Tire

Abstract

To provide a tire capable of achieving both wet braking performance when the tire is new and wet braking performance in a middle stage of wear.SOLUTION: In a tire 1, a land portion includes a hidden groove 4 which extends in a tire width direction without opening to a tread surface of a block 322, opens to a side surface on the outer side in the tire width direction of the block 322 at one end portion 43, and terminates inside the block 322 at the other end portion 44. Further, groove width W41 of the hidden groove 4 on the tread surface side of the block 322 is in a range of W41<W42 with respect to the groove width W42 of the hidden groove 4 on the groove bottom 42 side.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a tire, and more particularly to a tire capable of achieving both wet braking performance at the time of a new tire and in the mid-wear stage.

Background Art

[0002] In recent tires, there is a problem of improving the wet braking performance of the tire after the mid-wear stage. As a conventional tire related to such a problem, the technique described in Patent Document 1 is known.

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 both wet braking performance at the time of a new tire and in the mid-wear stage.

Means for Solving the Problems

[0005] To achieve the above object, a tire according to the present invention is a tire including a main groove and a land portion partitioned by the main groove, wherein the land portion extends in the tire width direction without opening to the tread surface of the land portion, and has a hidden groove that opens to the outer side surface of the land portion in the tire width direction at one end and terminates inside the land portion at the other end, and a groove width W41 of the hidden groove on the tread side of the land portion is in a range of W41 < W42 with respect to a groove width W42 of the hidden groove on the groove bottom side.

Effects of the Invention

[0006] In the tire according to the present invention, (1) since the hidden groove does not open to the tread surface of the land portion when the tire is new, compared with a configuration having additional fine grooves that open to the tread surface, the rigidity of the land portion when the tire is new is ensured, and the wet braking performance of the tire is ensured. Also, (2) when the hidden groove appears on the tread surface of the land portion in the middle wear stage where the groove depth of the main groove becomes shallow, the wet braking performance of the tire after the middle wear stage is ensured. Further, (3) since one end of the hidden groove, that is, the end on the outer side in the tire width direction, opens to the side surface on the outer side in the tire width direction of the land portion, the drainage performance of the hidden groove is ensured, and since the other end of the hidden groove, that is, the end on the inner side in the tire width direction, terminates inside the land portion, the rigidity of the land portion is ensured. Furthermore, (4) since the groove width W41 of the hidden groove on the tread side of the land portion, that is, on the top side of the hidden groove, is in the range of W41 < W42 with respect to the groove width W42 of the hidden groove on the groove bottom side, it is possible to achieve both ensuring the drainage performance of the hidden groove and ensuring the rigidity of the land portion from the middle wear stage to the end wear stage. Thus, there is an advantage that the wet braking performance of the tire from when it is new to the end wear stage is ensured.

Brief Description of the Drawings

[0007] [Figure 1] FIG. 1 is a cross-sectional view in the tire meridian direction showing the tire 1 according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view showing the tread surface of the tire described in FIG. 1. [Figure 3] FIG. 3 is an explanatory view showing the hidden groove of the tire described in FIG. 2. [Figure 4] FIG. 4 is a cross-sectional view taken along the line A of the block described in FIG. 3. [Figure 5] FIG. 5 is a cross-sectional view taken along the line B of the block described in FIG. 3. [Figure 6] FIG. 6 is a view taken along the line C of the block described in FIG. 3. [Figure 7] FIG. 7 is an explanatory view showing a modified example of the hidden groove described in FIG. 3. [Figure 8] FIG. 8 is an explanatory view showing a modified example of the hidden groove described in FIG. 3. [Figure 9]FIG. 9 is an explanatory diagram showing a modified example of the hidden groove shown in FIG. [Figure 10] FIG. 10 is an explanatory diagram showing a modified example of the hidden groove shown in FIG. [Figure 11] FIG. 11 is an explanatory diagram showing a modified example of the hidden groove shown in FIG. [Figure 12] FIG. 12 is an explanatory diagram showing a modified example of the hidden groove shown in FIG. [Figure 13] FIG. 13 is an explanatory diagram showing a modified example of the hidden groove shown in FIG. [Figure 14] FIG. 14 is an explanatory diagram showing a modified example of the hidden groove shown in FIG. [Figure 15] FIG. 15 is an explanatory diagram showing a modified example of the hidden groove shown in FIG. [Figure 16] FIG. 16 is an explanatory diagram showing a modified example of the hidden groove shown in FIG. [Figure 17] FIG. 17 is an explanatory diagram showing a modified example of the hidden groove shown in FIG. [Figure 18] FIG. 18 is an explanatory diagram showing a modified example of the hidden groove shown in FIG. [Figure 19] FIG. 19 is an explanatory diagram showing a modified example of the hidden groove shown in FIG. [Figure 20] FIG. 20 is an explanatory diagram showing a modified example of the hidden groove shown in FIG. [Figure 21] FIG. 21 is an explanatory diagram showing a modified example of the hidden groove shown in FIG. [Figure 22] FIG. 22 is an explanatory diagram showing a modified example of the hidden groove shown in FIG. [Figure 23] FIG. 23 is a table showing the results of performance tests on tires according to embodiments of the present invention. [Figure 24] FIG. 24 is a table showing the results of performance tests on tires according to embodiments of the present invention. [Figure 25] FIG. 25 is an explanatory diagram showing the test tire of the comparative example shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, the components of these embodiments include those that can be substituted and are obvious substitutes while maintaining the identity of the invention. Furthermore, the multiple modifications described in these embodiments can be arbitrarily combined within the scope obvious to those skilled in the art.

