JPH07266809A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To prevent toe and heel abrasion effectively, while holding drainage performance. CONSTITUTION:A pneumatic radial tire is so formed that a lot of blocks composed of a plurality of vertical grooves 2 extending in the tire circumferential direction and lateral grooves opening to between a vertical groove 2 and a vertical groove 2, and a vertical groove 2 and the outside of a shoulder grounding end 5, are arranged in the tire circumferential direction. A plurality of inclined sipes 9 which are approximately parallel to the tire equator TE and inclined in the depth direction are provided in the circumferential end parts of the blocks 6 coming in contact with the lateral grooves 3, 4 and their inclination angle in the depth direction is set to 10 deg.-40 deg. to a plane P which is parallel to the tire equator TE and perpendicular to the block treading face part 1 and their circumferential length L is set to 5-25% of the average block pitch length PB.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire having a block pattern, particularly to a heavy-duty pneumatic radial tire, and more particularly to prevention of toe and heel wear thereof.

[0002]

2. Description of the Related Art Conventionally, a pneumatic radial tire having a block pattern has a fatal toe and heel wear, that is, a tire circumferential front end (first contact area) and a tire circumferential rear end (block). In order to prevent uneven wear that occurs in a step shape in the last contact area), a so-called bridge is provided, which is shallower than the circumferential longitudinal groove of the block exclusively over part or the entire length of the lateral groove forming the block. This is because the shear force on the tread surface based on the relative speed difference between the vehicle speed and the tire circumferential speed and the shear force on the tread surface in the tire circumferential direction due to block deformation are reduced to the total of the latter. By reducing the force, the difference in shearing force between the front and rear ends of the block is reduced to prevent toe and heel wear (JP-B-57-9967).

[0003]

However, although it is preferable to provide such a bridge in terms of preventing toe and heel wear, it is obvious that the effective cross-sectional area of the lateral groove is reduced and the drainage is impaired. Is (a trade-off). This loses the technical significance in which the drainage is taken into consideration so that the block pattern is generally used for all weathers. And, depending on the height of the bridge, even in the very early stage of the wear, there is a problem in traction on a wet road.

An object of the present invention is to maintain drainage while
Moreover, it is to provide a pneumatic radial tire that can effectively prevent toe and heel wear.

[0005]

There are two main factors that cause toe and heel wear. One is the sum of the shearing force generated based on the relative speed difference between the vehicle speed and the tire peripheral speed, and the shearing forces generated by the load on the surface of the block tread surface in opposite circumferential directions at both ends in the circumferential direction.
Since both ends of the block in the circumferential direction are different from each other, that is, when the total sum of shear forces is different at both ends in the circumferential direction of the block, at the end where the total sum of shear forces is large, the slip against the friction force should be given to the deformation amount of the block. The slip is close to the saturated state, and the sum of the shear forces at the other end is relatively small with respect to the friction force, and the slip is smaller than the slip that should be given to the deformation amount of the block and is unsaturated. Therefore, a difference in slippage occurs with respect to the same frictional force, which appears as a difference in friction energy, resulting in a difference in wear, that is, a toe and heel.

Secondly, in a tire mounted on a drive shaft to which traction is applied, when the tread touches the road surface and then takes off, only the rear end portion is gradually separated from the road surface from the front end to the rear end of the block. Although the deformation due to the shearing force is maintained by the frictional force, the frictional force with the road surface of the block suddenly decreases, so that the deformation begins to return suddenly and the rear end of the block slides against the road surface. Caused by abrasion.

In order to prevent this, as described above, when uneven wear occurs, slippage occurs reliably between the block surface and the road surface, so it is necessary to set conditions under which this slippage does not occur. . For this, for example, there is a method of providing a bridge to reduce the shearing force due to the deformation, but it is difficult to maintain the all-season performance as a feature of the block pattern as described above.

Therefore, the frictional energy is reduced in a particularly worn portion of the circumferential end portion of the block to reduce the wear,
A method for reducing the difference in wear in one block must be taken.

Generally, the frictional energy e is expressed as the product of the frictional force F = W · μ and the slip amount S, where the load W is the friction coefficient μ, and the slip amount S is almost equal in one tire. Since it is considered to be constant and the load W is also constant, reducing the friction coefficient μ leads to a decrease in the friction energy e.

To reduce the friction coefficient μ, there is a method of changing the material of the tread rubber, but it is desirable to avoid lowering the friction coefficient μ in the wet road, and when all the friction coefficients μ of the block rubber are reduced, This is inconvenient because the total slip amount S becomes large and wear is rather increased.

