JP2002144826A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire for sharply reducing strain of the carcass folding-back part tail end and largely improving the durability of a bead part. SOLUTION: On an assembly cross section for filling internal pressure of 50 kPa in the standard rim by installing the tire in the standard rim, in a carcass body part, a ply part extending between an intersection P1 of a perpendicular Lv1 to the tire axis passing through the bead core outermost side position and the thickness center of body part and an intersection P2 of a perpendicular Lv2 lowering to the tire axis from the grounding width end of a tread part and the thickness center of the body part ply, has a projecting curved shape toward the tire outside, a carcass folding-back part has the folding-back tail end in an area extending up to a straight line L3 parallel to the tire axis passing through an intersection P3 of a perpendicular Lv3 to the tire axis passing through the center of a radius of curvature of a standard rim flange and the thickness center of the body part ply from a straight line L2 parallel to the tire axis passing through the intersection P2, the highest hardness rubber of stiffener rubber is run along the body part, and is arranged on the tire axis directional inside more than at least the perpendicular Lv1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly to a heavy-duty pneumatic tire for use in heavy vehicles such as trucks and buses, and more particularly, to a pneumatic tire with improved bead portion durability. About.

[0002]

2. Description of the Related Art A pneumatic tire to be mounted on a heavy vehicle of the type described at the beginning has a region from a bead portion corresponding to a ground contact portion to a sidewall portion in the vicinity thereof under rolling under load. , Causing a large fall. Along with this deformation, a large compressive strain is generated at and around the turn-up end of the carcass located at the bead, and in addition, a large in-section shear strain is generated at the turn-up end and its vicinity due to thrust from the flange of the rim. appear. These strains repeatedly act on the end of the folded portion many times during running of the tire. As a result, as the traveling of the tire progresses, a crack is generated at the end of the folded portion, and this crack develops into a separation failure of the folded portion.

Therefore, a tire 11 shown in the left half sectional view of FIG. 4 has been proposed which is effective in suppressing the occurrence of cracks at the end of the folded portion. That is, in FIG. 4, the biggest feature of the tire 11 is that the carcass line of the carcass main body portion 16 b between the position near the bead core 15 and the position near the cross-sectional width (maximum width) SW of the tire 11 is substantially equivalent to the case where the internal pressure is zero and the gauge pressure is zero. The point is that it is straight and set to a non-equilibrium shape. Note that the carcass line is a line connecting the thickness center of the carcass ply.

When a predetermined internal pressure is applied to the tire 11 mounted on the rim by the non-equilibrium-shaped carcass line, the substantially straight carcass line protrudes outwardly from the tire, and the carcass tension increases by that amount. As a result, the rigidity of the portion from the bead portion 14 to the sidewall portion 13 is increased, and in the portion, the fall of the tire 11 when a load is applied is reduced, and the distortion of the folded portion is reduced.

[0005]

However, in recent years, with the increase in the bending rate and the amount of heat generated due to the increase in the load burden on the tire 11, and the tendency of flattening, the carcass tension due to the straight carcass line has been increased. There is a limit to the improvement of rigidity.
s and nylon chafers 18n.

[0006] The combined use of these straight carcass lines and the reinforcing cord layers 18s, 18n results in a significant increase in the cross-sectional gauge and volume of the bead portion 14. They are,
Not only does the tire weight increase, but also the bead portion 14 which becomes thicker than that increases, while the rolling load of the tire decreases the falling degree, but the temperature increases further due to the increase in the amount of heat generated. In addition, due to the push-up by the flange of the rim, separation failure at the end of the reinforcing cord layer and separation failure along the tire radial direction of the reinforcing cord layer are likely to occur. In addition, the effect of suppressing the separation at the end of the folded portion becomes small, and on the contrary, the failure mode becomes complicated and the improvement of the bead portion durability becomes insufficient.

Therefore, in view of the above-mentioned problems, the invention described in claims 1 to 10 of the present invention has a folded portion in which, under rolling of a tire under a load, the strain is concentrated most and a separation failure occurs due to generation of a crack. To provide a pneumatic tire capable of minimizing edge distortion, increasing rigidity against falling down of a bead portion without disposing a reinforcing cord layer, and thereby highly improving bead portion durability. With the goal.

