Non-pneumatic tire with debris ejection features

Abstract

A non-pneumatic tire and method of manufacturing a non-pneumatic tire having a plurality of spokes with each spoke surfaces having a low surface roughness, each spoke forming a minimal angle in the axial direction to each adjacent spoke and the tire having a minimal spoke deflection when loaded to the maximum specified load, such tires suitable for on-road or off-road vehicles, including automobiles, light trucks, heavy trucks, all-terrain vehicles, zero turn radius lawn mowers, and military vehicles for operation in mud and / or snow conditions and possessing improved debris ejection properties.

Description

NON-PNEUMATIC TIRE WITH DEBRIS EJECTION FEATURESFIELD

[0001] This disclosure relates to non-pneumatic tires for on-road or off-road vehicles, including automobiles, light trucks, heavy trucks, all-terrain vehicles, zero turn radius lawn mowers, and military vehicles. Particularly, it relates to off-road vehicles which may require operation in mud and / or snow conditions.BACKGROUND

[0002] Non-pneumatic tires (“NPTs”) have advantages over pneumatic tires. NPTs are not pressure vessels, as are pneumatic tires. They cannot fail due to air pressure loss. As such, they have certain advantages in off-road conditions where rough terrain, obstacles and hazards may be encountered. Such conditions may cause flats in pneumatic tires that NPTs are not susceptible to.

[0003] NPTs use structural means to carry load. NPTs have certain advantages compared to compression-based NPTs. As a reference, US Patent 7,201,194 B2, owned by the current applicant, discloses aspects of tension based NPTs that are now commercialized as TWEEL NPTs. Tension-based NPT’s carry a majority of the load through an annular beam from the contact patch on the radial outer surface of the annular beam to the portion of the annular beam circumferentially opposite to the contact patch where the spokes of the annular support carries the load in tension to the hub. Compression-based NPTs on the other hand, carry more load in compression through the annular support between the contact patch and hub and do not carry a majority of the load in tension opposite the contact patch.

[0004] Pneumatic tires have sidewalls which are a positive attribute for off-road operation. Dirt, mud, and / or snow cannot enter the air-filled cavity defined by the tire crown, sidewall, and wheel. The open structure of a tension-based NPT has potential for entrance of mud, snow, or other into the cavities formed within the annular support between each of the spokes. This maycause issues related to tire function. Tire uniformity, stiffness, and / or fatigue performance may be adversely affected.

[0005] There is a current need for a tension -based NPT with features that enable and facilitate debris ejection.SUMMARY

[0006] The invention has general application for vehicles that use non-pneumatic tires. Specifically, application is especially suited to off-road vehicles that may operate in soft-soil, mud, or snow.

[0007] In at least one embodiment of the invention, there is provided a non-pneumatic tire comprising an annular beam, and an annular support extending radially inward from the annular beam, the annular support comprising a plurality of spokes that extend in the radial direction, connecting the inner surface of the annular beam to a rim without intersection with any ones of the other spokes. The spokes are sheet-like elements that extend from a first axial extent to a second axial extent of the non-pneumatic tire. An angle between one spoke and a circumferentially adjacent spoke is at least 1.0 degree in the axial direction. A spoke surface has a mean centerline roughness of no more than 0.30 microns. A deflection of the non-pneumatic tire over a spoke radial length when loaded to a rated maximum load is at least 0.15.

[0008] According to another embodiment of the invention, there is provided a process for forming a non-pneumatic tire, the non-pneumatic tire comprising an annular beam, and an annular support extending radially inward from the annular beam, said annular support comprising a plurality of spokes that extend in the radial direction, connecting the inner surface of the annular beam to a rim without intersection with any ones of the other spokes. The spokes are sheet-like elements that extend from a first axial extent to a second axial extent of the non- pneumatic tire. An angle between one spoke and a circumferentially adjacent spoke is at least 1.0 degree in the axial direction. A mold used for forming a spoke of the non-pneumatic tire has a grit finish of at least 300.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] A detailed description of embodiments is provided below, by way of example only, with reference to the accompanying drawings, in which:

[0010] Figure 1 is an exemplary NPT according to an embodiment of the invention.

[0011] Figure 2 is a side view of the exemplary NPT.

