JPS5926481B2 - Radial tires for large vehicles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to improve the durability and shape retention of radial tires for large vehicles such as trucks and buses.

Conventionally, steel cords have been used for the belt layer of radial tires used for trucks, buses, etc., and rayon, nylon, polyester, or steel cords have been used for the carcass plies, but each has its own characteristics in terms of durability and tire shape retention. It had some drawbacks.

Tires used on trucks and buses are normally filled with air pressure of 5 to 8 kg/cri to support heavy loads, but the tires flex when they touch the ground and return to their original shape when they are not in contact with the ground. The strain inside the tire and the local ply cord tension constantly increase and decrease, and as a result, the tire generates heat internally, causing a rise in temperature.

In addition, when steel wire cords are used for carcass plies, due to the above-mentioned strain and the repeated increase and decrease of cord tension, the steel wire cords may be damaged, especially in the upper part of the bead and part of the tire shoulder where such phenomena are severe. Strain is created between the filaments, and the friction between each filament causes the filaments to wear out.

In addition, the filled air of 5 to 8 kg7/cd permeates into the tire sidewall and accumulates in small gap spaces within the steel cord layer, causing the steel cord to rust due to moisture in the air.

The reduction in strength of the carcass ply cord due to such corrosion phenomenon is greater than the material deterioration caused by repeated deformation during use of the tire, and this is a major drawback to using steel wire for the carcass ply.

Furthermore, tires are subject to various types of trauma while driving, and when the trauma reaches the carcass ply, the moisture that has entered corrodes the steel cord, reducing its strength and adhesion to the rubber. This phenomenon of steel cord is a major disadvantage of steel cord compared to when organic fibers are used in carcass plies.

On the other hand, when an organic fiber cord is used for the carcass ply, since the modulus is low, the tire size increases as the tire runs due to the cord tension caused by the filling air pressure of 5 to 8 kg/crA.

In large vehicles such as trucks and buses, the rear axle is generally used with double wheels, so excessive tire growth will cause the side walls of the double tires to come into contact with each other, making them unusable. There are drawbacks.

Therefore, in order to reduce the tire width after growth, if the tire is vulcanized in advance with a narrow mold, that is, if the H/W (H = tire cross-sectional height, W - tire cross-sectional width) exceeds a certain limit. The durability of tires vulcanized using molds is significantly reduced.

Therefore, from the viewpoint of durability, it is not possible to narrow the tire width in advance.

Considering the advantages and disadvantages of the steel cord and organic fiber cord used as the carcass ply described above, an experiment was first conducted to examine the relationship between the carcass ply cord modulus (kg/mA) used and the growth of tire width.

The tires used in this experiment were 10.0O-20 (standard outer diameter 1042 to 1062 mm, maximum width 283 mm), and the carcass ply was determined by adjusting the carcass ply tension to 1/8 of the cord strength based on the tire's air pressure. It was designed to be.

The ply cords are manufactured so that the strength per unit width is almost equal, and the breaker uses 4 plies of 1.2 mm diameter steel cord.The breaker angle is 55° for the first layer, counting from the carcass side. The remaining three layers are general breaker layers arranged at 18 degrees and alternately intersecting each other.

Therefore, the number of carcass plies was selected depending on the strength of the material used.

The drum test conditions for this experiment were tire pressure 7.2.
5 kg/crA, load 2425 kg, speed 60 km/
h, mileage is approximately 15,000 km.

The results of this test are shown in the relationship curve of FIG.

In Figure 1, the horizontal axis is the carcass ply cord modulus (k
g/xi), and the growth of tire width and 2H are plotted on the vertical axis.
The relationship between the two is shown by taking the growth of +W.

In the figure, C is the carcass ply layer of the tire, B is the breaker layer, H is the tire cross-sectional height, W is the tire cross-sectional width, GW
The curve is a growth curve for a tire cross section of 1 m, indicated by a broken line, H
The W curve is the sum of 2H and W (2H+W) shown by the solid line.
This is the growth curve of

As this experimental result shows, the modulus of the organic fiber cord currently used as carcass ply is 8QOk.
g/- or less, the growth of 2H+W was 4 to 6%, and the growth of tire cross-sectional width W was 10.5 to 17.5%, which showed large growth.

Therefore, the size that can be used as tires for trucks and buses on multiple wheels and without problems after growth is, for example, 10.
For tires of size 00-20, the outer diameter should be 1055 mm and the width should be 270 mm.

Therefore, in order to use conventional strong tire cords made of nylon, polyester, rayon, etc. for the carcass ply and keep the dimensions after growth within the above range, the growth of the tire must be adjusted as shown in Figure 1. Since it is large, the outer diameter of the vulcanization mold is set to 1049.5 mm, and the width is as follows in the case of nylon cord.
225mm, 245 for rayon and polyester
There is a need to make it mm.

