JPS6345321B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a radial tire for passenger cars, and more specifically, by specifying the tread groove depth, groove bottom gauge, tread radius, tire maximum radius, and belt radius, it is possible to avoid problems with low internal pressure driving on ordinary roads or rough roads. This invention relates to a radial tire for passenger cars that improves the high speed performance of steel radial tires without causing any damage. Radial tires, which have superior handling stability and wear resistance compared to conventional bias tires for passenger cars, are rapidly becoming popular. Furthermore, the spread of radial tires is accelerating due to the desire for low fuel consumption due to the recent energy crisis. On the other hand, with the development of expressway networks in recent years, tires have come to be required to simultaneously run on so-called ordinary roads (including rough roads and slow roads) and at high speeds on expressways. Radial tires can fully demonstrate their high-speed performance for high-speed driving on expressways. However, on ordinary roads, rough roads, slow roads, etc.
Damage to the belt layer of steel radial tires is often a problem when running at extremely low internal pressures. This is because car drivers also try to keep their tire pressures high when driving on highways, but when driving on general roads, tire pressure management is inadequate and they often drive with low internal pressure. This is also due to this. In general, even what are called radial tires for passenger cars are full radial, due to differences in carcass structure.
Furthermore, depending on the cord material used in the belt layer, there are textile radials, steel radials, and radial tires that use both of these materials at the same time. The present invention relates to improvements in the tread structure of steel radial tires among these radial tires for passenger cars. Here is the "Toretsudo Department"
means the material and shape of each part throughout the tread, including the tread surface. That is, the materials of the captread, undertread, belt layer, carcass layer and inner liner,
It means shape. Figure 1 is a cross-sectional view of a radial tire, where 1 is a tread rubber, 2 is a belt layer, 3 is a carcass layer,
4 indicates a groove. 2A and 2B are enlarged views of the belt layer, A is a plan view, B is a sectional view, 2a is a second belt,
2b is the first belt, 5 is the cord part of the belt layer, 6
indicates the rubber part. As shown in FIG. 1, unlike a normal bias tire, a radial tire has a belt layer 2 in its tread surface to provide a hoop effect in the tire circumferential direction. This belt layer 2 is the main factor in improving the performance characteristics of the radial tire. for example,
It is precisely the belt layer 2 that maintains better handling stability than bias tires. As shown in FIG. 2, in steel radial tires for passenger cars, this belt layer is generally composed of a two-layer bias laminate made of steel cords. Specifically, these two-layer steel laminates are normally arranged so that their cords intersect with each other at an angle of 15° to 30° with respect to the tire circumferential direction. The width, that is, the belt width, is about 95 to 105% of the tread development width. Normally, when a tire rotates while touching the ground, the cord tension in the belt layer exhibits a different distribution shape depending on the location in the cross section of the tire. FIG. 3 is a graph showing the tension distribution of the cord on the crown center, and FIG. 4 is a graph showing the tension distribution of the cord near the belt edge. In the figure, the horizontal axis is the position in the tire circumferential direction, and the vertical axis is the cord tension. In Figure 3, the curve (solid line) P
indicates normal air pressure, curve (dashed line) P' indicates extremely low air pressure, and C indicates the contact area. The form of cord tension distribution will be explained with reference to FIG. First, the cord on the crown center has a tension value approximately equal to the initial cord tension, that is, the tension exerted on the cord by the air pressure filled in the tire, in the non-ground contact area (point a in the figure). However, when entering the contact area C, the cord tension shows a value larger than the initial cord tension (point b in the figure). Thereafter, the cord tension gradually decreases until the center of contact with the ground (point C in the figure) and reaches a minimum value at the center of contact with the ground. Furthermore, in the latter half of the contact area, a phenomenon opposite to the above-mentioned form is exhibited. That is, the path from