JP2009090692A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of enhancing the fall preventive performance when the tire is worn while ensuring the steering stability. <P>SOLUTION: L1 denotes the contour range of a tread surface 11, TDW denotes the tread development width, TR1 denotes the radius of curvature of a center part arc 31, TR2 denotes the radius of curvature of a shoulder side arc 32, OD denotes the outside diameter of the tire, SW denotes the total width, and β denotes the flatness ratio. The tread surface 11 is formed so that the value obtained by F1=L1/(TDW×0.5) is in a range of 0.64≤F1≤0.7; the value obtained by F2=TR1/OD is in a range of 1.2≤F2≤2.0; the value obtained by F3=TR2/TR1 is in a range of 0.1≤F3≤0.2; and the value obtained by F4=(β×TDW)/(100×SW) is in a range of 0.35≤F4≤0.48. In addition, cap tread 12 is formed of a plurality of rubber layers in which the 300% tensile modulus becomes smaller from the outer side in the tire radial direction to the inner side in the tire radial direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pneumatic tire. In particular, the present invention relates to a pneumatic tire having a tread surface whose cross-sectional shape is formed by a plurality of arcs.

  Pneumatic tires usually have different areas of use in the tread when running straight and when running on a curve, so the degree of wear of each part of the tread varies depending on the running situation, and uneven wear may occur. is there. Thus, some conventional pneumatic tires have an appropriate shape of the tread portion to reduce uneven wear. For example, in the pneumatic radial tire described in Patent Document 1, in order to make the contact pressure distribution uniform and the contact length distribution when the tread part contacts the ground, the crown shape of the tread part has a curvature. It is formed by three arcs having different radii, and the radius of curvature of the arc and the width of each arc in the tire width direction are within an appropriate range. Thereby, even when various traveling states are mixed, since the tread portion is uniformly worn along the crown width direction, uneven wear can be reduced.

JP-A-9-71107

  In the conventional pneumatic tire, as described above, the uneven wear is reduced by making the crown shape of the pneumatic tire an appropriate shape. However, when the crown shape is adjusted, the characteristics during running of the vehicle also change. For example, by adjusting the crown shape and adjusting the contact area in the vicinity of the shoulder portion in the tread portion, the maximum cornering force at the time of turning of the vehicle equipped with the pneumatic tire can be changed. This maximum cornering force contributes to vehicle handling stability and toppling prevention performance, which are contradictory, but in recent years there has been a trend toward higher center of gravity and lower flatness of pneumatic tires. Due to its strength, there is an increasing demand to maintain the fall prevention performance.

  For this reason, as a method for maintaining such a fall prevention performance, it is conceivable to adjust the crown shape to reduce the ground contact area near the shoulder portion and to reduce the maximum cornering force. However, even when the crown shape is adjusted and the fall prevention performance is maintained, the rigidity of the tread portion is improved as the tread portion wears, so that the fall prevention performance may be lowered. In order to secure such a fall prevention performance when the tread portion is worn, it is effective to reduce the rigidity of the tread portion. However, if the rigidity of the tread portion is reduced, the steering stability may be lowered. There is. Therefore, it has been very difficult to achieve both the fall prevention performance and the handling stability during wear.

  This invention is made | formed in view of the above, Comprising: It aims at providing the pneumatic tire which can improve the fall prevention performance at the time of abrasion, ensuring steering stability.

In order to solve the above-described problems and achieve the object, a pneumatic tire according to the present invention has sidewall portions at both ends in the tire width direction, and a cap tread on the outer side in the tire radial direction of the sidewall portions. And a tread surface, which is the surface of the cap tread when viewed in a meridional section, is formed of a plurality of arcs having different radii of curvature, and is assembled to a regular rim. In addition, in a state where 5% of the normal internal pressure is filled, the tread surface has a central arc located at the center in the tire width direction, and a shoulder side located at least outside the vehicle in the tire width direction of the central arc. An arc and a shoulder arc that forms a shoulder located at least at the end of the tread surface outside the vehicle in the tire width direction. The radius of curvature of the central arc is TR1, the radius of curvature of the shoulder side arc is TR2, and the contour range from the equator plane to the end of the central arc in the tire width direction is L1, The width of the tread surface that is the width of the tread surface in the tire width direction is defined as TDW, and the tire widths of the outermost portions in the tire width direction of the sidewall portions that are located opposite to each other in the tire width direction are opposed to each other. When the total width that is the width in the direction is SW, the tire outer diameter that is the diameter of the largest portion in the tire radial direction of the tread surface is OD, and the flatness is β, the contour range L1 F1 obtained by the following equation (1), which is a relational expression with the tread development width TDW, falls within the range of 0.64 ≦ F1 ≦ 0.7, and the curvature of the central arc is half F2 obtained by the following formula (2), which is a formula for calculating the ratio between the diameter TR1 and the tire outer diameter OD, falls within the range of 1.2 ≦ F2 ≦ 2.0, and the radius of curvature of the central arc F3 obtained by the following expression (3), which is an expression for determining the ratio between the TR1 and the radius of curvature TR2 of the shoulder-side arc, falls within the range of 0.1 ≦ F3 ≦ 0.2, and the flatness F4 obtained by the following formula (4), which is a relational expression between β, the tread development width TDW, and the total width SW, falls within the range of 0.35 ≦ F4 ≦ 0.48, and the cap tread is It is characterized by being formed of a plurality of rubber layers having a 300% tensile modulus that decreases from the outer side in the tire radial direction toward the inner side in the tire radial direction.
F1 = L1 / (TDW × 0.5) (1)
F2 = TR1 / OD (2)
F3 = TR2 / TR1 (3)
F4 = (β × TDW) / (100 × SW) (4)

  In the present invention, the relationship F1 between the contour range L1 and the tread development width TDW is calculated by the above formula, and F1 falls within the range of 0.64 ≦ F1 ≦ 0.7, and the radius of curvature TR1 of the central arc is By setting the ratio F2 to the tire outer diameter OD to be in the range of 1.2 ≦ F2 ≦ 2.0, the profile of the tread surface can be brought close to a flat shape. Thereby, for example, the ground contact area at the time of low load such as a rear tire of a front engine front drive (FF) vehicle can be increased, and the maximum cornering force at the time of low load can be increased. Therefore, it is possible to ensure steering stability at low loads.

