JP3145912B2 - Pneumatic radial tire for heavy loads - 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 radial tire capable of improving tire durability, particularly bead durability, while reducing rolling resistance.

[0002]

2. Description of the Related Art Conventionally, in order to reduce the rolling resistance of a pneumatic radial tire for heavy loads, for example, Japanese Patent Publication No.
No. 0083 proposes to intentionally remove the carcass profile from the so-called natural equilibrium shape.

[0005] As shown in FIG. 5, as shown in FIG. 5, when a tire is assembled to a regular rim and filled with a regular internal pressure, a distance of 15% of a tire sectional height H from a tire bead base line BL is obtained. B is a point on the carcass center line a that separates h from the tire radial outside, and BC is a line segment extending outward from the point B in the tire radial direction and intersecting with the carcass center line a at the point C. A straight line N parallel to the BC and tangent to the carcass center line a, a curvature radius Rn of a virtual reference arc (shown by a dotted line) tangent to the straight line N and having the line segment BC as a chord; The ratio of the contour curve extending to the vicinity of the maximum width position M to the radius of curvature R
One of the features is that (R / Rn) is 0.65 or more and 0.95 or less.

[0004] The above-mentioned proposal increases the bending deformation in the region above the side wall (tread side) by the above-described structure, and has an inverse correlation with the bending deformation and relatively reduces energy loss. It is expected to reduce large shear deformation and reduce rolling resistance as a whole.

[0005] Further, this proposal proposes that, with respect to the remaining partial contour curve of the carcass center line a having a single inflection point between the point B and the contour curve extending to the shoulder portion of the carcass center line a, It is required that the maximum separation distance f1 between the reference arc and the arc be set to 3 to 8 mm.

Accordingly, the above proposal provides a so-called inverted R shape in a region below the sidewall portion under normal internal pressure filling, thereby reducing energy consumption during tire load rolling.
Rolling resistance is reduced.

[0007]

By the way, when the profile of the outer surface of the tire is constant, the smaller the ratio (R / Rn) of the carcass center line a, the more the rubber around the shoulder part, especially the buttress part. The thickness can be reduced. Therefore, the above proposal can also reduce the thickness of the rubber at this portion, reduce the amount of heat generated by bending deformation, and improve the durability of the tire.

However, in the above proposal, since the center line a of the carcass around the bead portion needs to be separated from the reference arc approximating the natural equilibrium shape by at least 3 mm, preferably at least 4 mm inside the tire, Although the distortion at the bead portion becomes large and is suitable for reducing the rolling resistance, there is a problem in the durability of the bead portion.

Particularly, in a tubeless type heavy-load pneumatic radial tire in which the bead portion is extremely firmly fixed to the rim, setting a carcass profile separated from the equilibrium shape by 3 mm or more around the bead portion is difficult.
The carcass around the bead portion is significantly distorted, and when the carcass cord is a metal cord, the bead durability is remarkably deteriorated such that damage is easily induced.

[0010] In this regard, the above proposal adopts "700T x 20" as the regular rim of the specific example tire, and it is considered that a tube type tire is considered as an embodiment of the invention.

The present inventor has proposed a heavy-duty pneumatic radial tire that simultaneously satisfies the most required tire durability, especially bead portion durability, while reducing rolling resistance. The purpose is to provide. Further, the present invention can be preferably applied to a tubeless heavy-duty pneumatic radial tire in which the rim sheet in contact with the bead base of the tire is inclined at an angle of 12 ° or more with respect to the axial line of the tire.

[0012]

Means for Solving the Problems In the present invention, claim 1 is provided.
According to the invention described above, a folded portion that is folded back around a bead core is provided on a main body portion extending from a tread portion to a bead portion through a sidewall portion, and cords are arranged at an angle of 75 to 90 degrees with respect to the tire equator. Heavy-duty pneumatic radial tire comprising a carcass made of a carcass ply, and a belt layer made up of a plurality of belt plies arranged radially outward of the carcass and inside the tread portion, the tire including a tire shaft. In the meridional section, the tire is rim-assembled into a regular rim and the internal pressure of 5% of the normal internal pressure is filled.
When the internal pressure state is set, the deformation amount f at which the carcass main body is deformed outward or inward has a maximum value of 2.3 mm or less based on the carcass main body center line at the 5% internal pressure state, and In the 100% internal pressure state, a point B on the center line of the main body of the carcass at a distance h of 15% of the tire sectional height H from the bead base line of the tire to the tire radial outside, and from this point B, the tire A line BC extending radially outward and intersecting the center line of the carcass body at the point C, and a straight line N parallel to the line segment BC and in contact with the center line of the carcass body at its maximum width position M;
The curvature radius Rn of a virtual reference arc that is in contact with the straight line N and has the line segment BC as a chord, and the arc of the shoulder region extending from the point C to the vicinity of the maximum width position on the center line of the main body of the carcass. The ratio (R / Rn) to the radius of curvature R is
With 0.65 or more and 0.95 or less, the most
The amount of deformation fm at the large width position is more tight than the maximum width position M.
60-75% of the deformation amount fd of the area inside in the radial direction
And the carcass splice has a Taber stiffness index α per cord of 35 (g · cm) or less and
It is a pneumatic radial tire for heavy loads in which metal cords having a breaking strength of 800 to 1200 (N) are arranged.

