tire durability cannot be sufficiently achieved. The cord thread tension of the organic fiber cord thread (PET fiber cord thread) within the tire, forming the belt cover layer 8, is measured at two or more turns on the inside in the tire's width direction from the end of the strip material forming the belt cover layer.

[0024] In the present invention, the rise of the tire is controlled by the aforementioned properties of the PET fiber cord threads and the structure of the belt cover layer 8. In particular, the Sh / Ce ratio of the rise Ce in the central region A and the rise Sh in the shoulder region B is set to 0.85 to 1.15, preferably 0.95 to 1.00, while driving at 240 km / h. The "rise" is the difference between the tire's outer diameter in the reference state and the tire's outer diameter in the driving state (while driving at 240 km / h in the present invention) at the same location in the tire's width direction. In the present invention, the value in the reference state is the tire's outer diameter when driving at a speed of 40 km / h under the near-contact condition (load immediately before the tire touches the ground). Furthermore, the rise Ce in the central region A is measured at the position of the tire's equator CL.The rise Sh in shoulder area B is measured at the point shifted 1 mm outwards in the tire width direction from the boundary position between the center area A and shoulder area B (a position located 35% of the ground contact width W outwards from the tire equator CL). However, if the main groove is present in shoulder area B, the rise is measured at the point shifted 1 mm outwards in the tire width direction from the outer edge of the main groove that forms in shoulder area B in the tire width direction.

[0025] In this way, the Sh / Ce ratio of the Ce slope in the center area A (the position of the tire equator CL) and the Sh slope in the shoulder area B is adjusted to between 0.85 and 1.15 while driving at 240 km / h. This prevents the belt cover tension in the shoulder area from becoming excessively high, thus preventing belt edge separation and advantageously ensuring tire durability, while suppressing belt vibrations to effectively reduce road noise. However, if the Sh / Ce ratio is less than 0.85, belt vibration cannot be suppressed, and the road noise reduction effect cannot be expected.If the Sh / Ce ratio exceeds 1.15, the stress of the belt cover layer 8 in the shoulder area B becomes excessively high, belt edge separation is likely to occur and tire resistance may decrease.

[0026] In a case where polyethylene terephthalate fiber cord threads (PET fiber cord threads) are used as the organic fiber cord threads forming the belt cover layer 8, the PET fiber cord threads preferably have a heat shrink tension at 100 °C of 0.6 cN / tex or more. By adjusting the heat shrink tension at 100 °C in this way, road noise can be effectively reduced while maintaining the durability of the pneumatic tire more effectively and successfully. If the heat shrink tension of the PET fiber cord threads at 100 °C is less than 0.6 cN / tex, the ring action during driving cannot be sufficiently improved, and it is difficult to adequately maintain durability at high speeds. The upper limit of the heat shrink tension of the PET fiber cord threads at 100 °C is not subject to any specific restrictions, but is preferably, for example, 2.0 cN / tex.It should be noted that in one embodiment of the present invention, the heat shrink tension (cN / tex) at 100 °C is the heat shrink tension of a sample cord thread, measured with reference to the "Test procedure for chemical tire fiber cord threads" of JIS-L1017 and under the conditions of a sample length of 500 mm and heating to 100 °C for 5 minutes.

[0027] To obtain PET fiber cord threads with the aforementioned physical properties, for example, it is preferred to carry out the dip treatment properly. In other words, dip treatment with adhesive is performed on the PET fiber cord threads before a calendering process; however, in a normalization process after a two-bath treatment, it is preferred that an ambient temperature in the range of 210 °C to 250 °C is set and the cord tension in the range of 2.2 × 10 -2 N / tex up to 6.7 × 10 -2N / tex is set. Accordingly, the PET fiber cord threads can be given the desired physical properties, as described above. If the cord thread tension in the normalization process is less than 2.2 × 10 -2 If the N / tex value is low, the cord thread elasticity modulus is low, and therefore medium-frequency road noise cannot be sufficiently reduced. However, if the cord thread tension is greater than 6.7 × 10⁻⁶, the cord thread tension is significantly lower. -2 If N / tex is high, the cord thread elasticity modulus is high, and therefore the fatigue resistance of the cord threads is low.

[0028] The present invention is described below with reference to exemplary embodiments, but the scope of the present invention is not limited to these examples. Examples

[0029] Tires of the prior art example 1, comparative examples 1 to 7 and examples 1 to 6 were manufactured, and the tires had a tire size of 225 / 60R18 and exhibited the characteristics described in Fig. The basic structure shown in Table 1, and the elastic modulus of the organic fiber cord threads (PET fiber cord threads) forming the belt cover layer, at 100 °C under a load of 2.0 cN / dtex [cN / (tex·%)], the tire internal cord thread tension [cN / dtex], the belt cover layer structure and the Sh / Ce ratio of the rise Sh in the shoulder area and the rise Ce in the center area during driving at 240 km / h were changed as shown in Tables 1 and 2.

