JP5193502B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire that can achieve both high-speed durability and steering stability, in particular, a tire having a bias structure.

  High-performance passenger car tires have a particularly high rotational speed, and therefore the influence of centrifugal force is greater than that of tires for general commercial vehicles. For this reason, the tread portion of the tire may be deformed to increase the diameter, and the steering stability during high-speed traveling may be impaired.

  On the other hand, tires for commercial vehicles such as trucks and buses may have the same problem. That is, in this type of tire, since the thickness of the tread rubber is increased, the mass of the tread portion is inevitably increased, and the tread portion is expanded and deformed under the influence of centrifugal force even at a speed of about 100 km / h. Unfortunately, this can lead to tire failure.

For this reason, a spiral called a cap, a layer, or the like is formed by extending an organic fiber cord in the tread portion of the tire in the tread circumferential direction and spirally winding it in the tread width direction. Providing a reinforcing layer to suppress the diameter expansion deformation of the tread during rotation of the tire has been proposed and has been widely used.
Here, the cap means that the cord is spirally arranged over almost the entire width of the tread portion, and the layer is that in which the cord is spirally arranged only in the side region of the tread portion. Say.

  By the way, as a cord to be spirally arranged, conventionally, a nylon fiber cord has been generally used, but in recent years, as disclosed in Patent Documents 1 to 3 and the like, it is lightweight and has high strength. In addition, using an aromatic polyamide cord that does not stretch even at high temperatures, this enhances the effect on the tread part and more effectively suppresses the expansion of the tread part, resulting in maneuvering during high-speed rotation. Various techniques for improving stability and durability have been proposed.

  Also, for tires for heavy-duty vehicles such as trucks, buses, etc., as disclosed in Patent Documents 4 to 8, etc., the wavyly shaped steel cord is extended in the tread circumferential direction. It has been proposed to wind and arrange in a spiral.

In any of these cases, for example, this is formed by spirally winding a ribbon-like strip formed by integrally covering 1 to 10 cords arranged in parallel to each other with rubber. It has been confirmed that such a spiral reinforcing layer can effectively contribute to improvement of traction performance and braking performance in addition to high speed durability, steering stability and high load durability.
JP-A-7-186615 JP-A-7-276913 Japanese Patent Laid-Open No. 11-192809 JP-A-9-156315 JP-A-6-32108 JP-A-6-191219 Japanese Patent Laid-Open No. 7-17209 JP-A-8-188809

  With the recent increase in performance of vehicles, the frequency of high-speed traveling has increased, and as described above, the influence of centrifugal force due to high-speed traveling has increased for tires. Therefore, it is necessary to fully consider changes in the ground contact shape at low speeds and high speeds, and fluctuations in steering stability performance resulting therefrom.

  Also, the higher the belt rigidity, the worse the ride comfort, but the greater lateral force is generated, so for sports car tires, etc. Aimed at high rigidity members are generally used. In general, the structure using a steel belt has higher rigidity compared to the structure using organic fibers, which increases the lateral force generated by the tire, but on the other hand increases the weight, so it is particularly fast. There was a problem that the centrifugal force increased during traveling and the characteristics such as the ground contact shape changed at high speed.

  In addition, as the performance of vehicles increases, the demand for durability performance on tires is becoming stricter year by year.

  The failure that must be noted when the spiral reinforcing layer as described above is employed is first the winding end of the spiral reinforcing layer and peeling from the start of winding. On the other hand, it is necessary to pay attention to end processing (adhesiveness, not bringing the start and end of winding to the same position in the circumferential direction, etc.).

  The other is that since there is a large difference in rigidity between the highly rigid spiral reinforcing layer and its outer portion in the width direction, the strain is concentrated at a low rigidity and the cord is likely to break. This is a failure that frequently occurs particularly when a carcass ply having a bias structure is combined with a spiral reinforcing layer.

