JP5364259B2 - tire - Google Patents

Description

  The present invention relates to a tire, and more particularly, to a tire having reduced rolling resistance while maintaining wearability and steering stability.

  When a pneumatic tire mounted on a vehicle is driven, the tire undergoes various deformations such as rubber crushing deformation and collapse deformation in the contact surface area, and the rubber hysteresis loss caused by these deformations is considered as rolling resistance of the tire. appear. The tire rolling resistance directly affects the fuel consumption performance of the vehicle because the tire rolling resistance is improved when the tire rolling resistance is low. Therefore, there is a strong demand to further improve tire rolling resistance, including environmental problems on a global scale.

It is well known that this type of hysteresis loss has a high rate of occurrence from the tread portion of the tire. Therefore, conventionally, in order to reduce this kind of hysteresis loss, means such as applying a rubber having a small tan δ to the tread rubber has been taken. However, when tan δ is reduced, wear resistance and steering stability performance are inevitably lowered, and therefore, measures have been taken to suppress the tread deformation itself (Patent Document 1).
Japanese Patent Application Laid-Open No. 2001-206012

  However, generally, when rolling resistance is reduced, steering stability on a wet road surface tends to deteriorate. Accordingly, an object of the present invention is to provide a tire that effectively reduces rolling resistance while maintaining wearability and steering stability.

In order to achieve the above object, the present invention provides a tire including a pair of bead portions and a pair of sidewall portions, a tread portion, a carcass of one or more plies, a belt, and a tread rubber having a main groove . The groove bottom and groove wall of the main groove are covered with a rubber sheet having a higher elastic modulus than the tread rubber , and among the rubber sheets covering the main groove, at least tan δ of the groove bottom is 50% of tan δ of the tread rubber. There is provided a tire characterized by being less than or equal to 0.06 or less .

  Furthermore, the tire of the present invention is characterized in that the elastic modulus of the rubber sheet has a value 1.3 times or more higher than the elastic modulus of the tread rubber.

  Furthermore, the tire of the present invention is characterized in that the rubber sheet has a thickness within 10% of the width of the block defined by the main groove.

  Furthermore, the tire of the present invention is characterized in that the blending amount of carbon black in the rubber sheet is 35% by mass or less.

  Furthermore, the tire of the present invention is characterized in that the rubber composition constituting the rubber sheet and the rubber composition constituting the tread rubber are different.

  According to the present invention, by covering the groove bottom and groove wall of the main groove of the tire with a rubber sheet having a higher elastic modulus than the tread rubber, it is possible to reduce rolling resistance while maintaining wearability and steering stability. .

  Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a left half sectional view of a tire according to the present invention, and FIG. 2 is a schematic diagram showing the deformation behavior of the outermost layer of the tread during rolling of the tire. Reference numeral 10 denotes a tread rubber, and the tread rubber 10 includes a base rubber B and a cap rubber 14. Reference numeral 16 denotes a groove provided in the tread rubber (cap rubber 14), and the bottom and side surfaces of the groove 16 are covered with the rubber sheet 12.

  In FIG. 1, the rubber sheet 12 has physical properties having a higher elastic modulus than the cap rubber 14. This configuration is the same for the right half of the tire equator plane E including the following points.

The effects of the present invention will be described below with reference to FIG. When a load is applied to the tire, the most distorted portion in the tire is the outermost layer in the tire block. Thus, it is possible to suppress the deformation of the entire block when a high flexibility in the outermost layer portion, it is effective to decrease the rolling rising resistance and compatibility of the grip without any loss of elasticity of the whole tread Is possible.

