JPH0495504A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE:To improve groove-crack resistance and operating stability in a case where grooves on the tread part are deepen to prolong their life by devising a structure of belt layers consisting of four belt layers containing at least one set of cross-ply layers, and specifying the relationship between the groove-depths of plural main grooves. CONSTITUTION:In a cross section of the tread part T, four belt layers 8-11 are arranged on a carcass layer 7. In this case, first belt layers 8 most close to the carcass layer 7 are made up of steel cords, and arranged separately on both right and left sides. Second and third belt layers 9,10 are made of thick steel cords having a tensile strength of 280 to 300 kg, and form cross-ply layers in which the cords of both the layers cross each other Further, respective groove-depths t1, t2 of main grooves in the circumferential direction of the tire are set to meet the relationship I in relation to the groove-depth of the main groove in the cross-sectional direction of the tire.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a heavy-duty air conditioner with improved group crank resistance and handling stability when the grooves in the trend portion having a block pattern are deepened to extend the life. Regarding radial tires.

[Conventional technology]

Generally, in radial tires that have a belt layer made of steel cords placed in the trend part, the tread part is strengthened by the hoop effect, and at the same time, the movement of the trend when the tire contacts the ground is suppressed, so the amount of distortion at the groove bottom is small. .

For this reason, in the case of radial tires, it has been thought that group cranks, which frequently occur in tires with a bias structure, are less likely to occur.

However, in recent years, the groove depth of the block pattern heavy-duty pneumatic radial tires used as the rear wheels of trucks, buses, etc. has become increasingly deeper due to the market demand for longer life. It is true that increasing the groove depth will extend the wear life of the tire, but it has been found that when the groove depth exceeds 20 mm, unexpected group cranking occurs even in radial tires. In other words, as the groove depth increases, the center of gravity of the block in the trend section becomes higher, and even with the hoop effect of the steel belt layer described above, it becomes difficult to suppress the movement. As a result, the amount of strain occurring at the groove bottom increases, leading to group cracks.

Another problem is steering stability due to fluctuations during driving. As mentioned above, when the groove depth is increased and the center of gravity of the block is raised, a phase delay occurs in the transmission of the deformation of the trend surface, which increases the fluctuation phenomenon during running.
A problem has arisen in which the steering stability deteriorates significantly.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heavy-duty radial tire that suppresses the occurrence of group cracks and instability of handling due to the flaking phenomenon even when the groove depth is increased to increase wear life.

[Means to solve the problem]

The heavy-duty radial tire of the present invention which achieves such an object has five block rows each consisting of blocks separated by a main groove in the circumferential direction of the tire and a main groove in the cross-sectional direction of the tire arranged in the trend part. A radial tire in which the groove depth of the main groove in the cross-sectional direction is 20.0 mm or more, and has at least four belt layers including a pair of cross-ply layers in the area sandwiched between the carcass layer and the tread part,
The one set of cross-ply layers has a tensile strength of 280 to 300.
Kg thick steel cord, the belt layer closest to the carcass layer is made of steel cord, and the belt layer is separated on the left and right, and the main groove in the tire circumferential direction in the center part is made of steel cord. Depth 11 and groove depth tl of the main groove in the tire circumferential direction of the shoulder portion are 0.5≦1 with respect to the groove depth of the main groove in the tire cross-sectional direction. /1
≦0.7・・−・・・−・−−−−−1・−(1)0
．． 8≦tZ/l ≦0.9----------------------
- This can be achieved by satisfying the relationship (2).

The present invention is directed to a heavy-duty radial tire having five rows of blocks provided in its tread. This is because if there are four rows of blocks in a heavy-duty radial tire, the shape of the blocks is difficult to deform to a large extent, and therefore cannot be the object of the present invention. In addition, if the number of block rows is three or less, the number of grooves decreases and wet performance such as drainage performance deteriorates, resulting in poor marketability. Furthermore, if the number of block rows is six or more, the actual ground contact area will decrease, and even if the depth of the grooves is increased, the wear life of the tire cannot be improved.

FIGS. 1 and 2 show representative examples of heavy-duty radial tires according to the present invention.

A main groove 1 in the tire circumferential direction E-E' and a main groove 2 in the cross-sectional direction of the tire are formed in the tread portion, and five rows of blocks 3 are divided by these bidirectional grooves 1.2. Block rows B-IB-2B-3, B-4, and B-5 are formed in the tire circumferential direction.

In the cross section of the tread portion T, there are four belt layers 8 on top of the carcass layer 7. 9.10.11 are located. Among these four belt layers, the first belt layer 8 closest to the carcass layer 7 is preferably arranged in the tire circumferential direction E-
It is composed of steel cords with a cord angle of 40° to 70° with respect to E', and is arranged separately on both the left and right sides. The second and third belt layers 9 and 10 have a tensile strength of 280
Constructed from ~300 icg thick steel cord,
The cords of both layers cross each other at 10° to 30° with respect to the tire circumferential direction to form a cross-ply layer.

