Pneumatic tires

Abstract

To provide pneumatic tires capable of decreasing Cfmax when a vehicle turns at a large steering angle.SOLUTION: There is provided a pneumatic tire 1 that has a groove 505, extending in a predetermined direction within a predetermined range T outside grounding ends 501, 502, arranged at a tread, wherein the grounding ends 501, 502 are end parts of a grounding surface in a width direction of the tire 1 when 70% of a maximum load of a road index is placed on the tire 1 while the tire 1 has an internal pressure of 230 kPa, the predetermined range T is a range of a part outside the grounding ends 501, 502 in the width direction of the tire 1, and distances from the grounding ends 501, 502 are within a range of 8 to 15% of the width from one grounding end 501 to the other grounding end 502, the predetermined direction having an angle of 0 to 35° to a circumferential direction of the tire 1.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a pneumatic tire. [Background technology]

[0002] Conventionally, tires having grooves formed in the tread portion are known. For example, Patent Document 1 discloses a tire having grooves formed in the tread portion that go around the tire in the circumferential direction and that extend at a predetermined angle relative to the circumferential direction of the tire. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2006-069435 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been an increasing demand in the tire market for improved braking performance (μ), and improving μ improves Cfmax (maximum lateral force, coefficient of friction). However, when turning a vehicle with a large steering angle, if Cfmax is too high, the tires will have too much grip, causing the vehicle to roll significantly, and in particular in the case of vehicles with a high center of gravity such as minivans, the center of gravity of the vehicle will be located outside the outer wheel position, causing a significant loss of balance.

[0005] The present invention has been made in consideration of the above problems, and has an object to provide a pneumatic tire that is capable of lowering Cfmax when the vehicle is cornering with a large steering angle. [Means for solving the problem]

[0006] The pneumatic tire of the present invention is a pneumatic tire having a tread that constitutes the tread, which is the contact surface with the road surface, and the tread has grooves arranged in a predetermined direction within a predetermined range outside the ground contact edge, the ground contact edge being the end of the ground contact surface in the width direction of the tire when the internal pressure of the tire is set to 230 kPa and a load of 70% of the maximum load of the load index is applied to the tire, the predetermined range being the range of the outer part of the ground contact edges in the width direction of the tire, the distance from the ground contact edges being in the range of 8% to 15% of the width from one ground contact edge to the other ground contact edge in the width direction of the tire, and the predetermined direction being an angle between 0 degrees and 35 degrees with respect to the circumferential direction of the tire. Effect of the Invention

[0007] According to the present invention, it is possible to provide a pneumatic tire that is capable of lowering Cfmax when the vehicle is cornering with a large steering angle. [Brief description of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view in the tire width direction of a tire according to a first embodiment. [Diagram 2] 2 is a view of the tire of FIG. 1 as seen in the direction of arrow II when the vehicle is traveling straight. [Diagram 3] 2 is a view of the tire of FIG. 1 as seen in the direction of arrow II when the vehicle is turning leftward. [Figure 4] 2 is a view of a tire according to a second embodiment when a vehicle travels straight ahead, as viewed in the same direction as the arrow II in FIG. 1. [Diagram 5] 2 is a view of a tire according to a second embodiment when the vehicle is turning leftward, as viewed in the same direction as the arrow II in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a first embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a cross-sectional view of a tire 1 in the tire width direction. Fig. 2 is a view of the tire 1 in Fig. 1 as viewed in the direction of arrow II when the vehicle is traveling straight ahead. Fig. 3 is a view of the tire 1 in Fig. 1 as viewed in the direction of arrow II when the vehicle is turning. In the drawings, the symbol S1 indicates the tire equatorial plane. The tire equatorial plane S1 is a plane that is perpendicular to the tire rotation axis (tire meridian) and is located at the center in the tire width direction.

[0010] Here, the tire width direction is a direction parallel to the tire rotation axis, and is the left-right direction on the paper in the cross-sectional view of Fig. 1. In Fig. 1, this is illustrated as the tire width direction W. The inner side in the tire width direction is a direction approaching the tire equatorial plane S1. The outer side in the tire width direction is a direction moving away from the tire equatorial plane S1. For ease of explanation, the inner side in the vehicle width direction when the tire is mounted on the vehicle is defined as the left side in Fig. 1, and the outer side in the vehicle width direction when the tire is mounted on the vehicle is defined as the right side in Fig. 1.