In other words, when the tire is deformed by the ground contact, or when braking force and driving force are applied to the tire, the intersection layer of the carcass ply near the contact surface is pulled in the circumferential direction or the width direction, as if it is a pantograph Deformation that a square becomes a parallelogram is generated. On the other hand, the same tensile force is also applied to the spiral reinforcement layer, but the deformation of the spiral reinforcement layer is small due to its high rigidity, and its wrinkle is just outside the width direction of the spiral reinforcement layer. (The carcass ply must absorb the deformation that the spiral reinforcing layer should take on), so the carcass ply portion just outside the spiral reinforcing layer in the width direction is very A large deformation will occur.
In this case, one of the carcass plies where the ply cords cross each other restrains the movement of the other carcass ply. Therefore, the organic fiber ply cord has “high tensile rigidity but rigidity in the compression direction. In addition, the reinforcing structure formed by combining the spiral reinforcing layer and the car asply of the bias structure is liable to cause a failure due to the cord breakage of the carcass ply.

  On the other hand, in the case of a carcass ply with a radial structure, the ply cords are not interlaced. Since the deformation that the rubber stretches mainly occurs, the ply cord does not become an element that inhibits the expansion and contraction in the circumferential direction, and failure of the ply cord itself hardly occurs.

  In this way, the spiral reinforcement layer is superior in terms of durability when combined with the radial structure carcass ply, but there are advantages such as the unique ride comfort and uniformity of the ground contact shape that are characteristic of the bias structure carcass ply. When it is desired to make use of the above, it is necessary to employ means capable of enhancing durability using a biased carcass ply.

  Therefore, the present invention provides a pneumatic tire that can achieve high steering stability performance while solving the above-described problems of durability.

  The pneumatic tire according to the present invention includes a tread portion, a pair of sidewall portions that extend inward in the radial direction continuously to the respective side portions of the tread portion, and a bead portion that continues to the inner peripheral side of each sidewall portion. And two or more carcass plies in which a ply cord, which can be an organic fiber cord, for example, is arranged to extend in opposite directions with respect to the tire equatorial plane between at least two adjacent inner and outer carcass plies. Consisting of a carcass extending toroidally between a pair of bead cores arranged in the bead portion, and two or more belt layers arranged on the outer peripheral side of the crown region of the carcass, at least between the inner and outer two belt layers, Belts with belt cords extending in opposite directions with respect to the tire equator surface, and extending toward the tread circumferential direction on the outer circumference side of the belt In addition, for example, it is provided with one or more spiral reinforcing layers made of organic fiber cords such as aromatic polyamide cords or steel cords or other cords arranged spirally in the tread width direction. The ply cords that cross each other have an extension angle with respect to the tire equatorial plane at the inner peripheral side portion of the side edge of the widest belt layer in the range of 30 to 60 °, and at least one spiral reinforcing layer The width of the belt is in the range of 0.8 to 1.2 times the tread width, and a buffer rubber layer having a width in the range of 10 to 40 mm is interposed between the two carcass plies where the ply cords cross each other. Then, the buffer rubber layer is formed at least at the above-mentioned origin at a portion within a range of −10 to +30 mm from the side edge position of the spiral reinforcing layer to the outer side in the tread width direction. The ply interval between the two carcass plies, not including the thickness of the covering rubber on the ply, is 0.8 to 5.0 mm. As a range.

  In such a pneumatic tire, the cushion rubber layer is formed by the covered rubber of the carcass ply or the covered rubber of the spiral reinforcing layer, and the belt equator of each belt cord of the belt layer in which the belt cords cross each other. The belt cord of the innermost layer belt layer and the ply cord of the outermost layer carcass ply 1 on the tire equatorial plane regardless of whether they intersect each other. It is preferable that both of the cords extend in the same direction, and the extension angle of the cords with respect to the tire equatorial plane is 30 ° or less, and at least one belt of the belt layer in which the belt cords cross each other The cord is a steel cord, and in this case, a belt cord made of a steel cord is 0.15-0. It is preferable to form a steel single wire having a diameter of 25 mm or a cord obtained by twisting them.

