Pneumatic radial tires for passenger cars

Abstract

To provide a pneumatic radial tire for a passenger vehicle, capable of further improving fuel economy performance of the tire while curbing degradation of a ground contact shape when a camber angle is changed.SOLUTION: A pneumatic radial tire for a passenger vehicle has: a cross-sectional width SW and an outer diameter OD which satisfy a predetermined relation; a tread in which all grooves have a width of 2 mm or less and at least one block-shaped land section compartmentalized with 2 or more grooves in the tire circumferential direction and 2 or more grooves in a width direction is formed; and a predetermined falling height (or a predetermined relation with a ground contact length or a tread gauge).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a pneumatic radial tire for a passenger vehicle. [Background technology]

[0002] As a pneumatic radial tire for passenger cars with improved fuel economy, the present applicant has proposed a narrow-width, large-diameter pneumatic radial tire for passenger cars in which the tire cross-sectional width SW and the tire outer diameter OD have a predetermined relationship (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2011 / 135774 Brochure Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the development of vehicles for personal mobility has progressed, and it is conceivable to use narrow-width, large-diameter pneumatic radial tires for passenger cars such as those described above, especially tires with a small cross-sectional width SW.

[0005] However, when the tire cross-sectional width SW is small, there is a risk that the contact patch shape may deteriorate due to changes in the camber angle in particular.

[0006] On the other hand, narrow-width, large-diameter pneumatic radial tires for passenger cars like those mentioned above have high circumferential belt tension rigidity, which means they tend to exert higher contact pressure on the road surface compared to wide-width, low-profile tires of the same tire size and load capacity. Narrow-width, large-diameter tires have good hydroplaning performance due to this high contact pressure, combined with their narrow contact width, and can require less drainage groove area than conventional tires. Furthermore, the dominant factor in the rolling resistance of such narrow-width, large-diameter tires is strain energy loss due to compression strain in the tread area.

[0007] For example, a technology has been proposed that reduces the negative ratio to 20% or less, which improves the rigidity of the tread, reduces strain energy loss, and improves fuel economy. However, such a pattern with fewer grooves can lead to poor compliance with road surface irregularities, lowering the coefficient of friction on dry roads and increasing slippage, potentially resulting in a worsening of fuel economy and a worsening ride.

[0008] Therefore, an object of the present invention is to provide a pneumatic radial tire for passenger cars that can further improve the fuel economy of the tire while suppressing deterioration of the contact patch shape when the camber angle changes. [Means for solving the problem]

[0009] The gist and configuration of the present invention are as follows. (1) A pneumatic radial tire for a passenger vehicle having a tread, The tire has a cross-sectional width SW of less than 165 (mm), The ratio SW / OD of the tire's section width SW to its outer diameter OD is 0.26 or less, or the tire's section width SW (mm) and outer diameter OD (mm) satisfy the following relational expression: OD (mm) ≧ −0.0187 × SW (mm). 2 +9.15×SW(mm)-380(mm) The tire is mounted on a rim, inflated to a specified internal pressure, and unloaded. In the cross section in the tire width direction under the reference condition, a straight line passing through a point on the tread surface at the tire equatorial plane and parallel to the tire width direction is defined as m1, and a straight line passing through the contact edge E and parallel to the tire width direction is defined as m2. The distance in the tire radial direction between the straight lines m1 and m2 is defined as the drop height L. CR When the tread width of the tire is TW, the ratio L CR / TW is greater than 0.045, The tire is mounted on a rim, inflated to a specified internal pressure, and subjected to a maximum load. The grooves in the contact patch are composed only of grooves with a groove width of 2 mm or less. A pneumatic radial tire for passenger cars, characterized in that the contact patch has one or more block-shaped land portions defined by two or more circumferential grooves extending in the tire circumferential direction or extending at an inclination angle of less than 45° with respect to the tire circumferential direction, and two or more width grooves extending in the tire width direction or extending at an inclination angle of 45° or less with respect to the tire width direction.

[0010] Here, the term "ground contact edge" refers to both ends in the tire width direction of the ground contact surface when the tire is mounted on a rim, inflated to a specified internal pressure, and subjected to a maximum load. The term "tread width" refers to the distance in the tire width direction between the above-mentioned contact edges in a standard state in which the tire is mounted on a rim, inflated to a specified internal pressure, and no load is applied. Moreover, the "groove width" refers to the opening width in the above-mentioned reference state. Additionally, the term "tread surface" refers to the surface extending around the entire circumference of the tire that comes into contact with the road surface when the tire is mounted on a rim, inflated to the specified internal pressure, and subjected to the maximum load. Furthermore, the "block-shaped land portion" may not only be completely defined by two circumferential grooves and two widthwise grooves, but may also have interrupted portions when the two circumferential grooves and two widthwise grooves extend intermittently. Furthermore, "extending in the tire circumferential direction," "extending at an incline relative to the tire circumferential direction," "extending in the tire width direction," and "extending at an incline relative to the tire width direction" include extending in a straight line as well as in a zigzag or curved shape, and the inclination angle in this case is the inclination angle of the straight line connecting the end points. Furthermore, when a groove is disposed on the tire equatorial plane, the straight line m1 is drawn using an imaginary line that would be drawn if the groove were not present.

