Pneumatic radial tire for heavy vehicles

Abstract

A pneumatic radial tire for a heavy vehicle. A belt assembly of the tire has three belt plies, including first and second working plies and a third ply, the first and second working plies being sequentially positioned in the radially outward direction of the tire; the third ply is a transition ply between the carcass and the first working ply or a protective ply between the second working ply and the tread portion; the first working ply comprises a plurality of first steel cords arranged in parallel at a first angle [alpha] 1 within 15 to 30 degrees with respect to the tire circumferential direction, each first steel cord comprising a plurality of first steel wires; the second working ply comprises a plurality of second steel cords arranged in parallel within 15 to 30 degrees with respect to the tire circumferential direction at a second angle [alpha] 2, each second steel cord comprising a plurality of second steel wires, the second steel cords being inclined opposite the first steel cords with respect to the tire circumferential direction, the first and second working plies have a total ply strength, PStr, greater than 2.5 kN / mm and a total ply stiffness, PSti, greater than 1.4 kN * mm.

Description

Technical Field

[0001] The present invention relates to a pneumatic radial tire for a heavy vehicle, in particular a pneumatic radial tire having a belt package with three belt plies. Background Art

[0002] Pneumatic radial tires for heavy vehicles (such as heavy trucks or buses) typically have a belt package with four belt plies. Each of the four belt plies is a rubber ply embedded with steel cords. The four belt plies are a first working ply, a second working ply, a protection ply, and a transition ply respectively. The transition ply is arranged closest to the carcass of the pneumatic radial tire, the protection ply is arranged on the outermost side of the carcass, and the first working ply and the second working ply are arranged between the transition ply and the protection ply. The transition ply includes a plurality of steel cords which are arranged in parallel at a relatively large angle (such as greater than 40 degrees) with respect to the circumferential direction of the pneumatic radial tire. The first working ply includes a plurality of first steel cords which are arranged in parallel at a first angle α1 in the range of 15 degrees to 30 degrees with respect to the circumferential direction of the pneumatic radial tire, the second working ply includes a plurality of second steel cords which are arranged in parallel at a second angle α2 in the range of 15 degrees to 30 degrees with respect to the circumferential direction of the pneumatic radial tire, and the second steel cords are inclined in the opposite direction to the first steel cords with respect to the circumferential direction of the pneumatic radial tire. The protection ply includes a plurality of steel cords which are arranged in parallel at an angle with respect to the circumferential direction of the pneumatic radial tire.

[0003] In order to reduce the tire weight and lower the rolling resistance, one solution is to reduce the number of belt plies from four to three.

[0004] US 6,082,427 discloses a heavy-duty pneumatic radial tire which includes a belt composed of three rubberized cord plies, and the three rubberized cord plies include the innermost cord ply, the intermediate cord ply, and the outermost cord ply, wherein the elastic modulus of the coating rubber for the outermost cord ply is not less than 200 kgf / mm 2 .

[0005] US 7,712,501 discloses a heavy-duty tire including a belt composed of three cord plies, wherein the cords of the radially outer third ply are inclined at an angle of from 13 degrees to 23 degrees in one direction with respect to the equator line of the tire, the cords of the intermediate second ply are inclined at an angle of from 13 degrees to 23 degrees in a direction opposite to that of the radially outer third ply, and the cords of the radially inner first ply are arranged at an angle of from 30 degrees to 70 degrees in a direction opposite to that of the radially outer third belt ply, wherein the total strength of the three plies is in the range of from 120 kN / 5 cm to 170 kN / 5 cm, and the second ply has a relatively large ply strength in the range of from 52 kN / 5 cm to 64 kN / 5 cm. The ply strength S is obtained by multiplying the breaking force E of the cords and the number of cords N ( / 5 cm).

[0006] There is still a need to develop a pneumatic radial tire for heavy vehicles with better performance. SUMMARY OF THE INVENTION

[0007] An object of the present invention is to provide a pneumatic radial tire having a belt assembly with three belt plies, the pneumatic radial tire being for heavy vehicles and having a longer life.

