JP5837399B2 - Pneumatic radial tire for trucks and buses - Google Patents

Description

  The present invention relates to a pneumatic radial tire for trucks and buses (hereinafter, also simply referred to as “tire”), and more particularly, to a truck / vehicle that achieves weight reduction while avoiding a decrease in tire durability due to breakage of a metal wire. The present invention relates to a pneumatic radial tire for buses.

  Conventional typical radial tires for trucks and buses have a bead core provided on a pair of left and right bead parts, and extend from the crown part to both bead parts through both side parts, and are wound around the bead cores to bead parts. A radial carcass that is moored and a belt that is disposed outside the radial carcass in the radial direction of the crown portion of the tire are provided. This belt is composed of at least three belt layers, and these belt layers are formed by embedding metal cords arranged in parallel in rubber. Among the at least three belt layers, the second layer and the third layer, counted from the inner side in the tire radial direction, are in the same layer at an angle of about 10 to 30 ° with respect to the circumferential direction of the tire. In FIG. 2, a so-called cross belt layer is formed, which is arranged in parallel with each other, and is laminated so as to be opposite to each other across the tire equator line.

  The skeleton part of the radial tire is basically composed of a radial carcass and a belt disposed outside the crown part of the radial carcass. Or substantially 90 °, and the cord angle at the crown of the belt layer is approximately 10 ° to 30 ° with respect to the tire equator line, and the belt layer bears the circumferential tension generated by the air pressure. The radial carcass bears the tension. Generally, a radial tire belt is a tension member, and one of the important functions of the belt is to maintain a predetermined cross-sectional shape when the tire is filled with internal pressure, and to use the tire for a long time. Sometimes suppressing the tire diameter growth.

  In recent years, due to social demands for resource and energy saving, pneumatic tires for trucks and buses have been required to develop fuel-efficient tires, that is, tires with low rolling resistance, and the weight reduction of pneumatic radial tires for trucks and buses has been strong. It is requested. Reducing the mass of the belt is an effective means for reducing the weight of pneumatic tires for trucks and buses. To reduce the weight of the belt, the rubber-coated metal cord layer forming the belt is used. It is the simplest means to reduce the amount of metal cord driven. However, if the driving amount of the metal cord is reduced, the metal wire constituting the metal cord is likely to be broken due to compression fatigue, resulting in a problem that the durability performance of the tire is lowered.

Patent Document 1 satisfies the following (i) to (iii) as pneumatic radial tires for trucks and buses that can be reduced in weight while avoiding a decrease in the durability performance of the tires caused by broken metal wires Pneumatic radial tires for trucks and buses have been proposed. (I) The belt is formed of at least three rubber-coated metal cord layers formed by embedding metal cords arranged in parallel in rubber. (Ii) The metal cord of the innermost layer of the belt is a single twist in which filaments made of high carbon steel having a carbon content of 0.6 to 1.0 mass% and having a diameter of 0.10 to 0.40 mm are twisted together. It is a steel cord having a structure or a layer twist structure or a double twist structure. (Iii) The filament has a tensile strength of 100 to 230 kg / mm ² and a total elongation of 5% or more when cut. Further, in Patent Documents 2 to 5, metal wires having a flat cross-sectional shape have been proposed for the purpose of reducing the weight of the tire while preventing breakage of the metal wire which is a reinforcing material for the belt. A tire using the tire has been studied.

JP-A-11-59122 JP 2009-41170 A JP 2009-249663 A JP 2010-47877 A JP 2011-25595 A

  The pneumatic radial tire for trucks and buses described in Patent Document 1 has been reduced in weight compared to the conventional pneumatic radial tire for trucks and buses, but now there is an increasing demand for tire weight reduction. However, the tire described in Patent Document 1 is not necessarily sufficient, and further improvements are required. In Patent Documents 2 to 5, only a tire for a passenger car is examined, and a tire for trucks and buses with more severe use conditions is not examined.

  Accordingly, an object of the present invention is to provide a pneumatic radial tire for trucks and buses that achieves weight reduction while avoiding a decrease in durability of the tire due to breakage of a metal wire.

