A pneumatic radial tire for heavy vehicle

Abstract

A longer lifetime pneumatic radial tire having a belt package (125) with three belt plies for heavy vehicle is provided. The pneumatic radial tire has a tread portion (105), a carcass (120) comprising at least one carcass ply, a pair of bead portions, and a belt package located between the carcass and the tread portion, the belt package has 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 are located in sequence along the radially outward direction of the pneumatic radial tire; the third ply is either 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 comprises a plurality of first steel cords arranged in parallel with a first angle di relative to the circumferential direction of the pneumatic radial tire in a range of 15 to 30 degrees, each of the first steel cords comprises multiple first steel filaments; and the second working ply comprises a plurality of second steel cords arranged in parallel with a second angle relative to the circumferential direction of the pneumatic radial tire in a range of 15 to 30 degrees, each of the second steel cords comprises multiple second steel filaments, wherein the second steel cords are inclined oppositely to the first steel cords with respect to the circumferential direction of the pneumatic radial tire, wherein the total ply strength PStr of the first working ply and the second working ply is more than 2.5 kN / mm, and the total ply stiffness PSti of the first working ply and the second working ply is more than 1.4 kNxmm.

Description

[0001] Title A pneumatic radial tire for heavy vehicle

[0002] Description

[0003] Technical Field

[0004]

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

[0005] Background Art

[0006] [2] Pneumatic radial tire for heavy vehicle such as heavy truck or bus normally has a belt package with four belt plies. Each of four belt plies is a rubber ply embedded with steel cords. The four belt plies are separately a first working ply, a second working ply, a protection ply and a transition ply. The transition ply is arranged nearest to the carcass of the pneumatic radial tire, the protection ply is arranged at the outermost from the carcass, wherein the first working ply and the second working ply are arranged between the transition ply and the protection ply. The transition ply comprises a plurality of steel cords arranged in parallel with a relatively large angle such as more than 40 degrees relative to the circumferential direction of the pneumatic radial tire. The first working ply comprises a plurality of first steel cords arranged in parallel with a first angle ai relative to the circumferential direction of the pneumatic radial tire in a range of 15 to 30 degrees, the second working ply comprises a plurality of second steel cords arranged in parallel with a second angle a2 relative to the circumferential direction of the pneumatic radial tire in a range of 15 to 30 degrees, wherein the second steel cords are inclined oppositely to the first steel cords with respect to the circumferential direction of the pneumatic radial tire. The protection ply comprises a plurality of steel cords arranged in parallel with an angle relative to the circumferential direction of the pneumatic radial tire.

[0007] [3] For the purpose of tire weight reduction and lower rolling resistance, one solution is to reduce the number of belt ply from four to three.

[0008] [4] US 6,082,427 discloses a heavy duty pneumatic radial tire comprises a belt comprised of three rubberized cord layers including an innermost cord layer, a middle cord layer and an outermost cord layer, wherein the coating rubber for the outermost cord layer has a modulus of elasticity of not less than 200kgf / mm2.

[0009] [5] US 7,712,501 discloses a heavy duty tire comprising a belt consists of three plies of cords, wherein the cords of the radially outer third ply are inclined towards one direction at an angle of from 13 to 23 degrees with respect the tire equator, the cords of the intermediate second ply are inclined at an angle of from 13 to 23 degrees towards one direction being 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 to 70 degrees towards one direction being opposite to that of the radially outer third belt ply, wherein the total of strength of the three plies is in a range of from 120 to 170 kN / 5cm, the second ply has a relatively bigger ply strength in the range of 52 - 64 kN / 5cm. The ply strength S is obtained by multiplying the force at break E of a cord and the cord count N( / 5cm).

[0010] [6] Still need to develop a pneumatic radial tire for heavy vehicle with better performance.

[0011] Disclosure of Invention

[0012] [7] The object of the invention is to provide a pneumatic radial tire having a belt package with three belt plies for heavy vehicle with longer lifetime.

