pneumatic tires

Abstract

Pneumatic tires (1), comprising: a carcass layer (16) toroidally bridging a pair of tire bead sections (D) and a tread section (A) by a pair of sidewall sections (C); a total width SW and an outer diameter OD that satisfy the relationship SW / OD ≤ 0.3; an inner diameter ID and an outer diameter OD that satisfy the relationship ID / OD ≥ 0.7; wherein in a tire meridian cross-section on each side in the tire width direction with the equatorial plane (CL) of the tire in between an imaginary pair of first boundary lines (b1) passes through the intersection of an extension line of a shoulder arc (a1) and an extension line of a side arc (a2) and is perpendicular to the inner circumferential surface of the tire and an imaginary pair of second boundary lines (b2) passes through a rim inspection line (L) and is perpendicular to the inner circumferential surface of the tire; where areas between the first boundary lines (b1) and the second boundary lines (b2) are each first areas (R1) and areas further inside the second boundary lines (b2) in the tire radial direction are each second areas (R2); where the area X1 (mm 2 ) of the first region (R1) and the circumferential length Y1 (mm) of the inner circumferential surface of the first region (R1) have a ratio X1 / Y1 of 12 or greater and 30 or less; and where the area X2 (mm 2 ) of the second area (R2) and the circumferential length Y2 (mm) of the inner circumferential surface of the second area (R2) have a ratio X2 / Y2 of 10 or greater and 15 or less; where the reference points (P1, P2) are the intersection points of the first boundary lines (b1) on both sides in the tire width direction and a profile line of the outer circumferential surface of the tire, and a stretched tread width TDW is the length along the profile line between the two reference points (P1, P2); where a tread vertex (P3, T) is an intersection of the profile line and equatorial plane (CL) of the tire and an angle θ is an angle of a line segment connecting the reference point and the tread vertex (P3, T) relative to the tire width direction; wherein the stretched tread width TDW and a total width SW have a ratio TDW / SW of 0.8 or greater and 1 or less; and the angle θ is 1° or greater and 5° or less.

Description

Technical area

[0001] The present invention relates to a pneumatic tire having improved performance such as fuel economy performance. State of the art

[0002] There have been previous proposals for a pneumatic tire capable of reducing fuel consumption (see, for example, Patent Document 1).

[0003] In the technology disclosed in WO 2011 / 135774 A1, the circumferential air resistance of a tire is reduced by having a tire section width W and an outer diameter L with a W / L ratio of 0.25 or smaller, and by reducing the projected area of ​​the tire's front surface (relative to the projected area of ​​a pneumatic tire viewed from the rolling direction). Further related art documents include DE 689 12 097 T2, WO 02 / 030 687 A2, JP 2002-301 912 A, DE 10 2011 085 246 A1, EP 0 323 895 A1, and DE 29 26 159 A1. Summary of the inventionTechnical problem

[0004] Recently, there has been a demand for the development of a pneumatic tire capable of demonstrating high levels of performance in terms of steering stability and load endurance, as well as fuel economy. However, achieving all of these capabilities in a well-coordinated manner by simply controlling the W / L ratio remains unknown.

[0005] In view of the foregoing, it is an object of the present invention to provide a pneumatic tire having improved fuel economy performance, steering stability performance and load durability in a well-balanced manner. Solution to the problem

[0006] A pneumatic tire according to the present invention has a carcass layer toroidally bridging a pair of bead portions and a tread portion through a pair of sidewall portions; a total width SW and an outer diameter OD satisfy the relationship SW / OD ≤ 0.3; and an inner diameter ID and the outer diameter OD satisfy the relationship ID / OD ≥ 0.7.In a tire meridian cross-section, on each side in the tire width direction with the tire equatorial plane therebetween, a pair of imaginary first boundary lines pass through the intersection of an extension line of a shoulder arc and an extension line of a side arc and are perpendicular to the tire inner circumferential surface, and a pair of imaginary second boundary lines pass through the rim inspection line and are perpendicular to the tire inner circumferential surface; wherein regions between the first boundary lines and the second boundary lines are respectively first regions, and regions further inward from the second boundary lines in the tire radial direction are respectively second regions. The area X1 (mm. 2 ) of the first region and the circumferential length Y1 (mm) of the inner circumferential surface of the first region have a ratio X1 / Y1 of 12 or greater and 30 or less; and the area X2 (mm 2) of the first region and the circumferential length Y2 (mm) of the inner peripheral surface of the first region have a ratio X2 / Y2 of 10 or greater and 15 or less, wherein the reference points are the intersection points of the first boundary lines on both sides in the tire width direction and a profile line of the outer peripheral surface of the tire, and an extended tread width TDW is the length along the profile line between the two reference points; wherein a tread apex is an intersection point of the profile line and the equatorial plane of the tire, and an angle θ is an angle of a line segment connecting the reference point and the tread apex relative to the tire width direction; wherein the extended tread width TDW and a total width SW have a ratio TDW / SW of 0.8 or greater and 1 or less; and the angle θ is 1° or greater and 5° or less. Advantageous effects of the invention

[0007] In a pneumatic tire according to the present invention, the relationship of total width SW and outer diameter OD, the relationship of inner diameter ID and outer diameter OD, and the shape of predetermined regions in a tire meridian cross section are defined.