[0008]

According to a first aspect of the present invention, there is provided a tread portion having a pair of sidewall portions and a pair of bead portions connected to both sides of the tread portion. A carcass of a rubber-coated cord ply that reinforces each of these portions between bead cores embedded in each bead portion, and the carcass folds a carcass body portion between a pair of bead core inner portions and a bead core from inside to outside. A pneumatic tire having a turned-back portion and having a stiffener rubber extending in a tapered shape along the carcass body portion and the turned portion from the outer periphery of the bead core toward the end of the tread portion. The highest hardness rubber of the combined rubber is arranged along the carcass body from the bead core. The lowest hardness rubber is formed by arranging the pneumatic tire on its standard rim from the bead core along the turn-back portion, and the cross section of the tire and rim assembly filled with an internal pressure of 50 kPa at a gauge pressure is applied to the tire. , The carcass main body has an intersection P ₁ between a perpendicular Lv ₁ to the tire axis passing through the outermost position of the bead core and the center of the thickness of the main body ply.
If, ply portion extending between the intersection point P ₂ between the thickness center of the vertical line Lv ₂ and the main body ply down from contact width edge of the tread portion to the tire axis has a curved shape convex toward the outer side of the tire, and, carcass turnup portion, the intersection point P ₂ from the straight line parallel L ₂ and the tire axis through a perpendicular line Lv ₃ and the intersection P ₃ between the thickness center of the main body ply of the tire axis through the curvature center of the standard rim flange It has folded end in a region ranging until the tire axis and a straight line parallel L ₃ through the highest hardness rubber stiffener rubber is characterized by comprising accounting for at least the tire axial direction inside position from the perpendicular line Lv ₁ It is a pneumatic tire

Here, the standard rim is a JATMA YEAR BOOK
(2000), ETRTO SANDARDS MANUAL 2000, TRA (THE TIRE a
nd RIM ASSOCIATION INC.) YEAR BOOK (2000) and other rims.The JATMA standard uses the underlined rims in the applicable rim table specified for each tire type.
In ETRTO standard, it is defined for each TIRE SIZE / SECTION CODE
According to the MEASURING RIM WIDTH CODE, the TRA standard
In accordance with GN RIM WIDTH, the center of the radius of curvature of the flange of the standard rim is also the center of the radius of curvature on the side away from the tire and the tire among the positions described in these standards. The contact width of the tread portion is determined by mounting the tire on the above standard rim, filling the maximum internal pressure (gauge pressure) specified by the above standards, placing the tire perpendicular to the flat plate in a stationary state, and setting the maximum internal pressure corresponding to the maximum internal pressure. When the load (N) equivalent to the load capacity is applied, indicates the maximum linear distance in the tire axial direction at the contact surface with the flat plate,
The contact width end is an end indicating the maximum linear distance.

According to the first aspect of the present invention, there is provided a second aspect.
As in the invention described in the above, the minimum hardness rubber of the stiffener rubber has a lower hardness than the ply cord coating rubber hardness of the carcass, and the minimum hardness rubber moves the tire radial end of the highest hardness rubber in the tire radial direction. Having a terminal height extending beyond.

According to the first and second aspects of the present invention, as in the third aspect of the present invention, the minimum hardness rubber of the stiffener rubber has a shape extending beyond the end of the carcass turn-back portion in the tire radial direction. .

According to the first to third aspects of the present invention, as in the fourth aspect of the present invention, the carcass main body passes through the terminal of the highest hardness rubber of the stiffener rubber and extends inward in the tire radial direction from the normal line Lv _{4 of the} carcass main body. For the stiffener rubber located
The highest hardness rubber occupies an area within the range of 60 to 80% of the stiffener rubber area in the tire cross section.

Further, relates the invention described in claim 1, according to the invention described in claim 5, the carcass main body, 60 ° below with respect to the tire axis and parallel to the straight line passing through the intersection point P ₁ It has a tilt angle.

Further, according to the invention described in claims 1 to 5, as in the invention described in claim 6, the bead portion is provided with a reinforcing cord layer extending at least from the folded portion to the bead core. the radially outer terminal position of the side reinforcing cord layer, the following termination height of the highest hardness rubber stiffener rubber, and a tire axis parallel to the straight line L ₄ or through the outermost position of the bead core.