  Further, by calculating the ratio F3 between the radius of curvature TR1 of the central arc and the radius of curvature TR2 of the shoulder side arc by the above formula, so that F3 falls within the range of 0.1 ≦ F3 ≦ 0.2. For example, the ground contact width at the time of a high load such as a maximum load can be increased. Thereby, since the contact pressure can be made uniform, the wear resistance can be improved. Further, by calculating F4 which is the relationship between the flatness ratio β, the tread development width TDW, and the total width SW by the above formula, so that F4 falls within the range of 0.35 ≦ F4 ≦ 0.48, Since the tread deployment width can be narrowed, the contact area at the time of high load can be reduced. Thereby, since the maximum cornering force at the time of high load can be reduced, the fall prevention performance at the time of high load can be ensured.

  In addition, since the cap tread is formed of a plurality of rubber layers whose tensile modulus decreases by 300% as it goes from the outer side in the tire radial direction to the inner side in the tire radial direction, 300% in the initial stage of wear of the cap tread. A rubber layer having a high% tensile modulus can be grounded. Thereby, since the rigidity of the cap tread can be ensured before the cap tread is worn or in a state where the cap tread is not worn so much, the steering stability can be secured.

  Further, by forming the cap tread with a plurality of rubber layers having a 300% tensile modulus that decreases from the outer side in the tire radial direction toward the inner side in the tire radial direction, when the wear of the cap tread proceeds, A rubber layer having a low 300% tensile modulus can be grounded. Thereby, since the rigidity of the cap tread when the cap tread is worn can be reduced, the fall prevention performance at the time of wear can be improved. As a result, it is possible to improve the fall prevention performance during wear while ensuring the steering stability.

  Further, in the pneumatic tire according to the present invention, the plurality of rubber layers forming the cap tread are an outer rubber layer that is the rubber layer located on the outer side in the tire radial direction, and a tire radial direction of the outer rubber layer. An inner rubber layer located on the inner side, the 300% tensile modulus Mo of the outer rubber layer being in the range of (10 <Mo ≦ 15) MPa, The 300% tensile modulus Mi is characterized by being in the range of (5 ≦ Mi ≦ 10) MPa.

  In this invention, the cap tread is formed of the outer rubber layer and the inner rubber layer, and the 300% tensile modulus Mo of the outer rubber layer is within the range of (10 <Mo ≦ 15) MPa, and 300% of the inner rubber layer. The tensile modulus Mi is in the range of (5 ≦ Mi ≦ 10) MPa. Thereby, the rigidity of the cap tread when the wear of the cap tread is small can be ensured more reliably, and the rigidity of the cap tread when the wear of the cap tread is large can be more reliably reduced. As a result, it is possible to improve the fall prevention performance at the time of wear while ensuring the steering stability more reliably.

  In the pneumatic tire according to the present invention, the average thickness of the inner rubber layer is in the range of 30 to 70% of the thickness of the cap tread.

  In this invention, in order to make the average thickness of the inner rubber layer within a range of 30 to 70% of the thickness of the cap tread, the rigidity of the cap tread is ensured at the initial stage of wear, and the cap tread when wear progresses. The reduction in rigidity can be achieved more reliably. In other words, when the average thickness of the inner rubber layer is less than 30% of the thickness of the cap tread, even when the cap tread is worn, many outer rubber layers having a high 300% tensile modulus remain. There is a risk that the rigidity is difficult to reduce. Thereby, there exists a possibility that the fall prevention performance at the time of wear may become difficult to improve.

  In addition, if the average thickness of the inner rubber layer is greater than 70% of the cap tread thickness, the inner rubber layer with a low 300% tensile modulus is too thick, resulting in lower overall rigidity of the cap tread. There is a risk of passing. This may make it difficult to ensure steering stability in a state with little wear. Therefore, by setting the average thickness of the inner rubber layer within the range of 30 to 70% of the thickness of the cap tread, the cap tread has a rigidity at the initial stage of wear, and the cap tread has an improved thickness when the wear progresses. The rigidity can be more reliably reduced. As a result, it is possible to improve the fall prevention performance at the time of wear while ensuring the steering stability more reliably.

  In addition, the pneumatic tire according to the present invention passes through an end portion in the tire width direction of the central arc and is in contact with the central arc, and an end portion on the outer side in the tire width direction of the shoulder arc. And an angle α formed with a tangent line in contact with the shoulder portion arc is in a range of 35 ° ≦ α ≦ 60 °.

  In the present invention, by making the angle α described above within the range of 35 ° ≦ α ≦ 60 °, the angle change in the vicinity of the shoulder portion from the tread surface direction to the sidewall portion direction is increased, that is, It is possible to make the shoulder drop at a steep angle. As a result, it is possible to suppress the contact width from expanding at a high load and a high slip angle, so that the maximum cornering force at a high load can be more reliably reduced. As a result, the fall prevention performance can be improved more reliably.

