JP2007290453A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve braking performance by widening a grounding width and uniformizing grounding pressure distribution. <P>SOLUTION: As a tire shape for widening the grounding width, the ratio of a tire sectional width (SW) to a tread width (TW) is set to satisfy the following expression (1), and the sectional width (SW) to the standard center value sectional width (SW<SB>0</SB>) of a tire standard is set to satisfy the following expression (2). In order to uniformize the grounding pressure, when a Young's modulus in the center region 24C of a tread part 16 is assumed as Mc, and a Young's modulus in the middle region 24M as Mm, the Mc and Mm are set to satisfy the following expression (3). Expression (1) is 0.810≤TW/SW≤0.870, expression (2) is 0.990≤SW/SW<SB>0</SB>≤1.030, and expression (3) is 1.2≤Mm/Mc≤3.0. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire with improved braking performance.

  Conventionally, in a pneumatic radial tire, various measures have been taken to improve braking performance. For example, in Patent Document 1 below, the tread portion is divided into five regions, a center region in the center in the width direction, an intermediate region on both sides thereof, and a shoulder region on the outer side, and only the intermediate region has a high modulus rubber. It has been proposed to improve the braking performance by suppressing the deterioration of the contact pressure distribution by using. However, it is difficult to sufficiently improve the braking performance only by making the contact pressure distribution uniform.

Patent Document 2 listed below discloses a technique for achieving both tire rolling resistance and wet braking performance by optimally designing the tire ground contact shape and material configuration. A technique for improving the braking performance by making the distribution uniform is not disclosed.
JP-A-8-175108 Japanese Patent Laid-Open No. 60-15203

  In order to improve the braking performance, a tire shape and a tire structure that require a wide contact width and a uniform contact pressure in a braking state are required. On the other hand, in order to increase the contact width of the tire, it is generally necessary to increase the tread width. However, simply increasing the tread width widens the contact width, but the contact pressure distribution becomes uneven or lightweight. There is a problem that the resistance and the rolling resistance deteriorate.

  The present invention has been made in view of the above points, and by increasing the contact width by defining the tire shape, and by defining the Young modulus of the tread portion, the effect of increasing the contact width by the tire shape is achieved. An object of the present invention is to provide a pneumatic radial tire in which the contact pressure distribution is made uniform without loss, thereby improving the braking performance.

In the pneumatic radial tire according to the present invention, the tread portion is formed in the tire width direction, a center region through which the tire equatorial plane passes, an intermediate region formed on both sides of the center region, and further outside the intermediate region. A pneumatic radial tire divided into five regions with a shoulder region,
(1) The ratio (TW / SW) of the tread width (TW) to the cross-sectional width (SW) when the tire is mounted on a rim prescribed in the tire standard is in the range of 0.810 to 0.870,
(2) The ratio (SW / SW ₀ ) of the cross-sectional width (SW) to the standard center value cross-sectional width (SW ₀ ) of the tire standard is in the range of 0.990 to 1.030,
(3) The ratio (Mm / Mc) of the Young's modulus (Mm) of the rubber in the center region to the Young's modulus (Mc) of the rubber in the center region is in the range of 1.2 to 3.0. Is.

  According to the present invention, by defining the tire shape as in the above (1) and (2), the ground contact width of the tire can be widened. Further, by defining the rubber modulus distribution of the tread portion as in (3) above, it is possible to make the contact pressure distribution uniform while maintaining the effect of expanding the contact width by the tire shape. Therefore, the contact pressure distribution can be made uniform while widening the contact width, and the braking performance can be improved.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a cross-sectional view in the tread width direction of a pneumatic radial tire 10 according to an embodiment, showing a state where the pneumatic radial tire 10 is mounted on a rim 40 and filled with a specified internal pressure. The tire 10 includes a pair of left and right bead portions 12 and 12 and side wall portions 14 and 14 and a tread portion 16 straddling the both side wall portions 14. A carcass 18 locked by the portion 12 is provided, a belt 20 is provided on the tread portion 16 on the radially outer side of the carcass 18, and a tread rubber 22 is further provided on the radially outer side of the belt 20. Such a basic structure is the same as that of a general radial tire, and a detailed description thereof will be omitted.