Further, according to the invention described in claim 6, as in the invention described in claim 7, the terminal of the reinforcing cord layer along the carcass body is higher than the terminal height of the reinforcing cord layer on the turnback side, Regarding the invention described in claims 6 and 7,
As in the invention as set forth in claim 8, the reinforcing cord layer is made of a rubber coating layer of a steel cord inclined and arranged with respect to the tire radial direction, and is perpendicular to the steel cord at an end of the reinforcing cord layer along the folded portion. The value of the ratio of the arrangement interval to the cord outer diameter is in the range of 1.0 to 3.0.

Further, according to the invention described in claims 1 to 8, as in the invention described in claim 9, the carcass is provided with a rubber-coated ply portion of a radial arrangement code in a region extending between at least a pair of sidewall portions. In the cross section of a tire having a plane including the tire axis, the bead core-under carcass ply portion present in a region where two straight lines perpendicular to the bead base surface pass through the innermost and outermost sides of the bead core, , Which have an inclination angle in the range of 5 to 45 ° with respect to the plane.

According to the present invention, the steel cord is applied to the ply cord of the carcass, and the heavy load tire is applied to the pneumatic tire. Become.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a left half sectional view of a plane including a tire axis of an assembly in which a pneumatic tire and a rim of the present invention are filled with an internal pressure of 50 kPa, and FIG. 2 is a code see-through plane of a part of a reinforcing cord layer. FIG. 3 is a perspective view of the cord and the bead core of the carcass ply from the direction of arrow A shown in FIG.

In FIG. 1, a pneumatic tire (hereinafter referred to as a tire) 1 has a tread portion 2 and a pair of sidewall portions 3 (only one side is shown) and a pair of bead portions 4 (only one side is shown) connected to both sides thereof. Having. Also, tire 1
Has a carcass 6 extending between the bead cores 5 embedded in each bead portion 4, and the carcass 6 is
And a belt 7 is provided on the outer periphery of the carcass 6.
Further, the tire 1 includes a stiffener rubber 8. The stiffener rubber 8 is tapered from the bead core 5 to the end of the tread along the carcass 6 main body 6b and the turnback 6t. Note that the tire 1 is symmetrical on both sides with respect to the tire equatorial plane E.

The carcass 6 has a main body 6b extending between the insides of the pair of bead cores 5 and a folded portion 6t that turns around the bead cores 5 from the inside of the tire 1 to the outside. The carcass 6 has one or more rubber-coated cord plies, and the carcass 6 in the illustrated example is one ply. The carcass 6 has a rubber-coated ply portion of the radial arrangement code in at least a region between the pair of sidewall portions 3. As the ply cord of the carcass 6, a high modulus cord, particularly a steel cord, is suitable.

Here, the tire 1 is mounted on the standard rim R
(According to the above-mentioned standard), the cross section of the assembly of the tire 1 and the rim R in which the tire 1 is filled with an internal pressure of 50 kPa with a gauge pressure is (1) the main body 6b of the carcass 6 One axis of the tire passing through the outermost position (not shown)
The perpendicular line Lv ₁ and the ply thickness center and the Majiwa point of the main body 6b and the intersection P ₁ of the perpendicular line Lv ₂ and the body portion 6 down from the contact width end TE of the tread portion (according to the provisions) to the tire axis
When b ply thickness around the point where intersects the intersection P _2, ply portion of the carcass 6 main body 6b extending between the intersection point P ₁ and the point of intersection P ₂ has a curved shape convex toward the outer side of the tire 1 .

In the above cross section, (2) the folded portion 6t of the carcass 6 is defined by the outer contour arc (radius) of the flange Rf of the standard rim R from the straight line L ₂ parallel to the tire 1 axis passing through the intersection P _2. perpendicular Lv of the tire 1 axis passing through the center of curvature C of r) ₃ and the main body 6b of the ply turnup portion 6t terminates in a region extending between the up straight L ₃ parallel to the tire axis through the intersection point P ₃ of the thickness center 6tE Having. In this case, it shall include an upper straight line L ₂ on the straight line L _3.

When the tire 1 rolls under a load, the bead portion 4 immediately below the load causes a bending deformation having a deformation center outside the rotation axis of the tire 1 by pushing up the rim R from the flange Rf. . On the other hand, the sidewall portion 3 immediately below the load undergoes bending deformation having a deformation center inside the tire 1 in the rotation axis direction. Since these two types of deformation have different bending directions, there is a first inflection point in the main body 6b as viewed from the carcass line.