Further, the pneumatic tire according to the present invention is an equation for obtaining a ratio between the curvature radius TR1 of the central arc and the curvature radius SHR of the shoulder arc when the curvature radius of the shoulder arc is SHR. F5 calculated | required by the following formula | equation (5) becomes in the range of 0.025 <= F5 <= 0.035, It is characterized by the above-mentioned.
F5 = SHR / TR1 (5)

  In the present invention, the curvature radius of the shoulder portion can be reduced by setting the ratio F5 between the curvature radius TR1 of the central arc and the curvature radius SHR of the shoulder arc within the range of 0.025 ≦ F5 ≦ 0.035. Can be small. As a result, it is possible to suppress the contact width from expanding at a high load and a high slip angle, so that the maximum cornering force at a high load can be more reliably reduced. As a result, the fall prevention performance can be improved more reliably.

  The pneumatic tire according to the present invention has an effect that it is possible to improve the fall prevention performance at the time of wear while ensuring the steering stability.

  Hereinafter, an embodiment of a pneumatic tire according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily replaced by those skilled in the art or those that are substantially the same.

(Embodiment)
In the following description, the tire width direction refers to a direction parallel to the rotation axis of the pneumatic tire, the inner side in the tire width direction refers to the direction toward the equator in the tire width direction, and the outer side in the tire width direction refers to the tire. The direction opposite to the direction toward the equatorial plane in the width direction. Further, the tire radial direction refers to a direction orthogonal to the rotation axis, and the tire circumferential direction refers to a direction rotating around the rotation axis as a center of rotation.

  FIG. 1 is a meridional cross-sectional view showing a main part of a pneumatic tire according to the present invention. The pneumatic tire 1 shown in the figure has a tread portion 10 at the outermost portion in the tire radial direction when viewed in a meridional section. Further, a sidewall portion 15 is provided from the end of the tread portion 10 in the tire width direction, that is, from the vicinity of the shoulder portion 16 to a predetermined position on the inner side in the tire radial direction. That is, the sidewall portions 15 are provided at both ends of the pneumatic tire 1 in the tire width direction. Further, a bead portion 24 is provided on the inner side in the tire radial direction of the sidewall portion 15. The bead portions 24 are provided at two locations of the pneumatic tire 1, and are also provided on the opposite side of the equator plane 5 so as to be symmetric about the equator plane 5. For this reason, the bead part 24 is located on both sides in the tire width direction of the pneumatic tire 1. Also, the bead portion 24 provided in this way is provided with a bead core 25, and a bead filler 26 is provided outside the bead core 25 in the tire radial direction.

  A plurality of belt layers 21 are provided on the inner side of the tread portion 10 in the tire radial direction. A carcass 22 is continuously provided on the inner side in the tire radial direction of the belt layer 21 and on the equator plane 5 side of the sidewall portion 15. The carcass 22 is folded back outward in the tire width direction along the bead core 25 at the bead portion 24. Further, an inner liner 23 is formed along the carcass 22 on the inner side of the carcass 22 or on the inner side of the carcass 22 in the pneumatic tire 1.

  The tread portion 10 has a cap tread 12. The cap tread 12 is located outward in the tire radial direction in the tread portion 10 and is exposed to the outside of the pneumatic tire 1. Thus, the portion of the cap tread 12 exposed to the outside, that is, the surface of the cap tread 12 is formed as a tread surface 11.

  In the tread portion 10, when the pneumatic tire 1 is viewed in a meridional section, the surface of the cap tread 12 or the tread surface 11 that is the surface of the tread portion 10 is formed by a plurality of arcs having different curvature radii. ing. Specifically, the tread surface 11 has a central arc 31 and a shoulder-side arc 32 in a state where the pneumatic tire 1 is assembled on a normal rim and is filled with 5% of the normal internal pressure. The shoulder portion arc 33 is formed.

  Here, the regular rim is “standard rim” defined by JATMA, “Design Rim” defined by TRA, or “Measuring Rim” defined by ETRTO. The normal internal pressure is “maximum air pressure” defined by JATMA, the maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO. However, in the case of the pneumatic tire 1 for passenger cars, it is 180 kPa.

  Of the plurality of arcs forming the tread surface 11, the central arc 31 is located in the center of the tread surface 11 in the tire width direction, includes the equator plane 5, and the tire on the equator plane 5 is centered on the equator plane 5. It is formed on both sides in the width direction. The shape is an arc that is convex outward in the tire radial direction and has the largest diameter in the tire radial direction near the equatorial plane 5.

  Further, the shoulder-side arc 32 is located on the vehicle outer side in the tire width direction of the central arc 31 or at two places on both sides, and the shoulder-side arc 32 is convex outward in the tire radial direction. Further, the shoulder portion arc 33 is located outward of the shoulder side arc 32 in the tire width direction. The shoulder portion arc 33 forms the shoulder portion 16 and is an arc that protrudes outward in the tire radial direction.

  That is, the tread surface 11 has a shoulder-side arc 32 positioned on the outer side of the vehicle in the tire width direction of the central arc 31 located at the center in the tire width direction, or on both sides of the tread surface 11. The shoulder arc 33 is located on the vehicle outer side or on both sides. Further, the central arc 31 and the shoulder arc 32, and the shoulder arc 32 and the shoulder arc 33 are connected and continuously formed. Further, the radius of curvature TR1 of the central arc 31 positioned in this way, the radius of curvature TR2 of the shoulder side arc 32, and the radius of curvature SHR of the shoulder arc 33 are all different in size.

  In addition, the tire width direction vehicle outer side here refers to the outer side in the width direction of the vehicle among both ends in the tire width direction of the pneumatic tire 1 when the pneumatic tire 1 is mounted on a vehicle (not shown). The end on the side where it is located. In addition, when the pneumatic tire 1 is mounted on a vehicle, the tire width direction vehicle inner side refers to the inner side in the vehicle width direction, or the center in the vehicle width direction, of both ends of the pneumatic tire 1 in the tire width direction. The end on the side located in the direction.

