JPH0319803B2 - - 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 virtually deteriorating its vibration riding comfort characteristics among other tire performances. Regarding conventional so-called radial structure tires, which have generally been recognized as being practical, the results of analyzing the contribution of the factors that each constituent part of the tire has on its rolling resistance, as shown in Figure 1. It has been found that it can be handled as being distributed as approximately 34% in the tread area, 27% in the buttress area, 25% in the sidewall area, and 14% in the bead area. Here, the tread rubber has the largest contribution to the rolling resistance, so in order to reduce the internal friction of the tread rubber and thereby reduce the rolling resistance, the loss tangent (tan δ), loss elasticity, etc. It is best to deal with this by increasing the rubber distribution while lowering the impact modulus (G"). However, in this case, the undesirable However, this type of tire has the disadvantage of deteriorating its wet performance, which is one of its important characteristics. Figure 2 shows the effect of this point on rolling resistance and wet performance using the value of the rebound modulus of the tread rubber as an index. According to Figure 2, the above measures cannot be expected to dramatically improve rolling resistance unless additional measures are taken to prevent deterioration of wet performance.There are also measures that are particularly advantageous in maintaining wet performance. Therefore, in the end, the above measures are not very effective in reducing rolling resistance.The next best measure is to reduce internal friction in almost the same way as mentioned above regarding the characteristics of treaded rubber. Attempts have been made to apply this rubber compound to the sidewalls, but in reality, it not only only helps to improve rolling resistance by less than 3% at most, but also has poor damping properties against vibrations that occur in radial tires. This has the disadvantage of causing a deterioration of the tire's damping characteristics, which is accompanied by a disadvantage on the important ride comfort performance.Therefore, the vibration of the damping characteristics of the tire accounts for more than 3% of the rolling resistance without any deterioration of the vibration ride comfort characteristics. However, in addition to the above, it is also possible to reduce the weight of the tire and reduce rolling resistance by changing the structure from two layers to one layer per carcass, or by narrowing the width of the belt in particular. However, the degree of improvement was low, and the stiffness of the main parts of the tire, which is important for reinforcing the tire, decreased, resulting in a decrease in maneuverability and stability.
It is unavoidable that there are limits to its effectiveness. This invention departs from the conventional way of thinking and first focuses on the physical properties of the so-called coating rubber that covers the cord ply of the carcass of radial structure tires, which has not been considered at all in the past. As a result of research focusing on the more appropriate modulus at 25% elongation and dynamic elastic modulus, as a new perspective on rubber physical properties that is completely different from conventional methods such as modulus of elasticity or rebound modulus, This comes from the discovery that a significant reduction in rolling resistance can be advantageously achieved without deteriorating not only wet performance but also vibration ride comfort, handling stability performance, and durability. . Although it is expected that internal energy loss will be lowered by lowering the loss tangent of the coating rubber from the usual value of around 0.1, it will also have the disadvantage of significantly deteriorating the tire's vibration ride comfort due to deterioration of the damping characteristics. is inevitable. That is, this invention was developed as a result of fundamental investigation into the deformation state of the sidewall that occurs when a load is applied to a radial structure tire and the tire rolls. Here, sidewall deformation refers to bending deformation that occurs out of plane and shearing deformation that occurs in-plane. Particularly, shear deformation is small when directly under the load of a radial structure tire, but it affects the ground contact surface. In the vicinity where depressing and kicking occur, the deformation increases significantly to account for 75% of the total deformation, making a very large contribution overall, and is important in radial structure tires. Therefore, as a result of focusing on the strain caused by this shear deformation, that is, the shear strain, the inventors obtained the following important knowledge. In other words, the distribution of shear strain in the thickness direction in the sidewall section is maximum around the ply cords of the carcass, and the shear deformation of the sidewall is
Since the shear strain of the rubber disposed in the sidewall portion is almost determined by the tension of the carcass ply, it is said that the shear strain of the rubber placed in the sidewall portion is not dependent on its physical properties and is subjected to almost constant strain. Based on this new knowledge of constant strain, from the following equation showing the internal energy loss EL due to shear strain: EL=1/2Gγ ² ×Vol×tanδ...(1), loss tangent and loss elasticity can be calculated as in the conventional technology. Rather than changing the modulus or rebound modulus, the value of G in equation (1) is lowered by lowering the modulus at 25% elongation in the static case and lowering the dynamic modulus in the dynamic case. , it is possible to improve rolling resistance by reducing internal energy loss EL. In equation (1), γ is shear strain, Vol is volume, and tan δ is loss tangent. Taking into account that shear strain is greatest around the ply cords of the carcass, the above concept can be applied to the coating rubber covering the cord plies of the carcass to maximize effectiveness. The results summarized the effects of changing the modulus at 25% elongation and dynamic elastic modulus on the change in rolling resistance of the coating rubber of the cord ply of the carcass when the loss tangent value was fixed at 0.09 and 0.12. , 3rd a.