In the pneumatic tire according to the present invention, among two or more carcass plies, at least two adjacent carcass plies are extended by interlacing a ply cord between two adjacent carcass plies, so that the filling air pressure and load on the tire are increased. The carcass ply sufficiently supports the tension in the operation of the above, and the rigidity of the carcass as a tire case, mainly in the tread width direction, is enhanced, and excellent steering stability performance can be exhibited.
In other words, since a carcass ply having a radial structure and a single carcass ply having no crossing layer cannot sufficiently support air pressure, the rigidity in the tread width direction cannot be denied.

  Also, in this tire, by providing a belt composed of two or more belt layers, it is possible to ensure belt rigidity that cannot be provided by a single belt layer, and at least between the belt layers of the inner and outer layers. By crossing the cords, the in-plane rigidity of the belt can be increased and the road grip force can be increased.

  However, if the belt cords are only crossed, the treads are deformed due to contact with the ground, etc., and the crossing cords are easily deformed to expand and contract in the tread width direction as if they were panda graphs. A spiral reinforcing layer is arranged on the outer peripheral side of the belt, and this reinforcing layer functions as a replacement rod for the belt crossing cord to restrain the pantograph deformation of the crossing cord.

And here, by making the angle with respect to the tire equatorial plane in the inner circumferential side portion of the side edge of the widest belt layer, for example, the innermost layer belt layer, of the ply cords that cross each other, The required lateral rigidity can be ensured while ensuring a sufficient ground contact area.
That is, if it is less than 30 °, the out-of-plane rigidity of the carcass ply related to the vertical rigidity of the tire becomes too high, and the ground contact area becomes small, which is disadvantageous in terms of steering stability. If it exceeds, the ratio of the carcass ply to be borne by the internal pressure or the like becomes low, and sufficient lateral rigidity cannot be obtained.

Here, the ply cord angle at the inner peripheral side portion of the side edge of the widest belt layer is defined for the following reason.
One of them is tires especially for high-performance vehicles, in order to make the contact area as wide as possible, so that the tire crown shape is often very flat, and it is inevitable if the crown shape is flattened. In addition, the shape is sharply rounded from the tread portion to the sidewall portion. Therefore, when a load is applied to the tire, the tread is almost flat because it is close to a flat surface, so it does not flex, and therefore, deformation is borne at the sidewall portion. Therefore, the value of the ply cord crossing angle at the belt side portion greatly contributes to the rigidity related to tire deformation. Therefore, defining the ply angle at the side of the belt is most reasonable when designing a tire.

  Another reason is that the belt layer used in high-performance vehicle tires, in particular, is composed of members and cord angles that have extremely high rigidity to generate a high lateral force during cornering. (For example, steel or kepler). Therefore, in general, the crossing angle of the carcass ply, in which a member (nylon or the like) whose rigidity is lower than that of the belt is often used, does not make much sense in the tread portion within the range where the belt is disposed. Because. That is, the rigidity of the belt is overwhelmingly higher than the rigidity of the ply.

  Furthermore, in this tire, by providing at least one spiral reinforcing layer, it is possible to directly suppress the tread portion from expanding and deforming under the influence of the centrifugal force generated by high-speed traveling, thereby improving the steering stability performance. Can be improved. In addition, the change in speed of the ground contact shape due to speed can be reduced to improve running stability.

  And here, by making the width of at least one layer of such a spiral reinforcement layer into the range of 0.8 to 1.2 times the tread width, without causing an excessive increase in rigidity of the tread portion, The diameter expansion deformation of the tread portion can be effectively prevented.

