Patent Publication Number: US-2002005237-A1

Title: Tire for zero radius turns

Description:
[0001] This application claims the benefit of U.S. Provisional Application, Ser. No. 60/213,910, filed on Jun. 26, 2000, in Express Mail Label No. EL514600944US, by the same inventors, Carl Musat and Robert Davis, entitled TREAD FOR ZERO-TURN MOWER TIRE. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] I. Field of the Invention  
       [0003] This invention relates to the art of vehicle tires, and more specifically to tires used on zero radius turn vehicles, or ZTR vehicles, especially as related to the tire tread.  
       [0004] II. Background of the Invention  
       [0005] Vehicles that permit zero radius turns have been gaining widespread popularity. Such vehicles generally work well for their intended purpose and are able to rotate one drive wheel in a forward direction while simultaneously rotating a second drive wheel in a reverse direction.  
       [0006] One aspect of ZTR vehicles is that the vehicles may be operated to turn, or steer, wherein the vehicle rotates solely about one drive wheel. The tread of the tire, about which the vehicle is turning, may cause damage to underlying turf in that it is not rolling over the surface thereof but rather rotating under the tread of the tire. As many tire treads are designed for traction, especially for traditional non-ZTR vehicles, such tread configuration may be not suitable for turf where a ZTR vehicle is rotating about one of the drive wheels.  
       [0007] Another aspect of tires is that the tire treads for ZTR vehicles, and more specifically lawn tractors or mowers, play a critical role in the effectiveness of mowing lawns. It is desirous to have a tire that has excellent traction capabilities so that underlying vegetation of hills and uneven terrain can be mowed. It is also important to have adequate traction when turning the mower.  
       [0008] Therefore, there is a strong need in the art to solve the aforementioned problems. A need exists to provide tread for a tire, which provides traction control without causing significant damage to the underlying turf.  
       SUMMARY OF THE INVENTION  
       [0009] The present invention reduces all the aforementioned problems. A tire having a tread comprises a central raised rib having first and second lateral edges and extends about the tire in a generally circumferential manner. The central raised rib is substantially disposed on an equatorial plane of the tire. A plurality of transverse raised ribs has first and second radial edges and is axially disposed along a tread section width. Each of said transverse raised ribs is substantially V-shaped and connected to the central raised rib.  
       [0010] Accordingly, it is the object of the present invention to provide a tire having a tread wherein the plurality of transverse raised ribs and the central raised rib define a plurality of voids where each of the voids is defined between the first radial edge of one transverse raised rib, one of the lateral edges of the central raised rib, and the second radial edge of the next radially-spaced transverse raised rib.  
       [0011] Another object of the present invention is to provide a tire having a tread wherein the central raised rib and the transverse raised ribs to comprise a chamfer on the edges thereof for use of providing optimal traction for an associated vehicle.  
       [0012] Still yet, another object of the present invention is to provide a tire having a tread wherein the transverse raised ribs are integrally formed with the central raised rib.  
       [0013] Still yet, another object of the present invention is to provide a tire having a tread where each of the transverse raised ribs extends in a substantially equidistant length from the equatorial plane, across the tread section width of the tire and over a lateral edge such as the combination of the transverse raised ribs and central rib is substantially W-shaped in the axial direction.  
       [0014] Yet, another object of the present invention is to provide a tire having a tread wherein the central raised rib further comprises a tread depth being measured from a tire surface to a rib top, wherein the tread depth may range from approximately 0.25 inches to approximately 0.5 inches.  
       [0015] Still yet, another object of the present invention is to provide a tire having a tread wherein the V-shaped transverse raised ribs point in a rearwardly direction relative to a backend of an associated vehicle, meaning the tire is directional.  
       [0016] Another object of the present invention is to provide a tire having a tread wherein the tire is grooveless.  
       [0017] Still yet, another object of the present invention is to provide a tire having a tread wherein the ratio of the transverse rib width, trw, to center rib width, crw, is at least 1.5 to 1.  
       [0018] It is another object of the present invention is to provide a tire having a tread wherein the tread further comprises a net-to-gross ratio ranging from substantially 26% to 36%.  
