Patent Document

BACKGROUND 
       [0001]    Packaging for electronic products continues to move away from heavy and bulky metal enclosures for cost and weight-saving purposes. While plastic housings reduce cost and weight, plastic housings can be difficult to mount because plastics that are usable as housings are brittle and have relatively low elastic moduli. Mounting flanges or feet are easily crushed when the plastics they are made from are subjected to c compressive stress. Plastics are therefore somewhat ill-suited for use as housings or enclosures of electronic devices. 
         [0002]      FIG. 1  is a perspective view of a prior art housing  100  for electronic devices. The housing  100  is comprised of a plastic top portion  102  and a metallic lower portion  104 . Two mounting feet  106  are cantilevered, i.e., they project outwardly, from a side surface  107  of the housing  100 . The mounting feet  106  are structures that enable the housing  100  to be attached to a surface. 
         [0003]    Each mounting foot  106  is comprised of a plastic upper, generally cylindrically-shaped lug  108 . The lug  108  has a hole or cylinder, which receives a separately-made and separately installed metallic insert support  112 . The plastic lug  108  is attached to a second lug  110  that is metallic and which extends&#39; laterally away from the side  109  of a metallic lower portion  104  of the housing  100 . The metal insert  112  extends from the top of the plastic lug  108  to the bottom of the second metal lug  110 . 
         [0004]    The metal insert  112  is installed into the foot  106  to provide a structure that can withstand compressive loads applied to the foot  106  by fasteners, which are not shown. Fasteners extend through the insert  112  and through an attachment surface to which the housing  100  is mounted. The insert  112  thus prevents the plastic lug  108  from being crushed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a perspective view of a prior art housing with mounting feet having separately inserted metal supports; 
           [0006]      FIG. 2  is an exploded view of a combined metal cover and anti-crush hole inside a mounting foot; 
           [0007]      FIG. 3A  is bottom view of the structure depicted in  FIG. 2  after assembly; 
           [0008]      FIG. 3B  is a top view of the structure shown in  FIG. 2  after assembly; 
           [0009]      FIG. 4  is an exploded view of a combined metal cover and anti-crush hole formed as part of a mounting foot; 
           [0010]      FIG. 5  is cross sectional view of the structure shown in  FIG. 4  after assembly; 
           [0011]      FIG. 6  is a top view of an alternate embodiment of a metal cover and anti-crush hole, with the anti-crush hole located interior to a housing; 
           [0012]      FIG. 7  and  FIG. 8  are assembled and pre-assembled views of an alternate embodiment of a crush-resistant metal portion of a mounting foot; 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Prior art metal inserts  112  that are inserted separately require manual insertion. They are also relatively expensive to manufacture because they are typically formed by rolling a flat metal tab into a cylinder as shown. Reference numeral  114  identifies a seam formed by rolling the insert  112 . A housing having a combined metal cover and a crush-resistant or an anti-crush hole would be an improvement an improvement over the prior art. 
         [0014]    It is well known that the degree to which structures deform in response to an applied stress depends on the material&#39;s modulus of elasticity. When stress and strain are proportional to each other, deformation of a material is considered to be elastic. When a material is stressed to its proportional limit, deformation is plastic, i.e., the material does not return to its original shape. Stated another way, a material fails, when it is subjected to a stress that exceeds its proportional limit or yield strength. 
         [0015]    Plastics are generally less dense than metals. Plastics are also generally non-conductive. Another difference between plastics and metals is their elastic modulus. Plastics are not as strong as metals. 
         [0016]    Plastics that include low density polyethylene or LDPE, high density polyethylene (HDPE), polypropylene (PP) and polyvinyl chloride (PVC) have a modulus of elasticity of about 0.025×10 6  psi and about 5.0×10 6  psi. Light weight aluminum alloys however have elastic moduli of about 10×10 6  psi. Metals are therefore better able to withstand compressive loads. 
         [0017]      FIG. 2  is an exploded view of a housing  200  comprised of a plastic top portion  202  and a metallic bottom portion  204 . The plastic can be amorphous or polycrystalline. The housing  200  has crush-resistant or “anti-crush” supports  206  that extend from exterior sides of the housing  200 . 
