JP5797914B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to prevention of occurrence of cracks in a shoulder groove of a pneumatic tire in which a rib-like land portion is formed in a shoulder portion and improvement in uneven wear performance of a shoulder rib.

Conventionally, in a pneumatic tire in which a rib-like land portion (shoulder rib) continuous in the tire circumferential direction is formed on the shoulder portion, such as a heavy-duty pneumatic tire, a large load is applied to the shoulder rib during acceleration / deceleration or turning. Therefore, there is a problem that the shoulder rib is unevenly worn and cracks are easily generated in the shoulder groove.
As a method for suppressing uneven wear of the shoulder rib, for example, a method of changing the inclination of the wall surface facing the shoulder groove of the shoulder rib in the tire circumferential direction at a predetermined cycle has been proposed (for example, see Patent Document 1). .
On the other hand, as a method of reducing the occurrence of cracks in the shoulder groove, the groove bottom R of the shoulder groove is increased, or the wall surface facing the shoulder groove of the shoulder rib is inclined to the groove center side from the perpendicular of the shoulder rib tread surface. By providing a first inclined portion and a second inclined portion that is provided on the groove bottom side of the first inclined portion and is inclined further toward the groove center side than the first inclined portion, the rigidity of the shoulder rib is increased. A method of increasing the height has been proposed (see, for example, Patent Documents 2 and 3).

JP-A-9-11708 Japanese Patent Laid-Open No. 2005-193895 JP 2007-1434 A

However, in the method of changing the inclination of the wall surface of the shoulder rib at a predetermined cycle in the tire circumferential direction, although it is possible to reduce the occurrence of uneven wear to some extent, it is difficult to reduce the occurrence of shoulder groove cracks. . On the other hand, it is difficult to reduce the occurrence of uneven wear by the method of increasing the rigidity of the shoulder rib.
Further, in the method of providing the first and second inclined portions on the wall surface of the shoulder rib, the inclination change angle α which is the difference between the inclination angle θ ₁ of the first inclined portion and the inclination angle θ ₂ of the second inclined portion. = Θ ₂ −θ ₁ and the relationship between the depth D of the shoulder groove and the position d of the boundary between the first inclined portion and the second inclined portion can effectively reduce the groove bottom distortion at the time of riding on the curb. In addition to being unable to do so, wrinkles occurred at the boundary between the first inclined portion and the second inclined portion, and there was a risk that cracks would occur in the shoulder groove starting from this wrinkle.

  The present invention has been made in view of the conventional problems, and an object of the present invention is to provide a pneumatic tire that can sufficiently suppress uneven wear of shoulder ribs and can reduce the occurrence of cracks in shoulder grooves. .

The present invention relates to a shoulder land defined by a plurality of circumferential grooves extending along the circumferential direction of the tire on the tread surface of the tire and a shoulder groove located on the outermost side in the tire width direction of the circumferential grooves. A first inclined portion in which a groove wall surface on the shoulder land portion side of the shoulder groove is inclined toward the tire equatorial plane side with respect to a direction perpendicular to the tread surface of the shoulder land portion. And a second inclined portion that is inclined from the first inclined portion toward the tire equatorial plane at an inclination angle larger than the inclination angle of the first inclined portion and reaches the groove bottom of the shoulder groove. The inclination angle of the first inclined portion is constant in the tire circumferential direction, and the angle α formed by the first inclined portion and the second inclined portion changes along the tire circumferential direction, The second inclined part is arranged in the tire circumferential direction The said a plurality of sipes formed to open to the shoulder groove, the depth from the tire tread to the groove bottom of the shoulder groove from D, the tire tread and the second inclined portion and the first inclined portion When the depth to the boundary position is d, the maximum value of the angle α is α _max , and the minimum value of the angle α is α _min , the maximum value α _max and the minimum value α _min are (D−d ) ( Tan α _max −tan α _min ) ≧ 2.5 .
As a result, it is possible to suppress the wear of the shoulder part and the strain concentration on the shoulder bottom of the shoulder groove, and to suppress the increase of the shearing force when the lateral force is input, so the occurrence of rib tears and the uneven wear of the shoulder part Can be reliably suppressed.
In addition, since the above-mentioned restriction is provided for the maximum value α _max and the minimum value α _min of the angle α formed by the first inclined part and the second inclined part, the groove bottom distortion at the time of riding on the curb is reduced. The occurrence of cracks in the shoulder groove can be suppressed by relaxing.

