tire

Abstract

To provide a tire 2 that can attain improvement in noise performance, while securing necessary wet performance.SOLUTION: A tire 2 comprises a tread 4. A ratio of total widths of groove widths of four circumferential grooves 10 carved on the tread 4 to a grounding width of a reference grounding surface is 16.0% or more and 23.0% or less. A ratio (P100 / P80) of an equator grounding length P100 to a reference grounding length P80 is 1.25 or more and 1.40 or less, in the reference grounding surface. A crown land part 12c of the tread 4 is a plane land part on which a groove 8 is not carved.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to tires, particularly to passenger vehicle tires. [Background technology]

[0002] Grooves extending in the circumferential direction (hereinafter, circumferential grooves) are cut into the tread of a tire. When a tire runs on a wet road surface, the circumferential grooves contribute to the discharge of water present between the tire and the road surface. For example, by cutting circumferential grooves having a wide groove width (hereinafter, wide circumferential grooves) into the tread, the running performance on wet road surfaces (hereinafter, wet performance) is improved. However, wide circumferential grooves increase pattern noise. For this reason, improvement of wet performance is being studied while taking into account the impact on noise performance (for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-101040 A Summary of the Invention [Problem to be solved by the invention]

[0004] As hybrid and electric vehicles become more widespread, tires are required to have improved noise performance. In order to improve noise performance, the use of circumferential grooves with a narrow groove width (hereinafter, narrow circumferential grooves) is being considered. However, if narrow circumferential grooves are used to further improve noise performance, there is a concern that wet performance may be reduced.

[0005] The present invention has been made in consideration of the above circumstances, and has an object to provide a tire that can achieve improved noise performance while ensuring the necessary wet performance. [Means for solving the problem]

[0006] A tire according to one aspect of the present invention includes a tread that comes into contact with a road surface. The tread is formed with four circumferential grooves that are aligned in the axial direction, thereby forming five land portions. Among the five land portions, the land portion located at the center is a crown land portion, the land portions located on the outer sides are shoulder land portions, and the land portion located between the crown land portion and the shoulder land portion is a middle land portion. The tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 230 kPa, and a load of 70% of the regular load is applied to the tire as a vertical load, and the tread is brought into contact with a flat reference road surface, resulting in a contact surface that is a reference contact surface. The ratio of the total groove width of the four circumferential grooves to the contact width of the reference contact surface is 16.0% or more and 23.0% or less. In the reference ground contact surface, a ratio (P100 / P80) of an equatorial contact length P100 measured along the equator to a reference contact length P80 at a position corresponding to 80% of the contact width is 1.25 or more and 1.40 or less. The crown land portion is a plain land portion having no grooves.

[0007] Preferably, in the tire, a ratio of a land portion width of the crown land portion to a contact width of the reference contact surface is equal to or greater than 10.0% and is equal to or less than 13.0%.

[0008] Preferably, in the tire, a circumferential narrow groove is formed in the middle land portion, and a ratio of a groove depth of the circumferential narrow groove to a groove depth of the circumferential groove is 35% or more and 45% or less.

[0009] Preferably, in the tire, a ratio of a land portion width of the shoulder land portion to a land portion width of the crown land portion is equal to or greater than 160%.

[0010] Preferably, in the tire, a lateral groove is cut in the shoulder land portion. The lateral groove has an end portion in the shoulder land portion and extends from the end portion toward an end of the tread. Both edges of the lateral groove are rounded. Effect of the Invention

[0011] According to the present invention, a tire can be obtained that can achieve improved noise performance while ensuring the required wet performance. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a development view showing a part of a tread of a tire according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing a portion of the tire. [Diagram 3] FIG. 3 is an image showing the tire contact patch. [Figure 4] FIG. 4 is an enlarged cross-sectional view showing a lateral groove formed in a shoulder land portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[0014] In this disclosure, a state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to a standard internal pressure, and no load is applied to the tire is referred to as a standard state. In this disclosure, unless otherwise specified, the dimensions and angles of each part of the tire are measured in the standard state.

[0015] Genuine rim means the rim specified in the standard on which the tire is based. The "standard rim" included in the applicable rim in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are genuine rims.

[0016] Normal internal pressure means the internal pressure specified in the standard on which the tire is based. The "maximum air pressure" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are normal internal pressures. If the tire is for passenger cars, the normal internal pressure is 180kPa unless otherwise specified.

[0017] Normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0018] In this disclosure, pattern noise refers to noise in the 1000 Hz band that occurs in a tire traveling at a speed of 100 km / h. Pattern noise is mainly caused by air column resonance sound that occurs due to resonance of the air inside a pipe surrounded by the road surface and the circumferential groove, and is also called shear noise.

[0019] Fig. 1 shows a part of a tire 2 according to one embodiment of the present invention. This tire 2 is a tire for a passenger vehicle. Although not shown, this tire 2 is mounted on a rim. Air is filled inside the tire 2, and the internal pressure of the tire 2 is adjusted. This tire 2 is a pneumatic tire.

[0020] The tire 2 mounted on the rim is also called a tire-rim complex. The tire-rim complex includes a rim and the tire 2 mounted on the rim.

[0021] 1, the up-down direction is the circumferential direction of the tire 2, and the left-right direction is the axial direction of the tire 2. The direction perpendicular to the plane of the paper in FIG. 1 is the radial direction of the tire 2. In FIG.