[0030] In these examples, the belt cover layer has a seamless structure in which a strip formed by bundling an organic fiber cord thread (PET fiber cord thread) and its coating rubber is wound spirally in the tire's circumferential direction. The cord thread density in the strip is 50 cord threads / 50 mm. Furthermore, each organic fiber cord thread (PET fiber cord thread) has a structure of 1100 dtex / 2.

[0031] In each example, the modulus of elasticity [N / (tex·%)] at a load of 2.0 cN / dtex at 100 °C was calculated by performing a tensile test under conditions of a gripping interval of 250 mm and a tensile speed of 300 ± 20 mm / min according to the "Test methods for man-made fiber tire cords" of JIS-L1017 and converting the slope of the tangent at the point corresponding to the load of 2.0 cN / dtex on the load-strain curve into the value per tex. Furthermore, the tire-internal cord tension [cN / dtex] was determined by removing the tread rubber from tread section 1 to expose the belt cover, peeling the fiber cord from a predetermined length range of the belt cover, measuring the length of the peeled fiber cord after removal, and determining the amount of contraction relative to the length before removal.In particular, the average contraction value obtained from five cord threads located in the middle of the outermost belt layer was determined. Subsequently, the strain (%) corresponding to the degree of contraction was determined from the SS curve and measured by converting it to the value per dtex. The tension Ce was measured on five fiber cord threads located in the middle section of the outermost belt layer 7, and the tension Sh was measured on five fiber cord threads located in the shoulder section of the outermost belt layer 7.

[0032] For each example, the gradient Ce and the gradient Sh were calculated as follows. Each test tire was mounted on a wheel with a rim size of 18x7J, inflated with oxygen to an internal pressure of 230 kPa, and mounted on a drum tester equipped with a smooth-surface steel drum with a diameter of 1707 mm. The ambient temperature was controlled to 38 ±3 °C. The tire's outer diameter was measured in the reference condition (speed 40 km / h and near-contact condition (load just before the tire touches the ground) and the tire's outer diameter in the driving condition (speed 240 km / h, load 5.67 kN)). The difference (the value obtained by subtracting the value in the reference condition from the value in the driving condition) was calculated as the gradient. The gradient Ce in the mid-range was measured at the tire's equator, CL.The rise Sh in shoulder area B was measured at the point that was shifted 1 mm outwards in the tire width direction from the boundary position between the center area A and the shoulder area B (since the tire has the basic structure of . Fig. 1, the boundary position coincides with the outer edge in the tire width direction of the outermost main groove in the tire width direction).

[0033] The column “Belt Cover Layer Structure” in Table 1 indicates the number of the corresponding figure. Comparative example 6 shows a structure with only an edge cover layer and no complete cover layer (a structure in which the complete cover layer consists of Fig. 2A away) on.

[0034] These test tires were evaluated for road noise, resistance to damp heat and the presence of belt separation using the following evaluation methods, and the results are also shown in Tables 1 and 2. street noise

[0035] Each test tire was mounted on a wheel with a rim size of 18×7 J, as the front and rear wheels of a passenger car (front-wheel drive vehicle) with a 2.5 L engine, and inflated to a pressure of 230 kPa. A sound-collecting microphone was placed on the inside of the driver's seat window. A sound pressure level at or near the frequency of 315 Hz was measured when the vehicle was driven at an average speed of 50 km / h on a test track with an asphalt road surface. The evaluation results were based on a state-of-the-art example as a reference and indicated the amount of change (dB) relative to the reference. Resistance to humid heat

[0036] Each test tire was mounted on wheels with a rim size of 18×7 J, inflated with oxygen to an internal pressure of 230 kPa, and kept for 30 days in a chamber maintained at a temperature of 70 °C and a humidity of 95%. The pre-treated test tires were then mounted on a drum tester with a smooth steel drum and a diameter of 1707 mm, and the ambient temperature was controlled to 38 ±3 °C. The speed was increased from 120 km / h in 50 km / h increments over 24 hours, and the distance traveled until tire failure was measured. The evaluation results are expressed as index values ​​using the measured distances, with an index value of 100 assigned to the prior art example 1.Higher index values ​​indicate a longer distance that can be traveled before a tire failure occurs, and better resistance in humid heat. Presence of belt edge separation

