JPH064364B2 - Pneumatic radial tires for trucks and buses - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention mainly relates to trucks and buses, and particularly to air having a rib tire tread pattern which is widely used for purposes including high-speed driving on good roads. It is an object of the present invention to propose a new tread pattern for a filled radial tire, which is improved so as to effectively improve the wear life of the tire by effectively increasing the uneven wear resistance of the tread.

Generally, the rib type tread pattern is suitable for pneumatic radial tires for trucks and buses which are generally used for high-speed running on good roads.
Up to four, that is, a plurality of wide main grooves form (ribber number + 1) ribs.

However, with regard to the formation of the rib sections, so-called uneven wear frequently occurred on the shoulder ribs located outside the tread, even though consideration was given to making the contact pressure distribution across the width of the tread as uniform as possible. .

This uneven wear starts from an edge defect that begins to appear at the outer edge of the shoulder rib at the beginning of use of the tire, and with this as a core, shoulder wear wear over the entire shoulder rib, or local wear such as wavy wear, that is, uneven wear is caused. It develops into wear, and further, it goes through abnormal wear such as polygonal wear that crosses the wide main groove and spreads over the center rib to significantly impair the tread appearance. Wear life, vibration riding comfort, wet resistance, reusability, etc.) are significantly impaired.

(Prior Art) When the above-mentioned uneven wear is applied to the front wheel as the idle wheel, the occurrence degree is particularly severe in the tread half portion located outside the vehicle, and therefore it can be prevented by rotating the tire. However, it is difficult to execute because it is time-consuming, and the tread pattern that is difficult to adapt to rotation is also being improved, and it is not effective to avoid uneven wear.

Also, with the aim of making the wear uniform over the entire width of the tread and also improving the adhesion on the ground of the tire, two wide main grooves and several narrow auxiliary grooves are used together, Particularly, it is disclosed in Japanese Patent Publication No. 45-801 that the sub-grooves are arranged between the main grooves and between the main grooves and the tread ends at substantially the center.

However, it has been found that the combined use of the main groove and the sub groove is not practically effective in solving the uneven wear as described above.

On the other hand, in JP-A-58-194606, when the tread of a non-driving wheel tire for a truck bus is a square shoulder type in which both side edges are square, a so-called rail effect, which is a difficulty in operation, is caused. In order to avoid it, the side ribs that step down from the peripheral surface at both ends of the tread are divided by narrow circumferential grooves, and the top width of these side ribs is especially the maximum depth of the circumferential groove. Is almost equal to
Being able to increase lateral grounding force as well as with a round shoulder type tread, such as when taking the conventional solution of increasing the number of circumferential groups, results in a rib width between the groups Although it is disclosed according to the occurrence of uneven wear due to narrowing, localized wear such as shoulder drop wear caused by edge defects at the side edge of the tread, that is, uneven wear and abnormal wear due to its progress No mention is made of measures to prevent the progress of the development, and no such effect can be expected.

Furthermore, since the groove depth is deep enough and the rigidity of the tread rubber is relatively small at the time of new use and at the beginning of use, the movement of the rubber at the tread end portion becomes large when side force acts, and this tread end portion There is a possibility that the edge inside the narrow groove may be damaged early due to the step provided on the. In this way, if the edge is damaged in the initial stage of use, the uneven wear is significantly developed thereafter, which is a problem.

(Problems to be Solved by the Invention) The present invention advantageously reduces the progress of uneven tread wear, which is inevitable in pneumatic radial tires for trucks and buses having a rib type tread pattern as described above, to reduce tire wear. The purpose is to significantly improve the life.

(Means for Solving the Problems) The present invention has a plurality of wide main grooves extending along the outer circumference of a tire to allow a tread to have shoulder ribs on both sides under a substantially uniform contact pressure distribution over the width direction. , A small number of center ribs located between them, and at least one shoulder rib is provided with one sub-groove having a width narrower than that of the wide main groove adjacent to the shoulder rib. In a pneumatic radial tire having a rib type tread pattern, which is further divided into two ribs, the above sub groove is
There is a distance (B) equivalent to 25-40% of the width (A) of the shoulder rib measured from the edge of the tread, and the groove walls substantially contact only in the contact area due to the load rolling of the tire. By dividing the shoulder rib into an outer rib and an inner rib by an arrangement extending along the outer circumference of the tire with a groove width, the inner rib is sacrificed solely due to the difference in wear caused in the outer rib. This is a pneumatic radial tire for trucks and buses, which is characterized by reducing the development of uneven wear of the tread toward the side.

