JP4891614B2 - Pneumatic tire for running on rough terrain - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire for irregular terrain travel capable of enhancing the traction property on a soft road surface and the steering stability during the irregular terrain travel without impairing the traction property on a hard road surface. <P>SOLUTION: In a block B provided on a tread part 2, n (n&ge;1) pairs of small grooves 10 extending in the circumferential direction are formed in an axial block wall Wj in the direction opposite to the tire axial direction. In the small grooves 10, the groove sectional shape orthogonal to their longitudinal direction is substantially U-shaped with a groove bottom being an arc-shaped part 11. In addition, the angle &theta; with respect to a tread Bs at the groove center of the small grooves 10 is set to be &le;30&deg;. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a pneumatic tire for running on rough terrain that has improved steering stability during running on rough terrain.

  For pneumatic tires for motorcycles running on rough terrain with a block pattern in the tread, the block spacing is set wide for soft dirt road surfaces such as sand, and soft mud and sand are compressed and scratched. The traction is generated. On the other hand, on a hard dirt road surface, the traction is enhanced by increasing the frictional force with the road surface by setting the block interval narrow so as to increase the contact area between the road surface and the tread surface (block surface).

  However, in general, courses used for competitions include both soft road surfaces and hard road surfaces, which are mixed. In order to obtain an appropriate traction on such a course, both a scratching effect by the edge and wall surface of the block and a road surface frictional force by the block surface are required. Conventionally, block arrangement, number of blocks, block shape, etc. are set so that this scratching effect and road friction force can be obtained in good balance, but such methods have limitations and are higher in recent years It is difficult to meet the demand for traction.

Therefore, the present invention is based on the fact that the axial block wall facing the tire axial direction is provided with n-shaped (1 ≦ n ≦ 4) small grooves having a substantially U-shaped cross section and extending in the circumferential direction. An object of the present invention is to provide a pneumatic tire for rough terrain that can improve traction on a soft dirt road surface while ensuring high traction on a dirt road surface, and exhibit excellent steering stability.

Japanese Patent Laid-Open No. 11-151912 Japanese Patent Laid-Open No. 11-245631

In order to achieve the above object, the invention of claim 1 of the present application has a tread portion having a circumferential block wall facing in the tire circumferential direction and an axial block wall facing in the tire axial direction. And a pneumatic tire for running on rough terrain provided with a plurality of blocks whose tread surface has a substantially rectangular shape,
The axial block wall is provided with n-shaped (1 ≦ n ≦ 4) small grooves extending in the circumferential direction,
The small groove has a substantially U-shape in which the groove cross-sectional shape perpendicular to the length direction has an arc-shaped portion at the groove bottom,
In addition, the angle θ of the groove center with respect to the tread surface is set to 30 ° or less.

In the invention of claim 2, the small groove is formed in a range region between the tread surface and a position separated from the tread surface by 3/4 times the block height. is doing.
According to a third aspect of the present invention, both ends of the small groove are opened at a circumferential edge of the axial block wall.
According to a fourth aspect of the present invention, both end portions of the small groove are cut off from the circumferential edge of the axial block wall at a distance L in the circumferential direction, and the distance L is in the range of 1.5 to 6.0 mm. It is characterized by that.
According to a fifth aspect of the present invention, the small groove is characterized in that the angle θ with respect to the tread surface is set to 10 to 30 °.
According to a sixth aspect of the present invention, the groove depth h from the axial block wall of the small groove is shallower as the small groove on the block bottom side.
The invention according to claim 7 is characterized in that the small grooves are 2 to 4 and the angle θ is 15 to 30 °.
The invention according to claim 8 is characterized in that the small groove has 2 to 3 stripes and the angle θ is 15 to 25 °.

In the present invention, as described above, n-shaped (1 ≦ n ≦ 4) small grooves extending in the circumferential direction are formed on the axial block wall of the block wall facing the tire axial direction. Therefore, sand and mud are hardened in the small groove and the block is difficult to come off from the dirt road surface, and the reaction force increases the longitudinal force. Further, the small groove can exert an edge effect, can increase the contact area with sand and mud on the block wall surface, and can increase the adhesive frictional force. These synergistic effects can improve traction on soft dirt road surfaces.

  In addition, the load on the block increases along with the improvement of traction, and there is a tendency for block missing due to the small groove. However, this block chipping can be suppressed by making the small groove into a substantially U-shaped cross section.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a pneumatic tire 1 for traveling on rough terrain (hereinafter referred to as a tire 1) includes a carcass 6 extending from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, and a tire of the carcass 6. And a breaker 7 arranged radially outside and inside the tread portion 2. In this example, the case where the tire 1 is an off-road motorcycle tire is illustrated, and in the tire meridional section, the tread surface 2S is smoothly curved into a convex arc shape and between the tread edges Te and Te. The width of the tire is the maximum tire width. This ensures high turning performance. The “tread edge” means the position of the outer edge in the tire axial direction in the block farthest from the tire equator C in the tire axial direction.

