JP2007230400A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance rolling resistance performance while ensuring excellent bead durability. <P>SOLUTION: A bead core 5 comprises a core body 10 wound with a bead wire 5s; and a lapping rubber layer 11 for surrounding its periphery. A bead apex rubber 8 standing up from the bead core 5 comprises a hard lower apex part 12 and a soft upper apex part 13, the lower apex part 12 forms an L shape cross section comprising a bottom piece part 12B along an outer surface SU in a tire radial direction of the bead core 5 and a standing piece part 12A along a ply body part 6a of a carcass 6. Respective rubber hardness Hs1, Hs2 of the lapping rubber layer 11 and the lower apex part 12 are made to 76-88°. Height h1 in a radial direction of the standing piece part 12A is 15 mm or more and thickness t of the standing piece part 12A at 10 mm height position P0 is made to a range of 0.5-2.5 mm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pneumatic tire that is particularly suitable as a heavy-duty tire and can improve rolling resistance performance while ensuring excellent bead durability.

  In a pneumatic tire, when a load is applied, the bead portion is deformed so as to fall outward in the tire axial direction, and at that time, a compressive strain is generated on the side of the carcass ply folded portion. By repeating this compressive strain, the carcass cord of the ply turn-up portion is cord loose and induces bead damage. This bead damage is more likely to occur in heavy load tires such as trucks and buses with heavy loads.

  Therefore, conventionally, in heavy-duty tires, as shown in FIG. 6, a bead apex rubber b disposed between a ply main body portion a1 and a ply turn-back portion a2 of a carcass is provided in a radially inwardly lower direction made of hard rubber. A structure divided into an apex portion b1 and a radially outward upper apex portion b2 made of soft rubber is widely adopted (see, for example, Patent Document 1). In this structure, bead deformation is reduced by the hard lower apex portion b1, the compression strain is kept low, and the soft upper apex portion b2 can relieve stress on the carcass cord due to the compression strain. Code loose can be suppressed.

JP 2002-205508 A

  On the other hand, from the viewpoint of protecting environmental resources, in recent years, there has been a strong demand for improving rolling resistance performance even in the heavy duty tire. For this purpose, it is proposed to reduce the bead apex rubber b, in particular, the rubber volume of the hard lower apex portion b1 with a large energy loss. However, when the rubber volume of the lower apex part b1 is reduced, there arises a problem that the bead rigidity is lowered, the bead deformation amount is increased, and the bead durability is lowered.

  Therefore, the present inventor conducted research while paying attention to the wrapping rubber layer d disposed around the bead core c. As a result, when hard rubber is used for the wrapping rubber layer d, the lower apex portion b1 and the bead core c can be integrally coupled, and the force acting on the lower apex portion b1 is efficiently applied to the bead core c. It has been found that the bead deformation can be effectively suppressed integrally with the bead core c so that it can be transmitted well. It has also been found that the rubber volume of the lower apex portion b1 can be reduced, and the rolling resistance performance can be improved while ensuring high bead durability.

  That is, an object of the present invention is to provide a pneumatic tire capable of improving rolling resistance performance while ensuring high bead durability based on the use of hard rubber for the rubber layer for wrapping.

In order to achieve the above object, the invention of claim 1 of the present application includes a carcass made of a carcass ply having a ply body part extending from a tread part to a bead core of a bead part through a sidewall part, and radially outward from the bead core. A pneumatic tire comprising a bead apex rubber having a substantially triangular cross section extending,
The bead core is composed of a ring-shaped core body in which bead wires are wound in multiple rows and stages, and a wrapping rubber layer that prevents the bead wire from being separated by surrounding the core body,
The bead apex rubber is composed of a radially inner lower apex portion made of hard rubber, and a radially outer upper apex portion made of softer rubber than the lower apex portion,
The lower apex portion includes a bottom piece portion extending along the tire radial upper surface of the bead core, and a standing piece portion rising from a tire axial inner end of the bottom piece portion and extending outward in the tire radial direction along the ply main body portion. It has a cross-sectional L-shape,
Moreover, the rubber hardness Hs1 of the wrapping rubber layer and the rubber hardness Hs2 of the lower apex portion are in the range of 76 to 88 °,
The standing piece portion has a radial height h1 of 15 mm or more from a radial outer end of the core body at a radially outer end thereof,
Further, the thickness t of the upright piece portion sequentially decreases outward in the radial direction, and the upright piece at the height position P0 that is separated from the radially outer end of the core body by 10 mm radially outwardly. The thickness t0 of the part is in the range of 0.5 to 2.5 mm.