[0008] As a result, a pneumatic tire according to the present invention can improve fuel saving performance, steering stability performance and load durability in a well-balanced manner. Brief description of the drawings Fig. 1 is a tire meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. Fig. 2 is an enlarged tire meridian cross-sectional view of one side of the pneumatic tire in the Fig. 1 illustrated tire width direction. Description of the embodiment

[0009] Embodiments of the pneumatic tire according to the present invention (including a Basic Embodiment and Additional Embodiments 1 to 8) will now be described based on the drawings.

[0010] It should be noted that the present invention is not limited to these embodiments.

[0011] The components of the embodiments include components that can be readily replaced by those skilled in the art, as well as components that are substantially identical to the components of the embodiments. In addition, the various modes included in these embodiments can be combined as desired by one skilled in the art, within the scope of obviousness. [Basic embodiment]

[0012] A basic embodiment of the pneumatic tire according to the present invention will now be described.

[0013] In the following description, "tire radial direction" refers to a direction perpendicular to the rotation axis of a pneumatic tire; "tire radial direction inner side" refers to a side that is close to a rotation axis in the tire radial direction; and "tire radial direction outer side" refers to a side that is far from the rotation axis in the tire radial direction.

[0014] The “tire circumferential direction” refers to a circumferential direction with the axis of rotation as the central axis.

[0015] In addition, “tire width direction” refers to a direction parallel to the rotation axis; “tire width direction inner side” refers to a side located near a tire equatorial plane CL (tire equatorial line) in the tire width direction; and “tire width direction outer side” refers to a side located away from the tire equatorial plane CL (tire equatorial line) in the tire width direction.

[0016] It should be noted that “tire equatorial plane CL” (tire equatorial line) refers to a plane (line) perpendicular to the axis of rotation of the tire and passing through the center of the width of the tire.

[0017] In addition, the specifications included in this embodiment (e.g., rim size, specified air pressure, applied load) conform to international standards established by the International Organization for Standardization (ISO). However, if there is no ISO standard, the specifications conform to Japanese Industrial Standards (JIS). In addition, if there is an ISO standard but JIS has its own specifications that differ from ISO, the specifications conform to either an ISO or a JIS standard.

[0018] Fig. 1 is a tire meridian cross-sectional view illustrating a region between the tread portion and the bead portions of a pneumatic tire according to an embodiment of the present invention.

[0019] Namely, in the pneumatic tire illustrated in the drawing, the pairs of shoulder portions B, B, sidewall portions C, C and bead portions D, D are formed continuously with a tread portion A at the center.

[0020] Therefore, the portions of the tread portion A to the tire bead portions D, D extend continuously in the tire circumferential direction, respectively, and the pneumatic tire is formed with a toroidal shape.

[0021] In the Fig. 1, tire bead cores 12, bead fillers 14, a carcass layer 16, a belt layer 18, tread rubber 20, a pair of sidewall rubbers 22, 22 and an inner liner 24 are arranged as components of a pneumatic tire 1.

[0022] For example, the tire bead cores 12 have circularly wound bead wire structures in the tire circumferential direction, and the bead filler 14 arranged outwardly in the tire radial direction of the tire bead cores 12 is composed of a rubber material that is harder than other rubber materials to achieve superior steering stability performance.

[0023] The carcass layer 16 is an element bridged between tire bead cores 12, 12 on both sides in the tire width direction over the sections D, C, B, A, B, C, D and forms the frame of the tire.

[0024] In addition, although the Fig. 1 is configured with a single carcass, the present embodiment is not particularly limited, and the carcass layer 16 may be configured with a plurality of carcasses.

[0025] In addition, the fineness of the carcass cord in the present embodiment may be 1400 dtex / 2 or more and 2000 dtex / 2 or less, and preferably 1440 dtex / 2 or more and 1860 dtex / 2 or less.

[0026] In addition, the number of cords of the carcass cords per 50 mm in the tire width direction can be 40 or more and 50 or less.

[0027] The belt layer 18 is an element arranged outside the carcass layer 16 in the tire radial direction, which strongly tightens the carcass layer 16 and increases the rigidity of the tread portion A. The belt layer 18 is provided with a plurality of belts (two belts 18a, 18b in the Fig. 1 illustrated example), which are formed one after the other in the tire radial direction from the inside to the outside.

[0028] The belts 18a, 18b have a structure in which belt cord threads cross each other.

[0029] The tread rubber 20 is an outer covering member of the tire on the tread portion A, which mainly protects the carcass layer 16 and the belt layer 18 from wear and damage.

[0030] The sidewall rubbers 22 are tire outer covering members on the tire widthwise outer side of the tread rubber 20 in the areas from the shoulders B to the sidewall portions C, and are attached to the tire radial direction outer side or the tire widthwise outer side of the carcass layer 16.

[0031] During tire travel, the sidewall rubbers 22 resist repeated bending deformation, protect the carcass layer 16 from external force, and thereby prevent damage.