In addition, a bending deformation directed toward the inside of the tire 1 (a flattening deformation along a road surface) is also generated in a shoulder region where both ends of the tread portion 2 and each sidewall portion 3 are continuous under the load of the tire 1. A second inflection point exists between the tread portion 2 and the side wall portion 3 that causes a convex overhang deformation toward the outside of the tire 1 as seen in the carcass line in the main body portion 6b.

Compressive strain acts on the tire 1 radially inward (hereinafter referred to as radial direction) from the first inflection point and on the outer side in the radial direction outward from the second inflection point. It has been clarified that if the ends of the folded portion are located at these outer portions, a large compressive strain acts on the ends. In the conventional tire, since the end of the folded portion is positioned radially inward from the first inflection point, the action of the compressive strain is added to the action of the shear strain in the cross-section caused by pushing up from the flange Rf. A crack or separation failure has occurred at the end of the part.

Each of the first inflection point position and the second inflection point position fluctuates depending on conditions such as tire type, filling internal pressure (gauge pressure) and applied load, and is not constant. Therefore, under all conceivable conditions, the outside position range of the main body 6b where the compressive strain does not act reliably, that is, of the main body 6b existing between the first inflection point and the second inflection point. actually measuring the outside position range, the result of the analysis, either of the tire 1, strain reliably compression is found that has not occurred in the region extending between the straight line L ₂ supra up straight L _3.

[0027] It also ply portion of the body portion 6b over between the intersection point P ₁ and the point of intersection P ₂ is necessary prerequisite to have a curved shape convex toward the outer side of the tire 1. Under this condition, the folded portion 6t and the terminal 6tE are connected to the straight line L ₂
By placing the region spanning until the straight line L ₃ from not act is compressive strain in the turnup portion 6t end 6TE, and, since significantly reduce the action of shear strain in the cross section by pushing up from the flange Rf of the rim R , Folded part 6
The durability related to crack resistance and separation resistance of the 6tE at the t-terminus is dramatically improved. In addition, since the radial length of the folded portion 6t is greatly increased, the bending rigidity of the bead portion 4 is improved, which contributes to the improvement of the durability of the folded portion 6t and the terminal end 6tE.

However, the above-mentioned improvement in bending stiffness is achieved by the main body 6.
This causes an increase in the strain burden on the stiffener rubber 8 between the b and the folded portion 6t. This increase tends to cause a wide range of separation along the folded portion 6t, and the initial occurrence position of the failure is near the flange Rf of the rim R. It is determined that. Therefore, in order to prevent the initial occurrence of the separation failure, two or more stiffener rubbers 8 are used, and in the illustrated example, two types of rubbers 8-1 and 8 having different hardness are used.
-2, the highest hardness rubber 8-1 of the combined rubber is disposed along the bead core 5 along the carcass 6 main body 6b, and the lowest hardness rubber 8-2 is formed from the bead core 5 to the turn-back portion 6t. along allowed to relax the stress by disposing the highest hardness rubber 8-1, the tire 1 from at least the perpendicular line Lv ₁
It occupies a substantially triangular cross section at an axially inner position, which contributes to an increase in rigidity for suppressing the falling down.

Increasing the height of the highest hardness rubber 8-1 in the radial direction can further suppress the bead portion 4 from falling down, but the effect of the suppression is the highest hardness rubber having a substantially triangular cross section. 8-1 not the highest hardness rubber 8
In order to easily cause a crack between the radially outer end of -1 and the cord covering rubber of the main body 6b, the highest hardness rubber 8-1 is
It is desirable to set the radial height following termination 8-1E height of the straight line L _3.

As a result, the highest hardness rubber 8-1 is
The inconvenience of cracking b is eliminated. Here, the height refers to a height from a straight line that passes through the diameter position of the rim R and is parallel to the one axis of the tire, that is, a rim diameter line RL. The same applies hereinafter. In addition, in order to advantageously achieve the effect of suppressing falling, the highest hardness rubber 8-1 has a JIS A hardness of 75.
Suitably within the range of ９５95 °.

