JP2005022622A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire which can achieve low fuel consumption and improve brake performance at the same time, which conflict with each other. <P>SOLUTION: A Rolling Resistance Coefficient (RRC), in other words, the low fuel consumption and the brake performance, which conflict with each other, can be achieved and improved at the same time as follows. A tread is formed so as to have a dual layered structure composed of cap rubber layers arranged on both sides of the tread and a base rubber layer arranged inside the cap rubber layer. The cap rubber layer is divided into five regions in the direction of the width of the tire. Rubber moduli in the central region X, the intermediate region Y, and the shoulder region Z are set so as to satisfy X≤Z<Y, and a loss tangent (tan δ) are set so as to satisfy X≤Y<Z. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

 The present invention relates to a pneumatic tire that achieves both low fuel consumption and improved braking performance.

Rolling resistance in the tread portion of an automobile tire affects the fuel consumption of the vehicle. The tan δ (loss elastic modulus / storage elastic modulus) of the tread rubber indicates the degree of energy absorption. The smaller the tan δ, the lower the rolling resistance and the lower the fuel consumption.
On the other hand, braking performance is also important for the tire as various characteristics of the tire. It is known that the rubber modulus (rubber elastic modulus) is an important factor for this braking performance. The higher the rubber modulus, the better the braking performance.

However, attempts have been made to reduce fuel consumption by reducing the tan δ of the tread rubber. However, there is a possibility that the braking performance contradicting this, particularly performance degradation such as wetness, may occur. Attempts have been made to achieve both reduction in rolling resistance and braking performance by dividing the tire into a plurality of regions and dividing and arranging a characteristic tread rubber compound in each region.
In Patent Document 1, the tread rubber is divided into at least three in the tire axial direction, the rubber near the tire equatorial plane is made high elastic rubber, the rubber near the shoulder portion is made low elastic rubber, and tan δ of these rubbers is almost the same. A pneumatic tire is disclosed. Furthermore, in Patent Document 1, when the tread rubber is divided into four or more in the tire width direction, the dynamic elastic modulus of the rubber located in the middle between the rubber near the tire equator surface and the rubber near the shoulder portion is expressed as the two rubbers. It is described that it is preferable to set it to an intermediate value of the dynamic elastic modulus.
Japanese Patent Laid-Open No. 7-164821 (see paragraphs 0004 to 0009)

 However, the technique shown in Patent Document 1 is a method of reducing the rolling resistance of the entire tire while maintaining other performance such as wettability, and provides a pneumatic tire that can improve fuel consumption and reduce fuel consumption at the same time. Has not reached.

 Accordingly, an object of the present invention is to provide a pneumatic tire capable of simultaneously reducing the anti-rolling resistance and improving the braking performance.

 In order to achieve the above-mentioned object, the present inventor further advances the division of the tread rubber disclosed in Patent Document 1 into three in the tire width direction, the center region X through which the tire equatorial plane passes in the tire width direction, and the center The region is divided into five regions consisting of an intermediate region Y formed on both sides of the region and a shoulder region Z formed further outside the intermediate region. Of the rubber properties of each region, the rubber modulus and tan δ Focusing on the above, by changing these variously, we aimed to provide a pneumatic tire that simultaneously satisfies the contradictory reduction in rolling resistance and improved braking performance.

 As a result, the following knowledge was obtained. First, it has been found that the braking performance not only increases the modulus, but also greatly affects the contact pressure distribution. It has been found that the effects of the modulus and contact pressure distribution in each region in the tire width direction are more sensitive if the sensitivity of the shoulder region is higher than that of the center region and the modulus is increased in the shoulder region.

 Further, focusing on the RRC (Rolling Resistance Coefficient) related to the rolling resistance, the influence of tan δ was examined. As a result, the sensitivity in the center region was higher than that in the shoulder region, and It became clear that the effect of RRC on this would increase if the value was increased.

