JP4720359B2 - Pneumatic tire for icy and snowy roads - Google Patents

Description

  The present invention relates to a pneumatic tire for snowy and snowy roads having a run-flat function. More specifically, the present invention enables run-flat running on a road surface with a low coefficient of friction, such as ice, while avoiding an increase in mass and a decrease in productivity. The present invention relates to a pneumatic tire for icy and snowy roads.

  As a pneumatic tire having a run-flat function, for example, a reinforcing rubber layer having a crescent cross section is embedded in the sidewall portion, and a load in a zero pressure state is supported based on the rigidity of the reinforcing rubber layer. There is. However, in a pneumatic tire having such a run-flat function, the tire may not rotate when traveling on a road surface having a low friction coefficient such as an ice sheet in a zero pressure state. This is because, in the zero pressure state, the tread portion buckles inward in the tire radial direction, and the contact area is greatly reduced, so that a sufficient frictional force cannot be generated between the tire and the road surface. . That is, as shown in FIG. 4, in the zero pressure state, the tread portion of the pneumatic tire T tends to rise from the road surface R and the contact pressure tends to concentrate on the shoulder portion.

On the other hand, in a pneumatic tire with a run-flat function, a reinforcing layer made of steel cord or the like is embedded in the tread part to suppress buckling of the tread part, thereby driving performance on a road surface with a low coefficient of friction. Has been proposed (see, for example, Patent Document 1). However, when a reinforcing layer is added to the tread portion, there is a problem that the mass of the pneumatic tire increases or productivity decreases. Therefore, it is desired to improve the running performance on a road surface having a low friction coefficient without causing these disadvantages.
International Publication No. 03/024727 Pamphlet

  An object of the present invention is to provide a pneumatic tire for icy and snowy roads that enables run-flat running on a road surface having a low coefficient of friction such as an ice board while avoiding an increase in mass and a decrease in productivity.

In order to achieve the above object, an icy / snow road pneumatic tire according to the present invention is an icy / snow road pneumatic tire having a run-flat function, wherein the relationship between the tire cross-sectional width SW and the tread contact width TW is 0.5 ≦ TW. /SW≦0.8, a rubber layer A having a JIS-A hardness of 30 to 50 at 0 ° C. is disposed on the surface of the shoulder region outside the tread contact width TW , and the thickness of the rubber layer A is 5 mm or less. it is characterized in that the.

  In the present invention, the soft rubber layer A is disposed in a shoulder region outside the tread contact width TW, that is, a region that is not grounded in a normal internal pressure state but is grounded in a zero pressure state. Therefore, even if buckling occurs in the tread portion in the zero pressure state, a high frictional force can be generated between the tire and the road surface based on the rubber layer A. Thereby, run flat running on a road surface having a low coefficient of friction such as an ice plate becomes possible. Since the soft rubber layer A is not grounded in the normal internal pressure state, it does not adversely affect the running performance in the normal internal pressure state. Moreover, since it is not necessary to add a reinforcing layer for suppressing buckling to the tread portion, it is possible to avoid an increase in mass and a decrease in productivity.

In the present invention, the rubber layer B covered with the rubber layer A is disposed in the shoulder region, the 300% modulus of the rubber layer B is larger than the 300% modulus of the rubber layer A, and 300% of the rubber layer B. The modulus is preferably 8 MPa or more. By disposing the high modulus rubber layer B as the base of the rubber layer A, it is possible to prevent the land portion of the shoulder region from being greatly deformed during run flat running, and to improve the performance and durability on ice during run flat running. Can do. Here, the thickness of the rubber layer A is 5 mm or less . Moreover, it is desirable to arrange sipes extending in the tire width direction in the land portion existing in the shoulder region.

  In the present invention, a pneumatic tire having a run-flat function means that, for example, a reinforcing rubber layer having a crescent cross section is embedded in a sidewall portion, and a load in a zero pressure state is supported based on the rigidity of the reinforcing rubber layer. However, the load supporting structure is not particularly limited.

  The tire cross-sectional width SW is a cross-sectional width measured in a state where the tire is mounted on a standard rim in accordance with a method for measuring dimensions of a new tire specified in the JATMA Yearbook (2005 version). Further, the tread contact width TW is a contact width measured in a state where a tire is mounted on a standard rim in accordance with a method for measuring a static load radius specified in the JATMA Yearbook (2005 version). In other words, in the case of passenger car tires, the internal pressure is set to 180 kPa, and a mass corresponding to 88% of the maximum load capacity is loaded. In the case of other tires, the internal pressure is set to the maximum air pressure (the air pressure corresponding to the maximum load capacity), and the mass corresponding to the maximum load capacity is applied.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an icy and snowy road pneumatic tire according to an embodiment of the present invention, and FIG. 2 shows an enlarged main part thereof. In FIG. 1, 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. As shown in FIG. 1, two carcass layers 4 are mounted between a pair of bead portions 3 and 3, and ends of these carcass layers 4 are folded around the bead core 5 from the tire inner side to the outer side. . A bead filler 6 made of high-hardness rubber is disposed on the outer periphery of the bead core 5, and the bead filler 6 is wrapped by a folded portion of the carcass layer 4. On the inner side in the tire axial direction of the carcass layer 4 in the sidewall portion 2, a crescent-shaped reinforcing rubber layer 7 made of high-hardness rubber is disposed. Further, on the outer peripheral side of the carcass layer 4 in the tread portion 1, a two-layer belt layer 8 including a reinforcing cord inclined with respect to the tire circumferential direction is disposed. Further, a belt cover layer 9 including reinforcing cords oriented in the tire circumferential direction is disposed on the outer peripheral side of the belt layer 8.

