Abstract:
A brake drum configured for providing an visual indication of braking surface diameter safe operating limits while the brake drum is mounted on a vehicle that includes one or more axially-oriented indentations defined in the braking surface, each of which is defined to a depth that is less than or corresponds to the maximum safe operating diameter of the braking surface.

Description:
BACKGROUND 
     1. Field 
     The present invention relates generally to brake drums, and more particularly, to brake drums for heavy-duty vehicles having an external visual indication of whether braking surface diameter is within safe operating limits. 
     2. Description of the Problem and Related Art 
     A brake drum&#39;s maximum allowable braking surface diameter is the largest diameter that a brake drum&#39;s braking surface can be machined, or worn to, and still maintain satisfactory characteristics for safe and expected braking performance. It is a violation of Department of Transportation regulations to use a brake drum whose braking surface diameter exceeds the maximum allowable diameter. At this time, there is not an accurate method of determining whether a brake drum&#39;s braking surface diameter has worn to, or exceeded, the maximum allowable diameter while the brake drum is installed on a vehicle. Accordingly, the entire wheel must be removed from the vehicle and the brake drum surface diameter must be measured. It is both time consuming and expensive—not to mention safety issues involved with removing and reinstalling wheel end equipment—to remove a brake drum from an axle to determine whether or not a brake drum has worn to the point that the braking surface diameter exceeds the maximum allowable diameter. This can lead to brake drums being discarded and replaced sooner than needed, or it can lead to brake drums remaining in service after the braking surface diameter exceeds the maximum allowable diameter. 
     With reference to  FIGS. 6 and 6A  of the drawings, a prior art technique to permit visual inspection of brake surface diameter has used a notch  30  machined circumferentially around the braking surface at the lip of the drum for wear indication. This method, however, may provide misread inspections because of uneven wear of the brake linings and drum. A step is worn into the lining near the lip of the drum. This uneven wear leads to inaccurate evaluations of both lining wear and brake drum wear, leading to either early removal of a good brake drum, or worse, non-removal of a bad brake drum. 
     SUMMARY 
     The present disclosure is directed to a brake drum configured for accurate, visual indication of braking surface adequate thickness without removal from the vehicle on which it is installed. 
     For purposes of summarizing the invention, certain aspects, advantages, and novel features of the invention have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any one particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
     An exemplary brake drum includes a braking surface one or more axially oriented notches or indentations defined therein. The notches are defined from the inner edge of the braking surface rim and extend outwardly towards the brake drum hub and are formed to have a depth no greater than a depth corresponding to the maximum allowable diameter of the braking surface of the drum. 
     This and other embodiments will also become readily apparent to those skilled in the art from the following detailed description of the embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. 
         FIG. 1  is an inboard perspective view of an exemplary brake drum with wear indicator in braking surface in an unworn condition; 
         FIG. 2  is a section view of the exemplary brake drum of  FIG. 1  along line  2 ; 
         FIG. 3  is a section view of the exemplary brake drum of  FIG. 1  along line  3 ; 
         FIG. 3A  is an inset of the indicated portion of  FIG. 3 ; 
         FIG. 4  is an inboard view of an exemplary brake drum according to an embodiment of the invention with multiple wear indicator notches; 
         FIG. 5  is an inboard view of an exemplary brake drum according to an embodiment of the invention with multiple wear indicator notches; and 
         FIG. 6  is a section view of a prior art brake drum with a circumferentially oriented wear indicator notch; and 
         FIG. 6A  is an inset of the indicated portion of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     The various embodiments of the present invention and their advantages are best understood by referring to  FIGS. 1 through 6A  of the drawings. The elements of the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. Throughout the drawings, like numerals are used for like and corresponding parts of the various drawings. 
     This invention may be provided in other specific forms and embodiments without departing from the essential characteristics as described herein. The embodiments described above are to be considered in all aspects as illustrative only and not restrictive in any manner. The following claims rather than the foregoing description indicate the scope of the invention. 
     Furthermore, reference in the specification to “an embodiment,” “one embodiment,” “various embodiments,” or any variant thereof means that a particular feature or aspect of the invention described in conjunction with the particular embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases “in one embodiment,” “in another embodiment,” or variations thereof in various places throughout the specification are not necessarily all referring to its respective embodiment. Finally, as used in this description, terms such as “inner,” “outer,” “inboard” and “outboard” are to be understood as they relate to a vehicle on which the brake drum is mounted. 
     An exemplary brake drum  10  comprises a brake surface  15  made from cast iron or other friction and wear resistant material, a mounting plate  14  at the brake drum&#39;s outboard end  17  with mounting holes for mounting the drum to the hub of a vehicle axle, a wraparound, or shoulder portion  12 , and one or more squealer bands  13  circumscribing the brake drum. A brake drum  10  is typically used with a brake shoe  20 . In operation, the shoe is selectively applied to the braking surface  15  of the brake drum  10  through actuation of the brake. Brake drum  10  converts kinetic energy and potential energy of the vehicle into heat energy by providing a friction surface for the brake shoe thereby transmitting brake torque to the wheels and tires of the vehicle. 
     A notch  11 , or indentation, is defined in the braking surface  15  of the drum  10 , extending from the inner lip of the inboard end  16  axially toward the outboard end. The indentation  11  is formed with a depth d in relation to the braking surface  15  that corresponds to, or is within, the maximum allowable diameter  22  of the braking surface  15 . The indentation  11  extends outboard from inboard edge so that at least a portion of the area of the indentation  11  overlaps the area of the braking surface  15  that makes contact with the brake shoe. As the braking surface  15  is worn away through use, and the maximum diameter is reached, the indentation  11  is worn away, so that the indentation  11  no longer perceivable through visual or tactile inspection. 
     Since the indentation  11  is located on the inboard edge of the braking surface  15 , it may be inspected while the drum  10  is still mounted on the vehicle. Thus, if upon visual inspection, the indentation  11  can still be seen, the braking surface  15  is still within the maximum diameter. As illustrated in  FIGS. 4 and 5 , it is contemplated that a plurality of indentations  11  may be defined in the braking surface  15  as described above, at different locations about the circumference of the drum surface, that are generally accessible while the drum is installed on the vehicle, to increase the possible inspection locations. 
     Through the use of the aforementioned features, the inventive brake drum  10  provides a number of advantages. Because braking surface diameter may be easily visually inspected, a determination can be made by shop personnel, the driver, or law enforcement personnel. The brake drum will not have to be removed from the axle and measured to determine whether the braking surface has reached the maximum allowable diameter. This reduces vehicle down time, labor, and maintenance costs attributable to inspection. Lastly, use of the indentation  11  reduces likelihood of a brake drum remaining in service after the braking surface diameter has reached or exceeded the maximum allowable diameter. 
     As described above and shown in the associated drawings, the present invention comprises an integral braking surface wear indicator. While particular embodiments of the invention have been described, it will be understood, however, that the invention is not limited thereto, since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. It is, therefore, contemplated by the appended claims to cover any such modifications that incorporate those features or those improvements that embody the spirit and scope of the present invention.