[0022] The tire 2 has a tread 4 that comes into contact with the road surface. The tread 4 comes into contact with the road surface at its outer surface, i.e., a tread surface 6. The tread 4 is made of crosslinked rubber. The intersection of the tread surface 6 and the equatorial plane is the equator PC.

[0023] Although not described in detail, the tire 2 includes elements such as a sidewall, a bead, a carcass, and a belt in addition to the tread 4. Except for the tread pattern, the specifications of the elements constituting the tire 2 are equivalent to the specifications of elements generally used in passenger vehicle tires.

[0024] 1, the two-dot chain line PE indicates a position on the outer surface (more specifically, the tread surface 6) of the tire 2. The position PE corresponds to the axially outer end of the contact surface with the road surface of the tire 2. In this tire 2, the position PE on the outer surface that corresponds to the axially outer end of the contact surface with the road surface is referred to as the contact edge.

[0025] The contact patch for identifying the contact edge PE is obtained, for example, by using a contact patch shape measuring device (not shown). This contact patch is obtained by mounting the tire 2 on a rim (regular rim), adjusting the internal pressure of the tire 2 to 230 kPa, applying a load of 70% of the normal load as a vertical load to the tire 2 with the camber angle of the tire 2 set to 0°, and bringing the tire 2 into contact with a flat reference road surface. In the present disclosure, the contact patch obtained in this manner is referred to as the reference contact patch.

[0026] In Fig. 1, the double-headed arrow CW indicates the width of the reference ground contact patch, i.e., the contact width. This contact width CW is expressed as the axial distance from one ground contact edge PE to the other ground contact edge PE measured along the tread surface 6. The contact width CW may be identified in an image of the reference ground contact patch obtained by the above-mentioned ground contact shape measuring device.

[0027] Grooves 8 are cut into the tread 4, which constitute a tread pattern. As shown in FIG. 1, the tread pattern of the tire 2 is not symmetrical with respect to the equatorial plane. The tread pattern is an asymmetric pattern. In the plane of FIG. 1, the right side corresponds to the inner side in the width direction of the vehicle on which the tire 2 is mounted. The left side corresponds to the outer side in the width direction of the vehicle on which the tire 2 is mounted.

[0028] In this tire 2, among the grooves 8 constituting the tread pattern, the grooves 8 having a groove width of 1.5 mm or less are called narrow grooves. Narrow grooves are also called sipes. In this tire 2, the grooves 8 having a groove width exceeding 1.5 mm are called wide grooves. The grooves 8 constituting this tread pattern are composed of narrow grooves and wide grooves.

[0029] In this tire 2, the grooves 8 constituting the tread pattern include grooves 8 extending in the circumferential direction (hereinafter, circumferential grooves 10). The circumferential grooves 10 have a groove width of at least 3.0 mm. The circumferential grooves 10 are part of the wide grooves described above.

[0030] The tread 4 of the tire 2 is formed with four circumferential grooves 10 arranged in parallel in the axial direction. Of the four circumferential grooves 10, the circumferential groove 10 located on the outer side in the axial direction is the shoulder circumferential groove 10s. The circumferential groove 10 located on the inner side of the shoulder circumferential groove 10s in the axial direction is the middle circumferential groove 10m. The four circumferential grooves 10 include a pair of middle circumferential grooves 10m and a pair of shoulder circumferential grooves 10s.

[0031] In Fig. 1, the double-headed arrow GM indicates the groove width of the middle circumferential groove 10m. The double-headed arrow GS indicates the groove width of the shoulder circumferential groove 10s. The groove width of the circumferential groove 10 is represented by the shortest distance from one edge to the other edge of the circumferential groove 10. When the groove width of the circumferential groove 10 varies in the circumferential direction, the groove width is represented by the average value of the maximum groove width and the minimum groove width.

[0032] In this tire 2, four circumferential grooves 10 are formed in the tread 4, thereby forming five land portions 12 arranged in parallel in the axial direction. Of the five land portions 12, the land portion 12 located at the center in the axial direction is the crown land portion 12c. The crown land portion 12c is located on the equatorial plane. The land portion 12 located on the outer side in the axial direction is the shoulder land portion 12s. The shoulder land portion 12s includes the above-mentioned ground contact edge PE. The land portion 12 located between the crown land portion 12c and the shoulder land portion 12s in the axial direction is the middle land portion 12m.

[0033] The five land portions 12 include a crown land portion 12c, a pair of middle land portions 12m, and a pair of shoulder land portions 12s. The crown land portion 12c is between the left and right middle circumferential grooves 10m. The middle land portion 12m is between the middle circumferential groove 10m and the shoulder circumferential groove 10s. And the shoulder land portion 12s is between the shoulder circumferential groove 10s and the ground contact edge PE.

[0034] In FIG. 1, the double-headed arrow LC indicates the land width of the crown land portion 12c. The double-headed arrow LM indicates the land width of the middle land portion 12m. The double-headed arrow LS indicates the land width of the shoulder land portion 12s. The land width is represented by the shortest distance from one edge to the other edge of the land portion 12. When the land width varies in the circumferential direction, the land width is represented by the average value of the maximum land width and the minimum land width.

[0035] In this tire 2, the crown land portion 12c has no grooves 8. The crown land portion 12c is a plain land portion in which the grooves 8 are not formed.

[0036] Narrow grooves are formed in the middle land portion 12m. A circumferential narrow groove 14 and a dead-end narrow groove 16 are formed in the middle land portion 12m as narrow grooves. The circumferential narrow groove 14 is a narrow groove that extends in the circumferential direction. One circumferential narrow groove 14 is formed in the middle land portion 12m. The circumferential narrow groove 14 is located near the center of the middle land portion 12m in the axial direction.

