Patent Application
20120234451
1. Field of the Invention
The present invention relates to a pneumatic tire (hereinafter simply referred to as a “tire”), particularly a pneumatic tire suitable for heavy load.
2. Background Art
A radial tire for heavy load holds its shape by a binding force of a belt layer. However, in a tire having low aspect ratio, which is increasing recently, binding force is short in the conventional belt structure, and growth of an outer diameter in a tread shoulder part becomes large by running. The local growth of outer diameter gave rise to the problems of uneven wear in a shoulder part and delamination of belt edge.
In view of the above, a structure which increases binding force by arranging a belt reinforcing layer of small angle at the outside in a radial direction of a main action belt layer is proposed as shown in JP-A-03-200403 (1991). Furthermore, a structure in which a steel cord is arranged in a zigzag state between a marginal part of a belt layer and other marginal part thereof is proposed as shown in JP-A-08-183110 (1996).
However, in the structure shown in JP-A-03-200403 (1991), a certain extent of effect is obtained, but binding force still is short to a tire having low aspect ratio. Furthermore, the structure shown in JP-A-08-183110 (1996) aims at that a cut surface of a steel cord is not exposed at a belt edge. In the case that the number of zigzag is extremely reduced to decrease an angle of a belt, tension which receives load may be too larger than tensile strength of the steel cord, and there is a problem that breakage of a steel cord occurs.
As a result of various investigations in view of the above, the present inventors have developed a tire having improved durability and uneven wear resistance performance and free of occurrence of breakage of a steel cord while holding its shape, by a binding force of a belt layer.
The tire according to the present invention improves durability of a tire by spirally winding and arranging a steel cord of a reinforcing belt layer so as to nearly go around a tire from a marginal part of a belt layer to other marginal part thereof.
Specific constitution of the tire according to the present invention comprises a reinforcing belt arranged in a belt layer which goes around in a tire tread part in a tire circumferential direction, wherein the reinforcing belt comprises plural steel cords arranged in parallel over overall length thereof, covered with a rubber, the steel cord of the reinforcing belt is arranged such that an angle θ between the steel cord and a tire circumferential direction satisfies a range of 0.9πR≦W/tan θ≦1.1πR when a reinforcing belt width is W and a reinforcing belt diameter is R, the reinforcing belt in its developed state shows a parallelogram comprising circumferential direction sides having the same length, parallel to a tire circumferential direction, and inclined sides connecting edges of the circumferential direction sides, a length of the circumferential direction side is a circumferential length πR of the reinforcing belt, a length of the inclined side is a length of the steel cord, a distance of two circumferential direction sides is a reinforcing belt width W, and the steel cord is arranged in parallel to the inclined sides. Where the W/tan θ is smaller than 0.9πR, a hoop effect of the belt is difficult to be obtained. Where W/tan θ is larger than 1.1πR, a circumferential direction component of a steel cord angle becomes large, and breakage of the steel cord may occur by strain.
In the above constitution, two main working belts comprising a steel cord covered with a rubber are arranged up and down in the belt layer which goes around in a tire tread, and the reinforcing belt maybe arranged between the upper and lower two main working belts.
The tire may have a constitution that a diameter of the steel cord of the reinforcing belt is smaller than a diameter of the steel cord of the main working belt. In the case of such a constitution, a thickness of a tire can be decreased, resulting in low generation of heat. As a result, durability is improved.
Furthermore, the tire may have a constitution that a cut angle of the edge of the steel cord of the reinforcing belt is larger than an angle between the steel cord and a tire circumferential direction. The cut angle of the edge of the steel cord of the reinforcing belt is preferably from 20° to 90°. In the case that the cut angle of the edge of the steel cord of the reinforcing belt is 20° or more, a distance between the steel cord edges becomes large. As a result, separations between the steel cord and a rubber occurred at the edge of each steel cord are difficult to connect to each other.
The reinforcing belt may have a constitution that its width is wider than 65% of the overall width of a tire and is narrower than larger width of two main working belts. Where the width of the reinforcing layer is equal to or less than 65% of the overall width of a tire, growth of an outer diameter in a tread shoulder part is not suppressed. On the other hand, where the width of the reinforcing layer is wider than the larger width of the main working belts, the belt edge is located in a region of large deformation during loading. As a result, trouble is easy to occur.
The tire may have a constitution that an aspect ratio of a tire having the reinforcing belt arranged therein is 60% or less.
When the tire according to the present invention has the above constitution, each steel cord in the reinforcing belt has a spiral state nearly going around a tire, and the growth of an outer diameter is effectively suppressed. Furthermore, at the belt edge and in the belt, the rubber between the steel cords appropriately relaxes strain of the steel cord occurred by load applied to a tire. As a result, breakage of the steel cord can be prevented without using a special steel cord. Eventually, occurrence of delamination at the belt edge can be prevented, and a tire having excellent durability is obtained.