  The carcass 6 is formed of a plurality of (for example, two) carcass plies 6A in which organic fiber carcass cords are arranged at an angle of 15 to 45 ° in this example with respect to the tire circumferential direction. The carcass ply 6A increases tire rigidity by forming a cross ply structure in which carcass cords cross each other between plies. As the carcass 6, for example, a radial structure in which carcass cords are arranged at an angle of 75 to 90 ° with respect to the tire circumferential direction can be adopted. The carcass ply A is fixed to the bead core 5 by folding both ends around the bead core 5 from the inside to the outside.

  In the case of the cross-ply structure as in this example, the breaker 7 is mainly used for the purpose of protecting the carcass 6 from damage. In such a case, the breaker cord is usually formed by one or two breaker plies in which the breaker cord is arranged at an angle of, for example, 15 to 45 ° with respect to the tire circumferential direction, but may be omitted if necessary. In the case of the radial structure, the breaker 7 is formed by one or two breaker plies in which breaker cords are arranged at an angle of, for example, 0 to 30 ° with respect to the tire circumferential direction, and the tread portion 2 has a tag effect. To secure the necessary tire rigidity.

  Next, a block pattern in which a plurality of blocks B are protruded is employed for the tread portion 2. Although this block pattern is not particularly restricted, in this example, as shown in FIG. 2 developed in a plane, the row R1 of the first block B1 arranged on the tire equator C and the outer side thereof are arranged in the circumferential direction. Row R2 of second block B2, row R3 of third block B3 arranged in the circumferential direction further outside, row R4 of fourth block B4 arranged in the circumferential direction further outside thereof, and further It is composed of a total of 11 block rows including a row R5 of fifth blocks B5 arranged in the circumferential direction on the outer side and a row R6 of sixth blocks B6 arranged in the circumferential direction on the outer side.

  In the case of running on rough terrain, the block height H (shown in FIG. 4) of the block B is in the range of 10 to 20 mm, and the total area of the tread Bs which is the outer surface of the block is a ratio of the total tread area. The so-called land ratio is set in the range of 8 to 30%. As the block shape, the second block B2 is representatively described with reference to FIG. 3, and the circumferential block wall Ws facing the tire circumferential direction and the tire axial direction are opposed from the viewpoint of traction. An axial block wall Wj facing in the direction and the tread surface Bs having a substantially rectangular shape is used.

  Here, the “direction facing the tire circumferential direction” means a direction in which the angle θ1 with respect to the circumferential direction Fs is 60 ° or more, and the “direction facing the tire axial direction” means the tire axial direction. The direction in which the angle θ2 with respect to Fj is 60 ° or more is meant. The “substantially rectangular shape” includes a rectangle that is rectangular or square, and includes a rectangle whose four sides are surrounded by the circumferential block wall Ws and the axial block wall Wj. It can include a pentagon with one corner cut out at the other hypotenuse K. The hypotenuse K is preferably in a direction facing either the tire circumferential direction or the tire axial direction, but may not be opposed.

In the present invention, as shown in FIGS. 4 and 5, the block B is a block Bg with small grooves in which n-shaped (1 ≦ n ≦ 4) small grooves 10 extending in the circumferential direction are formed on the axial block wall Wj. It is comprised including. The small groove 10 has an angle θ of the groove center i with respect to the tread surface Bs of 30 ° or less. In this example, the small groove 10 is inclined at an angle θ of 10 to 30 °.

  In such a small grooved block Bg, since sand and mud are hardened in the small groove 10, the block Bg becomes difficult to come off from the dirt road surface, and the reaction force can increase the longitudinal force. Further, the small groove 10 can exert an edge effect by the groove side edge, can increase the contact area with sand and mud on the block wall surface, and can increase the adhesive frictional force. These synergistic effects can enhance traction on soft dirt road surfaces.