  Since the pneumatic tire includes the reinforcing rubber layer 7 having a crescent cross section in the sidewall portion 2, the pneumatic tire can support a load in a zero pressure state based on the rigidity of the reinforcing rubber layer 7. That is, this pneumatic tire has a run-flat function.

  In the pneumatic tire described above, the relationship between the tire cross-sectional width SW and the tread ground contact width TW is 0.5 ≦ TW / SW ≦ 0.8, and as shown in FIG. 2, the shoulder outside the tread ground contact width TW. A rubber layer A having a JIS-A hardness of 30 to 50 at 0 ° C. is disposed on the surface of the region.

  Thus, by arranging the soft rubber layer A in the shoulder region outside the tread contact width TW, even if buckling occurs in the tread portion 1 in the zero pressure state, the tire, road surface and Since a high frictional force can be generated during this period, it becomes possible to run flat on a road surface having a low coefficient of friction such as ice. Further, since the soft rubber layer A is not grounded in the normal internal pressure state, the running performance in the normal internal pressure state is not adversely affected. And since it is not necessary to add the reinforcement layer for suppressing a buckling to the tread part 1, the increase in mass resulting from such an additional reinforcement layer and the fall of productivity are not caused.

  Here, if the TW / SW is less than 0.5, the performance on ice in the normal internal pressure state becomes insufficient, and conversely if it exceeds 0.8, the ground contact area in the zero pressure state cannot be sufficiently obtained. Performance on ice during run-flat running will be insufficient. A preferable range of TW / SW is 0.65 to 0.80.

  Further, when the JIS-A hardness of the rubber layer A is less than 30, the wear resistance is lowered, and when it exceeds 50, the performance on ice becomes insufficient. A preferable range of the JIS-A hardness of the rubber layer A is 35 to 45. While the rubber layer A has a low hardness, the rubber layer C within the tread ground contact width TW may have a JIS-A hardness of 45 to 60 in consideration of performance on ice under normal internal pressure conditions.

  The thickness D of the rubber layer A is 5 mm or less, preferably 1 mm to 3 mm. When the thickness D of the rubber layer A exceeds 5 mm, the shoulder area block collapses due to the low-hardness rubber layer A when running on ice in a zero pressure state, and the ground contact area decreases, resulting in on-ice performance. May decrease. In order to increase the frictional force on ice, the rubber layer A may be blended with at least one selected from the group consisting of thermally expandable microcapsules, thermally expandable graphite, a foaming agent-containing resin, and short fibers.

  In the pneumatic tire, a rubber layer B covered with a rubber layer A is disposed in a shoulder region outside the tread contact width TW. The 300% modulus of the rubber layer B is larger than the 300% modulus of the rubber layer A, and the 300% modulus of the rubber layer B is set to 8 MPa or more, preferably in the range of 8 MPa to 18 MPa. By setting the 300% modulus of the rubber layer B to 8 MPa or more, it is possible to prevent the block in the shoulder region from being greatly deformed during run-flat running, and to improve the performance on ice and durability during run-flat running.

  FIG. 3 shows an example of a tread pattern employed in the pneumatic tire for an icy and snowy road. In FIG. 3, a plurality of vertical grooves 11 extending in the tire circumferential direction and a plurality of horizontal grooves 12 extending in the tire width direction are formed in the tread portion 1, and a plurality of blocks 13 are formed by the vertical grooves 11 and the horizontal grooves 12. And ribs 14 are defined. A plurality of sipes 15 extending in the tire width direction are provided in each land portion including the blocks 13 and the ribs 14. The sipe 15 contributes to the improvement of performance on ice by the edge effect. As shown in FIG. 3, when the sipe 15 is disposed also in the shoulder region outside the tread contact width TW, it is possible to sufficiently ensure the performance on ice during run-flat travel.

  However, the present invention is not limited to the tread pattern described above, and any pattern suitable for icy and snowy roads can be employed, and it is particularly preferable to employ a pattern having a block tone.

  In a pneumatic tire for an icy and snowy road having a tire size of 245 / 40R18 and a run-flat function, the tire is disposed on the surface of the shoulder region outside the tread contact width TW, the ratio TW / SW of the tire cross-section width SW and the tread contact width TW Conventional Example 1, Examples 1 to 8 in which the physical properties of the rubber layer A, the physical properties of the rubber layer B serving as the base of the rubber layer A, and the physical properties of the rubber layer C within the tread ground width TW are varied as shown in Table 1. Tires of Comparative Examples 1 to 5 were produced.

