JP2012254736A - Pneumatic tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve rolling resistance performance while maintaining bead durability.SOLUTION: In this pneumatic tire 1 for a heavy load, a bead core 5 is a substantially cross sectional hexagon including an inner side surface 5a. In a normal state and in a state that a rated load is applied, an angle formed of an inner side surface 5a of the bead core 5, and a rim seat surface 13 of a normal rim R is in 0±3 degrees. Bead apex rubber 8 comprises inner apex rubber 8A having a complex modulus of elasticity E*1 of 40 to 65 MPa and outer apex rubber 8B having a complex modulus of elasticity E*2 of 3 to 5 MPa. In addition, a height H1 of the inner apex rubber 8A, a height H2 of the outer apex rubber 8B, a thickness W1 of the bead apex rubber 8, and a tire cross sectional height Ho satisfy the following relationship; 0.1≤H1/Ho≤0.3, 0.35≤H2/Ho≤0.55, and 0.1≤W1/H2≤0.3.

Description

  The present invention relates to a heavy-duty pneumatic tire capable of improving rolling resistance performance while maintaining bead durability.

  As shown in FIG. 7A, conventionally, a tubeless type heavy-duty pneumatic tire a has a bead core c embedded in an approximately hexagonal cross section. Further, in the state before the internal pressure filling in which the tire a is assembled to the normal rim b (for example, the state in which the internal pressure is reduced to 5% of the normal internal pressure after filling the normal internal pressure), the inner radius of the bead core c in the tire radial direction is increased. The side surface c1 is designed to be substantially parallel to the rim seat surface b1 of the rim b, that is, the angle α1 formed by the inner side surface c1 and the rim seat surface b1 is substantially 0 degree.

  As a result, the fitting pressure between the bead core c and the rim b is uniformly increased at the inner portion of the bead core c, and an improvement in bead durability is expected. Related documents include the following (see Patent Document 1 below).

JP 2009-137035 A

  However, as exaggeratedly shown in FIG. 7B, when the heavy load pneumatic tire a is filled with the internal pressure, the bead core c is rotated clockwise in the figure by the tension f of the body portion d1 of the carcass ply d. And the angle α1 formed between the inner side surface c1 and the rim seat surface b1 tends to change to about 3 to 5 degrees. In such a bead core c, the fitting pressure with respect to the rim, in particular, the fitting pressure on the toe side of the bead portion is likely to be greatly reduced.

  For this reason, in this type of tire, the bead core c repeats rotational displacement around its center of gravity (hereinafter, such displacement may be simply referred to as “rotation”) during traveling, so that the expected bead durability is obtained. There was a problem that it was difficult.

  In addition, increasing the rubber volume of the bead apex rubber j extending from the bead core c in a tapered shape may increase the rigidity of the bead portion and improve the bead durability, but heat generation at the bead portion increases. There was also a problem that the rolling resistance performance deteriorated.

  The present invention has been devised in view of the actual situation as described above, and is a normal state in which a rim is assembled to a normal rim and is filled with a normal internal pressure, and a camber that is loaded with a normal load in this normal state. In both of the normal load application state with the ground contact at 0 degrees, the inner side surface of the bead core and the rim seat surface of the regular rim are substantially parallel, and the height and thickness of the inner apex rubber and outer apex rubber The main purpose is to provide a heavy-duty pneumatic tire capable of improving rolling resistance performance while maintaining bead durability on the basis of limiting the thickness to a predetermined range.

The invention according to claim 1 of the present invention is a carcass in which a body portion extending from a tread portion to a bead core of a bead portion through a sidewall portion is provided with a series of folded portions that fold around the bead core from the inner side to the outer side in the tire axial direction. A heavy duty pneumatic tire comprising a carcass made of ply and a bead apex rubber extending in a taper shape from the bead core between the main body portion and the folded portion, wherein the bead core is a bottom surface of the bead portion. A normal state in which the tire has a substantially hexagonal cross section with an inner surface in the radial direction of the tire extending along the rim, a rim assembled to a normal rim and filled with normal internal pressure, and a normal load is applied to the normal state. The rim seat of the inner rim of the bead core and the rim seat of the regular rim in a standard load state with a camber angle of 0 degrees The bead apex rubber is arranged on the inner side in the tire radial direction and the inner apex rubber having a complex elastic modulus E * 1 of 40 to 65 MPa, and the tire radius of the inner apex rubber. The outer apex rubber having a complex elastic modulus E * 2 of 3 to 5 MPa, the height H1 in the tire radial direction from the bead base line of the inner apex rubber, and the bead base line of the outer apex rubber The tire radial height H2, the thickness W1 of the folded end portion of the carcass ply of the bead apex rubber, and the tire cross-section height Ho satisfy the following relationship.
0.1 ≦ H1 / Ho ≦ 0.3
0.35 ≦ H2 / Ho ≦ 0.55
0.1 ≦ W1 / H2 ≦ 0.3

  Further, the invention according to claim 2 is that the sidewall rubber disposed on the outer side in the tire axial direction of the carcass includes an inner rubber portion disposed on the carcass side, and an outer rubber disposed on the outer side and forming a tire outer surface. The loss tangent tan δ1 of the inner rubber portion is smaller than the loss tangent tan δ2 of the outer rubber portion.

