JPH09240216A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the ground contact pressure at a tread terminal part and prevent a difference between the ground contact length at the tread end part and that of the central part from growing excessively large, by setting the radius of curvature of a circular arc arranged in a shoulder range is made less than a half of that of a circular arc arranged in the center range. SOLUTION: Such relationship as 1/2 Q1>R, 1/2 Q2>R between a radius of curvature R and radii of curvature Q1, Q2, relationship as 0.65W<=L<=0.85W, M=W between distance L, M and a distance W and relationship as 0.3J<=H<=0.6J between a drop height H and a drop height J are satisfied. However, after a tire is pressed on a flat plate, it is defined that an axial distance from the equator surface S of the tyre to the ground contact end P is W and distances from there to the most outside 33, 34 of respective ranges 31, 32 of center and shoulder are L, M respectively. And also radii of curvature of the first, second and third circular arcs are defined to Q1, Q2 and R, and drop heights from the tread center T at the most outside points 33, 34 are defined to H, J, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to passenger cars, vans,
The present invention relates to a pneumatic radial tire used for a relatively small automobile called a pickup / light truck, and particularly to a pneumatic radial tire having improved uneven wear resistance in a tread portion.

[0002]

2. Description of the Related Art A pneumatic radial tire mounted on an automobile, especially a relatively small automobile of the type described above, has a tread rubber at a tread end portion (both end portions in the width direction of the tread portion) at a tread central portion (tire equatorial plane). There is a tendency to wear more (proximate wear occurs) more rapidly than rubber in the vicinity). Here, such uneven wear is caused by the forced wear due to the ground contact pressure at the tread end portion being higher than the ground contact pressure at the tread central portion in the case of a tire having a high curve traveling frequency. In the case of frequently used tires, it is considered that the self-excited wear is caused by the fact that the ground contact length at the tread edge portion is considerably shorter than the ground contact length at the tread central portion. Then, when such uneven wear progresses and the tread end portion is dented, it is unavoidable to discard it as a used tire despite a large amount of unutilized rubber remaining in the tread central portion. Before the above-mentioned disposal, uneven wear generated at the end of the tread may extend to the central part of the tread and reduce steering stability and braking performance on a wet road surface.

For this reason, for a tire that frequently travels in a curve, the cross-sectional outer contour of the tread portion should be formed by a single arc having a small radius of curvature, while on the other hand, for a tire that frequently travels straight, the tread should be treaded. It is practiced to form the cross-sectional outer contour of the portion with a single arc having a large radius of curvature.

[0004]

However, since the above-mentioned improving means is an antinomy, it can only be effective for a tire having a high curve traveling frequency or a tire having a high straight traveling frequency. Moreover, the effect was not sufficient.

The present invention suppresses early wear at the tread edge regardless of whether the vehicle is mainly running in a curve or straight running, and the early wear is due to the steering stability and braking performance of the tire. It is an object of the present invention to provide a long-lived pneumatic radial tire that can effectively suppress the progress to the central portion of the tread, which greatly affects the above.

[0006]

[Means for Solving the Problems] In order to achieve such an object, the present inventor has conducted earnest research and found the following. That is, in order to suppress early wear at the tread end, lowering the ground contact pressure at the tread end to approach the ground contact pressure at the tread center, and the ground contact length at the tread end and the ground contact length at the tread center. It is effective to prevent the difference between the tread lengths from becoming too large, and in order to prevent the early wear that occurs at the tread edges from progressing to the tread central part, the change in the ground contact length at the tread central part is suppressed. It was found that it is effective to reduce

