tire

Abstract

To provide tire 2 that can achieve a reduction in air resistance while suppressing the impact on quietness and handling stability. [Solution] The tread 4 of the tire 2 is provided with circumferential grooves 10 and undulating portions 18. The undulating portions 18 are provided on the groove bottom surface 12 of the circumferential grooves 10. The undulating portions 18 are provided with conical elements 20. The conical elements 20 are either convex portions 22 or concave portions 24. The conical elements 20 are composed of a semi-conical SC or a part of a semi-conical SC. When the conical element 20 is a convex portion 22, the height Hc of the conical element 20 is lower than the groove depth DG of the circumferential grooves 10, and the inclination angle θc of the ridge line MLt of the conical element 20 is 75 degrees or less. When the conical element 20 is a concave portion 24, the depth Dr of the conical element 20 is shallower than the groove depth DG of the circumferential grooves 10, and the inclination angle θr of the valley line MLb of the conical element 20 is 75 degrees or less.

Description

Technical Field

[0001] The present invention relates to a tire.

Background Art

[0002] The air resistance of a tire affects the rolling resistance. In order to reduce the rolling resistance, reducing the air resistance of the tire has been considered. For reducing the air resistance, a tire provided with dimples on the side surface is disclosed in Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a tire capable of achieving reduction of air resistance while suppressing the influence on quietness and handling stability.

Means for Solving the Problems

[0005] The tire according to the present invention is equipped with a tread that contacts the road surface. The tread is equipped with a circumferential groove that extends continuously in the circumferential direction and an uneven portion provided on the groove bottom surface of the circumferential groove. The uneven portion is equipped with a plurality of conical elements arranged in the circumferential direction. The plurality of conical elements are convex portions that protrude from the groove bottom surface, or concave portions that are recessed from the groove bottom surface. Each of the plurality of conical elements is composed of a semi-cone having a semi-conical surface represented by a group of straight lines connecting a reference point and each point on the edge of a reference surface that does not include the reference point, or a part of the semi-cone. The edge of the reference surface constitutes a corner that includes the top of the convex portion or the bottom of the concave portion. The tip of the conical element is located on one side in the circumferential direction of the top of the convex portion or the bottom of the concave portion. When the conical element is a convex portion, the height of the conical element is lower than the groove depth of the circumferential groove, and the angle that the ridge of the convex portion makes with the groove bottom surface of the circumferential groove is 75 degrees or less. When the conical element is the recess, the depth of the conical element is shallower than the groove depth of the circumferential groove, and the angle that the valley line of the recess makes with respect to the groove bottom surface of the circumferential groove is 75 degrees or less. [Effects of the Invention]

[0006] According to the present invention, a tire can be obtained that can achieve a reduction in air resistance while suppressing the impact on quietness and handling stability. [Brief explanation of the drawing]

[0007] [Figure 1] This is an exploded view showing a portion of the tire tread according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view illustrating the structure of the grooves. [Figure 3] This is a cross-sectional view along line III-III in Figure 1. [Figure 4] This is a perspective view illustrating a semicone. [Figure 5] This is a perspective view illustrating the cone elements. [Figure 6] This is a perspective view illustrating variations of cone elements. [Figure 7]It is a perspective view for explaining a modified example of a conical element. [Figure 8] It is a development view showing a modified example of a conical element. [Figure 9] It is a cross-sectional view taken along line IX-IX of FIG. 3. [Figure 10] It is a cross-sectional view showing a modified example of a convex portion. [Figure 11] It is a cross-sectional view taken along line XI-XI of FIG. 3. [Figure 12] It is a cross-sectional view showing a modified example of a concave portion. [Figure 13] It is a cross-sectional view showing a modified example of a corrugated portion. [Figure 14] It is a cross-sectional view showing a modified example of a corrugated portion. [Figure 15] It is a development view showing a modified example of a corrugated portion. [Figure 16] It is a development view showing a modified example of a corrugated portion. [Figure 17] It is a cross-sectional view taken along line XVII-XVII of FIG. 16. [Figure 18] It is a development view showing a modified example of a corrugated portion. [Figure 19] It is a cross-sectional view taken along line XIX-XIX of FIG. 18. [Figure 20] It is a cross-sectional view taken along line XX-XX of FIG. 18. [Figure 21] It is a perspective view showing the convex portion P of Comparative Example 2.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, based on preferred embodiments, the present invention will be described in detail while appropriately referring to the drawings.

[0009] The tire of the present invention is assembled to a rim. Air is filled inside the tire, and the internal pressure of the tire is adjusted. The tire assembled to the rim is also called a tire-rim assembly. The tire-rim assembly includes a rim and a tire assembled to this rim.

[0010] In the present invention, the state where a tire is mounted on a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, and no load is applied to this tire is called the regular state.

[0011] In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in the regular state. The dimensions and angles of each part in the meridian cross-section of the tire that cannot be measured in the state where the tire is mounted on the regular rim are measured on the cut surface of the tire obtained by cutting the tire along the plane including the rotation axis. In this measurement, the tire is set so that the distance between the left and right beads matches the distance between the beads in the tire mounted on the regular rim. In addition, the structure of the tire that cannot be confirmed in the state where the tire is mounted on the regular rim is confirmed on the aforementioned cut surface.

[0012] The regular rim means the rim defined in the standard on which the tire depends. The "Standard Rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are regular rims.

[0013] The regular internal pressure means the internal pressure defined in the standard on which the tire depends. The "Maximum Air Pressure" in the JATMA standard, the "Maximum Value" published in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are regular internal pressures.

[0014] The regular load means the load defined in the standard on which the tire depends. The "Maximum Load Capacity" in the JATMA standard, the "Maximum Value" published in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are regular loads.

[0015] In this invention, the tread portion of a tire is the part of the tire that makes contact with the road surface. The bead portion is the part of the tire that is fitted onto the rim. The sidewall portion is the part of the tire that spans the space between the tread portion and the bead portion. The tire comprises the tread portion, a pair of bead portions, and a pair of sidewall portions.

[0016] [Practices that formed the basis of this invention] As mentioned earlier, a technique of adding dimples to the sidewall of a tire to reduce air resistance is known. If dimples are added not only to the sidewall but also to the tread, the tire may be able to further reduce air resistance. The tread area makes contact with the road surface. Adding dimples to the tread surface may reduce driving performance such as handling stability and ride comfort. The tread has grooves cut into it. The groove walls and bottom do not come into contact with the road surface. If dimples are placed in the grooves, the tire can minimize the impact of the dimples on driving performance. However, the groove width is narrow. It is difficult to place a sufficient number of dimples in the grooves to contribute to reducing air resistance. Therefore, the inventors diligently studied technologies other than dimples that could reduce air resistance while suppressing the impact on quietness and handling stability, and have completed the invention described below.

[0017] [Summary of Embodiments of the Invention] The present invention provides a tread that contacts a road surface, wherein the tread comprises a circumferential groove extending continuously in the circumferential direction and a relief portion provided on the groove bottom surface of the circumferential groove, the relief portion comprises a plurality of conical elements arranged in the circumferential direction, the plurality of conical elements being a convex portion protruding from the groove bottom surface or a concave portion recessed from the groove bottom surface, and each of the plurality of conical elements is composed of a semi-cone having a semi-cone represented by a group of lines connecting a reference point and each point on the edge of a reference plane that does not include the reference point, or a part of the semi-cone, and the edge of the reference plane is the top of the convex portion or A tire comprising a corner including the bottom of the recess, wherein the tip of the conical element is located on one side in the circumferential direction of the top of the convex portion or the bottom of the recess, and when the conical element is the convex portion, the height of the conical element is lower than the groove depth of the circumferential groove, and the angle that the ridge of the convex portion makes with respect to the groove bottom surface of the circumferential groove is 75 degrees or less, and when the conical element is the recess, the depth of the conical element is shallower than the groove depth of the circumferential groove, and the angle that the valley of the recess makes with respect to the groove bottom surface of the circumferential groove is 75 degrees or less.

