JP3441575B2 - Heavy duty pneumatic tires - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy duty pneumatic tire used for trucks, buses and the like having excellent wear resistance.

[0002]

2. Description of the Related Art In recent years, heavy duty pneumatic tires for trucks and buses have a flat radial shape due to a radial structure carcass and a belt layer that imparts a hoop effect to the carcass to maintain the tire shape and enhance tread rigidity. Is progressing.

As the belt layer, usually, a belt ply in which low elongation steel cords having an elongation at break of about 1 to 3% are arranged at an angle of about 10 to 35 with respect to the tire circumferential direction, It is formed by stacking three or four cords in a direction intersecting each other.

In such a heavy-duty pneumatic radial tire, the restraining force at the cut ends of the belt cord at both edges of the belt layer is weaker than that at the crown portion, and due to centrifugal force during high-speed rotation, this belt Lifting is likely to occur in which only the edges of the layers are lifted radially outward. In the crown portion of the belt layer, since the steel cords cross each other and are strongly arranged, the rigidity is extremely high, and the amount of lifting to the outside in the tire radial direction is extremely small.

Such lifting of both edges of the belt layer induces separation between the tread rubber and the belt layer, and, for example, in a tire mounted on a drive shaft,
As shown in FIG. 5 (A), the ground contact surface shape of the tread is
It has a drum shape with respect to the tire equator c.

As a result, the central portion of the tread where the ground contact pressure is lowered is liable to slip with respect to the road surface, leading to center wear which causes early wear of the tread crown portion. In a tire mounted on the front wheels, so-called shoulder drop wear is likely to occur at the shoulder portion.
The uneven wear tends to be promoted by the change in the ground contact shape due to the flattening of the tire.

Conventionally, as a means for preventing the lifting of both edges of the belt layer, from the viewpoint of mainly suppressing the lifting of the belt layer, both edges of the belt layer are made of a cord having a lower elasticity than the belt cord. Covering with bands arranged along the tire circumferential direction is performed.

[0008]

However, in the case of newly providing the band as described above, firstly, the productivity is drastically reduced due to the addition of the band winding process during the tire production process. Second, there is a problem that the weight of the tire increases.

Further, as described above, in the pneumatic radial tire for heavy load, the rigidity of the crown portion is remarkably enhanced by the belt layer of the low elongation steel cord, and as a result, the envelope characteristic for wrapping the protrusions on the road surface is poor. , It is pointed out that the ride is uncomfortable.

The inventors of the present invention have conducted a study from a completely different viewpoint from the conventional one, and as a result, the belt layer is made to be lifted up to the same degree as the lifting of the belt both edges so that other crowning performance is not deteriorated. By improving the structure, without deteriorating productivity and tire weight,
The present invention has been completed based on the finding that the tread contact surface shape can be changed to a drum shape to obtain a good contact pressure distribution and suppress uneven wear while improving the envelope characteristics.

As described above, the present invention provides a heavy-duty pneumatic tire capable of preventing uneven wear and improving envelope characteristics by obtaining a good ground pressure distribution on the tread surface. Has an aim.

[0012]

[Means for Solving the Problems] Claim 1 of the present invention
The described invention comprises a carcass that folds around a bead core of a bead part from a tread part through a sidewall part, and a belt layer composed of a plurality of belt plies arranged radially outside of the carcass and inside the tread part. A heavy-duty pneumatic tire, wherein the belt layer is at least the innermost first belt ply in the tire radial direction,
The first belt ply has second and third belt plies that are sequentially overlapped with each other on the outer side in the radial direction, and the first belt ply has a low extension cord having an elongation at break of 1 to 3%. The second and third belt plies are arranged at an angle of 40 ° or more and 70 ° or less with respect to the equator, and the second and third belt plies have a high elongation cord having an elongation at break of 4 to 10% with respect to the tire equator. The second belt ply and the third belt ply are arranged so as to be inclined at equal angles of not less than 10 ° and not more than 20 °, and the high-stretch cords are overlapped with each other so that the low-stretch cords and the high-stretch cords are high. The pneumatic tire for heavy loads is characterized in that the extension cords intersect in a triangle shape.

The aspect of the invention according to claim 2 has an aspect ratio of 50.
% Or more and 70% or less, and further, in the invention according to claim 3, the belt layer has a low extension cord having an elongation at break of 1 to 3% on the outer side in the radial direction of the third belt ply. It is characterized in that it has a fourth belt ply arranged at an angle of 10 ° or more and 20 ° or less with respect to the tire equator.