Further, according to the present invention, the extension direction of the sipe when viewed from the tire tread side is perpendicular to a straight line or a curve connecting a boundary point between the bottom of the shoulder groove and the second inclined portion. Features.
As a result, it is possible to suppress an increase in the shearing force acting on the shoulder rib when a lateral force is input while suppressing the occurrence of sipetea, and thus it is possible to further suppress the uneven wear of the shoulder rib.

In the present invention, when the length along the groove wall surface of the sipe is w, and the distance along the tire circumferential direction between the opening of the sipe and the opening of the sipe adjacent to the sipe is l , L and w satisfy 1.5 <(l / w) <4.
As a result, the sipe density in the groove wall of the shoulder groove can be optimized, so that the rigidity of the inclined portion can be secured and the occurrence of sipe tear can be suppressed, and the shear deformation at the time of lateral force input can be suppressed and the shoulder portion. The uneven wear can be suppressed.

Further, the present invention, the inclination angle of the first inclined portion is taken as theta _1, wherein the theta ₁ is in the range of _{0 ° ≦ θ 1 ≦ 10 °} , said angle alpha is, 0 ° ≦ α < It is characterized by being in the range of 25 °.
Thereby, while being able to suppress the uneven wear of a shoulder part and the distortion concentration in the groove bottom of a shoulder groove can be suppressed, the early wear and uneven wear of a shoulder rib can be reduced reliably.

Further, since d is set so as to satisfy 0.1 <(d / D) ≦ 0.6, uneven wear can be reduced while ensuring the rigidity of the shoulder rib.

  The summary of the invention does not list all necessary features of the present invention, and sub-combinations of these feature groups can also be the invention.

It is a figure showing an example of a pneumatic tire concerning an embodiment of the invention. It is a figure which shows the state of the inclination of the groove wall surface of a shoulder groove. It is a table | surface which shows the performance test result of the tire of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1A is a development view of a tread pattern of a pneumatic tire 10 according to the present embodiment, and FIG. 1B is a cross-sectional view taken along line AA in FIG.
In FIG. 1A, only the tread pattern on one side of the center line CL indicating the center in the width direction of the tread pattern is shown.
In each figure, 11 to 13 are circumferential grooves formed in the tread portion of the tire 10 along the tire circumferential direction, 11 is a center main groove located at the center in the tire width direction, and 12 is on the outermost side in the tire width direction. A shoulder groove 13 positioned is a second main groove formed between the center main groove 11 and the shoulder groove 12.
14 is a lug groove provided so as to cross the center main groove 11, and the central land portion row 16 composed of a plurality of central blocks 15 is defined by the lug groove 14, the center main groove 11 and the second main groove 13. Is done. Reference numeral 17 denotes a rib-like land portion defined by the second main groove 13 and the shoulder groove 12, 18 denotes a shoulder land portion located on the outermost side in the tire width direction of the shoulder groove 12, and 19 denotes the second main groove 13. Lug groove that opens in the rib-shaped land portion 17 and ends in the rib-shaped land portion 17, 20 is a sipe provided on the groove wall surface 12 a on the shoulder land portion side of the shoulder groove 12, and 21 and 22 are the rib-shaped land portion 17 and the center respectively. A sipe provided in the block 15.
Since the shoulder land portion 18 is a land portion continuous in the tire circumferential direction, the shoulder land portion 18 is hereinafter referred to as a shoulder rib 18, and the sipe 20 provided on the groove wall surface 12 a of the shoulder rib 18 is referred to as a groove wall sipe 20.

