JPH07232510A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE:To improve a cut resistant property of a tread part without lowering anti-shock burst performance by integrating an angle forming a tire equatorial surface of a cord of a first belt and a second belt nearest to a carcass layer between the tread part and the carcass layer of a radial tire and the extending direction. CONSTITUTION:This is a pneumatic radial tire laminating a belt layer 3 formed in a ring shape by way of aligning a plural number of steel cords between a tread part 1 and a carcass layer 2 in four layers, and when the belt layer at a position nearest to the carcass layer 2 to the belt layer at a position nearest to a tread rubber 4 are called as first to fourth belt, the extending direction and an angle of the cord of each of the belt layers are integral as R20-R20-L20-L20 from the first belt. 1 (Alphabets show right or left extending direction against a tire equatorial surface of the belt cord.) Generally, cut resistant performance is improved after anti-shock burst performance is maintained as a tire for a good road.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty radial tire mounted on a truck or a bus and used particularly under rough roads such as unpaved roads and gravel roads. Regarding improvement of cutting performance.

[0002]

2. Description of the Related Art The extension direction of a cord forming a carcass layer is approximately 90 degrees (radial direction) with respect to the equatorial plane of a tire, and a belt having high rigidity is provided on the carcass layer. In a radial tire in which the layers are arranged in a ring shape, there is a tendency that the tread portion is essentially susceptible to crack damage (so-called cut) by stepping on foreign matter, stones, etc. on the road surface during traveling. For this reason, in radial tires for heavy-duty vehicles, which are especially used for running on rough roads, it has been attempted to reduce the bending rigidity of the belt portion as a means for improving the cut resistance. For example, R50-R20-L20-L, which is a belt structure for good roads that has been generally adopted in the past.
20 (alphabet indicates the extending direction to the right or left of the belt cord relative to the equatorial plane of the belt, and the number indicates the angle to the tire equatorial plane of the code) to improve insufficient cut resistance. Therefore, the following cut resistant belt structure has been adopted. Conventional cut resistance improved belt structure example; (1) R20-L20-L20 (2) R50 (narrow belts are arranged at both ends of the tread)-
R20-L20-L20 (1) is intended to reduce bending rigidity by removing the first belt from the above-described good road belt structure. (2) is
When the tire gets over bumps such as foreign matter on the road surface, we aimed to reduce the rigidity of the central part of the tire tread to improve EP performance, which is a typical characteristic that represents the amount of impact force that the tire receives from the bumps. It is a thing.

[0003]

However, in the above-mentioned conventional belt structure having improved cut resistance, the bending rigidity of the belt is certainly lowered, the EP characteristics are improved, and the cutting is less likely to occur. On the other hand, since the tensile rigidity of the central portion of the belt is lowered, the tread portion is shock-barred due to the belt cord of each belt layer being cut due to the large deformation of the tread portion and the belt portion that receive from projections such as foreign matters. There is a problem that durability is deteriorated against a strike (a tire is damaged by an impact).

The present invention provides a heavy-duty pneumatic radial tire having a belt structure which improves the cut resistance of the tread portion without deteriorating the shock burst resistance under running conditions including rough road running. It is an object.

[0005]

In order to achieve the above object, in a heavy duty pneumatic radial tire of the present invention, as described in claim 1, a tread portion and a carcass layer of a toroidal tire. In a belt structure in which at least four belt layers in which a plurality of rubber-coated cords are arranged in a ring shape are laminated between and, the cord of the first belt closest to the carcass layer side is formed. The angle formed with the tire equatorial plane is substantially the same as the angle formed with the tire equatorial plane of the cord of the second belt adjacent to the first belt, and the cord of the first belt is
The extension direction of the cord is the same as the extension direction of the cord of the second belt. The crossing angle formed by the first belt and the second belt is assumed to be a projection foreign matter of any shape that the tire encounters on the road surface, and is 5 degrees from the inventor's many past experiences in practical use of the tire. It is preferably within. When the intersecting angle is 5 degrees or more, the bending rigidity of the belt in each direction tends to increase, and the tire is likely to be cut when riding on projection foreign matter. Therefore, this intersection angle is 5
Within the range, the angle formed by the code of the first belt and the tire equatorial plane is substantially the same as the angle formed by the code of the second belt and the tire equatorial plane.

