Pneumatic tire

Abstract

To provide a pneumatic tire that is configured so that reduction of rolling resistance and uneven wear in a shoulder region can be suppressed, even in a high load-type passenger automobile.SOLUTION: In a state where a pneumatic tire is mounted on a normal rim and is filled with normal internal pressure, a ratio A / B of a rectangular rate A at the time when a load corresponding to 130% of a maximum load is applied to the tire and a rectangular rate B at the time when a load corresponding to 100% of the maximum load is applied thereto is 100% or more and 110% or less. Respective tire standards of the normal rim, the normal internal pressure and the maximum load are based on ETRTO. The rectangular rate is L2 / L1, where a tread grounding length that is a length in a tire circumferential direction on a tire equator is set as L1 in a tire grounding surface shape and a tread grounding length that is a length in the tire circumferential direction at a position shifted by 10 mm from both ends of a grounding width in the tire grounding surface shape to inside is set as L2.SELECTED DRAWING: Figure 4B

Description

[Technical field]

[0001] The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire suitable for use on passenger vehicles with a relatively heavy load. [Background technology]

[0002] Conventionally, reducing rolling resistance has been one of the issues for pneumatic tires for vehicles. For example, a design in which the contact surface of the tread is rectangular is considered to be effective in reducing rolling resistance, but on the other hand, uneven wear is likely to occur in the shoulder regions near both ends of the contact surface shape in the width direction. Patent Document 1 shows a pneumatic tire that reduces rolling resistance and suppresses uneven wear in the shoulder regions by specifying the rectangular ratio of the tire at a load of 75% of the standard maximum load capacity (maximum load) within an appropriate range. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-111357 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, electric vehicles (EVs), which have become increasingly popular in recent years, are heavier than conventional engine-driven passenger cars. For this reason, such heavy-load vehicles require tires that reduce rolling resistance and suppress uneven wear in the shoulder area, even when the maximum load exceeds 100%, for example.

[0005] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide a pneumatic tire that reduces rolling resistance and suppresses uneven wear in the shoulder region even in the case of a heavy-load passenger vehicle. [Means for solving the problem]

[0006] When the pneumatic tire of the present invention is mounted on a regular rim and inflated to the regular internal pressure, the ratio A / B of the rectangularity ratio A at a load of 130% of the maximum load to the rectangularity ratio B at a load of 100% of the maximum load is 100% or more and 110% or less, wherein the regular rim, the regular internal pressure, and the maximum load are all those in accordance with the ETRTO tire standard, and the rectangularity ratio is L2 / L1, where L1 is the tread contact length, which is the circumferential length of the tire at the tire equator in the tire contact surface shape, and L2 is the tread contact length, which is the circumferential length of the tire at positions 10 mm inward from both ends of the contact width of the tire contact surface shape. Effect of the Invention

[0007] According to the present invention, it is possible to provide a pneumatic tire that reduces rolling resistance and suppresses uneven wear in the shoulder region, even in the case of a heavy-load passenger vehicle. [Brief description of the drawings]

[0008] [Figure 1] 1 is a half cross-sectional view in an axial direction of a pneumatic tire according to an embodiment. FIG. [Diagram 2] FIG. 1 is a diagram illustrating a tread pattern of a pneumatic tire according to an embodiment, and is a partial plan view of the tire. [Diagram 3] FIG. 2 is a simplified diagram showing the shape of a tire's contact patch, for explaining the rectangular ratio of the tire. [Figure 4A] FIG. 2 is a contour diagram (contour line map) showing the contact patch shape and the areas of high and low load when the tire of the embodiment is loaded with 100% of the maximum load according to the ETRTO standard. [Figure 4B] FIG. 2 is a contour diagram (contour line map) showing the contact patch shape and the areas of high and low load when a load of 130% of the maximum load according to the ETRTO standard is applied to the tire of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment will be described with reference to the drawings. Fig. 1 is a diagram showing the internal structure of a tire 1, which is a pneumatic tire for vehicles according to an embodiment, and shows a half cross section in the tire axial direction. This tire 1 is suitable as a tire for passenger cars, and is more suitable as a tire for EVs.

[0010] The cross-sectional view of FIG. 1 is an axial cross-sectional view of a tire 1 mounted on a standard rim (not shown) and inflated to a standard internal pressure in an unloaded state.