  As a result of intensive studies on the belt structure in order to solve the above problems, the present inventor has obtained the following knowledge. That is, among the at least three rubber-coated metal cord layers forming the belt, the so-called cross belt layers of the second layer and the third layer counted from the inner side in the radial direction have the above-described cross-sectional shape retention and diameter growth. Since it plays an important function of suppression, the amount of metal cord driving cannot be reduced easily. Therefore, in order to reduce the weight of the belt, it is essential to reduce the weight of the innermost layer of the belt, that is, the first layer belt counted from the inner side in the radial direction. As a result of further investigation based on such knowledge, it was found that the above-mentioned problem can be solved by using a reinforcing material for the first belt layer as a metal wire and optimizing the shape of the metal wire. The invention has been completed.

That is, the pneumatic radial tire for trucks and buses of the present invention includes a belt composed of at least three belt layers on the outer side in the tire radial direction of the crown portion of the radial carcass that forms a toroidal shape across a pair of left and right bead cores. In pneumatic radial tires for trucks and buses
The innermost belt layer of the belt is parallel and flat in the belt width direction so that the long diameter of the flat shape matches the belt width direction without twisting the metal wire having a flat shape in a cross section perpendicular to the longitudinal direction. Embedded in rubber at intervals,
The width W (mm) and thickness T (mm) of the flat metal wire are expressed by the following formula (1),
2.0 ≦ W / T ≦ 6.0 (1)
Satisfying the relationship represented by
The width direction bending rigidity WS (N · mm ² ) and the thickness direction bending rigidity TS (N · mm ² ) of the flat metal wire are expressed by the following formula (2):
5.0 ≦ WS / TS ≦ 35.0 (2)
Satisfying the relationship represented by
The number P (lines / 50 mm) of the flat metal wire for the innermost belt layer is expressed by the following formula (3),
−24.9 × Ln (W / T) + 53.7 ≦ P ≦ −34.4 × Ln (W / T) +83.3 (3)
(Wherein, the same as the above, and Ln represents a natural logarithm) is satisfied.

  In the present invention, the cross-sectional shape of the flat metal wire is preferably a track shape having a pair of parallel straight portions and a pair of arc portions that protrude outwardly and face each other. Further, in the present invention, the cross-sectional shape of the flat metal wire includes a pair of parallel straight portions, a pair of arc portions that are convexly opposed to each other, and further, from the straight portions to the arc portions. It is preferable that the track has a pair of arc portions at the transition portion.

  ADVANTAGE OF THE INVENTION According to this invention, the pneumatic radial tire for trucks and buses which implement | achieved weight reduction can be provided, avoiding the fall of the durability of the tire by bending of a metal wire.

1 is a cross-sectional view in one side in the width direction showing an example of a pneumatic radial tire for trucks and buses of the present invention. It is width direction sectional drawing which shows the example of the flat-shaped metal wire which concerns on this invention. It is width direction sectional drawing which shows the example of the flat-shaped metal wire which concerns on this invention. It is width direction sectional drawing which shows the example which twisted the conventional cross-section metal wire to 1 + 6 structure. It is a graph which shows the relationship between ratio W / T of the width | variety and thickness of a metal wire in each Example and a comparative example, ratio WS / TS of width direction bending rigidity, and thickness direction bending rigidity. It is a graph which shows the relationship between ratio W / T of the width | variety of the metal wire in each Example and a comparative example, and the number P of implantation.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a cross-sectional side view of a radial radial tire for trucks and buses according to a preferred embodiment of the present invention. As shown in the figure, a pneumatic radial tire 10 for trucks and buses according to the present invention extends to a bead core 1 provided on a pair of left and right bead parts 6 and both bead parts 6 from a crown part through both side wall parts 5, A belt comprising a radial carcass 2 wound around a bead core 1 and moored at a bead portion 6, and at least three layers (four layers in the illustrated example) of belt layers disposed on the radial outer side of the crown portion of the radial carcass 2 in the tire direction. 3, and a tread portion 4 reinforced by the above. In the present invention, the innermost belt layer is parallel to the belt width direction so that the long diameter of the flat shape coincides with the belt width direction without twisting the metal wire having a flat shape in a cross section orthogonal to the longitudinal direction. And it is buried in rubber with a space in the plane.