The fourth belt layer 11 is made of steel cord or aramid fiber cord, and has a thickness of 10" to 10" in the tire circumferential direction.
The cord angle is 30°.

This fourth belt layer 11 does not necessarily have to be made of steel cord like the other belt layers.

The belt layers 8, which are arranged separately on both the left and right sides, can increase the stiffness in the width direction of the trend from the center part toward the shoulder parts, thereby improving the steering stability. However, the belt layer 8 has a tensile strength of 280 to 300 because it reduces the absolute belt strength at the center part.
Belt layers 9 and 10, consisting of a pair of cross-ply layers constructed from Kg steel cord, compensate for this deficiency. As an example of the steel cord constituting such a belt layer 9.10, for example, the coat structure is 3 + 9.
A code of +15(0,23)''' can be mentioned.

The grooves provided in the tread portion T are such that the main groove 2 in the cross-sectional direction of the tire is 201 mm or more, more preferably 22.2 mm (28/32
'') For such a deep main groove 2, the groove depth t2 of the main groove 1 in the tire circumferential direction that divides the block row B-3 in the center part and the block row B-1 in the shoulder part.
and B-2, and the groove depth tl of the tire circumferential main groove 1 between B-4 and B-5 are based on the relationships of the above-mentioned equations (1) and (2), respectively.

Regarding the groove depth 1 of the tire circumferential main groove in the shoulder area, if 1+/1 is less than 0.5, wet performance such as braking performance on wet roads will be significantly reduced and the practical safety level will not be satisfied. It becomes impossible. Also, 1+/1 is 0
．． If it exceeds 7, the total length of cracks that occur at the groove bottom (length per crack x number of cracks) increases rapidly, exceeding the allowable range of cracks that occur when retreading a tire, and making it difficult to retread the tire. becomes incapable.

Further, regarding the groove depth t2 of the tire circumferential main groove in the center portion, if tz/t is less than 0.8, the wet performance will deteriorate and the practical safety level will not be satisfied. Further, when tz/l exceeds 0.9, the stiffness in the tire width direction of the trend portion cannot be increased sequentially from the center portion toward the shoulder portion, and the stiffness becomes discontinuous.

For this reason, it is not possible to improve the fluctuating feeling during driving, and the steering stability deteriorates.

〔Example〕

In the radial tire having the tread pattern shown in Fig. 1 and the tread section cross-sectional structure shown in Fig. 2,
The groove depth t2 of the tire circumferential main groove 1 in the center part is the same as the groove depth t of the tire cross-sectional main groove 2 in the shoulder part.
．． 2mm, and the groove depth tl of the main groove in the tire circumferential direction at the shoulder part is set to t1/t in equation (1), and each is 0.2
．． Four types of comparative tires changed to 0.40.6 and 0.9■.

Conventional tires (2), (2) and (2) were prepared in which the groove depth of all grooves distributed on the tread surface was 22.2 mm (t+/l = 1.0).

The size of these tires is the same 11 R2
It was set as 2,5-14PR.

A group crack generation test was conducted on each of the comparative tires I, n, III, rV and the conventional tire. The results were as shown in Figure 3.

Group Koo Koo: Size 22.5 x 8.2
Assemble on the rim of 5, 7. Filled with air pressure of OOkgf/cm", attached to the drive shaft of a 10 ton (2-D/4) panel vehicle, and loaded with JIS standard load, it was driven on a paved road (highway 62χ
, - Ship route 24χ, mountain road 14χ) 40-50km/h
The tire was driven for 50,000 km at an average speed of r, and the total length of cracks generated at the bottom of the main groove in the cross-sectional direction of the tire at the shoulder portion was measured.

As can be seen from FIG. 3, the total length of the crank increases rapidly from around 1+/1 exceeding 0.6. In addition, the allowable limit for cracks that occur when retreading tires (
It can be seen that in order to satisfy the requirement (the total crank length is 301 or less), t1/t must be 0.7 or more.

Also, if the groove depth of the tire circumferential main groove is made shallow,
It can be predicted that wet performance will deteriorate. To confirm this, we investigated the wet performance of the five types of tires mentioned above and found that t is half of t (t+/
l = 0.5) or less, the wet performance significantly decreased.

Next, t+/l = 0.6 was kept constant and the groove depth t2 of the center tire circumferential main groove was changed as shown in the table. Types of comparative tires V, VI■ and tires of the present invention I
, II was produced.

The comparison tire (2) was added to these five types of tires, and the group crank test using the actual vehicle, as well as the following handling stability test and wet performance test were conducted. The results were as shown in the table.

Driving skin test shoes: Assembled on a rim of size 22.5 x 8.25, 7. Fill with air pressure of OOkgf/cm2,
Mounted on the drive shaft of a 2-D flat body vehicle, loaded with a JIS standard load, and driven on a highway at a speed of 80 to 1100 K/hr, maneuvering with emphasis on the roll and fluctuation sensations. The sexual stability was evaluated.