[0011] A regular rim is a rim that is determined by the tire standard, and in the case of ETRTO, it is called "Measuring Rim." Regular internal pressure is the air pressure that is determined by the tire standard, and in the case of ETRTO, it is called "INFLATION PRESSURE." Regular internal pressure is usually 180kPa for passenger car tires, but 220kPa for tires that are labeled "Extra Load" or "Reinforced." For ETRTO, regular load is called "LOAD CAPACITY."

[0012] The internal structure of the tire 1 is basically symmetrical in a cross section in the tire axial direction. Fig. 1 shows a cross section of the right half of the tire 1, and the left half (not shown) has the same structure. In Fig. 1, the symbol S1 indicates the tire equatorial plane. The tire equatorial plane S1 is a plane perpendicular to the tire rotation axis and located at the center in the tire axial direction.

[0013] Here, the tire axial direction is a direction parallel to the tire rotation axis, and is the left-right direction on the paper in Fig. 1. In Fig. 1, this is illustrated as the tire axial direction X. The tire axially inner side is a direction approaching the tire equatorial plane S1, and is the left side on the paper in Fig. 1. The tire axially outer side is a direction away from the tire equatorial plane S1, and is the right side on the paper in Fig. 1.

[0014] The tire radial direction is a direction perpendicular to the tire rotation axis, and is the up-down direction on the paper in Fig. 1. In Fig. 1, this is illustrated as tire radial direction Y. The outer side in the tire radial direction is a direction away from the tire rotation axis, and is the upper side on the paper in Fig. 1. The inner side in the tire radial direction is a direction approaching the tire rotation axis, and is the lower side on the paper in Fig. 1.

[0015] As shown in FIG. 1, the tire 1 includes a pair of beads 10, a pair of sidewalls 20 extending radially outward from each of the pair of beads 10, a tread 30 disposed between the pair of sidewalls 20, a shoulder 40 which is a transition portion from the sidewalls 20 to the tread 30, a carcass ply 50 disposed spanning between the pair of beads 10, and an inner liner 60 disposed on the tire cavity side of the carcass ply 50.

[0016] The pair of beads 10 are disposed on both axial sides of the tire and on the inner ends in the radial direction of the tire. Each bead 10 has a bead core 11, a bead filler 12 extending from the bead core 11 to the outer side in the radial direction of the tire, and a rim strip rubber 13.

[0017] The bead core 11 is an annular member in which a rubber-coated metal bead wire is wound multiple times in the tire circumferential direction. The bead core 11 is a member that serves to fix the tire 1 filled with air to the rim. The bead filler 12 has a tapered shape that decreases in thickness as it extends from the tire radial inner side to the tire radial outer side. The bead filler 12 is provided to increase the rigidity of the peripheral portion of the bead 10 and ensure high maneuverability and stability. The bead filler 12 is made of, for example, rubber that is harder than the surrounding rubber members.

[0018] The rim strip rubber 13 further surrounds the outside of a carcass ply 50 that is provided surrounding the bead core 11 and the bead filler 12. The rim strip rubber 13 comes into contact with the inner surface of a rim on which the tire 1 is mounted.

[0019] The sidewall 20 includes a sidewall rubber 21 disposed axially outward of the carcass ply 50. The sidewall rubber 21 constitutes the circumferentially outer side surface of the tire 1. The sidewall rubber 21 is the portion that bends the most when the tire 1 performs its cushioning function, and flexible rubber having fatigue resistance is usually used for the sidewall rubber 21.

[0020] A rim line 21c protruding axially outward is formed on an inner end 21a in the tire radial direction of the sidewall rubber 21. The rim line 21c is a circular line extending along the tire circumferential direction.

[0021] The tread 30 includes an endless belt 31, a cap ply 34, and a tread rubber 37. The belt 31 is disposed on the outer side of the carcass ply 50 in the tire radial direction. The cap ply 34 is disposed on the outer side of the belt 31 in the tire radial direction. The tread rubber 37 is disposed on the outer side of the cap ply 34 in the tire radial direction.