[0018] The tire of the present invention can achieve a reduction in air resistance while suppressing the impact on quietness and handling stability. Although the mechanism by which this effect is achieved is not yet clear, it is presumed to be as follows.

[0019] The raised sections on the groove bottoms of the circumferential grooves generate minute longitudinal vortices. This causes fluctuations in the airflow over the tread surface. Specifically, the raised sections are comprised of multiple conical elements arranged circumferentially, each of which is composed of a semi-cone or a part of a semi-cone. In other words, the conical elements have a shape that tapers towards the tip. Some of the longitudinal vortices generated in the raised sections move from the circumferential grooves to the tread surface. This suppresses airflow separation downstream. This tire can reduce air resistance. The uneven surface alters the air density within the circumferential grooves. This expands the frequency range of air column resonance noise. The maximum sound pressure in a specific frequency band is reduced. The uneven surface can contribute to reducing air column resonance noise generated in the circumferential grooves. Furthermore, the uneven surface creates fluctuations in the water flow within the circumferential grooves during braking on wet road surfaces. This reduces the pressure loss of water within the circumferential grooves. Water flows more easily within the circumferential grooves even in downstream areas. The rate at which hydroplaning occurs increases. This tire can achieve a reduction in air resistance while suppressing the impact on quietness and handling stability.

[0020] Preferably, the angle that the longitudinal direction of the conical element makes with respect to the longitudinal direction of the circumferential groove is 45 degrees or less. In this case, the tire can further reduce air resistance while suppressing the impact on quietness and handling stability.

[0021] Preferably, when the conical element is a semicone, the projected shape of the conical element onto the groove bottom surface is the reference projected shape of the conical element, the projected shape of the undulation onto the groove bottom surface is composed of a combination of multiple reference projected shapes, and the ratio An / Aa of the projected area An of the undulation to the reference projected area Aa, which is expressed as the product of the projected area of ​​the reference projected shape and the number of conical elements constituting the undulation, is 10% or more and 100% or less. In this case, the tire can further reduce air resistance while suppressing the impact on quietness and handling stability.

[0022] Preferably, the conical element has ridges extending along its sides, the depth of which is 50% or less of the height of the conical element. In this case, the tire can further reduce air resistance while suppressing the impact on quietness and handling stability.

[0023] Thus, the tire of the present invention can achieve a reduction in air resistance while suppressing the impact on quietness and handling stability. This will be explained in detail below using the tire shown in Figure 1 as an example.

[0024] [Details of the Embodiments of the Invention]

[0025] Figure 1 is a plan view showing a portion of the tread 4 of a tire 2 according to one embodiment of the present invention. This tire 2 is a pneumatic tire for a passenger car.

[0026] Although the present invention will be explained using passenger car tires as an example, the tires to which the present invention can be applied are not limited to passenger car tires. The present invention can also be applied to tires for small trucks, truck and bus tires, motorcycle tires, and the like.

[0027] The direction indicated by the double arrow AD is the axial direction of tire 2. The axial direction of tire 2 means the direction parallel to the rotation axis of tire 2. The direction indicated by the double arrow CD is the circumferential direction of tire 2. The direction perpendicular to the plane of paper in Figure 1 is the radial direction of tire 2. The dashed line EL extending in the circumferential direction represents the equatorial plane of tire 2. In the axial direction, the direction approaching the equatorial plane is the axial inward direction of tire 2, and the direction moving away from the equatorial plane is the axial outward direction of tire 2. The direction indicated by arrow CD1 is the first circumferential direction side of tire 2, and the direction indicated by arrow CD2 is the second circumferential direction side of tire 2. The tread 4 of tire 2 makes contact with the road surface from the second circumferential direction side toward the first circumferential direction side. The second circumferential direction side is the first side of tire 2 to make contact, and the first circumferential direction side is the rear side of tire 2 to make contact.

[0028] This tire 2 is equipped with a tread 4. The tread 4 is made of cross-linked rubber. The tread 4 is located radially outward of the tire 2 and extends circumferentially. The outer surface of the tread 4 includes a tread surface 6. The tread 4 contacts the road surface at the tread surface 6. The tread 4 has a tread surface 6 that contacts the road surface.

[0029] In this invention, the internal structure of the tire 2 is not particularly limited. Although not described in detail, this tire 2 has an internal structure that is typical for passenger car tires. The tread 4 is one of the elements that make up this internal structure.

[0030] Tread 4 has grooves 8 cut into it. This forms the tread pattern. Tread 4 has a tread pattern.

[0031] Figure 2 shows a cross-section of groove 8. The main components of groove 8 will be explained based on Figure 2. The cross-section of the groove 8 is a cross-section along a plane perpendicular to the length direction of the groove 8. The direction indicated by the double arrow RD is the radial direction of the tire 2. The side indicated by arrow RD1 is the radially outer side of the tire 2, and the side indicated by arrow RD2 is the radially inner side of the tire 2. This groove 8 is a circumferential groove, which will be described later. The bottom surface of the circumferential groove of the present invention is provided with an uneven surface, but for the sake of explanation, the uneven surface is not shown in Figure 2.

[0032] The groove 8 comprises a groove bottom surface 8B and a pair of groove walls 8W. The groove bottom surface 8B shown in Figure 2 is flat. The groove bottom surface 8B may also be curved. The pair of groove walls 8W include the groove opening 8M of the groove 8. The groove walls 8W span between the groove opening 8M and the groove bottom surface 8B.

[0033] The groove width of groove 8 is represented by the shortest distance between a pair of groove walls 8W, namely the first groove wall 8W and the second groove wall 8W (hereinafter referred to as the groove wall distance). The groove wall distance is measured along a plane containing a pair of edges 8E that constitute the groove opening 8M, or along a plane parallel to this plane. The shortest distance from one edge 8E to the other edge 8E, measured along the plane containing the pair of edges 8E, is the groove width W of groove 8 in the groove opening 8M. The length indicated by the double arrow D is the groove depth of groove 8. The groove depth D of groove 8 is represented by the maximum distance from the groove bottom surface 8B to the plane containing the left and right edges 8E, measured along the normal of this plane. The direction of the normal of the plane containing the left and right edges 8E is the depth direction of groove 8.

[0034] The tread 4 of this tire 2 is provided with a plurality of circumferential grooves 10 as grooves 8. The plurality of circumferential grooves 10 are aligned in the axial direction and extend continuously in the circumferential direction. Each of the plurality of circumferential grooves 10 is provided with a groove bottom surface 12 and a pair of groove walls 14.

[0035] Figure 3 shows a cross-section of the circumferential groove 10 along the line III-III in Figure 1. The line III-III in Figure 1 is the center line of the groove width of the circumferential groove 10. Figure 3 shows a cross-section of the circumferential groove 10 along a plane perpendicular to the groove bottom surface 12 and containing the groove width center line. The length indicated by the double arrow DG is the groove depth of the circumferential groove 10.