  However, as the traction increases, the load on the block Bg increases, so that a crack or the like is generated from the bottom of the small groove 10 to easily cause damage such as block chipping. Therefore, in the small groove 10, as shown in FIG. 6, the groove cross-sectional shape perpendicular to the length direction needs to be formed in a substantially U shape with the groove bottom as the arc-shaped portion 11. The radius of curvature r of the arcuate portion 11 is preferably 0.5 mm or more, and the groove side edge of the small groove 10 is preferably a sharp edge in order to obtain an edge effect. The groove width W of the small groove 10 is preferably in the range of 1.5 to 8.0 mm, and the groove depth h of the small groove 10 from the axial block wall Wj is preferably in the range of 0.5 to 5.0 mm. Further, in the small groove 10, the straight line X passing through the deepest point 10a farthest from the axial block wall Wj and the width center point Pc on the axial block wall Wj is radially outward with respect to the axial block wall Wj. The angle [beta] is 60 to 120 [deg.], And if it is 60 [deg.] Or less, the block Bg is easily removed from the dirt road surface, and it is difficult to sufficiently increase the longitudinal force. If the angle β exceeds 120 °, it is difficult to remove the mold from the tire during vulcanization formation, which may cause block damage.

  Here, when the angle θ formed by the small groove 10 with the tread surface Bs exceeds 30 °, the effect of compacting the mud and sand is reduced, and the traction cannot be sufficiently increased. This angle θ can be set in a range of 0 to less than 10 ° as in this example in a normal tire for traveling on rough terrain. However, especially on hard road surfaces, the tendency of block chipping increases, so in a tire intended for this hard road surface, it is preferable to incline at the angle θ of 10 to 30 ° to improve crack resistance. If the radius of curvature r of the arcuate part 11 is less than 0.5 mm, it is difficult to prevent cracks at the groove bottom. If the groove width W is smaller than 1.5 mm and the groove depth h is smaller than 0.5 mm, the small groove size becomes too small to obtain the effect of improving the traction. When W is greater than 8.0 mm and the groove depth h is greater than 5.0 mm, the inclination causes a lack of strength of the block Bg.

  Next, in the small groove 10, it is preferable that both end portions 10 e of the small groove 10 are interrupted at a distance L in the circumferential direction from the circumferential edge Es of the axial block wall Wj. This is because, by separating the distance L, the rigidity of the edge portion at the circumferential edge Es is ensured. As a result, the lateral force during turning can be maintained by the edge effect, and the turning performance can be enhanced. Become. For this purpose, the distance L is preferably in the range of 1.5 to 6.0 mm. If the distance L is less than 1.5 mm, the rigidity of the edge portion becomes insufficient and the turning performance tends to be lowered. On the contrary, if it exceeds 6.0 mm, it is difficult to sufficiently improve the traction improvement effect by the small groove 10. In particular, in a tire for a soft road surface, as illustrated in FIG. 7, the distance L is set to 0 mm, and both ends 10e of the small groove 10 are opened at the circumferential edge Es of the axial block wall Wj. It is preferable to secure the maximum length of the small groove 10.

Moreover, it is preferable from a viewpoint of traction to form the said small groove | channel 10 by 1-4 , Preferably it is 2-4. However, as the traction increases, the load on the block Bg increases and the strain concentrates at the base portion, so that cracks and the like are likely to occur. Therefore, in order to avoid the occurrence of cracks and the like, the small groove 10 has a range region Q between the tread surface Bs and a position separated from the tread surface Bs by 3/4 times the block height H. It is preferable to form the region. For the same reason, it is preferable that the groove depth h of the small groove 10 is formed so as to be gradually shallower as the small groove 10 is arranged on the block bottom side. Further, for the same reason, it is also preferable that the groove width W of the small groove 10 is formed so as to become narrower sequentially as the small groove 10 is arranged on the block bottom side.

  In order to secure the block strength, for example, as illustrated in FIG. 8, a raised portion 12 may be provided on the axial block wall Wj, and the small groove 10 may be formed in the raised portion 12. At this time, it is preferable that the raised height h2 of the raised portion 12 is equal to the groove depth h of the small groove 10 or smaller than the groove depth h.

Next, the entire block B can be formed by the small grooved block Bg. However, as shown in FIG. 1, in the range from the tire equator C to the tread edge Te, the tread surface 2S has a crown area Yi on the tire equator C side, a shoulder area Yo on the tread edge Te side, and a middle area Yn therebetween. It is preferable that at least the block B arranged in the crown region Yi and the middle region Yn is formed by the small grooved block Bg when the three regions are virtually divided into equal widths. This is because the longitudinal force at the time of driving and braking is normally applied when the vehicle is traveling straight or when the vehicle body is not tilted significantly, such as the corner inlet and outlet during turning, and the crown region Yi that contacts the ground in this state and the middle It is preferable to employ the small grooved block Bg in the region Yn. However, since the entire tire sinks on the road surface on the soft road surface, it is preferable to use the small grooved block Bg for all the blocks B, particularly in a tire intended for this soft road surface. The tread surface 2S means a tread contour surface that smoothly connects the tread surface Bs of each block B. Also when the block B is placed over two regions Y, that is, when the block B is placed on the division line PL, the size of the area of the tread 2 divided by block piece by the separation line PL Are defined to be arranged in the region Y having the larger area. Accordingly, in this example, it is considered that the first and second blocks B1 and B2 are arranged in the crown region Yi, and the third and fourth blocks B3 and B4 are arranged in the middle region Yn. It is assumed that the fifth and sixth blocks B5 and B6 are arranged in the shoulder region Yo.

