JP3213127B2 - Pneumatic radial tires with excellent fuel efficiency - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire having improved fuel efficiency and improved uniformity and steering stability of wheels.

[0002]

2. Description of the Related Art Conventional pneumatic tires aimed at improving fuel efficiency generally use a rubber material having a small loss coefficient, increase a filling internal pressure, and reduce the number of layers of a reinforcing member. Is being done.

[0003]

However, in a rubber material having a small loss coefficient, the proportion of reinforcing material such as carbon in the rubber is reduced in order to reduce the hysteresis loss of the rubber in each part. In the tire using, the rigidity of each part is reduced, there is a disadvantage that the steering stability on a dry road surface is reduced, and when the filling internal pressure is increased to reduce energy loss due to distortion of the entire tire, There is a problem that the longitudinal spring constant of the tire is significantly increased and the uniformity of the wheel is reduced.

[0004] The present invention has been made as a result of studying to solve such problems of the prior art, and an object of the present invention is to use a rubber material having a small loss coefficient and apply it to a tire. Even if the filling internal pressure is increased, the steering stability on dry road surfaces can be increased and the uniformity of the wheels can be improved as compared with the conventional technology.
It is to provide a pneumatic radial tire with excellent fuel efficiency.

[0005] In other words, according to the present invention, the use of a rubber material having a small loss coefficient causes a reduction in steering stability on a dry road surface and an increase in wheel internal pressure due to an increase in internal pressure charged into a tire. The uniformity must be reduced. In particular, by improving the bead portion of the tire, a satisfactory wheel uniformity can be realized as a tire wheel with a pneumatic tire mounted on a standard rim, and a radial runout (hereinafter referred to as "RRO"). Abbreviated) and radial force variation (hereinafter referred to as “R
FV ”). Here, the improvement of the uniformity, on the other hand, minimizes fluctuations in the circumferential direction of the wheel, such as the shape of the contact surface, the contact area, and the position of the contact surface in the width direction during rolling of the tire wheel. By equalizing the generated force at any position in the circumferential direction,
Since the running stability of the vehicle is enhanced, according to the present invention, each of the steering stability and the wheel uniformity can be made more than enough to compensate for the aforementioned decrease.

[0006]

A pneumatic radial tire according to the present invention has a pair of sidewalls connected to a tread portion having a cap and base structure, and a bead portion connected to a radially inner end of each sidewall portion. And usually buried radial carcass composed of at least one carcass ply and a belt composed of at least two belt layers, up to 350 kP
a which can be used at a filling internal pressure of a, wherein the tan δ at 60 ° C. of the cap rubber of the tread portion is 0.08
Tan δ of the base rubber at 60 ° C.
02 to 0.07, the tan δ at 60 ° C. of the side wall rubber is set to 0.02 to 0.15, and the bead portion tightly fitted to the inclined bead sheet of the standard rim is fitted with the standard rim. Prior to contact between the outermost curved flange located in the width direction and the opposing outer surface of the bead portion, a bulging heel is provided over the entire periphery of the rounded concave portion adjacent to the outer side in the width direction of the inclined bead sheet. The swelling amount of the swelling heel is 2 mm or more, and the rubber hardness of the swelling heel is 65 degrees or more in JIS hardness.

Here, the standard rim means a split rim, 5
JA such as 15 ° deep rim, 15 ° deep rim, wide deep rim, etc.
A rim defined by TMA, TRA or the like shall be referred to as a rim. The standard rim includes an inclined bead sheet, a rounded concave portion successively extending outwardly in the width direction of the inclined bead sheet, and an outwardly curving rim. It may have a curved flange, and in some cases, an overhang flange between the curved flange and the corner recess. Here, the amount of bulging of the bulging heel means the amount of lateral bulging of the bulging heel when measured on the basis of a perpendicular to the tire center axis passing through the bead base point.

In this case, preferably, the elongation at break of the toe rubber of the bead toe located at the inner end in the width direction of the bead portion along the inclined bead sheet is 420 ± 50.
% And a 300% modulus of 200 ± 20.
kgf / cm ² .