[0036] The tread 4 of this tire 2 further comprises a raised section 18. The tread 4 comprises a circumferential groove 10 and a raised section 18. The raised section 18 is provided on the groove bottom surface 12 of the circumferential groove 10. The undulating section 18 comprises a plurality of conical elements 20. The plurality of conical elements 20 are arranged in the circumferential direction. There is no gap between two adjacent conical elements 20. The plurality of conical elements 20 of this undulating section 18 are arranged without spacing. The plurality of conical elements 20 may be arranged with spacing between them. If the plurality of conical elements 20 are arranged with spacing between them, the plurality of conical elements 20 are arranged in the circumferential groove 10 such that at least one conical element 20 is within the contact surface between the tire 2 and the road surface.

[0037] The multiple conical elements 20 provided on the undulating portion 18 are either convex portions 22 or concave portions 24. The convex portions 22 protrude from the groove bottom surface 12 of the circumferential groove 10. The concave portions 24 are recessed from the groove bottom surface 12 of the circumferential groove 10. The conical element 20 has a shape that tapers towards the tip 26, whether it is a convex portion 22 or a concave portion 24. The conical element 20 of this tire 2 is composed of a semicone or a part of a semicone, as described below.

[0038] Figure 4 shows an example of a semicone. The shape of a semicone is explained based on the semicone SC shown in Figure 4. The semi-conical SC comprises a reference point BP included in the groove bottom surface 12, a reference surface BS that stands upright relative to the groove bottom surface 12, and a side surface SS. The reference point BP is a point located away from the reference surface BS and not included in the reference surface BS. The side surface SS is a surface that spans between the reference point BP and the edge BSe of the reference surface BS. In Figure 4, the solid line SP is a straight line connecting the reference point BP and a point on the edge BSe of the reference surface BS. The side surface SS is represented by a group of straight lines connecting the reference point BP and each point on the edge BSe of the reference surface BS. The straight line SP is one of the straight lines included in this group of straight lines.

[0039] In the present invention, a convex portion 22 protruding from the groove bottom surface 12 or a concave portion 24 recessed from the groove bottom surface 12, among solids having a tapered shape, is called a semicone if it comprises a reference point BP included in the groove bottom surface 12, a reference surface BS that stands upright relative to the groove bottom surface 12 and does not include the reference point BP, and a side surface SS, where the side surface SS is represented by a group of lines connecting the reference point BP and each point of the edge BSe of the reference surface BS. The side surface SS of this solid is called a semipyramid surface.

[0040] The reference plane BS of the semi-cone SC shown in Figure 4 is a semicircle. This semi-cone SC has a semi-conical shape. There are no particular restrictions on the shape of the semi-cone, as long as it tapers from the reference plane BS toward the reference point BP. Examples of semi-conical shapes include a semi-elliptical cone, a semi-angular pyramid, a semi-bicone, a semi-bielliptical cone, and a semi-bigonal pyramid. The reference plane BS of a semi-conical semi-cone SC is the same semicircle as the reference plane BS of a semi-conical semi-cone SC. The reference plane BS of a semi-elliptical or semi-bielliptical semi-cone SC is an ellipse. The reference plane BS of a semi-conical semi-cone SC is a polygon.

[0041] Figure 5 is a perspective view showing the conical element 20 as the convex portion 22 shown in Figure 3. The conical element 20 comprises a tip 26, a base 28, and a side surface 30. The base surface 28 stands upright relative to the groove bottom surface 12 of the circumferential groove 10. The base surface 28 is positioned opposite the tip 26. The side surface 30 spans the space between the tip 26 and the base surface 28. The tip 26 of the conical element 20 shown in Figure 5 is a point and is contained within the groove bottom surface 12. This point, the tip 26, is positioned away from the bottom surface 28 and is not contained within the bottom surface 28. The solid line LS in Figure 5 is a straight line connecting the tip 26 to a point on the edge 28e of the bottom surface 28. The side surface 30 of this conical element 20 is represented by a group of straight lines connecting the point, the tip 26, to each point on the edge 28e of the bottom surface 28. In the cone element 20 shown in Figure 5, the point 26 corresponds to the reference point BP of the semicone SC, the base 28 corresponds to the reference plane BS of the semicone SC, and the side surface 30 corresponds to the semicone surface SS of the semicone SC. This cone element 20 is composed of a semicone SC.

[0042] Figure 6 shows a modified example of the cone element 20 shown in Figure 5. The tip 26 of this cone element 20 is composed of a surface rather than a point. The side surface 30 of this modified example is located further away from the base surface 28 than the tip 26 and is included in a surface represented by a group of lines connecting a point 32 included in the groove base surface 12 to each point on the edge 28e of the base surface 28. The solid line LSa is a line connecting point 32 to a point on the edge 28e of the base surface 28, and is one of the lines included in the group of lines.

[0043] In the modified example of the cone element 20 shown in Figure 6, point 32, which is located further away from the base surface 28 than the tip 26 of the cone element 20, corresponds to the reference point BP of the semicone SC. The base surface 28 corresponds to the reference plane BS of the semicone SC. The plane represented by the set of lines connecting point 32 and each point on the edge 28e of the base surface 28 corresponds to the semiconical surface SS of the semicone SC. The side surface 30 of this modified example is included in the semiconical surface SS. The modified example in Figure 6 is composed of a part of the semicone SC. In the cone element 20 shown in Figure 6, the shape of the base surface 28 and the shape of the tip 26, which is a surface, are similar to each other.

[0044] In Figure 5, the solid line CRt represents the boundary between the base 28 and the side surface 30, and is the corner of the cone element 20. The edge 28e of the base 28 and the edge 30e of the side surface 30 constitute the corner CRt of the cone element 20. The conical element 20 shown in Figure 5 is a solid enclosed by a base 28, a side surface 30, and the groove bottom surface 12 of the circumferential groove 10. Both ends Ce of the corner CRt of the conical element 20 are contained within the groove bottom surface 12 of the circumferential groove 10.

[0045] In Figure 5, the position indicated by the symbol T is the apex of the convex portion 22 of the conical element 20. The apex T is the position where the length from the groove bottom surface 12 to the edge 28e of the base surface 28 of the conical element is longest, measured along the normal to the groove bottom surface 12 of the circumferential groove 10. The apex T is included in the corner CRt of the conical element 20. In Figure 3, the length indicated by the double arrow Hc is the height of the conical element 20. The height Hc is the shortest distance from the groove bottom surface 12 to the apex T of the conical element 20.

[0046] In Figure 5, the solid line LBt is the normal to the groove bottom surface 12, passing through the apex T of the conical element 20. The position indicated by the sign CP is the intersection of the normal LBt and the groove bottom surface 12. The intersection point CP is called the shape reference point of the conical element 20. The straight line BL connecting this shape reference point CP and the reference point BP of the semi-cone SC that constitutes the conical element 20 is the reference line of the conical element 20. The reference line BL is contained within the groove bottom surface 12. The orientation of the reference line BL represents the length direction of the conical element 20. The straight line MLt connecting the reference point BP and the apex T is the edge of the conical element 20 as a convex portion 22. The angle θc in Figure 3 is the angle that the edge MLt makes with respect to the reference line BL. This angle θc is the angle that the edge MLt of the convex portion 22 makes with respect to the groove bottom surface 12 of the circumferential groove 10, and is also called the inclination angle θc of the edge MLt.