That is, as shown in FIG. 2A, when a compression load F is applied to a rubber block S of a normal tread, the rubber is not compressed as shown on the right side of FIG. block S is accompanied by deflection of a (mm) from the surface S ₀ position when unloaded, inflated in a direction perpendicular to the direction of action of the compressive load F. However, as shown in FIG. 2B, the same rubber block S ′ having the same shape as FIG. 2A in which the rubber sheet 12 is attached to the groove bottom and groove wall of the groove 16 provided in the cap rubber 14 is the same. When the compression load F is applied, the rubber sheet 12 works so as to suppress the swelling of the cap rubber 14 of the rubber block S ′, so that the bending amount b (mm) at that time is smaller than the bending amount a (mm). Become. That is, the relationship of a> b is established. This is because the rubber sheet 12 has higher elastic properties than the cap rubber 14 and has a larger deformation resistance against the compressive load than the cap rubber 14, so the rubber sheet 12 suppresses the compressive deformation of the cap rubber 14. Because it works like. As a result, the hysteresis of the tread rubber 10 is reduced and the rolling resistance can be reduced.

  Therefore, the elastic modulus of the outermost rubber sheet 12 used in the present invention is higher than that of the tread cap rubber 14. In particular, the elastic modulus of the rubber sheet 12 is preferably 1.3 times higher than the elastic modulus of the cap rubber 14. This is because if the elastic modulus of the rubber sheet 12 is 1.3 times higher than that of the cap portion of the tread, it is more advantageous in achieving the object of the present invention to reduce rolling resistance.

Further, if the elastic modulus of the rubber sheet 12 is large, the focus is distorted in the groove bottom when the block is distorted, the tanδ of the part is large, the rolling rising resistance is increased. Therefore in order to avoid such adverse effects, at least for the groove bottom, it is preferable to use a rubber having a small tanδ compared to tread rubber, thereby reducing the rolling rising resistance. Incidentally, not only the groove bottom only, it is more preferable that tanδ in groove walls to use a small rubber, thereby allowing further reduction of the rolling rising resistance. In this case, the tan δ of the rubber sheet 12 is preferably about 50% or less of the tan δ of the tread rubber, that is, the value of tan δ is preferably about 0.05 or less.

  Here, for example, the value of tan δ can be reduced by reducing the amount of reinforcing agent such as carbon black blended in the rubber of the rubber sheet. In addition, it is preferable that the compounding quantity of carbon black in this rubber sheet is 35 mass% to 20 mass% from the surface of ensuring elastic modulus.

  The thickness of the rubber sheet 12 is preferably within 10% of the width 18 of the block defined by the main groove 16 as shown in FIG. As a result, a sufficient contact area between the road surface and the tread rubber can be ensured, and excellent wear resistance and steering stability on a wet road surface can be exhibited. A specific preferable thickness of the rubber sheet is about 1 mm to 2 mm. The main groove may be a lateral groove for forming a lug or block in addition to the circumferential main groove shown in the figure.

  Moreover, in this invention, the composition of the rubber composition which comprises the rubber sheet 12 and the rubber composition which comprises the tread rubber 10 may differ. When the elastic modulus of the block surface is increased by using the same rubber composition as that of the tread rubber 10, the required physical properties are different between the rubber sheet 12 and the tread rubber 10, and therefore the vulcanization temperature needs to be set finely. . However, when different compositions are used, it is advantageous in that it is not necessary.

  The composition of the rubber sheet 12 used in the present invention is not particularly limited as long as the elasticity thereof is larger than the elastic modulus of the tread rubber 10, and a rubber composition containing a component normally used in this technical field. It can be. Specifically, natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber ( IIR) and other rubber components, fillers such as carbon black and silica, zinc white, stearic acid, sulfur, vulcanization accelerators, anti-aging agents, and other additives within a range that does not impair the purpose of the present invention. It can select and mix | blend suitably.

  The physical properties of the rubber sheet 12 can be adjusted by appropriately selecting the type of rubber component and compounding agent to be used and the compounding ratio thereof. Specifically, by increasing the blending amount of sulfur in the composition of the rubber sheet 12, the elasticity can be enhanced while maintaining the wear resistance. In order to secure the elastic modulus, the amount of sulfur is preferably 2.5 parts by mass or more. Further, by increasing the blending amount of the vulcanization accelerator of the rubber sheet 12, the elasticity can be increased by increasing the stitch density by crosslinking.

  Next, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples.