 Based on the above knowledge, it is possible to improve the braking performance by suppressing the deterioration of the contact pressure distribution by using rubber with high modulus only in the intermediate region where the sensitivity is low, not the shoulder region which is highly sensitive to the contact pressure distribution of the tire. In addition, it has been found that if the tan δ of the center region, which is highly sensitive to strain energy, is lowered, the RRC and braking performance that are contradictory can be improved at the same time.

  That is, the pneumatic tire according to the present invention has a tread portion in the tire width direction, a center region X through which the tire equatorial plane passes, an intermediate region Y formed on both sides of the center region, and an outer side of the intermediate region. Are divided into five regions, the rubber modulus of these regions is set to X ≦ Z <Y, and the loss tangent (tan δ) is set to X ≦ Y <Z. It is a feature.

 According to the above configuration, by setting the rubber modulus to X ≦ Z <Y, an increase in contact pressure in a highly sensitive shoulder region can be suppressed, braking performance can be improved, and front-rear rigidity can be increased. Further, by setting tan δ to X ≦ Y <Z, it is possible to reduce the rolling resistance in the center region.

 The tread portion may be a single layer structure or a multi-layer structure in the tire radial direction. However, in recent years, it is preferable to apply the present invention to a multi-layer structure that effectively exhibits various characteristics of the tire. That is, the tread portion has a two-layer structure of a cap rubber layer on the tread surface side and a base rubber layer disposed inside the tread portion, and the cap rubber layer has a center region, an intermediate region, and a shoulder in the tire width direction. In a pneumatic tire divided into five regions, it is preferable to apply each rubber modulus and tan δ of the region.

 As apparent from the above description, according to the present invention, the cap rubber layer is divided into five regions, the rubber moduli of the center region X, the intermediate region Y, and the shoulder region Z are set to X ≦ Z <Y, and the loss tangent By setting (tan δ) to X ≦ Y <Z, it is possible to improve both RRC, that is, the fuel consumption reduction and anti-braking performance.

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a main portion in the axial (width) direction of a radial tire in a tread portion of a pneumatic tire showing an embodiment of the present invention, and shows from a tire equatorial plane A to a tread end portion B on one side. Show.

 The radial tire 1 includes a sidewall portion (both not shown) extending radially outward from a pair of bead portions, a tread portion 2 connecting the upper ends thereof, and bead cores (not shown) at both ends along the inner periphery thereof. And a carcass 6 (partially shown) supported by being folded. Since the belt layer 7 is provided between the tread portion 2 and the carcass 6 and the reinforcing structure thereof is the same as that of a general radial tire, detailed description thereof is omitted.

 The tread portion 2 has a cap-base structure composed of two layers of a cap rubber layer 10 and a base rubber layer 11 located inside the cap rubber layer 10. A plurality of main grooves 12a and 12b (four main grooves in this embodiment) are formed on the outer peripheral surface of the cap rubber layer 10 so as to extend linearly or in a zigzag shape in the tire circumferential direction. However, normally, a lateral groove in a direction intersecting with the main grooves 12a and 12b, and further, an auxiliary groove connecting a sub-groove and a lateral groove narrower than the main groove in the tire circumferential direction are formed, and a predetermined tread pattern is formed. Is formed.

 The cap rubber layer 10 is formed with a center region X formed with the equator plane A as the center, an intermediate region Y formed with both sides of the center region X, and both sides with the intermediate region Y interposed therebetween. The shoulder region Z is divided into a total of five regions. Each part of the center region X, the intermediate region Y, and the shoulder region Z in the cap rubber layer 10 is indicated by 10x, 10y, and 10z.

 The rubber modulus of the center region X, the intermediate region Y, and the shoulder region Z is set to X ≦ Z <Y, and the loss tangent (tan δ) is set to X ≦ Y <Z.