[0047] Figure 7 is a perspective view showing the conical element 20 as the recess 24 shown in Figure 3. This conical element 20, like the conical element 20 described above as the convex portion 22, also comprises a tip 26, a base 28, and a side surface 30. The base surface 28 stands upright relative to the groove bottom surface 12 of the circumferential groove 10. The base surface 28 is positioned opposite the tip 26. The side surface 30 bridges the space between the tip 26 and the base surface 28. The tip 26 of the conical element 20 shown in Figure 7 is also a point and is included in the groove bottom surface 12. The side surface 30 of this conical element 20, like the side surface 30 of the conical element 20 as a convex portion 22, is also represented by a group of lines connecting the tip 26, which is a point, to each point on the edge 28e of the bottom surface 28. In the cone element 20 shown in Figure 7, the point 26 corresponds to the reference point BP of the semicone SC, and the side surface 30 corresponds to the semiconical surface SS of the semicone SC. This cone element 20 is also composed of a semicone SC.

[0048] In Figure 7, the portion indicated by the solid line CRb is the boundary between the base surface 28 and the side surface 30, and is the corner of the conical element 20 as a recess 24. The edge 28e of the base surface 28 and the edge 30e of the side surface 30 constitute the corner CRb. When there is no distinction between a corner CRb as a corner and a corner CRb as an angle, both corner CRb and corner CRb are represented as corner CR.

[0049] Since the conical element 20 shown in Figure 7 is a recess 24, the groove bottom surface 12 of the circumferential groove 10 on which the conical element 20 is placed is not shown. However, this conical element 20 is also a solid enclosed by its bottom surface 28, side surface 30, and the groove bottom surface 12 of the circumferential groove 10. Both ends Re of the corner CRb of the conical element 20 are included in the groove bottom surface 12 of the circumferential groove 10. In Figure 7, the position indicated by the symbol B is the bottom of the recess 24, which is the conical element 20. The bottom B is the position where the length from the groove bottom surface 12 to the edge 28e of the bottom surface 28 of the conical element is longest, measured along the normal to the groove bottom surface 12 of the circumferential groove 10. The bottom B is included in the corner CRb of the conical element 20. In Figure 3, the length indicated by the double arrow Dr is the depth of the conical element 20. The depth Dr is the shortest distance from the groove bottom surface 12 to the bottom B of the conical element 20.

[0050] The solid line LBb is the normal to the groove bottom surface 12, passing through the bottom B of the conical element 20. The intersection of this normal line LBb and the groove bottom surface 12 of the circumferential groove 10 is the shape reference point CP of the conical element 20 as a recess 24. If the groove bottom surface 12 cannot be identified, a plane containing the boundary between the bottom surface 28 and the groove bottom surface 12, and the boundary between the side surface 30 and the groove bottom surface 12, which constitute the mouth of the recess 24, is used as a virtual groove bottom surface, and the bottom B and shape reference point CP are identified. In Figure 7, the straight line BL connecting the shape reference point CP and the reference point BP of the semi-cone SC that constitutes the conical element 20 is the reference line of the conical element 20. The straight line MLb connecting the reference point BP and the base B is the valley line when the conical element 20 is a concave section 24. The angle θr in Figure 3 is the angle that the valley line MLb makes with respect to the reference line BL. This angle θc is the angle that the valley line MLb makes with respect to the groove bottom surface 12 of the circumferential groove 10, and is also called the inclination angle θr of the valley line MLb.

[0051] The conical elements 20 shown in Figures 5 and 7 are composed of a semi-conical shape. The conical elements 20 shown in Figures 5 and 7 have a semi-conical shape. The conical element 20 shown in Figure 6 is composed of a part of a semi-conical shape. In the conical element 20 shown in Figure 6, as mentioned above, the shape of the base 28 and the shape of the tip 26, which is a surface, are similar to each other. The conical element 20 shown in Figure 6 has a semi-frustoconical shape.

[0052] Figure 8 shows a modified example of the conical element 20. Although not described in detail, this conical element 20 is composed of a semi-conical shape. In this case, for the conical element 20 which is a convex portion 22, the cross-section of the conical element 20 along the plane containing the corner CRt of the conical element 20 corresponds to the base surface 28 of the conical element 20, i.e., the reference plane BS of the semi-conical SC. For the conical element 20 which is a concave portion 24, the cross-section of the conical element 20 along the plane containing the corner CRb of the conical element 20 corresponds to the reference plane BS of the semi-conical SC. Although not shown, even for the conical element 20 which is a semi-elliptical cone, the cross-section of the conical element 20 along the plane containing the corner CR of the conical element 20 corresponds to the reference plane BS of the semi-conical SC.

[0053] Figure 9 shows a cross-section of the conical element 20 along the line IX-IX in Figure 3. The line IX-IX in Figure 3 passes through a point where the length of the conical element 20 is halved. The cross-section of this conical element 20 is the cross-section of the convex portion 22. The cross-sectional shape of this conical element 20 is a semicircle. As mentioned above, this conical element 20 is composed of a semiconical hemi-cone. The cross-sectional shape of the conical element 20 shown in Figure 9 and the shape of the base 28 are similar to each other.

[0054] Figure 10 shows a modified example of the conical element 20 as the convex portion 22. Similar to Figure 9, Figure 10 shows a cross-section of the conical element 20 at a point where its length is halved. The cross-sectional shape of this modified example is semi-elliptical. This modified example consists of a semi-elliptical cone. The apex T, height Hc, ridge MLt, and inclination angle θc of this modified example are set in the same manner as the conical element 20 as the convex portion 22 shown in Figure 3, which has a semicircular cross-sectional shape. The conical element 20 shown in Figure 10 is provided in the circumferential groove 10 such that the minor axis of the semi-ellipse cross-sectional shape is contained within the groove bottom surface 12. Alternatively, the conical element 20 may be provided in the circumferential groove 10 such that the major axis of the semi-ellipse cross-sectional shape is contained within the groove bottom surface 12.

[0055] Figure 11 shows a cross-section of the conical element 20 along the line XI-XI in Figure 3. This cross-section of the conical element 20 is the cross-section of the recess 24. Figure 11, like Figure 9, shows a cross-section of the conical element 20 at a position where the length of the conical element 20 is halved. Figure 11 also shows the convex portion 22 located on the rear side of the recess 24. The cross-sectional shape of this conical element 20 is a semicircle. As mentioned above, this conical element 20, which serves as the recess 24, is also composed of a semi-conical hemicone.

[0056] Figure 12 shows a modified example of the conical element 20 as a recess 24. Similar to Figure 11, Figure 12 shows a cross-section of the conical element 20 at a point where its length is halved. The cross-sectional shape of this modified example is semi-elliptical. This modified example has a semi-elliptical cone. The base B, depth Dr, valley line MLb, and inclination angle θr of this modified example are set in the same manner as the conical element 20 as a recess 24 shown in Figure 3, which has a semicircular cross-sectional shape. The conical element 20 shown in Figure 12, like the conical element 20 shown in Figure 10, is provided in the circumferential groove 10 such that the minor axis of its semi-elliptical cross-sectional shape is contained within the groove bottom surface 12. Alternatively, the conical element 20 may be provided in the circumferential groove 10 such that the major axis of its semi-elliptical cross-sectional shape is contained within the groove bottom surface 12.

