Pneumatic radial tires for passenger cars

Abstract

To provide a pneumatic radial tire for a passenger vehicle, capable of improving silent performance thereof 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; only one circumferential main groove which is extended on a tread in a tire circumferential direction and is provided on a one-half side in a tread width direction, with an equatorial plane of the tire as a boundary, corresponding to an inner side of the vehicle when the tire is mounted thereon; and a predetermined falling height (or a relation with a ground contact length or a relation with a tread gauge).SELECTED DRAWING: Figure 2

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's cross-sectional width SW is small, there is a risk that the contact shape may deteriorate, especially due to changes in the camber angle. Furthermore, with growing concern about environmental issues in recent years, there is an increasing demand for quieter tires.

[0006] Therefore, an object of the present invention is to provide a pneumatic radial tire for passenger cars that can improve tire quietness while suppressing deterioration of the contact patch shape when the camber angle changes. [Means for solving the problem]

[0007] 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 tread surface has only one circumferential main groove extending in the tire circumferential direction, A pneumatic radial tire for passenger cars, characterized in that the circumferential main groove is provided in one half of the tread width direction on the inner side when mounted on a vehicle, with the tire equatorial plane as the boundary.

[0008] 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. 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. Moreover, the term "circumferential main groove" refers to a groove that extends in the tire circumferential direction and has a groove width (opening width) of 2 mm or more.

[0009] 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.

[0010] (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 tread surface has only one circumferential main groove extending in the tire circumferential direction, A pneumatic radial tire for passenger cars, characterized in that the circumferential main groove is provided in one half of the tread width direction on the inner side when mounted on a vehicle, with the tire equatorial plane as the boundary. 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 main 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 main groove did not exist.

[0011] (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, The tread surface has only one circumferential main groove extending in the tire circumferential direction, A pneumatic radial tire for passenger cars, characterized in that the circumferential main groove is provided in one half of the tread width direction on the inner side when mounted on a vehicle, with the tire equatorial plane as the boundary. 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. If the circumferential main 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 main groove were not present.

[0012] (4) A pneumatic radial tire for passenger cars according to any one of (1) to (3) above, wherein one or more widthwise sipes extending in the tread width direction or extending at an angle of 45° or less to the tread width direction, and / or one or more hole-like sipes having a diameter of 2 mm or less are provided in the land portion defined by the circumferential main groove and the tread edge and located on the tire equatorial plane. Here, the "tread edge" refers to the above-mentioned ground contact edge. Furthermore, the "diameter" of the hole-like sipe refers to the maximum diameter in a plan view.

[0013] (5) A pneumatic radial tire for passenger cars according to any one of (1) to (4) above, wherein one or more widthwise sipes extending in the tread width direction or extending at an angle of 45° or less to the tread width direction, and / or one or more hole-like sipes having a diameter of 2 mm or less are provided in the land portion on the inner side when mounted on the vehicle, which is defined by the circumferential main groove and the tread edge. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a pneumatic radial tire for passenger cars that can improve tire quietness while suppressing deterioration of the contact patch shape when the camber angle changes. [Brief explanation of the drawings]

[0015] [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 development view showing a tread pattern of a pneumatic radial tire for passenger cars according to one embodiment of the present invention. [Figure 4] 10A and 10B are schematic diagrams for explaining changes in the ground contact shape. [Figure 5] FIG. 10 is a schematic diagram for explaining a rectangularity ratio. [Figure 6] FIG. 10 is a development view showing another example of a tread pattern. [Figure 7] FIG. 10 is a development view showing yet another example of a tread pattern. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0017] 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.

[0018] 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 and 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] FIG. 3 is a development view showing a tread pattern of a pneumatic radial tire for passenger cars according to one embodiment of the present invention. As shown in FIGS. 2 and 3 , in this example, the tire 1 has only one circumferential main groove 6 extending in the tire circumferential direction on the contact surface of the tread 5. In this example, the circumferential main groove 6 extends straight in the tire circumferential direction, but it may extend in a zigzag or bent shape. The groove width (opening width) of the circumferential main groove 6 is not particularly limited, but may be, for example, 2 mm to 5 mm. The groove depth (maximum depth) of the circumferential main groove 6 is not particularly limited, but may be, for example, 3 mm to 6 mm. Here, in this embodiment, the circumferential main groove 6 is provided in one half of the tread width direction, which is on the inner side when mounted on a vehicle, with the tire equatorial plane CL as the boundary. In the illustrated example, the tire 1 does not have widthwise grooves extending in the tire width direction on the tread surface of the tread 5, but may have one or more widthwise grooves.

[0028] 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.

[0029] 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.

[0030] 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 4, 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 diagrammatically to the right of the arrow in Figure 4, and suppresses deterioration of the contact patch. Furthermore, narrow tires such as those described above have excellent drainage to the sides of the tire, so sufficient drainage can be ensured even when the tire has only one circumferential main groove 6. Furthermore, because such a circumferential main groove 6 is provided in one half of the tread width direction with the tire equatorial plane CL as the boundary, which is on the inner side when mounted on the vehicle, the distance over which air column resonance sound that may be generated in the circumferential main groove 6 travels to the outside of the vehicle is longer (compared to when the circumferential main groove 6 is provided in the outer half when mounted on the vehicle), and noise attenuation can improve quietness.