  As described above, the particularly preferred embodiment of the present invention has been described in detail. However, the present invention is not limited to the illustrated embodiment, and can be applied to a tire for a four-wheeled vehicle in addition to a tire for a motorcycle. The present invention can be carried out by modifying the embodiment.

  A tire for a motorcycle with a tire size of 110 / 90-19 having the tread pattern of FIG. 2 and the internal structure shown in FIG. 1 was made on the basis of the specifications of Table 1, and each sample tire was installed on the rear wheel. The vehicle was evaluated for traction, braking, and crack resistance. Each tire has substantially the same specifications except those listed in Table 1. In the first embodiment, the groove depth h is formed so that the smaller groove arranged on the block bottom side is sequentially shallower. In the second embodiment, the groove width W is formed narrower in the smaller groove arranged on the block bottom side. In the table, the groove depth h and the groove width W indicate the values of the small grooves arranged on the most tread surface side. The groove depth h and groove width W of the small groove closest to the block bottom are reduced to about 50% of the groove depth h and groove width W of the small groove closest to the tread surface. In other examples and comparative examples, each small groove has the same size.

(1) Traction and braking properties:
The tire is mounted on the rear wheel of a 250cc off-road motorcycle with a rim (WM 2.15 × 19) and internal pressure (80 kPa), and the traction and braking characteristics when driving off-road are evaluated by the driver's sensory evaluation. Comparative Example 1 is indicated by an index of 100. A larger index is better. The front wheels were 80 / 100-21 size tires with no small grooves in the block.

(2) Crack resistance:
The tires after running 30 km on the hard road surface and the medium road surface between the hard road surface and the soft road surface were inspected, and the occurrence of cracks in the block was investigated.

Examples, traction, it can be confirmed that an excellent braking property.

It is sectional drawing which shows one Example of the pneumatic tire for rough terrain travel of this invention. It is an expanded view which shows the tread pattern. It is a top view which expands and shows a block. It is a side view of the axial block wall which shows a small groove. It is sectional drawing of the axial block wall which shows a small groove. It is sectional drawing of the direction orthogonal to the length direction of a small groove. It is a side view of the axial direction block wall which shows the other example of a small groove. It is sectional drawing of the axial direction block wall which shows the other example of a small groove.

Explanation of symbols

2 Tread portion 10 Small groove 10e Both ends 11 of small groove Arc-shaped portion B Block Bs Tread surface Q Range region Ws Circumferential block wall Wj Axial block wall

Claims (8)

The tread portion is provided with a plurality of blocks having a circumferential block wall facing in the tire circumferential direction and an axial block wall facing in the tire axial direction, and the tread surface having a substantially rectangular shape. A pneumatic tire for running on rough terrain,
The axial block wall is provided with n-shaped (1 ≦ n ≦ 4) small grooves extending in the circumferential direction,
The small groove has a substantially U-shape in which the groove cross-sectional shape perpendicular to the length direction has an arc-shaped portion at the groove bottom,
In addition, a pneumatic tire for traveling on rough terrain, wherein an angle θ of the groove center of the small groove with respect to the tread is 30 ° or less.   2. The rough terrain according to claim 1, wherein the small groove is formed in a range region between the tread surface and a position separated from the tread surface by 3/4 times the block height. Pneumatic tire for running.   The pneumatic tire for rough terrain travel according to claim 1 or 2, wherein both ends of the small groove are opened at circumferential edges of the axial block wall.   The both ends of the small groove are interrupted by a distance L in the circumferential direction from the circumferential edge of the axial block wall, and the distance L is in the range of 1.5 to 6.0 mm. Item 3. A pneumatic tire for traveling on rough terrain according to item 1 or 2.   The pneumatic tire for rough terrain travel according to claim 1, wherein the small groove has an angle θ with respect to the tread of 10 to 30 °. The pneumatic tire for rough terrain travel according to any one of claims 1 to 5, wherein the groove depth h from the axial block wall of the small groove is shallower toward the small groove on the block bottom side.   The pneumatic tire for running on uneven terrain according to any one of claims 1 to 6, wherein the small grooves are 2 to 4 and the angle θ is 15 to 30 °.   The pneumatic tire for running on uneven terrain according to any one of claims 1 to 7, wherein the small groove has 2 to 3 strips, and the angle θ is 15 to 25 °.

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