3b and 3c. According to Figures 3a and 3c, in accordance with conventional practice, the modulus of the coating rubber of the cord ply at 25% elongation is measured at room temperature, which is the general measurement condition.
When the rolling resistance at 9.3Kgf/cm ² is expressed as 100 in index display, the modulus at 25% elongation is 6.0Kgf/cm ² or less and 2.0Kgf/cm ² or more under the same measurement conditions.
In particular, it is clear that by adjusting the range of 5.0 Kgf/cm ² to 3.0 Kgf/cm ² , it is possible to achieve a remarkable reduction and improvement in the rolling resistance of the tire to an index of 80 or less. Also, according to Figures 3b and 3d, as is conventional practice, the dynamic elastic modulus of the coating rubber of the cord ply was determined by a mechanical spectrometer (manufactured by Rheometrics) at 50°C - 15Hz, dynamic shear. Measured under the condition of strain amplitude 1%, 3×
Compared to when the rolling resistance is 100 when it is ¹⁰⁷ dyn/ ^cm2 , the dynamic elastic modulus under the same measurement conditions
2×10 ⁷ dyn/cm ² or less, 8×10 ⁶ dyn/cm ² or more, preferably 1.5×10 ⁷ dyn/cm ² or less, 9×10 ⁶ dyn/cm ²
It has become clear that by doing so, the rolling resistance of the tire can be reduced to an index of 80 or less. Therefore, the present invention provides a belt consisting of a plurality of cord layers arranged around the carcass by wrapping at least one ply carcass of organic fiber cords in a radial arrangement around a bead core and folding the carcass outward in the radial direction of the tire. In a pneumatic tire, the cord ply of the carcass is covered with outer skins of tread rubber on the outer periphery of the belt, sidewall rubber on both sides of the carcass, and chief rubber arranged below the belt. The modulus of the coated rubber at 25% elongation is under greenhouse conditions.
2.0Kgf/cm ² to 6.0Kgf/cm ² , and the dynamic elastic modulus was determined using a mechanical spectrometer at 50℃, 15
8× under the condition of dynamic shear strain amplitude 1% at Hz
A pneumatic radial tire characterized by having physical properties of 10 ⁶ dyn/cm ² to 2×10 ⁷ dyn/cm ² ,
In addition, the sidewall rubber outer skin was measured at 5×10 ⁶ dyn/cm ² to 2
having a dynamic modulus of 10 ⁷ dyn/cm ² ;
The sidewall rubber outer skin is provided with a shoulder rubber consisting of a rubber stock having a dynamic elastic modulus higher than that of the rubber but lower than that of the treaded rubber outer skin as part of the sidewall rubber outer skin, and the treaded rubber outer skin is bonded through this shoulder rubber. In addition, the tread rubber outer skin is wedge-shaped at the side edge, and is sandwiched between the radially outer end of the sidewall rubber outer skin and the shoulder rubber, and furthermore, the belt is located at the equator of the tire. However, at least two layers of metal cord intersect each other in an inclined arrangement at a relatively small angle, and the carcass folds have a fold height within 25% of the tire height, measured from the bead base, and the sidewall It is more preferable that the rubber enters inside the chief rubber disposed below and is in contact with the folded end of the carcass. With this invention, the modulus at 25% elongation is 2.0Kgf/
cm ² and the dynamic modulus of elasticity is less than 8×10 ⁶ dyn/cm ² , the ply layer consisting of cords arranged in one direction becomes too soft, making it nearly impossible to mold the tire. 6.0Kgf/cm ² , 2× each
If it exceeds 10 ⁷ dyn/cm ² , the effect of reducing rolling resistance will be poor, but if it is within these ranges, a practically sufficient effect can be expected. As mentioned above, the main purpose of this invention is to select the coating rubber for the carcass cord from a range of physical properties in which the modulus at 25% elongation and dynamic elastic modulus are rather low. There is a concern that the sidewall rubber tends to move more easily, distortion is concentrated there and cracks occur, and that this may lead to separation if this is noticeable. This can be easily solved by giving the elastic modulus. In other words, the degree of concentration of strain due to the increase in the amount of movement at the folded end of the carcass is related to the dynamic elastic modulus of the adjacent sidewall rubber, and as shown in Figure 4, the dynamic elasticity of the sidewall rubber increases. When the modulus is high, the degree of concentration of strain at the end of the ply is high, and when the dynamic elastic modulus of the sidewall rubber is also low, the concentration of strain is alleviated. Actually, the modulus of the carcass coating rubber at 25% elongation was 4.8Kgf/ ^cm2 , and the dynamic modulus was 1.4×