  This is because a sufficient effect can be obtained unless the spiral reinforcement layer has a width of 0.8 times or more of the tread width in order to suppress the expansion deformation of the tread portion due to the centrifugal force generated at high speed. This is because when the width is smaller than 0.8 times, the outside of the area covered with the spiral reinforcing layer is deformed by expanding the diameter, and the effect becomes sufficient. On the other hand, the width is 1.2. If the width is larger than twice, the spiral reinforcing layer becomes too wide, the rigidity of the tread portion becomes too high, the proper grounding of the tire is hindered, and the ground contact area becomes small, which is disadvantageous for the steering stability performance. .

  In addition, here, two carcass plies in which the ply cords cross each other in a portion within a range of −10 to +30 mm from the side edge position to the outer side in the tread width direction including the side edge of the spiral reinforcing layer. By providing a cushioning rubber layer with a width of 10 to 40 mm between them, a sufficient space is secured between the two carcass plies, and the deformation of one carcass ply is sufficiently restrained by the other carcass ply. The relaxation of the ply cord can effectively prevent the ply cord from being broken due to the compressive strain.

  In addition, such an effect by the shock-absorbing rubber layer is such that the arrangement area thereof is within a range of 10 mm from the inner side to 30 mm including the side edge position of the spiral reinforcing layer, and the width of the shock-absorbing rubber layer itself is Unless it is 10 mm or more and 40 mm or less, it will not be sufficient.

  Here, the width of the buffer rubber layer is set to a range of 10 to 40 mm. If it is less than 10 mm, the mutual restraint between the two carcass plies cannot be effectively relaxed, while if it exceeds 40 mm. In addition to an increase in the weight of the tire, there is a disadvantage that the amount of heat generation increases due to an increase in the rubber volume in a region where deformation is large.

  And this means that the ply spacing of the two carcass plies at the intervening portion of the buffer rubber layer, not including the thickness of the covering rubber on the plies, may be in the range of 0.8 to 5.0 mm. When the thickness is less than 0.8 mm, the restraint relaxation effect between the carcass plies cannot be fully exerted, and when the thickness exceeds 5.0 mm, it is interposed in a region with large deformation. Since the volume of the cushioning rubber becomes too large and the amount of heat generated increases, failure due to thermal factors is likely to occur.

  Here, when the buffer rubber layer is formed of a carcass ply covering rubber or a spiral reinforcing layer covering rubber, the buffer rubber layer may be adhered to the carcass ply or spiral reinforcing layer with a high strength. it can.

  That is, when the buffer rubber layer is made of the same type of rubber as the covering rubber of the carcass ply, it is possible to prevent the occurrence of interlayer cracks between adjacent rubbers, and the same as the covering rubber layer of the spiral reinforcing layer. If the cushioning rubber layer is pushed out between the plies and flows out to the side edge of the spiral reinforcement layer during molding or vulcanization of the tire, the rubber and cushioning rubber of the spiral reinforcement layer are placed on the side edge. It is possible to eliminate the possibility of the rubber interface being generated.

  In such a tire, as described in claim 3, when the extending angle of the belt layers where the belt cords cross each other with respect to the tire equatorial plane of each belt cord is in the range of 45 to 85 °, the tire The out-of-plane bending rigidity of the belt with respect to the circumferential direction is in an appropriate range, and a sufficient ground contact area can be ensured, and the envelope property at the time of stepping on the step is improved, and the riding comfort is improved.

  On the other hand, by giving the spiral reinforcement layer a width that is at least 0.8 times the tread width, virtually all air pressure can be borne by the bias ply and the spiral reinforcement layer where the ply cords cross. Therefore, there is no special problem even if the angle of the belt cord is increased and the air pressure cannot be borne.

