JPH0513841B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a heavy-duty pneumatic radial tire that has improved wear resistance without substantially impairing traction properties based on a block pattern. [Prior art] Heavy-duty pneumatic tires include conventional bias tires, which have a belt layer made of organic fiber cords such as nylon cords, as well as radial tires, which have a belt layer made of highly rigid cords such as metal cords. The demand for radial tires is rapidly increasing because they have many advantages over bias tires in terms of wear resistance and puncture resistance. On the other hand, tread patterns provided on heavy-duty pneumatic radial tires include rib patterns, rib-lug patterns, and block patterns. Figure 3 shows the actual ground contact area B relative to the total ground contact area A that each tread pattern generally has.
Compares the relationship between the ratio (hereinafter referred to as the actual ground contact area ratio) and tire performance (traction performance, wear resistance, rolling resistance (fuel efficiency)), and plots representative examples of each pattern. It is. Furthermore, as a special example, snow tires are shown as a reference example. As shown in Figure 3, the actual ground contact area ratio of the various tread patterns adopted in conventional heavy-duty pneumatic radial tires is 54-64% for block patterns and 65-75% for rib-lug patterns.
%, and the rib pattern was 72-82%. In addition, snow tires are characterized by a significantly smaller block rigidity of 48 to 52% in order to improve traction (braking and driving performance) on snowy and icy roads by lowering the block rigidity. In addition, Figure 3 shows tires of the same size.
10.00R 20-14PR, snow tires with an actual ground contact area ratio of 49%, tires with a block pattern of 62%,
Tires with a 72% rib lug pattern and tires with a 76% rib pattern are representative examples, and their rolling resistance is measured as a measure of fuel efficiency by the wear resistance, traction property, and indoor drum test described in Example 3 of the main text. The value is an index with rib pattern tires as standard (100) for abrasion resistance and rolling resistance, and for traction property,
It plots snow tires as a standard index (100) and connects them with curves for each performance. As is clear from Figure 3, the rib pattern and rib-lug pattern have a larger actual contact area ratio than the block pattern, so they have excellent wear resistance and can have a long life, so they are preferred for heavy-load applications. It had been. However, although rib patterns and rib lug patterns exhibit a certain level of traction performance on dry roads, on wet roads the actual contact area ratio is large, resulting in poor drainage, and on shallow snowy roads, the edge effect is low. The drawback was that it was unable to exhibit sufficient traction performance. On the other hand, since the block pattern has a smaller actual ground contact area ratio than the rib pattern or the rib lug pattern, it exhibits sufficiently high traction performance not only on dry roads but also on wet roads and shallow snowy roads.
Because it has such all-weather characteristics, it is gradually being welcomed as a vehicle that meets the recent demands for wider, larger volume, and faster transportation modes. However, this block pattern has a small actual ground contact area ratio, so it has lower wear resistance than rib patterns or rib-lug patterns, and its biggest drawback is that it cannot maintain a long life when used for heavy loads. [Problems to be Solved by the Invention] An object of the present invention is to provide a heavy-duty pneumatic radial tire having the above-mentioned block pattern, while substantially maintaining the traction properties of the block pattern, while improving the rib pattern and the rib lug pattern. To provide a heavy-duty pneumatic radial tire having comparable wear resistance. [Problems and Means for Solving the Problems] The present invention, which achieves the above objects, includes a plurality of belt layers made of metal cords between the carcass layer and the tread rubber part, and a plurality of circumferential grooves and width grooves on the tread surface. In a heavy-duty pneumatic radial tire in which a block pattern is arranged and the ratio of _the tread radius T _R to the tire width T _W is set _to 1.65 to 2.00, the tread surface is connected to the left and right shoulder edges. to the widthwise center of the circumferential groove located at the outermost side in the width direction among the plurality of circumferential grooves, respectively, into three areas: an outer area and a central area located between the two outer areas. Along with classifying,
The ratio I/L of the distance l to the tread width L is 0.20.
0.25, furthermore, the ratio of the actual ground contact area B to the total ground contact area A on the tread surface is in the range of 64 to 72%, and the groove ratio R _C of the center region of the groove ratio R _S of the outer region It is characterized in that the ratio R _S /R _C to R C is in the range of 0.5 to 0.7. As described above, although the tire of the present invention has a block pattern, the actual ground contact area ratio B/A of the entire tread surface is different from that of the conventional rib pattern shown in FIG.
The abrasion resistance is improved by increasing the range from 64 to 72%, which is similar to that of the rib rug pattern. If such a large actual ground contact area ratio is simply applied to a block pattern, the inherent traction properties of the block pattern will deteriorate due to a decrease in the groove ratio.However, in the present invention, the ratio I/L is 0.20 to 0.20.
By devising the groove ratio R _S in the outer region specified in the range of 0.25 and the groove ratio R _C in the central region of the tread surface, we made the groove ratio R _C in the central region similar to the conventional block pattern, while improving the groove ratio R C in the outer region. Groove ratio R _S /R _C = 0.5~
By making it particularly small within the range of 0.7, it is possible to maintain the original traction properties of the block pattern. In other words, the ground pressure on the tread surface of a heavy-duty pneumatic radial tire is distributed such that it is highest in the center region and lower in the outer regions, and the center region is more likely to generate large traction than the outer regions. ing. Furthermore, since the outer region has a smaller radius from the tire axis than the center region, the difference in circumferential speed when the tire is rolling causes it to slip on the road surface, making it more likely to wear out earlier than the center region. The present invention makes use of such characteristics and sets the groove ratio between the central region and the outer region in the above-mentioned relationship, thereby allocating traction performance mainly to the central region and providing wear resistance mainly to the outer region. This ensures the inherent traction properties of the block pattern, prevents early wear only in the outer region, and improves durability based on the fact that the actual ground contact area ratio of the entire tread is 64-72%. This made the abrasive effect even more advantageous. Here, the actual ground contact area ratio is the total ground contact area A of the actual ground contact area B of the tread surface (total area of the tire tread surface).