According to a second aspect of the present invention, the upper apex portion has a rubber hardness Hs3 of 50 to 60 ° and a difference (Hs2−Hs3) from the rubber hardness Hs2 of 20 to 38 °.
In the invention of claim 3, the wrapping rubber layer has a thickness i of 0.2 to 2.5 mm.
According to a fourth aspect of the present invention, the rubber hardness Hs2 of the lower apex portion is greater than the rubber hardness Hs1 of the wrapping rubber layer.
Further, the invention of claim 5 is characterized in that the thickness T of the bottom piece from the upper surface in the tire radial direction of the bead core decreases sequentially toward the outer side in the tire axial direction.
According to a sixth aspect of the present invention, the carcass ply includes a ply turn-up portion that is continuous with the ply main body portion and is turned around the bead core, and the ply turn-up portion is an outer surface in the tire axial direction of the upper apex portion. It is characterized by extending along the outer surface and being interrupted at the outer surface.
According to a seventh aspect of the present invention, the carcass ply includes a ply folding portion that is continuous with the ply body portion and is folded around the bead core, and the ply folding portion passes through the lower apex portion and the ply body. It is characterized by having a winding part extending toward the part.

  In the present specification, the rubber hardness means a durometer A hardness measured by a durometer type A based on JIS-K6253. Unless otherwise specified, the dimensions and the like of each part of the tire are values specified in a 50 kPa filling state in which the tire is assembled on a regular rim and filled with an internal pressure of 50 kPa. The “regular rim” is a rim determined by the standard for each tire in the standard system including the standard on which the tire is based. For example, JAMMA is a standard rim, TRA is “Design Rim”, or ETRTO. Then means "Measuring Rim".

  In the present invention, as described above, the bead core wrapping rubber layer is formed of a hard rubber having the same level as the lower apex portion. Therefore, the bead core and the lower apex portion can be integrally and firmly bonded via the lapping rubber layer. As a result, especially when the lower apex portion is L-shaped and the rubber volume is reduced, it becomes possible to effectively suppress bead deformation integrally with the bead core while improving rolling resistance performance. High bead durability can be secured.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a 50 kPa filling state when the pneumatic tire of the present invention is a heavy duty tire for trucks and buses, and FIGS. 2 and 3 are cross-sectional views showing an enlarged bead portion thereof. .

  In FIG. 1, a pneumatic tire 1 is disposed on a carcass 6 that extends from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, and on the radially outer side of the carcass 6 and inside the tread portion 2. A belt layer 7;

  The belt layer 7 is formed of two or more belt plies using a belt cord, and usually three to four belt plies in the case of a heavy duty tire. In this example, the belt layer 7 includes a first belt ply 7A on the innermost side in the radial direction in which steel cords are arranged at an angle of 60 ± 15 ° with respect to the tire circumferential direction, and 10 to 10 with respect to the tire circumferential direction. A case of a four-sheet structure including second to fourth belt plies 7B to 7D arranged at a small angle of 35 ° is illustrated. The belt plies 7 </ b> A to 7 </ b> D are provided with one or more places where the belt cords cross each other between the plies, and are superposed to enhance belt rigidity and reinforce the tread portion 2 with a tagging effect.

  The carcass 6 is formed of one or more, in this example, one carcass ply 6A in which carcass cords are arranged at an angle of 70 to 90 ° with respect to the tire circumferential direction. A steel cord is suitable as the carcass cord, but an organic fiber cord such as nylon, rayon, polyester, aromatic polyamide or the like is also used if necessary. The carcass ply 6 </ b> A includes a series of ply folding portions 6 b that are folded from the inner side to the outer side in the tire axial direction around the bead core 5 on both sides of the ply body portion 6 a that extends between the bead cores 5 and 5.

