JPH0655904A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To provide a pneumatic radial tire with enhanced belt durability without lowering wet grip performance or partial abrasion resistant property. CONSTITUTION:When a tire is inflated to the regular inner pressure from the state of noninflation of 5% of the regular inner pressure, the center region defined into the inside of two points P1, P1 separated by distance L determined by 0.25 TW<=L<0.50TW relative to tread grounding width TW on both the right and left sides along a tread part surface from the tread width center point P0 is grown outward in the radius direction. Respective shoulder regions on both outsides from the two points are constracted inward in the radial direction and constituted so as to change a radius of curvature R2 of a region formed between two middle points so as to contain two middle points P2, P2' corresponding to 1/2 of distance between the center point P0 and the shoulder end parts on both the right and left sides less than the radius of curvature R1 at the time of noninflation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire having improved belt durability, and more particularly to a heavy-duty pneumatic radial tire.

[0002]

2. Description of the Related Art A pneumatic radial tire has a plurality of ply belt layers arranged outside of at least one (ply) carcass layer composed of carcass cords arranged in a range of 90 ° ± 20 ° with respect to the tire circumferential direction. However, the shape of the belt layer is stabilized by the tension of these belt layers during inflation. Conventionally, in pneumatic radial tires for heavy loads,
When the rim is assembled to the regular rim and inflated, the tension T in the belt layer is designed to be uniformly distributed over the entire width direction as shown in FIG. Therefore, when the pneumatic radial tire for heavy load is inflated from 5% of the normal internal pressure to the normal internal pressure,
As shown in, in the tire meridian section, the dotted line 11
As shown by the solid line 12, the tread surface at 5% of the normal internal pressure indicated by indicates that the entire tread surface grows substantially uniformly outward in the tire radial direction as indicated by the solid line 12.

However, in the conventional radial tire, since the tension T is uniformly applied to the entire belt layer in this manner, the belt interlayer shearing at the widthwise end portion (edge portion) of the belt layer during running is extremely high. The force acts repeatedly. As a result, heat is generated at the edge portion of the belt layer, separation occurs between the cord and the coat rubber, and there is a problem that the belt durability is reduced.

Therefore, as a measure for suppressing such heat generation at the edge portion of the belt layer, a compound (rubber composition) having a low heat generation property is used as a tread rubber, or the gauge thickness of the shoulder portion is made as thin as possible. It was done. However, when using a compound with low heat generation, there is a problem that wet grip performance (road surface gripping performance on wet roads) is generally deteriorated, and unnecessarily thin gauge thickness of the shoulder part results in uneven wear resistance. There is a problem that the property is deteriorated and the shoulder portion is prematurely worn.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pneumatic radial tire having improved belt durability without deteriorating other tire characteristics, particularly a pneumatic radial tire suitable for heavy loads. To do.

[0006]

In order to achieve this object, the present invention provides that the tread portion inscribes at least one carcass layer over the bead portions on the left and right sides, and the carcass layer has an outer peripheral side in the tread portion. In a pneumatic radial tire in which a plurality of belt layers are arranged on the surface of the tread portion in the tire meridian section, when the tire is inflated from 5% of the normal internal pressure to the normal internal pressure, the tread width Inside the two points P ₁ and P ₁ separated from the center point P ₀ along the surface of the tread portion on both left and right sides by a distance L defined by 0.25TW ≦ L <0.50TW with respect to the tread ground contact width TW. Center area segmented grow on the outer side in the tire radial direction, each shoulder area of the two outer respectively from the two points P _1, P ₁ is contracted on the inner side in the tire radial direction, One the tread width center point P ₀ and center point P ₀ and two middle point P ₂ corresponding to 1/2 of the distance between the shoulder end portion of the left and right sides, respectively,
That P 'the two midpoint P ₂ to include, P _{2' 2} the radius of curvature R ₂ of the area formed between is configured to vary less than the radius of curvature R ₁ at the time of non-inflated Characterize.

As described above, according to the present invention, since the growth direction of the tread surface when inflated is determined, the tension distribution of the belt layer at the time of inflation is made as close to zero as possible at the edge portion, By suppressing the inter-belt shear force acting on the edge portion of the belt layer, it becomes possible to prevent separation. In addition, here, "regular internal pressure" is JATM
It means the internal pressure specified in A (Japanese Tire Standard). "5% of the normal internal pressure" is the internal pressure that keeps the tire mold almost in the same shape (normal state when not inflated).