The present invention has been made on the basis of such knowledge, and a pair of bead portions, a pair of sidewall portions extending outward from the bead portions in a substantially radial direction, and radii of the sidewall portions. With a tread portion that connects the outer ends in the direction, the outermost point of the grounding area when the assembly is mounted on a standard rim and filled with standard internal pressure and then pressed against a flat plate while applying a standard load is the grounding end P, and In a pneumatic radial tire in which the axial distance from the tire equatorial plane S to the ground contact end P when returned to the loaded state is a distance W, a standard rim is assembled and a standard internal pressure is filled in by a plane including the tire rotation axis. The outer contour of the tread portion when cut is composed of at least two kinds of arcs which are smoothly connected to each other and have different radii of curvature, and The outer contour of the tread portion divided into a center region consisting of at least one kind of arc and a shoulder region consisting of one kind of arc sequentially from the road surface S toward the ground contact end P has a center measured from the tire equatorial surface S, The distance to the outermost point of each shoulder area is L, M, the center, the radius of curvature of the arc in each shoulder area is Q, R, the center, the fall height from the tread center at the outermost point of each shoulder area, respectively. When represented by H and J, respectively, there is a relationship of 1 / 2Q> R between the radius of curvature Q and the radius of curvature R, and the distance L,
0.65W ≤ L ≤ 0.85W, M = between M and distance W
The relationship between W and the drop height H and the drop height J is
It is a pneumatic radial tire that satisfies the relationship of 0.3J ≦ H ≦ 0.6J.

First, according to the present invention, since the radius of curvature R of the circular arc arranged in the shoulder region is less than 1/2 of the radius of curvature Q of the circular arc arranged in the center region, the shoulder region extends outward in the axial direction. The diameter decreases rapidly as Here, this shoulder region is the tire equatorial plane S
It is an area outside the axial direction from the point separated by a distance L (0.65W to 0.85W) from the point where a high ground contact pressure was generated when traveling on a curve. Since the pressure is sharply reduced as it goes, the ground contact pressure generated in the shoulder area does not become so high even when the vehicle travels in a curve, and approaches the ground contact pressure in the center area.
As a result, even if the vehicle mainly travels along a curve, the shoulder area is prevented from being worn early. Moreover, in the present invention, in addition to the relationship described above, the fall height H is set to 0.6 times or less of the fall height J, so that a clear corner portion (bent portion) is generated at the boundary between the center region and the shoulder region, and The contact length in the center region is not so large because the radius of curvature Q of the arc in the center region maintains a large value at any position (exceeds twice the radius of curvature R of the arc in the shoulder region). It does not change, and thereby, even if the early wear occurs in the shoulder region, the early wear is suppressed from propagating toward the center region. Further, in the present invention, the falling height H is set to 0.3 times or more of the falling height J,
The difference between the ground contact length of the shoulder area and the ground contact length of the center area can be kept within the limit, which allows the shoulder area to wear early due to self-excited wear even when running straight ahead. Is suppressed.

According to the second aspect of the invention, it is possible to effectively suppress early wear in the shoulder region. Further, according to the third aspect, even if early wear occurs in the shoulder region, this early wear is blocked by the circumferential groove, and the progress to the center region is effectively suppressed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an assembly 13 of the tire 11 and the rim 12 when the pneumatic radial tire 11 is assembled to a standard rim 12 and then filled with a standard internal pressure, which is a plane including a rotation axis of the tire 11. It is the diagram which simplified the right half cross section among cross sections. Where the standard rim,
Standard internal pressure and standard load, which will be described later, refer to JATMA YE
It is based on the applicable rim and the pneumatic-load capacity correspondence table corresponding to the size of the radial ply tire defined in AR BOOK (1992, Japan Automobile Tire Manufacturers Association Standard).

1 and 2, reference numeral 11 denotes a pneumatic radial tire having a toroidal cross section.
Is provided with a pair of bead portions 17, a pair of sidewall portions 18 that respectively extend from the bead portions 17 toward the outer side in the substantially radial direction, and a tread portion 19 that connects the outer ends in the radial direction of the sidewall portions 18. There is. The tire 11 extends between the bead cores 20 embedded in the bead portion 17, and the radial carcass layer 21 that reinforces the sidewall portion 18 and the tread portion 19, and is arranged on the outer side in the radial direction of the carcass layer 21. , And a belt layer 22 that reinforces the tread portion 19.