[0022] The belt 31 is a member that reinforces the tread 30. The belt 31 of the embodiment has a two-layer structure including an inner belt 32 arranged on the outer side of the inner liner 60 in the tire radial direction, and an outer belt 33 arranged on the outer side of the inner belt 32 in the tire radial direction. Both the inner belt 32 and the outer belt 33 have a structure in which a plurality of belt cords such as steel cords are covered with rubber. The inner belt 32 is wider than the outer belt 33. By providing the belt 31, the rigidity of the tire 1 is ensured, and the contact of the tread 30 with the road surface is improved. Note that the belt 31 is not limited to a two-layer structure, and may have a single layer structure, or a three-layer structure or more.

[0023] The cap ply 34 is a member that reinforces the tread 30 together with the belt 31. The cap ply 34 has a structure in which a plurality of organic fiber cords having insulating properties, such as polyamide fiber, are covered with rubber. The cap ply 34 is wider than the belt 31 and covers the entire belt 31 from the tire outer surface side. An outer end 34a of the cap ply 34 in the tire axial direction is folded toward the tire cavity side to form a double layer, and this end 34a covers the outer ends 32a, 33a of the inner belt 32 and the outer belt 33 in the tire axial direction from the tire outer surface side. By providing the cap ply 34, it is possible to improve the durability of the tire 1 and reduce road noise during driving. The cap ply 34 is not limited to a single-layer structure as in the embodiment, but may have a two-layer structure or a three-layer structure or more.

[0024] The tread rubber 37 is disposed on the outer side of the cap ply 34 in the tire radial direction. The outer surface of the tread rubber 37 constitutes a tread surface 38 that comes into contact with the road surface. A tread pattern 39 is provided on the tread surface 38. An axially outer end 37a of the tread rubber 37 covers an axially outer end 21b of the sidewall rubber. The axially outer end 37a of the tread rubber 37 has a buttress 23a that protrudes axially outward.

[0025] Fig. 2 is a part of a plan view of the tire 1 shown in Fig. 1, and shows a tread surface 38 having a tread pattern 39. The tread pattern 39 is formed of a plurality of lands 70 and a plurality of grooves 80 formed between the lands 70 to partition the lands 70. The tread pattern 39 of the embodiment may be, for example, a rib-type pattern or a rib-lug-type pattern. Note that Fig. 2 shows the tire axial direction X and the tire circumferential direction C.

[0026] The tread pattern 39 has an asymmetrical pattern. The symbol S in Fig. 2 denotes the tire equator. The tire equator S is an imaginary line extending along the tire circumferential direction through the tire axial center of the tread surface 38. The tire equatorial plane S1 includes the tire equator S.

[0027] The land 70 includes two central lands, i.e., a first central land 71 and a second central land 72, and a first shoulder land 73 and a second shoulder land 74, which are disposed on both sides of the tire in the axial direction. The groove 80 includes a first main groove 81 between the first central land 71 and the second central land 72, a second main groove 82 between the first central land 71 and the first shoulder land 73, and a third main groove 83 between the second central land 72 and the second shoulder land 74.

[0028] The first central land 71 is wider than the second central land 72, i.e., the dimension in the tire axial direction is larger than that of the second central land 72. The first central land 71 has a plurality of inclined slits 71a arranged at intervals in the tire circumferential direction. The inclined slits 71a cross the first central land 71 in its width direction (corresponding to the tire axial direction) while inclining with respect to the tire circumferential direction. The first central land 71 also has a plurality of communicating slits 71b that intersect the inclined slits 71a and communicate with the inclined slits 71a. The first central land 71 further has a sipe 71c that communicates with the inclined slits 71a. The sipes 71c are formed in a pair on the left and right in FIG. 2, and the sipe 71c on the left side extends while curving along the tire circumferential direction, and the sipe 71c on the right side extends straight along the tire circumferential direction. The tire equator S passes through the first central land 71 to the right of the sipe 71c on the right side.

[0029] The second central land 72 has a plurality of inclined slits 72a inclined in substantially the same direction as the inclined slits 71a with respect to the tire circumferential direction. The inclined slits 72a open to the third main groove 83 and extend from the opening end toward the first main groove 81, but terminate before reaching the first main groove 81. The second central land 72 has a plurality of sipes 72c extending straight along the tire circumferential direction. These sipes 72c are disposed between the inclined slits 72a and are formed in a state in which they do not communicate with the inclined slits 72a.

