Aircraft tires with zoned tread

Description

Field of the Invention

[0001] This invention relates to pneumatic tires, and more particularly, to high-speed heavy load tires such as those used on aircraft.Background of the Invention

[0002] Current tire design drivers for an aircraft tire include designing the tire for high wear resistance. FIG. 2 illustrates a computer simulation of a comprehensive wear model showing the amount from various aircraft activities such as touch down, taxing, turning. The central part of the tire tread has the greatest wear. The outer lateral ends of the tire tread near the shoulder also have high wear. The state of the art of high wear resistant tire treads is to select tread compounds that have high stiffness or high abrasion resistance for improved wear resistance. However, the present inventors have discovered an improved wear resistant tread that is contrary to the state of the art.

[0003] US 9,809,058 B2 describes a tire in accordance with the preamble of claim 1.

[0004] Tires having a zoned tread with different rubber compositions are also known from US 2018 / 0326788 A1, EP 2159079 B1 and US 6,959,744 B2.Summary of the Invention

[0005] The invention relates to a tire in accordance with claim 1.

[0006] Dependent claims refer to preferred embodiments of the invention.

[0007] The invention provides in a first preferred aspect a pneumatic tire having a tread with a ground engaging outer surface, the tread having a first tread zone and a second tread zone, wherein the first tread zone includes a central portion of the tread and the second tread zone is located adjacent the first tread zone and on each lateral end of the tread, wherein the first tread zone is formed of a first rubber compound and the second tread zone is formed of a second rubber compound, wherein the first rubber compound has a G' (at 50% strain) in the range of 1.6 to 1.8 MPa.

[0008] The invention provides in a second preferred aspect a pneumatic tire having a tread with a ground engaging outer surface, the tread having a first tread zone and a second tread zone, wherein the first tread zone includes a central portion of the tread and the second tread zone is located adjacent the first tread zone and on each lateral end of the tread, wherein the first tread zone is formed of a first rubber compound and the second tread zone is formed of a second rubber compound, wherein the second rubber compound has a G' (at 100% strain) in the range of 0.80 to 0.83 MPa.Definitions

[0009] "Carcass" means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.

[0010] "Circumferential" means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.

[0011] "Cord" means one of the reinforcement strands of which the plies in the tire are comprised.

[0012] "Equatorial plane" and "EP" mean the plane perpendicular to the tire's axis of rotation and passing through the center of its tread.

[0013] "Ply" means a continuous layer of rubber-coated parallel cords.

[0014] "Radial" and "radially" mean directions radially toward or away from the axis of rotation of the tire.

[0015] "Radial-ply tire" means a belted or circumferentially restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65° and 90° with respect to the equatorial plane of the tire.Brief Description of the Drawings

[0016] The invention will be described by way of example and with reference to the accompanying drawings in which: FIG. 1 is a schematic cross-sectional view of a first embodiment of half of a zoned tire tread according to the invention; FIG. 2 is a computer model plot of tire tread wear indicator vs. y-coordinate; FIG. 3 is a computer model plot of relative G' vs. shoulder wear; FIG. 4 is a computer model plot of relative G' vs. centerline tread wear; and FIG. 5 is a computer model plot of overall wear of the tread having three different zoned tread compositions. Detailed Description of Preferred Embodiments of the Invention

[0017] FIG. 1 illustrates a cross-sectional view of one half of a pneumatic tire tread 10 of the present invention. The tire is symmetrical about the mid-circumferential plane so that only one half is illustrated. As shown, the tire tread 10 is for an aircraft tire, although the invention is also applicable to other uses such as truck or off the road tires.

[0018] The tire tread 10 defines an outer running surface 12 that includes a plurality of grooves 14, 16 separated by tread blocks or ribs. The tire tread 10 is zoned and has a first or central tread zone 30 formed of a first rubber compound and is located on the central or crown portion of the tire tread 10. The tire tread 10 further comprises a second or shoulder tread zone 40 formed of a second rubber compound. The second tread zone 40 is located axially outward of the first or central tread zone 30 on each lateral end of the tire tread 10. The second tread zone 40 extends from a tire tread interface 50 to the shoulder region terminating at the sidewall.

[0019] FIG. 2 illustrates a computer simulation of a comprehensive wear model illustrating the amount of wear caused by events such as takeoff, landing (touch down) taxing, turning, and braking. As shown in FIG. 2, in the shoulder tread zone 40 at the outer lateral ends of the tire tread 10, there is shown a large increase in wear.

[0020] FIG. 3 illustrates that shoulder wear for an aircraft tire correlates strongly with high strain G', or G' (measured at 50%-100% strain) with an R 2< >0.8. G' is the dynamic storage modulus and is a measurement of the viscoelastic properties of rubber compounds at various strain levels. G' is obtained using a Rubber Process Analyzer as RPA 2000 ™< from the Alpha Technologies. These measurements are made on green rubber. Using the RPA 2000 ™< , a strain sweep at 100°C at 1 Hz over a range of from 1% to 100% strain may be made.

