JPS6120442B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pneumatic tire, and more particularly to a belt reinforcing layer of a pneumatic tire such as a radial tire or a semi-radial tire having a plurality of belt reinforcing layers including a belt reinforcing layer with both ends bent inward in a cap tread portion. A rubber layer having characteristics advantageous for lowering the rolling resistance of the tire is arranged on both shoulders of the tread at a portion that approximately corresponds to the bent portion of the tire, and also approximately corresponds to the portion sandwiched between the bent ends. By arranging a rubber layer having good wet road running characteristics in the center of the tread, the tire can be provided with extremely good low rolling resistance properties and excellent wet road running properties at the same time. It concerns pneumatic tires. There are many performance requirements for automobile tires, but recently the most strongly demanded are fuel efficiency and safety. Among these, conventional methods for reducing the rolling resistance of tires that greatly contribute to the above-mentioned fuel efficiency are (1) reducing tire weight, (2) improving tire shape, (3) improving tire internal structure, (4) Individual proposals have been made, such as the use of compounds with low energy loss, and each has achieved some success. On the other hand, as the performance of vehicles increases, improving the dynamic characteristics on wet roads, which affects safety, is an essential characteristic of tires. However, generally speaking, reducing the aforementioned rolling resistance and improving dynamic characteristics on wet road surfaces are contradictory matters, and it is currently extremely difficult to impart these two characteristics to a tire at the same time. It is. For example, in order to reduce the rolling resistance,
Means of (4) above, in other words, if rubber with low energy loss is used as the constituent material of the tire, especially the tread rubber layer, in other words, a rubber with a small loss tangent (tan δ) that reduces the extent to which mechanical energy is lost due to heat generation, Although the effect of reducing rolling resistance can be obtained, if a rubber with a significantly small loss tangent is used for the entire tread rubber layer, the wet road surface motion characteristics will deteriorate, and in practice, a rubber with a sufficiently small loss tangent cannot be used. On the other hand, as the performance of vehicles increases, tire structures are becoming flatter to improve tire road holding, and the edges of the belt reinforcement layer are bent to improve high-speed durability. Measures are being taken to increase the stiffness of the shoulders. However, it has been found that these measures generally result in an increase in the ground contact pressure on both shoulders of the tread, as well as an increase in rolling resistance. That is, a pneumatic tire having a plurality of belt reinforcing layers including a belt reinforcing layer formed by bending the end of the belt reinforcing layer has a lower tread surface in the cross-sectional direction of the tire than a pneumatic tire having only an unbent belt reinforcing layer. The ground pressure distribution is markedly different. As shown in Figure 1, the ground pressure on the tread surface is high at both shoulders of the tread, which roughly corresponds to the bending part, and conversely, the ground pressure on the tread surface is high at the tread center, which roughly corresponds to the part sandwiched between the two ends of the belt. The ground pressure on the tread surface becomes lower, resulting in an increase in rolling resistance. Therefore, the present invention solves the above-mentioned problems at once, and in order to maintain good high-speed durability, a pneumatic tire having a belt reinforcing layer bent as described above has extremely good low rolling resistance characteristics. It is an object of the present invention to provide a pneumatic tire that can simultaneously provide excellent wet road motion characteristics. The feature is that the cap lead portion is sandwiched between the rubber layer A on both shoulders of the cap lead portion, which corresponds approximately to the bent portion of the bent belt reinforcing layer, and the bent end portions of the bent belt reinforcing layer. Divide the rubber layer B into the central part of the cap ret, which roughly corresponds to the
