JP3362237B2 - Heavy duty pneumatic tires - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty pneumatic tire having ribs defined by at least three main grooves, and in particular, a notch is formed in the side wall of the ribs to improve uneven wear resistance. The present invention relates to an improved pneumatic tire for heavy loads.

[0002]

2. Description of the Related Art Conventionally, many attempts have been made to reduce uneven wear of a heavy duty pneumatic tire.
For example, a tire having a rib formed on the side wall of a rib defined by a zigzag groove formed in the circumferential direction and having a variable inclination with respect to the tire tread surface has been attempted (Japanese Patent Publication No. 50-22282). Further, there is an attempt (Japanese Patent Publication No. 57-24242) to prevent step wear by providing a thin groove extending in the tire circumferential direction and making a round at a position slightly inside from the outer edge of the outermost rib. As further attempts thereafter, for example, in order to level the distribution of the shearing force proportional to the peripheral velocity of each portion in the width direction of the tread portion of the tire surface and reduce the difference in wear of each portion of the tread portion, The part where the tire peripheral speed is closer to the tread shoulder part has a smaller diameter than its adjacent parts and receives a large amount of friction energy from the road surface at the time of touchdown to cause wear, thereby accelerating the tire and increasing the peripheral speed. An attempt to form a sacrificial element on the tread portion (JP-A-2-15840)
No. 5, No. 2-225109).

[0003]

However, various problems remain in such conventional tires. That is, the former is effective against uneven wear such as river wear and step wear, but it is still insufficient to prevent uneven wear overall, and the latter requires additional elements. It accounts for a relatively large proportion of the ribs (land portion) on the tread surface, and there is a strong demand for weight reduction of tires due to the demands of recent social conditions. This is because there is a strong tendency to narrow the width as much as possible, which is disadvantageous in terms of wear resistance.

In view of the above-mentioned circumstances, the inventor of the present invention considers the cross-sectional shape of the main groove and the shape of each rib on the conventional tread surface in order to reduce the uneven wear phenomenon of the tread surface during running of the tire. In terms of correlation, we have made an earnest study on uneven wear resistance in each part of the tread surface. As a result, particularly in heavy-duty pneumatic tires having a rib pattern, one of the characteristic features of uneven wear is that the widthwise edge of the rib is 1 more than the portion near the center of the rib. There is manifestation of so-called river wear, which wears out in rapid succession so as to be continuous in the circumferential direction. Such a river wear phenomenon is imparted by the relative speed between the road surface and the tread surface of the tire, which is given by the difference between the tire peripheral speed and the vehicle speed, in order to secure steering stability, heat generation durability, etc. in the tire tread portion. Compared to the shearing force of the surface of the tread portion caused by the difference in the peripheral velocity of each portion in the tread width direction due to the so-called crown radius (curved surface), the rib is closer to the center of the rib like the outer edge of the rib. In a large part of the decrease in frictional force, the frictional force falls below the shearing force, causing slippage.This slippage phenomenon produces frictional energy, and the slippage part of the tread part, that is, the rib edge is selected. Wear, which is the starting point of the riverwear. Also, at this time, the greater the relative speed with the road surface, the faster the progress of the riverwear. In the case of general rib type tires, heavy loads for trucks and buses are often mounted on the front wheels (steering wheels).
Moreover, in the front tire, the relative speed to the road surface becomes larger in the portion closer to the shoulder portion where the peripheral speed is slower, so that the river wear also has a large number of main grooves near the shoulder and large.

As described above, the shearing force generated in the tire tread portion is generated by the shape of the tire and the relative speed difference between the tire and the vehicle, and the shearing force can be reduced or resisted. Increasing the frictional force to prevent slipping reduces the slippage between the tire and the road surface, that is, the friction energy.
Furthermore, an important point in the relationship between the tire, the road surface, and the speed is that the value of the shear force between the center of the tread tread portion in the width direction and the shoulder region shows different values in each part of the tread portion. The circumferential shear force distribution in the contact area also changes from zero at the start of contact to a specific value at which it begins to slip beyond the frictional force and increases toward the rear end of contact.

