JPS6214403B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pneumatic radial tire, and particularly aims to advantageously improve its rolling resistance without deteriorating other tire performances. According to the results of analyzing the contribution of the factors that each component of the tire has to the rolling resistance of conventional so-called radial structure tires, which have generally been recognized as being practical, the results are as shown in Figure 1. It was found that 34% of the tread area, 27% of the buttrest area, 25% of the sidewall area, and 14% of the bead area can be used as a tread area. Here, the treaded rubber has the largest contribution to the rolling resistance, and therefore, in order to reduce the internal friction of the treaded rubber and reduce the rolling resistance, the loss tangent (tan δ) and loss elasticity of the rubber are While lowering the impact modulus (G″), the impact resilience modulus (Resilience)
It is common to deal with this problem by using a rubber compound that increases the temperature. However, in this case, the disadvantage is that the wet performance, which is one of the important characteristics of this type of tire, deteriorates undesirably, depending on the degree to which the rolling resistance is improved. In this respect, FIG. 2 shows the effect on rolling resistance and wet performance using the value of the rebound modulus of the tread rubber as an index. Therefore, the above-mentioned measures cannot be expected to dramatically improve rolling resistance unless separate measures are taken to prevent deterioration of wet performance, and no particularly effective means for maintaining wet performance have been found, so in the end, they are not very effective. I can't give you anything. As a next-best measure, attempts have been made to apply a rubber compound that reduces internal friction to the sidewalls in a manner similar to that described above regarding the characteristics of treaded rubber, but in reality it only accounts for around 3% or less of the rolling resistance. Not only is this method only useful for improving the tire to a lesser extent, but it also has the drawback of deteriorating the damping characteristics of vibrations generated in the tire, which is accompanied by a disadvantage in terms of the important ride comfort performance of the tire. In addition, methods have been adopted to reduce tire weight and rolling resistance by changing the carcass structure from two layers to one, or by narrowing the width of the belt. It is unavoidable that there is a limit to its effectiveness, as it leads to a decrease in steering stability due to a decrease in the rigidity of the important main parts of the tire. Therefore, since it is inevitable to solve the problem of wet performance in radial tires, this invention focuses not on tread rubber, but especially on side rubber, in terms of vibration riding comfort performance such as loss tangent, loss modulus, and rebound modulus as mentioned above. As a new perspective on rubber physical properties, which is completely different from conventional methods that involve deterioration of
This comes from the discovery that it can be advantageously achieved without deteriorating not only wet performance but also vibration ride comfort performance, steering stability performance, etc. In other words, this invention was arrived at as a result of fundamental investigation into the deformation state of the sidewall that occurs when a load is applied to a radial tire. It has been newly discovered that deformation depends on tension, and that sidewall rubber is subject to almost constant strain, almost unaffected by its physical properties. In this constant strain state, the internal energy loss EL in the sidewall rubber is expressed by the following equation. EL=Σ1/2G'·ε ² ·v·tan δ Here, G' represents the dynamic elastic modulus, ε is the strain, v is the volume element of the sidewall rubber, and tan δ is the loss tangent. The dynamic elastic modulus G' is defined as a value measured by a mechanical spectrometer (manufactured by Rheometrics) under conditions of 50° C., 15 Hz, and dynamic shear strain amplitude of 1%. In accordance with the above equation, this invention reduces internal energy loss by lowering the dynamic elastic modulus G', rather than relying on tan δ, that is, the internal friction characteristics of the sidewall rubber, as in the prior art. This is based on new knowledge that it is significantly useful in reducing rolling resistance. In this invention, at least one ply