Tire with ribs made of thermoplastic elastomer

Abstract

A tire (10) is provided that has a plurality of circumferential ribs (12) that are made of thermoplastic elastomer with a height (h) that extends in a thickness direction and is between and including 3 millimeters to 6.5 millimeters. The thermoplastic elastomer has an average rigidity G* that is measured at 40° C under a stress of 0.7 MPa. Each one of the ribs (12) has a height to average rigidity ratio that is governed as follows: (h / G*) < 9 mm / MPa.

Description

DescriptionTitle of Invention: TIRE WITH RIBS MADE OF THERMOPLASTIC ELASTOMERFIELD OF THE INVENTION

[0001] The subject matter of the present invention relates to a tire that has ribs made of ther- moplastic elastomer. More particularly, the present application involves a tire with thermoplastic elastomer ribs that are short enough in height so that they have rolling resistance performance close to that of a tire that has a ground contacting tread made of standard tread rubber.BACKGROUND OF THE INVENTION

[0002] When the tread on tires has been depleted, it is known to replace the tread with new tread so that the carcass of the tire can be reused. One way to replace this tread is to produce pre-cured tread that is sized for the specific tire that is being retread. The depleted, remaining tread can be removed and this new tread can be attached to the carcass via a curing process. In this regard, uncured rubber can be placed onto the carcass and the new tread placed onto this uncured rubber. An autoclave can be used to cure this bonding layer so that the new tread is attached to the carcass. In an alternative method, the new tread that is provided can be uncured and placed onto the used carcass. This product can then be put into a mold which imparts architecture into the new tread and cures it to be a part of the resulting tire.

[0003] Although capable of adding new tread to an existing tire, such processes require one to have a press, mold, autoclave or other equipment capable of curing some portion of the product. This equipment can represent a significant investment for retreading fa- cilities and can be labor intensive. Still further, these techniques may require one to produce new tread that is specifically sized for installation onto an existing tire. A dedicated flat mold or circular mold must be produced for each tire size, and this increases the cost and complexity of retreading due to this extra tooling. The addition of a new tread to an existing carcass such that the newly added tread has the same ar- chitecture as the tread that was worn away also adds to the cost of the retreading process.BRIEF DESCRIPTION OF THE DRAWINGS

[0004] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: [Fig 1]

[0005] [Fig.l] is a cross-sectional view of a tire with worn tread.[Fig 2]

[0006] [Fig.2] is the tire of [Fig.1] with the worn tread removed to expose the underlay.[Fig 3]

[0007] [Fig.3] is the tire of [Fig.2] with ribs applied to the underlay.[Fig 4]

[0008] [Fig.4] is a perspective view of a rib that is formed by a plurality of strips of ther- moplastic elastomer.[Fig 5]

[0009] [Fig.5] is a perspective view of a rib that has sipes that extend into the rib from the outer surface.[Fig 6]

[0010] [Fig.6] is a cross-sectional view of a tire that has ribs attached to the tread rubber via adhesive.[Fig 7]

[0011] [Fig.7] is a cross-sectional view of a tire that has ribs attached to the tread rubber via connecting rubber through a curing process.[Fig 8]

[0012] [Fig.8] is a perspective view of a non-pneumatic tire that has ribs made of ther- moplastic elastomer applied thereon.[Fig 9]

[0013] [Fig.9] is a graph of the temperature versus the tan(b) value of a thermoplastic elastomer that can be used in the rib.[Fig 10]

[0014] [Fig.10] is a graph of the temperature versus the G* value of a thermoplastic elastomer that can be used in the rib and that represents rigidity.[Fig 11]

[0015] [Fig.11] is a graph of temperature versus the tan(b) / G*(1 / 3)value of a thermoplastic elastomer that can be used in the rib and that represents wet braking.[Fig 12]

[0016] [Fig.12] is a graph of deformation percentage versus the tan(6) at 23° C of a ther- moplastic elastomer that can be used in the rib and that represents rolling resistance.

[0017] The use of identical or similar reference numerals in different figures denotes identical or similar features.DETAILED DESCRIPTION OF THE INVENTION

[0018] Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, and not meant as a limitation of the invention. Forexample, features illustrated or described as part of one embodiment can be used with another embodiment to yield still a third embodiment. It is intended that the present invention include these and other modifications and variations.

[0019] The present invention provides for a tire 10 that has a plurality of circumferential ribs 12 that are made of thermoplastic elastomer and have a height (h) 14 that is from and including 3-6.5 millimeters. The thermoplastic elastomer that is used has an average rigidity G* that is measured at 40° Centigrade under a stress of 0.7 MPa. In order to achieve a desired rolling resistance of the tire 10, the thermoplastic ribs 12 are addi- tionally sized so that their height to average rigidity ratio is governed by the inequality (h / G*) < 9 mm / MPa. The tire 10 is constructed so that that ribs 12 are shorter and made of a more flexible material yet have a rolling resistance similar to tires 10 that include traditional tread rubber in their ground contacting portions. The ribs 12 can be featureless in some arrangements, and in other arrangements may have ornamental features on the outer surface 18, or can include sipes 40 or other features that extend from the outer surface 18 but do not extend into the full height (h) 14 of the ribs 12. When the ribs 12 are added onto an existing carcass 90 through a retread process, the architecture of the ribs 12 is not the same as that of the originally produced tire. The ribs 12 can be attached to the carcass 90 in various ways such as by thermoplastic welding, adhesives, or via curing process. The use of shorter ribs 12 that are made of a more hysteretic material may allow for the resulting tire 10 to have a rolling resistance that is comparable to that of tires 10 having conventional tread 12 rubber.