[0037] The dead-end narrow groove 16 has one end in the middle land portion 12m and extends from this end toward the circumferential groove 10. The dead-end narrow groove 16 is connected to the circumferential groove 10 at the other end. The dead-end narrow groove 16 is inclined with respect to the axial direction. In the tire 2, the dead-end narrow groove 16 provided in the middle land portion 12m is composed of an inner dead-end narrow groove 16u located inside the circumferential narrow groove 14 and an outer dead-end narrow groove 16s located outside the circumferential narrow groove 14 in the axial direction.

[0038] As shown in Fig. 1, the inclination direction of the inner dead-end narrow groove 16u is the same as that of the outer dead-end narrow groove 16s. The inclination angle of the inner dead-end narrow groove 16u is larger than that of the outer dead-end narrow groove 16s. The inclination direction of the inner dead-end narrow groove 16u in the middle land portion 12m (hereinafter also referred to as the first middle land portion 12m1) located on the inner side in the width direction of the vehicle is the same as the inclination direction of the inner dead-end narrow groove 16u in the middle land portion 12m (hereinafter also referred to as the second middle land portion 12m2) located on the outer side in the width direction of the vehicle.

[0039] In the present disclosure, when a narrow groove or a wide groove is inclined with respect to the axial direction, the inclination direction of the narrow groove or the wide groove is represented by the inclination direction of a straight line connecting both ends of the narrow groove or the wide groove with respect to the axial direction. The inclination angle of the narrow groove or the wide groove is represented by the angle that the straight line connecting both ends of the narrow groove or the wide groove makes with respect to the axial direction. The end of the narrow groove or the wide groove is specified at the center of the groove width of the narrow groove or the wide groove.

[0040] A plurality of inner dead-end narrow grooves 16u are formed in the middle land portion 12m. These inner dead-end narrow grooves 16u are arranged at intervals in the circumferential direction. A plurality of outer dead-end narrow grooves 16s are formed in the middle land portion 12m. These outer dead-end narrow grooves 16s are arranged at intervals in the circumferential direction. The aforementioned circumferential narrow groove 14 is located between the inner dead-end narrow groove 16u and the outer dead-end narrow groove 16s. The circumferential narrow groove 14 does not intersect with the inner dead-end narrow groove 16u. Circumferential thin groove 14 does not intersect with outer dead-end narrow groove 16s.

[0041] The shoulder land portion 12s is formed with a wide groove and a narrow groove. A lateral groove 18 is formed in the shoulder land portion 12s as a wide groove. The lateral groove 18 has one end in the shoulder land portion 12s and extends from this end toward an end (not shown) of the tread surface 6. The lateral groove 18 intersects with the ground contact edge PE. In the tire 2, the lateral groove 18 is inclined with respect to the axial direction. The inclination direction of the lateral groove 18 is opposite to the inclination direction of the outer dead-end narrow groove 16s formed in the middle land portion 12m. A plurality of lateral grooves 18 are formed in the shoulder land portion 12s. The lateral grooves 18 are arranged at intervals in the circumferential direction.

[0042] In the shoulder land portion 12s, a closed narrow groove 20 is formed as a narrow groove. The closed narrow groove 20 is entirely located in the shoulder land portion 12s. The closed narrow groove 20 is independent from the other grooves 8. The closed narrow groove 20 is inclined with respect to the axial direction. The inclination direction of the closed narrow groove 20 is the same as the inclination direction of the lateral groove 18.

[0043] In the tire 2, a plurality of closed narrow grooves 20 are formed in the shoulder land portion 12s. These closed narrow grooves 20 are arranged at intervals in the circumferential direction. In the tire 2, one or two closed narrow grooves 20 are arranged between one lateral groove 18 and another lateral groove 18 adjacent to the one lateral groove 18 in the circumferential direction.

[0044] In this tire 2, the shoulder land portion 12s located on the inner side in the vehicle width direction (hereinafter, the first shoulder land portion 12s1) is formed with an open narrow groove 22 as a narrow groove. In contrast, the shoulder land portion 12s located on the outer side in the vehicle width direction (hereinafter, the second shoulder land portion 12s2) is not formed with the open narrow groove 22.

[0045] The open narrow groove 22 extends from the end of the lateral groove 18 toward the shoulder circumferential groove 10s. The open narrow groove 22 connects the lateral groove 18 and the shoulder circumferential groove 10s. The open narrow groove 22 is inclined with respect to the axial direction. The inclination direction of the open narrow groove 22 is the same as the inclination direction of the lateral groove 18.

[0046] Fig. 2 shows a part of a cross section (hereinafter also referred to as a meridian cross section) of the tire 2 taken along a plane including the rotation axis (not shown) of the tire 2. In Fig. 2, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the paper surface of Fig. 2 is the circumferential direction of the tire 2. A tread surface 6 is shown in Fig. 2.

[0047] In a meridian cross section of the tire 2, the contour of the tread surface 6 is represented by a plurality of arcs with different radii. In this tire 2, the arcs representing the contour of the tread surface 6 include a crown arc, a pair of middle arcs, and a pair of shoulder arcs. Of the contour of the tread surface 6, the region represented by the crown arcs is the crown region Cr. The region represented by the middle arcs is the middle region Mi. The region represented by the shoulder arcs is the shoulder region Sh.