[0011] The above "rim" refers to the standard rim (Measuring Rim in the ETRTO Standards Manual, Design Rim in the TRA Year Book) for the applicable size that is described or will be described in the future, as an industrial standard in effect in the region where the tire is produced and used, such as the JATMA Year Book of the Japan Automobile Tire Manufacturers Association (JATMA) in Japan, the Standards Manual of the European Tyre and Rim Technical Organization (ETRTO) in Europe, or the Year Book of the Tire and Rim Association, Inc. (TRA) in the United States. (In other words, the "rim" in the above "wheel" includes not only current sizes but also sizes that may be included in the above industrial standards in the future. An example of a "size to be described in the future" is the size listed as "FUTURE DEVELOPMENTS" in the 2013 edition of the ETRTO.) However, in the case of a size not described in the above industrial standards, it refers to a rim with a width that corresponds to the bead width of the tire. Furthermore, "specified internal pressure" refers to the air pressure (maximum air pressure) that corresponds to the maximum load capacity of a single wheel for the applicable size and ply rating as specified in the above JATMA etc., and in the case of sizes not specified in the above industry standards, "specified internal pressure" refers to the air pressure (maximum air pressure) that corresponds to the maximum load capacity specified for each vehicle on which the tire is fitted. Furthermore, the "maximum load" refers to the load corresponding to the maximum load capacity.

[0012] (2) A pneumatic radial tire for a passenger vehicle having a tread, The tire has a cross-sectional width SW of less than 165 (mm), The ratio SW / OD of the tire's section width SW to its outer diameter OD is 0.26 or less, or the tire's section width SW (mm) and outer diameter OD (mm) satisfy the following relational expression: OD (mm) ≧ −0.0187 × SW (mm). 2 +9.15×SW(mm)-380(mm) The contact length on the tire equatorial plane is longer than the average contact length at a position 20% of the contact width inward from both contact edges in the tire width direction, The tire is mounted on a rim, inflated to a specified internal pressure, and subjected to a maximum load. The grooves in the contact patch are composed only of grooves with a groove width of 2 mm or less. A pneumatic radial tire for passenger cars, characterized in that the contact patch has one or more block-shaped land portions defined by two or more circumferential grooves extending in the tire circumferential direction or extending at an inclination angle of less than 45° with respect to the tire circumferential direction, and two or more width grooves extending in the tire width direction or extending at an inclination angle of 45° or less with respect to the tire width direction. Here, "contact length" refers to the length of the contact patch in the circumferential direction of the tire when the tire is mounted on a rim, inflated to the specified internal pressure, and subjected to the maximum load, and "contact width" refers to the maximum width of the contact patch in the width direction of the tire when the tire is mounted on a rim, inflated to the specified internal pressure, and subjected to the maximum load. In addition, when a circumferential groove is disposed at the position where the contact length is to be measured, the contact length is measured using an imaginary line that would be drawn if the circumferential groove were not present.

[0013] (3) A pneumatic radial tire for a passenger vehicle having a tread, The tire has a cross-sectional width SW of less than 165 (mm), The ratio SW / OD of the tire's section width SW to its outer diameter OD is 0.26 or less, or the tire's section width SW (mm) and outer diameter OD (mm) satisfy the following relational expression: OD (mm) ≧ −0.0187 × SW (mm). 2 +9.15×SW(mm)-380(mm) The gauge of the tread on the tire equatorial plane is larger than the average value of the gauge of the tread at positions 20% of the contact width inward in the tire width direction from both contact edges, A pneumatic radial tire for passenger cars, characterized in that the contact patch has one or more block-shaped land portions defined by two or more circumferential grooves extending in the tire circumferential direction or extending at an inclination angle of less than 45° with respect to the tire circumferential direction, and two or more width grooves extending in the tire width direction or extending at an inclination angle of 45° or less with respect to the tire width direction. The "gauge" refers to the gauge from the radially outermost reinforcing layer of the reinforcing layers arranged radially outward of the crown portion of the carcass to the tread surface, and is measured in the normal direction to the tread surface in the reference state. In addition, if the circumferential groove is present at the position where the gauge is measured, the gauge is measured using an imaginary line that would be drawn if the circumferential groove were not present.

[0014] (4) A pneumatic tire for passenger cars according to any one of (1) to (3) above, wherein the circumferential grooves are circumferential sipes having a groove width of 2 mm or less, and the widthwise grooves are widthwise sipes having a groove width of 2 mm or less, and the widthwise sipes are flat sipes.

[0015] (5) The pneumatic tire for passenger vehicles according to any one of (1) to (4) above, wherein the area of ​​the block-shaped land portion is 1 / 10 or less of the area of ​​the contact patch. The "area of ​​the block-shaped land portions" refers to the area of ​​the tread in a developed view.

[0016] (6) A pneumatic tire for passenger cars according to (5) above, which has a plurality of the block-shaped land portions, and the area of ​​80% or more of the block-shaped land portions is 1 / 10 or less of the area of ​​the contact patch.

[0017] (7) The pneumatic tire for passenger cars according to (6) above, wherein the maximum area of ​​the block-shaped land portion is 1 / 10 or less of the area of ​​the contact patch.

[0018] (8) The pneumatic radial tire for passenger cars according to any one of (1) to (7) above, wherein the widthwise grooves communicate with the ground contact ends on one or the other sides in the tire width direction.