[0009] [tire] 1 is a cross-sectional view in the tire meridian direction showing a tire 1 according to an embodiment of the present invention. The figure shows a cross-sectional view of one side region in the tire radial direction. In this embodiment, a pneumatic radial tire for light trucks will be described as an example of a tire.

[0010] In the figure, the tire meridian cross section is defined as a cross section of the tire cut by a plane including the tire rotation axis (not shown). The tire equatorial plane CL is defined as a plane that passes through the midpoint of the tire section width defined by JATMA and is perpendicular to the tire rotation axis. The tire width direction is defined as the direction parallel to the tire rotation axis, and the tire radial direction is defined as the direction perpendicular to the tire rotation axis.

[0011] The tire 1 has an annular structure centered on the tire rotation axis, and includes a pair of bead cores 11, 11, a pair of bead fillers 12, 12, a carcass layer 13, a belt layer 14, a tread rubber 15, a pair of sidewall rubbers 16, 16, and a pair of rim cushion rubbers 17, 17 (see Figure 1).

[0012] The pair of bead cores 11, 11 are formed by winding one or more steel bead wires in an annular and multiple pattern and are embedded in the bead portions to form the cores of the left and right bead portions. The pair of bead fillers 12, 12 are disposed on the outer periphery of the pair of bead cores 11, 11 in the tire radial direction, respectively, to reinforce the bead portions.

[0013] The carcass layer 13 has a single-layer structure consisting of one carcass ply or a multi-layer structure consisting of multiple carcass plies stacked together, and is toroidally laid between the left and right bead cores 11, 11 to form the tire framework. Both ends of the carcass layer 13 are wrapped around and secured to the outside in the tire width direction so as to enclose the bead cores 11 and the bead fillers 12. The carcass ply of the carcass layer 13 is formed by covering multiple carcass cords made of steel or organic fiber material (e.g., aramid, nylon, polyester, rayon, etc.) with coating rubber and rolling them, and has a cord angle (defined as the inclination angle of the carcass cords in the longitudinal direction relative to the tire circumferential direction) of 80 degrees or more and 100 degrees or less.

[0014] The belt layer 14 is formed by laminating a pair of cross belts 141 and 142, and is disposed so as to be wound around the outer periphery of the carcass layer 13.

[0015] The pair of cross belts 141, 142 are formed by coating a plurality of belt cords made of steel or organic fiber material with coating rubber and rolling them, and have a cord angle (defined as the inclination angle of the belt cords in the longitudinal direction with respect to the tire circumferential direction) of 15 degrees or more and 55 degrees or less in absolute value. The pair of cross belts 141, 142 have cord angles of opposite signs to each other, and are layered with the longitudinal directions of the belt cords crossing each other (so-called cross-ply structure). The pair of cross belts 141, 142 are layered and arranged on the outer side of the carcass layer 13 in the tire radial direction.

[0016] The tread rubber 15 is disposed on the outer periphery of the carcass layer 13 and the belt layer 14 in the tire radial direction to form the tread portion of the tire 1. Made of a rubber material with excellent ground contact characteristics and weather resistance, it is exposed over the entire outer periphery of the tire to form the tread surface. A pair of sidewall rubbers 16, 16 are disposed on the outer sides of the carcass layer 13 in the tire width direction to form left and right sidewall portions. A pair of rim cushion rubbers 17, 17 extend from the inner side in the tire radial direction of the left and right bead cores 11, 11 and the turned-up portions of the carcass layer 13 to the outer side in the tire width direction to form the rim fitting surface of the bead portion.

[0017] [Tread surface] FIG. 2 is a plan view showing the tread surface of the tire 1 shown in FIG. 1. The figure shows a tread surface having a typical rib-lug pattern. In the figure, the tire circumferential direction refers to the direction around the tire rotation axis. The symbol T indicates the tire contact edge, and the dimension symbol TW indicates the tire contact width. In the figure, the tire 1 has a tread surface that is approximately point-symmetric with the centerline point on the tire equatorial plane CL, so some of the symbols for the components in the right-hand region of the figure have been omitted.

[0018] As shown in FIG. 2, the tire 1 has main grooves 21, 22 and land portions 31, 32 defined by the main grooves 21, 22 on the tread surface.

