Patent Application
20070012393
The present invention is directed to a pneumatic tire. More specifically, the present invention is directed to a pneumatic tire comprising a belt reinforcing ply wherein the steel cords of the belt ply have a filament diameter of 0.45 to 0.65 mm and a minimum tensile strength.
For passenger vehicle tires, the belt plies of a tire perform multiple functions. Such functions include limiting tire growth, contributing to tire strength, achieving desirable foot print shape, stiffness characteristics affected tread wear, and, depending upon the structure of the cords therein, assisting in puncture resistance. To optimize the thickness of the belt ply and the desired strength of the belt ply, cords used to form the belt plies have conventionally been formed from filaments having a diameter in the range of 0.10 to 0.45 mm.
With the advent of steel filaments of greater tensile strength for given diameters, the industry has looked at various ways of using the greater tensile strength wires for reinforcement plies. These various methods have conventionally included reducing the wire diameter while using the same cord construction or using the same wire diameter while using fewer filaments to form the cord construction.
The present invention is directed to cord structures that take advantage of steel filaments having a very high tensile strength with acceptable cord fatigue strength.
The present invention is directed to a pneumatic tire having a belt ply wherein the ply cords are formed of multiple individual filaments having a diameter ranging from 0.45 to 0.65 mm, each filament having a tensile strength of at least −2000 D+4050 MPa, where D is the filament diameter in mm.
In another aspect of the invention, the filaments have a tensile strength of at least −2000 D+4400 MPa, thus being ultra tensile steel filaments. A preferred tire according to the invention has at least one belt ply wherein the cords are formed of filaments of ultra tensile steel having a diameter of 0.55 mm.
In another aspect of the invention, the cord has a structure selected from the group consisting of 1×, 2×, 3×, 4×, 5×, 6×, 7×, 8×, 11×, 12×, 1+2, 1+3, 1+4, 1+5, 1+6, 1+7, 1+8, 1+14, 2+2, 2+5, 2+6, 2+7, 2+8, 2+9, 2+10, 2+2+8, 2/2, ⅔, 2/4, ⅖, 2/6, 3+2, 3+3, 3+4, 3+6, 3+9, 3+9+15, 27×, 1+26, 4×4, 5/8/14, 7×2, 12+1, 3+9+1, 1+6+1, 2+6+1, 2+7+1, 2+8+1, 2+9+1, 2+10+1, 1+6+12, 2+2+8+1, 3+9+15+1, 27+1, 1+26+1 and 7×2+1.
The tires disclosed herein may be passenger vehicle tires, light truck tires, including Load Range B, C, D, E, and F tires, or radial medium truck (RMT) tires.
In another aspect of the invention, the belt structure has at least two reinforcing plies and the at least two plies are reinforced with the metallic cords formed of high tensile strength and large filament diameter. Alternatively, for the larger RMT tires, the belt structure may have at least three reinforcing plies and two of the at least three reinforcing plies are reinforced with the metallic cords.
Definitions
The following definitions are applicable to the present invention:
“High Tensile Strength Steel (HT)” means a carbon steel with a tensile strength of at least 3400 MPa @ 0.20 mm filament diameter;
“Super Tensile Strength Steel (ST)” means a carbon steel with a tensile strength of at least 3650 MPa @ 0.20 mm filament diameter, and may be characterized by the equation of TS=4050−2000 D, where D is the filament diameter;
“Ultra Tensile Strength Steel (UT)” means a carbon steel with a tensile strength of at least 4000 MPa @0.20 mm filament diameter; and may be characterized by the equation of TS=4400−2000 D, where D is the filament diameter; and
“Mega Tensile Strength Steel (MT)” means a carbon steel with a tensile strength of at least 4500 MPa @ 0.20 mm filament diameter, and may be characterized by the equation of TS=4900−2000 D, where D is the filament diameter.
The invention will be described by way of example and with reference to the accompanying drawings in which:
The following language is of the best presently contemplated mode or modes of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. The reference numerals as depicted in the drawings are the same as those referred to in the specification. For purposes of this application, the various embodiments illustrated in the figures each use the same reference numeral for similar components. The structures employed basically the same components with variations in location or quantity thereby giving rise to the alternative constructions in which the inventive concept can be practiced.
The tire 10 is a radial medium truck (RMT) tire. RMT tires are generally equipped on over-the-road, cargo vehicles. Such tires have an overall diameter ranging from about 30 inches (76.2 cm) to about 45 inches (114.3 cm), and most have a diameter in the range of 40 inches (88.9 cm) to about 45 inches (114.3 cm). Alternatively, the tire 10 may be either a passenger tire or light truck tire; such a tire having an overall maximum diameter of not greater than 35 inches (88.9 cm).
An inner liner 20 of low permeability material is disposed inwardly of the carcass plies 12, 14. Elastomeric sidewalls 22, 24 are disposed axially outwardly of the carcass structure. A circumferentially extending belt structure 26 is radially outward of the carcass plies 12, 14 in the crown region of the tire 10, underlying the tire tread 32. In the illustrated embodiment of
In accordance with the invention, the steel cords in at least one of the belt plies 28, 30 are formed of at least one steel filament having a filament diameter in the range of 0.45 to 0.65 mm and have a tensile strength at least equal to −2000 D+4050 MPa, where D is the diameter of the filaments forming the steel cord. Thus, the steel filaments are at least super tensile steel filaments, but instead of reducing the wire diameter to take advantage of the higher strength steel filaments, the diameter of the filaments is increased over conventional diameters. The larger diameter filaments permit the use of fewer filaments in the cords used in the belt structure. Preferably, the filament has a diameter in the range of 0.50 to 0.60 mm, and has a tensile strength of at least a super tensile strength steel. Most preferably, the filament has a diameter of about 0.55 mm and has a tensile strength of at least an ultra tensile strength steel.
These larger filament cords are most useful in the belt structure to enhance cut resistance properties of the belt structure and exhibit similar strength and ductility as the smaller diameter, larger number of filament cords. For use in the belt structure, preferred cord constructions are 1×, 2× (
In the above cord constructions, there is at least one filament having a diameter in the range of 0.45 to 0.65 mm. The cords may be constructed wherein all of the filaments in the cord have a diameter in the above range. The cords may also be constructed wherein all of the filaments have a diameter in the above range, but the filaments in the cord have at least two different diameters; for example, cord 1+6+12 may be constructed as 1×0.65+6×0.45+12×0.45. The cord may even include at least one filament having a diameter greater than 0.65 mm, for example: 1×0.85+6×0.65+12×0.65. For both of these non-limiting examples, an “open” cable is formed due to the greater diameter of the central filament. The cord may also include a filament having a diameter of less than 0.45 mm; this is most likely for cords of a wrapped construction wherein the +1 wrap cord has a diameter of less than 0.45 mm.
Additionally, any of the above cord constructions may be formed of either distinct layers having different lay lengths or formed as bunched cables wherein the filaments of the different layers are all twisted together at the same time resulting in the same lay length for the different layers.
In one embodiment of the present invention, the belt structure is composed of the two belt plies 28, 30 wherein the cords in both plies are reinforced with cords of the present invention. In another embodiment of the present invention, the belt structure includes a first, second, and third radially overlapped belts wherein the cords of the present invention are used in at least one of the belt plies. In preferred constructions, the outermost ply in the belt structure is the ply comprising the large filament wire cords. In any embodiment of the belt structure, any of the plies may be folded edge plies.
Sample cord constructions were prepared and tested against conventional, comparable cord constructions, see Table 1.
For cord constructions A-C, cord A is the conventional cord, while cords B and C are potential replacements for cord A. Cord B has 45% less filaments than cord A, but has a breaking load only 22% less than for cord A. Cord C has a 60% reduction in filaments from cord A, with a breaking load only 28% less than cord A.
For cord constructions D-F, cord D is the conventional cord, while cords E and F are potential replacements for cord D. Cord D has the same amount of filaments as cord E, but with a 40% increase in breaking load even though the tensile strength of the filament is reduced. Cord E has 35% fewer cord filaments, but has a 17% increase in breaking load.
For cord constructions G and H, potential replacement cord H has 25% fewer filaments, but a 5% increase in breaking load in comparison to conventional cord G. For cord constructions I and J, potential replacement cord J has the same number of filaments, a reduced filament tensile strength, but a 40% increase in breaking load. For cord constructions K and L, potential replacement cord L has ⅓ fewer filaments, with only a 6% decrease in breaking load.
Several embodiments of the cords formed with the high strength 0.55 diameter filaments were also tested for fatigue properties and found to have acceptable fatigue properties. With comparable steel areas for the larger filament diameter cord constructions, the cords have a lower linear density while providing comparable physical characteristics.
