JP2010120530A - Heavy load pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heavy load pneumatic tire capable of further reducing the rolling bearing resistance. <P>SOLUTION: In the heavy load pneumatic tire, a carcass extending toroidally between a pair of bead cores forms a skeleton, and a belt comprising a belt layer of at least three rubber-covered cords and a tread are provided on the outer side in the tire radial direction of the carcass. The belt has cord intersecting layers 4a, 4b by two layers adjacent to each other, and an outermost belt layer 4c located on the outermost side in the tire radial direction. The angle formed by a cord 4 cc of the outermost belt layer and a cord 4bc of the belt layer adjacent to the outermost belt layer is ≥10° and ≤90°, while the angle of inclination of the cord 4 cc of the outermost belt layer with respect to the tire equatorial plane is ≥30° and ≤44°. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a heavy duty pneumatic tire having reduced rolling resistance.

  When a pneumatic tire rolls under load, rolling resistance is generated due to deformation of the tread contact surface and the tire itself, which causes energy loss mainly in the form of thermal energy. Since this rolling resistance has a serious effect on the fuel consumption of the vehicle, various proposals for reducing the rolling resistance have been made. For example, it is known to use a rubber with a small loss tangent (tan δ) in the tread part, and to reduce the thickness of the tread part. However, when rubber with a small loss tangent is used, depending on the physical properties of the rubber There is a risk that wet performance and maneuverability may be reduced, and when the thickness of the tread portion is reduced, there is a risk that wear resistance and riding comfort may be reduced.

Further, in the pneumatic tire described in Patent Document 1, after the cross-sectional shape of the tire is flattened, the amount of shoulder descending of the ground contact edge of the tread portion with respect to the height of the center position in the tire width direction on the tread surface is determined. By increasing the width and making the crossing width of the crossing belt shorter than the grounding width of the tread portion, the deflection near the grounding end of the tread portion is increased. As a result, eccentric deformation near the center of the tread portion is increased, and shear deformation in the tire circumferential direction near the center of the tread portion is suppressed. In addition, the crossing width of the cross belt is shorter than the contact width of the tread portion, in other words, the cross belt is not positioned inside the tire radial direction near the contact end of the tread portion, thereby reducing the cross belt in the tire width direction. Due to this, shear deformation in the tire width direction in the vicinity of the ground contact end of the tread portion is suppressed. As a result, the strain energy loss of the tread rubber is reduced to reduce the rolling resistance.
JP 2006-1360 A

However, in the pneumatic tire described in Patent Document 1 described above, the strain energy loss of the rubber of the tread portion can be reduced, but the reduction of the strain energy loss of the rubber of the belt portion is insufficient, and further rolling resistance is reduced. It turns out that there is room for reduction.
Therefore, an object of the present invention is to provide a heavy-duty pneumatic tire that achieves further reduction in rolling resistance by reducing strain energy loss of rubber in the belt portion.

The gist of the present invention is as follows.
(1) A heavy-duty pneumatic tire having a carcass extending in a toroidal shape between a pair of bead cores and having a belt and a tread comprising a belt layer of at least three rubber-coated cords on the outer side in the tire radial direction of the carcass. In
The belt has a cord crossing layer composed of two layers adjacent to each other, and an outermost belt layer located on the outermost side in the tire radial direction,
The angle formed by the cord of the outermost belt layer and the cord of the belt layer adjacent to the outermost belt layer is 10 ° or more and 90 ° or less,
The inclination angle of the cord of the outermost belt layer with respect to the tire equatorial plane is 30 ° or more and 44 ° or less,
A heavy-duty pneumatic tire characterized by that.

Here, the cord crossing layer means an inclined belt layer having cord arrangements in which cords are arranged in different directions between two adjacent layers with the tire equatorial plane sandwiched therebetween and intersect each other.
In addition, the angle formed by the cord of the outermost belt layer and the cord of the belt layer adjacent to the outermost belt layer means an acute angle of an acute angle and an obtuse angle.

(2) The cord of the outermost belt layer is inclined in the same direction with respect to the cord of the belt layer adjacent to the outermost belt layer and the tire equatorial plane. Pneumatic tire.

  Here, inclining in the same direction means that in a coordinate system in which the tire width direction is the x-axis and the tire circumferential direction is the y-axis, the two cords are in the same quadrant when they are translated so as to pass the 0 coordinate. It means to exist within.

