Abstract:
A tire tread has at least one cavern formed in the sidewall of the traction elements of the tire. The cavern has a base with information therein to indicate the state of wear of the tire and a ceiling that is progressively worn away as the tread wears. Multiple caverns may be formed in the traction elements. If arranged in a series at progressively increasing or decreasing radial heights, the remaining tread life is communicated to an operator. If the caverns are located in different locations of the tread, relative wear patterns of the tire can also be indicated.

Description:
FIELD OF THE INVENTION 
   The present invention is directed to a tire tread including wear indicators. 
   BACKGROUND OF THE INVENTION 
   The use of treadwear indicators is not new and the use of treadwear indicators is mandated by law in many countries. A variety of such indicators are known. Once such type employs colored means, such as colored rubber or colored fibers, below the tread for a visual indicator of wear. Other types use tie-bar type elements in the tread grooves. When required by law, the upper surface of the tread wear indicator must be located at a height of 1.6 mm from the base of the groove in which the wear indicator is located. 
   The practical problem with the colored indicators of the type mentioned is that there is way for the operator to determine the level of wear until the tire is worn. When the tire employs the tie-bar type wear indicator, since the wear indicator is the same color as the remaining part of the tread, it can be difficult to determine the level of wear. 
   SUMMARY OF THE INVENTION 
   The invention is directed to a tire having wear indicators that assist the operator in determining the level of wear of a tire tread. 
   The invention is a tire tread for a vehicle tire. The tread has at least one tread element projecting from the base of the tread wherein the tread element has at least one radially extending side. The side of the tread element has a wear indicating cavern formed therein. The wear indicating cavern has a base located below the uppermost surface of the tread element when the tire is unworn. 
   In one aspect of the invention, the cavern has a base parallel to the uppermost surface of the element. The cavern may also have a roof that has a sloping configuration. The cavern may be formed in a variety of configurations. The configuration permits uniform wear of the cavern and slowly exposes information regarding the wear of the tread to the vehicle operator. The information regarding the wear of the tread is provided on the base of the cavern and may be in any form that communicates the tread wear to the user; i.e. it may be alpha-numeric, fractions, or symbols. The wear information may also be provided in colors. 
   In one aspect of the invention, the tread element is a circumferentially extending rib bounded by at least one circumferentially extending groove. In a tread having a rib, the caverns are formed to be open to the circumferentially extending groove. To allow for indication of the tread wear, the rib has a series of caverns formed therein. The caverns in the series are located at different radial heights along the rib side. 
   In another aspect of the invention, the tread element is a block formed by a plurality of circumferential and lateral grooves. The tread has multiple adjacent blocks wherein each block has a cavern therein. The caverns in adjacent blocks are located at different radial heights to indicate progressive tread wear. 
   Definitions 
   The following definitions are applicable to the present invention. 
   “Annular” means formed like a ring. 
   “Axial” and “axially” are used herein to mean lines or directions that are parallel to the axis of rotation of the tire. 
   “Circumferential” means lines or directions extending along the perimeter of the surface of the annular tire parallel to the Equatorial Plane (EP) and perpendicular to the axial direction. 
   “Groove” means an elongated void area in a tread that may extend circumferentially or laterally about the tread in a straight curved, or zigzag manner. Circumferentially and laterally extending grooves sometimes have common portions and may be sub classified as “wide”, “narrow”, or “slot”. The slot typically is formed by steel blades inserted into a cast or machined mold or tread ring therefor. In the appended drawings, slots are illustrated by single lines because they are so narrow. A “slot” is a groove having a width in the range from about 0.2% to 0.8% of the compensated tread width, whereas a “narrow groove” has a width in the range from about 0.8% to 3% of the compensated tread width and a “wide groove” has a width greater than 3% thereof. The “groove width” is equal to tread surface area occupied by a groove or groove portion, the width of which is in question, divided by the length of such groove or groove portion; thus, the groove width is its average width over its length. Grooves, as well as other voids, reduce the stiffness of tread regions in which they are located. Slots often are used for this purpose, as are laterally extending narrow or wide grooves. Grooves may be of varying depths in a tire. The depth of a groove may vary around the circumference of the tread, or the depth of one groove may be constant but vary from the depth of another groove in the tire. If such narrow or wide groove are of substantially reduced depth as compared to wide circumferential grooves which they interconnect, they are regarded as forming “tie bars” tending to maintain a rib-like character in the tread region involved. 
   “Inner” means toward the inside of the tire and “outer” means toward its exterior. 
   “Lateral” means an axial direction. 
   “Leading” means 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. 
   “Lugs” means discontinuous radial rows of tread rubber in direct contact with the road surface. 
   “Outer” means toward the tire&#39;s exterior. 
   “Radial” and “radially” are used to mean directions radially toward or away from the axis of rotation of the tire. 
   “Rib” means a circumferentially extending strip of rubber on the tread which is defined by at least one circumferential “wide groove” and either a second such groove or a lateral edge of the tread, the strip of rubber being laterally undivided by full-depth narrow or wide grooves. 
   “Tie-Bar” means an extra thickness of rubber at the bottom of a slot such that, in the location where the extra rubber is present, the slot depth is less than the slot depth at all other locations. Tie-bars stabilize a lug by limiting the independent movement of two portions of a lug that are separated by slots, while traction properties that are inherent in the use of slots are provided. 
   “Trailing” means 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 preferred direction of travel. 
   “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. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described by way of example and with reference to the accompanying drawings in which: 
       FIG. 1  illustrates a portion of a ribbed tire tread; 
       FIG. 2  is a cross sectional view of the ribbed tire tread along line  2 — 2  of  FIG. 1 ; 
       FIGS. 3A–3E  are various embodiment of the wear indicator cavern; 
       FIG. 4  illustrates a portion of a block tire tread; 
       FIG. 5  illustrates a portion of another block tire tread; and 
       FIG. 6  illustrates a portion of a lugged tire tread. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The following language is of the best presently contemplated mode or modes of carrying out the invention. This description is made for the purpose of illustrating the general principals of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
   A portion of a tire tread is illustrated in  FIG. 1 . The tread is characterized by at least one circumferentially extending groove  10  and adjacent ribs  12 . Each rib  12  has at least one radially extending sidewall  14  that faces the circumferential groove  10 . Those skilled in the art will appreciate that the tire tread may have more than one circumferential groove  10  and multiple continuous or non-continuous ribs  12 . 
   Located in the rib sidewall  14  is at least one tread wear indicating cavern  16 . The cavern  16  is defined by a base  18  that is a radially inner surface parallel to the outer surface of the rib  12  and a ceiling  20  that is a radially outer surface that connects with the cavern base  18 . The cavern  16  is spaced from the groove base  22  by a predetermined height, see  FIG. 2 . The rib  12  has a series of adjacent caverns  16 , arranged in a predetermined sequence. Herein illustrated, the adjacent caverns  16  are arranged in sequentially descending heights along the rib sidewall  14 . 
   When the tire is unworn, the uppermost cavern  24  is open to the tread surface  26  and the operator can locate the first wear indicator  16 . The adjacent caverns  16  are preferably radially overlapping, see  FIG. 2 . The slight overlapping of the adjacent caverns  16  assures that as the tire is wearing, the next cavern  16  appears as the preceding cavern  16  disappears. The overlapping provides the operator with continuous knowledge as to the level of tire wear. 
   At the base  18  of the cavern  16  is an indicator  28  that informs the operator of the wear condition of the tread. As illustrated, the indicator  28  is a number corresponding to the height, in mm&#39;s, of the cavern base  18  as measured from the groove base  22 . The indicator  28  may also be presented as a fraction, such as ⅞, ½, ¼, indicating the wear percentage of the tread, expressed relative to the original tread depth. Alternatively, any other symbol easily interpreted by the operator may be employed; such as a go, caution, and stop signs. The size of the indicator  28  has a maximum dimension of 2 to 6 mm, preferably 3 to 4 mm. 
   In the illustrated tread of FIG.  1 ., the caverns  16  are sequentially number from 2–7. Each number is the remaining tread depth in mm&#39;s. Adjacent to the caverns  16 , and located in the adjacent groove  10 , may be markings  30  that indicate the significance of the indicators  28  in the cavern base  18 . Such markings  30  may be absent from narrow grooves. 
   To increase visibility of the wear indicating caverns  16 , the selective use of color may be employed. The indicators  28  on the cavern base  18  may be made in a color contrasting with the tread color, for example, green, yellow, and red—colors internationally known for go, caution, and stop. The cavern base  18  itself may be formed in the contrasting color. While more complex to manufacture, the entire inside of the cavern  16  may be lined or formed in a contrasting color to emphasize the presence of the cavern  16 . Any markings  30  placed in the adjacent groove  10  may be provided in color. Additionally, the groove markings  30  may be presented in a raised or indented format, making accidental destruction of the groove markings  30  due to stones and other abrasive elements that enter the groove  10  less likely during normal tire use. 
     FIGS. 3   a – 3   e  illustrate a plurality of cavern configurations. Each FIG. shows a top view, cross section side view, and front view of the caverns  16 . The cavern  16  of  FIG. 3   a  has a quarter spherical shape, with the cavern ceiling  20  gradually sloping upwards to a maximum height at the cavern opening in the tread element sidewall  14 . The cavern  16  of  FIG. 3   b  has a conical shape, with the ceiling  20  have a constant slope to a maximum height and a tall opening. The cavern  16  of  FIG. 3C  is diamond shaped with the ceiling  20  formed in multiple sections, joining at the maximum height; the opening being diamond shaped. The cavern  16  of  FIG. 3D  is pyramidal shaped, formed from two sections, sloped to meet at the maximum height with a triangular opening. The cavern  16  of  FIG. 3E  is square shaped with a square opening. 
   A series of caverns  16  may be located in any position of the tread, either in center ribs, shoulder ribs, or in ribs located between the center and shoulder ribs. A series or individual wear indicator caverns  16  may be located in several positions across the width of the tread, providing information regarding the wear pattern of the tire. For example, if the wear indicator caverns  16  are located in the center and the shoulders, if the wear indicators caverns  16  show a lower number in one shoulder than the wear indicators caverns  16  in the opposing shoulder, than the wear is uneven across the tire. 
   Ideally, the series of caverns are located in multiple locations about the circumference of the tire tread. A minimum of two series of caverns  16  would be desired, with the maximum number of series in a tire tread optimized due to the cavern size and maintaining the tread pattern and tread performance characteristics. 
     FIG. 4  shows an alternative embodiment employing the tread wear indicator caverns  16 . A portion of a tread is shown, the tread having a plurality of blocks  32 . The blocks  32  are delineated by circumferential grooves  10  and lateral grooves  34  inclined at angles relative to each other. The blocks  32  may have any overall configuration desired by the tread designer. The sole requirement in accordance with the present invention is that the blocks  32  have radially extending sidewalls  36 ,  38 . 
   Located in one sidewall  36  of one of the tread blocks  32  is a tread wear indicator cavern  16 . At least one adjacent block  32  also has a wear indicator cavern  16 , the adjacent cavern  16  being located at a different radial height than the first cavern  16 . When aligned, the result is a series of wear indicator caverns  16  arranged at gradually ascending or descending radial heights. As previously discussed, the base  18  of the caverns  16  are marked in a manner so as to indicate the wear level of the tire and the adjacent groove  10  may be marked to highlight the presence of the caverns  16 . 
   Also, when forming the caverns  16  in blocks  32 , the caverns  16  may be formed in either leading or trailing sidewalls  38  of the blocks, see  FIG. 5 . At least two caverns  16  form this series of wear indicators. The caverns  16  are located at different radial heights and are also provided with marks  28  to indicate the wear level. When the caverns  16  are formed in either the leading or trailing sidewall  38  of the block  32  in conjunction with a series formed elsewhere, either in the trailing or leading sidewall  38  or along the circumferential sidewalls  36  of the blocks  32 , then determinations can be made regarding the wear pattern across the tread. Forming caverns  16  in both the leading and trailing sidewalls provides heel-and-toe wear information. 
   Wear indicators  16  located in the leading or trailing sidewalls  38  may also be located in axially adjacent tread blocks  32 , or if the tread pattern is an off-the-road or agricultural tread, the wear indicators  16  may be formed in axially extending lugs  40 , either the leading or trailing edges, see  FIG. 7 . Each series of caverns  16  may be identically arranged, or arranged in a manner to provide additional information regarding wear across the tread width. This is illustrated in the tread of  FIG. 7 . In a first series  42  of wear indicators  16 , the indicator  16  closest to the centerline CL of the tread has a base  18  at the greatest radial height from the tread base  46 . A second series  44  of wear indicators  16 , located on the opposing tread half from the first series  42 , is formed such that the cavern  16  with the greatest radial height from the tread base  46  is located farthest from the centerline CL. No matter what type of tread configuration is employed, or the intended use of the tread, the wear cavern indicators can be employed. 
   Regardless of what tread pattern is employed and where and how in the tread the wear cavern indicators  16  are used, the number of wear cavern indicators  16  in a single series should be at least three. Three indicators  16  will indicate the unworn tread, a mid-wear level of the tread, and a worn tread. The actual number used may be based on the percentage of remaining tread depth it is desired to communicate to the operator, i.e. one/half, two/thirds, three/fourths, or the actual depth in millimeters of tread remaining.