[0048] In FIG. 2, the position on the tread surface 6 represented by the symbol CM is the boundary between the crown region Cr and the middle region Mi. This boundary CM is the edge of the crown region Cr and also the inner end of the middle region Mi. The position on the tread surface 6 represented by the symbol MS is the boundary between the middle region Mi and the shoulder region Sh. This boundary MS is the outer end of the middle region Mi and the inner end of the shoulder region Sh. In FIG. 2, the position on the tread surface 6 represented by the symbol SE is the outer end of the shoulder region Sh. The outer end SE of the shoulder region Sh is located outside the ground contact edge PE in the axial direction.

[0049] The crown region Cr is disposed across the equatorial plane. The contour of the crown region Cr has an outwardly convex shape. In FIG. 2, an arrow TR1 indicates the radius of the crown arc (hereinafter, the first radius). Although not shown, the center of the crown arc is located on the equatorial plane.

[0050] Each middle region Mi is located outside the crown region Cr in the axial direction. The contour of the middle region Mi has an outwardly convex shape. In FIG. 2, the arrow TR2 indicates the radius of the middle arc (hereinafter, the second radius). The middle arc is in contact with the crown arc at the boundary CM. In this tire 2, the boundary CM is located on the outer surface of the middle land portion 12m. Specifically, the boundary CM is located between a position 5 mm away from the inner edge of the middle land portion 12m and a position 10 mm away from this inner edge.

[0051] Each shoulder region Sh is located outside the middle region Mi in the axial direction. The contour of the shoulder region Sh has an outwardly convex shape. In FIG. 2, the arrow TR3 indicates the radius of the shoulder arc (hereinafter, the third radius). The shoulder arc is in contact with the middle arc at the boundary MS. In this tire 2, the boundary MS is located on the outer surface of the shoulder land portion 12s. Specifically, the boundary MS is located between a position 5 mm away from the edge of the shoulder land portion 12s and a position 10 mm away from this edge.

[0052] In the tire 2, the contour of the tread surface 6 is configured such that the first radius TR1, the second radius TR3, and the third radius TR3 are different from each other. The tread surface 6 has a multi-radius contour shape. From the viewpoint of smoothly connecting the crown arc, the middle arc, and the shoulder arc, it is preferable that the first radius TR1, the second radius TR2, and the third radius TR3 satisfy the following formula (1). TR1>TR2>TR3 (1)

[0053] In the tire 2, the second radius TR2 is set in the range of 45% to 60% of the first radius TR1. The second radius TR2 is preferably set in the range of 50% to 55% of the first radius TR1. The third radius TR3 is set in the range of 15% to 30% of the first radius TR1. The third radius TR3 is preferably set in the range of 20% to 25% of the first radius TR1.

[0054] Fig. 3 shows an image of the contact patch of the tire 2. This image of the contact patch is the image of the reference contact patch mentioned above. In Fig. 3, the up-down direction corresponds to the circumferential direction of the tire 2, and the left-right direction corresponds to the axial direction of the tire 2. The direction perpendicular to the paper surface of Fig. 3 corresponds to the radial direction of the tire 2.

[0055] In Fig. 3, the dashed dotted line LP is a straight line corresponding to the equator PC of the tire 2 on the reference contact surface. When it is difficult to identify the equator PC on the reference contact surface, the axial center line of the reference contact surface is used as the straight line corresponding to the equator PC. The double-headed arrow P100 is the length of the intersection line between a plane including the line LP and the reference contact surface. The length P100 of this intersection line is the equatorial contact length measured along the equator PC on the reference contact surface.

[0056] In FIG. 3, the solid line LE is a straight line that passes through the ground contact edge PE and is parallel to the straight line LP. The solid line L80 is a straight line that is located between the straight lines LE and LP and is parallel to the straight lines LE and LP. The double-headed arrow A100 represents the axial distance from the straight line LP to the straight line LE. This distance A100 corresponds to the maximum width of the reference ground contact surface, that is, half of the ground contact width CW. The double-headed arrow A80 represents the axial distance from the straight line LP to the straight line L80. In the present disclosure, the ratio of the distance A80 to the distance A100 is set to 80%. That is, the straight line L80 represents a position that corresponds to 80% of the ground contact width CW of the reference ground contact surface. The double-headed arrow P80 is the length of the intersection line between the plane including the straight line L80 and the reference ground contact surface. In this tire 2, the length P80 of this intersection line is the reference ground contact length at a position that corresponds to 80% of the ground contact width CW on the reference ground contact surface.

[0057] In this tire 2, the equatorial contact length P100 and the reference contact length P80 are specified in the reference contact surface shown in Fig. 3, and the ratio (P100 / P80) of the equatorial contact length P100 to the reference contact length P80 is obtained. In this tire 2, this ratio (P100 / P80) is also referred to as a shape index F. Although not described in detail, the shape index F of this tire 2 is mainly controlled by adjusting the first radius TR1 of the crown arc, the second radius TR2 of the middle arc, and the third radius TR3 of the shoulder arc as arcs that represent the contour of the tread surface 6.

[0058] As described above, four circumferential grooves 10 are formed in the tread 4 of this tire 2. Like a tire with three circumferential grooves in the tread, this tire 2 ensures the total volume of the circumferential grooves 10 necessary to ensure good wet performance, while allowing the groove volume of each circumferential groove 10 to be set smaller than that of a tire with three circumferential grooves in the tread.