[0032] The inner liner 24 is a band-shaped rubber sheet member attached to the inner circumferential surface of the tire, which covers the carcass layer 16 and prevents oxidation by exposure of the carcass layer 16 and leakage of the air with which the tire is filled.

[0033] In a pneumatic tire 1 according to the present embodiment, which provides the above-described components 12, 14, 16, 18, 20, 22, 24, the vehicle installation direction may be specified or unspecified.

[0034] In addition, main grooves are provided on the surface of the tread portion A on the pneumatic tire 1 as shown in Fig. 1 illustrated (tread surface).

[0035] Here, main grooves refer to grooves with a width of 3 mm or more and a depth of 2.5 mm or more.

[0036] In addition, the main grooves described above include main grooves extending in each direction, which define various tread patterns formed on the tread surface.

[0037] Namely, the main grooves described above may be main grooves extending in the tire circumferential direction (hereinafter sometimes referred to as "main circumferential groove") or main grooves inclined in the tire circumferential direction (including main grooves extending in the tire width direction, hereinafter referred to as "inclined main grooves").

[0038] In addition, when the above-mentioned main grooves are inclined main grooves, such grooves naturally include main grooves for which at least one end is connected to the circumferential main grooves and main grooves which are not connected.

[0039] In addition, Fig. 1 illustrates four main grooves 26a, 26b, 26c and 26d as such main grooves.

[0040] Under such a premise, in the present embodiment, the total width SW, the outer diameter OD and the inner diameter ID are hereby defined as follows.

[0041] In particular, the total width SW (see Fig. 1) the maximum length of a pneumatic tire 1 in the width direction of the tire when mounted on a rim and inflated to a specified air pressure in the unloaded condition, including design features formed on the outer surface of the sidewall portions C. “Outer diameter OD” (see Fig. 1) is the maximum length in the tire radial direction when a pneumatic tire 1 is mounted on a rim.

[0042] “Inner diameter ID” (see Fig. 1) refers to a length that is usually defined as a length of the rim diameter minus the thickness of the rim.

[0043] In the present embodiment, the units of total width SW, outer diameter OD and inner diameter ID are all in mm.

[0044] Based on these definitions, in a pneumatic tire 1 of the present embodiment, the total width SW and the outer diameter OD satisfy the relationship SW / OD ≤ 0.3 and the inner diameter ID and the outer diameter OD satisfy the relationship ID / OD ≥ 0.7.

[0045] Next, in the present embodiment, as shown in Fig.1 illustrates, in a tire meridian cross-section, on each side in the tire width direction with the tire equatorial plane CL therebetween, a pair of imaginary first boundary lines b1 at the intersection point of an extension line of a shoulder arc a1 and an extension line of a side arc a2 and perpendicular to the tire inner peripheral surface, and a pair of imaginary second boundary lines b2 passing through the rim inspection line L and perpendicular to the tire inner peripheral surface; wherein regions between the first boundary lines b1 and the second boundary lines b2 are first regions R1, respectively, and regions further inward from the second boundary lines b2 in the tire radial direction are second regions R2, respectively.

[0046] Here, the shoulder arc a1 means an arc describing the contours of the road contact surface of the land portion provided on the outermost side of the tread portion A in the tire width direction, and the side arcs a2 mean arcs describing the contours of the sidewall profiles of the land portion provided on the outermost side of the tread portion A in the tire width direction.

[0047] In addition, although not illustrated in the present embodiment, profile lines on the tire outer circumference of a grade in which further arcs are laid between the shoulder arc a1 and the side arcs a2 are considered.

[0048] However, the present embodiments include exceptions in which the other arcs are not present, in which case the shoulder arc a1 and the side arcs a2 are adjacent.

[0049] Therefore, if the other arcs described above are not present, the intersection point of the extension line of the shoulder arc a1 described above and the extension lines of the side arcs a2 is replaced with the intersection point of shoulder arc a1 and the side arcs a2.

[0050] Based on these definitions, in a pneumatic tire 1 of the present embodiment, the area X1 (mm 2 ) of the first regions R1 and the circumferential length Y1 (mm) of the inner circumferential surfaces of the first regions R1 have a ratio X1 / Y1 of 12 or greater and 30 or less.

[0051] In addition, the area X2 (mm 2 ) of the second regions R2 and the circumferential length Y2 (mm) of the inner circumferential surfaces of the second regions have a ratio X2 / Y2 of 10 or greater and 15 or less. (effects and the like)

[0052] In the present embodiment, the total width SW and the outer diameter OD have a ratio SW / OD of 0.3 or less.

[0053] Therefore, it is possible to sufficiently narrow the overall width SW relative to the outer diameter OD, reducing the projected area of ​​the front of a tire. As a result, it is possible to reduce a tire's air resistance and improve fuel economy performance.

[0054] Typically, however, narrowing the overall width SW relative to the outer diameter OD reduces the length of the contact patch in the tire width direction. This results in a lack of sufficient cornering stiffness, making it difficult to achieve superior steering stability performance.

[0055] Therefore, in the present embodiment, the inner diameter ID and the outer diameter OD have a ratio ID / OD of 0.7 or greater, reducing the cross-sectional height.