The dynamic elastic modulus of the sidewall rubber was lowered to 10 ⁷ dyn/cm ² , and correspondingly ^the dynamic elastic modulus of ^the sidewall rubber was 2.3
Table 1 shows the results of examining the durability against separation at successively lower values of 10 ⁷ dyn/cm ² and 5×10 ⁶ dyn/cm ² . Here, separation durability is defined as high internal pressure (3.0
Kgf/cm ² ), a high load (200% load according to JIS regulations) is applied to the tire, and the distance traveled on the drum is compared. Table 1 shows the modulus at 25% elongation, dynamic modulus of elasticity, and dynamic modulus of side rubber of the coating rubber of the carcass cord ply, all compared with the conventional tire as a control using an index of 100. The larger the value, the better the durability.

[Table] According to this example, if the modulus at 25% elongation and dynamic elastic modulus of the coating rubber of the cord ply are lowered, but the suitability of the sidewall rubber is not considered, the durability will be 80 in terms of index. Although the dynamic elastic modulus of the sidewall rubber has decreased slightly up to now, it is clear that by simultaneously lowering the dynamic elastic modulus of the sidewall rubber, it is possible to not only sufficiently compensate for this disadvantage but also improve it. This is particularly preferable for carrying out the invention. Next, when considering the influence of the dynamic elastic modulus of this sidewall rubber on rolling resistance, as mentioned earlier, sidewall deformation depends on tension.
The sidewall rubber is subjected to almost constant strain regardless of its physical properties, and in such a constant strain state, the lower the modulus or dynamic elastic modulus of the side rubber, the lower the internal energy loss EL.
This, together with lowering the coating rubber's modulus at 25% elongation and dynamic elastic modulus, has a significant effect on reducing rolling resistance. In accordance with this invention, tires of 185/70SR14 size were made by varying the dynamic elastic modulus of the sidewall rubber, and their effects on rolling resistance were investigated. The results are summarized in Figure 5. According to this figure, when the rolling resistance when the dynamic elastic modulus of the sidewall rubber is 3 x 10 ⁷ dyn/cm ² or more is expressed as 100 in index form, the dynamic elastic modulus is 5.
The rolling of the tire can be improved by setting the tire to a range of × ^{10 6} dyn/cm ² or more and 2 × 10 ⁷ dyn/cm ² or less, more preferably 7 × 10 6 dyn/cm ² to 1.5 × 10 ⁷ dyn/cm ^{2 .} It is clear that a significant reduction and improvement in resistance up to an index of 90 can be achieved. What is advantageous in this invention is that the range of dynamic elastic modulus of the sidewall rubber that does not deteriorate durability covers the range of dynamic elastic modulus that improves rolling resistance. If the dynamic elastic modulus is less than 5×10 ⁶ dyn/cm ² , the sidewall rubber becomes excessively soft and difficult to manufacture, and cannot be put to practical use. As mentioned above, in this invention, it is preferable to select the sidewall rubber from a range in which the dynamic elastic modulus is particularly low, since the disparity increases markedly at the boundary between the sidewall rubber and the treaded rubber, which has much higher physical properties. That is, both the outer skins of the tread rubber and the sidewall rubber are joined to each other via a shoulder rubber having a rubber stock having a dynamic elastic modulus higher than that of the sidewall rubber but lower than that of the tread rubber. In this case, it is more desirable that the side end of the tread rubber be wedge-shaped and sandwiched between the radially outer end of the sidewall rubber and the shoulder rubber. This is effective under conditions where a large slip angle is applied during use of the tire. Under