Further, as described in claim 4, the belt cord of the innermost layer belt layer and the ply cord of the outermost layer carcass ply are both the same with respect to the tire equatorial plane regardless of whether they intersect each other. When the extension angle of these cords with respect to the tire equatorial plane is 30 ° or less, first, the innermost layer belt layer cord and the outermost layer carcass ply cord are interlaced. In some cases, in-plane shear strain is likely to occur between the side of the belt layer and the carcass ply, and there is a concern about durability. If the angle is in the same direction, when the force is applied, the belt layer Since the cord and the ply cord move in the same (close) direction, distortion hardly occurs.
Secondly, when belt cords and ply cords cross each other, the rigidity rapidly increases in those cord crossing regions, so that the rigidity step becomes large and easily becomes a failure nucleus, but these two cords are not crossed. Thus, since the rigidity gradually increases from the carcass to the outermost belt layer, there is an advantage that it is difficult to become the core of the failure.

  In any of the tires described above, when at least one of the belt layers of the belt layers where the belt cords cross each other is made of a steel cord, the in-plane rigidity of the belt is further increased and the road surface grip force is more effective. Can be increased.

And in this case, when the belt cord made of steel cord is composed of a steel single wire with a diameter of 0.15 to 0.25 mm, or a cord twisted of them, ensure sufficient rigidity inside and outside the surface, Excellent road surface grip can be demonstrated.
That is, if the cord diameter is less than 0.15 mm, the desired in-plane rigidity cannot be ensured and the road surface grip force cannot be reduced. On the other hand, if the cord diameter exceeds 0.25 mm, the belt is bent out of plane. Since the rigidity is increased and the ground contact area is reduced, the reduction of the grip force on the road surface at low loads cannot be denied.

FIG. 1 is a meridional direction sectional view of a tire showing an embodiment of the present invention. In the figure, 1 is a tread portion, and 2 is a radially inward continuous to each side portion of the tread portion 1. A pair of side wall portions extending, and 3 indicates a bead portion continuous on the inner peripheral side of each side wall portion 2.
4 indicates a pair of bead cores disposed in each bead portion, and 5 indicates a carcass extending between the bead cores 4 in a toroidal manner.

  The carcass 5 here is formed by two or more carcass plies, two inner and outer carcass plies 5a and 5b in the figure, and at least two adjacent inner and outer cars, the carcass lies 5a and 5b in the figure, A bias structure is formed by extending ply cords made of organic fiber cords or the like in opposite directions with respect to the tire equatorial plane E, for example, in line symmetry.

  In addition, here, on the outer peripheral side of the crown region of the bias carcass 5, two or more belt layers, in the figure, two inner and outer belt layers 6 a and 6 b, and adjacent to each other, these two layers are formed. A belt 6 in which the belt cords of the belt layers 6a and 6b extend in opposite directions with respect to the tire equatorial plane E, for example, axisymmetrically extending, is disposed on the outer peripheral side of the belt 6. A cord such as an organic fiber cord or a steel cord extends in the tread circumferential direction and is arranged in a spiral winding form in the tread width direction, and more than one layer covering the entire width of the belt 6, one layer in the figure The spiral reinforcement layer 7 is disposed, and the width of the spiral reinforcement layer 7, that is, the width L under the tire posture in which the tire is assembled to the applied rim and filled with the prescribed air pressure, is the same. 0.8 to 1.2 times the range of the tread width W at the bottom of the matter.

Here, “applicable rim” means a rim defined in the following standards according to the tire size, and “specified air pressure” means an air pressure defined in accordance with the maximum load capacity in the following standards. The maximum additional capacity refers to the maximum mass allowed to be loaded on the tire according to the following standards.
The air here can be replaced with an inert gas such as nitrogen gas or the like.

  The standard is an industrial standard valid for the region where tires are produced or used. For example, in the United States, “THE TIRE AND RIM ASSOCIATION INC. YEAR BOOK”, in Europe, “THE European Tire and Rim Technical Organization” STANDARDS MANUAL ", and in Japan, the Japan Automobile Tire Association" JATMA YEAR BOOK ".