[0019] The main groove is defined as a groove that is required to display a wear indicator as specified by JATMA. The main groove 21 has a maximum groove width of 4.0 mm or more and a maximum groove depth of 6.0 mm or more.

[0020] The groove width is measured as the distance between the opposing groove walls at the groove opening on the tread surface when the tire is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state. In a configuration in which the groove opening has a notch or chamfer, the groove width is measured using the intersection of an extension of the tread surface and an extension of the groove wall in a cross-sectional view parallel to the groove width direction and the groove depth direction as the endpoint.

[0021] The groove depth is measured as the distance from the tread surface to the groove bottom when the tire is mounted on a specified rim, inflated to a specified internal pressure, and under no load. If the tire has partial unevenness or sipes at the groove bottom, the groove depth is measured excluding these.

[0022] A specified rim is a "standard rim" as specified by JATMA, a "design rim" as specified by TRA, or a "measuring rim" as specified by ETRTO. Also, specified internal pressure is the "maximum air pressure" as specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" as specified by TRA, or the "inflation pressure" as specified by ETRTO. Also, specified load is the "maximum load capacity" as specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" as specified by TRA, or the "load capacity" as specified by ETRTO. However, in JATMA, for passenger car tires, the specified internal pressure is 180 kPa, and the specified load is 88% of the maximum load capacity at the specified internal pressure.

[0023] For example, in the configuration of Fig. 2, the tire 1 has three circumferential main grooves 21, 22 extending in the tire circumferential direction and four rows of land portions 31, 32 defined by these circumferential main grooves 21, 22. However, the tire 1 is not limited to this, and may have four or more circumferential main grooves and five or more rows of land portions (not shown). Also, in the configuration of Fig. 2, the circumferential main grooves 21, 22 have a straight shape. However, the tire is not limited to this, and the circumferential main grooves 21, 22 may have a zigzag shape or a bent shape (not shown).

[0024] 2, the first land portion 31 is a rib having a circumferentially continuous tread surface, and the second land portion 32 is a block row made up of a plurality of blocks 322 partitioned by a plurality of lug grooves 321. However, this is not limiting, and all of the land portions 31, 32 may be ribs or block rows (not shown).

[0025] In addition, in FIG. 2, the maximum ground contact width WL of the land portions 31, 32 is in the range of 0.15≦Wb1 / TW≦0.40 relative to the tire ground contact width TW, and preferably in the range of 0.17≦Wb1 / TW≦0.35.

[0026] The contact width of the land portion is measured as the linear distance in the axial direction of the tire at the contact surface between the land portion and the flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0027] The tire contact width TW is measured as the linear distance in the axial direction of the tire at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0028] The tire contact edge T is defined as the widest position in the axial direction of the tire at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0029] [Hidden trench on land] Fig. 3 is an explanatory diagram showing the hidden groove 4 of the tire 1 shown in Fig. 2. Fig. 3 shows a perspective view of a single block 322 having the hidden groove 4. Figs. 4 to 6 are a cross-sectional view taken from view A (Fig. 4), a cross-sectional view taken from view B (Fig. 5), and a view taken from view C (Fig. 6) of the block 322 shown in Fig. 3.

[0030] As shown in Fig. 2, the land portions 31, 32 have hidden grooves 4. In the configuration of Fig. 2, the first land portion 31 has a plurality of hidden grooves 4 arranged at predetermined intervals in the tire circumferential direction, and the second land portion 32 has a single hidden groove 4 in each of a plurality of blocks 322. Here, as an example, a hidden groove 4 formed in a single block 322 of the second land portion 32 will be described.

[0031] As shown in Figures 2 and 3, the hidden groove 4 is a groove embedded inside the land portions 31, 32, and extends in the tire width direction without opening onto the tread surfaces of the land portions 31, 32. Specifically, as shown in Figure 3, the apex 41 of the hidden groove 4 is positioned away from the tread surface of the land portion 32. With this configuration, the rigidity of the land portions 31, 32 is ensured when the tire is new, ensuring the wet braking performance of the tire. Furthermore, the hidden groove 4 appears on the tread surfaces of the land portions 31, 32 at the intermediate stage of wear when the groove depths of the main grooves 21, 22 become shallower, thereby ensuring the wet braking performance of the tire from the intermediate stage onwards. As a result, the wet braking performance of the tire is ensured from the time the tire is new to the final stage of wear.

[0032] 2 and 3, one end 43 of the hidden groove 4, i.e., the end on the outer side in the tire width direction, opens to the side surface of the land portions 31, 32 on the outer side in the tire width direction. This ensures the drainage performance of the hidden groove 4. Furthermore, the other end 44 of the hidden groove 4, i.e., the end on the inner side in the tire width direction, terminates inside the land portions 31, 32. This ensures the rigidity of the land portions 31, 32.

