JP2000142023A - Pneumatic radial tire for small truck - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire for a small truck having a flattening ratio of 85% or less capable of enhancing a rut wondering performance and a durability of a belt part without lowering a comfortability to ride and an abrasion resistance. SOLUTION: In a pneumatic radial tire for a small truck having a flattening ratio of 85% or less, a carcass layer 1 comprising at least one layer is laid between a pair of right and left bead portions 6, 6 and a belt layer 2 of two layer or more comprising a metal cord is buried in an outer periphery side of the carcass layer 1 in a tread portion 7. A ground contact width GCW of a tread at the time of a maximum air pressure and a maximum load of JATMA standard is 62-68% of a tire nominal width, a sum width SW of the tire is 142-148% of the ground contact width GCW of the tread and a width of the outermost belt layer 2 is 95-99% of the ground contact width GCW of the tread. A ratio b/a of a gauge a determined from a relation ship of the innermost layer 2 and the carcass layer 1 at a position corresponding to an end of the outermost belt layer 2 and a distance b is set to a range of 8-26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radial tire for a small truck, and more particularly to a radial tire for a small truck having a flattening ratio of 85% or less and simultaneously improving belt durability and rut wandering. It relates to a pneumatic radial tire.

[0002]

2. Description of the Related Art Conventional standard pneumatic radial tires for light trucks generally have an aspect ratio of more than 85%. However, since the regulation on loading by the Vehicle Transportation Law was relaxed, trucks with lower chassis and flattened tires with a flattening rate of 85% or less have been used as means for increasing the load of trucks. However, in the pneumatic radial tire for light trucks, since the tread portion is reinforced by a belt layer made of at least two metal cords, if the flatness is flattened to 85% or less, the tread width is increased with respect to the tire height. As the (belt layer width) becomes wider, the tread portion rigidity increases, and there is a problem that the rudder wandering property and the belt portion durability are reduced as compared with the conventional size tire.

As a measure to improve the rut wandering property, the tread contact width may be narrowed to reduce the tread rigidity. However, the load per unit area of the tread is increased, so that the belt durability is reduced. The drawback is that the wear resistance is further reduced and the wear resistance is also reduced. On the other hand, to improve the durability of the belt portion, the width of the belt layer may be increased, but this time, the rigidity of the tread portion is increased, so that the rut wandering property is reduced and the riding comfort is also reduced. Disadvantage occurs. In other words, rut wandering and belt durability are in conflict with each other, and it is extremely difficult to achieve both at the same time. Doing so was a more difficult problem.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the rut wandering property and the belt durability at the same time without lowering the abrasion resistance and ride comfort while keeping the flatness at 85% or less. It is an object of the present invention to provide a pneumatic radial tire for a light truck capable of performing the above-mentioned operations.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, a pneumatic radial tire for a light truck according to the present invention is provided.
At least one carcass layer is mounted between a pair of right and left bead portions, and two or more belt layers made of a metal cord are buried on the outer peripheral side of the carcass layer in a tread portion for a small truck having an aspect ratio of 85% or less. For pneumatic radial tires, it is mounted on a standard rim of JATMA standard, and the tread contact width (GCW) at the maximum air pressure and maximum load of the standard
62-68% of the nominal tire width, the maximum tire pressure, the total tire width (SW) at the maximum load is 142-148% of the tread contact width (GCW), and the outermost belt layer of the belt layers is The width is the tread contact width (GCW)
95-99% of the gauge (a) between the innermost belt layer and the carcass layer at a position corresponding to the end of the outermost belt layer, and the carcass layer is separated from the innermost belt layer The ratio (b / a) to the distance (b) from the point to the end of the outermost belt layer is set to 8 to 26.

[0006] Thus, the maximum air pressure of JATMA standard,
By specifying the tread contact width at maximum load, the total tire width, and the width of the outermost belt layer, and further specifying (b / a) determined by the gauge between the belt layer and the carcass layer, the abrasion resistance is improved. It is possible to improve both the rut wandering property and the durability of the belt portion without substantially affecting the riding comfort.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail with reference to the accompanying drawings. 1 and 2 illustrate a pneumatic radial tire for a small truck having an aspect ratio of 85% or less according to an embodiment of the present invention. In the figure, 1 is a carcass layer, 2 is a belt layer, 3 is a belt reinforcing layer, 6 is a bead portion, and 7 is a tread portion. Two carcass layers 1 composed of organic fiber cords are mounted between the pair of left and right bead portions 6 and 6. The inner and outer two carcass layers 1 form a cord angle of 75 ° to 90 ° with respect to the tire circumferential direction, and are arranged so that the cords cross each other between the layers. Of these, the inner carcass layer 1 has both ends in the tire width direction folded around the bead core 4 from the inside to the outside of the tire, and its terminal is wound up to the outside and above the beat filler 5. On the other hand, the outer carcass layer 1 is wound down so that both end portions respectively cover the outside of the beat filler 5 and the outside of the folded portion of the inner carcass layer 1. The organic fiber cord constituting the carcass layer 1 is not particularly limited, and examples thereof include nylon, polyester, and aramid fibers.