The invention according to claim 3 is the heavy duty pneumatic tire according to claim 2, wherein the loss tangent tan δ1 of the inner rubber portion and the loss tangent tan δ2 of the outer rubber portion satisfy the following relationship.
0.03 ≦ tan δ1 ≦ 0.06
0.07 ≦ tan δ2 ≦ 0.12

  According to a fourth aspect of the present invention, in the normal state, the height of the center of gravity of the bead core from the bead base line is 0.40 to 0.85 times the height of the rim flange. The heavy duty pneumatic tire according to any one of the above.

  According to a fifth aspect of the present invention, in the normal state, the bead core has a ratio (AW / CW) between a maximum width CW of the bead core parallel to the rim seat surface and a maximum thickness AW perpendicular to the maximum width. ) Is 0.2 to 0.7. The heavy duty pneumatic tire according to any one of claims 1 to 4.

  According to a sixth aspect of the present invention, the bead portion includes a bead apex rubber that tapers outward from the outer surface in the tire radial direction of the bead core in the tire radial direction, and the complex elastic modulus E * of the bead apex rubber. The heavy-duty pneumatic tire according to any one of claims 1 to 5, wherein 3 is 60 to 80 MPa.

  According to a seventh aspect of the present invention, in the regular state, a tire axial distance H from an inner end of the bead core in the tire axial direction to a bead heel point, and a width G of the bottom surface of the bead portion in the tire axial direction The heavy load pneumatic tire according to any one of claims 1 to 6, wherein the ratio (H / G) is 0.60 to 0.94.

  In the invention according to claim 8, in the normal state, the ratio (CW / G) of the maximum width CW of the bead core to the width G in the tire axial direction of the bottom surface of the bead portion is 0.50 to 0. The heavy-duty pneumatic tire according to any one of claims 1 to 7, wherein the pneumatic tire is .85.

  Further, in the invention according to claim 9, in an unloaded state in which a rim is assembled on a normal rim and an internal pressure of 5% of the normal internal pressure is filled, an angle θc with respect to the tire axial direction line of the inner surface of the bead core is: 9. The heavy duty pneumatic tire according to claim 1, wherein an angle θr with respect to a tire axial direction line of the rim seat surface is larger and a difference θc−θr is 2 to 8 degrees.

In the present specification, the complex elastic modulus and the loss tangent are values measured using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho under the following conditions in accordance with JIS-K6394.
Initial strain: 10%
Amplitude: ± 1%
Frequency: 10Hz
Deformation mode: Tensile Measurement temperature: 70 ° C

  The heavy-duty pneumatic tire of the present invention is a carcass ply provided with a series of folded portions that fold around the bead core from the inner side to the outer side in the tire axial direction on the main body part that extends from the tread part through the sidewall part to the bead core of the bead part. And a bead apex rubber extending in a tapered shape from the bead core between the carcass and the body portion and the folded portion.

  The bead core has a substantially hexagonal cross section having an inner side surface in the tire radial direction extending along the bottom surface of the bead portion, a normal state in which a normal rim is assembled and a normal internal pressure is filled, and this normal state In a standard load state in which a normal load is applied to the state and grounded at a camber angle of 0 degrees, the angle formed between the inner side surface of the bead core and the rim seat surface of the normal rim is limited to 0 degree ± 3 degrees.

  Thereby, the bead core can maintain largely the fitting pressure of the bead part with respect to a rim | limb in a wide range in both a normal state and a standard load load state. Therefore, in the heavy duty pneumatic tire of the present invention, rotation of the bead core during traveling can be suppressed, and as a result, bead durability can be improved.

  The bead apex rubber is arranged on the inner side in the tire radial direction and has an inner apex rubber having a complex elastic modulus E * 1 of 40 to 65 MPa, and on the outer side in the tire radial direction of the inner apex rubber and has a complex elastic modulus E * 2. Consists of 3 to 5 MPa outer apex.

  Such a bead apex rubber, when deforming the bead part, relaxes the shear stress acting on the folded part of the carcass ply by using an outer apex rubber having a small complex elastic modulus while ensuring sufficient bending rigidity, so that separation, etc. Effectively prevent damage and the like.

Further, a height H1 in the tire radial direction from the bead base line of the inner apex rubber, a height H2 in the tire radial direction from the bead base line of the outer apex rubber, and a turn-up end of the turn-up portion of the carcass ply of the bead apex rubber The thickness W1 and the tire cross-section height Ho satisfy the following relationship.
0.1 ≦ H1 / Ho ≦ 0.3
0.35 ≦ H2 / Ho ≦ 0.55
0.1 ≦ W1 / H2 ≦ 0.3

  Such a bead apex rubber can reduce the rubber volume as compared with the conventional one while ensuring the rigidity of the bead portion, and thus can suppress the heat generation of the bead portion and improve the rolling resistance performance. The reduction in the rubber volume of the bead apex rubber can be used for a part of the above-described improvement in the bead durability, so that the rolling resistance performance can be improved while maintaining the bead durability.