[0012] Figure 3 shows a section view of the exemplary NPT.

[0013] Figure 4 is a close-up of the section view, showing the cross section of two spokes.

[0014] Figure 5 shows the cross section of 4 spokes and a mold used to form the spokes.

[0015] Figure 6 is a simplified illustration of an NPT loaded to a rated load.

[0016] Figure 7 is a load vs. deflection plot of an NPT “Study Tire A” according to the invention.

[0017] Figure 8 is a picture of an NPT “Study Tire A” according to the invention, packed with mud before a mud ejection test.

[0018] Figure 9 is a picture of the mud-packed NPT “Study Tire A” from being weighed.

[0019] Figure 10 shows a picture of a perspective view of the NPT “Study Tire A” after the mud ejection test.

[0020] Figure 11 shows a picture of the side view of the NPT “Study Tire A” after the mud ejection test.

[0021] Figure 12 shows mud retention vs. distance for the NPT.

[0022] It is to be expressly understood that the description and drawings are only for purposes of illustrating certain embodiments and are an aid for understanding. They are not intended to and should not be limiting.DEFINITION OF TERMS

[0023] The following terms are defined as follows for this disclosure, with material properties referring to those at ambient temperature, unless otherwise noted:

[0024] ‘Hub” refers to any structure for supporting the tire and capable of attachment to a vehicle axis.

[0025] “Rated Load” of a tire is maximum tire load as specified by the manufacturer.

[0026] Tire vertical force vs. deflection and footprint measurements are performed according to SAEJ2704.

[0027] ‘NPT” is an acronym for non-pneumatic tire. Non-pneumatic tires support a load by structural means and do not possess an air chamber for the purpose of supporting the load. Non- pneumatic tires are not reliant on retaining air pressure for their performance.

[0028] “Ra” is the arithmetic average surface roughness according to ISO 1302.DETAILED DESCRIPTION OF EMBODIMENTS

[0029] Figure 1 shows an exemplary example of an NPT 100, in the size 26x9-14 as sold under the name X-Tweel UTV tire from Michelin. The tire defines a cylindrical coordinate system with radial direction R, circumferential direction 9, and axial direction Y. A convenient cartesian coordinate system has X as the direction of travel of the tire, Y as the axial direction, and Z as the vertical direction.

[0030] The tire comprises an annular beam. In this embodiment, the annular beam is supported by an annular support. The annular support portion comprises spokes that extend in the radial direction, connecting the radially inner surface of the annular beam to a rim 104 without intersection with any ones of the other spokes. Two circumferentially adjacent spokes are shown as spoke 102 and spoke 103.

[0031] The NPT may also comprise a central hub 105 that is configured for fixation to a vehicle. The hub and rim may be formed of an elastomer, or a metal, or any suitable combination thereof.

[0032] A side view of the NPT is shown in Figure 2. Spoke 102 and spoke 103 extend in the radial direction a distance SR. This is the radial distance from a radially inward surface 106 of the annular beam to a radially outward surface 107 of the rim.

[0033] The NPT has a vertical compliance. In preferred embodiments, the vertical compliance may approximate that of a pneumatic tire, such that the NPT provides shock absorption. The annular beam may be designed to flex in the contact area when the NPT rolls and carries a load, creating a contact patch area, like that of a pneumatic tire. As a result, the spokes may experience significant deformation.

[0034] The inventor has found that specific levels of spoke deformation may be combined with other design attributes to facilitate ejection of debris that may enter the open cavities between adjacent spokes. There are three separate design attributes that are preferably employed simultaneously in examples of the current invention, namely: spoke draft angle in the axial direction, spoke surface roughness, and vertical compliance. The inventor has discovered parameters related to each of the above for effective eject debris. These will now be disclosed in detail.Spoke draft angle

[0035] Figure 3 shows a section view of the NPT taken on line 3 - 3 in Figure 2 showing the spokes 102 and 103. It is evident that spoke 102 extends in the axial direction, at a small angle from parallel with the axial direction.

[0036] Figure 4 is a close-up of the cross section of spokes 102 and 103. Spoke 102 has a relatively constant thickness and is disposed at a small angle from axis Y. Similarly, spoke 103 has a relatively constant thickness and is disposed at a small angle from axis Y, but of opposite angle. An angle 0 is between spoke 102 and spoke 103. Angle 0 is measured in a plane which is both tangential to the circumferential direction of the tire and parallel to the axis of the tire.

