JP2013169870A - Pneumatic tire - Google Patents

Abstract

The present invention provides a pneumatic tire that improves both traction performance and lateral grip performance.
A pneumatic tire is formed with a tread pattern that is asymmetrical with respect to the tire equator and in which a mounting direction of the vehicle is designated. The tread rubber 2G includes an inner rubber layer 12 and an outer rubber layer 13, and the inner rubber layer 12 is made of a short fiber reinforced rubber FG in which short fibers 14 are blended. Moreover, the short fiber reinforced rubber FG is arranged on the vehicle inner side and the short fiber 14 is oriented at an angle of ± 15 ° with respect to the tire circumferential direction, and on the vehicle outer side and the short fiber 14 is And a vehicle outer side portion 16 oriented at an angle of ± 15 ° with respect to the tire axial direction.
[Selection] Figure 2

Description

  The present invention relates to a pneumatic tire suitable for running on rough terrain that can improve traction performance and lateral grip performance in, for example, rally and dirt trials.

  For example, in the case of racing rough terrain tires used in rally, dirt trials, etc., the traction performance that firmly grips the rough road surface and transmits the driving force to the road surface, and the skidding of the tire during turning It is important to achieve both the side grip performance for suppressing.

  For this reason, various proposals have been made regarding the block shape, groove shape, and the like in the tread pattern. Generally, a pneumatic tire is proposed in which a tread pattern on the inner side of the vehicle has many grooves extending in the tire axial direction, and a tread pattern on the outer side of the vehicle has many grooves extending in the tire circumferential direction. (See Patent Documents 1 and 2 below). Such a pneumatic tire is a tread pattern on the inner side of the vehicle in which a large ground load acts when traveling straight, and a tread pattern on the outer side of the vehicle in which a large ground load acts upon turning while a frictional force is exerted by an edge in the tire axial direction. Since the frictional force due to the tire circumferential edge is exhibited, both traction performance and lateral grip performance are achieved.

JP 2008-285004 A JP 2011-93391 A

  However, since the pneumatic tire as described above exhibits an edge effect due to the arrangement of the grooves, the pattern rigidity in the direction orthogonal to the longitudinal direction of the grooves is likely to decrease. That is, the tire circumferential rigidity in the tread pattern on the vehicle inner side and the tire axial rigidity in the tread pattern on the vehicle outer side are likely to decrease. And in such a tire, there existed a problem that the straight running stability and steering stability in particular on a paved road surface or a comparatively hard rough road surface fell.

  The present invention has been devised in view of the above problems, and is based on the fact that short fibers are arranged on the inner rubber layer of the tread rubber, and the orientation directions of the short fibers are different between the vehicle inner side and the vehicle outer side. The main object of the present invention is to provide a pneumatic tire with improved traction performance on a paved road surface and the like while achieving both traction performance and lateral grip performance on rough terrain.

  Among the present inventions, the invention according to claim 1 is a pneumatic tire in which the tread rubber disposed in the tread portion is formed with a tread pattern that is asymmetrical with respect to the tire equator and in which the mounting direction of the vehicle is specified. The tread rubber includes an inner rubber layer and an outer rubber layer disposed on the outer side in the tire radial direction of the inner rubber layer, and the inner rubber layer is a short fiber reinforced rubber in which short fibers are blended. And the short fiber reinforced rubber is disposed on the vehicle inner side than the tire equator when the vehicle is mounted and the short fiber is oriented at an angle of ± 15 ° with respect to the tire circumferential direction; The vehicle has a vehicle outer side portion that is arranged on the vehicle outer side than the tire equator when mounted and the short fibers are oriented at an angle of ± 15 ° with respect to the tire axial direction.

  The invention according to claim 2 is the pneumatic tire according to claim 1, wherein the short fiber reinforced rubber contains 5 to 20% by mass of the short fiber with respect to 100% by mass of a rubber component.