In the invention according to claim 4, the high-stretch cord forms a single-layer sheath by twisting one steel filament to be a core and its periphery (N-1). (Where N is 3 or more and 7 or less) has a 1+ (N-1) structure composed of steel filaments, and the steel filaments are preliminarily crimped prior to twisting and form a core. The steel filament and the steel filament forming the sheath are twisted so as to be replaced with each other.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a standard state (right-left symmetric section) of a heavy duty pneumatic tire that is assembled to a regular rim J defined by JIS, JATMA, etc. and is filled with standard internal pressure. The tread portion 2 to the sidewall portion are shown. Three
The carcass 6 whose both ends are folded back around the bead core 5 of the bead portion 4 is passed over the carcass 6 and
A tough belt layer 7 is wound around the outer side of the sheet with a hoop effect. In addition, the bead core 4 includes the bead core 5
A bead apex 9 made of hard rubber is provided on the outer side in the radial direction of the tire.

In this example, the pneumatic tire for heavy load has a ratio (H of the tire section height H to the tire section width W (H
Although the flatness ratio obtained from / W) is about 70%, the flatness ratio may be appropriately set within the range of 50% to 70%.

The carcass 6 is composed of at least one carcass ply having a radial structure in which organic fiber cords such as nylon, rayon, polyester or steel cords are arranged at an angle of 75 to 90 ° with respect to the tire equator C. It is configured. In this example, the carcass 6 has a one-piece structure in which steel cords are arranged at 90 ° with respect to the tire equator C.

Next, the belt layer 7 comprises a plurality of belt plies in which steel cords are arranged in parallel with each other,
In this example, the first belt ply 7A on the innermost side in the radial direction of the tire and the second, third, and fourth belt plies 7B, 7 that sequentially overlap the outer side of the first belt ply 7A in the radial direction.
4 illustrates a four-layer structure having C and 7D.

In the present embodiment, the width WB of the second belt ply 7B is the largest in the tire axial width of each belt ply, and this width WB is preferably about 80% to 95% of the tread width TW. .

The tire axial width of each belt ply is, next to the second belt ply 7B, the third belt ply 7C, the first belt ply 7A, and the fourth belt ply 7D in order from the largest one. Continuing, but not limited to this example, the width dimension can be set appropriately.

Further, as shown in FIG. 2, the first belt ply 7A has a low elongation cord 10 having an elongation at break of 1 to 3% at 40 ° or more and 70 ° or less with respect to the tire equator C. It is necessary to incline at a relatively large angle θ1.

More specifically, the low-stretch cord 10 is, for example, a steel cord having a (3 / .20 + 6 / .35) structure in which the number of twists is set so that the elongation at break is 2%. The ones arranged as 67 ° are used.
It should be noted that the number of embedded cords and the like can be variously set according to the required performance.

Next, the second and third belt plies 7
In B and 7C, the high-stretch cords 11 each having an elongation at break of 4 to 10% are arranged so as to be inclined with respect to the tire equator C at an equal angle (θ2 = θ3) of 10 ° or more and 20 ° or less. The second and third belt plies are stacked in such a manner that the high extension cords 11 intersect each other.

In this example, the high expansion cord 11 is
For example, a steel cord whose elongation at break is 6% is
= Θ3 = 18 ° is used.

Further, in the fourth belt ply 7D, the low elongation cord 10 having an elongation at break of 1 to 3% is used for the tire equator C.
With respect to the angle .theta.4 and inclined by an angle .theta.4 of 20.degree. In this example, the low extension cord 10 employs the same cord as the first belt ply 7A. The fourth belt ply 7D can be omitted.

Further, as shown in FIG. 6, the first, second and third
With the belt plies 7A, 7B, and 7C, the low extension cords 10 arranged at a relatively large angle with respect to the tire circumferential direction and the high extension cords 11 arranged at a relatively small angle with respect to the tire circumferential direction. , 11 to form a triangle-shaped cord intersection.

With the structure of the belt layer 7 as described above, when centrifugal force or the like due to high speed rotation is applied, the cord is not only lifted at both edge portions of the belt layer but also the tensile force acting on the cord at the crown portion. Stretching can occur and allow the entire belt layer to rise approximately radially outward.