carcass made of organic fiber cords arranged in a substantially radial plane of the tire is wound around a beat core and folded outward in the radial direction of the tire, and the carcass is wrapped around the carcass. This is a pneumatic tire with a body reinforcement that works in conjunction with a belt made of multiple cord layers arranged in a treaded rubber belt and sidewall rubber on both sides of the carcass. The present invention is a pneumatic radial tire characterized by having a dynamic elastic modulus of 5×10 ⁶ dyn/cm ² or more and 2×10 ⁷ dyn/cm ² or less. As mentioned above, the purpose of this invention is to select the sidewall rubber from a physical property range in which the dynamic elastic modulus G' is particularly low. Since the disparity increases significantly, it is necessary to place the buffer rubber in the buttress part, that is, to make both the outer skins of the treaded rubber and the sidewall rubber have a rubber stock with a dynamic elastic modulus higher than that of the sidewall rubber but lower than that of the treaded rubber. In practice, it is preferable to join the shoulder rubber to each other through the outer skin of the shoulder rubber, and in this case, assuming that the side end of the tread rubber is wedge-shaped, the radially outer end of the sidewall rubber and the shoulder rubber are sandwiched between the sidewall rubber and the shoulder rubber. Therefore, it is more desirable to have it located there. In all cases, it is customary to use as belts at least two layers of metal cord intersecting each other in an inclined arrangement at a relatively small angle to the equator of the tire, and to fold the carcass back from the bead base. In practice, it is recommended that the folding height be within 25% of the tire height. In accordance with this invention, radial tires of size 185/70SR14 were produced with various dynamic modulus G' of the sidewall rubber, and their effects on rolling resistance were investigated. 3
Shown in the figure. According to this figure, the dynamic elastic modulus G′ is 3×
When the rolling resistance at 10 ⁷ dyn/cm ² or more is expressed as 100 in index form, the value of G' should be 5 x 10 ⁶ dyn/cm ² or more and 2 x 10 ⁷ dyn/cm ² or less, especially 7. ×10 ⁶ ~1.5×
It is clear that by setting the tire to a range of 10 ⁷ dyn/cm ² , the rolling resistance of the tire can be significantly reduced and improved to reach an index of 110. If G' is less than 5×10 ⁶ dyn/cm ² , the sidewall will become soft and difficult to manufacture, making it impossible to put it into practical use. On the other hand, G′ is 2×10 ⁷ dyn/
It is clear from FIG. 3 that as soon as cm ² is exceeded, no improvement effect on the rolling resistance index can be brought about. Next, during use of the tire, under conditions where a large slip angle is applied, a situation occurs in which the contact area expands at the buttrest part, and at this time, the dynamic modulus of elasticity is low as described above.
If this part is formed with sidewall rubber having G', local wear will develop rapidly there, which is why it is necessary to interpose the outer skin of the shoulder rubber. . Advantageously, the above-mentioned problems can be overcome by the shoulder rubber having a dynamic modulus of elasticity higher than that of the sidewall rubber, G', but lower than that of the tread rubber. However, when the above-mentioned physical property values of the tread rubber are exceeded, the stiffness of the buttress portion becomes too high, and deformation in the sidewall is easily transmitted to the tread portion, which actually impedes improvement in rolling resistance. Further, according to the present invention, the effect of reducing rolling resistance by lowering the dynamic elastic modulus G' of the sidewall rubber is that the belt is composed of a highly rigid metal cord layer, and the folding of the carcass is of
This is more advantageously realized when the bending height of the sidewall is kept within 25% and the bending area of the sidewall is expanded as much as possible. In order to confirm the more specific effects of this invention, we tested the test tires whose general cross-section is shown in Fig. 4 for each size shown in Table 1, and determined that the dynamic elastic modulus of the sidewall rubber was 3 x 10 ⁷ dyn/ cm ² as a comparative example
A comparative test was conducted with an example of the present invention, which was set at 1.1×10 ⁷ dyn/cm ² . Here, the volume and tan δ of the sidewall rubber of each tire were already set to the same conditions.

