Abstract:
A folding side mirror for an automobile having a hinge structure with dissimilar metals while avoiding problems associated with galvanic corrosion. The hinge structure includes a spring and an inner base. The spring and inner base are formed from dissimilar metals, such as steel and magnesium, respectively. The spring is isolated from the inner base by a washer member, which is preferably formed from plastic.

Description:
FIELD OF THE INVENTION 
   The present invention generally pertains to a folding side mirror structure and, more particularly, toward improved folding side mirror structure that permits use of dissimilar metals. 
   DESCRIPTION OF RELATED ART 
   Assemblies including dissimilar metals, such as those having magnesium parts in combination with steel parts, suffer from galvanic corrosion. This inherent corrosion problem is exacerbated when the assembly is used in a wet environment. Due to these problems, the use of magnesium in automobiles has been rather limited, despite the weight savings and manufacturing efficiencies that could result from its implementation. 
   Folding automobile side mirrors are a particular application wherein galvanic corrosion resulting from the interaction of magnesium and steel has prevented the introduction of magnesium parts. For example, with reference to  FIG. 6 , a conventional folding automobile side mirror is shown to include an outer base  10 , a housing  12 , an inner base  14 , a bracket  16 , and a hinge structure formed between the bracket  16  and the inner base  14 . The inner base  14  provides a raised cylindrical wall  14   a , which serves as a pivot post. The pivot post  14   a  receives a plastic washer  20  and a metal push-on lock nut  22  at its upper end. The plastic washer  20  is provided to reduce noise that would otherwise be generated by contact between the metal nut  22  and a metal spring  24 , described hereinafter. The bracket  16  has inner and outer concentric cylindrical walls  16   a ,  16   b  that are interconnected by a base wall  16   c . The bracket&#39;s inner and outer concentric cylindrical walls  16   a ,  16   b  surround the raised cylindrical wall  14   a  of the inner base  14  and cooperate with the inner base cylindrical wall  14   a  to define an annular chamber  18  in which the biasing spring  24  is received. Thus, the biasing spring  24 , which urges the folding mirror into a lower position, is trapped in the annular chamber  18  between the washer  20  and the base wall  16   c  of the bracket  16 . 
   Insofar as the spring  24  is ordinarily made from steel, and due to the fact that the spring  24  is in direct contact with the bracket  16 , it is not possible to form the bracket  16  from magnesium. Moreover, the upwardly open annular chamber  18  receives and holds water that may be introduced into the folding mirror assembly (e.g. from rain, condensation, etc.), which would accelerate any galvanic corrosion should a steel/magnesium junction be present. Due in part to these problems, magnesium parts have not been incorporated into folding automobile side mirrors of the design illustrated in FIG.  6 . 
   There has also been proposed, as illustrated in  FIG. 7 , an alternative hinge design for folding automobile side mirrors. This proposed design also includes a bracket  40 , an inner base  42 , an outer base  44 , and a housing  46 . The bracket  40  includes inner and outer cylindrical walls  40   a ,  40   b  that are joined at their upper ends by an annular wall  40   c . In this configuration, the bracket&#39;s inner cylindrical wall  40   a  serves as the pivot post for the hinge. Between the pivot post  40   a  and the outer cylindrical wall  40   b , the inner base  42  provides an upwardly extending cylindrical wall  42   a , with an annular flange  42   b  extending inwardly from an upper end thereof. The inner edge of the annular flange  42   b  includes a downwardly extending lip  42   c , which serves to retain a spring  48  thereon, as described hereinafter. 
   A plastic washer  50  is placed over the lower end of the pivot post  40   a , and is held in place by a lock nut  52 . The spring  48  is received and retained between the washer  50  and the downwardly facing surface of the annular flange  42   b . Accordingly, the spring  48 , which is made of steel, is in direct contact with the inner base  42  at the annular flange  42   b.    
   Therefore, while the problems associated with water intrusion at the hinge (i.e., in the area of the spring) are reduced or eliminated with the alternative design shown in  FIG. 7 , the problem of galvanic corrosion resulting from contact between steel and magnesium would still be present should the inner base  42  be made from magnesium. Thus, in the alternative design of  FIG. 7  the inner base  42  has been formed from a material that is compatible with the steel spring  48 , such as steel, plastic, or aluminum. 
   Accordingly, there exists a need in the art for an improved folding automobile side mirror that is configured so as to permit at least some of the mirror components to be formed from magnesium. 