  The invention according to claim 3 is the pneumatic tire according to claim 1 or 2, wherein the short fiber has a length L of 0.1 to 5 mm and an outer diameter D of 1 to 100 µm.

  The invention according to claim 4 is the pneumatic tire according to any one of claims 1 to 3, wherein the thickness t1 of the inner tread rubber layer is 20 to 50% of the total thickness T of the tread rubber. It is.

  Further, in the invention according to claim 5, the tread pattern includes a ground surface that contacts the road surface and a groove that is recessed from the ground surface, and the total area S1 of the virtual ground surface that fills all the grooves, 5. The pneumatic tire according to claim 1, wherein a land ratio that is a ratio S <b> 2 / S <b> 1 with a total surface area S <b> 2 of the ground contact surface is 40 to 65%.

  In the pneumatic tire of the present invention, the inner rubber layer of the tread rubber is made of short fiber reinforced rubber in which short fibers are blended. Such a tread rubber increases the rigidity in the orientation direction of the short fibers, so that the rigidity of the tread portion can be improved with anisotropy.

  Further, the short fiber reinforced rubber is arranged on the vehicle inner side when the vehicle is mounted and the short fiber is oriented in the tire axial direction, and when the vehicle is worn, the short fiber is arranged on the vehicle outer side and the short fiber is oriented in the tire circumferential direction. A vehicle outer portion. Such a short fiber reinforced rubber improves the rigidity in the tire circumferential direction at the tread portion inside the vehicle, and improves the rigidity in the tire axial direction at the tread portion outside the vehicle. In addition to rough terrain, this provides excellent straight traction performance on the tread inside the vehicle on paved roads, etc., and excellent lateral grip performance when turning on the tread outside the vehicle. Is done.

It is a schematic top view when the vehicle with which the pneumatic tire of this embodiment was mounted on four wheels is viewed from above. It is sectional drawing which shows one Embodiment of the pneumatic tire of this invention. It is an expanded view which shows the tread pattern of this embodiment. It is an expanded sectional view of the tread part of FIG. It is an expanded view of the tread pattern which shows the orientation direction of the short fiber of an inner side rubber layer.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic top view of a vehicle M with the pneumatic tire 1 of this embodiment mounted on four wheels as viewed from above. The pneumatic tire 1 according to this embodiment includes a tread pattern that is asymmetrical with respect to the tire equator C. In order to maximize the action of the pattern, the tire 1 is designated with a direction of mounting on the vehicle. The pneumatic tire 1 of the present embodiment includes a right wheel 1R and a left wheel 1L. Further, the direction of mounting on the vehicle is displayed, for example, on the sidewall portion 3 of the tire 1 by characters or patterns (not shown).

  FIG. 2 is a tire meridian cross-sectional view including a tire shaft in a normal state of the pneumatic tire 1 of the present embodiment. In addition, the tread end Tei on the right side in the drawing is arranged inside the vehicle. Here, the normal state is a no-load state in which the tire is assembled on the normal rim and the normal internal pressure is filled. Hereinafter, unless otherwise specified, the dimensions of each part of the tire are values measured in this normal state.

  The “regular rim” is a rim determined for each tire in a standard system including a standard on which a tire is based. For example, JATMA is a standard rim, TRA is “Design Rim”, ETRTO Then "Measuring Rim". Furthermore, “regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is JATMA and the table “TIRE LOAD LIMITS AT” is TRA. Maximum value described in “VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” for ETRTO, but 180 kPa for tires for passenger cars.

  As shown in FIG. 2, the pneumatic tire 1 of the present embodiment includes a carcass 6 that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and the outer side in the tire radial direction of the carcass 6 and the tread. A belt layer 7 disposed inside the portion 2 and a bead apex rubber 8 that tapers outward from the bead core 5 in the radial direction of the tire are provided. In this example, the competition is used for running on rough terrain. A pneumatic tire for is shown.

