Abstract:
A pneumatic tire for use on row-crop field sprayers having lugs configured for providing improved traction, load-handling capability, and stability. The leading edge of each lug is curvilinear such that outside corners are absent. Elimination of outside corners removes stress concentration points that would otherwise degrade tire performance under the conditions of high loading and fast speed. The lugs provide a significant load-carrying capacity without sacrificing attributes such as wet and dry traction, tread cleaning and hard surface roading.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of application Ser. No. 10/324,662, filed Dec. 20, 2002, which is hereby incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to tires and, more specifically, to pneumatic tires for row-crop field sprayers and like agricultural machinery. 
       BACKGROUND OF THE INVENTION 
       [0003]    Self-propelled row-crop field sprayers are specialized agricultural machinery for applying liquids, such as fertilizers or insecticides, to crops planted and grown in multiple parallel rows. Adjacent pairs of rows are tightly spaced for maximizing the plant density of the row crop being grown. As a result, row-crop field sprayer tires have a narrow section width and a high aspect ratio so that the tire can travel within the intra-row space. Because row-crop field sprayers are extremely massive agricultural machines, their pneumatic tires must have the ability to carry large loads. Pneumatic tires for the row-crop field sprayer also have to have a large rim diameter so that the field sprayer can clear the plants in the crop rows. Moreover, the pneumatic tires must exhibit good traction in either wet or dry conditions. In addition, row-crop field sprayer tires must be designed to withstand hard surface roading as the row-crop field sprayer is moved on paved roads between fields at a transport speed significantly faster than the service speed in the field. 
         [0004]    As the spacing between adjacent rows has narrowed for increasing the crop density, a need has arisen for narrowed pneumatic tires for row-crop field sprayer service. Because the tire load increases as the footprint narrows, conventional agricultural pneumatic tires cannot satisfy the full range of performance and design parameters required for row-crop field sprayer service. In particular, the lugs of such conventional agricultural pneumatic tires experience adverse consequences, such as cracking, tearing or, at the least, irregular wear patterns, resulting from hard surface roading. 
         [0005]    The inferior performance of conventional agricultural pneumatic tires arises from the faceted leading edge of the lugs, which define outside corners that provide stress concentration points under the conditions of high loading and fast speed. The leading edge experiences a significantly larger strain than the lug&#39;s trailing edge so that the outside corners on the leading edge experience significant strains. In particular, tires having conventional lug widths are prone to deflection which creates cracking, tearing and irregular wear patterns. Therefore, conventional agricultural pneumatic tires for service with row-crop field sprayers are particularly susceptible to the aforementioned adverse consequences, which significantly reduce tire durability. 
         [0006]    For these and other reasons, it would be desirable to provide a pneumatic agricultural tire for row-crop field sprayer services that can provide adequate wet and dry traction, that can carry heavy loads on a narrow-width ground-contacting footprint, and that does not experience any significant adverse consequences due from hard surface roading. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention is directed to high-profile pneumatic tires for row-crop field sprayers, and like agricultural machinery having a high center of mass, that are capable of rolling between adjacent crop rows. A pneumatic tire constructed according to the principles of the invention includes a casing having an axis of rotation, and a tread disposed radially outward of the casing. The tread includes a circumferential inner tread and a plurality of lugs each projecting radially outward from the inner tread. Each of the lugs has a trailing edge, a leading edge that contacts the ground before the trailing edge as the tire rotates about the axis of rotation in a direction of travel, and a ground-contacting surface positioned between the leading edge and the trailing edge, the leading edge having a curvilinear contour that is free of outside edges. 
         [0008]    A pneumatic tire in accordance with the invention has lugs each with a curvilinear leading edge lacking outside corners. The elimination of outside corners eliminates structures that would otherwise operate as stress concentration points. As a result, stress lines are less likely to develop under high loading conditions, such as hard surface roading, which reduces the incidence of cracking and tearing and increases tire durability. A pneumatic tire constructed in accordance with the principles of the invention has a significantly increased lug contact area or net-to-gross ratio proximate the equatorial plane of the tire. The concomitant increase in the circumferential lug width significantly increases lug stability. Moreover, the lug pattern layout permits the number of lugs per unit tire circumference or pitch number to be increased, as compared with conventional pneumatic tires used in row-crop field sprayer service, for maximizing the contact area to improve performance under conditions of high loading. Pneumatic tires constructed in accordance with the principles of the invention provide a significant load-carrying capacity without sacrificing attributes such as wet and dry traction, tread cleaning and hard surface roading. In addition, pneumatic tires constructed in accordance with the principles of the invention improve ride and handling performance in hard surface roading by virtue of the increased circumferential lug overlap as compared with conventional pneumatic tires used in row-crop field sprayer service. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention. 