Therefore, the friction coefficient μ of the block rubber as a whole is high, and it is necessary to reduce the friction coefficient μ only in a portion where the friction energy e is large. In short, the “partial” coefficient of friction μ at the circumferential ends of the block where toe and heel wear occurs must be reduced, not the coefficient of friction μ of the entire block rubber.

Then, as a result of earnest research to realize this trade-off, according to the present invention, a special sipe is installed at the end of the block in the circumferential direction to reduce the wear energy e of the part even if there is no bridge. The amount of the "toe" portion having large wear is reduced to provide a so-called uneven wear tire having smooth wear.

That is, according to the present invention, a large number of blocks are formed in the tire circumferential direction by a plurality of vertical grooves extending in the tire circumferential direction, vertical grooves and vertical grooves, and vertical grooves and lateral grooves that open to the outside of the shoulder ground contact end. In the arranged pneumatic radial tire, in the circumferential direction end portion of the block in contact with the lateral groove, in the depth direction with respect to a plane that is substantially parallel to the equatorial direction, is parallel to the tire equator, and is perpendicular to the block tread portion. We adopted a structure that provides multiple inclined sipe.

The inclination angle of the inclined sipe is 10 ° to 4 with respect to a plane parallel to the tire equator and perpendicular to the block tread surface.
It is desirable to set it to 0 °. When the inclination angle is less than 10 °, it becomes insufficient to cause movement in the tire width direction at the end portion of the block circumferential direction to lower the friction coefficient μ.
On the other hand, if the angle exceeds °, the component of the movement (force) in the tire width direction weakens and the effect diminishes. In addition, the rigidity of the block decreases at the base of the small area near the inclined sipe, causing chipping, tearing, etc. Is likely to occur.

The same applies to the length of the inclined sipe. If the circumferential length of the inclined sipe is less than 5% of the average block pitch length, the tire width direction motion is caused at the block circumferential end portion. It becomes insufficient to reduce the friction coefficient μ, and if it exceeds 25%, the component of the movement in the tire width direction becomes weak, and chipping, tearing, etc. are likely to occur.

The depth of the inclined sipe is also an important factor, at least 50% or more of the lateral groove depth and 1 of the adjacent vertical groove depth.
A good depth is about 00%. When the depth of the lateral groove is less than 50%, it becomes insufficient to cause the movement in the tire width direction at the end portion in the circumferential direction of the block to lower the friction coefficient μ, and when the depth of the adjacent vertical groove exceeds 100%, the tire is The component of the movement in the width direction becomes weak, and chipping, tearing, etc. are likely to occur.

The interval between the inclined sipes is preferably 0.7 to 1.5 times the circumferential length of the sipes for the same reason as above. Therefore, when the length is less than 0.7 times the circumferential length of the sipe, the desired uneven wear preventing effect is poor.
If it exceeds 5 times, chips and tears will increase.

The sipe installed at the circumferential end of the block is not an inclined sipe extending substantially parallel to the tire equator as in the present invention, but a normal vertical sipe having a certain angle with respect to the tire equator. It can be considered to be a sipe, but if there is no inclination, the vertical component of the load causes the sipe and a small block surrounded by the sipe to fall in the tire width direction, that is, to positively move in the tire width direction and try to slip. Therefore, there is no effect of decreasing μ with respect to the circumferential frictional force. However, although a slight effect can be expected by generating a widthwise force when a circumferential force is applied, the rigidity resulting from the shape of the small block is partially different, so that it causes a complicated movement and rather a different shape. However, there is a problem in that the abrasion of the block is promoted, and the block is chipped or cracked.

[0019]

According to the pneumatic tire of the present invention, a block formed by a plurality of vertical grooves extending in the tire circumferential direction and vertical grooves and vertical grooves, and vertical grooves and lateral grooves that open to the outside of the shoulder ground contact end is provided in the tire circumferential direction. In a pneumatic radial tire arranged in a large number in the above, since the plurality of inclined sipes that are substantially parallel to the equatorial direction and are inclined in the depth direction are provided at the circumferential ends of the blocks in contact with the lateral grooves, this tire When the wheel is used as a steering wheel, the block in that portion, due to the vertical component of the load, particularly in the front end portion in the contact area, has a large component in the direction perpendicular to the rolling direction of the tire due to the inclined sipe. This motion in the right-angled direction has the function of lowering the friction coefficient against the circumferential force, and at the ground contact end of the block, the slip has already reached a saturated state, so only the friction force decreases and the friction energy decreases, but At the edges, the slip coefficient changes and increases as the friction coefficient decreases, as well as slippage. That is, wear decreases at the front end of the ground and partially offsets the increase / decrease at the rear end, so the wear decreases or increases somewhat, so the amount of wear at both ends decreases and uneven wear decreases. It becomes. When this tire is used as a drive wheel and a driving force is exerted, the same motion as the above occurs except that the action at the front end portion and the rear end portion of the contact area of the tire is reversed, and the following action is exerted. .