The rubber layer A has a relatively large dynamic elastic modulus _E'A and a relatively small dynamic loss _E''A , and has good low rolling resistance characteristics. This is because a rubber layer with a relatively small dynamic elastic modulus E' _B and a relatively large dynamic loss E'' _B and good wet road motion characteristics is arranged. The background and theory that led to the present invention will be explained below. The energy loss H when the tire rotates once is expressed as H∝E''/(E') ² + (E'') ² σ ² (1). Here, E′...Dynamic modulus of elasticity E″...Dynamic loss σ...Stress regulated by the reaction force of the tread It is recognized that even if a rubber having `` is disposed on the cap tread portion, that is, on the tread surface of the tire, a difference in energy loss H occurs due to a difference in stress σ. Therefore, f (E′, E″) in equation (1) = E″/(E′) ² + (E″) ² …
…Focusing on (2), fixing E′ and differentiating with respect to E″, we get ∂f(E′, E″)/∂E″ = (E′) ² + (E″) ² −E″・2E″/{ (E
') ² + (E'') ² } ² = (E') ² - (E'') ² / {(E') ² + (E''
) ² } ² , that is, E′=±E″, and equation (1) has an extreme value, but E′≦
In practice, it is almost impossible for E″, that is, tanδ≧1, so equation (2) becomes a simple increasing function. Also, the stress σ in equation (1) has a distribution according to the ground pressure on the tire tread surface. Needless to say, measures such as flattening the tire or bending the ends of the belt reinforcing layer increase the ground contact pressure on both shoulders of the tread, which increases the stress on both shoulders of the tread and reduces rolling. This will lead to an increase in dynamic resistance.At this point, even if rubber with a low loss tangent (tan δ) is placed over the entire tread surface as in the past, it may not be sufficiently effective depending on the structure. Depending on the structure, energy can only be effectively reduced by reducing equation (2) f(E′, E″) in areas where the stress (σ) is large. The present inventors have come to the conclusion that the loss H can be reduced. On the other hand, energy loss can be reduced by extremely reducing equation (2) f(E', E''), that is, by imparting extremely large E' and extremely small E'' to the rubber. Although it is possible to reduce the rolling resistance, it has not been possible to do so by disposing the rubber over the entire tread surface because this would reduce the wet road motion characteristics. Based on the above circumstances, the present inventors have developed dynamic elasticity at both shoulders of the tread where the ground pressure distribution of the tread is higher than the center of the tread, which approximately corresponds to the bent part of the belt reinforcing layer placed in order to maintain good high-speed durability performance. In addition to arranging rubber having good low rolling resistance characteristics with a relatively large coefficient E' and a relatively small dynamic loss E'', the bending of the bent belt reinforcing layer has a ground pressure distribution lower than that of both shoulders of the tread. The center of the tread, which roughly corresponds to the part sandwiched between the two ends, has a dynamic elastic modulus.
By arranging rubber with good wet road motion characteristics with a relatively small E' and a relatively large dynamic loss E'', it is possible to achieve good low rolling resistance characteristics and excellent wet road motion characteristics, which are contrary to the above-mentioned tradeoffs. We have now invented a pneumatic tire that can be added to a tire at the same time.The present invention will be explained below using examples with reference to the drawings.Figure 2 (first embodiment) and Figure 3 (second embodiment) ) As shown in FIG. , rubber layers A on both shoulder portions of the cap lead portion T approximately corresponding to the bent portions 6a of the bent belt reinforcing layer 6;
The belt reinforcing layer 6 is divided into a rubber layer B at the center of the cap lead T, which corresponds approximately to the portion sandwiched between the bent ends 6b of the belt reinforcing layer 6, and the rubber layer A has a dynamic elastic modulus _E'A. is relatively large and dynamic loss E″ _A is relatively small.
, the dynamic elastic modulus E′ _B is relatively small and the dynamic loss
It is constructed by arranging a rubber layer 7 having good wet road motion characteristics with a relatively large E″ _B . In the first embodiment shown in FIG. 2, the belt reinforcing layer G has both ends bent inward. The steel cable belt reinforcement layer 4 is placed on the bottom surface of the belt reinforcement layer 6.
It is configured by arranging. In this embodiment, the belt reinforcing layer 6 is made of a high elastic modulus organic synthetic fiber cord having a substantially negligible thermal shrinkage, a tensile strength of 10 g/d or more, and an elastic modulus of 1500 Kg/mm ² or more. For example, the ends of a cord, such as aramid, are folded inward without wrapping around other reinforcing layers. The rubber layer 7, which has good wet road motion characteristics, can be measured with a dynamic viscoelasticity measuring device (viscoelasticity spectrometer).
Dynamic elastic modulus E' measured at 20Hz, temperature 50℃, initial strain 20%, dynamic stress 2.4Kg/ ^cm2 is 25.3Kg/ ^cm2, and dynamic loss.