[0033] In addition, in FIG. 3, the groove width W41 of the hidden groove 4 on the tread side of the land portions 31 and 32, that is, on the top 41 side of the hidden groove 4, is in the range of W41 < W42 with respect to the groove width W42 of the hidden groove 4 on the groove bottom 42 side. Therefore, the groove width of the hidden groove 4 widens in the groove depth direction. Specifically, the groove width W41 of the hidden groove 4 on the tread side of the land portions 31 and 32 is in the range of 0.10 ≦ W41 / W42 ≦ 0.80 with respect to the groove width W42 of the hidden groove 4 on the groove bottom 42 side, and preferably in the range of 0.20 ≦ W41 / W42 ≦ 0.60. Thereby, ensuring the drainage of the hidden groove 4 from the mid-wear stage to the end-wear stage and ensuring the rigidity of the land portions 31 and 32 are compatible. Further, the groove width W41 of the hidden groove 4 on the tread side of the land portions 31 and 32 is in the range of 1.0 [mm] ≦ W41 ≦ 6.0 [mm], and preferably in the range of 2.0 [mm] ≦ W41 ≦ 6.0 [mm]. Also, the groove width W42 of the hidden groove 4 on the groove bottom 42 side is in the range of W42 ≦ 10.0 [mm], and preferably in the range of W42 ≦ 8.0 [mm].

[0034] The groove widths W41 and W42 of the hidden groove 4 are measured as the opening widths of the hidden groove 4 at one end 43 of the hidden groove 4, that is, the outer end in the tire width direction. Also, the groove width W41 of the hidden groove 4 on the tread side of the land portions 31 and 32 is measured as the maximum width of the opening width in the region of 15 [%] of the height H43 of the hidden groove 4 from the top 41 of the hidden groove 4. Further, the groove width W42 of the hidden groove 4 on the groove bottom 42 side is measured as the maximum width in the region of 15 [%] of the height H43 of the hidden groove 4 from the groove bottom 42 of the hidden groove 4.

[0035] The height H43 of the hidden groove 4 is measured as the maximum value of the opening height from the top 41 to the groove bottom 42 of the hidden groove 4 at one end 43 of the hidden groove 4.

[0036] Also, the groove width W42 of the hidden groove 4 on the groove bottom 42 side is in the range of 0.05 ≦ W42 / PL ≦ 0.50 with respect to the pitch length PL of the land portions 31 and 32 (see FIG. 2), and preferably in the range of 0.10 ≦ W42 / PL ≦ 0.30. Thereby, ensuring the drainage of the hidden groove 4 and ensuring the rigidity of the land portions 31 and 32 are compatible.

[0037] As shown in Figure 2, the pitch length PL of the land portions 31, 32 is measured as the pitch length of other lug grooves 311 or uneven portions formed in the land portion 31 when the land portion 31 is a rib, and is measured as the pitch length of the blocks 322 when the land portion 32 is a block row.

[0038] 6, when the land portion 32 is a row of blocks, the groove width W42 of the hidden groove 4 on the groove bottom 42 side is in the range of W42 / L22≦0.60, preferably W42 / L22≦0.40, relative to the circumferential length L22 of the block 322. This ensures the rigidity of the block 322.

[0039] 5 and 6, the height H43 of the hidden groove 4 at one end 43 is in the range of 0.55≦H43 / H2′≦0.95, and preferably 0.60≦H43 / H2′≦0.90, relative to the effective groove depth H2′ (dimension symbols omitted in the figures) of the main grooves 21, 22. The lower limit ensures that the hidden groove 4 improves drainage, and the upper limit ensures the rigidity of the land portions 31, 32.

[0040] The effective groove depth H2' of the main grooves 21, 22 is defined as the maximum groove depth H2 of the main grooves 21, 22 minus the height of the wear indicator (not shown).

[0041] Also, in FIG. 5 , the height H44 of the hidden groove 4 at the other end 44, i.e., the terminal end of the land portion 31, 32, is in the range of 0.10≦H44 / H43≦0.90, preferably 0.20≦H44 / H43≦0.80, relative to the height H43 of the hidden groove 4 at one end 43. Therefore, the height H44 of the hidden groove 4 at the other end 44 is lower than the height H43 of the hidden groove 4 at one end 43. For example, in the configuration of FIG. 5 , the height of the hidden groove monotonically decreases from one end 43 to the other end 44. With this configuration, the groove area of ​​the hidden groove 4 exposed to the tread surface increases as wear progresses, thereby appropriately improving drainage performance by the hidden groove 4. Furthermore, the mold release from the hidden groove 4 during tire vulcanization is improved.

[0042] The height H44 of the hidden groove 4 at the other end 44 is measured as the maximum height in a region 15% from the end point of the extension length L4 of the hidden groove 4 in the tire width direction.

[0043] The extension length L4 of the hidden groove 4 in the tire width direction is measured as the maximum value of the entire extension length of the hidden groove 4.

