JP2007045375A - Heavy load tubeless tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heavy load tubeless tire which enhances a rim assembling property and a toe chipping property while ensuring the high bead durability. <P>SOLUTION: A bead base surface SA of a tire 1 mounted on a 15° taper rim is inclined straight at the angle of α of 6-10° with respect to the bead base line BL. A chafer rubber 12 is divided into chafer rubber parts 13, 14 inside and outside the tire axial direction by a boundary line K extending from a starting point P1 on the bead base surface SA in an inclined manner outwardly in the tire axial direction. The length L1 from a toe point Qt of the starting point P1 is set to be in a range of 10-35% of the length L0 of the bead base surface, and in the inner chafer rubber part 13, the rubber hardness is set to be 60-70°, and the elongation at the breakage after the heat aging when the chafer rubber part is left for 72 hours at the temperature of 100°C is set to be 300-450%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heavy-duty tubeless tire capable of suppressing rubber chipping (tow chipping) in a bead toe portion when assembling a rim while maintaining bead durability.

  Since the heavy duty tubeless tire is used under high internal pressure and high load, it is necessary to fit the bead portion to the rim with high contact pressure. Therefore, as shown in FIG. 4, the bead base surface a1 of the tire is inclined at an angle θ larger than the inclination angle (15 °) of the rim surface on which the bead base surface a1 is mounted, and the toe of the bead portion a is A chafer rubber b that forms a bead skin made of hard rubber having a rubber hardness of about 80 ° is formed in a contact area with the rim that extends from the portion at to the bead outer surface ao through the heel portion ah. In the toe portion at, the chafer rubber b has a structure in which a standing piece b1 rising radially outward is provided in order to cover and protect the inner end c1 of the air-impermeable inner liner rubber c. ing.

  However, in such a tire, there is a problem that the toe portion at is caught on the rim flange when assembling the rim, and the rim assembling property is deteriorated or toe chipping is likely to occur. Particularly in tires having a long service period such as retreaded tires, the tendency of the toe chipping becomes more prominent because the rubber is hardened due to deterioration.

  Therefore, it is proposed to suppress toe chipping by reducing the rubber hardness of the chafer rubber to make it easy to stretch, but in such a case, a high contact pressure with the rim cannot be secured, and the bead deformation is large. This leads to a decrease in bead durability. In order to improve the rim assembly property, it is also devised to increase the inner diameter of the bead portion a. However, even in such a case, the contact pressure with the rim is reduced and the bead durability is lowered.

  As described above, there is a trade-off between the rim assembly property and the toe chipping property and the bead durability, and it is difficult to improve the rim assembly property and the toe chipping property while maintaining the bead durability.

  Therefore, the present invention deliberately reduces the inclination angle of the bead base surface to be lower than the inclination angle of the rim surface, and divides the chafer rubber into the tire axial direction inside and outside by a boundary line having a starting point on the bead base surface. It is an object of the present invention to provide a heavy-duty tubeless tire capable of improving rim assembling property and toe chipping property while ensuring high bead durability, based on specifying the rubber physical properties of the part.

JP 2002-52909 A

In order to achieve the above object, the invention of claim 1 of the present application includes a carcass ply extending from a tread portion through a sidewall portion to a bead core of a bead portion, and a bead base surface of a tire is provided on a rim surface of a 15 ° taper rim. A tubeless tire for heavy loads to be installed,
The bead portion includes a chafer rubber that forms the bead base surface, a bead outer surface connected to a heel point at an outer end in the tire axial direction of the bead base surface, and an inner surface of the bead connected to a toe point at an inner end in the tire axial direction. And
And in the meridional section of the tire when the distance between the heel points of the bead portions on both sides is set to the rim width W0 without attaching the tire to the rim,
The bead base surface is inclined at an angle α of 6 to 10 ° with respect to a bead base line in the tire axial direction passing through the heel point and has a substantially straight shape without bending,
The chafer rubber includes an inner chafer rubber portion and an outer chafer rubber portion that are divided inward and outward in the tire axial direction by a boundary line that inclines outward from the starting point P1 on the bead base surface in the tire radial direction. And the length L1 along the bead base surface from the toe point of the starting point P1 is in the range of 10 to 35% of the length L0 of the bead base surface,
The chafer rubber part has a rubber hardness (durometer A hardness) of 60 to 70 °, and an elongation at break after heat aging left at a temperature of 100 ° C. for 72 hours is set to 300 to 450%. Yes.