[0012] The outer contour of the tread portion 19 (the tread portion when the tire 11 is assembled to the standard rim 12 and filled with the standard internal pressure, and cut by a plane including the tire rotation axis.
The outer surface contour of 19 and also called the tread surface 25 is composed of a combination of at least two types of arcs 26 (three types of arcs of the first, second and third arcs 26a, 26b, 26c in this embodiment). And these first, second, and third arcs 26a, 26
b and 26c have different radii of curvature and are smoothly connected to each other. Here, “smoothly connected to each other” means that arcs that are adjacent to each other are in contact with each other, that is, two arcs have one common point, and arcs are connected so that the tangent line is shared at this point. Say. Further, the outer contour 25 of the tread portion 19 is divided into a center region 31 and a shoulder region 32 which are sequentially arranged from the tire equatorial plane S toward the ground contact end P, and the center region 31 has at least one kind of arc (this implementation In the form, it is composed of two kinds of arcs, a first arc 26a located on the inner side in the axial direction and a second arc 26b located on the outer side in the axial direction), while the shoulder region 32 has one kind of arc (the outermost side in this embodiment). Of the third circular arc 26c). Here, the grounding end P is the axial direction of the grounding area when the tire 11 is assembled to the standard rim 12 and the standard internal pressure is filled, and then the standard rim 12 is pressed against a flat plate parallel to the rotation axis of the tire 11 while applying a standard load. The outermost point.

Then, after the tire 11 is pressed against the flat plate as described above, the axial distance from the tire equatorial plane S to the ground contact end P when the tire 11 is separated from the flat plate and returned to the unloaded state is defined as a distance W, The distances from the tire equatorial plane S to the outermost points 33, 34 of the center and shoulder regions 31, 32 (same as the ground contact end P) are L, M, the center, and the shoulder regions 31 and 32, respectively. , Radiuses of curvature of the second circular arcs 26a, 26b and the third circular arc 26c are respectively Q1, Q2 and R, the outermost point 3 of each of the center, shoulder regions 31, 32.
Assuming that the falling heights from the tread center T at 3 and 34 are H and J, respectively, the radius of curvature R and the radii of curvature Q1 and Q2 are described.
, 1 / 2Q1> R, 1 / 2Q2> R, and 0.65 W≤L≤0 between the distances L and M and the distance W, respectively.
In addition to the relationship of 85 W and M = W, a relationship of 0.3 J ≦ H ≦ 0.6 J is further established between the falling height H and the falling height J.
Further, between the radius of curvature R and the distance W, 0.3 W ≦ R ≦
It is preferable to have a relationship of 1.3W. Here, in order to smoothly connect the first, second, and third arcs 26a, 26b, and 26c to each other, in this embodiment, the first arc 26a
Center of curvature on the tire equatorial plane S, and the second arc
The center of curvature of 26b is taken on a straight line connecting the connection point between the first and second arcs 26a and 26b and the center of curvature of the first arc 26a,
Furthermore, the center of curvature of the third circular arc 26c is set to the second and third circular arcs 26c.
It is arranged on a straight line connecting the connection point between b and 26c and the center of curvature of the second arc 26b. Incidentally, here, the outermost point 35 of the first circular arc 26a measured from the tire equatorial plane S (first
The distance to the connection point between the arc 26a and the second arc 26b) is K.

Reference numeral 37 denotes a circumferential groove formed on the outer circumference of the tread portion 19 and extending continuously in the circumferential direction. The circumferential groove 37 extends from the tire equatorial plane S toward the ground contact end P by a distance U. That is, it is preferable to arrange them at positions separated by 0.90 to 1.10 times the distance L. A plurality of known main grooves extending in the circumferential direction are formed in the tread portion 19, but these main grooves are not shown in FIGS. 1 and 2 because the drawings are complicated.