[0056] Therefore, it is possible to generate sufficient cornering force when turning a vehicle and consequently demonstrate superior steering stability performance.

[0057] Next, in the present embodiment, as described above, for specific regions (first regions and second regions) having the areas (X1, X2) and inner peripheral surfaces having peripheral lengths (Y1, Y2), the ratios (X1 / Y1, X2 / Y2) thereof are regulated. The ratio of the surface areas of the specific regions and the peripheral lengths of their inner peripheral surfaces, that is, the value of the surface areas of the specific regions divided by the peripheral lengths of the inner peripheral surfaces, is the value indicating the average value (average width) of the width measured along a direction perpendicular to the extending direction (the longitudinal direction) of these regions.

[0058] Therefore, this value can serve as an index expressing the stiffness and inflexibility in the deformation direction of the specific areas during tire rolling.

[0059] Typically, it is not possible to adequately secure sidewall areas capable of deformation during tire rolling when the ID / OD ratio of the inner diameter ID and outer diameter OD is increased, making it difficult to realize superior load resistance.

[0060] However, in the present embodiment, the first regions (second regions) have a ratio X1 / Y1 (ratio X2 / Y2) of 12 or greater (10 or greater), which makes it possible to secure sufficient rigidity in the deformation direction of the first regions (second regions) during tire rolling and to demonstrate superior steering stability performance.

[0061] In addition, the first areas (second areas) have a ratio X1 / Y1 (ratio X2 / Y2) of 12 or greater (10 or greater), which makes it possible to control the bending of predetermined areas during tire rolling and demonstrate superior load resistance.

[0062] On the other hand, the first areas (second areas) have a ratio X1 / Y1 (ratio X2 / Y2) of 30 or less (15 or less), which makes it possible to avoid an excessive increase in the center width, limit an increase in tire weight, and consequently demonstrate superior fuel saving performance.

[0063] Furthermore, it is possible to demonstrate these effects to a greater extent when the ratio X1 / Y1 (ratio X2 / Y2) is 14 (11) or greater and 28 (14) or less.

[0064] As shown above, a pneumatic tire according to the present embodiment makes it possible, in particular, to improve fuel saving performance, steering stability performance, and load durability by appropriately controlling the relationship between overall width SW and outer diameter OD, the relationship between inner diameter ID and outer diameter OD, and the shapes of predetermined regions in a tire meridian cross section in a well-coordinated manner.

[0065] Furthermore, a pneumatic tire according to the present embodiment can be obtained through ordinary manufacturing steps as shown above; that is, a tire material mixing step, a tire material processing step, a tire green compact molding step, a vulcanization step, an inspection step subsequent to the vulcanization step, etc.

[0066] When a pneumatic tire is manufactured according to the present invention, the tire green molding step and vulcanization are carried out such that a tire mounted on a rim and inflated to a predetermined air pressure after completion of the post-vulcanization inspection step satisfies the above-described relationship between the total width SW and the outer diameter OD, the relationship between the inner diameter ID and the outer diameter OD, and the shape of the predetermined regions in a tire meridian cross section. [Additional embodiments]

[0067] Next, additional embodiments 1 to 8, which can be optionally implemented in contrast to the basic embodiment of the pneumatic tire according to the present invention described above, will be described. (Additional Embodiment 1)

[0068] In the basic embodiment, if the Fig.1 illustrated area between the first pair of boundary lines b1, b1 is defined as a third area R3, have the area X3 (mm 2 ) of the third region R3 and the circumferential length Y3 (mm) of the inner circumferential surface of the third region R3 has a ratio X3 / Y3 of preferably 11 or greater and 15 or less (Additional Embodiment 1).

[0069] Here the value of the area X3 (mm 2 ) of the third region R3, divided by the circumferential length Y3 (mm) of the inner circumferential surface, the value indicating the mean value (average width) of width measured along a direction perpendicular to the extending direction (the tire width direction) of the third region R3.

[0070] Therefore, it is possible for this value to serve as an index for determining the stiffness in the deformation direction of the third region R3 during tire rolling and the maximum groove depth that can be established on the tread portion A.

[0071] From this point of view, the ratio X3 / Y3 of 11 or greater makes it possible to ensure an adequate depth of the grooves arranged on the tread portion A and consequently increases the tire drainage performance.

[0072] In addition, a ratio X3 / Y3 of 15 or less makes it possible to prevent an excessive increase in the thickness of the tread portion, limit the tire weight and consequently improve the rolling resistance and also the fuel economy performance.

[0073] In addition, the X3 / Y3 ratio of 15 or less makes it possible to restrict the thickness of the tread portion and inhibit the collapse of the land portion during turning of the vehicle, thereby further improving the steering stability performance.

[0074] Furthermore, it is possible to demonstrate these effects to a greater extent when the ratio X3 / Y3 is 12 or greater and 14 or less. (Additional Embodiment 2)

[0075] In the basic embodiment and an embodiment combining the basic embodiment with Additional Embodiment 1, the ratio X1 / Y1 is preferably larger than the ratio X2 / Y2 (Additional Embodiment 2).

[0076] The fact that the ratio X1 / Y1 is greater than the ratio X2 / Y2 makes it possible to further increase the average width of the first areas for which the bending stress during tire rolling is relatively large.