  In the tire of Conventional Example 1, a steel belt reinforcing layer for preventing buckling is added to the tread portion. On the other hand, the tires of Examples 1 to 8 and Comparative Examples 1 to 5 are not provided with a steel belt reinforcing layer. In the tires of Conventional Example 1 and Comparative Example 1, the tread portion is composed of only the rubber layer C without providing the rubber layers A and B. All the test tires have the same block-tread tread pattern, and a plurality of sipes extending in the tire width direction are formed on the land portion thereof. For the tire of Example 8, from the tread ground contact width TW. The sipe is also arranged in the land portion existing in the outer shoulder region, and the sipe is not arranged in the land portion of the shoulder region for other tires.

  These test tires were evaluated for on-ice braking performance, on-ice start performance, wear resistance, and mass by the following test methods, and the results are also shown in Table 1.

Ice braking performance:
The test tire is fitted to a wheel with a rim size of 18x8J and mounted on a domestic rear-wheel drive vehicle. ABS braking is performed from a running state of 40 km / h on an icy road under conditions of air pressure of 230 kPa, and completely The braking distance until stopping was obtained. Moreover, the valve core of one front wheel was pulled out, the tire internal pressure was set to 0 kPa, and the braking distance was obtained in the same manner as described above under these conditions. The evaluation results are shown as an index with the conventional example 1 as 100, using the reciprocal of the measured value. The larger the index value, the better the braking performance on ice.

Ice start performance:
A test tire is fitted to a wheel with a rim size of 18 x 8 J and mounted on a domestic rear-wheel drive vehicle. The valve core of one front wheel is removed, the tire internal pressure is set to 0 kPa, and the vehicle is slowed down from a state where it completely stops on an icy road. After starting the vehicle, the vehicle was gradually accelerated and the behavior of the tire adjusted to 0 kPa was observed. A case where the tire is rotating in the same manner as the other tires is indicated by “◯”, a case where the rotation is less than that of the other tires is indicated by “Δ”, and a case where the tire is not rotating is indicated by “X”.

Abrasion resistance:
A test tire is fitted to a wheel with a rim size of 18 × 8J and mounted on a domestically produced rear wheel drive vehicle. The valve core of one front wheel is pulled out to make the tire internal pressure 0 kPa. The amount of wear was confirmed. The case of an acceptable wear state is indicated by “OK”, and the case of an unacceptable wear state is indicated by “NG”.

mass:
The mass of the test tire was measured. The evaluation results are shown as an index with the conventional example 1 as 100, using the reciprocal of the measured value. A larger index value means lighter weight.

  As shown in Table 1, the tires of Examples 1 to 8 are lighter than Conventional Example 1, and can obtain results equivalent to Conventional Example 1 in terms of braking performance on ice, starting performance on ice, and wear resistance. did it. On the other hand, the tire of Comparative Example 1 was inferior to Conventional Example 1 in braking performance on ice in a zero pressure state. The tires of Comparative Examples 2 and 5 were inferior to Conventional Example 1 in braking performance on ice and starting performance on ice in a zero pressure state. The tire of Comparative Example 3 was inferior to Conventional Example 1 in braking performance on ice under normal internal pressure conditions. The tire of Comparative Example 4 was inferior in wear resistance to Conventional Example 1.

1 is a meridian cross-sectional view showing a pneumatic tire for an icy and snowy road according to an embodiment of the present invention. It is sectional drawing which shows the principal part of the pneumatic tire of FIG. FIG. 2 is a development view illustrating an example of a tread pattern of the pneumatic tire in FIG. 1. It is sectional drawing which shows the buckling state of the tread part in the conventional pneumatic tire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Bead filler 7 Reinforcement rubber layer 8 Belt layer 9 Belt cover layer 11 Vertical groove 12 Horizontal groove 13 Block 14 Rib 15 Sipe A, B, C Rubber layer SW Tire cross section Width TW Tread contact width

Claims (4)

In a pneumatic tire for a snowy and snowy road having a run-flat function, the relationship between the tire cross-sectional width SW and the tread ground contact width TW is 0.5 ≦ TW / SW ≦ 0.8, and the shoulder region outside the tread ground contact width TW A pneumatic tire for icy and snowy roads , wherein a rubber layer A having a JIS-A hardness of 30 to 50 at 0 ° C. is disposed on the surface , and the thickness of the rubber layer A is 5 mm or less .   A rubber layer B covered with the rubber layer A is disposed in the shoulder region, the 300% modulus of the rubber layer B is set larger than the 300% modulus of the rubber layer A, and the 300% modulus of the rubber layer B is increased. The pneumatic tire for icy and snowy roads according to claim 1, wherein the pressure is 8 MPa or more. The air for ice and snowy road according to claim 1 or 2, wherein the rubber layer A is blended with at least one selected from the group consisting of thermally expandable microcapsules, thermally expandable graphite, a foaming agent-containing resin, and short fibers. Enter tire.   The pneumatic tire for ice and snowy road according to any one of claims 1 to 3, wherein a sipe extending in a tire width direction is disposed in a land portion existing in the shoulder region.

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