JPH0429561B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heavy-duty radial tire having a rib-lug type tread pattern that prevents uneven wear near the lug grooves. Generally, pneumatic tires have tread patterns such as rib type, lug type, rib lug type, block type, and rib block type selected depending on the purpose. In heavy-duty radial tires, which are defined as radial ply tires for buses and buses, rib-lug type tread patterns are often used from the viewpoint of wet grip resistance, abrasion resistance, and the like. However, in the tread portion of such a rib lug pattern having lug grooves extending in the axial direction of the tire at both ends of the tread, so-called shoulder-drop wear often occurs in which both ends of the tread partially wear out first. In order to reduce shoulder drop wear, a large number of sipings are applied to both ends of the tread portion in the axial direction of the tire to make the movement of the rubber in these parts flexible, thereby reducing wear. Furthermore, it has been found that in tires with a tread pattern provided with lug grooves, not only so-called shoulder drop wear but also uneven wear occurs in which wear progresses particularly in the vicinity of the lug grooves. This is thought to be due to the fact that the tread surface near the lug grooves becomes the stepping-in and kick-off parts during running, and is subject to particularly severe deformation and strain, as well as the rubber rigidity in this area being relatively high. This phenomenon is particularly likely to occur when the groove walls of the lug groove are sloped and the lug groove has a V-shaped cross section. An object of the present invention is to provide a heavy-duty radial tire that reduces uneven wear at both ends of the tread by equalizing the rigidity and deformation strain of the tread surface near the lug grooves. The present invention provides at least three sipings at equal intervals, one end of which is open at the tread end, and extends in the axial direction of the tire and has approximately the same length on the lug surface, which is the part that is sandwiched in the lug groove. In the region of the lug surface between the nearest sipe and the lug groove, one end is open at the tread end and extends in the axial direction of the tire, and the length on the lug surface is smaller than the length of the sipe, and the other end auxiliary sipes are provided whose lengths are gradually increased in the depth direction and whose maximum length is larger than the length of the sipes by moving away from the tread ends as the sipes move away from the lug surface inwardly in the radial direction. This is a radial tire for heavy loads. The siping increases flexibility at the tread end portion and prevents shoulder drop wear, and since the auxiliary siping is close to the lug groove, it facilitates the movement of the rubber near the lug groove where deformation strain is large. In addition, the length is small on the surface of the lug and increases in the depth direction, which prevents chipping in the initial stage and
It facilitates the deformation of the rubber inside, alleviates deformation strain, suppresses heat generation, and suppresses increases in rigidity during wear. An embodiment of the present invention will be described below based on the drawings. FIG. 1 is a partial plan view of the tread surface of the tire of the present invention, FIG. 2 is an enlarged plan view of the end of the tread portion, and FIG. 3 is a sectional view taken along the line -- in FIG. In the figure, a heavy-duty radial tire 1 has a rib-lug type tread pattern, and the tread surface is provided with, for example, three zigzag vertical grooves G extending in the tire circumferential direction at the center of the tread to provide stable handling. lug grooves R extending in the axial direction of the tire are formed at regular intervals in the tire circumferential direction on both ends of the tread surface. In addition, this lug groove R has a V-shaped groove by making the groove wall slope at an angle of 15 to 40 degrees with respect to the tire radius line in order to prevent stones and soil from getting stuck and maintain traction performance. None, and the tip is tapered. In addition, the length r of the lug groove R is 8 to 20% of the tread width, as shown in Figure 1, as in a normal tire.
It is set to a certain degree. Further, on the lug surface, which is the range between the lug grooves R on the tread surface, at least three, in this example four, sipes C1, C2, C3, and C4 are provided spaced apart in the tire circumferential direction. . This siping C
1 to C4 have one end open at the tread end, extend in the axial direction of the tire, and are interrupted. This siping C1
~C4 is similar to conventional siping, and makes it easy for the rubber to move in the lugs between the lug grooves, making it flexible to prevent shoulder drop wear. The sipes C1 to C4 have substantially the same spacings a1, a2, and a3, and
The distance a0 from the sipes C1, C4 closest to the lug groove R to the lug groove R is also approximately the same. Length b of siping C1, C2, C3, C4
is shorter than the length r of the lug groove R, and the length b of the sipes C1 to C4 is usually 30 to 30 times the length r of the lug groove R.
The range shall be 80%. Furthermore, the siping C1, C closest to the lug groove R
A region A of the lug surface, which is the tread surface between the tread surface R and the lug groove R, is provided with auxiliary sipes D1 and D2 having one end open at the tread end. As shown in FIG. 3, the auxiliary sipes D1 and D2 have the other end a rear surface 2 whose length gradually increases in the depth direction as it moves away from the tread end as it moves radially inward from the tread surface.
has. Further, this inner surface 2 is preferably formed into an arcuate shape, thereby increasing the ratio of increase in the length of the auxiliary sipes D1 and D2 that appear on the lug surface as the tread portion wears. Reduce stiffness. The preferred radius R1 is 10 to 50 mm. The length d of the auxiliary sipes D1 and D2 on the lug surface is the length b of the sipes C1 to C4.
For example, the length d is shorter than the siping C
The length b should be in the range of 20 to 60% of the length b of 1 to C4. Further, the maximum length d0 of the bottom surface 3 of the auxiliary sipes D1 and D2 is 150 to 250% of the surface length d. The depth CD of the auxiliary sipes D1 and D2 is approximately the same depth as the sipes C1 to C4, for example, 7 to 7.
The range is 15 mm, which is approximately equal to the depth of the lug groove G. Although the lengths of the auxiliary sipes D1 and D2 gradually increase in the depth direction, they are formed to have a substantially constant length at a depth exceeding a predetermined depth l. Note that this depth l is usually 60% or more of the auxiliary siping depth CD and 100
%. This prevents the deep surface 2 and the bottom surface 3 from intersecting sharply and reduces stress concentration, and by making it 60% or more, a constant depth CD
In auxiliary siping, it is useful to gradually increase the length with wear. Since the auxiliary sipes D1 and D2 are disposed close to the lug groove R, they facilitate the movement of the rubber near the lug groove where deformation strain is particularly severe. Moreover, since the length b is small on the lug surface, it is possible to prevent the tread portion from chipping in the vicinity of the lug groove in the initial stage. The other end is a deep surface 2 that becomes further away from the tread end as it moves inwardly away from the surface. The other lug groove R
Like normal lug grooves, the groove cross section is V-shaped and the groove walls are sloped, resulting in the groove width decreasing in the depth direction. Although the length in the direction increases, the length of the auxiliary sipes D1 and D3 increases in the depth direction, and the maximum length _d0 is large, increasing the rigidity of the rubber near the lug groove R. This suppresses the movement of rubber inside the rubber. This alleviates the deformation strain and contributes to reducing the heat generation of the rubber, and also prevents the rigidity of the lugs from increasing even when the lug grooves become shallow due to wear on the tire surface. The auxiliary siping D1 of this configuration,
By providing D2, uneven wear that tends to occur near the lug groove R can be suppressed. Edges of lug grooves R of auxiliary siping D1, D2
The distance e from RE is preferably in the range of 20% to 70% of the distance a0 of the sipes C1 and C4, particularly preferably
It is in the range of 30-45%. This is because the deformation is especially severe at the edge RE, so it is necessary to reduce the rigidity of the region near the edge RE as much as possible. However, if the positions of the auxiliary sipes D1 and D2 are too close to the edge RE, the problem of rubber chipping will occur in this area, so the above range is set as a suitable range. Although the sipings C1 to C4 and the auxiliary sipings D1 and D4 are normally arranged in the axial direction of the tire, they may be arranged with a slight inclination. Example Tires with the tread patterns shown in FIGS. 1 and 2 were manufactured as trial tires for truck and bus radial tires of tire size 1000R and 20, and uneven wear was evaluated. As a comparative example, the tread pattern of the example without auxiliary siping was used.
The specifications of the sample tires are shown in Table 1.
Note that the length r of the lug groove R is 25 mm, and the width is 15 mm.
Uneven wear is defined as the amount of wear on the lug surface A from the edge of the lug groove to the siping closest to the edge for the comparative example product, and the amount of wear on the lug surface A from the edge of the lug groove to the siping closest to the edge, and for the example product, the amount of wear on the areas A1 and A2 where area A is divided by the auxiliary siping. Each was evaluated as the amount of wear (mm) after driving the actual vehicle. The results are shown in FIG. In FIG. 4, curve A shows the wear amount in the comparative example, and curves A1 and A2 show the wear amount in areas A1 and A2 in the example. From the figure, it can be seen that the wear of the example is significantly reduced. In addition, no chipping occurred in any of them. As described above, the heavy-duty radial tire of the present invention is basically equipped with auxiliary sipes that increase in length in the depth direction near the lug grooves, so that