Therefore, in order to reduce the rib surface wear near the shoulder, the frictional force near the shoulder is increased by improving the grounding property, and the shearing force in the grounding region increases from zero at the start of grounding to the direction at the end of grounding. Then, it becomes important to delay or eliminate the time to start slipping beyond the frictional force. For this purpose, it is necessary that the rib closer to the center of the tread tread portion has better flexibility with respect to the radial load on the tread portion to increase the flexure and to bear the load more than the shoulder. However,
In the conventional tire, the rib width is almost the same as that of the shoulder rib, which is often a little wider, and no special consideration is given to flexibility.

Therefore, the present invention is based on the above findings.
This is done in order to cope with this improvement. In the conventional tread structure, as shown in (a), (b) and (c) of FIG. 6, the cross section of the main groove 31 has an opening in the main groove. The width a is larger than the bottom surface width b, and in the same relationship, the base width c of the rib 33 is larger than the rib surface width d, and as a result, the rib width of the tread portion is more than the value that can be obtained. Since it is bad and has high rigidity, in the present invention, for example, a zigzag-shaped cut portion is provided in the side wall portion of the rib defined by the main groove in the tire circumferential direction, and the side wall of the rib is larger than the rib surface width. The width of the base portion of the rib having the cut portion formed in the portion is increased, and in the ratio of the two, the area closer to the center of the tread tread portion is formed to be larger than the other portion so that the center portion of the tread tread portion is formed. Flexible against flexural deformation It is referred to as its object to improve the uneven wear resistance and better than the flexibility of other regions.

[0008]

SUMMARY OF THE INVENTION Therefore, according to the present invention which meets the above object, at least three main grooves arranged at intervals along the tire circumferential direction are defined by the main grooves. A heavy-duty pneumatic tire having ribs formed on the outer surface of the tread portion, the surface width W _{1 of the} ribs,
At least one side wall portion of the rib surrounded by the main groove is formed with a plurality of notches having a depth and a width that increase toward the base portion of the rib connected to the bottom portion of the main groove. ₂ a, which has a relationship of W ₁ ≧ W _2, that the ratio of the W _{2 /} W ₁ of each rib is formed so as to be sequentially increased toward the center of the tread portion in the direction of the shoulder It is a feature. The center of the tread surface of the rib or at least close to this
The base width W ₂ of the rib at the position is 70 to the surface width W ₁ of the rib.
It is preferably 100%, and if the surface widths W _{1 of the} ribs excluding the shoulder ribs are formed to be equal, running stability and uneven wear resistance are good. Further, it is preferable that the notch formed on the side wall of the rib is a zigzag notch whose width and depth increase toward the base, and the number of pitches of the notch of the zigzag in this case is tread portion. It is suitable if it is 3 to 9% of the width W.

The rib in the present invention is a so-called land portion partitioned by a plurality of main grooves arranged in the circumferential direction. The rib has a width of 1.5 mm so that it can be easily closed when the tread is grounded. Even if it is divided by the thin sipe below or a block-like pattern divided by lateral grooves with a depth of 3 mm or less, it does not contribute to the flexibility of the rib in the vertical direction Be done.

[0010]