Next, the operation of the embodiment of the present invention will be described. First, it is considered that when the pneumatic radial tire 11 as described above is caused to travel around a curve, for example, a high ground contact pressure is generated at the tread end of the tire 11. However, in this embodiment, 0.65 W ≦ L ≦ between the distance L and the distance W as described above.
The relationship of 0.85W is provided, and the radius of curvature R and the radius of curvature Q1, Q2 are 1/2 × Q1> R, 1/2 × Q2> R.
That is, the region where the high ground contact pressure is likely to occur (the region outside in the axial direction from the point separated from the tire equatorial plane S by the distance L (0.65 W to 0.85 W), here, the shoulder region 32). Radius R of the third circular arc 26c arranged at
The first and second arcs 26 arranged in the center region 31.
The radius of curvature R of the region (shoulder region 32) is made sufficiently small by setting the radius of curvature of a and 26b to less than 1/2 of the radius of curvature Q1, Q2.
The diameter of is sharply reduced toward the outside in the axial direction. For this reason, even if the vehicle travels in a curve as described above, the ground contact pressure generated in the region (shoulder region 32) does not become so high and approaches the ground contact pressure of the center region 31. As a result, even if the vehicle mainly travels along a curve, the shoulder area 32 is prevented from being worn early. Here, if the distance L is less than 0.65 times the distance W, the width of the center region 31 which has a great influence on steering stability and braking performance on a wet road surface cannot be sufficiently secured, while Distance L
Is more than 0.85 times the distance W, the ground contact pressure at the axially outer end of the center region 31 (in the vicinity of the boundary with the shoulder region 32) becomes high, causing early wear in the center region 31. The distance L must be 0.65 times or more and 0.85 times or less as large as the distance W as described above. If the radius of curvature R is 1/2 or more of the radius of curvature Q, the shoulder region 32
The radius of curvature R cannot be made sufficiently small, which prevents the early wear in the shoulder region 32. Therefore, the radius of curvature R must be less than 1/2 of the radius of curvature Q as described above. I have to.

On the other hand, when the pneumatic radial tire 11 is run centering on straight running, a braking force is applied to the shoulder region 32 due to a difference in diameter between the center region 31 and the shoulder region 32 (contact length difference). There is a risk that premature wear will occur in the shoulder region 32, but in this embodiment, there is a relationship of 0.3 J ≦ H between the drop height H and the drop height J as described above. Since the fall height H is set to 0.3 times or more of the fall height J, the difference between the ground contact length of the shoulder area 32 and the ground contact length of the center area 31 can be kept within a limit, which allows straight running. Even if the vehicle travels around the center, it is possible to prevent the shoulder region 32 from being prematurely worn due to self-excited wear. Here, if the fall height H is less than 0.3 times the fall height J, the ground contact length in the shoulder region 32 is the center region.
The fall height H is 0.3 times larger than the fall height J because the shoulder area 32 is prematurely worn by self-excited wear when straight running because it becomes shorter than the ground contact length at 31 or the steering stability during cornering decreases. Must be above.

Between the radius of curvature R and the distance W,
0.3W ≦ R ≦ 1.3W, that is, the radius of curvature R of the arc 26c arranged in the shoulder region 32 is set to the distance W
If it is 0.3 times or more and 1.3 times or less, early wear in the shoulder region 32 can be suppressed more effectively. Here, when the radius of curvature R is less than 0.3 times the distance W, the ground contact length in the shoulder region 32 is the center region 31.
The contact length may be slightly shorter than the contact length in Fig. 1 and early wear due to self-excited wear is likely to occur, and a part of the shoulder region 32 may not contact the ground, resulting in deterioration of tire performance. This is because if it exceeds 1.3 times, the ground contact pressure in the shoulder region 32 becomes high and early wear may occur.

Although the early wear in the shoulder region 32 is suppressed as described above, if the early wear still occurs, this early wear tends to propagate toward the center region 31. However, in this embodiment, in addition to the above-described relationship, a relationship of H ≦ 0.6J is provided between the falling height H and the falling height J, that is, the falling height H is 0.6 times or less than the falling height J. It was. Therefore, a clear corner portion (bent portion) is generated at the boundary between the center region 31 and the shoulder region 32, and the ground contact length in the center region 31 is the first and second arcs 26a in the center region 31. 26
Since the curvature radii Q1 and Q2 of b maintain a large value at any position (exceeding twice the curvature radius R of the third arc 26c in the shoulder region 32), they do not change so much. , Shoulder area as described above
Even if 32 wear occurs early, it will be
The progress toward 31 is suppressed. Here, when the drop height H exceeds 0.6 times the drop height J, the above-mentioned corners become unclear and the early wear generated in the shoulder region 32 is suppressed from progressing to the center region 31. Since it becomes difficult, the drop height H must be less than 0.6 times the drop height J.