points c to e in the figure is followed. Therefore, on the crown center, the minimum cord tension is shown at the center of ground contact. This minimum value becomes smaller as the load applied to the tire increases. Furthermore, if the internal pressure is lowered, the entire distribution shape will slide downward on the vertical axis. Therefore, in the case of extremely low internal pressure and high load P', the cord tension may become negative (see the dotted line in Figure 3). Due to the tension having such distribution acting on the cord during one rotation of the tire and the repeated action of these forces, a large load is applied to the belt cord, which in turn reduces the durability of the belt cord. The cord tension distribution near the belt edge shown in Figure 4 shows an inversely symmetrical distribution with respect to the center of contact, but even in this case, the cord tension may become negative under extremely low internal pressure and high load conditions (not shown). sell. The tires actually mounted on a car are subject to loads such as braking, driving, and cornering forces, and due to the condition of the tread, the belt cord tension shows a more complicated distribution shape than the shapes shown in Figures 3 and 4. , these shapes are basically the dominant ones. Therefore, tires that have been used for a long time under conditions of extremely low internal pressure and high load may sometimes cause damage to this belt layer. The forms of damage to the belt layer include separation at the belt edge, delamination between belt layers, and damage to the belt cord itself. Various measures have been attempted so far to prevent damage to these belt layers. For example, as a measure for belt edge separation,
Publication No. 22202 describes that a rubber layer is interposed between the layers of the belt edge portion to reduce interlayer shearing force, which is the main cause of belt edge separation. As a measure against delamination between the belt laminations, there is a method of using a rubber material covering the cord to be made of a peel-resistant rubber material. Furthermore, measures have been taken to prevent damage to the belt cord itself, such as increasing the number of cords per belt width or increasing the strength of one cord. However, most of these countermeasures mainly involve accepting stress applied from the outside and attempting to solve the problem by strengthening the belt. In response to this, the inventors of the present invention aimed to improve the durability of the belt layer and its surroundings, that is, the entire tread section, and as a result of conducting research from the viewpoint of dispersing the stress applied to the belt cord, we found that the belt layer We discovered that it is necessary to optimally determine each factor of the structure of the tread part, which has a great influence.
This led to the present invention. Therefore, the purpose of the present invention is to create a radial tire for passenger cars that improves the high speed performance of steel radial tires without interfering with low internal pressure running by optimizing each factor that determines the structure of the tread portion. It is about providing. That is, the radial tire for passenger cars of the present invention is a radial tire in which grooves are carved in the tread portion having two belt layers, and the ratio d/t of the groove depth t to the groove bottom gauge d, and the tread radius R The product of _T and the ratio R _T /R of the tire maximum radius R, (d/t) x (R _T /R), is 0.35 or more, and the ratio of the tire radius R _T to the belt radius R _B is R _T /R. The gist of this is to keep R _B within the range of 1.13 to 1.20. The present invention will be explained in more detail below. First, let's explain about the TRETSU Radius R _T. When the tire makes contact with the ground, the tire shell, which has a double curvature, is deformed into a planar shape within the contact area of the tire. With this deformation, the radius of curvature in the circumferential direction of the tire and the radius of curvature in the cross-sectional direction of the tire each become infinite. In other words, it becomes flat against a flat road surface. At this time, considering the change in curvature due to bending deformation of the tire, if the radius of curvature before deformation is r ₀ and the radius of curvature after deformation is r ₁ , then the change in curvature K is K = 1/r ₀ -1/r ₁ = r ₁ - r ₀ /r ₀ r ₁ . If the curvature change K is large during ground contact deformation, a large amount of strain tends to be concentrated in the tread portion, especially in the belt layer under the grooves, leading to a decrease in the durability of the belt layer.