 The first boundary line 15 that divides the center region X and the intermediate region Y is formed along the bottom surface of the first main groove 12a closer to the center. The second boundary line 16 that divides the intermediate region Y and the shoulder region Z is set along the bottom surface of the second main groove 12b outside the first main groove 12a. The first boundary line 15 and the second boundary line 16 are formed in pairs at symmetrical positions with the equator plane A interposed therebetween. The first boundary line 15 and the second boundary line 16 may be formed on the land portion surface of the tread portion 2.

  According to the FEM analysis, the first boundary line 15 and the second boundary line 16 are arranged within a range of 5 to 60 when the equatorial plane is 0 and the position of the tread edge is 100. It has been found that it is preferable to position the second boundary line within the range of 30-90. Furthermore, when the 1st boundary line 15 was located in the range of 5-30, and the 2nd boundary line 16 was located in the range of 40-60, the more preferable result was obtained.

 The rubber modulus and loss tangent (tan δ) can be adjusted as appropriate by a combination of the type of polymer and carbon to be blended, the blending amount, the blending amount of silica, oil, and sulfur. Table 1 shows three blending examples. However, it goes without saying that the present invention is not limited to the formulation examples in Table 1.

  Next, examples of the pneumatic tire having the above-described configuration will be described. Table 2 shows the results of evaluation tests of RRC performance, braking performance, and ground pressure distribution of seven types of radial tires in which the modulus and tan δ of the cap rubber layer were changed. The tire size of the test tire is 185 / 65R15.

  In Table 2, Examples 1 to 3 and Comparative Example 4 show cases where the cap rubber layer is divided into 5 regions, and the modulus and tan δ of each region are variously changed. The five regions including the center region X, the intermediate region Y, and the shoulder region Z of the cap rubber layer 10 have the first boundary line 15 defined as “1” when the position of the equator plane A is 0 and the position of the tread end portion B is 100. 20 ”and the second boundary line 16 were set at the position“ 50 ”, respectively. Comparative Examples 1 to 3 show examples in which the cap rubber layer is composed of a single rubber, and the modulus and tan δ of the single rubber are variously changed.

 The modulus is the tensile stress (M100) at 100% elongation of the sample. The sample length is set to 20 mm according to JIS K6251 and stretched at 23 ° C. at 4 mm / min. The rate was determined. In Table 2, the tensile stress of 0.29 MPa is shown as an index 100.

 tan δ is represented by a ratio of loss elastic modulus and storage elastic modulus when a sample (20 mm × 5 mm × 1 mm) is given an initial strain of 5%, a frequency of 10 Hz, and a dynamic strain of 10% at 60 ° C., The index is displayed with tan δ = 0.2 as index 100.

  Further, RRC, braking performance and contact pressure distribution in Table 2 were determined as follows.

<RRC>
RRC (Rolling Resistance Coefficient) is a rolling resistance coefficient expressed as a coefficient obtained by dividing the rolling resistance by the load. In the measurement, the internal pressure was set to 200 kPa, the test tire assembled with a rim was set on a drum testing machine, the drum was run at a load of 505 kg and a speed of 80 km / h, and the rotational resistance was measured. The rotation resistance of the tire of Formulation 1) was indicated as an index 100, and the index was expressed as the rotation resistance of Comparative Example 1 / the rotation resistance of the evaluation tire. The larger the value of RRC, the lower the rolling resistance and the better the performance.

<Brake performance>
The braking performance was displayed as an index with the reciprocal of the ABS braking distance at a speed of 100 km / h in actual vehicle running as 100 and the braking distance of the tire of Comparative Example 1 (CAP formulation 1) as 100. The larger the value, the better the performance.

<Ground pressure distribution>
The contact pressure distribution indicates a numerical value (%) obtained by dividing the maximum contact pressure of the shoulder portion by the average pressure. The more uniform the tire in the tire width direction, the better the tire and the better the braking performance.