That is, the H/W ratio of the vulcanization mold is 1.20 for nylon cord and 1.20 for rayon and polyester.
It should be around 11.

However, this H/W ratio affects the durability of the tire, and the tire must be manufactured according to a certain range of standards.

Next, FIG. 2 shows the results of investigating the relationship between the H/W ratio of the vulcanization mold and the tire durability caused by this ratio.

The drum test conditions for this experiment were an air pressure of 7.5 kg.
/cri1 speed 100 km/h, load 2425
The tests were conducted under the condition of 88% kg x 88%, and the mileage until the breaker layer peeled off was compared using an index.

The structure of this experimental tire was as shown in FIG. 1, and was made of steel cord and nylon cord.
The experiment was carried out over the range of the above modulus codes, and the H/W ratio was changed.

The durability is expressed by comparing the tire durability index with H/W=1.01 as 100.

In the figure, the H/W ratio of the vulcanization mold is plotted on the horizontal axis, and the tire durability index is plotted on the vertical axis.

As this relationship curve shows, the H/W of the vulcanization mold is 1.0
When it reaches 6 or more, durability decreases rapidly.

Therefore, the H/W ratio is preferably 1.06 or less.

This H/W ratio is based on the tire size specification after running growth and the carcass ply cord modulus (kg/1n
77L), the H/W of the mold is automatically determined from the width growth (%) due to its modulus and the growth % of 2H+W.
is calculated, H/W of the mold = 1.06
In the case of , the modulus of the carcass ply cord is 200
It is about 0kg/-, and when H/W=1.06 or more, that is, 2000kg/7n7? In the case of a low modulus of less than L, the durability will be significantly reduced, so carcass ply cord should be
00kg/mt? This indicates that a high modulus cord with a higher modulus than is required.

Therefore, a carcass ply cord having a modulus of 2,000 kg/- or more can be used based on the durability index, but it is more preferable in the present invention to use a carcass ply cord with a modulus of 2,500 kg/- or more.

This invention solves the disadvantages of steel cord.
When using a high modulus fiber cord and using it on a double wheel as mentioned above, there are issues of contact between tires and the H of the vulcanization mold.
/W ratio within a certain standard range, the rubber quality around the fiber cord was investigated, and a pneumatic tire that satisfies both the problem of tire durability was investigated.

In other words, we use a vulcanization mold that does not have durability problems caused by the H/W ratio of the tire, increase durability by selecting a rubber material that is compatible around the fiber cord, and increase the durability of the high modulus fiber cord. The purpose of this invention is to provide a pneumatic tire that is free from the risk of contact with two-wheeled tires due to selection, and as stated in the header, provides a pneumatic tire that is excellent in durability and tire shape retention.

For example, in the case of a tire size of 10.00-20, a vulcanization mold with an outer diameter of 1049.5 mm, a width of 259 mm, and a H/W of 1.05 mm is used, and the fiber cord used for the tire carcass layer) y is used. If an organic fiber cord with a modulus of 2500 kg/in is used, the growth of 2H and W will be 2% and the growth of the convergence will be about 4% (see Figure 1 AtB), so the outer diameter after growth will be 1055 mm and the width. is 270 degrees, and a practically satisfactory tire can be obtained.

Therefore, in this invention, the substitute modulus is 2500 kg.
The first characteristic feature is that an organic fiber cord of /- or more is used in the carcass ply.

Also, outer diameter 1049.5mm, width 265mm, H/W
Using a medium 1.02 vulcanization mold, 37
If a cord modulus of 50 kg/ma and 4800 kg/m4 is used, the dimensions after running will be approximately 1055 mm in outer diameter, 270 mm in width, and 268 mm.

Regarding durability, the second requirement is the characteristics of the rubber in which the fiber cord is embedded.

Currently, the 100% modulus of embedded rubber used in carcass ply cords such as nylon, polyester, and rayon is approximately 15 to 35 kg/cwt.

But code modulus 2500'Q? If an organic fiber cord of /ma or more is buried in rubber with a 100% modulus within the above range, the modulus of the rubber will be insufficient, so a small peeling effect will occur in a part between the cord and the rubber during running. Durability tests have revealed that cracks occur in some parts of the rubber, causing failure.

In this invention, the modulus of the carcass ply cord is 25.
The second characteristic feature is to improve the durability of the tire by setting the 100% modulus of the embedded rubber of the carcass ply cord of 00 kg/m4 or more to a range as shown in the following formula.

That is, the cord diameter is DlnllL and the cord strength is T.
kg, the carcass ply cord embedded rubber is 100
It is desirable that the % modulus (Md100%) is in the range of .

In the formula, D-cord diameter (g), T-cord strength (kg)
It is.

However, 100% modulus of rubber means 100% rubber.
It is the elastic modulus of rubber measured and calculated during elongation (twice the original length), and the unit is kg/crA.

