JP2006111104A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To strongly suppress partial or whole arc-shaped deformation of a belt layer 43. <P>SOLUTION: The belt layer 43 of a pneumatic tire 31 is partially deformed into an arc-shape at the position of a main groove 52 when internal pressure is filled. If a reinforcing layer 57 buried with a steel cord extending in a substantially radial direction is provided, while geometrical moment of inertia of the steel cord is made larger than geometrical moment of inertia of circular cross section having the same cross-sectional area, a value of bending rigidity becomes higher than a conventional steel cord of circular cross section. As a result, the arc-shaped deformation is suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

    The present invention relates to a pneumatic tire provided with a reinforcing layer overlapping a belt layer.

    In general, since the pneumatic tire 11 is filled with a predetermined internal pressure, as shown in FIG. 13, the carcass layer 12 and the belt layer 13 constituting the pneumatic tire 11 receive the internal pressure and have a radius. Try to bulge outward in the direction. Here, in the carcass layer 12 and the belt layer 13 located in the ground contact area, the land portion 14 (ribs, blocks, etc.) overlaps with the land portion 14 so that the bulging deformation is restricted. However, the portion overlapping the main groove 15 between the land portions 14 does not have a land portion 14 that is stretched, and the reinforcement cord in the belt layer 13 is an angle of 10 to 40 degrees with respect to the tire equator And the bending rigidity in the width direction is low, so that it bulges and deforms so as to project in an arc shape toward the outside in the radial direction.

  When the carcass layer 12 and the belt layer 13 in the vicinity of the portion overlapping the main groove 15 are deformed in an arc shape in this way, the deformation is transmitted to the surrounding land portion 14 and compressed in the land portion 14 near the main groove 15. The amount is larger than the compression amount in the central portion of the land portion 14, and as a result, the contact pressure in the land portion 14 is high on both sides in the width direction in the vicinity of the main groove 15, whereas it is low in the central portion in the width direction and is uneven. As a result, there is a problem that steering stability is deteriorated and that both side portions in the width direction of the land portion 14 are worn earlier than the center portion, thereby causing uneven wear and lowering the wear resistance.

  Further, as a pneumatic tire 21 that can run safely even if the tire internal pressure leaks, a run with a reinforcing rubber layer 23 having a substantially crescent-shaped cross section disposed on the inner surface side of the sidewall portion 22 as shown in FIG. Flat tires have been proposed, but when run flat running with such pneumatic tires 21 (running with the tire internal pressure at 0) is performed, the sidewall portion 22 is crushed and bulges outward in the width direction. On the other hand, the entire tread portion 24 in the ground contact region is deformed in an arc shape toward the inside in the radial direction (the tread central portion is deformed so as to be lifted from the road surface). When the entire tread portion 24 is deformed in an arc shape in this way, the belt layer 25 in the tread portion 24 is similarly deformed in an arc shape, and as a result, heat generation at the tread end portion is increased and the sidewall portion 22 is also increased. There was a problem that the deformation in was promoted.

In order to solve such a problem, as described in Patent Document 1 below, for example, a large number of steel cords having an inclination angle with respect to the tire equator within a range of 70 to 90 degrees are embedded, and the width is wide. One reinforcing layer, which is wider than the distance between the outer wall surfaces of the two main grooves located on the outermost side in the direction, is placed on the belt layer so as to bend each steel cord in the reinforcing layer. It is conceivable that the steel cord is caused to function as a resisting high-stiffness beam, and the arc-shaped deformation is suppressed by functioning as a resistance against a compressive force or a tensile force generated by the arc-shaped deformation.
Japanese Patent Laid-Open No. 10-44712

    However, in such a conventional pneumatic tire, although the partial or total arc-shaped deformation of the belt layer described above can be suppressed to some extent, in recent years, the riding comfort of the vehicle has improved and the cost effectiveness has improved. However, there is a problem that conventional pneumatic tires as described above cannot sufficiently meet the demands. It was. In order to solve such a problem, it is conceivable to increase the diameter of the steel cord or increase the driving density. However, if this is done, the weight of the pneumatic tire increases, and thereby the initial steering angle is increased. The responsiveness of the vehicle is deteriorated, the vibration vibration of the vehicle after the lane change is deteriorated, the steering stability is lowered, and the manufacturing cost is increased.

  An object of the present invention is to provide a pneumatic tire capable of strongly suppressing partial or overall arc-shaped deformation of a belt layer without causing an increase in weight.