In the tire according to the present invention, the notch is formed from the outside of the side wall toward the base of the rib to reduce the cross-sectional area of the rib in the tire width direction, and the surface width W ₁ and the base width W of the rib are reduced. _By increasing the ratio W ₂ / W ₁ of ₂ from the center of the tread surface toward the shoulder, the rigidity (flexibility) of each rib in the radial direction of the tire is changed, so that uneven wear is caused as compared with the conventional tire. This is effective in blocking, and the fact that this flexibility in the radial direction of the tread decreases from the center of the tread surface toward the shoulder (increased rigidity in the radial direction of the tire) means that the load on the shoulder side rib is the same for the same load. This means that the share is increased and the frictional force is increased. Wear occurs because slip occurs when the shearing force based on the relative slip between the tire and the road surface exceeds the frictional force.
By applying the crown radius, the ribs near the shoulder where the shearing force is large act more effectively. As a method of changing the flexibility of the rib, there are a method of changing the rib width and a method of changing the rib height, that is, the groove depth. However, the latter is limited by the use and size of the tire. Generally, the former is easy to use. However, if the rib width closer to the center of the tread surface is narrowed to improve flexibility, the rib will be largely bent, and therefore,
In addition to the large shear strain in the width direction of the rib surface and the reduction of the frictional force in the circumferential direction, the ground pressure decreases and the product of it and the friction coefficient,
That is, due to the double action that the frictional force becomes smaller and the slippage becomes easier, uneven wear is likely to occur in a different shape in the rib near the center of the tread portion. Therefore, in the present invention,
The rib width is almost the same so that the rib strain on the rib surface is almost the same between the ribs, the flexibility is improved, and the flexibility of the rib base is reduced to reduce the surface shear strain. By making the tire larger than that of the conventional tire, the function of overcoming the drawbacks of the conventional tire is exhibited. That is, when the rib has a rectangular or trapezoidal cross-sectional shape (see FIG. 6C) like a conventional tire, the shear strain due to flexural deformation is maximum at the end of the rib surface (tread surface portion) during deformation under vertical load. However, in the rib of the tire according to the present invention, the base width W ₂ of the rib becomes smaller than that of the conventional tire by forming the notch whose depth and width increase toward the base side on the wall surface thereof. As a result, the deformation is transferred to the base side, so that the shear strain on the surface side is smaller than that on the base side of the conventional tire. This strain increases in the width direction of the rib as it approaches the end of the rib, and the movement of the rubber on the rib surface, which is proportional to the shear strain in the rib width direction, is the coefficient of friction in the circumferential direction in the direction perpendicular to that, that is, the friction. Although the force was reduced, it offsets the disadvantage of lowering the frictional force by increasing flexibility because it keeps the frictional force in a large state by reducing this shear strain, and the center of the tread tread Conventionally, the problem of uneven wear was small on the side, but it can be retained as it is.On the other hand, on the ribs near the shoulder, the shearing force exceeds the frictional force in the ground contact area due to the increase in the frictional force due to the increased load sharing and slippage. The start time is late, that is, the slip energy becomes small and the growth of riverwear is suppressed.
Also, the rib from the shoulder is smaller than the rib near the center of the tread surface, but a notch with a greater depth and width is provided on the rib base side to reduce the shear strain in the width direction on the rib surface and reduce the circumferential friction force. Since the decrease is suppressed, the shear strain in the width direction due to the increase in load sharing is offset to eliminate the problem.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the accompanying drawings.

1 to 5 are views of a tread portion of tires of respective examples according to the present invention, and FIG. 6 is a view of a tread portion of a conventional tire for comparison.

First, FIGS. 1 to 3 show an example in which a side wall portion of a rib is formed in a zigzag shape. FIG. 1 is a tread development view showing an example of a heavy duty pneumatic tire according to the present invention. 2 is a sectional view taken along line AA of FIG.
FIG. 3 is an enlarged partial sectional view of the rib side wall portion. In the figure, 1 is a tire, 2 is its tread portion, and 3 and 3'are four tires formed on the outer surface of the tread portion 2 along the tire circumferential direction, two on each side of the center X of the tread tread portion. The outermost main groove is 3 '. Reference numeral 4 is a rib defined by the respective main grooves 3, 3 ', and 4'is a so-called shoulder rib located at the outermost shoulder portions S, S'of the tread portion 2. Further, 5 is shoulder portions S ', S'on both ends of the tread portion 2.
6 is a belt ply.

