JPH03104706A - Steel radial tire for construction vehicle - Google Patents

Abstract

PURPOSE:To improve separation durability at the ends of a belt, and to reduce rolling resistance by constituting a tread reinforcement belt by laminating an extensible protective layer, nonextensible principal layers, and a nonextensible additional layer of a prescribed width, each of which has slantingly arranged cords and a specific breaking elongation, in this order from the radial-directional outside. CONSTITUTION:A tread reinforcement belt 2 is made up of an outermost protective layer 11 consisting of at least one layer of extensible cord, a plurality of principal layers 10 consisting of nonextensible cords on the outside thereof, and an additional layer 12 consisting of a nonextensible cord on the inner side thereof. In the protective layer 11, a high-elongation cord whose breaking elongation is 4.5 to 8% is arranged so as to have an inclination of 20 to 30deg. to the equatorial plane. In the principal part 10, nonextensible cords are arranged so as to have an inclination of 20 to 30deg. to the equatorial plane. The additional layer 12 is constituted by arranging a nonextensible cord in the inclination of 0deg., and also is positioned in the range of 1/2 to 1/5 of the maximum width of the principal layer 10. By this constitution, durability can be improved, and rolling resistance can be reduced.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The conditions for use of steel radial tires for construction vehicles are to improve both load and vehicle speed under the request of improving the productivity of transporting construction materials, ore, waste rock, etc. There is a growing tendency for tires to become more and more severe, and there is a need to improve the durability of the belt end separation in these types of tires in order to significantly reduce rolling resistance.

(Prior art) In order to improve belt durability, a layer of cords arranged at virtually 0 degrees with respect to the tire's equator plane, in particular a rubber coating layer of organic fiber cords, is arranged on the outer layer of the belt so that the tire's equator This was an example of suppressing the diameter or length of a belt by cross-layering rubber-coated cord layers arranged at an angle of 15 to 20 degrees with respect to the plane, but this is mainly used to control the diameter or length of a passenger car tire when running at high speed. Although it has been effective in reducing belt length and edge distortion, heavy-duty radial tires, in which steel cord is used as the main body of the belt, are especially useful for construction vehicles that mainly drive on rough terrain. The effectiveness of the belt in practical use is insufficient, and even if the outer cord of the belt is replaced with a steel cord, the tension load is especially severe on rough terrain, resulting in a state where the residual strength is significantly reduced. This is difficult to fit because there is a risk of the cord breaking due to the tread cut on a certain outer layer of the belt.

On the other hand, especially in flat pneumatic radial tires, between the carcass and the heel, a second belt having a wider width than a belt with non-stretchable or difficult-to-stretch cords arranged virtually parallel to the equator of the tire is used.
Regarding the arrangement of layers, JP-A-59-12440
As disclosed in Publication No. 8, this second layer is made wide to compensate for the lack of rigidity at both trend ends, so strain concentration tends to occur at the heel end, which has increased rigidity, making it difficult to drive on rough terrain. In use, there is a problem with durability due to belt end separation, and when the helt placed on this second layer is made of steel cord, the circumferential tensile rigidity as a whole becomes excessive, resulting in failure on uneven ground. When a tire runs over a rock or other surface, it can cause a burst due to cant, which is still unsuitable.

Furthermore, in Japanese Patent Application Laid-Open No. 54-126306, there is a gap between the shooting carcass and the playing force, which is narrower than the playing force.
In the longitudinal direction of the tire, the outside diameter is determined by arranging a limit tab made by overlapping two cord layers that intersect phase 7E and form a minimum angle F of the breaker other than zero degrees. Although it is disclosed that the circumferential tension caused by this limiter block is larger than the circumferential tension burden on the breaker, it is sufficient to suppress the outer diameter elongation caused by running. , since it does not have circumferential tensile stiffness,
Even if there is an effect of preventing separation at the end of the belt, it is not sufficient and does not have the effect of reducing rolling resistance.

(Problem to be solved by the invention) It is possible to maintain the separation durability of the belt end even when the belt is used under an excessive load on rough terrain, particularly rough terrain where coarse rock fragments are scattered. It is an object of the present invention to propose an excellent steel radial tire for construction vehicles that can realize a significant reduction in rolling resistance.