On the other hand, the lowest hardness rubber 8-2 is a rubber having a lower hardness than the ply cord coating rubber hardness of the carcass 6, and the terminal end 8-1E of the highest hardness rubber 8-1 is arranged in the radial direction. Set to the height of the end 8-2E extending beyond the height. Thus a minimum hardness rubber 8-2, even beyond the radial height of the straight line L _3, with respect to the ply cord coating rubber of the carcass 6 acts as a stress relaxation member. In this sense, the minimum hardness rubber 8
-2, the end 8-2E extends radially outward beyond the end 6tE of the folded portion 6t, so that the main body 6b
Function as a stress relaxation member between the
Separation resistance is improved over the entire area along the folded part 6t.

Further, for the stiffener rubber 8 located radially inward from the normal Lv ₄ of the carcass 6 main body 6b passing through the terminal end 8-1E of the highest hardness rubber 8-1, the highest hardness rubber 8-1
Is 60 of the stiffener rubber area in one section of the tire.
It occupies an area in the range of ８０80%. Thus, the suppression of the bead portion 4 from falling down and the relaxation of the stress at the folded portion 6t are appropriately harmonized. The area of the highest hardness rubber 8-1 is 6
If it is less than 0%, the fall of the bead portion 4 is not sufficiently suppressed, and if it exceeds 80%, the stress relieving effect of the folded portion 6t is insufficient.

Since the highest hardness rubber 8-1 and the lowest hardness rubber 8-2 have remarkably different hardnesses, there is a possibility that the two rubber bonding surfaces are separated. This peeling phenomenon occurs when the carcass 6 main body 6b
As a result, the strain is concentrated on the joint surface as a result of being protruded toward the outside of the tire 1, which is a dominant factor. To suppress to made the overhang, the angle of inclination of the main body portion 6b with respect to the tire 1 parallel to the axis lines L ₁ passing through the intersection point P ₁ the previous theta (inclination angle of the tangential line of the main body 6b at the intersection point P ₁ theta) It is effective to reduce. However, since the upper limit value of the inclination angle θ differs depending on the type of tire, the relationship between the inclination angle θ and the durability of various tires was experimentally analyzed and obtained. As a result, the inclination angle θ was 60 ° or less for all tire sizes. I was able to find out that it was appropriate to do it.

At the stepped portion and the kick-out portion of the tire 1 under the rolling load, the folded portion 6t of the ground contact portion is sheared in the circumferential direction, and this deformation may cause a separation failure at the folded portion 6t. In order to suppress the deformation, the bead portion 4 is provided with a reinforcing cord layer 9 extending at least from the folded portion 6t to the bead core 5. The reinforcing cord layer 9 shown in FIG. 1 reaches around the bead core 5 to the main body 6b. The position of the radially outer end 9Eo of the reinforcing cord layer 9 along the folded portion 6t is set to be equal to or less than the height of the terminal end 8-1E of the highest hardness rubber 8-1 and is parallel to the tire axis passing through the outermost position of the bead core 5. a straight line L ₄ or more.

The terminal 9Eo is connected to the terminal end 8-1E of the highest hardness rubber 8-1.
The reason for setting the height to be equal to or less than the height is that the area radially outward from the height of the terminal end 8-1E is easily deformed in the circumferential direction as a flexible area in the circumferential direction, and the circumferential deformation suppression is concentrated on the separation generation area of the folded portion 6t. This makes it harder to deform in the circumferential direction, because it is more effective in preventing separation. The cords of the reinforcing cord layer 9 are suitably arranged in an inclined arrangement within a range of 45 to 75 ° with respect to the radial direction.
Also, a terminal 9Eo higher than the terminal end 8-1E of the highest hardness rubber 8-1.
In this case, a large circumferential strain is generated in the portion, which causes a large compressive strain between the cord of the terminal 9Eo where the cords of the reinforcing cord layer 9 are arranged in an inclined arrangement and the covering rubber, thereby generating a crack at the cord end. It is incompatible.

Also, the end 9Ei of the reinforcing cord layer 9 along the main body 6b shown in FIG. 1 is made higher than the height of the terminal 9Eo of the reinforcing cord layer 9 on the folded portion 6t side. To increase the circumferential rigidity of the
The circumferential strain component of the compressive strain acting on the terminal 9Eo of the reinforcing cord layer 9 on the side along t is reduced, and the occurrence of cracks in the terminal 9Eo is suppressed.