One point to be noted in this invention is that
The ratio W ₂ / W ₁ of the rib surface width W ₁ to the base width W ₂ is formed so as to increase from the center line X of the tread tread surface portion toward the tire shoulder portions S and S ′. That is, according to this relationship, the flexibility of the tread portion is increased as it approaches the tread tread central area, so that the area near the tread tread central portion is more likely to bend with respect to the load, and the shoulder-side rib has a larger load sharing. Therefore, the frictional force of the rib near the shoulder increases and the time when the shearing force exceeds the frictional force and starts slipping in the ground contact area is delayed, that is, the slip energy becomes small and the growth of riverwear is suppressed. Is. Reference numeral 7 is a sipe with a thin notch, at least one end of which communicates with the main groove 3 between the ribs 4, and is engraved with being inclined in the same direction, but the depth thereof affects the flexibility of the rib. Without an average of 3 mm or a width that can be easily closed when grounded 1.
It is 5mm or less, and this sipe 7 apparently makes the rib 4
Has a block shape, but in the present invention, it is omitted in view of its function and effect, and all ribs are included. In the present invention, the surface width W _{1 of the} rib is the average width, and the base width W ₂ is the width between the valleys of the cut portion, and the peculiar maximum and minimum widths are Although not included, it is included in the scope of the basic technical idea of the present invention.

Another important point in the present invention is the shape of the side wall of the rib. For example, the side wall portion 4a of the rib 4 has a shape having a notch 4b formed by cutting at least one side wall portion 4a of the rib 4 toward the base of the side wall portion 4a in the tire width direction. It is essential that the notch 4b of the side wall 4a of the rib 4 is formed at least in the rib on the tread tread center line or the rib closest to the center line. Also,
The cut portion 4b is shown in FIG. 4 showing another embodiment of the present invention.
Further, as shown in FIG. 5, it may be provided only on one side wall portion of the side wall portion of the rib 4 ', or of course, a mixed cut portion on one side and both sides may be used. In addition, the base width W _{2 of} the rib 4 in the region including the tread tread center line or at a position close thereto, that is, the rib width W ₃ of the rib 4 at the base 4c.
The width excluding both depths D ₁ and D ₂ of the cut portion 4 b is preferably 70 to 100% of the rib surface width W ₁ .
In this case, if it exceeds 100%, the rigidity of the rib base side is not sufficiently reduced, and the shear strain on the rib surface cannot be reduced, so that the effect of preventing river wear is insufficient. On the other hand, if it is less than 60%, "wrinkles" due to buckling frequently occur in the rib base portion 4c, and cracks are likely to proceed.

Moreover, in this shape and structure, the main groove 3 gradually becomes zigzag as the tread wear progresses, so that it is effective for maintaining the steering stability on a wet road surface.

In this case, the cut pitch number P of the cut portions 4b of the rib side wall portion 4a is 3 to the tread width W.
9% is preferable. In this case, if it is less than 3%, the same pitch number P of the cut portions 4b becomes too small, the rigidity of the convex portion between the cut portions is reduced, the wear is abnormally delayed, and it remains in a streak shape or is chipped, resulting in appearance. On the other hand, if it exceeds 9%, on the other hand, the intervals of the same pitch number P become rough and the convex portions of the ribs with respect to the grooves are likely to be the base points of the river wear, as in the general zigzag pattern.

Next, the comparison test of the test tire will be specifically described.

(1) Contents of test tire / tread pattern: With respect to the tread patterns of the tires of Examples 1 and 2, and the rib width ratio, the ribs in the center area of the tread tread are used as the rib positional relationship. Center ribs, ribs located on the shoulders are shoulder ribs, and ribs in the middle between them are intermediate ribs. Further, the cutting pitch ratio of the main groove and the depth of the sipe (lateral groove) are measured and summarized in Table 1. Showed.・ Tire size: 10,000 R 20 ・ Rim size: 20 × 7.0 0-J ・ Air pressure: 7.25 kg / cm ²

(2) Test method-Test vehicle; truck vehicle (type: 10-ton long-distance transport truck) -Installation position: front wheel (steering wheel) -Load: 100% loading-Road surface condition: 100% paving-mileage 35,000 km ・ Traveling speed; 50-80 km / h ・ Uneven wear resistance; After traveling 35,000 km, the outer ends of both banks of the outermost main groove 3 '(corresponding to the side wall 4a of the rib 4) shown in FIG. ), The depths A ₁ , A ₂ and the widths B ₁ , B ₂
Is measured, and with the average value of A ₁ × B ₁ and A ₂ × B ₂ ,
The value of the comparative example was set to 100 and indexed. The smaller the number, the better.・ Abrasion resistance: (35,000km / T) x 100 (T; 35,000km
It is the value of the amount of wear after running, that is, the amount of decrease in groove depth, and is shown as an index with the value of the comparative example as 100. The larger the number, the better.