It is sectional drawing which shows the heavy-duty pneumatic tire of the normal state of this embodiment. It is an enlarged view of the bead part of FIG. (A) is a fragmentary sectional view of a normal state, (b) is a fragmentary sectional view of a standard load state. (A) is sectional drawing of a bead core, (b) is sectional drawing of the bead part of the free state of a tire. It is sectional drawing of the bead part in the unloaded state and normal state with which the internal pressure of 5% of normal internal pressure was filled. (a) is sectional drawing which shows the position of the contact part of a bead part and a rim | limb, (b) is a graph which shows the fitting pressure of the contact part of (a). (A) is sectional drawing before the internal pressure filling of the conventional heavy duty pneumatic tire, (b) is sectional drawing after the internal pressure filling.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a normal rim (hereinafter sometimes simply referred to as “rim”) R, and a heavy-duty pneumatic tire in a normal state in which the rim is assembled to the rim R and filled with normal internal pressure. Hereinafter, it may be simply referred to as “tire”.) A right half sectional view of the assembly with 1 is shown. Unless otherwise specified, dimensions and the like of each part of the tire are values specified in the normal state.

  The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, “Standard Rim” for JATMA, “Design Rim” for TRA, or ETRTO means "Measuring Rim".

  In addition, the “regular internal pressure” is an air pressure determined by each standard for each tire in the standard system including the standard on which the tire is based. TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES "Maximum value", ETRTO, "INFLATION PRESSURE".

  The tire 1 according to the present embodiment is provided with a toroidal carcass 6 that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and the carcass 6 on the outer side in the tire radial direction and inside the tread portion 2. A tubeless type having a belt layer 7 is shown.

  The carcass 6 is folded from the inner side to the outer side in the tire axial direction around the bead core 5 extending from the main body 6a and extending from the main body 6a to the bead core 5 of the bead part 4 through the sidewall part 3 from the tread part 2. In this embodiment, one or more carcass plies 6A including the folded portion 6b are formed.

  The carcass ply 6A is formed of a cord ply in which an array of carcass cords arranged in parallel is covered with a topping rubber, and the carcass cord is disposed at an angle of 70 to 90 degrees with respect to the tire equator C. As the carcass cord, a steel cord is preferably adopted.

  A bead apex rubber 8 extending in a tapered shape from the bead core 5 to the outer side in the tire radial direction is disposed between the main body portion 6a and the folded portion 6b of the carcass ply 6A, and the bead portion 4 is appropriately reinforced.

  The belt layer 7 includes, for example, an innermost belt ply 7A in which steel belt cords are arranged at an angle of, for example, about 60 ± 10 degrees with respect to the tire equator C; It is composed of four layers including belt plies 7B, 7C and 7D arranged at a small angle of about 35 degrees. Further, the belt layer 7 can enhance belt rigidity by providing one or more places where the belt cords cross each other between the plies, and strongly reinforces almost the entire width of the tread portion 2.

  As shown in an enlarged view in FIG. 2, the bead core 5 is formed in a substantially hexagonal cross section by winding a bead wire 11 having a circular cross section continuously in, for example, a multistage multi-row. For example, a steel cord is preferably used for the bead wire 11. However, the bead core 5 may be formed as an integrally molded product.

  A wrapping layer 12 is disposed on the bead core 5 of the present embodiment so as to surround the outer periphery thereof. As the wrapping layer 12, for example, various layers such as a rubber layer made only of a rubber material and a canvas layer made of a rubberized canvas cloth are appropriately adopted. Such a wrapping layer 12 serves to prevent the bead wire 11 from being loosened.

  Further, the bead core 5 of the present embodiment includes a tire radial inner surface 5a extending along the bottom surface 4a of the bead portion 4, a tire radial outer surface 5b facing the inner surface 5a, and a tire shaft extending therebetween. The inner side of the tire axial direction 5c that protrudes and bends in a lateral V shape toward the inner side in the tire axial direction and the inner side surface 5a and the outer side surface 5b are joined on the outer side in the tire axial direction and the outer side in the tire axial direction. It is formed in a flat hexagonal shape having a flat cross section having a tire axially outer surface 5d that protrudes and bends in a lateral V shape. Such a bead core 5 is excellent in form stability and helps to improve bead durability.

  The bottom surface 4a of the bead portion 4 is a section from a bead toe 4t that is an inner end of the bead portion in the tire axial direction to a bead heel point 4h that is an outer end of the bead portion 4 in the tire axial direction. Further, the bead heel point 4h is determined as an intersection with a bead base line BL that is a tire axial line passing through the position of the rim diameter in a normal state.