That is, as described above, in the conventional tire, at the rear end portion of the area where the tire is in contact with the ground, the block is deformed by the shearing force and the slip is suppressed to the minimum by the frictional force with the road surface. Indicates that when the ground contact is released at the front end of the block, the vertical load W is suddenly reduced, and the frictional force F = W · μ is reduced at the rear end of the block. Become. And this slip amount S
Changes much more due to a decrease in the load W, so that the friction energy e becomes rather large and the friction becomes uneven. Further, when the slip amount S changes in the larger direction, the shearing force on the block surface increases in proportion to the slip amount S, and this force also enhances the uneven wear. However, in the tire of the present invention, in the process of decreasing the vertical load W,
The rear end of the block is restored in the opposite manner to the process of deforming at the front end of the block, but at this time, the inclined sipe causes movement in the direction perpendicular to the tire rolling direction (however, the direction opposite to the front end that touches the ground). generate.

This movement of the component at right angles to the rolling direction of the tire makes the friction coefficient of that portion extremely small, so that in the reduced vertical load W and the increased slip amount S, only the friction coefficient μ is present. This reduces the friction energy e and reduces uneven wear.

Therefore, in the tire of the present invention, the coefficient of friction μ of the entire block rubber is not lowered, so that the coefficient of friction μ in the wet road does not decrease, and since no bridge is formed in the lateral groove, drainage performance is improved. It does not decrease. Also, it is not a normal vertical sipe that has a certain angle to the tire equator, but an inclined sipe that extends almost parallel to the tire equator, so the vertical force that always accompanies the load is effectively used and the sipe In addition to reducing the friction coefficient in the circumferential direction at the part, it often happens that cutting and cracking occur.

The inclination angle of the inclined sipe is 10 ° with respect to a plane parallel to the tire equator and perpendicular to the block tread surface.
To 40 °, the circumferential length of the inclined sipe is 5 to 25% of the block average pitch length, and the depth of the inclined sipe is at least 50% or more of the lateral groove depth and 100 of the adjacent vertical groove depth.
%, The tendency to cause the tire width direction motion at the block circumferential direction end to decrease the friction coefficient μ increases, and the component of the tire width direction motion (force) works well, so that the inclination sipe The rigidity of the block does not decrease at the base of the small area in the vicinity, and it is possible to prevent chipping, tearing, and the like.

[0024]

1 is a schematic view of a tread pattern showing an embodiment of a pneumatic radial tire according to the present invention, FIG. 2 is an enlarged view of a main part thereof, and FIG. 3 is a schematic side view of a main part viewed from the direction A in FIG. It is a figure.

In the figure, 1 is a tire tread, 2 is a plurality of vertical grooves extending in the tire circumferential direction, 3 and 4 are vertical grooves 2 respectively.
And the vertical groove 2, and the vertical groove 2 and the lateral groove that are open to the outside of the shoulder ground contact end 5, respectively. 6 is a plurality of these vertical grooves 2 and lateral grooves 3, 4
Blocks formed by and are arranged in a large number in the tire circumferential direction. P _B indicates the pitch length of the block 6.

Reference numeral 7 denotes a circumferential end portion of the block 6, and a tire equator TE is respectively provided at a block end portion 7a which is a first contact area and a block end portion 7b which is a final contact area of the circumferential end portion 7, respectively. A plurality of inclined sipes 8 that are substantially parallel to the direction and are inclined in the depth direction are installed. 9
Is a normal vertical sipe installed at the end of the block 6 on the vertical groove 2 side.

Both the block end 7a and the block end 7b of the inclined sipe 8 are, as shown in FIGS. 2 and 3, in the depth direction thereof, a plane P parallel to the tire equator TE and perpendicular to the block tread 1. On the other hand, it is formed with an inclination angle θ of 10 ° toward the tire equator TE direction. Further, in the inclined sipe 8, the circumferential length L is 15% of the block average pitch length P _B , and the interval SP of the inclined sipe 8 is
Is 1.2 times the circumferential length L.