On the outer peripheral side of the carcass layer 1 in the tread portion 7, two belt layers 2 made of metal cords having a cord angle of 10 to 40 ° with respect to the tire circumferential direction are arranged so that the metal cords intersect each other between the layers. Are arranged over one circumference of the tire. Further, at both ends of the belt layer 2, two belt reinforcing layers 3 each having a reinforcing cord wound endlessly at 0 ° in the tire circumferential direction are arranged. The belt reinforcing layer 3 suppresses the belt layer 2 from rising due to centrifugal force, and contributes to improving the durability of the belt portion.

In the pneumatic radial tire for a light truck according to the present invention, in the above-mentioned tire structure, the belt reinforcing layer is not always necessary, but at least one carcass layer and a belt layer made of a metal cord are provided. It is necessary that at least two layers are provided respectively.
In the present invention, in order to achieve the object of the present invention, in such a basic tire configuration, the following requirements are further applied.
Must be satisfied at the same time.

When the tire is mounted on a standard rim specified in JATMA (Japan Automobile Tire Association) standard, filled with the specified maximum air pressure, and loaded with the specified maximum load, the tire is grounded on a flat road surface. Tread contact width (GC
W) is 62 to 68% of the nominal tire width. The feature is that the tread contact width (GCW) is set to be smaller than that of a conventional tire. If the tread contact width (GCW) is wider than 68% of the nominal tire width, the tread portion rigidity increases, and the rut wandering property is reduced. However, if the tread contact width (GCW) is smaller than 62% of the nominal tire width, the load on the tread per unit contact area increases, and the wear resistance decreases.

Similarly, when the tire is mounted on a standard rim of JATMA standard, is filled with a standard maximum air pressure, and a maximum load specified by the standard is applied, the total tire width (SW) is 142 of the tread contact width (GCW). To 148%. The total tire width (SW) is adjusted to the tread contact width (GC
If it is greater than 148% of W), the tread contact width (GCW) becomes too small with respect to the tire total width (SW), so that the belt portion durability is reduced. However, when the total tire width (SW) is smaller than 142% of the tread contact width (GCW), the side wall portion becomes too short, the effect of absorbing the vibration from the road surface by the side wall portion is reduced, and the riding comfort is reduced. descend.

The width of the outermost belt layer among the plurality of belt layers is 95 to 99% of the tread contact width (GCW). As described above, the tread contact width (GCW) is set to be relatively narrower than the conventional tire, so if the width of the outermost belt layer is smaller than 95% of the tread contact width (GCW), The wear resistance of the tread portion becomes increasingly worse. However, if it is larger than 99% of the tread contact width (GCW),
Since the load on the belt layer end increases, the durability of the belt portion deteriorates.

A gauge (a) between the end of the innermost belt layer and the carcass layer at a position corresponding to the end of the outermost belt layer, and a point P at which the carcass layer starts to separate from the belt layer
To the distance (b) from the edge to the end of the outermost belt layer b /
Set a to 8 to 26. The ratio b / a represents the size (separation angle) at which the carcass layer separates from the innermost belt layer or the size of the triangular rubber layer interposed between both layers.
Is smaller than 8, the separation angle is large and the thickness of the triangular rubber layer is also large, so that ride comfort tends to be reduced. On the other hand, if b / a is larger than 26, the separation angle is extremely small and the triangular rubber layer becomes thin, so that the rudder wandering property tends to be reduced.

[0014]

[Example] 205 / 70R16 with the same tire size
Unified to 111 / 109L LT, tread contact width (G
CW), the total tire width (SW), the width of the outermost belt layer, and the ratio b / a between the gauge a and the distance b, respectively, as shown in Table 1 below. Comparative tires 1 to 8 were manufactured. Drum durability, rut wandering, riding comfort, and abrasion resistance were evaluated for these 14 test tires under the following measurement conditions. The results are shown in Table 1.