In the invention according to claim 2, the boundary line has a length L2 along the bead base surface from the toe point of the radially outer end point P2 within a range of 20 to 50% of the length L0 of the bead base surface. It is characterized by that.
According to a third aspect of the present invention, the outer chafer rubber portion has a rubber hardness (durometer A hardness) of 70 to 83 °.

  Since the present invention is configured as described above, it is possible to improve the rim assembly property and the toe chipping property while ensuring high bead durability.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a meridional section in a normal internal pressure state in which the heavy-duty tubeless tire of the present invention is assembled to a normal rim and filled with a normal internal pressure. 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, a standard rim for JATMA, “Design Rim” for TRA, or ETRTO means "Measuring Rim". The “regular internal pressure” is the air pressure specified by the tire for each tire. The maximum air pressure in the case of JATMA, the maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the case of TRA, If it is ETRTO, it means "INFLATION PRESSURE".

  In FIG. 1, a heavy-duty tubeless tire 1 (hereinafter referred to as a tire 1) is a tire assembled on a 15 ° taper rim, and is a carcass extending from a tread portion 2 to a sidewall portion 3 to a bead core 5 of a bead portion 4. 6 and a belt layer 7 disposed on the inner side of the tread portion 2 and on the outer side in the radial direction of the carcass 6.

  The belt layer 7 is formed of two or more belt plies (usually three or four in the case of a heavy load tire). In this example, the belt layer 7 includes an innermost belt ply 7A in which steel belt cords (steel cords) are arranged at an angle of 60 ± 10 ° with respect to the tire circumferential direction, and the tire circumferential direction. The belt plies 7B and 7C arranged at a small angle of 30 ° or less are shown as an example. By providing one or more points where the belt cords cross each other between the plies, the belt rigidity is increased. The tread portion 2 is reinforced.

  Further, the carcass 6 is provided with one or more ply turn-up portions 6b that are turned around from the bead core 5 to the outside in the tire axial direction at both ends of the ply main body portion 6a straddling the bead cores 5 and 5, in this example. It is formed from one carcass ply 6A. The carcass ply 6A has a so-called radial structure in which carcass cords are arranged at an angle of 70 to 90 ° with respect to the tire circumferential direction. As the carcass cord, in addition to the steel cord, an organic fiber cord such as nylon, polyester, rayon, aromatic polyamide or the like can be adopted.

  Next, FIG. 2 shows the bead portion 4 of the tire in a reference holding state in which the distance between the heel points Qh and Qh of the bead portions 4 on both sides is matched with the rim width W0 without attaching the tire to the rim. Indicates. The “heel point Qh” means an outer end in the tire axial direction of the bead base surface SA attached to the rim surface, and an inner end in the tire axial direction of the bead base surface SA is called a “toe point Qt”. A tire axial line passing through the heel point Qh is referred to as “bead base line BL”.

  As shown in FIG. 2, a bead apex rubber 8 extending in a radially outward direction from the bead core 5 is disposed between the ply main body portion 6a and the ply folded portion 6b of the carcass 6, The bead portion 4 is provided with a bead reinforcing layer 9 that wraps the bead core 5 around the U-shaped via the carcass 6 so as to wrap the ply main body portion 6a and the ply folding portion 6b. The bead reinforcing layer 9 is formed of a cord ply in which reinforcing cords such as steel cords are arranged at an angle of, for example, 15 to 60 ° with respect to the tire circumferential direction, and the bead portion 4 is reinforced in cooperation with the bead apex rubber 8. In addition, the bead rigidity is improved.

  Further, an inner liner rubber layer 10 forming a tire cavity surface is disposed on the inner side of the ply main body portion 6 a via an insulation rubber layer 11. The inner liner rubber layer 10 is made of an air impermeable rubber mainly composed of, for example, butyl rubber. The insulation rubber layer 11 is a highly adhesive rubber which is interposed between the inner liner rubber layer 10 and the ply main body 6a and extends inward and outward in the radial direction to increase the adhesive force between them. A rubber using natural rubber or the same rubber as the topping rubber of the carcass ply 6A is preferable. A radially inner end portion 11E of the insulation rubber layer 11 terminates at a substantially linear lower surface 11S in contact with the bead reinforcement layer 9. In this example, the lower surface 11S is parallel to the bead base surface SA.