As a result, the ground contact pressure distribution on the tread surface can be made substantially uniform, and the ground contact shape of the tread is an ideal drum shape as shown in FIG. 5 (B), especially center wear on the drive shaft of the vehicle. It is possible to prevent the occurrence of uneven wear.

Further, by adopting the constitution of the belt layer 7, it is possible to improve the envelope characteristic for wrapping the protrusions in the tread crown portion, and it is also possible to improve the riding comfort.

It should be noted that it is conceivable to adopt high extension cords for all of the first, second, third and fourth belt plies 7A, 7B, 7C and 7D, but in this case, the belt layer 7 The amount of movement becomes extremely large, the heat of the rubber is high, which causes the tire durability to be significantly reduced.
Experimental results have shown that it is not suitable for practical use.

It is also conceivable that the first and second belt plies 7A and 7B are made of high extension cords, and the third belt ply 7C is made of a low extension cord. In this case, the first and second belt plies 7A and 7B are used. Due to the difference in the arrangement angles θ1 and θ2 of the belt plies, the belt layer 7 is not uniformly stretched and distorted, and it is difficult to obtain a uniform tread contact pressure.

Incidentally, the first and third belt plies 7A, 7
Even if a high extension cord is adopted for C, the same problem as above cannot be caused and cannot be adopted, and low extension cord is adopted for all of the first, second and third belt plies 7A, 7B, 7C. In that case, the ground contact shape becomes distorted as in the conventional case, and the uneven wear suppressing effect is poor.

On the other hand, in the present invention, the low elongation cord 10 having a small elongation is provided with a relatively large angle θ in the tire circumferential direction.
The second and third belt plies 7B and 7C, which are arranged one by one, and have a high elongation cord 11 having a large elongation at a relatively small angle in the tire circumferential direction and having a bilaterally symmetrical structure.
By adopting the above, it is possible to eliminate all the above-mentioned problems.

The elongation at break of the high elongation cord 11 is 10
If it exceeds%, the original hoop effect of the belt layer cannot be exhibited,
It reduces the tire strength and cannot maintain the shape.

Further, as shown in FIG. 2, the belt cords of the first and second belt plies 7A and 7B are arranged in the same direction with respect to the tire equator C, in the present example, in the leftward upward direction, and The belt cords of the 3rd and 4th belt plies 7C and 7D are arranged in a direction different from the belt cords of the 1st and 2nd belt plies with respect to the tire equator C, that is, in the present example, arranged in an upward direction to the right. As a result, the number of plies is made equal on the left and right in the arrangement direction of the cords. Therefore, by providing the fourth belt ply 7D, the extension of the belt cord is also balanced left and right.

In the present example, the tread portion 2 is
As a tread groove extending in the tire circumferential direction, a crown groove 17 on the tire equator side and a shoulder groove 18 on the tread edge side
It is illustrated that the and are formed, and various shapes such as a linear shape and a zigzag shape can be adopted for this.

Next, as the high-stretch cord 11, for example, as shown in FIGS. 3 to 4, one steel filament to be the core 13 and a single-layer sheath 14 by being twisted around the steel filament are provided. It has a 1+ (N-1) structure consisting of (N-1) pieces (where N is 3 or more and 7 or less) of steel filaments to be formed, and the steel filaments are already wavy before being twisted. It is preferable that the steel filament forming the core 13 and the steel filament forming the sheath 14 are twisted so as to be replaced with each other.

The steel filament 12 (hereinafter,
(Simply referred to as a filament) is a steel wire that has been finely drawn and has been pre-wavy before being twisted. For example, the wire diameter d is 0.20 mm or more and 0.40.
The cord 11 is formed by twisting seven thin wires having a diameter of not more than mm and having the same diameter in this example.

As described above, by using the filaments which are preliminarily corrugated, a large number of gaps between the filaments are formed even after twisting, the permeability of the topping rubber can be enhanced, and the elongation of the cord can be increased. It can be preferably used for heavy-duty tires because it can be easily made large and the cord can be lightened.

The filament 12 forming the core 13
And the filaments 12 forming the sheath 14 are twisted in such a manner that they are interchanged with each other, and the twisting is roughly as follows.

