JP2002019419A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wandering performance. SOLUTION: This pneumatic tire has a shoulder block 6 along the tread edge E. The tread edge E is composed of a circular arc-shaped curved surface Re for smoothly continuing a buttress surface 9 and a tread surface 2 being a tire axial directional outside surface of the shoulder block 6 in a tire meridian cross section. The buttress surface 9 is characterized in that a buttress contour line 10 in a cylindrical cross section of a radius r with the tire axis as the center has a curved surface part 11 composed of a curved surface forming a circular arc-shaped curve projecting outside in the tire axial direction and having the circular arc-shaped curve approaching a straight line as the radius r reduces.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire capable of improving wandering performance.

[0002]

2. Description of the Related Art A pneumatic tire, particularly a heavy-duty radial tire filled with a high internal pressure and having a tread portion reinforced by a tough belt layer, has an increased shoulder rigidity. There is a tendency that a so-called wandering phenomenon in which the handle is taken away tends to occur. It is known that in order to suppress such a wandering phenomenon, that is, to improve the wandering performance, it is effective to lower the rigidity of the shoulder portion and shift the camber thrust to the plus side. Therefore, conventionally,
As shown in FIG. 7A, the contour of the tread edge TE in the meridional section is a small arc b1, that is, a so-called round shoulder is formed. Further, in order to further improve the wandering performance, as shown in FIG. 7 (B), a number of sipes s extending in the tire axial direction are provided at the round shoulder portion to reduce the rigidity of the tread edge. Has been done.

[0003]

However, FIG. 7 (B)
As shown in FIG. 2, the sipe s formed on the rounded tread edge TE can greatly improve the wandering performance, but the sipe s reduces the rigidity of the tread edge TE. Unusual wear such as heel & toe wear and shoulder drop wear is likely to occur in the shoulder portion starting from the portion, and damage such as chipping of rubber is likely to occur.

[0004] The inventors have conducted various studies to improve wandering performance while maintaining abrasion resistance in a pneumatic tire having a shoulder block at the tread edge. As a result, in addition to the round shouldering of the tread edge, the shape of the buttress surface of the shoulder block is improved, that is, the buttress profile in the cylindrical section having a radius r around the tire axis of the buttress surface is shifted in the tire axial direction. Form an arc-shaped curve that protrudes outward,
In addition, the stiffness of the tread edge is reduced without drastically reducing the rigidity of the shoulder block based on the provision of a curved surface portion having a curved surface in which the radius of curvature of the arc-shaped curve increases as the radius r decreases. I found out what could be done.

As described above, the present invention is directed to a pneumatic tire capable of effectively improving wandering performance without causing problems such as uneven wear, chipping of rubber, and a large decrease in contact width, particularly preferably for heavy loads. It aims to provide tires.

[0006]

In order to achieve the above-mentioned object, according to the present invention, the invention is characterized in that a vertical main groove extending continuously in the tire circumferential direction near the tread edge is provided on the tread surface. A pneumatic tire having a shoulder block arranged in the tire circumferential direction along the tread edge by providing the vertical main groove and a lateral groove extending from the tread edge, wherein the tread edge is A buttress surface, which is an outer surface of the shoulder block in the tire axial direction, and an arc-shaped curved surface that smoothly connects the tread surface, and the buttress surface is a buttress in a cylindrical section having a radius r around the tire axis. The outline is
It is characterized in that it has an arcuate curve that protrudes outward in the tire axial direction, and that the arcuate curve has a curved surface portion that approaches a straight line as the radius r decreases.

Such a pneumatic tire has a curved surface portion on the buttress surface of the shoulder block,
The rigidity of the tread edge side of the shoulder block can be alleviated in combination with the so-called round shoulder without drastically reducing the rigidity, and the wandering performance can be effectively improved without causing problems such as uneven wear and rubber chipping. . That is, for example, when the buttress surface of the shoulder block collides with the slope of the rutted road, since the rigidity of the shoulder block is optimized, the camber thrust of the tire in the direction of climbing this slope occurs, making it easy to get on and off the rut. It can be carried out.