[0019] (9) A pneumatic radial tire for passenger cars according to (4) above, having the widthwise sipes or perforated sipes having a diameter of 2 mm or less in the tire widthwise half portion bounded by the tire equatorial plane, which is on the outer side when mounted on a vehicle. The "diameter" of the hole-like sipe means the maximum diameter in a plan view. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a pneumatic radial tire for passenger cars that can further improve the fuel economy of the tire while suppressing deterioration of the contact patch shape when the camber angle changes. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic diagram showing the section width SW and the outer diameter OD of a tire. [Figure 2] 1 is a cross-sectional view in the tire width direction of a pneumatic radial tire for passenger cars according to one embodiment of the present invention. [Figure 3] 1 is a diagram showing a groove pattern arranged on a contact patch of a pneumatic radial tire for passenger cars according to one embodiment of the present invention. FIG. [Figure 4] FIG. 10 is a diagram showing a groove pattern arranged on the contact patch of a pneumatic radial tire for passenger cars according to another embodiment of the present invention. [Figure 5] FIG. 10 is a diagram showing a groove pattern arranged on the contact patch of a pneumatic radial tire for passenger cars according to another embodiment of the present invention. [Figure 6] 10A and 10B are schematic diagrams for explaining changes in the ground contact shape. [Figure 7] FIG. 10 is a schematic diagram for explaining a rectangularity ratio. DETAILED DESCRIPTION OF THE INVENTION

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0023] FIG. 1 is a schematic diagram showing the section width SW and the outside diameter OD of a tire. A pneumatic radial tire for passenger cars (hereinafter simply referred to as tire) according to one embodiment of the present invention has a tire section width SW of less than 165 mm, and a ratio SW / OD of the tire section width SW to the outer diameter OD of 0.26 or less, resulting in a narrow width / large diameter shape. By narrowing the tire section width SW compared to the tire outer diameter OD, air resistance can be reduced, and by increasing the tire outer diameter OD compared to the tire section width SW, deformation of the tread rubber near the tire's contact patch can be suppressed, reducing rolling resistance, thereby improving the tire's fuel economy. The SW / OD ratio is preferably 0.25 or less, and more preferably 0.24 or less. The above ratio is preferably satisfied when the tire internal pressure is 200 kPa or higher, more preferably 220 kPa or higher, and even more preferably 280 kPa or higher, because this allows for a reduction in rolling resistance. On the other hand, the above ratio is preferably satisfied when the tire internal pressure is 350 kPa or lower, because this allows for an improvement in ride comfort. Here, the tire cross-sectional width SW is preferably 105 to 145 mm, and more preferably 115 to 135 mm. Furthermore, the aspect ratio of the tire is more preferably 45 to 70, and even more preferably 45 to 65, when the cross-sectional width SW and the outer diameter OD of the tire satisfy the above ratio. Specific tire sizes are not particularly limited, but examples include 105 / 50R16, 115 / 50R17, 125 / 55R20, 125 / 60R18, 125 / 65R19, 135 / 45R21, 135 / 55R20, 135 / 60R17, 135 / 60R18, 135 / 60R19, 135 / 65R19, 145 / 45R21, 145 / 5 155 / 5R20, 145 / 60R16, 145 / 60R17, 145 / 60R18, 145 / 60R19, 145 / 65R19, 155 / 45R18, 155 / 45R21, 155 / 55R18, 155 / 55R19, 155 / 55R21, 155 / 60R17, 155 / 65R18, 155 / 70R17, or 155 / 70R19.

[0024] Alternatively, the tire has a section width SW of less than 165 mm, and the section width SW (mm) and the outer diameter OD (mm) of the tire satisfy the relationship: OD(mm)≧-0.0187×SW(mm) 2 +9.15×SW(mm)-380 It has a narrow width and large diameter. By satisfying the above relational expression, it is possible to reduce air resistance and rolling resistance, thereby improving the fuel economy of the tire. In the third aspect, the tire's section width SW and outer diameter OD satisfy the above-mentioned relational expression, and the ratio SW / OD is preferably 0.26 or less, more preferably 0.25 or less, and even more preferably 0.24 or less, because this can further improve the tire's fuel economy. The above relationship and / or ratio is preferably satisfied when the tire internal pressure is 200 kPa or higher, more preferably 220 kPa or higher, and even more preferably 280 kPa or higher, because this allows for a reduction in rolling resistance. On the other hand, the above relationship and / or ratio is preferably satisfied when the tire internal pressure is 350 kPa or lower, because this allows for an improvement in ride comfort. Here, the tire cross-sectional width SW is preferably 105 to 145 mm, and more preferably 115 to 135 mm. Furthermore, the aspect ratio of the tire is more preferably 45 to 70, and even more preferably 45 to 65, when the cross-sectional width SW and the outer diameter OD of the tire satisfy the above relational expression. Specific tire sizes are not particularly limited, but examples include 105 / 50R16, 115 / 50R17, 125 / 55R20, 125 / 60R18, 125 / 65R19, 135 / 45R21, 135 / 55R20, 135 / 60R17, 135 / 60R18, 135 / 60R19, 135 / 65R19, 145 / 45R21, 145 / 5 155 / 5R20, 145 / 60R16, 145 / 60R17, 145 / 60R18, 145 / 60R19, 145 / 65R19, 155 / 45R18, 155 / 45R21, 155 / 55R18, 155 / 55R19, 155 / 55R21, 155 / 60R17, 155 / 65R18, 155 / 70R17, or 155 / 70R19.