[0044] 5, the extension length L42 of the hidden groove 4 on the groove bottom 42 side is in the range of 0.30≦L42 / WL≦0.90, and preferably 0.40≦L42 / WL≦0.80, relative to the maximum ground contact width WL of the land portions 31, 32. The lower limit ensures that the hidden groove 4 improves drainage, and the upper limit ensures the rigidity of the land portions 31, 32.

[0045] The extension length L42 of the hidden groove 4 on the groove bottom 42 side is measured as the maximum extension length in the tire width direction in the region from the maximum depth position of the hidden groove 4 to 15[%] of the height H43 of the hidden groove 4.

[0046] 5, the extension length L41 of the hidden groove 4 on the tread side of the land portions 31, 32 (block 322 in FIG. 6), i.e., on the top 41 side of the hidden groove 4, is in the range of 0.10≦L41 / L42≦0.90, and preferably 0.25≦L41 / L42≦0.75, relative to the extension length L42 of the hidden groove 4 on the groove bottom 42 side. The lower limit ensures that the hidden groove 4 improves drainage, and the upper limit ensures the rigidity of the land portions 31, 32 in the middle stage of wear.

[0047] The extension length L41 of the hidden groove 4 on the apex 41 side is measured as the maximum extension length in the tire width direction in the region from the maximum height position of the hidden groove 4 to 15% of the height H43 of the hidden groove 4.

[0048] 6, the distance H41 from the tread surface of the land portions 31, 32 (block 322 in FIG. 6) to the top 41 of the hidden groove 4 is in the range of 0.05≦H41 / H2′≦0.45, and preferably in the range of 0.15≦H41 / H2′≦0.40, relative to the effective groove depth H2′ of the main grooves 21, 22. The above lower limit ensures the rigidity of the land portions 31, 32 in the early stage of wear, and the above lower limit ensures the improved drainage effect of the hidden groove 4 in the middle stage of wear.

[0049] Furthermore, the maximum groove depth H2 and horizontal tread width THW of the main grooves 21, 22 satisfy the condition 550≦H2×THW[mm^2]≦2500, and preferably satisfy the condition 700≦H2×THW[mm^2]≦2350. With this configuration, particularly when a green tire is vulcanized using a tire mold that can be separated in the tire axial direction, the removability of the tire mold from the main grooves 21, 22 and the hidden groove 4 is properly ensured.

[0050] [Variations] 7 to 22 are explanatory diagrams showing modified examples of the hidden groove 4 shown in Fig. 3. In these figures, the same components as those shown in Fig. 3 are given the same reference numerals, and their description will be omitted.

[0051] In the configuration of FIG. 3, the groove width of the hidden groove 4 is constant over the entire extension length L4 of the hidden groove 4 from one end 43 to the other end 44, as shown in FIG.

[0052] 7, the groove width of the hidden groove 4 may monotonically decrease from one end 43 to the other end 44. Furthermore, the groove cross-sectional area of ​​the hidden groove 4 may monotonically decrease from one end 43 to the other end 44. Such a configuration is preferable in that it improves the ease with which the molding die can be removed from the hidden groove 4 during tire vulcanization molding.

[0053] 3, the groove bottom 42 of the hidden groove 4 is horizontal to the tread surface of the block 322 as shown in FIG.

[0054] In contrast to this, as shown in Fig. 8, the groove bottom 42 of the hidden groove 4 may be inclined from one end 43 to the other end 44. For example, in the configuration of Fig. 8, the groove bottom 42 of the hidden groove 4 is inclined so that the groove depth of the hidden groove 4 decreases from one end 43 to the other end 44. This configuration is preferable in that it achieves both the drainage properties of the hidden groove 4 from the middle to final stages of wear and the rigidity of the land portions 31, 32.

[0055] 3, the height H44 of the hidden groove 4 at the other end 44 is lower than the height H43 of the hidden groove 4 at one end 43, as shown in FIG.

[0056] 9, the height of the hidden groove 4 may be constant over the entire extension length of the hidden groove 4. Also, as shown in FIG. 10, the height of the hidden groove 4 at the other end 44 may be zero.

[0057] In addition, in the configuration of Figure 3, as shown in Figure 5, the top 41 of the hidden groove 4 slopes linearly from the center of the block 322 toward the other end 44 of the hidden groove 4, so that the height of the hidden groove 4 gradually decreases.

[0058] 11 and 12, the height of the hidden groove 4 may be gradually reduced by curving the top 41 of the hidden groove 4 in an arc shape from the center of the block 322 toward the other end 44 of the hidden groove 4. Alternatively, as shown in FIG. 13, the height of the hidden groove 4 may be gradually reduced by curving the top 41 of the hidden groove 4 in a step shape from the center of the block 322 toward the other end 44 of the hidden groove 4.

[0059] In the configuration of FIG. 3, the other end 44 of the hidden groove 4 has a corner with an L-shaped cross section, as shown in FIG.

[0060] On the other hand, as shown in FIG. 14, the other end 44 of the hidden groove 4 may have an arc-shaped corner.