Further, the early wear generated in the shoulder region 32 progresses to the center region 31, in the vicinity of the boundary between the center region 31 and the shoulder region 32 where the ground contact length rapidly changes, specifically, the distance from the tire equatorial plane S. Since the above-mentioned circumferential groove 37 is formed at a position separated by 0.90 to 1.10 times L to divide the shoulder region 32 and the center region 31, the circumferential region 37 blocks the shoulder region 32 and further effectively suppresses the circumferential region 37. It Here, when the distance U from the tire equatorial plane S to the circumferential groove 37 is less than 0.90 times the distance L, the early wear generated in the shoulder region 32 causes the circumferential groove 37 to be arranged in the center region 31. The wet performance may be deteriorated because it can progress to the inner side in the axial direction to the position where it is present. On the contrary, if the distance U to the circumferential groove 37 exceeds 1.10 times the distance L, the circumferential direction is increased. Premature wear due to forced wear or self-excited wear occurs on the inner side of the groove 37 in the axial direction, and it becomes difficult to suppress the progress of wear to the center region 31.
37 is preferably arranged at a position separated from the tire equatorial plane S by 0.90 to 1.10 times the distance L.

As described above, regardless of whether the vehicle is mainly traveling in a curve or straight, the shoulder region 32
It is possible to suppress the early wear in the tire, and to effectively prevent the early wear from progressing to the center region 31 that has a great influence on the steering stability and the braking performance of the tire, and the tire 11 has a long life. can do.

[0021]

EXAMPLES The tires used in the uneven wear test described below are pneumatic radial tires for LT (light truck) of size 185R14, and the carcass layer is composed of one ply in which polyester cords are radially arranged. The belt layer is composed of a steel cord layer. Such a tire was assembled to a standard rim of 5.0J × 14, and a standard internal pressure of 300 kPa was filled in the tire to form an assembly. After a standard load of 600 kg was applied to this assembly to determine the ground contact end P, the load was returned to the unloaded state and the distance from the tire equatorial plane S to the ground contact end P was measured. The result, 67.5 mm, was taken as the distance W. .

In this uneven wear test, the conventional tire 1 in which the outer contour of the tread portion has a large radius of curvature (405.2 mm) and the conventional tire 1 having the outer contour of the tread portion having a small radius of curvature (252.3 mm) are used. Conventional tire 2 formed of an arc, test tires 1 to 3 and comparative tires 1 to 2 forming a first tire group, test tires 4 to 7 and comparative tires 3 to 6 forming a second tire group, Test tires 8 to 11 and comparative tires 7 to 10 forming the third tire group, test tires 12 to 15 and comparative tires 11 to 14 forming the fourth tire group, and test tires forming the fifth tire group. Test tires 16 to 19 and comparative tires 15 to 18 were prepared. Here, the specifications of the test tire 1 are as follows. That is, the distance K is
22.0 mm, distance L is 50.3 mm, distance M = W is 67.5 mm, distance U
Is 52.5 mm, the radius of curvature Q1 of the first arc is 349.4 mm, the radius of curvature Q2 of the second arc is 368.6 mm, and the radius of curvature R of the third arc is
61.7 mm, drop height J is 8.64 mm, ratio R / Q2 of radius of curvature R of the third arc and radius of curvature Q2 of the second arc is 0.167, distance L
The ratio L / W between the distance and the distance W is 0.745, and the ratio H / J of the falling height is
0.414, the ratio R / W of the radius of curvature R of the third arc and the distance W is 0.
914, the ratio U / L of the distance U and the distance L was 1.04. Further, each of the tires constituting the first tire group is one in which the value of R / Q2 among the specifications of the test tire 1 is changed as shown in Table 1 below. However, since only the value of R / Q2 cannot be changed, other specifications were also changed, but here, the changes of the other specifications are suppressed as much as possible.

[Table 1] Further, each of the tires constituting the second tire group is one in which only the L / W value among the specifications of the test tire 1 is changed as shown in Table 2 below. However, since only the value of L / W cannot be changed, other specifications were also changed, but here, the changes of the other specifications are suppressed as much as possible.

[Table 2] Further, each of the tires constituting the third tire group is
Of the specifications of the test tire 1, only the value of H / J was changed as shown in Table 3 below. However, since only the value of H / J cannot be changed, other specifications were also changed, but here, the changes of the other specifications are suppressed as much as possible.