[0025] The tire of this embodiment is a pneumatic radial tire for passenger cars, and is particularly suitable for use as a tire to be mounted on a vehicle for personal mobility.

[0026] Fig. 2 is a widthwise cross-sectional view of a pneumatic radial tire for passenger cars according to one embodiment of the present invention. Fig. 2 shows a widthwise cross-section of the tire in a standard state, in which the tire is mounted on a rim, inflated to a specified internal pressure, and no load is applied. As shown in Fig. 2, the tire 1 includes a carcass 3 made of a ply of radially arranged cords that extends toroidally between a pair of bead portions 2. The tire 1 also includes a belt 4 and a tread 5, which are made of two belt layers 4a and 4b in the illustrated example, arranged in this order on the radially outer side of the carcass 3.

[0027] In this example, a bead core 2a is embedded in each of the pair of bead portions 2. In the present invention, the cross-sectional shape and material of the bead core 2a are not particularly limited, and the bead core 2a may have a configuration that is normally used in pneumatic radial tires for passenger cars. In the present invention, the bead core 2a may be divided into a plurality of small bead cores. Alternatively, in the present invention, the bead core 2a may not be included.

[0028] The tire 1 in the illustrated example has a bead filler 2b with a generally triangular cross section on the tire radial outer side of the bead core 2a. The cross-sectional shape of the bead filler 2b is not limited to this example, and the material is not particularly limited either. Alternatively, the tire can be configured without the bead filler 2b to reduce its weight.

[0029] In this embodiment, the tire 1 may have a structure including a rim guard. Also, in this embodiment, additional members such as a rubber layer or a cord layer may be provided in the bead portion 2 for the purpose of reinforcement, etc. Such additional members may be provided in various positions relative to the carcass 3 and the bead filler 2b.

[0030] In the example shown in FIG. 2, the carcass 3 consists of one carcass ply. However, in the present invention, the number of carcass plies is not particularly limited and can be two or more. Also, in the example shown in FIG. 2, the carcass 3 has a carcass main body 3a that spans a pair of bead portions 2 in a toroidal shape, and a folded-up portion 3b that is folded back from the carcass main body 3a around the bead core 2a. On the other hand, in the present invention, the carcass folded-up portion 3b can be wrapped around the bead core 2a, or can be sandwiched between multiple divided small bead cores. In the illustrated example, the end 3c of the carcass folded-up portion 3b is located radially outward from the radially outer end of the bead filler 2b and radially inward from the maximum width position of the tire. This allows the tire to be lightweight while maintaining the rigidity of the sidewall portion. On the other hand, in the present invention, the end 3c of the carcass folded-up portion 3b may be located radially inward of the outer end of the bead filler 2b, or may be located radially outward of the maximum tire width position. Alternatively, the end 3c of the carcass folded-up portion 3b may have an envelope structure, being located radially inward of the end of the belt 4 (e.g., the end of the belt layer 4b) so as to be located between the carcass main body 2a and the belt 4 in the tire radial direction. Furthermore, when the carcass 3 is composed of multiple carcass plies, the positions of the end 3c of the carcass folded-up portion 3b (e.g., tire radial position) between the carcass plies may be the same or different. The end count of the cords in the carcass 3 is not particularly limited, but may be, for example, in the range of 20 to 60 cords per 50 mm. Various structures can also be adopted for the carcass line. For example, the maximum carcass width position in the tire radial direction may be closer to the bead portion 2 or closer to the tread 5. For example, the carcass maximum width position can be set in a range of 50% to 90% of the tire cross-sectional height outward from the bead base line in the tire radial direction. The "radial arrangement" is at an angle of 85° or more with respect to the tire circumferential direction, preferably 90° with respect to the tire circumferential direction.

[0031] The tire of this embodiment preferably has one or more inclined belt layers made of rubberized cords extending at an angle with respect to the tire circumferential direction, and two layers are most preferable in terms of balancing weight reduction and suppression of distortion of the contact patch shape. Note that a single belt layer may be used from the viewpoint of weight reduction, while three or more belt layers may be used from the viewpoint of suppressing distortion of the contact patch shape. In the example shown in FIG. 2 , of the two belt layers 4a, 4b, the width in the tire width direction of the radially outer belt layer 4b is smaller than the width in the tire width direction of the radially inner belt layer 4a. On the other hand, the width in the tire width direction of the radially outer belt layer 4b may be greater than or the same as the width in the tire width direction of the radially inner belt layer 4a. The width in the tire width direction of the belt layer with the largest width in the tire width direction (belt layer 4a in the illustrated example) is preferably 90 to 115% of the contact patch width, and particularly preferably 100 to 105% of the contact patch width. Note that the "contact patch width" refers to the distance in the tire width direction between the above-mentioned contact patch ends E. In this embodiment, metal cords, particularly steel cords, are most preferably used as the belt cords of the belt layers 4a and 4b. However, non-metallic cords, such as organic fiber cords (e.g., Kevlar (registered trademark)), can also be used. Steel cords are primarily composed of steel and may contain trace amounts of various elements, such as carbon, manganese, silicon, phosphorus, sulfur, copper, and chromium. In this embodiment, the belt cords of the belt layers 4a and 4b can be monofilament cords, cords made of multiple parallel filaments, or cords made of multiple twisted filaments. Various twist structures can be employed, including various cross-sectional structures, twist pitches, twist directions, and distances between adjacent filaments. Furthermore, cords made of twisted filaments of different materials can also be used. The cross-sectional structure is not particularly limited, and various twist structures, such as single twist, multi-layer twist, and multi-twist, can be used. In this embodiment, the inclination angle of the belt cords of the belt layers 4a, 4b with respect to the tire circumferential direction is preferably 10° or more. In this embodiment, the inclination angle of the belt cords of the belt layers 4a, 4b with respect to the tire circumferential direction is preferably high, specifically 20° or more with respect to the tire circumferential direction, preferably 35° or more, and particularly in the range of 55° to 85° with respect to the tire circumferential direction. By setting the inclination angle to 20° or more (preferably 35° or more), rigidity in the tire width direction can be increased, and steering stability performance, particularly during cornering, can be improved. In addition, shear deformation of the interlayer rubber can be reduced, thereby reducing rolling resistance.