[0059] Specifically, in the tire 2, the ratio (SG / CW) of the total width SG of the groove widths of the four circumferential grooves 10, i.e., the sum of the groove width GM of one middle circumferential groove 10m, the groove width GM of the other middle circumferential groove 10m, the groove width GS of one shoulder circumferential groove 10s, and the groove width GS of the other shoulder circumferential groove 10s, to the contact width CW of the reference contact surface is 16.0% or more and 23.0% or less.

[0060] Since the ratio (SG / CW) is 16.0% or greater, the circumferential groove 10 has a required groove volume. Since the circumferential groove 10 promotes the discharge of water present between the tire 2 and the road surface, required wet performance is ensured in the tire 2. From this viewpoint, the ratio (SG / CW) is preferably 17.0% or greater, and more preferably 17.5% or greater.

[0061] Since the ratio (SG / CW) is 23.0% or less, the circumferential groove 10 is prevented from having a groove volume larger than necessary. Since the generation of air column resonance sound is suppressed, pattern noise is reduced. In this tire 2, noise performance is improved. From this viewpoint, the ratio (SG / CW) is preferably 21.0% or less, and more preferably 20.0% or less.

[0062] As described above, in the tire 2, the shape index F is controlled by adjusting the first radius TR1 of the crown arc, the second radius TR2 of the middle arc, and the third radius TR3 of the shoulder arc, which are arcs that represent the contour of the tread surface 6. Specifically, the shape index F is 1.25 or more and 1.40 or less.

[0063] Since the shape index F is 1.25 or more, the shape of the ground contact surface can be rounded. In the tire 2 in a running state, the crown land portion 12c having the longest ground contact length first comes into contact with the road surface, the middle land portion 12m having the second longest ground contact length after the crown land portion 12c comes into contact with the road surface next, and then the shoulder land portion 12s having the shortest ground contact length comes into contact with the road surface, so that water present between the tire 2 and the road surface is effectively discharged from the axial center portion toward the outside. With this tire 2, good wet performance is obtained. In addition, since the impact when the tire 2 comes into contact with the road surface is mitigated, pattern noise is effectively reduced. From this viewpoint, the shape index F is preferably 1.30 or more.

[0064] Since the shape index F is 1.40 or less, the ground contact surface shape is prevented from being excessively rounded. In the tire 2, the ground contact pressure is suppressed from increasing locally in the crown land portion 12c. Since wear is prevented from progressing specifically in the crown land portion 12c, good wear resistance is maintained. From this viewpoint, the shape index F is preferably 1.35 or less.

[0065] As described above, the crown land portion 12c is a plain land portion that does not have grooves 8. The crown land portion 12c has higher rigidity than, for example, a crown land portion having fine grooves. Since the crown land portion 12c having sufficient rigidity is located on the equatorial plane, the tire 2 maintains good driving stability, specifically, good initial response.

[0066] In this tire 2, the ratio (SG / CW) is 16.0% or more and 23.0% or less, the shape index F expressed by the ratio (P100 / P80) is 1.25 or more and 1.40 or less, and the crown land portion 12c is a plain land portion. This tire 2 can achieve improved noise performance while suppressing the influence on driving stability and wear resistance and ensuring necessary wet performance.

[0067] In the tire 2, the ratio (LC / CW) of the land portion width LC of the crown land portion 12c to the contact width CW of the reference contact surface is preferably equal to or greater than 10.0% and is preferably equal to or less than 13.0%.

[0068] By setting the ratio (LC / CW) to 10.0% or more, the rigidity of the crown land portion 12c is appropriately ensured. Since the rigidity is well balanced between the crown land portion 12c and the middle land portion 12m or the shoulder land portion 12s, the tire 2 can ensure the necessary wet performance and improve the noise performance while maintaining good driving stability (particularly initial response) and wear resistance. From this viewpoint, the (LC / CW) is more preferably 10.6% or more, and even more preferably 11.3% or more.

[0069] By setting the ratio (LC / CW) to 13.0% or less, the middle circumferential groove 10m is disposed at an appropriate position in the axial direction. Since the middle circumferential groove 10m contributes to the discharge of water present between the tire 2 and the road surface, good wet performance is maintained in the tire 2. From this viewpoint, the ratio (LC / CW) is more preferably 12.5% ​​or less.

[0070] In the tire 2, the land portion width LC of the crown land portion 12c is preferably equal to or greater than 18 mm and is preferably equal to or less than 20 mm.

[0071] By setting the land width LC to 18 mm or more, the rigidity of the crown land portion 12c is appropriately ensured. Since the rigidity is well balanced between the crown land portion 12c and the middle land portion 12m or the shoulder land portion 12s, the tire 2 can ensure the necessary wet performance and improve noise performance while maintaining good driving stability (especially initial response) and wear resistance.

[0072] By setting the land portion width LC to 20 mm or less, the middle circumferential groove 10m is disposed at an appropriate position in the axial direction. The middle circumferential groove 10m contributes to the discharge of water present between the tire 2 and the road surface, so that the tire 2 maintains good wet performance.

[0073] In the tire 2, the ratio (LS / LC) of the land width LS of the shoulder land portion 12s to the land width LC of the crown land portion 12c is preferably 160% or more. This ensures the rigidity of the shoulder land portion 12s. In the tire 2, good driving stability (particularly, limit performance) is obtained. From this viewpoint, the ratio (LS / LC) is more preferably 165% or more. From the viewpoint of ensuring the rigidity of the crown land portion 12c and maintaining good initial responsiveness, and from the viewpoint of ensuring the groove volume and maintaining good wet performance, the ratio (LS / LC) is preferably 185% or less, more preferably 175% or less, and even more preferably 170% or less.