The passing level in this case is 71 points to 72 points.

Standing 6 Yu Kamibi Kansei Shun: Built on a rim of size 22.5 x 8.25, filled with air pressure of 7.00 kgf / cm,
Speed 6 on wet road under JIS standard load
The friction coefficient at 0 Kn+/hr was measured. The measurement results were expressed as an index value, with the measured value of the comparative tire ■ being set as 100.

As shown in the table, there was no significant difference in the occurrence of cracks in the main groove in the cross-sectional direction of the tire in the shoulder area.

Regarding the steering stability, the comparative tire (2) has the worst groove depth t2 of the main groove in the tire circumferential direction at the center portion, which is the same as the groove depth t of the main groove in the cross-sectional direction of the tire at the shoulder portion. However, the comparative tires (2) and (3), in which the t2 was relatively shallow, did not show a significant decrease. This is because the comparative tire (2) had discontinuous stiffness in the tire width direction, so the movement of the tread surface at the time of contact with the ground lacked lance.

Furthermore, for comparison tires ■ and ■, the total stiffness in the width direction of the tire including the belt layer and tread portion is almost uniform, and the fact that there is no discontinuity in stiffness does not have much influence on the evaluation results. It can be said that there was no impact. Therefore, for handling stability, the stiffness in the tire width direction in the trend section must be uniform, or the stiffness must increase sequentially from the center section to the shoulder section, as in the tires I and ■ according to the present invention. Therefore, tz/
t needs to be 0.9 or less.

However, considering wet performance, the coefficient of friction on wet roads starts to decrease when the groove depth t2 of the main groove in the tire circumferential direction at the center section is about half of the groove depth t of the main groove in the cross-sectional direction of the tire at the shoulder section. As in the comparison tires ■ and ■, the groove depth t2 of the tire circumferential main groove in the center portion
When the depth becomes 20χ to 40χ with respect to t, the coefficient of friction decreases significantly to a level that poses a safety problem. Therefore, in terms of safety margin, b/l needs to be 0.8 or more.

〔Effect of the invention〕

According to the present invention, five rows of blocks are arranged in the trend part, and the groove depth of the main groove in the cross-sectional direction of the tire in the shoulder part is set to 20.
．． A radial tire having at least four belt layers with a thickness of 0 mm or more and including one set of cross ply layers in the region sandwiched between the carcass layer and the trend part, wherein the one set of cross ply layers has a tensile strength of 280 to 300 Kg. The belt layer is made of thick steel cord, the closest belt layer to the carcass layer is made of steel cord, and the belt layer is separated on the left and right, and the main groove in the tire circumferential direction at the center has a groove depth t2. and the groove depth t of the main groove in the tire circumferential direction of the shoulder portion, and the groove depth of the main groove in the cross-sectional direction of the tire, by satisfying the relationships of equations (1) and (2) described above. Even if the groove depth in the block pattern is increased to increase the wear life, it is possible to suppress the occurrence of group cranking, and it is also possible to suppress the flaking phenomenon during running and improve the steering stability.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing an example of the tread pattern of the pneumatic radial tire for heavy loads of the present invention, Fig. 2 is a sectional view of Fig. 1, and Fig. 3 is the groove depth of the main groove in the cross-sectional direction of the tire in the shoulder region. 2 is a graph showing the relationship between the ratio 1+/1 of the groove depth tl of the main groove in the tire circumferential direction of the shoulder portion to the depth tl of the tire and the total length of cranks generated at the groove bottom of the main groove in the cross-sectional direction of the tire in the shoulder portion. 1.2...Main groove, 3...Block, B-L B-
2゜B-3, B-4, B-5...Block row, 7...
・Carcass layer, 8. 9.10.11...belt layer,
t2... Groove depth of the tire circumferential main groove in the center part, 1
．． ...Groove depth of the main groove in the tire circumferential direction at the shoulder part, t
...Groove depth of the main groove in the cross-sectional direction of the tire at the shoulder part, T
...Trend Department.

Claims (1)

[Scope of Claims] Five rows of blocks each consisting of blocks separated by a main groove in the circumferential direction of the tire and a main groove in the cross-sectional direction of the tire are arranged in the tread portion, and the groove depth of the main groove in the cross-sectional direction of the tire is 20
．． 0 mm or more, and includes one set of cross-ply layers in the area sandwiched between the carcass layer and the tread portion.
In the radial tire having a belt layer of 1.
The cross-ply layers of the set are made of thick steel cords with a tensile strength of 280 to 300 kg, the belt layer closest to the carcass layer is made of steel cords, and the belt layers are separated on the left and right sides, and the center portion The groove depth t_2 of the main groove in the circumferential direction of the tire and the groove depth t_1 of the main groove in the tire circumferential direction of the shoulder portion are 0.5≦t_1/ A pneumatic radial tire for heavy loads that satisfies the following relationships: t≦0.7 (1) 0.8≦t_2/t≦0.9 (2).