JP2002067624A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wear resistance. SOLUTION: On the tread surface 2, a plurality of longitudinal grooves 3 extending along the circumference of the tire having the tread 2, and latitudinal grooves 4 are provided, which form block patterns. The blocks comprise crown blocks Bcr, the areal center of gravity of the blocks Bcr's surface being placed within a crown area Cr occupying 50% of a tread grounding width TW having its center line of the tire equator C, and shoulder blocks Bsh, the areal center of gravity of the blocks Bsh's surface being placed within a shoulder area Sh occupying both right and left outside of the above crown area Cr. The circumferential stiffness Kcr of the above crown blocks Bcr is to be 245.0 to 270.0 (N/mm), and the circumferential stiffness Ksh of the above shoulder blocks Bsh is to be 137.0 to 197.0 (N/mm).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a pneumatic tire capable of improving abrasion performance.

[0002]

2. Description of the Related Art In recent years,
With respect to tires mounted on driving wheels and the like, block patterns are being adopted to improve the driving force. Especially in heavy duty tires used for heavy vehicles such as trucks and buses, the mainstream is a lug pattern with so-called lug grooves that extend from the tread edge in the tire axial direction and terminate. Is rapidly shifting to a block pattern capable of exhibiting a larger driving force.

[0003] However, a tire having a block pattern has a problem that the rigidity of the tread surface tends to be smaller than that of a tire having a lug pattern or the like, so that the abrasion resistance is reduced and uneven wear easily occurs. In particular, in the case of tires used under a large load such as heavy load tires, the rear surface side of the block on which a large shear force is applied during vehicle braking, and the road surface of the block on which a large shear force is applied when driving the vehicle Heel and toe wear, in which wear is concentrated on the first arrival side, is likely to occur. In addition, since the distribution of the action of the contact pressure and the lateral force is different between the crown region, which is the central portion of the tread surface, and the shoulder regions on both sides, the appearance of wear in each region also differs, and the tread surface is uniformly formed. It is difficult to wear.

The present invention has been devised in view of the above situation. In a block pattern, a crown block in which the area center of gravity of the block surface is located in the crown region, and an area center of gravity of the block surface in the shoulder region are located. Pneumatic tires that can prevent uneven wear and uniform tread surface wear and improve wear resistance, especially pneumatic tires for heavy loads, based on setting the rigidity of each block with the shoulder block to the optimum value It is intended to provide.

[0005]

According to the first aspect of the present invention, a plurality of vertical grooves extending in the circumferential direction of a tire, a land portion between the vertical grooves, and the vertical grooves are formed on a tread surface. A pneumatic tire having a block pattern provided with a lateral groove for dividing a land portion between the tread edge and the tread edge into blocks, wherein the block has a tread contact width of 5% with respect to the tire equator.
A crown block in which the area center of gravity of the block surface is located in the 0% crown region, and a shoulder block in which the area center of gravity of the block surface is located in the shoulder regions which are regions on both sides of the crown region, and the following formula (1) )
When defining the circumferential stiffness K of the block (when the block has siping, it is corrected by equation (2)), the circumferential stiffness Kcr of each crown block is 245.0 to
270.0 (N / mm), and the circumferential rigidity Ksh of each of the shoulder blocks is 137.0 to 197.0 (N / m).
m).

(Equation 3)

(Equation 4) Here, F: tangential force in the circumferential direction at the time of contact with the ground (N) y: circumferential displacement of the block (mm) h: height of the block (mm) E: Young's modulus of the block rubber (Pa) I: cross section 2 of the block Next moment (mm ⁴ ) A: Cross-sectional area of block (mm ² ) G: Shear rigidity of block rubber (= E / 3) (Pa) W: Width of block in the tire axial direction (mm) L: Tiping shaft of siping Length of directional component (mm) hs: Depth of siping (mm) n: Number of siping (number)

The circumferential rigidity K of the crown block
It is desirable that the ratio (Kcr / Ksh) between cr and the circumferential rigidity Ksh of the shoulder block be 1.25 to 1.95.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a development view of a tread surface 2 of a heavy-duty radial tire mounted on driving wheels of heavy vehicles such as trucks and buses as the pneumatic tire of the present embodiment. In the figure, a heavy-load radial tire (hereinafter sometimes simply referred to as a “tire”) has a plurality of longitudinal grooves 3 extending in the tire circumferential direction on a tread surface 2 and a land portion between the longitudinal grooves 3. And a horizontal groove 4 which divides a land portion between the vertical groove 3 and the tread edge E serving as a ground contact end into blocks B.