The structure of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a meridional direction sectional explanatory view of an example of a pneumatic radial tire of the present invention designed for heavy loads. In FIG. 1, a carcass layer 2 is mounted between the bead portions 1 and 1, and the end portions of the carcass layer 2 are respectively folded around the bead core 3 from the inside of the tire to the outside and wound up. ing. This carcass layer 2
Is made of steel cord or organic fiber cord. Two or more carcass layers 2 may be provided. In the tread portion 4, outside the carcass layer 2, four belt layers 5a, 5b, 5 made of steel cord are formed.
c and 5d are annularly arranged over the circumference of the tire.
The first belt layer 5a counted from the carcass layer 2 in the tread surface direction is mainly for improving the bending rigidity of the tread, and its cord angle with respect to the tire circumferential direction is about 40 ° to 75 °. On the other hand, the second belt layer 5b and the third belt layer 5c are mainly provided as tensile strength layers in the tire circumferential direction, and the cord angles thereof are 10 ° to 30 °, respectively, and between the plies. The cords intersect each other and the cord directions are opposite to each other. The fourth belt layer 5d is mainly provided as a protective layer for the inner belt layer and is not always necessary. The cord angle is about 20 °.
Incidentally, the above-mentioned four belt layers 5a, 5b, 5c, 5d
Among them, the second belt layer 5b and the third belt layer 5c have a relationship in which the plies cross each other, but the first belt layer 5a and the second belt layer 5 are
In b, and the third belt layer 5c and the fourth belt layer 5d, the cords may or may not intersect with each other between the plies.

The tire of the present invention thus constructed is
When assembled on a regular rim and inflated from 5% of the regular internal pressure to the regular internal pressure, as shown in FIG. 2, the tread surface changes from the dotted line 11 to the solid line 12 in the tire meridian direction cross section, as shown in FIG. From the center point P ₀ to the point P ₁ having a length L along the tread surface in the shoulder direction, the point P ₁ grows outward in the radial direction of the tire, while from the point P ₁ to the shoulder end 13 (edge) on the opposite side. Shrink inward in the tire radial direction. That is, the tread surface in the center region from the tread width center point P ₀ to the point P ₁ having the length L in the shoulder portion direction grows (expands) outward in the tire radial direction, but from the point P ₁ to the shoulder end portion. The tread surface in the shoulder area up to 13 contracts inward in the tire radial direction. Therefore, the point P ₁ is a point where the tread surface neither grows nor shrinks. Further, the tread radius of the tread surface passing through the tread width center point P ₀ and the center point P ₀ and the midpoints P ₂ and P ₂ ′ between the shoulder end portions 13 and the shoulder end portions 13 respectively is such that before inflation. Will be smaller than.

Further, in the above-described structure, the maximum growth length f ₁ of the center region and the maximum contraction length f ₂ of the shoulder region when inflated to the normal internal pressure are such that f ₁ is larger than 0.5 mm. , F ₂ should be larger than 0.2 mm. As described above, the change in the tread surface when the tire is inflated to the normal internal pressure shows that the center area from the tread width center point P ₀ to the point P _{1 in the} shoulder portion direction grows outward in the tire radial direction. The shoulder region from P ₁ to the shoulder end 13 is made to shrink inward in the tire radial direction, and 3 of P ₀ , P ₂ and P ₂ ′ is used.
By changing the radius of the surface of the central portion of the tread consisting of points to be small, the tension distribution in the tire width direction of the belt layers 5a, 5b, 5c, and 5d is high in the center region as shown in FIG. Tension T at the shoulder edge
Can be substantially zero. Therefore, the shear strain between the belt layers at the edge portion can be minimized.

Further, in the above-mentioned structure, when a load (standard load stipulated by JATMA) is applied to the tire to roll the tire, the change in the shear strain generated between the belt layers is shown in FIG.
As described above, by changing the distance L of the point P ₁ as described above, the shear strain a of the edge portion between the belt layers when no load is applied and the shear strain b of the edge portion between the belt layers when loaded are different, and It can be seen that the difference t also changes significantly.