  The rim R of the present embodiment includes a rim sheet Rs that receives the bottom surface 4a of the bead portion 4, and a rim flange that protrudes from the outer end of the rim sheet Rs in the tire axial direction while smoothly curving outward in the tire radial direction and outward in the tire axial direction. And Rf.

  The rim seat Rs is a 15-degree taper rim inclined at an angle θr of about 15 degrees from the inner side in the tire axial direction toward the outer side toward the outer side in the tire radial direction. Note that “approximately 15 degrees” allows an error in manufacturing, and may be in a range of 15 degrees ± 1 degree.

  In the tire 1 of the present embodiment, a normal load shown in FIG. 3A and a normal load shown in FIG. 3B in a normal load state in which a normal load is loaded and grounded at a camber angle of 0 degrees. In both cases, the angle θ1 formed by the inner side surface 5a of the bead core 5 and the rim seat surface 13 which is the outer surface of the rim seat Rs is limited to 0 ° ± 3 °.

  Here, the “regular load” is a load determined by each standard for each tire in a standard system including the standard on which the tire is based. “JATMA” is “maximum load capacity”, and “TRA”. The maximum value listed in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES”. If ETRTO, “LOAD CAPACITY”.

  As shown in FIG. 2, when the bead core 5 is formed of a wound body of the bead wire 11, the inclination of the inner side surface 5a of the bead core 5 is a common tangent line SL passing through each bead wire 11 aligned with the inner side surface 5a. Determined by When the common tangent line SL cannot be drawn, for convenience, among the bead wires 11 arranged on the inner surface 5a, the inner bead wire 11ai positioned on the innermost side in the tire axial direction and the outermost position positioned on the outermost side in the tire axial direction. It is specified by a tangent line in contact with the bead wire 11ao.

  As shown in FIGS. 3A and 3B, such a bead core 5 maintains a large fitting pressure of the bead portion 4 with respect to the rim R in a wide range both in a normal state and a standard load load state. it can. Therefore, the tire 1 of the present invention suppresses the rotation of the bead core 5 and effectively increases the bending rigidity of the bead portion 4 during traveling, thereby improving bead durability and rolling resistance performance.

  In the conventional heavy load tire, even when the angle θ1 formed by the inner side surface 5a of the bead core 5 and the rim seat surface 13 which is the outer surface of the rim seat Rs is 0 ° ± 3 ° in a normal state, The bead core 5 was rotated by the action of the load, and the angle θ1 was not maintained at 0 ° ± 3 °.

  However, as a result of various experiments and analyzes by the inventors, as shown in FIG. 4A, when the bead core 5 is formed, the inner surface 5a is oriented in the direction in which the inner diameter increases toward the outer side in the tire axial direction. And an angle θc of 20 ° ± 2 °, preferably 20 ° ± 1 °, more preferably 20 ° with respect to the tire axial direction line, both in the normal state and the standard weighted load state It was found that the angle θ1 can be within a range of 0 ° ± 3 °.

  Further, in addition to the angle θc of the inner side surface 5a of the bead core 5, as shown in FIG. 4 (b), at least the bead core 5 of the inner side surface 5a and the bottom surface 4a of the bead portion 4 in the free state of the tire. The angle θa between the inner side surface 5a and the inner bottom surface 4a1 positioned inward in the tire radial direction is preferably 0 ° or more, more preferably 3 ° or more, and it is formed to be 10 ° or less, more preferably 7 ° or less. It is also important that

  As described above, the tire 1 including the bead core 5 whose inner surface 5a has the angle θc of 20 degrees ± 2 degrees is assembled to the rim R and has a normal internal pressure of 5 as indicated by a solid line in FIG. % Of the inner surface 5a of the bead core 5 with respect to the tire axial direction in a no-load state in which the internal pressure is filled (% after filling the normal internal pressure, and the internal pressure is reduced to 5% of the normal internal pressure), the rim seat of the rim R It becomes larger than the angle θr of the surface 13 with respect to the tire axial direction.

  For this reason, the angle θ1 (θc−θr) formed between the inner side surface 5a of the bead core 5 and the rim seat surface 13 is about 5 ° ± 3 °, more preferably about 5 ° ± 2 °. In the present specification, the angles θc and θr are positive in the direction of inclination in which the outer shape increases toward the outer side in the tire axial direction.

  Next, when the normal internal pressure is filled, the bead core 5 rotates clockwise in the drawing by the tensile force F2 of the carcass ply 6A outward in the tire radial direction, as indicated by a virtual line in FIG. As a result, the angle θc of the inner side surface 5a of the bead core 5 is reduced, and the angle θ1 formed by the inner side surface 5a and the rim seat surface 13 is 0 ° ± 3 °, preferably 0 ° ± 2 °, more preferably 0 ° ± 1. Decrease to a degree.

  Further, in the tire 1 of the present embodiment, as shown in FIGS. 3A and 3B, even when the normal load is applied in a normal state, the angle θ1 does not substantially change and remains as it is. The angle can be maintained.