  FIG. 2 shows a cross-sectional view of an example of a flat metal wire 20 according to the present invention. Conventionally, in general, the reinforcing material used for the innermost layer belt is a metal obtained by twisting together metal wires 40 having a substantially circular cross-sectional shape perpendicular to the length direction as shown in FIG. It was a code (1 + 6 structure in the illustrated example). However, in the present invention, the metal wire 20 used for the innermost layer belt is characterized in that its cross section is flat as shown in FIG. Since the innermost layer belt has a relatively low angle of inclination with respect to the tire equatorial plane, that is, the angle formed with the carcass cord, the metal wire used for the innermost layer belt is a metal wire of another belt layer. More susceptible to compression strain. Therefore, folding resistance is important. A flat metal wire as shown in FIG. 2 is less deformed when repeatedly subjected to compressive strain than a metal cord, so that it does not easily fold and becomes a durable belt. In addition, since the metal wire having a flat cross section has a smaller thickness than the metal cord, the thickness of the belt layer can be reduced and the weight of the tire can be reduced.

In the present invention, the width W (mm) and the thickness T (mm) of the flat metal wire are expressed by the following formula (1).
2.0 ≦ W / T ≦ 6.0 (1)
It is necessary to satisfy the relationship expressed by If W / T is less than 2.0, WS / TS, which will be described later, is too low, and the folding resistance is lowered. On the other hand, when W / T exceeds 6.0, it becomes difficult to manufacture the metal wire.

Furthermore, in the present invention, the width-direction bending rigidity WS (N · mm ² ) and the thickness-direction bending rigidity TS (N · mm ² ) of the flat metal wire are expressed by the following formula (2),
5.0 ≦ WS / TS ≦ 35.0 (2)
It is also necessary to satisfy the relationship expressed by When WS / TS is less than 5.0, the deformation of the metal wire is increased when compressive strain is applied to the metal wire, and the bending resistance is lowered. On the other hand, if WS / TS exceeds 35.0, the W / T will inevitably increase, making it difficult to produce a metal wire.

Furthermore, the number P (lines / 50 mm) of the flat metal wire to the innermost layer belt is expressed by the following formula (3),
−24.9 × Ln (W / T) + 53.7 ≦ P ≦ −34.4 × Ln (W / T) +83.3 (3)
(Wherein W and T are the same as those described above, and Ln represents a natural logarithm). If the number P to be driven is less than −24.9 × Ln (W / T) +53.7, the weight resistance is excessively reduced, so that the folding resistance is lowered. On the other hand, when the number P to be driven exceeds −34.4 × Ln (W / T) +83.3, it is disadvantageous for weight reduction.

Specifically, as a cross-sectional shape of the flat metal wire 20, for example, as shown in FIG. 2, a pair of parallel straight portions 11, a pair of arc portions 12 that are convex and opposed to the outside, Preferably, the track shape has In this case, the radius of curvature R (mm) of the arc portion 12 is preferably the following formula (4) with respect to the thickness T (mm):
0.6354 × T ≦ R ≦ 0.77 × T + 0.019 (4)
The relationship expressed by When the radius of curvature R of the arc portion 12 is less than 0.6354 × T, the radius of curvature is too small, and therefore shear stress generated at the bonding interface between the metal wire and the rubber is locally increased, which may cause separation. There is. On the other hand, when the radius of curvature R exceeds 0.77 × T + 0.019, the shear stress generated at the bonding interface between the metal wire and the rubber in the boundary region between the straight portion 11 and the arc portion 12 is locally increased. There is a risk of separation.