[0008] According to an aspect of the present invention, there is provided a pneumatic radial tire for heavy vehicles. The pneumatic radial tire has a tread portion, a carcass, a pair of bead portions, and a belt assembly. The carcass includes at least one carcass ply. The belt assembly is located between the carcass and the tread portion. The belt assembly has three belt plies. The three belt plies include a first working ply, a second working ply, and a third ply. The first working ply and the second working ply are sequentially positioned along the radially outward direction of the pneumatic radial tire, that is, the first working ply is relatively closer to the carcass than the second working ply. The third ply is a transition ply located between the carcass and the first working ply or a protection ply located between the second working ply and the tread portion. The first working ply includes a plurality of first steel cords. The plurality of first steel cords are arranged in parallel at a first angle α1 in the range of from 15 degrees to 30 degrees with respect to the circumferential direction of the pneumatic radial tire. Each of the first steel cords includes at least one first steel wire, preferably including a plurality of first steel wires. And the second working ply includes a plurality of second steel cords. The plurality of second steel cords are arranged in parallel at a second angle α2 in the range of from 15 degrees to 30 degrees with respect to the circumferential direction of the pneumatic radial tire. Each of the second steel cords includes at least one second steel wire, preferably including a plurality of second steel wires, wherein the second steel cords are inclined in a direction opposite to that of the first steel cords with respect to the circumferential direction of the pneumatic radial tire, wherein the total ply strength PS of the first working ply and the second working ply trGreater than 2.5 kN / mm, and the total ply stiffness PS of the first working ply and the second working ply ti Greater than 1.4 kN×mm, the total ply strength PSt tr and the total ply stiffness PS ti Are calculated by the following formulas respectively:

[0009] PS tr = EPD1 × BL1 × cos 2 α1 / 100000 + EPD2 × BL2 × cos 2 α2 / 100000,

[0010] PSti = EPD1 × CS1 × cos 2 α1 / 100000 + EPD2 × CS2 × cos 2 α2 / 100000,

[0011] Wherein,

[0012] EPD1 is the number of ends per decimeter of the first working ply with at least 50 ends per decimeter, EPD2 is the number of ends per decimeter of the second working ply with at least 50 ends per decimeter, and

[0013] BL1 is the average breaking load of the first steel cord of at least 2300 Newtons, BL2 is the average breaking load of the second steel cord of at least 2300 Newtons, and

[0014] CS1 is the cord stiffness of the first steel cord of at least 1100 N×mm 2 The cord stiffness of the second steel cord of at least 1100 N×mm 2 CS2, and the cord stiffness CS is calculated by the following formula,

[0015] CS = ΣE × N × π × d 4 / 64, wherein

[0016] E is the elastic modulus of steel of 206000 expressed in MPa,

[0017] d is the wire diameter in the range of 0.15 mm to 0.55 mm,

[0018] N is the total number of wires of the steel cord.

[0019] The present invention provides a new solution for a pneumatic radial tire for heavy vehicles with a longer life, and the pneumatic radial tire has a belt assembly with three belt plies.

[0020] As the number of belt plies in a pneumatic radial tire for heavy vehicles is reduced from four to three, in order to make the strength of the belt assembly of a tire with three belt plies consistent with that of an existing tire with four belt plies, the common practice is to increase the ply strength of each belt ply. Each belt ply includes a first working ply, a second working ply, or a third ply as a transition ply or a protection ply, and the ply strength is calculated by multiplying the cord strength by the EPD. Different from common understanding and common practice, the inventor found that the strength of the belt assembly is mainly determined by the total strength of the working plies, while the third ply as a transition ply or a protection ply contributes less to the strength of the belt assembly; in addition, the inventor found that the ply strength of a working ply depends not only on the steel cord strength and the EPD, but also on the inclination angle of the steel cords. Therefore, the inclination angle of the steel cords in the working ply should be considered as one of the factors in the ply strength calculation, because the steel cords in the working ply are always arranged parallel to each other at an angle (i.e., the inclination angle) with respect to the circumferential direction of the pneumatic radial tire, and when the tire is running, the steel cords in the working ply are subjected to a tensile force in a direction along the circumferential direction of the pneumatic radial tire. The present invention provides a new solution for calculating the ply strength of a working ply by considering the influence of the inclination angle of the steel cords, and the present invention provides a new solution with a higher total ply strength PS tr of the first working ply and the second working ply, and this total ply strength PS tr is greater than 2.5 kN / mm, far higher than that of the existing working plies, compensating for the insufficient contribution of the third ply as a transition ply or a protection ply. Therefore, the pneumatic radial tire with three belt plies has sufficient total strength of the belt assembly and can thus be used for heavy vehicles.