[0006]

In the belt structure of the present invention, at least four or more belt layers are provided to withstand a large impact input from the road surface on rough roads, and the code angle of the first belt is
Since the cord angle is substantially the same as the cord angle of the second belt and is in the same direction, on the tire inner surface side (carcass side) that receives the largest bending stress when the protrusion is pushed into the tread portion, The first belt and the second belt are arranged so as not to intersect with each other, and as a result, the bending rigidity is small and sufficient flexibility can be exhibited against protrusions of various shapes and foreign matter.
Therefore, when the tire rides on the protrusions or foreign substances, deformation occurs such that the tire tread rubber and the belt integrally wrap these protrusions or foreign substances to reduce the impact force (projection reaction force) from the protrusions or foreign substances. . As a result, the local tension applied to the tread rubber is reduced, and the cut is less likely to occur. On the other hand, in the conventional tire, since the crossing angle between the first belt and the second belt is large, the flexural rigidity of the belt layer located on the tire inner surface side is large and the tire lacks the ability to wrap projections or foreign matter on the road surface. Is flipped up and receives a large impact force (projection reaction force), and the relatively soft tread rubber receives a large local tension between the rigid belt and the hard road surface based on the impact force, causing crack damage. It tends to occur.

Further, the belt structure according to the conventional cutting improvement technique, that is, R20-L20-L20 or R50.
In the case of (narrow width) -R20-L20-L20, if the outermost belt cord is cut due to running on a rough road,
The remaining belt layers can resist the tire internal pressure and the external force from the road surface. In the tire center part, there are only two R20-L20 cord crossing layers, and this crossing layer is When a protrusion or foreign matter is pushed into the tread, the bending stress becomes the largest, and it is located closest to the inner surface of the tire, resulting in a large tensile stress state (in other words, a tension state of the thread) and the impact during tire rolling. When subjected to specific dynamic stress, the cord is in a state of being easily broken. on the other hand,
In the belt structure of the present invention, the intersecting layer (R20-) that holds the shape of the tire against the filling internal pressure and the external force from the road surface.
L20) is always composed of a second belt and a third belt, and the second belt is located at a position closest to the inner surface side of the tire where the bending stress is greatest when protrusions or foreign matter are pushed into the tread portion. The crossing layer (R20-L20) is not arranged because the first belt layer having the crossing angle of ± 5 degrees or less and which does not substantially become the crossing layer is arranged, so that the crossing layer has a large tensile stress state (so to speak, a yarn). The structure is such that the shock burst of the tire is unlikely to occur even if it receives a shocking dynamic stress when the tire rolls.

[0008]

EXAMPLES The present invention will be specifically described below with reference to examples. The tire of the example was experimentally manufactured with a tire size of 1000R20, 14RP. The belt structure of the embodiment has a ring-shaped belt in which a plurality of steel cords are arranged between the tread portion (1) and the carcass layer (2) of the tire as schematically shown in FIG. It is a laminate of four layers (3).
Here, the belt layer closest to the carcass layer will be referred to as the first belt in the following order, and the belt layer closest to the tread rubber (4) will be referred to as the fourth belt. Further, the cord extending direction and the angle of each belt layer are R20-R20-L20-L20 in order from the first belt according to the present invention. Further, in order to carry out a comparative test to be described later with the tire of this example, a tire of a comparative example according to a conventional technique was prototyped. The belt structure of Comparative Example (1) is mainly used for good road tires as described above.
As shown schematically in FIG. 1, the tire of the embodiment of FIG. 1 and the belt layer have the same cross-sectional shape, the type of cord and the material of the covering rubber, and the number of laminated layers are the same. Unlike the present invention, the angle is R50-R20-L in order from the first belt.
20-L20. Further, the belt structure of Comparative Example (2) is a conventional cut resistance improved belt structure, and as shown schematically in FIG. Although the material of the covering rubber is the same, the number of laminated belts is three, and the extending direction and the angle of the cord of each belt layer are R20-L20-L20. Further, in the tires of these comparative examples, all the tire constituent members other than the belt structure have the same specifications and materials as the tires of the examples.