To reduce the curvature change K, if r ₀ = r ₁ then K =
0, it is necessary to make r ₀ as close to r ₁ as possible. Here, r ₁ is the radius of curvature of the road surface, that is, almost infinite, so bringing r ₀ closer to r ₁ means making the radius of curvature r ₀ of the tire closer to infinity. Here, the radius of curvature of a tire includes both the radius of curvature in the tire circumferential direction and the radius of curvature in the cross-sectional direction of the tire, but the radius of curvature in the tire circumferential direction is substantially determined by the tire dimensions. On the other hand, since it is possible to change the radius of curvature in the cross-sectional direction, it can be understood that in order to reduce the amount of change in curvature before and after tire deformation, it is better to increase the radius of curvature in the tire cross-sectional direction. Next, the physical properties of the tread rubber and the rubber thickness of the tire tread will be explained. Generally, in a passenger car tire, the depth t of the groove cut in the tread portion is approximately 8 mm, and the thickness from the groove bottom to the belt layer is called the groove bottom gauge d. If the groove bottom gauge d is thin, the stress concentration acting on the bottom of the groove within the tire contact area is likely to be directly transmitted to the belt layer, and larger compressive stress will act on the belt cord. There is a risk that the force will act and cause damage to the belt cord. Furthermore, if the groove bottom gauge d is thin, there is a risk that damage sustained at the groove bottom is likely to directly reach the belt layer. By increasing the thickness of the groove bottom gauge d, the groove bottom T
It is possible to alleviate stress concentration without directly transmitting it to the belt layer. The effects of the present invention will be explained below with reference to Examples. Examples and Comparative Examples Tires with different tire shape factors were manufactured,
Table 1 shows the results of these indoor drum durability tests. In Table 1, tires No. 5, 7, and 8 are examples of the present invention, and tires No. 1, 2, 3, 4, 6, and 9 are comparative examples.

[Table] The measurement method for the trellis radius R _T in the table was performed as follows. In other words, the outer shape of the tread of a tire filled with the JIS design standard air pressure is measured using plaster, and the tread development width is measured with respect to the radial tangent on the tire crown center (this straight line is parallel to the tire rotation axis). A perpendicular line is drawn to this tangent from both the left and right ends (P ₁ and P ₂ in Figure 1), and the average value of the distances δ ₁ and δ ₂ from each end to each intersection is set as δ=δ ₁ +δ ₂ /2. Also, a straight line perpendicular to the tangent line on the crown center (this is the center line of the tire cross section).
A perpendicular line is drawn from the left and right end points P ₁ and P ₂ to this straight line, and the average value of the lengths l ₁ and l ₂ of the perpendicular lines is l=l ₁ +l ₂ /2. At this time, the average tire radius
R _T is expressed as follows. R _T = l ² + δ ² /2δ Tret radius measured in this way
In R _T , No. 1 to 3 in Table 1 are the training radius.
R _T is 248mm, No.4~6 is 300mm, No.7, 8 is 360mm
mm, No.9 is 380mm. As for the indoor drum durability test conditions, for the example size 195/70HR14 of the tire of the present invention,
Internal pressure P = 1.2Kg/cm ² and camber angle fixed at -6°,
The slip angle is changed from -5° to 5° and the applied load is changed from 100 to 700 kg at the same time in a rectangular waveform. In other words, we conducted a durability evaluation test under conditions that reproduced the driving conditions of an actual vehicle using an indoor drum testing machine. Also,
The traveling speed is V=25.2 Km/hr. The results of the indoor drum durability test conducted under these conditions are also shown in FIG. Figure 5 shows the horizontal axis and the vertical axis, respectively, which are the main factors of the durability of the belt part, the radius radius R _T and the groove bottom gauge d.