[0021] Similar to the above description, the stiffness of a working ply depends not only on the stiffness of the steel cords and the EPD, but also on the inclination angle of the steel cords, that is, the inclination angle of the steel cords in the working ply should be considered as one of the factors in the ply stiffness calculation. The present invention provides a new solution for calculating the ply stiffness of a working ply by considering the influence of the inclination angle of the steel cords, and the present invention provides a new solution with a higher total ply stiffness PS ti of the first working ply and the second working ply, and this total ply stiffness PS ti is greater than 1.4 kN×mm, far higher than that of the existing working plies, compensating for the insufficient contribution of the third ply as a transition ply or a protection ply. Therefore, the pneumatic radial tire with three belt plies has sufficient total stiffness of the belt assembly and can thus be used for heavy vehicles.

[0022] Since the number of belt plies is reduced from 4 to 3, the hoop effect between the two working plies is correspondingly reduced, and this results in an increase in the maximum shear stress between the two working plies and an increase in the maximum shear stress in the shoulder insert. Therefore, cracks in the working plies spread inwards, which may increase the risk of tire burst, or cracks in the working plies spread outwards, which may increase the risk of shoulder separation. According to the present invention, the total ply strength PS tr and the total ply stiffness PS ti of the first working ply and the second working ply are increased, that is, PS tr is greater than 2.5 kN / mm and PS ti is greater than 1.4 kN×mm, so that the hoop effect between the two working plies is improved. Therefore, the maximum shear stress between the two working plies and the maximum shear stress in the shoulder insert are reduced, and thus the life of the tire is improved and extended. In addition, since the maximum shear stress between the two working plies and the maximum shear stress in the shoulder insert are reduced, rubber deformation and heat generation are reduced. Therefore, the rolling resistance coefficient and the maximum temperature at the shoulder are reduced.

[0023] The pneumatic radial tire of the present invention is for heavy vehicles, especially for tubeless heavy vehicles.

[0024] Preferably, the total ply strength PS tr of the first working ply and the second working ply is greater than or equal to 2.7 kN / mm. More preferably, the total ply strength PS tr of the first working ply and the second working ply is in the range of 2.9 kN / mm to 3.5 kN / mm. This enables a pneumatic radial tire with three belt plies to have a belt assembly with very high strength for heavy vehicles.

[0025] Preferably, the total ply stiffness PS ti of the first working ply and the second working ply is greater than or equal to 1.6 kN×mm. More preferably, the total ply stiffness PS ti of the first working ply and the second working ply is in the range of 1.6 kN×mm to 2.5 kN×mm. This high total ply stiffness of the working plies significantly improves the hoop effect between the two working plies, especially for a pneumatic radial tire with three belt plies, which has a belt assembly with very high total strength.

[0026] Each of the three belt plies, including the first working ply, the second working ply, or the third ply, is an impregnated cord ply, i.e., a rubber ply embedded with steel cords arranged in parallel, while the steel cords are arranged at a certain inclination angle with respect to the circumferential direction of the pneumatic radial tire. For example, for the working ply, the inclination angle is from 15 degrees to 30 degrees, and for the third ply, the inclination angle is from 20 degrees to 80 degrees. The inclination direction of the first steel cords in the first working ply is opposite to the inclination direction of the second steel cords in the second working ply. When the third ply is a transition ply, the inclination direction of the steel cords in the third ply is the same as the inclination direction of the steel cords in the adjacent first working ply; or, when the third ply is a protection ply, the inclination direction of the steel cords in the third ply is opposite to or the same as the inclination direction of the steel cords in the adjacent second working ply.

[0027] According to the present invention, the number of ends per decimeter ('EPD') of each working ply is at least 50 ends per decimeter, and both EPD1 and EPD2 are at least 50 ends per decimeter. By doing so, combined with the predetermined average breaking load of the steel cords and the cord inclination angle, a high ply strength of the desired working ply can be achieved. Preferably, EPD1 and / or EPD2 are in the range of 55 ends per decimeter to 70 ends per decimeter.

[0028] Preferably, EPD1 is the same as EPD2. Alternatively, EPD1 and EPD2 are different.