Next, in order to verify the effect of the belt structure of the present invention, a comparative test was carried out using the tires of the above-mentioned examples and comparative examples. First, in order to confirm the cut resistance of the tire tread rubber, the tire is pressed against a hemispherical steel projection, and the impact absorption capacity (cut resistance) of the tire is evaluated by the amount of load (projection reaction force) received by the projection. did. Specifically, tires 1000R20, 14PR filled with JIS standard normal internal pressure are attached to the Amsler compression tester, while a hemispherical projection made of steel having a predetermined radius is fixed on the lifting table of the Amsler tester, The central portion of the tread portion of the tire is pressed against the protrusion, and the load received by the protrusion is measured as the protrusion reaction force. A tire having a small protrusion reaction force has a large impact absorption capacity and is advantageous in cut resistance. From the results shown in FIG. 3, the protrusion reaction force received by the tire of the belt structure of the example and the tire of the comparative example (2) is small for various protrusion radii, and therefore the tread portion of the tires of these two tires is not cut. It can be seen that the generation can be sufficiently suppressed. Further, the number of cuts that penetrated the tire tread rubber and reached the belt was measured and compared between the example tire and the comparative example (1) tire by mounting the tire on an actual vehicle and running on a bad road. Figure 4
As shown in, tire size 1000R20,14PR,
After running 30,000 km on a rough road under the conditions of an internal pressure of 9 kg / cm ² , a load of 250% in accordance with JIS standard, and a dump truck mounted on all positions of two rear wheels, the tire of the example is the tire of the comparative example (1). It was found that the number of cuts that reached the belt was extremely small compared to the above, and it was very excellent.

Next, in order to confirm the shock burst resistance of the tire, the tire was attached to an Amsler tire compression tester, and a round bar having a diameter of 19 mm was erected and fixed on the floor surface of the lower surface of the tire. Destruction energy from the load applied to the tire shaft and the moving distance of the tire shaft until the center of the tire tread is pressed to the top and the tread rubber and belt are penetrated.
(So-called plunger energy) was measured. As shown in FIG. 5, the results show that the tires of the examples of the present invention maintain the same breaking energy as the tires for good roads of the comparative example (1). On the other hand, the breaking energy of the tire of Comparative Example (2) having the improved cut resistance structure according to the prior art is reduced by 20%, which is disadvantageous to the tire shock burst.

[0011] In summary of the above test results, the good road tire of Comparative Example (1) is not capable of running on bad roads in terms of cut resistance, and the conventional example of Comparative Example (2) has the same cut resistance. In the tire having the improved structure, good results can be obtained in terms of cut resistance, but it is disadvantageous in shock burst resistance and is not suitable for running on rough roads. It was confirmed that while maintaining the same strike performance as that of a tire for good roads, the cut resistance was further improved and it was able to withstand running on bad roads.

Under the condition that shock burst resistance is not so important as running on bad roads, for example, on running on a semi-good road where the impact load from the road surface is relatively mild, the central portion of the tire of the first belt in the above embodiment is set. A belt structure whose cross section is schematically shown in FIG. 6 that has been omitted can also be used as the category of the present invention. In this case, the shock burst resistance performance is located midway between the tire having the conventional cut resistance improvement structure described in [Prior Art] and the tire of the above embodiment, and the cut resistance performance is the same as that of the above embodiment. Will be equivalent.

[0013]

With the belt structure of the present invention, the level of shock burst resistance performance is maintained at the same level as the belt structure for tires for good roads, which has a proven track record in this respect, and at the same time, it has extremely excellent cut resistance performance on rough roads. It is possible to obtain an excellent radial tire for heavy loads.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a belt structure of the present invention.

FIG. 2 (a) is a schematic sectional view of a belt structure of Comparative Example (1) according to a conventional technique.

FIG. 2 (b) is a schematic sectional view of a belt structure of Comparative Example (2) according to a conventional technique.

FIG. 3 is a diagram comparing projection reaction forces of belt structures.

FIG. 4 is a diagram comparing the occurrence states of tread cuts caused by actual vehicle running.

FIG. 5 is a diagram comparing the breaking energy of each belt structure.

FIG. 6 is a schematic sectional view showing another embodiment of the present invention.

[Explanation of symbols]

 1 tread part 2 carcass layer 3 belt layer 4 tread rubber

Claims (1)

[Claims] 1. A belt structure formed by laminating at least four belt layers in which a plurality of rubber-coated cords are arranged in parallel in a ring shape between a tread portion and a carcass layer of an annular tire. In, the angle formed with the tire equatorial plane of the code of the first belt closest to the carcass layer side is substantially the same as the angle formed with the tire equatorial plane of the code of the second belt adjacent to the first belt. A heavy-duty pneumatic radial tire having a belt structure, which is the same and in which the extending direction of the cord of the first belt is the same as the extending direction of the cord of the second belt.