   SUMMARY OF THE INVENTION 
   The present invention is directed toward an improved folding automobile side mirror assembly that is formed, at least partially, from magnesium. The present invention is further directed toward an improved hinge assembly for a folding automobile side mirror assembly that limits water intrusion and retention within the mirror assembly. The present invention is further directed toward such an improved hinge assembly that permits use of dissimilar metals, such as magnesium and steel, while minimizing risks associated with galvanic corrosion. 
   In accordance with the present invention, a folding automobile side mirror assembly, includes an outer base, an inner base, a bracket, upper and lower washer members, a lock nut, and a spring. The outer base is secured to a surface of a vehicle; the inner base and the bracket are disposed within a mirror housing that is pivotally secured to the outer base. The inner base includes an upstanding cylindrical wall that has an annular wall member extending inwardly therefrom while the bracket includes inner and outer cylindrical walls that are connected at upper ends thereof by an upper wall member. 
   In further accordance with the present invention, the upstanding cylindrical wall of the inner base is received between the inner and outer cylindrical wall members of the bracket. The upper and lower washer members are secured around inner cylindrical wall of the bracket and each includes a radially extending flange. The radially extending flange of the upper washer member is in engagement with the annular wall member of the inner base upstanding cylindrical wall. The lower washer member is disposed at a location spaced from the upper washer member and is held in place by the lock nut. 
   In further accordance with the present invention, the spring is disposed around the inner cylindrical wall and is in engagement with the radially extending flanges of the upper and lower washer members. The inner base is formed from a first metal and the spring is formed from a second metal, with the first and second metals being dissimilar and subject to galvanic corrosion. Preferably, magnesium or an alloy thereof is used as the first metal and steel is used as the second metal. The upper washer member is disposed between inner base and the spring and prevents galvanic corrosion therebetween. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and further features of the invention will be apparent with reference to the following description and drawings, wherein: 
       FIG. 1  is a front and top perspective view of a folding automobile mirror incorporating the present invention; 
       FIG. 2  is a rear and left perspective view of the folding automobile mirror shown in  FIG. 1 ; 
       FIG. 3  is a top plan view of the folding automobile mirror of  FIGS. 1-2 , with the folded mirror being shown in dashed lines; 
       FIG. 4  is a cross sectional view of the mirror according to the present invention, as seen along line  4 — 4  of  FIG. 3 ; 
       FIG. 5  is a cross sectional view of the mirror according to the present invention, as seen along line  5 — 5  of  FIG. 3 ; 
       FIG. 6  is a cross sectional view of a conventional folding mirror assembly; and, 
       FIG. 7  is a cross sectional view of another known folding mirror assembly. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to  FIGS. 1-3 , a folding automobile mirror assembly  1001   s  shown to include an outer base  102  and a mirror housing  104 . The mirror housing  104  is pivotally secured to the outer base  102  such that the mirror housing  104  may be manually moved from an outwardly extended or normal position to a folded or storage position. The storage position is illustrated in dashed lines in FIG.  3 . Conventionally, the mirror housing  104  will move vertically upward slightly from a normal vertical position to a raised vertical position as the mirror housing  104  pivots from the normal position toward the storage position. The mirror housing hinge assembly includes a spring that biases the mirror housing toward the normal vertical position and away from the raised vertical position so as to provide resistance to the pivoting movement. The folding automobile side mirror assembly disclosed to this point is conventional in appearance and function, and will be described hereinafter as it relates to the improved hinge structure of the present invention. 
   With reference to  FIGS. 4 and 5 , the mirror assembly  100  is shown to include a spring  108 , a bracket  110 , an inner base  112 , an upper washer member  114 , a lower washer member  116 , and a lock nut  118 . The spring  108  and lock nut  118  are preferably formed from steel, while the bracket  110 , upper and lower washer members  114 ,  116 , the outer base  102 , and the housing  104  are formed from plastic or other materials that are not subject to galvanic corrosion. Alternatively, the housing  104  and outer base  102  may be formed from metal, such as aluminum. The inner base  112  is preferably formed from magnesium or alloys thereof and, therefore, in the illustrated embodiment must be protected from both water and contact with steel due to the threat of galvanic corrosion. 
   Although the present invention is particularly concerned with structures and methods to permit use of magnesium and alloys thereof in assemblies that are ordinarily used in wet environments and in the presence of other steel parts, it is more broadly concerned with structures and methods that permit the use of dissimilar metals that would otherwise be subject to galvanic corrosion. Accordingly, the present invention, although described herein with reference to the preferred embodiment (which employs a part made from magnesium used in a mirror assembly incorporating steel), is not to be limited to this specifically described and presently preferred embodiment. Rather, it is considered apparent that one skilled in the art, with knowledge of the present invention, would be capable of altering the materials used (i.e., to use another combination of dissimilar metals that would otherwise be susceptible to galvanic corrosion) without departing from the scope and spirit of the present invention. 