As shown in FIG. 1 (b), the pneumatic tire 10 of the present invention has a wall surface on the shoulder groove 12 side of the shoulder rib 18, that is, a groove wall surface 12 a on the side located on the tire width direction end side of the shoulder groove 12. The tire is inclined toward the equator. The groove wall surface 12 a has different inclination angles on the tread surface 18 t side of the shoulder rib 18 and the groove bottom 12 b side of the shoulder groove 12. The inclination angle refers to an angle formed by a straight line k perpendicular to the tread surface 18t of the shoulder rib 18 and the groove wall surface 12a, which is indicated by a single oblique line in FIG.
Hereinafter, the tread surface 18t side of the shoulder rib 18 of the groove wall surface 12a is referred to as a first inclined portion 121, and the groove bottom 12b side of the shoulder groove 12 is referred to as a second inclined portion 122. The position p at which the inclination angle changes is referred to as the boundary between the first inclined portion 121 and the second inclined portion 122, and the depth d from the tread 18t of the shoulder rib 18 to the boundary p is referred to as the boundary depth. As shown in FIG. 1A, the line P connecting the boundaries p is a straight line parallel to the tire circumferential direction.
The inclination angle θ ₁ of the first inclined portion 121 is constant in the tire circumferential direction. In this example, the inclination angle θ ₁ is in the range of 0 ° ≦ θ ₁ ≦ 10 °.
The second inclined portion 122 is further inclined to the tire equatorial plane side by an angle α with respect to the first inclined portion 121. This angle α is hereinafter referred to as an inclination change angle. The inclination angle θ ₂ of the second inclined portion 122 is θ ₂ = θ ₁ + α.

In this example, since the inclination change angle α is changed along the tire circumferential direction, the inclination angle θ ₂ of the second inclined portion 122 changes along the tire circumferential direction. When the inclination angle theta ₂ periodically increased and decreased, as shown in FIG. 1, the groove bottom 12b and the curve Q connecting the boundary point q of the second inclined portion 122 of the shoulder groove 12 is corrugated .
The position m closest to the straight line P, which is the intersection of the alternate _long and short dash line Lm and the curve Q in FIG. 2A, is the position of the minimum value α _min of the inclination change angle α, and the alternate _long and short dash line L _M and the curve Q The position M where the curve Q is farthest from the straight line P is the position of the maximum value α _max of the inclination change angle α.
FIG. 2B is a cross-sectional view when the position of the maximum inclination angle α _max of the inclination change angle α is viewed from the position where the inclination change angle α is the minimum value α _min , and reference numeral 20 in FIG. .
As shown in FIG. 2A, one end of the groove wall sipe 20 opens into the shoulder groove 12 and the other end terminates in the second inclined portion 122. A plurality of groove wall sipes 20 are arranged along the tire circumferential direction so that the extending direction when viewed from the tire tread side is perpendicular to the curve Q.
Thus, it is important to form the groove wall sipe 20 so that the groove wall sipe 20 and the curve Q are perpendicular to each other. That is, when the groove wall sipe 20 and the curve Q are not perpendicular to each other, a so-called sipe tear in which a crack occurs from the groove wall sipe 20 may occur. Therefore, as in this example, if the inclination angle of the groove wall sipe 20 is changed in accordance with the change in the inclination change angle α, and the groove wall sipe 20 is formed so that the groove wall sipe 20 and the curve Q are perpendicular to each other. In addition to ensuring the necessary rigidity, it is possible to obtain a shearing force suppressing effect at the time of lateral force input, and it is possible to suppress the occurrence of sipetea.