[0029] According to the present invention, the steel cords in the working ply should have a high breaking load, so the steel cords in the working ply should have a high average breaking load. Both BL1 and BL2 are at least 2300 Newtons. Preferably, both BL1 and BL2 are in the range of 2300 Newtons to 3500 Newtons. Preferably, BL1 is the same as BL2. Alternatively, BL1 and BL2 are different.

[0030] Preferably, the steel cords in the working ply (i.e., the first steel cords in the first working ply and / or the second steel cords in the second working ply) have a 1×n construction, where n is 5 or 6. Alternatively, the steel cords in the working ply (i.e., the first steel cords in the first working ply and / or the second steel cords in the second working ply) have an n+m construction, n is from 1 to 4, and m is from 3 to 10. The first steel cords and the second steel cords can have the same or different constructions.

[0031] To obtain a high cord breaking load, each wire in the steel cord (i.e., each first wire in the first steel cord and / or each second wire in the second steel cord) has a diameter d in the range of 0.35 mm to 0.45 mm and an ultra-high or extremely high tensile strength TS, where TS ≥ 4100 - 2000×d MPa. Preferably, 4200 - 2000×d ≤ TS ≤ 4800 - 2000×d MPa.

[0032] By using wires with ultra-high tensile strength (ST) or extremely high tensile strength (UT) and large diameters, the total number N of wires in the steel cord for achieving a high total ply stiffness can be no more than 14. Preferably, N is in the range of 5 to 14.

[0033] According to the present invention, the ply stiffness of each working ply is mainly related to the EPD of the working ply, the cord stiffness CS, and the cord inclination angle. To achieve a high ply stiffness, based on a predetermined EPD and cord inclination angle, the cord stiffness of each steel cord in the working ply is at least 1100 N×mm 2 . Preferably, the cord stiffness of the first steel cord CS1 and / or the cord stiffness of the second steel cord CS2 is in the range of 1700 N×mm 2 to 2600 N×mm 2 .

[0034] According to the present invention, the third ply is a transition ply located between the carcass and the first working ply or a protective ply located between the second working ply and the tread portion, and it can be any one of the existing transition plies or any one of the existing protective plies for a pneumatic radial tire having three belt plies or four belt plies.

[0035] The third ply has a ply strength much smaller than that of the first working ply or the second working ply, such as 1.67 kN / mm or even smaller. The third ply has a ply stiffness much smaller than that of the first working ply or the second working ply, such as 0.81 kN×mm or even smaller. The EPD of the third ply does not exceed 45 ends per decimeter, or even does not exceed 40 ends per decimeter.

[0036] The rubber compound for the belt ply including the first working ply, the second working ply, and the third ply can be any one of the existing rubber compounds. The rubber compounds for different plies can be the same or different.

[0037] The rubber gauge of each belt ply can be any one of the rubber gauges in the rubber gauges in the art, such as 0.4 mm to 0.8 mm. Description of the Drawings

[0038] Figure 1 is a partial cross-sectional view of the tire of the present invention.

[0039] Figure 2 is a partial plan view of the belt assembly showing the steel cord arrangement.

[0040] Figure 3 is a partial front view of the first working ply showing the ends of the steel cords. Detailed Description

[0041] As Figure 1 shown, the pneumatic radial tire for heavy vehicles includes a tread portion 105, a pair of sidewall portions 110, a pair of bead portions (not shown), a carcass 120 extending between the bead portions, and a belt assembly 125 located between the carcass 120 and the tread portion 105.

[0042] The carcass 120 has a carcass ply having steel cords arranged parallel at an angle of 90 degrees with respect to the circumferential direction of the pneumatic radial tire. The carcass ply extends between the bead portions while passing through the sidewall portions 110 and the tread portion 105.

[0043] As Figure 2 shown, the belt assembly 125 has three belt plies. The third ply 205 as a transition ply is the innermost ply on top of the carcass 120, the first working ply 210 is on top of the third ply 205, and the second working ply 215 is on top of the first working ply 210. The steel cords in each ply are arranged parallel at a certain angle with respect to the circumferential direction A - A of the pneumatic radial tire. The first steel cords 220 in the first working ply 210 have an inclination angle α1 of 18 degrees with respect to the circumferential direction A - A of the pneumatic radial tire, the second steel cords 225 in the second working ply 215 have an inclination angle α2 of 18 degrees with respect to the circumferential direction A - A of the pneumatic radial tire, and the steel cords in the third ply 205 have an inclination angle of 60 degrees with respect to the circumferential direction A - A of the pneumatic radial tire. As Figure 3 shown, the first working ply 210 has first steel cords 220 with a structure of 1×6 and a rubber gauge of 0.45 mm.

[0044] Table 1 summarizes the FEM modeling comparison results between the examples of the present invention and the comparative examples in a tire of size 12R22.5.

[0045] Table 1

[0046]

[0047] * “100” is the reference score.

[0048] The calculation method of the average breaking load of the steel cord is as follows:

[0049] - Take out a rubber block with three steel cords inside from the belt carcass ply (such as the working carcass ply), ensuring that the length of the steel cords in the rubber block is greater than 30 cm; then remove the surface rubber of the rubber block until the three steel cords are wrapped by thin and smooth rubber, ensuring that the three steel cords are still inside the rubber block without any separation from the rubber of the rubber block or exposure outside the rubber of the rubber block; thus obtain a thin block sample with two long sides and two short sides, where the block sample has three steel cords, two of the three steel cords are side steel cords, and one steel cord is the middle steel cord;

[0050] - Remove a part of the two side steel cords from the block sample by cutting from a position 8 cm away from one end of the block sample until another position 8 cm away from the other end of the block sample, while keeping the middle steel cord undamaged; thus obtain an I-shaped test sample, that is, two end parts and a relatively narrow middle part;

[0051] - Clamp the two end parts of the test sample by two clamps (Zwick type 8303-10kN) respectively, and conduct a tensile test by a tensile testing machine. The conditions of the tensile test are: tensile speed 50 mm / min, preload 10 N; and the load at the time of fracture of the middle steel cord is the breaking load of the steel cord;

[0052] - Repeat sample preparation and testing, and take the average value by calculating 8 valid data of the breaking load of the steel cord. This average value is used as the average breaking load of the steel cord in the belt carcass ply. "Valid data" means that the steel cord breaks at any part of the middle steel cord between the two clamps, rather than at the clamped part of the middle steel cord.

[0053] The test method for the tensile strength of the steel wire:

[0054] - Take out a steel cord from the belt carcass ply (such as the working carcass ply) without causing any damage to the steel cord, ensuring that the length of the steel cord is greater than 30 cm;

[0055] - Remove each steel wire from the steel cord without causing any damage to the steel wire; select a single steel wire, and clamp two end portions of the single steel wire respectively by two clamps (Zwick type 8303 - 10kN), and conduct a tensile test through a tensile testing machine. The conditions of the tensile test are: tensile speed 50mm / min, preload 10N, and the load at which the steel wire breaks is the breaking load of the steel wire; calculate the tensile strength of the steel wire by dividing the breaking load of the steel wire by the cross-sectional area of the steel wire, and this tensile strength is used as the tensile strength of the single steel wire; conduct tensile tests and calculations on each single steel wire, and calculate the average value, and this average value is used as the average value of the tensile strength of the steel wires of the steel cord.

[0056] Steel wire diameter test method: Completely remove the rubber from the surface of the steel wire, and conduct the test according to the diameter test method in Chinese standard GB / T 33159 - 2016.