  Further, the inner and outer two carcass plies 5a, 5b of the ply cords crossing each other with respect to the tire equatorial plane E at the innermost side portion of the widest belt layer, in the figure, the side edge of the inner layer side belt layer 6a The extension angle is in the range of 30 to 60 °, more preferably 45 to 60 °, and the ply cord intersects with each other between the two carcass plies 5a and 5b measured in the tread width direction to 10 to 10. A buffer rubber layer 8 having a width in the range of 40 mm, in particular, a range of 20 to 40 mm, is interposed, and this buffer rubber layer 8 starts from the side edge position of the spiral reinforcing layer 7. In the outer side of the tread width direction, within the range of −10 to +30 mm, it is arranged so as to overlap with the spiral reinforcing layer 7 at least at the starting point, and at the interposed portion of the buffer rubber layer 8. The ply interval between the carcass plies 5a and 5b without including the thickness of the covering rubber is set to 0.8 to 5.0 mm, more preferably 2.0 to 5.0 mm.

  In such a tire, more preferably, the buffer rubber layer 8 is formed of the covering rubber of the carcass plies 5a and 5b or the covering rubber of the spiral reinforcing layer 7, and preferably, the belt cords are crossed with each other. The extending angle of the belt layers 6a and 6b to the tire equatorial plane E of each belt cord is in the range of 45 to 85 °.

  Also preferably, the innermost belt layer, in the drawing, the belt cord of the inner layer side belt layer 6a, the outermost layer carcass ply, in the drawing, the ply cord of the outer layer side carcass ply 5b, both in the same direction with respect to the tire equatorial plane E And the extension angle of each cord with respect to the tire equatorial plane is 30 ° or less.

  In this case, if the extension angle with respect to the tire equatorial plane exceeds 30 °, the interlaminar shear strain between the belt layer and the carcass ply increases, and the durability may be lowered.

  By the way, in such a tire, when at least one of the belt cords of the belt layers where the belt cords cross each other is a steel cord, the road surface grip force can be effectively increased as described above. This is particularly noticeable when the belt cord made of steel cord is formed of a steel single wire having a diameter of 0.15 to 0.25 mm or a cord in which they are twisted.

A comparative test was performed on each of high speed durability and steering stability of an example tire described below and the following conventional tire, which will be described in detail below.
All tires were 245 / 40R18 in size.

Conventional tire 1
There are two carcass plies having the structure shown in FIG. 2 and straddling between a pair of bead cores in a toroidal shape. The carcass ply uses a twisted nylon cord with a diameter of 0.5 mm, and both are radial (angle with respect to the tire equatorial plane is 90 degrees). The carcass is folded around the bead core

  The belt is composed of two belt layers intersecting at the same angle of 35 degrees with respect to the tire circumferential direction on the radial carcass. Both belt layers are made of steel cord. As this steel cord, one obtained by twisting three single wires of steel having a diameter of 0.2 mm and driving them at a driving interval of 1.2 mm was used. The width of the belt layer was set such that one belt (inner layer side) was 235 mm and two belts (outer layer side) were 225 mm with respect to a tread width of 245 mm.

On the outer peripheral side of this belt, a spiral reinforcing layer was disposed by winding an aromatic polyamide (trademark Kevlar) around the equator plane so that it was substantially 0 degrees. The Kevlar has twisted Kevlar cords having a diameter of 0.7 mm arranged at a driving interval of 1.0 mm. The spiral reinforcing layer was disposed so as to cover the entire belt, and was 255 mm wider than the tread width.
The tread was provided with a predetermined groove.

Conventional tire 2
The radial carcass of the conventional tire 1 is changed to a bias carcass.
The ply cord was molded so as to intersect at about 60 degrees with respect to the tire equatorial plane, just below the side edge position of the inner belt layer of the two belt layers.