(Means for Solving the Problems) This invention provides an air-conditioning system in which a tread reinforcing belt having a laminate structure of at least four layers, which surrounds the outer periphery of the crown portion of a carcass made of radially arranged steel cords and serves as a rubber coating for the steel cords, is arranged. In radial tires,
The tread reinforcing helt is substantially inextensible and has an inclined array cord of 20 to 30' with respect to the equatorial plane of the tire.
jS consisting of at least two layers intersecting each other across the equator 1ni, a trunk layer, and an elongation 1'1. 20 to 20 to the equatorial plane of the tire.
consisting of at least one layer of cords arranged at an angle of 30', a protective layer disposed on the main layer, and a middle layer of substantially non-extensible cords arranged at an angle of LO° with respect to the equatorial plane of the tire; , an additional (Jn) layer disposed in contact with the layer closest to the carcass among the main layers, and the additional layer has a width within the range of 1/2 to 1/5 of the maximum width of the main layer. 11' in the crown center area! This is a steel radial tire for construction vehicles, which is specially designed for use in heavy-duty vehicles.

Here, the additional layer is arranged to surround the layer closest to the carcass among the main layers, and the additional layer is arranged between the layer closest to the carcass among the main layers and the carcass. desirable.

Now, Fig. 1 shows the cross section of the steel radial tire for construction vehicles according to the present invention on the left. The sidewall portion or 6 is a bead core, 7 is a bead chafer, and 8 is a rim.

The carcass 1 has, according to custom, a turn-up section 9 in which a radially arranged steel cord rubber covering layer is wound around a bead core 6 from the inside to the outside, and a bead chafer 7 is attached to this turn-up area.

The tread reinforcing belt 2 also has a laminated structure of at least four layers surrounding the outer periphery of the crown portion of the carcass l and rubber coating of the steel cord according to the customary practice. The layer 11 and the additional layer 12 are arranged separately.

The main material JIIWIO is substantially non-extensible (elongation at break: 1
．． 5 to 3.0%, more preferably 1.8 to 2.8%), and the cords are laminated at an angle of 20 to 30 degrees with respect to the equatorial plane of the tire and intersect with each other while sandwiching the equatorial plane. It consists of at least 2N.

The protective layer 11 is made of a so-called high elongation cord having an elongation at break of 4.5 to 8%, preferably 5.5 to 7%, with a tensile strength of 20 to 3
It consists of at least one layer arranged in a 0' tilted arrangement, and when there are two or more layers, they are stacked in a direction in which the cords intersect between the layers.

The additional layer 12 is substantially non-extensible (elongation at break equal to that of the main layer) and consists of a layer of cords arranged at virtually 0° with respect to the equatorial plane of the tire, and is substantially inextensible (elongation at break equal to that of the main layer) and consists of a layer of cords arranged at virtually 0° with respect to the equatorial plane of the tire. It is placed in contact with the layer closest to , but its placement width is
It is located in the crown center region within a range of 172 to 1/5 of the maximum width of the main trunk layer 10.

Regarding the additional layer 12, the arrangement in contact with the layer of the main layer IO closest to the carcass 1 means the arrangement surrounding the layer and intervening within the layer of the main trunk 110, or the arrangement intervening between the layer and the carcass. Furthermore, one of the main layers closest to the carcass I may be hollowed out, and the arrangement may be such that the hollowed out portion occupies the space.

In addition, regarding the cord arrangement of additional layer construction 2, the actual distance of 0° with respect to the tire's equatorial plane means that a large number of cord elements braided into endless loops with the same predetermined diameter are arranged side by side in a concentric cylindrical shape and coated with rubber. In addition to being used in a ring shape, it is also used as a wire ring with a series of tightly wound cylindrical cords coated with rubber, and a pair of right-handed and left-handed wire loops are used concentrically side by side. It also includes cases.

(Function) Since the additional layer is composed of substantially inextensible cords arranged at an angle of 0 degrees with respect to the equatorial plane of the tire, it is possible to significantly increase the circumferential tensile rigidity of the tread reinforcing belt 2 as a whole. Therefore, the outer diameter or length of the tire is hardly changed due to running of the tire, and as a result, the interlaminar shear strain at the end of the tread reinforcing belt 2 is significantly reduced, which significantly contributes to improving the durability of the belt. , resulting in a significant reduction in tire rolling resistance.

However, on the other hand, this suppression of the outer diameter length causes high tension in the additional layer, and the stress range up to breakage is narrow.
When a safety effort such as receiving a cut in the trend part 3 occurs due to riding on a rock, etc., it can be sufficiently buffered only by the main layer 10, and there is a good chance that the cord of the additional Jil 2 will break. Therefore, in order to avoid this, it is necessary to arrange the protective layer 1l on the main layer 10.

Here, it is important that the additional layer 12 consists of only a single layer; if the additional layer 12 is made of two or more layers, the gauge becomes thicker, and by filling in the step, the cross-sectional shape of the main layer 10 is changed. It is necessary to insert a rubber stock to keep it flat (otherwise, air pockets may occur), and as a result the overall gauge of the tread section 3 increases, heat generation increases, and the temperature of the tread section 3 rises. Therefore, disadvantageous heat separation of the tread reinforcing belt 2 is inevitable.