  The carcass 6 includes one or a plurality of carcass plies 6A and 6B in the present embodiment. The carcass plies 6A and 6B are made of a cord ply in which a carcass cord is covered with a thin topping rubber. Further, the carcass cord is disposed to be inclined with respect to the tire equator C at an angle of 60 ° to 90 °, for example. As the carcass cord, an organic fiber cord such as polyester cord, nylon, rayon, or aramid is preferably used.

  Each of the carcass plies 6A and 6B includes a toroid-shaped main body portion 6a extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and a tire shaft extending around the bead core 5 connected to the main body portion 6a. And a folded portion 6b that is folded from the inner side to the outer side and extends outward in the tire radial direction.

  The belt layer 7 includes a belt ply in which belt cords are arranged at an angle of, for example, 10 to 45 ° with respect to the tire equator C, and is formed of two belt plies 7A and 7B in this example. The belt layer 7 has a belt cord that intersects with each other between the plies, thereby increasing the belt rigidity and firmly reinforcing almost the entire width of the tread portion 2. As the belt cord, for example, a highly elastic organic fiber cord such as aramid or rayon is adopted.

  The bead apex rubber 8 is made of hard rubber, is disposed between the main body portion 6a and the folded portion 6b, and extends in a tapered manner from the bead core 5 outward in the tire radial direction. Thereby, the bead part 4 and the sidewall part 3 are reinforced.

  FIG. 3 is a development view showing an example of the tread pattern TP of the present embodiment. The tread pattern TP includes a ground surface 10 that contacts the road surface and a groove 9 that is recessed from the ground surface 10. Further, the ground contact surface 10 is formed by a tread surface of a block 11 separated by the groove 9.

  Among the tread patterns TP, the tread pattern TPi disposed on the vehicle inner side than the tire equator C preferably includes a groove 9A extending parallel to the tire axial direction. As a result, a large frictional force due to the edge in the tire axial direction is exhibited, and the traction performance during straight traveling can be improved. In addition, the tread pattern TPo disposed on the vehicle outer side than the tire equator C desirably includes a groove 9B that extends while inclining with respect to the tire axial direction. Thereby, the effect of a large frictional force at the time of turning can be exerted by the edge in the tire circumferential direction, and the lateral grip performance can be improved.

  The tread pattern TP has a land ratio of preferably 40% or more, more preferably 50% or more, and preferably 65% or less, more preferably 55% or less. The land ratio is a ratio S2 / S1 of the total area S1 of the virtual ground plane filling all the grooves 9 and the total surface area S2 of the ground plane 10, and if it is smaller than 40%, block chipping occurs. If it exceeds 55%, the running performance on rough terrain may be reduced.

  Further, when the groove depth d1 of the groove 9 is reduced, drainage performance may be reduced and wet performance may be reduced. When the groove depth d1 is increased, rigidity of the block 11 may be reduced and steering stability may be reduced. . From such a viewpoint, the groove depth d1 is preferably 9 mm or more, more preferably 10 mm or more, and preferably 12 mm or less, more preferably 11 mm or less.

  FIG. 4 shows an enlarged cross-sectional view of the tread portion 2. The tread rubber 2G disposed on the outer side of the belt layer 7 includes an inner rubber layer 12 and an outer rubber layer 13 disposed on the outer side in the tire radial direction of the inner rubber layer 12, and in this embodiment, two layers. Composed.

  In the present embodiment, the inner rubber layer 12 is disposed in contact with the belt layer 7 or via an insulation rubber (not shown) and extends in the tire axial direction. Such an inner rubber layer 12 can improve the rigidity of the tread portion 2 in cooperation with the belt layer 7.

  The inner rubber layer 12 is made of a short fiber reinforced rubber FG in which short fibers 14 are blended. When the short fiber reinforced rubber FG is extruded before vulcanization, the short fibers 14 are oriented in the rubber extrusion direction, so that the elastic modulus of the rubber in this orientation direction is improved.

  Examples of the short fiber 14 include nylon, polyester, aramid, and other organic fibers such as rayon, vinylon, cotton, cellulose resin, and crystalline polybutadiene. These may be used alone or in combination of two or more. Can also be used.