  In the tire 10 of the present embodiment, the tread rubber 22 is composed of two layers of a cap rubber layer 24 on the ground surface side and a base rubber layer 26 on the carcass 18 side. On the outer peripheral surface of the cap rubber layer 24, a plurality of (here, four) main grooves 28A, 28B extending in a straight line shape or a zigzag shape in the tire circumferential direction are provided.

  The tread portion 16, more specifically, the cap rubber layer 24, in the tire width direction, the center region 24C through which the tire equatorial plane A passes by the four main grooves 28A and 28B, and both sides of the center region 24C. The intermediate regions 24M and 24M are formed and the shoulder regions 24S and 24S at both ends formed further outside the intermediate region 24M are divided into five regions. More specifically, the boundary 30 between the center region 24C and the intermediate region 24M is provided along the groove bottoms of the two main grooves 28A and 28A closer to the center, and the boundary 32 between the intermediate region 24M and the shoulder region 24S. Are respectively provided along the groove bottoms of the two outer main grooves 28B, 28B.

  The boundaries 30 and 32 between these regions are not necessarily in the main grooves 28A and 28B, and may be provided on the land portion surface of the tread portion 16. In particular, when the number of grooves is not four, all the boundaries cannot be provided in the main groove, and therefore, for example, the respective regions can be defined by dividing the tread width into five equal parts. As for the arrangement of the boundaries 30 and 32, when the position of the tire equatorial plane A is 0 and the position of the tread end B is 100, the boundary 30 between the center region 24C and the intermediate region 24M is 5 to 60, more preferably 5 to 30. It is preferable that the boundary 32 between the intermediate region 24M and the shoulder region 24S is positioned within the range of 30 to 90, more preferably 40 to 60.

In the above configuration, in the present embodiment, the tire shape for widening the contact width is designed as follows. That is, the ratio of the cross-sectional width (SW) to the tread width (TW) when the tire is mounted on the specified rim is determined so as to satisfy the following formula (1), and the cross-sectional width (SW) is set to the center of the tire standard. It is determined so as to satisfy the following formula (2) with respect to the value sectional width (SW ₀ ).

0.810 ≦ TW / SW ≦ 0.870 (1)
0.990 ≦ SW / SW ₀ ≦ 1.030 (2).

  Here, the cross-sectional width (SW) is a cross-sectional width when the tire 10 is mounted on the rim 40 specified in the tire standard, and is a width excluding patterns and characters on the tire side surface (a linear distance between sidewalls). (See FIG. 1). More specifically, after the tire 10 is attached to the rim 40 and filled with the prescribed air pressure to the inner pressure, and the bead portion 12 is accurately assembled to the rim 40, the tire shape is substantially the same as the unfilled state of the inner pressure. It is a cross-sectional width in a no-load state when the internal pressure is reduced to 50 kPa. Hereinafter, this cross-sectional width is sometimes referred to as “specified rim assembly cross-sectional width”.

  Further, the tread width (TW) is a linear distance between both ends of the tread pattern portion of the tire in the same state as when the cross-sectional width (SW) is measured (see FIG. 1).

Furthermore, the standard center value cross-sectional width (SW ₀ ) of the tire standard is the design center value (design dimension) of the cross-sectional width described in the tire standard (the design center value is the value at the time of specified air pressure filling) Is). The tire standard is determined by an industrial standard effective in the region where the tire is produced or used. For example, JATMA of the Japan Automobile Tire Association in Japan, TRA (The Tire and Rim Association) in the United States, There are ETRTO (European Tire and Rim Technical Organization) in Europe and Australia TRA (The Tire and Rim Association of Australia) in Australia, which are determined according to the destination of the tire to be designed.

  In the above formula (1), when TW / SW is smaller than the lower limit, the effect of expanding the contact width cannot be obtained, and the uniformity of the contact pressure is also impaired. On the other hand, if TW / SW is larger than the upper limit, weight reduction and rolling resistance are deteriorated, and uniformity of the ground pressure is also impaired.