This crossing angle increases as it approaches the tread center (the reason why this angle increases is due to the tire molding method. Ply layers and other members cut at a predetermined angle are bonded together in a cylindrical shape. A raw cover is constructed by stacking a member in which a belt, spiral layer, tread rubber, etc. are bonded together in a cylindrical shape, and a tubular air bag is placed inside the raw cover to inflate the ply. In this process of inflating, the drum can (cylindrical) shape swells into a donut shape with a higher order curvature, and the expansion rate increases as it approaches the tread center, The crossing angle of ply increases.)
The structure is the same as that of the conventional tire 1 except that the carcass is a bias.

Example tire The tire shown in FIG. 1 has two carcass plies between the pair of bead cores in a toroidal shape. The carcass ply uses a twisted nylon cord having a diameter of 0.5 mm, and both are bias plies. The ply cord was molded so as to cross at exactly 60 degrees with respect to the tire equatorial plane at a position directly below the side edge of one belt layer described later.

  A buffer rubber layer was disposed between the carcass plies. The place and width were set to a width within a range of 5 mm inward from the side edge of the spiral reinforcing layer and 25 mm in the outward direction.

  The thickness of the buffer rubber layer was set to 2 mm after vulcanization (completion) of the tire. The material of the buffer rubber layer was the same type as the carcass ply coding rubber, and a rubber sheet was sandwiched between the plies when the tire was molded.

  Two belt layers intersecting at the same angle of 35 degrees with respect to the tire equatorial plane were arranged on the outer peripheral side of the carcass. For these steel cord belt layers, three steel wires having a diameter of 0.2 mm were twisted and driven at a driving interval of 1.2 mm. The width of the belt layer was set such that one belt (inner layer side) was 235 mm and two belts (outer layer side) were 225 mm with respect to a tread width of 245 mm.

On the outer peripheral side of this belt, a spiral reinforcing layer was disposed by winding an aromatic polyamide (trademark Kevlar) around the equator plane so that it was substantially 0 degrees. The Kevlar has twisted Kevlar cords having a diameter of 0.7 mm arranged at a driving interval of 1.0 mm. The spiral reinforcing layer was disposed so as to cover the entire belt layer, and was 255 mm wider than the tread width.
The tread was provided with a predetermined groove (same as conventional tires 1 and 2).

In order to confirm the effects of the conventional tires 1 and 2 and the example tires described above, an indoor test was performed.
First, the durability was confirmed. Table 1 shows the results of high-speed durability evaluation.
Here, the high-speed durability test was performed on a testing machine that can simulate actual vehicle running indoors, generally called a drum testing machine. The test conditions were an air pressure (250 kPa), a load (5 kPa) and a camber angle (-1 degree) simulating an actual vehicle. The speed started from 150 km / h, and the speed was increased stepwise every 10 minutes in 10 km increments, and the speed at which the failure occurred was recorded.
The higher the speed at which the failure occurred, the higher the durability.

  As described above, it was confirmed that the example tire had high-speed durability equivalent to that of the conventional tire 1 while being a bias ply. When the failure mode after the test was observed, it was as follows.

・ Conventional tire 1: Failure is caused by cracks in the circumferential direction starting from the side edges of the steel belt layer.
In addition, when the crack progressed to the spiral reinforcement layer on the belt and a part of the spiral reinforcement layer was peeled off, the testing machine detected a failure and stopped.
The internal pressure was maintained even after the test machine was stopped.
-Conventional tire 2: The ply cord broke at the outer portion of the side edge of the spiral reinforcing layer, the internal pressure leaked and burst at once.
-Example tire: A failure mode in which cracks starting from the side edges of the steel belt layer spread between the spiral reinforcing layer and partly peeled off as in the conventional tire 1.
Even after stopping the test machine, there is no leakage of internal pressure as with the conventional tire 1.