[Table] In Figure 4, 1 is the tread rubber, 2 is the belt, 3 is the carcass, 4 is the sidewall rubber,
5 is shoulder rubber, 6 is bead core, B
is the baseline, H is the tire height, and T is the carcass folding height. To test the rolling resistance of tires, each test tire was pressed against a drum with a diameter of 1707 mm under a load of 445 kgf.
After rotating once until the speed exceeds 100Km/h, immediately release the clutch and continue to drive at 100Km/h during the slow rotation.
The degree of deceleration at 50 km/h was also expressed as an index using a reciprocal number, with the performance of the conventional example (control) set as 100, for comparison. In other words, the rolling resistance index is determined by the dynamic elastic modulus of the sidewall rubber of each sample tire being 3
When the rolling resistance (Kg) of the conventional example (Table 2), which is 10 ⁷ dyn/cm ² , is set as 100, the rolling resistance index of the example is calculated as the rolling resistance (Kg) of the conventional example/rolling resistance of the example. resistance (Kg) x 10
Displayed as 0. The internal filling pressure of each test tire was kept uniform at 1.7 kg ^f /cm ² . The test results are shown in Table 2.

[Table] * The larger the rolling resistance index, the greater the rolling resistance reduction effect.
As compared above, the present invention achieves a reduction in rolling resistance of approximately several percent, sometimes reaching 10%, under typical practical vehicle speeds. Next, using each tire of test number 1 as a representative, we compared the wet performance on a concrete road surface (skid number SN = 35, which indicates road surface roughness) and an asphalt road surface (skin number SN = 50). was indistinguishable from the comparison tires. The wet performance index is a comparison of the distance it takes to apply the brakes and stop when driving at 60 km/h, and the repulsion elasticity of the tread rubber is 40%, and the tire size.
185/70 The stopping distance (27.5 m) of a tire with SR14 and T/H of 0.53 is taken as an index of 100, and the wet index of a tire with a different tread rubber impact resilience is 27.5/of a tire with an other tread rubber impact resilience. It is expressed as stopping distance from 60 km/h x 100. Furthermore, each of the representative tires mentioned above was tested for vibration ride quality by comparing the magnitude of the force generated on the tire's rotating shaft during rotation on a test drum with protrusions, and the following results were obtained.

[Table] That is, the tire according to the present invention is not accompanied by virtually any deterioration in vibration ride comfort performance. In addition, similar representative tires were tested to compare their cornering power, and when the handling performance of the comparative tires was expressed as an index of 100, the tire of the present invention had an index of 101, and almost the same performance was obtained. The steering performance index of the present invention is: Cornering power of the present invention/74.2 (Kg/deg) When the cornering power (74.2 Kg/deg) of the comparison tire is taken as 100, the steering performance index of the present invention is: Cornering power of the present invention/74.2 (Kg/deg)
It is expressed as ×100. As described above, according to the present invention, by selecting physical property values for the sidewall rubber that are different from the conventional ones, the rolling resistance of the tire can be dramatically improved.
However, it is possible to advantageously reduce and improve wet performance, vibration riding comfort performance, and steering stability without actually causing any deterioration.

[Brief explanation of the drawing]

Figure 1 is a tire cross-sectional view showing the contribution of factors to rolling resistance of each part of a general radial tire.
Figure 2 is a graph showing the effect of the impact modulus of tread rubber on rolling resistance and wet performance. Figure 3 is a graph showing the influence of the impact modulus of tread rubber on rolling resistance under various dynamic moduli of sidewall rubber. FIG. 4 is a general cross-sectional view of a radial tire to which the present invention is advantageously applied. 1...Tread rubber, 2...Belt, 3...Carcass, 4...Side wall rubber, 5...Shoulder rubber, 6...Bead core, B...Bead base, H...Tire height, T...Turn height difference.

Claims (1)

[Claims] 1. At least one ply carcass made of organic fiber cords arranged substantially within the radial plane of the tire is wound around a bead core and folded outward in the radial direction of the tire, and the carcass is A pneumatic tire having a body reinforcement that works in cooperation with a belt consisting of a plurality of cord layers arranged around the circumference, and a pneumatic tire having outer skins of tread rubber around the outer circumference of the belt and sidewall rubber on both sides of the carcass, The sidewall rubber has a dynamic elastic modulus of 5×
A pneumatic radial tire characterized by having physical properties of 10 ⁶ dyn/cm ² or more and 2×10 ⁷ dyn/cm ² or less. 2. The outer skins of the tread rubber and the sidewall rubber are joined to each other through the outer skin of the shoulder rubber, which has a rubber stock having a dynamic elastic modulus higher than that of the sidewall rubber but lower than that of the tread rubber. tire. 3. The tire according to claim 2, wherein the side end of the tread rubber is wedge-shaped and is located between the radially outer end of the sidewall rubber and the shoulder rubber. 4. A tire according to claim 1, 2 or 3, wherein the belt is at least two layers of metal cords crossing each other in an inclined arrangement at a relatively small angle to the equator of the tire. 5. The tire according to claim 1, 2, 3 or 4, wherein the carcass folds have a fold height within 25% of the tire height as measured from the bead base.