As is apparent from FIG. 4A showing the AA cross section of FIG. 3, the high extension cord 11 has one filament 12a as the core 13 and the remaining six filaments 12b and 12c around it. , 12d, 12e, 12f, 1
2 g are adjacent to each other to form the sheath 14. For easy understanding, the filaments 12 ... Show a state in which they are in contact with each other, but in reality, the filaments 12 ...
Are pre-stressed, so there are partially spaced parts.

Further, the high extension cord 11 has a cross section B- in FIG.
As is clear from FIG. 4 (B) showing B, among the six filaments 12 forming the sheath 14, the filament 12g moves outward in the radial direction of the cord and is located between the filaments 12b and 12g. A void S is formed in the hollow space S, and the filament 12a forming the core 13 can be exposed by forming the void S.

Further, the arrangement of the filaments shown in FIGS. 4 (C) and 4 (D) is changed to FIG. 4 (E) showing a cross section taken along the line EE of FIG.
As can be seen from the above, the core 13 and the sheath 14 until now are
The filament 12f forming the core is located, and the filament 12a forming the core 13 until now forms a part of the sheath 14.

Therefore, during the period from FIG. 4 (A) to FIG. 4 (E), the filaments 12a and 12f, which respectively formed the core 13 and the sheath 14, form the interchanged portion 15 which interchanges each other.

Similarly, the other filaments 12b, 12
Also in c, 12d, 12e, and 12g, the sheath 1 is sequentially
4, the core 13 is replaced, and the series of replacement of the filament 12 is completed. The filaments 12 may be exchanged in a fixed order, or may be exchanged randomly.

The filament 12 has a replacement pitch PC for switching between the sheath 14 and the core 13, for example, 1.0 times or more the twist pitch P1 of the sheath 14 and 10.0.
It can be twisted in the range of not more than double.

In such a high extension cord 11, the filaments 12 of the core 13 and the filaments of the sheath 14 can be made substantially equal in length by exchanging the filaments 12 between the sheath 14 and the core 13. As a result, the strain can be prevented from concentrating on the core filament, and the cord 11
It can be preferably used as a belt cord of a heavy-duty tire that is subjected to a high load and a high internal pressure because it can enhance the durability.

In addition, such a high-stretch cord 11 can promote the permeation of rubber into the core 13 in combination with the curling of the filament 12 in the replacement portion, and enhance the corrosion resistance of the cord. And the occurrence of distortion due to residual air,
It is preferable in that the strength can be prevented from lowering.

In the conventional structure in which the core is specified as one filament, the filaments of the core 13 are not twisted, and as a result, there is little friction with other filaments forming the sheath 14, and the core is not changed as the tire runs. The cord of this example is likely to come off, but the filament of the core is not specified, and a sufficient frictional force can be secured in all filaments, core omission can be effectively prevented, and the durability of the cord can be further improved, which is preferable. .

It is needless to say that, as the high-expansion cord, a cord having no interchanged portion can be adopted in addition to the above cords.

[0051]

EXAMPLES Tire sizes are 11 / 70R22.5, and multiple types of pneumatic tires for heavy load (Examples 1 to 4 and Comparative Examples 1 to 4) having specifications as shown in FIG. 1 and Table 1 are used. Along with making a prototype, the following tests were performed to evaluate these performances.

A) Plunger index This is a tire strength test. Test tires with regular rims (2
A plunger destruction test according to JIS D4230 was carried out under the condition that the rim was assembled into 2.5 × 7.50 V) and the internal pressure of 8.0 ksc was filled. The breaking energy at that time was compared by an index with Comparative Example 1 as 100. The larger the value, the better.

B) Apply a load 1.4 times the maximum load specified in HTLC JIS,
The speed is increased by 10 km / H every 2 hours from the speed of 0 km / H, and the speed until the tire is destroyed and the running time at that speed are obtained, and both are separated by a hyphen. The higher the speed and the higher the time, the better.

C) Tire weight The weight of each tire is measured and is shown as an index with Comparative Example 1 being 100. The smaller the index, the better.

(D) Abrasion index 10 ton bus A test tire was mounted on the rear wheel of a 2-D vehicle by rim assembly (tire load: 2500 kgf), and the groove depth of the crown groove was 3.2 mm (about 16 mm when new). The traveling distance until reaching was measured, and it was displayed as an index with Comparative Example 1 being 100. The larger the index, the better.

