JPH0342309A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE:To restrain generation of crack to improve durability of a bead part by arranging a thin rubber layer of lower modulus than that of a rubber chafer on the outside in the axial direction of the rubber chafer in the territory in which the bead part contacts and separates to a rim at rolling movement of a tire under load. CONSTITUTION:The bead part 4 of a tire 1 is formed so that a bead rubber 46 is mounted between the folding back part 13 of a carcass layer 11 and a rubber chafer 36 contacted with a rim 5 and extended. The extreme end of the folding back part 13 is arranged on the outside in the radial direction from the extreme end of a rim flange 14. In the above-stated constitution, on the outside in the axial direction of the rubber chafer 36 in the territory S in which the outer surface of a bead part 4 contacts and separates to the curved part 41 of the rim flange 14 at rolling movement of the tire 1 under load, a thin rubber layer 43 having lower modulus than that of the rubber chafer 36 and sufficient flexural property is arranged. Hereby, generation of the crack in the rubber chafer 36 in the territory S is efficiently restrained to improve durability of the bead part 4.

Description

DETAILED DESCRIPTION OF THE INVENTION -1 The present invention relates to a heavy-duty pneumatic radial tire for use on trucks, industrial vehicles, construction vehicles, etc.

[Kudachi Katsukatsu] A conventional heavy-duty pneumatic radial tire has, for example, a cylindrical tread section, a pair of sidewall sections extending radially inward from both ends of the tread section, and a pair of sidewall sections extending radially inward from both ends of the tread section. a pair of bead portions connected to the ends and seated on the rim, the bead portions bead ringing both ends of a carcass layer consisting of at least one carcass ply in which a metal cord extending substantially in the meridian direction is embedded. a rubber chafer that is folded axially outward around the carcass layer and extends in contact with the folded part of the carcass layer and the rim;
It is known that a bead rubber is interposed between the rim flange and the rim flange, and the tip of the folded portion is located radially outward from the tip of the rim flange.

Here, as mentioned above, the outer surface of the tire bead, especially the outer surface of the area that repeatedly contacts and separates from the rim flange during load rolling (contact/separation area), has a large Repeated shear strain acts on the outer surface of the bead, but since a rubber chafer made of rubber that has excellent rim slippage resistance but slightly poor crack resistance is placed on the outer surface of the bead, tire wear is reduced. At the middle stage, minute cracks occur one after another on the outer surface of the rubber chafer in the contact/separation region due to the repeated shear strain. When microcracks occur on the outer surface of the rubber chafer in this way, stress concentrates at the deepest part of these microcracks, which allows the cracks to easily propagate in the thickness direction and reach the inner surface of the rubber chafer. However, there is a problem in that cracks sometimes pass through the rubber chafer and reach the bead rubber and carcass layer, damaging the entire bead portion. Such problems become more noticeable as the lifespan of tires becomes longer, and moreover, these problems become more noticeable in tires to which a large load is applied, that is, in heavy-duty tires.

An object of the present invention is to provide a heavy-duty pneumatic radial tire that can effectively suppress the occurrence of cracks and improve bead durability.

This objective can be distantly achieved by arranging a thin rubber layer having a lower modulus than the rubber chafer on the axially outer side of the rubber chafer in the contact/separation region of the heavy-duty pneumatic radial tire.

New Year's Day When the tire is run as mentioned above, the outer surface of the bead,
In particular, large repeated shear strains act on the outer surface of the contact/separation region. For this reason, in the present invention, a thin rubber layer is disposed on the axially outer side of the rubber chafer in the contact/separation region, and the thin rubber layer is exposed on the outer surface of the contact/separation region instead of the rubber chafer. Here, since the thin rubber layer has a lower modulus than the rubber chafer, the rubber chafer
The crack resistance is better, and as a result, microcracks caused by the repeated shear strain do not occur in the thin rubber layer even in the middle stage of tire wear. When the thin rubber layer mentioned above wears away due to rim misalignment with the rim flange and the rubber chafer is exposed on the outer surface of the bead, microcracks may begin to occur in the rubber chafer. This makes it possible to suppress the generation of microcracks in the contact/separation region until the material wears out. Even if cracks occur, if they occur late, the time from crack occurrence to complete wear will be shortened, so the crank will not be able to grow too deep, and as a result, the bead portion will not be damaged.

Fruit 1 (defeated) Hereinafter, one embodiment of the present invention will be described based on the drawings.