From the result of FIG. 4, in the present invention, the point P ₁
Ratio of length L to tread contact width TW
Let TW be 0.25 TW ≦ L <0.50 TW. Preferably, 0.25 TW ≤ L ≤ 0.38 TW. In FIG. 4, t is the difference between the shear strains a and b of the edge portion of the belt layer before and after the load is applied to the tire, and has a correlation with the energy loss.
As can be seen from FIG. 4, when L is 0.50 TW or more, the shear strain at the time of the standard load suddenly increases. 0.25T
If it is less than W, the shear strain under standard load does not become large, but it is difficult to make it less than 0.25 TW in terms of tire production.

FIG. 4 shows the tire size 11R 22.5 14
2 is a measurement result of the shear strain at the edge portion of the belt layer for the heavy-duty pneumatic radial tire having the tire structure shown in FIG. 1 by PR. The shear strain of the belt layer edge part here is
It was measured between the second belt layer 5b and the third belt layer 5c, which act as a tension-resistant layer in the tire circumferential direction, and is the portion where the largest shear strain occurs in the belt layer.

In the tire of the present invention having the above-mentioned structure, the radius of curvature R _c of the center region of the carcass line at the time of non-inflation of 5% of the regular internal pressure is set to the maximum width BW of the belt layer when assembled to the regular rim. It can be obtained by setting as follows in relation to. That is, as shown in FIG. 1, a point B on the innermost carcass layer corresponding to the center point P ₀ of the tread and the maximum width belt layer on both sides in the tire width direction from this point B, that is, the belt layer of the belt layer 5b in FIG. 1 / width BW
The radius of curvature _Rc (mm) of the carcass line passing through the three points A and A'on the innermost carcass layer 6 apart satisfies the following formula, and the distance from the points A and A'to both shoulder ends is The radius of curvature R _s (mm) of the carcass line is to be smaller than the radius of curvature R _c . In addition, R
_s is the radius of curvature of the carcass line when the rim is assembled to the regular rim and 5% of the regular internal pressure is not inflated. R _c = C · (W / H) ⁶ (where C is a constant in the range of 500 to 700, W is the tire maximum width (mm) at normal internal pressure filling, and H is the tire cross-section height at normal internal pressure filling ( The radius of curvature R _c of the carcass line set by the above equation is significantly larger than that of the conventional tire, and is characterized by being almost linear. Therefore, when the tire is inflated, the center area of the tread surface grows outward in the tire radial direction, and the shoulder area contracts inward in the tire radial direction. For reference, in the conventional pneumatic radial tire, C in the above formula is in the range of about 70 to 250, so that the entire tread surface grows substantially uniformly outside in the tire radial direction.

[0015]

[Example] Tire size is 11R 22.5 14PR,
Tire structure; Fig. 1, cord of carcass layer 2; Steel cord, belt layer 5a; Steel cord, cord angle 58
°, width 145 mm, belt layer 5b; steel cord, cord angle 18 °, width 175 mm, belt layer 5c; steel cord, cord angle 18 °, width 155 mm, belt layer 5d;
Steel cord, cord angle 18 °, width 70 mm, belt layers 5a and 5b are in the same cord direction as the tire circumferential direction,
5b and 5c are opposite to the tire circumferential direction in the cord direction, and 5c
The tires of the present invention and conventional tires having the following different specifications were manufactured with the same points that 5 and 5d are in the same cord direction with respect to the tire circumferential direction. The belt durability of each tire was evaluated by the measurement method described below. The results are shown in Table 1.

The tire of the present invention. C = 530. W = 265mm. H = 240mm. R _c = 960 mm. R
_s = 75 mm. TW = 188mm. BW = 175mm. When the tire is assembled to the regular rim and inflated from 5% of the regular internal pressure to the regular internal pressure, the position of the point P ₁ of the tread surface is L = 75 mm (L / TW = 0.4),
The center region inside the point P ₁ grows outward in the tire radial direction, and the shoulder region outside the point P ₁ contracts inward in the tire radial direction.

Conventional tire. As shown in FIG. 3, the growth of the tread surface when the tire is assembled on the regular rim and inflated from 5% of the regular internal pressure to the regular internal pressure, the entire tread surface grows outward in the tire radial direction. C = 199. W = 265mm. H = 240mm. R _c = 360 mm. R
_s = 85 mm. TW = 188mm.