In the present embodiment, a total of three longitudinal grooves 3 are provided, and a central longitudinal groove 3a extending substantially on the tire equator C.
And outer vertical grooves 3b, 3b arranged on both sides thereof. In the present embodiment, each of the vertical grooves 3a and 3b has a zigzag shape in the tire circumferential direction and extends continuously over one circumference of the tire. However, it is needless to say that the shape of the vertical groove 3 is not limited to the illustrated shape, but may be changed to various shapes such as a smooth wavy shape or a straight shape. The groove width of each of the vertical grooves 3a, 3b is, for example, 4.5 to 8.0% of the tread contact width TW, more preferably 5.5 to 5.5, for example, in order to sufficiently exhibit drainage.
It is desirable to be 8.0%.

The tread contact width TW is determined between a tread edge E, which is a contact end when the tire is assembled on a regular rim, filled with a regular internal pressure, and a regular load is applied to contact a flat surface. This is the distance in the tire axial direction. The regular rim is a rim defined for each tire in a standard system including a standard on which the tire is based. For example, a standard rim for JATMA, a "Design Rim" for TRA, or an ETRTO. If you have "Measur
ing Rim ". The normal internal pressure is an air pressure determined for each tire in a standard system including a standard on which the tire is based. Table "TIRE LOAD LIMITS AT VA"
RIOUS COLD INFLATION PRESSURES "
In the case of TRTO, it is "INFLATION PRESSURE", but when the tire is for a passenger car, the pressure is 180 KPa. Further, the normal load is a load defined for each tire 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 INFLATI
ON PRESSURES ", maximum value for ETRTO
LOAD CAPACITY ".

In the present embodiment, the lateral grooves 4 are, in this example, lateral grooves 4a, 4a which can be divided into blocks by connecting the longitudinal grooves 3, 3 with a land portion between the longitudinal grooves 3, 3; Outer lateral groove 4 that can divide the land between tread edge E and tread edge E into blocks
b, 4b. Each said lateral groove 4a,
4b has a groove width of, for example, 4.0 to 7.5% of the tread contact width TW so that the drainage property can be sufficiently exhibited.
More preferably, it is desirable to set it to 4.5 to 7.5%. Each of the lateral grooves 4a and 4b may be formed in various shapes such as a straight line extending along the tire axis direction and a zigzag shape inclined with respect to the tire axis direction as in the present embodiment. Further, the lateral groove 4 of the present example exemplifies a partition that forms a vertically long block in which the tire circumferential direction length is larger than the tire axial direction length by making the arrangement pitch in the tire circumferential direction relatively large. are doing.

The block B defined on the tread surface 2 by the longitudinal groove 3, the lateral groove 4, and the tread edge E forms a crown having a range of 50% of the tread contact width around the tire equator C in the tire axial direction. A crown block Bcr in which the area center of gravity G1 of the block surface is located in the region Cr; and a shoulder region Sh which is a region on both outer sides of the crown region Cr.
And the shoulder block Bsh where the area center of gravity G2 of the block surface is located. In the present embodiment, the block sandwiched between the central longitudinal groove 3a and the outer longitudinal groove 3b forms the crown block Bcr, and the block sandwiched between the outer longitudinal groove 3b and the tread edge E is the shoulder block. Configure Bsh.

In the tire 1 of the present embodiment, when the circumferential stiffness K of the block is defined by the following equation (1) (when the block has siping, it is corrected by the equation (2)), the crown blocks Bcr Circumferential rigidity Kcr of 2
45.0 to 270.0 (N / mm), and the circumferential rigidity Ksh of each of the shoulder blocks Bsh is 137.0 to 19
It is one of the features to be set to 7.0 (N / mm).