Therefore, when this tire is used as a steered wheel, the blocks 6 in the contact area of the blocks 6 in the contact area of the blocks 6 are moved in the tire rolling direction by the inclined sipes 8 based on the vertical component of the load. On the other hand, a large right angle component motion is generated. When the tire is used as a drive wheel, the block ends 7a and 7b in the contact area of the block 6 are
In addition to the same movement as above, the grounded state is released,
In the process of decreasing the vertical load W, the block end portion 7b is restored in the opposite manner to the process of deforming at the block end portion 7a, and at this time, the inclined sipe 8 moves in the direction perpendicular to the tire rolling direction (however, it is grounded). Direction opposite to the end). The movement of the component at right angles to the tire rolling direction makes the friction coefficient of that portion extremely small, and in the reduced vertical load W and the increased slip amount S, only the friction coefficient μ decreases, Reduce friction energy e,
Reduces uneven wear.

Next, tire size 10.00R20 14PR and rim size 20 × with various inclination angles θ of the inclined sipe changed.
A tire with 7.00 and an air pressure of 0.725MP was prototyped and mounted on the front wheels (steering wheels) and rear wheels (driving wheels) of a truck for running on good roads, and the load was subjected to a constant volume load test to perform an uneven wear resistance test.

In this test, as shown in FIG. 7, the uneven wear amount h (mm) of the block end 7b on the surface of the block 6 after running 70,000 km is measured and evaluated. In the figure, 3,
Reference numeral 7b is the same reference numeral as that of the above-described embodiment, and is a lateral groove and a block end portion which open in the vertical grooves 2 and 2, respectively. The vertical groove 2 and the lateral groove 4 opening to the shoulder ground contact end 5 were also tested in the same manner, and the lateral groove 3 and the lateral groove 3 were comprehensively evaluated.

In FIG. 4, the horizontal axis represents the inclination angle θ of the inclined sipe, and the vertical axis represents the uneven wear index, showing the relationship between them. The uneven wear index is obtained by similarly testing a normal vertical sipe with an inclination angle of 0 ° (circumferential length is 15% of the block average pitch length) under the same conditions, and the uneven wear amount h (mm) is 100. As, the uneven wear index at each inclination angle θ is plotted. Also, the uneven wear characteristics in which the circumferential length L of the inclined sipe is changed to the ratio with respect to the block pitch length P _B and variously changed are evaluated. At this time, P _B uses the average pitch length. The smaller the uneven wear index, the better the uneven wear resistance. The block average pitch length P
_B means the average pitch length when different pitch lengths are used for one tire for noise reduction measures.

Block end 7a and block end 7b
As a result of testing a tire having no sipe, the uneven wear index of this tire was 105 to 108.

As shown in FIG. 4, the uneven wear index of each of the tires having sipes formed at the circumferential ends of the block is lower than that of the tire having no sipes formed at the circumferential ends of the block. In particular, in the case of the tire of the present invention in which the inclined sipe is formed, the effect of improving the uneven wear resistance is recognized as compared with the normal vertical sipe, and in particular, the inclination angle θ of the inclined sipe is 1
It is recognized that a range of 0-40 ° is suitable. 40
Even if the angle exceeds 50 °, the uneven wear resistance is good as shown in FIG. 4, but when the tire after running 70,000 km is observed, chipping, tearing, etc. occur at the base of the small area near the inclined sipe. It's been found.

Further, from FIG. 4, the circumferential length L of the inclined sipe is shown.
It is recognized that the uneven wear resistance is good even when the length is gradually increased, but the uneven wear resistance is sharply improved especially from the point where the circumferential length L is 5%, and the uneven wear resistance is longer than that. The improvement effect is gradually increasing. However, if it exceeds 25%,
On the tire after running 70,000 km, chipping, tearing, etc. were observed.

Tires in which the interval SP of the inclined sipes was changed were also prototyped and tested under the same conditions as described above. However, when the tire length was less than 0.7 times the circumferential length L of the sipes, the uneven wear preventing effect was poor. It was confirmed that when it exceeds 1.5 times, chips and tears increase.

The present invention is not limited to the above embodiment. For example, as shown in FIG. 5, the inclined sipes formed at the circumferential end portions of the block 6 can be formed at the block end portions 7a and the block end portions 7b as inclination angles in mutually opposite directions. That is, the inclined sipe 8 of the block end 7a is cut outward in the tire width direction, and the block end 7 is cut.
The configuration is such that the inclined sipe 8 of b is cut in the tire equator TE direction. As a result, when the vertical load W is reduced when the block is grounded, the block end portion 7b is changed to the block end portion 7a.
Corresponding to the restoration in the opposite manner to the process of deforming with the, the block end 7a and the block end 7b generate motions at right angles in directions opposite to each other with respect to the tire rolling direction, and As in the case, the friction energy e is reduced to prevent uneven wear.