In this specification, the above-mentioned Taber
The sex index is, as shown in FIG. 4, a length of 5 cm from the fixed end.
Applying force to the end of the cord b that extends, the opening angle of the end becomes 15
Defined as the moment value (gcm) when と き
Justify.

Further, in the invention according to claim 2, the tire
The center line of the main body of the carcass in the meridional section is
Changes from 5% internal pressure state to the 100% internal pressure state
Sometimes, on the tire radial direction outside of the maximum width position M
The deformation amount fu of the area is greater than the deformation amount fm at the maximum width position M.
Small and substantially zero, and at maximum width position M
The deformation fd of the area inside the tire radial direction is the maximum width
It is characterized in that it is larger than the deformation amount fm at the position M.

According to a third aspect of the present invention, the carcass
The ply has a Taber stiffness index α of 16 to 33 (g · c
2. A metal cord according to claim 1, wherein the metal cords are arranged in the order of m).
Or a pneumatic radial tire for heavy loads according to 2 .

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. The pneumatic radial tire for heavy loads according to the present invention includes a carcass 6 that is folded back around the bead core 5 of the bead portion 4 from the tread portion 2 via the sidewall portion 3 and is locked radially outside the carcass 6 and inside the tread portion. The tubeless type is mainly used for trucks, buses and the like, and is attached to a 15 ° deep rim.

The carcass 6 includes a main body 6a extending from the tread portion 2 to the bead portion 4 through the sidewall portion 3;
In this example, a turn-back portion 6b connected to the main body and turned around the bead core 5 from inside to outside in the tire axial direction.
And

The carcass 6 has a radial structure in which carcass cords are arranged at an angle of 75 ° to 90 ° with respect to the tire equator CL, and is composed of one or more carcass plies,
As the carcass cord, a metal cord can be preferably used. Note that an organic fiber cord such as nylon, rayon, or polyester can be used as necessary.

In this embodiment, the carcass 6 is composed of one carcass ply, and has a Taber stiffness index of 35 (g · cm) or less, preferably 16 to 33 (g · cm) as a carcass cord. The use of a soft metal cord facilitates the bending of the cord, as described later, and helps prevent carcass damage.

Next, the belt layer 7 is composed of two or more belt cords, such as 4
The tread portion 2 is formed of a plurality of belt plies, giving a tightening effect to the carcass 6 and increasing the rigidity of the tread portion 2. And as the belt cord, like the carcass cord,
Metal cords are preferred, and organic fiber cords such as nylon, polyester, rayon and the like may be used as necessary.
Note that, in this example, the belt layer 7 is formed of a metal cord 4
It is composed of a plurality of belt plies.

A hard rubber, for example, having a JISA hardness of 70, is provided between the main body 6a and the folded portion 6b of the carcass 6.
A bead apex 9, which is made of a rubber composition of about 95 degrees and extends radially outward in the tire radial direction in a meridional section of the tire, is provided to reinforce the bead portion 4. It is preferable that the bead portion 4 is provided with a chafer or the like and is appropriately reinforced.

The pneumatic radial tire for heavy load according to the present invention has a tire meridional section including a tire shaft,
As shown in FIG. 2, the center line 6c of the carcass body 6a is set to a normal internal pressure from a 5% internal pressure state (shown by a dashed line) in which the rim is assembled to a normal rim and filled with an internal pressure of 5% of the normal internal pressure. When a filled 100% internal pressure state (shown by a solid line) is reached, the maximum value of the deformation amount f that deforms outward or inward is 2.3 mm or less.

As described above, by setting the upper limit of the maximum value of the deformation amount f of the carcass 6 due to the internal pressure filling to a very small range, the distortion generated in the carcass 6 can be reduced. Damage can be suppressed.