It is the ratio to Also, what is the groove ratio?
It is the ratio of the groove area of each region in plan view to the total area of each region in plan view. In addition, the groove ratio R _S set in both the left and right outer areas
may be the same on both the left and right sides, or may have different values on the left and right sides, as long as the relationship with the groove ratio R _C of the central region described above is maintained. Hereinafter, the present invention will be explained with reference to the drawings. FIG. 1 shows an example of a tread pattern provided in a heavy-duty pneumatic radial tire of the present invention, and FIG. 2 is a sectional view taken along the line A--A in FIG. 1. The radial tire E has a plurality of belt layers 6 made of metal cords between the carcass layer 5 and the tread rubber layer _T1 . The surface of Toledo T _S ,
That is, the tread surface is divided into a plurality of ribs 2 by a plurality of circumferential grooves 1 and 4, and these ribs 2 are divided into a plurality of width direction grooves 3 to form a block pattern consisting of a large number of blocks 11. has been done. In this block pattern, outer regions on both left and right sides are divided by the distance l from the left and right shoulder edges 10 to the groove width center of the outermost circumferential groove 4, and a center area has been formed. The actual ground contact area ratio of a tread surface with such a block pattern is 64 to 72.
%, preferably in the range of 68-70%, so as to improve the overall wear resistance of the tread. Furthermore, since the block rigidity is improved as a whole, rolling resistance can be reduced and fuel efficiency can be improved. If the actual ground contact area ratio is less than 64%, it is not possible to expect better wear resistance than the conventional block pattern. Moreover, if it is larger than 72%, the groove width will be significantly reduced, so for example, the groove ratio R _C in the center area and the groove ratio R _S in the outer area are set within the range of the present invention described above. Even if the block pattern is improved, it becomes difficult to maintain the original traction performance of the block pattern. The block pattern in the present invention has an actual ground contact area ratio in a large range as described above.
While the groove ratio R _C in the center area is approximately the same as that of conventional tires, the groove ratio R _S in the outer area is significantly reduced.
The groove ratio in the center area is R _S / _{R C and} it is 0.5.
It is set in the range of ~0.7. This setting maintains the original traction properties of the block pattern, prevents premature wear (uneven wear) only in the shoulder area (outer area), and increases the actual ground contact area ratio of the entire tread surface. This makes the improvement in wear resistance based on this effect even more effective. In the tire of the present invention having the above-described block pattern, the ratio _TR / _TW of _{the tread radius TR to the tire width TW is} set in the range of 1.65 to 2.00. This range is substantially the same as that of conventional tires, but if this ratio T _R /T _W is smaller than 1.65, uneven wear in the shoulder portion (outer region) becomes large.
For this reason, even if the groove ratio R _S in the outer region is set to be smaller than the groove ratio R _C in the central region as in the present invention, it is difficult to improve the wear resistance of the entire tread surface. Also, T _R / T _W is 2.00
If it exceeds this, the rubber thickness in the shoulder portion becomes too thick, which increases heat generation in the shoulder portion during running, which tends to cause edge separation of the belt layer and reduces durability. Further, in the present invention, the distance l dividing the outer region has a ratio I/L to the tread width L.
It is set in the range of 0.20 to 0.25. I/L
If it is less than 0.20, uneven wear of the shoulder portion will increase, and as above, it will be difficult to ensure the wear resistance of the entire tread. Furthermore, when I/L exceeds 0.25, the amount of rubber in the shoulder portion increases, and as described above, heat generation during running increases, which induces separation of the belt edges and reduces durability. In the block pattern illustrated in Fig. 1, in order to improve on-snow performance, the circumferential grooves 1 and the width grooves 3 intersect at one place in the central region to form an almost cross shape. The width direction groove 3 may intersect with the outermost circumferential groove 4 at the boundary between the outer region and the center region in a substantially crisscross pattern. Example 1 The tire size is 10.00 R 20-14PR, and the first
It has the block pattern shown in the figure, and the actual ground contact area ratio B/A = 68.2%, the groove ratio R _C = 38.5%, and the R _S =
21.8% (both left and right), I/L = 0.20, tread width
The same point is T _W = 273 mm, and the tread radius is
By changing T _R , the ratio T _R / to the tread width T _W
Six types of heavy-duty radial tires were manufactured with different T _W values as shown in Table 1. The shoulder wear and durability of these tires were measured under the following measurement conditions, and the results shown in Table 1 were obtained. Shoulder wear: Install the tire on a 2-2D (test vehicle) and check the air pressure.
On the road with 7.25Kg/cm ² and a load of 2500Kg/1 tire.
After driving 20,000km, we measured the amount of wear on the shoulder part (outer area) of the tread surface compared to when it was new. The evaluation result is performed using the reciprocal of the measured value, and T _R /
It is expressed as an index using a tire with T _W = 1.80 as the standard (100). The smaller the index, the greater the shoulder wear. Durability: Indoor drum test (air pressure 7.25Kg/ ^cm2 , speed 81
Km/h), run for 24 hours with an initial load of 2700 kg,
After that, while increasing the load by 20% every 24 hours,
The distance traveled until the tire broke was measured. The evaluation results are expressed as an index based on T _R /T _W =1.80 (100), and the larger the index, the better the durability.