The above formula (2) is basically based on the same reason as the above formula (1), that is, if SW / SW ₀ is smaller than the lower limit, the uniformity of the ground pressure is impaired, When it is larger than the upper limit, weight reduction and rolling resistance are deteriorated, and uniformity of the contact pressure is also impaired.

  When actually using a tire, it may not be mounted on a rim prescribed in the tire standard, but if the prescribed rim assembly cross-sectional width satisfies the above formulas (1) and (2), Even if the cross-sectional width when mounted on a use rim having a different rim width does not satisfy the above formulas (1) and (2), the above-described effects can be obtained.

  In the present embodiment, the modulus distribution of the tread portion 16 is designed as follows as a tire structure for achieving uniform contact pressure without affecting the contact width. That is, when the Young modulus of the cap rubber layer 24 in the center region 24C is Mc and the Young modulus of the cap rubber layer 24 in the intermediate region 24M is Mm, the following equation (3) is satisfied.

1.2 ≦ Mm / Mc ≦ 3.0 (3)
Here, the Young's modulus is the tensile stress (M100) at 100% elongation obtained by the JIS K6251 vulcanized rubber tensile test method, set to a sample length of 20 mm, and stretched at 23 ° C. at 4 mm / min. And obtained from the obtained stress-strain curve.

  In the above formula (3), if Mm / Mc is smaller than the lower limit, the effect of improving the contact pressure uniformity is reduced, and if it is greater than the upper limit, the contact pressure in the intermediate region 24M becomes too high and the contact pressure is made uniform. However, it is damaged. A more preferable lower limit of Mm / Mc is 2.0 or more.

  The Young modulus Ms of the cap rubber layer 24 in the shoulder region 24S is not particularly limited, but is preferably equal to or greater than the Young modulus of the center region 24C and smaller than the Young modulus of the intermediate region 24M (Mc <= Ms <Mm).

As described above, according to this embodiment, in terms of defined within a predetermined range with respect to prescribed rim section width SW specification center section width SW ₀ and the prescribed rim section width SW and the tread width TW By defining the ratio, it is possible to effectively widen the ground contact width depending on the tire shape. In addition, by defining the Young modulus distribution of the tread portion as described above, the contact pressure can be effectively equalized without impairing the contact width expansion effect due to the tire shape. Thus, since the contact width is wide and the contact pressure can be made uniform, the braking performance can be effectively improved.

  With respect to pneumatic radial tires for passenger cars having a cross-sectional structure shown in FIG. 1 with a tire size of 215 / 55R17 93V, tires of Examples and Comparative Examples were produced. The shape and structure of each tire were designed as shown in Table 1 below, and the configurations other than those shown in Table 1 were the same.

  The tire-free section width in Table 1 is a section width in a free state in which the tire is not mounted on the rim. Further, the specified rim assembly cross-sectional width SW and tread width TW are obtained by attaching each tire to a specified rim 17 × 7 JJ (rim width = 7.0 inches) of JATMA standard and filling the specified standard air pressure = 180 kPa with internal pressure. It is a measured value when the air pressure is reduced to 50 kPa. Each tire has a bead portion interval of 7.25 inches in a free state, and the bead portion interval is narrowed by the rim assembly, so that the prescribed rim assembly cross-sectional width is smaller.

The standard center value section width SW _{0 in} Table 1 is the design center value (design dimension) of the section width described in the JATMA standard.

TW / SW in the formula (1) in Table 1 is a ratio between the tread width TW and the specified rim assembly sectional width SW, and SW / SW ₀ in the formula (2) is the specified rim assembly sectional width SW. it is the ratio of the specification center section width SW _0.

Regarding the configuration of the tread cap rubber layer 24, Comparative Examples 1 to 3 and Comparative Example 6 use the same rubber in the entire width direction (formulation 1 shown in Table 2 below). In other Comparative Examples and Examples, The region 24C and the shoulder region 24S were left as they were (compound 1), and the rubber in the intermediate region 24M was changed as shown in Table 1 (compounds 2 to 4 shown in Table 2).