[0013] [8] According the aspect of the invention, a pneumatic radial tire for heavy vehicle is provided. The pneumatic radial tire has a tread portion, a carcass comprising at least one carcass ply, a pair of bead portions, and a belt package located between the carcass and the tread portion, the belt package has 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 are located in sequence along the radially outward direction of the pneumatic radial tire, i.e. the first working ply is relatively close to the carcass than the second working ply; the third ply is either 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 comprises a plurality of first steel cords arranged in parallel with a first angle ai relative to the circumferential direction of the pneumatic radial tire in a range of 15 to 30 degrees, each of the first steel cords comprises at least one first steel filament preferably multiple first steel filaments; and the second working ply comprises a plurality of second steel cords arranged in parallel with a second angle a2 relative to the circumferential direction of the pneumatic radial tire in a range of 15 to 30 degrees, each of the second steel cords comprises at least one second steel filament preferably multiple second steel filaments, wherein the second steel cords are inclined oppositely to the first steel cords with respect to the circumferential direction of the pneumatic radial tire, wherein the total ply strength PStr of the first working ply and the second working ply is more than 2.5 kN / mm, and total ply stiffness PSti of the first working ply and the second working ply is more than 1 .4 kNxmm, the total ply strength PStr and the total ply stiffness PSti are separately calculated by the following formulas:

[0014] PStr = EPDixBLixcos2ai / 100000 + EPD2xBI_2xcos2a2 / 100000, PSti = EPDixCSi xcos2ai / 100000 + EPD2xCS2xcos2a2 / 100000, Wherein,

[0015] EPDi is the number of ends per decimeter of the first working ply of at least 50 ends per decimeter, EPD2 is the number of ends per decimeter of the second working ply of at least 50 ends per decimeter, and

[0016] BL1 is the average breaking load of the first steel cords of at least 2300 Newton, BL2 is the average breaking load of the second steel cords of at least 2300 Newton, and

[0017] CS1 is the cord stiffness of the first steel cord of at least 1100 Nxmm2, CS2 is the cord stiffness of the second steel cord of at least 1100 Nxmm2, the cord stiffness CS is calculated by the formula,

[0018] CS = ZExNx7ixd4 / 64, wherein

[0019] - E is the steel elastic modulus of 206000 expressed in MPa,

[0020] - d is the steel filament diameter in the range of 0.15 to 0.55mm,

[0021] - N is the total number of steel filament of steel cord.

[0022] [9] The invention provides a new solution of longer lifetime pneumatic radial tire having a belt package with three belt plies for heavy vehicle.

[0023]

[0010] With the reduction of the number of belt ply from four to three for a pneumatic radial tire for heavy vehicle, for making the strength of the belt package of tire with three belt plies being consistent with the existing tire with four belt plies, the common practice is increasing the ply strength of every belt ply, including the first working ply, the second working ply or the third ply of either the transition ply or the protection ply, and the ply strength is calculated by multiplying the cord strength and EPD. Different from the common understanding and common practice, the inventors find that the strength of the belt package is mainly determined by the total strength of the working plies, while the third ply of either the transition ply or the protection ply contributes less to the strength of the belt package; futhermore, the inventors find that the ply strength of one working ply is depending on not only the steel cord strength and EPD but also the inclination angle of steel cord, as thus the inclination angle of steel cord in the working ply shall be considered as one of the factors for ply strength calculation, because the steel cords in the working ply are always arranged in parallel with an angle relative to the circumferential direction of the pneumatic radial tire (i.e. inclination angle), while the steel cords in the working ply are subjected to a tensile force which is in a direction along the circumferential direction of the pneumatic radial tire when the tire is running. The invention provides a new solution of calculating the ply strength of one working ply by considering the affect of the inclination angle of steel cord, and the invention provides of a new solution of higher total ply strength PStr of the first working ply and the second working ply of more than 2.5 kN / mm, much higher than the existing working plies, as a compensation to the insufficient contribution from the third ply of either the transition ply or the protection ply. As a result, the pneumatic radial tire with three belt plies has sufficient total strength of the belt package and thereby available for heavy vehicle.