Further, in the present invention, since the inclined sipes may be formed at the circumferential end portions of the blocks substantially parallel to the tire equator direction, as shown in FIG. 6, the inclined sipes are bent in a substantially V shape. Sipe 8 is okay. In this way, in the case of the inclined sipe 8 that is bent from the main part of the sipe in a substantially V shape to form the opening ends to the lateral grooves 3 and 4, the opening ends to the lateral grooves 3 and 4 that are not at right angles to the tire equator TE are. The sipe portion has a small chip, a tear, and the like at right angles to the lateral grooves 3 and 4, and a main portion of the sipe is substantially parallel to the tire equator TE, thereby exerting an effect of preventing uneven wear.

It is desirable that the inclined sipes are formed at both ends of the block in the circumferential direction, that is, at both ends of the block. However, when the tire rotation direction is specified, the purpose is fulfilled. It can also be limited to one of the sides. Also, the block that forms the inclined sipe,
It is not necessary to cover the entire area of the tire, and only the block on the shoulder ground contact end side that is most likely to occur may be used.

[0039]

As described above, according to the present invention, a block formed by a plurality of vertical grooves extending in the tire circumferential direction, vertical grooves and vertical grooves, and vertical grooves and lateral grooves that open to the outside of the shoulder ground contact end is used for the tire. In a pneumatic radial tire arranged in a large number in the circumferential direction, a pneumatic radial in which a plurality of inclined sipes that are substantially parallel to the tire equatorial direction and are inclined in the depth direction are installed at the circumferential ends of the blocks in contact with the lateral grooves. Since it is a tire, it is possible to effectively prevent toe and heel wear while maintaining drainage.

Since the material of the tread rubber is not changed, the friction coefficient μ on the wet road of the tire as a whole
In addition, since it is an inclined sipe rather than a vertical sipe, the effect of improving the uneven wear resistance is particularly remarkable.

[Brief description of drawings]

FIG. 1 is a schematic view of a tread pattern showing an embodiment of a pneumatic radial tire according to the present invention.

FIG. 2 is an enlarged view of the main part.

FIG. 3 is a schematic side view of a main part viewed from the direction A in FIG.

FIG. 4 is a diagram showing a relationship between an inclination angle θ of an inclined sipe and an uneven wear index.

FIG. 5 is an enlarged view of an essential part of a block showing another embodiment in which a tilt sipe having a tilt angle θ in the opposite direction is installed.

FIG. 6 is a schematic view of a tread pattern showing another embodiment in which a substantially V-shaped inclined sipe is installed.

FIG. 7 is a schematic cross-sectional view showing an uneven wear state at a block end portion.

[Explanation of symbols]

1 Tread portion 2 Vertical groove 3 Horizontal groove 4 Horizontal groove 5 Shoulder ground end 6 Block 7 Circumferential end 7a Block end 7b Block end 8 Inclined sipe 9 Vertical sipe W Vertical load P _B Average block pitch θ Inclined angle of inclined sipe L Circumferential length of inclined sipe TE Tire equator SP Distance between inclined sipe

Claims (4)

[Claims] 1. A pneumatic tire in which a plurality of blocks formed by a plurality of vertical grooves extending in the tire circumferential direction, vertical grooves and vertical grooves, and vertical grooves and lateral grooves opening to the outside of the shoulder ground contact end are arranged in the tire circumferential direction. In the radial tire, a pneumatic radial tire in which a plurality of inclined sipes that are substantially parallel to the tire equatorial direction and are inclined in the depth direction are installed at the circumferential ends of the blocks that are in contact with the lateral grooves. 2. The pneumatic radial tire according to claim 1, wherein, in the depth direction, the inclined sipe has an inclination angle θ of 10 ° to 40 ° with respect to a plane parallel to the tire equator and perpendicular to the block tread surface. . 3. The pneumatic radial tire according to claim 1, wherein the circumferential length L of the inclined sipe is 5 to 25% of the block average pitch length P _B. 4. The pneumatic radial tire according to claim 1, 2 or 3, wherein the interval SP between the inclined sipes is 0.7 to 1.5 times the circumferential length of the sipes.