Mechanism for fitting lens to an extension
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a lighting device for a vehicle. More particularly, the present invention relates to an improvement of a mechanism disposed in a lighting device of the foregoing type for preliminarily fitting a lens to an extension before an assembly of the lens and the extension is firmly fitted to a housing of a lighting device, and wherein the extension is disposed in the lighting device for the purpose of covering a part of the lighting device unnecessary to be visually seen by anybody. 
     2. Background Art 
     To facilitate understanding of the present invention, a typical conventional mechanism of the foregoing type will briefly be described below with reference to FIG. 2. With the conventional mechanism, since the direction of fitting a lens 91 to an extension 92 largely differs from the direction of the lens 91 to a housing 93 of a lighting device (not shown), it is practically impossible to fit the lens 91 to the extension 92 after the extension 92 latter is preliminarily fitted to the housing 93. For this reason, the lens 91 is first fitted to the extension 92 to form an assembly and, thereafter, the assembly of the lens 91 and the extension 92 is fitted to the housing 93. 
     To assure that the lens 91 is reliably fitted to the extension 92, a part of the lens 91 is extended from a housing fitting foot portion 91a to form an auxiliary foot portion 91b so that the lens 91 is firmly secured to the extension 92 by fixing the auxiliary foot portion 91b to the extension 92 at plural locations by tightening a plurality of screws as shown in FIG. 2. 
     With the conventional mechanism constructed in the above-described manner, since there arises a necessity for fixing the auxiliary foot portion 9lb to the housing fitting foot portion 91a with the aid of a plurality of screws before an assembly of the lens 91 and the extension 92 is firmly fitted to the housing 93 of the lighting device, a lens fitting operation is achieved in a complicated manner with an increased number of steps, resulting in the lighting device being produced at an increased cost. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the aforementioned background. 
     An object of the present invention is to provide a mechanism for preliminarily fitting a lens to an extension to form an assembly, before the assembly of the lens and the extension is firmly fitted to a housing of a lighting device for a vehicle, and wherein a lens fitting operation can easily be achieved at a reduced cost without a necessity for tightening any screws or the like. 
     The present invention provides a mechanism for preliminarily fitting a lens to an extension before an assembly of the lens and the extension is firmly fitted to a housing of a lighting device for a vehicle, wherein the mechanism includes at least one fitting hole formed through an auxiliary foot portion extending from a housing fitting foot portion of the lens, and a boss in the form of a tapered pin-shaped projection extended from the extension, the boss being located at a position corresponding to that of the fitting hole through which the boss is inserted. 
     In addition, the mechanism includes a flange portion which extends from the upper end of the extension to be held between the lens and the housing in a clamped state when the assembly of the lens and the extension is fixed to the housing. 
     In practice, a lens fitting operation is performed by inserting the boss into the fitting hole while the flange portion is placed on the upper surface of one of the side walls defining a lens receiving groove formed at the upper end of the housing of the lighting device. 
     In a case where there is no possibility that water such as rain water or the like can enter into the interior of a lighting chamber of the lighting device, the fitting hole may be formed directly through the housing fitting foot portion. 
     Other objects, features and advantages of the present invention will become apparent from a reading of the following description which has been made in conjunction with the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary sectional view of a mechanism for preliminarily fitting a lens to an extension before an assembly of the lens and the extension is firmly fitted to a housing of a lighting device according to an embodiment of the present invention. 
     FIG. 2 is a fragmentary sectional view of a conventional mechanism of the foregoing type. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, reference numeral 1 designates a lens and reference numeral 2 designates an extension. Similar to the conventional mechanism described above with reference to FIG. 2, the lens 1 is preliminarily fitted to the extension 2 before an assembly of the lens 1 and the extension 2 is fitted to a housing 3 of a lighting device (not shown) for a vehicle. A characterizing feature of the mechanism of the present invention is that a housing fitting foot portion 11 of the lens 1 includes an auxiliary foot portion 13 through which at least one fitting hole 12 is formed. As seen in FIG. 1, the housing fitting foot portion 11 extends from the main light-passing portion of the lens 1, and the auxiliary foot portion 13 and its fitting hole 12 are formed more interiorly of the housing 3 of the lighting device. 
     In addition, the extension 2 includes a boss 21 in the form of a tapered pin-shaped projection at the position corresponding to that of the fitting hole 12. While the boss 21 is inserted into the fitting hole 12, the lens 1 can be attached to and detached from the extension 2 as desired. The reason why the lens 1 includes the above described auxiliary foot portion 13 is that if a fitting hole 12 is formed directly on the housing fitting foot portion 11, there arises a problem that water such as rain water or the like could enter into interior of the lighting chamber of the lighting device through the fitting hole 12. Therefore, when there is no possibility that water invasion occurs, the fitting hole 12 may be formed directly on the housing fitting foot portion 11. 
     In addition, the extension 2 includes a flange portion 22 in the region along the upper portion of the periphery thereof, i.e., at the upper part thereof in the embodiment of FIG. 1. 
     In practice, a lens fitting operation is performed in the following manner. 
     First, the lens 1 is preliminarily fitted to the extension 2 to form an assembly, and thereafter, the housing fitting foot portion 11 is received in a lens receiving groove 31 of the housing 3, so that the foot portion 11 is firmly held in the lens receiving groove 31 using a thermoplastic adhesive 4. On completion of the lens fitting operation, the flange 22 is held between the inner surface of the lens 1 and the upper surface of one of the side walls defining the lens receiving groove 31 in a clamped state, whereby the lens 1 is firmly secured to the housing 3 of the lighting device with the aid of the flange portion 22 in cooperation with the boss 21 fitted into the fitting hole 12. 
     While the present invention has been described above with respect to a single preferred embodiment thereof, it should of course be understood that the present invention should not be limited only to this embodiment but various change or modification may be made without any departure from the scope of the present invention as defined by the appended claims.