[0024]

[0011] As the same the explanation above, the stiffness of one working ply is depending on not only the steel cord stiffenss and EPD but also the inclination angle of steel cord, i.e. the inclination angle of steel cord in the working ply shall be considered as one of the factors for ply stiffness calculation. The invention provides a new solution of calculating the ply sstiffness of one working ply by considering the affect of the inclination angle of steel cord, and the invention provides of a new solution of higher total ply stiffness PSti of the first working ply and the second working ply of more than 1.4 kNxmm, much higher than the existing working plies, as a compensation to the insufficient contribution from the third ply of either the transition ply or the protection ply. As a result, the pneumatic radial tire with three belt plies has sufficient total stiffness of the belt package and thereby available for heavy vehicle.

[0025]

[0012] With the reduction of the number of belt ply from four to three, the hoop effect between the two working plies decreases accordingly, and this results in an increased maximum shear stress between the two working plies and an increased maximum shear stress in the tire shoulder insert, as thus either the cracks of the working plies spread inwards which may lead to the increase of the risk of tire burst, or the cracks of the working plies spread outwards which may lead to the increase of the risk of tire shoulder separation. According to the invention, the increase of the total ply strength PStr and the total ply stiffness PSti of the first working ply and the second working ply, i.e. PStr of more than 2.5 kN / mm and PSti of more than 1 .4 kNxmm, makes the hoop effect of the two working plies being improved, as a result the maximum shear stress between the two working plies and the maximum shear stress in the shoulder insert are reduced, thereafter the lifetime of the tire is improved and extended. Further more, the rubber deformation and the heat generation are reduced, since the maximum shear stress between the two working plies and the maximum shear stress in the shoulder insert are reduced. As thus the rolling resistance coefficient and the highest temperature at shoulder are reduced.

[0026]

[0013] The invention pneumatic radial tire is for heavy vehicle, in particular for the tubeless heavy vehicle.

[0027]

[0014] Preferably the total ply strength PStr of the first working ply and the second working ply is more than and equal to 2.7 kN / mm. More preferably the total ply strength PStr of the first working ply and the second working ply is in the range of 2.9 to 3.5 kN / mm. This makes the pneumatic radial tire with three belt plies having a very high strength of the belt package for heavy vehicle.

[0015] Preferably the total ply stiffness PSti of the first working ply and the second working ply is more than and equal to 1 .6 kNxmm. More preferably the total ply stiffness PSti of the first working ply and the second working ply is in the range of 1 .6 to 2.5 kNxmm. Such high total ply stiffness of the working plies makes the hoop effect between the two working plies being sigificantly improved, in particular for the pneumatic radial tire with three belt plies having a very high total strength of the belt package.

[0028]

[0016] Each of the three belt plies including first working ply, a second working ply or a third ply is rubberized cord ply, i.e. a rubber ply embedded with steel cords which are arranged in parallel, while the steel cords are arranged in a certain inclination angle relative to the circumferential direction of the pneumatic radial tire, for example 15 to 30 degrees for working ply, and 20 to 80 degrees for the third ply. 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. The inclination direction of the steel cords in the third ply is the same as the inclination direction of the steel cords in the first working ply which is adjacent to, when the third ply is a transition ply; or, 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 second working ply which is adjacent to, when the third ply is a protection ply.

[0029]

[0017] According to the invention, the number of ends per decimeter (‘EPD’) of each working ply is at least 50 ends per decimeter, that both EPDi and EPD2 are at least 50 ends per decimeter. By doing this, the desired high ply strength of the working ply can be reached, in combination of predetermined average breaking load of steel cords and cord inclination angle. Preferably, EPD1 and / or EPD2 is in the range of 55 to 70 ends per decimeter.

[0030]

[0018] Perferably EPD1 is the same as EPD2. Alternativley, EPD1 and EPD2 are different.