[0011] The tire radial direction is a direction perpendicular to the tire rotation axis, and is the up-down direction on the paper in Fig. 1. In Fig. 1, this is illustrated as tire radial direction R. The tire radial outer side is a direction away from the tire rotation axis, and is the upper side on the paper in Fig. 1. The tire radial inner side is a direction approaching the tire rotation axis, and is the lower side on the paper in Fig. 1.

[0012] The cross-sectional view in Fig. 1 is a cross-sectional view in the tire width direction (cross-sectional view including the tire meridian) of the tire 1 mounted on a standard rim and inflated to a standard internal pressure in an unloaded state. The standard rim refers to a standard rim determined by JATMA for the tire size. The standard internal pressure is, for example, 180 kPa when the tire 1 is for a passenger car.

[0013] The tire 1 of this embodiment includes a pair of beads 2 provided on both sides in the tire width direction, sidewalls 3 extending radially outward from each of the beads 2, and an annular tread 4 extending in the circumferential direction of the tire 1, which is connected to the radially outward parts of each of the sidewalls 3 and constitutes a tread surface that is a contact surface with the road surface. A shoulder portion 50 is formed on the outer side of the tread 4 in the tire width direction.

[0014] The bead 2 is configured to include a bead core 21 formed into a bundled ring shape by winding a rubber-coated metal bead wire multiple times, and a rubber bead filler 22 with the bead core 21 embedded inside. The bead core 21 is a member for fixing the tire 1 filled with air to the rim (rim flange) of a wheel (not shown). The bead filler 22 is a member for increasing the rigidity of the periphery of the bead to ensure high maneuverability and stability.

[0015] Carcass plies (23, 27) that form the framework of the tire 1 are embedded inside the tire 1. The carcass ply (23, 27) is configured by a double carcass ply in which a first carcass ply 23 and a second carcass ply 27 are overlapped, but the carcass ply (23, 27) may be a single layer or three or more layers.

[0016] 1 and 2, the tread 4 includes a belt 26 embedded radially outward of the carcass plies (23, 27), and a tread rubber 28 that is disposed radially outward of the belt 26 while embedding the belt 26 and has an outer surface that serves as a contact surface, and the tread rubber 28 includes a plurality of main grooves 41, 42, 43 that extend continuously in the tire circumferential direction and go around the tire 1. The main grooves 41, 42, 43 extend continuously in the tire circumferential direction.

[0017] Of the multiple main grooves 41, 42, 43, the pair of main grooves 41, 42 arranged on the outermost sides in the tire width direction constitute shoulder main grooves 41, 42. More specifically, the shoulder main groove 41 on the vehicle inner side constitutes the inner shoulder main groove 41 as an inner main groove, and the shoulder main groove 42 on the vehicle outer side constitutes the outer shoulder main groove 42 as an outer main groove. The main groove 43 arranged between the pair of shoulder main grooves 41, 42 constitutes the center main groove 43.

[0018] The tread 4 includes an inner shoulder land portion 51, an outer shoulder land portion 52, an inner center land portion 53, and an outer center land portion 54.

[0019] The inner shoulder land portion 51 is formed by a land portion defined by the shoulder main groove 41 and a ground contact edge 501. The outer shoulder land portion 52 is formed by a land portion defined by the shoulder main groove 42 and a ground contact edge 502. As shown in FIG. 2, grooves 46, 47 and sipes 48, 49 are formed in the inner shoulder land portion 51 and the outer shoulder land portion 52, respectively.

[0020] Here, the ground contact edges 501 and 502 refer to the ends of the ground contact surface in the tire width direction when the tire is loaded with 70% of the maximum load of the load index while traveling straight and the tire is under an internal pressure of 230 kPa. Therefore, for example, as will be described later, when a vehicle equipped with tire 1 turns left as shown in Fig. 3, the part of the range indicated by T on the outer side in the tire width direction than ground contact edge 502 (to the right of ground contact edge 502 in Fig. 3) also comes into contact with the ground.

[0021] The inner center land portion 53 is formed by a land portion defined by adjacent main grooves 41, 43. The outer center land portion 54 is formed by a land portion defined by adjacent main grooves 42, 43. As shown in FIG. 2, slits 551, 552, 553 are formed in the inner center land portion 53 and the outer center land portion 54, respectively.