[0020] [Fig.1] shows a tire 10 that can be a heavy duty truck tire for use with 18 wheelers, garbage trucks, fire trucks, school busses, or box trucks. The tire 10 may be a steer tire, a drive tire, a trailer tire, or an all position tire. The tire 10 could be a light truck tire or a passenger car tire. The tire 10 includes a casing / carcass 90 onto which a worn tread 36 is disposed thereon. The lateral / axial direction 26 of the tire 20 is parallel to a central axis 34. The radial direction 28, which is also known as the thickness direction 28, of the tire 10 is perpendicular to the central axis 34, and the tread 36 is located farther from the central axis 34 in the thickness direction 28 than the carcass 90. The tread 36 extends all the way around the carcass 90 in the longitudinal direction 24 of the tire 10 and circles the central axis 360 degrees. The worn tread 36 has a series of circumferential grooves and ribs disposed thereon, and can have any design and may additionally or alternatively feature lateral grooves, sipes, notches, blocks and any other architecture. Although shown as a truck tire 10, it is to be understood that this is for illustrative purposes only and the tire 10 may be a passenger car tire 10 in other embodiments.

[0021] The tire 10 has a crown 16 that engages the road surface, and a pair of sidewalls 96, 98 that extend from the crown 16 in the thickness direction 28 and are separated fromone another on opposite sides of the tire 10 in the lateral direction 26. A first bead 100 is located at the end of the first sidewall 96, and a second bead 102 is located at the end of the second sidewall 98 in the thickness direction 28. The first beads 100, 102 each include a bead core that is made up of a steel rod and padding gum. The bead cores with the rod function to hold the tire 10 onto the rim and maintain its strength to withstand internal stresses from inflation on the rim to prevent slipping. Surrounding the bead cores are wrapping tissue that can be made of nylon in some embodiments. The steel rods are shown as a single piece and have a rectangular cross-sectional shape. This single piece can actually be many rods arranged together in the shape of a rectangle.

[0022] The tire 10 includes a tissue designated as a reinforcement ply 104 that is located within the first bead 100 and extends through the first sidewall 96 and crown 16 and into the second sidewall 98 and into the second bead 102. The reinforcement ply 104 wraps around the first bead core and has a portion that can be called a return casing ply that is embedded within the bead filler of the first bead 100. The opposite end of the re- inforcement ply 104 likewise wraps around the padding gum and steel rod in the second bead 102 and terminates within the bead filler of the second bead 102. The re- inforcement ply 104 provides strength and flexibility to the tire 10, and it is the supporting structure for the inflation pressure which carries the load of the tire 10. The reinforcement ply 104 is a composite material that includes metal cords and a rubber mix.

[0023] Another element of the tire 10 that extends from the first bead 100 to the second bead 102 is an inner liner 82 that is inside of the first bead 100 and forms a portion of the exterior of the first bead 100 and extends to the sidewall 96. The inner liner 82 then extends across the entire inner side of the crown 16 in the lateral direction 26 before extending into and forming the inner side of the second sidewall 98 and a part of the exterior surface of the second bead 102. The inner liner 82 in the second bead 102 is arranged in a similar mirror-image manner to its presence in the first bead 100. The inner liner 82 is made of a material that is fluid tight so that fluid between the tire 10 and rim is maintained therein for purposes of maintaining inflation pressure of the tire 10. The inner liner 82 controls air retention, has low temperature cracking resistance, and has good flex fatigue resistance. The inner liner 82 can be made of a single layer or may be multi-layered. The inner liner 82 forms the inward exterior surface of the sidewalls 96 and 98.

[0024] The first sidewall 96 has a tread wall 84 that is located at the axial end of the tire 10 and extends from the first sidewall 96 and into the crown 16. The tread wall 84 is made of a different rubber composition than other portions of the first sidewall 96 and forms a portion of the exterior surface of the tire 10. The tread wall 86 is on the opposite endof the tread rubber 88 in the lateral direction 26 and engages the second sidewall 98 and may be a mirror image and configured the same as the tread wall 84 as discussed. The tread walls 84, 86 are made of a different material than the tread rubber 88 and have a hysteresis different than that of the tread rubber 88.