[0009]

In the pneumatic radial tire with excellent fuel efficiency, the internal pressure of the tire is increased up to 350 kPa to reduce the loss due to tire distortion, and the tread is reduced. By using a material having a small loss coefficient for each of the portion and the sidewall portion, the hysteresis loss of each portion is reduced. Here, the maximum filling internal pressure of the tire is 3
If the value is more than 50 kPa, the riding comfort to the vehicle is greatly deteriorated. Therefore, here, the value is limited to 350 kPa.

Here, the tan δ at 60 ° C. of the cap rubber constituting the tread portion is set to 0.08 to 0.5.
22 and tan at 60 ° C. of the base rubber.
By setting δ in the range of 0.02 to 0.07, sufficient fuel economy can be achieved without lowering uneven wear resistance and durability. In other words, when the tan δ of the cap rubber is less than 0.08, the uneven wear becomes severe,
If it exceeds 0.22, it is difficult to sufficiently improve the fuel efficiency. If the tan δ of the base rubber is less than 0.02, a decrease in durability due to cracks at the bottom of the groove, cuts and the like will be evident. When the ratio exceeds 07, it is difficult to improve the fuel efficiency.

Further, here, the side wall rubber is
Assuming that tan δ at 60 ° C. is 0.02 to 0.15,
It improves fuel economy without reducing durability due to side cracks and the like.

When the fuel efficiency of the tire is reduced as described above, as described above, the uniformity of the tire wheels decreases due to an increase in the longitudinal spring constant caused by increasing the internal pressure of the tire. In addition, since the use of a rubber material having a small loss coefficient reduces the rigidity of each component, the steering stability on a dry road surface is reduced. In order to provide further improvement, the bead portion has a rounded recess adjacent to the widthwise outer side of the inclined bead seat prior to contact with the curved flange of the standard rim and the opposing outer surface of the bead portion when the tire rim is assembled. Is provided with a bulging heel which is in close contact with the entire circumference.

According to this, when the rim assembly of the tire proceeds, first, the bulging heel comes into close contact with the rounded concave portion of the standard rim, and then the outer surface of the bead portion is curved under the compression deformation of the bulging heel. Because it will contact the flange,
By making the contact state between the bead portion outer surface and the curved flange or the like sufficiently uniform over the entire circumference, the center axis of the tire can be aligned with the center axis of the standard rim with high accuracy, and therefore, the RRO, that is, the tire wheel The fluctuation of the radial reaction force when the tire wheel is rotated under a constant deflection, ie, RF
V is effectively suppressed, and the uniformity of the wheels is greatly improved. And such improvement of uniformity also makes the ground contact state at the time of rolling of the tire wheel sufficiently uniform over the entire circumference, and makes the force generated by the tire wheel almost constant at any position in the circumferential direction. As a result, the running stability of the vehicle and, consequently, the steering stability are also effectively improved.

Here, the bulging amount of the bulging heel is 2 m.
By setting m or more, complete embedding of the rounded concave portion by the bulging heel can be ensured, but if the bulging amount is too large, the movement of the bead portion outer surface with respect to the curved flange increases, Since there is a possibility that rim abrasion may become severe, it is preferable to limit the rim to 4 mm. The rubber hardness of the bulging heel is 65 in JIS hardness.
By setting the degree or more, the bulging heel can be firmly fitted and fixed to the corner round recess, and the bulging heel can lead to uniform contact with the corner round recess all around. If the hardness is too hard,
A sufficient amount of compressive deformation between the rim and the rim cannot be ensured, which may cause a problem in airtightness.

In addition, in this tire, the bead toe located at the inner end in the width direction along the inclined bead sheet of the bead portion has an elongation at break of the toe tip rubber of 420 ± 50.
% And the 300% modulus is 200 ± 20 kgf / c
In the case of m ² , it is possible to effectively prevent the bead from falling down, further improve the steering stability, and prevent the rim of the tire bead from being rubbed.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view in the tire width direction showing an embodiment of the present invention, in which 1 indicates a tread portion. The tread portion 1 is composed of a cap rubber layer 1a and a base rubber layer 1b. A pair of left and right sidewall portions 2 is formed continuously on a side portion of the tread portion 1, and each of the sidewall portions 2 The bead portion 3 is provided continuously at the inner end in the radial direction.

