JPH02270607A - Pneumatic radial tire for automobile - Google Patents

Abstract

PURPOSE:To release shock applied from a road surface with a tread portion so as to especially improve riding comfortableness economically by reducing the thickness of a tread rubber at the ground end of a shoulder than that at the center of a crown portion and also specifying the ratio of the thickness. CONSTITUTION:A tire E is provided with a tread portion 1 having a crown portion 2 and a shoulder portion 4, and a belt layer 3 interposed between a carcass layer 7 and the lower portion of the tread portion 1. The width WL of the belt layer 3 is set to be larger than the width W at the grounded area W of the tread portion 1. In this case, a relation of b/a<=0.95 holds, wherein (a) is a thickness of a tread rubber of the crown portion 2 in the ground area W of the tread portion 1 and (b) is a thickness of a tread rubber in the ground edge 4a of the shoulder portion 4. The thickness of the tread rubber is liable to be smoothly reduced ranging from the crown portion 2 to the ground edge 4a of the shoulder 4.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a pneumatic radial tire for passenger cars.More specifically, by improving the tread portion where the impact force from the road surface is first transmitted, the impact force is transferred to the belt layer. , relates to a pneumatic radial tire for passenger cars that improves ride comfort by relaxing the air in the tread before being transmitted to the carcass layer.

[Prior art]

-Mu radial tires are superior to bias tires in basic tire characteristics such as handling stability and wear resistance. However, on the other hand, radial tires
This has the disadvantage that the ride comfort is inferior to that of bias tires due to the fact that a very rigid belt layer is placed on the tread portion of the carcass layer in which reinforcing cords are arranged in the radial direction.

In order to improve the poor riding comfort of such radial tires, improvements such as reducing the rigidity of the belt layer have been proposed. However, since all of these methods change the rigidity of the skeleton that makes the radial tire's original features come true, they end up impairing the radial tire's original strengths of handling stability and wear resistance.

[Problem to be solved by the invention]

In view of the above-mentioned conventional problems, an object of the present invention is to improve the driving stability and wear resistance of radial tires by focusing on the trend portion where the impact force of the road surface is first transmitted. An object of the present invention is to provide a pneumatic radial tire that improves comfort.

[Means for Solving the Problems] In the pneumatic radial tire of the present invention which achieves the above objects, the thickness of the tread rubber on the belt layer of the crown portion in the ground contact area of the tread portion is a, If the thickness of the Lund rubber on the belt layer at the shoulder contact end is b, the ratio of each rubber thickness a and b is b / a ≦ 0.95, and the thickness of the tread rubber is from the crown to the shoulder. It is characterized by a smooth decreasing change over the ground contact end.

The present invention has been achieved by focusing on the tread portion to which the impact force of the road surface is first transmitted, instead of the tire frame portion. In conventional radial tires, the thickness of the trend rubber is generally greater at the shoulder contact end than at the crown, but in the present invention,
The thickness of the tread rubber is set in a relationship opposite to the conventional one, and is varied within a predetermined range as described above. By varying the thickness of the tread rubber in this way, it is possible to reduce the impact force from the road surface in the tread before it is transmitted to the belt layer and carcass layer, improving ride comfort. It is.

In the present invention, it goes without saying that the thickness of the tread rubber may be changed within the known thickness range applied to conventional radial tires for passenger cars.

That is, as is well known, the thickness of the tread rubber of a radial tire for a passenger car is usually 8 to 181 mm, but it is sufficient to keep it within this range, and there is no need for a special rubber thickness. isn't it.

Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 shows an example of a pneumatic radial tire E for a passenger car according to the present invention.

1 is a tread part, 2 is a crown part of this tread part 1,
Further, 4 is a shoulder portion of this tread portion 1. 3 is a belt i, which is disposed below the trend part 1 so as to be sandwiched between it and the carcass layer 7.

In such a configuration, the width of the belt layer 3 is configured to be larger than the width WL of the ground contact area W of the tread portion 1. This configuration of the belt layer 3 further improves the steering stability and wear resistance inherent in the radial tire.

Further, if the thickness of the trend rubber at the center of the crown part 2 in the ground contact area W of the tread part l is a, and the thickness of the tread rubber at the ground contact end 4a of the shoulder part 4 is b, then these rubber thicknesses a and the ratio of b/a≦0.9
There is a relationship of 5.

Furthermore, the thickness of the tread rubber changes smoothly from the crown portion 2 to the ground contact end 4a of the shoulder portion 4.

By changing the tread rubber thickness so that it gradually decreases from the center of the crown part to the contact edge of the shoulder part, as is clear from the experimental examples described later, the impact force from the road surface is reduced to the belt layer 3. , it is relaxed in the tread portion 1 before being transmitted to the carcass layer 7, making it possible to improve riding comfort. In particular, when the width of the belt layer 3 is larger than IIWL of the ground contact area of the tread portion 1, as in the case of the illustrated radial tire, the ride comfort generally deteriorates significantly. This deterioration can be alleviated by changing the thickness of the tread rubber.

In the radial tire of the present invention, the thickness of the tread rubber from the center of the crown part 2 to the ground contact edge of the shoulder part 4 changes smoothly as described above. It is necessary to maintain the structure of the belt layer 3, and it goes without saying that the belt layer 3 should not change to the extent that it is exposed to the tire surface (including the groove bottom).