[0031]

[0019] According to the invention, the breaking load of the steel cord in the working ply shall be high, and accordingly the average breaking load of the steel cords in the working ply shall be high. Both BL1 and BL2 are at least 2300 Newton. Preferably both BL1 and BL2 are in the range of 2300- 3500 Newton. Perferably BLi is the same as BL2. Alternativley, BL1 and Bl_2 are different.

[0032]

[0020] Preferably the steel cord in the working ply, i.e. the first steel cord in the first working ply and / or the second steel cord in the second working ply, has a construction of 1xn, wherein n is 5 or 6. Alternatively, the steel cord in the working ply, i.e. the first steel cord in the first working ply and / or the second steel cord in the second working ply, has a construction of n+m, n is 1 to 4, m is 3 to 10. The first steel cord and the second steel cord may have the same or different construction.

[0033]

[0021] For obtaining a high cord breaking load, each steel filament of the steel cord, i.e., each first steel filament of the first steel cord and / or each second steel filament of the second steel cord has a diameter d in the range of 0.35-0.45mm and a super high or ultra high tensile strength TS, TS>4100- 2000xd MPa. Preferably 4200-2000xd<TS<4800-2000xd MPa.

[0034]

[0022] With the use of steel filament with super tensile strength (ST) or ultra tensile strength (UT) and big diameter, the total number of steel filament of steel cord N could be no more than 14 for realizing high total ply stiffness. Preferably N is in the range of 5 to 14.

[0035]

[0023] According to the invention, the ply stiffness of each working ply is mainly relating to the EPD of working ply, the cord stiffness CS and the cord inclination angle. To reach high ply stiffness, based on the predetermined EPD and the cord inclination angle, the cord stiffness of each steel cord in working ply is at least 1100 Nxmm. Perferably, 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 to 2600 Nxmm2.

[0036]

[0024] According to the present invention, the third ply is either 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, and it could anyone of existing transition ply or anyone of existing protection ply for pneumatic radial tire with three belt plies or four belt plies.

[0037]

[0025] The third ply has a ply strength much smaller than the first working ply or the second working ply, for example 1 .67 kN / mm or even smaller. The third ply has a ply stiffness much smaller than the first working ply or the second working ply, for example 0.81 kNxmm or even smaller. The third ply has an EPD of no more than 45 ends per decimeter, or even not more than 40 ends per decimeter.

[0038]

[0026] The rubber compound for the belt plies including the first working ply, the second working ply and the third ply can be anyone of existing rubber compound. The rubber compound for the different ply can be the same or different.

[0039]

[0027] The rubber gauge of each belt ply can be anyone of rubber gauge in the field, for example 0.4 - 0.8 mm.

[0040] Brief Description of Figures in the Drawings

[0041]

[0028] Figure 1 is the partial cross-section view of the invention tire.

[0042]

[0029] Figure 2 is the partial plan view of the belt package showing steel cord arrangement.

[0043]

[0030] Figure 3 is the partial front view of the first working ply showing the ends of steel cord.

[0044] Mode(s) for Carrying Out the Invention

[0045]

[0031] As shown in figure 1 , the pneumatic radial tire for heavy vehicle comprises 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 package 125 located between the carcass 120 and the tread portion 105.

[0046]

[0032] The carcass 120 has one carcass ply with steel cords arranged in parallel with an angle relative to the circumferential direction of the pneumatic radial tire at 90 degrees. The carcass ply extends between the bead portions while through the sidewall portions 110 and tread portion 105.

[0047]

[0033] As shown in Figure 2, the belt package 125 has three belt plies. The third ply 205 as a transition ply is the innermost ply on top of carcass 120, the first working ply 210 is on top of the third ply 205, the second working ply 215 is on top of the first working ply 210. The steel cords in each ply are arranged in parallel with a certain angle relative 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 ai of 18 degrees relative 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 a2 of 18 degrees relative to the circumferential direction A-A of the pneumatic radial tire, the steel cords in the third ply 205 have an inclination angle of 60 degrees relative to the circumferential direction A-A of the pneumatic radial tire. As shown in Figure 3, the first working ply 210 has first steel cords 220 with a construction of 1x6, the rubber gauge is 0.45mm.