In the present invention, in particular, as shown in FIG. 3, a pair of parallel straight line portions 21, a pair of arc portions 22 that are convexly opposed to each other, and a straight portion 21 to a circular arc portion 22. It is preferable to use a flat-shaped metal wire 30 having a track-shaped cross-sectional shape having another pair of arc portions 23 at a portion that transitions to. By making the cross-sectional shape in this way, the folding resistance can be effectively improved. In this case, the radius of curvature Ra (mm) of the arc portion 22 is preferably the following formula (5) with respect to the thickness T (mm):
0.5 × T ≦ Ra ≦ 0.77 × T + 0.019 (5)
It is assumed that the relational expression represented by If the radius of curvature Ra is less than 0.5 × T, the radius of curvature is too small, so that the shear stress generated at the bonding interface between the metal wire and the rubber is locally increased, and separation tends to occur. On the other hand, if the curvature radius Ra exceeds 0.77 × T + 0.019, the shear stress generated at the bonding interface between the metal wire and the rubber in the boundary region with the arc portion 23 is locally increased, and separation is likely to occur. Become.

Furthermore, the radius of curvature Rb of the arc portion 23 is preferably the following formula (6) with respect to the thickness T (mm):
T ≦ Rb ≦ 2.5 × T (6)
It is assumed that the relational expression represented by When the radius of curvature Rb of the arc is less than T, the radius of curvature is too small, so that the local distortion of the arc portion 23 becomes large at the time of large bending deformation, and the wire is likely to be broken at the time of sudden turning of the vehicle. End up. On the other hand, when the curvature radius Rb exceeds 2.5 × T, the shear stress generated at the bonding interface between the metal wire and the rubber is locally increased in the boundary area between the arc portion 22 of the wire and separation is likely to occur. Become. In addition, the strain generated at the time of large bending deformation in the boundary region with the straight portion 21 is locally increased, and the metal wire is likely to be broken at the time of sudden turning of the vehicle.

  The flat-shaped metal wire according to the present invention is rolled between rollers in the latter half of the wire drawing process using the conventional equipment and process for producing a metal wire having a normal circular cross section as it is, or It is possible to manufacture economically and easily by flattening by passing a flat hole die or the like.

  The pneumatic radial tire for trucks and buses of the present invention may be any metal wire used for the innermost layer belt layer as long as it satisfies the above conditions, and the structure of the other belt layers is not particularly limited, and is publicly known. A structure can be adopted. The details of the tire structure and the material of each member are not particularly limited, and can be appropriately selected from conventionally known ones. For example, a tread pattern is appropriately formed on the surface of the tread portion 4, a bead filler (not shown) is disposed outside the bead core 1 in the tire radial direction, and an inner liner is disposed in the innermost layer of the tire. Furthermore, in the tire of the present invention, as the gas filled in the tire, it is possible to use normal or air having a changed oxygen partial pressure, or an inert gas such as nitrogen.

Hereinafter, the present invention will be described in more detail with reference to examples.
<Examples 1-4, Comparative Examples 1-4, and Conventional Examples 1 and 2>
The innermost layer belt inclined at an angle of 52 ° to the right with respect to the tire equator plane was applied to a truck / bus pneumatic radial tire (tire size: 11R22.5) having the structure shown in FIG. For the innermost layer belts of the tires of Examples 1 to 4 and Comparative Examples 1 to 4, metal wires conforming to the specifications shown in the code specification columns of Tables 1 and 2 below were used. As shown in FIG. 4, the tires of Conventional Examples 1 and 2 are metal cords obtained by twisting a conventional metal wire having a circular cross section into a 1 + 6 structure. The belt layers other than the innermost belt layer used a 1 + 6 twisted cord.

  Each performance test was carried out according to the following for each obtained tire. The results are also shown in Tables 1 and 2 below. FIG. 5 is a graph showing the relationship between the ratio W / T of the width and thickness of the metal wire and the ratio WS / TS of the width direction bending stiffness and the thickness direction bending stiffness in each example and comparative example. The graph which shows the relationship between ratio W / T of the width | variety of thickness and the number P of driving | operations is shown in FIG. Note that the two straight lines in the graph of FIG. 5 and the two curves in the graph of FIG. 6 correspond to the upper limit value and the lower limit value of the equations (2) and (3), respectively.