In FIG. 2, the reinforcing cord layer 9 is composed of a steel cord 9sc and its covering rubber 9cg so as to improve the circumferential rigidity. At this time, at the terminal 9Eo the reinforcing cord layer 9, the value of the ratio d ₂ / d ₁ for cable OD d ₁ of SEQ distance d ₂ which is perpendicular to the steel cord 9sc 1.
Within the range of 0 to 3.0. As a result, the occurrence of a crack failure from the terminal 9Eo of the reinforcing cord layer 9 is prevented, and
The effect of suppressing the circumferential deformation of t can be achieved at a high level. When the value of the ratio d ₂ / d ₁ is less than 1.0, since the rubber interval d ₂ is smaller than the cord end diameter d ₁ of the cut end of the steel cord not bonded to rubber, a crack nucleus is easily connected, and separation failure occurs. If the ratio exceeds 3.0, the effect of improving the circumferential rigidity becomes insufficient, and all of them are unsuitable.

The carcass 6 of the tire 1 described above includes both a case where the carcass 6 is composed of a rubber-coated ply having a radial arrangement cord and a case where the carcass 6 is composed of a ply described below. That is,
1 and 3, the carcass 6 has a bead core-under carcass ply portion 6p which passes through the innermost and outermost sides of the bead core 5 and is located between two straight lines VLi and VLo perpendicular to the bead base surface 4B. , And a slant cord 6pC array obliquely crossing a plane P (see FIG. 3) including one axis of the tire.

The inventor has clarified that the position where the degree of constraint of the carcass 6 on the bead core 5 is the highest around the bead core 5 is immediately below the bead core 5. To be more precise, the position where the contribution of the degree of constraint is the highest is the area below the bead core 5 sandwiched by the two straight lines VLi and VLo. Below the bead core 5 refers to the inside of the bead core 5 as viewed in the radial direction of the tire 1.

According to this elucidation, a radial ply having a cord arrangement in which the carcass 6 crosses under the bead core 5 perpendicularly to the circumferential direction in which the bead core 5 extends has a small degree of restraint of the carcass 6 on the bead core 5, It can be seen that the behavior of pulling out the carcass 6 from the bead core 5 occurs relatively easily due to the fall of the bead portion 4.

On the other hand, the tire 1 in which the carcass ply portion 6p has the inclination cord 6pC arrangement has the inclination cord 6pC
Of the tire 1 having a carcass 6 made of a rubber-coated ply of a radial array cord, the degree of restraint of the carcass 6 on the bead core 5 is large because the cross-sectional length of the carcass 6 with respect to the bead core 5 is long and the carcass 6 has a high resistance to the pull-out force. It is much higher than that. As a result, not only when the internal pressure is applied to the tire 1 but also when the bead portion 4 falls under the rolling load of the tire 1, the in-section shear strain acting on the entire area along the turn-back portion 6t is greatly reduced. The generation and propagation of cracks along the folded portion 6t can be suppressed, which ultimately contributes to the improvement of the durability of the bead portion 4.

When the reinforcing cord layer 9 is applied, the region between the two straight lines VLi and VLo below the bead core 5 is:
With respect to the plane P, it is preferable to arrange the cords 9sc which are inclined in the direction opposite to the inclination direction of the cords 6pC of the carcass ply portion 6p. In other words, it is preferable that the code 6pC and the code 9sc be arranged so as to intersect each other with the plane P interposed therebetween. With this cord crossing configuration, the rigidity of the carcass 6 in the pulling-out direction is further improved, which contributes to the improvement of the degree of constraint of the carcass 6 on the bead core 5. In FIG. 3, the code 9sc is indicated by a two-dot chain line.

Further, the cord 6pC of the carcass ply portion 6p below the bead core 5 has an inclination angle α within the range of 5 to 45 ° with respect to the plane P. If the inclination angle α is less than 5 °, the effect cannot be sufficiently exerted.
If the angle exceeds 5 °, the rigidity in the direction along the plane P becomes too low, so that the shear strain between the bead core 5 and the carcass ply portion 6p and the shear strain between the carcass ply portion 6p and the reinforcing cord layer 9 both increase. As a result,
Any of them is unsuitable because a separation failure is likely to occur between them. Due to this kind of separation failure, cord 6pC rubs and breaks between adjacent parts,
Eventually, the tire 1 may burst. The inclination angle β of the reinforcing cord layer 9 with respect to the plane P of the cord 9SC is desirably in the range of 45 to 75 ° described above.