Here, a radial carcass 4 composed of a single carcass ply is provided extending in a toroidal manner, and its respective side end portions are arranged from the inside around a bead core 5 embedded in the bead portion 3. A belt 6 composed of two belt layers 6a and 6b is disposed on the outer side of the crown portion of the radial carcass 4 and on the inner side of the tread portion 1 to reinforce the tire. .

Further, the maximum applicable internal pressure is increased from 200 kPa to 3 kPa.
In this tire up to 50 kPa, the tan δ at 60 ° C. of the cap rubber is 0.08 to 0.22, and the tan δ of the base rubber at 60 ° C. is 0.02 to 0.22.
0.07, and the similar tan δ of the sidewall rubber forming the sidewall portion 2 is set to 0.02.
０．１0.15. Here, as described above, all of these tan δ are within a range in which the hysteresis loss of each part is reduced and the fuel efficiency is improved, while the reduction in wear resistance, durability and the like can be effectively prevented.

Further, in this tire, a bulging heel 7 is provided at a bead heel portion of the bead portion 3 in order to improve the uniformity of the tire wheel. FIG. 2 is a cross-sectional view of a main part showing how to attach the bead part 3 provided with the bulging heel 7 and the tire to the standard rim, in which 8 is a standard rim, and 9 is an inclined bead seat thereof. Reference numeral 10 denotes a rounded concave portion located adjacent to the widthwise outside of the inclined bead sheet 9, reference numeral 11 denotes a projecting flange projecting radially outward from the rounded concave portion 10, and reference numeral 12 denotes a projecting flange. FIG. 4 shows curved flanges that continuously and outwardly bend outwardly in the width direction and the radial direction, respectively, of the overhang flange 12. Here, the overhang flange 11 may be omitted depending on the type of the standard rim 8.

The swelling amount d of the swelling heel 7 at the time of vulcanization molding of the tire is determined by extending the inclined bead sheet 9 toward the rounded concave portion in the widthwise cross section of the standard rim 8 as shown in the figure. Corresponding to the intersection point P of the imaginary straight line 1 and the imaginary straight line m that is in contact with the curved flange 12 and orthogonal to the central axis of the standard rim 8 in the standard rim without the overhang flange 11 and the overhang flange 11 that is continuous with It is determined based on a perpendicular line n passing through a bead base point Q planned for the tire design and descending from the bead base point Q to the tire center axis, and the bulging amount d is 2 mm or more here.

Further, here, the rubber hardness of the bulging heel 7 is set to 65 degrees or more in JIS hardness, and the bead portion 3
The toe tip rubber 13 of the bead toe located at the inner end in the width direction along the inclined bead sheet 9, a hook-shaped toe tip in which the portion along the inclined bead sheet 9 is extended somewhat toward the rounded concave side in the figure. The elongation at break of the rubber 13 is set to 420 ± 50%, and the 300% modulus is set to 200 ± 20 kg.
As f / cm ² , toughness is imparted to the toe rubber 13 together with hardness.

The tire bead portion 3 constructed as described above usually has an intersection P between the straight line 1 and the straight line m as described above.
Rim diameter D defined by the diameter of a circle whose radius is the distance from the center axis of the standard rim 8 to the rim 8, and an appropriate interference is given to the rim diameter D. For each bead portion, the bead portions are partially and successively passed over the outer periphery of the curved flange 12 of the standard rim 3 to drop both bead portions 3 into the drop or well of the standard rim 8 once. The subsequent mounting of the tire to the rim 8 is carried out by filling the tire with air until a specified internal pressure is reached,
As shown by an arrow in FIG. 2, the bead portion 3 is pushed outward along the inclined bead sheet 9 until the outer surface thereof contacts the curved flange 12.