       [0019] Further, another object of the present invention is to provide a tread wherein the netto-gross ratio is substantially 31%.  
       [0020] Yet, another object of the present invention is to provide a tire having a tread wherein an angle is formed between the first lateral edge of the central raised rib and the first radial edge of the transverse raised rib such that the angle may range from substantially 45 degrees to 85 degrees.  
       [0021] Further, another object of the present invention is to provide a tread wherein a radius interconnects the first lateral edge of the central raised rib and the first radial edge of the transverse raised rib.  
       [0022] Still, another object of the present invention is to provide a tire having a tread wherein a an angle is formed between the first lateral edge of the central raised rib and second radial edge of the transverse raised rib such that the angle ranges substantially 85 degrees to 125 degrees.  
       [0023] Another object of the present invention is to provide a tire having a tread wherein the radius interconnects the first lateral edge of the central rib and the second radial edge of the transverse rib.  
       [0024] Further, another object of the present invention is to provide a tire having a tread wherein the radius interconnecting the first lateral edge of the central rib and second radial edge of the transverse rib is substantially 0.5 inches.  
       [0025] Still yet, another object of the present invention is to provide a tire having a tread wherein the second radial edge comprises a connection end for connecting the second radial edge to the central raised rib, wherein each of the V-shaped transverse ribs further comprises an outer vertex and an inner vertex wherein the inner vertex has a vertex angle that may range from substantially 85 degrees to 125 degrees.  
       [0026] Yet, another object of the present invention is to provide improved traction for a zero turn radius vehicle.  
       [0027] It is another object of the present invention is to provide minimization of tearing of the associated turf.  
       DEFINITION SECTION  
       [0028] “Axial” and “axially” are used herein to refer to lines or directions that are parallel to the axis of rotation of the tire.  
       [0029] “Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.  
       [0030] “Radial” and “radially” are used to mean directions perpendicular to the axis of rotation of the tire.  
       [0031] “Lateral” means an axial direction.  
       [0032] “Footprint” means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under normal load and pressure, including the area occupied by the tread elements.  
       [0033] “Net-to-gross” means the total area of ground contracting tread elements within the footprint divided by the gross area of the footprint.  
       [0034] “Rib” means a strip of rubber on the tread, which protrudes in a normal direction relative to the tire surface.  
       [0035] “Equatorial plane” means the plane perpendicular to the tire&#39;s axis of rotation and passing through the center of its tread. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0036] The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein:  
     [0037]FIG. 1 is a perspective view of a Zero Turn Radius vehicle.  
     [0038]FIG. 1 a  is a perspective view of the present invention.  
     [0039]FIG. 2 is a side elevational view of the present invention.  
     [0040]FIG. 3 is a cross-sectional view of FIG. 2 taken along lines  3 - 3 .  
     [0041]FIG. 4 is a front elevational view of the present invention.  
     [0042]FIG. 5 is a schematic drawing the tread pattern of the present invention.  
     [0043]FIG. 6 is a perspective view of the transverse raised ribs.  
     [0044]FIG. 6 a  is a cross section view of the transverse raised ribs taken at A-A′. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0045] The present invention relates to tires  10  used on a Zero Turn Radius vehicle  1 , which may include tractors and mowers, and especially as related to mowers utilizing independent drive units. The independent drive units provide the ZTR vehicle  1  with the ‘zero-turn-radius’ maneuverability. As ‘zero-turn-radius’ vehicles are well known in the art, as such will not be described further.  
     [0046] With reference to FIGS. 1 through 5, a tire  10  is shown having a pair of lateral edges  14  and a pair of sidewalls  18 . Each of the sidewalls  18  communicates with one of the lateral edges  14 . A tire tread  20  having a tread section width  42 , shown most clearly in FIG. 3, is disposed substantially equidistantly between the pair of lateral edges  14 . An equatorial plane  12  is defined as being located perpendicular to an axis of rotation of the tire  10  and passing substantially through the center of the tread  20  as shown in Figures. The tread  20  is comprised of a central raised rib  22  fashioned along the outer periphery of the tire  10  in a generally circumferential manner, as depicted clearly in FIG. 1 a  and  4 . Additionally, the central raised rib  22  has first and second lateral edges  24 ,  26 , which define an axial width  28  of the central raised rib  22 . The dimensions of the axial width  28 , referred to as aw, will be discussed in greater detail in a subsequent paragraph. However, as with any dimension disclosed herein, any width may be utilized for the central raised rib  22  as long as adequate traction is maintained without causing significant damage to the underlying turf.  