    Such an object is to extend between the beads in a toroidal shape and to form a carcass layer made of at least one carcass ply, to be arranged radially outside the carcass layer, and to make a belt layer made of at least two belt plies, and the carcass ply. In a pneumatic tire provided with a tread having a plurality of main grooves formed on the outer periphery thereof and arranged on the outer side in the radial direction of the layer and the belt layer, a plurality of tires having an inclination angle with respect to the tire equator within a range of 60 to 90 degrees A reinforcing layer having a width wider than the interval between the outer wall surfaces of the two main grooves positioned on the outermost side in the width direction is provided to overlap the belt layer, The vertical axis is substantially parallel to the tire tangential direction, and the cross-sectional shape of each reinforcing element is the cross-sectional secondary mode of a circular cross section having the same cross-sectional area with respect to the neutral axis. This can be achieved by making the shape larger than the element.

  As described above, the belt layer tends to be deformed in an arc shape partly at the position of the main groove by internal pressure or entirely by run-flat running. In the present invention, the interval between the main grooves on the outermost side in the width direction is A wider reinforcing layer is placed over the belt layer, and steel cords with high Young's modulus that are almost perpendicular to the main groove are embedded in the reinforcing layer, so each steel cord crosses all the main grooves. It functions as a highly rigid beam that resists partial arcuate deformation at the main groove position, and also functions as a highly rigid beam that resists arcuate deformation of the entire tread portion.

  Moreover, in the present invention, the cross-sectional secondary moment of each steel cord is made larger than the cross-sectional secondary moment of the circular cross section having the same cross-sectional area, so that the value of the bending rigidity can be calculated without changing the diameter and driving density. Can be made higher than that of a conventional steel cord having a circular shape, and the effect of suppressing the arc-shaped deformation described above becomes stronger. These steel cords also have a tensile force generated on the convex side from the neutral axis of the bending (usually located in the vicinity of the radially innermost belt ply) or a compressive force generated on the concave side due to the arc-shaped deformation. It also functions as a resistance against. For this reason, partial or overall arc-shaped deformation of the belt layer is strongly suppressed without incurring an increase in weight, thereby improving the handling stability and durability of the pneumatic tire easily and reliably, Production costs can be reduced.

And as a shape where the value of the cross-sectional secondary moment is larger than the cross-sectional secondary moment of the circular cross-section, the cross-sectional shape as described in claims 2 to 5 can be cited, and such a shape Is easy to manufacture.
Here, due to variations in manufacturing, the direction in which the bending rigidity of the steel cord is maximized, that is, the long axis of the ellipse, the long side of the rectangle, or the extending direction of the longitudinally extending portion is inclined with respect to the tire radial direction. However, if the inclination angle is within 30 degrees, arc-shaped deformation can be strongly suppressed, and thus the inclination within this range is allowed. In addition, as long as it exists in this angle range, the inclination angle may vary for every steel cord.

Embodiment 1 of the present invention will be described below with reference to the drawings.
1 and 2, 31 is a pneumatic radial tire mounted on a high-performance passenger car or the like. The pneumatic tire 31 includes a pair of bead portions 33 each embedded with a ring-shaped bead 32, and these bead portions 33. Side wall portions 34 respectively extending outward in the substantially radial direction from each other, and a substantially cylindrical tread portion 35 for connecting the radially outer ends of the sidewall portions 34 to each other.

  The pneumatic tire 31 has a carcass layer 38 that reinforces the sidewall portion 34 and the tread portion 35 by extending between the beads 32 in a toroidal shape, and both end portions of the carcass layer 38 surround the bead 32. It is folded back from the axially inner side toward the axially outer side. The carcass layer 38 is composed of at least one carcass ply 39 in this case, and the carcass ply 39 intersects the tire equator S at a cord angle of 70 to 90 degrees, that is, in the radial direction (meridian direction). It is constructed by rubber coating a number of reinforcing cords 40 made of nylon, aromatic polyamide, steel, etc., and as a result, the reinforcing cords 40 are embedded in the carcass ply 39. Become.