FIG. 1 shows a tire size 1000 to which the present invention is applied.
An example of the tread pattern of a heavy-duty pneumatic radial tire of R20 is shown in a partially developed plane, and a cross section is shown in FIG.

Regarding the internal structure of the tire, a radial carcass, a highly rigid belt arranged to surround the crown portion thereof, and a tread rubber that surrounds the outer peripheral portion thereof are very common as a tire of this type. Detailed description is omitted.

The tread 1 has a plurality of (three in this example) wide main grooves 2 extending in a zigzag shape along the outer periphery thereof, so that the tread 1
Two shoulder ribs 3 located on both outer sides of the tread 1 and a few in the center of the tread 1 (two in this example)
It is divided into the center ribs 4 of.

Width T of the tread 1 is 200m
m, the radius of curvature of the outer peripheral surface of the tread in the tire axial section, the so-called crown R is 520 mm, and the width W ₂ of the main groove ₂ is 11
mm, therefore the average width of the ribs 3, 4 is approximately 42 mm and the depth d ₂ of the wide main groove ₂ is 14 mm.

The wide main groove 2 is provided in the contact area when the tire rolls under load.
The groove walls are so wide that they do not come into contact with each other, and the width W ₂ is preferably 4 to 8% of the width T of the ground contact area of the tread.
And

The shoulder rib 3 does not include a lateral groove in the rotational axis direction of the tire that substantially impedes continuity in the circumferential direction.

Each shoulder rib 3 is further divided into an outer rib 6 and an inner rib 7 by one narrow sub-groove 5 extending in a zigzag shape along the tire circumferential direction, and the sub-groove 5 has a tread width T. 3% or less, more preferably 0.3 to 2%, and at least 30% of the groove width of the wide main groove 2 is preferable.

The sub-groove 5 has a distance B from the tread edge 10 of 25% to 40% of the width A of the shoulder rib 3, that is, 0.25 ≦ (B /
A) It is arranged in a position such that ≦ 0.4. It is more preferably 30% or less.

The width of the outer rib 6 and the inner rib 7 divided by the sub-width 5 on the shoulder rib 3 is smaller than the width W ₄ of the center rib 4 in order to balance the ground pressure. To most preferred.

In the illustrated example, the sub groove 5 extending in a zigzag shape has a zigzag pitch P of 23 mm and a point height H of 3 mm. The rib width is measured when the ridgeline of the rib is zigzag-shaped and the center of swing of the zigzag-shaped ridgeline is taken as the end of the rib.

In FIG. 2, the sub-groove 5 is not necessarily provided substantially perpendicular to the tread surface, and may be cut so as to form a small angle α with respect to the normal line n of the tread surface which is erected in the groove opening. Most preferably, as shown in FIG. 2, it is preferable to incline outward at an angle α of 20 ° or less with respect to the normal line n (α is 8 ° in this example).

As mentioned above, the uneven wear of the shoulder ribs 3 is particularly severe in the tread half located outside the vehicle when the tire is mounted on the vehicle. It goes without saying that the tire can be mounted and used so that the shoulder rib 3 provided only on the rib and having the sub-groove 5 is on the outside of the vehicle.

(Operation) The inventors have established a mechanism of uneven wear that grows and develops with the edge drop defect in the shoulder rib of the tread as a starting point, and develops the contact pressure distribution and the frictional force (shear force) between the road surface. Various studies were conducted on the size and the like.

First, the edge drop defect occurs when the tire receives a side force due to a reaction force from the ground due to the cornering operation, and the ground contact pressure at the outer edge of the shoulder rib 3 locally becomes high, resulting in the largest slip.

Generally, the wear amount V is V = A × E, (A: wear amount per unit wear energy,
E: wear energy), where wear energy E is E = ∫F · dl (F: friction force, dl: slip amount), and friction force F is F = μ × P (μ: friction coefficient) , P: ground pressure).