Referring to the progress of such a rim assembly in the case of a conventional pneumatic tire having no bulging heel as shown in FIG. 3, the beat portion 21 moves outward on the inclined bead seat. As a result, the interference for the bead increases and the degree of tight fitting can be increased, but the frictional resistance of the bead portion 21 that hinders the movement is
Since it is not always uniform over the entire circumference, the outer surface of the bead portion 21 is removed from the rim 8 before the bead heel 22 reaches the rounded concave portion 10 in the portion where the frictional resistance is large.
The bead heel 22 will approach the rounded corner recess 10 against the resistance to compressive deformation starting there. However, in this case, the position and volume of the gap 23 that often occurs between the bead heel 22 and the rounded corner recess 10 often become uneven on the circumference of the standard rim 8, and such a state occurs once. Then, the air trapped in the gap,
Since the further movement of the bead portion 21 along the inclined bead seat 9 is restrained by the increase in the pressure, the rim assembling work is likely to be discontinued, and therefore, the pneumatic tire itself has sufficient uniformity. Despite being vulcanized, R as a tire wheel
The RO increased, and as a result, the RFV increased.

On the other hand, in the inventive tire provided with the bulging heel 7, the bulging heel 7 is first fitted with the rounded concave portion 10
Then, as shown in FIG. 2, the bead portion outer surface comes into contact with the curved flange 12 under the compressive deformation of the swelling heel 7, and the rim assembling operation is completed in a state where moderate pressure is applied thereto. Therefore, the above-described gap does not occur between the outer surface of the bead portion and the standard rim 8, and the center axis of the tire is easily and accurately aligned with the center axis of the standard rim 8. Therefore, the RRO as the tire wheel is reduced, and the RFV is effectively suppressed.

Thus, according to the pneumatic tire, particularly its bead structure, the decrease in wheel uniformity caused by the increase in the internal pressure of the tire is always prevented from being reduced by the tire bead portion 3 to the standard rim 8. Use of a rubber material that can be completely improved by realizing proper assembly and that can be effectively improved, and that has a small loss factor due to the improvement of running stability of the vehicle based on the improvement of its wheel uniformity Therefore, the decrease in steering stability due to the above can be more than sufficiently covered.

Here, the bulging amount d of the bulging heel 7 is
In a normal passenger car tire, the thickness is preferably 2 to 4 mm in order to improve the wheel uniformity while preventing rim rubbing on the outer surface of the bead portion, and the JIS hardness of the bulging heel 7 is 65 to 80 mm. The degree is preferable in order to improve the wheel uniformity while securing sufficient airtightness.

Further, in this tire, the elongation at break of the toe tip rubber 13 is set to 420 ± 50% and 300%
By setting the modulus to 200 ± 20 kgf / cm ² , as described above, the rim of the bead portion 3 can be prevented from being rubbed, and the steering stability can be further improved.
Here, when the elongation at break is less than 370%, there is a high possibility that toe chipping occurs in the bead toe. On the other hand, when the value exceeds 470%, the bead portion 3 is effectively prevented from falling down. And these things imply that the 300% modulus is 220 kgf / cm ²
The same applies to the case where the value exceeds 180 kg / cm ² and the case where the value is less than 180 kgf / cm ² .

Comparative Example 1 The rolling resistance coefficient (RRC) index for each of the inventive tire, the comparative tire, and the conventional tire is described below.
The following describes comparative tests on wheel uniformity and steering stability on dry roads.供 Test tire A tire having a size of 175 / 70R13 was applied to a 5J × 13 standard rim. Here, the radial carcass is composed of one carcass ply made of a 1000 d / 2 PET cord, the angle of the PET cord with respect to the tire circumferential direction is 90 °, and the belt is 1 × 4.
, And each metal cord was extended at an angle of 20 ° with respect to the tire circumferential direction in a direction crossing each other between the layers. Inventive Tire The tan δ at 60 ° C. of the cap rubber in the tread portion is 0.11, the tan δ of the base rubber is 0.03, and the tan δ of the sidewall rubber is 0.07.
And the bulging amount of the bulging heel is 2 mm. In addition,
The applied internal pressure was 250 kPa. ○ Comparison tire: tan δ of cap rubber is 0.27, ta of base rubber is
n δ is set to 0.08, tan δ of the sidewall rubber is set to 0.16, and the bead heel has a normal shape in which the heel does not bulge. The applied internal pressure is 200
kPa. ○ Conventional tire Same as the inventive tire except that the bead heel has a normal shape in which the heel does not bulge. ◎ Test method The RRC index was such that a drum having a steel smooth surface with an outer diameter of 1707.6 mm and a width of 350 mm was rotated at 0 to 180 km / h, and the tire was loaded with 300 kg of tire.
The RRC is measured by the elliptic method, and the uniformity of the wheel is determined by actually measuring the RFV and RRO, and the steering stability on a dry road surface The test runs on a test course at high speeds (100-1
(60 km / h) was evaluated based on the feeling of the test driver.試 験 Test results Each test was performed on eight tires at a time and the average value was determined. The results are shown in Table 1. The larger the index value in the table, the better the result.