     [0047] With continued reference to FIGS. 1 through 5, a plurality of transverse raised ribs  30  is shown having first and second radial edges  32 ,  34 . The transverse raised ribs  30  are axially spaced along the tread section width  42  on opposite sides thereof where each of the transverse raised ribs  30  is substantially V-shaped and connected with the central raised rib  22 . As shown in FIGS. 1 a ,  2 ,  4  and  5 , the transverse raised ribs  30  are extended from and are integrally formed with the central raised rib  22  defining a plurality of voids  48 . As best seen in FIG. 5, each of the voids  48  is defined between the first radial edge  32  of one transverse raised rib  30 , one of the lateral edges  24  or  26  of the central raised rib  22 , and the second radial edge  34  at the next radially space transverse raised rib  30 . This formation, as detailed in the figures, maximizes traction for the mower especially as related to the zero-turn-radius tractors.  
     [0048] With continued reference to FIGS. 1 a ,  2  and  4 , the transverse raised ribs  30  are disposed in pairs in a radial direction about the tire circumference. In the preferred embodiment, each transverse raised rib  30  of each pair is oppositely disposed about the central raised rib  22 . In this manner, the transverse raised ribs  30  of each pair are aligned directly opposite each other. The transverse raised ribs  30  extend in a substantially equidistant length from the equatorial plane  12 , across the tread section width  42  of the tire  10  and over to the lateral edge  14  of the tire  10  such that the combination of the transverse raised ribs  30  and central rib  22  is substantially W-shaped in the axial direction. Therefore the transverse raised ribs  30  are symmetric about the equatorial plane  12 . In this manner, the transverse raised ribs  30  disposed directly opposite on each side of the central raised rib  22  are not staggered with respect to each other. However, it is also contemplated that the ribs  30 ,  30  may be disposed in a staggered or offset relationship about the equatorial plane  12 .  
     [0049] Referencing all of the Figures, it is noted at this point that the tire  10  is preferably grooveless. That is to say that the tread  20  including the central raised rib  22  and transverse raised ribs  30  do not have grooves fashioned therein. In other words, the surface  46  of the tire  10  includes voids  48  and has protrusions extending therefrom in the way of transverse raised ribs  30  and a central rib  22  but does not contain grooves fashioned into any of the surfaces described above. In this manner, the tire  10  and the tire tread  20  is grooveless.  
     [0050] Referencing again FIG. 5 and also FIG. 6 and  6   a , in the preferred embodiment of the present invention, the net-to-gross ratio is minimized to reduce the contact with the turf. This allows for optimal wear of the tire tread  20  along the central raised rib  22 . The ratio of the area of the raised ribs  22  and  30  to the void area  48  is optimized as shown clearly depicted in FIG. 5. The net-to-gross ratio may have a general range between 26% and 36%. However, it is contemplated in an alternate embodiment that the net-to-gross ratio may extend from 20% to 50%. More precisely, the net-to-gross of the preferred embodiment is substantially 31%. FIGS. 6 and 6 a , depict the raised ribs  22  and  30  having a chamfer  50  fashioned on the edges thereof for use in providing optimal traction for the tires  10  of the vehicle  1  of the present invention, and especially as related to the traction of the tires  10  in the reverse direction. The chamfer  50  may be fashioned at any angle chosen with sound engineering judgment, but in the preferred embodiment is fashioned at substantially 45 degrees. It is noted that the net-to-gross ratio is calculated related to the surface area of the tread  20  that is not chamfered. In other words, the area of the raised ribs  22  and  30  that has been chamfered is not included in calculating the net-to-gross ratio. In this manner, the net-to-gross may increase as the tire tread  20  wears with use because the area of the tread  20  will increase due to the chamfered edges  50 . Therefore, the net-to-gross calculated herein is a net-to-gross ratio of the new or substantially un-used tire  10 .  