  43 is a belt layer disposed radially outside the carcass layer 38, and this belt layer 43 is formed by laminating a plurality (here, two) of belt plies 44, 45, and these belt plies 44, 45 is constituted by rubber coating non-stretchable reinforcing cords 46, 47 made of, for example, a large number of steels and aromatic polyamides. As a result, the reinforcing cords 46, 47 are contained in these belt plies 44, 45. Will be buried. These reinforcing cords 46 and 47 are inclined at an angle of 10 to 40 degrees with respect to the tire equator S, and at least two belt plies 44 and 45 are inclined in the opposite direction with respect to the tire equator S and intersect each other. ing.

  51 is a tread made of rubber disposed radially outward of the carcass layer 38 and the belt layer 43. The outer periphery of the tread 51 has a plurality of wide and substantially four main grooves extending substantially in the circumferential direction. 52 is formed. Here, these main grooves 52 may extend linearly as in this embodiment, but may also be bent in a zigzag shape, and at a slight angle with respect to the circumferential direction, for example, about 30 degrees. It may be inclined and have a substantially C shape. Thus, when the main groove 52 is formed on the outer periphery of the tread 51, a land portion 54, here, a rib is defined between the tread end and the main groove 52 and between the adjacent main grooves 52. Here, there is a case where a lateral groove extending substantially in the tire width direction and intersecting the main groove 52 is formed on the outer periphery of the tread 51. In this case, the land portion 54 is a block.

  Then, after filling the pneumatic tire 31 with a predetermined internal pressure and then rolling on the road surface, among the carcass layer 38 and the belt layer 43 in the ground contact region, in the vicinity of the portion overlapping the main groove 52 As described above, the land portion 54 that functions as a tension does not exist, and the bending rigidity of the belt layer 43 is a relatively low value. Therefore, the belt layer 43 is deformed so as to protrude partially in an arc shape outward in the radial direction. try to.

  For this reason, in this embodiment, between the belt layer 43 and the carcass layer 38, which is spaced radially inward from the neutral axis of bending (usually located in the vicinity of the radially innermost belt ply 44). The reinforcing layer 57 is disposed so as to overlap the belt layer 43. The width W of the reinforcing layer 57 is wider than the interval M between the outer wall surfaces 52a of the two main grooves 52 positioned on the outermost side in the width direction, and the reinforcing layer 57 is overlaid on all the main grooves 52. A large number of steel cords 58 having a high Young's modulus extending in a direction substantially perpendicular to the main groove 52, here a monofilament, in which an inclination angle K with respect to the tire equator S is in the range of 60 to 90 degrees in the reinforcing layer 57 The code is buried.

  In this way, each steel cord 58 in the reinforcing layer 57 resists partial arcuate deformation at the position of the main groove 52 across all the main grooves 52 as shown in the test results described later. Therefore, partial arc-shaped deformation at all main groove 52 positions is strongly suppressed. Such a suppression function becomes greater as the tilt angle K approaches 90 degrees. If the width W of the reinforcing layer 57 is wider than the tread width, cracks are likely to occur at the outer end in the width direction of the reinforcing layer 57. Therefore, the width W of the reinforcing layer 57 may be narrower than the tread width. preferable.

  Moreover, in this embodiment, as shown in FIG. 3, the cross-sectional shape of each steel cord 58 is an ellipse that is easy to manufacture, and the neutral axis of the steel cord 58 is tangential to the tire circumferential direction. Are arranged so that the major axis C of the ellipse is along the tire radial direction, and thereby the secondary moment of inertia of each steel cord 58 with respect to the neutral axis of the cross section is the same cross-sectional area. It is set to be larger than the second moment of section of a certain circular section. As a result, the value of the bending rigidity of the steel cord 58 functioning as a beam can be made higher than that of a conventional steel cord having a circular cross section without changing the diameter and driving density, and thereby the main groove described above. Partial arcuate deformation at 52 positions can be strongly suppressed without causing an increase in weight. At this time, since the inclination angle K of the steel cord 58 with respect to the tire equator S has the above-described value, the bending rigidity of the reinforcing layer 57 is strengthened in the tire width direction, and the tire circumferential direction hardly changes.

  Here, due to variations in manufacturing, the direction in which the bending rigidity of the steel cord 58 is maximized, here, the major axis C of the ellipse may be inclined with respect to the tire radial direction as shown in FIG. However, if the inclination angle A is within 30 degrees, the arc-shaped deformation can be strongly suppressed, and thus the inclination within this range is allowed. It should be noted that the inclination angle may vary for each steel cord 58 as long as it is within this angle range. In addition to the monofilament cord, the steel cord 58 may be a twisted cord formed by twisting several steel filaments 59 as shown in FIG.