  As shown in FIG. 2, the bead core 5 includes, for example, a ring-shaped core body 10 having a polygonal cross section in which steel bead wires 5 s are wound in multiple rows and stages, and the bead wires 5 s are surrounded by surrounding the core body 10. And a rubber layer 11 for wrapping that prevents the above-mentioned variation.

  As the wrapping rubber layer 11, a rubber layer formed only of a rubber material and a rubber layer containing a wrapping cord in which a wrapping cord is embedded in the rubber material can be suitably employed. As the rubber of the wrapping rubber layer 11, a hard rubber having a rubber hardness Hs1 in the range of 76 to 88 ° is used. The conventional lapping rubber layer has a rubber hardness of 70 ° or less, and in the present invention, a hard rubber is used as compared with the conventional rubber layer. Further, the thickness i (shown in FIG. 3) of the wrapping rubber layer 11 is preferably in the range of 0.2 to 2.5 mm as in the conventional case.

  The bead core 5 includes a radial lower surface SL facing the rim sheet Js surface of the rim J, a radial upper surface SU parallel to the lower surface SL, and a tire axial outer surface that connects between the outer edges in the tire axial direction of the lower surface SL and the upper surface SU. The cross-sectional polygonal shape which has a core outer peripheral surface which consists of SO and tire axial direction inner side surface SI which connects between the tire axial direction inner edges of said lower surface SL and upper surface SU is made. In particular, in this example, the case where the outer side surface SO and the inner side surface SI each have a flat hexagonal cross section made of a curved surface, and the lower surface SL is substantially parallel to the rim sheet Js. The fitting force with the rim J is increased over a wide range. In this example, the rim J is a tubeless 15 ° taper rim. Therefore, the lower surface SL is inclined at an angle of approximately 15 ° with respect to the tire axial line.

  Next, a bead apex rubber 8 having a substantially triangular cross section extending radially outward from the bead core 5 is disposed between the ply body portion 6a and the ply turn-up portion 6b of the carcass 6. The bead apex rubber 8 extends beyond the outer end 6be of the ply turn-up portion 6b outward in the radial direction. That is, the ply turn-up portion 6b extends along the tire axial direction outer surface of the bead apex rubber 8 and is interrupted at the outer surface. In this example, the radial height H1 from the bead base line BL of the outer end 8e of the bead apex rubber 8 is in the range of 26 to 50% of the tire cross-section height H0.

  The bead apex rubber 8 includes a radially inward lower apex portion 12 made of a hard rubber having a rubber hardness Hs2 in the range of 76 to 88 °, and a radially outer portion made of a softer rubber than the lower apex portion 12. The upper apex portion 13 is formed. In this example, the rubber hardness Hs3 of the upper apex portion 13 is in the range of 50 to 60 °, and the difference in hardness (Hs2−Hs3) from the rubber hardness Hs2 is 20 to 38 °, preferably 26 to 38. °. Thereby, the stress which acts on a carcass cord can be relieve | moderated with respect to the compressive strain by the side of the ply folding | turning part 6b accompanying bead deformation.

  The lower apex portion 12 rises from the inner end in the tire axial direction of the bottom piece portion 12B along the tire radial upper surface SU of the bead core 5 and outwards in the tire radial direction along the ply main body portion 6a. It is formed in an L-shaped cross section composed of a standing piece portion 12A that extends.

  Thus, in the present invention, first, the wrapping rubber layer 11 of the bead core 5 is formed of a hard rubber having the same level as that of the lower apex portion 12. Accordingly, the core body 10 and the lower apex portion 12 can be integrally and firmly bonded via the lapping rubber layer 11. Secondly, the lower apex portion 12 is formed in an L-shaped cross section having a standing piece portion 12A that rises along the ply main body portion 6a. As a result, the bead deformation falling to the outside in the tire axial direction can be effectively suppressed by integrating the lower apex portion 12 and the core body 10, and high bead durability can be secured. In addition, since the rubber lower volume is reduced such that the hard lower apex portion 12 having a large energy loss has an L-shaped cross section, the rolling resistance performance can be improved at the same time.