[0022] Further, the tread 4 is provided with grooves 505 extending in a predetermined direction within a predetermined range T outside the ground contact ends 501, 502, as shown by the area surrounded by a dashed line in Fig. 2 etc. Specifically, as shown in Fig. 2 etc., the predetermined range T is a range in a portion that does not come into contact with the ground when a vehicle equipped with the tire 1 travels straight, as shown in Fig. 2, and is a range in a portion that comes into contact with the ground when a vehicle equipped with the tire 1 turns at an angle of about 10° to the left and makes a turn, as shown in Fig. 3.

[0023] More specifically, the predetermined range T is a range on the outer side of the ground contact ends 501, 502 in the width direction of the tire 1 (the left side of the ground contact end 501 and the right side of the ground contact end 502 in FIG. 2), and means a range T in which the distance from the ground contact ends 501, 502 in the width direction of the tire 1 is 8% to 15% of the width from one ground contact end 501 to the other ground contact end 502 in the width direction of the tire 1. This is because if the distance from the ground contact ends 501, 502 is less than 8%, Cfmax (maximum lateral force, coefficient of friction) will be lowered more than necessary. Also, if the distance from the ground contact ends 501, 502 exceeds 15%, the effect of lowering Cfmax when the vehicle is turning cannot be obtained.

[0024] The predetermined direction is a direction that forms an angle of 0 degrees or more and 35 degrees or less with respect to the circumferential direction of the tire 1. That is, the circumferential direction of the tire 1 includes one circumferential direction (clockwise direction) and the other circumferential direction (counterclockwise direction) opposite to the one circumferential direction, and it is sufficient that the angle formed with respect to either one of the circumferential directions is 0 degrees or more and 35 degrees or less. If the angle formed with respect to the circumferential direction exceeds 35 degrees, the pressure from the road surface on the edge of the opening of the groove 505 does not increase, making it difficult to reduce the braking performance (μ). A more preferable direction is a direction that forms an angle of 0 degrees or more and 15 degrees or less with respect to either one of the circumferential directions. If the angle is 15 degrees or less, the braking performance (μ) can be sufficiently reduced.

[0025] As shown in FIG. 2 etc., the groove 505 extends continuously in the circumferential direction of the tire 1 and goes around the tire 1. In this case, the angle of the above-mentioned predetermined direction with respect to the circumferential direction of the tire 1 is 0 degrees. The depth of the groove 505 may be 0.5 mm or more, and is 1.5 mm in this embodiment. The width of the groove 505 may be 0.5 mm or more, and is 4.0 mm in this embodiment. This is because if the width of the groove 505 is less than 0.5 mm, it is not possible to sufficiently reduce the contact area during cornering.

[0026] Next, a second embodiment of the present disclosure will be described with reference to the drawings. Fig. 4 is a view of a tire 1A as seen in the same direction as the arrow II in Fig. 1. Fig. 5 is a view of the tire 1A as seen in the same direction as the arrow II in Fig. 1 when the vehicle is turning.

[0027] In the second embodiment, the configuration of the groove 505A is mainly different from that of the groove 505 in the first embodiment. In addition, the configurations of the other grooves 46A and sipes 48A, 49A, 55A, etc. are different from those of the grooves 46, 47, sipes 48, 49, etc. in the first embodiment. Since the other configurations are the same as those in the first embodiment, they are illustrated with the same reference numerals and the description is omitted. Specifically, as shown in FIG. 4, a plurality of sipes 55A are formed in the inner center land portion 53A and the outer center land portion 54A. In the inner shoulder land portion 51A and the outer shoulder land portion 52A, the sipes 48A, 49A extending in the width direction of the tire 1A and the groove 505A extending so as to straddle the ends of the sipes 48A and the ends of the sipes 49A on the outer sides in the width direction of the tire 1A are formed. In addition, between adjacent grooves 505A in the circumferential direction of tire 1A, sipes 48A extending in the width direction of tire 1A and grooves 46A extending further from the ends of sipes 48A are formed. Groove 505A extends in a direction forming an angle of 35 degrees with respect to the circumferential direction of tire 1A. Groove 505A has a depth of 0.5 mm and a width of 2.0 mm.

