Abstract:
In an uneven wear-resisting heavy duty pneumatic tire tread including main grooves; land areas separated by grooves; and a stepped zone, within a land portion, located radially inside the tread contour line and bounded by narrow grooves, having a first lowered radial depth forming a wear-sacrificing portion, the improvement comprises at least a radially-directed circumferential portion of one of two radially outermost circumferentially-extending ground contact areas of the land portion, laterally terminating into one of the stepped zone grooves, with a circumferentially relieved first portion, the maximum depth thereof having a second lowered surface depth, with respect to the tread contour line, this second lowered surface depth differing from the first lowered surface depth, the relieved portion taking the shape of a surface of revolution, with the laterally directed surface thereof being one of a straight, curved, undulating, stepped, and scalloped line.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Technical Field  
           [0002]    The invention pertains to improved heavy duty pneumatic tires, particularly for use in drive wheel and steered wheel applications, the improvement relating to increasing uneven wear resistance.  
           [0003]    2. Background Information  
           [0004]    Radial carcass structures are often utilized in the construction of heavy duty pneumatic tires and the use of such constructions in trucks or busses, particularly in driven or driving wheels, and especially in steered wheels, so-called uneven wear often occurs, particularly in the shoulder portions of such tires, long before the tires reach the end of their projected life span.  
           [0005]    In order to reduce the incidents of uneven wear of such tire treads, there have been many proposed solutions, including contour configurations, tread patterns, grooving and siping arrangements, as well as combinations thereof. Some countermeasures, particularly those set forth in U.S. Pat. Nos. 5,131,444 and 5,445,201, both assigned to Bridgestone Corporation, which are incorporated herein by reference in their entireties, have provide significant improvements. These tire tread configurations utilize discrete, stepped, recessed zones in land portions thereof wherein each stepped zone has its outer circumferential surface located radially inside a contour line of the tread, when viewed in section, with these stepped portions being bounded on opposite sides thereof by narrow grooves. The noted stepped zones or portions have a lowered radial depth and define an uneven wear-sacrificial or equalization portion or rib which contacts the ground within the ground-contacting area of the tire footprint for supporting a load exerted upon the tire.  
           [0006]    Further additional prior art proposed solutions to the noted uneven tread wear problem are believed to be set forth in the following U.S. Pat. Nos.: 5,115,850; 5,293,918; 5,323,825; 5,345,988; 5,665,184; 5,833,780; 5,891,276 and 6,112,787.  
           [0007]    Although these tire and their various proposed constructions may provide partial solutions to the existing uneven wear problems, the need still exists for a heavy duty pneumatic tire, as previously defined, having a radial construction that provides increased resistance to the occurrence of the noted uneven and/or irregular tire wear.  
         BRIEF SUMMARY OF THE INVENTION  
         [0008]    The present invention builds upon the structures set forth in previously discussed U.S. Pat. Nos. 5,131,444, 5,445,201 and provide additional countermeasures against the uneven wear phenomenon. More particularly, the present invention is utilized in a heavy duty pneumatic tire adapted for substantially preventing uneven wear including circumferential main grooves in a tread along the circumference thereof; land portions defined and separated by the main grooves; and a stepped zone located within a land portion having a substantially flat, radial outer top surface located radially inside a contour line of the tread, the contour line being defined by radially outer surfaces of the land portions, as viewed in section, the stepped zone extending substantially continuously in the circumferential direction within a land portion and being bounded on opposite sides by narrow grooves, preferably having substantially equal depths, the stepped portion having a first lowered radial depth, wherein a wear-sacrificing portion is formed by the noted radially outer top surface of the stepped zone, with the wear-sacrificing portion contacting the ground within the tread ground-contacting area for supporting a load exerted upon the tire, wherein the improvement comprises at least a laterally-directed portion, of one of the two radially outermost circumferentially-extending ground contact areas of said land portion laterally terminating into the narrow grooves bounding the stepped zone, the ground contacting area portion having a first circumferentially relieved portion, with a maximum depth of the first relieved portion occurring at the intersection of the ground contacting area portion and one of the narrow grooves, the maximum depth of the first taper having a second lowered surface depth, with respect to the sectional contour line of the tread, the second lowered depth differing from the first lowered depth. The other of the two radial outermost circumferentially-extending ground contacting surfaces of the opposing land portions, that laterally terminates into the other of the narrow grooves bounding the stepped zone, having a second relieved portion, with a maximum depth of the second relieved portion thereof occurring at the intersection of the other ground contacting surface and the other narrow groove, the maximum depth of the second relieved portion having a third lowered surface depth, with respect to the sectional contour line of the tread, with the third lowered surface depth differing from the first lowered surface depth.  