(Equation 5)

(Equation 6) Here, F: tangential force in the circumferential direction at the time of contact with the ground (N) y: circumferential displacement of the block (mm) h: height of the block (mm) E: Young's modulus of the block rubber (Pa) I: cross section 2 of the block Next moment (mm ⁴ ) A: Cross-sectional area of block (mm ² ) G: Shear rigidity of block rubber (= E / 3) (Pa) W: Width of block in the tire axial direction (mm) L: Tiping shaft of siping Length of directional component (mm) hs: Depth of siping (mm) n: Number of siping (number)

As a result of various experiments by the inventors, each block constituting the block pattern has an optimum circumferential rigidity against wear, and the crown block Bcr and the shoulder block Bsh are different from each other. It was found that the value was different. In particular, it has been found that the crown block Bcr to which a high contact pressure always acts requires higher circumferential rigidity than the shoulder block Bsh, and the value is also limited to a substantially constant range. Further, in the pneumatic tire of the present invention, the heel and toe wear of each block is reduced by limiting the circumferential rigidity of each of the crown block Bcr and the shoulder block Bsh to an optimum constant range, and the crown block Bcr and the shoulder block Bsh are further reduced. The wear speed with Bsh is approximated, and the tread surface is worn almost uniformly.

For example, as shown in FIG. 2A, the block B can be modeled in a pseudo manner as a cantilever supported on the inner end side in the tire radial direction. By applying the bending and shearing of the beam to such a model, the circumferential rigidity K of the block is specified not by actual measurement but by approximate calculation. However, as shown in FIG. 2B, when a siping 7 having no substantial groove width is formed in the block B, the rigidity in the circumferential direction is reduced. The above equation (2) modified by empirical rules such as experiments in consideration of the influence of siping is used. In addition, since actual blocks include various shapes such as those having complicated shapes, individual rigidities in the circumferential direction can be calculated using a quadrature method, coordinate transformation, or the like.

The inventors conducted experiments by changing the circumferential rigidity of the crown block Bcr and the shoulder block Bsh in various block patterns. First, the basic patterns (tire size: 11R) shown in FIGS.
A heavy-duty tire having 22.5) was prototyped according to the specifications in Table 1, and the circumferential rigidity, heel and toe wear amount, and driving force on a wet road surface of each block were examined. Figure 1,
3 and 4 are block patterns, and FIG. 5 is a lag pattern. Example 2 has the same pattern as Comparative Example 2, but differs from Comparative Example 2 in that a rubber whose Young's modulus is increased by 20% is used for the tread rubber. The amount of heel and toe abrasion was determined by riming each tire (7.
50 × 22.5), fill the internal pressure of 850kPa, and attach it to two driving wheels of 2-D ・ D2 truck with constant load (10 tons) to perform road test on general roads. When the groove depth of the vertical groove 3a (the lug pattern is the same as the lug groove, the same applies hereinafter) reaches 70% of the new groove depth, as shown in FIG. The amount m was measured and evaluated by the average value.
In the road test, the vehicle traveled until the groove depth substantially disappeared. In FIG. 1, the groove width and the groove depth were as shown in the figure.

In order to check the driving force on a wet road surface, the test vehicle (constant load) is run on a test course having a low μ road surface with a water film thickness of 0.5 mm.
The traction was measured. A traction force of 15 kN or more passes.
Table 1 shows the test results.

[0017]

[Table 1]

As a result of the test, in the tires of Examples 1 and 2 included in the present invention, the heel and toe wear of each block is small, and the difference is small.
It can be confirmed that the driving force on a wet road surface is excellent.

On the other hand, in Comparative Examples 1 and 2 in which the circumferential rigidity Kcr of the crown block Bcr is less than 245.0 (N / mm), the heel and toe wear amount is large, and the wear resistance is improved. You can see that it was not done. This is because the crown block Bcr that exists
It is probable that heel and toe wear rapidly occurred in the crown region due to low circumferential rigidity of the tire. FIG. 7 shows the relationship between the groove depth of the vertical groove and the traveling distance as a result of the road test.
During the road test, the heel-and-toe wear of the crown block progressed rapidly during the road test, and the center area where the crown area was worn rapidly developed, resulting in a remarkable appearance defect. ing. In Comparative Example 3 having a lug pattern, it can be confirmed that the driving force on a wet road surface is inferior.

Even in a tire having a block pattern, the circumferential rigidity Kcr of the crown block Bcr is 2
If it is greater than 70.0 (N / mm), the circumferential rigidity of the crown block Bcr becomes excessive, and the shoulder block B
It is not preferable because wear is concentrated on sh and there is a problem that braking performance is reduced. From such a viewpoint, the circumferential rigidity Kcr of the crown block Bcr is 248.0 to 26.
It is preferably 7.0 (N / mm).