[0032] In the illustrated example, the tread rubber constituting the tread 5 consists of a single layer. However, in this embodiment, the tread rubber constituting the tread 5 may be formed by stacking multiple different rubber layers in the tire radial direction. The multiple rubber layers may have different tangent loss, modulus, hardness, glass transition temperature, material, etc. The thickness ratio of the multiple rubber layers in the tire radial direction may vary in the tire width direction, and only the bottom of the circumferential main groove may be a rubber layer different from its surroundings. The tread rubber constituting the tread 5 may be formed by multiple rubber layers that are different in the tire width direction. The multiple rubber layers may have different tangent loss, modulus, hardness, glass transition temperature, material, etc. The width ratio of the multiple rubber layers in the tire width direction may vary in the tire radial direction, and only limited regions, such as the vicinity of the circumferential main groove, the vicinity of the tread edge, the shoulder land portion, or the center land portion, may be a rubber layer different from its surroundings.

[0033] The tire 1 of this embodiment has an inner liner 8 on the inner surface 7 of the tire (also simply referred to as the tire inner surface 7). The thickness of the inner liner 8 is preferably about 1.5 mm to 2.8 mm. This is because it can effectively reduce interior noise in the range of 80 to 100 Hz. The air permeability coefficient of the rubber composition constituting the inner liner 8 is 1.0×10 -14 cc·cm / (cm 2·s·cmHg) or more, 6.5×10 -10 cc·cm / (cm 2 ·s·cmHg) or less is preferable.

[0034] FIG. 3 is a diagram showing a groove pattern arranged on the contact patch of a pneumatic radial tire for passenger cars according to one embodiment of the present invention. 3, in this example, when the tire 1 is mounted on a rim, inflated to a specified internal pressure, and subjected to a maximum load, the grooves 6a, 6b in the contact patch are configured only with grooves 6 having a groove width of 2 mm or less. In this embodiment, the grooves 6a, 6b are sipes having a groove width (opening width) of 2 mm or less, but they can also be narrow grooves.

[0035] As shown in Fig. 3, the tire 1 has, in its contact patch, two or more circumferential grooves 6a extending in the tire circumferential direction or extending at an inclination angle of less than 45° with respect to the tire circumferential direction, and two or more widthwise grooves 6b extending in the tire width direction or extending at an inclination angle of 45° or less with respect to the tire width direction. In this embodiment, the circumferential grooves 6a are circumferential sipes having a groove width of 2 mm or less, and the widthwise grooves 6b are widthwise sipes having a groove width of 2 mm or less. In this example, the circumferential sipes 6a and the widthwise sipes 6b are flat sipes. "Flat" means that the groove width is approximately constant from the opening to the groove bottom, but the groove bottom may have a curvature, or the groove bottom may be a so-called flask-shaped sipe with a widened width. Furthermore, the sipes may be such that at least a portion of the depth of the sipe is closed when the tire is in contact with the ground, and for example, either or both of the circumferential sipe 6a and the widthwise sipe 6b may be so-called three-dimensional sipes in which the inner wall surface of the sipe is uneven along the depth direction.

[0036] In the illustrated example, the circumferential sipes 6a extend in the tire circumferential direction, but may extend at an angle relative to the tire circumferential direction. Also, in the illustrated example, the widthwise sipes 6b extend in the tire width direction, but may extend at an angle relative to the tire width direction. In the illustrated example, there are four circumferential sipes 6a and three widthwise sipes 6b in the contact surface, but the number of circumferential sipes 6a may be two or more in the contact surface, and the number of widthwise sipes 6b may also be two or more in the contact surface, and are not limited to the above numbers. In this example, there are two or more circumferential grooves 6a that extend intersecting with two or more widthwise grooves 6b, and there are also two or more widthwise grooves 6b that extend intersecting with two or more circumferential grooves 6a.

[0037] The tire 1 of this embodiment has one or more (six in the illustrated example) block-shaped land portions 9 defined by two or more circumferential grooves (circumferential sipes in this example) 6a and two or more widthwise grooves (widthwise sipes in this example) 6b. In the illustrated example, the block-shaped land portion 9 is rectangular (in this developed view).