Therefore, the wear amount increases as the ground contact pressure increases and the slip amount increases, and as described above, the ground contact pressure increases and the slip amount also increases. Is unavoidable.

This edge drop defect occurs at the portion subjected to the side force, and this becomes the core, and a difference in the radius of gyration during tire running occurs between the shoulder rib surface where the edge drop defect does not occur and the wear surface where the edge drop defect occurs. By that,
During straight running, wear due to so-called dragging occurs and a wear step appears, which is usually called (diameter difference wear).

After that, the edge drop defect and the diameter difference wear due to the side force repeatedly occur, so that the wear step expands in the depth direction and in the rib width direction to reach the shoulder drop wear over the entire shoulder rib 3.

Also, the same edge drop defect is the starting point, and unevenness on the circumference of the side force input acting on a part around the shoulder rib 3, unevenness of the outer diameter of the shoulder rib 3 such as rim fitting property, etc. In combination, irregular and non-uniform input acts on the outer edge of the shoulder rib 3, so that the wear growth rate in the width direction of the shoulder rib 3 is different over the entire circumference of the shoulder rib 3 to cause wavy friction in which the wear surface has a wavy shape. Reach

This corrugated wear is blocked by the wide main groove 2 and the unevenness of the shoulder rib 3 is gradually made to progress to the above-mentioned shoulder drop wear, or it extends beyond the wide main groove to the center rib and is made non-circular. Develops into polygonal wear.

With the progress of such uneven wear, in the tread pattern according to the present invention, the position of the sub-groove 5 arranged on the shoulder rib 3 is remarkably reduced under proper arrangement.

That is, the shoulder rib 3 measured from the edge of the tread 1
By dividing the shoulder ribs 3 into the outer ribs 6 and the inner ribs 7 with the arrangement of the sub-grooves 5 extending along the outer periphery of the tire with a gap B corresponding to 25 to 40% with respect to the width A of The outer rib 6 has a sacrificial action based on the difference in diameter wear starting from the edge drop defect, which advantageously promotes not only the uneven wear to the inner rib but also the spread to the center rib. This is avoided, and the step difference between the outer rib 6 and the inner rib 7 due to this sacrificial action is maintained continuously during use of the tire.

Thus, the outer rib 6 receives a lower average grounding pressure and a shearing force in the width direction than the inner rib 7 when subjected to the side force exerted on the running tire. The shearing force concentrated on the edge is also dispersed and significantly reduced.

The distribution of the average ground pressure and the shearing force in the width direction of the outer rib 6 is reduced by adjusting the sub-groove 5 so that the width A of the shoulder rib 3 is smaller than that of the shoulder rib 3.
It is practically not brought under the excessive distance B from the edge of the tread 1 which exceeds 40%, and when it is less than 25%, the ground contact pressure at the outer end of the inner rib 7 becomes relatively large, which is unsuitable. Is.

In short, the uneven wear that occurs in the shoulder ribs 3 and further develops is mainly due to the side force generated during cornering and the local edge drop defect at the side edge of the shoulder ribs 3 due to the dragging during straight running. Along with the outer circumference of the rib 3 and in the width direction and the depth direction, the edge drop defect grows and develops to uneven wear. On the other hand, according to the present invention, the shoulder rib 3 has a narrow width. Shoulder rib 3 with one sub groove 5
Therefore, by dividing the outer rib 6 having an appropriate width from the inner rib 7, the progress of uneven wear due to the occurrence of the uneven wear nucleus is effectively suppressed.

That is, the auxiliary groove 5 arranged at the specific position appropriately reduces the ground contact pressure applied to the side end of the outer rib 6 of the shoulder rib 3 when the side force acts, and the edge drop that becomes the core of the uneven wear is reduced. In addition to reducing the occurrence of the defect itself, by optimizing the difference in the shearing force generated in the outer rib 6 and the inner rib 7 in the width direction and along the outer circumference of the rib,
That is, by reducing the shearing force generated in the outer ribs in the width direction and increasing the shearing force along the outer circumference of the tread, the outer ribs 6 have a sacrificial effect of being worn first, and the outer ribs 6 come into contact with the inner ribs while the outer ribs 6 are running. By effectively reducing the force applied to 7 and separating the inner rib 7 by the sub-groove 5,
This contributes to effectively reducing the progress of uneven wear generated from the tread end portion on the shoulder rib 3.