(3) The heavy-duty pneumatic tire described in (1) or (2) above, wherein at least the tan δ of the rubber on the tread surface is 0.15 or less at 60 ° C. and 1% strain.

(4) The heavy-duty pneumatic tire according to any one of (1) to (3), wherein the belt is composed of four belt layers.

(5) Among the belt layers constituting the belt, the cord of the innermost belt layer located on the innermost side in the tire radial direction and the cord of the outermost belt layer intersect with each other in the opposite directions with respect to the tire equatorial plane. The heavy-duty pneumatic tire according to any one of (1) to (4), wherein the pneumatic tire extends in a direction.

(6) The inclination angle of the cord of the innermost belt layer located on the innermost side in the tire radial direction with respect to the tire equator plane among the belt layers constituting the belt, and the inclination angle of the cord of the outermost belt layer with respect to the tire equator plane The heavy-duty pneumatic tire according to any one of the above (1) to (5), wherein the difference is within 5 °.

  According to the present invention, it is possible to provide a heavy-duty pneumatic tire with further reduced rolling resistance, which is very effective for the recent demand for energy saving.

Hereinafter, an embodiment of a heavy duty pneumatic tire (hereinafter referred to as a tire) of the present invention will be described in detail with reference to the drawings.
In FIG. 1, a tire 1 has a carcass 3 extending in a toroidal shape between a pair of bead cores 2 as a skeleton, and at least three layers, in the illustrated example, a three-layer rubber-coated belt on the outer side in the tire radial direction. It comprises a belt 4 and a tread 5 consisting of layers 4a, 4b, 4c.

FIG. 2 is a belt development view where the tread rubber of the tire shown in FIG. 1 is cut out and subjected to a step-down cut. The cord arrangement of each belt layer will be described with reference to FIG.
The three belt layers 4a, 4b, and 4c are arranged in this order from the inner side in the tire radial direction. The inclination angle α of the cord 4ac of the belt layer 4a with respect to the tire equator plane CL is the same as the inclination angle β of the cord 4bc of the belt layer 4b with respect to the tire equator plane CL, and the cord 4ac of the belt layer 4a is the cord 4bc of the belt layer 4b. And the tire equatorial plane CL. In this way, the belt layers 4a and 4b form two adjacent cord crossing layers 4a and 4b.
The cord crossing layer is a direction in which the cords are different from each other with the tire equatorial plane CL sandwiched between two adjacent layers, that is, on the paper surface of FIG. And inclined belt layers having cord arrangements crossing each other.
Further, the angle formed by the cord 4cc of the belt layer 4c, which is the outermost belt layer located on the outermost side in the tire radial direction, and the cord 4bc of the belt layer 4b adjacent to the belt layer 4c, that is, the difference in inclination angle | β− γ | is 10 ° or more and 90 ° or less, and the inclination angle γ of the cord 4cc of the belt layer 4c with respect to the tire equatorial plane CL is 30 ° or more and 44 ° or less.

FIG. 3 is a development view of a belt of a tire according to a preferred embodiment of the present invention. The four belt layers 4a, 4b, 4c, and 4d are arranged in this order from the inner side in the tire radial direction. The inclination angle β of the cord 4bc of the belt layer 4b with respect to the tire equator plane CL is the same as the inclination angle γ of the cord 4cc of the belt layer 4c with respect to the tire equator plane CL, and the cord 4bc of the belt layer 4b is the cord 4cc of the belt layer 4c. And the belt layers 4b and 4c form a cord crossing layer.
Similarly to the case of the three belt layers described above, the cord 4dc of the belt layer 4d, which is the outermost belt layer located on the outermost side in the tire radial direction, and the cord 4cc of the belt layer 4c adjacent to the belt layer 4d, , That is, the difference in inclination angle | δ−γ | is 10 ° to 90 °, and the inclination angle γ of the cord 4dc of the belt layer 4d with respect to the tire equatorial plane CL is 30 ° to 44 °. It is important to be. Hereinafter, the reason will be described.