[Table] of.
The movement of the tread rubber becomes easy, and uneven wear and chipping on the lug surfaces near the lug grooves can be effectively suppressed.

[Brief explanation of drawings]

Fig. 1 is a partial plan view of the tread portion of the tire of the present invention, Fig. 2 is an enlarged plan view of the end of the tread portion, Fig. 3 is a cross-sectional view of Figs. 1 and 2, and Fig. 4 is the mileage distance. It is a graph showing the relationship between the amount of uneven wear and the amount of uneven wear. R...Lug groove, C1, C2, C3, C4...Siping, D1, D2...Auxiliary siping.

Claims (1)

[Claims] 1. In a heavy-duty radial tire having a rib-lug type tread pattern with lug grooves extending in the axial direction of the tire at both ends of the tread, one end is open at the tread ends and at least one groove extending in the axial direction of the tire has approximately the same length. Three sipes are provided at equal intervals in the circumferential direction of the tire, and one end is open at the tread end and extends in the axial direction of the tire, and a lug is provided in the region of the lug surface between the sipe closest to the lug groove and the lug groove. An auxiliary siping is provided whose length on the surface is smaller than the length of the siping, and whose length gradually increases as it moves away from the lug surface inward in the radial direction, and whose maximum length is larger than the length of the siping. A radial tire for heavy loads.