         [0018]    The supports  206  are hereinafter referred to as mounting feet. A mounting foot is formed by the joinder or assembly of a top plastic portion  208  of the housing  200  and a metal bottom portion  210  of the housing  200 . The metallic bottom portion  210  is formed to provide a metal, load-bearing insert, which when inserted into a plastic sleeve or cylinder resists crushing when a compressive stress is applied to the foot  206 . 
         [0019]    When viewed from the top, the foot  206  has a form reminiscent of a stilted arch. As used herein, “stilted arch” refers to an arch having a semi-circular rounded portion with straight legs or stilts that extend away from the ends of the semi-circular portion. In  FIG. 2 , the plastic top portion  208  of the mounting foot  206  has an arch-shaped portion identified by reference numeral  212 . Plastic straight legs or stilts  214  extend laterally away from a side surface  215  of the plastic top portion  202  of the housing  200 . 
         [0020]    A cylindrical hole  218  is formed in the plastic top portion  208  of the foot  206 . The circular-cross section hole  218  formed into the end of the foot  206  imbues the top portion  208  of the foot  206  with a structure that is cylindrical and formed from the plastic material surrounding the cylindrical hole  218 . Reference numeral  220  identifies what is considered to be the outer circumference of a “cylinder” of material in the plastic top portion  208  of the foot  206 . The plastic top portion  208  is thus considered to have a first cylindrical part  220  of the mounting foot  206 . 
         [0021]    The bottom portion  210  of the foot  206  is metallic. It therefore has an elastic modulus much greater than the plastic top portion  202 . 
         [0022]    The bottom portion  210  is comprised of a relatively thin, stilted arch-shaped tab portion  216  that extends laterally away from a side surface  222  of the metallic bottom portion  204 . 
         [0023]    The bottom portion  204  including the metal tab  216  is formed by stamping. A cylinder  224  extends upwardly from the tab  216  is also formed by a stamping process known as deep drawing. Being formed by stamping, the metal cylinder  224  is seamless. And, unlike prior art inserts that are stamped and rolled and therefore not really circular, the cross sectional shape of the stamped metallic cylinder  224  can be made into a nearly perfect circle. 
         [0024]    In addition to being seamless and having nearly perfect circular cross sections, in one embodiment, the stamped metallic cylinder  224  has an outside diameter that tapers, or which has a “draft.” The outside diameter at the top of the cylinder  224  is slightly less than the outside diameter of the cylinder  224  where it meets the tab  216 . Providing a draft to the cylinder  224  facilitates assembly of the two pieces  202  and  204  to each other. In other embodiments, the cylinder  224  outside diameter is constant. 
         [0025]    The bottom or lower end of the cylinder  224  is surrounded by a relatively flat or planar annulus  225 , which meets the plastic “cylinder”  220  portion of the plastic top portion  202 . The metallic cylinder  224  has a height that is substantially equal to or slightly greater than the thickness of the plastic first cylindrical part  220  of the plastic top portion  208 . 
         [0026]    By deep drawing the metal lower portion  204 , it is possible to stamp a lower metal panel  204  having a metallic second cylinder  224 , the outside diameter of which is just equal to the inside diameter of the hole  218  in the plastic upper portion of the foot  206 . The metallic second cylinder  224  also has an inside diameter  226  selected to correspond to the outside diameter of a fastener used to attach the housing  200  to a surface. Fasteners are not shown in  FIG. 2  for clarity. A complete housing  200  with a crush-resistant mounting foot  206  is formed when the plastic top portion  202  is joined with the bottom metallic portion  204 . 
         [0027]      FIG. 3A  is a bottom view of the housing  200  shown in  FIG. 2 .  FIG. 3B  is a top view of the housing  200 . 
         [0028]    Together,  FIGS. 2 ,  3 A and  3 B show that the metallic cylinder  224  of the bottom portion  204  extends orthogonally from the tab  226  and extends completely through the thickness of the plastic top portion  208  of the foot  206 . Unlike prior art metal inserts that are inserted manually and which have seams, the metallic cylinder  224  slides into the first plastic cylindrical part  220 . The metallic cylinder  224 , which extends through the first cylindrical part  220  and which has an elastic modulus greater than that of the plastic, significantly limits deformation of the first cylindrical portion responsive to a compressive load compressed on the foot  206  by a fastener. The metallic cylinder  224  thus provides the mounting foot  206  with an anti-crush hole. 