[0057] The undulating portion 18 shown in Figure 3 comprises conical elements 20, each consisting of a convex portion 22 and a concave portion 24. The shape of the conical element 20 as a concave portion 24 is the same as the shape of the conical element 20 as a convex portion 22. The convex portions 22 and concave portions 24 are arranged alternately in the circumferential direction. As shown in Figure 13, all of the conical elements 20 constituting the undulating portion 18 may be convex portions 22. As shown in Figure 14, all of the conical elements 20 constituting the undulating portion 18 may be concave portions 24.

[0058] As described above, the conical elements 20 of this tire 2 are composed of a semi-cone or a part of a semi-cone. Each of the multiple conical elements 20 provided on the undulating portion 18 is composed of a semi-cone SC having a semi-cone SS represented by a group of straight lines connecting a reference point BP and each point on the edge BSe of the reference plane BS that does not include the reference point BP, or a part of this semi-cone SC, where the edge BSe of the reference plane BS constitutes a corner CRt including the apex T of the convex portion 22 or a corner CRb including the bottom B of the concave portion 24. When the conical element 20 is a convex portion 22, the height Hc of the conical element 20 is lower than the groove depth DG of the circumferential groove 10, and the inclination angle θc of the ridge line MLt of the conical element 20 is 75 degrees or less. When the conical element 20 is a concave portion 24, the depth Dr of the conical element 20 is shallower than the groove depth DG of the circumferential groove 10, and the inclination angle θr of the valley line MLb of the conical element 20 is 75 degrees or less.

[0059] In this tire 2, the raised portion 18 provided on the groove bottom surface 12 generates minute longitudinal vortices. This causes fluctuations in the airflow on the surface of the tread 4. As mentioned above, the raised portion 18 is equipped with a plurality of conical elements 20 arranged in the circumferential direction, and each of the plurality of conical elements 20 is composed of a semi-cone or a part of a semi-cone. In other words, the conical elements 20 have a shape that tapers towards the tip 26. The conical elements 20 promote the movement of the longitudinal vortices generated in the raised portion 18 from the circumferential groove 10 to the tread surface 6. Since a portion of the longitudinal vortices generated in the raised portion 18 moves from the circumferential groove 10 to the tread surface 6, separation of the airflow downstream is suppressed. This tire 2 can reduce air resistance.

[0060] The undulating portion 18 changes the air density within the circumferential groove 10. This expands the frequency range of the air column resonance sound. The maximum sound pressure in a specific frequency band is reduced. The undulating portion 18 can contribute to reducing the air column resonance sound generated in the circumferential groove 10. This tire 2 has good quietness. The undulating sections 18 further create fluctuations in the water flow within the circumferential grooves 10 during braking on wet road surfaces. This reduces the pressure loss of water within the circumferential grooves 10, thereby promoting water flow within the grooves 10. Water flows more easily within the circumferential grooves 10 even in the downstream areas. As a result, the rate at which hydroplaning occurs increases. This tire 2 has good handling stability even on wet road surfaces.

[0061] This tire 2 can achieve a reduction in air resistance while minimizing the impact on quietness and handling stability.

[0062] In the undulating portion 18 shown in Figure 3, all conical elements 20 constituting the undulating portion 18 are provided on the groove bottom surface 12 such that their tips 26 are positioned on the leading side. The tip 26 of the conical element 20 as a convex portion 22 is located on the second circumferential direction side of the apex T of the convex portion 22, and the tip 26 of the conical element 20 as a concave portion 24 is located on the second circumferential direction side of the bottom B of the concave portion 24. In this tire 2, the tip 26 of the conical element 20 only needs to be located on one circumferential side of the apex T of the convex portion 22 or the bottom B of the concave portion 24, and the tip 26 of the conical element 20 may also be located on the first circumferential direction side of the apex T of the convex portion 22 or the bottom B of the concave portion 24. The tip 26 of the conical element 20 may be located on both sides of the apex T of the convex portion 22 or the bottom B of the concave portion 24 in the circumferential direction. From the viewpoint of effective generation of longitudinal vortices, it is preferable that the tip 26 of the conical element 20 as a convex portion 22 is located on the second circumferential direction side of the apex T of the convex portion 22, and the tip 26 of the conical element 20 as a concave portion 24 is located on the second circumferential direction side of the bottom B of the concave portion 24. In other words, it is preferable that all conical elements 20 constituting the undulating portion 18 are provided on the groove bottom surface 12 such that their tips 26 are located on the leading side.

[0063] As mentioned above, when the conical element 20 is a convex portion 22, the height Hc of the conical element 20 is lower than the groove depth DG of the circumferential groove 10. Specifically, the ratio Hc / DG of the height Hc of the conical element 20 to the groove depth DG of the circumferential groove 10 is preferably between 1% and 75%. Setting the ratio Hc / DG to 1% or more promotes the generation of minute longitudinal vortices. The conical elements 20 promote the movement of longitudinal vortices from the circumferential grooves 10 to the tread surface 6, thereby suppressing airflow separation downstream. This tire 2 can reduce air resistance. Since changes in air density within the circumferential grooves 10 become more likely, the air column resonance noise generated in the circumferential grooves 10 is reduced. This tire 2 has good quietness. Since the pressure loss of water within the circumferential grooves 10 is reduced, water flow within the circumferential grooves 10 is promoted, and the rate at which hydroplaning occurs increases. This tire 2 can maintain good handling stability on wet road surfaces. From these viewpoints, a ratio Hc / DG of 30% or more is more preferable, and 45% or more is even more preferable. By setting the ratio Hc / DG to 75% or less, a moderate longitudinal vortex is generated. Since airflow separation is suppressed, tire 2 can maintain low air resistance. Tire 2 can maintain good quietness because it can sustain the effect of reducing air column resonance noise. Since the pressure loss reduction effect is sustained, tire 2 can maintain good handling stability on wet road surfaces. From these viewpoints, a ratio Hc / DG of 60% or less is more preferable, and 55% or less is even more preferable.

[0064] As mentioned above, when the conical element 20 is a convex portion 22, the inclination angle θc of the ridge line MLt of the conical element 20 is 75 degrees or less. This generates a moderate longitudinal vortex. Since airflow separation is suppressed, the tire 2 can maintain low air resistance. The tire 2 can maintain good quietness because it can sustain the effect of reducing air column resonance noise. Since the pressure loss reduction effect is sustained, the tire 2 can maintain good handling stability on wet road surfaces. From these viewpoints, it is preferable that the inclination angle θc is 45 degrees or less. The inclination angle θc should be greater than 0 degrees, and no preferred lower limit for the angle θc is set.

[0065] As mentioned above, when the conical element 20 is a recess 24, the depth Dr of the conical element 20 is shallower than the groove depth DG of the circumferential groove 10. Specifically, the ratio Dr / DG of the depth Dr of the conical element 20 to the groove depth DG of the circumferential groove 10 is preferably 1% or more and 75% or less. Setting the ratio Dr / DG to 1% or more promotes the generation of minute longitudinal vortices. The conical elements 20 promote the movement of longitudinal vortices from the circumferential grooves 10 to the tread surface 6, thereby suppressing airflow separation downstream. This tire 2 can reduce air resistance. Since changes in air density within the circumferential grooves 10 become more likely, the air column resonance noise generated in the circumferential grooves 10 is reduced. This tire 2 has good quietness. Since the pressure loss of water within the circumferential grooves 10 is reduced, water flow within the circumferential grooves 10 is promoted, and the rate at which hydroplaning occurs increases. This tire 2 can maintain good handling stability on wet road surfaces. From these viewpoints, a ratio of 30% or more is more preferable, and 45% or more is even more preferable. By setting the ratio Dr / DG to 75% or less, a moderate longitudinal vortex is generated. Since airflow separation is suppressed, tire 2 can maintain low air resistance. Tire 2 can maintain good quietness because it can sustain the effect of reducing air column resonance noise. Since the pressure loss reduction effect is sustained, tire 2 can maintain good handling stability on wet road surfaces. From these viewpoints, a ratio of 60% or less is more preferable, and 55% or less is even more preferable.