The test results are shown below. In the figure, the ○ mark indicates that the belt cord was not damaged as a result of the test under the present test conditions, the 〓 mark indicates that the belt cord was slightly damaged, and the ● mark indicates that the belt cord was damaged. Further, each number corresponds to the tire number in Table 1. From FIG. 5, it can be seen that the groove bottom gauge and the tread radius have a large influence on durability. For example, tires No. 3 and 6 with a groove bottom gauge of 3 mm,
8, the larger the training radius, the less the degree of cord damage. Similarly, tires with constant radius, for example R _T = 248mm
In Nos. 1, 2, and 3, when the gauge under the groove becomes thicker, cord damage tends to disappear. Similarly, it can be seen that a similar tendency exists in the cases where the training radius R _T =300 and 360. These trends are completely consistent with the reasons given above. FIG. 6 is made dimensionless by dividing the vertical and horizontal axes of FIG. 5 by the groove depth t and the tire maximum rotation radius R, respectively. The curve in the figure (d/tR _T /R=
0.35), there is a tendency for steel cord damage to occur below the curve, and no damage to the steel cord above the curve. However, among the measures taken to improve the durability of the tread section during low internal pressure running,
The present inventors have discovered that making the groove gauge thicker than necessary reduces the inherent high speed performance of steel radial tires. This is presumed to be because if the groove gauge is made thicker than necessary, the heat dissipation effect in the tread portion, particularly in the vicinity of the belt layer, deteriorates. Furthermore, from the viewpoint of saving resources in response to the recent energy crisis, it is becoming difficult to simply increase the thickness of the groove bottom gauge due to demands for lighter tires, lower fuel consumption, etc. The inventors of the present invention further studied the shape of the belt layer and found a relationship between the belt radius R _B in the cross section of the tire and the tire radius R _T described above. By satisfying these relationships, it has become possible to provide a steel radial tire that can withstand low internal pressure running on public roads while maintaining the high speed performance of a steel radial tire. The method for measuring the belt radius R _B here is the same as the method for measuring the belt radius R _T. In other words,
The radius of the circular arc passing through the three points, the midpoint of the two belt layers on the crown center and the midpoint of both No. 2 belt edge parts, is defined as belt radius R _B. The ratio of this tretz radius to belt radius R _T /
High-speed durability tests were conducted on tires with different R _B values, and the results are shown in Table 1. The test conditions were tires of 195/70HR14 size, internal pressure P = 2.1Kg/cm ² , load 524Kg, preliminary running for 2 hours at speed V = 81Km/hr, and then every 30 minutes from V = 121Km/hr. Increase the speed by 8km/hr and drive until the tire breaks.
The distance traveled was determined. The results are shown in the rightmost column of Table 1. Furthermore, FIG. 7 plots the travel distance versus the radius ratio R _T /R _B. Previous test conditions ()
In this case, tire No. 9 had no cord damage (〇), but under this test condition (), the mileage was lower than tire No. 6.
tires. Furthermore, although the No. 5 tire and the No. 9 tire have the same tread gauge, the No. 5 tire has better high-speed durability. These results show that it is possible to improve high-speed durability by limiting the belt radius R _T and the belt radius R _B , and in order to increase the mileage to 1040 km or more, R _T /R _B must be 1.13 to 1.13. You can see that it needs to be in the range of 1.20. From the above, in order to obtain durability during low internal pressure running, it is necessary to
The product of R _T divided by the groove depth t and the tire maximum radius R, that is, the tread shape factor _d /tR
The ratio _of R _T and belt radius R _B is 1.13 to 1.20 _.
By doing so, it has become possible for the first time to provide a tire that can enjoy the high speed performance of a steel radial tire without interfering with low internal pressure driving on ordinary roads or rough roads.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a radial tire, Figure 2 A,
B is an enlarged view of the belt layer, A is a plan view, B is a cross-sectional view, Figures 3 and 4 are tension distribution diagrams of steel cords, Figure 5 is a graph showing the relationship between tread radius and groove bottom gauge, and Figure 6 The figure shows the radius ratio (R _T /R)
FIG. 7 is a graph showing the relationship between radius ratio (R _T /R _B ) and travel distance. 1... Treaded rubber, 2... Belt layer, 3...
carcass layer, 4... groove, 5... steel cord,
6...Rubber part, t...Groove depth, d...Groove bottom gauge, R _T ...Treat radius, R...Tire maximum radius, R _B ...Belt radius.

Claims (1)

[Claims] 1. In a radial tire in which a groove is carved in the tread portion having two belt layers, the depth t of the groove is
The product of the ratio d/t between tread radius R _T and the tire maximum radius R, (d/t) x (R _{T /} R), is 0.35 or more, and A radial tire for a passenger car, characterized in that the ratio R _T /R _B of the training radius R _T and the belt radius R _B is within the range of 1.13 to 1.20.