  A side arc 34 is formed on the outer side of the shoulder arc 33 in the tire width direction. The side portion arc 34 is located on the outer side in the tire width direction of the shoulder portion arc 33 and is connected to the shoulder portion arc 33, and is formed from the shoulder portion arc 33 toward the sidewall portion 15.

  In addition, sidewall portions 15 are provided at two locations on the inner side in the tire radial direction of the tread portion 10 at both ends in the tire width direction of the pneumatic tire 1. The meridional cross section is curved so as to be convex outward in the tire width direction. In addition, since the two sidewall portions 15 are curved so as to protrude outward in the tire width direction, the two sidewall portions 15 are farthest from the equator plane 5 in the tire width direction among the sidewall portions 15. The distance between the portions in the tire width direction is the total width of the pneumatic tire 1.

The tread surface 11 of the pneumatic tire 1 formed as described above is formed in a predetermined shape. That is, each part of the pneumatic tire 1 has a contour range L1 as a width in the tire width direction from the center arc end point 35 which is an end of the center arc 31 in the tire width direction to the equator plane 5, and the pneumatic tire 1 The outer diameter of the tire 1, that is, the tire outer diameter that is the diameter of the largest portion in the tire radial direction of the tread surface 11 is OD, and the tread deployment width that is the width of the tread surface 11 in the tire width direction is TDW. To do. When each part of the pneumatic tire 1 is defined in this way, the tread surface 11 obtains the relationship between the contour range L1 and the tread development width TDW by the following equation (6), and F1 obtained by the equation (6) is While being within the range of 0.64 ≦ F1 ≦ 0.7, the ratio between the radius of curvature TR1 of the central arc 31 and the tire outer diameter OD is obtained by the following equation (7), and F2 obtained by the equation (7) is obtained. Is in a range of 1.2 ≦ F2 ≦ 2.0. Furthermore, the tread surface 11 calculates | requires ratio of the curvature radius TR1 of the center part arc 31 and the curvature radius TR2 of the shoulder side arc 32 by the following formula | equation (8), and F3 calculated | required by the formula (8) is 0.1. It is formed so as to be within the range of ≦ F3 ≦ 0.2.
F1 = L1 / (TDW × 0.5) (6)
F2 = TR1 / OD (7)
F3 = TR2 / TR1 (8)

  FIG. 2 is a detailed view of part A of FIG. As shown in FIG. 2, the tread development width TDW is a distance between the virtual tread ends 47 positioned on both ends in the tire width direction of the tread portion 10 as a tread development width TDW. That is, in the meridional section of the pneumatic tire 1, the shoulder side arc extension which is a virtual line obtained by extending one shoulder side arc 32 outward in the tire width direction among the shoulder side arcs 32 positioned on both sides in the tire width direction. The intersection of the line 45 and the side part arc extension line 46 which is a virtual line obtained by extending the side part arc 34 connected to the shoulder part arc 33 formed continuously with the shoulder side arc 32 outward in the tire radial direction. Is a virtual tread end 47. Since the virtual tread ends 47 are formed on both ends in the tire width direction, the distance between the virtual tread ends 47 in the tire width direction is defined as a tread development width TDW.

Furthermore, when the flat rate of the pneumatic tire 1 is β and the total width in the tire width direction of the pneumatic tire 1 is SW, the relationship between the flat rate β, the tread deployment width TDW, and the total width SW is expressed by the following equation: The pneumatic tire 1 is formed so that F4 obtained by (9) and F4 obtained by the equation (9) falls within the range of 0.35 ≦ F4 ≦ 0.48.
F4 = (β × TDW) / (100 × SW) (9)

  Still further, the pneumatic tire 1 passes through the central arc end point 35 and has a central arc tangent 41 that is a tangent to the central arc 31 and an end of the shoulder arc 33 on the outer side in the tire width direction. Among the plurality of angles formed when the shoulder portion arc tangent 42 passing through the shoulder portion arc end point 36 and intersecting with the shoulder portion arc 33 intersects with the center portion arc tangent 41 in the tire radial direction. The angle α located on the outer side and on the outer side in the tire width direction of the shoulder arc tangent line 42 is in a range of 35 ° ≦ α ≦ 60 °.

Further, in the pneumatic tire 1, the ratio of the curvature radius TR1 of the central arc 31 and the curvature radius SHR of the shoulder arc 33 is obtained by the following equation (10), and F5 obtained by the equation (10) is 0.00. The tread surface 11 is formed so as to be in the range of 025 ≦ F5 ≦ 0.035.
F5 = SHR / TR1 (10)

  FIG. 3 is an explanatory diagram of the cap tread of the pneumatic tire shown in FIG. 1. The cap tread 12 included in the tread portion 10 is formed of two rubber layers having different 300% tensile moduli according to JIS-K6251. Of the two rubber layers, the rubber layer positioned on the outer side in the tire radial direction is An outer rubber layer 13 is formed, and the rubber layer located on the inner side in the tire radial direction of the outer rubber layer 13 is an inner rubber layer 14.

  The two rubber layers have a 300% tensile modulus that decreases from the outer side in the tire radial direction toward the inner side in the tire radial direction, and the inner rubber layer 14 has a lower tensile modulus than the 300% tensile modulus of the outer rubber layer 13. The 300% tensile modulus is lower. Specifically, when the 300% tensile modulus of the outer rubber layer 13 is Mo and the 300% tensile modulus of the inner rubber layer 14 is Mi, the 300% tensile modulus Mo of the outer rubber layer 13 is (10 <Mo ≦ 15) It is in the range of MPa, and the 300% tensile modulus Mi of the inner rubber layer 14 is in the range of (5 ≦ Mi ≦ 10) MPa.