[0037] Figure 5 discloses a schematic of a mold profile that may be employed for forming spokes 102 and 103, as well as the plurality of spokes comprised in the NPT. The mold profile may comprises a repeating wedge geometry near one axial extent of the mold profile and a second repeating wedge geometry on the opposite axial extent. These may be formed from a left mold half 201 and a right mold half 202. Each mold half may be actuated along the axial axis Y as shown by the dashed arrow. When the mold is closed, the wedges form a mold civility corresponding to the spokes. The spokes may then be formed from any suitable molding operation.

[0038] For some NPT’s according to the invention, a thermoplastic injection operation may be used. In this case, the inventor has found that a spoke material may be a thermoplastic copolymer. For other NPT’s according to the invention, a thermoset casting operation may be used. In this case, the inventor has found that a spoke material may be a polyurethane.

[0039] The draft angle aids efficient demolding, i.e., the removal of the NPT from the mold, after the spoke material has been cured. Even a small angle 0, such as 0.5 degrees, may be sufficient for demolding and allow the spokes to function essentially as if there were no inclination angle from the Y axis.

[0040] However, for efficient debris ejection, the inventor has found that the included draft angle 0 is very important. Surprisingly, even small changes in 0 have profound impacts on mud ejection. An ejection force may be directly related to the tangent of the draft angle, meaning that the ejection force is doubled when going from 0.5 degree to 1.0 degree of total draft angle. The inventor has found that draft angle 0 must be at least 1.0 degree for mud ejection. Preferably the angle 0 should be at least 2.0 degrees. In other cases, angle 0 of at least 3.0 degrees provides even better mud ejection, and in other cases, even more.Spoke surface roughness

[0041] Spoke draft angle is necessary but not sufficient for efficient debris ejection. The inventor has also found spoke surface roughness must be small; or, similarly stated, the spoke surface must be very smooth. As with spoke draft angle, relatively small changes may have significant impacts.

[0042] The inventor has found that the spoke surface roughness may be characterized by Ra, which is the arithmetic mean deviation of the surface profile. Small Ra corresponds to smoother surfaces. ISO 1302 defines this and other parameters for surface finish.

[0043] The spoke surface roughness may be measured in any suitable way. One instrument that is acceptable is the non-contacting Nanovea ST400.

[0044] The inventor has found that the spoke roughness must be no higher than Ra = 0.23 microns; in other cases, 0.10 microns; and in other cases, even less.

[0045] Mold surface finish relates strongly to spoke surface roughness. The smoother the mold finish, the lower the spoke surface roughness will be. The inventor has found that the mold surface used to form the spokes should be polished to a grit finish of 400; in other cases, to a finish of 500; and in other cases, even more.Vertical compliance

[0046] Figure 6 shows a deformed geometry of a simplified finite element model of an embodiment of the invention. The model has an outer radius Ro and a spoke radial length SR. When loaded to a design load, it deflects 8. An open cavity in the NPT is defined by spoke 103, the radially inward portion of the shear beam 106, spoke 102, and the radially outward portion of the hub 107. The volume defined by this cavity changes as the NPT rolls and the spokes deflect. Away from the contact area, the volume is at a maximum. In the contact area, the volume is at a minimum. The volume is “compressed” in the radial direction as the shear beam flattens into contact. Furthermore, the spokes flex and move not only in the radial direction, but also in the circumferential direction.

[0047] The inventor has found that this behavior is also of first order importance for debris ejection. When combined with a spoke surface that has very low roughness Ra = 30 microns or less, with an included draft angle 0 between adjacent spokes of at least 1 degree, the inventor has found that the deflection 8 at a rated load of the NPT must be at least a certain percentage of the spoke radial length SR.

[0048] For efficient mud ejection, the deflection of the spoke (8) over the length of the spoke (SR), written as 8 / SR, should be no less than 0.15; in other cases, no less than 0.20; in other cases, no less than 0.25; and in other cases, even more.