[0025] Included within the crown 16 is a cushion layer 92 that is located on top of the rein- forcement ply 104 in the crown 16 and provides a flat surface onto which the belt layers 94 can be disposed. The cushion layer 92 is made of rubber and engages the re- inforcement ply 104, the belt layers 94, the belt edge layer 112, and the belt edge layer 114. The belt layers 94 are within the crown 16 and are made up of three belts. Although the belt layers 94 are shown as including three belts, any number of belts in the belt layer 94 can be present in other embodiments. The belts of the belt layer 94 provide reinforcement in the crown 16 for improved wear and cornering power. The steel belts allow the tire 10 to maintain its shape. Belt edge layers 112 and 114 act as wedges between the belt layers 94 and the tread rubber 88 to dampen stresses and are present for endurance performance of the tire 10. The radial centerline 106 is located at the middle of the tire 10 in the lateral direction 26, and all of the belts of the belt layer 94 extend across the radial centerline 106 so that their lateral midpoints are likewise at the radial centerline 106 so that half of their widths are on one side of the lateral centerline 106 in the lateral direction 26.

[0026] The crown 16 includes tread rubber 88 that acts as an undertread layer that is located below and engages the underlay 22 in the thickness direction 28 and is in engagement with the belt layer 94. The tread rubber 88 extends along the majority of the entire crown 16 in the lateral direction 26. The tread rubber 88 layer may be made of a material that minimize heat generation from the tread 36 and steel belts in the belt layers 94. The tread rubber 88 can also function as an oil migration barrier, provide desirable tack, and have low hysteresis. However, these properties can be eliminated or modified in various tires 10 as desired. An underlay 22 engages the tread rubber 88 and tread 36 and is between these two components in the thickness direction 28. The underlay 22 is made of thermoplastic elastomer and has left terminal side and a right terminal side in the lateral direction 26. The underlay 22 can be originally attached to the tread 36 and tread rubber 88 via a conventional curing process in which heat and pressure in a mold are used to adhere these components to one another. The tread 36 is situated on top of the underlay 22 so that the grooves of the tread 36 have bottoms made of the tread 36 and are not made by the underlay 22 itself so that the underlay 22 is not exposed but is completely covered from the left to right terminal sides. In the embodiment shown in [Fig.l], some areas of the underlay 22 proximate to the left and right terminal sides 38, 40 are uncovered by the tread 36, but this need not be the case in other configurations of the tire 10.

[0027] The tread 36 may be worn to a point that it is at the end of its useful life. Alter- natively, the tread 36 may have abnormal wear such that replacement by the owner of the tire 10 is desired. Instead of throwing the tire 10 away, the tire 10 may be subjected to a retreading process in which new tread is added to the used, current carcass 90 to extend the life of the tire 10. To retread the tire 10, the worn tread 36 is ground away so that it is removed to expose the underlay 22 as shown in [Fig.2]. The exposed underlay 22 is then the outer surface of the tire 10, and is the portion of the tire 10 farthest from the central axis 34 in the thickness direction 28. The underlay 22 has an underlay width that extends from the left terminal side to the right terminal side in the lateral direction 26. If enough of the underlay 22 is present, the sculpture element 10 can then be applied. However, if some of the underlay 22 is removed in the process, or if additional underlay 22 is desired, extra thermoplastic elastomer can be added to existing thermoplastic elastomer of the underlay 22 to achieve a desired level of underlay 22. The addition of this extra thermoplastic elastomer to the already existing underlay 22 is an optional step in the method.

[0028] The ribs 12 are attached to the underlay 22 via thermoplastic welding so that the ground contacting portion of the ribs 12 is located outward from the underlay 22 in the thickness direction 28. [Fig.3] shows the ribs 12 attached to the underlay 22 so that a new tread is formed on the used carcass 90. The ribs 12 have an outer surface 18 that is the surface of the ribs 12 that are farthest from the central axis 34 in the thickness direction 28 and that is the ground contacting portion of the ribs 12. The commonly known welding process that attaches two metals together is not used to attach the underlay 22 and the ribs 12 because of the flexibility and softness of the two materials. Thermoplastic welding may employ heated tool welding, laser welding, electro- magnetic welding, or non-contact infrared welding to attach the thermoplastic elastomers of the ribs 12 and the underlay 22. Thermoplastic welding introduces heat into the weld to attach the components 12 and 22, and in some instances this heat may be made by mechanical movement. Linear vibration following bringing the two components 12, 22 into contact under pressure can be employed. In other instances, spin welding or ultrasonic welding can be used as the thermoplastic welding techniques to join the components 12 and 22. In other instances, an external heat source from hot plate welding, hot bar welding, impulse welding, hot gas welding, or extrusion welding can be used as the thermoplastic welding process to attach the two components 12 and 22. Electromagnetic welding that uses resistive implants, induction, high frequency welding or infrared welding may be used as the ther- moplastic welding technique to attach the components 12 and 22. Still further, the ther- moplastic welding used to attach components 12, 22 to one another can be laser welding in which a focused beam of intense radiation is used to melt the thermoplasticelastomers in the components 12, 22 at the joint region to result in attachment of the ribs 12 to the underlay 22.