  Further, due to the partial arc-shaped deformation at the position of the main groove 52 described above, a tensile force is generated on the convex side of the bending neutral axis and a compressive force is generated on the concave side. Since the steel cord 58 in the reinforcing layer 57 disposed radially inward from the neutral axis functions as a resistance, the aforementioned arc-shaped deformation is further suppressed. For this reason, the handling stability and wear resistance of the pneumatic tire 31 can be improved easily and reliably, and the production cost can be reduced. Further, the distance between the steel cords 58 embedded in the reinforcing layer 57 is preferably 5 mm or more. The reason is that if the distance between adjacent steel cords 58 is 5 mm or more, the arc-shaped deformation of the belt layer 43 can be strongly suppressed while reducing the weight.

  FIG. 6 is a diagram showing Embodiment 2 of the present invention. In this embodiment, the cross-sectional shape of the steel cord 63 made of a monofilament cord is a rectangle that is easy to manufacture, and the steel cord 63 is arranged such that the long side B of the rectangle is along the tire radial direction. Even in this case, as in the first embodiment, each steel cord 63 functioning as a beam has a large second moment of section, and the bending stiffness is higher than that of a conventional steel cord having a circular section. As a result, the partial arc-shaped deformation at the position of the main groove 52 described above can be strongly suppressed without causing an increase in weight.

  FIG. 7 is a diagram showing Embodiment 3 of the present invention. In this embodiment, the cross-sectional shape of the steel cord 65 made of a monofilament cord is integrally connected to one longitudinally extending portion 66 extending in the tire radial direction and the radially inner and outer ends of the longitudinally extending portion 66, and the tire circumferential direction It is comprised from the two laterally extending parts 67 and 68 extended in the tangential direction with respect to this, and is made into the I-shape with easy manufacture as a whole. Even in this case, as in the first embodiment, each steel cord 65 functioning as a beam has a large cross-sectional secondary moment, and the bending rigidity value is higher than that of a conventional steel cord having a circular cross section. As a result, the partial arc-shaped deformation at the position of the main groove 52 described above can be strongly suppressed without causing an increase in weight.

  FIG. 8 is a diagram showing Embodiment 4 of the present invention. In this embodiment, the cross-sectional shape of the steel cord 70 made of a monofilament cord has two longitudinally extending portions 71 and 72 extending in the tire radial direction and overlapping each other, and both ends at the radial center of the longitudinally extending portions 71 and 72. Are integrally connected and formed of one laterally extending portion 73 that extends in a tangential direction with respect to the tire circumferential direction, and has an H shape that is easy to manufacture as a whole. Even in this case, as in the first embodiment, each steel cord 70 functioning as a beam has a large second moment of section, and the value of bending rigidity is higher than that of a conventional steel cord having a circular section. As a result, the partial arc-shaped deformation at the position of the main groove 52 described above can be strongly suppressed without causing an increase in weight.

  Even when the steel cords 63, 65, and 70 have a rectangular, I-shaped, and H-shaped cross-section as in the second, third, and fourth embodiments, as in the first embodiment, variation during manufacturing is also possible. Thus, in the direction in which the bending rigidity of the steel cords 63, 65, and 70 is maximized, in the rectangle, the long sides C, I, and H, the longitudinally extending portions 66, 71, 72 are in the tire radial direction. In this case as well, in this case, if the inclination angle A is within 30 degrees, the arc-shaped deformation can be strongly suppressed, so that the inclination within this range is allowed.

  And the above-mentioned test result was obtained by the following tests. In this test, as shown in FIG. 9, a reinforcing layer 77 in which a large number of steel cords 75 made of monofilaments having a circular cross section and a diameter of 0.98 mm are embedded is arranged at the center in the thickness direction of the rubber sheet 74. A steel cord 75 made of a monofilament having an elliptical cross section, a long axis C length of 1.6 mm, and a short axis length of 0.6 mm is formed at the center of the test piece 1 and the rubber sheet 74 in the thickness direction. Twist six steel filaments with a cross-section of a diameter of 0.4 mm in the center of the thickness direction of the rubber sheet 74 and the test piece 2 in which one reinforcing layer 77 is embedded in the thickness direction. Therefore, a large number of steel cords 75 with an ellipse with a major axis C of 1.6 mm and a minor axis length of 1.0 mm are embedded with the major axis C aligned in the thickness direction. In the test piece 3 in which one reinforcing layer 77 is arranged, and in the center of the rubber sheet 74 in the thickness direction, A reinforcing layer 77 in which a steel cord 75 made of a monofilament having a rectangular surface and a long side B of 1.5 mm and a short side of 0.5 mm is embedded with the long side B aligned in the thickness direction. A test piece 4 arranged in one layer was prepared.