[0077] Therefore, it is possible to inhibit the bending of the side wall portions C and consequently further improve the load resistance. (Additional Embodiment 3)

[0078] Fig.2 is an enlarged tire meridian cross-sectional view of one side of the pneumatic tire in the Fig. 1 illustrated tire width direction.

[0079] In the basic embodiment and an embodiment which, as in Fig.2 illustrates the basic embodiment combined with the additional embodiment 1 or 2, in a tire meridian cross section, when a tread apex T is defined as the intersection point of a profile line of an outer peripheral surface of the tire and an equatorial plane of the tire CL, a pair of imaginary third boundary lines b3 perpendicular to the inner peripheral surface of the tire respectively pass through positions on the outer peripheral surface of the tire at a distance 0.25 times the tire section height SH from the tread apex, and every fourth region is defined as a region between the second boundary lines b2 and third boundary lines b3, then a maximum tire thickness position in the first regions R1 is preferably present in the fourth region (additional embodiment 3).

[0080] Here, “fourth areas R4” refers to portions located inward in the tire radial direction, within the first areas R1 specified as areas between the first gauge lines b1 and second gauge lines b2.

[0081] In addition, the tire section height SH is the value obtained by subtracting the tire inner diameter ID from the tire outer diameter OD divided by 2.

[0082] In addition, “maximum tire thickness” refers to the length of the longest line segment that can be drawn perpendicular to the inner circumferential surface of the tire within the first areas R1.

[0083] By having the maximum thickness positions in the first regions R1 within the fourth regions R4, it is possible to increase the thickness of the fourth regions R4 for which the bending stress during tire rolling is large even within the first regions R1, and further increase the load resistance. (Additional Embodiment 4)

[0084] In the basic embodiment and an embodiment which, as in Fig.2 illustrates the basic embodiment combined with the additional embodiments 1 to 3, in a tire meridian cross section, when a tread apex T is defined as the intersection point of a profile line of an outer peripheral surface of the tire and an equatorial plane of the tire CL, a pair of imaginary third boundary lines b4 perpendicular to the inner peripheral surface of the tire respectively pass through positions on the outer peripheral surface of the tire at a distance 0.5 times the tire section height SH from the tread apex T, and every fifth region is defined as a region between the first boundary lines b1 and fourth boundary lines b4, then there is a variation in the tire thickness in the fifth regions R5 of preferably 2 mm or less (additional embodiment 4).

[0085] Here, “fifth areas R5” refers to portions located outward in the tire radial direction, within the first areas R1 specified as areas between the first gauge lines b1 and second gauge lines b2.

[0086] The variation of the tire thickness in the fifth regions R5 is 2 mm or less and, in particular, makes it possible to avoid excessively increasing fluctuation in the tire thickness in the fifth regions, to inhibit local stress in a part of the fifth regions during tire rolling and, consequently, to further increase the load resistance.

[0087] Furthermore, it is possible to demonstrate these effects to a greater extent when the variation of tire thickness in the fifth areas R5 is 1 mm or less. (Additional Embodiment 5)

[0088] In the basic embodiment and an embodiment which, as in Fig. 1 and Fig.2, combining the basic embodiment with at least one additional embodiment 1 to 4, crescent-shaped side reinforcing rubber 28 can be arranged in a tire meridian cross section within the tire width direction of the carcass layer 16 (additional embodiment 5).

[0089] Here, sidewall rubber 28 is harder rubber compared to sidewall rubber 22 and is normally used in run-flat tires.

[0090] When crescent-shaped side reinforcing rubber 28 is arranged within the carcass layer 16 in the tire width direction, it is possible to further reduce deformation of the shoulder portion B and the sidewall portions C during tire rolling and hence further improve load resistance.

[0091] In addition, if the Fig. 1 and Fig.2, the side reinforcing rubber 28 prevents flexion of the tire even when the tire is punctured and the air pressure drops to 100 kPa or below, making it possible to travel a certain distance at a constant speed. (Additional Embodiment 6)

[0092] In an embodiment combining the basic embodiment with at least one Additional Embodiment 5, the loss tangent (tan δ) of the side reinforcing rubber at 60°C is preferably 0.01 or greater and 0.1 or less (Additional Embodiment 6).

[0093] In the present invention, the loss tangent (tan δ) is measured using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisaku-sho, Ltd.) under conditions of 20 Hz frequency, initial strain 10%, dynamic strain ±2%, and a temperature of 60 °C in accordance with JIS-K6394.

[0094] In general, the loss tangent (tan δ) can express an index of energy loss along with a so-called loss modulus. In the present embodiment, the loss tangent (tan δ) of the side reinforcing rubber at 60°C is 0.1 or less, which makes it possible to suppress heat buildup during tire rolling in the areas from the sidewall portions B to the sidewall portions C.

[0095] As a result, it is possible to further reduce rolling resistance and improve fuel economy performance, limit wear caused by heat buildup, and further improve load durability. (Additional Embodiment 7)

[0096] In an embodiment combining the basic embodiment with at least one Additional Embodiment 5, the loss tangent (tan δ) of the side reinforcing rubber at 20°C is preferably 60 or greater and 80 or less (Additional Embodiment 7).