[0029] The thermoplastic welding therefore heat welds the thermoplastic elastomer of the underlay 22 to the thermoplastic elastomer that makes up the ribs 12 without having to use a curing system to vulcanize the connection between the ribs 12 and the underlay 22, such as would be the case in the commonly known cold retreading process. A press or autoclave is thus not necessary to have on hand in order to attach the ribs 12 to the underlay 22. The ribs 12 could be extruded directly onto the underlay 22 and then heat welded after they are formed via extrusion. Alternatively, the ribs 12 could be formed via an extrusion process at a separate location and then transported to the tire 10 and applied to the underlay 22.

[0030] The ribs 12 are designated generally by the reference number 12, and are described in greater detail using the reference numbers 50, 52, 54, 56, 58. The first rib 50 is located at the left terminal side of the underlay 22 and can cover this left terminal side. The width of the first rib 50 is less than the underlay 22 width and is positioned on the underlay 22 at a spot such that the first rib serves as a first shoulder rib of the tire 10. The underlay 22 has an underlay length that is the total length of the underlay 22 in the longitudinal direction 24 and extends completely around the central axis 34 in the lon- gitudinal direction 24. The first rib 50 has a length in the longitudinal direction 24 that is the same as the underlay 22 length as it likewise extends completely around the central axis 34 in the longitudinal direction 24. It is to be understood that these lengths are measured in degrees, and not in millimeters or other length units, because these components 22, 50 are designed for extending around the central axis 34 and are located at different distances from the central axis 34 in the thickness direction 28 so that they will have the same degree extension but different length unit extensions.

[0031] The first rib 50 extends so as to completely encircle the underlay 22 in the lon- gitudinal direction 24 so that it can contact itself from end to end. Multiple ribs 12 can be produced in the same way as the first rib 50 and can be attached via thermoplastic welding to the underlay 22 to form the tread as shown in [Fig.3]. In this regard, the second rib 52 is made of thermoplastic elastomer that is atached to the underlay 22 via thermoplastic welding. The second rib 52 has a length that is the same as the underlay 22 length in that both lengths extend the same amount (360 degrees) about the central axis 34. The second rib 52 has a width that is less than the underlay 22 width, and in some instances may be the same as the width of the first rib 50. The second rib 52 is spaced from the first rib 50 and is not in contact therewith and is positioned as a first intermediate rib of the tread of the tire 10. The space between the first and second ribs 50, 52 forms a circumferential groove 60 that is a shoulder groove of the tread and the bottom 62 of the shoulder groove 60 is the top of the underlay 22 which is thus notcovered by any of the ribs 12 of the tread and is exposed. The circumferential groove 60 is defined by the first rib 50, second rib 52, and underlay 22.

[0032] A radial centerline 106 is present in the tire 10 at the midway point in the lateral direction 26. A third rib 54 is located on the underlay 22 at the radial centerline 106 such that half of the third rib 54 is on one side of the radial centerline 106 and the other half is on the other in the lateral direction 26. The remaining ribs 12 in the tread 10 include this third rib 54, the fourth rib 56 and the fifth rib 58 and these elements can all be constructed in the same manner as the first rib 50. The third, fourth and fifth ribs 54, 56, 58 can all be made of thermoplastic elastomer that is designed for engaging the road surface and may be the same material as the first and second ribs 50, 52. The third, fourth, and fifth ribs 54, 56, 58 all include thermoplastic elastomer and are ther- moplastic welded onto the underlay 22. The third, fourth, and fifth ribs 54, 56, 58 all extend the same amount as one another and the other ribs 50, 52 around the central axis 34 and are the same lengths as that of the underlay length as all of these elements circle the central axis 34 completely 360 degrees. Still further, the third, fourth, and fifth rib 54, 56, 58 widths are all smaller than the underlay 22 width.

[0033] The center rib 54 is located in the center of the tread such that the radial centerline 106 is located in the center rib 54. The inboard and outboard orientations as described herein are with reference to this radial centerline 106 in which an inboard orientation means something is located towards or closer to the radial centerline 106 in the lateral direction 26, and in which an outboard orientation means that something is located farther away from or moving away from the radial centerline 106 in the lateral direction 26.

[0034] The various ribs 50, 52, 54, 56, 58 can be thermoplastic welded onto the underlay 22 to attach them to the tire 10. The third rib 54 forms a center rib of the tread and is spaced from the second rib 52 in the lateral direction 26 and does not engage the second rib 52. A first center groove is formed between the second and third ribs 52, 54 and the bottom of the first center groove is defined by the underlay 22 which is exposed and not covered by any of the ribs 12. On the opposite side of the third rib 54 in the lateral direction 26 is the fourth rib 56 which is spaced from and not in en- gagement with the third rib 54. The two ribs 54, 56 form a second center groove on the opposite side of the radial centerline 106 as is the first center groove, and the bottom of the second center groove is defined by the exposed underlay 22. The fifth rib 58 is po- sitioned at and over the right terminal side and forms a second shoulder rib of the tread. The fifth rib 58 is spaced from and free from engagement with the fourth rib 56 and forms with it and the exposed underlay 22 a second shoulder groove. The combined widths of all of the ribs 50, 52, 54, 56, 58 are less than the underlay 22 width. The five ribs 50, 52, 54, 56, 58 form a tread on the used carcass 90 and allowthe carcass 90 to be reused.