  In the cap tread 12, the average thickness Di of the inner rubber layer 14 in the meridional cross-sectional view of the pneumatic tire 1 is in the range of 30 to 70% of the thickness D of the cap tread 12. In addition, the thickness D of the cap tread 12 here is an average thickness of the cap tread 12. Moreover, since the average thickness Di of the inner rubber layer 14 is an average value of the thickness of the entire inner rubber layer 14, the thickness of the inner rubber layer 14 is partially 30 to 30 mm of the thickness D of the cap tread 12. It may be outside the range of 70%.

  When the pneumatic tire 1 is mounted on a vehicle and travels, the pneumatic tire 1 rotates while the tread surface 11 positioned below the tread surface 11 contacts the road surface (not shown). When the vehicle is traveling, the tread surface 11 is in contact with the road surface in this way, so that a load due to the weight of the vehicle acts on the tread surface 11. The load acting on the tread surface 11 varies depending on the traveling state of the vehicle, and during cornering when traveling at low speed, the load acting on the tread surface 11 is relatively low and traveling at high speed. At the time of lane change or cornering, the load acting on the tread surface 11 is relatively high.

  When the vehicle travels, the tread surface 11 contacts the road surface while the load acting in this way changes. However, since the tread surface 11 is deformed by the acting load, the cornering force in each state according to the deformation of the tread surface 11. The maximum value, i.e., the maximum cornering force, changes.

  Specifically, when the load acting on the tread surface 11 is low, the tread surface 11 is not easily deformed, but the tread surface 11 of the pneumatic tire 1 according to the embodiment has the contour range L1 and the tread deployment width TDW. F1 is in the range of 0.64 ≦ F1 ≦ 0.7, and the ratio F2 between the radius of curvature TR1 of the central arc 31 and the tire outer diameter OD is 1.2 ≦ It is in the range of F2 ≦ 2.0. Thereby, for example, when the pneumatic tire 1 is used as a rear tire of an FF vehicle, the shape of the tread surface 11 at the time of low load becomes close to a flat shape, and the ground contact area at the time of low load becomes wide.

  That is, by setting the ratio F2 between the curvature radius TR1 of the central arc 31 and the tire outer diameter OD to be 1.2 or more, the curvature radius TR1 of the central arc 31 can be appropriately increased, and F2 Is set to 2.0 or less, it is possible to suppress the difference in the radius of curvature between the central arc 31 and the shoulder-side arc 32 from becoming too large, and a large stress acts near the central arc end point 35. Can be suppressed.

  Further, by setting F1 which is the relationship between the contour range L1 and the tread development width TDW to be 0.64 or more, the range in which the central arc 31 having a large curvature radius is formed in the tire width direction is increased. By making F1 0.7 or less, the formation range of the shoulder-side arc 32 in the tire width direction can be secured, and the radius of curvature from the central arc 31 to the shoulder arc 33 is gentle. Can be made smaller.

  Thus, F1 which is the relationship between the contour range L1 and the tread development width TDW is set within the range of 0.64 ≦ F1 ≦ 0.7, and the radius of curvature TR1 of the central arc 31 and the tire outer diameter OD are By setting the ratio F2 within the range of 1.2 ≦ F2 ≦ 2.0, the profile of the tread surface 11 can be brought close to a flat shape. For this reason, the ground contact area at the time of low load can be increased, and the maximum cornering force at the time of low load can be increased. Therefore, it is possible to ensure steering stability at low loads. In particular, the rear tire of the FF vehicle is light, and the rear tire has a low load. However, the rear corner is improved by increasing the maximum cornering force when the rear tire is under a low load. Thereby, in FF vehicle, steering stability becomes higher. In addition, by increasing the contact area at the time of low load in this way, the frictional force between the tread surface 11 and the road surface can be improved, and the braking performance can be improved.

  When the load acting on the tread surface 11 is large, the tread surface 11 is easily deformed, but the pneumatic tire 1 has a radius of curvature TR1 of the central arc 31 and a radius of curvature TR2 of the shoulder side arc 32. Since the ratio F3 is in the range of 0.1 ≦ F3 ≦ 0.2, the ground contact width at the time of high load can be appropriately increased.

  That is, by making the ratio F3 of the curvature radius TR1 of the central arc 31 and the curvature radius TR2 of the shoulder side arc 32 to be 0.1 or more, the curvature radius of the shoulder side arc 32 is suppressed from becoming too small. it can. As a result, when the shoulder arc 32 on the tread surface 11 is grounded under a heavy load, the ground can be grounded with an appropriate grounding width, and the grounding width can be appropriately widened under a heavy load. Further, by setting the ratio F3 between the curvature radius TR1 of the central arc 31 and the curvature radius TR2 of the shoulder side arc 32 to be 0.2 or less, it is possible to prevent the curvature radius of the shoulder side arc 32 from becoming too large. it can. Thereby, it can suppress that the tread surface 11 spreads too much due to the part of the shoulder side circular arc 32 in the tread surface 11 grounding at the time of high load.

  For this reason, when a high load is applied to the tread surface 11 such as at the maximum load of the pneumatic tire 1, the contact width can be appropriately increased, and the contact pressure can be made uniform. Thereby, an improvement in wear resistance can be achieved. Further, by making the contact pressure uniform, the frictional force with the road surface can be improved, so that the braking performance can be improved. The maximum load referred to here is the “maximum load capacity” specified by JATMA, the maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” specified by TRA, or “LOAD CAPACITY” specified by ETRTO. is there.

  In addition, when the load acting on the tread surface 11 is large, the tread surface 11 is easily deformed, but the pneumatic tire 1 has F4 which is a relationship among the flatness β, the tread deployment width TDW, and the total width SW. Since it is within the range of 0.35 ≦ F4 ≦ 0.48, the ground contact area is not so wide even under heavy loads.