The tire 1 described above is suitable for heavy duty pneumatic tires, especially truck and bus tires.
Particularly, the structure is effective for a tubeless tire.

[0045]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A radial ply tire for trucks and buses is a tubeless tire having a size of 275 / 70R22.5. The construction of Examples 1 to 24 is shown in FIGS. 1 and 2, and the construction of Examples 24 to 29 is shown in FIG. 1 to FIG. Carcass 6 is a one-ply rubber-coated steel cord layer,
The reinforcing cord layer 9 is a single rubber-coated steel cord layer. The height and rubber hardness common to each example are as follows. Height from a rim diameter line RL linear L ₁ = 29 mm, height from a rim diameter line RL linear L ₂ = 154 mm, height from a rim diameter line RL linear L ₃ = 54 mm, the linear L ₄ rim Height from diameter line RL = 9 mm, JIS A hardness of highest hardness rubber 8-1 = 85 °, JIS A hardness of cord covering rubber of carcass 6 = 70 °, Diameter d ₁ of steel cord 9sc of reinforcing cord layer 9 = 1.
0mm, height of the highest hardness rubber end 8-1E = 41mm. Other specifications are shown in Tables 1 to 3. All the heights are heights from the rim diameter line RL, and the rubber hardness is JIS A value.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

The tires of Comparative Examples 1 to 3 and the conventional tire were all matched with the tires of the example except for the specifications different from those of the example. All of these tires were used as test tires, and these tires were used as standard rims 8.25 specified by JATMA YEAR BOOK (2000).
× 22.5, filled with an internal pressure of the maximum air pressure of 900 kPa specified by JATMA, and a bead durability test was performed using a drum. The applied load is 56.9 kN, which is twice the maximum load capacity of 2900 (kg mass) when wearing DUAL specified by JATMA, and each test tire is pressed against the drum rotating at a speed of 60 km / h, and the bead portion In addition, the distance traveled before the failure occurred in the folded portion was measured, and the failure mode was also confirmed. The speed was 60 km / h.

The measurement result of the running distance is as follows.
The index is set to 00, and the larger the index, the better. The results are shown in Tables 1 to 3 together with the failure modes. In each table, the bead portion durability or folded portion durability is abbreviated as drum durability, and the failure type is PES for the separation at the end of the folded portion and SP for the separation along the folded portion along the folded portion. Layer 9 Terminal Separation is Layer 9 ES
P, and the separation between the highest hardness rubber 8-1 and the lowest hardness rubber 8-2 was represented by the inter-hard rubber SP. Burst is bead breaking.

From the results shown in Tables 1 to 3, it can be seen that the tires of the examples generally have significantly improved bead portion durability compared with the conventional tires, and that the end height of the folded portion or the highest hardness rubber is obtained. It can be seen that the tire of the comparative example in which the arrangement is inappropriate does not exhibit the same bead durability as the conventional tire.

[0052]

According to the first to tenth aspects of the present invention, the end portion of the folded portion is greatly increased, and the arrangement of the highest hardness rubber among the stiffener rubbers is optimized. In other words, the durability of the bead portion can be remarkably improved, and
The use of the reinforcing cord layer can provide a pneumatic tire that can further improve the bead portion durability.

[Brief description of the drawings]

FIG. 1 50 kP for the pneumatic tire and rim of the present invention
FIG. 4 is a left half sectional view of a plane including a tire axis of the assembly filled with the internal pressure of FIG.

FIG. 2 is a perspective plan view of a part of a reinforcing cord layer of the present invention.