  When the bead core 5 as described above is used, it is necessary to further analyze why the angle θ1 falls within the range of 0 ° ± 3 ° in both the normal state and the standard load state. As one cause, it is presumed that the region where the fitting pressure between the bottom surface 4a of the bead portion 4 and the rim seat surface 13 is high increases.

  FIG. 6 shows the bead portion 4 and the rim R in a normal state for a heavy-duty tire (11R22.5) in which the angle θc of the inner surface of the bead core is 15 degrees (comparative product) and 20 degrees (example product). The result of having measured the fitting pressure (contact pressure) of each is shown. In FIG. 6B, the vertical axis indicates the fitting pressure, and the horizontal axis indicates the position of the contact portion between the bottom surface 4a of the bead portion 4 and the rim seat surface 13 of the rim R shown in FIG. The larger the value, the inner side in the tire axial direction (bead toe 4t side).

  The fitting pressure was measured by a surface pressure distribution measurement system I-SCAN (manufactured by Nitta Corporation) in the normal state. As is clear from FIG. 6B, it can be seen that in the tire 1 of the present embodiment, a portion with a high fitting pressure spreads toward the bead toe 4t side. It is considered that such a change in the fitting pressure distribution contributes to the maintenance of the angle θ1 (shown in FIG. 4) as described above.

  As shown in FIG. 3B, originally, in the standard load state, the side wall portion 3 is bent so as to protrude outward in the tire axial direction, and accordingly, the outside of the folded portion 6b of the bead portion 4 is bent. The rubber portion 4o is pressed outward in the tire radial direction by the rim flange Rf. By the pressing of the rubber, the folded portion 6b of the carcass ply 6A is also pushed outward in the tire radial direction, and as a result, a tensile force F1 that rotates the bead core 5 counterclockwise in the drawing is generated.

  However, like the tire 1 of the present embodiment, the fitting pressure between the bottom surface 4a of the bead portion 4 and the rim seat surface 13 is increased over a wide range, particularly on the bead toe 4t side, thereby overcoming the tensile force F1 of the carcass ply 6A. Presumed to prevent rotation.

  As described above, the tire 1 according to this embodiment can rotate the bead core 5 even when the tire rolls because the bead core 5 can exhibit an excellent fitting force to the normal rim R even in a normal state and a normal load load state. Can be suppressed. Therefore, the tire 1 can prevent the rotation of the bead core 5 and suppress the movement of the bead portion 4, prevent damage to the bead portion 4 and energy loss, and improve bead durability and rolling resistance performance.

  In order to exhibit the above action more effectively, the angle θ1 is preferably 0 degree ± 2 degrees, more preferably 0 degree ± 1 degree, and further preferably 0 degree in a normal state and a standard load application state. It is desirable.

  As shown in FIG. 1, in the normal state, the height Ha of the bead core 5 from the bead base line BL can be set as appropriate. However, if the height Ha is small, the rubber thickness W2 between the bead core 5 and the rim R cannot be sufficiently secured, and cracks may occur in the bottom surface 4a of the bead portion 4 and the like. On the other hand, if the height Ha is too large, the fitting pressure to the rim R may not be sufficiently increased, and problems such as rim detachment are likely to occur. From such a viewpoint, the height Ha is preferably 0.40 times or more, more preferably 0.5 times or more, and further preferably 0.55 times or more the height Hb of the rim flange Rf. Preferably, it is 0.85 times or less, more preferably 0.75 times or less, and still more preferably 0.70 times or less.

  Further, as shown in FIG. 2, when the ratio (AW / CW) between the maximum width CW of the bead core 5 and the maximum thickness AW perpendicular to the maximum width CW is small in the normal state, the rigidity of the bead core 5 is reduced. There is a possibility that it cannot be secured sufficiently. Conversely, even if the ratio (AW / CW) is large, the pressure between the bottom surface 4a of the bead portion 4 and the rim seat surface 13 may not be increased over a wide range. From such a viewpoint, the ratio (AW / CW) is preferably 0.2 or more, more preferably 0.30 or more, still more preferably 0.40 or more, and preferably 0.7 or less. Preferably it is 0.65 or less, more preferably 0.60 or less.

  Further, in a normal state, the ratio of the tire axial distance H from the inner end 5i of the bead core 5 in the tire axial direction to the bead heel point 4h to the width G of the bottom surface 4a of the bead portion 4 in the tire axial direction (H / If G) is small, the rubber volume on the bead toe 4t side becomes excessively large, which may reduce the bead durability. On the other hand, even if the ratio (H / G) is large, the rubber volume on the bead toe 4t side becomes excessively small, and there is a possibility that defects such as cracks may occur. From such a viewpoint, the ratio (H / G) is preferably 0.60 or more, more preferably 0.70 or more, and preferably 0.94 or less, more preferably 0.85 or less. .

  From the same viewpoint, the ratio (CW / G) between the maximum width CW of the bead core 5 and the width G in the tire axial direction of the bottom surface 4a of the bead portion 4 is preferably 0.50 or more, more preferably 0.60 or more. Desirably, it is preferably 0.85 or less, more preferably 0.75 or less.