(3) Test result The test results are shown in Table 1. Margin below

[0022]

[Table 1]

As is clear from the table, the examples are superior in both uneven wear resistance and wear resistance to the comparative examples, and in particular, the uneven wear resistance is about three times as high as that of the comparative examples. I understand.

[0024]

As described above, according to the present invention, in the relation between the rib surface width W ₁ and the rib base width W ₂ , the depth increases on at least one side wall of the rib as it becomes closer to the base. Since the notch is formed so that W ₁ ≧ W ₂ and the ratio of W ₂ / W ₁ is gradually increased from the shoulder portion toward the equatorial plane, the effective effective area of the tread portion is reduced to improve resistance. The flexibility is greater in the equatorial plane region of the tread portion by simply forming the notch in the rib side wall without adversely affecting wearability, so it is appropriate for displacement under vertical load by the crown radius of the tread portion. It is effective for preventing and reducing river wear because it increases the frictional force of the rib near the shoulder where uneven wear is likely to occur and reduces slippage, especially for high-speed running on paved roads. Tire durability It is an extremely effective.

[Brief description of drawings]

FIG. 1 is a development view of a tire tread portion showing an example of an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is an enlarged partial cross-sectional explanatory view of the rib side wall portion of FIG.

FIG. 4 is a development view of a tire tread portion showing another embodiment of the present invention.

5 is a cross-sectional view taken along the line AA of FIG.

FIG. 6 is a view showing an example of a conventional tire, in which (a) is a development view of the tread portion of the left half of the tire, and (b) is (a).
6 is a sectional view taken along the line D-D in FIG.

FIG. 7 is an explanatory diagram showing uneven wear resistance and wear resistance.

[Explanation of symbols]

1 tire 2 tread portion 3 main groove 3'outermost main groove 3a main groove bottom 3b main groove opening 4 rib 4a rib side wall 4b rib notch 4c rib base 4d rib surface 4'shoulder rib 5 sub Groove 6 Belt ply 7 Sipe P Cut pitch W Tread width W ₁ Rib surface width W ₂ Rib base width W ₃ Rib base width not including cut depth D ₁ , D ₂ Cut depth X Tread tread center S, S'shoulder

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B60C 11 / 04,11 / 13

Claims (5)

(57) [Claims] 1. A heavy-duty pneumatic tire in which at least three main grooves arranged at intervals along the tire circumferential direction and ribs defined by the main grooves are formed on the outer surface of the tread portion. A notch formed on the surface width W ₁ of the rib and on at least one of the side walls of the rib surrounded by the main groove, the depth and width of which increase as the distance to the base of the rib connecting to the bottom of the main groove increases. The width W _{2 of the} rib having a large number of ribs has a relationship of W ₁ ≧ W ₂ , and the ratio of W ₂ / W ₁ of each rib is gradually increased from the center of the tread surface to the shoulder. A heavy-duty pneumatic tire characterized by being formed as follows. 2. A method according to claim preparative Red tread portion width W ₂ of the base of Li blanking in at least close center or to the can, characterized in that 70 to 100% of the surface width W ₁ of the rib 1 The pneumatic tire for heavy load described. 3. The tread is located on the outermost shoulder portion.
Heavy duty pneumatic tire according to claim 1 or 2, wherein the surface width W ₁ of the rib excluding the shoulder rib is a rib that is formed to be almost equal. 4. A heavy duty pneumatic tire according to claim 1, 2 or 3, wherein the forming a large number of cut portions of the zigzag shape as the width and depth widens near base to the side wall portion of the Li blanking. 5. The heavy load according to claim 4 , wherein the number of pitches of the zigzag-shaped notch formed on at least the base of the side wall of the rib is 3 to 9% of the tread width W. Pneumatic tires.