[0048]

[0034] Table 1 summaries a comparison from FEM modelling between the invention examples and the comparative examples, in the tire with a size of 12R22.5.

[0035] Table 1

[0049] “100” is a reference score

[0050]

[0036] Average breaking load of steel cord calculation method is:

[0051] - take out a rubber block having three steel cords inside from the belt ply such as the working ply, make sure the steel cords in the rubber block have a length of more than 30cm; and then remove the surface rubber of the rubber block until the three steel cords are enveloped with a thin and smooth rubber, make sure that the three steel cords are still inside the rubber block without any separation from or any exposure out of rubber of the rubber block; as thus a thin block sample with two long sides and two short sides is obtained, wherein the block sample has three steel cords, and two of them are side steel cords and one is the middle steel cord;

[0052] - remove part of the two side steel cords from the block sample by cutting starting from one spot of 8 cm distance away from one end of the block sample until another spot of 8 cm distance away from the other end of the block sample, while the middle steel cord is kept without any damage; as thus a test sample with l-shape is obtained, i.e. , two end portions and a relatively narrow middle portion;

[0053] - clamp the two end portions of the test sample separately by two clamps (Zwick type 8303 - 10kN), and do tensile testing by tensile testing machine, and the tensile test conditions are: tensile speed of 50mm / min, pre-load of 10N; and the load at which the middle steel cord breaks is the breaking load of the steel cord;

[0054] - repeat sample making and testing, and take 8 effective data of steel cord breaking load to calculate the average as the average breaking load of steel cords of the belt ply, “effective data” means the steel cord breaks at any portion of the middle steel cord between the two clamps but not the clamped portion of the middle steel cord.

[0055]

[0037] Steel filament tensile strength test method:

[0056] - take out one steel cord from the belt ply such as the working ply without any damage to the steel cord, make sure the steel cord has a length of more than 30cm;

[0057] - take out every steel filament from the steel cord without any damage to the steel filament; select one individual steel filament and clamp the two end portions of that individual steel filament separately by two clamps (Zwick type 8303 - 10kN), and do tensile testing by tensile testing machine, and the tensile test conditions are: tensile speed of 50mm / min, pre-load of 10N, and the load at which the steel filament breaks is the breaking load of the steel filament; calculate the tensile strength of the steel filament by dividing the filament breaking load by the steel filament cross-sectional area as the tensile strength of the individual steel filament; do the tensile test and calculation on every individual steel filament and calculate the average as the tensile strength of the steel filament of steel cord.

[0058]

[0038] Steel filament diameter test method: remove rubber completely from the steel filament surface, and follow the diameter test method in Chinese standard GB / T 33159-2016.