[0061] In addition, in the configuration of Figure 3, as shown in Figure 6, the side wall of the hidden groove 4 at one end 43 has a linear shape that is inclined in the tire circumferential direction, so that the groove width of the hidden groove 4 increases from the top 41 to the groove bottom 42.

[0062] Alternatively, as shown in Fig. 15, the side wall of the hidden groove 4 at one end 43 may have an arc shape that bulges in the tire circumferential direction, or as shown in Fig. 16, the side wall of the hidden groove 4 at one end 43 may have an arc shape that is recessed in the tire circumferential direction. Also, as shown in Fig. 17, the side wall of the hidden groove 4 at one end 43 may have a step shape that widens from the top 41 of the hidden groove 4 toward the groove bottom 42.

[0063] In the configuration of FIG. 3, as shown in FIG. 6, the top portion 41 of the hidden groove 4 has a U-shape or a trapezoidal shape, and thus has a flat top surface.

[0064] In contrast to this, as shown in Figure 18, the top 41 of the hidden groove 4 may have a V-shape, or as shown in Figure 19, the top 41 of the hidden groove 4 may have an arc shape that convex toward the tread side of the block 322.

[0065] In the configuration of FIG. 3, as shown in FIG. 6, the groove bottom 42 and the left and right groove walls (reference numerals omitted in the drawing) of the hidden groove 4 have a flat shape.

[0066] On the other hand, as shown in Fig. 20, the groove bottom 42 of the hidden groove 4 may have a partial recess, or as shown in Fig. 21, the side wall of the hidden groove 4 may have a partial recess. Also, as shown in Fig. 22, the groove bottom 42 of the hidden groove 4 may have an arc shape recessed in the groove depth direction.

[0067] In addition, in the configuration of Figure 3, the hidden groove 4 is formed in a single block 322 of the second land portion 32, and one end 43 opens to the wall surface of the block 322 on the outer side in the tire width direction, i.e., the groove wall of the shoulder main groove 21.

[0068] In contrast, as shown in FIG. 2, the hidden groove 4 may be formed in the rib of the first land portion 31, and one end portion 43 may open to the buttress portion of the tire.

[0069] In the configuration of FIG. 2, the land portions 31 and 32 only have lug grooves 311 and 321. However, it is not limited to this, and the land portions 31 and 32 may have additional sipes or fine grooves (not shown).

[0070] [Effect] As described above, [1] this tire 1 includes main grooves 21 and 22, and land portions 31 and 32 partitioned by the main grooves 21 and 22 (see FIG. 2). Further, the land portions 31 and 32 extend in the tire width direction without opening to the tread surface of the land portions 31 and 32 (block 322 in FIG. 3), open to the side surface outside the tire width direction of the land portions 31 and 32 at one end portion 43, and have a hidden groove 4 that terminates inside the land portions 31 and 32 at the other end portion 44. Further, the groove width W41 of the hidden groove 4 on the tread side of the land portions 31 and 32 is in the range of W41 < W42 with respect to the groove width W42 of the hidden groove 4 on the groove bottom 42 side (see FIG. 3).

[0071] In such a configuration, (1) since the hidden groove 4 does not open to the tread surfaces of the land portions 31 and 32 when the tire is new, compared with a configuration having additional fine grooves that open to the tread surface (refer to the comparative example in FIG. 25 described later), the rigidity of the land portions 31 and 32 when the tire is new is ensured, and the wet braking performance of the tire is ensured. Also, (2) when the groove depths of the main grooves 21 and 22 become shallow in the midwear stage, the hidden groove 4 appears on the tread surfaces of the land portions 31 and 32, thereby ensuring the wet braking performance of the tire after the midwear stage. Further, (3) since one end portion 43 of the hidden groove 4, that is, the end portion on the outer side in the tire width direction, opens to the side surface on the outer side in the tire width direction of the land portions 31 and 32, the drainage performance of the hidden groove 4 is ensured. Also, since the other end portion 44 of the hidden groove 4, that is, the end portion on the inner side in the tire width direction, terminates inside the land portions 31 and 32, the rigidity of the land portions 31 and 32 is ensured. Furthermore, (4) since the groove width W41 of the hidden groove 4 on the tread surface side of the land portions 31 and 32, that is, on the top portion 41 side of the hidden groove 4, is in the range of W41 < W42 with respect to the groove width W42 of the hidden groove 4 on the groove bottom 42 side, it is possible to achieve both ensuring the drainage performance of the hidden groove 4 and ensuring the rigidity of the land portions 31 and 32 from the midwear stage to the endwear stage. Thus, there is an advantage that the wet braking performance of the tire is ensured from when the tire is new to the endwear stage.

[0072] Also, [2] in this tire 1, in the tire 1 described in [1] above, the groove width W42 of the hidden groove 4 on the groove bottom 42 side (refer to FIGS. 3 and 4) is in the range of 0.05 ≦ W42 / PL ≦ 0.50 with respect to the pitch length PL of the land portions 31 and 32 (refer to FIG. 2). Thereby, there is an advantage that both ensuring the drainage performance of the hidden groove 4 and ensuring the rigidity of the land portions 31 and 32 can be achieved.