[0074] In this tire 2, from the viewpoint of achieving a good balance between initial responsiveness and limit performance, the ratio (LM / LC) of the land width LM of the middle land portion 12m to the land width LC of the crown land portion 12c is preferably 105% or more and 110% or less.

[0075] In this tire 2, the groove width GM of the middle circumferential groove 10m is preferably equal to or wider than the groove width GS of the shoulder circumferential groove 10s. Specifically, the ratio (GM / GS) of the groove width GM to the groove width GS is preferably 1.0 or more. This allows water present between the tire 2 and the road surface to be effectively discharged. As described above, in this tire 2, the shape of the ground contact surface can be rounded, so by setting this ratio (GM / GS) to 1.0 or more, water present between the tire 2 and the road surface can be more effectively discharged from the axial center portion toward the outside. In this tire 2, good wet performance is obtained. From this viewpoint, this ratio (GM / GS) is more preferably 1.1 or more. From the viewpoint that the shoulder circumferential groove 10s can effectively contribute to drainage, this ratio (GM / GS) is preferably 1.5 or less, more preferably 1.4 or less.

[0076] In this tire 2, when the groove width GM of the middle circumferential groove 10m is the same as the groove width GS of the shoulder circumferential groove 10s or when this groove width GM is wider than this groove width GS, from the viewpoint of further improving noise performance, the ratio (GM / CW) of the groove width GM to the contact width CW of the reference contact surface is preferably 6.0% or less, more preferably 5.5% or less, and even more preferably 5.0% or less. From the viewpoint of ensuring the necessary wet performance, this ratio (GM / CW) is preferably 4.0% or more, more preferably 4.2% or more, and even more preferably 4.5% or more. Note that, when the groove width GS of the shoulder circumferential groove 10s is wider than the groove width GM of the middle circumferential groove 10m, from the viewpoint of further improving noise performance, the ratio (GS / CW) of the groove width GS to the contact width CW of the reference contact surface is preferably 6.0% or less, more preferably 5.5% or less, and even more preferably 5.0% or less. From the standpoint of ensuring necessary wet performance, this ratio (GS / CW) is preferably equal to or greater than 4.0%, more preferably equal to or greater than 4.2%, and even more preferably equal to or greater than 4.5%.

[0077] 2, the double arrow DM indicates the groove depth of the middle circumferential groove 10m, the double arrow DS indicates the groove depth of the shoulder circumferential groove 10s, and the double arrow DG indicates the groove depth of the circumferential narrow groove 14.

[0078] In the tire 2, the ratio (DG / DM) of the groove depth DG of the circumferential narrow groove 14 to the groove depth DM of the middle circumferential groove 10m is preferably 35% or more and 45% or less.

[0079] By setting the ratio (DG / DM) to 35% or more, the middle land portion 12 m has appropriate flexibility. Since the impact when the tire 2 contacts the road surface is mitigated, pattern noise is effectively reduced. In this tire 2, noise performance is improved. From this viewpoint, the ratio (DG / DM) is more preferably 36% or more, and further preferably 37% or more.

[0080] By setting the ratio (DG / DM) to 45% or less, the rigidity of the middle land portion 12 m is appropriately maintained. Good initial responsiveness is maintained in the tire 2. From this viewpoint, the ratio (DG / DM) is more preferably 44% or less, and further preferably 43% or less.

[0081] In the tire 2, the shoulder circumferential groove 10s has a groove depth DS that is approximately the same as the groove depth DM of the middle circumferential groove 10m. Specifically, the ratio (DS / DM) of the groove depth DS of the shoulder circumferential groove 10s to the groove depth DM of the middle circumferential groove 10m is preferably 0.9 or more and preferably 1.1 or less. The ratio of the groove depth DM of the middle circumferential groove 10m to the thickness of the tread 4 measured along the equatorial plane is set in the range of 0.80 to 0.95.

[0082] Fig. 4 shows a cross section of the tire 2 taken along line IV-IV in Fig. 1. Fig. 4 shows a cross section of a lateral groove 18 provided in the shoulder land portion 12s.

[0083] The lateral groove 18 of the shoulder land portion 12s includes a groove bottom 24 and a pair of groove walls 26 extending from the groove bottom 24 toward the tread surface 6. The boundary between the groove wall 26 and the tread surface 6 is an edge 28 of the lateral groove 18. As shown in FIG. 4, both edges 28 of the lateral groove 18 are rounded.

[0084] As shown in FIG. 1, the lateral groove 18 extends in a substantially axial direction. The edges 28 of the lateral groove 18 also extend in a substantially axial direction. As described above, the edges 28 on both sides of the lateral groove 18, in other words, the edge 28 located on the leading side and the edge 28 located on the trailing side in the running state of the tire 2, are rounded. The rounded edges 28 contribute to mitigating the impact when the tire 2 comes into contact with the road surface. In the tire 2, the generation of noise caused by the lateral groove 18 is suppressed. The tire 2 can further improve the noise performance. From this viewpoint, in the tire 2, it is preferable that the edges 28 on both sides of the lateral groove 18 provided in the shoulder land portion 12s are rounded.

[0085] 4, the arrow Ra indicates the radius of rounding of one edge 28. The arrow Rb indicates the radius of rounding of the other edge 28.