[0035] The ribs 50, 52, 54, 56, 58 could all be sized and shaped identically or could be dif- ferently sized and shaped in other embodiments. The method eliminates the curing step that would otherwise be used to attach the new tread onto the used carcass 90. A facility that retreads tires 10 can have a reduced variety of sizes of ribs 12 to retread all tire 10 sizes since dedicated, exactly sized treads are not needed for each tire 10 size and type. The retreading facilities need not have an autoclave or other curing equipment on hand to attach the new tread to the carcass 90 since thermoelectric welding is used as the attachment step.

[0036] As stated, the ribs 12 are made of thermoplastic elastomers. In some embodiments, the rib 12 is made completely of a thermoplastic elastomer and no other material. Ther- moplastic elastomers are sometimes referred to as thermoplastic rubbers, and are a class of copolymers or a physical mix of polymers that consist of materials with both thermoplastic and elastomeric properties. When constituted as a physical mix of polymers, the mix can include both a plastic and a rubber material. The ribs 12 can be centrally manufactured with standardized features such as sipes, blocks, notches or other architectural elements. These large series of ribs 12 can be shipped to dealer or retread establishments that are close to the customer. Only one, two, or three different widths of the various ribs 12 could be provided to be used with tires 10 having varying widths. Five or six different variants of the ribs 12 that are used as the center rib or ribs could also be provided. The ribs 12 that are provided may have the same cross- sectional shape, or some could have one rounded side while others have both straight sides so that some can be used as the shoulder ribs while the ones with both straight sides can be used as both intermediate and center ribs.

[0037] The rib 12 can be a single piece of thermoplastic elastomer that is extruded or otherwise produced as a one piece element. The length of the rib 12 will be greater than its width or height (h). The rib 12 could be provided in other, various formats. [Fig.4] shows an embodiment of the construction of the rib 12 in which it is produced from a plurality of smaller strips 40. These strips 40 have a length and width that is the same as that of the resulting rib 12, but their heights are not as large. Each one of the strips 40 is made of a thermoplastic elastomer, and five strips 40 are stacked on top of one another to form the resulting rib 12. The strips 40 are attached to subsequent strips 40 in the stack via thermoplastic welding to form a resultant rib 12 that is constructed via thermoplastic welding. Although five strips 40 are shown, any number of strips 40 can be present in the rib 12 in other embodiments.

[0038] The ribs 12 can have outer surfaces 18 that are completely featureless, and such ribs 12 when placed into the tire 10 form a tread known as a slick, but there will be circum- ferential grooves located between the ribs 12 that form the outer surface 18. The outersurface 18 in other embodiments could have ornamentation features located thereon. In yet other embodiments, the ribs 12 could have architectural features such as notches or sipes 42. One such embodiment of a rib 12 is shown with reference to [Fig.5] in which sipes 42 extend from the outer surface 18 into the rib 12. Sipes 42 are present within the ground contacting outer surface 18 and are voids in the rib 12 that have a length in the longitudinal direction that is 2 millimeters or less. Sequential sipes 42 can be spaced equally from one another along the length of the rib 12. The width of the sipes 42 in the lateral direction 26 extend completely across the entire width of the tread 12. With respect to the depth of the sipes 42, their depth in the thickness direction 28 is smaller than the height (h) 14. The extension of the sipes 42 in the thickness direction 28 is 2 millimeters or less. In some embodiments, the sipes 42 have a depth in the thickness direction 28 that is less than or equal to one half of the height (h) 14.

[0039] [Fig.6] shows another embodiment of the tire 10 in which the ribs 12 are again made of thermoplastic elastomer. However, the construction of the tire 10 is different from that as previously discussed in that the underlay 22 is not present. The underlay 22 could be removed during the grinding process in preparing the tire 10 for retreading, or the underlay 22 may have never been present within the tire 10 as originally formed. Regardless, the ribs 12 are attached to the tread rubber 88 in the crown 16 without the presence of the underlay 22. The ribs 12 are attached through the use of an adhesive 44 that attaches each one of the ribs 50, 52, 54, 56 to the tread rubber 88. In the disclosed embodiment, four ribs 50, 52, 54, 56 are present instead of five ribs as previously disclosed. It is to be understood that any number of ribs 12 can be present within the tire 10 in other embodiments. The ribs 12 are spaced from one another and not in en- gagement with one another such that circumferential grooves are formed between successive ribs 12, and these grooves have bottoms defined by the tread rubber 88 and not by the thermoplastic elastomer of the ribs 12 or the adhesive 44. The circum- ferential groove 60 is defined by the successive ribs 50, 52 and the exposed tread rubber 88 at the bottom 62. The other grooves in the tread can be formed in a similar manner. The adhesive 44 does not extend all the way across the entire width of the tread rubber 88 in the lateral direction 26, but is only present where the ribs 12 are located. In this regard, the bottoms 62 of the grooves 60 do not include adhesive 44 but are instead free from adhesive, although it is to be understood that some adhesive 44 could seep or otherwise be present on the bottom 62, and could form part of the sidewalls of the groove 60 especially at the contact point between the rib 12 and the tread rubber 88.