[Table 3] Further, each of the tires constituting the fourth tire group is one in which only the R / W value of the specifications of the test tire 1 is changed as shown in Table 4 below. However, since only the value of R / W cannot be changed, other specifications were also changed, but here, the changes of the other specifications are suppressed as much as possible.

[Table 4] In addition, each of the tires forming the fifth tire group is
Among the specifications of the test tire 1, only the U / L value was changed as shown in Table 5 below. However, since only the value of U / L cannot be changed, other specifications were also changed, but here, the changes of the other specifications are suppressed as much as possible.

[Table 5]

Next, after each of the tires was mounted on a small truck, a good track of about half and half for curve running and straight running was run for 20,0
An uneven wear test was conducted after traveling for 00 km, and the results are shown in Table 6 below.

[Table 6] Here, in the evaluation method of the uneven wear test, the amount of wear of the tread portion after the traveling of the distance is measured, and the amount of wear Sm in the shoulder region Cm in the center region is measured.
And the ratio of the maximum wear amount Ma to the minimum wear amount Mi at the three main groove positions in the center region were determined. Here, the closer these values are to 1.0, the better the uneven wear resistance and the ability to prevent the early wear generated in the shoulder region from progressing to the center region. Then, as is clear from Table 6, in each of the test tires embodying the present invention, the ratio of the wear amount in the shoulder region to the wear amount in the center region Sm / Cm, and the maximum wear amount in the center region are the minimum. The ratio Ma / Mi to the amount of wear is
It can be seen that both are improved over the conventional tires and better than the comparative tires.

[0024]

As described above, according to the present invention, it is possible to suppress early wear at the tread end portion regardless of whether the vehicle is mainly traveling in a curve or straight. It is possible to effectively suppress the progress of wear to the central portion of the tread, which greatly affects the steering stability and braking performance of the tire.

[Brief description of drawings]

FIG. 1 is a right half sectional view showing an embodiment of the present invention.

FIG. 2 is an enlarged explanatory view showing an outer contour of a tread portion.

[Explanation of symbols]

 11 ... Pneumatic radial tire 12 ... Standard rim 17 ... Bead part 18 ... Sidewall part 19 ... Tread part 25 ... Outer contour 26 ... Arc 31 ... Center area 32 ... Shoulder area 33 ... Outermost point 34 ... Outermost point 37 ... Circumferential groove

Claims (3)

[Claims] 1. A standard structure comprising a pair of bead portions, a pair of sidewall portions extending outward from the bead portions in a substantially radial direction, and a tread portion connecting the radially outer ends of the sidewall portions. After the rim is assembled and filled with standard internal pressure, the outermost point of the ground contact area when pressed against a flat plate while applying a standard load is set as the ground contact end P, and from the tire equatorial plane S when returned to the unloaded state, In a pneumatic radial tire having an axial distance to the ground contact end P as a distance W, the outer contour of the tread portion when cut by a plane including the tire rotation axis in a state where the tire is mounted on a standard rim and filled with standard internal pressure, has a radius of curvature. Of at least two types of arcs smoothly connected to each other, and at least one type sequentially from the tire equatorial plane S toward the ground contact end P. The outer contours of the tread section divided into the center region consisting of the circular arc and the shoulder region consisting of one kind of circular arc are the distances from the tire equatorial plane S to the outermost points of the center and shoulder regions, respectively, L and M. , The radius of curvature of the arc in each of the center and shoulder regions is represented by Q and R, and the fall heights from the tread center at the outermost points of each of the center and shoulder regions are represented by H and J, respectively, the radius of curvature Q and the curvature. The relationship of 1 / 2Q> R with the radius R, and the distance L,
0.65W ≤ L ≤ 0.85W, M = between M and distance W
The relationship between W and the drop height H and the drop height J is
A pneumatic radial tire characterized by satisfying the relationship of 0.3J ≦ H ≦ 0.6J. 2. The pneumatic radial tire according to claim 1, wherein the outer contour of the tread portion satisfies the relationship of 0.3 W ≦ R ≦ 1.3 W between the radius of curvature R and the distance W. 3. A pneumatic groove according to claim 1, wherein a circumferential groove continuously extending in the circumferential direction is formed at a position separated from the tire equatorial plane S toward the ground contact end P by 0.90 to 1.10 times the distance L. Radial tires.