In this example, the groove wall sipes 20 are evenly arranged in the tire circumferential direction, but the groove wall sipes 20 may be unevenly arranged. In this case, it is preferable not to arrange the groove wall sipes 20 at random, but to keep the sipe interval 1 constant at least in the range of a constant length (for example, 30 mm) in the tire circumferential direction. In addition, the sipe space | interval l says the distance along the tire circumferential direction between the opening parts of the groove wall sipes 20 and 20 adjacent to each other.
Further, if the length (hereinafter referred to as length) along the groove wall surface 12a of the groove wall sipe 20 is w and the sipe interval is l, l and w satisfy 1.5 <(l / w) <4. It is preferable to satisfy.
When the groove wall sipes 20 are unevenly arranged, as shown in FIG. 2A, the length of the k-th groove wall sipes 20 (k) is w _k , and the groove wall sipes 20 ( k) and the adjacent groove wall sipe 20 (k-1) and groove wall sipe 20 (k + 1) as l _{k, k-1} , l _{k, k + 1} respectively, w _k , l _{k, k−1} , l _{k, k + 1} satisfy 1.5 <(l _{k, k−1} / w _k ) <4 and 1.5 <(l _{k, k + 1} / w _k ) <4. It is preferable to satisfy.
(L / w) is 1.5 or less, that is, the density of the groove wall sipe 20 is too high, or the length of the groove wall sipe 20 is long. When the total volume of the sipe 20 is increased, the rigidity of the second inclined portion 122 is not sufficient, and as a result, there is a possibility that sipe tear occurs when a large lateral force is input. On the other hand, (l / w) is 4 or more, i.e., the density of the groove wall sipe 20 is too low, or the length of the groove wall sipe 20 is too short. If the total volume of the groove wall sipe 20 is reduced, the rigidity of the second inclined portion 122 is too high, and the shear force suppression effect at the time of lateral force input is not sufficient, and as a result, the uneven wear suppression effect of the shoulder portion is not sufficient. Therefore, it is preferable to set l and w so as to satisfy 1.5 <(l / w) <4.

The range of the inclination change angle α is preferably 0 ° ≦ α <25 °. This is because when the inclination change angle α is 25 ° or more, wrinkles are generated at the boundary p between the first inclined portion 121 and the second inclined portion 122, and the wrinkles cause cracks in the shoulder groove 12.
In the present example, by making the inclination angle θ ₁ of the first inclined portion 121 constant and changing the inclination angle θ ₂ of the second inclined portion 122, the uneven wear of the shoulder rib 18 from the initial stage to the middle stage of wear. After the middle stage of wear, the second inclined portion 122 whose inclination angle θ ₂ changes in the tire circumferential direction is exposed to the tire tread side, so that the strain concentration at the groove bottom 12b of the shoulder groove 12 is reduced. I try to suppress it.

In this example, the difference between the maximum value α _max and the minimum value α _min of the inclination change angle α (specifically, the difference between the tangent of the maximum value α _{max and} the tangent of the minimum value α _min ) is expressed by the following equation: By providing the restriction as shown in (1), the occurrence of cracks in the shoulder groove 12 is suppressed.
This limitation is the groove depth D of the shoulder groove 12 measured from the tread surface 18t of the shoulder rib 18, and the first inclined portion 121 and the second inclined portion 122 from the tread surface 18t. It depends on the boundary depth d which is the distance to the boundary p.
(D−d) · (tan α _max −tan α _min ) ≧ 2.5 (1)
Hereinafter, (tan α _max −tan α _min ) = Δ.
When (D−d) Δ is less than 2.5, the groove bottom distortion at the time of curb climbing is not sufficient, and cracks are likely to occur in the shoulder groove 12.
Note that (tan α _max −tan α _min ) is multiplied by (D−d) because the volume of the second inclined portion 122 increases as the difference between the groove depth D and the boundary depth d increases. Therefore, by increasing the change amount of the inclination change angle α correspondingly, strain concentration at the groove bottom 12b of the shoulder groove 12 is suppressed.

Moreover, in this example, the uneven wear of the shoulder rib 18 is further suppressed by adding a restriction as shown in the following formula (2) between the groove depth D and the boundary depth d of the shoulder groove 12. The effect and the effect of reducing the occurrence of cracks in the shoulder groove 12 are further improved.
0.1 <(d / D) ≦ 0.6 (2)
That is, when (d / D) is 0.1 or less, the boundary between the first inclined portion 121 and the second inclined portion 122 is exposed at the initial stage of wear, and a groove swing shape appears on the tread surface of the shoulder rib 18. For this reason, uneven wear is likely to occur, and if (d / D) exceeds 0.6, the volume of the second inclined portion 122 becomes small, so that strain concentration at the groove bottom 12b of the shoulder groove 12 cannot be sufficiently suppressed. Because.