[0097] In the present invention, “JIS hardness” means durometer hardness as measured according to JIS K-6253 using a Type A durometer at a temperature of 20 °C.

[0098] The JIS-A hardness of the reinforced rubber at 20 °C of 60 or more makes it possible to increase the rigidity of the areas from the shoulder portions B to the sidewall portions C and suppress deformation during tire rolling.

[0099] As a result, it is possible to suppress the wear caused by the improved rigidity and further improve the load resistance.

[0100] In addition, the JIS-A hardness of the reinforced rubber at 20 °C of 80 or less makes it possible to avoid an excessive increase in rigidity in the areas from shoulder sections B to sidewall sections C and consequently increase ride comfort. (Additional Embodiment 8)

[0101] As in Fig.1, reference points P1, P2 are defined as intersection points of the first boundary lines b1 and a profile line of the outer peripheral surface of the tire on both sides in the tire width direction, and a stretched tread width (TDW) is defined as the length along the profile line on the outer peripheral surface of the tire between the two reference points P1, P2.

[0102] In addition, as in Fig. 1, the intersection point P3 of the profile line of the outer peripheral surface of the tire and the equatorial plane of the tire CL is defined as the tread apex P3, and an angle θ is defined as an angle of the line segment connecting the reference points P1 (P2) and the tread apex P3 relative to the tire width direction.

[0103] Under such a premise, in the basic embodiment and an embodiment combining the basic embodiment with at least one Additional Embodiment 1, the stretched tread width TDW and the total width SW have a ratio TDW / SW of 0.8 or greater and less than 1, and the angle θ is 1° or greater and 5° or less (Additional Embodiment 8).

[0104] In addition, the Fig. 1 is an exaggerated size compared to the actual dimension in order to clarify how to take the angle θ, and should not be assumed to be the actual size in the present embodiment.

[0105] The TDW / SW ratio of 0.8 or greater makes it possible to ensure adequate contact width, simplify the generation of cornering force and consequently further improve steering stability performance.

[0106] In addition, the TDW / SW ratio of less than 1 enables adequate rolling resistance reduction effects to be realized and fuel saving performance to be further improved.

[0107] Next, the angle θ of 1° or more makes it possible to prevent an excessive increase in contact pressure in the areas on the outside in the tire width direction of the Fig. 1 illustrated tread section A and to further improve the steering stability performance.

[0108] In addition, the angle θ of 5° or smaller makes it possible to avoid an excessive increase in contact pressure in the areas in the center of the tire width direction of the tread portion A and further improve the steering stability performance.

[0109] Furthermore, it is possible to demonstrate these respective effects to a greater extent when the ratio TDW / SW is 0.86 or greater and 0.98 or less and the angle θ is 2° or greater and 4° or less. Examples

[0110] Pneumatic tires were manufactured according to Comparative Examples 1 to 2 and Application Examples 1 to 11 with tire size 155 / 55R20, wherein each of the components (except for side reinforcing rubber 28) in Fig.1 and wherein the conditions shown in Table 1-1, 1-2 or 1-3 are met (total width SW, outer diameter OD, inner diameter ID, the ratio X1 / Y1, where X1 is an area of ​​a first region R1 and Y1 is a circumferential length of an inner circumferential surface, the ratio X2 / Y2, where X2 is an area of ​​a second region R2 and Y2 is a circumferential length of an inner circumferential surface, the ratio X3 / Y3, where X3 is an area of ​​a third region R3 and Y3 is a circumferential length of an inner circumferential surface Y3, the position of maximum tire thickness in the first region R1, variation of tire thickness in the fifth region, presence or absence of side reinforcing rubber 22, loss tangent (tan δ) of side reinforcing rubber at 60 °C, JIS-A hardness of side reinforcing rubber at 20 °C, the ratio TDW / SW, where TDW is an extended tread width and SW is a total width SW, and angle θ).

[0111] In contrast, a pneumatic tire was manufactured in a prior art example with tire size 205 / 55R16 and each of the components in Fig. 1 (except for side reinforcing rubber 28), and met the conditions shown in Table 1-1.

[0112] Therefore, each of these test tires prepared in Prior Art Example, Comparative Examples 1 to 2, and Application Examples 1 to 11 was evaluated for fuel economy performance, steering stability performance, and load durability.

[0113] The results are also shown in Table 1-1 to Table 1-3. (Fuel saving performance)

[0114] Each test tire was mounted on a rim and installed on a front-wheel drive vehicle with an 1800 cc displacement. After the vehicle was driven 50 times around a 2 km test track at a speed of 100 km / h, the fuel consumption rate was calculated. Then, using the fuel consumption rate of the prior art example as a reference (100), the fuel economy improvement rate was calculated for each application example.

[0115] Higher numerical values ​​indicate higher fuel economy performance. (steering stability)

[0116] Each test tire was mounted on a rim and installed on a front-wheel-drive vehicle with an 1800 cc engine. The vehicle was then driven three times around a 2 km test track while simultaneously changing lanes. A functional evaluation was obtained from three drivers, and the average of the evaluation values ​​was calculated.