Claims

1. A pneumatic radial tire for a heavy vehicle, the pneumatic radial tire having a tread portion, a carcass, a pair of bead portions, and a belt assembly, the carcass including at least one carcass ply, the belt assembly being located between the carcass and the tread portion, the belt assembly having three belt plies, the three belt plies including a first working ply, a second working ply, and a third ply, the first working ply and the second working ply being sequentially positioned along a radially outward direction of the pneumatic radial tire, the third ply being a transition ply located between the carcass and the first working ply or a protection ply located between the second working ply and the tread portion, the first working ply includes a plurality of first steel cords, the plurality of first steel cords being arranged in parallel at a first angle α1 in a range of 15 degrees to 30 degrees with respect to the circumferential direction of the pneumatic radial tire, each of the first steel cords including a plurality of first steel wires, and the second working ply includes a plurality of second steel cords, the plurality of second steel cords being arranged in parallel at a second angle α2 in a range of 15 degrees to 30 degrees with respect to the circumferential direction of the pneumatic radial tire, each of the second steel cords including a plurality of second steel wires, and the second steel cords are inclined in a direction opposite to that of the first steel cords with respect to the circumferential direction of the pneumatic radial tire, and It is characterized in that The total cord ply strength PS of the first working cord ply and the second working cord ply tr is greater than 2.5 kN / mm, and the total cord ply stiffness PS of the first working cord ply and the second working cord ply ti is greater than 1.4 kN×mm. The total cord ply strength PS tr and the total cord ply stiffness PS ti are calculated by the following formulas respectively: PS tr = EPD1 × BL1 × cos 2 α1 / 100000 + EPD2 × BL2 × cos 2 α2 / 100000, PSti = EPD1 × CS1 × cos 2 α1 / 100000 + EPD2 × CS2 × cos 2 α2 / 100000, wherein, EPD1 is the number of ends per decimeter of the first working ply with at least 42 ends per decimeter, EPD2 is the number of ends per decimeter of the second working ply with at least 42 ends per decimeter, and BL1 is the average breaking load of the first steel cords of at least 2300 Newtons, BL2 is the average breaking load of the second steel cords of at least 2300 Newtons, and CS1 is the cord stiffness of the first steel cord of at least 1100 N×mm 2 and CS2 is the cord stiffness of the second steel cord of at least 1100 N×mm 2 The cord stiffness CS is calculated by the following formula CS = ΣE × N × π × d 4 / 64, where E is the elastic modulus of steel of 206000 expressed in MPa, d is the wire diameter in a range of 0.15 mm to 0.55 mm, N is the total number of steel wires of the steel cords of at least 4.

2. The pneumatic radial tire for heavy vehicles according to claim 1, wherein The total ply strength PS of the first working ply and the second working ply tr is greater than or equal to 2.7 kN / mm.

3. The pneumatic radial tire for heavy vehicles according to claim 2, characterized in that, The total ply strength PS tr of the first working ply and the second working ply ranges from 2.9 kN / mm to 3.5 kN / mm.

4. The pneumatic radial tire for heavy vehicles according to any one of claims 1 to 3, characterized in that, The total ply stiffness PS of the first working ply and the second working ply ti is greater than or equal to 1.6 kN×mm.

5. The pneumatic radial tire for heavy vehicles according to claim 4, wherein The total ply stiffness PS of the first working ply and the second working ply ti ranges from 1.6 kN×mm to 2.5 kN×mm.

6. The pneumatic radial tire for heavy vehicles according to any one of claims 1 to 5, characterized in that, Each of the first steel wires of the first steel cords and / or each of the second steel wires of the second steel cords has a diameter d in a range of 0.35 mm to 0.45 mm and a tensile strength TS, TS≥4100 - 2000×d MPa.

7. The pneumatic radial tire for heavy vehicles according to claim 6, characterized in that, Each of the first steel wires of the first steel cords and / or each of the second steel wires of the second steel cords has a tensile strength TS, 4200 - 2000×d MPa≤TS≤4800 - 2000×d MPa.

8. The pneumatic radial tire for heavy vehicles according to any one of claims 1 to 7, characterized in that, The range of N is 5 to 14.

9. The pneumatic radial tire for heavy vehicles according to any one of claims 1 to 8, characterized in that, The first steel cords and / or the second steel cords have a 1×n structure, where n is 5 or 6.

10. The pneumatic radial tire for heavy vehicles according to any one of claims 1 to 8, characterized in that, The first steel cords and / or the second steel cords have an n + m structure, n is 1 to 4, and m is 3 to 10.

11. The pneumatic radial tire for heavy vehicles according to any one of claims 1 to 10, characterized in that, The range of EPD1 and / or EPD2 is 48 to 65 ends per decimeter.

12. The pneumatic radial tire for heavy vehicles according to claim 11, characterized in that, The range of EPD1 and / or EPD2 is 50 to 60 ends per decimeter.

13. The pneumatic radial tire for heavy vehicles according to any one of claims 1 to 12, characterized in that, The range of the BL1 and / or the BL2 is from 2500 Newtons to 3200 Newtons.

14. The pneumatic radial tire for heavy vehicles according to any one of claims 1 to 13, characterized in that, The range of the CS1 and / or the CS2 is from 1500 to 2500.

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