E) Uneven wear amount of front and rear wheels A test tire is attached to each of the front and rear wheels of a 2-D vehicle (front load: 2725 kgf, rear load: 2500 kg).
f), for front tires, mileage of 20,000 km and 5
The shoulder drop wear amount (mm) at 10,000 km was measured, and is shown in the upper and lower rows. For rear wheel tires, the center wear amount (mm) obtained by subtracting the groove depth of the crown from the groove depth of the shoulder groove was measured at mileages of 20,000 km and 50,000 km respectively. Shows. The smaller the uneven wear amount, the better.

(F) Ride comfort Test tires were mounted on all the wheels of the vehicle shown in (e) above, and the tire test course was run to perform sensory evaluation by the driver. The evaluation is indicated by an index with Comparative Example 1 being 100, and the larger the value, the better. Table 1 shows the test results, and Table 2 shows the types of cords.

[0058]

[Table 1]

[0059]

[Table 2]

As a result of the test, it was confirmed that each of the example tires can suppress uneven wear and that the riding comfort can be equal to or improved as compared with the conventional one. In particular, code B in Table 2
It has been confirmed that in Examples 1 to 3 in which No. 1 is adopted, the strength of the tire can be improved by utilizing the characteristics of the cord.
It was also confirmed that the ground contact surface shape was drum-shaped as shown in FIG. 5 (B). In addition, it has been confirmed that the above effects can be exhibited in a size other than the tire size of this example.

On the contrary, Comparative Examples 1 to 3 have a small effect of suppressing uneven wear, and Comparative Example 4 which does not use a low stretch cord can suppress uneven wear, but the tire strength is remarkably lowered, which is preferable. Absent.

[0062]

As described above, the heavy duty pneumatic tire of the present invention can prevent uneven wear by obtaining a good contact pressure distribution on the tread surface. In the invention according to claim 4, as a result of devising the structure of the high-stretch cords of the second and third belt plies, the durability of the cords and the tire strength can be improved.

[Brief description of drawings]

FIG. 1 is a tire cross-sectional view showing an embodiment of the present invention.

FIG. 2 is a diagram showing a developed belt layer.

FIG. 3 is a plan view showing an example of a high expansion cord.

4A to 4E are cross-sectional views showing an example of a high expansion cord.

5A and 5B are diagrams for explaining the shape of a ground plane.

FIG. 6 is a conceptual diagram showing a triangle cross-shaped body of a belt cord.

[Explanation of symbols]

2 tread section 3 Side wall part 4 bead part 5 bead core 6 carcass 7 Belt layer 7A First belt ply 7B Second belt ply 7C Third belt ply 7D 4th belt ply 10 Low extension cord 11 High extension cord

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Claims (4)

(57) [Claims] 1. A carcass which folds around a bead core of a bead part from a tread part through a side wall part, and a belt layer composed of a plurality of belt plies arranged radially outside the carcass and inside the tread part. A heavy-duty pneumatic tire, wherein the belt layer includes at least a first innermost belt ply in the radial direction of the tire and second and third belt plies that sequentially overlap radially outward of the first belt ply. And the first belt ply has an elongation at break of 1 to 3
% Low extension cords are arranged at an angle of 40 ° or more and 70 ° or less with respect to the tire equator, and the second and third belt plies have an elongation at break of 4 to 4
The 10% high extension cords are arranged so as to be inclined with respect to the tire equator at the same angle of 10 ° or more and 20 ° or less, and the second and third belt plies are oriented so that the high extension cords intersect each other. A pneumatic tire for heavy loads, characterized in that the low-expansion cord and the high-expansion cord intersect each other in a triangle shape by being overlapped with each other. 2. The pneumatic tire for heavy loads according to claim 1, wherein the pneumatic tire for heavy loads has a flatness of 50% or more and 70% or less. 3. The belt layer has a low extension cord having an elongation at break of 1 to 3% on the outer side in the radial direction of the third belt ply at an angle of 10 ° or more and 20 ° or less with respect to the tire equator. The heavy-duty pneumatic tire according to claim 1, comprising a fourth belt ply that is inclined and arranged. 4. The high-stretch cord comprises one steel filament serving as a core and twisted around the steel filament to form a single-layer sheath (N-1) (however, N).
Has a 1+ (N-1) structure consisting of steel filaments of 3 or more and 7 or less), and the steel filaments are preliminarily corrugated prior to twisting and have formed a core with steel filaments. The heavy-duty pneumatic tire according to claim 1, wherein the steel filaments forming the sheath are twisted in such a manner that they are exchanged with each other.