     [0051] With reference again to FIG. 5, in the preferred embodiment, the depth of the tread  20  from the ground-engaging surface of the raised ribs  22  and  30  to the surface of the void  48  is substantially 0.35 inches. However, the depth of the raised ribs  22 ,  30 , or the tread depth, may range from 0.25 to 0.5 inches.  
     [0052] With continued reference to FIG. 5, A first radial edge angle  58  is formed between the first lateral edge  24  of the central raised rib  22  and the first radial edge  32  of the transverse raised rib  30 . The first radial edge angle  58  may range from substantially 45 degrees to 85 degrees. As shown in FIG. 5, the first radial edge angle  58  is approximately 65 degrees, but may reside within the range of 45 to 85 degrees. A first radius  62  interconnects the first lateral edge  24  of the central raised rib  22  and the first radial edge  32  of the transverse raised rib  30 . The first radius  62  is substantially 0.25 inches to correlate with the 65 degree first radial edge angle  58 . On the opposite side of the transverse raised rib  30 , a second radial edge angle  60  is formed between the first lateral edge  24  of the central raised rib  22  and second radial edge  34  of the transverse raised rib  30 . The second radial edge angle  60  may range from substantially 85 degrees to 125 degrees. As shown in FIG. 5, the second radial edge angle  60  is approximately 105 degrees. A second radius  64  interconnects the first lateral edge  24  of the central raised rib  22  and the second radial edge  34  of the transverse raised rib  30 . The second radius  64  is substantially 0.5 inches to correlate with 105-degree angle of the second radial edge angle  60 .  
     [0053] Referencing again all of the FIGS. 1 through 5, each transverse rib  30  comprises first and second connection ends  36 ,  38  for connecting the transverse raised rib  30  to the central rib  22 . Additionally, each transverse raised rib  30  has a distal end  40 , which extends over to the lateral edge  14  of the tire  10 . The transverse ribs  30  further comprise an outer vertex  52  and an inner vertex  54  wherein the inner vertex  54  has a vertex angle  56  ranging from substantially 85 degrees to 125 degrees. As shown in FIG. 5, the inner vertex angle  56  is substantially 105 degrees. A ratio is defined of the radial distance from the second connection end  38  to the inner vertex  54 , iv, to the radial distance from the second connection end  38  to the outer vertex  52 , ov, which may be substantially within the range of 0.73 to 0.79. This range provides for optimal performance of the tire tread  20 . However, the ratio iv/ov may generally range from substantially 0.65 to 0.87. Of course these radial distances, the vertex angle  56 , and first and second radial angles  32 ,  34  may be any dimension chosen with sound engineering judgment provided that traction is maintained and damage to the underlying turf is minimal. As is evident from these angles and radial distances, the V-shaped transverse raised ribs  30  point in a rearwardly direction relative to a backend of the associated vehicle  1 , meaning the tire  10  is directional.  
     [0054] Referencing again FIGS. 1 through 5, in the preferred embodiment, the tread section width  42  may range between substantially 7.5 inches and substantially 8.12 inches, but is not limited thereto. Additionally, the plurality of transverse raised ribs  30  extends a distance, which may range from substantially 7.2 inches to substantially 7.8 inches measured from one distal end  40  of one transverse raised rib  30  to the distal end  40  of the opposing transverse raised rib  30 . In this manner, the ratio, trw/tsw, of the transverse rib width trw, to the tread section width tsw, is substantially within the range of 0.93 to 0.99. However, the ratio trw/tsw may range from between 0.87 to 1.05. The transverse rib  30  width, trw, and the axial width  28 , aw, of the center rib  22  also form a ratio trw/aw, which is at least 1.5 to 1. In some instances it may be 2 to 1 or even 5 to 1. The present embodiment described herein provides for optimal performance of the zero-turn-radius vehicle  1  while minimizing tearing of the turf on which the vehicle  1  is traversing.  
     [0055] The preferred embodiments have been described, hereinabove. It will be apparent to those skilled in the art that the above methods may incorporate changes and modifications without departing from the general scope of this invention. It is intended to include all such modifications and alterations in so far as they come within the scope of the appended claims or the equivalents thereof.