[0040] [Fig.7] discloses another tire 10 in accordance with the present invention that again features ribs 12 made of thermoplastic elastomer. The attachment of the ribs 12 to the carcass 90 in this embodiment is made via a curing process. In this regard, the underlay22 is not present as it is either ground off during the retread process or is not present in the tire 10 as originally formed. Strips of connecting rubber 46, which are uncured rubber, are placed at locations on the cured tread rubber 88 at which ribs 12 are desired to be located. The uncured connecting rubber 46 does not extend across the entire width of the tread rubber 88 in the lateral direction 26 but is intermittently spaced from successive strips of connecting rubber 46. The ribs 12 are placed upon the strips of connecting rubber 46, and this assembly is then placed into a mold or autoclave so that the connecting rubber 46 is cured. This curing causes the ribs 12 to be attached to the tread rubber 88 via the now cured connecting rubber 46. The resulting tread thus features ribs 12 that extend in the longitudinal direction 24 completely around the tire 10 and are spaced from successive ribs 12 in the lateral direction 26 and not in en- gagement therewith so that circumferential grooves 60 are formed between the ribs 12 completely around the longitudinal length of the tire 10. The height 14 is greater than the height of the connecting rubber 46 in the thickness direction 28.

[0041] The tire 10 illustrated in [Fig.8] is a non-pneumatic tire 10 in which the carcass 90 has a support structure 66 that is a series of spokes that are attached on their inner ends to a hub 70 and on their outer ends to a shear beam 68. The central axis 34 extends through the center of the hub 70 and is the inward most portion of the tire 10 in the thickness direction 28. The underlay 22 is included on the shear beam 68, and when the tread on the shear beam 68 is worn to the end of its useful life can be replaced with one or more of the ribs 12. These ribs 12 can be attached to the thermoplastic elastomer of the underlay 22 using the techniques as previously discussed. Multiple ribs 12 can be applied to the underlay 22 to construct the tread. The tire 10 onto which the ribs 12 are attached can thus be a pneumatic tire 10 as previously mentioned, or a non-pneumatic tire 10 as presently discussed. The tire 10 could also be a solid tire 10, which are sometimes found on construction vehicles, material handling vehicles, and lawncare vehicles. The ribs 12 formed on the tire 10 are featureless and are five in number forming intermittent circumferential grooves and the tire 10 can be described as a slick. Although described as being utilized with the retreading of a used tire 10, the method could also be used to form a tire 10 that can be an original equipment man- ufactured tire 10 that is produced and goes onto a new vehicle.

[0042] Hysteresis can be measured by the tan(6) value of the rubber making up the rib 12. The loss factor “tan(b)” is a dynamic property of the rubber compound. It is measured on a viscosity analyzer (Metravib V A4000) according to Standard ASTM D5992-96. The response of a test specimen consisting of two cylindrical pellets each 2 mm thick and one centimeter in diameter is recorded (the test specimen is made from samples taken from a tire mid-way up the height of the zone concerned as close as possible to the region of the equatorial plane in a region that is thick enough to be able to form thetest specimen), the specimen being subjected to simple alternating sinusoidal shear loadings at a frequency of 10 Hz, at a temperature of 60° C. The sweep covers amplitude of deformation from 0.1% to 25% peak to peak (on the outbound cycle) then from 25% to 1 % peak to peak (on the return cycle). The results that are used here are the loss factor tan(b) and the complex dynamic shear modulus. The complex dynamic shear modulus is denoted “G*25” in reference to the 25% strain applied during the test. During the outbound cycle, the maximum value of tanb that is observed is denoted “max tan(b)”.

[0043] The modulus, sometimes referred to as the complex shear modulus, may be denoted by the designation G*. The modulus G* of the particular material may be measured with the material at 60 degrees centigrade and may be expressed in units of mega pascals (MPa). The dynamic property G* may be measured on a Metravib Model VA400 ViscoAnalyzer Test System in accordance with ASTM D5992-96. The response of a sample of vulcanized material (double shear geometry with each of two 10 mm diameter cylindrical samples being 2 mm thick) can be recorded as it was being subjected to an alternating single sinusoidal shearing stress of a constant 0.7 MPa and at a frequency of 10 Hz over a temperature sweep from -60 °C to 100 °C with the tem- perature increasing at a rate of 1.5 °C / min. The shear modulus G* at 40 °C may be captured. As used herein, unless otherwise noted, the shear modulus G* at 40 °C is de- termined in accordance with ASTM 5992-96 and expressed in MPa. As used herein, the term “modulus” or “modulus G*” may also be referred to as or known as the complex shear modulus G* at 40 °C, or as the shear modulus G* at 40 °C, or as G* complex shear modulus at 40 °C. In so far as the ASTM 5992-96 may require the G* to be measured at a different temperature, such as at 60 °C, the measurement at 40 °C could be substituted with same in order to arrive at the G* measured at this tem- perature.

