Abstract:
A tire is provided having a tread region that includes continuous ribs which extend diagonally across the transverse direction of the tire. Partial sipes are provided at the trailing edges of the ribs. Full sipes can also be provided with the partial sipes. The ribs may form various patterns such as e.g., an S-shaped pattern, chevron pattern, and others. The tire provides improved traction performance over non-diagonal ribs while still providing desirable rolling resistance performance and control of irregular wear.

Description:
PRIORITY CLAIM 
       [0001]    This application claims the benefit of priority of U.S. Provisional Patent Application No. 61/706,923, filed Sep. 28, 2012, which is incorporated herein by reference for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The subject matter of the present disclosure relates generally to a tire having ribs that fully or partially extend diagonally across the transverse direction of the tread region and have a plurality of sipes defined in the trailing edge of the ribs. 
       BACKGROUND OF THE INVENTION 
       [0003]    Tires having continuous ribs oriented parallel to the longitudinal direction of the tread are commonly used on e.g., commercial vehicles. A common placement of such designs on commercial vehicles can include the steer tire positions on a commercial truck. Ribs constructed in such a manner can provide rolling resistance performance that is much better than e.g., tread patterns having blocks or non-continuous ribs. Improved rolling resistance performance can provide better fuel efficiency, a particularly desirable feature in view of increasing fuel costs. 
         [0004]    One challenge with ribs oriented parallel to the longitudinal direction, however, is relatively poor traction performance. This characteristic results from e.g., the lack of transverse edges that provide grip as the tire rolls over the road surface. Thus, tires having such rib construction are typically not used on e.g., the drive tires of commercial vehicles. Instead, as stated above, such tires are commonly placed in the steer positions where a high level of longitudinal traction is not required. 
         [0005]    Additionally, such longitudinally oriented ribs are subject to irregular wear. As used herein, “irregular wear” means that the wearing of the ribs is not uniform from rib to rib. Such irregular wear can e.g., shorten the life of the tread and create unwanted vibrations as the tire rolls across the road surface. Although siping can be added to reduce such irregular wear, such can also adversely affect rolling resistance performance. 
         [0006]    Accordingly, a ribbed tire that provides desired rolling resistance and traction performance would be useful. More particularly, a tire that can provide the rolling resistance performance of a continuous rib while also providing needed traction performance would be beneficial. Such a tire that can also be provided with features for preventing or reducing irregular wear would also be very useful. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a tire having a tread region that includes continuous ribs that fully or partially extend diagonally across the transverse direction of the tire. Partial sipes are provided at the trailing edges of the ribs. Full sipes can also be provided along with the partial sipes. The ribs may form various patterns such as e.g., an S-shaped pattern, chevron pattern, and others. The tire provides improved traction performance over non-diagonal ribs while still providing desirable rolling resistance performance and control of irregular wear. Additional objects and advantages of embodiments of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention. 