[0028] Next, tire 1 according to the first embodiment was evaluated as Example 1, tire 1A according to the second embodiment was evaluated as Example 2, and a conventional tire was prepared and evaluated as Comparative Example 1, in which grooves 505 extending in the predetermined direction described above are not arranged in the predetermined range T on the outside of ground contact ends 501, 502, and the other configuration is the same as that of Example 1. Also, a conventional tire was prepared and evaluated as Comparative Example 2, in which grooves 505A extending in the predetermined direction described above are not arranged in the predetermined range T on the outside of ground contact ends 501A, 502A, and the other configuration is the same as that of Example 2.

[0029] <Rolling resistance rating (RRC)> A test tire having a tire size of 205 / 60R16 92H was mounted on a standard rim with an air pressure of 230 kPa, and an evaluation test was conducted on the rolling resistance. In the rolling resistance test, a uniaxial drum testing machine for measuring rolling resistance was used to measure the rolling resistance at a load of 400 kg and a speed of 60 km / h. The rolling resistance of the test tire of Comparative Example 1 was assigned an index of 100, and the tire of Example 1 was evaluated based on this index.

[0030] <Evaluation of braking distance> A test tire with a tire size of 205 / 60R16 92H was mounted on a standard rim at an air pressure of 230 kPa, and an evaluation test was conducted on the braking distance. In this evaluation test, the tire was mounted on a test vehicle (a front-wheel drive minivan with an engine displacement of 2000 cc) and driven on a dry road surface, and braking force was applied by the ABS (Antilock Brake System) at a speed of 100 km / h, and the braking distance when the vehicle stopped at a speed of 0 km / h was evaluated. The braking distance of the test tire of Comparative Example 1 was set as an index of 100, and the tire of Example 1 was evaluated as an index.

[0031] <Cornering power (CP) evaluation> A drum tester with a diameter of 2500 mm was used to measure the cornering force generated in tire 1 of 205 / 60R16 92H with an internal pressure of 230 kPa and a load of 70% of the maximum load of the load index, and a cornering power evaluation test was performed by determining the cornering power at a slip angle of 1 degree. The result of Comparative Example 1 was set to 100 and the evaluation was performed using an index.

[0032] <Evaluation of maximum cornering force (Cfmax)> A test tire with a size of 205 / 60R16 92H was mounted on a standard rim with an air pressure of 230kPa, and was driven at a speed of 80km / h. A load of 70% of the maximum load of the load index was applied to the tire. Using a flat belt cornering tester, the maximum cornering force (Cfmax) was measured as the steering angle was gradually increased, and an evaluation test was conducted on the maximum cornering force. The result of Comparative Example 1 was set to 100 and the evaluation was performed using an index.

[0033] [Table 1] [Table 2]

[0034] As shown in Table 1, in Example 1, the Cfmax value was lower than that of Comparative Example 1, which is a conventional configuration, but it can be seen that similar performance to Comparative Example 1 was obtained in terms of RCC, braking distance, and CP.

[0035] Also, as shown in Table 2, in Example 2, although it does not reach Example 1, it is possible to set a lower Cfmax value than Comparative Example 1, which is a conventional configuration. And, as in Example 1, it can be seen that in all of RCC, braking distance, and CP, performance similar to that of Comparative Example 2 is obtained, and not inferior to Comparative Example 2.

[0036] That is, in Example 1, as described above, groove 505 extends in a direction that forms an angle of 0 degrees with respect to the circumferential direction of tire 1, groove 505 has a depth of 1.5 mm, and groove 505 has a width of 4.0 mm. Also, in Example 2, as described above, groove 505A extends in a direction that forms an angle of 35 degrees with respect to the circumferential direction of tire 1A, groove 505A has a depth of 0.5 mm, and groove 505A has a width of 2.0 mm.

[0037] Therefore, it can be seen that good results can be obtained in both this embodiment 1 and this embodiment 2, in which the groove depth is 0.5 mm or more, and that good results can be obtained in both this embodiment 1 and this embodiment 2, in which the groove width is between 1.0 mm and 4.0 mm.

[0038] The tire 1 of the present embodiment provides the following advantages. In the tread of the tire 1 (1A) according to this embodiment, a groove 505 (505A) is arranged extending in a predetermined direction within a predetermined range T (TA) outside the ground contact ends 501, 502 (501A, 502A). The ground contact ends 501, 502 (501A, 502A) are ends of the ground contact surface in the width direction of the tire 1 (1A) when the internal pressure of the tire 1 (1A) is set to 230 kPa and a load of 70% of the maximum load of the load index is applied to the tire 1 (1A). The predetermined range T (TA) is the tire 1 (1A). The specified direction is the range of the outer part of the ground contact ends 501, 502 (501A, 502A) in the width direction of the tire 1 (1A), the distance from the ground contact ends 501, 502 (501A, 502A) is the width from one ground contact end 501, 502 (501A, 502A) to the other ground contact end 501, 502 (501A, 502A) in the width direction of the tire 1 (1A), i.e., a range of 8% to 15% of the ground contact width of the tire, and the specified direction is a direction that forms an angle of 0 degrees to 35 degrees with respect to the circumferential direction of the tire 1 (1A).