[0117] Then, an index evaluation was performed based on the results measured using the prior art example as a reference (100).

[0118] Higher index values ​​indicate better steering stability. (Load resistance)

[0119] Load resistance tests specified by JISD-4230 were conducted using a drum testing machine for drum diameters of 1707 mm.

[0120] During these tests, the load was increased by 20% of the maximum load capacity every five hours and the distance traveled at the time of tire failure was measured.

[0121] Then, the endurance improvement rate was calculated based on the measured results using the prior art example as a reference, and the index evaluation was performed using the prior art example as a reference (100).

[0122] Higher index values ​​indicate better load resistance.

[0123] The results are shown in Tables 1-1, 1-2 and 1-3. [Table 1-1] Example of the state of the art Application example 1 Application example 2 Application example 3 Application example 4 SW / OD ratio 0,33 0,24 0,24 0,24 0,24 ID / OD ratio 0,64 0,74 0,74 0,74 0,74 Ratio X1 / Y1 11 14 14 20 20 Ratio X2 / Y2 9 15 15 12 12 Ratio X3 / Y3 10 10 13 13 13 Positions of maximum thickness of the tire in first areas R1 Fourth areas R outer Fourth areas R outer Fourth areas R outer Fourth areas R outer Fourth areas R inner Variation of tire thickness in fifth areas R5 (mm) 3 3 3 3 3 Presence of side-reinforcing rubber No No No No No Loss tangent (tan δ) of side-reinforcing rubber at 60 °C JIS-A hardness of side-reinforcing rubber at 20 °C - - - - - TDW / SW ratio 0,75 0,75 0,75 0,75 0,75 Angle θ (°) 6 6 6 6 6 (Fuel saving performance) 100 100,3 100,3 100,3 100,3 Steering stability performance 100 105 110 110 110 Load resistance 100 110 110 115 117 [Table 1-2] Application example 5 Application example 6 Application example 7 Application example 8 Application example 9, according to the invention SW / OD ratio 0,24 0,24 0,24 0,24 0,24 ID / OD ratio 0,74 0,74 0,74 0,74 0,74 Ratio X1 / Y1 20 20 20 20 20 Ratio X2 / Y2 12 12 12 12 12 Ratio X3 / Y3 13 13 13 13 13 Positions of maximum width of the tire in first areas R1 Fourth areas R inner Fourth areas R inner Fourth areas R inner Fourth areas R inner Fourth areas R inner Variation of tire thickness in fifth areas R5 (mm) 2 2 2 2 2 Presence of side-reinforcing rubber No Available Available Available Available Loss tangent (tan δ) of side-reinforcing rubber at 60 °C 0,12 0,08 0,08 0,08 0,08 JIS-A hardness of side-reinforcing rubber at 20 °C - 0,11 0,09 0,09 0,09 TDW / SW ratio 0,75 0,75 0,75 0,9 0,9 Angle θ (°) 6 6 6 6 4 (Fuel saving performance) 100,3 100,2 100,2 100,2 100,2 Steering stability performance 110 110 110 110 115 Load resistance 120 123 124 125 125 [Table 1-3] Application example 10 Application example 11 Comparison example 1 Comparison example 2 SW / OD ratio 0,24 0,24 0,24 0,24 ID / OD ratio 0,74 0,74 0,74 0,74 Ratio X1 / Y1 30 14 11 20 Ratio X2 / Y2 15 15 9 9 Ratio X3 / Y3 10 15 10 10 Positions of maximum thickness of the tire in first areas R1 Fourth areas R outer Fourth areas R outer Fourth areas R outer Fourth areas R outer Change in tire thickness in fifth areas R5 (mm) 3 3 3 3 Presence of side-reinforcing rubber No No No No Loss tangent (tan δ) of side-reinforcing rubber at 60 °C JIS-A hardness of side-reinforcing rubber at 20 °C - - - - TDW / SW ratio 0,75 0,75 0,75 0,75 Angle θ (°) 6 6 6 6 (Fuel saving performance) 100,3 100,3 100,3 100,3 Steering stability performance 110 115 95 110 Load resistance 110 110 95 97

[0124] According to Tables 1-1, 1-2 and 1-3, a pneumatic tire according to Application Examples 1 to 11 within the technical scope of the present invention (the relationship of total width SW and outer diameter OD, the relationship of inner diameter ID and outer diameter OD and the shape of predetermined regions in a tire meridian cross section satisfy predetermined conditions) improves fuel economy performance, steering stability performance and load durability in a well-balanced manner better than the pneumatic tire in the prior art example.

[0125] On the other hand, the tire in Comparative Example 1 has a ratio X1 / Y1, ratio X2 / Y2 and ratio X3 / Y3 and a tire size of 155 / 55R20 like the prior art example, and therefore, the fuel saving performance is improved, but the steering stability performance and load durability are reduced.