[0066] As mentioned above, when the conical element 20 is a concave 24, the inclination angle θr of the valley line MLb of the conical element 20 is 75 degrees or less. This generates a moderate longitudinal vortex. Since airflow separation is suppressed, the tire 2 can maintain low air resistance. The tire 2 can maintain good quietness because it can sustain the effect of reducing air column resonance noise. Since the pressure loss reduction effect is sustained, the tire 2 can maintain good handling stability on wet road surfaces. From these viewpoints, it is preferable that the inclination angle θr is 45 degrees or less. The inclination angle θr only needs to be greater than 0 degrees, and no preferred lower limit for the angle θr is set.

[0067] As mentioned above, the conical elements 20 provided on the undulating portion 18 are either convex portions 22 or concave portions 24. It is preferable that the undulating portion 18 of this tire 2 is provided with convex portions 22 as conical elements 20. There is a concern that the convex portions 22 will obstruct the airflow in the circumferential grooves 10, leading to increased air resistance for the tire 2. However, as mentioned above, the conical elements 20 of this tire 2 have a shape that tapers from the bottom surface 28 towards the front 26, generating longitudinal vortices. The generation of these longitudinal vortices suppresses the separation of airflow downstream. This tire 2 can reduce air resistance even though the undulating portion 18 is provided with convex portions 22 as conical elements 20.

[0068] From the viewpoint of effective generation of longitudinal vortices, it is more preferable that the undulating portion 18 further comprises concave portions 24 as conical elements 20 in addition to the convex portions 22. In this case, it is even more preferable that the convex portions 22 and concave portions 24 are arranged alternately in the circumferential direction. And it is particularly preferable that the convex portions 22 and concave portions 24 are arranged alternately in the circumferential direction without any gaps between them.

[0069] Figure 15 shows a modified example of the undulating portion 18. This modified example of the undulating portion 18 also includes convex portions 22 and concave portions 24 as conical elements 20, with the convex portions 22 and concave portions 24 being arranged alternately in the circumferential direction. As shown in Figure 15, the tire 2 can have the conical elements 20 positioned at an angle with respect to the longitudinal direction of the circumferential groove 10.

[0070] In Figure 15, angle θt represents the angle that the reference line BL of the conical element 20 makes with respect to the longitudinal direction of the circumferential groove 10. This angle θt represents the angle that the longitudinal direction of the conical element 20 makes with respect to the longitudinal direction of the circumferential groove 10 (hereinafter referred to as the inclination angle of the conical element 20).

[0071] The inclination angle θt of the conical element 20 is preferably 45 degrees or less. This promotes the generation of minute but non-uniform longitudinal vortices. This suppresses airflow separation downstream. This tire 2 can reduce air resistance. Because the air density in the circumferential groove 10 changes in various ways due to the minute longitudinal vortices, air column resonance noise is reduced. This tire 2 has good quietness. Because the pressure loss of water in the circumferential groove 10 is reduced, the rate at which hydroplaning occurs increases. This tire 2 can maintain good handling stability on wet road surfaces. From these viewpoints, the inclination angle θt of the conical element 20 is more preferably 25 degrees or less. This inclination angle θt is particularly preferably 0 degrees.

[0072] When the reference line BL of the conical element 20 is inclined with respect to the longitudinal direction of the circumferential groove 10, it is preferable that the direction of the inclination of the reference line BL of the rear conical element 20 is opposite to the direction of the inclination of the reference line BL of the front conical element 20. This suppresses airflow separation on the downstream side, so that the tire 2 can reduce air resistance. Air column resonance noise is reduced, so the tire 2 has good quietness. The rate at which hydroplaning occurs is increased, so the tire 2 can maintain good handling stability on wet road surfaces.

[0073] When the direction of the inclination of the reference line BL of the rear-facing conical element 20 is opposite to the direction of the inclination of the reference line BL of the leading-facing conical element 20, it is preferable that the inclination angle θt of the reference line BL of the rear-facing conical element 20 is the same as the inclination angle θt of the reference line BL of the leading-facing conical element 20. This suppresses airflow separation on the downstream side, so the tire 2 can reduce air resistance. Air column resonance noise is reduced, so the tire 2 has good quietness. The rate at which hydroplaning occurs is increased, so the tire 2 can maintain good handling stability on wet road surfaces.

[0074] Figure 16 shows a modified example of the undulating portion 18. Figure 17 shows a cross-section of this modified example of the undulating portion 18 along the line XVII-XVII in Figure 16.

[0075] This modified example, the undulating section 18, also comprises multiple conical elements 20. This undulating section 18 also includes convex portions 22 and concave portions 24 as conical elements 20, with the convex portions 22 and concave portions 24 alternating in the circumferential direction. Each conical element 20 has a shape that tapers from the base 28 towards the tip 26. The conical elements 20 are not semi-conical, but rather semi-frustoconical. These conical elements 20 are composed of a part of a semi-conical semi-cone.

[0076] These undulating sections 18 also generate minute but non-uniform longitudinal vortices, which suppresses airflow separation downstream. This allows the tire 2 to reduce air resistance. These undulating sections 18 alter the air density within the circumferential grooves 10. This reduces the maximum sound pressure in a specific frequency band. As air column resonance noise is reduced, the tire 2 exhibits good quietness. These undulating sections 18 reduce water pressure loss within the circumferential grooves 10. As the rate at which hydroplaning occurs increases, the tire 2 can maintain good handling stability on wet surfaces. The tire 2, which employs the undulating section 18 shown in Figure 16, can also reduce air resistance while suppressing the impact on quietness and handling stability.

[0077] As mentioned above, the conical elements 20 that constitute the undulating portion 18 shown in Figure 16 have a semi-frustoconical shape. The projected shape of these conical elements 20 onto the groove bottom surface 12 is an isosceles trapezoid. As suggested by the configuration of the undulation portion 18 shown in Figure 16, the projected shape of this undulation portion 18 onto the groove bottom surface 12 has a configuration in which multiple isosceles trapezoidal projection shapes are arranged without gaps. In the case of a conical element 20 having a semiconical shape, the projected shape of the conical element 20 onto the groove bottom surface 12 is an isosceles triangle. As mentioned above, the conical element 20 that constitutes this undulation portion 18 is composed of a part of a semiconical semi-cone. The projected shape of this undulation portion 18 is obtained by arranging multiple isosceles triangle projection shapes, which are the projected shapes of semicones, with overlapping shapes.

[0078] As described above, the conical elements 20 that constitute the undulating portion 18 are composed of semicones or parts of semicones. In the present invention, when the conical elements 20 are semicones, the projection shape of the conical elements 20 onto the groove bottom surface 12 is the basic projection shape. As described above, the undulating portion 18 is composed of a combination of multiple conical elements 20. The projection shape of the undulating portion 18 onto the groove bottom surface 12 is composed of a combination of multiple basic projection shapes.

[0079] In this tire 2, the projected area An of the projection shape of the undulating portion 18 onto the groove bottom surface 12, and the reference projected area Aa, which is expressed as the product of the projected area of ​​the basic projection shape and the number of conical elements 20 constituting the undulating portion 18, are effectively controlled, taking into consideration quietness, handling stability, and the impact on air resistance. Specifically, the ratio An / Aa of the projected area An of the projection shape of the undulating portion 18 onto the groove bottom surface 12 to the reference projected area Aa is preferably between 10% and 100%.

[0080] By setting the ratio An / Aa to 10% or more, minute but non-uniform longitudinal vortices are generated, thereby suppressing airflow separation downstream. This tire 2 can reduce air resistance. The undulations 18 change the air density within the circumferential grooves 10, reducing air column resonance noise. This tire 2 has good quietness. The undulations 18 reduce the water pressure loss within the circumferential grooves 10, increasing the rate at which hydroplaning occurs. This tire 2 can maintain good handling stability on wet road surfaces. From this viewpoint, a ratio of 45% or more is more preferable. By setting the ratio An / Aa to 100% or less, a moderate longitudinal vortex is generated. Since airflow separation is suppressed, tire 2 can maintain low air resistance. Tire 2 can maintain good quietness because it can sustain the effect of reducing air column resonance noise. Since the pressure loss reduction effect is sustained, tire 2 can maintain good handling stability on wet roads. From this viewpoint, a ratio of 55% or less is more preferable. A ratio of An / Aa of 100% means that the cone elements 20 are arranged in the undulating portion 18 as shown in Figure 1, for example.

[0081] Figure 18 shows a modified example of the undulating section 18. Figure 19 shows a cross-section of this modified example of the undulating section 18 along the line XIX-XIX in Figure 18. Figure 20 shows a cross-section of this modified example of the undulating section 18 along the line XX-XX in Figure 19.

[0082] This modified form, the undulating section 18, also comprises multiple conical elements 20. This undulating section 18 also includes convex portions 22 and concave portions 24 as conical elements 20, with the convex portions 22 and concave portions 24 alternating in the circumferential direction. Each conical element 20 has a shape that tapers from the base 28 towards the tip 26. The conical elements 20 have a semi-conical shape.

[0083] In this modified example, both the convex portion 22 and the concave portion 24 of the conical element 20 are provided with a ridge 34 on the side surface 30. The ridge 34 extends straight along the side surface 30 of the conical element 20. The ridge 34 bridges the gap between the tip 26 of the conical element 20 and the edge 30e of the side surface 30.

[0084] The ridge 34 is a groove. The ridge 34 can contribute to generating longitudinal vortices that are minute but of non-uniform size. This ridge 34 can also contribute to causing changes in the air density within the circumferential groove 10. Furthermore, this ridge 34 can also contribute to reducing the pressure loss of water within the circumferential groove 10. In other words, by carving ridges 34 into the side surface 30 of the conical element 20, the tire 2 can sufficiently reduce air resistance while effectively suppressing the impact on quietness and handling stability. From this viewpoint, it is preferable that the conical element 20 of the tire 2 is provided with ridges 34 extending along its side surface 30.

[0085] In Figures 19 and 20, the length indicated by the double-headed arrow Dt represents the depth of the ridge 34. The depth Dt of the ridge 34 is measured at the edge 30e of the side surface 30 of the conical element 20.

[0086] In the conical element 20 as the convex portion 22, the depth Dt of the ridge 34 is preferably 50% or less of the height Hc of the conical element 20. This allows the ridge 34 to effectively contribute to generating minute but non-uniform longitudinal vortices, causing changes in the air density within the circumferential groove 10, and reducing the pressure loss of water within the circumferential groove 10. This tire 2 can sufficiently reduce air resistance while effectively suppressing the impact on quietness and handling stability. From this viewpoint, it is more preferable that the depth Dt of the ridge 34 is 40% or less of the height Hc of the conical element 20. From the viewpoint that the tire 2 can effectively sustain the airflow separation suppression effect, air column resonance noise reduction effect, and pressure loss reduction effect of the ridge 34, it is preferable that the depth Dt of the ridge 34 is 20% or more of the height Hc of the conical element 20.

[0087] In the conical element 20 as the recess 24, similar to the conical element 20 as the convex portion 22, the depth Dt of the ridge 34 is preferably 50% or less of the depth Dr of the conical element 20. This allows the ridge 34 to effectively contribute to generating minute but non-uniform longitudinal vortices, causing changes in air density within the circumferential groove 10, and reducing water pressure loss within the circumferential groove 10. This tire 2 can sufficiently reduce air resistance while effectively suppressing the impact on quietness and handling stability. From this viewpoint, it is more preferable that the depth Dt of the ridge 34 is 40% or less of the depth Dr of the conical element 20. From the viewpoint that the tire 2 can effectively sustain the airflow separation suppression effect, air column resonance noise reduction effect, and pressure loss reduction effect of the ridge 34, it is preferable that the depth Dt of the ridge 34 is 20% or more of the depth Dr of the conical element 20.

[0088] As shown in Figure 18, each cone element 20 is provided with two ridges 34. The number of ridges 34 provided on a cone element 20 may be one or three or more. The number of ridges 34 provided on a cone element 20 is determined appropriately, taking into consideration the specifications of the cone element 20.

[0089] In this undulating section 18, it is preferable that the ridge 34 is provided in one of the two zones 30z when the side surface 30 of the conical element 20 is divided into two zones 30z by a ridge line MLt or a valley line MLb. This allows the ridge 34 to effectively contribute to generating longitudinal vortices of minute but non-uniform size, causing changes in the air density within the circumferential groove 10, and reducing the pressure loss of water within the circumferential groove 10. This tire 2 can sufficiently reduce air resistance while effectively suppressing the impact on quietness and handling stability.

[0090] When a ridge 34 is provided in one zone 30z of the side surface 30 of the conical element 20, as shown in Figure 18, when the zone 30z on one groove wall 14a side (hereinafter referred to as the first groove wall 14a side) of the circumferential groove 10 is designated as the first zone 30z1, and the zone 30z on the other groove wall 14b side (second groove wall 14b side) is designated as the second zone 30z2, it is more preferable that the ridge 34 provided on the side surface 30 of the conical element 20 is provided in the first zone 30z1 for the conical element 20 as a convex portion 22, and in the second zone 30z2 for the conical element 20 as a concave portion 24. This allows the ridge 34 to effectively contribute by generating longitudinal vortices of minute but non-uniform size, causing changes in the air density within the circumferential groove 10, and reducing the pressure loss of water within the circumferential groove 10. This tire 2 can more effectively suppress the impact on quietness and handling stability while more sufficiently reducing air resistance.

[0091] As is clear from the above description, the present invention provides a tire that can achieve a reduction in air resistance while suppressing the impact on quietness and handling stability. [Examples]

[0092] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0093] [Examples 1-17 and Comparative Examples 1-6] Tires (tire size = 195 / 65R15) of Example 1-17 and Comparative Example 1-6 were obtained, with undulations having the specifications shown in Table 1-5 below provided in the circumferential grooves. In the "Shape" column of Table 1-5, "C" indicates that the cone element has a semiconical shape, "EC" indicates that it has a semi-elliptical pyramidal shape, "BC" indicates that the cone element has a semi-biconical shape, "BEC" indicates that it has a semi-bielliptical pyramidal shape, and "CT" indicates that the cone element has a semi-frustum-shaped cone. The circumferential grooves in Comparative Example 1 do not have any undulating sections. In Examples 1-3 and Comparative Examples 3-4, all conical elements constituting the undulating portion are convex. The conical elements constituting the undulations in Examples 4-17 and Comparative Examples 5-6 consist of convex and concave portions, and the undulations are configured such that the convex and concave portions are arranged alternately in the circumferential direction. In Comparative Example 2, instead of conical elements, the undulating portion has convex portions P, as shown in Figure 18, arranged circumferentially without spacing, similar to the conical elements in Example 1. The shape of the convex portions P is a triangular prism.

[0094] [Air resistance] The prototype tire was mounted on a standard rim and inflated to an internal pressure of 230 kPa. This tire was then mounted on a test vehicle. With one driver in the vehicle, it was driven at 100 km / h on a dry circuit. Fuel consumption was calculated over 50 laps, and the distance traveled per liter of fuel was determined. The results are shown in Table 1-5 below, using an index with Comparative Example 1 set to 100. A higher value indicates lower fuel consumption and lower tire air resistance.

[0095] [Quietness] A prototype tire was mounted on a standard rim and inflated to an internal pressure of 230 kPa. This tire was then mounted on a test vehicle. With one driver in the vehicle, the air column resonance sound of the circumferential groove was measured while the test vehicle traveled on a dry road surface at a speed of 100 km / h. The results are shown in Table 1-5 below, expressed as an index with the reciprocal of the energy of the air column resonance sound of Comparative Example 1 set to 100. A higher value indicates a lower air column resonance sound and superior quietness.

[0096] [Handling Stability (WET)] The prototype tire was mounted on a standard rim and inflated to an internal pressure of 230 kPa. This tire was then mounted on a test vehicle. With one driver in the vehicle, it was driven onto a wet road surface with a 1 mm deep water film. The hydroplaning rate was calculated from the deceleration from a speed of 100 km / h to a complete stop. The results are shown in Table 1-5 below, using an index with Comparative Example 1 set to 100. A higher value indicates that hydroplaning is less likely to occur and that the vehicle has superior handling stability on wet roads.

[0097] [total] The sum of the indices obtained from each evaluation was calculated. The results are shown in the "Total" column of Table 1-5 below. A higher number is preferable.

[0098] [Table 1]

[0099] [Table 2]

[0100] [Table 3]

[0101] [Table 4]

[0102] [Table 5]

[0103] As shown in Table 1-5, the embodiments demonstrate that air resistance reduction is achieved while suppressing the impact on quietness and handling stability. The advantages of the present invention are clear from these evaluation results. [Industrial applicability]

[0104] The technologies described above, which can reduce air resistance while suppressing the impact on quietness and handling stability, can be applied to various types of tires.

[0105] [Note] The present invention includes the following embodiments.

[0106] [1] A road surface having a tread that contacts the road surface, the tread having a circumferential groove that extends continuously in the circumferential direction and a relief portion provided on the groove bottom surface of the circumferential groove, the relief portion having a plurality of conical elements arranged in the circumferential direction, the plurality of conical elements being a convex portion that protrudes from the groove bottom surface or a concave portion that is recessed from the groove bottom surface, the plurality of conical elements each being a semi-cone having a semi-cone represented by a group of straight lines connecting a reference point and each point on the edge of a reference plane that does not include the reference point, or a part of the semi-cone, the edge of the reference plane being the top of the convex portion or A tire comprising a corner including the bottom of the recess, wherein the tip of the conical element is located on one side in the circumferential direction of the top of the convex portion or the bottom of the recess, and when the conical element is the convex portion, the height of the conical element is lower than the groove depth of the circumferential groove, and the angle that the ridge of the convex portion makes with respect to the bottom surface of the circumferential groove is 75 degrees or less, and when the conical element is the recess, the depth of the conical element is shallower than the groove depth of the circumferential groove, and the angle that the valley of the recess makes with respect to the bottom surface of the circumferential groove is 75 degrees or less. [2] The tire according to [1] above, wherein the angle that the longitudinal direction of the conical element makes with respect to the longitudinal direction of the circumferential groove is 45 degrees or less. [3] The tire according to [1] or [2] above, wherein the projection shape of the conical element onto the groove bottom surface when the conical element is a semicone is the reference projection shape of the conical element, the projection shape of the undulation onto the groove bottom surface is formed by combining a plurality of the reference projection shapes, and the ratio An / Aa of the projection area An of the projection shape of the undulation to the reference projection area Aa, which is expressed as the product of the projection area of ​​the reference projection shape and the number of conical elements constituting the undulation, is 10% or more and 100% or less. [4] The tire according to any one of [1] to [3] above, wherein the conical element has a ridge extending along its side, and the depth of the ridge is 50% or less of the height of the conical element. [Explanation of Symbols]

[0107] 2... Tires 4. Tread 6. Tread surface 10...Circumferential groove 12... Groove bottom surface 14.. Ditch wall 18... undulating part 20... Cone elements 22···Convex part 24...recess 26... The tip of the cone element 20 28... Base of cone element 20 30... Side view of cone element 20 32... points 34.. Ridge

Claims

1. Equipped with a tread that makes contact with the road surface, The tread comprises a circumferential groove that extends continuously in the circumferential direction, and an undulating portion provided on the groove bottom surface of the circumferential groove. The aforementioned undulating portion comprises a plurality of conical elements arranged in the circumferential direction, The multiple conical elements are convex portions that protrude from the bottom surface of the groove, or concave portions that are recessed from the bottom surface of the groove. Each of the multiple conical elements is a semicone having a semiconical surface represented by a group of lines connecting a reference point and each point on the edge of a reference plane that does not include the reference point, or is composed of a part of the semicone. The edge of the reference surface constitutes a corner including the top of the protrusion or the bottom of the recess, The tip of the conical element is located on one side in the circumferential direction of the top of the convex portion or the bottom of the concave portion. If the conical element is the convex portion, the height of the conical element is lower than the groove depth of the circumferential groove, and the angle that the ridge of the convex portion makes with respect to the groove bottom surface of the circumferential groove is 75 degrees or less. When the conical element is the recess, the depth of the conical element is shallower than the groove depth of the circumferential groove, and the angle that the valley line of the recess makes with respect to the groove bottom surface of the circumferential groove is 75 degrees or less. tire.

2. The angle that the longitudinal direction of the conical element makes with respect to the longitudinal direction of the circumferential groove is 45 degrees or less. The tire according to claim 1.

3. When the conical element is a semicone, the projected shape of the conical element onto the bottom surface of the groove is the reference projected shape of the conical element. The projection shape of the undulation onto the groove bottom surface is formed by combining a plurality of the reference projection shapes, The ratio An / Aa of the projected area An of the projected shape of the relief portion to the reference projected area Aa, which is expressed as the product of the projected area of ​​the reference projected shape and the number of cone elements constituting the relief portion, is 10% or more and 100% or less. The tire according to claim 1 or 2.

4. The conical element is provided with a ridge extending along its side surface, The depth of the ridge is 50% or less of the height of the conical element. The tire according to claim 1 or 2.

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