JP5072071B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire having a tread having a block formed by a main groove extending in the tire circumferential direction and a lug groove intersecting the main groove, and more specifically, a heavy duty pneumatic tire having a small flatness ratio. The present invention relates to a pneumatic tire that can improve wear resistance.

  In heavy-duty pneumatic tires used in buses, trucks, construction vehicles, etc., wet grip properties and traction are achieved by forming a block with a main groove extending in the tire circumferential direction and a lug groove intersecting the main groove. Many tread patterns with improved properties are employed (see Patent Document 1).

  However, in a tire having a block pattern, the kicking side of the block is greatly deformed in the tire circumferential direction when entering the contact area, and as a result of repeating the movement of restoring to the original shape due to the elasticity of rubber when coming out of the contact area, There is a problem that uneven wear on the kicking side of the block, so-called heel and toe wear, occurs. Particularly in the case of heavy-duty tires, because of the high internal pressure and high load, the rubber between the tread base, that is, the bottom surface of the lug groove and the belt layer, extends in the tire circumferential direction (traveling direction) and deforms. Since the kicking side of the block bulges in the tire circumferential direction as a result of the deformation, the frictional work amount (integral value of the product of the shear strain on the tread surface and the slipping amount) increases, and the kicking side wears. Furthermore, in the case of ultra-flat tires with a flatness ratio of 55% or less, compared to general-purpose tires with a flatness ratio of about 70%, the belt tension at the time of filling with internal pressure increases, so the amount of compressive deformation at the base of the tread increases. Increase in the tire circumferential direction (distortion) of the base portion increases, and the amount of bulging in the tire circumferential direction on the kicking side of the block increases accordingly. There is.

Japanese Patent No. 3086034

  The present invention has been made to solve such problems, the purpose of which is to suppress the elongation of the base portion of the tread in the tire circumferential direction in a pneumatic tire having a block in the tread. This is to reduce the amount of bulging of the block in the tire circumferential direction and improve the wear resistance.

According to the first aspect of the present invention, a plurality of main grooves extending in the tire circumferential direction, a plurality of lug grooves that intersect the plurality of main grooves and do not intersect with each other, and a block defined by the main grooves and the lug grooves are used as treads. A pneumatic tire provided, wherein a slit extending in a tire width direction is provided only on a bottom surface of the lug groove.
According to a second aspect of the present invention, in the pneumatic tire according to the first aspect, the surface area of the bottom surface of the lug groove is greater than 1.0 times the surface area of the bottom surface of the lug groove when the slit is not provided. It is a pneumatic tire characterized by being smaller than 6 times.
The invention of claim 3 is the pneumatic tire according to claim 1 or 2, characterized in that the depth of the slit is greater than 0.04 times and less than 0.32 times the depth of the lug groove. It is a pneumatic tire.
The invention according to claim 4, in the pneumatic tire according to any one of claims 1 to 3, the distance is the lag between the projecting end of irregularities adjacent formed on the bottom surface of said lug groove by providing said slit It is a pneumatic tire characterized by being larger than 0.1 times and smaller than 0.3 times the width of the groove.

(Function)
According to the present invention, by providing the slit on the bottom surface of the lug groove, the free surface area of the base portion of the tread is increased, so that the out-of-plane deformation of the base portion in the radial direction when the block is kicked out is promoted. As a result, since the elongation of the base portion in the tire circumferential direction is reduced, the swelling of the block in the tire circumferential direction is reduced. Further, the slit disturbs the air flow on the bottom surface of the lug groove, and the air flow takes heat away, thereby improving the heat dissipation of the lug groove.

According to the present invention, in a pneumatic tire having a block in the tread, by suppressing the extension of the base portion of the tread in the tire circumferential direction, the amount of swelling in the tire circumferential direction on the kicking side of the block is reduced, Abrasion resistance can be improved. Moreover, the heat dissipation of a lug groove can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a development view of a part of a tread pattern of a pneumatic tire according to an embodiment of the present invention, and FIG. 2 is a perspective view showing two blocks 12 adjacent in the circumferential direction in FIG.