           [0010]      FIG. 1  is a perspective view of a pneumatic tire according to the principles of the invention. 
           [0011]      FIG. 2  is an end view of the pneumatic tire of  FIG. 1 . 
           [0012]      FIG. 3  is a side view of the pneumatic tire of  FIG. 1 . 
           [0013]      FIG. 4  is an enlarged view of a portion of  FIG. 2 . 
           [0014]      FIG. 5  is a cross-sectional view of the pneumatic tire of  FIG. 1 . 
           [0015]      FIG. 6  is a top view of a single lug of the tire of  FIG. 4 . 
       
    
    
     DEFINITIONS 
       [0016]    “Axial” and “axially” means the lines or directions that are parallel to the axis of rotation of the tire. 
         [0017]    “Axially Inward” means in an axial direction toward the equatorial plane. 
         [0018]    “Axially Outward” means in an axial direction away from the equatorial plane. 
         [0019]    “Bead” means the circumferentially substantially inextensible metal wire assembly that forms the core of the bead area, and is associated with holding the tire to the rim. 
         [0020]    “Carcass” means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads. 
         [0021]    “Casing” means the carcass, belt structure, beads, sidewalls, and other components of the tire excepting the tread and the undertread. 
         [0022]    “Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction. 
         [0023]    “Equatorial Plane” (EP) means the plane perpendicular to the tire&#39;s axis of rotation and passing through the center of its tread. 
         [0024]    “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. 
         [0025]    “Inner” means toward the inside of the tire. 
         [0026]    “Lateral Edge” means the axially outermost edge of the tread as defined by a plane parallel to the equatorial plane and intersecting the outer ends of the axially outermost traction lugs at the radial height of the inner tread surface. 
         [0027]    “Leading” refers to a portion or part of the tread that contacts the ground first, with respect to a series of such parts or portions, during rotation of the tire in the direction of travel. 
         [0028]    “Lugs” refer to discontinuous radial rows of tread rubber in direct contact with the road surface. 
         [0029]    “Net-to-Gross Ratio” means the ratio of the normally loaded and normally inflated tire tread rubber that makes contact with a hard flat surface, divided by the area of the tread, including non-contacting portions such as grooves as measured around the entire circumference of the tire. 
         [0030]    “Outer” means toward the tire&#39;s exterior. 
         [0031]    “Pitch” means a section of the tread in the circumferential direction that is repeated around the outer circumference of the tire. Normally, a pitch contains a load-bearing element or lug that contact the road surface and an adjacent channel which separates adjacent lugs. 
         [0032]    “Pneumatic Tire” means a laminated mechanical device of generally toroidal shape, usually an open-torus, having beads and a tread and made of rubber, chemicals, fabric and steel or other materials. When mounted on the wheel of a motor vehicle, the tire through its tread provides traction and contains the fluid that sustains the vehicle load. 
         [0033]    “Radial” and “Radially” mean directions radially toward or away from the axis of rotation of the tire. 
         [0034]    “Section Height” (SH) means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane. 
         [0035]    “Section Width” (SW) means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after it has been inflated at normal pressure for 24 hours, but unloaded, excluding elevations of the sidewalls due to labeling, decoration or protective bands. 
         [0036]    “Shoulder” means the upper portion of sidewall just below the tread edge. 
         [0037]    “Sidewall” means that portion of a tire between the tread and the bead area. 
         [0038]    “Trailing” refers to a portion or part of the tread that contacts the ground last, with respect to a series of such parts or portions, during rotation of the tire in the direction of travel. 
         [0039]    “Tread” means a molded rubber component which, when bonded to a tire casing, includes that portion of the tire that comes into contact with the road when the tire is normally inflated and under normal load. 
         [0040]    “Tread Width or Tread Arc Width” means the arc length of the tread surface in the axial direction, that is, in a plane parallel to the axis of rotation of the tire. 