[0037] After performing the aforementioned resistance test in moist heat, each test tire was disassembled, and the presence of separation (belt edge separation) in the belt surface layer was visually inspected. The evaluation result is indicated as "Yes" if belt edge separation was present and "No" if no belt edge separation was present. [Table 1-1] Example of the state of the art 1 Comparative example 1 Comparative example 2 Comparative example 3 modulus of elasticity cN / (tex·%) 2,0 6,0 5,8 3,2 Cord thread tension in the tire cN / dtex 0,7 0,7 0,7 0,7 Belt cover layer structure Fig. 2B Fig. 2B Fig. 2B Fig. 2B Sh / Ce ratio 0,80 0,80 0,80 0,90 road noise level dB 0 -3,0 -2,8 -0,5 Resistance to humid heat Index value 100 81 85 90 Presence of belt edge separation No Yes Yes Yes [Table 1-2] Comparative example 4 Comparative example 5 Comparative example 6 modulus of elasticity cN / (tex·%) 4,5 4,5 4,5 Cord thread tension in the tire cN / dtex 0,7 0,7 0,7 Belt cover layer structure Fig. 2B Fig. 2B Without a complete top layer Sh / Ce ratio 0,80 1,20 0,70 road noise level dB -0,2 -1,8 -1,8 Resistance to humid heat Index value 95 87 87 Presence of belt edge separation Yes Yes No [Table 2-1] Comparative example 7 Example 1 Example 2 Example 3 modulus of elasticity cN / (tex·%) 4,5 3,8 5,3 5,0 Cord thread tension in the tire cN / dtex 0,7 0,7 0,7 0,7 Belt cover layer structure Fig. 2C Fig. 2B Fig. 2B Fig. 2B Sh / Ce ratio 0,83 0,87 0,98 0,95 road noise level dB -1,8 -1,5 -2,8 -2,5 Resistance to humid heat Index value 87 105 110 112 Presence of belt edge separation Yes No No No [Table 2-2] Example 4 Example 5 Example 6 modulus of elasticity cN / (tex·%) 4,5 4,5 4,5 Cord thread tension in the tire cN / dtex 1,8 0,9 0,9 Belt cover layer structure Fig. 2B Fig. 2B Fig. 2B Sh / Ce ratio 0,96 0,99 1,15 road noise level dB -2,0 -2,9 -3,0 Resistance to humid heat Index value 123 120 122 Presence of belt edge separation No No No

[0038] As can be seen from Tables 1 and 2, the tires of Examples 1 to 6 exhibited reduced road noise and improved resistance to humid heat compared to the prior art example 1 as a reference. On the other hand, in the tires of Comparative Examples 1 and 2, because the modulus of elasticity of the polyethylene terephthalate fiber cord threads forming the belt cover was high at a load of 2.0 cN / dtex at 100 °C, resistance to humid heat deteriorated, and belt edge separation occurred. Since the modulus of elasticity of the polyethylene terephthalate fiber cord threads forming the belt cover was low at a load of 2.0 cN / dtex at 100 °C in the tire of Comparative Example 3, road noise could not be sufficiently reduced, resistance to humid heat deteriorated, and belt edge separation occurred.In comparative example 4, because the Sh / Ce ratio was low, road noise could not be sufficiently reduced, resistance to humid heat deteriorated, and belt edge separation occurred. In comparative example 5, because the Sh / Ce ratio was high, resistance to humid heat deteriorated, and belt edge separation occurred. In comparative example 6, because the complete surface course was not provided, road noise could not be sufficiently reduced, and resistance to humid heat deteriorated. In comparative example 7, because the number of layers of the belt surface course in the shoulder area exceeded two, resistance to humid heat deteriorated, and belt edge separation occurred. List of reference symbols 1 tread section 2 Side wall section 3 bead section 4 Carcass layer 5 bead core 6 bead fillers 7th belt layer 8 Belt cover layer 8a Full top layer 8b Edge cover layer CL tire equator E Ground contact edge A medium area B Shoulder area

Claims

[1] Pneumatic tires, including: a tread section(1) extending in a circumferential direction of the tire and having a ring shape; a pair of sidewall sections (2) which are arranged on both sides of the running surface section (1); a pair of bead sections (3) which are each arranged on an inside sidewall section (2) in a tire radial direction; a carcass layer (4) arranged between the pair of bead sections (3); a plurality of belt layers (7) arranged on an outer circumferential side of the carcass layer (4) in the tread section (1); and a belt reinforcement layer (8) arranged on an outer circumferential side of the belt layers (7), wherein the belt cover layer (8) is formed by spirally winding an organic fiber cord thread covered with coating rubber along the circumferential direction of the tire, wherein the organic fiber cord thread is a polyethylene terephthalate fiber cord thread whose modulus of elasticity at a load of 2.0 cN / dtex at 100 °C is in the range of 3.5 cN / (tex·%) to 5.5 cN / (tex·%), wherein the belt cover layer (7) includes at least one complete cover layer (8a) covering an entire width direction of the belt layer (7), wherein the number of layers of the belt cover layer (8) in a shoulder area (B) located on both sides in the tire width direction is 2 or less, and a Sh / Ce ratio of an increase in Sh in the shoulder area (B) and The increase Ce at a tire equator position (CL) during driving at 240 km / h is 0.85 to 1.

15. [2] Pneumatic tire according to claim 1, wherein the internal tire cord tension of the organic fiber cord thread is 0.9 cN / dtex or more.

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