[0086] In this tire 2, from the viewpoint that the rounded edge 28 can effectively contribute to reducing noise, the rounding radius Ra of one edge 28 is preferably equal to or greater than 0.5 mm and equal to or less than 1.5 mm. From the same viewpoint, the rounding radius Rb of the other edge 28 is preferably equal to or greater than 0.5 mm and equal to or less than 1.5 mm.

[0087] As described above, according to the present invention, a tire 2 can be obtained that can achieve improved noise performance while ensuring necessary wet performance. EXAMPLES

[0088] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0089] [Example 1] A pneumatic tire for passenger cars (tire size=205 / 55R16 91V) having the basic structure shown in FIG. 1 and the specifications shown in Table 1 below was obtained.

[0090] In this Example 1, the number of land portions formed in the tread is five. This tread is a 5-rib pattern tread. The ratio (GM / CW) of the groove width GM of the middle circumferential groove to the ground contact width CW of the reference ground contact surface was 5.0%. The ratio (SG / CW) of the total width SG of the circumferential groove to the ground contact width CW was 18.8%. The shape index F was 1.30. The ratio (LC / CW) of the land width LC of the crown land portion to the ground contact width CW was 12.5%. The ratio (DG / DM) of the groove depth DG of the circumferential narrow groove to the groove depth DM of the middle circumferential groove was 39%. The ratio (LS / LC) of the land width LS of the shoulder land portion to the land width LC of the crown land portion was 170%. The ratio (LM / LC) of the land width LM of the middle land portion to the land width LC of the crown land portion was 105%. The ground contact width CW was 160 mm.

[0091] [Comparative Example 1] Comparative Example 1 is a conventional tire. In this Comparative Example 1, the number of land portions formed in the tread is four. The tread of this Comparative Example 1 is a four-rib pattern tread.

[0092] Of the three circumferential grooves engraved in the tread, the one located in the center is called the middle circumferential groove, and the two circumferential grooves located outside the middle circumferential groove are called shoulder circumferential grooves. The land portion between the middle circumferential groove and the shoulder circumferential groove is called the middle land portion, and the land portion located outside the shoulder circumferential groove is called the shoulder land portion. In this comparative example 1, a crown land portion located on the equatorial plane is not provided.

[0093] The ratio (GM / CW) of the groove width GM of the middle circumferential groove to the ground contact width CW was 6.3%. This ratio (GM / CW) corresponds to the ratio (GM / CW) of Example 1. The ratio (SG / CW) of the total width SG of the circumferential groove to the ground contact width CW was 17.7%. This ratio (SG / CW) corresponds to the ratio (SG / CW) of Example 1. The shape index F was 1.25. This shape index F corresponds to the shape index F of Example 1. The ratio (LM / CW) of the land portion width LM of the middle land portion to the ground contact width CW was 13.0%. This ratio (LM / CW) corresponds to the ratio (LC / CW) of Example 1. The ratio (DG / DM) of the groove depth DG of the circumferential narrow groove engraved in the middle land portion to the groove depth DM of the middle circumferential groove was 47%. This ratio (DG / DM) corresponds to the ratio (DG / DM) of Example 1. The ratio (LS / LM) of the land width LS of the shoulder land portion to the land width LM of the middle land portion was 214%. This ratio (LS / LM) corresponds to the ratio (LS / LC) of Example 1.

[0094] [Example 2-3] Tires of Examples 2-3 were obtained in the same manner as in Example 1, except that the groove width GS and the land width LS were changed to set the ratio (SG / CW) and the ratio (LS / LC) as shown in Table 1 below.

[0095] [Example 4] A tire of Example 4 was obtained in the same manner as Example 1, except that the groove width GM and the land width LS were changed to set the ratio (GM / CW), ratio (SG / CW), and ratio (LS / LC) as shown in Table 1 below.

[0096] [Comparative Example 2-3] A tire of Comparative Example 2-3 was obtained in the same manner as in Example 1, except that the groove width GM, groove width GS, and land width LS were changed to set the ratio (GM / CW), ratio (SG / CW), and ratio (LS / LC) as shown in Tables 1 and 2 below.

[0097] [Example 5] A tire of Example 5 was obtained in the same manner as Example 1, except that the land width LC, land width LM, groove width GS, and land width LS were changed to set the ratio (SG / CW), ratio (LC / CW), ratio (LS / LC), and ratio (LM / LC) as shown in Table 2 below.

[0098] [Example 6] A tire of Example 6 was obtained in the same manner as in Example 1, except that the shape index F was set as shown in Table 2 below.

[0099] [Examples 7-8] Tires of Examples 7 and 8 were obtained in the same manner as in Example 1, except that the groove depth DG was changed to make the ratio (DG / DM) as shown in Table 2 below.

[0100] [Handling stability (initial response)] The prototype tire was mounted on a rim (size = 6.0J) and filled with air so that the internal pressure of the tire was 240 kPa. In a flat belt testing machine, the slip angle was set to 0.5° and the load was set to 4.22 kN, and the tire was run at a speed of 60 km / h to measure the cornering force. The results are shown as an index in Table 1-2 below. The higher the value, the better the initial responsiveness. In this evaluation, an index of 90 or more is acceptable as it is deemed that the required initial responsiveness is ensured.

[0101] [Handling stability (limit performance)] The prototype tire was mounted on a rim (size = 6.0J) and air was filled to adjust the internal pressure of the tire to 240kPa. The tire was mounted on a test vehicle (passenger car (minivan type)). The limit speed was measured when the test vehicle turned around a steady circle with a radius of 60m on a test course with a dry asphalt road surface. The results are shown as an index in Table 1-2 below. The higher the value, the better the limit performance.