[0038] As shown in FIG. 2, in this embodiment, in the tire width direction cross section in the reference state, a straight line passing through a point on the tread surface at the tire equatorial plane CL and parallel to the tire width direction is defined as m1, a straight line passing through the ground contact edge E and parallel to the tire width direction is defined as m2, and the distance in the tire radial direction between the straight lines m1 and m2 is defined as the drop height L. CR When the tread width of tire 1 is TW, the ratio L CR / TW is greater than 0.045 (Configuration 1). The following describes the effects of the pneumatic radial tire for passenger cars according to this embodiment.

[0039] The pneumatic radial tire for passenger cars of this embodiment is a narrow-width, large-diameter tire in which the tire's section width SW and outer diameter satisfy the above-mentioned relationship, and has a narrow section width SW of less than 165 (mm). Such a tire can particularly reduce air resistance and also reduce rolling resistance, thereby improving the tire's fuel efficiency. On the other hand, as shown schematically on the left side of the arrow in Figure 6, with such tires, when the camber angle changes, such as during cornering, the contact patch shape becomes too elongated, which can deteriorate the contact patch shape and reduce handling stability, etc. In contrast, in the tire of this embodiment, the ratio L CR The / TW is set to more than 0.045. This results in a tire with a relatively round crown shape, which allows the contact patch to be rounded, with the contact patch length at the shoulders shorter than at the center. This prevents the contact patch from becoming too elongated when the camber angle changes, as shown schematically to the right of the arrow in Figure 6, and suppresses deterioration of the contact patch. Furthermore, narrow tires such as those described above are excellent at draining water to the sides of the tire, so even if they only have grooves 6a, 6b with a groove width of 2 mm or less, sufficient drainage can be ensured. However, with such a pattern with fewer grooves, there is a risk that the ability to follow road surface irregularities may deteriorate, as described above. In contrast, in this embodiment, the contact patch has one or more block-shaped land portions 9 defined by two or more circumferential grooves 6a extending in the tire circumferential direction or extending at an inclination angle of less than 45° relative to the tire circumferential direction, and two or more widthwise grooves 6b extending in the tire width direction or extending at an inclination angle of 45° or less relative to the tire width direction, thereby reducing the compression rigidity (compared to a pattern without grooves). Furthermore, in the tire 1 of this embodiment, the grooves in the contact patch are composed only of grooves with a groove width of 2 mm or less, so that the contact area can be secured (compared to patterns having grooves with a groove width of more than 2 mm), and the average contact pressure applied to the tread rubber can be reduced. Note that the tread rubber is preferably formulated with a low-loss rubber that is typically used in eco-tires. In this way, by reducing the compression stiffness while maintaining a low contact pressure, the tire's ability to follow the road surface can be improved. This can prevent a decrease in the effective rolling resistance, further improving fuel economy. It can also prevent a decrease in ride comfort. In this example, the circumferential sipes 6a and the widthwise sipes 6b are provided, but the same effects can be obtained even if narrow grooves are used. Furthermore, as described above, the block-shaped land portion may be completely defined by two circumferential grooves and two widthwise grooves, and may have an interrupted portion when the two circumferential grooves and two widthwise grooves extend intermittently. For example, the block-shaped land portion may be completely defined by a virtual line that is assumed to extend continuously.

[0040] The above ratio L CR It is more preferable that the ratio L / TW is 0.05 or more, because this can further suppress the deterioration of the ground contact shape. On the other hand, from the viewpoint of reducing rolling resistance, CR / TW is preferably 0.1 or less.

[0041] FIG. 7 is a schematic diagram illustrating the contact shape. In another embodiment, the contact length L1 on the tire equatorial plane CL is longer than the average value ((L2 + L3) / 2) of the contact lengths L2 and L3 at tire widthwise positions P1 and P2, which are 20% of the contact width inward from both contact edges E in the tire widthwise direction (Configuration 2). Even in this case, the contact shape can be made rounder, with the contact length at the shoulders being shorter than that at the center. This prevents the contact shape from becoming too elongated when the camber angle changes, as shown schematically to the right of the arrow in FIG. 6, and suppresses deterioration of the contact shape. Preferably, the contact length L1 is 1.1 times or more the average value of the contact lengths L2 and L3. On the other hand, from the perspective of uneven wear performance, the contact length L1 is preferably 1.5 times or less the average value of the contact lengths L2 and L3.

[0042] In another embodiment, as shown in FIG. 2, the tread gauge G1 at the tire equatorial plane is greater than the average value ((G2 + G3) / 2) of the tread gauges G2 and G3 at positions P1 and P2, which are 20% of the contact width inward from both contact edges E in the tire width direction (Configuration 3). This results in a tire with a relatively rounded crown shape, allowing the contact shape to be rounded with the contact length of the shoulders shorter than that of the center. This prevents the contact shape from becoming too elongated when the camber angle changes, as schematically shown to the right of the arrow in FIG. 6, and suppresses deterioration of the contact shape. Furthermore, the thin gauge at positions P1 and P2 increases the tread rigidity at these positions, which is advantageous for improving steering stability during cornering. Preferably, the gauge G1 is 1.1 times or more the average value of the gauges G2 and G3. On the other hand, from the standpoint of uneven wear performance, the gauge G1 is preferably 1.5 times or less the average value of the gauges G2 and G3.