  The bead portion 4 is provided with a chafer rubber 12 that forms a bead skin. The chafer rubber 12 includes a base portion 12A forming the bead base surface SA, an outer standing portion 12o forming a bead outer surface So connected to the bead base surface SA at the heel point Qh, and the toe base to the bead base surface SA. The inner liner rubber layer 10 is covered and protected by the inner standing piece 12i that forms the inner surface Si of the bead continuous at the point Qt.

  In the tire according to the present embodiment, in the reference holding state, the bead base surface SA is substantially straight and has an angle α of 6 to 10 ° with respect to the bead base line BL. Inclined.

  As shown in FIG. 4, the conventional bead base surface has a curved surface that is inclined in two steps at two angles θ larger than the inclination angle (15 °) of the rim surface. The bead base surface is formed of a single slope that does not bend. Moreover, the angle α of the bead base surface SA with respect to the bead base line BL is reduced to 10 ° or less, which is smaller than the inclination angle of the rim surface. Therefore, the inner diameter of the tire at the toe point Qt is increased, and the catch when the rim flange is moved over is reduced, and the rim assembly property is improved. The tire inner diameter (heel diameter) Dh at the heel point Qh is in the range of 99.2 to 99.6% of the rim diameter, as in the prior art, and thereby the fitting force with the rim is ensured. However, when the angle α is less than 6 °, the amount by which the toe point Qt side is lifted from the rim surface becomes excessive during internal pressure filling or load application. As a result, the fitting with the rim is insufficient, the bead deformation becomes large, and the bead durability is lowered. Therefore, it is necessary to set the angle α in the range of 6 to 10 °.

  Further, in the present embodiment, as shown in an enlarged view in FIG. 3, the chafer rubber 12 extends from the starting point P1 on the bead base surface SA toward the outer side in the tire radial direction and extends outward in the tire axial direction. Thus, it is divided into chafer rubber portions 13 and 14 inside and outside in the tire axial direction. At this time, the outer chafer rubber portion 14 is formed of a hard rubber having a rubber hardness Hs2 (durometer A hardness) in the range of 70 to 83 ° in order to increase the contact pressure with the rim and obtain a sufficient fitting force. is doing. On the other hand, the inner chafer rubber portion 13 is formed of a slightly soft rubber having a rubber hardness Hs1 (durometer A hardness) in the range of 60 to 70 ° and smaller than the rubber hardness Hs2, and at a temperature of 100 ° C. The elongation at break after heat aging after standing for 72 hours is set in the range of 300 to 450%.

  Thus, the chafer rubber 12 is divided into two, and the chafer rubber portion 13 on the toe side is formed of a soft rubber. Therefore, even when caught on the rim flange, it can be flexibly deformed, and coupled with the increase in the tire inner diameter at the toe point Qt, the toe chipping property can be effectively suppressed in a new tire or a tire with a short use period. Therefore, the difference in rubber hardness (Hs2−Hs1) is preferably 8.0 ° or more.

  However, in a tire having a long service period such as a retread tire, for example, the rubber is hardened due to deterioration, so that it is not possible to sufficiently suppress toe chipping. Therefore, it is necessary to use a rubber excellent in heat aging resistance in which the elongation at break after heat aging that is allowed to stand at a temperature of 100 ° C. for 72 hours is 300 to 450%. If the elongation is less than 300%, toe chipping in a retreaded tire or the like cannot be sufficiently suppressed. Conversely, if it exceeds 450%, bead deformation tends to increase.

  In order to effectively exhibit such an effect, the length L1 along the bead base surface SA between the starting point P1 of the boundary line K and the toe point Qt is set to the bead base surface of the bead base surface SA. It is important that the length is in the range of 10 to 35% of the length L0 along the SA. This is because when the length L1 exceeds 35%, the ratio of the chafer rubber portion 13 in the base portion 12A becomes excessive, and a sufficient contact pressure with the rim surface, that is, a fitting force with the rim can be secured. Because it disappears. On the other hand, if it is less than 10%, the effect of suppressing toe chipping is not sufficiently exhibited. For the same reason, the length L2 along the bead base surface SA from the toe point Qt of the radially outer end point P2 of the boundary line K is set to a range of 20 to 50% of the length L0 of the bead base surface. Is preferred. If the length difference (L2−L1) is too small, the boundary line K is shortened, and delamination tends to occur at the boundary line K. Therefore, the difference (L2−L1) is preferably 20% or more of the length L0. Positioning the outer end point P2 of the boundary line K on the interface J between the chafer rubber 12 and the insulation rubber layer 11 is preferable for suppressing delamination. The rubber hardness Hs3 of the insulation rubber layer 11 is smaller than the rubber hardness Hs1 of the inner chafer rubber portion 13.