[0030] The first shoulder land 73 has multiple transverse slits 73a spaced apart in the tire circumferential direction. The transverse slits 73a extend in a zigzag pattern along the tire axial direction and cross the first shoulder land 73 in its width direction. The first shoulder land 73 has multiple sipes 73c that extend in a curved manner in the tire circumferential direction. These sipes 73c are arranged between the transverse slits 73a and are not connected to the transverse slits 73a.

[0031] The second shoulder land 74 has a plurality of transverse slits 74a spaced apart in the tire circumferential direction. The transverse slits 74a extend while curving along the tire axial direction and cross the second shoulder land 74 in its width direction. The second shoulder land 74 has a plurality of sipes 74c extending straight along the tire circumferential direction. These sipes 74c are disposed between the transverse slits 74a and are formed so as not to communicate with the transverse slits 74a.

[0032] The first main groove 81 divides the first central land 71 and the second central land 72. The first main groove 81 extends straight in the tire circumferential direction. The second main groove 82 divides the first central land 71 and the first shoulder land 73. The second main groove 82 extends in a zigzag shape along the tire circumferential direction. The third main groove 83 divides the second central land 72 and the second shoulder land 74. The third main groove 83 extends straight in the tire circumferential direction.

[0033] The above-mentioned slits are grooves with a width exceeding 1 mm, and the sipes are grooves with a width of 1 mm or less. The main grooves are grooves that are wider than the slits and are formed in an annular shape around the entire circumference of the tire.

[0034] 1, the shoulder 40 is a portion where the sidewall 20 transitions to the tread 30. The shoulder 40 includes an end 37a of the tread rubber 37 on the outer side in the tire axial direction.

[0035] The carcass ply 50 is laid between a pair of beads 10. The carcass ply 50 is embedded inside the tire 1 in a manner that the carcass ply 50 passes between the pair of beads 10, through a pair of sidewalls 20, a pair of shoulders 40, and the tire cavity side of the tread 30. In the tread 30, a belt 31 is disposed on the outer side of the carcass ply 50 in the tire radial direction.

[0036] The carcass ply 50 includes a plurality of ply cords (not shown) that form the framework of the tire 1. The plurality of ply cords extend, for example, along a plane along the tire axial direction, and are arranged side by side in the tire circumferential direction. The ply cords are made of insulating organic fiber cords such as polyester or polyamide. The carcass ply 50 is formed by covering the plurality of ply cords with rubber.

[0037] The carcass ply 50 includes a ply main body 50A and a pair of turned-up portions 50B. The ply main body 50A is a portion that extends from the tread 30 through a pair of shoulders 40 and a pair of sidewalls 20 toward the axially inner side of each of the pair of beads 10. The pair of turned-up portions 50B are portions that are folded back toward the radially outer side of the tire by being wound from the ply main body 50A around each of the pair of bead cores 11, and extend along the sidewalls 20.

[0038] The ply body 50A is disposed on the inner side of the belt 31 and the shoulder pad 41 in the tread 30 in the tire radial direction, and on the inner side of the sidewall rubber 21 in the tire axial direction in the sidewall 20. The turned-up portion 50B is wound around the bead core 11 from the inner side to the outer side in the tire axial direction, and then extends outward in the tire radial direction along the sidewall 20, and reaches the outer end of the tread 30 in the tire axial direction. The part of the turned-up portion 50B that is outer in the tire radial direction than the bead filler 12 is overlapped on the outer side of the ply body 50A in the tire axial direction. The end of the turned-up portion 50B is sandwiched between the outer end of the belt 31 in the tire axial direction and the ply body 50A, and the tip 50b is located axially inner than the axial tip 33b of the outer belt 33.

[0039] The rim strip rubber 13 of the bead 10 described above surrounds the end of the carcass ply 50 on the inner side in the radial direction of the tire, the end winding around the bead core 11 .

[0040] Although the carcass ply 50 in the embodiment has a single layer structure, the carcass ply 50 may have two layers, or three or more layers. When the carcass ply 50 has a single layer structure, it is preferable in that the tire 1 can be made lighter.

[0041] The inner liner 60 covers the inner surface of the ply body portion 50A of the carcass ply 50 between a pair of beads 10 to form the tire cavity surface. The inner liner 60 of the embodiment has a two-layer structure having a first inner liner 61 on the tire cavity side and a second inner liner 62 overlapped on the tire outer surface side of the first inner liner 61. Each of the inner liners 61, 62 is made of air permeability resistant rubber. The inner liner 60 prevents air in the tire cavity from leaking to the outside. The inner liner 60 may have a single-layer structure instead of a two-layer structure. At the tire radial inner part of the bead 10 on the tire axial inner side, the rim strip rubber 13 covers the inner liner 60 to form a part of the tire cavity surface.

[0042] In the tire 1 of the embodiment, a reinforcing rubber layer 65 is provided from the radially outer portion of the sidewall 20 through the shoulder 40 to the axially outer portion of the tread 30. The reinforcing rubber layer 65 is sandwiched between the second inner liner 62 and the ply main body portion 50A of the carcass ply 50.

[0043] Here, the rubber used for the bead filler 12 has a hardness higher than at least the sidewall rubber 21 and the inner liner 60. The hardness of the rubber is a hardness measured by "JIS K6253-3:2012 durometer hardness type A".

[0044] For example, when the hardness of the sidewall rubber 21 is used as a standard, the hardness of the bead filler 12 is preferably about 1.2 to 2.3 times the hardness of the sidewall rubber 21. The hardness of the rim strip rubber 13 is more preferably about 1 to 1.6 times the hardness of the sidewall rubber 21. By setting the hardness in this range, a balance between the flexibility of the tire and the rigidity in the vicinity of the bead 10 can be ensured.

[0045] The above is the internal structure and tread pattern 39 of the tire 1 according to the embodiment. This tire 1 has the following characteristics regarding the rectangular ratio when in contact with the road surface. Note that the regular rim, regular internal pressure, and maximum load described below are in accordance with the ETRTO tire standards.

[0046] The rectangularity of a tire indicates the degree of rectangularity of the tire's contact patch when the tire is mounted on a standard rim, inflated to the standard internal pressure, and in contact with the road surface. It is the ratio of the circumferential length of the tire contact patch at a position 10 mm inward from both axial ends of the tire to the circumferential length of the tire at the axial center of the tire's contact patch, i.e., at the tire equator.

[0047] Fig. 3 is a simplified diagram showing the tire contact patch shape and is a diagram for explaining the rectangular ratio of the tire. In Fig. 3, in the contact patch shape F of the tread surface 38 of the tire 1 of the embodiment, the tread contact length in the tire circumferential direction on the tire equator S is indicated by L1, the tread contact length in the tire circumferential direction at a position 10 mm inward from both ends of the contact width W is indicated by L2, and the rectangular ratio is L2 / L1. Note that the actual L2 may differ between the left and right, so the average of both is taken.

[0048] In the embodiment, when the tire 1 is mounted on a standard rim and inflated to the standard internal pressure, the rectangularity ratio L2 / L1 at a load of 130% of the maximum load is defined as A, and the rectangularity ratio L2 / L1 at a load of 100% of the maximum load is defined as B, and the ratio A / B is specified as being 100% or more and 110% or less.

[0049] When the A / B is 100% or more and 110% or less, uneven wear of the shoulder 40 including the first shoulder land 73 and the second shoulder land 74 is suppressed under high load, thereby improving steering stability. Furthermore, by suppressing uneven wear of the shoulder 40, distortion is less likely to occur in the shoulder 40, and as a result, rolling resistance is reduced. Note that when the A / B is below 100%, the shoulder 40 is less likely to contact the ground, resulting in reduced steering stability. On the other hand, when the A / B is above 110%, the shoulder 40 is more susceptible to wear and uneven wear is more likely to occur.

[0050] As described above, the tire 1 of the embodiment is suitable for passenger cars, and is particularly suitable as a tire for EVs. In general, the rectangularity ratio of a tire for passenger cars at 100% load of the maximum load of the tire standard ETRTO is about 0.8 to 1 (80% to 100). In tires for high-load vehicles such as EVs, the greater the load (for example, about 130% of the maximum load), the greater the load on the shoulder, and the more likely the ground contact surface shape becomes square or drum-shaped. If the ground contact surface shape becomes square rather than elliptical, excessive load is applied to the shoulder, and uneven wear of the shoulder is likely to occur. However, as in the tire 1 of the embodiment, when the ratio A / B between the rectangularity ratio A at 130% load of the maximum load and the rectangularity ratio B at 100% load of the maximum load is 100% to 110%, the squareness of the ground contact surface shape is suppressed. This suppresses uneven wear of the shoulder 40, improving steering stability and reducing rolling resistance.