[0126] The tire in Comparative Example 2 only had the ratio X1 / Y1 larger than that in the prior art example, and therefore had insufficient improvement effects for load resistance. List of reference symbols 1 pneumatic tire 12 tire bead core 14 bead fillers 16 carcass layers 18 Belt layer 18A, 18B belt 20 Tread rubber 22 Sidewall rubber 24 Inner core 26A, 26B, 26C, 26D main groove 28 Side reinforcing rubber A tread section B shoulder section C Side wall section CL Equatorial plane of the tire D Tire bead section ID inner diameter OD outer diameter P1, P2 reference points P3 tread vertex R1 First Area R2 Second Area R3 Third Area R4 Fourth Area R5 Fifth Area SW total width TDW Stretched tread width Y1 Circumferential length of the inner circumferential surface of the first areas Y2 Circumferential length of the inner circumferential surface of the second areas Y3 Circumferential length of the inner circumferential surface of the second areas A1 shoulder arch A2 side sheet B1 First boundary line B2 Second boundary line B3 Third boundary line B4 Fourth boundary line θ angle

Claims

[1] Pneumatic tyre (1), comprising: a carcass layer (16) toroidally bridging a pair of tire bead portions (D) and a tread portion (A) by a pair of sidewall portions (C); a total width SW and an outer diameter OD satisfying the relationship SW / OD ≤ 0.3; an inner diameter ID and outer diameter OD that satisfy the relationship ID / OD ≥ 0.7; wherein, in a tire meridian cross-section on each side in the tire width direction with the equatorial plane (CL) of the tire therebetween, an imaginary pair of first boundary lines (b1) passes through the intersection of an extension line of a shoulder arc (a1) and an extension line of a side arc (a2) and is perpendicular to the inner peripheral surface of the tire, and an imaginary pair of second boundary lines (b2) passes through a rim check line (L) and is perpendicular to the inner peripheral surface of the tire; wherein regions between the first boundary lines (b1) and the second boundary lines (b2) are each first regions (R1) and regions further inside from the second boundary lines (b2) in the tire radial direction are each second regions (R2); where the area X1 (mm 2 ) of the first region (R1) and the circumferential length Y1 (mm) of the inner circumferential surface of the first region (R1) have a ratio X1 / Y1 of 12 or greater and 30 or less; and where the area X2 (mm 2 ) of the second region (R2) and the circumferential length Y2 (mm) of the inner circumferential surface of the second region (R2) have a ratio X2 / Y2 of 10 or greater and 15 or less; wherein the reference points (P1, P2) are the intersection points of the first boundary lines (b1) on both sides in the tire width direction and a profile line of the outer peripheral surface of the tire, and an extended tread width TDW is the length along the profile line between the two reference points (P1, P2); wherein a tread apex (P3, T) is an intersection point of the profile line and equatorial plane (CL) of the tire and an angle θ is an angle of a line segment connecting the reference point and the tread apex (P3, T) relative to the tire width direction; wherein the stretched tread width TDW and a total width SW have a ratio TDW / SW of 0.8 or greater and 1 or less; and the angle θ is 1° or greater and 5° or less. [2] A pneumatic tire (1) according to claim 1, wherein the area between the pair of first boundary lines (b1) is a third area (R3), wherein for the area X3 (mm 2 ) of the third region (R3) and the circumferential length Y3 (mm) of the inner circumferential surface of the third region (R3) is a ratio X3 / Y3 of 11 or greater and 15 or less. [3] A pneumatic tire (1) according to claim 1 or 2, wherein the ratio X1 / Y1 is greater than the ratio X2 / Y2. [4] A pneumatic tire (1) according to any one of claims 1 to 3, wherein in a tire meridian cross-section, a tread apex (P3, T) is the intersection point of a profile line of an outer peripheral surface of the tire and an equatorial plane (CL) of the tire, a pair of imaginary third boundary lines (b3) are perpendicular to the inner peripheral surface of the tire and each pass through positions on the outer peripheral surface of the tire at a distance of 0.25 times the tire section height from the tread apex (P3, T), each fourth region (R4) is a region between the second boundary line (b2) and the third boundary line (b3), a position of maximum tire thickness being present in the first region (R1) in the fourth regions (R4). [5] A pneumatic tire (1) according to any one of claims 1 to 4, wherein in a tire meridian cross section, a tread apex (P3, T) is the intersection point of a profile line of an outer peripheral surface of the tire and an equatorial plane (CL) of the tire, a pair of imaginary third boundary lines (b3) are perpendicular to the inner peripheral surface of the tire and each pass through positions on the outer peripheral surface of the tire at a distance of 0.5 times the tire section height from the tread apex (P3, T), each fifth region (R5) is a region between the first boundary line (b1) and the fourth boundary line (b4), a variation of the tire thickness in the fifth region (R5) is 2 mm or less. [6] Pneumatic tire (1) according to one of claims 1 to 5, wherein in a tire meridian cross section, sickle-shaped side-reinforcing rubber is arranged inside in the tire width direction of the carcass layer (16). [7] A pneumatic tire (1) according to claim 6, wherein the loss tangent (tan δ) of the side reinforcing rubber at 60°C is 0.01 or greater and 0.1 or less. [8] A pneumatic tire (1) according to claim 6 or 7, wherein the JIS-A hardness of the side reinforcing rubber at 20°C is 60 or more and 80 or less.

Images