[0008] The curved surface portion may be constituted by a curved surface in which the radius of curvature of the arc-shaped curve gradually increases as the radius r decreases. Preferably, forming the curved surface portion from the tread edge to the tire radially inward region is particularly effective for preventing wandering. Further, a flat portion in which the buttress contour line forms a straight line may be formed inside the curved surface portion in the tire radial direction. Thereby, the rigidity of the shoulder block can be further optimized. More preferably, the curved surface portion has a radius of curvature of the arc-shaped curve at the tread edge of 1.5 to 4.5 times the length L of the shoulder block in the tire circumferential direction.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings, taking a heavy-load radial tire (hereinafter, sometimes simply referred to as "tire") as an example. FIG. 1 is a schematic cross-sectional view of a tread portion of a tire in which an internal structure is omitted, and FIG. 2 is a developed view of the tread surface. The tread surface 2 has a longitudinal main groove 3 extending continuously in the tire circumferential direction. ,
A horizontal groove 4 intersecting with the vertical main groove 3 is formed.

In the present embodiment, a plurality of vertical main grooves 3 are arranged. That is, the vertical main grooves 3 are, for example, a pair of vertical main grooves 3a, 3a arranged on both sides of the tire equator C, and a pair of outer main grooves 3a arranged on each outer side in the tire axial direction and closest to the tread edge E. The tread surface 2 includes four vertical main grooves 3b and 3b. Each of the vertical main grooves 3 has a zigzag shape in the tire circumferential direction and is formed continuously in the tire circumferential direction, but can be changed in various shapes such as a linear shape or a sine wave shape.

In the present embodiment, the horizontal groove 4 is a first horizontal groove 4a which connects between the inner vertical main grooves 3a, 3a, and extends outward in the tire axial direction from the inner vertical main groove 3a and extends to the outer vertical main groove 3a. Groove 3
b, the second lateral groove 4 that terminates without communication with b
b, a third lateral groove 4c extending inward in the tire axial direction from the outer vertical main groove 3b and terminating without communication with the inner vertical main groove 3a, and a tire shaft extending from the outer vertical main groove 3b. 4th extending outward in the direction and opening at the tread edge E
That include the lateral groove 4d. Note that the second and third
The lateral grooves 4b and 4c are connected by the narrow groove 16 in this example.

The width and depth of each of the vertical main grooves 3 and each of the horizontal grooves 4 can be variously set as required. For example, the groove width of the vertical main groove 3 is 2.0% of the tread contact width TW.
As described above, the content is more preferably 2.5% or more, and in the case of a heavy load tire 1 as in this example, it is particularly preferable that the tire 1 is continuously formed with a width of at least 5 mm or more. It is desirable that the width of each lateral groove 4 be, for example, 1.5% or more of the tread contact width TW. Preferably, the depth of the vertical main groove 3 is, for example, 5 to 12% of the tread contact width TW, and the depth of the lateral groove 4 is, for example, 2 to 12% of the tread contact width TW.

The tread contact width TW is the outermost tread edge E when the tire is rim-assembled on a regular rim, and the tire is grounded on a plane by applying a regular internal pressure and a regular load.
It is determined as the distance in the tire axial direction between E. At this time, the “regular rim” is a rim that is defined for each tire in the standard system including the standard on which the tire is based,
For example, a standard rim for JATMA and "Design for TRA
Rim "or" Measuring Rim "in the case of ETRTO." Normal internal pressure "is the air pressure specified for each tire in the standard system including the standard on which the tire is based. If it is the highest air pressure, if TRA, the table "TIRE LOAD LIMITS AT VARIOUSCOLD INFLATIO
N PRESSURES ", the maximum value in ETRTO is" INFLA
TION PRESSURE ", but 180 kPa if the tire is for a passenger car. In addition," regular load "means the load specified by each standard in the standard system including the standard on which the tire is based. For JATMA, the maximum load capacity and for TRA, the table "TIRE LOAD LIMITS AT
VARIOUS COLD INFLATION PRESSURES "
For ETRTO, specify "LOAD CAPACITY".

The tire 1 of this embodiment has a fourth lateral groove extending on the tread surface 2 and extending between the outer vertical main groove 3b and the outer vertical main groove 3b and the tread edge E. 4d
And a shoulder row 6 defined by the tread edge E and a row of blocks arranged in the tire circumferential direction. In the present invention, if the shoulder block 6 is provided, other portions of the tread surface 2 can be formed arbitrarily. In this example, the central block 5 is provided between the vertical main grooves 3a and 3a, and A rib-shaped portion 7 is formed between the vertical main groove 3a and the outer vertical main groove 3b.