  In order to effectively exhibit such an effect, as shown in an enlarged view in FIG. 3, the radial height of the radially outer end of the standing piece 12A from the radially outer end of the core body 10 is shown. h1 is 15 mm or more. Further, the thickness t of the upright piece portion 12A is gradually decreased outward in the radial direction, and at a height position P0 that is separated from the outer radial end of the core body 10 by 10 mm radially outward. The thickness t0 of the upright piece 12A is in the range of 0.5 to 2.5 mm.

  Here, when the rubber hardness Hs1 of the wrapping rubber layer 11 is less than 76 °, the force acting on the lower apex portion 12 is not effectively transmitted to the core body 10, and the rubber hardness Hs2 of the lower apex portion 12 is 76. If it is less than 0 °, the lower apex portion 12 itself is easily deformed, and in any case, the effect of suppressing bead deformation is not achieved. Further, even when the height h1 of the upright piece 12A is less than 15 mm and the thickness t0 is less than 0.5 mm, the reinforcement by the lower apex portion 12 becomes insufficient, and the effect of suppressing bead deformation cannot be achieved. . Note that the radial height H2 from the bead base line BL at the radially outer end of the upright piece portion 12A may be 250% or more of the rim flange height Hf from the bead base line BL. To preferred. Further, as the thickness t of the upright piece portion 12A sequentially decreases radially outward, the rigidity step with the upper apex portion 13 is reduced, and the upright end portion 12A of the upright piece portion 12A is reduced in the radial direction. Damage from the starting point is suppressed.

  If the rubber hardness Hs1 of the wrapping rubber layer 11 is greater than 88 ° and the rubber hardness Hs2 of the lower apex portion 12 is greater than 88 °, the energy loss increases and the rolling resistance performance is sufficiently improved. Can not be. On the other hand, if the thickness t0 of the upright piece portion 12A is larger than 2.5 mm, the rubber volume of the lower apex portion 12 is not sufficiently reduced, and the rolling resistance performance is not sufficiently improved.

  From such a viewpoint, in the rubber hardness Hs1 and Hs2, the lower limit value is preferably set to 76 ° or more, and the upper limit value is preferably set to 88 ° or less. In the thickness t0, the lower limit value is more preferably 1.0 mm or more, and the upper limit value is more preferably 2.0 mm or less. The upper limit of the height h1 is preferably 30 mm or less from the viewpoint of rolling resistance performance.

  In the bottom piece 12B, the thickness T of the bead core 5 from the upper surface SU in the radial direction of the tire is sequentially decreased toward the outer side in the tire axial direction in order to reduce the rubber volume while exhibiting the effect of suppressing bead deformation. Is preferable.

  In order to further strengthen the connection between the lower apex portion 12 and the core body 10, the gap portion between the inner side surface SI of the bead core 5 and the ply turn-up portion 6b, and the outer side surface SO and the ply of the bead core 5. The rubber disposed in the gap between the folded portion 6b is preferably formed of rubber having the same composition as the lower apex portion 12, or the same rubber having a rubber hardness Hs (76 to 88 °).

  The wrapping rubber layer 11 and the lower apex portion 12 can be formed of rubber having the same composition. However, from the viewpoint of suppressing bead deformation, it is preferable that the rubber hardness Hs2 of the lower apex portion 12 is larger than the rubber hardness Hs1 of the wrapping rubber layer 11 (Hs2> Hs1).

  Next, reference numeral 20 in FIG. 2 denotes a bead reinforcing layer that surrounds the bead core 5 in a U shape via the carcass 6. The bead reinforcing layer 20 is formed of a steel cord ply in which steel reinforcing cords are arranged at an angle of 10 to 60 ° with respect to the tire circumferential direction, and is an inner portion extending along the inner side surface in the tire axial direction of the ply main body portion 6a. From the piece 20a, it passes through the inside of the bead core 5 in the radial direction and is formed in a U-shaped cross section having an outer piece 20b that rises radially outward along the outer side surface of the ply turn-up portion 6b. Thereby, the bead part 4 is reinforced. The radial height Da from the bead base line BL at the radially outer end of the inner piece 20a and the radial height Db from the bead base line BL at the radially outer end of the outer piece 20b are the rim, respectively. The flange height Hf is in the range of 150 to 300%, and if it is less than 150%, the reinforcing effect is insufficient. Conversely, if it exceeds 300%, the outer end of the inner piece 20a and the outer end of the outer piece 20b are damaged as starting points. Is likely to occur.