  In order to reduce rolling resistance, it is necessary to perform eccentric deformation when the tire rolls. First, this eccentric deformation will be described with reference to FIG. When the tire rolls, two deformations, that is, eccentric deformation shown in FIG. 4 (a) and ring deformation shown in FIG. 4 (b) are combined. In the figure, the dotted line represents the outer shape of the tire before deformation, and the solid line represents the outer shape of the tire during rolling. In the case of the eccentric deformation shown in FIG. 4A, since the rotation center is biased, the tread portion is less deformed and the energy loss is small. On the other hand, in the case of the ring deformation shown in FIG. 4B, the energy loss is large because the tread portion is largely deformed. Thus, in order to reduce the amount of deformation of the tread portion and reduce the energy loss of rubber, it is necessary to perform eccentric deformation when the tire rolls.

Therefore, when the inventors analyzed in detail the conventional tire flattened in order to increase the eccentric deformation at the time of rolling of the tire using the finite element method (FEM), It was found that the strain energy loss corresponding to the rolling resistance is small in the tread rubber portion from the belt layer to the tread surface, but the strain energy loss of the rubber between the belt layers is not small. Therefore, it was considered that a further reduction in rolling resistance can be achieved by reducing the strain energy loss of the rubber of the belt, and the object of the present invention.
In order to analyze this cause, the cord angle of each belt was examined in a tire having a belt composed of four belt layers as shown in FIG. FIG. 5 shows the belt 4 and the tread 5 when the tire 1 is viewed from the side, and the arrows indicate the traveling direction of the tire. The belt layers 4a, 4b, 4c, and 4d, which have a curvature when no load is applied, are pressed against the flat road surface 10 during the load rolling shown in FIG. At this time, the neutral plane of bending (indicated by the dotted line in the figure) is between the cord crossing layers 4b and 4c, so the belt layer 4a inside the cord crossing layers 4b and 4c in the tire radial direction is pulled in the tire circumferential direction. The belt layer 4d on the outer side in the tire radial direction is compressed in the tire circumferential direction. Referring to the cord inclination angles of the belts of the conventional tire shown in Table 1, the belt layers 4c and 4d have the same cord inclination angle, and the belt layer 4d, which is the outermost belt layer located on the outermost side in the tire radial direction. Since the cord inclination angle is close to the tire circumferential direction, even if it is subjected to circumferential compression at the time of load due to bending deformation, the cord has high rigidity and is not compressed. For this reason, it was found that a large shear was generated between the belt layers 4c and 4d, which caused a loss of strain energy.
In order to improve this, the belt layer 4d may be easily compressed in the circumferential direction, and for this purpose, the inclination angle of the cord of the belt layer 4d with respect to the circumferential direction (tire equatorial plane) is increased, thereby I came up with the idea that it should be made less susceptible to rigidity. As an example, the cord inclination angle of each belt of the tire according to the present invention is also shown in Table 1.

Next, an internal pressure of 700 kPa and a load of 2.45 kPa were applied to the tire (size: 11R22.5), and the result of FEM analysis of the rolling resistance as a tire wheel assembled to the rim (size: 7.50) is shown in FIGS. Shown in
In FIG. 6, the horizontal axis represents the angle difference (δ−γ) between the inclination angle γ of the belt layer 4 c with respect to the tire equator plane CL of the cord 4 cc and the inclination angle δ with respect to the tire equator plane CL of the cord 4 dc of the belt layer 4 d. Yes, the vertical axis represents the rolling resistance when this angular difference is changed from −20 ° to 120 ° as an index. That is, when this angle difference becomes negative, γ> δ. The index is expressed as an index with the rolling resistance when the inclination angle γ of the cord 4cc of the belt layer 4c is equal to the inclination angle δ of the cord 4dd of the belt layer 4d (γ = δ) as 100, and the rolling resistance is smaller when the numerical value is smaller. Represents that.

  FIG. 6 shows that the rolling resistance is reduced by 2% when the angular difference is 10 °, and the rolling resistance can be effectively reduced when the angular difference is in the range of 10 ° to 98 °. In particular, when the angle difference is in the range of 20 ° to 95 °, it can be seen that the measurement variation of the rolling resistance in the actual tire is greatly improved over 2%, and the effect is great. In addition, when the angle difference is more than 90 °, it is preferable from the viewpoint of reducing rolling resistance, but there is a problem in that the shear strain during loading increases between the belt layers 4c and 4d, and separation between the belt layers is likely to occur. Therefore, in the present invention, the angle difference is defined in the range of 10 ° to 90 °.