  Here, these test pieces 1 to 4 are squares each having a length of 200 mm and a thickness of 2 mm. In addition, in each test piece 1 to 4, the tire equator S (on one side of the rubber sheet 74) 10 pieces were manufactured while changing the crossing angle K of the steel cord 75 with respect to the tire equator S (along a parallel straight line) by 10 degrees from 0 degrees to 90 degrees. Further, the intervals between the steel cords 75 in each of the test pieces 1 to 4 were all 10 mm, and their weights were substantially the same because their cross-sectional areas were substantially the same.

  Next, both side ends of the test pieces 1 to 4 are supported from below by a pair of horizontal support members 78 extending in parallel to the tire equator S and separated by 200 mm, and then the center of the test pieces 1 to 4 in the width direction. A load was applied by placing a weight 79 having a paperweight shape (square column shape) of 9.8 N extending parallel to the tire equator S on the top. Then, the maximum deflection amount immediately below the weight 79 when the load as described above is applied to each test piece is measured, and the reciprocal of the maximum deflection amount of the test piece 1 whose crossing angle K is 90 degrees is bent. The strength index is shown as 100 in FIG. Here, the maximum deflection amount of the test piece 1 having the crossing angle K of 90 degrees was 28 mm. From this test result, when the crossing angle K is in the range of 60 to 90 degrees, the bending strength is maintained at a high value, and when the steel cord 75 has a shape having a large second moment of section, It can be understood that the bending strength can be effectively increased as compared with the case of a circular cross section.

  In FIGS. 1 and 2 again, 81 is a pair of auxiliary layers which are arranged at both ends in the width direction of the belt layer 43 on the outer side in the radial direction, and are composed of at least one auxiliary ply 82. A reinforcing cord 83 made of an organic fiber that extends substantially in the circumferential direction, such as nylon or polyester, is embedded.

    FIG. 11 is a diagram showing Embodiment 5 of the present invention. In this embodiment, a relatively hard reinforcing rubber layer 85 having a substantially crescent cross section is provided on the inner surface side of the sidewall portion 34, so that air that can travel safely even if the tire internal pressure leaks is provided. In this pneumatic tire 86, the auxiliary layer 81 is omitted, and the carcass layer 38 is composed of two carcass plies 39. Then, when run flat running (running with the tire internal pressure being 0) is performed with such a pneumatic tire 86, the sidewall portion 34 is crushed and bulged and deformed outward in the width direction. The tread portion 35 (belt layer 43) tends to deform in an arc shape inward in the radial direction.

  However, in this embodiment, the cross section of the steel cord 58 in the reinforcing layer 57 disposed radially inward of the belt layer 43, specifically between the belt layer 43 and the carcass layer 38, is elliptical as in the first embodiment. By making the rectangular, I-shaped, and H-shaped, the cross-sectional secondary moment of the steel cord 58 is increased, and the long axis of the ellipse, the long side of the rectangle, the I-shaped, and the H-shaped vertical Since the extending portion is aligned along the tire radial direction, the value of the bending rigidity of the steel cord 58 functioning as a beam is higher than that of the conventional steel cord having a circular cross section. Arc-shaped deformation can be strongly suppressed without causing an increase in weight. Other configurations and operations are the same as those of the first embodiment.

    Next, Test Example 1 will be described. In this test, a conventional reinforcing tire 1 in which no reinforcing layer is arranged and a single reinforcing layer in which a steel cord having a circular cross section and a crossing angle K of 90 degrees is embedded between a belt layer and a carcass layer. A prepared comparative tire 1 and an implementation tire 1 in which a single reinforcing layer in which a steel cord having an elliptical cross section and an intersection angle K of 90 degrees was embedded were arranged between a belt layer and a carcass layer were prepared.

  Here, each of the tires described above was a tire for a high-performance passenger car, and the size was 215 / 55R15. As shown in FIGS. 1 and 2, the tire skeleton structure has a carcass layer composed of one carcass ply in which a nylon cord intersecting the tire equator S at 90 degrees is embedded, and the tire equator S. The belt layer is composed of two belt plies embedded with steel cords crossing in opposite directions at 25 degrees, and the auxiliary layer is embedded with nylon cords extending substantially parallel to the tire equator S. .