these conditions, the ground contact expands at the buttrest part of the tire, and at this time, if this part is formed of a sidewall with a low dynamic elastic modulus as described above, rapid local wear may occur there. There is the joy of progress, and it is desirable to interpose the above-mentioned shoulder rubber here. Advantageously, the above problems can be overcome by having the shoulder rubber have a dynamic modulus higher than that of the sidewall rubber, but lower than that of the tread rubber. However, when the above 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. Furthermore, according to the present invention, rolling resistance is improved by lowering the modulus and dynamic elastic modulus at 25% elongation of the coating rubber that covers the cord ply, and by lowering the dynamic elastic modulus of the sidewall rubber accordingly. This effect is more advantageously realized when the belt is composed of a highly rigid metal cord layer and when the carcass folding height is kept within 25% of the tire height to extend the flexing area of the sidewall as much as possible. Ru. It should be noted here that in tires used in normal practical use, if the folding height of the carcass is low, the folding end of the carcass will not be directly adjacent to the sidewall rubber, as shown in Figure 6. Therefore, in such a structure, it is not possible to achieve the effect of reducing the modulus at 25% elongation and dynamic elastic modulus of the coating rubber of the cord ply, thereby reducing durability. However, when the folded height of the carcass ply is within 25% of the tire height, the side rubber enters inside the chief rubber placed below it and directly contacts the folded end of the ply, creating the structure shown in FIG. 7. In Figures 6 and 7, 1 is the tread rubber, 2 is the belt, 3 is the carcass, 4 is the sidewall rubber, 5 is the shoulder rubber, 6 is the bead core, 7 is the chief rubber, B is the baseline, and H is the Tire height, T represents carcass folding height. To confirm the specific effects of this invention
The test results for 185/70SR14 size tires are listed below. First, the modulus of the coating rubber that covers the cord ply of the carcass is 9.3 kgf at 25% elongation.
cm ² and a dynamic elastic modulus of 3 x 10 ⁷ dyn/cm ² compared to a conventional tire, the rubber composition consists mainly of natural rubber, the amount of aroma oil mixed in is adjusted, and the amount of carbon black is kept to a small amount, resulting in a 25% modulus at elongation. 4.8Kg
f/cm ² and a dynamic elastic modulus of 1.4×10 ⁷ dyn/cm ² The results of testing the tire of Example 1 of this invention are shown in the second example.
Shown in the table. The coating rubber formulations for the conventional tire and Example 1 described above were as follows, and the loss tangent was 0.09 in both cases. Conventional tire Example 1 NR 80 Parts by weight 100 parts SBR # 1500 20 - HAF 5 45 Spindle oil 12 22 Stearic acid 2 2 Zn0 7 3 Anti-aging (RD-S) 0.8 0.8 〃 Accelerator Nobs 0.3 〃 0.3 〃 Accelerator DM 0.3 〃 0.15 〃 Iou 3.0 〃 3.0 〃 Here, the characteristics and dimensions of the tire components other than the carcass coating rubber were all set to the same conditions.

[Table] Next, in the same comparison with the conventional tire, the modulus at 25% elongation of the coating rubber that covers the cord ply of the carcass is 4.8 Kgf/cm ² and the dynamic modulus is 1.4×10 ⁷ dyn/cm ² In addition, the dynamic elastic modulus of the sidewall rubber is 1.1×, compared to 3×10 ⁷ dyn/cm ² for conventional tires.
Table 3 shows the results of a comparative test of rolling resistance with Example 2 of the present invention, which was lowered to 10 ⁷ dyn/cm ² .

[Table] Furthermore, in the same comparison with conventional tires, the modulus of the carcass coating rubber at 25% elongation is
4.8Kgf/cm ² , dynamic elastic modulus is 1.4×10 ⁷ dyn/cm ² , and the dynamic elastic modulus of sidewall rubber is
In addition to setting the tire height to 1.1×10 ⁷ dyn/cm ² , the ratio of the folding height T of the carcass to the tire height H was lowered from 0.53 in conventional tires to 0.18, and the side rubber was placed inside the rubber chief. Table 4 shows the rolling resistance comparison test results with Example 3.

[Table] Here, the rolling resistance test for tires is diameter 1707.