[Table] From Table 1, if T _R /T _W is 1.65 to 2.00,
It can be seen that both shoulder wear and durability are satisfied. Example 2 The tire size is 10.00 R 20-14PR, and the first
It has a block pattern as shown in the figure, and the groove ratio R _C = 38.5%, R _S = 21.8% (both left and right),
T _R /T _W = 1.83, tread width L = 202 mm, the distance l was changed as shown in Table 2, and the actual ground contact area ratio B/A was changed accordingly. We manufactured a radial tire for heavy loads. The shoulder wear and durability of these tires were measured under the same measurement conditions as in Example 1, and the results shown in Table 2 were obtained.

[Table] From Table 2, it can be seen that when I/L is in the range of 0.20 to 0.25, both shoulder wear and durability are satisfied. Example 3 The tire size is 10.00 R 20-14PR, and the first
A heavy load radial tire of the present invention and a conventional heavy load radial tire having the block pattern shown in the figure and the specifications shown in Table 3 were manufactured. The wear resistance and traction properties of both tires were measured under the following measurement conditions, and the results shown in Table 4 were obtained. The tire of the present invention and the conventional tire are different in distance l, groove ratios R _C , R _S , and actual ground contact area ratios B/A, I/L, T _R /T _W, as shown in Table 3. , other structural elements were kept the same. Wear resistance: The vehicle was run under the same conditions as the shoulder wear in Example 1, and evaluated using the average value of the amount of tread wear in the center region and the amount of tread wear in the outer region. The results in Table 4 show the travel distance per unit wear amount of 1 mm, and the larger the distance, the better the wear resistance. Traction performance: The traction force on a snowy road and the braking performance on a dry paved road were measured under the following conditions, and a comprehensive evaluation was made using both measured values, which was expressed as an index with the conventional tire as the standard (100). The larger the index, the better. The traction force on a snowy road is calculated by attaching tires to the test vehicle and pulling the towed vehicle with the brakes applied.The force just before the tires of the test vehicle start spinning is applied to the rope connecting the two vehicles. It was measured using a load cell installed in Braking performance on a general dry paved road was determined by measuring the coefficient of friction (μ-Slide) when the tires were locked and slid when a test vehicle equipped with tires was braked from a speed of 60 km/h.