In Figure 1.2, l is a heavy-duty pneumatic radial tire used on trucks, buses, industrial vehicles, construction vehicles, etc., and this tire l has a cylindrical tread part 2 and a tread part 2. A pair of sidewall portions 3 extending substantially radially inward from both axial ends of the rim 5 and a pair of bead portions 4 continuous to the radial inner end of each sidewall portion 3. The tire 1 is mounted on the rim 5 by being seated on the bead seat portion 6 of the tire. Further, the tire 1 has a toroidal carcass layer 11 extending from one bead part 4 to the other bead part 4 and reinforcing each part, and both ends of this carcass layer 11 have bead rings at the bead part 4. 12 from the inside in the axial direction to the outside to form a folded portion 13. The tip (outer end in the radial direction) of each folded portion 13 is located radially outward than the tip (outer end in the radial direction) of the rim flange 14 when the tire 1 is assembled on the rim 5. It extends to a position slightly beyond the maximum width position H of l. The carcass layer 11 is composed of at least one carcass ply 15, and a large number of metal cords, for example, steel cords, extending substantially in the meridional cross-sectional direction (radial direction) are embedded in each carcass ply 15. Further, a rubber filler 21 is provided in the bead portion 4 between the center portion of the carcass layer 11 and the folded portion 13, and the rubber filler 21 is tapered toward the outside in the radial direction, and the inner end of each rubber filler 21 in the radial direction is formed into a bead. It is fixed to the outer end surface of the ring 12, and its radially outer end is located radially outward from the tip of the folded portion 13.

These rubber fillers 21 can be composed of multiple types of rubber, and in this embodiment, they are arranged on the inner end side in the radial direction, have a substantially triangular shape, and have a high modulus (100%
Modulus during expansion is 70~IQOKg/C:rn')
a first rubber part 22 made of rubber, and a second rubber part 23 made of rubber with a relatively low modulus (modulus at 100% elongation of 16 to 28 Kg/C:m'') arranged on the outer end side in the radial direction. A belt layer 26 is disposed on the tread portion 2 on the radially outer side of the carcass layer 11, and this belt layer 26 has a plurality of belt plies 27 attached to it.
It is composed of J1 layer. A large number of metal cords, for example, steel cords, which are inclined with respect to the tire equatorial plane 28, are buried in each belt ply 27. At least two of these belt plies 27 are arranged such that the metal cords embedded therein intersect with each other. A top tread 31 is disposed on the radially outer tread portion 2 of the belt layer 2G, and a known pattern is embossed on the outer surface of the top tread 31. Such patterns include a lug type in which a plurality of lateral grooves are separated by a predetermined distance in the circumferential direction, thereby defining ridges between the lateral grooves, or a lug type in which ridges are formed between the lateral grooves; A plurality of longitudinal grooves are formed that intersect with the groove, are separated by a predetermined distance in the axial direction, and extend in the circumferential direction,
A block-type structure in which block-shaped ridges are defined by these horizontal grooves and vertical grooves is preferably used.

An inner liner 35 is attached to the inner surface of the carcass layer 11 from one bead portion 4 to the other bead portion 4, and this inner liner 35 is made of air-impermeable rubber. Reference numeral 36 denotes rubber chafers disposed on the bead portion 4 and extending along the rim 5. These rubber chafers 36 are used to protect the bead seat portion 6 and the rim flange 1 when the tire l is assembled on the rim 5.
contact at least 4. These rubber chafer-36
is from the bead toe 37 to the bead heel 38 of the bead portion 4.
The axial portion 39 extends substantially axially toward the bead seat portion 6, and the radial portion 40 extends substantially radially from the bead heel 38 toward the sidewall portion 3. whereas the radial section 40 only contacts the rim flange 14 at its inner end.