  The steel cord embedded in the reinforcing layer of the comparative tire 1 is composed of a monofilament having a circular cross section and a diameter of 0.98 mm, while the steel cord embedded in the reinforcing layer of the working tire 1 has a cross section. The ellipse is composed of a monofilament having a major axis C of 1.6 mm and a minor axis of 0.6 mm, and the major axis C extends in the tire radial direction. Further, the width W of the reinforcing layer is set to 150 mm, and the steel cord is driven at an interval of 10 mm in any reinforcing layer.

  After each tire is filled with an internal pressure of 200 kPa and installed in an indoor testing machine, it is slowly rotated twice on the road surface at a slip angle of 3 degrees while applying a 5 kN vertical load, In the state, the cross section immediately under the load was photographed with X-rays, and the maximum deformation amount of the steel cord in the inner belt ply overlapped with the outermost main groove in the width direction was measured. As a result, the maximum deformation amount was 0.8 mm for the conventional tire 1 and 0.4 mm for the comparative tire 1, but it was drastically reduced to 0.2 mm or less for the implementation tire 1.

  In addition, each tire described above was mounted on a passenger car, and the steering stability was evaluated by a test driver. As a result, in the lane change from 60km / h straight running, the implemented tire 1 is evaluated to react very quickly and move sharply, and the comparative tire 1 is better than the conventional tire 1, It was evaluated that it did not reach the implementation tire 1. When the test driver gave the evaluation a score of 100, the score was 50 for the conventional tire 1, 70 for the comparative tire 1, and 90 for the implementation tire 1.

    Next, Test Example 2 will be described. In this test, a conventional tire 2 in which no reinforcing layer is disposed and a reinforcing layer having a width of 160 mm in which a steel cord having a rectangular cross section and a crossing angle K of 90 degrees is embedded are disposed between the belt layer and the carcass layer. An example tire 2 arranged in one layer and a reinforcing layer having a width of 160 mm in which a steel cord having an H-shaped cross section and a crossing angle K of 90 degrees is embedded is arranged between the belt layer and the carcass layer. Implementation tire 3 was prepared.

  Here, each of the tires described above is a run-flat tire for a passenger car in which a relatively hard reinforcing rubber layer having a substantially crescent cross section is disposed on the inner surface side of the sidewall portion, and the size is 225 / 50R16. . Further, as shown in FIG. 11, the skeleton structure of these tires includes a carcass layer composed of two carcass plies embedded with a nylon cord that intersects the tire equator S at 90 degrees, and a tire equator S of 25. And a belt layer composed of two belt plies embedded with steel cords crossing in opposite directions at a degree.

  In addition, the steel cord of the reinforcing layer in the implementation tire 2 is composed of a monofilament having a rectangular section with a long side B of 3 mm and a short side of 1.5 mm, and the long side B is in the tire radial direction. On the other hand, the steel cord of the reinforcing layer in the implementation tire 3 is composed of a monofilament having an H-shaped cross section having a height of 3 mm, a width of 3 mm, and a uniform thickness of 0.6 mm, and a longitudinally extending portion. Extends in the tire radial direction. In the implementation tires 2 and 3, steel cords were embedded in the reinforcing layer at intervals of 20 mm.

  Next, after mounting each of these tires on an indoor testing machine with an internal pressure of 0 (atmospheric pressure), slowly rotate 2 times on the road surface at a slip angle of 0 degrees (straight running) while applying a vertical load of 5 kN. In a stationary state after rotation, the cross section immediately under the load was photographed with X-rays, and the amount of lift U from the road surface of the tread outer surface at the tire equator (see FIG. 14) was measured. As a result, when the lift amount U in the conventional tire 2 is an index of 100, both of the tires 2 and 3 can be effectively suppressed to 50. Here, the index 100 was 22 mm. Further, the side wall portion was crushed less in the tires 2 and 3 than in the conventional tire 2.