         [0008]    In one exemplary embodiment, the present invention provides a tire defining longitudinal, radial, and transverse directions. The tire includes a pair of opposing shoulders spaced apart along the transverse direction. A tread region extends between the shoulders. The tread region includes a plurality of ribs separated by grooves and extending from one of the shoulders to the other of the shoulders. Each of the ribs has a rib length and a rib width. Along the rib length, each of the ribs forms a non-zero angle α from the longitudinal direction. Relative to the direction of tire rotation, each of the ribs includes a leading edge and a trailing edge—where the leading edge is the edge that rolls through the contact patch first. The trailing edge defines a plurality of partial sipes spaced apart along the length of the rib. The partial sipes have a sipe length SL that is less than the rib width. The leading edge does not have any partial sipes. 
         [0009]    In another exemplary embodiment, the present invention provides a tire defining a centerline and defining longitudinal and transverse directions. The tire includes a pair of opposing shoulders spaced apart along the transverse direction. A tread region extends between the shoulders. The tread region includes a first plurality of ribs separated by grooves and extending from one of the shoulders to substantially the centerline of the tread region. A second plurality of ribs is also separated by grooves and extends from another of the shoulders to substantially the centerline of the tread region so as to approach the first plurality of ribs. Each of the first plurality and second plurality of ribs have a rib length and a rib width. The first plurality of ribs forms a non-zero, positive angle+α 1  from the longitudinal direction along their rib length. The second plurality of ribs forms a non-zero, negative angle −α 2  from the longitudinal direction along their rib length. Each of the first and second plurality of ribs includes a leading edge and a trailing edge. Each trailing edge defines a plurality of partial sipes spaced apart along the length of the rib. The partial sipes have a sipe length SL that is less than the rib width. The leading edge does not have any partial sipes. 
         [0010]    In still another exemplary embodiment, the present invention provides a tire that defines longitudinal, radial, and transverse directions. The tire includes a pair of opposing shoulders spaced apart along the transverse direction. A tread region extends between the shoulders. The tread region has a rolling tread width RTW. The tread region includes a plurality of ribs separated by grooves and extending along the tread region. Each of the ribs having a rib length RL and a rib width RW. Along the rib length RL each of the ribs forms a non-zero angle α from the longitudinal direction and the value of RL*cos(α) is about 40 percent of the rolling tread width RTW or greater. Each of the ribs includes a leading edge and a trailing edge. The trailing edge defines a plurality of partial sipes spaced apart along the length of the rib. The partial sipes have a sipe length SL that is less than the rib width RW. The leading edge does not have any partial sipes. 
         [0011]    These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    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: 
           [0013]      FIG. 1  illustrates a perspective view of an exemplary embodiment of a tire of the present invention. 
           [0014]      FIG. 2  is a close up, perspective view of a portion of the tread region of the exemplary embodiment of  FIG. 1 . 
           [0015]      FIG. 3  is a cross-sectional view of a portion of the tread region of the exemplary embodiment of  FIG. 1 . 
           [0016]      FIG. 4  is a close-up, perspective view of a portion of an exemplary embodiment of a tread of the present invention with hidden features shown in dashed lines. 
           [0017]      FIGS. 5 ,  6 ,  7 , and  8  are perspective views of additional exemplary embodiments of the present invention. 
           [0018]      FIG. 9  is a close up, perspective view of a portion of the tread region of another exemplary embodiment of the present invention. 
           [0019]      FIGS. 10-12  are graphs of certain data as will be further described below. 
           [0020]      FIG. 13  is a close up, perspective view of a portion of the tread region of another exemplary embodiment of the present invention. 
       