In FIG. 7, the horizontal axis represents the inclination angle δ of the cord 4dc of the belt layer 4d with respect to the tire equatorial plane CL, and the vertical axis represents the rolling resistance when the inclination angle δ is changed, expressed as an index. . The index is expressed as an index with the inclination angle of the conventional tire being 18 ° as 100, and the smaller the numerical value, the smaller the rolling resistance.
From FIG. 7, when the inclination angle δ is 30 °, the rolling resistance is reduced by 3%, and when the inclination angle δ is in the range of 30 ° to 44 °, the measurement variation of the rolling resistance in the actual tire exceeds 2%. It can be seen that the rolling resistance can be effectively reduced. The most preferable inclination angle is 40 °.

In the above description, reference has been made to an example in which the belt structure has four layers as shown in FIG. 3 and the belt layers 4b and 4c form a cord crossing layer. The same applies to the belt structure in which the belt layers 4a and 4b constitute a cord crossing layer.
Further, not only in the case of the four-layer belt configuration, but also in the case of the belt configuration including the three-layer belt layers 4a, 4b, and 4c as shown in FIGS. The belt layer 4c which is the outer belt layer is hardly compressed in the circumferential direction, and a large shear strain is generated between the belt layers 4b and 4c, resulting in a large strain energy loss. Therefore, it is effective to increase the inclination angle of the cord of the belt layer 4c so that the belt layer 4c is easily compressed in the circumferential direction.

Hereinafter, further preferred embodiments of the tire of the present invention will be described.
Of the belt layers 4a, 4b and 4c constituting the belt 4, the cord 4cc of the outermost belt layer 4c located on the outermost side in the tire radial direction is the same as the cord 4bc of the belt layer 4b adjacent to the outermost belt layer 4c and the tire equator. Inclination in the same direction with respect to the surface CL is suitable for improving belt durability.
Note that, in the coordinate system in which the tire width direction is the x-axis and the tire circumferential direction is the y-axis, when the two cords are translated so as to pass the 0 coordinate, the two cords are in the same quadrant. Means to exist.

  At least the tan δ of the rubber on the tread surface (so-called cap rubber) is preferably 0.15 or less at 60 ° C. and 1% strain. As described above, the rolling resistance can be further reduced by using the rubber having a low tan δ on the surface of the tread portion while reducing the energy of the rubber of the belt portion. The reason why the above range is specified is that when tan δ exceeds 0.15, the effect of reducing energy loss may be low.

Among the belt layers constituting the belt, the cord of the innermost belt layer located on the innermost side in the tire radial direction and the cord of the outermost belt layer located on the outermost side in the tire radial direction are opposite to each other with respect to the tire equatorial plane. It is preferable to extend in a direction intersecting with.
Referring to FIG. 2, the cord 4ac of the innermost belt layer 4a and the cord 4cc of the outermost belt layer 4c extend in directions intersecting with the tire equatorial plane CL in opposite directions. 3 and 8, the cord 4ac of the innermost belt layer 4a and the cord 4dc of the outermost belt layer 4d extend in directions opposite to each other with respect to the tire equatorial plane CL. is doing. With this configuration, the belt layer 4a effectively suppresses deformation of the belt layer 4b and the belt layer 4d of 4c effectively suppresses the shear strain between the belt layers 4b and 4c, thereby improving the belt durability. .

Further, the difference between the inclination angle of the cord of the innermost belt layer with respect to the tire equator plane and the inclination angle of the cord of the outermost belt layer with respect to the tire equator plane is preferably within 5 °.
Referring to FIG. 2, the difference between the inclination angle α of the cord 4ac of the innermost belt layer 4a with respect to the tire equator plane CL and the inclination angle γ of the cord 4cc of the outermost belt layer 4c with respect to the tire equator plane CL | α −γ | ≦ 5 °, and with reference to FIGS. 3 and 8, the inclination angle α of the cord 4ac of the innermost belt layer 4a with respect to the tire equatorial plane CL, and the cord 4dc of the outermost belt layer 4d. The difference from the inclination angle δ with respect to the tire equatorial plane CL is | α−δ | ≦ 5 °. With this configuration, the member preparation of the belt layers 4a and 4d is facilitated, and the manufacturing cost can be reduced.