Thus, in the embodiment, the groove wall surface 12a on the shoulder rib 18 side of the shoulder groove 12 is inclined with respect to the tire equator surface side at the inclination angle θ ₁ and the first inclined portion 121. The second inclined portion 122 is further inclined by an angle α, and the second inclined portion 122 opens into the shoulder groove 12 so that the extension direction when viewed from the tire tread side is the shoulder groove. Since the plurality of groove wall sipes 20 perpendicular to the curve Q connecting the boundary points between the twelve groove bottoms 12b and the second inclined portions 122 are arranged in the tire circumferential direction, It is possible to suppress wear and to suppress strain concentration at the groove bottom 12b from the middle to the end, and to suppress an increase in shearing force when a lateral force is input, thus generating rib tears and uneven wear on the shoulder. It is possible to reliably suppressed.
At this time, if the groove wall sipe 20 is formed so that the length w along the groove wall surface and the interval l in the tire circumferential direction satisfy 1.5 <(l / w) <4, the occurrence of sipe tear is suppressed. However, uneven wear of the shoulder portion can be suppressed.
When the angle (inclination change angle) α is 0 ° ≦ α <25 °, the shoulder groove 12 has a groove depth D and a boundary depth d, the maximum value α of the inclination change angle α The inclination angles θ ₁ and θ ₂ of the first and second inclined portions 121 and 122 are set so that _max and the minimum value α _min satisfy (D−d) (tan α _max −tan α _min ) ≧ 2.5. If set, the uneven wear characteristic of the shoulder rib 18 can be improved, and the occurrence of cracks in the shoulder groove 12 can be effectively reduced.
Further, since the boundary depth d is in the range of 0.1 <(d / D) ≦ 0.6, the effect of suppressing the uneven wear of the shoulder rib 18 and the effect of reducing the occurrence of cracks in the shoulder groove 12 are further improved. .

The tire of the present invention shown in FIG. 1 (Inventions 1 and 2), a tire whose groove wall surface on the shoulder land portion side of the shoulder groove has no inclined portion (conventional example), and (D−d) Δ is 2. Less than 5 tires (Comparative Example 1), tires (d / D) of 0.1 or less (Comparative Example 2), (d / D) exceeds 0.6, and (l / w) is A tire having a tire of 1.5 or less (Comparative Example 3) and a tire having (l / w) of 4 or more (Comparative Example 4) are prepared, and each of the tires is mounted on a test vehicle. The results of performing a performance test on the number of occurrences of cracks in the shoulder groove and sipe tear characteristics are shown in the tables of FIGS.
Tire 1 of the present invention: (l / w) = 2.9, (d / D) = 0.4, (D−d) Δ = 3.1
Tire 2 of the present invention: (l / w) = 2.9, (d / D) = 0.4, (D−d) Δ = 2.7
The tire size is a 295 / 75R22.5 steel tire that is the main size in North America, the rim used is 8.25x22.55 (standard rim size), and the tire internal pressure and load are the TRA normal internal pressure and normal load.
The uneven wear characteristics are as follows: 3 users prepared 16 vehicles each, 32 test tires each, 3 users prepared a total of 96 tires, whether or not uneven wear initial nuclei occurred in the shoulder-in area, Market evaluation was conducted on the subsequent uneven wear progress. In the market evaluation, in order to avoid the influence of error factors other than between specifications as much as possible, the vehicle alignment, the driving route, the internal pressure management state, etc. were managed uniformly under the test vehicle within the same user. Moreover, the following travel distance was set and evaluated as a standard of the travel distance at the time of evaluation of each tire.
1st Survey; 30,000 miles 2nd Survey; 80,000 miles 3rd Survey; 130,000 Miles 4th Survey; 180,000 Miles The tire is subjected to a deterioration test. That is, the tire is allowed to deteriorate sufficiently by leaving the tire for 7 days in a test chamber called a thermostatic chamber where the room temperature is maintained at 80 ° C. After that, set a tire that has undergone a deterioration test on the test vehicle, raise the belt end temperature of the shoulder to 65 ° C by normal running or circular turning, and then ride the tire on a 15cm curb with an angle of 15 °. The superiority or inferiority of the tire was determined by the number of rides up to.
Moreover, the occurrence level of cypetea was evaluated by the presence or absence of cypetea after traveling 180,000 miles.
In this test, the type of rubber used was unchanged between specifications.
Since the number of occurrences of rib tear is the number of rides up to failure, the higher the number, the better the rib tear characteristics.
Since the partial wear vol. Is a partial wear ratio per unit volume, a smaller value is better.
As is clear from the table of FIG. 3, it was confirmed that all the tires according to the present invention were free from sipe tear and excellent in rib tear characteristics as well as in uneven wear characteristics. .
In contrast, in the tire (Comparative Example 1) where (D−d) Δ is less than 2.5, the rib tear characteristics and the uneven wear characteristics are slightly improved as compared with the conventional example, but the characteristics of the tire according to the present invention are as follows. There was no improvement.
Moreover, in the tire (d / D) of 0.1 or less (Comparative Example 2), although the rib tear characteristic is improved, the uneven wear characteristic is lower than that of the conventional example, and (l / w) is 1.5 or less. In the tire (comparative example 3) in which (d / D) exceeded 0.6, the uneven wear was small in the initial stage, but the rib tear characteristic and the uneven wear characteristic were almost the same as the conventional example.
Moreover, in the tire (Comparative Example 4) in which (l / w) exceeds 4.0, there is no sipe tear and the rib tear characteristics are also improved. However, after the middle period, it was confirmed that the effect of suppressing uneven wear was insufficient.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the embodiment. It is apparent from the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