<Inner layer belt mass>
The mass per unit area of the innermost belt used in each test tire was measured, and the index was displayed with the conventional example 1 as 100. The smaller this value, the smaller the inner layer belt mass and the lighter the weight, but 75 or less is required to meet social demands.

<Folding resistance test>
Each test tire was mounted on a regular rim, loaded with a load of 1000 kg on an indoor drum tester under a filling internal pressure of 1 atm, and after traveling 5000 km, the tire was dissected and 50 cords of the innermost belt were collected. The number of bent metal wires was measured. The folding resistance is the number of occurrences of folding with respect to the number of collected samples expressed in%, and the larger the number, the lower the folding resistance.

  As shown in Tables 1 and 2 above, in the tires of Examples 1 to 4 that satisfy the conditions of the present invention, there is no breakage of the metal wire, and a weight reduction of 25% or more is achieved as compared with the conventional example 1. Yes. On the other hand, the tire of Conventional Example 2 was broken because the number of cords driven in the tire of Conventional Example 1 was reduced. In the tire of Comparative Example 1, the ratio W / T between the width and the thickness of the metal wire was small, and the ratio WS / TS between the width direction bending stiffness and the thickness direction bending stiffness was too small, and the fold occurred. The tire of Comparative Example 2 was broken because the inner layer belt was too light. In the tire of Comparative Example 3, since the ratio of the width and the thickness of the metal wire is large, it is difficult to manufacture the metal wire, and cracks are generated in the cross section of the metal wire at the metal wire processing stage. Furthermore, the tire of the comparative example 4 has a result that the weight reduction of 25% or more compared with the conventional example 1 is not achieved.

DESCRIPTION OF SYMBOLS 1 Bead core 2 Radial carcass 3 Belt 4 Tread part 5 Side wall part 6 Bead part 10 Pneumatic radial tire for trucks and buses 11, 21 Straight part 12, 22, 23 Arc part 20, 30, 40 Metal wire W Metal wire width T thickness of metal wire R radius of curvature Ra of arc portion 12 of metal wire radius of curvature Rb of arc portion 22 of metal wire Rb radius of curvature of arc portion 23 of metal wire

Claims (3)

In a pneumatic radial tire for trucks and buses including a belt composed of at least three belt layers on the outer side in the tire radial direction of a crown portion of a radial carcass that forms a toroidal shape across a pair of left and right bead cores,
The innermost belt layer of the belt is parallel and flat in the belt width direction so that the long diameter of the flat shape matches the belt width direction without twisting the metal wire having a flat shape in a cross section perpendicular to the longitudinal direction. Embedded in rubber at intervals,
The width W (mm) and thickness T (mm) of the flat metal wire are expressed by the following formula (1),
2.0 ≦ W / T ≦ 6.0 (1)
Satisfying the relationship represented by
The width direction bending rigidity WS ( N · mm ² ) and the thickness direction bending rigidity TS ( N · mm ² ) of the flat metal wire are expressed by the following formula (2),
5.0 ≦ WS / TS ≦ 35.0 (2)
Satisfying the relationship represented by
The number P (lines / 50 mm) of the flat metal wire for the innermost belt layer is expressed by the following formula (3),
−24.9 × Ln (W / T) + 53.7 ≦ P ≦ −34.4 × Ln (W / T) +83.3 (3)
A pneumatic radial tire for trucks and buses satisfying a relationship expressed by the same formula (wherein, Ln represents a natural logarithm).   2. The air for trucks and buses according to claim 1, wherein the cross-sectional shape of the flat metal wire is a track shape having a pair of parallel straight portions and a pair of arc portions projecting outwardly to face each other. Entering radial tire.   The cross-sectional shape of the flat metal wire is a pair of parallel straight portions, a pair of arc portions that protrude outward from each other, and a pair of portions that transition from the straight portions to the arc portions. 3. A pneumatic radial tire for trucks and buses according to claim 2, wherein the pneumatic tire has a circular arc part.

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