  If the blending amount of the short fibers 14 with respect to the rubber component of the short fiber reinforced rubber FG is small, the rigidity improvement effect may be reduced, and if it is large, the inner rubber layer 12 is likely to be peeled off, and block breakage may occur. There is. From such a viewpoint, it is desirable that the short fiber 14 is contained in an amount of preferably 5% by mass or more, more preferably 10% by mass or more, with respect to 100% by mass of the rubber component of the short fiber reinforced rubber FG. The content is preferably 20% by mass or less, more preferably 15% by mass or less.

  If the length L of the short fiber 14 is reduced, the rigidity improvement effect may be reduced. If the length L is increased, the adhesion with the outer rubber layer 13 and the belt layer 7 is reduced, and the block 11 is cracked or chipped. There is a risk. From such a viewpoint, the length L is preferably 0.1 mm or more, more preferably 1.5 mm or more, and preferably 5 mm or less, more preferably 3.5 mm or less.

  Further, if the outer diameter D of the short fiber 14 is reduced, the rigidity improving effect may be reduced. If the outer diameter D is increased, the adhesiveness with the outer rubber layer 13 and the belt layer 7 is reduced and the durability of the block 11 is improved. May decrease. From such a viewpoint, the outer diameter D is preferably 1 μm or more, more preferably 40 μm or more, and preferably 100 μm or less, more preferably 60 μm or less.

  FIG. 5 is a development view showing the orientation direction of the short fibers 14 of the inner rubber layer 12. The tread pattern TP is displayed with a virtual line. As shown in FIG. 5, the short fiber reinforced rubber FG is arranged on the vehicle inner side than the tire equator C when the vehicle is mounted, and the short fibers 14 are oriented at an angle of ± 15 ° with respect to the tire circumferential direction. It has a vehicle inner side portion 15 and a vehicle outer side portion 16 that is arranged on the vehicle outer side than the tire equator when the vehicle is mounted and in which the short fibers 14 are oriented at an angle of ± 15 ° with respect to the tire axial direction.

  Such a vehicle inner portion 15 exhibits a large rigidity with respect to the tire circumferential direction, and improves the traction performance when traveling straight. In particular, when the pattern rigidity in the tire circumferential direction is reduced by the groove 9A as in the present embodiment, the vehicle inner side portion 15 effectively reinforces the rigidity in the tire circumferential direction, and the edge effect of the groove 9A. Combined with traction performance is improved.

  Further, the vehicle outer portion 16 exhibits a large rigidity with respect to the tire axial direction, and improves the lateral grip performance during turning. In particular, when the pattern rigidity in the tire axial direction is reduced by the groove 9B, the vehicle outer side portion 16 effectively reinforces the rigidity in the tire axial direction, and combined with the edge effect of the groove 9B, the side grip Performance is improved. Therefore, the vehicle inner portion 15 and the vehicle outer portion 16 can improve both the traction performance and the lateral grip performance of the tire 1 as a whole.

  The short fibers 14 of the vehicle inner side portion 15 are preferably oriented at an angle of ± 10 °, more preferably at an angle of ± 5 ° with respect to the tire circumferential direction. Thereby, the rigidity in the tire circumferential direction can be further improved. Further, from the same viewpoint, the short fibers 14 of the vehicle outer side portion 16 are preferably oriented at an angle of ± 10 °, more preferably at an angle of ± 5 ° with respect to the tire axial direction. In addition, the said orientation means that 80% or more of the short fibers 14 mix | blended with the vehicle inner side part 15 and the vehicle outer side part 16 exists in the range of the said angle in consideration of rubber processing technology.

  The outer rubber layer 13 is disposed in contact with the inner rubber layer 12 and appears on the outer surface 2S of the tread portion 2. Such an outer rubber layer 13 prevents the inner rubber layer 12 from appearing on the outer surface 2S of the tread portion 2 and suppresses cracking of the inner rubber layer 12 and the like.