[0102] [Noise performance] The prototype tire was mounted on a rim (size = 6.0J) and filled with air to an internal pressure of 240 kPa. The noise level (dB) in the 1000 Hz range was measured when the tire was run at a speed of 100 km / h using a drum testing machine (drum diameter = 1.7 m). The sound level meter was set up in accordance with JASO C606-81. The results are shown as an index in Table 1-2 below. The higher the value, the more the generation of hissing noise is suppressed and the better the noise performance. In this evaluation, an index greater than 100 is deemed to have achieved improved noise performance.

[0103] [Wear resistance] The prototype tire was mounted on a rim (size = 6.0J) and filled with air so that the internal pressure of the tire was 230 kPa. The wear energy of the land portion was measured using a wear energy measuring device. The load applied to the tire was set to 4.22 kN. The results are shown as an index in Table 1-2 below. The smaller the value, the smaller the wear energy and the better the wear resistance.

[0104] [Wet performance (WET)] A prototype tire was mounted on a rim (size = 6.0J) and air was filled to adjust the tire's internal pressure to 240kPa. The tire was mounted on a test vehicle (passenger car (minivan type)). The test vehicle was driven on a test course with a wet road surface (water film thickness = 1mm). The test vehicle was traveling at a speed of 100km / h when the brakes were applied, and the distance traveled from when the brakes were applied until the vehicle came to a stop (braking distance) was measured. The results are shown as an index in Table 1-2 below. The smaller the value, the shorter the braking distance and the better the tire's wet performance. In this evaluation, an index of 105 or less is acceptable as it is deemed to have the necessary wet performance.

[0105] [Table 1]

[0106] [Table 2]

[0107] As shown in Table 1-2, in Comparative Example 2, good wet performance was obtained, but the noise performance was not at an acceptable level. In Comparative Example 3, good noise performance was obtained, but the wet performance was not at an acceptable level. In contrast, in the Examples, an acceptable level of wet performance was obtained, and improvement in noise performance was confirmed. In other words, in the Examples, improvement in noise performance was achieved while ensuring the necessary wet performance. From these evaluation results, the superiority of the present invention is clear. [Industrial Applicability]

[0108] The technology described above that can achieve improved noise performance while ensuring necessary wet performance can be applied to various types of tires. [Explanation of symbols]

[0109] 2. Tires 4. Tread 6. Tread surface 8...Groove 10, 10s, 10m...Circumferential groove 12, 12c, 12m, 12m1, 12m2, 12s, 12s1, 12s2...Land 14... Circumferential narrow groove 18. Yokomizo 24...groove bottom 26 Groove wall 28. Edge

Claims

1. A tire having a tread that comes into contact with a road surface, The tread is formed with four circumferential grooves arranged in parallel in the axial direction, thereby forming five land portions in the tread, Among the five land portions, a land portion located at the center is a crown land portion, a land portion located on an outer side is a shoulder land portion, and a land portion located between the crown land portion and the shoulder land portion is a middle land portion, The tire is mounted on a standard rim, the internal pressure is adjusted to 230 kPa, and a load of 70% of the standard load is applied as a vertical load. The tire is brought into contact with a flat standard road surface, and the contact surface is the standard contact surface. A ratio of a total width of the groove widths of the four circumferential grooves to a ground contact width of the reference ground contact surface is 17.5% or more and 20.0% or less, In the reference contact surface, a ratio (P100 / P80) of an equatorial contact length P100 measured along the equator to a reference contact length P80 at a position corresponding to a width of 80% of the contact width is 1.30 or more and 1.35 or less, the crown land portion is a plain land portion having no grooves; Among the four circumferential grooves, two circumferential grooves located on axially outer sides are shoulder circumferential grooves, and two circumferential grooves located between the two shoulder circumferential grooves are middle circumferential grooves, a groove width of the middle circumferential groove is equal to or wider than a groove width of the shoulder circumferential groove, a ratio of a groove width of the middle circumferential groove to a ground contact width of the reference ground contact surface is 4.2% or more and 5.0% or less; tire.

2. a ratio of a land width of the crown land portion to a ground contact width of the reference ground contact surface is 10.0% or more and 13.0% or less; 2. The tire of claim 1.

3. A circumferential narrow groove is formed in the middle land portion, A ratio of the groove depth of the circumferential narrow groove to the groove depth of the circumferential groove is 35% or more and 45% or less.

3. A tire according to claim 1 or 2.

4. a ratio of a width of the shoulder land portion to a width of the crown land portion is 160% or more; A tire according to any one of claims 1 to 3.

5. A lateral groove is formed in the shoulder land portion, The lateral groove has an end portion within the shoulder land portion and extends from the end portion toward an end of the tread, The edges of both sides of the lateral groove are rounded. A tire according to any one of claims 1 to 4.

6. A ratio of a land width of the middle land portion to a land width of the crown land portion is 105% or more and 110% or less. A tire according to any one of claims 1 to 5.

7. A circumferential narrow groove and a dead-end narrow groove having one end within the middle land portion and connected to the circumferential groove at the other end are engraved in the middle land portion, the dead-end narrow groove is composed of an inner dead-end narrow groove located axially inside the circumferential narrow groove and an outer dead-end narrow groove located axially outside the circumferential narrow groove, The circumferential groove does not intersect with either the inner dead-end groove or the outer dead-end groove. A tire according to any one of claims 1 to 6.

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