JPH02234810A - Heavy duty radial tire of pneumatic type - Google Patents

Abstract

PURPOSE:To secure excellent braking and driving performance by forming a tread from rubber compound with high hardness, arranging a number of blocks with cuts on the tread surface, and giving the grounding area a specific share in the tread surface. CONSTITUTION:On the tread surface of a tire a plurality of blocks 3 are partitioned by main and aux. grooves 1, 2 in such an arrangement as alongside the tire circumference E-E'. Each block 3 is provided with at least one shallow cut 4 in parallel with the axis of tire rotation. The tread rubber constituting the blocks 3 is formed from rubber compound having a JIS-A hardness of 67-74 at -10 deg.C. The grounding area shall range 62-66% of the tread surface. This prevents tumbling of each block 3 with large shearing force at the time of braking, and excellent braking and driving performance are secured by edge effect.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pneumatic radial tire for heavy loads, typified by tires for trunks, buses, and the like.

[Conventional technology]

Conventional heavy-duty pneumatic radial tires (hereinafter referred to as heavy-duty tires) designed to improve braking and driving performance on icy and snowy roads have a large number of blocks 3 arranged on the tread surface, as shown in Figure 2. And some of them brosoku 3
It was common to have a spike pin 5 driven into the hole.

Rubber with low hardness is used for the cap tread rubber of this tire, which provides frictional force due to its adhesive properties.
The scratching effect of the spike bin 5 provided braking and driving performance on icy and snowy roads. However, cap treads made of a rubber composition with low rubber hardness tend to suffer uneven wear, and have the disadvantage that their performance deteriorates in the middle stage of wear. Furthermore, the spike bins driven into the blocks damage the road surface when driving on dry roads, creating dust pollution, which has become a social problem.

In order to eliminate dust pollution caused by spiked tires, there is an urgent need to develop studless tires that do not use the spike pins, and various studless tires have been proposed. These proposed studless tires use a rubber composition with low hardness at low temperatures as the tread rubber in order to improve the low-temperature properties of the tread, and from a structural standpoint, the blocks arranged on the tread surface are equipped with sipes. There are some types that have a thin cut called a tire approximately parallel to the axis of rotation of the tire. In other words, there is a system that improves braking and driving performance on icy and snowy roads by imparting low-temperature properties to blocks segmented by sipes and effectively exerting the edge effect of the block at low temperatures.

However, in the case of heavy-duty tires that have a high compressive force on the tread and a large pressure distribution, the hardness of the blocks is low, which tends to cause uneven wear. The strength of the block decreased, the block collapsed due to the shearing force applied to the block during braking, the desired edge effect could not be achieved, and good braking and driving performance on icy and snowy roads could not be achieved.

[Problem to be solved by the invention]

The object of the present invention is to provide a heavy-duty tire, especially a tire for icy and snowy roads, that exhibits excellent braking and driving performance without uneven wear in a tire for icy and snowy roads in which thin cuts are made in blocks arranged on the tread surface. The goal is to provide the following.

[Means to solve the problem]

The heavy-duty tire of the present invention has a large number of blocks made of a rubber composition having a JIS-A hardness of 67 to 74 at -10°C arranged on its tread surface, and the surface of these blocks is arranged so as to have a hardness relative to the tire rotation axis. The tread is characterized by forming substantially parallel thin cuts, and setting the ground contact area ratio of the tread surface to 62% to 66χ.

FIG. 1 is a plan view of a tread pattern of a heavy-duty tire showing an embodiment of the present invention.

As shown in the figure, a large number of blocks 3 partitioned by a plurality of main grooves 1 and a plurality of sub-grooves 2 are arranged along the tire circumferential direction E-E' on the tread surface, and the blocks 3
At least one thin notch 4 is formed in the. These thin cuts 4 are provided substantially parallel to the axis of rotation of the tire.

In the present invention, the tread rubber constituting the block 3 has a JIS-A hardness of 67 to 7 at -10°C.
It is necessary that the rubber composition is No. 4. In heavy-duty tires for trucks and buses, where the tread has high compression rigidity and large pressure distribution, if the rubber hardness is less than 67, the block will collapse due to the shear force applied to the block during braking, and the edge effect will affect performance on ice and snow. cannot be fully demonstrated. On the other hand, when the rubber hardness exceeds 74, the adhesion of the tread surface to the road surface deteriorates, making it impossible to obtain good performance on icy and snowy roads.

Rubber compositions with such hardness are produced by appropriately selecting the types and mixing ratios of rubber components, and the types and amounts of chemicals added to the rubber components, such as carbon black, anti-aging agents, vulcanizing agents, and vulcanization aids. and can be obtained by making adjustments.

Furthermore, the tire of the present invention, in which the tread surface is made of tread rubber with high hardness, needs to have a ground contact area ratio within the range of 62% to 66χ.

Here, the ground contact area ratio refers to a value calculated by measuring the ground contact area of the tread contact area when the tread contacts the flat plate under the conditions of maximum air pressure and maximum load specified by JATMA, and according to the following formula.