[0044] The use of a rib 12 made of thermoplastic elastomer may result in a tire 10 that does not perform the same as a tire 10 with tread made of standard tread rubber. This may be because thermoplastic elastomer is more flexible than tread rubber and if it is of the same height as the tread rubber, may result in a tire 10 that does not have as good rolling resistance performance. In order to design a tire 10 that has certain performance characteristics be the same as or even better than a tire 10 made of tread rubber, the ribs 12 can be designed so as to have a height (h) 14 that is not as high as a tire 10 that includes tread rubber as the outer surface 18. The height (h) 14 in some embodiments may be between and including 3-6.5 millimeters. In other embodiments, the height (h) 14 may be between and including 3-4 millimeters, 3-5 millimeters, 3-6 millimeters, 6-6.5 millimeters, 5-6.5 millimeters, 4-6.5 millimeters, 4-6 millimeters, or 5-6 mil- limeters. To further define the tread design, the rigidity of the thermoplastic elastomercan be taken into account to achieve the desired performance properties of the tread 10. The rigidity is expressed by using the G* value at 40 °C under a stress of 0.7 MPa. The height (h) 14 of the rib 12 can be further refined by selecting it according to the following inequality:

[0045] [Fig.9] shows a graph of temperature in degrees centigrade versus the tan(b) for both a tire 10 incorporating the thermoplastic elastomer into the ribs 12 and a tire 10 that in- corporates regular tread rubber as the ground contacting element instead of ribs 12 that are made of thermoplastic elastomer. This regular tread rubber tire 10 may be a Michelin ® Primacy ® 4 Grand Touring Summer tire manufactured by Michelin North America, Inc. having offices at 1 Parkway S, Greenville, South Carolina, 29615, USA. This reference tire 10 is designated as PCY 4 OE in [Fig.9]. The tire 10 as described herein that includes thermoplastic elastomer in the ribs 12 is designated as “subject” in [Fig.9]. At various temperatures the tan(b) value was recorded for both tires 10, and the PCY 4 OE reference tire has a higher hysteresis which corresponds with a higher tan(b) value for temperatures from -12° C to 12° C as compared to the subject tire 10. The subject tire 10 had a higher hysteresis and thus a higher tan(b) at temperatures outside of this range.

[0046] The rigidity of the materials making up the subject tire 10 and the PCY 4 OE tire 10 are compared at different temperatures in [Fig.10]. The rigidity is measured as the value G* and is expressed in units of MPa, and [Fig.10] shows the PCY 4 OE having a higher G* than the subject tire 10 at all temperatures.

[0047] Fig. 11 is a graph of temperature versus the expression tan(6) for again the subject C*l / 3 tire 10 and a reference tire 10 that is again the PCY 4 OE. The tan(6) values that are used in Fig. 11 are measured at a deformation of 10%, and the G* values are those that are measured at different degrees centigrade under a stress of 0.7 MPa. The numbers present in Figs. 9 and 10 for the tan(6) values and the G* values for the subject and reference tires 10 are pulled at each temperature and put into the expression tan(S) to G*l / 3 plot the two curves shown in Fig. 11. The graph of Fig. 11 shows the wet braking per- formance of the materials of the subject and reference tires 10. In particular, the wet braking performance of the tire 10 is the area under the curve taken in a temperature range from -8° C - 20° C. The subject tire 10 has a higher curve than the reference tire 10 in Fig. 11 and therefore has more area 110 under the curve between this range of temperatures. The wet braking performance of the subject tire 10 is the averageintegral of tan© measured from -8° C to 20° C, and this average integral may be greater than 0.4 in some embodiments. In other embodiments this average integral, which is the area 110, may be greater than 0.37, 0.38. 0.39, 0.35, 0.33, 0.41, 0.42, 0.43 or 0.44. The wet grip performance of the subject material may be better than the wet grip performance of the reference material.

[0048] Fig. 12 shows the rolling resistance of the tire 10. The values in Fig. 12 are obtained at a temperature of 23° C. The tan(6) at 23° C at various deformations are ploted on the graph for both the subject material and the reference material that are in the tires 10. The reference tire 10 is again the PCY 4 OE. The deformation values on the x-axis represent the percentage of deformation of the material being tested. The most extreme value on the far right hand side of the x-axis is 100% deformation, and the lowest value noted on the far left hand side of the x-axis is at 0.01% deformation of the sample. A higher tan(6) value represents a greater rolling resistance. Since the tan(6) changes at different percentages of deformation, in order to design the tread having the thermoplastic elastomer so that it has an equivalent rolling resistance to the tread of the reference tire 10 a single one of the tan(5) values should be selected. This tan(6) value may be the maximum tan(6) that is present in the range from 0.01% to 100% de- formation and in [Fig.12] is 0.22 for the subject tire 10 material and 0.16 for the reference tire 10 material. It is therefore the case that the material of the subject tire 10 will yield a higher rolling resistance than the material making up the reference tire 10.

[0049] At the tire 10 operating temperature which can be 40° C, the rigidity G* expressed as the tan(6) of the subject tire 10 material is 0.6 MPa and that of the reference tire 10 material is 0.86 MPa. If the reference tire 10 has a height of 7.5 millimeters, and if one wanted to provide a height (h) 14 of the subject tire 10 that has an equivalent rolling resistance, this height (h) 14 can be calculated by solving the equation height (h) 14 = reference height X (subject G* / reference G*) = 7.5 mm X (0.6 MPa / 0.86 MPa) = 7.5 mm X (0.697) = 5.2 mm. The tire 10 can be provided with ribs 12 having a height (h) 14 that is 5.2 mm so that its resulting rolling resistance is equivalent to the standard rubber tread tire 10 that does not have thermoplastic elastomer in its tread portion that engages the ground.

[0050] The designed tire 10 need not have a rolling resistance that is exactly the same as that of the reference tire 10, but could be within 95% of the rolling resistance. One in- equality that may be used to calculate the height (h) 14 of the ribs 12 of the tire 10 is as follows: < ^-2 mm where the max tan(8) is the largest tan(6) for the subject tiremax tan (S)10 material between the 0.01% to 100% deformation range.

[0051] The ribs 12 that are formed in the resulting tire 10 can be simplified from otherdesigns in that they may be featureless slicks that are not as stiff as tread having standard rubber that engages the ground, but are shorter in height (h) 14 to compensate to achieve acceptable rolling resistance performance. Although described as being fea- tureless, notches could be added to the ribs 12, or any other architectural feature could be added to the ribs 12, as desired and it is to be understood that the ribs 12 need not be featureless in all embodiments.

[0052] While the present subject matter has been described in detail with respect to specific embodiments and methods thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents to such embodiments. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations and / or additions to the present subject matter as would be apparent.

Claims

Claims

1. A tire, comprising: a plurality of circumferential ribs that extend in a longitudinal direction around a central axis, wherein the ribs are made of thermoplastic elastomer and have a height (h) that extends in a thickness direction and that is between and including 3 millimeters to 6.5 millimeters, wherein the thermoplastic material has an average rigidity G* that is measured at 40° C under a stress of 0.7 MPa; wherein each one of the ribs has a height to average rigidity ratio that is governed as follows:

2. The tire as set forth in claim 1, wherein the thermoplastic elastomer has a plurality of tan(b) values measured at 10% deformation at different degrees of Centigrade temperature, and wherein the thermoplastic elastomer has a plurality of average rigidity G* values that are measured at different degrees of Centigrade temperature; wherein the thermoplastic elastomer has a wet braking performance as follows: an average integral of tan(a) measured from -8° C to 20° C > 0.4.

3. The tire as set forth in claim 1 or 2, wherein the thermoplastic elastomer has a max tan(b) at 23 degrees of Centigrade temperature that is the highest tan(6) value found over a range of deformation that is between and including 0.01% to 100%; wherein the height (h) of the ribs is governed as follows: 12

4. The tire as set forth in any one of claims 1-3, wherein the ribs are produced through an extrusion process.

5. The tire as set forth in any one of claims 1-4, wherein each one of the ribs is composed of a plurality of strips of the thermoplastic elastomer that are heat welded together to form the ribs.

6. The tire as set forth in any one of claims 1-5, wherein the tire has an underlay that is made of thermoplastic elastomer that extends in the longitudinal direction around the central axis and extends in a lateral direction, wherein the ribs are attached to the underlay via ther-moplastic welding, wherein the ribs are spaced from one another in the lateral direction and not in engagement with one another such that cir- cumferential grooves are defined between successive ones of the ribs and the bottoms of the circumferential grooves are defined by the underlay.

7. The tire as set forth in any one of claims 1-5, wherein a crown of the tire has tread rubber, and further comprising adhesive that attaches the ribs to the tread rubber.

8. The tire as set forth in any one of claims 1-5, wherein a crown of the tire has tread rubber, and further comprising connecting rubber that is located between the ribs and the tread rubber in the thickness direction, wherein curing is used to cure the connecting rubber and attach the ribs to the tread rubber via the connecting rubber.

9. The tire as set forth in any one of claims 1-8, wherein the ribs have an outer surface that is a ground engaging surface of the tire, wherein the ribs do not have any voids that extend deeper than 2 millimeters in the thickness direction into the ribs from the outer surface.

10. The tire as set forth in any one of claims 1-8, wherein the ribs have an outer surface that is a ground engaging surface of the tire, wherein the outer surface is featureless.

11. The tire as set forth in any one of claims 1-10, wherein the tire is a pneumatic tire.

12. The tire as set forth in any one of claims 1-10, wherein the tire is a solid tire.

13. The tire as set forth in any one of claims 1-10, further comprising: a support structure that has spokes; and a shear beam located outward in the thickness direction from the support structure; wherein the ribs are located outward in the thickness direction from the shear beam.

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