[0043] In the present disclosure, it is sufficient that any one or more of the above configurations 1 to 3 is satisfied, and any two or all three may be satisfied.

[0044] The area of ​​the block-shaped land portion 9 (one block-shaped land portion) is preferably 1 / 10 or less of the area of ​​the ground contact patch, more preferably there are multiple block-shaped land portions 9 and for 80% or more of the block-shaped land portions 9, the area of ​​one block-shaped land portion 9 is 1 / 10 or less of the area of ​​the ground contact patch, and even more preferably the area of ​​the block-shaped land portion 9 with the largest area among the multiple block-shaped land portions 9 is 1 / 10 or less of the area of ​​the ground contact patch. This is because by reducing the area of ​​each block-shaped land portion 9, it is possible to pack the blocks closer together, further improving the ability to follow the road surface and more effectively achieving the above-mentioned effects.

[0045] Although narrow tires are advantageous in preventing macro-drainage phenomena such as hydroplaning, when the volume of the grooves is reduced, it is difficult to ensure localized drainage at the block contact surface, or so-called micro-drainage performance, and further improvements in wet performance were required. In this embodiment, as shown in Fig. 3, the widthwise grooves communicate with the ground contact edge on one or the other side in the tire width direction (in this example, they communicate with the ground contact edges on both sides), thereby improving local drainage of the ground contact patch, so-called micro drainage performance, and further improving wet performance.

[0046] It is also preferable to have widthwise sipes or perforated sipes with a diameter of 2 mm or less in the tire widthwise half bounded by the tire equatorial plane, which will be on the outer side when mounted on a vehicle, because this can appropriately reduce the compression rigidity of the block-shaped land portions on the outer side when mounted on a vehicle and make the ground contact pressure uniform.

[0047] FIG. 4 is a diagram showing a groove pattern arranged on the ground contact patch of a pneumatic radial tire for passenger cars according to another embodiment of the present invention. In the example shown in FIG. 4, circumferential grooves (circumferential sipes) 6a extend at an angle relative to the tire circumferential direction, and widthwise grooves (widthwise sipes) 6b extend at an angle relative to the tire width direction. In this example, the circumferential grooves and widthwise grooves intersect at approximately right angles, so the block-shaped land portions 9 are rectangular (as viewed in development), but this is not limiting. On the other hand, it is preferable that two or more circumferential grooves are parallel to each other and two or more widthwise grooves are parallel to each other, so that the block-shaped land portions 9 are rectangular (as viewed in development). However, for example, they can also be parallelogram-shaped (as viewed in development). In this case, it is preferable that the angle of the smallest corner among the four corners is 45° or greater to prevent the corners from being too acute.

[0048] Fig. 5 is a diagram showing a groove pattern arranged on the ground contact patch of a pneumatic radial tire for passenger cars according to another embodiment of the present invention. In the example shown in Fig. 5, the circumferential grooves 6a extend in the tire circumferential direction, but the widthwise grooves have two types of widthwise grooves 6b1, 6b2 that have different inclination directions with respect to the tire width direction and extend so as to intersect with each other, which is different from the pattern shown in Fig. 4. In this example, the block-shaped land portions 9 are triangular (in this developed view). According to the pattern shown in Fig. 5, the block-shaped land portions can be arranged more densely, further improving the road surface followability and more effectively achieving the above-mentioned effects.

[0049] Here, for example, when the block-shaped land portion 9 is rectangular or parallelogram-shaped, the ratio of the shortest side to the longest side of the block-shaped land portion 9 is preferably 0.7 or more. This is because, particularly when there are a plurality of block-shaped land portions 9 in the ground contact surface, the effect of the block-shaped land portions 9 supporting each other can be obtained more uniformly in all directions.

[0050] <Tire and rim assembly> The tire-rim assembly herein is formed by mounting the above-mentioned pneumatic radial tire for passenger cars onto a rim. This tire-rim assembly can achieve the same effects as those described for the above-mentioned pneumatic radial tire for passenger cars. In this case, the internal pressure of the tire-rim assembly is preferably 200 kPa or more, more preferably 220 kPa or more, and even more preferably 280 kPa or more. This is because a high internal pressure can further reduce rolling resistance. On the other hand, the internal pressure of the tire-rim assembly is preferably 350 kPa or less, because this can improve ride comfort.

[0051] <How to use pneumatic radial tires for passenger cars> The method for using a pneumatic radial tire for passenger cars herein uses the above-mentioned pneumatic radial tire for passenger cars. According to this method for using a pneumatic radial tire for passenger cars, the same effects as those described for the pneumatic radial tire for passenger cars can be obtained. In this case, the internal pressure is preferably 200 kPa or more, more preferably 220 kPa or more, and even more preferably 280 kPa or more. This is because a high internal pressure can further reduce rolling resistance. On the other hand, it is preferable to use an internal pressure of 350 kPa or less, because this can improve ride comfort.