That is, in the case of tires for icy and snowy roads, the tread thereof is usually composed of a rubber composition having a JIS-A hardness of 57 to 66 at -10°C, and a contact area ratio of 50% to 60χ.
In contrast, the tread of the tire of the present invention has high JIS-A hardness and low adhesion to the road surface, as described above. For this reason, it is necessary to increase the contact area ratio of the tread surface as described above and reduce the contact pressure per unit area to increase its adhesion and improve braking and driving performance on icy and snowy roads. It is.

Further, the tire of the present invention whose tread is made of the above-mentioned high hardness rubber composition exhibits excellent braking and driving performance due to the edge effect of the thin cuts by providing thin cuts on the surface of the blocks on the tread surface. Can be done.

The interval between these thin cuts is not particularly limited, but is preferably 8 to 16 mm. In addition, the depth of the thin cut should be 50% or more of the leading depth, especially for ice and snow roads, as per JIS D4202-1982 r.
In Explanation Table 9 on page 11 of ``Specification Explanation of Automotive Tires'', Extra Heavy tread (EHT) in the section of maximum groove depth mm.
) is preferably the value stated in the column.

The spacing and depth of these thin cuts may be constant for all blocks or may vary from block to block. Furthermore, in terms of tire performance on icy and snowy roads, it is preferable that at least one end of the thin cut reaches the edge of the block. Preferably, both ends of the thin cut reach the edge of the block, as shown in FIG. The direction of this thin cut only needs to be substantially parallel to the rotational axis of the tire, so it may have a slight angle to the rotational axis, and the shape can also be a straight line, curved line, or broken line. Can be shaped.

Hereinafter, the tire of the present invention will be specifically explained using Examples, Conventional Examples, and Comparative Examples.

The braking performance, driving performance, uneven wear resistance, and JISA rubber hardness were each evaluated by the following methods.

Each tire is actually installed on all wheels of a large vehicle (2/D), and braking is applied from 40Kn+/h on compressed snow and frozen roads, and the braking distance is evaluated. The results are set as 100 for conventional tires. Expressed as an index. The larger this number is, the better the braking performance is.

Each tire is actually mounted on the drive wheel of a base 22 large vehicle (2/D),
The vehicle was climbed up a slope on a snow-compacted road from an initial speed of 30 km/h and evaluated based on the time required, and the results were expressed as an index with the conventional tire set at 100. The larger this value is, the better the drive performance is.

■1st performance: A large vehicle (2/D) was equipped with each tire on all wheels, and the third test was carried out after driving 15,000 km on a course with high braking and driving performance.
The heel-and-toe height difference t of the block shown in the figure was measured and evaluated, and the results were expressed as an index with the conventional tire set at 100. The larger this value is, the better the uneven wear resistance is.

Two-person performance: Measured in accordance with the method specified in JIS-K 6301.

Examples, Comparative Examples 1 and 2, Conventional Example Three types of tires were created with the JIS-A hardness, ground contact area ratio, spacing and depth of thin cuts, and tread pattern changed as shown in the table, and the drive performance of each was changed. , braking performance, uneven wear resistance and crank resistance were evaluated, and the results shown in the table were obtained.

These tires all had the same size, tread width, and leading depth, and were as follows.

Tire size: IOOOR 20 14PR Tread width: 210mm Lead depth: 19.9n+m In the conventional tire, 60 spike bins were driven into the block without forming thin cuts in the block.

(The following is a blank space) From the table, the tires of the present invention are superior to conventional tires in both braking/driving performance and uneven wear resistance, whereas the comparative tires have poor braking performance on icy and snowy roads. , and was found to be inferior in drive performance and wear resistance.

In addition, the deformation state of the block during braking was observed for the tire of the present invention and the comparative tire, and the results were as shown in FIGS. 4 and 5. In the case of the comparison tire, the edge e of the block 3 is deformed and rounded, and the edge effect is lost, whereas the edge e of the block 3 of the tire of the present invention is not substantially deformed and shows a good edge effect. I can see that you are doing it.

〔Effect of the invention〕

According to the present invention, in a pneumatic tire for heavy loads, the tread is made of a high hardness rubber composition, thereby preventing blocks from collapsing due to the large shearing force applied during braking in the case of the pneumatic tires for heavy loads. This ensures braking and driving performance through the edge effect, improving uneven wear resistance, and increasing the contact area ratio of the tread surface to ensure tread surface adhesion, improving braking and driving performance on icy and snowy roads. can be improved.

Further, the synergistic effect of the above-mentioned excellent edge effect and adhesion makes it possible to make the tire studless.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing an example of the tread pattern of the tire of the present invention, Fig. 2 is a plan view showing an example of the tread pattern of a conventional heavy-duty tire, and Fig. 3 shows the measurement points for uneven wear resistance. The cross-sectional views of the block shown in FIGS. 4 and 5 are cross-sectional views showing the deformed state of the block during braking of the tire of the present invention and the comparative tire, respectively. 1... Main groove, 2... Minor groove, 3... Blossom, 4...
...notch, e...edge part. Figure 3

Claims (1)

[Claims] The tread rubber has a JIS-A hardness of 67 at -10°C.
-74, a large number of blocks are arranged on the tread surface, thin cuts are formed in these blocks substantially parallel to the axis of rotation of the tire, and the ground contact area ratio of the tread surface is 62%. A pneumatic radial tire for heavy loads with ~66%.