  That is, the minimum necessary tread development width TDW with respect to the total width SW can be secured by setting F4, which is the relationship between the flat rate β, the tread development width TDW, and the total width SW, to be 0.35 or more. In addition, by setting F4 to be 0.48 or less, the tread development width TDW with respect to the total width SW of the pneumatic tire 1 can be reduced. For this reason, when the high load is acting on the tread surface 11, such as at the maximum load of the pneumatic tire 1, an increase in the contact area can be reduced, and the maximum cornering force at the time of the high load can be reduced. Therefore, it is possible to ensure the fall prevention performance at the time of high load.

  That is, the ratio F3 between the radius of curvature TR1 of the central arc 31 and the radius of curvature TR2 of the shoulder side arc 32 is in the range of 0.1 ≦ F3 ≦ 0.2, and the flatness β and the tread development width are set. By making F4, which is the relationship between the TDW and the total width SW, within the range of 0.35 ≦ F4 ≦ 0.48, it is possible to reduce the contact area from becoming too large at the time of high load and at the time of high load. The ground contact width can be increased moderately and the ground contact area can be kept within an appropriate range.

  In addition, since the cap tread 12 is formed of two rubber layers having a 300% tensile modulus that decreases from the outer side in the tire radial direction toward the inner side in the tire radial direction, the cap tread 12 is in an initial wear stage. Then, the rubber layer having a high 300% tensile modulus can be grounded. Thereby, since the rigidity of the cap tread 12 can be ensured before the cap tread 12 is worn or in a state where the cap tread 12 is not worn much, the steering stability can be ensured.

  Further, by forming the cap tread 12 with two rubber layers having a 300% tensile modulus that decreases from the outer side in the tire radial direction toward the inner side in the tire radial direction, wear of the cap tread 12 has progressed. In this case, the rubber layer having a low 300% tensile modulus can be grounded. Thereby, since the rigidity of the cap tread 12 when the cap tread 12 is worn can be lowered, the fall prevention performance at the time of wear can be improved. As a result, it is possible to improve the fall prevention performance during wear while ensuring the steering stability.

  Further, the cap tread 12 is formed by the outer rubber layer 13 and the inner rubber layer 14 having different 300% tensile modulus, and the 300% tensile modulus Mo of the outer rubber layer 13 is in the range of (10 <Mo ≦ 15) MPa. The 300% tensile modulus Mi of the inner rubber layer 14 is in the range of (5 ≦ Mi ≦ 10) MPa. Thereby, the rigidity of the cap tread 12 when the wear of the cap tread 12 is small can be ensured more reliably, and the rigidity of the cap tread 12 when the wear of the cap tread 12 is large can be more reliably reduced. Can do. As a result, it is possible to improve the fall prevention performance at the time of wear while ensuring the steering stability more reliably.

  In addition, since the average thickness Di of the inner rubber layer 14 is within the range of 30 to 70% of the thickness D of the cap tread 12, securing of the rigidity of the cap tread 12 in the initial stage of wear and progress of wear have progressed. In this case, the reduction in the rigidity of the cap tread 12 can be more reliably achieved. That is, when the average thickness Di of the inner rubber layer 14 is less than 30% of the thickness D of the cap tread 12, even when the cap tread 12 is worn, there are many outer rubber layers 13 having a high 300% tensile modulus. Since it remains, there exists a possibility that the rigidity of the cap tread 12 may become difficult to reduce. Thereby, there exists a possibility that the fall prevention performance at the time of wear may become difficult to improve. When the average thickness Di of the inner rubber layer 14 is thicker than 70% of the thickness D of the cap tread 12, the inner rubber layer 14 having a low 300% tensile modulus is too thick. There is a possibility that the overall rigidity becomes too low. This may make it difficult to ensure steering stability in a state with little wear.

  Therefore, by making the average thickness Di of the inner rubber layer 14 within the range of 30 to 70% of the thickness D of the cap tread 12, the wear progressed while ensuring the rigidity of the cap tread 12 in the initial stage of wear. In this case, the rigidity of the cap tread 12 can be more reliably reduced. As a result, it is possible to improve the fall prevention performance at the time of wear while ensuring the steering stability more reliably.

  Further, the ratio F3 between the radius of curvature TR1 of the central arc 31 and the radius of curvature TR2 of the shoulder-side arc 32 is in the range of 0.1 ≦ F3 ≦ 0.2, so that the ground contact width at the time of high load is appropriately set. Since the rubber that forms the tread surface 11, that is, the rubber that forms the cap tread 12, can be widened, the frictional force between the tread surface 11 and the road surface is ensured even when rubber having low rolling characteristics is used. be able to. That is, for example, even when rubber with a small tan δ value is used for the cap tread 12, the frictional force between the tread surface 11 and the road surface can be ensured, so that the braking performance can be ensured. Therefore, regardless of the type of rubber used for the cap tread 12, the braking performance can be ensured. As a result, the braking performance can be improved more reliably. In addition, since the braking performance can be ensured regardless of the type of rubber used for the cap tread 12 as described above, the choice of materials can be increased, and inexpensive rubber can be selected. . As a result, the manufacturing cost can be reduced.