When the maximum value of the deformation amount f exceeds 2.3 mm, the distortion of the carcass around the bead portion tends to increase, and the effect of improving the durability of the bead portion can be exerted. More preferably, the maximum value of the deformation amount f is 1.5 mm or less.

In such a heavy-duty pneumatic radial tire, the center line 6c of the main body of the carcass 6 has the following contour in the 100% internal pressure state where the rim is assembled to the regular rim.

As shown in FIG. 3, a point B on the center line 6c of the carcass main body, which is separated from the bead base line BL of the tire by a distance h of 15% of the tire cross-sectional height H to the outside in the tire radial direction, A line segment extending outward from the point B in the tire radial direction and intersecting with the carcass main body center portion 6c at the point C is BC, and the carcass main body center line 6c parallel to this line segment BC and the carcass maximum width position M , A radius of curvature Rn of an imaginary reference arc V tangent to the straight line N and having the line segment BC as a chord (the straight line N contacts the point E), and the maximum width of the carcass from the point C The ratio (R / Rn) of the contour curve extending to the vicinity of the position to the radius of curvature R is 0.
It is 65 or more and 0.95 or less. The expression "extends to the vicinity of the position of the maximum width of the carcass" means that the curve extends from the point C as a curve having a radius of curvature R of at least 30 degrees or more, preferably 40 degrees or more.

That is, in the present invention, as described above, while the maximum value of the deformation f of the carcass 6 during the internal pressure filling process is restricted to a small value, the main body center line 6c radially outward from the maximum width position M of the carcass 6 is controlled. Is greatly deviated from the natural equilibrium shape. Note that the reference curve V is naturally
Although the carcass contour of the pneumatic tire based on the natural equilibrium shape is originally different from the equilibrium shape, the carcass contour at the main body centerline 6 radially outside the maximum width position M of the carcass is 6
It is known that c is very close to the arc of the reference curve V. The present invention can increase the bending deformation in the upper region of the sidewall portion by the technical configuration as described above, and reduce the shearing deformation having an inverse correlation with the bending deformation and having a relatively large energy loss. This makes it possible to reduce the thickness of rubber around the buttress portion, reduce heat generation, and improve durability while reducing rolling resistance as a whole. Moreover, the bead portion 4 is improved in durability as a result of the reduced distortion of the carcass 6 as described above. More preferably, the ratio (R / Rn) may be 0.65 to 0.70.

In this embodiment, as shown in FIG. 2, the pneumatic radial tire for heavy load is such that the carcass main body center line 6c in the tire meridional section changes from the 5% internal pressure state to the 100% When changing to the internal pressure state, the deformation amount fu of the region U outside the maximum width position M in the tire radial direction is smaller than the deformation amount fm at the maximum width position M and substantially zero, and Position M
The deformation amount fd of the region D inside the tire radial direction is larger than the deformation amount fm at the maximum width position.

Thus, the carcass body center line 6c
And the maximum deformation amount fd of the area D in the tire radial direction from the maximum width position M is increased, thereby increasing the rigidity of the bead portion 4 without impairing the durability. As a result, the steering performance can be improved by increasing the cornering power and the like. Note that the deformation amount fm at the maximum width position is 60 to 75% of the fd.
The degree is preferred.

Since the carcass profile deviated from the above natural equilibrium shape has a large distortion, it is apt to be refused from the viewpoint of durability, and has been generally used as a carcass cord for a heavy load tire. When a metal cord has a high rigidity and produces a profile that largely deviates from the natural equilibrium shape, a carcass cord is forcibly bent to cause damage to the carcass cord.

Therefore, in the present invention, the Taber stiffness index α is 35 (g · c) as the carcass cord as described above.
m) or less, more preferably 16 to 33 (g · cm), and a soft and easy-to-work metal cord having a breaking strength of 800 to 1200 (N) (for example, 3 / 0.2 mm + 7 /
By adopting 0.23 mm), there is an advantage that the carcass profile can be easily formed without imposing an unreasonable load on the cord and the productivity can be improved.

The metal cord (7 × 4 / 0.175, or 3 + 9 / 0.0) used in the conventional carcass cord is used.
23) is, for example, a Taber stiffness index α of 40 to 4
8 (g · cm), and the breaking strength is 1300-165
Since it is 0 (N), it is understood that the code is clearly different from the code of the present embodiment.

[0033]

[Example] The tire size is 10.00 R22.5,
Rim size: 7.50 x 22.5 (15 ° deep rim),
Tire of the present invention having an internal pressure of 8.0 kg / cm ² (Examples 1 to 3)
6) and comparative tires (Comparative Examples 1 to 4) not included in the present invention were prototyped, and their performances were compared by the following tests.