[0052] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, in the above example, the tire is symmetrical with respect to the tire equatorial plane CL except for the groove arrangement, but it may have asymmetrical portions. For example, the contact patch lengths L2 and L3 may be different from each other. Also, for example, the gauges G2 and G3 may be different from each other. Various other modifications and variations are possible. [Explanation of symbols]

[0053] 1: Passenger car pneumatic radial tires (tires), 2: bead portion, 2a: bead core, 2b: bead filler, 3: carcass, 4: belt; 4a, 4b: belt layer; 5: tread; 6: circumferential main groove; 7: tire inner surface; 8: inner liner; 9: Block-shaped land portion, CL: Tire equatorial plane

Claims

1. A pneumatic radial tire for a passenger vehicle having a tread, The tire has a cross-sectional width SW of less than 165 (mm), The ratio SW / OD of the tire's section width SW to its outer diameter OD is 0.26 or less, or the tire's section width SW (mm) and outer diameter OD (mm) satisfy the following relational expression: OD (mm) ≧ −0.0187 × SW (mm). ２ +9.15 × SW (mm) -380 (mm) is satisfied, In a cross section in the tire width direction under a reference condition in which the tire is mounted on a rim, inflated to a specified internal pressure, and unloaded, a straight line passing through a point on the tread surface at the tire equatorial plane and parallel to the tire width direction is defined as m1, and a straight line passing through the ground contact edge E and parallel to the tire width direction is defined as m2. The distance in the tire radial direction between the straight lines m1 and m2 is defined as the drop height L. ＣＲ When the tread width of the tire is TW, the ratio L ＣＲ / TW is greater than 0.045, When the tire is mounted on a rim, inflated to a specified internal pressure, and subjected to a maximum load, the grooves in the contact patch are composed only of grooves having a groove width of 2 mm or less, The ground contact patch has one or more block-shaped land portions defined by two or more circumferential grooves extending in the tire circumferential direction or extending at an inclination angle of less than 45° with respect to the tire circumferential direction, and two or more width grooves extending in the tire width direction or extending at an inclination angle of 45° or less with respect to the tire width direction, A pneumatic radial tire for passenger cars, wherein the block-shaped land portions have a triangular shape in a plan view.

2. A pneumatic radial tire for a passenger vehicle having a tread, The tire has a cross-sectional width SW of less than 165 (mm), The ratio SW / OD of the tire's section width SW to its outer diameter OD is 0.26 or less, or the tire's section width SW (mm) and outer diameter OD (mm) satisfy the following relational expression: OD (mm) ≧ −0.0187 × SW (mm). ２ +9.15 × SW (mm) -380 (mm) is satisfied, The contact patch length on the tire equatorial plane is longer than the average contact patch length at a position 20% of the contact patch width inward from both contact patch edges in the tire width direction, When the tire is mounted on a rim, inflated to a specified internal pressure, and subjected to a maximum load, the grooves in the contact patch are composed only of grooves having a groove width of 2 mm or less, The ground contact patch has one or more block-shaped land portions defined by two or more circumferential grooves extending in the tire circumferential direction or extending at an inclination angle of less than 45° with respect to the tire circumferential direction, and two or more width grooves extending in the tire width direction or extending at an inclination angle of 45° or less with respect to the tire width direction, A pneumatic radial tire for passenger cars, wherein the block-shaped land portions have a triangular shape in a plan view.

3. A pneumatic radial tire for a passenger vehicle having a tread, The tire has a cross-sectional width SW of less than 165 (mm), The ratio SW / OD of the tire's section width SW to its outer diameter OD is 0.26 or less, or the tire's section width SW (mm) and outer diameter OD (mm) satisfy the following relational expression: OD (mm) ≧ −0.0187 × SW (mm). ２ +9.15 × SW (mm) -380 (mm) is satisfied, The gauge of the tread on the tire equatorial plane is larger than the average value of the gauge of the tread at positions spaced 20% of the contact width from both contact edges toward the inside in the tire width direction, The ground contact patch has one or more block-shaped land portions defined by two or more circumferential grooves extending in the tire circumferential direction or extending at an inclination angle of less than 45° with respect to the tire circumferential direction, and two or more width grooves extending in the tire width direction or extending at an inclination angle of 45° or less with respect to the tire width direction, A pneumatic radial tire for passenger cars, wherein the block-shaped land portions have a triangular shape in a plan view.

4. The circumferential groove is a circumferential sipe having a groove width of 2 mm or less, and the widthwise groove is a widthwise sipe having a groove width of 2 mm or less, and the widthwise sipe is a flat sipe. A pneumatic tire for passenger cars according to any one of claims 1 to 3.

5. The pneumatic tire for passenger vehicles according to any one of claims 1 to 4, wherein an area of ​​the block-shaped land portion is 1 / 10 or less of an area of ​​the contact patch.

6. 6. The pneumatic tire for passenger vehicles according to claim 5, wherein the tire has a plurality of the block-shaped land portions, and the area of ​​80% or more of the block-shaped land portions is 1 / 10 or less of the area of ​​the ground contact patch.

7. The pneumatic tire for passenger vehicles according to claim 6, wherein the maximum area of ​​the block-shaped land portion is 1 / 10 or less of the area of ​​the ground contact patch.

8. The pneumatic radial tire for passenger cars according to any one of claims 1 to 7, wherein the widthwise grooves communicate with a ground contact end on one or the other side in the tire width direction.

9. 5. The pneumatic radial tire for passenger cars according to claim 4, wherein the widthwise sipes or perforated sipes having a diameter of 2 mm or less are provided in a half portion in the tire width direction bounded by the tire equatorial plane, which is on the outer side when mounted on a vehicle.

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