  Further, the minimum rubber thickness t under the bead core of the outer chafer rubber portion 14 is 1.5 to 3.5 mm, thereby suppressing the cracking of the chafer rubber 12 under the bead core and the fitting force with the rim. Highly secured.

  In addition, the effect of this application is effectively exhibited with the tire whose said length L0 of bead base surface SA was 20-28 mm. 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 tire (245 / 70R19.5) having the structure shown in FIG. 1 was prototyped based on the specifications shown in Table 1, and the rim assembly property, toe chipping property, and bead durability of each sample tire were tested. It was described in.

(1) Rim assembly ability;
Ten general workers assemble a sample tire on a rim (7.50 × 19.5) using a rim assembly machine (hydraulic tire changer). It was evaluated as “good”. And the ratio of “good” in the whole was displayed. Higher values are better.

(2) Toe deficiency;
After filling the inner tire (850 kPa) to the rim-assembled sample tire, 10 tires (corresponding to old products) that were left to stand for 7 days under the condition of a temperature of 100 ° C. were prepared. Then, the reciprocal of the occurrence rate of toe chipping when the rims (7.50 × 19.5) were assembled / removed on the rims (7.50 × 19.5) for each used tire equivalent tire was displayed as an index with Comparative Example 1 as 100. Higher values are better. In order to verify the toe chipping property under more disadvantageous conditions, a zigzag circumferential groove having a depth of 5 mm is formed at the tip of the rim flange.

(3) Bead durability;
Using a drum tester, the vehicle was run under conditions of internal pressure (850 kPa), load (43.89 KN), and speed (20 km / h), and the running time until tire damage occurred was an index with Comparative Example 1 as 100. it's shown. The greater the value, the better the durability.

  It can be confirmed that the tires of the examples have improved toe chipability without impairing the rim assembly property and bead durability.

It is sectional drawing which shows one Example of the tubeless tire for heavy loads of this invention. It is sectional drawing which expands and shows a bead part. It is sectional drawing which expands and shows the principal part further. It is sectional drawing which illustrates the bead part of the conventional tire.

Explanation of symbols

2 Tread portion 3 Side wall portion 4 Bead portion 5 Bead core 6A Carcass ply 12 Chafer rubber portion 13 Chafer rubber portion 14 Chafer rubber portion outside BL Bead base line K Boundary line Qh Heel point Qt Toe point SA Bead base surface Si Bead inner surface So bead Outside

Claims (3)

A heavy duty tubeless tire comprising a carcass ply extending from a tread portion through a sidewall portion to a bead core of a bead portion, and having a bead base surface of the tire mounted on a rim surface of a 15 ° taper rim,
The bead portion includes a chafer rubber that forms the bead base surface, a bead outer surface connected to a heel point at an outer end in the tire axial direction of the bead base surface, and an inner surface of the bead connected to a toe point at an inner end in the tire axial direction. And
And in the meridional section of the tire when the distance between the heel points of the bead portions on both sides is set to the rim width W0 without attaching the tire to the rim,
The bead base surface is inclined at an angle α of 6 to 10 ° with respect to a bead base line in the tire axial direction passing through the heel point and has a substantially straight shape without bending,
The chafer rubber includes an inner chafer rubber portion and an outer chafer rubber portion that are divided inward and outward in the tire axial direction by a boundary line that inclines outward from the starting point P1 on the bead base surface in the tire radial direction. And the length L1 along the bead base surface from the toe point of the starting point P1 is in the range of 10 to 35% of the length L0 of the bead base surface,
The inner chafer rubber part is characterized in that its rubber hardness (durometer A hardness) is 60 to 70 °, and the elongation at break after thermal aging after standing for 72 hours at a temperature of 100 ° C. is 300 to 450%. Heavy duty tubeless tire.   The boundary line has a length L2 along the bead base surface from the toe point of the radially outer end point P2 in a range of 20 to 50% of the length L0 of the bead base surface. Item 1. A heavy-duty tubeless tire according to item 1.   The heavy duty tubeless tire according to claim 1 or 2, wherein the outer chafer rubber part has a rubber hardness (durometer A hardness) of 70 to 83 °.

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