[0051] In the tire 1 of the embodiment, the tread length L1 under 130% load is preferably 112% to 120% of the tread length L1 under 100% load. Furthermore, the tread length L2 under 130% load is preferably 115% to 125% of the tread length L2 under 100% load. With these characteristics, the A / B ratio is likely to be 100% to 110%.

[0052] The tire 1 according to the embodiment described above provides the following advantages.

[0053] (1) When a tire 1 according to the embodiment is mounted on a regular rim and inflated to the regular internal pressure, the ratio A / B between the rectangularity ratio A at a load of 130% of the maximum load and the rectangularity ratio B at a load of 100% of the maximum load is 100% or more and 110% or less. However, the regular rim, regular internal pressure, and maximum load are all those according to the ETRTO tire standard, and the rectangularity ratio is L2 / L1, where L1 is the tread length, which is the circumferential length of the tire at the tire equator in the tire contact surface shape, and L2 is the tread length, which is the circumferential length of the tire at positions 10 mm inward from both ends of the contact width of the tire contact surface shape.

[0054] As a result, the contact patch shape F is prevented from becoming squarish even under heavy load, uneven wear of the shoulder 40 is suppressed, and handling stability is improved while rolling resistance is reduced.

[0055] (2) In the tire 1 according to the above embodiment (1), the tread contact length L1 under a 130% load is preferably 112% to 120% of the tread contact length L1 under a 100% load.

[0056] As a result, the contact patch shape F is prevented from becoming squarish even under heavy load, uneven wear of the shoulder 40 is suppressed, and handling stability is improved while rolling resistance is reduced.

[0057] (3) In the tire 1 according to the above embodiments (1) and (2), the tread contact length L2 under a 130% load is preferably 115% to 125% of the tread contact length L2 under a 100% load.

[0058] As a result, the contact patch shape F is prevented from becoming squarish even under heavy load, uneven wear of the shoulder 40 is suppressed, and handling stability is improved while rolling resistance is reduced.

[0059] (4) The tire 1 according to the above embodiments (1) to (3) is suitable for use on passenger cars.

[0060] In other words, in the tire 1 of the embodiment, even when subjected to a load of 130%, which is a high load for passenger vehicles such as EVs, the squaring of the contact patch shape F is suppressed, uneven wear of the shoulder 40 is suppressed, improving handling stability and reducing rolling resistance.

[0061] Although specific embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and even if modifications and improvements are made within the scope of the present invention, they will still be included in the scope of the present invention.

[0062] Although the tire 1 of the above embodiment is for passenger cars, the configuration of this tire 1 can be adopted as a tire for heavy-duty passenger cars such as SUVs and EVs, or for various vehicles other than passenger cars, such as trucks and buses. Also, the tire 1 of the above embodiment is suitable as a tire with a round shoulder shape in which the shoulder 40 is curved and rounded. EXAMPLES

[0063] Examples will be described below. Seven tires of a simulation model were prepared, which have the same internal configuration as the above embodiment, but have different rectangular ratios A / B. For each tire, the tread length L1, which is the tire circumferential length on the tire equator in the tire ground contact surface shape, and the tread length L2, which is the tire circumferential length at a position 10 mm inward from both ends of the ground contact width of the tire ground contact surface shape, were measured at 100% load and 120% load, which are the maximum loads in the TRA standard. Each tire was mounted on a regular rim in the TRA standard, and inflated to a regular internal pressure. The rectangular ratio L2 / L1 at 100% load is B, and the rectangular ratio L2 / L1 at 120% load is A. Table 1 shows the rectangular ratios B and A, and also lists the ratio A / B of the rectangular ratios B and A in %. Note that TW100 and TW120 in Table 1 mean 100% load and 120% load, respectively, of the maximum loads in the TRA standard.

[0064] [Table 1]

[0065] The tires with the ratios of rectangularity A and B: A / B of 100%, 105%, and 110% are respectively Examples 1 to 3 which satisfy the provisions of the present invention. The tires with the ratios of rectangularity A and B: A / B of 90%, 95%, 115%, and 120% are respectively Comparative Examples 1 to 4 which are outside the provisions of the present invention.