If the circumferential rigidity Ksh of the shoulder block Bsh is smaller than 137.0 (N / mm), the rigidity of the shoulder region is reduced, so that wear is concentrated on the shoulder block Bsh, so-called shoulder wear. The shoulder block Bsh has a higher wear rate than the crown block Bcr, making it difficult to uniformly wear the tread surface. Conversely, if the circumferential stiffness Ksh of the shoulder block Bsh is larger than 197.0 (N / mm), the stiffness of the shoulder region Sh is reduced to the crown region.
It becomes excessive with respect to the rigidity of Cr, and the wear speed of the shoulder block Bsh becomes smaller than that of the crown block Bcr, making it difficult to uniformly wear the tread surface.

It is particularly preferable that the ratio (Kcr / Ksh) of the circumferential rigidity Kcr of the crown block to the circumferential rigidity Ksh of the shoulder block be 1.25 to 1.9.
5, more preferably 1.35 to 1.85. Thereby, the crown block B
The difference in the wear rate between cr and the shoulder block Bsh can be further minimized, and uniform wear of the tread surface can be achieved. In addition, shoulder block Bsh, crown block B
As is apparent from the equation (1), the circumferential rigidity of cr is the Young's modulus of the block rubber, the shear rigidity, the height of the block,
It can be easily adjusted by variously changing the sectional area of the block.

[0023]

As described above, the pneumatic tire of the present invention regulates the stiffness in the circumferential direction of the crown block and the shoulder block within a certain range, thereby reducing the heel and toe wear of the crown block and the shoulder block. The difference in wear rate between the blocks can be reduced and the tread surface can be uniformly worn.

[Brief description of the drawings]

FIG. 1 is a developed view showing a tread surface of a pneumatic tire according to the present embodiment in a developed manner.

FIGS. 2A and 2B are perspective views schematically showing blocks.

FIG. 3 is a development view of a tread surface of the pneumatic tire of Comparative Example 1.

FIG. 4 is a development view of a tread surface of the pneumatic tires of Comparative Example 2 and Example 2.

FIG. 5 is a development view of a tread surface of a pneumatic tire of Comparative Example 3.

FIG. 6 is a sectional view of a block showing a method for measuring a heel and toe wear amount.

FIG. 7 is a graph showing a relationship between a groove depth of a longitudinal groove and a traveling distance.

[Description of Signs] 2 Tread portion 3 Vertical groove 3a Central vertical groove 3b Outside vertical groove 4 Horizontal groove 4a Horizontal groove 4b Outside horizontal groove Bcr Crown block Bsh Shoulder block

Claims (2)

[Claims] 1. A plurality of vertical grooves extending in the tire circumferential direction on a tread surface, a land portion between the vertical grooves, and a horizontal groove dividing a land portion between the vertical grooves and the tread edge into blocks. A pneumatic tire having a block pattern provided with: a crown block in which an area center of gravity of a block surface is located in a crown region of 50% of a tread contact width around a tire equator; A shoulder block in which the area center of gravity of the block surface is located in a shoulder region which is an outer region, and a circumferential rigidity K of the block according to the following equation (1) (when the block has siping, corrected by the equation (2)) Is defined, the circumferential rigidity Kcr of each crown block is 245.0 to 270.0 (N / mm), and the circumferential rigidity of each shoulder block is The sh 13
A pneumatic tire characterized by having a value of 7.0 to 197.0 (N / mm). (Equation 1) (Equation 2) Here, F: tangential force in the circumferential direction at the time of contact with the ground (N) y: circumferential displacement of the block (mm) h: height of the block (mm) E: Young's modulus of the block rubber (Pa) I: cross section 2 of the block Next moment (mm ⁴ ) A: Cross-sectional area of block (mm ² ) G: Shear rigidity of block rubber (= E / 3) (Pa) W: Width of block in the tire axial direction (mm) L: Tiping shaft of siping Length of directional component (mm) hs: Depth of siping (mm) n: Number of siping (number) 2. The circumferential rigidity Kcr of the crown block.
Of the shoulder block in the circumferential direction Ksh (K
The pneumatic tire according to claim 1, wherein cr / Ksh) is set to 1.25 to 1.95 and is used for heavy-duty vehicles.