Evaluation method of belt edge heat generation : Tires having holes with a diameter of 3 mm from the tread surface were formed in the edge portion of the belt layer 5b having the maximum width and the edge portion of the belt layer 5c located outside the belt layer 5c. It was mounted on a vehicle and run for 2 hours at a speed of 80 km / h under standard load. After running, the belt durability was evaluated by measuring the temperatures at the edge portions of the belt layer 5b having the maximum width and the outermost layer 5c. The evaluation results are expressed as an index with the measured temperature of the conventional tire being 100. As can be seen from Table 1, the tire of the present invention does not have an increase in the temperature of the edge portion of the belt layer as compared with the conventional tire, and the result shows that the tire of the present invention is superior in belt durability to the conventional tire. You can see that

[0019]

As described above, according to the present invention, the change in the tread surface when inflated causes the center area from the tread width center point P ₀ to the point P ₁ to grow outward in the tire radial direction. Since the shoulder region from P ₁ to the shoulder end portion is configured to shrink inward in the tire radial direction, the belt interlayer shear strain acting on the belt layer edge portion is brought into a state close to zero, and therefore durability against separation of the belt layer is achieved. It is possible to improve the property.

[Brief description of drawings]

FIG. 1 is a meridional direction cross-sectional explanatory view of an example of a pneumatic radial tire designed for heavy load according to the present invention.

FIG. 2 is an explanatory view showing a growth direction of a tread surface in a meridional section of a pneumatic radial tire of the present invention when inflated.

FIG. 3 is an explanatory diagram showing a growth direction of a tread surface when a conventional pneumatic radial tire is inflated when a meridional direction is cut.

[Fig. 4] Shear strain (%) and L / TW at the edge of the belt layer
FIG.

FIG. 5 is an explanatory diagram showing a tension distribution of a belt layer in the pneumatic radial tire of the present invention.

FIG. 6 is an explanatory diagram showing a tension distribution of a belt layer in a conventional pneumatic radial tire.

[Explanation of symbols]

1 bead part, 2 carcass layer, 3 bead core,
4 tread portion, 5a first belt layer, 5b
2nd belt layer, 5c 3rd belt layer,
5d First belt layer.

Claims (2)

[Claims] 1. A pneumatic radial tire in which a tread portion inscribes at least one carcass layer over the bead portions on both left and right sides, and a plurality of belt layers are arranged on the outer peripheral side of the tread portion of the carcass layer, the tire comprising: When the tire is inflated from the non-inflated state of 5% of the normal internal pressure to the normal internal pressure, the surface of the tread portion in the meridian section tread width center point P ₀
From the center on the right and left sides along the surface of the tread portion, inside the two points P ₁ and P ₁ separated from each other by a distance L defined by 0.25TW ≦ L <0.50TW with respect to the tread ground contact width TW. The area grows outward in the tire radial direction, the shoulder areas on both outsides of the two points P ₁ and P ₁ respectively contract inward in the tire radial direction, and the tread width center point P ₀ and the center point P ₀ A region formed between the two midpoints P ₂ and P ₂ ′ so as to include two midpoints P ₂ and P ₂ ′ corresponding to ½ of the distance between the left and right shoulder ends, respectively. Pneumatic radial tire configured such that the radius of curvature R ₂ thereof is smaller than the radius of curvature R ₁ when not inflated. 2. In a non-inflated state, a point B corresponding to the tread width center point P ₀ of the carcass layer and the maximum width BW of the belt layer on both left and right sides from the point B, respectively.
The radius of curvature R _c (mm) of the carcass line in the center area formed between the two points A and A ′ including the two points A and A ′ that are separated by 1/6 R _c = C ・ (W
/ H) ⁶ [where C is a constant in the range of 500 to 700, W is the tire maximum width (mm) at normal internal pressure filling, and H is the tire cross-section height (mm) at normal internal pressure filling] Has a size
The pneumatic radial tire according to claim 1, wherein a radius of curvature R _s of the carcass line in the shoulder region on both outer sides of the two points A and A'is smaller than the radius of curvature R _c .