  As shown in FIG. 1, the bead apex rubber 8 of the present embodiment includes an inner apex rubber 8A disposed on the inner side in the tire radial direction and an outer apex rubber 8B disposed on the outer side in the tire radial direction of the inner apex rubber 8A. It consists of.

  The inner apex rubber 8A has an inner surface 8Aa in the tire radial direction connected to the bead core 5 and extends outwardly in the tire radial direction. Further, the inner side surface 8Ai and the outer side surface 8Ao of the inner apex rubber 8A in the tire axial direction are curved in an arc shape that is convex inward in the tire axial direction. The complex elastic modulus E * 1 of the inner apex rubber 8A is set to 40 to 65 MPa.

  Further, the outer apex rubber 8B is disposed in a region surrounded by the outer surface 8Ao of the inner apex rubber 8A, the main body portion 6a of the carcass ply 6A, and the folded portion 6b, and extends outwardly in the tire radial direction. The complex elastic modulus E * 2 of the outer apex rubber 8B is set to 3 to 5 MPa, which is smaller than the complex elastic modulus E * 1 of the inner apex rubber 8A.

  Such a bead apex rubber 8 can relieve the shear stress acting on the folded portion 6b of the carcass ply 6A in the low-elasticity outer apex rubber 8B while ensuring sufficient bending rigidity when the bead portion 4 is deformed. Etc. can be effectively prevented.

Further, in the present embodiment, the height H1 of the inner apex rubber 8A in the tire radial direction from the bead base line BL, the height H2 of the outer apex rubber 8B in the tire radial direction from the bead base line BL, and the bead apex rubber 8 The thickness W1 and the tire cross-section height Ho at the turn-up end 6be of the turn-up portion 6b of the carcass ply 6A satisfy the following relationship.
0.1 ≦ H1 / Ho ≦ 0.3
0.35 ≦ H2 / Ho ≦ 0.55
0.1 ≦ W1 / H2 ≦ 0.3

  Since such a bead apex rubber 8 can secure the bending rigidity of the bead portion 4 and can reduce its rubber volume compared to the conventional one, heat generation of the bead portion 4 can be effectively suppressed, and rolling resistance performance can be improved. It can be further improved. Further, the reduction in the rubber volume of the bead apex rubber 8 can alleviate the distortion that tends to concentrate on the sidewall portion 3, and can prevent damage such as cracks in the sidewall portion 3.

  Note that the decrease in the bending rigidity of the bead portion 4 due to the decrease in the rubber volume of the bead apex rubber 8 is part of the improvement in the bead durability due to the bead core 5, and thus the bead durability is maintained.

  When the ratio of the height H1 of the inner apex rubber 8A to the tire cross-section height Ho (H1 / Ho) exceeds 0.3, the thickness W1 of the outer apex rubber 8B decreases, and the carcass ply 6A The distortion of the folded end 6be of the folded portion 6b cannot be sufficiently relaxed, and the bead durability may be lowered. Conversely, if the ratio (H1 / Ho) is less than 0.1, the bending rigidity of the bead portion 4 cannot be sufficiently increased, and the bead durability may be reduced. From such a viewpoint, the ratio (H1 / Ho) is more preferably 0.25 or less, and more preferably 0.15 or more.

  Furthermore, if the ratio (H2 / Ho) between the height H2 of the outer apex rubber 8B and the tire cross-section height Ho exceeds 0.55, there is a possibility that strain is concentrated on the sidewall portion 3 to cause cracks. In addition, there is a possibility that the heat generation of the bead portion 4 is increased and the rolling resistance performance is deteriorated. Conversely, if the ratio (H2 / Ho) is less than 0.35, the bending rigidity of the bead portion 4 cannot be sufficiently increased, and the bead durability may be lowered. From such a viewpoint, the ratio (H2 / Ho) is more preferably 0.50 or less, and more preferably 0.40 or more.

  From the same viewpoint, the ratio (W1 / H2) between the thickness W1 of the bead apex rubber 8 and the height H2 of the outer apex rubber 8B is more preferably 0.25 or less, and more preferably 0.00. 15 or more is desirable.

  Moreover, when the complex elastic modulus E * 1 of the inner apex rubber 8A is less than 40 MPa, the bending rigidity of the bead portion 4 may not be sufficiently increased. On the contrary, if the complex elastic modulus E * 1 exceeds 65 MPa, the heat generation of the bead portion 4 cannot be sufficiently suppressed, and the rolling resistance performance may not be improved. From such a viewpoint, the complex elastic modulus E * 1 is more preferably 50 MPa or more, and more preferably 60 MPa or less.

  From the same viewpoint, the complex elastic modulus E * 2 of the outer apex rubber 8B is more preferably 3.5 MPa or more, and more preferably 4.5 MPa or less.