         [0029]      FIG. 4  is an exploded view of one mounting foot  206  that extends from sides of upper and lower portions of a housing  200  depicted in  FIG. 2 .  FIG. 4  also shows a fastener, comprised of a bolt  401  and hex nut  403 , positioned to fasten the two portions of the housing  200  together. 
         [0030]    The thickness  402  of the plastic upper portion  208  of the foot  206  is shown to be substantially equal to the height  404  of the metallic second cylinder  224 . Since the height  404  of the inner cylinder  224  is at least equal to and preferably slightly greater than the thickness  402  of the upper portion  208 , insertion of the inner cylinder  224  into the cylindrical hole  218  provides a metallic structure inside a plastic structure with the metallic structure bearing load applied to the mounting foot  206  by a fastener  406 . Tightening the hex nut  403  on the bolt  401  exerts compressive force on the metallic inner cylinder  224  but not on the plastic outer cylinder. In one embodiment, the thickness  402  is slightly less than the height  404  to enable the metallic second cylinder  224  to engage a compressive load before the plastic. 
         [0031]      FIG. 5  is a cross sectional view of the assembled foot  206  depicted in  FIG. 4 . The bolt  401  and hex nut  403  are shown assembled to each other and attach the housing  200  to a surface  502 , such as a surface of a metal chassis of an automobile or other vehicle. By inserting a metal cylinder into the plastic cylinder, compressive stress on the plastic cylinder is significantly reduced or even eliminated. 
         [0032]      FIG. 6  is a top view of an alternate embodiment of a housing  600  formed from a plastic top portion and a metal bottom portion. Unlike the supports  206  described above and which extend outwardly from sidewalls of a housing, an anti-crush support  602  is located within the exterior side walls  604  the housing  600 . 
         [0033]      FIG. 7  is an exploded view of the housing  600  depicted in  FIG. 6  and showing the structure of the interior-located support  602 . A plastic outer cylinder  704  of the support  602  is formed through the plastic top portion  702  of the housing  600 . The plastic outer cylinder  704  has an inside diameter  706  large enough to slide over, i.e., receive, a seamless and metallic inner cylinder  708  formed by stamping, and preferably deep drawing. The metallic cylinder  708  is stamped as part of a metallic plate from which a metallic bottom portion  710  of the housing  600  is formed. As with the embodiment described above, the metallic inner cylinder  708  can be formed with a slight draft or taper to facilitate assembly of the housing portions. 
         [0034]    The metallic inner cylinder  708  has a central hole  712  large enough to receive a fastener, such as a bolt  714 . When the plastic top portion  702  is joined to the metallic bottom portion  710 , the metallic inner cylinder  708  extends all the way through the plastic outer cylinder  704  as described above with regard to the exterior foot  206 . 
         [0035]      FIG. 8  is a side view of the assembled housing  600  of  FIG. 6 . A bolt  714  is shown inserted into the hole  712  that exists in the metallic inner cylinder  708 . The bolt  714  also extends through a thin, flat panel  800  to which the housing  600  is attached by tightening the hex nut  716  on the bolt  714 . 
         [0036]    When the fastener  712  and nut  714  are tightened, compressive stress is applied to the metallic inner cylinder  706 . The plastic outer cylinder  704  is thus spared from force that might otherwise permanently deform, i.e., crush, the plastic top portion  702  of the housing  600 . 
         [0037]    In the embodiments described above and depicted in the figures, the cylinders have circular cross sections. Alternate and equivalent embodiments include “cylinders” that have non-circular cross sections, such as square, triangular and rectangular cross sections. 
         [0038]    Those of ordinary skill in the art will recognize that a light-weight housing can be constructed with robust mounting supports by using supports formed from both plastic and metallic components. A metallic insert inside a plastic outer portion is able to withstand compressive loads greater than having a plastic portion. 
         [0039]    The foregoing description is for purposes of illustration only. The true scope of the disclosure is set forth in the appurtenant claims.

Technology Category: 5