In the tire according to the present embodiment, as shown in FIG. 1, in a tire meridian section including the tire axis, the tread edge E has a buttress surface 9 which is the outer surface of the shoulder block 6 in the tire axial direction. The tread surface 2
Are formed from an arc-shaped curved surface Re that smoothly connects the above-mentioned and the so-called round shoulder. The tire 1 having such a round shoulder can reduce the rigidity of the tread edge E in a well-balanced and appropriate manner, and is useful for shifting the camber thrust to the plus side. This can contribute to improving wandering performance. It is particularly desirable that such a curved surface Re be formed by an arc having a radius of curvature R1 having a center on the tire inner side, for example, 2 to 6%, more preferably 3 to 5% of the tread contact width TW. If the radius of curvature R1 of the arc is less than 2% of the tread contact width TW, it tends to be difficult to reduce the high rigidity of the tread edge E. There is a problem that a large decrease is easily caused.

In the tire 1, the buttress surface 9 of the shoulder block 6 is formed as shown in FIGS. 3, 4, 5 (A),
As shown in (B), the radius r around the tire axis CP
The buttress contour line 10 in the cylindrical section K has a curved surface portion 11 having a curved surface convex toward the outside in the tire axial direction, and a curved surface portion 11 having a curved surface that becomes closer to a straight line as the radius r decreases. , The tread edge E
Fig. 1 shows an example provided in the tire radially inner region.

As a result, the shoulder block 6 can reduce the rigidity of the tread edge E without drastically reducing its rigidity, and can shift the camber thrust to the plus side. Here, the camber thrust (CT) is, as shown in FIG. 6, a force in a direction perpendicular to the traveling direction generated when the tire 1 is rolled while being tilted at the camber angle θ, and in the tilted direction. It is expressed as plus when working and negative when working in the opposite direction. For a tire having a positive camber thrust value, for example, when the tread edge E collides with the slope of the rutted road, an axial force acting on the tire acts on the tire to smoothly get on and off the rut. Therefore, the wandering performance can be improved.

In order to remarkably improve such wandering performance, the curved surface portion 11 forms the arc-shaped curve from an arc, and for example, as the radius r decreases, the radius of curvature of the arc gradually increases. It can be composed of a curved surface that is large. In this case, the radius of curvature R2 of the arc-shaped curve at the tread edge E is 1.5 to 4.5 times, more preferably 2.0 to 4.5 times the length L of the shoulder block 6 in the tire circumferential direction (shown in FIG. 2). A value of 4.0 is particularly desirable in that an optimal arc-shaped curve corresponding to the shape of the shoulder block 6 can be obtained, and the camber thrust can be efficiently increased.

The ratio (R2 / R1) of the radius of curvature R2 of the arc-shaped curve at the tread edge E to the radius of curvature R1 of the curved surface Re of the tread edge E is, for example, 4 to 4.
0, more preferably 8 to 25. If this ratio (R2 / R1) is less than 4, the wear resistance tends to decrease due to a large decrease in the contact width and the amount of tread rubber, and if it exceeds 40, the rigidity of the tread edge E will increase. Cannot be relaxed, and it tends to be difficult to improve the wandering performance. In the case where the arc of the arc-shaped curve 11 is a composite arc formed by combining a plurality of arcs, the average radius of curvature can be substantially determined. When the tread edge E is formed by the curved surface Re as in the present example, “the radius of curvature R2 of the arc-shaped curve at the tread edge E” at the intersection of the curved surface Re and the tread surface 2.
Can be determined.

In the present invention, the wandering performance can be improved by forming such a curved surface portion 11 in the buttress portion 9 of the shoulder block 6. Therefore, in this embodiment, the tread edge E is attached to the tire axial direction. Does not have a sipe. For this reason, the occurrence of chipping of the rubber of the shoulder block 6 and uneven wear caused by the sipe can be effectively prevented, and the life of the tire can be extended.

Further, the shoulder block 6 may form the curved surface portion 11 in a height range ha in the tire radial direction of at least 60% or more, preferably 80% or more, more preferably 100% of the block height H. desirable. When the range ha of the curved surface portion 11 is less than 60% of the block height H, the effect of appropriately reducing the rigidity of the shoulder block 6 on the tread edge E side and improving the wandering performance is relatively reduced. On the contrary, even if it exceeds 100%, the effect of improving the wandering performance will level off.

Further, a flat portion 12 in which the buttress contour line 10 forms a straight line may be formed inside the curved surface portion 11 in the tire radial direction. That is, FIGS. 5A to 5C respectively show the buttress contour lines 10 when the radius r of the cylindrical section K is sequentially reduced. As shown in FIG. At 12, the buttress outline 10 appears as a straight line. In such a tire 1, for example, as the tire wears, the tread edge E of the shoulder block 6 can be gradually changed from an arc-shaped curve to a straight line. This is particularly preferable as a heavy-duty tire for all seasons running on a road or the like.