  Further, in the present embodiment, the side wall rubber 3G extending from the outer side in the tire axial direction of the carcass 6 to the inner and outer sides in the tire radial direction is disposed on the inner side of the carcass 6 and on the outer side of the tire rubber surface. And an outer rubber portion 17 that forms Further, the loss tangent tan δ1 of the inner rubber portion 16 is set to be smaller than the loss tangent tan δ2 of the outer rubber portion 17.

  Thus, since the side wall rubber 3G can effectively prevent heat generation and energy loss in the inner rubber part 16, it can reduce rolling resistance due to bending distortion of the side wall part 3. Accordingly, the side wall rubber 3G can improve the rolling resistance performance more effectively by the synergistic effect of the bead core 5 and the bead apex rubber 8.

  On the other hand, since the loss tangent tan δ2 of the outer rubber portion 17 is set larger than the loss tangent tan δ1 of the inner rubber portion 16, it is possible to maintain the rigidity of the sidewall portion 3 and suppress the occurrence of damage such as cracks. .

  If the loss tangent tan δ1 of the inner rubber portion 16 is large, the rolling resistance performance may not be sufficiently improved. On the other hand, even if the loss tangent tan δ1 is too small, there is a possibility that damage such as cracks may occur due to a decrease in rigidity of the sidewall portion 3. From such a viewpoint, the loss tangent tan δ1 is preferably 0.06 or less, more preferably 0.05 or less, and preferably 0.03 or more, more preferably 0.04 or more.

  Further, if the loss tangent tan δ2 of the outer rubber portion 17 is small, the sidewall portion 3 may be damaged such as cracks. On the contrary, even if the loss tangent tan δ2 is too large, the rigidity of the sidewall portion 3 is excessively increased, and the rolling resistance performance may not be sufficiently improved. From such a viewpoint, the loss tangent δ2 of the outer rubber portion 17 is preferably 0.07 or more, more preferably 0.08 or more, preferably 0.12 or less, more preferably 0.11 or less. Is desirable.

  The inner rubber portion 16 extends from the inner side surface 8Bi of the outer apex rubber 8B in the tire axial direction to the outer side in the tire radial direction along the main body portion 6a of the carcass ply 6A, and an outer end 16o thereof is near the outer end 7t of the belt layer 7. Terminate with Such an inner rubber portion 16 can reduce heat generation and energy loss over a wide range of the sidewall portion 3, and can improve rolling resistance performance.

  If the length L1 of the inner rubber portion 16 in the tire radial direction between the inner end 16i and the outer end 16o in the tire radial direction is small, the above-described action may not be sufficiently exhibited. Conversely, even if the length L1 is too large, the rigidity of the tread portion 2 and the bead portion 4 may be reduced. From such a viewpoint, the length L1 is preferably 50% or more, more preferably 60% or more, and preferably 80% or less, more preferably 70% or less of the tire cross-section height Ho.

  The outer rubber portion 17 includes an outer surface 8Bo in the tire axial direction of the outer apex rubber 8B and an outer surface 18o in the tire radial direction of the chafer rubber 18 disposed on the bead portion 4, and an outer surface in the tire axial direction of the inner rubber portion 16. And the outer end 17o covers the side end surface 2Go in the tire axial direction of the tread rubber 2G and terminates without reaching the tread ground contact end 2t. Such an outer rubber portion 17 can increase the rigidity of the sidewall portion 3 over a wide range extending to the tread portion 2.

  If the length L2 in the tire radial direction between the inner end 17i and the outer end 17o in the tire radial direction of the outer rubber portion 17 is small, there is a possibility that the above-described effect cannot be sufficiently exhibited. On the other hand, even if the length L2 is too large, the outer rubber portion 17 may come into contact with the rim R and cause damage due to running. From such a viewpoint, the length L2 is preferably 70% or more of the tire cross-section height Ho, more preferably 75% or more, and preferably 90% or less, more preferably 85% or less.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

A heavy-duty pneumatic tire having the basic structure shown in FIG. 1 and provided with a bead core, a bead apex rubber, and a side wall rubber having the specifications shown in Table 1 was manufactured, and their performance was tested.
The common specifications are as follows.
Tire size: 11R22.5
Rim size: 7.50 x 22.5
Rim flange height Hb: 12.7 mm
Tire cross section height Ho: 240 mm
Angle θr of the rim seat surface of the regular rim with respect to the tire axial direction: 15 degrees Inner rubber portion length L1: 140 mm
Length L2 of outer rubber part 17: 190 mm
Ratio (L1 / Ho): 58.3%
Ratio (L2 / Ho): 80%
The test method is as follows.

<Bead durability 1>
Using a drum testing machine, each sample tire is assembled to the rim, filled with an internal pressure of 800 kPa, and run at a speed of 30 km / h under the condition of a load of 88.26 kN until the bead part is damaged. The running time of was measured. A result is an index | exponent which sets the comparative example 1 to 100, and shows that it is excellent in durability, so that a numerical value is large.

<Bead durability 2>
After heating the rim flange of the rim to 130 degrees, each test tire was assembled into a rim and evaluated in the same manner as in the bead durability 1.