   With further reference to  FIGS. 4-5 , the inner base  112  and the bracket  110  cooperate with the spring  108 , washer members  114 ,  116 , and lock nut  118  to define a hinge assembly  106 . To that end, the bracket  110  includes an inner cylindrical wall  110   a , which defines a pivot post of the hinge assembly  106 , an outer cylindrical wall  110   b , and an upper wall member  110   c  that interconnects the upper ends of the bracket&#39;s inner and outer cylindrical walls  110   a ,  110   b . The inner and outer cylindrical walls  110   a ,  110   b  are open at their bottom ends and spaced apart from one another to define a cylindrical chamber (annular in cross section) that receives an upstanding cylindrical wall  112   a  from the inner base  112 . The upstanding cylindrical wall  112   a  is disposed adjacent an inner surface of the outer cylindrical wall  110   a  of the bracket  110 , and includes an annular wall member  112   b  at its upper end that projects inwardly toward the outer surface of the bracket&#39;s inner cylindrical wall  110   a . The annular wall member  112   b  is disposed adjacent a lower surface of the bracket&#39;s upper wall member  110   c , as illustrated. An inner edge of the annular wall member  112   b  terminates in a downwardly extending lip  112   c , which is positioned near the outer surface of the bracket&#39;s inner cylindrical wall  110   a.    
   The upper washer member  114 , which is generally L-shaped in cross section, is pushed on over the inner cylindrical wall  110   a  of the bracket  110  so as to have an elongated cylindrical leg  114   a  extending along the outer surface of the brackets inner cylindrical wall  110   a  and an annular rim  114   b  extending away from the inner cylindrical wall  110   a  and toward the inner surface of the inner base upstanding cylindrical wall  112   a . Preferably, as best seen in  FIG. 5 , the downwardly extending lip  112   c  of the inner base  112  engages an upper surface of the upper washer member  114  at a location adjacent the intersection of the elongated cylindrical leg  114   a  and the annular rim  114   b.    
   The lower washer member  116 , which is pushed on over the inner cylindrical wall  110   a  of the bracket member  110  but retained at a location spaced downwardly from the upper washer member  114  a predetermined amount, is preferably identical to the upper washer member  114  but is inverted relative to the upper washer member  114 . To that end, the lower washer member  116  has an elongated cylindrical leg  116   a  extending along the outer surface of the bracket&#39;s inner cylindrical wall  110   a  and an annular rim  116   b  extending away from the inner cylindrical wall  110   a  and toward the inner surface of the inner base upstanding cylindrical wall  112   a.    
   The spring  108  is received between the upper and lower washer members  114 ,  116  and, more particularly, is in engagement with the annular rims  114   b ,  116   b  of the washer members  114 ,  116 . The spring  108  is held in compression so as to exert a downward force on the lower washer member  116  and the bracket  110  and thereby help to retain the bracket  110  in engagement with the inner base  112 . 
   The lock nut  118 , which is pushed on over the lower end of the bracket inner cylindrical wall  110   a , is downwardly adjacent and in face-to-face contact with the lower surface of the lower washer member annular rim  116   b . To facilitate assembly and retention, the bracket inner cylindrical wall  110   a  preferably includes a circumferential groove into which an inwardly projection flange from the lock nut  118  is snap-fittingly inserted. The groove and flange cooperate to hold the lock nut  118  in place, and thereby retain the spring  108  in a compressed or biasing condition. 
   As noted hereinbefore, the spring  108  is preferably formed from steel, which is conventional. However, the inner base  112  is formed from magnesium. While the hinge assembly  106  is protected from water intrusion due to its closed upper end (via the bracket wall  110   c ), there would ordinarily still remain direct steel to magnesium contact at the flange  112   b  where the upper end of the spring  108  contacts the inner base  112 . However, in the assembly according to the present invention, such corrosive contact is precluded by the placement of the upper washer member  114  therebetween. Accordingly, by introduction of the upper washer member  114  in this particular location, the damaging effects of galvanic corrosion are prevented and it is now possible to make the inner base  112  out of magnesium in an application in which, heretofore, the use of magnesium parts was impossible. 
   While the present invention has been described hereinbefore with particularity, it is considered apparent that the present invention is capable of numerous modifications, rearrangements, and substitutions of parts and, accordingly is not limited to the preferred embodiment specifically disclosed herein. Rather, the present invention is only to be defined by the claims appended hereto.