[0073] Also, [3] in this tire , in the tire 1 described in [1] or [2] above, the groove width W41 of the hidden groove 4 on the tread surface side of the land portions 31 and 32 is in the range of 0.10 ≦ W41 / W42 ≦ 0.80 with respect to the groove width W42 of the hidden groove 4 on the groove bottom 42 side (refer to FIGS. 3 and 6). Thereby, there is an advantage that both ensuring the drainage performance of the hidden groove 4 and ensuring the rigidity of the land portions 31 and 32 can be achieved from the midwear stage to the endwear stage.

[0074] [4] In addition, in the tire 1 described in any one of [1] to [3] above, the height H43 of the hidden groove 4 at one end 43 is in the range of 0.55≦H43 / H2′≦0.95 relative to the effective groove depth H2′ (dimension symbols omitted in the drawings; see symbol H2 in FIG. 6) of the main grooves 21, 22. The lower limit ensures the effect of improving drainage by the hidden groove 4, while the upper limit has the advantage of ensuring the rigidity of the land portions 31, 32.

[0075] [5] In addition, in the tire 1 described in any one of [1] to [4] above, the height H44 of the hidden groove 4 at the other end 44 is in the range of 0.10≦H44 / H43≦0.90 relative to the height H43 of the hidden groove 4 at one end 43 (see FIG. 5). With this configuration, the groove area of ​​the hidden groove 4 exposed to the tread surface increases as wear progresses, which has the advantage of appropriately improving drainage performance by the hidden groove 4. Another advantage is that the mold can be more easily removed from the hidden groove 4 during vulcanization molding of the tire.

[0076] [6] In the tire 1 according to any one of the above [1] to [5], the extension length L42 of the hidden groove 4 on the groove bottom 42 side is in the range of 0.30≦L42 / WL≦0.90 relative to the maximum contact width WL of the land portions 31, 32 (see FIG. 5). The lower limit ensures the effect of improving drainage by the hidden groove 4, and the upper limit has the advantage of ensuring the rigidity of the land portions 31, 32.

[0077] [7] In the tire 1 described in any one of [1] to [6] above, the extension length L41 of the hidden groove 4 on the tread side of the land portions 31, 32 is in the range of 0.10≦L41 / L42≦0.90 relative to the extension length L42 of the hidden groove 4 on the groove bottom 42 side (see FIG. 5). The lower limit ensures the effect of improving drainage by the hidden groove 4, and the upper limit has the advantage of ensuring the rigidity of the land portions 31, 32 in the middle stage of wear.

[0078] [8] In the tire 1 according to any one of the above [1] to [7], the groove width W41 of the hidden groove 4 on the tread side of the land portions 31, 32 is in the range of 1.0 mm≦W41≦6.0 mm (see FIGS. 3 and 6). This has the advantage of optimizing the groove width W41 of the hidden groove 4 on the tread side.

[0079] [9] In the tire 1 described in any one of [1] to [8] above, the distance H41 (see FIG. 6) from the tread surface of the land portions 31, 32 to the apex 41 of the hidden groove 4 is in the range of 0.10≦H41 / H2′≦0.45 relative to the effective groove depth H2′ (dimension symbols omitted in the drawing) of the main grooves 21, 22. The lower limit ensures the rigidity of the land portions 31, 32 in the early stage of wear, and the lower limit has the advantage of ensuring the improved drainage effect of the hidden groove 4 in the middle stage of wear.

[0080]

[10] In the tire 1 according to any one of the above [1] to [9], the groove width W42 of the hidden groove 4 on the groove bottom 42 side monotonically decreases from one end 43 to the other end 44 (see FIG. 7). This has the advantage of improving the ease with which the molding die can be removed from the hidden groove 4 during tire vulcanization molding.

[0081]

[11] In the tire 1 according to any one of the above items [1] to

[10] , the height of the hidden groove 4 decreases monotonically from one end 43 to the other end 44 (see FIGS. 3 and 5). This has the advantage of achieving both the drainage properties of the hidden groove 4 and the rigidity of the land portions 31, 32 from the middle to final stages of wear.

[0082]

[12] In the tire 1 described in any one of [1] to

[11] above, the maximum groove depth H2 (see FIG. 5) of the main grooves 21, 22 and the horizontal tread width THW (see FIG. 1) satisfy the condition 550≦H2×THW[mm^2]≦2500. This configuration has the advantage that the removability of the tire molding mold from the main grooves 21, 22 and the hidden groove 4 is properly ensured, particularly when a green tire is vulcanized using a tire molding mold that can be separated in the tire axial direction.