  The tread pattern includes a plurality of (six in the drawing) main grooves 2 extending in the tire circumferential direction (hereinafter abbreviated as the circumferential direction) and a large number (two in the drawing) extending in the tire width direction (hereinafter abbreviated as the width direction). A large number of plan views formed by the lug grooves 4 of FIG. Here, although the main groove 2 extends straight in the circumferential direction, it may extend in the circumferential direction in a zigzag shape, for example. Similarly, the lug groove 4 may be extended in the width direction in a zigzag shape. The main groove 2 may be disposed on the tire equator CL.

  A slit 22 is formed in a region of the lug groove 4 other than the region intersecting with the main groove 2, in other words, a bottom surface of a region that divides the circumferential edge of the block 12. For convenience, in this figure, the slits 22 are shown only on the bottom surfaces of the two regions that define the peripheral edge of the block on the left end, but the slits 22 are provided on the bottom surfaces of the regions that define the peripheral edge of the other blocks. Is formed. However, it is not necessary to form in the area | region which divides the circumferential direction edge of all the blocks 12. FIG.

  As shown in FIG. 2, in the present embodiment, four constant width slits 22 extend straight in the width direction of the bottom surface of the lug groove 4. Both ends of each slit 22 extend to a position reaching the end of the main groove 2 in the width direction, and open to the main groove 2. In this specification, the slit means an elongated cut such as a groove.

  FIG. 3 is a cross-sectional view in the width direction of the bottom surface of the lug groove 4 and its base portion in the tire radial direction. FIG. 4 shows how the base portion of the lug groove is deformed when the block is kicked out in FIG. It is a figure for demonstrating. In these drawings, the portion to which the leftward hatching is attached is the base portion.

  As shown in FIG. 3, the cross-sectional shape of the slit 22 is an isosceles triangle (more precisely, an isosceles inverted triangle). As described above, since the unevenness is formed in the lug groove 4 by providing the slit 22 on the bottom surface of the lug groove 4, the surface area of the bottom surface of the lug groove 4 is increased compared to the case where the slit 22 is not provided. Since the bottom surface of the lug groove 4 is the free surface of the base portion 13, the free surface area of the base portion 13 is also wider than when no slit 22 is provided.

Since the kicking side of the block 12 of the tread portion having the above configuration is compressed from the tread side when it contacts the road surface, the base portion 13 extends in the circumferential direction and deforms. At this time, the free surface of the base portion 13, in other words, the bottom surface of the lug groove 4 is deformed out of plane in the radial direction. In the present embodiment, as shown in FIG. 4, the virtual plane B ₁ connecting the radial tip of the bottom surface of the lug groove 4 (the uneven protrusion formed on the bottom surface of the lug groove 4 by the slit 22) is caused by out-of-plane deformation. the virtual surface B _2. Here, in this embodiment, since the free surface area of the base portion 13 is widened by the slits 22, out-of-plane deformation of the base portion 13 is promoted, so that the elongation of the base portion 13 in the circumferential direction is reduced. As a result, the amount of swelling of the block 12 in the circumferential direction on the kick-out side is also reduced, and the friction work during kick-out is reduced, so that the wear resistance is improved.

  The slit 22 is formed on the bottom surface of the lug groove 4 so that the surface area of the bottom surface of the lug groove 4 does not reach 3.6 times, preferably larger than 1.5 times and smaller than 2.5 times compared to the case where it is not formed. It is formed to be wide in the range. If it becomes 3.6 times or more, not only the effect of promoting the out-of-plane deformation of the base portion 13 will not be improved, but also the volume of the rubber will increase and the heat dissipation will deteriorate, and the bottom surface of the lug groove 4 will be greatly distorted It becomes. On the other hand, when the ratio is 1.0 or less, the rubber of the base portion 13 escapes in the circumferential direction, so that it becomes impossible to promote out-of-plane deformation. Therefore, it is preferable that the range be larger than 1.0 times and smaller than 3.6 times. Here, the above-mentioned magnification may be set to the same value or different values for the individual areas that define the circumferential edge of the block 12.

The depth h ₂ of the slit 22 is set to a range larger than 0.04 times and smaller than 0.32 times, preferably larger than 0.1 times and smaller than 0.2 times the depth h ₁ of the lug grooves 4. This is because the surface area does not increase sufficiently when it is 0.04 times or less, and the distortion of the bottom surface of the lug groove 4 increases when it is 0.32 times or more.