Since the conventional tire 1 has a radial carcass structure, a failure due to the compression deformation of the ply cord does not occur outside the spiral reinforcing layer by the mechanism described above. Although a failure occurred starting from the side edge of the steel belt layer, the internal pressure could be maintained even when a failure clearly seen in the appearance occurred.
Since the conventional tire 2 has a bias carcass structure, the ply cord is broken by the above-described mechanism, resulting in a failure.
The ply failure is more serious than the side failure of the belt that progresses step by step. If a part of the ply failure breaks, the internal pressure is suddenly released and a burst occurs.

  On the other hand, it was confirmed that the example tires have the same durability as the conventional tire 1 while suppressing the failure of the ply cord. This is because the gauge between the layers is sufficient in the range where the cushioning rubber layer exists, and by reducing the mutual restraint of the carcass ply, even if the tire is subjected to deformation or braking / driving force due to ground contact, This is thought to be because the compression distortion in the applied chord direction was reduced.

Next, in order to see the steering stability performance, the maximum value of the cornering force was tested on the same indoor test machine.
The maximum value of the cornering force was measured when a slip angle was given to the tire during running under the conditions of constant speed (100 km / h), air pressure (250 kPa), load (5 kPa), camber (-1 degree). .
The maximum value of the cornering force when a triangular wave having a gentle slope was input from 0 degree to 5 degrees was recorded and compared.
The results are shown as an index in Table 2. The larger the index value, the better the result.

As described above, the example tire generates a cornering force equivalent to that of the conventional tire 2, and it can be seen that the example tire can achieve both durability and steering stability performance.
The cornering force of the conventional tire 2 and the example tire is higher than that of the conventional tire 1 because both have a biased carcass structure, so that the in-plane shear rigidity of the entire grounding range (tread) is increased.

1 is a meridian cross-sectional view of a tire showing an embodiment of the present invention. It is sectional drawing similar to FIG. 1 which shows the structure of the conventional tire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Bead core 5 Carcass 5a, 5b Carcass ply 6 Belt 6a, 6b Belt layer 7 Spiral reinforcement layer 8 Buffer rubber layer E Tire equatorial plane L Width of buffer rubber layer W Tread width

Claims (5)

Two or more tread parts, a pair of side wall parts and bead parts, and at least two adjacent carcass plies arranged with ply cords extending in opposite directions with respect to the tire equatorial plane The carcass ply consists of a carcass extending toroidally between a pair of bead cores and two or more belt layers arranged on the outer periphery of the crown area of the carcass. A belt arranged extending in opposite directions with respect to the surface, and one or more spiral reinforcing layers made of cords arranged extending in the tread circumferential direction on the outer circumferential side of the belt. A pneumatic tire,
The ply cords that cross each other have an extension angle with respect to the tire equatorial plane at the inner peripheral side portion of the side edge of the widest belt layer in the range of 30 to 60 °, and at least the width of the spiral reinforcing layer The tread width ranges from 0.8 to 1.2 times, and a cushion rubber layer having a width of 10 to 40 mm is interposed between two carcass plies in which ply cords cross each other. The side portion of the spiral reinforcing layer is the starting point, and the portion within the range of −10 to +30 mm in the outer direction in the tread width direction from there is disposed at least overlapping the starting point, and the cushion rubber layer is interposed. A pneumatic tire in which the ply distance between two carcass plies is in the range of 0.8 to 5.0 mm.   The pneumatic tire according to claim 1, wherein the buffer rubber layer is formed of a covered rubber of a carcass ply or a covered rubber of a spiral reinforcing layer.   The pneumatic tire according to claim 1 or 2, wherein the belt layer in which the belt cords cross each other has an extension angle of each belt cord with respect to the tire equatorial plane in a range of 45 to 85 °. The pneumatic tire according to any one of claims 1 to 3 , wherein at least one of the belt layers of the belt layers in which the belt cords cross each other is a steel cord. The pneumatic tire according to claim 4 , wherein the belt cord made of a steel cord is constituted by a steel single wire having a diameter of 0.15 to 0.25 mm or a cord obtained by twisting them.

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