Claims

Claims1 . A pneumatic radial tire for heavy vehicle, said pneumatic radial tire having a tread portion, a carcass comprising at least one carcass ply, a pair of bead portions and a belt package located between said carcass and said tread portion, said belt package having three belt plies including a first working ply, a second working ply and a third ply, said first working ply and said second working ply being located in sequence along the radially outward direction of said pneumatic radial tire, said third ply being either a transition ply located between said carcass and said first working ply or a protection ply located between said second working ply and said tread portion, said first working ply comprising a plurality of first steel cords arranged in parallel with a first angle ai relative to the circumferential direction of said pneumatic radial tire in a range of 15 to 30 degrees, each of said first steel cords comprising multiple first steel filaments, and said second working ply comprising a plurality of second steel cords arranged in parallel with a second angle a2 relative to the circumferential direction of said pneumatic radial tire in a range of 15 to 30 degrees, each of said second steel cords comprising multiple second steel filaments, and said second steel cords being inclined oppositely to said first steel cords with respect to the circumferential direction of said pneumatic radial tire, and characterized in that the total ply strength PStr of said first working ply and said second working ply is more than 2.5 kN / mm, and the total ply stiffness PSti of said first working ply and said second working ply is more than 1 .4 kNxmm, said total ply strength PStr and said total ply stiffness PSti are separately calculated by the following formulas:PStr = EPDi xBLi xcos2ai / 100000 + EPD2xBI_2xcos2a2 / 100000, PSti = EPDi xCSixcos2ai / 100000+ EPD2xCS2xcos2a2 / 100000, Wherein,EPDi is the number of ends per decimeter of said first working ply of at least 42 ends per decimeter, EPD2 is the number of ends per decimeter of said second working ply of at least 42 ends per decimeter, andBLi is the average breaking load of said first steel cords of at least 2300 Newton, BL2 is the average breaking load of said second steel cords of at least 2300 Newton, andCS1 is the cord stiffness of said first steel cord of at least 1100 Nxmm2, CS2 is the cord stiffness of said second steel cord of at least 1100 Nxmm2, the cord stiffness CS is calculated by the formula, CS = ZExNx7ixd4 / 64, whereinE is the steel elastic modulus of 206000 expressed in MPa, d is the steel filament diameter in the range of 0.15 to 0.55mm, N is the total number of steel filament of steel cord of at least 4.

2. A pneumatic radial tire for heavy vehicle as claimed in claim 1 , characterized in that said total ply strength PStr of said first working ply and said second working ply is more than or equal to 2.7 kN / mm.

3. A pneumatic radial tire for heavy vehicle as claimed in claim 2, characterized in that said total ply strength PStr of said first working ply and said second working ply is in the range of 2.9 to 3.5 kN / mm.

4. A pneumatic radial tire for heavy vehicle as claimed in any one of claims 1 to 3, characterized in that said total ply stiffness PSti of said first working ply and said second working ply is more than or equal to 1 .6 kNxmm.

5. A pneumatic radial tire for heavy vehicle as claimed in claim 4, characterized in that said total ply stiffness PSti of said first working ply and said second working ply is in the range of 1 .6 to 2.5 kNxmm.

6. A pneumatic radial tire for heavy vehicle as claimed in any one of claims 1 to 5, characterized in that each of said first steel filaments of said first steel cord and / or each of said second steel filaments of said second steel cord has a diameter d in the range of 0.35-0.45mm and a tensile strength TS, TS>4100- 2000xd MPa.

7. A pneumatic radial tire for heavy vehicle as claimed in claim 6, characterized in that each of said first steel filaments of said first steel cord and / or each of said second steel filaments of said second steel cord has a tensile strength TS, 4200-2000xd<TS<4800-2000xd MPa.

8. A pneumatic radial tire for heavy vehicle as claimed in any one of claims 1 to 7, characterized in that said N is in the range of 5 to 14.

9. A pneumatic radial tire for heavy vehicle as claimed in any one of claims 1 to 8, characterized in that said first steel cord and / or said second steel cord has a construction of 1xn, wherein n is 5 or 6.

10. A pneumatic radial tire for heavy vehicle as claimed in any one of claims 1 to 8, characterized in that said first steel cord and / or said second steel cord has a construction of n+m, n is 1 to 4, m is 3 to 10.11 . A pneumatic radial tire for heavy vehicle as claimed in any one of claims 1 to 10, characterized in that said EPDi and / or said EPD2 is in the range of 48 to 65 ends per decimeter.

12. A pneumatic radial tire for heavy vehicle as claimed in claim 11 , characterized in that said EPD1 and / or said EPD2 is in the range of 50 to 60 ends per decimeter.

13. A pneumatic radial tire for heavy vehicle as claimed in any one of claims 1 to12, characterized in that said BL1 and / or said BL2 is in the range of 2500 to 3200 Newton.

14. A pneumatic radial tire for heavy vehicle as claimed in any one of claims 1 to13, characterized in that said CS1 and / or said CS2 is in the range of 1500 to

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