  As described above, according to the present invention, it is possible to simultaneously improve the uneven wear characteristics of the shoulder rib and reduce the occurrence of cracks in the shoulder groove, so that the durability performance of the tire can be greatly improved.

DESCRIPTION OF SYMBOLS 10 Pneumatic tire, 11 Center main groove, 12 Shoulder groove, 12a Groove wall surface, 12b Groove bottom, 13 2nd main groove, 121 1st inclination part, 122 2nd inclination part,
14 lug grooves, 15 central blocks, 16 central land rows, 17 rib-shaped land portions,
18 shoulder land (shoulder rib), 18t tread, 19 lug groove,
20 groove wall sipe, 21 rib sipe, 22 central block sipe.

Claims (5)

A plurality of circumferential grooves extending along the tire circumferential direction on the surface of the tread of the tire, and a shoulder land portion defined by a shoulder groove located on the outermost side in the tire width direction of the circumferential grooves. In a pneumatic tire
The groove wall surface on the shoulder land portion side of the shoulder groove is
A first inclined portion inclined toward the tire equatorial plane with respect to a direction perpendicular to the tread surface of the shoulder land portion, and a tire having an inclination angle greater than an inclination angle of the first inclined portion from the first inclined portion A second inclined portion that inclines toward the equator plane and reaches the groove bottom of the shoulder groove,
The inclination angle of the first inclined portion is constant in the tire circumferential direction,
An angle α formed by the first inclined portion and the second inclined portion changes along the tire circumferential direction,
A plurality of sipes that are arranged in the tire circumferential direction and that open to the shoulder grooves are formed in the second inclined portion ,
The depth from the tire tread to the groove bottom of the shoulder groove is D,
The depth from the tire tread to the position of the boundary between the first inclined portion and the second inclined portion is d,
When the maximum value of the angle α is α _max and the minimum value of the angle α is α _min ,
The maximum value α _max and the minimum value α _min are
A pneumatic tire characterized by satisfying (D−d) (tan α _max −tan α _min ) ≧ 2.5 .   The extending direction of the sipe when viewed from the tire tread side is perpendicular to a straight line or a curve connecting a boundary point between the bottom of the shoulder groove and the second inclined portion. Pneumatic tire described in 2.   When the length of the sipe along the groove wall surface is w, and the distance along the tire circumferential direction between the sipe opening and the sipe opening adjacent to the sipe is l, the l and w The pneumatic tire according to claim 1 or 2, wherein 1.5 satisfies (l / w) <4. When the inclination angle of the first inclined portion is θ ₁ ,
The θ ₁ is in a range of 0 ° ≦ θ ₁ ≦ 10 °, and the angle α is in a range of 0 ° ≦ α <25 °. 5. Pneumatic tires . The pneumatic tire according to claim 1 , wherein d satisfies 0.1 <(d / D) ≦ 0.6.

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