[0031] 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.

[0032] Furthermore, the groove width (opening width) of the circumferential main groove 6 is preferably 20% or less of the ground contact width, and more preferably 15% or less. This is because it is possible to ensure the area of ​​the inner land portion when the tire is mounted on a vehicle. For the same reason, the negative ratio of the entire tread surface is preferably 20% or less, and more preferably 15% or less. "Negative rate" refers to the ratio of the area of ​​grooves (circumferential main grooves and widthwise grooves) with a groove width of 2 mm or more to the area of ​​the tread surface when the tread is viewed in a developed state. Furthermore, on the inside of the vehicle, the width in the tire width direction of the land portion defined by the tread edge and the circumferential main groove 6 is preferably 20% or more, more preferably 25% or more, of the contact width. This is because it can reduce the load bearing rate and contact pressure concentration of the land portion and suppress uneven wear. It also suppresses buckling near the circumferential main groove 6, which has the effect of improving ground contact.

[0033] FIG. 5 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. 4, 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.

[0034] 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. 4, 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.

[0035] 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.

[0036] 6 is a development view showing another example of a tread pattern. In this example, one or more widthwise sipes 9 (9a) extending in the tread width direction or extending at an angle of 45° or less with respect to the tread width direction, and / or one or more hole-like sipes with a diameter of 2 mm or less are provided in land portions defined by the circumferential main grooves 6 and the tread edges and located on the tire equatorial plane CL (in the illustrated example, the widthwise sipes 9 (9a) are provided). According to this configuration, the compression rigidity of the land portion located on the tire equatorial plane CL can be appropriately reduced, thereby making the ground contact pressure uniform. Here, the term "sipe" in the width direction sipe refers to a sipe with a sipe width (opening width) of less than 2 mm.

[0037] 7 is a development view showing yet another example of a tread pattern. In this example, one or more widthwise sipes 9 (9b) extending in the tread width direction or extending at an angle of 45° or less with respect to the tread width direction, and / or one or more hole-like sipes with a diameter of 2 mm or less are provided in the land portion defined by the circumferential main groove 6 and the tread edge on the inner side when mounted on a vehicle (in the illustrated example, the widthwise sipes 9 (9b) are provided). This configuration can reduce input from road irregularities and improve NVH performance. The sipe depth (maximum depth) of the widthwise sipes 9a, 9b and the hole-like sipes is not particularly limited, but may be, for example, 2 to 6 mm. The pitch interval of the widthwise sipes 9a, 9b in the tire circumferential direction is not particularly limited, but may be, for example, 10 to 40 mm.

[0038] <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.

[0039] <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.

[0040] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. For example, in the above examples, the tire is symmetrical with respect to the tire equatorial plane CL, except for the presence or absence of circumferential main grooves. However, the tire may have an asymmetrical portion. For example, the contact 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]

[0041] 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: Width direction sipe, 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, The tread surface has only one circumferential main groove extending in the tire circumferential direction, The circumferential main groove is provided in one half of a tread width direction on an inner side when mounted on a vehicle, the half being bounded by a tire equatorial plane, A pneumatic radial tire for passenger cars, characterized in that one or more widthwise sipes extending in the tread width direction or extending at an angle of 45° or less with respect to the tread width direction, and / or one or more perforated sipes having a diameter of 2 mm or less are provided only in land portions defined by the circumferential main grooves and the tread edges and located on the tire equatorial plane, and the widthwise sipes extend across the tire equatorial plane.

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 positions in the tire width direction that are 20% of the contact patch width inward from both contact patch edges in the tire width direction, The tread surface has only one circumferential main groove extending in the tire circumferential direction, The circumferential main groove is provided in one half of a tread width direction on an inner side when mounted on a vehicle, the half being bounded by a tire equatorial plane, A pneumatic radial tire for passenger cars, characterized in that one or more widthwise sipes extending in the tread width direction or extending at an angle of 45° or less with respect to the tread width direction, and / or one or more perforated sipes having a diameter of 2 mm or less are provided only in land portions defined by the circumferential main grooves and the tread edges and located on the tire equatorial plane, and the widthwise sipes extend across the tire equatorial plane.

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 tread surface has only one circumferential main groove extending in the tire circumferential direction, The circumferential main groove is provided in one half of a tread width direction on an inner side when mounted on a vehicle, the half being bounded by a tire equatorial plane, A pneumatic radial tire for passenger cars, characterized in that one or more widthwise sipes extending in the tread width direction or extending at an angle of 45° or less with respect to the tread width direction, and / or one or more perforated sipes having a diameter of 2 mm or less are provided only in land portions defined by the circumferential main grooves and the tread edges and located on the tire equatorial plane, and the widthwise sipes extend across the tire equatorial plane.

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