In a tire such as the above-mentioned radial tire of the present invention, in which the tread rubber thickness a of the Claran portion 2 and the tread rubber thickness b of the shoulder portion ground contact edge 4a have an irregular relationship such that a > b, the tire It is difficult to live out the full lifespan. Here, the tire life is FMVSS Nα10
9, this is the point in time when the shallow groove amount (groove height from the groove bottom) of the groove due to wear reaches 1.6 mm. The complete lifespan of a tire means that the grooves in the crown part and the grooves in the end of the shoulder part wear out substantially evenly.
This is the case when it reaches mm.

In a radial tire with irregular tread rubber thickness as described above, suppose that the groove depth d of the groove 6 located at the shoulder ground contact edge 4a is smaller than the groove depth C of the groove 5 of the crown section 2. When the groove 6 of the shoulder grounding end 4a
Since the shallow groove amount reaches 1.61 earlier than the groove 5 of the crown portion 2, the complete life cannot be completed.

Therefore, in order to extend the life of the tire having the above-mentioned irregular tread rubber thickness, it is necessary to change the groove depth d(1) of the groove 6 of the shoulder portion grounding edge 4a to the groove depth d(1) of the groove 6 near the center of the crown portion 2. For the groove depth e (mm), d
It is preferable to have a relationship of ≧C1.6 mm.

In addition, since stress concentrates at the groove bottom and group cranking is likely to occur, the groove 5 of the crown part 2 and the shoulder part 4
It is desirable that the thickness of each of the adjacent grooves 6 from the groove bottom to the belt N3 is 1.81 mm or more. That is, the groove depth c (mm) near the center of the crown portion 2,
The groove depth d (mn+) near the shoulder portion 4 is a-C for the tread rubber thicknesses a and b (mm), respectively.
It is desirable that the relationship is 20,81,b-d≧1,8n+n+.

〔Example〕

Below, specific experimental examples of the present invention tire and a comparative tire will be explained.

The tire size was set to 165 SR13, and the ratio W, /L between the width of the ground contact area and the width of the belt layer was set to 1.02, and the thickness of the shoulder end was set to 1.02. Ratio b of tread rubber thickness b /
A large number of radial tires with various a were manufactured. Among these, tires with b/a of 0.95 or less are tires of the present invention, and tires with b/a exceeding 0.95 are comparative tires.

The ride comfort of these tires was evaluated by measuring the impact force using an impact force measurement tester under the following experimental conditions.

Internal pressure: 1.7 Kgf/cm" Load: 300 Kg Speed: 60 Km/hr Protrusion: Radius 101 By plotting the above measurement results, the graphs in FIGS. 2 and 3 were obtained.

In FIG. 2, the horizontal axis represents the ratio b/a of the tread rubber thickness of each tire, and the vertical axis represents the impact force. The shaded area in the figure shows the range of variation in the measured values multiple times. FIG. 3 shows the slope (differential coefficient) of the curve corresponding to the median value of the dispersion shown in FIG. This chart was created to make it easier to clearly confirm the impact buffering effect caused by changes in the value of the tread rubber thickness ratio b/'a.

As is clear from FIGS. 2 and 3, b/a
Comparative tires with a value of more than 0.95 had a much larger change in impact force (slope of the curve) than the tires of the present invention, which had a value of 0.95 or less, and the ride comfort deteriorated rapidly. Recognize.

That is, conventional radial tires generally have b/a
b value is 1.0 or more, but corresponds to this conventional tire.
It can be seen that the tire of the present invention has improved ride comfort compared to the comparative tire with /a=1.0 or more.

〔Effect of the invention〕

As described above, the present invention focuses on the tread portion where the impact force from the road surface is first transmitted, and the thickness of the tread rubber is made smaller at the shoulder contact end than at the center of the crown portion, and within a predetermined range. By specifying this, it becomes possible to reduce the impact force from the road surface in the tread before it is transmitted to the belt layer and carcass layer, thereby impairing the inherent advantages of radial tires such as handling stability and wear resistance. Riding comfort can be improved without any problems.

Furthermore, since the present invention improves ride comfort simply by changing the thickness of the tread rubber, it is extremely economical compared to conventional shock mitigation means that modify the rigidity of the belt layer.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view illustrating the radial tire of the present invention, and FIG. 2 is a graph (graph) showing the relationship between the tread rubber thickness ratio a/b and impact force of each tire manufactured in the example.
FIG. 3 is a diagram (graph) showing the slope of the curve corresponding to the median variation of the curve in FIG. DESCRIPTION OF SYMBOLS 1... Tread part, 2... Crown part, 3... Belt layer, 4... Part of sigilda. Figure 1

Claims (1)

[Claims] If the thickness of the tread rubber on the belt layer at the center of the crown part in the ground contact area of the tread part is a, and the thickness of the tread rubber on the belt layer at the ground contact end of the shoulder part is b, A pneumatic radial tire for a passenger car, in which the ratio of the rubber thicknesses a and b is b/a≦0.95, and the thickness of the tread rubber is smoothly decreased from the crown portion to the shoulder portion contacting edge.