As described in detail above, in the present invention, the category of the tire is not limited to the above-described example,
It can be used for various categories of pneumatic tires such as for light trucks. It is desirable to form a buttress surface 9 including the curved surface portion 11 on all the shoulder blocks 6 of the tire.
If it is provided in 70% or more of the total number, the wandering performance can be improved.

[0024]

Next, an embodiment of the present invention will be described. The tire having the structure shown in FIG. 2 and having the shoulder block 6 according to FIG.
A 14PR heavy load radial tire was prototyped based on the specifications in Table 1, and the wandering performance and wear performance of each test tire were tested. The curved surface part is a buttress contour line at the tread edge as an arc with a radius of curvature of 110 mm,
And buttress contour line straight at the groove bottom position of the lateral groove,
A curved surface in which the radius of curvature of the buttress contour edge is smoothly changed between them. The tread edge was rounded by an arc having a radius of curvature of 8 mm.

The wandering performance is determined by assembling a test tire with a rim of 22.5 × 7.50 rim at an internal pressure of 700 kPa and loading a 20-ton loaded 2-D / 4 10-ton vehicle. It was mounted on wheels and traveled on a rutted road provided on the test course, and the driver's sensuality was evaluated with emphasis on how the handle was taken on the rutted road. The wear performance was determined by mounting each test tire on the front wheel of the vehicle and measuring 4000
After traveling 0 km, the uneven wear of the shoulder block and the lack of rubber at the tread edge were visually observed. These test results were evaluated in the following three stages: ：: good △: normal ×: bad

As an object for comparing the effects of the present invention,
A tire of Comparative Example 1 having a round shoulder and a buttress profile edge being straight over the entire buttress surface of the shoulder block, and a sipe spaced in the tire circumferential direction at the tread edge of the shoulder block of the tire of Comparative Example 1 The tire of Comparative Example 2 was also tested. Table 1 shows the test results.

[0027]

[Table 1]

As a result of the test, it can be confirmed that the tires of Example and Comparative Example 2 have better wandering performance than the tire of Comparative Example 1. However, in the tire of Comparative Example 2, the tread edge of the shoulder block was rapidly worn, and one-sided abrasion was observed. In addition, some rubber chips between sipes were found. On the other hand, it was confirmed that the pneumatic tire of the example according to the present invention improved the wandering performance without impairing the wear performance.

[0029]

As described above, the pneumatic tire according to the present invention can effectively improve wandering performance without causing uneven wear and chipping of rubber.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a tread portion of a tire showing one embodiment of the present invention.

FIG. 2 is a development view of a tread surface showing one embodiment of the present invention.

FIG. 3 is a perspective view schematically showing the shoulder block.

FIG. 4 is a diagram illustrating a cross section of a cylinder.

FIGS. 5A to 5C are cross-sectional views of a shoulder block having different buttress radiuses r.

FIG. 6 is a diagram illustrating camber thrust.

FIGS. 7A and 7B are diagrams illustrating a conventional technique.

[Explanation of symbols]

 Reference Signs List 2 tread surface 3 vertical main groove 4 lateral groove 6 shoulder block 9 buttress surface 10 buttress contour line 11 arc-shaped curve 12 flat portion 15 inclined surface portion 16 chamfered portion 17 narrow groove E tread edge K cylindrical section

Claims (4)

[Claims] 1. A tread surface having a vertical main groove extending continuously in the tire circumferential direction near a tread edge and a horizontal groove extending from the vertical main groove to the tread edge. A pneumatic tire formed with shoulder blocks arranged in the tire circumferential direction along an edge, wherein the tread edge is a buttress surface that is an outer surface of the shoulder block in the tire axial direction in a tire meridional section including a tire axis. The buttress surface is a circular arc shape in which a buttress profile in a cylindrical cross section with a radius r around the tire axis is convex outward in the tire axial direction. It is characterized in that the arc-shaped curve has a curved surface portion formed of a curved surface approaching a straight line as the radius r is reduced. Pneumatic tire. 2. The pneumatic tire according to claim 1, wherein the curved surface portion has a curved surface in which the radius of curvature of the arc-shaped curve increases as the radius r decreases. 3. The buttress surface includes the curved surface portion in a radially inner region from the tread edge to the tire radial direction, and the buttress contour line is a straight line inside the curved surface portion in the tire radial direction. The pneumatic tire according to claim 1 or 2, further comprising: 4. The curved surface portion has a radius of curvature of the arc-shaped curve at the tread edge set to 1.5 to 4.5 times the length L of the shoulder block in the tire circumferential direction. Item 4. The pneumatic tire according to any one of Items 1 to 3.