[0049] The inventors have reduced to practice an exemplary NPT “Study Tire A.” This NPT has:• 8 / SR = 0.20• Ra = 0.26 microns• 0 = 2 degrees

[0050] Tire A was prototyped and tested in load vs. deflection, shown in Figure 7. A rated load of Tire A is 325 kg. A deflection at this load is 23 mm. Debris ejection at this deflection will be optimal; however, off-road vehicles are often used in muddy conditions when loaded lessthan the maximum permissible tire load. As such, the inventor tested Tire A at a condition where the tire load was only 58% that of the rated load of 325 kg.

[0051] Study Tire A was tested for mud ejection performance by the inventor using the following test protocol:• Honda Pioneer UTV was used as test vehicle.• Left front tire position load was measured with Tire A installed at left front position.• Tire A was dismounted and weighed.• Tire A was packed with mud, shown in Figure 8.• Tire A with packed mud was weighed, shown in Figure 9.• Tire A was mounted on the test vehicle in left front position.• Test vehicle was driven at 40 kph for 200 meters.• Tire A was dismounted and weighed.• Test vehicle was driven for 400 m.• Tire A was again dismounted and weighed.• Test vehicle was driven for 200 m, for a total of 1000m.• Tire A was again dismounted and weighed.

[0052] Figure 10 shows a perspective view of Tire A after 1000 meters of operation and Figure 11 show a side view of the same tire. As shown in Figures 10 and 11, the spoke cavities are now largely free of mud. Thus, even in a relatively lightly loaded condition, this exemplary example of the current invention ejected the vast majority of mud after 1000 meters operation. This occurred when starting from a rather impossible condition of being 100% packed with mud.

[0053] By appropriate simple math, the percent of mud ejected was calculated as a function of distance traveled. Results are shown in Figure 12. At test beginning, Tire A spoke cavities were 100% full of mud - about 37 kg total of mud. After 1000 meters, only about 17% (about 6 kg) of mud was left. The inventor has found that after 2 km or more of driving in normal operation are sufficient to eject over 95% of the mud. Results depend on speed and other factors. Nevertheless, this level of performance has been observed to match customer needs.

[0054] It is to be understood that the disclosures herein may be combined with other design features and are not meant to be limiting in any means. Spoke initial curvature in the R-6 plane, variations in spoke thickness in the radial direction and / or in the lateral direction may be used in the context of this invention. Spokes which do not fully traverse the lateral extents of the hub and / or shear beam may also be employed.

Claims

We claim:1 . A non-pneumatic tire having a plurality of spokes with improved debris ejection, the non-pneumatic tire rotatable about an axis and having a radial direction extending perpendicular the axis, a circumferential direction extending perpendicular the radial direction and perpendicular to the axis, the non-pneumatic tire further comprising: an annular beam having a radially inner surface and a radial outer surface; and a rim radially inward from the annular beam; an annular support extending radially inward from the annular beam, said annular support comprising the plurality of spokes which extend in the radial direction, the plurality of spokes connecting the inner surface of the annular beam to the rim, each of the plurality of spokes configured to not intersect with any other of the plurality of spokes, each of the plurality of spokes configured as sheet-like elements extending from a first axial extent to a second axial extent of the non-pneumatic tire, wherein each spoke of the plurality of spokes defines an angle between itself and a circumferentially adjacent spoke of the plurality of spokes which is at least 2.0 degree in the axial direction and wherein a spoke surface has a mean centerline roughness of no more than 0.30 microns and wherein a deflection of the non- pneumatic tire over a spoke radial length when loaded to a rated maximum load is at least 0.15.

2. The non-pneumatic tire of claim 1 wherein the deflection of the non-pneumatic tire over a spoke radial length when loaded to a maximum load is at least 0.20.

3. The non-pneumatic tire of claim 1 wherein the deflection of the non-pneumatic tire over a spoke radial length when loaded to a maximum load is at least 0.25.

4. The non-pneumatic tire of any one of the above claims wherein spoke surface has a mean centerline roughness no more than 0.23 microns.

5. The non-pneumatic tire of any one of the above claims wherein spoke surface has a mean centerline roughness no more than 0.10 microns.

6. The non-pneumatic tire of any one of the above claims wherein the angle defined between each spoke of the plurality of spokes and the circumferentially adjacent spoke is at least 3.0 degrees in the axial direction.

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