The clutch was disengaged after the drum of mm was rotated once, and the degree of deceleration during the forward rotation was compared. The internal filling pressure of the test tires was 1.7 Kgf/cm ² and the load was 445 Kg, all of which were made uniform. Next, using the tires of Example 2 as a representative, concrete road surface (skid No. SN representing road surface roughness =
35) and asphalt road surface (SN = 50), the tires of this invention were indistinguishable from conventional tires. Furthermore, vibration and ride quality tests were conducted on the above representative tires by comparing the magnitude of the force generated on the rotating shaft of the tire during rotation on a test drum with protrusions, and the following results were obtained.

[Table] In other words, the tire according to the present invention is not accompanied by virtually any deterioration in vibration riding comfort performance. In addition, when comparing the cornering power of similar representative tires and expressing the handling performance of the conventional tire as an index of 100, the tire of this invention had an index of 102.
Almost the same results were obtained. Finally, the high internal pressure (3.0Kg/
cm ² ) As a result of comparing the distance traveled on the drum under high load (200% load of JIS regulations), the result was 99 when the conventional tire was set as 100, and there was also a deterioration in durability. It was clear that there was no such thing. As described above, according to the present invention, the rolling resistance of the tire can be dramatically improved by selecting physical property values that are different from the conventional ones for the coating rubber that covers the cord ply of the carcass, which has not been considered at all in the past. Moreover, it is advantageous because not only wet performance but also required characteristics of tires such as vibration ride comfort performance and steering stability performance are not actually deteriorated.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the contribution rate of each part of the tire to rolling resistance, Figure 2 is a graph of the relationship between rolling resistance index and wet performance index using the rebound modulus of tread rubber as an index, and Figures 3a, b, c, and d The figure is a diagram showing the effects of the modulus and dynamic modulus of elasticity at 25% elongation of the coating rubber of the cord ply on reducing rolling resistance. Figure 4 shows the dynamic modulus of the sidewall rubber and the strain concentration at the ply end. FIG. 5 is a graph showing the influence on the rolling resistance index, and FIGS. 6 and 7 are cross-sectional views of tires showing examples. 1... Tread rubber, 2... Belt, 3... Carcass, 4... Side wall rubber, 5... Shoulder rubber, 6... Bead core, 7... Chief rubber, T... Turning height.

Claims (1)

[Claims] 1. A carcass consisting of at least one ply of radially arranged organic fiber cords is wound around a bead core and folded outward in the radial direction of the tire, and a plurality of cord layers are arranged surrounding the carcass. In a pneumatic tire, the pneumatic tire has a body reinforcement that works in cooperation with a belt, and has outer skins consisting of tread rubber around the outer periphery of the belt, sidewall rubber on both sides of the carcass, and Chufur rubber arranged below the cord ply of the carcass. The coating rubber that covers it has a modulus of 2.0Kg at room temperature when 25% elongated.
f/cm ² to 6.0 Kgf/cm ² , and the dynamic elastic modulus is 8×10 ⁶ dyn/ under the conditions of dynamic shear strain amplitude of 1% at 50°C and 15 Hz using a mechanical spectrometer.
A pneumatic radial tire characterized by having physical properties of cm ² to 2×10 ⁷ dyn/cm ² . 2. In the pneumatic radial tire described in claim 1, the sidewall rubber outer skin is measured by a mechanical spectrometer at 50°C and 15Hz.
5× under the condition of dynamic shear strain amplitude of 1% at
A tire with a dynamic elastic modulus of 10 ⁶ dyn/cm ² to 2×10 ⁷ dyn/cm ² . 3. In the pneumatic radial tire described in claim 2, the sidewall rubber skin has a shoulder rubber whose dynamic elastic modulus is higher than that of the rubber, but lower than that of the tread rubber skin. A tire that is provided as part of a rubber outer skin and is made by joining a treaded rubber outer skin via this shoulder rubber. 4. In the pneumatic radial tire described in claim 3, the tread rubber outer skin has a wedge shape at the side end, and is arranged to be sandwiched between the radially outer end of the sidewall rubber outer skin and the shoulder rubber. . 5. In the pneumatic radial tire described in any one of claims 1 to 4,
A tire wherein the belt is at least two layers of metal cord intersecting each other in an oblique arrangement at a relatively small angle relative to the equator of the tire. 6. In the pneumatic radial tire described in any one of claims 1 to 5,
A tire in which the carcass turn-up height is within 25% of the tire height as measured from the bead base, and the sidewall rubber enters inside the chief rubber placed below and contacts the turn-up end of the carcass. .