E″ is 11.6Kg/cm ² , and the rubber layer 8 having good low rolling resistance has a dynamic elastic modulus E′ of 40.1.
Kg/cm ² , the dynamic loss E″ is 6.4 Kg/cm ² .As shown in the figure, both bent ends 6 of the belt reinforcing layer 6
The rubber layer 7 having good wet road motion characteristics is disposed in a portion B that approximately corresponds to the portion sandwiched between the belt reinforcing layer 6, and the rubber layer 7 having the good wet road movement characteristics is placed in both shoulder portions A of the tread surface that approximately correspond to the bent portions 6a of the belt reinforcing layer 6. A rubber layer 8 having low rolling resistance characteristics is disposed. It goes without saying that the above-mentioned rubber layers 7 and 8 may be bonded together in advance or may be bonded together on a molding machine. Note that 3 in the figure is the carcass layer. Next, a second embodiment shown in FIG. 3 will be described. In this embodiment, the belt reinforcing layer G, both the belt reinforcing layer 6 whose both ends are bent inward, and the other belt reinforcing layer 4 are made of a steel cable belt. As shown in the figure, the belt reinforcing layer 4 is formed so as to be wrapped around the bent portion 6a of the belt reinforcing layer 6. The rubber layer 7, which has good wet road motion characteristics, is measured at a frequency of 20 using a dynamic viscoelasticity measuring device (viscoelasticity spectrometer).
Hz, temperature 50℃, initial fundamental strain 20% dynamic stress 24Kg/ ^cm2 , the dynamic elastic modulus E' is 25.3Kg/ ^cm2 , and the dynamic loss E'' is
11.6 Kg/cm ² , and the rubber layer 8 having good low rolling resistance properties has a dynamic elastic modulus E′ of 40.1 Kg/cm ²
Then, the dynamic loss E'' is 6.4 Kg/cm ^2.As shown in the figure, the portion B approximately corresponds to the portion sandwiched between the bent ends 6b of the belt reinforcing layer 6 to approximately below the bottom of the groove 5. The rubber layer 7 having good wet road motion characteristics
is arranged, and the bent portion 6 of the belt reinforcing layer 6
The rubber layer 8 having the above-mentioned good low rolling resistance characteristics is arranged from both shoulder portions A of the tread surface approximately corresponding to portions A to a portion close to the belt reinforcing layer G. Next, the results of the experiment will be explained. Table 1 below shows the values of dynamic elastic modulus E', dynamic loss E'', and rolling resistance (ratio) of the present invention tire, conventional tire, and comparative tire, as well as the wet road dynamic characteristics as substitute characteristics for the wet road motion characteristics. Road braking distance compared to conventional tires
It is expressed as a ratio of 100. (The smaller the rolling resistance value and wet road braking distance values, the better)

[Table] Tire size is 195/70HR14 Load 400Kg Air pressure
1.9Kg/cm ² The average value was taken from 60Km/hr to 130Km/hr. 1 in the table is a dynamic viscoelasticity measuring instrument (viscoelasticity spectrometer) at a frequency of 20Hz and a temperature of 50℃ and an initial strain of 20%.
The dynamic elastic modulus E′ measured at a dynamic stress of 2.4 Kg/cm ² is
A conventional tire that uses a rubber layer on the entire tread surface with a tire weight of 34.8 Kg/cm ² and a dynamic loss E″ of 11.1 Kg/cm ² , and its rolling resistance and wet road braking distance are each 100. 2 has a dynamic elastic modulus E′ of 25.3Kg/cm ² and a dynamic loss
Comparative example tire whose entire tread surface is made of rubber with extremely good wet road dynamic properties with an E″ of 11.6 Kg/cm ² .No. 3 is a comparative tire with a dynamic elastic modulus E′ of 40.1 Kg/cm ² and a dynamic loss
Comparative example tire in which rubber, which is extremely advantageous for low rolling resistance and has an E″ of 6.4 Kg/cm ² , is used on the entire tread surface. 4 is an example tire of the present invention shown in FIG. When the rate E′ is 25.3Kg/cm ² , the dynamic loss
A rubber layer 7 with extremely good wet road movement characteristics with an E″ of 11.6 Kg/cm ² is attached to the bent end 6b of the belt reinforcing layer 6.