       DETAILED DESCRIPTION 
       [0041]    Although the invention will be described next in connection with certain embodiments, the invention is not limited to practice in any one specific type of row-crop field sprayer. It is contemplated that the pneumatic tires of the invention can be used with a variety of agricultural machinery having a high center of gravity and a large mass, including but not limited to row-crop field sprayers. Exemplary row-crop field sprayers with which the pneumatic tires of the invention can be used are commercially available, for example, from the Model 4710 and Model 6700 Self-Propelled Sprayers manufactured by John Deere (Moline, Ill.) and the New Holland Model SF550 self-propelled sprayer manufactured by CNH Global N.V. (Lake Forest, Ill.), and such commercially available row-crop field sprayers can be equipped with pneumatic tires constructed in accordance with the present invention. The description of the invention is intended to cover all alternatives, modifications, and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims. 
         [0042]    With reference to  FIGS. 1-5 , a pneumatic agricultural tire  10  constructed according to the principles of the invention includes a casing  12  and a tread  14 . Tire  10  has an axis of rotation (R)  24 , an equatorial plane (EP)  26 , a maximum section width (SW)  28 , and a rim diameter (D)  30 . Casing  12  includes a pair of sidewalls  16 ,  18 , a cord-reinforced rubber-coated carcass  20  and a pair of annular beads  21 ,  22 . Carcass  20  includes one or more carcass plies  23  extending circumferentially about the axis of rotation  24  of the tire anchored at opposite ends to a corresponding one of beads  21 ,  22  and one or more belt plies  25  disposed radially outward from the carcass plies  23 . 
         [0043]    Tread  14  includes a pattern of ground-engaging lugs  32  disposed radially outward of the carcass  20 , in which each of the lugs  32  projects radially outwardly from an inner tread  34 , which extends circumferentially about the tire  10 . The lugs  32  have a depth measured relative to the inner tread  34 , which may be the depth classified as an R1 depth by the Tire and Rim Association, Inc. (Copley, Ohio). Discharge channels  40  between adjacent pairs of the lugs  32  extend axially toward a corresponding one of two opposite shoulders or lateral edges  42 ,  44  of tread  14  for clearing accumulated mud and the like from the volumetric space between the lugs  32 . 
         [0044]    The lugs  32  are arranged into two sets  36 ,  38  that extend circumferentially about the tread  14  with a uniform pitch. The sets  36 ,  38  of lugs  32  are symmetrical relative to the equatorial plane  26  or, equivalently, symmetrically positioned between the lateral edges  42 ,  44 . Each lug  32  of each set  36 ,  38  has an outer lateral wall  46  that depends transversely from a radially-outermost ground-contacting surface  48  to merge with a corresponding one of the two sidewalls  16 ,  18  at the lateral edges  42 ,  44 . Each lug  32  has a leading wall  50  that intersects surface  48  along a leading edge  51 , an inner lateral wall  52 , and a trailing wall  54  that intersects surface  48  along a trailing edge  56 . Each of the walls  50 ,  52  and  54  extends radially inward from surface  48  to the inner tread  34 . 
         [0045]    With reference to  FIGS. 4 and 6 , leading wall  50  is a smooth curvilinear surface and leading edge  51  is a smooth curvilinear line each free of outside corners. The elimination of outside corners from leading wall  50  removes structures from tire  10  that would otherwise serve as stress concentration points that are a potential source for the development of stress lines. As a result, tire  10  has a reduced likelihood of experiencing cracking and tearing and has an improved tire durability under high loading conditions, such as hard surface roading. In particular, leading edge  51  has a concave curve segment  51   a  and a convex curve segment  51   b  adjoining the concave curve segment  51   a . The concave curve segment  51   a  extends along at least a majority of the length of leading edge  51 . 
         [0046]    The radially-outermost ground-contacting surface  48  of each lug  32  may be partitioned into an inner section  48   a  and an outer section  48   b . Outer section  48   b  extends generally laterally from a junction  57  with lateral wall  52  approximately one-half of the distance from junction  57  to the equatorial plane  26 . Inner section  48   a  extends inwardly from a junction  59  with outer section  48   b  toward the equatorial plane  26  and extends approximately one-half of the distance from the junction  57  to the equatorial plane  26 . The tread  14  is directional in that the tire  10  is designed to rotate about axis of rotation  24  in the rotational direction indicated by arrow  55  ( FIG. 1 ) such that leading edge  51  of each lug  32  contacts the ground before the trailing edge  56 . 
         [0047]    With continued reference to  FIGS. 4 and 6 , sections  48   a  and  48   b  are inclined relative to equatorial plane  26  with different inclination angles. Specifically and with regard to section  48   a , a tangent line  60  intersecting leading edge  51  at the inflection point where the curvature of leading edge  51  changes from concave to convex is inclined at an angle, α, of about 61°±2°, measured relative to an axial line  61  extending perpendicular to the equatorial plane  26 . A lobe  53  is defined on section  48   a  proximate to the equatorial plane  26 . With regard to section  48   b , a tangent line  62  intersecting leading edge  51  at junction  57  is inclined at an angle, β, of about 29°±2°, measured relative to an axial line  63  extending perpendicular to equatorial plane  26 . This set of angles provides a significant circumferential lug overlap that improves ride and handling performance in hard surface roading. For example, the lugs  32  operate for reducing vibration during hard surface roading. The lesser inclination of tangent line  62  operates for improving performance parameters, such as traction, of pneumatic tire  10  when operating on a soft surface, such as ground. The steeper inclination angle of tangent line  60  increases the mechanical bracing and deflection resistance of lug  32  to a circumferentially-directed force result from surface  48  contacting the ground. In other words, each lug  32  can apply a greater stiffening force opposing the ground-contact force due to the inclination angle of tangent line  60 . 
         [0048]    With continued reference to  FIG. 4 , a portion of the inner section  48   a  crosses the equatorial plane  26  near the lateral wall  52  such that each lug  32  extends in an axial direction over 50% of the maximum section width  28 . As a result, the lugs  32  are self-reinforcing by operating to stabilize one another due to the circumferential overlap in the tire footprint among adjacent lugs  32 . The constructive reinforcement of adjacent lugs  32  significantly reduces tire vibration during hard surface roading because each lug  32  operates to stabilize an adjacent later-contacting lug  32 , which are less likely to deflect as a result of surface contact as each lug  32  serially enters and exits the elliptical zone defined by the tire footprint. However, the extent of the overlap is limited so that the cleaning of soil from between the channels  40  between adjacent pairs of lugs  32  is not significantly affected. 
         [0049]    Section  48   b  of surface  48  has an approximately uniform width, W, that is increased by a slight flaring, γ, in the circumferential direction of less than about 3° and is present for aesthetic purposes. Section  48   a  of surface  48  is flared with a circumferential dimension that increases in a direction from junction  59  toward the equatorial plane  26 . As a result, the dimension of section  48   a  in the circumferential direction is significantly greater than the width of section  48   b . The flaring of section  48   a  increases the effective circumferential dimension of lug  32  near the equatorial plane  26  and cooperates in providing lobe  53 . The flaring of section  48   a  may be, for example, at an angle, χ, of about 13.5°±2°. The flaring of section  48   a  increases the surface or lug contact area proximate the equatorial plane  26 , which increases the load-carrying capability of the pneumatic tire  10  on hard and soft surfaces. It follows that the increased lug contact area effectively increases the net-to-gross ratio of tire  10  relative to conventional pneumatic tires for service with row-crop field sprayers. The increase in the circumferential lug width of section  48   a  also significantly enhances lug stability against deflection. 
         [0050]    The presence of lobe  53  causes the apportionment of the net-to-gross ratio to vary as compared with a lug  32  having a uniform circumferential dimension or width. Specifically, tread  14  may be apportioned into three circumferential regions or zones,  64 ,  66  and  68 , each of which extends one-third of the perpendicular axial distance between junction  57  and a junction between surface  48  and surface  52 . The proportion of the net-to-gross ratio provided by a portion of surface  48  encompassed by zone  64  to the net-to-gross provided by surface  48  encompassed by zone  68  is greater than 1.29, and typically is about 1.55 or larger. These values are significantly higher than the same ratio for conventional pneumatic tires intended for row-crop sprayer service. The net-to-gross ratio of tread  14 , including all three zones  64 ,  66 , and  68 , is greater than 24% and, in certain embodiments, is about 27% or larger. 
         [0051]    While the present invention has been illustrated by the description of one or more embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of applicants&#39; general inventive concept.