[0083] Applies to In this embodiment, as described above, a pneumatic tire has been described as an example of a tire. However, the present invention is not limited to this, and the configuration described in this embodiment can be applied to other tires as desired within the scope of what is obvious to those skilled in the art. Examples of other tires include airless tires and solid tires. [Example]

[0084] 23 and 24 are tables showing the results of performance tests of tires according to embodiments of the present invention, and Fig. 25 is an explanatory view showing the test tire of the comparative example shown in Fig. 23.

[0085] In this performance test, several types of test tires were evaluated for (1) wet braking performance when the tires were new and (2) wet braking performance when the tires were 50% worn. The test tires, measuring 145 / 80R12 80 / 78N, were mounted on rims measuring 12x4.00B, and the test tires were pressurized to 260 kPa (front tires) and 350 kPa (rear tires) and subjected to the specified JATMA load. The test tires were also mounted on all four wheels of a rear-wheel drive van, which served as the test vehicle.

[0086] To evaluate wet braking performance, a test vehicle is driven on an asphalt road covered with 1mm of water, and the braking distance is measured from an initial speed of 100km / h. Based on the measurement results, an index rating is then given, with the comparative example being assigned a standard rating of 100. The higher the rating, the better.

[0087] The test tire of the example has the configuration shown in Figures 1 to 6, and the land portions 31, 32 have hidden grooves 4 that open at one end 43 to the outer side surface of the land portions 31, 32 in the tire width direction and terminate at the other end 44 inside the land portions 31, 32. The tread horizontal width THW is 114 mm, and the tire ground contact width TW is 110 mm. The ground contact width WL of the land portions 31, 32 is 25 mm, and the average pitch length PL of the land portions 31, 32 is 24 mm. The maximum groove depth H2 of the main grooves 21, 22 is 8.5 mm, and the effective groove depth H2' is 6.9 mm.

[0088] The test tire of the comparative example is the test tire of Example 1, in which the land portions 31, 32 have, instead of the hidden grooves 4, thin slit-like grooves that penetrate the land portions 31, 32 in the tire width direction.

[0089] As the test results show, the test tires of the examples exhibit good wet braking performance both when the tires are new and when they are 50% worn. [Explanation of symbols]

[0090] 1 tire; 11 bead core; 12 bead filler; 13 carcass layer; 14 belt layer; 141, 142 cross belt; 15 tread rubber; 16 sidewall rubber; 17 rim cushion rubber; 21, 22 main groove; 21 circumferential main groove; 31, 32 land portion; 311 lug groove; 321 lug groove; 322 block; 4 hidden groove; 41 top; 42 groove bottom; 43 one end; 44 other end

Claims

1. A tire having a main groove and a land portion defined by the main groove, The land portion includes a hidden groove that extends in the tire width direction without opening onto the tread surface of the land portion, opens onto a side surface of the land portion on the outer side in the tire width direction at one end, and terminates inside the land portion at the other end, and A tire characterized in that a groove width W41 of the hidden groove on the tread side of the land portion is in a range of W41<W42 with respect to a groove width W42 of the hidden groove on the groove bottom side.

2. The tire according to claim 1, wherein a groove width W42 of the hidden groove on the groove bottom side is in a range of 0.05≦W42 / PL≦0.50 relative to a pitch length PL of the land portion.

3. The tire according to claim 1, wherein a groove width W41 of the hidden groove on the tread side of the land portion and a groove width W42 of the hidden groove on the groove bottom side are in a range of 0.10≦W41 / W42≦0.

80.

4. 2. The tire according to claim 1, wherein a height H43 of the hidden groove at the one end is in a range of 0.55≦H43 / H2′≦0.95 relative to an effective groove depth H2′ of the main groove.

5. The tire according to claim 1, wherein a height H44 of the hidden groove at the other end and a height H43 of the hidden groove at the one end are in a range of 0.10≦H44 / H43≦0.

90.

6. The tire according to claim 1, wherein an extension length L42 of the hidden groove on the groove bottom side is in a range of 0.30≦L42 / WL≦0.90 relative to a maximum ground contact width WL of the land portion.

7. The tire according to claim 1, wherein an extension length L41 of the hidden groove on the tread side of the land portion and an extension length L42 of the hidden groove on the groove bottom side are in a range of 0.10≦L41 / L42≦0.

90.

8. The tire according to claim 1, wherein a groove width W41 of the hidden groove on the tread side of the land portion is in a range of 1.0 mm≦W41≦6.0 mm.

9. 2. The tire according to claim 1, wherein a distance H41 from the tread surface of the land portion to the top of the hidden groove is in a range of 0.10≦H41 / H2′≦0.45 relative to an effective groove depth H2′ of the main groove.

10. The tire according to claim 1 , wherein a groove width W42 of the hidden groove on the groove bottom side monotonically decreases from the one end toward the other end.

11. The tire according to claim 1 , wherein the height of the hidden groove monotonically decreases from the one end toward the other end.

12. The tire according to claim 1, wherein the maximum groove depth H2 of the main groove and the horizontal tread width THW satisfy the condition 550≦H2×THW [mm^2]≦2500.

Images