<Evaluation results>
As shown in Table 2, in the comparative example using a single rubber as the cap rubber layer, the modulus / tan δ was set lower in the comparative example 1 than in the comparative example 1 and the modulus / tan δ in the comparative example 2 and the comparative example 3 than in the comparative example 1. Is set. In the RRC and braking performance of Comparative Examples 1 to 3, the lower the modulus / tan δ, the softer the rubber and the worse the braking performance, but the RRC becomes better and the fuel consumption is reduced.

 Comparative Example 4 is an example in which the cap rubber layer is divided into five regions, and the modulus and tan δ of each region are set higher toward the shoulder region from the center region. That is, in this example, the rubber modulus is set to X ≦ Y <Z and tan δ is set to X ≦ Y <Z.

 In Comparative Example 4, the modulus of the center region is set similarly to Comparative Example 1 (30%), and the shoulder region is set to 170 (%). Therefore, the braking performance is higher than that of Comparative Example 1 (index). Although it is “115” in terms of conversion, the braking performance is inferior to that of Comparative Example 3 in which the index is set to 170 (%) with a single rubber. This is presumably because the contact pressure distribution became non-uniform (index “90”) as a result of increasing the rubber modulus of the shoulder portion.

 On the other hand, in Examples 1 to 3, the rubber modulus is X ≦ Z <Y, and tan δ is X ≦ Y <Z. In any of Examples 1 to 3, the rubber modulus of the intermediate region Y is higher than that of the shoulder region Z, and tan δ is sequentially increased from the center region to the shoulder region. As a result, the balance between braking performance and RRC is improved as compared with Comparative Example 4.

 This is considered to be due to the use of rubber having a high modulus only in the intermediate region Y having a low sensitivity, not in the shoulder region Z having a high sensitivity to the tire contact pressure distribution. Further, since the center region X is highly sensitive to strain energy, tan δ in this portion is set low to reduce rolling resistance.

 FIG. 2 is a graph comparing the relationship between braking performance and fuel consumption performance, with the vertical axis representing braking performance and the horizontal axis representing RRC. In this graph, for braking performance and RRC, Examples 1 to 3 (shown as “invention product” in the figure) and Comparative Examples 1 to 4 (shown as “conventional structure” in the figure) are associated with each other. It is a thing. Each can be expressed as linear, and the line segments of Examples 1 to 3 are compared to Comparative Examples 1 to 4 of the conventional structure, and the result is that they are moved substantially parallel to the upper right direction. It can be seen that it is better than that.

 Thus, by setting the rubber modulus of the center region X, the intermediate region Y, and the shoulder region Z to X ≦ Z <Y and setting the loss tangent (tan δ) to X ≦ Y <Z, the RRC and the braking performance can be improved. A balance of contradictory performance can be achieved.

Sectional drawing of the principal part of the radial tire which shows embodiment of this invention Graph showing the relationship between braking performance and fuel efficiency

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radial tire 2 Tread part 6 Carcass 7 Belt layer 10 Cap rubber layer 11 Base rubber layer 15 First boundary line 16 Second boundary line A Tire equatorial plane B Tread edge X Center area Y Middle area Z Shoulder area

Claims (2)

The tread portion is composed of a center region X through which the tire equatorial plane passes in the tire width direction, an intermediate region Y formed on both sides of the center region, and a shoulder region Z formed further outside the intermediate region. A pneumatic tire characterized by being divided into two regions, wherein the rubber modulus of these regions is set to X ≦ Z <Y, and the loss tangent (tan δ) is set to X ≦ Y <Z. The tread portion has a two-layer structure of a cap rubber layer on the tread surface side and a base rubber layer disposed inside the tread portion, and the cap rubber layer has a center region X through which the tire equatorial plane passes in the tire width direction. And an intermediate region Y formed on both sides of the center region, and a shoulder region Z formed further outside the intermediate region, and the rubber modulus of these regions is X ≦ Z < A pneumatic tire characterized by being set to Y and having a loss tangent (tan δ) set to X ≦ Y <Z.

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