The effect of the distance B from the tread edge 10 on the shoulder rib 3 of the auxiliary groove 5 on the average ground pressure and the axial shearing force as shown in FIG. 1 will be explained in more detail by actually running results.

Shoulder rib 3 of tread 1 when side force of about 300 kg acts on the tread end 10 of the tire when a vehicle equipped with a tire size of 1000R20 and 3 groove tires is running.
FIG. 3 shows the average ground contact pressure from the time when the upper outer rib 6 and the inner rib 7 are stepped on to the time when they are pushed out. When the position of the sub groove 5 is 30% in B / A, it is indicated by a circle, and the average ground pressure P ₆ of the outer rib ₆ is sufficiently lower than the average ground pressure P ₇ of the inner rib 7. Further, this average ground pressure P ₆ is the third
Compared with the average ground pressure P ₆₀ of the outer rib 6 when the sub groove position shown in the figure for comparison is 50% in B / A, it is also sufficiently low. The average ground pressures P ₇ and P ₇₀ of the inner rib 7 are almost the same.

Also, when a side force of about 300 kg is applied to the tread 1 of the tire during running, the axial shearing force generated on the outer rib 6 and the inner rib 7 of the shoulder rib 3 of the tread 1 also affects the shoulder rib 3 of the auxiliary groove 5. The position B / A above results in the state shown in FIG.

That is, the position of the sub groove is 30% in B / A (indicated by a circle in the figure)
And outer rib 6 when B / A is 50% (shown by the diamond mark in the figure)
Comparing the above axial shear forces, it can be seen that the case where B / A is 30% is sufficiently low, and the side force is not concentrated at the outer rib 6 end, that is, the tread end.

The effect of B / A on the average ground pressure shown in FIG. 3 and the axial shearing force shown in FIG.
Pneumatic radial tires for buses are almost the same when they are different. For example, the tire size is 1000R20 and the groove is 4 grooves. The results are shown in Figs. 5 and 6, and the tire size is 750R20. The case of three grooves is shown in FIGS. 7 and 8, and the case of four grooves of the same size is shown in FIGS. 9 and 10, respectively.

Next, the uneven wear starting from the above-mentioned edge drop defect and its suppression will be described in more detail with reference to FIGS. 11 to 13.

(1) Edge drop defect (a) When sub-groove 5 is not provided on shoulder rib 3 (No. 11)
Fig. A) Axial shearing force τ is generated as shown in Fig. 11B (a) due to the collapse of the tread rubber during loading (solid line). Further, when the side force is input, the load on the input side becomes large like τ ₁ and τ _{2 in} FIG. 11B (b). (Dashed line) Here, + is taken toward the central part of the tread.

(b) When the shoulder rib 3 is provided with a groove G having a width equal to that of the main groove (Fig. 12A), the axial shearing force τ is also as shown in Fig. 12B (A) due to the crushing of the tread rubber when loaded. Are generated in the dividing ribs by the groove G, respectively. Rib rigidity when inputting side force
Since it is lower than that in (a), the bending deformation increases,
The load at the end of each partition rib on the input side is larger than in the case of (a), as shown in FIG. 12B (b).

(c) When the sub-groove 5 is provided on the shoulder rib 3 (Fig. 13A) When the load is applied, the sub-groove 5 closes and closes as shown in Fig. 13B (a) to prevent the tread rubber around the sub-groove from being crushed. , The shear force of this part is smaller than that of (b) and approaches 0. When the side force is input, the auxiliary groove 5 is closed (b)
The shoulder rib 3 behaves as a unit in comparison with the above. In addition, the presence of the sub-groove 5 reduces the entire amount of bending deformation (deformation is divided) as compared with (a), and the increase in the axial shearing force τ at the shoulder outer end is small.