  When manufacturing radial tires for trucks and buses (size: 11R22.5), unvulcanized rubber sheets for high-elastic rubber sheets are bonded to the surface of unvulcanized tread rubber in the raw tire molding process and vulcanized. Later, a tire in which the groove bottom and the groove wall of the main groove formed in the tread rubber were covered with a highly elastic rubber sheet having a thickness of 1.5 mm was manufactured as an example tire. On the other hand, a normal tire in which the groove bottom and the groove wall of the main groove are not covered with the high-elasticity rubber sheet was also manufactured and used as a comparative tire. The rubber composition and physical properties of the rubber sheet and tread rubber are shown in Table 1 as Formulations 1 and 2. Table 1 also shows the results of examining the rolling resistance, wear resistance, and steering stability on wet surfaces of these tires.

(1) Rolling resistance A standard rim 7.5 × 22.5 was assembled, filled with an internal pressure of a maximum air pressure of 750 kPa, and the rolling resistance at a speed of 80 km / h was measured under a load of 24.5 kN. The rolling resistance value in the comparative example was set to 100, and the evaluation in the examples was evaluated relative to the index.

(2) Abrasion The tire of the example and the tire of the comparative example were mounted on a vehicle, and the amount of wear was calculated from the measurement of the remaining groove after traveling 100,000 km. As a result, travel distance / (groove depth before travel−groove depth after travel) was calculated, and the evaluation value in the comparative example was set to 100, and the evaluation in the examples was evaluated relative to the index. It shows that it is excellent in abrasion resistance, so that a numerical value is large.

(3) Steering stability Steering stability is controlled by a test driver on a wet road surface, with driving performance, braking performance, steering wheel response, road surface grip during steering, and controllability after exceeding the slip limit. Judgment was made comprehensively based on the evaluation and the stopping distance from 80 km / h. The value of the steering stability in the comparative example was set to 100, and the evaluation in the examples was evaluated relative to the index. When the difference between the indices is ± 1 to 5, it is a level that can be judged by the test driver, and when the difference exceeds ± 5, it is a level that can be judged by a general user. Each tire performance index indicates that the larger the value, the better the performance.

  As shown in Table 1, in the tire of the example, the rolling resistance was greatly improved. In addition, it was confirmed that the wear resistance and steering stability were sufficiently maintained, and the intended effect was achieved in the present invention.

  In a pneumatic tire, by covering the groove bottom and groove wall of the main groove of the tread with a rubber sheet having a higher elastic modulus than the tread rubber, it is possible to reduce rolling resistance while maintaining wearability and steering stability. . Since the pneumatic tire of the present invention has low rolling resistance, it is effective for keeping the fuel consumption of the vehicle low, and thus contributes greatly to the development of an environment-friendly vehicle.

It is a partial longitudinal cross-sectional view of the tire of this invention. It is a schematic diagram which shows the deformation | transformation behavior of the tread outermost layer at the time of tire rolling.

Explanation of symbols

B Base rubber 10 Tread rubber 12 Rubber sheet 14 Cap rubber 16 Groove 18 Block width

Claims (5)

In a tire including a pair of bead portions and a pair of sidewall portions, a tread portion, a carcass of one or more plies, a belt, and a tread rubber having a main groove, the groove bottom and groove wall of the main groove are formed on the tread. We covered with a rubber sheet having a high elastic modulus of rubber, of rubber sheet covering the main groove, tan [delta of at least the groove bottom is less than 50% of the tan [delta of the tread rubber, and is 0.06 or less A tire characterized by that.   The tire according to claim 1, wherein the elastic modulus of the rubber sheet has a value 1.3 times or more higher than the elastic modulus of the tread rubber.   The tire according to claim 1 or 2, wherein the rubber sheet has a thickness within 10% of a width of a block defined by the main groove.   The tire according to any one of claims 1 to 3, wherein a compounding amount of carbon black in the rubber sheet is 35% by mass or less.   The tire according to any one of claims 1 to 4, wherein the rubber composition constituting the rubber sheet and the rubber composition constituting the tread rubber are different in composition.

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