  Reference numeral 21 in FIG. 2 denotes a clinch rubber for preventing rim displacement, and is formed of, for example, rubber having a rubber hardness Hs4 of 70 to 79 ° and softer than the wrapping rubber layer 11 and having excellent wear resistance. In this example, the clinching rubber 21 includes a clinching base portion 21A that forms the outer surface of the bead portion 4 and rises from the bead heel portion to a height position that extends radially outward from the upper end of the rim flange. And a clinching bottom portion 21B extending from 21A to the bead toe portion. A flexible sidewall rubber 22 that forms the outer surface of the sidewall portion 3 is connected to the clinch base portion 21A via a boundary line K. In this example, the boundary line K is inclined radially outward from the bead heel portion to the outer surface of the bead portion 4. Accordingly, the clinch rubber 21 has a radially outermost point on the outer surface of the bead portion 4, and a height H3 of the outermost point from the bead base line BL is larger than the rim flange height Hf, and The lower apex portion 12 is set to be smaller than the radial height H2.

  Further, in this example, in order to suppress the carcass cord loose from the outer end 6be of the ply folding portion 6b, the ply folding portion 6b is sandwiched from inside and outside in the tire axial direction so as to cover and protect the outer end 6be. Rubber layers 23i and 23o are provided. The protective rubber layers 23i and 23o are made of rubber that is softer than the upper apex portion 13 and harder than the sidewall rubber 22, and relaxes and absorbs stress acting on the ply turn-up portion 6b, thereby suppressing the carcass cord loose. sell.

  FIG. 4 shows another embodiment of the present invention. In this example, the clinching rubber 21 has a boundary line K with the sidewall rubber 22 from the lower point 21a on the outer surface of the bead portion 4 to the outer surface of the bead apex rubber 8 or the outer surface of the protective rubber layer 23o. A case is shown in which the upper upper point 21b is inclined radially outward toward the inner side in the tire axial direction. The height H4 of the lower point 21a from the bead base line BL is larger than the rim flange height Hf. In this example, the height H4 is set smaller than the radial height H2 of the lower apex portion 12. is doing.

  FIG. 5 shows still another embodiment of the present invention. In this example, the ply turn-up portion 6b of the carcass 6 includes a main portion 30 that bends along the tire axial direction inner side surface SI, the radial direction lower surface SL, and the tire axial direction outer side surface SO of the bead core 5, and the main portion. 30, the bead core 5 has a so-called wind structure in which the vicinity of the upper surface SU in the radial direction of the bead core 5 includes a winding portion 31 that inclines toward the ply main body 6 a. The winding portion 31 passes through the lower apex portion 12 and is interrupted in the lower apex portion 12.

  In the wind structure, it is preferable that an auxiliary cord layer 33 for pressing the winding portion is formed on the outer side in the tire radial direction of the winding portion 31 in order to restrain the winding portion 31 and prevent springback of the carcass cord. . The auxiliary cord layer 33 is formed of a wound body in which a steel cord 33w is spirally wound in the tire circumferential direction, thereby suppressing a spring back without applying a type to the carcass cord, and reducing the strength of the cord due to the type. While preventing, the said winding part 31 can be stably hold | maintained at the intended shape.

  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 tire having a tire size of 11R22.5 having the structure shown in FIG. 1 was prototyped based on the specifications shown in Table 1, and the bead durability and rolling resistance performance of each sample tire were tested and compared. The specifications other than those listed in Table 1 are the same. In each tire, the bead apex rubber has a radial height H1 of 165% of the tire cross-section height H0, and the thickness i of the lapping rubber layer is 1.0 mm. It is.