<Rolling resistance performance>
Using a rolling resistance tester, rolling resistance was measured under the following conditions. Evaluation was made with an index with Comparative Example 1 as 100. The smaller the value, the smaller the rolling resistance and the better.
Internal pressure: 800 kPa
Load: 29.42kN
Speed: 80km / h

<Sidewall durability (SFC performance)>
Each test tire is assembled on the rim, filled with 800 kPa of internal pressure, mounted on the rear wheel of a 10-pile 2-D car, and the regular road / highway in the fixed volume state, the groove depth of the tread part Was run until it reached 20% of the new product, and the number and size of cracks in the sidewall were visually confirmed. Evaluation was made with an index with Comparative Example 1 as 100. The smaller the numerical value, the smaller the number of cracks.
The test results are shown in Table 1.

  As a result of the test, it was confirmed that the heavy-duty pneumatic tire of the example can improve rolling resistance performance while maintaining bead durability.

1 Pneumatic tire for heavy loads 5 Bead core 8 Bead apex rubber R rim

Claims (9)

A carcass made of a carcass ply provided with a series of folded portions that folds the bead core around from the inner side to the outer side in the tire axial direction on the main body part from the tread part through the sidewall part to the bead core of the bead part;
A heavy-duty pneumatic tire comprising a bead apex rubber extending from the bead core in a tapered shape between the main body portion and the folded portion,
The bead core is substantially hexagonal in cross section having an inner surface in the tire radial direction extending along the bottom surface of the bead portion,
In the normal state in which the rim is assembled to the normal rim and the normal internal pressure is filled, and in the normal load state in which a normal load is applied to the normal state and the camber angle is 0 degrees,
The angle formed by the inner side surface of the bead core and the rim seat surface of the regular rim is 0 ° ± 3 °,
The bead apex rubber is arranged on the inner side in the tire radial direction and has an inner apex rubber having a complex elastic modulus E * 1 of 40 to 65 MPa, and the inner apex rubber is arranged on the outer side in the tire radial direction and has a complex elastic modulus E * 2 It consists of 3-5 MPa outer apex rubber,
The height H1 of the inner apex rubber from the bead base line in the tire radial direction, the height H2 of the outer apex rubber from the bead base line in the radial direction of the tire, and the folded end of the folded portion of the carcass ply of the bead apex rubber The heavy-duty pneumatic tire is characterized in that the thickness W1 and the tire cross-section height Ho satisfy the following relationship.
0.1 ≦ H1 / Ho ≦ 0.3
0.35 ≦ H2 / Ho ≦ 0.55
0.1 ≦ W1 / H2 ≦ 0.3 The sidewall rubber disposed on the outer side in the tire axial direction of the carcass includes an inner rubber portion disposed on the carcass side, and an outer rubber portion disposed on the outer side and forming a tire outer surface,
The heavy duty pneumatic tire according to claim 1, wherein a loss tangent tan δ1 of the inner rubber portion is smaller than a loss tangent tan δ2 of the outer rubber portion. The heavy duty pneumatic tire according to claim 2, wherein the loss tangent tan δ1 of the inner rubber portion and the loss tangent tan δ2 of the outer rubber portion satisfy the following relationship.
0.03 ≦ tan δ1 ≦ 0.06
0.07 ≦ tan δ2 ≦ 0.12   4. The heavy duty pneumatic engine according to claim 1, wherein, in the normal state, the height of the center of gravity of the bead core from the bead base line is 0.40 to 0.85 times the height of the rim flange. tire.   In the normal state, the bead core has a ratio (AW / CW) of a maximum width CW of the bead core parallel to the rim seat surface to a maximum thickness AW perpendicular to the maximum width of 0.2 to 0.7. The heavy duty pneumatic tire according to any one of claims 1 to 4. The bead portion includes a bead apex rubber extending in a tapered shape from an outer surface in the tire radial direction of the bead core to the outer side in the tire radial direction,
The pneumatic tire for heavy loads according to any one of claims 1 to 5, wherein the bead apex rubber has a complex elastic modulus E * 3 of 60 to 80 MPa.   In the normal state, the ratio (H / G) of the tire axial distance H from the inner end of the bead core in the tire axial direction to the bead heel point and the width G of the bottom surface of the bead portion in the tire axial direction is 0. The heavy duty pneumatic tire according to any one of claims 1 to 6, which is 60 to 0.94.   The ratio (CW / G) between the maximum width CW of the bead core and the width G in the tire axial direction of the bottom surface of the bead portion in the normal state is 0.50 to 0.85. The heavy duty pneumatic tire according to any one of the above.   In an unloaded state in which a rim is assembled on a normal rim and filled with an internal pressure of 5% of the normal internal pressure, the angle θc with respect to the tire axial direction line of the inner surface of the bead core is an angle with respect to the tire axial direction line of the rim seat surface The heavy duty pneumatic tire according to any one of claims 1 to 8, wherein the tire is larger than θr and the difference θc-θr is 2 to 8 degrees.

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