In other words, compared to the limiter block mentioned earlier regarding the conventional technology, the amount of steel cord needed to achieve the same strength is approximately 1/2, which is advantageous in terms of material costs and processes. The circumferential tensile rigidity of the limiter block is greater than that of a two-layer limiter block, and the cost performance is high.

If the arrangement width of the addition 1'512 is too wide, the rubber distortion at the end of the tread reinforcing helt 2 will increase, and it will also be easy to cause ceviel sagging, so the width of the addition 1'512 is the maximum width of the main layer 10.
On the other hand, if it is less than 1/5, it will not be sufficient to suppress the outside diameter I length of the shoulder part when the tire is running, so improving the belt end separation durability will also improve the rolling resistance. It cannot help reduce the

Here, rolling resistance increases significantly because the outer diameter or length of the tire occurs concentratedly at the center of the crown, which increases the strain of the heel end rubber under load, thereby increasing the strain energy of the entire crown. .

The additional layer 12 increases the circumferential tensile rigidity of the tread reinforcing belt 2, making the tread 3 more susceptible to cuts in its placement area, so it is necessary to place it as far away from the surface of the tread 3 as possible. Also, when the tire rides on a rock or the like and bends along the circumference of the trend part, the circumferential tension acts stronger the closer to carcass 1, so in order to avoid cord breakage due to this, carcass 1 It is necessary to keep away from it.

In this sense, it is necessary to select the placement of the additional layer 12 between the carcass and the main layer depending on the usage conditions of the tire, so that the operation of the construction vehicle is relatively slow. If there are many small broken rock fragments and the area is easily covered by them, but it is easy to be cut, the former is the case, and there are many rocks that are too large to be wrapped within the contact area of the tread portion 2. The latter are each more advantageously suited to the field.

In this invention, at least two steel cord layers are used as the main layer, and the main layer is two or more layers laminated with the cord directions intersecting in order to mainly bear the required performance of the belt 2 for reinforcing the trend section. A single layer cannot bring out the desired performance, and if the above cord direction is less than 20 degrees with respect to the tire's equatorial plane, interlayer shear strain at the end of the belt will increase, resulting in poor belt durability. On the other hand, if the angle exceeds 30°, the circumferential tensile rigidity of the belt decreases and rolling resistance increases, making it unsuitable.

For the protective layer 1l, a so-called high elongation cord with a breaking elongation of 4.5 to 8% is used, but when the cord angle defined in the same way as above is smaller than 20°, the interlaminar shear at the belt end Distortion increases and Hert I'1
1 [On the one hand, it has the disadvantage of poor durability, but if it exceeds 30°, the circumferential tensile rigidity of the helt decreases and rolling resistance increases, so it is not suitable.

(Example) The cross-sectional structure of a tire size 18.00 R25 shown in FIG.
Figure 3(a) shows a test tire in which the lamination arrangement of the tread reinforcing belt 2 is slightly different. In (b), a trial was made along with a comparative tire having a stacked arrangement of Helt 2' according to the conventional technology.

Here, the ply of carcass 1 has (7X7)XO. 21
Sudir cord represented by +1 (tensile strength 400
Driving a single layer consisting of 20 kgf/pieces/5cm
The cord angle with respect to the tire's equatorial plane was set at 90°, and the tire was arranged in a radial arrangement.

Regarding the tread reinforcing helt 2, (7 x 7) Xo. 21+1
20 steel cords (tensile strength 400 kgf/cord, breaking strength 2.5%) were used at 20 cords/5 cm.
As the protective layer 11, 18 pieces of (3 x 7) x 0.23 Stino records (bow tension 170 kgf/piece, breaking elongation 6.8%) were used in a length of 75 cm. Both the boat layer 11 and the tire are arranged in such a manner that the cord angle with respect to the equatorial plane of the tire is 23 degrees, and the additional layers are arranged in such a manner that the cord angle is virtually 0 degrees, as shown in FIG. In the example of a), the inclination from the layer closer to carcass 1 is upward to the right, upward to the left, upward to the right, upward to the left, and upward to the right: 3 main layers, 2 protective layers, and a follow-up layer jl'1
In the same figure (b), there is an additional layer 1 between the main layers 10 on the upper right and upper left.
2, the main layer lo on the upper right side and the guarantee layer 11 on the upper left side, making a total of 5 layers, and Figure 2 (C
) is convenient in that the L layer of the main layer 10 closest to the carcass 1 is hollowed out and the additional layer 12 is filled in there, and this is arranged diagonally in a pair of upper right layers sandwiching it on the left and right, upper left, upper right, and upper left. Surrounding the main layer 10 of 4 layers, upper left, upper right, 2
A total of 6 layers are laminated using 8IIJ11 layers.