[0039] This makes it possible to reduce the contact area when the vehicle turns, and to increase the average contact pressure on the contact surface. As a result, it becomes possible to reduce the coefficient of friction. Cfmax is calculated by "lateral friction coefficient x vertical load", and since it becomes possible to reduce the coefficient of friction as described above, it becomes possible to lower Cfmax when the vehicle turns with a large steering angle. Furthermore, since groove 505 (505A) is arranged in the steady-state non-contact portion, it becomes possible to avoid impairing maneuverability and braking performance in the steady state.

[0040] In the tire 1 (1A) according to the present embodiment, the predetermined direction is a direction that forms an angle of 0 degrees or more and 15 degrees or less with respect to the circumferential direction of the tire 1 (1A). This allows the braking performance (μ) to be sufficiently reduced. This allows the Cfmax to be sufficiently reduced.

[0041] In the tire 1 (1A) according to this embodiment, the groove 505 (505A) goes around the tire 1 (1A) in the circumferential direction. This means that the groove 505 (505A) is present at any position in the circumferential direction of the tire 1 (1A), making it possible to lower Cfmax.

[0042] In addition, in the tire 1 (1A) according to this embodiment, the depth of the groove 505 (505A) is 0.5 mm or more. This makes it possible to sufficiently increase the non-ground contact area when the vehicle is turning. As a result, it becomes possible to sufficiently reduce Cfmax.

[0043] In addition, in the tire 1 (1A) according to this embodiment, the width of the groove 505 (505A) is 1.0 mm or more and 4.0 mm or less. This makes it possible to sufficiently widen the non-ground contact area when the vehicle is turning. As a result, it becomes possible to sufficiently lower Cfmax.

[0044] The present invention is not limited to the above embodiment, and even if modifications and improvements are made within the scope of the present invention, the modifications and improvements are included in the scope of the present invention. For example, in the first embodiment, the groove 505 extends continuously around the tire 1 in the circumferential direction, but the present invention is not limited to this configuration. The groove only needs to be formed around the tire in the circumferential direction, and therefore, for example, the groove may be discontinuous around the tire in the circumferential direction, or may be zigzag-shaped around the tire in the circumferential direction. [Explanation of symbols]

[0045] 1. 1A Tire 4, 4A Tread 501, 501A, 502, 502A ground end 505, 505A Groove T, TA specified range

Claims

1. A pneumatic tire having a tread having a tread surface that contacts a road surface, The tread has grooves extending in a predetermined direction within a predetermined range on the outer side of the ground contact edge, The ground contact edge is an edge of the ground contact surface in the width direction of the tire when the internal pressure of the tire is set to 230 kPa and a load of 70% of the maximum load of the load index is applied to the tire, the predetermined range is a range of an outer portion of the ground contact end in the width direction of the tire, the range being from a portion that is 8% to a portion that is 15% of a width from one ground contact end to the other ground contact end in the width direction of the tire, the predetermined direction is a direction that forms an angle with respect to the circumferential direction of the tire of equal to or greater than 0 degrees and equal to or less than 35 degrees, The groove extends across ends of a pair of sipes extending in the tire width direction in the shoulder land portion.

2. The pneumatic tire according to claim 1 , wherein the predetermined direction is a direction forming an angle of 0 degrees or more and 15 degrees or less with respect to a circumferential direction of the tire.

3. The pneumatic tire according to claim 1 or 2, wherein the groove extends around the entire circumference of the tire in a circumferential direction.

4. The pneumatic tire according to claim 3 , wherein the groove is continuous in the circumferential direction of the tire.

5. The pneumatic tire according to claim 3 or 4, wherein the groove has a depth of 0.5 mm or more.

6. The pneumatic tire according to any one of claims 3 to 5, wherein the groove has a width of 1.0 mm or more and 4.0 mm or less.

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