The dynamic elastic modulus E′ is 40.1Kg/cm ² and the dynamic loss E″ is 6.4Kg/cm ^{2 .}
This is a tire in which a rubber layer 8, which is extremely advantageous for low rolling resistance, is arranged on the tread shoulder A. As is clear from the results of measuring rolling resistance and wet road braking distance for these tires 1 to 4,
The rolling resistance value and wet road braking distance of conventional tire 1 are
100, whereas the dynamic elastic modulus E′ is 25.3Kg/
The tire of Comparative Example ² , in which rubber with a dynamic loss E″ of 11.6 Kg/cm ² is arranged over the entire tread, has an excellent wet road braking distance of 89, but a rolling resistance of 119.
The tire of Comparative Example 3, in which rubber with a dynamic modulus of elasticity E′ of 40.1 Kg/cm ² and a dynamic loss E″ of 6.4 Kg/cm ² is arranged over the entire tread, has a low rolling resistance. Although the resistance is excellent at 82, the wet road braking distance is inferior at 108.On the other hand, as in the embodiment shown in Fig. 1 of the present invention, the dynamic elastic modulus E' is 25.3 Kg/cm ² and the dynamic loss E ″ is 11.6Kg/
A rubber layer 7 having good wet road motion characteristics of 40.1 Kg/cm ² and a dynamic elastic modulus E' of 40.1 Kg/cm ² and a dynamic loss E''
The tire 4 of the present invention, in which the rubber layer 8, which is extremely advantageous for low rolling resistance of 6.4 kg/cm ² , is arranged on the belt bending portion 6a, has a good rolling resistance of 87, and a wet road braking distance of 95. It was confirmed through experiments that this was a good result. As described above, the present invention is such that the cap lead portion is sandwiched between the rubber layer A at both shoulder portions of the cap lead portion that substantially corresponds to the bent portion of the bent belt reinforcing layer, and the bent end portions of the bent belt reinforcing layer. The rubber layer A is divided into a rubber layer B at the center of the cap lead portion, which approximately corresponds to the
, the dynamic elastic modulus E′ _A is relatively large and the dynamic loss
A rubber layer having good low rolling resistance characteristics with a relatively small E″ _A is disposed, and the rubber layer B has a
Since the dynamic elastic modulus _E'B is relatively small and the dynamic loss _E''B is relatively large, a rubber layer with good wet road motion characteristics is arranged, so that the fibers can be woven as described above to achieve good high-speed durability. A pneumatic tire with a folded belt reinforcement layer has extremely low rolling resistance and
Excellent wet road motion characteristics can be imparted at the same time.

[Brief explanation of the drawing]

Figure 1 shows the ground contact pressure of a 195/70HR14 tire with an air pressure of 1.9 Kg/cm ² and a load of 520 Kg/cm ² on both treads approximately corresponding to the belt bending part of the belt reinforcing layer with both ends bent inward. Figures 2 and 3 show the results of measurement at the shoulder and the central part of the tread, which roughly corresponds to the part sandwiched between the bent ends.
The figures are cross-sectional views showing each embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Bead part, 2...Side wall part, 6...Belt reinforcing layer with both ends bent inward, 6a...Bent part, 6b...Both bent ends, 7...Rubber layer with good wet road motion characteristics, 8...Good quality Rubber layer with low rolling resistance characteristics, T...Cap lead part, G...
Belt reinforcement layer.

Claims (1)

[Claims] 1. In a pneumatic tire having a pair of bead portions and a pair of sidewall portions, and having a plurality of belt reinforcing layers including an inwardly bent belt reinforcing layer at the cap tread portion, the cap tread portion is attached to the bent belt reinforcing layer. The cap lead is divided into a rubber layer A on both shoulders of the cap lead, which roughly corresponds to the bent part, and a rubber layer B in the center of the cap lead, which roughly corresponds to the part sandwiched between the folded ends of the folded belt reinforcing layer. The rubber layer A has a relatively large dynamic elastic modulus _E'A and a relatively small dynamic loss _E''A , and has good low rolling resistance characteristics. , the dynamic elastic modulus E′ _B is relatively small and the dynamic loss
A pneumatic tire with a rubber layer that has a relatively large E″ _B and has good wet road motion characteristics.