FIG. 3 is a perspective view of a cord and a bead core of the carcass ply from the direction of arrow A shown in FIG. 1;

FIG. 4 is a left half sectional view of a conventional tire.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Side wall part 4 Bead part 4B Bead base surface 5 Bead core 6 Carcass 6b Body part 6t Folding part 6p Carcass ply part under bead core 6pC Carcass ply part code 7 Belt 8 Stiffener rubber 8-1 Highest hardness rubber 8-2 Minimum hardness rubber 9 Reinforcement cord layer 9sc Reinforcement cord layer cord E Tire equatorial plane

Claims (10)

[Claims] 1. A tread portion and a pair of treads connected on both sides thereof
Having a sidewall portion and a pair of bead portions,
Each part spans between bead cores embedded in each bead part.
A carcass of a rubber-coated cord ply for reinforcing
The carcass is a carcass book between the inside of a pair of bead cores.
Folding around body and bead core from inside to outside
And a bead core extending from the outer periphery of the bead core to the end of the tread portion.
The tapered shape extends along the carcass body and the folded part
In a pneumatic tire provided with a stiffener rubber, two or more types of stiffener rubbers have different hardnesses from each other.
The highest hardness rubber of the united rubber
Is placed along the carcass body from the bead core,
Low-hardness rubber is placed along the turn from the bead core.
Assemble the above pneumatic tire on its standard rim,
Between the rim and the tire, which has an internal pressure of 50kPa
In the cross section of the assembly, the carcass body is the tire that passes through the outermost position of the bead core.
Perpendicular to axis (Lv₁) And the center of the body ply thickness
Point (P₁ ) And from the tread edge to the tire axis
Vertical line (Lv_Two) And the center of thickness of the body ply
(P_Two ) And the ply part facing the outside of the tire
The carcass folded portion has a convex curved shape and the intersection (P_Two ) Tire axis passing
Straight line (L_Two) From the standard rim flange song
Perpendicular to the tire axis passing through the center of the radius (Lv_Three) And main unit
Intersection with the center of the ply thickness (P_Three ) And the tire axis passing through
Parallel straight line (L _Three End)
The maximum hardness rubber of the stiffener rubber is at least
Line (Lv₁).
And a pneumatic tire. 2. The lowest hardness rubber of the stiffener rubber has a lower hardness than the ply cord coating rubber hardness of the carcass, and the lowest hardness rubber extends in the direction beyond the tire radial end of the highest hardness rubber. The tire of claim 1 having an extended end height. 3. The tire according to claim 1, wherein the minimum hardness rubber of the stiffener rubber has a shape extending beyond the end of the carcass turn-back portion in the tire radial direction. 4. A stiffener rubber located inward in the tire radial direction from a normal line (Lv ₄ ) of the carcass main body passing through the end of the highest hardness rubber of the stiffener rubber. An area in the range of 60 to 80% of
A tire according to any one of the preceding claims. 5. The tire according to claim 1, wherein the carcass body has an inclination angle of not more than 60 ° with respect to a straight line parallel to the tire axis passing through the intersection (P ₁ ). 6. The bead portion is provided with a reinforcing cord layer extending at least from the folded portion to the bead core, and a radially outer terminal position of the folded portion-side reinforcing cord layer is set at the end of the highest hardness rubber of the stiffener rubber. and less height, and, according to claim 5 comprising a higher tire axis parallel to the straight line passing through the outermost position of the bead core (L ₄₎
A tire according to any one of the preceding claims. 7. The tire according to claim 6, wherein a terminal of the reinforcing cord layer along the carcass main body is higher than a terminal height of the reinforcing cord layer on the folded side. 8. The reinforcing cord layer is composed of a rubber coating layer of a steel cord arranged obliquely with respect to the tire radial direction, and at a terminal of the reinforcing cord layer along the turn-back portion, an outer cord having an arrangement interval orthogonal to the steel cord is provided. The value of the ratio to the diameter is 1.
The tire according to claim 6 or 7, wherein the value is in the range of 0 to 3.0. 9. The carcass has a rubber-coated ply portion of a radial array cord at least in a region extending between a pair of sidewall portions, and has a tire core having an innermost portion and an outermost portion in a tire cross section in a plane including a tire axis. , A bead core-under carcass ply portion present in an area sandwiched by two straight lines perpendicular to the bead base surface has an inclined cord arrangement obliquely crossing the plane,
The tire according to any one of claims 1 to 8, wherein the tire has an inclination angle in a range of 5 to 45 ° with respect to the plane. 10. The tire according to claim 1, wherein a steel cord is applied to a ply cord of the carcass, and a heavy duty tire is applied to a pneumatic tire.