    
    
       [0021]    The use of the same or similar reference numerals in the figures denotes same or similar features. 
       DETAILED DESCRIPTION 
       [0022]    For purposes of describing the invention, reference now will 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, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
         [0023]      FIG. 1  illustrates an exemplary embodiment of a tire  100  constructed according to the present invention. Tire  100  defines a transverse direction T that is parallel to the axis of rotation A. A radial direction R extends from the axis of rotation A and is perpendicular thereto. Tire  100  also defines a longitudinal direction L ( FIGS. 6 and 7 ) that is perpendicular to both the transverse direction T and radial direction R at any point along the tread region  102  of tire  100 . Longitudinal direction L is also tangent to a circumferential direction C of tire  100  at any point along tread region  102 . 
         [0024]    Tire  100  includes a pair of opposing shoulders  104  and  110  spaced apart from each other along transverse direction T. Tread region  102  extends between shoulders  104  and  110  along transverse direction T and also extends circumferentially around tire  100 . Tread region may include e.g., notches  146  of other features along each shoulder of tire  100 . Tire  100  also includes a pair of sidewalls  112  and  114  on opposing sides of tire  100 . 
         [0025]    Tread region  102  includes a plurality of ribs  106  separated by grooves  108 . Each of the ribs  106  has a rib length RL and a rib width RW. Ribs  106  each extend diagonally from one shoulder  104  to the other shoulder  110 . Although shown for this embodiment as uninterrupted across the entire rib length RL, the present invention includes exemplary embodiments where one or more ribs may be interrupted along their rib length RL by grooves or other features. 
         [0026]    As shown in  FIGS. 1 and 2 , each rib  106  has a rib length RL that forms a non-zero angle α (45 degrees in  FIGS. 1 and 20  degrees in  FIG. 5 ) from the longitudinal direction L. For example, in certain exemplary embodiments, the absolute value of angle α is in the range of about 10 degrees to about 60 degrees. In still other embodiments, the absolute value of angle α is about 20 degrees or about 60 degrees. It should be noted that in  FIG. 1  as viewed by the reader, ribs  106  extend diagonally upward from left to right and provide for a positive angle α from the longitudinal direction L, which can be denoted as +α as shown in  FIG. 1 . However, in other embodiments, ribs  106  extend downwardly from left to right and still form a non-zero angle α from the longitudinal direction L. In such instance, angle α will provide for a negative angle α, which can be denoted as −α as shown in  FIG. 2 . Regardless of which directions for ribs  106  are used, the absolute value of angle α is in the range of about 10 degrees to about 60 degrees for these exemplary embodiments as previously stated. 
         [0027]    Continuing now with  FIGS. 1 ,  2 , and  3  ribs  106  each have a leading edge  116  and a trailing edge  118  as defined by rolling direction RD, where the leading edge  116  is the first edge to enter the contact patch as the tire rolls and the vehicle moves in a forward direction. More particularly, the configuration of ribs  106  provides tire  100  with a directional tread pattern. As such, when a vehicle equipped with tire  100  is moving in a forward direction, leading edge  116  of a rib  106  contacts the road surface before trailing edge  118  as tire  100  moves along rolling direction RD and each rib  106  moves through the contact patch. 
         [0028]    Trailing edge  118  of each rib  106  defines a plurality of partial sipes  120  that are spaced apart along rib length RL. Partial sipes  120  are “partial” meaning they each have sipe length SL shorter than rib width RW such that they do not extend fully across rib width RW of rib  106 . Each partial sipe  120  is spaced apart along the direction of rib length RL from an adjacent partial sipe  120  by a spacing S. Each partial sipe  120  has a sipe depth SD. For this exemplary embodiment, spacing distance S is less than about 1.5 times sipe depth SD. In turn, sipe depth SD is at least about 50 percent of the height H of ribs  106  along the radial direction R. ( FIG. 3 ). Partial sipes  120  also have a sipe length SL that is at least about 50 percent of the spacing S between partial sipes  120 . 
         [0029]    Referring specifically to  FIG. 2 , partial sipes  120  each form an acute angle β from the transverse direction T. Angle β has an absolute value in the range of about zero degrees to about 45 degrees. It should be noted that in  FIG. 2  as viewed by the reader, ribs  106  extend diagonally upward from left to right such that angle β has a positive value denoted +β. However, in other embodiments, ribs  106  extend downwardly from left to right and will still form an acute angle −β from the transverse direction T having an absolute value in the range of about zero degrees to about 45 degrees. 
         [0030]    Along sipe depth SD, partial sipes  120  can be straight as shown in  FIG. 3 . Alternatively, various features may be added to assist with durability, wear rate, and irregular wear in other embodiments of the invention. For example, as shown in  FIG. 4 , sipes  120  could include one or more waves or undulations  122  along radial direction R. Other types of shear locking features may be used as well. Undulations or other shear locking features may also be provided along sipe length SL. 
         [0031]    A variety of shapes and/or orientations may be used with the diagonal ribs  106  that will provide tire  100  with different appearances. In  FIG. 1 , the diagonal ribs  106  of tire  100  are relatively straight along rib length RL.  FIG. 5  provides another exemplary embodiment of tire  100  in which ribs  106  are provided at a different angle α from the longitudinal direction L. Other configurations may also be used. For example, ribs  106  may be provided with a slight curvature so to create an overall corkscrew or S-shape for each rib  106 . 
         [0032]      FIGS. 6 ,  7 , and  8  each show additional exemplary embodiments of tire  100  where diagonal ribs are arranged to create chevron patterns. More particularly, for each embodiment, tire  100  includes a first plurality of ribs  124  separated by grooves  126  and extending from shoulder  104  to substantially the centerline C/L of tread region  102 . Tire  100  also includes a plurality of ribs  128  separated by grooves  130  and extending from the other shoulder  110  to substantially the centerline C/L of tread region  102  so as to meet ribs  124 . For the embodiments of tire  100  shown in  FIGS. 6 and 7 , grooves  126  and  130  meet at centerline C/L whereas in  FIG. 8  grooves  126  and  130  are offset from each other at centerline C/L. In still other embodiments of the invention, grooves  126  and  130  may approach each other without necessarily touching and/or without meeting only at the centerline C/L. 
         [0033]    First plurality of ribs  124  each have a rib length RL and a rib width RW. Along their rib length RL, ribs  124  are positioned at a non-zero, positive angle +α 1  from the longitudinal direction L. Second plurality of ribs  128  each have a rib length RL and a rib width RW. Along their rib length RL, second plurality of ribs  128  are positioned at a non-zero, negative angle −α 2  from the longitudinal direction L. For each exemplary embodiment shown, the absolute value of angle α x  for ribs  124  and  128  is identical. However, in other exemplary embodiments of the invention, the absolute values of α 1  and α 2  may be different or non-equal. Comparing  FIGS. 6 and 7 , the absolute value used for angle α is greater in  FIG. 7 . Other values may be used to provide a different appearance. As with the exemplary embodiment of  FIG. 1 , the absolute value of angle α is in the range of about 10 degrees to about 60 degrees. 
         [0034]    In a manner also similar to the exemplary embodiment of  FIG. 1 , ribs  124  each have a leading edge  132  and a trailing edge  134 . A plurality of partial sipes  136  are defined by trailing edge  134  in a manner similar to partial sipes  120 . Ribs  128  each have a leading edge  138  and a trailing edge  140 . A plurality of partial sipes  142  are defined by trailing edge  140  in a manner similar to partial sipes  120  but with an opposite orientation. For each of the embodiments of  FIGS. 6 ,  7 , and  8 , partial sipes  136  and  142  have a spacing S, a sipe depth SD, and a sipe width SW as previously described with regard to the embodiment of  FIG. 1 . Similarly, partial sipes  136  and  142  form an acute angle β (+β or −β) from the transverse direction, wherein angle β has an absolute value in the range of about 0 to about 45 degrees. 
         [0035]    Chevron patterns other than what is shown in e.g.,  FIGS. 6 ,  7 , and  8  may be used as well for the ribs of tire  100 . For example, the chevron pattern may be oriented 90 degrees from what is shown in these figures. U.S. Design Pat. No. 352,486 provides an example of such an orientation. 
         [0036]    The above description has provided examples of tire  100  with partial sipes—i.e. sipes extending from the trailing edge and partially across the width of a respective rib. However, the present invention includes full width sipes as well. For example,  FIG. 9  provides a view similar to the embodiment of  FIG. 2  except partial sipes  120  alternate with full width sipes  121 . For sipes  121 , aspects such as the sipe depth SD, angle β, and undulations can be provided in a manner similar to that previously described with regard to the embodiment of  FIGS. 1 and 2 . Patterns other than alternating between full width sipes  121  and partial sipes  120  may also be used. For example,  FIG. 13  provides another exemplary embodiment for the tread of tire  100  in which multiple, partial sipes  120  are positioned between full width sipes  121  as shown. 
         [0037]    The rib length RL for the exemplary embodiment of  FIGS. 1 and 5  is such that ribs  106  extend substantially or completely across the rolling tread width RTW of tread region  102 . In  FIGS. 6 ,  7 , and  8 , rib length RL of ribs  124  or  128  extends only partially across the rolling tread width RTW such that rib length RL is less than that of the exemplary embodiments of  FIGS. 1 and 5 . As used herein, rolling tread width RTW is the width of the tread—as measured along transverse direction T—that is in contact with the ground surface as the tire moves through the contact patch. For all exemplary embodiments of the invention described above, the product of the rib length RL and the cosine of angle α is equal to, or greater than, about 40 percent of the rolling tread width RTW. This can also be expressed as RL*cos(α) is the same, or greater than, about 40 percent of the rolling tread width RTW. 
         [0038]    Rolling resistance measurements were conducted for five different tires A through E constructed according to various exemplary embodiments of the invention as identified in TABLE I below. Rolling resistance was measured on a drum at maximum nominal loads and pressures at about 90 kilometers per hour. All tires had a tread having the same void volume ratio. The notches referenced in Table I are notches such as notches  146  shown in  FIG. 1  and located on the exterior shoulders of tire  100 . For tires A through D, each tire was tested without notches or partial sipes, with notches but not partial sipes, and with notches and partial sipes. RR as referenced in Table I refers to rolling resistance coefficients expressed in values of Kg/T (kilograms of resistance force/ton of load). 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Tire A 
                 Tire B 
                 Tire C 
                 Tire D 
                 Tire E 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Rib description 
                 α = 20°/ 
                 α = 45°/ 
                 /α/ = 25°/ 
                 /α/ = 45°/ 
                 7 straight ribs 
               
               
                   
                 CorkScrew 
                 CorkScrew 
                 Chevron 
                 Chevron 
               
               
                 RR with no 
                 3.62 
                 3.41 
                 3.62 
                 3.54 
                 3.67 
               
               
                 notches or sipes 
               
               
                 RR with notches 
                 3.72 
                 3.5 
                 3.81 
                 3.72 
               
               
                 but no sipes 
               
               
                 RR with notches 
                 3.68 
                 3.55 
                 3.85 
                 3.72 
               
               
                 and 20 mm sipes 
               
               
                   
               
             
          
         
       
     
         [0039]    As shown, for tires A through D, an unexpected result occurs in that the addition of partial sipes did not increase rolling resistance RR. 
         [0040]      FIGS. 10 ,  11  and  12  provide graphs of for contact force measurements taken along the trailing edge of a rib of an exemplary embodiment of a tire of the present invention while the tire was submitted to a driving torque. Each figure includes an inset I depicting the location of sensor S.  FIG. 10  represents a plot for a tire having ribs  148  without siping.  FIGS. 11 and 12  represent plots for a tire having ribs  148  with partial sipes  150  with a sensor S positioned on different sides of partial sipe  150  as shown. In these figures, Fx represents a force along longitudinal direction L, Fy represents a force along the transverse direction T, and Fz represents a force normal to the road surface. As shown in  FIGS. 10 ,  11 , and  12 , the addition of partial sipe  150  leads to a reduction of contact force and stress in the kickout area—particularly in the area behind the sipe as shown in  FIG. 11 . 
         [0041]    By using the ratio of tangential force divided by the normal force (Ft/Fz), a sliding potential can be represented by the duration this Ft/Fz ratio exceeds some given threshold. This threshold would be akin to the coefficient of friction and would depend on many factors such as the type of ground, tread compound, temperature, sliding speed, etc. For purposes of further describing the invention, a threshold of 0.8 was selected for analysis. Multiplying this sliding potential by the Fz force gives a value that would be roughly proportional to the frictional dissipated energy and can be viewed as a form of a wear indicator. Accordingly, the product of the sliding length potential multiplied by force Fz measured for an exemplary embodiment of a tire having an angle α of twenty degrees for its diagonal ribs was determined. 
         [0042]    Unexpectedly, the results indicated a benefit for partial sipes on the trailing edge for a driving torque condition. The lead edge of the rib showed a significant amount of wear potential under driving, free rolling, and braking conditions, but such was merely an edge effect that goes away in the first miles of wear and then stabilizes. Under the free rolling and braking conditions, no benefit was seen with the trailing edge sipes, which makes the design of the present invention more beneficial for the drive axle positions. However, importantly the trailing edge sipes showed no detrimental effects under these conditions, particularly under the braking conditions. This is a very good result because braking conditions are typically when abnormal wear can be initiated and propagated. 
         [0043]    Finite element analysis (FEA) was also used to predict the wear of trailing edge sipes through modeling of a single rib having a rib width RW of 50 mm. As with above, frictional sliding was used as a wear indicator but was calculated from the FEA by the dot product of the displacement vector (sliding) and tangential force vector for each time step and summed for each node. 
         [0044]    The FEA revealed that under driving torque, ribs with only partial sipes or ribs with both partial and full sipes will reduce the wear prediction at the trailing edge. Sipes having a sipe length SL of 20 mm reduced the wear only at the trailing edge whereas the full width sipes showed a tendency to reduce wear of the overall rib. Smaller sipe spacings S of 15 mm concentrated the wear reduction even more along the trailing edge and had a more uniform wear along the leading edge. 
         [0045]    FEA analysis also revealed that full width sipes can be used to improve the overall wear rate while trailing edge sipes can be used to target wear rate reduction at the trailing edge. Ribs which combine both full and partial width sipes can be used to accomplish both of these effects. Accordingly, FEA was used to analyze a diagonal rib (with a of 20 degrees) having full width siping and ribs having both full and partial siping with sipe lengths SL and spacing S as indicated in Table II below. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE II 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 SW = combinations 
                 SW = combination 
               
               
                   
                 Solid 
                 SW = 20 mm, 
                 SW = full, 
                 SW = 20 mm, 
                 of full width and 
                 of full width and 
               
               
                   
                 rib 
                 S = 30 mm 
                 S = 30 mm 
                 S = 15 mm 
                 10 mm, S = 15 mm 
                 7.5 mm, S = 15 mm 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Driving 
                 100 
                 86 
                 66 
                 81 
                 68 
                 70 
               
               
                 Braking 
                 91 
                 85 
                 85 
                 95 
                 88 
                 93 
               
               
                 50/50 
                 97 
                 87 
                 77 
                 90 
                 79 
                 83 
               
               
                 braking/driving 
               
               
                 10/90 
                 99 
                 87 
                 68 
                 83 
                 70 
                 72 
               
               
                 braking/driving 
               
               
                   
               
             
          
         
       
     
         [0046]    The values shown are percents relative to the solid rib having a width of 50 mm under driving torque conditions. A lower number represents a slower (i.e. better) wear rate. As shown, the full width siping without partial width siping provided the best overall wear performance for both driving and breaking A wear penalty appears when partial width siping is added to the trailing edge, but this penalty decreases as the use of the tire becomes dominated by a driving torque—indicating such design is best suited for drive axle applications. Even though full width siping alone appears to provide an improvement in wear life, it will negatively affect rolling resistance. However, the addition of partial sipes on the trailing edge provides an improvement to wear and irregular wear without negatively impacting rolling resistance. 
         [0047]    While the present subject matter has been described in detail with respect to specific exemplary 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 readily apparent to one of ordinary skill in the art using the teachings disclosed herein.