The preferred embodiment of the tire according to the present invention is described in detail below by reference to the accompanying drawings.
As shown in
In the first embodiment, when the parallelogram reinforcing belt 10 shown in
The steel cords are provided in parallel to the inclined sides 13 and 14 in
The reinforcing belt 10 is cut at 10° of the cut angle of the edge of the steel cord, which is larger than 6.1° which is the angle θ1 between the steel cord and the tire circumferential direction. Thus, when the reinforcing belt 10 is cut at an angle between the steel cord and the tire circumferential direction of θ1 or more, a distance L between a lower part 17a′ of a cord edge 17a of a steel cord 17 and an upper part 17b′ of a cord edge 17b of the steel cord 17 becomes large as shown in
As shown in
In the second embodiment, when the parallelogram reinforcing belt 20 shown in
The steel cords are provided in parallel to the inclined sides 23 and 24 in
As shown in
In the third embodiment, when the parallelogram reinforcing belt 30 shown in
The steel cords are provided in parallel to the inclined sides 33 and 34 in
The fact that the steel cords of the reinforcing belt are preferably arranged such that the angle θ between the steel cord and the tire circumferential direction satisfies a range of 0.9πR≦W/tan θ≦1.1πR when a width of a reinforcing belt is W and a diameter of a reinforcing belt is R, the fact that the reinforcing belt is preferably arranged between upper and lower two main working belts, and the fact that the reinforcing belt preferably has the constitution that its width is wider than 65% of the overall width of the tire and is narrower than the wider length of the two main working belts, as shown in the above each embodiment are clarified by the following Comparative Tests 1 and 2 in which the tire of Example (1) based on the first embodiment, the tire of Example (2) based on the second embodiment and the tire of Example (3) based on the third embodiment are prepared.
Using the tires according to Examples (1), (2) and (3), Comparative Tests are conducted in the following manners. That is, to confirm durability of the conventional tire, three tires of Examples (1), (2) and (3) according to the present invention, and two tires of Comparative Examples (1) and (2), a tire having a tire size of 445/50R22.5 (tire overall width 445 mm) is used as a test tire, the test tire is mounted to a wheel having a rim size of 22.5×14.00, the wheel is attached to a drum testing machine as air pressure 1,000 kPa, and running test is carried out under the conditions of a speed of 40 km/h and a load of 54.4 kN. Running distance until the tire is broken is measured. The evaluation results are shown by the index in which the conventional example is 100. The results mean that durability of a belt is excellent as the index value is large. To confirm uneven wear resistance performance of the above six tires, after running 80,000 km on a dry road surface, a width of a step wear part occurred in a shoulder rib edge is measured, and the reverse number is indicated as an index. Furthermore, steel cords of the reinforcing belt are extracted from the tire after completion of the durability test, and the presence or absence of breakage of the steel cords is confirmed.
The Conventional Example is that the reinforcing belt in which W/tan θ is 0.9πR is arranged outside in a radial direction of two main working belts C1 and C2, as shown in
Measurement results of Comparative Test 1 are shown in Table 1. In Table 1, the unit of a reinforcing belt width is mm. As a result of Comparative Test, Examples (1), (2) and (3) in which W/tan θ is fallen in a range of 0.9πR≦W/tan θθ1.1πR each are that durability and uneven wear resistance performance are improved as compared with those of the Conventional Example. Comparative Example (1) in which W/tan θ is less than 0.9πR is that durability and uneven wear resistance performance are lowered as compared with those of the Conventional Example. Comparative Example (2) in which W/tan θ exceeds 1.1πR is that breakage of steel cord occurred. Therefore, good results are obtained in Examples (1), (2) and (3) by that W/tan θ is fallen in a range of 0.9πR≦W/tan θ≦1.1πR and a reinforcing belt is arranged between the main working belts C1 and C2.
Comparative Test 2 is conducted in the same manner as in Comparative Test 1, except that W/tan θ in Comparative Examples (1) and (2) and Examples (1), (2) and (3) is 1.0πR and the width of the reinforcing belt is sequentially widened, and durability and uneven wear resistance performance are measured. The measurement results of Comparative Test 2 are shown in Table 2. In Table 2, the unit of the reinforcing belt width is mm. As a result of Comparative Test 2, Comparative Example (1) in which the reinforcing belt width is narrower than any of widths of the main working belts is that durability and uneven wear resistance performance are lower than those of the Conventional Example. Furthermore, Comparative Example (2) in which the reinforcing belt width is wider than any of widths of the main working belts is that durability is lower than those of the Conventional Example. Therefore, good results are obtained in Examples (1), (2) and (3) by that the reinforcing belt width is wider than 65% of the overall width of the tire and is narrower than the wider width of the main working belt C1.
The tire according to the present invention is not limited to the above embodiments, and various embodiments are possible in a range which does not deviate from the constitution described in the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-061196 | Mar 2011 | JP | national |