[0021] Additionally, FIG. 3 illustrates the shoulder wear rate for various compounds having different stiffness levels. FIG. 3 illustrates that the shoulder wear rate is lowest for the softer compounds, i.e., lower G' values at high strain. In one embodiment, G' of the second rubber compound for the shoulder or second tread zone 40 is selected to have a G' (at 100% strain) in the range of from 0.81 to 0.83 MPa, and more preferably 0.82 MPa. In a second embodiment, G' of the second rubber compound for the shoulder or second tread zone 40 is selected to have a G' (at 50% strain) in the range of 1.024 to 1.028 MPa, and more preferably 1.026 MPa.

[0022] FIG. 4 illustrates the centerline wear rate for the tire tread 10 versus G' at various strain levels. From FIG. 4, it has been determined that centerline wear correlates strongly with G' at 100% strain. Centerline wear is reduced for compounds higher in stiffness, i.e., higher values of G' (at 100% strain). Thus, for the first or central tread zone 30 it is preferred that the G' (100%) of the first rubber compound be in the range of 1.2 to 1.4 MPa, and more preferably 1.3 MPa. Additionally, for the first or central tread zone 30 it is preferred that the G' (at 50% strain) of the first rubber compound be in the range of 1.6 to 1.8 MPa, more preferably, 1.7 MPa.

[0023] FIG. 5 illustrates the overall wear rate of the tire tread 10 using first and second tread zones 30, 40 for different types of compounds. Thus, tread zoning improves the wear balance of the tire tread 10, while slightly improving centerline tread wear.

[0024] Accordingly, and in order to improve the overall wear rate of the tire tread 10, it is desired to have a first or central tread zone 30 formed of a first rubber compound having a G' (50%) at least 150% greater than the G' (at 50% strain) of the second rubber compound, and more preferably, at least 170% greater than the G' (at 50% strain) of the second rubber compound.

[0025] The first rubber compound is selected to have a greater stiffness than the second rubber compound so as to provide the tread with greater wear resistance along the first or central tread zone 30, and the second rubber compound provides the tread with a softer compound that reduces shoulder wear. The interface 50 or dividing line between the first and second tread zones 30, 40 is determined from modeling analysis such as shown in FIG. 2. As shown in FIG. 5, the tread wear is highest at the outer lateral ends of the tread, and lower in the central portion of the tread. For a typical tire tread, the first or central tread zone 30 is preferably at least 50-70% of the total tread arc width, and the combined outer lateral ends are preferably at least 30-50% of the total tread arc width.

Claims

1. A pneumatic tire having a tread with an outer surface defined for ground contact, the tread having a first tread zone (30) and a second tread zone (40), wherein the first tread zone (30) includes a central portion of the tread and wherein the second tread zone (40) is located laterally adjacent the first tread zone (40), preferably on both lateral sides of the first tread zone (30), wherein the first tread zone (30) is formed of a first rubber compound and the second tread zone (40) is formed of a second rubber compound different from the first rubber compound, and wherein the first rubber compound has a dynamic storage modulus G', measured at 100°C, 1 Hz and at 50% strain in the range of from 1.6 to 1.8 MPa, characterized in that the second rubber compound has a dynamic storage modulus G', measured at 100°C, 1 Hz and 100% strain in the range of from 0.75 to 0.90 MPa or in that the second rubber compound has a dynamic storage modulus G', measured at 100°C, 1 Hz and at 50% strain in the range of from 1 to 1.05 MPa.

2. The tire of claim 1 wherein the first rubber compound has a dynamic storage modulus G', measured at 100°C, 1 Hz and at 100% strain in the range of from 1.2 to 1.4 MPa.

3. The tire of claim 1 or 2 wherein the second rubber compound has a dynamic storage modulus G', measured at 100°C, 1 Hz and at 50% strain in the range of from 1.024 to 1.028 MPa.

4. The tire of at least one of the previous claims wherein the second rubber compound has a dynamic storage modulus G', measured at 100°C, 1 Hz and at 100% strain in the range of from 0.80 to 0.83 MPa5. The tire of at least one of the previous claims wherein the first rubber compound has a dynamic storage modulus G', measured at 100°C, 1 Hz and at 50% strain in the range of from 1.6 to 1.7 MPa6. The tire of at least one of the previous claims wherein the axial width of the first tread zone (30) is in the range of 50-70%, preferably 60% to 70%, of the axial width of the tread.

7. The tire of at least one of the previous claims wherein the second tread zone (40) is located laterally adjacent the first tread zone (40) on both lateral sides of the first tread zone (30) and has a total axial width in the range of from 50% to 30%, preferably 40% to 30%, of the tread.

8. The tire of at least one of the previous claims wherein the tire (10) is an aircraft tire.