Further, by providing the slit 22, the circumferential interval L ₂ between the protrusions of the plurality of projections and depressions formed on the bottom surface of the lug groove 4 is in a range larger than 0.1 times and smaller than 0.3 times the width L ₁ of the lug groove 4. Set. If it is 0.1 times or less, the slit 22 is likely to crack, and if it is 0.3 times or more, the surface area of the lug groove 4 cannot be sufficiently increased. The distance L ₂ is also the distance between the deepest portions of the slits 22 adjacent in the circumferential direction (the distance between the vertices of two adjacent inverted triangles in FIG. 3). 4 is also the interval between the corresponding slopes formed in 4 (the interval between the corresponding hypotenuses of two adjacent inverted triangles in FIG. 3). Therefore, it can be said that these are the circumferential intervals of the slits 22.

  FIG. 5 shows a modification in which the slit is formed so as to extend in the circumferential direction. In this example, six slits 23 having a constant width extend straight in the circumferential direction of the bottom surface of the lug groove 4. As shown in this figure, when the slit 23 extends in the circumferential direction, the slit 23 itself is resistant to cracks. On the other hand, as shown in FIG. 2, when the slit 22 extends in the width direction, the slit 22 disturbs the air flow on the bottom surface of the lug groove 4, and the air flow takes heat away. The heat dissipation is improved.

  In addition, although the cross-sectional shape of the slits 22 and 23 demonstrated above is a triangle, you may make it a polygon other than a circular arc or a triangle. Moreover, you may form a slit diagonally instead of parallel to the circumferential direction or the width direction. Furthermore, you may form so that the edge of a slit may not open to the main groove 2. FIG. In addition, slits having different cross-sectional shapes, lengths, widths, orientations, and the like may be mixed in one region that divides the circumferential edge of the block 12.

[Example]
In order to confirm the effect of the present invention, an example tire and a comparative tire were made as prototypes, and a heel and toe wear test was performed on an actual vehicle. The size of both the example tire and the comparative example tire was “495 / 45R22.5”, and the internal pressure was set to 900 kPa. The tread pattern of the example tire is shown in FIGS. 1 and 2, and the comparative example tire is a pattern in which the slit 22 is not formed in the lug groove 4 in FIGS.
The test was carried out by mounting the example tire and the comparative example tire on the drive shaft of a 2D vehicle, traveling 50000 km at a load of 5800 kg, and measuring the actual amount of wear (difference from when new) after traveling. The measurement results are shown in Table 1 below. The numerical values in this table are indices based on the comparative tire as 100, and the larger the numerical value, the better the wear resistance.

  From the test results shown in this table, the wear resistance of the example tires was significantly improved (approximately 60%) than the wear resistance of the comparative example tires, and it was proved that the effect of the present invention was extremely large.

It is a partial development view of the tread pattern of the pneumatic tire of the embodiment of the present invention. It is a perspective view which shows two blocks adjacent to the circumferential direction in FIG. It is sectional drawing of the bottom face of the lug groove of FIG. 1, and the base part of the radial inside. In FIG. 3, it is a figure for demonstrating a mode that the base part of a lug groove deform | transforms when kicking out a block. It is a figure which shows the modification which formed the slit so that it might extend in the circumferential direction.

Explanation of symbols

  2 ... main groove, 4 ... lug groove, 12 ... block, 22, 23 ... slit.

Claims (4)

A pneumatic tire having a tread having a plurality of main grooves extending in the tire circumferential direction, a plurality of lug grooves that intersect the plurality of main grooves and do not intersect each other, and a block that is partitioned by the main grooves and the lug grooves. And
A pneumatic tire characterized in that a slit extending in the tire width direction is provided only on the bottom surface of the lug groove. The pneumatic tire according to claim 1,
A pneumatic tire characterized in that the surface area of the bottom surface of the lug groove is greater than 1.0 times and less than 3.6 times the surface area of the bottom surface of the lug groove when the slit is not provided. In the pneumatic tire according to claim 1 or 2,
The pneumatic tire according to claim 1, wherein a depth of the slit is greater than 0.04 times and less than 0.32 times the depth of the lug groove. In the pneumatic tire according to any one of claims 1 to 3,
The distance between adjacent protrusions formed on the bottom surface of the lug groove by providing the slit is greater than 0.1 times and less than 0.3 times the width of the lug groove. Enter tire.

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