[0066] Next, the steering stability, RRC (rolling resistance coefficient), and wear were evaluated for each tire of Examples 1 to 3 and Comparative Examples 1 to 4. Each evaluation was performed by applying a 100% load (750 kgf) according to the ETRTO standard to the tire. The results are shown in Table 2.

[0067] The evaluation methods for the steering stability, RRC, and wear are as follows. The steering stability was evaluated by evaluating the wobble when steering the steering wheel while the vehicle equipped with the tire was running. The RRC was evaluated by mounting one tire on a drum-type tire testing machine and measuring the rolling resistance coefficient. The steering stability and RRC were both evaluated when the tire was first mounted (when the tire was in a new state). The wear was measured by measuring the friction energy when the tire was running after running a specified distance of 12,000 km. In Table 2, the evaluations of the steering stability, RRC (rolling resistance coefficient), and wear are each given an index of 100 for each value of Example 1, and the other values ​​are compared with Example 1 to give an index evaluation. That is, an index of 100 is used as the standard, and an index below 100 indicates a worse evaluation, and an index above 100 indicates a better evaluation.

[0068] [Table 2]

[0069] According to Table 2, when the ratio of the rectangularity rate: A / B is below 100%, the steering stability is deteriorated as in Comparative Examples 1 and 2, and when it is 100% or more, it is good as in Examples 1 to 3 and Comparative Examples 3 and 4. On the other hand, when the ratio of the rectangularity rate: A / B is above 110%, the steering stability is deteriorated as in Comparative Examples 3 and 4, and when it is 110% or less, it is good as in Examples 1 to 3 and Comparative Examples 1 and 2. That is, the steering stability is not satisfied in Comparative Examples 1 and 2, and the RRC and abrasion are not satisfied in Comparative Examples 3 and 4. In contrast, the results of Examples 1 to 3 are satisfactory in all evaluations. Therefore, it was confirmed that even when a high load of about 130% of the maximum load is applied according to the ETRTO standard, if the ratio of the rectangularity rate at a load of 130% of the maximum load to the rectangularity rate at a load of 100% of the maximum load: A / B is 100% or more and 110% or less, the steering stability, RRC, and abrasion properties are all good.

[0070] Figures 4A and 4B are both of tires of Example 2, and Figure 4A is a contour diagram (contour map) showing the contact patch shape and the high and low load areas at a load of 100% of the maximum load according to the ETRTO standard, and Figure 4B is a contour diagram showing the contact patch shape and the high and low load areas at a load of 130% of the maximum load according to the ETRTO standard. The high and low loads indicate high and low loads, with black indicating high and low loads, and white indicating low and high loads. The high and low loads indicate high and low contact pressure against the road surface.

[0071] As shown in these figures, in the tire of Example 2, there is no significant change in contact pressure, including at the shoulder, and no significant bias in contact pressure is observed, even under a maximum load of 100% or 130%. Therefore, even under a high load, uneven wear in the shoulder is suppressed and rolling resistance is reduced. [Explanation of symbols]

[0072] 1...Tire (pneumatic tire) 10...Bead 20…Sidewall 30…Tread 38…Tread surface 39…Tread pattern 40…Shoulder F…Contact surface shape S…Tire equator W…Ground width

Claims

1. A pneumatic tire, A pneumatic tire in which, when mounted on a standard rim and inflated to a standard internal pressure, the ratio A / B of a rectangularity ratio A at a load of 130% of a maximum load to a rectangularity ratio B at a load of 100% of a maximum load is 100% or more and 110% or less. However, the regular rim, the regular internal pressure, and the maximum load are those based on the ETRTO tire standard, and the rectangular ratio is L2 / L1, where L1 is the tread contact length, which is the circumferential length of the tire at the tire equator in the tire contact surface shape, and L2 is the tread contact length, which is the circumferential length of the tire at a position 10 mm inward from both ends of the contact width of the tire contact surface shape.

2. The pneumatic tire according to claim 1 , wherein the tread contact length L1 under a 130% load is equal to or greater than 112% and equal to or less than 120% of the tread contact length L1 under a 100% load.

3. 3. The pneumatic tire according to claim 1, wherein the tread contact length L2 under a 130% load is equal to or greater than 115% and equal to or less than 125% of the tread contact length L2 under a 100% load.

4. The pneumatic tire according to claim 1 or 2, which is for a passenger car.

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