           [0009]    In further a embodiment of the invention, the first and second relieved portions, as viewed in elevation, have the general shape of laterally-directed surfaces of revolution, wherein at least one of these surfaces, when viewed in section, is one of a chamfer and a taper, which in turn can take the shape of either a substantially straight line, a curved line, an undulating line, a stepped line or a scalloped line.  
           [0010]    In another embodiment of this invention, at least one of the first and second relieved portions, as viewed in elevation, has the general shape of a laterally directed truncated cone.  
           [0011]    In yet further embodiments of this invention, the angles of the first and second relieved portions, relative to the tire contour surface, leading to the second and third relieved portions, are different and/or are oppositely directed and/or and have converging angles and/or fall within specified ranges, and/or specific angulations.  
           [0012]    In additional embodiments of this invention, the lateral extents of the first and second relieved portions, are different, and can extend over all or but portions of their associated ground contacting area portions.  
           [0013]    In yet other embodiments of this invention, the depths of the second and third lowered surfaces are less than the depth of the first lowered surface and fall within specified limits relative to the tread depth and each other.  
           [0014]    Finally, in still other embodiments of this invention, the improvements thereof, relative to the widths of the ground contacting areas, the first and second lowered depths and the angulations of the noted truncated cones are set forth in four respective relationships that are set forth below the illustration appearing in FIG. 4B.  
           [0015]    The foregoing advantages, construction and operation of the present invention will become more readily apparent from the following description and the several accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0016]    A preferred embodiment of the invention, illustrative of the best mode in which the inventor has contemplated applying the principles thereof, is set forth in the following description and is shown in the drawings as well as being particularly pointed out and set forth in the appended claims.  
         [0017]    [0017]FIG. 1 is a front elevational view of a pneumatic tire having the improved equalization control rib contained within the tire tread portion thereof;  
         [0018]    [0018]FIG. 2 is a greatly enlarged plan elevational or developed view of the encircled portion of FIG. 1;  
         [0019]    [0019]FIG. 3 is an enlarged fragmentary sectional and simplified view of the tire tread, taken along line  3 - 3  of FIG. 1;  
         [0020]    [0020]FIG. 4A is a further enlarged and simplified fragmentary view of the left one half portion of the tire tread of FIG. 3, terminating at the mid-circumferential centerline of the tire; and  
         [0021]    [0021]FIG. 4B is another version of FIG. 4A but is further denominated with definitions, constraints, ranges and four relationships pertaining to the claimed lateral ranges, relief depths and relief angulations.  
         [0022]    Similar numerals refer to similar parts throughout the drawings. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    Turning now to the drawings, particularly in FIGS. 1 and 2, there are shown a front elevational view and an enlarged plan elevational or developed view of a left hand principal portion  12   b  of a tread  12  respectively, of a heavy duty radial pneumatic tire  10  incorporating the present invention. Tire  10  includes a circumferential center rib or land portion  14  that is axially separated from adjacent intermediate rib or land portions  16  by circumferentially directed main grooves  18 . The improved opposed shoulder or circumferential edge land portions  20  of this invention are laterally spaced from their respective adjacent improved intermediate rib portions  16  by the known stepped zone control rib  22  of this invention, as best seen in the enlarged fragmentary sectional view of the tire tread in FIGS. 3, 4A and  4 B. It should be noted that since FIG. 4B shows angulations and dimensions etc., similar to those of FIG. 4A, in terms of relationships or ratios, the corresponding such angulations and/or dimensions are stated herein, on occasion, within double parenthesis for ease of understanding.  
         [0024]    A review of FIG. 3 will show that the mid-circumferential center line or plane  24  separates tread portion  12  into allochiral or mirror-image tread halves  12   a  (right) and  12   b  (left) and therefore, in the interest of brevity, only tread portion  12   b  will be discussed in detail with reference to FIGS. 4A and 4B which set forth enlarged simplified fragmentary views of left tread half  12   b  ((W)).  
         [0025]    As best seen in FIGS. 2, 3,  4 A and  4 B, control rib  22  is laterally or axially spaced from adjacent shoulder rib  20  by a narrow outer circumferential straight groove  26  and similarly spaced from adjacent intermediate rib  16  by a narrow inner circumferential straight groove  28 . Narrow outer groove  26  may have a radially inwardly-directed diminishing variable cross sectional width while narrow inner groove  28  has a preferably constant cross sectional width. The terminus or radially inner radii end of each of grooves  18 ,  26  and  28  abuts a theoretical radial inner (broken) line  30  (FIG. 4A) joining said groove radii, with line  30  being substantially parallel with a theoretical outer line  32  (FIG. 4A) joining the largest radial outwardly-directed dimensions of shoulder rib  20 , starting at circumferential line  34  (FIG. 2), and intermediate rib  16 , starting at line  36  (FIG. 2), with both lines  34  and  36  being seen only as points in FIG. 4A, and which will be discussed in more detail hereinafter.  
         [0026]    Turning now specifically to FIGS. 2, 4A and  4 B, in the illustrated embodiment of this invention, an axially inwardly-directed annular portion or band area  40   a , ((C 3 (C 1 W )), stippled in FIG. 2, of about one half of the axial or lateral width of shoulder rib  20 , ((C 1 W)) starting at line  34  and terminating at line  56 , (which also defines the intersection of area  40  with the edge portion of the axial outer wall of narrow groove  26 ), is tapered, relieved or chamfered, as at  40   b , in any desired manner, relative to theoretical outer line  32 , at an included angle ((θ′)) of about 14 to 16 degrees. Outer line  32  forms a lateral portion of the theoretical sectional contour line (not shown per se) of tread portion  12   b  ((W)). The axial extent or width of band portion  40  extends about 19% of the axial width of tread portion  12   b . Similarly, an axially outwardly-directed annular band portion or area  42   a  ((C 4 (C 2 W)), stippled in FIG. 2, of about one half of the axial width of intermediate rib  16 , staring at line  36  and terminating at line  60 , (which also defines the intersection of area  42  with the edge portion of the inner wall of narrow groove  28 ), is similarly also tapered, relieved or chamfered, as at  42   b , relative to theoretical outer line  32 , at an included angle ((θ′)) of about 21 to 23 degrees. The lateral extent or width of band portion  42  extends about 12% of the axial width of tread portion  12   b . It will be clear from FIG. 4A that relieved band portions  40  and  42  are oppositely angularly-directed or sloped toward brake control rib  22  in a converging manner.  
         [0027]    In another embodiment of this invention, the entire lateral or axial extent of at least one of band portions  40  or  42  of shoulder ribs  30  and intermediate rib  16 , respectively is chamfered, tapered or relieved, taking the shape of one of a substantially straight line, as illustrated, or a curved line, an undulating line, a stepped line and a scalloped line, etc. as desired. Relieved band portions  40  and/or  42 , as viewed in elevation, also have the general shape of laterally directed first and second truncated cones, respectively. Furthermore, band portions  40  and/or  42 , as viewed in elevation, are also surfaces of revolution taking one or more of the shapes defined directly hereinabove.  
         [0028]    In a further embodiment of this invention, the lateral extents of at least one of band portions  40  and  42  extend for less than the previously noted about one half of the width of ribs  20  and  16 . See relationships ( 1 ) and ( 2 ) in FIG. 4B. The respective angulations of band portions  40  and  60  of ribs  16  and  20 , respectively, ((θ, θ′)) will of course change, depending on the axial extents thereof. See relationship ( 4 ) in FIG. 4B.  
         [0029]    Continuing with FIGS. 2 and 4A, and with reference to known equalizer control rib  22 , the flat radially-outermost or top surface  44  thereof (stippled in FIG. 2) may be tapered, relieved or chamfered, relative to the axial outer wall or side surface of rib  22  via an angular annular surface  46  between top surface  44  and a rib outer wall surface  48  but the shape, per se, of rib  22  forms no part of the present invention.  
         [0030]    Furthermore, in the illustrated embodiment of this invention, control rib top surface  44  is located radially inwardly a predetermined distance ((C 5 D)), relative to outer theoretical line  32 , (which may also be defined as a portion of the continuous theoretical, but not the actual, contour line of tread portion  12   b ), about 17% of the thickness or depth  54  ((D)) of tread portion  12   b , which is also equivalent to the radial extent or depth of main groove  18  ((D)). In addition, the maximum amount of chamfer or relief of shoulder rib portion  40 , at line  56  ((C 6 D)), at groove  26 , relative to outer theoretical line  32 , is about 10% of noted tread thickness  54 . The maximum amount of chamfer or relief of shoulder rib portion  42 , at line  60  ((C 6 D)), at groove  28 , relative to outer theoretical line  32 , is also about 10% of noted tread thickness  54  but it need not be the same as that of shoulder rib portion  40 . In addition, relative to an intermediate theoretical line  62 , perpendicularly connecting lines  56  and  60  (shown as points in FIG. 4A), equalizer control rib outer surface  44  is located radially-inwardly ((distance C 5 D-C 6 D)) thereof about 7%, with reference to noted tread thickness  54 . Finally, relative to outer theoretical line  32 , surface  44  is located radially inwardly thereof about 17%, with reference to noted tread thickness  54 . See relationship ( 3 ) in FIG. 4B.  
         [0031]    A viewing of FIG. 4A will make it clear that inner, intermediate and outer theoretical lines  30 ,  62  and  32  are in fact substantially parallel and that the maximum radial inward relief of chamfered shoulder rib and intermediate rib portions  40 ,  42  occurs at lines  56  and  60 , respectively, and that lines  62  and  30  are thus located radially inwardly of the theoretical contour line of tread  12 , while line  32  is coincident with a portion thereof. The radial distance between lines  32  and  62  corresponds to about 10% of tread thickness  54 , representing a graduated or smooth and oppositely-directed decrease from lines  34  and  36  to lines  56  and  60 , respectively. Similarly, control rib top surface  44  is, in turn, located radially inwardly, relative to line  62 , a further distance corresponding to 7% of noted tread thickness  54 , thus representing one discrete stepped zone. In addition, surface  44 , relative to line  32 , is thus located radially inwardly, thereof a total of about 17% of tread thickness  54 , this representing the combination of the defined gradual step ((C 6 D)) and the noted discrete step ((C 5 D-C 6 D)).  
         [0032]    Turning now principally to FIG. 4A, the maximum width of groove  26  is about 6%; the width of groove  28  is about 3%; and the maximum width of groove  18  is about 11% of the axial width of tread portion  12   b . In addition the axial widths of shoulder rib  20 , intermediate rib  16  and one half of center rib  14  are about 38%, 25% and 11% respectively, of the axial extent of tread portion  12   b . Finally, the combination of the axial extents of relieved surfaces  40  and  42 , together with braking rib top surface  44 , the portion relieved from surface  44 , as well as the maximum width of groove  26  and the width of groove  28 , which together also constitute the axial extent of theoretical outer line  32  (joining lines  34  and  36 ), comprise about 48% of the axial extent of tread portion  12   b . The total axial extent of relieved rib areas  40  and  42  (whose maximum relief depth is about 10% of noted tread thickness  54 ) comprises about 31% of the axial extent of tread portion  12   b  as well as about 66% of the axial extent of theoretical outer line  32 . The total axial extent of control rib  22 , together with the axial extents or lateral widths of adjacent grooves  26  and  28 , (whose minimum relief depth, relative to line  32 , is about 10% of noted tread thickness  54 ), and which also constitutes the axial extent of intermediate theoretical line  62 , comprises about 16% of the axial extent of tread portion  12   b  as well as about 34% of the axial extent of theoretical outer line  32 .  
         [0033]    It has been determined that the prior art&#39;s utilization of but a single discrete stepped zone, such as lowered surface level “δ” in U.S. Pat. Nos. 5,131,444 and 5,445,201, while reducing uneven tread wear and irregular tread wear, still did not fully reduce the phenomenon in these tread designs, particularly on steered and/or driven wheels of heavy duty vehicles. The present invention, in the illustrated embodiment thereof, further reduces such uneven and irregular tread wear by utilizing, in addition to the known discrete radial (first) stepped zone between the equalizing control rib upper surface  44  and intermediate theoretical line  62 , intermediate graduated or chamfered (second and third) steps emanating at circumferential lines  34 ,  36  of adjacent shoulder and intermediate ribs  20  and  16 , respectively. These relieved, tapered or chamfered surfaces  40  and  42 , extending from theoretical line  32  to theoretical line  62 , terminate and are maximized at their intersections with narrow grooves  26  and  28 , respectively and represent about 10% of noted tread thickness  54 . These chamfers etc. are laterally spread out, in the illustrated embodiment of this invention, over about 50% of the noted tread thickness  54 . Stated in the alternative, in the noted embodiment, the chamfer angles ((θ,θ′)) relative to line  32 , range from about 14 to 16 and 21 to 23 degrees for surfaces  40  and  42 , respectively. It is preferred that the about 7% depth difference between first step (about 17%) and the second and third steps (about 10%), respectively, be equated to no less than about 1 mm. It is believed that the theory of operation of the tire itself remains substantially similar to that espoused in noted U.S. Pat. Nos. 5,131,444 and 5,445,201.  
         [0034]    The benefits of the improvements of the present invention, with respect to the widths of the relieved portions  40  and  42 , the first and second lowered surface depths as well as the angulations of first ((θ)) and second ((θ′)) relieved portions ((C 3 (C 1 W)) and ((C 4 (C 2 W)), are set forth graphically in FIG. 4B together with four relationships that serve to define the noted relationships. For ease of understanding, these four relationships, which pertain to the dimensions and angulations in FIG. 4B have been included as a part of FIG. 4B.  
         [0035]    Uneven wear is additionally believed to be reduced by chamfering equalizer control rib top surface  44  at its axially outermost corner, i.e., at the previous intersection of top surface  44  (adjacent shoulder rib  20 ) and the axially outermost surface of brake control rib outer wall  48 , which consequently results in sloping surface  46  that joins surfaces  44  and  48 . As noted, the chamfering of control rib  22  forms no part of the present invention.  
         [0036]    Turning now to FIG. 3, particularly the latter, shoulder rib  20  includes, on its shoulder side  70 , a known laterally-extending shoulder indentation groove extending angularly into tire shoulder side  70 . The axial or lateral extent of groove  74  is limited due to the proximity of the underlying tread reinforcement belts or plies (not shown here for the sake of simplicity). It is the known function of shoulder indentation groove  74  to permit additional deflection of an axial outer annular edge portion of shoulder rib  20  as tire  10  rotates through its footprint, i.e., during the rotation of the tire under load and forms no part of the present invention.  
         [0037]    It should be understood that those skilled in the tire art will readily appreciate that the improved construction of this invention is not limited for utilization with only straight circumferentially-directed tread ribs of constant width but is also capable of being utilized with undulating and zig-zag ribs and varying width ribs together with their associated grooves grooves. In addition, the tread ribs, as well as the equalization control rib(s) need not be circumferentially continuous but could be provided with any desired lateral grooves and/or sipes and cuts, such as for example, those indicated in FIGS. 1 and 2. If desired the improved construction of this invention can be used in adjacent tread land areas other and/or in conjunction with those of the shoulder and intermediate ribs.  
         [0038]    In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed.  
         [0039]    Moreover, the description and illustration of the invention is but an example and the invention is not limited to the exact details shown and/or described.