  In addition, after mounting each of the above-described tires on a rear-wheel drive passenger car, the internal pressure is reduced to 0 by removing the valve on the right wheel of the rear wheel, while the remaining three tires are filled with an internal pressure of 220 kPa. The run-flat run was run counterclockwise on the oval course of about 3 km per lap at a constant speed of 90 km / h until the tire on the right side of the rear wheel failed and it became difficult to run. Assuming that the running distance of the conventional tire 2 at this time is an index of 100, the running distance has increased to 370 for the implementation tire 2 and to 350 for the implementation tire 3. Here, the index 100 was 60 km.

  In the above-described embodiment, the reinforcing layer 57 is arranged in the radial direction of the belt layer 43, that is, between the belt layer 43 and the carcass layer 38.In the present invention, as shown in FIG. It may be disposed radially outside the belt layer 43, that is, between the belt layer 43 and the tread 51, or when the carcass layer 38 is composed of two carcass plies 39, between the carcass plies 39. You may make it arrange | position to.

  The present invention can be applied to the industrial field of pneumatic tires.

1 is a meridian cross-sectional view of a pneumatic tire showing Embodiment 1 of the present invention. It is a partially broken top view of a tread part. It is circumferential direction sectional drawing of a reinforcement layer. It is circumferential direction sectional drawing of the other example of a reinforcement layer. It is sectional drawing which shows the other example of a steel cord. It is circumferential direction sectional drawing of the reinforcement layer which shows Embodiment 2 of this invention. It is circumferential direction sectional drawing of the reinforcement layer which shows Embodiment 3 of this invention. It is circumferential direction sectional drawing of the reinforcement layer which shows Embodiment 4 of this invention. It is a perspective view of a test piece. It is a graph which shows a test result. It is meridian sectional drawing of the pneumatic tire which shows Embodiment 5 of this invention. It is meridian sectional drawing which shows the other example of a pneumatic tire. It is a partial molecular meridian cross-sectional view showing a cross-sectional shape of a conventional pneumatic tire at the time of ground contact. It is meridian sectional drawing which shows the cross-sectional shape at the time of the run flat running of the conventional pneumatic tire.

Explanation of symbols

31 ... Pneumatic tire 32 ... Bead
38 ... Carcass layer 39 ... Carcass ply
43 ... Belt layer 44, 45 ... Belt ply
51 ... Tread 52 ... Main groove
52a… Outer wall surface 57… Reinforcing layer
58 ... Steel cord S ... Tire equator K ... Inclination angle M ... Spacing W ... Width A ... Inclination angle

Claims (6)

    A carcass layer made of at least one carcass ply extending in a toroidal manner between the beads, a belt layer made of at least two belt plies arranged radially outward of the carcass layer, and the radius of the carcass layer and the belt layer In a pneumatic tire provided with a tread with a plurality of main grooves formed on the outer periphery on the outer side in the direction, a large number of steel cords with an inclination angle with respect to the tire equator in the range of 60 to 90 degrees are embedded A reinforcing layer having a width wider than the distance between the outer wall surfaces of the two main grooves positioned on the outermost side in the width direction is superimposed on the belt layer, and the neutral axis of the cross section of the steel cord is the tire tangential direction The cross-sectional shape of each steel cord is substantially parallel, and the cross-sectional secondary moment of a circular cross-section whose cross-sectional secondary moment about the neutral axis is the same cross-sectional area. A pneumatic tire characterized by having a shape that is larger than the tire.     2. The pneumatic tire according to claim 1, wherein the steel cord has an elliptical cross-sectional shape and the steel cord is disposed such that a major axis of the ellipse is along a tire radial direction.     The pneumatic tire according to claim 1, wherein the steel cord has a rectangular cross-sectional shape, and the steel cord is disposed such that a long side of the rectangle is along a tire radial direction.     The cross-sectional shape of the steel cord is composed of one longitudinally extending portion extending in the tire radial direction and two laterally extending portions integrally connected to the radially inner and outer ends of the longitudinally extending portion and extending in the tire tangential direction, The pneumatic tire according to claim 1, wherein the pneumatic tire is I-shaped as a whole.     The steel cord has a cross-sectional shape in which two longitudinally extending portions extending in the tire radial direction and overlapping each other, and one laterally extending portion extending in the tire tangential direction at both ends integrally connected to the radial center of the longitudinally extending portion, The pneumatic tire according to claim 1, wherein the pneumatic tire has an H shape as a whole.     The pneumatic tire according to any one of claims 2 to 5, wherein an inclination angle of the major axis of the ellipse, a long side of the rectangle, or a longitudinally extending portion with respect to a tire radial direction is within 30 degrees.

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