(1) Bead durability:
Using a drum tester, the bead was damaged by running at a speed of 30 km / h under conditions of rim (7.50 × 22.5), internal pressure (700 kPa), and longitudinal load (3 times 27.25 kN). The running time until it was measured was measured.

(2) Rolling resistance performance;
Using a rolling resistance tester, rolling resistance was measured under the conditions of rim (7.50 × 22.5), internal pressure (700 kPa), longitudinal load (27.25 kN), and speed (80 km / h). The tires are shown as an index with 100 as the tire. A smaller index is better.

  As shown in the table, it was confirmed that the tires of Examples could improve rolling resistance performance while ensuring high bead durability.

It is sectional drawing which shows one Example of the pneumatic tire of this invention. It is sectional drawing which expands and shows the bead part. It is sectional drawing which expands and shows a bead part further. It is sectional drawing which shows the other Example of a bead part. It is sectional drawing which shows the further another Example of a bead part. It is sectional drawing explaining the conventional bead structure.

Explanation of symbols

2 Tread part 3 Side wall part 4 Bead part 5 Bead core 5s Bead wire 6 Carcass 6A Carcass ply 6a Ply main part 6b Ply turn part 8 Bead apex rubber 10 Core main body 11 Lapping rubber layer 12 Lower apex part 12A Standing piece part 12B Bottom piece part 13 Upper Apex Club

Claims (7)

A pneumatic comprising a carcass made of a carcass ply having a ply main body extending from a tread portion to a bead core of a bead portion and a bead apex rubber having a substantially triangular cross section extending radially outward from the bead core. Tire,
The bead core is composed of a ring-shaped core body in which bead wires are wound in multiple rows and stages, and a wrapping rubber layer that prevents the bead wire from being separated by surrounding the core body,
The bead apex rubber is composed of a radially inner lower apex portion made of hard rubber, and a radially outer upper apex portion made of softer rubber than the lower apex portion,
The lower apex portion includes a bottom piece portion extending along the tire radial upper surface of the bead core, and a standing piece portion rising from a tire axial inner end of the bottom piece portion and extending outward in the tire radial direction along the ply main body portion. It has a cross-sectional L-shape,
Moreover, the rubber hardness Hs1 of the wrapping rubber layer and the rubber hardness Hs2 of the lower apex portion are in the range of 76 to 88 °,
The standing piece portion has a radial height h1 of 15 mm or more from a radial outer end of the core body at a radially outer end thereof,
Further, the thickness t of the upright piece portion sequentially decreases outward in the radial direction, and the upright piece at the height position P0 that is separated from the radially outer end of the core body by 10 mm radially outwardly. A pneumatic tire characterized in that the thickness t0 of the portion is in the range of 0.5 to 2.5 mm.   The pneumatic tire according to claim 1, wherein the upper apex portion has a rubber hardness Hs3 of 50 to 60 ° and a difference (Hs2-Hs3) from the rubber hardness Hs2 of 20 to 38 °.   The pneumatic tire according to claim 1 or 2, wherein the wrapping rubber layer has a thickness i of 0.2 to 2.5 mm.   The pneumatic tire according to any one of claims 1 to 3, wherein a rubber hardness Hs2 of the lower apex portion is larger than a rubber hardness Hs1 of the wrapping rubber layer.   The pneumatic tire according to any one of claims 1 to 4, wherein a thickness T of the bottom piece portion from the upper surface in the tire radial direction of the bead core decreases sequentially toward the outer side in the tire axial direction.   The carcass ply includes a ply turn-up portion that is connected to the ply main body portion and is turned around the bead core. The ply turn-up portion extends along the tire axial direction outer surface of the upper apex portion and extends to the outer surface. The pneumatic tire according to claim 1, wherein the pneumatic tire is interrupted at a point.   The carcass ply includes a ply turn-up portion that is connected to the ply main body portion and is turned around the bead core. The ply turn-up portion has a winding portion extending toward the ply main body portion through the lower apex portion. The pneumatic tire according to claim 1, wherein the pneumatic tire is provided.

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