【table】

【table】

[Table] As is clear from Table 4, the tire of the present invention:
Compared to conventional tires, wear resistance has improved by 12%, but traction performance has only decreased by 4%.
It can be seen that there is no problem in practical use. Example 4 The tire size is 10.00 R 20-14PR, and the first
It has the block pattern shown in the figure, and T _R /T _W =
500mm/273mm=1.83, I/L=42mm/202mm=
0.21, R _S /R _C = 0.61, and the groove ratio
R _S (same ratio of left and right), R _C and actual ground contact area B/A
Five types of heavy-duty radial tires were manufactured, each having different values as shown in Table 5. The wear resistance and traction properties of these tires were measured under the same measurement conditions as in Example 3.
The results shown in the table were obtained. However, the wear resistance and traction properties in Table 5 are expressed as an index with a tire with B/A=60.2 as the standard (100).

Table 5 shows that by setting the actual ground contact area ratio B/A in the range of 64 to 72%, the wear resistance can be improved without substantially impairing the traction performance. Example 5 The tire size is 10.00 R 20-14PR, and the first
It has the block pattern shown in the figure, and T _R /T _W =
500mm/273mm=1.83, I/L=42mm/202mm=
0.21, actual ground contact area ratio = 68.4%, and by changing the groove ratio R _S (same left and right ratio) and R _C , the ratio R _S /R _C will be different as shown in Table 6. We manufactured five types of heavy-duty radial tires. The traction properties of these tires were measured under the same measurement conditions as in Example 3, and
When the wear resistance as shoulder wear was measured under the same measurement conditions as in Table 6, the results shown in Table 6 were obtained. However, the wear resistance and traction properties in Table 6 are expressed as an index with a tire having R _S /R _C =0.61 as the standard (100).

【table】

〔Effect of the invention〕

The present invention provides a heavy-duty pneumatic radial tire provided with a block pattern, which uses the above-described structure to improve wear resistance while maintaining the good traction properties inherent to the block pattern, thereby making it possible to extend the life of the tire.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of a tread pattern provided in a heavy-duty pneumatic radial tire of the present invention, FIG. 2 is a sectional view taken along the first arrow A-A, and FIG. 3 is a diagram showing various tread patterns. FIG. 3 is a diagram showing the relationship between the actual ground contact area ratio of the tires and their wear resistance, traction properties, and rolling resistance (fuel efficiency). 1... Circumferential groove, 3... Width direction groove, 4... (Outermost) circumferential groove, 5... Carcass layer, 6... Belt layer,... Outer region,... Central region.

Claims (1)

[Scope of Claims] 1. A plurality of belt layers made of metal cords are provided between the carcass layer and the tread rubber portion, and a block pattern defined by a plurality of circumferential grooves and width direction grooves is arranged on the tread surface, In a heavy-duty pneumatic radial tire in which the ratio of the tread radius T _R to the tire width T _W is T _R /T _W of 1.65 to 2.00, the tread surface is separated from the left and right shoulder edges by the width of each of the plurality of circumferential grooves. It is divided into three regions, an outer region and a central region located between the two outer regions, according to the distance l to the widthwise center of the circumferential groove located at the outermost side in the direction, and
The ratio I/L of the distance l to the tread width L is 0.20.
0.25, furthermore, the ratio of the actual ground contact area B to the total ground contact area A on the tread surface is set in the range of 64 to 72%, and the groove ratio R _C of the center region of the groove ratio R _S of the outer region A pneumatic radial tire for heavy loads with a ratio R _S / R _C in the range of 0.5 to 0.7.