  If the thickness t1 of the inner rubber layer 12 is reduced, the rigidity improving effect may be reduced. If the thickness t1 is increased, the thickness of the outer rubber layer 13 may be reduced and the wear resistance of the block 11 may be reduced. . From such a viewpoint, the thickness t1 is preferably 20% or more, more preferably 30% or more, and preferably 50% or less, more preferably 40% with respect to the total thickness T of the tread rubber 2G. The following is desirable.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  A pneumatic tire having the basic structure shown in FIG. 2 and having a size of 205 / 65R15 was prototyped based on the specifications shown in Table 1. Each sample tire uses nylon as a short fiber. Each sample tire was tested for traction performance, side grip performance, lap time, and block durability. Further, as Comparative Example 1, the same test was performed for a tire in which short fibers are not disposed on the inner rubber layer. The test method is as follows.

<Traction performance, side grip performance>
Each of the test tires assembled on a rim with a rim size of 7J x 15 was mounted on all wheels of a four-wheel drive vehicle with a displacement of 2000cc, and a test run was conducted on a dirt trial course with 1.5km per lap. ”And“ lateral grip performance ”were evaluated by sensory evaluation with a test driver. The results are expressed in a five-point method with 5 points as the perfect score, and the larger the value, the better. The evaluation contents of each item are as follows.
Traction performance: Evaluate grip performance when driving force is applied. Side grip performance: Evaluate grip performance when turning.

<Lap time>
Under the above conditions, the lap time for one round of the dirt trial course was measured. In addition, the result was measured twice and the favorable result is displayed.

<Block durability>
After the lap time measurement, the presence or absence of uneven wear, cracks, and chipping of the blocks of each test tire was visually evaluated. The results are expressed in a five-point method with 5 points as the perfect score, and the larger the value, the better.
The test results are shown in Table 1.

  As shown in the table, it can be confirmed that in the tires of the examples, both the traction performance and the lateral grip performance are improved and the lap time is shortened.

5 Bead core 6 Carcass 7 Belt layer 8 Bead apex rubber 9 Groove 10 Ground surface 11 Block 12 Inner rubber layer 13 Outer rubber layer 14 Short fiber 15 Vehicle inner portion 16 Vehicle outer portion

Claims (5)

A pneumatic tire in which a tread pattern arranged in a tread rubber, which is asymmetrical with respect to the tire equator and designated for mounting on a vehicle, is formed on a tread rubber disposed in a tread portion,
The tread rubber includes an inner rubber layer, and an outer rubber layer disposed on the outer side in the tire radial direction of the inner rubber layer,
The inner rubber layer is made of a short fiber reinforced rubber containing short fibers,
Moreover, the short fiber reinforced rubber is disposed on the vehicle inner side than the tire equator when the vehicle is mounted, and the vehicle inner side portion in which the short fibers are oriented at an angle of ± 15 ° with respect to the tire circumferential direction,
A pneumatic tire characterized by having a vehicle outer portion disposed outside the tire equator when mounted on the vehicle and having the short fibers oriented at an angle of ± 15 ° with respect to the tire axial direction.   The pneumatic tire according to claim 1, wherein the short fiber reinforced rubber contains 5 to 20% by mass of the short fiber with respect to 100% by mass of a rubber component.   The pneumatic tire according to claim 1 or 2, wherein the short fibers have a length L of 0.1 to 5 mm and an outer diameter D of 1 to 100 µm.   The pneumatic tire according to any one of claims 1 to 3, wherein a thickness t1 of the inner tread rubber layer is 20 to 50% of a total thickness T of the tread rubber. The tread pattern has a ground surface that contacts the road surface, and a groove that is recessed from the ground surface,
The land ratio, which is a ratio S2 / S1, of the total area S1 of the virtual ground plane filling all the grooves and the total surface area S2 of the ground plane is 40 to 65%. The described pneumatic tire.

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