In addition, the arrangement width W of the additional layer 12 is 0.3 with respect to the maximum width w, sX of the main layer 10 in both cases of FIGS. 2(a) and 2(c).
5 times, and 0.3 times in the case of Fig. 2 (C).

On the other hand, in the comparative example shown in FIG. 3(a), the upper right
Main r# layer 10 consisting of four layers: upper left, upper right, and upper left
' and a protective layer ll with two layers laminated in the order of upper right and upper left
′, and in the comparative example shown in FIG.
In addition to the protective layer 11'' similar to that shown in FIG. 3(a), the center of the crown of the carcass is set at 0% relative to the maximum width W of the main layer 10'' (not shown in the figure) on the inside of the main layer 110''. A so-called ξta block I3 was arranged in which 2N cords were arranged with a steep slope of 5 degrees with respect to the tire's equatorial plane over an arrangement width equivalent to 35w, and crossed each other from the carcass side upward to the left and upward to the right. This is an example.

These test tires were manufactured and subjected to a belt end separation durability test and a rolling resistance test in the following manner.

Wiping test conditions Belt end separation it Ku BK %1 diameter 5II
Each test tire, mounted on a regular rim and filled with the regular air pressure, was run at a running speed of 20k on the indoor drum tester in step 1.
m/h constant, the test was first started with 80% of the normal load to remove residual stress, and after a break-in run, the normal load was applied, and then the load was gradually increased to 10%, and the belt Signs of peeling and cracking at the edges of the tread were detected by detecting bulges appearing near the edges of the tread, and the distance traveled (test time) up to this point was used as the standard for evaluation.

Rolling resistance test on an indoor drum testing machine with a diameter of 5 m at a speed of 10 k++
/h, after running for one hour under regular load, compare the current of the drum drive motor (DC) when forcing the test tire to rotate under regular load and when that load is removed. The difference in current value was used as an index.

The results of the above tests are summarized in the table below.

Next, for the tire of Example 1 with the belt configuration shown in FIG. A summary of the results of investigating the effects on the belt end separation durability when changing over a range of .6 and 5 was obtained as shown in Figure 4.

(Effects of the Invention) According to the present invention, heavy-duty construction vehicles are used that are forced to carry excessive loads on rough terrain, especially rough terrain where coarse and sharp rock fragments are present. The durability of steel radial tires can be enhanced with reduced rolling resistance.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a steel radial tire for construction vehicles, Fig. 2 is an explanatory drawing of the belt structure according to the present invention, Fig. 3 is an explanatory drawing illustrating a conventional belt structure, and Fig. 4 is an explanatory drawing of the belt structure according to the present invention. 3 is a graph showing the influence of the arrangement width of additional layers of a belt on performance. l... Carcass 2... Trend reinforcing belt 3... Tread part 4... Bead part 5
...Side wall part 6...Bead core 10...
・Main layer 11...Protective layer 12...Additional layer Fig. 2 (a) 2 (b) Fig. 3 Fig. 4 0 01 0.2 0.3 04 0.50'' Belt width/maximum Entering belt l1l crystal of

Claims (1)

[Scope of Claims] 1. A pneumatic radial tire in which a tread reinforcing belt having a laminate structure of at least four layers surrounds the outer periphery of the crown portion of a carcass made of radially arranged steel cords and serves as a rubber coating for the steel cords. , the tread reinforcing belt is substantially inextensible, and has a main layer consisting of at least two layers in which cords arranged at an angle of 20 to 30 degrees with respect to the equatorial plane of the tire intersect with each other across the equatorial plane; A protective layer having an elongation in the range of 4.5 to 8% and consisting of at least one layer of cords arranged at an angle of 20 to 30 degrees with respect to the equatorial plane of the tire, disposed on the main layer; Consisting of only a single layer of cords that are substantially non-stretchable and aligned at virtually 0° with respect to the equatorial plane of the tire, with an additional layer disposed in contact with the layer of said main layer closest to the carcass. , the additional layer is 1/2 to 1/2 of the maximum width of the main layer.
A steel radial tire for a construction vehicle, characterized in that the tire is located in the crown center region with a width within the range of 5. 2. The tire according to claim 1, wherein the additional layer is arranged to surround the layer closest to the carcass among the main layers. 3. The tire according to claim 1, wherein the additional layer is interposed between the carcass and the layer closest to the carcass among the main layers.