The tire of the present invention and the conventional tire were prototyped according to the specifications described later, and the rolling resistance index was measured.
Each of the test tires has four belt layers 4a, 4b, 4c, and 4d as shown in FIG. 3, which are arranged in this order from the inner side in the tire radial direction. Table 2 shows the cord inclination angle of each belt layer of each test tire.
Moreover, regarding the rubber material of the tread surface (cap) of each test tire, “Conventional” in Table 2 means that the tan δ of the rubber is 0.20 at 60 ° C. and 1% strain, “Low loss” means that the tan δ of the rubber is 0.12 at 60 ° C. and 1% strain.

  Each test tire (size: 11R22.5) was assembled to a rim (size: 7.50) to form a tire wheel. It was. The rolling resistance of the tire was measured with a drum tester (outer diameter: 1.7 m, smooth steel) at a load of 2.45 kN and a speed of 80 km / h. This rolling resistance measurement is based on ISO18164. The measurement results were indexed with the rolling resistance of the conventional tire 1 as 100. It shows that rolling resistance is so small that this index | exponent is small.

  As can be seen from Table 2, it can be seen that the invention example tires 1 and 3 have a reduced rolling resistance index compared to the conventional example tire 1. Moreover, when rubber | gum with small tan-delta is used for the tread surface, it turns out that the rolling resistance index of the invention example tire 2 is reducing compared with the conventional example tire 2. FIG.

  Therefore, by defining the inclination angle of the cord of the belt layer, it is possible to achieve a reduction in rolling resistance, and furthermore, by using rubber with a small tan δ on the tread surface, it is possible to provide a tire with further enhanced this effect. I understood.

It is a figure which shows the cross section of the width direction of the tire according to this invention. FIG. 2 is a belt development view of the tire shown in FIG. 1. It is a belt development view of a tire concerning a suitable embodiment of the present invention. It is a figure for demonstrating eccentric deformation and ring deformation. It is a figure for demonstrating the belt deformation | transformation at the time of load rolling. It is a graph showing the rolling resistance index | exponent with respect to the angle difference ((delta)-(gamma)) of the code | cord | chord of a belt layer. It is a graph showing the rolling resistance index with respect to the inclination angle of the cord of the outermost belt layer. It is a belt development view of a tire concerning other suitable embodiments of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tire 2 Bead core 3 Carcass 4 Belt 4a, 4b, 4c, 4d Belt layer 4ac, 4bc, 4cc, 4dc Belt layer cord 10 Road surface

Claims (6)

In a heavy duty pneumatic tire comprising a carcass extending in a toroidal shape between a pair of bead cores, and a belt composed of at least three rubber-coated belt layers and a tread on the outer side in the tire radial direction of the carcass,
The belt has a cord crossing layer composed of two layers adjacent to each other, and an outermost belt layer located on the outermost side in the tire radial direction,
The angle formed by the cord of the outermost belt layer and the cord of the belt layer adjacent to the outermost belt layer is 10 ° or more and 90 ° or less,
The inclination angle of the cord of the outermost belt layer with respect to the tire equatorial plane is 30 ° or more and 44 ° or less,
A heavy-duty pneumatic tire characterized by that.   The heavy load pneumatic tire according to claim 1, wherein the cord of the outermost belt layer is inclined in the same direction with respect to the cord of the belt layer adjacent to the outermost belt layer and the tire equatorial plane.   3. The heavy duty pneumatic tire according to claim 1, wherein at least the tan δ of the rubber on the tread surface is 0.15 or less at 60 ° C. and 1% strain. 4.   The heavy duty pneumatic tire according to any one of claims 1 to 3, wherein the belt is composed of four belt layers.   Of the belt layers constituting the belt, the cord of the innermost belt layer located on the innermost side in the tire radial direction and the cord of the outermost belt layer extend in directions intersecting with the tire equatorial plane in opposite directions. The heavy-duty pneumatic tire according to any one of claims 1 to 4, wherein the pneumatic tire is used.   Of the belt layers constituting the belt, the difference between the inclination angle of the cord of the innermost belt layer located on the innermost side in the tire radial direction with respect to the tire equator plane and the inclination angle of the cord of the outermost belt layer with respect to the tire equator plane Is within 5 °, the heavy duty pneumatic tire according to any one of claims 1 to 5.

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