The tip (outer end in the radial direction) of the radial portion 40 extends to a position slightly radially outward from the tip of the rim flange 14. The rubber chafer 36 has a 100% elongation modulus of 32 to 80 kg/
Constructed from Ctn' rubber with good rim slippage resistance. A thin rubber layer 43 having a lower modulus and greater flexibility than the rubber kneefer 36 is disposed on the axially outer side of the outer end of the radial portion 40, and only the inner end of this rubber layer 43 is It is in contact with the rim flange 14. Here, the contact/separation area S (the separation point R of the tire 1 from the rim flange 14 in the radial direction) where the outer surface of the bead portion 4 repeatedly contacts and separates from the curved portion 41 of the rim flange 14 when the tire l is rolled under load. The narrow ring-shaped region included in the inner end corresponds to a part of the outer end of the radial portion 40, so
The rubber layer 43 is disposed on the outer side of the rubber chafer 36 in the axial direction in the contact/separation region S. Here, the above-mentioned separation point R is the point where the rim flange 14 and the outer surface of the bead portion 4 are always in contact when the tire 1 is assembled to the rim 5 and the tire is filled with the normal internal pressure and no load is applied. This refers to the outer limit position in the radial direction, and the modulus of the rubber layer 43 described above is less than or equal to the modulus of the rubber constituting the side tread 44 described later, specifically 100%, in order to effectively prevent the occurrence of minute cranks. It is preferable that the elongation modulus is within the range of 14 to 28 Kg/Crn'. It becomes a form. Further, the thickness a of the rubber layer 43 is 0.5 to 2.0 m+
It is preferable to keep it within the range of a, because the wall thickness a
If it is less than 0.5 mm, the rubber layer 43 will wear out quickly due to rim displacement, and the effect of delaying the generation of microcracks will be small. This is because the rigidity is lowered and the bead portion 4 falls down significantly. Here, since the modulus is an index of crack resistance, the rubber layer 43 with a lower modulus than the rubber chafer 36 has better crack resistance than the rubber chafer 36. In particular, when the modulus is lower than the side tread 44, the crack resistance is improved. The performance is improved compared to the side tread 44. Bead rubber 48 is interposed between the radial part 40 and the folded part 13 of the rubber chafer 36, and these bead rubbers 4G are part of the side tread 44 disposed on the axially outer side of the carcass layer 11 in the sidewall part 3. ie, a radially inner end. The side tread 44 has a radially outer end extending to both ends of the top tread 31 and a radially inner end extending to the vicinity of the curved portion 41 of the rim flange 14, and has a 100% elongation modulus of 14 to 28 kg/
Cm'' is made of rubber with excellent flexibility. When the tire 1 as described above is run, large repeated shearing strains occur on the outer surface of the bead portion 4, especially on the outer surface of the contact/separation region S. However, since the rubber layer 43 with good crack resistance is exposed on the outer surface of the contact/separation area S where this large shear strain acts, microcracks do not occur even in the middle stage of wear. When the rubber layer 43 is worn out due to rim displacement, the rubber chafer 36
may be exposed and microcracks may begin to occur,
Until this rubber layer 43 is worn out, the generation of microcracks in the contact/separation region S can be suppressed. Even if microcracks occur, if they occur late, the period from the occurrence of the cracks to complete wear of the top tread 31 will be shortened, so the cracks will not be able to grow very deep, and as a result, the bead portion 4 will be damaged. There is nothing to do.Next, a test example will be explained. In this test, the 100% extension modulus in the contact/separation region was 50K.
g/Cml, and a comparative tire with a rubber chafer exposed on the outer surface, and a rubber chafer in the same area with a 100% elongation modulus of 11Kg/CrIf on the outside in the axial direction.
50 comparative tires and 30 test tires were prepared to which the present invention was applied by disposing a rubber layer with a certain thickness of 0.81 mm. Here, the size of each tire is 38.00R51, and the structure of each tire is the same as in the previous example. To explain briefly, the cord structure of the carcass layer is 7×(7+1
2) It consists of one carcass ply in which +1 steel cords are arranged in the radial direction, and the folded part of this carcass layer extends to a position slightly beyond the maximum width position of the tire. In addition, the belt layer is arranged between the top tread with a lug pattern formed on the outer surface and the carcass layer,
It is a known non-stretchable material with a metal cord embedded therein.

Furthermore, the rubber filler has a 100% elongation modulus of 85.
It consists of a first rubber part made of hard rubber with a modulus of 1.3 Kg/Crn' and a second rubber part made of relatively soft rubber with a modulus of 1!3 Kg/Crn', and the first rubber part is close to the bead ring. The second rubber portion is disposed radially inwardly, while the second rubber portion is disposed radially outwardly, spaced apart from the bead ring. In addition, rubber chafers are made of zero-order rubber with a 100% elongation modulus of 50 kg/Crrf.As a result of installing each of these tires on a 170-ton dump truck and having the truck work at a copper mine, the comparative tires were Almost! In /3, a bead failure occurred due to a crack that occurred in the contact/separation area during the wear life of the top tread, but in the test tire, only two similar bead failures occurred. Met.

As explained above, according to the present invention, it is possible to effectively suppress the occurrence of cracks in the rubber chafer in the contact/separation area, and the durability of the bead portion of the tire can be dramatically improved. I can do it.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a meridian sectional view showing one embodiment of the present invention;
The figure is a meridian cross-sectional view of the vicinity of the bead. l...Pneumatic radial tire for heavy loads 2...Tread part 3...Side wall part 4...Bead part 5...Rim 11...Carcass layer
12...Bead ring 13...Folded part
14...Rim flange 15...Carcass ply 3
6...Rubber chafer-43...Thin rubber layer
4B... Bead rubber S... Contact/separation area

Claims (1)

[Claims] The tread includes a cylindrical tread portion, a pair of sidewall portions extending radially inward from both ends of the tread portion, and a pair of bead portions connected to the radial inner end of each sidewall portion and seated on the rim. The bead portion consists of folding both ends of a carcass layer consisting of at least one carcass ply in which a metal cord extending substantially in the meridian direction is embedded axially outward around the bead ring, and connecting the folded portion of the carcass layer with the rim. A heavy-duty pneumatic radial tire in which a bead rubber is interposed between a rubber chafer extending along the rim flange, and the tip of the folded portion is located radially outward from the tip of the rim flange. A thin rubber layer with a lower modulus than the rubber chafer is placed on the axially outer side of the rubber chafer in the contact/separation region that repeatedly contacts and separates from the rim during motion, thereby suppressing the occurrence of cracks in the contact/separation region. A pneumatic radial tire for heavy loads that is characterized by: