GB1600068A

GB1600068A - Heavy duty pneumatic tyre

Info

Publication number: GB1600068A
Application number: GB8332/78A
Authority: GB
Original assignee: Uniroyal GmbH
Current assignee: Uniroyal GmbH
Priority date: 1977-03-10
Filing date: 1978-03-02
Publication date: 1981-10-14
Also published as: SE7802340L; FR2383028B1; BE864707A; CA1100858A; FR2383028A1; DE2710446C2; DE2710446A1; AU3350378A; AU515426B2; JPS53114105A

Description

(54) A HEAVY DUTY PNEUMATIC TIRE (71) We, UNIROYAL GMBH, a corporation organized under the laws of the District Court of Aachen, Federal Republic of Germany, having an office at D-5100 Aachen 1, Huettenstrasse 7, Federal Republic of Germany, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to pneumatic vehicle tires and more particularly to novel bead and shoulder area constructions for heavy duty pneumatic tires which reduce ply edge separation.

In the case of all vehicle tires containing plies of rubberized or similar metallic reinforcement elements there arise problems, in particular at the edges of the plies. During the manufacturing of the tire, sharp metallic cutting edges may have been created along those edges of the plies which are cut during the manufacturing process. This holds true in particular for large vehicle tires designed for heavy duty applications since the dimensions of the steel cords used for such tires exceed by a multiple those of the steel cords utilized in passenger car tires. The extent of potential damage is of corresponding magnitude.

It will be possible to gain an understanding of the problem by looking at the various stages of tire manufacture. The cord fabric used for the tire is manufactured in the form of a web of considerable length and is, essentially, steel or metallic cords embedded in a rubber compound. The various cord plies for the carcass and for the reinforcement belt are cut from this web at a bias in the form of strips of a certain width. This cutting creates exposed, steel surfaces along the edges of the plies. Moreover, along the cut edges, the plies exhibit bared steel cord ends of different lengths which, as a result of squeezing and bending action in the course of the cutting operation, are irregularly deformed.

In the finished tire, these edges constitute a problem of considerable significance. The tire components adjacent these reinforced plies generally are rubber compounds that are highly unsuited for constant contact with such bare steel edges under operational loads.

Because of the multiplicity of forces to which the finished tire is subjected during operation, there result inherent movements of the individual tire components with respect to one another so that the edges of the cord plies and the adjoining tire components tend to rub against one another. The result is a break-down of the adjacent rubber components and, in addition, separation of the cord from the rubber at the edges of the plies. This results, ultimately, in the complete destruction of the tire.

Attempts have been made to eliminate the hazards of separation in a steel cord carcass or to minimize its effects. For instance, the ends of the carcass flipper may be hemmed on both side with rubber strips. Different arrangements of filler strips in the form of inserts of varying hardness in the bead area have been proposed in attempts to prevent failures and separations at the turnup portions when the tire is deformed due to load. An element made of rubber of medium softness can be used to cover the ends of the turnup and to reduce the friction between the hard rubber ply of the bead and the balance of the tire components.

In the shoulder area of the tire, specifically with regard to the edges of the reinforcement belt plies beneath the tread profile protective methods have been advanced which show end cushions under the tread adjacent the ply edges. There is known a construction in which a cushion element is composed of rubber and elongated shaped particles. The edges of the plies may be covered with rubber profiles.

The use of rubber strips as a covering means is unsatisfactory with regard both to the edges of the turnup and belt since rubber strips may, after prolonged use, separate from the adjacent tire components and thus be unable effectively to prevent separations in the edges.

Moreover, such rubber strips create, particularly in the tire bead, an inherent weakness.

According to the present invention we provide a pneumatic tire comprising a pair of annular bead cores; sidewalls; a carcass of at least one ply of rubberized metallic cord fabric having its end portions wrapped radially around the bead cores to form turnups which are axially displaced from the remaining portions of the carcass; in which in each bead core region an annular apex strip is disposed between the carcass and the turnup, the annular apex strip extending radially of and from the bead core and, along its axially inward surface, contacting the carcass; and a bead cushion element of a soft rubber compound having high restorability and a Shore A hardness less than that of the apex strip and the carcass, fills the space between the apex strip and the turnup, envelops the terminal edge of the turnup and extends radially outwardly beyond the apex strip and the turnup into the sidewall thereby isolating the terminal edge of the turnup from the carcass ply and rendering the bead and lower sidewall portion of the pneumatic tire more flexible to inhibit separation of the cords at the terminal edge.

The cushion elements may have a Shore A hardness of from 50 to 650.

In one embodiment of the invention, reinforcement strips of rubberized metallic cord fabric are wrapped around the bead cores to form radial extensions of the turnups. The terminal edges of these strips are also enveloped by the cushion elements. The terminal edges of the reinforcement strips may be spaced from the terminal edges of the turnups, but still be enveloped by the cushion elements.

The pneumatic tire may include a tread portion connected to the carcass and defining a pair of shoulders where the edges of the tread portion meet the carcass; a reinforcing belt assembly positioned between the tread portion and the carcass including at least two plies of rubberised metallic cord fabric; and in each shoulder, a shoulder cushion element of a soft rubber compound having high restorability and a Shore A hardness less than that of the tread portion, sidewalls and plies, enveloping the edges of the plies.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter regarded as the invention herein, it is believed that the invention will be better understood from the following description when read in conjunction with the accompanying drawings, in which: Figure 1 is an enlarged partial cross-sectional view of one half of a pneumatic tire constructed in accordance with embodiments of the present invention Figure 2 is a view similar to Figure 1 showing other embodiments of the present invention and Figure 3 is a partial cross-sectional view of a bead portion of a further embodiment of the present invention.

As used in the specification and the claims, the terms "axially inward" and "axially outward" are used with reference to a sidewall of the tire, that is, "axially inward" refers to a vector extending from the sidewalls to the opposite sidewall. Conversely, "axially outward" refers to a vector extending outwardly away from the sidewall. The terms "radially inward" and "radially outward" are used with reference to the axis of rotation of the tire, that is, "radially inward" refers to a vector extending from the tread profile of the tire to the axis, while. the term "radially outward" refers to a vector extending from the axis toward the tread profile.

Referring now to the drawings, there is shown in Figure 1 in partial section one half of a pneumatic tire constructed in accordance with embodiments of the present invention identified by the reference numeral 10. The tire 10 is a size 12.00 R 20 truck tire on a shoulder rim 11. While only one half of the tire is illustrated, it is to be understood that the half not illustrated is the same as that illustrated but opposite in hand. The tire 10 includes a ground engaging tread portion 12 extending circumferentially of the tire and a sidewall portion 14 extending from the lateral edge 16 of the tread 12 to a bead portion 18. A carcass 20 of at least one ply of rubberized steel cord fabric extends circumferentially about the tire 10 beneath the thread 12. The cords in the carcass 20 are arranged radially, i.e., substantially 90" to a circumferential direction of the tire. The end 22 of the carcass play is wrapped radially outwardly about a bead core 24 to form a turnup or carcass flipper 26.

Extending circumferentially of the tire and radially above the bead core 24 between the turnup 26 and the carcass ply 20 is a hard rubber annular reinforcement or apex strip 28.

The apex strip 28 is substantially at its base 30 as wide as the bead core 24 and, as shown, may encompass the bead core. It tapers smoothly and gradually to a point at its radially outer extermity 32. In addition, the apex strip 28 abuts the carcass ply 20 substantially along the entire axially inward side 34 of the apex strip as shown.

Wrapped about the bead core 24 and in direct over-lapping relationship with the turnup 26 may be a reinforcement strip 36 of rubberized steel cord fabric. The axially outward terminal edge 38 of the reinforcement strip 36 is positioned radially outwardly of the terminal edge 40 of the turnup 26 so that the reinforcement strip 36 forms a radially outward extension of the turnup. The steel cords in the reinforcement strip 36 are oriented with respect to the equatorial axis X-X of the tire so as to create an angle a with the steel cords of the carcass ply. As mentioned hereinabove, the cords in the carcass ply 20 extend at an angle of substantially 90" with respect to the equatorial axis X-X and the cords in the reinforcing strip 36 may lie at an angle of 60 with respect to the axis.

In accordance with one embodiment of the present invention, an annular rubber cushion element or insert 42 encompasses the radially outward terminal edge 40 of the turnup 26 and if a reinforcement strip 36 is provided, its terminal edge 38. The cushion element 42 abuts the axially outer edge 44 of the apex strip 28 and the carcass ply 20 as well as the sidewall 14. The cushion element 42 is formed of a rubber compound, hereinafter described in detail, which when vulcanized, has a hardness less than the hardness of the surrounding rubber components. For example, the cushion element 42 may have a Shore A hardness of approximately 60 , with the adjoining rubber portion of the apex strip 28, as well as the rubber coating of the carcass ply 20 and the reinforcement strip 36 being significantly harder, for instance, of a Shore A hardness of 80".

With continued reference to Figure 1, it can be seen that the radially outward terminal edges 28 and 40 of the reinforcement strip 36 and the turnup 26 respectively are located approximately in the center of the cushion element 42. Preferably, the cushion element 42 has a cross-sectional shape of a lentil and is, at its thickest point, a multiple of the thickness of the cords in the carcass ply and the reinforcement strip.

The cushion element 42 tapers to a point 46 at its radially inward extermity adjacent the apex strip 28 and to a point 48 at its radially outward extremity adjacent the carcass ply 20.

The distance, measured radially, that the point 46 is from the terminal edge 38 of the reinforcement strip 36 is the same as the distance point 48 is from the same edge.

With continued reference to Figure 1, a reinforcement belt 50 includes a plurality of superimposed plies 52, 54 and 56 of rubberized steel cord, and a protector ply 58. The edges 60 and 62 of the plies 52 and 54 respectively are encased in a soft rubber cushion element 64 formulated in accordance with the present invention. The cushion element 64 has sickle-shaped cross sectional configuration and is situated axially inwardly of the shoulder 16. The cushion element 64 extends axially inwardly between the ply 52 and the carcass ply 20 to a point proximate the equatorial axis X-X of the tire as well as radially inwardly into the sidewall 14 of the tire. In this construction, the cushion element 64 prevents contact between the steel cord ends at the edges 60 and 62 of the plies 52 and 54 and the carcass ply 20 and eliminates separation in the ply edges.

According to an alternative arrangement of the structure illustrated in Figure 1, respresented in Figure 2, one half of a pneumatic truck tire 70 is mounted on a 15 shoulder rim 71 and includes a carcass ply 72 containing radially oriented rubberized steel cords. The carcass ply 72 is wrapped about a bead core 74 which may have a hexagonal cross-section configuration as shown. In this embodiment, the radially outward terminal edge 76 of the turnup 78 is separated, i.e., axially spaced, from the radially outward edge 80 of the reinforcement strip 82. Both the edge 76 and the edge 80 are encased in a cushion element 84, which is similar in configuration to cushion element 42. The cushion element 84 is substantially wider than the cushion element 42 due to the spaced relationship of the edges 76 and 80.

Also illustrated in Figure 2 is an alternative construction for the cushion element associated with the reinforcement belt. Identified by the reference numeral 86, the cushion element extends axially inwardly not only between the ply 88 and the carcass ply 72, but also between the ply 88 and the immediately adjacent ply 89.

A further embodiment of the present invention is illustrated in Figure 3 in which the carcass ply 90 is wrapped radially outwardly about a bead core 92. The radially outward terminal edge 94 of the turnup 96 and the terminal edge 98 of the reinforcement strip 100 are adjacent one another and bear against the sidewall 102. The cushion element 104 is positioned between the terminal edges 94 and 98 and the carcass ply 90 to maintain the edges in axially spaced relationship to the carcass ply 90.

While both Figures 1 and 2 contain details of cushion elements for the bead areas and shoulder areas of a pneumatic tire, it is to be appreciated that the scope of the present invention is not limited to a pneumatic tire containing cushion elements in the shoulder areas.

Furthermore a tire can combine the bead area construction of either Figure 1 or Figure 3 with the shoulder area construction of Figure 2, or the bead area construction of either Figure 2 of Figure 3 with the shoulder area construction of Figure 1.

The rubber compounds for the above described cushion-elements in the bead area and for the cushion elements in the shoulder area of the tire and their vulcanization process are selected so that the elements provide elevated rebound elasticity and high adhesivity to the steel cord extremities. Preferably, these cushion elements have, as noted hereinabove, a comparatively low hardness compared with the surrounding components of the bead and of the tire sidewall a low permanent set and a low development of heat under dynamic deformation.

Preferably, the highly restorable vulcanized cushion elements have a rebound elasticity, determined according to German Industrial Standards DIN 53,512 of 55 to 65%. The Shore A hardness of these elements as discussed above lies in the range of 50C to 65 , and in particular around 60".

The cushion elements in accordance with the invention contain additives promoting the adhesion of rubber to steel, e.g., known materials such as resorcinol and methylene group donors, for instance resorcinol-formaldehyde resins and 2-nitro-2-methyl-1-propanol or 1-aza-3,7-dioxy-5-hydroxymethyl-dicyclo (3,3,0) octane, as well as active silicic acid.

Preferably resorcinol, hexamethylene tetramine and active silicic acid are used. These additives insure firm bonding of the exposed steel at the edges with the rubber surrounding them.

Table 1 is an example, without limitation, of a rubber enwrapping compound from which the elements may be formed with the quantities being given in parts by weight with respect to 100 parts natural rubber.

TABLE 1 100 parts natural rubber 20-30 parts reinforcing carbon black 2.5-3.5 parts sulfur 5-10 parts active silicic acid 1-3 parts resorcinol 1-2.5 parts hexamethylene tetramine The vulcanized products contain other standard additives such as zinc oxide, zinc stearate, processing oils, adhesive cement, antioxidants, antiozonants, and accelerators.

Preferred compounds are compounds in which the rubber portion consists of natural rubber (NR). However, likewise suitable are mixtures of natural rubber with butadiene rubbers (BR), e.g., cis-1,4-polybutadiene rubber. Suitable compounding ratios of the rubber components are 30 to 100 parts, preferably at least 80 parts, of natural rubber per 70 to 0 parts of the butadiene rubber component. The preferred amount of carbon black is at around 25 parts and the preferred amount of sulfur at about 3 parts. The active silicic acid is preferably applied at the lower limit of the above-mentioned range, in other words, one uses preferably quantities of approximately 5 parts of only slightly increased amounts.

Resorcinol is appropriately applied in an amount of approximately 2.5 parts and hexamethylene tetramine suitably in an amount of approximately 2 parts.

For an accelerator, N-cyclohexyl-2-benzothiazyl-sulfenamide can be used. Depending on the type of rubber that has been selected, one can use other suitable accelerators, such as the sulfenamide type.

The cushion elements are manufactured in the following manner. The cut and weighed raw rubber is first masticated in a kneader. It is then processed to a carbon black masterbatch by incorporating the following additives: silicic acid and resorcinol, processing oil, zinc compounds, carbon black, and the other additives, and mixing in a kneader. The resultant mixture is rolled out in sheet form, weighed, and cut to size in charges.

Subsequently, the CBS accelerator and the HMT are added to the masterbatch. Following further processing in a kneader, renewed rolling, and cutting, the rubber material eventually assumes the form of a strip that can be used for tire building.

The manufacture of the tire involves the building up of the individual tire components on a tire building machine. First, a cylindrical protector ply, made of rubber, is placed on a drum. Next the bead reinforcement strips as well as the steel cord carcass are positioned over the proctector ply. A bead ring, a filler, and a rubber cushion element of the above-described compound, are placed on each side. The carcass extremities are then flipped over into the inflated building state of the carcass. Pressed onto the ends of the turnup are additional strips of rubber made out of the above-described compound.

Following covering of the edges by means of a rim protecting band made of natural rubber, the carcass is completed. In a subsequent building process, this carcass body is endowed with the shape of a toroid by way of inflation.

Onto same, one applies and forces on under pressure, in the area of the later tire shoulder, additional rubber strips made out of the above-described compound and, in the crown area, the required belt plies made of steel cord, and then the tire sidewalls and, finally, the tread or the other way round. The resultant raw tire is finally vulcanized under pressure and heat in a heated press mold of a vulcanization press and endowed with its shape as a finished tire.

The optimum choice of the components results on the one hand an elevated cross-linking density of the rubber and thus the favorable adhesion properties of the rubber cushion elements at the steel cord extremities, and on the other hand, the desirability that the elements be capable of absorbing a high portion of the deformation energy created during tire operation. As a result of the elevated adhesive strength, the rubber cushion elements and the steel cords combine to form a unit that effectively resists deterioration. The bonding creates a functional unit which is capable of absorbing a high portion of deformation energy and which reduces the effects of friction between the tire components by cushioning the movements of the steel cord ends and isolating the ends from other tire components.

In this context, truck tires having rubber cushion elements of the type disclosed herein failed to show any separation at the edegs of the plies under the highly unfavorable operating conditions to which they were subjected in bench as well as in road tests.

WHAT WE CLAIM IS: 1. A pneumatic tire comprising a pair of annular bead cores; sidewalls; a carcass of at least one ply of rubberized metallic cord fabric having its end portions wrapped radially around the bead cores to form turnups which are axially displaced from the remaining portions of the carcass; in which in each bead core region an annular apex strip is disposed between the carcass and the turnup, the annular apex strip extending radially of and from the bead core and, along its axially inward surface, contacting the carcass; and a bead cushion element of a soft rubber compound having high restorability and a Shore A hardness less than that of the apex strip and the carcass, fills the space between the apex strip and the turnup, envelops the terminal edge of the turnup and extends radially outwardly beyond the apex strip and the turnup into the sidewall thereby isolating the terminal edge of the turnup from the carcass ply and rendering the bead and lower sidewall portion of the pneumatic tire more flexible to inhibit separation of the cords at the terminal edge.

2. A pneumatic tire according to claim 1, and including, in each bead core region, a reinforcement strip of rubberized metallic cord fabric wrapped about the bead core and forming a radially outward extension of the turnup, the bead cushion element also enveloping the terminal edge of the reinforcement strip.

3. A pneumatic tire according to claim 2, in which, in each bead core region, the terminal edge of the turnup is axially spaced from the terminal edge of the reinforcement strip in the bead cushion element.

4. A pneumatic tire according to claim 2, in which, in each bead core region, the terminal edges of the turnup and the reinforcement strip are positioned substantially at the cross-sectional midpoint of the bead cushion element.

5. A pneumatic tire according to any one of the preceding claims in which each bead cushion element has a lentil cross-sectional configuration having at its thickest point, a width equal to a multiple of the thickness of the metallic cords.

6. A pneumatic tire according to any one of claims 1 to 5 and including a tread portion connected to the carcass and defining a pair of shoulders where the edges of the tread portion meet the carcass: a reinforcing belt assembly positioned between the tread portion and the carcass including at least two plies of rubberised metallic cord fabric; and in each shoulder, a shoulder cushion element of a soft rubber compound having high restorability and a Shore A hardness less than that of the tread portion, sidewalls and plies, enveloping the edges of the plies.

7. A pneumatic tire according to claim 6 in which each shoulder cushion element has a sickle cross-sectional configuration extending from the edges of the plies, radially inwardly into the respective sidewall, and having at its thickest point a thickness equal to a multiple of the thickness of the cords in the plies.

8. A pneumatic tire according to any one of the preceding claims in which any or all of the cushion elements have a Shore A hardness of from 50 to 650.

9. A pneumatic tire according to any of the preceding claims in which any or all of the cushion elements have a Shore A hardness of about 60".

10. A pneumatic tire according to any one of the preceding claims in which any or all of the cushion elements have a rebound elasticity of from 55 to 65% determined according to German Industrial Standards DIN 53,512.

11. A pneumatic tire according to any one of the preceding claims in which any or all of the cushion elements are the vulcanization products of a compound comprising; (a) from 20 to 30 parts reinforcing carbon black; (b) from 2.5 to 3.5 parts sulfur;

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. finally, the tread or the other way round. The resultant raw tire is finally vulcanized under pressure and heat in a heated press mold of a vulcanization press and endowed with its shape as a finished tire. The optimum choice of the components results on the one hand an elevated cross-linking density of the rubber and thus the favorable adhesion properties of the rubber cushion elements at the steel cord extremities, and on the other hand, the desirability that the elements be capable of absorbing a high portion of the deformation energy created during tire operation. As a result of the elevated adhesive strength, the rubber cushion elements and the steel cords combine to form a unit that effectively resists deterioration. The bonding creates a functional unit which is capable of absorbing a high portion of deformation energy and which reduces the effects of friction between the tire components by cushioning the movements of the steel cord ends and isolating the ends from other tire components. In this context, truck tires having rubber cushion elements of the type disclosed herein failed to show any separation at the edegs of the plies under the highly unfavorable operating conditions to which they were subjected in bench as well as in road tests. WHAT WE CLAIM IS:

1. A pneumatic tire comprising a pair of annular bead cores; sidewalls; a carcass of at least one ply of rubberized metallic cord fabric having its end portions wrapped radially around the bead cores to form turnups which are axially displaced from the remaining portions of the carcass; in which in each bead core region an annular apex strip is disposed between the carcass and the turnup, the annular apex strip extending radially of and from the bead core and, along its axially inward surface, contacting the carcass; and a bead cushion element of a soft rubber compound having high restorability and a Shore A hardness less than that of the apex strip and the carcass, fills the space between the apex strip and the turnup, envelops the terminal edge of the turnup and extends radially outwardly beyond the apex strip and the turnup into the sidewall thereby isolating the terminal edge of the turnup from the carcass ply and rendering the bead and lower sidewall portion of the pneumatic tire more flexible to inhibit separation of the cords at the terminal edge.

(c) from 5 to 10 parts active silicic acid; (d) from 1 to 3 parts resorcinol; and (e) from 1 to 2.5 parts hexamethylene tetramine; all being parts by weight based on 100 parts rubber.

12. A pneumatic tire according to claim 11, in which said compound further includes zinc ozide. zinc stearate, processing oil, adhesive cement, antioxidants and antiozonants.

13. A pneumatic tire according to claim 11 or claim 12 in which said compound further includes accelerators.

14. A pneumatic tire according to any one of the preceding claims in which any or all of the cushion elements are formed from a mixture of natural rubber and butadiene rubber, which the natural rubber being present in quantities of 30 to 100 parts by weight of the mixture, and butadiene rubber being present in quantities of 70 to 0 parts by weight.

15. A pneumatic tire according to claim 14 in which the butadiene rubber is cis-1,4-polybutadiene rubber.

16. A pneumatic tire according to claim 14 or claim 15 in which the natural rubber is present in quantities of at least 80 parts by weight.

17. A pneumatic tire having a bead region substantially as herein described and as shown in any one Figure of the accompanying drawings.

18. A pneumatic tire substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings, or to either of those Figures as modified by Figure 3 of the accompanying drawings.