JP2005132247A - Pneumatic radial-ply tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial-ply tire capable of compatibly establishing the braking performance and its counter-performance (anti-wear performance, rolling resistance performance, etc.) by introducing a special shape to the tread surface profile. <P>SOLUTION: At the tread surface of this pneumatic radial-ply tire in its width direction section, the relation of Y/X to X, where X represents the tire width direction distance from the tread center CL and Y does the drop-in amount in the tire radial direction from the tread center CL, has a first, a second, and a third region in the area from the tread center CL to the grounding end E with the 80-% load of the normal design load according to JATMA, wherein the second region lies in the extent 1/2W to W, where W represents the tire width direction distance from the tread center to the grounding end, and further the tread surface is formed so that the gradient in each region when the above described relation is subjected to a linear, first-order approximation in each region meets the conditions β<α, β<γ, and α<γ. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pneumatic radial tire, and more particularly to its tread surface shape.

  Generally, the tread surface shape of a pneumatic radial tire is configured by connecting a plurality of arcs from a center portion to a shoulder portion. At that time, in the conventional radial tire, the plurality of arcs are connected so as to be in smooth contact with each other, that is, the adjacent arcs are generally connected by a contact so that they have a common tangent line. .

  For example, in Patent Document 1, the outer peripheral line of the tread portion includes an arc-shaped crown center region having a center of curvature inward in the tire radial direction, and a crown shoulder portion region continuous therewith. A radial tire is disclosed in which the ratio (R2 / R1) of the curvature radius (R1) of the region and the curvature radius (R2) of the crown shoulder region is in the range of 0.5 to 1.0.

  In Patent Document 2, the tread surface is formed by three arcs of curvature radii R1, R2 and R3 from the tread center to the shoulder portion, and each arc and the width of the region formed by each arc are defined. , Radial tires each designed to have a specific relationship are disclosed.

  Patent Document 3 discloses a radial tire in which the tread surface is composed of four or more arcs connected from the center portion to the shoulder portion, and the radius of curvature of adjacent arcs is designed to have a specific relationship. ing.

Furthermore, Patent Document 4 discloses a radial tire in which the tread outer ring shape has three or more curvature radii that smoothly contact each other from the center portion of the tire crown toward the shoulder portion, and have a specific relationship therebetween. Is disclosed.
Japanese Patent Laid-Open No. 10-315710 JP-A-5-229308 JP-A-6-191223 JP 2001-191733 A

  As described above, in the conventional pneumatic radial tire, the tread surface is formed by connecting the plurality of arcs at the contact points so as to smoothly contact each other. However, with such a conventional tread surface shape, it has not been easy to achieve both braking performance and anti-back performance (for example, wear performance and rolling resistance performance).

  That is, for example, conventionally, in order to improve the braking performance, the ground contact shape of the tire at the time of high load is a square type as shown in FIG. 4B, and the ground contact pressure in the tire width direction is made uniform. In this case, however, it is necessary to reduce the tread crown radius. As shown in FIG. 4 (a), the tire ground contact shape becomes a round shape under the load equivalent to the actual vehicle, and the wear performance and rolling resistance performance decrease. End up. Therefore, the tread crown radius cannot be extremely reduced. On the other hand, in order to improve the wear performance, if the tire ground contact shape is designed to be a square shape as shown in FIG. As shown in (d), the ground contact shape does not extend in the width direction at the shoulder end but grows in the tire circumferential direction, the pressure distribution in the tire width direction becomes non-uniform, and particularly the contact pressure at the shoulder portion increases. The braking performance will deteriorate.

  Therefore, in order to achieve both the braking performance and the anti-wear performance and rolling resistance performance, the tire ground contact shape is the square shape shown in FIG. It is desirable to use the square shape shown in FIG. 4B in which the ground contact area is increased while maintaining the ground contact shape.

  The present invention has been made in view of the above points, and by making the tread surface shape a unique shape unprecedented, both braking performance and anti-wear performance such as wear performance and rolling resistance performance are compatible. An object of the present invention is to provide a pneumatic radial tire that can be used.

  The pneumatic radial tire according to the present invention has a tire width direction distance from the tread center on the tread surface in the tire width direction cross section as X, and the amount of depression in the tire radial direction from the tread center as Y. The Y / X relationship has three regions, a first region, a second region, and a third region, between the tread center and the ground contact edge at 80% of the JATMA design normal load, and the second region is the tread center. When the distance in the tire width direction from the contact point to the ground contact edge is W, it is in the range of 1/2 W to W, and the gradient of the first region when the relationship in each region is linearly approximated by α , Where the slope of the second region is β and the slope of the third region is γ, it has a tread surface that satisfies β <α and β <γ.

  In the pneumatic radial tire of the present invention, it is preferable that the tread surface further satisfies α <γ.

  In addition, the surface shape of the tread in the present invention is an outer shape at the time of filling a minute internal pressure, and the minute internal pressure is 30 kPa. Further, the reason why the ground contact end at 80% of the JATMA design normal load is defined is that this often coincides with the ground contact end at an actual vehicle equivalent load. That is, the actual vehicle equivalent load is a load applied to the front single shaft of the vehicle to be evaluated, and this load is often 80% of the design normal load of JATMA (Japan Automobile Tire Association).

  In the pneumatic radial tire of the present invention, the tire ground contact shape may be a square shape with a large contact area while maintaining the ground contact shape even at a heavy load while maintaining a square shape at a load equivalent to an actual vehicle. Therefore, it is possible to achieve both braking performance and anti-wear performance such as wear performance and rolling resistance performance.

  Hereinafter, a pneumatic radial tire according to an embodiment of the present invention will be described with reference to the drawings.

  The pneumatic radial tire of the present embodiment is characterized by the surface shape of the tread, and the shape is defined as follows.

  As shown in FIG. 1 (a), the distance in the tire width direction from the tread center CL (the distance from a point Q on the tread surface to the tread center CL) on the tread surface in the cross section in the width direction of the pneumatic radial tire is expressed as X. And Y is the amount of depression in the tire radial direction from the tread center CL (the distance in the tire radial direction between the point Q on the tread surface CL and the point P on the tread surface CL at the tread center CL). And the value of X and Y / X is plotted about several arbitrary points Q on the tread surface, and the relationship shown in FIG.1 (b) is obtained. In the example of FIG. 1B, the sampling interval of X is 5 mm from the tread center CL to 20 mm, and 2 mm from 20 mm to the grounding end, but is not limited to this. For example, the tread width The interval may be 1 mm as a whole.

  In the pneumatic radial tire according to the present embodiment, the relationship of Y / X with respect to X is between the tread center CL and the ground contact E at 80% of the JATMA design normal load as shown in FIG. , The first region, the second region, and the third region. More specifically, as shown in FIG. 1 (b), two singular points A and B (points that are boundaries between regions where Y / X increases tend to be different) are generated in the XY / X distribution. With these as a boundary, the first region is defined from the tread center CL to the singular point A, the second region is defined from the singular point A to the singular point B, and the third region is defined from the singular point B to the ground contact E. Here, in the second region, when the distance in the tire width direction from the tread center CL to the ground contact E is W (that is, when the 80% load of the JATMA design normal load is applied), the ground contact width is 2W. ), Within the range of 1/2 W to W from the tread center CL, that is, the shoulder side range T between the position of W / 2 from the tread center CL and the ground contact E.

  Then, when the point sequence in each of the above regions is linearly linearly approximated, the gradient of the first region is α, the gradient of the second region is β, and the gradient of the third region is γ, β <α, And it is designed to satisfy β <γ. More preferably, α <γ is further satisfied.

  Such a regulation of the slope is not found in the conventional pneumatic radial tire described above. That is, when a tread surface is formed by connecting a plurality of arcs so that they touch each other smoothly as in the prior art, the gradient of each region of the XY / X distribution is the case of two regions. , Α <β, or β <α, and even when there are three regions, it is normal that α <β <γ or γ <β <α.

Here, linear linear approximation is performed as follows. That is, in the graph of FIG. 1B, the horizontal axis is x, the vertical axis is y, and the number of plotted points is n. For each xy value, for example, the i-th value is (x _i , y _i ).

  Assuming that the relationship between x and y is a linear relationship, the relationship is expressed as follows.

y = a ₁ x + a ₀ (1)
The coefficients a ₁ and a ₀ of this equation (1) are obtained by the least square method. The least square method is a method for obtaining each coefficient so that the sum of squares of the residual is minimized, and the residual here is a difference between the estimated value and the measured value. The residual sum of squares S is

And that this sum of squares is the smallest

Therefore, if the coefficients a ₁ and a ₀ are obtained from the above equation (2), the gradients α, β, and γ are given by the calculated coefficient a ₁ .

  According to the present embodiment, by interposing the second region having a small gradient as described above in the shoulder side range T, the tread outer shape line is effectively lifted by the shoulder portion, and the tire touches down at the time of an actual vehicle equivalent load. The shape can be a square shape as shown in FIG. 4 (c), and even when the load is increased, the ground contact shape is maintained and the ground contact area is increased to increase the contact pressure distribution even at high loads. Uniformity can be achieved.

  FIG. 2 is a half sectional view in the tire width direction showing an example of a tread shape according to the present embodiment.

  In this example, the tread surface is formed from four arcs of curvature radii R1, R2, R3, and R4 from the tread center CL to the ground contact E.

  The arc of R1 forming the central portion including the tread center CL and the arc of R2 adjacent to the outside thereof are connected using point 1 as a contact. More specifically, the center of the arc of R1 is on the tread center line CL, the center of the arc of R2 exists on a straight line connecting the point 1 and the center of the arc R1, and the arcs of R1 and R2 The tangent slope at point 1 is set to be the same. Also, the arc of R3 and the arc of R4 adjacent to the outside thereof are also connected with the point 3 as a contact point, but the arc of R2 and the arc of R3 adjacent to the outside of the arc are the point 2 as an intersection instead of a contact point. It is connected. That is, the center of the arc of R3 is not on the straight line connecting the point 2 and the center of the arc R2, but is located on the outer side in the tire width direction, and accordingly, the point 2 of the arc of R2 and the arc of R3 The tangents at are set to have different slopes.

  Further, the point 2 is designed to exist within a shoulder side range T of ½ W to W from the tread center CL with respect to the distance W from the tread center CL to the ground contact E. In addition, the radius of curvature of the arcs of R2 and R3 adjacent to each other via this point 2 is set to R2> R3.

  Thus, in this example, in the shoulder side range T, an area composed of two arcs R2 and R3 connected at the intersections that are not contact points is provided, and the tread outline is lifted outward by the arc R3. The arc R3 is positioned on the outer side in the tire radial direction with respect to the extension line of the inner arc R2, and the outer arc R3 has a smaller radius of curvature than the inner arc R2.

  As a result, the relationship of Y / X with respect to X has three regions, the first region, the second region, and the third region, as shown in FIG. 1B, and is linearly approximated within each region. The gradient satisfies the above β <α, β <γ, and α <γ. More specifically, since the Y / X values near the intersection (point 2) of the arc R2 and the arc R3 have different tendencies from the Y / X values in the first and second regions before and after that, X− A region peculiar to the Y / X distribution is generated, and the singular point A and the singular point B exist. That is, the second region is formed due to the intersection (point 2).

  In the example of FIG. 2, the discontinuous point connected by the intersection point is set to the point 2 that is the intersection point of the arc R2 and the arc R3. However, the present invention is not limited to this, and the point is the boundary between the arc R3 and the arc R4. It can also be set at the boundary of another arc, such as 3. In the example of FIG. 2, the tread surface is formed by four arcs, but the number of arcs is not limited to four, and may be three, two, or five or more.

  The pneumatic radial tire according to the present embodiment has the same basic structure as that of the conventional tire, i.e., a bead portion including a pair of left and right bead cores, and a sidewall portion extending radially outward from the bead portion. A carcass disposed radially inward of the tread portion, and then locked by a bead core at the bead portion through the side wall portions on both sides, and the carcass in the tread portion. The belt layer is arranged on the outside in the radial direction.

  For a pneumatic radial tire having a tire size of 225 / 45R17 and a contact width of 2W = 176 mm, the tire of Example 1 having the configuration shown in FIG. Here, R1 = 900 mm, R2 = 500 mm, R3 = 130 mm, R4 = 30 mm, and the position of the point 2 was 60 mm from the tread center CL. With respect to this tire, the XY / X distribution was determined as shown in FIG. 1 (b). The width G1 of the first region, the width G2 of the second region, the width G3 of the third region, and these The gradients α, β, and γ of the regions G1, G2, and G3 are as shown in Table 1 below.

  For comparison, tires of the control and the conventional example were produced. Both the control tire and the conventional tire have tread surfaces formed by connecting four arcs at the contact points. The conventional tire improves braking performance compared to the control tire. Is improved by a conventional method (a method of bringing the grounding shape closer to a round shape while maintaining the connection between the contacts). More specifically, in the control, the radius of curvature of each arc from the center side of the tread is r1 = 900 mm, r2 = 650 mm, r3 = 190 mm, r4 = 30 mm, and in the conventional example, the radius of curvature of each arc from the center side of the tread is r1. = 900 mm, r2 = 650 mm, r3 = 150 mm, r4 = 30 mm. When the XY / X distribution was determined for the tires of the control and the conventional example, the distribution had two regions, and the widths G1 and G2 and the gradients α and β of each region were as shown in Table 1 below. It was. An XY / X distribution of a conventional tire is shown in FIG.

  Each tire obtained was evaluated for braking performance and wear performance. The results are shown in Table 1. Each evaluation method is as follows.

-Braking performance: Rim used = 17 x 7.5 JJ, air pressure = 220 kPa, mounted on a 2500 cc passenger car, accelerated to 100 km / h in the run-up section, maintained test speed in the initial speed adjustment section, braking start point At the same time, the brake pedal was pressed quickly and strongly, and maintained until it stopped. Then, the stopping distance was measured, and the index was evaluated with the control tire as 100. The larger the index, the better the braking performance.

Wear performance: Used rim = 17 × 7.5JJ, air pressure = 220 kPa, mounted on a 2500 cc passenger car, and traveled 20,000 km on a test course. Then, the wear amount of the tread center portion and the shoulder portion was measured, and the wear ratio of the center portion / shoulder portion was calculated. The smaller the wear ratio, the better (that is, uniform wear). A larger index indicates better wear performance.

  As shown in Table 1, in the conventional improved method (conventional example), although the braking performance was improved, the wear performance was worse against the control. On the other hand, in the tire of Example 1, the braking performance could be improved without impairing the wear performance.

  Tire size of 185 / 65R15, contact width 2W = 130 mm About the pneumatic radial tire of Example 2, the tire of Example 2 which has each dimension shown in following Table 2 was produced. For comparison, control tires having the dimensions shown in Table 2 below and conventional tires were prepared.

About each obtained tire, braking performance and rolling resistance performance were evaluated. The results are shown in Table 2. In addition, the evaluation method of braking performance was the same as that in the above-described evaluation method, with rim used = 15 × 6JJ, air pressure = 210 kPa. The rolling resistance performance was evaluated according to SAE J1269.

  As shown in Table 2, in the conventional improved method (conventional example), although the braking performance was improved, the rolling resistance performance was worse against the control. In contrast, in the tire of Example 2, the braking performance could be improved without impairing the rolling resistance performance.

(A) is a half part sectional view of a tire width direction cross section showing a tread surface shape of a pneumatic radial tire, and (b) is a graph showing an XY / X distribution related to a tread surface shape of a tire according to the present embodiment. It is. 1 is a half sectional view of a tire width direction cross section showing a tread surface shape of a tire according to an example of the present embodiment. It is a graph which shows XY / X distribution regarding the tread surface shape of the conventional tire. (A) And (c) is a tire grounding shape figure at the time of a load equivalent to a real vehicle, (b) And (d) is a tire grounding shape figure at the time of high load.

Claims (2)

  On the tread surface in the tire width direction cross section, when the distance in the tire width direction from the tread center is X and the amount of depression in the tire radial direction from the tread center is Y, the relationship of Y / X to X is JATMA from the tread center. There are three regions, a first region, a second region, and a third region, up to the ground contact end at 80% of the design normal load, and the second region is a distance in the tire width direction from the tread center to the ground contact end. Is within a range of ½ W to W, where W is a linear first-order approximation of the relationship in each region, α is the gradient of the first region, β is the gradient of the second region, A pneumatic radial tire having a tread surface that satisfies β <α and β <γ, where γ is a gradient of the third region.   The pneumatic radial tire according to claim 1, wherein the tread surface further satisfies α <γ.

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