As described above, by providing the shoulder ribs 3 with the auxiliary grooves 5 that come into contact with each other when the load is applied, the concentration of force on the tread edge when side force is applied is suppressed and dispersed, whereby the edge drop of the outer rib 6 occurs. The occurrence of the defect itself can be suppressed. By the sub-groove 5 that comes into contact when the load rolls,
The concentration of force on the outer edge of the inner rib 7 is also suppressed, and the occurrence of edge drop defects at this portion is also suppressed.

(2) Sacrificial action Although the edge drop defect is extremely slow compared to the conventional case shown in FIG. 11A, it is unavoidable that the outer rib 6 occurs as shown in FIG. 14, but the outer diameter is slightly reduced. A step is generated due to the difference in wear centered on the broken portion. At this time, the outer rib 6 having a low ground contact pressure is worn earlier (sacrificing action) because the shearing force along the outer circumference of the tread 1 increases with an increase in the step amount, while the inner rib 7 has a higher ground contact pressure and the outer circumference of the tread. Wear is suppressed because no shearing force is generated along.
In this way, the outer ribs 6 are preferentially worn to widen the wear step, but the step is maintained there when reaching a limit in the ground contact surface where the outer rib does not contact the ground.

(3) Why does wear due to sacrificial action not progress inside the sub-groove (a) When no sub-groove is provided (Figs. 14A and 14B) The difference in diameter due to the step difference is initially generated when the edge drop defect occurs. Although the wear progresses in the depth direction due to wear and does not exceed a certain step, the progress of the wear in the width direction reveals that between the part that is worn down and the other part is as shown in FIG. 14B. As shown in FIG. Since the step-down portion contacts the road surface within the ground contact surface during load rolling, bending deformation d occurs in the axial direction with the convex portion as a fulcrum. Therefore, when the side force is applied, the ground contact pressure of the convex portion p becomes extremely high and wears (the same principle as the edge drop defect), and the wear gradually progresses inward of the shoulder ribs 3, and finally To reach the main groove 2.

(b) In case of providing a narrow groove (FIGS. 15A and B) Even when the outer rib 6 stepped down due to the sacrificial action comes into contact with the road surface within the ground contact surface, the auxiliary groove 5 prevents the inner rib 7 from contacting. Since it is continuous, bending deformation with the end of the inner rib 7 as a fulcrum is less likely to occur, so that an increase in ground contact pressure can be suppressed even when a side force is applied. Therefore, the re-emergence of nuclei is prevented.

(4) Progress of overall wear As described above, the outer rib 6 is lowered due to the sacrificial action.

Although the step is maintained at a constant position, microscopically, it is repeated wear due to the difference in diameter and wear due to side force. That is, if the difference in diameter wear becomes excessive and the step becomes larger than a certain level, the wear of the entire tread inside the sub-groove including the inner rib 7 due to the side force is prioritized, and the inside of the fine groove becomes too worn and the step becomes more than a certain level. If it becomes smaller, the difference in wear will be given priority, and the step will be increased again. By repeating such behavior, it is possible to achieve uniform wear until the end of wear while keeping the level difference substantially constant.

As for the diameter difference wear (striking wear), as shown in FIG. 16, the outer diameters (R1 and R
When there is a portion forming 2), the large diameter portion R1 has a small diameter portion R2.
The ground contact pressure is higher than that of the above, and the large diameter part rotates and advances with almost no slippage with the road surface. Therefore, the distance traveled by the large-diameter portion R1 is substantially the distance traveled by the tire as a unit. On the other hand, although the outer diameter of the small diameter portion R2 is small, the distance traveled during one rotation must be equal to the distance traveled by Taya as a unit, that is, the distance traveled by the large diameter portion R1 in one rotation. Therefore, a deviation occurs in the small diameter portion where the ground contact pressure is low. Due to this deviation, a shearing force acts in the tangential direction on the outer circumference of the tire, so that the small diameter portion is preferentially worn.

Such a phenomenon in which a portion having a small outer diameter is preferentially worn is called diameter difference wear.

Example An interior having a tread pattern of a type in which four ribs are divided by three wide main grooves 2 equivalent to those shown in FIGS. track of the same size 10.00R20 structures were compared with those of Comparative tire C ₁ -C ₅ the effect of the tire I ₁ ~I ₃ of the present invention by several prepared radial tires for buses.