[Table 1]

[Comparative Example 2] Other comparative tests on the same performances as in Comparative Example 1 will be described below. ◎ Test tire A tire having a size of 185 / 65R14 was applied to a 6J × 14 standard rim. Here, the radial carcass is 10
A single carcass ply made of a 00d / 2 PET cord has an angle of 90 ° with respect to the tire circumferential direction, and the belt has a two-layer belt layer made of a 1 × 3 metal cord. , And the respective metal cords were extended to cross each other between the layers at an angle of 20 ° with respect to the tire circumferential direction. O Inventive tire The tan δ at 60 ° C. of the cap rubber in the tread portion was 0.11, the tan δ similar to that of the base rubber was 0.03, and the tan δ of the sidewall rubber was 0.07.
And the bulging amount of the bulging heel is 2 mm. In addition,
The filling internal pressure was 300 kPa. ○ Comparison tire: tan δ of cap rubber is 0.27, ta of base rubber is
n δ is set to 0.08, tan δ of the sidewall rubber is set to 0.16, and the bead heel has a normal shape in which the heel does not bulge. Filling pressure is 200kPa
And ○ Conventional tire Same as the inventive tire except that the bead heel is of a normal shape in which the heel does not bulge. ◎ Test method The RRC index was obtained in the same manner as described above, except that the tire pressing force was 400 kg. The uniformity of the wheels and the steering stability on dry road surfaces were respectively
It was determined in the same manner as described above.試 験 Test results The results of each test are shown in Table 2 in the same manner as in Table 1.

[Table 2]

[0030]

As is apparent from the above comparative example, according to the present invention, the fuel economy is sufficiently achieved, especially due to the presence of the bulging heel, and the uniformity of the wheels and the dry road surface The steering stability of the vehicle can be effectively improved.

[Brief description of the drawings]

FIG. 1 is a sectional view in the tire width direction showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a main part of the rim of the tire illustrated in FIG. 1;

FIG. 3 is a cross-sectional view of a main part showing a rim assembly procedure of a conventional tire.

[Explanation of symbols]

 Reference Signs List 1 dread part 1a cap rubber layer 1b base rubber layer 2 side wall part 3 bead part 4 radial carcass 5 bead core 6 belt 7 bulging heel 8 standard rim 9 inclined bead seat 10 corner round recess 11 overhang flange 12 curved flange P intersection Q bead Base point d Swell amount

Claims (2)

(57) [Claims] 1. A tread portion having a cap and base structure, a pair of sidewall portions connected to the tread portion, and a bead portion connected to a radially inner end of each sidewall portion. A pneumatic radial tire that can be used, wherein a tan δ at 60 ° C. of the cap rubber of the tread portion is provided.
From 0.08 to 0.22, and the ta of the base rubber at 60 ° C.
n δ is set to 0.02 to 0.07, and tan δ of the sidewall rubber at 60 ° C. is set to 0.02 to 0.15.
The bead portion tightly fitted to the inclined bead sheet of the standard rim, the curved flange located on the outermost side in the width direction of the standard rim, and the contact with the bead portion outer surface facing the inclined flange, A bulging heel is provided on the rounded concave portion adjacent to the outer side of the bead in the width direction so as to be in close contact with the bead over its entire circumference. The bulging amount of the bulging heel is 2 mm or more. A pneumatic radial tire with excellent fuel efficiency of 65 degrees or more in hardness. 2. The bead toe positioned at the inner end in the width direction along the inclined bead sheet of the bead portion has an elongation at break of 420 to 50% of the toe rubber and a 300% modulus of 200 to 20 kgf / cm. ^{2. The} pneumatic radial tire according to claim 1, which is excellent in fuel efficiency.