  In Table 2, the Young's modulus of each formulation was expressed as an index with formulation 1 as 100.

  For each tire produced above, the contact width, contact pressure dispersion, weight, rolling resistance, and braking performance were measured and evaluated. Each measuring method is as follows.

-Ground contact width: 5880 N (= JATMA maximum load × 0.8 × 1... Equivalent to the vertical load applied to each tire wheel during braking on a tire mounted on a rim of 17 × 7 JJ and having an air pressure of 180 kPa. 15) was loaded, and the contact width (maximum length in the direction perpendicular to the circumferential direction of the tread portion contact surface) was measured. The larger the index, the wider the contact width and the better.

-Ground pressure dispersion: 5880N (= JATMA maximum load x 0.8 x 1) equivalent to the vertical load applied to each tire wheel during braking on a tire mounted on a rim of 17 x 7 JJ and having an air pressure of 180 kPa .15) and calculate the vertical ground pressure and the average ground pressure at each measurement point in the ground plane, and calculate the square of all the square points of the difference between the ground pressure and the average ground pressure at each measurement point. A value obtained by dividing the total by the total number of measurement points was obtained, and this value was expressed as an index with Comparative Example 1 taken as 100, as ground pressure dispersion. The smaller the index, the more uniform and improved the contact pressure.

-Weight: The tire weight before assembling the rim was measured and displayed as an index with Comparative Example 1 taken as 100. The smaller the index, the lighter and better.

-Rolling resistance: It measured based on SAE J1269, and displayed by the index | exponent which set the comparative example 1 to 100. The smaller the index, the smaller the rolling resistance and the better.

-Braking performance: Each tire was mounted on a 2500 cc passenger car, the stopping distance from a speed of 100 km / h was measured, and displayed as an index with Comparative Example 1 as 100. The smaller the index, the better.

  The results are as shown in Table 1. Compared with Comparative Example 1 as a control, Comparative Example 2 in which Formula (1) was below the lower limit, Comparative Example 3 in which Formula (1) exceeded the upper limit, and Formula (3 ) Is below the lower limit, Comparative Example 4 and Comparative Example 6, and Comparative Example 5 where Expression (3) exceeds the upper limit, Comparative Example 7, which satisfies only Expression (3), and Expression (1) and Expression (3) are satisfied. In Comparative Example 8 that does not satisfy the formula (2), in all cases, sufficient results cannot be obtained in reducing the weight and rolling resistance, expanding the ground contact width, and making the ground pressure distribution uniform. The braking performance improvement effect was also insufficient. On the other hand, in Examples 1 to 3 that satisfy the above formulas (1) to (3), the grounding width is increased and the grounding pressure is made uniform without greatly reducing the weight and rolling resistance. As a result, an excellent braking performance improvement effect was recognized.

  As described above, according to the present invention, the braking performance can be improved, so that the present invention is suitably used for various pneumatic radial tires.

1 is a cross-sectional view in the width direction of a pneumatic radial tire according to an embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Pneumatic radial tire, 16 ... Tread part, 24 ... Cap rubber layer, 24C ... Center area | region, 24M ... Middle area | region, 24S ... Shoulder area | region, A ... Tire equatorial plane, SW ... Specified rim assembly cross-sectional width, TW ... Tread Width, R ... Rim width

Claims (1)

In the tire width direction, the tread portion has five regions: a center region through which the tire equator plane passes, an intermediate region formed on both sides of the center region, and a shoulder region formed further outside the intermediate region. Divided pneumatic radial tires,
(1) The ratio (TW / SW) of the tread width (TW) to the cross-sectional width (SW) when the tire is mounted on a rim prescribed in the tire standard is in the range of 0.810 to 0.870,
(2) The ratio (SW / SW ₀ ) of the cross-sectional width (SW) to the standard center value cross-sectional width (SW ₀ ) of the tire standard is in the range of 0.990 to 1.030,
(3) The ratio (Mm / Mc) of the Young's modulus (Mm) of the rubber in the central region to the Young's modulus (Mc) of the rubber in the central region is in the range of 1.2 to 3.0. Pneumatic radial tire.

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