The number of sub-grooves 5 is one for each of the shoulder ribs 3, and the depth d ₅ , width W ₅ , and inclination angle α are 12 mm, 1.5 mm, and 8 °, respectively. The zigzag pitch P of the groove is 23 mm and the point height H is 3 mm.

Each tire has a tread width T of 200 mm and a crown R of 5
20 mm, the depth d ₂ and the width W ₂ of the wide main groove 2 were 14 mm and 11 mm, respectively, and the ratio B / A of the distance B to the width A on the shoulder rib 3 was varied as shown in Table 1.

The comparative tires C _{1 to} C ₄ are the same as those shown in FIGS. 1 and 2 except that the sub-groove arrangement is incompatible and C ₅ has no sub-groove.

100% good road with these tires, average speed 80km /
h, the actual vehicle running test under the condition of specified load, 50,000km
The results of examining the uneven wear at the time of running are as follows.

The uneven wear of the shoulder ribs 3 basically proceeds from edge drop defects to shoulder drop wear, corrugated wear, and polygonal wear as described above.
The extension that was pulled from the outer peripheral part where uneven wear of No. 1 toward the tread end following the crown shape at the time of new article,
The gap between the cross-sectional contour of the tread that actually causes uneven wear is defined as the uneven wear region, and the maximum depth on the tire outer circumference of this uneven wear region is measured as the step amount (mm). The area in the tire cross section of the region was measured as an uneven wear area (mm ² ), and the index of the result of the tire I ₁ of the present invention was set to 100 for these measurement results, together with a visual observation of the uneven wear condition, Listed in Table 1.

As is clear from these results, the tires I _{1 to} I of the present invention are
₃ is able to reduce the fall height due to wear of the entire shoulder rib 3, Comparative tire C _1, C _2,
Almost no uneven wear as seen in the shoulder ribs 3 of C ₃ , C ₄ and C ₅ occurred. It should be noted that the wear itself due to the sacrificial action that occurs in the outer rib 6 does not pose a serious problem in terms of appearance and performance.

(Effects of the Invention) As described above, according to the present invention, it is possible to advantageously reduce uneven wear of a pneumatic radial tire for trucks and buses having a rib type tread pattern, particularly shoulder ribs and even center ribs. However, the wear life of the tire as a whole can be significantly improved.

[Brief description of drawings]

1 and 2 are a development view and a cross-sectional view of a main part of a tread showing an example of a pneumatic radial tire for trucks and buses according to the present invention, and FIGS. 3 to 10 are subordinates on respective shoulder ribs 3. Comparative graphs showing the relationship between the groove position and the average contact pressure and the axial shearing force FIGS. 11 to 16 are explanatory views of wear behavior. 1 ... Tread 2 ... Wide main groove 3 ... Shoulder rib 4 ... Center rib 5 ... Sub groove 6 ... Outer rib 7 ... Inner rib 10 ... Side edge of tread A ... Shoulder rib width B ... Distance from sub tread end

 ─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-58-194606 (JP, A) JP-A-56-157606 (JP, A) JP-A-55-44028 (JP, A) JP-A-54- 136002 (JP, A)

Claims (1)

[Claims] 1. A tread with a plurality of wide main grooves extending along the outer periphery of a tire under a substantially uniform contact pressure distribution across the width of the tread, and a plurality of shoulder ribs located on both sides of the shoulder rib. The rib-type tread is further divided into two by dividing one of the center ribs into at least one shoulder rib and arranging one sub-groove having a width narrower than that of the adjacent wide main groove. In a pneumatic radial tire having a pattern, the auxiliary groove has a distance (B) corresponding to 25 to 40% with respect to the width (A) of the shoulder rib measured from the edge of the tread,
In addition, by dividing the shoulder rib into an outer rib and an inner rib by an arrangement that extends along the outer periphery of the tire with a groove width in which the groove walls substantially contact each other only in the contact area due to the load rolling of the tire, A pneumatic radial tire for trucks and buses, which is characterized by reducing the progress of uneven wear of the tread toward the inner ribs under the sacrificial effect based on the difference in diameter wear caused by the ribs.