(1) Rolling resistance Using a rolling resistance tester, a speed of 80 km / h and a load of 272
The rolling resistance was measured at 5 kgf.
It was indicated by an index of 0. The larger the index, the smaller the rolling resistance and the better.

(2) New bead durability Using a drum tester, under a load of 7200 kgf and a speed of 20
The sample tire was rotated at a low speed of km / h, and the time until the bead portion was broken or the crack became large was measured. The larger the index, the better the bead durability. In this test, since the speed is low, no damage occurs near the buttress portion, and the durability of the bead portion can be checked.

(3) Maneuverability The test tires were mounted on a 2-D4 vehicle (10 tons loaded) with rims assembled, and evaluated by a 100-point method in 5-point increments depending on the driver's sensuality. The larger the value, the better. Table 1 shows the carcass and belt configurations (common to each tire), and Table 2 shows the test results.

[0037]

[Table 1]

[0038]

[Table 2]

As a result of the test, it can be confirmed that the tire of the example has improved bead durability while reducing rolling resistance. When the ratio (R / Rn) is more than 0.95 (Comparative Example 2) and when the ratio (R / Rn) is less than 0.65 (Comparative Example 1), both are bent in the region above the sidewall. The deformation cannot be increased, and the effect of reducing the rolling resistance is small. When the maximum value of the deformation amount f exceeds 2.3 mm (Comparative Examples 3 and 4), it can be confirmed that the bead durability is also poor.

[0040]

As described above, the pneumatic radial tire for heavy load according to the present invention can increase the durability of the bead portion while reducing the rolling resistance. According to the third aspect of the invention, productivity can be improved.

[Brief description of the drawings]

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

FIG. 2 is a conceptual diagram showing a center line of a main body of a carcass according to the present invention.

FIG. 3 is a conceptual diagram showing a center line of a main body of a carcass according to the present invention.

FIG. 4 is a diagram illustrating a Taber stiffness index.

FIG. 5 is a cross-sectional view showing a contour of a conventional carcass.

[Explanation of symbols]

 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6a Carcass main part 6b Carcass turnback part 6c Main part center line 7 Belt layer

Claims (3)

(57) [Claims] A main body extending from the tread portion to the bead portion through the side wall portion and having a folded portion which is folded back around the bead core and is arranged at an angle of 75 to 90 ° with respect to the tire equator. Heavy-duty pneumatic radial tire, comprising: a carcass made of a carcass ply made in the following manner; and a belt layer made up of a plurality of belt plies arranged radially outside the carcass and inside the tread portion, the tire including a tire shaft. In the meridional section, the tire was assembled to the regular rim and filled with the normal internal pressure from the 5% internal pressure state where the internal pressure was filled with 5% of the normal internal pressure.
When the internal pressure state is set to 00%, the amount f of deformation of the carcass body outward or inward is 2.3 mm, which is the maximum value based on the center line of the carcass main body in the 5% internal pressure state.
In addition, in the state of 100% internal pressure, the tire section height H with respect to the tire bead base line
A point B on the carcass body centerline at a distance h of 15% to the outside in the tire radial direction, a line extending from this point B to the tire radial direction outside and intersecting with the carcass body centerline at a point C A straight line N parallel to this line segment BC and tangent to the center line of the carcass body at its maximum width position M; a curvature of a virtual reference arc tangent to the straight line N and having the line segment BC as a chord; The ratio (R / Rn) of the radius Rn to the radius of curvature R of the arc of the shoulder region extending from the point C to the vicinity of the maximum width position on the center line of the carcass body portion is:
0.65 or more and 0.95 or less, and the carcass splice has a Taber stiffness index α per cord of 35 (g · cm) or less and a breaking strength.
A pneumatic radial tire for heavy loads , wherein metal cords having a degree of 800 to 1200 (N) are arranged. 2. The center line of the carcass main body in the tire meridional section is shifted from the 5% internal pressure state to the 100%
%, The deformation amount fu in the region radially outside the tire from the maximum width position M is smaller than the deformation amount fm at the maximum width position M and substantially zero. The heavy-load pneumatic radial tire according to claim 1, wherein the deformation amount fd in a region radially inward of the tire from the position M is larger than the deformation amount fm at the maximum width position M. 3. The carcass ply has a Taber stiffness index.
α is 16 to 33 (gcm)
The pneumatic radial tire for heavy loads according to claim 1 or 2, wherein: