Abstract:
The Vented Brake Drum has a pattern of through holes arranged around it circumferentially, the holes intersecting the inside cylindrical braking surface radially of the inner surface as well as intersecting the outside surface of the drum. The holes may be drilled into the finished drum or cast into the drum prior to machining the inner braking surface of the drum, to present a smooth albeit perforated internal circumferential surface (ID) to the arcuate brake lining.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of copending U.S. application Ser. No. 14/018,343, filed Sep. 4, 2013, which claims the benefit of U.S. Provisional Application Ser. No. 61/699,740, filed Sep. 11, 2012 and U.S. Provisional Application Ser. No. 61/727,535, filed Nov. 16, 2012, hereby incorporated in their entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to drum brakes for vehicles and more particularly to brake drum designs for cooler operation. 
     The conventional brake drum as shown in  FIGS. 1, 2 and 3  has a solid cylindrical shape, and the internal surface (the internal diameter or “ID”) is a smooth, contiguous or unperforated cylinder against which the brake lining of a semicircular brake shoe (not shown) is frictionally engaged for braking. The images are for a 16.5×7 brake drum which is the most common size steel alloy or gray iron brake drum for heavy-duty tractors and trailers. 
     Brake drums are known to have been formed with external or internal fins to assist in cooling the drums. U.S. Pat. Nos. 3,127,959; 6,698,557 and 8,181,753 disclose various such approaches. The concept of drilling holes through the wall thickness of a braking surface has thus far been restricted to disc brake rotors, which are flat. However, this concept has never been applied to S-CAM brake drums which are a completely different braking system than disc brake rotors. For instance, the brake rotor system uses a caliper to squeeze a rotating disk, thus engaging the frictional surfaces. In contrast, the brake drum system uses an internal shoe to apply radial pressure to the cylindrical brake drum surface. 
     Brake fade occurs after repeated or sustained application of drum brakes which creates a high temperature condition and contributes to a reduction of stopping power. Significant improvement in brake performance can be obtained by optimizing the thermal performance of the brake drum. Although conventional brake drums continue to perform successfully in the field, a need remains for a brake drum design which maintains cooler temperatures than the conventional brake drum. 
     SUMMARY OF INVENTION 
     The Vented Brake Drum concept of the present invention utilizes drilled or cast-in openings—such as holes or slots—extending depthwise through the otherwise solid wall of the cylindrical drum portion of a typical brake drum. Basically, the drum has a pattern of through holes arranged circumferentially, the holes intersecting the inside cylindrical braking surface radially of the inner surface as well as intersecting the outside surface of the drum. The holes may be drilled into the finished drum or cast into the drum prior to machining the inner braking surface of the drum, to present a smooth, albeit perforated, internal circumferential surface (ID) to the arcuate brake lining. 
     This invention improves cooling of the drum brake and reduces brake fade. Other features and advantages will become apparent from the following detailed description which proceeds with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1, 2 and 3  are perspective views of a conventional brake drum. 
         FIGS. 4, 5 and 6  are perspective views of a first embodiment of a ventilated brake drum according to the invention. 
         FIGS. 7 and 8  are perspective views of second and third embodiments of a ventilated brake drum according to the invention. 
         FIG. 9  is a perspective view of a fourth embodiment of a ventilated brake drum according to the invention. 
         FIG. 10  is a cross-sectional view of the fourth embodiment of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIGS. 1-3 , a conventional brake drum  10  is a cylindrical structure which, in use, rotates about an axis  11  in a rotation direction  15 . The brake drum  10  comprises an annular outboard wheel-mounting portion  12  having a ring of wheel-bolt holes  13 , an annular inboard rim portion  14  axially opposite the hub portion, and a drum portion  16  having a cylindrical shape extending between the hub portion and the rim portion. The drum portion  16  has a circumferential outer surface  18 , and a cylindrical internal braking surface  20  against which a brake lining of a semicircular brake shoe (not shown) can be frictionally engaged for braking. 
     A first embodiment of the invention, shown in  FIGS. 4-6 , is incorporated in a brake drum  10 A, like drum  10  but with the further features next described. In accordance with the invention, a series of spaced-apart vent openings  22 A are formed in the drum portion  16  of the brake drum. These openings extend depthwise through the drum portion  16  from the outer surface  18  to the internal braking surface  20 . The series of vent openings  22 A are distributed in a pattern  24 A that is repeated circumferentially around the drum portion. In the first embodiment, the vent openings  22 A are cylindrical in shape, with an example diameter of 0.5 inch (1.25 cm.) and arranged in a diamond pattern  24 A, repeated circumferentially around the drum portion  16 . 
     A second embodiment of vented brake drum  10 B shown in  FIG. 7  is generally similar to the first embodiment but has a different pattern  24 B of vent openings repeated circumferentially around the drum portion. In this embodiment, the pattern  24 B of openings  22 B is in the form of a line oriented diagonally across the internal braking surface. That is, each line of half dozen vent openings follows a helical path across the direction of rotation  15  of the drum portion  16 . 
     A third embodiment of vented brake drum  10 C shown in  FIG. 8  is generally similar to the second embodiment but has a different shape of vent openings. In this embodiment, the vent openings are formed as slots  22 C having an oblong shape. 
     Various shapes, sizes and patterns of vent openings can be used. In the third embodiment, the slots  22 C are oriented diagonally across the internal braking surface and as a repeating pattern of openings in the form of a line oriented diagonally across the internal braking surface. The slots could alternatively be positioned in a diamond pattern. Or the slots could be aligned with the direction of rotation  15  of the brake drum. 
     A fourth embodiment of vented brake drum  10 D shown in  FIG. 9  is generally similar to the third embodiment, but has a different orientation of the vent openings or slots  22 D. In this embodiment, the individual slots  22 D are oriented circumferentially along the internal braking surface  20 , i.e., with the direction  15  of rotation. 
     In the fourth embodiment,  10 D, as shown in  FIG. 9 , the vent openings  22 D each have an oblong shape oriented circumferentially along the internal braking surface  20 . The oblong vent openings  22 D are arranged in a repeated pattern  24 D in the form of a line oriented diagonally across the internal braking surface  20 . The openings  22 D extend depthwise, or radially, between the circumferential outer surface  18  and the internal braking surface  20 . Each opening  22 D includes a chamfer  26  about the periphery of the opening on the circumferential outer surface  18  as shown in  FIGS. 9 and 10 . 
     In the illustrated embodiments, the openings are oriented depthwise along a radial line from the axis of the drum portion, and have parallel sides. Alternatively, the holes or slots could be canted relative to the radial line. As a further alternative, the holes or slots can have sides that are tapered toward one another; that is, have nonparallel sides. These parameters can be varied and combined to enhance their ventilation effect in the rotating brake drum. 
     Advantages of the vent openings in this vented brake drum over the standard solid brake drum include the following:
         1. Increases heat dissipation, thus improving the thermal performance and reducing brake fade   2. Creates a path for dissipation of hot gases inside the brake drum to the exterior surroundings   3. Provides a method of brake dust removal by creating an unobstructed path between the inside braking surface to the exterior surroundings   4. Reduces drum weight   5. The circumferential orientation of the slots and the chamfer around the periphery of each slot help to reduce stress concentrations and heat check cracks.       

     The vent openings can either be drilled into the brake drum or preferably cast into the drum. The hole size, shape and pattern can vary to optimize ventilation. The accompanying drawings are intended to illustrate the concept and are not restricted to the pattern or number of holes distributed around the circumference of the brake drum. This vented brake drum concept will apply to any size S-CAM brake drum, as well as any other brake drum, without restriction. 
     Having illustrated and described various embodiments, it should be appreciated that the invention can be modified in arrangement and detail. We claim all embodiments within the scope of the following claims.