  Moreover, since the angle α formed by the central arc tangent 41 and the shoulder arc tangent 42 is in the range of 35 ° ≦ α ≦ 60 °, the fall prevention performance can be improved more reliably. That is, by making the angle α formed by the central arc tangent 41 and the shoulder arc tangent 42 to be 35 ° or more, the change in angle in the vicinity of the shoulder portion 16 from the tread surface 11 direction to the sidewall portion 15 direction is increased. be able to. That is, the shoulder fall of the shoulder portion 16 can be made a steep angle. Further, by setting the angle α formed by the central arc tangent 41 and the shoulder arc tangent 42 to 60 ° or less, the rigidity in the vicinity of the shoulder arc 33 can be secured. As a result, the shoulder portion 16 can be prevented from being deformed and many portions of the shoulder portion 16 are grounded at a high load and at a high slip angle, and the shoulder portion 16 is deformed and grounded. Expansion of the area can be suppressed. Therefore, the maximum cornering force at the time of high load can be more reliably reduced. As a result, the fall prevention performance can be improved more reliably.

  Further, since F5 which is the ratio of the curvature radius TR1 of the central arc 31 and the curvature radius SHR of the shoulder arc 33 is in the range of 0.025 ≦ F5 ≦ 0.035, the fall prevention performance is more sure. Can be improved. That is, by setting the ratio F5 between the radius of curvature TR1 of the central arc 31 and the radius of curvature SHR of the shoulder arc 33 to 0.025 or more, the rigidity in the vicinity of the shoulder arc 33 can be secured. Further, by setting the ratio F5 between the radius of curvature TR1 of the central arc 31 and the radius of curvature SHR of the shoulder arc 33 to 0.035 or less, the shoulder fall of the shoulder 16 can be made a steep angle. As a result, it is possible to prevent the shoulder portion 16 from being deformed and many portions of the shoulder portion 16 from being grounded at a high load and at a high slip angle, and the contact area can be expanded by the deformation of the shoulder portion 16. Can be suppressed. Therefore, the maximum cornering force at the time of high load can be more reliably reduced. As a result, the fall prevention performance can be improved more reliably.

  In the pneumatic tire 1 according to the embodiment, the cap tread 12 is formed by two rubber layers of the outer rubber layer 13 and the inner rubber layer 14, but the cap tread 12 has three or more rubber layers. May be formed. The cap tread 12 may be of any number as long as it is formed of a plurality of rubber layers having a 300% tensile modulus that decreases from the outer side in the tire radial direction toward the inner side in the tire radial direction. By forming the cap tread 12 in this way, the rigidity can be reduced as the cap tread 12 is worn while the rigidity is secured at the initial stage of wear. Prevention performance can be improved.

  Hereinafter, the performance evaluation test performed on the pneumatic tire 1 of the present invention and the pneumatic tire of the comparative example compared with the pneumatic tire 1 of the present invention will be described. The performance evaluation test was conducted for the fall prevention performance and the handling stability.

  The test method was performed by assembling a 205 / 45R17 size pneumatic tire 1 to a rim and mounting the pneumatic tire 1 on a vehicle with a displacement of 1500 cc for test running. As for the evaluation method of each test item, as for the fall prevention performance, a pneumatic tire 1 at the time of 50% wear is prepared as a pneumatic tire 1 to be tested, and the vehicle equipped with this pneumatic tire 1 is specified in ISO 3888-2. A double lane change test (elk test) was performed, and the fall prevention performance was judged by whether or not the vehicle wheel lifted up. In this determination, the case where the wheel did not lift up at the test speed of 60 km / h was evaluated as “good”, the case where the wheel was lifted up was evaluated as “poor”, and when the determination was “good”, it was determined that the fall prevention performance was excellent. .

  As for steering stability, a test course having a flat circuit is mounted on a vehicle equipped with a pneumatic tire 1 for performing a performance evaluation test. The vehicle travels at a speed of 60 to 100 km / h during lane change and cornering. Sensory evaluation was conducted by three specialized panelists on steering performance and stability during straight running. The evaluation results are indicated by an index with the steering stability of a comparative example described later as 100, and the larger the index, the better the steering stability. Further, this steering stability has a superior difference when the index has a difference of 3 points or more.

  As for the pneumatic tire 1 for performing this test, five types of the present invention and one type of comparative example to be compared with the present invention are tested by the above method. In the pneumatic tire 1 to be tested, in the present inventions 1 to 5, F1, F2, F3, and F4 are all in the above-described ranges, that is, (0.64 ≦ F1 ≦ 0.7), (1.2 ≦ F2). ≦ 2.0), (0.1 ≦ F3 ≦ 0.2), and (0.35 ≦ F4 ≦ 0.48). On the other hand, in the comparative example, F1 and F3 are out of the range of (0.64 ≦ F1 ≦ 0.7) and (0.1 ≦ F3 ≦ 0.2). Moreover, these pneumatic tires 1 have the same values for F1, F2, F3, and F4 in the present invention 1, the present invention 2, and the present inventions 3 to 5, respectively. Further, in the comparative example, the cap tread 12 is formed of a rubber layer made of one type of tensile modulus, while the present inventions 1 to 5 include the inner rubber layer 14 and the outer rubber layer 13 with a 300% tensile modulus Mi. , Mo are different from each other, and the tensile modulus Mi of the inner rubber layer 14 is lower than the tensile modulus Mo of the outer rubber layer 13. Moreover, in this invention 1-5, the ratio of the average thickness of the inner side rubber layer 14 with respect to the thickness of the cap tread 12 differs, respectively.

  These comparative examples and the pneumatic tires 1 of the present invention 1 to 5 are subjected to an evaluation test by the above method, and the results obtained are shown in Table 1.

  As apparent from the above test results shown in Table 1, F1, F2, F3, and F4 are set to (0.64 ≦ F1 ≦ 0.7), (1.2 ≦ F2 ≦ 2.0), (0 ..Ltoreq.F3.ltoreq.0.2) and (0.35.ltoreq.F4.ltoreq.0.48), even if 50% wear occurs, the profile of the tread surface 11 changes from the state before wear. Therefore, it is difficult to ensure the fall prevention performance (comparative example). On the other hand, by forming the cap tread 12 from the inner rubber layer 14 and the outer rubber layer 13, and making the 300% tensile modulus Mi of the inner rubber layer 14 lower than the 300% tensile modulus Mo of the outer rubber layer 13, Since the rigidity at the time of wear can be lowered while securing the rigidity of the cap tread 12 before wear, the fall prevention performance when the cap tread 12 is worn can be improved while securing the steering stability at the initial stage of wear. (Invention 1-5).