Drum durability: An index of belt portion durability, in which each test tire has an air pressure of 600 kPa and a load of 1
Drum diameter 17 at a speed of 120 km / h as 0.69 kN
A running distance was measured when the belt was run on a 07 mm drum until the belt portion was broken. The measurement results are shown as index values with the measured value of the conventional tire being 100. The larger the index value, the better the drum durability (belt portion durability).

Rudder wandering property: Each test tire was mounted on a small truck having a maximum loading capacity of 2 ton under an air pressure of 600 kPa, and evaluated by a feeling test by a test driver when the vehicle was driven out of the rut while traveling on a rutted road surface. The evaluation results are shown as points where the conventional tire has 6 points. The larger the score, the better the rut wandering performance.

Ride comfort: Each test tire is inflated at an air pressure of 600 k.
It was mounted on a small truck having a maximum loading capacity of 2 tons as Pa and evaluated by a feeling test by a test driver when traveling on a road surface provided with unevenness. The evaluation results are shown as points where the conventional tire has 6 points. The greater this score, the better the ride comfort.

Abrasion resistance: Each test tire was compressed to an air pressure of 600 k.
It was mounted on a small truck having a maximum loading capacity of 2 tons as Pa, and the amount of wear after traveling 10,000 km on a test course was measured. The measurement result was evaluated by the reciprocal, and was indicated by an index value with the reciprocal of the measurement value of the conventional tire being 100. The greater the index value, the better the wear resistance.

[0019]

[Table 1] As is clear from Table 1, the tires 1 to 5 of the present invention have improved rut wandering property and drum durability (belt part durability) as compared with conventional tires. In addition, the same ride comfort as the conventional tire was maintained, and the wear resistance was hardly reduced.

On the other hand, since the comparative tire 1 has a tread contact width (GCW) larger than that specified in the present invention, the rut wandering property is reduced, and the comparative tire 2 is smaller than specified according to the present invention. This improves rut wandering,
Abrasion resistance is reduced. The comparative tire 3 has poor ride comfort because the total tire width (SW) is smaller than the stipulation of the present invention. The comparative tire 5 has poor wear resistance because the outermost belt layer has a width smaller than that specified in the present invention. On the contrary, the comparative tire 6 has wide drums and rut wandering properties because it is wide. Further, the comparative tire 7 has the gauge a and
The ratio b / a to the distance b is larger than the specification of the present invention, and
On the contrary, since the comparative tire 8 is wide, no remarkable improvement effect is seen compared with the conventional tire.

[0021]

As described above, according to the present invention, J
Specify the ATMA standard maximum air pressure, tread contact width at maximum load, total tire width, width of outermost belt layer, and innermost belt layer and carcass layer at positions corresponding to the ends of the outermost belt layer. Since the ratio (b / a) of the gauge (a) and the distance (b) obtained from the relationship between
The belt durability and the rut wandering property can be improved without substantially impairing the riding comfort and wear resistance while keeping the flatness at 85% or less.

[Brief description of the drawings]

FIG. 1 is a half sectional view of a pneumatic radial tire for a small truck according to an embodiment of the present invention.

FIG. 2 is a sectional view of an essential part of the pneumatic radial tire of FIG.

[Explanation of symbols]

 Reference Signs List 1 carcass layer 2 belt layer 3 belt reinforcing layer 4 bead core 5 bead filler 6 bead section 7 tread section

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) B60C 9/22 B60C 9/22 A 15/00 15/00 B

Claims (3)

[Claims] 1. An aspect ratio of 85% wherein at least one carcass layer is mounted between a pair of left and right bead portions, and two or more belt layers made of a metal cord are buried on the outer peripheral side of the carcass layer in a tread portion. The following pneumatic radial tires for light trucks are mounted on JATMA standard rims, and the maximum air pressure and the tread contact width (GCW) at the time of maximum load of the same standard are 62 to 68% of the tire nominal width, and the maximum The tire total width (SW) at the time of air pressure and maximum load is 142 to 148% of the tread contact width (GCW), and the width of the outermost belt layer among the belt layers is 95 to 99 of the tread contact width (GCW). %, A gauge (a) between the innermost belt layer and the carcass layer at a position corresponding to the end of the outermost belt layer, and the carcass layer is separated from the innermost belt layer A pneumatic radial tire for a light truck, wherein a ratio (b / a) of a distance (b / a) from a point to an end of the outermost belt layer is set to 8 to 26. 2. The pneumatic radial tire for a light truck according to claim 1, wherein two carcass layers are provided so that carcass cords intersect each other between the layers. 3. The pneumatic radial tire for a light truck according to claim 1, wherein a belt reinforcing layer made of a reinforcing cord extending in a tire circumferential direction is arranged on each outer periphery of both ends of the belt layer.