In addition, in order to find the minimum required 100% modulus of the rubber around the T/D and ply cord, 10.0
OR20, 14PR tires are filled with an air pressure of 9 kg/rst, which is higher than the normal air pressure of 7 and 25 kg/crA, in order to accelerate the failure situation of the tires, and 4 types with different 100% modulus (22, 27, 35, 43kg/c
Durability indoor test (st) rubber was used as a parameter (
The results of the drum running test are shown in Figure 3.

The selection of carcass cord modulus in Fig. 3 is 2500 kg/mi and 5100 kg/mi.
This study was carried out within the following scope.

For cord modulus of 2500 kg/-, cord strength T = 145 kg, 63 kg, 42 kg, cord diameter D = 1.2 mrn, 0.8 mm, 0.65 m1
T/D = 121.78.8.65 For cord modulus of 5100 kg/mi, cord strength T = 180 kg, 82 kg, 55 kg - cord diameter D = 1.2 mm 10.8 mm, 0.65 mm.

T/D = 150.103.84.6 As mentioned above, for the T/D value at a carcass cord modulus of 2500 ky/m4 or more, use a rubber within the range according to the formula for calculating the 100% modulus of the rubber of this invention. By doing so, we found out how to achieve the required mileage.

The behavior of the tire in such tests is due to deformation due to load, increase in cord tension, and pressure from the inner tire surface due to the air pressure inside the tire.If the above 100% rubber modulus is low, the rubber near the inner surface of the tire becomes ply The cord is permanently deformed as it moves into the tire through the gap, and the rubber layer on the inside surface of the tire that is in contact with the ply cord becomes extremely thin.Finally, the rubber and cord separate at this part, and the rubber part Cracks occur.

Approximately 15,000k on the drum under the above drum test conditions
It is clear from past experience that if there is no abnormality during Wl driving, no failure will occur during actual vehicle driving.

Therefore, from Figure 3, 15,000 km. If we calculate the 100% modulus of the rubber that can be run as the lower limit, it will be as follows.

Next, in order to find the upper limit of the 100% modulus of rubber, 10. C) With OR20,14PR tires, 2 kg lower than the normal air pressure to facilitate the failure situation.
The results of an indoor durability test conducted at an air pressure of /crA are shown in FIG.

It is clear from past experience that when the ply cord adhesive force retention rate drops to 70% under these conditions, a tire that has already been traveled for more than 2000 m can withstand use even in actual vehicle driving.

If a rubber with a higher modulus than necessary is used, the stress at the interface between the ply cord and the rubber increases due to load deformation, and the adhesive force between the cord and the rubber decreases significantly during running.

From Figure 4, 100 rubber that can run for more than 7n in 2000
When calculating the % modulus, it becomes.

For example, code modulus 5100 kg/mlA,
Cord diameter D = 0.8 mm, :7-cord strong T
= 82 kg ply cord is used for the carcass, and the modulus of the rubber in which the carcass is buried is 20 kg/crA, which is currently widely used, and 35 to 61 kg/cn based on the calculation formula of this invention. Among the range, the durability indoor test result when using 100% modulus rubber of 45 kg/crti is 10.0OR2
0.14 PH tire, the former had cracks in the rubber at the upper part of the bead, at the separation between the cord and the rubber, and at the inner surface of the tire in a part of the shoulder.

With the latter tire of this invention, no abnormality was observed even when running at approximately 15,000 kWl.

Further, when a rubber with a 100% modulus of 75 kg/crtH was used, the adhesive strength retention rate after running 2000 km was reduced to 62%, indicating a decrease in durability compared to the tire of the present invention.

As explained above, the tire of the present invention exhibits excellent effects, and in order to obtain a suitable tire with excellent durability and tire shape retention, the modulus of the organic fiber cord should be increased to 2500 kg/m17. Based on the above, it is necessary to set the 100% modulus of the rubber in which it is embedded within the range determined by the above formula.

[Brief explanation of the drawing]

Figure 1-A shows the carcass ply cord modulus (k
g/xi), the growth (%) of the tire width (W), and the tire width after running (= GW). Figure 1-B shows the carcass ply cord modulus (kg
2H+W diagram of platinum mold. Figure 2 is the relationship curve between the H/W ratio of the tire vulcanization mold and the tire durability index, and Figure 3 is the relationship between the ratio of ply cord strength/ply cord thickness 11 and tire mileage. The curve shown in FIG. 4 is a relationship curve between the T/D and the running distance until the ply cord adhesion retention rate decreases to 70%.

Claims (1)

[Scope of Claims] 1. In a pneumatic tire having a pair of beads and a carcass layer fixed to the beads and extending parallel or almost parallel to the radial direction of the tire, the carcass layer has a weight of 2,500 kg/- or more. A radial tire for a large vehicle, which uses an organic fiber cord with a modulus of Modulus (kgloA) D...Cord diameter (im) T...Cord strength (kg).