  Therefore, as is clear from these test results, F1, F2, F3, and F4 are set to (0.64 ≦ F1 ≦ 0.7), (1.2 ≦ F2 ≦ 2.0), (0.1 ≦ F3 ≦ 0.2) and (0.35 ≦ F4 ≦ 0.48), and 300% tensile modulus decreases as the cap tread 12 moves from the tire radial direction outer side toward the tire radial direction inner side. By forming the plurality of rubber layers, it is possible to improve the fall prevention performance at the time of wear while ensuring the steering stability.

  As described above, the pneumatic tire according to the present invention is useful when the tread surface as viewed in the meridional section is formed by a plurality of arcs, and in particular, the tread surface is formed by three types of arcs. Suitable if you are.

1 is a meridional cross-sectional view showing a main part of a pneumatic tire according to the present invention. FIG. 2 is a detailed view of part A in FIG. 1. It is explanatory drawing of the cap tread of the pneumatic tire shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 5 Equatorial surface 10 Tread part 11 Tread surface 12 Cap tread 13 Outer rubber layer 14 Inner rubber layer 15 Side wall part 16 Shoulder part 21 Belt layer 22 Carcass 23 Inner liner 24 Bead part 25 Bead core 26 Bead filler 31 Central part Arc 32 Shoulder side arc 33 Shoulder arc 34 Side arc 35 Center arc end point 36 Shoulder arc end point 41 Central arc tangent 42 Shoulder arc tangent 45 Shoulder side arc extension 46 Side arc extension line 47 Virtual tread end

Claims (5)

There are sidewall portions at both ends in the tire width direction, and a tread portion having a cap tread is provided on the outer side in the tire radial direction of the sidewall portion, and when viewed in a meridional section, the surface of the cap tread A pneumatic tire in which a certain tread surface is formed by a plurality of arcs having different radii of curvature,
In a state in which the rim is assembled to the normal rim and filled with 5% of the normal internal pressure, the tread surface has a central arc located at the center in the tire width direction, and at least the vehicle outer side in the tire width direction of the central arc. Is formed by a shoulder-side arc positioned at a shoulder portion arc that forms a shoulder portion positioned at least on the outer side of the vehicle in the tire width direction of the tread surface,
The radius of curvature of the central arc is TR1,
The radius of curvature of the shoulder side arc is TR2,
The contour range that is the width from the equator plane to the end of the central arc in the tire width direction is L1,
The tread development width, which is the width of the tread surface in the tire width direction, is TDW
The total width that is the width in the tire width direction of the outermost portions in the tire width direction among the sidewall portions that are located and opposed at both ends in the tire width direction is SW,
The tire outer diameter which is the diameter of the largest portion in the tire radial direction of the tread surface is defined as OD,
When the flatness ratio is β,
F1 obtained by the following formula (1), which is a relational expression between the contour range L1 and the tread development width TDW, falls within the range of 0.64 ≦ F1 ≦ 0.7,
F2 obtained by the following equation (2), which is an equation for obtaining the ratio of the radius of curvature TR1 of the central arc and the tire outer diameter OD, is in the range of 1.2 ≦ F2 ≦ 2.0,
F3 obtained by the following equation (3), which is an equation for obtaining the ratio of the radius of curvature TR1 of the central arc and the radius of curvature TR2 of the shoulder side arc, is in the range of 0.1 ≦ F3 ≦ 0.2. Become
Furthermore, F4 obtained by the following equation (4), which is a relational expression between the flatness ratio β, the tread development width TDW, and the total width SW, falls within the range of 0.35 ≦ F4 ≦ 0.48,
The pneumatic tire is characterized in that the cap tread is formed of a plurality of rubber layers having a 300% tensile modulus that decreases from the radially outer side to the radially inner side of the tire.
F1 = L1 / (TDW × 0.5) (1)
F2 = TR1 / OD (2)
F3 = TR2 / TR1 (3)
F4 = (β × TDW) / (100 × SW) (4) The plurality of rubber layers forming the cap tread are an outer rubber layer that is the rubber layer positioned on the outer side in the tire radial direction, and the rubber layer that is positioned on the inner side in the tire radial direction of the outer rubber layer. Consisting of an inner rubber layer,
The outer rubber layer has a 300% tensile modulus Mo in the range of (10 <Mo ≦ 15) MPa, and the inner rubber layer has a 300% tensile modulus Mi in the range of (5 ≦ Mi ≦ 10) MPa. The pneumatic tire according to claim 1, wherein   The pneumatic tire according to claim 2, wherein an average thickness of the inner rubber layer is in a range of 30 to 70% of a thickness of the cap tread. A tangent passing through an end of the central arc in the tire width direction and in contact with the central arc;
The angle α formed between the shoulder portion arc and the tangent line passing through the outer end in the tire width direction and in contact with the shoulder portion arc is in the range of 35 ° ≦ α ≦ 60 °. The pneumatic tire according to any one of claims 1 to 3. When the curvature radius of the shoulder arc is SHR,
F5 obtained by the following formula (5), which is a formula for obtaining the ratio of the radius of curvature TR1 of the central arc and the radius of curvature SHR of the shoulder arc, is in the range of 0.025 ≦ F5 ≦ 0.035. The pneumatic tire according to claim 1, wherein the pneumatic tire is a tire.
F5 = SHR / TR1 (5)

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